Cross-talk between transforming growth factor-β₁ and muscarinic M₂ receptors augments airway smooth muscle proliferation

Impact of obesity on airway remodeling in asthma: pathophysiological insights and clinical implications

The prevalence of obesity among asthma patients has surged in recent years, posing a significant risk factor for uncontrolled asthma. Beyond its impact on asthma severity and patients' quality of life, obesity is associated with reduced lung function, increased asthma exacerbations, hospitalizations, heightened airway hyperresponsiveness, and elevated asthma-related mortality. Obesity may lead to metabolic dysfunction and immune dysregulation, fostering chronic inflammation characterized by increased pro-inflammatory mediators and adipocytokines, elevated reactive oxygen species, and reduced antioxidant activity. This chronic inflammation holds the potential to induce airway remodeling in individuals with asthma and obesity. Airway remodeling encompasses structural and pathological changes, involving alterations in the airway's epithelial and subepithelial layers, hyperplasia and hypertrophy of airway smooth muscle, and changes in airway vascularity. In individuals with asthma and obesity, airway remodeling may underlie heightened airway hyperresponsiveness and increased asthma severity, ultimately contributing to the development of persistent airflow limitation, declining lung function, and a potential increase in asthma-related mortality. Despite efforts to address the impact of obesity on asthma outcomes, the intricate mechanisms linking obesity to asthma pathophysiology, particularly concerning airway remodeling, remain incompletely understood. This comprehensive review discusses current research investigating the influence of obesity on airway remodeling, to enhance our understanding of obesity's role in the context of asthma airway remodeling.

Airway smooth muscle in contractility and remodeling of asthma: potential drug target mechanisms

INTRODUCTION

Asthma is characterized by enhanced airway contractility and remodeling where airway smooth muscle (ASM) plays a key role, modulated by inflammation. Understanding the mechanisms by which ASM contributes to these features of asthma is essential for the development of novel asthma therapies.

AREAS COVERED

Inflammation in asthma contributes to a multitude of changes within ASM including enhanced airway contractility, proliferation, and fibrosis. Altered intracellular calcium ([Ca²⁺]_i) regulation or Ca²⁺ sensitization contributes to airway hyperreactivity. Increased airway wall thickness from ASM proliferation and fibrosis contributes to structural changes seen with asthma.

EXPERT OPINION

ASM plays a significant role in multiple features of asthma. Increased ASM contractility contributes to hyperresponsiveness, while altered ASM proliferation and extracellular matrix production promote airway remodeling both influenced by inflammation of asthma and conversely even influencing the local inflammatory milieu. While standard therapies such as corticosteroids or biologics target inflammation, cytokines, or their receptors to alleviate asthma symptoms, these approaches do not address the underlying contribution of ASM to hyperresponsiveness and particularly remodeling. Therefore, novel therapies for asthma need to target abnormal contractility mechanisms in ASM and/or the contribution of ASM to remodeling, particularly in asthmatics resistant to current therapies.

Role of Airway Smooth Muscle in Inflammation Related to Asthma and COPD

Airway smooth muscle contributes to both contractility and inflammation in the pathophysiology of asthma and COPD. Airway smooth muscle cells can change the degree of a variety of functions, including contraction, proliferation, migration, and the secretion of inflammatory mediators (phenotype plasticity). Airflow limitation, airway hyperresponsiveness, β₂-adrenergic desensitization, and airway remodeling, which are fundamental characteristic features of these diseases, are caused by phenotype changes in airway smooth muscle cells. Alterations between contractile and hyper-contractile, synthetic/proliferative phenotypes result from Ca²⁺ dynamics and Ca²⁺ sensitization. Modulation of Ca²⁺ dynamics through the large-conductance Ca²⁺-activated K⁺ channel/L-type voltage-dependent Ca²⁺ channel linkage and of Ca²⁺ sensitization through the RhoA/Rho-kinase pathway contributes not only to alterations in the contractile phenotype involved in airflow limitation, airway hyperresponsiveness, and β₂-adrenergic desensitization but also to alteration of the synthetic/proliferative phenotype involved in airway remodeling. These Ca²⁺ signal pathways are also associated with synergistic effects due to allosteric modulation between β₂-adrenergic agonists and muscarinic antagonists. Therefore, airway smooth muscle may be a target tissue in the therapy for these diseases. Moreover, the phenotype changing in airway smooth muscle cells with focuses on Ca²⁺ signaling may provide novel strategies for research and development of effective remedies against both bronchoconstriction and inflammation.

Exploring the role of nerves in asthma; insights from the study of cough

Cough in asthma predicts disease severity, prognosis, and is a common and troublesome symptom. Cough is the archetypal airway neuronal reflex, yet little is understood about the underlying neuronal mechanisms. It is generally assumed that symptoms arise because of airway hyper-responsiveness and/or airway inflammation, but despite using inhaled corticosteroids and bronchodilators targeting these pathologies, a large proportion of patients have persistent coughing. This review focuses on the prevalence and impact of cough in asthma and explores data from pre-clinical and clinical studies which have explored neuronal mechanisms of cough and asthma. We present evidence to suggest patients with asthma have evidence of neuronal dysfunction, which is further heightened and exaggerated by both bronchoconstriction and airway eosinophilia. Identifying patients with excessive coughing with asthma may represent a neuro-phenotype and hence developing treatment for this symptom is important for reducing the burden of disease on patients' lives and currently represents a major unmet clinical need.

In Vivo Allergen-Activated Eosinophils Promote Collagen I and Fibronectin Gene Expression in Airway Smooth Muscle Cells via TGF-β1 Signaling Pathway in Asthma

Eosinophils infiltration and releasing TGF-β1 in the airways has been implicated in the pathogenesis of asthma, especially during acute episodes provoked by an allergen. TGF-β1 is a major mediator involved in pro-inflammatory responses and fibrotic tissue remodeling in asthma. We aimed to evaluate the effect of in vivo allergen-activated eosinophils on the expression of COL1A1 and FN in ASM cells in asthma. A total of 12 allergic asthma patients and 11 healthy subjects were examined. All study subjects underwent bronchial challenge with D. pteronyssinus allergen. Eosinophils from peripheral blood were isolated before and 24 h after the bronchial allergen challenge using high-density centrifugation and magnetic separation. Individual co-cultures of blood eosinophils and immortalized human ASM cells were prepared. The TGF-β1 concentration in culture supernatants was analyzed using ELISA. Gene expression was analyzed using qRT-PCR. Eosinophils integrins were suppressed with linear RGDS peptide before co-culture with ASM cells. Results: The expression of TGF-β1 in asthmatic eosinophils significantly increased over non-activated asthmatic eosinophils after allergen challenge, p < 0.001. The TGF-β1 concentration in culture supernatants was significantly higher in samples with allergen-activated asthmatic eosinophils compared to baseline, p < 0.05. The effect of allergen-activated asthmatic eosinophils on the expression of TGF-β1, COL1A1, and FN in ASM cells was more significant compared to non-activated eosinophils, p < 0.05, however, no difference was found on WNT-5A expression. The incubation of allergen-activated asthmatic eosinophils with RGDS peptide was more effective compared to non-activated eosinophils as the gene expression in ASM cells was downregulated equally to the same level as healthy eosinophils.

