Homeostatic glucocorticoid signaling in airway smooth muscle: A roadmap to asthma pathogenesis.

Homeostasis is the self-regulating process by which the body maintains internal stability within a narrow physiological range (i.e., "normality") as it dynamically adjusts to disruptive influences. Thus, whereas homeostasis maintains bodily health, disrupted homeostasis at the tissue or systemic level leads to disease. Airway smooth muscle (ASM) is the pivotal site of disrupted homeostasis in asthma. While extensive research has greatly expanded our understanding of ASM behavior under pro-asthmatic conditions, the cellular signaling mechanisms that underlie ASM homeostasis under these conditions remain elusive. Based on a broad collection of published studies, a homeostasis mechanism intrinsic to ASM and exhibited under inflammatory and non-inflammatory pro-asthmatic conditions is identified herein. Central to this mechanism is the novel unifying concept that the pro-asthmatic-exposed ASM can independently generate its own active glucocorticoid (i.e., cortisol), produce its own newly activated glucocorticoid receptors for the steroid, and, accordingly, use this molecular strategy to homeostatically prevent induction of the asthmatic state. This article addresses the experimental evidence that underlies the proposed homeostatic glucocorticoid signaling mechanism in ASM, followed by a discussion and depiction of the feed-forward and feedback intrinsic ASM signaling circuitry that constitutes the homeostatic state. The proposed mechanism offers a practical roadmap for future basic and translational research aimed at identifying potential key site(s) of disrupted ASM homeostasis leading to asthma.

Constitutively active signaling by the G protein ßγ-subunit mediates intrinsically increased phosphodiesterase-4 activity in human asthmatic airway smooth muscle cells.

Signaling by the Gßγ subunit of Gi protein, leading to downstream c-Src-induced activation of the Ras/c-Raf1/MEK-ERK1/2 signaling pathway and its upregulation of phosphodiesterase-4 (PDE4) activity, was recently shown to mediate the heightened contractility in proasthmatic sensitized isolated airway smooth muscle (ASM), as well as allergen-induced airway hyperresponsiveness and inflammation in an in vivo animal model of allergic asthma. This study investigated whether cultured human ASM (HASM) cells derived from asthmatic donor lungs exhibit constitutively increased PDE activity that is attributed to intrinsically upregulated Gßγ signaling coupled to c-Src activation of the Ras/MEK/ERK1/2 cascade. We show that, relative to normal cells, asthmatic HASM cells constitutively exhibit markedly increased intrinsic PDE4 activity coupled to heightened Gßγ-regulated phosphorylation of c-Src and ERK1/2, and direct co-localization of the latter with the PDE4D isoform. These signaling events and their induction of heightened PDE activity are acutely suppressed by treating asthmatic HASM cells with a Gßγ inhibitor. Importantly, along with increased Gßγ activation, asthmatic HASM cells also exhibit constitutively increased direct binding of the small Rap1 GTPase-activating protein, Rap1GAP, to the α-subunit of Gi protein, which serves to cooperatively facilitate Ras activation and, thereby, enable enhanced Gßγ-regulated ERK1/2-stimulated PDE activity. Collectively, these data are the first to identify that intrinsically increased signaling via the Gßγ subunit, facilitated by Rap1GAP recruitment to the α-subunit, mediates the constitutively increased PDE4 activity detected in asthmatic HASM cells. These new findings support the notion that interventions targeted at suppressing Gßγ signaling may lead to novel approaches to treat asthma.

Pro-asthmatic cytokines regulate unliganded and ligand-dependent glucocorticoid receptor signaling in airway smooth muscle.

