The critical role of calpain versus caspase activation in excitotoxic injury induced by nitric oxide.
The pathogenesis of various acute and chronic neurodegenerative disorders has been linked to excitotoxic processes and excess generation of nitric oxide. We investigated the deleterious effects of calpain activation in nitric oxide-elicited neuronal apoptosis. In this model, nitric oxide triggers apoptosis of murine cerebellar granule cells by an excitotoxic mechanism requiring glutamate exocytosis and receptor-mediated intracellular calcium overload. Here, we found that calcium-dependent cysteine proteases, calpains, were activated early in apoptosis of cerebellar granule cells exposed to nitric oxide. Release of the proapoptogenic factors cytochrome c and apoptosis-inducing factor from mitochondria preceded neuronal death. However, caspases-3 was not activated. We observed that procaspase-9 was cleaved by calpains to proteolytically inactive fragments. Inhibition of calpains by different synthetic calpain inhibitors or by adenovirally mediated expression of the calpastatin inhibitory domain prevented mitochondrial release of cytochrome c and apoptosis-inducing factor, calpain-specific proteolysis and neuronal apoptosis. We conclude that (i) signal transduction pathways exist that prevent the entry of neurons into a caspase-dependent death after mitochondrial release of cytochrome c and (ii) that calpain activation links nitric oxide-triggered excitotoxic events with the execution of caspase-independent apoptosis in neurons.
Volbracht
Christiane
C
Institute of Molecular and Cell Biology (IMCB), Singapore. cvo@lundbeck.com
Chua
Boon Tin
BT
Ng
Chee Peng
CP
Bahr
Ben A
BA
Hong
Wanjin
W
Li
Peng
P
D000818:Animals; D017209:Apoptosis; D051033:Apoptosis Inducing Factor; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D002154:Calpain / Q000378:metabolism*; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D002478:Cells, Cultured; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D045304:Cytochromes c / Q000378:metabolism; D004789:Enzyme Activation; D005420:Flavoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008928:Mitochondria / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D009498:Neurotoxins / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D010447:Peptide Hydrolases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D026422:S-Nitrosoglutathione / Q000494:pharmacology
D051033:Apoptosis Inducing Factor; D002135:Calcium-Binding Proteins; D005420:Flavoproteins; D008565:Membrane Proteins; D009498:Neurotoxins; D020030:Nitric Oxide Donors; C494830:AIFM1 protein, mouse; D009569:Nitric Oxide; D026422:S-Nitrosoglutathione; C033668:calpastatin; D045304:Cytochromes c; D010447:Peptide Hydrolases; D002154:Calpain; C506434:Casp9 protein, mouse; D053453:Caspase 9; D020169:Caspases