Potentiation of beta-adrenoceptor function in bovine tracheal smooth muscle by inhibition of protein kinase C

Cooperativity between β-agonists and c-Abl inhibitors in regulating airway smooth muscle relaxation

Current therapeutic approaches to avoid or reverse bronchoconstriction rely primarily on β2 adrenoceptor agonists (β-agonists) that regulate pharmacomechanical coupling/cross bridge cycling in airway smooth muscle (ASM). Targeting actin cytoskeleton polymerization in ASM represents an alternative means to regulate ASM contraction. Herein we report the cooperative effects of targeting these distinct pathways with β-agonists and inhibitors of the mammalian Abelson tyrosine kinase (Abl1 or c-Abl). The cooperative effect of β-agonists (isoproterenol) and c-Abl inhibitors (GNF-5, or imatinib) on contractile agonist (methacholine, or histamine) -induced ASM contraction was assessed in cultured human ASM cells (using Fourier Transfer Traction Microscopy), in murine precision cut lung slices, and in vivo (flexiVent in mice). Regulation of intracellular signaling that regulates contraction (pMLC20, pMYPT1, pHSP20), and actin polymerization state (F:G actin ratio) were assessed in cultured primary human ASM cells. In each (cell, tissue, in vivo) model, c-Abl inhibitors and β-agonist exhibited additive effects in either preventing or reversing ASM contraction. Treatment of contracted ASM cells with c-Abl inhibitors and β-agonist cooperatively increased actin disassembly as evidenced by a significant reduction in the F:G actin ratio. Mechanistic studies indicated that the inhibition of pharmacomechanical coupling by β-agonists is near optimal and is not increased by c-Abl inhibitors, and the cooperative effect on ASM relaxation resides in further relaxation of ASM tension development caused by actin cytoskeleton depolymerization, which is regulated by both β-agonists and c-Abl inhibitors. Thus, targeting actin cytoskeleton polymerization represents an untapped therapeutic reserve for managing airway resistance.

Role of PKCζ-NADPH oxidase signaling axis in PKCα-mediated Giα2 phosphorylation for inhibition of adenylate cyclase activity by angiotensin II in pulmonary artery smooth muscle cells

We sought to determine the mechanism by which angiotensin II (AngII) inhibits isoproterenol induced increase in adenylate cyclase (AC) activity and cyclic adenosine monophosphate (cAMP) production in bovine pulmonary artery smooth muscle cells (BPASMCs). Treatment with AngII stimulates protein kinase C-ζ (PKC-ζ), nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and PKC-α activities, and also inhibits isoproterenol induced increase in AC activity and cAMP production in the cells. Pertussis toxin pretreatment eliminates AngII caused inhibition of isoproterenol induced increase in AC activity without a discernible change in PKC-ζ, NADPH oxidase, and PKC-α activities. Treatment of the cells with AngII increases α2 isoform of Gi (Giα2) phosphorylation; while pretreatment with chemical and genetic inhibitors of PKC-ζ and NADPH oxidase attenuate AngII induced increase in PKC-α activity and Giα2 phosphorylation, and also reverse AngII caused inhibition of isoproterenol induced increase in AC activity. Pretreatment of the cells with chemical and genetic inhibitors of PKC-α attenuate AngII induced increase in Giα2 phosphorylation and inhibits isoproterenol induced increase in AC activity without a discernible change in PKC-ζ and NADPH oxidase activities. Overall, PKCζ-NADPH oxidase-PKCα signaling axis plays a crucial role in Giα2 phosphorylation resulting in AngII-mediated inhibition of isoproterenol induced increase in AC activity in BPASMCs.

Second M3 muscarinic receptor binding site contributes to bronchoprotection by tiotropium

BACKGROUND AND PURPOSE

The bronchodilator tiotropium binds not only to its main binding site on the M₃ muscarinic receptor but also to an allosteric site. Here, we have investigated the functional relevance of this allosteric binding and the potential contribution of this behaviour to interactions with long-acting β-adrenoceptor agonists, as combination therapy with anticholinergic agents and β-adrenoceptor agonists improves lung function in chronic obstructive pulmonary disease.

EXPERIMENTAL APPROACH

ACh, tiotropium, and atropine binding to M₃ receptors were modelled using molecular dynamics simulations. Contractions of bovine and human tracheal smooth muscle strips were studied.

