Allergic airway inflammation induces tachykinin peptides expression in vagal sensory neurons innervating mouse airways

Current understanding of Bordetella-induced cough

Typical pathogenic bacteria of the genus Bordetella cause respiratory diseases, many of which are characterized by severe coughing in host animals. In human infections with these bacteria, such as whooping cough, coughing imposes a heavy burden on patients. The pathophysiology of this severe coughing had long been uncharacterized because convenient animal models that reproduce Bordetella-induced cough have not been available. However, rat and mouse models were recently shown as useful for understanding, at least partially, the causative factors and the mechanism of Bordetella-induced cough. Many types of coughs are induced under various physiological conditions, and the neurophysiological pathways of coughing are considered to vary among animal species, including humans. However, the neurophysiological mechanisms of the coughs in different animal species have not been entirely understood, and, accordingly, the current understanding of Bordetella-induced cough is still incomplete. Nevertheless, recent research findings may open the way for the development of prophylaxis and therapeutic measures against Bordetella-induced cough.

Therapeutic efficacy of topical blockade of substance P in experimental allergic red eye

PURPOSE

Allergic conjunctivitis is the most common cause leading to ocular redness (OR). Herein, using an animal model of allergic OR, we evaluated the therapeutic efficacy of topical blockade of substance P (SP) in treating red eye.

METHODS

Allergic OR was induced in guinea pigs with topical histamine. Ocular SP was blocked using a specific SP receptor (neurokinin-1 receptor, NK1R) antagonist, L-703,606, via topical application 10 min before or 10 min after histamine instillation. Animal eyes were examined and a series of images were taken for up to 60 min post-OR induction. The severity of redness was analyzed using the quantitative ocular redness index (ORI). At the end of clinical examination, conjunctival tissues were collected for histological examination of conjunctival blood vessels and infiltrating eosinophils and neutrophils. In addition, SP concentration was quantified in the tear fluid and expression levels of inflammatory cytokines were assessed in the conjunctival tissues.

RESULTS

Topical histamine application successfully induced red eye, evidenced by the significantly increased ORI during the observation period, with peak values at 10 min, along with significantly increased levels of SP in the tears. Topical treatment with L-703,606, either before histamine application or at the time of peak ORI, effectively reduced ORI and suppressed conjunctival blood vessel dilation, along with decreased eosinophil and neutrophil infiltration, and inflammatory cytokine expression in the conjunctiva, as well as reduced SP levels in the tears.

CONCLUSIONS

Topical blockade of SP effectively prevents and treats allergy-related ocular redness by suppressing blood vessel dilation and allergic inflammation.

The Mechanism of Pertussis Cough Revealed by the Mouse-Coughing Model

Pertussis, also known as whooping cough, is a contagious respiratory disease caused by the Gram-negative bacterium Bordetella pertussis. This disease is characterized by severe and uncontrollable coughing, which imposes a significant burden on patients. However, its etiological agent and the mechanism are totally unknown because of a lack of versatile animal models that reproduce the cough. Here, we present a mouse model that reproduces coughing after intranasal inoculation with the bacterium or its components and demonstrate that lipooligosaccharide (LOS), pertussis toxin (PTx), and Vag8 of the bacterium cooperatively function to cause coughing. Bradykinin induced by LOS sensitized a transient receptor potential ion channel, TRPV1, which acts as a sensor to evoke the cough reflex. Vag8 further increased bradykinin levels by inhibiting the C1 esterase inhibitor, the major downregulator of the contact system, which generates bradykinin. PTx inhibits intrinsic negative regulation systems for TRPV1 through the inactivation of G_i GTPases. Our findings provide a basis to answer long-standing questions on the pathophysiology of pertussis cough.

The impact of influenza pulmonary infection and inflammation on vagal bronchopulmonary sensory neurons

Influenza A virus (IAV) is rapidly detected in the airways by the immune system, with resident parenchymal cells and leukocytes orchestrating viral sensing and the induction of antiviral inflammatory responses. The airways are innervated by heterogeneous populations of vagal sensory neurons which also play an important role in pulmonary defense. How these neurons respond to IAV respiratory infection remains unclear. Here, we use a murine model to provide the first evidence that vagal sensory neurons undergo significant transcriptional changes following a respiratory IAV infection. RNA sequencing on vagal sensory ganglia showed that IAV infection induced the expression of many genes associated with an antiviral and pro-inflammatory response and this was accompanied by a significant increase in inflammatory cell recruitment into the vagal ganglia. Assessment of gene expression in single-vagal sensory neurons confirmed that IAV infection induced a neuronal inflammatory phenotype, which was most prominent in bronchopulmonary neurons, and also evident in some neurons innervating other organs. The altered transcriptome could be mimicked by intranasal treatment with cytokines and the lung homogenates of infected mice, in the absence of infectious virus. These data argue that IAV pulmonary infection and subsequent inflammation induces vagal sensory ganglia neuroinflammation and this may have important implications for IAV-induced morbidity.

Mini review: Neural mechanisms underlying airway hyperresponsiveness

Neural changes underly hyperresponsiveness in asthma and other airway diseases. Afferent sensory nerves, nerves within the brainstem, and efferent parasympathetic nerves all contribute to airway hyperresponsiveness. Inflammation plays a critical role in these nerve changes. Chronic inflammation and pre-natal exposures lead to increased airway innervation and structural changes. Acute inflammation leads to shifts in neurotransmitter expression of afferent nerves and dysfunction of M₂ muscarinic receptors on efferent nerve endings. Eosinophils and macrophages drive these changes through release of inflammatory mediators. Novel tools, including optogenetics, two photon microscopy, and optical clearing and whole mount microscopy, allow for improved studies of the structure and function of airway nerves and airway hyperresponsiveness.

