IL-17A Contributes to the Pathogenesis of Endometriosis by Triggering Proinflammatory Cytokines and Angiogenic Growth Factors

Endometriosis is a chronic, inflammatory disease characterized by the growth of endometrial tissue in aberrant locations outside the uterus. Neo-angiogenesis or establishment of new blood supply is one of the fundamental requirements of endometriotic lesion survival in the peritoneal cavity. IL-17A is emerging as a potent angiogenic and pro-inflammatory cytokine involved in the pathophysiology of several chronic inflammatory diseases such as rheumatoid arthritis and psoriasis. However, sparse information is available in the context of endometriosis. In this study, we demonstrate the potential importance of IL-17A in the pathogenesis and pathophysiology of endometriosis. The data show a differential expression of IL-17A in human ectopic endometriotic lesions and matched eutopic endometrium from women with endometriosis. Importantly, surgical removal of lesions resulted in significantly reduced plasma IL-17A concentrations. Immunohistochemistry revealed localization of IL-17A primarily in the stroma of matched ectopic and eutopic tissue samples. In vitro stimulation of endometrial epithelial carcinoma cells, Ishikawa cells and human umbilical vein endothelial cells with IL-17A revealed significant increase in angiogenic (VEGF, IL-8), pro-inflammatory (IL-6, IL-1β) and chemotactic cytokines (G-CSF, CXCL12, CXCL1, CX3CL1). Furthermore, IL-17A promoted tubulogenesis of HUVECs plated on matrigel in a dose-dependent manner. Thus we provide the first evidence that endometriotic lesions produce IL-17A and that the removal of the lesion via laparoscopic surgery leads to the significant reduction in the systemic levels of IL-17A. Taken together, our data shows a likely important role of IL-17A in promoting angiogenesis and pro-inflammatory environment in the peritoneal cavity for the establishment and maintenance of endometriosis lesions.