Transforming growth factor β1 increases fibronectin deposition through integrin receptor α5β1 on human airway smooth muscle

Background: Integrin receptors signal to and from the extracellular matrix. Altered expression of the integrin receptors, such as the fibronectin receptor alpha(5)beta(1), might be implicated in extracellular matrix accumulation in airway remodeling in asthma. Objective: We examined the effect of TGF-beta stimulation on integrin alpha(5)beta(1), expression and the role of alpha(5)beta(1), in fibronectin deposition and proliferation. Methods: Integrin subunit alpha(5) and PI expression in airway smooth muscle (ASM) from subjects with and without asthma was examined by means of PCR and flow cytometry. The effect of blocking alpha(5)beta(1) receptor on ASM proliferation to FBS was assessed by using the 3-(4,5-dimethylthiazol-2-yl)-2,5diphenyltetrazolium assay. Cells were stimulated with TGF-beta in the presence or absence of extracellular signal-regulated kinase, phosphoinositide-3 kinase, or p38 inhibitors and antibodies to the alpha(5) and beta(1) subunits. The effect of blocking alpha(5)beta(1) receptor on fibronectin deposition was assessed by means of immunocytochemistry. Results: Proliferation of ASM cells from asthmatic and nonasthmatic subjects was inhibited by blocking the fibronectin receptor subunit alpha(5)beta(1). TGF-beta-induced alpha(5)beta(1) was extracellular signal-regulated kinase dependent but not phosphoinositide-3 kinase or p38 dependent. Blockade of the 041 receptor inhibited TGF-beta-induced fibronectin matrix deposition. Conclusion: Through its increased expression by the profibrotic stimulus TGF-beta, integrin alpha(5)beta(1) might be important in regulating fibronectin deposition.