Mitochondria-Peroxisome Fatty Acid Oxidation in Obesity

描述(由申请人提供)：这项研究的长期目标是更好地了解骨骼肌缺陷(SKM)，这些缺陷导致肥胖明显的发病率和死亡率。有证据表明，肥胖与SKM脂质氧化能力降低有关，这可能是肌肉胰岛素抵抗和糖尿病发展的关键。具体地说，肥胖者的SKM具有线粒体(MitOSKM)氧化长链脂肪酸(LCFA)的能力受损。然而，线粒体外机制对受损的MitOSKM脂肪酸代谢的潜在作用一直没有得到很好的研究。在肝脏中，过氧化物酶体通过将LCFA链缩短为酰基肉碱，在防止细胞脂肪酸过度积累方面发挥着特有的作用，后者被线粒体更有效地氧化。在瘦肉和肥胖动物的肝脏中，化学抑制肝细胞CPT-1(线粒体LCFA输入的限速酶)与过氧化物体数量的增加有关。肝外组织中的过氧化体也对LCFA代谢改变的状态做出反应，因为接受降血脂药物治疗的动物表现出明显的心肌过氧化体活性增加。我们提出了过氧化体在SKM脂代谢中的类似作用，并假设当脂肪酸的MitOSKM氧化受损时，过氧化体氧化将增强以补偿。精瘦受试者的耐力运动训练(EET)和肥胖者的降血脂药物治疗会刺激SKM脂肪酸的氧化。我们的第二个假设是，肥胖受试者的SKM将通过提高现有的MitOSKM对LCFA完全氧化的过氧化体贡献来对提高脂代谢的治疗做出反应。我们的具体目标是1)确定过氧化体活性对肥胖与瘦骨骼肌LCFA氧化的贡献，以及2)确定肥胖与瘦SKM中过氧化体-线粒体氧化能力的代谢灵活性程度。方法：我们将通过1)利用电子显微镜/免疫细胞化学和脂肪酸氧化的放射性同位素评估来定量肥胖和瘦受试者后肢(啮齿动物)和腹直肌(人)SKM组织中过氧体/线粒体对LCFA代谢的贡献，以及2)确定(在啮齿动物中)EET(8周)和药物治疗(3周)单独和/或与EET联合使用是否可以改善LCFA代谢的过氧体和MitOSKM能力。这些研究将1)进一步阐明过氧化体氧化在肥胖和糖尿病中的作用2)有助于确定治疗肥胖和其他血脂异常疾病的新疗法3)为我们的学生提供有价值的研究培训和4)为后续的RO1应用生成数据。

DESCRIPTION (provided by applicant): The Iong-term objective of this research is to better understand the defects in skeletal muscle (SKM) that contribute to the morbidity and mortality evident with obesity. There is evidence that obesity is associated with a reduced capacity for SKM lipid oxidation, which could be critical to the development of muscle insulin resistance and diabetes. Specifically, SKM from obese subjects possess an impaired mitochondrial (MitOSKM) capacity to oxidize long-chain fatty acids (LCFA). However, the potential for extra-mitochondrial mechanisms to respond to impaired MitOSKM fatty acid metabolism has been poorly investigated. In the liver, peroxisomes play an obligate role in defending against excess accumulation of cellular fatty acids by chain-shortening LCFA to acyl-carnitines, which are oxidized more efficiently by the mitochondria. In support, chemical inhibition of hepatocyte CPT-1 (rate limiting enzyme in mitochondrial LCFA import) in lean and the livers of obese animals are associated with elevated numbers of peroxisomes. Peroxisomes in extra-hepatic tissues are also responsive to states of altered LCFA metabolism as animals treated with hypolipidemic agents demonstrate clear increases in myocardial peroxisomal activity. We are proposing a similar role for peroxisomes in SKM lipid metabolism, and hypothesize that when MitOSKM oxidation of fatty acids is impaired, peroxisomal oxidation will be enhanced to compensate. Endurance exercise training (EET) in lean subjects and pharmacological treatment with hypolipidemic agents in obese subjects stimulate SKM fatty acid oxidation. Our secondary hypothesis is that SKM from obese subjects will be responsive to treatments that elevate lipid metabolism by elevating peroxisomal contributions toward complete oxidation of LCFA by existing MitOSKM Our Specific Aims are 1) To determine the contributions of peroxisomal activity toward LCFA oxidation in obese vs. lean skeletal muscle and 2) To determine the extent of metabolic flexibility of peroxisomal-mitochondrial oxidative capacity in obese vs. lean SKM. Methods: We will address these aims by 1) quantifying peroxisomal/mitochondrial contributions toward LCFA metabolism in SKM biopsies from hindlimb (rodent) and rectus abdominus (human) muscles of obese vs. lean subjects using electron microscopy/ immunocytochemistry and radioisotope assessment of fatty acid oxidation and 2) determining (in rodents) whether EET (8 weeks) and pharmacological treatment (3 weeks) with hypolipidemic agents (alone and/or in combination with EET) can improve the peroxisomal and MitOSKM capacity to metabolize LCFA. These investigations will 1) further elucidate the role of peroxisomal oxidation in obesity and diabetes 2) aid in the identification of new therapies for the treatment of obesity and other dyslipidemic diseases 3) provide valuable research training for our students and 4) generate data for subsequent RO1 applications.