SCODiA Report by MLBI Lab

Single-Cell Transcriptomic Analysis Reveals Condition-Specific Cellular Dysregulation and Intercellular Communication in Mouse Colon Inflammatory Bowel Disease

This single-cell RNA sequencing analysis of mouse colon tissue reveals profound cellular and molecular changes in acute colitis (AC) and chronic colitis (CC) compared to healthy controls (HC), consistent with Inflammatory Bowel Disease (IBD) / Colitis. Key findings include significant shifts in immune cell populations, such as expanded B cells and plasma cells in chronic colitis and an increase in pro-inflammatory M1 macrophages in both disease states. Intestinal epithelial cells exhibit markers of barrier dysfunction and cellular stress, while widespread upregulation of inflammatory pathways, cell-cell adhesion molecules, and extracellular matrix remodeling interactions characterize the inflamed colon, highlighting distinct yet overlapping pathogenic mechanisms in AC and CC.

Contents

0. Dataset overview
1. UMAP Visualization of Cell Identity and Experimental Conditions
2. Major Cell Type Score UMAP Visualization
3. Marker Gene Expression Across Colon Cell Subsets
4. Minor Cell Type Population Analysis in Mouse Colon
5. Lymphoid Cell Subset Population Analysis in Colonic Inflammation
6. T Cell Subset Population Dynamics in Mouse Colon Conditions (AC, CC vs. HC)
7. Macrophage Subset Population Analysis Across Colon Conditions
8. Macrophage Subset Population Shifts Across Inflammatory Conditions in Colon
9. Comparative Analysis of Cell-Cell Interaction Patterns in Mouse Colon Under Healthy and Inflammatory Conditions
10. Condition-Specific Cell-Cell Interaction Patterns in Mouse Colon IBD Model
11. Intestinal Epithelial Cell Surfaceome Markers in Colitis Conditions (AC, CC) vs. Healthy Control (HC)
12. Macrophage Condition-Specific Surfaceome Markers in Colitis
13. Fibroblast Condition-Specific Surfaceome Markers in Mouse Colon
14. T cell CD4+ Surfaceome Marker Analysis in Mouse Colon Colitis Models
15. Gene Ontology Analysis of Intestinal Epithelial Cells in Colitis Conditions (AC, CC) and Healthy State
16. Gene Set Enrichment Analysis (GSEA) of Colon Cell Types in Inflammatory Conditions
17. Discussion
18. Query List

0. Dataset overview

Dataset Summary:

• AnnData Dimensions: This dataset contains 84,594 cells and 21,984 genes.
• Observed Columns (Cell Metadata): Includes 'sample', 'condition', 'sample_ext', 'celltype_major', 'celltype_minor', 'celltype_subset', and 'cluster'.
• Variable Columns (Gene Metadata): Contains 'gene_id' and 'variable_genes'.
• Species and Tissue: The data is from mouse colon tissue.
• Conditions: The experimental conditions are 'AC', 'CC', and 'HC' (Healthy Control).
• Cell Type Annotations:
• celltype_major: Myeloid cell, T cell, B cell, Stromal cell, Endothelial cell, unassigned, Intestinal Epithelial cell, Plasma cell.
• celltype_minor: Macrophage, ILC, B cell, Fibroblast, T cell CD4+, Endothelial cell, unassigned, Intestinal Epithelial cell, NK cell, Dendritic cell, Plasma cell, Smooth muscle cell, T cell CD8+.
• celltype_subset: A more granular classification including Macrophage (M1), ILC2, B cell (Follicular), Fibroblast, T cell (Treg), Endothelial cell, unassigned, Endothelial tip cell, T cell (Th1), Macrophage (M2C), Lymphatic Endothelial cell, ILCreg, Macrophage (M2B), Microfold cell, NK cell, B cell (Memory), T cell (Th22), Macrophage (M2D), T cell (Th9), Enterocyte, T cell (CD4 Naive), T cell (CD4 Memory), ILC3, T cell (Th17), DC (Plasmacytoid), DC (Inflammatory), ILC1, Plasma cell, T cell (Tfh), T cell (Th2), Macrophage (M2A), B cell (MZ), DC (Classical), Smooth muscle cell, Tuft cell, Goblet cell, B cell (Breg), T cell (CD8 Exhausted), T cell (CD8 Memory), T cell (Cytotoxic), T cell (CD8 Naive), Crypt cell, Paneth cell, Enterochromaffin cell, Enteroendocrine cell.
• Tumor and CNV Status: Tumor identification was not requested, and CNV estimates are not available in this dataset.
• Reference Condition: 'HC' is used as the reference for comparative analyses (DEG_vs_ref, GSEA_vs_ref, GSA_vs_ref_up).
• Precomputed Results: The dataset includes precomputed results for Cell-Cell Interaction (CCI), Differential Expression Genes (DEG), Gene Set Enrichment Analysis (GSEA), and Gene Ontology (GSA/GO), with versions comparing conditions against the rest or against the reference condition.
• Inferred Biological Context: The dataset is inferred to be related to Inflammatory Bowel Disease (IBD) / Colitis, based on the mouse colon tissue, experimental conditions (AC, CC vs. HC), and available immune/epithelial cell type analyses.

1. UMAP Visualization of Cell Identity and Experimental Conditions

[Analysis Visualization Results]...

Analysis Overview

This analysis presents Uniform Manifold Approximation and Projection (UMAP) plots for the single-cell RNA-seq dataset, providing a visual overview of the cellular landscape. The UMAP dimensionality reduction technique allows for the visualization of high-dimensional gene expression data in a two-dimensional space, where cells with similar transcriptional profiles cluster together. These plots are colored by condition, sample, celltype_major, celltype_minor, and celltype_subset to assess the overall data structure, the quality of cell type annotations, and the distribution of cells across different experimental conditions and individual samples.

Visual Summary

• Condition UMAP: The plot shows distinct, yet overlapping, distributions of cells across the three conditions: 'AC' (Acute Colitis), 'CC' (Chronic Colitis), and 'HC' (Healthy Control). While some cell clusters appear to be predominantly associated with specific conditions (e.g., 'HC' cells forming more distinct clusters in certain regions, indicating healthy-specific cell states), there is also significant intermixing, particularly between 'AC' and 'CC', suggesting shared cell populations or inflammatory processes. This indicates that while there are condition-specific cellular changes, some cellular states are common across the disease spectrum.
• Sample UMAP: This visualization displays the distribution of individual samples (e.g., AC1, AC2, AC3). Cells from samples within the same condition generally co-localize, suggesting consistency across biological replicates and a minimal impact of strong sample-specific batch effects that might otherwise drive artificial separation of samples. The sample distribution reinforces the patterns observed in the condition UMAP, showing both shared and distinct regions among conditions.
• Celltype_major UMAP: The major cell types (e.g., Myeloid cell, T cell, B cell, Intestinal Epithelial cell, Stromal cell) are clearly resolved into well-separated clusters on the UMAP. This indicates that the primary cell type annotations are robust and reflect distinct transcriptional identities. The 'unassigned' category is minimal and scattered, which is a positive indicator of high-quality annotation coverage.
• Celltype_minor UMAP: Moving to a finer granularity, the minor cell types (e.g., Macrophage, T cell CD4+, Fibroblast) also show excellent separation, typically forming sub-clusters within their respective major cell type groups. This confirms the ability to distinguish more specialized cell populations based on their gene expression profiles.
• Celltype_subset UMAP: At the most granular level, celltype_subset annotations (e.g., Macrophage (M1), T cell (Treg), Enterocyte, Goblet cell) demonstrate fine-grained resolution, with numerous distinct sub-clusters representing highly specific cell states or differentiation lineages. This level of detail is crucial for in-depth biological investigations, especially in complex tissues like the colon.

Biological Interpretation

The UMAP visualizations collectively provide a robust foundation for subsequent analyses in the context of Inflammatory Bowel Disease (IBD)/Colitis.

• High-Resolution Cell Type Identification: The strong separation of cell types across all annotation levels (major, minor, subset) confirms the high quality of the single-cell data and the annotation pipeline. This detailed cell typing is essential for dissecting the complex cellular ecosystem of the colon in healthy and inflammatory states. The identification of various immune cell subsets (e.g., macrophage subtypes, T helper subsets, B cell subtypes) and intestinal epithelial cell populations (e.g., Enterocytes, Goblet cells, Paneth cells, Tuft cells) provides the necessary granularity to investigate their specific roles in disease pathogenesis.
• Condition-Associated Cellular Landscape Changes: The distinct yet overlapping distributions of cells across 'AC', 'CC', and 'HC' conditions suggest that while the colon maintains some core cellular components across states, there are significant condition-specific alterations in cell population composition or transcriptional states. The separation of some 'HC' cells from disease conditions might indicate healthy-specific cellular programs that are lost or altered during inflammation. Conversely, the extensive overlap between 'AC' and 'CC' could point to shared inflammatory responses or transitional cell states between acute and chronic colitis. Further differential abundance and differential expression analyses will be critical to pinpoint which specific cell types are altered in quantity or gene expression in response to these inflammatory conditions.
• Data Integrity and Reliability: The consistency observed across individual samples within the same condition (as shown in the sample UMAP) increases confidence that the observed condition-specific differences are biologically driven rather than artifacts of experimental batch effects. This robust data structure allows for reliable comparisons between healthy and disease states.

Annotation Notes

The UMAP plots confirm the high quality and distinctness of the cell type annotations provided in the AnnData object. The clear separation of cell populations from major to subset levels indicates that the clustering and annotation processes have successfully captured biologically meaningful cell identities. The minimal presence of 'unassigned' cells further reinforces the comprehensiveness of the current cell type assignments. These UMAPs serve as a critical validation step, ensuring that downstream analyses, such as differential gene expression or cell-cell interaction studies, will be performed on accurately defined cell populations.

2. Major Cell Type Score UMAP Visualization

[Analysis Visualization Results]...

Analysis Overview

This analysis visualizes the expression scores for various major cell types across the entire single-cell dataset on a UMAP embedding. The purpose is to assess the distinctness and spatial organization of cell populations based on predefined gene signatures for each major cell type (HiCAT_major_score), and to corroborate the overall celltype_major annotation. This provides an important quality control step for cell type assignment and reveals the global cellular landscape of the mouse colon under study.

Visual Summary

The UMAP plots illustrate the distribution of scores for individual major cell types, with warmer colors (yellow/green) indicating higher scores and cooler colors (purple) indicating lower scores. The final plot shows the assigned celltype_major for comparison.

• Distinct Cluster Formation: For most major cell types such as T cell, Plasma cell, B cell, Myeloid cell, Endothelial cell, Stromal cell, and Intestinal Epithelial cell, high scores localize predominantly to specific, well-separated clusters within the UMAP. This indicates that these cell types form distinct populations with characteristic gene expression profiles.

Cell Type Localization

• T cells and B cells each occupy large, distinct regions, suggesting robust identification of adaptive immune cell compartments.
• Myeloid cells show strong scores in a cluster separate from T and B cells, consistent with their distinct immune functions.
• Plasma cells form a relatively smaller but distinct cluster, often appearing in close proximity to B cell clusters, which is biologically expected given their lineage.
• Intestinal Epithelial cells form a large, central cluster, reflecting their abundance and critical role in the colon lining.
• Endothelial cells and Stromal cells also show clear clustering, indicating their distinct mesenchymal and vascular identities within the tissue.

Less Prominent or More Diffuse Cell Types

• Mast cells, Enteric glia cells, and Enteric neurons show lower overall scores and tend to occupy smaller or more diffuse regions compared to the major immune or epithelial populations. This could be due to lower cell numbers in the dataset, less distinct transcriptional profiles, or inherent biological rarity. For instance, Enteric neurons have very low scores across the UMAP (max ~0.175), suggesting they are either rare or poorly represented by the scoring gene set in this dataset, or highly specialized.
• Overall Coherence: The individual cell type score plots align well with the celltype_major annotation UMAP (bottom right panel), where distinct colors represent the final major cell type assignments. This visual congruence supports the accuracy and confidence in the celltype_major assignments derived from the data.

Biological Interpretation

The strong localization of high major cell type scores to distinct clusters on the UMAP embedding confirms that the cellular populations in this mouse colon dataset are well-resolved and transcriptionally distinct. This is crucial for downstream analyses, especially in the context of Inflammatory Bowel Disease (IBD)/Colitis, where precise identification of immune and structural cell types is paramount.

• Immune Cell Heterogeneity: The clear separation of T cells, B cells, Plasma cells, and Myeloid cells highlights the diverse immune landscape of the colon, which is highly relevant to IBD. Changes in the proportions or activation states of these cells are central to intestinal inflammation.
• Structural Cell Integrity: The identification of distinct Intestinal Epithelial cells, Endothelial cells, and Stromal cells provides the foundational cellular context for understanding disease pathology. Alterations in epithelial barrier function, vascular integrity, and stromal support are critical aspects of colitis.
• Annotation Confidence: The high congruence between the major cell type scores and the final celltype_major annotations increases confidence in the cell type assignments. This robust annotation is essential for reliable differential gene expression, pathway enrichment, and cell-cell interaction analyses that will follow, particularly when comparing disease conditions (AC, CC) to healthy controls (HC).

Annotation Notes

• The visualization effectively validates the celltype_major annotations by demonstrating that cells assigned to a particular major type also express high scores for the corresponding gene signatures.
• While most major cell types are clearly delineated, further investigation might be warranted for cell types with lower overall scores or more diffuse distributions (e.g., Enteric glia cells, Enteric neurons) to ensure their accurate representation and to understand if their gene signatures are fully captured. This could involve exploring minor cell type annotations or specific marker genes if these populations are critical to the biological question.
• The clear separation of cell populations forms a solid basis for investigating condition-specific changes in cell composition and activity within the IBD context.

3. Marker Gene Expression Across Colon Cell Subsets

[Analysis Visualization Results]...

Analysis Overview

This analysis presents a marker expression dot plot for various cell subsets (celltype_subset) identified within the mouse colon single-cell RNA-seq dataset. The plot visualizes the expression of a curated set of marker genes across these cell populations, with dot size representing the fraction of cells within a group expressing the gene and dot color intensity indicating the mean expression level of the gene in that group. The primary objective of this visualization is to assess the fidelity of the cell type annotations by examining whether the observed gene expression patterns align with known cell type-specific markers.

Visual Summary

The dot plot effectively delineates distinct marker expression profiles for most of the identified celltype_subset populations.

• Cell Type Specificity: Many cell subsets exhibit highly specific marker expression. For instance, B cell subsets (Breg, Follicular, MZ, Memory) strongly express canonical B cell markers like *Cd79a* and *Ebf1*. T cell subsets universally show high expression of T cell receptor components like *Cd3d* and *Cd3e*, with further differentiation by co-receptors such as *Cd4* (CD4+ T cells) or *Cd8a*/*Cd8b1* (CD8+ T cells), and specific transcription factors like *Foxp3* for T cell (Treg).
• Epithelial Cell Diversity: Intestinal Epithelial Cell subsets, including Crypt cell, Enterocyte, Goblet cell, Microfold cell, and Paneth cell, show characteristic marker expression. For example, Goblet cell displays strong *Muc2* expression, Enterocyte expresses *Vil1* and *Ceacam1*, and Paneth cell shows *Lyz1*.
• Stromal and Endothelial Markers: Fibroblast cells are clearly marked by extracellular matrix-related genes such as *Col1a1* and *Dcn*, while Smooth muscle cell populations show strong expression of contractile proteins like *Acta2* and *Myh11*. Endothelial cells (General, Tip, Lymphatic) uniformly express *Pecam1* and *Cdh5*, with *Prox1* specifically enriched in Lymphatic Endothelial cell.
• Immune Cell Lineages: Myeloid cells (Macrophage and Dendritic cell subsets) generally express pan-myeloid markers like *Cd68* and *Itgam*, with further refinement by subset-specific genes. ILC and NK cells display markers such as *Il2rg* and *Nkg7*. Plasma cells are clearly distinguished by immunoglobulin chain genes like *Jchain* and *Ighm*.
• Common Markers: A distinct section on the right highlights genes expressed broadly across many cell types (e.g., *Ptprc* (CD45) as a pan-hematopoietic marker, MHC Class II genes like *H2-Aa*, *H2-Ab1* on antigen-presenting cells). This panel helps distinguish broadly expressed genes from truly cell-type-specific markers.

Biological Interpretation

The observed marker expression patterns largely validate the celltype_subset annotations provided in the dataset, confirming the presence and distinct identities of various cell populations in the mouse colon.

• Immune Cell Heterogeneity: The clear segregation of B, T, Macrophage, Dendritic, ILC, and NK cell subsets by their canonical markers (e.g., *Cd19* for B cells, *Cd3e* for T cells, *Cd68* for macrophages, *Flt3* for dendritic cells) indicates a robust classification of the immune landscape within the colon. The identification of specific T cell subsets (e.g., T cell (Treg) by *Foxp3*, T cell (Th2) by *Gata3*) and macrophage subtypes suggests a detailed understanding of the immune response, which is particularly relevant in the context of colonic inflammation (IBD/Colitis).
• Epithelial Barrier Components: The specific expression of markers for diverse intestinal epithelial cell types underscores the complexity and specialized functions of the gut lining. Crypt cells expressing stem/progenitor markers like *Lrig1* are crucial for regeneration, while Goblet cells (*Muc2*) maintain the mucus barrier, Paneth cells (*Lyz1*) contribute to innate immunity, and Enterocytes (*Vil1*) are responsible for absorption. The presence of Microfold cells and Tuft cells (e.g., *Dclk1*) further highlights specialized epithelial functions, potentially involved in antigen sampling or immune modulation.
• Stromal Support System: The distinct expression of *Col1a1* by Fibroblasts and *Acta2* by Smooth muscle cells accurately identifies the mesenchymal components of the colon, which play crucial roles in tissue structure, wound healing, and immune cell recruitment. The differentiation of endothelial cell types, including Lymphatic Endothelial cell (*Prox1*), indicates the comprehensive characterization of the vascular and lymphatic networks supporting the colon.

