Enhanced mtDNA repair capacity protects pulmonary artery endothelial cells from oxidant-mediated death

Abstract

In rat cultured pulmonary arterial (PA), microvascular, and venous endothelial cells (ECs), the rate of mitochondrial (mt) DNA repair is predictive of the severity of xanthine oxidase (XO)-induced mtDNA damage and the sensitivity to XO-mediated cell death. To examine the importance of mtDNA damage and repair more directly, we determined the impact of mitochondrial overexpression of the DNA repair enzyme, Ogg1, on XO-induced mtDNA damage and cell death in PAECs. PAECs were transiently transfected with an Ogg1-mitochondrial targeting sequence construct. Mitochondria-selective overexpression of the transgene product was confirmed microscopically by the observation that immunoreactive Ogg1 colocalized with a mitochondria-specific tracer and, with an oligonucleotide cleavage assay, by a selective enhancement of mitochondrial Ogg1 activity. Overexpression of Ogg1 protected against both XO-induced mtDNA damage, determined by quantitative Southern analysis, and cell death as assessed by trypan blue exclusion and MTS assays. These findings show that mtDNA damage is a direct cause of cell death in XO-treated PAECs.