Endometriosis: disease pathophysiology and the role of prostaglandins

Endometriosis is considered to be a polygenic disease with a complex, multifactorial aetiology that affects about 10% of women in the reproductive age. Women with endometriosis have symptoms that include chronic pelvic pain, dysmenorrhoea and dyspareunia, significantly reducing their quality of life. Endometriosis is also the primary cause of infertility in women, with the prevalence rate ranging from 20% to 50%. The high prevalence and severe outcomes of this disease have made it a major public health concern in modern society. Currently, the mechanism(s) responsible for the initiation and promotion of this disease remains obscure. In this review, we focus on the expression, regulation and action of prostaglandins in the cellular and molecular mechanisms that contribute to the development and/or maintenance of endometriosis.     

Could DNA hydroxymethylation be crucial in influencing steroid hormone signaling in endometrial biology and endometriosis?

Endometriosis affects 10% of reproductive‐aged women. It is characterized by the growth of the endometrium, outside the uterus and is associated with infertility and chronic abdominal pain. Lack of noninvasive diagnostic tools and early screening tests results in delayed treatment and subsequently increased disease severity. Endometriosis is a disease associated with a deregulated hormonal response, therefore, understanding the molecular mechanisms that govern this hormonal interplay is of paramount importance. DNA methylation is an epigenetic mark that regulates gene expression and is often associated with genes that code for steroid receptors and enzymes associated with estrogen synthesis and metabolism in endometriosis. DNA hydroxymethylation, which is structurally similar to methylation but functionally different, is a biologically critical mechanism that is also known to regulate gene expression. Ten Eleven Translocation (TET) proteins mediate hydroxymethylation. However, the role of DNA hydroxymethylation or TETs in the endometrium remains relatively unexplored. Currently, the “gold standard” technique used to study methylation patterns is bisulfite genomic sequencing. This technique also detects hydroxymethylation but fails to distinguish between the two, thereby limiting our understanding of these two processes. The presence of TETs in the male and female reproductive tract and its contribution to endometrial cancer makes it an important factor to study in endometriosis. This review summarizes the role of DNA methylation in aberrant steroid hormone signaling and hypothesizes that hydroxymethylation could be a factor influencing hormonal instability seen in endometriosis.     

Emerging hallmarks of endometriosis metabolism: A promising target for the treatment of endometriosis

Endometriosis, characterized by ectopic endometrium growth in the extrauterine environment, is one of the most notable diseases of the female reproductive system. Worldwide, endometriosis affects nearly 10 % of women in their reproductive years and causes a significant decline in quality of life. Despite extensive investigations of endometriosis over the past years, the mechanisms of endometriosis pathogenesis remain unclear. In recent years, metabolic factors have increasingly been considered factors in endometriosis. There is compelling evidence regarding the progress of endometriosis in the context of severe metabolic dysfunction. Hence, the curative strategies and ongoing attempts to conquer endometriosis might start with metabolic pathways. This review focuses on metabolic mechanisms and summarizes current research progress. These findings provide valuable information for the non-intrusive diagnosis of the disease and may contribute to the understanding of the pathogenesis of endometriosis.     

Molecular dysregulations underlying the pathogenesis of endometriosis

Endometriosis is a crippling disease characterized by the presence of endometrium-like tissue or scar outside the uterine cavity, commonly confined to the peritoneal and serosal surfaces of the pelvic organs. 10–15% of women in reproductive age are estimated to be affected by endometriosis. Most of these patients present with infertility and suffer from pelvic pain. The benign disease rarely progresses to malignancy. Regardless of its high prevalence, the pathogenesis of the disease is not fully understood. Treatment options for endometriosis are limited and are often based on a symptomatic approach. The unavailability of proper diagnostic approaches, fewer therapeutic options, and sparse understanding of molecular alterations are responsible for the continued disease burden. Exploring the molecular elements causing the pathogenesis of endometriosis may lead to a number of breakthroughs in the treatment of the illness, such as the discovery of new biomarkers for diagnosis and therapeutic targets that can be a guide to better prognosis and reduced recurrence. The goal of this review is to provide the reader a critical understanding of the disease by summarizing the genetic, immunological, hormonal, and epigenetic deregulations that support the molecular basis for development of endometriotic cyst, with a special focus on the study models needed to analyze these changes in the endometriotic microenvironment.     

