Role of the JNK pathway in NMDA-mediated excitotoxicity of cortical neurons

Abstract

Excitotoxic insults induce c-Jun N-terminal kinase (JNK) activation, which leads to neuronal death and contributes to many neurological conditions such as cerebral ischemia and neurodegenerative disorders. The action of JNK can be inhibited by the Dretro-inverso form of JNK inhibitor peptide (D-JNKI1), which totally prevents death induced by N-methyl-D-aspartate (NMDA) in vitro and strongly protects against different in vivo paradigms of excitotoxicity. To obtain optimal neuroprotection, it is imperative to elucidate the prosurvival action of D-JNKI1 and the death pathways that it inhibits. In cortical neuronal cultures, we first investigate the pathways by which NMDA induces JNK activation and show a rapid and selective phosphorylation of mitogen-activated protein kinase kinase 7 (MKK7), whereas the only other known JNK activator, mitogen-activated protein kinase kinase 4 (MKK4) In many nervous system disorders, including cerebral ischemia, traumatic brain injury and neurodegenerative diseases, overactivation of N-methyl-d-aspartate (NMDA) receptors leads to neuronal damage, resulting in neuronal loss and consequent severe neurological impairment. This cascade of neuronal injury, referred to as 'excitotoxicity', is still only partly understood. Dying neurons activate complex signal transduction events to trigger their death program, and the c-Jun N-terminal kinase (JNK) pathway plays an important role in this process. 1 D-retro-inverso form of JNK inhibitor (D-JNKI1) is an extremely potent neuroprotectant against excitotoxicity of cortical neurons and against different in vivo paradigms of neurodegeneration. [2][3][4] The active part of this peptide contains a retro-inverso form of a 20-amino-acid sequence (JBD 20 ) from the JNK-binding domain (JBD) of the scaffold protein JNK-interacting protein-1 (IB1/JIP-1), and it blocks the access of JNK to many of its targets. [5][6][7] Recently, Negri et al. 8,9 performed a detailed re-examination of the JBD-containing proteins and identified 19 different substrates of JNK. They then proved in a cell-free assay that the JBD 20 sequence prevented interactions and phosphorylations by JNK of nine of these targets. Among these nine substrates, we have studied the following four that might participate in regulating the death of cortical neurons: (1) MADD/DENN (MAPK-activating death domain-containing protein/differentially expressed in normal and neoplastic cells); (2-3) mitogen-activated protein kinase kinase 4 (MKK4) and mitogen-activated protein kinase kinase 7 (MKK7), the two direct upstream activators of JNK and (4) the scaffold protein IB1/JIP-1.,In particularly, MADD/DENN was identified as a substrate for JNK3, 10 the isoform most clearly involved in excitotoxicity 11,12 and mostly expressed in the brain. [10][11][12] Increasing evidence supports a strong correlation between low MADD/ DENN expression and neuronal loss. 13,14 MKK4 and MKK7 are the only known JNK activators. In some cell types, MKK4 activates JNK primarily by stress stimuli and MKK7 by inflammatory cytoki...

Dopaminergic and Glutamatergic Signaling Crosstalk in Huntington's Disease Neurodegeneration: The Role of p25/Cyclin-Dependent Kinase 5

“…JNK activation is not associated with NMDA and SKF38393-mediated neurotoxicity in STHdh Q111 cells Activation of the JNK may contribute to neuronal cell death after excitotoxicity (Brecht et al, 2005;Centeno et al, 2007). To investigate the potential role of the JNK pathway in the neurotoxic effect of NMDA and SKF38393, wild-type STHdh Q7 and mutant STHdh Q111 striatal cells were treated with 500 M NMDA or 100 M SKF38393, and the levels of total and phospho-JNK were determined by Western blot analysis.…”

Death and survival of neuronal and astrocytic cells in ischemic brain injury: a role of autophagy

“…Each gene is alternatively spliced to produce one or two variants of 46 and 54 kDa, which generates a total of at least 10 JNK isoforms with potentially different pro-survival and pro-death roles [51] . Among its pro-death roles, JNK has been shown to be important for neuronal death after excitotoxic stress because of its involvement in necrosis and apoptosis [52][53][54] . In cerebral ischemia, JNK has become an accepted target for neuroprotection because small-molecule inhibitors [55] or cell-penetrating peptides [56,57] such as D-JNKI1 (d-c-Jun N-terminal kinase 1 inhibitor), a cell-permeable peptide inhibitor of the JNK pathway, have been shown to be a powerful neuroprotective agent after focal cerebral ischemia in adult mice and young rats.…”

Regulation of axon growth by the JIP1-AKT axis

“…5D). Studies in non-neuronal cells have shown that JNK phosphorylation of JIP1 controls its ability to bind to AKT (Song and Lee, 2005a;Song and Lee, 2005b), whereas in cortical neurons treated with NMDA, it is reported that inhibition of JNK activity can stabilize JIP1 (Centeno et al, 2007). This suggested that glutamate stimulation induces JNK phosphorylation of JIP1 thus causing the dissociation of the JIP1-AKT complex and subsequent destabilization of the proteins in the growth cone.…”

“…Glutamate is the major excitatory neurotransmitter in the central nervous system and the principal neurotransmitter of cortical efferent systems (Fonnum, 1984). Previous studies have demonstrated that JIP1 can be regulated following stimulation of the N-methyl-D-aspartate (NMDA) class of glutamate receptors (Kim et al, 2002;Kennedy et al, 2007;Centeno et al, 2007). We exposed developing cultured neurons to glutamate and this led to a reduction in JIP1 protein levels that could be rescued by the NMDA receptor antagonist MK-801, but not by the AMPA/kainate antagonist CNQX (Fig.…”