Store-operated calcium entry is required for sustained contraction and Ca2+ oscillations of airway smooth muscle

IL-37 protects against house dust mite-induced airway inflammation and airway epithelial barrier dysfunction via inhibiting store-operated calcium entry

BACKGROUND

Airway epithelial barrier dysfunction has been proved to contribute to the development of type 2 inflammation of asthma. Interleukin (IL)-37 is a negative regulator of immune responses and allergic airway inflammation. However, whether IL-37 has any effect on airway epithelial barrier has been unknown.

METHODS

We evaluated the role of IL-37 in both mouse model and cultured 16HBE cells. Histology and ELISA assays were used to evaluate airway inflammation. FITC-dextran permeability assay was used to evaluate the airway epithelial barrier function. Immunofluorescence, western blot and quantitative Real-Time PCR (RT-PCR) were used to evaluate the distribution and expression of tight junction proteins. RT-PCR and Ca2+ fluorescence measurement were used to evaluate the mRNA expression and activity of store-operated calcium entry (SOCE).

RESULTS

IL-37 inhibited house dust mite (HDM)-induced airway inflammation and decreased the levels of IgE in serum and type 2 cytokines in bronchoalveolar lavage fluid (BALF) compared to asthmatic mice. IL-37 protected against HDM-induced airway epithelial barrier dysfunction, including reduced leakage of FITC-dextran, enhanced expression of TJ proteins, and restored the membrane distribution of TJ proteins. Moreover, IL-37 decreased the level of IL-33 in the BALF of asthmatic mice and the supernatants of HDM-treated 16HBE cells. IL-37 decreased the peak level of Ca2+ fluorescence induced by thapsigargin and HDM, and inhibited the mRNA expression of Orai1, suggesting an inhibiting effect of IL-37 on SOCE in airway epithelial cells.

CONCLUSION

IL-37 plays a protective role in airway inflammation and HDM-induced airway epithelial barrier dysfunction by inhibiting SOCE.

Precision cut lung slices: an integrated ex vivo model for studying lung physiology, pharmacology, disease pathogenesis and drug discovery

Precision Cut Lung Slices (PCLS) have emerged as a sophisticated and physiologically relevant ex vivo model for studying the intricacies of lung diseases, including fibrosis, injury, repair, and host defense mechanisms. This innovative methodology presents a unique opportunity to bridge the gap between traditional in vitro cell cultures and in vivo animal models, offering researchers a more accurate representation of the intricate microenvironment of the lung. PCLS require the precise sectioning of lung tissue to maintain its structural and functional integrity. These thin slices serve as invaluable tools for various research endeavors, particularly in the realm of airway diseases. By providing a controlled microenvironment, precision-cut lung slices empower researchers to dissect and comprehend the multifaceted interactions and responses within lung tissue, thereby advancing our understanding of pulmonary pathophysiology.

Calcium Signaling in Airway Epithelial Cells: Current Understanding and Implications for Inflammatory Airway Disease

Airway epithelial cells play an indispensable role in protecting the lung from inhaled pathogens and allergens by releasing an array of mediators that orchestrate inflammatory and immune responses when confronted with harmful environmental triggers. While this process is undoubtedly important for containing the effects of various harmful insults, dysregulation of the inflammatory response can cause lung diseases including asthma, chronic obstructive pulmonary disease, and pulmonary fibrosis. A key cellular mechanism that underlies the inflammatory responses in the airway is calcium signaling, which stimulates the production and release of chemokines, cytokines, and prostaglandins from the airway epithelium. In this review, we discuss the role of major Ca2+ signaling pathways found in airway epithelial cells and their contributions to airway inflammation, mucociliary clearance, and surfactant production. We highlight the importance of store-operated Ca2+ entry as a major signaling hub in these processes and discuss therapeutic implications of targeting Ca2+ signaling for airway inflammation.

Ca2+ dynamics in interstitial cells: foundational mechanisms for the motor patterns in the gastrointestinal tract

The gastrointestinal (GI) tract displays multiple motor patterns that move nutrients and wastes through the body. Smooth muscle cells (SMCs) provide the forces necessary for GI motility, but interstitial cells, electrically coupled to SMCs, tune SMC excitability, transduce inputs from enteric motor neurons, and generate pacemaker activity that underlies major motor patterns, such as peristalsis and segmentation. The interstitial cells regulating SMCs are interstitial cells of Cajal (ICC) and PDGF receptor (PDGFR)α+ cells. Together these cells form the SIP syncytium. ICC and PDGFRα+ cells express signature Ca2+-dependent conductances: ICC express Ca2+-activated Cl- channels, encoded by Ano1, that generate inward current, and PDGFRα+ cells express Ca2+-activated K+ channels, encoded by Kcnn3, that generate outward current. The open probabilities of interstitial cell conductances are controlled by Ca2+ release from the endoplasmic reticulum. The resulting Ca2+ transients occur spontaneously in a stochastic manner. Ca2+ transients in ICC induce spontaneous transient inward currents and spontaneous transient depolarizations (STDs). Neurotransmission increases or decreases Ca2+ transients, and the resulting depolarizing or hyperpolarizing responses conduct to other cells in the SIP syncytium. In pacemaker ICC, STDs activate voltage-dependent Ca2+ influx, which initiates a cluster of Ca2+ transients and sustains activation of ANO1 channels and depolarization during slow waves. Regulation of GI motility has traditionally been described as neurogenic and myogenic. Recent advances in understanding Ca2+ handling mechanisms in interstitial cells and how these mechanisms influence motor patterns of the GI tract suggest that the term "myogenic" should be replaced by the term "SIPgenic," as this review discusses.

Inherent differences of small airway contraction and Ca2+ oscillations in airway smooth muscle cells between BALB/c and C57BL/6 mouse strains

BALB/c and C57BL/6 mouse strains are widely used as animal model in studies of respiratory diseases, such as asthma. Asthma is characterized by airway hyperresponsiveness, which is eventually resulted from the excessive airway smooth muscle (ASM) contraction mediated by Ca²⁺ oscillations in ASM cells. It is reported that BALB/c mice have inherently higher airway responsiveness, but show no different contractive response of tracheal ring as compared to C57BL/6 mice. However, whether the different airway responsiveness is due to the different extents of small airway contraction, and what's underlying mechanism remains unknown. Here, we assess agonist-induced small airway contraction and Ca²⁺ oscillations in ASM cells between BALB/c and C57BL/6 mice by using precision-cut lung slices (PCLS). We found that BALB/c mice showed an intrinsically stronger extent of small airway narrowing and faster Ca²⁺ oscillations in ASM cells in response to agonists. These differences were associated with a higher magnitude of Ca²⁺ influx via store-operated Ca²⁺ entry (SOCE), as a result of increased expression of SOCE components (STIM1, Orai1) in the ASM cells of small airway of BALB/c mice. An established mathematical model and experimental results suggested that the increased SOC current could result in increased agonist-induced Ca²⁺ oscillations. Therefore, the inherently higher SOC underlies the increased Ca²⁺ oscillation frequency in ASM cells and stronger small airway contraction in BALB/c mice, thus higher airway responsiveness in BALB/c than C57BL/6 mouse strain.

Exercise Reduces Airway Smooth Muscle Contraction in Asthmatic Rats via Inhibition of IL-4 Secretion and Store-Operated Ca2+ Entry Pathway

PURPOSE

Increased evidence has shown that aerobic exercise reduces airway hyperresponsiveness in asthmatic individuals. However, the underlying mechanisms of action remain elusive. This study aimed to investigate the effect of exercise on airway smooth muscle (ASM) contractile function in asthmatic rats, and uncover the possible involvement of interleukin 4 (IL-4) and the store-operated Ca²⁺ entry (SOCE) pathway.

