DNA damage and nonhomologous end joining in excitotoxicity: Neuroprotective role of DNA-PKcs in kainic acid-induced seizures

Abstract

DNA repair plays a critical, but imprecisely defined role in excitotoxic injury and neuronal survival throughout adulthood. We utilized an excitotoxic injury model to compare the location and phenotype of degenerating neurons in mice (strain 129-C57BL) deficient in the catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs), an enzyme required for nonhomologous end joining (NHEJ). Brains from untreated adult heterozygous and DNA-PKcs null mice displayed comparable cytoarchitecture and undetectable levels of cell death. By day 1, and extending through 4 days following kainic acid-induced seizures, brains from DNA-PKcs null mice showed widespread neurodegeneration that encompassed the entire hippocampal CA1-CA3 pyramidal cell layer, entorhinal cortex, and lateral septum, with relative sparing of the dentate gyrus granule cell layer and hilus, as judged by toluidine blue, Fluoro-Jade B, and terminal dUTP nick end labeling staining. In contrast, seizure-related neurodegeneration in heterozygous littermates was limited to the CA3 region of the hippocampus. NeuN and calbindin staining revealed a selective decrease in the number and density of NeuN-positive neurons in the pyramidal layers of degenerating regions in both heterozygous and DNA-PKcs null mice. To elucidate the mechanisms leading to cell death, we examined an involvement of the p53 pathway, known to be induced by DNA damage. Addition of pifithrin-alpha, a p53 inhibitor, or expression of a dominant-negative p53 rescued neurons from kainate-induced excitotoxic cell death in primary cortical cultures derived from wildtype, DNA-PKcs heterozygous, or DNA-PKcs null neonatal mice. Moreover, pifithrin-alpha prevented kainate-induced loss of mitochondrial membrane potential, dendrite degeneration, and cell death. Results suggest that NHEJ plays a neuroprotective role in excitotoxicity, within the perforant, Schaffer collateral, hippocampal-septal, and temperoammonic pathways, in part by repairing DNA damage that would otherwise result in activation of a p53-dependent apoptotic cascade.

Comparative assessment of the apoptotic potential of silver nanoparticles synthesized by Bacillus tequilensis and Calocybe indica in MDA-MB-231 human breast cancer cells: targeting p53 for anticancer therapy

“…112 Neema et al suggested that p53-dependent neuronal death involves a drop in MTP, which reflects both a loss in the integrity of mitochondria and an increase in mitochondrial membrane permeability. 113 As described from an earlier study, the inner MTP decreases during apoptosis. Thus, the …”

Pathologies Associated with the p53 Response

“…PFTa was also shown to protect against neuron degeneration induced by 6-Hydroxydopamine (Biswas et al 2005;Liang et al 2007), proteasome inhibitors (Nair et al 2006), and the herbicide paraquat (a suspected etiologic factor in the development of Parkinson's disease) (Yang and Tiffany-Castiglioni 2008). Moreover, PFTa inhibited glutamate-and kainite (an analog of glutamate)-induced p53-mediated neuronal death (Morrison et al 1996;Xiang et al 1998;Liu and Zhu 1999;Culmsee et al 2001;Neema et al 2005) and protected mouse synaptosomes against excitotoxic injuries (Gilman et al 2003).…”

Sublethal Doses of β-Amyloid Peptide Abrogate DNA-dependent Protein Kinase Activity

“…Moreover, neurons have low levels of antioxidant enzymes, thus particularly susceptible to the damaging and highly toxic effects of ROS (94). DNA-PK exerts a protec-tive function under different cell death conditions, including oxidative stress and excitotoxicity (71,73). Hence, it is possible that exposure to nonlethal oxidative injuries in the presence of A␤, a hallmark of AD pathology, elicits neuronal cell death by suppression of DNA-PK anti-apoptotic function, contributing to the neurodegenerative process.…”