Xbp1s-Hrd1-Nrf2信号通路调控DCD供肾缺血再灌注损伤

Ischemia-reperfusion injury (IRI) damages the function of kidney donor and therefore limits the outcome in donation after circulation death (DCD) kidney transplantation. The critical causes of the IRI include high production of oxygen free radical and decrease of endogenous oxygen free radical scavenger such as Nrf2. Nrf2 significantly up-regulates the expression of NOX4 that acts as antioxidation; we have verified that Xbp1 expression can be increased by the enhanced endoplasmic reticulum stress (ERS) induced by IRI and result in improvement of the down-stream Hrd1; three-dimension analysis on Nrf2 molecule indicates that its degradation may depend on Hrd1 ubiquitination. Taken together, we hypothesize that: Xbp1s-Hrd1-Nrf2, recognized as a novel signal pathway, holds critical mechanism on IRI; down-regulation of its initial factor Xbp1 can modulate this pathway to increase NOX4 expression resulting in kidney graft protection. Herein, the expression of the three key molecules is planned to be modulated to verify the existence of this pathway and clarify its effects using the models of hypoxia/re-oxygenation, orthotopic IRI and DCD syngeneic kidney transplantation. This work provides novel mechanism and molecular treatment strategy for DCD kidney donor protection.

在心脏死亡器官捐献（DCD）移植中，供体缺血再灌注损伤(IRI)严重影响供肾功能和移植效果。氧自由基生成过多和内源性氧自由基清除剂(如NOX4)合成减少是DCD供肾发生IRI的重要原因。已知Nrf2显著促进NOX4表达，发挥抗氧化作用；我们证实IRI诱导内质网应激强化Xbp1s生成,导致下游Hrd1增多；Nrf2分子三维构象分析提示其降解可能依赖Hrd1泛素化。由此设想：Xbp1s-Hrd1-Nrf2作为一条新发现的信号通路，是肾脏IRI的关键机制；下调始动因子Xbp1s可以调控该信号通路，增加NOX4表达，保护DCD供肾。本项目拟通过对全通路关键分子的干预，证实此信号通路的存在；并在体外缺氧/复氧模型、在体原位IRI模型及DCD同系肾脏移植模型三个层面，验证Xbp1s-Hrd1-Nrf2信号通路的效应，为保护DCD供肾提供新的理论基础和分子治疗策略。

肾缺血再灌注（IR）损伤与内质网应激（ERS）和线粒体功能障碍有关，会导致氧化应激诱导的急性肾损伤 （AKI）。X盒结合蛋白1（XBP1）是一种ERS反应蛋白，可能在IR诱导的AKI中发挥突出作用。本研究揭示了XBP1及其下游靶标HRD1通过调节NRF2/HO-1介导的活性氧（ROS）信号传导参与ERS与线粒体功能障碍之间的互作。由于NRF1/HO-1的表达增强和肾脏中ROS的减少，XBP1表达减少的小鼠（杂合Xbp1+/-）对IR诱导的AKI具有抗性。肾上皮细胞中XBP1的下调导致HRD1表达降低，NRF2/HO-1功能增加，同时抗氧化反应增强。此外，HRD1作为E3连接酶，通过泛素化-降解途径促进NRF2的下调，NRF2上的QSLVPDI基序构成了其与HRD1相互作用的活性位点。因此，我们的研究结果揭示了XBP1/HRD1在调节应激条件下肾脏中NRF2 / HO-1抗氧化功能的重要生理作用。靶向XBP1-HRD1-NRF2通路的分子治疗方法可能是治疗肾IR损伤的潜在有效手段。