Stromal cells of endometriosis fail to produce paracrine factors that induce epithelial 17beta-hydroxysteroid dehydrogenase type 2 gene and its transcriptional regulator Sp1: a mechanism for defective estradiol metabolism

Inflammatory Changes after Medical Suppression of Suspected Endometriosis for Implantation Failure: Preliminary Results

Unexplained euploid embryo transfer failure (UEETF) is a frustrating and unanswered conundrum accounting for 30 to 50% of failures in in vitro fertilization using preimplantation genetic testing for aneuploidy (PGT-A). Endometriosis is thought by many to account for most of such losses and menstrual suppression or surgery prior to the next transfer has been reported to be beneficial. In this study, we performed endometrial biopsy in a subset of women with UEETF, testing for the oncogene BCL6 and the histone deacetylase SIRT1. We compared 205 PGT-A cycles outcomes and provide those results following treatment with GnRH agonist versus controls (no treatment). Based on these and previous promising results, we next performed a pilot randomized controlled trial comparing the orally active GnRH antagonist, elagolix, to oral contraceptive pill (OCP) suppression for 2 months before the next euploid embryo transfer, and monitored inflammation and miRNA expression in blood, before and after treatment. These studies support a role for endometriosis in UEETF and suggest that medical suppression of suspected disease with GnRH antagonist prior to the next transfer could improve success rates and address underlying inflammatory and epigenetic changes associated with UEETF.

Effect of Oral Contraceptive Use in Relation to Fertile Years on the Risk of Endometriosis in Women with Primary Infertility: A Ten-Year Single-Centre Retrospective Analysis

Background and Objectives: Oral contraceptives (OCs) are usually used to treat endometriosis; however, the evidence is inconsistent about whether OC use in the past, when given to asymptomatic women, is protective against the development of future disease. We aimed to assess the relationship between the use of OCs and the likelihood of discovering endometriosis, considering the length of time under OCs during their fertile age. Materials and Methods: This was a monocentric retrospective cohort study in a tertiary-care University Hospital (Department of Human Reproduction, Division of Gynaecology and Obstetrics, University Medical Centre Ljubljana, Slovenia) carried out from January 2012 to December 2022. Reproductive-aged women scheduled for laparoscopic surgery for primary infertility and subsequent histopathological diagnosis of endometriosis were compared to women without an endometriosis diagnosis. They were classified based on the ratio of years of OC use to fertile years in four subgroups: never, <25%, between 25 and 50%, and >50. Results: In total, 1923 women (390 with and 1533 without endometriosis) were included. Previous OC use was higher in those with endometriosis than controls (72.31% vs. 58.64%; p = 0.001). Overall, previous OC usage was not related to histopathological diagnosis of endometriosis (aOR 1.06 [95% CI 0.87-1.29]). Women who used OCs for less than 25% of their fertile age had reduced risk of rASRM stage III endometriosis (aOR 0.50 [95% CI 0.26-0.95]; p = 0.036) or superficial implants (aOR 0.88 [95% CI 0.58-0.95]; p = 0.040). No significant results were retrieved for other rASRM stages. Using OCs for <25%, between 25 and 50%, or >50% of fertile age did not increase the risk of developing superficial endometriosis, endometriomas, or DIE. Conclusions: When OCs are used at least once, histological diagnoses of endometriosis are not increased. A protective effect of OCs when used for less than 25% of fertile age on superficial implants may be present. Prospective research is needed to corroborate the findings due to constraints related to the study's limitations.

Autophagy regulation and redox perturbation by transcrocetin suppress the growth of endometriosis

Until non-hormonal therapeutic targets for endometriosis are suggested, we focused on mitochondrial function and autophagy regulation in the disease. Transcrocetin is a carotenoid and retinoic acid with high antioxidant potency and antiproliferative effects in several diseases. In this study, we demonstrated the therapeutic mechanisms of transcrocetin in endometriosis using the End1/E6E7 and VK2/E6E7 cell lines. Transcrocetin suppressed the viability and proliferation of these cell lines and did not affect the proliferation of normal uterine stromal cells. p21 Waf1/Cip1 as a cell cycle regulator and target of p53, were increased by transcrocetin and caused the G1 arrest via inhibition of cyclin-dependent kinase activity, which might further cause cell death. Furthermore, we confirmed endoplasmic reticulum stress and calcium ion dysregulation in the cytosol and mitochondrial matrix, disrupting the mitochondrial membrane potential. Mitochondrial bioenergetics were suppressed by transcrocetin, and oxidative phosphorylation-related gene expression was downregulated. Moreover, the proliferation of End1/E6E7 and VK2/E6E7 cells was regulated by transcrocetin-induced oxidative stress. Finally, we verified the impairment of autophagic flux following pre-treatment with chloroquine. Therefore, transcrocetin may be a potent therapeutic alternative for endometriosis.

A Preliminary Investigation of the Roles of Endometrial Cells in Endometriosis Development via In Vitro and In Vivo Analyses

Endometriosis is a complex gynecological disease that affects more than 10% of women in their reproductive years. While surgery can provide temporary relief from women's pain, symptoms often return in as many as 75% of cases within two years. Previous literature has contributed to theories about the development of endometriosis; however, the exact pathogenesis and etiology remain elusive. We conducted a preliminary investigation into the influence of primary endometrial cells (ECs) on the development and progression of endometriosis. In vitro studies, they were involved in inducing Lipopolysaccharide (LPS) in rat-isolated primary endometrial cells, which resulted in increased nuclear factor-kappa B (NF-κB) and vascular endothelial growth factor (VEGF) mRNA gene expression (quantitative polymerase chain reaction analysis, qPCR) and protein expression (western blot analysis). Additionally, in vivo studies utilized autogenic and allogeneic transplantations (rat to rat) to investigate endometriosis-like lesion cyst size, body weight, protein levels (immunohistochemistry), and mRNA gene expression. These studies demonstrated that estrogen upregulates the gene and protein regulation of cytoskeletal (CK)-18, transforming growth factor-β (TGF-β), VEGF, and tumor necrosis factor (TNF)-α, particularly in the peritoneum. These findings may influence cell proliferation, angiogenesis, fibrosis, and inflammation markers. Consequently, this could exacerbate the occurrence and progression of endometriosis.

