LEPTIN REGULATION OF BETA CELL PROLIFERATION

Baylor College Of Medicine, Houston TX

Investigators

Linked publications, trials & patents

Abstract

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 fluorescence imaging. Revealing leptin effects on calcium levels in delta cells will position future studies to define the signals downstream of LepR that lead to SST secretion. Define transcriptional mechanisms of leptin action in delta cells. Our preliminary data suggest delta cell expression of Stat3 is required for leptin-induced SST secretion. Islets from SST-Cre;Stat3-fl/fl (dStat3 KO) mice exhibit a significantly blunted secretion of SST when treated with leptin compared to control islets. - We will block STAT3 during islet perifusion in the presence of leptin in human (STAT3 inhibitor, TTI-101; Tvardi Therapeutics) or mouse (dStat3 KO) islets to assess the impacts on hormone secretion. - Human islets treated with leptin +/- STAT3 inhibitor (TTI-101) will be subjected to scRNA-seq analysis (expertise previously established as part of a separate manuscript in prep) to determine the delta cell specific gene targets of leptin-STAT3 signaling that define delta cell activities. We will also uncover other transcription factors and close key knowledge gaps that define the regulation of delta cells. Significance. Our proposed studies will reveal leptin stimulates JAK-STAT signaling in delta cells to ready SST secretion, which suppresses beta cell insulin secretion. Leptin is a critical regulator of energy balance and glucose homeostasis and therefore, these findings will provide key insights into leptin action during physiologic (post-prandial) and pathologic (obesity, diabetes) states. We will also determine the potential translational benefits of STAT3 inhibition. Our revised premise focused on islet function combined with new preliminary data using innovative tools will significantly strengthen our new R01 application for late 2022 or early 2023. Our proposed studies for the next year will reveal new biology about delta cells and define molecular and transcriptional mechanisms through which leptin regulates islet function.