Role of Nrf2 in Alveolar Epithelial Cell Regeneration During Lung Repair

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Impaired repair of alveolar epithelium after acute lung injury (ALI) can lead to heightened inflammatory response and tissue repair do not normally resolve. Studies in this application will test the hypothesis that impaired lung repair after injury is the result of GSH/AKT signaling imbalance in type 2 alveolar epithelial cells (AEC2s) regulated by cyto-protection and pro-survival transcription factor, Nrf2. We found that global deletion of Nrf2 impairs lung repair after sub-lethal pro-oxidant (hyperoxia)-induced ALI. Using conditional mutant Nrf2 ("floxed") mouse model to determine the contribution of lung resident cellular stress to acute lung and repair, we found that deletion of Nrf2 in lung epithelium impaired the resolution of ALI in a manner similar to that observed in Nrf2-null mice, suggesting that lung epithelial-Nrf2 signaling regulates pro-resolution response and lung repair. In agreement with this result, we found that primary AEC2s lacking Nrf2 (Nrf2-/-AEC2s) proliferate poorly due to oxidative stress and G2/M (not G1/M) cell cycle arrest. Interestingly, mitigating oxidative stress in Nrf2-/-AEC2s by exogenous N-acetyl-cysteine, but it failed to rescue G2/M arrest. In contrast, exogenous GSH mitigated stress, activated AKT signaling and restored proliferation in Nrf2-/-AEC2s. Preliminary 3D cell culture experiments showed reduced size of "alveolospheres" formation by AEC2s isolated from Nrf2+/+ mice exposed to sub-lethal (48-h) hyperoxia compared to room air counterparts. AEC2s from Nrf2-/- mice exposed to either room air or hyperoxia formed disorganized and reduced number of "alveolospheres". Nrf2-/-AEC2s supplemented with GSH exhibited improved alveolosphere formation, but not efficient AEC2/1 trans-differentiation. In this project, we test hypothesize that AEC2-specific Nrf2 regulated signaling is essential for tipping the equilibrium towards either for optimal GSH/AKT- dependent AEC2 proliferation and GSH/AKT-independent AEC2/1 trans-differentiation. We will use multiple approaches to provide a mechanistic test of this hypothesis including the use of AEC2-tissue- specific loss-of-function (Nrf2-/-AEC2) and gain-of-function (Nrf2 inhibitor Keap1-/-AEC2) mouse models and small molecule Nrf2 activators. The Specific Aims to be pursued are: 1) to determine the mechanisms and role of Nrf2 regulated GSH/AKT-mediated signaling in the mechanisms of optimal AEC2 proliferation and AEC2/1 trans-differentiation, 2) to address in vivo the role of AEC2-specific Nrf2 as a pro-survival and pro-regenerative mechanism after ALI, and 3) to test the postulate that Nrf2 activation will accelerate AEC repair post-injury. Hyperoxia is used widely in the treatment of pulmonary diseases (such as COPD and ARDS), but its effects on the repair lung alveolar epithelium in these patients are not clearly understood. Likewise, abnormal repair of lung alveolar epithelium caused by bacterial infection is a major health concern. Thus, the studies proposed are of major scientific and clinical importance to critically ill ALI/ARDS patients.