Alcohol induces muscle autophagy by a novel AMPK independent PI3K mediated mechan

描述（由申请人提供）：近三分之二的美国成年人不同程度地饮酒。过量饮酒最广为人知的临床后果是酒精性肝病的发展。然而，肌肉质量和功能的减少是酒精性肝病以及酒精对骨骼肌的直接影响的结果。骨骼肌质量损失或肌肉减少是酒精性肝病的主要组成部分，并对生存、生活质量和其他肝病并发症的发展产生不利影响。尽管人们认识到酒精相关的肌肉损失和肌病比肝脏疾病的发生率高5倍，但目前还没有预防或逆转这一过程的治疗选择。酒精性肝病中肌肉减少的潜在机制之一是骨骼肌蛋白质合成的减少。然而，仅仅蛋白质合成受损是不够的，蛋白质分解的增加是肌肉质量损失发生的必要条件。骨骼肌中的蛋白质分解要么发生在蛋白酶体中，要么发生在自噬中。自噬是一个过程，通过这个过程，修饰的有毒蛋白质和受损的细胞器被分解，产物被回收。我们已经证明酒精不会改变蛋白酶体的活性，但会增加骨骼肌的自噬。本研究旨在了解酒精性肝病中自噬增加的机制及其病理生理作用。一种综合的方法将用于对患有不同严重程度酒精性肝病的人类受试者、喂食乙醇的小鼠和暴露于酒精的C2C12肌肉细胞的研究。酒精被代谢为乙醛，乙醛与丙二醛结合，由酒精引起的脂质过氧化反应产生，改变富含赖氨酸的蛋白质。肌肉蛋白富含赖氨酸，它们很可能经历这种修饰（加合物）。这些蛋白质需要被降解，因为它们具有细胞毒性。由于蛋白酶体途径未被激活，而自噬被激活，我们假设酒精诱导骨骼肌自噬来降解这些修饰的蛋白质。我们还观察到mTOR的关键抑制剂mTOR被抑制，而诱导自噬的AMPK在肌肉中不受酒精的影响。这伴随着蛋白磷酸酶2A （PP2A）的激活，使mTOR失活。拟议的研究将使我们能够识别这种新的AMPK独立的、PI3K-PP2A依赖的肌肉自噬激活。确定自噬增加的机制将有助于确定酒精性肝病肌肉减少症的潜在新治疗靶点。我们将通过两个特定的目的来检验这一假设，以证明在酒精性肝病中，通过新的信号通路，自噬降解肌肉中的蛋白质加合物的形成。这些研究将使用一系列全面的模型，包括酒精性肝病患者的肌肉组织，喂食乙醇的小鼠和暴露于乙醇的肌肉细胞，这将为更详细的机制研究和新疗法奠定基础，以逆转这些患者的肌肉减少症。

DESCRIPTION (provided by applicant): Nearly two thirds of adult Americans drink alcohol in varying amounts. The best known clinical consequence of excess alcohol use is the development of alcoholic liver disease. However, reduction in muscle mass and function are a consequence of both alcoholic liver disease as well as a direct effect of alcohol on the skeletal muscle. Loss of skeletal muscle mass or sarcopenia is a major component of alcoholic liver disease and adversely affects survival, quality of life and development of other complications of liver disease. Despite recognition that alcohol related muscle loss and myopathy are five times more frequent than liver disease, there are no therapeutic options to prevent or reverse this process. One of the potential mechanisms responsible for sarcopenia in alcoholic liver disease is the reduction in skeletal muscle protein synthesis. However, impaired protein synthesis alone is not enough and an increase in protein breakdown is necessary for loss of muscle mass to occur. Protein breakdown in the skeletal muscle occurs either in the proteasome or by autophagy, a process by which modified and toxic proteins and damaged organelles are broken down and the products recycled. We have shown that alcohol does not alter proteasome activity but increases autophagy in skeletal muscle. The present studies aim towards understanding the mechanisms responsible for increased autophagy and its pathophysiological role in alcoholic liver disease. A comprehensive approach will be used with studies in human subjects with varying severity of alcoholic liver disease, mice fed ethanol and C2C12 muscle cells exposed to alcohol. Alcohol is metabolized to acetaldehyde that in combination with malondialdehyde, generated by lipid peroxidation in response to alcohol, modifies proteins that are rich in lysine. Muscle proteins are rich in lysine, they are likely to undergo this modification (adducts). These proteins need to be degraded since they are cytotoxic. Since the proteasome pathway is not activated, while autophagy is, we hypothesize that alcohol induces skeletal muscle autophagy to degrade these modified proteins. We also observed that mTOR, a critical inhibitor of mTOR is inhibited while AMPK, that induces autophagy is unaltered by alcohol in the muscle. This was accompanied by activation of protein phosphatase 2A (PP2A) that inactivates mTOR. The proposed studies will permit us to identify this novel AMPK independent, PI3K-PP2A dependent activation of autophagy in the muscle. Identifying the mechanism of increased autophagy will permit identification of potential novel therapeutic targets for sarcopenia of alcoholic liver disease. We will examine this hypothesis by 2 specific aims to demonstrate the formation of the protein adducts in the muscle that are degraded by autophagy via novel signaling pathway in alcoholic liver disease. A comprehensive array of models including muscle tissue from patients with alcoholic liver disease, mice fed ethanol and muscle cells exposed to ethanol will be used for these studies that will lay the foundation for more detailed mechanistic studies and new therapies to reverse sarcopenia in these patients.