KEY RESULTS

Molecular dynamics simulation revealed extracellular vestibule binding of tiotropium, and not atropine, to M₃ receptors as a secondary low affinity binding site, preventing ACh entry into the orthosteric binding pocket. This resulted in a low (allosteric binding) and high (orthosteric binding) functional affinity of tiotropium in protecting against methacholine-induced contractions of airway smooth muscle, which was not observed for atropine and glycopyrrolate. Moreover, antagonism by tiotropium was insurmountable in nature. This behaviour facilitated functional interactions of tiotropium with the β-agonist olodaterol, which synergistically enhanced bronchoprotective effects of tiotropium. This was not seen for glycopyrrolate and olodaterol or indacaterol but was mimicked by the interaction of tiotropium and forskolin, indicating no direct β-adrenoceptor-M₃ receptor crosstalk in this effect.

CONCLUSIONS AND IMPLICATIONS

We propose that tiotropium has two binding sites at the M₃ receptor that prevent ACh action, which, together with slow dissociation kinetics, may contribute to insurmountable antagonism and enhanced functional interactions with β-adrenoceptor agonists.

Targeting acetylcholine receptor M3 prevents the progression of airway hyperreactivity in a mouse model of childhood asthma

Asthma often progresses into adulthood from early-life episodes of adverse environmental exposures. However, how the injury to developing lungs contributes to the pathophysiology of persistent asthma remains poorly understood. In this study, we identified an age-related mechanism along the cholinergic nerve-airway smooth muscle (ASM) axis that underlies prolonged airway hyperreactivity (AHR) in mice. We showed that ASM continued to mature until ∼3 wk after birth. Coinciding with postnatal ASM maturation, there was a critical time window for the development of ASM hypercontractility after cholinergic stimulation. We found that allergen exposure in neonatal mice, but not in adult mice, elevated the level and activity of cholinergic nerves (termed neuroplasticity). We demonstrated that cholinergic neuroplasticity is necessary for the induction of persistent AHR after neonatal exposure during rescue assays in mice deficient in neuroplasticity. In addition, early intervention with cholinergic receptor muscarinic (ChRM)-3 blocker reversed the progression of AHR in the neonatal exposure model, whereas β2-adrenoceptor agonists had no such effect. Together, our findings demonstrate a functional relationship between cholinergic neuroplasticity and ASM contractile phenotypes that operates uniquely in early life to induce persistent AHR after allergen exposure. Targeting ChRM3 may have disease-modifying benefits in childhood asthma.-Patel, K. R., Bai, Y., Trieu, K. G., Barrios, J., Ai, X. Targeting acetylcholine receptor M3 prevents the progression of airway hyperreactivity in a mouse model of childhood asthma.

Phorbol 12,13-dibutyrate-induced protein kinase C activation triggers sustained contracture in human myometrium in vitro

BACKGROUND

Although physiologic transition from rhythmic contractions to uterine retraction postpartum remains a poorly understood process, it has been shown that the latter is essential in the prevention of hemorrhage and its negative consequences.

OBJECTIVE

To investigate the transition from oscillatory contractions to tonic contracture in human myometrium after delivery, a mechanism purported to facilitate postpartum hemostasis. Protein kinase C (PKC) plays a key regulatory role in human uterine contractions because it can prevent dephosphorylation of regulatory proteins and sensitize the contractile machinery to low Ca²⁺. Thus, activation of PKC by phorbol 12,13-dibutyrate (PDBu) may act as a strong uterotonic agent.

STUDY DESIGN

Uterine biopsies were obtained from consenting women undergoing elective caesarian delivery at term without labor (N = 19). Isometric tension measurements were performed on uterine strips (n = 114). The amplitudes and area under the curve of phasic contractions and tonic responses were measured and compared. A total of 1 μM PDBu was added to the isolated organ baths, and maximal tension of the uterine contracture was determined in the absence and presence of either 1 μM of staurosporine, 100 nM nifedipine, or 10 μM cyclopiazonic acid to assess the role of PKC and calcium sensitivity on uterine contractility.

RESULTS

On the addition of PDBu on either basal or oxytocin-induced activity, consistent contractures were obtained concomitant with complete inhibition of phasic contractions. After a 30-minute incubation period, the mean amplitude of the PDBu-induced tone represented 65.3% of the amplitude of spontaneous contraction. Staurosporine, a protein kinase inhibitor, induced a 91.9% inhibition of PDBu contractures, a process not affected by nifedipine or cyclopiazonic acid, thus indicating that this mechanism is largely Ca²⁺ independent.

