MAPT and Alzheimer disease: Although the phosphorylation of GSK-3β at Ser9 has an inhibitory role in GSK3β activity, there have been several reports suggesting induction of oxidative stress and inactivation of PP2A increase GSK-3β phsphorylation at Ser9 and activity via another alterative pathway such as a calpain activation, which is important for tau phosphorylation in AD brain31, 45, 46, 47, 48, 49, 50.