Transforming Growth Factor β1 Function in Airway Remodeling and Hyperresponsiveness. The Missing Link?

An overview of high-mobility group box 1, a potent pro-inflammatory cytokine in asthma

High-mobility group box 1 (HMGB1), also called amphoterin, HMG1 and p30, is a highly conserved protein between different species that has various functions in nucleus such as stabilization of nucleosome formation, facilitation of deoxyribonucleic acid (DNA) bending and increasing the DNA transcription, replication and repair. It has also been indicated that HMGB1 acts as a potent pro-inflammatory cytokine with increasing concentrations in acute and chronic inflammatory diseases. Asthma is a common chronic respiratory disease associated with high morbidity and mortality rates. One central characteristic in its pathogenesis is airway inflammation. Considering the inflammatory role of HMGB1 and importance of inflammation in asthma pathogenesis, a better understanding of this protein is vital. This review describes the structure, cell surface receptors, signaling pathways and intracellular and extracellular functions of HMGB1, but also focuses on its inflammatory role in asthma. Moreover, this manuscript reviews experimental and clinical studies that investigated the pathologic role of HMGB1.

Transforming Growth Factor-β1 Decreases β2-Agonist-induced Relaxation in Human Airway Smooth Muscle

Helper T effector cytokines implicated in asthma modulate the contractility of human airway smooth muscle (HASM) cells. We have reported recently that a profibrotic cytokine, transforming growth factor (TGF)-β1, induces HASM cell shortening and airway hyperresponsiveness. Here, we assessed whether TGF-β1 affects the ability of HASM cells to relax in response to β₂-agonists, a mainstay treatment for airway hyperresponsiveness in asthma. Overnight TGF-β1 treatment significantly impaired isoproterenol (ISO)-induced relaxation of carbachol-stimulated, isolated HASM cells. This single-cell mechanical hyporesponsiveness to ISO was corroborated by sustained increases in myosin light chain phosphorylation. In TGF-β1-treated HASM cells, ISO evoked markedly lower levels of intracellular cAMP. These attenuated cAMP levels were, in turn, restored with pharmacological and siRNA inhibition of phosphodiesterase 4 and Smad3, respectively. Most strikingly, TGF-β1 selectively induced phosphodiesterase 4D gene expression in HASM cells in a Smad2/3-dependent manner. Together, these data suggest that TGF-β1 decreases HASM cell β₂-agonist relaxation responses by modulating intracellular cAMP levels via a Smad2/3-dependent mechanism. Our findings further define the mechanisms underlying β₂-agonist hyporesponsiveness in asthma, and suggest TGF-β1 as a potential therapeutic target to decrease asthma exacerbations in severe and treatment-resistant asthma.

In Vivo Allergen-Activated Eosinophils Promote Collagen I and Fibronectin Gene Expression in Airway Smooth Muscle Cells via TGF-β1 Signaling Pathway in Asthma

Eosinophils infiltration and releasing TGF-β1 in the airways has been implicated in the pathogenesis of asthma, especially during acute episodes provoked by an allergen. TGF-β1 is a major mediator involved in pro-inflammatory responses and fibrotic tissue remodeling in asthma. We aimed to evaluate the effect of in vivo allergen-activated eosinophils on the expression of COL1A1 and FN in ASM cells in asthma. A total of 12 allergic asthma patients and 11 healthy subjects were examined. All study subjects underwent bronchial challenge with D. pteronyssinus allergen. Eosinophils from peripheral blood were isolated before and 24 h after the bronchial allergen challenge using high-density centrifugation and magnetic separation. Individual co-cultures of blood eosinophils and immortalized human ASM cells were prepared. The TGF-β1 concentration in culture supernatants was analyzed using ELISA. Gene expression was analyzed using qRT-PCR. Eosinophils integrins were suppressed with linear RGDS peptide before co-culture with ASM cells. Results: The expression of TGF-β1 in asthmatic eosinophils significantly increased over non-activated asthmatic eosinophils after allergen challenge, p < 0.001. The TGF-β1 concentration in culture supernatants was significantly higher in samples with allergen-activated asthmatic eosinophils compared to baseline, p < 0.05. The effect of allergen-activated asthmatic eosinophils on the expression of TGF-β1, COL1A1, and FN in ASM cells was more significant compared to non-activated eosinophils, p < 0.05, however, no difference was found on WNT-5A expression. The incubation of allergen-activated asthmatic eosinophils with RGDS peptide was more effective compared to non-activated eosinophils as the gene expression in ASM cells was downregulated equally to the same level as healthy eosinophils.

Mechanical forces induce an asthma gene signature in healthy airway epithelial cells

Bronchospasm compresses the bronchial epithelium, and this compressive stress has been implicated in asthma pathogenesis. However, the molecular mechanisms by which this compressive stress alters pathways relevant to disease are not well understood. Using air-liquid interface cultures of primary human bronchial epithelial cells derived from non-asthmatic donors and asthmatic donors, we applied a compressive stress and then used a network approach to map resulting changes in the molecular interactome. In cells from non-asthmatic donors, compression by itself was sufficient to induce inflammatory, late repair, and fibrotic pathways. Remarkably, this molecular profile of non-asthmatic cells after compression recapitulated the profile of asthmatic cells before compression. Together, these results show that even in the absence of any inflammatory stimulus, mechanical compression alone is sufficient to induce an asthma-like molecular signature.

