Glucocorticoids inhibit proliferation, cyclin D1 expression, and retinoblastoma protein phosphorylation, but not activity of the extracellular-regulated kinases in human cultured airway smooth muscle

Asthma therapy and airway remodeling

Asthma is characterized by variable degrees of chronic inflammation and structural alterations in the airways. The most prominent abnormalities include epithelial denudation, goblet cell metaplasia, subepithelial thickening, increased airway smooth muscle mass, bronchial gland enlargement, angiogenesis, and alterations in extracellular matrix components, involving large and small airways. Chronic inflammation is thought to initiate and perpetuate cycles of tissue injury and repair in asthma, although remodeling may also occur in parallel with inflammation. In the absence of definite evidence on how different remodeling features affect lung function in asthma, the working hypothesis should be that structural alterations can lead to the development of persistent airway hyperresponsiveness and fixed airway obstruction. It is still unanswered whether and when to begin treating patients with asthma to prevent or reverse deleterious remodeling, which components of remodeling to target, and how to monitor remodeling. Consequently, efforts are being made to understand better the effects of conventional anti-inflammatory therapies, such as glucocorticosteroids, on airway structural changes. Animal models, in vitro studies, and some clinical studies have advanced present knowledge on the cellular and molecular pathways involved in airway remodeling. This has encouraged the development of biologicals aimed to target various components of airway remodeling. Progress in this area requires the explicit linking of modern structure-function analysis with innovative biopharmaceutical approaches.

KCa3.1 Ca2+ activated K+ channels regulate human airway smooth muscle proliferation

Airway smooth muscle cell hyperplasia contributes to airway remodeling and hyperreactivity characteristic of asthma. Changes to potassium channel activity in proliferating human airway smooth muscle (HASM) cells have been described, but no regulatory role in proliferation has been attributed to them. We sought to investigate the expression of the intermediate conductance calcium-activated potassium channel K(Ca)3.1 in HASM cells and investigate its role in proliferation. Smooth muscle cells derived from human airways were grown in vitro and K(Ca)3.1 channel expression was measured using Western blot, RT-PCR, and patch clamp electrophysiology. Pharmacologic inhibitors of the channel were used in assays of cellular proliferation, and flow cytometry was used to identify cell cycle regulation. HASM cells expressed K(Ca)3.1 channel mRNA, protein, and activity with up-regulation evident after transforming growth factor-beta stimulation. Pharmacologic inhibition of K(Ca)3.1 led to growth arrest in cells stimulated to proliferate with mitogens. These inhibitors did not cause cellular toxicity or induce apoptosis. We have demonstrated, for the first time, the expression of K(Ca)3.1 channels in HASM cells. In addition, we have shown that K(Ca)3.1 channels are important in HASM cell proliferation, making these channels a potential therapeutic target in airway remodeling.

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.

Mechanisms of induction of airway smooth muscle hyperplasia by transforming growth factor-beta

Airway smooth muscle (ASM) hyperplasia is a characteristic feature of the asthmatic airway, but the underlying mechanisms that induce ASM hyperplasia remain unknown. Because transforming growth factor (TGF)-beta is a potent regulator of ASM cell proliferation, we determined its expression and mitogenic signaling pathways in ASM cells. We obtained ASM cells by laser capture microdissection of bronchial biopsies and found that ASM cells from asthmatic patients expressed TGF-beta1 mRNA and protein to a greater extent than nonasthmatic individuals using real-time RT-PCR and immunohistochemistry, respectively. TGF-beta1 stimulated the growth of nonconfluent and confluent ASM cells either in the presence or absence of serum in a time- and concentration-dependent manner. The mitogenic activity of TGF-beta1 on ASM cells was inhibited by selective inhibitors of TGF-beta receptor I kinase (SD-208), phosphatidylinositol 3-kinase (PI3K, LY-294002), ERK (PD-98059), JNK (SP-600125), and NF-kappaB (AS-602868). On the other hand, p38 MAPK inhibitor (SB-203580) augmented TGF-beta1-induced proliferation. To study role of the Smads, we transduced ASM cells with an adenovirus vector-expressing Smad4, Smad7, or dominant-negative Smad3 and found no involvement of these Smads in TGF-beta1-induced proliferation. Dexamethasone caused a dose-dependent inhibition in TGF-beta1-induced proliferation. Our findings suggest that TGF-beta1 may act in an autocrine fashion to induce ASM hyperplasia, mediated by its receptor and several kinases including PI3K, ERK, and JNK, whereas p38 MAPK is a negative regulator. NF-kappaB is also involved in the TGF-beta1 mitogenic signaling, but Smad pathway does not appear important.

Inhaled corticosteroid prevents the thickening of airway smooth muscle in murine model of chronic asthma

Airway smooth muscle growth contributes to the mechanism of airway hyperresponsiveness (AHR) in asthma. Although current steroid use demonstrates anti-inflammatory activity, there is little reported on the action of corticosteroid on smooth muscle of the asthmatic airway. The present study investigated the effect of inhaled corticosteroid on the thickening of airway smooth muscle in bronchial asthma. 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 a week for 3 months. Mice were treated intranasally with fluticasone during the OVA challenge. Mice chronically exposed to OVA developed sustained eosinophilic airway inflammation compared with control mice. In addition, the mice chronically exposed to OVA developed features of airway remodeling, including thickening of the peribronchial smooth muscle layer. Intranasal administration of fluticasone inhibited the development of eosinophilic inflammation, and importantly, thickening of the smooth muscle layer. Moreover, intranasal fluticasone treatment reduced the transforming growth factor (TGF)-beta 1 level in bronchoalveolar lavage fluid and regulated active TGF-beta 1 signaling with a reduction in the expression of phospho-Smad2/3 and the concomitant up-regulation of Smad7 in lung tissue sections. These results suggest that intranasal administration of fluticasone can modulate the remodeling of airway smooth muscle via regulation of TGF-beta 1 production and active TGF-beta 1 signaling.

Regulation of airway smooth muscle alpha-actin expression by glucocorticoids

Airway smooth muscle hypertrophy appears to be present in severe asthma. However, the effect of corticosteroids on airway smooth muscle cell size or contractile protein expression has not been studied. We examined the effects of dexamethasone, fluticasone, and salmeterol on contractile protein expression in transforming growth factor (TGF)-beta-treated primary bronchial smooth muscle cells. Dexamethasone and fluticasone, but not salmeterol, each reduced expression of alpha-smooth muscle actin and the short isoform of myosin light chain kinase. Steady-state alpha-actin mRNA level and stability were unchanged, consistent with posttranscriptional control. Fluticasone significantly decreased alpha-actin protein synthesis following treatment with the transcriptional inhibitor actinomycin D, indicative of an inhibitory effect on mRNA translation. Fluticasone also significantly increased alpha-actin protein turnover. Finally, fluticasone reduced TGF-beta-induced incorporation of alpha-actin into filamentous actin, cell length, and cell shortening in response to ACh and KCl. We conclude that glucocorticoids reduce human airway smooth muscle alpha-smooth muscle actin expression and incorporation into contractile filaments, as well as contractile function, in part by attenuation of mRNA translation and enhancement of protein degradation.

Collagen impairs glucocorticoid actions in airway smooth muscle through integrin signalling

BACKGROUND AND PURPOSE

Airway wall remodelling in asthma is characterised by a number of structural changes, including an increase in the volume of airway smooth muscle (ASM), and the abundance of the extracellular matrix (ECM) protein, collagen, is increased. We have investigated the mechanism of collagen-induced glucocorticoid resistance of proliferation, and migration of ASM.

EXPERIMENTAL APPROACH

ASM cultured from human airways has been seeded on to either type I monomeric collagen or a laminin pentapeptide, YIGSR. The role of alpha2beta1 integrin in the collagen-induced glucocorticoid resistance was investigated using a function blocking monoclonal antibody.

KEY RESULTS

Culture of ASM on collagen I, but not laminin, led to a greater proliferative response that was insensitive to regulation by dexamethasone (100 nM). The anti-migratory effects of the glucocorticoid, fluticasone propionate (1 nM) were also impaired by contact of ASM with collagen. The impaired anti-mitogenic action of dexamethasone was associated with a failure to reduce the levels of the rate-limiting cell cycle regulatory protein, cyclin D1. When signalling through the alpha2beta1 integrin was reduced, dexamethasone-mediated reductions in proliferation and cyclin D1 levels were restored.

CONCLUSIONS AND IMPLICATIONS

In the collagen-rich microenvironment of the inflamed and fibrotic asthmatic airway, integrin/ECM interactions may contribute to glucocorticoid resistance.

