Folate deficiency exacerbates apoptosis by inducing hypomethylation and resultant overexpression of DR4 together with altering DNMTs in Alzheimer's disease.

Abstract

This study was to evaluate patterns of gene expression and promoter methylation of DR4 from peripheral circulating blood lymphocytes of AD patients and folate-deficiency medium cultured neuroblast cells, and also expression levels of DNMT1, DNMT3a, and MECP2. Blood samples of 25 pairs of AD patients and age- and sex-matched controls were collected. SH-SY5Y cells were cultured with folate-deficiency medium. Bisulfite cloning coupled with sequencing was employed to analyze methylation levels of DR4 gene promoters, and quantitative real time PCR (qRT-PCR) was used to detect gene expression levels of DR4, and also DNA methyltransferase 1 (DNMT1), DNA methyltransferase 3a (DNMT3a) and methyl CpG binding protein 2 (MECP2). Folate concentration was calculated in serum of blood samples. 3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyl tetrazolium (MTT) assay was used to analyze cell viability. The results showed that, the promoter of DR4 was hypomethylated in AD patients and cells cultured in folate-deficiency medium and had site-specific changes (P < 0.05), and these sites were mostly at or nearby some key transcription factor binding sites. Accordance with the hypomethylation, increased expression level of DR4 was observed (P < 0.05). DNMT1 and DNMT3a mRNA level were elevated (P < 0.05) in AD patients and folate deficient medium cultured cells compared with controls (P < 0.05), together with lower folate concentration in AD. MTT assay showed that folate deficiency inhibited cell growth. In summary, folate deficiency can induce apoptosis by increasing DR4 expression with DNA promoter hypomethylation in AD, together with upregulating DNMTs expression, which may be associated with folate deficiency-induced DNA damage.