Knockdown of AMPA receptor GluR2 expression causes delayed neurodegeneration and increases damage by sublethal ischemia in hippocampal CA1 and CA3 neurons

Considerable evidence suggests that Ca2+-permeable AMPA receptors are criti cal mediators of the delayed, selective neuronal death associated with tran sient global ischemia and sustained seizures. Global ischemia suppresses mR NA and protein expression of the glutamate receptor subunit GluR2 and incre ases AMPA receptor-mediated Ca2+ influx into vulnerable neurons of the hipp ocampal CA1 before the onset of neurodegeneration. Status epilepticus suppr esses GluR2 mRNA and protein in CA3 before neurodegeneration in this region . To examine whether acute downregulation of the GluR2 subunit, even in the absence of a neurological insult, can cause neuronal cell death, we perfor med GluR2 "knockdown" experiments. Intracerebral injection of antisense oli godeoxynucleotides targeted to GluR2 mRNA induced delayed death of pyramida l neurons in CA1 and CA3. Antisense-induced neurodegeneration was preceded by a reduction in GluR2 mRNA, as indicated by in situ hybridization, and in GluR2 protein, as indicated by Western blot analysis. GluR2 antisense supp ressed GluR2 mRNA in the dentate gyrus but did not cause cell death. The AM PA receptor antagonist 6-cyano-7-nitroquinoxiline-2,3-dione (CNQX) and the Ca2+-permeable AMPA receptor channel blocker 1-naphthyl acetyl spermine pro tected against antisense-induced cell death. This result indicates that ant isense-induced cell death is mediated by Ca2+-permeable AMPA receptors. Glu R2 antisense and brief sublethal global ischemia acted synergistically to c ause degeneration of pyramidal neurons, consistent with action by a common mechanism. These findings demonstrate that downregulation of GluR2 is suffi cient to induce delayed death of specific neuronal populations.