MMP-12 Inhibits Inverse Eosinophilic Inflammation-Mediated Bronchial Fibrosis in Murine Models of Pulmonary Airway Obstruction

Matrix metalloproteinases (MMPs) are a major group of proteases known to regulate the turnover of the extracellular matrix (ECM). We observed that induced MMP-12 promotes eosinophilic inflammation-related epithelial cell mesenchymal transition (EMT), bronchial fibrosis, and airway obstruction in an allergen-exposed mouse model of chronic airway diseases in allergen-exposed mice and in airway-specific CC10-IL-13-overexpressed mice. Our histological analysis showed that the parabronchial and perivascular accumulation of eosinophils, fibroblasts, and collagen is significantly decreased in MMP-12^−/− allergen-exposed mice and airway-specific rtTA-MMP-12^−/−CC-10-IL-13-overexpressed mice compared to allergen-exposed wild-type mice and rtTA-CC10-IL-13-overexpressed mice. ELISA and Western blot analyses validated these histological findings, demonstrating that EMT and profibrotic protein levels were significantly decreased in allergen-challenged MMP-12^−/− mice and rtTA-MMP-12^−/−CC10-IL-13-overexpressed mice in comparison to the allergen-exposed wild-type mice and rtTA-CC10-IL-13-overexpressed mice. In addition, we also observed that allergen-challenged MMP-12^−/− mice have improved resistance and compliance compared to allergen-challenged wild-type mice. Most importantly, we show that treatment with MMP-12 inhibitors (PF-00356231 and MMP408) restricts the induction and progression of bronchial fibrosis and airway restrictions in allergen-exposed mice and airway-specific rtTA-CC10-IL-13 mice compared to the respective control mice. Taken together, the novelty of these findings lie in the fact that induced MMP-12 regulates eosinophilic inflammation-induced bronchial fibrosis and associated airway restriction, which may be reduced by treatment with MMP-12 inhibitors.