Alveolar epithelial cell (AEC) apoptosis, arising from mitochondrial dysfunction and mitophagy defects, is important in mediating idiopathic pulmonary fibrosis (IPF). Our group established a role for the mitochondrial (mt) DNA base excision repair enzyme, 8-oxoguanine-DNA glycosylase 1 (mtOGG1), in preventing oxidant-induced AEC mtDNA damage and apoptosis and showed that OGG1-deficient mice have increased lung fibrosis. Herein, we determined whether mice overexpressing the mtOGG1 transgene (mtOgg1tg) are protected against lung fibrosis and whether AEC mtOGG1 preservation of mtDNA integrity mitigates phosphatase and tensin homolog-induced putative kinase 1 (PINK1) deficiency and apoptosis. Compared with wild type (WT), mtOgg1tg mice have diminished asbestos- and bleomycin-induced pulmonary fibrosis that was accompanied by reduced lung and AEC mtDNA damage and apoptosis. Asbestos and H2O2 promote the MLE-12 cell PINK1 deficiency, as assessed by reductions in the expression of PINK1 mRNA and mitochondrial protein expression. Compared with WT, Pink1-knockout (Pink1-KO) mice are more susceptible to asbestos-induced lung fibrosis and have increased lung and alveolar type II (AT2) cell mtDNA damage and apoptosis. AT2 cells from Pink1-KO mice and PINK1-silenced (siRNA) MLE-12 cells have increased mtDNA damage that is augmented by oxidative stress. Interestingly, mtOGG1 overexpression attenuates oxidant-induced MLE-12 cell mtDNA damage and apoptosis despite PINK1 silencing. mtDNA damage is increased in the lungs of patients with IPF as compared with controls. Collectively, these findings suggest that mtOGG1 maintenance of AEC mtDNA is crucial for preventing PINK1 deficiency that promotes apoptosis and lung fibrosis. Given the key role of AEC apoptosis in pulmonary fibrosis, strategies aimed at preserving AT2 cell mtDNA integrity may be an innovative target.
Keywords: OGG1; PINK1; alveolar epithelial cell; mitochondrial DNA damage; oxidative stress; pulmonary fibrosis.