The endoplasmic reticulum (ER) stress response participates in many chronic inflammatory and autoimmune diseases. In the current study, we sought to examine the contribution of ER stress transducers in the pathogenesis of three principal facets of allergic asthma: inflammation, airway fibrosis, and airways hyperresponsiveness.
House Dust Mite (HDM) was used as an allergen for in vitro and in vivo challenge of primary human and murine airway epithelial cells. ER stress transducers were modulated using specific small interfering RNAs (siRNAs) in vivo. Inflammation, airway remodeling, and hyperresponsiveness were measured by total bronchoalveolar lavage (BAL) cell counts, determination of collagen, and methacholine responsiveness in mice, respectively.
Challenge of human bronchiolar and nasal epithelial cells with HDM extract induced the ER stress transducer, activating transcription factor 6 α (ATF6α) as well as protein disulfide isomerase, ERp57, in association with activation of caspase-3. SiRNA-mediated knockdown of ATF6α and ERp57 during HDM administration in mice resulted in a decrease in components of HDM-induced ER stress, disulfide mediated oligomerization of Bak, and activation of caspase-3. Furthermore, siRNA-mediated knockdown of ATF6α and ERp57 led to decreased inflammation, airway hyperresponsiveness and airway fibrosis.
Collectively, our work indicates that HDM induces ER stress in airway epithelial cells and that ATF6α and ERp57 play a significant role in the development of cardinal features of allergic airways disease. Inhibition of ER stress responses may provide a potential therapeutic avenue in chronic asthma and sub-epithelial fibrosis associated with loss of lung function.
Allergen; HDM; Unfolded protein response; ER stress; Apoptosis; Asthma; Airway fibrosis
Overactivation of nuclear factor κB (NF-κB) orchestrates airway eosinophilia, but does not dampen airway hyperresponsiveness in asthma. NF-κB repression by arsenic trioxide (As2O3) contributes to apoptosis of eosinophils (EOS) in airways. Here we provide evidence that As2O3 abrogates allergen (OVA)-induced airway eosinophilia by modulating the expression of IκBα, an NF-κB inhibitory protein, and decreases the airway hyperresponsiveness.
Using a murine model of asthma, the airway hyperresponsiveness was conducted by barometric whole-body plethysmography. Airway eosinophilia, OVA-specific IgE in serum, and chemokine eotaxin and RANTES (regulated upon activation, normal T cell expressed and secreted) in bronchoalveolar lavage fluid were measured by lung histology, Diff-Quick staining, and ELISA. Chemokine-induced EOS chemotactic activity was evaluated using EOS chemotaxis assay. Electrophoretic mobility shift assay and Western blot analysis were performed to assess pulmonary NF-κB activation and IκBα expression, respectively.
As2O3 attenuated the allergen-induced serum IgE, chemokine expression of eotaxin and RANTES, and the EOS recruitment in bronchoalveolar lavage fluid, which is associated with an increased IκBα expression as well as a decreased NF-κB activation. Also, As2O3 suppressed the chemotaxis of EOS dose-dependently in vitro. Additionally, As2O3 significantly ameliorated the allergen-driven airway hyperresponsiveness, the cardinal feature underlying asthma.
These findings demonstrate an essential role of NF-κB in airway eosinophilia, and illustrate a potential dissociation between airway inflammation and hyperresponsiveness. As2O3 likely exerts its broad anti-inflammatory effects by suppression of NF-κB activation through augmentation of IκBα expression in asthma.
Allergic asthma is characterized by airway hyperresponsiveness and pulmonary eosinophilia, and may be mediated by T helper (Th) lymphocytes expressing a Th2 cytokine pattern. Interleukin (IL) 12 suppresses the expression of Th2 cytokines and their associated responses, including eosinophilia, serum immunoglobulin E, and mucosal mastocytosis. We have previously shown in a murine model that antigen- induced increases in airway hyperresponsiveness and pulmonary eosinophilia are CD4+ T cell dependent. We used this model to determine the ability of IL-12 to prevent antigen-induced increases in airway hyperresponsiveness, bronchoalveolar lavage (BAL) eosinophils, and lung Th2 cytokine expression. Sensitized A/J mice developed airway hyperresponsiveness and increased numbers of BAL eosinophils and other inflammatory cells after single or repeated intratracheal challenges with sheep red blood cell antigen. Pulmonary mRNA and protein levels of the Th2 cytokines IL-4 and IL-5 were increased after antigen challenge. Administration of IL-12 (1 microgram/d x 5 d) at the time of a single antigen challenge abolished the airway hyperresponsiveness and pulmonary eosinophilia and promoted an increase in interferon (IFN) gamma and decreases in IL-4 and IL-5 expression. The effects of IL-12 were partially dependent on IFN-gamma, because concurrent treatment with IL-12 and anti-IFN-gamma monoclonal antibody partially reversed the inhibition of airway hyperresponsiveness and eosinophilia by IL-12. Treatment of mice with IL-12 at the time of a second antigen challenge also prevented airway hyperresponsiveness and significantly reduced numbers of BAL inflammatory cells, reflecting the ability of IL-12 to inhibit responses associated with ongoing antigen-induced pulmonary inflammation. These data show that antigen-induced airway hyperresponsiveness and inflammation can be blocked by IL-12, which suppresses Th2 cytokine expression. Local administration of IL-12 may provide a novel immunotherapy for the treatment of pulmonary allergic disorders such as atopic asthma.
