title: Critical role of calpain I in mitochondrial release of apoptosis-inducing factor in ischemic neuronal injury.
abstract: Loss of mitochondrial membrane integrity and release of apoptogenic factors are a key step in the signaling cascade leading to neuronal cell death in various neurological disorders, including ischemic injury. Emerging evidence has suggested that the intramitochondrial protein apoptosis-inducing factor (AIF) translocates to the nucleus and promotes caspase-independent cell death induced by glutamate toxicity, oxidative stress, hypoxia, or ischemia. However, the mechanism by which AIF is released from mitochondria after neuronal injury is not fully understood. In this study, we identified calpain I as a direct activator of AIF release in neuronal cultures challenged with oxygen-glucose deprivation and in the rat model of transient global ischemia. Normally residing in both neuronal cytosol and mitochondrial intermembrane space, calpain I was found to be activated in neurons after ischemia and to cleave intramitochondrial AIF near its N terminus. The truncation of AIF by calpain activity appeared to be essential for its translocation from mitochondria to the nucleus, because neuronal transfection of the mutant AIF resistant to calpain cleavage was not released after oxygen-glucose deprivation. Adeno-associated virus-mediated overexpression of calpastatin, a specific calpain-inhibitory protein, or small interfering RNA-mediated knockdown of calpain I expression in neurons prevented ischemia-induced AIF translocation. Moreover, overexpression of calpastatin or knockdown of AIF expression conferred neuroprotection against cell death in neuronal cultures and in hippocampal CA1 neurons after transient global ischemia. Together, these results define calpain I-dependent AIF release as a novel signaling pathway that mediates neuronal cell death after cerebral ischemia.
authors.affiliation: Department of Neurology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
authors.forename: Guodong
authors.initials: G
authors.lastname: Cao
authors.forename: Juan
authors.initials: J
authors.lastname: Xing
authors.forename: Xiao
authors.initials: X
authors.lastname: Xiao
authors.forename: Anthony K F
authors.initials: AK
authors.lastname: Liou
authors.forename: Yanqin
authors.initials: Y
authors.lastname: Gao
authors.forename: Xiao-Ming
authors.initials: XM
authors.lastname: Yin
authors.forename: Robert S B
authors.initials: RS
authors.lastname: Clark
authors.forename: Steven H
authors.initials: SH
authors.lastname: Graham
authors.forename: Jun
authors.initials: J
authors.lastname: Chen
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D051033:Apoptosis Inducing Factor / Q000378:metabolism*; D001921:Brain / Q000166:cytology; D002154:Calpain / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D004195:Disease Models, Animal; D016521:Electrophoresis, Gel, Pulsed-Field / Q000379:methods; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D005947:Glucose / Q000172:deficiency; D006801:Humans; D000860:Hypoxia / Q000378:metabolism* / Q000503:physiopathology; D020287:In Situ Nick-End Labeling / Q000379:methods; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000378:metabolism; D009474:Neurons / Q000473:pathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014162:Transfection / Q000379:methods
chemical_list: D051033:Apoptosis Inducing Factor; D004791:Enzyme Inhibitors; D024101:Mitochondrial Proteins; D002154:Calpain; D005947:Glucose