Annotation Notes

Based on the marker expression patterns, the celltype_subset annotations appear to be highly reliable and well-supported by known biological markers. The plot demonstrates a high degree of specificity for most cell types, with minimal ambiguous overlap in unique marker expression. The strategy of plotting both lineage-defining markers and more specific subset markers provides confidence in the granular cell type assignments. The distinct clustering of marker expression within related cell families (e.g., different B cell subsets sharing core B cell markers but showing subtle differences in others) further confirms the hierarchical annotation structure. This strong validation of cell identities forms a solid foundation for subsequent analyses, particularly those investigating condition-specific changes in gene expression or cell-cell interactions.

4. Minor Cell Type Population Analysis in Mouse Colon

[Analysis Visualization Results]...

Analysis Overview

This analysis presents a population bar plot illustrating the relative abundance of minor cell types across individual samples within three experimental conditions: Acute Colitis (AC), Chronic Colitis (CC), and Healthy Control (HC). The goal is to identify shifts in cell composition that may be indicative of disease states or inflammatory processes in the colon.

Visual Summary

The stacked bar plots display the percentage contribution of each minor cell type to the total cell population within each sample.

• Dominant Cell Types: Across all conditions and samples, B cells, Dendritic cells, Endothelial cells, Fibroblasts, and Intestinal Epithelial cells appear to constitute the largest proportions of the cell populations. B cells (dark red) consistently represent a substantial fraction, particularly in CC and HC.

Condition-Specific Trends:

• B cells: Show a notable increase in relative proportion in the CC condition compared to both AC and HC. In CC, B cells comprise roughly 30-50% of the population, whereas in AC and HC, they are generally below 20-30%.
• Dendritic cells and Endothelial cells: Appear to maintain relatively stable proportions across all conditions.
• Fibroblasts: Seem to be a substantial component across all conditions, perhaps slightly lower in CC compared to AC and HC, but this is less pronounced.
• Intestinal Epithelial cells: The proportion of Intestinal Epithelial cells (light orange) appears relatively consistent across AC and HC, but might be slightly diminished in some CC samples (e.g., CC1, CC2) relative to the prominent B cell expansion.
• T cells (CD4+ and CD8+): Both CD4+ T cells (light green) and CD8+ T cells (teal) show a modest presence, with no immediately striking large-scale changes visible at this resolution, though they appear present in all conditions.
• Macrophages, NK cells, Plasma cells, Smooth muscle cells, and ILCs: These cell types are present in smaller proportions across the samples. Macrophages (light yellow) show a consistent, albeit minor, presence. Plasma cells (pale green) are detectable and appear slightly elevated in CC samples compared to AC and HC, coinciding with the B cell expansion.
• Sample Variability: There is some variability in cell type proportions between individual samples within each condition, particularly noticeable in the AC and CC groups (e.g., AC3 shows a relatively higher proportion of Intestinal Epithelial cells compared to AC1 and AC2).

Biological Interpretation

The observed shifts in minor cell type populations provide insights consistent with an inflammatory bowel disease (IBD) context, specifically colitis.

• B cell and Plasma Cell Expansion in Colitis: The most striking observation is the increased relative abundance of B cells and Plasma cells in the Chronic Colitis (CC) condition. This is highly consistent with chronic inflammation, where sustained immune activation leads to robust humoral immune responses, characterized by B cell proliferation and differentiation into antibody-secreting plasma cells https://pubmed.ncbi.nlm.nih.gov/30595304/.
• Inflammatory Infiltrates: While not as dramatically shifted as B cells, the presence of various immune cells (Dendritic cells, Macrophages, T cells, ILCs, NK cells) across all conditions, and their potentially subtle increases in AC and CC, reflects the immune cell infiltration characteristic of intestinal inflammation https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8949021/.
• Epithelial and Stromal Context: The consistent presence of Intestinal Epithelial cells and Fibroblasts suggests that despite inflammation, the basic tissue architecture components are still represented. A relative decrease in Intestinal Epithelial cells in the inflamed conditions could indicate epithelial damage or loss, a hallmark of IBD. Fibroblasts play a critical role in tissue remodeling and fibrosis in chronic inflammation, and their consistent presence underscores their involvement in the colon's response to injury.
• Acute vs. Chronic States: The distinct profile of CC (higher B cells/plasma cells) compared to AC and HC suggests a more pronounced or prolonged immune activation in the chronic phase, which is expected in progressive inflammatory disease.

Clinical or Translational Implications

The changes in cell type composition identified here have several potential clinical and translational implications for IBD/Colitis:

• Biomarkers of Disease Activity/Stage: The substantial increase in B cell and plasma cell populations, particularly in Chronic Colitis, could serve as a cellular biomarker for disease chronicity or severity. Monitoring these cell populations could offer insights into disease progression or response to therapy.
• Therapeutic Targets: The prominent role of B cells and plasma cells in CC suggests that therapeutic strategies targeting humoral immunity (e.g., B cell depletion therapies or plasma cell-specific inhibitors) might be particularly effective in chronic inflammatory states of the colon https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9345711/.
• Understanding Pathogenesis: These population shifts reinforce the understanding of the distinct immune responses in acute versus chronic phases of colitis, highlighting the transition from acute inflammatory infiltrates to more organized adaptive immune responses.

5. Lymphoid Cell Subset Population Analysis in Colonic Inflammation

[Analysis Visualization Results]...

Analysis Overview

This analysis presents a stacked bar plot visualizing the relative proportions of lymphoid cell subsets (including T cells, ILCs, and NK cells as defined by celltype_subset within the T cell major cell type) across different samples and experimental conditions. The data is derived from single-cell RNA-seq of mouse colon tissue, comparing two inflammatory conditions, AC and CC, against a healthy control (HC). Each bar represents an individual sample, normalized to 100%, allowing for direct comparison of subset compositions.

Visual Summary

The plot effectively illustrates the proportional distribution of various lymphoid subsets across the AC, CC, and HC conditions.

• Overall Composition: In healthy control (HC) samples, the lymphoid compartment exhibits a diverse composition, with notable contributions from T cell (CD4 Memory), T cell (CD4 Naive), T cell (CD8 Memory), and T cell (Treg) populations, alongside various ILC subsets (ILC1, ILC2, ILC3, ILCreg) and NK cells.
• ILC Subsets (ILC1, ILC2, ILC3, ILCreg): There appears to be a general trend of slightly reduced proportions of ILCs (represented by the darker red hues at the bottom of the bars) in both AC and CC inflammatory conditions compared to HC. This reduction is visually consistent across most samples within the AC and CC groups.

T Helper Cell Subsets (Th1, Th2, Th9, Th17, Th22, Tfh):

• T cell (Th1) and T cell (Th17) populations (light green segments) seem to be maintained or show a subtle increase in their relative proportions in AC and CC conditions compared to HC, particularly in some AC samples (e.g., AC3) and CC samples.
• Other T helper subsets such as T cell (Th2) and T cell (Tfh) show relatively stable or minor fluctuations.
• Regulatory T cells (Treg): The T cell (Treg) population (dark blue segment at the top) generally maintains a consistent proportion across all conditions and samples, with no prominent changes immediately apparent.
• CD4 and CD8 T cell populations: T cell (CD4 Memory) and T cell (CD4 Naive) (various orange tones) together constitute a substantial portion of the lymphoid compartment. While their overall contribution remains high, there might be subtle shifts in their relative balance between naïve and memory phenotypes in diseased states. Similarly, CD8 T cell subsets (CD8 Naive, CD8 Memory, Cytotoxic, Exhausted; yellow tones) are present but form a smaller segment, without clear condition-specific enrichment.

Biological Interpretation

The observed shifts in lymphoid cell populations provide valuable insights into the immune responses occurring in the colon under inflammatory conditions (AC and CC), consistent with the inferred context of Inflammatory Bowel Disease (IBD)/Colitis.

• Reduced ILCs in Inflammation: The apparent decrease in ILC subsets (ILC1, ILC2, ILC3, ILCreg) in AC and CC conditions is a noteworthy finding. ILCs are critical innate immune cells that reside in mucosal tissues and play essential roles in maintaining gut barrier integrity and orchestrating early immune responses [PubMed search: Innate Lymphoid Cells IBD gut immunity]. A reduction in these protective populations, particularly ILC3s which produce IL-22 crucial for epithelial repair, could contribute to impaired barrier function and dysregulated immune responses characteristic of IBD [PubMed search: ILC3 IL-22 IBD].
• Sustained Pro-inflammatory T Helper Responses: The maintenance or slight increase in T cell (Th1) and T cell (Th17) populations in AC and CC aligns with the known pathogenesis of IBD, where a dysregulated Th1- and Th17-mediated inflammatory response is often observed [PubMed search: Th1 Th17 IBD pathogenesis]. Th1 cells produce IFN-γ, while Th17 cells produce IL-17 and IL-22, all potent pro-inflammatory cytokines that drive chronic intestinal inflammation.
• Treg Stability: The seemingly stable proportion of T cell (Treg) cells suggests that the overall suppressive capacity, as indicated by their relative numbers, might not be severely compromised or significantly expanded in these inflammatory conditions. However, a stable proportion amid increasing effector T cell activity could still imply an *imbalance* and insufficient suppression of inflammation.

Clinical or Translational Implications

Understanding the dynamic changes in lymphoid cell populations during colonic inflammation has several clinical and translational implications:

• Biomarker Potential: The specific shifts in ILC and T helper cell proportions could serve as potential biomarkers for assessing disease activity, monitoring therapeutic efficacy, or stratifying patients with different inflammatory profiles in IBD. For instance, a decrease in specific ILC subsets or an increase in Th1/Th17 proportions might indicate active inflammation.
• Therapeutic Targets: The data highlights specific cell types that could be targeted for therapeutic intervention. Strategies aimed at restoring beneficial ILC populations (e.g., via cytokine administration like IL-22 for ILC3s) or dampening excessive Th1/Th17 responses could be explored.
• Disease Heterogeneity: The variability observed between individual samples within the AC and CC conditions suggests that even within similar disease states, there might be heterogeneity in the immune cell landscape, which could influence disease progression and response to treatment. This underscores the importance of personalized medicine approaches in IBD.

6. T Cell Subset Population Dynamics in Mouse Colon Conditions (AC, CC vs. HC)

[Analysis Visualization Results]...

Analysis Overview

This analysis investigates the proportional representation of various T cell subsets (derived from celltype_subset) across three conditions: 'AC', 'CC', and 'HC' (Healthy Control). The goal is to identify statistically significant differences in these cell proportions between conditions, particularly in the context of inferred Inflammatory Bowel Disease (IBD) / Colitis. Box plots visualize the distribution of celltype proportions for each subset, with p-values indicating the statistical significance of pairwise comparisons between conditions (using a p-value cutoff of 0.1).

Visual Summary

The box plots illustrate the proportions of seven T cell subsets. Statistically significant changes (p < 0.1) are observed in several populations, predominantly showing increases in 'AC' and 'CC' conditions compared to 'HC'.

1. T cell (CD4 Memory): Both 'AC' (p=0.00651) and 'CC' (p=0.0204) conditions exhibit significantly higher proportions of CD4 Memory T cells compared to 'HC'. There is no significant difference between 'AC' and 'CC' (p=0.224).
2. T cell (CD8 Exhausted): The 'AC' condition shows a significantly elevated proportion of CD8 Exhausted T cells when compared to 'HC' (p=0.00931) and also to 'CC' (p=0.00931). Proportions in 'CC' and 'HC' are very low, almost negligible.
3. Th2: Both 'AC' (p=0.0807, borderline significance) and 'CC' (p=0.0198) conditions display significantly increased Th2 cell proportions relative to 'HC'. No significant difference is observed between 'AC' and 'CC'.
4. Th22: The 'AC' condition has a significantly higher proportion of Th22 cells compared to 'HC' (p=0.03). Differences between 'AC' and 'CC' (p=0.11) and 'CC' and 'HC' (p=0.157) are not statistically significant at the 0.1 cutoff.
5. Th17: The 'CC' condition shows a significantly increased proportion of Th17 cells compared to 'HC' (p=0.0311). No significant differences are noted between 'AC' and 'HC' (p=0.135) or 'AC' and 'CC' (p=0.449).
6. Treg: The 'CC' condition has a statistically higher proportion of Treg cells compared to 'HC' (p=0.0535, borderline significance). No significant differences are found between 'AC' and 'HC' (p=0.158) or 'AC' and 'CC' (p=0.45).
7. Tfh: The 'CC' condition exhibits a borderline significantly higher proportion of Tfh cells compared to 'HC' (p=0.0675). Other comparisons are not significant.

Biological Interpretation

The observed shifts in T cell subset proportions align with an inflammatory immune response characteristic of Inflammatory Bowel Disease (IBD) or colitis, as inferred from the data context.

• General Immune Activation: The significant increase in T cell (CD4 Memory) populations in both 'AC' and 'CC' conditions relative to 'HC' suggests a broad activation of the adaptive immune system and the establishment of immune memory in response to persistent antigenic stimulation within the inflamed colon. This is a common feature of chronic inflammatory conditions.

Pro-inflammatory Responses:

• The elevation of Th22 cells in 'AC' compared to 'HC' suggests a potential role in mucosal immunity and tissue repair but can also contribute to inflammation. Th22 cells produce IL-22, which is critical for maintaining epithelial barrier integrity and promoting tissue regeneration, but dysregulation can exacerbate inflammation [1].
• The significant increase in Th17 cells in 'CC' compared to 'HC' is a hallmark of many autoimmune and inflammatory diseases, including IBD [2]. Th17 cells produce IL-17 and IL-22, driving robust inflammatory responses and contributing to tissue damage in chronic inflammation.
• Th2 cells are also elevated in both 'AC' and 'CC'. While traditionally associated with allergic responses, Th2 responses in the gut can also contribute to mucosal inflammation and goblet cell hyperplasia, particularly in certain forms of colitis [3].
• Immune Exhaustion in 'AC': The pronounced increase in T cell (CD8 Exhausted) cells specifically in 'AC' compared to 'CC' and 'HC' is a notable finding. CD8 T cell exhaustion is characterized by impaired effector function and sustained expression of inhibitory receptors, typically occurring during chronic infections or cancer. In the context of chronic inflammation like IBD, T cell exhaustion might represent an attempt by the immune system to limit excessive inflammation, or it could reflect persistent antigen exposure leading to dysfunctional effector cells [4]. This suggests that 'AC' might represent a more chronic or severe inflammatory state than 'CC'.

Regulatory and Follicular Helper T Cells in 'CC':

• The borderline increase in Treg cells in 'CC' compared to 'HC' is often observed in inflammatory settings as a compensatory mechanism to suppress excessive immune responses and maintain immune homeostasis [5]. Their presence could indicate an ongoing but perhaps somewhat controlled inflammatory process in 'CC'.
• The borderline increase in Tfh cells in 'CC' compared to 'HC' suggests enhanced B cell help and germinal center responses, potentially contributing to antibody production and humoral immunity in this condition. Tfh cells are crucial for effective antibody responses, which can be relevant in certain IBD subtypes where autoantibodies or specific antibody responses are observed [6].

In summary, both 'AC' and 'CC' conditions demonstrate immune activation, with 'AC' showing signs of T cell exhaustion, potentially indicating a more protracted or unresolved inflammatory state. 'CC' exhibits characteristics of Th17-driven inflammation alongside compensatory regulatory responses and active humoral immunity. These distinct T cell profiles suggest differing immunopathological mechanisms or stages of disease progression between 'AC' and 'CC'.

Clinical or Translational Implications

Understanding the distinct T cell subset dynamics in 'AC' and 'CC' could have implications for disease classification and targeted therapeutic strategies in IBD.

• Targeted Therapies for Inflammation: The robust Th17 response in 'CC' suggests that therapies targeting the IL-17 pathway might be particularly effective in this specific condition. Similarly, pathways associated with Th2 or Th22 activity could be considered in 'AC' and 'CC', respectively.
• Immunomodulation in Chronic Disease: The presence of CD8 Exhausted T cells in 'AC' opens avenues for immunomodulatory approaches aimed at revitalizing T cell function, similar to strategies used in chronic infections or cancer. Restoring functional anti-inflammatory or anti-pathogen responses in these exhausted cells could be beneficial.
• Biomarker Discovery: The distinct T cell signatures could serve as biomarkers to differentiate between 'AC' and 'CC' conditions, potentially guiding personalized treatment decisions or assessing disease severity and progression. For instance, the ratio of exhausted T cells to other effector populations could be indicative of disease chronicity or therapeutic responsiveness.

References

1. Th22 cells: A search for "Th22 cells gut inflammation" on PubMed provides relevant literature. PubMed search: Th22 cells gut inflammation
2. Th17 cells in IBD: A search for "Th17 cells inflammatory bowel disease" on PubMed provides extensive literature. PubMed search: Th17 cells inflammatory bowel disease
3. Th2 cells in colitis: A search for "Th2 cells colitis" on PubMed provides relevant literature. PubMed search: Th2 cells colitis
4. T cell exhaustion in chronic inflammation: A search for "T cell exhaustion chronic inflammation" on PubMed provides relevant literature. PubMed search: T cell exhaustion chronic inflammation
5. Treg cells in IBD: A search for "Treg cells inflammatory bowel disease" on PubMed provides extensive literature. PubMed search: Treg cells inflammatory bowel disease
6. Tfh cells in IBD: A search for "Tfh cells inflammatory bowel disease" on PubMed provides relevant literature. PubMed search: Tfh cells inflammatory bowel disease

7. Macrophage Subset Population Analysis Across Colon Conditions

[Analysis Visualization Results]...

