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: 10322660
• 负责人: Michael Karin
• 金额: $ 41.77万
• 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 2023-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/10322660
• 关键词: Ablation; Active Sites; Adaptor Signaling Protein; Adipose tissue; Affect; Benign; Binding; Binding Proteins; CASP2 gene; Cells; Cholesterol; Chronic; 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; simple steatosis; 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.

项目总结 非酒精性脂肪性肝病(NAFLD)是一种常见的代谢性疾病，其发病率在美国超过 30%。虽然NAFLD表现为良性脂肪变性，但在大约15%-20%的患者中，它表现为更多 侵袭型--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 人们对此知之甚少，但建议依赖内质网应激。事实上，通过喂食MUP-uPA小鼠，它们是 肝细胞特异性尿激酶型纤溶酶原激活物(UPA)表达易导致肝脏内质网应激 高脂饮食(HFD)我们建立了一种可靠的NASH模型，该模型很容易进展为肝细胞癌 (肝细胞癌)。高脂饲料喂养的MUP-uPA小鼠表现出内质网应激依赖和固醇反应元件的持续激活 结合蛋白(SREBP)1和2，控制新生脂肪生成(DNL)和胆固醇的生物合成。 值得注意的是，SREBP1和2在MUP-uPA肝脏中保持激活，没有任何反馈抑制的迹象，这 关闭它们在脂类细胞中的活动。在NAFLD和肝脏中，DNL也慢性升高 游离胆固醇的积累被认为是将单纯性脂肪变性转化为NASH的原因。研究肝脏ER是如何 应激导致SREBP的持续激活，我们发现了一个以前未知的途径，其中caspase-2 (Casp2)，其表达是内质网应激诱导的，导致1位点蛋白酶(S1P)的结构性激活， 从而在内质网中启动不依赖于SCAP的SREBP切割。Casp2介导的细胞分裂和激活 NASH患者中似乎存在S1P和MUP-uPA中Casp2的基因消融或药物抑制 小鼠阻止肝脏脂肪变性和NASH的发展。要完全建立这条途径的机械性方面 以及它在肝脏脂肪变性中的作用，我们将研究它在肝脏特异性SCAP基因敲除小鼠和 确定肝脏特异性Casp2消融是否影响外周脂肪和改善能量消耗 除了预防HFD诱导的肝脏脂肪变性及其进展为NASH外。我们还将生成敲门声 表达Casp2抗性(C2R)形式的S1P并确定它们是否受到ER- 应激导致肝脏脂肪变性和脂肪组织扩张。AS内质网应激介导的Casp2激活和 S1P的切割似乎依赖于TP53的活性，这导致了Casp2激活剂PIDD的诱导，我们将 检测TP53和PIDD在Casp2依赖的S1P裂解、SREBP1/2激活和肝脏中的作用 脂肪变性，从而建立了癌症外TP53的关键代谢功能。最后，我们将研究 假设依赖Casp2的S1P-SREBP激活通路的原始功能是促进 在营养过剩时期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激活在肝脏脂肪变性和NASH中的作用的同时，这些研究将 揭示了选择性胰岛素抵抗这一鲜为人知的现象，在这种现象中，肝脏DNL 尽管胰岛素信号减弱，但仍保持高水平。