Pattern-recognition receptors in endometriosis: A narrative review

Endometriosis is closely associated with ectopic focal inflammation and immunosuppressive microenvironment. Multiple types of pattern recognition receptors (PRRs) are present in the innate immune system, which are able to detect pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) in both intracellular and external environments. However, the exact role of PRRs in endometriosis and the underlying molecular mechanism are unclear. PRRs are necessary for the innate immune system to identify and destroy invasive foreign infectious agents. Mammals mainly have two types of microbial recognition systems. The first one consists of the membrane-bound receptors, such as toll-like receptors (TLRs), which recognize extracellular microorganisms and activate intracellular signals to stimulate immune responses. The second one consists of the intracellular PRRs, including nod-like receptors (NLRs) and antiviral proteins retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA-5) with helix enzyme domain. In this review, we mainly focus on the key role of PRRs in the pathological processes associated with endometriosis. PRRs recognize PAMPs and can distinguish pathogenic microorganisms from self, triggering receptor ligand reaction followed by the stimulation of host immune response. Activated immune response promotes the transmission of microbial infection signals to the cells. As endometriosis is characterized by dysregulated inflammation and immune response, PRRs may potentially be involved in the activation of endometriosis-associated inflammation and immune disorders. Toll-like receptor 2 (TLR2), toll-like receptor 3 (TLR3), toll-like receptor 4 (TLR4), nod-like receptor family caspase activation and recruitment domain (CARD) domain containing 5 (NLRC5), nod-like receptor family pyrin domain containing 3 (NLRP3), and c-type lectin receptors (CLRs) play essential roles in endometriosis development by regulating immune and inflammatory responses. Absent in melanoma 2 (AIM2)-like receptors (ALRs) and retinoic acid-inducible gene I-like receptors (RLRs) may be involved in the activation of endometriosis-associated immune and inflammation disorders. PRRs, especially TLRs, may serve as potential therapeutic targets for alleviating pain in endometriosis patients. PRRs and their ligands interact with the innate immune system to enhance inflammation in the stromal cells during endometriosis. Thus, targeting PRRs and their new synthetic ligands may provide new therapeutic options for treating endometriosis.

In vitro modeling of endometriosis and endometriotic microenvironment - Challenges and recent advances

Endometriosis is a chronic condition with high prevalence in reproductive age women, defined as the growth of endometrial tissue outside the uterine cavity, most commonly on the pelvic peritoneum. The ectopic endometrial lesions exist in a unique microenvironment created by the interaction of epithelial, stromal, endothelial, glandular, and immune cell components, dominated by inflammatory, angiogenic, and endocrine signals. Current research is directed at understanding the complex microenvironment of the lesions and its relationship with different endometriosis stages, phenotypes, and disease symptoms and at the development of novel diagnostic and therapeutic concepts that minimalize the undesirable side effects of current medical management. Recreating pathophysiological cellular and molecular mechanisms and identifying clinically relevant metrics to assess drug efficacy is a great challenge for the experimental disease models. This review summarizes the complete range of available in vitro experimental systems used in endometriotic studies, which reflect the multifactorial nature of the endometriotic lesion. The article discusses the simplistic in vitro models such as primary endometrial cells and endometriotic cell lines to heterogeneous 2D co-cultures, and recently more common, 3D systems based on self-organization and controlled assembly, both in microfluidic or bioprinting methodologies. Basic research models allow studying fundamental pathological mechanisms by which menstrual endometrium adheres, invades, and establishes lesions in ectopic sites. The advanced endometriosis experimental models address the critical challenges and unsolved problems and provide an approach to drug screening and medicine discovery by mimicking the complicated behaviors of the endometriotic lesion.

Site-Specific Regulation of Sulfatase and Aromatase Pathways for Estrogen Production in Endometriosis

Endometriosis is a highly prevalent gynecological disease characterized by lesions in different sites. Regulation of specific estrogen pathways may favor the formation of distinct microenvironments and the progression of endometriosis. However, no study has simultaneously evaluated the gene and protein regulation of the main estrogen-synthesizing enzymes in endometriosis. Thus, our goals were to study the relationship between gene and protein expression of aromatase (CYP19A1 or ARO), steroid sulfatase (STS), and hydroxysteroid 17-beta dehydrogenase (HSD17B1) in superficial (SUP), ovarian (OMA), and deep infiltrating (DIE) endometriotic lesion sites as well as in the eutopic endometrium of patients with (EE) and without (control) endometriosis in the same and large cohort of patients. The site-specific expression of these enzymes within different cells (glandular and stromal components) was also explored. The study included 108 patients surgically diagnosed with endometriosis who provided biopsies of EE and endometriotic lesions and 16 disease-free patients who collected normal endometrium tissue. Our results showed that CYP19A1 was detected in all endometriosis tissues and was in higher levels than in control. Unique patterns of the STS and HSD17B1 levels showed that they were most closely regulated in all tissues, with manifestation at greater levels in DIE compared to the other endometriotic lesion sites, OMA and SUP. Gene and protein expression of ARO, STS, and HSD17B1 occurred at different rates in endometriotic sites or EE. The distinctive levels of these estrogen-synthesizing enzymes in each endometriotic site support the hypothesis of a tissue microenvironment that can both influence and be influenced by the expression of different estrogenic pathways, locally affecting the availability of estrogen needed for maintenance and progression of endometriotic lesions.

Endometriosis is a chronic systemic disease: clinical challenges and novel innovations

Endometriosis is a common disease affecting 5-10% of women of reproductive age globally. However, despite its prevalence, diagnosis is typically delayed by years, misdiagnosis is common, and delivery of effective therapy is prolonged. Identification and prompt treatment of endometriosis are essential and facilitated by accurate clinical diagnosis. Endometriosis is classically defined as a chronic, gynaecological disease characterised by endometrial-like tissue present outside of the uterus and is thought to arise by retrograde menstruation. However, this description is outdated and no longer reflects the true scope and manifestations of the disease. The clinical presentation is varied, the presence of pelvic lesions is heterogeneous, and the manifestations of the disease outside of the female reproductive tract remain poorly understood. Endometriosis is now considered a systemic disease rather than a disease predominantly affecting the pelvis. Endometriosis affects metabolism in liver and adipose tissue, leads to systemic inflammation, and alters gene expression in the brain that causes pain sensitisation and mood disorders. The full effect of the disease is not fully recognised and goes far beyond the pelvis. Recognition of the full scope of the disease will facilitate clinical diagnosis and allow for more comprehensive treatment than currently available. Progestins and low-dose oral contraceptives are unsuccessful in a third of symptomatic women globally, probably as a result of progesterone resistance. Oral gonadotropin-releasing hormone (GnRH) antagonists constitute an effective and tolerable therapeutic alternative when first-line medications do not work. The development of GnRH antagonists has resulted in oral drugs that have fewer side-effects than other therapies and has allowed for rapid movement between treatments to optimise and personalise endometriosis care. In this Review, we discuss the latest understanding of endometriosis as a systemic disease with multiple manifestations outside the parameters of classic gynaecological disease.

