氟西汀下调葡萄糖-6-磷酸酶表达致肝脏脂代谢异常机制研究

Depression is a chronic disease with high prevalence and high recurrence rate. Drug therapy is the main treatment for anti-depression, however, the hepatic lipid metabolism abnormalities induced by drug leads to the treatment interruption, so the mechanism is urgent to investigate. Fluoxetine (FLX) is one of the most widely used antidepressant. Our previous study showed that FLX could induce hepatic lipid accumulation and inhibit the expression of G6PC significantly both in vitro and in vivo, but there’s no effect on fatty acid transporters 2, 5. Further studies showed that FLX down-regulated the expression of PPARα, an upstream transcription factor of G6PC, in mouse primary hepatocytes without any significantly effect on other upstream transcription factors or their target genes. Meanwhile, FLX can prevent the upregulation of PPARα and G6PC against PPARα agonists. In view of the fact that G6PC is a key enzyme in gluconeogenesis, and the decline of its function or expression can enhances the production of de novo synthesis of fatty acids raw materials, then induce the liver lipid accumulation. In our study, combined with clinical samples, the role of G6PC in the abnormality of liver lipid metabolism caused by FLX both in vitro and in vivo will be evaluated, and the mechanism of FLX down-regulate G6PC through PPARα will be clarified. Meanwhile, the effective strategy to improve the abnormality of liver lipid metabolism caused by FLX will be explored, which provides a theoretical basis and a viable treatment plan.

抑郁症是一种高患病率、高复发率的慢性疾病。药物治疗是抗抑郁的主要手段，但药物引起的脂代谢异常易导致治疗中断，因此迫切需要阐明其发生机制。氟西汀(FLX)是主要抗抑郁药物之一，我们前期体内外研究发现，FLX诱发肝细胞脂质蓄积，下调G6PC表达，但对肝脏脂肪酸转运蛋白2/5无影响。进一步研究显示，FLX下调小鼠原代肝细胞中G6PC上游转录因子PPARα的表达，且抑制PPARα激动剂对PPARα及G6PC的上调，但对其他转录因子及其靶基因无明显影响。鉴于G6PC为糖异生过程的关键酶，其功能或表达的下降可加剧脂肪酸从头合成，诱发肝脏脂质蓄积。本研究将结合临床样本，从细胞和整体水平证实FLX通过抑制G6PC的表达，引起肝脏脂代谢异常，阐明FLX经PPARα下调肝脏G6PC机制，寻找改善FLX引起肝脏脂代谢异常的有效策略，为提高临床FLX的依从性提供理论依据和可行的治疗方案。

氟西汀(FLX)作为选择性五羟色胺再摄取抑制剂代表药物之一，是治疗抑郁症的一线药物。然而氟西汀诱导的脂代谢紊乱限制了其临床使用，并降低病人的依从性。有研究表明新生脂肪酸的增加在肝脏甘油三酯积累和非酒精性脂肪肝发生中起着重要作用。在本研究中，我们首先证实了氟西汀可诱导原代小鼠肝细胞、HepG2细胞和小鼠肝脏的脂质积累。但血浆TG无变化。通过分析原代小鼠肝细胞给药后脂代谢相关基因变化，显示脂肪酸摄取转运体Fabp1和Fatp2/5 mRNA表达无影响，而Cd36的mRNA表达明显下降，糖异生关键酶磷酸烯醇式丙酮酸羧激酶 (PEPCK) 的mRNA表达没有明显变化，而葡萄糖-6-磷酸酶（G6PC，G6Pase）的mRNA水平呈浓度依赖性下降，G6Pase蛋白表达显著减少，肝细胞中G6Pase产物葡萄糖生成量明显下降。小鼠长期给药8周后，亦发现肝脏脂肪酸摄取转运体表达量无明显变化，肝脏中G6Pase mRNA及蛋白水平显著降低，G6Pase产物葡萄糖明显低于对照组，而底物葡萄糖-6-磷酸呈剂量依赖性增加，脂肪酸从头合成的底物乙酰辅酶A在给药组的小鼠肝脏中略有增加，以上结果提示氟西汀诱导肝脏脂质积累可能与G6Pase表达降低和脂肪从头生成增加有关。为进一步探究氟西汀抑制G6pase相关机制，我们考察了FLX给药后小鼠肝组织中G6pase上游转录因子变化，显示法尼酯X受体（FXR）有明显的下降，其下游Cyp7a1有上升的趋势，但其他G6PC上游转录因子无显著变化。同时，小鼠原代肝细胞中，FLX亦可抑制mFxr经典激动剂对FXR及G6PC上调作用，且两者联合共孵育，FLX诱导的脂质蓄积明显改善。因此，我们推测氟西汀通过抑制核激素受体FXR，下调了肝脏G6Pase的表达，随后增强了葡萄糖向脂肪酸的转化，促进脂肪酸的从头合成，最终导致肝脏脂肪变性，从而为提高氟西汀临床依从性提供可能的干预靶点。