Genetic associations of Nrf2-encoding NFE2L2 variants with Parkinson's disease - a multicenter study.

BACKGROUND: The transcription factor Nrf2, encoded by the NFE2L2 gene, is an important regulator of the cellular protection against oxidative stress. Parkinson's disease is a neurodegenerative disease highly associated with oxidative stress. In a previously published study, we reported associations of NFE2L2 haplotypes with risk and age at onset of idiopathic Parkinson's disease in a Swedish discovery material and a Polish replication material. Here, we have extended the replication study and performed meta-analyses including the Polish material and four new independent European patient-control materials. Furthermore, all SNPs included in the haplotype windows were investigated individually for associations with Parkinson's disease in meta-analyses including all six materials. METHODS: Totally 1038 patients and 1600 control subjects were studied. Based on previous NFE2L2 haplotype associations with Parkinson's disease, five NFE2L2 tag SNPs were genotyped by allelic discrimination and three functional NFE2L2 promoter SNPs were genotyped by sequencing. The impact of individual SNPs and haplotypes on risk and age at onset of Parkinson's disease were investigated in each material individually and in meta-analyses of the obtained results. RESULTS: Meta-analyses of NFE2L2 haplotypes showed association of haplotype GAGCAAAA, including the fully functional promoter haplotype AGC, with decreased risk (OR = 0.8 per allele, p = 0.012) and delayed onset (+1.1 years per allele, p = 0.048) of Parkinson's disease. These results support the previously observed protective effect of this haplotype in the first study. Further, meta-analyses of the SNPs included in the haplotypes revealed four NFE2L2 SNPs associated with age at onset of Parkinson's disease (rs7557529 G > A, -1.0 years per allele, p = 0.042; rs35652124 A > G, -1.1 years per allele, p = 0.045; rs2886161 A > G, -1.2 years per allele, p = 0.021; rs1806649 G > A, +1.2 years per allele, p = 0.029). One of these (rs35652124) is a functional SNP located in the NFE2L2 promoter. No individual SNP was associated with risk of Parkinson's disease. CONCLUSION: Our results support the hypothesis that variation in the NFE2L2 gene, encoding a central protein in the cellular protection against oxidative stress, may contribute to the pathogenesis of Parkinson's disease. Functional studies are now needed to explore these results further.

A novel ARC gene polymorphism is associated with reduced risk of Alzheimer's disease.

Alzheimer's disease (AD) is the most common neurodegenerative disease, and is clinically characterized by cognitive disturbances and the accumulation of the amyloid ß (Aß) peptides in plaques in the brain. Recent studies have shown the links between AD and the immediate-early gene Arc (activity-regulated cytoskeleton-associated protein), involved in synaptic plasticity and memory consolidation. For example, AD mouse models show a decreased expression of Arc mRNA in the brain. In additional, acute Aß application to brain slices leads to a widespread ARC protein diffusion, unlike the normal defined localization to synapses. In this study, we investigated genetic variation in human ARC and the risk of developing AD. To this end, we genotyped 713 subjects diagnosed with AD and 841 controls without dementia. ARC was sequenced in a group of healthy individuals, and seven previously known SNPs and three novel SNPs were identified. Two of the newly found SNPs were intronic and one, +2852(G/A), was located in the 3'UTR. Three tag SNPs were selected, including the novel SNP +2852(G/A), to relate to risk of AD, Mini Mental State Examination (MMSE) scores and cerebrospinal fluid (CSF) biomarker levels of total tau (T-tau), hyperphosphorylated tau181 (P-tau(181)) and Aß(1-42). The AA genotype of the newly found 3'-UTR SNP +2852(A/G), was associated with a decreased risk of AD (p (c) = 0.005; OR = 0.74; 95 % CI: 0.61-0.89). No associations of single SNPs or haplotypes with MMSE score or CSF biomarkers were found. Here we report a novel ARC SNP associated with a reduced risk of developing AD. To our knowledge, this is the first study associating a gene variant of ARC with any disease. The location of the SNP within the 3'UTR indicates that dendritic targeting of ARC mRNA could be involved in the molecular mechanisms underlying this protective function. However, further investigation of the importance of this SNP for ARC function, ARC processing and the pathology of AD is needed.

Association of Nrf2-encoding NFE2L2 haplotypes with Parkinson's disease.

