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: 8820262
• 负责人: Lei Yin
• 金额: $ 33.74万
• 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/8820262
• 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; 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）：非酒精性肝脂肪变性，也称为脂肪肝，是由于肝细胞中脂肪过度积累所致，是最常见的肝脏疾病，影响普通人群的 10-30%。脂肪肝也被认为是代谢综合征的一个组成部分，与胰岛素抵抗、肥胖和糖尿病有关。近35%的脂肪肝患者会出现慢性炎症、纤维化，最终导致肝衰竭，并且脂肪肝尚无有效的治疗方法。因此，了解脂肪肝发生的分子机制势在必行。我们的初步研究表明，损伤特异性 DNA 结合蛋白 1 (DDB1) E3 连接酶在高脂饮食 (HFD) 诱导的脂肪肝的发生过程中发挥着至关重要的作用。特别是，我们发现肝脏 DDB1 蛋白水平在肥胖条件下升高。肝脏特异性删除 Ddb1 可保护小鼠免受 HFD 诱导的脂肪堆积，并选择性抑制肝脏中糖酵解和脂肪生成基因的表达。在原代小鼠肝细胞中，Ddb1 敲低可抑制从头脂肪生成速率，降低甘油三酯含量，并阻断脂肪生成关键调节因子碳水化合物反应元件结合蛋白 (ChREBP) 的活性。在机制水平上，我们发现了DDB1通过泛素化降解O-GlcNAcase (OGA)来间接调节ChREBP蛋白O-GlcNAc糖化和稳定性的证据。尽管 DDB1 作为 CUL4A E3 连接酶复合物的关键组成部分在 DNA 损伤反应中已得到充分研究，但其代谢作用仍然未知。根据初步数据，我们假设 DDB1 E3 连接酶通过激活 ChREBP 介导的肝脏脂肪生成来促进脂肪肝的发生。为了检验这一假设，我们提出了三个相互关联的具体目标。目标 1：确定 DDB1 E3 连接酶是否促进脂肪从头生成并通过 ChREBP 导致肥胖相关脂肪肝。目标 2：测试 DDB1 E3 连接酶是否通过降解肥胖中的 OGA 蛋白来促进 O-GlcNAcNA 酰化和 ChREBP 的稳定性。目标 3：研究 AMPK 通路如何介导肥胖发展过程中肝脏 DDB1 表达的营养调节。该提案寻求深入了解 DDB1 E3 连接酶的代谢作用。具体来说，我们预计确定 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该揭示营养过剩导致脂肪积累的基本机制，并为治疗脂肪肝疾病提供潜在的新治疗途径。