Acid-Sensing Ion Channel 1a Contributes to Airway Hyperreactivity in Mice

Progressive tauopathy disrupts breathing stability and chemoreflexes during presumptive sleep in mice

Rationale: Although sleep apnea occurs in over 50% of individuals with Alzheimer's Disease (AD) or related tauopathies, little is known concerning the potential role of tauopathy in the pathogenesis of sleep apnea. Here, we tested the hypotheses that, during presumptive sleep, a murine model of tauopathy (rTg4510) exhibits: 1) increased breathing instability; 2) impaired chemoreflex function; and 3) exacerbation of these effects with tauopathy progression. Methods: rTg4510 mice initially develop robust tauopathy in the hippocampus and cortex, and eventually progresses to the brainstem. Type I and II post-sigh apnea, Type III (spontaneous) apnea, sigh, and hypopnea incidence were measured in young adult (5-6 months; n = 10-14/group) and aged (13-15 months; n = 22-24/group) non-transgenic (nTg), monogenic control tetracycline transactivator, and bigenic rTg4510 mice using whole-body plethysmography during presumptive sleep (i.e., eyes closed, curled/laying posture, stable breathing for >200 breaths) while breathing room air (21% O2). Peripheral and central chemoreceptor sensitivity were assessed with transient exposures (5 min) to hyperoxia (100% O2) or hypercapnia (3% and 5% CO2 in 21% O2), respectively. Results: We report significant increases in Type I, II, and III apneas (all p < 0.001), sighs (p = 0.002) and hypopneas (p < 0.001) in aged rTg4510 mice, but only Type III apneas in young adult rTg4510 mice (p < 0.001) versus age-matched nTg controls. Aged rTg4510 mice exhibited profound chemoreflex impairment versus age matched nTg and tTA mice. In rTg4510 mice, breathing frequency, tidal volume and minute ventilation were not affected by hyperoxic or hypercapnic challenges, in striking contrast to controls. Histological examination revealed hyperphosphorylated tau in brainstem regions involved in the control of breathing (e.g., pons, medullary respiratory column, retrotrapezoid nucleus) in aged rTg4510 mice. Neither breathing instability nor hyperphosphorylated tau in brainstem tissues were observed in young adult rTg4510 mice. Conclusion: Older rTg4510 mice exhibit profound impairment in the neural control of breathing, with greater breathing instability and near absence of oxygen and carbon-dioxide chemoreflexes. Breathing impairments paralleled tauopathy progression into brainstem regions that control breathing. These findings are consistent with the idea that tauopathy per se undermines chemoreflexes and promotes breathing instability during sleep.

Hyperresponsiveness to Extracellular Acidification-Mediated Contraction in Isolated Bronchial Smooth Muscles of Murine Experimental Asthma

PURPOSE

Extracellular acidification is a major component of tissue inflammation, including airway inflammation. The extracellular proton-sensing mechanisms are inherent in various cells including airway structural cells, although their physiological and pathophysiological roles in bronchial smooth muscles (BSMs) are not fully understood. In the present study, to explore the functional role of extracellular acidification on the BSM contraction, the isolated mouse BSMs were exposed to acidic pH under contractile stimulation.

METHODS AND RESULTS

The RT-PCR analyses revealed that the proton-sensing G protein-coupled receptors were expressed both in mouse BSMs and cultured human BSM cells. In the mouse BSMs, change in the extracellular pH from 8.0 to 6.8 caused an augmentation of contraction induced by acetylcholine. Interestingly, the acidic pH-induced BSM hyper-contraction was further augmented in the mice that were sensitized and repeatedly challenged with ovalbumin antigen. In this animal model of asthma, upregulations of G protein-coupled receptor 68 (GPR68) and GPR65, that were believed to be coupled with Gq and Gs proteins respectively, were observed, indicating that the acidic pH could cause hyper-contraction probably via an activation of GPR68. However, psychosine, a putative antagonist for GPR68, failed to block the acidic pH-induced responses.

