Small Peptide Inhibitor Of JNK3 Protects Against MPP~+/MPTP Induced Dopaminergic Injury Via Inhibiting The ASK1/JNK3 Signaling Pathway

Parkinson’s disease (PD) is a neurodegenerative disorder, with symptoms that include bradykinesia, akinesia, rigidity and tremor. The featured pathological change of PD is the selective and progressive loss of dopaminergic neurons in substantia nigra of midbrain and the formation of Lewy body. Idopahtic PD results from the degeneration and loss of dopaminergic neurons from the substantia nigra.Now, treatment for PD is mainly drug use with Levodopa complex, which can not delay the progression of disease. Therefore, it is urgent to seek and discover a new drug to protect the dopaminergic neurons against the injury to stop the progression of PD.Increasing evidences prove that the activation of the c-Jun N-terminal protein kinase3 (JNK3) is implicated in dopaminergic neuronal death triggered in PD. Apoptosis signal-regulating kinase 1 (ASK1), a member of the mitogen-activated protein kinase (MAPK) kianase kinase family, is an upstream activator of JNK3. ASK1 can be activated in response to diverse stress, and then activation of ASK1 trigger the ASK1/JNK3 signaling pathway. Activated JNK3 in turn phosphorylates its substrates including c-Jun and Bcl-2 and so on, leading to apoptosis and neuronal death. In the present study proved that β-arrestin2, a member of JNK scaffolds family, is a key factor for the activation of ASK1/JNK3 signaling pathway. It functions as a scafford protein and carries ASK1, JNK3 and MKK4 to form a cascade. And this cascade is critical for JNK3 activation.The JNK3-binding domain of β-arrestin2 is located at residues of N terminus of JNK3. Therefore, the ASK1/JNK3 signaling pathway is an important therapeutic target for prevention of dopaminergic neuronal death induced PD.On the basis of the above results, we synthesized the 10-mer peptide (Cys-Ser-Glu-Pro-Thr-Leu-Asp-Val-Lys-Ile), which is same with the N-terminal of JNK3. Then we fused this 10-mer peptide with the Tat peptide (Tyr-Gly-Arg-Lys-Lys-Arg-Arg-Gln-Arg-Arg-Arg) originated from the cell-membrane transduction domain of HIV-1 to obtain a 21-amino acid fusion peptide, named JNK3-N-Tat. The peptide was evaluated in Vitro and in Vivo to ascertain its feature as an inhibitor of JNK3.Our results snowed that treatment of SH-SY5Y or primary cultured neuron with MPP+ could trigger the activation of ASK1/JNK3 signaling pathway. The studies both in vivo and in vitro showed that this peptide alone was sufficient to cross the membrane to cell body and across the blood brain barrier to the central nervous system. The small peptide, which named JNK3-N-Tat, was sufficient to decrease the activation of JNK3 via pertubing the binding between β-arrestin2 and JNK3 in MPP+/MPTP indued injury in both cell and mouse PD model. And JNK3-N-Tat was capable of protecting dopaminergic neurons against MPTP-induced injury.These findings have important implications in understanding of the biology of JNK3 and its role in the pathogenesis of Parkinson’s disease. As significant neuroprotection was achieved by JNK3-N-Tat at the onset of PD, JNK3-N-Tat shows great clinical relevancy and provides a novel way for the treatment of PD.