[DC-derived exosomes induce osteogenic differentiation of mesenchymal stem cells]

This study was aimed to investigate the effect of dendritic cell-derived exosome (DCex) on in vitro osteoblast differentiation of human bone marrow mesenchymal stem cells (hBM-MSC). DCex were harvested from the DC culture supernatants by ultracentrifugation. The morphology of DCex was observed by using transmission electron microscopy and the surface marker expression was detected by flow cytometry. MSCs at passage 3 were used in this study. DCex incorporation into MSCs was observed under a confocal microscope. MSCs were either exposed to DCex (10 µg/ml) or the standard osteogenic induction condition. The cells cultured in complete medium were served as the control. The expression levels of Runt related transcription factor 2 (Runx2) were detected by real-time and standard PCR. The cellular alkaline phosphatase (ALP) activity was also detected. The results showed that the DCex were spherical or oval membrane vesicles with diameters of about 40-100 nm under transmission electron microscope. The DCex expressed surface molecules specific for DCs, including CD83, CD86, CD80, and HLA-DR. After cultured for 7 days, the MSCs treated with DCex highly expressed Runx2 as compared with the control group (P < 0.05). After cultured for 14 days, ALP activity of the DCex-treated MSCs was markedly higher than the control group (P < 0.01), though it was lower than that of MSCs treated with standard inductive agents. It is concluded that DCex can induce MSCs to differentiate into osteoblasts. The detailed investigations are needed to clarify the underlying mechanisms.