Project Summary Inflammatory bowel disease (IBD) is a chronic inflammatory condition of the digestive tract with an uncertain etiology. At present, treatment of IBD is limited to 5-aminosalicylates, corticosteroids, and immunosuppressants, including azathioprine and 6-mercaptopurine. Because specific and curative treatments with acceptable toxicity and side effect profiles are lacking, there remains a demand for the development of effective therapeutic approaches. Of significant importance to the present application are our findings from previous studies, which demonstrated that bacterial products, such as fMLP and MDP, could be transported by the intestinal epithelial oligopeptide transporter, PepT1. Once taken up into the cytosol, these small bacterial peptides initiate an inflammatory response. These bacterial peptides can also interact directly with immune cells. Since immune cells, including macrophages, also express PepT1, they have the capacity to take up small bacterial peptides, which can then interact with the NBS- LRR family of intracellular receptors (e.g., NOD2) that mediate intracellular recognition of microbes and their products. Thus, together with the inflammatory response initiated at the epithelial level, these small bacterial peptides in immune system cells may lead to an inflammatory cascade that results in tissue damage. Our overall hypothesis is that PepT1 plays a critical role in regulating the immune response by serving as a gateway for bacterial products. The initial aim of this proposal is to investigate the induction of PepT1 expression in colonic epithelial cells. Secondly, we will investigate the role of immune cell-expressed PepT1 in intestinal inflammation using chimeric mice. Finally, PepT1 will be used to target the anti-inflammatory tripeptide, KPV, to inflamed colonic epithelial and immune cells. The project will involve a variety of biochemical and molecular approaches at both the in vitro and in vivo level. The proposed study will generate new insights that will be key to the design and development of therapeutic strategies to ameliorate intestinal inflammatory conditions, including IBD. More than one million adults and children in the United States suffer from IBD. New therapeutic strategies based on a better understanding of the pathogenesis of IBD will improve the clinical care of patients with this disorder.