New concepts on the etiology of endometriosis

Endometriosis is a serious, chronic disorder where endometrial tissue grows outside the uterus, causing severe pelvic pain and infertility. It affects 11% of women. Endometriosis is a multifactorial disorder of unclear etiology, although retrograde menstruation plays a major role. It has a genetic component with over 40 genetic risk factors mapped, although their mechanism of action is still emerging. New evidence suggests a role for retrograde menstruation of endometrial stem/progenitor cells, now that identifying markers of these cells are available. Recent lineage tracing and tissue clearing microscopy and 3D reconstruction has provided new understanding of endometrial glandular structure, particularly the horizontal orientation and interconnection of basalis glands. New sequencing technologies, particularly whole genome DNA sequencing are revealing somatic mutations, including in cancer driver genes, in normal and eutopic endometrium of patients with endometriosis, as well as ectopic endometriotic lesions. Methylome sequencing is offering insight into the regulation of genes and the role of the environmental factors. Single cell RNA sequencing reveals the transcriptome of individual endometrial cells, shedding new light on the diversity and range of cellular subpopulations of the major cell types present in the endometrium and in endometriotic lesions. New endometrial epithelial organoid cultures replicating glandular epithelium are providing tractable models for studying endometriosis. Organoids derived from menstrual fluid offer a non-invasive source of endometrial tissue and a new avenue for testing drugs and developing personalized medicine for treating endometriosis. These new approaches are rapidly advancing our understanding of endometriosis etiology.

The Role of Platelets in the Pathogenesis and Pathophysiology of Adenomyosis

Widely viewed as an enigmatic disease, adenomyosis is a common gynecological disease with bewildering pathogenesis and pathophysiology. One defining hallmark of adenomyotic lesions is cyclic bleeding as in eutopic endometrium, yet bleeding is a quintessential trademark of tissue injury, which is invariably followed by tissue repair. Consequently, adenomyotic lesions resemble wounds. Following each bleeding episode, adenomyotic lesions undergo tissue repair, and, as such, platelets are the first responder that heralds the subsequent tissue repair. This repeated tissue injury and repair (ReTIAR) would elicit several key molecular events crucial for lesional progression, eventually leading to lesional fibrosis. Platelets interact with adenomyotic cells and actively participate in these events, promoting the lesional progression and fibrogenesis. Lesional fibrosis may also be propagated into their neighboring endometrial-myometrial interface and then to eutopic endometrium, impairing endometrial repair and causing heavy menstrual bleeding. Moreover, lesional progression may result in hyperinnervation and an enlarged uterus. In this review, the role of platelets in the pathogenesis, progression, and pathophysiology is reviewed, along with the therapeutic implication. In addition, I shall demonstrate how the notion of ReTIAR provides a much needed framework to tether to and piece together many seemingly unrelated findings and how it helps to make useful predictions.

“Iron triangle” of regulating the uterine microecology: Endometrial microbiota, immunity and endometrium

The uterus is the core place for breeding new life. The balance and imbalance of uterine microecology can directly affect or even dominate the female reproductive health. Emerging data demonstrate that endometrial microbiota, endometrium and immunity play an irreplaceable role in regulating uterine microecology, forming a dynamic iron triangle relationship. Up to nowadays, it remains unclear how the three factors affect and interact with each other, which is also a frontier topic in the emerging field of reproductive tract microecology. From this new perspective, we aim to clarify the relationship and mechanism of the interaction of these three factors, especially their pairwise interactions. Finally, the limitations and future perspectives of the current studies are summarized. In general, these three factors have a dynamic relationship of mutual dependence, promotion and restriction under the physiological or pathological conditions of uterus, among which the regulatory mechanism of microbiota and immunity plays a role of bridge. These findings can provide new insights and measures for the regulation of uterine microecology, the prevention and treatment of endometrial diseases, and the further multi-disciplinary integration between microbiology, immunology and reproductive medicine.

