IL-17A enhances IL-13 activity by enhancing IL-13-induced signal transducer and activator of transcription 6 activation.

BACKGROUND: Increased IL-17A production has been associated with more severe asthma; however, the mechanisms whereby IL-17A can contribute to IL-13-driven pathology in asthmatic patients remain unclear. OBJECTIVE: We sought to gain mechanistic insight into how IL-17A can influence IL-13-driven responses. METHODS: The effect of IL-17A on IL-13-induced airway hyperresponsiveness, gene expression, mucus hypersecretion, and airway inflammation was assessed by using in vivo models of IL-13-induced lung pathology and in vitro culture of murine fibroblast cell lines and primary fibroblasts and human epithelial cell lines or primary human epithelial cells exposed to IL-13, IL-17A, or both. RESULTS: Compared with mice given intratracheal IL-13 alone, those exposed to IL-13 and IL-17A had augmented airway hyperresponsiveness, mucus production, airway inflammation, and IL-13-induced gene expression. In vitro, IL-17A enhanced IL-13-induced gene expression in asthma-relevant murine and human cells. In contrast to the exacerbating influence of IL-17A on IL-13-induced responses, coexposure to IL-13 inhibited IL-17A-driven antimicrobial gene expression in vivo and in vitro. Mechanistically, in both primary human and murine cells, the IL-17A-driven increase in IL-13-induced gene expression was associated with enhanced IL-13-driven signal transducer and activator of transcription 6 activation. CONCLUSIONS: Our data suggest that IL-17A contributes to asthma pathophysiology by increasing the capacity of IL-13 to activate intracellular signaling pathways, such as signal transducer and activator of transcription 6. These data represent the first mechanistic explanation of how IL-17A can directly contribute to the pathogenesis of IL-13-driven pathology.

Enhanced protection from fibrosis and inflammation in the combined absence of IL-13 and IFN-γ.

Persistent or dysregulated IL-13 responses are key drivers of fibrosis in multiple organ systems, and this identifies this cytokine as an important therapeutic target. Nevertheless, the mechanisms by which IL-13 blockade leads to the amelioration of fibrosis remain unclear. Because IFN-γ exhibits potent anti-fibrotic activity, and IL-4Rα signalling antagonizes IFN-γ effector function, compensatory increases in IFN-γ activity following IL-13/IL-4Rα blockade might contribute to the reduction in fibrosis. To investigate the role of IFN-γ, we developed novel IL-13(-/-) /IFN-γ(-/-) double cytokine-deficient mice and examined disease progression in models of type 2-driven fibrosis. As predicted, we showed that fibrosis in the lung and liver are both highly dependent on IL-13. We also observed increased IFN-γ production and inflammatory activity in the tissues of IL-13-deficient mice. Surprisingly, however, an even greater reduction in fibrosis was observed in IL-13/IFN-γ double deficient mice, most notably in the livers of mice chronically infected with Schistosoma mansoni. The increased protection was associated with marked decreases in Tgfb1, Mmp12, and Timp1 mRNA expression in the tissues; reduced inflammation; and decreased expression of important pro-inflammatory mediators such as TNF-α. Experiments conducted with neutralizing monoclonal antibodies to IL-13 and IFN-γ validated the findings with the genetically deficient mice. Together, these studies demonstrate that the reduction in fibrosis observed when IL-13 signalling is suppressed is not dependent on increased IFN-γ activity. Instead, by reducing compensatory increases in type 1-associated inflammation, therapeutic strategies that block IFN-γ and IL-13 activity simultaneously can confer greater protection from progressive fibrosis than IL-13 blockade alone. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Exposure to allergen and diesel exhaust particles potentiates secondary allergen-specific memory responses, promoting asthma susceptibility.