Selective Progesterone Receptor Modulators-Mechanisms and Therapeutic Utility

Selective progesterone receptor modulators (SPRMs) are a new class of compounds developed to target the progesterone receptor (PR) with a mix of agonist and antagonist properties. These compounds have been introduced for the treatment of several gynecological conditions based on the critical role of progesterone in reproduction and reproductive tissues. In patients with uterine fibroids, mifepristone and ulipristal acetate have consistently demonstrated efficacy, and vilaprisan is currently under investigation, while studies of asoprisnil and telapristone were halted for safety concerns. Mifepristone demonstrated utility for the management of endometriosis, while data are limited regarding the efficacy of asoprisnil, ulipristal acetate, telapristone, and vilaprisan for this condition. Currently, none of the SPRMs have shown therapeutic success in treating endometrial cancer. Multiple SPRMs have been assessed for efficacy in treating PR-positive recurrent breast cancer, with in vivo studies suggesting a benefit of mifepristone, and multiple in vitro models suggesting the efficacy of ulipristal acetate and telapristone. Mifepristone, ulipristal acetate, vilaprisan, and asoprisnil effectively treated heavy menstrual bleeding (HBM) in patients with uterine fibroids, but limited data exist regarding the efficacy of SPRMs for HMB outside this context. A notable class effect of SPRMs are benign, PR modulator-associated endometrial changes (PAECs) due to the actions of the compounds on the endometrium. Both mifepristone and ulipristal acetate are effective for emergency contraception, and mifepristone was approved by the US Food and Drug Administration (FDA) in 2012 for the treatment of Cushing's syndrome due to its additional antiglucocorticoid effect. Based on current evidence, SPRMs show considerable promise for treatment of several gynecologic conditions.

Progesterone receptor ligands for the treatment of endometriosis: the mechanisms behind therapeutic success and failure

BACKGROUND

Despite intense research, it remains intriguing why hormonal therapies in general and progestins in particular sometimes fail in endometriosis.

OBJECTIVE AND RATIONALE

We review here the action mechanisms of progesterone receptor ligands in endometriosis, identify critical differences between the effects of progestins on normal endometrium and endometriosis and envisage pathways to escape drug resistance and improve the therapeutic response of endometriotic lesions to such treatments.

SEARCH METHODS

We performed a systematic Pubmed search covering articles published since 1958 about the use of progestins, estro-progestins and selective progesterone receptor modulators, to treat endometriosis and its related symptoms. Two reviewers screened the titles and abstracts to select articles for full-text assessment.

OUTCOMES

Progesterone receptor signalling leads to down-regulation of estrogen receptors and restrains local estradiol production through interference with aromatase and 17 beta-hydroxysteroid dehydrogenase type 1. Progestins inhibit cell proliferation, inflammation, neovascularisation and neurogenesis in endometriosis. However, progesterone receptor expression is reduced and disrupted in endometriotic lesions, with predominance of the less active isoform (PRA) over the full-length, active isoform (PRB), due to epigenetic abnormalities affecting the PGR gene transcription. Oxidative stress is another mechanism involved in progesterone resistance in endometriosis. Among the molecular targets of progesterone in the normal endometrium that resist progestin action in endometriotic cells are the nuclear transcription factor FOXO1, matrix metalloproteinases, the transmembrane gap junction protein connexin 43 and paracrine regulators of estradiol metabolism. Compared to other phenotypes, deep endometriosis appears to be more resistant to size regression upon medical treatments. Individual genetic characteristics can affect the bioavailability and pharmacodynamics of hormonal drugs used to treat endometriosis and, hence, explain part of the variability in the therapeutic response.

WIDER IMPLICATIONS

Medical treatment of endometriosis needs urgent innovation, which should start by deeper understanding of the disease core features and diverse phenotypes and idiosyncrasies, while moving from pure hormonal treatments to drug combinations or novel molecules capable of restoring the various homeostatic mechanisms disrupted by endometriotic lesions.

Genetic, Epigenetic, and Steroidogenic Modulation Mechanisms in Endometriosis

Endometriosis is a chronic gynecological disease, affecting up to 10% of reproductive-age women. The exact cause of the disease is unknown; however, it is a heritable condition affected by multiple genetic, epigenetic, and environmental factors. Previous studies reported variations in the epigenetic patterns of numerous genes known to be involved in the aberrant modulation of cell cycle steroidogenesis, abnormal hormonal, immune and inflammatory status in endometriosis, apoptosis, adhesion, angiogenesis, proliferation, immune and inflammatory processes, response to hypoxia, steroidogenic pathway and hormone signaling are involved in the pathogenesis of endometriosis. Accumulating evidence suggest that various epigenetic aberrations may contribute to the pathogenesis of endometriosis. Among them, DNA methyltransferases, histone deacetylators, and non-coding microRNAs demonstrate differential expression within endometriotic lesions and in the endometrium of patients with endometriosis. It has been indicated that the identification of epigenetic differences within the DNA or histone proteins may contribute to the discovery of a useful prognostic biomarker, which could aid in the future earlier detection, timely diagnosis, and initiation of a new approach to the treatment of endometriosis, as well as inform us about the effectiveness of treatment and the stage of the disease. As the etiology of endometriosis is highly complex and still far from being fully elucidated, the presented review focuses on different approaches to identify the genetic and epigenetic links of endometriosis and its pathogenesis.

Endometriosis

Pelvic endometriosis is a complex syndrome characterized by an estrogen-dependent chronic inflammatory process that affects primarily pelvic tissues, including the ovaries. It is caused when shed endometrial tissue travels retrograde into the lower abdominal cavity. Endometriosis is the most common cause of chronic pelvic pain in women and is associated with infertility. The underlying pathologic mechanisms in the intracavitary endometrium and extrauterine endometriotic tissue involve defectively programmed endometrial mesenchymal progenitor/stem cells. Although endometriotic stromal cells, which compose the bulk of endometriotic lesions, do not carry somatic mutations, they demonstrate specific epigenetic abnormalities that alter expression of key transcription factors. For example, GATA-binding factor-6 overexpression transforms an endometrial stromal cell to an endometriotic phenotype, and steroidogenic factor-1 overexpression causes excessive production of estrogen, which drives inflammation via pathologically high levels of estrogen receptor-β. Progesterone receptor deficiency causes progesterone resistance. Populations of endometrial and endometriotic epithelial cells also harbor multiple cancer driver mutations, such as KRAS, which may be associated with the establishment of pelvic endometriosis or ovarian cancer. It is not known how interactions between epigenomically defective stromal cells and the mutated genes in epithelial cells contribute to the pathogenesis of endometriosis. Endometriosis-associated pelvic pain is managed by suppression of ovulatory menses and estrogen production, cyclooxygenase inhibitors, and surgical removal of pelvic lesions, and in vitro fertilization is frequently used to overcome infertility. Although novel targeted treatments are becoming available, as endometriosis pathophysiology is better understood, preventive approaches such as long-term ovulation suppression may play a critical role in the future.