Peripheral and central mechanisms of cough hypersensitivity

Chronic cough is a difficult to treat symptom of many respiratory and some non-respiratory diseases, indicating that varied pathologies can underpin the development of chronic cough. However, clinically and experimentally it has been useful to collate these different pathological processes into the single unifying concept of cough hypersensitivity. Cough hypersensitivity syndrome is reflected by troublesome cough often precipitated by levels of stimuli that ordinarily don't cause cough in healthy people, and this appears to be a hallmark feature in many patients with chronic cough. Accordingly, a strong argument has emerged that changes in the excitability and/or normal regulation of the peripheral and central neural circuits responsible for cough are instrumental in establishing cough hypersensitivity and for causing excessive cough in disease. In this review, we explore the current peripheral and central neural mechanisms that are believed to be involved in altered cough sensitivity and present possible links to the mechanism of action of novel therapies that are currently undergoing clinical trials for chronic cough.

Airway Innervation and Plasticity in Asthma

Airway nerves represent a mechanistically and therapeutically important aspect that requires better highlighting in the context of diseases such as asthma. Altered structure and function (plasticity) of afferent and efferent airway innervation can contribute to airway diseases. We describe established anatomy, current understanding of how plasticity occurs, and contributions of plasticity to asthma, focusing on target-derived growth factors (neurotrophins). Perspectives toward novel treatment strategies and future research are provided.

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.

Vagal Afferent Innervation of the Airways in Health and Disease

Vagal sensory neurons constitute the major afferent supply to the airways and lungs. Subsets of afferents are defined by their embryological origin, molecular profile, neurochemistry, functionality, and anatomical organization, and collectively these nerves are essential for the regulation of respiratory physiology and pulmonary defense through local responses and centrally mediated neural pathways. Mechanical and chemical activation of airway afferents depends on a myriad of ionic and receptor-mediated signaling, much of which has yet to be fully explored. Alterations in the sensitivity and neurochemical phenotype of vagal afferent nerves and/or the neural pathways that they innervate occur in a wide variety of pulmonary diseases, and as such, understanding the mechanisms of vagal sensory function and dysfunction may reveal novel therapeutic targets. In this comprehensive review we discuss historical and state-of-the-art concepts in airway sensory neurobiology and explore mechanisms underlying how vagal sensory pathways become dysfunctional in pathological conditions.

Allergic airway inflammation induces migration of mast cell populations into the mouse airway

Mast cells (MCs) and airway nerves play an important role in allergic asthma. However, little is known about the MCs and their interaction with airway nerves during allergic airway inflammation. This study aims to investigate the distribution and proliferation of MC populations in different lung compartments, along with the association of mast cells with nerve endings, using a house dust mite (HDM) model for allergic airway inflammation. BALB/c mice were exposed to HDM extract intranasally (25 μg/50 μl) for 5 consecutive days a week over 7 weeks. Immunofluorescence and Edu stains were used to examine the colocalisation of MCs and nerves and the proliferation of MCs, respectively. HDM treatment caused an increased migration of MCs into bronchi, alveolar parenchyma and airway vessels. The proportions of tryptase-chymase expressing MC (MC_TC) increased significantly in the bronchi and the alveolar parenchyma but not in the vascular tissues, by allergic airway inflammation. The association of MCs with nerves was found only in the bronchi and there were no changes in comparison of controls to HDM-treated animals. The present study shows a strong migration of tryptase expressing MC (MC_T) and MC_TC into the bronchi and the alveolar parenchyma, as well as of MC_T in the vascular compartment under HDM treatment. This supports the hypothesis that these mast cell populations may contribute to allergic airway inflammation.

Immunohistochemical characterization of the jugular (superior vagal) ganglion in the pig

The study was carried out on three 4-month old female pigs. All the animals were deeply anesthetized and transcardially perfused with 4% buffered paraformaldehyde (pH 7.4). Left and right superior vagal ganglia (SVG) were collected and processed for immunofluorescence labeling method. The preparations were examined under a Zeiss LSM 710 confocal microscope equipped with adequate filter block. Neurons forming SVG were round or oval in shape with a round nucleus in the center. The majority of them (52%) were medium (M) (31-50 μm in diameter) while 7% and 41% were small (S) (up to 30μm in diameter) or large (L) (above 50 μm in diameter) in size, respectively. Double-labeling immunofluorescence revealed that SVG neurons stained for CGRP (approx. 57%; among them 37%, 9% and 54% were M, S and L in size, respectively), SP (14.5%; 72.4% M, 3.4% S, 24.2% L), VACHT (26%; 63% M, 24% S and 13% L), GAL (14%; 57% M, 29% S, 14% L), NPY (12%; 53% M, 12% S, 35% L), Met-Enk (5%; 40% M, 6% S and 54% L), PACAP (15%; 52% M, 24% S and 24% L), VIP (6.3%; 67% M, 8% S and 25% L), and NOS-positive (6%; 31% M and 69% L). The most abundant populations of intraganglionic nerve fibers were those which stained for CGRP or GAL, whereas only single SP-, PACAP- or Met-ENK-positive nerve terminals were observed.

Decreased Migration of Dendritic Cells into the Jugular-Nodose Ganglia by the CXCL12 Neutraligand Chalcone 4 in Ovalbumin-Sensitized Asthmatic Mice

OBJECTIVE

The chemokine CXCL12 interacting with the CXC receptor 4 (CXCR4) has been reported to play a role in the development and progression of bronchial asthma, but its mechanism of action is still unknown. The objective of this study was to assess the effect of the CXCL12 neutraligand chalcone 4 on the migration of dendritic cells (DCs) in a murine model of allergic airway inflammation.