Analysis Overview

This analysis provides a population bar plot illustrating the relative proportions of different macrophage subsets (Macrophage (M1), Macrophage (M2A), Macrophage (M2B), Macrophage (M2C), and Macrophage (M2D)) within the colon tissue samples. The data is stratified by experimental conditions: 'AC', 'CC' (representing distinct disease states, likely inflammatory), and 'HC' (Healthy Control), and further broken down by individual samples within each condition. This visualization helps to identify shifts in macrophage polarization that may be associated with disease.

Visual Summary

The bar plot displays the percentage contribution of each macrophage subset to the total macrophage population for each sample.

• Macrophage (M1) Dominance in Disease Conditions: In both 'AC' and 'CC' conditions, Macrophage (M1) (maroon bars) constitutes the largest fraction of the macrophage population, consistently ranging approximately between 35-40% across all 'AC' and 'CC' samples. In contrast, in the 'HC' condition, Macrophage (M1) accounts for a visibly smaller proportion, roughly 20-25% of the total macrophages.
• Reduction of Macrophage (M2D) in Disease Conditions: Macrophage (M2D) (teal bars) shows a notable decrease in its relative abundance in both 'AC' and 'CC' conditions (approximately 10-15%) compared to the 'HC' condition, where it represents a larger fraction (approximately 20-30%).
• Distribution of Other M2 Subsets: Macrophage (M2A) (orange bars) remains a minor component across all conditions and samples. Macrophage (M2B) (light yellow) and Macrophage (M2C) (pale yellow) together form a significant portion, particularly in the 'HC' condition, where Macrophage (M2C) appears to be a major M2 component. While these M2 subsets are still present in 'AC' and 'CC', their relative contributions shift due to the increased M1 and decreased M2D populations.
• Overall Shift: The data indicates a clear shift in macrophage polarization from a more balanced profile in healthy controls towards a pro-inflammatory phenotype dominated by M1 macrophages, coupled with a reduction in M2D macrophages, in both 'AC' and 'CC' disease conditions.

Biological Interpretation

Macrophages are central to immune responses and tissue homeostasis in the colon. Their polarization into distinct functional subsets, such as pro-inflammatory M1 and anti-inflammatory/pro-resolving M2 macrophages, is critical in inflammatory conditions like IBD/Colitis.

• Pro-inflammatory Skewing in Colitis: The observed increase in Macrophage (M1) populations in the 'AC' and 'CC' conditions is highly indicative of a pro-inflammatory environment. M1 macrophages are known to produce pro-inflammatory cytokines (e.g., TNF-$\alpha$, IL-1$\beta$, IL-6) and mediators (e.g., iNOS), contributing to tissue damage and perpetuating inflammation characteristic of IBD [1].
• Alterations in M2 Subsets: The decrease in Macrophage (M2D) in 'AC' and 'CC' conditions compared to 'HC' suggests a shift away from certain anti-inflammatory or immunoregulatory functions. While M2 subsets generally promote tissue repair and resolve inflammation, specific M2 subtypes (like M2C, associated with efferocytosis and immune suppression, and M2D, implicated in angiogenesis and immune modulation) have distinct roles. A reduction in M2D could signify an impaired ability to resolve inflammation or an altered immune-suppressive landscape in the diseased colon.
• Disease Progression and Macrophage Plasticity: The consistent macrophage polarization pattern across 'AC' and 'CC' samples suggests that both conditions involve a similar fundamental inflammatory macrophage response, likely characterized by an imbalance favoring pro-inflammatory activation. This highlights the plasticity of macrophages and their significant role in dictating the inflammatory state of the colon during colitis.

Clinical or Translational Implications

• Diagnostic/Prognostic Biomarker Potential: The distinct shift in macrophage subsets, particularly the elevated M1 population and reduced M2D population, could serve as potential cellular biomarkers for assessing disease activity or distinguishing active inflammation from remission in IBD patients.
• Therapeutic Targeting of Macrophage Polarization: Modulating macrophage polarization represents a promising therapeutic strategy for inflammatory bowel diseases. Interventions aimed at suppressing M1 macrophage activation or enhancing the populations/functions of specific anti-inflammatory M2 subsets (such as M2D or other M2 subtypes that are reduced or dysfunctional in disease) could help restore immune homeostasis and promote mucosal healing in colitis [2]. Understanding the specific drivers behind the M1 skewing and M2D reduction in AC and CC conditions could inform the development of targeted therapies.

---

References:

1. M1 Macrophage roles in IBD: For general information on M1 macrophage involvement in inflammation and IBD: https://pubmed.ncbi.nlm.nih.gov/?term=M1+macrophage+inflammation+IBD
2. Macrophage polarization as therapeutic target in IBD: For insights into therapeutic strategies targeting macrophage polarization in IBD: https://pubmed.ncbi.nlm.nih.gov/?term=macrophage+polarization+IBD+therapy

8. Macrophage Subset Population Shifts Across Inflammatory Conditions in Colon

[Analysis Visualization Results]...

Analysis Overview

This analysis investigates the proportional changes of specific macrophage subsets, Macrophage (M1) and Macrophage (M2B), across different conditions (Healthy Control: HC; Inflammatory Conditions: AC, CC) in mouse colon single-cell RNA-seq data. Box plots illustrate the celltype proportions, with statistical significance indicated for pairwise comparisons between conditions. The goal is to identify statistically significant shifts in macrophage populations that may reflect alterations in the immune microenvironment during inflammatory states.

Visual Summary

Figure 1: Macrophage Subset Proportions Across Conditions

Macrophage (M1) Proportions

• HC vs. AC: The proportion of Macrophage (M1) cells significantly increases from HC to AC (p=0.0381). The median proportion rises from approximately 28.5% in HC to about 37.5% in AC.
• HC vs. CC: Similarly, Macrophage (M1) proportions are significantly elevated in CC compared to HC (p=0.0276). The median proportion in CC is around 39.5%, demonstrating a similar increase to AC.
• AC vs. CC: There is no statistically significant difference in Macrophage (M1) proportions between AC and CC (p=0.458), suggesting both inflammatory conditions induce a comparable expansion of this subset.

Macrophage (M2B) Proportions

• HC vs. AC: The proportion of Macrophage (M2B) cells shows an increasing trend from HC to AC, with median values around 26.5% in HC and 29.5% in AC, but this difference does not reach statistical significance (p=0.161).
• HC vs. CC: In contrast to M1, Macrophage (M2B) proportions are significantly *decreased* in CC compared to HC (p=0.0346). The median proportion drops to approximately 25.5% in CC.
• AC vs. CC: A statistically significant decrease in Macrophage (M2B) proportion is observed from AC to CC (p=0.0346), indicating a reduction in this subset in the CC condition relative to AC.

Biological Interpretation

The observed shifts in macrophage subsets provide key insights into the immune landscape of the colon during inflammatory conditions.

• Elevated M1 Macrophages in Inflammation: Macrophage (M1) cells are traditionally characterized as pro-inflammatory macrophages, pivotal in initiating and sustaining immune responses, pathogen clearance, and tissue damage through the production of pro-inflammatory cytokines. The significant increase in M1 proportions in both AC and CC conditions compared to healthy controls strongly suggests a robust pro-inflammatory shift in the colon microenvironment during these disease states, consistent with the inferred context of Inflammatory Bowel Disease (IBD) or Colitis.
• Divergent M2B Macrophage Dynamics: Macrophage (M2B) cells are a less uniformly defined M2 subtype, capable of both pro- and anti-inflammatory functions, often associated with immune complex stimulation. The non-significant increase in M2B in AC compared to HC might reflect a complex or transitional response where some regulatory or immune complex-mediated activity is initiated. However, the significant *decrease* of M2B in CC compared to both HC and AC is notable. This could indicate a suppression or alteration of this particular M2 phenotype in the CC condition, potentially suggesting a different inflammatory or immunoregulatory phase compared to AC. A reduction in certain M2 subsets could impair anti-inflammatory processes or tissue repair mechanisms, further contributing to disease pathology in CC.
• Differential Macrophage Polarization in AC vs. CC: The distinct changes in M1 and M2B populations between AC and CC suggest that these two conditions, while both inflammatory, may represent different stages or types of colonic inflammation. Both conditions show an M1-dominant inflammatory response compared to HC. However, the significant reduction of M2B in CC, while AC shows a non-significant increase, highlights potential differences in their immunoregulatory mechanisms or disease progression.

Clinical or Translational Implications

These findings have several potential clinical and translational implications:

• Biomarkers for Disease States: The distinct changes in M1 and M2B macrophage proportions could serve as cellular biomarkers for different inflammatory states or disease activity in IBD/Colitis. For instance, a high M1 proportion would consistently indicate inflammation, while the M2B profile might help differentiate between AC and CC conditions.
• Therapeutic Targeting of Macrophage Polarization: Given the critical role of macrophages in shaping intestinal inflammation, modulating macrophage polarization could be a promising therapeutic strategy. Strategies to dampen M1 activation or restore beneficial M2 subsets (if M2B is indeed beneficial in some contexts or if other M2 types are affected) could be explored to control chronic inflammation and promote tissue healing.
• Understanding Disease Heterogeneity: The differential macrophage profiles between AC and CC underscore the heterogeneity of inflammatory conditions. Recognizing these cellular shifts can help in understanding disease mechanisms and potentially lead to more precise, condition-specific therapeutic interventions. For example, therapies that might be effective in mitigating the M1-driven inflammation in AC might need to be complemented by strategies addressing the unique M2B dynamics observed in CC.

9. Comparative Analysis of Cell-Cell Interaction Patterns in Mouse Colon Under Healthy and Inflammatory Conditions

[Analysis Visualization Results]...

Analysis Overview

This analysis presents dot plots visualizing cell-cell interaction (CCI) patterns across three conditions: acute colitis (AC), chronic colitis (CC), and healthy control (HC) in mouse colon tissue. These interactions were inferred using CellPhoneDB. The plots highlight the significance (-log10(p)) and strength (log2(mean) expression) of ligand-receptor interactions between various cell types. The goal is to identify common and condition-specific CCI signatures that may contribute to inflammatory bowel disease (IBD) pathology.

Visual Summary

The three dot plots display the top 80 significant cell-cell interactions for each condition (AC, CC, HC). The size of each dot represents the -log10(p-value), with larger dots indicating higher statistical significance. The color intensity of each dot corresponds to the log2(mean) expression level of the ligand-receptor pair, where brighter (more yellow) colors denote stronger interaction potential.

Key visual observations:

• Healthy Control (HC): The HC plot shows fewer and generally weaker interactions compared to the inflammatory conditions. While some baseline interactions are present, particularly involving Fibroblasts and Endothelial cells (e.g., FN1-integrin complexes), the overall landscape is less dense and less intense, reflecting a quiescent tissue state.
• Acute Colitis (AC): This condition exhibits a marked increase in both the number and intensity of cell-cell interactions compared to HC. Prominent interactions include various integrin complexes (e.g., FN1-integrin, COL6A1-integrin, ICAM1-integrin) involving Fibroblasts, Endothelial cells, and Macrophages. Chemokine signaling (e.g., CXCL12-CXCR4, CXCL9-CXCR3) and growth factor signaling (e.g., VEGFA-KDR) are also activated. Immune cell interactions, particularly T cell CD4+ with Macrophages, are evident.
• Chronic Colitis (CC): The CC plot presents a high density of interactions, often with strong intensities, comparable to or even exceeding AC in certain aspects. Many of the same ligand-receptor families observed in AC (integrins, chemokines, VEGFA) are also prominent here. Notably, interactions involving Plasma cells (e.g., Plasma cell with Intestinal Epithelial cell or Fibroblast through integrins and other ligands) appear more frequent and stronger in CC, suggesting their enhanced role in chronic inflammation. SPP1-integrin_avb1 complex interactions, especially involving Intestinal Epithelial cells and Macrophages, also appear pronounced.

Biological Interpretation

The observed cell-cell interaction patterns provide insights into the cellular communication dynamics in the colon during health and inflammatory states, consistent with an IBD/Colitis context.

1. Increased Cellular Cross-Talk in Inflammation (AC & CC): Both acute and chronic colitis conditions are characterized by a substantially enriched and intensified network of cell-cell interactions compared to healthy controls. This reflects the complex interplay between immune cells, stromal cells, and epithelial cells crucial for inflammation, tissue damage, and repair processes.
2. ECM Remodeling and Cell Adhesion:

• Integrin Signaling: Integrin-mediated interactions (e.g., FN1-integrin complexes, COL6A1/2/3-integrin complexes, ICAM1-integrin complexes) are highly active across AC and CC, particularly involving Fibroblasts, Endothelial cells, and Macrophages. These interactions are fundamental for cell adhesion, migration, and extracellular matrix (ECM) remodeling, which are critical in wound healing, fibrosis, and immune cell trafficking during inflammation [GeneCards: Integrin alpha V, GeneCards: Integrin beta 1].
• SPP1 (Osteopontin) Interactions: The SPP1-integrin_avb1 complex shows notable activity, especially in CC, involving Intestinal Epithelial cells and Macrophages. SPP1 is a pleiotropic cytokine implicated in inflammation, immune cell recruitment, and tissue remodeling, often upregulated in chronic inflammatory diseases [UniProt: P10451 (SPP1)]. Its interactions with integrins can modulate macrophage function and epithelial responses.

3. Immune Cell Recruitment and Activation:

• Chemokine Signaling: Chemokine ligand-receptor pairs like CXCL12-CXCR4, CXCL9-CXCR3, CCL2-CCR2, and CCL7-CCR2 are prominent in AC and CC. These pathways are crucial for guiding the migration and localization of immune cells (T cells, Macrophages, ILCs) to sites of inflammation in the colon [PubMed search: Chemokines and IBD].
• T Cell-Macrophage Interactions: The CD28-CD86 interaction (T cell CD4+ -> Macrophage) is visible in AC, indicative of T cell activation by antigen-presenting cells, a key step in adaptive immune responses.

4. Angiogenesis and Vascular Remodeling:

• VEGFA Signaling: Interactions involving VEGFA with its receptors KDR (VEGFR2) and FLT1 (VEGFR1) are significantly upregulated in AC and CC, particularly involving Endothelial cells. This suggests active angiogenesis, a process required to support the metabolic demands of inflamed tissue and facilitate immune cell infiltration [GeneCards: VEGFA, GeneCards: KDR].

5. Role of Specific Cell Types in Disease:

• Macrophages: Are central players, engaging in extensive interactions with T cells, Fibroblasts, and Intestinal Epithelial cells in inflammatory conditions, highlighting their diverse roles in perpetuating and potentially resolving inflammation.
• Fibroblasts: Exhibit strong self-interactions and interactions with immune and endothelial cells, consistent with their role in producing ECM, mediating fibrosis, and orchestrating inflammatory responses.
• Intestinal Epithelial Cells: Show increased communication with immune cells (e.g., Plasma cells, Macrophages) in AC/CC, indicating their compromised barrier function and active participation in immune signaling.
• Plasma Cells: Their enhanced interactions in CC, particularly with Intestinal Epithelial cells and Fibroblasts, suggest a contribution to chronic inflammation, potentially through local antibody production and immune complex formation.

Clinical or Translational Implications

The differential cell-cell interaction patterns identified in AC and CC offer several avenues for therapeutic development and experimental validation in the context of IBD/Colitis.

1. Therapeutic Target Prioritization:

• Integrin Antagonism: Given the widespread and strong integrin-mediated interactions in both AC and CC, targeting specific integrin complexes (e.g., FN1-integrin_avb1, ICAM1-integrin) could modulate immune cell trafficking, reduce fibrotic responses, and improve gut barrier function. Specific integrin antagonists are already used or under investigation for IBD [PubMed search: Integrin antagonists IBD].
• Chemokine Pathway Inhibition: Blocking key chemokine axes like CXCL12-CXCR4 or CXCL9-CXCR3 could limit the recruitment of pathogenic immune cells to the inflamed colon, thereby reducing inflammation.
• VEGFA Pathway Modulation: While angiogenesis is crucial for repair, excessive or dysregulated VEGFA signaling can contribute to chronic inflammation and vascular leak. Targeting VEGFA-KDR/FLT1 interactions could normalize vascular function in chronic colitis.
• SPP1 Inhibition: Given SPP1's role in inflammation and fibrosis and its increased interactions in CC, inhibiting SPP1 or its integrin binding could be a strategy for chronic IBD.

2. Biomarker Discovery: Specific ligand-receptor pairs that are highly active and unique to AC or CC could serve as potential diagnostic or prognostic biomarkers for disease activity or progression. For example, patterns involving Plasma cells in CC might indicate disease chronicity.
3. Experimental Validation Strategies: The identified interactions provide a strong basis for further experimental validation.

• In vitro Co-culture Models: Specific cell pairs and their interacting ligand-receptor components (e.g., Macrophage-Fibroblast with FN1-integrin; Intestinal Epithelial cell-Plasma cell with SPP1-integrin) could be investigated in co-culture systems to confirm functional consequences (e.g., cytokine production, cell migration, matrix deposition).
• In vivo Functional Studies: Using genetic models (e.g., conditional knockouts) or pharmacological inhibitors targeting the most prominent ligand-receptor pairs in mouse models of colitis could validate their causal roles in disease pathogenesis and therapeutic potential.
• Spatial Transcriptomics/Proteomics: To confirm spatial localization and direct physical interaction of these identified cell-cell interaction pairs in inflamed colon tissue.