BACKGROUND: Oxidative stress is heavily implicated in the pathogenic process of Parkinson's disease. Varying capacity to detoxify radical oxygen species through induction of phase II antioxidant enzymes in substantia nigra may influence disease risk. Here, we hypothesize that variation in NFE2L2 and KEAP1, the genes encoding the two major regulators of the phase II response, may affect the risk of Parkinson's disease. METHODS: The study included a Swedish discovery case-control material (165 cases and 190 controls) and a Polish replication case-control material (192 cases and 192 controls). Eight tag single nucleotide polymorphisms representing the variation in NFE2L2 and three representing the variation in KEAP1 were chosen using HapMap data and were genotyped using TaqMan Allelic Discrimination. RESULTS: We identified a protective NFE2L2 haplotype in both of our European case-control materials. Each haplotype allele was associated with five years later age at onset of the disease (p = 0.001) in the Swedish material, and decreased risk of PD (p = 2 x 10(-6)), with an odds ratio of 0.4 (95% CI 0.3-0.6) for heterozygous and 0.2 (95% CI 0.1-0.4) for homozygous carriers, in the Polish material. The identified haplotype includes a functional promoter haplotype previously associated with high transcriptional activity. Genetic variation in KEAP1 did not show any associations. CONCLUSION: These data suggest that variation in NFE2L2 modifies the Parkinson's disease process and provide another link between oxidative stress and neurodegeneration.

Association of the RAGE G82S polymorphism with Alzheimer's disease.

The receptor for advanced glycation end-products (RAGE) has been implicated in several pathophysiological processes relevant to Alzheimer's disease (AD), including transport and synaptotoxicity of AD-associated amyloid beta (Abeta) peptides. A recent Chinese study (Li et al. in J Neural Transm 117:97-104, 2010) suggested an association between the 82S allele of the functional single nucleotide polymorphism (SNP) G82S (rs2070600) in the RAGE-encoding gene AGER and risk of AD. The present study aimed to investigate associations between AGER, AD diagnosis, cognitive scores and cerebrospinal fluid AD biomarkers in a European cohort of 316 neurochemically verified AD cases and 579 controls. Aside from G82S, three additional tag SNPs were analyzed to cover the common genetic variation in AGER. The 82S allele was associated with increased risk of AD (P (c) = 0.04, OR = 2.0, 95% CI 1.2-3.4). There was no genetic interaction between AGER 82S and APOE epsilon4 in producing increased risk of AD (P = 0.4), and none of the AGER SNPs showed association with Abeta(42), T-tau, P-tau(181) or mini-mental state examination scores. The data speak for a weak, but significant effect of AGER on risk of AD.

Association of NFE2L2 and KEAP1 haplotypes with amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a degenerative motor neuron syndrome influenced by oxidative stress. The transcription factor Nrf2 and its repressor Keap1 constitute an important defence system in cellular protection against oxidative stress. Here we hypothesize that common genetic variations in the genes NFE2L2 and KEAP1, encoding Nrf2 and Keap1, may influence the risk and phenotype of ALS. Five hundred and twenty-two Swedish patients with sporadic ALS (SALS) and 564 Swedish control subjects were studied. Eight tag SNPs in NFE2L2 and three tag SNPs in KEAP1 were genotyped by allelic discrimination and three functional NFE2L2 promoter SNPs were genotyped by sequencing. One NFE2L2 haplotype (GGGAC) was associated with decreased risk of SALS (OR = 0.62 per allele, p = 0.003) and one haplotype in KEAP1 (CGG) was associated with later SALS onset (+3.4 years per allele, p = 0.015). When stratified by subgroup, one haplotype in NFE2L2, GAGCAGA including three functional promoter SNPs associated with high Nrf2 protein expression, was associated with 4.0 years later disease onset per allele in subgroup ALS (p = 0.008). In conclusion, these results suggest that variations in NFE2L2 and KEAP1, encoding two central proteins in cellular oxidative stress defence, may influence SALS pathogenesis.

SILAC zebrafish for quantitative analysis of protein turnover and tissue regeneration.

Defective tissue regeneration is thought to contribute to several human diseases, including neurodegenerative disorders, heart failure and various lung diseases. Boosting the regenerative capacity has been suggested a possible therapeutic approach. Methods to metabolically label newly synthesized proteins in vivo with stable isotopic forms of amino acids holds promise for the study of protein turnover and tissue regeneration that are fundamental to the sustained life of all organisms. Here, we used the "stable isotope labeling with amino acids in cell culture" (SILAC) approach to explore normal protein turnover and tissue regeneration in adult zebrafish. The ratio of labeled and unlabeled proteins/peptides in specific organs of zebrafish fed a SILAC diet containing (13)C(6)-labeled lysine was determined by liquid chromatography and tandem mass spectrometry. Labeling was highest in tissues with high regenerative capacity, including intestine, liver, and fin, whereas brain and heart displayed the lowest labeling. Proteins with high degree of labeling were mainly involved in catalytic or transport activity pathways. The technique also verified increased protein synthesis during regeneration of the caudal fin following amputation. This newly developed SILAC zebrafish model constitutes a novel tool to analyze tissue regeneration in an animal model amenable to genetic and pharmacologic manipulation.

Proteomics profiling of single organs from individual adult zebrafish.