To elucidate the regulation of glucocorticoid receptor (GR) signaling under pro-asthmatic conditions, cultured human airway smooth muscle (HASM) cells were treated with proinflammatory cytokines or GR ligands alone and in combination, and then examined for induced changes in ligand-dependent and -independent GR activation and downstream signaling events. Ligand stimulation with either cortisone or dexamethsone (DEX) acutely elicited GR translocation to the nucleus and, comparably, ligand-independent stimulation either with the Th2 cytokine, IL-13, or the pleiotropic cytokine combination, IL-1ß/TNFα, also acutely evoked GR translocation. The latter response was potentiated by combined exposure of cells to GR ligand and cytokine. Similarly, treatment with either DEX or IL-13 alone induced GR phosphorylation at its serine-211 residue (GR(Ser211)), denoting its activated state, and combined treatment with DEX+IL-13 elicited heightened and sustained GR(Ser211) phosphorylation. Interestingly, the above ligand-independent GR responses to IL-13 alone were not associated with downstream GR binding to its consensus DNA sequence or GR transactivation, whereas both DEX-induced GR:DNA binding and transcriptional activity were significantly heightened in the presence of IL-13, coupled to increased recruitment of the transcriptional co-factor, MED14. The stimulated GR signaling responses to DEX were prevented in IL-13-exposed cells wherein GR(Ser211) phosphorylation was suppressed either by transfection with specific serine phosphorylation-deficient mutant GRs or treatment with inhibitors of the MAPKs, ERK1/2 and JNK. Collectively, these novel data highlight a heretofore-unidentified homeostatic mechanism in HASM cells that involves pro-asthmatic cytokine-driven, MAPK-mediated, non-ligand-dependent GR activation that confers heightened glucocorticoid ligand-stimulated GR signaling. These findings raise the consideration that perturbations in this homeostatic cytokine-driven GR signaling mechanism may be responsible, at least in part, for the insensirtivity to glucocorticoid therapy that is commonly seen in individuals with severe asthma.

IL-13-induced changes in endogenous glucocorticoid metabolism in the lung regulate the proasthmatic response.

Endogenous glucocorticoid (GC) activation is regulated by the intracellular GC-activating and -inactivating enzymes 11ß-hydroxysteroid dehydrogenase (11ß-HSD)1 and 11ß-HSD2, respectively, that catalyze interconversion of inert cortisone and its bioactive metabolite cortisol. Because endogenous GCs are critically implicated in suppressing the asthmatic state, this study examined the roles of the 11ß-HSD enzymes in regulating GC activation and bronchoprotection during proasthmatic stimulation. Airway hyperresponsiveness to methacholine and inflammation were assessed in rabbits following inhalation of the proasthmatic/proinflammatory cytokine IL-13 with and without pretreatment with the 11ß-HSD inhibitor carbenoxolone (CBX). Additionally, IL-13-induced changes in 11ß-HSD isozyme expression and GC metabolism were examined in epithelium-intact and -denuded tracheal segments and peripheral lung tissues. Finally, the effects of pretreatment with CBX or 11ß-HSD2-targeted siRNAs were investigated with respect to cortisol prevention of IL-13-induced airway constrictor hyperresponsiveness and eotaxin-3 production by airway epithelial cells. IL-13-exposed rabbits exhibited airway hyperresponsiveness, inflammation, and elevated bronchoalveolar lung fluid levels of eotaxin-3. These responses were inhibited by pretreatment with CBX, suggesting a permissive proasthmatic role for 11ß-HSD2. Supporting this concept, extended studies demonstrated that 1) IL-13-treated tracheal epithelium and peripheral lung tissues exhibit upregulated 11ß-HSD2 activity, 2) the latter impairs cortisone-induced cortisol accumulation and the ability of administered cortisol to prevent both IL-13-induced heightened airway contractility and eotaxin-3 release from epithelial cells, and 3) these proasthmatic responses are prevented by cortisol administration in the presence of 11ß-HSD2 inhibition. Collectively, these data demonstrate that the proasthmatic effects of IL-13 are enabled by impaired endogenous GC activation in the lung that is attributed to upregulation of 11ß-HSD2 in the pulmonary epithelium.

G Protein ßγ-subunit signaling mediates airway hyperresponsiveness and inflammation in allergic asthma.

