Myocardial Protein Synthesis After Alcohol Intoxication

描述(由申请者提供)：本项目的长期目标是了解酒精摄入导致酒精性心肌疾病特有的肌原纤维损伤的机制。酗酒仍然是美国最常见的药物滥用形式。酗酒与过早死亡率增加有关，部分原因是患上酒精引起的心肌病，约35%长期饮酒过量的人被诊断患有这种疾病。导致酒精依赖心肌功能障碍的机制是多因素的，但心肌蛋白表达的改变似乎是一个主要机制。在当前资助期间完成的研究表明，饮酒在mRNA翻译水平上抑制了心脏中蛋白质的合成速度。通过了解mRNA翻译过程中的变化，有望开发新的策略来对抗与慢性酒精中毒相关的心肌结构和功能的病理改变。我们描述了蛋白质合成过程中的两个调节步骤，即活性elF4E-elF4G复合体的形成和延伸过程，这两个步骤在一定程度上导致了慢性酒精中毒期间蛋白质合成的抑制，而急性酒精中毒只影响活性elF4E-elF4G复合体的形成。我们假设，通过mTOR的正常信号通路负责维持在对照动物中观察到的蛋白质合成的这两个步骤的功能，但乙醇摄入严重损害了这两个步骤的功能。这种净效应通过包括收缩蛋白在内的心肌蛋白表达的改变来体现。我们进一步假设，无论是通过急性灌胃或进食氨基酸来提供给酒精灌胃的大鼠，都可以刺激mTOR，导致蛋白质合成速度的加快。即将到来的项目期的实验设计旨在检验如下假设：1)饮酒使mTOR活性降低，导致4E-BP1和S6K1去磷酸化，从而通过减少活性elF4G-elF4E复合体的形成而限制心肌蛋白质合成；2)补充氨基酸刺激mTOR活性可逆转酒精引起的心肌蛋白质合成抑制；3)慢性饮酒抑制蛋白质合成，改变心肌蛋白质的表达；4)基因消融mTOR可引起心肌的功能和生化紊乱，与慢性饮酒时观察到的情况类似。总体而言，这项研究设计将建立酒精滥用导致心肌蛋白质合成减少的机制。

DESCRIPTION (provided by applicant): The long-term goal of this project is to understand the mechanisms by which alcohol consumption induces myofibrillar damage characteristic of alcoholic heart muscle disease. Alcoholism remains the most common form of drug abuse in the United States. Alcohol abuse is associated with an increased premature mortality partly resulting from the development of an alcohol-induced cardiomyopathy, a condition diagnosed in approximately 35% of whose individuals who chronically consume excessive amounts of alcohol. The mechanisms leading to alcohol-dependent myocardial dysfunction are multifactorial, but altered expression of myocardial proteins appears as a central mechanism. Studies completed during the current funding period established that alcohol consumption inhibits rates of protein synthesis in heart at the level of mRNA translation. By understanding the alterations in the process of mRNA translation it is hoped that new strategies could be developed to combat the pathologic derangements in cardiac muscle structure and function associated with chronic alcoholism. We delineated two regulatory steps in the process of protein synthesis, the formation of an active elF4E-elF4G complex and the process of elongation that are responsible, in part, for the inhibition of protein synthesis during chronic alcohol administration, whereas acute alcohol intoxication only affects the formation of an active elF4E-elF4G complex. We hypothesize that the normal signaling path-way through mTOR responsible for maintaining the functioning of these two steps in protein synthesis at rates observed in control animals is severely compromised by ethanol intake. The net effect is manifested through alterations in the expression of myocardial proteins including contractile proteins. We further hypothesize that provision of amino acids either through acute gavage or meal feeding to rats administered alcohol can stimulate mTOR leading to an acceleration of rates of protein synthesis. The experimental design for the forthcoming project period addresses the following Specific Aims in order to test the hypothesis that: 1) Alcohol consumption reduces mTOR activity resulting in dephosphorylation of 4E-BP1 and S6K1, thereby limiting myocardial protein synthesis by reducing formation of active elF4G-elF4E complex; 2) Stimulating mTOR activity with aminp acid supplementation reverses the alcohol-induced inhibition of myocardial protein synthesis; 3) Inhibition of protein synthesis in response to chronic alcohol feeding shifts myocardial protein expression; and 4) Genetic ablation of mTOR causes functional and biochemical derangements in the myocardium similar to those observed with chronic alcohol intake. Overall, the research design will establish the mechanism by which myocardial protein synthesis is reduced in response to alcohol abuse.