Like tumor metastases, endometriotic implants require neovascularization to proliferate and invade into ectopic sites within the host. Endometrial tissue, with its robust stem cell populations and remarkable regenerative capabilities, is a rich source of proangiogenic factors. Among the most potent and extensively studied of these proteins, vascular endothelial growth factor has emerged as a critical vasculogenic regulator in endometriosis. Accordingly, angiogenesis of the nascent endometriotic lesion has become an attractive target for novel medical therapeutics and strategies to inhibit vascular endothelial growth factor action. Vascular endothelial growth factor gene regulation in endometrial and endometriosis cells by nuclear receptors, other transcription factors, and also by infiltrating immune cells is emphasized. New data showing that oxidative and endoplasmic reticulum stress increase vascular endothelial growth factor expression are provided. Finally, we review the clinical implications of angiogenesis in this condition and propose potential antiangiogenic therapies that may become useful in the control or eradication of endometriotic lesions. Keywords VEGF; uterus; endothelial Etiology of EndometriosisEndometriosis is a common gynecological disorder defined by the proliferation of endometrial glands and stroma outside the confines of the uterine cavity. The disease affects 5% to 10% of all reproductive-aged women and the prevalence rises to 20% to 50% in infertile women. Genetic factors influence susceptibility to endometriosis; however, the mode of hereditary transmission is complex and likely multifactorial. 1 Sib-pair linkage analyses in 1176 families of affected British and Australian women identified a susceptibility locus on chromosome 10q26 locus. 2 A number of other genetic aberrancies, particularly single nucleotide polymorphisms in relevant nuclear receptors (eg, estrogen receptor-α 3 and estrogen receptor-β 4 ), cytokines, 5 and even in the vascular endothelial growth factor (VEGF) coding sequence per se in Korean 6 and South Indian populations 7 are associated with an increased odds ratio of endometriosis prevalence.Arguments persist over the histogenic etiology of endometriosis; however, the implantation hypothesis put forward by Sampson more than 80 years ago is the most widely accepted. 8 Retrograde menstruation, 9 with subsequent intraperitoneal spillage 10 and mesothelial

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Activin A and related proteins (inhibins, follistatin [FS], follistatin-related gene [FLRG], endometrial bleeding associated factors [ebaf]) are involved in the complex mechanisms allowing the establishment and the maintenance of pregnancy. As a consequence of ovarian progesterone stimuli, activin A is expressed and secreted by the stromal endometrial cells, which locally induces the decidualization process, a prerequisite for implantation. Moreover, activin A does influence the implantation phase, also enhancing cytotrophoblast differentiation, indirectly, by increasing the expression of other molecules involved in embryo implantation, such as matrix metalloproteinases (MMPs) and leukemia inhibitory factor (LIF). The local derangement of activin A pathway in some pregnancy disorders (incomplete and complete miscarriages, recurrent abortion, and ectopic pregnancy [EP]) further sustains the hypothesis that activin A and its related proteins play a relevant role in the establishment of pregnancy.

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Activin A is a dimeric protein that regulates endometrial functions by signaling at its receptors, namely type I (ActRI) and type II (ActRII). Nodal is an activin competitor that requires the coreceptor cripto to assemble its signaling pathway through ActRI and ActRII. In the current study, we evaluated the expression of activin A, ActRII, nodal, and cripto in eutopic and ectopic endometrium collected from women with ovarian endometrioma (n = 15) and in eutopic endometrium of healthy participants (n = 15). Eutopic endometrial samples were evaluated according to the stage of menstrual cycle. Total RNA was extracted from tissue homogenates and analyzed by real-time polymerase chain reaction (PCR). Activin A messenger RNA (mRNA) expression in eutopic endometrium of patients with endometriosis was significantly higher than in controls (P < .001) with a 10.2-fold and 7.3-fold increase in the proliferative and secretory phases, respectively. ActRII and nodal mRNA expression were found to be similar in patients with and without endometriosis, while cripto mRNA was markedly lower in eutopic (fold change = 0.03 at proliferative phase, P < .001) and ectopic endometrium (fold change = 0.14, P < .001) of women with endometriosis compared with eutopic endometrium from healthy controls. In conclusion, the altered endometrial expression of activin A and cripto during the menstrual cycle and the differences observed in the endometriotic tissue support the involvement of the activin system in endometrial changes of women with endometriosis.

