Evidence for polymerase gamma, POLG1 variation in reduced mitochondrial DNA copy number in Parkinson's disease.

BACKGROUND: It remains unclear whether the mtDNA content is related to the clinicopathological prognosis in Parkinson's disease (PD). METHODS/RESULTS: We analyzed the copy number of mtDNA using quantitative real-time PCR in 414 cases with PD and 231 healthy subjects from mainland of China. The level of mtDNA was significantly decreased in PD patients' peripheral blood as compared to that of healthy controls (p < 0.001). Furthermore, lower mtDNA copy number was more frequently detected (75%) in the older onset age group (≥ 50 years old) than that in (49%) the younger group (<50 years old, p = 0.007), suggesting mtDNA content might be an important genetic event in PD progression. Using direct sequencing, we examined the mutations in the D-loop region of mtDNA in 318 PD patients. The results revealed that 17% of the PD patients carried mutations in the D-loop of mtDNA, and 55% of these mutations were heteroplasmic. In addition, PD patients harboring AA + AA genotype of c.2070-12T > A and c.2070-64G > A in POLG1 along with mutations in POLG1 had a significantly lower copy number of mtDNA than those of PD patients without POLG1 alterations. CONCLUSIONS: Our results provided evidence for a significantly lower of mtDNA copy number in PD patients and POLG1 variation for reducing mtDNA copy number in PD.

Four novel rare mutations of PLA2G6 in Chinese population with Parkinson's disease.

BACKGROUND: Mutations in the phospholipase A2 Group 6 (PLA2G6) gene have been identified in autosomal recessive neurodegenerative diseases classified as infantile neuroaxonal dystrophy and neurodegeneration with brain iron accumulation. Recently, PLA2G6 was also reported as the causative gene for early-onset PARK14-linked dystonia-parkinsonism. METHODS/RESULTS: To address whether PLA2G6 mutations are also an important cause of PD, we screened sequence variants of PLA2G6 in 250 PD patients and 550 controls in a Chinese Han populations. We identified four sequence changes: a coding synonymous c.1959T>A transition of exon13 in one patient, two missense mutations c.1966C>G in exon13 and c.2077C>G in exon14 in two different patients, which caused two amino acids change Leu656Val and Leu693Val respectively. We also found a frame-shift mutation P.His597fx69 in exon 12 in one patient. These four rare variants were not represented in 550 control individuals. Furthermore, we found that WT PLA2G6 enzyme hydrolyzed phospholipids while mutant PLA2G6 with P.His597fx69 frame-shift caused loss of enzyme activity, exhibiting less than 6% of the specific activity in phospholipase assays compared to that of WT PLA2G6. Mutant PLA2G6 with Leu656Val and Leu693Val decreased their activity by 45% and 35% in phospholipase assay respectively. CONCLUSIONS: We identified four rare PLA2G6 mutations in 250 PD patients, enlarging the spectrum of PLA2G6 mutations in PD. Although PLA2G6 mutations account for only a small fraction of PD patients in Chinese populations, these mutations impair catalytic activity of their phospholipids-hydrolyzing function. These results indicate that PLA2G6 mutations maybe PD-causing in Chinese Han populations.

Association of mitochondrial DNA polymerase γ gene POLG1 polymorphisms with parkinsonism in Chinese populations.

BACKGROUND: Mitochondrial DNA polymerase gamma (POLG1) mutations were associated with levodopa-responsive Parkinsonism. POLG1 gene contains a number of common nonsynonymous SNPs and intronic regulatory SNPs which may have functional consequences. It is of great interest to discover polymorphisms variants associated with Parkinson's disease (PD), both in isolation and in combination with specific SNPs. MATERIALS AND METHODS: We conducted a case-control study and genotyped twenty SNPs and poly-Q polymorphisms of POLG1 gene including in 344 Chinese sporadic PD patients and 154 healthy controls. All the polymorphisms of POLG1 we found in this study were sequenced by PCR products with dye terminator methods using an ABI-3100 sequencer. Hardy-Weinberg equilibrium and linkage disequilibrium (LD) for association between twenty POLG1 SNPs and PD were calculated using the program Haploview. PRINCIPAL RESULTS: We provided evidence for strong association of four intronic SNPs of the POLG1 gene (new report: c.2070-12T>A and rs2307439: c.2070-64G>A in intron 11, P = 0.00011, OR = 1.727; rs2302084: c.3105-11T>C and rs2246900: c.3105-36A>G in intron 19, P = 0.00031, OR = 1.648) with PD. However, we did not identify any significant association between ten exonic SNPs of POLG1 and PD. Linkage disequilibrium analysis indicated that c.2070-12T>A and c.2070-64G>A could be parsed into one block as Haplotype 1 as well as c.3105-11T>C and c.3105-36A>G in Haplotype 2. In addition, case and control study on association of POLG1 CAG repeat (poly-Q) alleles with PD showed a significant association (P = 0.03, OR = 2.16) of the non-10/11Q variants with PD. Although intronic SNPs associated with PD didn't influence POLG1 mRNA alternative splicing, there was a strong association of c.2070-12T>A and c.2070-64G>A with decreased POLG1 mRNA level and protein levels. CONCLUSIONS: Our findings indicate that POLG1 may play a role in the pathogenesis of PD in Chinese populations.

