Cholesterol biosynthesis pathway intermediates and inhibitors regulate glucose-stimulated insulin secretion and secretory granule formation in pancreatic beta-cells.
Cholesterol biosynthesis pathway intermediates and inhibitors regulate glucose-stimulated insulin secretion and secretory granule formation in pancreatic beta-cells.
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DOI：
10.1210/en.2010-0623
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发表时间：
2010-10
期刊：
影响因子：
4.8
通讯作者：
Miho Tsuchiya;M. Hosaka;T. Moriguchi;Shaojuan Zhang;M. Suda;Hiromi Yokota-Hashimoto;K. Shinozuka;T. Takeuchi
中科院分区：
文献类型：
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作者：
Miho Tsuchiya;M. Hosaka;T. Moriguchi;Shaojuan Zhang;M. Suda;Hiromi Yokota-Hashimoto;K. Shinozuka;T. Takeuchi
据报道，胆固醇在内分泌分泌颗粒(SG)膜中含量丰富。在这项研究中，我们研究了胆固醇生物合成中间体和抑制剂在胰岛素分泌和SG形成机制中的作用。向细胞供应胆固醇有两种途径：一种是通过新生生物合成，另一种是通过低密度脂蛋白受体介导的内吞作用。我们发现，β-羟基-β-甲基戊二酰辅酶A抑制剂洛伐他汀能减少β-细胞胰岛素的分泌和含量，但不会减少培养上清液中的脂蛋白。胆固醇生物合成的中间体甲戊酸、角鲨烯和香叶基焦磷酸促进了葡萄糖刺激的胰岛素分泌，前两者增加了胰岛素的含量。在大鼠胰岛灌流实验中也证实了香叶基香叶基焦磷酸对葡萄糖刺激的胰岛素分泌的促进作用。在形态上，甲戊酸和角鲨烯在不影响其大小的情况下增加了SGS的种群。相反，洛伐他汀增加了SG的大小，减少了积累胰岛素的致密核，导致胰岛素含量下降。此外，胰岛素以结构性的方式分泌，表明调节的胰岛素分泌被破坏。由于分泌型颗粒素III是一种胆固醇结合蛋白，与基于胆固醇组成的SG定位一致，因此分泌型颗粒素III可能与胰岛素的蓄积机制有关。尽管SG膜具有较高的胆固醇组成，但在蔗糖密度梯度分级中，使用脂筏-住宅蛋白fltillin和荧光胆固醇-硅-芘探针作为标记，我们无法找到抗洗涤剂的膜区域。我们认为，高胆固醇组成的SG膜在40-50摩尔%，是胰岛素分泌和SG形成功能的关键。
Cholesterol is reportedly abundant in the endocrine secretory granule (SG) membrane. In this study, we examined the involvement of cholesterol biosynthesis intermediates and inhibitors in insulin secretion and SG formation mechanisms. There are two routes for the supply of cholesterol to the cells: one via de novo biosynthesis and the other via low-density lipoprotein receptor-mediated endocytosis. We found that insulin secretion and content are diminished by β-hydroxy-β-methylglutaryl-coenzyme A inhibitor lovastatin but not by lipoprotein depletion from the culture medium in MIN6 β-cells. Cholesterol biosynthesis intermediates mevalonate, squalene, and geranylgeranyl pyrophosphate enhanced glucose-stimulated insulin secretion, and the former two increased insulin content. The glucose-stimulated insulin secretion-enhancing effect of geranylgeranyl pyrophosphate was also confirmed in perifusion with rat islets. Morphologically, mevalonate and squalene increased the population of SGs without affecting their size. In contrast, lovastatin increased the SG size with reduction of insulin-accumulating dense cores, leading to a decrease in insulin content. Furthermore, insulin was secreted in a constitutive manner, indicating disruption of regulated insulin secretion. Because secretogranin III, a cholesterol-binding SG-residential granin-family protein, coincides with SG localization based on the cholesterol composition, secretogranin III may be associated with insulin-accumulating mechanisms. Although the SG membrane exhibits a high cholesterol composition, we could not find detergent-resistant membrane regions using a lipid raft-residential protein flotillin and a fluorescent cholesterol-Si-pyrene probe as markers on a sucrose-density gradient fractionation. We suggest that the high cholesterol composition of SG membrane with 40-50 mol% is crucial for insulin secretion and SG formation functions.