Transcriptomic changes during TGF-β-mediated differentiation of airway fibroblasts to myofibroblasts

Asthma is the most common chronic lung disease in children and young adults worldwide. Airway remodelling (including increased fibroblasts and myofibroblasts in airway walls due to chronic inflammation) differentiates asthmatic from non-asthmatic airways. The increase in airway fibroblasts and myofibroblasts occurs via epithelial to mesenchymal transition (EMT) where epithelial cells lose their tight junctions and are transdifferentiated to mesenchymal cells, with further increases in myofibroblasts occurring via fibroblast-myofibroblast transition (FMT). Transforming growth factor (TGF)-β is the central EMT- and FMT-inducing cytokine. In this study, we have used next generation sequencing to delineate the changes in the transcriptome induced by TGF-β treatment of WI-38 airway fibroblasts in both the short term and after differentiation into myofibroblasts, to gain an understanding of the contribution of TGF-β induced transdifferentiation to the asthmatic phenotype. The data obtained from RNAseq analysis was confirmed by quantitative PCR (qPCR) and protein expression investigated by western blotting. As expected, we found that genes coding for intermediates in the TGF-β signalling pathways (SMADs) were differentially expressed after TGF-β treatment, SMAD2 being upregulated and SMAD3 being downregulated as expected. Further, genes involved in cytoskeletal pathways (FN1, LAMA, ITGB1) were upregulated in myofibroblasts compared to fibroblasts. Importantly, genes that were previously shown to be changed in asthmatic lungs (ADAMTS1, DSP, TIMPs, MMPs) were similarly differentially expressed in myofibroblasts, strongly suggesting that TGF-β mediated differentiation of fibroblasts to myofibroblasts may underlie important changes in the asthmatic airway. We also identified new intermediates of signalling pathways (PKB, PTEN) that are changed in myofibroblasts compared to fibroblasts. We have found a significant number of genes that are altered after TGF-β induced transdifferentiation of WI-38 fibroblasts into myofibroblasts, many of which were expected or predicted. We also identified novel genes and pathways that were affected after TGF-β treatment, suggesting additional pathways are activated during the transition between fibroblasts and myofibroblasts and may contribute to the asthma phenotype.

Exhaled TGF-β1 levels before and after an exercise challenge in asthmatic and healthy children, and during exacerbation

BACKGROUND

There is conflicting data regarding the role of transforming growth factor-β1 (TGF-β1) in the pathogenesis of airway hyper-reactivity and asthma exacerbation.

OBJECTIVE

To investigate the role of exhaled-TGF-β1 in exercise-induced bronchospasm (EIB) in asthmatic and nonasthmatic healthy children, and in asthma exacerbation and asthma control.

METHODS

The exhaled-TGF-β1 levels of 56 stable asthmatic children and 15 nonasthmatic healthy children were evaluated before and 30 min after an exercise challenge. The exhaled-TGF-β1 levels of 20 additional children with asthma exacerbation were evaluated.

RESULTS

While no significant difference in the exhaled-TGF-β1 levels was found at the baseline, exhaled-TGF-β1 levels after the exercise challenge were significantly higher in the non-EIB (n = 31) asthmatics when compared to the asthmatic children with EIB (n = 25) (p = 0.04). Although there was a statistically significant increase in the concentration of the exhaled-TGF-β1 after the exercise challenge in the non-EIB asthmatics (p = 0.008), the concentration of the TGF-β1 was not increased after the exercise challenge in EIB + asthmatics. The exhaled-TGF-β1 was significantly correlated with the ACT score (p = 0.01, r = 0.49) and the baseline FEV₁ level (p = 0.02, r = 0.35). The exhaled-TGF-β1 levels were significantly higher in the stable asthmatic children when compared to the nonasthmatic children (p < 0.0001). There was no significant difference in exhaled-TGF-β1 levels after the exercise challenge in the nonasthmatics. The exhaled-TGF-β1 levels were significantly lower in those children with asthma exacerbation when compared to the stable asthmatic children (p = 0.0003).

CONCLUSION

Our results suggest that TGF-β1 may play a role in suppressing airway reactivity and its deficiency is associated with asthma exacerbation.

Tetrandrine Ameliorates Airway Remodeling of Chronic Asthma by Interfering TGF-β1/Nrf-2/HO-1 Signaling Pathway-Mediated Oxidative Stress

Background

Imbalanced oxidative stress and antioxidant defense are involved in airway remodeling in asthma. It has been demonstrated that Tetrandrine has a potent role in antioxidant defense in rheumatoid arthritis and hypertension. However, the correlation between Tetrandrine and oxidative stress in asthma is utterly blurry. This study aimed to investigate the role of Tetrandrine on oxidative stress-mediated airway remolding.

Materials and Methods

Chronic asthma was established by ovalbumin (OVA) administration in male Wistar rats. Histopathology was determined by HE staining. Immunofluorescence was employed to detect the expression of α-SMA and Nrf-2. Level of oxidative stress and matrix metalloproteinases were examined by ELISA kits. Cell viability and cell cycle of primary airway smooth muscle cells (ASMCs) were evaluated by CCK8 and flow cytometry, respectively. Signal molecules were detected using western blot.

Results

Tetrandrine effectively impairs OVA-induced airway inflammatory and airway remodeling by inhibiting the expression of CysLT1 and CysLTR1. The increase of oxidative stress and subsequent enhancement of MMP9 and TGF-β1 expression were rescued by the administration of Tetrandrine in the rat model of asthma. In in vitro experiments, Tetrandrine markedly suppressed TGF-β1-evoked cell viability and cell cycle promotion of ASMCs in a dose-dependent manner. Furthermore, Tetrandrine promoted Nrf-2 nuclear transcription and activated its downstream HO-1 in vivo and in vitro.