Recent studies in transgenic mice have revealed that expression of a dominant negative form of the transcription factor GATA-3 in T cells can prevent T helper cell type 2 (Th2)-mediated allergic airway inflammation in mice. However, it remains unclear whether GATA-3 plays a role in the effector phase of allergic airway inflammation and whether antagonizing the expression and/or function of GATA-3 can be used for the therapy of allergic airway inflammation and hyperresponsiveness. Here, we analyzed the effects of locally antagonizing GATA-3 function in a murine model of asthma. We could suppress GATA-3 expression in interleukin (IL)-4–producing T cells in vitro and in vivo by an antisense phosphorothioate oligonucleotide overlapping the translation start site of GATA-3, whereas nonsense control oligonucleotides were virtually inactive. In a murine model of asthma associated with allergic pulmonary inflammation and hyperresponsiveness in ovalbumin (OVA)-sensitized mice, local intranasal administration of fluorescein isothiocyanate–labeled GATA-3 antisense oligonucleotides led to DNA uptake in lung cells associated with a reduction of intracellular GATA-3 expression. Such intrapulmonary blockade of GATA-3 expression caused an abrogation of signs of lung inflammation including infiltration of eosinophils and Th2 cytokine production. Furthermore, treatment with antisense but not nonsense oligonucleotides induced a significant reduction of airway hyperresponsiveness in OVA-sensitized mice to levels comparable to saline-treated control mice, as assessed by both enhanced pause (PenH) responses and pulmonary resistance determined by body plethysmography. These data indicate a critical role for GATA-3 in the effector phase of a murine asthma model and suggest that local delivery of GATA-3 antisense oligonucleotides may be a novel approach for the treatment of airway hyperresponsiveness such as in asthma. This approach has the potential advantage of suppressing the expression of various proinflammatory Th2 cytokines simultaneously rather than suppressing the activity of a single cytokine.
GATA-3; antisense DNA; asthma; T cells; Th2 cytokines
The pathogenesis of allergic airway inflammation in asthmatic patients is complex and characterized by cellular infiltrates and activity of many cytokines and chemokines. Both the transcription factor hypoxia inducible factor-1 (HIF-1) and chemokine CCL2 have been shown to play pivotal roles in allergic airway inflammation. The interrelationship between these two factors is not known. We hypothesized that the expression of HIF-1 and CCL2 may be correlated and that the expression of CCL2 may be under the regulation of HIF-1. Several lines of evidence are presented to support this hypothesis.
The effects of treating wild-type OVA (ovalbumin)-sensitized/challenged mice with ethyl-3,4-dihydroxybenzoate (EDHB), which upregulate HIF, on CCL2 expression, were determined. Mice conditionally knocked out for HIF-1β was examined for their ability to mount an allergic inflammatory response and CCL2 expression in the lung after intratracheal exposure to ovalbumin. The association of HIF-1α and CCL2 levels was also measured in endobronchial biopsies and bronchial fluid of asthma patients after challenge.
We show that both HIF-1α and CCL2 were upregulated during an OVA (ovalbumin)-induced allergic response in mice. The levels of HIF-1α and CCL2 were significantly increased following treatment with a pharmacological agent which upregulates HIF-1α, ethyl-3,4-dihydroxybenzoate (EDHB). In contrast, the expression levels of HIF-1α and CCL2 were decreased in the lungs of mice that have been conditionally knocked out for ARNT (HIF-1β) following sensitization with OVA when compared to levels in wild type mice. In asthma patients, the levels of HIF-1α and CCL2 increased after challenge with the allergen.
These data suggest that CCL2 expression is regulated, in part, by HIF-1 in the lung. These findings also demonstrate that both CCL2 and HIF-1 are implicated in the pathogenesis of allergic airway inflammation.
Allergic airway inflammation; Asthma; Hypoxia inducible factor-1; CCL2; Arylhydrocarbon receptor nuclear translocator
NF-kB is a critical transcription factor for the production of many inflammatory cytokines. It is activated in the airway epithelium of human asthmatics and in mice after allergic stimulation. To examine the role of NF-kB activation in allergic inflammation we generated transgenic mouse lines that allowed for the inducible stimulation of NF-kB in airway epithelial cells. After allergic sensitization with ovalbumin and alum, mice were challenged daily with ovalbumin aerosols and NF-kB was activated in airway epithelium by administration of doxycycline. Enhancement of airway epithelial NF-kB expression alone did not lead to increased airway responsiveness to methacholine. However induction of epithelial NF-kB during allergic inflammation caused airway hyperresponsiveness, increased airway neutrophilic and lymphocytic inflammation and goblet cell hyperplasia. Accompanying the exaggerated inflammation was an increase in the cytokines, G-CSF, IL-15, and KC. Interestingly, the counter regulatory interleukin, IL-10, was suppressed by NF-kB activation. The epithelial NF-kB dependent modulation of these cytokines provides a plausible explanation for the increased inflammation seen with overexpression of NF-kB. Modulation of airway epithelial NF-kB activation enhances the airway hyperresponsiveness and mucus secretion found in the mouse lung during allergic inflammation. NF-kB represents a potential target for pharmacologic intervention in human asthma.