CONCLUSION

Pharmacologic activation of PKC leads to a significant contracture of the myometrium. Together, these data suggest that the up-regulation of PKC plays a physiologic role in the modulation of uterine contracture after delivery. A switch from phasic to strong tonic contractions potentially may facilitate postpartum hemostasis.

The evidence on tiotropium bromide in asthma: from the rationale to the bedside

Severe and poorly controlled asthma still accounts for a great portion of the patients affected. Disease control and future risk management have been identified by international guidelines as the main goals in patients with asthma. The need for new treatment approaches has led to reconsider anticholinergic drugs as an option for asthma treatment. Tiotropium is the first anticholinergic drug that has been approved for children and adults with poorly controlled asthma and is currently considered as an option for steps 4 and 5 of the Global Initiative for Asthma. In large randomized clinical trials enrolling patients with moderate to severe asthma, add-on therapy with tiotropium has demonstrated to be efficacious in improving lung function, decreasing risk of exacerbation and slowing the worsening of disease; accordingly, tiotropium demonstrated to be non inferior compared to long acting beta-agonists in the maintenance treatment along with medium to high inhaled corticosteroids. In view of the numerous ancillary effects acting on inflammation, airway remodeling, mucus production and cough reflex, along with the good safety profile and the broad spectrum of efficacy demonstrated in different disease phenotypes, tiotropium can represent a beneficial alternative in the therapeutic management of poorly controlled asthma. The present extensive narrative review presents the pharmacological and pathophysiological basis that guided the rationale for the introduction of tiotropium in asthma treatment algorithm, with a particular focus on its conventional and unconventional effects; finally, data on tiotropium efficacy and safety. from recent randomized clinical trials performed in all age categories will be extensively discussed.

Tiotropium for the treatment of asthma in adolescents

INTRODUCTION

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

Bronchodilators, receptors and cross-talk: Together is better?

The most widely used maintenance therapies in chronic obstructive pulmonary disease (COPD) are long-acting muscarinic antagonists (LAMAs), and a number of these drugs are now available in combination with long-acting β2-agonists (LABAs). LAMAs inhibit the parasympathetic muscarinic pathway, while LABAs, as sympathomimetics, reduce airway smooth muscle (ASM) tone. As well as directly controlling the constriction and relaxation of ASM, muscarinic and adrenergic receptors are found on inflammatory cells, and drugs that target these receptors may also reduce inflammation in COPD. Evidence suggests that the muscarinic and adrenergic pathways cross-talk at the level of neuronal input to the ASM via second-messenger pathways within ASM cells. Although the cross-talk is not completely understood, pharmacologically targeting both pathways in COPD can maximize bronchodilation. Combining LAMAs and LABAs demonstrated improved efficacy compared with the individual therapies and so, for greater convenience, several fixed-dose combinations for once-daily use have been developed. These fixed-dose combinations demonstrate improvements in both lung-function and patient-reported outcomes compared with well-established monotherapies, with similar tolerability profiles to the individual agents.

β3-Adrenoceptor-mediated relaxation of rat and human urinary bladder: roles of BKCa channels and Rho kinase

Previous studies suggest that the large-conductance Ca(2+)-activated K(+) (BKCa) channel and Rho-kinase play major roles in the control of urinary bladder tone. Here, we investigated their involvement in β-adrenoceptor (AR)-mediated relaxation of rat and human bladder. Concentration-response curves of isoprenaline and mirabegron-induced bladder relaxation were generated against passive tension and KCl- and carbachol-induced tone, in the absence or presence of the BKCa channel inhibitor iberiotoxin (100 nM) or the Rho-kinase inhibitor Y27,632 (1 μM). Myosin light chain (MLC) phosphorylation was studied by Western blot. In rat, iberiotoxin only slightly altered isoprenaline- and mirabegron-induced relaxation against KCl-induced tone but attenuated relaxation by both agonists against carbachol-induced tone. Y27,632 enhanced isoprenaline- or mirabegron-induced relaxation only against carbachol-induced tone. In humans, iberiotoxin slightly enhanced relaxation by both agonists against carbachol-induced pre-contraction. Y27,632 did not change isoprenaline-induced relaxation but enhanced that by mirabegron. Under passive tension, MLC phosphorylation was markedly reduced by both β-AR agonists, an effect insensitive to Y27,632. In the presence of carbachol, both β-AR agonists increased MLC phosphorylation, an effect reduced by Y27,632 only in the presence of 1 μM carbachol. These results indicate that the extent of BKCa channel and Rho-kinase involvement in relaxation induced by β-AR agonists depends on pre contractile stimulus and species.