Mouse model of surgically-induced endometriosis by auto-transplantation of uterine tissue

Endometriosis is a chronic, painful disease whose etiology remains unknown. Furthermore, treatment of endometriosis can require laparoscopic removal of lesions, and/or chronic pharmaceutical management of pain and infertility symptoms. The cost associated with endometriosis has been estimated at 22 billion dollars per year in the United States. To further our understanding of mechanisms underlying this enigmatic disease, animal models have been employed. Primates spontaneously develop endometriosis and therefore primate models most closely resemble the disease in women. Rodent models, however, are more cost effective and readily available. The model that we describe here involves an autologous transfer of uterine tissue to the intestinal mesentery (Figure 1) and was first developed in the rat and later transferred to the mouse. The goal of the autologous rodent model of surgically-induced endometriosis is to mimic the disease in women. We and others have previously shown that the altered gene expression pattern observed in endometriotic lesions from mice or rats mirrors that observed in women with the disease. One advantage of performing the surgery in the mouse is that the abundance of transgenic mouse strains available can aid researchers in determining the role of specific components important in the establishment and growth of endometriosis. An alternative model in which excised human endometrial fragments are introduced to the peritoneum of immunocompromised mice is also widely used but is limited by the lack of a normal immune system which is thought to be important in endometriosis. Importantly, the mouse model of surgically induced endometriosis is a versatile model that has been used to study how the immune system, hormones and environmental factors affect endometriosis as well as the effects of endometriosis on fertility and pain.     

The possible anti-inflammatory role of circulating human leukocyte antigen levels in women with endometriosis after treatment with danazol and leuprorelin acetate depot

BACKGROUND: Endometriosis is defined as an inflammatory condition of the female reproductive tract, a state often associated with infertility and miscarriage. Many exogenously administered factors (treatments) control the disease via as yet unknown pathways. Possible candidate molecules involved in these mechanisms could be the serum-soluble human leukocyte antigens (sHIA) that have been detected in a variety of human body fluids and that are associated with several diseases. AIMS: We here examine how danazol and leuprorelin acetate depot treatments exert their anti-inflammatory action. It is plausible that subtle alterations mediated by these treatments and in relation to sHLA may explain the pathophysiology of endometriosis and provide insights towards new therapeutic protocols. METHODS: Indirect enzyme-linked immunosorbent assay (ELISA), using specific monoclonal antibodies, determined serum-soluble class-I and class-II HLA levels. ELISA readings from treated women were compared with normal healthy subjects. RESULTS: Serum-soluble class-I and class-II HLA levels are statistically significantly lower (P < 0.001) in women with endometriosis than in the control groups. However, danazol but not leuprorelin acetate depot administration augments soluble HLA class I and class II (P < 0.01 and P < 0.001, respectively) to normal levels during the treatment period, an increase that may account for the anti-inflammatory effect and the remission observed. CONCLUSIONS: It is shown that one of the underlying causes of endometriosis may be the lack of both circulating class-I and class-II antigen levels. Danazol administration acts via an induced release of these antigens, whose presence correlates with the degree of the inflammatory alleviation obtained. We thus provide evidence that the inflammatory state of the disease appears to be associated with soluble HLA levels because, 3 months after ceasing therapy, the circulating antigens in the serum return to the same levels that correspond to the pathological condition.     

A baboon model for endometriosis: implications for fertility

Endometriosis is one of the most common causes of chronic pelvic pain and infertility in women in the reproductive age group. Although the existence of this disease has been known for over 100 years our current knowledge of its pathogenesis and the pathophysiology of its related infertility remains unclear. Several reasons contribute to our lack of knowledge, the most critical being the difficulty in carrying out objective long-term studies in women. Thus, we and others have developed a model of this disease in the non-human primate, the baboon (Papio anubis). Intraperitoneal inoculation of autologous menstrual endometrium results in the development of endometriotic lesions with gross morphological characteristics similar to those seen in the human. Multiple factors have been implicated in endometriosis-associated infertility. We have described aberrant levels of factors involved in multiple pathways important in the establishment of pregnancy, in the endometrium of baboons induced with endometriosis. Specifically, we have observed dysregulation of proteins involved in invasion, angiogenesis, methylation, cell growth, immunomodulation, and steroid hormone action. These data suggest that, in an induced model of endometriosis in the baboon, an increased angiogenic capacity, decreased apoptotic potential, progesterone resistance, estrogen hyper-responsiveness, and an inability to respond appropriately to embryonic signals contribute to the reduced fecundity associated with this disease.     