Conclusion

Tetrandrine attenuates airway inflammatory and airway remodeling in rat model of asthma and TGF-β1-induced cell proliferation of ASMCs by regulating oxidative stress in primary ASMCs, suggesting that Tetrandrine possibly is an effective candidate therapy for asthma.

Insulin resistance mediates high-fat diet-induced pulmonary fibrosis and airway hyperresponsiveness through the TGF-β1 pathway

Prior studies have reported the presence of lung fibrosis and enhanced airway hyperresponsiveness (AHR) in mice with high-fat-diet (HFD)-induced obesity. This study evaluated the role of TGF-β1 in HFD-induced AHR and lung fibrosis in a murine model. We generated HFD-induced obesity mice and performed glucose and insulin tolerance tests. HFD mice with or without ovalbumin sensitization and challenge were also treated with an anti-TGF-β1 neutralizing antibody. AHR to methacholine, inflammatory cells in the bronchoalveolar lavage fluid (BALF), and histological features were evaluated. Insulin was intranasally administered to normal diet (ND) mice, and in vitro insulin stimulation of BEAS-2b cells was performed. HFD-induced obesity mice had increased insulin resistance, enhanced AHR, peribronchial and perivascular fibrosis, and increased numbers of macrophages in the BALF. However, they did not have meaningful eosinophilic or neutrophilic inflammation in the lungs compared with ND mice. The HFD enhanced TGF-β1 expression in the bronchial epithelium, but we found no differences in the expression of interleukin (IL)−4 or IL-5 in lung homogenates. Administration of the anti-TGF-β1 antibody attenuated HFD-induced AHR and lung fibrosis. It also attenuated goblet cell hyperplasia, but did not affect the AHR and inflammatory cell infiltration induced by OVA challenge. The intranasal administration of insulin enhanced TGF-β1 expression in the bronchial epithelium and lung fibrosis. Stimulating BEAS-2b cells with insulin also increased TGF-β1 production by 24 h. We concluded that HFD-induced obesity-associated insulin resistance enhances TGF-β1 expression in the bronchial epithelium, which may play an important role in the development of lung fibrosis and AHR in obesity.

Insulin resistance may be an important causative factor underlying the increased risk of asthma and other respiratory issues in obese individuals. Obesity doubles the likelihood of developing asthma, with symptoms that are more difficult to control than in non-obese patients. The connection between these conditions is poorly understood, but researchers led by Jung-Won Park, Yonsei University College of Medicine, Seoul, South Korea, have identified a potential mechanism. They demonstrated that a signaling molecule called TGF-β1 contributes to airway sensitivity and tissue scarring in a mouse model of diet-induced obesity. Subsequent experiments showed that treatment with insulin also gives rise to increased TGF-β1 production in the mouse lung. Since insulin resistance is a common feature of obesity, resulting in abnormally high levels of circulating insulin, this could also account for the increased risk of respiratory problems.

Role of TRPC1 channels in pressure-mediated activation of airway remodeling

Background

Bronchoconstriction and cough, a characteristic of the asthmatic response, leads to development of compressive stresses in the airway wall. We hypothesized that progressively pathological high mechanical stress could act on mechanosensitive cation channels, such as transient receptor potential channel 1 (TRPC1) and then contributes to airway remodeling.

Methods

We imitate the pathological airway pressure in vitro using cyclic stretch at 10 and 15% elongation. Ca²⁺ imaging was applied to measure the activity of TRPC1 after bronchial epithelial cells exposed to cyclic stretch for 0, 0.5, 1, 1.5, 2, 2.5 h. To further clarify the function of channnel TRPC1 in the process of mechano-transduction in airway remodeling, the experiment in vivo was implemented. The TRPC1 siRNA and budesonide were applied separately to asthmatic models. The morphological changes were measured by HE and Massion method. The expression levels of TRPC1 were evaluated by real-time PCR, western blot and immunohistochemistry. The protein expression level of IL-13, TGF-β₁ and MMP-9 in BALF were measured by ELISA.

Results

The result showed that cyclic stretch for 15% elongation at 1.5 h could maximize the activity of TRPC1 channel. This influx in Ca²⁺ was blocked by TRPC1 siRNA. Higher TRPC1 expression was observed in the bronchial epithelial layer of ovalbumin induced asthmatic models. The knockdown of TRPC1 with TRPC1 siRNA was associated with a hampered airway remodeling process, such as decreased bronchial wall thickness and smooth muscle hypertrophy/hyperplasia, a decreased ECM deposition area and inflammation infiltration around airway wall. Meantime, expression of IL-13, TGF-β₁ and MMP-9 in OVA+TRPC1 siRNA also showed reduced level. TRPC1 intervention treatment showed similar anti-remodeling therapeutic effect with budesonide.

Conclusions

These results demonstrate that most TRPC1 channels expressed in bronchial epithelial cells mediate the mechanotransduction mechanism. TRPC1 inducing abnormal Ca²⁺ signal mediates receptor-stimulated and mechanical stimulus-induced airway remodeling. The inhibition of TRPC1 channel could produce similar therapeutic effect as glucocortisteroid to curb the development of asthmatic airway remodeling.

Extracellular Matrix Component Remodeling in Respiratory Diseases: What Has Been Found in Clinical and Experimental Studies?