Retinoid signaling controlled by SRC-2 in decidualization revealed by transcriptomics

Establishment of a successful pregnancy requires not only implantation of a healthy embryo into a receptive uterus but also progesterone receptor (PGR)-dependent transformation of endometrial stromal cells (ESCs) into specialized decidual cells. Decidual cells support the developing embryo and are critical for placentation. We have previously shown that a known transcriptional coregulator of the PGR, steroid receptor coactivator-2 (SRC-2), is a critical driver of endometrial decidualization in both human and mouse endometrium. However, the full spectrum of genes transcriptionally controlled by SRC-2 in decidualizing ESCs has not been identified. Therefore, using an RNA- and chromatin immunoprecipitation-sequencing approach, we have identified the transcriptome of decidualizing human ESCs (hESCs) that requires SRC-2. We revealed that the majority of hESC genes regulated by SRC-2 are associated with decidualization. Over 50% of SRC-2-regulated genes are also controlled by the PGR. While ontology analysis showed that SRC-2-dependent genes are functionally linked to signaling processes known to underpin hESC decidualization, cell membrane processes were significantly enriched in this analysis. Follow-up studies showed that retinoid signaling is dependent on SRC-2 during hESC decidualization. Specifically, SRC-2 is required for full induction of the retinol transporter, stimulated by retinoic acid 6 (STRA6), which is essential for hESC decidualization. Together our findings show that a critical subset of genes transcriptionally reprogramed by PGR during hESC decidualization requires SRC-2. Among the multiple genes, pathways and networks that are dependent on SRC-2 during hESC decidualization, first-line analysis supports a critical role for this coregulator in maintaining retinoid signaling during progesterone-driven decidualization.

The Endometriotic Tumor Microenvironment in Ovarian Cancer

Women with endometriosis are at increased risk of developing ovarian cancer, specifically ovarian endometrioid, low-grade serous, and clear-cell adenocarcinoma. An important clinical caveat to the association of endometriosis with ovarian cancer is the improved prognosis for women with endometriosis at time of ovarian cancer staging. Whether endometriosis-associated ovarian cancers develop from the molecular transformation of endometriosis or develop because of the endometriotic tumor microenvironment remain unknown. Additionally, how the presence of endometriosis improves prognosis is also undefined, but likely relies on the endometriotic microenvironment. The unique tumor microenvironment of endometriosis is composed of epithelial, stromal, and immune cells, which adapt to survive in hypoxic conditions with high levels of iron, estrogen, and inflammatory cytokines and chemokines. Understanding the unique molecular features of the endometriotic tumor microenvironment may lead to impactful precision therapies and/or modalities for prevention. A challenge to this important study is the rarity of well-characterized clinical samples and the limited model systems. In this review, we will describe the unique molecular features of endometriosis-associated ovarian cancers, the endometriotic tumor microenvironment, and available model systems for endometriosis-associated ovarian cancers. Continued research on these unique ovarian cancers may lead to improved prevention and treatment options.

The significance and evolution of menstruation

Historically, the evolutionary origins of menstruation have been based on two theories: the ability to eliminate infectious agents carried to the uterus with spermatozoa and the comparative conservation of energy with menstruation compared to its absence. In the menstruating species, more recent theories have identified spontaneous decidualization as the key adaptive mechanism. Spontaneous decidualization is seen as a mechanism to provide the mother with protection from the invasive characteristics of the embryo. Physiologically, menstruation involves complex interactions of inflammation and vascular mechanisms to stabilize the endometrium and allow a regulated loss of endometrial tissues and blood. A variety of human illnesses can be better understood as vulnerabilities associated with these evolutionary developments, including recurrent pregnancy loss, placenta accreta, ectopic pregnancy, endometriosis, adenomyosis, dysmenorrhea, and chronic pelvic pain. While the evolutionary aspects of these diseases indicate why such illnesses can occur, in some instances, they also provide a basis for treatment, prevention and future research direction.

Progestins for the Treatment of Endometriosis: An Update

Endometriosis is a gynecological condition that affects approximately 10% of women of reproductive age, including 25–40% of infertile women. Dysmenorrhea, dyspareunia and chronic pelvic pain are the most common symptoms. Currently available medical therapies for endometriosis do not cure the disease, but are directed at symptom relief, typically utilizing the hormone responsiveness of endometriotic tissue to induce lesion atrophy. Unfortunately, pain relapse after treatment suspension is a common event. Treatment with pharmacological therapies for endometriosis should be conceived in terms of years, thus agents that must be withdrawn after a few months due to poor tolerability or severe metabolic side effects do not greatly benefit women with symptomatic endometriosis. The characteristics of progestins render this class an ideal pharmacological choice for administration over extended periods. The present paper will review the rationale for using progestins and their mechanism of action in endometriosis. Thereafter, the results obtained by various progestins in the treatment of endometriosis will be evaluated (danazol, gestrinone, norethisterone acetate, desogestrel, cyproterone acetate, megestrol acetate, medroxyprogesterone acetate, and levonorgestrel). A progestin called dienogest, recently introduced for the treatment of endometriosis, will be given special focus, describing its mechanism of action and clinical results.

Retinoid Metabolism in Endometriosis

Endometriosis is an estrogen-dependent disease in which progesterone resistance and inflammation have been found to be major mechanisms responsible for its development and progression. When compared to eutopic endometrium, key molecules have been found to be differentially expressed, which contribute to these mechanisms. One pathway that is aberrant in endometriotic tissue when compared to eutopic endometrium is the retinoic acid signaling pathway. This review focuses on the role of the retinoid signaling pathway in endometriosis and summarizes evidence that supports the use of retinoid compounds for the stimulation of pro-apoptotic activity in these cells.

