Cdk5 suppression blocks SIRT1 degradation via the ubiquitin-proteasome pathway in Parkinson's disease models

The NAD⁺-dependent protein deacetylase sirtuin 1 (SIRT1), a member of the sirtuin family, may have a neuroprotective effect in multiple neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS). Many studies have suggested that overexpression-induced or resveratrol-treated activation of SIRT1 could significantly ameliorate several neurodegenerative diseases in mouse models. However, the type of SIRT1, protein expression levels and underlying mechanisms remain unclear, especially in PD. In this study, the results demonstrated that SIRT1 knockout markedly worsened the movement function in MPTP-lesioned animal model of PD. SIRT1 expression was found to be markedly decreased not only in environmental factor PD models, neurotoxin MPP⁺-treated primary culture neurons and MPTP-induced mice but also in genetic factor PD models, overexpressed α-synuclein-A30PA53T SH-SY5Y stable cell line and hm²α-SYN-39 transgenic mouse strain. Importantly, the degradation of SIRT1 during MPP⁺ treatment was mediated by the ubiquitin-proteasome pathway. Furthermore, the results indicated that cyclin-dependent kinase 5 (Cdk5) was also involved in the decrease of SIRT1 expression, which could be efficiently blocked by the inhibition of Cdk5. In conclusion, our findings revealed that the Cdk5-dependent ubiquitin-proteasome pathway mediated degradation of SIRT1 plays a vital role in the progression of PD.     

Gene co-expression network analysis for identifying genetic markers in Parkinson's disease - a three-way comparative approach

Parkinson's disease (PD) is a neurodegenerative disorder involving progressive deterioration of dopaminergic neurons. Although few genetic markers for familial PD are known, the etiology of sporadic PD remains poorly understood. Microarray data was analysed for induced pluripotent stem cells (iPSCs) derived from PD patients and mature neuronal cells (mDA) differentiated from these iPSCs. Combining expression and semantic similarity, a highly-correlated PD interactome was constructed that included interactions of established Parkinson's disease marker genes. A novel three-way comparative approach was employed, delineating topologically and functionally important genes. These genes showed involvement in pathways like Parkin-ubiquitin proteosomal system (UPS), immune associated biological processes and apoptosis. Of interest are three genes, eEF1A1, CASK, and PSMD6 that are linked to PARK2 activity in the cell and thereby form attractive candidate genes for understanding PD. Network biology approach delineated in this study can be applied to other neurodegenerative disorders for identification of important genetic regulators.     

Association of the COQ2 V393A Variant with Parkinson's Disease: A Case-Control Study and Meta-Analysis

Both Parkinson’s disease (PD) and multiple system atrophy (MSA) are neurodegenerative diseases of uncertain etiology, but they show similarities in their pathology and clinical course. The fact that the gene encoding α-synuclein is associated with both diseases also suggests that they share some genetic determinants. Recent studies in Japan associating MSA with a variant in the COQ2 gene led us to question whether variants in the COQ2 gene are associated with PD in Han Chinese in a case-control study. A total of 564 patients with PD were genotyped using the ligase detection rection, together with 484 gender- and age-matched healthy subjects. The M128V and R387X variants of COQ2 were not detected in patients or controls; instead, we detected only the heterozygous V393A variant (CT genotype). The frequency of the CT genotype encoding the V393A mutation was significantly higher in patients PD (4.08%) than in controls (1.86%), corresponding to an odds ratio of 2.24 (95%CI 1.03 to 4.90, p = 0.037). The frequency of the C allele of the V393A variant was significantly higher in patients with PD than in controls (OR 2.22, 95%CI 1.02 to 4.82, p = 0.039), and this was also observed in a meta-analysis of studies from mainland China, Taiwan and Japan. Subgroup analysis of our data showed that the V393A variant was significantly associated with early-onset PD (OR 3.71, 95%CI 1.51 to 9.15, p = 0.002) but not with late-onset disease (OR 1.65, 95%CI 0.69 to 3.95, p = 0.260). Gender was not significantly associated with either genotype or minor allele frequencies. In conclusion, our findings show for the first time that the V393A variant in the COQ2 gene increases risk of PD among the population of east Asia. These results, combined with research on Japanese, lend genetic support to the hypothesis that oxidative stress underlies pathogenesis of both PD and MSA.     

