EFFECTS OF STATUS EPILEPTICUS ON MECHANISMS OF DNA REPAIR
Abstract number :
2.053
Submission category :
Year :
2002
Submission ID :
1642
Source :
www.aesnet.org
Presentation date :
12/7/2002 12:00:00 AM
Published date :
Dec 1, 2002, 06:00 AM
Authors :
Karen Gale, Dawn Selby, Samantha Crowe, Timothy Jorgensen, Sunghan Yoo, Alexei Kondratyev. Department of Pharmacology, Georgetown University, Washington, DC; Interdisciplinary Program in Neuroscience, Georgetown University, Washington, DC; Department of R
RATIONALE: Excitotoxicity associated with status epilepticus (SE) leads to severe DNA damage which is the cause of death in a significant population of neurons. Studies of the mechanisms of DNA damage after excitotoxic insults have been extensive, but very little is known about the competing function of DNA repair under these conditions. We hypothesized that the up- or down-regulation of DNA repair mechanisms may be an important determinant of vulnerability to excitotoxic neuronal death. In this study we examined changes in the levels of subunit of DNA-dependent protein kinase, Ku70, following 2 hr of continuous SE in rats. This subunit is considered to be responsible for binding to double strand breaks in the DNA and thereby mobilizing DNA repair activity. In addition, we evaluated DNA repair activity in the same tissue using an in vitro assay system. We also determined protein levels of p21/waf (a p53-dependent mediator of DNA repair) following SE.
METHODS: SE was induced in adult male Sprague-Dawley rats by kainic acid (12 mg/kg ip) and terminated after a 2 hr duration with diazepam (30 mg/kg ip). Protein levels of Ku70 and p21 were determined by Western blotting at several time points during the 72 hr after seizure termination. In addition, at selected time points we performed an in vitro end-joining assay for DNA repair activity.
RESULTS: In the hippocampus, a 36% decrease in Ku70 protein level was found at 48 hr and this decrease remained significant up to 72 hr after SE termination. At 24 hr, there was an increase in DNA end-joining activity, but no change in Ku70 protein level. SE resulted in 4-5 fold upregulation of p21/waf protein at 24-72 hr post seizure.
CONCLUSIONS: Our results indicate that components of the DNA repair cascade are activated shortly after SE-evoked injury with subsequent depletion as the injury progresses toward cell death. This provides initial evidence that regulation of DNA repair mechanisms may represent a target for manipulating the vulnerability of neurons to excitotoxic insults. The possibility that neuroprotective strategies may activate DNA repair is now under investigation.