Megasphaera Elesdenii Dysregulates Colon Epithelial Homeostasis, Aggravates Colitis-Associated Tumorigenesis

Altered gut microbiota has evidenced to be associated with colitis and colonic tumorigenesis, however bacteria-driven mechanism underlying inflammation-related colon pathologies remains undetermined. This study identifies a previously overlooked genus, Megasphaera, is highly abundant in inflammatory bowel diseases (IBD) and colorectal cancer (CRC) cohorts. A Megasphaera species, M. elsdenii reshapes colonic immunity by triggering dendritic cell (DC)-mediated Th1 and Th17 inflammation. Mechanistically, M. elsdenii and its lipopolysaccharide triggers DC activation via TLR4/NF-κB/IRF4 pathway. Accordingly, in Tlr4^-/- mice, M. elsdenii colonization cannot expand colonic infiltration of DCs and fails to induce Th1 and Th17 responses in. In a Shanghai CRC cohort with a 100% detective rate for Megasphaera, the species of Megasphaera significantly dominated in early onset CRC patients (<50 years old) rather than late-onset CRC (≥50 years old). M. elsdenii and M. elsdenii-enriched microbiota exacerbate colonic inflammation and tumorigenesis in azoxymethane (AOM)/dextran sodium sulfate (DSS)-induced murine colitis-associated cancer model. Taken together, this study uncovers a pathogenic role of Megasphaera in developing colonic tumorigenesis via activating DC-mediated inflammation.