Objective:
One of the first clinically detectable changes in the vasculature during atherogenesis is the accumulation of cholesterol within the vessel wall. Hypercholesterolemia is characterized by dysfunctional endothelial-dependent vessel relaxation and impaired NOS3 function. Since DNA methylation at gene promoter regions strongly suppresses gene expression, we postulated that high-fat/high-cholesterol diet suppresses endothelial NOS3 through promoter DNA methylation.
Methods:
Domestic male pigs were fed control diet (CD) or isocaloric high fat and high cholesterol diet (HC; 12% fat and 1.5% cholesterol) for 2, 4, 8 or 12 weeks prior to tissue collection. Furthermore, to determine the effects of risk factor withdrawal, an additional group of swine received HC for 12 weeks and then CD for 8 weeks; a control group received HC continuously for 20 weeks. Endothelial cells were harvested from common carotid aorta. In parallel in vitro studies, cultured human aortic endothelial cells (HAEC) were treated with human LDL, GW3956 (LXR agonist) and RG108 (DNA methyltransferase [DNMT] inhibitor). In cells from both sources, DNA methylation at the NOS3 promoter was measured using methylation specific pyro sequencing, and endothelial gene expression was measured using RT PCR.
Results:
HC diet increased plasma cholesterol level from 75 mg/dl on CD to a plateau of about 540 mg/dl within 2 weeks. Endothelial NOS3 expression was significantly reduced (71±9 % of CD) after 4 weeks of HC, a level sustained at subsequent time points. Withdrawal of HC for 8 weeks did not recover NOS3 expression. After 12-week HC, the NOS3 promoter was hypermethylated. Withdrawal of HC did not reverse NOS3 promoter methylation. In vitro treatment of HAEC with human LDL (200 mg/dl total cholesterol) or GW3956 (5μM) suppressed NOS3 mRNA to 50% and 30% respectively, suggesting that LXR/RXR is involved in suppression of NOS3. Nitric oxide production was consistently suppressed by GW3959. Both could be reversed through inhibition of DNMTs by RG108.
Conclusions:
DNA methylation and LXR/RXR pathway can mediate the HC-suppression of endothelial NOS3. The study identifies novel pharmaceutical targets in treating endothelial dysfunction. Crosstalk between these pathways is under investigation.
Chlamydia pneumoniae and Hyperlipidemia Are Co-Risk Factors for Atherosclerosis: Infection Prior to Induction of Hyperlipidemia Does Not Accelerate Development of Atherosclerotic Lesions in C57BL/6J Mice