Airway Innervation and Plasticity in Asthma

Airway nerves represent a mechanistically and therapeutically important aspect that requires better highlighting in the context of diseases such as asthma. Altered structure and function (plasticity) of afferent and efferent airway innervation can contribute to airway diseases. We describe established anatomy, current understanding of how plasticity occurs, and contributions of plasticity to asthma, focusing on target-derived growth factors (neurotrophins). Perspectives toward novel treatment strategies and future research are provided.

Immune induction of airway remodeling

Airway remodeling is accepted to be a determining component within the natural history of asthma. It is a phenomenon characterized by changes in the airways structures that marches in parallel with and can be influenced by airway inflammation, floating at the interface between both natural and adaptive immunity and physical and mechanical cells behavior. In this review we aimed to highlight the comprehensive, yet not exhaustive, evidences of how immune cells induce, regulate and adapt to the recognized markers of airway remodeling. Mucous cell hyperplasia, epithelial dysfunction and mesenchymal transition, extracellular matrix protein synthesis and restructuration, fibroblast to myofibroblast transition, airway smooth muscle proliferation, bioactive and contractile properties, and vascular remodeling encompass complex physiopathological mechanisms that can be induced, suppressed or regulated by different cellular and molecular pathways. Growth factors, cytokines, chemokines and adhesion molecules expressed or derived either from the immune network of cells infiltrating the asthmatic airways and involving T helper lymphocytes, immune lymphoid cells, dendritic cells, eosinophils, neutrophils, mast cells or by the structural components such as epithelial cells, fibroblasts, myocytes, airway smooth muscle cells concur with protein cellular matrix component and metalloproteases in modifying the airway structure in a detrimental way. The consequences in lung function decline, fixed airway obstruction and clinical severity of the disease suggest the possibility of identify among the immune molecular pathway of remodeling some biological parameters or signal pathway to be either a good tracer for monitoring the disease evolution or a target for hypothetical phenotypes and endotypes. In the era of personalized medicine, a biomarker of remodeling might predict a response to small-molecule inhibitors or biologicals potentially targeting a fundamental aspect of asthma pathogenesis that impacts on the low responsiveness to airway inflammation directed treatments.

Association of Autoantibodies against M2-Muscarinic Acetylcholine Receptor with Atrial Fibrosis in Atrial Fibrillation Patients

Objectives

To investigate the association of serum autoantibodies against M2-muscarinic acetylcholine receptor (anti-M2-R) with atrial fibrosis in long-standing persistent atrial fibrillation (AF) patients.

Methods

Twenty-four long-standing persistent AF patients, scheduled to undergo hybrid ablation surgery, were enrolled in the study. Twenty-six patients with sinus rhythm, scheduled to undergo coronary artery bypass grafting surgery, were enrolled into the non-AF group. We detected serum anti-M2-R levels. Left atrial appendages were subjected to histological and molecular biological assays. Patients in the AF group received follow-up for two years.

Results

The AF group showed significantly higher serum anti-M2-R levels compared to the non-AF group (496.2 ± 232.5 vs. 86.3 ± 25.7 pmol/L, p < 0.001). The AF group exhibited severe fibrosis in the left atrial appendages, as indicated by increased collagen volume fraction (45.2 ± 4.7% vs. 27.6 ± 8.3%, p < 0.001), and higher levels of collagen I (0.52 ± 0.04 vs. 0.24 ± 0.06, p < 0.001) and collagen III (0.51 ± 0.07 vs. 0.36 ± 0.09, p < 0.001). TGF-β1 and CTGF were also upregulated in the AF group. A positive correlation between serum anti-M2-R levels and fibrosis of the left atrial appendage and fibrogenic indexes was observed.

Conclusions

Serum anti-M2-R levels are higher in AF patients and are associated with the severity of atrial fibrosis. In addition, serum anti-M2-R levels are positively correlated to TGF-β1 and CTGF expression in the left atrial appendage.

The mode of action of anticholinergics in asthma

Acetylcholine binds to muscarinic receptors to play a key role in the pathophysiology of asthma, leading to bronchoconstriction, increased mucus secretion, inflammation and airway remodelling. Anticholinergics are muscarinic receptor antagonists that are used in the treatment of chronic obstructive pulmonary disease and asthma. Recent in vivo and in vitro data have increased our understanding of how acetylcholine contributes to the disease manifestations of asthma, as well as elucidating the mechanism of action of anticholinergics. This review assesses the latest literature on acetylcholine in asthma pathophysiology, with a closer look at its role in airway inflammation and remodelling. New insights into the mechanism of action of anticholinergics, their effects on airway remodelling, and a review of the efficacy and safety of long-acting anticholinergics in asthma treatment will also be covered, including a summary of the latest clinical trial data.

Pre-clinical data suggest that anticholinergics can reduce acetylcholine-induced airway inflammation and remodellinghttp://ow.ly/xqAQ30loP8F

Comparison between montelukast and tiotropium as add-on therapy to inhaled corticosteroids plus a long-acting β2-agonist in for patients with asthma

Objective: Asthma often remains uncontrolled despite treatment with inhaled corticosteroids (ICS) alone or with ICS plus a long-acting β₂-agonist (LABA). The recommended alternative is the addition of either montelukast or tiotropium. The aim of this study was to compare the effects of montelukast and tiotropium on airway inflammation and remodeling in persistent asthma. Methods: Eighty-seven patients with asthma were treated with budesonide and formoterol (640/18 μg); then, the patients were randomly allocated to three groups to receive oral montelukast (10 mg/day), inhaled tiotropium (5 μg/day), or no add-on to the maintenance therapy for 48 weeks. Fractional exhaled nitric oxide (FeNO) and pulmonary function were measured, and quantitative computed tomography was performed. Results: Compared to the maintenance therapy, add-on montelukast significantly decreased FeNO (p < 0.05) and improved airflow obstruction (p < 0.05), whereas airway dimensions remained unchanged. Changes in FeNO were significantly correlated with changes in FEV₁ (r = -0.71, p < 0.001). In contrast, the addition of tiotropium significantly decreased airway wall area corrected for body surface area (WA/BSA) (p < 0.05), decreased wall thickness (T/√BSA) (p < 0.05) and improved airflow obstruction (p < 0.05) with no change in FeNO. Changes in WA/BSA and T/√BSA were significantly correlated with the change in percentage predicted FEV₁ (r = -0.84, p < 0.001 and r = -0.59, p < 0.01, respectively). Conclusions:Adding either montelukast or tiotropium to ICS/LABA may provide additive benefits with respect to the pulmonary function and airway inflammation or remodeling in patients with asthma.

Methacholine induces extracellular matrix production by human airway smooth muscle cells through β-catenin signaling

Altered extracellular matrix (ECM) production by airway smooth muscle cells (ASMCs) is an important feature of airway remodeling. Muscarinic receptor agonists contribute to ECM production in vivo, but the mechanisms involved remain unclear. This study attempted to investigate the role of methacholine in promoting ECM production by human ASMCs (HASMCs) and the underlying mechanism. We found that methacholine induced the expression of collagen I protein and multiple ECM genes. β-catenin signaling was activated in this process upon GSK3β phosphorylation, leading to upregulation of total and active β-catenin. Silencing β-catenin by specific small interfering RNA (siRNA) or with the β-catenin inhibitor, PKF115-584, decreased collagen I expression. Conversely, overexpression of active β-catenin by adenoviruses carrying the S33Y-β-catenin mutant increased the methacholine-induced collagen I expression. Furthermore, methacholine induced TGF-β expression in HASMCs, while pan-TGF-β-neutralizing antibody only partially decreased collagen I expression. These findings suggest that methacholine induced ECM production through β-catenin signaling and partially through TGF-β.

