Reinoud Gosens

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

Excessive airway obstruction is the cause of symptoms and abnormal lung function in asthma. As airway smooth muscle (ASM) is the effecter controlling airway calibre, it is suspected that dysfunction of ASM contributes to the pathophysiology of asthma. However, the precise role of ASM in the series of events leading to asthmatic symptoms is not clear. It is not certain whether, in asthma, there is a change in the intrinsic properties of ASM, a change in the structure and mechanical properties of the noncontractile components of the airway wall, or a change in the interdependence of the airway wall with the surrounding lung parenchyma. All these potential changes could result from acute or chronic airway inflammation and associated tissue repair and remodelling. Anti-inflammatory therapy, however, does not “cure” asthma, and airway hyperresponsiveness can persist in asthmatics, even in the absence of airway inflammation. This is perhaps because the therapy does not directly address a fundamental abnormality of asthma, that of exaggerated airway narrowing due to excessive shortening of ASM. In the present study, a central role for airway smooth muscle in the pathogenesis of airway hyperresponsiveness in asthma is explored.

Inhibition of allergen-induced airway remodelling by tiotropium and budesonide: a comparison

Chronic inflammation in asthma and chronic obstructive pulmonary disease drives pathological structural remodelling of the airways. Using tiotropium bromide, acetylcholine was recently identified as playing a major regulatory role in airway smooth muscle remodelling in a guinea pig model of ongoing allergic asthma. The aim of the present study was to investigate other aspects of airway remodelling and to compare the effectiveness of tiotropium to the glucocorticosteroid budesonide. Ovalbumin-sensitised guinea pigs were challenged for 12 weeks with aerosolised ovalbumin. The ovalbumin induced airway smooth muscle thickening, hypercontractility of tracheal smooth muscle, increased pulmonary contractile protein (smooth-muscle myosin) abundance, mucous gland hypertrophy, an increase in mucin 5 subtypes A and C (MUC5AC)-positive goblet cell numbers and eosinophilia. It was reported previously that treatment with tiotropium inhibits airway smooth muscle thickening and contractile protein expression, and prevents tracheal hypercontractility. This study demonstrates that tiotropium also fully prevented allergen-induced mucous gland hypertrophy, and partially reduced the increase in MUC5AC-positive goblet cell numbers and eosinophil infiltration. Treatment with budesonide also prevented airway smooth muscle thickening, contractile protein expression, tracheal hypercontractility and mucous gland hypertrophy, and partially reduced MUC5AC-positive goblet cell numbers and eosinophilia. This study demonstrates that tiotropium and budesonide are similarly effective in inhibiting several aspects of airway remodelling, providing further evidence that the beneficial effects of tiotropium bromide might exceed those of bronchodilation.

The WNT signaling pathway from ligand secretion to gene transcription: molecular mechanisms and pharmacological targets.

Wingless/integrase-1 (WNT) signaling is a key pathway regulating various aspects of embryonic development; however it also underlies several pathological conditions in man, including various cancers and fibroproliferative diseases in several organs. Investigating the molecular processes involved in (canonical) WNT signaling will open new avenues for generating new therapeutics to specifically target diseases in which WNT signaling is aberrantly regulated. Here we describe the complexity of WNT signal transduction starting from the processes involved in WNT ligand biogenesis and secretion by WNT producing cells followed by a comprehensive overview of the molecular signaling events ultimately resulting in enhanced transcription of specific genes in WNT receiving cells. Finally, the possible targets for therapeutic intervention and the available pharmacological inhibitors for this complex signaling pathway are discussed.

Activation of WNT / β-Catenin Signaling in Pulmonary Fibroblasts by TGF-β1 Is Increased in Chronic Obstructive Pulmonary Disease

Background Chronic obstructive pulmonary disease (COPD) is characterized by abnormal extracellular matrix (ECM) turnover. Recently, activation of the WNT/β-catenin pathway has been associated with abnormal ECM turnover in various chronic diseases. We determined WNT-pathway gene expression in pulmonary fibroblasts of individuals with and without COPD and disentangled the role of β-catenin in fibroblast phenotype and function. Methods We assessed the expression of WNT-pathway genes and the functional role of β-catenin, using MRC-5 human lung fibroblasts and primary pulmonary fibroblasts of individuals with and without COPD. Results Pulmonary fibroblasts expressed mRNA of genes required for WNT signaling. Stimulation of fibroblasts with TGF-β1, a growth factor important in COPD pathogenesis, induced WNT-5B, FZD8, DVL3 and β-catenin mRNA expression. The induction of WNT-5B, FZD6, FZD8 and DVL3 mRNA by TGF-β1 was higher in fibroblasts of individuals with COPD than without COPD, whilst basal expression was similar. Accordingly, TGF-β1 activated β-catenin signaling, as shown by an increase in transcriptionally active and total β-catenin protein expression. Furthermore, TGF-β1 induced the expression of collagen1α1, α-sm-actin and fibronectin, which was attenuated by β-catenin specific siRNA and by pharmacological inhibition of β-catenin, whereas the TGF-β1-induced expression of PAI-1 was not affected. The induction of transcriptionally active β-catenin and subsequent fibronectin deposition induced by TGF-β1 were enhanced in pulmonary fibroblasts from individuals with COPD. Conclusions β-catenin signaling contributes to ECM production by pulmonary fibroblasts and contributes to myofibroblasts differentiation. WNT/β-catenin pathway expression and activation by TGF-β1 is enhanced in pulmonary fibroblasts from individuals with COPD. This suggests an important role of the WNT/β-catenin pathway in regulating fibroblast phenotype and function in COPD.

