CDK5 and Alzheimer disease: Consistent with these findings, another recent study demonstrated that Aβ upregulates tau hyperphosphorylation as well as tau kinases, including GSK-3β, cyclin-dependent kinase 5 (CDK-5), proline-directed kinase (PDK), and casein kinase II, in vitro and in a model of AD (Takashima et al., 1993; Vintém et al., 2009; Oliveira et al., 2015; Wu et al., 2018).