Global DNA methylation analysis of human atherosclerotic plaques reveals extensive genomic hypomethylation and reactivation at imprinted locus 14q32 involving induction of a miRNA cluster

Aims We conducted a genome-wide analysis to identify differentially methylated genes in atherosclerotic lesions. Methods DNA methylation at promoters, exons and introns was identified by massive parallel sequencing. Gene expression was analysed by microarrays, qPCR, immunohistochemistry and western blots. Results Globally, hypomethylation of chromosomal DNA predominates in atherosclerotic plaques and two-thirds of genes showing over 2.5-fold differential in DNA methylation are up-regulated in comparison to healthy mammary arteries. The imprinted chromatin locus 14q32 was identified for the first time as an extensively hypomethylated area in atherosclerosis with highly induced expression of miR127, -136, -410, -431, -432, -433 and capillary formation-associated gene RTL1. The top 100 list of hypomethylated promoters exhibited over 1000-fold enrichment for miRNAs, many of which mapped to locus 14q32. Unexpectedly, also gene body hypermethylation was found to correlate with stimulated mRNA expression. Conclusion Significant changes in genomic methylation were identified in atherosclerotic lesions. The most prominent gene cluster activated via hypomethylation was detected at imprinted chromosomal locus 14q32 with several clustered miRNAs that were up-regulated. These results suggest that epigenetic changes are involved in atherogenesis and may offer new potential therapeutic targets for vascular diseases.