METHODS

A 21-day ovalbumin (OVA)-induced allergic-airway TH2 inflammation model in BALB/c mice was used. Four groups were sensitized with OVA adsorbed on alum and challenged either with OVA or saline for 4 days. Mice were treated intranasally with chalcone 4 (300 nmol/kg body weight) or solvent 2 h before each OVA or saline challenge; 24 h after the last challenge, CD11c+F4/80- DCs were counted in the bronchoalveolar lavage. Jugular-nodose ganglion complex (JNC) sections were sampled, and for immunofluorescence staining, cryocut sections were prepared. MHC II+F4/80- DCs as well as calcitonin gene-related peptide (CGRP)- and substance P (SP)-positive neuronal cell bodies were analyzed.

RESULTS

In OVA-challenged mice, chalcone 4 caused a significantly decreased DC/neuron ratio in the JNC from 51.7% in solvent-treated to 32.6% in chalcone 4-treated mice. In parallel, chalcone 4 also decreased the DC population in BALF from 11.5 × 103 cells in solvent to 4.5 × 103 cells in chalcone 4-treated mice. By contrast, chalcone 4 had no effect on the expression of the neuropeptides CGRP and SP in JNC.

CONCLUSION

This study reported the CXCL12 neutraligand chalcone 4 to affect DC infiltration into the airways and airway ganglia as well as to decrease airway eosinophilic inflammation and, therefore, validated CXCL12 as a new target in allergic disease models of asthma.

Regulator Versus Effector Paradigm: Interleukin-10 as Indicator of the Switching Response

The interleukin-10 (IL-10) is generally considered as the most important cytokine with anti-inflammatory properties and one of the key cytokines preventing inflammation-mediated tissue damage. In this respect, IL-10 producing cells play a crucial role in the outcome of infections, allergy, autoimmune reactions, tumor development, and transplant tolerance. Based on recent findings with regard to the mentioned clinical conditions, this review attempts to shed some light on the IL-10 functions, considering this cytokine as inherent inducer of the switching immunity. While acute infections and vaccinations are associated by IL-10 enhanced during few weeks, chronic parasitoses, tumor diseases, allergen-specific immunotherapy, transplants, and use of immune-suppressor drugs show an increased IL-10 level along months or years. With regard to autoimmune pathologies, the IL-10 increase is prevalently observed during early stages, whereas the successive stages are characterized by reaching of immune equilibrium independently to disease's activity. Together, these findings indicate that IL-10 is mainly produced during transient immune conditions and the persistent IL-10-related effect is the indication/prediction (and maybe effectuation) of the switching immunity. Actual knowledge emphasizes that any manipulation of the IL-10 response for treatment purposes should be considered very cautiously due to its potential hazards to the immune system. Probably, the IL-10 as potential switcher of immunity response should be used in association with co-stimulatory immune effectors that are necessary to determine the appropriate deviation during treatment of respective pathologies. Hopefully, further findings would open new avenues to study the biology of this "master switch" cytokine and its therapeutic potential.

TRP channels and traffic-related environmental pollution-induced pulmonary disease

Environmental pollutant exposures are major risk factors for adverse health outcomes, with increased morbidity and mortality in humans. Diesel exhaust (DE) is one of the major harmful components of traffic-related air pollution. Exposure to DE affects several physiological systems, including the airways, and pulmonary diseases are increased in highly populated urban areas. Hence, there are urgent needs to (1) create newer and lesser polluting fuels, (2) improve exhaust aftertreatments and reduce emissions, and (3) understand mechanisms of actions for toxic effects of both conventional and cleaner diesel fuels on the lungs. These steps could aid the development of diagnostics and interventions to prevent the negative impact of traffic-related air pollution on the pulmonary system. Exhaust from conventional, and to a lesser extent, clean fuels, contains particulate matter (PM) and more than 400 additional chemical constituents. The major toxic constituents are nitrogen oxides (NOx) and polycyclic aromatic hydrocarbons (PAHs). PM and PAHs could potentially act via transient receptor potential (TRP) channels. In this review, we will first discuss the associations between DE from conventional as well as clean fuel technologies and acute and chronic airway inflammation. We will then review possible activation and/or potentiation of TRP vanilloid type 1 (TRPV1) and ankyrin 1 (TRPA1) channels by PM and PAHs. Finally, we will discuss and summarize recent findings on the mechanisms whereby TRPs could control the link between DE and airway inflammation, which is a primary determinant leading to pulmonary disease.

Steroid Treatment Reduces Allergic Airway Inflammation and Does Not Alter the Increased Numbers of Dendritic Cells and Calcitonin Gene-Related Peptide-Expressing Neurons in Airway Sensory Ganglia

OBJECTIVES

Our previous data demonstrated that allergic airway inflammation induces migration of dendritic cells (DC) into airway sensory jugular and nodose ganglia (jugular-nodose ganglion complex; JNC). Here we investigated the effects of steroid treatment regarding the expression and migration of DC and calcitonin gene-related peptide (CGRP)-immunoreactive neurons of vagal sensory ganglia during allergic airway inflammation.

METHODS

A house dust mite (HDM) model for allergic airway inflammation was used. The mice received 0.3 mg fluticasone propionate per kilogram of body weight in the last 9 days. JNC slices were analyzed on MHC II, the neuronal marker PGP9.5, and the neuropeptide CGRP.

