Molecular pathways underlying lung-brain axis signaling in asthma: Relevance for psychopathology and neuroinflammation.

BACKGROUND: Accumulating evidence indicates that asthma has systemic effects and affects brain function. Although airway inflammation is proposed to initiate afferent communications with the brain, the signaling pathways have not been established. OBJECTIVE: We sought to identify the cellular and molecular pathways involved in afferent lung-brain communication during airway inflammation in asthma. METHODS: In 23 adults with mild asthma, segmental bronchial provocation with allergen (SBP-Ag) was used to provoke airway inflammation and retrieve bronchoalveolar lavage fluid for targeted protein analysis and RNA sequencing to determine gene expression profiles. Neural responses to emotional cues in nodes of the salience network were assessed with functional magnetic resonance imaging at baseline and 48 hours after SBP-Ag. RESULTS: Cell deconvolution and gene coexpression network analysis identified 11 cell-associated gene modules that changed in response to SBP-Ag. SBP-Ag increased bronchoalveolar lavage eosinophils and expression of an eosinophil-associated module enriched for genes related to TH17-type inflammation (eg, IL17A), as well as cell proliferation in lung and brain (eg, NOTCH1, VEGFA, and LIF). Increased expression of genes in this module, as well as several TH17-type inflammation-related proteins, was associated with an increase from baseline in salience network reactivity. CONCLUSIONS: Our results identify a specific inflammatory pathway linking asthma-related airway inflammation and emotion-related neural function. Systemically, TH17-type inflammation has been implicated in both depression and neuroinflammation, with impacts on long-term brain health. Thus, our data emphasize that inflammation in the lung in asthma may have profound effects outside of the lung that may be targetable with novel therapeutic approaches.

Development of Adaptive Immunity and Its Role in Lung Remodeling.

Asthma is characterized by airflow limitations resulting from bronchial closure, which can be either reversible or fixed due to changes in airway tissue composition and structure, also known as remodeling. Airway remodeling is defined as increased presence of mucins-producing epithelial cells, increased thickness of airway smooth muscle cells, angiogenesis, increased number and activation state of fibroblasts, and extracellular matrix (ECM) deposition. Airway inflammation is believed to be the main cause of the development of airway remodeling in asthma. In this chapter, we will review the development of the adaptive immune response and the impact of its mediators and cells on the elements defining airway remodeling in asthma.

Neuroimaging and biomarker evidence of neurodegeneration in asthma.

BACKGROUND: Epidemiologic studies have shown that Alzheimer's disease (AD) and related dementias (ADRD) are seen more frequently with asthma, especially with greater asthma severity or exacerbation frequency. OBJECTIVE: To examine the changes in brain structure that may underlie this phenomenon, we examined diffusion-weighted magnetic resonance imaging (dMRI) and blood-based biomarkers of AD (phosphorylated tau 181, p-Tau181), neurodegeneration (neurofilament light chain, NfL), and glial activation (glial fibrillary acidic protein, GFAP). METHODS: dMRI data were obtained in 111 individuals with asthma, ranging in disease severity from mild to severe, and 135 healthy controls. Regression analyses were used to test the relationships between asthma severity and neuroimaging measures, as well as AD pathology, neurodegeneration, and glial activation, indexed by plasma p-Tau181, NfL, and GFAP, respectively. Additional relationships were tested with cognitive function. RESULTS: Asthma participants had widespread and large-magnitude differences in several dMRI metrics, which were indicative of neuroinflammation and neurodegeneration, and which were robustly associated with GFAP and, to a lesser extent, NfL. The AD biomarker p-Tau181 was only minimally associated with neuroimaging outcomes. Further, asthma severity was associated with deleterious changes in neuroimaging outcomes, which in turn were associated with slower processing speed, a test of cognitive performance. CONCLUSIONS: Asthma, particularly when severe, is associated with characteristics of neuroinflammation and neurodegeneration, and may be a potential risk factor for neural injury and cognitive dysfunction. There is a need to determine how asthma may affect brain health and whether treatment directed toward characteristics of asthma associated with these risks can mitigate these effects.

Airway fibrin formation cascade in allergic asthma exacerbation: implications for inflammation and remodeling.

