PGC-1 and Muscle Mitochondrial Dysfunction in Diabetes

描述(申请人提供)：胰岛素抵抗是肥胖和2型糖尿病患者骨骼肌的特征，被广泛认为是2型糖尿病发病机制中的一个重要因素。最近，人们认识到骨骼肌线粒体功能障碍与胰岛素抵抗密切相关。这些线粒体异常包括Krebs循环活性、电子传递、氧化能力和氧化燃料(碳水化合物与脂肪)选择方面的缺陷。越来越多的证据表明，心肌细胞内的脂质，包括甘油三酯、脂肪酸(FFA)、脂肪酰胆碱和神经酰胺，抑制了胰岛素受体信号转导，并导致胰岛素抵抗。综上所述，这些发现导致了一个总体假设，即肌肉线粒体氧化脂肪酸的能力降低会导致各种脂肪酸代谢物的积累，进而抑制胰岛素受体信号和胰岛素作用。到目前为止，胰岛素抵抗肌肉线粒体氧化能力下降的机制还不清楚。我们提出的证据表明，在胰岛素抵抗肌肉中，过氧化体增殖物激活受体(PPAR)-γ共激活因子-1(PGC-1)和核呼吸因子(NRF)-1的表达减少是导致参与电子传递和氧化磷酸化的一系列核编码线粒体基因表达协同减少的原因。在这个项目中，我们将确定骨骼肌中PGC-1和/或NRF-1表达的变化是否可以预测骨骼肌中核编码的线粒体基因表达、线粒体功能、脂质含量和胰岛素受体信号的变化方向。具体地说，我们建议：1)通过减少肌肉中PGC-1/NRF-1的表达来确定血浆FFA浓度的实验性增加是否也减少了核编码的线粒体基因的表达，并增加了心肌细胞内甘油三酯、脂肪酰辅酶A和神经酰胺的浓度。2)确定使用Acipimox治疗的实验性血浆FFA降低是否增加了PGC-1/NRF-1的表达，同时增加了核编码的线粒体基因的表达。3)确定运动(肌肉收缩)是否增加胰岛素抵抗受试者肌肉中PGC-1和NRF-1的表达。4)确定PPAR-γ激动剂治疗是否增加胰岛素抵抗患者骨骼肌中PGC-1/NRF-1的表达。我们将检验这一假设，即PPAR-γ激动剂诱导的PGC-1/NRF-1表达增加预示着核编码线粒体基因的表达增加，并降低心肌细胞内甘油三酯、脂肪酰辅酶A和神经酰胺的浓度。5)确定在墨西哥裔美国人中，PGC-1基因常见的单核苷酸多态性是否与PGC-1表达降低或胰岛素抵抗有关。

DESCRIPTION (provided by applicant): Insulin resistance characterizes skeletal muscle from patients with obesity and type 2 diabetes mellitus and is widely considered to be an important factor in the pathogenesis of type 2 diabetes. Recently, it has become appreciated that mitochondrial dysfunction in skeletal muscle is found in tandem with insulin resistance. These mitochondrial abnormalities include defects in Krebs cycle activity, electron transport, oxidative capacity, and selection of oxidative fuel (carbohydrate vs. fat). A body of evidence is accumulating suggesting that intramyocellular lipids, including triglycerides, fatty acids (FFA), fatty acyI-CoAs, and ceramides inhibit insulin receptor signaling and cause insulin resistance. Taken together, these findings lead to the overall hypothesis that decreased capacity of muscle mitochondria to oxidize fatty acids leads to an accumulation of various fatty acid metabolites that in turn inhibit insulin receptor signaling and insulin action. Up to this point, the mechanism of decreased mitochondrial oxidative capacity in insulin resistant muscle has been unclear. We present evidence indicating that decreased expression of peroxisome proliferator activated receptor (PPAR)-gamma coactivator-1 (PGC-1) and nuclear respiratory factor (NRF)-1 in insulin resistant muscle is responsible for a coordinate reduction of expression of a wide array of nuclear-encoded mitochondrial genes involved in electron transport and oxidative phosphorylation. In this project we will determine whether changes in PGC-1 and/or NRF-1 expression in skeletal muscle predict the direction of changes in expression of nuclear-encoded mitochondrial genes, mitochondrial function, and lipid content and insulin receptor signaling in skeletal muscle. Specifically, we propose: 1) To determine whether an experimental increase in plasma FFA concentrations using a lipid infusion that decreases PGC-1/NRF-1 expression in muscle also decreases expression of nuclear-encoded mitochondrial genes and increases intramyocellular triglyceride, fatty acyl CoA, and ceramide concentrations. 2) To determine whether an experimental decrease in plasma FFA using Acipimox treatment increases PGC-1/NRF-1 expression in concert with increased expression of nuclear encoded mitochondrial genes. 3) To determine whether physical exercise (muscle contraction) increases PGC-1 and NRF-1 expression in muscle of insulin resistant subjects. 4) To determine whether treatment with a PPAR-gamma agonist increases PGC-1/NRF-1 expression in skeletal muscle from insulin resistant patients. We will test the hypothesis that a PPAR-gamma agonist-induced increase in PGC-1/NRF-1 expression predicts increased expression of nuclear-encoded mitochondrial genes and decreased intramyocellular triglyceride, fatty acyl CoA, and ceramide concentrations. 5) To determine whether common single nucleotide polymorphisms in the PGC-1 gene are associated with decreased PGC-1 expression or insulin resistance in Mexican Americans.