METHODS

In this study, chicken ovalbumin was used to induce asthma in male Sprague-Dawley rats. The exercise group received moderate-intensity aerobic exercise training for 4 weeks. IL-4 concentrations in bronchoalveolar lavage fluid (BALF) samples were evaluated by enzyme linked immunosorbent assay. The contractile function of the ASM was investigated using tracheal ring tension experiments and intracellular Ca²⁺ imaging techniques. Western blot analysis was used to evaluate expression levels of calcium-release activated calcium (CRAC) channel protein (Orai) and stromal interaction molecule 1 (STIM1) in ASM.

RESULTS

Our data showed that the carbachol-stimulated, SOCE-mediated contraction of rat ASM was significantly increased in asthmatic rats, which could be abolished by exercise. Pharmacological studies revealed that GSK5498A and BTP-2, selective blockers of CRAC channels significantly inhibited SOCE-induced ASM contraction. In addition, exercise inhibited the up-regulation of IL-4 in BALF as well as STIM1 and Orai expression in the ASM of asthmatic rats. In line with these observations, we demonstrated that pretreatment of the ASM with IL-4 up-regulated the expression level of STIM1, Orai1 and Orai2, thereby promoting SOCE-mediated ASM contraction.

CONCLUSIONS

The data in this study reveal that aerobic exercise may improve the ASM contractile function in asthmatic rats by inhibiting IL-4 secretion and by down-regulating the expression of STIM1, Orai1 and Orai2, thus decreasing excessive SOCE-mediated ASM contraction in asthmatic rats.

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.

Menthol flavoring in e-cigarette condensate causes pulmonary dysfunction and cytotoxicity in precision cut lung slices

E-cigarette consumption is under scrutiny by regulatory authorities due to concerns about product toxicity, lack of manufacturing standards, and increasing reports of e-cigarette- or vaping-associated acute lung injury. In vitro studies have demonstrated cytotoxicity, mitochondrial dysfunction, and oxidative stress induced by unflavored e-cigarette aerosols and flavoring additives. However, e-cigarette effects on the complex lung parenchyma remain unclear. Herein, the impact of e-cigarette condensates with or without menthol flavoring on functional, structural, and cellular responses was investigated using mouse precision cut lung slices (PCLS). PCLS were exposed to e-cigarette condensates prepared from aerosolized vehicle, nicotine, nicotine + menthol, and menthol e-fluids at doses from 50 to 500 mM. Doses were normalized to the glycerin content of vehicle. Video-microscopy of PCLS revealed impaired contractile responsiveness of airways to methacholine and dampened ciliary beating following exposure to menthol-containing condensates at concentrations greater than 300 mM. Following 500 mM menthol-containing condensate exposure, epithelial exfoliation in intrabronchial airways was identified in histological sections of PCLS. Measurement of lactate dehydrogenase release, mitochondrial water-soluble-tetrazolium salt-1 conversion, and glutathione content supported earlier findings of nicotine or nicotine + menthol e-cigarette-induced dose-dependent cytotoxicity and oxidative stress responses. Evaluation of PCLS metabolic activity revealed dose-related impairment of mitochondrial oxidative phosphorylation and glycolysis after exposure to menthol-containing condensates. Taken together, these data demonstrate prominent menthol-induced pulmonary toxicity and impairment of essential physiological functions in the lung, which warrants concerns about e-cigarette consumer safety and emphasizes the need for further investigations of molecular mechanisms of toxicity and menthol effects in an experimental model of disease.

Glucose- and glutamine-dependent bioenergetics sensitize bone mechanoresponse after unloading by modulating osteocyte calcium dynamics

Disuse osteoporosis is a metabolic bone disease resulting from skeletal unloading (e.g., during extended bed rest, limb immobilization, and spaceflight), and the slow and insufficient bone recovery during reambulation remains an unresolved medical challenge. Here, we demonstrated that loading-induced increase in bone architecture/strength was suppressed in skeletons previously exposed to unloading. This reduction in bone mechanosensitivity was directly associated with attenuated osteocytic Ca2+ oscillatory dynamics. The unloading-induced compromised osteocytic Ca2+ response to reloading resulted from the HIF-1α/PDK1 axis-mediated increase in glycolysis, and a subsequent reduction in ATP synthesis. HIF-1α also transcriptionally induced substantial glutaminase 2 expression and thereby glutamine addiction in osteocytes. Inhibition of glycolysis by blockade of PDK1 or glutamine supplementation restored the mechanosensitivity in those skeletons with previous unloading by fueling the tricarboxylic acid cycle and rescuing subsequent Ca2+ oscillations in osteocytes. Thus, we provide mechanistic insight into disuse-induced deterioration of bone mechanosensitivity and a promising therapeutic approach to accelerate bone recovery after long-duration disuse.

ORAI Calcium Channels: Regulation, Function, Pharmacology, and Therapeutic Targets

The changes in intracellular free calcium (Ca2+) levels are one of the most widely regulators of cell function; therefore, calcium as a universal intracellular mediator is involved in very important human diseases and disorders. In many cells, Ca2+ inflow is mediated by store-operated calcium channels, and it is recognized that the store-operated calcium entry (SOCE) is mediated by the two partners: the pore-forming proteins Orai (Orai1-3) and the calcium store sensor, stromal interaction molecule (STIM1-2). Importantly, the Orai/STIM channels are involved in crucial cell signalling processes such as growth factors, neurotransmitters, and cytokines via interaction with protein tyrosine kinase coupled receptors and G protein-coupled receptors. Therefore, in recent years, the issue of Orai/STIM channels as a drug target in human diseases has received considerable attention. This review summarizes and highlights our current knowledge of the Orai/STIM channels in human diseases and disorders, including immunodeficiency, myopathy, tubular aggregate, Stormorken syndrome, York platelet syndrome, cardiovascular and metabolic disorders, and cancers, as well as suggesting these channels as drug targets for pharmacological therapeutic intervention. Moreover, this work will also focus on the pharmacological modulators of Orai/STIM channel complexes. Together, our thoughtful of the biology and physiology of the Orai/STIM channels have grown remarkably during the past three decades, and the next important milestone in the field of store-operated calcium entry will be to identify potent and selective small molecules as a therapeutic agent with the purpose to target human diseases and disorders for patient benefit.

Transition behavior of the seizure dynamics modulated by the astrocyte inositol triphosphate noise

Epilepsy is a neurological disorder with recurrent seizures, which convey complex dynamical characteristics including chaos and randomness. Until now, the underlying mechanism has not been fully elucidated, especially the bistable property beneath the epileptic random induction phenomena in certain conditions. Inspired by the recent finding that astrocyte GTPase-activating protein (G-protein)-coupled receptors could be involved in stochastic epileptic seizures, we proposed a neuron-astrocyte network model, incorporating the noise of the astrocytic second messenger, inositol triphosphate (IP3) that is modulated by G-protein-coupled receptor activation. Based on this model, we have statistically analyzed the transitions of epileptic seizures by performing repeatable simulation trials. Our simulation results show that the increase in the IP3 noise intensity induces depolarization-block epileptic seizures together with an increase in neuronal firing frequency, consistent with corresponding experiments. Meanwhile, the bistable states of the seizure dynamics were present under certain noise intensities, during which the neuronal firing pattern switches between regular sparse spiking and epileptic seizure states. This random presence of epileptic seizures is absent when the noise intensity continues to increase, accompanying with an increase in the epileptic depolarization block duration. The simulation results also shed light on the fact that calcium signals in astrocytes play significant roles in the pattern formations of the epileptic seizure. Our results provide a potential pathway for understanding the epileptic randomness in certain conditions.

