Abstract
The respiratory epithelium forms an important barrier against inhaled pollutants and microorganisms, and its barrier function is often compromised during inflammatory airway diseases. Epithelial activation of hypoxia-inducible factor-1 (HIF-1) represents one feature of airway inflammation, but the functional importance of HIF-1 within the respiratory epithelium is largely unknown. Using primary mouse tracheal epithelial (MTE) cells or immortalized human bronchial epithelial cells (16HBE14o-), we evaluated the impact of HIF-1 activation on loss of epithelial barrier function during oxidative stress. Exposure of either 16HBE14o- or MTE cells to H(2)O(2) resulted in significant loss of transepithelial electrical resistance and increased permeability to fluorescein isothiocyanate-dextran (4 kDa), and this was attenuated significantly after prior activation of HIF-1 by preexposure to hypoxia (2% O(2); 6 h) or the hypoxia mimics CoCl(2) or dimethyloxalylglycine (DMOG). Oxidative barrier loss was associated with reduced levels of the tight junction protein occludin and with hyperoxidation of the antioxidant enzyme peroxiredoxin (Prx-SO(2)H), events that were also attenuated by prior activation of HIF-1. Involvement of HIF-1 in these protective effects was confirmed using the pharmacological inhibitor YC-1 and by short-hairpin RNA knockdown of HIF-1α. The protective effects of HIF-1 were associated with induction of sestrin-2, a hypoxia-inducible enzyme known to reduce oxidative stress and minimize Prx hyperoxidation. Together, our results suggest that loss of epithelial barrier integrity by oxidative stress is minimized by activation of HIF-1, in part by induction of sestrin-2.