MODULATING PHYSIOLOGIC EFFECTS OF PHOSPHOLIPID METABOLISM IN OBESITY AND DIABETES

描述（由申请人提供）：运动是治疗糖尿病和肥胖的理想方法，但依从性较差，骨骼肌收缩如何降低代谢性疾病风险尚不清楚。脂质代谢异常有助于2型糖尿病的病理生理，但对于脂质、肌肉功能和代谢失代偿之间的关系尚无一致的解释。出乎意料的是，脂肪酸合成酶（FAS）在动物和人类的骨骼肌中都是由高脂肪喂养和肥胖引起的。Sarco/内质网钙atp酶（SERCA）对正常肌肉功能至关重要。骨骼肌FAS缺乏导致高脂饮食引起的肌肉无力，因为FAS需要通过决定肌浆网（SR）的磷脂组成来维持SERCA的活性。在幼鼠中，高脂肪饮食是引起虚弱的必要条件。同样的表型由于同样的机制发生在衰老小鼠肌肉FAS缺乏吃低脂食物。FAS与磷脂合成酶胆碱/乙醇胺磷酸转移酶1 （CEPT1）相连。高脂肪喂养诱导骨骼肌CEPT1表达。骨骼肌CEPT1缺乏导致高脂肪饮食引起的肌肉无力，其机制与FAS缺乏相同：SR磷脂组成改变导致SERCA活性降低。肌肉中的FAS和CEPT1似乎主要将脂质输送到SR，因为在FAS缺陷或CEPT1缺陷的肌肉中，对线粒体功能、PPAR激活、内质网应激或其他过程没有影响。FAS还与过氧化物酶体脂质合成有关。这一过程的最后一步是由过氧化物酶体还原酶激活PPAR （peexrap）介导的，该酶是根据其在非肌肉组织中的特性克隆并命名的。PexRAP是一种能够合成常规磷脂的多功能酶，PexRAP缺失小鼠肌肉SR的磷脂组成与FAS和CEPT1缺失小鼠肌肉SR的磷脂组成相似。在肥胖人群中，FAS和CEPT1是协调调节的。这一途径受到体重减轻的动态调节，并与胰岛素刺激的葡萄糖处理有关。质谱分析表明，在fas缺陷、cept1缺陷和peexrap缺陷小鼠以及人类代谢综合征的肌肉中，SR磷脂特征也受到类似的影响。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联系，以改善肥胖和糖尿病患者的健康。我们将验证骨骼肌中涉及FAS、peexrap和CEPT1的内源性磷脂合成途径的假设，以维持代谢应激环境下的肌肉功能。这一假设将通过解决四个目标来验证：(1)定义小鼠饮食和运动变化对骨骼肌肌浆网和钙处理的脂肪生成介导变化的动力学。(2)将FAS、peexrap和CEPT1与导致培养细胞中肌浆网组成和功能改变的共同磷脂合成途径联系起来。(3)确定小鼠骨骼肌中peexrap基因失活是否会改变肌浆网的组成和功能，从而影响肌力和葡萄糖代谢。(4)通过确定代谢综合征患者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。实现这一应用程序的目标可以提供对有效治疗的生化障碍的新理解，为健康肥胖人群的代谢妥协提供新的生物标志物，并通过重新定位国家推进转化科学中心（NCATS）药物收集（NPC）提供治疗糖尿病的可行靶点。

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).