Serum follistatin is increased in women with endometriosis and allows clear distinction between endometrioma and other benign ovarian cysts. Follistatin has the sensitivity and specificity to become a useful clinical marker of ovarian endometrioma.

Steroid hormones, cytokines, and growth factors have a major role in evoking local endometrial changes needed for trophoblast implantation. In the present study, the effect of interleukin-1beta (IL-1beta), 17-beta estradiol (E2), and progesterone (Pr) on activin A and follistatin (FS) secretion from cultured human endometrial stromal cells (HESCs) is evaluated. HESCs were obtained from healthy human endometrial samples (n = 8) collected from healthy women. The cells were cultured and stimulated with E2 (10(-7) M, 10(-6)M), Pr (10(-7)M, 10(-6)M), IL-1beta (500 pg/mL), IL-1beta (500 pg/mL) + E2 (10(-6)M), and IL-1beta (500 pg/mL) + Pr (10(-6)M). Activin A and FS secretion and mRNA expression were assayed by enzyme-linked immunosorbent assay and semiquantitative reverse transcriptase-polymerase chain reaction, respectively. Pr (10(-7) M, 10(-6) M) significantly increased activin A secretion and mRNA expression from HESCs, but E2 did not show remarkable effects. The addition of IL-1beta (P< .001), IL- 1beta + E2 (P < .01), and IL-1beta + Pr (P< .001). significantly stimulated activin A secretion and mRNA expression, compared to untreated cells. Activin A expression and secretion after the coincubation of IL-1beta+ Pr were significantly higher than after IL-1betaand IL-1beta+ E2 stimuli ( P< .01 and P< .001, respectively). Neither Pr nor E2 and IL-1beta had a significant effect on FS secretion and expression. IL-1betaand Pr stimulated activin A but not FS secretion from cultured HESCs, and the effect of IL-1betawas augmented by Pr. These findings, together with the evidence that activin A is involved in trophoblast implantation, suggest the existence of a complex cross-talk by which the ovary, through Pr secretion, and the embryo, through IL-1beta production, may trigger the endometrial induction of activin A and consequently timing implantation.

Urocortin (UCN) is a 40-amino acid neuropeptide sharing 45% sequence homology with corticotropin-releasing factor (CRF). The human endometrium expresses both UCN and CRF, and CRF/UCN receptors type-1 (CRF-R1) and -2 (CRF-R2). CRF-R1 activation inhibits cell growth and proliferation of a tumor cell line derived from the human endometrium, and the UCN signaling pathway has been implicated in tumorigenesis of several tissues. Therefore, we investigated whether UCN mRNA and peptide are expressed by human endometrial adenocarcinoma, and whether their expression changes compared to controls. Samples of well (grade 1; nZ6 endometrioid adenocarcinoma, of whom nZ1 with squamous differentiation, and nZ1 clear-cell carcinoma) and poorly differentiated (grade 3; nZ3 endometrioid adenocarcinoma) endometrial adenocarcinoma were collected from nine women (age range 61-79 years) enrolled at the time of diagnosis. Healthy endometrium was collected from postmenopausal women (controls; nZ13; age range 64-78 years), who underwent hysterectomy for uterine prolapse. Immunohistochemistry was used to evaluate cellular UCN localization, with the intensity of immunostaining scored on a subjective scale. Quantitative real-time reverse transcriptase (RT)-PCR analysis was used to estimate mRNA expression changes and restriction analysis was used to confirm PCR products identity. UCN mRNA expression was significantly reduced (P!0$0001) in endometrial adenocarcinoma than in healthy controls. Immunoreactive UCN was found in luminal and glandular epithelial cells in healthy, but not in neoplastic samples. UCN mRNA and peptide expressions are decreased in endometrial adenocarcinoma. These data and the evidence that endometrial cancer expresses UCN receptors and UCN is involved in tumorigenesis of several tissues together suggest a role for UCN in endometrial tumoral cell growth and proliferation.