Regulatory T cells (Treg) play a decisive role in many diseases including asthma and allergen-induced lung inflammation. However, little progress has been made developing new therapeutic strategies for pulmonary disorders. In the current study we demonstrate that cytokine:antibody complexes of IL-2 and anti-IL-2 mAb reduce the severity of allergen-induced inflammation in the lung by expanding Tregs in vivo. Unlike rIL-2 or anti-IL-2 mAb treatment alone, IL-2:anti-IL-2 complexes dampened airway inflammation and eosinophilia while suppressing IL-5 and eotaxin-1 production. Mucus production, airway hyperresponsiveness to methacholine, and parenchymal tissue inflammation were also dramatically reduced following IL-2:anti-IL-2 treatment. The suppression in allergic airway disease was associated with a marked expansion of Tregs (IL-10+CD4+CD25+ and Foxp3+CD4+CD25+) in the tissues, with a corresponding decrease in effector T cell responses. The ability of IL-2:anti-IL-2 complexes to suppress airway inflammation was dependent on Treg-derived IL-10, as IL-10+/+, but not IL-10-/- Tregs, were capable of mediating the suppression. Furthermore, a therapeutic protocol using a model of established airway allergy highlighted the ability of IL-2:anti-IL-2 complexes to expand Tregs and prevent successive airway inflammation and airway hyperresponsiveness. This study suggests that endogenous Treg therapy may be a useful tool to combat the rising incidence of allergic airway disease.
Rationale: Ventilator-induced lung injury (VILI) significantly contributes to mortality in patients with acute respiratory distress syndrome, the most severe form of acute lung injury. Understanding the molecular basis for response to cyclic stretch (CS) and its derangement during high-volume ventilation is of high priority.
Objectives: To identify specific molecular regulators involved in the development of VILI.
Methods: We undertook a comparative examination of cis-regulatory sequences involved in the coordinated expression of CS-responsive genes using microarray analysis. Analysis of stretched versus nonstretched cells identified significant enrichment for genes containing putative binding sites for the transcription factor activating transcription factor 3 (ATF3). To determine the role of ATF3 in vivo, we compared the response of ATF3 gene–deficient mice to wild-type mice in an in vivo model of VILI.
Measurements and Main Results: ATF3 protein expression and nuclear translocation is increased in the lung after mechanical ventilation in wild-type mice. ATF3-deficient mice have greater sensitivity to mechanical ventilation alone or in conjunction with inhaled endotoxin, as demonstrated by increased cell infiltration and proinflammatory cytokines in the lung and bronchoalveolar lavage, and increased pulmonary edema and indices of tissue injury. The expression of stretch-responsive genes containing putative ATF3 cis-regulatory regions was significantly altered in ATF3-deficient mice.
Conclusions: ATF3 deficiency confers increased sensitivity to mechanical ventilation alone or in combination with inhaled endotoxin. We propose ATF3 acts to counterbalance CS and high volume–induced inflammation, dampening its ability to cause injury and consequently protecting animals from injurious CS.
mechanotransduction; transcriptional profiling; acute respiratory distress syndrome; bioinformatics; transgenic mice
Obesity is an important risk factor for asthma but the mechanistic basis for this association is not well understood. In the current study, the impact of obesity on lung inflammatory responses after allergen exposure was investigated. C57BL/6 mice maintained on a high-fat diet (HFD) or a normal diet (ND) after weaning were sensitized and challenged with cockroach allergen (CRA). Airway inflammation was assessed based on inflammatory cell recruitment, measurement of lung Th1-Th2 cytokines, chemokines, eicosanoids, and other proinflammatory mediators as well as airway hyperresponsiveness (AHR). CRA-challenged mice fed a HFD exhibited significantly decreased allergen-induced airway eosinophilia along with reduced lung IL-5, IL-13, LTC4, CCL11, and CCL2 levels as well as reduced mucus secretion and smooth muscle mass compared to ND fed mice. However, allergen-challenged HFD fed mice demonstrated significantly increased PAI-1 and reduced PGE2 levels in the lung relative to corresponding ND fed mice. Interestingly, saline-exposed HFD fed mice demonstrated elevated baseline levels of TGF-α1, arginase-1, hypoxia-inducible factor-1α, and lung collagen expression associated with decreased lung function compared to corresponding ND fed mice. These studies indicate that a HFD inhibits airway eosinophilia while altering levels of PAI-1 and PGE2 in response to CRA in mice. Further, a HFD can lead to the development of lung fibrosis even in the absence of allergen exposure which could be due to innate elevated levels of specific profibrotic factors, potentially affecting lung function during asthma.
allergic inflammation; fibrogenic factors; obesity; reduced eosinophilia; Th2 cytokines
Background: Humans with asthma display considerable heterogeneity with regard to T helper (Th) 2–associated eosinophilic and Th17-associated neutrophilic inflammation, but the impact of the environment on these different forms of asthma is poorly understood.
Objective: We studied the nature and longevity of asthma-like responses triggered by inhalation of allergen together with environmentally relevant doses of inhaled lipopolysaccharide (LPS).
Methods: Ovalbumin (OVA) was instilled into the airways of mice together with a wide range of LPS doses. Following a single OVA challenge, or multiple challenges, animals were assessed for pulmonary cytokine production, airway inflammation, and airway hyperresponsiveness (AHR).
