Role of mitochondria in neurodegenerative diseases

我们探讨了线粒体在帕金森病（PD）中的作用。家族性帕金森病中至少有两个突变的基因产物PINK1和Parkin介导有缺陷线粒体的自噬清除，这表明帕金森病的一个原因是线粒体质量控制受损。PINK1是一种位于线粒体上的激酶，而Parkin是一种通常位于细胞质中的E3泛素连接酶。在线粒体损伤时，Pink1将细胞质内的Parkin招募到线粒体中介导线粒体自噬，揭示了哺乳动物细胞中Pink1在Parkin上游起作用的细胞生物学途径。我们发现PINK1在细胞中快速翻转。在健康的线粒体中，PINK1组成性地进入内膜并被蛋白酶PARL降解，并维持在非常低的水平。当线粒体受到损伤时，PINK1的输入和降解被阻止，从而使其在线粒体外膜上积累。因此，PINK1作为线粒体功能的传感器。当PINK1聚集在受损细胞器的线粒体外膜上时，它从细胞质中招募Parkin到线粒体。Parkin募集需要PINK1激酶活性，但参与这一过程的PINK1底物尚不清楚。一旦进入线粒体，Parkin泛素化线粒体蛋白，包括gtpase Mfn1和2。泛素化的Mfn1和mf2因蛋白体降解而丧失，从而阻止受损线粒体与健康线粒体融合，从而使它们分离以供处置。Parkin在其他线粒体蛋白上形成的泛素链似乎是自噬消除线粒体的信号。我们发现蛋白体和AAA atp酶、p97/VCP、optinurin或NDP52和ATG5是Parkin介导的线粒体自噬所必需的，进一步表明泛素在Parkin介导的线粒体自噬中的重要性。为了证实这一模型，我们发现，在含有含有野生型线粒体DNA的功能性线粒体和COX1基因线粒体DNA突变的功能失调线粒体的杂交细胞中，增加Parkin表达选择性地消除了受损的线粒体，并为野生型线粒体DNA的繁殖提供了丰富的资源。基于这些结果，我们预测刺激PINK1/Parkin通路可能促进线粒体质量控制，并可能对线粒体疾病和某些形式的帕金森病患者具有潜在的治疗益处。积累线粒体DNA突变的动物模型证实了Parkin介导质量控制并拯救受损线粒体神经元的模型。我们已经开始筛选化学文库，以确定刺激PINK1表达和Parkin易位的药物。我们还完成了RNAi筛选，以鉴定参与PINK1向线粒体募集Parkin和Parkin刺激线粒体自噬体吞噬的基因产物。

We have explored the role of mitochondria in Parkinson's disease (PD). At least two gene products mutated in familial PD, PINK1 and Parkin, are now known to mediate autophagic removal of defective mitochondria suggesting that one cause of PD is an impairment of mitochondrial quality control. PINK1 is a kinase located on mitochondria whereas Parkin is an E3 ubiquitin ligase normally located in the cytosol. Upon mitochondrial damage Pink1 recruits cytosolic Parkin to mitochondria to mediate mitophagy revealing a cell biology pathway in mammalian cells where Pink1 works upstream of Parkin. We have found that PINK1 is rapidly turned over in cells. In healthy mitochondria PINK1 is constitutively imported into the inner membrane and degraded by the protease PARL, and maintained at very low levels. When mitochondria sustain damage PINK1 import and degradation is prevented allowing its accumulation on the outer mitochondrial membrane. Thus PINK1 acts as a sensor of mitochondria function. When PINK1 accumulates on the outer mitochondrial membrane of damaged organelles it recruits Parkin to mitochondria from the cytosol. Parkin recruitment requires PINK1 kinase activity but the substrate of PINK1 involved in this process remains unknown. Once on the mitochondria, Parkin ubiquitinates mitochondrial proteins including the GTPases Mfn1 and 2. The loss of ubiqutinated Mfn1 and 2 by proteosomal degradation prevents damaged mitochondria from fusing with healthy mitochondria thereby segregating them fordisposal. The ubiquitin chains Parkin forms on other mitochondrial proteins appear to signal the elimination of mitochondria by autophagy. We found that the proteosome and the AAA ATPase, p97/VCP, Optineurin or NDP52 and ATG5 are required for Parkin mediated mitophagy further indicating the importance of ubiquitin in Parkin mediated mitophagy. Corroborating this model we have found that in cybrid cells that contain a mixture of functional mitochondria with wild type mitochondrial DNA and dysfunctional mitochondria with a mutation in mitochondrial DNA in the COX1 gene, increasing Parkin expression selectively eliminates the damaged mitochondria and enriches for the propagation of wild type mitochondrial DNA. Based on these results we predict that stimulation of the PINK1/Parkin pathway may facilitate mitochondrial quality control and may be of potential therapeutic benefit for patients with mitochondrial diseases and certain forms of Parkinson's disease. An animal model that accumulates mitochondrial DNA mutations corroborates the model that Parkin mediates quality control and rescues neurons of damaged mitochondria. We have begun screening chemical libraries to identify agents that stimulate PINK1 expression and Parkin translocation. We have also completed RNAi screens to identify gene products participating in PINK1 recruitment of Parkin to mitochondria and Parkin stimulation of autophagosome engulfment of mitochondria.