BACKGROUND: Airway remodeling in patients with asthma, which leads to a decline in pulmonary function, is likely the result of repeated exacerbations often provoked by aeroallergen exposures. Aeroallegen exposure triggers a stereotypic response orchestrated by growth factor cytokines and other protein mediators. This results in a late-phase allergic reaction characterized by vascular permeability, recruitment of activated leukocytes, and activation of structural cells of the airway. The spectrum of protein mediators and their functions are incompletely understood. METHODS: Bronchoalveolar lavage fluid (BALF) samples were obtained from 12 volunteers who exhibited robust eosinophilic recruitment following segmental bronchial provocation with allergen (SBP-Ag). We systematically identified and quantified proteins in BALF using high-performance liquid chromatography-high-resolution mass spectrometry (LC-MS/MS) followed by pathway analysis and correlations with airway physiology. RESULTS: Pairwise analysis of protein abundance in BALF pre- vs post-SBP-Ag revealed that 55 proteins were upregulated and 103 proteins were downregulated. We observed enrichment of groups of proteins mapping to hemostasis/fibrin clot, platelet activation, lipoprotein assembly, neutrophil degranulation proteins, and acute-phase inflammation-airway remodeling pathways. The abundances of F2 and Fibrinogen γ (FGG) correlated with eosinophil numbers, whereas SERPINA3 negatively correlated with change in FeNO. The coagulation proteins F2 and KNG negatively correlated with FN1 an index of airway remodeling. Interestingly, patients with lower FEV1 showed distinct allergen-induced patterns of 8 BALF proteins, including MUC1, alarmins (HSPB1), and actin polymerization factors. CONCLUSIONS: Protein abundance of the fibrin formation cascade, platelet activation and remodeling are associated with late-phase leukocyte numbers and markers of remodeling. Patients with lower FEV1 have distinct dynamic responses to allergen.

Increased IL-6 and Potential IL-6 trans-signalling in the airways after an allergen challenge.

BACKGROUND: In asthma, IL-6 is a potential cause of enhanced inflammation, tissue damage and airway dysfunction. IL-6 signalling is regulated by its receptor, which is composed of two proteins, IL-6R and GP130. In addition to their membrane form, these two proteins may be found as extracellular soluble forms. The interaction of IL-6 with soluble IL-6R (sIL-6R) can trigger IL-6 trans-signalling in cells lacking IL-6R. Conversely, the soluble form of GP130 (sGP130) competes with its membrane form to inhibit IL-6 trans-signalling. OBJECTIVES: We aimed to analyse IL-6 trans-signalling proteins in the airways of subjects after an allergen challenge. METHODS: We used a model of segmental bronchoprovocation with an allergen (SBP-Ag) in human subjects with allergy. Before and 48 h after SBP-Ag, bronchoalveolar lavages (BALs) allowed for the analysis of proteins in BAL fluids (BALFs) by ELISA, and membrane proteins on the surface of BAL cells by flow cytometry. In addition, we performed RNA sequencing (RNA-seq) and used proteomic data to further inform on the expression of the IL-6R subunits by eosinophils, bronchial epithelial cells and lung fibroblasts. Finally, we measured the effect of IL-6 trans-signalling on bronchial fibroblasts, in vitro. RESULTS: IL-6, sIL-6R, sGP130 and the molar ratio of sIL-6R/sGP130 increased in the airways after SBP-Ag, suggesting the potential for enhanced IL-6 trans-signalling activity. BAL lymphocytes, monocytes and eosinophils displayed IL-6R on their surface and were all possible providers of sIL-6R, whereas GP130 was highly expressed in bronchial epithelial cells and lung fibroblasts. Finally, bronchial fibroblasts activated by IL-6 trans-signalling produced enhanced amounts of the chemokine, MCP-1 (CCL2). CONCLUSION AND CLINICAL RELEVANCE: After a bronchial allergen challenge, we found augmentation of the elements of IL-6 trans-signalling. Allergen-induced IL-6 trans-signalling activity can activate fibroblasts to produce chemokines that can further enhance inflammation and lung dysfunction.

The peptidyl-prolyl isomerase Pin1 facilitates cytokine-induced survival of eosinophils by suppressing Bax activation.

