REVIEW ARTICLE: Three-Dimensional Culture of Endometrial Cells: An In Vitro Model of Endometriosis

Strategies for modelling endometrial diseases

Each month during a woman's reproductive years, the endometrium undergoes vast changes to prepare for a potential pregnancy. Diseases of the endometrium arise for numerous reasons, many of which remain unknown. These endometrial diseases, including endometriosis, adenomyosis, endometrial cancer and Asherman syndrome, affect many women, with an overall lack of efficient or permanent treatment solutions. The challenge lies in understanding the complexity of the endometrium and the extensive changes, orchestrated by ovarian hormones, that occur in multiple cell types over the period of the menstrual cycle. Appropriate model systems that closely mimic the architecture and function of the endometrium and its diseases are needed. The emergence of organoid technology using human cells is enabling a revolution in modelling the endometrium in vitro. The goal of this Review is to provide a focused reference for new models to study the diseases of the endometrium. We provide perspectives on the power of new and emerging models, from organoids to microfluidics, which have opened up a new frontier for studying endometrial diseases.

Endometriosis: current challenges in modeling a multifactorial disease of unknown etiology

Endometriosis is a chronic inflammatory hormone-dependent condition associated with pelvic pain and infertility, characterized by the growth of ectopic endometrium outside the uterus. Given its still unknown etiology, treatments usually aim at diminishing pain and/or achieving pregnancy. Despite some progress in defining mode-of-action for drug development, the lack of reliable animal models indicates that novel approaches are required. The difficulties inherent to modeling endometriosis are related to its multifactorial nature, a condition that hinders the recreation of its pathology and the identification of clinically relevant metrics to assess drug efficacy. In this review, we report and comment endometriosis models and how they have led to new therapies. We envision a roadmap for endometriosis research, integrating Artificial Intelligence, three-dimensional cultures and organ-on-chip models as ways to achieve better understanding of physiopathological features and better tailored effective treatments.

In-vitro models of human endometriosis

Endometriosis is one of the most common benign gynecological diseases in women of reproductive age worldwide. In past decades, a number of in-vitro models have been used to investigate the pathology and therapeutic methods for the treatment of endometriosis. The current review summarized the majority of currently available in-vitro models, which utilize a variety of cell or tissues types, including endometriotic cell lines, primary endometrial stromal cells, endometrial stem cells, endometrial explants, peritoneal explants and immune cells. These cells or tissues are cultured individually, co-cultured in 2D or 3D systems with various matrices or cultured in chicken chorioallantotic membranes and amniotic membranes culture systems. These models are able to represent one or more aspects of the process of endometriosis. These models are helpful and can be used to investigate the development of endometriosis and the underlying mechanisms of this disorder in detail, and help investigators select appropriate models for their experiments. Recently, the new concept of endometriosis as a fibrotic condition will lead research to investigate the differentiation of myofibroblasts and the development of fibrosis in endometriotic lesions, which will increase the development of novel models that can be used to investigate endometriotic fibrosis.

Effects of histone methyltransferase inhibition in endometriosis

Although the histone methyltransferase EZH2 and its product H3K27me3 are well studied in cancer, little is known about their role and potential as therapeutic targets in endometriosis. We have previously reported that endometriotic lesions are characterized by global enrichment of H3K27me3. Therefore, we aimed to (1) characterize the expression levels of EZH2 in endometriotic tissues; (2) assess H3K27me3 enrichment in candidate genes promoter regions; and (3) determine if pharmacological inhibition of EZH2 impacts migration, proliferation, and invasion of endometriotic cells. Immunohistochemistry of an endometriosis-focused tissue microarray was used to assess the EZH2 protein levels in tissues. Chromatin immunoprecipitation-qPCR was conducted to assess enrichment of H3K27me3 in candidate gene promoter regions in tissues. Immunofluorescence was performed to assess the effect of an EZH2-specific pharmacological inhibitor on H3K27me3 global enrichment in cell lines. To measure effects of the inhibitor in migration, proliferation, and invasion in vitro we used Scratch, BrdU, and Matrigel assays, respectively. Endometriotic lesions had significantly higher EZH2α nuclear immunostaining levels compared to eutopic endometrium from patients (glands, stroma) and controls (glands). H3K27me3 was enriched within promoter regions of candidate genes in some but not all of the endometriotic lesions. Inhibition of EZH2 reduced H3K27me3 levels in the endometriotic cells specifically, and also reduced migration, proliferation but not invasion of endometriotic epithelial cells (12Z). These findings support future preclinical studies to determine in vivo efficacy of EZH2 inhibitors as promising nonhormonal treatments for endometriosis, still an incurable gynecological disease.