RESULTS

Allergic airway inflammation increased the numbers of DC and CGRP-expressing neurons in the JNC significantly in comparison to the controls (DC/neurons: HDM 44.58 ± 1.6% vs. saline 33.29 ± 1.6%, p < 0.05; CGRP-positive neurons/total neurons: HDM 30.65 ± 1.9% vs. saline 19.49 ± 2.3%, p < 0.05). Steroid treatment did not have any effect on the numbers of DC and CGRP-expressing neurons in the JNC compared to HDM-treated mice.

CONCLUSIONS

The present findings indicate an important role of DC and CGRP-containing neurons in the pathogenesis of allergic airway inflammation. However, steroid treatment did not have an effect on the population of DC and neurons displaying CGRP in the JNC, whereas steroid treatment was found to suppress allergic airway inflammation.

Allergic airway inflammation induces the migration of dendritic cells into airway sensory ganglia

BACKGROUND

A neuroimmune crosstalk between dendritic cells (DCs) and airway nerves in the lung has recently been reported. However, the presence of DCs in airway sensory ganglia under normal and allergic conditions has not been explored so far. Therefore, this study aims to investigate the localisation, distribution and proliferation of DCs in airway sensory ganglia under allergic airway inflammation.

METHODS

Using the house dust mite (HDM) model for allergic airway inflammation BALB/c mice were exposed to HDM extract intranasally (25 μg/50 μl) for 5 consecutive days a week over 7 weeks. With the help of the immunohistochemistry, vagal jugular-nodose ganglia complex (JNC) sections were analysed regarding their expression of DC-markers (MHC II, CD11c, CD103), the neuronal marker PGP 9.5 and the neuropeptide calcitonin gene-related peptide (CGRP) and glutamine synthetase (GS) as a marker for satellite glia cells (SGCs). To address the original source of DCs in sensory ganglia, a proliferation experiment was also carried in this study.

RESULTS

Immune cells with characteristic DC-phenotype were found to be closely located to SGCs and vagal sensory neurons under physiological conditions. The percentage of DCs in relation to neurons was significantly increased by allergic airway inflammation in comparison to the controls (HDM 51.38 ± 2.38% vs. control 28.16 ± 2.86%, p < 0.001). The present study also demonstrated that DCs were shown to proliferate in jugular-nodose ganglia, however, the proliferation rate of DCs is not significantly changed in the two treated animal groups (proliferating DCs/ total DCs: HDM 0.89 ± 0.38%, vs. control 1.19 ± 0.54%, p = 0.68). Also, increased number of CGRP-positive neurons was found in JNC after allergic sensitisation and challenge (HDM 31.16 ± 5.41% vs. control 7.16 ± 1.53%, p < 0.001).

CONCLUSION

The present findings suggest that DCs may migrate from outside into the ganglia to interact with sensory neurons enhancing or protecting the allergic airway inflammation. The increase of DCs as well as CGRP-positive neurons in airway ganglia by allergic airway inflammation indicate that intraganglionic DCs and neurons expressing CGRP may contribute to the pathogenesis of bronchial asthma. To understand this neuroimmune interaction in allergic airway inflammation further functional experiments should be carried out in future studies.

Detection of mouse cough based on sound monitoring and respiratory airflow waveforms

Detection for cough in mice has never yielded clearly audible sounds, so there is still a great deal of debates as to whether mice can cough in response to tussive stimuli. Here we introduce an approach for detection of mouse cough based on sound monitoring and airflow signals. 40 Female BALB/c mice were pretreated with normal saline, codeine, capasazepine or desensitized with capsaicin. Single mouse was put in a plethysmograph, exposed to aerosolized 100 µmol/L capsaicin for 3 min, followed by continuous observation for 3 min. Airflow signals of total 6 min were recorded and analyzed to detect coughs. Simultaneously, mouse cough sounds were sensed by a mini-microphone, monitored manually by an operator. When manual and automatic detection coincided, the cough was positively identified. Sound and sound waveforms were also recorded and filtered for further analysis. Body movements were observed by operator. Manual versus automated counts were compared. Seven types of airflow signals were identified by integrating manual and automated monitoring. Observation of mouse movements and analysis of sound waveforms alone did not produce meaningful data. Mouse cough numbers decreased significantly after all above drugs treatment. The Bland-Altman and consistency analysis between automatic and manual counts was 0.968 and 0.956. The study suggests that the mouse is able to present with cough, which could be detected by sound monitoring and respiratory airflow waveform changes.

The effects of nociceptin peptide (N/OFQ)-receptor (NOP) system activation in the airways

The heptadecapeptide nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand for the N/OFQ peptide (NOP) receptor. It is cleaved from a larger precursor identified as prepronociceptin (ppN/OFQ). NOP is a member of the seven transmembrane-spanning G-protein coupled receptor (GPCR) family. ppN/OFQ and NOP receptors are widely distributed in different human tissues. Asthma is a complex heterogeneous disease characterized by variable airflow obstruction, bronchial hyper-responsiveness and chronic airway inflammation. Limited therapeutic effectiveness of currently available asthma therapies warrants identification of new drug compounds. Evidence from animal studies suggests that N/OFQ modulates airway contraction and inflammation. Interestingly up regulation of the N/OFQ-NOP system reduces airway hyper-responsiveness. In contrast, inflammatory cells central to the inflammatory response in asthma may be both sources of N/OFQ and respond to NOP activation. Hence paradoxical dysregulation of the N/OFQ-NOP system may potentially play an important role in regulating airway inflammation and airway tone. To date there is no data on N/OFQ-NOP expression in the human airways. Therefore, the potential role of N/OFQ-NOP system in asthma is unknown. This review focuses on its physiological effects within airways and potential value as a novel asthma therapy.

