Impaired Acyl-CoA Synthetase-Muscle Lipid Oxidation in African American Women

描述(申请人提供)：肥胖已成为一种流行的健康威胁，在非裔美国人(AAW)比高加索人(CW)女性中的流行率更高。尽管环境因素可能会有影响，但很明显，AAW患者的肥胖也是内在的生化缺陷造成的。我们已经证明，肥胖的AAW与CW相比，肌肉脂肪酸氧化(FAO)显著降低。这一点很重要，因为肌肉FAO的减少会导致生物活性脂的积累，而生物活性脂与胰岛素抵抗和糖尿病密切相关。尽管这些发现意义重大，但解释种族/民族特定代谢功能障碍的细胞机制仍不明确。然而，利用放射性标记脂肪酸的组合，我们的研究小组现在发现了肥胖AAW患者骨骼肌粮农组织中存在的一种特定缺陷。在肌肉匀浆中，我们已经证明在肥胖的AAW和CW中，由酰基辅酶A合成酶(ACSL)激活的棕榈酸酯到其酰基辅酶A衍生物的作用受到更大程度的损害。我们还证明了从肥胖的AAW和CW获得的原代培养的心肌细胞中棕榈酸酯氧化受到了损害，这表明ACSL活性降低是一种遗传的、种族特有的特征。令人惊讶的是，这种代谢功能障碍可能在非肥胖者AAW中预先存在，他们也表现出棕榈酸酯氧化的抑制率。我们推测，AAW患者骨骼肌FAO的损伤是由于酰基辅酶A合成酶的缺陷，该酶是在线粒体运输和氧化之前激活脂肪酸所需的酶。这一缺陷很可能是导致这一种族女性肥胖和糖尿病发病率较高的原因。然而，在瘦CW中，耐力运动训练(EET)刺激肌肉氧化长链脂肪酸的能力。我们的第二个假设是，由于ACSL活性的正常化，AAW将通过增加骨骼肌氧化脂质的能力来对EET做出反应。为了验证我们的假设，我们提出了以下具体目标：1)从AAW中确定导致骨骼肌脂肪酸氧化能力降低的ACSL的细胞位置和特异性异构体(S)2)通过确定ACSL活性受损改变并导致肌肉胰岛素抵抗的特定肌内脂肪种类来扩展我们的发现1)利用小干扰RNA和腺病毒转染技术，我们将在人类骨骼肌细胞中证明ACSL活性受损是AAW的一种遗传功能障碍，纠正后可恢复脂肪酸氧化和胰岛素作用；4)通过有氧运动训练，确定AAW中ACSL活性扩大的可能性，以及随后骨骼肌的氧化能力。我们的长期目标是明确AAW诱发肥胖和糖尿病的细胞机制(S)。这项研究具有临床意义，因为研究结果可能会导致发现治疗AAW中肥胖和糖尿病的新治疗策略。

DESCRIPTION (provided by applicant): Obesity has become an epidemic health threat, the prevalence which is greater among African-American (AAW) than Caucasian (CW) women. Although environmental factors may be influential, it is apparent that inherent biochemical defects also underlie obesity in AAW. We have demonstrated that muscle fatty acid oxidation (FAO) is significantly lower in obese AAW vs. CW. This is important as reductions in muscle FAO leads to accumulation of bioactive lipids, which is strongly associated with insulin resistance and diabetes. Despite the significance of these findings, the cellular mechanisms to explain the racial/ethnic specific metabolic dysfunction remain undefined. However, using combinations of radiolabeled fatty acids, our research group has now identified a specific defect in skeletal muscle FAO present in obese AAW. In muscle homogenates, we have demonstrated that activation of palmitate to its acyl-CoA derivative by acyl-CoA synthetase (ACSL) is impaired to a greater extent in obese AAW vs. CW. We have also demonstrated that palmitate oxidation is impaired in cultured primary myocytes obtained from obese AAW vs. CW, suggesting that reduced ACSL activity is an inherited, race specific trait. Startlingly, this metabolic dysfunction may pre- exist in non-obese AAW, who also exhibit suppressed rates of palmitate oxidation. We hypothesize that the impairment in skeletal muscle FAO in AAW is due to a defect in acyl-CoA synthetase, the enzyme required for activating fatty acids prior to transport and oxidation in the mitochondria. This defect likely contributes to the greater incidence of obesity and diabetes in this racial group of women. However, in lean CW, endurance exercise training (EET) stimulates the muscle's capacity to oxidize long-chain fatty acids. Our secondary hypothesis is that AAW will respond to EET by increasing the capacity of skeletal muscle to oxidize lipids, due in part to a normalization of ACSL activity. To test our hypothesis, we propose the following specific aims: 1) to determine the cellular site and specific isoform(s) of ACSL responsible for reducing the fatty acid oxidative capacity of skeletal muscle from AAW 2) to extend our findings from specific aim 1 by determining the specific intramuscular lipid species that are altered by impaired ACSL activity and which contribute to muscle insulin resistance 3) using siRNA and adenovirus transfection technologies, we will demonstrate in human skeletal muscle cells that impaired ACSL activity is an inherited dysfunction in AAW which when corrected can restore fatty acid oxidation and insulin action and 4) to determine the potential for expanding ACSL activity and subsequently the oxidative capacity of skeletal muscle in AAW by aerobic exercise training. Our long term objective is to define the cellular mechanism(s) which pre-dispose AAW to obesity and diabetes. This research is clinically relevant as findings are likely to lead to the discovery of new therapeutic strategies for the treatment of obesity and diabetes in AAW.