NADPH oxidase-4 mediates myofibroblast activation and fibrogenic responses to lung injury

The mechanisms that lead to idiopathic pulmonary fibrosis, or lung scarring, is not clear. Victor Thannickal and his colleagues have now provided further insight by showing that induction of NOX4, an enzyme that creates reactive oxygen species, is required for the progression of the disease. Their findings suggest NOX4 as a potential target to treat this common ailment that currently has no proven treatment options. Members of the NADPH oxidase (NOX) family of enzymes, which catalyze the reduction of O2 to reactive oxygen species, have increased in number during eukaryotic evolution1,2. 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 elucidated3,4. The best established physiological role of NOX enzymes is in host defense against pathogen invasion in diverse species, including plants5,6. The prototypical member of this family, NOX-2 (gp91phox), is expressed in phagocytic cells and mediates microbicidal activities7,8. Here we report a role for the NOX4 isoform in tissue repair functions of myofibroblasts and fibrogenesis. Transforming growth factor-β1 (TGF-β1) induces NOX-4 expression in lung mesenchymal cells via SMAD-3, a receptor-regulated protein that modulates gene transcription. NOX-4–dependent generation of hydrogen peroxide (H2O2) is required for TGF-β1–induced myofibroblast differentiation, extracellular matrix (ECM) production and contractility. NOX-4 is upregulated in lungs of mice subjected to noninfectious injury and in cases of human idiopathic pulmonary fibrosis (IPF). Genetic or pharmacologic targeting of NOX-4 abrogates fibrogenesis in two murine models of lung injury. These studies support a function for NOX4 in tissue fibrogenesis and provide proof of concept for therapeutic targeting of NOX-4 in recalcitrant fibrotic disorders.