Results: Mice instilled with OVA together with very low doses (≤ 10–3 μg) of LPS displayed modest amounts of Th2 cytokines, with associated airway eosinophilia and AHR after a single challenge, and these responses were sustained after multiple OVA challenges. When the higher but still environmentally relevant dose of 10–1 μg LPS was used, mice initially displayed similar Th2 responses, as well as Th17-associated neutrophilia. After multiple OVA challenges, however, the 10–1 μg LPS animals also accumulated large numbers of allergen-specific T regulatory (Treg) cells with high levels of inducible co-stimulatory molecule (ICOS). As a result, asthma-like features in these mice were shorter-lived than in mice sensitized using lower doses of LPS.
Conclusions: The nature and longevity of Th2, Th17, and Treg immune responses to inhaled allergen are dependent on the quantity of LPS inhaled at the time of allergic sensitization. These findings might account in part for the heterogeneity of inflammatory infiltrates seen in lungs of asthmatics.
Citation: Whitehead GS, Thomas SY, Cook DN. 2014. Modulation of distinct asthmatic phenotypes in mice by dose-dependent inhalation of microbial products. Environ Health Perspect 122:34–42; http://dx.doi.org/10.1289/ehp.1307280
Maladaptive, Th2-polarized inflammatory responses are integral to the pathogenesis of allergic asthma. As regulators of T cell activation, dendritic cells (DCs) are important mediators of allergic asthma, yet the precise signals which render endogenous DCs “pro-asthmatic”, and the extent to which these signals are regulated by the pulmonary environment and host genetics, remains unclear. Comparative phenotypic and functional analysis of pulmonary DC populations in mice susceptible (A/J), or resistant (C3H) to experimental asthma, revealed that susceptibility to airway hyperresponsiveness is associated with preferential myeloid DC (mDC) allergen uptake, and production of Th17-skewing cytokines (IL-6, IL-23), whereas resistance is associated with increased allergen uptake by plasmacytoid DCs. Surprisingly, adoptive transfer of syngeneic HDM-pulsed bone marrow derived mDCs (BMDCs) to the lungs of C3H mice markedly enhanced lung IL-17A production, and rendered them susceptible to allergen-driven airway hyperresponsiveness. Characterization of these BMDCs revealed levels of antigen uptake, and Th17 promoting cytokine production similar to that observed in pulmonary mDCs from susceptible A/J mice. Collectively these data demonstrate that the lung environment present in asthma-resistant mice promotes robust pDC allergen uptake, activation, and limits Th17-skewing cytokine production responsible for driving pathologic T cell responses central to the development of allergen-induced airway hyperresponsiveness.
Rationale: There is conflicting information about the development and resolution of airway inflammation and airway hyperresponsiveness (AHR) after repeated airway exposure to allergen in sensitized mice.
Methods: Sensitized BALB/c and C57BL/6 mice were exposed to repeated allergen challenge on 3, 7, or 11 occasions. Airway function in response to inhaled methacholine was monitored; bronchoalveolar lavage fluid inflammatory cells were counted; and goblet cell metaplasia, peribronchial fibrosis, and smooth muscle hypertrophy were quantitated on tissue sections. Bone marrow–derived dendritic cells were generated after differentiation of bone marrow cells in the presence of growth factors.
Results: Sensitization to ovalbumin (OVA) in alum, followed by three airway exposures to OVA, induced lung eosinophilia, goblet cell metaplasia, mild peribronchial fibrosis, and peribronchial smooth muscle hypertrophy; increased levels of interleukin (IL)-4, IL-5, IL-13, granulocyte-macrophage colony–stimulating factor, transforming growth factor-β1, eotaxin-1, RANTES (regulated on activation, normal T-cell expressed and secreted), and OVA-specific IgG1 and IgE; and resulted in AHR. After seven airway challenges, development of AHR was markedly decreased as was the production of IL-4, IL-5, and IL-13. Levels of IL-10 in both strains and the level of IL-12 in BALB/c mice increased. After 11 challenges, airway eosinophilia and peribronchial fibrosis further declined and the cytokine and chemokine profiles continued to change. At this time point, the number of myeloid dendritic cells and expression of CD80 and CD86 in lungs were decreased compared with three challenges. After 11 challenges, intratracheal instillation of bone marrow–derived dendritic cells restored AHR and airway eosinophilia.
Conclusions: These data suggest that repeated allergen exposure leads to progressive decreases in AHR and allergic inflammation, through decreases in myeloid dendritic cell numbers.
airway hyperresponsiveness; chronic asthma; cytokine; dendritic cells; eosinophil
IL-22 is a Th17/Th22 cytokine that is increased in asthma. However, recent animal studies showed controversial findings in the effects of IL-22 in allergic asthma. To determine the role of IL-22 in ovalbumin-induced allergic inflammation we generated inducible lung-specific IL-22 transgenic mice. Transgenic IL-22 expression and signaling activity in the lung were determined. Ovalbumin (OVA)-induced pulmonary inflammation, immune responses, and airway hyperresponsiveness (AHR) were examined and compared between IL-22 transgenic mice and wild type controls. Following doxycycline (Dox) induction, IL-22 protein was readily detected in the large (CC10 promoter) and small (SPC promoter) airway epithelial cells. IL-22 signaling was evidenced by phosphorylated STAT3. After OVA sensitization and challenge, compared to wild type littermates, IL-22 transgenic mice showed decreased eosinophils in the bronchoalveolar lavage (BAL), and in lung tissue, decreased mucus metaplasia in the airways, and reduced AHR. Among the cytokines and chemokines examined, IL-13 levels were reduced in the BAL fluid as well as in lymphocytes from local draining lymph nodes of IL-22 transgenic mice. No effect was seen on the levels of serum total or OVA-specific IgE or IgG. These findings indicate that IL-22 has immune modulatory effects on pulmonary inflammatory responses in allergen-induced asthma.
