Gene Expression Profile of Human Airway Epithelium Induced by Hyperoxia In Vivo

Abstract

Hyperoxia leads to oxidative modification and damage of macromolecules in the respiratory tract with loss of biological functions. Given the lack of antioxidant gene induction with acute exposure to 100% oxygen, we hypothesized that clearance pathways for oxidatively modified proteins may be induced and serve in the immediate cellular response to preserve the epithelial layer. To test this, airway epithelial cells were obtained from individuals under ambient oxygen conditions and after breathing 100% oxygen for 12 h. Gene expression profiling identified induction of genes in the chaperone and proteasome-ubiquitin-conjugation pathways that together comprise an integrated cellular response to manage and degrade damaged proteins. Analyses also revealed gene expression changes associated with oxidoreductase function, cell cycle regulation, and ATP synthesis. Increased HSP70, protein ubiquitination, and intracellular ATP were validated in cells exposed to hyperoxia in vitro. Inhibition of proteasomal degradation revealed the importance of accelerated protein catabolism for energy production of cells exposed to hyperoxia. Thus, the human airway early response to hyperoxia relies predominantly upon induction of cytoprotective chaperones and the ubiquitin-proteasome-dependent protein degradation system to maintain airway homeostatic integrity.Keywords: airways; gene expression; hyperoxia; proteasome; ubiquitin Oxygen, one of the most abundant elements in our world, is essential for the oxidation of organic compounds to generate the energy needed to sustain life. Under ambient conditions, reactive oxygen species (ROS) are generated at a low level in lung cells during aerobic metabolism. To minimize the oxidant injury that is a consequence of aerobic life, the human lung is endowed with an integrated antioxidant system, which detoxifies reactive products (1-4). However, excessive ROS may overwhelm the antioxidant system and result in damage to major cellular components, including membrane lipids, proteins, carbohydrates, and DNA (1,(5)(6)(7)(8). The pathophysiologic consequences of this injury may include cell death, and tissue inflammation and damage. This is particularly evident during conditions of increased oxygen exposure for medical therapy (4, 9, 10). The bronchial epithelium is particularly vulnerable to the effects of airborne oxidative stress as the moist mucosal surface of the airway is in direct contact with the environment (11). Hyperoxia leads to oxidant injury in the respiratory tract, which is manifest as acute tracheobronchitis with edema and decrease in mucocili-(Received in original form July 8, 2005 and in final form May 4, 2006 ) This study was supported by AI70649, HL60917, and M01 RR018390 from the National Center for Research Resources. A.C. was supported by grants from the Collège des Professeurs de Pneumologie.Correspondence and requests for reprints should be addressed to Serpil C. (12,13). Oxidative damage of proteins and loss of biological function is one defined end-point of hyperoxic inj...

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