ABSTRACT Idiopathic Pulmonary fibrosis (IPF) is a devastating interstitial lung disease (ILD) characterized by disruption of distal lung architecture that results in scar formation, abnormal gas exchange, and respiratory failure. Barriers to better IPF outcomes have included an incomplete understanding of its pathophysiologic underpinnings and a dearth of translationally relevant preclinical models. However, identification of rare genetic variants in the alveolar epithelial type 2 (AT2) cell-restricted Surfactant Protein C (SP-C) gene (SFTPC) in subsets of PF patients has been part of a paradigm shift in which dysfunctional AT2 cells serve as a proximal driver of IPF. Coupled with the recent identification of a population of “reprogrammed” AT2 cells in human IPF lungs deficient in classic AT2 transcriptional programs and enriched in profibrotic mediators, new opportunities are emerging for therapeutic discovery for IPF. Our prior in vitro modeling demonstrated that IPF-associated SFTPC mutations produce aberrant SP-C proprotein isoforms that functionally disrupt epithelial cell quality control (QC) yielding 2 phenotypes: “ER stressed” from misfolding (“BRICHOS”) mutant with activation of all 3 signaling arms (ATF6, IRE1, PERK) of the unfolded protein response (UPR) or impaired autophagy / mitophagy secondary to proSP-C mistrafficking (“Non-BRICHOS”) mutants. The prior funding period provided proof of concept for a seminal role for disrupted AT2 QC showing that expression of either non-BRICHOS (SftpcI73T) or BRICHOS (SftpcC121G) mutants in mouse lung epithelia are each sufficient to evoke a spontaneous fibrotic phenotype with recapitulation of IPF defining elements. We also showed that SftpcC121G mice develop marked activation of AT2 UPR with emergence of a reprogrammed transition state. Our Preliminary Data show that mutant SftpcI73T expression in vivo causes AT2 glycolytic reprogramming, altered mitochondrial dynamics (biogenesis, fission, and respiration) and emergence of the aberrant AT2 transition state. Thus, this renewal application now seeks to mechanistically understand how imbalanced UPR signaling and metabolism each contribute to AT2 reprogramming and promotion of a fibrotic niche. Leveraging our Sftpc mouse PF models, we will first use mutant SftpcC121G as a model substrate for disruption of proteostasis while genetically and pharmacologically interrogating UPR signaling focusing on IRE1α and ATF6 to define their impact on AT2 proteostasis, cell states, and progenitor function [Specific Aim 1]. Then using SftpcI73T mice we will define downstream consequences of disrupted AT2 organellar QC for metabolic reprogramming and mitochondrial dynamics with contextualization of their impact on pathological AT2 endophenotypes and fibrotic remodeling [Specific Aim 2]. Proof of concept studies for each Aim using patient derived human induced Pluripotent Stem Cell AT2 (iPSC-AT2) expressing these mutants will provide translation of preclinical data t...