Cyclin-dependent kinase 5 (Cdk5 physiology and pathology)

我们已经开始使用TFP5来研究它在PD中的治疗作用。帕金森病（PD）是一种慢性神经退行性疾病，其特征是黑质多巴胺神经元丢失，纹状体多巴胺水平下降，从而导致锥体外系运动功能障碍。最近的证据表明，细胞周期蛋白依赖性激酶5 （Cdk5）在包括PD在内的几种神经退行性疾病中被不适当激活。迄今为止，在不影响正常Cdk5活性的情况下，特异性抑制Cdk5过动的策略尚未成功。此前，我们报道了TFP5肽在阿尔茨海默病（AD）动物模型中具有神经保护作用。在这里，我们发现TFP5/TP5选择性抑制Cdk5/p25在体内和体外的过度激活，挽救了1-甲基- 4-苯基-1,2,3,6-四氢吡啶（MPTP/MPP+）诱导的PD小鼠模型黑质纹状体多巴胺能神经退行性变。TP5肽治疗也阻断纹状体多巴胺消耗，改善MPTP治疗后的步态功能障碍。TFP5/TP5肽的神经保护作用也与神经炎症和细胞凋亡的显著减少有关。在这里，我们展示了TFP5/TP5肽选择性抑制Cdk5/p25过度激活，这表明该激酶是减少帕金森病神经退行性变的潜在治疗靶点。

We have began to use TFP5 to study its therapeutic role in PD. Parkinsons disease (PD) is a chronic neurodegenerative disorder characterized by the loss of dopamine neurons in the substantia nigra, decreased striatal dopamine levels, and consequent extrapyramidal motor dysfunction. Recent evidence indicates that cyclin-dependent kinase 5 (Cdk5) is inappropriately activated in several neurodegenerative conditions including PD. To date, strategies to specifically inhibit Cdk5 hyperactivity have not been successful without affecting normal Cdk5 activity. Previously, we reported that TFP5 peptide has neuroprotective effects in animal models of Alzheimer's disease (AD). Here, we show that TFP5/TP5 selective inhibition of Cdk5/p25 hyperactivation in vivo and in vitro, rescues nigrostriatal dopaminergic neurodegeneration induced by 1-methyl- 4-phenyl-1,2,3,6-tetrahydropyridine (MPTP/MPP+),in a mouse model of PD. TP5 peptide treatment also blocked dopamine depletion in the striatum and improved gait dysfunction after MPTP administration. The neuroprotective effect of TFP5/TP5 peptide is also associated with marked reduction in neuroinflamation and apoptosis. Here, we show selective inhibition of Cdk5/p25 hyperactivation by TFP5/TP5 peptide, which identifies the kinase as a potential therapeutic target to reduce neurodegeneration in Parkinson's disease. Because of its involvement in PD, Cdk5/p25 has been identified as a prime therapeutic target for PD. Accordingly, compounds like roscovitine, an inhibitor targeting the ATP binding site in Cdk5 and other cell cycle kinases, have been studied as potential therapeutic agents, however, these drugs are toxic. Our approach to this problem, based on structure and kinetics of the Cdk5/p25complex, resulted in the production of several small truncated peptides of p35, which competed with p25 binding and inhibited Cdk5 hyperactivation in vitro. A small peptide, P5, comprising 24 aa, specifically inhibited Cdk5/p25 activity in cultured cortical neurons, reduced hyperphosphorylated tau and apoptosis, without affecting the normal endogenous Cdk5/p35 activity, nor the activity of several cell cycle kinases (Zheng et al., 2005, Zheng et al., 2010a).The P5 peptide was modified as TFP5 with a transactivator of transcription (Tat) peptide conjugated at the C terminus to facilitate passage through the blood-brain barrier, and fluoresceinisothiocyanate (FITC; a green fluorescent tag) attached at the N terminus as a marker. When injected intraperitoneally into 5XFAD AD model mice, significantly reduced Cdk5/p25 hyperactivity, hyperphosphorylated tau and rescued behavior deficits of spatial working memory and motor deficits (Shukla et al., 2013). Moreover, TFP5 also reduced toxicity in cortical neurons exposed to high glucose (Binukumar et al., 2014). We now find the intraperitoneal injection of TP5 (TFP5 without FITC) into MPTP-induced mice effectively blocks degeneration of dopamine neurons in the SNpc, and almost completely prevents the loss of striatal dopamine and its metabolites. The peptide treatment also ameliorates the MPTP-induced behavioral deficits, inhibits neuroinflamation in vivo and protects MPP+ neurotoxicity in vitro.These results suggest that TFP5/TP5 may be effective in the treatment of Parkinsons disease. We believe TFP5 acts on multiple pathways inhibiting hyper activation of Cdk5 and other kinases involved in inducing neuropathologies to reduce / prevent neurodegenerative phenotypes.