Resolving Resident Colonic Muscularis Macrophage Diversity and Plasticity During Colitis
Background: Immune cell populations within the intestinal muscularis propria are poorly resolved during colitis. Maintaining homeostasis in this unique niche is of critical importance, highlighted by the poorer prognosis of inflammatory bowel disease associated with inflammation in the muscularis propria. Methods: This study utilizes single-cell RNA sequencing to survey the immune cell populations within the muscularis propria of normal colon and DSS-induced colitis. Results: In naïve conditions, transcriptional duality is observed in MMf with two major supopulations: conventional resident Cx3cr1+ MMfs and Lyve1+ MMfs. During colitis, significant changes occur within the muscularis propria, with increases in B-cells, T-cells, monocytes, neutrophils, and dendritic cells. Unlike in the mucosa, single cell transcriptomics indicates that resident MMfs are retained during colitis and exhibit plasticity toward an inflammatory profile. Lyve1+ MMfs, which express anti-inflammatory marker CD163, are absent during colitis. In contrast, resident Cx3cr1+ MMfs remain during colitis. Conclusions: Our findings provide a resource for understanding the immune system in the muscularis propria niche during colitis and resolve the heterogeneity and origins of proinflammatory MMfs during colitis by demonstrating the plasticity of the persistent MMf population. Overall design: To induce acute colitis B6 mice were provided ad libitum access to drinking water containing 2.5% DSS (36,000 - 50,000 Da, MP Biomedicals, CA) for 7 days before sacrifice. Naïve mice and littermates exposed to DSS to induce colitis of each gender were euthanized and colons collected for isolation of the muscularis propria to analyze leukocytes and enteric glia.