ABSTRACT
17ß-Estradiol (E2) attenuates hypoxia-induced pulmonary hypertension (HPH) through estrogen receptor (ER)-dependent effects, including inhibition of hypoxia-induced endothelial cell proliferation; however, the mechanisms responsible for this remain unknown. We hypothesized that the protective effects of E2 in HPH are mediated through hypoxia-inducible factor 1α (HIF-1α)-dependent increases in ERß expression. Sprague-Dawley rats and ERα or ERß knockout mice were exposed to hypobaric hypoxia for 2-3 weeks. The effects of hypoxia were also studied in primary rat or human pulmonary artery endothelial cells (PAECs). Hypoxia increased expression of ERß, but not ERα, in lungs from HPH rats as well as in rat and human PAECs. ERß mRNA time dependently increased in PAECs exposed to hypoxia. Normoxic HIF-1α/HIF-2α stabilization increased PAEC ERß, whereas HIF-1α knockdown decreased ERß abundance in hypoxic PAECs. In turn, ERß knockdown in hypoxic PAECs increased HIF-2α expression, suggesting a hypoxia-sensitive feedback mechanism. ERß knockdown in hypoxic PAECs also decreased expression of the HIF inhibitor prolyl hydroxylase 2 (PHD2), whereas ERß activation increased PHD2 and decreased both HIF-1α and HIF-2α, suggesting that ERß regulates the PHD2/HIF-1α/HIF-2α axis during hypoxia. Whereas hypoxic wild-type or ERα knockout mice treated with E2 demonstrated less pulmonary vascular remodeling and decreased HIF-1α after hypoxia compared with untreated hypoxic mice, ERß knockout mice exhibited increased HIF-2α and an attenuated response to E2 during hypoxia. Taken together, our results demonstrate a novel and potentially therapeutically targetable mechanism whereby hypoxia, via HIF-1α, increases ERß expression and the E2-ERß axis targets PHD2, HIF-1α, and HIF-2α to attenuate HPH development.
