Synergistic Proinflammatory Responses by IL-17A and Toll-Like Receptor 3 in Human Airway Epithelial Cells

Ruxolitinib inhibits poly(I:C) and type 2 cytokines-induced CCL5 production in bronchial epithelial cells: A potential therapeutic agent for severe eosinophilic asthma

Rationale

Severe eosinophilic asthma is characterized by airway eosinophilia and corticosteroid‐resistance, commonly overlapping with type 2 inflammation. It has been reported that chemokine (C‐C motif) ligand 5 (CCL5) is involved in the exacerbation of asthma by RNA virus infections. Indeed, treatment with a virus‐associated ligand and a T helper type 2 cell (Th2) cytokine can synergistically stimulate CCL5 production in bronchial epithelial cells. We aimed to evaluate the mechanisms underlying CCL5 production in this in vitro model and to assess the potential of Janus kinase 1 (JAK1) as a novel therapeutic target via the use of ruxolitinib.

Methods

We stimulated primary normal human bronchial epithelial (NHBE) cells and BEAS‐2B cells with poly(I:C) along with interleukin‐13 (IL‐13) or IL‐4, and assessed CCL5 production. We also evaluated the signals involved in virus‐ and Th2‐cytokine‐induced CCL5 production and explored a therapeutic agent that attenuates the CCL5 production.

Results

Poly(I:C) stimulated NHBE and BEAS‐2B cells to produce CCL5. Poly(I:C) and IL‐13 increased CCL5 production. Poly(I:C)‐induced CCL5 production occurred via the TLR3–IRF3 and IFNAR/JAK1–phosphoinositide 3‐kinase (PI3K) pathways, but not the IFNAR/JAK1–STATs pathway. In addition, IL‐13 did not augment poly(I:C)‐induced CCL5 production via the canonical IL‐13R/IL‐4R/JAK1–STAT6 pathway but likely via subsequent TLR3‐IRF3‐IFNAR/JAK1‐PI3K pathways. JAK1 was identified to be a potential therapeutic target for severe eosinophilic asthma. The JAK1/2 inhibitor, ruxolitinib, was demonstrated to more effectively decrease CCL5 production in BEAS‐2B cells than fluticasone propionate.

Conclusion

We have demonstrated that JAK1 is a possible therapeutic target for severe corticosteroid‐resistant asthma with airway eosinophilia and persistent Th2‐type inflammation, and that ruxolitinib has potential as an alternative pharmacotherapy.

Influenza A virus enhances ciliary activity and mucociliary clearance via TLR3 in airway epithelium

Background

Viral respiratory tract infections, such as influenza A virus (IAV), are common and life-threatening illnesses worldwide. The mechanisms by which viruses are removed from the respiratory tract are indispensable for airway host defense. Mucociliary clearance is an airway defense mechanism that removes pathogens from the respiratory tract. The coordination and modulation of the ciliary beating of airway epithelial cells play key roles in maintaining effective mucociliary clearance. However, the impact of respiratory virus infection on ciliary activity and mucociliary clearance remains unclear.

Methods

Tracheal samples were taken from wild-type (WT) and Toll-like receptor 3 (TLR3)-knockout (KO) mice. Transient organ culture of murine trachea was performed in the presence or absence of IAV, polyI:C, a synthetic TLR3 ligand, and/or reagents. Subsequently, cilia-driven flow and ciliary motility were analyzed. To evaluate cilia-driven flow, red fluorescent beads were loaded into culture media and movements of the beads onto the tracheal surface were observed using a fluorescence microscope. To evaluate ciliary motility, cilia tips were labeled with Indian ink diluted with culture medium. The motility of ink-labeled cilia tips was recorded by high-speed cameras.

Results

Short-term IAV infection significantly increased cilia-driven flow and ciliary beat frequency (CBF) compared with the control level in WT culture. Whereas IAV infection did not elicit any increases of cilia-driven flow and CBF in TLR3-KO culture, indicating that TLR3 was essential to elicit an increase of cilia-driven flow and CBF in response to IAV infection. TLR3 activation by polyI:C readily induced adenosine triphosphate (ATP) release from the trachea and increases of cilia-driven flow and CBF in WT culture, but not in TLR3-KO culture. Moreover, blockade of purinergic P2 receptors (P2Rs) signaling using P2R antagonist, suramin, suppressed polyI:C-mediated increases of cilia-driven flow and CBF, indicating that TLR3-mediated ciliary activation depended on released extracellular ATP and the autocrine ATP-P2R loop.

