Glutathione peroxidase 3 localizes to the epithelial lining fluid and the extracellular matrix in lung fibrosis

Abstract

Aberrant antioxidant activity contributes to the pathogenesis of interstitial lung diseases (ILD). The composition of the extracellular matrix (ECM) is affected by oxidative stress, but extracellular antioxidant defense mechanisms in ILD are incompletely understood.

Here, relative abundance and detergent solubility of extracellular antioxidant enzymes were extracted from a proteomic dataset of bleomycin-induced lung fibrosis in C57BL/6N mice. Glutathione peroxidase (Gpx) activity was measured in bronchoalveolar lavage fluid (BALF) and immunofluorescent stainings were performed to address distribution of Gpx3 in the lung. Regulation of GPX3 by TGF-β1, TNF-α, and menadione was assessed in primary human bronchial epithelial cells (phBEC) and lung fibroblasts (phLF) by qPCR and ELISA. Finally, GPX3 levels were measured in BALF from ILD patients by ELISA.

Sod3, Gpx3, and Gpx activity were increased in BALF of mice subjected to bleomycin-induced lung fibrosis. In total lung tissue, only Gpx3, but not Sod3, was upregulated. Quantitative detergent solubility profiles indicated that Gpx3, but not Sod3, associated with ECM proteins. Immunofluorescence analysis showed that Gpx3 was expressed by bronchial epithelial cells and interstitial fibroblasts and localized to the basement membrane and interstitial ECM in mouse and human lung tissue. GPX3 expression in phBEC and phLF was downregulated by TNF-α, but more variably regulated by TGF-β1 and menadione. BALF of some ILD patients contained high levels of GPX3.

Hence, levels of the extracellular antioxidant enzyme GPX3 are variably increased in ILD. Upregulation of GPX3 might protect the ECM from oxidative damage in ILD.