SM蛋白与Syt-7调控胰岛素分泌颗粒融合的机制研究

葡萄糖刺激的胰岛素分泌障碍是2型糖尿病的主要病理特征之一。在钙离子触发下，胰岛素分泌颗粒与细胞膜融合将胰岛素释放到细胞外。除SNARE外，胰岛素分泌颗粒融合还需要Sec-1/Munc18（SM）蛋白和钙信号蛋白Syt-7来调控。目前已发现多达7种SNARE蛋白和3种SM蛋白参与了这一复杂过程。SM蛋白、Syt-7是如何调控胰岛素分泌颗粒融合的还不清楚。我们在预实验中发现3种SM蛋白在胰岛素分泌中的保守功能是促进SNARE蛋白介导的囊泡融合，但每一个SM蛋白有其特异的调控机制。Syt-7通过和t-SNARE蛋白、脂质结合，与SM蛋白一起协同调控胰岛素分泌颗粒融合。本项目将通过膜蛋白功能重组技术和细胞实验系统地研究SM蛋白、Syt-7与SNARE结合调控胰岛素分泌颗粒融合的机制，揭示GLP-1磷酸化融合蛋白对胰岛素分泌的影响，为认识2型糖尿病的产生机制和以胰岛素分泌为靶治疗糖尿病提供新思路。

Impairment in glucose-stimulated insulin secretion is a hallmark of type 2 diabetes. Intracellular insulin is released through Ca2+-triggered insulin granule fusion. Insulin granule fusion is mediated by SNARE, Sec1/Munc18 (SM) proteins and the Ca2+-binding factor Syt-7. The SNARE-SM machinery of insulin granule fusion is considerably complex, seven SNARE proteins and three SM proteins are involved in this process. It remains unknown how SM proteins and Syt-7 act in concert to regulate insulin granule fusion. In our preliminary studies, we identified that the conserved function of SM proteins in insulin secretion is acceleration of SNARE-mediated vesicle fusion, although each of them has divergent mechanisms. We observed that Syt-7 bound to t-SNAREs and phosphatidylserine in a Ca2+-dependent manner, and Syt-7 and SM proteins cooperatively promote insulin granule fusion. In this proposal, we will use in vitro functional reconstitution assays and cell-based experiments to investigate the regulatory mechanisms of SM proteins and Syt-7 in SNARE-dependent insulin granule fusion. We will uncover how insulin secretion is modulated by GLP-1-induced fusion protein phosphorylations. This work will help to understand the molecular basis of type 2 diabetes and identify new drug targets from the regulation of insulin secretion.