Inhibiting pro-death NMDA receptor signaling dependent on the NR2 PDZ ligand may not affect synaptic function or synaptic NMDA receptor signaling to gene expression

Center for Integrative Physiology, University of Edinburgh, Edinburgh, UK.
Channels (Austin, Tex.) (Impact Factor: 2.32). 02/2009; 3(1):12-5. DOI: 10.4161/chan.3.1.7864
Source: PubMed


NMDA receptors (NMDARs) mediate ischemic brain damage, in part through interactions of the PDZ ligand of NR2 subunits with the PDZ domain proteins PSD-95 and neuronal nitric oxide synthase located within the NMDAR signaling complex. We have recently shown that this PDZ ligand-dependent pathway promotes neuronal death via p38 activation. A peptide mimetic of the NR2B PDZ ligand (TAT-NR2B9c) reduces p38-mediated death in vitro and p38-dependent ischemic damage in vivo. In the absence of the PDZ ligand-p38 pathway, such as in TAT-NR2B9c-treated neurons, or in NMDAR-expressing non-neuronal cells, NMDAR-dependent excitotoxicity is mediated largely by JNK and requires greater Ca2+ influx. A major reason for blocking pro-death signaling events downstream of the NMDAR as an anti-excitotoxic strategy is that it may spare physiological synaptic function and signaling. We find that neuroprotective doses of TAT-NR2B9c do not alter the frequency of spontaneous synaptic events within networks of cultured cortical neurons nor is mini-EPSC frequency altered. Furthermore, TAT-NR2B9c does not inhibit the capacity of synaptic NMDAR activity to promote neuroprotective changes in gene expression, including the upregulation of PACAP via CREB, and suppression of the pro-oxidative FOXO target gene Txnip. Thus, while the NR2 PDZ ligand does not account for all the excitotoxic effects of excessive NMDAR activity, these findings underline the value of the specific targeting of death pathways downstream of the NMDAR.