Pathogenesis of endometriosis: natural immunity dysfunction or autoimmune disease?

Endometriosis is a chronic inflammatory disease, characterized by implantation and growth of endometrial tissue outside the uterine cavity. This disabling condition is considered one of the most frequent diseases in gynecology, affecting 15-20% of women in their reproductive life. Pelvic endometriosis, the most common form of the disease, is associated with increased secretion of pro-inflammatory cytokines, neo-angiogenesis, intrinsic anomalies of the refluxed endometrium and impaired function of cell-mediated natural immunity. Recently, endometriosis has also been considered to be an autoimmune disease, owing to the presence of autoantibodies, the association with other autoimmune diseases and recurrent immune-mediated abortion. These findings are in apparent contradiction with the reduced cell-mediated natural immunity observed during the disease. In this review, we focus on the multiple processes underlying the complex pathogenesis of endometriosis, with particular emphasis on the role played by the immune system with the induction of autoimmunity.     

RhoA/ROCK pathway mediates the effect of oestrogen on regulating epithelial‐mesenchymal transition and proliferation in endometriosis

Endometriosis is a benign gynaecological disease appearing with pelvic pain, rising dysmenorrhoea and infertility seriously impacting on 10% of reproductive‐age females. This research attempts to demonstrate the function and molecular mechanism of RhoA/ROCK pathway on epithelial‐mesenchymal transition (EMT) and proliferation in endometriosis. The expression of Rho family was abnormally changed in endometriotic lesions; in particular, RhoA and ROCK1/2 were significantly elevated. Overexpression of RhoA in human eutopic endometrial epithelial cells (eutopic EECs) enhanced the cell mobility, epithelial‐mesenchymal transition (EMT) and proliferation, and RhoA knockdown exhibited the opposite function. Oestrogen up‐regulated the RhoA activity and expression of RhoA and ROCK1/2. RhoA overexpression reinforced the effect of oestrogen on promoting EMT and proliferation, and RhoA knockdown impaired the effect of oestrogen. oestrogen receptor α (ERα) was involved with the regulation of oestrogen on EMT and proliferation and up‐regulated RhoA activity and expression of RhoA and ROCK1/2. The function of ERα was modulated by the change in RhoA expression. Furthermore, phosphorylated ERK that was enhanced by oestrogen and ERα promoted the protein expression of RhoA/ROCK pathway. Endometriosis mouse model revealed that oestrogen enhanced the size and weight of endometriotic lesions. The expression of RhoA and phosphorylated ERK in mouse endometriotic lesions was significantly elevated by oestrogen. We conclude that abnormal activated RhoA/ROCK pathway in endometriosis is responsible for the function of oestrogen/ERα/ERK signalling, which promoted EMT and proliferation and resulted in the development of endometriosis.     

Genomewide linkage study in 1,176 affected sister pair families identifies a significant susceptibility locus for endometriosis on chromosome 10q26

Endometriosis is a common gynecological disease that affects up to 10% of women in their reproductive years. It causes pelvic pain, severe dysmenorrhea, and subfertility. The disease is defined as the presence of tissue resembling endometrium in sites outside the uterus. Its cause remains uncertain despite >50 years of hypothesis-driven research, and thus the therapeutic options are limited. Disease predisposition is inherited as a complex genetic trait, which provides an alternative route to understanding the disease. We seek to identify susceptibility loci, using a positional-cloning approach that starts with linkage analysis to identify genomic regions likely to harbor these genes. We conducted a linkage study of 1,176 families (931 from an Australian group and 245 from a U.K. group), each with at least two members--mainly affected sister pairs--with surgically diagnosed disease. We have identified a region of significant linkage on chromosome 10q26 (maximum LOD score [MLS] of 3.09; genomewide P = .047) and another region of suggestive linkage on chromosome 20p13 (MLS = 2.09). Minor peaks (with MLS > 1.0) were found on chromosomes 2, 6, 7, 8, 12, 14, 15, and 17. This is the first report of linkage to a major locus for endometriosis. The findings will facilitate discovery of novel positional genetic variants that influence the risk of developing this debilitating disease. Greater understanding of the aberrant cellular and molecular mechanisms involved in the etiology and pathophysiology of endometriosis should lead to better diagnostic methods and targeted treatments.     

