Department of Cell Biology, Neurobiology and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226.
HHMI, Yale University School of Medicine, New Haven, CT 06510.
Proc Natl Acad Sci U S A. 2021 Aug 10;118(32). doi: 10.1073/pnas.2021764118.
Pancreatic β cells operate with a high rate of membrane recycling for insulin secretion, yet endocytosis in these cells is not fully understood. We investigate this process in mature mouse β cells by genetically deleting dynamin GTPase, the membrane fission machinery essential for clathrin-mediated endocytosis. Unexpectedly, the mice lacking all three dynamin genes (, , ) in their β cells are viable, and their β cells still contain numerous insulin granules. Endocytosis in these β cells is severely impaired, resulting in abnormal endocytic intermediates on the plasma membrane. Although insulin granules are abundant, their release upon glucose stimulation is blunted in both the first and second phases, leading to hyperglycemia and glucose intolerance in mice. Dynamin triple deletion impairs insulin granule exocytosis and decreases intracellular Ca responses and granule docking. The docking defect is correlated with reduced expression of Munc13-1 and RIM1 and reorganization of cortical F-actin in β cells. Collectively, these findings uncover the role of dynamin in dense-core vesicle endocytosis and secretory capacity. Insulin secretion deficiency in the absence of dynamin-mediated endocytosis highlights the risk of impaired membrane trafficking in endocrine failure and diabetes pathogenesis.
胰岛β细胞通过高速的膜循环来进行胰岛素分泌，但目前对于这些细胞中的内吞作用还不完全了解。我们通过基因敲除网格蛋白介导的内吞作用所必需的膜分裂机械蛋白——GTP 酶 dynamin，来研究成熟的小鼠β细胞中的这个过程。出乎意料的是，缺乏β细胞中所有三种 dynamin 基因（，，）的小鼠是存活的，并且它们的β细胞中仍然含有大量的胰岛素颗粒。这些β细胞中的内吞作用严重受损，导致质膜上出现异常的内吞中间产物。尽管胰岛素颗粒丰富，但在葡萄糖刺激下它们的释放受到阻碍，导致第一和第二阶段的高血糖和葡萄糖不耐受。 dynamin 三重缺失会损害胰岛素颗粒的胞吐作用，并降低细胞内 Ca 反应和颗粒对接。对接缺陷与 Munc13-1 和 RIM1 的表达减少以及β细胞中皮质 F-肌动蛋白的重组有关。总的来说，这些发现揭示了 dynamin 在致密核心囊泡内吞作用和分泌能力中的作用。缺乏 dynamin 介导的内吞作用导致胰岛素分泌缺陷，这突出了在内分泌功能衰竭和糖尿病发病机制中膜运输受损的风险。
