TFP5/TP5 peptide provides neuroprotection in the MPTP model of Parkinson's disease

Binukumar BK , Harish C. Pant

National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA

INVITED REVIEW

TFP5/TP5 peptide provides neuroprotection in the MPTP model of Parkinson's disease

Binukumar BK , Harish C. Pant*

National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA

Cyclin-dependent kinase 5 (Cdk5) is a member of the serine-threonine kinase family of cyclin-dependent kinases. Cdk5 is critical to normal mammalian nervous system development and plays important regulatory roles in multiple cellular functions. Recent evidence indicates that Cdk5 is inappropriately activated in several neurodegenerative conditions, including Parkinson's disease (PD). 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. During neurotoxicity, p35 is cleaved to form p25. Binding of p25 with Cdk5 leads deregulation of Cdk5 resulting in number of neurodegenerative pathologies. To date, strategies to specifically inhibit Cdk5 hyperactivity have not been successful without affecting normal Cdk5 activity. Here we show that inhibition of p25/Cdk5 hyperactivation through TFP5/TP5, truncated 24-aa peptide derived from the Cdk5 activator p35 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 neuroinflammation and apoptosis. Here we show inhibition of Cdk5/p25-hyperactivation by TFP5/TP5 peptide, which identifies Cdk5/p25 as a potential therapeutic target to reduce neurodegeneration in PD.

cyclin-dependent kinase 5; Parkinson's disease; neurodegeneration; therapeutic target; TP5 TFP5/ TP5 peptide; MPTP

Introduction

Cyclin dependent kinase-5 (Cdk5), a family member of the cyclin dependent kinases, plays a pivotal role in the nervous system development and function. Cdk5 was first purified as one (TPKII) of two tau protein kinases, namely TPKI and TPKII, from a bovine brain microtubule fraction (Ishiguro et al., 1992), as neuronal cdc2-like kinase from bovine brain extracts (Lew et al., 1992), and as a Lys-Ser-Pro (KSP) sequence phosphorylating kinase from rat spinal cord (Shetty et al., 1993). We had also identified kinase and phosphatase players regulating neurofilament and tau phosphorylation in mammalian and squid neurons (Floyd et al., 1991; Veeranna et al., 1998; Veeranna et al., 2000; Grant and Pant, 2004), identified Cdk5 as a principal kinase phosphorylating KSP sites in neurofilament subunit (NFH) tail domains (Sharma et al., 1998), and in a collaborative study of a Cdk5 knockout, demonstrated its key role in neuronal development, function and survival (Ohshima et al., 1996). Initially, its activity was found to be restricted to neurons in the central nervous system due to the expression of neuronal specific activators p35 and p39. However, in the last decade p35 distribution and Cdk5 activity have been found in a growing number of tissues such as the testis, pancreas, cornea and most recently in glial cells of the brain (Kesavapany et al., 2007).

