Neuronal expression of the DNA repair protein Ku 70 after ischemic preconditioning corresponds to tolerance to global cerebral ischemia.
OBJECTIVE
Oxidative stress after ischemia/reperfusion has been shown to induce DNA damage and subsequent DNA repair activity. Ku 70/86, multifunctional DNA repair proteins, bind to broken DNA ends and trigger a DNA repair pathway. We investigated the involvement of these proteins in the development of neuronal tolerance to global cerebral ischemia after ischemic preconditioning.


METHODS
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. Ku expression was also examined by immunohistochemistry and Western blot analysis.


RESULTS
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 Ku proteins in CA1 neurons; however, ischemic preconditioning induced neuronal Ku 70 expression 1 to 3 days later. Western blot confirmed an increase in Ku 70 in this region at the same time.


CONCLUSIONS
The temporal and spatial expression of Ku 70 corresponded to tolerance of the hippocampal CA1 neurons to subsequent ischemia, suggesting the involvement of Ku proteins in the development of neuronal tolerance after ischemic preconditioning.
Sugawara
T
T
Department of Neurosurgery, Program in Neurosciences, Stanford University School of Medicine, CA 94305-5487, USA.
Noshita
N
N
Lewén
A
A
Kim
G W
GW
Chan
P H
PH
D000818:Animals; D034961:Antigens, Nuclear; D001253:Astrocytes / Q000378:metabolism / Q000473:pathology; D001784:Blood Gas Analysis; D001794:Blood Pressure; D015153:Blotting, Western; D002545:Brain Ischemia / Q000378:metabolism* / Q000473:pathology; D002452:Cell Count; D002467:Cell Nucleus / Q000378:metabolism; D004265:DNA Helicases; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D006624:Hippocampus / Q000098:blood supply / Q000378:metabolism / Q000473:pathology; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D019194:Ischemic Preconditioning; D000072200:Ku Autoantigen; D008297:Male; D009474:Neurons / Q000378:metabolism* / Q000473:pathology; D009687:Nuclear Proteins / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley
D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; C000606511:Xrcc6 protein, rat; D000072200:Ku Autoantigen