View Abstract

A7598 - Role of Mitochondrial DNA Damage in Aberrant Airway Remodeling and Repair Post Inhalation Lung Injury
Author Block: S. Aggarwal1, I. Ahmad2, A. Lam3, H. Paiste1, M. N. Gillespie4, S. Matalon3; 1Anesthesiology, University of Alabama at Birmingham, Birmingham, AL, United States, 2Anesthesiology and Perioperative Medicine, University of Alabama at Birmingham, Birmingham, AL, United States, 3University of Alabama at Birmingham, Birmingham, AL, United States, 4Univ of South Alabama College of Med, Mobile, AL, United States.
RATIONALE: Chronic pulmonary deficiencies due to aberrant remodeling and repair may cause severe morbidity and mortality in patients who survive acute inhalation injury (AII). Pulmonary fibrosis and emphysema are irreversible chronic events after AII that compromise lung function. Surprisingly, the mechanism(s) involved in chronic lung damage after AII are unclear. We previously showed that exposure to the oxidant halogen-gases, bromine (Br2) and chlorine (Cl2) result in oxidative lung injury. Free radicals produced during oxidative stress can damage mitochondrial DNA (mtDNA) due to its proximity to the electron transport chain, a lack of a histone protective shield overlying the mtDNA, and limited DNA repair mechanisms. Mitochondrial DNA damage is an early event in oxidant exposed cells that contributes to the inflammatory response. Therefore, we hypothesized that mtDNA damage underlie chronic lung damage post inhalation injury and therefore enhancing mtDNA repair can be a useful therapeutic approach to mitigate the lung pathology. METHODS: We exposed adult C57BL/6 mice to Cl2 or Br2 (400ppm for 30min) and return them to room air. On days 1, 7, 14, and 21 post exposure, we measured markers of lung injury (inflammatory cells and plasma protein levels in bronchial-alveolar lavage fluid), evaluated histological lung changes, fluid extravastion into the lung, and airway resistance and compliance. We also evaluated the lung parenchyma for pro-fibrotic and emphysematous remodeling by measuring lung collagen levels, alveolar septal damage, and alveolar mean linear intercept. We assessed lung mtDNA damage by measuring lesion frequency in the 16kb mtDNA. Finally, we determined whether the administration of the DNA repair enzyme, 8-oxoguanine-DNA glycosylase 1 (OGG1), attached to a mitochondrial targeting signal (OGG1 fusion protein) post halogen gas exposure, enhanced mtDNA repair, mitigated chronic lung injury and improved survival. RESULTS: On days 14 and 21 post halogen exposure, C57BL/6 mice had an increase in collagen levels around bronchioles suggesting peribronchiolar fibrosis. Lung function showed an obstructive lung phenotype (increased lung compliance, alveolar septal damage, and increased alveolar size) indicative of emphysema. Lung mtDNA was damaged on day 1 post exposure, while treatment with the OGG1 fusion protein 6 hour post halogen exposure, attenuated mtDNA damage, abrogated chronic lung injury and reduced mortality. CONCLUSION: Together, the data demonstrates for the first time that a brief exposure to an oxidant gas results in peribronchial fibrosis and emphysema due to mtDNA damage and establishes the therapeutic potential of OGG1 fusion protein in its treatment.