NRF2 protects lung epithelial cells from wood smoke particle toxicity

Wildfire smoke is a potential source of oxidative stress in lung epithelial tissue. The response to oxidative stress is controlled by the transcription factor NRF2, which is the central regulator of antioxidant gene expression. If wood smoke particle (WSP) exposure induces reactive oxygen species (ROS) in epithelial cells, then NRF2 may protect against pathological conditions resulting from increased oxidative stress through changes in gene expression. We used two lung epithelial cell lines to test this hypothesis in vitro: A549, which harbor a mutation resulting in constitutive activation of NRF2, and BEAS-2B, which show limited NRF2 activity under basal conditions, but high inducibility during oxidative stress. In BEAS-2B cells, WSP exposure leads to increased cellular ROS, activation of NRF2, and upregulation of the NRF2 target genes NQO1, GCLM, and SRXN1. WSP exposure also increased ROS in A549 cells, although NRF2 activation and antioxidant gene upregulation were less robust as both were basally high in this cell line. Overall, the degree of ROS induction by WSP across cell lines is dependent upon NRF2 activity, and a similar pattern was observed for WSP cytotoxicity. WSP also sensitized both cell lines to the ferroptosis inducer erastin in a manner that is correlated with NRF2 activity. Knockout of NRF2 in A549 resulted in higher WSP-induced ROS generation, cytotoxicity, and erastin sensitivity. Taken together, these results suggest that NRF2 serves as a protective factor against wood smoke induced ROS and oxidative stress in lung epithelial cells.