CONCLUSION

These findings suggest that extracellular acidification contributes to the airway hyperresponsiveness, a characteristic feature of bronchial asthma. Further studies are required to identify the receptor(s) responsible for sensing extracellular protons in BSM cells.

The Role of ASIC1a in Inflammatory Immune Diseases: A Potential Therapeutic Target

It is acknowledged that chronic inflammation is associated with a rise in extracellular proton concentrations. The acid-sensing ion channel 1a (ASIC1a) belongs to the extracellular H⁺-activated cation channel family. Recently, many studies have been conducted on ASIC1a and inflammatory immune diseases. Here, in this review, we will focus on the role of ASIC1a in several inflammatory immune diseases so as to provide new perspectives for clinical treatment.

Advancing Lung Immunology Research: An Official American Thoracic Society Workshop Report

The mammalian airways and lungs are exposed to a myriad of inhaled particulate matter, allergens, and pathogens. The immune system plays an essential role in protecting the host from respiratory pathogens, but a dysregulated immune response during respiratory infection can impair pathogen clearance and lead to immunopathology. Furthermore, inappropriate immunity to inhaled antigens can lead to pulmonary diseases. A complex network of epithelial, neural, stromal, and immune cells has evolved to sense and respond to inhaled antigens, including the decision to promote tolerance versus a rapid, robust, and targeted immune response. Although there has been great progress in understanding the mechanisms governing immunity to respiratory pathogens and aeroantigens, we are only beginning to develop an integrated understanding of the cellular networks governing tissue immunity within the lungs and how it changes after inflammation and over the human life course. An integrated model of airway and lung immunity will be necessary to improve mucosal vaccine design as well as prevent and treat acute and chronic inflammatory pulmonary diseases. Given the importance of immunology in pulmonary research, the American Thoracic Society convened a working group to highlight central areas of investigation to advance the science of lung immunology and improve human health.

Influence of SARS-CoV-2 on airway mucus production: A review and proposed model

Coronavirus disease 2019 (COVID-19) is a worldwide pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that has affected millions of lives. Individuals who survive severe COVID-19 can experience sustained respiratory symptoms that persist for months after initial infection. In other airway diseases, abnormal airway mucus contributes to sustained airway symptoms. However, the impact of SARS-CoV-2 on airway mucus has received limited attention. In the current review, we assess literature describing the impact of SARS-CoV-2 on airway pathophysiology with specific emphasis on mucus production. Accumulating evidence suggests that the 2 major secreted airway mucin glycoproteins, MUC5AC and MUC5B, are abnormal in some patients with COVID-19. Aberrations in MUC5AC or MUC5B in response to SARS-CoV-2 infection are likely due to inflammation, though the responsible mechanisms have yet to be determined. Thus, we also provide a proposed model highlighting mechanisms that can contribute to acute and sustained mucus abnormalities in SARS-CoV-2, with an emphasis on inflammatory cells and mediators, including mast cells and histamine. Last, we bring to light the challenges of studying abnormal mucus production in SARS-CoV-2 infections and discuss the strengths and limitations of model systems commonly used to study COVID-19. The evidence to date suggests that ferrets, nonhuman primates, and cats may have advantages over other models to investigate mucus in COVID-19.

Analysis of Airway Vagal Neurons

Internal organs, including the airway, are innervated by neurons of the autonomic and sensory nervous systems. The airway-innervating sensory neurons primarily originate from the vagus nerve, whose cell bodies are found, in rodents, in the jugular and nodose ganglia complex (JNC). About half of these sensory neurons expressed the heat-sensing ion channel TRPV1 and evolved to limit tissue damage by detecting chemical, mechanical, or thermal threats and to initiate protective airway reflexes such as coughing and bronchoconstriction. They also help monitor the host homeostasis by sensing nutrients, pressure, and O₂ levels and help mount airway defenses by controlling immune and goblet cell activity. To better appreciate the scope of the physiological role and pathological contributions of these neurons, we will review gain and loss-of-function approaches geared at controlling the activity of these neurons. We will also present a method to study transcriptomic changes in airway-innervating neurons and a co-culture approach designed to understand how nociceptors modulate immune responses.

