Fibrinolysis in LPS-induced chronic airway disease

To examine the role of the fibrinolytic system in LPS-induced airway disease, we compared the effect of a chronic LPS challenge in plasminogen activator inhibitor-deficient (C57BL/6J^PAI-1-/-) mice and wild-type (WT) C57BL/6J mice. Physiological and biological assessments were performed, immediately after, and 4 wk after an 8-wk exposure to LPS or saline. Immediately after the LPS exposure, WT mice had increased estimates of airway reactivity to methacholine compared with C57BL/6J^PAI-1-/- mice; however, airway inflammation was similar in both LPS-exposed groups. Significant increases in both active transforming growth factor (TGF)-β1 and active matrix metalloproteinase (MMP)-9 was detected after LPS exposure in WT but not C57BL/6J^PAI-1-/- mice. C57BL/6J^PAI-1-/- mice showed significantly less TGF-β1 in the lavage and higher MMP-9 in the lung tissue than WT mice at the end of exposure and 4 wk later. After LPS exposure, both WT and C57BL/6J^PAI-1-/- mice had substantial expansion of the subepithelial area of the medium [diameter (d) = 90-129 μm]- and large (d > 129 μm)-size airways when compared with saline-exposed mice. Subepithelial fibrin deposition was prevalent in WT mice but diminished in C57BL/6J^PAI-1-/-. PAI-1 expression by nonciliated bronchial epithelial cells was enhanced in LPS-exposed WT mice compared with the saline-exposed group. Four weeks after LPS inhalation, airway hyperreactivity and the expansion of the subepithelial area in the medium and large airways persisted in WT but not C57BL/6J^PAI-1-/- mice. We conclude that an active fibrinolytic system can substantially alter the development and resolution of the postinflammatory airway remodeling observed after chronic LPS inhalation.