TGFβ1 Mediates Alcohol-Induced Nrf2 Suppression in Lung Fibroblasts

BackgroundChronic alcohol ingestion induces the expression of transforming growth factor beta-1(TGF1), inhibits nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-mediated activation of the antioxidant response element (ARE), depletes alveolar glutathione pools, and potentiates acute lung injury. In this study, we examined the mechanistic relationship between TGF1 and Nrf2-ARE signaling in the experimental alcoholic lung. MethodsWild-type mice were treatedalcohol in drinking water for 8weeks and their lungs were assessed for Nrf2 expression. In parallel, mouse lung fibroblasts were culturedalcohol and treated +/- sulforaphane (SFP; an activator of Nrf2), +/- TGF1, +/- TGF1 neutralizing antibody, and/or +/- activin receptor-like kinase 5 inhibitors (to block TG1 receptor signaling) and then analyzed for the expression of Nrf2, Kelch-like ECH-associated protein 1 (Keap1) and TGF1, Nrf2-ARE activity, and the expression of the Nrf2-ARE-dependent antioxidants glutathione s-transferase theta 2 (GSTT2) and glutamate-cysteine ligase catalytic subunit (GCLC). Finally, silencing RNA (siRNA) of Nrf2 was then performed prior to alcohol exposure and subsequent analysis of TGF1 expression. ResultsAlcohol treatment in vivo or in vitro decreased Nrf2 expression in murine whole lung and lung fibroblasts, respectively. In parallel, alcohol exposure in vitro decreased Keap1 gene and protein expression in lung fibroblasts. Furthermore, alcohol exposure increased TGF1 expression but decreased Nrf2-ARE activity and expression of the ARE-dependent genes for GSTT2 and GCLC. These effects of alcohol were prevented by treatment with SFP; in contrast, Nrf2 SiRNA expression exacerbated alcohol-induced TGF1 expression. Finally, TGF1 treatment directly suppressed Nrf2-ARE activity whereas blocking TGF1 signaling attenuated alcohol-induced suppression of Nrf2-ARE activity. ConclusionsAlcohol-induced oxidative stress is mediated by TGF1, which suppresses Nrf2-ARE-dependent expression of antioxidant defenses and creates a vicious cycle that feeds back to further increase TGF1 expression. These effects of alcohol can be mitigated by activation of Nrf2, suggesting a potential therapy in individuals at risk for lung injury due to alcohol abuse.