Ramalingam Latha, Oh Eunjin, Thurmond Debbie C
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
Diabetologia. 2014 Jul;57(7):1476-84. doi: 10.1007/s00125-014-3227-7. Epub 2014 Apr 6.
AIMS/HYPOTHESIS: Insulin secretion from pancreatic beta cells and insulin-stimulated glucose uptake into skeletal muscle are processes regulated by similar isoforms of the soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) and mammalian homologue of unc-18 (Munc18) protein families. Double C2 domain β (Doc2b), a SNARE- and Munc18-interacting protein, is implicated as a crucial effector of glycaemic control. However, whether Doc2b is naturally limiting for these processes, and whether Doc2b enrichment might exert a beneficial effect upon glycaemia in vivo, remains undetermined.
Tetracycline-repressible transgenic (Tg) mice engineered to overexpress Doc2b simultaneously in the pancreas, skeletal muscle and adipose tissues were compared with wild-type (Wt) littermate mice regarding glucose and insulin tolerance, islet function in vivo and ex vivo, and skeletal muscle GLUT4 accumulation in transverse tubule/sarcolemmal surface membranes. SNARE complex formation was further assessed using Doc2b overexpressing L6-GLUT4-myc myoblasts to derive mechanisms relatable to physiological in vivo analyses.
Doc2b Tg mice cleared glucose substantially faster than Wt mice, correlated with enhancements in both phases of insulin secretion and peripheral insulin sensitivity. Heightened peripheral insulin sensitivity correlated with elevated insulin-stimulated GLUT4 vesicle accumulation in cell surface membranes of Doc2b Tg mouse skeletal muscle. Mechanistic studies demonstrated Doc2b enrichment to enhance syntaxin-4-SNARE complex formation in skeletal muscle cells.
CONCLUSIONS/INTERPRETATION: Doc2b is a limiting factor in SNARE exocytosis events pertinent to glycaemic regulation in vivo. Doc2b enrichment may provide a novel means to simultaneously boost islet and skeletal muscle function in vivo in the treatment and/or prevention of diabetes.
目的/假设：胰腺β细胞分泌胰岛素以及胰岛素刺激葡萄糖摄取进入骨骼肌，这些过程受可溶性N - 乙基马来酰亚胺敏感因子附着蛋白受体（SNARE）和unc - 18哺乳动物同源物（Munc18）蛋白家族的相似亚型调控。双C2结构域β（Doc2b）是一种与SNARE和Munc18相互作用的蛋白，被认为是血糖控制的关键效应因子。然而，Doc2b在这些过程中是否天然受限，以及Doc2b富集是否可能对体内血糖产生有益影响，仍未确定。
将经四环素抑制的转基因（Tg）小鼠与野生型（Wt）同窝小鼠进行比较，这些转基因小鼠经工程改造可在胰腺、骨骼肌和脂肪组织中同时过表达Doc2b，比较内容包括葡萄糖和胰岛素耐受性、体内和体外胰岛功能，以及骨骼肌横管/肌膜表面膜中葡萄糖转运蛋白4（GLUT4）的积累情况。使用过表达Doc2b的L6 - GLUT4 - myc成肌细胞进一步评估SNARE复合体的形成，以推导与体内生理学分析相关的机制。
Doc2b转基因小鼠清除葡萄糖的速度明显快于野生型小鼠，这与胰岛素分泌两个阶段的增强以及外周胰岛素敏感性的提高相关。外周胰岛素敏感性增强与Doc2b转基因小鼠骨骼肌细胞表面膜中胰岛素刺激的GLUT4囊泡积累增加相关。机制研究表明，Doc2b富集可增强骨骼肌细胞中Syntaxin - 4 - SNARE复合体的形成。
结论/解读：Doc2b是体内与血糖调节相关的SNARE胞吐事件中的一个限制因素。Doc2b富集可能为在糖尿病治疗和/或预防中同时增强体内胰岛和骨骼肌功能提供一种新方法。
