Detection of apoptosis by DAPI staining

U87 cells at a density of 5.0×10⁴ viable cells/cm² were cultured in the incubator and treated with 10 µM Aβ_1–42 at 37°C for 48 h. Apoptosis was detected using DAPI staining (Beyotime Institute of Biotechnology). Normal cells exhibit a round nucleus uniformly stained with clear margin, while apoptotic cells exhibit abnormal nucleus margin and the condensed chromosomes. Following fixation with 4% PFA for 20 min at room temperature and treatment with 1X TPBS (0.5% Triton-X-100) for 10 min on ice, cells were stained with DAPI solution for 15 min at room temperature. Images were acquired using a fluorescence microscope at ×100 and ×200 magnification (Eclipse Ti-S; Nikon Corporation).