The pregnancy-augmented uterine vasodilation is linked to increased AT₂R (angiotensin type-2 receptor) that mediates the vasodilatory effects of angiotensin II. However, the mechanisms controlling AT₂R expression during pregnancy remain unclear. Estrogens are known to play a role in vascular adaptations during pregnancy. We hypothesized that estrogen stimulates uterine artery AT₂R expression via ER (estrogen receptor)-β-dependent transcription in a pregnancy-specific endothelium-dependent manner. Plasma estradiol levels increased and peaked in late pregnancy and returned to prepregnant levels post-partum, correlating with uterine artery AT₂R and ERβ upregulation. Estradiol stimulated AT₂R mRNA expression in endothelium-intact but not endothelium-denuded late pregnant and nonpregnant rat uterine artery ex vivo. Consistently, estradiol stimulated AT₂R mRNA expression in late pregnant but not nonpregnant primary human uterine artery endothelial cells in vitro, which was abolished by ER antagonist ICI 182,780. Higher ERα protein bound to ER-responsive elements in AT₂R promoter in the nonpregnant arteries whereas higher ERβ bound in the pregnant state. ERα protein levels were similar but higher ERβ protein levels were expressed in pregnant versus nonpregnant human uterine artery endothelial cells. Estradiol stimulation recruited ERα to the AT₂R promoter in the nonpregnant state and ERβ to the AT₂R promoter in pregnancy; however, only ERβ recruitment mediated transactivation of the AT₂R reporter gene in pregnant human uterine artery endothelial cells. Estradiol-induced AT₂R expression was abolished by the specific ERβ (not ERα) antagonist 4-[2-Phenyl-5,7-bis(trifluoromethyl)pyrazolo[1,5-a]pyrimidin-3-yl]phenol (PHTPP) and mimicked by the specific ERβ (not ERα) agonist 2,3-bis(4-Hydroxyphenyl)-propionitrile (DPN) in pregnant human uterine artery endothelial cells in vitro. This study demonstrates a novel role of pregnancy-augmented ERβ in AT₂R upregulation in the uterine artery and provides new insights into the mechanisms underlying uterine vascular adaptation to pregnancy.

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