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。PINK1作为线粒体功能的感受器，Parkin诱导这些受损的线粒体被清除。积累线粒体DNA突变的动物模型证实了帕金参与质量控制并将神经元从受损的线粒体中拯救出来的模型。我们进行了全基因组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。 1)基因筛选使我们在Parkin-/-和PINK1-/-小鼠中发现了强烈的炎症表型，当与突变小鼠杂交时，这些突变小鼠随着年龄的增长而积累线粒体DNA突变。这种炎症可以通过同时失去STING来完全挽救，STING是一种I型干扰素对胞浆DNA反应的中央调节因子。在老年Parkin-/-；突变小鼠中观察到SNC中DA神经元的丢失和运动缺陷，也可以通过失去刺痛而获救，这表明炎症促进了这种表型。在与一个拥有大量PINK1和Parkin突变PD患者队列的德国领先研究小组的合作下，我们发现，双等位Parkin突变患者的循环细胞因子水平也高于健康对照组或特发性PD患者。此外，这些双等位Parkin和PINK1患者的线粒体DNA循环水平高于健康对照组或特发性帕金森病患者。这些结果支持PINK1和Parkin介导的有丝分裂抑制先天免疫作为预防帕金森病的一种方式的模型。 2)与小鼠和人相比，果蝇Parkin基因的隐性突变表现出严重的身体和运动缺陷，这是由于线粒体过度损伤导致的，导致肌肉缺陷和多巴胺能神经元的进行性退化。天然免疫信号通路包括SING和NF-kB通路在果蝇中是保守的，然而，天然免疫信号在PINK1/Parkin突变果蝇病理中的作用尚未确定。我们发现，保守的免疫调节剂刺痛介导了Parkin功能表型的丧失。产生了两个遗传独立的刺痛和Parkin双基因敲除菌株。删除带刺显著降低了主要的Parkin Null苍蝇表型的外显率，包括飞行肌肉缺陷、机翼姿势和攀爬能力。令人惊讶的是，Parkin突变果蝇潜在的线粒体形态缺陷也在这些双重突变系中被抑制。 3)我们探索了线粒体损伤和线粒体DNA释放到胞浆下游的刺痛是如何激活天然免疫的。我们发现了一个新的和意想不到的功能，在激活Lc3的脂肪作用，这是经典的认为与双膜自噬小体有关。我们没有像以前的主要模型那样诱导自噬，而是在单膜高尔基体结合膜上发现了刺脂类化合物LC3。我们和其他人正在探索这一新步骤在叮咬活动中的先天免疫功能。

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. PINK1 acts as a sensor of mitochondria function and Parkin induced the elimination of those damaged mitochondria. An animal model that accumulates mitochondrial DNA mutations corroborates the model that Parkin mediates quality control and rescues neurons from damaged mitochondria. We preformed full genome RNAi screens to identify gene products participating in PINK1 recruitment of Parkin to mitochondria and Parkin stimulation of autophagosome engulfment of mitochondria. 1) The genetic screens led us to identify a strong inflammatory phenotype in both Parkin-/- and PINK1-/- mice when crossed with Mutator mice, which accumulate mitochondrial DNA mutations with age. This inflammation is completely rescued by concurrent loss of STING, a central regulator of the type I Interferon response to cytosolic DNA. The loss of DA neurons from the SNc and the motor defect observed in aged Parkin-/-; Mutator mice are also rescued by loss of STING, suggesting that inflammation facilitates this phenotype. In collaboration with a leading German group with large cohorts of PINK1 and Parkin mutant PD patients we discovered that people with biallelic Parkin mutations also display elevated circulating cytokines at levels higher than either healthy controls or those with idiopathic PD. Furthermore, these biallelic Parkin and PINK1 patients had higher circulating levels of mitochondrial DNA than either healthy controls or idiopathic PD patients. These results support the model that PINK1- and Parkin-mediated mitophagy restrains innate immunity as a way to prevent PD. 2) In contrast to mice and man, recessive mutations in Parkin in Drosophila melanogaster display severe physical and locomotion defects caused by excess mitochondria damage, leading to muscle defects and progressive degeneration of dopaminergic neurons. Innate immunity pathways including STING and NF-kB pathways are conserved in flies, however, the role of innate immune signaling in Pink1/Parkin mutant fly pathology has not been established. We found the conserved immunity regulator STING mediates the Parkin loss of function phenotypes. Two genetically independent STING and Parkin double knockout strains were generated. Deletion of STING with significantly reduces the penetrance of the major Parkin null fly phenotypes including flight muscle defects, wing posture, and climbing ability. Surprisingly, the underlying mitochondria morphology defects in Parkin mutant flies were also suppressed in these double mutant lines. 3) We explored how STING, functioning downstream of mitochondrial damage and mtDNA release into the cytosol, activates innate immunity. We discovered a new and unanticipated function of STING in activating the lipidation of LC3, which is classically thought to be linked to double membrane autophagosomes. Instead of inducing autophagy as had been the dominant model, we found STING lipidates LC3 onto single membrane Golgi associated membranes. The innate immune function of this novel step in STING activity is being explored by us and others.