Wnt/β-catenin signaling links embryonic lung development and asthmatic airway remodeling

Embryonic lung development requires reciprocal endodermal-mesodermal interactions; mediated by various signaling proteins. Wnt/β-catenin is a signaling protein that exhibits the pivotal role in lung development, injury and repair while aberrant expression of Wnt/β-catenin signaling leads to asthmatic airway remodeling: characterized by hyperplasia and hypertrophy of airway smooth muscle cells, alveolar and vascular damage goblet cells metaplasia, and deposition of extracellular matrix; resulting in decreased lung compliance and increased airway resistance. The substantial evidence suggests that Wnt/β-catenin signaling links embryonic lung development and asthmatic airway remodeling. Here, we summarized the recent advances related to the mechanistic role of Wnt/β-catenin signaling in lung development, consequences of aberrant expression or deletion of Wnt/β-catenin signaling in expansion and progression of asthmatic airway remodeling, and linking early-impaired pulmonary development and airway remodeling later in life. Finally, we emphasized all possible recent potential therapeutic significance and future prospectives, that are adaptable for therapeutic intervention to treat asthmatic airway remodeling.

Transforming Growth Factor β1 Function in Airway Remodeling and Hyperresponsiveness. The Missing Link?

The pathogenesis of asthma includes a complex interplay among airway inflammation, hyperresponsiveness, and remodeling. Current evidence suggests that airway structural cells, including bronchial smooth muscle cells, myofibroblasts, fibroblasts, and epithelial cells, mediate all three aspects of asthma pathogenesis. Although studies show a connection between airway remodeling and changes in bronchomotor tone, the relationship between the two remains unclear. Transforming growth factor β1 (TGF-β1), a growth factor elevated in the airway of patients with asthma, plays a role in airway remodeling and in the shortening of various airway structural cells. However, the role of TGF-β1 in mediating airway hyperresponsiveness remains unclear. In this review, we summarize the literature addressing the role of TGF-β1 in airway remodeling and shortening. Through our review, we aim to further elucidate the role of TGF-β1 in asthma pathogenesis and the link between airway remodeling and airway hyperresponsiveness in asthma and to define TGF-β1 as a potential therapeutic target for reducing asthma morbidity and mortality.

The PDE4 inhibitor CHF-6001 and LAMAs inhibit bronchoconstriction-induced remodeling in lung slices

Combination therapy of PDE4 inhibitors and anticholinergics induces bronchoprotection in COPD. Mechanical forces that arise during bronchoconstriction may contribute to airway remodeling. Therefore, we investigated the impact of PDE4 inhibitors and anticholinergics on bronchoconstriction-induced remodeling. Because of the different mechanism of action of PDE4 inhibitors and anticholinergics, we hypothesized functional interactions of these two drug classes. Guinea pig precision-cut lung slices were preincubated with the PDE4 inhibitors CHF-6001 or roflumilast and/or the anticholinergics tiotropium or glycopyorrolate, followed by stimulation with methacholine (10 μM) or TGF-β₁ (2 ng/ml) for 48 h. The inhibitory effects on airway smooth muscle remodeling, airway contraction, and TGF-β release were investigated. Methacholine-induced protein expression of smooth muscle-myosin was fully inhibited by CHF-6001 (0.3-100 nM), whereas roflumilast (1 µM) had smaller effects. Tiotropium and glycopyrrolate fully inhibited methacholine-induced airway remodeling (0.1-30 nM). The combination of CHF-6001 and tiotropium or glycopyrrolate, in concentrations partially effective by themselves, fully inhibited methacholine-induced remodeling in combination. CHF-6001 did not affect airway closure and had limited effects on TGF-β₁-induced remodeling, but rather, it inhibited methacholine-induced TGF-β release. The PDE4 inhibitor CHF-6001, and to a lesser extent roflumilast, and the LAMAs tiotropium and glycopyrrolate inhibit bronchoconstriction-induced remodeling. The combination of CHF-6001 and anticholinergics was more effective than the individual compounds. This cooperativity might be explained by the distinct mechanisms of action inhibiting TGF-β release and bronchoconstriction.

Cyclic peptide *CRRETAWAC* attenuates fibronectin-induced cytokine secretion of human airway smooth muscle cells by inhibiting FAK and p38 MAPK

α5β1 integrin is highly expressed in airway smooth muscle cells and mediate the adhesion of airway smooth muscle cells to fibronectin to regulate airway remodelling in asthma. This study aimed to investigate the effects of synthetic cyclic peptide *CRRETAWAC* on fibronectin‐induced cytokine secretion of airway smooth muscle cells and the underlying mechanism. Human airway smooth muscle cells were isolated and treated with fibronectin, IL‐13, *CRRETAWAC* peptide, α5β1 integrin‐blocking antibody, FAK inhibitor or p38 MAPK inhibitor. The transcription and secretion of eotaxin‐1 and RANTES were detected by real‐time PCR and ELISA, respectively. The phosphorylation of FAK and MAPKs including p38, ERK1/2 and JNK1/2 was detected by Western blot analysis. The transcription and secretion of eotaxin‐1 and RANTES increased in airway smooth muscle cells cultured in fibronectin‐coated plates. However, α5β1 integrin‐blocking antibody, *CRRETAWAC* peptide, FAK inhibitor or p38 MAPK inhibitor significantly reduced mRNA levels and the secretion of eotaxin‐1 and RANTES in airway smooth muscle cells cultured in fibronectin‐coated plates. In addition, the phosphorylation of FAK and p38 MAPK was significantly increased in airway smooth muscle cells cultured in fibronectin‐coated plates compared to the cells cultured in uncoated plates and was significantly reduced in airway smooth muscle cells treated with *CRRETAWAC* peptide. Fibronectin induces cytokine synthesis and secretion of airway smooth muscle cells. Peptide *CRRETAWAC* antagonizes fibronectin‐induced cytokine synthesis and secretion of airway smooth muscle cells via the inhibition of FAK and p38 MAPK, and is a potential agent for the therapy of asthma.

Tiotropium for the treatment of asthma in adolescents

INTRODUCTION

Asthma is a prevalent disease affecting millions of individuals. Despite receiving guideline therapy with inhaled corticosteroids (ICS) with or without a long-acting β₂-agonist (LABA), a proportion of patients remain symptomatic or have suboptimal lung function. There is therefore an unmet need for additional therapies to improve asthma control. The long-acting anticholinergic tiotropium, delivered via the Respimat inhaler, is approved for the treatment of asthma in the EU, the USA, and other countries. Phase III investigation in adults has demonstrated that tiotropium improves lung function and asthma control, with a safety profile comparable with that of placebo. Areas covered: Clinical trials in adolescent patients (aged 12-17 years) with moderate or severe symptomatic asthma have shown that tiotropium Respimat as add-on to ICS, with or without other maintenance therapies, is a well-tolerated and efficacious bronchodilator showing trends toward improved asthma control, similar to data in adult patients. Expert opinion: Tiotropium Respimat may be of benefit as add-on maintenance therapy to medium- or high-dose ICS with or without LABA; however, further data are needed to directly compare the efficacy of ICS plus tiotropium versus ICS plus LABA in adolescents with symptomatic asthma, and to establish the long-term effects on airway modeling.

