Résumé
The recent discovery of a new isoform of estrogen receptor (ER) beta has prompted the reexamination of estrogen action on target organs. Here, we describe the endometrial expression of human ER beta and compare its distribution with that of ER alpha in the endometrial functional zone. Using immunocytochemistry with well characterized polyclonal antibodies against ER beta, we have detected specific ER beta expression in all endometrial compartments (glandular, stromal, and vascular); the specificity of the immunostaining is confirmed by lack of staining of the uterine sections with anti-ER beta antibodies previously incubated with peptide preparation. The highest levels of ER beta expression are observed in epithelial cells during the periovulatory period (days 14 and 15), as well as in stromal cells and cells of the Vascular wall in the late-secretory phase; both smooth muscle cells and endothelial cells express ER beta, as deduced from immunocytochemistry and RT-PCR analysis. ER beta staining is usually low compared with that of ER alpha, except at days 24-26. The presence of ER beta in decidualized stromal cells is deduced from immunocytochemistry using antismooth alpha -actin and anti-ER beta antibodies or from RT-PCR analysis of ER beta and insulin-like growth factor-BP transcripts in the same cells; the presence of ER beta -positive stromal cells located close to vascular smooth muscle cells during this period suggests some specific role of this receptor during decidualization. ER alpha is also present in the cells of the endometrial vascular wall, in addition to the nuclei of glandular epithelial and stromal cells. Vascular ER alpha expression is highest during the periovulatory period, suggesting a regulation by estradiol, and a role in vascular function. Moreover, different Variations of ER beta and ER alpha in arterioles might have implications for the modulation of vascular function, possibly of vascular tone, during the menstrual cycle. Finally, these data suggest that ER beta may have important roles in endometrial function, in addition to the well known role of ER alpha in endometrial proliferation and differentiation.