Altered retinoid signaling compromises decidualization in human endometriotic stromal cells

Decidualization alters multiple molecular pathways in endometrium to permit successful embryo implantation. We have reported that paracrine factors, including retinoids, secreted from progesterone-treated endometrial stromal cells, act on nearby epithelial cells to induce the estradiol metabolizing enzyme HSD17B2. This same induction is not seen in endometriotic stromal cells. We have also shown significant differences in retinoid uptake, metabolism and action in endometriotic tissue and stromal cells compared to normal endometrium. Here, we characterize retinoid signaling during decidualization in these cells. Endometrial and endometriotic cells were isolated, cultured and incubated and decidualized. Genes involved in retinoid metabolism and trafficking were examined using RT-PCR and Western blotting. Prolactin, a decidualization marker, was also examined. We found that both endometrial and endometriotic stromal cells express all intracellular proteins involved in retinoid uptake and metabolism. Decidualization significantly reduced the expression of the genes responsible for retinoid uptake and shuttling to the nucleus. However, expression of CRBP1, an intracellular carrier protein for retinol, increased, as did RBP4, a carrier protein for retinol in the blood, which can function in a paracrine manner. Secreted RBP4 was detected in the media from decidualized endometrial cells but not from endometriotic cells. We believe that retinoid trafficking in endometrial stromal cells during decidualization may shift to favor paracrine rather than intracrine signaling, which may enhance signaling to the adjacent epithelium. There is blunting of this signaling in endometriotic cells. These alterations in retinoid signaling may help explain the decidualization defects and deficient estradiol inactivation (via HSD17B2) seen in endometriosis.

Inflammation influences steroid hormone receptors targeted by progestins in endometrial stromal cells from women with endometriosis

Endometriosis is an estrogen-dependent disease characterised by the growth of endometrial epithelial and stromal cells outside the uterus creating a chronic inflammatory environment that further contributes to disease progression. The first choice treatment for endometriosis is currently progestin mediated hormone modulation. In addition to their progestogenic activity however, progestins also have the potential to bind to other nuclear receptors influencing their local activity on endometriotic cells. This local activity will be dependent on the steroid hormone receptor expression that occurs in endometrial cells in a chronic inflammatory environment. We therefore aimed to quantify receptors targeted by progestins in endometrial stromal cells after exposure to inflammation. Using primary endometrial stromal cells isolated from women with endometriosis we examined the mRNA and protein expression of the progesterone receptors A and B, membrane progesterone receptors 1 and 2, androgen receptors, mineralocorticoid receptors and glucocorticoid receptors after exposure to the inflammatory cytokines tumor necrosis factor α (TNFα) and interleukin 1β (IL-1β). The results indicate that both cytokines reduced the expression of progesterone receptors and increased the expression of the glucocorticoid receptors in the endometrial stromal cells. The change in expression of progestin targets in endometrial stromal cells in an inflammatory environment could contribute to the progesterone resistance observed in endometriotic cells and ultimately influence the design of hormonal therapies aimed at treating this disease.

Type 2 17-β hydroxysteroid dehydrogenase as a novel target for the treatment of osteoporosis

Low estradiol level in postmenopausal women is implicated in osteoporosis, which occurs because of the high bone resorption rate. Estrogen formation is controlled by 17-β hydroxysteroid dehydrogenase 17-β HSD enzymes, where 17-β HSD type 1 contributes in the formation of estradiol, while type 2 catalyzes its catabolism. Inhibiting 17-β HSD2 can help in increasing estradiol concentration. Several promising 17-β HSD2 inhibitors that can act at low nanomolar range have been identified. However, there are some specific challenges associated with the application of these compounds. Our review provides an up-to-date summary of the current status and recent progress in the production of 17-β HSD2 inhibitors as well as the future challenges in their clinical application.

Pathophysiology and Immune Dysfunction in Endometriosis

Endometriosis is an estrogen-dependent, chronic, proinflammatory disease prevalent in 10% of women of reproductive age worldwide. Characterized by the growth of endometrium-like tissue in aberrant locations outside of the uterus, it is responsible for symptoms including chronic pelvic pain, dysmenorrhea, and subfertility that degrade quality of life of women significantly. In Canada, direct and indirect economic cost of endometriosis amounts to 1.8 billion dollars, and this is elevated to 20 billion dollars in the United States. Despite decades of research, the etiology and pathophysiology of endometriosis still remain to be elucidated. This review aims to bring together the current understanding regarding the pathogenesis of endometriosis with specific focus on mechanisms behind vascularization of the lesions and the contribution of immune factors in facilitating lesion establishment and development. The role of hormones, immune cells, and cytokine signaling is highlighted, in addition to discussing the current pharmaceutical options available for management of pain symptoms in women with endometriosis.

Potential role of aromatase inhibitors in the treatment of endometriosis

Endometriosis is an estrogen-dependent chronic inflammatory disease affecting 5%–10% of reproductive-age women, with a prevalence of 5%–50% in infertile women and >33% of women with chronic pelvic pain. Third-generation aromatase inhibitors (AIs) are approved adjuvants for the treatment of estrogen receptor-positive breast cancer. Molecular studies have revealed the presence of aromatase P450, the key enzyme in the biosynthesis of ovarian estradiol, inside the endometriotic tissue, indicating local synthesis of estradiol. Thereby, AIs represent an appealing medical option for the management of different aspects of this enigmatic disease, especially pelvic pain and infertility. Accordingly, this review aims to evaluate the potential role of AIs in the treatment of endometriosis-associated symptoms, mainly pain and infertility. Notably, several studies have demonstrated that the combination of AIs with conventional therapy as oral contraceptive pills, progestins, or gonadotropin-releasing hormone analogs can be used to control endometriosis-associated pain and pain recurrence in premenopausal women, particularly those with pain due to rectovaginal endometriosis refractory to other medical or surgical treatment. Some case reports have shown promising results in the treatment of postmenopausal endometriosis as first-line treatment, when surgery is contraindicated, or as second-line treatment in the case of postoperative recurrence. Third-generation AIs, especially letrozole, have challenged clomiphene citrate as an ovulation-induction agent in patients with polycystic ovary syndrome and in cases of unexplained infertility. However, few studies are available regarding the use of AIs to treat endometriosis-associated infertility. Therefore, larger multicenter randomized trials using AIs for the treatment of endometriosis-associated infertility are needed to clarify its effect. The safety of AIs for ovulation induction or superovulation has generated a lively discussion. Data from recent retrospective and prospective studies have supported its safety.

Oestrogen-induced angiogenesis promotes adenomyosis by activating the Slug-VEGF axis in endometrial epithelial cells

Adenomyosis is an oestrogen-dependent disease characterized by the invasion of endometrial epithelial cells into the myometrium of uterus, and angiogenesis is thought to be required for the implantation of endometrial glandular tissues during the adenomyotic pathogenesis. In this study, we demonstrate that compared with eutopic endometria, adenomyotic lesions exhibited increased vascularity as detected by sonography. Microscopically, the lesions also exhibited an oestrogen-associated elevation of microvascular density and VEGF expression in endometrial epithelial cells. We previously reported that oestrogen-induced Slug expression was critical for endometrial epithelial–mesenchymal transition and development of adenomyosis. Our present studies demonstrated that estradiol (E2) elicited a Slug-VEGF axis in endometrial epithelial cells, and also induced pro-angiogenic activity in vascular endothelial cells. The antagonizing agents against E2 or VEGF suppressed endothelial cells migration and tubal formation. Animal experiments furthermore confirmed that blockage of E2 or VEGF was efficient to attenuate the implantation of adenomyotic lesions. These results highlight the importance of oestrogen-induced angiogenesis in adenomyosis development and provide a potential strategy for treating adenomyosis through intercepting the E2-Slug-VEGF pathway.

