Role of stromal and epithelial estrogen receptors in vaginal epithelial proliferation, stratification, and cornification

Estradiol 17-beta (E-2) induces epithelial proliferation, stratification, and cornification in vaginal epithelium. Our aim was to determine the respective roles of epithelial and stromal estrogen receptor-alpha (ER alpha) in these E-2-induced events. Vaginal epithelium (E) and stroma (S) from adult ER alpha knockout (ko) and wild-type (wt) neonatal Balb/c mice were enzymatically separated and used to produce four types of tissue recombinants in which epithelium, stroma, or both lack functional ERa. Tissue recombinants were grafted into female nude mice, which were subsequently ovariectomized and treated with oil or E,. In response to E, treatment, grafts prepared with wt-S (wt-S + wt-E and wt-S + ko-E) showed similar large increases in epithelial labeling index, indicating that E, stimulated epithelial proliferation despite a lack of epithelial ERa in wt-S + ko-E tissue recombinants. Conversely, in tissue recombinants prepared with ko-S (ko-S + wt-E and ko-S + ko-E), epithelial labeling index remained at baseline levels after E-2 or oil treatment, even though epithelial ER alpha were detected in ko-S + wt-E grafts. Epithelial cornification was present in wt-S + wt-E grafts from E-2-treated hosts, whereas epithelium in all other tissue recombinants failed to cornify. Grafts composed of wt-S + wt-E from E-2-treated hosts had highly stratified epithelium, whereas epithelial thickness was reduced almost 60% in wt-S + ko-E tissue recombinants grown in E-2-treated hosts and was atrophic in all other tissue recombinants. In addition, cytokeratin 10, a marker of epithelial differentiation, was strongly expressed in wt-S + wt-E tissue recombinants grown in E-2-treated hosts but was markedly reduced or absent in all other tissue recombinants. These results indicate that E-2-induced vaginal epithelial proliferation is mediated indirectly through stromal ER alpha, consistent with our recent findings in uterus. Conversely, both epithelial and stromal ER alpha are required for E-2 induced cornification and normal epithelial stratification. These are the first known functions attributed to epithelial ER alpha in vivo and the first time any epithelial response to E-2 has been shown to involve both stromal and epithelial ER alpha.