The role of CDK6 in Alzheimer's Disease

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Summary Cellular senescence has recently emerged as a fundamental aging mechanism contributing to Alzheimer’s Disease (AD). None of the numerous clinical trials to treat aging related diseases has been able to demonstrate beneficial impact on patients. Moreover, the lack of a preclinical model of aging progression is a barrier to therapeutic development. By using our Cdk6 mouse models and biochemical analyses, we have found that mice lacking the CDK6 protein (KO) or its kinase domain (K43M) replicated many features of human aging. In contrast, mice with constitutive kinase activity (R31C) had opposite phenotypes observed in KO/K43M mice. We have also discovered senescent cells in the hippocampus and entorhinal cortex (EC) regions of KO/K43M brains but not in those of WT/R31C brains at the age of 7 months. Although R31C mutation confers cells with constitutive kinase activity, it does not enhance tumor susceptibility, which makes our proposed study more feasible. Combined with other specific effects of CDK6 on production of the Neural Stem Cells (NSCs)6 and antioxidants14, induction of angiogenesis19, and mediating Notch1 signaling pathway which is involved in inhibition of Aβ5 production, all the evidence described leads us to hypothesize that CDK6 kinase activity is required for inhibiting the development of AD, and therefore enhancing CDK6 kinase activity or targeting its effectors could be a novel therapeutic intervention in the treatment of AD. The long-term goal of our studies is to validate CDK6 as an attractive target for aging related AD, with the aim of identifying the novel therapeutic target genes regulated by CDK6 in AD. The short-term goal of this proposal is to focus on central aims to define the cells attribute to senescence (Aim 1) and to determine the molecular mechanism(s) whereby CDK6 affects senescence in the defined senescent cells (Aim 2). Guided by solid preliminary data, the central hypothesis will be tested in two specific Aims: (Aim1) Defining the cells which attributed to the senescence in hippocampus and EC by flow cytometry, immunohistochemistry, RT-PCR, and Western Blotting. (Aim 2a): Determining the requirement of CDK6 for self-renewal and differentiation of the NSCs by isolating undifferentiated NSCs positive for Nestin and Sox-2 and then by performing self-renewal and differentiation assays as described8,9. Quantification of expressed markers will be determined by Flow cytometry analysis, Western Blotting, and immunohistochemistry; (Aim 2b): Determining the cell autonomous effect of CDK6 on senescence by re-expression of CDK6 specifically on the defined senescent cells to observe if re-expression of CDK6 can reverse the senescence observed in KO brain; (Aim 2c): Determining if loss of CDK6 kinase activity in mice may trigger oxidative stress and the inflammatory cascades known to induce neuroinflammation. Overall, the proposed studies will generate adequate data to support the design and initiation of experimental approaches designed for the next phase.