9-cis-RA 促进RXRα的SUMO化修饰增加MRP3表达减轻阻塞性黄疸肝损伤的机制

Obstructive jaundice (OJ) liver damage increased perioperative complications and mortality, to explore the injury mechanism of OJ and effective treatment has important clinical significance. Excessive ROS induced by the accumulation of the hydrophobic bile acid is the important pathological mechanism of liver damage caused by OJ.Our previous study confirmed firstly that vitamin A could allevate oxidative stress during OJ, to improve the liver function. Multiple resisance drug protein 3(MRP3) contributes to accumulate the excretion of bile acid. It was shown by our preliminary experiments that compensatory expression of MRP3 is limited, 9-cis-RA, a metabolic product of vitamin A can promote the expression of MRP3 and inhibit the generation of ROS during OJ. Meanwhile 9-cis–RA is also the ligand of retinoic acid nuclear receptor alpha, could reduce RXR alpha: RAR alpha dimers formation by modifying the SUMO. RXR alpha: RAR alpha vision dimers can inhibit the expression of MRP3 via transcription factor SP1.So we propose a hypothesis that 9-cis-RA may promote SUMOylation of RXRα, reduce the formation of RXR alpha: RAR alpha, reduce the inhibition of SP1, stimulate the expression of MRP3, reduce the accumulation of bile acid and inhibit the generation of ros, attenuating liver injury.

阻塞性黄疸（OJ）肝损伤增加了围手术期并发症和死亡率，探索其损伤机制和有效地治疗手段具有重要的临床意义。疏水性胆汁酸蓄积诱导ROS过度产生是阻黄肝损伤的重要病理机制。我们先前研究率先发现维生素A可以减轻阻黄时的氧化应激，改善肝功能。胆汁酸转运体MRP3有助于疏水性胆汁酸的排出，减轻肝损伤。预实验发现阻黄时MRP3代偿性表达增加但有时限性，维生素A代谢活性产物9-cis-RA可以促进MRP3的表达，同时抑制ROS的产生。9-cis-RA又是视黄酸核受体RXRα的配体，能通过SUMO修饰减少RXRα：RARα异二聚体的形成。RXRα：RARα异二聚体通过转录因子SP1可以抑制MRP3的表达。我们推测9-cis-RA通过以下通路抑制ROS的产生并改善肝功能：9-cis-RA→RXRα的SUMO修饰↑→RXRα：RARα异二聚体↓→SP1↑→MRP3↑→疏水性胆汁酸蓄积↓→ROS↓→肝损伤减轻。

肝脏是vitamin A类物质的代谢和储存场所，胆汁淤积时，肝内vitamin A类物质含量明显下降。课题组前期研究表明vitamin A类物质能够缓解阻塞性黄疸肝损伤，但其机制不明。据此，本研究探索vitamin A的代谢产物9-cis-retinoic acid在阻塞性黄疸肝损伤中的作用及其机制。本项目首先探索 9-cis-retinoic acid 对胆汁淤积肝损伤的保护作用。通过尾静脉注射 9-cis-retinoic acid 治疗胆总管结扎小鼠 10 天，评估比较对照组与实验组肝功能指标和肝脏组织学改变情况。结果发现9-cis-retinoic acid治疗组能够降低转氨酶水平，减轻肝组织损伤和胆管反应。在细胞水平，9-cis-retinoic acid减轻胆汁酸对肝细胞的毒性作用。其次通过qRT-PCR、western blot、IHC 等方法检测9-cis-retinoic acid治疗小鼠肝脏组织内 MRP3 的表达水平。在细胞水平探索9-cis-retinoic acid对肝细胞内MRP3表达的影响。结果发现9-cis-retinoic acid促进MRP3的表达。最后，研究RXRα的 SUMO 化修饰及其对 MRP3 的影响，探讨9-cis-retinoic acid对 RXRα的 SUMO 化修饰的影响，结果发现9-cis-retinoic acid抑制RXRα的SUMO化修饰，促进MRP3的表达。综上，本研究结果发现在胆汁淤积时，9-cis-retinoic acid通过抑制核受体RXRα的SUMO化修饰增加MRP3的表达，从而缓解胆汁淤积肝损伤。