Effect of M. elsdenii on gene expression of bone marrow derived dendritic cells

Bacteria-driven mechanism underlying inflammation-related colon pathologies remains undetermined. We identified that Megasphaera elsdenii (M. elsdenii), was highly abundant in inflammatory bowel diseases (IBD) and colorectal cancer (CRC) cohorts. To understand the possible mechanism by which M. elsdenii affects DC function, we sequenced BMDC RNAs with and without M. elsdenii treatment.. A subset of genes involved in immune activation, inflammation and antigen presentation, including Il1b, Ifng, Il23, Il12, Cd40, Icos, Cd80, H2-M2 and H2-K2, were increased by M. elsdenii, whereas genes related to immunosuppression (Arg1, Mrc1, Cd163) were downregulated. Enrichment analysis of the KEGG pathway and GO term showed that the Toll-like receptor (TLR) signaling pathway and NF-κB signaling pathway in BMDCs were notably upregulated by M. elsdenii. We further performed western blot, receptor inhibitors and shRNA assays, and showed that M. elsdenii promotes DC maturation and activation through TLR4 ligation, leading to the activation of NF-κB and IRF4 and subsequent induction of pro-inflammatory cytokines and co-stimulatory molecules.