The mechanisms by which cytokine signals prevent the activation and mitochondrial targeting of the proapoptotic protein Bax are unclear. Here we show, using primary human eosinophils, that in the absence of the prosurvival cytokines granulocyte-macrophage colony-stimulating factor and interleukin 5, Bax spontaneously underwent activation and initiated mitochondrial disruption. Inhibition of Bax resulted in less eosinophil apoptosis, even in the absence of cytokines. Granulocyte-macrophage colony-stimulating factor induced activation of the kinase Erk1/2, which phosphorylated Thr167 of Bax; this facilitated new interaction of Bax with the prolyl isomerase Pin1. Blockade of Pin1 led to cleavage and mitochondrial translocation of Bax and caspase activation, regardless of the presence of cytokines. Our findings indicate that Pin1 is a key mediator of prosurvival signaling and is a regulator of Bax function.

Eosinophil cytolysis on Immunoglobulin G is associated with microtubule formation and suppression of rho-associated protein kinase signalling.

BACKGROUND: The presence of eosinophils in the airway is associated with asthma severity and risk of exacerbations. Cell-free eosinophil granules are found in tissues in eosinophilic diseases, including asthma. This suggests that eosinophils have lysed and released cellular content, likely harming tissues. OBJECTIVE: The present study explores the mechanism of CD32- and αMß2 integrin-dependent eosinophil cytolysis of IL3-primed blood eosinophils seeded on heat-aggregated immunoglobulin G (HA-IgG). METHODS: Cytoskeletal events and signalling pathways potentially involved in cytolysis were assessed using inhibitors. The level of activation of the identified events and pathways involved in cytolysis was measured. In addition, the links between these identified pathways and changes in degranulation (exocytosis) and adhesion were analysed. RESULTS: Cytolysis of IL3-primed eosinophils was dependent on the production of reactive oxygen species (ROS) and downstream phosphorylation of p-38 MAPK. In addition, formation of microtubule (MT) arrays was necessary for cytolysis and was accompanied by changes in MT dynamics as measured by phosphorylation status of stathmin and microtubule-associated protein 4 (MAP4), the latter of which was regulated by ROS production. Reduced ROCK signalling preceded cytolysis, which was associated with eosinophil adhesion and reduced migration. CONCLUSION AND CLINICAL RELEVANCE: In this CD32- and αMß2 integrin-dependent adhesion model, lysing eosinophils exhibit reduced migration and ROCK signalling, as well as both MT dynamic changes and p-38 phosphorylation downstream of ROS production. We propose that interfering with these pathways would modulate eosinophil cytolysis and subsequent eosinophil-driven tissue damage.

Matrix Metalloproteinase-9-Dependent Release of IL-1ß by Human Eosinophils.

Asthma is often associated with airway eosinophilia, and therapies targeting eosinophils are now available to treat severe eosinophilic asthma. Eosinophilic asthma is often due to a type-2 immune response and production of IL-5, which leads to eosinophilopiesis and recruitment of mature eosinophils in the airways. A concomitant type-2 and type-17 response has been reported in some individuals. IL-17 may be enhanced by IL-1ß production and can lead to neutrophilic inflammation. In fact, both eosinophilic and neutrophilic (mixed granulocytic) inflammation are simultaneously present in a large population of patients with asthma. In monocyte/macrophage cell populations, release of mature IL-1ß occurs via toll-like receptor ligand-induced activation of the inflammasome. Within the inflammasome, a cascade of events leads to the activation of caspase-1, which cleaves pro-IL-1ß protein into a mature, releasable, and active form. We have demonstrated that eosinophils can release IL-1ß in a Toll-like receptor ligand-independent fashion. The objective of this study was to determine the mechanisms underlying the production and maturation of IL-1ß in cytokine-activated eosinophils. Using eosinophils from circulating blood and from bronchoalveolar lavage fluid after an airway allergen challenge, the present study demonstrates that cytokine-activated eosinophils express and release a bioactive form of IL-1ß with an apparent size less than the typical 17 kDa mature form produced by macrophages. Using a zymography approach and pharmacological inhibitors, we identified matrix metalloproteinase-9 (MMP-9) as a protease that cleaves pro-IL-1ß into a ~15 kDa form and allows the release of IL-1ß from cytokine-activated eosinophils. Therefore, we conclude that activated eosinophils produce MMP-9, which causes the release of IL-1ß in an inflammasome/caspase-1-independent manner. The production of IL-1ß by eosinophils may be a link between the eosinophilic/type-2 immune response and the neutrophilic/type-17 immune response that is often associated with a more severe and treatment-refractory type of asthma.

