Establishment of Endometriotic Models: The Past and Future

Establishment of Endometriotic Models: The Past and Future

Endometriosis is a chronic and debilitating disease that affects approximately 6% to 10% of women during their reproductive age. It is characterized by the presence of endometrioid epithelial and stromal cells outside the uterus, primarily in the pelvic cavity, and is classified into three main categories: peritoneal, ovarian, and deep infiltrating endometriosis (DIE). Patients with endometriosis often experience symptoms such as pelvic pain, dysmenorrhea, deep dyspareunia, ovarian cysts, and infertility. Additionally, they face an increased risk of developing epithelial ovarian cancer. Despite extensive research over the past century, the etiology of endometriosis remains unclear, and current treatments are limited to pain management, hormonal interventions, and surgery.

The exploration of the pathophysiology and development of novel therapies for endometriosis heavily relies on the establishment of reliable endometriotic models. Over the past decade, various models have been developed, including animal models, endometriotic cell lines, and, more recently, endometrial organoids. These models have played a crucial role in advancing our understanding of the disease and have provided valuable tools for preclinical research.

In Vitro Cell Models

In vitro cell models, particularly endometriotic cell lines, have been instrumental in studying the cellular and molecular mechanisms underlying endometriosis. These cell lines are derived from endometriotic lesions and have been used to investigate various aspects of the disease, including inflammation, immune response, gene expression, and therapeutic interventions.

Characteristics of Endometriotic Primary Cells

Primary cells derived from endometriotic lesions have been used to study the invasive properties of endometriotic cells. Gaetje et al. reported that E-cadherin-negative epithelial cells from endometriotic primary cells are invasive and can be distinguished from fibroblasts and stromal cells by their expression of cytokeratin. These cells, characterized as cytokeratin+/E-cadherin-, are believed to play a significant role in the development and invasion of endometriosis. However, primary cells have a limited lifespan, which has led to the development of immortalized cell lines for long-term studies.

Endometriotic Epithelial Cell Line 145T

The endometriotic epithelial cell line (EEC) 145T was established from peritoneal biopsies and transformed using the Simian virus 40 (SV40) T antigen. This cell line is invasive, cytokeratin+/E-cadherin-, and expresses both estrogen receptor (ER) and progesterone receptor (PR). EEC145T has a lifespan of approximately 35 passages, but it begins to lose its invasive properties and cytokeratin expression after around 25 passages. This cell line has been used to study the role of ovarian cancer antigen CA125 in cell adhesion.

EEC10Z, EEC11Z, EEC12Z, and EEC49Z

Zeitvogel et al. established several endometriotic cell lines from peritoneal endometriotic biopsies, including EEC10Z, EEC11Z, EEC12Z, and EEC49Z. These cell lines were immortalized using the SV40 T antigen and exhibit both stromal and epithelial-like features. Notably, EEC12Z has been widely used in endometriosis research, with over 40 studies utilizing this cell line. These cell lines have been instrumental in studying the role of N-cadherin in invasion and migration, as well as in exploring gene expression profiles and cytokine production.

EMosis-CC/TERT1 and EMosis-CC/TERT2

Bono et al. developed immortalized epithelial cell lines from ovarian endometrioma, known as EMosis-CC/TERT1 and EMosis-CC/TERT2. These cell lines were created by co-transfecting cyclinD1, cdk4, and hTERT genes to overcome premature senescence. These cell lines have been used to study the carcinogenesis of ovarian endometrioma and the pharmacologic mechanisms of dienogest.

EEC16 and EEC16-TERT

Brueggmann et al. established the EEC16 cell line from ovarian surface endometriosis lesions. This cell line exhibits epithelial morphology with mesenchymal markers and has been used to study the transcriptome of endometriotic cells. Lawrenson et al. further developed the EEC16-TERT cell line by immortalizing EEC16 with hTERT. This cell line has been used to study the pathogenesis of endometriosis-associated ovarian cancer (EAOC) and the role of Src activation in disease progression.

