Role of mitochondria in neurodegenerative diseases

我们已经探索了线粒体在帕金森病（PD）中的作用。目前已知家族性PD中至少有两种突变的基因产物PINK 1和Parkin介导缺陷线粒体的自噬去除，这表明PD的一个原因是线粒体质量控制受损。PINK 1是位于线粒体上的激酶，而Parkin是通常位于细胞溶质中的E3泛素连接酶。 在线粒体损伤后，Pink 1将胞质Parkin招募到线粒体中以介导线粒体自噬，揭示了哺乳动物细胞中Pink 1在Parkin上游工作的细胞生物学途径。我们发现PINK 1在细胞中迅速翻转。 在健康的线粒体中，PINK 1组成性地输入到内膜中并被蛋白酶PARL降解，并维持在非常低的水平。 当线粒体遭受损伤时，PINK 1的输入和降解被阻止，允许其在线粒体外膜上积累。 因此，PINK 1充当线粒体功能的传感器。当PINK 1在受损细胞器的线粒体外膜上积累时，它会从细胞质中招募帕金到线粒体中。帕金募集需要PINK 1激酶活性，但参与这一过程的PINK 1底物仍然未知。一旦在线粒体上，帕金泛素化线粒体蛋白，包括GTP酶Mfn 1和2。 蛋白体降解导致的泛素化Mfn 1和2的丢失阻止了受损线粒体与健康线粒体的融合，从而将它们分离以进行处理。帕金在其他线粒体蛋白上形成的泛素链似乎是通过自噬消除线粒体的信号。我们发现蛋白体和AAA ATP酶p97/VCP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。 证实了该模型，我们发现在含有功能性线粒体与野生型线粒体DNA和功能障碍性线粒体与COX 1基因中线粒体DNA突变的混合物的胞质杂种细胞中，增加帕金表达选择性地消除受损的线粒体并富集野生型线粒体DNA的繁殖。 基于这些结果，我们预测刺激PINK 1/Parkin通路可能有助于线粒体质量控制，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。 我们已经开始筛选化学文库，以确定刺激PINK 1表达和帕金易位的药物。 我们还完成了RNAi筛选，以鉴定参与PINK 1将Parkin募集到线粒体和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, 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. 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.