Compelling evidence indicates that two autosomal recessive Parkinson’s disease genes, PINK1 (PARK6) and Parkin (PARK2), co-operate to mediate the autophagic clearance of damaged mitochondria (mitophagy). Mutations in the F-box domain containing protein Fbxo7 (PARK15) also cause early onset autosomal recessive Parkinson’s disease by an unknown mechanism. Here we show that Fbxo7 participates in mitochondrial maintenance through direct interaction with PINK1 and Parkin and plays a role in Parkin-mediated mitophagy. Cells with reduced Fbxo7 expression show deficiencies in Parkin mitochondrial translocation, ubiquitination of mitofusin 1 and mitophagy. In Drosophila, ectopic overexpression of Fbxo7 rescued loss of Parkin supporting a functional relationship between the two proteins. Parkinson’s disease-causing mutations in Fbxo7 interfere with this process, emphasising the importance of mitochondrial dysfunction in Parkinson’s disease pathogenesis.
Genetic analysis of Parkinson disease (PD) has identified several genes whose mutation causes inherited parkinsonism, as well as risk loci for sporadic PD. PTEN-induced kinase 1 (PINK1) and parkin, linked to autosomal recessive PD, act in a common genetic pathway regulating the autophagic degradation of mitochondria, termed mitophagy. We undertook a genome-wide RNAi screen as an unbiased approach to identify genes regulating the PINK1/Parkin pathway. We identified several genes that have a conserved function in promoting mitochondrial translocation of Parkin and subsequent mitophagy, most notably sterol regulatory element binding transcription factor 1 (SREBF1), Fbox and WD40 domain protein 7 (FBXW7), and other components of the lipogenesis pathway. The relevance of mechanisms of autosomal recessive parkinsonism to sporadic PD has long been debated. However, with the recent identification of SREBF1 as a risk locus for sporadic PD, our findings suggest a common mechanistic link between autosomal recessive and sporadic PD, and underscore the importance of mitochondrial homeostasis. P arkinson disease (PD) is an age-related neurodegenerative disease caused principally by the loss of midbrain dopaminergic neurons, resulting in motor disturbances, such as postural instability, resting tremor, and bradykinesia, as well as other nonmotor symptoms. Current therapeutic strategies alleviate symptoms by the replacement of dopamine, with variable efficacy and substantial side effects. However, there are currently no established curative, preventative, or disease-modifying interventions, stemming from a poor understanding of the molecular mechanisms of pathogenesis. Genetic analyses have identified causative mutations for autosomal dominant and recessive forms of familial parkinsonism. Functional studies of these genes have provided great insight into potential pathogenic mechanisms of inherited forms of PD; however, it is unclear how these may relate to the more common sporadic forms of PD. To gain insight into the genetic influence in sporadic PD, genome-wide association studies (GWASs) have revealed several loci that are significantly associated with the occurrence of PD, and so are considered potential risk factors. However, we lack mechanistic insight into how many of the associated risk loci may contribute to pathogenesis.Mitochondrial dysfunction has long been considered a key contributing factor in the pathogenesis of PD, with evidence from postmortem tissue, epidemiological studies, and genetics. In particular, a body of evidence indicates that two genes linked to recessive parkinsonism, PTEN-induced kinase 1 (PINK1) and parkin, act in a common pathway to regulate mitochondrial turnover, providing an attractive hypothesis for the impact of mitochondrial homeostasis on pathogenesis (1). The process of mitophagy to degrade dysfunctional mitochondria has been extensively studied using uncoupling agents to dissipate the mitochondrial membrane potential (ΔΨm) (2). Following loss of ΔΨm, PINK1 accumulates on the outer mit...
Mutations in PINK1, a mitochondrially targeted serine/threonine kinase, cause autosomal recessive Parkinson's disease (PD). Substantial evidence indicates that PINK1 acts with another PD gene, parkin, to regulate mitochondrial morphology and mitophagy. However, loss of PINK1 also causes complex I (CI) deficiency, and has recently been suggested to regulate CI through phosphorylation of NDUFA10/ND42 subunit. To further explore the mechanisms by which PINK1 and Parkin influence mitochondrial integrity, we conducted a screen in Drosophila cells for genes that either phenocopy or suppress mitochondrial hyperfusion caused by pink1 RNAi. Among the genes recovered from this screen was ND42. In Drosophila pink1 mutants, transgenic overexpression of ND42 or its co-chaperone sicily was sufficient to restore CI activity and partially rescue several phenotypes including flight and climbing deficits and mitochondrial disruption in flight muscles. Here, the restoration of CI activity and partial rescue of locomotion does not appear to have a specific requirement for phosphorylation of ND42 at Ser-250. In contrast to pink1 mutants, overexpression of ND42 or sicily failed to rescue any Drosophila parkin mutant phenotypes. We also find that knockdown of the human homologue, NDUFA10, only minimally affecting CCCP-induced mitophagy, and overexpression of NDUFA10 fails to restore Parkin mitochondrial-translocation upon PINK1 loss. These results indicate that the in vivo rescue is due to restoring CI activity rather than promoting mitophagy. Our findings support the emerging view that PINK1 plays a role in regulating CI activity separate from its role with Parkin in mitophagy.
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