Figure 3.

Internalization is independent of clathrin- and caveolin-mediated endocytosis or macropynocytosis. (A) Exosomes were added to recipient cells and incubate at 37°C or 4°C for 1 h. The temperature affects exosomal uptake with a significant decrease of luciferase activity at 4 degrees suggesting an energy-dependent process rather than passive membrane uptake (^*p > 0.05). (B–D) Represent the % of internalization of exosomes with and without pharmacological treatment. The cells were pretreated with the following drug were used: CPZ 9 μg/ml (clathrin-dependent pathway inhibitor), nystatin 25 μg/ml (non-clathrin, caveolar-related pathway inhibitor) and Cytocholasin D 2 μM (macropinocytosis inhibitor) and add again with the exosomes. The luciferase signal was measured 1h later. None of the inhibitors significantly blocked the exosomal uptake (P > 0.05, n.s). Data were obtained from 3 independent experiments and are expressed as the % uptake relative to the control recipient cell. Values are the mean ± S.E.M.