Airway Hyperresponsiveness In Asthma Research Articles

SRF Overexpression, A Double Trouble that May Underlie Airway Hyperresponsiveness in Asthma.

SRF Overexpression, A Double Trouble that May Underlie Airway Hyperresponsiveness in Asthma.

The impact of eosinophilia on high fat diet-induced obesity and airway hyperresponsiveness

Hypothesis/Rationale: Eosinophils contribute to both adipose tissue metabolic homeostasis in obesity and airway hyperresponsiveness in asthma, but the role of eosinophils in obesity-related airway hyperresponsiveness is not understood. Considering that metabolic disorders increase the susceptibility to airway hyperresponsiveness in obese individuals, we investigated whether adipose eosinophils play a protective role in obesity-related airway hyperresponsiveness. Methods: Wild type (WT) and transgenic mice that overexpress interleukin 5 in peripheral T cells (+IL5T) were fed a high fat (61.6% fat) or normal chow (13.6% fat) diet for 19 weeks. Body weight, body fat, fasting glucose and insulin, and bronchoconstriction in response to inhaled serotonin were measured. The number of eosinophils were counted using flow cytometry in lung, adipose, and blood from transgenic WT and +IL5T mice with GFP-expressing eosinophils. Data: High fat diet significantly increased body weight and body fat in both WT and +IL5T mice, however +IL5T mice gained less weight and body fat than the WT mice. High fat diet increased fasting glucose, fasting insulin, and nerve-mediated airway responsiveness to inhaled serotonin in only the WT mice. On a normal chow diet, +IL5T mice had significantly more eosinophils in lung, blood, and adipose, and high fat diet further increased eosinophils in +IL5T adipose tissue. Acute administration of 1.29 U/kg (i.p.) insulin to a WT mouse on a normal chow diet significantly potentiated airway hyperresponsiveness to inhaled serotonin. Summary of results: Eosinophils in adipose tissue prevented high fat diet increases in circulating glucose and insulin, resulting in less body weight and body fat. This reduction in insulin by eosinophils in adipose tissue prevented obesity-related airway hyperresponsiveness. Conclusions: Insulin is a key modulator of obesity-related airway hyperresponsiveness. Eosinophils in adipose tissue play an important role in preventing obesity-related airway hyperresponsiveness by modulating insulin levels. Funding: NIH HL164474, NIH HL163087. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Downregulation of protein phosphatase 2Aα in asthmatic airway smooth muscle.

Airway smooth muscle cell (ASM) is renowned for its involvement in airway hyperresponsiveness through impaired ASM relaxation and bronchoconstriction in asthma, which poses a significant challenge in the field. Recent studies have explored different targets in ASM to alleviate airway hyperresponsiveness, however, a sizeable portion of patients with asthma still experience poor control. In our study, we explored protein phosphatase 2 A (PP2A) in ASM as it has been reported to regulate cellular contractility by controlling intracellular calcium ([Ca2+]i), ion channels, and respective regulatory proteins. We obtained human ASM cells and lung tissues from healthy and patients with asthma and evaluated PP2A expression using RNA-Seq data, immunofluorescence, and immunoblotting. We further investigated the functional importance of PP2A by determining its role in bronchoconstriction using mouse bronchus and human ASM cell [Ca2+]i regulation. We found robust expression of PP2A isoforms in human ASM cells with PP2Aα being highly expressed. Interestingly, PP2Aα was significantly downregulated in asthmatic tissue and human ASM cells exposed to proinflammatory cytokines. Functionally, FTY720 (PP2A agonist) inhibited acetylcholine- or methacholine-induced bronchial contraction in mouse bronchus and further potentiated isoproterenol-induced bronchial relaxation. Mechanistically, FTY720 inhibited histamine-evoked [Ca2+]i response and myosin light chain (MLC) phosphorylation in the presence of interleukin-13 (IL-13) in human ASM cells. To conclude, we for the first time established PP2A signaling in ASM, which can be further explored to develop novel therapeutics to alleviate airway hyperresponsiveness in asthma.NEW & NOTEWORTHY This novel study deciphered the expression and function of protein phosphatase 2Aα (PP2Aα) in airway smooth muscle (ASM) during asthma and/or inflammation. We showed robust expression of PP2Aα in human ASM while its downregulation in asthmatic ASM. Similarly, we demonstrated reduced PP2Aα expression in ASM exposed to proinflammatory cytokines. PP2Aα activation inhibited bronchoconstriction of isolated mouse bronchi. In addition, we unveiled that PP2Aα activation inhibits the intracellular calcium release and myosin light chain phosphorylation in human ASM.