Airway smooth muscle function in asthma

Known to have affected around 340 million people across the world in 2018, asthma is a prevalent chronic inflammatory disease of the airways. The symptoms such as wheezing, dyspnea, chest tightness, and cough reflect episodes of reversible airway obstruction. Asthma is a heterogeneous disease that varies in clinical presentation, severity, and pathobiology, but consistently features airway hyperresponsiveness (AHR)—excessive airway narrowing due to an exaggerated response of the airways to various stimuli. Airway smooth muscle (ASM) is the major effector of exaggerated airway narrowing and AHR and many factors may contribute to its altered function in asthma. These include genetic predispositions, early life exposure to viruses, pollutants and allergens that lead to chronic exposure to inflammatory cells and mediators, altered innervation, airway structural cell remodeling, and airway mechanical stress. Early studies aiming to address the dysfunctional nature of ASM in the etiology and pathogenesis of asthma have been inconclusive due to the methodological limitations in assessing the intrapulmonary airways, the site of asthma. The study of the trachealis, although convenient, has been misleading as it has shown no alterations in asthma and it is not as exposed to inflammatory cells as intrapulmonary ASM. Furthermore, the cartilage rings offer protection against stress and strain of repeated contractions. More recent strategies that allow for the isolation of viable intrapulmonary ASM tissue reveal significant mechanical differences between asthmatic and non-asthmatic tissues. This review will thus summarize the latest techniques used to study ASM mechanics within its environment and in isolation, identify the potential causes of the discrepancy between the ASM of the extra- and intrapulmonary airways, and address future directions that may lead to an improved understanding of ASM hypercontractility in asthma.

Imidazobenzodiazepine PI320 Relaxes Mouse Peripheral Airways by Inhibiting Calcium Mobilization

Asthma is a common respiratory disease characterized, in part, by excessive airway smooth muscle (ASM) contraction (airway hyperresponsiveness). Various GABA_AR (γ-aminobutyric acid type A receptor) activators, including benzodiazepines, relax ASM. The GABA_AR is a ligand-operated Cl^- channel best known for its role in inhibitory neurotransmission in the central nervous system. Although ASM cells express GABA_ARs, affording a seemingly logical site of action, the mechanism(s) by which GABA_AR ligands relax ASM remains unclear. PI320, a novel imidazobenzodiazepine designed for tissue selectivity, is a promising asthma drug candidate. Here, we show that PI320 alleviates methacholine (MCh)-induced bronchoconstriction in vivo and relaxes peripheral airways preconstricted with MCh ex vivo using the forced oscillation technique and precision-cut lung slice experiments, respectively. Surprisingly, the peripheral airway relaxation demonstrated in precision-cut lung slices does not appear to be GABA_AR-dependent, as it is not inhibited by the GABA_AR antagonist picrotoxin or the benzodiazepine antagonist flumazenil. Furthermore, we demonstrate here that PI320 inhibits MCh-induced airway constriction in the absence of external Ca², suggesting that PI320-mediated relaxation is not mediated by inhibition of Ca²⁺ influx in ASM. However, PI320 does inhibit MCh-induced intracellular Ca²⁺ oscillations in peripheral ASM, a key mediator of contraction that is dependent on sarcoplasmic reticulum Ca²⁺ mobilization. Furthermore, PI320 inhibits peripheral airway constriction induced by experimentally increasing the intracellular concentration of inositol triphosphate (IP₃). These novel data suggest that PI320 relaxes murine peripheral airways by inhibiting intracellular Ca²⁺ mobilization in ASM, likely by inhibiting Ca²⁺ release through IP₃Rs (IP₃ receptors).

Ca2+ signalling in interstitial cells of Cajal contributes to generation and maintenance of tone in mouse and monkey lower esophageal sphincters

KEY POINTS

The lower esophageal sphincter (LES) generates contractile tone preventing reflux of gastric contents into the esophagus. LES smooth muscle cells (SMCs) display depolarized membrane potentials facilitating activation of L-type Ca²⁺ channels. Interstitial cells of Cajal (ICC) express Ca²⁺ -activated Cl^- channels encoded by Ano1 in mouse and monkey LES. Ca²⁺ signaling in ICC activates ANO1 currents in ICC. ICC displayed spontaneous Ca²⁺ transients in mice from multiple firing sites in each cell and no entrainment of Ca²⁺ firing between sites or between cells. Inhibition of ANO1 channels with a specific antagonist caused hyperpolarization of mouse LES and inhibition of tone in monkey and mouse LES muscles. Our data suggest a novel mechanism for LES tone in which Ca²⁺ transient activation of ANO1 channels in ICC generates depolarizing inward currents that conduct to SMCs to activate L-type Ca²⁺ currents, Ca²⁺ entry and contractile tone.

ABSTRACT

The lower esophageal sphincter (LES) generates tone and prevents reflux of gastric contents. LES smooth muscle cells (SMCs) are relatively depolarized, facilitating activation of Ca_v 1.2 channels to sustain contractile tone. We hypothesised that intramuscular interstitial cells of Cajal (ICC-IM), through activation of Ca²⁺ -activated-Cl^- channels (ANO1), set membrane potentials of SMCs favorable for activation of Ca_v 1.2 channels. In some gastrointestinal muscles, ANO1 channels in ICC-IM are activated by Ca²⁺ transients, but no studies have examined Ca²⁺ dynamics in ICC-IM within the LES. Immunohistochemistry and qPCR were used to determine expression of key proteins and genes in ICC-IM and SMCs. These studies revealed that Ano1 and its gene product, ANO1 are expressed in c-Kit⁺ cells (ICC-IM) in mouse and monkey LES clasp muscles. Ca²⁺ signaling was imaged in situ, using mice expressing GCaMP6f specifically in ICC (Kit-KI-GCaMP6f). ICC-IM exhibited spontaneous Ca²⁺ transients from multiple firing sites. Ca²⁺ transients were abolished by CPA or caffeine but were unaffected by tetracaine or nifedipine. Maintenance of Ca²⁺ transients depended on Ca²⁺ influx and store reloading, as Ca²⁺ transient frequency was reduced in Ca²⁺ free solution or by Orai antagonist. Spontaneous tone of LES muscles from mouse and monkey was reduced ∼80% either by Ani9, an ANO1 antagonist or by the Ca_v 1.2 channel antagonist nifedipine. Membrane hyperpolarisation occurred in the presence of Ani9. These data suggest that intracellular Ca²⁺ activates ANO1 channels in ICC-IM in the LES. Coupling of ICC-IM to SMCs drives depolarization, activation of Ca_v 1.2 channels, Ca²⁺ entry and contractile tone. Abstract figure legend Proposed mechanism for generation of contractile tone in the lower esophageal sphincter (LES). Interstitial cells of Cajal (ICC) in the LES generate spontaneous, stochastic Ca²⁺ transients via Ca²⁺ release from the endoplasmic reticulum (ER). The Ca²⁺ transients activate ANO1 Cl- channels causing Cl- efflux (inward current). ANO1 currents have a depolarizing effect on ICC (+++s inside membrane) and this conducts through gap junctions (GJ) to smooth muscle cells (SMCs). Input from thousands of ICC results in depolarized membrane potentials (-40 to -50 mV) which is within the window current range for L-type Ca²⁺ channels. Activation of these channels causes Ca²⁺ influx, activation of contractile elements (CE) and development of tonic contraction. This article is protected by copyright. All rights reserved.

Transient receptor potential cation channel subfamily V (TRPV) and its importance in asthma

Transient receptor potential (TRP) ion channels play critical roles in physiological and pathological conditions. Increasing evidence has unveiled the contribution of TRP vanilloid (TRPV) family in the development of asthma. The TRPV family is a group (TRPV1-TRPV6) of polymodal channels capable of sensing thermal, acidic, mechanical stress, and osmotic stimuli. TRPVs can be activated by endogenous ligands including, arachidonic acid derivatives or endocannabinoids. While TRPV1-TRPV4 are non-selective cation channels showing a predominance for Ca2+ over Na + influx, TRPV5 and TRPV6 are only Ca2+ permeable selective channels. Asthma is a chronic inflammatory bronchopulmonary disorder involving airway hyperresponsiveness (AHR) and airway remodeling. Patients suffering from allergic asthma display an inflammatory pattern driven by cytokines produced in type-2 helper T cells (Th2) and type 2 innate lymphoid cells (ILC2s). Ion channels are essential regulators in airway smooth muscle (ASM) and immune cells physiology. In this review, we summarize the contribution of TRPV1, TRPV2, and TRPV4 to the pathogenesis of asthma. TRPV1 is associated with hypersensitivity to environmental pollutants and chronic cough, inflammation, AHR, and remodeling. TRPV2 is increased in peripheral lymphocytes of asthmatic patients. TRPV4 contributes to ASM cells proliferation, and its blockade leads to a reduced eosinophilia, neutrophilia, as well as an abolished AHR. In conclusion, TRPV2 may represent a novel biomarker for asthma in children; meanwhile, TRPV1 and TRPV4 seem to be essential contributors to the development and exacerbations of asthma. Moreover, these channels may serve as novel therapeutic targets for this ailment.