The tight regulation of Cdk5 activity is achieved through the specific cellular localization of its major activator p35. With an N-terminal myristoylation sequence of the activator, which anchor the membranes, Cdk5 activity is therefore restricted and localized to this region of the cell. When a neurotoxic insult involving amyloid-β peptides, 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP), reactive oxygen species (ROS) or glutamate is initiated, there is an increase in intracellular calcium, which then activates the calcium-dependent protease calpain. Calpain cleaves p35 into a p10 product that is still anchored to the membrane and a p25 moiety that is a potent hyperactivator of Cdk5. p25 is now free to move around the neuronal compartments and the net effect is that Cdk5 is hyperactivated by p25 leading to hyper phosphorylation of the substrates. To confound the misery of the neuron, p25 has a very strong affinity to Cdk5 but also has a longer half-life than its parent p35 protein, which leads to an aberrant hyperactivation of Cdk5 (Kesavapany et al., 2007). The result of this is an abnormal phosphorylation of cytoskeletal proteins, such as the microtubule-associated protein tau and neurofilaments (NFs) and the hyperphosphorylation of these cytoskeletal proteins are found in pathological hallmarks of a number of neurodegenerative diseases including Alzheimer's disease (AD), Parkinson's disease(PD) and amyotrophic lateral sclerosis (ALS). One type of such lesion in AD is the neurofibrillary tangles (NFTs) where the epitopes found to be phosphorylated in these inclusions are readily hyperphosphorylated by Cdk5/ p25. Lewy bodies, the inclusions found in PD brain, contain deposits of α-synuclein and phosphor NF-H (Hill et al., 1991; Spillantini et al., 1997) and Cdk5 (Brion et al., 1995; Nakamura et al., 1997; Smith et al., 2003), while inclusions in the spinal cord contain hyperphosphorylated aggregated NF-H (Bajaj et al., 1998, 1999). In PD, early involvement of Cdk5 in the disease pointed to its presence in Lewy bodies (Nakamura et al., 1997). Since then, experiments using MPTP to induce dopaminergic neuronal loss showed that the downstream effector of this is Cdk5 (Smith et al., 2003; Alvira et al., 2006). Upon MPTP treatment, calpains produces p25 and hyperactive Cdk5 (Cdk5/p25) phosphorylates the transcription factor myocyte enhancer factor 2 (MEF2) to inactivate it. The inactivation of MEF2 causes neuronal loss (Smith et al., 2006). In a recent report, Cdk5 has been shown to interact with and phosphorylate Parkin, a protein that contains E3-ubiquitin ligase activity. Mutations in Parkin are responsible for a large percent of autosomal recessive juvenile parkinsonism cases. Cdk5 phosphorylation of Parkin decreased its auto-ubiquitination activity and a phospho-deficient mutant of Parkin displayed increased ubiquitination towards itself as well as its substrates synphilin and α-synuclein, both constituents of Lewy body inclusions in PD. The results showed that Cdk5 activity is important in regulating inclusion formation and accumulations of toxic Parkin substrates in a PD paradigm (Avraham et al., 2007).

Evolution of CIP, P5 and TFP5/TP5

Current strategies to produce inhibitors of kinase activity target ATP binding regions of the kinases. However, since all kinases depend on these regions as a mode of action, the specificity of this approach has often been called into question. ‘Normal' p35-mediated Cdk5 activity, as mentioned before, is required for the proper formation and function of the nervous system and thus, only aberrant p25-mediated Cdk5 hyperactivity must be targeted and ATP analogues would not be useful in this paradigm. Indeed, known inhibitors such as butyralactone, olomoucine and roscovitine all inhibit normal as well as aberrant Cdk5 activity. While attempting to fully characterize the behavior of p25 and its subsequent hyperactivation of Cdk5, we identified CIP (126a.a. residues), a truncated fragment of the Cdk5 regulator, p35, which specifically inhibited hyperactive Cdk5/ p25 (Amin et al., 2002; Sundaram et al., 2013), presumed to contribute to the pathology of AD (Patrick et al., 1999; Smith and Tsai, 2002; Tsai et al., 2004).

A further fine-tuning of these studies has identified a smaller, 24-aa peptide (termed P5) derived by serial truncation of CIP. This 24-aa peptide (termed P5) has been shown to inhibit Cdk5/p25 activity in transfected human embryonic kidney 293 (HEK) cells and primary neurons without affecting normal Cdk5/p35 or other Cdks (Zheng et al., 2002, 2005, 2007, 2010; Kesavapany et al., 2007). Subsequently, P5, modified as TFP5 so as to penetrate the blood-brain barrier after intraperitoneal injections in AD model mice, inhibited abnormal Cdk5/p25 hyperactivity and significantly rescued AD pathology in AD model mice (Shukla et al., 2013). Moreover, TFP5 also reduced toxicity in cortical neurons exposed to high glucose (Binukumar et al., 2014).

TFP5 Treatment Inhibits MPP+-induced Inflammation and Apoptosis in Mesencephalic Primary Cultures

