title: The characterisation of endometrial epithelial stem/progenitor cells
Creators: name: Al-Iamee, Hannan
Publisher: name: University of Liverpool Repository
Year: 2013

description: The highly regenerative nature of the human endometrium has caused much speculation over the existence of resident stem/progenitor cells (SPCs) within this tissue. Endometrial SPCs may be associated with a variety of gynaecological pathologies such as endometriosis. Although common, little is known about the pathogenesis of this condition and the lack of defining markers of putative endometrial SPCs makes the isolation and analysis of these cells difficult. The well characterised endometrial stromal stem cells are only able to regenerate a stromal cell population of the endometrium in 3D in vitro or animal xenograft models. This suggests that there is a separate endometrial epithelial SPC that gives rise to the endometrial epithelial cells, including the glands and the surface epithelium. SSEA-1, a surface glycolipid expressed by embryonic stem cells (ESCs), has recently been identified as a possible endometrial epithelial progenitor cell marker by our lab. However, the gene expression profile of the SSEA-1+ endometrial epithelial cells has yet to be assessed. With the use of qPCR, we aimed to further characterise the SSEA-1+ endometrial epithelial cell population by assessing their gene expression profile for common markers of stemness and an undifferentiated state when grown in both 2D and 3D culture. As abnormal endometrial SPCs are speculated to be involved in the pathogenesis of endometriosis, we further investigated the gene profile of SSEA-1 expressing endometrial epithelial cells in this condition. Within the normal endometrium, we found no differences between the levels of stem cell markers expressed by the SSEA-1+ and SSEA-1- epithelial cell populations grown in 2D culture. Significant up-regulation of markers of differentiation, ERα and PR, within the SSEA-1- cells confirmed the existence of a more differentiated cell state within this population. SSEA-1+ epithelial cells grown in 2D culture exhibited significantly higher levels of stem cell marker expression in patients with endometriosis than those with a normal endometrium, confirming their association with this disease. When grown in 3D culture endometrial epithelial cells form gland-like structures also called spheroids/organoids, similar to those seen within the endometrium. 3D Matrigel culture mimics the endometrium and the stem cell niche in vivo and therefore acts as a better culture system to preserve stemness and accurately reflects in vivo physiology. Unlike the 2D culture, SSEA-1+ epithelial cells grown in 3D culture exhibited a clear up-regulation of markers of stemness when compared to the SSEA-1- cell population, in both normal and endometriosis tissue. This difference was more pronounced in cells taken from women with endometriosis, again indicating its link with this condition. High levels of ERα and stable levels of PR expression indicated elements of oestrogen responsiveness and progesterone resistance within the 3D cultured SSEA-1+ epithelial cells taken from women with endometriosis, and are known features of endometriosis. These findings provide further evidence to suggest that endometrial epithelial SPCs are contained within the SSEA-1+ cell population displaying greater stem cell activity than the SSEA-1- population, but only when grown in 3D culture which mimicks their in vivo environment. This highlighted the significance of the surrounding stem cell niche in preserving stemness and preventing differentiation. Furthermore, our study demonstrats that this sub-population of SSEA-1+ epithelial SPCs are in some way involved in the pathogenesis of endometriosis.