Rho-Kinase Inhibition of Active Force and Passive Tension in Airway Smooth Muscle: A Strategy for Treating Airway Hyperresponsiveness in Asthma.

Rho-kinase inhibitors have been identified as a class of potential drugs for treating asthma because of their ability to reduce airway inflammation and active force in airway smooth muscle (ASM). Past research has revealed that, besides the effect on the ASM's force generation, rho-kinase (ROCK) also regulates actin filament formation and filament network architecture and integrity, thus affecting ASM's cytoskeletal stiffness. The present review is not a comprehensive examination of the roles played by ROCK in regulating ASM function but is specifically focused on passive tension, which is partially determined by the cytoskeletal stiffness of ASM. Understanding the molecular basis for maintaining active force and passive tension in ASM by ROCK will allow us to determine the suitability of ROCK inhibitors and its downstream enzymes as a class of drugs in treating airway hyperresponsiveness seen in asthma. Because clinical trials using ROCK inhibitors in the treatment of asthma have yet to be conducted, the present review focuses on the in vitro effects of ROCK inhibitors on ASM's mechanical properties which include active force generation, relaxation, and passive stiffness. The review provides justification for future clinical trials in the treatment of asthma using ROCK inhibitors alone and in combination with other pharmacological and mechanical interventions.

Mechanism of anion exchange and small-molecule inhibition of pendrin

Pendrin (SLC26A4) is an anion exchanger that mediates bicarbonate (HCO3−) exchange for chloride (Cl−) and is crucial for maintaining pH and salt homeostasis in the kidney, lung, and cochlea. Pendrin also exports iodide (I−) in the thyroid gland. Pendrin mutations in humans lead to Pendred syndrome, causing hearing loss and goiter. Inhibition of pendrin is a validated approach for attenuating airway hyperresponsiveness in asthma and for treating hypertension. However, the mechanism of anion exchange and its inhibition by drugs remains poorly understood. We applied cryo-electron microscopy to determine structures of pendrin from Sus scrofa in the presence of either Cl−, I−, HCO3− or in the apo-state. The structures reveal two anion-binding sites in each protomer, and functional analyses show both sites are involved in anion exchange. The structures also show interactions between the Sulfate Transporter and Anti-Sigma factor antagonist (STAS) and transmembrane domains, and mutational studies suggest a regulatory role. We also determine the structure of pendrin in a complex with niflumic acid (NFA), which uncovers a mechanism of inhibition by competing with anion binding and impeding the structural changes necessary for anion exchange. These results reveal directions for understanding the mechanisms of anion selectivity and exchange and their regulations by the STAS domain. This work also establishes a foundation for analyzing the pathophysiology of mutations associated with Pendred syndrome.

Interleukin 31 receptor α promotes smooth muscle cell contraction and airway hyperresponsiveness in asthma

Asthma is a chronic inflammatory airway disease characterized by airway hyperresponsiveness (AHR), inflammation, and goblet cell hyperplasia. Multiple cytokines, including IFNγ, IL-4, and IL-13 are associated with asthma; however, the mechanisms underlying the effects of these cytokines remain unclear. Here, we report a significant increase in the expression of IL-31RA, but not its cognate ligand IL-31, in mouse models of allergic asthma. In support of this, IFNγ, IL-4, and IL-13 upregulated IL-31RA but not IL-31 in both human and mice primary airway smooth muscle cells (ASMC) isolated from the airways of murine and human lungs. Importantly, the loss of IL-31RA attenuated AHR but had no effect on inflammation and goblet cell hyperplasia in mice challenged with allergens or treated with IL-13 or IFNγ. We show that IL-31RA functions as a positive regulator of muscarinic acetylcholine receptor 3 expression, augmenting calcium levels and myosin light chain phosphorylation in human and murine ASMC. These findings identify a role for IL-31RA in AHR that is distinct from airway inflammation and goblet cell hyperplasia in asthma.