Airway hyperresponsiveness in asthma: lessons from in vitro model systems and animal models

Airway hyperresponsiveness (AHR) is a hallmark clinical symptom of asthma. At least two components of AHR have been identified: 1) baseline AHR, which is persistent and presumably caused by airway remodelling due to chronic recurrent airway inflammation; and 2) acute and variable AHR, which is associated with an episodic increase in airway inflammation due to environmental factors such as allergen exposure. Despite intensive research, the mechanisms underlying acute and chronic AHR are poorly understood. Owing to the complex variety of interactive processes that may be involved, in vitro model systems and animal models are indispensable to the unravelling of these mechanisms at the cellular and molecular level. The present paper focuses on a number of translational studies addressing the emerging central role of the airway smooth muscle cell, as a multicompetent cell involved in acute airway constriction as well as structural changes in the airways, in the pathophysiology of airway hyperresponsiveness.

Tiotropium inhibits pulmonary inflammation and remodelling in a guinea pig model of COPD

Airway remodelling and emphysema are major structural abnormalities in chronic obstructive pulmonary disease (COPD). In addition, pulmonary vascular remodelling may occur and contribute to pulmonary hypertension, a comorbidity of COPD. Increased cholinergic activity in COPD contributes to airflow limitation and, possibly, to inflammation and airway remodelling. This study aimed to investigate the role of acetylcholine in pulmonary inflammation and remodelling using an animal model of COPD. To this aim, guinea pigs were instilled intranasally with lipopolysaccharide (LPS) twice weekly for 12 weeks and were treated, by inhalation, with the long-acting muscarinic receptor antagonist tiotropium. Repeated LPS exposure induced airway and parenchymal neutrophilia, and increased goblet cell numbers, lung hydroxyproline content, airway wall collagen and airspace size. Furthermore, LPS increased the number of muscularised microvessels in the adventitia of cartilaginous airways. Tiotropium abrogated the LPS-induced increase in neutrophils, goblet cells, collagen deposition and muscularised microvessels, but had no effect on emphysema. In conclusion, tiotropium inhibits remodelling of the airways as well as pulmonary inflammation in a guinea pig model of COPD, suggesting that endogenous acetylcholine plays a major role in the pathogenesis of this disease.

Noncanonical WNT-5A signaling regulates TGF-β-induced extracellular matrix production by airway smooth muscle cells

Transforming growth factor β (TGF‐β), a key mediator of fibrotic responses, is increased in asthma and drives airway remodeling by inducing expression of extracellular matrix (ECM) proteins. We investigated the molecular mechanisms underlying TGF‐β‐induced ECM expression by airway smooth muscle cells and demonstrate a novel link between TGF‐β and Wingless/integrase 1 (WNT) signaling in ECM deposition. Airway smooth muscle expresses abundant WNT ligands, with the noncanonical WNT‐5A being the most profoundly expressed. Interestingly, WNT‐5A shows ~2‐fold higher abundance in airway smooth muscle cells isolated from individuals with asthma than individuals without asthma. WNT‐5A is markedly induced in response to TGF‐β (4–16‐fold; EC50 0.3 ng/ml) and is required for collagen and fibronectin expression by airway smooth muscle. WNT‐5A engages noncanonical WNT signaling pathways, as inhibition of Ca2+ and c‐Jun N‐terminal kinase (JNK) signaling attenuated this TGF‐β response, whereas the canonical WNT antagonist Dickkopf 1 (DKK‐1) did not. Accordingly, WNT‐5A induced JNK phosphorylation and nuclear translocation of nuclear factor of activated T cells c1 (NFATc1). Furthermore, silencing of the WNT‐5A receptors Frizzled 8 (FZD8) and RYK attenuated TGF‐β‐induced ECM expression. Collectively, these findings demonstrate that noncanonical WNT‐5A signaling is activated by and necessary for TGF‐β‐induced ECM production by airway smooth muscle cells, which could have significance in asthma pathogenesis.—Kumawat, K., Menzen, M. H., Bos, I. S. T., Baarsma, H. A., Borger, P., Roth, M., Tamm, M., Halayko, A. J., Simoons, M., Prins, A., Postma, D. S., Schmidt, M., and Gosens, R. Noncanonical WNT‐5A signaling regulates TGF‐β‐induced extracellular matrix production by airway smooth muscle cells. FASEB J. 27, 1631–1643 (2013). www.fasebj.org

Rho kinase inhibitors: A novel therapeutical intervention in asthma?

