A novel selective cell-permeable peptide disrupts presynaptic JNK2-STX1a interaction, providing neuroprotection and preventing glutamate-mediated excitotoxicity

L-glutamate is the major excitatory neurotransmitter in the central nervous system of vertebrates. By playing a dual role as amino acid and neurotransmitter, glutamate fulfils a large array of physiological functions supporting neuronal development and cognitive performances. Consequently, the alteration of glutamate signaling entails profound detrimental effects that give rise to disease conditions, including excitotoxicity induced by cerebral ischemia. Since plenty of reports have so far investigated the effects of cerebral ischemia at postsynaptic sites, little is known concerning the mechanisms activated by the ischemic injury at the presynaptic terminal. NMDA receptors have been classically implicated in both postsynaptic and presynaptic pathways sustaining excitotoxicity, but only recently their intracellular association with the c-Jun N-terminal kinase (JNK) has also been involved in such pathological mechanisms. Our previous findings already underlined a specific and unique involvement of the JNK2 isoform as a pivot player in glutamate release, when focusing on presynaptic sites. In the present dissertation we furthermore unveil the selective protein-protein interaction between JNK2 and Syntaxin-1a (STX1a), emphasizing their unexplored contribution in the docking and release of synaptic vesicles at the basis of the NMDA-evoked excitotoxicity. On purpose, we have developed JGRi1, a cell-permeable peptide able to selectively disrupt JNK2/STX1a interplay and pharmacologically prevent the downstream ischemic cascade. To uphold our hypothesis, we tested JGRi1 in several experimental settings, achieving a convincing neuroprotective effect also in a murine model of ischemia over a conveniently long therapeutic window. Conclusively, we analysed the presence of three single nucleotide polymorphisms (SNPs) on the STX1A gene in a cohort of stroke patients, evidencing a haplotype correlated with increased susceptibility to cerebral ischemia. Overall, we here confirm JNK fundamental implication in glutamate release at presynaptic level, moreover presenting for the first time JGRi1, a selective inhibitor of the JNK2/STX1a interaction that may represent a new therapeutic tool able to modulate glutamate overflow in various conditions, including neurodegenerative diseases and ischemia-linked pathologies