MiR-23b controls TGF-β1 induced airway smooth muscle cell proliferation via direct targeting of Smad3

BACKGROUND

MicroRNAs are small yet versatile gene tuners that regulate a variety of cellular processes, including cell growth and proliferation. Here we report that miR-23b inhibited airway smooth muscle cells (ASMCs) proliferation through directly targeting of Smad3.

METHODS

We obtained ASMCs by laser capture microdissection of normal and asthmatic mice lung tissues. Mice ASMCs were cultured and induced by TGF-β1. The implication between TGF-β1 and miR-23b in ASMCs were detected by RT-PCR. The effects of miR-23b on ASMCs proliferation and apoptosis were assessed by transient transfection of miR-23b mimics and inhibitor. The expression of Smad3 in ASMCs were detected by RT-PCR and Western blotting analysis. Dual-Luciferase Reporter Assay System will be applied to identify whether Smad3 is a target gene of miR-23b.

RESULTS

TGF-β1 and miR-23b mRNA expression of in-situ bronchial ASMCs collected by laser capture microdissection were increased in asthmatic mice compared to non-asthma controls. This is accompanied by an increase in miR-23b mRNA expression in TGF-β1 induced ASMCs. miR-23b up-regulation significantly inhibited TGF-β1-induced ASMCs proliferation and promoted apoptosis. MiR-23b negatively regulates the expression of Smad3 in ASMCs. Dual-Luciferase Reporter Assay System demonstrated that Smad3 was a direct target of miR-23b.

CONCLUSIONS

MiR-23b may function as an inhibitor of asthma airway remodeling by suppressing ASMCs proliferation via direct targeting of Smad3.

Selective targeting of CREB-binding protein/β-catenin inhibits growth of and extracellular matrix remodelling by airway smooth muscle

BACKGROUND AND PURPOSE

Asthma is a heterogeneous chronic inflammatory disease, characterized by the development of structural changes (airway remodelling). β-catenin, a transcriptional co-activator, is fundamentally involved in airway smooth muscle growth and may be a potential target in the treatment of airway smooth muscle remodelling.

EXPERIMENTAL APPROACH

We assessed the ability of small-molecule compounds that selectively target β-catenin breakdown or its interactions with transcriptional co-activators to inhibit airway smooth muscle remodelling in vitro and in vivo.

KEY RESULTS

ICG-001, a small-molecule compound that inhibits the β-catenin/CREB-binding protein (CBP) interaction, strongly and dose-dependently inhibited serum-induced smooth muscle growth and TGFβ1-induced production of extracellular matrix components in vitro. Inhibition of β-catenin/p300 interactions using IQ-1 or inhibition of tankyrase 1/2 using XAV-939 had considerably less effect. In a mouse model of allergic asthma, β-catenin expression in the smooth muscle layer was found to be unaltered in control versus ovalbumin-treated animals, a pattern that was found to be similar in smooth muscle within biopsies taken from asthmatic and non-asthmatic donors. However, β-catenin target gene expression was highly increased in response to ovalbumin; this effect was prevented by topical treatment with ICG-001. Interestingly, ICG-001 dose-dependently reduced airway smooth thickness after repeated ovalbumin challenge, but had no effect on the deposition of collagen around the airways, mucus secretion or eosinophil infiltration.

CONCLUSIONS AND IMPLICATIONS

Together, our findings highlight the importance of β-catenin/CBP signalling in the airways and suggest ICG-001 may be a new therapeutic approach to treat airway smooth muscle remodelling in asthma.

Where does current and future pediatric asthma treatment stand? Remodeling and inflammation: Bird's eye view

Airway remodeling is the chronic outcome of inflammation in asthma and a point of intervention between pediatric and adult ages. Pediatric asthma has been of great interest in the efforts to find a valuable time to interrupt remodeling. Various experimental and clinical research have assessed the effect of current therapeutic modalities on airway remodeling in asthma and many new agents are being developed with promising results. The heterogeneity in the results of these studies may lie in the heterogeneity of pathogenesis leading to asthma and remodeling; underlying the need for individualized treatment of the unique pathogenetic characteristics of each child's asthma. The aim of this review is to summarize the evidence about the influence of current and future therapeutic modalities in the concept of inflammation and remodeling in pediatric asthma. Pediatr Pulmonol. 2016;51:1422-1429. © 2016 Wiley Periodicals, Inc.

Different anti-remodeling effect of nilotinib and fluticasone in a chronic asthma model

BACKGROUND/AIMS

Inhaled corticosteroids are the most effective treatment currently available for asthma, but their beneficial effect against airway remodeling is limited. The tyrosine kinase inhibitor nilotinib has inhibitory activity against c-kit and the platelet-derived growth factor receptor. We compared the effects of fluticasone and nilotinib on airway remodeling in a chronic asthma model. We also examined whether co-treatment with nilotinib and fluticasone had any synergistic effect in preventing airway remodeling.

METHODS

We developed a mouse model of airway remodeling, including smooth muscle thickening, in which ovalbumin (OVA)-sensitized female BALB/c-mice were repeatedly exposed to intranasal OVA administration twice per week for 3 months. Mice were treated with fluticasone and/or nilotinib intranasally during the OVA challenge.

RESULTS

Mice chronically exposed to OVA developed eosinophilic airway inflammation and showed features of airway remodeling, including thickening of the peribronchial smooth muscle layer. Both fluticasone and nilotinib attenuated airway smooth muscle thickening. However, only nilotinib suppressed fibrotic changes, demonstrating inhibition of collagen deposition. Fluticasone reduced pro-inflammatory cells, such as eosinophils, and several cytokines, such as interleukin 4 (IL-4), IL-5, and IL-13, induced by repeated OVA challenges. On the other hand, nilotinib reduced transforming growth factor β1 levels in bronchoalveolar lavage fluid and inhibited fibroblast proliferation significantly.

CONCLUSIONS

These results suggest that fluticasone and nilotinib suppressed airway remodeling in this chronic asthma model through anti-inflammatory and anti-fibrotic pathways, respectively.

Inactivated Pseudomonas aeruginosa inhibits hypoxia-induced pulmonary hypertension by preventing TGF-β1/Smad signaling

Pseudomonas aeruginosa is one of the common colonizing bacteria of the human body and is an opportunistic pathogen frequently associated with respiratory infections. Inactivated P. aeruginosa (IPA) have a variety of biological effects against inflammation and allergy. Transforming growth factor-β (TGF-β) signaling plays a critical role in the regulation of cell growth, differentiation, and development in a wide range of biological systems. The present study was designed to investigate the effects of IPA on TGF-β/Smad signaling in vivo, using a hypoxia-induced pulmonary hypertension (PH) rat model. Sprague Dawley rats (n=40) were exposed to 10% oxygen for 21 days to induce PH. At the same time, IPA was administered intravenously from day 1 to day 14. Mean pulmonary artery pressure (mPAP) and the right ventricle (RV) to left ventricle plus the interventricular septum (LV+S) mass ratio were used to evaluate the development of PH. Vessel thickness and density were measured using immunohistochemistry. Primary arterial smooth muscle cells (PASMCs) were isolated and the proliferation of PASMCs was assayed by flow cytometry. The production of TGF-β1 in cultured supernatant of PASMCs was assayed by ELISA. The expression levels of α-smooth muscle actin (α-SMA), TGF-β1 and phospho-Smad 2/3 in PASMCs were assayed by western blot. Our data indicated that IPA attenuated PH, RV hypertrophy and pulmonary vascular remodeling in rats, which was probably mediated by restraining the hypoxia-induced overactive TGF-β1/Smad signaling. In conclusion, IPA is a promising protective treatment in PH due to the inhibiting effects on TGF-β1/Smad 2/3 signaling.

