Fig. 2

Fibril-like structures in endocytic organelles of wild-type neurons treated with Aβ1-42. a Wt primary neurons treated at 12 DIV with Aβ for 48 h induced fibril-like structures in endocytic organelles with Aβ1-42. BSA-gold was added to cells 2 h before fixation to delineate endocytic organelles (marked with asterisk). Scale bar 500 nm. High magnification image to the right, scale bar 100 nm. b Aβ1-42 peptides incubated in vitro at 37 °C for 1 h to induce fibril formation, imaged with EM. Scale bar 100 nm. c BSA-gold (white arrows) was found in the cytosol in Aβ1-42 treated neurons, indicating loss of endolysosomal impermeability due to Aβ1-42. Scale bar 500 nm. d OC antibody labelling for fibrillar oligomers and/or fibrils is seen in a vesicular pattern in processes after 45 min treatment with 0.5 μM of Aβ1-42 and colocalizes with human Aβ antibody 6E10 confirming that fibrils consist of the added human Aβ1-42. Scale bar 10 μm. e Feeding 0.5 μM of Aβ1-42 to wt primary neurons at 12 DIV at 24 h vs 48 h. At 24 h most of the OC labelling was also antibody 6E10 positive. At 48 h the outer aspects of OC positive structures were 6E10 negative. Scale bar 20 μm. f Weak surface labelling of non-permeabilized neurons shows that OC and 6E10 antibody positive structures were intracellular after 24 h of treatment with Aβ1-42 (upper panel). At 48 h extracellular OC antibody labelling was now more visible consistent with penetration of the plasma membrane by the elongated OC positive fibrils (middle panel). Strong OC and 6E10 antibody labelling of permeabilized cells after fixation but before immunolabelling, shows that the vast majority of added human Aβ1-42 (antibody 6E10) and OC antibody positive fibrils and/or fibrillar oligomers are inside neurons (lower panel). Scale bar 20 μm. g After 48 h of treatment with 0.5 μM Aβ1-42, OC antibody labelling was seen extending out from LAMP1-positive structures in the processes. The image shows OC with the superimposed colocalizing channel for LAMP1 and OC. For the complete image with separate channels see Additional file 3: S2A. Scale bar 20 μm