Nrf2 activation protects against intratracheal LPS induced mouse/murine acute respiratory distress syndrome by regulating macrophage polarization

The transcription factor nuclear factor E2-related factor 2 (Nrf2) is known to control the expression of antioxidant response elements and cytoprotective genes and modulate inflammatory response, helping to ameliorate damage in many diseases. Exactly how Nrf2 regulates innate inflammatory homeostasis remains unclear. In this study, we provide in vitro and in vivo evidence that Nrf2 plays a crucial role in macrophage polarization and acute respiratory distress syndrome (ARDS). We conducted in vitro experiments using a mouse alveolar macrophage cell line as well as primary cultures of macrophages in which cells were exposed to lipopolysaccharide (LPS) or interferon-γ in order to mimic ARDS, in the presence or absence of the Nrf2 activator tert-butylhydroquinone (tBHQ). Using siRNA-mediated Nrf2 knockdown, we showed that Nrf2 inhibited the inflammatory response by promoting M2 macrophage polarization and inhibiting M1 macrophage polarization. At the same time, tBHQ activated Nrf2-mediated inhibition of the p65 nuclear factor-κB pathway and activation of peroxisome proliferator-activated receptor-γ, which play important roles in regulating macrophage polarization. We also conducted in vivo experiments in which mice were given tBHQ with or without intratracheal LPS, then their survival was monitored, lung injury was assessed using histology, and levels of pro- and anti-inflammatory cytokines were assayed in the lungs and serum. Activation of Nrf2 with tBHQ dramatically reduced LPS-induced mortality and lung injury, down-regulated pro-inflammatory mediators and up-regulated anti-inflammatory mediators. These results suggest that Nrf2 can help prevent ARDS progression by promoting M2 polarization of macrophages. Interfering with Nrf2 may be an effective strategy for reprogramming macrophage polarization in order to treat ARDS.