BACKGROUND: Exposure to traffic pollution particulate matter, predominantly diesel exhaust particles (DEPs), increases the risk of asthma and asthma exacerbation; however, the underlying mechanisms remain poorly understood. OBJECTIVE: We sought to examine the effect of DEP exposure on the generation and persistence of allergen-specific memory T cells in asthmatic patients and translate these findings by determining the effect of early DEP exposure on the prevalence of allergic asthma in children. METHODS: The effect of DEPs on house dust mite (HDM)-specific memory responses was determined by using an asthma model. Data from children enrolled in the Cincinnati Childhood Allergy and Air Pollution Study birth cohort were analyzed to determine the effect of DEP exposure on asthma outcomes. RESULTS: DEP coexposure with HDM resulted in persistent TH2/TH17 CD127(+) effector/memory cells in the lungs, spleen, and lymph nodes of adult and neonatal mice. After 7 weeks of rest, a single exposure to HDM resulted in airway hyperresponsiveness and increased TH2 cytokine levels in mice that had been previously exposed to both HDM and DEPs versus those exposed to HDM alone. On the basis of these data, we examined whether DEP exposure was similarly associated with increased asthma prevalence in children in the presence or absence of allergen exposure/sensitization in the Cincinnati Childhood Allergy and Air Pollution Study birth cohort. Early-life exposure to high DEP levels was associated with significantly increased asthma prevalence among allergic children but not among nonallergic children. CONCLUSION: These findings suggest that DEP exposure results in accumulation of allergen-specific TH2/TH17 cells in the lungs, potentiating secondary allergen recall responses and promoting the development of allergic asthma.

Diesel exhaust particle induction of IL-17A contributes to severe asthma.

BACKGROUND: IL-17A has been implicated in severe forms of asthma. However, the factors that promote IL-17A production during the pathogenesis of severe asthma remain undefined. Diesel exhaust particles (DEPs) are a major component of traffic-related air pollution and are implicated in asthma pathogenesis and exacerbation. OBJECTIVE: We sought to determine the mechanism by which DEP exposure affects asthma severity using human and mouse studies. METHODS: BALB/c mice were challenged with DEPs with or without house dust mite (HDM) extract. Airway inflammation and function, bronchoalveolar lavage fluid cytokine levels, and flow cytometry of lung T cells were assessed. The effect of DEP exposure on the frequency of asthma symptoms and serum cytokine levels was determined in children with allergic asthma. RESULTS: In mice exposure to DEPs alone did not induce asthma. DEP and HDM coexposure markedly enhanced airway hyperresponsiveness compared with HDM exposure alone and generated a mixed T(H)2 and T(H)17 response, including IL-13(+)IL-17A(+) double-producing T cells. IL-17A neutralization prevented DEP-induced exacerbation of airway hyperresponsiveness. Among 235 high DEP-exposed children with allergic asthma, 32.2% had more frequent asthma symptoms over a 12-month period compared with only 14.2% in the low DEP-exposed group (P = .002). Additionally, high DEP-exposed children with allergic asthma had nearly 6 times higher serum IL-17A levels compared with low DEP-exposed children. CONCLUSIONS: Expansion of T(H)17 cells contributes to DEP-mediated exacerbation of allergic asthma. Neutralization of IL-17A might be a useful potential therapeutic strategy to counteract the asthma-promoting effects of traffic-related air pollution, especially in highly exposed patients with severe allergic asthma.

Dynamic regulation of platelet-derived growth factor receptor α expression in alveolar fibroblasts during realveolarization.

Although the importance of platelet-derived growth factor receptor (PDGFR)-α signaling during normal alveogenesis is known, it is unclear whether this signaling pathway can regulate realveolarization in the adult lung. During alveolar development, PDGFR-α-expressing cells induce α smooth muscle actin (α-SMA) and differentiate to interstitial myofibroblasts. Fibroblast growth factor (FGF) signaling regulates myofibroblast differentiation during alveolarization, whereas peroxisome proliferator-activated receptor (PPAR)-γ activation antagonizes myofibroblast differentiation in lung fibrosis. Using left lung pneumonectomy, the roles of FGF and PPAR-γ signaling in differentiation of myofibroblasts from PDGFR-α-positive precursors during compensatory lung growth were assessed. FGF receptor (FGFR) signaling was inhibited by conditionally activating a soluble dominant-negative FGFR2 transgene. PPAR-γ signaling was activated by administration of rosiglitazone. Changes in α-SMA and PDGFR-α protein expression were assessed in PDGFR-α-green fluorescent protein (GFP) reporter mice using immunohistochemistry, flow cytometry, and real-time PCR. Immunohistochemistry and flow cytometry demonstrated that the cell ratio and expression levels of PDGFR-α-GFP changed dynamically during alveolar regeneration and that α-SMA expression was induced in a subset of PDGFR-α-GFP cells. Expression of a dominant-negative FGFR2 and administration of rosiglitazone inhibited induction of α-SMA in PDGFR-α-positive fibroblasts and formation of new septae. Changes in gene expression of epithelial and mesenchymal signaling molecules were assessed after left lobe pneumonectomy, and results demonstrated that inhibition of FGFR2 signaling and increase in PPAR-γ signaling altered the expression of Shh, FGF, Wnt, and Bmp4, genes that are also important for epithelial-mesenchymal crosstalk during early lung development. Our data demonstrate for the first time that a comparable epithelial-mesenchymal crosstalk regulates fibroblast phenotypes during alveolar septation.

