IL-13 dampens human airway epithelial innate immunity through induction of IL-1 receptor-associated kinase M

Interleukin-37 attenuates aortic valve lesions by inhibiting N6-methyladenosine-mediated interleukin-1 receptor-associated kinase M degradation

AIMS

Calcific aortic valve disease (CAVD) has become an increasingly important global medical problem without effective pharmacological intervention. Accumulating evidence indicates that aortic valve calcification is driven by inflammation. Interleukin-1 receptor-associated kinase M (IRAK-M) is a well-known negative regulator of inflammation, but its role in CAVD remains unclear.

METHODS AND RESULTS

Here, we stimulated aortic valve interstitial cells (AVICs) with low-dose lipopolysaccharide (LPS) to mimic the inflammatory response in aortic valve calcification and observed the expression pattern of IRAK-M. Furthermore, we generated IRAK-M-/- mice to explore the effect of IRAK-M deficiency on the aortic valve in vivo. Additionally, overexpression and knockdown experiments were performed to verify the role of IRAK-M in AVICs. Methylated RNA immunoprecipitation-quantitative polymerase chain reaction was used to detect the N6-methyladenosine (m6A) level of IRAK-M, and recombinant interleukin (IL)-37-treated AVICs were used to determine the regulatory relationship between IL-37 and IRAK-M. We found that IRAK-M expression was upregulated in the early stages of inflammation as part of a negative feedback mechanism to modulate the immune response. However, persistent inflammation increased overall m6A levels, ultimately leading to reduced IRAK-M expression. In vivo, IRAK-M-/- mice exhibited a propensity for aortic valve thickening and calcification. Overexpression and knockdown experiments showed that IRAK-M inhibited inflammation and osteogenic responses in AVICs. In addition, IL-37 restored IRAK-M expression by inhibiting m6A-mediated IRAK-M degradation to suppress inflammation and aortic valve calcification.

CONCLUSION

Our findings confirm that inflammation and epigenetic modifications synergistically regulate IRAK-M expression. Moreover, IRAK-M represents a potential target for mitigating aortic valve calcification. Meanwhile, IL-37 exhibited inhibitory effects on CAVD development both in vivo and in vitro, giving us hope that CAVD can be treated with drugs rather than surgery.

Comprehensive single-cell RNA-sequencing study of Tollip deficiency effect in IL-13-stimulated human airway epithelial cells

OBJECTIVE

Toll-interacting protein (Tollip) suppresses excessive pro-inflammatory signaling, but its function in airway epithelial responses to IL-13, a key mediator in allergic diseases, remains unclear. This study investigates Tollip knockdown (TKD) effects in primary human airway epithelial cells using single-cell RNA sequencing, providing the first single-cell analysis of TKD and the first exploring its interaction with IL-13.

RESULTS

IL-13 treatment upregulated key genes, including SPDEF, MUC5AC, POSTN, ALOX15, and CCL26, confirming IL-13's effects and validating our methods. IL-13 reduced TNF-α signaling and epithelial-mesenchymal transition in certain cell types, suggesting a dual role in promoting type 2 inflammation while suppressing Th1-driven inflammation. Tollip deficiency alone significantly amplified TNF-α signaling and inflammatory pathways in goblet, club, and suprabasal cells. Comparisons between TKDIL13 vs IL13 and TKD vs CTR revealed that IL-13 does not substantially alter Tollip deficiency response in most cell types, reinforcing findings in TKD vs CTR. Tollip deficiency alters the response to IL-13 in a cell-type-specific manner, strongly downregulating TNF-α signaling in goblet cells but only weakly in basal and club cells. Tollip deficiency enhances IL-13's suppression of Th1 inflammatory responses in goblet cells. These novel insights in Tollip-IL-13 interactions offer potential therapeutic targets for asthma and related diseases.

Targeting IL-13 and IL-4 in Asthma: Therapeutic Implications on Airway Remodeling in Severe Asthma

Asthma is a chronic respiratory disorder affecting individuals across all age groups. It is characterized by airway inflammation and remodeling and leads to progressive airflow restriction. While corticosteroids remain a mainstay therapy, their efficacy is limited in severe asthma due to genetic and epigenetic alterations, as well as elevated pro-inflammatory cytokines interleukin-4 (IL-4), interleukin-13 (IL-13), and interleukin-5 (IL-5), which drive structural airway changes including subepithelial fibrosis, smooth muscle hypertrophy, and goblet cell hyperplasia. This underscores the critical need for biologically targeted therapies. This review systematically examines the roles of IL-4 and IL-13, key drivers of type-2 inflammation, in airway remodeling and their potential as therapeutic targets. IL-4 orchestrates eosinophil recruitment, immunoglobulin class switching, and Th2 differentiation, whereas IL-13 directly modulates structural cells, including fibroblasts and epithelial cells, to promote mucus hypersecretion and extracellular matrix (ECM) deposition. Despite shared signaling pathways, IL-13 emerges as the dominant cytokine in remodeling processes including mucus hypersecretion, fibrosis and smooth muscle hypertrophy. While IL-4 primarily amplifies inflammatory cascades by driving IgE switching, promoting Th2 cell polarization that sustain cytokine release, and inducing chemokines to recruit eosinophils. In steroid-resistant severe asthma, biologics targeting IL-4/IL-13 show promise in reducing exacerbations and eosinophilic inflammation. However, their capacity to reverse established remodeling remains inconsistent, as clinical trials prioritize inflammatory biomarkers over long-term structural outcomes. This synthesis highlights critical gaps in understanding the durability of IL-4/IL-13 inhibition on airway structure and advocates for therapies combining biologics with remodeling-specific strategies. Through the integration of mechanistic insights and clinical evidence, this review emphasizes the need for long-term studies utilizing advanced imaging, histopathological techniques, and patient-reported outcomes to evaluate how IL-4/IL-13-targeted therapies alter airway remodeling and symptom burden, thereby informing more effective treatment approaches for severe, steroid-resistant asthma.

Degradation of IL-4Ralpha by Immunoproteasome: implication in airway type 2 inflammation and hyperresponsiveness

Introduction

Immunoproteasome (IP) is induced by pro-inflammatory stimuli such as interferon gamma to regulate inflammation and immunity. Asthma patients with airway type 2 high inflammation (e.g., IL-13) demonstrate more eosinophils and airway hyperresponsiveness (AHR) with less interferon gamma. The role of IP in regulating airway eosinophilic inflammation and AHR has not been investigated.

Methods

This study was aimed to determine how IP regulates type 2 inflammation and AHR using LMP7 (a subunit of IP) deficient mouse lungs, precision-cut lung slices (PCLS), and cultured human airway epithelial cells treated with IL-13 in the absence or presence of an IP inhibitor ONX-0914 or exogenous IP.

Results

LMP7 KO mouse lungs had significantly more IL-4Rα protein expression than the wildtype (WT) mice. Following IL-13 treatment in PCLS, LMP7 KO mice had significantly more airway contraction than WT mice, which was coupled with increased eotaxin-2 levels. IP inhibition by ONX-0914 in IL-13 treated human airway epithelial cells resulted in significantly more IL-4Rα protein expression and eotaxin-3 release. IP inhibition in human PCLS significantly increased AHR.

Conclusion

Collectively, these data demonstrated that IP promotes degradation of IL-4Rα, while inhibits type 2 inflammation and AHR. Enhancement of IP expression or activity may serve as an alternative approach to reduce the severity of type 2 inflammation and AHR.

Toll-Interacting Protein Down-Regulation by Cigarette Smoke Exposure Impairs Human Lung Defense against Influenza A Virus Infection

Cigarette smoking is a primary cause of chronic obstructive pulmonary disease (COPD). Smokers have a higher risk of influenza-related mortality, but the underlying mechanisms remain unclear. Toll-interacting protein (TOLLIP), an immune regulator, inhibits influenza A virus (IAV) infection, but its regulation in COPD has not been well understood. We sought to determine if cigarette smoke (CS) exposure down-regulates TOLLIP expression via epigenetic mechanisms, including histone methylation. TOLLIP and histone-methylating enzymes enhancer of zeste homolog 1/2 (EZH1/2) were measured in healthy and COPD human lungs, human airway epithelial cells cultured under submerged and air-liquid interface conditions, and precision-cut lung slices (PCLSs) exposed to CS with or without IAV infection. EZH1/2 siRNA and inhibitors were used to investigate their effects on TOLLIP expression. In patients with COPD, TOLLIP levels decreased, whereas EZH1 and EZH2 expression increased. Repeated CS exposure decreased TOLLIP and increased EZH1, EZH2, H3K27me3, and IAV levels in human airway epithelial cells and PCLSs. EZH1/2 siRNA or their pharmacologic inhibitor valemetostat tosylate in part restored TOLLIP and reduced IAV levels in CS-exposed airway epithelial cells and PCLSs. Our findings suggest that repeated CS exposure during viral infection reduced TOLLIP levels and increased viral load in part through EZH1/EZH2-H3K27me3-mediated epigenetic mechanisms. Targeting EZH1 and EZH2 may serve as one of the potential therapeutic strategies to restore TOLLIP expression and host defense against viral infections in patients with COPD.