Sirtuin 2 (SIRT2) Enhances 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Nigrostriatal Damage via Deacetylating Forkhead Box O3a (Foxo3a) and Activating Bim Protein

Sirtuins are NAD-dependent protein deacetylases that were shown to have beneficial effects against age-related diseases. SIRT2 is a strong deacetylase that is highly expressed in brain. It has been associated with neurodegenerative diseases. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a dopaminergic neurotoxin that replicates most of the clinical features of Parkinson disease (PD) and produces a reliable and reproducible lesion of the nigrostriatal dopaminergic pathway and neurodegeneration after its systemic administration. Chronic administration of MPTP induces lesion via apoptosis. We show here that SIRT2 deacetylates Foxo3a, increases RNA and protein levels of Bim, and as a result, enhances apoptosis in the MPTP model of PD. We also show that neurodegeneration induced by chronic MPTP regimen is prevented by genetic deletion of SIRT2 in mouse. Deletion of SIRT2 leads to the reduction of apoptosis due to an increase in acetylation of Foxo3a and a decrease in Bim levels. We demonstrate that SIRT2 deacetylates Foxo3a, activates Bim, and induces apoptosis only in 1-methyl-4-phenylpyridinium-treated cells. Therefore, designing SIRT2 inhibitors might be helpful to develop effective treatments for PD.     

中国汉族两个马凡综合征家系FBN1基因的一个新插入突变和一个复发点突变

目的:明确两个中国北方汉族马凡综合征(Marfan syndrome,MFS)家系的临床特点,并对其进行基因诊断。方法:对两个家系进行家系调查和系谱分析,应用聚合酶链式反应-DNA测序方法对原纤维蛋白1基因(Fibrillin-1,FBN1)的所有外显子进行测序。应用Swiss-model、Polyphen-2和SIFT软件对发现的变异位点进行功能预测。结果:两个家系均呈常染色显性遗传特点,在家系1患者中发现一个新的插入突变,即第13外显子1691位碱基处插入碱基A(1691 ins A),导致蛋白在第571位氨基酸处翻译提前终止。此外,在家系2患者中发现一个已知的点突变,即第27外显子第3463位碱基由G变为A(3463 GA),导致第1155位氨基酸由天冬氨酸变为天冬酰胺。这两个变异位点在家系的健康人及50例健康对照中均未出现。功能预测发现这两个变异位点均可能会影响FBN1蛋白的结构或功能。结论:在两个MFS家系中发现一个新插入突变位点(1691 ins A)和一个已知点突变位点(3463 GA),为扩大FBN1基因的突变谱及进一步阐明FBN1基因突变在MFS中的作用提供理论依据。     

Targeted Exon Capture and Sequencing in Sporadic Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that results in progressive degeneration of motor neurons, ultimately leading to paralysis and death. Approximately 10% of ALS cases are familial, with the remaining 90% of cases being sporadic. Genetic studies in familial cases of ALS have been extremely informative in determining the causative mutations behind ALS, especially as the same mutations identified in familial ALS can also cause sporadic disease. However, the cause of ALS in approximately 30% of familial cases and in the majority of sporadic cases remains unknown. Sporadic ALS cases represent an underutilized resource for genetic information about ALS; therefore, we undertook a targeted sequencing approach of 169 known and candidate ALS disease genes in 242 sporadic ALS cases and 129 matched controls to try to identify novel variants linked to ALS. We found a significant enrichment in novel and rare variants in cases versus controls, indicating that we are likely identifying disease associated mutations. This study highlights the utility of next generation sequencing techniques combined with functional studies and rare variant analysis tools to provide insight into the genetic etiology of a heterogeneous sporadic disease.     

