Fig. 1

APOE ε4-expressing induced neurons (iNs) from patients with Alzheimer’s disease (AD). a Schematic depiction of the generation of directly converted iNs from the fibroblasts of patients with AD. To induce APOE ε4 isoforms at the time point of the amyloid-seeding stage, doxycycline was added at day 7 (amyloid-seeding stage) and 14 (amyloid-progressive stage). b Relative intensity of  Aβ (6E10) oligomers in the iNs of healthy controls at different time points. Data represent mean ± SEM. ANOVA-test; n = 5 per sample. c Relative intensity of amyloid oligomers (6E10) in AD patient iNs harboring PSEN1 (left) and PSEN2 (right) mutation at different time points. Data represent mean ± SEM. ANOVA-test, *P < 0.05, **P < 0.01; n = 5 per sample. d Western blot analysis of APOE ε4 in AD patient-derived iNs treated with doxycycline at different time points. e Immunofluorescence for TUJ1 and NEUN to confirm AD patient iNs on day 25. Scale bar,  20 µm. f Quantification of TUJ1⁺/NeuN⁺ cells at amyloid-seeding and amyloid-aggregation stages. Data represent mean ± SEM. ANOVA-test, *P < 0.05; n = 3 per sample. g Immunostaining of MAP2- and VGLUT1-positive cells in APOE ε4-expressing AD patient-derived iNs on day 25. Scale bars, 50 µm. h Quantification of MAP2⁺/VGLUT1⁺ cells at amyloid-seeding and amyloid-aggregation stages. Data represent mean ± SEM. ANOVA-test, *P < 0.05; n = 3 per sample. i Immunostaining of Synapsin1- and VGLUT1-positive cells in AD patient iNs. Scale bar, 20 µm. j Number of Synapsin⁺/VGLUT1⁺ puncta in each condition. Data represent mean ± SEM. ANOVA-test, *P < 0.05; n = 5 per sample. k Fluorescence-activated cell-sorting analysis of Synapsin–RFP-positive cells from AD fibroblasts harboring PSEN1 mutation, AD patient iNs, and APOE ε4-expressing patient iNs. l Quantification of Synapsin–RFP-positive cells in each condition. Data represent mean ± SEM. ANOVA-test, *P < 0.05; n = 3 per sample. + APOE4 (day 7): AD patient iNs expressing APOE ε4 from day 7; + APOE4 (day 14): AD patient iNs expressing APOE ε4 from day 14; -APOE4: AD patient iNs with no APOE ε4 expression