Characterization of a flexible AAV-DTR/DT mouse model of acute epithelial lung injury

Background & aim: Recurring epithelial injury and aberrant repair are considered as a major driver of idiopathic pulmonary fibrosis (IPF) leading to chronic inflammation, fibroblast activation and ultimately to scarring and stiffening of the lung. As decline of lung function is the first reported symptom by IPF patients and occurs once fibrosis is firmly established, animal models are required to study early disease-driving mechanisms. Methods: We developed a novel and flexible mouse model of acute epithelial injury based on adeno-associated virus (AAV) variant 6.2 mediated expression of the human diphtheria toxin receptor (DTR). Following intratracheal administration of diphtheria toxin (DT), a cell-specific death of bronchial epithelial and alveolar epithelial type II cells can be observed. Results: Detailed characterization of the AAV-DTR/DT mouse model revealed increasing cell numbers in bronchoalveolar lavage (BAL; macrophages, neutrophils, and atypical cells) and elevation of apoptotic cells and infiltrated leukocytes in lung tissue, which were dependent of viral genome load and DT dose. Cytokine levels in BAL fluid showed different patterns dependent of viral genome load with IFNγ, TNFα, and IP-10 increasing and IL-5 and IL-6 decreasing, while lung function was not affected. Additionally, laser-capture microdissection-based proteomics of bronchial and alveolar epithelium showed upregulated immune and inflammatory response in all epithelial cell regions and extracellular matrix deposition in infiltrated alveoli, while proteins involved in pulmonary surfactant synthesis, alveolar fluid clearance and alveolar-capillary barrier were downregulated in the parenchyma. Conclusion: Our novel AAV-DTR/DT model resembles specific aspects of pulmonary diseases like IPF and acute respiratory distress syndrome.