The laminin b 1-competing peptide YIGSR induces a hypercontractile , hypoproliferative airway smooth muscle phenotype in an animal model of allergic asthma

Background: Fibroproliferative airway remodelling, including increased airway smooth muscle (ASM) mass and contractility, contributes to airway hyperresponsiveness in asthma. In vitro studies have shown that maturation of ASM cells to a (hyper)contractile phenotype is dependent on laminin, which can be inhibited by the laminincompeting peptide Tyr-Ile-Gly-Ser-Arg (YIGSR). The role of laminins in ASM remodelling in chronic asthma in vivo, however, has not yet been established. Methods: Using an established guinea pig model of allergic asthma, we investigated the effects of topical treatment of the airways with YIGSR on features of airway remodelling induced by repeated allergen challenge, including ASM hyperplasia and hypercontractility, inflammation and fibrosis. Human ASM cells were used to investigate the direct effects of YIGSR on ASM proliferation in vitro. Results: Topical administration of YIGSR attenuated allergen-induced ASM hyperplasia and pulmonary expression of the proliferative marker proliferating cell nuclear antigen (PCNA). Treatment with YIGSR also increased both the expression of sm-MHC and ASM contractility in salineand allergen-challenged animals; this suggests that treatment with the laminin-competing peptide YIGSR mimics rather than inhibits laminin function in vivo. In addition, treatment with YIGSR increased allergen-induced fibrosis and submucosal eosinophilia. Immobilized YIGSR concentration-dependently reduced PDGF-induced proliferation of cultured ASM to a similar extent as laminincoated culture plates. Notably, the effects of both immobilized YIGSR and laminin were antagonized by soluble YIGSR. Conclusion: These results indicate that the laminin-competing peptide YIGSR promotes a contractile, hypoproliferative ASM phenotype in vivo, an effect that appears to be linked to the microenvironment in which the cells are exposed to the peptide. Background Airway inflammation, airway obstructive reactions and development of transient airway hyperresponsiveness are primary features of acute asthma [1,2]. In addition, structural changes in the airway wall are thought to contribute to a decline of lung function and development of persistent airway hyperresponsiveness in chronic asthma [1,3]. These structural changes include goblet cell metaplasia and mucous gland hyperplasia, increased vascularity, altered deposition of the extracellular matrix (ECM) proteins and accumulation of contractile airway smooth muscle (ASM) cells [1,4-7]. ASM cells can contribute to airway remodelling as they retain the ability for reversible phenotypic switching, enabling them to exhibit variable contractile, proliferative, migratory and synthetic states [8,9]. In vitro, modulation to a proliferative phenotype results from exposure of ASM cells to mitogenic stimuli, leading to increased proliferative activity and decreased contractile function [10-12]. * Correspondence: b.g. j.dekkers@rug.nl Department of Molecular Pharmacology, University of Groningen, Groningen, Netherlands Full list of author information is available at the end of the article Dekkers et al. Respiratory Research 2010, 11:170 http://respiratory-research.com/content/11/1/170 © 2010 Dekkers et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Removal of growth factors, for example by serum deprivation in the presence of insulin, results in maturation of the cells to a contractile phenotype, characterized by increased expression of contractile protein markers, increased contractile function and increased expression of laminin a2, b1 and g1 chains [8,13-15]. Laminins are basement membrane ECM components composed of heterotrimers of a, b and g chains. Five laminin a-, three band three g-chains have been identified in mammals, which form at least fifteen different laminin isoforms [16]. Various laminin chains are expressed in the lung and expression appears to be tissueand developmental stage-dependent [17]. In adult asthmatics, expression of laminin a2 and b2 chains in the airways is increased [18,19]. In addition, asthmatics with compromised epithelial integrity show increased laminin g2 chain expression in the airways [19]. Laminins appear to be essential for lung development and are important determinants of ASM function. Laminin a1 and a2 chains are required for pulmonary branching and differentiation of naïve mesenchymal cells into ASM [16,20,21]. Primary ASM cells cultured on laminin-111 (laminin-1) are retained in a hypoproliferative phenotype, associated with high expression levels of contractile proteins [22]. This is of functional relevance as the induction of a hypocontractile ASM phenotype by PDGF can be prevented by co-incubation with laminin-111 [11]. Increased expression of endogenous laminin-211 (laminin-2) is essential for ASM cell maturation [14], and studies from our laboratory show that laminin-211 is essential for the induction of a hypercontractile, hypoproliferative ASM phenotype by prolonged insulin exposure [15]. Recently, in an animal model of chronic allergic asthma we showed that ASM remodelling can be inhibited by the integrin-blocking peptide Arg-Gly-Asp-Ser (RGDS) [23], which contains the RGD-binding motif present in ECM proteins like fibronectin, collagens and laminins [24,25]. The specific role of laminins in ASM remodelling in vivo, however, remains to be determined. Therefore, using a guinea pig model of chronic asthma, we explored the role of laminins in ASM remodelling in vivo, by treating the animals with the specific soluble laminin-competing peptide Tyr-Ile-Gly-Ser-Arg (YIGSR), a binding motif present in the b1 chain of laminins [26].