Alveolar Epithelial Stress Signaling in Lung Fibrosis

Pulmonary fibrosis (PF) is a devastating and progressive lung disease with a rising incidence and prevalence and minimally effective therapies. PF pathology is characterized by aberrant mesenchymal and epithelial populations that disrupt the normal alveolar lung architecture. In the alveolar epithelium in human PF and murine PF models, a subset of Alveolar Type 2 (AT2) cells lose their quintessential transcriptional program, entering but failing to exit an “aberrant transitional” state between AT2 and Alveolar Type 1 (AT1) cells. These cells are found in proximity to pathological collagen producing fibroblasts and they are transcriptionally enriched in fibrotic mediators, suggesting they may pathogenically activate alveolar fibroblasts. Why these aberrant transitional AT2s arise, why they fail to differentiate to AT1s, and how they contribute to fibrosis is not understood. We have identified that the aberrant transitional AT2s are enriched in the PKR-like ER kinase (PERK) cell stress pathway and its downstream Integrated Stress Response (ISR). How PERK-ISR signaling relates to the emergence and persistence of the aberrant AT2s and to the epithelial contribution to fibrogenesis is also not known. In this proposal we will answer these questions by utilizing complimentary in vivo models of lung fibrosis with a human model system. For our murine models, we use mice that express a human PF-associated mutation in the AT2 restricted Surfactant Protein C gene (SftpcMut mice) where intrinsic AT2 stress pathways initiate spontaneous lung fibrosis without a “second hit” lung injury and the established Bleomycin (Bleo) fibrosis model of extrinsic AT2 activation and lung fibrosis. Our human system is an induced pluripotent stem cell (iPSC)-based AT2 (iAT2s) model from a PF patient harboring a SFTPCMut. In both murine models we have found that AT2s are enriched in PERK-ISR signaling as they enter and persist in the aberrant transitional state. We have developed a strategy to sort the most fibrogenic aberrant transitional AT2s from the mouse lung and found that in ex vivo co-culture systems these cells induce a fibrotic response in alveolar fibroblasts. We also discovered that SFTPCMut iAT2s develop an aberrant transitional gene signature and are enriched in PERK-ISR signaling and profibrotic mediators. We will now test our hypothesis that PERK-ISR signaling promotes AT2s to enter and restrains their exit from an aberrant transitional state that contributes to lung fibrosis by pathogenically activating alveolar fibroblasts. We will [Specific Aim 1] determine how aberrant transitional epithelial cells directly contribute to fibrosis and test our hypothesis that an altered alveolar niche signaling circuit initiated by the aberrant transitional epithelial cells promotes fibrotic tissue remodeling. We will [Specific Aim 2] define how PERK-ISR signaling impacts epithelial differentiation and promotes fibrosis and test our hypothesis that PERK-ISR signaling contributes to AT2 persistence in the aberrant transitional state. When completed these studies will fill critical knowledge gaps in PF biology by defining the direct contribution of the aberrant transitional cell to fibrosis and the mechanistic impact of the targetable PERK-ISR pathway in PF pathogenesis. Project Number: 5R01HL172975-02 | Fiscal Year: 2026 | NIH Institute/Center: National Heart Lung and Blood Institute (NHLBI) | Principal Investigator: Jeremy Katzen | Institution: UNIVERSITY OF PENNSYLVANIA, PHILADELPHIA, PA | Award Amount: $667,795 | Activity Code: R01 | Study Section: Pulmonary Injury, Repair, and Remodeling Study Section (PIRR)[PIRR] View on NIH RePORTER: https://reporter.nih.gov/project-details/5R01HL17297502