Control of Lipogenesis and Hepatic Steatosis by Caspase-2

Caspase-2 对脂肪生成和肝脂肪变性的控制

• 批准号: 9886239
• 负责人: Michael Karin
• 金额: $ 41.64万
• 依托单位: UNIVERSITY OF CALIFORNIA, SAN DIEGO
• 依托单位国家: 美国
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-03-15 至 2022-12-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9886239
• 关键词: Ablation; Active Sites; Adaptor Signaling Protein; Adipose tissue; Affect; Benign; Binding; Binding Proteins; CASP2 gene; Cells; Cholesterol; Chronic; Cleaved cell; Complex; Consumption; Cues; Death Domain; Development; Diet; Down-Regulation; Endoplasmic Reticulum; Energy Metabolism; Fatty Liver; Fatty acid glycerol esters; Feedback; Fructose; Genes; Genetic; Genetic Transcription; Golgi Apparatus; Hepatic; Hepatocyte; High Fat Diet; Hypoxia; Incidence; Inflammation; Insulin; Insulin Resistance; Knock-in Mouse; Knockout Mice; Light; Lipids; Liver; Malignant Neoplasms; Mediating; Membrane; Metabolic; Metabolic Diseases; Modeling; Mus; Mutant Strains Mice; N-terminal; Nutritional; Obesity; Pathway interactions; Patients; Peptide Hydrolases; Peripheral; Pharmacology; Phosphorylation; Preparation; Prevention; Primary carcinoma of the liver cells; Production; Protein Activation Pathway; Protein Isoforms; Protein Precursors; Proteins; Proteolysis; Proto-Oncogene Proteins c-akt; Refractory; Regulation; Resistance; Response Elements; Role; SCAP protein; Signaling Protein; Site; Starvation; Sterols; Sucrose; Tertiary Protein Structure; Testing; Tissue Expansion; Tissues; Triglycerides; Type 2 diabetic; Unsaturated Fatty Acids; Up-Regulation; Urokinase; Vesicle; adenoviral-mediated; cholesterol biosynthesis; endoplasmic reticulum stress; experimental study; feeding; improved; in vivo; insulin signaling; interest; lipid biosynthesis; lipid metabolism; non-alcoholic fatty liver disease; nonalcoholic steatohepatitis; nutrition; prevent; protein activation; protein complex; protein transport; reconstitution; response; site-1 protease; stressor; uptake; western diet

PROJECT SUMMARY Non-alcoholic fatty liver disease (NAFLD) is a common metabolic disorder whose US incidence exceeds 30%. While NAFLD manifests as benign steatosis, in about 15-20% of patients it assumes a much more aggressive form – non-alcoholic steatohepatitis (NASH). The switch from benign simple steatosis to NASH is poorly understood, but was suggested to depend on ER stress. Indeed, by feeding MUP-uPA mice, which are prone to liver ER stress caused by hepatocyte-specific urokinase plasminogen activator (uPA) expression, a high-fat diet (HFD) we established a faithful model of NASH that readily progresses to hepatocellular carcinoma (HCC). HFD-fed MUP-uPA mice show ER-stress-dependent and persistent activation of sterol response element binding proteins (SREBP) 1 and 2, which control de novo lipogenesis (DNL) and cholesterol biosynthesis. Notably, SREBP1 and 2 remain activated in the MUP-uPA liver without any sign of feedback inhibition, which shuts down their activity in lipid-loaded cells. DNL is also chronically elevated in NAFLD and hepatic accumulation of free cholesterol was suggested to convert simple steatosis to NASH. Investigating how liver ER stress causes persistent SREBP activation, we uncovered a previously unknown pathway in which caspase-2 (Casp2), whose expression is ER-stress-inducible, leads to constitutive activation of site 1 protease (S1P), thereby initiating SCAP-independent SREBP cleavage in the ER. Casp2-mediated cleavage and activation of S1P seems to occur in NASH patients and genetic ablation or pharmacological inhibition of Casp2 in MUP-uPA mice blocks hepatic steatosis and NASH development. To fully establish the mechanistic aspects of this pathway and its role in hepatic steatosis, we will investigate whether it functions in liver-specific SCAP knockout mice and determine whether liver-specific Casp2 ablation affects peripheral adiposity and improves energy expenditure in addition to preventing HFD-induced hepatic steatosis and its progression to NASH. We will also generate knockin mice that express a Casp2-resistant (C2R) form of S1P and determine whether they are protected from ER- stress induced hepatic steatosis and adipose tissue expansion. As ER-stress-mediated Casp2 activation and S1P cleavage seem to depend on Tp53 activity, which results in induction of the Casp2 activator PIDD, we will examine the role of Tp53 and PIDD in Casp2-dependent S1P cleavage, SREBP1/2 activation, and hepatic steatosis, thereby establishing a key metabolic function for Tp53 outside of cancer. Finally, we will examine the hypothesis that the original function of the Casp2-dependent S1P-SREBP activation pathway was to promote energy storage in the form of liver fat during periods of hypernutrition in preparation for long-term starvation. While clarifying the role of Casp2-mediated SREBP activation in hepatic steatosis and NASH, these studies will shed new light on the poorly understood phenomenon of selective insulin resistance, in which hepatic DNL remains elevated despite diminished insulin signaling.