Since the Gßγ subunit of Gi protein has been importantly implicated in regulating immune and inflammatory responses, this study investigated the potential role and mechanism of action of Gßγ signaling in regulating the induction of airway hyperresponsiveness (AHR) in a rabbit model of allergic asthma. Relative to non-sensitized animals, OVA-sensitized rabbits challenged with inhaled OVA exhibited AHR, lung inflammation, elevated BAL levels of IL-13, and increased airway phosphodiesterase-4 (PDE4) activity. These proasthmatic responses were suppressed by pretreatment with an inhaled membrane-permeable anti-Gßγ blocking peptide, similar to the suppressive effect of glucocorticoid pretreatment. Extended mechanistic studies demonstrated that: 1) corresponding proasthmatic changes in contractility exhibited in isolated airway smooth muscle (ASM) sensitized with serum from OVA-sensitized+challenged rabbits or IL-13 were also Gßγ-dependent and mediated by MAPK-upregulated PDE4 activity; and 2) the latter was attributed to Gßγ-induced direct stimulation of the non-receptor tyrosine kinase, c-Src, resulting in downstream activation of ERK1/2 and its consequent transcriptional upregulation of PDE4. Collectively, these data are the first to identify that a mechanism involving Gßγ-induced direct activation of c-Src, leading to ERK1/2-mediated upregulation of PDE4 activity, plays a decisive role in regulating the induction of AHR and inflammation in a rabbit model of allergic airway disease.

Mechanism of glucocorticoid protection of airway smooth muscle from proasthmatic effects of long-acting beta2-adrenoceptor agonist exposure.

BACKGROUND: Chronic use of long-acting beta2-adrenergic receptor agonists (LABAs), resulting in beta2-adrenergic receptor desensitization, has been associated with increased asthma morbidity. When LABAs are used in combination with inhaled glucocorticoids, however, asthma control is improved, raising the following question: Do glucocorticoids inhibit the proasthmatic mechanism that mediates altered contractility in LABA-exposed airway smooth muscle (ASM)? OBJECTIVE: This study aimed to identify the potential protective role and mechanism of action of glucocorticoids in mitigating the effects of prolonged LABA exposure on ASM constrictor and relaxation responsiveness. METHODS: Cultured human ASM cells and isolated rabbit ASM tissues were examined for induced changes in agonist-mediated cyclic adenosine monophosphate accumulation, constrictor and relaxation responsiveness, and expression of specific glucocorticoid-regulated molecules after 24-hour exposure to the LABA salmeterol in the absence and presence of dexamethasone. RESULTS: Salmeterol-exposed ASM exhibited impaired cyclic adenosine monophosphate and relaxation responses to isoproterenol and increased acetylcholine-induced contractility. These proasthmatic effects of prolonged LABA exposure were attributed to upregulated phosphodiesterase 4 (PDE4) activity and were ablated by pretreatment with dexamethasone. Further studies demonstrated that (1) dexamethasone suppressed activation of the mitogen-activated protein kinases extracellular signal-regulated kinases 1 and 2 (ERK1/2), which upregulate PDE4 expression in salmeterol-exposed ASM; and (2) the inhibitory actions of dexamethasone on salmeterol-induced ERK1/2 activation and resultant PDE4-mediated changes in ASM responsiveness were prevented by gene silencing or pharmacologic inhibition of dexamethasone-induced expression of mitogen-activated protein kinase phosphatase 1, an endogenous deactivator of ERK1/2 signaling. CONCLUSION: Glucocorticoids prevent the adverse proasthmatic effects of prolonged LABA exposure on airway responsiveness as a result of glucocorticoid-induced upregulation of mitogen-activated protein kinase phosphatase 1, which inhibits proasthmatic ERK1/2 signaling in the LABA-exposed ASM.

Current concepts on the use of glucocorticosteroids and beta-2-adrenoreceptor agonists to treat childhood asthma.

PURPOSE OF REVIEW: This article reviews current concepts regarding the clinical and scientific rationale for the combined use of glucocorticosteroids and beta-2-adrenoreceptor (beta2AR) agonists in the treatment of childhood asthma. RECENT FINDINGS: Several studies have demonstrated that inhaled corticosteroids (ICS) and beta2AR agonists are the most effective medications for the management of asthma in children. Given substantial evidence of an increased clinical benefit when these agents are used together, new studies are being pursued to establish the efficacy and safety of this combinational therapy in infants and children. Ongoing research is also investigating the mechanisms of beta2AR and glucocorticosteroids signaling and their molecular interactions. This new knowledge will likely lead to novel therapeutic approaches to asthma control. SUMMARY: There is increasing evidence demonstrating that the combination of long-acting beta2AR agonists and ICS may be more effective than high-dose ICS therapy alone in the management of children with uncontrolled asthma. In addition, the use of a single inhaler containing ICS and a quick-acting beta2AR agonist might be a convenient alternative to prevent and treat asthma exacerbations. Future investigations should be designed to more specifically evaluate the efficacy and safety of these therapies in the different asthmatic phenotypes of infants and children.

