缺氧诱导因子2alpha在肝脏胆固醇代谢中作用的研究

Hypercholesterolemia is one of the most important risk factors for cardiovascular disease.Epidemiological investigations suggest an increased incidence of hypercholesterolemia and atherosclerosis in patients with chronic intermittent hypoxia.However, the underlying mechanism is elusive. Hypoxia -inducible factor (HIF) is the major mediator for cellular adapative responses to hypoxia. Previous studies demonstrate that activation of HIF2alpha in liver accelerates steatohepatitis via augmenting steatosis, inflammation and fibrosis. Our preliminary data revealed that activation of HIF2alpha increased and knockout of HIF2alpha decreased cholesterol levels both in liver and serum. We also found that HIF2alpha activation led to decreased FXR protein level and activity. Our results showed that activation of HIF2alpha increased and knockout of HIF2alpha decreased the expression of miRNA103(miR-103), which may bind to the 3'-UTR of FXR and suppress FXR translation. Promoter analysis and chromatin-immunoprecipitation (ChIP)assay showed that HIF2alpha can bind to hypoxia-responsive element (HRE) binding site in pre-miR-103 promoter region, suggesting miR-103 may be a new target gene of HIF2alpha. Therefore, we hypothesized that HIF2alpha and its target gene miR-103 was implicated in liver cholesterol accumulation and hypercholesterolemia via downregulating FXR expression and its downstream genes. The research plan will identify a new HIF2alpha-regulated pathway in liver cholesterol metabolism, and provide potential therapeutic targets for dyslipidemia and cardiovascular disease.

流行病学显示慢性间歇性缺氧增加高胆固醇血症和动脉粥样硬化发生，但机制不清。缺氧诱导因子（HIF）是介导细胞对缺氧适应性反应的关键转录因子。最近研究显示肝脏中HIF2a激活可通过诱发脂肪肝、炎症和纤维化加速脂肪肝性肝炎的发展。我们前期数据表明激活HIF2a可通过抑制与胆固醇代谢密切相关的法尼酯衍生物X受体（FXR）活性而诱导肝脏胆固醇代谢紊乱和高胆固醇血症，敲除HIF2a则改善之。我们还进一步发现HIF2a可增加miR-103的表达，启动子序列分析和ChIP实验显示miR-103可能是HIF2a新的靶基因；而FXR3'-UTR上存在miR-103的结合序列。据此我们提出假说：HIF2a通过上调miR-103，促进miR-103与FXR3'-UTR结合，抑制FXR表达和活性，引起肝脏胆固醇代谢紊乱和高胆固醇血症。对此进行深入研究，将有助于认识HIF2a的新功能和提供治疗高胆固醇血症的潜在新靶点

流行病学显示慢性间歇性低氧可促进高胆固醇血症和动脉粥样硬化的发生发展，但机制不清。低氧诱导因子（HIF）是介导细胞适应性低氧反应的主要核转录因子之一。我们的研究结果显示，肝脏中HIF2a活化可通过诱导肝细胞脂肪变、炎症和纤维化加速非酒精性脂肪性肝炎的发生发展；激活肝脏HIF2a可上调其靶基因pre-miR-103，成熟形式的miR-103通过靶向胆固醇代谢关键性核转录因子法尼酯衍生物X受体（FXR）3’-UTR，降低FXR的活性，从而抑制胆固醇向胆盐的转化，促进肝脏胆固醇代谢紊乱和高胆固醇血症的发生发展，而敲除肝细胞HIF2则可逆转上述过程；此外，通过代谢组学发现，激活肝细胞HIF2a，可明显增加溶血磷脂酰乙醇胺（LPE16:0和LPE18:0）在循环血中的蓄积，其机制为FXR转录活性降低，其靶基因Chpt1和Pemt的mRNA水平和蛋白水平明显下降，进而使磷脂酰乙醇胺PE向磷脂酰胆碱PC的转化减少；而增加的LPE16:0和LPE18:0有可能作为Cd1d识别的内源性抗原，激活肝脏中的iNKT细胞，进一步加重脂肪性肝炎的发生发展。该研究为高胆固醇血症该项目支持下，发表共同责任作者SCI文章2篇（Circulation和Pharmacology&Therapeutics），单独责任作者中文核心期刊1篇，共同作者SCI文章9篇，另有2篇责任作者SCI文章在修稿中。该研究丰富了高胆固醇血症和脂肪性肝炎的发生机制，并为临床治疗提供了潜在靶点。