Increased AKT or MEK1/2 activity influences progesterone receptor levels and localization in endometriosis

CONTEXT

Endometriosis is characterized by progesterone resistance and hyperactivity of the AKT and MAPK pathways. Kinases can cause posttranslational modifications of the progesterone receptor (PR) to influence cellular localization and protein stability.

OBJECTIVE

The objective of this study was to determine whether the increased AKT or MAPK kinase-1/2 (MEK1/2) activity observed in endometriotic stromal cells (OSIS) from ovarian endometriomas influences levels of PR protein. In turn, the effects of inhibiting AKT or MEK1/2 in the presence of the progestin R5020 on cell viability were investigated.

RESULTS

Inhibiting AKT with MK-2206 or MEK1/2 with U0126 for 24 hours in the absence of R5020 increased total and nuclear PRA and PRB protein levels in OSIS but not in eutopic endometrial stromal cells from disease-free patients from disease-free patients. MK-2206 and R5020 decreased OSIS viability and increased apoptosis. Trends toward decreased volumes of sc grafted endometriosis tissues were demonstrated with MK-2206 and progesterone.

CONCLUSIONS

Inhibition of AKT or MEK1/2 increased total and nuclear PR protein in OSIS. MK-2206 and R5020 decreased OSIS viability and increased apoptosis. The AKT and MAPK pathways may be potential molecular targets for the treatment of endometriosis.

Interplay between Misplaced Müllerian-Derived Stem Cells and Peritoneal Immune Dysregulation in the Pathogenesis of Endometriosis

In the genetic regulation of Müllerian structures development, a key role is played by Hoxa and Wnt clusters, because they lead the transcription of different genes according to the different phases of the organogenesis, addressing correctly cell-to-cell interactions, allowing, finally, the physiologic morphogenesis. Accumulating evidence is suggesting that dysregulation of Wnt and/or Hox genes may affect cell migration during organogenesis and differentiation of Müllerian structures of the female reproductive tract, with possible dislocation and dissemination of primordial endometrial stem cells in ectopic regions, which have high plasticity to differentiation. We hypothesize that during postpubertal age, under the influence of different stimuli, these misplaced and quiescent ectopic endometrial cells could acquire new phenotype, biological functions, and immunogenicity. So, these kinds of cells may differentiate, specializing in epithelium, glands, and stroma to form a functional ectopic endometrial tissue. This may provoke a breakdown in the peritoneal cavity homeostasis, with the consequent processes of immune alteration, documented by peripheral mononuclear cells recruitment and secretion of inflammatory cytokines in early phases and of angiogenic and fibrogenic cytokines in the late stages of the disease.

Progesterone action in endometrial cancer, endometriosis, uterine fibroids, and breast cancer

Progesterone receptor (PR) mediates the actions of the ovarian steroid progesterone, which together with estradiol regulates gonadotropin secretion, prepares the endometrium for implantation, maintains pregnancy, and differentiates breast tissue. Separation of estrogen and progesterone actions in hormone-responsive tissues remains a challenge. Pathologies of the uterus and breast, including endometrial cancer, endometriosis, uterine fibroids, and breast cancer, are highly associated with estrogen, considered to be the mitogenic factor. Emerging evidence supports distinct roles of progesterone and its influence on the pathogenesis of these diseases. Progesterone antagonizes estrogen-driven growth in the endometrium, and insufficient progesterone action strikingly increases the risk of endometrial cancer. In endometriosis, eutopic and ectopic tissues do not respond sufficiently to progesterone and are considered to be progesterone-resistant, which contributes to proliferation and survival. In uterine fibroids, progesterone promotes growth by increasing proliferation, cellular hypertrophy, and deposition of extracellular matrix. In normal mammary tissue and breast cancer, progesterone is pro-proliferative and carcinogenic. A key difference between these tissues that could explain the diverse effects of progesterone is the paracrine interactions of PR-expressing stroma and epithelium. Normal endometrium is a mucosa containing large quantities of distinct stromal cells with abundant PR, which influences epithelial cell proliferation and differentiation and protects against carcinogenic transformation. In contrast, the primary target cells of progesterone in the breast and fibroids are the mammary epithelial cells and the leiomyoma cells, which lack specifically organized stromal components with significant PR expression. This review provides a unifying perspective for the diverse effects of progesterone across human tissues and diseases.

Aromatase inhibitors for the treatment of endometriosis

OBJECTIVE

To review the use of aromatase inhibitors (AIs) for the treatment of endometriosis.

DESIGN

Literature review.

CONCLUSION(S)

Most studies show that in reproductive-age women, the combination of AI with conventional therapy alleviates endometriosis-related pain. In postmenopausal women, using an AI alone has been shown to be an effective treatment, although more studies are needed in this subgroup. Side effects of using AIs appear to be tolerable in most women, although special consideration should be given to monitoring bone mineral density. More studies need to be done examining pregnancy rates and outcomes after AI treatment for endometriosis. In addition, larger randomized clinical trials using AIs need to be done. In summary, AIs may be effective in treating endometriosis-related chronic pelvic pain in both reproductive-age and postmenopausal women.

Estrogen biosynthesis and signaling in endometriosis

Endometriosis is an estrogen-dependent gynecological disease where endometrium-like tissue grows outside uterine cavity. Endometriotic cell proliferation is stimulated by estrogens acting predominantly via their nuclear receptors. Estrogen receptors (ESR1, ESR2) are ligand activated transcription factors whose activation is dependent on the cell-specific dynamic expression of the receptors, on the interacting proteins and on the ligand availability. The different types of endometriotic lesions, peritoneal, deep, and ovarian endometriosis, may respond to estrogens differentially due to differences in the expression of the receptors and interacting proteins, and due to potential differences in the ligand availability regulated by the local estrogen synthesis. This review summarizes the current knowledge of estrogen synthesizing enzymes and estrogen receptors in different types of endometriosis lesions. Further studies are still needed to define the possible differences in steroid metabolism in different types of endometriotic lesions.

