Molecular genetic analysis of the alpha-synuclein and the parkin gene in Parkinson's disease in Finland

Role of mitochondria DNA A10398G polymorphism on development of Parkinson's disease: A PRISMA-compliant meta-analysis

BACKGROUND

Parkinson's disease (PD) is characterized by memory loss and multiple cognitive disorders caused primarily by neurodegeneration. However, the preventative effects of the mitochondrial A10398G DNA polymorphism remain controversial. This meta-analysis comprehensively assessed evidence on the influence of the mitochondrial DNA A10398G variant on PD development.

METHODS

The PubMed, EMBASE, EBSCO, Springer Link, and Web of Science databases were searched from inception to May 31, 2020. We used a pooled model with random effects to explore the effect of A10398G on the development of PD. Stata MP version 14.0 was used to calculate the odds ratios and 95% confidence intervals (CIs) from the eligible studies to assess the impact of mitochondrial DNA A10398G on PD development.

RESULTS

The overall survey of the populations showed no significant association between mitochondrial DNA A10398G polymorphism (G allele compared to A allele) and PD (odds ratio = 0.85, 95% CI = 0.70-1.04, p = 0.111); however, a significant association between the mutation and PD was observed in the Caucasian population (odds ratio = 0.71, 95% CI = 0.58-0.87, p = 0.001). A neutral effect was observed in the Asian population (odds ratio = 1.10, 95% CI = 0.94-1.28, p = 0.242).

CONCLUSIONS

The results of this meta-analysis showed the potential protective effect of the mitochondrial DNA A10398G polymorphism on the risk of developing PD in the Caucasian population. Studies with better designs and larger samples with intensive work are required to validate these results.

Twenty years since the discovery of the parkin gene

Nearly 20 years have passed since we identified the causative gene for a familial Parkinson's disease, parkin (now known as PARK2), in 1998. PARK2 is the most common gene responsible for young-onset Parkinson's disease. It codes for the protein Parkin RBR E3 ubiquitin-protein ligase (PARK2), which directly links to the ubiquitin-proteasome as a ubiquitin ligase. PARK2 is involved in mitophagy, which is a type of autophagy, in collaboration with PTEN-induced putative kinase 1 (PINK1). The PINK1 gene (previously known as PARK6) is also a causative gene for young-onset Parkinson's disease. Both gene products may be involved in regulating quality control within the mitochondria. The discovery of PARK2 as a cause of young-onset Parkinson's disease has had a major impact on other neurodegenerative diseases. The involvement of protein degradation systems has been implicated as a common mechanism for neurodegenerative diseases in which inclusion body formation is observed. The discovery of the involvement of PARK2 in Parkinson's disease focused attention on the involvement of protein degradation systems in neurodegenerative diseases. In this review, we focus on the history of the discovery of PARK2, the clinical phenotypes of patients with PARK2 mutations, and its functional roles.

SNCA mutation p.Ala53Glu is derived from a common founder in the Finnish population

Mutations in SNCA are rare causes of familial Parkinson's disease (PD). We have previously described a novel p.Ala53Glu mutation in 2 Finnish families. To assess this mutation's frequency among Finnish PD patients, we screened 110 PD patients (mean age-of-onset 60 years) from Western Finland by Sanger sequencing of the third coding exon of SNCA. In addition, a sample of 47 PD subjects (mean age-of-onset 53 years) originating from Southern and Eastern Finland were studied using next-generation sequencing covering SNCA. Only one new individual with the p.Ala53Glu mutation was identified, confirming that this mutation is a rare cause of PD in the Finnish population. To search for a possible common origin of the p.Ala53Glu mutation, haplotype analysis was conducted in 2 families and in a patient from a third family (6 affected subjects) using both STR markers and a genome-wide SNP array. The results show that patients with the p.Ala53Glu mutation share a haplotype spanning a minimum of 5.7 Mb suggesting a common founder.

