PNPLA3 in Susceptibility and Resistance to Fatty Liver Disease

项目摘要 这个项目的目标是确定脂肪肝(FLD)的代谢和分子基础，这是一种新兴的 健康问题，几乎没有治疗选择。脂肪肝一直是我们实验室的主要研究重点。 2004年，我们进行了第一次以人群为基础的肝甘油三酯(TG)含量(HTGC)的调查 不同祖先的样本，达拉斯心脏研究(DHS)。肝脏脂肪变性被发现是强烈的 受血统(西班牙裔；欧洲和非洲)和肥胖的影响，但即使在个人之间也有很大的差异 他们在血统和体重指数(BMI)方面都是匹配的。我们利用人类遗传学来鉴定第一个和 临床上对FLD影响最大的遗传风险因子变异：PNPLA3(148M)。这种变异使人容易患上 酒精性和非酒精性脂肪肝的全光谱。在同一项研究中，我们发现 PNPLA3(148m)，我们还发现了PNPLA3的另一个变异S453I，它与hTGC降低相关； 这种变异几乎只存在于非洲人后裔中，这是患病率最低的群体 是FLD的。这两个变异加在一起可以解释大约70%与祖先相关的HTGC差异。 尽管在阐明148M变异的致病机制方面取得了重大进展，但 在小鼠身上成功地进行了关于潜在治疗途径的概念验证研究，以对抗 148M的作用，关于变异的病理生物学以及它与FLD的关系的重要问题仍然存在 无人回答或有争议的。因此，我们将重点解决三个关键问题：1)如何 PNPLA3(148m)逃避泛素化和降解？2)148m变异体是如何影响TG水解度的？ 3)PNPLA3-S453I是如何降低肝脏甘油三酯含量和保护FLD的？其中的每一个问题 构成了一个特定的目标。我们将利用尖端技术来克服重要限制 在我们和其他人解决这些问题所使用的先前方法中。在目标1中，我们将使用CRISPR/CAS9 失活筛选以鉴定泛素化PNPLA3的E3连接酶。在AIM 2中，我们将使用高度可调的 系统来控制蛋白质在翻译水平的表达，以及一种灵敏的荧光素酶重组试验来 生物化学定义PNPLA3、ATGL和ABHD5之间的相互作用在生理上相关 细胞内的浓度。在AIM 3中，我们将开发第一个PNPLA3(S453I)小鼠模型，以确定 VARIANT降低HTGC。由于PNPLA3跨越残基453的区域在小鼠中不存在，我们将替换 利用CRISPR-CAS9技术将小鼠基因与包含S453I变异体的人类微型基因结合在一起。这些 小鼠将被用来确定这种错义变异是如何导致肝脏甘油三酯水平降低的。 这些研究结合在一起，有望揭示出新的途径和过程， 治疗手法预防和治疗PNPLA3相关性FLD。

Project Summary The goal of this project is to define the metabolic and molecular basis of fatty liver disease (FLD), a burgeoning health problem with few therapeutic options. Fatty liver disease has been a major focus of our laboratory since 2004, when we undertook the first survey of hepatic triglyceride (TG) content (HTGC) in a population-based sample of different ancestries, the Dallas Heart Study (DHS). Hepatic steatosis was found to be strongly influenced by ancestry (Hispanics>European>African) and adiposity, but varied widely even among individuals who were matched for ancestry and body mass index (BMI). We used human genetics to identify the first and most clinically impactful genetic risk factor variant for FLD: PNPLA3(148M). This variant confers susceptibility to the full spectrum of both alcoholic and nonalcoholic FLD. In the same study in which we identified PNPLA3(148M), we also identified another variant in PNPLA3, S453I, that is associated with reduced HTGC; this variant is present almost exclusively in individuals of African descent, the group with the lowest prevalence of FLD. These two variants together account for ~70% of ancestry-related differences in HTGC. Despite having made significant progress elucidating the pathogenic mechanism of the 148M variant, and having performed successful proof-of-concept studies in mice of potential therapeutic avenues to combat the effects of 148M, important questions regarding the pathobiology of the variant and how it is related to FLD remain unanswered or disputed. Accordingly, we will focus this application on three critical questions: 1) How does PNPLA3(148M) evade ubiquitylation and degradation? 2) How does the 148M variant impair TG hydrolysis? and 3) How does PNPLA3-S453I lower hepatic TG content and protect against FLD? Each of these questions constitutes a Specific Aim. We will take advantage of cutting edge technologies to overcome important limitations in prior methods used by us and others to address these questions. In AIM 1 we will use a CRISPR/Cas9 inactivation screen to identify the E3-ligase that ubiquitylates PNPLA3. In AIM 2 we will use a highly tunable system to control protein expression at the level of translation, and a sensitive, luciferase reconstitution assay to biochemically define the interactions among PNPLA3, ATGL, and ABHD5 at physiologically relevant concentrations in cells. In AIM 3 we will develop the first mouse model of PNPLA3(S453I) to determine how the variant lowers HTGC. Since the region of PNPLA3 spanning residue 453 is not present in mice, we will replace the mouse gene with a human mini-gene containing the S453I variant using CRISPR-Cas9 technology. These mice will be used to determine how this missense variant results in lower hepatic TG levels. These studies, when taken together, hold the promise of revealing new pathways and processes that can be therapeutically manipulated for the prevention and treatment of PNPLA3-related FLD.