Abstract TMP35: Neural Recovery Following Cerebral Ischemia is Exacerbated by Loss of DNA Polymerase-Beta

Abstract

Oxidative DNA damage (ODD) after cerebral ischemia/reperfusion injury occurs rapidly and has been implicated in the patholgenesis of ischemic injury. Ischemic ODD in the brain are primarly characterized as apurinic/apyrimidinic (AP) sites and single strand breaks (SSB). Following ODD, key enzymes in the base excision-repair (BER) pathway including AP endonuclease-1 (APE1) and the DNA polymerase-beta (PolyB) are critical to repair AP sites and SSB, and to mitigate cellular damage. Global knockout of either APE1 or PolyB leads to embryonic lethality. We have previously demonstrated that conditional deletion of APE1 in the adult heightens sensitivity to ischemic injury. PolyB is a highly inducible gene, and its expression is increased after sublethal brain injury, yet the contribution of PolyB to ischemic brain recovery remains unknown. PolyB conditional knockout (cKO) mice were generated by subjecting PolyB-CAG-CreER mice to tamoxifen administration for 5 days. Transient middle cerebral artery occlusion (tMCAO) was induced for 45 min following STAIR guidelines, and behavioral recovery and grey/white matter injury were assessed by over 35 days after ischemia. Cortical action field potentials (CAFP) and compound action potentials (CAP) were used to assess functional integrity of grey and white matter. PolyB cKO mice were significantly impaired up to 35 days after ischemic injury compared to WT mice, displaying exacerbated neuronal tissue loss, extensive demyelination in the CC/EC, and diminished CAFP and CAP compared to WT mice. In addition, accumulation of AP sites and SSBs were evident in the ischemic PolyB cKO. These results were compared to to APE1 cKO ischemic outcomes. PolyB cKO was associated with PARP1 activation, NAD + depletion, necrotic neuronal cell death, and neuronal release of HMGB1, and PJ34, a specific PARP-1 inhibitor, significantly improved stroke outcomes in PolyB cKO mice. Along with APE1, PolyB plays an essential role in ischemic brain recovery in both grey and white matter. However, the molecular mechanisms between exacerbation of injury in ischemic neurons by PolyB vs APE1 may be distinct. DNA base excision repair pathway may potentially serve as a therapeutic target for long-term neurological recovery after stroke.