Erythropoietin and erythropoietin receptor expression in human endometrium throughout the menstrual cycle

Erythropoietin (Epo) is an important regulator of erythropoiesis. Recent studies have demonstrated non-classical sites of Epo and Epo-receptor (Epo-R) expression, suggesting new physiological roles unrelated to erythropoiesis. Other studies have shown that the mouse uterus expresses Epo and its receptor, and produces Epo protein in an estrogen-dependent manner. We therefore hypothesized that Epo is one of the growth factors involved in cyclic endometrial changes. We determined Epo and Epo-R mRNA expression in isolated endometrial epithelial and stromal cells using RT-PCR. While both Epo and Epo-R were detected in all samples of isolated epithelial cells analysed throughout the menstrual cycle, neither one was detected in isolated stromal cells. In addition, using quantitative real-time RT-PCR with the TaqMan detection system, we showed that isolated epithelial cells had higher Epo mRNA levels in the secretory phase than in the proliferative phase. Immunohistochemical analyses revealed that Epo and Epo-R protein expression in glandular epithelial cells was increased during the mid-proliferative phase and was maintained during the late proliferative and the early, mid- and late secretory phases. These findings suggest that Epo may be involved in cyclic proliferation and differentiation of endometrial glandular epithelial cells, acting in an autocrine manner. In addition, we also hypothesize that ovarian steroids may stimulate Epo production in human endometrial glandular epithelial cells.