Changes in extracellular matrix (ECM) components in the lungs are associated with the progression of respiratory diseases, such as asthma, chronic obstructive pulmonary disease (COPD), and acute respiratory distress syndrome (ARDS). Experimental and clinical studies have revealed that structural changes in ECM components occur under chronic inflammatory conditions, and these changes are associated with impaired lung function. In bronchial asthma, elastic and collagen fiber remodeling, mostly in the airway walls, is associated with an increase in mucus secretion, leading to airway hyperreactivity. In COPD, changes in collagen subtypes I and III and elastin, interfere with the mechanical properties of the lungs, and are believed to play a pivotal role in decreased lung elasticity, during emphysema progression. In ARDS, interstitial edema is often accompanied by excessive deposition of fibronectin and collagen subtypes I and III, which can lead to respiratory failure in the intensive care unit. This review uses experimental models and human studies to describe how inflammatory conditions and ECM remodeling contribute to the loss of lung function in these respiratory diseases.

MicroRNA-744 Inhibits Proliferation of Bronchial Epithelial Cells by Regulating Smad3 Pathway via Targeting Transforming Growth Factor-β1 (TGF-β1) in Severe Asthma

BACKGROUND Bronchial epithelial cells proliferation plays a pivotal role in airway remodeling in children with severe asthma. MicroRNAs (miRNAs) have gained great attention for many diseases, including asthma. The purpose of this study was to explore the mechanisms that underlie miR-744 modulating bronchial epithelial cells proliferation in severe asthma in children. MATERIAL AND METHODS Bronchial epithelial cells were isolated from bronchial biopsies of normal controls and asthmatic subjects. miR-744 and transforming growth factor-ß1 (TGF-ß1) expressions were measured by quantitative reverse transcription PCR (qRT-PCR). Proliferating cell nuclear antigen (PCNA), phosphorylation or total of mothers against decapentaplegic homolog3 (Smad3) and production of Smad anchor for receptor activation (SARA) were measured via Western blot analysis. A link between miR-744 and TGF-ß1 was probed by luciferase activity and RNA immunoprecipitation. Cell proliferation was evaluated using the Cell Proliferation Assay Kit. RESULTS Severe asthma showed a significantly elevated cell proliferation rate and reduced abundance of miR-744, which in turn inhibited cell proliferation of bronchial epithelial cells. In particular, TGF-ß1 might be a candidate target of miR-744, and enrichment of miR-744 lowered the expression of TGF-ß1 at mRNA and protein levels. Indeed, overexpression of miR-744 lowered the proliferation rate of bronchial epithelial cells via driving TGF-ß1. Moreover, addition of miR-744 limited phosphorylation of Smad3 but reversed SARA protein abundance by regulating TGF-ß1. CONCLUSIONS The presence of miR-744 repressed bronchial epithelial cells proliferation through mediating the Smad3 pathway by modulating TGF-ß1, providing a promising therapeutic approach for epithelial function in severe asthma.

Regulation of IL-17A and implications for TGF-β1 comodulation of airway smooth muscle remodeling in severe asthma

Severe asthma develops as a result of heightened, persistent symptoms that generally coincide with pronounced neutrophilic airway inflammation. In individuals with severe asthma, symptoms are poorly controlled by high-dose inhaled glucocorticoids and often lead to elevated morbidity and mortality rates that underscore the necessity for novel drug target identification that overcomes limitations in disease management. Many incidences of severe asthma are mechanistically associated with T helper 17 (T_H17) cell-derived cytokines and immune factors that mediate neutrophilic influx to the airways. T_H17-secreted interleukin-17A (IL-17A) is an independent risk factor for severe asthma that impacts airway smooth muscle (ASM) remodeling. T_H17-derived cytokines and diverse immune mediators further interact with structural cells of the airway to induce pathophysiological processes that impact ASM functionality. Transforming growth factor-β1 (TGF-β1) is a pivotal mediator involved in airway remodeling that correlates with enhanced T_H17 activity in individuals with severe asthma and is essential to T_H17 differentiation and IL-17A production. IL-17A can also reciprocally enhance activation of TGF-β1 signaling pathways, whereas combined T_H1/T_H17 or T_H2/T_H17 immune responses may additively impact asthma severity. This review seeks to provide a comprehensive summary of cytokine-driven T cell fate determination and T_H17-mediated airway inflammation. It will further review the evidence demonstrating the extent to which IL-17A interacts with various immune factors, specifically TGF-β1, to contribute to ASM remodeling and altered function in T_H17-driven endotypes of severe asthma.

Bu-Shen-Yi-Qi formula ameliorates airway remodeling in murine chronic asthma by modulating airway inflammation and oxidative stress in the lung

Bu-Shen-Yi-Qi formula (BSYQF) could suppress chronic airway inflammation according to previous studies. However, there is relatively little direct experimental evidence to evaluate the effects of BSYQF treatment on airway remodeling in chronic asthma. Recent evidence suggests that oxidative stress is involved in airway inflammation and airway remodeling in chronic asthma. BSYQF which includes various of chemical components having antioxidant effects, could be beneficial in attenuating airway remodeling in chronic asthma. The purpose of this study was to elucidate the effect of BSYQF treatment on airway remodeling and investigate its potential mechanisms in chronic asthma. To develop the murine models of chronic asthma, BALB/c mice were sensitized and challenged to ovalbumin for 8 weeks. BSYQF (5, 10, 20 g raw herbs/kg body weight) or tiotropium bromide (0.1 mM) were administered orally and intranasal instillation, respectively. The effect of BSYQF on pulmonary inflammation and remodeling was evaluated. The parameters of oxidative stress in the lung were analyzed. BSYQF treatment reduced airway hyperresponsiveness (AHR), Th2 response including IL-4, IL-13, and OVA-specific IgE and IgG1, transforming growth factor-β (TGF-β), vascular endothelium growth factor (VEGF), airway inflammation and airway remodeling including smooth muscle thickening and peribronchial collagen deposition. As for oxidative stress, BSYQF treatment reduced reactive oxygen species (ROS), Malondialdehyde (MDA), NO, and the expression of inducible nitric oxide synthase (iNOS), but increased significantly glutathione (GSH) /Oxidized glutathione(GSSH) ratios in the lung, restored mitochondrial ultrastructural changes of bronchial epithelia and ATP levels in the lung. In summary, this study suggested that BSYQF treatment ameliorated airway remodeling and alleviated asthmatic features in chronic asthma models. Anti-inflammatory and antioxidant effect of BSYQF may explain why BSYQF has effects on preventing airway remodeling.