ORAI1 regulates sustained cytosolic free calcium fluctuations during breast cancer cell apoptosis and apoptotic resistance via a STIM1 independent pathway

Excessive rapid increases in cytosolic free Ca²⁺ have a clear association with the induction of cancer cell death. Whereas, characterizing the Ca²⁺ signaling events that occur during the progression of the apoptotic cascade over a period of hours or days, has not yet been possible. Now using genetically encoded Ca²⁺ indicators complemented with automated epifluorescence microscopy we have shown that staurosporine-induced apoptosis in MDA-MB-231 breast cancer cells was associated with delayed development of cytosolic free Ca²⁺ fluctuations, which were then maintained for 24 h. These cytosolic free Ca²⁺ fluctuations were dependent on the Ca²⁺ channel ORAI1. Silencing of ORAI1, but not its canonical activators STIM1 and STIM2, promoted apoptosis in this model. The pathway for this regulation implicates a mechanism previously associated with the migration of cancer cells involving ORAI1, the chaperone protein SigmaR1, and Ca²⁺ -activated K⁺ channels.

Ca2+ transients in ICC-MY define the basis for the dominance of the corpus in gastric pacemaking

Myenteric interstitial cells of Cajal (ICC-MY) generate and actively propagate electrical slow waves in the stomach. Slow wave generation and propagation are altered in gastric motor disorders, such as gastroparesis, and the mechanism for the gradient in slow wave frequency that facilitates proximal to distal propagation of slow waves and normal gastric peristalsis is poorly understood.  Slow waves depend upon Ca2+-activated Cl- channels (encoded by Ano1). We characterized Ca2+ signaling in ICC-MY in situ using mice engineered to have cell-specific expression of GCaMP6f in ICC. Ca2+ signaling differed in ICC-MY in corpus and antrum. Localized Ca2+ transients were generated from multiple firing sites and were organized into Ca2+ transient clusters (CTCs). Ca2+ transient refractory periods occurred upon cessation of CTCs, but a relatively higher frequency of Ca2+ transients persisted during the inter-CTC interval in corpus than in antrum ICC-MY. The onset of Ca2+ transients after the refractory period was associated with initiation of the next CTC. Thus, CTCs were initiated at higher frequencies in corpus than in antrum ICC-MY. Initiation and propagation of CTCs (and electrical slow waves) depends upon T-type Ca2+ channels, and durations of CTCs relied upon L-type Ca2+ channels. The durations of CTCs mirrored the durations of slow waves. CTCs and Ca2+ transients between CTCs resulted from release of Ca2+ from intracellular stores and were maintained, in part, by store-operated Ca2+ entry. Our data suggest that Ca2+ release and activation of Ano1 channels both initiate and contribute to the plateau phase of slow waves.

Store-operated Calcium Entry-associated Regulatory Factor Regulates Airway Inflammation and Airway Remodeling in Asthma Mice Models

BACKGROUND

Store-operated calcium entry (SOCE) is involved in the pathogenesis of airway inflammation and remodeling in asthma. Store-operated calcium entry-associated regulatory factor (SARAF) can down-regulate SOCE.

OBJECTIVE

We sought to investigate the role of SARAF in the regulation of airway inflammation and remodeling in asthma mice models, as well as in the functional regulation of human airway smooth muscle cells (hASMCs).

METHODS

Balb/c mice were sensitized and challenged with ovalbumin to establish the asthma mice models. Mice were transfected with lentivirus, which expressed the SARAF gene + GFP or the negative control gene + GFP. Airway resistance was measured with the animal pulmonary function system. Airway inflammation and remodeling were evaluated via histological staining. In vitro cultured hASMCs were transfected with scrambled small interfering RNA(siRNA) or SARAF-specific siRNA respecitvely. The proliferation, migration rate, hypertrophy and SOCE activity of hASMCs were examined with cell counting kit 8, wound healing test, bright field imaging and Ca²⁺ fluorescence imaging, respectively. SARAF expression was measured by quantitative real-time-PCR.

RESULTS

Asthma mice models showed decreased SARAF mRNA expression in the lungs. SARAF overexpression attenuated airway inflammation, resistance and also remodeling. Downregulation of SARAF expression with siRNA promoted the proliferation, migration, hypertrophy and SOCE activity in hASMCs.

CONCLUSIONS

SARAF plays a protective role against airway inflammation and remodeling in asthma mice models by blunting SOCE; SARAF may also be a functional regulating factor of hASMCs.

Nimodipine inhibits intestinal and aortic smooth muscle contraction by regulating Ca2+-activated Cl- channels

Nimodipine is a clinically used dihydropyridine L-type calcium channel antagonist that effectively inhibits transmembrane Ca2+ influx following the depolarization of smooth muscle cells, but the detailed effect on smooth muscle contraction is not fully understood. Ca2+-activated Cl- channels (CaCCs) in vascular smooth muscle cells (VSMCs) may regulate vascular contractility. We found that nimodipine can inhibit transmembrane protein 16A (TMEM16A) activity in a concentration-dependent manner by cell-based fluorescence-quenching assay and short-circuit current analysis, with an IC50 value of ~5 μM. Short-circuit current analysis also showed that nimodipine prevented Ca2+-activated Cl- current in both HT-29 cells and mouse colonic epithelia accompanied by significantly decreased cytoplasmic Ca2+ concentrations. In the absence of extracellular Ca2+, nimodipine still exhibited an inhibitory effect on TMEM16A/CaCCs. Additionally, the application of nimodipine to CFTR-expressing FRT cells and mouse colonic mucosa resulted in mild activation of CFTR-mediated Cl- currents. Nimodipine inhibited basolateral CCh-activated K+ channel activity with no effect on Na+/K+-ATPase activity. Evaluation of intestinal smooth muscle contraction showed that nimodipine inhibits intestinal smooth muscle contractility and frequency, with an activity pattern that was similar to that of non-specific inhibitors of CaCCs. In aortic smooth muscle, the expression of TMEM16A in thoracic aorta is higher than that in abdominal aorta, corresponding to stronger maximum contractility in thoracic aorta smooth muscle stimulated by phenylephrine (PE) and Eact. Nimodipine completely inhibited the contraction of aortic smooth muscle stimulated by Eact, and partially inhibited the contraction stimulated by PE. In summary, the results indicate that nimodipine effectively inhibits TMEM16A/CaCCs by reduction transmembrane Ca2+ influx and directly interacting with TMEM16A, explaining the mechanisms of nimodipine relaxation of intestinal and aortic smooth muscle contraction and providing new targets for pharmacological applications.

Development of Store-Operated Calcium Entry-Targeted Compounds in Cancer

Store-operated Ca²⁺ entry (SOCE) is the major pathway of Ca²⁺ entry in mammalian cells, and regulates a variety of cellular functions including proliferation, motility, apoptosis, and death. Accumulating evidence has indicated that augmented SOCE is related to the generation and development of cancer, including tumor formation, proliferation, angiogenesis, metastasis, and antitumor immunity. Therefore, the development of compounds targeting SOCE has been proposed as a potential and effective strategy for use in cancer therapy. In this review, we summarize the current research on SOCE inhibitors and blockers, discuss their effects and possible mechanisms of action in cancer therapy, and induce a new perspective on the treatment of cancer.

