Glutamate potentiates the toxicity of mutant Cu/Zn-superoxide dismutase in motor neurons by postsynaptic calcium-dependent mechanisms.
Mutations in the Cu/Zn-superoxide dismutase (SOD-1) gene are responsible for a subset of familial cases of amyotrophic lateral sclerosis. Using a primary culture model, we have demonstrated that normally nontoxic glutamatergic input, particularly via calcium-permeable AMPA/kainate receptors, is a major factor in the vulnerability of motor neurons to the toxicity of SOD-1 mutants. Wild-type and mutant (G41R, G93A, or N139K) human SOD-1 were expressed in motor neurons of dissociated cultures of murine spinal cord by intranuclear microinjection of plasmid expression vector. Both a general antagonist of AMPA/kainate receptors (CNQX) and a specific antagonist of calcium-permeable AMPA receptors (joro spider toxin) reduced formation of SOD-1 proteinaceous aggregates and prevented death of motor neurons expressing SOD-1 mutants. Partial protection was obtained by treatment with nifedipine, implicating Ca2+ entry through voltage-gated calcium channels as well as glutamate receptors in potentiating the toxicity of mutant SOD-1 in motor neurons. Dramatic neuroprotection was obtained by coexpressing the calcium-binding protein calbindin-D28k but not by increasing intracellular glutathione levels or treatment with the free radical spin trap agent, N-tert-butyl-alpha-phenylnitrone. Thus, generalized oxidative stress could have contributed in only a minor way to death of motor neurons expressing the mutant SOD-1. These studies demonstrated that the toxicity of these mutants is calcium-dependent and provide direct evidence that calcium entry during neurotransmission, coupled with deficiency of cytosolic calcium-binding proteins, is a major factor in the preferential vulnerability of motor neurons to disease.
Roy
J
J
Montreal Neurological Institute and Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec, Canada H3A 2B4.
Minotti
S
S
Dong
L
L
Figlewicz
D A
DA
Durham
H D
HD
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D064092:Calbindin 1; D064026:Calbindins; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology; D020746:Calcium Channels, L-Type; D002478:Cells, Cultured; D003497:Cyclic N-Oxides; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000166:cytology; D018698:Glutamic Acid / Q000494:pharmacology*; D005978:Glutathione / Q000378:metabolism; D007736:Kynurenic Acid / Q000494:pharmacology; D051379:Mice; D009046:Motor Neurons / Q000737:chemistry / Q000201:enzymology*; D016296:Mutagenesis / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009498:Neurotoxins / Q000494:pharmacology; D009589:Nitrogen Oxides / Q000494:pharmacology; D018384:Oxidative Stress / Q000502:physiology; D018091:Receptors, AMPA / Q000502:physiology; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D013111:Spider Venoms / Q000494:pharmacology; D013116:Spinal Cord / Q000166:cytology; D013482:Superoxide Dismutase / Q000235:genetics* / Q000378:metabolism; D013569:Synapses / Q000737:chemistry / Q000201:enzymology*
C576498:CALB1 protein, human; C576499:Calb1 protein, mouse; D064092:Calbindin 1; D064026:Calbindins; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D003497:Cyclic N-Oxides; D018691:Excitatory Amino Acid Antagonists; D016166:Free Radical Scavengers; C044936:JSTX spider toxin; D009419:Nerve Tissue Proteins; D009498:Neurotoxins; D009589:Nitrogen Oxides; D018091:Receptors, AMPA; D064030:S100 Calcium Binding Protein G; D013111:Spider Venoms; C029217:phenyl-N-tert-butylnitrone; D018698:Glutamic Acid; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D015763:2-Amino-5-phosphonovalerate; D013482:Superoxide Dismutase; D005978:Glutathione; D007736:Kynurenic Acid; D002118:Calcium