Nebulized Inhalation of Anti-Nerve Growth Factor Microspheres Inhibits Airway Remodeling in an Ovalbumin-Induced Rat Asthma Model

BACKGROUND

Airway remodeling is considered an important factor in refractory and uncontrollable asthma. Previous studies have confirmed that anti-nerve growth factor (NGF) antibody can ameliorate airway remodeling. However, whether nebulized inhalation of anti-NGF microspheres (NANM) can inhibit airway remodeling is not clear. The purpose of this study was to investigate the effects of NANM on ovalbumin (OVA)-induced airway remodeling, and the mechanisms involved.

METHODS

Anti-NGF microspheres were produced using a polymer alloy method. OVA was used to establish a rat model of asthma airway remodeling. Rats were treated with inhalation atomized anti-NGF antibody or NANM. Airway inflammation, airway reactivity, and airway remodeling were measured. Lung tissue P-Smad₃ and tumor growth factor (TGF)-β₁ mRNA and protein expression were also measured.

RESULTS

The anti-NGF antibody microsphere encapsulation rate was high, and the release time was long. NANM markedly attenuated OVA-induced airway remodeling, such as collagen deposition, average pulmonary resistance, the WAm/Pbm, WAt/Pbm, and Wcol/Pbm ratios (WAt, bronchial wall area; Pbm, perimeter of basement membrane; WAm, smooth muscle wall area; Wcol, airway collagen fiber area). Compared with the anti-NGF antibody group and the OVA group, the expression of TGF-β₁ mRNA, TGF-β₁ protein, and P-Smad₃ in the NANM group were markedly decreased.

CONCLUSIONS

NANM ameliorated OVA-induced airway remodeling, partly through regulation of the TGF-β₁/Smad₃ pathway.

IRAK-M Associates with Susceptibility to Adult-Onset Asthma and Promotes Chronic Airway Inflammation

IL-1R-associated kinase (IRAK)-M regulates lung immunity during asthmatic airway inflammation. However, the regulatory effect of IRAK-M differs when airway inflammation persists. A positive association between IRAK-M polymorphisms with childhood asthma has been reported. In this study, we investigated the role of IRAK-M in the susceptibility to adult-onset asthma and in chronic airway inflammation using an animal model. Through genetic analysis of IRAK-M polymorphisms in a cohort of adult-onset asthma patients of Chinese Han ethnicity, we identified two IRAK-M single nucleotide polymorphisms, rs1624395 and rs1370128, genetically associated with adult-onset asthma. Functionally, the top-associated rs1624395, with an enhanced affinity to the transcription factor c-Jun, was associated with a higher expression of IRAK-M mRNA in blood monocytes. In contrast to the protective effect of IRAK-M in acute asthmatic inflammation, we found a provoking impact of IRAK-M on chronic asthmatic inflammation. Following chronic OVA stimulation, IRAK-M knockout (KO) mice presented with significantly less inflammatory cells, a lower Th2 cytokine level, a higher IFN-γ concentration, and increased percentage of Th1 cells in the lung tissue than wild type mice. Moreover, lung dendritic cells (DC) from OVA-treated IRAK-M KO mice expressed a higher percentage of costimulatory molecules PD-L1 and PD-L2. Mechanistically, in vitro TLR ligation led to a greater IFN-γ production by IRAK-M KO DCs than wild type DCs. These findings demonstrated a distinctive role of IRAK-M in maintaining chronic Th2 airway inflammation via inhibiting the DC-mediated Th1 activation and indicated a complex role for IRAK-M in the initiation and progression of experimental allergic asthma.

Genes and Pathways Regulating Decline in Lung Function and Airway Remodeling in Asthma

Asthma is a common disorder of the airways characterized by airway inflammation and by decline in lung function and airway remodeling in a subset of asthmatics. Airway remodeling is characterized by structural changes which include airway smooth muscle hypertrophy/hyperplasia, subepithelial fibrosis due to thickening of the reticular basement membrane, mucus metaplasia of the epithelium, and angiogenesis. Epidemiologic studies suggest that both genetic and environmental factors may contribute to decline in lung function and airway remodeling in a subset of asthmatics. Environmental factors include respiratory viral infection-triggered asthma exacerbations, and tobacco smoke. There is also evidence that several asthma candidate genes may contribute to decline in lung function, including ADAM33, PLAUR, VEGF, IL13, CHI3L1, TSLP, GSDMB, TGFB1, POSTN, ESR1 and ARG2. In addition, mediators or cytokines, including cysteinyl leukotrienes, matrix metallopeptidase-9, interleukin-33 and eosinophil expression of transforming growth factor-β, may contribute to airway remodeling in asthma. Although increased airway smooth muscle is associated with reduced lung function (i.e. forced expiratory volume in 1 second) in asthma, there have been few long-term studies to determine how individual pathologic features of airway remodeling contribute to decline in lung function in asthma. Clinical studies with inhibitors of individual gene products, cytokines or mediators are needed in asthmatic patients to identify their individual role in decline in lung function and/or airway remodeling.