Inflammatory disease status and response to TNF blockade are associated with mechanisms of endotoxin tolerance

The mechanisms of endotoxin tolerance (ET), which down-regulate inflammation, are well described in response to exogenous toll-like receptor ligands, but few studies have focused on ET-associated mechanisms in inflammatory disease. As blocking TNF can attenuate the development of ET, the effect of anti-TNF on the expression of key ET-associated molecules in inflammatory auto-immune disease was measured; changes in inflammatory gene expression were confirmed using an ET bioassay. The expression of immunomodulatory molecules was measured in a murine model of arthritis treated with anti-TNF and the expression of ET-associated molecules was measured in whole blood in rheumatoid arthritis (RA) and ankylosing spondylitis (AS) patients, before and after therapy. The expression of ET-associated genes was also measured in RA patient monocytes before and after therapy, in anti-TNF responders and non-responders. Tnfaip3, Ptpn6 and Irak3 were differentially expressed in affected paws, spleens, lymph nodes and circulating leucocytes in experimental murine arthritis treated with anti-TNF. Prior to therapy, the expression of TNFAIP3, INPP5D, PTPN6, CD38 and SIGIRR in whole blood differed between human healthy controls and RA or AS patients. In blood monocytes from RA patients, the expression of TNFAIP3 was significantly reduced by anti-TNF therapy in non-responders. Prior to therapy, anti-TNF non-responders had higher expression of TNFAIP3 and SLPI, compared to responders. Although the expression of TNFAIP3 was significantly higher in RA non-responders prior to treatment, the post-treatment reduction to a level similar to responders did not coincide with a clinical response to therapy.

IRAK-M has effects in regulation of lung epithelial inflammation

BACKGROUND

Epithelial barrier is important for asthma development by shaping immune responses. Airway expressing-IL-1 receptor-associated kinase (IRAK)-M of Toll-like receptor pathway was involved in immunoregulation of airway inflammation through influencing activities of macrophages and dendritic cells or T cell differentiation. Whether IRAK-M has effect on cellular immunity in airway epithelial cells upon stimulation remains unclear.

METHODS

We modeled cellular inflammation induced by IL-1β, TNF-α, IL-33, and house dust mite (HDM) in BEAS-2B and A549 cells. Cytokine production and pathway activation were used to reflect the effects of IRAK-M siRNA knockdown on epithelial immunity. Genotyping an asthma-susceptible IRAK-M SNP rs1624395 and measurement of serum CXCL10 levels were performed in asthma patients.

RESULTS

IRAK-M expression was significantly induced in BEAS-2B and A549 cells after inflammatory stimulation. IRAK-M knockdown increased the lung epithelial production of cytokines and chemokines, including IL-6, IL-8, CXCL10, and CXCL11, at both mRNA and protein levels. Upon stimulation, IRAK-M silencing led to overactivation of JNK and p38 MAPK in lung epithelial cells. While antagonizing JNK or p38 MAPK inhibited increased secretion of CXCL10 in IRAK-M silenced-lung epithelium. Asthma patients carrying G/G genotypes had significantly higher levels of serum CXCL10 than those carrying homozygote A/A.

CONCLUSION

Our findings suggested that IRAK-M has effect on lung epithelial inflammation with an influence on epithelial secretion of CXCL10 partly mediated through JNK and p38 MAPK pathways. IRAK-M modulation might indicate a new insight into asthma pathogenesis from disease origin.

IRAK-M Regulates Proliferative and Invasive Phenotypes of Lung Fibroblasts

Lung fibroblasts play an important role in subepithelial fibrosis, one feature for airway remodeling. IL-1 receptor-associated kinase (IRAK)-M was shown to involve fibrosis formation in airways and lung through regulation of inflammatory responses. IRAK-M is expressed by lung fibroblasts, whether IRAK-M has direct impact on lung fibroblasts remains unclear. In this investigation, we evaluated in vitro effect of IRAK-M on phenotypes of lung fibroblasts by silencing or overexpressing IRAK-M. Murine lung fibroblasts (MLg) were stimulated with house dust mite (HDM), IL-33, and transforming growth factor (TGF) β1. Techniques of small interfering RNA or expression plasmid were employed to silence or overexpress IRAK-M in MLg fibroblast cells. Proliferation, migration, invasiveness, and fibrosis-related events were evaluated. Significant upregulation of IRAK-M expression in MLg cells was caused by these stimuli. Silencing IRAK-M significantly increased proliferation, migration, and invasiveness of lung fibroblasts regardless of stimulating conditions. By contrast, IRAK-M overexpression significantly inhibited proliferation and motility of MLg lung fibroblasts. IRAK-M overexpression also significantly decreased the expression of fibronectin, collagen I, and α-SMA in MLg cells. Under stimulation with TGFβ1 or IL-33, IRAK-M silencing reduced MMP9 production, while IRAK-M overexpression increased MMP9 production. Modulation of IRAK-M expression affected cytokines production, either decreased or increased expression of TNFα and CXCL10 by the cells regardless of stimulation. Our in vitro data reveal that IRAK-M directly impacts on lung fibroblasts through modulation of cellular motility, release of inflammatory, and fibrotic cytokines of lung fibroblasts. These might suggest a new target by regulation of IRAK-M in slowing airway remodeling.

Trends and factors associated with influenza vaccination in subjects with asthma: analysis of the Korea National Health and Nutrition Examination Survey between 2010 and 2019

BACKGROUND

Despite the importance of influenza vaccination, its rates in subjects with asthma are suboptimal, especially in the young population.

METHODS

Among 72,843 adults aged ⩾18 years from the Korea National Health and Nutrition Examination Survey conducted between 2010 and 2019, 1643 with asthma were included. The yearly trends and factors associated with influenza vaccination were analyzed in subjects with asthma. In addition, stratified analyses were performed by age group (<65 versus ⩾65 years).

RESULTS

During the study period, the overall influenza vaccination rate among subjects with asthma fluctuated from 51.0% to 64.3%, with a consistently higher vaccination rate in elderly subjects than in young subjects. Among young subjects with asthma, factors positively associated with influenza vaccination were female sex [adjusted odds ratio (aOR) = 1.66, 95% confidence interval (CI) = 1.11-2.49], current asthma being treated (aOR = 1.69, 95% CI = 1.14-2.50), history of pulmonary tuberculosis (aOR = 2.01, 95% CI = 1.04-3.87), and dyslipidemia (aOR = 1.86, 95% CI = 1.05-3.30). However, unmarried subjects showed an inverse relationship (aOR = 0.50, 95% CI = 0.34-0.75). In elderly subjects, unmarried status (aOR = 0.52, 95% CI = 0.29-0.94), being underweight (aOR = 0.29, 95% CI = 0.09-0.97), and having a low income (aOR = 0.42, 95% CI = 0.18-0.97) were factors negatively associated with influenza vaccination.

CONCLUSION

In the last 10 years, influenza vaccination rates have still been insufficient in subjects with asthma, particularly in young subjects. Considering the factors that are influencing the vaccination rates of young subjects, public policies to increase influenza vaccination rates in subjects with asthma need to be established urgently.

Tollip interaction with STAT3: a novel mechanism to regulate human airway epithelial responses to type 2 cytokines

BACKGROUND

Toll-interacting protein (Tollip) is one of the key negative regulators in host innate immunity. Genetic variation of Tollip has been associated with less Tollip expression and poor lung function in asthmatic patients, but little is known about the role of Tollip in human airway type 2 inflammatory response, a prominent feature in allergic asthma.

