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（T2DM）中几乎是普遍存在的，在已知的致糖尿病危险因素中，胰岛素抵抗是T2DM发展的最大预测价值之一。因此，旨在逆转骨骼肌胰岛素抵抗的干预措施可能有效地预防和治疗这种疾病。toll样受体（TLR） 4和该受体下游的炎症通路[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，目前尚不清楚胰岛素抵抗患者骨骼肌中是否有异常的TLR4信号。本研究的目的是研究TLR4是否与人类骨骼肌胰岛素抵抗的机制有关。利用胰岛素钳技术和肌肉活检，以及原代人肌肉细胞培养系统，我们计划验证TLR4信号升高在脂质介导的胰岛素抵抗发病机制中起重要作用的假设。提出以下目的：1)确定胰岛素抵抗受试者是否存在TLR4表达/含量异常和骨骼肌中TLR4驱动信号异常，以及这是否预示着胰岛素信号和胰岛素敏感性异常；2)确定在生理范围内循环游离脂肪酸（FFAs）的实验升高是否会增加TLR4的表达/含量，并刺激瘦正常葡萄糖耐量（胰岛素敏感）受试者肌肉中TLR4驱动的信号传导；3)确定抗脂药acpimox导致的FFAs减少是否改善了胰岛素抵抗（肥胖和T2DM）受试者肌肉中的TLR4信号；4)确定TLR4是否介导ffa诱导的人肌管胰岛素抵抗。这些研究将对人类肌肉中脂质诱导的胰岛素抵抗的分子机制产生新的见解。肥胖和2型糖尿病患者的骨骼肌对胰岛素（一种有助于将血糖水平维持在正常范围内的激素）的作用有抵抗力。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TLR4的蛋白质的组织水平升高可能在肥胖和2型糖尿病患者的胰岛素抵抗中起作用。在这个项目中，我们计划研究这种蛋白（TLR4）是否参与人体肌肉中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.