Overexpression of human copper/zinc-superoxide dismutase in transgenic animals attenuates the reduction of apurinic/ apyrimidinic endonuclease expression in neurons after in vitro ischemia and after transient global cerebral ischemia Purnima Narasimhan, Taku Sugawara, Jing Liu, Takeshi Hayashi, Nobuo Noshita and Pak H. Chan Department of Neurosurgery, Department of Neurology and Neurological Sciences and Program in Neurosciences, Stanford University School of Medicine, Stanford, California, USA Abstract Oxidative stress after ischemia/reperfusion has been shown to induce DNA damage and subsequent DNA repair activity. Apurinic/apyrimidinic endonuclease (APE) is a multifunctional protein in the DNA base excision repair pathway which repairs apurinic/apyrimidinic sites in DNA. We investigated the involvement of oxidative stress and expression of APE in neurons after oxygen–glucose deprivation and after global cerebral ischemia. Our results suggest that overexpression of human copper/zinc-superoxide dismutase reduced oxidative stress with a subsequent decrease in APE expression. Pro- duction of oxygen free radicals and inhibition of the base excision repair pathway may play pivotal roles in the cell death pathway after ischemia. Keywords: cell death, DNA repair, hypoxia, ischemia, neu- rons. J. Neurochem. (2005) 93, 351–358. Apurinic/apyrimidinic endonuclease (APE)/redox factor-1 (Ref-1) is a key enzyme in the base excision repair pathway which aids in the repair of damaged bases of DNA (Bennett et al. 1997). DNA lesions occur by genotoxic exposures such as ionizing radiation, alkylating agents and availability of reactive oxygen species (ROS). DNA glycosylases followed by the repair of the resulting apurinic/apyrimidinic (AP) site by APE activity remove the damaged base. Endonuclease and 3¢-phosphodiesterase, two key APE activities, are important for the repair of DNA damage. In vitro studies have shown a constitutive expression of APE in neurons of the mammalian CNS (Ono et al. 1995) and recent reports have shown that APE expression is responsive to oxidative stress. An increase in APE expression leads to increases in the binding activity of several redox-sensitive transcription factors such as nuclear factor-kappa B (NF-jB) and AP1. These transcription factors play important roles in controlling oxidative stress response and cell proliferation (Ho and Ames 2002). APE expression has been shown to be transiently up-regulated by non-toxic levels of ROS at the transcrip- tional level (Grosch et al. 1998; Ramana et al. 1998) in mammalian cells. This increase in APE-1 expression is correlated with increased cellular resistance to oxidizing agents. Moreover, induction of APE expression was demon- strated in HT29 colon cancer cells after hypoxia/reoxygen- ation. Other in vitro studies in non-neuronal cells have shown that APE expression is induced by hypoxia at both the mRNA and protein levels (Yao et al. 1995). Oxidative species are generated in cells by various pathophysiological processes such as inflammatory activation. ROS include partially reduced oxygen species, namely superoxide anion, H 2 O 2 and the hydroxyl radical, and have been implicated in the development of neurological disorders and brain dys- function. Growing evidence suggests the involvement of DNA damage and repair in cell death mechanisms after Resubmitted manuscript received November 16, 2004; accepted December 6, 2004. Address correspondence and reprint requests to Pak H. Chan, PhD, Neurosurgical Laboratories, Stanford University, 1201 Welch Road, #P314, Stanford, CA 94305-5487, USA. E-mail: phchan@stanford.edu Abbreviations used: AP, apurinic/apyrimidinic; APE, apurinic/apyri- midinic endonuclease; MEM, minimum essential medium; NF-jB, nuclear factor-kappa B; OGD, oxygen–glucose deprivation; Ref-1, redox factor-1; ROS, reactive oxygen species; SOD1, human copper/zinc- superoxide dismutase; Tg, transgenic; WT, wild-type. Journal of Neurochemistry , 2005, 93, 351–358 doi:10.1111/j.1471-4159.2005.03039.x Ó 2005 International Society for Neurochemistry, J. Neurochem. (2005) 93, 351–358 351