Functional inhibition of PAR2 alleviates allergen-induced airway hyperresponsiveness and inflammation

Cathepsin S: A key drug target and signalling hub in immune system diseases

The lysosomal cysteine protease cathepsin S supports host defence by promoting the maturation of MHC class-II proteins. In contrast, increased cathepsin S activity mediates tissue destructive immune responses in autoimmune and inflammatory diseases. Therefore, cathepsin S is a key target in drug discovery programs. Here, we critically reviewed the specific mechanisms by which cathepsin S mediates autoimmune and hyperinflammatory responses to identify new targets for therapeutic immunomodulation. To this end, we performed literature review utilizing PubMed, drug database of US FDA, European Medicines Agency and the Drug-Gene Interaction Database. Cathepsin S destroys T cell epitopes and reduces endogenous antigen diversity, impairing negative selection of autoreactive T cells that could recognize these epitopes. Moreover, cathepsin S critically regulates inflammatory disease severity by generating proinflammatory molecules (PAR-1, PAR-2, IL-36γ, Fractalkine, Endostatin, Ephrin-B2), inactivating anti-inflammatory mediators (SLPI) and degrading molecules involved in antimicrobial and immunomodulatory responses (surfactant protein-A, LL-37, beta-defensins), inter-endothelial/-epithelial barrier function, gene repair and energy homeostasis. These pathways could be targeted by repositioning of existing drugs. These findings suggest that inhibiting cathepsin S or a specific downstream target of cathepsin S by repositioning of existing drugs could be a promising strategy for treating autoimmune and inflammatory diseases. Current cathepsin S inhibitors in clinical trials face challenges, highlighting the need for innovative inhibitors that function effectively in various cellular compartments with differing pH levels, without targeting the shared catalytic site of cysteine cathepsins.

Protease-activated receptor 2: A promising therapeutic target for women's cancers

Cancers affecting women, such as breast, uterine, ovarian, endometrial, and cervical cancers, have become increasingly prevalent. The growing incidence and death rates associated with these cancers warrant the development of innovative and alternative approaches to current treatments. This article investigates the association of women's cancers with a molecular target known as protease-activated receptor 2 (PAR2), a G protein-coupled receptor that is expressed on the surface of cancer cells. Expression levels of the PAR2 gene were curated from publicly available databases, and PAR2 was found to be significantly overexpressed in tissues from patients with breast, uterine, ovarian, endometrial, or cervical cancer compared with normal tissues. PAR2 overexpression has been previously linked to tumor progression and, in some cases, tumor growth. Activation of PAR2 by either endogenous proteases or synthetic agonists triggers certain downstream intracellular signaling pathways that have been associated with tumor progression, cell migration and invasion, angiogenesis, and apoptosis of cancer cells. Although recent advances have led to identification of several PAR2 antagonists, none has yet been developed for human use. Additionally, PAR2 inhibition has been shown to increase the efficacy of chemotherapeutic drugs, allowing them to be potentially used at less toxic doses in combination therapies for cancer. The present work briefly summarizes the current status of PAR2 as a potential therapeutic target for treating women's cancers. SIGNIFICANCE STATEMENT: This article highlights potential roles for protease-activated receptor 2 (PAR2) in cancers affecting women. Overexpression of the PAR2 gene in women's cancers is associated with various oncogenic processes, such as tumor progression, cell migration, and invasion, ultimately contributing to poorer patient prognoses. Given the increasing incidence of women's cancers, there is an urgent need to develop novel therapeutic drugs, and PAR2 represents a promising target for developing new treatments.

Protease-Activated Receptor 2 in inflammatory skin disease: current evidence and future perspectives

Protease-activated receptor-2 (PAR2) is a class-A G protein-coupled receptor (GPCR) activated by serine proteases and is expressed by multiple tissues, including the skin. PAR2 is involved in the skin inflammatory response, promoting Th2 inflammation, delaying skin barrier repair, and affecting the differentiation of keratinocytes. It also participates in the transmission of itch and pain sensations in the skin. Increasing evidence indicates that PAR2 plays an important role in the pathogenesis of inflammatory skin diseases such as acne vulgaris, rosacea, psoriasis, and atopic dermatitis. Additional focus will be placed on potential targeted therapies based on PAR2. The Goal of this review is to outline the emerging effects of PAR2 activation in inflammatory skin disease and highlight the promise of PAR2 modulators.

Circumferential Stenosis of the Second Part of the Duodenum Caused by Eosinophilic Gastroenteritis

Isolated eosinophilic gastroenteritis (EGE) of the second part of the duodenum is rare. We herein report a case of EGE limited to the second part of the duodenum that caused circumferential stenosis due to massive wall thickening. A boring biopsy was useful to verify the accumulation of eosinophils. Induction of remission by prednisolone was accompanied by a marked reduction in the mRNA expression of interleukin-6, C-C motif chemokine ligand 17 (CCL17), and CCL26 without any reduction in prototypical EGE-associated T helper type 2 cytokines (IL-5, IL-13). Thus, the enhanced expression of IL-6, CCL17, and CCL26 might be involved in the development of EGE in this case.