Serum Periostin Levels: A Potential Serologic Marker for Toluene Diisocyanate-Induced Occupational Asthma

PURPOSE

Toluene diisocyanate (TDI) is a leading cause of occupational asthma (OA). Periostin is a matricellular protein implicated in type 2 immunity-driven asthma. Its pathogenic role in TDI-OA has not been completely elucidated. The present study was performed to investigate the role of periostin in TDI-OA.

MATERIALS AND METHODS

Serum periostin levels were measured in subjects with TDI-OA, asymptomatic TDI-exposure controls (AECs), non-occupational asthmatics (NAs), and unexposed normal controls (NCs). To understand the mechanism by which TDI induces periostin production, primary small airway epithelial cells (SAECs) were cultured under stimulation of TDI and neutrophils from asthmatic patients.

RESULTS

Fifty-three subjects with TDI-OA, 71 AECs, 67 NAs, and 83 NCs were enrolled. Serum periostin levels were significantly higher in TDI-OA subjects than in AECs (p=0.001), NAs (p<0.001), and NCs (p<0.001). In TDI-exposed subjects (TDI-OA and AEC), the PC₂₀ methacholine levels were significantly lower in subjects with a higher periostin level than in those with a lower periostin level. TDI exposure did not increase periostin production directly by SAECs; however, periostin production increased significantly after co-culture with TDI and neutrophils, which was suppressed by an antioxidant. In addition, increased release of TGF-β1 was noted from SAECs when exposed to TDI and neutrophils, which was also suppressed by an antioxidant.

CONCLUSION

These results suggest that an increased periostin level may contribute to the progression of airway inflammation to remodeling in TDI-exposed workers. A high serum periostin level is a potential serologic marker of the phenotype of TDI-OA.

Fibroblast-to-myofibroblast transition in bronchial asthma

Bronchial asthma is a chronic inflammatory disease in which bronchial wall remodelling plays a significant role. This phenomenon is related to enhanced proliferation of airway smooth muscle cells, elevated extracellular matrix protein secretion and an increased number of myofibroblasts. Phenotypic fibroblast-to-myofibroblast transition represents one of the primary mechanisms by which myofibroblasts arise in fibrotic lung tissue. Fibroblast-to-myofibroblast transition requires a combination of several types of factors, the most important of which are divided into humoural and mechanical factors, as well as certain extracellular matrix proteins. Despite intensive research on the nature of this process, its underlying mechanisms during bronchial airway wall remodelling in asthma are not yet fully clarified. This review focuses on what is known about the nature of fibroblast-to-myofibroblast transition in asthma. We aim to consider possible mechanisms and conditions that may play an important role in fibroblast-to-myofibroblast transition but have not yet been discussed in this context. Recent studies have shown that some inherent and previously undescribed features of fibroblasts can also play a significant role in fibroblast-to-myofibroblast transition. Differences observed between asthmatic and non-asthmatic bronchial fibroblasts (e.g., response to transforming growth factor β, cell shape, elasticity, and protein expression profile) may have a crucial influence on this phenomenon. An accurate understanding and recognition of all factors affecting fibroblast-to-myofibroblast transition might provide an opportunity to discover efficient methods of counteracting this phenomenon.

TGF-β1-Induced Airway Smooth Muscle Cell Proliferation Involves TRPM7-Dependent Calcium Influx via TGFβR/SMAD3

BACKGROUND

TRPM7 in mast cells plays a key role in asthma. However, the effect of TRPM7 on TGF-β1-induced airway smooth muscle cell (ASMC) proliferation remains unclear. Therefore, we designed this study to explore whether TRPM7 is involved in TGF-β1-induced ASMC proliferation.

METHODS

An asthmatic mouse model was established, and the expressions of TGF-β1 and TRPM7 in mice lungs were detected using enzyme-linked immunosorbent assay (ELISA) and western blotting. In addition, murine ASMCs were cultured and stimulated with TGF-β1. Possible TGF-β1 and TRPM7 interactions were examined using RT-PCR and western blotting analyses with ASMCs. The effect of TRPM7 knockdown on ASMC calcium influx was assessed by the fluorescent indicator indo-1. MTT and flow cytometry were applied to evaluate the effects of TRPM7 knockdown on ASMC proliferation and apoptosis.

RESULTS

TGF-β1 elevated the expression of TRPM7 via TGFβR/SMAD3. Knocking down TRPM7 decreased the intracellular Ca²⁺ concentration and cellular proliferation of ASMCs, although apoptosis remained unaffected.

CONCLUSIONS

Our initial findings suggest that TRPM7 inhibition may prevent asthma-induced airway remodeling.

