Jinfeng Li

Male-Specific Association between Dopamine Receptor D4 Gene Methylation and Schizophrenia

Objective The goal of our study was to investigate whether DRD4 gene DNA methylation played an important role in the susceptibility of Han Chinese SCZ. Methods Using the bisulphite pyrosequencing technology, DNA methylation levels of 6 CpG dinucleotides in DRD4 CpG island were measured among 30 paranoid SCZ patients, 30 undifferentiated SCZ patients, and 30 age- and gender-matched healthy controls. Results Strong correlation was observed among the six CpG sites (r>0.5, P<0.01), thus average methylation levels were applied thereafter. Our results indicated that there was a significant association between DRD4 methylation and the risk of SCZ (P = 0.003), although there was no significant difference in DRD4 methylation between the two SCZ subtypes (P = 0.670). A breakdown analysis by gender showed that the significant association of DRD4 methylation and SCZ was driven by males (P<0.001) but not by females (P = 0.835). DRD4 methylation was significantly associated with p300 in male SCZ patients (r = −0.543, P = 0.005) but not in female SCZ patients (r = 0.110, P = 0.599). Moreover, receiver operating characteristic (ROC) curves showed DRD4 methylation was able to predict the status of SCZ in males [area under curve (AUC) = 0.832, P = 0.002] but not in females (AUC = 0.483, P = 0.876). Finally, a further expression experiment showed that DRD4 methylation in the gene body was positively associated with gene expression, although the exact mechanism of gene regulation remained unknown for this interesting DRD4 methylation. Conclusion The gender disparity in the DRD4 DNA methylation provides novel insights into the pathogenesis of SCZ.

Elevation of peripheral BDNF promoter methylation links to the risk of Alzheimer's disease.

Brain derived neurotrophic factor (BDNF) has been known to play an important role in various mental disorders or diseases such as Alzheimers disease (AD). The aim of our study was to assess whether BDNF promoter methylation in peripheral blood was able to predict the risk of AD. A total of 44 AD patients and 62 age- and gender-matched controls were recruited in the current case-control study. Using the bisulphite pyrosequencing technology, we evaluated four CpG sites in the promoter of the BDNF. Our results showed that BDNF methylation was significantly higher in AD cases than in the controls (CpG1: p = 10.021; CpG2: p = 0.002; CpG3: p = 0.007; CpG4: p = 0.005; average methylation: p = 0.004). In addition, BDNF promoter methylation was shown to be significantly correlated with the levels of alkaline phosphatase (ALP), glucose, Lp(a), ApoE and ApoA in males (ALP: r = −0.308, p = 0.042; glucose: r = −0.383, p = 0.010; Lp(a): r = 0.333, p = 0.027; ApoE: r = −0.345, p = 0.032;), ApoA levels in females (r = 0.362, p = 0.033), and C Reactive Protein (CRP) levels in both genders (males: r = −0.373, p = 0.016; females: r = −0.399, p = 0.021). Our work suggested that peripheral BDNF promoter methylation might be a diagnostic marker of AD risk, although its underlying function remains to be elaborated in the future.

Body Mass Index and Risk of Parkinson’s Disease: A Dose-Response Meta-Analysis of Prospective Studies

Background A number of epidemiologic studies examining the relationship between body mass index (BMI) and the future occurrence of Parkinson’s disease (PD) reported largely inconsistent findings. We conducted a dose-response meta-analysis of prospective studies to clarify this association. Methods Eligible prospective studies were identified by a search of PubMed and by checking the references of related publications. The generalized least squares trend estimation was employed to compute study-specific relative risks (RR) and 95% confidence intervals (CI) for an increase in BMI of 5 kg/m2, and the random-effects model was used to compute summary RR and 95% CI. Results A total of 10 prospective studies were included in the final analysis. An increase in BMI of 5 kg/m2 was not associated with PD risk, with a summary RR of 1.00 (95% CI = 0.89-1.12). Results of subgroup analysis found similar results except for a week positive association in studies that adjusted for alcohol consumption (RR = 1.13, 95% CI = 0.99-1.29), and a week inverse association in studies that did not (RR = 0.90, 95% CI = 0.78-1.04). In a separate meta-analysis, no significant association between overweight (25 kg/m2 ≤ BMI ≤29.9 kg/m2), obesity (BMI≥30 kg/m2) or excess weight (BMI≥25 kg/m2) and PD risk was observed. Conclusion This meta-analysis does not support the notion that higher BMI materially increases PD risk. However, a week positive BMI-PD association that may be masked by confounders still cannot be excluded, and future prospective studies with a good control for potential confounding factors are needed.

