CDK5 and Alzheimer disease: For instance, Aβ oligomers may activate protein kinases such as glycogen synthase kinase-3β (GSK-3β), Ca2+-dependent calmodulin kinase IIα (CaMKIIα) and cyclin-dependent kinase 5 (CDK5) that are able to directly phosphorylate tau proteins at AD-related sites 7-9.