Galectin-1 Overexpression in Endometriosis and Its Regulation by Neuropeptides (CRH,UCN) Indicating Its Important Role in Reproduction and Inflammation

Endometriosis is an inflammatory disease of women of reproductive age featured by the presence of ectopic endometrium and is strongly related to infertility. Galectins, carbonhydrate-binding proteins, have been found to have pro- or anti-inflammatory roles in the reproductive tract and in pathological conditions concerning infertility. Galectin-1, which is expressed at endometrium and decidua, plays a major role in implantation and trophoblast invasion. Also, the neuropeptides, corticotropin releasing hormone (CRH) and urocortin (UCN) and their receptors are expressed in eutopic and ectopic endometrium showing a differential expression pattern in endometriotic women compared to healthy ones. The aim of this study was to examine the galectin-1 expression in endometriotic lesions and compare its expression in eutopic endometrium of endometriotic and healthy women. Furthermore, we examined the effect of CRH and UCN in galectin-1 expression in Ishikawa cell line and macrophages and investigated the implication of CRHR1 in these responses. Eutopic and ectopic endometrium specimens, Ishikawa cell line and mice macrophages were used. Immunohistochemistry and western blot analysis were performed in order to identify galectin-1 expression in ectopic and eutopic endometrium of women with and without endometriosis and the regulatory effect of CRH and UCN on galectin-1 expression. This study presents for the first time that galectin-1 is overexpressed in endometriotic lesions compared to eutopic endometrium of endometriotic women and is more abundantly expressed in eutopic endometrium of disease women compared to healthy ones. Furthermore, it is shown that CRH and UCN upregulate galectin-1 expression in Ishikawa cell line and macrophages and this effect is mediated through CRHR1. These results suggest that galectin-1 might play an important role in endometriosis pathology and infertility profile of women suffering from endometriosis by being at the same time regulated by CRH and UCN interfering in the immune disequilibrium which characterizes this pathological condition.     

Autophagy in endometriosis: Friend or foe?

Endometriosis is a chronic, estrogen-dependent disease and characterized by the implantation of endometrial glands and stroma deep and haphazardly into the outside the uterine cavity. It affects an estimated 10% of the female population of reproductive age and results in obvious reduction in health-related quality of life. Unfortunately, there is no a consistent theory for the etiology of endometriosis. Furthermore, the endometriosis is hard to diagnose in early stage and the treatment methods are limited. Importantly, emerging evidence has investigated that there is a close relationship between endometriosis and autophagy. However, autophagy is a friend or foe in endometriosis is puzzling, the precise mechanism underlying autophagy in endometriosis has not been fully elucidated yet. Here, we provide an integrated view on the acquired findings of the connections between endometriosis and autophagy. We also discuss which may contribute to the abnormal level of autophagy in endometriosis.     

Oestrogen induces epithelial‐mesenchymal transition in endometriosis via circ_0004712/miR‐148a‐3p sponge function

Endometriosis is a common, chronic gynaecologic disease affecting up to 10% of women in their reproductive age and leading to pain and infertility. Oestrogen (E₂)‐induced epithelial‐mesenchymal transition (EMT) process has been considered as a key factor of endometriosis development. Recently, the dysregulated circular RNAs (circRNAs) have been discovered in endometriosis tissues. However, the molecular mechanism of circRNAs on the E₂‐induced EMT process in endometriosis is still unknown. Here, we demonstrated that circ_0004712 up‐regulated by E₂ treatment in endometrial epithelial cells. Knock‐down the expression of circ_0004712 significantly suppressed E₂‐induced cell migration activity. Meanwhile, we identified miR‐148a‐3p as a potential target miRNA of circ_0004712. Inhibited the expression of miR‐148a‐3p could recovered the effect of circ_0004712 knock‐down in E₂‐treated endometrial epithelial. Furthermore, Western blot assay showed that E₂ treatment could increase the expression and activity of β‐catenin, snail and N‐cadherin and reduce the expression of E‐cadherin. The expression and activity of β‐catenin pathway were recovered by circ_0004712 knock‐down or miR‐148a‐3p overexpression. Altogether, the results demonstrate that circ_0004712/miR‐148a‐3p plays an important role in E₂‐induced EMT process in the development of endometriosis, and the molecular mechanism may be associated with the β‐catenin pathway. This work highlighted the importance of circRNAs in the development of endometriosis and provide a new biomarker for diagnosis and therapies.     

