Identification and Characterisation of Endometrial Stem/Progenitor Cells

Background: To identify specific markers of functional humanand mouse endometrial epithelial progenitor cells (eEPs) andmesenchymal stem cells (eMSCs) and determine their identityand location. Our hypothesis was that endometrial stem/progenitorcells would be located in the basalis layer of humanendometrium not shed during menstruation, which is responsiblefor providing cells to repair and regenerate endometriumeach month.Materials and Methods: Hysterectomy tissue was obtainedfrom women who had not been taking hormones for ۳ months.Single cell suspensions were prepared by enzyme digestion andmechanical means. A candidate approach to identify human eMSCsusing MSC and perivascular markers was used. For humanendometrial eEPs, gene profiling of EpCAM magnetic beadsorted pre- and post-menopausal endometrial cells was usedto identify differentially expressed adhesion molecules. Clonogenicity,serial cloning and differentiation assays were usedto assess the efficacy of candidate markers. In mice, label retentionof BrdU and a telomerase reporter mouse (mTert-GFP)were used to identify mouse endometrial eEPs and eMSCs.Results: Co-expression of CD۱۴۰b and CD۱۴۶ enriched for asmall population (۱.۵%) of clonogenic stromal cells with MSCproperties and showed their perivascular niche in the basalisand functionalis. A single perivascular marker, SUSD۲ comprised۴% of endometrial stromal cells with MSC propertiesand reconstituted stromal tissue in vivo. Of ۲۲ differentially expressedadhesion molecules, ۱۱ were upregulated in basalis-likepostmenopausal endometrial epithelial cells, including CDH۲and CDH۳. Functional assays showed that clonogenic, selfrenewingand organoid-forming epithelial cells were N-cadherin+,but not P-cadherin+ cells. N-cadherin+ cells were located inthe gland bases in the basalis. In mice, epithelial label retainingcells (LRC) were located in the luminal epithelium and initiatedendometrial regeneration in response to estrogen in estrogendepleted mice. Stromal LRC were near the endometrial-myometrialjunction around some vessels. MTert-GFP+ cells werepredominantly leukocytes, but a small population of luminalepithelial cells and endothelial cells were identified.Conclusions: Human and mouse endometrium contains smallpopulations of functional epithelial progenitor cells and MSC.Our markers for these stem/progenitor cells allows their quantificationin tissue and menstrual blood to assess their role inendometrial proliferative disorders and their purification forfurther characterisation or use in cell-based therapies.