MyD88-mediated signaling in myo-/fibroblasts is required for control of macrophage maturation under mucosal tolerance in the gut

Abstract Introduction Colonic myo-/fibroblasts (MFs) are cells of mesenchymal origin in a healthy gut are among the key players in the mucosal tolerance that involve MF-restricted MyD88 signaling. MFs and macrophages interact in colonic tissue. However, the mechanisms of MF mediated regulation of macrophages under intestinal mucosal tolerance has emerging evidence. We hypothesized that MF-restricted MyD88 signaling regulates macrophage maturation under colonic mucosal tolerance. Methods RNAseq, qRT-PCR, H&E, and flow cytometry was used for analysis of colonic tissue/cell derived from B6ACTA2CreMyD88fl/fl, B6Col1a2CreMyD88fl/fl and B6RagCol1a2CreMyD88fl/fl MF-specific conditional KO mice. Results MF-specific deletion of MyD88 in vivo resulted in the development of microcolitis and was associated with dysbiotic decrease in Firmicutes to Bacteroidetes bacterial ratio, a hallmark of intestinal inflammation. This process was associated with the increase in colonic expression of genes linked to the inflammatory activity of myeloid cells and accumulation of immature monocyte-derived macrophages. In vitro deletion of MyD88 from MFs (isolated from MF-specific MyD88 conditional KO mice) resulted in changes of basal and TLR4 mediated pathways involved in myeloid cell migration/maturation and inflammation. Using MF-macrophage co-cultures we demonstrated the MF-restricted MyD88 signaling suppresses myeloid cell inflammatory activity. Conclusion Intrinsic MyD88 signaling within colonic mesenchymal cells is critical to control myeloid cell differentiation and inflammatory activity under mucosal tolerance in the gut. Supported by CTSA/TL1 5TL1TR001440-04 UTMB Institute for Translational Science and R01 DK103150 National Institute of Diabetes and Digestive and Kidney Diseases.