Uterine epithelial estrogen receptor α is dispensable for proliferation but essential for complete biological and biochemical responses

Female fertility requires estrogen to specifically stimulate estrogen receptor α (ERα)-dependent growth of the uterine epithelium in adult mice, while immature females show proliferation in both stroma and epithelium. To address the relative roles of ERα in mediating estrogen action in uterine epithelium versus stroma, a uterine epithelial-specific ERα knockout (UtEpiαERKO) mouse line was generated by crossing Esr mice with Wnt7a-Cre mice. Expression of Wnt7a directed Cre activity generated selective deletion of ERα in uterine epithelium, and female UtEpiαERKO are infertile. Herein, we demonstrate that 17β-estradiol (E₂)- induced uterine epithelial proliferation was independent of uterine epithelial ERα because DNA synthesis and up-regulation of mitogenic mediators were sustained in UtEpiαERKO uteri after E₂ treatment. IGF-1 treatment resulted in ligand-independent ER activation in both wildtype (WT) and UtEpiαERKO and mimicked the E₂ stimulatory effect on DNA synthesis in uterine epithelium. Uterine epithelial ERα was necessary to induce lactoferrin, an E₂-regulated secretory protein selectively synthesized in the uterine epithelium. However, loss of uterine epithelial ERα did not alter the E₂-dependent progesterone receptor (PR) down-regulation in epithelium. Strikingly, the uterine epithelium of UtEpiαERKO had robust evidence of apoptosis after 3 d of E₂ treatment. Therefore, we surmise that estrogen induced uterine hyperplasia involves a dispensable role for uterine epithelial ERα in the proliferative response, but ERα is required subsequent to proliferation to prevent uterine epithelial apoptosis assuring the full uterine epithelial response, illustrating the differential cellular roles for ERα in uterine tissue and its contribution during pregnancy.