Pro-inflammatory mechanisms of muscarinic receptor stimulation in airway smooth muscle

Abstract

BackgroundAcetylcholine, the primary parasympathetic neurotransmitter in the airways, plays an important role in bronchoconstriction and mucus production. Recently, it has been shown that acetylcholine, by acting on muscarinic receptors, is also involved in airway inflammation and remodelling. The mechanism(s) by which muscarinic receptors regulate inflammatory responses are, however, still unknown.MethodsThe present study was aimed at characterizing the effect of muscarinic receptor stimulation on cytokine secretion by human airway smooth muscle cells (hASMc) and to dissect the intracellular signalling mechanisms involved. hASMc expressing functional muscarinic M2 and M3 receptors were stimulated with the muscarinic receptor agonist methacholine, alone, and in combination with cigarette smoke extract (CSE), TNF-α, PDGF-AB or IL-1β.ResultsMuscarinic receptor stimulation induced modest IL-8 secretion by itself, yet augmented IL-8 secretion in combination with CSE, TNF-α or PDGF-AB, but not with IL-1β. Pretreatment with GF109203X, a protein kinase C (PKC) inhibitor, completely normalized the effect of methacholine on CSE-induced IL-8 secretion, whereas PMA, a PKC activator, mimicked the effects of methacholine, inducing IL-8 secretion and augmenting the effects of CSE. Similar inhibition was observed using inhibitors of IκB-kinase-2 (SC514) and MEK1/2 (U0126), both downstream effectors of PKC. Accordingly, western blot analysis revealed that methacholine augmented the degradation of IκBα and the phosphorylation of ERK1/2 in combination with CSE, but not with IL-1β in hASMc.ConclusionsWe conclude that muscarinic receptors facilitate CSE-induced IL-8 secretion by hASMc via PKC dependent activation of IκBα and ERK1/2. This mechanism could be of importance for COPD patients using anticholinergics.

Regulation of airway inflammation and remodeling by muscarinic receptors: Perspectives on anticholinergic therapy in asthma and COPD

“…Furthermore, methacholine strongly augmented cigarette smoke extract (CSE) induced IL-8 release ). In line with findings in epithelial cells, IL-8 release induced by stimulation with methacholine and CSE in airway smooth muscle is ERK1/2 and NF-κB dependent (Oenema et al, 2010a).…”

Pharmacology and Therapeutics of Bronchodilators

“…M 3 mAChRs also mediate dilation of airway blood vessels, an action that has been demonstrated to be an endothelium-dependent mechanism (Belmonte, 2005). Moreover, they facilitate cigarette smoke extract-induced interleukin (IL)-8 secretion by human ASM cells via protein kinase C (PKC)-dependent activation of nuclear factor of light polypeptide gene enhancer in B cells (NF-B), inhibitor ␣ and extracellular signal-regulated kinase 1/2 (Oenema et al, 2010).…”

Pharmacological Interference With Protein-protein Interactions of Akinase Anchoring Proteins as a Strategy for the Treatment of Disease

“…The mRNA expression of IL--8 positively correlates with COPD progression in lung biopsies [159]. Cigarette smoke represents a major risk factor of COPD and induced IL--8 release from inflammatory cells, structural lung cells and airway smooth muscle (ASM) cells [160]. cAMP compartmentalization is involved in important features of COPD such as inflammation and airway remodeling.…”