BMS‑345541 inhibits airway inflammation and epithelial‑mesenchymal transition in airway remodeling of asthmatic mice

The present study aimed to investigate the possible effects and regulatory mechanism of the inhibitor of nuclear factor‑κB kinase complex β subunit (IKKβ) inhibitor BMS‑345541 on airway inflammation, airway remodeling and epithelial‑mesenchymal transition (EMT) in an ovalbumin (OVA) exposure asthma model in mice. The asthma mouse model was generated by sensitization and challenge with OVA. BMS‑345541/dimethyl sulfoxide (DMSO) was administered perorally dairy in two therapeutic groups throughout the entire OVA challenge process. At 24 h following the last challenge, airway hyperresponsiveness (AHR) and airway inflammation were examined, and serum, bronchoalveolar lavage fluid (BALF) and lung samples were collected. Lung tissue was stained and assessed for pathological changes. The total number and classification of inflammatory cells in the BALF were examined. Levels of transforming growth factor β1 (TGFβ1) in the serum and BALF were measured using an enzyme‑linked immunosorbent assay. The differential expression of EMT regulators E‑cadherin and vimentin was detected by immunohistochemical staining, reverse transcription‑quantitative polymerase chain reaction analysis and western blot analysis. The results showed that OVA successfully induced allergic asthma. The asthmatic mice had AHR, airway inflammation, airway remodeling, a high expression of TGFβ1, and evidence of EMT. Following BMS‑345541 treatment, there was significant inhibition of pathophysiological signs, including increased pulmonary eosinophilia infiltration, mucus hypersecretion and AHR. Treatment with BMS‑345541 significantly reduced levels of TGFβ1. In addition, BMS‑345541 notably downregulated the expression of vimentin and increased the expression of E‑cadherin. These data suggested that the increased secretion of TGFβ1 induced by asthmatic inflammation can lead to EMT, and the IKKβ inhibitor BMS‑345541 may alter airway remodeling by preventing EMT in an OVA asthma model. Therefore, IKKβ inhibitors require investigation as potential asthma therapies.

Effects of ozone stimulation of bronchial epithelial cells on proliferation and collagen synthesis of co-cultured lung fibroblasts

Ozone (O₃) as a major air pollutant is widely recognized for causing pathological changes of the airway system. However, it is not clear whether O₃ exposure of bronchial epithelial cells (BECs) influences the proliferation and collagen synthesis of submucosal fibroblasts and contributes to the pathogenesis of airway remodeling in diseases, including asthma. In the present study, a co-culture method was applied to culture human lung fibroblasts (HLFs) with human bronchial epithelial cells (HBECs) that were pre-stimulated with O₃. Following co-culture for up to 24 h, the proliferation of HLFs was measured using MTT colorimetry. Furthermore, the collagen synthesis capacity of HLFs was determined by the level of hydroxyproline. In addition, the protein expression levels of cytokines, including transforming growth factor (TGF)-β1, tumor necrosis factor (TNF)-α and prostaglandin E2 (PGE2) were assessed. Results indicated that the proliferation of HLFs co-cultured with HBECs was significantly inhibited when compared with HLFs cultured alone (P<0.05). By contrast, co-culture with O₃-stimulated HBECs significantly promoted the proliferation of HLFs compared with the HLFs cultured alone or those cultured with HBECs but no O₃ stimulation, respectively (P<0.05 and P<0.01). Furthermore, similar effects were observed regarding the collagen synthesis capacity of HLFs co-cultured with HBECs for 24. In the supernatant, TGF-β1 concentration was continuously increased over 24 h, whereas the concentration of PGE2 increased and plateaued between 12 to 24 h and TNF-α concentration was not significantly altered during the assessed time period. To conclude, the present results suggest that O₃ pre-exposure of HBECs may promote the transformation of HLFs from the typical inhibitory state into a promoting state with respect to proliferation and collagen synthesis, which may likely occur through a mechanism that influences the balance between pro- and anti-inflammatory factors, including TGF-β1 and PGE2. The present findings may improve the understanding of the mechanism involved in O₃-induced airway remodeling from a novel perspective of maintenance/loss of steady-state function of the airway epithelium.

TGF-β1 Evokes Human Airway Smooth Muscle Cell Shortening and Hyperresponsiveness via Smad3

Transforming growth factor β1 (TGF-β1), a cytokine whose levels are elevated in the airways of patients with asthma, perpetuates airway inflammation and modulates airway structural cell remodeling. However, the role of TGF-β1 in excessive airway narrowing in asthma, or airway hyperresponsiveness (AHR), remains unclear. In this study, we set out to investigate the direct effects of TGF-β1 on human airway smooth muscle (HASM) cell shortening and hyperresponsiveness. The dynamics of AHR and single-cell excitation-contraction coupling were measured in human precision-cut lung slices and in isolated HASM cells using supravital microscopy and magnetic twisting cytometry, respectively. In human precision-cut lung slices, overnight treatment with TGF-β1 significantly augmented basal and carbachol-induced bronchoconstriction. In isolated HASM cells, TGF-β1 increased basal and methacholine-induced cytoskeletal stiffness in a dose- and time-dependent manner. TGF-β1-induced single-cell contraction was corroborated by concomitant increases in myosin light chain and myosin phosphatase target subunit 1 phosphorylation levels, which were attenuated by small interfering RNA-mediated knockdown of Smad3 and pharmacological inhibition of Rho kinase. Strikingly, these physiological effects of TGF-β1 occurred through a RhoA-independent mechanism, with little effect on HASM cell [Ca2+]i levels. Together, our data suggest that TGF-β1 enhances HASM excitation-contraction coupling pathways to induce HASM cell shortening and hyperresponsiveness. These findings reveal a potential link between airway injury-repair responses and bronchial hyperreactivity in asthma, and define TGF-β1 signaling as a potential target to reduce AHR in asthma.

