Estrogen receptor-α agonists promote angiogenesis in human myometrial microvascular endothelial cells

The relative role of the two estrogen receptors, ERα and ERβ, in mediating angiogenic responses in adult human endothelium is unknown. The aim of this study was to determine whether novel ERα-selective agonists, propyl pyrazole triol (PPT) and the tetrahydrochrysene (R,R-THC), up-regulate the expression of vascular endothelial growth factor receptor-2 (VEGFR-2), and promote VEGF-stimulated endothelial cell proliferation in primary cultures of adult female microvascular endothelial cells co-expressing endogenous ERα and ERβ. Confluent primary cultures of microvascular endothelial cells isolated from human myometrium were incubated with 17β-estradiol (1 and 10 nM), PPT (10 nM to 3 μM), or R,R-THC (10 nM to 3 μM) for 18 hours and VEGFR-2 expression measured by biotin-VEGF ₁₆₅ binding and flow cytometry. Endothelial cell proliferation was assessed in microvascular endothelial cells after incubation with 17β-estradiol (10 nM), PPT (100 nM), and R,R-THC (100 nM) for 6 days using a tetrazolium-based bioassay. Both PPT and R,R-THC increased VEGFR-2 expression on myometrial microvascular endothelial cells in a dose-dependent manner, reaching a maximum at 1 μM. Approximately 40% of myometrial microvascular endothelial cell isolates only express ERβ and do not express ERα, and in these neither PPT, R,R-THC, nor 17β-estradiol increased VEGF binding. PPT- or R,R-THC-stimulated increase in VEGF binding was significantly different between ERα ⁺ and ERα ^- microvascular endothelial cell samples (P <. 001 and P <. 05, respectively). PPT, R,R-THC, and 17β-estradiol significantly augmented VEGF-stimulated microvascular endothelial cell proliferation in ERα ⁺ (P <. 05), but not in ERα ^- samples. This angiogenic effect of 17β-estradiol on adult female microvascular endothelial cells is mediated by ERα, rather than ERβ.