Vasoactive intestinal peptide is upregulated in women with endometriosis and chronic pelvic pain

PROBLEM

Chronic pelvic pain (CPP) causes compromised the quality of life in women with endometriosis and is often attributed to local inflammation and ingrowth of nerve fibers. In this pilot study, we aimed to investigate whether the inflammation-related vasoactive intestinal peptide (VIP) and interleukin (IL)-6 were increased in affected patients.

METHOD OF STUDY

Endometrial and endometriotic tissue biopsy specimens, and serum and peritoneal fluid (PF) samples, were obtained from 85 endometriosis patients and 53 controls. VIP and IL-6 analysis and measurement of microvessel density in tissue were performed using immunohistochemistry, Western blotting, RT-qPCR, and ELISA.

RESULTS

Compared with controls, VIP transcript and protein levels were increased in endometrium from endometriosis patients and further elevated in patients with CPP. In addition, microvessel density, a measurement of angiogenic activity, was increased in the endometrium and in endometriosis lesions in the same subset of patients. Serum and PF levels of VIP and IL-6 were higher in women with endometriosis and CPP compared with endometriosis patients who reported no chronic pain.

CONCLUSION

Vasoactive intestinal peptide is upregulated in endometriosis patients reporting chronic pain. Increased microvessel density in tissue and peritoneal fluid concentrations of IL-6 indicate an elevated inflammation in the pelvic microenvironment of these patients.

Organ-on-a-Chip Systems for Women's Health Applications

Biomedical research, for a long time, has paid little attention to the influence of sex in many areas of study, ranging from molecular and cellular biology to animal models and clinical studies on human subjects. Many studies solely rely on male cells/tissues/animals/humans, although there are profound differences in male and female physiology, which can significantly impact disease mechanisms, toxicity of compounds, and efficacy of pharmaceuticals. In vitro systems have been traditionally very limited in their capacity to recapitulate female-specific physiology and anatomy such as dynamic sex-hormone levels and the complex interdependencies of female reproductive tract organs. However, the advent of microphysiological organ-on-a-chip systems, which attempt to recreate the 3D structure and function of human organs, now gives researchers the opportunity to integrate cells and tissues from a variety of individuals. Moreover, adding a dynamic flow environment allows mimicking endocrine signaling during the menstrual cycle and pregnancy, as well as providing a controlled microfluidic environment for pharmacokinetic modeling. This review gives an introduction into preclinical and clinical research on women's health and discusses where organ-on-a-chip systems are already utilized or have the potential to deliver new insights and enable entirely new types of studies.

Three-dimensional culture of differentiated endometrial stromal cells to oligodendrocyte progenitor cells (OPCs) in fibrin hydrogel

