-derived metabolites protect mice against colonic inflammation.

Gut microbiota-derived metabolites play a pivotal role in the maintenance of intestinal immune homeostasis. Here, we demonstrate that the human commensal possesses a specific metabolic fingerprint, consisting predominantly of the tryptophan catabolite indole-3-propionic acid (IPA), the branched-chain acids (BCFAs) isobutyrate and isovalerate and the short-chain fatty acids (SCFAs) acetate and propionate. Mono-colonization of germ-free mice with (CS mice) affected colonic mucosal immune cell phenotypes, including up-regulation of gene expression, and increased abundance of transcriptionally active colonic tuft cells and Foxp3 regulatory T cells (Tregs). In DSS-induced colitis, conventional mice suffered severe inflammation accompanied by loss of colonic crypts. These symptoms were absent in CS mice. In conventional, but not CS mice, bulk RNAseq analysis of the colon revealed an increase in inflammatory and Th17-related gene signatures. -derived IPA reduced IL-17A protein expression by suppressing mTOR activity and by altering ribosome-related pathways in Th17 cells. Additionally, BCFAs and SCFAs generated by enhanced the activity of Tregs and increased the production of IL-22, which led to protection from colitis. Collectively, we identified as a therapeutically relevant probiotic bacterium that might be employed in patients with inflammatory bowel disease (IBD).