Conclusions

IAV infection readily increases ciliary activity and cilia-driven flow via TLR3 activation in the airway epithelium, thereby hastening mucociliary clearance and “sweeping” viruses from the airway as an initial host defense response. Mechanically, extracellular ATP release in response to TLR3 activation promotes ciliary activity through autocrine ATP-P2R loop.

Interleukin-36 in Infectious and Inflammatory Skin Diseases

Interleukin-36 (IL-36) comprises to a cytokine family consisting of four isoforms IL-36α, IL-36β, IL-36γ, and IL-36 receptor antagonist (IL-36 Ra). These IL-36 cytokines, in turn, belong to the IL-1 superfamily. The IL-36 receptor (IL-1R6) is functional as a heterodimer formed of IL-1R6 and IL-1 receptor accessory protein (IL-1RAcP). IL-36α, IL-36β, and IL-36γ are regarded as pro-inflammatory ligands and IL-36 Ra as well as IL-38 as anti-inflammatory ligands of IL-1R6. IL-36 cytokines are mainly expressed on the barrier sites of the body e.g., bronchial, intestinal, and dermal epithelium. One of their most important biological functions is the bridging of innate and adaptive immune responses. A disturbed balance between pro-inflammatory and anti-inflammatory branches easily leads to inflammation of the corresponding tissue. The most prominent example for an altered IL-36 expression is the spectrum of psoriasis. In addition to inflammatory dermatoses, IL-36 also seems to play a role in infectious dermatoses. Microbial triggers, especially Staphylococcus aureus infection, increase the production of pro-inflammatory IL-36 cytokines and initiate/promote the inflammation of skin lesions. Due to the discovery of IL-36 as an important immune mediator, it has already been possible to develop important diagnostic tools for dermatitis. Not only in the field of inflammatory skin diseases, but also in pulmonary and intestinal inflammation, there is evidence that IL-36 cytokines might have diagnostic and/or therapeutic relevance.

Distinct roles for MDA5 and TLR3 in the acute response to inhaled double-stranded RNA

The airway epithelial barrier is critical for preventing pathogen invasion and translocation of inhaled particles into the lung. Epithelial cells also serve an important sentinel role after infection and release various pro-inflammatory mediators that recruit and activate immune cells. Airway epithelial barrier disruption has been implicated in a growing number of respiratory diseases including viral infections. It is thought that when a pathogen breaks the barrier and gains access to the host tissue, pro-inflammatory mediators increase, which further disrupts the barrier and initiates a vicious cycle of leak. However, it is difficult to study airway barrier integrity in vivo, and little is known about relationship between epithelial barrier function and airway inflammation. Current assays of pulmonary barrier integrity quantify the leak of macromolecules from the vasculature into the airspaces (or “inside/out” leak). However, it is also important to measure the ease with which inhaled particles, allergens, or pathogens can enter the subepithelial tissues (or “outside/in” leak). We challenged mice with inhaled double stranded RNA (dsRNA) and explored the relationship between inside/out and outside/in barrier function and airway inflammation. Using wild-type and gene-targeted mice, we studied the roles of the dsRNA sensors Toll Like Receptor 3 (TLR3) and Melanoma Differentiation-Associated protein 5 (MDA5). Here we report that after acute challenge with inhaled dsRNA, airway barrier dysfunction occurs in a TLR3-dependent manner, whereas leukocyte accumulation is largely MDA5-dependent. We conclude that airway barrier dysfunction and inflammation are regulated by different mechanisms at early time points after exposure to inhaled dsRNA.