Endometrial Stromal Cell Line St-T1b

Samalecos et al. established the St-T1b cell line by immortalizing primary endometrial stromal cells with hTERT. This cell line has been used to study the decidualization process and the role of microRNAs in endometriosis. Although St-T1b cells do not respond to progestin alone, they can be induced to undergo decidualization with the addition of cyclic AMP (cAMP).

Epithelial Progenitors and Mesenchymal Stem Cells

The presence of epithelial progenitors and mesenchymal stem cells (MSCs) in the endometrium has been proposed as a potential mechanism for the development of endometriosis. These cells are believed to be shed during retrograde menstruation and establish endometriotic implants in the peritoneal cavity. Studies have shown that ectopic MSCs from patients with endometriosis exhibit increased angiogenesis, migration, and invasion compared to eutopic MSCs. These cells have been used to study the pathogenesis of endometriosis and to explore non-hormonal therapies, such as sorafenib.

Endometrial Organoids

Endometrial organoids (EOs) are three-dimensional (3D) structures derived from endometrial epithelial stem cells that mimic the architecture and physiology of the endometrium. EOs have emerged as a promising model for studying endometriosis, as they can maintain the phenotypic and genetic characteristics of the original tissue over long-term expansion. Turco et al. and Boretto et al. were among the first to report the successful culture of EOs from both mouse and human endometrium. These organoids have been used to study hormone responsiveness, gene expression profiles, and drug screening in endometriosis.

In Vivo Models

In vivo models, particularly animal models, have been essential for studying the etiology, pathophysiology, and treatment of endometriosis. These models allow researchers to investigate the effects of endometriosis on fertility, pain, and other clinical outcomes that cannot be fully replicated in vitro.

Non-Human Primates

Non-human primates (NHPs), such as rhesus monkeys and baboons, are the only species other than humans that experience spontaneous endometriosis. These animals have reproductive anatomy and physiology similar to humans, making them valuable models for studying the disease. Induced endometriosis models in baboons have been created by injecting autologous menstrual effluent into the pelvic cavity. These models have been used to explore the pathophysiology of endometriosis and to test potential therapies.

Rodent Models

Rodent models, including rats and mice, are widely used in endometriosis research due to their low cost, ease of handling, and the ability to perform genetic manipulations. The rat autologous model, developed by Vernon and Wilson, involves suturing uterine tissue to the peritoneum to induce endometriosis. This model has been used to study the association between endometriosis and pelvic pain, as well as to test novel therapies such as cisplatin and letrozole.

Mouse models, including patient-derived xenografts (PDX) and syngeneic models, have been used to study the immune system’s role in endometriosis and to explore the effects of genetic manipulations. These models have provided valuable insights into the mechanisms of endometriosis-associated pain and the potential for immune-modulating therapies.

Conclusions and Perspectives

Endometriosis is a complex and heterogeneous disease that significantly impacts the quality of life of affected women. The establishment of reliable endometriotic models has been crucial for advancing our understanding of the disease and for developing novel therapies. Traditional models, including cell lines and animal models, have provided valuable insights into the cellular and molecular mechanisms of endometriosis. However, these models have limitations, such as genetic instability, ethical concerns, and differences between animal and human physiology.

The development of endometrial organoids represents a significant advancement in endometriosis research. These 3D structures can maintain the genetic and phenotypic characteristics of the original tissue, making them ideal for studying disease mechanisms and for drug screening. Organoids have the potential to complement traditional models and to provide a more comprehensive understanding of endometriosis.

Future research should focus on understanding the pathogenesis of endometriosis, identifying disease subtypes, and developing non-invasive diagnostic methods and non-hormonal treatments. The establishment of an endometriosis organoid biobank could facilitate these efforts by providing a platform for studying patient-specific disease mechanisms and for testing personalized therapies.

In conclusion, the establishment of endometriotic models has been essential for advancing our understanding of endometriosis and for developing novel treatments. The integration of traditional models with emerging technologies, such as organoids, holds great promise for improving the diagnosis, treatment, and management of this debilitating disease.

doi.org/10.1097/CM9.0000000000000885

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