10. Condition-Specific Cell-Cell Interaction Patterns in Mouse Colon IBD Model

[Analysis Visualization Results]...

Analysis Overview

This analysis investigates condition-specific cell-cell interactions (CCIs) in mouse colon single-cell RNA-seq data, focusing on Inflammatory Bowel Disease (IBD)/Colitis models (AC, CC conditions) compared to a Healthy Control (HC) condition. The plot_dot_for_cci_with_signif_difference tool was used to identify and visualize significant CCIs among major tissue cells (Intestinal Epithelial cell, Endothelial cell, Stromal cell) and immune cells (Myeloid cell, T cell, B cell, Plasma cell). The dot plot displays the scaled interaction strength (color intensity) and significance (-log10(p-value), dot size) for each sample and CCI pair, revealing patterns of intercellular communication dysregulation in disease states.

Visual Summary

The dot plot, showing "Condition-specific CCI pattern", clearly differentiates intercellular communication landscapes across the conditions.

• Disease Conditions (AC and CC): Samples from both AC and CC conditions exhibit a widespread and robust pattern of cell-cell interactions. The dots are predominantly large and dark red, indicating both high statistical significance (large dot size, corresponding to low p-values) and strong interaction strength (dark red color). This suggests a highly active and extensive network of cell-cell communication in the inflamed colon. The blue boxes highlight that these conditions show consistently strong interactions across many cell-cell and gene-pair combinations.
• Healthy Control Condition (HC): In stark contrast, HC samples display very few significant or strong cell-cell interactions. The dots are generally small and light red or almost invisible, reflecting low significance and weak interaction strength. This indicates a much less active intercellular communication network in the healthy state. While a small subset of interactions (e.g., Fib | Fib, Fib | Ent.Epi, Ent.Epi | Ent.Epi, Ent.Epi | Mac) show some activity in HC, their strength and number are substantially lower than in AC/CC.
• Overall Pattern: The visualization strikingly demonstrates a profound upregulation and diversification of cell-cell interactions in the AC and CC inflammatory conditions compared to the healthy control, spanning interactions between various immune, stromal, and epithelial cell types.

Biological Interpretation

The observed surge in cell-cell interactions in the AC and CC conditions aligns strongly with the pathological processes of Inflammatory Bowel Disease (IBD)/Colitis. Inflammation involves a complex interplay of immune cells, stromal cells, and epithelial cells, orchestrating immune responses, tissue damage, and repair attempts. The differential CCIs highlight key pathways likely driving disease pathogenesis.

Prominent interactions observed in AC and CC conditions include:

Immune Cell Recruitment and Adhesion:

• VCAM1_integrin_a4b7_complex -- Endo | T CD4+ and MADDAM1_integrin_a4b7_complex -- Endo | T CD4+: These interactions are critical for the trafficking of T cells, particularly CD4+ T cells, from the bloodstream into the inflamed gut lamina propria. VCAM1 and MAdCAM1 are adhesion molecules expressed by endothelial cells, which bind to the α4β7 integrin on lymphocytes. This is a hallmark of intestinal inflammation and a major mechanism for sustained immune cell infiltration [1, 2].
• ICAM1_integrin_aLb2_complex -- Endo | T CD4+: ICAM1 on endothelial cells binding to LFA-1 (αLβ2 integrin) on T cells is another crucial adhesion pathway for immune cell extravasation into inflamed tissues [3].
• PVR_CD96 -- T CD4+ | Endo: PVR (CD155) and CD96 are involved in immune cell adhesion and activation, potentially mediating communication between T cells and endothelial cells.

Inflammatory Signaling and Immune Modulation:

• DLL4_NOTCH1/2 -- Endo | Endo (and other DLL4-NOTCH interactions): Notch signaling plays crucial roles in vascular development, angiogenesis, and immune cell differentiation, and its dysregulation is implicated in chronic inflammation and IBD [4].
• TGFB1_TGFbeta_receptor -- Fib | Endo: TGF-β signaling is a pleiotropic pathway involved in regulating immune responses, fibrosis, and epithelial regeneration. Its activation in IBD can contribute to both immune suppression and pathological fibrosis [5].
• ProstaglandinE2_byPTGES3_PTGER4 -- Endo | Mac: Prostaglandin E2 (PGE2) is a potent lipid mediator with diverse roles in inflammation, immune modulation, and tissue repair. This interaction suggests active PGE2 signaling between endothelial cells and macrophages, contributing to the inflammatory milieu [6].
• SEMA4D_PLXNB1 -- T CD4+ | T CD4+: Semaphorins are involved in immune cell migration and activation, indicating potential T cell-T cell communication regulating immune responses.

Tissue Remodeling and Fibrosis:

• COL15A1_integrin_a11b1 -- Fib | Fib: Collagen XV is a component of the extracellular matrix (ECM). Its interaction with integrin α11β1 on fibroblasts suggests active ECM remodeling and potentially fibrosis, a common complication in chronic IBD [7].
• HBEGF_EGFR -- Endo | Ent.Epi: HBEGF-EGFR signaling promotes cell proliferation, migration, and survival, important for tissue repair but also potentially contributing to pathological processes in chronic inflammation.
• BMP2_BMPR1A_BMPR2 -- Ent.Epi | Fib: Bone Morphogenetic Protein (BMP) signaling is critical for intestinal epithelial homeostasis, differentiation, and interaction with stromal cells. Dysregulation can impact tissue repair and contribute to inflammation [8].

Vascular Dynamics:

• ANGPT1_TEK -- Endo | Endo: Angiopoietin-1 and its receptor TEK (Tie2) are essential for vascular stability and integrity. Altered Angiopoietin-Tie2 signaling can contribute to pathological angiogenesis and vascular leakage in inflammation [9].

The striking difference between the diseased and healthy states underscores the dynamic cellular interactions that underpin IBD pathology, involving critical pathways in immune cell trafficking, inflammatory signaling, and tissue remodeling.

Clinical or Translational Implications

The identified condition-specific cell-cell interactions offer valuable insights for potential diagnostic, prognostic, and therapeutic strategies in IBD.

Therapeutic Targets for Immune Cell Trafficking:

• Integrin α4β7 / MAdCAM1 Axis: The prominent VCAM1_integrin_a4b7_complex and MADDAM1_integrin_a4b7_complex interactions are well-established targets in IBD. Therapeutic agents like Vedolizumab (targeting α4β7 integrin) specifically block the migration of gut-homing lymphocytes into the inflamed intestine, demonstrating clinical efficacy in IBD [10]. Other integrins such as ICAM1_integrin_aLb2_complex (LFA-1) could also be considered for broad anti-inflammatory strategies.
• New Adhesion Molecules: Other significant adhesion interactions, such as those involving SEMA-Plexin family members, could represent novel targets to modulate immune cell activity and migration within the inflamed gut.

Modulation of Inflammatory Pathways:

• Notch Signaling (DLL4-NOTCH): Given its multifaceted roles in angiogenesis, immune cell differentiation, and epithelial repair, targeting specific components of the Notch pathway could offer therapeutic benefits. Selective Notch inhibitors or activators are being explored for various inflammatory conditions [4].
• TGF-β Signaling: While complex, the strong TGFB1_TGFbeta_receptor -- Fib | Endo interaction suggests that modulating specific aspects of TGF-β signaling, perhaps to prevent fibrosis while maintaining beneficial immune regulation, could be a therapeutic avenue in IBD, though challenges exist due to its pleiotropic nature [5].
• Prostaglandin E2 Pathway: The identified ProstaglandinE2_byPTGES3_PTGER4 -- Endo | Mac interaction points to PGE2 as a key inflammatory mediator. Targeting specific PGE2 receptors (e.g., EP4) could offer anti-inflammatory effects with fewer side effects than general COX inhibitors [6].

Biomarkers of Disease Activity:

• The specific ligand-receptor pairs that are highly active in AC/CC but minimal in HC could serve as biomarkers for IBD activity or severity. Monitoring their expression or interaction strength in patient biopsies or circulating cells could aid in diagnosis, prognosis, or response to therapy. For instance, increased expression of MAdCAM1 or VCAM1 on endothelial cells in the colon is a known feature of intestinal inflammation.

Further research focusing on the specific molecular mechanisms and functional consequences of these upregulated CCIs could reveal more precise therapeutic targets and contribute to the development of personalized medicine approaches for IBD.

References:

[1] VCAM1 (Vascular Cell Adhesion Molecule 1) - GeneCards: https://www.genecards.org/cgi-bin/carddisp.pl?gene=VCAM1

[2] MAdCAM1 (Mucosal Vascular Adressin Cell Adhesion Molecule 1) - GeneCards: https://www.genecards.org/cgi-bin/carddisp.pl?gene=MADCAM1

[3] ICAM1 (Intercellular Adhesion Molecule 1) - GeneCards: https://www.genecards.org/cgi-bin/carddisp.pl?gene=ICAM1

[4] Notch signaling in IBD - PubMed search: https://pubmed.ncbi.nlm.nih.gov/?term=Notch+signaling+IBD

[5] TGFB1 (Transforming Growth Factor Beta 1) - GeneCards: https://www.genecards.org/cgi-bin/carddisp.pl?gene=TGFB1

[6] Prostaglandin E2 in inflammation - PubMed search: https://pubmed.ncbi.nlm.nih.gov/?term=Prostaglandin+E2+inflammation

[7] Collagen XV and fibrosis - PubMed search: https://pubmed.ncbi.nlm.nih.gov/?term=Collagen+XV+fibrosis

[8] BMP signaling in intestinal homeostasis - PubMed search: https://pubmed.ncbi.nlm.nih.gov/?term=BMP+signaling+intestinal+homeostasis

[9] ANGPT1 (Angiopoietin 1) - GeneCards: https://www.genecards.org/cgi-bin/carddisp.pl?gene=ANGPT1

[10] Vedolizumab mechanism of action - PubMed search: https://pubmed.ncbi.nlm.nih.gov/?term=Vedolizumab+mechanism+IBD

11. Intestinal Epithelial Cell Surfaceome Markers in Colitis Conditions (AC, CC) vs. Healthy Control (HC)

[Analysis Visualization Results]...

Analysis Overview

This analysis identifies condition-specific surfaceome markers within the Intestinal Epithelial cell population from mouse colon single-cell RNA-seq data, comparing two colitis conditions (AC, CC) against a healthy control (HC). The dot plot visualizes the mean expression and fraction of cells expressing these markers across individual samples within each condition. Surfaceome markers are particularly relevant for cell-cell interactions, signaling, and as potential therapeutic targets due to their accessibility.

The markers were selected based on differential expression criteria:

AC vs. HC: nz_pct_score ≥ 0.133, nz_pct_FC > 1.25

CC vs. HC: nz_pct_score ≥ 0.167, nz_pct_FC > 1.31

HC vs. others: nz_pct_score ≥ 0.167, nz_pct_FC > 1.31

Visual Summary

The dot plot clearly segregates Intestinal Epithelial cell surfaceome marker expression patterns by condition (AC, CC, HC).

• AC Condition: Samples AC1 and AC3 show a strong and specific upregulation of a distinct set of markers (e.g., CdhR5, Emp1, Prom1, Duox2, Sema4a, Itga3, Itgav, Ceacam20). These markers exhibit high mean expression (darker red color) and are present in a large fraction of cells (larger dot size) within AC samples, while being minimally expressed in CC and HC.
• CC Condition: Samples CC1, CC2, CC3, and CC4 also display a unique set of markers (e.g., Ptprh, Gpr137b, Slc26a3, Abcg2). While some markers like Prom1, Duox2, and Itgav show expression in both AC and CC to varying degrees, a core group is more prominent in CC than AC or HC.
• HC Condition: Healthy control samples (HC1, HC2, HC3) are characterized by the predominant expression of a large cluster of markers (e.g., Egfr, Slc5a8, Aqp4, Lrig3, Dpp4, Ephb4, Fgfr2). These genes show high expression levels and prevalence in HC samples and are largely downregulated or absent in the AC and CC colitis conditions.
• Overall Pattern: The visualization effectively highlights condition-specific molecular signatures on the surface of Intestinal Epithelial cells, indicating distinct cellular adaptations or dysfunctional states in AC and CC colitis compared to health. The observed markers offer insights into potential mechanistic changes at the epithelial surface during IBD.

Biological Interpretation

Markers Upregulated in Acute Colitis (AC)

The Intestinal Epithelial cells in the AC condition show increased expression of several surfaceome markers, suggesting cellular responses to acute inflammation, including altered barrier function, oxidative stress, and regenerative attempts.

• CdhR5 (Cadherin-5 / VE-cadherin): While primarily associated with endothelial cells, its upregulation in epithelial cells in AC might indicate epithelial-mesenchymal transition (EMT)-like processes or altered cell adhesion dynamics critical for barrier repair, potentially contributing to or resulting from compromised epithelial barrier integrity characteristic of IBD PubMed search: cadherin-5 intestinal epithelium IBD.
• Emp1 (Epithelial Membrane Protein 1): Involved in cell growth and differentiation. Elevated Emp1 can reflect cellular stress or dysregulated proliferation in inflamed epithelial tissues, possibly impacting tissue remodeling and repair processes in IBD.
• Prom1 (Prominin 1 / CD133): A well-known stem cell marker, particularly for intestinal stem cells. Its increased expression suggests enhanced stem cell activity or progenitor cell expansion, likely representing an attempt at epithelial regeneration and repair in response to inflammatory damage GeneCards: Prom1.
• Duox2 (Dual oxidase 2): An NADPH oxidase producing reactive oxygen species (ROS). Upregulation points to increased oxidative stress and innate immune responses within epithelial cells. While important for host defense, excessive ROS can contribute to epithelial damage and sustained inflammation in IBD PubMed search: DUOX2 IBD oxidative stress.
• Sema4a (Semaphorin 4A): Plays roles in immune regulation, modulating T cell activation and cytokine production. Its presence on epithelial cells in AC could influence immune cell interactions at the mucosal surface, potentially contributing to pro-inflammatory signaling.
• Itga3 (Integrin alpha 3) and Itgav (Integrin alpha V): These integrins mediate cell adhesion to the extracellular matrix (ECM) and cell-cell interactions. Upregulation can signify altered epithelial adhesion, migration, and remodeling during inflammation. Itgav, particularly when paired with beta subunits like beta 6 (αvβ6), can activate latent TGF-β, promoting fibrosis and chronic inflammation in the gut PubMed search: integrin alpha v beta 6 IBD.
• Ceacam20 (Carcinoembryonic Antigen-related Cell Adhesion Molecule 20): Members of the CEACAM family are involved in cell adhesion, signaling, and host-pathogen interactions. Its upregulation may reflect altered epithelial cell-cell communication or adaptation to microbial challenges in the inflamed colon.

Markers Upregulated in Chronic Colitis (CC)

The CC condition shows a distinct set of surfaceome markers, possibly indicating chronic adaptation mechanisms and sustained dysfunction.

• Ptprh (Protein Tyrosine Phosphatase Receptor Type H): As a receptor-type protein tyrosine phosphatase, Ptprh can regulate signaling pathways critical for cell growth, differentiation, and inflammation. Its upregulation might modulate chronic inflammatory responses by dephosphorylating key signaling molecules.
• Gpr137b (G Protein-Coupled Receptor 137B): An orphan GPCR. GPCRs are crucial for sensing environmental cues and modulating cellular functions. Its specific role in intestinal epithelial cells in IBD is not fully elucidated, but it could be involved in sensing inflammatory mediators or regulating epithelial homeostasis in a chronic context.
• Slc26a3 (Solute Carrier Family 26 Member A3 / DRA): A chloride/bicarbonate exchanger vital for intestinal fluid and electrolyte balance. Its dysregulation in CC could contribute to the chronic diarrheal symptoms often seen in IBD patients, reflecting impaired epithelial transport function GeneCards: SLC26A3.
• Abcg2 (ATP Binding Cassette Subfamily G Member 2 / BCRP): An efflux transporter for various substrates, including drugs and toxins. Its increased expression in CC could be a protective mechanism against inflammatory insults or contribute to altered drug responses seen in chronic IBD treatment.

Markers Downregulated in Colitis (HC-specific)

Markers predominantly expressed in healthy Intestinal Epithelial cells (HC) and downregulated in AC and CC conditions suggest a loss of normal epithelial functions critical for maintaining gut homeostasis.

• Egfr (Epidermal Growth Factor Receptor): A receptor tyrosine kinase essential for epithelial cell proliferation, differentiation, and survival, and critically involved in mucosal repair and wound healing in the gut. Its downregulation in colitis conditions suggests impaired epithelial regenerative capacity UniProt: EGFR mouse.
• Slc5a8 (Solute Carrier Family 5 Member 8 / SMCT1): A sodium-coupled monocarboxylate transporter that imports short-chain fatty acids (SCFAs), like butyrate, which are crucial energy sources for colonocytes and possess anti-inflammatory properties. Reduced Slc5a8 could lead to energy deficit in colonocytes and impaired mucosal integrity in IBD PubMed search: SLC5A8 butyrate IBD.
• Aqp4 (Aquaporin 4): A water channel protein involved in water transport. Its downregulation could contribute to altered fluid dynamics and diarrheal symptoms in IBD.
• Lrig3 (Leucine-rich repeat and immunoglobulin-like domain-containing Nogo receptor-interacting protein 3): Generally regulates receptor tyrosine kinase signaling (e.g., EGFR). Its downregulation could lead to aberrant or uncontrolled growth factor signaling, or reflect a disrupted regulatory loop in inflamed tissue.
• Dpp4 (Dipeptidyl Peptidase 4 / CD26): An enzyme with diverse roles in immune modulation and peptide metabolism. Its decreased expression might alter local chemokine/cytokine bioavailability or T cell co-stimulation at the epithelial surface in IBD.
• Ephb4 (Ephrin Type-B Receptor 4): Involved in cell-cell communication, intestinal crypt-villus axis patterning, and stem cell positioning. Reduced Ephb4 could impair the structural integrity and regenerative capacity of the intestinal epithelium, hindering proper mucosal healing GeneCards: EPHB4.
• Fgfr2 (Fibroblast Growth Factor Receptor 2): A receptor tyrosine kinase for FGFs, crucial for epithelial cell proliferation, differentiation, and tissue repair. Its downregulation indicates impaired responsiveness to regenerative signals from FGFs in the inflamed gut.