The model organism zebrafish (Danio rerio) is extensively utilized in studies of developmental biology but is also being investigated in the context of a growing list of human age-related diseases. To facilitate such studies, we here present protein expression patterns of adult zebrafish organs, including blood, brain, fin, heart, intestine, liver, and skeletal muscle. Protein extracts were prepared from the different organs of two zebrafish and analyzed using liquid chromatography coupled to high-resolution tandem mass spectrometry. Zebrafish tissue was digested directly after minimal fractionation and cleaned up (the shotgun approach). Proteins were identified using Mascot software. In total, 1394 proteins were identified of which 644 were nonredundant. Of these, 373 demonstrated an organ-specific expression pattern and 57 had not been shown on protein level before. These data emphasize the need for increased research at the protein level to facilitate the selection of candidate proteins for targeted quantification and to refine systematic genetic network analysis in vertebrate development, biology, and disease.

Ubiquitin carboxy-terminal hydrolase L1 (UCHL1) S18Y polymorphism in Alzheimer's disease.

Alzheimer's disease (AD) is characterized by protein aggregates, i.e. senile plaques and neurofibrillary tangles. The ubiquitin-proteasome system has been proposed a role in proteolytic removal of these protein aggregates. Ubiquitin carboxy-terminal hydrolase L1 (UCHL1) is a de-ubiquitinating enzyme with important functions in recycling of ubiquitin. The S18Y polymorphism of the UCHL1 gene confers protection against Parkinson's disease. In this study, the genotype and allele frequencies of the UCHL1 S18Y polymorphism were investigated in 452 AD patients and 234 control subjects, recruited from four memory clinics in Sweden. Using a binary logistic regression model including UCHL1 allele A and APOE epsilon4 allele positivity, age and sex as covariates with AD diagnosis as dependent variable, an adjusted OR of 0.82 ([95% CI 0.55-1.24], P = 0.35) was obtained for a positive UCHL1 allele A carrier status. The present study thus do not support a protective effect of the UCHL1 S18Y polymorphism against AD.

Nrf2-encoding NFE2L2 haplotypes influence disease progression but not risk in Alzheimer's disease and age-related cataract.

Alzheimer's disease (AD) and age-related cataract, disorders characterized by protein aggregation causing late-onset disease, both involve oxidative stress. We hypothesize that common variants of NFE2L2 and KEAP1, the genes encoding the main regulators of the Nrf2 system, an important defence system against oxidative stress, may influence risk of AD and/or age-related cataract. This case-control study combines an AD material (725 cases and 845 controls), and a cataract material (489 cases and 182 controls). Genetic variation in NFE2L2 and KEAP1 was tagged by eight and three tag single nucleotide polymorphisms (SNPs), respectively. Single SNPs and haplotypes were analyzed for associations with disease risk, age parameters, MMSE and AD cerebrospinal fluid biomarkers. NFE2L2 and KEAP1 were not associated with risk of AD or cataract. However, one haplotype allele of NFE2L2 was associated with 2 years earlier age at AD onset (p(c)=0.013) and 4 years earlier age at surgery for posterior subcapsular cataract (p(c)=0.019). Another haplotype of NFE2L2 was associated with 4 years later age at surgery for cortical cataract (p(c)=0.009). Our findings do not support NFE2L2 or KEAP1 as susceptibility genes for AD or cataract. However, common variants of the NFE2L2 gene may affect disease progression, potentially altering clinically recognized disease onset.

Kinesin light chain 1 gene haplotypes in three conformational diseases.

A functional intracellular transport system is essential to maintain cell shape and function especially in elongated cells, e.g. neurons and lens fibre cells. Impaired intracellular transport has been suggested as a common pathological mechanism for age-related diseases characterised by protein aggregation. Here, we hypothesise that common genetic variation in the transport protein kinesin may influence the risk of Parkinson's disease (PD), Alzheimer's disease (AD) and age-related cataract. This case-control study involves a PD material (165 cases and 190 controls), an AD material (653 cases and 845 controls) and a cataract material (495 cases and 183 controls). Genetic variation in the kinesin light chain 1-encoding gene (KLC1) was tagged by six tag single nucleotide polymorphisms (SNPs). Single SNPs and haplotypes were analysed for associations with disease risk, age parameters, mini-mental state examination scores and cerebrospinal fluid biomarkers for AD using logistic or linear regression. Genetic variation in KLC1 did not influence risk of PD. Weak associations with risk of AD were seen for rs8007903 and rs3212079 (P (c) = 0.04 and P (c) = 0.02, respectively). Two SNPs (rs8007903 and rs8702) influenced risk of cataract (P (c) = 0.0007 and P (c) = 0.04, respectively). However, the allele of rs8007903 that caused increased risk of AD caused reduced risk of cataract, speaking against a common functional effect of this particular SNP in the two diseases. Haplotype analyses did not add significantly to the associations found in the single SNP analyses. Altogether, these results do not convincingly support KLC1 as a major susceptibility gene in any of the studied diseases, although there is a small effect of KLC1 in relation to cataract.