Impact of dysbiotic and symbiotic catabolism of luminal amino acids on intestinal epithelial barrier function and inflammation

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Over 3 million adults in the U.S. suffer from inflammatory bowel diseases (IBD), which encompasses Crohn’s disease (CD) and ulcerative colitis (UC). IBD is characterized by dysbiotic gut microbiota, compromised epithelial barrier function, chronic intestinal inflammation, and increased mucosal cytokines. Epithelial barrier function is regulated by a series of intercellular junctions that encompass the tight junction (TJ), adherens junction, and desmosomes. Disruption of the critical epithelial barrier allows access of luminal contents to immunologically privileged compartments, thereby contributing to IBD pathogenesis. The dysbiotic gut microbiota-induced mucosal inflammation perturbs intercellular junctions and epithelial homeostatic properties, thereby resulting in a compromised epithelial barrier. However, our knowledge of the molecular basis of commensal-stimulated intercellular junction proteins’ function, epithelial homeostasis, and restoration of the compromised epithelial barrier during intestinal inflammation is very limited. Thus, the overall goals of this proposal are to identify mechanisms by which specific commensal bacteria and bacterial metabolic products regulate functions of intercellular junction proteins, and protect from epithelial barrier compromise and injury. Our preliminary data determined that the symbiotic Bacteroides uniformis predominantly catabolizes arginine to produce polyamine spermidine, which promotes a healthy barrier. In contrast, dysbiotic Proteobacterial species E. coli predominantly catabolizes lysine to synthesize polyamine cadaverine, which impairs gut permeability. Bacterial polyamines are aliphatic amines that regulate multiple cellular processes. Based on our preliminary data, we hypothesize that microbial polyamines regulate epithelial barrier functions by activating TRPV and regulating TJ SUMOylation, a post-translational modification of claudin and ZO proteins in the gut epithelial barrier. Polyamines can activate Transient Receptor Potential Receptors (TRPVs) to regulate cellular functions. In Aim 1, we will dissect the symbiotic polyamine-activated TRPV1 and dysbiotic cadaverine-elicited TRPV3-mediated TJ regulatory processes. In Aim 2, we will elucidate microbial polyamine-driven SUMOylation of TJ proteins eventuating in the perturbed barrier function. Finally, in Aim 3, we will determine the impact of small molecules and luminal metabolites, which inhibit cadaverine synthesizing enzymes of the dysbiotic gut bacteria and thereby dampen intestinal inflammation. This project is both conceptually and technically innovative. It will employ the creative use of Trpv1 and Trpv3 knockout mice and a novel pathogen-specific antibacterial agent. The investigation of the effects of gut bacterially produced polyamines on epithelial TRPV and TJ SUMOylation approach is novel. Completion of these studies will provide clear insights into the molecular basis of intestinal epithelial barrier regulation by commensals’ amino acid catabolism and engender new ideas and proof-of-principle of exploiting commensal bacterial metabolites to develop therapeutics for IBD and other gastrointestinal diseases, a high NIDDK research priority.