Future Efforts to Strengthen 1R01DK128098-01A1 My goal for the next year is to define molecular and transcriptional mechanisms that govern leptin regulation of islet delta cell functions. The delta cell has emerged as an important regulator of islet function through paracrine actions of somatostatin (SST) that inhibit alpha and beta cells. However, we know little about endocrine signals that perform gene expression and metabolic outcomes in delta cells. Leptin suppresses insulin secretion; however, the leptin receptor (LepR) is exclusively expressed on delta cells of human islets, suggesting leptin may act indirectly on beta cells. Our preliminary data demonstrate for the first time that leptin stimulates SST secretion from human islets which, in turn, decreases insulin secretion from the beta cell. Thus, we propose a model whereby leptin serves as a negative feedback regulator of beta cell insulin secretion by stimulating SST release from delta cells. We will build out our model by achieving the following goals: Cement our central hypothesis that leptin stimulates delta cell SST secretion to inhibit beta cell function. Our preliminary data demonstrate that leptin stimulates SST secretion from human and mouse islets, which suppresses insulin secretion under static conditions. We will employ islet perifusion studies to test dynamic changes in hormone secretion and paracrine signaling that, ultimately, better model in vivo islet responses. - I will visit Duke University to learn islet perifusion from Drs. Jonathan Campbell and David D’Alessio. These efforts will empower me to define dynamic islet responses and paracrine signals following exposure to leptin. - I will leverage new expertise in islet perifusion to define the delta cell specific effects of leptin (loss of function: SST-Cre;LepR-lp/lp mice (previously generated) or siRNA-mediated LepR deletion in human islets) and consequent paracrine effects of SST on insulin and glucagon secretion. These data will firmly establish the premise for my new R01 application that leptin suppresses beta cell function through stimulation of delta cell SST secretion. Define molecular mechanisms of leptin action in delta cells. Islet hormone release involves membrane depolarization and an elevation in intracellular calcium to mediate hormone exocytosis. Although leptin signaling through LepR involves tyrosine kinase activity and JAK-STAT signaling, there is evidence in neurons that leptin increases intracellular calcium (PMID: 30304668). Here, we will test whether leptin increases calcium in delta cells to mediate SST secretion. - I set up a collaboration with Dr. Mark Huising to determine if leptin stimulated SST secretion involves classical exocytotic signals, most notably increased intracellular calcium. Islets expressing the calcium indicator GCaMP6 in delta cells (SST-Cre;Rosa26-lsl-GCaMP; PMID: 28380380, PMID: 27408771) ) will be treated with leptin and GCaMP6 activation will be read out by fluorescen...