Ruth Grümmer

Endometriosis is a common gynaecological disease, defined as the presence of endometrial tissue outside the uterus, causing pelvic pain and subfertility in ∼10% of women of reproductive age. Current therapies lead to pain relief, however, do not address the causes and entail severe side effects. Still little is known about the pathogenic processes leading to the development and maintenance of endometriosis. Because endometriosis occurs spontaneously only in humans and some non-human primates, animal models of induced endometriosis have been developed and are of high value for the evaluation of pathophysiological mechanisms underlying the development of this disease. These experimental models include the autotransplantation of uterine fragments into the peritoneal cavity of rodents and non-human primates or the heterotransplantation of human endometrial or endometriotic tissue to immunodeficient mice or onto the chicken chorioallantoic membrane (CAM). This review describes the animal models for endometriosis and assesses their different potentials and limitations in regard to endometriosis research, with the aim of developing novel non-invasive diagnostic tools and improved strategies for the treatment of endometriosis in women.

Background During the female reproductive cycle, follicular development and corpus luteum formation crucially depend on the fast generation of new blood vessels. The importance of granulosa cells and follicular fluid in controlling this angiogenesis is still not completely understood. Vascular endothelial growth factor (VEGF) produced by granulosa cells and secreted into the follicular fluid plays an essential role in this process. On the other hand, soluble VEGF receptor-1 (sFlt-1) produced by endothelial cells acts as a negative modulator for the bioavailability of VEGF. However, the regulation of sFlt-1 production remains to be determined. Methods We analyzed the influence of human follicular fluid obtained from FSH-stimulated women as well as of human granulosa cell conditioned medium on sFlt-1 production in and release from human umbilical vein endothelial cells (HUVEC) in vitro. Soluble Flt-1 gene expression was determined by RT-PCR analysis, amount of sFlt-1-protein was quantified by Sandwich-ELISA. Results Human follicular fluid as well as granulosa cell-conditioned medium significantly inhibit the production of sFlt-1 by endothelial cells on a posttranscriptional level. Treatment of cultured granulosa cells with either hCG or FSH had not impact on the production of sFlt-1 inhibiting factors. We further present data suggesting that this as yet unknown sFlt-1 regulating factor secreted by granulosa cells is not heat-sensitive, not steroidal, and it is of low molecular mass (< 1000 Da). Conclusion We provide strong support that follicular fluid and granulosa cells control VEGF availability by down regulation of the soluble antagonist sFlt-1 leading to an increase of free, bioactive VEGF for maximal induction of vessel growth in the ovary.

A precise regulation of angiogenesis is a prerequisite for an adequate maturation of ovarian follicles. Despite the production of vascular endothelial growth factor (VEGF) by granulosa cells in antral follicles, angiogenesis is restricted to the theca cell layer. The maturing follicle remains avascular before ovulation, implying regulatory mechanisms which prevent premature follicular vascularization. In order to investigate the role of follicular fluid and of granulosa cells in the regulation of endothelial gene expression, human umbilical vein endothelial cells (HUVECs) were incubated in vitro with media conditioned with human follicular fluid obtained from individual patients undergoing oocyte retrieval for in vitro fertilization procedures or with culture medium conditioned by human granulosa cells respectively. Using microarray technology, the gene expression pattern was compared between untreated monolayers of HUVECs and HUVECs treated either with follicular fluid or with granulosa cell conditioned media. We identified a total of 15 genes that were significantly up-regulated and 11 genes that were significantly down-regulated in endothelial cells treated with follicular fluid at least 2.5-fold in more than 70% of comparisons. Up-regulated genes involved in angiogenesis were the anti-angiogenic factors gro-beta (16.5-fold), angiopoietin-2 (3.9-fold), alpha-2-macroglobulin (24.3-fold) and the pro-angiogenic factors E-selectin (5.3-fold) and vascular cell adhesion molecule-1 (VCAM-1) (4.4-fold), whereas a significant down-regulation of the pro-angiogenic genes fibulin-5 (3.5-fold) and elastin (14.9-fold) could be observed. Culturing of HUVECs with conditioned medium from cultured human luteinized granulosa cells demonstrated a similar regulatory pattern of gene expression for fibulin-5, elastin, gro-beta, and E-selectin. The gene regulation in endothelial cells by follicular fluid could be confirmed by RT-PCR for gro-beta, angiopoietin-2, elastin, fibulin-5, and E-selectin. The present work reveals that compounds secreted by granulosa cells lead to the expression of anti-angiogenic factors on the transcript level in endothelial cells and thus could help to explain the temporal and spatial discrepancy between the high expression of VEGF and the restricted angiogenesis in the preovulatory follicle.

BACKGROUND: The current medical treatment of endometriosis, a common gynaecological disease, is still associated with a high recurrence rate. To establish an appropriate in-vivo model to evaluate new therapeutic strategies we validated the nude mouse model for the intraperitoneal cultivation of human endometrial tissue. METHODS: Human endometrium of the proliferative phase was implanted into the peritoneal cavity of normal cycling and ovariectomized athymic mice and of cycling non-obese diabetic (NOD)-severe combined immuno-deficiency (SCID) mice. Morphology, proliferation, differentiation, and angiogenesis in the ectopic endometrium at different time points after implantation was investigated. RESULTS: Adhesion of endometrial fragments was observed from day 2 onwards. The lesions persisted for up to 28 days revealing a well preserved glandular morphology. The glandular epithelium maintained cytokeratin expression even after 14 days of culture. With progressing culture, glands exhibited vimentin staining in combination with a decrease of surrounding stromal cells. Proliferation of glandular epithelium could be demonstrated throughout the investigated period of 28 days, whereas expression of oestrogen and progesterone receptors was maintained only in endometriotic lesions grown in cycling but not in ovariectomized mice. Neoangiogenesis occurred from day 4 onwards, independent from the intraperitoneal localization of the ectopic lesions. CONCLUSIONS: This in-vivo model is a promising tool to test the effect of compounds such as different hormone agonists/antagonists or anti-angiogenic factors to develop new therapeutic concepts in endometriosis.