Airway remodeling and airway smooth muscle in asthma

Airway remodeling in asthma has been recognized as structural changes of airways such as smooth muscle hypertrophy (an increase in size of airway smooth muscle cells) and hyperplasia (an increase in the number of airway smooth muscle cells), thickening and fibrosis of sub-epithelial basement membrane, hypertrophy of bronchial glands, goblet cell hyperplasia, and thickening of airway epithelium. In these pathological changes, airway smooth muscle remodeling has been recognized as one of the most important factors related to in vitro and in vitro airway responsiveness and the severity of asthma. Both hypertrophy and hyperplasia have been shown in asthmatic airways by morphometrical analyses, although there is a wide variation in the contribution of each mechanism in each patient. Such changes could also be recognized as a phenotypic modulation of airway smooth muscle. On the background of airway smooth muscle remodeling, the existence of several contributing factors, such as inflammatory mediators, growth factors, cytokines, extra-cellular matrix proteins, and genetic factors have been suggested. On the other hand, recent studies revealed that airway smooth muscle could also be a source of inflammatory mediators promoting airway inflammation. In this article, the recent understanding in the mechanisms of airway smooth muscle remodeling in asthma, its relations to airway inflammation and airway physiology, and possible usefulness of early intervention with inhaled glucocorticoids have been discussed.

Airway smooth muscle as a regulator of immune responses and bronchomotor tone

The traditional view of airway smooth muscle (ASM) in asthma, as a purely contractile tissue, seems to be inadequate. Compelling evidence now suggests that ASM plays an important role in regulating bronchomotor tone, in perpetuating airway inflammation, and in remodeling of the airways. This article reviews three distinct functions of ASM cells: the process of excitation-contraction coupling, with a particular focus on the role of cytokines in modulating calcium responses; the processes of smooth muscle cell proliferation and migration; and the synthetic and immunomodulatory function of ASM cells. This article also discusses how altered synthetic function contributes to airway remodeling.

The Glucocorticoid Receptor Represses Cyclin D1 by Targeting the Tcf-β-Catenin Complex

The ability of glucocorticoids (GCs) to regulate cell proliferation plays an important role in their therapeutic use. The canonical Wnt pathway, which promotes the proliferation of many cancers and differentiated tissues, is an emerging target for the actions of GCs, albeit existing links between these signaling pathways are indirect. By screening known Wnt target genes for their ability to respond differently to GCs in cells whose proliferation is either positively or negatively regulated by GCs, we identified c-myc, c-jun, and cyclin D1, which encode rate-limiting factors for G(1) progression of the cell cycle. Here we show that in U2OS/GR cells, which are growth-arrested by GCs, the glucocorticoid receptor (GR) represses cyclin D1 via Tcf-beta-catenin, the transcriptional effector of the canonical Wnt pathway. We demonstrate that GR can bind beta-catenin in vitro, suggesting that GC and Wnt signaling pathways are linked directly through their effectors. Down-regulation of beta-catenin by RNA interference impeded the expression of cyclin D1 but not of c-myc or c-jun and had no significant effect on the proliferation of U2OS/GR cells. Although these results revealed that beta-catenin and cyclin D1 are not essential for the regulation of U2OS/GR cell proliferation, considering the importance of the Wnt pathway for proliferation and differentiation of other cells, the repression of Tcf-beta-catenin activity by GR could open new possibilities for tissue-selective GC therapies.

The proliferative status of thyrotropes is dependent on modulation of specific cell cycle regulators by thyroid hormone

In this report we have examined changes in cell growth parameters, cell cycle effectors, and signaling pathways that accompany thyrotrope growth arrest by thyroid hormone (TH) and growth resumption after its withdrawal. Flow cytometry and immunohistochemistry of proliferation markers demonstrated that TH treatment of thyrotrope tumors resulted in a reduction in the fraction of cells in S-phase that is restored upon TH withdrawal. This is accompanied by dephosphorylation and rephosphorylation of retinoblastoma (Rb) protein. The expression levels of cyclin-dependent kinase 2 and cyclin A, as well as cyclin-dependent kinase 1 and cyclin B, were decreased by TH, and after withdrawal not only did these regulators of Rb phosphorylation and mitosis increase in their expression but so too did the D1 and D3 cyclins. We also noted a rapid induction and subsequent disappearance of the type 5 receptor for the growth inhibitor somatostatin with TH treatment and withdrawal, respectively. Because somatostatin can arrest growth by activating MAPK pathways, we examined these pathways in TtT-97 tumors and found that the ERK pathway and several of its upstream and downstream effectors, including cAMP response element binding protein, were activated with TH treatment and deactivated after its withdrawal. This led to the hypothesis that TH, acting through increased type 5 somatostatin receptor, could activate the ERK pathway leading to cAMP response element binding protein-dependent decreased expression of critical cell cycle proteins, specifically cyclin A, resulting in hypophosphorylation of Rb and its subsequent arrest of S-phase progression. These processes are reversed when TH is withdrawn, resulting in an increase in the fraction of S-phase cells.

Stimulus-dependent glucocorticoid-resistance of GM-CSF production in human cultured airway smooth muscle

For a subpopulation of asthmatics, symptoms persist even with high doses of glucocorticoids. Glucocorticoids reduce the levels of the proinflammatory and fibrogenic cytokine, granulocyte-macrophage colony-stimulating factor (GM-CSF) produced by human cultured airway smooth muscle (ASM). We have contrasted the effects of a synthetic glucocorticoid, dexamethasone, on thrombin- and IL-1alpha-stimulated GM-CSF production in human ASM cells. Although IL-1alpha stimulated three-fold higher levels of GM-CSF mRNA and protein compared to thrombin, dexamethasone concentration-dependently reduced IL-1alpha-stimulated GM-CSF more potently and to a greater extent than the response to thrombin. This pattern of glucocorticoid regulation was also observed at the GM-CSF mRNA level and was reproduced with other glucocorticoids such as fluticasone propionate. IL-1alpha and thrombin stimulated NF-kappa B-dependent luciferase expression equally. Dexamethasone treatment reduced luciferase expression stimulated by both IL-1alpha and thrombin. The GM-CSF mRNA half life was markedly prolonged by IL-1alpha compared to thrombin. This IL-1alpha-induced GM-CSF mRNA stability was prevented by either dexamethasone or the p38(MAPK) inhibitor, SB203580, neither of which influenced GM-CSF mRNA stability in thrombin-treated cells. Dexamethasone inhibited p38(MAPK) phosphorylation in IL-1alpha-stimulated ASM, whereas thrombin does not stimulate p38(MAPK) phosphorylation. These data suggest that the mechanism underlying the greater potency and efficacy of glucocorticoids in reducing GM-CSF synthesis stimulated by IL-1alpha depends on inhibition of the involvement of p38(MAPK)-induced increases in GM-CSF message stability.

Regulation of human airway mesenchymal cell proliferation by glucocorticoids and beta2-adrenoceptor agonists

Altered rates of cell proliferation play important roles in the pathogenesis of a variety of conditions, including cancer, inflammation and several airway and cardiovascular diseases. One of the most consistently observed changes in asthmatic airways is an increased volume of airway smooth muscle (ASM), that has been explained by proliferation, hypertrophy, extracellular matrix deposition within the smooth muscle bundles, and more recently, the migration of mesenchymal precursor cells to the airways. The best characterised of these is proliferation of ASM cells. In vitro studies suggest that the proliferation is driven by various mitogens, and ECM proteins found in asthma, such as collagen type I. Therefore, we compared the anti-mitogenic actions of two classes of anti-asthma agents, the glucocorticoids and the beta2-adrenoceptor agonists, in ASM cells grown on collagen type I. Culture on collagen type I prevented the anti-mitogenic actions of glucocorticoids, but not beta2-adrenoceptor agonists. In contrast, glucocorticoids are efficacious in regulating ASM production of GM-CSF, whereas beta2-adrenoceptor agonists are without effect. Therefore, combination therapy may have increased efficacy over glucocorticoids alone in controlling remodelling events due to complementary actions of the two classes of compounds.

