Alcohol Intake and Hepatic Fat Metabolism

描述（由申请人提供）：酒精性肝病（ALD）在美国和全世界都是一个严重的公共卫生问题。ALD由慢性饮酒引起，开始时为单纯脂肪变性，其特征是肝细胞中脂质（主要是甘油三酯（TG））的过度积累。单纯性脂肪变性患者的一部分进展为酒精性脂肪性肝炎（ASH），可进一步进展为纤维化，最终导致肝硬化和肝细胞癌。我们研究的基本假设是，对ALD疾病易感性的差异反映了肝脏脂质代谢的个体差异。由于没有针对ALD的直接治疗方法，因此更好地了解酒精性脂肪肝发展的机制对于开发有效的阻断ALD的干预措施至关重要。该应用程序的总体目标是获得对ALD发展早期事件的新理解。本研究将通过实验解决的具体假设是，肝脏TG水解失调和TG合成失调在酒精性脂肪变性的发展中起重要作用。由于脂肪肝的定义意味着肝脏中过多的TG积累，我们建议研究与TG积累相关的两个最近的代谢步骤，TG合成和降解。我们所有的研究都将在小鼠身上进行，并将包括4周的慢性喂养，包括含酒精或等热量无酒精的lieber - decarli饮食配方。这些研究还将利用腺病毒表达或敲低一些肝脂肪酶和TG合成酶的结构，以及我们早期发表的关于脂肪酶在饮食诱导（高脂肪饮食）肝脂肪变性中的作用的研究中获得的其他实验方案和专业知识。在具体目标1中，我们建议评估几种不同的肝脂肪酶在酒精性脂肪肝的发展/预防中的作用。尽管进行该Aim所需的绝大多数实验方案都在PI的实验室中得到了很好的建立，但由于在Specific Aim 1中提出的四种脂肪酶中的一种的正常生理作用尚未得到很好的确定，因此该特异性Aim有一个探索性因素。特异性目的2将探讨二酰基甘油酰基转移酶1和2 （DGAT1和DGAT2）的具体作用，这两种基因上不同的肝酶催化TG合成的最后一步，在酒精性脂肪肝的发展中。我们的初步数据证实，在酒精喂养小鼠的肝脏中，DGAT1和DGAT2的表达都升高了大约2倍。在具体目标2中提出的研究将定义DGAT1和dgat2在ALD发展的早期阶段的具体作用。

DESCRIPTION (provided by applicant): Alcoholic liver disease (ALD) is a serious public health problem in the US, and throughout the entire world. ALD results from chronic alcohol consumption and starts as simple steatosis, characterized by an over accumulation of lipid, primarily triglycerides (TG), in hepatocytes. A subset of subjects with simple steatosis progress to alcoholic steatohepatitis (ASH), which can further progress to fibrosis, eventually leading to cirrhosis and hepatoculluar carcinoma. The underlying general hypothesis for our studies is that the difference in susceptibility to ALD disease reflects individual variation in hepatic lipid metabolism. Since there are no direct treatments available for ALD, understanding better the mechanisms underlying alcoholic fatty liver development is crucial for developing effective interventions for blocking ALD. The overall goal of this application is to gain new understanding of the early events in ALD development. The specific hypothesis that will be addressed experimentally in this proposal is that dysregulated hepatic TG hydrolysis and dysregulated TG synthesis have important contributory roles in the development of alcoholic steatosis. Since a fatty liver by definition implies excessive hepatic TG accumulation, we are proposing to investigate the 2 most proximal metabolic steps associated with TG accumulation, TG synthesis and degradation. All of our studies will be carried out in mice and will involve chronic feeding, for 4 weeks, of either the alcohol-containing or the isocaloric alcohol-free control Leiber-DeCarli diet formulations. These studies will also make use of adenoviral expression or knockdown constructs for a number of hepatic lipases and TG synthesizing enzymes, as well as other experimental protocols and expertise gained in our earlier published studies of the role of lipases in diet-induced (high fat diet) hepatic steatosis. In Specific Aim 1, we propose to evaluate the roles that several different hepatic lipases may have in the development/prevention of alcohol-induced fatty liver. Although the great majority of experimental protocols needed for undertaking this Aim are well established in the PI's laboratory, there is an exploratory element to this Specific Aim since the normal physiological role of one of the four lipases proposed for study in Specific Aim 1 is not well established. Specific Aim 2 will explore the specific roles that diacylglycerol acyltransferase 1 and 2 (DGAT1 and DGAT2), the two genetically distinct hepatic enzymes that catalyze the final step of TG synthesis, have in the development of alcoholic fatty liver. Our preliminary data establish that both DGAT1 and DGAT2 expression are elevated, by approximately 2-fold, in livers of alcohol-fed mice. Investigations proposed in Specific Aim 2 will define the specific actions of DGAT1 and DGAT 2 in the early stages of ALD development. PUBLIC HEALTH RELEVANCE: Alcoholic liver disease (ALD) is an important public health problem in the United States. An early event in the development of ALD is excessive accumulation of fat (triglyceride) in the liver. We propose to investigate how chronic alcohol consumption influences the actions of specific enzymes that are importantly involved in the synthesis and breakdown of fat in the liver. Our investigations will help establish the biochemical roles these enzymes have in facilitating alcohol-induced excessive fat accumulation in the liver. In addition, our studies may identify enzymes that can be targeted pharmacologically to block the early events that ultimately result in ALD. This may be important for preventing or retarding alcohol-induced liver disease.