Functional α7 nicotinic receptors in human airway smooth muscle increase intracellular calcium concentration and contractility in asthmatics.

Although nicotinic acetylcholine receptors (nAChRs) are commonly associated with neurons in the brain and periphery, recent data indicate that they are also expressed in non-neuronal tissues. We recently found the alpha7 (α7nAChR) subunit is highly expressed in human airway smooth muscle (hASM) with substantial increase in asthmatics, but their functionality remains unknown. We investigated the location and functional role of α7nAChRs in hASM cells from normal versus mild-moderate asthmatic patients. Immunostaining and protein analyses showed α7nAChR in the plasma membrane including in asthmatics. In asthmatic hASM, patch-clamp recordings revealed significantly higher functional homomeric α7nAChR channels. Real-time fluorescence imaging showed nicotine, via α7nAChR, increases intracellular Ca2+ ([Ca2+]i) independent of ACh effects, particularly in asthmatic hASM, while cellular traction force microscopy showed nicotine-induced contractility including in asthmatics. These results indicate functional homomeric and heteromeric nAChRs that are increased in asthmatic hASM, with pharmacology that likely differ owing to different subunit interfaces that form the orthosteric sites. nAChRs may represent a novel target in alleviating airway hyperresponsiveness in asthma.NEW & NOTEWORTHY Cigarette smoking and vaping exacerbate asthma. Understanding the mechanisms of nicotine effects in asthmatic airways is important. This study demonstrates that functional alpha7 nicotinic acetylcholine receptors (α7nAChRs) are expressed in human airway smooth muscle, including from asthmatics, and enhance intracellular calcium and contractility. Although a7nAChRs are associated with neuronal pathways, α7nAChR in smooth muscle suggests inhaled nicotine (e.g., vaping) can directly influence airway contractility. Targeting α7nAChR may represent a novel approach to alleviating airway hyperresponsiveness in asthma.

Excitatory cholinergic responses in mouse primary bronchial smooth muscle require both Ca2+ entry via l-type Ca2+ channels and store operated Ca2+ entry via Orai channels

Malfunctions in airway smooth muscle Ca2+-signalling leads to airway hyperresponsiveness in asthma and chronic obstructive pulmonary disease. Ca2+-release from intracellular stores is important in mediating agonist-induced contractions, but the role of influx via l-type Ca2+ channels is controversial. We re-examined roles of the sarcoplasmic reticulum Ca2+ store, refilling of this store via store-operated Ca2+ entry (SOCE) and l-type Ca2+ channel pathways on carbachol (CCh, 0.1–10 µM)-induced contractions of mouse bronchial rings and intracellular Ca2+ signals of mouse bronchial myocytes. In tension experiments, the ryanodine receptor (RyR) blocker dantrolene (100 µM) reduced CCh-responses at all concentrations, with greater effects on sustained rather than initial components of contraction. 2-Aminoethoxydiphenyl borate (2-APB, 100 μM), in the presence of dantrolene, abolished CCh-responses, suggesting the sarcoplasmic reticulum Ca2+ store is essential for contraction. The SOCE blocker GSK-7975A (10 µM) reduced CCh-contractions, with greater effects at higher (e.g. 3 and 10 µM) CCh concentrations. Nifedipine (1 µM), abolished remaining contractions in GSK-7975A (10 µM). A similar pattern was observed on intracellular Ca2+-responses to 0.3 µM CCh, where GSK-7975A (10 µM) substantially reduced Ca2+ transients induced by CCh, and nifedipine (1 µM) abolished remaining responses. When nifedipine (1 µM) was applied alone it had less effect, reducing tension responses at all CCh concentrations by 25% - 50%, with greater effects at lower (e.g. 0.1 and 0.3 µM) CCh concentrations. When nifedipine (1 µM) was examined on the intracellular Ca2+-response to 0.3 µM CCh, it only modestly reduced Ca2+ signals, while GSK-7975A (10 µM) abolished remaining responses. In conclusion, Ca2+-influx from both SOCE and l-type Ca2+ channels contribute to excitatory cholinergic responses in mouse bronchi. The contribution of l-type Ca2+ channels was especially pronounced at lower doses of CCh, or when SOCE was blocked. This suggests l-type Ca2+ channels might be a potential target for bronchoconstriction under certain circumstances.

