Alcohol Intake and Hepatic Fat Metabolism

描述(申请人提供)：酒精性肝病(ALD)在美国和整个世界都是一个严重的公共卫生问题。ALD是由长期饮酒引起的，最初是单纯性脂肪变性，特征是肝细胞中脂肪过度堆积，主要是甘油三酯(TG)。部分单纯性脂肪变性的受试者进展为酒精性脂肪性肝炎(ASH)，可进一步发展为纤维化，最终导致肝硬变和肝癌。我们研究的基本假设是，ALD疾病易感性的差异反映了肝脂代谢的个体差异。由于酒精性脂肪肝没有直接的治疗方法，因此更好地了解酒精性脂肪肝发生的机制对于开发有效的干预措施来阻断酒精性脂肪肝至关重要。此应用程序的总体目标是对ALD开发中的早期事件有新的理解。在这项建议中，将通过实验解决的具体假设是，肝脏甘油三酯降解和甘油三酯合成失调在酒精性脂肪变性的发生发展中起着重要的作用。由于脂肪肝的定义意味着肝脏TG过度堆积，我们建议研究与TG堆积、TG合成和降解相关的最近端的两个代谢步骤。我们的所有研究都将在小鼠身上进行，并将包括长期喂养含酒精或不含等热量酒精的对照Leiber-DeCarli饮食配方，为期4周。这些研究还将利用一些肝脏脂肪酶和甘油三酯合成酶的腺病毒表达或敲除结构，以及我们早期发表的关于脂肪酶在饮食诱导(高脂肪饮食)肝脏脂肪变性中的作用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酶在酒精性脂肪肝的发生/预防中可能起到的作用。尽管完成这一目标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确立，但由于在特定目标1中建议研究的四种脂肪酶中的一种的正常生理作用还没有很好地确定，所以对这一特定目标有一个探索性的因素。具体目标2将探讨甘油二酯酰基转移酶1和2(DGAT1和DGAT2)在酒精性脂肪肝发生发展中的具体作用。我们的初步数据表明，在酒精喂养的小鼠的肝脏中，DGAT1和DGAT2的表达都增加了大约2倍。在具体目标2中提出的调查将确定DGAT1和DGAT2在ALD发展的早期阶段的具体作用。 公共卫生相关性：酒精性肝病(ALD)在美国是一个重要的公共卫生问题。ALD发展的早期事件是脂肪(甘油三酯)在肝脏中过度堆积。我们建议调查长期饮酒如何影响特定酶的活动，这些酶在肝脏脂肪的合成和分解中起重要作用。我们的研究将有助于确定这些酶在促进酒精诱导的肝脏过度脂肪积累方面所起的生化作用。此外，我们的研究可能确定可以在药理学上靶向阻止最终导致ALD的早期事件的酶。这对于预防或延缓酒精性肝病可能很重要。

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.