Stimulus‐dependent glucocorticoid‐resistance of GM‐CSF production in human cultured airway smooth muscle

Abstract

1 For a subpopulation of asthmatics, symptoms persist even with high doses of glucocorticoids. Glucocorticoids reduce the levels of the proinflammatory and fibrogenic cytokine, granulocytemacrophage colony-stimulating factor (GM-CSF) produced by human cultured airway smooth muscle (ASM). We have contrasted the effects of a synthetic glucocorticoid, dexamethasone, on thrombin-and IL-1a-stimulated GM-CSF production in human ASM cells. 2 Although IL-1a stimulated three-fold higher levels of GM-CSF mRNA and protein compared to thrombin, dexamethasone concentration-dependently reduced IL-1a-stimulated GM-CSF more potently and to a greater extent than the response to thrombin. This pattern of glucocorticoid regulation was also observed at the GM-CSF mRNA level and was reproduced with other glucocorticoids such as fluticasone propionate. 3 IL-1a and thrombin stimulated NF-kB-dependent luciferase expression equally. Dexamethasone treatment reduced luciferase expression stimulated by both IL-1a and thrombin. 4 The GM-CSF mRNA half life was markedly prolonged by IL-1a compared to thrombin. This IL-1a-induced GM-CSF mRNA stability was prevented by either dexamethasone or the p38 MAPK inhibitor, SB203580, neither of which influenced GM-CSF mRNA stability in thrombin-treated cells. Dexamethasone inhibited p38 MAPK phosphorylation in IL-1a-stimulated ASM, whereas thrombin does not stimulate p38 MAPK phosphorylation. 5 These data suggest that the mechanism underlying the greater potency and efficacy of glucocorticoids in reducing GM-CSF synthesis stimulated by IL-1a depends on inhibition of the involvement of p38 MAPK -induced increases in GM-CSF message stability.

Airway smooth muscle dynamics: a common pathway of airway obstruction in asthma

“…However, there are differences amongst mitogens in their susceptibility to regulation, with thrombin responses appearing to be more readily regulated than those to stronger mitogens, such as FGF-b. Although stimulus-dependency of inhibition by glucocorticoids is also observed for cytokine production, this response is more readily regulated when thrombin, rather than IL-1a, is the stimulus [110].…”

“…The working hypothesis is that this is due to a reduction in airway inflammation [314], which indirectly changes the stimulation and the micro-environment of ASM, leading to reduced airway narrowing at a given dose of inhaled agonist. However, smooth muscle itself responds to steroids by changing its expression of a host of genes that are involved in cell adhesion, proliferation, ECM formation, cell signalling, cytokine production and signal-transduction molecules regulating smooth muscle responsiveness [315][316][317][318]. It can be postulated that this also influences the structure of the cytoskeleton and the arrangement of contractile proteins, and thus affects the muscle's ability to adapt to length or force perturbation [319].…”

Anti-inflammatory functions of glucocorticoid-induced genes

“…Targets of such regulation include COX-2 (Chivers et al, 2006;Lasa et al, 2001;Newton et al, 1998;Ristimaki et al, 1996), TNF (Han et al, 1990;Kontoyiannis et al, 1999;Swantek et al, 1997), vascular endothelial growth factor (Gille et al, 2001), interferon β (Peppel et al, 1991), colony stimulating factor 2 (CSF2) (Bergmann et al, 2004;Tobler et al, 1992;Tran et al, 2005), IL-5 (Staples et al, 2003), IL-6 (Amano et al, 1993;Tobler et al, 1992), IL-1α and -1β (Amano et al, 1993;Lee et al, 1988), inducible nitric oxide synthase (Korhonen et al, 2002) and several chemokines (Berkman et al, 1995;Brach et al, 1992;Chang et al, 2001;Chaudhary and Avioli, 1996;Chivers et al, 2006;Mukaida et al, 1991;Poon et al, 1999;Stellato et al, 1999;Tobler et al, 1992). The majority of these mRNAs have in common the presence of adenylate/uridylate-rich elements (AREs) in their 3' untranslated regions (UTRs).…”

IL-17 enhances IL-1β-mediated CXCL-8 release from human airway smooth muscle cells

“…Supernatants were collected at different time points (24 and 48 h), centrifuged for 7 min at 4°C to remove cellular debris, and stored at Ϫ80°C before ELISA. To test the effect of mRNA synthesis inhibitor actinomycin D (Act D) on CXCL-8 mRNA or protein release, 5 g/ml was added to serum-deprived HASMC 30 min before stimulation with IL-17 (1 ng/ml), IL-1␤ (1 ng/ml), or both (40). Supernatants were recovered at 24 and 48 h and processed as described above.…”