The PPARgamma ligand, rosiglitazone, reduces airways hyperresponsiveness in a murine model of allergen-induced inflammation

There is considerable interest in the role of peroxisome proliferator activated receptors (PPARs) as ligand-activated transcription factors in the airways. This study examines the effects of a potent synthetic PPARgamma ligand, rosiglitazone (RG), in a murine model of allergen-induced inflammation, to explore its potential regulation of airways inflammation, structure and function. C57BL/6 mice were sensitised with ovalbumin (OVA, 50 microg i.p., days 0, 12) and challenged with aerosolized OVA (1% w v(-1), 30 min day(-1)) for 7 days (days 20-26). Mice were treated with RG (5 mg kg(-1) i.p.) or vehicle during the challenge period. The OVA challenge induced increases in leukocyte number and MMP-2 activity in bronchoalveolar lavage fluid and in goblet cell number in lung tissue obtained on Day 27. RG failed to inhibit inflammatory cell infiltration, MMP-2 activity or goblet cell hyperplasia. Respiratory resistance in response to methacholine (MCh i.v.) was greater in OVA-challenged mice than saline-challenged mice and this airways hyperresponsiveness (AHR) was reduced by RG. However, RG did not affect MCh-induced contraction in isolated guinea-pig tracheal rings, nor did it influence the airway obstruction induced by MCh in saline-challenged mice, so a direct effect on airway obstruction is unlikely. These data suggest that RG modulates AHR in this model, by a mechanism that is also potentially independent of an anti-inflammatory action.

Mitogen-activated protein kinases and asthma

Mitogen-activated protein kinases (MAPKs) are evolutionary conserved enzymes which play a key role in signal transduction mediated by cytokines, growth factors, neurotransmitters and various types of environmental stresses. In the airways, these extracellular stimuli elicit complex inflammatory and structural changes leading to the typical features of asthma including T cell activation, eosinophil and mast cell infiltration, as well as bronchial hyperresponsiveness and airway remodelling. Because MAPKs represent an important point of convergence for several different signalling pathways, they affect multiple aspects of normal airway function and also significantly contribute to asthma pathophysiology. Therefore, this review focuses on the crucial involvement of MAPKs in asthma pathogenesis, thus also discussing their emerging role as molecular targets for anti-asthma drugs.

Quantitative phase microscopy: A new tool for investigating the structure and function of unstained live cells

1. The optical transparency of unstained live cell specimens limits the extent to which information can be recovered from bright-field microscopic images because these specimens generally lack visible amplitude-modulating components. However, visualization of the phase modulation that occurs when light traverses these specimens can provide additional information. 2. Optical phase microscopy and derivatives of this technique, such as differential interference contrast (DIC) and Hoffman modulation contrast (HMC), have been used widely in the study of cellular materials. With these techniques, enhanced contrast is achieved, which is useful in viewing specimens, but does not allow quantitative information to be extracted from the phase content available in the images. 3. An innovative computational approach to phase microscopy, which provides mathematically derived information about specimen phase-modulating characteristics, has been described recently. Known as quantitative phase microscopy (QPM), this method derives quantitative phase measurements from images captured using a bright-field microscope without phase- or interference-contrast optics. 4. The phase map generated from the bright-field images by the QPM method can be used to emulate other contrast image modes (including DIC and HMC) for qualitative viewing. Quantitative phase microscopy achieves improved discrimination of cellular detail, which permits more rigorous image analysis procedures to be undertaken compared with conventional optical methods. 5. The phase map contains information about cell thickness and refractive index and can allow quantification of cellular morphology under experimental conditions. As an example, the proliferative properties of smooth muscle cells have been evaluated using QPM to track growth and confluency of cell cultures. Quantitative phase microscopy has also been used to investigate erythrocyte cell volume and morphology in different osmotic environments. 6. Quantitative phase microscopy is a valuable, new, non-destructive, non-interventional experimental tool for structural and functional cellular investigations.

Factors controlling airway smooth muscle proliferation in asthma

Airway smooth muscle proliferation has been the focus of considerable attention, as it is a quantitatively important component of the airway wall remodeling response in asthma and has been suggested as a suitable target for the development of novel anti-asthma agents. Such agents are considered likely to reduce airway hyperresponsiveness and, consequently, airway obstruction, resulting in fewer symptoms and exacerbations. Identifying suitable drug targets has proved an elusive goal, as no dominant molecular mechanism for remodeling has emerged. Moreover, recent findings raise some doubt as to whether smooth muscle proliferation per se is the explanation of the increase in smooth muscle cell number in asthma, with alternative explanations including the proposal that cells migrate either from the interstitial compartment or from a circulating precursor stem cell population. Therefore, drug targeting of migration responses should be considered as an alternative approach to regulating the smooth muscle component of airway wall remodeling.

Synthetic responses in airway smooth muscle

Human airway smooth muscle (ASM) has several properties and functions that contribute to asthma pathogenesis, and increasing attention is being paid to its synthetic capabilities. ASM can promote the formation of the interstitial extracellular matrix, and in this respect, ASM from asthmatic subjects compared with normal subjects responds differently, both qualitatively and quantitatively. Thus, ASM cells are important regulating cells that potentially contribute to the known alterations within the extracellular matrix in asthma. In addition, through integrin-directed signaling, extracellular matrix components can alter the proliferative, survival, and cytoskeletal synthetic function of ASM cells. ASM also functions as a rich source of biologically active chemokines and cytokines that are capable of perpetuating airway inflammation in asthma and chronic obstructive pulmonary disease by promoting recruitment, activation, and trafficking of inflammatory cells in the airway milieu. Emerging evidence shows that airway remodeling may also be a result of the autocrine action of secreted inflammatory mediators, including T(H)2 cytokines, growth factors, and COX-2-dependent prostanoids. Finally, ASM cells contain both beta(2)-adrenergic receptors and glucocorticoid receptors and may represent a key target for beta(2)-adrenergic receptor agonist/corticosteroid interactions. Combinations of long-acting beta(2)-agonists and corticosteroids appear to have additive and/or synergistic effects in inhibiting inflammatory mediator release and the migration and proliferation of ASM cells.

Proliferative aspects of airway smooth muscle

Increased airway smooth muscle (ASM) mass is perhaps the most important component of the airway wall remodeling process in asthma. Known mediators of ASM proliferation in cell culture models fall into 2 categories: those that activate receptors with intrinsic receptor tyrosine kinase activity and those that have their effects through receptors linked to heterotrimeric guanosine triphosphate-binding proteins. The major candidate signaling pathways activated by ASM mitogens are those dependent on extracellular signal-regulated kinase and phosphoinositide 3'-kinase. Increases in ASM mass may also involve ASM migration, and in culture, the key signaling mechanisms have been identified as the p38 mitogen-activated protein kinase and the p21-activated kinase 1 pathways. New evidence from an in vivo rat model indicates that primed CD4(+) T cells are sufficient to trigger ASM and epithelial remodeling after allergen challenge. Hyperplasia has been observed in an equine model of asthma and may account for the increase in ASM mass. Reduction in the rate of apoptosis may also play a role. beta(2)-Adrenergic receptor agonists and glucocorticoids have antiproliferative activity against a broad spectrum of mitogens, although it has become apparent that mitogens are differentially sensitive. Culture of ASM on collagen type I has been shown to enhance proliferative activity and prevent the inhibitory effect of glucocorticoids, whereas beta(2)-agonists are minimally affected. There is no evidence that long-acting beta(2)-agonists are more effective than short-acting agonists, but persistent stimulation of the beta(2)-adrenergic receptor probably helps suppress growth responses. The maximum response of fluticasone propionate against thrombin-induced proliferation is increased when it is combined with salmeterol.

Airway mucosal thickening and bronchial hyperresponsiveness induced by inhaled beta 2-agonist in mice

BACKGROUND

Patients with chronic persistent asthma require frequent use of inhaled beta(2)-agonist, which may result in aggravation of asthma symptoms. Our recent in vitro study has shown that beta(2)-agonist stimulates the growth of human airway epithelial cell lines.

STUDY OBJECTIVE

To determine whether beta(2)-agonist likewise affects airway epithelial cell proliferation in vivo and, if so, what the mechanism of action is, we examined the effect of salbutamol on the morphology of murine airways.

METHODS

Seventy-two BALB/c mice were administered aerosolized salbutamol using "flow-through" nose-only inhalation chambers at daily doses of 0.2 to 20 microg for up to 6 weeks. Morphology of tracheal mucosa, labeling of epithelial cells with 5-bromo-2'-deoxyuridine (BrdU), and bronchial responsiveness were assessed.