Substance P antagonist improves both obesity and asthma in a mouse model

BACKGROUND

Evidence suggests a causal relationship between obesity and asthma; however, the underlying mechanisms remain unknown. Substance P (SP), involved in neurogenic inflammation by acting through its receptor NK1-R, seems to participate in obese-asthma phenotype in mice.

OBJECTIVES

To evaluate the effect of a selective substance P receptor antagonist on a mouse model of diet-induced obesity and asthma.

METHODS

Diet-induced obese Balb/c mice were sensitized and challenged with ovalbumin (OVA) and treated with a selective NK1-R antagonist or placebo. Serum glucose, insulin, IL-6, resistin, and OVA-specific IgE levels were quantified. A score for peribronchial inflammation in lung histology was used. Cells were counted in bronchoalveolar lavage fluid. Adipocyte sizes were measured.

RESULTS

Ovalbumin-obese mice treated with NK1-R antagonist had lower weight (P = 0.0002), reduced daily food intake (P = 0.0021), reduced daily energy intake (P = 0.0021), reduced surface adipocyte areas (P < 0.0001), lower serum glucose (P = 0.04), lower serum insulin (P = 0.03), lower serum IL-(P = 0.0022), lower serum resistin (P = 0.0043), lower serum OVA-specific IgE (P = 0.035), and lower peribronchial inflammation score (P < 0.0001) than nontreated OVA-obese mice. We observed an interaction between obesity, allergen sensitization, and treatment with NK1-R antagonist for metabolic and systemic biomarkers, and for allergen sensitization and bronchial inflammation, showing a synergy between these variables.

CONCLUSION & CLINICAL RELEVANCE

In an experimental model of obesity and asthma in mice, NK1-R blockade improved metabolic and systemic biomarkers, as well as allergen sensitization and bronchial inflammation. These positive effects support a common pathway in the obese-asthma phenotype and highlight SP as a target with potential clinical interest in the obese-asthma epidemics.

Neurogenic inflammation in allergen-challenged obese mice: A missing link in the obesity-asthma association?

AIM

A number of studies have shown an association between obesity and asthma. Controversy remains on the mechanisms supporting this association. In this study we aimed to assess neurogenic inflammation in a model of diet-induced obesity and allergen-challenged mice.

METHODS

High fat diet-induced (HFD) obese Balb/c mice were sensitized and challenged with ovalbumin (OVA). Glucose, insulin, OVA-specific IgE and substance P (SP), and the main tachykinin involved in neurogenic inflammation, were quantified in sera. Cell counts were performed in bronchoalveolar lavage fluid (BALF). The extent of peribronchial infiltrates was estimated on lung tissue sections and inflammation was score based on inflammatory cell counts surrounding the bronchi.

RESULTS

Obesity per se and allergen-sensitization per se increased serum SP (P = .027, P = .004, respectively). Further increased was observed in obese-sensitized mice (P = .007). Obese-sensitized mice also showed higher insulin (P = .0016), OVA-specific IgE (P = .016), peribronchial inflammatory score (P = .045), and tendency for higher glycemia. The interaction of obesity and asthma on SP levels was confirmed (P = .005, R(2) = 0.710). SP was positively correlated with metabolic (glycemia, r = 0.539, P = .007) and allergic inflammation parameters (BALF eosinophils, r = 0.445, P = 0.033; BALF mast cells, r = 0.574, P = .004; peribronchial inflammation score, r = 0.661, P < .001; and OVA-specific IgE, r = 0.714, P < .001).

CONCLUSIONS

Our findings provide support to the neurogenic inflammation link between obesity and asthma in mice. These two conditions independently increased SP and the presence of both pathologies further increased this level. Neurogenic inflammation may be a previously unrecognized mechanism beyond the obese-asthma phenotype. Further studies are need to confirm this role of SP in human obesity-asthma association.

The neuropeptide calcitonin gene-related peptide affects allergic airway inflammation by modulating dendritic cell function

BACKGROUND

The neuropeptide calcitonin gene-related peptide (CGRP) is released in the lung by sensory nerves during allergic airway responses. Pulmonary dendritic cells (DC) orchestrating the allergic inflammation could be affected by CGRP.

OBJECTIVE

To determine the immunomodulatory effects of CGRP on DC function and its impact on the induction of allergic airway inflammation.

METHODS

CGRP receptor expression on lung DC was determined by RT-PCR and immunofluorescence staining. The functional consequences of CGRP receptor triggering were evaluated in vitro using bone marrow-derived DC. DC maturation and the induction of ovalbumin (OVA)-specific T cell responses were analysed by flow cytometry. The in vivo relevance of the observed DC modulation was assessed in a DC-transfer model of experimental asthma. Mice were sensitized by an intrapharyngeal transfer of OVA-pulsed DC and challenged with OVA aerosol. The impact of CGRP pretreatment of DC on airway inflammation was characterized by analysing differential cell counts and cytokines in bronchoalveolar lavage fluid (BALF), lung histology and cytokine responses in mediastinal lymph nodes.

RESULTS

RT-PCR, immunofluorescence and cAMP assay demonstrated the expression of functionally active CGRP receptors in lung DC. RT-PCR revealed a transcriptional CGRP receptor down-regulation during airway inflammation. CGRP specifically inhibited the maturation of in vitro generated DC. Maturation was restored by blocking with the specific antagonist CGRP(8-37) . Consequently, CGRP-pretreated DC reduced the activation and proliferation of antigen-specific T cells and induced increased the numbers of T regulatory cells. The transfer of CGRP-pretreated DC diminished allergic airway inflammation in vivo, shown by reduced eosinophil numbers and increased levels of IL-10 in BALF.