OBJECTIVE

Our goal was to determine the role and underlying mechanisms of Tollip in human airway epithelial responses such as eotaxin to type 2 cytokine IL-13.

METHODS

Tollip deficient primary human airway epithelial cells from 4 healthy donors were generated by the gene knockdown approach and stimulated with IL-13 to measure activation of transcription factor STAT3, and eotaxin-3, an eosinophilic chemokine.

RESULTS

Following IL-13 treatment, Tollip deficient cells had significantly higher levels of STAT3 activation and eotaxin-3 than the scrambled control counterpart, which was reduced by a STAT3 inhibitor. Interaction between Tollip and STAT3 proteins was identified by co-immunoprecipitation.

CONCLUSION

Our results, for the first time, suggest that Tollip inhibits excessive eotaxin-3 induction by IL-13, in part through the interaction and inhibition of STAT3. These findings lend evidence to the potential of a STAT3 inhibitor as a therapeutic target, especially for type 2 inflammation-high asthmatics with Tollip deficiency.

IRAK-M knockout promotes allergic airway inflammation, but not airway hyperresponsiveness, in house dust mite-induced experimental asthma model

Background

IL-1 receptor associated-kinase (IRAK)-M, expressed by airway epithelium and macrophages, was shown to regulate acute and chronic airway inflammation exhibiting a biphasic response in an OVA-based animal model. House dust mite (HDM) is a common real-life aeroallergen highly relevant to asthma pathogenesis. The role of IRAK-M in HDM-induced asthma remains unknown. This study was aimed to investigate the effect of IRAK-M on allergic airway inflammation induced by HDM using IRAK-M knockout (KO) mice and the potential underlying mechanisms.

Methods

IRAK-M KO and wild-type (WT) mice were sensitized and challenged with HDM. The differences in airway inflammation were evaluated 24 hours after the last challenge between the two genotypes of mice using a number of cellular and molecular biological techniques. In vitro mechanistic investigation was also involved.

Results

Lung expression of IRAK-M was significantly upregulated by HDM in the WT mice. Compared with the WT controls, HDM-treated IRAK-M KO mice showed exacerbated infiltration of inflammatory cells, particularly Th2 cells, in the airways and mucus overproduction, higher epithelial mediators IL-25, IL-33 and TSLP and Th2 cytokines in bronchoalveolar lavage (BAL) fluid. Lung IRAK-M KO macrophages expressed higher percentage of costimulatory molecules OX40L and CD 80 and exhibited enhanced antigen uptake. However, IRAK-M KO didn’t impact the airway hyperreactivity (AHR) indirectly induced by HDM.

Conclusions

The findings indicate that IRAK-M protects allergic airway inflammation, not AHR, by modifying activation and antigen uptake of lung macrophages following HDM stimulation. Optimal regulation of IRAK-M might indicate an intriguing therapeutic avenue for allergic airway inflammation.

Analysis of interleukin-1 receptor associated kinase-3 (IRAK3) function in modulating expression of inflammatory markers in cell culture models: A systematic review and meta-analysis

BACKGROUND

IRAK3 is a critical modulator of inflammation in innate immunity. IRAK3 is associated with many inflammatory diseases, including sepsis, and is required in endotoxin tolerance to maintain homeostasis of inflammation. The impact of IRAK3 on inflammatory markers such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in cell culture models remains controversial.

OBJECTIVE

To analyse temporal effects of IRAK3 on inflammatory markers after one- or two-challenge interventions in cell culture models.

METHODS

A systematic search was performed to identify in vitro cell studies reporting outcome measures of expression of IRAK3 and inflammatory markers. Meta-analyses were performed where sufficient data were available. Comparisons of outcome measures were performed between different cell lines and human and mouse primary cells.

RESULTS

The literature search identified 7766 studies for screening. After screening titles, abstracts and full-texts, a total of 89 studies were included in the systematic review.

CONCLUSIONS

The review identifies significant effects of IRAK3 on decreasing NF-κB DNA binding activity in cell lines, TNF-α protein level at intermediate time intervals (4h-15h) in cell lines or at long term intervals (16h-48h) in mouse primary cells following one-challenge. The patterns of TNF-α protein expression in human cell lines and human primary cells in response to one-challenge are more similar than in mouse primary cells. Meta-analyses confirm a negative correlation between IRAK3 and inflammatory cytokine (IL-6 and TNF-α) expression after two-challenges.

Single-Cell and Population Transcriptomics Reveal Pan-epithelial Remodeling in Type 2-High Asthma

The type 2 cytokine-high asthma endotype (T2H) is characterized by IL-13-driven mucus obstruction of the airways. To further investigate this incompletely understood pathobiology, we characterize IL-13 effects on human airway epithelial cell cultures using single-cell RNA sequencing, finding that IL-13 generates a distinctive transcriptional state for each cell type. Specifically, we discover a mucus secretory program induced by IL-13 in all cell types which converts both mucus and defense secretory cells into a metaplastic state with emergent mucin production and secretion, while leading to ER stress and cell death in ciliated cells. The IL-13-remodeled epithelium secretes a pathologic, mucin-imbalanced, and innate immunity-depleted proteome that arrests mucociliary motion. Signatures of IL-13-induced cellular remodeling are mirrored by transcriptional signatures characteristic of the nasal airway epithelium within T2H versus T2-low asthmatic children. Our results reveal the epithelium-wide scope of T2H asthma and present candidate therapeutic targets for restoring normal epithelial function.

Interleukin 1 Receptor-Like 1 (IL1RL1) Promotes Airway Bacterial and Viral Infection and Inflammation

Interleukin 1 receptor-like 1 (IL1RL1), also known as suppression of tumorigenicity 2 (ST2), is the receptor for interleukin 33 (IL-33) and has been increasingly studied in type 2 inflammation. An increase in airway IL-33/ST2 signaling in asthma has been associated with eosinophilic inflammation, but little is known about the role of ST2 in neutrophilic inflammation. Airway Mycoplasma pneumoniae and human rhinovirus (HRV) infections are linked to neutrophilic inflammation during acute exacerbations of asthma. However, whether ST2 contributes to M. pneumoniae- and HRV-mediated airway inflammation is poorly understood. The current study sought to determine the functions of ST2 during airway M. pneumoniae or HRV infection. In cultured normal human primary airway epithelial cells, ST2 overexpression (OE) increased the production of neutrophilic chemoattractant IL-8 in the absence or presence of M. pneumoniae or HRV1B infection. ST2 OE also enhanced HRV1B-induced IP-10, a chemokine involved in asthma exacerbations. In the M. pneumoniae-infected mouse model, ST2 deficiency, in contrast to sufficiency, significantly reduced the levels of neutrophils following acute (≤24 h) infection, while in the HRV1B-infected mouse model, ST2 deficiency significantly reduced the levels of proinflammatory cytokines KC, IP-10, and IL-33 in bronchoalveolar lavage (BAL) fluid. Overall, ST2 overexpression in human epithelial cells and ST2 sufficiency in mice increased the M. pneumoniae and HRV loads in cell supernatants and BAL fluid. After pathogen infection, ST2-deficient mice showed a higher level of the host defense protein lactotransferrin in BAL fluid. Our data suggest that ST2 promotes proinflammatory responses (e.g., neutrophils) to airway bacterial and viral infection and that blocking ST2 signaling may broadly attenuate airway infection and inflammation.