Bradykinin in asthma: Modulation of airway inflammation and remodelling

Bradykinin, a pro-inflammatory molecule, and its related peptides have been studied for their effects on acute reactions in upper and lower airways, where they can be synthesised and metabolized after exposure to different stimuli including allergens and viral infection. Bradykinin B₁ and B₂ receptors are constitutively expressed in the airways on several residential and/or immune cells. Their expression can also be induced by inflammatory mediators, usually associated with eosinophil and neutrophil recruitment, such as IL-4, IL-13, TNF-α, IL-6 and IL-8, via intracellular MAPK and NF-κB signalling. In turn, the latters up-regulate both bradykinin receptors. Bradykinin activates epithelial/endothelial and immune cells, neurons and mesenchymal cells (such as fibroblasts, myofibroblasts and smooth muscle cells), which are implicated in the development of airway chronic inflammation, responsiveness and remodelling (a major feature of severe asthma). This review highlights the role of bradykinin and its receptors in respect to chronic inflammatory response involving eosinophils/neutrophils and to vascular/matrix-related airway remodelling in asthmatic airways. This scenario is especially important for understanding the mechanisms involved in the pathogenesis of eosinophilic and/or neutrophilic asthma and hence their therapeutic approach.

Safer approaches to therapeutic modulation of TGF-β signaling for respiratory disease

The transforming growth factor (TGF)-β cytokines play a central role in development and progression of chronic respiratory diseases. TGF-β overexpression in chronic inflammation, remodeling, fibrotic process and susceptibility to viral infection is established in the most prevalent chronic respiratory diseases including asthma, COPD, lung cancer and idiopathic pulmonary fibrosis. Despite the overwhelming burden of respiratory diseases in the world, new pharmacological therapies have been limited in impact. Although TGF-β inhibition as a therapeutic strategy carries great expectations, the constraints in avoiding compromising the beneficial pleiotropic effects of TGF-β, including the anti-proliferative and immune suppressive effects, have limited the development of effective pharmacological modulators. In this review, we focus on the pathways subserving deleterious and beneficial TGF-β effects to identify strategies for selective modulation of more distal signaling pathways that may result in agents with improved safety/efficacy profiles. Adverse effects of TGF-β inhibitors in respiratory clinical trials are comprehensively reviewed, including those of the marketed TGF-β modulators, pirfenidone and nintedanib. Precise modulation of TGF-β signaling may result in new safer therapies for chronic respiratory diseases.

Interleukin-37 alleviates airway inflammation and remodeling in asthma via inhibiting the activation of NF-κB and STAT3 signalings

Asthma is a common respiratory inflammatory disorder disease of childhood, and airway smooth muscle cells (ASMCs) play an important role in this disease. Recently, studies have found that interleukin (IL)-37 inhibits allergic airway inflammation of asthmatic mouse models. The aim of this study was to investigate the exact mechanism of IL-37 in asthma. In this study, we found recombinant human IL-37 protein significantly reduced ovalbumin (OVA)-induced airway hyperresponsiveness, inflammatory cell infiltration, the epithelial-mesenchymal-transition (EMT) process, and levels of IL-4, IL-6 and IL-13, but increased interferon (IFN)-γ expression. Moreover, IL-37 treatment remarkably inhibited transforming growth factor (TGF)-β1-induced cell proliferation, migration, EMT, and inflammatory response in ASMCs. IL-37 notably upregulated IκB expression and downregulated levels of NF-κB p65, phospho-NF-κB p65, STAT3 and phospho-STAT3 both in OVA-induced mice and in TGF-β1-stimulated ASMCs. The effects of IL-37 on TGF-β1-induced ASMCs were abrogated by STAT3 upregulation. Additionally, PDTC, a NF-κB inhibitor, showed the similar effects as IL-37 in ASMCs. In conclusion, IL-37 may alleviate airway inflammation and remodeling in asthma through suppressing the activation of NF-κB and STAT3.

Role of PIM2 in allergic asthma

T cell-associated inflammation, particularly type 2 inflammation, has an important role in asthma pathogenesis, which is suppressed by regulatory T cells (Tregs). Proviral integration site for Moloney murine leukemia virus 2 (PIM2), a member off the serine/threonine kinase family, promotes the growth and survival of T cells and influences the function of Treg cells. However, whether PIM2 affects asthma pathogenesis remains unclear. Peripheral blood mononuclear cells and Treg cells from asthmatic and healthy subjects were obtained, and the expression level of PIM2 was measured by reverse transcription-quantitative polymerase chain reaction and immunocytochemistry. In addition, BALB/c female mice sensitized and challenged by ovalbumin were used as an asthma model, and PIM2 inhibitor was injected during the challenge period to observe the effect of PIM2 on asthma. The asthma symptoms were recorded, and airway hyper-responsiveness (AHR), expression levels of cytokines in the serum or bronchoalveolar lavage fluid (BALF), and the number of BALF leukocytes were evaluated. In addition, hematoxylin and eosin staining and immunohistochemistry of lung tissues was performed. The results demonstrated that PIM2 was overexpressed in patients with asthma in natural Treg cells. Inhibition of PIM2 attenuated asthma symptoms, and improved AHR and airway inflammation compared with asthmatic mice without inhibition of PIM2. In addition, expression levels of interleukin (IL)-10 and forkhead box protein 3 (FOXP3) in BALF were increased following PIM2 inhibition (IL-10, 470.3±21.78 vs. 533.7±25.55 pg/ml, P<0.05; FOXP3, 259±4.68 vs. 279.3±3.68 pg/ml; asthma and PIM2 inhibition groups, respectively; P<0.05). In conclusion, PIM2 may exhibit an important role in asthma pathogenesis and exacerbate AHR, airway inflammation and asthma symptoms. These effects of PIM2 may be dependent on Treg cells and the secretion of IL-10 by Tregs. The results of the present study suggest that PIM2 may be a potential target molecule for asthma treatment.