MAPT and Alzheimer disease: To determine if there was aberrant PAD-pathway signaling in the AD-tau neurons, we immunostained PBS, Con, or AD-tau treated neurons for a marker of active GSK3β (aGSK3β; non-phospho-Ser9 GSK3β antibody;) and a marker of phospho-Ser422 tau (pS422 antibody) to identify pathological tau inclusions (Fig. 6A–D).