Neural tissue engineering is one of the most promising strategies for treatment of nerve tissue injuries. Three-dimensional (3D) environment mimics in vivo conditions for cells. 3D distribution and growth of the cells within the scaffold are both important for neural tissue engineering. In this study, endometrial stromal cell-derived oligodendrocyte progenitor cells (EnSC-derived OPCs) were cultured in fibrin gel and cell differentiation and viability were evaluated after 8 days of post-culture. The structural and mechanical characteristics of fibrin gel-like scaffold were examined with rheological analysis. EnSCs were isolated from donor tissue and were induced to OPCs with growth factors (FGF2/EGF/PDGF-AA) for 12 days, then were cultured in fibrin gel with Triiodothyronine (T3) medium for another 8 days. The viability of cells was analyzed using MTT assay for a period of 8 days culturing in a fibrin matrix. Structure of fibrin matrix and cell morphology was analyzed with SEM. TEM, immunostaining and quantitative RT-PCR was performed for OPCs markers after cell culturing in fibrin matrix. Cell viability is enhanced in fibrin matrix after 8 days. SEM and TEM show that cells are in good integration with nano-fibers. Moreover, immunohistochemistry and quantitative RT-PCR of OPCs differentiation markers showed that Olig2, Sox10, PDGFRa, CNP, and A2B5 are expressed after 8 days culturing within fibrin matrix. Fibrin can provide a suitable 3-D scaffold for EnSCs differentiated cells for the regeneration of CNS.

Perfusion culture enhanced human endometrial stromal cell growth in alginate-multivalent integrin α5β1 ligand scaffolds

A method to functionalize alginate by introducing monomeric or self-assembling (tetrameric) fibronectin (FN) domains is described, leading to a functional scaffold, which is used for three dimensional (3D) culture of human endometrial stromal cells (EnSCs). EnSCs encapsulated in the functional alginate were cultured under perfusion using the TissueFlex® platform, a multiple parallel microbioreactor system for 3D cell culture. The effect of the novel scaffold and the effect of perfusion were examined. Cell viability, proliferation, and extracellular matrix (ECM) deposition were determined and the results compared with those obtained with cells encapsulated in non-functionalized alginate, and also those without perfusion. Staining for focal adhesions and actin showed maximal cell adhesion only for alginate-tetrameric FN scaffolds under perfusion, associated with a significant increase in cell number over 7 days culture; in contrast to poor cell adhesion and a decrease in cell number for non-functionalized alginate scaffolds (irrespective of perfused/static culture) and 3D static culture (irrespective of the scaffold). Conjugation of alginate to FN was an absolute requirement to attenuate the loss of cell metabolic activity over 7 days culture. ECM deposition for blank alginate and alginate-monomeric FN was similar, but increased around 2-fold and 3-fold for alginate-tetrameric FN under static and perfusion culture, respectively. It is concluded that the requirement for EnSC engagement with multivalent integrin α5β1 ligands and perfused culture are both essential as a first step toward endometrial tissue engineering.

Simvastatin induces apoptosis and alters cytoskeleton in endometrial stromal cells

CONTEXT

Statins are competitive inhibitors of 3-hydroxy-3methylglutaryl-coenzyme A reductase, with antimitotic, antioxidant, antiinflammatory, and immunomodulatory properties. Recent studies have shown that statins reduce the growth of human endometrial stromal (HES) cells and protect from the development of endometriosis in animal models.

OBJECTIVES

The present study was conducted to evaluate the effects of simvastatin on apoptosis and cytoskeleton of HES cells.

DESIGN AND SETTING

In vitro experiments were performed in the university research laboratory.

PATIENTS

HES cells were obtained from endometrial biopsies collected from nine subjects in the proliferative phase of their menstrual cycle.

MAIN OUTCOME MEASURES

The effect of simvastatin (10 and 30 mum) and/or geranylgeranyl pyrophosphate (GGPP, 30 mum) on caspase 3 and 7 activity, DNA fragmentation, and HES cell morphology was evaluated.

RESULTS

Simvastatin induced significant time- and concentration-dependent apoptotic effects on HES cells as determined by increased activity of executioner caspases and DNA fragmentation. Simvastatin also caused profound alterations in HES cell morphology and F-actin cytoskeleton. This effect was abrogated by geranylgeranyl pyrophosphate, an important product of the mevalonate pathway.

CONCLUSIONS

Simvastatin induces apoptosis and disruption of the cytoskeleton of HES cells by reducing isoprenylation in cultures of human endometrial stroma. The present findings may lead to the development of novel treatments for endometriosis involving statins.