Encouraged by our previous results and Cdk5 involvement in PD, Cdk5/p25 has been identified as a prime therapeutic target for PD. In a recent study the efficacy of the TFP5 peptide was tested in a PD model (Binukumr et al., 2015). Consistent with previous studies, we observed 24 hours of MPP+incubation induces Cdk5 hyperactivation in mesencephalic primary cultures. Pretreatment and coincubation with TFP5, however, was sufficient to significantly reduce the elevated activity. Because the Cdk5/ p25 inhibitor TFP5 was effective at blocking deregulated kinase activity, we further tested whether the effect can be replicated in primary dopaminergic neurons from mesencephalic cultures. The number of tyrosine hydroxylase (TH) positive neurons and the length of TH-positive neurites were significantly reduced after MPP+treatment. In contrast, treatment with TFP5 effectively attenuated MPP+induced toxicity in dopaminergic neurons. Scrambled peptide control however, had no protective effect on these cells. Taken together, those results demonstrate that TFP5 has a neuroprotective effect in cell culture models of dopaminergic neurodegeneration. We also investigated the anti inflammatory action of TFP5, primary neuron-glia cultures from mouse midbrains with TFP5 or scrambled peptide. It is evident that treatment with MPP+increased the expression of both F4/F8 and GFAP, astocytic marker compared with the control, whereas treatment with TFP5 ameliorates these effects. Scrambled peptide had no effect compared with MPP+treatment. Further we examined the effect of TFP5 on MPP+induced apoptosis by measuring caspase-3 activation and cytochrome c release in the mixed cultures. Treatment of mesencephalic primary cultures with MPP+for 24 hours resulted in robust activation of caspase-3 and cytochrome c release. TFP5 significantly inhibited the increased levels of caspase-3 and cytochrome c. To confirm further the antiapoptotic function of TFP5, we determined the expression levels of Bcl-2. MPP+treatment significantly decreased the protein level of Bcl-2. This result is in line with previous reports (Liu et al., 2010). Treatments with TFP5 significantly increased Bcl-2 expression. Together, these results showed that TFP5 treatment has antiapoptotic effects in mesencephalic primary culture.

Dopaminergic Neurons are Protected from Cell Death by TP5 after MPTP Induction

As a more effective test of the efficacy of TFP5 as a therapy for PD, we used an in vivo model system. For the initial sets of experiments, animals were injected intraperitoneally (i.p.) with a single TFP5 injection, 40 mg/ kg every day for 9 days. On day 2, TFP5-treated animals received four doses of MPTP. We found that the dose of TFP5 was inadequate; TFP5-treated animals did not show significant inhibition of Cdk5/p25-deregulated activity compared with the MPTP group accordingly, we increased the dose to a single, 80 mg/kg i.p. injection every day for 9 days. We used the peptide without the FITC tag (TP5) since TFP5 aggregates at higher concentration. In this case, TP5 pretreatment produced significant inhibition of Cdk5/p25 kinase activity. MPTP treatment also reduced the number of TH-positive neurons by 77% compared with saline-treated controls. Mice that received daily treatments of TP5 at 80 mg/kg showed an increase of TH-positive neurons in the SNpc. The neuroprotective effect of TP5 was dose dependent, as a 40 mg/kg dose of TP5 failed to protect dopamine neurons due to MPTP toxicity. Moreover, scrambled peptide did not show any dopaminergic neuroprotection compared with the MPTP group. MPTP injections also caused significant decreases in the level of dopamine and its metabolites in the striatal region of MPTP-injected mice. MPTP-induced dopamine and homovanillic acid (HVA) depletion was attenuated almost to control levels in mice treated with TP5. Taken together, these results suggest that TP5 can improve neurochemical deficits in the MPTP mouse model of PD.

