Role of PNPLA3 in Fatty Liver Disease

描述（由申请人提供）：非酒精性脂肪性肝病（NAFLD）是一种新兴的健康问题，影响了美国三分之一的成年人和越来越多的儿童。该疾病的过程始于肝脏中甘油三酯（TG）的积累（脂肪变性），在某些个体中会引起炎症反应（脂肪性肝炎），可进展为肝硬化，并可能发展为肝癌。虽然各种因素（例如，尽管在横断面研究中发现NAFLD与肥胖、胰岛素抵抗相关，但NAFLD的发病机制仍然知之甚少，并且治疗选择目前非常有限。我们的研究小组已经采取了遗传方法来确定导致NAFLD的因果因素。最近，我们发现了一个错义突变（I148 M）在patatin样磷脂酶结构域的蛋白质，PNPLA 3是强烈相关的肝TG含量和肝损伤。这种变异在西班牙裔美国人中最常见，这是肝脏脂肪变性患病率最高的群体，在脂肪变性频率最低的非洲裔美国人中最不常见。随后的研究证实了我们的发现，并表明PNPLA 3-I148 M变异体在活检证实的脂肪性肝炎和酒精相关性肝硬化受试者中富集。因此，PNPLA 3被认为是全谱NAFLD以及酒精性肝硬化的促成因素。 关于PNPLA 3的生理作用以及这种酶的遗传变异如何促进肝脏TG积累、炎症和纤维化的基本问题仍然存在。本申请的总体目标是阐明PNPLA 3在脂肪肝疾病中的作用。为此，我们将使用经典的生物化学和生理学的组合加上国家的最先进的质谱在小鼠与遗传定义的PNPLA 3功能的变化，以确定底物和产品的酶，在脂质代谢中的作用PNPLA 3和其关联的TG积累和肝损伤的分子基础。将使用两种互补的方法来鉴定PNPLA 3的生物底物：i）使用纯化的酶的候选底物方法（Aim 1a）和在遗传修饰的小鼠中的比较脂质组学方法（Aim 1b），以鉴定通过PNPLA 3活性的变化而改变的脂质。在目的2中，我们将使用我们的小鼠模型来检查PNPLA 3-I148 M对肝脂质代谢的影响。目的3着重于鉴定PNPLA 3-I148 M促进TG在肝脏中积累的分子机制。最后，在目的4中，我们将建立小鼠模型，其中研究PNPLA 3促进肝脏炎症和纤维化的机制。 通过阐明PNPLA 3的生物学作用和I148 M突变赋予脂肪肝疾病易感性的机制，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NAFLD。

DESCRIPTION (provided by applicant): Nonalcoholic fatty liver disease (NAFLD) is a burgeoning health problem that affects one-third of adults and an increasing number of children in the U.S. The disease process begins with the accumulation of triglyceride (TG) in the liver (steatosis), which in some individuals elicits an inflammatory response (steatohepatitis) that can progress to cirrhosis, and possibly liver cancer. Although various factors (e.g., obesity, insulin resistance) are associated with NAFLD in cross-sectional studies, the pathogenesis of NAFLD remains poorly understood and therapeutic options are currently very limited. Our group has taken a genetic approach to identify causal factors that contribute to NAFLD. Recently, we identified a missense mutation (I148M) in patatin-like phospholipase domain-containing protein, PNPLA3 that is strongly associated with both hepatic TG content and hepatic injury. The variant is most common in Hispanics, the group with the greatest prevalence of hepatic steatosis and least common in African-Americans who have the lowest frequency of steatosis. Subsequent studies have confirmed our findings and showed that the PNPLA3-I148M variant is enriched in subjects with biopsy-proven steatohepatitis and with alcohol-related cirrhosis. Thus, PNPLA3 is implicated as a contributing factor in the full spectrum of NAFLD as well as alcoholic cirrhosis. Basic questions remain regarding the physiological role of PNPLA3 and how genetic variation in this enzyme promotes hepatic TG accumulation, inflammation and fibrosis. The overall goal of this application is to elucidate the role of PNPLA3 in fatty liver disease. To this end, 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 function to identify the substrates and products of the enzyme, the role in PNPLA3 in lipid metabolism and the molecular basis for its association with TG accumulation and liver damage. Two complementary approaches will be used to identify the biological substrate(s) of PNPLA3: i) a candidate substrate approach using purified enzyme (Aim 1a) and a comparative lipidomic approach in genetically- modified mice (Aim 1b) to identify lipids that are altered by changes in PNPLA3 activity. In Aims 2 we will use our mouse models to examine effects of PNPLA3-I148M on hepatic lipid metabolism. Aim 3 focuses on identifying molecular mechanisms by which PNPLA3-I148M promotes TG accumulation in the liver. Finally, in Aim 4 we will establish a mouse model in which to investigate the mechanisms by which PNPLA3 contributes to hepatic inflammation and fibrosis. By elucidating the biological role of PNPLA3 and the mechanisms by which the I148M mutation confers susceptibility to fatty liver disease, the experiments outlined in this proposal will provide new insight 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 NAFLD.