Deleting MyD88 signaling in myeloid cells promotes development of adenocarcinomas of the colon

Intestinal myeloid cells are not only essential for keeping local homeostasis, but also play an important role in regulating the occurrence of colitis and colitis-associated cancer (CAC). In these diseases, the manner in which the myeloid cells work and which molecular pathways influence them are still not fully understood. In our study, we discovered that MyD88 signaling in colonic myeloid cells participates in the development of CAC. Myeloid MyD88-deficient mice showed greater susceptibility to azoxymethane (AOM)/dextran sodium sulfate (DSS)-induced CAC, as evidenced by the increase in the number and sizes of tumors. Myeloid MyD88 deletion markedly increased production of pro-inflammatory and pro-tumor cytokines; recruitment of more IL-1β producing-neutrophils in colon from bone marrow; increased in epithelial cell apoptosis and decreased in epithelial cell proliferation; enhancement of colon mucosal expression of COX-2, p-STAT3, β-catenin, and cyclinD1; induction of further DNA damage and β-catenin mutation. To sum up, these results suggest that myeloid MyD88 signaling protects the intestine from tumorigenesis during the development of CAC.