HGF/HGFR Axis and Fatty Liver Disease

HGF/HGFR 轴与脂肪肝疾病

• 批准号: 9077861
• 负责人: Reza Zarnegar
• 金额: $ 34.65万
• 依托单位: UNIVERSITY OF PITTSBURGH AT PITTSBURGH
• 依托单位国家: 美国
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-04-01 至 2020-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9077861
• 关键词: Albumins; Alcoholic Hepatitis; Automobile Driving; Biological; Cell Death; Cell Survival; Cells; Cessation of life; Cirrhosis; Clinical; Coupled; Data; Defect; Disease; Event; Fatty Liver; Fatty acid glycerol esters; Fibrosis; Glucose; Growth Factor Receptors; HGF gene; Hepatic; Hepatocyte; High Fat Diet; Homeostasis; Human; In Vitro; Inflammation; Inflammatory; Insulin; Insulin Receptor; Insulin Resistance; Liver; Liver Failure; Liver diseases; MET gene; Malignant neoplasm of liver; Mediating; Mediator of activation protein; Metabolic; Metabolic syndrome; Metabolism; Modification; Molecular; Mus; Necrosis; Non-Insulin-Dependent Diabetes Mellitus; Pathology; Pathway interactions; Phosphotransferases; Play; Process; Proteasome Inhibition; Protein Kinase; Protein Tyrosine Kinase; Public Health; RIPK1 gene; Regulation; Resistance; Role; Series; Signal Transduction; Site-Directed Mutagenesis; System; Testing; Transgenic Mice; Tyrosine; Up-Regulation; base; cancer type; cell growth; feeding; gain of function; glucose metabolism; hepatic necrosis; in vivo Model; insight; lipid metabolism; liver inflammation; liver injury; loss of function; meetings; mouse model; non-alcoholic; non-alcoholic fatty liver; nonalcoholic steatohepatitis; novel; prevent; public health relevance; receptor function; research study; response; restoration

 DESCRIPTION (provided by applicant): Fatty Liver Disease (FLD) is a leading public health problem in the U.S. and elsewhere. Liver parenchymal cells (hepatocytes) play an essential role in regulating glucose and fat homeostasis which is believed to be achieved by the proper action of the Insulin-Insulin Receptor (I-IR) axis. Dysregulation of this pathway in Type 2 Diabetes (T2D) can result in non-alcoholic FLD (NAFLD) - a disorder showing a spectrum of pathologies from hepatocyte fat accumulation (steatosis), inflammation and necrosis of steatotic hepatocytes (NASH), fibrosis, cirrhosis and liver cancer that are not well understood at the molecular level. Hepatic insulin resistance is believed to be a driver of this process and results from lack of optimum insulin receptor (IR) function in hepatocytes. Recently, we established that the Hepatocyte Growth Factor (HGF)-MET signaling axis controls hepatic glucose and fat metabolism and is essential for optimum hepatic insulin response. Given the fact that the HGF-MET signaling axis not only controls metabolism but also modulates cell growth and survival (i.e. suppression of cell death), we propose that diminished HGF-MET signalling (that is, "HGF Resistance") in the liver acts as a double-edged sword causing a vicious cycle of hepatocyte metabolic derangement coupled with an inability to overcome (or survive) liver damage provoked by insults such as lipotoxicity. RIPK1 (Receptor Interacting Protein Kinase 1) has emerged as the master switch that dictates inflammation and necrosis. Based on our groundbreaking preliminary data examining the impact of the HGF- MET axis on RIPK1 in hepatocytes, we hypothesize that, under normal conditions in hepatocytes, the HGF-MET axis negatively regulates RIPK1 enzymatic activity through directly tyrosine phosphorylating RIPK1 promoting RIPK1 proteosomal degradation in order to protect hepatocytes from RIPK1's pro- inflammatory and pro-necrotic actions, and that, in the setting of hepatocyte lipotoxicity and NAFLD, reduced and defective HGF-MET signaling results in escape of RIPK1 from HGF-MET-mediated negative regulation unleashing RIPK1-dependent hepatocyte inflammation and necrotic cell death. We propose that restoration of HGF-MET signaling will negate this effect. We outline three specific aims to test this novel hypothesis. Aim 1 - we will investigate the functional consequences of tyrosine phoshorylation of RIPK1 by MET using site directed mutagenesis and in vitro hepatocytic cell cuture systems to establish that this modification results in inhibition of RIPK1 enzymatic activity and promotes its proteosomal degradation - hence, RIPK1 mediated inflammation and necrosis are prevented. We will also test the hypothesis that disruption of MET signaling results in uncontrolled RIPK1 activity unleashing RIPK1- mediated hepatocyte death. The molecular mechanisms that regulate RIPK1 are not well understood. We have discovered that MET directly tyrosine phosphorylates RIPK1 on Tyr384 downregulating RIPK1 kinase activity and marking it for proteosomal degradation. Thus, studies under this aim will decipher the molecular regulation of RIPK1 by the tyrosine kinase growth factor receptor MET. Aim 2 - we will directly test our hypothesis that HGF-MET mediated regulation of RIPK1 has biological and pathological implications to liver homeostasis in the setting of fatty liver disease using loss- and gain-of-function mouse models. We believe that HGF-MET insufficiency caused by lipotoxicity exacerbates RIPK1-induced liver inflammation and necrosis and that restoration of HGF-MET signaling will negate this effect. We have discovered that RIPK1 is upregulated and HGF/MET are downregulated in human and mouse fatty liver. The molecular mechanisms that drive progression of fatty liver disease are not well understood. We propose that reduced HGF/MET signaling in fatty hepatocytes causes RIPK1 to escape MET-mediated negative regulation driving RIPK1-induced hepatocyte necrosis. We will induce fatty liver disease (by feeding a high fat diet) in liver specific loss-of function (using LMETKO and LRIPK1 KO) and gain- of-function (Albumin-HGF Transgenic) mouse models. Aim 3 - we will determine the molecular basis of RIPK1 upregulation in hepatocytes by lipotoxicity. We hypothesize that any defect in HGF/MET signaling provoked by lipotoxicity will promote RIPK1 accumulation. Liptoxicity may also stabilizes RIPK1 via direct inhibition of the proteasome. We will perform a series of comprehensive experiments using a hepatocyte culture system and in vivo models to test if one or both of these pathways are active to define the molecular bases of RIPK1 dysregulation in fatty liver disease. The proposed studies will establish a new paradigm by which tyrosine kinase growth factor receptor systems like HGF-Met prevent hepatic inflammation and necrosis by downmodulating the pro-inflammatory and pro- death activity of RIPK1. Our studies will provide rationale for manipulating these key mediators (HGF-MET and RIPK1) in the clinical setting of inflammatory hepatic conditions such as NASH or alcoholic hepatitis.