Ca2+ signaling driving pacemaker activity in submucosal interstitial cells of Cajal in the murine colon

Interstitial cells of Cajal (ICC) generate pacemaker activity responsible for phasic contractions in colonic segmentation and peristalsis. ICC along the submucosal border (ICC-SM) contribute to mixing and more complex patterns of colonic motility. We show the complex patterns of Ca²⁺ signaling in ICC-SM and the relationship between ICC-SM Ca²⁺ transients and activation of smooth muscle cells (SMCs) using optogenetic tools. ICC-SM displayed rhythmic firing of Ca²⁺transients ~ 15 cpm and paced adjacent SMCs. The majority of spontaneous activity occurred in regular Ca²⁺ transients clusters (CTCs) that propagated through the network. CTCs were organized and dependent upon Ca²⁺ entry through voltage-dependent Ca²⁺ conductances, L- and T-type Ca²⁺ channels. Removal of Ca²⁺ from the external solution abolished CTCs. Ca²⁺ release mechanisms reduced the duration and amplitude of Ca²⁺ transients but did not block CTCs. These data reveal how colonic pacemaker ICC-SM exhibit complex Ca^2+-firing patterns and drive smooth muscle activity and overall colonic contractions.

Extracellular Vesicles Derived from Human Umbilical Cord Mesenchymal Stem Cells Protect Liver Ischemia/Reperfusion Injury by Reducing CD154 Expression on CD4+ T Cells via CCT2

As a cause of postoperative complications and early hepatic failure after liver transplantation, liver ischemia/reperfusion injury (IRI) still has no effective treatment during clinical administration. Although the therapeutic potential of mesenchymal stem cells (MSCs) for liver IRI has been previously shown, the underlying mechanisms are not completely clear. It is accepted that MSC-derived extracellular vesicles (MSC-EVs) are newly uncovered messengers for intercellular communication. Herein, it is reported that umbilical cord-derived MSCs (UC-MSCs) improve liver IRI in mice through their secreted EVs. It is also visualized that UC-MSC-EVs mainly concentrate in liver after 6 h of reperfusion. Furthermore, UC-MSC-EVs are found to significantly modulate the membranous expression of CD154 of intrahepatic CD4+ T cells, which is an initiation of inflammatory response in liver and can aggravate liver IRI. Mechanistically, protein mass spectrum analysis is performed and it is revealed that Chaperonin containing TCP1 subunit 2 (CCT2) enriches in UC-MSC-EVs, which regulates the calcium channels to affect Ca2+ influx and suppress CD154 synthesis in CD4+ T cells. In conclusion, these results highlight the therapeutic potential of UC-MSC-EVs in attenuating liver IRI. This finding suggests that CCT2 from UC-MSC-EVs can modulate CD154 expression of intrahepatic CD4+ T cells during liver IRI through the Ca2+-calcineurin-NFAT1 signaling pathway.

Folium Sennae and emodin reverse airway smooth muscle contraction

The objective of this project was to find a bronchodilatory compound from herbs and clarify the mechanism. We found that the ethanol extract of Folium Sennae (EEFS) can relax airway smooth muscle (ASM). EEFS inhibited ASM contraction, induced by acetylcholine, in mouse tracheal rings and lung slices. High-performance liquid chromatography assay showed that EEFS contained emodin. Emodin had a similar reversal action. Acetylcholine-evoked contraction was also partially reduced by nifedipine (a selective inhibitor of L-type voltage-dependent Ca²⁺ channels, LVDCCs), YM-58483 (a selective inhibitor of store-operated Ca²⁺ entry, SOCE), as well as Y-27632 (an inhibitor of Rho-associated protein kinase). In addition, LVDCC- and SOCE-mediated currents and cytosolic Ca²⁺ elevations were inhibited by emodin. Emodin reversed acetylcholine-caused increases in phosphorylation of myosin phosphatase target subunit 1. Furthermore, emodin, in vivo, inhibited acetylcholine-induced respiratory system resistance in mice. These results indicate that EEFS-induced relaxation results from emodin inhibiting LVDCC, SOCE, and Ca²⁺ sensitization. These findings suggest that Folium Sennae and emodin may be new sources of bronchodilators.

Effect of Calcium and Vitamin D Co-supplementation on Blood Pressure: A Systematic Review and Meta-Analysis

PURPOSE

Vitamin D and calcium insufficiency has been related to elevated blood pressure (BP) and cardiovascular complications. This systematic review and meta-analysis investigates the effect of calcium and vitamin D co-supplementation on BP.

METHODS

A systematic search was conducted of electronic databases, including Web of Sciences, MEDLINE, Scopus, EMBASE, and the Cochrane Library, along with searches of gray literature and reference lists from included trials. There were no language restrictions, and the databases were searched from inception to October 2019. Randomized controlled trials, using calcium and vitamin D co-supplementation and reporting mean systolic BP and/or diastolic BP (DBP) with SDs, were included in the systematic review. Articles were evaluated independently by 2 researchers based on inclusion and exclusion criteria. A random effects model was conducted to synthesize the data.

FINDINGS

Eight trials were included in the meta-analysis. Meta-analysis of these 8 trials indicated a nonsignificant reduction in systolic BP in the calcium and vitamin D co-supplementation group compared with control (standardized mean difference, -0.23; 95% CI, -0.52 to 0.06). Conversely, there was a statistically significant decrease in DBP (standardized mean difference, -0.29; 95% CI, -0.55 to -0.02). Subgroup analysis suggested that young adults achieve a greater reduction in DBP than other age groups.

IMPLICATIONS

Calcium and vitamin D co-supplementation can modulate DBP and should be investigated more specifically in large, well-designed trials of hypertensive populations. (Clin Ther. 2020;42:XXX-XXX) © 2020 Elsevier HS Journals, Inc.

Roles of LRRC26 as an auxiliary γ1-subunit of large-conductance Ca2+-activated K+ channels in bronchial smooth muscle cells

In visceral smooth muscle cells (SMCs), the large-conductance Ca²⁺-activated K⁺ (BK) channel is one of the key elements underlying a negative feedback mechanism that is essential for the regulation of intracellular Ca²⁺ concentration. Although leucine-rich repeat-containing (LRRC) proteins have been identified as novel auxiliary γ-subunits of the BK channel (BKγ) in several cell types, its physiological roles in SMCs are unclear. The BKγ expression patterns in selected SM tissues were examined using real-time PCR analyses and Western blotting. The functional contribution of BKγ1 to BK channel activity was examined by whole cell patch-clamp in SMCs and heterologous expression systems. BKγ1 expression in mouse bronchial SMCs (mBSMCs) was higher than in other several SMC types. Coimmunoprecipitation and total internal reflection fluorescence imaging analyses revealed molecular interaction between BKα and BKγ1 in mBSMCs. Under voltage-clamp, steady-state activation of BK channel currents at pCa 8.0 in mBSMCs occurred in a voltage range comparable to that of reconstituted BKα/BKγ1 complex. However, this range was much more negative than in mouse aortic SMCs (mASMCs) or in HEK293 cells expressing BKα alone and β-subunit (BKβ1). Mallotoxin, a selective activator of BK channel that lacks BKγ1, dose-dependently activated BK currents in mASMCs but not in mBSMCs. The abundant expression of BKγ1 in mBSMCs extensively facilitates BK channel activity to keep the resting membrane potential at negative values and prevents contraction under physiological conditions.

Sarcoplasmic reticulum and calcium signaling in muscle cells: Homeostasis and disease

The sarco/endoplasmic reticulum is an extensive, dynamic and heterogeneous membranous network that fulfills multiple homeostatic functions. Among them, it compartmentalizes, stores and releases calcium within the intracellular space. In the case of muscle cells, calcium released from the sarco/endoplasmic reticulum in the vicinity of the contractile machinery induces cell contraction. Furthermore, sarco/endoplasmic reticulum-derived calcium also regulates gene transcription in the nucleus, energy metabolism in mitochondria and cytosolic signaling pathways. These diverse and overlapping processes require a highly complex fine-tuning that the sarco/endoplasmic reticulum provides by means of its numerous tubules and cisternae, specialized domains and contacts with other organelles. The sarco/endoplasmic reticulum also possesses a rich calcium-handling machinery, functionally coupled to both contraction-inducing stimuli and the contractile apparatus. Such is the importance of the sarco/endoplasmic reticulum for muscle cell physiology, that alterations in its structure, function or its calcium-handling machinery are intimately associated with the development of cardiometabolic diseases. Cardiac hypertrophy, insulin resistance and arterial hypertension are age-related pathologies with a common mechanism at the muscle cell level: the accumulation of damaged proteins at the sarco/endoplasmic reticulum induces a stress response condition termed endoplasmic reticulum stress, which impairs proper organelle function, ultimately leading to pathogenesis.

