Influence of 2-Methoxyestradiol and Sex on Hypoxia-Induced Pulmonary Hypertension and Hypoxia-Inducible Factor-1-α

Background-Women are at greater risk of developing pulmonary arterial hypertension, with estrogen and its downstream metabolites playing a potential role in the pathogenesis of the disease. Hypoxia-inducible factor-1-alpha (HIF1 alpha) is a pro-proliferative mediator and may be involved in the development of human pulmonary arterial hypertension. The estrogen metabolite 2-methoxyestradiol (2ME2) has antiproliferative properties and is also an inhibitor of HIF1 alpha. Here, we examine sex differences in HIF1 alpha signaling in the rat and human pulmonary circulation and determine if 2ME2 can inhibit HIF1 alpha in vivo and in vitro. Methods and Results-HIF1 alpha signaling was assessed in male and female distal human pulmonary artery smooth muscle cells (hPASMCs), and the effects of 2ME2 were also studied in female hPASMCs. The in vivo effects of 2ME2 in the chronic hypoxic rat (male and female) model of pulmonary hypertension were also determined. Basal HIF1 alpha protein expression was higher in female hPASMCs compared with male. Both factor-inhibiting HIF and prolyl hydroxylase-2 (hydroxylates HIF leading to proteosomal degradation) protein levels were significantly lower in female hPASMCs when compared with males. In vivo, 2ME2 ablated hypoxia-induced pulmonary hypertension in male and female rats while decreasing protein expression of HIF1 alpha. 2ME2 reduced proliferation in hPASMCs and reduced basal protein expression of HIF1 alpha. Furthermore, 2ME2 caused apoptosis and significant disruption to the microtubule network. Conclusions-Higher basal HIF1 alpha in female hPASMCs may increase susceptibility to developing pulmonary arterial hypertension. These data also demonstrate that the antiproliferative and therapeutic effects of 2ME2 in pulmonary hypertension may involve inhibition of HIF1 alpha and/or microtubular disruption in PASMCs.