Transmembrane protease, serine 4 (TMPRSS4) is upregulated in IPF lungs and increases the fibrotic response in bleomycin-induced lung injury

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive lung disease characterized by epithelial cell activation, expansion of the fibroblast population and excessive extracellular matrix accumulation. The mechanisms are incompletely understood but evidence indicates that the deregulation of several proteases contributes to its pathogenesis. Transmembrane protease serine 4 (TMPRSS4) is a novel type II transmembrane serine protease that may promote migration and facilitate epithelial to mesenchymal transition (EMT), two critical processes in the pathogenesis of IPF. Thus, we hypothesized that over-expression of TMPRSS4 in the lung could promote the initiation and/or progression of IPF. In this study we first evaluated the expression and localization of TMPRSS4 in IPF lungs by real time PCR, western blot and immunohistochemistry. Then we examined the lung fibrotic response in wild-type and TMPRSS4 deficient mice using the bleomycin-induced lung injury model. We found that this protease is upregulated in IPF lungs, where was primarily expressed by epithelial and mast cells. Paralleling the findings in vivo, TMPRSS4 was expressed by alveolar and bronchial epithelial cells in vitro and unexpectedly, provoked an increase of E-cadherin. No expression was observed in normal human or IPF lung fibroblasts. The lung fibrotic response evaluated at 28 days after bleomycin injury was markedly attenuated in the haplodeficient and deficient TMPRSS4 mice. By morphology, a significant reduction of the fibrotic index was observed in KO and heterozygous mice which was confirmed by measurement of collagen content (hydroxyproline: WT: 164±21.1 μg/lung versus TMPRSS4 haploinsufficient: 110.2±14.3 μg/lung and TMPRSS4 deficient mice: 114.1±24.2 μg/lung (p<0.01). As in IPF, TMPRSS4 was also expressed in epithelial and mast cells. These findings indicate that TMPRSS4 is upregulated in IPF lungs and that may have a profibrotic role.