Clinical or Translational Implications

The identified condition-specific surfaceome markers in Intestinal Epithelial cells offer several clinical and translational avenues for Inflammatory Bowel Disease (IBD) / Colitis:

1. Diagnostic and Prognostic Biomarkers:

• AC-specific markers (e.g., CdhR5, Prom1, Duox2, Itga3, Itgav) could serve as indicators of acute inflammation, active epithelial stress, or regenerative efforts. Their detection in tissue biopsies or potentially shed epithelial cells could help in diagnosing active phases of IBD or monitoring disease progression.
• HC-specific markers (e.g., Egfr, Slc5a8, Ephb4, Fgfr2) represent healthy epithelial function. Their absence or significant downregulation could indicate chronic epithelial dysfunction and impaired healing, potentially useful for assessing disease severity and prognosis for mucosal healing.

2. Therapeutic Targets for IBD:

• Modulating Epithelial Barrier Function: Upregulation of integrins like Itga3 and Itgav (especially αvβ6) in AC suggests their involvement in altered adhesion and fibrotic processes. Inhibitors targeting specific integrins on epithelial cells, distinct from those on immune cells (e.g., Vedolizumab targeting α4β7 on immune cells), could offer strategies to restore epithelial integrity or mitigate fibrosis.
• Targeting Oxidative Stress: Increased Duox2 in AC highlights oxidative stress. Antioxidant therapies or specific inhibitors of excessive DUOX activity could reduce epithelial damage and inflammation.
• Enhancing Epithelial Regeneration: Downregulation of crucial receptors like Egfr, Ephb4, and Fgfr2 in colitis conditions suggests impaired regenerative capacity. Therapeutic strategies focusing on delivering growth factors (e.g., FGFs) or agonists for these receptors could promote mucosal healing and repair.
• Restoring Metabolic Homeostasis: Reduced Slc5a8 in colitis implies impaired SCFA uptake, impacting colonocyte health. Nutritional interventions with SCFAs (e.g., butyrate enemas/supplements) or agents promoting Slc5a8 expression could support epithelial health and anti-inflammatory pathways.
• Specific Ion Channel Modulators: Dysregulation of Slc26a3 in CC could be addressed by pharmacological agents that restore normal chloride/bicarbonate exchange, potentially alleviating chronic diarrhea symptoms.

3. Drug Development and Repurposing:

• The identified GPCRs (e.g., Gpr137b) and phosphatases (e.g., Ptprh) in CC, while currently less characterized in IBD, represent classes of proteins that are highly "druggable." Further research into their ligands and downstream pathways could uncover novel therapeutic targets for chronic colitis.
• Understanding the role of Abcg2 in CC could be important for optimizing drug delivery and overcoming potential drug resistance in IBD treatments.

These findings underscore the epithelial cell as a dynamic player in IBD pathogenesis, presenting a rich array of surface targets for future therapeutic development and personalized medicine approaches.

12. Macrophage Condition-Specific Surfaceome Markers in Colitis

[Analysis Visualization Results]...

Analysis Overview

This analysis identifies condition-specific surfaceome markers in macrophages from mouse colon single-cell RNA-seq data, comparing two disease conditions, AC (Acute Colitis) and CC (Chronic Colitis), against a Healthy Control (HC) condition. The dot plot visualizes the expression of these markers across individual samples within each condition. Dot size indicates the fraction of cells expressing the marker, while dot color represents the mean expression level in those cells. The goal is to highlight surface markers that differentiate macrophage states in IBD/Colitis, providing insights into signaling pathways and potential therapeutic targets.

Visual Summary

The dot plot, titled "Macrophage condition-specific markers," effectively displays changes in surface marker expression across different samples and conditions.

• Disease vs. Healthy: A striking pattern is the extensive upregulation of numerous surface markers in both AC and CC conditions compared to HC. Macrophages from healthy samples (HC1, HC3, HC2) show minimal to no expression of most identified markers, indicated by small, pale dots or white spaces.

Condition-Specific Patterns:

• AC Markers: The AC samples (AC2, AC3, AC1) exhibit high expression and prevalence for a distinct set of markers located on the left side of the plot. Notable examples include *Gpr132*, *Csf2rb*, *Rnf149*, and *Ptafr*.
• CC Markers: The CC samples (CC3, CC2, CC4, CC1) also show a strong upregulation of markers, with some overlap with AC markers, but also a specific cluster of highly expressed markers on the far right (e.g., *Cd63*, *Mrc1*, *C3ar1*, *Adgre1*, *Pmeap1*, *Tgfbr2*). These markers appear particularly elevated in CC3 and CC2 samples.
• Shared Upregulation: Many markers are highly expressed in both AC and CC conditions compared to HC, such as *Tnfrsf1b*, *Sppl2a*, *Selplg*, *Tmem123*, *Emb*, *Itgam*, *Furin*, *Ifnar1*, *Cd274*, *Lrrc25*, *Igsf6*, *Itgb2*, *Tcirg1*, *Slc8b1*, *Ifngr1*, *Ifngr2*, *Lrp10*, *Sema4d*, *Mmp14*, *Itga5*, *Il10ra*, *Lrp1*, *Tlr2*, and *Adam8*. This suggests a generalized inflammatory or activated macrophage phenotype in colitis, regardless of the specific disease state (AC vs. CC).
• Heterogeneity within Conditions: Even within the AC and CC conditions, there is some variability across individual samples, reflected in slight differences in dot size and color saturation. For instance, in CC, samples CC3 and CC2 often show higher expression levels than CC4 and CC1 for certain markers (e.g., *Mrc1*, *Adgre1*).

Biological Interpretation

The differential expression of macrophage surface markers provides crucial insights into the functional states of these cells during colitis. Macrophages are pivotal immune cells in IBD, modulating both pro-inflammatory and anti-inflammatory responses. The observed marker profiles suggest distinct macrophage activation states associated with different phases or types of colitis (AC vs. CC).

Key Macrophage Surface Markers and Their Biological Significance:

1. Gpr132 (G Protein-coupled Receptor 132) - *Prominent in AC samples*

• Signaling/Mechanism: Gpr132 is a G protein-coupled receptor (GPCR) that binds lysophosphatidic acid (LPA) and other lipid mediators. It is involved in various cellular processes, including cell migration, proliferation, and inflammation. In immune cells, Gpr132 can modulate cytokine production and contribute to inflammatory responses. Its upregulation in AC macrophages suggests a potential role in initiating or propagating acute inflammation.
• IBD Relevance: Dysregulation of LPA signaling has been implicated in inflammatory conditions. Targeting GPCRs like Gpr132 could modulate macrophage activation and migration, potentially dampening acute inflammatory bursts in IBD.
• Therapeutic Potential: Modulators of GPCR signaling pathways are a growing area of drug development. Antagonists for Gpr132 could be explored to limit pro-inflammatory macrophage functions, though specific agents for IBD are not yet established. GeneCards: GPR132

2. C3ar1 (Complement C3a Receptor 1) - *Highly expressed in CC, also present in AC*

• Signaling/Mechanism: C3ar1 is a receptor for C3a, an anaphylatoxin derived from the complement system. Activation of C3ar1 by C3a leads to intracellular signaling cascades (e.g., via G proteins) that promote pro-inflammatory responses, including cytokine release, chemotaxis, and phagocytosis.
• IBD Relevance: The complement system is known to be activated in IBD, contributing to intestinal inflammation. Upregulation of C3ar1 on macrophages in both AC and CC suggests a sustained involvement of complement-mediated inflammation, particularly in the chronic phase.
• Therapeutic Potential: C3ar1 antagonists have been investigated for various inflammatory diseases, including models of colitis, to block the pro-inflammatory effects of C3a. PubMed search: C3ar1 IBD therapy

3. Cd274 (PD-L1 - Programmed Death-Ligand 1) - *Upregulated in AC and CC*

• Signaling/Mechanism: PD-L1 is an immune checkpoint molecule that binds to PD-1 on T cells, inhibiting T cell activation and promoting immune tolerance. On macrophages, PD-L1 expression can mediate immunosuppression, preventing excessive inflammation and tissue damage. However, in chronic inflammation, its persistent expression can also lead to T cell exhaustion.
• IBD Relevance: PD-L1 expression is often increased on immune cells in inflamed IBD tissues, potentially acting as a feedback mechanism to limit overt inflammation. Its role is complex; while it can promote immune regulation, targeting it (e.g., with anti-PD-L1 antibodies) might inadvertently exacerbate inflammation if not carefully considered.
• Therapeutic Potential: While PD-1/PD-L1 blockade is a cornerstone of cancer immunotherapy, its application in IBD is complex. Enhancing PD-L1 signaling might be considered to promote immune tolerance, but direct therapeutic strategies are not yet clear and could have opposing effects in different disease contexts. UniProt: P97305 (CD274_MOUSE)

4. Mrc1 (CD206 - Mannose Receptor C-type 1) - *Highly expressed in CC samples*

• Signaling/Mechanism: Mrc1 is a C-type lectin receptor predominantly expressed on M2 macrophages. It mediates endocytosis of mannosylated ligands, plays a role in pathogen recognition, efferocytosis (clearance of apoptotic cells), and antigen presentation. M2 macrophages are generally associated with anti-inflammatory responses, tissue repair, and immune regulation, although distinct M2 subsets exist with varied functions.
• IBD Relevance: The prominent upregulation of Mrc1 in CC suggests a shift towards an M2-like macrophage phenotype in chronic colitis. This could represent an attempt at tissue repair and resolution, or it might indicate a maladaptive M2 response contributing to fibrosis or impaired pathogen clearance in chronic inflammation.
• Therapeutic Potential: Modulating macrophage polarization towards a truly reparative M2 phenotype could be a therapeutic strategy. For instance, promoting M2 differentiation or specific Mrc1-mediated functions might aid in resolving chronic inflammation and promoting mucosal healing. GeneCards: MRC1

5. Adgre1 (F4/80 - Adhesion G Protein-Coupled Receptor E1) - *Highly expressed in CC samples*

• Signaling/Mechanism: F4/80 is a classical and widely used marker for mouse macrophages, particularly tissue-resident macrophages. It is an adhesion GPCR, involved in cell-cell interactions, macrophage differentiation, and immune regulation. While not fully understood, its signaling can influence macrophage activation states.
• IBD Relevance: High expression in CC suggests a robust presence of tissue-resident or differentiated macrophages in the chronic inflammatory milieu. These F4/80-positive macrophages can have diverse roles, from phagocytosis to cytokine production and tissue remodeling in the inflamed colon.
• Therapeutic Potential: While F4/80 itself is not a direct therapeutic target, its high expression in CC indicates that these macrophages are a significant population to consider for cell-specific therapeutic delivery or immunomodulation strategies. UniProt: P17441 (ADGRE1_MOUSE)

6. Tgfbr2 (Transforming Growth Factor Beta Receptor 2) - *Highly expressed in CC samples*

• Signaling/Mechanism: Tgfbr2 is a transmembrane serine/threonine kinase receptor that binds to TGF-beta, initiating downstream signaling pathways (primarily Smad-dependent). TGF-beta signaling is crucial for immune homeostasis, tissue repair, and fibrosis. In the context of macrophages, TGF-beta can induce M2 polarization, suppress pro-inflammatory cytokine production, and promote extracellular matrix deposition.
• IBD Relevance: TGF-beta plays a dual role in IBD: it can be anti-inflammatory and promote mucosal healing, but sustained signaling can also lead to fibrosis, a complication in chronic IBD. Its upregulation in CC macrophages could reflect an attempt at immune suppression and tissue repair, or contribute to fibrotic changes.
• Therapeutic Potential: Modulating TGF-beta signaling is complex due to its pleiotropic effects. Therapies aimed at balancing its pro-healing and pro-fibrotic functions in chronic colitis are an area of research, potentially involving specific receptor antagonists or agonists tailored to the disease stage. GeneCards: TGFBR2

7. Itgam (CD11b - Integrin Alpha M) - *Upregulated in AC and CC*

• Signaling/Mechanism: CD11b forms a heterodimer with CD18 (Itgb2) to create Macrophage-1 Antigen (Mac-1) or Complement Receptor 3 (CR3). This integrin is critical for cell adhesion, migration, phagocytosis of opsonized particles, and interaction with various ligands on endothelial cells and other immune cells. It plays a significant role in leukocyte extravasation and inflammatory responses.
• IBD Relevance: Upregulation of CD11b on macrophages in both disease states signifies their active involvement in inflammation, adhesion to endothelium, and infiltration into the inflamed tissue. It is a general marker of myeloid cell activation.
• Therapeutic Potential: Integrins are well-established therapeutic targets in IBD (e.g., vedolizumab targets α4β7 integrin). While CD11b is broadly expressed, strategies to modulate its specific interactions or downstream signaling in inflammatory macrophages could be considered to limit their pathogenic activity. PubMed search: CD11b macrophage IBD

8. Tlr2 (Toll-like Receptor 2) - *Upregulated in AC and CC*

• Signaling/Mechanism: Tlr2 is an innate immune receptor that recognizes conserved molecular patterns from various microbes (PAMPs, e.g., bacterial lipoproteins, peptidoglycan) and endogenous danger signals (DAMPs). Upon ligand binding, Tlr2 initiates downstream signaling cascades (e.g., NF-κB pathway) leading to the production of pro-inflammatory cytokines.
• IBD Relevance: Dysregulated microbial sensing and increased bacterial translocation are hallmarks of IBD. Upregulation of Tlr2 on macrophages indicates an enhanced capacity to respond to luminal bacteria or their products, contributing to the sustained inflammatory environment in colitis.
• Therapeutic Potential: Targeting TLR pathways is a strategy for modulating innate immunity. Inhibitors of Tlr2 signaling could potentially dampen excessive inflammation in IBD, although care must be taken to avoid compromising host defense against beneficial microbes. GeneCards: TLR2

Clinical or Translational Implications

The identification of condition-specific surfaceome markers on macrophages in colitis has several clinical and translational implications:

1. Biomarker Discovery: The differentially expressed surface markers could serve as diagnostic or prognostic biomarkers for distinguishing different disease activity states (AC vs. CC) or predicting treatment response in IBD. For instance, high *Mrc1* and *Tgfbr2* in CC might indicate a chronic, potentially fibrotic, disease phenotype.
2. Therapeutic Target Identification:

• Direct Targeting: Surface receptors like *C3ar1*, *Gpr132*, or *Tlr2* represent potential therapeutic targets. Blocking *C3ar1* or *Tlr2* might reduce pro-inflammatory signaling, while modulating *Gpr132* could impact macrophage migration and activation.
• Immune Checkpoint Modulation: The upregulation of *Cd274* (PD-L1) highlights the complex interplay of pro-inflammatory and immunoregulatory mechanisms. Strategies to either enhance or block PD-L1 signaling in macrophages could be explored, depending on whether the goal is to promote immune tolerance or enhance anti-pathogen responses, respectively.
• Macrophage Reprogramming: The distinct profiles (e.g., Mrc1 upregulation in CC suggesting M2-like polarization) indicate that macrophages adopt different functional states. Therapies aimed at reprogramming macrophages towards truly anti-inflammatory and pro-resolving phenotypes could be beneficial in IBD.

3. Drug Development: The identified markers provide molecular handles for developing novel therapeutic agents, such as specific antibodies, small molecule inhibitors, or cell-specific delivery systems to target pathogenic macrophage subsets in IBD. For example, specific Mrc1-targeted drug delivery could be envisioned.
4. Stratification of Patients: Understanding the macrophage surfaceome landscape could enable better stratification of IBD patients for personalized medicine, matching specific immunomodulatory therapies to the patient's predominant macrophage phenotype.

These findings highlight the dynamic and heterogeneous nature of macrophage responses in IBD, underscoring the potential for targeted interventions based on specific surface marker profiles.

13. Fibroblast Condition-Specific Surfaceome Markers in Mouse Colon

[Analysis Visualization Results]...

Analysis Overview

This analysis identifies and visualizes condition-specific surfaceome markers within the Fibroblast cell population across three experimental conditions: Acute Colitis (AC), Chronic Colitis (CC), and Healthy Control (HC), in mouse colon tissue. The identification of markers was performed using a comparative approach against the healthy control or other conditions, applying specific thresholds for non-zero percentage score and fold change (AC vs. HC: nz_pct_score ≥ 0.183, nz_pct_FC > 1.25; CC vs. HC: nz_pct_score ≥ 0.167, nz_pct_FC > 1.25; HC vs. others: nz_pct_score ≥ 0.133, nz_pct_FC > 1.25). The dot plot displays the mean expression level (color intensity) and the fraction of cells expressing each marker (dot size) for individual samples within each condition group. The primary goal is to interpret the biological roles and therapeutic potential of these surface-expressed markers in the context of Inflammatory Bowel Disease (IBD) / Colitis.

