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

Abstract

In asthma, basic fibroblast growth factor (FGF-2) plays an important (patho)physiological role. This study examines the effects of FGF-2 on the transforming growth factor-b (TGF-b)-stimulated differentiation of airway smooth muscle (ASM) cells in vitro. The differentiation of human ASM cells after incubation with TGF-b (100 pM) and/ or FGF-2 (300 pM) for 48 hours was assessed by increases in contractile protein expression, actin-cytoskeleton reorganization, enhancements in cell stiffness, and collagen remodeling. FGF-2 inhibited TGF-b-stimulated increases in transgelin (SM22) and calponin gene expression (n ¼ 15, P , 0.01) in an extracellular signal-regulated kinase 1/2 (ERK1/2) signal transduction-dependent manner. The abundance of ordered a-smooth muscle actin (a-SMA) filaments formed in the presence of TGF-b were also reduced by FGF-2, as was the ratio of F-actin to G-actin (n ¼ 8, P , 0.01). Furthermore, FGF-2 attenuated TGF-b-stimulated increases in ASM cell stiffness and the ASM-mediated contraction of lattices, composed of collagen fibrils (n ¼ 5, P , 0.01). However, the TGF-b-stimulated production of IL-6 was not influenced by FGF-2 (n ¼ 4, P . 0.05), suggesting that FGF-2 antagonism is selective for the regulation of ASM cell contractile protein expression, organization, and function. Another mitogen, thrombin (0.3 U ml 21), exerted no effect on TGF-b-regulated contractile protein expression (n ¼ 8, P . 0.05), a-SMA organization, or the ratio of F-actin to G-actin (n ¼ 4, P . 0.05), suggesting that the inhibitory effect of FGF-2 is dissociated from its mitogenic actions. The addition of FGF-2, 24 hours after TGF-b treatment, still reduced contractile protein expression, even when the TGF-b-receptor kinase inhibitor, SB431542 (10 mM), was added 1 hour before FGF-2. We conclude that the ASM cell differentiation promoted by TGF-b is antagonized by FGF-2. A better understanding of the mechanism of action for FGF-2 is necessary to develop a strategy for therapeutic exploitation in the treatment of asthma.Keywords: airway wall remodeling; a-smooth muscle actin; asthma; cytoskeleton; transgelin Airway wall remodeling (AWR) contributes to airway dysfunction in asthma. AWR comprises an array of persistent tissue structural changes that are thought to occur through a process of injury and dysregulated repair, linked to chronic airway inflammation. Features of AWR include the increased deposition of extracellular matrix (ECM), airway smooth muscle (ASM) hyperplasia and hypertrophy, mucous cell metaplasia, and angiogenesis (1). The deposition of collagens I and III in the subepithelial layer and within smooth muscle bundles by airway mesenchyma increases airway wall thickness and reduces airway wall distensibility (2, 3). An effective anti-remodeling treatment is expected to reduce airway reactivity and symptoms in asthma (4, 5).Transforming growth factor-b (TGF-b) is an important mediator of AWR in asthma. TGF-b stimulates ASM cells to differentiate into a more contractile and hypertrophic phenotype (6, 7). TGF-b ...

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“…TGF-b1 increases contractile protein expression in HASM, fibroblasts, and myofibroblasts. TGF-b1 induces the expression of SM22, calponin, a-SMA, MLCK, and Ca 21 pathway proteins in HASM cells, subsequently mediating enhancements in cell stiffness, actin-cytoskeleton reorganization, and contractility (87,104,105). In addition, mast cell-derived TGF-b1 may modulate the phenotype of HASM cells, promoting their differentiation into a more contractile phenotype and subsequently enhancing agonist-induced contraction (106).…”

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