TP5 Suppresses MPTP-induced Astroglial and Microglial Activation in vivo

Microglial activation has been implicated in the propagation of SNpc neurotoxicity in multiple animal models of PD. Post-mortem analysis of idiopathic PD patients revealed strong immunoreactivity for CD68, a marker of phagocytic microglia (Croisier et al., 2005; Vroon et al., 2007). Administration of MPTP has been reliably shown to induce this phagocytic microglia phenotype in the SNpc of mice (Vroon et al., 2007; Chung et al., 2010, 2011). Previous studies reported in addition the presence of reactive microglia in MPTP-treated SN exhibiting nigral DA neuronal degeneration (Wu et al., 2003; Block et al., 2007). Accordingly, we investigated whether a TP5 injection regimen can inhibit MPTP-induced glial activation in the SNpc in vivo. Consistent with earlier reports (Wu et al., 2003), numerous GFAP-positive reactive astrocytes and CD11b-positive (activated) microglia were observed in MPTP-treated SNpc compared with saline and scrambled peptide controls. TP5 treatment mitigated these effects of MPTP. Scrambled peptide had no effects on glial activation compared with the MPTP group. Post-mortem analysis of human PD tissue showed that microglia are immunoreactive for multiple proinflammatory cytokines, including tumor necrosis factor α (TNF-α) and interleukin-1β (IL-1β; McGeer and McGeer, 2004). Further, mice that are genetically altered to inhibit cytokine production or are deficient in receptors for these cytokines provide neuroprotection in the SNpc after MPTP exposure (Klevenyi et al., 1999; Sriram et al., 2002). Thus we examined whether MPTP-induced expression of IL-1β and TNF-α in the SN was affected by TP5. The results showed that the levels of TNF-α protein and IL-1β were significantly increased in the midbrain of MPTP-treated mice compared with saline controls. Treatment with TP5 inhibited these MPTP-induced effects, reducing levels of TNF-α and IL-1β ～50%. Here, too, scrambled peptide had no effects. Further we examined whether TFP5 protects against neurobehavioral deficits caused by MPTP. We observed a marked decrease in total distance traveled after MPTP treatment (85%), which was restored ～30% after TP5 treatment. We see that TP5 significantly improved MPTP-induced hypolocomotion.

Our recent data for the first time identify that intraperitoneal injection of peptide, TP5 into MPTP-induced mice effectively blocks degeneration of dopamine neurons in the SNpc and prevents the loss of striatal dopamine and its metabolites. The peptide treatment also ameliorates the MPTP-induced behavioral deficits, inhibits neuroinflammation in vivo, and protects against MPP+neurotoxicity in vitro. These results suggest that TFP5/ TP5 may be effective in the treatment of Parkinson's disease.

Author contributions: All the authors reviewed the literature and drafted the review.

Conflicts of interest: The authors declare no competing financial interests.

Alvira D, Tajes M, Verdaguer E, Acuña-Castroviejo D, Folch J, Camins A, Pallas M (2006) Inhibition of the cdk5/p25 fragment formation may explain the antiapoptotic effects of melatonin in an experimental model of Parkinson's disease. J Pineal Res 40:251-258.

Amin ND, Albers W and Pant HC (2002) Cyclin-dependent kinase 5 (cdk5) activation requires interaction with three domains of p35. J Neurosci Res 67:354-362.

Avraham E, Rott R, Liani E, Szargel R, Engelender S (2007) Phosphorylation of parkin by the cyclin-dependent kinase 5 at the linker region modulates the E3 ubiquitin-ligase activity and parkin aggregation. J Biol Chem 282:12842-12850.

Bajaj NP, Al-Sarraj ST, Anderson V, Kibble M (1998) Cyclin-dependent kinase-5 is associated with lipofuscin in motor neurones in amyotrophic lateral sclerosis. Neurosci Lett 245:45-48.

Bajaj NP, al-Sarraj ST, Leigh PN, Anderson V, Miller CC (1999) Cyclin dependent kinase-5 (CDK-5) phosphorylates neurofilaments heavy (NF-H) chain to generate epitopes for antibodies that label neurofilament accumulations in amyotrophic lateral sclerosis (ALS) and is present in affected motor neurones in ALS. Prog Neuropsychopharmacol Biol Psychiatry 23:833-850.

Binukumar B, Shukla V, Amin ND, Grant P, Bhaskar M, Skuntz S, Steiner J, Pant HC (2015) Peptide (TFP5/TP5), derived from Cdk5 activator P35, provides neuroprotection in the MPTP model of Parkinson's disease. Mol Biol Cell 26:4478-4491

Brion JP, Couck AM (1995) Cortical and brainstem-type Lewy bodies are immunoreactive for the cyclin-dependent kinase 5. Am J Pathol 147:1465-1476.

Chung YC, Kim SR, Jin BK (2010) Paroxetine prevents loss of nigrostriatal dopaminergic neurons by inhibiting brain inflammation and oxidative stress in an experimental model of Parkinson's disease. J Immunol 185:1230-1237.

Chung YC, Bok E, Huh SH, Park JY, Yoon SH, Kim SR, Kim YS, Maeng S, Park SH, Jin BK (2011) Cannabinoid receptor type 1 protects nigrostriatal dopaminergic neurons against MPTP neurotoxicity by inhibiting microglial activation. J Immunol 187:6508-6517.

