Oxidative DNA Damage is Concurrently Repaired by BER and APE1-initiated NHEJ in Cortical Neurons.

AIMS Accumulating studies have suggested that base excision repair (BER) is the major repair pathway of oxidative DNA damage in neurons, and neurons are deficient in other DNA repair pathways, including nucleotide excision repair and homologous recombination repair. However, some studies have demonstrated that neurons could efficiently repair glutamate- and menadione-induced double-strand breaks (DSBs), suggesting that the DSB repair mechanisms might be implicated in neuronal health. In this study, we hypothesised that BER and non-homologous end join (NHEJ) work together to repair oxidative DNA damage in neurons. METHODS Immunohistochemistry and confocal microscopy were employed to examine the co-localization of AP endonuclease 1 (APE1), histone variant 2AX (γH2AX), and phosphorylated p53-binding protein (53BP1). APE1 inhibitor and shRNA were respectively applied to suppress APE1 activity and protein expression to determine the correlation of APE1 and DSB formation. The neutral comet assay was used to determine and quantitate the formation of DSB. RESULTS Both γH2AX and 53BP1 were upregulated and co-localized with APE1 in the nuclei of rat cortical neurons subjected to menadione-induced oxidative insults. Phospho53BP1 foci were efficiently abolished, but γH2AX foci persisted following the suppression of APE1 activity. Comet assays demonstrated that inhibition of APE1 decreased the DSB formation. CONCLUSIONS Our results indicate that APE1 can engage the NHEJ mechanism in the repair of oxidative DNA damage in neurons. These findings provide insights into the mechanisms underlying the efficient repair of oxidative DNA damage in neurons despite the high oxidative burden.