Macrophages alternatively activated by endometriosis-exosomes contribute to the development of lesions in mice

STUDY QUESTION: Do exosomes play a role in the pathogenesis of endometriosis in a murine model? SUMMARY ANSWER: Exosomes from endometriosis (EMS) can alternatively activate macrophages and thus contribute to the development of lesions in mice. WHAT IS KNOWN ALREADY: The pathogenesis of endometriosis, an inflammatory disease, possibly involves peritoneal macrophages. Exosomes are recognized as a new communicator among cells and a key modulator in several inflammatory diseases. STUDY DESIGN, SIZE, DURATION: We performed in vitro and in vivo experiments to demonstrate the role of exosomes in modulating macrophages. RAW264.7 cells (macrophages) were used to examine the effects of exosomes on macrophages in vitro. An experiment was also conducted in vivo, as follows. Fifty C57BL/6 female mice were randomly allocated to five control and five experimental groups (n = 5/group). The experimental group was injected i.p. with EMS-exosomes derived from eutopic stromal cells, starting on Day-7 then every day for 1 week. The control group received CON-exosomes from mice without endometriosis. Peritoneal macrophages were assessed over the next 6 days. On Day 0, all mice were injected i.p. with endometrium to establish the endometriosis model. On Day 14, all mice were sacrificed, ectopic lesions were counted and measured. PARTICIPANTS/MATERIALS, SETTING, METHODS: Exosomes were isolated from endometrial stromal cells (ESCs) by ultracentrifugation and characterized through transmission electron microscopy, nanoparticle tracking analysis and western blot. After treatment with exosomes, the polarization and phagocytic ability of the macrophages were detected by flow cytometry analysis, immunofluorescent staining and RT-PCR. C57BL/6 mice were utilized to establish an endometriosis model by i. p. injection of endometrial segments. MAIN RESULTS AND THE ROLE OF CHANCE: After treatment with EMS-exosomes, the macrophages were polarized into an M2-like phenotype and their phagocytic ability decreased (P < 0.05 versus treatment with CON-exosomes). The total weight and volume of the lesions in mice treated with EMS-exosomes significantly increased compared with those in mice treated with CON-exosomes (P < 0.05). The infiltration of M2-like macrophages was enhanced in the EMS-exosome group (P < 0.001 versus treatment with CON-exosomes). LARGE SCALE DATA: N/A LIMITATIONS, REASONS FOR CAUTION: Detection of endometriosis following exosome treatment was only performed in a murine endometriosis model. Clinical data and additional mechanism studies must be conducted to understand the role of exosomes in the pathogenesis of endometriosis. WIDER IMPLICATIONS OF THE FINDINGS: This study emphasizes the importance of EMS-exosomes in the pathogenesis of endometriosis. Further investigations on the exosome signaling pathways may contribute to the development of effective treatments for endometriosis.