Chronic asthma is often associated with neutrophilic infiltration in the airways. Neutrophils contain elastase, a potent secretagogue in the airways, nonetheless the role for neutrophil elastase as well as neutrophilic inflammation in allergen-induced airway responses is not well defined. In this study, we have investigated the impact of neutrophil elastase inhibition on the development of allergic airway inflammation and airway hyperresponsiveness (AHR) in previously sensitized and challenged mice.
BALB/c mice were sensitized and challenged (primary) with ovalbumin (OVA). Six weeks later, a single OVA aerosol (secondary challenge) was delivered and airway inflammation and airway responses were monitored 6 and 48 hrs later. An inhibitor of neutrophil elastase was administered prior to secondary challenge.
Mice developed a two-phase airway inflammatory response after secondary allergen challenge, one neutrophilic at 6 hr and the other eosinophilic, at 48 hr. PAR-2 expression in the lung tissues was enhanced following secondary challenge, and that PAR-2 intracellular expression on peribronchial lymph node (PBLN) T cells was also increased following allergen challenge of sensitized mice. Inhibition of neutrophil elastase significantly attenuated AHR, goblet cell metaplasia, and inflammatory cell accumulation in the airways following secondary OVA challenge. Levels of IL-4, IL-5 and IL-13, and eotaxin in BAL fluid 6 hr after secondary allergen challenge were significantly suppressed by the treatment. At 48 hr, treatment with the neutrophil elastase inhibitor significantly reduced the levels of IL-13 and TGF-β1 in the BAL fluid. In parallel, in vitro IL-13 production was significantly inhibited in spleen cells from sensitized mice.
These data indicate that neutrophil elastase plays an important role in the development of allergic airway inflammation and hyperresponsiveness, and would suggest that the neutrophil elastase inhibitor reduced AHR to inhaled methacholine indicating the potential for its use as a modulator of the immune/inflammatory response in both the neutrophil- and eosinophil-dominant phases of the response to secondary allergen challenge.
Neutrophil; Elastase; Airway; Hyperresponsiveness; Asthma
There is convincing evidence that endoplasmic reticulum (ER) stress is implicated in the pathogenesis of diabetes and its complications; however, the mechanisms are not fully understood. This study aimed to dissect the role and signalling pathways of activating transcription factor 4 (ATF4) in ER-stress-associated endothelial inflammation and diabetic retinopathy.
ER stress and ATF4 activity were manipulated by complementary pharmacological and genetic approaches in cultured retinal endothelial (TR-iBRB) cells. Diabetes was induced by streptozotocin in heterozygous Atf4 knockout and wild-type mice. ER stress markers, inflammatory cytokines and adhesion molecules, activation of the signal transducer and activator of transcription 3 (STAT3) pathway, and retinal vascular permeability were measured.
High-glucose treatment resulted in rapid induction of ER stress, activation of ATF4, and increased production of inflammatory factors in TR-iBRB cells. Suppressing ER stress or inhibiting ATF4 activity markedly attenuated high-glucose-induced production of intercellular adhesion molecule 1, TNF-α and vascular endothelial growth factor. Conversely, enhancing ER stress or overexpressing Atf4 was sufficient to induce endothelial inflammation, which was, at least in part, through activation of the STAT3 pathway. Furthermore, knockdown of the Stat3 gene or inhibiting STAT3 activity restored ER homeostasis in cells exposed to high glucose and prevented ATF4 activation, suggesting that STAT3 is required for high-glucose-induced ER stress. Finally, we showed that downregulation of Atf4 significantly ameliorated retinal inflammation, STAT3 activation and vascular leakage in a mouse model of type 1 diabetes.
Taken together, our data reveal a pivotal role of ER stress and the ATF4/STAT3 pathway in retinal endothelial inflammation in diabetic retinopathy.
Activating transcription factor 4; Diabetic retinopathy; Endoplasmic reticulum; Endothelial cells; Inflammation
Allergic asthma is characterized by airway hyperresponsiveness, inflammation, and a cellular infiltrate dominated by eosinophils. Numerous epidemiological studies have related the exacerbation of allergic asthma with an increase in ambient inhalable particulate matter from air pollutants. This is because inhalable particles efficiently deliver airborne allergens deep into the airways, where they can aggravate allergic asthma symptoms. However, the cellular mechanisms by which inhalable particulate allergens (pAgs) potentiate asthmatic symptoms remain unknown, in part because most in vivo and in vitro studies exploring the pathogenesis of allergic asthma use soluble allergens (sAgs). Using a mouse model of allergic asthma, we found that, compared with their sAg counterparts, pAgs triggered markedly heightened airway hyperresponsiveness and pulmonary eosinophilia in allergen-sensitized mice. Mast cells (MCs) were implicated in this divergent response, as the differences in airway inflammatory responses provoked by the physical nature of the allergens were attenuated in MC-deficient mice. The pAgs were found to mediate MC-dependent responses by enhancing retention of pAg/IgE/FcεRI complexes within lipid raft–enriched, CD63+ endocytic compartments, which prolonged IgE/FcεRI-initiated signaling and resulted in heightened cytokine responses. These results reveal how the physical attributes of allergens can co-opt MC endocytic circuitry and signaling responses to aggravate pathological responses of allergic asthma in mice.