Variants of DENND1B associated with asthma in children.

BACKGROUND: Asthma is a complex disease that has genetic and environmental causes. The genetic factors associated with susceptibility to asthma remain largely unknown. METHODS: We carried out a genomewide association study involving children with asthma. The sample included 793 North American children of European ancestry with persistent asthma who required daily inhaled glucocorticoid therapy and 1988 matched controls (the discovery set). We also tested for genomewide association in an independent cohort of 917 persons of European ancestry who had asthma and 1546 matched controls (the replication set). Finally, we tested for an association between 20 single-nucleotide polymorphisms (SNPs) at chromosome 1q31 and asthma in 1667 North American children of African ancestry who had asthma and 2045 ancestrally matched controls. RESULTS: In our meta-analysis of all samples from persons of European ancestry, we observed an association, with genomewide significance, between asthma and SNPs at the previously reported locus on 17q21 and an additional eight SNPs at a novel locus on 1q31. The SNP most strongly associated with asthma was rs2786098 (P=8.55x10(-9)). We observed replication of the association of asthma with SNP rs2786098 in the independent series of persons of European ancestry (combined P=9.3x10(-11)). The alternative allele of each of the eight SNPs on chromosome 1q31 was strongly associated with asthma in the children of African ancestry (P=1.6x10(-13) for the comparison across all samples). The 1q31 locus contains the 1q31 locus contains DENND1B, a gene expressed by natural killer cells and dendritic cells. DENND1B protein is predicted to interact with the tumor necrosis factor α receptor [corrected]. CONCLUSIONS: We have identified a locus containing DENND1B on chromosome 1q31.3 that is associated with susceptibility to asthma.

Mechanism regulating proasthmatic effects of prolonged homologous beta2-adrenergic receptor desensitization in airway smooth muscle.

Use of long-acting beta(2)-adrenergic receptor (beta2AR) agonists to treat asthma incurs an increased risk of asthma morbidity with impaired bronchodilation and heightened bronchoconstriction, reflecting the adverse effects of prolonged homologous beta2AR desensitization on airway smooth muscle (ASM) function. Since phosphodiesterase 4 (PDE4) regulates ASM relaxation and contractility, we examined whether the changes in ASM function induced by prolonged homologous beta2AR desensitization are attributed to altered expression and action of PDE4. Cultured human ASM cells and isolated rabbit ASM tissues exposed for 24 h to the long-acting beta2AR agonist salmeterol exhibited impaired acute beta2AR-mediated cAMP accumulation and relaxation, respectively, together with ASM constrictor hyperresponsiveness. These proasthmatic-like changes in ASM function were associated with upregulated PDE4 activity due to enhanced expression of the PDE4D5 isoform and were prevented by pretreating the ASM preparations with the PDE4 inhibitor rolipram or with inhibitors of either PKA or ERK1/2 signaling. Extended studies using gene silencing and pharmacological approaches demonstrated that: 1) the mechanism underlying upregulated PDE4D5 expression following prolonged beta2AR agonist exposure involves PKA-dependent activation of G(i) protein signaling via its betagamma-subunits, which elicits downstream activation of ERK1/2 and its induction of PDE4D5 transcription; and 2) the induction of PDE4 activity and consequent changes in ASM responsiveness are prevented by pretreating the beta2AR agonist-exposed ASM preparations with inhibitors of G(i)-betagamma signaling. Collectively, these findings identify that the proasthmatic changes in ASM function resulting from prolonged homologous beta2AR desensitization are attributed to upregulated PDE4 expression induced by G(i)-betagamma-mediated cross-talk between the PKA and ERK1/2 signaling pathways.

Th2 cytokine-induced upregulation of 11beta-hydroxysteroid dehydrogenase-1 facilitates glucocorticoid suppression of proasthmatic airway smooth muscle function.