CONCLUSIONS AND CLINICAL RELEVANCE

CGRP inhibits DC maturation and allergen-specific T cell responses, which affects the outcome of the allergic airway inflammation in vivo. This suggests an additional mechanism by which nerve-derived mediators interfere with local immune responses. Thus, CGRP as an anti-inflammatory mediator could represent a new therapeutic tool in asthma therapy.

Phenotypic distinctions between neural crest and placodal derived vagal C-fibres in mouse lungs

Two major types of nociceptors have been described in dorsal root ganglia (DRGs). In comparison, little is known about the vagal nociceptor subtypes. The vagus nerves provide much of the capsaicin-sensitive nociceptive innervation to visceral tissues, and are likely to contribute to the overall pathophysiology of visceral inflammatory diseases. The cell bodies of these afferent nerves are located in the vagal sensory ganglia referred to as nodose and jugular ganglia. Neurons of the nodose ganglion are derived from the epibranchial placodes, whereas jugular ganglion neurons are derived from the neural crest. In the adult mouse, however, there is often only a single ganglionic structure situated alone in the vagus nerve. By employing Wnt1Cre/R26R mice, which express β-galactosidase only in neural crest derived neurons, we found that this single vagal sensory ganglion is a fused ganglion consisting of both neural crest neurons in the rostral portion and non-neural crest (nodose) neurons in the more central and caudal portions of the structure. Based on their activation and gene expression profiles, we identified two major vagal capsaicin-sensitive nociceptor phenotypes, which innervated a defined target, namely the lung in adult mice. One subtype is non-peptidergic, placodal in origin, expresses P2X2 and P2X3 receptors, responds to α,β-methylene ATP, and expresses TRKB, GFRα1 and RET. The other phenotype is derived from the cranial neural crest and does not express P2X2 receptors and fails to respond to α,β-methylene ATP. This population can be further subdivided into two phenotypes, a peptidergic TRKA(+) and GFRα3(+) subpopulation, and a non-peptidergic TRKB(+) and GFRα1(+) subpopulation. Consistent with their similar embryonic origin, the TRPV1 expressing neurons in the rostral dorsal root ganglia were more similar to jugular than nodose vagal neurons. The data support the hypothesis that vagal nociceptors innervating visceral tissues comprise at least two major subtypes. Due to distinctions in their gene expression profile, each type will respond to noxious or inflammatory conditions in their own unique manner.

Modulation of sensory nerve function and the cough reflex: understanding disease pathogenesis

To cough is a protective defence mechanism that is vital to remove foreign material and secretions from the airways and which in the normal state serves its function appropriately. Modulation of the cough reflex pathway in disease can lead to inappropriate chronic coughing and an augmented cough response. Chronic cough is a symptom that can present in conjunction with a number of diseases including chronic obstructive pulmonary disease (COPD) and asthma, although often the cause of chronic cough may be unknown. As current treatments for cough have proved to exhibit little efficacy and are largely ineffective, there is a need to develop novel, efficacious and safe antitussive therapies. The underlying mechanisms of the cough reflex are complex and involve a network of events, which are not fully understood. It is accepted that the cough reflex is initiated following activation of airway sensory nerves. Therefore, in the hope of identifying novel antitussives, much research has focused on understanding the neural mechanisms of cough provocation. Experimentally this has been undertaken using chemical or mechanical tussive stimuli in conjunction with animal models of cough and clinical cough assessments. This review will discuss the neural mechanisms involved in the cough, changes that occur under pathophysiological conditions and and how current research may lead to novel therapeutic opportunities for the treatment of cough.

On the putative role of transient receptor potential cation channels in asthma

The mammalian transient receptor potential (TRP) superfamily consists of 28 mammalian TRP cation channels, which can be subdivided into six main subfamilies: the TRPC ('Canonical'), TRPV ('Vanilloid'), TRPM ('Melastatin'), TRPP ('Polycystin'), TRPML ('Mucolipin') and the TRPA ('Ankyrin') groups. Increasing evidence has accumulated during the previous few years that links TRP channels to the cause of several diseases or to critically influence and/or determine their progress. This review focuses on the possible role of TRP channels in the aetiology of asthmatic lung disease.

The role of neuro-immune cross-talk in the regulation of inflammation and remodelling in asthma

Despite recent advances in the development of anti-asthmatic medication, asthma continues to be a major health problem worldwide. The symptoms of asthmatic patients include wheezing, chest tightness, cough and shortness of breath, which, together with airway hyperresponiveness, previously have been attributed to a dysfunction of airway nerves. However, research in the last two decades identified Th2-sensitization and the subsequent allergic reaction to innocuous environmental antigens as a basic immunological mechanism leading to chronic airway inflammation. Recent evidence suggests that the development of allergic asthma is influenced by events and circumstances in early childhood and even in utero. Allergen, ozone or stress exposure, as well as RSV infection in early life could be able to induce irreversible changes in the developing epithelial-mesenchymal trophic unit of the airways. The co-existence of chronic inflammation and neural dysfunction have recently drawn attention to the involvement of interaction pathways between the nervous and the immune system in the airways. Intensive basic research has accumulated morphological as well as functional evidence for the interaction between nerves and immune cells. Neuropeptides and neurotrophins have come into focus of attention as the key mediators of neuro-immune interactions, which lead to the development of several pharmacological compounds specifically targeting these molecules. This review will integrate our current knowledge on the involvement of neuro-immune pathways in asthma on the cellular and molecular level. It will summarize the results of pharmacological studies addressing the potential of neuropeptides and neurotrophins as novel therapeutic targets in asthma.