Sputum cell IL-1 receptor expression level is a marker of airway neutrophilia and airflow obstruction in asthmatic patients.

BACKGROUND: Various clinical, biologic, or physiologic markers of asthma have been used to identify patient clusters and potential targets for therapy. However, these identifiers frequently overlap among the different asthma groups. For instance, both eosinophil and neutrophil counts are often increased in the airways of asthmatic patients despite their typical association with type 2 and type 17 immune response, respectively. OBJECTIVES: We sought to determine whether inflammatory gene expression is related to patterns of airway inflammation and lung function and identify molecular markers for neutrophilic asthma. METHODS: Expression levels of 17 genes characterizing type 1, type 2, and type 17 lymphocytes were measured in sputum samples from 48 participants with asthma. The relationships between gene expression levels and sputum cell differentials or measures of pulmonary function were examined by using partial least squares regression. RESULTS: Gene expression levels were strongly associated with cell differentials, explaining 71% of variation in eosinophil counts and 64% of variation in neutrophil counts. The 3 genes with the strongest relationships to sputum neutrophil counts were IL1R1 (standardized regression coefficient [ß] = +0.27, P = .005), IL1RAP (ß = +0.32, P = .0004), and IL4R (ß = +0.29, P = .002). Higher expression levels of IL1R1, IL1RAP, and IL4R were associated with reduced FEV1/forced vital capacity ratio (ß = -0.11, -0.08, and -0.10; P = .005, .07, and .05). CONCLUSION: IL-1 receptor appears to be a marker of neutrophilic inflammation and airflow obstruction in patients with asthma, who have a wide range of disease severity. The IL-1 pathway might contribute to airway neutrophilia and is a potential therapeutic target in patients with neutrophilic asthma.

Proteomic and Phosphoproteomic Changes Induced by Prolonged Activation of Human Eosinophils with IL-3.

Purified human eosinophils treated for 18-24 h with IL-3 adopt a unique activated phenotype marked by increased reactivity to aggregated immunoglobulin-G (IgG). To characterize this phenotype, we quantified protein abundance and phosphorylation by multiplexed isobaric labeling combined with high-resolution mass spectrometry. Purified blood eosinophils of five individuals were treated with IL-3 or no cytokine for 20 h, and comparative data were obtained on abundance of 5385 proteins and phosphorylation at 7330 sites. The 1150 proteins that were significantly up-regulated ( q < 0.05, pairwise t test with Benjamini-Hochberg correction) by IL-3 included the IL3RA and CSF2RB subunits of the IL-3 receptor, the low-affinity receptor for IgG (FCGR2B), 96 proteins involved in protein translation, and 55 proteins involved in cytoskeleton organization. Among the 703 proteins that decreased were 78 mitochondrial proteins. Dynamic regulation of protein phosphorylation was detected at 4218 sites. These included multiple serines in CSF2RB; Y694 of STAT5, a key site of activating phosphorylation downstream of IL3RA/CSF2RB; and multiple sites in RPS6KA1, RPS6, and EIF4B, which are responsible for translational initiation. We conclude that IL-3 up-regulates overall protein synthesis and targets specific proteins for up-regulation, including its own receptor.

Mepolizumab Attenuates Airway Eosinophil Numbers, but Not Their Functional Phenotype, in Asthma.

RATIONALE: Mepolizumab, an IL-5-blocking antibody, reduces exacerbations in patients with severe eosinophilic asthma. Mepolizumab arrests eosinophil maturation; however, the functional phenotype of eosinophils that persist in the blood and airway after administration of IL-5 neutralizing antibodies has not been reported. OBJECTIVES: To determine the effect of anti-IL-5 antibody on the numbers and phenotypes of allergen-induced circulating and airway eosinophils. METHODS: Airway inflammation was elicited in participants with mild allergic asthma by segmental allergen challenge before and 1 month after a single intravenous 750-mg dose of mepolizumab. Eosinophils were examined in blood, bronchoalveolar lavage, and endobronchial biopsies 48 hours after challenge. MEASUREMENTS AND MAIN RESULTS: Segmental challenge without mepolizumab induced a rise in circulating eosinophils, bronchoalveolar lavage eosinophilia, and eosinophil peroxidase deposition in bronchial mucosa. IL-5 neutralization before allergen challenge abolished the allergen-induced rise in circulating eosinophils and expression of IL-3 receptors, whereas airway eosinophilia and eosinophil peroxidase deposition were blunted but not eliminated. Before mepolizumab treatment, bronchoalveolar lavage eosinophils had more surface IL-3 and granulocyte-monocyte colony-stimulating factor receptors, CD69, CD44, and CD23 and decreased IL-5 and eotaxin receptors than blood eosinophils. This activation phenotype indicated by bronchoalveolar lavage eosinophil surface markers, as well as the release of eosinophil peroxidase by eosinophils in the bronchial mucosa, was maintained after mepolizumab. CONCLUSIONS: Mepolizumab reduced airway eosinophil numbers but had a limited effect on airway eosinophil activation markers, suggesting that these cells retain functionality. This observation may explain why IL-5 neutralization reduces but does not completely eradicate asthma exacerbations. Clinical trial registered with www.clinicaltrials.gov (NCT00802438).