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

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

The pharmacological rationale for combining muscarinic receptor antagonists and β-adrenoceptor agonists in the treatment of airway and bladder disease

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Muscarinic receptors increase smooth muscle tone in airways and urinary bladder.

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β-Adrenoceptors relax smooth muscle tone and oppose muscarinic contraction.

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Opposition involves transmitter release, signal transduction and receptor expression.

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This supports the combined use of muscarinic antagonists and β-adrenoceptor agonists.

Muscarinic receptor antagonists and β-adrenoceptor agonists are used in the treatment of obstructive airway disease and overactive bladder syndrome. Here we review the pharmacological rationale for their combination. Muscarinic receptors and β-adrenoceptors are physiological antagonists for smooth muscle tone in airways and bladder. Muscarinic agonism may attenuate β-adrenoceptor-mediated relaxation more than other contractile stimuli. Chronic treatment with one drug class may regulate expression of the target receptor but also that of the opposing receptor. Prejunctional β₂-adrenoceptors can enhance neuronal acetylcholine release. Moreover, at least in the airways, muscarinic receptors and β-adrenoceptors are expressed in different locations, indicating that only a combined modulation of both systems may cause dilatation along the entire bronchial tree. While all of these factors contribute to a rationale for a combination of muscarinic receptor antagonists and β-adrenoceptor agonists, the full value of such combination as compared to monotherapy can only be determined in clinical studies.

Emerging role of long acting muscarinic antagonists for asthma

Acetlycholine is involved in the control of airway smooth muscle constriction and in recruitment of inflammatory cells via neuronal and paracrine effects on muscarinic type 3 receptors. Long acting muscarinic antagonists (LAMA) are well established in guidelines for COPD but are not currently licensed for use in asthma. There are emerging data from key clinical trials to show that LAMA may confer bronchodilator effects and improved control when used in addition to inhaled corticosteroid (ICS) alone or in conjunction with long acting β-adrenoceptor agonists (LABA). Further studies in persistent asthmatic patients are required to evaluate ICS sparing effects of LAMA looking particularly at airway hyper-responsiveness and surrogate inflammatory markers, in addition to evaluation of possible synergy between LAMA and LABA when given together. Future possible development of combination inhalers comprising ICS/LAMA or ICS/LAMA/LABA will require long term studies looking at asthma control and exacerbations in both adult and paediatric patients.

Active components of ginger potentiate β-agonist-induced relaxation of airway smooth muscle by modulating cytoskeletal regulatory proteins

β-Agonists are the first-line therapy to alleviate asthma symptoms by acutely relaxing the airway. Purified components of ginger relax airway smooth muscle (ASM), but the mechanisms are unclear. By elucidating these mechanisms, we can explore the use of phytotherapeutics in combination with traditional asthma therapies. The objectives of this study were to: (1) determine if 6-gingerol, 8-gingerol, or 6-shogaol potentiate β-agonist-induced ASM relaxation; and (2) define the mechanism(s) of action responsible for this potentiation. Human ASM was contracted in organ baths. Tissues were relaxed dose dependently with β-agonist, isoproterenol, in the presence of vehicle, 6-gingerol, 8-gingerol, or 6-shogaol (100 μM). Primary human ASM cells were used for cellular experiments. Purified phosphodiesterase (PDE) 4D or phospholipase C β enzyme was used to assess inhibitory activity of ginger components using fluorescent assays. A G-LISA assay was used to determine the effects of ginger constituents on Ras homolog gene family member A activation. Significant potentiation of isoproterenol-induced relaxation was observed with each of the ginger constituents. 6-Shogaol showed the largest shift in isoproterenol half-maximal effective concentration. 6-Gingerol, 8-gingerol, or 6-shogaol significantly inhibited PDE4D, whereas 8-gingerol and 6-shogaol also inhibited phospholipase C β activity. 6-Shogaol alone inhibited Ras homolog gene family member A activation. In human ASM cells, these constituents decreased phosphorylation of 17-kD protein kinase C-potentiated inhibitory protein of type 1 protein phosphatase and 8-gingerol decreased myosin light chain phosphorylation. Isolated components of ginger potentiate β-agonist-induced relaxation in human ASM. This potentiation involves PDE4D inhibition and cytoskeletal regulatory proteins. Together with β-agonists, 6-gingerol, 8-gingerol, or 6-shogaol may augment existing asthma therapy, resulting in relief of symptoms through complementary intracellular pathways.