A polymorphism in a let-7 microRNA binding site of KRAS in women with endometriosis

Endometriosis is found in 5-15% of women of reproductive age and is more frequent in relatives of women with the disease. Activation of KRAS results in de novo endometriosis in mice, however, activating KRAS mutations have not been identified in women. We screened 150 women with endometriosis for a polymorphism in a let-7 microRNA (miRNA) binding site in the 3'-UTR of KRAS and detected a KRAS variant allele in 31% of women with endometriosis as opposed to 5% of a large diverse control population. KRAS mRNA and protein expression were increased in cultured endometrial stromal cells of women with the KRAS variant. Increased KRAS protein was due to altered miRNA binding as demonstrated in reporter assays. Endometrial stromal cells from women with the KRAS variant showed increased proliferation and invasion. In a murine model, endometrial xenografts containing the KRAS variant demonstrated increased proliferation and decreased progesterone receptor levels. These findings suggest that an inherited polymorphism of a let-7 miRNA binding site in KRAS leads to abnormal endometrial growth and endometriosis. The LCS6 polymorphism is the first described genetic marker of endometriosis risk.

Endometriosis expresses a molecular pattern consistent with decreased retinoid uptake, metabolism and action

BACKGROUND

Retinoic acid (RA) regulates key biological processes, including differentiation, apoptosis and cell survival. RA mediates induction of 17 beta-hydroxysteroid dehydrogenase type 2 mRNA, catalyzing the conversion of estradiol to estrone, in endometrium but not endometriosis because of a defect in endometriotic stromal cells. This defect may involve both the uptake and metabolism of RA. In this study, we analyze the expression of genes involved in RA signaling in normal endometrium and endometriosis.

METHODS

Tissue and stromal cells from ovarian endometriomas and eutopic endometrium from disease-free women were collected. Real-time reverse transcription-polymerase chain reaction was used to measure mRNA levels. Western blotting was used to evaluate protein expression.

RESULTS

We found that endometriotic tissue and stromal cells demonstrated significantly decreased mRNA expression of the major genes involved in RA signaling, including STRA6, CRBP1, ALDH1A2, CRABP2 and FABP5. We found increased levels of CYP26B1, responsible for RA metabolism. Nuclear extracts showed that RARα, RXRα and PPARβ/δ were underexpressed in both tissues and stromal cells from endometriotic tissue. Differences in protein levels were confirmed by western blotting.

CONCLUSIONS

Endometriosis is characterized by a gene expression pattern suggesting a decrease in uptake and metabolism of RA. Because RA is integral in regulating key biological processes involved in cell survival, this alteration could partially explain the resistance to apoptosis found in endometriosis.

Effect of primary human endometrial stromal cells on epithelial cell receptivity and protein expression is dependent on menstrual cycle stage

BACKGROUND

Successful implantation requires a receptive endometrium. We hypothesized that effects of endometrial stromal cells (ESC) on epithelial cell receptivity and trophoblast-endometrium interaction are menstrual cycle dependent.

METHODS

An endometrial in vitro 3D co-culture model of primary human ESC with the endometrial epithelial cell line (RL95-2) was constructed. Co-cultures were prepared using primary ESC from biopsies taken before the window of implantation (ESCbw) and during the window of implantation (ESCw), on cycle days 10-17 and 19-23, respectively. RL95-2 served as a constant parameter upon which the influence of ESC from different phases of the cycle was investigated. proMMP-2 (MMP, matrix metalloproteinase) and proMMP-9 secretion was tested in response to progesterone. Progesterone receptor B (PR-B) and plexin B1 protein expression and mRNA levels were investigated using immunofluorescence and RT-PCR, respectively.

RESULTS

Progesterone increased proMMP-2 secretion in primary ESCbw (P = 0.0046) but decreased proMMP-2 and proMMP-9 secretion in ESCw (P < 0.0005). In the presence of ESCbw, JAR spheroid attachment rate to overlying RL95-2 cells was decreased (P < 0.0001), whereas in the presence of ESCw, attachment rate was unchanged. Progesterone treatment restored epithelial cell receptivity in co-culture with ESCbw (P = 0.00004). A correlation between spheroid attachment rate and plexin B1 mRNA level was observed (P = 0.01). PR-B protein and mRNA level were influenced by the interplay between RL95-2 and stromal cells.

CONCLUSION

The effects of human primary ESC on epithelial cell receptivity and trophoblast-endometrium interaction depended upon whether the ESC were taken before or during the window of implantation.

Altered retinoid uptake and action contributes to cell survival in endometriosis

CONTEXT

Retinoic acid (RA) controls multiple biological processes via exerting opposing effects on cell survival. Retinol uptake into cells is controlled by stimulated by RA 6 (STRA6). RA is then produced from retinol in the cytosol. Partitioning of RA between the nuclear receptors RA receptor α and peroxisome-proliferator-activated receptor β/δ is regulated by cytosol-to-nuclear shuttling proteins cellular RA binding protein 2 (CRABP2) and fatty acid binding protein 5 (FABP5), which induce apoptosis or enhance survival, respectively. The roles of these mechanisms in endometrium or endometriosis remain unknown.

OBJECTIVE

The aim was to determine the regulation of retinoid uptake and RA action in primary stromal cells from endometrium (n = 10) or endometriosis (n = 10).

RESULTS

Progesterone receptor was necessary for high STRA6 and CRABP2 expression in endometrial stromal cells. STRA6, which was responsible for labeled retinoid uptake, was strikingly lower in endometriotic cells compared to endometrial cells. CRABP2 knockdown in endometrial cells increased survival, and FABP5 knockdown in endometriotic cells decreased survival without altering the expression of downstream nuclear retinoic acid receptor α and peroxisome-proliferator-activated receptor β/δ.

CONCLUSIONS

In endometrial stromal cells, progesterone receptor up-regulates expression of STRA6 and CRABP2, which control retinol uptake and growth-suppressor actions of RA. In endometriotic stromal cells, decreased expression of these genes leads to decreased retinol uptake and dominant FABP5-mediated prosurvival activity.

Deregulation of LOXL1 and HTRA1 gene expression in endometriosis

Endometriosis is a gynecologic disease characterized by the presence of endometrial tissue outside the uterine cavity. Although 15% of the female population in reproductive age is affected by endometriosis, its pathogenesis remains unclear. According to the most accepted pathogenesis hypothesis, endometrial fragments from the menstrual phase are transported through the uterine tubes to the peritoneal cavity, where they undergo implantation and growth, invading adjacent tissues. However, the establishment of the disease requires that endometrial cells present molecular characteristics favoring the onset and progression of ectopic implantation. In this investigation, we analyzed the differential gene expression profiles of peritoneal and ovarian endometriotic lesions compared to the endometrial tissue of nonaffected women using rapid subtraction hybridization (RaSH). In our study, this method was applied to samples of endometriotic lesions from affected women and to biopsies of endometrium of healthy women without endometriosis, where we could identify 126 deregulated genes. To evaluate the expression of genes found by RaSH method, we measured LOXL1, HTRA1, and SPARC genes by real-time polymerase chain reaction. Significant different expression was obtained for HTRA1 and LOXL1, upregulated in the ectopic endometrium, suggesting that these genes are involved in the physiopathology of endometriosis and may favor the viability of endometrial cells at ectopic sites.