Phosphoinositide 3-kinase (PI3K)/Akt pathway is linked to the development of asthma. Anti-malarial drug artesunate is a semi-synthetic derivative of artemisinin, the principal active component of a medicinal plant Artemisia annua, and has been shown to inhibit PI3K/Akt activity. We hypothesized that artesunate may attenuate allergic asthma via inhibition of the PI3K/Akt signaling pathway.
Female BALB/c mice sensitized and challenged with ovalbumin (OVA) developed airway inflammation. Bronchoalveolar lavage fluid was assessed for total and differential cell counts, and cytokine and chemokine levels. Lung tissues were examined for cell infiltration and mucus hypersecretion, and the expression of inflammatory biomarkers. Airway hyperresponsiveness was monitored by direct airway resistance analysis. Artesunate dose-dependently inhibited OVA-induced increases in total and eosinophil counts, IL-4, IL-5, IL-13 and eotaxin levels in bronchoalveolar lavage fluid. It attenuated OVA-induced lung tissue eosinophilia and airway mucus production, mRNA expression of E-selectin, IL-17, IL-33 and Muc5ac in lung tissues, and airway hyperresponsiveness to methacholine. In normal human bronchial epithelial cells, artesunate blocked epidermal growth factor-induced phosphorylation of Akt and its downstream substrates tuberin, p70S6 kinase and 4E-binding protein 1, and transactivation of NF-κB. Similarly, artesunate blocked the phosphorylation of Akt and its downstream substrates in lung tissues from OVA-challenged mice. Anti-inflammatory effect of artesunate was further confirmed in a house dust mite mouse asthma model.
Artesunate ameliorates experimental allergic airway inflammation probably via negative regulation of PI3K/Akt pathway and the downstream NF-κB activity. These findings provide a novel therapeutic value for artesunate in the treatment of allergic asthma.
ORMDL3 (orosomucoid like 3) has been strongly linked with asthma in genetic association studies. As allergen challenge induces lung ORMDL3 expression in WT mice, we have generated human ORMDL3 Zona Pellucida 3 Cre (hORMDL3zp3-Cre) mice that overexpress human ORMDL3 universally to investigate the role of ORMDL3 in regulating airway inflammation and remodeling. These hORMDL3zp3-Cre mice have significantly increased levels of airway remodeling including increased airway smooth muscle, subepithelial fibrosis, and mucus. hORMDL3zp3-Cre mice had spontaneous increased AHR to methacholine compared to WT mice. This increased airway remodeling was associated with selective activation of the Unfolded Protein Response pathway transcription factor ATF6 (but not Ire1 or PERK). The ATF6 target gene SERCA2b, implicated in airway remodeling in asthma, was strongly induced in the lungs of hORMDL3zp3-Cre mice. In addition, increased levels of expression of genes associated with airway remodeling (TGF-β1, ADAM8) were detected in airway epithelium of these mice. Increased levels of airway remodeling preceded increased levels of airway inflammation in hORMDL3zp3-Cre mice. hORMDL3zp3-Cre mice had increased levels of IgE, with no change in levels of IgG, IgM, and IgA. These studies provide evidence that ORMDL3 plays an important role in vivo in airway remodeling potentially through ATF6 target genes such as SERCA2b, and/or through ATF6 independent genes (TGF-β1, ADAM8).
Antigen desensitization through oral tolerance is becoming an increasingly attractive treatment option for allergic diseases. However, the mechanism(s) by which tolerization is achieved remain poorly defined. In this study we endeavored to induce oral tolerance to cockroach allergen (CRA: a complex mixture of insect components) in order to ameliorate asthma-like, allergic pulmonary inflammation.
We compared the pulmonary inflammation of mice which had received four CRA feedings prior to intratracheal allergen sensitization and challenge to mice fed PBS on the same time course. Respiratory parameters were assessed by whole body unrestrained plethysmography and mechanical ventilation with forced oscillation. Bronchoalveolar lavage fluid (BAL) and lung homogenate (LH) were assessed for cytokines and chemokines by ELISA. BAL inflammatory cells were also collected and examined by light microscopy.