The anti-inflammatory actions of endogenous glucocorticoids (GCs) are regulated by the activities of the GC-activating and -inactivating enzymes, 11beta-hydroxysteroid dehydrogenase (11beta-HSD)-1 and 11beta-HSD2, respectively, that catalyze the interconversion of the inert GC, cortisone, and its bioactive derivative, cortisol. Proinflammatory cytokines regulate 11beta-HSD1 expression in various cell types and thereby modulate the bioavailability of cortisol to the glucocorticoid receptor (GR). Since endogenous GCs reportedly attenuate the airway asthmatic response to allergen exposure, we investigated whether airway smooth muscle (ASM) exhibits cytokine-induced changes in 11beta-HSD1 expression that enable the ASM to regulate its own bioavailability of GC and, accordingly, the protective effect of GR signaling on airway function under proasthmatic conditions. Human ASM cells exposed to the primary proasthmatic T helper type 2 (Th2) cytokine, IL-13, exhibited upregulated expression of 11beta-HSD1, an effect that was attributed to activation of the transcription factor, AP-1, coupled to MAPK signaling via the ERK1/2 and JNK pathways. The induction of 11beta-HSD1 expression and its oxoreductase activity by IL-13 (also IL-4) served to amplify the conversion of cortisone to cortisol by the cytokine-exposed ASM and, hence, heighten GR-mediated transcriptional activation. Extended studies demonstrated that this amplified 11beta-HSD1-dependent GC activation enabled physiologically relevant concentrations of cortisone to exert enhanced protection of ASM tissues from the proasthmatic effects of IL-13 on ASM constrictor and relaxation responsiveness. Collectively, these novel findings identify a Th2 cytokine-driven homeostatic feedback mechanism in ASM that enhances its responsiveness to endogenous GCs by upregulating 11beta-HSD1 activity, thereby curtailing the adverse effects of the proasthmatic cytokine on airway function.

Prolonged heterologous beta2-adrenoceptor desensitization promotes proasthmatic airway smooth muscle function via PKA/ERK1/2-mediated phosphodiesterase-4 induction.

Beta2-adrenergic receptor (beta2AR) agonists acutely relieve bronchoconstriction via cAMP-mediated relaxation of airway smooth muscle (ASM). Airway constrictor responsiveness may be significantly heightened, however, following protracted exposure to these agents, presumably reflecting the effects of beta2AR desensitization in ASM accompanying prolonged cAMP signaling. Because cAMP phosphodiesterase (PDE) activity can significantly modulate ASM contractility, we investigated the mechanism regulating PDE expression and its potential role in mediating changes in agonist-induced constrictor and relaxation responsiveness in ASM following its heterologous beta2AR desensitization by prolonged exposure to cAMP-elevating agents. Isolated rabbit ASM tissues and cultured human ASM cells treated for 24 h with the receptor- or nonreceptor-coupled cAMP-stimulating agent, prostaglandin E(2) (PGE(2)) or forskolin, respectively, exhibited constrictor hyperresponsiveness to acetylcholine and impaired beta2AR-mediated relaxation and cAMP accumulation. These proasthmatic-like changes in ASM function were associated with upregulated PDE4 activity, reflective of increased transcription of the PDE4D5 isoform, and were prevented by pretreatment of the ASM with a PDE4 inhibitor. Extended studies using gene silencing and pharmacological approaches to inhibit specific intracellular signaling molecules demonstrated that the mechanism underlying PGE(2)-induced transcriptional upregulation of PDE4D5 involves PKA-dependent activation of G(i) protein signaling via the betagamma-subunits, the latter eliciting downstream activation of ERK1/2 and its consequent induction of PDE4D5 transcription. Collectively, these findings identify that beta2AR desensitization in ASM following prolonged exposure to cAMP-elevating agents is associated with proasthmatic-like changes in ASM responsiveness that are mediated by upregulated PDE4 expression induced by activated cross talk between the PKA and ERK1/2 signaling pathways.

Superantigen presentation by airway smooth muscle to CD4+ T lymphocytes elicits reciprocal proasthmatic changes in airway function.

