Role of DNA repair proteins in development of the tolerance after ischemic preconditioning

点击翻译按钮获取中文摘要

Oxidative stress after ischemia/reperfusion has been shown to induce DNA damage and subsequent DNA repair activity. The DNA repair enzyme, apurinic/apyrimidinic endonuclease (or redox effector factor-1, APE/Ref-1), is involved in base excision repair of apurinic/apyrimidinic sites after oxidative DNA damage. We investigated the involvement of this protein in the development of neuronal tolerance to global cerebral ischemia after ischemic preconditioning. Adult male Sprague-Dawley rats were subjected to either 5 minutes of lethal global ischemia with or without 3 minutes of sublethal ischemic preconditioning or 3 minutes of ischemia only. Neuronal injury was histologically assessed, and DNA damage was visualized by in situ labeling of DNA fragmentation and DNA gel electrophoresis. APE expression was also examined by immunohistochemistry and Western blot analysis. Hippocampal CA1 neurons underwent DNA-fragmented cell death 3 days after 5 minutes of ischemia. However, these neurons showed a strong tolerance to 5 minutes of ischemia 1 to 3 days after ischemic preconditioning. Immunohistochemistry showed virtually no constitutive expression of APE proteins in CA1 neurons ; however, ischemic preconditioning induced neuronal APE expression 1 to 3 days later. Western blot confirmed an increase in Ku 70 in this region at the same time. The temporal and spatial expression of APE corresponded to tolerance of the hippocampal CA1 neurons to subsequent ischemia, suggesting the involvement of APE protein in the development of neuronal tolerance after ischemic preconditioning.