RESULTS

Exposure to salbutamol increased the thickness of tracheal epithelial layer and the number of BrdU-positive epithelial cells in a dose- and time-dependent manner: the values in mice receiving 20 microg salbutamol for 6 weeks were 247% and 642%, respectively, of those in control animals receiving saline solution alone. These effects were inhibited by the mitogen-activated protein (MAP) kinase kinase inhibitors PD98059 and U0126. Salbutamol also caused a decrease in the provocative concentration of methacholine to achieve 400% of baseline enhanced pause. Combined treatment with inhaled budesonide attenuated salbutamol-induced airway morphologic changes and bronchial hyperresponsiveness.

CONCLUSION

beta(2)-agonist stimulates proliferation of airway epithelial cells and produces airway wall thickening in vivo via MAP kinase-dependent pathway, and these effects are prevented by inhaled corticosteroid.

Dysfunctional interaction of C/EBPalpha and the glucocorticoid receptor in asthmatic bronchial smooth-muscle cells

BACKGROUND

Increased proliferation of bronchial smooth-muscle cells may lead to increased muscle mass in the airways of patients with asthma. The antiproliferative effect of glucocorticoids in bronchial smooth-muscle cells in subjects without asthma is mediated by a complex of the glucocorticoid receptor and the CCAAT/enhancer binding protein alpha (C/EBPalpha). We examined the signaling pathway controlling the inhibitory effect of glucocorticoids on cell proliferation and interleukin-6 synthesis in bronchial smooth-muscle cells of subjects with asthma and those without asthma.

METHODS

Lines of bronchial smooth-muscle cells were established from cells from 20 subjects with asthma, 8 subjects with emphysema, and 26 control subjects. Cell proliferation was determined by means of cell counts and [3H]thymidine incorporation. Signal transduction was studied by means of an electrophoretic DNA mobility-shift assay, a supershift electrophoretic-mobility assay, immunoblotting, use of C/EBPalpha antisense oligonucleotides, and use of a human C/EBPalpha expression vector. Interleukin-6 release was determined by means of an enzyme-linked immunosorbent assay.

RESULTS

Glucocorticoids activated the glucocorticoid receptor and inhibited serum-induced secretion of interleukin-6 in bronchial smooth-muscle cells from both subjects with asthma and those without asthma; however, glucocorticoids inhibited proliferation only in bronchial smooth-muscle cells from subjects without asthma. C/EBPalpha protein was detected by immunoblotting in all bronchial smooth-muscle cells from subjects without asthma but not in those with asthma, whereas the protein was expressed in lymphocytes from both groups of subjects. C/EBPalpha antisense oligonucleotides or the glucocorticoid-receptor inhibitor mifepristone reversed the antiproliferative effect of glucocorticoids in bronchial smooth-muscle cells from subjects without asthma. When bronchial smooth-muscle cells from subjects with asthma were transiently transfected with an expression vector for human C/EBPalpha, two forms of the protein were expressed, and subsequent administration of glucocorticoids inhibited cell proliferation.

CONCLUSIONS

We hypothesize that a cell-type-specific absence of C/EBPalpha is responsible for the enhanced proliferation of bronchial smooth-muscle cells derived from subjects with asthma and that it explains the failure of glucocorticoids to inhibit proliferation in vitro.

Contribution of the p38MAPK signalling pathway to proliferation in human cultured airway smooth muscle cells is mitogen-specific

We have investigated the role of p38MAPK in human airway smooth muscle (HASM) proliferation in response to thrombin and bFGF. The regulation of cyclin D1 mRNA, cyclin D1, cyclin E and p21Cip1 protein levels, and the extent of retinoblastoma protein (pRb) phosphorylation in response to activation of p38MAPK have also been examined. Two distinct inhibitors of p38MAPK, SB 203580 (10 microm) and SB 202190 (10 microm), prevented bFGF (0.3-3 nm)-stimulated cell proliferation, but had no effect on the response to thrombin (0.3-3 U ml(-1)). In cells incubated with thrombin or bFGF for 20 h, there was an increase in p38MAPK phosphorylation in response to bFGF, but not to thrombin. Thrombin and bFGF-stimulated increases in ERK phosphorylation and cyclin D1 mRNA and protein levels were not influenced by SB 203580 pre-treatment. Similarly, cyclin E and p21Cip1 protein levels, measured after 20 h incubation with mitogen, did not appear to be regulated by SB 203580 (10 microm). Although both thrombin and bFGF significantly increased levels of pRb phosphorylation, SB 203580 (10 microm) inhibited only bFGF-stimulated pRb phosphorylation. In addition, SB 203580 (10 microm) selectively inhibited bFGF-stimulated DNA synthesis, suggesting that the antimitogenic actions of SB 203580 on pRb phosphorylation cause cell cycle arrest at late G1 phase. In conclusion, these results indicate that p38MAPK is involved in bFGF-, but not in thrombin-stimulated HASM proliferation. The activation of the p38MAPK pathway by bFGF, but not by thrombin, regulates the phosphorylation of pRb without influencing cyclin D1 expression.

PPAR gamma ligands, 15-deoxy-delta12,14-prostaglandin J2 and rosiglitazone regulate human cultured airway smooth muscle proliferation through different mechanisms

The influence of two peroxisome proliferator-activated receptor gamma (PPARgamma) ligands, a thiazolidinedione, rosiglitazone (RG) and the prostaglandin D2 metabolite 15-deoxy-Delta(12,14)-prostaglandin J2 (15d-PGJ2) on the proliferation of human cultured airway smooth muscle (HASM) was examined. The increases in HASM cell number in response to basic fibroblast growth factor (bFGF, 300 pm) or thrombin (0.3 U ml-1) were significantly inhibited by either RG (1-10 microM) or 15d-PGJ2 (1-10 microM). The effects of RG, but not 15d-PGJ2, were reversed by the selective PPARgamma antagonist GW9662 (1 microM). Neither RG nor 15d-PGJ2 (10 microM) decreased cell viability, or induced apoptosis, suggesting that the regulation of cell number was due to inhibition of proliferation, rather than increased cell death. Flow-cytometric analysis of HASM cell cycle distribution 24 h after bFGF addition showed that RG prevented the progression of cells from G1 to S phase. In contrast, 15d-PGJ2 caused an increase in the proportion of cells in S phase, and a decrease in G2/M, compared to bFGF alone. Neither RG nor 15d-PGJ2 inhibited ERK phosphorylation measured 6 h post mitogen addition. The bFGF-mediated increase in cyclin D1 protein levels after 8 h was reduced in the presence of 15d-PGJ2, but not RG. Although both RG and 15d-PGJ2 can inhibit proliferation of HASM irrespective of the mitogen used, only the antiproliferative effects of RG appear to be PPARgamma-dependent. The different antimitogenic mechanisms of 15d-PGJ2 and synthetic ligands for PPARgamma may be exploited to optimise the potential for these compounds to inhibit airway remodelling in asthma. British Journal of Pharmacology (2004) 141, 517-525. doi:10.1038/sj.bjp.0705630

Increased P27KIP1 protein expression in the dentate gyrus of chronically stressed rats indicates G1 arrest involvement

Various chronic stress paradigms decrease new cell proliferation in the hippocampal dentate gyrus, yet the exact underlying mechanism is still unclear. In the first gap (G1) phase of the cell cycle, both stimulatory and inhibitory signals derived from the extracellular environment converge. Corticosteroids, which increase during stress and are well-known anti-mitotics, cause cells in vitro to arrest in the G1 phase. Following 3 weeks of unpredictable stress, we therefore expected a change in protein expression of various important G1 cell cycle regulators in the adult rat subgranular zone. Using quantitative immunocytochemistry, we show that particularly cyclin-dependent kinase inhibitor p27Kip1 expression is significantly increased. In addition, 3 weeks of recovery after stress normalized the numbers of p27Kip1-expressing cells, consistent with the recovered adult cell proliferation in these animals. P27Kip1-positive cells do not overlap with GFAP-staining and only to a limited extent with Ki-67-expressing cells. Numbers of cyclin E- and cyclin D1-expressing cells did not change after chronic stress. These results indicate that chronic stress causes cycling cells in the adult hippocampus to arrest in G1, thereby providing more mechanistic insight in the stress-induced decrease in cell proliferation.

