Menstrual endometrium and individual endometrial stromal and epithelial cells are unique in their ability to adhere to and invade peritoneal mesothelium

Abstract

Objective: Using an in vitro model of the early endometriotic implant, we have demonstrated that mechanically dispersed aggregates of proliferative and secretory phase endometrium adhere to intact mesothelium of peritoneal explants within one hour and invade into the submesothelial extracellular matrix (ECM) within 24 hours. We have also demonstrated that dispersed cultured endometrial stromal (ESCs) and endometrial epithelial cells (EECs) adhere to and invade mesothelial cell (MC) monolayer cultures in a similar time period. The purpose of the present study was to evaluate the unique potential of human menstrual shed endometrium (MSE) and individual ESCs and EECs to adhere to and invade peritoneal mesothelial explants in vitro Design: In vitro study in a university based laboratory. Materials/Methods: Antegrade MSE was collected from volunteers. ESC and EEC cultures were established from MSE, proliferative, and secretory phase endometrium. Myometrial cells (MYOs) in culture served as controls. Peritoneal explants were obtained from 6–8 week old ICR outbread mice. MSE aggregates, isolated endometrial cells from culture and MYOs were labeled with chloromethylbenzoylaminotetramethylrhodamine and peritoneum was labeled with chloromethylfluorscein diacetate. MSE aggregates, isolated endometrial cells and MYOs were cultured on the mesothelial surface of peritoneal explants. Cultures were interrupted at 1 and 24 hours. Confocal laser scanning microscopy (CLSM) was performed taking 5 micron optical sections of the peritoneal explants. Orthogonal sections and a three-dimensional model were reconstructed Results: Fragments of MSE adhered to intact peritoneal mesothelium at 1 hour, but no transmesothelial invasion was observed. At 24 hours, MSE fragments showed transmesothelial invasion into the peritoneal ECM. Invasion by the intact MSE fragments was characterized by extension of pseudopodia from individual cells within the aggregate. The depth of invasion of MSE fragments ranged from 0 (i.e. the same level as the MC basement membrane) to 8 microns at 24 hours. Individual ESCs and EECs from cultured MSE, proliferative and secretory endometrium adhered to, but did not invade at 1 hour. At 24 hours, the depth of invasion of the cultured ESCs and EECs was similar to that observed for the MSE aggregates. Endometrial cells invaded the mesothelium by extending cell processes between mesothelial cell junctions. In contrast to the MSE aggregates and individual endometrial cells, MYOs adhered to intact peritoneal mesothelial explants at one hour, but no transmesothelial invasion was observed after 24 hours in culture Conclusions: These findings demonstrate that MSE aggregates and individual ESCs and EECs from cultured MSE, proliferative and secretory endometrium adhere to and invade intact peritoneal mesothelium. The absence of invasion by MYOs suggests that MSE and individual endometrial cells are unique in their ability to interact with peritoneal mesothelium. This interaction appears to be mediated by ESCs and EECs suggesting that both cell types are involved in the genesis of the early endometriotic lesion. Supported by: Endometriosis Association Grant.