PXR-lncRNA H19通路在利福平致肝细胞脂质代谢紊乱中的作用及机制

Nuclear receptor PXR plays an important role in the regulation of hepatic lipid metabolism. Previous studies have pointed out that both PXR activation and silencing promote lipid metabolism disorder in hepatocytes, which lead to lipid accumulation, hepatic steatosis and other hepatic diseases. The molecular mechanism of PXR-mediated lipid metabolism is complicated. At present, the role of lncRNAs in PXR-mediated lipid metabolism is still unknown. Our previous studies have found that lncRNA H19 was upregulated by rifampicin in HepaRG and Huh7 cells, and was associated with rifampicin-induced increase of lipid levels. In addition, knockdown the expression of H19 significantly reduced the induction of lipid levels as well as the expression of FABP4 and FGFBP1 genes by rifampicin, but did not affect the expression of PXR. These results suggest that rifampicin-induced lipid metabolism disorder is mediated by upregulation of H19 via PXR activation. In this study, the regulating role as well as molecular mechanisms of PXR-H19 pathway in rifampicin-induced hepatic lipid metabolism disorder will be investigated. The detection of DNA methylation and histone modifications will be performed to investigate the epigenetic mechanisms in the upregulation of H19 by PXR activation. RNA pull down and FISH analysis will be performed to study the role of PXR-H19 pathway in regulation of FABP4 and other genes correlated with lipid metabolism. This study will provide a new insight into PXR-mediated lipid metabolism disorders caused by drugs, and suggest PXR-H19 pathway might be a potential target in the prevention of drug-induced hepatic steatosis and other liver diseases.

核受体PXR在肝脏脂质代谢中具有重要的调节作用，激活或抑制PXR均能导致肝细胞脂质代谢紊乱而造成脂质聚积和脂肪肝等，其分子机制较为复杂。目前未见有lncRNA参与PXR调控脂质代谢的报道。我们前期研究发现，利福平激活PXR能显著上调lncRNA H19的表达并且与肝细胞脂质代谢改变有关。下调H19明显降低利福平所致的脂质水平升高及脂肪酸结合蛋白FABP4等的表达而不影响PXR表达。基于此，我们提出利福平通过激活PXR上调H19进而调控FABP4等的表达，从而引起肝细胞脂质代谢紊乱的科学假设。本课题拟通过分子生物学实验明确PXR-H19通路与利福平诱导肝细胞脂质代谢紊乱的关系，探讨利福平诱导H19表达上调以及PXR-H19通路调控FABP4等表达的机制，以系统阐明PXR-H19通路调控利福平致肝细胞脂质代谢紊乱的分子机制，为药源性肝脏疾病的研究提供新的思路和依据。

核受体PXR作为异源物质的感受器不仅调控药物在肝脏中的代谢，还影响脂质等内源性物质的生物转化过程。本课题从体外和体内水平分别探讨了PXR在药物诱导肝细胞脂质代谢紊乱中的作用及潜在机制：①PXR在丙戊酸钠诱导HepG2细胞脂质堆积中的作用及机制；②利福平激活PXR对Huh7细胞中H19的表达及脂质代谢的影响；③PXR激活对C57BL/6小鼠肝脏脂质代谢及转录组的影响。研究结果：①丙戊酸钠可上调HepG2细胞中PXR和FABP4的表达，扰动PXR或FABP4的表达水平均可影响丙戊酸钠引起的肝细胞脂肪变性，且丙戊酸钠对FABP4的诱导表达受到PXR的调控；②利福平可上调Huh7细胞中H19的表达，抑制PXR能够降低H19的表达以及细胞中的脂质含量，抑制H19也可降低细胞的脂质含量，但外源性表达PXR或H19并不影响Huh7细胞中的脂质含量以及相关的脂质代谢基因的表达；③PXR激活可显著上调小鼠肝脏中的脂质含量以及甘油三酯水平，转录组学分析提示PXR激活对肝脏的众多脂质代谢通路有显著影响。本研究通过不同模型探讨并验证了PXR调控肝细胞脂质代谢紊乱的作用及潜在机制，为研究PXR调控药源性肝脏疾病提供了新的线索和依据。