MAPT and Alzheimer disease: To detect tau seeding activity in AD and related tauopathies’ brain extracts above by seeded-tau aggregation assay, we treated HEK-293FT/HA-3R-tau151-391 or HA-4R-tau151-391 cells with these brain extracts for 42 h and analyzed RIPA-insoluble and -soluble tau (Fig. 3f).