Tiotropium for the treatment of asthma: a drug safety evaluation

INTRODUCTION

Tiotropium, a once-daily long-acting anticholinergic bronchodilator, has recently been approved for use in the treatment of asthma in a number of countries, including the EU and the USA, and was incorporated into the 2015 update of the Global Initiative for Asthma treatment guidelines. Here we review safety data from published clinical trials to help inform the use of tiotropium in the treatment of patients with asthma.

AREAS COVERED

Safety data from recently published clinical trials, which compared tiotropium with placebo or an active control, were reviewed. Trials included children, adolescents, and adults across severities of symptomatic asthma, and assessed tiotropium delivered via the Respimat and HandiHaler devices.

EXPERT OPINION

Based on the reviewed scientific evidence, tiotropium is a safe and well-tolerated long-acting anticholinergic bronchodilator for use in the treatment of asthma. In the trials assessed, the safety of tiotropium was found to be comparable with that of placebo and alternative therapeutic options, including a doubling in the dose of inhaled corticosteroids and the long-acting β2-agonist salmeterol.

Combination therapy of tiotropium and ciclesonide attenuates airway inflammation and remodeling in a guinea pig model of chronic asthma

Background

The long-acting anticholinergic tiotropium has recently been registered for the treatment of asthma, and its use is associated with a reduction in exacerbation frequency. Anti-inflammatory and anti-remodeling effects of tiotropium have been demonstrated in in vitro and in vivo models. Because tiotropium treatment is used in combination with inhaled corticosteroids, potential additive effects between the two would be clinically relevant. Therefore, the aim of this study was to investigate additive effects between tiotropium and ciclesonide on airway inflammation and remodeling in guinea pig models of asthma.

Methods

Guinea pigs (n = 3–8/group) were sensitized and challenged with ovalbumin in an acute (single challenge) and a chronic model (12 weekly challenges) of allergic asthma. Animals were treated with vehicle, nebulized tiotropium (0.01–0.3 mM) and/or intranasally instilled ciclesonide (0.001–1 mg/kg) before each challenge. Bronchoalveolar lavage fluid and lungs were collected for analysis of airway inflammation and remodeling.

Results

Tiotropium and ciclesonide treatment, alone or in combination, did not inhibit airway inflammation in the acute asthma model. In a dose-finding study, low doses of tiotropium and ciclesonide inhibited airway eosinophilia and airway smooth muscle thickening in the chronic asthma model. Threshold doses of 0.01 mM tiotropium (nebulizer concentration) and 0.01 mg/kg ciclesonide were selected to investigate potential additive effects between both drugs. At these doses, tiotropium and ciclesonide did not inhibit airway eosinophilia or airway smooth muscle thickening when administered alone, but significantly inhibited these allergen-induced responses when administered in combination.

Conclusions

Combined treatment with low doses of tiotropium and ciclesonide inhibits airway inflammation and remodeling in a guinea pig model of chronic asthma, suggesting that combined treatment with anticholinergics and corticosteroids may have anti-inflammatory and anti-remodeling activity in allergic airway diseases. Since tiotropium is registered as a therapy for asthma added on to corticosteroid treatment, these beneficial effects of the combination therapy may be clinically relevant.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-016-0327-6) contains supplementary material, which is available to authorized users.

Differential deposition of fibronectin by asthmatic bronchial epithelial cells

Altered ECM protein deposition is a feature in asthmatic airways. Fibronectin (Fn), an ECM protein produced by human bronchial epithelial cells (HBECs), is increased in asthmatic airways. This study investigated the regulation of Fn production in asthmatic or nonasthmatic HBECs and whether Fn modulated HBEC proliferation and inflammatory mediator secretion. The signaling pathways underlying transforming growth factor (TGF)-β1-regulated Fn production were examined using specific inhibitors for ERK, JNK, p38 MAPK, phosphatidylinositol 3 kinase, and activin-like kinase 5 (ALK5). Asthmatic HBECs deposited higher levels of Fn in the ECM than nonasthmatic cells under basal conditions, whereas cells from the two groups had similar levels of Fn mRNA and soluble Fn. TGF-β1 increased mRNA levels and ECM and soluble forms of Fn but decreased cell proliferation in both cells. The rate of increase in Fn mRNA was higher in nonasthmatic cells. However, the excessive amounts of ECM Fn deposited by asthmatic cells after TGF-β1 stimulation persisted compared with nonasthmatic cells. Inhibition of ALK5 completely prevented TGF-β1-induced Fn deposition. Importantly, ECM Fn increased HBEC proliferation and IL-6 release, decreased PGE2 secretion, but had no effect on VEGF release. Soluble Fn had no effect on cell proliferation and inflammatory mediator release. Asthmatic HBECs are intrinsically primed to produce more ECM Fn, which when deposited into the ECM, is capable of driving remodeling and inflammation. The increased airway Fn may be one of the key driving factors in the persistence of asthma and represents a novel, therapeutic target.

Research and development of bronchodilators for asthma and COPD with a focus on G protein/KCa channel linkage and β2-adrenergic intrinsic efficacy

Bronchodilators are used to improve symptoms and lung function in asthma and COPD. Airway smooth muscle tone is regulated by both muscarinic and β2-adrenergic receptor activity. Large-conductance Ca(2+)-activated K(+) (KCa) channels are activated by β2-adrenergic receptor agonists, via Gs, and suppressed by muscarinic receptor antagonists via Gi. This functional antagonism converges on the G protein/KCa channel linkages. Membrane potential regulated by KCa channels contributes to airway smooth muscle tension via Ca(2+) influx passing through voltage-dependent Ca(2+) (VDC) channels. The Gs/KCa/VDC channel linkage is a key process in not only physiological effects, but also in dysfunction of β2-adrenergic receptors and airway remodeling. Moreover, this pathway is involved in the synergistic effects between β2-adrenergic receptor agonists and muscarinic receptor antagonists. Intrinsic efficacy is also an important characteristic for both maintenance and loss of β2-adrenergic action. Allosteric modulators of G protein-coupled receptors contribute not only to this synergistic effect between β2-adrenergic and muscarinic M2 receptors, but also to intrinsic efficacy. The effects of weak partial agonists are suppressed by lowering receptor number, disordering receptor function, and enhancing functional antagonism; in contrast, those of full or strong partial agonists are not suppressed. Excessive exposure to full agonists causes β2-adrenergic desensitization; in contrast, exposure to partial agonists does not cause desensitization. Intrinsic efficacy may provide the rationale for the clinical use of β2-adrenergic receptor agonists in asthma and COPD. In conclusion, the G protein/KCa linkage and intrinsic efficacy (allosteric effects) may be therapeutic targets for research and development of novel agents against both airway obstruction and airway remodeling.