OPRK1 promoter hypermethylation increases the risk of Alzheimer’s disease

As a member of the opioid family, κ-opioid receptors play important role in cognitive and learning functions. The purpose of this study was to evaluate the association of OPRK1 promoter methylation with Alzheimers disease (AD). OPRK1 DNA methylation levels of 48 cases and 58 well matched controls were measured using the bisulphite pyrosequencing technology. Our results showed that there was a significant correlation between three CpG sites on the OPRK1 promoter region (r>=0.715, p<0.001). Thus, the mean methylation value of the three CpG sites was used for the case-control comparison. And our results showed there was a significantly higher OPRK1 promoter methylation in AD cases than in controls (p=0.006, adjusted p=0.012). Subsequent luciferase reporter assay showed the CpGs containing fragment of OPRK1 promoter significantly increased the expression of reporter gene (Fold=2.248, p=0.0235). In summary, our results suggested that OPRK1 promoter hypermethylation might increase the risk of AD through its regulation on the gene expression of OPRK1.

Elevated OPRD1 promoter methylation in Alzheimer’s disease patients

Aberrant DNA methylation has been observed in the patients with Alzheimer’s disease (AD), a common neurodegenerative disorder in the elderly. OPRD1 encodes the delta opioid receptor, a member of the opioid family of G-protein-coupled receptors. In the current study, we compare the DNA methylation levels of OPRD1 promoter CpG sites (CpG1, CpG2, and CpG3) between 51 AD cases and 63 controls using the bisulfite pyrosequencing technology. Our results show that significantly higher CpG3 methylation is found in AD cases than controls. Significant associations are found between several biochemical parameters (including HDL-C and ALP) and CpG3 methylation. Subsequent luciferase reporter gene assay shows that DNA fragment containing the three OPRD1 promoter CpGs is able to regulate gene expression. In summary, our results suggest that OPRD1 promoter hypermethylation is associated with the risk of AD.

DNA methylation patterns of protein-coding genes and long non-coding RNAs in males with schizophrenia

Schizophrenia (SCZ) is one of the most complex mental illnesses affecting ~1% of the population worldwide. SCZ pathogenesis is considered to be a result of genetic as well as epigenetic alterations. Previous studies have aimed to identify the causative genes of SCZ. However, DNA methylation of long non-coding RNAs (lncRNAs) involved in SCZ has not been fully elucidated. In the present study, a comprehensive genome-wide analysis of DNA methylation was conducted using samples from two male patients with paranoid and undifferentiated SCZ, respectively. Methyl-CpG binding domain protein-enriched genome sequencing was used. In the two patients with paranoid and undifferentiated SCZ, 1,397 and 1,437 peaks were identified, respectively. Bioinformatic analysis demonstrated that peaks were enriched in protein-coding genes, which exhibited nervous system and brain functions. A number of these peaks in gene promoter regions may affect gene expression and, therefore, influence SCZ-associated pathways. Furthermore, 7 and 20 lncRNAs, respectively, in the Refseq database were hypermethylated. According to the lncRNA dataset in the NONCODE database, ~30% of intergenic peaks overlapped with novel lncRNA loci. The results of the present study demonstrated that aberrant hypermethylation of lncRNA genes may be an important epigenetic factor associated with SCZ. However, further studies using larger sample sizes are required.