The morbidity of inflammatory bowel disease (IBD) stems from its effect on electrolytes, nutrients and fluid absorption;thus, patients with IBD sustain malabsorption and diarrhea with attendant malnutrition and weight loss. It has long been held that once chronic intestinal inflammation has occurred, malabsorption and diarrhea are the inevitable results. However, in the previous funding cycle of this proposal we demonstrated that malabsorption and diarrhea are not the irrevocable end results of chronic intestinal inflammation, but actively regulated processes. We focused on the regulation of Na-glucose co-transport (SGLT1) and Na-amino acid co-transport (NAcT), which are not only important for nutrient assimilation, but also the absorption of Na. We determined that upstream mast cells, inducible nitric oxide, and arachidonic acid were common pathways of extra cellular regulation of these 2 co-transporters. However, further downstream while prostaglandin E2 (PGE2) mediated the inhibition of SGLT1, leukotriene D4 (LTD4) mediated the inhibition of NAcT. We also demonstrated that the mechanism of inhibition of SGLT1 was secondary to a decrease in co-transporter numbers while that of NAcT was secondary to altered co-transporter affinity during chronic enteritis. Having demonstrated the unique extra cellular regulation of SGLT1 and NAcT in the chronically inflamed intestine, the next logical step is the overall aim of this proposal: Determine the intracellular mechanism of regulation and the molecular alterations of SGLT1 and NAcT during chronic enteritis. Specifically, we will determine intracellular G protein, 2nd messenger and protein kinase pathways, which regulate SGLT1 and NAcT during chronic enteritis. Then we will decipher the unique molecular alterations of SGLT1 and NAcT mediated by the respective intracellular pathways in the chronically inflamed intestine. Successful completion of these studies will provide novel and valuable information for the overall hypothesis of this proposal: Unique intracellular mechanisms of regulation result in the unique changes in SGLT1 and NAcT in the chronically inflamed intestine. This knowledge will provide the basis for new and more efficacious treatment modalities for the most common morbidities of IBD specifically, malabsorption, diarrhea and malnutrition.
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