Flavored e-liquids increase cytoplasmic Ca2+ levels in airway epithelia

E-cigarettes are noncombustible, electronic nicotine-delivery devices that aerosolize an e-liquid, i.e., nicotine, in a propylene glycol-vegetable glycerin vehicle that also contains flavors. While the effects of nicotine are relatively well understood, more information regarding the potential biological effects of the other e-liquid constituents is needed. This is a serious concern, because e-liquids are available in >7,000 distinct flavors. We previously demonstrated that many e-liquids affect cell growth/viability through an unknown mechanism. Since Ca²⁺ is a ubiquitous second messenger that regulates cell growth, we characterized the effects of e-liquids on cellular Ca²⁺ homeostasis. To better understand the extent of this effect, we screened e-liquids for their ability to alter cytosolic Ca²⁺ levels and found that 42 of 100 flavored e-liquids elicited a cellular Ca²⁺ response. Banana Pudding (BP) e-liquid, a representative e-liquid from this group, caused phospholipase C activation, endoplasmic reticulum (ER) Ca²⁺ release, store-operated Ca²⁺ entry (SOCE), and protein kinase C (PKCα) phosphorylation. However, longer exposures to BP e-liquid depleted ER Ca²⁺ stores and inhibited SOCE, suggesting that this e-liquid may alter Ca²⁺ homeostasis by short- and long-term mechanisms. Since dysregulation of Ca²⁺ signaling can cause chronic inflammation, ER stress, and abnormal cell growth, flavored e-cigarette products that can elicit cell Ca²⁺ responses should be further screened for potential toxicity.

NS8593 inhibits Ca2+ permeant channels reversing mouse airway smooth muscle contraction

AIMS

This study focused on investigating whether NS8593 reverses airway smooth muscle (ASM) contraction and the underlying mechanism.

MAIN METHODS

ASM contraction in mouse tracheal rings and lung slices was measured. Currents mediated by voltage dependent Ca²⁺ channels (VDCCs) and ACH-activated channels were measured using the whole-cell patch-clamp technique in single tracheal smooth muscle cells (TSMCs). Intracellular Ca²⁺ level and cell length were measured using an LSM 700 laser confocal microscope and a Zen 2010 software. Mouse respiratory system resistance (Rrs) was assessed using a FlexiVent FX system.

KEY FINDINGS

High K⁺ (80 mM K⁺) and ACH induced ASM contraction in mouse tracheal rings and lung slices, which was partially relaxed by nifedipine (blocker of L-type VDCCs, LVDCCs), YM-58483 (blocker of store-operated Ca²⁺ entry (SOCE), transient receptor potential C3 (TRPC3) and TRPC5 channels), respectively. However, the contraction was completely reversed by NS8593, whereas, slightly relaxed by formoterol. ACH activated inward currents, which displayed linear and reversed around 0 mV, indicating the currents were mediated by non-selective cation channels (NSCCs). Moreover, these currents were blocked by YM-58483. In addition, such currents were abolished by NS8593, implicating that NS8593 inhibits the same channels. Besides, NS8593 inhibited increases of intracellular Ca²⁺ and the associated cell shortening. Finally, NS8593 inhibited ACH-induced increases of mouse respirator system resistance (Rrs).

SIGNIFICANCE

Our results indicate that NS8593 inhibits LVDCCs and NSCCs, resulting in decreases of intracellular Ca²⁺ and then leading to ASM relaxation. These data suggest that NS8593 might be a new bronchodilator.

Regulation of Airway Smooth Muscle Contraction in Health and Disease

Airway smooth muscle (ASM) extends from the trachea throughout the bronchial tree to the terminal bronchioles. In utero, spontaneous phasic contraction of fetal ASM is critical for normal lung development by regulating intraluminal fluid movement, ASM differentiation, and release of key growth factors. In contrast, phasic contraction appears to be absent in the adult lung, and regulation of tonic contraction and airflow is under neuronal and humoral control. Accumulating evidence suggests that changes in ASM responsiveness contribute to the pathophysiology of lung diseases with lifelong health impacts.Functional assessments of fetal and adult ASM and airways have defined pharmacological responses and signaling pathways that drive airway contraction and relaxation. Studies using precision-cut lung slices, in which contraction of intrapulmonary airways and ASM calcium signaling can be assessed simultaneously in situ, have been particularly informative. These combined approaches have defined the relative importance of calcium entry into ASM and calcium release from intracellular stores as drivers of spontaneous phasic contraction in utero and excitation-contraction coupling.Increased contractility of ASM in asthma contributes to airway hyperresponsiveness. Studies using animal models and human ASM and airways have characterized inflammatory and other mechanisms underlying increased reactivity to contractile agonists and reduced bronchodilator efficacy of β₂-adrenoceptor agonists in severe diseases. Novel bronchodilators and the application of bronchial thermoplasty to ablate increased ASM within asthmatic airways have the potential to overcome limitations of current therapies. These approaches may directly limit excessive airway contraction to improve outcomes for difficult-to-control asthma and other chronic lung diseases.

Imaging elemental events of store-operated Ca2+ entry in invading cancer cells with plasmalemmal targeted sensors

STIM1- and Orai1-mediated store-operated Ca²⁺ entry (SOCE) constitutes the major Ca²⁺ influx in almost all electrically non-excitable cells. However, little is known about the spatiotemporal organization at the elementary level. Here, we developed Orai1-tethered or palmitoylated biosensor GCaMP6f to report subplasmalemmal Ca²⁺ signals. We visualized spontaneous discrete and long-lasting transients ('Ca²⁺ glows') arising from STIM1-Orai1 in invading melanoma cells. Ca²⁺ glows occurred preferentially in single invadopodia and at sites near the cell periphery under resting conditions. Re-addition of external Ca²⁺ after store depletion elicited spatially synchronous Ca²⁺ glows, followed by high-rate discharge of asynchronous local events. Knockout of STIM1 or expression of the dominant-negative Orai1-E106A mutant markedly decreased Ca²⁺ glow frequency, diminished global SOCE and attenuated invadopodial formation. Functionally, invadopodial Ca²⁺ glows provided high Ca²⁺ microdomains to locally activate Ca²⁺/calmodulin-dependent Pyk2 (also known as PTK2B), which initiates the SOCE-Pyk2-Src signaling cascade required for invasion. Overall, the discovery of elemental Ca²⁺ signals of SOCE not only unveils a previously unappreciated gating mode of STIM1-Orai1 channels in situ, but also underscores a critical role of the spatiotemporal dynamics of SOCE in orchestrating complex cell behaviors such as invasion. This article has an associated First Person interview with the first author of the paper.

ORAI channels in cellular remodeling of cardiorespiratory disease

Cardiorespiratory disease, which includes systemic arterial hypertension, restenosis, atherosclerosis, pulmonary arterial hypertension, asthma, and chronic obstructive pulmonary disease (COPD) are highly prevalent and devastating diseases with limited therapeutic modalities. A common pathophysiological theme to these diseases is cellular remodeling, which is contributed by changes in expression and activation of ion channels critical for either excitability or growth. Calcium (Ca²⁺) signaling and specifically ORAI Ca²⁺ channels have emerged as significant regulators of smooth muscle, endothelial, epithelial, platelet, and immune cell remodeling. This review details the dysregulation of ORAI in cardiorespiratory diseases, and how this dysregulation of ORAI contributes to cellular remodeling.

