Sirtuin 1 Promotes Hyperoxia-Induced Lung Epithelial Cell Death Independent of NF-E2-Related Factor 2 Activation

Lung epithelial cell damage accompanied by death is a cardinal feature of toxicant- and prooxidant-induced acute lung injury. The transcription factor nuclear factor (erythroid-derived 2)-like 2 (NEF2L2 or NRF2) activates several antioxidant enzymes (AOEs) and prosurvival genes in response to oxidant stress, and its deficiency enhances susceptibility to hyperoxic lung injury and other oxidant-induced lung pathologies. Sirtuin 1 (SIRT1) regulates cell growth and survival in response to both physiological and pathological stresses by selectively deacetylating multiple proteins required for chromatin remodeling and transcription; therefore, we sought to examine potential SIRT1-NRF2 cross-talk in the regulation of AOE expression during hyperoxia-induced lung epithelial cell death. Unexpectedly, pharmacological inhibition or small interfering RNA-mediated depletion of SIRT1 caused a reduction in cell death, accompanied by reduced levels of NRF2-dependent AOE expression in chronic hyperoxia. NRF2 acetylation was markedly and transiently higher in cells exposed to acute (6 h) hyperoxia. Sirtinol blocked this acute effect, but NRF2 acetylation was low or undetectable in cells exposed to chronic hyperoxia (24-36 h) both with and without sirtinol. SIRT1 activation by resveratrol augmented hyperoxia-induced death in cells with NRF2 deficiency. SIRT1 inhibition or depletion led to a reduced activation of the cell-death executioner caspase 3, whereas caspase inhibition prevented death. Consistent with these results, sirtinol attenuated hyperoxia-induced lung alveolar permeability and toxicity in vivo. Collectively, these results reveal that, in chronic hyperoxia, SIRT1 promotes hyperoxia-induced lung epithelial cell damage and death by altering pro- and antiapoptotic balance, not by dampening optimal NRF2-dependent AOE expression.