Progesterone and transforming growth factor-beta coordinately regulate suppression of endometrial matrix metalloproteinases in a model of experimental endometriosis.

Endometriosis is a benign, though aggressive, disease of the female reproductive tract that consists of endometrial stromal and epithelial cells growing at an extrauterine site. Although it is widely accepted that the majority of cases of endometriosis result from the ectopic implantation of refluxed menstrual tissue, the precise mechanisms by which this disease becomes established are not well understood. Matrix metalloproteinases (MMPs), enzymes which are important for extracellular matrix turnover, have recently been implicated in the development of endometriosis. MMPs appear to be overexpressed in endometriotic lesions, but expression levels decrease following successful medical therapy. Intriguingly, although transforming growth factor-beta (TGF-beta) mediates progesterone suppression of specific endometrial MMPs, this growth factor is overexpressed in women with endometriosis. In the current study, we used an established experimental model of endometriosis to explore MMP regulation by TGF-beta. Our findings indicate that blocking the action of TGF-beta opposes progesterone-mediated suppression of MMPs and blocks the ability of this steroid to prevent experimental endometriosis. However, we also show that the action of TGF-beta does not lead to a sustained suppression of MMPs as observed following progesterone treatment. Taken together, our data suggest that in the absence of a normal progesterone response, common in ectopic lesions of endometriosis, sensitivity to TGF-beta may be altered, resulting in a failure to regulate MMPs.     

The putative role of cell adhesion molecules in endometriosis: can we learn from tumour metastasis?

Endometriosis, one of the most frequent diseases in gynaecology, is a considerable threat to the physical, psychological and social integrity of women. The etiology and pathogenesis of this important disease, defined as the ectopic location of endometrium-like glandular epithelium and stroma outside the uterine cavity, is poorly understood. Clinical observations and in vitro experiments imply that endometriotic cells are invasive and able to metastasize. Analogous to tumour metastasis, it is likely that cell adhesion molecules are central for the invasion and metastasis of endometriotic cells. Investigation of these molecules in endometriosis should increase our understanding of the molecular mechanisms involved in the pathogenesis of this disease.     

Stem cells: are they the answer to the puzzling etiology of endometriosis?

Endometriosis is a chronic benign disease characterized by the presence of abnormally located tissue resembling the endometrium with glands and stroma. This disease has a high degree of morbidity due to chronic pelvic pain and infertility. The disease is likely to be polygenic and multifactorial, but the exact pathogenic mechanisms are still not entirely clear. Recently, adult stem cells have been identified in several tissues, including the endometrium. These cells are probably involved in the regenerative ability of the endometrial cycle, and also in the pathogenesis of proliferative gynaecological diseases, such as endometriosis. The identification of stem cells in animal and human tissues is very complex and the putative stem cells are supposed to be found through several assays such as clonogenicity, label-retaining cells, "side-population" cells, undifferentiation markers, and cellular differentiation. Bone marrow-derived stem cells transplanted into humans and animals have also been identified in eutopic endometrium and endometriotic implants. This review evaluates the available evidence regarding stem/progenitor cells in the human endometrium and explores the possible involvement of these cells in the etiology of endometriosis.     

Computational identification and analysis of functional polymorphisms involved in the activation and detoxification genes implicated in endometriosis

Endometriosis is a complex disorder of the female reproductive system where endometrial tissue embeds and grows at extrauterine location leading to inflammation and pain. Hundreds of polymorphisms in several genes have been studied as probable risk factors of this debilitating disease. Bioinformatics tools have come a long way in augmenting the search for putative functional polymorphisms in human diseases. In this study we have explored 16 genes involved in the detoxification of xenobiotic chemicals that are implicated in endometriosis by utilising publically available programs like SIFT, Polyphen, Panther, FastSNP, SNPeffect and PhosSNP. The variations among different ethnic populations of the SNPs were studied. We then calculated the extent to which bioinformatics based predictions are concurrent with real world epidemiological, genotyping studies using a set of SNPs that have been studied in endometriosis case–control studies. Our study shows that there is a significant positive correlation (r = 0.569, p < 0.005) between the summary of the predicted scores taken from 4 different servers and the odds ratio found from epidemiological studies. This report has identified and catalogued various deleterious SNPs that could be important in endometriosis and could aid in further analysis by in vitro and in vivo methods for the better understanding of the disease pathophysiology.