Nociceptor neurons promote IgE class switch in B cells

Nociceptors, the high-threshold primary sensory neurons that trigger pain, interact with immune cells in the periphery to modulate innate immune responses. Whether they also participate in adaptive and humoral immunity is, however, not known. In this study, we probed if nociceptors have a role in distinct airway and skin models of allergic inflammation. In both models, the genetic ablation and pharmacological silencing of nociceptors substantially reduced inflammatory cell infiltration to the affected tissue. Moreover, we also found a profound and specific deficit in IgE production in these models of allergic inflammation. Mechanistically, we discovered that the nociceptor-released neuropeptide Substance P help triggered the formation of antibody secreting cells and their release of IgE. Our findings suggest that nociceptors, in addition to their contributions to innate immunity, play a key role in modulating the adaptive immune response, particularly B cell antibody class switching to IgE.

Modulation of Vagal Sensory Neurons via High Mobility Group Box-1 and Receptor for Advanced Glycation End Products: Implications for Respiratory Viral Infections

Vagal sensory neurons contribute to the symptoms and pathogenesis of inflammatory pulmonary diseases through processes that involve changes to their morphological and functional characteristics. The alarmin high mobility group box-1 (HMGB1) is an early mediator of pulmonary inflammation and can have actions on neurons in a range of inflammatory settings. We hypothesized that HMGB1 can regulate the growth and function of vagal sensory neurons and we set out to investigate this and the mechanisms involved. Culturing primary vagal sensory neurons from wildtype mice in the presence of HMGB1 significantly increased neurite outgrowth, while acute application of HMGB1 to isolated neurons under patch clamp electrophysiological investigation produced inward currents and enhanced action potential firing. Transcriptional analyses revealed the expression of the cognate HMGB1 receptors, Receptor for Advanced Glycation End products (RAGE) and Toll-like Receptor 4 (TLR4), in subsets of vagal sensory neurons. HMGB1-evoked growth and electrophysiological responses were significantly reduced in primary vagal sensory neurons harvested from RAGE deficient mice and completely absent in neurons from RAGE/TLR4 double deficient mice. Immunohistochemical analysis of vagal sensory neurons collected from mice after intranasal infection with murine pneumovirus or influenza A virus (IAV), or after intratracheal administration with the viral mimetic PolyI:C, revealed a significant increase in nuclear-to-cytoplasm translocation of HMGB1 compared to mock-inoculated mice. Neurons cultured from virus infected wildtype mice displayed a significant increase in neurite outgrowth, which was not observed for neurons from virus infected RAGE or RAGE/TLR4 deficient mice. These data suggest that HMGB1 can enhance vagal sensory neuron growth and excitability, acting primarily via sensory neuron RAGE. Activation of the HMGB1-RAGE axis in vagal sensory neurons could be an important mechanism leading to vagal hyperinnervation and hypersensitivity in chronic pulmonary disease.

Inhibition of TRPA1 reduces airway inflammation and hyperresponsiveness in mice with allergic rhinitis

This study was conducted to investigate whether a transient receptor potential ankyrin 1 (TRPA1) antagonist (HC-030031) can reduce airway inflammation and hyperresponsiveness in a murine allergic rhinitis (AR) model. BALB/c mice were sensitized and challenged by ovalbumin (OVA) to induce AR. HC-030031 or vehicle was administrated to mice via intraperitoneal injection prior to OVA challenges. Nose-scratching events, histopathologic alterations of the airways, and bronchial hyperresponsiveness (BHR) were assessed. Differential cells and proinflammatory cytokines in the nasal lavage (NAL) and bronchoalveolar lavage (BAL) fluid were measured. Expressions of TRPA1 in nasal mucosa were examined by immunohistochemistry. TRPA1-expressing vagal neurons were labeled by immunofluorescent staining. HC-030031-treated AR mice had markedly reduced type-2 inflammation in nasal mucosa and ameliorated-nose-scratching events than AR mice received vehicle. HC-030031 treatment also dramatically reduced leucocyte numbers and IL-8 level in the BAL fluid, inhibited lower airway remodeling and fibrosis, and nearly abolished BHR. HC-0300031 treatment significantly inhibited the upregulated number of TRPA1 expressing nasal epithelial cells and TRPA1 expressing sensory neurons, leading to downregulation of SP in both upper and lower airways. Targeting TRPA1 may represent a promising strategy for treating AR and AR-related asthma.

