Manuel Menéndez

Profile of microRNAs in the plasma of Parkinson's disease patients and healthy controls

The pathological hallmark of Parkinson’s disease (PD) is the loss of dopaminergic neurons and the presence of Lewy bodies and Lewy neurites in the substantia nigra pars compacta, corpus striatum and brain cortex [1]. PD is a complex disease caused by the interaction of genetic/ inherited and environmental/acquired risk factors [2]. MicroRNAs (miRNAs) are small RNAs that control gene expression by binding to the 30 UTRs of mRNAs [3]. Postmortem analysis of brain tissues and in vitro studies have identified several miRNAs implicated in PD. MiR-133b was shown to be downregulated in PD brains and to promote the survival of dopaminergic neurons [4]. MiR-433 was related with PD through targeting the FGF20, which in turn regulates the expression of a-synuclein [5]. MiR-7 targets a-synuclein and could regulate oxidative stress and cell death, while miR-184 and let-7 regulate dopaminergic neurons survival and activity [6, 7]. Recently, a miRNA profiling of PD brains identified early downregulation of miR-34b/c, modulating mitochondrial function in areas with pathological affectation [8]. Plasma (circulating) miRNAs have been proposed as biomarkers for several diseases and aging [9, 10]. Our aim was to characterize the plasma miRNA profile in PD patients and healthy controls, to determine its usefulness as a biomarker for PD. The study was approved by the Ethical Committee of Hospital Universitario Central de Asturias (HUCA) in accordance with the ethical standards of the Declaration of Helsinki and all the participants signed an informed consent. The study cohort consisted of sexand age-matched healthy controls (n = 25; mean age 67.6; 52 % males) and patients (n = 31; mean age 63.9; 55 % males) who fulfilled the PD-clinical diagnosis criteria [11]. None of the patients were receiving drugs for PD-treatment or had a diagnosis of cardiovascular or tumor disease. Full details of the experimental procedure are available as supplementary material. Briefly, blood was collected in tubes with EDTA, centrifuged and plasma was aliquoted (350 ll). A total of 2 pg of a synthetic Arabidopsis thaliana miRNA (Ath-miR-159a; 5 ll of a 0.4 pg/ll dilution) was immediately added and each aliquot stored at -80 C until use. Ath-miR-159a was used as control of the extraction process (supplementary material). Total plasma RNA was extracted (TRIzol LS Reagent, Ambion) and resuspended in 25 ll of RNAse-free water. Five ll of each sample were retrotranscribed (RT) with the Megaplex RT primers Human pool A and TaqMan microRNA Reverse transcription kit (Applied Biosystems). Three ll of the RT product were pre-amplified with the Megaplex Preamp primers Human pool A and TaqMan Universal Master Mix no AmpErase UNG (Applied Biosystems). All the preamplifications were assayed with a custom Ath-miR-159a Taqman assay in an ABI 7500 Real-Time PCR (Applied Electronic supplementary material The online version of this article (doi:10.1007/s00415-013-6900-8) contains supplementary material, which is available to authorized users.

Analysis of the Micro-RNA-133 and PITX3 Genes in Parkinson's Disease

MicroRNAs are small RNA sequences that negatively regulate gene expression by binding to the 3′ untranslated regions of mRNAs. MiR‐133b has been implicated in Parkinsons disease (PD) by a mechanism that involves the regulation of the transcription factor PITX3. The variation in these genes could contribute to the risk of developing PD. We searched for DNA variants in miR‐133 and PITX3 genes in PD patients and healthy controls from Spain. We found common DNA variants in the three miR‐133 genes. Genotyping of a first set of patients (n = 777) and controls (n = 650) showed a higher frequency of homozygous for a miR‐133b variant (−90 del A) in PD‐patients (6/575; 1%) than in healthy controls (0/650) (P = 0.03). However, this association was not confirmed in a second set of patients (1/250; 0.4%) and controls (2/210; 1%). No common PITX3 variants were associated with PD, although a rare missense change (G32S) was found in only one patient and none of the controls. In conclusion, we report the variation in genes of a pathway that has been involved in dopaminergic neuron differentiation and survival. Our work suggests that miR‐133 and PITX3 gene variants did not contribute to the risk for PD.

A search for SNCA 3' UTR variants identified SNP rs356165 as a determinant of disease risk and onset age in Parkinson's disease.

Alpha-synuclein gene (SNCA) polymorphisms have been associated with the common sporadic form of Parkinson’s disease (PD). We searched for DNA variants at the SNCA 3′ UTR through single strand conformation analysis and direct sequencing in a cohort of Spanish PD patients and controls. We have genotyped the rs356165 SNCA 3′ UTR polymorphism in a total of 1,135 PD patients and 772 healthy controls from two Spanish cohorts (Asturias and Navarre). We identified six SNCA 3′ UTR variants. Single nucleotide polymorphism (SNP) rs356165 was significantly associated with PD risk in the Spanish cohort (p = 0.0001; odd ratio = 1.37, 95%CI = 1.19–1.58). This SNP was also significantly associated with early age at onset of PD. Our work highlights rs356165 as an important determinant of the risk of developing PD and early age at onset and encourages future research to identify a functional effect on SNCA expression.

