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A7150 - Peroxisome Proliferator-Activated Receptor γ-Mediated Regulation of Glutathione Peroxidase 3 in COPD
Author Block: A. Banno, A. Reddy, S. Lakshmi, S. Kim, R. C. Reddy; University of Pittsburgh, Pittsburgh, PA, United States.
Rationale: COPD is characterized by bronchial inflammation and overproduction of reactive oxygen species (ROS). Increased ROS, which cause oxidative stress and resulting tissue injury, are considered major contributors to COPD pathogenesis. Glutathione peroxidase 3 (GPx3), an antioxidant expressed in the lungs, scavenges hydrogen peroxide and organic hydroperoxides and is thus a major factor in protecting tissues against oxidative damage. Methods: Expression and activity of peroxisome proliferator-activated receptor γ (PPARγ), GPx3, and factors associated with inflammation and oxidative stress were measured in lung tissue samples and bronchial epithelial cells (HBEs) from COPD patients and controls. For in vitro studies, inflammation was induced in normal HBEs by cigarette smoke extract (CSE). Some cells were treated with the synthetic PPARγ agonist rosiglitazone (Rosi) whereas other cells were subjected to the PPARγ antagonist GW9662 or siRNA-mediated PPARγ knockdown. Effects of these treatments on GPx3, inflammation, and oxidative stress were measured by standard biochemical and molecular biological assays. Results: Expression and activity of PPARγ and GPx3 were strongly downregulated in lung tissue samples and HBEs from COPD patients while those of the pro-inflammatory transcription factor NF-κB, along with ROS production, were upregulated. In vitro, CSE treatment of normal HBEs similarly decreased PPARγ expression and increased inflammation-induced oxidative stress. These changes were accompanied by a variety of inflammation-associated features including upregulated NF-κB activity. CSE-treatment likewise reduced GPx3 expression and activity in normal HBEs, further augmenting ROS production. Molecular studies identified direct interaction between PPARγ and the PPAR response element (PPRE) within the GPx3 promoter. This interaction enhanced GPx3 expression and activity, reducing ROS and thus alleviating oxidative stress. Complementary PPARγ activation and inactivation studies in CSE-treated normal HBEs revealed that the antioxidant effects of PPARγ were mediated largely via modulation of GPx3 expression. Conclusions: Our data demonstrate that PPARγ regulates basal as well as induced expression of GPx3 and highlight the significance of GPx3 in PPARγ-mediated protection against oxidative stress and damage in the lungs.