Abstract
Neurological disabilities following traumatic brain injury (TBI) may be due to excitotoxic neuronal loss. The excitotoxic loss of neurons following TBI occurs largely due to hyperactivation of N-methyl-d-aspartate receptors (NMDARs), leading to toxic levels of intracellular Ca(2+). The axon guidance and outgrowth protein collapsin response mediator protein 2 (CRMP2) has been linked to NMDAR trafficking and may be involved in neuronal survival following excitotoxicity. Lentivirus-mediated CRMP2 knockdown or treatment with a CRMP2 peptide fused to HIV TAT protein (TAT-CBD3) blocked neuronal death following glutamate exposure probably via blunting toxicity from delayed calcium deregulation. Application of TAT-CBD3 attenuated postsynaptic NMDAR-mediated currents in cortical slices. In exploring modulation of NMDARs by TAT-CBD3, we found that TAT-CBD3 induced NR2B internalization in dendritic spines without altering somal NR2B surface expression. Furthermore, TAT-CBD3 reduced NMDA-mediated Ca(2+) influx and currents in cultured neurons. Systemic administration of TAT-CBD3 following a controlled cortical impact model of TBI decreased hippocampal neuronal death. These findings support TAT-CBD3 as a novel neuroprotective agent that may increase neuronal survival following injury by reducing surface expression of dendritic NR2B receptors.
Highlights
collapsin response mediator protein 2 (CRMP2) is an axonal guidance protein that has been linked to NMDA receptor-mediated excitotoxicity
Lentivirus-mediated Knockdown of CRMP2 Is Neuroprotective—Our initial findings show that TAT-CBD3 protects neurons from an excitotoxic insult but raise some important questions: 1) is the neuroprotection due to inhibition of CRMP2, and 2) does the activity of TAT-CBD3 require CRMP2 to be present? To address if the neuroprotection was due to CRMP2, we reduced endogenous CRMP2 expression by transducing cortical neurons with lentiviral particles containing shRNA targeting CRMP2 or a scramble shRNA sequence at 2 DIV, a viral knockdown approach that knocks down Ͼ85% of CRMP2, as reported by us previously [16]
We describe the neuroprotective effects of a novel peptide (CBD3) derived from the CRMP2 protein
Summary
CRMP2 is an axonal guidance protein that has been linked to NMDA receptor-mediated excitotoxicity. Systemic administration of TAT-CBD3 following a controlled cortical impact model of TBI decreased hippocampal neuronal death These findings support TAT-CBD3 as a novel neuroprotective agent that may increase neuronal survival following injury by reducing surface expression of dendritic NR2B receptors. Ca2ϩ influx through NMDARs5 is thought to be an integral mediator of excitotoxicity because antagonists of these receptors have been shown to be neuroprotective in animal models of traumatic brain injury (TBI) and ischemia-induced excitotoxicity [2, 3]. In addition to its role in axon growth, recent studies by our laboratory have characterized a novel role for CRMP2 in regulating synaptic transmission through interactions with Ca2ϩ channels (16 –19) These biochemical and membrane trafficking studies demonstrated that CRMP2 modulates Ca2ϩ channel activity via alterations in surface expression. We demonstrate that a CRMP2 peptide down-regulates dendritic surface expression of NMDARs and protects against neurotoxicity in cell-based assays and in TBI
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