RNA-sequencing analysis of lung primary fibroblast response to eosinophil-degranulation products predicts downstream effects on inflammation, tissue remodeling and lipid metabolism.

BACKGROUND: The association of eosinophils with inflammation and tissue remodeling is at least partially due to their release of toxic granule proteins and other mediators, including cytokines. Tissue remodeling and consequent functional defects are affected by activity of connective tissue fibroblasts. Exaggerated fibroblast activation, accumulation and change of phenotype may lead to fibrosis and loss of tissue function. So far, little information has been reported on how eosinophils affect inflammation and tissue remodeling via the activation of fibroblasts. We have recently shown that eosinophil activation with IL-3 led to a robust eosinophil degranulation on immunoglobin-G (IgG) coated plates. Thus, in the present study, we analyze the effects of IL-3-activated eosinophil degranulation products on primary human lung fibroblasts (HLF) using whole transcriptome sequencing. METHODS: Conditioned media was obtained from eosinophils that were pre-activated with IL-3 or IL-5 and subsequently cultured for 6 h on IgG to induce degranulation. This conditioned media was added on human lung fibroblasts (HLF) for 24 h and the cell lysates were then subjected to whole transcriptome sequencing to identify global changes in gene expression. Differentially expressed genes were analyzed using the Ingenuity Pathway Analysis (IPA), and validated by qPCR. RESULTS: In HLF, the expression level of 300 genes was changed by conditioned media from IL-3-activated eosinophils compared to control fibroblast cultures. Among these 300 genes, the expression level of 35 genes coding for known proteins was upregulated by IL-3- versus IL-5-pre-activated eosinophils. Of the 35 upregulated genes, IPA identified C3, CH25H, CXCL1, CXCL8, CYP1A1, ICAM1, IL6 and UCN2 as having downstream functions on inflammation, tissue remodeling and lipid synthesis. This analysis combined with previous RNA sequencing analyses of eosinophils suggest IL-1ß, OSM and TNFSF12 as potential upstream regulators of fibroblasts. CONCLUSIONS: This study has identified several novel pro-inflammatory and pro-remodeling mediators produced by fibroblasts in response to activated eosinophils. These findings may have significant implications on the role of eosinophil/fibroblast interactions in eosinophilic disorders.

Essential Mechanisms of Differential Activation of Eosinophils by IL-3 Compared to GM-CSF and IL-5.

Compelling evidence has demonstrated that the eosinophils bring negative biological outcomes in several diseases, including eosinophilic asthma and hypereosinophilic syndromes. Eosinophils produce and store a broad range of toxic proteins and other mediators that enhance the inflammatory response and lead to tissue damage. For instance, in asthma, a close relationship has been demonstrated between increased lung eosinophilia, asthma exacerbation, and loss of lung function. The use of an anti-IL-5 therapy in severe eosinophilic asthmatic patients is efficient to reduce exacerbations. However, anti-IL-5-treated patients still display a relatively high amount of functional lung tissue eosinophils, indicating that supplemental therapies are required to damper the eosinophil functions. Our recent published works suggest that compared to IL-5, IL-3 can more strongly and differentially affect eosinophil functions. In this review, we summarize our and other investigations that have compared the effects of the three ß-chain receptor cytokines (IL-5, GM-CSF and IL-3) on eosinophil biology. We focus on how IL-3 differentially activates eosinophils compared to IL-5 or GM-CSF.