A Joint Model of Random Forest and Artificial Neural Network for the Diagnosis of Endometriosis

Endometriosis (EM), an estrogen-dependent inflammatory disease with unknown etiology, affects thousands of childbearing-age couples, and its early diagnosis is still very difficult. With the rapid development of sequencing technology in recent years, the accumulation of many sequencing data makes it possible to screen important diagnostic biomarkers from some EM-related genes. In this study, we utilized public datasets in the Gene Expression Omnibus (GEO) and Array-Express database and identified seven important differentially expressed genes (DEGs) (COMT, NAA16, CCDC22, EIF3E, AHI1, DMXL2, and CISD3) through the random forest classifier. Among these DEGs, AHI1, DMXL2, and CISD3 have never been reported to be associated with the pathogenesis of EMs. Our study indicated that these three genes might participate in the pathogenesis of EMs through oxidative stress, epithelial–mesenchymal transition (EMT) with the activation of the Notch signaling pathway, and mitochondrial homeostasis, respectively. Then, we put these seven DEGs into an artificial neural network to construct a novel diagnostic model for EMs and verified its diagnostic efficacy in two public datasets. Furthermore, these seven DEGs were included in 15 hub genes identified from the constructed protein–protein interaction (PPI) network, which confirmed the reliability of the diagnostic model. We hope the diagnostic model can provide novel sights into the understanding of the pathogenesis of EMs and contribute to the clinical diagnosis and treatment of EMs.

The Role of mTOR and eIF Signaling in Benign Endometrial Diseases

Adenomyosis, endometriosis, endometritis, and typical endometrial hyperplasia are common non-cancerous diseases of the endometrium that afflict many women with life-impacting consequences. The mammalian target of the rapamycin (mTOR) pathway interacts with estrogen signaling and is known to be dysregulated in endometrial cancer. Based on this knowledge, we attempt to investigate the role of mTOR signaling in benign endometrial diseases while focusing on how the interplay between mTOR and eukaryotic translation initiation factors (eIFs) affects their development. In fact, mTOR overactivity is apparent in adenomyosis, endometriosis, and typical endometrial hyperplasia, where it promotes endometrial cell proliferation and invasiveness. Recent data show aberrant expression of various components of the mTOR pathway in both eutopic and ectopic endometrium of patients with adenomyosis or endometriosis and in hyperplastic endometrium as well. Moreover, studies on endometritis show that derangement of mTOR signaling is linked to the establishment of endometrial dysfunction caused by chronic inflammation. This review shows that inhibition of the mTOR pathway has a promising therapeutic effect in benign endometrial conditions, concluding that mTOR signaling dysregulation plays a critical part in their pathogenesis.

[Adenomyosis pathophysiology: An unresolved enigma]

Adenomyosis is a chronic benign uterine disease characterized by the presence of endometrial glands and stroma within the myometrium. It is a heterogeneous disease, presenting various clinical forms, depending on the location of the ectopic lesions within the myometrium. Adenomyosis can be responsible for several symptoms such as dysmenorrhea, abnormal uterine bleeding and/or infertility. Its pathophysiology is a real conundrum and several theories have been proposed: development of adenomyosis lesion could initiate de novo from Mullerian rests or from stem cells. Moreover, multiple factors could be involved in initiating lesions, including specific hormonal, immune and/or genetic changes. The objective of this review is to provide an update on adenomyosis pathophysiology, in particular on the various theories proposed concerning the invasion of the myometrium by endometrial cells and the inducing mechanisms, and to study the link between the physiopathology, the symptoms and the medical treatments.

Epithelial-to-mesenchymal transition contributes to the downregulation of progesterone receptor expression in endometriosis lesions

Endometriosis is a common, estrogen-dependent disease, in which endometrial tissue grows in the peritoneal cavity. These lesions often express low levels of progesterone receptors (PR), which potentially play an important role in the insufficient response to progestin treatment. Here, we uncover an interconnection between the downregulated PR expression and the epithelial-to-mesenchymal transition (EMT) in endometriotic lesions. The majority of ectopic epithelial glands (93.1 %, n = 67/72) display heterogeneous states of EMT by immunohistochemistry staining. Interestingly, low PR expression associated with high N-cadherin expression, a hallmark of EMT. In order to gain mechanistic insights, we performed in vitro functional assays with the endometriotic epithelial cell lines EM'osis and 12Z. TGF-β-induced EMT, marked by elevations of CDH2 and SNAI1/2, led to a significant downregulation of PR gene expression in both cell lines. In contrast, silencing of SNAI1 in EM'osis and of SNAI1 plus SNAI2 in 12Z elevated PR gene expression significantly. We found that not only in vitro, but also in the epithelial component of endometriotic lesions strong expression of SNAI1/2 concurred with weak expression of PR. In summary, these results suggested the negative correlation association of the heterogeneous states of EMT and suppressed PR expression in endometriotic lesions. Our functional assays indicate that EMT contributes to the downregulation of PR expression via the upregulation of EMT-TFs, like SNAI1 and SNAI2, which may ultimately lead to progesterone resistance.