Bronchoprotection by olodaterol is synergistically enhanced by tiotropium in a guinea pig model of allergic asthma

The novel once-daily β₂-agonist bronchodilator drug olodaterol has recently been shown to be effective in patients with allergic asthma for >24 hours. An increased cholinergic tone common to these patients may decrease the effectiveness of β₂-agonists. This could provide a rationale for combination therapy with olodaterol and the long-acting anticholinergic tiotropium to aim for a once-daily treatment regimen. In guinea pigs, we evaluated the protective effects of olodaterol, alone and in combination with tiotropium, on airway responsiveness to histamine, which is partially mediated by a cholinergic reflex mechanism. In addition, using a guinea pig model of acute allergic asthma, we examined the cooperative effects of these bronchodilators on allergen-induced early (EAR) and late (LAR) asthmatic reactions, airway hyper-responsiveness (AHR) to histamine, and airway inflammation. It was demonstrated that the protective effect of olodaterol against histamine-induced bronchoconstriction was synergistically enhanced and prolonged in the presence of tiotropium. In addition, tiotropium synergistically augmented both the reversal of and the protection against the allergen-induced AHR after the EAR by olodaterol. Olodaterol and tiotropium were highly effective in inhibiting the magnitude of the allergen-induced EAR and LAR, and both reactions were fully inhibited by the combination of these drugs. It is remarkable that these effects were not associated with an effect on inflammatory cell infiltration in the airways. In conclusion, the results indicate that combination therapy with olodaterol and tiotropium may be highly effective in the treatment of allergen-induced asthmatic reactions and AHR.

Role of PKC-ζ in NADPH oxidase-PKCα-Giα axis dependent inhibition of β-adrenergic response by U46619 in pulmonary artery smooth muscle cells

Treatment of bovine pulmonary artery smooth muscle cells (BPASMCs) with U46619 attenuated isoproterenol caused stimulation of adenyl cyclase activity and cAMP production. Pretreatment with SQ29548 (Tp receptor antagonist), apocynin (NADPH oxidase inhibitor) and Go6976 (PKC-α inhibitor) eliminated U46619 caused attenuation of isoproterenol stimulated adenyl cyclase activity. Pretreatment with SQ29548 and apocynin prevented U46619 induced increase in NADPH oxidase activity, PKC-α activity and Giα phosphorylation. However, pretreatment with CZI, a PKC-ζ inhibitor, markedly, but not completely, inhibited U46619 induced increase in NADPH oxidase activity, PKC-α activity, Giα phosphorylation and also significantly eliminated U46619 caused attenuation of isoproterenol stimulated adenyl cyclase activity. Pretreatment with Go6976 inhibited U46619 induced increase in Giα phosphorylation, but not PKC-ζ activity and NADPH oxidase activity. Pretreatment with pertussis toxin eliminated U46619 caused attenuation of isoproterenol stimulated adenyl cyclase activity without any discernible change in PKC-ζ, NADPH oxidase and PKC-α activities. Transfection of the cells with Tp, PKC-ζ and PKC-α siRNA duplexes corroborate the findings observed with their respective pharmacological inhibitors on the responses produced by U46619. Taken together, we suggest involvement of PKC-ζ in U46619 caused attenuation of isoproterenol stimulated β-adrenergic response, which is regulated by NADPH oxidase-PKCα-Giα axis in pulmonary artery smooth muscle cells.

A new perspective on muscarinic receptor antagonism in obstructive airways diseases

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

Muscarinic receptors on airway mesenchymal cells: novel findings for an ancient target

Since ancient times, anticholinergics have been used as a bronchodilator therapy for obstructive lung diseases. Targets of these drugs are G-protein-coupled muscarinic M(1), M(2) and M(3) receptors in the airways, which have long been recognized to regulate vagally-induced airway smooth muscle contraction and mucus secretion. However, recent studies have revealed that acetylcholine also exerts pro-inflammatory, pro-proliferative and pro-fibrotic actions in the airways, which may involve muscarinic receptor stimulation on mesenchymal, epithelial and inflammatory cells. Moreover, acetylcholine in the airways may not only be derived from vagal nerves, but also from non-neuronal cells, including epithelial and inflammatory cells. Airway smooth muscle cells seem to play a major role in the effects of acetylcholine on airway function. It has become apparent that these cells are multipotent cells that may reversibly adopt (hyper)contractile, proliferative and synthetic phenotypes, which are all under control of muscarinic receptors and differentially involved in bronchoconstriction, airway remodeling and inflammation. Cholinergic contractile tone is increased by airway inflammation associated with asthma and COPD, resulting from exaggerated acetylcholine release as well as increased expression of contraction related proteins in airway smooth muscle. Moreover, muscarinic receptor stimulation promotes proliferation of airway smooth muscle cells as well as fibroblasts, and regulates cytokine, chemokine and extracellular matrix production by these cells, which may contribute to airway smooth muscle growth, airway fibrosis and inflammation. In line, animal models of chronic allergic asthma and COPD have recently demonstrated that tiotropium may potently inhibit airway inflammation and remodeling. These observations indicate that muscarinic receptors have a much larger role in the pathophysiology of obstructive airway diseases than previously thought, which may have important therapeutic implications.