Cysteinyl-maresin 3 inhibits IL-13 induced airway hyperresponsiveness through alternative activation of the CysLT1 receptor

BackgroundCysteinyl-maresins, also known as maresin-conjugates in tissue regeneration (MCTRs), are recently discovered lipid mediators proposed to reduce airway inflammation. ObjectiveTo investigate the influence of MCTRs on IL-13-induced airway hyperresponsiveness in isolated human and mice airways. MethodsBefore responsiveness to contractile agonists were assessed in myographs, human small bronchi were cultured for 2 days and mouse tracheas were cultured for 1–4 days. During the culture procedure airways were exposed to interleukin (IL)-13 in the presence or absence of MCTRs. Signalling mechanisms were explored using pharmacologic agonists and antagonists, and genetically modified mice. ResultsIL-13 treatment increased contractions to histamine, carbachol and leukotriene D4 (LTD4) in human small bronchi, and to 5-hydroxytryptamine (5-HT) in mouse trachea. In both preparations, co-incubation of the explanted tissues with MCTR3 reduced the IL-13 induced enhancement of contractions. In mouse trachea, this inhibitory effect of MCTR3 was blocked by three different CysLT1 receptor antagonists (montelukast, zafirlukast and pobilukast) during IL-13 exposure. Likewise, MCTR3 failed to reduce the IL-13-induced 5-HT responsiveness in mice deficient of the CysLT1 receptor. However, co-incubation with the classical CysLT1 receptor agonist LTD4 did not alter the IL-13-induced 5-HT hyperreactivity. ConclusionsMCTR3, but not LTD4, decreased the IL-13-induced airway hyperresponsiveness by activation of the CysLT1 receptor. The distinct actions of the two lipid mediators on the CysLT1 receptor suggest an alternative signalling pathway appearing under inflammatory conditions, where this new action of MCTR3 implicates potential to inhibit airway hyperresponsiveness in asthma.

Association of Tumor Necrosis Factor-α and Myeloperoxidase enzyme with Severe Asthma: A comparative study.

Tumor necrosis factor-alpha (TNF-α) may stimulate airway hyperresponsiveness in asthma, which is also affected by neutrophils activity. The latter can be determined indirectly by evaluating myeloperoxidase (MPO) activity. The insufficient studies that investigated the combined association of serum TNF-α and MPO with asthma was objective of this study. A case-control study included 110-asthmatics besides 92-controls. All participants underwent venous sampling for TNF-α and MPO immunoassays. A percentage of predicted "forced expiratory volume in one second (FEV1%)", and the "peak expiratory flow rate (PEF/L)" of all participants were verified. The statistical analyses had done using SPSS V-25. The accuracy, specificity, sensitivity, and significance of both biomarkers to distinguish asthma examined "under the ROC-curves". High TNF-α levels observed among the controls(p-0.006), opposing the higher MPO levels among the patients(p-0.00). There were nonsignificant variations of two biomarkers between the treatment groups and nonsignificant correlations of MPO with FEV1 and PEF. There was a significant correlation of MPO with the TNF-α levels of all participants. The TNF-α showed lower sensitivity, specificity, and accuracy to diagnose asthma. There were no MPO differences according to asthma levels. The TNF-α was higher among the severe asthmatics significantly. TNF-α may be a contributory particle for neutrophilic inflammation of severe asthma. MPO levels were significantly higher among asthmatics, whereas TNF-α levels were lower. TNF-α levels were higher among those with severe compared to mild/moderate asthma. The MPO level has a significant predictive capacity compared to TNF-α for distinguishing asthma from healthy subjects.

Overuse of Short-Acting Beta-2 Agonists (SABAs) in Elite Athletes: Hypotheses to Explain It.

