Impact Of Dysbiotic And Symbiotic Catabolism Of Luminal Amino Acids On Intestinal Epithelial Barrier Function And Inflammation

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 gut microbiota is intricately linked with many gastrointestinal disorders, including IBD and colorectal cancer. We previously reported that the injured intestinal mucosa specifically enriches a mucosa-associated microbial consortium, which promotes restoration of epithelial barrier function. 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 protein 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. My recently completed K01 award laid a foundation for my rigorous training in metabolome and cell biology of gut barrier function. In this R01 proposal, 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, which regulate multiple cellular processes. Based on our preliminary data, we posit that the microbial polyamines regulate epithelial barrier functions by stimulating translational and post-translational modifications of TJ proteins. We will specifically examine the role of bacterial polyamine in regulating translational and post-translational modification and the function of TJ claudin and ZO proteins in the gut epithelial barrier. We will dissect the symbiotic polyamine-activated TRPV1 and TRPV3-mediated TJ regulatory processes. We will elucidate microbial polyamine-driven SUMOylation of TJ proteins eventuating in the perturbed barrier function. Also, we will determine the impact of small molecules and luminal metabolites, which inhibit cadaverine synthesizing enzymes of dysbiotic gut bacteria and thereby dampen intestinal inflammation. Thus, these studies will provide 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.