Function and Mechanism of DDB1-CUL4A E3 Ligase in Liver Lipid Metabolism

DDB1-CUL4A E3连接酶在肝脏脂质代谢中的功能和机制

• 批准号: 8697500
• 负责人: Lei Yin
• 金额: $ 33.82万
• 依托单位: UNIVERSITY OF MICHIGAN AT ANN ARBOR
• 依托单位国家: 美国
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-04-01 至 2019-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8697500
• 关键词: 5' -AMP-activated protein kinase; Affect; Animals; Binding Proteins; CUL4A gene; Carbohydrates; Cells; Chronic; Complex; DNA Damage; DNA-Binding Proteins; Data; Deposition; Development; Diabetes Mellitus; Diet; Elements; Fatty Liver; Fatty acid glycerol esters; Fibrosis; Gene Expression; Gene Targeting; General Population; Genes; Glucose; Health; Hepatic; Hepatocyte; In Vitro; Inflammation; Insulin Resistance; Knockout Mice; Leptin; Ligase; Lipids; Liver; Liver Failure; Liver diseases; Mediating; Metabolic; Metabolic syndrome; Modeling; Molecular; Mus; Nutrient; Nutritional; Obesity; Pathogenesis; Pathway interactions; Patients; Phosphorylation; Play; Prevalence; Prevention; Proteins; Regulation; Research; Role; Scheme; Testing; Triglycerides; Ubiquitination; base; cullin 4A; effective therapy; feeding; improved; lipid biosynthesis; lipid metabolism; liver injury; non-alcoholic; non-alcoholic fatty liver; novel; novel therapeutics; peptide O-linked N-acetylglucosamine-beta-N-acetylglucosaminidase; protein expression; public health relevance; response; therapeutic target; tool; transcription factor; ubiquitin-protein ligase

DESCRIPTION (provided by applicant): Non-alcoholic liver steatosis, also called fatty liver, is due to excessive fat accumulation in hepatocytes and is the most common liver disease affecting 10-30% of the general population. Fatty liver is also regarded as a component of metabolic syndrome, and is associated with insulin resistance, obesity, and diabetes. Nearly 35% of patients with fatty liver develop chronic inflammation, fibrosis, and eventual liver failure and there is no effective treatment for fatty liver disease. Therefore, it is imperative to understand the molecular mechanisms underlying the development of fatty liver. Our preliminary studies demonstrate that the damage-specific DNA binding protein 1 (DDB1) E3 ligase plays a crucial role in the development of high-fat diet (HFD)-induced fatty liver. In particular, we discovered that liver DDB1 protein levels were elevated under obese conditions. Liver-specific deletion of Ddb1 protects mice from the HFD-induced fat accumulation and selectively suppresses glycolytic and lipogenic gene expression in the liver. In primary mouse hepatocytes, Ddb1 knockdown represses de novo lipogenesis rate, reduces triglyceride content, and blocks the activity of a key regulator of lipogenesis, carbohydrate responsive- element binding protein (ChREBP). At the mechanistic level, we uncovered evidence that DDB1 indirectly regulates the ChREBP protein O-GlcNAcylation and stability by degrading O-GlcNAcase (OGA) through ubiquitination. Although DDB1 has been well-studied in the context of DNA damage response as a critical component of the CUL4A E3 ligase complex, its metabolic actions remain unknown. Based upon the preliminary data, we hypothesize that DDB1 E3 ligase contributes to the development of fatty liver by activating ChREBP-mediated hepatic lipogenesis. To test this hypothesis, we propose three inter- connected specific aims. Aim 1: Determine whether the DDB1 E3 ligase promotes de novo lipogenesis and contributes to obesity-associated fatty liver via ChREBP. Aim 2: Test whether DDB1 E3 ligase promotes O- GlcNAcylation and stability of ChREBP via degrading OGA protein in obesity. Aim 3: Investigate how the AMPK pathway mediates nutritional regulation of hepatic DDB1 expression during the obesity development. This proposal seeks an in-depth understanding of the metabolic role of DDB1 E3 ligase. Specifically, we anticipate identifying how DDB1 E3 ligase regulates de novo lipogenesis in the liver and induces fatty liver through ChREBP. Accomplishment of these research objectives should reveal fundamental mechanisms by which nutrient excess leads to fat accumulation and provide potential novel therapeutic avenues to treat fatty liver disease.

描述（由申请人提供）：非酒精性肝脏脂肪变性，也称为脂肪肝，是由于肝细胞中脂肪的积累过多，是影响普通人群10-30％的最常见肝病。脂肪肝也被视为代谢综合征的组成部分，与胰岛素抵抗，肥胖和糖尿病有关。脂肪肝脏患者中，近35％的患者会出现慢性炎症，纤维化和最终肝衰竭，并且没有有效治疗脂肪肝病。因此，必须了解脂肪肝发育的基础机制。我们的初步研究表明，损伤特异性的DNA结合蛋白1（DDB1）E3连接酶在高脂饮食（HFD）诱导的脂肪肝的发展中起着至关重要的作用。特别是，我们发现在肥胖条件下，肝脏DDB1蛋白水平升高。 DDB1的肝脏特异性缺失可保护小鼠免受HFD诱导的脂肪积累的影响，并有选择地抑制肝脏中的糖酵解和脂乐基因表达。在原发性小鼠肝细胞中，DDB1敲低抑制从头脂肪生成率，降低甘油三酸酯的含量，并阻止脂肪生成，碳水化合物响应元素结合蛋白（CHREBP）的关键调节剂的活性。在机械水平上，我们发现了DDB1间接调节CHREBP蛋白O-Glcnacylation和稳定性，通过泛素化降解O-Glcnacase（OGA）。尽管DDB1在DNA损伤响应的背景下是CUL4A E3连接酶复合物的关键组成部分进行了充分研究，但其代谢作用仍然未知。基于初步数据，我们假设DDB1 E3连接酶通过激活Chrebp介导的肝脂肪生成来有助于脂肪肝的发展。为了检验这一假设，我们提出了三个相互联系的特定目的。 AIM 1：确定DDB1 E3连接酶是否促进从头脂肪生成，并通过Chrebp促进与肥胖相关的脂肪肝。 AIM 2：测试DDB1 E3连接酶是否通过在肥胖症中降解OGA蛋白来促进Chrebp的O- Glcnacylation和稳定性。目标3：研究AMPK途径如何介导肥胖发育过程中肝DDB1表达的营养调节。该提案寻求对DDB1 E3连接酶代谢作用的深入了解。具体而言，我们预计DDB1 E3连接酶如何调节肝脏中的从头脂肪生成并通过Chrebp诱导脂肪肝。这些研究目标的实现应揭示营养过量导致脂肪积累的基本机制，并提供潜在的新型治疗途径来治疗脂肪肝病。