IL-3 Maintains Activation of the p90S6K/RPS6 Pathway and Increases Translation in Human Eosinophils.

IL-5 is a major therapeutic target to reduce eosinophilia. However, all of the eosinophil-activating cytokines, such as IL-5, IL-3, and GM-CSF, are typically present in atopic diseases, including allergic asthma. As a result of the functional redundancy of these three cytokines on eosinophils and the loss of IL-5R on airway eosinophils, it is important to take IL-3 and GM-CSF into account to efficiently reduce tissue eosinophil functions. Moreover, these three cytokines signal through a common ß-chain receptor but yet differentially affect protein production in eosinophils. Notably, the increased ability of IL-3 to induce the production of proteins, such as semaphorin-7A, without affecting mRNA levels suggests a unique influence of IL-3 on translation. The purpose of this study was to identify the mechanisms by which IL-3 distinctively affects eosinophil function compared with IL-5 and GM-CSF, with a focus on protein translation. Peripheral blood eosinophils were used to study intracellular signaling and protein translation in cells activated with IL-3, GM-CSF, or IL-5. We establish that, unlike GM-CSF or IL-5, IL-3 triggers prolonged signaling through activation of ribosomal protein S6 (RPS6) and the upstream kinase 90-kDa ribosomal S6 kinase (p90S6K). Blockade of p90S6K activation inhibited phosphorylation of RPS6 and IL-3-enhanced semaphorin-7A translation. Furthermore, in an allergen-challenged environment, in vivo phosphorylation of RPS6 and p90S6K was enhanced in human airway compared with circulating eosinophils. Our findings provide new insights into the mechanisms underlying differential activation of eosinophils by IL-3, GM-CSF, and IL-5. These observations identify IL-3 and its downstream intracellular signals as novel targets that should be considered to modulate eosinophil functions.

Airway factor XIII associates with type 2 inflammation and airway obstruction in asthmatic patients.

BACKGROUND: Coagulation Factor XIII (FXIII) plays an important role in wound healing by stabilizing fibrin clots and cross-linking extracellular matrix proteins. FXIII is expressed in cells of the monocyte/macrophage and dendritic cell lineages in response to type 2 cytokines. OBJECTIVE: We sought to determine the association between FXIII and asthma pathobiology. METHODS: We analyzed the expression of FXIII mRNA and protein levels in bronchoalveolar lavage samples obtained before and after segmental allergen challenge from patients with mild asthma and in induced sputum samples collected from patients with mild-to-moderate and severe asthma. RESULTS: FXIII mRNA and protein levels were highly upregulated in bronchoalveolar cells and fluid after allergen challenge and mRNA levels correlated with protein levels. In sputum of asthmatic patients, FXIII expression was positively correlated with type 2 immune response and dendritic cell markers (CD209 and CD207). FXIII expression was also associated with increased airflow limitation (FEV1/forced vital capacity and residual volume/total lung capacity ratios) and greater reversibility to ß-agonists. CONCLUSIONS: FXIII expression was upregulated in the airways of asthmatic patients after allergen exposure. Expression in the sputum of asthmatic patients correlated with the type 2 immune response and airflow limitation. Excessive activity of FXIII could contribute to the pathophysiology of airway obstruction in asthmatic patients.

Human eosinophil activin A synthesis and mRNA stabilization are induced by the combination of IL-3 plus TNF.

Eosinophils contribute to immune regulation and wound healing/fibrosis in various diseases, including asthma. Growing appreciation for the role of activin A in such processes led us to hypothesize that eosinophils are a source of this transforming growth factor-ß superfamily member. Tumor necrosis factor-α (TNF) induces activin A by other cell types and is often present at the site of allergic inflammation along with the eosinophil-activating common ß (ßc) chain-signaling cytokines (interleukin (IL)-5, IL-3, granulocyte-macrophages colony-stimulating factor (GM-CSF)). Previously, we established that the combination of TNF plus a ßc chain-signaling cytokine synergistically induces eosinophil synthesis of the remodeling enzyme matrix metalloproteinase-9. Therefore, eosinophils were stimulated ex vivo by these cytokines and in vivo through an allergen-induced airway inflammatory response. In contrast to IL-5+TNF or GM-CSF+TNF, the combination of IL-3+TNF synergistically induced activin A synthesis and release by human blood eosinophils. IL-3+TNF enhanced activin A mRNA stability, which required sustained signaling of pathways downstream of p38 and extracellular signal-regulated kinase mitogen-activated protein kinases. In vivo, following segmental airway allergen challenge of subjects with mild allergic asthma, activin A mRNA was upregulated in airway eosinophils compared with circulating eosinophils, and ex vivo, circulating eosinophils tended to release more activin A in response to IL-3+TNF. These data provide evidence that eosinophils release activin A and that this function is enhanced when eosinophils are present in an allergen-induced inflammatory environment. Moreover, these data provide the first evidence for posttranscriptional control of activin A mRNA. We propose that an environment rich in IL-3+TNF will lead to eosinophil-derived activin A, which has an important role in regulating inflammation and/or fibrosis.

