NADPH Oxidase-4 Mediates Myofibroblast Activation and Fibrogenic Responses to Lung Injury

Abstract

The NADPH oxidase (NOX) family of enzymes, which catalyze the reduction of O ₂ to form reactive oxygen species (ROS), have increased in number during eukaryotic evolution 1, 2. Seven isoforms of the NOX gene family have been identified in mammals; however, specific roles of NOX enzymes in mammalian physiology and pathophysiology have not been fully elucidated 3, 4. The best established physiological role of NOX enzymes is in host defense against pathogen invasion in diverse species, including plants 5, 6. The prototypical member of this family, NOX2 (gp91 ^phox ), is expressed in phagocytic cells and mediates microbicidal activities 7, 8. Here, we report a role for the NOX4 isoform in tissue repair functions of myofibroblasts and fibrogenesis. Transforming growth factor-β1 (TGF-β1) induces NOX4 expression in lung mesenchymal cells by a SMAD3-dependent mechanism. NOX4-dependent generation of hydrogen peroxide (H ₂O ₂) is required for TGF-β1-induced myofibroblast differentiation, extracellular matrix (ECM) production, and contractility. NOX4 is upregulated in lungs of mice subjected to non-infectious injury and in human idiopathic pulmonary fibrosis (IPF). Genetic or pharmacologic targeting of NOX4 abrogates fibrogenesis in two different murine models of lung injury. These studies support a novel function for NOX4 in tissue fibrogenesis and provide proof-of-concept for therapeutic targeting of NOX4 in recalcitrant fibrotic disorders.