Drastic shift from positive to negative estrogen effect on bone morphogenetic protein signaling in pulmonary arterial endothelial cells under hypoxia.

Background: To investigate the possible role of sex hormones in the pathogenesis of pulmonary arterial hypertension (PAH), the effect of beta-estradiol (E2) on bone morphogenetic protein (BMP) signaling, a key signaling pathway involved in PAH, was studied in human pulmonary arterial endothelial cells (HPAEC). Methods and Results: BMP signaling molecules, including BMP receptor, Smad1/5/8 and Id1, were studied in HPAEC under 1% O-2 (hypoxia) and 21% O-2 (normoxia) as well as the effect of hypoxia-inducible factor (HIF)-1 alpha expression in the presence of E2 on BMP signaling. The effects of an estrogen receptor(ER) antagonist (ICI 182,780) and cycloheximide, and the interaction of ER with Smad or HIF-1 alpha were also studied. In the presence of E2, BMP signaling was augmented under normoxia but suppressed under hypoxia. HIF-1 alpha accumulation suppressed BMP signaling, whereas HIF-1 alpha inhibition augmented signaling. These effects were cancelled by 101 182,780. Moreover, binding between ER, HIF-1 alpha and phosphorylated (p)-Smad1/5/8 proteins occurred only under hypoxia. On inhibition of de novo synthesis with cycloheximide, however, p-Smad1/5/8 expression was suppressed only under normoxia. Conclusions: The effects of E2 on BMP signaling in HPAEC altered depending on O-2 concentration and different mechanisms may be involved. BMP and sex hormones may play an important role in PAH development.