Microbial products serving as superantigens (SAgs) have been implicated in triggering various T cell-mediated chronic inflammatory disorders, including severe asthma. Given earlier evidence demonstrating that airway smooth muscle (ASM) cells express MHC class II molecules, we investigated whether ASM can present SAg to resting CD4(+) T cells, and further examined whether this action reciprocally elicits proasthmatic changes in ASM responsiveness. Coincubation of CD4(+) T cells with human ASM cells pulsed with the SAg, staphylococcal enterotoxin A (SEA), elicited adherence and clustering of class II and CD3 molecules at the ASM/T cell interface, indicative of immunological synapse formation, in association with T cell activation. This ASM/T cell interaction evoked up-regulated mRNA expression and pronounced release of the Th2-type cytokine, IL-13, into the coculture medium, which was MHC class II dependent. Moreover, when administering the conditioned medium from the SEA-stimulated ASM/T cell cocultures to isolated naive rabbit ASM tissues, the latter exhibited proasthmatic-like changes in their constrictor and relaxation responsiveness that were prevented by pretreating the tissues with an anti-IL-13 neutralizing Ab. Collectively, these observations are the first to demonstrate that ASM can present SAg to CD4(+) T cells, and that this MHC class II-mediated cooperative ASM/T cell interaction elicits release of IL-13 that, in turn, evokes proasthmatic changes in ASM constrictor and relaxant responsiveness. Thus, a new immuno-regulatory role for ASM is identified that potentially contributes to the pathogenesis of nonallergic (intrinsic) asthma and, accordingly, may underlie the reported association between microbial SAg exposure, T cell activation, and severe asthma.

Regulation of Toll-like receptor 4-induced proasthmatic changes in airway smooth muscle function by opposing actions of ERK1/2 and p38 MAPK signaling.

Activation of Toll-like receptors (TLRs) on immune surveillance cells in the lung has been implicated in the pathobiology of allergic asthma, a condition associated with altered airway smooth muscle (ASM) contractility. Because ASM is known to directly respond to various proasthmatic stimuli, the potential role of TLR signaling in ASM in regulating airway expression of the proasthmatic phenotype was investigated. Cultured human ASM cells were found to express TLR4 and TLR9 mRNA transcripts and, whereas TLR9 stimulation had little effect, TLR4 activation with LPS elicited significant increases in IL-6 release and evoked proasthmatic-like changes in the constrictor and relaxation responsiveness of isolated rabbit ASM tissues. Complementary studies further demonstrated that the ASM responses to LPS were associated with activation of the ERK1/2 and p38 MAPK signaling pathways, IKK-mediated activation of NF-kappaB, and coupling of phosphorylated ERK1/2 with the p65 subunit of NF-kappaB. Moreover, the induced NF-kappaB activity and changes in ASM responsiveness were prevented in LPS-exposed ASM that were pretreated with inhibitors of ERK1/2 signaling, whereas inhibition of p38 MAPK augmented the proasthmatic responses to LPS. Finally, activation of p38 MAPK with anisomycin prevented both the LPS-induced stimulation of ERK1/2-mediated NF-kappaB activity and associated changes in ASM responsiveness. Collectively, these data support the novel concept that TLR4 activation in ASM elicits changes in ASM function that are regulated by opposing effects of MAPK signaling, wherein LPS-induced ERK1/2 activation mediates NF-kappaB-dependent proasthmatic-like changes in ASM function, whereas coactivation of p38 MAPK serves to homeostatically downregulate the proasthmatic effects of ERK1/2 activation.

Proasthmatic effects and mechanisms of action of the dust mite allergen, Der p 1, in airway smooth muscle.