Genetic analysis of SNCA coding mutation in Chinese Han patients with Parkinson disease

Parkinson disease (PD) is the second most common progressive neurodegenerative disorder. It is characterized by selective loss of dopamine-producing neurons and aggregation of alpha-synuclein (SNCA) in neurons of particular brain regions. At least 20 loci and 15 disease-causing genes have been identified. Rare missense or multiplication mutations in the SNCA gene have been reported to be involved in some familial and sporadic cases of PD. More recently, two novel pathogenic missense mutations (p.H50Q and p.G51D) were identified in the SNCA gene. To evaluate whether mutation(s) in the coding region of SNCA gene is related to PD in Chinese population, we investigated the SNCA gene in 502 PD patients of Chinese Han ethnicity from Mainland China. No pathogenic mutation was identified in the coding region of the gene. A known G to A transition (c.306 + 66G>A, rs10005233) in the intron 4, which does not potentially change splicing, was identified. Our data indicate that mutations in the coding region of the SNCA gene are not likely to be a common cause of PD in Chinese population.

Genetic variants and animal models in SNCA and Parkinson disease

Parkinson disease (PD; MIM 168600) is the second most common progressive neurodegenerative disorder characterized by a variety of motor and non-motor features. To date, at least 20 loci and 15 disease-causing genes for parkinsonism have been identified. Among them, the α-synuclein (SNCA) gene was associated with PARK1/PARK4. Point mutations, duplications and triplications in the SNCA gene cause a rare dominant form of PD in familial and sporadic PD cases. The α-synuclein protein, a member of the synuclein family, is abundantly expressed in the brain. The protein is the major component of Lewy bodies and Lewy neurites in dopaminergic neurons in PD. Further understanding of its role in the pathogenesis of PD through various genetic techniques and animal models will likely provide new insights into our understanding, therapy and prevention of PD.

Stable isotope labeling and label-free proteomics of Drosophila parkin null mutants

Parkinson's disease (PD) is characterized by loss of dopaminergic neurons in the substantia nigra and formation of intracytoplasmic Lewy bodies (LBs). Loss-of-function mutations in parkin which encodes an E3 ubiquitin protein ligase contribute to a predominant cause of a familial form of PD termed autosomal recessive juvenile Parkinsonism (AR-JP). Drosophila parkin null mutants display muscle degeneration and mitochondrial dysfunction, providing an animal model to study Parkin-associated molecular pathways in PD. To define protein alterations involved in Parkin pathogenesis, we performed quantitative proteomic analyses of Drosophila parkin null mutants and age-matched controls utilizing both global internal standard technology (GIST) and extracted ion chromatogram peak area (XICPA) label-free approaches. A total of 375 proteins were quantified with a minimum of two peptide identifications from the combination of the XICPA and GIST measurements applied to two independent biological replicates. Sixteen proteins exhibited significant alteration. Seven of the dysregulated proteins are involved in energy metabolism, of which six were down-regulated. All five proteins involved in transporter activity exhibited higher levels, of which larval serum protein 1alpha, larval serum protein 1beta, larval serum protein 1gamma, and fat body protein 1 showed >10-fold up-regulation and substantially higher level of fat body protein 1 was confirmed by Western blot analysis. These findings suggest that abnormalities in energy metabolism and protein transporter activity pathways may be associated with the pathogenesis of Parkin-associated AR-JP.

NF-κB contributes to 6-hydroxydopamine-induced apoptosis of nigral dopaminergic neurons through p53

To evaluate the contribution of NF-kappaB and the NF-kappaB target gene p53 to nigral dopaminergic neuron degeneration in rodent models of Parkinson's disease, time-course of dopaminergic neuron loss as well as changes in the expression of some NF-kappaB-regulated proapoptotic proteins were assayed after unilateral infusion of 6-hydroxydopamine into rat medial forebrain bundle. Substantial loss of tyrosine hydroxylase immunoreactivity in nigral was observed 24 h after 6-hydroxydopamine treatment. The degenerative processes began 12 h after 6-hydroxydopamine administration as evidenced by a positive silver staining. Apoptotic death of dopaminergic neurons was suggested by the appearance of TUNEL-positive nuclei in substantia nigra and internucleosomal DNA fragmentation as detected by agarose gel electrophoresis. NF-kappaB activation in dopaminergic neurons as revealed by immunohistochemistry and electrophoresis mobility shift assay, began at 12 h after 6-hydroxydopamine administration. Levels of c-Myc and p53 immunoreactivities increased after 6-hydroxydopamine treatment, mainly in dopaminergic neurons as indicated by co-localization with tyrosine hydroxylase immunoreactivity. Blockade of NF-kappaB nuclear translocation with recombinant cell-permeable peptide NF-kappaB SN50 inhibited NF-kappaB nuclear translocation and p53 induction. SN50 and the p53 antagonist pifithrin-alpha significantly reduced nigral dopaminergic neuron degeneration. These results suggest that NF-kappaB activation contributes, at least in part, to oxidative stress-induced degeneration of dopaminergic neurons through a NF-kappaB-dependent p53-signaling pathway.