Bronchial inflammation induced PKCζ over-expression: involvement in mechanical properties of airway smooth muscle

Protein kinase C variants (PKCs) have been involved in the control of airway smooth muscle (ASM) tone, and abnormalities in PKC-dependent signaling have been associated with respiratory diseases such as asthma. In this study, the role of atypical PKCζ in airway hyperresponsiveness was investigated, using an in-vitro model of TNFα-treated human bronchi and an in vivo guinea pig model of chronic asthma. Our results demonstrated that PKCζ-specific inhibition produced a significant increase in isoproterenol sensitivity in TNFα-treated bronchi and ovalbumin (OVA)-sensitized guinea pig bronchi. The role of epoxy-eicosanoids, known to exert anti-inflammatory effects in lung, on PKCζ expression and activity in these models was evaluated. An enhanced PKCζ protein expression was delineated in TNFα-treated bronchi when compared with control (untreated) and epoxy-eicosanoid-treated bronchi. Measurements of Ca(2+) sensitivity, performed in TNFα-treated bronchi, demonstrated that treatment with myristoylated (Myr) PKCζ peptide inhibitor resulted in significant reductions of pCa-induced tension. Epoxy-eicosanoid treatments had similar effects on Ca(2+) sensitivity in TNFα-treated bronchi. In control and epoxy-eicosanoid-treated bronchi, the phosphorylated forms of p38MAPK and CPI-17 were significantly decreased compared with the TNFα-treated bronchi. An enhanced expression of PKCζ was ascertained in our in-vivo model of allergic asthma. Hence an increased Ca(2+) sensitivity could be explained by the phosphorylation of p38-MAPK, which in turn leads to phosphorylation and activation of the CPI-17 regulatory protein. This process was reversed upon treatment with the Myr-PKCζ-peptide inhibitor. The present data provide relevant evidence regarding the role of PKCζ in human and rodent models of airways inflammation.

Pre-treatment with α-hederin increases β-adrenoceptor mediated relaxation of airway smooth muscle

Preparations of ivy leaves dry extract with secretolytic and bronchiolytic efficacy are widely used for the treatment of acute and chronic obstructive airway diseases. The mechanism by which ivy preparations improve lung functions is not fully understood. Here, we tested the influence of the three main saponins of ivy, α-hederin, hederacoside C and hederagenin, on the contraction and relaxation behaviour of isolated bovine tracheal smooth muscle strips by isometric tension measurements. None of the tested compounds altered histamine or methacholine-induced contraction of the smooth muscle strips. In contrast, the isoprenaline-induced relaxation of 100μM methacholine precontracted muscle strips was significantly enhanced when pre-treated with 1μM of α-hederin for 18h. The pre-treatment with hederacoside C or hederagenin had no effect on isoprenaline-induced relaxation. For the first time the bronchiolytic effect of α-hederin was demonstrated by isometric tension measurements using bovine tracheal smooth muscle strips. α-Hederin increases isoprenaline-induced relaxation indirectly, probably by inhibiting heterologous desensitization induced by high concentrations of muscarinic ligands like methacholine.

