Background: Endometriosis, characterized by the presence of functional endometrial tissues outside the uterus, is one of the most common gynecological disorders. Endometrial mesenchymal stem cells (MSCs) are crucial for the occurrence and development of endometriosis. Ectopic endometrial MSCs exist in the peritoneal cavity. Thus, the bioactive factors in endometriotic peritoneal fluid may regulate the biological behaviors of endometrial MSCs.
Methods: In this study, after assessing the concentration of Activin A in peritoneal fluid using ELISA, we isolated and cultured endometrial MSCs and investigated whether Activin A stimulated endometrial MSCs to differentiate into myofibroblasts and clarified the underlying mechanisms by quantitative real-time PCR, Western blot analysis, immunofluorescent staining, RNA interference and Chromatin immunoprecipitation. We also employed the inhibitors of Activin A to explore the possibility of suppressing the development of fibrosis in endometriosis using primary endometrial MSCs cultures and a mouse model of endometriosis.
Results: Here, we revealed that Activin A significantly elevated in endometriotic peritoneal fluid and activin receptor-like kinase (ALK4), the specific receptor for Activin A, obviously enhanced in ectopic endometrial MSCs compared with eutopic endometrial MSCs from women with or without endometriosis. Next, we found that Activin A drived myofibroblast differentiation of endometrial MSCs, with extremely enhanced expression of connective tissue growth factor (CTGF). CTGF was shown to be required for Activin A-induced expression of ACTA2, COL1A1 and FN1 in endometrial MSCs. CTGF induction by Activin A in endometrial MSCs involved the activation of Smad2/3, as evidenced by the phosphorylation and nuclear translocation of Smad2/3 as well as the binding of Smad2/3 to CTGF promoter. Furthermore, Smad/CTGF pathway in endometrial MSCs required activation of STAT3 while independent of PI3K, JNK and p-38 pathways. In addition, we also demonstrated that inhibition of Activin A pathway impeded myofibroblast differentiation of endometrial MSCs and ameliorated fibrosis in endometriosis mice.
Conclusions: Activin A promotes myofibroblast differentiation of endometrial mesenchymal stem cells via STAT3-dependent Smad/CTGF pathway. The results provided the first evidence that STAT3 acted as a crucial Activin A downstream mediator to regulate CTGF production. Our data may supplement the stem cell theory of endometriosis and provide the experimental basis to treat endometriosis-associated fibrosis by manipulating Activin A signaling.
Keywords: Activin a; Endometriosis; Fibrosis; Peritoneal fluid; SUSD2.