Overexpression of Substance P in pig airways increases MUC5AC through an NF-kβ pathway

Substance P (SP) is a tachykinin that regulates airway mucous secretion in both health and disease. Our study aimed to determine whether overexpression of SP without pre‐existing inflammation was sufficient to induce changes in mucin secretion and transport in small airways. Utilizing porcine precision‐cut lung slices, we measured the impact of AAV‐mediated overexpression of SP on airway physiology ex vivo. Immunofluorescence signal intensity for MUC5AC was significantly increased in SP‐overexpressed precision‐cut lung slices compared to GFP controls. No difference in MUC5B signal intensity between treatments was detected. SP‐overexpressed precision‐cut lung slices also exhibited decreased IL10 mRNA, an important inhibitor of mucous cell metaplasia. Overt deficits in mucociliary transport were not noted, though a trend for decreased mean transport speed was detected in methacholine‐challenged airways overexpressing SP compared to GFP controls. Pharmacologic inhibition of the NF‐kβ pathway abrogated the effects of overexpression of SP on both MUC5AC and IL10. Collectively, these data suggest that overexpression of SP in the absence of existing inflammation increases MUC5AC via activation of the NF‐kβ pathway. Thus, these data further highlight SP as a key driver of abnormal mucous secretion and underscore NF‐kβ signaling as a pathway of potential therapeutic intervention.

Airway cholinergic history modifies mucus secretion properties to subsequent cholinergic challenge in diminished chloride and bicarbonate conditions

NEW FINDINGS

What is the central question of this study? What is the impact of airway cholinergic history on the properties of airway mucus secretion in a cystic fibrosis-like environment? What is the main finding and its importance? Prior cholinergic challenge slightly modifies the characteristics of mucus secretion in response to a second cholinergic challenge in a diminished bicarbonate and chloride transport environment. Such modifications might lead to retention of mucus on the airway surface, thereby potentiating exacerbations of airway disease.

ABSTRACT

Viral infections precipitate exacerbations in many airway diseases, including asthma and cystic fibrosis. Although viral infections increase cholinergic transmission, few studies have examined how cholinergic history modifies subsequent cholinergic responses in the airway. In our previous work, we found that airway resistance in response to a second cholinergic challenge was increased in young pigs with a history of airway cholinergic stimulation. Given that mucus secretion is regulated by the cholinergic nervous system and that abnormal airway mucus contributes to exacerbations of airway disease, we hypothesized that prior cholinergic challenge would also modify subsequent mucus responses to a secondary cholinergic challenge. Using our established cholinergic challenge-rechallenge model in pigs, we atomized the cholinergic agonist bethanechol or saline control to pig airways. Forty-eight hours later, we removed tracheas and measured mucus secretion properties in response to a second cholinergic stimulation. The second cholinergic stimulation was conducted in conditions of diminished chloride and bicarbonate transport to mimic a cystic fibrosis-like environment. In pigs previously challenged with bethanechol, a second cholinergic stimulation produced a mild increase in sheet-like mucus films; these films were scarcely observed in animals originally challenged with saline control. The subtle increase in mucus films was not associated with changes in mucociliary transport. These data suggest that prior cholinergic history might modify mucus secretion characteristics with subsequent stimulation in certain environmental conditions or disease states. Such modifications and/or more repetitive stimulation might lead to retention of mucus on the airway surface, thereby potentiating exacerbations of airway disease.