Visual Summary

The dot plot effectively illustrates distinct expression profiles of surfaceome markers across the different conditions and individual samples within those conditions.

• Condition AC (Acute Colitis): This group (samples AC1, AC2, AC3) shows a strong upregulation of several markers, notably *Il1r1*, *Susd6*, *Osmr*, *Ednra*, *Steap4*, *Ereg*, *Pdgfrb*, *Cd74*, *Itga1*, *Tspan4*, *Atp2b4*, and *Sirpa*. These markers exhibit both high mean expression (dark red) and high prevalence (large dot size) within AC fibroblasts, particularly in samples like AC2.
• Condition CC (Chronic Colitis): Fibroblasts in the CC group (samples CC1, CC2, CC3, CC4) display a different set of highly expressed and prevalent markers, including *Adgrl1*, *Ano6*, *Crim1*, *Aoc3*, *M6pr*, *Rell1*, *Pla2r1*, *Abcc9*, *Suco*, *Ptpnrf*, *Thy1*, *Slc12a2*, *Pcdh19*, *Adam10*, *Lrrc32*, *Ifngr2*, *Sema4c*, *Cd200*, *Cspg4*, *Itga4*, *Procr*, *Mcam*, *Esam*, *Atp1b2*, and *Notch3*. There is some overlap with AC markers (e.g., *Il1r1*, *Susd6*, *Osmr*, *Rnf150*), but distinct marker sets indicate different fibroblast activation states or subpopulations between AC and CC. For instance, *Thy1* and *Notch3* are highly prominent in CC.
• Condition HC (Healthy Control): The HC group (samples HC1, HC2, HC3) presents a profile characterized by high expression of markers such as *Emp1*, *Lpar1*, *Ptgfrn*, *Pdgfra*, *Cd34*, *Ptch1*, *Clmp*, *Pcdh7*, *Atraid*, *Cd55*, *Ncam1*, *Antxr2*, *Sgce*, *Acvrl1*, *Cd248*, *PcsK5*, *Ghr*, *Ackr3*, *Rnf130*, *F3*, *Gpcr5a*, *Gpc3*, *Lepr*, *Scn7a*, *Ramp2*, *Slco3a1*, *Slc29a1*, *P2ry14*, *Robo2*, *Fzd2*, *Tm7sf3*, *Rgmb*, *Gpr153*, *Smo*, *Ptger4*, *Reck*, *Cadm3*, *Tpcn1*, and *Mpzl1*. These markers are largely absent or expressed at very low levels in the AC and CC conditions, suggesting their roles in maintaining healthy fibroblast phenotype and colonic homeostasis.

Overall, the plot clearly delineates condition-specific fibroblast populations based on their surfaceome expression, reflecting distinct cellular responses and roles during acute inflammation, chronic inflammation, and health.

Biological Interpretation

Condition AC (Acute Colitis) Specific Markers

Fibroblasts in acute colitis show a significant upregulation of markers associated with immediate inflammatory responses, immune cell interaction, and early tissue remodeling.

• Il1r1 (Interleukin-1 receptor type 1): As the receptor for pro-inflammatory cytokines IL-1α and IL-1β, high expression of *Il1r1* indicates that AC fibroblasts are highly responsive to IL-1 signaling. This engagement activates downstream pathways like NF-κB and MAPK, promoting the production of other inflammatory mediators and driving the acute inflammatory response. Fibroblast-mediated IL-1 signaling contributes to the recruitment of immune cells and exacerbates inflammation in the colon [PubMed search: IL1R1 IBD fibroblast].
• Osmr (Oncostatin M Receptor): Upregulation of *Osmr* suggests that AC fibroblasts are sensitive to Oncostatin M (OSM), an IL-6 family cytokine often elevated in acute inflammation. OSM-OSMR signaling can activate JAK/STAT3 pathways, leading to fibroblast proliferation, migration, and production of extracellular matrix components and inflammatory molecules, contributing to acute tissue remodeling and inflammation [GeneCards: OSMR].
• Ereg (Epiregulin): Epiregulin is a ligand for the Epidermal Growth Factor Receptor (EGFR). Its increased expression in AC fibroblasts might contribute to a pro-proliferative and migratory phenotype, essential for initial wound healing and repair but potentially also fueling dysregulated tissue growth and remodeling characteristic of acute inflammatory states in the colon [PubMed search: Epiregulin IBD colon].
• Pdgfrb (Platelet-derived growth factor receptor beta): PDGFRβ signaling is a critical driver of fibroblast activation, proliferation, and differentiation into myofibroblasts, which are key cellular players in early fibrotic processes and tissue repair. Its high expression in AC fibroblasts suggests active involvement in matrix production and tissue remodeling, even in the acute phase of colitis [GeneCards: PDGFRB].
• Itga1 (Integrin alpha 1): Integrin α1 (part of VLA-1) binds to collagen and laminin. Its upregulation signifies enhanced fibroblast adhesion to and interaction with the extracellular matrix, facilitating cell migration and contributing to changes in tissue architecture during acute inflammation and early repair [UniProt: ITGA1].
• Sirpa (Signal regulatory protein alpha): SIRPα is a transmembrane glycoprotein that interacts with CD47, mediating cell-cell communication. In inflammatory contexts, SIRPα on fibroblasts can influence immune cell functions, potentially regulating macrophage activity and immune surveillance, indicating a role in acute immune modulation [GeneCards: SIRPA].

Condition CC (Chronic Colitis) Specific Markers

Fibroblasts in chronic colitis exhibit markers associated with sustained inflammation, fibrosis, and altered immune interactions, pointing towards persistent tissue remodeling and immune dysregulation.

• Thy1 (CD90): High expression of *Thy1* is often associated with activated myofibroblasts and can promote fibrotic processes by mediating cell-cell and cell-matrix interactions, influencing cell adhesion, migration, and signaling. In chronic colitis, *Thy1* positive fibroblasts may contribute significantly to intestinal fibrosis and tissue stiffness [GeneCards: THY1].
• Adgrl1 (Adhesion G protein-coupled receptor L1): As an adhesion GPCR, *Adgrl1* can play roles in cell adhesion, migration, and mechanosensing. Its upregulation in CC fibroblasts might contribute to altered cellular interactions within the inflamed chronic colon microenvironment, potentially affecting tissue remodeling and inflammatory signaling [PubMed search: Adhesion GPCR IBD fibroblast].
• Ifngr2 (Interferon gamma receptor 2): *Ifngr2* forms part of the receptor for IFN-γ, a potent pro-inflammatory cytokine central to type 1 immune responses. Increased *Ifngr2* expression suggests that CC fibroblasts are highly responsive to IFN-γ, which can induce pro-inflammatory gene expression, regulate immune cell activity, and potentially influence anti-fibrotic or pro-fibrotic outcomes depending on the specific context and duration of signaling in chronic inflammation [GeneCards: IFNGR2].
• Notch3: Notch signaling, including Notch3, is crucial for cell fate, proliferation, and differentiation. In chronic inflammatory conditions, activated Notch3 signaling in fibroblasts can promote their differentiation into myofibroblasts and enhance extracellular matrix production, actively contributing to fibrosis and architectural distortion seen in chronic IBD [PubMed search: Notch3 IBD fibrosis].
• Mcam (CD146): MCAM (CD146) is an adhesion molecule involved in cell-cell adhesion, migration, and angiogenesis. Its expression on CC fibroblasts might facilitate their migration, interaction with endothelial cells, and recruitment of immune cells to sites of chronic inflammation, perpetuating the inflammatory cycle [UniProt: MCAM].
• Slc12a2 (Solute carrier family 12 member 2, NKCC1): NKCC1 is a co-transporter that regulates intracellular ion concentrations and cell volume. In chronic inflammation, altered ion homeostasis via NKCC1 can influence cell proliferation, migration, and inflammatory signaling in various cell types, including fibroblasts. Its role in maintaining cell function under inflammatory stress in CC fibroblasts could be significant [GeneCards: SLC12A2].

Condition HC (Healthy Control) Specific Markers

The markers highly expressed in healthy control fibroblasts likely represent pathways crucial for maintaining normal colonic stromal homeostasis, quiescent fibroblast states, and protective functions.

• Emp1 (Epithelial Membrane Protein 1): *Emp1* is involved in cell growth and differentiation. Its robust expression in HC fibroblasts suggests a role in maintaining the quiescent state or normal homeostatic functions of healthy stromal cells, potentially indicating a protective or regulatory role in tissue maintenance [GeneCards: EMP1].
• Lpar1 (Lysophosphatidic Acid Receptor 1): LPAR1 is a G protein-coupled receptor for lysophosphatidic acid (LPA). LPA signaling can influence cell proliferation, migration, and survival. In healthy fibroblasts, *Lpar1* might be involved in basal cellular functions and responsiveness to local cues that maintain tissue integrity and normal cell turnover [GeneCards: LPAR1].
• Pdgfra (Platelet-derived growth factor receptor alpha): Unlike PDGFRβ, PDGFRα is often associated with quiescent or progenitor fibroblast populations and plays a role in maintaining the normal fibroblast pool. Its high expression in HC fibroblasts suggests its importance in stromal development, maintenance, and perhaps preserving a less activated, non-fibrotic phenotype [GeneCards: PDGFRA].
• Cd55 (Complement Decay-Accelerating Factor, DAF): *Cd55* is a complement regulatory protein that protects host cells from complement-mediated damage. High expression in healthy colon fibroblasts is crucial for maintaining immune homeostasis, preventing uncontrolled complement activation, and protecting the gut from inflammatory damage under normal conditions [UniProt: CD55].
• Smo (Smoothened, Frizzled-related protein): SMO is a key component of the Hedgehog signaling pathway, vital for embryonic development and adult tissue homeostasis, including stem cell maintenance and stromal-epithelial interactions. Its expression in healthy fibroblasts suggests a role in maintaining normal colon architecture, crypt integrity, and regulating fibroblast behavior in a non-inflammatory state [GeneCards: SMO].
• Ptger4 (Prostaglandin E Receptor 4, EP4): PTGER4 is a receptor for prostaglandin E2 (PGE2). PGE2-EP4 signaling has diverse effects, often anti-inflammatory and pro-resolving, involved in maintaining gut barrier function and modulating immune responses. Its high expression in healthy fibroblasts might contribute to maintaining a tolerogenic microenvironment and tissue integrity [GeneCards: PTGER4].

Clinical or Translational Implications

The identification of condition-specific surfaceome markers on fibroblasts provides valuable insights into the pathophysiology of IBD/Colitis and opens avenues for therapeutic development.

Therapeutic Targets in AC and CC (Inflammatory Conditions)

The upregulated surfaceome markers in AC and CC fibroblasts represent potential therapeutic targets to modulate inflammation and fibrosis:

• Targeting IL-1 Signaling: The prominence of *Il1r1* in AC fibroblasts suggests that inhibiting IL-1 signaling could be beneficial. Therapeutic agents like Anakinra (an IL-1R antagonist) or Canakinumab (an anti-IL-1β antibody) could be explored to dampen fibroblast-driven acute inflammatory responses.
• Modulating Fibrotic Pathways: *Pdgfrb* in AC and *Thy1*, *Notch3* in CC are strong indicators of fibroblast activation and pro-fibrotic programs. Targeting PDGFRβ using small molecule inhibitors (e.g., Imatinib off-label, or more specific PDGFRβ inhibitors in development) or Notch signaling with gamma-secretase inhibitors or pathway-specific modulators could mitigate fibrosis, a major complication of chronic IBD.
• Interfering with OSM-OSMR Axis: *Osmr* upregulation in AC suggests that blocking OSM-OSMR signaling, potentially with neutralizing antibodies against OSM or OSMR, could reduce inflammation and associated tissue remodeling.
• Targeting Adhesion and Migration: Markers like *Itga1* (AC) and *Mcam* (CC) play roles in cell adhesion and migration. Inhibitors targeting these adhesion molecules could potentially reduce fibroblast trafficking to inflammatory sites or their interactions with immune cells. This is conceptually similar to vedolizumab, which targets α4β7 integrin on immune cells, but here the focus is on fibroblast-specific targets.

Diagnostics and Prognostics

• These condition-specific markers could serve as biomarkers to distinguish between different stages of colitis (acute vs. chronic) or to assess disease activity and progression. For instance, high levels of *Il1r1* might indicate an acute inflammatory flare, while *Thy1* or *Notch3* might point to ongoing chronic inflammation and fibrosis.
• They could also be used to identify subpopulations of fibroblasts with distinct functional roles in IBD, which might respond differently to therapies.

Markers for Healthy Fibroblast Maintenance

The HC-specific markers like *Emp1*, *Lpar1*, *Pdgfra*, *Cd55*, *Smo*, and *Ptger4* offer insights into the biology of healthy quiescent fibroblasts.

• Understanding how these pathways are downregulated in IBD could inform strategies to restore tissue homeostasis. For example, interventions aimed at promoting CD55 expression or enhancing beneficial PGE2-EP4 signaling could potentially protect against inflammation or promote resolution.
• *Pdgfra* as a marker for healthy, quiescent fibroblasts could be important for distinguishing between homeostatic and activated fibroblast populations in research and therapeutic development.

Further validation through functional studies (e.g., *in vitro* assays, *in vivo* disease models) would be crucial to confirm the specific roles of these markers and their utility as therapeutic targets or diagnostic tools in IBD.

14. T cell CD4+ Surfaceome Marker Analysis in Mouse Colon Colitis Models

[Analysis Visualization Results]...

Analysis Overview

This analysis presents a dot plot illustrating the expression of surfaceome markers in CD4+ T cells across different conditions (AC: Acute Colitis, CC: Chronic Colitis, and HC: Healthy Control) within the mouse colon. The markers were identified as differentially expressed when comparing each condition against the healthy control (HC) or against other conditions. The filtering criteria for marker identification focused on genes with significant non-zero percentage scores and fold changes, ensuring the selected markers are highly relevant to the specific conditions. This provides insights into condition-specific phenotypic changes in CD4+ T cells, which are critical immune cells in the context of Inflammatory Bowel Disease (IBD) / Colitis.

Visual Summary

The dot plot visualizes mean expression (color intensity, red gradient) and the fraction of cells expressing each gene (dot size) for individual samples grouped by condition (AC, CC, HC).

• Condition-Specific Clustering: A clear pattern emerges where markers cluster into two main groups: those predominantly expressed in inflammatory conditions (AC and CC) and those more expressed in the healthy control (HC). The red boxes highlight these distinct groups of markers.

Markers Elevated in AC and CC (Inflammatory Conditions):

• Genes such as Itga4, Icam1, Adora2a, Tnfrsf9, and Cd3d show higher mean expression and are expressed in a larger fraction of cells in the AC and CC samples compared to HC. This indicates an upregulation of these surface markers in CD4+ T cells during active colitis.
• Within AC and CC, there appears to be some variability between samples (e.g., AC3 showing somewhat lower expression for some inflammatory markers compared to AC1/AC2), but the overall trend is clear.

Markers Elevated in HC (Healthy Control Condition):

• Conversely, markers like Cd69, Cd28, Ccr7, Atp1b3, S1pr1, Emp3, and Bsg exhibit higher mean expression and cell fraction in the HC samples. This suggests a different activation or homing profile for CD4+ T cells in the healthy colon.
• Expression of these HC-dominant markers is noticeably low or absent in most AC and CC samples.
• Overall Intensity and Fraction: The color scale (mean expression) and dot size scale (fraction of cells) indicate that many of these condition-specific markers are not only expressed at higher levels but also by a substantial proportion of CD4+ T cells within their respective conditions, reinforcing their biological significance.

Biological Interpretation

The differential expression of these surfaceome markers on CD4+ T cells provides key insights into their functional states and roles in the context of colonic inflammation.

Markers Upregulated in Inflammatory Conditions (AC, CC)

These markers are associated with T cell activation, migration, and retention in inflamed tissues, characteristic features of IBD/Colitis.

• Itga4 (CD49d): Integrin alpha 4.
• Signaling/Mechanism: Itga4 forms heterodimers with integrin beta 1 (VLA-4, CD49d/CD29) or beta 7 (alpha4beta7 integrin). VLA-4 binds to VCAM-1, mediating T cell adhesion to endothelial cells and migration into inflamed tissues. Alpha4beta7 integrin specifically binds to MAdCAM-1, facilitating T cell homing to the gut. This upregulation in AC/CC suggests enhanced T cell recruitment to the inflamed colon.
• IBD/Colitis Relevance: Increased Itga4 expression drives the infiltration of pathogenic T cells into the intestinal mucosa, a hallmark of IBD. Blocking this pathway reduces inflammation.
• References: GeneCards: ITGA4
• Icam1 (CD54): Intercellular Adhesion Molecule 1.
• Signaling/Mechanism: Icam1 is a ligand for leukocyte function-associated antigen-1 (LFA-1, CD11a/CD18) on T cells. It plays a crucial role in immune synapse formation, T cell activation, and transmigration of leukocytes across the endothelium into inflamed tissues. Its upregulation is a common feature of inflammation, enhancing immune cell adhesion and infiltration.
• IBD/Colitis Relevance: Elevated ICAM-1 facilitates persistent inflammation by promoting the recruitment and activation of immune cells in the gut.
• References: GeneCards: ICAM1

Adora2a (Adenosine A2a Receptor)

• Signaling/Mechanism: Adora2a is a G protein-coupled receptor that binds extracellular adenosine. Activation of Adora2a on immune cells often leads to immunosuppressive effects by increasing intracellular cAMP, which can inhibit cytokine production and T cell proliferation. However, in certain chronic inflammatory contexts, its complex role can include promoting inflammation or dampening excessive responses. Its upregulation here might reflect an attempt to regulate inflammation or a specific pro-inflammatory role in the inflamed colon.
• IBD/Colitis Relevance: Adenosine signaling, via Adora2a, is implicated in regulating gut inflammation, with its effects being context-dependent.
• References: GeneCards: ADORA2A
• Tnfrsf9 (4-1BB, CD137): Tumor Necrosis Factor Receptor Superfamily Member 9.
• Signaling/Mechanism: Tnfrsf9 is a costimulatory receptor expressed on activated T cells. Upon binding its ligand (4-1BBL), it delivers a signal that enhances T cell proliferation, survival, and cytokine production, augmenting the effector functions of CD4+ T cells.
• IBD/Colitis Relevance: Activation of 4-1BB on T cells can contribute to immune-mediated tissue damage in chronic inflammation.
• References: GeneCards: TNFRSF9
• Cd3d: Component of the T cell receptor (TCR) complex.
• Signaling/Mechanism: Cd3d, along with other CD3 subunits (CD3G, CD3E), is essential for surface expression of the TCR and signal transduction upon antigen recognition. While constitutively expressed on T cells, its elevated presence here might reflect an activated state or altered TCR expression patterns in the inflamed environment.
• IBD/Colitis Relevance: Essential for T cell-mediated immunity in the gut; its expression level in activated cells can be indicative of their responsiveness.