The use of short-acting beta-2 agonists (SABAs) is more common in elite athletes than in the general population, especially in endurance sports. The World Anti-Doping Code places some restrictions on prescribing inhaled β2-agonists. These drugs are used in respiratory diseases (such as asthma) that might reduce athletes’ performances. Recently, studies based on the results of the Olympic Games revealed that athletes with confirmed asthma/airway hyperresponsiveness (AHR) or exercise-induced bronchoconstriction (EIB) outperformed their non-asthmatic rivals. This overuse of SABA by high-level athletes, therefore, raises some questions, and many explanatory hypotheses are proposed. Asthma and EIB have a high prevalence in elite athletes, especially within endurance sports. It appears that many years of intensive endurance training can provoke airway injury, EIB, and asthma in athletes without any past history of respiratory diseases. Some sports lead to a higher risk of asthma than others due to the hyperventilation required over long periods of time and/or the high environmental exposure while performing the sport (for example swimming and the associated chlorine exposure). Inhaled corticosteroids (ICS) have a low efficacy in the treatment of asthma and EIB in elite athletes, leading to a much greater use of SABAs. A significant proportion of these high-level athletes suffer from non-allergic asthma, involving the th1-th17 pathway.

LIGHT - LTßR Signaling is Essential for Airway Smooth Muscle Remodeling and Asthmatic Airway Hyperresponsiveness

Airway hyperresponsiveness (AHR) and dysregulation of airway smooth muscle cells (ASM) is central to the severity of asthma. However which molecules control ASM in asthmatics is still largely unclear. High levels of the cytokine TNFSF14/LIGHT have been linked to asthma severity and lower baseline FEV1 %predicted, implying signals through either of its receptors, LTbR and HVEM, could directly control ASM dysfunction. We aimed to determine whether signaling via LTbR or HVEM from LIGHT controls ASM hyperreactivity.

Effect of TRPV1 and TRPV4 genes polymorphisms on the development of airway hyperresponsiveness in patients with asthma

Introduction. A change in the level of relative humidity of the inhaled air can lead to the appearance of symptoms of airway hyperresponsiveness (AHR) in patients with asthma. Allelic variations of the TRPV genes encoding osmotic receptors may serve as an internal factor predisposing to the development of respiratory manifestations in response to an osmotic trigger.Aim. The aim of the study was to establish the contribution of some single nucleotide polymorphisms (SNPs) of TRPV1 and TRPV4 to the development of osmotic AHR in asthma patients.Materials and methods. Three hundred patients with mild and moderate asthma were enrolled in the study. Osmotic AHR was diagnosed using bronchoprovocation tests with inhalation of distilled water, hypertonic saline (4.5% NaCl) or by treadmill exercise challenge test. Three SNPs (rs222747, rs224534 и rs8065080) of TRPV1 and two SNPs (rs6606743, rs7971845) of TRPV4 were geno- typed.Results. Carriage of the AA genotype for rs6606743 was associated with a lower probability of developing hypo-osmotic-induced bronchospasm. This result was confirmed in recessive (OR 0.43 95% CI [0.19; 0.94], p=0.02) and Logadditive (OR 0.62 95% CI [0.4; 0.96], p=0.03) inheritance models. Besides, in patients with the AA genotype, a less pronounced decrease in all basic parameters of lung function was observed as compared with GG and ΔG genotypes (ΔFVC, ΔPEF and ΔFEF75 - p<0.01; ΔFEV1 ΔFEV1/FVC, ΔFEF50 and ΔMMEF - p<0.001).Conclusion. A protective effect of the AA genotype for rs6606743 of TRPV4 was revealed in relation to the formation of hypoosmotic AHR.

Inhibiting ATG5 mediated autophagy to regulate endoplasmic reticulum stress and CD4+ T lymphocyte differentiation: Mechanisms of acupuncture’s effects on asthma