Acid exposure disrupts mucus secretion and impairs mucociliary transport in neonatal piglet airways

Tenacious mucus produced by tracheal and bronchial submucosal glands is a defining feature of several airway diseases, including cystic fibrosis (CF). Airway acidification as a driving force of CF airway pathology has been controversial. Here we tested the hypothesis that transient airway acidification produces pathologic mucus and impairs mucociliary transport. We studied pigs challenged with intra-airway acid. Acid had a minimal effect on mucus properties under basal conditions. However, cholinergic stimulation in acid-challenged pigs revealed retention of mucin 5B (MUC5B) in the submucosal glands, decreased concentrations of MUC5B in the lung lavage fluid, and airway obstruction. To more closely mimic a CF-like environment, we also examined mucus secretion and transport following cholinergic stimulation under diminished bicarbonate and chloride transport conditions ex vivo. Under these conditions, airways from acid-challenged pigs displayed extensive mucus films and decreased mucociliary transport. Pretreatment with diminazene aceturate, a small molecule with ability to inhibit acid detection through blockade of the acid-sensing ion channel (ASIC) at the doses provided, did not prevent acid-induced pathologic mucus or transport defects but did mitigate airway obstruction. These findings suggest that transient airway acidification early in life has significant impacts on mucus secretion and transport properties. Furthermore, they highlight diminazene aceturate as an agent that might be beneficial in alleviating airway obstruction.

Profiling of how nociceptor neurons detect danger - new and old foes

The host evolves redundant mechanisms to preserve physiological processing and homeostasis. These functions range from sensing internal and external threats, creating a memory of the insult and generating reflexes, which aim to resolve inflammation. Impairment in such functioning leads to chronic inflammatory diseases. By interacting through a common language of ligands and receptors, the immune and sensory nervous systems work in concert to accomplish such protective functions. Whilst this bidirectional communication helps to protect from danger, it can contribute to disease pathophysiology. Thus, the somatosensory nervous system is anatomically positioned within primary and secondary lymphoid tissues and mucosa to modulate immunity directly. Upstream of this interplay, neurons detect danger, which prompts the release of neuropeptides initiating (i) defensive reflexes (ranging from withdrawal response to coughing) and (ii) chemotaxis, adhesion and local infiltration of immune cells. The resulting outcome of such neuro-immune interplay is still ill-defined, but consensual findings start to emerge and support neuropeptides not only as blockers of T_H 1-mediated immunity but also as drivers of T_H 2 immune responses. However, the modalities detected by nociceptors revealed broader than mechanical pressure and temperature sensing and include signals as various as cytokines and pathogens to immunoglobulins and even microRNAs. Along these lines, we aggregated various dorsal root ganglion sensory neuron expression profiling datasets supporting such wide-ranging sensing capabilities to help identifying new danger detection modalities of these cells. Thus, revealing unexpected aspects of nociceptor neuron biology might prompt the identification of novel drivers of immunity, means to resolve inflammation and strategies to safeguard homeostasis.

Neuropeptides in asthma, chronic obstructive pulmonary disease and cystic fibrosis

The nervous system mediates key airway protective behaviors, including cough, mucus secretion, and airway smooth muscle contraction. Thus, its involvement and potential involvement in several airway diseases has become increasingly recognized. In the current review, we focus on the contribution of select neuropeptides in three distinct airway diseases: asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis. We present data on some well-studied neuropeptides, as well as call attention to a few that have not received much consideration. Because mucus hypersecretion and mucus obstruction are common features of many airway diseases, we place special emphasis on the contribution of neuropeptides to mucus secretion. Finally, we highlight evidence implicating involvement of neuropeptides in mucus phenotypes in asthma, COPD and cystic fibrosis, as well as bring to light knowledge that is still lacking in the field.

The vagal ganglia transcriptome identifies candidate therapeutics for airway hyperreactivity

Mainstay therapeutics are ineffective in some people with asthma, suggesting a need for additional agents. In the current study, we used vagal ganglia transcriptome profiling and connectivity mapping to identify compounds beneficial for alleviating airway hyperreactivity (AHR). As a comparison, we also used previously published transcriptome data from sensitized mouse lungs and human asthmatic endobronchial biopsies. All transcriptomes revealed agents beneficial for mitigating AHR; however, only the vagal ganglia transcriptome identified agents used clinically to treat asthma (flunisolide, isoetarine). We also tested one compound identified by vagal ganglia transcriptome profiling that had not previously been linked to asthma and found that it had bronchodilator effects in both mouse and pig airways. These data suggest that transcriptome profiling of the vagal ganglia might be a novel strategy to identify potential asthma therapeutics.