Role of dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene 1 in protein kinase A- and protein kinase C-mediated regulation of the steroidogenic acute regulatory protein expression in mouse Leydig tumor cells: mechanism of action

Dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene 1 (DAX-1) is an orphan nuclear receptor that has been demonstrated to be instrumental to the expression of the steroidogenic acute regulatory (StAR) protein that regulates steroid biosynthesis in steroidogenic cells. However, its mechanism of action remains obscure. The present investigation was aimed at exploring the molecular involvement of DAX-1 in protein kinase A (PKA)- and protein kinase C (PKC)-mediated regulation of StAR expression and its concomitant impact on steroid synthesis using MA-10 mouse Leydig tumor cells. We demonstrate that activation of the PKA and PKC pathways, by a cAMP analog dibutyryl (Bu)2cAMP [(Bu)2cAMP] and phorbol 12-myristate 13-acetate (PMA), respectively, markedly decreased DAX-1 expression, an event that was inversely correlated with StAR protein, StAR mRNA, and progesterone levels. Notably, the suppression of DAX-1 requires de novo transcription and translation, suggesting that the effect of DAX-1 in regulating StAR expression is dynamic. Chromatin immunoprecipitation studies revealed the association of DAX-1 with the proximal but not the distal region of the StAR promoter, and both (Bu)2cAMP and PMA decreased in vivo DAX-1-DNA interactions. EMSA and reporter gene analyses demonstrated the functional integrity of this interaction by showing that DAX-1 binds to a DNA hairpin at position -44/-20 bp of the mouse StAR promoter and that the binding of DAX-1 to this region decreases progesterone synthesis by impairing transcription of the StAR gene. In support of this, targeted silencing of endogenous DAX-1 elevated basal, (Bu)2cAMP-, and PMA-stimulated StAR expression and progesterone synthesis. Transrepression of the StAR gene by DAX-1 was tightly associated with expression of the nuclear receptors Nur77 and steroidogenic factor-1, demonstrating these factors negatively modulate the steroidogenic response. These findings provide insight into the molecular events by which DAX-1 influences the PKA and PKC signaling pathways involved in the regulation of the StAR protein and steroidogenesis in mouse Leydig tumor cells.

CPI-17 silencing-reduced responsiveness in control and TNF-alpha-treated human bronchi

Under pathophysiologic conditions, the modulation of Ca2+ sensitivity and reactivity of bronchial smooth muscle is controlled by protein kinase C-dependent phosphorylation of the newly described protein, CPI-17. The goal of the present study was to assess the key role of this regulatory protein in airway hyperresponsiveness (AHR) using control and TNF-alpha-treated human bronchi as well as a specific siRNA duplex against human CPI-17 transcripts. Validity of a mixed transfection strategy was assessed using the reversible permeabilization method to introduce X-TremeGene (X-TG)-siRNA complexes in an overreactive model of human bronchi treated with TNF. Data demonstrate that X-TG-siRNA complexes targeted against CPI-17 transcripts resulted in a reduction in mRNA and specific protein expression in human bronchial tissues. This approach revealed that overall reactivity of bronchial smooth muscle to methacholine was reduced, while their relaxing responses to beta2-agonist were increased, when compared with responses triggered in control TNF-alpha-treated bronchi. Quantification analysis showed that Ca2+ -sensitivity in both untreated and TNF-alpha-treated bronchi were largely reduced upon transfection with human CPI-17 siRNA-X-TremeGene complexes, while Western blot analysis corroborated the decrease in CPI-17 and MLC phosphorylation levels in pretreated human bronchi. Identical results were obtained upon treatment with an antiinflammatory eicosanoid, 14,15-EET, known to inhibit CPI-17 phosphorylation. Together these results are consistent with a key molecular role for CPI-17 in AHR, in the absence of bronchial wall remodeling.

Investigation into the signal transduction pathway via which heat stress impairs intestinal epithelial barrier function

BACKGROUND AND AIMS

Intact protein absorption is thought to be a causative factor in several intestinal diseases, such as food allergy, celiac disease and inflammatory bowel disease. However, the mechanism remains unclear. The aim of this study was to characterize a novel signal transduction pathway via which heat stress compromises intestinal epithelial barrier function.

METHODS

Heat stress was carried out by exposing confluent human intestinal epithelial cell line T84 cell monolayers to designated temperatures (37-43 degrees C) for 1 h. Transepithelial electric resistance (TER) and permeability to horseradish peroxidase (HRP, molecular weight = 44 000) were used as indicators to assess the intestinal epithelial barrier function. Phosphorylated myosin light chain (MLC), MLC kinase (MLCK) and protein kinase C (PKC) protein of the T84 cells were evaluated in order to identify the signal transduction pathway in the course of heat stress-induced intestinal epithelial barrier dysfunctions.

RESULTS

The results showed that exposure to heat stress significantly increased intact protein transport across the intestinal epithelial monolayer; the amount of phospho-PKC, phospho-MLCK and phospho-MLC proteins in T84 cells decreased significantly at 41 degrees C and 43 degrees C although they increased at 39 degrees C. The heat stress-induced T84 monolayer barrier dysfunction was inhibited by pretreatment with PKC inhibitor, MLCK inhibitor, or HSP70.

