Abstract 049: Promoter Methylation of Glucocorticoid Receptor Gene Is Associated with Subclinical Cardiovascular Disease: a Monozygotic Twin Study

Abstract

Background: Epigenetic mechanisms are increasingly being recognized as a key factor in the pathogenesis of cardiovascular disease (CVD). Endothelial dysfunction assessed by brachial artery flow-mediated dilation (FMD) is a marker for early atherosclerotic CVD, a predictor of future cardiovascular events. The glucocorticoid receptor gene (NR3C1) regulates a variety of biological processes including cardiovascular, metabolic, immunologic, and homeostatic functions. Genetic polymorphisms in NR3C1 have been associated with atherosclerosis and several cardiometabolic risk factors. However, no study has yet investigated the potential role of NR3C1 promoter methylation in atherosclerosis. Objective: To examine the potential association between NR3C1 promoter methylation and FMD in a monozygotic (MZ) twin sample. Method: We studied 84 male-male monozygotic twin pairs drawn from the Vietnam Era Twin Registry. These twin pairs were recruited by the Emory Twins Heart Study, which investigates psychological, behavioral and biological risk factors for subclinical cardiovascular disease using a twin design. The twins were free of a self-reported previous diagnosis of cardiovascular disease at the time of enrollment. Brachial artery FMD was measured by ultrasound. The methylation levels of 25 CpG residues in the NR3C1 promoter region in peripheral blood leukocytes was quantified by bisulfite pyrosequencing. The association between DNA methylation variation and FMD was examined using nonparametric regression by regressing the intra-pair difference in FMD on the intra-pair difference in DNA methylation level at each CpG site, separately, adjusting for potential confounders including age, smoking, body mass index (BMI), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), blood glucose level and systolic blood pressure. Multiple testing was controlled by the false discovery rate. Results: Mean methylation level of the 25 CpG sites encompassing the NR3C1 promoter region was 2.1%. Methylation levels at 7 of the 25 CpG residues were significantly associated with FMD. On average, a 10% increase in mean methylation was associated with a 0.13 increase in FMD (95% CI: 0.09–0.17; p <0.0001) after controlling for confounding factors. Conclusion: Increased promoter methylation of NR3C1 is significantly associated with decreased risk for subclinical atherosclerosis assessed by FMD. Given the critical role of this gene in regulating hypothalamic-pituitary-adrenal axis (HPA) function, it is possible that aberrant promoter methylation of this gene may affect atherogenesis through its influence on the HPA system, a mechanism known to be involved in cardiovascular disease.