ObjectiveAsthma is characterized by airway hyperresponsiveness(AHR), inflammation and remodeling. Autophagy and endoplasmic reticulum stress(ERS) are dysregulated in asthma, and ATG5 has attracted wide attentions a representative gene of autophagy. Previous evidence shows that acupuncture may treat asthma by regulating the immune environment.However,the precise mechanism involved in acupuncture’s effects on asthma is unclear. Thus, we investigated the inner-relationships of acupuncture and ATG5-mediated autophagy, ERS and CD4+ T lymphocyte differentiation in asthma. MethodsOvalbumin (OVA)-sensitized and challenged ATG5+/- and ATG5-/-mice with asthma were treated by acupuncture at Dazhui(GV14),Feishu(BL13) and Zusanli(ST36),and sacrificed the next day.Then blood and bronchoalveolar lavage fluid (BALF)samples were collected to determine inflammatory cell counts and cytokine levels. Lung tissue samples were obtained for histological examination, and the spleen was harvested for flow cytometry. ResultsCompared with the untreated group, acupuncture decreased BALF inflammatory cell counts and AHR in OVA-induced mice.Acupuncture decreased autophagy-related protein and mRNA (ATG5,Beclin-1,p62 and LC3B)amounts and ERS-related protein (p-PERK, p-IRE-1,Grp78, and ATF6)levels as well as autophagosome formation in lung tissue, concomitant with increased IFN-γ and decreased IL-4, IL-17 and TGF-β amounts in BALF.Consistently, the imbalance of CD4+ T lymphocyte subsets(Th1/Th2 and Treg/Th17) was also corrected by acupuncture.Meanwhile, AHR and inflammation were decreased in ATG5-/- mice compared with ATG+/-animals,without affecting the therapeutic effect of acupuncture. ConclusionAcupuncture reduces airway inflammation and AHR in asthma by inhibiting ATG5-mediated autophagy to regulate endoplasmic reticulum stress and CD4+T lymphocyte differentiation.

Diacylglycerol Kinase Inhibition Reduces Airway Contraction by Negative Feedback Regulation of Gq-Signaling.

Exaggerated airway smooth muscle (ASM) contraction regulated by the Gq family of G protein-coupled receptors causes airway hyperresponsiveness in asthma. Activation of Gq-coupled G protein-coupled receptors leads to phospholipase C (PLC)-mediated generation of inositol triphosphate (IP3) and diacylglycerol (DAG). DAG signaling is terminated by the action of DAG kinase (DGK) that converts DAG into phosphatidic acid (PA). Our previous study demonstrated that DGKζ and α isoform knockout mice are protected from the development of allergen-induced airway hyperresponsiveness. Here we aimed to determine the mechanism by which DGK regulates ASM contraction. Activity of DGK isoforms was inhibited in human ASM cells by siRNA-mediated knockdown of DGKα and ζ, whereas pharmacological inhibition was achieved by pan DGK inhibitor I (R59022). Effects of DGK inhibition on contractile agonist-induced activation of PLC and myosin light chain (MLC) kinase, elevation of IP3, and calcium levels were assessed. Furthermore, we used precision-cut human lung slices and assessed the role of DGK in agonist-induced bronchoconstriction. DGK inhibitor I attenuated histamine- and methacholine-induced bronchoconstriction. DGKα and ζ knockdown or pretreatment with DGK inhibitor I resulted in attenuated agonist-induced phosphorylation of MLC and MLC phosphatase in ASM cells. Furthermore, DGK inhibition decreased Gq agonist-induced calcium elevation and generation of IP3 and increased histamine-induced production of PA. Finally, DGK inhibition or treatment with DAG analog resulted in attenuation of activation of PLC in human ASM cells. Our findings suggest that DGK inhibition perturbed the DAG:PA ratio, resulting in inhibition of Gq-PLC activation in a negative feedback manner, resulting in protection against ASM contraction.

Epithelial expression and role of secreted STC1 on asthma airway hyperresponsiveness through calcium channel modulation

