Mammalian Target of Rapamycin and Insulin Resistance

描述（由申请人提供）：大约1800万美国人患有糖尿病，每年直接医疗费用估计为920亿美元。2型糖尿病约占所有糖尿病的90-95%。虽然2型糖尿病的病因尚不清楚，但胰岛素抵抗是该疾病的一个常见因素。由于骨骼肌是胰岛素介导的葡萄糖处理的主要部位，胰岛素抵抗被认为部分是由于骨骼肌对循环胰岛素增加的适当反应能力的缺陷。本提案的目的是确定哺乳动物雷帕霉素靶点（mTOR）是否在骨骼肌胰岛素抵抗的发展中起作用。mTOR是一种营养敏感和胰岛素应答的丝氨酸/苏氨酸激酶，控制mRNA翻译和细胞生长。最近的细胞培养研究表明，激活mTOR通路抑制胰岛素信号转导，促进胰岛素抵抗。我们的第一个假设是，激活mTOR介导的信号转导将在骨骼肌中产生胰岛素抵抗，这一过程将被雷帕霉素逆转，雷帕霉素是一种高度特异性的mTOR抑制剂。具体目标#1将检查mtor介导的信号传导对骨骼肌胰岛素作用的影响。我们将通过mTOR依赖的胰岛素受体底物-1 （IRS-1）丝氨酸磷酸化来确定与氨基酸一起培养肌肉是否会产生胰岛素抵抗。IRS-1丝氨酸磷酸化被认为通过降低IRS-1酪氨酸磷酸化和促进IRS-1降解来促进胰岛素抵抗。我们还将研究氨基酸激活mTOR对胰岛素促进蛋白激酶B (PKB) Thr308和Ser473磷酸化能力的影响。PKB在这些位点上的磷酸化是充分发挥激酶活性和刺激葡萄糖转运所必需的。我们的初步数据表明，激活mTOR信号可以减少胰岛素刺激的骨骼肌中PKB Ser473磷酸化，这一过程被雷帕霉素所消除。最后，具体目标#1将确定激活mTOR信号与氨基酸是否会降低胰岛素招募GLUT4到细胞表面和刺激骨骼肌葡萄糖运输的能力。我们的第二个假设是与饮食诱导的胰岛素抵抗相关的高胰岛素血症构成性地激活mTOR。特定目标#2将检查高脂肪饮食小鼠肌肉中Ser2448上mTOR的磷酸化，并与对照组进行比较。Ser2448是mTOR中的一个位点，其磷酸化与激酶活性增加有关。这些研究的结果将为胰岛素抵抗的发展提供新的见解，并可能导致使用mTOR抑制剂作为2型糖尿病的新治疗方法。

DESCRIPTION (provided by applicant): Approximately 18 million Americans have diabetes resulting in an estimated $92 billion in direct medical costs per year. Type 2 diabetes mellitus accounts for approximately 90-95% of all diabetes. Although the cause of type 2 diabetes is unknown, one common factor of the disease is insulin resistance. Since skeletal muscle is the primary site for insulin-mediated glucose disposal, insulin resistance is thought to be due, in part, to a defect in skeletal muscle's ability to respond appropriately to increases in circulating insulin. The goal of this proposal is to determine whether or not the mammalian target of rapamycin (mTOR) plays a role in the development of skeletal muscle insulin resistance. mTOR is a nutrient sensitive and insulin responsive serine/threonine kinase that controls mRNA translation and cellular growth. Recent cell culture studies have demonstrated that activating the mTOR pathway inhibits insulin signal transduction and promotes insulin resistance. Our first hypothesis is that activating mTOR-mediated signal transduction will produce insulin resistance in skeletal muscle, a process that will be reversed by rapamycin, a highly specific inhibitor of mTOR. Specific aim #1 will examine the effects of mTOR-mediated signaling on insulin action in skeletal muscle. We will determine if incubating muscle with amino acids produces insulin resistance by an mTOR dependent serine phosphorylation of the insulin receptor substrate-1 (IRS-1). Serine phosphorylation of IRS-1 is thought to promote insulin resistance by decreasing IRS-1 tyrosine phoshorylation and promoting IRS-1 degradation. We will also examine the effects of activating mTOR with amino acids on insulin's ability to promote the phosphorylation of protein kinase B (PKB) on Thr308 and Ser473. Phosphorylation of PKB on these sites is necessary for full kinase activity and the stimulation of glucose transport. Our preliminary data indicate activating mTOR signaling reduces insulin-stimulated PKB phosphorylation on Ser473 in skeletal muscle, a process that is abolished by rapamycin. Finally, specific aim #1 will determine if activating mTOR signaling with amino acids decreases insulin's ability to recruit GLUT4 to the cell surface and stimulate glucose transport in skeletal muscle. Our second hypothesis is that the hyperinsulinemia associated with diet-induced insulin resistance constitutively activates mTOR. Specific aim #2 will examine the phosphorylation of mTOR on Ser2448 in muscles from mice subjected to a high fat diet compared to controls. Ser2448 is a site in mTOR whose phosphorylation is associated with increased kinase activity. The results from these studies will provide new insights into factors that play a role in the development of insulin resistance and possibly lead to the use of mTOR inhibitors as novel treatments for type 2 diabetes.