IL-17A Attenuates IFN-λ Expression by Inducing Suppressor of Cytokine Signaling Expression in Airway Epithelium

IFN-λ is a cytokine expressed in epithelial tissues and plays a central role in antiviral mucosal immune response. The expression of IFN-λ in the airway is impaired in chronic airway diseases (e.g., asthma, chronic obstructive pulmonary disease), which renders patients susceptible to viral infection. IL-17A is associated with asthma and chronic obstructive pulmonary disease pathogenesis; however, IL-17A regulation of IFN-λ expression remains unclear. The aim of the current study is to clarify IL-17A-mediated regulatory mechanisms of IFN-λ expression in human airway epithelial cells. In this study, we have shown that polyinosinic:polycytidylic acid (polyI:C) and influenza A virus (IAV) infection increased IFN-λ expression at mRNA and protein levels in primary cultures of normal human bronchial epithelial cells, whereas IL-17A attenuated polyI:C- or IAV-induced IFN-λ expression. IFN-λ receptor 1 knockdown and a JAK inhibitor, ruxolitinib, attenuated polyI:C-induced IFN-λ expression, confirming that a positive autocrine feedback loop, the IFN-λ receptor-JAK-STAT pathway, was involved in IFN-λ expression. In Western blotting analysis, we demonstrated that polyI:C and IAV infection induced STAT1 phosphorylation in normal human bronchial epithelial cells, whereas IL-17A suppressed polyI:C- or IAV-mediated STAT1 phosphorylation. Furthermore, we found that cotreatment with IL-17A and polyI:C or IAV infection synergistically increased suppressor of cytokine signaling (SOCS)1 and SOCS3 expression. SOCS1 small interfering RNA and SOCS3 small interfering RNA negated the inhibitory effect of IL-17A in polyI:C-induced IFN-λ expression by restoring attenuated STAT1 phosphorylation. Taken together, these findings indicate that IL-17A attenuates virus-induced IFN-λ expression by enhancing SOCS1 and SOCS3 expression to inhibit autocrine signaling loops in human airway epithelial cells.

IL-13 regulates IL-17C expression by suppressing NF-κB-mediated transcriptional activation in airway epithelial cells

The cytokine interleukin (IL)-17C is highly expressed in epithelial tissues and involved in innate immune responses; however, the regulation of IL-17C expression in the airways remains poorly understood. Here, we show that IL-1β strongly induces both IL-17C mRNA and protein expression in primary normal human bronchial epithelial cells. Conversely, IL-13 significantly reduced the IL-1β-induced IL-17C expression. Attenuation of the nuclear factor (NF)-κB-signaling pathway using an NF-κB-subunit p65-specific small-interfering RNA (siRNA), reduced IL-1β-induced IL-17C expression, demonstrating the importance of NF-κB signaling in IL-17C regulation. The inhibitory effects of IL-13 on IL-17C expression were abolished when the Janus kinase (JAK)/signal transducer and activator of transcription 6 (STAT6)-signaling pathway was impaired, using either the JAK inhibitor ruxolitinib or a STAT6-specific siRNA. Western blot analysis demonstrated that IL-1β promoted both IκB-α phosphorylation and degradation, and p65 nuclear translocation. Although IL-13 induced STAT6 phosphorylation and nuclear translocation, it did not affect the activation of the IL-1β-mediated NF-κB-pathway. Using chromatin immunoprecipitation, we confirmed that IL-1β enhanced p65 binding to regions within the IL-17C promoter that flank putative NF-κB-binding sites (-130/-120 and -157/-147). Interestingly, IL-13 treatment reduced the IL-1β-mediated p65 binding to these regions. These findings demonstrate that NF-κB-mediated transcriptional mechanisms are critically involved in the IL-1β-mediated IL-17C induction, and that IL-13 negatively regulates this induction by suppressing NF-κB-based transcriptional activation.

Regulation of airway inflammation and remodeling in asthmatic mice by TLR3/TRIF signal pathway

This paper aims to investigate the effect of Toll-like receptors 3 (TLR3)/TIR-domain-containing adapter-inducing interferon-β (TRIF) signal pathway on the airway inflammation and remodeling in asthmatic mice. C57BL/6 and TLR3^-/- mice were randomly divided into three groups (10 mice per group), including Control group (mice inhaled phosphate buffer saline (PBS)), Asthma group (mice inhaled ovalbumin (OVA)) and polyriboinosinic-ribocytidylic acid (poly (I: C)) group (asthmatic mice were injected intraperitoneally with TLR3 agonist poly (I: C)). Hematoxylin-eosin (HE) staining, Wright-Giemsa staining, Enzyme-linked immunosorbent assay (ELISA), Immunohistochemistry, Hydroxyproline assay, quantitative real time polymerase chain reaction (qRT-PCR) and Western blot were used to assess for the indices of airway inflammation and remodeling. In terms of WT mice, all asthma groups with or without the addition of poly (I: C) showed exaggerated inflammation and remodeling in the airways as compared to Control group, which were more seriously in poly (I: C) group than Asthma group. Furthermore, we observed the significant inhibition of airway inflammation and remodeling in the TLR3^-/- mice in both Asthma no matter with or without addition of poly (I: C) than the WT mice. TLR3 knockout could obviously relieve the airway inflammation and remodeling in asthma through inhibiting TLR3/TRIF signaling pathway.

