Role of PNPLA3 in Fatty Liver Disease

描述（由申请人提供）：脂肪肝（FLD）是一种新兴的健康问题，影响美国三分之一的成年人和越来越多的儿童。FLD的两种最常见形式是非酒精性肝病（NAFLD）和酒精性肝病（ALD）。这两种疾病开始都是肝脏中甘油三酯（TG）的积累（脂肪变性），在某些个体中，这会引发炎症反应[非酒精性脂肪性肝炎（NASH）或酒精性脂肪变性（ASH）]，可进展为肝硬化和肝癌。在这两种疾病中阻止疾病进展的治疗选择非常有限。FLD治疗的发展受到以下因素的阻碍：对该病分子基础的认识有限，缺乏人类疾病进展的非侵入性标志物，以及缺乏准确概括人类FLD发病机制的动物模型。 作为解决这些障碍的第一步，我们的研究小组使用人类遗传学来鉴定导致FLD的基因。我们在patatin样磷脂酶结构域蛋白PNPLA 3中发现了一个错义突变（I148 M），该突变与肝脏TG含量和炎症密切相关。我们发现，这种变异在西班牙裔美国人中非常常见，他们在美国的NAFLD患病率最高。超过50项独立研究证实并扩展了我们的发现，表明PNPLA 3-I148 M在患有活检证实的脂肪性肝炎、肝硬化和肝细胞癌的个体中富集，这些个体都是由于ALD和NAFLD引起的。因此，PNPLA 3被认为是NAFLD和ALD全谱中的一个促成因素，表明这两种形式的FLD不仅具有共同的病理特征，而且具有共同的分子机制。 最近，我们在第二个基因TM 6SF 2中发现了一种遗传变异，该基因使人对脂肪变性和炎症易感。该基因中的错义变体与独立于PNPLA 3的肝TG含量增加相关。该基因的功能尚不清楚。 在本申请中，我们将使用经典的生物化学和生理学加上最先进的质谱法在PNPLA 3和TM 6SF 2功能发生遗传定义变化的小鼠中进行组合，以阐明这两种蛋白质的生理作用以及它们促进肝脏脂肪积累和炎症的分子机制。我们将利用这些发现来开发小鼠模型，更准确地再现人类NAFLD和ALD，并为临床前测试提供改进的试剂。 相关性：通过阐明PNPLA 3和TM 6SF 2的生物学作用以及这些蛋白质中的变体赋予FLD易感性的机制，本提案中概述的实验将为继续增加患病率的主要人类疾病的发病机制提供新的见解。我们的最终目标是开发新的方法和策略来诊断，预防和治疗FLD。

DESCRIPTION (provided by applicant): Fatty liver disease (FLD) is a burgeoning health problem that affects one-third of adults and an increasing number of children in the U.S. The two most common forms of FLD are nonalcoholic liver disease (NAFLD) and alcoholic liver disease (ALD). Both disorders begin with accumulation of triglyceride (TG) in the liver (steatosis), which in some individuals elicits an inflammatory response [nonalcoholic steatohepatitis (NASH) or alcoholic steatosis (ASH)] that can progress to cirrhosis and liver cancer. Therapeutic options to arrest disease progression in both disorders are very limited. The development of treatments for FLD has been hampered by limited appreciation of the molecular underpinnings of the disease, the lack of noninvasive markers of disease progression in humans, and a paucity of animal models that accurately recapitulate the pathogenesis of human FLD. As a first step to address these obstacles, our group used human genetics to identify genes that contribute to FLD. We identified a missense mutation (I148M) in patatin-like phospholipase domain-containing protein, PNPLA3, which is strongly associated with both hepatic TG content and inflammation. We showed that the variant is very frequent in Hispanics, who have the highest prevalence of NAFLD in the United States. Over 50 independent studies have confirmed and extended our findings to show that PNPLA3-I148M is enriched in individuals with biopsy-proven steatohepatitis, cirrhosis, and hepatocellular carcinoma both due to ALD and NAFLD. Thus, PNPLA3 is implicated as a contributing factor in the full spectrum of both NAFLD and ALD, suggesting that these two forms of FLD share not only pathological features but also molecular mechanisms in common. Recently, we identified a genetic variant in a second gene, TM6SF2, that confers susceptibility to both steatosis and inflammation. A missense variant in this gene is associated with increased hepatic TG content independently of PNPLA3. The function of this gene is unknown. In this application we will use a combination of classical biochemistry and physiology plus state-of-the-art mass spectrometry in mice with genetically-defined changes in PNPLA3 and TM6SF2 function to elucidate the physiological roles of these two proteins and the molecular mechanisms by which they promote hepatic fat accumulation and inflammation. We will leverage these findings to develop mouse models that more accurately recapitulate human NAFLD and ALD and provide improved reagents for pre-clinical testing. RELEVANCE: By elucidating the biological roles of PNPLA3 and TM6SF2 and the mechanisms by which variants in these proteins confer susceptibility to FLD, the experiments outlined in this proposal will provide new insights into the pathogenesis of a major human disease that continues to increase in prevalence. Our ultimate goal is to develop new approaches and strategies to diagnose, prevent, and treat FLD.