Leigh syndrome caused by a novel m.4296G>A mutation in mitochondrial tRNA isoleucine

Leigh syndrome is a severe neurodegenerative disease with heterogeneous genetic etiology. We report a novel m.4296G>A variant in the mitochondrial tRNA isoleucine gene in a child with Leigh syndrome, mitochondrial proliferation, lactic acidosis, and abnormal respiratory chain enzymology. The variant is present at >75% heteroplasmy in blood and cultured fibroblasts from the proband, <5% in asymptomatic maternal relatives, and is absent in 3000 controls. It is located in the highly conserved anticodon region of tRNA(Ile) where three other pathogenic changes have been described. We conclude that there is strong evidence to classify m.4296G>A as a pathogenic mutation causing Leigh syndrome.     

神经退化性疾病生物能量代谢和氧化应激研究进展

衰老是导致几种常见的神经系统退化性疾病的主要危险因素,包括帕金森氏病（Ｐａｒｋｉｎｓｏｎ’ｓ ｄｉｓｅａｓｅ ＰＤ）,肌萎缩性侧索硬化（Ａｍｙｏｔｒｏｐｈｉｃ ｌａｔｅｒａｌ ｓｃｌｅｒｏｓｉｓ,ＡＬＳ）,早老性痴呆（Ａｌｚｈｅｉｍｅｒ’ｓ ｄｉｓｅａｓｅ ＡＤ）和亨廷顿氏病（Ｈｕｎｔｉｎｇｔｏｎ’ｓ ｄｉｓｅａｓｅ ＨＤ）。最近研究表明,神经退化性疾病涉及到线粒体缺陷,氧化应激等因素。在脑和其它组织中,老化可导致线粒体功能的损伤和氧化损伤的增强。ＰＤ病人中,已发现线粒体复合酶体Ⅰ活性降低,氧化损伤增加和抗氧化系统活性的改变。在几例家族性ＡＬＳ病人中,也发现Ｃｕ、Ｚｎ超氧化物歧化酶（Ｃｕ,Ｚｎ ＳＯＤ）基因的突变,导致Ｃｕ、Ｚｎ超氧化物歧化酶活性减低;散发的ＡＬＳ病人氧化损伤增高。在ＨＤ病人中已发现能量代谢异常     

Non-synonymous GIGYF2 variants in Parkinson’s disease from two Asian populations

Mutations in the GIGYF2 gene at the PARK11 locus have recently been reported in Parkinson’s disease (PD). However, the pathogenicity of some of these mutations has been debated. We conducted a comprehensive genetic analysis of the entire GIGYF2 gene in a cohort of young onset and familial PD patients, followed up with screening of specific variants in a separate group of PD and healthy controls. A total of 850 study subjects [450 Parkinson’s disease (PD) patients and 400 controls] from two Asian countries were included. Our analysis revealed 17 variants distributed across the entire GIGYF2 gene. Ten of these were novel variants out of which eight were non-synonymous (all heterozygous). Out of these eight, half were novel polymorphic variants (0.2–2%) whereas four were novel non-synonymous variants which were not detected in healthy controls. The seven PD patients with non-synonymous variants had a mean age and age at onset of 55.3 and 50.9 years. All had typical features of PD and only one had a positive family history. The collective frequency of these non-synonymous variants was higher in PD compared to controls (1.6 vs. 0%, P = 0.016, relative risk 1.9, 95% CI 1.2, 1.9). None of the previously reported pathogenic mutations in Italian and French patients were present in our cohort. Our data suggest that GIGYF2 is unlikely to play a major role in our Asian populations. Rare non-synonymous variants appeared to be enriched in our PD patients compared to healthy controls. However, in vivo functional studies and segregation analysis in large pedigrees will be needed to determine if these single heterozygous variants represent rare mutations, risk alleles or benign polymorphisms.