Immunological changes associated with adenomyosis: a systematic review

BACKGROUND

Adenomyosis is a benign gynecological disorder associated with subfertility, pelvic pain and abnormal uterine bleeding that have significant consequences for the health and quality of life of women. Histologically, it is defined as the presence of ectopic endometrial islets within the myometrium. Its pathogenesis has not yet been elucidated and several pieces of the puzzle are still missing. One process involved in the development of adenomyosis is the increased capacity of some endometrial cells to infiltrate the myometrium. Moreover, the local and systemic immune systems are associated with the onset of the disease and with maintaining it. Numerous observations have highlighted the activation of immune cells and the release of immune soluble factors in adenomyosis. The contribution of immunity occurs in conjunction with hormonal aberrations and activation of the epithelial to mesenchymal transition (EMT) pathway, which promotes migration of endometrial cells. Here, we review current knowledge on the immunological changes in adenomyosis, with the aim of further elucidation of the pathogenesis of this disease.

OBJECTIVE AND RATIONALE

The objective was to systematically review the literature regarding the role of the immune system in development of adenomyosis in the inner and the outer myometrium, in humans.

SEARCH METHODS

A systematic review of published human studies was performed in MEDLINE, EMBASE and Cochrane Library databases from 1970 to February 2019 using the combination of Medical Subject Headings (MeSH): Adenomyosis AND ('Immune System' OR 'Gonadal Steroid Hormones'), and free-text terms for the following search terms (and their variants): Adenomyosis AND (immunity OR immune OR macrophage OR 'natural killer cell' OR lymphocyte* OR leucocyte* OR HLA OR inflammation OR 'sex steroid' OR 'epithelial to mesenchymal transition' OR 'EMT'). Studies in which no comparison was made with control patients, without adenomyosis (systemic sample and/or eutopic endometrium), were excluded.

OUTCOMES

A total of 42 articles were included in our systematic review. Changes in innate and adaptive immune cell numbers were described in the eutopic and/or ectopic endometrium of women with adenomyosis compared to disease-free counterparts. They mostly described an increase in lymphocyte and macrophage cell populations in adenomyosis eutopic endometrium compared to controls. These observations underscore the immune contributions to the disease pathogenesis. Thirty-one cytokines and other markers involved in immune pathways were studied in the included articles. Pro-inflammatory cytokines (interleukin (IL) 6, IL1β, interferon (IFN) α, tumor necrosis factor α, IFNγ) as well as anti-inflammatory or regulatory mediators (IL10, transforming growth factor β…) were found to be elevated in the eutopic endometrium and/or in the ectopic endometrium of the myometrium in women with adenomyosis compared to controls. Moreover, in women affected by adenomyosis, immunity was reported to be directly or indirectly linked to sex steroid hormone aberrations (notably changes in progesterone receptor in eutopic and ectopic endometrium) in three studies and to EMT in four studies.

WIDER IMPLICATIONS

The available literature clearly depicts immunological changes that are associated with adenomyosis. Both systemic and local immune changes have been described in women affected by adenomyosis, with the coexistence of changes in inflammatory as well as anti-inflammatory signals. It is likely that these immune changes, through an EMT mechanism, stimulate the migration of endometrial cells into the myometrium that, together with an endocrine imbalance, promote this inflammatory process. In light of the considerable impact of adenomyosis on women's health, a better understanding of the role played by the immune system in adenomyosis is likely to yield new research opportunities to better understand its pathogenesis.

Epithelial-Mesenchymal Transition in Endometriosis-When Does It Happen?

