Genome-wide DNA methylation analysis in permanent atrial fibrillation

Atrial fibrillation (AF) is a highly heterogeneous genetic disease; however, the pathogenesis of AF cannot be explained by genetic variants alone. DNA methylation is a heritable method of gene expression regulation, and may be a potential regulatory mechanism in AF. Therefore, in the present study, the genome-wide DNA methylation pattern in cells derived from the left atrium of patients with permanent AF (n=7) was compared with that of healthy heart donors (n=4) with a normal sinus rhythm (SR). Enriched biological functions of the differentially methylated genes were assessed. Integrated analysis of genome-wide methylation and mRNA expression profiles was performed, and reverse transcription quantitative-polymerase chain reaction (RT-qPCR) was used to determine the expression levels of four selected genes. A total of 417 differentially methylated CpG sites were identified in the fibrillating atrium (P<0.05; vertical bar beta vertical bar>0.17); the majority of which were located in gene-body and intergenic regions outside of CpG islands. Aberrantly methylated genes participated in the activation of inflammation, sodium and potassium ion transport, fibrosis and the reduction of lipid metabolism. Hypermethylation in the AF susceptible loci, paired-like homeodomain transcription factor 2 (chromosome 4q25) and coiled-coil domain containing 141 (chromosome 2q31), as well as hypomethylation in the calcium voltage-gated channel subunit alpha 1C (chromosome 12p13) locus, were identified in all patients with AF. Of the 420 upregulated and 567 downregulated genes previously identified in patients with AF relative to those with normal SR (fold-change >2.0; P <= 0.05), 12 genes were hypomethylated and eight genes were hypermethylated in each group, respectively (vertical bar beta vertical bar>0.2: P<0.05). RT-qPCR analysis of four of these genes supported the modulatory effect of DNA methylation on gene expression. These results suggest that DNA methylation-mediated regulation of gene expression may serve an important role in AF pathogenesis, and several susceptible AF CpG loci were identified which may be involved in the initiation of AF.