Croisier E, Moran LB, Dexter DT, Pearce RK, Graeber MB (2005) Microglial inflammation in the parkinsonian substantia nigra: relationship to alpha-synuclein deposition. J Neuroinflammation 2:14.

Floyd CC, Grant P, Gallant PE, Pant HC (1991) Principal neurofilament-associated protein kinase in squid axoplasm is related to casein kinase I. J Biol Chem 266:4987-4994.

Grant P, Pant HC (2004) Topographic regulation of phosphorylation in giant neurons of the squid, Loligo pealei: role of phosphatases. J Neurobiol 58:514-528.

Hill WD, Lee VM, Hurtig HI, Murray JM, Trojanowski JQ (1991) Epitopes located in spatially separate domains of each neurofilaments subunit are present in Parkinson's disease Lewy bodies. J Comp Neurol 309:150-160.

Ishiguro K, Omori A, Takamatsu M, Sato K, Arioka M, Uchida T (1992) Phosphorylationsites on tau by tau proteinkinaseI, a bovine derived kinase generating an epitope of paired helical filaments. Neurosci Lett 148:202-206.

Julien JP (2001) Deregulation of Cdk5 in a mouse model of ALS: toxicity alleviated by perikaryal neurofilament inclusions. Neuron 30:135-147.

Kesavapany S, Zheng YL, Amin N, Pant HC (2007) Peptides derived from Cdk5 activator p35, specifically inhibit deregulated activity of Cdk5. Biotechnol J 2:978-987.

Lew J, Beaudette K, Litwin CM, Wang JH (1992) Purification and characterization of a novel proline-directed protein kinase from bovine brain. J Biol Chem 267:13383-13390.

Liberatore GT, Jackson-Lewis V, Vukosavic S, Mandir AS, Vila M, McAuliffe WG, Dawson VL, Dawson TM, Przedborski S (1999) Inducible nitric oxide synthase stimulates dopaminergic neurodegeneration in the MPTP model of Parkinson disease. Nat Med 5:1403-1409.

Nakamura S, Kawamoto Y, Nakano S, Akiguchi I, Kimura J (1997) p35nck5a and cyclin-dependent kinase 5 colocalize in Lewy bodies of brains with Parkinson's disease. Acta Neuropathol 94:153-157.

Ohshima T, Ward JM, Huh CG, Longenecker G, Veeranna, Pant HC, Brady RO, Martin LJ, Kulkarni AB (1996) Targeted disruption of the cyclin-dependent kinase 5 gene results in abnormal corticogenesis, neuronal pathology and perinatal death. Proc Natl Acad Sci U S A 93:11173-11178.

Patrick GN, Zukerberg L, Nikolic M, de la Monte, S, Dikkes P, Tsai LH (1999). Conversion of p35 to p25 deregulates Cdk5 activity and promotes neurodegeneration. Nature 402:615-622.

Qu D, Rashidian J, Mount MP, Aleyasin H, Parsanejad M, Lira A, Haque E, Zhang Y, Callaghan S, Daigle M, Park DS (2007) Role of Cdk5-mediated phosphorylation of Prx2 in MPTP toxicity and Parkinson's disease. Neuron 55:37-52.

Sharma P, Barchi JJ, Jr Huang X, Amin ND, Jaffe H, Pant HC (1998) Site-specific phosphorylation of Lys-Ser-Pro repeat peptides from neurofilament H by cyclindependent kinase 5: structural basis for substrate recognition. Biochemistry 37:4759-4766.

Shetty KT, Link WT, Pant HC (1993) cdc2-like kinase from rat spinal cord specifically phosphorylates KSPXK motifs in neurofilament proteins: isolation and characterization. Proc Natl Acad Sci U S A 90:6844-6848.

Shukla V, Zheng YL, Mishra SK, Amin ND, Steiner J, Grant P, Kesavapany S, Pant HC (2013). A truncated peptide from p35, a Cdk5 activator, prevents Alzheimer's disease phenotypes in model mice. FASEB J 27:174-186.

Smith PD, Crocker SJ, Jackson-Lewis V, Jordan-Sciutto KL (2003) Cyclin-dependent kinase 5 is a mediator of dopaminergic neuron loss in a mouse model of Parkinson's disease. Proc Natl Acad Sci U S A 100:13650-13655.

