Nuclear factor, erythroid 2 related factor 2 (Nrf2) belongs to the Cap'n'collar/basic region leucine zipper (CNC-bZIP) transcription factor family, and is activated by diverse oxidants, pro-oxidants, antioxidants, and chemopreventive agents. After phosphorylation and dissociation from the cytoplasmic inhibitor, Kelch-like ECH-associated protein 1 (Keap1), Nrf2 translocates to the nucleus and binds to an antioxidant response element (ARE). Through transcriptional induction of ARE-bearing genes that encode antioxidant-detoxifying proteins, Nrf2 activates cellular rescue pathways against oxidative injury, inflammation/immunity, apoptosis, and carcinogenesis. ARE-driven genes include direct antioxidants (e.g., GPx), thiol metabolism-associated detoxifying enzymes (e.g., GSTs), stress-response genes (e.g., HO-1), and others (e.g., PSMB5). Application of nrf2 germ-line mutant mice elucidated protective roles for Nrf2 in various models of human disorders in the liver, lung, kidney, brain, and circulation. In the lung, deficiency of nrf2 augmented injury caused by bleomycin and environmental oxidants including hyperoxia, diesel exhaust particles, and cigarette smoke. Microarray analyses of lungs from nrf2-deficient and -sufficient mice identified Nrf2-dependent genes that might be critical in pulmonary protection. Observations from these studies highlight the importance of the Nrf2-antioxidant pathway and may provide new therapeutic strategies for acute respiratory distress syndrome, idiopathic pulmonary fibrosis, cancer, and emphysema in which oxidative stress is implicated.

The molecular mechanisms of pulmonary fibrosis are poorly understood, although reactive oxygen species are thought to have an important role. NRF2 is a transcription factor that protects cells and tissues from oxidative stress by activating protective antioxidant and detoxifying enzymes. We hypothesized that NRF2 protects lungs from injury and fibrosis induced by bleomycin, an anti‐neoplastic agent that causes pulmonary fibrosis in susceptible patients. To test this hypothesis, mice with targeted deletion of Nrf2 ( Nrf2 ^‒/‒ ) and wild‐type ( Nrf2 ^+/+ ) mice were treated with bleomycin or vehicle, and pulmonary injury and fibrotic responses were compared. Bleomycin‐induced increases in lung weight, epithelial cell death, and inflammation were significantly greater in Nrf2 ^‒/‒ mice than in Nrf2 ^+/+ mice. Indices of lung fibrosis (hydroxyproline content, collagen accumulation, fibrotic score, cell proliferation) were significantly greater in bleomycin‐treated Nrf2 ^‒/‒ mice, compared with Nrf2 ^+/+ mice. NRF2 expression and activity were elevated in Nrf2 ^+/+ mice by bleomycin. Bleomycin caused greater up‐regulation of several NRF2‐inducible antioxidant enzyme genes and protein products in Nrf2 ^+/+ mice compared with Nrf2 ^‒/‒ mice. Further, bleomycin‐induced transcripts and protein levels of lung injury and fibrosis markers were significantly attenuated in Nrf2 ^+/+ mice compared with Nrf2 ^‒/‒ mice. Results demonstrated that NRF2 has a critical role in protection against pulmonary fibrosis, presumably through enhancement of cellular antioxidant capacity. This study has important implications for the development of intervention strategies against fibrosis.

Rationale: The NF-E2 related factor 2 (Nrf2)–antioxidant response element (ARE) pathway is essential for protection against oxidative injury and inflammation including hyperoxia-induced acute lung injury. Microarray expression profiling revealed that lung peroxisome proliferator activated receptor γ (PPARγ) induction is suppressed in hyperoxia-susceptible Nrf2-deficient (Nrf2−/−) mice compared with wild-type (Nrf2+/+) mice. PPARγ has pleiotropic beneficial effects including antiinflammation in multiple tissues. Objectives: We tested the hypothesis that PPARγ is an important determinant of pulmonary responsivity to hyperoxia regulated by Nrf2. Methods: A computational bioinformatic method was applied to screen potential AREs in the Pparg promoter for Nrf2 binding. The functional role of a potential ARE was investigated by in vitro promoter analysis. A role for PPARγ in hyperoxia-induced acute lung injury was determined by temporal silencing of PPARγ via intranasal delivery of PPARγ-specific interference RNA and by administration of a PPARγ ligand 15-deoxy-Δ12,14-prostaglandin J2 in mice. Measurements and Main Results: Deletion or site-directed mutagenesis of a potential ARE spanning -784/-764 sequence significantly attenuated hyperoxia-increased Pparg promoter activity in airway epithelial cells overexpressing Nrf2, indicating that the -784/-764 ARE is critical for Nrf2-regulated PPARγ expression. Mice with decreased lung PPARγ by specific interference RNA treatment had significantly augmented hyperoxia-induced pulmonary inflammation and injury. 15 Deoxy-Δ12,14-prostaglandin J2 administration significantly reduced hyperoxia-induced lung inflammation and edema in Nrf2+/+, but not in Nrf2−/− mice. Conclusions: Results indicate for the first time that Nrf2-driven PPARγ induction has an essential protective role in pulmonary oxidant injury. Our observations provide new insights into the therapeutic potential of PPARγ in airway oxidative inflammatory disorders.

Rationale: Respiratory syncytial virus (RSV) is the most frequent cause of significant lower respiratory illness in infants and young children, but its pathogenesis is not fully understood. The transcription factor Nrf2 protects lungs from oxidative injury and inflammation via antioxidant response element (ARE)-mediated gene induction. Objectives: The current study was designed to determine the role of Nrf2-mediated cytoprotective mechanisms in murine airway RSV disease. Methods: Nrf2-deficient (Nrf2−/−) and wild-type (Nrf2+/+) mice were intranasally instilled with RSV or vehicle. In a separate study, Nrf2+/+ and Nrf2−/− mice were treated orally with sulforaphane (an Nrf2-ARE inducer) or phosphate-buffered saline before RSV infection. Measurements and Main Results: RSV-induced bronchopulmonary inflammation, epithelial injury, and mucus cell metaplasia as well as nasal epithelial injury were significantly greater in Nrf2−/− mice than in Nrf2+/+ mice. Compared with Nrf2+/+ mice, significantly attenuated viral clearance and IFN-γ, body weight loss, heightened protein/lipid oxidation, and AP-1/NF-κB activity along with suppressed antioxidant induction was found in Nrf2−/− mice in response to RSV. Sulforaphane pretreatment significantly limited lung RSV replication and virus-induced inflammation in Nrf2+/+ but not in Nrf2−/− mice. Conclusions: The results of this study support an association of oxidant stress with RSV pathogenesis and a key role for the Nrf2-ARE pathway in host defense against RSV.