We have recently reported homozygous mutations in the PINK1 gene in three consanguineous families with early-onset parkinsonism (EOP) linked to the PARK6 locus. To further evaluate the pathogenic role of PINK1 in EOP and to draw genotype-phenotype correlates, we performed PINK1 mutation analysis in a cohort of Italian EOP patients, mostly sporadic, with onset younger than 50 years of age. Seven of 100 patients carried missense mutations in PINK1. Two patients had two PINK1 mutations, whereas in five patients only one mutation was identified. Age at onset was in the fourth-fifth decade (range, 37-47 years). The clinical picture was characterized by a typical parkinsonian phenotype with asymmetric onset and rare occurrence of atypical features. Slow progression and excellent response to levodopa were observed in all subject. Two of 200 healthy control individuals also carried one heterozygous missense mutation. The identification of a higher number of patients (5%) than controls (1%) carrying a single heterozygous mutation, along with previous positron emission tomography studies demonstrating a preclinical nigrostriatal dysfunction in PARK6 carriers, supports the hypothesis that haploinsufficiency of PINK1, as well as of other EOP genes, may represent a susceptibility factor toward parkinsonism. However, the pathogenetic significance of heterozygous PINK1 mutations still remains to be clarified.
Mutations in the PINK1 gene cause autosomal recessive Parkinson's disease. The PINK1 gene encodes a protein kinase that is mitochondrially cleaved to generate two mature isoforms. In addition to its protective role against mitochondrial dysfunction and apoptosis, PINK1 is also known to regulate mitochondrial dynamics acting upstream of the PD-related protein Parkin. Recent data showed that mitochondrial Parkin promotes the autophagic degradation of dysfunctional mitochondria, and that stable PINK1 silencing may have an indirect role in mitophagy activation. Here we report a new interaction between PINK1 and Beclin1, a key pro-autophagic protein already implicated in the pathogenesis of Alzheimer's and Huntington's diseases. Both PINK1 N-and C-terminal are required for the interaction, suggesting that full-length PINK1, and not its cleaved isoforms, interacts with Beclin1. We also demonstrate that PINK1 significantly enhances basal and starvation-induced autophagy, which is reduced by knocking down Beclin1 expression or by inhibiting the Beclin1 partner Vps34. A mutant, PINK1 W437X , interaction of which with Beclin1 is largely impaired, lacks the ability to enhance autophagy, whereas this is not observed for PINK1 G309D , a mutant with defective kinase activity but unaltered ability to bind Beclin1. These findings identify a new function of PINK1 and further strengthen the link between autophagy and proteins implicated in the neurodegenerative process. Parkinson's disease (PD) is a frequent neurodegenerative disorder resulting from massive degeneration of the dopaminergic neurons in the substantia nigra. Although most cases are sporadic, several genes are known to cause familial PD, especially with early onset. 1 Mutations in the PINK1 gene are the second most frequent cause of autosomal recessive PD after those in the Parkin gene. 2,3 The PINK1 gene encodes a serine-threonine kinase with an N-terminal mitochondrial import sequence, first characterized as a protein aimed at maintaining mitochondrial integrity and preventing apoptosis in response to cellular stressors. 2,[4][5][6][7][8] This neuroprotective role is partly exerted through phosphorylation of the mitochondrial chaperon, TRAP1, although cytoplasm-restricted PINK1 was also shown to protect against MPTP damage. 9,10 The full-length PINK1 (PINK1-FL) is processed within mitochondria to generate two mature proteins; 4,11 all three isoforms localize both to the mitochondria and cytosol, their relative ratio being regulated by several factors. [10][11][12][13] Increasing data have demonstrated that absence of functional PINK1 induces abnormalities of mitochondrial morphology. 6,14,15 In several studies (mostly in Drosophila), PINK1 was shown to promote fission acting upstream of the Fis1-Drp1 machinery, and the mitochondrial phenotype observed in PINK1 knockout flies or silenced cells was associated to reduced fission. 16,17 Subsequent studies in mammalian cell systems contradicted these results, demonstrating that mutant or silenced PINK1 resulted in incre...
Parkinson’s disease (PD) is characterized by accumulation of α-synuclein and degeneration of neuronal populations in cortical and subcortical regions. Mitochondrial dysfunction has been considered a potential unifying factor in the pathogenesis of the disease. Mutations in genes linked to familial forms of PD, including SNCA encoding α-synuclein and PINK1, have been shown to disrupt mitochondrial activity. We investigated the mechanisms through which mutant Pink1 might disrupt mitochondrial function in neuronal cells with α-synuclein accumulation. For this purpose, a neuronal cell model of PD was infected with virally-delivered Pink1, and was analyzed for cell survival, mitochondrial activity and calcium flux. Mitochondrial morphology was analyzed by confocal and electron microscopy. These studies showed that mutant (W437X) but not wildtype Pink1 exacerbated the alterations in mitochondrial function promoted by mutant (A53T) α-synuclein. This effect was associated with increased intracellular calcium levels. Co-expression of both mutant Pink1 and α-synuclein led to alterations in mitochondrial structure and neurite outgrowth that were partially ameliorated by treatment with Cyclosporine A, and completely restored by treatment with the mitochondrial calcium influx blocker Ruthenium Red, but not with other cellular calcium flux blockers. Our data suggest a role for mitochondrial calcium influx in the mechanisms of mitochondrial and neuronal dysfunction in PD. Moreover, these studies support an important function for Pink1 in regulating mitochondrial activity under stress conditions.
Heterozygous rare variants in the PINK1 gene, as well as in other genes causing autosomal recessive parkinsonism, have been reported both in patients and healthy controls. Their pathogenic significance is uncertain, but they have been suggested to represent risk factors to develop Parkinson disease (PD). The few large studies that assessed the frequency of PINK1 heterozygotes in cases and controls yielded controversial results, and the phenotypic spectrum is largely unknown. We retrospectively analyzed the occurrence of PINK1 heterozygous rare variants in over 1100 sporadic and familial patients of all onset ages and in 400 controls. Twenty patients and 6 controls were heterozygous, with frequencies (1.8% vs. 1.5%) not significantly different in the two groups. Clinical features of heterozygotes were indistinguishable to those of wild-type patients, with mean disease onset 10 years later than in carriers of two mutations but worse disease progression. A meta-analysis indicated that, in PINK1 heterozygotes, the PD risk is only slightly increased with a non significant odds ratio of 1.62. These findings suggest that PINK1 heterozygous rare variants play only a minor susceptibility significance should be kept distinct from that of homozygous/compound heterozygous mutations, that cause parkinsonism inherited in a mendelian fashion.
We analyzed the PINK1 gene in 58 patients with early-onset Parkinsonism and detected the homozygous mutation W437X in 1 patient. The clinical phenotype was characterized by early onset (22 years of age), good response to levodopa, early fluctuations and dyskinesias, and psychiatric symptoms. The mother, heterozygote for W437X mutation, was affected by Parkinson's disease and 3 further relatives were reported affected, according to an autosomal dominant transmission.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.