Smith PD, Mount MP, Shree R, Callaghan, Park DS (2006) Calpain-regulated p35/cdk5 plays a central role in dopaminergic neuron death through modulation of the transcription factor myocyte enhancer factor 2. J Neurosci 26:440-447.

Spillantini MG, Schmidt ML, Lee VM, Trojanowski JQ, Jakes R, Goedert M (1997) Alpha-synuclein in Lewy bodies. Nature 388:839-840.

Sriram K, Matheson JM, Benkovic SA, Miller DB, Luster MI, O'Callaghan JP (2002). Mice deficient in TNF receptors are protected against dopaminergic neurotoxicity: implications for Parkinson's disease. FASEB J 16:1474-1476.

Sundaram JR, Poore CP, Sulaimee NH, Pareek T, Asad AB, Rajkumar R, Cheong WF, Wenk MR, Dawe GS, Chuang KH, Pant HC, Kesavapany S (2013) Specific inhibition of p25/Cdk5 activity by the Cdk5 inhibitory peptide reduces neurodegeneration in vivo. J Neurosci 33:334-343.

Takahashi M, Amin N, Grant P, Pant HC (1995) P13suc1 associates with a cdc2-like kinase in a multimeric cytoskeletal complex in squid axoplasm. J Neurosci 15:6222-6229.

Tseng HC, Zhou Y, Shen Y, Tsai LH (2002) A survey of Cdk5 activator p35 and p25 levels in Alzheimer's disease brains. FEBS Lett 523:58-62.

Veeranna, Shetty KT, Takahashi M, Grant P, Pant HC (2000) Cdk5 and MAPK are associated with complexes of cytoskeletal proteins in rat brain. Brain Res Mol Brain Res 76:229-236.

Veeranna, Amin ND, Ahn NG, Jaffe H, Winters CA, Grant P, Pant HC (1998) Mitogen activated protein kinases (Erk1,2) phosphorylate Lys-Ser-Pro (KSP) repeats in neurofilament proteins NF-H and NF-M. J Neurosci 18:4008-4021.

Vroon A, Drukarch B, Bol JG, Cras P, Breve JJ, Allan SM, Relton JK, Hoogland PV, Van Dam AM (2007) Neuroinflammation in Parkinson's patients and MPTP-treated mice is not restricted to the nigrostriatal system: microgliosis and differential expression of interleukin-1 receptors in the olfactory bulb. Exp Gerontol 42:762-771.

Wu DC, Teismann P, Tieu K, Vila M, Jackson-Lewis V, Ischiropoulos H, Przedborski S (2003) NADPH oxidase mediates oxidative stress in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinson's disease. Proc Natl Acad Sci U S A 100:6145-6150.

Zheng Y, Kesavapany S, Gravell M, Hamilton RS, Schubert M, Amin N, Albers W, Grant P, Pant HC (2005) A Cdk5 inhibitory peptide reduces tau hyperphosphorylation and apoptosis in neurons. Embo J 24:209-220.

Zheng YL, Li BS, Amin ND, Albers W, Pant HC (2002) A peptide derived from cyclindependent kinase activator (p35) specifically inhibits Cdk5 activity and phosphorylation of tau protein in transfected cells. Eur J Biochem 269:4427-4434.

Zheng YL, Li BS, Kanungo J, Kesavapany S, Amin N, Grant P, Pant HC (2007) Cdk5 Modulation of Mitogen-activated Protein Kinase Signaling Regulates Neuronal Survival. Mol Biol Cell 18:404-413.

Zheng YL, Amin ND, Hu YF, Rudrabhatla P, Shukla V, Kanungo J, Kesavapany S, Grant P, Albers W, Pant HC (2010) A 24-residue peptide (p5), derived from p35, the Cdk5 neuronal activator, specifically inhibits Cdk5-p25 hyperactivity and tau hyperphosphorylation. J Biol Chem 285:34202-34212.

10.4103/1673-5374.182681 http://www.nrronline.org/

How to cite this article: Binukumar BK, Pant HC (2016) TFP5/TP5 peptide provides neuroprotection in the MPTP model of Parkinson's disease. Neural Regen Res 11(5)∶698-701.

*Correspondence to: Harish C. Pant, Ph.D., panth@ninds.nih.gov.

Accepted: 2016-04-15