Dexamethasone inhibits early regenerative response of rat liver after cold preservation and transplantation

Regeneration is crucial for the recovery of hepatic mass following liver transplantation. Glucocorticoids, immunosuppressive and antiinflammatory agents commonly used in transplantation, are known to inhibit the expression of specific cytokines and growth factors. Some of these proteins, namely tumor necrosis factor alpha (TNF-alpha) and interleukin 6 (IL-6), play a critical role in the initiation of liver regeneration. Following cold preservation and reperfusion of the transplanted liver, the normal recovery process is marked by increased expression of TNF-alpha and IL-6, followed by activation of cytokine-responsive transcription factors and progression of the cell cycle resulting in hepatocyte proliferation. We hypothesized that glucocorticoids may influence the repair mechanisms initiated after extended cold preservation and transplantation. Using a rat orthotopic liver transplant model, recipient animals were treated with dexamethasone at the time of transplantation of liver grafts with prolonged cold storage (16 hours). Treatment with dexamethasone suppressed and delayed the expression of TNF-alpha and IL-6 compared with animals receiving no treatment and attenuated downstream nuclear factor kappaB (NF-kappaB), signal transduction and activator of transcription 3 (STAT3), and activation protein 1 (AP-1) activation. This suppression was accompanied by poor cell-cycle progression, delayed cyclin D1 nuclear transposition, and impaired hepatocyte proliferation by BrdU uptake. Histologically, the liver grafts in treated animals demonstrated more injury than controls, which appeared to be necrosis, rather than apoptosis. In conclusion, these data provide evidence that the administration of glucocorticoids at the time of transplantation inhibits the initiation of the regenerative process and may have a deleterious effect on the recovery of liver grafts requiring significant regeneration. This may be particularly relevant for transplantation of partial liver grafts in the living donor setting.

Mitogenic signaling pathways in airway smooth muscle

Increased airway smooth muscle mass has been demonstrated in patients with asthma, bronchopulmonary dysplasia and most recently, cystic fibrosis. These observations emphasize the need for further knowledge of the events involved in airway smooth muscle mitogenesis and hypertrophy. Workers in the field have developed cell culture systems involving tracheal and bronchial myocytes from different species. An emergent body of literature indicates that mutual signal transduction pathways control airway smooth muscle cell cycle entry across species lines. This article reviews what is known about mitogen-activated signal transduction in airway myocytes. The extracellular signal regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI 3-kinase) pathways appear to be key positive regulators of airway smooth muscle mitogenesis; recent studies have also demonstrated specific roles for reactive oxygen and the JAK/STAT pathway. It is also possible that growth factor stimulation of airway smooth muscle concurrently elicits signaling through negative regulatory intermediates such as p38 mitogen-activated protein (MAP) kinase and protein kinase C (PKC) delta, conceivably as a defense against extreme growth.

Airway smooth muscle: immunomodulatory cells that modulate airway remodeling?

Although the pathogenesis of asthma remains unclear, substantial progress has been made over the past decades in the characterization of airway inflammation as a pathogenetic mechanism in asthma. New evidence suggests that airway smooth muscle (ASM), the most important cell modulating bronchomotor tone, plays an important immunomodulatory role in the orchestration and perpetuation of airway inflammation. Evidence now suggests that the signaling pathways that modulate leukocyte function may be disparate from those found in resident effector cells such as ASM, fibroblasts and epithelial cells. Further investigation and understanding of the critical signaling pathways that modulate ASM cell release, secretion of chemokines/cytokines and expression of cell adhesion molecules (CAMs) may offer new therapeutic approaches in the treatment of asthma.

Differential inhibition of thrombin- and EGF-stimulated human cultured airway smooth muscle proliferation by glucocorticoids

The present study compared the effects of glucocorticoids on thrombin- and EGF-stimulated proliferation in human cultured airway smooth muscle (ASM) to identify pathways that may be differentially regulated by glucocorticoids. Mitogenic responses to thrombin were inhibited by extracellular-regulated kinase (ERK 1/2) and phosphoinositide 3-kinase (PI3K) inhibitors, whereas mitogenic responses to EGF were inhibited by ERK 1/2 and PI3K inhibitors as well as by the p38 mitogen activated protein kinase inhibitor, SB203580 (10 microM). Mitogenic responses to thrombin were more sensitive to inhibition by dexamethasone (Dex) or fluticasone propionate (FP) than were those to EGF. Elevated cyclin D1 protein and mRNA levels induced by thrombin and EGF were attenuated equally by glucocorticoids. The protein or mRNA levels of the cyclin-dependent kinase inhibitors (cdki) p21(Cip1), p27(Kip1) were unaffected by Dex treatment of ASM cells treated with mitogens. The resistance of EGF-induced proliferation to inhibition by glucocorticoids is not associated with a failure to regulate cyclin D1 induction, nor does it appear to be explained by differential regulation of the levels of the cdki's, p21(Cip1) and p27(Kip1).

Cyclic AMP-mobilizing agents and glucocorticoids modulate human smooth muscle cell migration

Hyperplasia and cell migration of smooth muscle are features of both airway and pulmonary vascular diseases. The precise cellular and molecular mechanisms that regulate smooth muscle migration in the lungs remain unknown. In this study, we examined the effect of cAMP-mobilizing agents and steroids on smooth muscle cell migration. Platelet-derived growth factor (PDGF), transforming growth factor-alpha, vascular endothelial growth factor, and basic fibroblast growth factor significantly stimulated cell migration in pulmonary vascular smooth muscle (PVSM) cells. Airway smooth muscle (ASM) migration was also stimulated by PDGF, transforming growth factor-alpha, and basic fibroblast growth factor, but vascular endothelial growth factor was without effect. Interestingly, the smooth muscle mitogen thrombin did not stimulate migration of either cell type. Agents capable of elevating intracellular cAMP inhibited basal (unstimulated) cell migration in both cell types, whereas their effects on PDGF-stimulated migration were more variable. Prostaglandin E2, salmeterol, and the phosphodiesterase type 4 inhibitor cilomolast inhibited basal ASM and PVSM migration by 30-60%. Prostaglandin E2 and cilomolast also inhibited PDGF-stimulated migration of ASM and PVSM cells, but salmeterol was without effect. Preincubation of ASM cells with dexamethasone or fluticasone inhibited basal and PDGF-stimulated migration, and enabled an inhibitory effect of salmeterol on PDGF-induced cell migration. Steroids alone did not stimulate cAMP production or cAMP/PKA-dependent gene transcription (CRE-Luc activity), but slightly augmented salmeterol-stimulated CRE-Luc activity. Collectively, these findings demonstrate that cAMP-mobilizing agents and steroids modulate human smooth muscle cell migration, likely by distinct mechanisms.

IFN-gamma inhibits human airway smooth muscle cell proliferation by modulating the E2F-1/Rb pathway

Elucidating the factors that inhibit the increase in airway smooth muscle (ASM) mass may be of therapeutic benefit in asthma. Here, we investigated whether interferon-gamma (IFN-gamma), a potent inducer of growth arrest in various cell types, regulates mitogen-induced ASM cell proliferation. IFN-gamma (1-100 U/ml) was found to markedly decrease both DNA synthesis and ASM cell number induced by the mitogens epidermal growth factor (EGF) and thrombin. Interestingly, IFN-gamma had no effect on mitogen-induced activation of three major mitogenic signaling pathways, phosphatidylinositol 3-kinase, p70(S6k), or mitogen-activated protein kinases. Mitogen-induced expression of cell cycle regulator cyclin D1 was increased by IFN-gamma, whereas no effect was observed on degradation of p27(Kip1). Expression array analysis of 23 cell cycle-related genes showed that IFN-gamma inhibited EGF-induced increases in E2F-1 expression, whereas induction of c-myc, cyclin D2, Egr-1, and mdm2 were unaffected. Induction of E2F-1 protein and Rb hyperphosphorylation after mitogen stimulation was also suppressed by IFN-gamma. In addition, IFN-gamma decreased activation of cdk2 and expression of cyclin E, upstream signaling molecules responsible for Rb hyperphosphorylation in the late G1 phase. IFN-gamma also increased levels of IFI 16 protein, whose mouse homolog p202 has been associated with growth inhibition. Together, our data indicate that IFN-gamma is an effective inhibitor of ASM cell proliferation by blocking transition from G1-to-S phase by acting at two different levels: modulation of cdk2/cyclin E activation and inhibition of E2F-1 gene expression.