Tollip Inhibits ST2 Signaling in Airway Epithelial Cells Exposed to Type 2 Cytokines and Rhinovirus

The negative immune regulator Tollip inhibits the proinflammatory response to rhinovirus (RV) infection, a contributor to airway neutrophilic inflammation and asthma exacerbations, but the underlying molecular mechanisms are poorly understood. Tollip may inhibit IRAK1, a signaling molecule downstream of ST2, the receptor of IL-33. This study was carried out to determine whether Tollip downregulates ST2 signaling via inhibition of IRAK1, but promotes soluble ST2 (sST2) production, thereby limiting excessive IL-8 production in human airway epithelial cells during RV infection in a type 2 cytokine milieu (e.g., IL-13 and IL-33 stimulation). Tollip- and IRAK1-deficient primary human tracheobronchial epithelial (HTBE) cells and Tollip knockout (KO) HTBE cells were generated using the shRNA knockdown and CRISPR/Cas9 approaches, respectively. Cells were stimulated with IL-13, IL-33, and/or RV16. sST2, activated IRAK1, and IL-8 were measured. A Tollip KO mouse model was utilized to test if Tollip regulates the airway inflammatory response to RV infection in vivo under IL-13 and IL-33 treatment. Following IL-13, IL-33, and RV treatment, Tollip-deficient (vs. -sufficient) HTBE cells produced excessive IL-8, accompanied by decreased sST2 production but increased IRAK1 activation. IL-8 production following IL-13/IL-33/RV exposure was markedly attenuated in IRAK1-deficient HTBE cells, as well as in Tollip KO HTBE cells treated with an IRAK1 inhibitor or a recombinant sST2 protein. Tollip KO (vs. wild-type) mice developed exaggerated airway neutrophilic responses to RV in the context of IL-13 and IL-33 treatment. Collectively, these data demonstrate that Tollip restricts excessive IL-8 production in type 2 cytokine-exposed human airways during RV infection by promoting sST2 production and inhibiting IRAK1 activation. sST2 and IRAK1 may be therapeutic targets for attenuating excessive neutrophilic airway inflammation in asthma, especially during RV infection.

Sialylation of MUC4β N-glycans by ST6GAL1 orchestrates human airway epithelial cell differentiation associated with type-2 inflammation

Although type-2-induced (T2-induced) epithelial dysfunction is likely to profoundly alter epithelial differentiation and repair in asthma, the mechanisms for these effects are poorly understood. A role for specific mucins, heavily N-glycosylated epithelial glycoproteins, in orchestrating epithelial cell fate in response to T2 stimuli has not previously been investigated. Levels of a sialylated MUC4β isoform were found to be increased in airway specimens from asthmatic patients in association with T2 inflammation. We hypothesized that IL-13 would increase sialylation of MUC4β, thereby altering its function and that the β-galactoside α-2,6-sialyltransferase 1 (ST6GAL1) would regulate the sialylation. Using human biologic specimens and cultured primary human airway epithelial cells (HAECs),we demonstrated that IL-13 increases ST6GAL1-mediated sialylation of MUC4β and that both were increased in asthma, particularly in sputum supernatant and/or fresh isolated HAECs with elevated T2 biomarkers. ST6GAL1-induced sialylation of MUC4β altered its lectin binding and secretion. Both ST6GAL1 and MUC4β inhibited epithelial cell proliferation while promoting goblet cell differentiation. These in vivo and in vitro data provide strong evidence for a critical role for ST6GAL1-induced sialylation of MUC4β in epithelial dysfunction associated with T2-high asthma, thereby identifying specific sialylation pathways as potential targets in asthma.

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.

Identification, characterisation and preliminary functional analysis of IRAK-M in grass carp (Ctenopharyngodon idella)

Interleukin-1 receptor-associated kinase (IRAK) family members play important roles in myeloid differentiation primary response 88 (MyD88)-dependent toll-like receptor (TLR) signaling, the crucial innate immune pathway in vertebrates. In the present study, the IRAK family gene IRAK-M (also called IRAK3) from grass carp (Ctenopharyngodon idella) was cloned and characterised. IRAK-M was mainly enriched in the spleen, and the significantly altered expression was observed after grass carp reovirus (GCRV) infection. Subcellular localisation showed that IRAK-M protein distributed uniformly in the entire cell and co-localised with MyD88 in the cytoplasm of transfected cells. Additionally, the interaction between IRAK-M and MyD88 was confirmed by bimolecular fluorescence complementation (BiFC) system. Moreover, deficient of IRAK-M in C. idella kidney cell line (CIK) with small interference RNA (siRNA) upregulated polyinosinic:polycytidylic acid (poly(I:C))-induced inflammatory cytokines production, including interleukin 8 (IL-8), IL-6, and tumour necrosis factor α (TNF-α), which reveals that IRAK-M functions as a negative regulator of inflammatory cytokines. Taken together, our results demonstrate that IRAK-M gene plays an important role in innate immune regulation and provide new insights into understanding the functional characteristics of the IRAK-M in teleosts.

Immunoproteasomes as a novel antiviral mechanism in rhinovirus-infected airways

Rhinovirus (RV) infection is involved in acute exacerbations of asthma and chronic obstructive pulmonary disease (COPD). RV primarily infects upper and lower airway epithelium. Immunoproteasomes (IP) are proteolytic machineries with multiple functions including the regulation of MHC class I antigen processing during viral infection. However, the role of IP in RV infection has not been explored. We sought to investigate the expression and function of IP during airway RV infection. Primary human tracheobronchial epithelial (HTBE) cells were cultured at air-liquid interface (ALI) and treated with RV16, RV1B, or interferon (IFN)-λ in the absence or presence of an IP inhibitor (ONX-0914). IP gene (i.e. LMP2) deficient mouse tracheal epithelial cells (mTECs) were cultured for the mechanistic studies. LMP2-deficient mouse model was used to define the in vivo role of IP in RV infection. IP subunits LMP2 and LMP7, antiviral genes MX1 and OAS1 and viral load were measured. Both RV16 and RV1B significantly increased the expression of LMP2 and LMP7 mRNA and proteins, and IFN-λ mRNA in HTBE cells. ONX-0914 down-regulated MX1 and OAS1, and increased RV16 load in HTBE cells. LMP2-deficient mTECs showed a significant increase in RV1B load compared with the wild-type (WT) cells. LMP2-deficient (compared with WT) mice increased viral load and neutrophils in bronchoalveolar lavage (BAL) fluid after 24 h of RV1B infection. Mechanistically, IFN-λ induction by RV infection contributed to LMP2 and LMP7 up-regulation in HTBE cells. Our data suggest that IP are induced during airway RV infection, which in turn may serve as an antiviral and anti-inflammatory mechanism.

Comparison of pro- and anti-inflammatory responses in paired human primary airway epithelial cells and alveolar macrophages

Background

Airway epithelial cells and alveolar macrophages (AMs) are the first line of defense in the lung during infection. Toll-like receptor (TLR) agonists have been extensively used to define the regulation of inflammation in these cells. However, previous studies were performed in non-paired airway epithelial cells and AMs. The major goal of our study was to compare the pro- and anti-inflammatory responses of paired human primary airway epithelial cells and AMs to TLR3 and TLR4 agonists.

Methods

Tracheobronchial epithelial cells (TBEC) and AMs from four smokers and four non-smokers without lung disease were cultured with or without Poly(I:C) (PIC) (a TLR3 agonist) or LPS (a TLR4 agonist) for 4, 24 and 48 h. The immune responses of paired cells were compared.

Results

TBEC and AMs showed stronger pro-inflammatory cytokine (e.g., IL-8) responses to PIC and LPS, respectively. TLR3 and TLR4 mRNA levels were similar in non-stimulated TBEC and AMs. However, PIC stimulation in AMs led to sustained up-regulation of the immune negative regulators Tollip and A20, which may render AMs less sensitive to PIC stimulation than TBEC. Unlike AMs, TBEC did not increase NF-κB activation after LPS stimulation. Interestingly, smoking status was correlated with less TLR3 and IRAK-M expression in non-stimulated TBEC, but not in AMs. PIC-stimulated TBEC and LPS-stimulated AMs from smokers vs. non-smokers produced more IL-8. Finally, we show that expression of A20 and IRAK-M is strongly correlated in the two paired cell types.

Conclusions

By using paired airway epithelial cells and AMs, this study reveals how these two critical types of lung cells respond to viral and bacterial pathogen associated molecular patterns, and provides rationale for modulating immune negative regulators to prevent excessive lung inflammation during respiratory infection.

Electronic supplementary material

The online version of this article (10.1186/s12931-018-0825-9) contains supplementary material, which is available to authorized users.

