• Roxana Wasnick, Martina Korfei, Katarzyna Piskulak, Ingrid Henneke, Jochen Wilhelm, Poornima Mahavadi, Ruth Charlotte Dartsch, von der BeckDanielD0000-0003-1946-9303University of Giessen and Marburg Lung Center (UGMLC), member of the German Center for Lung Research (DZL), 35392 Giessen, Germany., Miriam Koch, Irina Shalashova, Astrid Weiss, Oleksiy Klymenko, Ingolf Askevold, Ludger Fink, Heiko Witt, Holger Hackstein, Elie El Agha, Saverio Bellusci, Walter Klepetko, Melanie Königshoff, Oliver Eickelberg, Ralph Theo Schermuly, Thomas Braun, Werner Seeger, Clemens Ruppert, and Andreas Guenther.
• University of Giessen and Marburg Lung Center (UGMLC), member of the German Center for Lung Research (DZL), 35392 Giessen, Germany.
• Am. J. Respir. Crit. Care Med. 2023 Feb 1; 207 (3): 283299283-299.

AbstractRationale: Although type II alveolar epithelial cells (AEC2s) are chronically injured in idiopathic pulmonary fibrosis (IPF), they contribute to epithelial regeneration in IPF. Objectives: We hypothesized that Notch signaling may contribute to AEC2 proliferation, dedifferentiation characterized by loss of surfactant processing machinery, and lung fibrosis in IPF. Methods: We applied microarray analysis, kinome profiling, flow cytometry, immunofluorescence analysis, western blotting, quantitative PCR, and proliferation and surface activity analysis to study epithelial differentiation, proliferation, and matrix deposition in vitro (AEC2 lines, primary murine/human AEC2s), ex vivo (human IPF-derived precision-cut lung slices), and in vivo (bleomycin and pepstatin application, Notch1 [Notch receptor 1] intracellular domain overexpression). Measurements and Main Results: We document here extensive SP-B and -C (surfactant protein-B and -C) processing defects in IPF AEC2s, due to loss of Napsin A, resulting in increased intra-alveolar surface tension and alveolar collapse and induction of endoplasmic reticulum stress in AEC2s. In vivo pharmacological inhibition of Napsin A results in the development of AEC2 injury and overt lung fibrosis. We also demonstrate that Notch1 signaling is already activated early in IPF and determines AEC2 fate by inhibiting differentiation (reduced lamellar body compartment, reduced capacity to process hydrophobic SP) and by causing increased epithelial proliferation and development of lung fibrosis, putatively via altered JAK (Janus kinase)/Stat (signal transducer and activator of transcription) signaling in AEC2s. Conversely, inhibition of Notch signaling in IPF-derived precision-cut lung slices improved the surfactant processing capacity of AEC2s and reversed fibrosis. Conclusions: Notch1 is a central regulator of AEC2 fate in IPF. It induces alveolar epithelial proliferation and loss of Napsin A and of surfactant proprotein processing, and it contributes to fibroproliferation.

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