Human endometrium contains rare clonogenic, self-renewing epithelial cells that differentiate into gland-like structures, but their identity and location are unknown. Epithelium of Premenopausal (PreM) basalis and Postmenopausal (PostM) endometrium have similar gene profiles.1 We hypothesized that endometrial epithelial progenitor cells are located in basalis glands. Our aim was to identify a surface marker purifying human endometrial epithelial progenitor cells with clonogenic activity and determine their in vivo niche.
An unbiased gene profiling approach was used to identify differentially expressed surface marker genes between fresh EpCAM-magnetic bead-selected basalis-like epithelial cells from PostM endometrium compared with predominantly functionalis epithelial cells from PreM endometrium and validated by qRT-PCR. Clonogenicity and self-renewal assays assessed stem/progenitor cell properties of magnetic bead-sorted N-cadherin+ and N-cadherin- epithelial cells. The phenotype and location of N-cadherin+ cells was assessed by mulitcolour immunofluorescence and confocal microscopy on full thickness human endometrium.
CDH2 (N-cadherin gene) was one of 11 surface markers highly expressed in PostM compared to PreM endometrial epithelial cells. N-cadherin+ epithelial cells from PreM endometrium were more clonogenic than N-cadherin- cells (n=12, P=0.003) and showed greater capacity for serial cloning (n=7). N-cadherin immunolocalised to the lateral and apical membrane of epithelial cells in the bases of glands in PreM basalis endometrium and PostM gland profiles. N-cadherin+ cells co-expressed cytokeratin, ERα, E-cadherin and vimentin, but not SSEA-1 or SOX9 (basalis epithelial markers), which localized on gland profiles proximal to N-cadherin+ cells. N-cadherin+ cells were quiescent (Ki-67-) in the basalis and in PostM endometrial glands.
We identified the first marker of human endometrial epithelial progenitor cells and their location in the bases of the glands, and identified a potential hierarchy of epithelial differentiation in the basalis. The molecular and cellular characteristics of epithelial progenitor cells and their role in endometrial proliferative disorders can now be investigated.