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

项目总结/摘要 包括肥胖症、代谢综合征和2型糖尿病在内的主要疾病都与 具有胰岛素抵抗并因此损害葡萄糖稳态。一个关键的维护 空腹和进食条件下的葡萄糖稳态是亚细胞葡萄糖代谢的适当控制。 葡萄糖转运蛋白GLUT 4在肌肉和脂肪细胞中的分布。在禁食条件下， 细胞表面的GLUT 4数量限制了葡萄糖进入肌肉和脂肪细胞的摄取， 允许循环中的葡萄糖作为大脑的燃料。饭后，对胰岛素的反应， 细胞表面的GLUT 4数量通过一个称为GLUT 4的过程显著增加 易位这有利于葡萄糖的吸收，并促进80-90%的摄入量的处置。 葡萄糖转化为肌肉和脂肪。此外，GLUT 4易位也是葡萄糖增加的原因 骨骼肌对运动的反应。AS 160是一种Rab GT3激活蛋白（Rab GAP）及其最近发现的相关Tbc 1d 1，在亚细胞免疫调节中发挥重要作用。 GLUT 4的分布，如在培养的脂肪和肌肉细胞以及特定的骨骼肌中所建立的， 小鼠它们负责在基础条件下GLUT 4的有效细胞内滞留，如 以及GLUT 4从滞留中的释放和GLUT 4向细胞表面的易位 胰岛素和锻炼。AS 160和Tbc 1d 1的作用尚未在体内进行评估。 AS 160缺失小鼠（AS 160敲除小鼠）的初步数据表明， AS 160在调节脂肪细胞而非骨骼肌中的葡萄糖摄取中发挥重要作用。 Tbc 1d 1基因敲除小鼠正在产生中，这些小鼠尚未获得初步结果。 小鼠考虑到Tbc 1d 1在某些骨骼肌类型中以较高水平表达， Tbc 1d 1可能是骨骼肌中GLUT 4易位的主要调节因子。我们的假设 AS 160和Tbc 1d 1在调节亚细胞内 GLUT 4在不同细胞类型中的分布。拟议研究的具体目标是 通过分析葡萄糖稳态和葡萄糖代谢的调节来确定AS 160和Tbc 1d 1的作用。 在基础条件下和对以下条件的响应下，GLUT 4在肌肉和脂肪细胞中的亚细胞分布 在AS 160敲除、Tbc 1d 1敲除和双AS 160/Tbc 1d 1敲除小鼠中，胰岛素和运动。 因此，我们的研究将阐明维持葡萄糖的基本机制。 体内平衡它将进一步为验证AS 160和Tbc 1d 1提供关键信息， 药物的目标是改善葡萄糖稳态和预防胰岛素抵抗的并发症。

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.