CRA feeding prior to allergen sensitization and challenge led to a significant improvement in respiratory health. Airways hyperreactivity measured indirectly via enhanced pause (Penh) was meaningfully reduced in the CRA-fed mice compared to the PBS fed mice (2.3 ± 0.4 vs 3.9 ± 0.6; p = 0.03). Directly measured airways resistance confirmed this trend when comparing the CRA-fed to the PBS-fed animals (2.97 ± 0.98 vs 4.95 ± 1.41). This effect was not due to reduced traditional inflammatory cell chemotactic factors, Th2 or other cytokines and chemokines. The mechanism of improved respiratory health in the tolerized mice was due to significantly reduced eosinophil numbers in the bronchoalveolar lavage fluid (43300 ± 11445 vs 158786 ± 38908; p = 0.007) and eosinophil specific peroxidase activity in the lung homogenate (0.59 ± 0.13 vs 1.19 ± 0.19; p = 0.017). The decreased eosinophilia was likely the result of increased IL-10 in the lung homogenate of the tolerized mice (6320 ± 354 ng/mL vs 5190 ± 404 ng/mL, p = 0.02).
Our results show that oral tolerization to CRA can improve the respiratory health of experimental mice in a CRA-induced model of asthma-like pulmonary inflammation by reducing pulmonary eosinophilia.
It is well-established that bacterial and viral infections have an exacerbating effect on allergic asthma, particularly aggravating respiratory symptoms, such as airway hyperresponsiveness (AHR). The mechanism by which these infections alter AHR is unclear, but some studies suggest that Toll-like receptors (TLRs) play a role. In this study, we investigated the impact of TLR3 and TLR4 ligands on AHR and airway inflammation in a model of pre-established allergic inflammation. Female BALB/c mice were sensitised and challenged intranasally (i.n.) with either PBS or ovalbumin (OVA) and subsequently i.n. challenged with poly (I:C) (TLR3) or LPS (TLR4) for four consecutive days. The response to methacholine was measured in vivo; cellular and inflammatory mediators were measured in blood, lung tissue and broncheoalveolar lavage fluid (BALF). OVA challenge resulted in an increase in AHR to methacholine, as well as increased airway eosinophilia and TH2 cytokine production. Subsequent challenge with TLR agonists resulted in a significant increase in AHR, but decreased TLR-specific cellular inflammation and production of immune mediators. Particularly evident was a decline in LPS-induced neutrophilia and neutrophil-associated cytokines following LPS and poly (I:C) treatment. The present data indicates that TLRs may play a pivotal role in AHR in response to microbial infection in allergic lung inflammation. These data also demonstrate that aggravated AHR occurs in the absence of an exacerbation in airway inflammation and that allergic inflammation impedes a subsequent inflammatory response to TLRs. These results may parallel clinical signs of microbial asthma exacerbation, including an extended duration of illness and increased respiratory symptoms.
Chlamydia pneumoniae is associated with chronic inflammatory lung diseases like bronchial asthma and chronic obstructive pulmonary disease. The existence of a causal link between allergic airway disease and C. pneumoniae is controversial. A mouse model was used to address the question of whether preceding C. pneumoniae lung infection and recovery modifies the outcome of experimental allergic asthma after subsequent sensitization with house dust mite (HDM) allergen. After intranasal infection, BALB/c mice suffered from pneumonia characterized by an increased clinical score, reduction of body weight, histopathology, and a bacterial load in the lungs. After 4 weeks, when infection had almost resolved clinically, HDM allergen sensitization was performed for another 4 weeks. Subsequently, mice were subjected to a methacholine hyperresponsiveness test and sacrificed for further analyses. As expected, after 8 weeks, C. pneumoniae-specific antibodies were detectable only in infected mice and the titer was significantly higher in the C. pneumoniae/HDM allergen-treated group than in the C. pneumoniae/NaCl group. Intriguingly, airway hyperresponsiveness and eosinophilia in bronchoalveolar lavage fluid were significantly lower in the C. pneumoniae/HDM allergen-treated group than in the mock/HDM allergen-treated group. We did observe a relationship between experimental asthma and chlamydial infection. Our results demonstrate an influence of sensitization to HDM allergen on the development of a humoral antibacterial response. However, our model demonstrates no increase in the severity of experimental asthma to HDM allergen as a physiological allergen after clinically resolved severe chlamydial lung infection. Our results rather suggest that allergic airway disease and concomitant cellular changes in mice are decreased following C. pneumoniae lung infection in this setting.
Pim kinases are a family of serine/threonine kinases whose activity can be induced by cytokines involved in allergy and asthma. These kinases play a role in cell survival and proliferation, but have not been examined, to the best of our knowledge, in the development of allergic disease. This study sought to determine the role of Pim1 kinase in the development of allergic airway responses. Mice were sensitized and challenged with antigen (primary challenge), or were sensitized, challenged, and rechallenged with allergen in a secondary model. To assess the role of Pim1 kinase, a small molecule inhibitor was administered orally after sensitization and during the challenge phase. Airway responsiveness to inhaled methacholine, airway and lung inflammation, cell composition, and cytokine concentrations were assessed. Lung Pim1 kinase concentrations were increased after ovalbumin sensitization and challenge. In the primary allergen challenge model, treatment with the Pim1 kinase inhibitor after sensitization and during airway challenges prevented the development of airway hyperresponsiveness, eosinophilic airway inflammation, and goblet cell metaplasia, and increased Th2 cytokine concentrations in bronchoalveolar fluid in a dose-dependent manner. These effects were also demonstrated after a secondary allergen challenge, where lung allergic disease was established before treatment. After treatment with the inhibitor, a significant reduction was evident in the number of CD4+ and CD8+ T cells and concentrations of cytokines in the airways. The inhibition of Pim1 kinase was effective in preventing the development of airway hyperresponsiveness, airway inflammation, and cytokine production in allergen-sensitized and allergen-challenged mice. These data identify the important role of Pim1 kinase in the full development of allergen-induced airway responses.
