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STUDY QUESTION: Is there a specific surface marker that identifies human endometrial epithelial progenitor cells with adult stem cell activity using in vitro assays? SUMMARY ANSWER: N-cadherin isolates clonogenic, self-renewing human endometrial epithelial progenitor cells with high proliferative potential that differentiate into cytokeratin(+) gland-like structures in vitro and identifies their location in some cells of gland profiles predominantly in basalis endometrium adjacent to the myometrium. @@@ WHAT IS KNOWN ALREADY: Human endometrium contains a small population of clonogenic, self-renewing epithelial cells with high proliferative potential that differentiate into large gland-like structures, but their identity and location is unknown. Stage-specific embryonic antigen-1 (SSEA-1) distinguishes the epithelium of basalis from functionalis and is a marker of human post-menopausal (Post-M) endometrial epithelium. @@@ STUDY DESIGN, SIZE, DURATION: Prospective observational study of endometrial epithelial cells obtained from hysterectomy samples taken from 50 pre-menopausal (Pre-M) and 24 Post-M women, of which 4 were from women who had taken daily estradiol valerate 2 mg/day for 8 weeks prior. @@@ PARTICIPANTS/MATERIALS, SETTING, METHODS: Gene profiling was used to identify differentially expressed surface markers between fresh EpCAM (Epithelial Cell Adhesion Molecule)-magnetic bead-selected basalis-like epithelial cells from Post-M endometrium compared with predominantly functionalis epithelial cells from Pre-M endometrium and validated by qRT-PCR. In vitro clonogenicity and self-renewal assays were used to assess the stem/progenitor cell properties of magnetic bead-sorted N-cadherin(+) and N-cadherin(-) epithelial cells. The cellular identity, location and phenotype of N-cadherin(+) cells was assessed by dual colour immunofluorescence and confocal microscopy for cytokeratin, proliferative status (Ki-67), ERa, SSEA-1, SOX9 and epithelial mesenchymal transition (EMT) markers on full thickness human endometrium. @@@ MAIN RESULTS AND THE ROLE OF CHANCE: CDH2 (N-cadherin gene) was one of 11 surface molecules highly expressed in PostM compared to Pre-M endometrial epithelial cells. N-cadherin(+) cells comprise a median 16.7% (n = 8) and 20.2% (n = 5) of Pre-M endometrial epithelial cells by flow cytometry and magnetic bead sorting, respectively. N-cadherin(+) epithelial cells from Pre-M endometrium were more clonogenic than N-cadherin(-) cells (n = 12, P = 0.003), underwent more population doublings (n = 7), showed greater capacity for serial cloning (n = 7) and differentiated into cytokeratin(+) gland-like organoids. N-cadherin immunolocalised to the lateral and apical membrane of epithelial cells in the bases of glands in the basalis of Pre-M endometrium and Post-M gland profiles, co-expressing cytokeratin, ERa but not SSEA-1 or SOX9, which localized on gland profiles proximal to N-cadherin(+) cells. N-cadherin(+) cells were quiescent (Ki-67(-)) in the basalis and in Post-M endometrial glands and co-localized with EMT markers vimentin and E-cadherin. @@@ LARGE SCALE DATA: The raw and processed data files from the gene microarray have been deposited in the National Center for Biotechnology Information Gene Expression Omnibus data set with accession number GSE35221. @@@ LIMITATIONS, REASONS FOR CAUTION: This is a descriptive study in human endometrium only using in vitro stem cell assays. The differential ability of N-cadherin(+) and N-cadherin(-) cells to generate endometrial glands in vivo was not determined. A small number of uterine tissues analysed contained adenomyosis for which N-cadherin has been implicated in epithelial-EMT. @@@ WIDER IMPLICATIONS OF THE FINDINGS: A new marker enriching for human endometrial epithelial progenitor cells identifies a different and potentially more primitive cell population than SSEA-1, suggesting a potential hierarchy of epithelial differentiation in the basalis. Using N-cadherin as a marker, the molecular and cellular characteristics of epithelial progenitor cells and their role in endometrial proliferative disorders including endometriosis, adenomyosis and thin dysfunctional endometrium can be investigated.
