Department of Cell Biology, Yale University School of Medicine, New Haven, CT, USA.
Department of Bioengineering, Key Laboratory of Biomedical Engineering of Ministry of Education, Zhejiang University, Hangzhou, China.
J Cell Mol Med. 2017 Nov;21(11):2950-2962. doi: 10.1111/jcmm.13207. Epub 2017 May 25.
Type 2 diabetes is caused by defects in both insulin sensitivity and insulin secretion. Glucose triggers insulin secretion by causing exocytosis of insulin granules from pancreatic β-cells. High circulating cholesterol levels and a diminished capacity of serum to remove cholesterol from β-cells are observed in diabetic individuals. Both of these effects can lead to cholesterol accumulation in β-cells and contribute to β-cell dysfunction. However, the molecular mechanisms by which cholesterol accumulation impairs β-cell function remain largely unknown. Here, we used total internal reflection fluorescence microscopy to address, at the single-granule level, the role of cholesterol in regulating fusion pore dynamics during insulin exocytosis. We focused particularly on the effects of cholesterol overload, which is relevant to type 2 diabetes. We show that excess cholesterol reduced the number of glucose-stimulated fusion events, and modulated the proportion of full fusion and kiss-and-run fusion events. Analysis of single exocytic events revealed distinct fusion kinetics, with more clustered and compound exocytosis observed in cholesterol-overloaded β-cells. We provide evidence for the involvement of the GTPase dynamin, which is regulated in part by cholesterol-induced phosphatidylinositol 4,5-bisphosphate enrichment in the plasma membrane, in the switch between full fusion and kiss-and-run fusion. Characterization of insulin exocytosis offers insights into the role that elevated cholesterol may play in the development of type 2 diabetes.
2 型糖尿病是由胰岛素敏感性和胰岛素分泌缺陷引起的。葡萄糖通过引起胰腺β细胞中胰岛素颗粒的胞吐作用来触发胰岛素分泌。在糖尿病患者中，观察到循环胆固醇水平升高和血清从β细胞中去除胆固醇的能力降低。这两种效应都可能导致β细胞中胆固醇积累，并导致β细胞功能障碍。然而，胆固醇积累损害β细胞功能的分子机制在很大程度上仍然未知。在这里，我们使用全内反射荧光显微镜在单个颗粒水平上解决胆固醇在调节胰岛素胞吐过程中融合孔动力学中的作用。我们特别关注与 2 型糖尿病相关的胆固醇过载的影响。我们表明，过量胆固醇减少了葡萄糖刺激的融合事件数量，并调节了完全融合和亲吻-跑融合事件的比例。对单个胞吐事件的分析显示出不同的融合动力学，在胆固醇过载的β细胞中观察到更聚集和复合胞吐作用。我们提供了证据表明 GTPase 动力蛋白的参与，该蛋白部分受胆固醇诱导的质膜中磷脂酰肌醇 4,5-二磷酸的富集调节，在完全融合和亲吻-跑融合之间的转换中起作用。胰岛素胞吐作用的特征提供了关于升高的胆固醇在 2 型糖尿病发展中可能起作用的见解。
