Investigating the role of peritoneal mesothelial cells in endometriosis lesion formation

To study the impact of primary peritoneal mesothelial cell (PMC) origin on endometrial stromal cell (ESC) coupling and invasion as an in vitro model of endometriosis lesion formation. PMCs from endometriosis and control patients were derived from tissue explants. Cell identity was confirmed using immunofluorescence. Endometriosis samples were further categorized by their origin from actual endometriotic lesions and non-lesion areas of peritoneum. Intercellular coupling was measured by Calcein dye transfer using the parachute method, linked to an automated image capturing system. Invasion assays were conducted using a modified Boyden Chamber with a PMC monolayer on the insert. Statistical analysis was performed by unpaired Mann Whitney test. PMCs from both control and endometriosis patients showed similar induction of ESC coupling. Regardless of PMC origin, ESCs from endometriosis patients consistently had greater coupling response than those from controls (p = 0.05). We did not detect a difference in ESC invasion across PMC monolayers derived from endometriosis or control patients. However, there was significantly reduced ESC invasion across PMCs derived from lesion tissue compared to non-lesion areas of peritoneum from the same patient (p = 0.02). Additionally, we found a difference in the effect of endometrial epithelial cells (EECs) on ESC invasion depending on PMC monolayer origin. While endometrial cell (ESCs or EECs) origin had a dramatic effect on coupling and invasion, the origin of the mesothelial cells did not. The exception being a difference in PMC influence on the interactions between EECs and ESCs during invasion, whether taken from a control or endometriosis patient. Overall, this supports the hypothesis that the major driving factor in endometriosis lesion formation comes from the endometrium rather than the peritoneum. However, while endometrial cells may be the primary determinant of lesion formation, mesothelial cells do have an active role (e.g. induction of intercellular coupling with ESCs), which requires a level of function that appeared to be compromised in endometriotic lesions.