 描述（由申请人提供）：脂肪肝（FLD）是美国和其他地方的主要公共卫生问题。肝实质细胞（肝细胞）在调节葡萄糖和脂肪稳态中起重要作用，这被认为是通过胰岛素-胰岛素受体（I-IR）轴的适当作用来实现的。2型糖尿病（T2 D）中该途径的失调可导致非酒精性FLD（NAFLD）-一种显示出肝细胞脂肪蓄积（脂肪变性）、脂肪变性肝细胞（NASH）炎症和坏死、纤维化、肝硬化和肝癌等一系列病理学的疾病，这些病理学在分子水平上尚未得到充分了解。肝胰岛素抵抗被认为是这一过程的驱动因素，并且是由于肝细胞中缺乏最佳胰岛素受体（IR）功能所致。最近，我们确定肝细胞生长因子（HGF）-MET信号轴控制肝脏葡萄糖和脂肪代谢，并且对于最佳肝脏胰岛素反应至关重要。鉴于HGF-MET信号轴不仅控制代谢，而且调节细胞生长和存活，（即细胞死亡的抑制），我们提出减少HGF-MET信号传导（即，肝细胞生长因子耐药性（“HGF耐药性”）是一把双刃剑，导致肝细胞代谢紊乱的恶性循环，（或存活）由诸如脂毒性的损伤引起的肝损伤。RIPK 1（受体相互作用蛋白激酶1）已成为支配炎症和坏死的主开关。基于我们研究肝细胞中HGF-MET轴对RIPK 1的影响的开创性初步数据，我们假设，在肝细胞的正常条件下，HGF-MET轴通过直接酪氨酸磷酸化RIPK 1促进RIPK 1蛋白体降解来负调节RIPK 1酶活性，以保护肝细胞免受RIPK 1的促炎和促坏死作用，并且，在肝细胞脂毒性和NAFLD的情况下，减少的和有缺陷的HGF-MET信号传导导致RIPK 1从HGF-MET介导的负调控中逃逸，释放RIPK 1依赖性肝细胞炎症和坏死细胞死亡。我们认为HGF-MET信号的恢复将抵消这种作用。我们概述了三个具体的目标来测试这个新的假设。目的1 -我们将使用定点突变和体外肝细胞培养系统研究MET对RIPK 1酪氨酸磷酸化的功能后果，以确定这种修饰导致RIPK 1酶活性的抑制并促进其蛋白体降解-因此，RIPK 1介导的炎症和坏死被预防。我们还将检验MET信号传导的中断导致不受控制的RIPK 1活性释放RIPK 1介导的肝细胞死亡的假设。调节RIPK 1的分子机制还不清楚。我们已经发现MET直接酪氨酸磷酸化Tyr 384上的RIPK 1，下调RIPK 1激酶活性并标记其蛋白体降解。因此，在此目标下的研究将破译酪氨酸激酶生长因子受体MET对RIPK 1的分子调控。目的2 -我们将直接测试我们的假设，即HGF-MET介导的RIPK 1调节对脂肪肝疾病中肝脏稳态具有生物学和病理学意义，使用功能丧失和获得小鼠模型。我们认为，由脂毒性引起的HGF-MET不足加剧了RIPK 1诱导的肝脏炎症和坏死，HGF-MET信号传导的恢复将抵消这种作用。我们已经发现，在人类和小鼠脂肪肝中，RIPK 1上调，HGF/MET下调。推动脂肪肝疾病进展的分子机制尚不清楚。我们认为，脂肪肝细胞中HGF/MET信号的减少导致RIPK 1逃避MET介导的负调控，从而驱动RIPK 1诱导的肝细胞坏死。我们将诱导脂肪肝疾病（通过喂养高脂肪饮食）在肝脏特定的损失， 功能（使用LMETKO和LRIPK 1 KO）和功能获得（白蛋白-HGF转基因）小鼠模型。目的3 -我们将通过脂毒性确定肝细胞中RIPK 1上调的分子基础。我们推测，任何由脂毒性引起的HGF/MET信号传导缺陷都会促进RIPK 1的积累。脂毒性也可以通过直接抑制蛋白酶体来稳定RIPK 1。我们将使用肝细胞培养系统和体内模型进行一系列综合实验，以测试这些途径中的一个或两个是否活跃，以确定脂肪肝疾病中RIPK 1失调的分子基础。所提出的研究将建立一种新的范例，通过该范例，酪氨酸激酶生长因子受体系统如HGF-Met通过下调RIPK 1的促炎和促死亡活性来预防肝脏炎症和坏死。我们的研究将为在炎症性肝病（如NASH或酒精性肝炎）的临床环境中操纵这些关键介质（HGF-MET和RIPK 1）提供理论依据。