Identification of germ cell-specific VASA and IFITM3 proteins in human ovarian endometriosis

Endometriosis is a gynaecological disorder that affects 6-10 % of female population. It is characterized by the presence of endometrial tissue outside the uterus, most often in the pelvic peritoneum or ovaries. Recent studies have indicated that mesenchymal endometrial stem cells might get involved in endometriosis progression. Although germ line stem cells have been proved to exist in the ovary, their involvement in ovarian endometriosis has not been investigated. In this preliminary report we aimed to identify germinal stem cell markers in ovarian endometriosis.

Ten paraffin-embedded ovarian endometriosis samples were screened for germ cell-specific proteins DDX4 (VASA) and IFITM3, and its relation with stem cell marker OCT4, proliferation marker PCNA and estrogen receptor alpha (ESR1), by immunohistochemistry, immunofluorescence and PCR. DDX4 and IFITM3 proteins were expressed in isolated cells and clusters of cells in the cortical region of ovarian endometriotic cysts. DDX4 and IFITM3 co-localized in cells from endometriotic stroma, and DDX4/IFITM3-expressing cells were positive for ESR1, OCT4 and PCNA. No cells expressing neither DDX4 nor IFITM3 were detected in normal endometrial tissue.

The identification of germ cell-specific proteins DDX4 and IFITM3 provides the first evidence of ovarian-sourced cells in ovarian endometriotic lesions and opens up new directions towards understanding the still confusing pathogenesis of endometriosis.