Ethanol, Protein Catabolism and Liver Cell Injury

描述（由申请方提供）：乙醇具有肝毒性，因为其代谢转化为与蛋白质反应的化合物，从而改变其生物活性。乙醇脱氢酶（ADH）和细胞色素P-450 2 E1（CYP 2 E1）催化乙醇氧化为乙醛。CYP 2 E1的催化作用还导致其他反应性物质的形成增加，包括超氧化物和羟乙基自由基，它们参与产生羟基自由基、过亚硝酸盐和脂质过氧化物的二级反应。这些代谢物破坏蛋白质的活性，包括蛋白酶体，这是一种多催化酶，对于降解受损和错误折叠的蛋白质以及严格控制调节蛋白的细胞内含量是必不可少的。我们的研究已经检查了乙醇对蛋白酶体功能的影响及其在肝损伤、细胞调节和信号转导中的作用。这些研究使用了组成型表达ADH和CYP 2 E1的重组Hep G2（VL-17 A）细胞，并将乙醇代谢为肝细胞。当VL-17 A细胞长时间暴露于乙醇时，蛋白酶体活性降低，并且这种酶活性的降低依赖于乙醇代谢。这一发现的重要性在于，蛋白酶体活性的下降可导致多种效应，其中包括细胞信号传导的减少、转录因子的稳定和蛋白质质量控制的显著破坏。对于我们的继续调查，我们建议检查蛋白酶体在乙醇引起的脂肪变性，无论是在培养的细胞和体内的可能作用。此外，我们提出的证据乙醇诱导的蛋白质聚集体在我们培养的肝癌细胞模型的积累。我们假设乙醇诱导的氧化应激抑制肝细胞中蛋白酶体的活性，从而影响Egr-1和其他参与脂肪变性的调节蛋白的水平。此外，蛋白酶体抑制破坏蛋白质质量控制，从而导致细胞内蛋白质聚集。为了检验这一假设，我们提出了以下具体目的：目的1将表征乙醇代谢培养细胞中乙醇引起的脂肪生成转录因子Egr-1和SREBP-1的诱导，并确定Egr-1在乙醇引起的脂肪变性中的必要性。目的2研究乙醇对小鼠肝脏脂肪生成转录因子的诱导作用.目的3将检查乙醇暴露后形成的蛋白质聚集体是否是蛋白酶体的有效底物或抑制剂，以及这些聚集体是否可以通过蛋白酶体活化消除。公共卫生相关性：从拟议的调查中获得的见解将扩大我们对乙醇肝毒性机制的了解。拟议的实验方法检查了一个高度调节的细胞蛋白水解系统，这是一个潜在的治疗靶点，以减轻由大量饮酒引起的器官损伤。

DESCRIPTION (provided by applicant): Ethanol is hepatotoxic because it is metabolically converted to compounds that react with proteins to alter their biological activities. Ethanol oxidation by alcohol dehydrogenase (ADH) and cytochrome P-450 2E1 (CYP2E1) catalyze the conversion of ethanol to acetaldehyde. Catalysis by CYP2E1 also leads to enhanced formation of other reactive species including superoxide and hydroxyethyl radicals, which participate in secondary reactions producing hydroxy radicals, peroxynitrite, and lipid peroxides. These metabolites disrupt the activity of proteins, including the proteasome, a multicatalytic enzyme that is indispensable for degrading damaged and misfolded proteins and for tightly controlling the intracellular content of regulatory proteins. Our research has examined the effects of ethanol on proteasome function and its role in hepatic injury, cell regulation and signal transduction. Theses studies have used recombinant Hep G2 (VL-17A) cells that constitutively express both ADH and CYP2E1 and metabolize ethanol comparably to liver cells. When VL-17A cells are exposed to ethanol for extended periods, proteasome activity decreases and this decrease in enzyme activity is dependent on ethanol metabolism. The importance of this finding is that a decline in proteasome activity can result in a variety of effects, among which are a reduction in cell signaling, stabilization of transcription factors and a significant disruption of protein quality control. For our continued investigations, we propose to examine the possible role of the proteasome in ethanol-elicited steatosis, both in cultured cells and in vivo. Furthermore, we present evidence for the ethanol-induced accumulation of protein aggregates in our cultured hepatoma cell model. We hypothesize that ethanol-induced oxidative stress suppresses proteasome activity in liver cells, thereby affecting the levels of Egr-1 and other regulatory proteins involved in steatosis. Additionally, proteasome suppression disrupts protein quality control, thereby causing intracellular protein aggregation in cells. To test this hypothesis, we propose the following Specific Aims: Aim 1 will characterize the ethanol- elicited induction of the lipogenic transcription factors, Egr-1 and SREBP-1 in ethanol metabolizing cultured cells and determine the essentiality of Egr-1 in ethanol-elicited steatosis. Aim 2 will characterize the ethanol- elicited induction of lipogenic transcription factors in mouse liver. Aim 3 will examine whether protein aggregates that form in response to ethanol exposure are effective substrates or inhibitors of the proteasome and whether such aggregates can be eliminated by proteasome activation. PUBLIC HEALTH RELEVANCE: The insights gained from the proposed investigation will expand our knowledge of the mechanisms of ethanol hepatotoxicity. The proposed experimental approach examines a highly regulated cellular proteolytic system that is a potential therapeutic target to alleviate organ damage caused by heavy alcohol consumption.