Reepithelialization of the uterine surface arises from endometrial glands: evidence from a functional mouse model of breakdown and repair.

The human endometrium is highly regenerative undergoing monthly cycles of growth and regression. Endometrial repair after menses is a critical component of the cycle; however, little is understood about the mechanisms behind this rapid process. Adult stem/progenitor cells identified in human and mouse endometrium may be responsible for its remarkable regenerative capacity; however, a functional role for stem/progenitor cells in menstruation is yet to be established. This study aimed to identify label retaining cells as candidate epithelial stem or progenitor cells involved in the rapid reepithelization of the uterine surface in our functional mouse model of endometrial breakdown and repair. Adult mice were pulse labeled with bromodeoxyuridine before endometrial breakdown and repair was induced. Throughout endometrial breakdown and repair, very rapid dilution of bromodeoxyuridine label was observed in the luminal epithelium, whereas label within the glandular epithelium remained constant. Importantly, glandular epithelial cells were shown to proliferate selectively in response to endometrial repair, and the majority strongly expressed estrogen receptor-alpha at this time. This is the first study to demonstrate a functionally diverse response during endometrial repair from the anatomically connected luminal and glandular epithelium and highlights the likelihood that the endometrial glands are the residence of epithelial progenitor cells contributing to reepithelialization of the uterine surface after menses.