CDK5 and Alzheimer disease: To determine how two pathogenic pathways triggered by Aβ influence the neuronal cell death process, we subsequently investigated the role of Aβ at the level of cell cycle regulatory proteins including cyclin 2, cyclin 4, CDK2, CDK4 and CDK5, which are known as critical regulators of neuronal cell death in AD patients (Frade and Ovejero-Benito, 2015; Liu et al., 2016).