NRF2 is a transcription factor important in the protection against carcinogenesis and oxidative stress through antioxidant response element (ARE)-mediated transcriptional activation of several phase 2 detoxifying and antioxidant enzymes. This study was designed to determine the role of NRF2 in the pathogenesis of hyperoxic lung injury by comparing pulmonary responses to 95-98% oxygen between mice with site-directed mutation of the gene for NRF2 (Nrf2-/-) and wild-type mice (Nrf2+/+). Pulmonary hyperpermeability, macrophage inflammation, and epithelial injury in Nrf2-/- mice were 7.6-fold, 47%, and 43% greater, respectively, compared with Nrf2+/+ mice after 72 h hyperoxia exposure. Hyperoxia markedly elevated the expression of NRF2 mRNA and DNA-binding activity of NRF2 in the lungs of Nrf2+/+ mice. mRNA expression for ARE- responsive lung antioxidant and phase 2 enzymes was evaluated in both genotypes of mice to identify potential downstream molecular mechanisms of NRF2 in hyperoxic lung responses. Hyperoxia-induced mRNA levels of NAD(P)H:quinone oxidoreductase 1 (NQO1), glutathione-S-transferase (GST)-Ya and -Yc subunits, UDP glycosyl transferase (UGT), glutathione peroxidase-2 (GPx2), and heme oxygenase-1 (HO-1) were significantly lower in Nrf2-/- mice compared with Nrf2+/+ mice. Consistent with differential mRNA expression, NQO1 and total GST activities were significantly lower in Nrf2-/- mice compared with Nrf2+/+ mice after hyperoxia. Results demonstrated that NRF2 has a significant protective role against pulmonary hyperoxic injury in mice, possibly through transcriptional activation of lung antioxidant defense enzymes.

Cellular oxidative and electrophilic stress triggers a protective response in mammals regulated by NRF2 (nuclear factor (erythroid-derived) 2-like; NFE2L2) binding to deoxyribonucleic acid-regulatory sequences near stress-responsive genes. Studies using Nrf2-deficient mice suggest that hundreds of genes may be regulated by NRF2. To identify human NRF2-regulated genes, we conducted chromatin immunoprecipitation (ChIP)-sequencing experiments in lymphoid cells treated with the dietary isothiocyanate, sulforaphane (SFN) and carried out follow-up biological experiments on candidates. We found 242 high confidence, NRF2-bound genomic regions and 96% of these regions contained NRF2-regulatory sequence motifs. The majority of binding sites were near potential novel members of the NRF2 pathway. Validation of selected candidate genes using parallel ChIP techniques and in NRF2-silenced cell lines indicated that the expression of about two-thirds of the candidates are likely to be directly NRF2-dependent including retinoid X receptor alpha (RXRA). NRF2 regulation of RXRA has implications for response to retinoid treatments and adipogenesis. In mouse, 3T3-L1 cells’ SFN treatment affected Rxra expression early in adipogenesis, and knockdown of Nrf2-delayed Rxra expression, both leading to impaired adipogenesis.

We recently used positional cloning to identify the transcription factor Nrf2 (NF-E2 related factor 2) as a susceptibility gene in a murine model of oxidant-induced acute lung injury (ALI). NRF2 binds to antioxidant response elements (ARE) and up-regulates protective detoxifying enzymes in response to oxidative stress. This led us to investigate NRF2 as a candidate susceptibility gene for risk of development of ALI in humans. We identified multiple single nucleotide polymorphisms (SNPs) by resequencing NRF2 in ethnically diverse subjects, and one (-617 C/A) significantly (P<0.001) diminished luciferase activity of promoter constructs containing the SNP and significantly decreased the binding affinity (P<0.001) relative to the wild type at this locus (-617 CC). In a nested case-control study, patients with the -617 A SNP had a significantly higher risk for developing ALI after major trauma (OR 6.44; 95% CI 1.34, 30.8; P=0.021) relative to patients with the wild type (-617 CC). This translational investigation provides novel insight into the molecular mechanisms of susceptibility to ALI and may help to identify patients who are predisposed to develop ALI under at risk conditions, such as trauma and sepsis. Furthermore, these findings may have important implications in other oxidative stress related illnesses.