Pathogenesis of endometriosis--current research.

Proliferative, secretory and menstrual endometrial cells of both the stroma and epithelium adhere to intact peritoneal mesothelium and mesothelial monolayers. Endometrial attachment to the mesothelium appears to occur rapidly (within 1 h) and transmesothelial invasion occurs between 1 and 18-24 h. These results demonstrate that the mesothelium is not a 'no-stick' surface and indicates that molecules present at the surface of the mesothelium are involved in the pathogenesis of the early endometriotic lesion. The inhibition of endometrial cell adherence to peritoneal mesothelium by hyaluronidase indicates that CD44-hyaluronan binding is at least one of the mechanisms involved in the pathogenesis of endometriosis. We believe that investigation of mesothelial cell adhesion molecules is central to understanding the pathogenesis of endometriosis.

Time series analysis of transmesothelial invasion by endometrial stromal and epithelial cells using three-dimensional confocal microscopy.

OBJECTIVE: To evaluate endometrial adhesion and invasion of peritoneal mesothelium. DESIGN: Descriptive study using confocal laser-scanning microscopy. SETTING: University-based laboratory. PATIENT(S): Women undergoing surgery for benign conditions. INTERVENTION(S): Fluorescence-labeled peritoneal mesothelial cells (PMCs) were grown on coverslips. Fluorescence-labeled endometrial stromal cells (ESCs) and epithelial cells (EECs) and myometrial cells (Myos) were plated on the PMCs. Cultures were examined at 1, 6, 12, and 24-27 hours with differential interference contrast and confocal laser-scanning microscopy. MAIN OUTCOME MEASURE(S): Demonstration of adherence and invasion of endometrial cells through peritoneal mesothelium. RESULT(S): At 1 hour, there was adherence of the ESCs, EECs, and Myos on the perimeter of PMCs. There was no invasion by the Myos. By 6 hours, ESCs and EECs spread over the surface of the PMCs and extended cell processes through PMC junctions. Extension of pseudopodia under the PMCs followed. By 12 hours, there was vacuolization and lifting of PMCs that had been undermined by endometrial cells. CONCLUSION(S): This is the first time-phase study to demonstrate adherence and the process of invasion of endometrial cells through the mesothelium. The application of three-dimensional confocal laser-scanning microscopy is a novel technique that can be used to further examine mechanisms involved in the pathogenesis of the early endometriotic lesion.

Culture of menstrual endometrium with peritoneal explants and mesothelial monolayers confirms attachment to intact mesothelial cells.

BACKGROUND: To evaluate adhesion of menstrual endometrium (ME) to intact peritoneal mesothelium. METHODS: Explants of peritoneum were cultured for 1 h with ME (n = 6). Specimens were serially sectioned for haematoxylin and eosin stain and immunohistochemistry using an anti-cytokeratin antibody to label mesothelium. Confocal laser scanning microscopy (CLSM) was performed to identify an intact layer of mesothelial cells (MC) underlying sites of ME attachment. Also, ME and MC were labelled with Cell-Tracker dyes. ME was cultured with mesothelial monolayers for 1 h (n = 10). Cultures were examined with differential interference contrast and CLSM. Optical sections were taken and a three-dimensional model was constructed. RESULTS: In the peritoneal explants, ME adhered to intact mesothelium. There was no evidence of transmesothelial invasion. CLSM of sections of the explants demonstrated an intact monolayer of cytokeratin positive cells below the sites of ME implantation. Cytokeratin negative and positive ME cells adhered to mesothelial cells. Likewise, the ME attached to cultured mesothelium. Orthogonal sections and three-dimensional reconstruction confirmed an intact monolayer of mesothelium underlying ME attachment sites. CONCLUSIONS: This study confirms that ME adheres rapidly to intact peritoneal mesothelium. Further studies are needed that characterize the mechanisms of ME adhesion to, and migration through, mesothelial cells.

The alpha(2)beta(1) and alpha(3)beta(1) integrins do not mediate attachment of endometrial cells to peritoneal mesothelium.

OBJECTIVE: To evaluate the possible role of mesothelial alpha(2)beta(1) and alpha(3)beta(1) integrins in the attachment of endometrial stromal cells (ESCs) and endometrial epithelial cells (EECs). DESIGN: In vitro study. SETTING: University medical center. PATIENT(S): Women of reproductive age (n = 26). MAIN OUTCOME MEASURE(S): Mesothelial cells were grown on collagen IV. Endometrial stromal cells and EECs were plated on mesothelial cells for 1 hour. Before plating, mesothelial cells or endometrial cells were incubated with antibodies to alpha2, alpha3, and beta1 integrin subunits. The effect of these antibodies on ESC and EEC binding to collagen IV and collagen I was also examined. The expression of collagen I, collagen IV, fibronectin, and laminin by cultured ESCs and EECs was examined. RESULT(S): The anti-integrin antibodies had no effect on endometrial binding to mesothelium. The beta1 integrin antibody decreased binding of ESCs and EECs to the collagen matrices. In culture, ESCs and EECs expressed collagen I, collagen IV, fibronectin, and laminin to varying degrees. CONCLUSION(S): The initial adhesion of ESCs and EECs to mesothelium is not mediated by beta1 integrins. In contrast, ESC and EEC attachment to collagen IV and collagen I, which are present in the submesothelial extracellular matrix, is mediated by beta1 integrins.

An in vitro model to study the pathogenesis of the early endometriosis lesion.

OBJECTIVE: To determine if whole fragments of endometrium can adhere to peritoneum with intact mesothelium. DESIGN: Tissue culture and immunohistochemical study. SETTING: University Medical Center. PATIENTS: Reproductive-age women undergoing surgery for benign conditions. INTERVENTIONS: Whole explants of human peritoneum from the anterior abdominal wall and the posterior surface of the uterus were cultured with whole fragments of mechanically dispersed endometrium. MAIN OUTCOME MEASURES: Adhesion of endometrial fragments to the surface of the peritoneum was evaluated. Adherent fragments of endometrium were identified using the dissecting microscope and by performing serial sections of the peritoneum explants for light and confocal laser-scanning microscopy. Immunohistochemical staining of the mesothelium with antibodies to cytokeratin and vimentin was used to ensure an intact layer of mesothelium beneath the endometrial implants. Transmission electron microscopy was also used to evaluate the adhesion of endometrium to the mesothelium. RESULTS: Endometrium was identified attached to the surface of the peritoneum. After 18-24 hours of culture, the majority of implants did not have identifiable mesothelium beneath them, but most had intact mesothelium running up to the point of attachment. Approximately 10% of the endometrial implants had intact mesothelium at the site of attachment. After 1 hour of culture, both endometrial stromal and epithelial cells were attached to intact mesothelium in nearly all cases. Early transmesothelial invasion involves endometrial stromal cells. CONCLUSIONS: Endometrial stromal and epithelial cells can attach to the intact mesothelial surface of the peritoneum. Endometrial stromal cell invasion through the mesothelium occurs in less than 18-24 hours.