Hypoxia Represses ER-α Expression and Inhibits Estrogen-Induced Regulation of Ca2+-Activated K+ Channel Activity and Myogenic Tone in Ovine Uterine Arteries
Causal Role of DNA Methylation
Previous in vivo study demonstrated that chronic hypoxia during gestation was associated with estrogen receptor-α (ER-α) gene repression in ovine uterine arteries. Yet, it remains undetermined whether hypoxia had a direct effect and if DNA methylation played a causal role in hypoxia-mediated ER-α gene repression. Thus, this study tested the hypothesis that prolonged hypoxia has a direct effect and increases promoter methylation resulting in ER-α gene repression and inhibition of estrogen-mediated adaptation of uterine vascular tone. Uterine arteries isolated from nonpregnant and pregnant sheep were treated ex vivo with 21.0% O2 and 10.5% O2 for 48 hours. Hypoxia significantly increased ER-α promoter methylation at both specificity protein-1 and upstream stimulatory factor binding sites, decreased specificity protein-1 and upstream stimulatory factor binding to the promoter, and suppressed ER-α expression in uterine arteries of pregnant animals. Of importance, the effects of hypoxia were blocked by a methylation inhibitor 5-aza-2′-deoxycytidine. In addition, hypoxia abrogated steroid hormone–mediated increase in ER-α expression and inhibited the hormone-induced increase in large-conductance Ca2+-activated K+ channel activity and decrease in myogenic tone in uterine arteries of nonpregnant animals, which were reversed by 5-aza-2′-deoxycytidine. The results provide novel evidence of a direct effect of hypoxia on heightened promoter methylation that plays a causal role in ER-α gene repression and ablation of steroid hormone–mediated adaptation of uterine arterial large conductance Ca2+-activated K+ channel activity and myogenic tone in pregnancy.
- Received February 3, 2015.
- Revision received March 3, 2015.
- Accepted April 23, 2015.
- © 2015 American Heart Association, Inc.