Role of TLR4 on insulin resistance in human muscle

描述（由申请人提供）：骨骼肌胰岛素抵抗在2型糖尿病（T2 DM）中几乎是普遍的，在已知的致糖尿病风险因素中，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可能有效预防和治疗这种疾病。Toll样受体（TLR）4和该受体下游的炎性通路[IKK/IkB/NFkB和c-jun n-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，尚不清楚胰岛素抵抗受试者是否在骨骼肌中具有异常TLR 4信号传导。本研究的目的是检查TLR 4是否与人类受试者骨骼肌胰岛素抵抗的潜在机制有关。使用胰岛素钳夹技术与肌肉活检，和原代人肌肉细胞培养系统，我们计划测试的假设，升高的TLR 4信号在脂质介导的胰岛素抵抗的发病机制中起着重要作用。1）确定胰岛素抵抗受试者是否在骨骼肌中具有异常的TLR 4表达/含量和TLR 4驱动的信号传导，以及这是否预测胰岛素信号传导和胰岛素敏感性的异常; 2）确定循环游离脂肪酸（FFA）的实验性升高是否在生理范围内，增加TLR 4表达/含量并刺激TLR 4驱动的肌肉信号传导，（胰岛素敏感）受试者; 3）确定由抗脂肪分解药物Acipimox引起的FFA的减少是否改善了来自胰岛素抵抗的肌肉中的TLR 4信号传导。（肥胖和T2 DM）受试者; 4）确定TLR 4是否介导人肌管中FFA诱导的胰岛素抗性。这些研究将对人体受试者中脂质诱导的肌肉胰岛素抵抗的分子机制产生新的见解。肥胖和2型糖尿病受试者的骨骼肌对胰岛素的作用具有抵抗性，胰岛素是一种激素，有助于将葡萄糖水平维持在正常范围内。然而，肌肉中胰岛素抵抗的原因尚不清楚。最近在动物身上进行的研究表明，一种名为TLR 4的蛋白质的组织水平增加可能在肥胖和2型糖尿病患者的胰岛素抵抗中发挥作用。在这个项目中，我们计划研究这种蛋白质（TLR 4）是否参与了人体肌肉胰岛素抵抗的分子机制。

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.