Single-cell and bulk transcriptomics reveals M2d macrophages as a potential therapeutic strategy for mucosal healing in ulcerative colitis.

Mucosal healing is essential for treating ulcerative colitis (UC), which results from imbalanced macrophage polarization and dysregulated inflammatory responses. However, the mechanisms of cellular communication and signal transduction that regulate mucosal healing among macrophage subtypes require further investigation. We use bulk and single-cell RNA sequencing analysis to reveal that macrophage subtypes vary in different UC states. At the same time, chemokine and angiogenesis signaling is strongly associated with M2 macrophage's infiltrated proportion. To get more insight into subtypes of macrophages in mucosal healing, we divided macrophages into M1, M2b, and M2d macrophages. Based on the differentially expressed genes (DEGs) between M2d and M1 macrophages, KEGG and GO analysis highlights M2d macrophages' ability to alleviate inflammation and promote epithelial healing. Trajectory analysis revealed opposite differentiation of macrophage subsets between UC and healthy groups, with M1 and M2d macrophages coexisting in the same differentiation branch under UC conditions. Along the pseudotime axis, CCL3 and VEGFA expression increased in UC, while IL10RA remained stable in UC but increased in healthy controls. CellChat identified CCL3-CCR1 has strong communication between M1 and M2d macrophages, while the IL10 signaling pathway is activated explicitly in M2d macrophages to mitigate inflammation and promote epithelial healing. We also speculate that high levels of VEGFA activate endothelial cells expressing VEGFR and worsen inflammation. To conclude, we suggested IL10 and VEGF signaling in M2d macrophages as potential therapeutic targets for mucosal healing. However, it is necessary to establish reliable methods for isolating and purifying M2d macrophages before these targets can be effectively utilized.