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

Abstract

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-beta1 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-beta1. In this study, we examined the effects of FGF-1 on TGF-beta1-induced EMT. A549 and RLE-6TN (human and rat) alveolar epithelial-like cell lines were stimulated with TGF-beta1 for 72 h, and then, in the presence of TGF-beta1, were cultured with FGF-1 plus heparin for an additional 48 h. After TGF-beta1 treatment, epithelial cells acquired a spindle-like mesenchymal phenotype with a substantial reduction of E-cadherin and cytokeratins and concurrent induction of alpha-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-beta1 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-beta1-induced EMT is reversed by FGF-1 and suggest therapeutic approaches to target this process in IPF.

Transforming Growth Factor–β–Induced Differentiation of Airway Smooth Muscle Cells Is Inhibited by Fibroblast Growth Factor–2

“…Furthermore, TGFb-stimulated increases in IL-6 concentrations, which are dependent on Smad2/3 signaling (37), were also not attenuated by FGF-2. In contrast to our observations in ASM cells, FGF-2 (or FGF-1) inhibits TGF-b-stimulated Smad 2/3 phosphorylation in aortic interstitial valvular cells (38) and in alveolar epithelial-like cell lines (20). However, TGF-b-stimulated Smad2/3 phosphorylation in nucleus pulposus cells is not attenuated by FGF-2 (39).…”

“…Similarly, acidic FGF (FGF-1) inhibits the differentiation (and transdifferentiation) of lung epithelial cells and fibroblasts into myofibroblasts (20,21). Although FGF-2 is a potent mitogen of ASM cells (16), the lack of antagonism of TGF-b-stimulated contractile protein gene expression and organization by the powerful mitogens thrombin and FCS is not consistent with the idea that the antagonism of TGF-b's effects is secondary to mitogenic signaling.…”

“…FGF-2 may prevent ASM cell differentiation into a more contractile phenotype (maturation), as has been reported for corneal fibroblasts (18) and microvascular pericytes (19). Acidic fibroblast growth factor (FGF-1) also inhibits the TGF-b-stimulated differentiation (or transdifferentiation) of lung epithelial cells and fibroblasts (20,21). We present evidence of the antagonistic effects of FGF-2 on ASM cell differentiation into a more contractile phenotype in response to TGF-b, and show that this inhibitory effect is dissociated from the mitogenic actions of FGF-2.…”

Inhibition of α-SMA by the Ectodomain of FGFR2c Attenuates Lung Fibrosis

“…Furthermore, TGF-β and FGF-2 might cooperate with each other and regulate the EMT of various types of cells in microenvironments during cancer progression (18,37). However, there have been contrary reports, including results that suggest that TGF-β1-induced EMT is reversed by FGF-1 in IPF (19).…”

“…Nevertheless, some studies have led to a different conclusion. For example, FGF-1 was found to display antifibrotic functions by downregulating collagen expression and antagonizing some of the profibrotic effects of TGF-β (7,16,19).…”