9 METABOLIC UTILIZATION OF PROPANEDIOL BY ADHERENT-INVASIVE E. COLI REGULATES INTESTINAL TISSUE IMMUNITY

While the molecular mechanisms by which the microbiome modulates mucosal immunity in Crohn’s disease (CD) are still largely unknown, recent data highlight the involvement of specific diet- and bacterial-derived metabolites in the regulation of intestinal immune cell activation and differentiation. We have recently shown that Adherent-Invasive E.coli (AIEC), which are enriched in CD patients, are sufficient to induce intestinal Th17 cells. Although AIEC lack pathogenic factors including type III secretion systems, many CD-derived isolates express virulence-associated metabolic enzymes including propanediol dehydratase (PduC), which enables AIEC to use fucose-derived propanediol as an alternate carbon source in the gut. We found that pduC is enriched in the microbiome and among E. coli genomes in CD patients compared to healthy controls. With fucosylated oligosaccharides on the surface of intestinal epithelial cells, we hypothesized that this propanediol utilization pathway provides AIEC a competitive advantage for epithelial cell adherence and intestinal immune cell activation. To evaluate the physiologic contribution of pduC to mucosal Th17 induction, we generated a pduC-deficient (ΔpduC) mutant of a CD-derived, AIEC isolate. Deletion of pduC resulted in reduced inflammatory Th17 cells and attenuated weight loss following T cell transfer colitis. Using genetic mouse models, we found that CX₃CR1⁺ mononuclear phagocytes are required for this AIEC-mediated Th17 induction and IL-10 is required to restrain pduC-dependent dextran sodium sulfate (DSS)-induced colitis. Using a catalytically-inactive mutant, we determined that PduC metabolic activity was required for this immune phenotype. Cell-free supernatants from WT AIEC (but not the isogenic, pduC-deficient clone) promoted ex vivo Th17 cell polarization and metabolomics analysis (LC-MS) of these supernatants defined PduC-dependent metabolites capable of promoting Th17 polarization. These studies reveal a link between AIEC microbial metabolism and inflammatory Th17 cells with the potential to serve as a therapeutic target in the treatment of Crohn’s disease.