Mesenchymal stem cell-secreted extracellular vesicles carrying TGF-β1 up-regulate miR-132 and promote mouse M2 macrophage polarization

The effects of mesenchymal stem cells (MSCs) on different types of diseases are controversial, and the inner mechanisms remain unknown, which retards the utilization of MSCs in disease therapy. In this study, we aimed to elucidate the mechanisms of MSCs-extracellular vesicles (EVs) carrying transforming growth factor-beta 1 (TGF-beta 1) in M2 polarization in mouse macrophages via the microRNA-132 (miR-132)/E3 ubiquitin ligase myc binding protein 2 (Mycbp2)/tuberous sclerosis complex 2 (TSC2) axis. Mouse MSCs were isolated for adipogenic and osteogenic induction, followed by co-culture with mouse macrophages RAW264.7. Besides, mouse macrophages RAW264.7 were co-cultured with MSCs-EVs in vitro, where the proportion of macrophages and inflammation were detected by flow cytometry and ELISA. The experimental data revealed that MSCs-EVs promoted M2 polarization of macrophages, and elevated interleukin (IL)-10 expression and inhibited levels of IL-1 beta, tumour necrosis factor (TNF)-alpha and IL-6. MSC-EV-treated macrophages RAW264.7 increased TGF-beta 1 expression, thus elevating miR-132 expression. MiR-132 directly bound to Mycbp2, as confirmed by luciferase activity assay. Meanwhile, E3 ubiquitin ligase Mycbp2 could ubiquitinate TSC2 protein. Furthermore, silencing TGF-beta 1 inhibited M2 polarization of MSC-EV-treated macrophages. Taken conjointly, this study provides evidence reporting that MSC-secreted EVs carry TGF-beta 1 to promote M2 polarization of macrophages via modulation of the miR-132/Mycbp2/TSC2 axis.