Endothelial exosomes stimulate migration of endothelial cells and angiogenesis. (A) Shown is an example of the cell migration assay. Borders of the scratch at t = 0 are indicated with solid lines, borders after migration at t = 6 hours with dotted lines. (B) Quantitation of HMEC cell migration assay after incubation with, respectively, (1) basal medium (basal,−); (2) conditioned medium (cond, comp.); (3) exosome-depleted conditioned medium (cond, depl.); (4) exosome-depleted conditioned medium after re-addition of exosomes (cond, re-add.); (5) reconstituted conditioned medium with 10 × concentrated exosomes (cond, 10×); and (6) purified exosomes resuspended in basal medium (basal, +). Values are normalized to condition 1 (n = 5 ± SD, ANOVA). Shown are (C) an example image of the in vitro angiogenesis assay, and (D) quantitation of mean tube lengths in the endothelial cell network formed after incubation with (1) basal medium (basal,−); (2) conditioned medium (cond, comp.); and (3) purified exosomes resuspended in basal medium (basal, +). Tubule lengths are indicated relative to condition 1 (n = 5 ± SD, ANOVA). Shown are (E) an illustrative image of a cell-seeded bead with angiogenic sprouts and (F) quantitation of average total sprout length per bead upon incubation with (1) basal medium (basal,−); (2) conditioned medium (cond, comp.); and (3) purified exosomes resuspended in basal medium (basal, +). Bars = 100 μm.