Localization of γ-glutamylcysteine synthetase messenger rna expression in lungs of smokers and patients with chronic obstructive pulmonary disease

Abstract

Cigarette smoking results in an oxidant/antioxidant imbalance in the lungs and inflammation, which are considered to be key factors in the pathogenesis of chronic obstructive pulmonary disease (COPD). Glutathione (GSH) is an important protective antioxidant in lung epithelial cells and epithelial lining fluid. De novo GSH synthesis in cells occurs by a two-enzyme process. The rate-limiting enzyme is γ-glutamylcysteine synthetase (γ-GCS), in which the heavy subunit (HS) constitutes most of its catalytic activity. The localization and expression of γ-GCS-HS in specific lung cells as well as possible differences in its expression between smokers with and without COPD have not yet been studied. The purpose of this study was to investigate γ-GCS-HS expression using messenger RNA in situ hybridization in peripheral lung tissue. We studied 23 current or ex-smokers with similar smoking histories with ( n = 11; forced expiratory volume in 1 s [FEV 1] < 75% predicted) or without COPD ( n = 12; FEV 1 < 84% predicted). We assessed the relations between pulmonary γ-GCS-HS expression, FEV 1 and transforming growth factor-β1 (TGFβ 1), because TGFβ 1 can modulate γ-GCS-HS expression in lung epithelial cells. Gamma-GCS-HS is predominantly expressed by airway and alveolar epithelial cells, alveolar CD68+ cells (macrophages), and endothelial cells of both arteries and veins. In subjects with COPD, semiquantitative analysis revealed higher levels of γ-GCS-HS messenger RNA in alveolar epithelium (1.5 times, p < .04) and a trend for a higher expression in bronchiolar epithelium (1.3 times, p = .075) compared with subjects without COPD. We did not observe a significant correlation between airway and alveolar epithelial γ-GCS-HS expression and TGFβ 1 expression ( r = .20), FEV 1 percentage predicted ( r = .18), or FEV 1/forced vital capacity ratio ( r = .14; p > .05). Our results show that γ-GCS-HS is localized, particularly in lung epithelium, and shows higher expression in smokers with COPD. This suggests a specific role for enhanced GSH synthesis as a mechanism to provide an adaptive response against oxidative stress in patients with COPD.