Mesothelial cell-associated hyaluronic acid promotes adhesion of endometrial cells to mesothelium.

OBJECTIVE: To evaluate the role of hyaluronic acid in the attachment of endometrial cells to mesothelium. DESIGN: In vitro study of adhesion of endometrial stromal and epithelial cells to mesothelial cells. SETTING: University medical center. PATIENT(S): Reproductive-age women without endometriosis undergoing surgery for benign conditions. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): The effect of hyaluronidase treatment of mesothelial cells or endometrial cells on adhesion of (51)Cr labeled endometrial stromal and epithelial cells to monolayers of mesothelium was evaluated. The expression of CD44, the hyaluronate receptor, was evaluated by western blot. RESULT(S): Hyaluronidase pretreatment of mesothelial cells decreased the binding of endometrial stromal and epithelial cells to mesothelium by 39% (P< .02) and 31% (P< .03), respectively. There was no effect on endometrial cell binding to mesothelial cells or to collagen IV when the endometrial cells were pretreated with hyaluronidase. CD44 expression by endometrial stromal and epithelial cells was demonstrated by western blot. CONCLUSIONS: This study demonstrates that mesothelial cell-associated hyaluronic acid is involved in attachment of endometrial stromal and endometrial epithelial cells to the mesothelium. We hypothesize that binding of hyaluronic acid by endometrial cells is involved in the pathogenesis of the early endometriotic lesion.

Composition of the extracellular matrix of the peritoneum.

OBJECTIVE: To localize the extracellular matrix proteins collagen I, collagen IV, fibronectin, and laminin in the peritoneal membrane. STUDY DESIGN: Peritoneal biopsies (n = 13) from the anterior abdominal wall and the uterine serosa (n = 3) were incubated with antibodies to collagen IV, laminin, collagen I, and fibronectin. Specimens were examined using light and confocal laser scanning microscopy. RESULTS: All of the extracellular matrix (ECM) proteins were present immediately under the mesothelium. Collagen (Col) IV and laminin (LM) were seen in the smooth muscle of microvascular structures, in the subendothelial basement membrane, and were present in a fascicular pattern in the peritoneal stroma. Collagen I was distributed diffusely in the peritoneal stroma. Fibronectin was also present in the subendothelial basement membrane. CONCLUSIONS: The resolution of the confocal microscope allowed for localization of extracellular matrix proteins in relation to the mesothelium. The presence of collagen IV, laminin, collagen I, and fibronectin under the mesothelium suggests that cells invading the peritoneum must have the ability to degrade and remodel this matrix.

Short-term culture of peritoneum explants confirms attachment of endometrium to intact peritoneal mesothelium.

OBJECTIVE: To evaluate the initial adhesion of endometrium to the peritoneum. DESIGN: Descriptive study using light and confocal laser-scanning microscopy, immunohistochemistry, and transmission electron microscopy. SETTING: University-based laboratory. PATIENT(S): Women without endometriosis undergoing surgery for benign conditions. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Explants of peritoneum (n = 20), prepared from four patients, were cultured for 1 hour with mechanically dispersed proliferative or secretory endometrium. Peritoneum was cultured with endometrium from the same patient. Specimens were fixed and serially sectioned for hematoxylin and eosin stain, immunohistochemistry using an anti-cytokeratin monoclonal antibody, and transmission electron microscopy. RESULT(S): In 17 of 20 explants, endometrium was adherent to intact mesothelium. There was no evidence of transmesothelial invasion at any sites of attachment. Although in most cases endometrium was adherent to mesothelium via endometrial stroma, there were many sites of endometrial epithelium-mesothelium attachment. Confocal laser scanning microscopy demonstrated an intact monolayer of cytokeratin-positive cells below the sites of endometrial implantation. Transmission electron microscopy demonstrated intact, viable, mesothelial cells below sites of attachment. CONCLUSION(S): This study demonstrates that endometrium rapidly adheres to intact peritoneal mesothelium. In addition, this study demonstrates that endometrial epithelial cells, as well as stroma, can attach to mesothelium. Further studies are needed that characterize the mechanism of endometrial-mesothelial cell adhesion.

Expression of the alpha2beta1 and alpha3beta1 integrins at the surface of mesothelial cells: a potential attachment site of endometrial cells.

OBJECTIVE: To localize alpha2beta1 and alpha3beta1 integrins in the cell membrane of peritoneal mesothelium in vivo and in vitro. DESIGN: Descriptive study using confocal and two-photon laser-scanning microscopy. SETTING: University-based laboratory. PATIENT(S): Women without endometriosis undergoing surgery for benign conditions. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Peritoneal biopsies (n = 9) and mesothelial monolayer cultures (n = 4) were incubated with antibodies to the alpha2 and alpha3 subunits and to the intact alpha2beta1 and alpha3beta1 integrins. Specimens were examined with laser-scanning microscopy. RESULT(S): The alpha2 and alpha3 subunits and the intact alpha2beta1 and alpha3beta1 integrins were identified at the base of the mesothelial cells (i.e., toward the basement membrane). There was also expression of the alpha2 and alpha3 subunits and the intact alpha2beta1 and alpha3beta1 integrins at the cell surface (i.e., toward the peritoneal cavity). CONCLUSION(S): The resolution of the confocal and two-photon laser-scanning microscope enabled localization of integrins in mesothelial cells. The presence of alpha2beta1 (collagen-laminin receptor) and alpha3beta1 integrins (collagen-laminin-fibronectin receptor) at the base of mesothelial cells suggests a role for these molecules in adhesion to the basement membrane. The presence of these molecules at the cell surface suggests a potential locus for cell adhesion in such processes as endometriosis and cancer metastasis.

Mesothelium expression of integrins in vivo and in vitro.

OBJECTIVE: To characterize the expression of alpha subunits of integrin adhesion molecules in peritoneal tissue in vivo and in vitro. METHOD: Peritoneum from the anterior abdominal wall (n = 22) and the serosa of the posterior uterus (n = 11) was obtained from women of reproductive age without endometriosis who were undergoing surgery for benign conditions. Immunohistochemical studies were performed on serial sections of peritoneum from the anterior abdominal wall, the uterine serosa, mesothelial monolayer cultures, and peritoneum explants from the abdominal wall using monoclonal antibodies to alpha subunits of integrin adhesion molecules. Electron microscopy was performed to localize these adhesion molecules in the mesothelium. RESULTS: The mesothelial expression of alpha integrin subunits was identical in the anterior peritoneum and uterine serosa. In vivo the mesothelium strongly expressed alpha 2 and alpha 3 and variably expressed alpha 6. In the monolayer cultures there was moderate/strong staining for alpha 2, alpha 3, and alpha 5; there was minimal expression of alpha v. In the explants there was moderate/strong expression of alpha 2, alpha 3, alpha 5, and alpha v; alpha 6 was variably expressed. The ultrastructure of the mesothelium was unique in the anterior peritoneum, uterine serosa, and the monolayer cultures. The integrin subunits were distributed throughout the cytoplasm, were expressed in the plasma membrane, and were present on the surface (i.e., towards the peritoneal cavity) of the mesothelium. CONCLUSION: Integrins are expressed by the mesothelium of the peritoneum. The mesothelium expression of integrins in vivo differs from that of the mesothelium integrin expression in monolayer culture and explant culture.