Gastric X/A Like Cells in Health and Diseases

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Project Abstract New insights from our studies and others indicate that the gastric mucosa may sense overall energy balance and control metabolic rate through fine-tuning the production of two counteracting hormones: ghrelin and nesfatin-1, in X/A like cells. Ghrelin, a 28-amino acid gastric peptide hormone, was originally identified as an orexigenic factor, and is the only known circulating hormone able to initiate food intake. X/A like cells has been discovered to also secrete the anorexigenic hormone nesfatin-1. Our data indicate that the balance of ghrelin and nesfatin-1 secretion regulates nutrient intake. Our studies also indicate that the mechanistic target of rapamycin (mTOR) signaling pathway in the gastric mucosa plays a critical role in the coordination of nutrient availability, ingestive behavior and metabolic activity. Based on these observations, we hypothesize that mTOR signaling regulates fuel sensing via gastric X/A like endocrine cells. This signaling pathway coordinates overall energy balance by differential regulation of the orexigenic hormone ghrelin and the anorexigenic hormone nesfatin-1. We propose 3 specific aims to investigate the function of the gastric mTOR pathway in the production of these peptides and thus their effects on appetite control and energy expenditure. Aim 1 is designed to test the hypothesis that organismal fuel status affects phosphorylation of mTOR in gastric X/A like cells, and that mTOR signaling differentially regulates ghrelin and nesfatin-1 production. Aim 2 will first examine the alternative AMPK-HDAC5-mTOR signaling pathway in the regulation of ghrelin and nesfatin-1. We will then test the hypothesis that S6K1 and 4EBP1 are mTOR downstream molecules regulating the reciprocal translation of ghrelin and nesfatin-1. Aim 3 will demonstrate that gastric mTOR signaling affects food intake, energy expenditure and body weight in mice vial acyl-ghrelin and nesfatin-1. Completion of this proposal will advance our understanding of the interaction between gastric X/A like cells and nutrient intake. These findings suggest a completely new therapeutic approach directed at gastric sites.