IL-13 induces periostin and eotaxin expression in human primary alveolar epithelial cells: Comparison with paired airway epithelial cells

Alveolar epithelial cells are critical to the pathogenesis of pulmonary inflammation and fibrosis, which are associated with overexpression of type 2 cytokine IL-13. IL-13 is known to induce the production of profibrotic (e.g., periostin) and pro-inflammatory (e.g., eotaxin-3) mediators in human airway epithelial cells, but it remains unclear if human primary alveolar epithelial cells increase periostin and eotaxin expression following IL-13 stimulation. The goals of this study are to determine if alveolar epithelial cells increase periostin and eotaxin expression upon IL-13 stimulation, and if alveolar and airway epithelial cells from the same subjects have similar responses to IL-13. Paired alveolar and airway epithelial cells were isolated from donors without any lung disease, and cultured under submerged or air-liquid interface conditions with or without IL-13. Up-regulation of periostin protein and mRNA was observed in IL-13-stimulated alveolar epithelial cells, which was comparable to that in IL-13-stimulated paired airway epithelial cells. IL-13 also increased eotaxin-3 expression in alveolar epithelial cells, but the level of eotaxin mRNA was lower in alveolar epithelial cells than in airway epithelial cells. Our findings demonstrate that human alveolar epithelial cells are able to produce periostin and eotaxin in responses to IL-13 stimulation. This study suggests the need to further determine the contribution of alveolar epithelial cell-derived mediators to pulmonary fibrosis.

Critical Role of IRAK-M in Regulating Antigen-Induced Airway Inflammation

Asthma is an airway epithelium disorder involving allergic lung inflammation. IL-1 receptor-associated kinase M (IRAK-M) is a negative regulator of Toll-like receptor (TLR) signaling on airway epithelial cells and macrophages, and it is known to limit the overproduction of cytokines during the inflammatory process. However, the direct role of IRAK-M in asthma pathogenesis is unclear. In the present study, we found a significant elevation of IRAK-M expression in mouse lungs after ovalbumin (OVA) exposure. Compared with wild-type mice, IRAK-M knockout (KO) mice responded to OVA challenge with significantly worse infiltration of airway inflammatory cells, greater airway responsiveness, higher proinflammatory cytokine levels in lung homogenates, and more prominent T-helper cell type 2 (Th2) and Th17 deviation. OVA exposure also induced higher activities of dendritic cells (DCs) and macrophages from IRAK-M KO mouse lungs. Furthermore, adoptive transfer of either IRAK-M KO bone-marrow-derived DCs or macrophages into wild-type mice aggravated OVA-induced airway inflammation. In vitro experiments showed that IRAK-M KO naive CD4⁺ T cells were more prone to differentiate into Th17 cells, but not regulatory T cells. Consistently, activation of IκBζ was significantly increased in the absence of IRAK-M, facilitating Th17 polarization. These findings suggest that IRAK-M plays a crucial role in the regulation of allergic airway inflammation by modifying the function of airway epithelia, DCs, and macrophages, and the differentiation of naive CD4⁺ T cells. Modulation of IRAK-M may provide a novel target for the control of asthma.

Overproduction of growth differentiation factor 15 promotes human rhinovirus infection and virus-induced inflammation in the lung

Human rhinovirus (HRV) is the most common virus contributing to acute exacerbations of chronic obstructive pulmonary disease (COPD) nearly year round, but the mechanisms have not been well elucidated. Recent clinical studies suggest that high levels of growth differentiation factor 15 (GDF15) protein in the blood are associated with an increased yearly rate of all-cause COPD exacerbations. Therefore, in the current study, we investigated whether GDF15 promotes HRV infection and virus-induced lung inflammation. We first examined the role of GDF15 in regulating host defense and HRV-induced inflammation using human GDF15 transgenic mice and cultured human GDF15 transgenic mouse tracheal epithelial cells. Next, we determined the effect of GDF15 on viral replication, antiviral responses, and inflammation in human airway epithelial cells with GDF15 knockdown and HRV infection. Finally, we explored the signaling pathways involved in airway epithelial responses to HRV infection in the context of GDF15. Human GDF15 protein overexpression in mice led to exaggerated inflammatory responses to HRV, increased infectious particle release, and decreased IFN-λ2/3 (IL-28A/B) mRNA expression in the lung. Moreover, GDF15 facilitated HRV replication and inflammation via inhibiting IFN-λ1/IL-29 protein production in human airway epithelial cells. Lastly, Smad1 cooperated with interferon regulatory factor 7 (IRF7) to regulate airway epithelial responses to HRV infection partly via GDF15 signaling. Our results reveal a novel function of GDF15 in promoting lung HRV infection and virus-induced inflammation, which may be a new mechanism for the increased susceptibility and severity of respiratory viral (i.e., HRV) infection in cigarette smoke-exposed airways with GDF15 overproduction.

Interleukin-1 receptor-associated kinase 3 downregulation in peripheral blood mononuclear cells attenuates immunosuppression in sepsis

Sepsis is the leading cause of mortality in intensive care units due to complex inflammatory immune responses and immunosuppression. Recent studies have indicated that the negative regulator of toll like receptors, interleukin-1 receptor-associated kinase 3 (IRAK-3/IRAK-M), serves an important role in immunosuppression during sepsis. In the current study, a cecal ligation puncture model was established in mice using lipopolysaccharide secondary challenge to simulate immunosuppression in sepsis. Peripheral blood mononuclear cells (PBMCs) from this model were then used to evaluate the expression and function of IRAK-M. The results demonstrated that silencing of IRAK-M expression in PBMCs from immunosuppressed mice partially restored the production of pro-inflammatory cytokines. By introducing PBMCs transfected with small-interfering RNA targeting IRAK-M into septic immunosuppressed mice, the survival rate was improved with an increase in splenic CD4⁺ and CD8⁺ T cells and a decrease in T cell apoptosis. In conclusion, downregulation of IRAK-M reversed the effects of sepsis on the production of inflammatory cytokines in PBMCs, and improved the survival of septic immunosuppressed mice. These results provide a basis for future studies investigating the immunological mechanisms underlying immune suppression in sepsis.

Effect of IRAK-M on Airway Inflammation Induced by Cigarette Smoking

Background

IRAK-M, negatively regulating Toll-like receptor, is shown the dual properties in the varied disease contexts. We studied the effect of IRAK-M deficiency on cigarette smoking- (CS-) induced airway inflammation under acute or subacute conditions in a mouse model.

Methods

A number of cellular and molecular techniques were used to detect the differences between IRAK-M knockout (KO) and wild type (WT) mice exposed to 3-day or 7-week CS.

Results

Airway inflammation was comparable between IRAK-M KO and WT mice under 3-day CS exposure. Upon short-term CS exposure and lipopolysaccharide (LPS) inhalation, IRAK-M KO mice demonstrated worse airway inflammation, significantly higher percentage of Th17 cells and concentrations of proinflammatory cytokines in the lungs, and significantly elevated expression of costimulatory molecules CD40 and CD86 by lung dendritic cells (DCs) or macrophages. Conversely, 7-week CS exposed IRAK-M KO mice demonstrated significantly attenuated airway inflammation, significantly lower concentrations of proinflammatory cytokines in the lungs, significantly increased percentage of Tregs, and lower expression of CD11b and CD86 by lung DCs or macrophages.

Conclusions

IRAK-M plays distinctive effect on CS-induced airway inflammation, and influences Treg/Th17 balance and expression of costimulatory molecules by DCs and macrophages, depending on duration and intensity of stimulus.

Regulation of MUC5B Expression in Idiopathic Pulmonary Fibrosis

The gain-of-function mucin 5B (MUC5B) promoter variant, rs35705950, confers the largest risk, genetic or otherwise, for the development of idiopathic pulmonary fibrosis; however, the mechanisms underlying the regulation of MUC5B expression have yet to be elucidated. Here, we identify a critical regulatory domain that contains the MUC5B promoter variant and has a highly conserved forkhead box protein A2 (FOXA2) binding motif. This region is differentially methylated in association with idiopathic pulmonary fibrosis, MUC5B expression, and rs35705950. In addition, we show that this locus binds FOXA2 dynamically, and that binding of FOXA2 is necessary for enhanced expression of MUC5B. In aggregate, our findings identify novel targets to regulate the expression of MUC5B.