Markers Upregulated in Healthy Control Conditions (HC)

These markers typically reflect states of T cell quiescence, recirculation, or regulatory functions in a non-inflamed environment.

• Cd69: Early activation marker, but also a tissue residency marker.
• Signaling/Mechanism: Cd69 is rapidly expressed upon T cell activation, but it can also promote retention of T cells in lymphoid organs and non-lymphoid tissues by downregulating S1pr1. Its higher expression in HC might indicate a population of quiescent tissue-resident memory T cells or T cells recently activated but retained in the healthy colon for immune surveillance.
• IBD/Colitis Relevance: In a healthy context, CD69+ T cells might represent immune surveillance or a local regulatory population.
• References: GeneCards: CD69
• Cd28: T cell costimulatory receptor.
• Signaling/Mechanism: Cd28 is a critical costimulatory molecule on T cells, binding to CD80 (B7-1) and CD86 (B7-2) on antigen-presenting cells (APCs). This interaction delivers a "second signal" necessary for full T cell activation, proliferation, and cytokine production. Its presence in HC T cells suggests they are fully competent for activation.
• IBD/Colitis Relevance: Essential for the initiation and maintenance of adaptive immune responses.
• References: GeneCards: CD28
• Ccr7: Chemokine (C-C motif) Receptor 7.
• Signaling/Mechanism: Ccr7 is a chemokine receptor crucial for T cell homing to secondary lymphoid organs (lymph nodes and Peyer's patches) in response to its ligands CCL19 and CCL21. High expression often marks naive T cells or central memory T cells that recirculate through lymphoid tissues. Its higher expression in HC suggests T cells are actively recirculating or have a naive/central memory phenotype.
• IBD/Colitis Relevance: Its low expression in AC/CC could imply T cells are retained in inflamed tissue or adopt a different homing phenotype.
• References: GeneCards: CCR7
• S1pr1: Sphingosine-1-phosphate Receptor 1.
• Signaling/Mechanism: S1pr1 is a G protein-coupled receptor that mediates T cell egress from lymphoid organs into the circulation, responding to an S1P gradient. Downregulation of S1pr1, often induced by inflammation or CD69, leads to T cell retention in tissues. Its higher expression in HC CD4+ T cells suggests they retain the capacity for recirculation.
• IBD/Colitis Relevance: S1PR1 agonists are used as immunomodulators to prevent lymphocyte egress from lymph nodes.
• References: GeneCards: S1PR1
• Atp1b3: Na+/K+-ATPase subunit beta-3.
• Signaling/Mechanism: This is a subunit of the sodium-potassium pump, essential for maintaining cellular ion gradients and membrane potential. While not a primary immune-specific receptor, its differential expression can reflect altered metabolic states or membrane dynamics of T cells in different conditions.

Emp3 (Epithelial Membrane Protein 3)

• Signaling/Mechanism: Emp3 belongs to the peripheral myelin protein 22 (PMP22) family, involved in cell adhesion and growth. Its function in T cells is less well-characterized compared to other markers, but its presence might imply a role in cell-cell interactions or tissue maintenance in the healthy state.
• Bsg (Basigin, CD147): Extracellular Matrix Metalloproteinase Inducer (EMMPRIN).
• Signaling/Mechanism: Bsg is a transmembrane glycoprotein involved in a wide range of cellular processes including cell adhesion, migration, and the induction of matrix metalloproteinases (MMPs) which remodel the extracellular matrix. It can also act as a costimulatory molecule for T cells. Its presence in HC T cells might signify a basal level of tissue interaction or immune readiness.
• IBD/Colitis Relevance: CD147 is implicated in inflammatory processes and T cell activation.
• References: GeneCards: BSG

Clinical or Translational Implications

The identified condition-specific surfaceome markers on CD4+ T cells present promising avenues for therapeutic intervention and biomarker development in IBD/Colitis.

Therapeutic Targets in Inflammatory Conditions:

• Itga4 (CD49d): The strong upregulation of Itga4 in AC/CC highlights its critical role in T cell trafficking to the inflamed gut. Therapeutic agents targeting Itga4 or its heterodimers are already clinically relevant. For example, Vedolizumab specifically targets the α4β7 integrin, blocking T cell migration to the gut, and is approved for IBD treatment. Natalizumab, targeting α4 integrin, is also effective but carries a broader risk profile due to its impact on CNS trafficking. These findings support the continued exploration and refinement of anti-integrin therapies.
• Icam1 (CD54): While no ICAM-1 specific drugs are widely used for IBD, the elevated expression of Icam1 suggests that strategies to modulate leukocyte-endothelial interactions could be beneficial. This could involve exploring agents that interfere with LFA-1/ICAM-1 binding to reduce T cell infiltration and activation.
• Tnfrsf9 (4-1BB): As a costimulatory molecule, 4-1BB agonists are primarily developed for cancer immunotherapy. However, its upregulation in colitis suggests that blocking the 4-1BB pathway might dampen pathogenic T cell responses in autoimmune conditions. Further research into 4-1BB antagonism could be relevant for severe IBD.

Biomarkers for Disease Activity and Prognosis:

• The distinct expression profiles of markers like Itga4, Icam1 (upregulated in disease) and Ccr7, S1pr1 (downregulated in disease) could serve as biomarkers to assess disease activity, monitor treatment response, or stratify patients. For instance, high levels of Itga4 on circulating T cells might indicate a predisposition for gut homing and more severe disease.

Understanding Disease Pathogenesis:

• The shift from S1pr1/Ccr7-high (recirculating/quiescent) T cells in HC to Itga4/Icam1-high (adherent/activated) T cells in AC/CC illustrates a fundamental mechanism of T cell recruitment and retention in the inflamed colon. Understanding the precise triggers for these phenotypic changes could lead to novel therapeutic strategies aimed at restoring immune homeostasis. For instance, modulating S1P receptor pathways (e.g., with S1PR modulators like ozanimod, an S1PR1 agonist, that prevents lymphocyte egress from lymph nodes, thus reducing circulating lymphocytes) could be considered, though with caution as their action is complex.

15. Gene Ontology Analysis of Intestinal Epithelial Cells in Colitis Conditions (AC, CC) and Healthy State

[Analysis Visualization Results]...

Analysis Overview

This analysis presents Gene Ontology (GO) enrichment results for Intestinal Epithelial cells, comparing two colitis conditions (AC and CC) against a healthy control (HC), and the healthy control against the combined colitis conditions (AC and CC). The analysis is based on genes found to be significantly up-regulated in the respective comparison. The results are visualized as bar plots showing the top enriched terms, ordered by their statistical significance (-log(p-val) and -log(q-val)). The objective is to identify key biological processes and pathways dysregulated in Intestinal Epithelial cells during colitis, and those characteristic of a healthy state.

Visual Summary

The visualizations consist of three bar plots, each detailing GO term enrichment for up-regulated differentially expressed genes (DEGs) in Intestinal Epithelial cells under different comparative conditions:

1. AC_vs_HC (Colitis AC vs. Healthy Control): This plot shows terms up-regulated in the AC colitis condition compared to HC. Prominently enriched terms include "Tight junction," "Adherens junction," "NOD-like receptor signaling pathway," "TNF signaling pathway," "Focal adhesion," "Chemokine signaling pathway," and "IL-17 signaling pathway." Pathways related to viral infections (Human papillomavirus, Human cytomegalovirus, Hepatitis B) and PI3K-Akt and NF-kappa B signaling are also highly ranked.
2. CC_vs_HC (Colitis CC vs. Healthy Control): This plot displays terms up-regulated in the CC colitis condition compared to HC. Top enriched terms include "Protein processing in endoplasmic reticulum," "Mucin type O-glycan biosynthesis," "Salmonella infection," "Lysosome," "TNF signaling pathway," and "Chagas disease (American trypanosomiasis)." Pathways like "Autophagy," "Bacterial invasion of epithelial cells," "Regulation of actin cytoskeleton," "FoxO signaling pathway," and "Fc gamma R-mediated phagocytosis" also show significant enrichment.
3. HC_vs_others (Healthy Control vs. Colitis conditions AC+CC): This plot highlights terms up-regulated in healthy Intestinal Epithelial cells compared to the combined colitis conditions. Key enriched terms are "Ribosome," "Oxidative phosphorylation," pathways associated with neurodegenerative diseases (Parkinson, Alzheimer, Huntington disease, which often reflect mitochondrial/metabolic health), "Thermogenesis," "Non-alcoholic fatty liver disease (NAFLD)," and various metabolic pathways (Valine, leucine and isoleucine degradation, TCA cycle, Fatty acid elongation/degradation). Processes related to RNA transport, RNA degradation, cell cycle, and mismatch repair are also highly ranked.

Across all plots, a higher bar length signifies greater statistical significance (smaller p-value and q-value). The top terms generally show strong enrichment with both -log(p-val) and -log(q-val) being high, indicating robust and reproducible findings.

Biological Interpretation

The Gene Ontology analysis provides crucial insights into the functional state of Intestinal Epithelial cells (IECs) in different conditions within the colon, consistent with an Inflammatory Bowel Disease (IBD) / Colitis context.

Colitis Conditions (AC and CC) vs. Healthy Control (HC)

Both AC and CC conditions show significant dysregulation in IECs, but with notable distinctions:

• AC Colitis (vs. HC): The prominence of "Tight junction" and "Adherens junction" pathways being up-regulated suggests a heightened epithelial response to maintain or repair barrier integrity, or possibly a dysregulated attempt at barrier formation, which is a hallmark of IBD pathogenesis PubMed Search: "intestinal barrier dysfunction IBD". The strong enrichment of "NOD-like receptor signaling pathway," "TNF signaling pathway," "Chemokine signaling pathway," and "IL-17 signaling pathway" directly points to an activated innate and adaptive immune response within IECs, driving inflammation. This activation is a central mechanism in colitis GeneCards: TNF. The enrichment of viral infection pathways (e.g., HPV, CMV) could indicate a broad activation of anti-viral innate immune responses, or potentially a response to general microbial dysbiosis rather than specific viral infection, often observed in inflammatory settings.
• CC Colitis (vs. HC): In contrast, CC colitis emphasizes cellular stress responses such as "Protein processing in endoplasmic reticulum," "Autophagy," and "Lysosome" pathways. These are indicative of cells dealing with misfolded proteins, cellular damage, and increased turnover, common features in chronic inflammation. The upregulation of "Mucin type O-glycan biosynthesis" could reflect an altered mucus layer composition or increased production as a protective response, which is often compromised in colitis PubMed Search: "mucin layer IBD". The terms "Salmonella infection" and "Bacterial invasion of epithelial cells" highlight a potentially impaired epithelial defense leading to increased host-pathogen interactions or an exaggerated immune response to commensal bacteria, a key feature of IBD. "Fc gamma R-mediated phagocytosis" further suggests a robust immune effector function in IECs, potentially in response to microbial threats or immune complexes.

Healthy Control (HC) vs. Colitis Conditions (AC+CC)

The pathways up-regulated in healthy IECs define their homeostatic functions:

• HC (vs. others): The strong enrichment of "Ribosome" and "Oxidative phosphorylation" pathways signifies active protein synthesis and robust energy metabolism, essential for the high turnover and absorptive functions of IECs. The presence of core metabolic pathways like "Valine, leucine and isoleucine degradation," "TCA cycle," and lipid metabolism pathways (e.g., "Fatty acid elongation/degradation") confirms efficient nutrient processing and energy generation. Furthermore, enrichment of "Cell cycle" and "Mismatch repair" pathways indicates active cell proliferation and DNA damage repair mechanisms, crucial for maintaining epithelial integrity and preventing pathological changes. The appearance of neurodegenerative disease pathways (Parkinson, Alzheimer) often points to healthy mitochondrial function and cellular stress resilience in a healthy state, as these pathways are often linked to metabolic dysfunction and oxidative stress when dysregulated.

The comparative analysis reveals distinct molecular signatures in IECs: AC colitis appears to be characterized by active inflammation and barrier response, while CC colitis exhibits prominent cellular stress and altered host-microbial interactions. Healthy IECs, in contrast, prioritize fundamental metabolic and maintenance processes.

Clinical or Translational Implications

These findings have several potential clinical and translational implications for IBD/Colitis:

• Therapeutic Targets: The consistent upregulation of "TNF signaling pathway" in both AC and CC conditions reinforces its established role in IBD and validates anti-TNF therapies. The involvement of "IL-17 signaling pathway" in AC suggests that IL-17 inhibitors could be particularly beneficial for specific colitis subtypes. Targeting pathways related to tight and adherens junctions could offer novel strategies to restore epithelial barrier function.
• Disease Stratification: The distinct GO enrichment profiles for AC and CC suggest that these conditions may represent different stages or types of colitis with unique underlying biological mechanisms. This could facilitate more precise disease stratification, leading to tailored therapeutic approaches. For instance, CC patients might benefit more from interventions that support cellular resilience, reduce ER stress, or modulate mucus production, whereas AC patients might respond better to direct anti-inflammatory agents targeting specific cytokine pathways.
• Biomarker Discovery: The enriched pathways and their constituent up-regulated genes could serve as potential biomarkers for disease activity, severity, or therapeutic response. Monitoring the activity of pathways like "Mucin type O-glycan biosynthesis" or markers of ER stress could offer insights into disease progression or remission.
• Epithelial Protection: The cellular stress pathways observed in CC colitis highlight the importance of therapies that protect and support intestinal epithelial cell health, beyond purely immune-suppressive strategies. This could include nutritional interventions or agents that enhance ER proteostasis or autophagy.

16. Gene Set Enrichment Analysis (GSEA) of Colon Cell Types in Inflammatory Conditions

[Analysis Visualization Results]...

Analysis Overview

This analysis presents Gene Set Enrichment Analysis (GSEA) results across various cell types in the mouse colon under two inflammatory conditions (AC and CC) compared to a healthy control (HC). The dot plot visualizes the Normalized Enrichment Score (NES) and statistical significance (-log(p-val)) for 120 selected gene sets, providing insights into activated or suppressed biological pathways in specific cell populations during colitis.

Visual Summary

The dot plot displays GSEA results, with each dot representing a gene set enriched or depleted in a specific cell type under a given condition comparison. The x-axis categorizes results by cell type (e.g., B cell, Macrophage, Intestinal Epithelial cell) and comparison (AC vs HC, CC vs HC, and HC vs others). The y-axis lists 120 distinct biological pathways.

• Color Scale (NES): The RdBu_r colormap is used, where red dots indicate pathways significantly upregulated (positive NES) in the test condition relative to HC, and blue dots indicate downregulation (negative NES). Darker shades of red or blue represent stronger enrichment/depletion, while lighter shades indicate weaker effects.
• Dot Size (-log(p-val)): The size of each dot is proportional to the -log(p-val), meaning larger dots correspond to more statistically significant enrichment or depletion. Small, light grey dots generally represent pathways that did not pass the significance threshold or have low enrichment scores.
• Overall Pattern: A prominent pattern of widespread pathway dysregulation is observed in both AC_vs_HC and CC_vs_HC comparisons across multiple cell types, especially immune cells. Many pathways show consistent trends (up- or downregulation) between AC and CC conditions, suggesting shared underlying inflammatory mechanisms. The 'HC_vs_others' comparisons often display inverse patterns to the disease conditions, as expected, highlighting processes characteristic of the healthy state.

Biological Interpretation

The GSEA results provide strong evidence for widespread inflammation and cellular dysregulation in the colon under AC and CC conditions, consistent with an Inflammatory Bowel Disease (IBD) or colitis-like state.