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    • "Based on recent observations on the neuroprotective properties of cationic CPPs, we view it as likely that TAT itself is the active neuroprotective component in TAT-NR2B9c. Like TAT alone, TAT-NR2B9c has only modest neuroprotective efficacy in vitro, which can easily be overcome by increasing the severity of excitotoxicity (Martel et al., 2009). "
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    ABSTRACT: Several recent studies have demonstrated that TAT and other arginine-rich cell penetrating peptides (CPPs) have intrinsic neuroprotective properties in their own right. Examples, we have demonstrated that in addition to TAT, poly-arginine peptides (R8 to R18; containing 8-18 arginine residues) as well as some other arginine-rich peptides are neuroprotective in vitro (in neurons exposed to glutamic acid excitotoxicity and oxygen glucose deprivation) and in the case of R9 in vivo (after permanent middle cerebral artery occlusion in the rat). Based on several lines of evidence, we propose that this neuroprotection is related to the peptide's endocytosis-inducing properties, with peptide charge and arginine residues being critical factors. Specifically, we propose that during peptide endocytosis neuronal cell surface structures such as ion channels and transporters are internalised, thereby reducing calcium influx associated with excitotoxicity and other receptor-mediated neurodamaging signalling pathways. We also hypothesise that a peptide cargo can act synergistically with TAT and other arginine-rich CPPs due to potentiation of the CPPs endocytic traits rather than by the cargo-peptide acting directly on its supposedly intended intracellular target. In this review, we systematically consider a number of studies that have used CPPs to deliver neuroprotective peptides to the central nervous system (CNS) following stroke and other neurological disorders. Consequently, we critically review evidence that supports our hypothesis that neuroprotection is mediated by carrier peptide endocytosis. In conclusion, we believe that there are strong grounds to regard arginine-rich peptides as a new class of neuroprotective molecules for the treatment of a range neurological disorders. Copyright © 2015. Published by Elsevier Inc.
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    • "ressing pro - death p38 signal - ling and CREB shut - off ( Aarts et al . , 2002 ; Martel et al . , 2012 ; Soriano et al . , 2008 ) . Also , unlike conventional NMDAR antagonists , NA - 1 / Tat - NR2B9c did not interfere with activity - dependent synaptic potentiation , nor synaptic NMDAR - dependent neuroprotective sig - nalling via Akt or CREB ( Martel et al . , 2009a ; Soriano et al . , 2008 ) . Moreover NA - 1 / Tat - NR2B9c was shown to be effective post - treatment in reducing lesion size and improving outcome follow - ing stroke in the non - human primate brain ( Cook et al . , 2012 ) . NA - 1 has also advanced to human clinical trials for iatrogenic stroke after endovascular aneurysm repair ( H"
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    ABSTRACT: N-methyl-d-aspartate receptors (NMDARs) are ligand-gated ion channels (‘ionotropic’ receptors) activated by the major excitatory neurotransmitter, l-glutamate. While the term ‘the NMDAR’ is often used it obscures the fact that this class of receptor contains within it members whose properties are as different as they are similar. This heterogeneity was evident from early electrophysiological, pharmacological and biochemical assessments of the functional properties of NMDARs and while the molecular basis of this heterogeneity has taken many years to elucidate, it indicated from the outset that the diversity of NMDAR phenotypes could allow this receptor family to subserve a variety of functions in the mammalian central nervous system. In this review we highlight some recent studies that have identified structural elements within GluN2 subunits that contribute to the heterogeneous biophysical properties of NMDARs, consider why some recently described novel pharmacological tools may permit better identification of native NMDAR subtypes, examine the evidence that NMDAR subtypes differentially contribute to the induction of long-term potentiation and long-term depression and discuss how through the use of chimeric proteins additional insights have been obtained that account for NMDAR subtype-dependency of physiological and pathophysiological signalling. This article is part of the Special Issue entitled ‘Glutamate Receptor-Dependent Synaptic Plasticity’.
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    • "Interestingly, this agrees with the finding that Tat-NR2B9c application caused a small yet significant potentiating effect on CRE-dependent reporter gene expression (Martel et al. 2009) downstream of NMDAR activation. Thus, Tat- NR2B9c may provide significant neuroprotection by maintaining trophic, CREB-dependent transcription during ischaemia. "
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    ABSTRACT: NMDA-type glutamate receptors mediate both trophic and excitotoxic signalling in CNS neurons. We have previously shown that blocking NMDAR-PSD95 interactions provides significant protection from excitotoxicity and in vivo ischemia; however the mechanism of neuroprotection is unclear. Here we report that blocking PSD-95 interactions with the Tat-NR2B9c peptide enhances a Ca(2+) -dependent protective pathway converging on CREB activation. We provide evidence that Tat-NR2B9c neuroprotection from oxygen glucose deprivation and NMDA toxicity occurs in parallel with the activation of calmodulin kinase signalling and is dependent on a sustained phosphorylation of the CREB transcription factor and its activator CaMKIV. Tat-NR2B9c-dependent neuroprotection and CREB phosphorylation are blocked by co-application of CaM kinase (KN93 and STO-609) or CREB (KG-501) inhibitors, and by siRNA knockdown of CaMKIV. These results are mirrored in vivo in a rat model of permanent focal ischemia. Tat-NR2B9c application significantly reduces infarct size and causes a selective and sustained elevation in CaMKIV phosphorylation; effects which are blocked by co-administration of KN93. Thus calcium-dependent nuclear signalling via CaMKIV and CREB is critical for neuroprotection via NMDAR-PSD95 blockade, both in vitro and in vivo. This study highlights the importance of maintaining neuronal function following ischemic injury. Future stroke research should target neurotrophic and pro-survival signal pathways in the development of novel neuroprotective strategies. © 2013 International Society for Neurochemistry, J. Neurochem. (2013) 10.1111/jnc.12176.
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