CONCLUSION

Heat stress can induce intestinal epithelial barrier dysfunction via the PKC and MLC signal transduction pathway.

Cysteinyl-leukotrienes in the regulation of beta2-adrenoceptor function: an in vitro model of asthma

Background

The response to β₂-adrenoceptor agonists is reduced in asthmatic airways. This desensitization may be in part due to inflammatory mediators and may involve cysteinyl-leukotrienes (cysteinyl-LTs). Cysteinyl-LTs are pivotal inflammatory mediators that play important roles in the pathophysiology of asthma, allergic rhinitis, and other inflammatory conditions. We tested the hypothesis that leukotriene D₄ (LTD₄) and allergen challenge cause β₂-adrenoceptor desensitization through the activation of protein kinase C (PKC).

Methods

The isoproterenol-induced cAMP accumulation was evaluated in human airway smooth muscle cell cultures challenged with exogenous LTD₄ or the PKC activator phorbol-12-myristate-13-acetate with or without pretreatments with the PKC inhibitor GF109203X or the CysLT₁R antagonist montelukast. The relaxant response to salbutamol was studied in passively sensitized human bronchial rings challenged with allergen in physiological salt solution (PSS) alone, or in the presence of either montelukast or GF109203X.

Results

In cell cultures, both LTD₄ and phorbol-12-myristate-13-acetate caused significant reductions of maximal isoproterenol-induced cAMP accumulation, which were fully prevented by montelukast and GF109203X, respectively. More importantly, GF109203X also prevented the attenuating effect of LTD₄ on isoproterenol-induced cAMP accumulation. In bronchial rings, both montelukast and GF109203X prevented the rightward displacement of the concentration-response curves to salbutamol induced by allergen challenge.

Conclusion

LTD₄ induces β₂-adrenoceptor desensitization in human airway smooth muscle cells, which is mediated through the activation of PKC. Allergen exposure of sensitized human bronchi may also cause a β₂-adrenoceptor desensitization through the involvement of the CysLT₁R-PKC pathway.

Control by cholinergic mechanisms

In the respiratory tract acetylcholine is neurotransmitter in ganglia and postganglionic parasympathetic nerves, but in addition is paracrine mediator released from various non-neuronal cells. Almost every cell type present in the respiratory tract expresses nicotinic and muscarinic receptors and therefore appears to be a target for acetylcholine. The present review describes the mechanisms of synthesis and release of acetylcholine from neuronal and non-neuronal cells and the differential control mechanisms. The different cholinoceptors, multiple nicotinic and muscarinic receptors and their signalling are outlined and their involvement in the modulation of the function of various target cells, smooth muscles, nerves, surface epithelial, secretory cells, fibroblasts and inflammatory cells is discussed in detail.

Protein kinase C potentiates homologous desensitization of the beta2-adrenoceptor in bovine tracheal smooth muscle

Preincubation (30 min) of bovine tracheal smooth muscle with various concentrations (0.1, 1 and 10 microM) of fenoterol decreased isoprenaline-induced maximal relaxation (E(max)) of methacholine-contracted preparations in a concentration dependent fashion, indicating desensitization of the beta(2)-adrenoceptor. Preincubation with 1 microM of the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) caused a small but significant decrease in isoprenaline-induced E(max), indicating activated PKC-mediated heterologous beta(2)-adrenoceptor desensitization. To investigate the capacity of activated PKC to regulate homologous desensitization, we incubated the smooth muscle strips with the combination of both 1 microM PMA and 1 microM fenoterol. This combined treatment synergistically decreased the isoprenaline-induced maximal relaxation, as compared to the individual effects of PMA and fenoterol alone, indicating a common pathway for heterologous and homologous desensitization. Moreover, the specific PKC-inhibitor 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl) maleimide (GF 109203X) markedly increased the potency and E(max) of isoprenaline for all conditions used, including control conditions, and the synergistic effects of PMA and fenoterol were completely prevented. In conclusion, the present study demonstrates that homologous desensitization of the beta(2)-adrenergic receptor can be enhanced by PKC activation. For the first time we have provided evidence that this concept is functionally operative in airway smooth muscle, and it may explain the reduced bronchodilator response to beta(2)-adrenoceptor agonists in patients with asthma during a severe exacerbation.