LXR-Dependent Cholesterol Sensing

LXR 依赖性胆固醇传感

• 批准号: 10586056
• 负责人: Ira G Schulman
• 金额: $ 47.64万
• 依托单位: UNIVERSITY OF VIRGINIA
• 依托单位国家: 美国
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-04-01 至 2026-03-31
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10586056
• 关键词: Adult; Affect; Agonist; Binding; Biological Models; Cardiovascular Diseases; Cell model; Cells; Cholesterol; Cholesterol Homeostasis; Chronic Disease; Cirrhosis; Collagen; Coupled; Deposition; Diet; Dominant-Negative Mutation; Enterobacteria phage P1 Cre recombinase; Event; Fatty Acids; Fatty acid glycerol esters; Fibrosis; Gene Expression; Genes; Genetic; Genetic Transcription; Heart Diseases; Hepatic; Hepatic Stellate Cell; Hepatocyte; Heterozygote; Human; Immune; Impairment; Individual; Inflammation; Inflammatory; LXRalpha protein; Ligands; Link; Liver; Liver Failure; Liver diseases; Mus; Mutation; Myeloid Cells; Non-Insulin-Dependent Diabetes Mellitus; Pathogenesis; Pathologic; Pathology; Patients; Phenotype; Phenylalanine; Population; Primary carcinoma of the liver cells; Process; Risk; Role; Severity of illness; Signal Transduction; Testing; Time; Tissues; Transcriptional Activation; Transcriptional Coactivator with PDZ-Binding Motif; Transcriptional Regulation; Triglycerides; Tryptophan; United States; cell type; chronic liver disease; experimental study; fatty liver disease; immune cell infiltrate; insight; lipid metabolism; liver inflammation; mouse model; non-alcoholic fatty liver disease; nonalcoholic steatohepatitis; novel; overexpression; pharmacologic; response; selective expression; sensor; single-cell RNA sequencing; tool

Project Summary: Non-alcoholic fatty liver disease (NAFLD) is estimated to affect 25% of the adult population in the United States and approximately 25% of NAFLD patients progress to non-alcoholic steatohepatitis (NASH), characterized by liver inflammation, hepatocyte ballooning, and fibrosis. Importantly, NASH increases the risks for cirrhosis, hepatocellular carcinoma, and liver failure. The processes that trigger the progression of NAFLD to NASH or even if there is a true stepwise progression from one pathological state to the other remain to be determined. NAFLD is associated with increases in liver triglycerides and elevated rates of fatty acid synthesis. Nevertheless, since most NAFLD patients do not have NASH, it is not clear if elevated fatty acids alone are sufficient to promote inflammation and fibrosis. Cholesterol is also increased in the livers of patients with NASH and non-esterified cholesterol correlates with disease severity. We reasoned that a unique approach to unraveling the roles of cholesterol in chronic liver diseases would be to reversibly disrupt cholesterol sensing. Liver x receptor alpha (LXRα) functions as an important cholesterol sensor that regulates hepatic fat and cholesterol metabolism at the transcriptional level in response to the direct binding of cholesterol derivatives. To disrupt cholesterol sensing we have generated mouse lines that change tryptophan 441 of LXRα to phenylalanine (W441F). W441F disrupts binding of endogenous cholesterol derived LXR ligands while still allowing transcription regulation by potent synthetic agonists providing a unique tool that blocks the ability of LXRα to sense cholesterol while still allowing pharmacological control. When fed a high fat/high cholesterol diet LXRα W441F mice rapidly (within 4 weeks) develop pathologies associated with NASH. Strikingly W441F mice have decreased hepatic triglycerides but large increases in cholesterol. Therefore, NASH-like phenotypes can arise in the absence of elevated hepatic triglycerides (“cholesterol-dependent NASH”). We hypothesize that decreased LXR activity in W441F hepatocytes leads to cholesterol accumulation which serves as the initiating event promoting inflammation and fibrosis. Furthermore, we propose that elevated hepatic cholesterol promotes NASH, at least in part, via cholesterol-dependent activation of the transcriptional coactivator with PDZ binding motif (TAZ, Wwtr1). TAZ is over expressed in livers of human NASH patients and promotes inflammation and fibrosis when over expressed in mouse models. Finally, our ability to re-establish LXR activity in W441F mice using pharmacological agents provides a unique opportunity to determine if cholesterol- dependent NASH can be reversed. Taken together our proposed studies will provide new insights into the mechanisms by which elevated cholesterol levels contribute to the pathogenesis of NASH and other chronic diseases.

项目概要： 据估计，美国 25% 的成年人口患有非酒精性脂肪肝 (NAFLD) 大约 25% 的 NAFLD 患者进展为非酒精性脂肪性肝炎 (NASH)， 其特征是肝脏炎症、肝细胞膨胀和纤维化。重要的是，NASH 增加了风险 用于肝硬化、肝细胞癌和肝功能衰竭。触发 NAFLD 进展的过程 NASH 或即使存在从一种病理状态到另一种病理状态的真正逐步进展，仍有待确定 决定。 NAFLD 与肝脏甘油三酯的增加和脂肪酸合成率的升高有关。 然而，由于大多数 NAFLD 患者没有 NASH，因此尚不清楚脂肪酸升高是否会单独导致 NASH。 足以促进炎症和纤维化。 NASH 患者肝脏中的胆固醇也会增加 非酯化胆固醇与疾病严重程度相关。我们认为，一种独特的方法 揭示胆固醇在慢性肝病中的作用将是可逆地破坏胆固醇感应。 肝脏 x 受体 α (LXRα) 是一种重要的胆固醇传感器，可调节肝脂肪和 转录水平上的胆固醇代谢响应胆固醇衍生物的直接结合。 为了破坏胆固醇感应，我们培育了将 LXRα 的色氨酸 441 改变为 苯丙氨酸（W441F）。 W441F 破坏内源性胆固醇衍生的 LXR 配体的结合，同时仍然 允许通过有效的合成激动剂进行转录调节，提供了一种独特的工具来阻止 LXRα 能够感知胆固醇，同时仍允许药物控制。 当喂食高脂肪/高胆固醇饮食时，LXRα W441F 小鼠迅速（4 周内）发育 与 NASH 相关的病理。令人惊讶的是，W441F 小鼠的肝甘油三酯降低了，但 胆固醇增加。因此，NASH 样表型可能在肝功能不升高的情况下出现。 甘油三酯（“胆固醇依赖性 NASH”）。我们假设 W441F 中 LXR 活性降低 肝细胞导致胆固醇积累，这是促进胆固醇积累的起始事件 炎症和纤维化。此外，我们认为肝脏胆固醇升高会促进 NASH 至少部分是通过具有 PDZ 结合基序的转录共激活因子的胆固醇依赖性激活 （TAZ，Wwtr1）。 TAZ 在人类 NASH 患者的肝脏中过度表达，并促进炎症和 在小鼠模型中过度表达时会导致纤维化。最后，我们在 W441F 中重建 LXR 活性的能力 使用药物制剂的小鼠提供了一个独特的机会来确定胆固醇是否 依赖性NASH是可以逆转的。综上所述，我们提出的研究将为以下问题提供新的见解： 胆固醇水平升高导致 NASH 和其他慢性疾病发病机制的机制 疾病。