Center for Perinatal Biology, Division of Pharmacology, Department of Basic Sciences, Loma Linda University, School of Medicine, Loma Linda, CA 92350, USA.
Hypertension. 2012 Sep;60(3):697-704. doi: 10.1161/HYPERTENSIONAHA.112.198242. Epub 2012 Jul 9.
Estrogen receptor-α (ERα) plays a key role in the adaptation of increased uterine blood flow in pregnancy. Chronic hypoxia is a common stress to maternal cardiovascular homeostasis and causes increased risk of preeclampsia. Studies in pregnant sheep demonstrated that hypoxia during gestation downregulated ERα gene expression in uterine arteries. The present study tested the hypothesis that hypoxia causes epigenetic repression of the ERα gene in uterine arteries via heightened promoter methylation. Ovine ERα promoter of 2035 bp spanning from -2000 to +35 of the transcription start site was cloned. No estrogen or hypoxia-inducible factor response elements were found at the promoter. Two transcription factor binding sites, USF(-15) and Sp1(-520), containing CpG dinucleotides were identified, which had significant effects on the promoter activity. The USF element binds transcription factors USF1 and USF2, and the Sp1 element binds Sp1, as well as ERα through Sp1. Deletion of the Sp1 site abrogated 17β-estradiol-induced increase in the promoter activity. In normoxic control sheep, CpG methylation at the Sp1 but not the USF site was significantly decreased in uterine arteries of pregnant as compared with nonpregnant animals. In pregnant sheep exposed to long-term high-altitude hypoxia, CpG methylation at both Sp1 and USF sites in uterine arteries was significantly increased. Methylation inhibited transcription factor binding and the promoter activity. The results provide evidence of hypoxia causing heightened promoter methylation and resultant ERα gene repression in uterine arteries and suggest new insights of molecular mechanisms linking gestational hypoxia to aberrant uteroplacental circulation and increased risk of preeclampsia.
雌激素受体-α（ERα）在妊娠期间增加子宫血流的适应中起着关键作用。慢性缺氧是母体心血管稳态的常见应激源，并增加子痫前期的风险。在妊娠绵羊中的研究表明，妊娠期间的缺氧会下调子宫动脉中的 ERα 基因表达。本研究检验了这样一个假设，即缺氧通过增强启动子甲基化导致子宫动脉中 ERα 基因的表观遗传抑制。克隆了跨越转录起始位点+35 至-2000 的 2035bp 的绵羊 ERα 启动子。在启动子上未发现雌激素或缺氧诱导因子反应元件。鉴定出两个转录因子结合位点，USF（-15）和 Sp1（-520），含有 CpG 二核苷酸，对启动子活性有显著影响。USF 元件结合转录因子 USF1 和 USF2，而 Sp1 元件结合 Sp1 以及通过 Sp1 结合 ERα。Sp1 位点的缺失消除了 17β-雌二醇诱导的启动子活性增加。在正常氧合对照绵羊中，与非妊娠动物相比，妊娠期间子宫动脉中 Sp1 而非 USF 位点的 CpG 甲基化显著降低。在长期高海拔缺氧暴露的妊娠绵羊中，子宫动脉中 Sp1 和 USF 位点的 CpG 甲基化均显著增加。甲基化抑制转录因子结合和启动子活性。这些结果提供了证据表明缺氧导致子宫动脉中启动子甲基化增加和 ERα 基因抑制，并提示了与妊娠缺氧相关的异常胎盘循环和子痫前期风险增加的分子机制的新见解。
