Absence of Thy-1 results in TGF-β induced MMP-9 expression and confers a profibrotic phenotype to human lung fibroblasts

Fibroblasts differ in a variety of phenotypic features, including the expression of Thy-1 a glycophosphatidylinositol-linked glycoprotein. Fibroblasts in idiopathic pulmonary fibrosis (IPF) are Thy-1 negative, whereas most fibroblasts from normal lungs are Thy-1 positive. However, the functional consequences of the absence of Thy-1 are not fully understood. We analyzed the expression of Thy-1 in several primary fibroblasts lines derived from IPF, hypersensitivity pneumonitis (HP), and normal human lungs. We found that a high proportion, independently of their origin, expressed Thy-1 in vitro. We identified a primary culture of HP fibroblasts, which did not express Thy-1, and compared several functional activities between Thy-1 (-) and Thy-1 (+) fibroblasts. Thy-1 (-) fibroblasts were smaller (length: 41.3 +/- 20.8 mu versus 83.1 +/- 40 mu), showed increased proliferative capacity and enhanced PDGF-induced transmigration through collagen I (59.9% versus 42.2% over control under basal conditions, P<0.01). Likewise, Thy-1 (-) fibroblasts either spontaneously or after TGF-beta stimulation demonstrated stronger contraction of collagen matrices (eg, 0.17 +/- 0.03 versus 0.6 +/- 0.05 cm(2) after TGF-beta stimulation at 24 h; P<0.01). Thy-1 (-) lung fibroblasts stimulated with TGF-beta 1 expressed MMP-9, an enzyme that is usually not produced by lung fibroblasts. TGF beta-induced MMP-9 expression was reversible upon re-expression of Thy-1 after transfection with full-length Thy-1. beta-glycan, a TGF-beta receptor antagonist abolished MMP-9 expression. TGF-beta 1-induced MMP-9 in Thy-1 (-) fibroblasts depended on the activation of ERK1/2 signaling pathway. Finally, we demonstrated that fibroblasts from IPF fibroblastic foci, which do not express Thy-1 exhibit strong staining for immunoreactive MMP-9 protein in vivo. These findings indicate that loss of Thy-1 in human lung fibroblasts induces a fibrogenic phenotype. Laboratory Investigation (2011) 91, 1206-1218; doi:10.1038/labinvest.2011.80; published online 16 May 2011