Development of a non-infectious rat model of acute exacerbation of idiopathic pulmonary fibrosis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive interstitial lung disease with severe pulmonary fibrosis. The main cause of IPF-associated death is acute exacerbation of IPF (AE-IPF). This study aims to develop a rat model of AE-IPF by two intratracheal perfusions with bleomycin (BLM).

METHODS

Ninety male Sprague Dawley (SD) rats were randomized into three groups: an AE-IPF model group (BLM + BLM group), an IPF model group (BLM group), and a normal control group. Rats in the BLM + BLM group underwent a second perfusion with BLM on day 28 after the first perfusion with BLM. Rats in the other two groups received saline as the second perfusion. Six rats in each group were sacrificed on day 31, day 35, and day 42 after the first perfusion, respectively. Additional 18 rats in each group were observed for survival.

RESULTS

Rats in the BLM + BLM group had significantly worse pulmonary alveolar inflammation and fibrosis than rats in the BLM group. Rats in the BLM + BLM group also developed large amounts of hyaline membrane, showed high levels of albumin (ALB) and various inflammatory factors in the bronchoalveolar lavage fluid (BALF), and had markedly increased lung water content. Furthermore, rat survival was reduced in the BLM + BLM group. The pathophysiological characteristics of rats in the BLM + BLM group resemble those of patients with AE-IPF.

CONCLUSIONS

A second perfusion with BLM appears to induce acute exacerbation of pulmonary fibrosis and may be used to model AE-IPF in rats.

Targeted inhibition of Six1 attenuates allergic airway inflammation and remodeling in asthmatic mice

Asthma is an inflammatory disease of the airways, characterized by lung eosinophilia, mucus hypersecretion by goblet cells and airway hyperresponsiveness to inhaled allergens. The purpose of this study was to evaluate the effects of Six1 on airway inflammation and remodeling and the underlying mechanisms in a murine model of chronic asthma. Female BALB/c mice were randomly divided into four groups: phosphate-buffered saline control, ovalbumin (OVA)-induced asthma group, OVA+siNC and OVA+siSix1. In this mice model, Six1 expression level was significantly elevated in OVA-induced asthma of mice. Additionally, downregulation of Six1 dramatically decreased OVA-challenged inflammation, infiltration, and mucus production. Moreover, silencing of Six1 resulted in decreased levels of immunoglobulin E and inflammatory mediators and reduced inflammatory cell accumulation, as well as inhibiting the expression of important mediators including matrix metalloproteinase MMP-2 and MMP-9, which is related to airway remodeling. Further analysis indicated that silencing of Six1 can significantly inhibit NF-kB pathway activation in the lungs. .In conclusion, these findings indicated that the downregulation of Six1 effectively inhibited airway inflammation and reversed airway remodeling, which suggest that Six1 represents a promising therapeutic strategy for human allergic asthma.

The roles and functional mechanisms of interleukin-17 family cytokines in mucosal immunity

The mucosal immune system serves as our front-line defense against pathogens. It also tightly maintains immune tolerance to self-symbiotic bacteria, which are usually called commensals. Sensing both types of microorganisms is modulated by signalling primarily through various pattern-recognition receptors (PRRs) on barrier epithelial cells or immune cells. After sensing, proinflammatory molecules such as cytokines are released by these cells to mediate either defensive or tolerant responses. The interleukin-17 (IL-17) family members belong to a newly characterized cytokine subset that is critical for the maintenance of mucosal homeostasis. In this review, we will summarize recent progress on the diverse functions and signals of this family of cytokines at different mucosal edges.