Immunomodulatory Molecule IRAK-M Balances Macrophage Polarization and Determines Macrophage Responses during Renal Fibrosis

Activation of various innate immune receptors results in IL-1 receptor-associated kinase (IRAK)-1/IRAK-4-mediated signaling and secretion of proinflammatory cytokines such as IL-12, IL-6, or TNF-α, all of which are implicated in tissue injury and elevated during tissue remodeling processes. IRAK-M, also known as IRAK-3, is an inhibitor of proinflammatory cytokine and chemokine expression in intrarenal macrophages. Innate immune activation contributes to both acute kidney injury and tissue remodeling that is associated with chronic kidney disease (CKD). Our study assessed the contribution of macrophages in CKD and the role of IRAK-M in modulating disease progression. To evaluate the effect of IRAK-M in chronic renal injury in vivo, a mouse model of unilateral ureteral obstruction (UUO) was employed. The expression of IRAK-M increased within 2 d after UUO in obstructed compared with unobstructed kidneys. Mice deficient in IRAK-M were protected from fibrosis and displayed a diminished number of alternatively activated macrophages. Compared to wild-type mice, IRAK-M-deficient mice showed reduced tubular injury, leukocyte infiltration, and inflammation following renal injury as determined by light microscopy, immunohistochemistry, and intrarenal mRNA expression of proinflammatory and profibrotic mediators. Taken together, these results strongly support a role for IRAK-M in renal injury and identify IRAK-M as a possible modulator in driving an alternatively activated profibrotic macrophage phenotype in UUO-induced CKD.

MUC18 regulates IL-13-mediated airway inflammatory response

OBJECTIVE

To evaluate the effects of MUC18 on IL-13-mediated airway inflammatory responses in human airway epithelial cells and in mice.

MATERIALS

Primary normal human tracheobronchial epithelial (HTBE) cells, wild-type (WT) and Muc18 knockout (KO) mice, and mouse tracheal epithelial cells (mTECs) were utilized.

TREATMENT

Cultured HTBE cells treated with MUC18 siRNA or MUC18 expressing lentivirus were incubated with IL-13 (10 ng/mL) for 24 h. Mice were intranasally instilled with 500 ng of IL-13 for 3 days. mTECs were treated with IL-13 (10 ng/mL) for 3 days.

METHODS

PCR was used to measure mRNA expression. Western Blot and ELISAs were used to quantify protein expression. Cytospins of bronchoalveolar lavage (BAL) cells were used to obtain leukocyte differentials.

RESULTS

MUC18 siRNA reduced IL-13-mediated eotaxin-3 (183 ± 44 vs. 380 ± 59 pg/mL, p < 0.05), while MUC18 overexpression increased IL-13-mediated eotaxin-3 (95 ± 3 vs. 58 ± 3 pg/mL, p < 0.05) in HTBE cells. IL-13-treated Muc18 KO mice had a lower percentage of neutrophils in BAL than WT mice (25 ± 3 vs. 35 ± 3%, p = 0.0565).

CONCLUSIONS

These results implicate MUC18 as a potential enhancer of airway inflammation in a type 2 cytokine (e.g., IL-13) milieu.

A novel mouse model of conditional IRAK-M deficiency in myeloid cells: application in lung Pseudomonas aeruginosa infection

Myeloid cells such as macrophages are critical to innate defense against infection. IL-1 receptor-associated kinase M (IRAK-M) is a negative regulator of TLR signaling during bacterial infection, but the role of myeloid cell IRAK-M in bacterial infection is unclear. Our goal was to generate a novel conditional knockout mouse model to define the role of myeloid cell IRAK-M during bacterial infection. Myeloid cell-specific IRAK-M knockout mice were generated by crossing IRAK-M floxed mice with LysM-Cre knock-in mice. The resulting LysM-Cre⁺/IRAK-M^fl/wt and control (LysM-Cre^-/IRAK-M^fl/wt) mice were intranasally infected with Pseudomonas aeruginosa (PA). IRAK-M deletion, inflammation, myeloperoxidase (MPO) activity and PA load were measured in leukocytes, bronchoalveolar lavage (BAL) fluid and lungs. PA killing assay with BAL fluid was performed to determine mechanisms of IRAK-M-mediated host defense. IRAK-M mRNA and protein levels in alveolar and lung macrophages were significantly reduced in LysM-Cre⁺/IRAK-M^fl/wt mice compared with control mice. Following PA infection, LysM-Cre⁺/IRAK-M^fl/wt mice have enhanced lung neutrophilic inflammation, including MPO activity, but reduced PA load. The increased lung MPO activity in LysM-Cre⁺/IRAK-M^fl/wt mouse BAL fluid reduced PA load. Generation of IRAK-M conditional knockout mice will enable investigators to determine precisely the function of IRAK-M in myeloid cells and other types of cells during infection and inflammation.

MUC18 Regulates Lung Rhinovirus Infection and Inflammation

Background

MUC18 is upregulated in the lungs of asthma and COPD patients. It has been shown to have pro-inflammatory functions in cultured human airway epithelial cells during viral infections and in mice during lung bacterial infections. However, the in vivo role of MUC18 in the context of viral infections remains poorly understood. The goal of this study is to define the in vivo function of MUC18 during respiratory rhinovirus infection.

Methods

Muc18 wild-type (WT) and knockout (KO) mice were infected with human rhinovirus 1B (HRV-1B) and sacrificed after 1 day to determine the inflammatory and antiviral responses. To examine the direct effects of Muc18 on viral infection, tracheal epithelial cells isolated from WT and KO mice were grown under air-liquid interface and infected with HRV-1B. Finally, siRNA mediated knockdown of MUC18 was performed in human airway epithelial cells (AECs) to define the impact of MUC18 on human airway response to HRV-1B.

Results

Both viral load and neutrophilic inflammation were significantly decreased in Muc18 KO mice compared to WT mice. In the in vitro setting, viral load was significantly lower and antiviral gene expression was higher in airway epithelial cells of Muc18 KO mice than the WT mice. Furthermore, in MUC18 knockdown human AECs, viral load was decreased and antiviral gene expression was increased compared to controls.

Conclusions

Our study is the first to demonstrate MUC18’s pro-inflammatory and pro-viral function in an in vivo mouse model of rhinovirus infection.

Tollip SNP rs5743899 modulates human airway epithelial responses to rhinovirus infection

BACKGROUND

Rhinovirus (RV) infection in asthma induces varying degrees of airway inflammation (e.g. neutrophils), but the underlying mechanisms remain unclear.

OBJECTIVE

The major goal was to determine the role of genetic variation [e.g. single nucleotide polymorphisms (SNPs)] of Toll-interacting protein (Tollip) in airway epithelial responses to RV in a type 2 cytokine milieu.

METHODS

DNA from blood of asthmatic and normal subjects was genotyped for Tollip SNP rs5743899 AA, AG and GG genotypes. Human tracheobronchial epithelial (HTBE) cells from donors without lung disease were cultured to determine pro-inflammatory and antiviral responses to IL-13 and RV16. Tollip knockout and wild-type mice were challenged with house dust mite (HDM) and infected with RV1B to determine lung inflammation and antiviral response.

RESULTS

Asthmatic subjects carrying the AG or GG genotype (AG/GG) compared with the AA genotype demonstrated greater airflow limitation. HTBE cells with AG/GG expressed less Tollip. Upon IL-13 and RV16 treatment, cells with AG/GG (vs. AA) produced more IL-8 and expressed less antiviral genes, which was coupled with increased NF-κB activity and decreased expression of LC3, a hallmark of the autophagic pathway. Tollip co-localized and interacted with LC3. Inhibition of autophagy decreased antiviral genes in IL-13- and RV16-treated cells. Upon HDM and RV1B, Tollip knockout (vs. wild-type) mice demonstrated higher levels of lung neutrophilic inflammation and viral load, but lower levels of antiviral gene expression.

CONCLUSIONS AND CLINICAL RELEVANCE

Our data suggest that Tollip SNP rs5743899 may predict varying airway response to RV infection in asthma.

Activator protein 1 promotes the transcriptional activation of IRAK-M

Interleukin-1 receptor-associated kinase M (IRAK-M) is a well-known negative regulator for Toll-like receptor signaling, which can regulate immune homeostasis and tolerance in a number of pathological settings. However, the mechanism for IRAK-M regulation at transcriptional level remains largely unknown. In this study, a 1.4kb upstream sequence starting from the major IRAK-M transcriptional start site was cloned into luciferase reporter vector pGL3-basic to construct the full-length IRAK-M promoter. Luciferase reporter plasmids harboring the full-length and the deletion mutants of IRAK-M were transfected into 293T and A549 cells, and their relative luciferase activity was measured. The results demonstrated that activator protein 1(AP-1) cis-element plays a crucial role in IRAK-M constitutive gene transcription. Silencing of c-Fos and/or c-Jun expression suppressed the IRAK-M promoter activity as well as its mRNA and protein expressions. As a specific inhibitor for AP-1 activation, SP600125 also significantly suppressed the basal transcriptional activity of IRAK-M, the binding activity of c-Fos/c-Jun with IRAK-M promoter, and IRAK-M protein expression. Taken together, the result of this study highlights the importance of AP-1 in IRAK-M transcription, which offers more information on the role of IRAK-M in infectious and non-infectious diseases.