Epithelial-mesenchymal transition (EMT) is an important process of cell remodeling characterized by the gradual loss of the epithelial phenotype and progressive gain of a mesenchymal phenotype. EMT is not an all-or-nothing process, but instead a transition of epithelial to mesenchymal cells with intermediate cell states. Recently, EMT was described in endometriosis, and many EMT-specific pathways like Twist, Snail, Slug, Zinc finger E-box-binding homeobox 1/2 (ZEB1/2), E/N-cadherin, keratins, and claudins are involved. However, as pointed out in this review, a comparison of the eutopic endometrium of women with and without endometriosis yielded only subtle changes of these EMT markers. Furthermore, only very few alterations in cell-cell contacts could be found but without changes in the epithelial phenotype. This suggests only a partial EMT which is not a prerequisite for the detachment of endometrial cells and, thus, not critical for the first step(s) in the pathogenesis of endometriosis. In contrast, the majority of changes in the EMT-related marker expression were found in the ectopic endometrium, especially in the three endometriotic entities, ovarian, peritoneal, and deep infiltrating endometriosis (DIE), compared with the eutopic endometrium. In this review, we examine the most important EMT pathways described in endometriosis and propose that partial EMT might result from the interaction of endometrial implants with their surrounding microenvironment.

The Prognostic Significance of Eukaryotic Translation Initiation Factors (eIFs) in Endometrial Cancer

Whilst the role of eukaryotic translation initiation factors (eIFs) has already been investigated in several human cancers, their role in endometrial cancer (EC) is relatively unknown. In the present retrospective study, 279 patients with EC (1180 samples) were included (mean age: 63.0 years, mean follow-up: 6.1 years). Samples were analysed for expression of 7 eIFs subunits (eIF2α, eIF3c, eIF3h, eIF4e, eIF4g, eIF5, eIF6) through immunohistochemistry and western blotting. Fifteen samples of healthy endometrium served as controls. Density and intensity were assessed and mean combined scores (CS) calculated for each patient. Upon immunohistochemistry, median eIF5 CS were significantly higher in EC as compared with non-neoplastic tissue (NNT, p < 0.001), whilst median eIF6 CS were significantly lower in EC (p < 0.001). Moreover, eIF5 (p = 0.002), eIF6 (p = 0.032) and eIF4g CS (p = 0.014) were significantly different when comparing NNT with EC grading types. Median eIF4g CS was higher in type II EC (p = 0.034). Upon western blot analysis, eIF4g (p < 0.001), peIF2α (p < 0.001) and eIF3h (p < 0.05) were significantly overexpressed in EC, while expression of eIF3c was significantly reduced in EC as compared with NNT (p < 0.001). The remaining eIFs were non-significant. Besides tumour stage (p < 0.001) and patient's age (p < 0.001), high eIF4g CS-levels were independently associated with poor prognosis (HR: 1.604, 95%CI: 1.037-2.483, p = 0.034). The other eIFs had no prognostic significance. Notably, the independent prognostic significance of eIF4g was lost when adding tumour type. Considering the difficulties in differentiating EC type I and II, eIF4g may serve as a novel prognostic marker indicating patient outcome.

Cellular Components Contributing to Fibrosis in Endometriosis: A Literature Review

Endometriosis-related fibrosis represents a complex phenomenon with underlying mechanisms yet to be clarified. Fibrosis is consistently present in all disease forms and contributes to classic endometriosis-related symptoms of pain and infertility. The purpose of this literature review was to examine the role of various cellular populations and biologic mechanisms and signaling pathways in inducing fibrogenesis of endometriotic lesions. A search was performed through PubMed and MEDLINE for animal and human studies published in English in the last 23 years that examined fibrosis in superficial, ovarian, and deep infiltrating endometriosis. The main cell types found to be involved in the development of fibrosis were platelets, macrophages, ectopic endometrial cells, and sensory nerve fibers. Interactions among each of the cell types contribute to the production of fibrosis through the production of soluble factors, mostly transforming growth factor-β but also other cytokines and neuropeptides. Cell types known to be critical to the pathophysiology of endometriosis also contribute to fibrogenesis, thus supporting the theory that fibrosis is an inherent part of endometriosis.

Anti-inflammatory cytokines in endometriosis

Although the pathogenesis of endometriosis is not fully understood, it is often considered to be an inflammatory disease. An increasing number of studies suggest that differential expression of anti-inflammatory cytokines (e.g., interleukin-4 and -10, and transforming growth factor-β1) occurs in women with endometriosis, including in serum, peritoneal fluid and ectopic lesions. These anti-inflammatory cytokines also have indispensable roles in the progression of endometriosis, including by promoting survival, growth, invasion, differentiation, angiogenesis, and immune escape of the endometriotic lesions. In this review, we provide an overview of the expression, origin, function and regulation of anti-inflammatory cytokines in endometriosis, with brief discussion and perspectives on their future clinical implications in the diagnosis and therapy of the disease.