Identification of a risk haplotype of the alpha-synuclein gene in Japanese with sporadic Parkinson's disease

alpha-Synuclein is one of the main components of Lewy bodies, a pathological marker of Parkinson's disease (PD). Certain missense mutations of the alpha-synuclein gene cause familial PD, but the role of the gene in sporadic PD is still controversial. We scrutinized polymorphisms of the alpha-synuclein gene in a Japanese population and investigated their associations with sporadic cases of PD. The 5' flanking region to intron 2 of the alpha-synuclein gene (3.8 kb) and two polymorphisms in intron 4 previously reported in Caucasian sporadic cases of PD were analyzed in 185 sporadic PD and 191 controls. Five novel single nucleotide polymorphisms (SNPs), 16 reported SNPs, and one reported polynucleotide polymorphism (PNP) were found. Most of the polymorphisms examined were in linkage disequilibrium. Significant associations with PD were found in 15 of 21 SNPs, especially in intron 1 (IVS1+155 TmAn PNP and the IVS1+719 C>T SNP, P < 0.0001). Haplotype analysis showed that T10A7-A-A and T11A6-G-G haplotypes at three loci (IVS1+155 - IVS1+273 - IVS1+608) were strongly negative and positive risk factors of sporadic PD, respectively (odds ratios were 0.23 [95% confidence interval, 0.16-0.32] and 1.51 [95% confidence interval, 1.29-1.75]). In conclusion, our findings indicate that genetic variations of the alpha-synuclein gene affect the development of sporadic PD.

Study of Association between α-Synuclein Gene Polymorphism and Methamphetamine Psychosis/Dependence

Methamphetamine (MAP) dissipates proton gradients across the membranes of synaptic vesicles, enhances cytoplasmic dopamine (DA) concentrations, and causes calcium-independent, nonvesicular DA release into synapses. MAP is taken into the cytosol by the dopamine transporter (DAT) on the synaptic terminals of DA neurons, and endogenous DA is concurrently released through the transporter by carrier exchange mechanisms, resulting in a robust increase in DA concentration in the synaptic clefts. The enhanced DA release through DAT by MAP is the main mechanism for the reinforcing effects of MAP. The complexes of alpha-synuclein and DAT facilitate membrane clustering of the DAT, thereby accelerating DA uptake in vitro. alpha-Synuclein has been shown to be overexpressed in the midbrain DA neurons of chronic cocaine abusers. The present study was performed to study the association between the alpha-synuclein gene polymorphisms and MAP psychosis/dependence in Japanese population. Since the T10A7 polymorphic site at the 5' end of the noncoding exon 1' in the alpha-synuclein gene is highly polymorphic, we analyzed the noncoding exon 1' and intron 1, including this polymorphic site by sequencing. We confirmed four single nucleotide polymorphisms (SNPs) within 1.38 kbp of the T10A7 polymorphic site. No significant difference was found in genotype or allele frequencies in the T10A7 polymorphic site between MAP psychotic/dependent and control subjects. We found significant association between three SNPs in the vicinity of this polymorphic site in intron 1 and MAP psychosis/dependence in female subjects, but not in males. These results suggest an association of the alpha-synuclein gene polymorphisms with MAP psychosis/dependence in our female subjects. Further analyses are necessary to clarify the gender difference, by using a larger sample size and/or different ethnic groups, as well as functional variations in the alpha-synuclein gene.