Magnetic Nanodrug Delivery Through the Mucus Layer of Air-Liquid Interface Cultured Primary Normal Human Tracheobronchial Epithelial Cells

Superparamagnetic iron oxide (Fe₃O₄) and highly anisotropic barium hexaferrite (BaFe₁₂O₁₉) nanoparticles were coated with an anti-inflammatory drug and magnetically transported through mucus produced by primary human airway epithelial cells. Using wet planetary ball milling, dl-2-amino-3-phosphonopropionic acid-coated BaFe₁₂O₁₉ nano-particles (BaNPs) of 1-100 nm in diameter were prepared in water. BaNPs and conventional 20-30-nm Fe₃O₄ nanoparticles (FeNPs) were then encased in a polymer (PLGA) loaded with dexamethasone (Dex) and tagged for imaging. PLGA-Dex-coated BaNPs and FeNPs were characterized using dynamic light scattering (DLS), transmission electron microscopy (TEM), and superconducting quantum interference device (SQUID) magnetometry. Both PLGA-Dex-coated BaNPs and FeNPs were transferred to the surface of a ~100-μm thick mucus layer of air-liquid interface cultured primary normal human tracheobronchial epithelial (NHTE) cells. Within 30 min, the nanoparticles were pulled successfully through the mucus layer by a permanent neodymium magnet. The penetration time of the nanomedicine was monitored using confocal microscopy and tailored by varying the thickness of the PLGA-Dex coating around the particles.

Cistrome-based Cooperation between Airway Epithelial Glucocorticoid Receptor and NF-κB Orchestrates Anti-inflammatory Effects

Antagonism of pro-inflammatory transcription factors by monomeric glucocorticoid receptor (GR) has long been viewed as central to glucocorticoid (GC) efficacy. However, the mechanisms and targets through which GCs exert therapeutic effects in diseases such as asthma remain incompletely understood. We previously defined a surprising cooperative interaction between GR and NF-κB that enhanced expression of A20 (TNFAIP3), a potent inhibitor of NF-κB. Here we extend this observation to establish that A20 is required for maximal cytokine repression by GCs. To ascertain the global extent of GR and NF-κB cooperation, we determined genome-wide occupancy of GR, the p65 subunit of NF-κB, and RNA polymerase II in airway epithelial cells treated with dexamethasone, TNF, or both using chromatin immunoprecipitation followed by deep sequencing. We found that GR recruits p65 to dimeric GR binding sites across the genome and discovered additional regulatory elements in which GR-p65 cooperation augments gene expression. GR targets regulated by this mechanism include key anti-inflammatory and injury response genes such as SERPINA1, which encodes α1 antitrypsin, and FOXP4, an inhibitor of mucus production. Although dexamethasone treatment reduced RNA polymerase II occupancy of TNF targets such as IL8 and TNFAIP2, we were unable to correlate specific binding sequences for GR or occupancy patterns with repressive effects on transcription. Our results suggest that cooperative anti-inflammatory gene regulation by GR and p65 contributes to GC efficacy, whereas tethering interactions between GR and p65 are not universally required for GC-based gene repression.

Trehalose-mediated autophagy impairs the anti-viral function of human primary airway epithelial cells

Human rhinovirus (HRV) is the most common cause of acute exacerbations of chronic lung diseases including asthma. Impaired anti-viral IFN-λ1 production and increased HRV replication in human asthmatic airway epithelial cells may be one of the underlying mechanisms leading to asthma exacerbations. Increased autophagy has been shown in asthmatic airway epithelium, but the role of autophagy in anti-HRV response remains uncertain. Trehalose, a natural glucose disaccharide, has been recognized as an effective autophagy inducer in mammalian cells. In the current study, we used trehalose to induce autophagy in normal human primary airway epithelial cells in order to determine if autophagy directly regulates the anti-viral response against HRV. We found that trehalose-induced autophagy significantly impaired IFN-λ1 expression and increased HRV-16 load. Inhibition of autophagy via knockdown of autophagy-related gene 5 (ATG5) effectively rescued the impaired IFN-λ1 expression by trehalose and subsequently reduced HRV-16 load. Mechanistically, ATG5 protein interacted with retinoic acid-inducible gene I (RIG-I) and IFN-β promoter stimulator 1 (IPS-1), two critical molecules involved in the expression of anti-viral interferons. Our results suggest that induction of autophagy in human primary airway epithelial cells inhibits the anti-viral IFN-λ1 expression and facilitates HRV infection. Intervention of excessive autophagy in chronic lung diseases may provide a novel approach to attenuate viral infections and associated disease exacerbations.

Enterococcus faecalis lipoteichoic acid suppresses Aggregatibacter actinomycetemcomitans lipopolysaccharide-induced IL-8 expression in human periodontal ligament cells

Periodontitis is caused by multi-bacterial infection and Aggregatibacter actinomycetemcomitans and Enterococcus faecalis are closely associated with inflammatory periodontal diseases. Although lipopolysaccharide (LPS) of A. actinomycetemcomitans (Aa.LPS) and lipoteichoic acid of E. faecalis (Ef.LTA) are considered to be major virulence factors evoking inflammatory responses, their combinatorial effect on the induction of chemokines has not been investigated. In this study, we investigated the interaction between Aa.LPS and Ef.LTA on IL-8 expression in human periodontal ligament (PDL) cells. Aa.LPS, but not Ef.LTA, substantially induced IL-8 expression at the protein and mRNA levels. Interestingly, Ef.LTA suppressed Aa.LPS-induced IL-8 expression without affecting the binding of Aa.LPS to Toll-like receptor (TLR) 4. Ef.LTA reduced Aa.LPS-induced phosphorylation of mitogen-activated protein kinases, including ERK, JNK and p38 kinase. Furthermore, Ef.LTA inhibited the Aa.LPS-induced transcriptional activities of the activating protein 1, CCAAT/enhancer-binding protein and nuclear factor-kappa B transcription factors, all of which are known to regulate IL-8 gene expression. Ef.LTA augmented the expression of IL-1 receptor-associated kinase-M (IRAK-M), a negative regulator of TLR intracellular signaling pathways, in the presence of Aa.LPS at both the mRNA and protein levels. Small interfering RNA silencing IRAK-M reversed the attenuation of Aa.LPS-induced IL-8 expression by Ef.LTA. Collectively, these results suggest that Ef.LTA down-regulates Aa.LPS-induced IL-8 expression in human PDL cells through up-regulation of the negative regulator IRAK-M.

IRAK-M promotes alternative macrophage activation and fibroproliferation in bleomycin-induced lung injury

Idiopathic pulmonary fibrosis is a devastating lung disease characterized by inflammation and the development of excessive extracellular matrix deposition. Currently, there are only limited therapeutic intervenes to offer patients diagnosed with pulmonary fibrosis. Although previous studies focused on structural cells in promoting fibrosis, our study assessed the contribution of macrophages. Recently, TLR signaling has been identified as a regulator of pulmonary fibrosis. IL-1R-associated kinase-M (IRAK-M), a MyD88-dependent inhibitor of TLR signaling, suppresses deleterious inflammation, but may paradoxically promote fibrogenesis. Mice deficient in IRAK-M (IRAK-M(-/-)) were protected against bleomycin-induced fibrosis and displayed diminished collagen deposition in association with reduced production of IL-13 compared with wild-type (WT) control mice. Bone marrow chimera experiments indicated that IRAK-M expression by bone marrow-derived cells, rather than structural cells, promoted fibrosis. After bleomycin, WT macrophages displayed an alternatively activated phenotype, whereas IRAK-M(-/-) macrophages displayed higher expression of classically activated macrophage markers. Using an in vitro coculture system, macrophages isolated from in vivo bleomycin-challenged WT, but not IRAK-M(-/-), mice promoted increased collagen and α-smooth muscle actin expression from lung fibroblasts in an IL-13-dependent fashion. Finally, IRAK-M expression is upregulated in peripheral blood cells from idiopathic pulmonary fibrosis patients and correlated with markers of alternative macrophage activation. These data indicate expression of IRAK-M skews lung macrophages toward an alternatively activated profibrotic phenotype, which promotes collagen production, leading to the progression of experimental pulmonary fibrosis.