Bronchoconstriction and airway biology: potential impact and therapeutic opportunities

Recent work has demonstrated that mechanical forces occurring in the airway as a consequence of bronchoconstriction are sufficient to not only induce symptoms but also influence airway biology. Animal and human in vitro and in vivo work demonstrates that the airways are structurally and functionally altered by mechanical stress induced by bronchoconstriction. Compression of the airway epithelium and mechanosensing by the airway smooth muscle trigger the activation and release of growth factors, causing cell proliferation, extracellular matrix protein accumulation, and goblet cell differentiation. These effects of bronchoconstriction are of major importance to asthma pathophysiology and appear sufficient to induce remodeling independent of the inflammatory response. We review these findings in detail and discuss previous studies in light of this new evidence regarding the influence of mechanical forces in the airways. Furthermore, we highlight potential impacts of therapies influencing mechanical forces on airway structure and function in asthma.

Acetylcholine beyond bronchoconstriction: roles in inflammation and remodeling

Acetylcholine is the primary parasympathetic neurotransmitter in the airways, where it not only induces bronchoconstriction and mucus secretion, but also regulates airway inflammation and remodeling. In this review, we propose that these effects are all primarily mediated via the muscarinic M3 receptor. Acetylcholine promotes inflammation and remodeling via direct effects on airway cells, and via mechanical stress applied to the airways sequential to bronchoconstriction. The effects on inflammation and remodeling are regulated by both neuronal and non-neuronal acetylcholine. Taken together, we believe that the combined effects of anticholinergic therapy on M3-mediated bronchoconstriction, mucus secretion, inflammation, and remodeling may account for the positive outcome of treatment with these drugs for patients with chronic pulmonary obstructive disease (COPD) or asthma.

Anticholinergics/antimuscarinic drugs in asthma

Anticholinergic alkaloids have been used for thousands of years for the relief of bronchoconstriction and other respiratory symptoms, and their use in the treatment of chronic obstructive pulmonary disease is well established. Acetylcholine, acting through muscarinic receptor (M) receptor, modulates multiple physiologic functions pertinent to asthma including airway muscle tone, mucus gland secretion, and various parameters of inflammation and remodeling. In addition, activation of M receptors may inhibit beta2 adrenoreceptor. These observations offer the rationale for the use of M receptors antagonists in the treatment of asthma. Short-acting antimuscarinic agents may be effective alone or in combination with short-acting beta agonists for the relief of acute symptoms. Long-acting antimuscarinic agents have emerged as potentially useful in the long-term treatment of difficult-to-control asthma. This review will analyze the mechanisms of action and therapeutic role of antimuscarinic agents on asthma including current guidelines regarding antimuscarinic drugs, recent studies in asthma, special populations to consider, and possible predictors of response.

L-thyroxine promotes a proliferative airway smooth muscle phenotype in the presence of TGF-β1

Hypothyroidism may reduce, whereas hyperthyroidism may aggravate, asthma symptoms. The mechanisms underlying this relationship are largely unknown. Since thyroid hormones have central roles in cell growth and differentiation, we hypothesized that airway remodeling, in particular increased airway smooth muscle (ASM) mass, may be involved. To address this hypothesis, we investigated the effects of triiodothyronine (T3) and l-thyroxine (T4) in the absence and presence of the profibrotic transforming growth factor (TGF)-β1 on human ASM cell phenotype switching. T3 (1-100 nM) and T4 (1-100 nM) did not affect basal ASM proliferation. However, when combined with TGF-β1 (2 ng/ml), T4 synergistically increased the proliferative response, whereas only a minor effect was observed for T3. In line with a switch from a contractile to a proliferative ASM phenotype, T4 reduced the TGF-β1-induced contractile protein expression by ∼50%. Cotreatment with T3 reduced TGF-β1-induced contractile protein expression by ∼25%. The synergistic increase in proliferation was almost fully inhibited by the integrin αvβ3 antagonist tetrac (100 nM), whereas no significant effects of the thyroid receptor antagonist 1-850 (3 μM) were observed. Inhibition of MEK1/2, downstream of the integrin αvβ3, also inhibited the T4- and TGF-β1-induced proliferative responses. Collectively, the results indicate that T4, and to a lesser extent T3, promotes a proliferative ASM phenotype in the presence of TGF-β1, which is predominantly mediated by the membrane-bound T4 receptor αvβ3. These results indicate that thyroid hormones may enhance ASM remodeling in asthma, which could be of relevance for hyperthyroid patients with this disease.

Integrins: therapeutic targets in airway hyperresponsiveness and remodelling?

Integrins are a group of transmembrane heterodimeric proteins that mediate cell-cell and cell-extracellular matrix (ECM) interactions. Integrins have been under intense investigation for their role in inflammation in asthma. Clinical trials investigating integrin antagonists, however, have shown that these compounds are relatively ineffective. Airway remodelling is another pathological feature of asthma that is thought to make an important contribution to airway hyperresponsiveness (AHR) and lung function decline. Recent studies have identified integrins as important players in this process, with a particular role for β1 and αv integrins. Here we review the role of these integrins in airway remodelling and hyperresponsiveness in obstructive airway disease and their potential as pharmacological targets for future treatment.

The acetylcholine signaling network of corneal epithelium and its role in regulation of random and directional migration of corneal epithelial cells

PURPOSE

Because cholinergic drugs are used in ophthalmology and cholinergic stimulation has been shown to facilitate epithelialization of mucocutaneous wounds, we performed a systematic analysis of components of the cholinergic network of human and murine corneal epithelial cells (CECs) and determined the role of autocrine and paracrine acetylcholine (ACh) in regulation of CEC motility.

METHODS

We investigated the expression of ACh receptors at the mRNA and protein levels in human immortalized CECs, localization of cholinergic molecules in normal and wounded murine cornea, and the effects of cholinergic drugs on CEC directional and random migration in vitro, intercellular adhesion, and expression of integrin αV and E-cadherin.

RESULTS

We demonstrated that corneal epithelium expresses the ACh-synthesizing enzyme choline acetyltransferase, the ACh-degrading enzyme acetylcholinesterase, two muscarinic ACh receptors (mAChRs), M3 and M4, and several nicotinic ACh receptors (nAChRs), including both α7- and α9-made homomeric nAChRs and predominantly the α3β2±α5 subtype of heteromeric nAChRs. Wounding affected the expression patterns of cholinergic molecules in the murine corneal epithelium. Constant stimulation of CECs through both muscarinic and nicotinic signaling pathways was essential for CEC survival and both directional and random migration in vitro. Both α7 and non-α7 nAChRs elicited chemotaxis, with the α7 signaling exhibiting a stronger chemotactic effect. Cholinergic stimulation of CECs upregulated expression of the integrin and cadherin molecules involved in epithelialization. We found synergy between the proepithelialization signals elicited by different ACh receptors expressed in CECs.

CONCLUSIONS

Simultaneous stimulation of mAChRs and nAChRs by ACh may be required to synchronize and balance ionic and metabolic events in a single cell. Localization of these cholinergic enzymes and receptors in murine cornea indicated that the concentration of endogenous ACh and the mode of its signaling differ among corneal epithelial layers. Elucidation of the signaling events elicited upon agonist binding to corneal mAChRs and nAChRs will be crucial for understanding the mechanisms of ACh signaling in CECs, which has salient clinical implications.

Beyond TGFβ--novel ways to target airway and parenchymal fibrosis

Within the lungs, fibrosis can affect both the parenchyma and the airways. Fibrosis is a hallmark pathological change in the parenchyma in patients with idiopathic pulmonary fibrosis (IPF), whilst in asthma or chronic obstructive pulmonary disease (COPD) fibrosis is a component of the remodelling of the airways. In the past decade, significant advances have been made in understanding the disease behaviour and pathogenesis of parenchymal and airway fibrosis and as a result a variety of novel therapeutic targets for slowing or preventing progression of these fibrotic changes have been identified. This review highlights a number of these targets and discusses the potential for treating parenchymal or airway fibrosis through these mediators/pathways in the future.