MiRNA Profile in the Substantia Nigra of Parkinson’s Disease and Healthy Subjects

The deregulation of several microRNAs (miRNAs) has been associated with neurodegenerative processes, including Parkinson’s disease (PD). Our aim was to characterize the level of miRNAs in the substantia nigra (SN) of PD patients and healthy donors. This is an important issue to characterize new putative markers and therapeutic targets for PD. RNA was extracted from the SN of postmortem PD (n = 8) and healthy (n = 4) subjects, and the level of 733 human miRNAs was assayed with TaqMan low-density arrays (TLDAs). Overall, there was a miRNA downregulation in the SN of patients. The mean level of 11 miRNAs was significantly different (p < 0.05) between patients and controls, with 10 downregulated among the patients. MiR-198, -135b, -485-5p, and -548d were the best candidates and were quantified with individual TaqMan assays in the 12 samples. MiR-135b showed the most significant difference between patients and healthy donors. The bioinformatic analysis suggested that this miRNA could bind to genes implicated in several neurodegenerative pathways.

Late-onset Alzheimer's disease is associated with mitochondrial DNA 7028C/haplogroup H and D310 poly-C tract heteroplasmy

There is growing evidence that mitochondria play an important role in the pathogenesis of late-onset Alzheimers disease (LOAD) [1]. Certain haplogroups defined by combinations of common mitochondrial DNA (mtDNA) single-nucleotide polymorphisms (SNPs) have been associated with longevity and age-related diseases. Recent studies reported a significant association between haplogroup H and LOAD [2–4] (supplementary Table 1). Differences between the mtDNA SNPs/haplogroups in the efficiency of oxygen consumption and ATP and ROS production could partly explain these associations [5]. Although the relative risk attributed to this haplogroup was low (<1.5) in all the studies, this could have important implications considering the high incidence of LOAD at the population level. It is therefore very important to determine the influence of mtDNA polymorphisms in LOAD by studying large cohorts from different populations. We report the results from Asturias (northern Spain) based on a total of 500 LOAD patients and 500 controls (Supplementary file). The mtDNA 7028C was significantly more frequent among the patients (p=0.001; OR=1.52, 95% CI=1.18– 1.95; Table 1). Allele frequencies for the other six SNPs that defined the mitochondrial haplogroups did not differ between patients and controls (data not shown). Haplogroup H (defined by 7028C) was significantly more frequent among the patients (Supplementary file). Multiple logistic regression with apolipoprotein E gene (APOE)-ε4 and mtDNA 7028C status, age, and gender as covariates showed that APOE-ε4 and 7028C were associated with LOAD. We found a synergistic effect between the two risk variants: the OR for APOE-ε4 + 7028C (OR=5.30, 95% CI=3.72–7.54) was higher than the OR for each separately. The non-APOE-ε4 + 7028T had a protective effect (OR= 0.43; 95%CI=0.33–0.75). Patients and controls were classified as D310 7C or D310 >7C (poly-C tract at position 310 of the mtDNA, Supplementary file). We found a significantly higher frequency of the >7C alleles among the patients (Table 1). Electronic supplementary material The online version of this article (doi:10.1007/s10048-011-0295-4) contains supplementary material, which is available to authorized users. E. Coto (*) : J. Gómez :B. Alonso :A. I. Corao :M. Díaz : V. Álvarez Genética Molecular-Laboratorio de Medicina, Hospital Universitario Central Asturias, 33006 Oviedo, Spain e-mail: eliecer.coto@sespa.princast.es

Alpha-synuclein transcript isoforms in three different brain regions from Parkinson's disease and healthy subjects in relation to the SNCA rs356165/rs11931074 polymorphisms

Mutations in the alpha-synuclein (SNCA) gene cause autosomal dominant Parkinsons disease (PD). Common SNCA polymorphisms have been associated with the risk of developing PD. Abnormal expression and post-translational modification of SNCA has been found in PD-brains. In addition to a full length transcript (SNCA-140) there are three short isoforms (SNCA-98, -112, and -126) that could be prone to aggregation. The association between SNCA polymorphisms and PD could be explained through an increased expression of these alternative transcripts. Our aim was to measure the different SNCA transcripts in the substantia nigra (SN), cerebellum (CB), and occipital cortex (OC) from PD-patients (n=9) and healthy subjects (n=6). In addition, we determined whether two SNCA polymorphisms (SNPs rs356165 and rs11931074) were related to differences in transcript isoform expression. PD brain tissues showed higher levels of the three short transcripts in the SN, but only SNCA-112 and SNCA-98 were significantly increased in the CB of patients vs. controls (p=0.02, p=0.03). The genotyping of a large cohort of PD-patients and controls showed that haplotype rs356165-A+rs11931074-G had a protective effect (OR=0.71; CI=0.59-0.83), while the G-T haplotype increased the risk for PD (OR=1.44; CI=1.06-1.96). We did not find significant differences for the SNCA levels between the haplotypes. In conclusion, we found statistically significant higher levels of the SNCA-112 and SNCA-98 transcripts in the CB of PD brains, and a trend toward higher levels of the short transcript isoforms in the SN of PD brains.

