Collagen remodelling by airway smooth muscle is resistant to steroids and ß2-agonists.

Bi-directional interactions between airway smooth muscle (ASM) and the altered extracellular matrix (ECM) may influence airway wall remodelling and ASM function in asthma. We have investigated the capacity of cultured human ASM to reorganise the structure of three-dimensional collagen gels and the effects of endothelin (ET)-1 and agents used to treat asthma. Human ASM cells were cast in type I collagen gels. Reductions in gel area over 72 h were determined in the absence and presence of ET-1 and potential inhibitors, steroids and ß2-adrenoceptor agonists. Changes in gel wet weights and hydroxyproline content were measured and ASM gel morphology was examined by scanning electron microscopy. Cell density-dependent reductions in gel area were augmented by ET-1, mediated via ET(A) receptors. This process was not associated with ASM contraction or proliferation, but was consistent with ASM tractional remodelling and migration leading to collagen condensation rather than collagen degradation within gels. The collagen remodelling by ASM was unaffected by salbutamol and/or budesonide. This study demonstrates an additional potential role for ASM in ECM regulation and dysregulation in airways disease that is resistant to steroids and ß2-adrenoceptor agonists. Therapy-resistant collagen condensation within ASM bundles may facilitate ECM-ASM interactions and contribute to increased internal airways resistance.

Collagen impairs glucocorticoid actions in airway smooth muscle through integrin signalling.

BACKGROUND AND PURPOSE: Airway wall remodelling in asthma is characterised by a number of structural changes, including an increase in the volume of airway smooth muscle (ASM), and the abundance of the extracellular matrix (ECM) protein, collagen, is increased. We have investigated the mechanism of collagen-induced glucocorticoid resistance of proliferation, and migration of ASM. EXPERIMENTAL APPROACH: ASM cultured from human airways has been seeded on to either type I monomeric collagen or a laminin pentapeptide, YIGSR. The role of alpha2beta1 integrin in the collagen-induced glucocorticoid resistance was investigated using a function blocking monoclonal antibody. KEY RESULTS: Culture of ASM on collagen I, but not laminin, led to a greater proliferative response that was insensitive to regulation by dexamethasone (100 nM). The anti-migratory effects of the glucocorticoid, fluticasone propionate (1 nM) were also impaired by contact of ASM with collagen. The impaired anti-mitogenic action of dexamethasone was associated with a failure to reduce the levels of the rate-limiting cell cycle regulatory protein, cyclin D1. When signalling through the alpha2beta1 integrin was reduced, dexamethasone-mediated reductions in proliferation and cyclin D1 levels were restored. CONCLUSIONS AND IMPLICATIONS: In the collagen-rich microenvironment of the inflamed and fibrotic asthmatic airway, integrin/ECM interactions may contribute to glucocorticoid resistance.

The PPARgamma ligand, rosiglitazone, reduces airways hyperresponsiveness in a murine model of allergen-induced inflammation.

There is considerable interest in the role of peroxisome proliferator activated receptors (PPARs) as ligand-activated transcription factors in the airways. This study examines the effects of a potent synthetic PPARgamma ligand, rosiglitazone (RG), in a murine model of allergen-induced inflammation, to explore its potential regulation of airways inflammation, structure and function. C57BL/6 mice were sensitised with ovalbumin (OVA, 50 microg i.p., days 0, 12) and challenged with aerosolized OVA (1% w v(-1), 30 min day(-1)) for 7 days (days 20-26). Mice were treated with RG (5 mg kg(-1) i.p.) or vehicle during the challenge period. The OVA challenge induced increases in leukocyte number and MMP-2 activity in bronchoalveolar lavage fluid and in goblet cell number in lung tissue obtained on Day 27. RG failed to inhibit inflammatory cell infiltration, MMP-2 activity or goblet cell hyperplasia. Respiratory resistance in response to methacholine (MCh i.v.) was greater in OVA-challenged mice than saline-challenged mice and this airways hyperresponsiveness (AHR) was reduced by RG. However, RG did not affect MCh-induced contraction in isolated guinea-pig tracheal rings, nor did it influence the airway obstruction induced by MCh in saline-challenged mice, so a direct effect on airway obstruction is unlikely. These data suggest that RG modulates AHR in this model, by a mechanism that is also potentially independent of an anti-inflammatory action.