Impact of extracellular matrix and strain on proliferation of bovine airway smooth muscle

1. The proliferation of airway smooth muscle (ASM) and collagen deposition are major contributors to airway remodelling in asthma that may be an important component of airway hyperresponsiveness. The ratio of collagen to laminin in asthma is increased as a result of fibrosis. 2. We investigated the effects of the extracellular matrix proteins laminin and collagen type I, as well as airway cell elongation (mechanical strain), on the proliferative responses of cultured bovine ASM cells and the impact of these biomechanical influences on glucocorticoid antimitogenic actions. 3. Bovine ASM cells were cultured onto a flexible silastic membrane coated with laminin or collagen. Cells were pretreated with dexamethasone (100 nmol/L) prior to incubation with the mitogen basic fibroblast growth factor (bFGF) for 72 h, at which time cells were enumerated. Cells were either subjected to mechanical strain (cell elongation) by stretching the flexible silastic membrane or were grown under static conditions. 4. Culture on collagen without elongation enhanced ASM proliferation compared with cells grown on laminin. Cells grown on laminin and subjected to 4% elongation did not respond to the mitogenic actions of bFGF. 5. Dexamethasone-mediated inhibition of bFGF-induced proliferation was unaffected by the extracellular matrix on which cells were seeded, or the degree of cell elongation. 6. These data support the hypothesis that the asthmatic airway wall microenvironment (collagen, reduced airway strain) enhances the proliferation of ASM cells.

Collagen-induced resistance to glucocorticoid anti-mitogenic actions: a potential explanation of smooth muscle hyperplasia in the asthmatic remodelled airway

Glucocorticoids (GCS) inhibit mitogenesis of airway smooth muscle (ASM) cells grown on plastic. We have now evaluated the effects of GCS on proliferation of ASM grown on extracellular matrix proteins (ECM) abundant in noninflamed airways (laminin) and in fibrotic asthmatic airways (collagen type I). Dexamethasone inhibited basic fibroblast growth factor (bFGF)-induced proliferation in cells maintained on laminin, but not collagen. Cells grown on collagen were resistant to the anti-mitogenic actions of fluticasone propionate. In addition, dexamethasone did not inhibit thrombin-induced proliferation. Thus, resistance induced by collagen is not dependent on the mitogen and appears to be a class effect on GCS. The inhibition of bFGF-induced granulocyte-macrophage colony-stimulating factor production was unaffected by the ECM type on which cells were grown. The impaired anti-mitogenic activity of GCS in cells maintained on collagen may be due to a lack of efficacy against the collagen-amplified mitogenesis, rather than any defect in responsiveness that is specific to glucocorticoid receptor mechanisms.

Protease-activated receptor (PAR)-independent growth and pro-inflammatory actions of thrombin on human cultured airway smooth muscle

(1) Thrombin, a mitogen for human cultured airway smooth muscle (HASM), has many actions that have been attributed to activation of protease-activated receptor (PARs). However, the role of PARs in the proliferative action has not been clearly identified. Moreover, thrombin elicits cytokine production in a number of cell types, but these effects have not been characterized in human ASM. (2) Thrombin (0.03-3 U ml(-1))-stimulated increases in the levels of the pro-inflammatory and fibrogenic cytokine, granulocyte-macrophage colony-stimulating factor (GM-CSF) were observed over the same concentration range observed for thrombin-stimulated mitogenesis. (3) Inhibition of thrombin proteolytic activity, with either D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone (PPACK)- or hirudin-treated thrombin (0.3 U ml(-1)) or in the presence of the thrombin serine protease-selective inhibitor, SDZ 217-766 (0.15 micro M), reduced the thrombin-stimulated GM-CSF levels by 91+/-3, 65+/-12 and 83+/-9% (n=8, P<0.05), respectively. PPACK treatment, hirudin and SDZ 217-766 inhibited thrombin-stimulated increase in cell number by 70+/-8, 63+/-11 and 69+/-8%, respectively. (4) PAR-selective peptides SFLLRN (PAR1; 10 micro M), SLIGKV (PAR2; 10 micro M), GYPGQV (PAR4; 100 micro M) or the combination of SFLLRN and GYPGQV elicited mitogenic responses of only 15% of that to thrombin and surprisingly, had no effect on GM-CSF levels (n=8). Nevertheless, inhibition of thrombin responses by pertussis toxin (50 ng ml(-1)) suggests that the PAR-independent actions also involve a G-protein-coupled receptor. (5) PAR1 receptor expression was evident by immunohistochemistry and these receptors were coupled to increases in intracellular calcium, but not to the phosphorylation of ERK or the increases in cyclin D1 protein levels that are essential for cell proliferation. Cross-desensitization of intracellular calcium increases by thrombin and the PAR1-selective peptide provides evidence that the PAR1 receptor responds to both ligands. (6) The failure of PAR-selective peptides to mimic thrombin responses together with the inhibition of thrombin responses by serine protease inhibitors suggest the involvement of novel proteolytic receptor targets for thrombin-induced mitogenesis and cytokine production.

Molecular mechanisms of corticosteroid actions in chronic inflammatory airway diseases

Although corticosteroids have been used for a long time as a very effective therapy of airway inflammatory diseases such as asthma, only recently the molecular basis of their mechanism of action has begun to be elucidated. These hormones exert their biological and pharmacological actions by binding to cytoplasmic receptors that, upon activation, translocate to the nucleus where they interact with specific genomic sequences thus modulating gene expression. However, many glucocorticoid effects responsible for their anti-inflammatory and anti-asthmatic activity take place irrespectively of receptor binding to DNA. In particular, ligand-bound glucocorticoid receptors can repress several different pro-inflammatory genes by physically associating, via protein-protein interactions, with various transcription factors and with the macromolecular complexes implicated in regulation of chromatin structure and function. In this regard, an important role is played by the influences of corticosteroids on the intrinsic histone acetyltransferase and deacetylase functions of coactivators and corepressors, respectively. Furthermore, the signal transduction pathways mediated by mitogen-activated protein kinases are newly recognized, key targets of glucocorticoids. Indeed, these enzymatic cascades are crucially involved in the regulation of gene expression in that they are essential for the activity of a high number of transcription factors. Therefore, the recent advances made in such a rapidly growing research field are providing new insights into the mode of action of corticosteroids, thereby also unveiling novel promising therapeutic strategies directly targeted to the molecular events underlying the inflammatory, immune, and apoptotic processes implicated in the pathogenesis of asthma and other airway diseases.

Pharmacotherapy and airway remodelling in asthma?

Over the last few decades attention has largely focused on airway inflammation in asthma, but more recently it has been appreciated that there are important structural airway changes which have been grouped together under the term "airway remodelling". It is only now that questions have been asked about the impact of treatment on these structural changes. This review examines the nature of these structural airway changes, the mechanisms of their generation, their potential consequences, and what is known about the ability of anti-asthma treatments to modulate these changes.

In vivo and in vitro effects of SAR 943, a rapamycin analogue, on airway inflammation and remodeling

No current therapy is considered to be satisfactory for severe asthma, and alternative approaches are still required for what is a major unmet medical need. In this study, we compared the effect of a rapamycin derivative, SAR 943, with budesonide, using a murine model of lung inflammation and remodeling. Allergen challenge of ovalbumin-sensitized BALB/c mice induced an increase in the levels of interleukin-5 and interleukin-4; numbers of eosinophil, neutrophil, and lymphocyte; cellular fibronectin; lung epithelial cell proliferation and mucus hypersecretory phenotype; as well as hyperreactivity to methacholine. Both SAR 943 and budesonide, when given intranasally 1 hour before and 24 hours after the aerosol challenge, inhibited all of these parameters with a similar potency (effective dose 50% of 1 mg/kg). In primary cultured smooth muscle cells from human airways, SAR 943 dose dependently inhibited epidermal growth factor-induced proliferation but did not affect the basal cell proliferation. Neither the basal nor stimulated proliferation of a human bronchial epithelial cell line (16HBE14o-) was affected by SAR 943. In conclusion, SAR 943 is as effective as budesonide in inhibiting both lung inflammation and remodeling in a murine model of asthma. Hence, this class of compound could offer beneficial effects in patients with severe asthma.

Airway smooth muscle: an immunomodulatory cell

Asthma is characterized in part by reversible airflow obstruction, hyperresponsiveness, and inflammation. Chronic obstructive pulmonary disease, which includes chronic bronchitis, emphysema, and possibly bronchiectasis, is defined as predominantly irreversible airflow obstruction associated with abnormal airway inflammation. Traditional concepts concerning airway inflammation have focused on trafficking leukocytes and on the effects of inflammatory mediators, cytokines, and chemokines secreted by these cells. Airway smooth muscle, the major effector cell responsible for bronchomotor tone, has been viewed as a target tissue responding to neurohumoral control and inflammatory mediators. New evidence, however, suggests that airway smooth muscle may secrete cytokines and chemokines and express cellular adhesion molecules that are important in modulating submucosal airway inflammation. Other new evidence suggests that beta-adrenergic agents may inhibit some but not all of the inflammatory responses. In certain circumstances, increasing levels of cyclic adenosine monophosphate in the cytosol of airway smooth muscle promote the secretion of other cytokines or chemokines. The cellular and molecular mechanisms that regulate the immunomodulatory functions of airway smooth muscle may offer new and important therapeutic targets in treating these common lung diseases.

