CDK5 and Alzheimer disease: Indeed, analysis of AD brain tissue showed that protein kinases such as glycogen synthase kinase 3β (GSK3β), P25/Cyclin-dependent kinase 5 (Cdk5), as well as mitogen-activated protein kinases (MAPKs), such as extracellular signal-regulated MAP kinase (ERK) 1⁄2 pathway, the c-Jun-N-terminal kinase (JNK) pathway, and the p38 pathway, are increased in expression and/or activity [14].