Fig. 3

Tau is localized inside exosomes. a Neuron-derived exosomes were incubated with increasing concentrations of NaCl to detach proteins peripherally attached to the membrane. Tau is detected with the pan-Tau antibody K9JA. HSC70 and Alix were examined as exosomal markers. Lines on the right indicate Tau protein, Alix and HSC70. M.W. markers are shown on the left. Note that exosomal Tau levels are not changed by NaCl treatment (lanes 1–5), similar to exosomal markers HSC70 and Alix, indicating that Tau is not peripherally attached to the exosomal membrane surface. b Proteinase K protection assay. Neuron-derived exosomes treated with or without 50 ng proteinase K (Prot K) in the presence or absence of 1% saponin (Sapo) for 5 min or 1 h at 37 °C, followed by western blot analysis. Note that Tau is strongly reduced (5 min) or even absent (1 h) in exosomes treated with both Prot K and Sapo, compared with treatment with Prot K alone, indicating that the exosomal membrane protects Tau against Prot K digestion