CDK5 and Alzheimer disease: HPA axis dysfunction, abnormalities in the CRF system and glutamate systems, neuro-inflammation, aberrant immune activity, dysbiosis of the gut microbiota, downregulation of neurotrophic factors, synaptic degeneration, and changes in the activity and expression of GSK3β, CDK5, and PP2A in response to chronic stress are all of great significance in the pathogenesis of AD.