CDK5 and Alzheimer disease: Tau can be phosphorylated by different protein kinases such as the members of the MAPK family (JNK, p38 and Erk1/2), GSK-3β, and cyclin-dependent kinase 5 (cdk5), while protein phosphatase (PP) 2A plays a major role in regulating dephosphorylating of the hyperphosphorylated tau isolated from the AD brains [143–147].