Epithelial EGF receptor signaling mediates airway hyperreactivity and remodeling in a mouse model of chronic asthma.

Increases in the epidermal growth factor receptor (EGFR) have been associated with the severity of airway thickening in chronic asthmatic subjects, and EGFR signaling is induced by asthma-related cytokines and inflammation. The goal of this study was to determine the role of EGFR signaling in a chronic allergic model of asthma and specifically in epithelial cells, which are increasingly recognized as playing an important role in asthma. EGFR activation was assessed in mice treated with intranasal house dust mite (HDM) for 3 wk. EGFR signaling was inhibited in mice treated with HDM for 6 wk, by using either the drug erlotinib or a genetic approach that utilizes transgenic mice expressing a mutant dominant negative epidermal growth factor receptor in the lung epithelium (EGFR-M mice). Airway hyperreactivity (AHR) was assessed by use of a flexiVent system after increasing doses of nebulized methacholine. Airway smooth muscle (ASM) thickening was measured by morphometric analysis. Sensitization to HDM (IgG and IgE), inflammatory cells, and goblet cell changes were also assessed. Increased EGFR activation was detected in HDM-treated mice, including in bronchiolar epithelial cells. In mice exposed to HDM for 6 wk, AHR and ASM thickening were reduced after erlotinib treatment and in EGFR-M mice. Sensitization to HDM and inflammatory cell counts were similar in all groups, except neutrophil counts, which were lower in the EGFR-M mice. Goblet cell metaplasia with HDM treatment was reduced by erlotinib, but not in EGFR-M transgenic mice. This study demonstrates that EGFR signaling, especially in the airway epithelium, plays an important role in mediating AHR and remodeling in a chronic allergic asthma model.

Early growth response-1 suppresses epidermal growth factor receptor-mediated airway hyperresponsiveness and lung remodeling in mice.

Transforming growth factor (TGF)-alpha and its receptor, the epidermal growth factor receptor, are induced after lung injury and are associated with remodeling in chronic pulmonary diseases, such as pulmonary fibrosis and asthma. Expression of TGF-alpha in the lungs of adult mice causes fibrosis, pleural thickening, and pulmonary hypertension, in addition to increased expression of a transcription factor, early growth response-1 (Egr-1). Egr-1 was increased in airway smooth muscle (ASM) and the vascular adventitia in the lungs of mice conditionally expressing TGF-alpha in airway epithelium (Clara cell secretory protein-rtTA(+/-)/[tetO](7)-TGF-alpha(+/-)). The goal of this study was to determine the role of Egr-1 in TGF-alpha-induced lung disease. To accomplish this, TGF-alpha-transgenic mice were crossed to Egr-1 knockout (Egr-1(ko/ko)) mice. The lack of Egr-1 markedly increased the severity of TGF-alpha-induced pulmonary disease, dramatically enhancing airway muscularization, increasing pulmonary fibrosis, and causing greater airway hyperresponsiveness to methacholine. Smooth muscle hyperplasia, not hypertrophy, caused the ASM thickening in the absence of Egr-1. No detectable increases in pulmonary inflammation were found. In addition to the airway remodeling disease, vascular remodeling and pulmonary hypertension were also more severe in Egr-1(ko/ko) mice. Thus, Egr-1 acts to suppress epidermal growth factor receptor-mediated airway and vascular muscularization, fibrosis, and airway hyperresponsiveness in the absence of inflammation. This provides a unique model to study the processes causing pulmonary fibrosis and ASM thickening without the complicating effects of inflammation.

Type 2 immunity is protective in metabolic disease but exacerbates NAFLD collaboratively with TGF-ß.