Solitary Cholinergic Stimulation Induces Airway Hyperreactivity and Transcription of Distinct Pro-inflammatory Pathways

Airway hyperreactivity is a hallmark feature of asthma and can be precipitated by airway insults, such as ozone exposure or viral infection. A proposed mechanism linking airway insults to airway hyperreactivity is augmented cholinergic transmission. In the current study, we tested the hypothesis that acute potentiation of cholinergic transmission is sufficient to induce airway hyperreactivity. We atomized the cholinergic agonist bethanechol to neonatal piglets and forty-eight hours later measured airway resistance. Bethanechol-treated piglets displayed increased airway resistance in response to intravenous methacholine compared to saline-treated controls. In the absence of an airway insult, we expected to find no evidence of airway inflammation; however, transcripts for several asthma-associated cytokines, including IL17A, IL1A, and IL8, were elevated in the tracheas of bethanechol-treated piglets. In the lungs, prior bethanechol treatment increased transcripts for IFNγ and its downstream target CXCL10. These findings suggest that augmented cholinergic transmission is sufficient to induce airway hyperreactivity, and raise the possibility that cholinergic-mediated regulation of pro-inflammatory pathways might contribute.

Early childhood trajectories of separation anxiety: Bearing on mental health, academic achievement, and physical health from mid-childhood to preadolescence

BACKGROUND

Separation anxiety disorder is the most prevalent childhood anxiety condition, but no study assessed children for separation anxiety at preschool age and followed them longitudinally and directly until mid-childhood/early adolescence.

METHODS

Multi-informant (children, teachers, family), multipoint (at age 8, 10, 12, 13) assessments of 1,290 children of the Quebec Longitudinal Study of Child Development, who had been categorized between age 1.5 and 6 into four specific separation anxiety trajectories (1, low-persistent; 2, low-increasing; 3, high-decreasing, and the less common: 4, high-increasing) by growth mixture modeling. Participants in the high-increasing trajectory were compared to participants in the other three trajectories for: (a) child's internalizing and externalizing problem behavior; (b) physical health; (c) academic achievement; (d) maternal anxiety.

RESULTS

Multivariate analyses of variance/covariance at separate time points showed the high-increasing trajectory mostly associated with: (a) higher internalizing, but not externalizing, behavior; (b) worse academic achievement (most consistently by comparisons to the normative low-persistent trajectory; (c) higher rates of maternal panic/agoraphobic anxiety; (d) worse physical health (most consistently by comparisons to the low-persistent trajectory). The high-increasing trajectory had twofold to threefold higher incidences of physical illnesses than the normative low-persistent group; this was specific for headaches at age 12 years, chronic asthma at age 10 and 13, and having received asthma-related medication during the past 12 months.

CONCLUSIONS

High-increasing separation anxiety in preschool maintains longitudinal relationships to independent health and academic outcomes, at least until preadolescence. This knowledge can inform the deployment of clinical resources at the earlier signs of the more impairing manifestations.

Simple and reproducible approaches for the collection of select porcine ganglia

BACKGROUND

The anatomy and physiology of the pig nervous system is more similar to humans compared to traditional rodent models. This makes the pig an attractive model to answer questions relating to human health and disease. Yet the technical and molecular tools available to pig researchers are limited compared to rodent researchers.

NEW METHOD

We developed simple and rapid methods to isolate the trigeminal, nodose (distal vagal), and dorsal root ganglia from neonatal pigs. We selected these ganglia due to their broad applicability to basic science researchers and clinicians.

RESULTS

Use of these methods resulted in reproducible isolation of all three types of ganglia as validated by histological examination.

COMPARISON WITH EXISTING METHOD(S)

There are currently no methods that describe a step-by-step protocol to isolate these porcine ganglia.

CONCLUSIONS

In conclusion, these methods for ganglia collection will facilitate and accelerate future neuroscience investigations in pig models of human disease.