MODULATING PHYSIOLOGIC EFFECTS OF PHOSPHOLIPID METABOLISM IN OBESITY AND DIABETES

描述(申请人提供)：运动是治疗糖尿病和肥胖症的理想疗法，但依从性差，骨骼肌收缩如何降低代谢性疾病风险尚不清楚。脂代谢异常参与了2型糖尿病的病理生理过程，但对于脂类、肌肉功能和代谢失代偿之间的关系尚无统一的解释。令人意外的是，在动物和人类中，高脂饮食和肥胖都会在骨骼肌中诱导脂肪酸合成酶(FAS)。肌浆网/内质网钙ATPase(SERCA)对正常肌肉功能至关重要。骨骼肌Fas缺乏导致高脂肪饮食诱导的肌肉无力，因为Fas是通过确定肌浆网(SR)的磷脂组成来维持SERCA活性的。在幼鼠中，需要高脂肪饮食才能引起虚弱。由于相同的机制，同样的表型也出现在肌肉Fas缺乏的衰老小鼠身上，吃的是低脂肪食物。Fas与磷脂合成酶胆碱/乙醇胺磷酸转移酶1(CEPT1)相连。高脂饮食可诱导骨骼肌CEPT1表达。骨骼肌CEPT1缺乏通过与Fas缺乏相同的机制导致高脂肪饮食诱导的肌肉无力：改变SR磷脂组成，导致SERCA活性降低。肌肉中的Fas和CEPT1对线粒体功能、PPAR激活、内质网应激或其他过程没有影响，无论是Fas缺陷的肌肉还是CEPT1缺陷的肌肉，Fas和CEPT1似乎主要将脂质输送到SR。Fas还与过氧化脂质合成有关。这一过程的最后一步是由Peroxisomal Reductase Activing PPAR(PexRAP)介导的，PexRAP是根据其在非肌肉组织中的特性克隆和命名的。PexRAP是一种能合成常规磷脂的多功能酶，PexRAP缺陷小鼠肌肉SR的磷脂组成反映了Fas和CEPT1缺陷小鼠肌肉SR的磷脂组成。在肥胖人群中，Fas和CEPT1是协同调节的。这一途径受体重减轻的动态调节，并与胰岛素刺激的葡萄糖处置有关。质谱仪分析表明，SR磷脂信号在Fas缺陷、CEPT1缺陷和PexRAP缺陷小鼠的肌肉中受到类似的影响，在人类代谢综合征中也是如此。这项应用的长期目标是描述饮食、肥胖、衰老和肌肉功能之间的这种新的联系，以改善肥胖和糖尿病患者的健康。我们将验证这样一种假设，即涉及骨骼肌中Fas、PexRAP和CEPT1的内源性磷脂合成途径通过脂类来维持代谢应激背景下的肌肉功能。这一假说将通过解决四个目标来验证：(1)确定小鼠骨骼肌肌浆网和钙处理因饮食和运动变化而发生的生脂调节变化的动力学。(2)使Fas、PexRAP和CEPT1参与共同的磷脂合成途径，导致培养细胞肌浆网组成和功能改变。(3)确定小鼠骨骼肌中PexRAP的基因失活是否会改变肌浆网的组成和功能，从而影响力量和葡萄糖代谢。(4)通过确定患有代谢综合征的人肌浆网的组成和功能是否发生改变，将这些观察结果转化为人类。实现这项应用的目标可以提供对有效治疗的生化障碍的新理解，提供在其他健康的肥胖者中进展到代谢障碍的新的生物标记物，并通过重新定位可通过国家先进转化科学中心(NCATS)药物收藏(NPC)获得的药物来提供治疗糖尿病的可行目标。

DESCRIPTION (provided by applicant): Exercise is an ideal therapy for diabetes and obesity, but compliance is poor and how skeletal muscle contraction decreases metabolic disease risk is poorly understood. Abnormal lipid metabolism contributes to the pathophysiology of type 2 diabetes, but there is no consensus explanation for the relationship between lipids, muscle function, and metabolic decompensation. Unexpectedly, fatty acid synthase (FAS) is induced in skeletal muscle by high fat feeding and obesity in both animals and humans. Sarco/endoplasmic reticulum calcium ATPase (SERCA) is critical for normal muscle function. Skeletal muscle FAS deficiency causes high fat diet-induced muscle weakness because FAS is required to maintain SERCA activity by determining the phospholipid composition of the sarcoplasmic reticulum (SR). In young mice, a high fat diet is required to elicit weakness. The same phenotype due to the same mechanism occurs in aging mice with muscle FAS deficiency eating a low fat chow diet. FAS is linked to the phospholipid synthetic enzyme choline/ethanolamine phosphotransferase 1 (CEPT1). High fat feeding induces CEPT1 in skeletal muscle. Skeletal muscle CEPT1 deficiency causes high fat diet-induced muscle weakness through the same mechanism as FAS deficiency: altered SR phospholipid composition leading to decreased SERCA activity. FAS and CEPT1 in muscle appear to channel lipids predominantly to the SR since there is no effect on mitochondrial function, PPAR activation, ER stress or other processes in either FAS-deficient or CEPT1-deficient muscle. FAS is also linked to peroxisomal lipid synthesis. The final step in this process is mediated by Peroxisomal Reductase Activating PPAR (PexRAP), cloned and named based on its properties in nonmuscle tissue. PexRAP is a multifunctional enzyme capable of conventional phospholipid synthesis, and the phospholipid composition of muscle SR in PexRAP-deficient mice mirrors that of muscle SR in FAS and CEPT1 deficiency. In obese humans, FAS and CEPT1 are coordinately regulated. This pathway is dynamically modulated by weight loss, and related to insulin stimulated glucose disposal. Mass spectrometry analyses indicate that the SR phospholipid signature is similarly affected in muscle in FAS-deficient, CEPT1-deficient, and PexRAP- deficient mice, and in human metabolic syndrome. The long-term objective of this application is to characterize this novel link between diet, obesity, aging, and muscle function to improve the health of people with obesity and diabetes. We will test the hypothesis that an endogenous phospholipid synthetic pathway involving FAS, PexRAP, and CEPT1 in skeletal muscle channels lipids to maintain muscle function in the setting of metabolic stress. This hypothesis will be tested by addressing four aims: (1) To define the dynamics of lipogenic-mediated changes in skeletal muscle sarcoplasmic reticulum and calcium handling in response to changes in diet and exercise in mice. (2) To implicate FAS, PexRAP, and CEPT1 in a common phospholipid synthetic pathway leading to altered sarcoplasmic reticulum composition and function in cultured cells. (3) To determine if genetic inactivation of PexRAP in the skeletal muscle of mice alters the composition and function of the sarcoplasmic reticulum to affect strength and glucose metabolism. (4) To translate these observations to humans by determining if the composition and function of the sarcoplasmic reticulum is altered in people with the metabolic syndrome. Achieving the goals of this application could deliver new understanding of biochemical impediments to effective treatments, deliver novel biomarkers of progression to metabolic compromise in otherwise healthy obese people, and deliver viable targets for treating diabetes by repositioning drugs available through the National Center for Advancing Translational Sciences (NCATS) Pharmaceutical Collection (NPC).