Endometriosis : involvement of stem cells and clinical impact

Abstract: Introduction: Endometriosis is a common gynaecological disease affecting up to 10% of women of reproductive age. The women suffer from severe abdominal pain and infertility as a consequence of the chronic inflammation. The disease has also been associated with an increased risk of cancer, in particular endometrial and ovarian cancer. Endometriosis represents an important socioeconomic burden as the condition is associated with productivity loss, medical and surgical treatments including assisted reproduction, and a compromised quality of life. The pathophysiology of endometriosis is not fully understood, and as of today we are unable to identify women at risk for cancer development and offer them a tailor-made prophylactic treatment. Aims: The overall aim of this thesis is to explore some of the mechanisms that have an important influence on clinical impact, in particular infertility and the risk of developing endometriosis-associated cancer. The mechanisms enabling endometriotic lesion establishment are explored in an in vitro experimental model and the methylation profile of the fertility-regulating gene HOXA10 is investigated in eutopic and ectopic endometrium. This study also attempts to identify the molecular link between endometriotic stem cells and the development of ovarian cancer by exploring CSC-specific markers and their molecular signatures, and gene expression profile of cancer-correlated molecules in different endometrial compartments. Results: Significant changes were found in the endometrium of women with endometriosis compared to healthy controls. The first study demonstrated the expression of ApoE, ITGB2, ITGB7, LAMC1, CD24, and JAM-1 in women with and without endometriosis. Also, some of the molecules showed a significant altered expression upon comparing endometrium from women with and without endometriosis, as well as eutopic and ectopic endometrium of women with endometriosis. ApoE and JAM-1 were decreased in both proliferative and secretory phase in endometrium from women with endometriosis, and mRNA expression of LAMC1 was reduced in endometrium from endometriosis patients compared with controls in the proliferative phase. CD24 expression was significantly expressed in eutopic and ectopic endometrium in women with endometriosis. In the second study, we found a significant hypermethylation of the HOXA10 gene in eutopic secretory endometrium in women with endometriosis compared with controls. When comparing the methylation profile in patients suffering from ovarian endometriosis with patients presenting extra-ovarian disease, we could not demonstrate any significant correlation between methylation status and stage of disease. The third study demonstrated that mesenchymal endometrial stem cells from women with endometriosis showed an active S-phase as well as an up-regulation of PTEN, VEGF-α, and decreased BCL2 gene-expression compared to controls. A subset of potentially ‘high-risk’ patients could be identified showing a significant up-regulation of genes involved in reprogramming SOX2, NANOG; cancer metabolism TP53, K-ras; and epithelial- mesenchymal transition genes TGF-α and SNAI1. TP53 turned out to play the role of a master regulator. When comparing monolayer to 3D spheroid cultures, an increased coexpression of CSC surface markers CD44 and CD133 was seen, and the chemo-sensitivity assay performed in a 3D-tumour microenvironment revealed increased tumour invasion in the ‘high-risk’ group. In the fourth study, we found a significant difference in the expression of genes that correlated with endometrial malignant transformation in both endometrial stromal and glandular compartments in endometriosis patients compared with controls. Conclusions: Our results shed light on the molecular linkage to the etiology of endometriosis and malignant transformation of endometriosis, as well as providing useful information relevant to endometriosis-associated infertility and pathogenesis.