PROJECT SUMMARY Chronic respiratory diseases including pulmonary fibrosis (PF) are substantial causes of morbidity and mortality among veteran populations. Most patients with progressive PF die of respiratory failure or require lung transplantation within 5 years of diagnosis, and currently available therapies only modestly slow disease progression, underscoring an urgent need for new and more effective therapies that halt disease progression and/or promote functional lung regeneration. Dysfunctional repair of the alveolar epithelium following recurrent/chronic injury has been hypothesized as central to PF pathogenesis, and our prior work and preliminary data demonstrate that that lung epithelium in PF is characterized by accumulation of cells in abnormal differentiation states similar to regeneration-associated transitional cells observed in mice, suggesting that persistence of typically transient cell-states may be driver of disease pathogenesis. Using single-cell transcriptomics, genetic lineage-tracing studies, recurrent injury-models together with human and mouse organoid models, our preliminary data demonstrate that there is aberrant and persistent activation of hypoxia-inducible-factor-2 (Hif2) in the distal lung epithelium following recurrent injury. Preventing or blocking Hif2 activity protects against proximal-like epithelial metaplasia and experimental lung fibrosis and enhances alveolar epithelial cell maturation. We hypothesize that recurrent injury to regenerating airway-derived progenitor cells prevents AEC maturation via persistent activation of HIF2, which cooperates with the ETS family of transcription factors to direct ectopic “proximal-like” cell fates and potentiate local profibrotic signaling. Our specific aims are: 1) To test whether targeted Hif-inhibition can ameliorate experimental lung fibrosis, 2) To investigate the mechanisms through which localized Hif-activation regulates niche-specific profibrotic signaling, and 3) To determine whether HIF2:ETS interactions mediate HIF-regulation of regenerating epithelial cell fate and profibrotic signaling. Integrating transgenic mouse models, human and mouse organoid studies, and state-of-the-art spatial-transcriptomic and multiomic approaches, these studies will determine whether hypoxia or non-hypoxic mechanisms drive Hif activation following recurrent injury, test whether targeted inhibition/deletion of Hif1α/Hif2α or both can prevent and/or enhance resolution of lung fibrosis, determine the mediators through which epithelial Hif2 promotes local fibroblast activation, and define the interacting partners by which Hif2 regulates fate and function of regenerating AECs. Together, these experiments will determine crucial insights into the “upstream” mechanisms linking dysfunctional alveolar repair to lung fibrosis, and establish HIF2 as a novel therapeutic target to interrupt the PF pathobiology and promote functional alveolar regeneration.