Insulin resistance in the pathogenesis of NASH

描述（由申请人提供）：在美国，大约三分之一的成年人被诊断患有脂肪肝。约10%的患者会发展为非酒精性脂肪性肝炎（NASH）及相关合并症。因此，了解本病的病理生理学是十分必要的。NASH发病机制目前的解释是基于“两击假说”，即肝脂肪变性最初发生（第一次击中），易发生脂质过氧化和炎症，导致肝炎、细胞凋亡、纤维化，最终肝硬化（第二次击中）。这种疾病与胰岛素抵抗之间的关系一直存在争议，主要是因为缺乏可复制的动物模型。我们描述了一种将NASH发病机制与癌胚抗原相关细胞粘附分子1 （CEACAM1）联系起来的新机制，CEACAM1是一种通过介导肝脏胰岛素清除来调节胰岛素敏感性的蛋白质。它也是一种抗炎信号分子。肝脏特异性CEACAM1失活导致胰岛素抵抗、内脏肥胖和肝脏甘油三酯产生和输出增加。在初步数据中，我们发现：(i)内脏型肥胖患者的CEACAM1水平降低；（ii）在高脂肪饮食等引发炎症的条件下，转基因小鼠中CEACAM1的显性阴性抑制会产生nash样综合征；（iii）转基因小鼠肝脏中CEACAM1的过表达可防止高脂肪饮食引起的胰岛素抵抗和内脏性肥胖。我们假设肝脏CEACAM1的减少是NASH发展的关键机制。为了验证这一假设，我们建议研究CEACAM1的肝脏特异性零突变是否会导致胰岛素抵抗（Aim 1），并在高脂肪饮食后易患NASH （Aim 2）。在Aim 2中，我们还将通过研究肝脏Ceacam1功能丧失和获得的小鼠，寻求确定NASH发展的信号通路。我们将研究CEACAM1在NASH模型中的恢复是否能逆转肝脏胰岛素抵抗、炎症、脂质过氧化和纤维化。在Aim 3中，我们将研究CEACAM1在NASH发展中的分子靶点和效应分子。基于一个新的假设，我们将测试线粒体甘油三酯转移蛋白（MTP）在这一过程中的作用。这些实验的结果将确定胰岛素抵抗与肝大脂肪变性、炎症和与NASH相关的细胞损伤之间的新机制。他们还将确定CEACAM1作为NASH的分子生物标志物以及预防和治疗NASH的潜在靶点。公共卫生相关性：非酒精性脂肪性肝炎（NASH）的发病率预计将与肥胖流行同步上升。由于NASH经常进展为肝硬化，并且正在成为美国肝移植的主要原因，因此了解其机制势在必行。该病以肝大脂肪变性、炎症和纤维化为特征。它经常与其他常见的代谢异常相关，如胰岛素抵抗、内脏肥胖和肝脏脂肪变性，但胰岛素抵抗在NASH发病机制中的作用一直存在争议，主要是由于缺乏合适的动物模型。我们提出了一种新的NASH机制，与癌胚抗原相关细胞粘附分子1 （CEACAM1）有关，CEACAM1是一种蛋白质，其失活会导致胰岛素抵抗、血脂异常、肝脏脂肪变性和炎症。该提案旨在验证肝脏CEACAM1的减少构成NASH发展的早期机制的假设。这些实验的结果将确定胰岛素抵抗与肝大脂肪变性、炎症和与NASH相关的细胞损伤之间的新机制。这将确定肝脏CEACAM1的减少作为NASH的分子生物标志物以及预防和治疗NASH的潜在靶点。

DESCRIPTION (provided by applicant): About one third of adults in the United States are diagnosed with fatty liver disease. About 10% will proceed to develop nonalcoholic steatohepatitis (NASH), and associated co-morbidities. Thus, it is imperative to understand the pathophysiology of the disease. NASH pathogenesis is currently explained on the basis of the "two-hit" hypothesis, in which hepatic steatosis develops initially (first hit) and predisposes to lipid peroxidation and inflammation, leading to hepatitis, apoptosis, fibrosis and ultimately, cirrhosis (second hit). Association between the disease and insulin resistance has been disputed, largely because of the lack of a replicate animal model. We describe a novel mechanism linking NASH pathogenesis to the Carcino-Embryonic Antigen-related Cell Adhesion Molecule 1 (CEACAM1), a protein that regulates insulin sensitivity by mediating hepatic insulin clearance. It also acts as an anti-inflammatory signaling molecule. Liver-specific inactivation of CEACAM1 causes insulin resistance, visceral obesity and increased triglyceride production and output from liver. In preliminary data, we show that: (i) CEACAM1 levels are reduced in humans with visceral obesity; (ii) dominant-negative inhibition of CEACAM1 in transgenic mice yields a NASH-like syndrome under conditions that trigger inflammation, such as high-fat diet; while (iii) overexpression of CEACAM1 in liver of transgenic mice prevents insulin resistance and visceral obesity in response to high fat diet. We hypothesize that reduction in hepatic CEACAM1 constitutes a key mechanism in NASH development. To test this hypothesis, we propose to investigate whether liver-specific null mutation of CEACAM1 causes insulin resistance (Aim 1) and predisposes to NASH in response to high-fat diet (Aim 2). In Aim 2, we will also seek to identify the signaling pathways responsible for NASH development by studying mice with hepatic Ceacam1 loss- and gain-of-function. We will examine whether CEACAM1 restoration in NASH models reverses hepatic insulin resistance, inflammation, lipid peroxidation and fibrosis. In Aim 3, we will investigate the molecular target(s) and effector(s) of CEACAM1 responsible for NASH development. Based on a novel hypothesis, we will test the role of Mitochondrial Triglyceride Transfer Protein (MTP) in this process. The results of these experiments will define novel mechanisms linking insulin resistance with hepatic macrosteatosis, inflammation and cell injury associated with NASH. They will also identify CEACAM1 as a molecular biomarker of NASH as well as a potential target for its prevention and treatment. PUBLIC HEALTH RELEVANCE: The incidence of Nonalcoholic Steatohepatitis (NASH) is expected to rise in parallel to the obesity epidemic. Because NASH frequently progresses to liver cirrhosis, and is becoming the leading cause of liver transplant in the US, it is imperative to understand its mechanisms. The disease is characterized by hepatic macrosteatosis, inflammation and fibrosis. It is frequently associated with other common metabolic abnormalities, such as insulin resistance, visceral obesity and liver steatosis, but the role of insulin resistance in the pathogenesis of NASH has been disputed, largely owing to the lack of a suitable animal model. We propose a novel mechanism of NASH, linked to the Carcino-Embryonic Antigen-related Cell Adhesion Molecule 1 (CEACAM1), a protein the inactivation of which causes insulin resistance, dyslipidemia, liver steatosis and inflammation. The proposal seeks to test the hypothesis that reduction in hepatic CEACAM1 constitutes an early mechanism in NASH development. The results of these experiments will define novel mechanisms linking insulin resistance and hepatic macrosteatosis, inflammation and cell injury associated with NASH. This will identify reduction in hepatic CEACAM1 as a molecular biomarker of NASH as well as a potential target for its prevention and treatment.