p38 Mitogen-Activated Protein Kinase is Involved in the Pathogenesis of Endometriosis by Modulating Inflammation, but not Cell Survival

Background: Local pro-inflammatory environment and enhanced cell survival contribute to the endometriosis development. A serine/threonine kinase p38 mitogen-activated protein kinase (MAPK) mediates intracellular signaling of cytokine production, cell proliferation, and apoptosis in different cell types. The current study compares p38 MAPK activity in normal endometrium and endometriosis, and assesses role(s) of p38 MAPK on cytokine production and cell survival in endometriosis. Methods: Immunohistochemical levels of total and phosphorylated (active) p38 MAPK as well as its correlation with interleukin 8 (IL-8) expression, and cell proliferation and apoptosis were compared in normal human endometrium and endometriosis. The action of p38 MAPK on pro-inflammatory cytokine-induced IL-8 and monocyte chemotactic protein (MCP)-1 expression in endometriotic cells were assessed by enzyme-linked immunosorbent assay. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell survival, 5-bromo-2′-deoxyuridine incorporation, and Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling assays were used to determine the function of p38 MAPK in cultured human endometriotic stromal cell proliferation and apoptosis. Results: p38 MAPK activity was significantly higher in both eutopic and ectopic endometria compared to normal endometria during late proliferative and early secretory phases (P < .05). Increased p38 MAPK activity in endometriotic cells correlated with IL-8 expression (Pearson correlation coefficient r = 0.83, P < .01), but not with apoptosis in vivo. The pro-inflammatory cytokines IL-1β and tumor necrosis factor (TNF)-α induced activation of p38 MAPK. Inhibition of p38 MAPK activity blocked IL-1β and TNF-α-induced IL-8 and MCP-1 secretion in cultured endometriotic stromal cells (P < .05), but did not impact on endometriotic cell survival. Conclusions: These results suggest that rather than modulating cell survival, increased p38 MAPK activity in endometriotic cells contributes to the pathogenesis of endometriosis by promoting the local inflammatory milieu.