FGF-1 reverts epithelial-mesenchymal transition induced by TGF-β1 through MAPK/ERK kinase pathway

Idiopathic pulmonary fibrosis (IPF) is a progressive and lethal lung disease characterized by the expansion of the fibroblast/myofibroblast population and aberrant remodeling. However, the origin of mesenchymal cells in this disorder is still under debate. Recent evidence indicates that epithelial-mesenchymal transition (EMT) induced primarily by TGF-β1 plays an important role; however, studies regarding the opposite process, mesenchymal-epithelial transition, are scanty. We have previously shown that fibroblast growth factor-1 (FGF-1) inhibits several profibrogenic effects of TGF-β1. In this study, we examined the effects of FGF-1 on TGF-β1-induced EMT. A549 and RLE-6TN (human and rat) alveolar epithelial-like cell lines were stimulated with TGF-β1 for 72 h, and then, in the presence of TGF-β1, were cultured with FGF-1 plus heparin for an additional 48 h. After TGF-β1 treatment, epithelial cells acquired a spindle-like mesenchymal phenotype with a substantial reduction of E-cadherin and cytokeratins and concurrent induction of α-smooth muscle actin measured by real-time PCR, Western blotting, and immunocytochemistry. FGF-1 plus heparin reversed these morphological changes and returned the epithelial and mesenchymal markers to control levels. Signaling pathways analyzed by selective pharmacological inhibitors showed that TGF-β1 induces EMT through Smad pathway, while reversion by FGF-1 occurs through MAPK/ERK kinase pathway, resulting in ERK-1 phosphorylation and Smad2 dephosphorylation. These findings indicate that TGF-β1-induced EMT is reversed by FGF-1 and suggest therapeutic approaches to target this process in IPF.