Lack of association between protocadherin 11-X/Y (PCDH11X and PCDH11Y) polymorphisms and late onset Alzheimer's disease.

A recent genome-wide association study (GWA) reported a significant association between single nucleotide polymorphisms (SNPs) at the PCDH11X gene and late-onset Alzheimers disease (LOAD). Our research was designated to replicate this association, including non previously analyzed PCDH11X and PCDH11Y SNPs. We genotyped four PCDH11X and one PCDH11Y SNPs in a total of 420 LOAD patients and 350 healthy controls from Spain. Allele and genotype frequencies did not differ between patients and controls for the five SNPs, even after correcting by gender, age, and APOE-ε4 status. Our data were in agreement with recent reports that failed to confirm the association between PCDH11X polymorphisms and LOAD, and extended the lack of association to common PCDH11Y variants.

Myocyte enhancing factor-2A in Alzheimer's disease: genetic analysis and association with MEF2A-polymorphisms.

Polymorphisms at different genes have been proposed as determinants of the risk for developing late-onset Alzheimers disease (LOAD). Among the several candidate genes are those that encode proteins involved in neuronal degeneration/survival. Studies of primary neuronal cultures supported that members of the myocyte enhancing factor-2 (MEF2) family of transcription factors have an anti-apoptotic effect, regulating the expression of proteins involved in neuronal survival and differentiation. We analysed the MEF2A gene in a total of 357 patients (mean age 72 years, range 60-97 years). Among others, a Pro279Leu in exon 8 and a polyglutamine (CAG) repeat polymorphisms in exon 12 were found. These variants were also genotyped in 495 healthy controls (>50 years old), and the frequencies were statistically compared. Eight patients were 279L (six P/L and two L/L), compared to only one control (2% vs. 0.2%; p=0.004, OR=11.32). There was a significantly higher frequency of 279L-carriers among APOE epsilon4+ (7/154=4.5%), compared to epsilon4- (1/203) (p=0.02). In conclusion, our work suggests that the variation at the MEF2A gene could be involved in the risk of developing LOAD. Because MEF2 has been related with neuronal survival, and the 279L allele has been related with a reduction in the transcriptional activation activity of MEF2A, the effect of this allele could be mediated through a down-regulation of antiapoptotic genes.

The screening of the 3'UTR sequence of LRRK2 identified an association between the rs66737902 polymorphism and Parkinson's disease.

Mutations in the leucine-rich repeat kinase 2 gene (LRRK2) are the most common genetic determinants of familial and sporadic Parkinson’s disease (PD). Most of the mutational screenings analyzed the exon-coding sequence. Our aim was to determine whether LRRK2 3′ untranslated region (UTR) variants were associated with the risk of developing PD in a large cohort of patients (n=743) and controls (n=523) from Spain. We identified a total of 12 3′UTR variants (two new). Single-nucleotide polymorphism (SNP) rs66737902 C allele was overrepresented in patients (P=0.005; odds ratio=1.47). This SNP was in linkage disequilibrium with the p.R1441G mutation, but the association remained significant among mutation-negative cases. We found a significant lower level of the LRRK2 transcript in the Substantia nigra (SN) of PD postmortem donors (n=9) who were rs66737902 C carriers (P=0.01). This SNP was predicted to affect a binding site for miR-138-2-3p. We showed that this microRNA was expressed in all the SN samples. In conclusion, we found a significant association between SNP rs66737902 and the risk of developing PD. This effect on PD risk could be explained by differences in LRRK2 transcript levels between the two alleles.

The Sp1/Egr1-tandem repeat polymorphism in the 5-lipoxygenase gene promoter is not associated with late onset Alzheimer disease.

Arachidonate 5-lipoxygenase plays an important role in the synthesis of leukotrienes. Leukotrienes are inflammatory mediators, and inflammation has been implicated in the pathogenesis of Alzheimer disease. A polymorphism in the ALOX5 promoter consisting on 3 to 6 tandem-repeats of a Sp1/Egr1 binding motif (GGGCGG)n, has been related with the amount of gene expression. To verify the association between this polymorphism and the risk for late-onset Alzheimer disease we genotyped a total of 291 patients (mean age 74±7 y) and 300 controls (mean age 73±8 y). We found alleles of 3 to 6 repeats, and allele and genotype frequencies did not differ between patients and controls. These frequencies did not differ between patients according to the APOE genotype (ϵ34+ϵ44 vs. ϵ23+ϵ33). Together, our results indicate that the Sp1/Egr1-repeat polymorphism in the ALOX5 promoter is not a genetic marker for the risk of developing late-onset Alzheimer disease.