Is TRPV1 a useful target in respiratory diseases?

This review focuses on the transient receptor potential vanilloid 1 (TRPV1). TRPV1 is a non-selective cation channel predominantly expressed in the cell membranes of sensory afferent fibers, which are activated multi-modally. In the mammalian respiratory system, immunohistochemical and electrophysiological studies have revealed heterogeneous localizations of TRPV1 channels in the airways and their presence in pleural afferents. TRPV1 channels in afferents are not only involved with sensory inputs, but also release several neuropeptides upon stimulation. These processes trigger pathophysiological effects (e.g. reflex bronchoconstriction, hypersecretion, cough, etc.) that cause various symptoms of airway diseases. Recent studies have identified several endogenous and exogenous substances that can activate TRPV1 in the lung. Because of its key role in initiating inflammatory processes, TRPV1 receptor antagonists have been proposed as therapeutic candidates. Therefore, a critical update of recent therapeutic results is also given in this review.

Nasobronchial interaction mechanisms in allergic airways disease

PURPOSE OF REVIEW

During the past few decades, the incidence of sensitization to inhaled allergens as well as allergic airways disease has grown steadily. Genetic and environmental factors are recognized as etiologic factors in the development of allergic airway disease, with allergic rhinitis often preceding the development of asthma. Allergic rhinitis is considered a risk factor for the development of asthma, and almost all allergic asthmatic patients have rhinitis. Insight into the risk factors responsible for allergic airways disease and the interaction between the involved organs results in a better diagnostic and therapeutic approach in global airway allergy syndrome.

RECENT FINDINGS

Recent studies have shown that local tissue factors, such as microbial stimuli and systemic inflammatory mechanisms, play a role in the clinical expression of the allergic airway syndrome. In addition, impaired nasal function affects the lower airways of asthmatic patients via different pathways. To date, most human and animal data point towards a systemic pathway linking the upper and lower airways, involving both bloodstream and bone marrow. Recent clinical trials and current guidelines underline the importance of an integrated treatment strategy involving both ends of the respiratory tract.

SUMMARY

This review provides an overview of recent epidemiological and immunopathologic evidence concerning the link between upper and lower airways in allergic disease and its therapeutic implications.

Central and peripheral mechanisms of narcotic antitussives: codeine-sensitive and -resistant coughs

Narcotic antitussives such as codeine reveal the antitussive effect primarily via the mu-opioid receptor in the central nervous system (CNS). The kappa-opioid receptor also seems to contribute partly to the production of the antitussive effect of the drugs. There is controversy as to whether delta-receptors are involved in promoting an antitussive effect. Peripheral opioid receptors seem to have certain limited roles. Although narcotic antitussives are the most potent antitussives at present, certain types of coughs, such as chronic cough, are particularly difficult to suppress even with codeine. In guinea pigs, coughs elicited by mechanical stimulation of the bifurcation of the trachea were not able to be suppressed by codeine. In gupigs with sub-acute bronchitis caused by SO2 gas exposure, coughing is difficult to inhibit with centrally acting antitussives such as codeine. Some studies suggest that neurokinins are involved in the development of codeine-resistant coughs. However, evidence supporting this claim is still insufficient. It is very important to characterize opiate-resistant coughs in experimental animals, and to determine which experimentally induced coughs correspond to which types of cough in humans. In this review, we describe the mechanisms of antitussive effects of narcotic antitussives, addressing codeine-sensitive and -resistant coughs, and including our own results.

Gene and protein expression of protease-activated receptor 2 in structural and inflammatory cells in the nasal mucosa in seasonal allergic rhinitis

BACKGROUND

Protease-activated receptor 2 (PAR 2) has been shown to be responsible for trypsin and mast cell tryptase-induced airway inflammation. Here, the present study aimed to explore the expression of PAR 2 in the nasal mucosa of seasonal allergic rhinitis (SAR).

METHODS

Study subjects were recruited for the study by medical history, physical examination and laboratory screening tests. Using immunohistochemistry, laser-assisted cell picking and subsequently real-time PCR, nasal mucosa biopsies of SAR patients were investigated for PAR 2 gene and protein expression in complex tissues of the nasal mucosa.

RESULTS

Gene and protein expression of PAR 2 was firstly detected in nasal mucosa of SAR patients. The relative gene expression level of PAR 2 was significantly increased in complex tissues of the nasal mucosa of SAR (6.21+/-4.02 vs. controls: 1.38+/-0.86, P=0.004). Moreover, PAR 2 mRNA expression in epithelial cells (SAR: 4.78+/-4.64 vs. controls: 0.84+/-0.61, P=0.003) but not in mucus (SAR: 1.51+/-1.15 vs. controls: 1.35+/-1.02, P=0.78) and endothelial cells (SAR: 1.20+/-0.57 vs. controls: 1.73+/-1.30, P=0.5) was found to be significantly changed in the nasal mucosa in SAR. Using double immunohistochemistry the present study demonstrated that the total numbers of mast cells (P=0.0003) and eosinophils (P=0.03) and the numbers of eosinophils expressing PAR 2 (P=0.006) were significantly elevated in the nasal mucosa of SAR compared with the controls.

CONCLUSION

The abundant presence and distribution of gene and protein expression of PAR 2 in different cell types in the nasal mucosa under normal situation, the increased expression of PAR 2 in epithelial cells and the increased number of eosinophils with PAR 2 suggest that PAR 2 may contribute to the pathogenesis of allergic diseases such as SAR.