Mitochondrial regulation of airway smooth muscle functions in health and pulmonary diseases

Mitochondria are important for airway smooth muscle physiology due to their diverse yet interconnected roles in calcium handling, redox regulation, and cellular bioenergetics. Increasing evidence indicates that mitochondria dysfunction is intimately associated with airway diseases such as asthma, IPF and COPD. In these pathological conditions, increased mitochondrial ROS, altered bioenergetics profiles, and calcium mishandling contribute collectively to changes in cellular signaling, gene expression, and ultimately changes in airway smooth muscle contractile/proliferative properties. Therefore, understanding the basic features of airway smooth muscle mitochondria and their functional contribution to airway biology and pathology are key to developing novel therapeutics for airway diseases. This review summarizes the recent findings of airway smooth muscle mitochondria focusing on calcium homeostasis and redox regulation, two key determinants of physiological and pathological functions of airway smooth muscle.

Protease-activated receptor 2 activates CRAC-mediated Ca2+ influx to cause prostate smooth muscle contraction

Protease activated receptor 2 (PAR2) is a G-protein coupled receptor that contributes to prostate fibrosis and lower urinary tract symptoms (LUTS). In addition to fibrosis, aberrant smooth muscle tone in the prostate has been hypothesized to play a role. We therefore examined PAR2 expression in primary human prostate smooth muscle cells (PSMC) and studied the downstream signaling effects of PAR2 activation. Signaling pathways involved in the process were assessed using the PAR2 activating peptide SLIGKV-NH2. We show that PAR2 is expressed in PSMC and that PAR2 activation mediates a biphasic elevation in intracellular Ca²⁺ and phosphorylation of myosin light chain 20 (MLC20), causing cellular contraction as assessed in a gel contraction assay. Intracellular Ca²⁺ flux was inhibited by a phosphoinositide hydrolysis inhibitor, U73122, showing a requirement for phospholipase C β (PLCβ) activation. PSMC expressed mRNA for L-type voltage dependent Ca²⁺ channels (VDCC) as well as Ca²⁺ release activated channels (CRAC), a hitherto unreported finding. Secondary intracellular Ca²⁺ oscillations were abrogated only by BTP2, the CRAC channel inhibitor, but not by nifedipine, an inhibitor of VDCC. These data suggest that, PAR2 activation and subsequent Ca²⁺ entry through CRAC channels are important mechanisms in prostate smooth muscle contraction.

A novel GABAA receptor ligand MIDD0301 with limited blood-brain barrier penetration relaxes airway smooth muscle ex vivo and in vivo

Airway smooth muscle (ASM) cells express GABA A receptors (GABA_ARs), and previous reports have demonstrated that GABA_AR activators relax ASM. However, given the activity of GABA_ARs in central nervous system inhibitory neurotransmission, concern exists that these activators may lead to undesirable sedation. MIDD0301 is a novel imidazobenzodiazepine and positive allosteric modulator of the GABA_AR with limited brain distribution, thus eliminating the potential for sedation. Here, we demonstrate that MIDD0301 relaxes histamine-contracted guinea pig ( P < 0.05, n = 6-9) and human ( P < 0.05, n = 6-10) tracheal smooth muscle ex vivo in organ bath experiments, dilates mouse peripheral airways ex vivo in precision-cut lung-slice experiments ( P < 0.001, n = 16 airways from three mice), and alleviates bronchoconstriction in vivo in mice, as assessed by the forced-oscillation technique ( P < 0.05, n = 6 mice). Only trace concentrations of the compound were detected in the brains of mice after inhalation of nebulized 5 mM MIDD0301. Given its favorable pharmacokinetic properties and demonstrated ability to relax ASM in a number of clinically relevant experimental paradigms, MIDD0301 is a promising drug candidate for bronchoconstrictive diseases, such as asthma.

Functional mechanism of tracheal relaxation, antiasthmatic, and toxicological studies of 6-hydroxyflavone

Previously, we described tracheal rat rings relaxation by several flavonoids, being 6-hydroxyflavone (6-HOF) the most active derivative of the series. Thus, its mechanism of action was determined in an ex vivo tracheal rat ring bioassay. The anti-asthmatic effect was assayed in in vivo OVAlbumin (OVA)-sensitized guinea pigs. Finally, the toxicological profile of 6-HOF was studied based on Organization of Economic Cooperation and Development guidelines with modifications. 6-HOF-induced relaxation appears to be related with receptor-operated calcium channel and voltage-operated calcium channel blockade as the main mechanism of action, and also through the production of relaxant second messengers NO and cGMP. Molecular docking supports that 6-HOF acts as calcium channel blocker and by activation of nitric oxide synthase. In addition, the in vivo anti-asthmatic experiments demonstrate the dose-dependent significant anti-allergic effect of 6-HOF induced by OVA, with best activity at 50 /kg. Finally, toxicological studies determined a LD50 > 2,000 mg/kg and, after 28 day of treatment with 6-HOF (50 mg/kg) by intragastric route, mice did not exhibit evidence of any significant toxicity. In conclusion, experiments showed that 6-HOF exerts significant relaxant activity through calcium channel blockade, and possibly, by NO/cGMP-system stimulation on rat trachea, which interferes with the contraction mechanism of smooth muscle cells in the airways. In addition, the flavonoid shows potential anti-asthmatic properties in an anti-allergic pathway. Furthermore, because the pharmacological and safety evidence, we propose this flavonoid as lead for the development of a novel therapeutic agent for the treatment of asthma and related respiratory diseases.

TGF-β1-Induced Airway Smooth Muscle Cell Proliferation Involves TRPM7-Dependent Calcium Influx via TGFβR/SMAD3

BACKGROUND

TRPM7 in mast cells plays a key role in asthma. However, the effect of TRPM7 on TGF-β1-induced airway smooth muscle cell (ASMC) proliferation remains unclear. Therefore, we designed this study to explore whether TRPM7 is involved in TGF-β1-induced ASMC proliferation.

METHODS

An asthmatic mouse model was established, and the expressions of TGF-β1 and TRPM7 in mice lungs were detected using enzyme-linked immunosorbent assay (ELISA) and western blotting. In addition, murine ASMCs were cultured and stimulated with TGF-β1. Possible TGF-β1 and TRPM7 interactions were examined using RT-PCR and western blotting analyses with ASMCs. The effect of TRPM7 knockdown on ASMC calcium influx was assessed by the fluorescent indicator indo-1. MTT and flow cytometry were applied to evaluate the effects of TRPM7 knockdown on ASMC proliferation and apoptosis.

RESULTS

TGF-β1 elevated the expression of TRPM7 via TGFβR/SMAD3. Knocking down TRPM7 decreased the intracellular Ca²⁺ concentration and cellular proliferation of ASMCs, although apoptosis remained unaffected.

CONCLUSIONS

Our initial findings suggest that TRPM7 inhibition may prevent asthma-induced airway remodeling.

Cigarette smoke up-regulates PDE3 and PDE4 to decrease cAMP in airway cells

BACKGROUND AND PURPOSE

cAMP is a central second messenger that broadly regulates cell function and can underpin pathophysiology. In chronic obstructive pulmonary disease, a lung disease primarily provoked by cigarette smoke (CS), the activation of cAMP-dependent pathways, via inhibition of hydrolyzing PDEs, is a major therapeutic strategy. Mechanisms that disrupt cAMP signalling in airway cells, in particular regulation of endogenous PDEs, are poorly understood.

EXPERIMENTAL APPROACH

We used a novel Förster resonance energy transfer (FRET) based cAMP biosensor in mice in vivo, ex vivo precision cut lung slices (PCLS) and in human cell models, in vitro, to track the effects of CS exposure.