A useful cell system for studying the regulation of 17HSD/KSR type 2 activity and expression in ovarian epithelial cancer

17β-Hydroxysteroid dehydrogenase/17-ketosteroid reductase (17HSD/KSR) activity and 17HSD/KSR types 1, 2, 4, and 5 mRNA levels were characterized in ovarian cancer cell lines derived from patients unexposed to radiation or chemotherapy. Activity was at the limit of detection in TOV-112D and TOV-21G cells. Activity in OV-90 was comparable to that in human placental tissue, was predominantly microsomal and was 17HSD/KSR type 2-like in substrate specificity and inhibition patterns. In monolayers, conversion of testosterone (T) to androstenedione (A) was 12-fold greater than that of A to T. Reduction of fetal bovine serum to 0.3% in the culture medium had no effect on 17β-HSD activity. Significant levels of type 1 and type 2 mRNAs were observed in OV-90 while only trace amounts were detected in TOV-21G. In contrast, type 4 mRNA levels were comparable for OV-90 and TOV-21G. Type 5 mRNA was detected in both cell lines but its level in OV-90 was twice that of TOV-21G. In OV-90, the type 2-like activity was predominant even though the type 5 mRNA level was 2.5-fold higher than that of the type 2. OV-90 cells may be a useful system for studying the regulation of 17HSD/KSR type 2 activity and expression in ovarian epithelial cancer.

17Beta-hydroxysteroid dehydrogenase-2 deficiency and progesterone resistance in endometriosis

Estradiol (E2) stimulates the growth and inflammation in the ectopic endometriotic tissue that commonly resides on the pelvic organs. Several clinical and laboratory-based observations are indicative of resistance to progesterone action in endometriosis. The molecular basis of progesterone resistance in endometriosis may be related to an overall reduction in the levels of progesterone receptor (PR). In normal endometrium, progesterone acts via PR on stromal cells to induce secretion of paracrine factor(s) that in turn stimulate neighboring epithelial cells to express the enzyme 17beta-hydroxysteroid dehydrogenase type 2 (HSD17B2). HSD17B2 is an extremely efficient enzyme and rapidly metabolizes the biologically potent estrogen E2 to weakly estrogenic estrone. In endometriotic tissue, progesterone is incapable of inducing epithelial HSD17B2 expression due to a defect in stromal cells. The inability of endometriotic stromal cells to produce progesterone-induced paracrine factors that stimulate HSD17B2 may be due to the very low levels of PR observed in vivo in endometriotic tissue. The end result is deficient metabolism of E2 in endometriosis giving rise to high local concentrations of this mitogen. The molecular details of this physiological paracrine interaction between the stroma and epithelium in normal endometrium and its lack thereof in endometriosis are discussed.

Estrogen metabolism and action in endometriosis

Endometriosis is a complex estrogen-dependent disease that is defined as the presence of endometrial glands and stroma outside the uterine cavity. The etiology of endometriosis is multifactorial and includes complex interactions of genetic, immunological, hormonal and environmental factors. Many theories have been proposed, but no single theory can explain all aspects of endometriosis, suggesting that endometriosis is a heterogeneous disease. This review presents the current theories on the pathogenesis of endometriosis, followed by an overview on estrogen metabolism in normal endometrium and diseased endometrium of endometriosis patients. The potential role of aberrant expression of individual estrogen-metabolizing enzymes is discussed, and a model mechanism for increased formation of estradiol is presented separately for different types of endometriosis. The disturbed expression of estrogen receptors in endometriosis is detailed, and the estrogen biosynthetic enzymes and receptors are discussed as novel therapeutic targets for the treatment of endometriosis.

The non-human primate model of endometriosis: research and implications for fecundity

The development of an animal model of endometriosis is crucial for the investigation of disease pathogenesis and therapeutic intervention. These models will enhance our ability to evaluate the causes for the subfertility associated with disease and provide a first-line validation of treatment modulators. Currently rodents and non-human primate models have been developed, but each model has their limitations. The aim of this manuscript is to summarize the current findings and theories on the development of endometriosis and disease progression and the effectiveness of therapeutic targets using the experimental induced model of endometriosis in the baboon (Papio anubis).

17Beta-hydroxysteroid dehydrogenase enzymes and breast cancer

Sex steroids play an important role in the development and differentiation in several tissues. Biologically active hormones that are locally converted in endocrine organs in the tissue where they exert their effects without release into extracellular space is a field of endocrinology that has been called intracrinology. In pre-menopausal women the ovary is the main source of estrogens, but in post-menopausal women the estrogen production as main site of synthesis moves to peripheral tissues and almost all of the sex steroids are synthesised from precursors of adrenal origin. In breast cancer 60-80% of the tumors express high levels of oestrogen receptor (ER) alpha which gives estrogen a proliferative effect. Breast tumors tend to have a higher intratumoral estrogen concentration than normal breast tissue and plasma, and in situ synthesis and the metabolism of estrogens is believed to be of great importance for the development and progression of the disease. The activity of estrogen metabolizing enzymes in breast are mainly aromatase, estrone sulfatases and 17HSD enzymes. 17HSD1 and 17HSD2 are the family members known to be of main importance in breast cancer. High expression of 17HSD1 has been associated to poor prognosis in breast cancer and late relapse among patients with ER-positive tumors. One of the mechanisms behind high 17HSD1 expression is gene amplification. Low or absent expression of 17HSD2 is associated to decreased survival in ER-positive breast cancer. 17HSD14 is one of the latest discovered 17HSD enzymes, transfection of 17HSD14 in human breast cancer cells significantly decreased the levels of estradiol in the culture medium. Low expression of 17HSD14 mRNA expression in breast cancer was correlated to decreased survival. The understanding of intratumoral synthesis of sex steroids in breast cancer is crucial to understand the disease both in pre- and post-menopausal women. Further studies are desirable to state the direct role of these enzymes in breast cancer and which patients that may benefit from new therapeutic strategies targeting 17HSD enzymes. The new inhibitors targeting 17HSD1 have shown promising results in pre-clinical studies to have clinical potential in the future.