Muscarinic receptor subtype-specific effects on cigarette smoke-induced inflammation in mice

Abstract

Cholinergic tone contributes to airflow obstruction in chronic obstructive pulmonary disease. Accordingly, anticholinergics are effective bronchodilators by blocking the muscarinic M 3 receptor on airway smooth muscle. Recent evidence indicates that acetylcholine also contributes to airway inflammation. However, which muscarinic receptor subtype(s) regulates this process is unknown.In this study, the contribution of the M 1 , M 2 and M 3 receptor subtypes to cigarette smoke-induced airway inflammation was investigated by exposing muscarinic receptor subtype deficient mice to cigarette smoke for 4 days.In wild-type mice, cigarette smoke induced an increase in macrophages, neutrophils and lymphocytes in bronchoalveolar lavage fluid. Neutrophilic inflammation was higher in M 1 -/-and M 2 -/-mice compared to wild-type mice, but lower in M 3 -/-mice. Accordingly, the release of keratinocyte-derived chemokine (KC), monocyte chemotactic protein-1 and interleukin-6 was higher in M 1 -/-and M 2 -/-mice, and reduced in M 3 -/-mice. Markers of remodelling were not increased after cigarette smoke exposure. However, M 3 -/-mice had reduced expression of transforming growth factor-b1 and matrix proteins. Cigarette smoke-induced inflammatory cell recruitment and KC release were also prevented by the M 3 -receptor selective antagonist 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide (4-DAMP) in wild-type mice.Collectively, our data indicate a pro-inflammatory role for the M 3 receptor in cigarette smoke-induced neutrophilia and cytokine release, yet an anti-inflammatory role for M 1 and M 2 receptors. @ERSpublications Inhibition of the muscarinic M 3 receptor prevents inflammation in response to cigarette smoke exposure in mice

Anti-inflammatory effects of targeted lung denervation in patients with COPD

“…This aligns well with the reduction in TGF-β we have previously found in muscarinic M 3 receptor knock-out mice [8], and with the human data from the UPLIFT (Understanding Potential Long-term Impacts on Function with Tiotropium) trial, where tiotropium reduced lung function decline in a subgroup of patients [11].…”

“…It has been shown that lipopolysaccharide-induced and cigarette smoke-induced inflammation and remodelling can be inhibited by anticholinergic treatment or by knock-out of the muscarinic M 3 receptor [7,8].…”

Acetylcholine beyond bronchoconstriction: roles in inflammation and remodeling

“…Therefore, impaired clearance of detrimental smoke particles from the airways after knock out of the M 1 receptor could underlie the enhanced inflammatory response observed in M 1 R -/-animals. This is further supported by a marked induction in the release of the cytokines IL-6 and monocyte chemoattractant protein-1 (MCP-1) in M 1 R -/-animals compared with wildtype animals [23] (Figure 1). …”

“…This is important from a therapeutic perspective, because it would imply that prevention of bronchoconstriction might prevent airway remodeling in asthma. However, it seems unlikely that the entire anti-inflammatory and remodeling activity of anticholinergics is due to these biomechanical effects, as in the above mentioned studies bronchoconstriction was selectively coupled to remodeling, and not to inflammation, whereas anticholinergics and M 3 receptor knockout have clear anti-inflammatory effects on neutrophilic inflammation [4,23]. Moreover, over the past decades, it has become clear that acetylcholine is not only released as a neurotransmitter from nerve terminals, but also as a hormone from non-neuronal cells, including epithelial cells and inflammatory cells, acting in an autocrine and/or paracrine manner [2,14].…”

“…Studies in muscarinic receptor subtype-deficient mice support a role for the M 3 receptor in inflammation in response to cigarette smoke [23]. Knock-out of the M 3 receptor or inhibition using the M 3 receptor preferring antagonist 4-DAMP prevented the inflammatory response induced by cigarette smoke in mice, characterized by reduced numbers of neutrophils and reduced expression of the neutrophil chemotactic factor KC [interleukin (IL)-8 in humans] [23].…”