KEY RESULTS

Under fenoterol stimulation, FRET responses to cilostamide were significantly increased in in vivo, ex vivo PCLS exposed to CS and in human airway smooth muscle cells exposed to CS extract. FRET signals to rolipram were only increased in the in vivo CS model. Under basal conditions, FRET responses to cilostamide and rolipram were significantly increased in in vivo, ex vivo PCLS exposed to CS. Elevated FRET signals to rolipram correlated with a protein up-regulation of PDE4 subtypes. In ex vivo PCLS exposed to CS extract, rolipram reversed down-regulation of ciliary beating frequency, whereas only cilostamide significantly increased airway relaxation of methacholine pre-contracted airways.

CONCLUSION AND IMPLICATIONS

Exposure to CS, in vitro or in vivo, up-regulated expression and activity of both PDE3 and PDE4, which affected real-time cAMP dynamics. These mechanisms determine the availability of cAMP and can contribute to CS-induced pulmonary pathophysiology.

Secondary Metabolites in Allergic Plant Pollen Samples Modulate Afferent Neurons and Murine Tracheal Rings

Plant pollens are strong airborne elicitors of asthma. Their proteinaceous allergens have been studied intensively, but little is known about a possible contribution of pollen secondary metabolites to the nonallergic exacerbation of asthma. Pollen samples originating from 30 plant species were analyzed by HPLC coupled to PDA, ESIMS, and ELSD detectors and off-line NMR spectroscopy. Polyamine conjugates, flavonoids, and sesquiterpene lactones were identified. Polyamine conjugates were characteristic of all Asteraceae species. The presence of sesquiterpene lactones in Asteraceae pollen varied between species and pollen lots. All plant pollen, including those from non-Asteraceae species, contained to some extent electrophiles as determined by their reaction with N-acetyl-l-cysteine. Selected pollen extracts and pure compounds were tested in murine afferent neurons and in murine tracheal preparations. Tetrahydrofuran extracts of Ambrosia artemisiifolia and Ambrosia psilostachya pollen and a mixture of sesquiterpene lactones coronopilin/parthenin increased the intracellular Ca²⁺ concentration in 15%, 32%, and 37% of cinnamaldehyde-responsive neurons, respectively. In organ bath experiments, only the sesquiterpene lactones tested induced a weak dilatation of naïve tracheas and strongly lowered the maximal methacholine-induced tracheal constriction. A tetrahydrofuran extract of A. psilostachya and coronopilin/parthenin led to a time-dependent relaxation of the methacholine-preconstricted trachea. These results provide the first evidence for a potential role of pollen secondary metabolites in the modulation of the tracheal tone.

Airway smooth muscle dysfunction in Pompe (Gaa-/- ) mice

Pompe disease is an autosomal recessive disorder caused by a deficiency of acid α-glucosidase (GAA), an enzyme responsible for hydrolyzing lysosomal glycogen. Deficiency of GAA leads to systemic glycogen accumulation in the lysosomes of skeletal muscle, motor neurons, and smooth muscle. Skeletal muscle and motor neuron pathology are known to contribute to respiratory insufficiency in Pompe disease, but the role of airway pathology has not been evaluated. Here we propose that GAA enzyme deficiency disrupts the function of the trachea and bronchi and this lower airway pathology contributes to respiratory insufficiency in Pompe disease. Using an established mouse model of Pompe disease, the Gaa^-/- mouse, we compared histology, pulmonary mechanics, airway smooth muscle (ASM) function, and calcium signaling between Gaa^-/- and age-matched wild-type (WT) mice. Lysosomal glycogen accumulation was observed in the smooth muscle of both the bronchi and the trachea in Gaa^-/- but not WT mice. Furthermore, Gaa^-/- mice had hyporesponsive airway resistance and bronchial ring contraction to the bronchoconstrictive agents methacholine (MCh) and potassium chloride (KCl) and to a bronchodilator (albuterol). Finally, calcium signaling during bronchiolar smooth muscle contraction was impaired in Gaa^-/- mice indicating impaired extracellular calcium influx. We conclude that GAA enzyme deficiency leads to glycogen accumulation in the trachea and bronchi and impairs the ability of lower ASM to regulate calcium and respond appropriately to bronchodilator or constrictors. Accordingly, ASM dysfunction may contribute to respiratory impairments in Pompe disease.

Role of transient receptor potential vanilloid 1 in the modulation of airway smooth muscle tone and calcium handling

Asthma is a common disorder characterized, in part, by airway smooth muscle (ASM) hyperresponsiveness. Transient receptor potential vanilloid 1 (TRPV1) is a nonselective cation channel expressed on airway nerve fibers that modulates afferent signals, resulting in cough, and potentially bronchoconstriction. In the present study, the TRPV1 transcript was detected by RT-PCR in primary cultured human ASM cells, and the TRPV1 protein was detected in ASM of human trachea by immunohistochemistry. Proximity ligation assays suggest that TRPV1 is expressed in the sarcoplasmic reticulum membrane of human ASM cells in close association with sarco/endoplasmic reticulum Ca²⁺-ATPase-2. In guinea pig tracheal ring organ bath experiments, the TRPV1 agonist capsaicin led to ASM contraction, but this contraction was significantly attenuated by the sodium channel inhibitor bupivacaine (n = 4, P < 0.05) and the neurokinin-2 receptor antagonist GR-159897 (n = 4, P < 0.05), suggesting that this contraction is neutrally mediated. However, pretreatment of guinea pig and human ASM in organ bath experiments with the TRPV1 antagonist capsazepine inhibited the maintenance phase of an acetylcholine-induced contraction (n = 4, P < 0.01 for both species). Similarly, capsazepine inhibited methacholine-induced contraction of peripheral airways in mouse precision-cut lung slice (PCLS) experiments (n = 4-5, P < 0.05). Although capsazepine did not inhibit store-operated calcium entry in mouse ASM cells in PCLS (n = 4-7, P = nonsignificant), it did inhibit calcium oscillations (n = 3, P < 0.001). These studies suggest that TRPV1 is expressed on ASM, including the SR, but that ASM TRPV1 activation does not play a significant role in initiation of ASM contraction. However, capsazepine does inhibit maintenance of contraction, likely by inhibiting calcium oscillations.

The relative contributions of store-operated and voltage-gated Ca2+ channels to the control of Ca2+ oscillations in airway smooth muscle

KEY POINTS

Agonist-dependent oscillations in the concentration of free cytosolic calcium are a vital mechanism for the control of airway smooth muscle contraction and thus are a critical factor in airway hyper-responsiveness. Using a mathematical model, closely tied to experimental work, we show that the oscillations in membrane potential accompanying the calcium oscillations have no significant effect on the properties of the calcium oscillations. In addition, the model shows that calcium entry through store-operated calcium channels is critical for calcium oscillations, but calcium entry through voltage-gated channels has much less effect. The model predicts that voltage-gated channels are less important than store-operated channels in the control of airway smooth muscle tone.

ABSTRACT

Airway smooth muscle contraction is typically the key mechanism underlying airway hyper-responsiveness, and the strength of muscle contraction is determined by the frequency of oscillations of intracellular calcium (Ca²⁺ ) concentration. In airway smooth muscle cells, these Ca²⁺ oscillations are caused by cyclic Ca²⁺ release from the sarcoplasmic reticulum, although Ca²⁺ influx via plasma membrane channels is also necessary to sustain the oscillations over longer times. To assess the relative contributions of store-operated and voltage-gated Ca²⁺ channels to this Ca²⁺ influx, we generated a comprehensive mathematical model, based on experimental Ca²⁺ measurements in mouse precision-cut lung slices, to simulate Ca²⁺ oscillations and changes in membrane potential. Agonist-induced Ca²⁺ oscillations are accompanied by oscillations in membrane potential, although the membrane potential oscillations are too small to generate large Ca²⁺ currents through voltage-gated Ca²⁺ channels, and thus have little effect on the Ca²⁺ oscillations. Ca²⁺ entry through voltage-gated channels only becomes important when the cell is depolarized (e.g. by a high external K⁺ concentration). As a result, agonist-induced Ca²⁺ oscillations are critically dependent on Ca²⁺ entry through store-operated channels but do not depend strongly on Ca²⁺ entry though voltage-gated channels.