airway hyperresponsiveness; inflammation; Pim1 kinase; T cells
Asthma is associated with airway hyperresponsiveness and enhanced T-cell number/activity on one hand and increased levels of exhaled nitric oxide (NO) with expression of inducible NO synthase (iNOS) on the other hand. These findings are in paradox, as NO also relaxes airway smooth muscle and has immunosuppressive properties. The exact role of the endothelial NOS (eNOS) isoform in asthma is still unknown. We hypothezised that a delicate regulation in the production of NO and its bioactive forms by eNOS might be the key to the pathogenesis of asthma.
The contribution of eNOS on the development of asthmatic features was examined. We used transgenic mice that overexpress eNOS and measured characteristic features of allergic asthma after sensitisation and challenge of these mice with the allergen ovalbumin.
eNOS overexpression resulted in both increased eNOS activity and NO production in the lungs. Isolated thoracic lymph nodes cells from eNOS overexpressing mice that have been sensitized and challenged with ovalbumin produced significantly less of the cytokines IFN-γ, IL-5 and IL-10. No difference in serum IgE levels could be found. Further, there was a 50% reduction in the number of lymphocytes and eosinophils in the lung lavage fluid of these animals. Finally, airway hyperresponsiveness to methacholine was abolished in eNOS overexpressing mice.
These findings demonstrate that eNOS overexpression attenuates both airway inflammation and airway hyperresponsiveness in a model of allergic asthma. We suggest that a delicate balance in the production of bioactive forms of NO derived from eNOS might be essential in the pathophysiology of asthma.
Airflow in the lungs of patients with allergic asthma is impaired by excessive mucus production and airway smooth muscle contractions. Elevated levels of the cytokines IL-4 and IL-13 are associated with this pathology. In vitro studies have suggested that IL-4 receptor alpha (IL-4Rα) signalling on smooth muscle cells is critical for airway inflammation and airway hyperresponsiveness.
In order to define the contribution of IL-4 and IL-13 to the onset of asthmatic pathology the role of their key receptor IL-4Rα in smooth muscle cells was examined in vivo.
By using transgenic SMC-MHCcreIL-4Rα−/lox mice deficient for IL-4Rα in smooth muscle cells, in vivo effects of impaired IL-4Rα signalling in smooth muscle cells on the outcome of asthmatic disease were investigated for the first time. Allergic asthma was introduced in mice by repeated sensitisation with ovalbumin/aluminium hydroxide on days 0, 7 and 14 followed by intranasal allergen challenge on days 21–23. Mice were investigated for the presence of airway hyperresponsiveness, airway inflammation, allergen specific antibody production, Th2 type cytokine responses and lung pathology.
Airway hyperresponsiveness, airway inflammation, mucus production, Th2 cytokine production and specific antibody responses were unaffected in SMC-MHCcreIL-4Rα−/lox mice when compared to control animals.
The impairment of IL-4Rα on smooth muscle cells had no effect on major aetiological markers of allergic asthma. These findings suggest that IL-4Rα responsiveness in airway smooth muscle cells during the early phase of allergic asthma is not, as suggested, necessary for the outcome of the disease.
Therapies targeting the IL-4Rα might have no direct effect on smooth muscle cells in an allergic asthma response.
Smooth muscle cell; Allergy; Asthma; Cytokine Receptors; IL-4; IL-13; gene-deficient mice
Identifying therapeutic drugs that block the release or effects of T-helper type 2 (Th2) cytokines after allergen exposure is an important goal for the treatment of allergic inflammatory diseases including asthma. We recently showed, using a murine model of allergic airway inflammation, that poly(ADP-ribose) polymerase (PARP) plays an important role in the pathogenesis of asthma-related lung inflammation. PARP inhibition, by single injection of a novel inhibitor, thieno[2,3-c]isoquinolin-5-one (TIQ-A), before ovalbumin (OVA) challenge, prevented airway eosinophilia in C57BL/6 mice with concomitant suppression of Th2 cytokine production and mucus secretion.
To evaluate the efficacy of the drug when it is given after OVA challenge for its possible therapeutic potential.
This study was conducted using a murine model of allergic airway inflammation.
A single injection of TIQ-A (6 mg/kg) one or 6 h post-allergen challenge conferred similar reduction in OVA challenge-induced eosinophilia. More significantly, post-allergen challenge administration of the drug exerted even better suppression on the production of IL-4, IL-5, IL-13, and IgE and prevented airway hyperresponsiveness to inhaled-methacholine. The significant decrease in IL-13 was accompanied by a complete absence of airways mucus production indicating a potential protection against allergen-induced airway remodelling.
The coincidence of the inflammation trigger and the time of drug administration appear to be important for the drug’s more pronounced protection. The observed time window for efficacy, 1 or 6 h after allergen challenge may be of great clinical interest. These findings may provide a novel therapeutic strategy for the treatment of allergic airway inflammation, including asthma.
airway hyperresponsiveness; allergy; cytokines; eosinophils; inflammation; interleukin; lung; mucus; PARP; therapeutic potential