Overexpression of Copper/Zinc Superoxide Dismutase in Transgenic Rats Protects Vulnerable Neurons against Ischemic Damage by Blocking the Mitochondrial Pathway of Caspase Activation

• Published in: The Journal of neuroscience 2002-01, Vol.22 (1), p.209-217
• Main Authors: Sugawara, Taku, Noshita, Nobuo, Lewen, Anders, Gasche, Yvan, Ferrand-Drake, Michel, Fujimura, Miki, Morita-Fujimura, Yuiko, Chan, Pak H
• Format: Article
• Language: English
• Subjects: Animals; Animals, Genetically Modified; Apoptosis - physiology; Brain Ischemia - enzymology; Brain Ischemia - pathology; Carrier Proteins - metabolism; Caspase 3; Caspase 9; Caspase Inhibitors; Caspases - metabolism; Cytochrome c Group - metabolism; Cytoprotection - physiology; DNA Damage - physiology; Enzyme Inhibitors - pharmacology; Gene Expression; Hippocampus - blood supply; Hippocampus - enzymology; Hippocampus - pathology; Immunohistochemistry; Male; Mitochondria - enzymology; Mitochondrial Proteins - metabolism; Neurons - enzymology; Neurons - pathology; Rats; Rats, Sprague-Dawley; Signal Transduction - physiology; Superoxide Dismutase - biosynthesis; Superoxide Dismutase - genetics; Superoxide Dismutase-1; Superoxides - metabolism
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/jneurosci.22-01-00209.2002

Mitochondria are known to be involved in the early stage of apoptosis by releasing cytochrome c, caspase-9, and the second mitochondria-derived activator of caspases (Smac). We have reported that overexpression of copper/zinc superoxide dismutase (SOD1) reduced superoxide production and ameliorated neuronal injury in the hippocampal CA1 subregion after global ischemia. However, the role of oxygen free radicals produced after ischemia/reperfusion in the mitochondrial signaling pathway has not been clarified. Five minutes of global ischemia was induced in male SOD1-transgenic (Tg) and wild-type (Wt) littermate rats. Cytosolic expression of cytochrome c and Smac and activation of caspases were evaluated by immunohistochemistry, Western blot, and caspase activity assay. Apoptotic cell death was characterized by DNA nick end and single-stranded DNA labeling. In the Wt animals, early superoxide production, mitochondrial release of cytochrome c, Smac, and cleaved caspase-9 were observed after ischemia. Active caspase-3 was subsequently increased, and 85% of the hippocampal CA1 neurons showed apoptotic DNA damage 3 d after ischemia. Tg animals showed less superoxide production and cytochrome c and Smac release. Subsequent active caspase-3 expression was not evident, and only 45% of the neurons showed apoptotic DNA damage. A caspase-3 inhibitor (N-benzyloxycarbonyl-val-ala-asp-fluoromethyl ketone) reduced cell death only in Wt animals. These results suggest that overexpression of SOD1 reduced oxidative stress, thereby attenuating the mitochondrial release of cytochrome c and Smac, resulting in less caspase activation and apoptotic cell death. Oxygen free radicals may play a pivotal role in the mitochondrial signaling pathway of apoptotic cell death in hippocampal CA1 neurons after global ischemia.