Asthma is characterized by airway hyperresponsiveness (AHR), inflammation, and airway remodeling. Airway hyperresponsiveness results from enhanced airway smooth muscle (ASM) contraction potentially under the control of an epithelium-derived relaxing factor (EpDRF). However, relatively rare is known about EpDRF. We aimed to elucidate the role of epithelium-derived stanniocalcin-1 (STC1) on AHR and ASM contraction. Stanniocalcin-1 levels in the serum of asthmatic patients and healthy volunteers and in bronchoalveolar lavage fluid (BALF) from ovalbumin (OVA)-challenged mice were measured by ELISA. The effects of exogenous STC1 on AHR and on inflammation were examined in mice. IL-13 modulation of STC1 mRNA and protein levels was studied in human bronchial epithelial cell lines (16HBE). The function of STC1 on Ca2+ influx and ASM contraction was examined ex vivo. Serum STC1 was decreased in asthma (n=93) compared with healthy volunteers (1071±30.4 vs 1414±75.1pg/ml, p<0.0001, n=23) and correlated with asthma control (p=0.0270), lung function (FEV1, p=0.0130), and serum IL-13 levels (p=0.0009). Treatment of ten asthmatic subjects with inhaled corticosteroids/long-acting beta2-agonists (ICS/LABA) for 1year enhanced STC1 expression which correlated with improved asthma control (p=0.022). STC1 was mainly expressed in bronchial epithelium and intranasal administration of recombinant human STC1 (rhSTC1) reduced AHR and inflammation in mice. IL-13 suppressed STC1 release from 16HBE, whereas rhSTC1 blocked store-operated Ca2+ entry (SOCE) by suppressing stromal interaction molecule 1 (STIM1) and further inhibited ASM cell contractility by suppressing Ca2+ -dependent myosin light chain (MLC) phosphorylation. Our data indicate that STC1 deficiency in asthmatic airways promotes STIM1 hyperactivity, enhanced ASM contraction, and AHR. STC1 may be a candidate EpDRF.

Inhaled triple therapy and airway hyperresponsiveness in persistent asthma

Adding a long-acting muscarinic antagonist (LAMA) is recommended in the guidelines for a patient with asthma not controlled on inhaled corticosteroid (ICS)/long-acting β-agonist (LABA). The change in forced expiratory volume in 1 second (FEV1) resulting from the addition of LAMA to ICS/LABA may be relatively small or less than the minimal clinically important difference, and as such, improved airway caliber is not the primary mechanism for a reduction in exacerbations with LAMA therapy. 1 Lipworth B.J. Emerging role of long acting muscarinic antagonists for asthma. Br J Clin Pharmacol. 2014; 77: 55-62 Crossref PubMed Scopus (33) Google Scholar Exacerbations are, in part, determined by the effects on airway hyperresponsiveness (AHR) in which a LAMA might be expected to confer additional airway smooth muscle–stabilizing effects when added to ICS/LABA. 2 Currie G.P. Jackson C.M. Ogston S.A. Lipworth B.J. Airway-stabilizing effect of long-acting beta2-agonists as add-on therapy to inhaled corticosteroids. Qjm. 2003; 96: 435-440 Crossref PubMed Scopus (23) Google Scholar Aside from effects on airway smooth muscle, there may be neuronal and paracrine actions of LAMAs that may reduce exacerbations. 1 Lipworth B.J. Emerging role of long acting muscarinic antagonists for asthma. Br J Clin Pharmacol. 2014; 77: 55-62 Crossref PubMed Scopus (33) Google Scholar Indirect challenge tests with agents such as mannitol are thought to be more physiological than direct agents such as histamine or methacholine in that they better reflect the underlying inflammation status as opposed to the function of airway smooth muscle alone. 3 Nair P. Martin J.G. Cockcroft D.C. et al. Airway hyperresponsiveness in asthma: measurement and clinical relevance. J Allergy Clin Immunol Pract. 2017; 5: 649-659.e2 Abstract Full Text Full Text PDF PubMed Scopus (52) Google Scholar

Exercise-induced alterations in phospholipid hydrolysis, airway surfactant, and eicosanoids and their role in airway hyperresponsiveness in asthma.