Interaction between glucocorticoids and beta2 agonists on bronchial airway smooth muscle cells through synchronised cellular signalling

BACKGROUND

Increased airway smooth muscle bulk is a pathological feature of asthma. Asthma is well controlled by the combined inhalation of glucocorticoids and beta2-adrenoceptor agonists. The basic molecular mechanism of the interaction of the two drugs on proliferation of airway smooth muscle cells is yet to be identified. Our aim was to elucidate how glucocorticoids and beta2 agonists affect the growth of human bronchial airway smooth muscle cells.

METHODS

We assessed the effect of formoterol and budesonide on the activation and function of transcription factors by immunohistochemistry, western blotting, DNA mobility shift assay, and a luciferase reporter gene assay. The effect of the drugs and the involvement of specific transcription factors on cell proliferation was ascertained by direct cell count and confirmed by thymidine incorporation.

FINDINGS

Both classes of drugs (10(-8) mol/L) activated C/EBP-alpha and the glucocorticoid receptor with different kinetic profiles, and inhibited proliferation. The combination of lower doses of drugs (10(-12) to 10(-9) mol/L) resulted in a synchronised activation of the transcription factors and an enhanced antiproliferative effect. The action of the drugs alone or in combination on transcription-factor activity and proliferation was suppressed by either depletion of C/EBP-alpha or in the presence of a glucocorticoid-receptor blocker.

INTERPRETATION

Our findings could provide one explanation for the interaction of beta2 agonists and glucocorticoids at a molecular level, and indicate that the concentration of inhaled glucocorticoids can be reduced when combined with beta2 agonists, minimising the side-effects of the drugs.

Glucocorticoids inhibit lung cancer cell growth through both the extracellular signal-related kinase pathway and cell cycle regulators

Glucocorticoids inhibit the proliferation of various cell types, but the mechanism of this inhibition remains unclear. We investigated the effect of dexamethasone on non-small cell lung cancer cell growth and cell cycle progression. We showed that dexamethasone suppresses the proliferation of A549 and Calu-1 cells, with accumulation of cells in G1/G0 stage of the cell cycle, as determined by fluorescence-activated cell sorter analysis. Western blot analysis confirmed that this is associated with hypophosphorylation of retinoblastoma protein. Using Western blot analysis and in vitro kinase assays, we found that dexamethasone results in decreased activity of CDK2 and 4, decreased levels of cyclin D, E2F, and Myc, and increased levels of the CDK inhibitor p21(Cip1). In addition, we found that dexamethasone decreases activity of extracellular signal-related kinase (ERK)/mitogen-activated protein kinase (MAPK). The kinetics of all these changes indicate that inhibition of the ERK/MAPK pathway precedes the cell cycle effects, suggesting that regulation of this MAPK-signaling pathway may be an alternative mechanism for glucocorticoid-induced cell cycle arrest and growth inhibition.

Regulation of airway smooth muscle cyclin D1 transcription by protein kinase C-delta

The precise mechanism by which protein kinase C-delta (PKCdelta) inhibits cell cycle progression is not known. We investigated the regulation of cyclin D1 transcription by PKCdelta in primary bovine airway smooth muscle cells. Overexpression of the active catalytic subunit of PKCdelta attenuated platelet-derived growth factor (PDGF)-mediated transcription from the cyclin D1 promoter, whereas overexpression of a dominant-negative PKCdelta increased promoter activity. A PKCdelta-specific pseudosubstrate increased cyclin D1 protein abundance. To determine the transcriptional mechanism by which PKCdelta negatively regulates cyclin D1 expression, we transiently transfected cells with cDNAs encoding cyclin D1 promoter 5' deletions and site mutations in the context of a -66 promoter fragment. We found that the -57 to -52 CRE/ATF2 site functions as a basal level and PDGF enhancer, whereas the -39 to -30 nuclear factor-kappaB site functions as a basal level suppressor. Further, PDGF and PKCdelta responsiveness of the cyclin D1 promoter was maintained following 5' deletion to the Ets-containing -22 minimal promoter. Finally, using electrophoretic mobility gel shift and reporter assays, we determined that PKCdelta inhibits CRE/ATF2 binding and transactivation, activates nuclear factor-kappaB binding and transactivation, and attenuates Ets transactivation. These data suggest that PKCdelta attenuates cyclin D1 promoter activity via the regulation of three distinct cis-acting regulatory elements.

2-Methoxyestradiol and analogs as novel antiproliferative agents: analysis of three-dimensional quantitative structure-activity relationships for DNA synthesis inhibition and estrogen receptor binding

2-Methoxyestradiol (2-MEO), a metabolite of estrogen, is an attractive lead compound for the development of novel antitumor and anti-inflammatory agents, because it embodies antiproliferative and antiangiogenic activities in one molecule. However, the affinity of 2-MEO for the estrogen receptor would lead to undesirable side effects. As a prelude to the design of 2-MEO-like compounds with an optimal activity profile, we assayed 2-MEO and a series of analogs for their ability to cause G(1) cell-cycle arrest (by measuring inhibition of DNA synthesis in human cultured airway smooth muscle) and to inhibit binding of [(3)H]estradiol at the estrogen receptor (ER; from rat uterine smooth muscle). One compound, a diacetoxy enediol derivative, was identified with reasonable potency for DNA synthesis (pIC(50) = 5.97) but showed negligible affinity for the ER (pIC(50) < 5). Three-dimensional quantitative structure-activity relationships were developed for these activities using comparative molecular field analysis (CoMFA) techniques. Comparison of optimized CoMFA models revealed distinct structural requirements for DNA synthesis inhibition and ER binding. For example, DNA synthesis inhibition is enhanced by electropositive substitutions in the 2-position below the plane of the steroid A-ring, whereas ER binding is favored by electronegative substitution in this position. Similarly, DNA synthesis inhibition correlates negatively with increased steric bulk in regions clustered around the A and B rings; changes in steric bulk in these regions has little correlation with ER binding. These observations will guide the design of new analogs with improved potency for desired characteristics (e.g., DNA synthesis inhibition) with minimal unwanted activities (e.g., ER binding).

Expression of cyclin D1/2 in the lungs of strain A/J mice fed chemopreventive agents

Male strain A mice were fed a diet containing chemopreventive agents. After 1 and 3 weeks on the diets, lung nuclear fractions were examined for expression of cyclin D1/2 with western blot analysis. In animals fed a diet containing a mixture of myoinositol and dexamethasone, a treatment found previously to be effective in preventing the development of tobacco smoke-induced lung tumors in A/J mice, cyclin D1/2 expression was reduced to 30-40% of control levels. A similar decrease in cyclin D1/2 expression was found when animals were fed either myoinositol or dexamethasone alone. Paradoxically, tobacco smoke by itself had a similar effect on cyclin D1/2 expression. On the other hand, several agents that had been previously found not to be effective against tobacco smoke carcinogenesis [phenethyl isothiocyanate, 1,4-phenylenebis(methylene)selenoisocyanate, N-acetylcysteine, acetylsalicylic acid, D-limonene and beta carotene] did not decrease cyclin D1/2 expression after 1 or 3 weeks of feeding. It was concluded that expression of cyclin D1/2 might be a potentially useful marker in the identification of chemopreventive agents for tobacco smoke and could be of some help in the evaluation of their effects.

Effects of glucocorticoids on activation of c-jun N-terminal, extracellular signal-regulated, and p38 MAP kinases in human pulmonary endothelial cells

Mitogen-activated protein kinases (MAPK) play a central role in signal transduction by regulating many nuclear transcription factors involved in inflammatory, immune, and proliferative responses. The aim of this study was to investigate, in human pulmonary endothelial cells, the effects of synthetic glucocorticosteroids on activation of c-jun N-terminal kinases, extracellular signal-regulated kinases, and p38 subgroups of the MAPK family. Human microvascular endothelial cells from lung were stimulated for 2 h with either H(2)O(2) (2 mM), IL-1beta (10 ng/mL), or tumour necrosis factor-alpha (10 ng/mL). Under these conditions, a remarkable increase in the phosphorylation pattern of c-jun N-terminal kinases, extracellular signal-regulated kinases 1/2, and p38 was detected. Pretreatment for 12 h with dexamethasone (100 nM) was able to prevent phosphorylation-dependent MAPK activation in stimulated cells, without substantially affecting the expression levels of these enzymes. Our results suggest that inhibition of MAPK signaling pathways in human pulmonary endothelial cells may significantly contribute, by interfering with activation of several different transcription factors, to the antiinflammatory and immunosuppressive effects of glucocorticosteroids.

