Role of mitochondria in neurodegenerative diseases

我们探讨了线粒体在帕金森病(PD)中的作用。在家族性帕金森病中，至少有两种基因产物发生突变，即PINK1和Parkin，目前已知它们可以介导缺陷线粒体的自噬移除，这表明帕金森病的一个原因是线粒体质量控制的损害。PINK1是一种位于线粒体上的激酶，而Parkin是一种E3泛素连接酶，通常位于胞浆中。在线粒体受损时，PINK1将胞质Parkin招募到线粒体以介导有丝分裂吞噬，揭示了PINK1在Parkin上游工作的哺乳动物细胞的细胞生物学途径。我们发现PINK1在细胞内迅速翻转。在健康的线粒体中，PINK1被结构性地输入到内膜，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，PINK1的输入和降解被阻止，允许其在线粒体膜外膜上积聚。因此，PINK1是线粒体功能的感受器。当PINK1聚集在受损细胞器的线粒体膜外时，它会将Parkin从胞浆招募到线粒体中。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。一旦在线粒体上，Parkin泛素化线粒体蛋白，包括GTP酶Mfn1和2。蛋白酶体降解导致泛量化的Mfn1和2的丢失阻止了受损的线粒体与健康的线粒体融合，从而将它们分离处理。帕金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，蛋白小体和AAA ATPase p97/VCP是Parkin介导的有丝分裂所必需的，进一步表明泛素在Parkin介导的有丝分裂中的重要性。证实了这一模型，我们发现，在含有功能线粒体和野生型线粒体DNA以及功能失调的线粒体和COX1基因线粒体DNA突变的混合胞质细胞中，Parkin表达的增加选择性地消除了受损的线粒体，并丰富了野生型线粒体DNA的繁殖。基于这些结果，我们预测，刺激PINK1/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优势。我们已经开始筛选化学文库，以确定刺激PINK1表达和Parkin易位的试剂。我们还完成了RNAi筛选，以确定参与PINK1将Parkin募集到线粒体和Parkin刺激自噬小体吞噬线粒体的基因产物。

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.