Nonalcoholic fatty liver disease (NAFLD) is now the most common progressive liver disease in developed countries and is the second leading indication for liver transplantation due to the extensive fibrosis it causes. NAFLD progression is thought to be tied to chronic low-level type 1 inflammation originating in the adipose tissue during obesity; however, the specific immunological mechanisms regulating the progression of NAFLD-associated fibrosis in the liver are unclear. To investigate the immunopathogenesis of NAFLD more completely, we investigated adipose dysfunction, nonalcoholic steatohepatitis (NASH), and fibrosis in mice that develop polarized type 1 or type 2 immune responses. Unexpectedly, obese interleukin-10 (IL-10)/IL-4-deficient mice (type 1-polarized) were highly resistant to NASH. This protection was associated with an increased hepatic interferon-γ (IFN-γ) signature. Conversely, IFN-γ-deficient mice progressed rapidly to NASH with evidence of fibrosis dependent on transforming growth factor-ß (TGF-ß) and IL-13 signaling. Unlike increasing type 1 inflammation and the marked loss of eosinophils seen in expanding adipose tissue, progression of NASH was associated with increasing eosinophilic type 2 liver inflammation in mice and human patient biopsies. Finally, simultaneous inhibition of TGF-ß and IL-13 signaling attenuated the fibrotic machinery more completely than TGF-ß alone in NAFLD-associated fibrosis. Thus, although type 2 immunity maintains healthy metabolic signaling in adipose tissues, it exacerbates the progression of NAFLD collaboratively with TGF-ß in the liver.

Dual targeting of MEK and PI3K pathways attenuates established and progressive pulmonary fibrosis.

Pulmonary fibrosis is often triggered by an epithelial injury resulting in the formation of fibrotic lesions in the lung, which progress to impair gas exchange and ultimately cause death. Recent clinical trials using drugs that target either inflammation or a specific molecule have failed, suggesting that multiple pathways and cellular processes need to be attenuated for effective reversal of established and progressive fibrosis. Although activation of MAPK and PI3K pathways have been detected in human fibrotic lung samples, the therapeutic benefits of in vivo modulation of the MAPK and PI3K pathways in combination are unknown. Overexpression of TGFα in the lung epithelium of transgenic mice results in the formation of fibrotic lesions similar to those found in human pulmonary fibrosis, and previous work from our group shows that inhibitors of either the MAPK or PI3K pathway can alter the progression of fibrosis. In this study, we sought to determine whether simultaneous inhibition of the MAPK and PI3K signaling pathways is a more effective therapeutic strategy for established and progressive pulmonary fibrosis. Our results showed that inhibiting both pathways had additive effects compared to inhibiting either pathway alone in reducing fibrotic burden, including reducing lung weight, pleural thickness, and total collagen in the lungs of TGFα mice. This study demonstrates that inhibiting MEK and PI3K in combination abolishes proliferative changes associated with fibrosis and myfibroblast accumulation and thus may serve as a therapeutic option in the treatment of human fibrotic lung disease where these pathways play a role.

Rapamycin decreases airway remodeling and hyperreactivity in a transgenic model of noninflammatory lung disease.

Airway hyperreactivity (AHR) and remodeling are cardinal features of asthma and chronic obstructive pulmonary disease. New therapeutic targets are needed as some patients are refractory to current therapies and develop progressive airway remodeling and worsening AHR. The mammalian target of rapamycin (mTOR) is a key regulator of cellular proliferation and survival. Treatment with the mTOR inhibitor rapamycin inhibits inflammation and AHR in allergic asthma models, but it is unclear if rapamycin can directly inhibit airway remodeling and AHR, or whether its therapeutic effects are entirely mediated through immunosuppression. To address this question, we utilized transforming growth factor-α (TGF-α) transgenic mice null for the transcription factor early growth response-1 (Egr-1) (TGF-α Tg/Egr-1(ko/ko) mice). These mice develop airway smooth muscle thickening and AHR in the absence of altered lung inflammation, as previously reported. In this study, TGF-α Tg/Egr-1(ko/ko) mice lost body weight and developed severe AHR after 3 wk of lung-specific TGF-α induction. Rapamycin treatment prevented body weight loss, airway wall thickening, abnormal lung mechanics, and increases in airway resistance to methacholine after 3 wk of TGF-α induction. Increases in tissue damping and airway elastance were also attenuated in transgenic mice treated with rapamycin. TGF-α/Egr-1(ko/ko) mice on doxycycline for 8 wk developed severe airway remodeling. Immunostaining for α-smooth muscle actin and morphometric analysis showed that rapamycin treatment prevented airway smooth muscle thickening around small airways. Pentachrome staining, assessments of lung collagen and fibronectin mRNA levels, indicated that rapamycin also attenuated fibrotic pathways induced by TGF-α expression for 8 wk. Thus rapamycin reduced airway remodeling and AHR, demonstrating an important role for mTOR signaling in TGF-α-induced/EGF receptor-mediated reactive airway disease.