Alcohol Intake and Hepatic Fat Metabolism

描述（由申请人提供）：酒精性肝病（ALD）是美国和整个世界的严重公共卫生问题。ALD由慢性饮酒引起，开始为简单的脂肪变性，其特征在于脂质（主要是甘油三酯（TG））在肝细胞中过度积累。患有单纯性脂肪变性的受试者亚组进展为酒精性脂肪性肝炎（ASH），其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，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ALD没有直接的治疗方法，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干预措施来阻断ALD至关重要。本申请的总体目标是获得对ALD发展早期事件的新理解。在本提案中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具有重要的贡献作用。由于脂肪肝的定义意味着过度的肝脏TG积累，我们建议研究与TG积累，TG合成和降解相关的2个最接近的代谢步骤。我们的所有研究都将在小鼠中进行，并将涉及长期喂养含酒精或不含等热量酒精的对照Leiber-DeCarli饮食制剂4周。这些研究还将利用腺病毒表达或敲低构建体用于许多肝脂肪酶和TG合成酶，以及我们早期发表的脂肪酶在饮食诱导（高脂饮食）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诱导的脂肪肝的发展/预防中可能发挥的作用。尽管PI实验室已充分确立了实施该目标所需的绝大多数实验方案，但由于具体目标1中拟定研究的4种脂肪酶之一的正常生理作用尚未充分确立，因此该具体目标仍存在探索性因素。具体目标2将探讨二酰基甘油酰基转移酶1和2（DGAT 1和DGAT 2），催化TG合成的最后一步的两种遗传上不同的肝酶，在酒精性脂肪肝的发展中的具体作用。我们的初步数据表明，DGAT 1和DGAT 2的表达升高，约2倍，在酒精喂养的小鼠的肝脏。具体目标2中提出的研究将定义DGAT 1和DGAT 2在ALD开发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.