title: Cell death after spinal cord injury is exacerbated by rapid TNF alpha-induced trafficking of GluR2-lacking AMPARs to the plasma membrane.
abstract: Glutamate, the major excitatory neurotransmitter in the CNS, is implicated in both normal neurotransmission and excitotoxicity. Numerous in vitro findings indicate that the ionotropic glutamate receptor, AMPAR, can rapidly traffic from intracellular stores to the plasma membrane, altering neuronal excitability. These receptor trafficking events are thought to be involved in CNS plasticity as well as learning and memory. AMPAR trafficking has recently been shown to be regulated by glial release of the proinflammatory cytokine tumor necrosis factor alpha (TNFalpha) in vitro. This has potential relevance to several CNS disorders, because many pathological states have a neuroinflammatory component involving TNFalpha. However, TNFalpha-induced trafficking of AMPARs has only been explored in primary or slice cultures and has not been demonstrated in preclinical models of CNS damage. Here, we use confocal and image analysis techniques to demonstrate that spinal cord injury (SCI) induces trafficking of AMPARs to the neuronal membrane. We then show that this effect is mimicked by nanoinjections of TNFalpha, which produces specific trafficking of GluR2-lacking receptors which enhance excitotoxicity. To determine if TNFalpha-induced trafficking affects neuronal cell death, we sequestered TNFalpha after SCI using a soluble TNFalpha receptor, and significantly reduced both AMPAR trafficking and neuronal excitotoxicity in the injury penumbra. The data provide the first evidence linking rapid TNFalpha-induced AMPAR trafficking to early excitotoxic secondary injury after CNS trauma in vivo, and demonstrate a novel way in which pathological states hijack mechanisms involved in normal synaptic plasticity to produce cell death.
authors.affiliation: Brain and Spinal Injury Center, Department of Neurological Surgery, University of California, San Francisco, San Francisco, California 94110, USA.
authors.forename: Adam R
authors.initials: AR
authors.lastname: Ferguson
authors.forename: Randolph N
authors.initials: RN
authors.lastname: Christensen
authors.forename: John C
authors.initials: JC
authors.lastname: Gensel
authors.forename: Brandon A
authors.initials: BA
authors.lastname: Miller
authors.forename: Fang
authors.initials: F
authors.lastname: Sun
authors.forename: Eric C
authors.initials: EC
authors.lastname: Beattie
authors.forename: Jacqueline C
authors.initials: JC
authors.lastname: Bresnahan
authors.forename: Michael S
authors.initials: MS
authors.lastname: Beattie
mesh_terms: D000818:Animals; D016923:Cell Death / Q000235:genetics / Q000502:physiology; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005260:Female; D006801:Humans; D008845:Microinjections; D009473:Neuronal Plasticity / Q000235:genetics / Q000502:physiology; D021381:Protein Transport / Q000235:genetics / Q000502:physiology; D051381:Rats; D020318:Rats, Long-Evans; D018091:Receptors, AMPA / Q000032:analysis / Q000172:deficiency* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000008:administration & dosage; D013119:Spinal Cord Injuries / Q000378:metabolism* / Q000473:pathology; D014409:Tumor Necrosis Factor-alpha / Q000008:administration & dosage / Q000502:physiology*
chemical_list: D018091:Receptors, AMPA; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; C104722:glutamate receptor ionotropic, AMPA 2