title: Caspase-mediated degradation of AMPA receptor subunits: a mechanism for preventing excitotoxic necrosis and ensuring apoptosis.
abstract: Activation of ionotropic glutamate receptors of the AMPA and NMDA subtypes likely contributes to neuronal injury and death in various neurodegenerative disorders. Excitotoxicity can manifest as either apoptosis or necrosis, but the mechanisms that determine the mode of cell death are not known. We now report that levels of AMPA receptor subunits GluR-1 and GluR-4 are rapidly decreased in cultured rat hippocampal neurons undergoing apoptosis in response to withdrawal of trophic support (WTS), whereas levels of NMDA receptor subunits NR1, NR2A, and NR2B are unchanged. Exposure of isolated synaptosomal membranes to "apoptotic" cytosolic extracts resulted in rapid degradation of AMPA receptor subunits. Treatment of cells and synaptosomal membranes with the caspase inhibitors prevented degradation of AMPA receptor subunits, demonstrating a requirement for caspases in the process. Calcium responses to AMPA receptor activation were reduced after withdrawal of trophic support and enhanced after treatment with caspase inhibitors. Vulnerability of neurons to excitotoxic necrosis was decreased after withdrawal of trophic support and potentiated by treatment with caspase inhibitors. Our data indicate that caspase-mediated degradation of AMPA receptor subunits occurs during early periods of cell stress and may serve to ensure apoptosis by preventing excitotoxic necrosis.
authors.affiliation: Sanders-Brown Research Center on Aging and Department of Anatomy and Neurobiology, University of Kentucky, Lexington 40536, USA.
authors.forename: G W
authors.initials: GW
authors.lastname: Glazner
authors.forename: S L
authors.initials: SL
authors.lastname: Chan
authors.forename: C
authors.initials: C
authors.lastname: Lu
authors.forename: M P
authors.initials: MP
authors.lastname: Mattson
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D020169:Caspases / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D018698:Glutamic Acid / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology; D016202:N-Methylaspartate / Q000494:pharmacology; D009336:Necrosis; D019579:Neocortex / Q000166:cytology; D009410:Nerve Degeneration / Q000139:chemically induced / Q000201:enzymology; D009414:Nerve Growth Factors / Q000494:pharmacology; D009474:Neurons / Q000737:chemistry / Q000201:enzymology* / Q000473:pathology*; D018696:Neuroprotective Agents / Q000494:pharmacology; D009498:Neurotoxins / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA / Q000032:analysis / Q000378:metabolism*; D013574:Synaptosomes / Q000737:chemistry / Q000201:enzymology
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D002118:Calcium; D020169:Caspases; D018690:Excitatory Amino Acid Agonists; D018698:Glutamic Acid; D016202:N-Methylaspartate; D009414:Nerve Growth Factors; D018696:Neuroprotective Agents; D009498:Neurotoxins; D018091:Receptors, AMPA; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; C104724:glutamate receptor ionotropic, AMPA 4