Mechanical ventilation augments bleomycin-induced epithelial- mesenchymal transition through the Src pathway

Mechanical ventilation used in patients with acute respiratory distress syndrome (ARDS) can damage pulmonary epithelial cells by producing inflammatory cytokines and depositing excess collagen. Src participates in plasminogen activator inhibitor-1 (PAI-1) and transforming growth factor-beta 1(TGF-beta 1) production during the fibroproliferative phase of ARDS, which involves a process of epithelial-mesenchymal transition (EMT). The mechanisms regulating interactions between mechanical ventilation and EMT are unclear. We hypothesized that EMT induced by high-tidal volume (V-T) mechanical stretch-augmented lung inflammation occurs through upregulation of the Src pathway. Five days after administering bleomycin to simulate acute lung injury (ALI), male C57BL/6 mice, either wild-type or Src-deficient, aged 3 months, weighing between 25 and 30 g, were exposed to low-V-T (6 ml/kg) or high-V-T (30 ml/kg) mechanical ventilation with room air for 1-5 h. Nonventilated mice were used as control subjects. We observed that high-V-T mechanical ventilation increased microvascular permeability, PAI-1 and TGF-beta 1 protein levels, Masson's trichrome staining, extracellular collagen levels, collagen gene expression, fibroblast accumulation, positive staining of alpha-smooth muscle actin and type I collagen, activation of Src signaling and epithelial apoptotic cell death in wild-type mice (P<0.05). Decreased staining of the epithelial marker, Zonula occludents-1, was also observed. Mechanical stretch-augmented EMT and epithelial apoptosis were attenuated in Src-deficient mice and pharmacological inhibition of Src activity by PP2 (P<0.05). Our data suggest that high-V-T mechanical ventilation-augmented EMT after bleomycin-induced ALI partially depends on the Src pathway.