Notch1 Induces Defective Epithelial Surfactant Processing and Pulmonary Fibrosis

Science and Research

RATIONALE: Although alveolar epithelial cells type II (AEC2) are chronically injured in Idiopathic Pulmonary Fibrosis (IPF), they contribute to epithelial regeneration in IPF. OBJECTIVES: We hypothezised that Notch signaling may contribute to AEC2 proliferation, de-differentiation 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, qPCR, proliferation- and surface activity- analysis to study epithelial differentiation, proliferation and matrix deposition in vitro (AEC2 cell lines, primary murine/human AEC2), ex vivo (human IPF-derived precision cut lung slices; IPF-PCLS) and in vivo (bleomycin-, pepstatin-application, Notch1 ICD overexpression) Measurements and Main Results: We document here extensive surfactant protein (SP)-B/C processing defects in IPF AEC2, due to loss of Napsin A, resulting in increased intra-alveolar surface tension and alveolar collapse and induction of ER-stress in AEC2. 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/Stat signaling in AEC2. Conversely, inhibition of Notch signaling in IPF-PCLS improved surfactant processing capacity of AEC2s and reversed fibrosis. CONCLUSION: Notch1 is a central regulator of AEC2 fate in IPF. It induces alveolar epithelial proliferation, loss of Napsin A and of surfactant proprotein processing and it contributes to fibroproliferation.