Different Effects of Homocysteine and Oxidized Low Density Lipoprotein on Methylation Status in the Promoter Region of the Estrogen Receptor α Gene

Abstract

We investigated the effects of homocysteine (Hcy) and oxidized low density lipoprotein (ox-LDL) on DNA methylation in the promoter region of the estrogen receptor alpha (ERalpha) gene, and its potential mechanism in the pathogenesis of atherosclerosis. Cultured smooth muscle cells (SMCs) of humans were treated by Hcy and ox-LDL with different concentrations for different periods of time. The DNA methylation status was assayed by nested methylation-specific polymerase chain reaction, the lipids that accumulated in the SMCs and foam cell formations were examined with Oil red O staining. The proliferation of SMCs was assayed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method. The results showed that ox-LDL in moderate concentrations (10-40 mg/L) induced de novo methylation in the promoter region of the ERalpha gene of SMCs. However, high concentrations (50 mg/L) of ox-LDL, resulted in demethylation of ERalpha. The Hcy treatment resulted in de novo methylation in the promoter region of the ERalpha gene with a concentration- and treating time-dependent manner, and a dose-dependent promoting effect on SMC proliferation. These data indicated that the two risk factors for atherosclerosis had the function of inducing de novo methylation in the promoter region of the ERalpha gene of SMCs. However, high concentrations (50 mg/L) of ox-LDL induced demethylation, indicating that different risk factors of atherosclerosis with different potency might cause different aberrant methylation patterns in the promoter region of the ERalpha gene. The atherogenic mechanism of Hcy might involve the hypermethylation of the ERalpha gene, leading to the proliferation of SMCs in atherosclerotic lesions.