Estrogen Receptor β, But Not Estrogen Receptor α, Is Present in the Vascular Endothelium of the Human and Nonhuman Primate Endometrium1

Estrogen action is dependent upon the presence of specific ligand-activated receptors in target tissues. The aim of the present experiments was to compare the spatial and temporal pattern of expression of estrogen receptor β (ERβ) with that of ERα in full thickness endometrial samples (from the superficial to the basal zone) obtained from both women and rhesus macaques. Immunohistochemical localization with specific antibodies revealed that ERα and ERβ were both expressed in nuclei of the glands and stroma. Consistent with previous studies, expression of ERα declined in the glands and stroma of the functionalis during the secretory phase. The luminal epithelium also displayed positive immunoreactivity for ERβ. Expression of ERβ declined in glandular cell nuclei, but not stroma, within the functionalis during the late secretory phase. Levels of expression of ERα and ERβ in all cellular compartments remained unchanged in the basalis. Both receptor subtypes were detected on Western blots using proteins extracted from uterine samples obtained throughout the menstrual cycle. There was a striking contrast between the pattern of expression of ERα and ERβ in the vascular endothelium and the perivascular cells surrounding endometrial blood vessels; only ERβ was present in the endothelial cell population, although both forms of ER were expressed in perivascular cells. We conclude that estrogen action(s) within the vascular endothelium in the endometrium may be mediated via direct binding to the ERβ isoform and that these cells could therefore be a target for agonists or antagonists that selectively target the β form of the ER.