Hyperoxia activates ATM independent from mitochondrial ROS and dysfunction

Emily A Resseguie,Rhonda J Staversky,Paul S Brookes,Michael A O’Reilly

doi:10.1016/j.redox.2015.04.012

Emily A Resseguie, Rhonda J Staversky + Show 2 more

Open Access

https://doi.org/10.1016/j.redox.2015.04.012

Copy DOI

Journal: Redox Biology	Publication Date: May 2, 2015
Citations: 79	License type: cc-by

Affiliation: University of Rochester

Abstract

High levels of oxygen (hyperoxia) are often used to treat individuals with respiratory distress, yet prolonged hyperoxia causes mitochondrial dysfunction and excessive reactive oxygen species (ROS) that can damage molecules such as DNA. Ataxia telangiectasia mutated (ATM) kinase is activated by nuclear DNA double strand breaks and delays hyperoxia-induced cell death through downstream targets p53 and p21. Evidence for its role in regulating mitochondrial function is emerging, yet it has not been determined if mitochondrial dysfunction or ROS activates ATM. Because ATM maintains mitochondrial homeostasis, we hypothesized that hyperoxia induces both mitochondrial dysfunction and ROS that activate ATM. In A549 lung epithelial cells, hyperoxia decreased mitochondrial respiratory reserve capacity at 12h and basal respiration by 48h. ROS were significantly increased at 24h, yet mitochondrial DNA double strand breaks were not detected. ATM was not required for activating p53 when mitochondrial respiration was inhibited by chronic exposure to antimycin A. Also, ATM was not further activated by mitochondrial ROS, which were enhanced by depleting manganese superoxide dismutase (SOD2). In contrast, ATM dampened the accumulation of mitochondrial ROS during exposure to hyperoxia. Our findings suggest that hyperoxia-induced mitochondrial dysfunction and ROS do not activate ATM. ATM more likely carries out its canonical response to nuclear DNA damage and may function to attenuate mitochondrial ROS that contribute to oxygen toxicity.

Highlights

Oxygen is an essential element of cellular respiration, as it is the final electron acceptor in a process that generates ATP
To determine when hyperoxia affects mitochondrial function in A549 human lung epithelial cells, the oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) were simultaneously measured in cells exposed to room air or hyperoxia for 12, 24, and 48 h
The concomitant increase in ECAR is reflected in the decreased OCR/ECAR ratio seen at 12–48 h of hyperoxia (Fig. 1B)

Summary

Introduction

Oxygen is an essential element of cellular respiration, as it is the final electron acceptor in a process that generates ATP. Mitochondria generate reactive oxygen species (ROS) when oxygen reacts with electrons that escape the electron transport chain (ETC) in the inner mitochondrial membrane. The free radical theory of aging proposes a vicious cycle in which mitochondrial ROS damage mitochondrial DNA (mtDNA), leading to improper coding of ETC proteins and dysfunction that further increases ROS [1]. Between mitochondrial ROS, mtDNA damage, and respiratory dysfunction. MtDNA is thought to be quite susceptible to oxidative stress induced by mitochondrial dysfunction because it is in close proximity to the inner mitochondrial membrane [3]. To prevent oxidative stress and mtDNA damage under normal physiological conditions, mitochondrial ROS are quenched, in part, by the mitochondrial isoform of superoxide dismutase (SOD2), thioredoxin, peroxiredoxin and glutathione systems [4,5]

Methods

Results

Conclusion