Lung remodeling mechanisms in chronic lung diseases

PURPOSE OF REVIEW

To summarize the new knowledge on tissue remodeling in the context of lung diseases. Tissue remodeling includes changes in cells: differentiation; response to growths factors, hormones, or environmental factors; and composition of the extracellular matrix. So, can one trigger cause them all or are they independently regulated?

RECENT FINDINGS

New evidence from clinical and experimental studies strengthened the view that a susceptibility to remodeling can be initiated in early life and be re-activated by environmental triggers later in life. Many studies further support the idea that TGF-β plays the central role in the pathogenesis of remodeling and fibrosis. However, the activation pathways and the end-effect of TGF-β activation seems to be distinctive of disease and effecter cell specific patterns. The existing animal models do not properly reflect the human disease and thus have to be further improved.

SUMMARY

The central role of TGF-β on pathological mechanisms leading to remodeling and fibrosis has been further confirmed. However, the questions of why TGF-β is activated as well as its disease and cell type specific mode of action remain to be answered. Based on clinical data redefining the term 'tissue remodeling' in a disease and cell type specific way should be considered.

Pharmacologic characterization of GSK-961081 (TD-5959), a first-in-class inhaled bifunctional bronchodilator possessing muscarinic receptor antagonist and β2-adrenoceptor agonist properties

The objective of the present studies was to characterize the pharmacologic properties of GSK-961081 [TD-5959; (R)-1-(3-((2-chloro-4-(((2-hydroxy-2-(8-hydroxy-2-oxo-1,2-dihydroquinolin-5-yl)ethyl)amino)methyl)-5-methoxyphenyl)amino)-3-oxopropyl) piperidin-4-yl [1,1'-biphenyl]-2-ylcarbamate], a novel first-in-class inhaled bifunctional compound possessing both muscarinic antagonist (MA) and β2-adrenoceptor agonist (BA) properties (MABA). In competition radioligand binding studies at human recombinant receptors, GSK-961081 displayed high affinity for hM2 (Ki = 1.4 nM), hM3 muscarinic receptors (Ki = 1.3 nM) and hβ2-adrenoceptors (Ki = 3.7 nM). GSK-961081 behaved as a potent hβ2-adrenoceptor agonist (EC50 = 0.29 nM for stimulation of cAMP levels) with 440- and 320-fold functional selectivity over hβ1- and hβ3-adrenoceptors, respectively. In guinea pig isolated tracheal tissues, GSK-961081 produced smooth muscle relaxation through MA (EC50 = 50.2 nM), BA (EC50=24.6 nM), and MABA (EC50 = 11 nM) mechanisms. In the guinea pig bronchoprotection assay, inhaled GSK-961081 produced potent, dose-dependent inhibition of bronchoconstrictor responses via MA (ED50 = 33.9 µg/ml), BA (ED50 = 14.1 µg/ml), and MABA (ED50 = 6.4 µg/ml) mechanisms. Significant bronchoprotective effects of GSK-961081 were evident in guinea pigs via MA, BA, and MABA mechanisms for up to 7 days after dosing. The lung selectivity index of GSK-961081 in guinea pigs was 55- to 110-fold greater than that of tiotropium with respect to systemic antimuscarinic antisialagogue effects and was 10-fold greater than that of salmeterol with respect to systemic β2-adrenoceptor hypotensive effects. These preclinical findings studies suggest that GSK-961081 has the potential to be a promising next-generation inhaled lung-selective bronchodilator for the treatment of airway diseases, including chronic obstructive pulmonary disease.

Airway smooth muscle in asthma: linking contraction and mechanotransduction to disease pathogenesis and remodelling

Asthma is an obstructive airway disease, with a heterogeneous and multifactorial pathogenesis. Although generally considered to be a disease principally driven by chronic inflammation, it is becoming increasingly recognised that the immune component of the pathology poorly correlates with the clinical symptoms of asthma, thus highlighting a potentially central role for non-immune cells. In this context airway smooth muscle (ASM) may be a key player, as it comprises a significant proportion of the airway wall and is the ultimate effector of acute airway narrowing. Historically, the contribution of ASM to asthma pathogenesis has been contentious, yet emerging evidence suggests that ASM contractile activation imparts chronic effects that extend well beyond the temporary effects of bronchoconstriction. In this review article we describe the effects that ASM contraction, in combination with cellular mechanotransduction and novel contraction-inflammation synergies, contribute to asthma pathogenesis. Specific emphasis will be placed on the effects that ASM contraction exerts on the mechanical properties of the airway wall, as well as novel mechanisms by which ASM contraction may contribute to more established features of asthma such as airway wall remodelling.

β-catenin as a regulator and therapeutic target for asthmatic airway remodeling

INTRODUCTION

Pathological alteration in the airway structure, termed as airway remodeling, is a hallmark feature of individuals with asthma and has been described to negatively impact lung function in asthmatics. Recent studies have raised considerable interest in the regulatory role of β-catenin in remodeling asthmatic airways. The WNT/β-catenin signaling pathway is the key to normal lung development and tightly coordinates the maintenance of tissue homeostasis under steady-state conditions. Several studies indicate the crucial role of β-catenin signaling in airway remodeling in asthma and suggest that this pathway may be activated by both the growth factors and mechanical stimuli such as bronchoconstriction.

AREAS COVERED

In this review, we discuss recent literature regarding the mechanisms of β-catenin signaling activation and its mechanistic role in asthmatic airway remodeling. Further, we discuss the possibilities of therapeutic targeting of β-catenin.

EXPERT OPINION

The aberrant activation of β-catenin signaling by both WNT-dependent and -independent mechanisms in asthmatic airways plays a key role in remodeling the airways, including cell proliferation, differentiation, tissue repair and extracellular matrix production. These findings are interesting from both a mechanistic and therapeutic perspective, as several drug classes have now been described that target β-catenin signaling directly.

Muscarinic M₃ receptors contribute to allergen-induced airway remodeling in mice

Asthma is a chronic obstructive airway disease, characterized by inflammation and remodeling. Acetylcholine contributes to symptoms by inducing bronchoconstriction via the muscarinic M3 receptor. Recent evidence suggests that bronchoconstriction can regulate airway remodeling, and therefore implies a role for the muscarinic M3 receptor. The objective of this work was to study the contribution of the muscarinic M3 receptor to allergen-induced remodeling using muscarinic M3 receptor subtype-deficient (M3R(-/-)) mice. Wild-type (WT), M1R(-/-), and M2R(-/-) mice were used as controls. C57Bl/6 mice were sensitized and challenged with ovalbumin (twice weekly for 4 wk). Control animals were challenged with saline. Allergen exposure induced goblet cell metaplasia, airway smooth muscle thickening (1.7-fold), pulmonary vascular smooth muscle remodeling (1.5-fold), and deposition of collagen I (1.7-fold) and fibronectin (1.6-fold) in the airway wall of WT mice. These effects were absent or markedly lower in M3R(-/-) mice (30-100%), whereas M1R(-/-) and M2R(-/-) mice responded similarly to WT mice. In addition, airway smooth muscle and pulmonary vascular smooth muscle mass were 35-40% lower in saline-challenged M3R(-/-) mice compared with WT mice. Interestingly, allergen-induced airway inflammation, assessed as infiltrated eosinophils and T helper type 2 cytokine expression, was similar or even enhanced in M3R(-/-) mice. Our data indicate that acetylcholine contributes to allergen-induced remodeling and smooth muscle mass via the muscarinic M3 receptor, and not via M1 or M2 receptors. No stimulatory role for muscarinic M3 receptors in allergic inflammation was observed, suggesting that the role of acetylcholine in remodeling is independent of the allergic inflammatory response, and may involve bronchoconstriction.

