416. A xenotransplantation model for investigating the role of human endometrial stem/progenitor cells in endometriosis

Endometriosis is a major cause of infertility in women. Recent evidence suggests that stem/progenitor cells are present in human endometrium which may be responsible for its remarkable regenerative capacity.1 In mouse endometrium, candidate epithelial and stromal stem/progenitor cells have been identified as label retaining cells (LRC).2 We hypothesised that endometrial stem/progenitor cells gain access to the peritoneal cavity in menstrual debris where they establish ectopic endometriosis lesions in women who develop endometriosis3. Our aim was to identify LRC in human endometrial tissues transplanted into an ectopic site in immunocompromised mice. Endometrium was dissected into pieces (1x1 mm × depth of endometrium) from hysterectomy tissues from ovulating women (n = 7) and transplanted beneath the kidney capsule of ovariectomised NOD/SCID mice. One week later, mice were administered a single 100 ng oestradiol valerate (E2) injection and 50 ug/g BrdU (6 ip injections over 3 days) to label proliferating endometrial cells with BrdU. E2 injections were given fortnightly to induce weekly cycles of endometrial growth and regression and to chase out the BrdU. Mice were sacrificed after 6–12 weeks chase and the explants examined for LRC and other markers by immunofluorescence. Endometrial explants underwent major remodelling during the BrdU pulse-chase, and cells in both glands and stroma underwent proliferation (PCNA+). Rare LRC were identified in the human endometrial epithelium and stroma. Epithelial LRC were ER-α negative while some stromal LRC were ER-α+ by confocal microscopy. Immunostaining of the LRC for ER-β, α-smooth muscle actin and human endometrial stromal stem/progenitor cell markers (CD146, PDGFR-β)4 will further characterise these candidate stem/progenitor cell populations in ectopic endometrium. This preliminary study suggests that combining the LRC technique with xenotransplantation of human endometrial tissue into a well vascularised ectopic site may provide a novel model for investigating the role of endometrial epithelial and stromal stem/progenitor cells in the pathogenesis of endometriosis. (1) Chan RWS et al. (2004). Biology of Reproduction. 70:1738–1750 (2) Chan RWS, Gargett CE (2006). Stem Cells 24:1529–1538 (3) Gargett CE (2007) Human Reproduction Update 13:87–101 (4) Schwab KE, Gargett CE (2007) Human Reproduction 22:2903–2911