BACKGROUND: House dust mite allergen exposure is a key risk factor for the development of allergic asthma. Beyond provoking immune cell-mediated allergic responses, house dust mite allergens were recently shown to exert direct effects on airway structural cells secondary to their intrinsic protease activities. OBJECTIVE: This study tested the hypothesis that house dust mite allergen exposure can produce changes in airway responsiveness through a direct effect on airway smooth muscle (ASM). METHODS: Isolated rabbit ASM tissues were exposed to the house dust mite allergen, Der p 1, and induced changes in ASM responsiveness and activation of mitogen-activated protein kinase (MAPK) signaling pathways were examined under different experimental conditions. RESULTS: The observations demonstrated the following: (1) Der p 1 exposure elicited enhanced constrictor responses and impaired relaxation responses in the ASM tissues, (2) these proasthmatic-like effects of Der p 1 were attributed to its intrinsic cysteine protease activity, and (3) the induced changes in ASM responsiveness were associated with activation of both the extracellular signal-regulated kinase (ERK) 1/2 and the p38 MAPK signaling pathways. Additionally, specific blockade of ERK1/2 signaling was found to prevent the Der p 1-induced changes in ASM responsiveness, whereas inhibition of p38 MAPK signaling enhanced the proasthmatic-like action of Der p 1, with the latter effect a result of augmented activation of ERK1/2. CONCLUSION: These findings are the first to demonstrate that the dust mite allergen, Der p 1, can directly elicit changes in ASM responsiveness that are associated with activation of MAPK signaling, wherein proasthmatic effects induced by Der p 1 are attributed to activation of ERK1/2, whereas coactivation of p38 MAPK exerts a homeostatic action by negatively regulating ERK1/2 signaling.

Autocrine regulation of airway smooth muscle responsiveness.

Bronchial asthma is characterized by airway inflammation, exaggerated airway narrowing to bronchoconstrictor agonists, and attenuated beta-adrenoceptor-mediated airway relaxation. Various cytokines/chemokines have been implicated in the pathogenesis of the airway inflammatory response, and certain cytokines, most notably including specific Th2-type cytokines and IL-1beta, have been shown to directly regulate airway smooth muscle (ASM) responsiveness. Recent evidence supports the concept that the ASM itself has the capacity to endogenously express a number of these cytokines under specific conditions of ASM sensitization. Moreover, these cytokines were found to act in an autocrine manner on the ASM to evoke the 'pro-asthmatic' phenotype of altered airway responsiveness. This cytokine-driven autocrine signaling mechanism in ASM may be triggered by either Fc receptor activation in the atopic (IgE-mediated) sensitized state or by ASM exposure to specific viral respiratory pathogens, most notably including rhinovirus. Furthermore, the autocrine-induced changes in ASM responsiveness are attributed to altered receptor-coupled transmembrane signaling in the sensitized ASM, resulting in perturbed expression and release of second messenger molecules that regulate ASM contraction and relaxation. Collectively, this evidence identifies mechanisms intrinsic to the ASM itself, including autocrine pro-inflammatory signaling and altered receptor/G protein-coupled second messenger activation, that importantly contribute to phenotypic expression of the changes in ASM responsiveness that characterize the asthmatic state.

T lymphocyte-mediated changes in airway smooth muscle responsiveness are attributed to induced autocrine release and actions of IL-5 and IL-1beta.

BACKGROUND: Bidirectional stimulatory cross-talk was recently found to exist between activated T cells and airway smooth muscle (ASM) cells, a process that involves coligation of specific cellular adhesion-costimulatory molecules that results in the induction of proasthmatic-like changes in ASM responsiveness. OBJECTIVE: The present study examined whether the cooperative intercellular signaling between activated T cells and ASM cells is coupled to the induced expression and actions of IL-5 and IL-1beta. METHODS: Agonist-induced constrictor and relaxant responses were examined in rabbit ASM segments exposed to resting and anti-CD3-activated T cells in the absence and presence of either an anti-IL-5 receptor mAb or the recombinant human IL-1 receptor antagonist. In addition, mRNA and protein expression of IL-5 and IL-1beta were assayed under control and anti-CD3-stimulated conditions. RESULTS: Relative to inactive T cells, incubation of ASM tissues with anti-CD3-activated T cells induced proasthmatic-like changes in agonist-mediated ASM responsiveness. This T cell-induced perturbation in ASM responsiveness was ablated by pretreating the tissues with either an anti-IL-5 receptor mAb or IL-1 receptor antagonist. Moreover, exposure of ASM cells to anti-CD3-activated T cells elicited an initial increased mRNA expression and release of IL-5, followed by an enhanced expression and release of IL-1beta, and the induced release of these cytokines was prevented in ASM cells that were pretreated with an anti-IL-5 receptor mAb. CONCLUSION: Collectively, these observations provide new evidence demonstrating that exposure of naive ASM cells to activated T cells induces the sequential release of IL-5 and IL-1beta from the ASM cells and that the latter cytokines act in an autocrine manner to elicit the proasthmatic phenotype of altered ASM responsiveness.