Crosstalk between beta-2-adrenoceptor and muscarinic acetylcholine receptors in the airway

The M3 and M2 muscarinic acetylcholine receptors (mAChRs) and beta-2-adrenoceptors (β2ARs) are important regulators of airway cell function, and drugs targeting these receptors are among the first line drugs in the treatment of the obstructive lung diseases asthma and chronic obstructive lung disease (COPD). Cross-regulation or crosstalk between mAChRs and β2ARs in airway smooth muscle (ASM) helps determine the contractile state of the muscle, thus airway diameter and resistance to airflow. In this review we will detail mAChR and β2AR-signaling and crosstalk, focusing on events in the ASM cell but also addressing the function of these receptors in other cell types that impact airway physiology. We conclude by discussing how recent advances in GPCR pharmacology offer a unique opportunity to fine tune mAChR and β2AR signaling and their crosstalk, and thereby produce superior therapeutics for obstructive lung and other diseases.

M2 Muscarinic acetylcholine receptor modulates rat airway smooth muscle cell proliferation

Airways chronic inflammatory conditions in asthma and COPD are characterized by tissue remodeling, being smooth muscle hyperplasia, the most important feature. Non-neuronal and neuronal Acetylcholine acting on muscarinic receptors (MAChRs) has been postulated as determinant of tissue remodeling in asthma and COPD by promoting proliferation and phenotypic changes of airway smooth muscle cells (ASMC). The objective was to evaluate proliferative responses to muscarinic agonist as carbamylcholine (Cch) and to identify the MAchR subtype involved. ASMC were isolated from tracheal fragments of Sprague-Dawley rats by enzymatic digestion. Proliferation assays were performed by MTS-PMS method. Viability was confirmed by trypan blue exclusion method. Mitogens as, epidermal growth factor (EGF), Tumor necrosis factor-alpha (TNF-α) and fetal bovine serum (FBS) increased ASMC proliferation (p < 0.05, n = 5). Cch alone increased ASMC proliferation at 24 and 48 hrs. However, combination of Cch with other mitogens exhibited a dual effect, synergistic proliferation effect in the presence of EGF (5 ng/mL) and 5% FBS and inhibiting the proliferation induced by 10% FBS, EGF (10 ng/mL) and TNF-α (10 ng/mL). To determine the MAChR subtype involved in these biological responses, a titration curve of selective muscarinic antagonists were performed. The Cch stimulatory and inhibitory effects on ASCM proliferation was blocked by AF-DX-116 (M2AChR selective antagonist), in greater proportion than 4-DAMP (M3AChR selective antagonist), suggesting that the modulation of muscarinic agonist-induced proliferation is M2AChR mediated responses. Thus, M2AChR can activate multiple signal transduction systems and mediate both effects on ASMC proliferation depending on the plethora and variable airway microenvironments existing in asthma and COPD.

Airway smooth muscle in airway reactivity and remodeling: what have we learned?

It is now established that airway smooth muscle (ASM) has roles in determining airway structure and function, well beyond that as the major contractile element. Indeed, changes in ASM function are central to the manifestation of allergic, inflammatory, and fibrotic airway diseases in both children and adults, as well as to airway responses to local and environmental exposures. Emerging evidence points to novel signaling mechanisms within ASM cells of different species that serve to control diverse features, including 1) [Ca(2+)]i contractility and relaxation, 2) cell proliferation and apoptosis, 3) production and modulation of extracellular components, and 4) release of pro- vs. anti-inflammatory mediators and factors that regulate immunity as well as the function of other airway cell types, such as epithelium, fibroblasts, and nerves. These diverse effects of ASM "activity" result in modulation of bronchoconstriction vs. bronchodilation relevant to airway hyperresponsiveness, airway thickening, and fibrosis that influence compliance. This perspective highlights recent discoveries that reveal the central role of ASM in this regard and helps set the stage for future research toward understanding the pathways regulating ASM and, in turn, the influence of ASM on airway structure and function. Such exploration is key to development of novel therapeutic strategies that influence the pathophysiology of diseases such as asthma, chronic obstructive pulmonary disease, and pulmonary fibrosis.

Pathology of asthma

Asthma is a serious health and socioeconomic issue all over the world, affecting more than 300 million individuals. The disease is considered as an inflammatory disease in the airway, leading to airway hyperresponsiveness, obstruction, mucus hyper-production and airway wall remodeling. The presence of airway inflammation in asthmatic patients has been found in the nineteenth century. As the information in patients with asthma increase, paradigm change in immunology and molecular biology have resulted in an extensive evaluation of inflammatory cells and mediators involved in the pathophysiology of asthma. Moreover, it is recognized that airway remodeling into detail, characterized by thickening of the airway wall, can be profound consequences on the mechanics of airway narrowing and contribute to the chronic progression of the disease. Epithelial to mesenchymal transition plays an important role in airway remodeling. These epithelial and mesenchymal cells cause persistence of the inflammatory infiltration and induce histological changes in the airway wall, increasing thickness of the basement membrane, collagen deposition and smooth muscle hypertrophy and hyperplasia. Resulting of airway inflammation, airway remodeling leads to the airway wall thickening and induces increased airway smooth muscle mass, which generate asthmatic symptoms. Asthma is classically recognized as the typical Th2 disease, with increased IgE levels and eosinophilic inflammation in the airway. Emerging Th2 cytokines modulates the airway inflammation, which induces airway remodeling. Biological agents, which have specific molecular targets for these Th2 cytokines, are available and clinical trials for asthma are ongoing. However, the relatively simple paradigm has been doubted because of the realization that strategies designed to suppress Th2 function are not effective enough for all patients in the clinical trials. In the future, it is required to understand more details for phenotypes of asthma.

A new perspective on muscarinic receptor antagonism in obstructive airways diseases

Acetylcholine has traditionally only been regarded as a neurotransmitter of the parasympathetic nervous system, causing bronchoconstriction and mucus secretion in asthma and COPD by muscarinic receptor activation on airway smooth muscle and mucus-producing cells. Recent studies in experimental models indicate that muscarinic receptor stimulation in the airways also induces pro-inflammatory, pro-proliferative and pro-fibrotic effects, which may involve activation of airway structural and inflammatory cells by neuronal as well as non-neuronal acetylcholine. In addition, mechanical changes caused by muscarinic agonist-induced bronchoconstriction may be involved in airway remodeling. Crosstalk between muscarinic receptors and β2-adrenoceptors on airway smooth muscle causes a reduced bronchodilator response to β2-agonists, and a similar mechanism could possibly apply to the poor inhibition of inflammatory and remodeling processes by these drugs. Collectively, these findings provide novel perspectives for muscarinic receptor antagonists in asthma and COPD, since these drugs may not only acutely affect cholinergic airways obstruction, but also have important beneficial effects on β2-agonist responsiveness, airway inflammation and remodeling. The clinical relevance of these findings is presently under investigation and starting to emerge.