项目概要 非酒精性脂肪肝（NAFLD）是一种常见的代谢性疾病，其在美国的发病率超过 30%。虽然 NAFLD 表现为良性脂肪变性，但在大约 15-20% 的患者中，它假设有更多的脂肪变性。 侵袭性形式——非酒精性脂肪性肝炎（NASH）。从良性单纯性脂肪变性到 NASH 的转变是 知之甚少，但建议取决于 ER 压力。事实上，通过喂养 MUP-uPA 小鼠， 容易出现由肝细胞特异性尿激酶纤溶酶原激活剂 (uPA) 表达引起的肝脏 ER 应激， 高脂肪饮食 (HFD) 我们建立了一个忠实的 NASH 模型，该模型很容易进展为肝细胞癌 （肝癌）。 HFD 喂养的 MUP-uPA 小鼠表现出内质网应激依赖性的甾醇反应元件的持续激活 结合蛋白 (SREBP) 1 和 2，控制从头脂肪生成 (DNL) 和胆固醇生物合成。 值得注意的是，SREBP1 和 2 在 MUP-uPA 肝脏中保持激活状态，没有任何反馈抑制的迹象，这 关闭它们在脂质负载细胞中的活性。 NAFLD 和肝病患者的 DNL 也长期升高 游离胆固醇的积累被认为可以将单纯性脂肪变性转化为 NASH。研究肝脏 ER 如何 压力导致持续的 SREBP 激活，我们发现了一个以前未知的途径，其中 caspase-2 (Casp2) 的表达是 ER 应激诱导型，导致位点 1 蛋白酶 (S1P) 的组成型激活， 从而在 ER 中启动不依赖于 SCAP 的 SREBP 裂解。 Casp2 介导的裂解和激活 S1P 似乎发生在 NASH 患者中，MUP-uPA 中 Casp2 的基因消除或药物抑制 小鼠可阻止肝脂肪变性和 NASH 的发展。充分建立该途径的机制方面 及其在肝脂肪变性中的作用，我们将研究它是否在肝脏特异性 SCAP 敲除小鼠中发挥作用，以及 确定肝脏特异性 Casp2 消融是否会影响外周脂肪并改善能量消耗 除了预防 HFD 诱导的肝脂肪变性及其进展为 NASH 之外。我们还将生成敲击 表达 Casp2 抗性 (C2R) 形式的 S1P 的小鼠，并确定它们是否受到 ER- 的保护 应激引起的肝脂肪变性和脂肪组织扩张。由于 ER 应激介导的 Casp2 激活和 S1P 裂解似乎依赖于 Tp53 活性，这会导致 Casp2 激活剂 PIDD 的诱导，我们将 检查 Tp53 和 PIDD 在 Casp2 依赖性 S1P 裂解、SREBP1/2 激活和肝脏中的作用 脂肪变性，从而建立 Tp53 在癌症之外的关键代谢功能。最后，我们将检查 假设 Casp2 依赖性 S1P-SREBP 激活途径的原始功能是促进 在营养过剩期间以肝脏脂肪的形式储存能量，为长期饥饿做准备。 在阐明 Casp2 介导的 SREBP 激活在肝脂肪变性和 NASH 中的作用的同时，这些研究将 为人们知之甚少的选择性胰岛素抵抗现象提供了新的线索，其中肝脏 DNL 尽管胰岛素信号减弱，但仍保持升高。