Downstream target genes of the neuropeptide S-NPSR1 pathway

The neuropeptide S (NPS)-NPS receptor 1 (NPSR1) pathway has recently been implicated in the pathogenesis of asthma. The purpose of this study was to identify downstream gene targets regulated by NPSR1 upon NPS stimulation. A total of 104 genes were found significantly up-regulated and 42 down-regulated by microarray analysis 6 h after NPS administration. By Gene Ontology enrichment analysis, the categories 'cell proliferation', 'morphogenesis' and 'immune response' were among the most altered. A TMM microarray database comparison suggested a common co-regulated pathway, which includes JUN/FOS oncogene homologs, early growth response genes, nuclear receptor subfamily 4 members and dual specificity phosphatases. The expression of four up-regulated genes, matrix metallopeptidase 10 (MMP10), INHBA (activin A), interleukin 8 (IL8) and EPH receptor A2 (EPHA2), exhibited a significant NPS dose-response relationship as confirmed by quantitative reverse-transcriptase-PCR and for MMP10 by immunoassay. Immunohistochemical analyses revealed that MMP10 and TIMP metallopeptidase inhibitor 3 (TIMP3) were both strongly expressed in bronchial epithelium, and macrophages and eosinophils expressed MMP10 in asthmatic sputum samples. Because remodeling of airway epithelium is a feature of chronic asthma, the up-regulation of MMP10 and TIMP3 by NPS-NPSR1 signaling may be of relevance in the pathogenesis of asthma.

Stress induces substance P in vagal sensory neurons innervating the mouse airways

BACKGROUND

Tachykinins-like substance P (SP) have been shown to play an important role in initiating and perpetuating airway inflammation. Furthermore, they are supposed to be released into tissues in response to stress.

OBJECTIVE

The aim of this study was to investigate the effects of stress alone or in combination with allergic airway inflammation on SP expression in sensory neurons innervating the mouse airways.

METHODS

Balb/c mice were systemically sensitized to ovalbumin (OVA), followed by allergen aerosol exposure, and compared with non-sensitized controls. Additionally, OVA-sensitized and -challenged and non-sensitized mice were exposed to sound stress. SP expression in airway-specific and overall vagal sensory neurons of the jugular and nodose ganglion complex was analysed using retrograde neuronal tracing in combination with immunohistochemistry. Preprotachykinin A (PPT-A) mRNA, the precursor for SP, was quantified in lung tissue by real-time PCR. Bronchoalveolar lavage (BAL) fluid was obtained, and cell numbers and differentiation were determined.

RESULTS

Stress and/or allergic airway inflammation significantly increased SP expression in retrograde-labelled vagal sensory neurons from the mouse lower airways compared with controls [stress: 15.7+/-0.8% (% of retrograde-labelled neurons, mean+/-SEM); allergen: 17.9+/-0.4%; allergen/stress: 13.1+/-0.7% vs. controls: 6.3+/-0.3%]. Similarly, SP expression increased in overall vagal sensory neurons identified by the neuronal marker protein gene product (PGP) 9.5 [stress: 9.3+/-0.6% (% of PGP 9.5-positive neurons, means+/-SEM); allergen: 12.5+/-0.4%; allergen/stress: 10.2+/-0.4% vs. controls: 5.1+/-0.3%]. Furthermore, stress significantly increased PPT-A mRNA expression in lung tissue from OVA-sensitized and -challenged animals, and immune cells were identified as an additional source of SP in the lung by immunohistochemistry. Associated with enhanced neuronal SP expression, a significantly higher number of leucocytes were found in the BAL following allergen exposure. Further, stress significantly increased allergen-induced airway inflammation identified by increased leucocyte numbers in BAL fluids.

CONCLUSION

The central event of sound stress leads to the stimulation of SP expression in airway-specific neurons. However, in sensitized stressed mice an additional local source of SP (probably inflammatory cells) might enhance allergic airway inflammation.

Plasticity of peripheral mechanisms of cough

The cough reflex pathway is characterized by a remarkable plasticity often resulting in a persistent and uncontrollable urge to cough during airway inflammation. In many instances cough becomes up regulated to the extent that ceases to fulfill its defensive role in protecting the airways. The exact mechanisms underlying this plasticity are unknown and likely involves a variety of factors influencing the function of the peripheral and central nervous system. This review outlines the evidence of increased cough sensitivity during airway disease. This is followed by a discussion of the peripheral mechanisms involved including the potential role of inflammatory mediators, neutrophins and changes in the airway mucosal structure. A greater understanding of the mechanisms leading to enhanced cough should lead to the development of more effective therapeutic strategies.

Pulmonary sensory and reflex responses in the mouse

Mouse model research is proliferating because of its readiness for genetic manipulation. Little is known about pulmonary vagal afferents in mice, however. The purpose of this study was to determine whether their pulmonary afferents are similar to those in large animals. Single-unit activity was recorded in the cervical vagus nerve of anesthetized, open-chest, and mechanically ventilated mice. We evaluated airway sensory activity in 153 single units; 141 were mechanosensitive, with 134 inflation receptors and 7 deflation receptors. The remaining 12 receptors were chemosensitive and mechanically insensitive, showing low basal firing frequency and behaving like C-fiber or high-threshold Adelta-receptors. In separate studies, phrenic activity was recorded as an index of respiratory drive to assess pulmonary reflexes. Lung inflation produced a typical Hering-Breuer reflex, and intravenous injection of phenylbiguanide produced the typical chemoreflex resulting in apnea, bradycardia, and hypotension. These reflexes were blocked by bilateral vagotomy. We conclude that mice possess a similar set of airway sensors and pulmonary reflexes as typically found in larger animals.