Electronic cigarette liquid increases inflammation and virus infection in primary human airway epithelial cells

Background/Objective

The use of electronic cigarettes (e-cigarettes) is rapidly increasing in the United States, especially among young people since e-cigarettes have been perceived as a safer alternative to conventional tobacco cigarettes. However, the scientific evidence regarding the human health effects of e-cigarettes on the lung is extremely limited. The major goal of our current study is to determine if e-cigarette use alters human young subject airway epithelial functions such as inflammatory response and innate immune defense against respiratory viral (i.e., human rhinovirus, HRV) infection.

Methodology/Main Results

We examined the effects of e-cigarette liquid (e-liquid) on pro-inflammatory cytokine (e.g., IL-6) production, HRV infection and host defense molecules (e.g., short palate, lung, and nasal epithelium clone 1, SPLUNC1) in primary human airway epithelial cells from young healthy non-smokers. Additionally, we examined the role of SPLUNC1 in lung defense against HRV infection using a SPLUNC1 knockout mouse model. We found that nicotine-free e-liquid promoted IL-6 production and HRV infection. Addition of nicotine into e-liquid further amplified the effects of nicotine-free e-liquid. Moreover, SPLUNC1 deficiency in mice significantly increased lung HRV loads. E-liquid inhibited SPLUNC1 expression in primary human airway epithelial cells. These findings strongly suggest the deleterious health effects of e-cigarettes in the airways of young people. Our data will guide future studies to evaluate the impact of e-cigarettes on lung health in human populations, and help inform the public about potential health risks of e-cigarettes.

MUC18 Differentially Regulates Pro-Inflammatory and Anti-Viral Responses in Human Airway Epithelial Cells

OBJECTIVE

MUC18 or CD146, a transmembrane glycoprotein, is mainly expressed by endothelial cells and smooth muscle cells where it serves as a cell-cell adhesion molecule. We have found MUC18 up-regulation in airway epithelial cells of patients with asthma and chronic obstructive pulmonary disease (COPD). However, the function of MUC18 in airway epithelial cells remains unclear. In the present study, we tested the hypothesis that MUC18 exerts a pro-inflammatory function during stimulation with a viral mimic polyI:C or human rhinovirus infection.

METHODS

Normal human primary airway epithelial cells were transduced with lentivirus encoding MUC18 cDNA to over-express MUC18 or with GFP (control), and treated with polyI:C or HRV for detection of pro-inflammatory cytokine IL-8 and anti-viral gene IFN-β. Additionally, we performed cell culture of human lung epithelial cell line NCIH292 cells to determine the mechanisms of MUC18 function.

RESULTS

We found that MUC18 over-expression promoted IL-8 production, while it inhibited IFN-β expression following polyI:C stimulation or HRV infection. Increased phosphorylation of MUC18 serines was observed in MUC18 over-expressing cells. Reduction of MUC18 serine phosphorylation by inhibiting ERK activity was associated with less production of IL-8 following polyI:C stimulation.

CONCLUSIONS

Our results for the first time demonstrate MUC18's pro-inflammatory and anti-viral function in human airway epithelial cells.

Interleukin-1 receptor-associated kinase M (IRAK-M) promotes human rhinovirus infection in lung epithelial cells via the autophagic pathway

Human rhinovirus (HRV) is the most common viral etiology in acute exacerbations of asthma. However, the exact mechanisms underlying HRV infection in allergic airways are poorly understood. IL-13 increases interleukin-1 receptor associated kinase M (IRAK-M) and subsequently inhibits airway innate immunity against bacteria. However, the role of IRAK-M in lung HRV infection remains unclear. Here, we provide the first evidence that IRAK-M over-expression promotes lung epithelial HRV-16 replication and autophagy, but inhibits HRV-16-induced IFN-β and IFN-λ1 expression. Inhibiting autophagy reduces HRV-16 replication. Exogenous IFN-β and IFN-λ1 inhibit autophagy and HRV-16 replication. Our data indicate the enhancing effect of IRAK-M on epithelial HRV-16 infection, which is partly through the autophagic pathway. Impaired anti-viral interferon production may serve as a direct or an indirect (e.g., autophagy) mechanism of enhanced HRV-16 infection by IRAK-M over-expression. Targeting autophagic pathway or administrating anti-viral interferons may prevent or attenuate viral (e.g., HRV-16) infections in allergic airways.

Failure of respiratory defenses in the pathogenesis of bacterial pneumonia of cattle

The respiratory system is well defended against inhaled bacteria by a dynamic system of interacting layers, including mucociliary clearance, host defense factors including antimicrobial peptides in the epithelial lining fluid, proinflammatory responses of the respiratory epithelium, resident alveolar macrophages, and recruited neutrophils and monocytes. Nevertheless, these manifold defenses are susceptible to failure as a result of stress, glucocorticoids, viral infections, abrupt exposure to cold air, and poor air quality. When some of these defenses fail, the lung can be colonized by bacterial pathogens that are equipped to evade the remaining defenses, resulting in the development of pneumonia. This review considers the mechanisms by which these predisposing factors compromise the defenses of the lung, with a focus on the development of bacterial pneumonia in cattle and supplemented with advances based on mouse models and the study of human disease. Deepening our understanding of how the respiratory defenses fail is expected to lead to interventions that restore these dynamic immune responses and prevent disease.

Human neutrophil elastase degrades SPLUNC1 and impairs airway epithelial defense against bacteria

Background

Acute exacerbations of chronic obstructive pulmonary disease (AECOPD) are a significant cause of mortality of COPD patients, and pose a huge burden on healthcare. One of the major causes of AECOPD is airway bacterial (e.g. nontypeable Haemophilus influenzae [NTHi]) infection. However, the mechanisms underlying bacterial infections during AECOPD remain poorly understood. As neutrophilic inflammation including increased release of human neutrophil elastase (HNE) is a salient feature of AECOPD, we hypothesized that HNE impairs airway epithelial defense against NTHi by degrading airway epithelial host defense proteins such as short palate, lung, and nasal epithelium clone 1 (SPLUNC1).

Methodology/Main Results

Recombinant human SPLUNC1 protein was incubated with HNE to confirm SPLUNC1 degradation by HNE. To determine if HNE-mediated impairment of host defense against NTHi was SPLUNC1-dependent, SPLUNC1 protein was added to HNE-treated primary normal human airway epithelial cells. The in vivo function of SPLUNC1 in NTHi defense was investigated by infecting SPLUNC1 knockout and wild-type mice intranasally with NTHi. We found that: (1) HNE directly increased NTHi load in human airway epithelial cells; (2) HNE degraded human SPLUNC1 protein; (3) Recombinant SPLUNC1 protein reduced NTHi levels in HNE-treated human airway epithelial cells; (4) NTHi levels in lungs of SPLUNC1 knockout mice were increased compared to wild-type mice; and (5) SPLUNC1 was reduced in lungs of COPD patients.

Conclusions

Our findings suggest that SPLUNC1 degradation by neutrophil elastase may increase airway susceptibility to bacterial infections. SPLUNC1 therapy likely attenuates bacterial infections during AECOPD.

Advances in environmental and occupational disorders in 2012

The year 2012 produced a number of advances in our understanding of the effect of environmental factors on allergic diseases, identification of new allergens, immune mechanisms in host defense, factors involved in asthma severity, and therapeutic approaches. This review focuses on the articles published in the Journal in 2012 that enhance our knowledge base of environmental and occupational disorders. Identification of novel allergens can improve diagnostics, risk factor analysis can aid preventative approaches, and studies of genetic-environmental interactions and immune mechanisms will lead to better therapeutics.

Advances in mechanisms of allergy and clinical immunology in 2012

Manuscripts published in the "Mechanisms of allergy and clinical immunology" section of the Journal of Allergy and Clinical Immunology during 2012 enhanced our knowledge of the involvement of cytokines and other mediators in allergic disorders and described novel approaches for understanding mechanisms of allergic and immunologic diseases. Also published were articles focused on mechanisms of allergen-specific immunotherapy and the development of novel antiallergic treatments, as well as strategies to achieve tolerance to allergens. The highlights of these studies and their potential clinical implications are summarized in this review.