Targeting a Tau Kinase Cdk5, Cyclin-Dependent Kinase: A Blood-Based Diagnostic Marker and Therapeutic Earmark for Alzheimer’s Disease

Protein kinases are important molecules of Alzheimer's Disease (AD), driving neuronal demise and the emergence of the disease's destructive hallmarks. Cdk5 has recently been highlighted as a key therapeutic target for AD. This study evaluated the expression levels of Cdk5 and Mcl1 (Cdk5's substrate) in blood samples of 61 AD, 55 Mild Cognitive Impairment (MCI), and 57 Geriatric Controls (GC), and explored the in vitro inhibition of Cdk5. The serum levels of Cdk5 and Mcl1 were measured by Surface Plasmon Resonance (SPR) and verified by Western blot and RT-PCR. Molecular modeling and simulation studies were used to identify a potent hit targeting Cdk5 and validated by binding studies using SPR. The peptide rescue effect was analyzed by MTT assay in the AD cellular model. SPR analysis revealed a significant change in Cdk5 and Mcl1 levels in the serum samples of AD and MCI compared to GC. Results were validated by Western blot and RT-PCR. Binary logistic regression analysis revealed that the concentration of both Cdk5 and Mcl1 was independently associated with disease after adjusting for certain parameters. ROC analysis established an optimum diagnostic cutoff value for Cdk5 [24.97 ng/µL (AUC-0.90)] and Mcl1 [23.08 ng/µL (AUC-0.94)] with high sensitivity and specificity. The peptide YCWS strongly binds to Cdk5's ATP binding site, confirmed by molecular modeling and SPR. In the AD cellular model, peptide YCWS rescued neurotoxicity, increased Mcl1 levels, and reduced destructive hallmarks by inhibiting Cdk5. It can be concluded that Cdk5 is a promising molecule as a circulatory biomarker for the diagnosis of the early stages of AD, and its peptide inhibitor YCWS is a potential therapeutic agent.