hiPSC-derived neurons, including MGE cell-derived GABAergic neurons, in culture were washed with PBS and collected in the presence of a high-detergent buffer consisting of 50 mM Tris, 150 mM sodium chloride, 2% Nonidet P-40, 1% sodium deoxycholate, 4% sodium dodecyl sulfate, and supplemented with complete protease inhibitor cocktail (Roche), phosphatase inhibitor cocktail 1 (P2850, Sigma), and phosphatase inhibitor cocktail 2 (P5726, Sigma). The total protein in cell lysates was quantitated with the BCA protein assay kit (#23227, Pierce). In some experiments, the media were also collected for analysis of apoE and soluble APP levels by western blot. The samples were separated by SDS-PAGE on 4−20% Bis-Tris polyacrylamide gels (Life Technologies) or Criterion XT 4–12% Bis-Tris gels (Bio-Rad) and transferred to nitrocellulose membranes (Bio-Rad). The membranes were then blocked in Odyssey Blocking Buffer (PBS) (LI-COR) and probed with the following primary antibodies: apoE (178479, Calbiochem), actin (A5060, Sigma), Tuj1 (MAB1637, EMD Millipore; MRB-435P, Covance), GFAP (Z0334, Dako), PHF1 (gift from Peter Davies), AT8 (MN1020, Thermo Fisher Scientific), AT180 (MN1040, Thermo Fisher Scientific), AT270 (MN1050, Thermo Fisher Scientific), Tau-5 (577801, EMD Millipore),