Immune Cell Activation and Inflammation:

• Pro-inflammatory Signaling: Key pathways such as "Cytokine-cytokine receptor interaction," "Toll-like receptor signaling pathway," "MAPK signaling pathway," and "JAK-STAT signaling pathway" are significantly upregulated (red, large dots) across various immune cell types, including Macrophages, T cell CD4+, Dendritic cells, and ILCs, in both AC and CC conditions compared to HC. This indicates robust activation of innate and adaptive immune responses R1: [https://pubmed.ncbi.nlm.nih.gov/?term=cytokine+signaling+IBD].
• Immune Cell Trafficking: "Chemokine signaling pathway" and "Leukocyte transendothelial migration" are also significantly upregulated in immune cells (Macrophages, T cells, Dendritic cells) and Endothelial cells, highlighting active recruitment and infiltration of immune cells into the inflamed tissue.
• T Cell and B Cell Responses: "T cell receptor signaling pathway" and "Th17 cell differentiation" are enriched in T cell CD4+ populations, suggesting an active pro-inflammatory T cell response, with Th17 cells being major contributors to IBD pathogenesis R2: [https://pubmed.ncbi.nlm.nih.gov/31331776/]. Similarly, "B cell receptor signaling pathway" is activated in B cells, indicating their involvement in the inflammatory process.
• Phagocytosis: "Fc gamma R-mediated phagocytosis" is upregulated in Macrophages and Dendritic cells, reflecting enhanced phagocytic activity crucial for clearing cellular debris and pathogens in inflammation.

Intestinal Epithelial Barrier Dysfunction:

• Compromised Integrity: In Intestinal Epithelial cells, pathways related to cell-cell adhesion like "Adherens junction" and "Focal adhesion" are significantly downregulated (blue, large dots) in both AC and CC vs HC. This suggests a disruption of the epithelial barrier, a critical feature in IBD pathogenesis that leads to increased gut permeability R3: [https://pubmed.ncbi.nlm.nih.gov/?term=intestinal+epithelial+barrier+dysfunction+IBD].
• Cellular Stress: "Protein processing in endoplasmic reticulum" and "Peroxisome" pathways are upregulated in Intestinal Epithelial cells, indicative of cellular stress and altered metabolic demands in response to chronic inflammation.

Metabolic Reprogramming:

• "Glycolysis / Gluconeogenesis" and "Pentose phosphate pathway" are upregulated in various immune cells (Macrophages, T cell CD4+, Dendritic cells) and Fibroblasts in both disease conditions. This suggests a metabolic shift, particularly towards glycolysis (the Warburg effect), which is characteristic of activated immune cells and plays a role in sustaining inflammation R4: [https://pubmed.ncbi.nlm.nih.gov/33130638/].

Distinctions Between AC and CC:

• While many pathways show common trends between AC and CC, subtle differences exist. For example, "Wnt signaling pathway" is notably upregulated in Intestinal Epithelial cells in AC vs HC but not consistently in CC vs HC. This might point to differing regenerative capacities, specific inflammatory triggers, or distinct phases of the disease between these two conditions.

Clinical or Translational Implications

The detailed GSEA findings highlight several key biological processes that could serve as diagnostic markers or therapeutic targets in IBD/Colitis.

• Targeting Inflammation: The consistent upregulation of cytokine, MAPK, JAK-STAT, and Toll-like receptor signaling pathways across multiple immune cell types reinforces the utility of current anti-inflammatory therapies (e.g., biologics targeting specific cytokines, JAK inhibitors) and suggests avenues for developing novel agents that modulate these pathways.
• Restoring Barrier Function: The observed downregulation of adherens junction and focal adhesion pathways in intestinal epithelial cells underscores the importance of therapeutic strategies aimed at preserving or restoring the epithelial barrier, which could mitigate antigen exposure and subsequent inflammation.
• Immune Cell Modulation: Specifically targeting Th17 differentiation or the metabolic reprogramming of immune cells could offer more refined immunomodulatory approaches, potentially reducing systemic side effects associated with broader immunosuppression.
• Disease Subtyping: The subtle differences observed between AC and CC conditions, such as in Wnt signaling within IECs, suggest that these conditions may represent distinct disease phenotypes or stages. Further investigation could lead to biomarker discovery for subtyping colitis and guiding personalized treatment regimens.

17. Discussion

The single-cell analysis of mouse colon tissues under acute colitis (AC) and chronic colitis (CC) conditions, when compared to healthy controls (HC), provides a comprehensive view of the cellular and molecular landscape of Inflammatory Bowel Disease (IBD) / Colitis. A consistent theme across both inflammatory conditions is a pronounced immune activation and dysregulation of cellular functions.

Widespread Immune Activation and Population Shifts: Both AC and CC exhibit a robust inflammatory response. Population analysis revealed a notable increase in B cell and plasma cell proportions in chronic colitis (CC), suggesting a robust humoral immune response central to chronic inflammation. Macrophages showed a significant skew towards a pro-inflammatory M1 phenotype in both AC and CC, indicating their central role in initiating and perpetuating inflammation. Furthermore, specific T cell subsets showed dynamic changes; AC was characterized by increased CD4 Memory and CD8 Exhausted T cells, while CC displayed elevations in Th17, Th2, Treg, and Tfh populations, reflecting a complex interplay of effector and regulatory responses. Intriguingly, ILC subsets appeared to be reduced in both inflammatory conditions, which could impair innate protective mechanisms and barrier integrity. GSEA results consistently underscored the activation of pro-inflammatory signaling pathways such as Cytokine-cytokine receptor interaction, Toll-like receptor, MAPK, and JAK-STAT pathways across various immune cell types, supporting a generalized immune hyper-responsiveness in disease.

Compromised Epithelial Barrier and Cellular Stress: Intestinal Epithelial Cells (IECs), critical for gut homeostasis, displayed significant dysfunction in colitis. GSEA indicated a downregulation of Adherens junction and Focal adhesion pathways in IECs from both AC and CC, pointing towards a compromised epithelial barrier. GSA further elucidated condition-specific epithelial stress: AC IECs showed upregulation of Tight junction and Adherens junction pathways (possibly a dysregulated repair effort) alongside NOD-like receptor and IL-17 signaling, reflecting active inflammatory engagement. In contrast, CC IECs were enriched for pathways related to Protein processing in endoplasmic reticulum, Autophagy, Lysosome, and bacterial invasion, suggesting chronic cellular stress, impaired protein homeostasis, and altered host-microbe interactions. Surfaceome analysis of IECs highlighted the loss of crucial homeostatic markers like EGFR, Slc5a8, Ephb4, and Fgfr2 in disease, which are vital for regeneration and metabolic health, further contributing to impaired mucosal healing.

Dynamic Cell-Cell Communication: A striking finding was the profound upregulation and diversification of cell-cell interactions (CCI) in AC and CC. Integrin-mediated interactions (e.g., VCAM1-integrin_α4β7, MAdCAM1-integrin_α4β7, ICAM1-integrin_αLβ2) involving endothelial cells, T cells, and macrophages were highly active, driving immune cell trafficking into the inflamed colon. Chemokine signaling (e.g., CXCL12-CXCR4, CCL2-CCR2) also contributed to immune cell recruitment. Furthermore, interactions involving VEGFA with its receptors indicated active angiogenesis, supporting the metabolic demands of inflammation. Fibroblasts, central to tissue remodeling, showed strong interactions and expressed markers like PDGFRβ in AC and Thy1, Notch3 in CC, suggesting their active role in both early remodeling and chronic fibrosis. SPP1-integrin_αvβ1 complex interactions, particularly in CC, hinted at multifaceted roles in immune modulation and tissue remodeling.

Distinct Features of Acute vs. Chronic Colitis: While sharing many inflammatory hallmarks, AC and CC presented distinct cellular and molecular signatures. AC appeared to be characterized by a more pronounced early inflammatory response, T cell exhaustion (CD8 Exhausted), and increased Th22 cells, alongside fibroblast markers (Il1r1, Osmr, Ereg) indicative of acute inflammatory signaling and early repair. CC, conversely, showed signs of more sustained adaptive immunity (B/plasma cell expansion, Th17, Tfh), distinct macrophage surface markers (Mrc1, Adgre1, C3ar1, Tgfbr2) reflecting M2-like polarization and complement activation, and fibroblast markers (Thy1, Notch3) strongly associated with fibrosis. The differential epithelial stress responses observed in GSA further emphasize these distinct pathological trajectories.

In conclusion, this single-cell analysis reveals a highly dynamic and heterogeneous immune landscape in colonic inflammation, driven by specific cell population shifts, altered intercellular communication, and distinct molecular programs within key cell types. The identified condition-specific markers and pathways provide critical insights into IBD pathogenesis and offer potential avenues for targeted therapeutic interventions.

Hypotheses:

1. Increased B cell and Plasma cell proportions, particularly in chronic colitis (CC), drive sustained humoral immunity and contribute to chronic inflammation through local antibody production and immune complex formation.
2. The significant upregulation of integrin-mediated cell-cell interactions (e.g., VCAM1-α4β7, MAdCAM1-α4β7) in both acute and chronic colitis (AC/CC) is a primary mechanism for pathogenic immune cell infiltration and perpetuates intestinal inflammation.
3. Distinct fibroblast activation states, characterized by specific surface markers (e.g., IL-1R1/OSMR in AC vs. Thy1/Notch3 in CC), mediate differential tissue remodeling, immune cell interaction, and fibrotic progression between acute and chronic colitis.
4. Dysregulation and loss of homeostatic markers (e.g., EGFR, SLC5A8) and increased cellular stress pathways (e.g., ER protein processing, autophagy) in Intestinal Epithelial cells contribute to compromised barrier function and impaired mucosal healing in colitis.
5. The shift towards an M1-dominant macrophage phenotype in both AC and CC, coupled with a decrease in specific M2D or M2B populations in CC, directly contributes to pro-inflammatory cytokine production and hindered resolution of inflammation.

Potential therapeutic targets:

1. α4β7 Integrin (on T cells): Upregulated Itga4 (CD49d, part of α4β7) in CD4+ T cells, and prominent VCAM1-α4β7 / MAdCAM1-α4β7 interactions with endothelial cells, indicate a crucial role in T cell gut-homing and infiltration in both acute and chronic colitis. Evidence: Marker gene analysis for T cell CD4+ (Section 14) and cell-cell interaction analysis (Section 10). Validation: Assess efficacy of α4β7 integrin inhibitors (e.g., Vedolizumab) in reducing T cell infiltration and inflammation in mouse colitis models, measuring clinical scores, histology, and T cell numbers by flow cytometry.
2. IL-1 Signaling (via IL1R1 on Fibroblasts): Strong upregulation of Il1r1 on acute colitis (AC) fibroblasts indicates their high responsiveness to pro-inflammatory IL-1 cytokines, contributing to acute inflammation and early tissue remodeling. Evidence: Fibroblast condition-specific marker analysis (Section 13). GSA for Intestinal Epithelial cells in AC shows enrichment of IL-17 signaling pathway, which is often cross-regulated with IL-1. Validation: Test IL-1R antagonists (e.g., Anakinra) in acute colitis models to evaluate reduction in fibroblast activation, inflammatory cytokine production, and disease severity.
3. PDGFRβ (on Fibroblasts): Elevated Pdgfrb on acute colitis (AC) fibroblasts suggests active fibroblast activation, proliferation, and differentiation into myofibroblasts, which are key processes in early fibrotic changes and tissue remodeling. Evidence: Fibroblast condition-specific marker analysis (Section 13). Validation: Evaluate specific PDGFRβ inhibitors in preventing or reversing early fibrosis and inflammatory responses in acute and chronic colitis models, assessing collagen deposition and myofibroblast markers.
4. Notch3 Signaling (on Fibroblasts): High Notch3 expression on chronic colitis (CC) fibroblasts indicates its role in promoting myofibroblast differentiation and enhancing extracellular matrix production, actively contributing to fibrosis, a major complication in chronic IBD. Evidence: Fibroblast condition-specific marker analysis (Section 13) and discussion of its role in fibrosis. Validation: Use gamma-secretase inhibitors or specific Notch3 pathway antagonists in chronic colitis models to assess their impact on fibrosis, tissue stiffness, and disease progression.
5. C3a Receptor 1 (C3ar1 on Macrophages): C3ar1 is highly expressed on macrophages in chronic colitis (CC), suggesting that sustained complement activation contributes to pro-inflammatory responses, chemotaxis, and phagocytosis in chronic inflammation. Evidence: Macrophage condition-specific marker analysis (Section 12). Validation: Test C3ar1 antagonists in chronic colitis models to determine their ability to reduce macrophage-mediated inflammation and tissue damage, and assess effects on complement activation markers.

Follow-up validation ideas:

1. Validate cell population shifts (e.g., B cell/Plasma cell expansion, Macrophage M1 increase, ILC decrease, T cell subset changes) using flow cytometry or immunohistochemistry on colon biopsies from mouse models and human IBD patients.
2. Confirm identified cell-cell interactions (e.g., VCAM1-α4β7, MAdCAM1-α4β7, DLL4-NOTCH, TGFB1-TGFbeta_receptor) via spatial transcriptomics (e.g., Visium, MERFISH) to show co-localization and proximity of interacting cells and ligands/receptors in situ, followed by in vitro co-culture assays to assess functional outcomes (e.g., cytokine production, cell migration).
3. Functionally test the role of identified surface markers (e.g., Itga4, Mrc1, Thy1, EGFR, Slc5a8) by genetic perturbation (CRISPR/shRNA) or pharmacological modulation in in vitro cell line models (e.g., primary colon epithelial cells, macrophages, fibroblasts) and ex vivo colon organoid cultures to assess changes in cell adhesion, proliferation, differentiation, and inflammatory responses.
4. Verify the activity of enriched pathways (e.g., TNF, IL-17, NOD-like receptor, ER stress, metabolic reprogramming) using targeted reporter assays, western blot, or qPCR in isolated cell populations from inflamed colon tissue, and evaluate the efficacy of pathway-specific inhibitors in in vivo colitis models.
5. Use a separate cohort of mouse colitis models (e.g., DSS-induced or TNBS-induced) or human IBD biopsy samples to validate the identified markers and pathways as diagnostic or prognostic biomarkers for acute vs. chronic inflammation or response to therapy.

Limitations:

This study is based on a mouse model of colitis, and findings may not fully translate to the complex and heterogeneous pathology of human IBD. While conditions are labeled 'AC' and 'CC', the precise nature, inducing agents, or specific experimental protocols defining these states are not provided, limiting detailed etiological interpretation. Single-cell RNA sequencing provides a snapshot of gene expression; dynamic processes and causal relationships inferred from the data require further functional validation. Cell type annotations, while robust, are based on clustering and known markers, and finer functional states or rare populations might be missed. Lastly, cell-cell interaction and gene set enrichment analyses are computational inferences based on gene expression, and direct protein-level interaction or pathway activity needs experimental confirmation.

18. Query List

1. Show and save UMAPs for condition, sample, major cell type, minor cell type, and celltype_subset in two columns.
2. Show major cell type scores on UMAP and save the result.
3. Show and save a marker expression dot plot for celltype_subset. SET target_cell = None and var_group_rotation = 45. Leave all other arguments at their default values.
4. Show and save a population bar plot of minor cell types.
5. Show and save a population bar plot of T cell subsets.
6. Show and save box plots of T cell subset populations with statistically significant differences between conditions, if any. Choose ncols based on the total number of panels.
7. Show and save a population bar plot of macrophage subsets.
8. Show and save box plots of macrophage subset populations with statistically significant differences between conditions, if any. Choose ncols based on the total number of panels.
9. Show and save cell-cell interaction patterns. Select at most 80 cell-cell interactions per group.
10. Find cell-cell interactions involving major tissue cells, immune cells and stromal cells that differ significantly between conditions, show them as a dot plot, and save the result. Set max_n_items_per_group to 60. For each interaction identified under each condition, using the provided dataset context (Inflammatory Bowel Disease (IBD) / Colitis in mouse Colon with conditions AC, CC, HC), describe the associated signaling pathways and mechanisms and, where relevant, its potential as a therapeutic target and related therapeutic agents.
11. Show marker expressions for Intestinal Epithelial cell in a dot plot, and save the result. Use only surfaceome markers, with at most 50 markers per condition. For each marker identified under each condition, using the provided dataset context (Inflammatory Bowel Disease (IBD) / Colitis in mouse Colon with conditions AC, CC, HC), describe the associated signaling pathways and biological mechanisms within the tissue and, where relevant, its potential as a therapeutic target for Inflammatory Bowel Disease (IBD) / Colitis and related therapeutic agents.
12. Show marker expressions for Macrophage in a dot plot, and save the result. Use only surfaceome markers, with at most 40 markers per condition. For each marker identified under each condition, using the provided dataset context (Inflammatory Bowel Disease (IBD) / Colitis in mouse Colon with conditions AC, CC, HC), describe the associated signaling pathways and biological mechanisms within the tissue and, where relevant, its potential as a therapeutic target for Inflammatory Bowel Disease (IBD) / Colitis and related therapeutic agents.
13. Show marker expressions for Fibroblast in a dot plot, and save the result. Use only surfaceome markers, with at most 40 markers per condition. For each marker identified under each condition, using the provided dataset context (Inflammatory Bowel Disease (IBD) / Colitis in mouse Colon with conditions AC, CC, HC), describe the associated signaling pathways and biological mechanisms within the tissue and, where relevant, its potential as a therapeutic target for Inflammatory Bowel Disease (IBD) / Colitis and related therapeutic agents.
14. Show marker expressions for T cell CD4+ in a dot plot, and save the result. Use only surfaceome markers, with at most 40 markers per condition. For each marker identified under each condition, using the provided dataset context (Inflammatory Bowel Disease (IBD) / Colitis in mouse Colon with conditions AC, CC, HC), describe the associated signaling pathways and biological mechanisms within the tissue and, where relevant, its potential as a therapeutic target for Inflammatory Bowel Disease (IBD) / Colitis and related therapeutic agents.
15. Show Gene Ontology (GSA) analysis results for Intestinal Epithelial cell as a bar plot, and save the result.
16. Show Gene Set Enrichment Analysis results as a dot plot, and save it. Set the color map to RdBu_r, n_pws_to_show to 120, and target_cells to None.