Fig. 2.

TD-sEVs up-regulate VEGFR-2 expression and promote in vitro endothelial cell migration and angiogenesis. a Up-regulating of VEGFR-2 expression in HUVECs incubated with various concentrations of TD-sEVs (25, 50 and 100 μg/ml), 100 μg/ml NT-sEVs, or vehicle control (PBS) after 48 h. Columns represent means of three different experiments; bars represent SD. ns: non-significant (P > 0.05), **P < 0.01, ***P < 0.001. b Promoting effects of different concentrations of TD-sEVs on the proliferation rate of HUVECs at time points 24 and 48 h. No significant difference in the cell proliferation rate was observed between NT-sEVs-treated and control PBS-treated cells at various time points. Points represent means of three experiments; bars represent SD. c Representative micrographs of monolayer wounding assay in HUVECs treated with 100 μg/ml TD-sEVs, 100 μg/ml NT-sEVs, or vehicle control (PBS) at the time of scratch wounding (0 h), 24 and 48 h thereafter. d Quantitative analysis of wound closure at different time points indicated the promoting effects of TD-sEVs on the migration rates of HUVECs compared to those of cells treated with NT-sEVs or vehicle control (PBS). e Representative micrographs showing the effects of TD-sEVs on the capability of endothelial cells to form the capillary-like tube structures in vitro after 24 h. Quantitative analysis of the tube lengths (f) and branch points (g) of HUVECs following treatment with 100 μg/ml TD-sEVs or vehicle control (PBS) were calculated in three randomly selected fields. ns: non-significant, *P < 0.05, **P < 0.01, ***P < 0.001