The mechanisms responsible for driving endogenous airway hyperresponsiveness (AHR) in the form of exercise-induced bronchoconstriction (EIB) are not fully understood. We examined alterations in airway phospholipid hydrolysis, surfactant degradation, and lipid mediator release in relation to AHR severity and changes induced by exercise challenge. Paired induced sputum (n = 18) and bronchoalveolar lavage (BAL) fluid (n = 11) were obtained before and after exercise challenge in asthmatic subjects. Samples were analyzed for phospholipid structure, surfactant function, and levels of eicosanoids and secreted phospholipase A2 group 10 (sPLA2-X). A primary epithelial cell culture model was used to model effects of osmotic stress on sPLA2-X. Exercise challenge resulted in increased surfactant degradation, phospholipase activity, and eicosanoid production in sputum samples of all patients. Subjects with EIB had higher levels of surfactant degradation and phospholipase activity in BAL fluid. Higher basal sputum levels of cysteinyl leukotrienes (CysLTs) and prostaglandin D2 (PGD2) were associated with direct AHR, and both the postexercise and absolute change in CysLTs and PGD2 levels were associated with EIB severity. Surfactant function either was abnormal at baseline or became abnormal after exercise challenge. Baseline levels of sPLA2-X in sputum and the absolute change in amount of sPLA2-X with exercise were positively correlated with EIB severity. Osmotic stress ex vivo resulted in movement of water and release of sPLA2-X to the apical surface. In summary, exercise challenge promotes changes in phospholipid structure and eicosanoid release in asthma, providing two mechanisms that promote bronchoconstriction, particularly in individuals with EIB who have higher basal levels of phospholipid turnover.

Airway smooth muscle and airway hyperresponsiveness in asthma: mechanisms of airway smooth muscle dysfunction.

Airway smooth muscle plays a pivotal role in modulating bronchomotor tone. Modulation of contractile and relaxation signaling is critical to alleviate the airway hyperresponsiveness (AHR) associated with asthma. Emerging studies examining the phenotype of ASM in the context of asthma provide rich avenues to develop more effective therapeutics to attenuate the AHR associated with the disease.

PKCε stimulation of TRPV1 orchestrates carotid body responses to asthmakines.

Key points We have previously shown that carotid body stimulation by lysophosphatidic acid elicits a reflex stimulation of vagal efferent activity sufficient to cause bronchoconstriction in asthmatic rats.Here, we show that pathophysiological concentrations of asthma‐associated prototypical Th2 cytokines also stimulate the carotid bodies.Stimulation of the carotid bodies by these asthmakines involves a PKCε–transient receptor potential vanilloid 1 (TRPV1) signalling mechanism likely dependent on TRPV1 S502 and T704 phosphorylation sites.As the carotid bodies’ oxygen sensitivity is independent of PKCε–TRPV1 signalling, systemic blockade of PKCε may provide a novel therapeutic target to reduce allergen‐induced asthmatic bronchoconstriction.Consistent with the therapeutic potential of blocking the PKCε–TRPV1 pathway, systemic delivery of a PKCε‐blocking peptide suppresses asthmatic respiratory distress in response to allergen and reduces airway hyperresponsiveness to bradykinin. The autonomic nervous system orchestrates organ‐specific, systemic and behavioural responses to inflammation. Recently, we demonstrated a vital role for lysophosphatidic acid in stimulating the primary autonomic oxygen chemoreceptors, the carotid bodies, in parasympathetic‐mediated asthmatic airway hyperresponsiveness. However, the cacophony of stimulatory factors and cellular mechanisms of carotid body activation are unknown. Therefore, we set out to determine the intracellular signalling involved in carotid body‐mediated sensing of asthmatic blood‐borne inflammatory mediators. We employed a range of in vitro and rat in situ preparations, site‐directed mutagenesis, patch‐clamp, nerve recordings and pharmacological inhibition to assess cellular signalling. We show that the carotid bodies are also sensitive to asthma‐associated prototypical Th2 cytokines which elicit sensory nerve excitation. This provides additional asthmatic ligands contributing to the previously established reflex arc resulting in efferent vagal activity and asthmatic bronchoconstriction. This novel sensing role for the carotid body is mediated by a PKCε‐dependent stimulation of transient receptor potential vanilloid 1 (TRPV1), likely via TRPV1 phosphorylation at sites T704 and S502. Importantly, carotid body oxygen sensing was unaffected by blocking either PKCε or TRPV1. Further, we demonstrate that systemic PKCε blockade reduces asthmatic respiratory distress in response to allergen and airway hyperresponsiveness. These discoveries support an inflammation‐dependent, oxygen‐independent function for the carotid body and suggest that targeting PKCε provides a novel therapeutic option to abate allergic airway disease without altering life‐saving autonomic hypoxic reflexes.