Role of Rab GAPs AS160 and Tbc1d1 in GLUT4 translocation and glucose homeostasis

项目摘要/摘要 主要疾病包括肥胖、代谢综合征和2型糖尿病。 患有胰岛素抵抗，从而损害了血糖稳态。维护的关键是 禁食和进食条件下的葡萄糖稳态是对亚细胞的适当控制。 葡萄糖转运蛋白GLUT4在肌肉和脂肪细胞中的分布。在禁食条件下， 细胞表面的GLUT4数量限制了肌肉和脂肪细胞对葡萄糖的吸收，因此 使循环中的葡萄糖成为大脑的燃料。餐后，作为对胰岛素的反应， 通过一种被称为GLUT4的过程，细胞表面的GLUT4数量显著增加 易位。这促进了葡萄糖的吸收，并促进了80%-90%的摄入 葡萄糖转化为肌肉和脂肪。此外，GLUT4易位也是导致血糖增加的原因 骨骼肌对运动的摄取反应。AS160，Rab GTP酶激活蛋白(Rab GAP)及其最近发现的近亲Tbc1d1在亚细胞调控中发挥重要作用 GLUT4在培养的脂肪、肌肉细胞和特定的骨骼肌中的分布 老鼠。它们负责在基础条件下GLUT4在细胞内的有效保留，如 以及从GLUT4的滞留和移位到细胞表面释放GLUT4作为反应 胰岛素和锻炼。AS160和Tbc1d1在体内的作用尚未得到评估。 AS160缺失的小鼠(AS160基因敲除小鼠)的初步数据表明 AS160在调节脂肪细胞的葡萄糖摄取中起重要作用，但在骨骼肌中不起作用。 Tbc1d1基因敲除小鼠正在产生，目前还没有初步结果 老鼠。考虑到Tbc1d1在某些类型的骨骼肌中表达水平较高，它是 Tbc1d1可能是骨骼肌GLUT4易位的主要调节因子。我们的假设 AS160和Tbc1d1在亚细胞的调节中发挥着重要且可能是独特的作用 GLUT4在不同细胞类型中的分布。拟议研究的具体目标是 通过分析糖稳态和Tbc1d1的调节来确定AS160和Tbc1d1的作用 基础状态下GLUT4在肌肉和脂肪细胞中的亚细胞分布 AS160基因敲除小鼠、Tbc1d1基因敲除小鼠和AS160/Tbc1d1基因敲除小鼠的胰岛素和运动。 因此，我们的研究将阐明维持血糖的基本机制 动态平衡。它将进一步为AS160和Tbc1d1的验证提供关键信息 以改善血糖稳态和预防胰岛素抵抗继发并发症为目标的药物。

Project Summary/Abstract Major diseases including obesity, the metabolic syndrome, and type 2 diabetes, are associated with insulin resistance and consequently impaired glucose homeostasis. A key to the maintenance of glucose homeostasis under fasting and fed conditions is the proper control of the subcellular distribution of the glucose transporter GLUT4 in muscle and fat cells. Under fasting conditions a low number of GLUT4 at the cell surface limits the uptake of glucose into muscle and fat cells and thus allows the circulating glucose to be available as fuel for the brain. After a meal, in response to insulin, the number of GLUT4 at the cell surface is dramatically increased, through a process known as GLUT4 translocation. This facilitates glucose uptake and promotes the disposal of 80-90% of the ingested glucose into muscle and fat. In addition, GLUT4 translocation is also responsible for increased glucose uptake in skeletal muscles in response to exercise. AS160, a Rab GTPase activating protein (Rab GAP), and its recently identified relative Tbc1d1, play important roles in the regulation of the subcellular distribution of GLUT4, as established in cultured fat and muscle cells and specific skeletal muscles in mice. They are responsible for the efficient intracellular retention of GLUT4 under basal conditions, as well as the release of GLUT4 from retention and translocation of GLUT4 to the cell surface in response to insulin and exercise. The roles of AS160 and Tbc1d1 have not yet been evaluated in vivo. Preliminary data with mice in which AS160 had been deleted (AS160 knockout mice), suggest an essential role for AS160 in the regulation of glucose uptake in adipocytes, but not in skeletal muscles. Tbc1d1 knockout mice are being generated and no preliminary results are yet available from these mice. Considering that Tbc1d1 is expressed at higher levels in some skeletal muscle types, it is possible that Tbc1d1 is the major regulator of GLUT4 translocation in skeletal muscles. Our hypothesis is that AS160 and Tbc1d1 play important and possibly unique roles in the regulation of the subcellular distribution of GLUT4 in different cell types. The specific aims of the proposed research are to determine the roles of AS160 and Tbc1d1 by analyzing glucose homeostasis and the regulation of the subcellular distribution of GLUT4 in muscle and fat cells under basal conditions and in response to insulin and exercise in AS160 knockout, Tbc1d1 knockout, and double AS160/Tbc1d1 knockout mice. Our research will thus elucidate fundamental mechanisms contributing to the maintenance of glucose homeostasis. It will further provide crucial information towards the validation of AS160 and Tbc1d1 as drug targets to improve glucose homeostasis and prevent ensuing complications of insulin resistance.