A Cdk5 inhibitory peptide reduces tau hyperphosphorylation and apoptosis in neurons

Abstract

The extracellular aggregation of amyloid b (Ab) peptides and the intracellular hyperphosphorylation of tau at specific epitopes are pathological hallmarks of neurodegenerative diseases such as Alzheimer's disease (AD). Cdk5 phosphorylates tau at AD-specific phospho-epitopes when it associates with p25. p25 is a truncated activator, which is produced from the physiological Cdk5 activator p35 upon exposure to Ab peptides. We show that neuronal infections with Cdk5 inhibitory peptide (CIP) selectively inhibit p25/ Cdk5 activity and suppress the aberrant tau phosphorylation in cortical neurons. Furthermore, Ab 1À42 -induced apoptosis of these cortical neurons was also reduced by coinfection with CIP. Of particular importance is our finding that CIP did not inhibit endogenous or transfected p35/ Cdk5 activity, nor did it inhibit the other cyclin-dependent kinases such as Cdc2, Cdk2, Cdk4 and Cdk6. These results, therefore, provide a strategy to address, and possibly ameliorate, the pathology of neurodegenerative diseases that may be a consequence of aberrant p25 activation of Cdk5, without affecting 'normal' Cdk5 activity.

Roles of heat-shock protein 90 in maintaining and facilitating the neurodegenerative phenotype in tauopathies

“…Of particular importance are cdk5 and mutant Tau (mTau), as demonstrated by the fact that either modulation of cdk5 complex activity or mutant TauP301L expression leads to alleviation of the transformed phenotype. In concordance with these observations, cdk5 inhibitors were found to reduce Tau phosphorylation and apoptosis in neurons (9,12,13). A role of the cdk5/p35 complex in the genetic etiology of early onset AD was recently suggested (14).…”

A 24-Residue Peptide (p5), Derived from p35, the Cdk5 Neuronal Activator, Specifically Inhibits Cdk5-p25 Hyperactivity and Tau Hyperphosphorylation

“…Immunocytochemistry-Immunocytochemistry analysis was performed as described previously (23). Briefly, cells were fixed on coverslips for 30 min at room temperature in 4% paraformaldehyde in PBS and then permeabilized and blocked in 5% FBS with 0.1% Triton X-100 in 1ϫ PBS for 1 h. The coverslips were incubated overnight at 4°C with primary antibodies diluted in blocking buffer.…”

“…It reduces Tau hyperphosphorylation and protects transfected HEK cells and neurons from apoptosis induced by Cdk5-p25 (23,27,(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42). To produce a smaller and more effective inhibitory peptide of Cdk5-p25 for potential therapeutic use, we designed and constructed five short peptides in GST vectors, as shown in Fig.…”

“…Indeed, increased levels of p25 and Cdk5 activity have been reported in AD brains. The finding that p25 may be toxic comes from studies of cortical neurons treated with ␤-amyloid (A␤), a key marker of AD pathology, where p35 is converted to p25 accompanied by activated Cdk5, Tau hyperphosphorylation, and apoptosis (22,23).Expression of the Cdk5-p25 complex seems to be primarily responsible for the Tau pathology and suggests that a therapeutic approach directed specifically at this target might prove successful (24 -26). For most of these studies, however, the focus has been on aminothiazol compounds resembling roscovitine, a kinase inhibitor that competes with the ATP binding site in Cdk5 and other kinases.…”

“…Indeed, increased levels of p25 and Cdk5 activity have been reported in AD brains. The finding that p25 may be toxic comes from studies of cortical neurons treated with ␤-amyloid (A␤), a key marker of AD pathology, where p35 is converted to p25 accompanied by activated Cdk5, Tau hyperphosphorylation, and apoptosis (22,23).…”