Specific Targeting of Pro-Death NMDA Receptor Signals with Differing Reliance on the NR2B PDZ Ligand

Abstract

NMDA receptors (NMDARs) mediate ischemic brain damage, for which interactions between the C termini of NR2 subunits and PDZ domain proteins within the NMDAR signaling complex (NSC) are emerging therapeutic targets. However, expression of NMDARs in a non-neuronal context, lacking many NSC components, can still induce cell death. Moreover, it is unclear whether targeting the NSC will impair NMDAR-dependent prosurvival and plasticity signaling. We show that the NMDAR can promote death signaling independently of the NR2 PDZ ligand, when expressed in non-neuronal cells lacking PSD-95 and neuronal nitric oxide synthase (nNOS), key PDZ proteins that mediate neuronal NMDAR excitotoxicity. However, in a non-neuronal context, the NMDAR promotes cell death solely via c-Jun N-terminal protein kinase (JNK), whereas NMDAR-dependent cortical neuronal death is promoted by both JNK and p38. NMDARdependent pro-death signaling via p38 relies on neuronal context, although death signaling by JNK, triggered by mitochondrial reactive oxygen species production, does not. NMDAR-dependent p38 activation in neurons is triggered by submembranous Ca 2ϩ , and is disrupted by NOS inhibitors and also a peptide mimicking the NR2B PDZ ligand (TAT-NR2B9c). TAT-NR2B9c reduced excitotoxic neuronal death and p38-mediated ischemic damage, without impairing an NMDAR-dependent plasticity model or prosurvival signaling to CREB or Akt. TAT-NR2B9c did not inhibit JNK activation, and synergized with JNK inhibitors to ameliorate severe excitotoxic neuronal loss in vitro and ischemic cortical damage in vivo. Thus, NMDAR-activated signals comprise pro-death pathways with differing requirements for PDZ protein interactions. These signals are amenable to selective inhibition, while sparing synaptic plasticity and prosurvival signaling.

Abnormal Activity of the MAPK- and cAMP-Associated Signaling Pathways in Frontal Cortical Areas in Postmortem Brain in Schizophrenia

“…In fact, relatively small changes are perhaps not unexpected, as more substantial changes in expression of these proteins are associated with oncogenic, apoptotic, and excitotoxic events (Huang et al, 2009;Kim and Choi, 2010;Soriano et al, 2008;von Engelhardt et al, 2007;Wagner and Nebreda, 2009). …”

Interaction of Postsynaptic Density Protein-95 with NMDA Receptors Influences Excitotoxicity in the Yeast Artificial Chromosome Mouse Model of Huntington's Disease

“…Another apoptotic pathway downstream of PSD-95 is through binding to synaptic Ras-GTPase activating protein, known to regulate synaptic plasticity and neuronal apoptosis through p38 -MAPK signaling (Kim et al, 1998;Rumbaugh et al, 2006). Notably, NMDARdependent p38 activation relies on neuronal context and is disrupted by Tat-NR2B9c (Soriano et al, 2008). Additional experiments are required to fully elucidate signaling pathways mediating enhanced excitotoxicity in YAC HD MSNs.…”

Identification of a small-molecule inhibitor of the PICK1 PDZ domain that inhibits hippocampal LTP and LTD

“…This is not surprising, given the impressive functional diversity of these proteins that allows for selective inhibition or activation of distinct disease-modulating signaling pathways. Nevertheless, receptor activation or blockade will inevitably affect the entire ensemble of signaling pathways to which the receptor is coupled and thereby often cause not only beneficial effects but also unwanted side effects (2,3). An attractive alternative would be to develop medicines that instead target protein-protein interactions in a specific intracellular signaltransduction pathway (4,5).…”

“…Blocking the PDZ interaction between the NMDA glutamate receptor and PSD-95 with membrane-permeable peptides results in selective inhibition of neuronal nitric oxide synthase (nNOS) activation, which is expected to reduce ischemic brain injury during stroke (2,3). In cancer, recent evidence suggests that blocking the PDZ domains of Na + /H + exchanger regulatory factor 1 (NHERF-1), dishevelled, or AF-6 might be interesting therapeutic approaches (9)(10)(11).…”