Modulation of Host-Microbe Interactions by Extracellular Purines in the Gastrointestinal Lumen

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Project Summary/Abstract Over 3 million people in the United States carry a diagnosis of inflammatory bowel disease (IBD), a chronic and incurable condition of unknown cause that carries with it significant morbidity and healthcare costs. Intestinal dysbiosis is a hallmark of IBD that contributes to its pathogenesis, though specific mechanisms underlying this observation are lacking. As a gastroenterologist and physician scientist, the candidate seeks to elucidate specific molecular mechanisms that mediate host-microbe interactions that drive IBD with the ultimate goal of translating these findings into clinical applications. The proposed research builds on the candidate's published observations that adenosine (Ado) regulates colonization and virulence of the Salmonella enterica serovar Tyhpimurium and will provide the candidate with the additional training necessary to move forward as an independent investigator. Whereas it has been shown that Ado signaling in the GI mucosa promotes resolution of inflammation, the actions of Ado on the intestinal microbiota have not been examined. The proposed research tests the hypothesis that extracellular Ado produced in the gastrointestinal mucosa influences the composition and metabolism of the intestinal microbiota through inhibition of the bacterial stringent response (SR) to inhibit dysbiosis and promote intestinal homeostasis. This hypothesis is explored through three aims: In Aim 1, the mechanism by which Ado inhibits growth of enteric bacteria will be defined. Preliminary data show that Ado inhibits bacterial growth by inducing amino acid auxotrophies through suppression of the SR, a global bacterial adaptation to nutritional stress. The mechanisms underlying this observation will be determined through metabolomic and transcriptomic analyses of bacterial mutants deficient in purine metabolism. Aim 2 will elucidate the mechanisms by which Ado promotes intestinal homeostasis by modulating the intestinal microbiota. A novel mouse model wherein intestinal epithelial cells lack the ability to generate extracellular Ado (conditional knockout of ecto-5'-nucleotidase) will be used to assess how Ado shapes the intestinal microbiota. Murine fecal microbial transfer (FMT)-IBD will be used to examine the role of Ado in promoting intestinal homeostasis by shaping the intestinal microbiota. Finally, Aim 3 presents a translational application of the mechanisms under study by demonstrating that exogenously administered purines can alter intestinal homeostasis in an analogous manner to naturally-occurring purines in the intestine. The proposed work will be performed under the mentorship of Drs. Sean Colgan and Andrés Vázquez-Torres at the University of Colorado, who have extensive expertise in the role of adenosine in gastrointestinal inflammation and the role of nucleotide metabolism in the pathogenesis of enteric infectious diseases, respectively. This mentoring team is ideally suited to the proposed research, which is situated at the intersection of each of their areas of expertise and will provide the candidate with necessary additional training in the areas of murine models of IBD, metabolomic analysis, microbiology, and microbiome analysis.