Cognitive impairment and the associated risk factors among the elderly in the Shanghai urban area: a pilot study from China.

OBJECTIVES: Our study aimed to investigate the prevalence of cognitive impairment(CI) and the associated risk factors among elderly people in Shanghai urban area, China. METHODS: A population-based survey was conducted among people aged 55 years or older in urban areas of Shanghai. Face-to-face interviews were carried out to collect information including demographic characteristics, medical history, and medication use, etc. The validated Chinese version of the Mini-Mental State Examination(MMSE) was used to screen subjects with CI, and the criteria of CI were adjusted for education levels. RESULTS: A total of 3,176 home-living residents (≥55 years old) were included in the study. Among them, 266 people (102 men and 164 women) were identified as cognition impaired, with a prevalence of 8.38% (266/3,176, 95% CI: (8.26, 8.49)) for both genders, 9.21% (102/1,107,95% CI: (9.18, 9.33)) for men and 7.93% (164/2,069, 95% CI: (7.80, 8.09)) for women, respectively. Furthermore, we found that several significant risk factors, including social factors(education, number of children, marriage status, and family structure), physiological factors (age, blood glucose level, and obesity), factors on living styles(physical exercise, diet & chronic diseases), and genetic factor(ApoE), associated with CI onset. CONCLUSIONS: This study confirms the high prevalence of CI among the elderly population in the Shanghai urban in China, similar to previous epidemiologic studies in Western countries. The putative risk factors associated with CI merit further investigated.

Glyphosate induced cell death through apoptotic and autophagic mechanisms.

Herbicides have been recognized as the main environmental factor associated with human neurodegenerative disorders such as Parkinson's disease(PD). Previous studies indicated that the exposure to glyphosate, a widely used herbicide, is possibly linked to Parkinsonism, however the underlying mechanism remains unclear. We investigated the neurotoxic effects of glyphosate in differentiated PC12 cells and discovered that it inhibited viability of differentiated PC12 cells in dose-and time-dependent manners. Furthermore, the results showed that glyphosate induced cell death via autophagy pathways in addition to activating apoptotic pathways. Interestingly, deactivation of Beclin-1 gene attenuated both apoptosis and autophagy in glyphosate treated differentiated PC12 cells, suggesting that Beclin-1 gene is involved in the crosstalk between the two mechanisms.

Extracellular signal-regulated kinase is involved in alpha-synuclein-induced mitochondrial dynamic disorders by regulating dynamin-like protein 1.

Compounding evidence suggests that alpha-synuclein (SNCA) plays an important role in the pathogenesis of Parkinson's disease (PD) by inducing neurotoxicity. Mitochondria are highly dynamic organelles that undergo fusion and fission processes, the imbalance of which has been viewed as a key trigger for PD. However, the underlying relationship between SNCA and mitochondrial dynamics remains unclear. This study demonstrated that SNCA overexpression not only altered mitochondrial morphology, but also significantly increased the translocation of mitochondrial fission protein dynamin-like protein 1 (DLP1). To further investigate the mechanism of SNCA's effect on mitochondrial dynamics, the proteomic technique, stable isotope labeling of amino acid in cell cultures (SILAC), was used. The extracellular signal-regulated kinase (ERK) was confirmed to be involved in the regulation of DLP1 and SNCA-mediated neurotoxicity. Finally, additional results demonstrated that SNCA inducing both mitochondrial dynamic disorders and neurotoxicity could be ameliorated by curcumin through ERK inhibition, which implied that the agent could be used to prevent and treat PD in the future.

Verification of expressions of Kir2 as potential peripheral biomarkers in lymphocytes from patients with Parkinson's disease.

Prior studies have reported gene expression alterations in peripheral blood lymphocytes (PBLs) obtained from patients with Parkinson's disease (PD) as compared to healthy controls. These alterations can not only be regarded as potential biomarkers, but also enhance understanding of the pathogenic mechanism of PD. In the present study, the gene expression levels of dopamine receptor (D2, D3), inward rectified potassium channels subunits Kir2 (Kir2.1, Kir2.2, Kir2.3, Kir2.4) and ATP-sensitive potassium channel subunit Kir6.2 in PBLs were analyzed using quantitative real-time PCR among 20 PD patients with medication, 10 PD patients without medication and 16 healthy controls, respectively. The results showed that there was a significantly decrease of the D2, D3 mRNA expression in PBLs of PD patients compared with that in healthy controls. The four inward rectified potassium channels Kir2.1, Kir2.2, Kir2.3, and Kir2.4 mRNA expression in PBLs from PD patients were also significantly down-regulated than that from age-matched healthy controls. However, there was no apparent difference in expression of another potassium channel Kir6.2 mRNA between PD patients and healthy controls. We proposed that the Kir2 potassium channels mRNA on blood lymphocytes may be regarded as a potential biomarker for PD screening.