Effects of growth factors and extracellular matrix on survival of human airway smooth muscle cells

Airway remodeling complicates longstanding asthma. It is characterized by an increase in the number of airway smooth muscle cells (SMCs) as well as an increase in and alteration of the type of extra-cellular matrix (ECM) in the airways. Although the number of SMCs in the airways depends on the balance of cell proliferation and cell death, studies to date have concentrated on factors affecting SMC proliferation. Here we report the first study on airway SMC survival factors: these cells receive a strong survival signal, which is not dependent on the known growth factor mitogens. We identified the ECM factors fibronectin, laminin, and collagens I and IV as important anti-apoptotic elements, and characterized the expression of the ECM receptors (integrins) on cultured SMC. Functionally blocking antibody and peptide studies revealed the alpha(5)beta(1) integrin to be an important transducer of the ECM-derived survival signal in these cells. Confocal microscopy confirmed the striking effects that discrete ECM factors have on SMC phenotype, notably the cytoskeleton. In summary, our data improves the understanding of the mechanisms underlying airway remodeling by outlining the key survival factors for airway SMC and by highlighting the impact of the cell-matrix interactions on cell death and phenotype.

Invited review: the circle of life: cell cycle regulation in airway smooth muscle

Severe asthma is characterized by increased airway smooth muscle (ASM) mass, due predominantly to ASM hyperplasia. Diverse stimuli, which include growth factors, plasma- or inflammatory cell-derived mediators, contractile agonists, cytokines, and extracellular matrix proteins, induce ASM proliferation. Mitogens act via receptor tyrosine kinase, G protein-coupled receptors, or cytokine receptors, to activate p21ras and stimulate two parallel signaling pathways in ASM cells, namely, the extracellular signal-regulated kinase (ERK) or the phosphatidylinositol 3-kinase (PI3K) pathways. ERK and PI3K regulate cell cycle protein expression and thus modulate cell cycle traversal. ERK activation and downstream effectors of PI3K, such as Rac1 and Cdc42, stimulate expression of cyclin D1, a key regulator of G(1) progression in the mammalian cell cycle. In addition, PI3K activates 70-kDa ribosomal S6 kinase, an enzyme that also regulates the translation of many cell cycle proteins, including the elongation factor E2F. The present review examines the mitogens and critical signal transduction pathways that stimulate ASM cell proliferation. Further study in this area may reveal new therapeutic targets to abrogate ASM hyperplasia in diseases such as asthma and chronic obstructive pulmonary disease.

Airway wall remodelling and hyperresponsiveness: modelling remodelling in vitro and in vivo

Airway wall remodelling contributes to the airway hyperresponsiveness that characterizes asthma. An increase in airway smooth muscle (ASM) volume is quantitatively important in the overall remodelling response and may be considered as a target for new therapeutic approaches to chronic asthma. ASM volume increases result from both hypertrophic as well as hyperplastic growth, the latter having been more extensively investigated. There are relatively few in vivo models available for analysis of the underlying mechanism(s) or their regulation by drugs. Human ASM in culture has been used to investigate potential stimuli for ASM proliferation and the signal transduction pathways that subserve these responses. The mitogen-activated protein kinase (MAPK) family members, ERK 1/2 and the phosphoinositol-3-kinase (PI3K) pathways each contribute to the signalling of G1 progression/S-phase entry in ASM. Glucocorticoids and beta(2)-adrenoceptor agonists attenuate, but do not prevent proliferative responses of ASM. Thus, there is scope for improved pharmacological control of this chronic and progressive aspect of asthma pathogenesis.

Thrombin-stimulated DNA synthesis in human cultured airway smooth muscle occurs independently of products of cyclo-oxygenase or 5-lipoxygenase

Arachidonic acid (AA) liberation and metabolism via cyclo-oxygenase or lipoxygenases may be an important regulatory pathway for mitogenic signalling in human cultured airway smooth muscle (ASM) cells. In cytokine-treated cells, thrombin markedly enhances production of the anti-mitogenic arachidonic acid metabolite, PGE(2). In this study, in the absence of cytokines, we examined the role of endogenous AA metabolism in thrombin-stimulated ASM DNA synthesis. Selective inhibitors of cyclo-oxygenase of 5-lipoxygenase metabolism had no significant effect on 0.3 U/ml thrombin-stimulated DNA synthesis. However, the non-selective, redox-active lipoxygenase inhibitors NDGA and BWA4C inhibited thrombin-stimulated DNA synthesis. Under basal conditions, and following stimulation by thrombin, the levels of the AA metabolites PGE(2), TxA(2), and LTC(4), remained below assay detection limits. Exogenous addition of AA, LTD(4), or 5-, 12-, and 15-HETE and HpETE metabolites had no consistent or substantial stimulatory effect on either basal or thrombin-stimulated DNA synthesis. These data suggest that the non-selective lipoxygenase inhibitors influence DNA synthesis via effects unrelated to lipoxygenase inhibition. The lack of detection of AA metabolites, the lack of influence of selective antagonists/inhibitors of the AA pathway, and the failure of selected AA metabolites to either enhance or directly stimulate DNA synthesis suggest that in the absence of cytokines, cyclo-oxygenase and lipoxygenase metabolism has little role in signalling of human ASM DNA synthesis by thrombin.

The production of extracellular matrix proteins by human passively sensitized airway smooth-muscle cells in culture: the effect of beclomethasone

Airway remodeling is a key feature of persistent asthma. Part of the remodeling process involves the laying down of extracellular matrix (ECM) proteins within the airways. In this study we compared the production of ECM proteins by human airway smooth-muscle (ASM) cells in culture after exposure to 10% serum from an asthmatic individual or 10% serum from a nonasthmatic individual with or without beclomethasone (0.01 to 100 nM). Enzyme-linked immunosorbent assays were done with antibodies to human fibronectin; perlecan; elastin; the laminin beta(1), gamma(1), beta(2), alpha(1) chains; thrombospondin; chondroitin sulfate; collagen types I, III, IV, and V; versican; and decorin. Serum from the asthmatic individual, when compared with that from the nonasthmatic individual, caused a significant increase in the production of fibronectin, perlecan, laminin gamma(1), and chondroitin sulfate. Beclomethasone caused a significant reduction in the number of cells exposed to serum from either the asthmatic or nonasthmatic individual, but did not reverse the increase in ECM protein induced by the former. These results suggest an interaction between the ASM and the allergic process that may alter components of the airway wall in asthma, and that corticosteroids may not prevent the fibrosis induced by resident cells within the airways.

The importance of ERK activity in the regulation of cyclin D1 levels and DNA synthesis in human cultured airway smooth muscle

The relationship between persistent ERK (extracellular signal-regulated kinase) activity, cyclin D1 protein and mRNA levels and cell cycle progression in human cultured airway smooth muscle was examined in response to stimulation by ET-1 (endothelin-1), thrombin and bFGF (basic fibroblast growth factor). Thrombin (0.3 and 3 u ml(-1)) and bFGF (0.3 and 3 nM) increased ERK activity for more than 2 h and increased cell number, whereas ET-1 (100 nM) transiently stimulated ERK activity and was non-mitogenic. The MEK1 (mitogen-activated ERK kinase) inhibitor, PD 98059 (30 microM), inhibited both ERK phosphorylation and activity, and either prevented (thrombin 0.3 and 3 u ml(-1), bFGF 300 pM) or attenuated (bFGF 3 nM) DNA synthesis. Thrombin and bFGF increased both cyclin D1 mRNA and protein levels. PD 98059 decreased cyclin D1 protein levels stimulated by the lower but not higher thrombin concentrations. Moreover, increases in cyclin D1 mRNA levels were unaffected by PD 98059 pretreatment, irrespective of the mitogen or its concentration, suggesting that inhibition of cyclin D1 protein levels occurred by a post-transcriptional mechanism. These findings indicate that the control of cyclin D1 protein levels may occur independently of the MEK1/ERK signalling pathways. The inhibition of S phase entry by PD 98059 at higher thrombin concentrations appears to result from effects on pathways downstream or parallel to those regulating cyclin D1 protein levels. These findings suggest heterogeneity in the signalling of DNA synthesis in human cultured airway smooth muscle.