Role of TLR4 on insulin resistance in human muscle

描述(申请人提供)：骨骼肌胰岛素抵抗在2型糖尿病(T2 DM)中几乎是普遍存在的，在已知的糖尿病危险因素中，胰岛素抵抗对T2 DM的发展具有最大的预测价值。因此，旨在逆转骨骼肌胰岛素抵抗的干预措施很可能在预防和治疗这种疾病方面有效。Toll样受体(TLR4)及其下游的炎症通路[IKK/IKB/NFkB和c-Jun氨基末端激酶(JNK)]最近被认为与脂质诱导的胰岛素抵抗的发病机制有关。然而，目前尚不清楚胰岛素抵抗患者的骨骼肌中是否存在异常的TLR4信号。这项研究的目的是研究TLR4是否与人体骨骼肌胰岛素抵抗的机制有关。利用肌肉活组织的胰岛素钳夹技术和原代人类肌肉细胞培养系统，我们计划检验TLR4信号升高在脂质介导的胰岛素抵抗发病机制中发挥重要作用的假设。这些研究的目的如下：1)确定胰岛素抵抗受试者骨骼肌中是否存在TLR4的异常表达/内容以及TLR4驱动的信号传导是否可预测胰岛素信号和胰岛素敏感性的异常；2)确定在一定生理范围内循环中游离脂肪酸(FFA)的实验性升高是否会增加TLR4在瘦肉正常糖耐量(胰岛素敏感)受试者肌肉中的表达/含量，并刺激TLR4驱动的信号转导；3)确定由降脂药物Acipimox带来的FFA减少是否可改善胰岛素抵抗(肥胖和T2 DM)受试者肌肉中的TLR4信号；4)确定TLR4是否介导了FFA诱导的人肌管胰岛素抵抗。这些研究将对人类受试者肌肉中脂质诱导的胰岛素抵抗的分子机制产生新的见解。肥胖症和2型糖尿病患者的骨骼肌对胰岛素的作用具有抵抗力，胰岛素是一种激素，有助于将血糖水平保持在正常范围内。然而，肌肉中胰岛素抵抗的原因还不是很清楚。最近在动物身上进行的研究表明，一种名为TLR4的蛋白质组织水平的增加可能在肥胖症和2型糖尿病患者的胰岛素抵抗中起到了作用。在这个项目中，我们计划研究这种蛋白(TLR4)是否与人类受试者肌肉中胰岛素抵抗的分子机制有关。

DESCRIPTION (provided by applicant): Skeletal muscle insulin resistance is nearly universal in type 2 diabetes (T2DM), and of the known diabetogenic risk factors, insulin resistance has one of the greatest predictive values for the development of T2DM. Therefore, interventions designed to reverse skeletal muscle insulin resistance are likely to be effective in preventing and treating this disease. Toll-like receptor (TLR) 4 and inflammatory pathways downstream of this receptor [IKK/IkB/NFkB and c-jun n-terminal kinase (JNK)] have been recently implicated in the pathogenesis of lipid-induced insulin resistance. However, it is not known whether insulin resistant subjects have abnormal TLR4 signaling in the skeletal muscle. The goal of this study is to examine whether TLR4 is implicated in the mechanism underlying skeletal muscle insulin resistance in human subjects. Using the insulin clamp technique with muscle biopsies, and a primary human muscle cell culture system, we plan to test the hypothesis that elevated TLR4 signaling plays an important role in the pathogenesis of lipid-mediated insulin resistance. The following Aims are proposed: 1) Determine whether insulin resistant subjects have abnormal TLR4 expression/content and TLR4-driven signaling in skeletal muscle and whether this predicts abnormalities in insulin signaling and insulin sensitivity; 2) Determine whether an experimental elevation in circulating free fatty acids (FFAs) within a physiologic range, increases TLR4 expression/content and stimulates TLR4-driven signaling in muscle from lean normal glucose tolerant (insulin-sensitive) subjects; 3) Determine whether the reduction of FFAs, brought about the antilipolytic drug Acipimox, improves TLR4 signaling in muscle from insulin resistant (obese and T2DM) subjects; 4) Determine whether TLR4 mediates FFA-induced insulin resistance in human myotubes. These studies will yield new insights into the molecular mechanisms responsible for lipid-induced insulin resistance in muscle from human subjects.The skeletal muscle from subjects with obesity and type 2 diabetes is resistant to the effect of insulin, a hormone, which helps maintain glucose levels within a normal range. However, the cause for the insulin resistance in muscle is not well known. Recent studies done in animals suggest that increased tissue levels of a protein called TLR4 may play a role in the insulin resistance present in subjects with obesity and type 2 diabetes. In this project we plan to examine whether this protein (TLR4) is involved in the molecular mechanisms responsible for insulin resistance in muscle from human subjects.