Muscarinic M₃receptors on structural cells regulate cigarette smoke-induced neutrophilic airway inflammation in mice

Abstract

Anticholinergics, blocking the muscarinic M3 receptor, are effective bronchodilators for patients with chronic obstructive pulmonary disease. Recent evidence from M(3) receptor-deficient mice (M(3)R(-/-)) indicates that M3 receptors also regulate neutrophilic inflammation in response to cigarette smoke (CS). M(3) receptors are present on almost all cell types, and in this study we investigated the relative contribution of M(3) receptors on structural cells vs. inflammatory cells to CS-induced inflammation using bone marrow chimeric mice. Bone marrow chimeras (C56Bl/6 mice) were generated, and engraftment was confirmed after 10 wk. Thereafter, irradiated and nonirradiated control animals were exposed to CS or fresh air for four consecutive days. CS induced a significant increase in neutrophil numbers in nonirradiated and irradiated control animals (4- to 35-fold). Interestingly, wild-type animals receiving M(3)R(-/-) bone marrow showed a similar increase in neutrophil number (15-fold). In contrast, no increase in the number of neutrophils was observed in M3R(-/-) animals receiving wild-type bone marrow. The increase in keratinocyte-derived chemokine (KC) levels was similar in all smoke-exposed groups (2.5- to 5.0-fold). Microarray analysis revealed that fibrinogen-α and CD177, both involved in neutrophil migration, were downregulated in CS-exposed M(3)R(-/-) animals receiving wild-type bone marrow compared with CS-exposed wild-type animals, which was confirmed by RT-qPCR (1.6-2.5 fold). These findings indicate that the M(3) receptor on structural cells plays a proinflammatory role in CS-induced neutrophilic inflammation, whereas the M(3) receptor on inflammatory cells does not. This effect is probably not mediated via KC release, but may involve altered adhesion and transmigration of neutrophils via fibrinogen-α and CD177.

Acetylcholine beyond bronchoconstriction: roles in inflammation and remodeling

“…Interestingly, wildtype animals receiving M 3 R -/-bone marrow cells showed a similar increase in neutrophil number, suggesting that the M 3 receptor on inflammatory cells is not involved in the pro-inflammatory effect of acetylcholine. By contrast, no increase in the number of neutrophils was observed in M 3 R -/-animals receiving wildtype bone marrow cells, suggesting a critical role for airway structural cells in the pro-inflammatory effect of acetylcholine [28].…”

“…As is evident from the various in vitro studies described above, both structural cells and inflammatory cells can contribute to the pro-inflammatory effects of acetylcholine, and it is not known whether this effect is primarily mediated via M 3 receptors on structural cells or via M 3 receptors on inflammatory cells. Recently, using bone marrow chimeric animals, it was shown that this is primarily mediated via M 3 receptors on structural cells [28]. Exposure to cigarette smoke induced neutrophilic inflammation in non-irradiated and irradiated control animals.…”

A role for muscarinic receptors in neutrophil extracellular trap formation and levamisole-induced autoimmunity

“…Evidence from M3 muscarinic receptor-deficient mice indicates that this receptor regulates neutrophilic inflammation in response to cigarette smoke. In murine models of asthma, antagonism of M3 alleviates airway hyperresponsiveness, neutrophil-mediated inflammation, and airway remodeling (49). As mentioned above, M3 receptor signaling may also play a causal role in specific idiopathic autoimmune diseases.…”

Effect of aclidinium bromide on cough and sputum symptoms in moderate-to-severe COPD in three phase III trials

“…In contrast, cough frequency was independently associated with being a current smoker, smoking history, sputum production and neutrophilic inflammation 39. A recent study has demonstrated that M3 receptors may play a proinflammatory role in cigarette smoke-induced inflammation in animal models of COPD, suggesting another potential mechanism by which LAMAs may improve cough in patients with COPD 44. This is further supported by preclinical studies that have shown LAMAs can reduce neutrophils and inflammatory mediators, such as interleukin-6, tumour necrosis factor-α and interferon-γ, in cigarette smoke-exposed animal models 45…”