IRE1α-Parkin信号通路在多巴胺能神经元线粒体自噬障碍及凋亡中的作用机制

Parkinson's Disease (PD) is the second most common neurodegenerative disorder following Alzheimer's Disease. Impaired mitochondrial autophagy and sustained endoplasmic reticulum(ER) stress-activated unfolded protein response (UPR) play key roles in the pathogenesis of PD; however, how sustained UPR participates in the mitochondrial autophagy is unclear. Inositol-requiring enzyme 1α (IRE1α) is one of the main and most evolutionarily conserved UPR signaling molecules. Several lines of evidence showed that UPR may play an important role in the mitochondrial autophagy. Recent studies have shown that sustained UPR impaired autophagic flux via IRE1α mediated pathway; however, the precise mechanisms remain unknown. Our previous data showed that both parkin protein and mRNA levels were decreased in 6-OHDA-induced PD in vitro model; while silencing IRE1α, the expression of parkin was up-regulated. The finding suggests that the sustained UPR may downregulate the expression of parkin; while IRE1α may be the key mediator leading to the mitochondrial autophagy in PD. The loss of parkin function is responsible for the majority of autosomal recessive Parkinsonism for its key roles in mitochondrial autophagy. In addition, studies have shown that both mitochondrial autophagy dysfuntion and loss of parkin lead to the mitochondria-dependent neuronal apoptosis. Therefore, in this study, we aim to investigate the cruical role of IRE1α in downregulating parkin expression and the possible underlying mechanisms in PD experimental models. Furthermore, we would like to identify if the IRE1α/parkin signal pathways results in impaired mitochondrial autophagy and subsequent mitochondria-dependent neuronal apoptosis. In conclusion, this study would provide a potential and novel mediator, i.e. IRE1α, a clue for the development of an alternative approach to the treatment of PD.

帕金森病(PD)是一种严重的神经退化疾病，线粒体自噬障碍及持续性内质网应激激活的未折叠蛋白反应(UPR)在PD发病机制中发挥关键作用，肌醇需求激酶1α(IRE1α)是UPR中的一个关键分子，然而IRE1α及UPR在PD线粒体自噬障碍中的作用尚不清楚。我们工作显示6-羟多巴胺(6-OHDA）介导的PD细胞模型parkin蛋白及其mRNA含量减少，而沉默UPR关键上游分子IRE1α时,parkin表达上调，提示持续性UPR可能通过IRE1α下调parkin的表达，IRE1α可能是导致多巴胺能(DA）神经元线粒体自噬障碍的关键机制。我们将在PD小鼠及细胞模型中明确IRE1α通过调节parkin,导致parkin介导的线粒体自噬障碍，进而导致线粒体依赖性神经元凋亡。本项目从新的角度揭示持续性UPR是导致DA神经元凋亡的机制,明确IRE1α-parkin是其中的关键通路,为PD的治疗提供新的分子靶点。

帕金森病(PD)是一种严重的神经退化疾病，线粒体自噬障碍及持续性内质网应激激活的未折叠蛋白反应(UPR)在PD发病机制中发挥关键作用，肌醇需求激酶1α(IRE1α)是 UPR中的一个关键分子，然而IRE1α及UPR在PD线粒体自噬障碍中的作用尚不清楚。我们工作显示6-羟多巴胺(6-OHDA）介导的PD细胞模型parkin蛋白及其mRNA含量减少，而沉默UPR关键上游分子IRE1α时,parkin表达上调，提示持续性UPR可能通过IRE1α下调parkin的表达，IRE1α可能是导致多巴胺能(DA）神经元线粒体自噬障碍的关键机制。同时，研究通过建立MPTP处理的PD小鼠模型发现，PD小鼠黑质纹状体中存在IRE1α上调及parkin下调。利用保护线粒体功能的药物（NBP）处理PD小鼠后，黑质TH较单纯PD小鼠增加。且黑质纹状体中存在IRE1α下调及parkin上调，P-α-Synuclein、p-tau、α-Synuclein oligomer、Parp1、Poly ADP Ribose在PD小鼠中较健康对照明显增加，NBP处理后的PD小鼠脑组织该指标均下降，提示NBP可能减弱PD小鼠中的IRE1α-parkin参与的线粒体凋亡，并减少病理性蛋白生成。此外，通过研究发现MPTP处理的PD小鼠中纤连蛋白（FN）和纤维蛋白原（FG）水平在脑内增加，且与IBA-1(小胶质细胞），p-tau(ser369), a-synuclein, parp-1均存在共定位。FN,FG的立体定位注射更可加重PD的病理表型及PARP1相关的线粒体功能障碍。此外，我们通过临床研究发现，低LDL-C以及增高的纤维蛋白原（fibrinogen）是帕金森病痴呆合并2型糖尿病病人（PD-DMD）最显著的风险因素；血浆SOD水平，hsCRP水平可作为评估PD严重性的标志物。基于本研究在IRE1α，parkin，PARP1等方面的发现，我们可进一步了解PD中线粒体功能障碍的潜在机制及影响因子，为帕金森病的治疗和诊断提供新的策略和重大的指导意义。