Mind-body interactions in the regulation of airway inflammation in asthma: A PET study of acute and chronic stress.

BACKGROUND: Psychological stress has long been recognized as a contributing factor to asthma symptom expression and disease progression. Yet, the neural mechanisms that underlie this relationship have been largely unexplored in research addressing the pathophysiology and management of asthma. Studies that have examined the mechanisms of this relationship in the periphery suggest that it is the superimposition of acute stress on top of chronic stress that is of greatest concern for airway inflammation. METHODS: We compared asthmatic individuals with high and low levels of chronic life stress in their neural and peripheral physiological responses to the Trier Social Stress Test and a matched control task. We used FDG-PET to measure neural activity during performance of the two tasks. We used both circulating and airway-specific markers of asthma-related inflammation to assess the impact of acute stress in these two groups. RESULTS: Asthmatics under chronic stress had a larger HPA-axis response to an acute stressor, which failed to show the suppressive effects on inflammatory markers observed in those with low chronic stress. Moreover, our PET data suggest that greater activity in the anterior insula during acute stress may reflect regulation of the effect of stress on inflammation. In contrast, greater activity in the mid-insula and perigenual anterior cingulate seems to reflect greater reactivity and was associated with greater airway inflammation, a more robust alpha amylase response, and a greater stress-induced increase in proinflammatory cytokine mRNA expression in airway cells. CONCLUSIONS: Acute stress is associated with increases in markers of airway inflammation in asthmatics under chronic stress. This relationship may be mediated by interactions between the insula and anterior cingulate cortex, that determine the salience of environmental cues, as well as descending regulatory influence of inflammatory pathways in the periphery.

Human airway eosinophils exhibit preferential reduction in STAT signaling capacity and increased CISH expression.

Allergic asthma, a chronic respiratory disorder marked by inflammation and recurrent airflow obstruction, is associated with elevated levels of IL-5 family cytokines and elevated numbers of eosinophils (EOS). IL-5 family cytokines elongate peripheral blood EOS (EOS(PB)) viability, recruit EOS(PB) to the airways, and, at higher concentrations, induce degranulation and reactive oxygen species generation. Although airway EOS (EOS(A)) remain signal ready in that GM-CSF treatment induces degranulation, treatment of EOS(A) with IL-5 family cytokines no longer confers a survival advantage. Because the IL-5 family receptors have common signaling capacity, but are uncoupled from EOS(A) survival, whereas other IL-5 family induced endpoints remain functional, we tested the hypothesis that EOS(A) possess a JAK/STAT-specific regulatory mechanism (because JAK/STAT signaling is critical to EOS survival). We found that IL-5 family-induced STAT3 and STAT5 phosphorylation is attenuated in EOS(A) relative to blood EOS from airway allergen-challenged donors. However, IL-5 family-induced ERK1/2 phosphorylation is not altered between EOS(A) and EOS from airway allergen-challenged donors. These observations suggest EOS(A) possess a regulatory mechanism for suppressing STAT signaling distinct from ERK1/2 activation. Furthermore, we found, in EOS(PB), IL-5 family cytokines induce members of the suppressors of cytokine signaling (SOCS) genes, CISH and SOCS1. Additionally, following allergen challenge, EOS(A) express significantly more CISH and SOCS1 mRNA and CISH protein than EOS(PB) counterparts. In EOS(PB), long-term pretreatment with IL-5 family cytokines, to varying degrees, attenuates IL-5 family-induced STAT5 phosphorylation. These data support a model in which IL-5 family cytokines trigger a selective downregulation mechanism in EOS(A) for JAK/STAT pathways.