In asthma, inflammatory mediators that are released in the airways by recruited inflammatory cells and by resident structural cells result in airway hyperresponsiveness caused by increased bronchoconstriction. In addition, chronic inflammation appears to drive remodelling of the airways that contributes to the development of fixed airway obstruction and airway hyperresponsiveness in chronic asthma. Airway remodelling includes several key features such as excessive deposition of extracellular matrix proteins in the airway wall (fibrosis) and increased abundance of contractile airway smooth muscle encircling the airways. Current asthma therapy fails to inhibit these features satisfactorily. This review focuses on Rho kinase as a potential drug target in asthma, as compelling evidence from animal models and ex vivo studies suggests a central role for this enzyme and its associated signalling in acute and chronic airway hyperresponsiveness.

Allergic sensitization enhances the contribution of Rho-kinase to airway smooth muscle contraction

Repeated allergen challenge has been shown to increase the role of Rho‐kinase in airway smooth muscle (ASM) contraction. We considered the possibility that active allergic sensitization by itself, that is, without subsequent allergen exposure, could be sufficient to enhance Rho‐kinase‐mediated ASM contraction. Guinea pigs were actively IgE‐sensitized to ovalbumin (OA), using Al(OH)3 as adjuvant. Contractile responsiveness to Gq‐coupled receptor agonists (methacholine, histamine or PGF2α) was investigated in tracheal rings. No effect of sensitization was observed on basal‐ and methacholine‐induced myogenic tone. In contrast, potency of histamine and PGF2α increased, that is, EC50 decreased, after OA‐sensitization by 2.6‐ and 4.7‐fold, respectively, without effect on maximal contraction (Emax). Basal tone in preparations from both control and OA‐sensitized animals was strongly decreased in the presence of the Rho‐kinase inhibitor (+)‐(R)‐trans‐4‐(1‐aminoethyl)‐N‐(4‐pyridyl) cyclohexane carboxamide (Y‐27632) (1 μM). In control preparations, the Emax and potency of histamine were unaffected by Y‐27632, but were decreased for PGF2α (by 38.2% and 2.0‐fold, respectively). However, in preparations from OA‐sensitized animals, Y‐27632 induced a significant reduction in Emax (33.5%) and potency (2.3‐fold) of histamine and of PGF2α (48.3% and 6.6‐fold, respectively), normalizing the OA‐sensitization‐induced increase in sensitivity toward these agonists. We also investigated the contribution of Rho‐kinase in vivo by measuring airway responsiveness toward inhaled histamine in permanently instrumented, unanaesthetized control and OA‐sensitized guinea pigs. Treatment with Y‐27632 by inhalation (5 mM, nebulizer concentration) decreased airway responsiveness toward histamine both in control and OA‐sensitized animals. However, the histamine PC100 ratio pre/post Y‐27632 inhalation was significantly smaller in OA‐sensitized animals as compared to control animals, indicating an enhanced contribution of Rho‐kinase. Expression of RhoA, an upstream activator of Rho‐kinase, was significantly increased (2.6‐fold) in lung homogenates of OA‐sensitized guinea pigs compared to control animals, as determined by Western analysis. In conclusion, the results show a receptor‐dependent role of Rho‐kinase in agonist‐induced ASM contraction. The contribution of Rho‐kinase to contractile airway responsiveness, both in vivo and ex vivo, is augmented after active allergic sensitization, as a consequence of increased expression of RhoA presumably. Inhibition of the RhoA/Rho‐kinase pathway may be considered a useful pharmacotherapeutical target in allergy and asthma.

Muscarinic M3 receptor stimulation increases cigarette smoke-induced IL-8 secretion by human airway smooth muscle cells

Acetylcholine is the primary parasympathetic neurotransmitter in the airways and is known to cause bronchoconstriction and mucus secretion. Recent findings suggest that acetylcholine also regulates aspects of remodelling and inflammation through its action on muscarinic receptors. In the present study, we aimed to determine the effects of muscarinic receptor stimulation on cytokine production by human airway smooth muscle cells (primary and immortalised cell lines). The muscarinic receptor agonists carbachol and methacholine both induced modest effects on basal interleukin (IL)-8 and -6 secretion, whereas the secretion of RANTES, eotaxin, vascular endothelial growth factor-A and monocyte chemoattractant protein-1 was not affected. Secretion of IL-8 and -6 was only observed in immortalised airway smooth muscle cells that express muscarinic M3 receptors. In these cells, methacholine also significantly augmented IL-8 secretion in combination with cigarette smoke extract in a synergistic manner, whereas synergistic effects on IL-6 secretion were not significant. Muscarinic M3 receptors were the primary subtype involved in augmenting cigarette smoke extract-induced IL-8 secretion, as only tiotropium bromide and muscarinic M3 receptor subtype selective antagonists abrogated the effects of methacholine. Collectively, these results indicate that muscarinic M3 receptor stimulation augments cigarette smoke extract-induced cytokine production by airway smooth muscle. This interaction could be of importance in patients with chronic obstructive pulmonary disease.