Association of single nucleotide polymorphisms in the F2RL1 gene with clinical and inflammatory characteristics of patients with asthma

BACKGROUND

Proteinase-activated receptor 2 (PAR-2) is a G-protein coupled receptor associated with many inflammatory diseases, including asthma. We have shown an association between PAR-2 expression in peripheral blood monocytes and asthma severity as well as blood PAR-2 mRNA level and lung function. Since F2RL1 (the gene encoding PAR-2) polymorphisms affect PAR-2 expression, we hypothesize they may affect asthma severity.

METHODS

We recruited 76 subjects with asthma of varying severity and collected clinical (FEV1 [% predicted], FEV1/FVC, IgE) and immunological (PAR-2 mRNA, blood eosinophils) disease parameters. We also genotyped these individuals for 3 F2RL1 SNPs (-45C/T, -149C/G, c.621C/T).

RESULTS

We found that the F2RL1 SNP "C" allele of -45C/T (rs1529505) was associated with PAR-2 mRNA and blood eosinophils. F2RL1 SNP c.621C/T (rs631465) was associated with PAR-2 mRNA. The F2RL1 SNP -149C/G (rs2242991) had no association with any of the parameters studied. This study identified one F2RL1 SNP rs1529505 is associated with parameters of asthma, but not asthma severity.

CONCLUSION

Larger studies are needed to further elucidate the role of PAR-2 in the pathophysiology of asthma and the influence of genetic variation.

Blockade of Proteinase-Activated Receptor 2 (PAR2) Attenuates Neuroinflammation in Experimental Autoimmune Encephalomyelitis

Proteinase-activated receptor-2 (PAR2), which modulates inflammatory responses, is elevated in the central nervous system in multiple sclerosis (MS) and in its murine model, experimental autoimmune encephalomyelitis (EAE). In PAR2-null mice, disease severity of EAE is markedly diminished. We therefore tested whether inhibiting PAR2 activation in vivo might be a viable strategy for the treatment of MS. Using the EAE model, we show that a PAR2 antagonist, the pepducin palmitoyl-RSSAMDENSEKKRKSAIK-amide (P2pal-18S), attenuates EAE progression by affecting immune cell function. P2pal-18S treatment markedly diminishes disease severity and reduces demyelination, as well as the infiltration of T-cells and macrophages into the central nervous system. Moreover, P2pal-18S decreases granulocyte-macrophage colony-stimulating factor (GM-CSF) production and T-cell activation in cultured splenocytes and prevents macrophage polarization in vitro. We conclude that PAR2 plays a key role in regulating neuroinflammation in EAE and that PAR2 antagonists represent promising therapeutic agents for treating MS and other neuroinflammatory diseases. SIGNIFICANCE STATEMENT: Proteinase-activated receptor-2 modulates inflammatory responses and is increased in multiple sclerosis lesions. We show that the proteinase-activated receptor-2 antagonist palmitoyl-RSSAMDENSEKKRKSAIK-amide reduces disease in the murine experimental autoimmune encephalomyelitis model of multiple sclerosis by inhibiting T-cell and macrophage activation and infiltration into the central nervous system, making it a potential treatment for multiple sclerosis.

Platelet-activating factor and protease-activated receptor 2 cooperate to promote neutrophil recruitment and lung inflammation through nuclear factor-kappa B transactivation

Although it is well established that platelet-activated receptor (PAF) and protease-activated receptor 2 (PAR2) play a pivotal role in the pathophysiology of lung and airway inflammatory diseases, a role for a PAR2-PAFR cooperation in lung inflammation has not been investigated. Here, we investigated the role of PAR2 in PAF-induced lung inflammation and neutrophil recruitment in lungs of BALB/c mice. Mice were pretreated with the PAR2 antagonist ENMD1068, PAF receptor (PAFR) antagonist WEB2086, or aprotinin prior to intranasal instillation of carbamyl-PAF (C-PAF) or the PAR2 agonist peptide SLIGRL-NH2 (PAR2-AP). Leukocyte infiltration in bronchoalveolar lavage fluid (BALF), C-X-C motif ligand 1 (CXCL)1 and CXCL2 chemokines, myeloperoxidase (MPO), and N-acetyl-glycosaminidase (NAG) levels in BALF, or lung inflammation were evaluated. Intracellular calcium signaling, PAFR/PAR2 physical interaction, and the expression of PAR2 and nuclear factor-kappa B (NF-КB, p65) transcription factor were investigated in RAW 264.7 cells stimulated with C-PAF in the presence or absence of ENMD1068. C-PAF- or PAR2-AP-induced neutrophil recruitment into lungs was inhibited in mice pretreated with ENMD1068 and aprotinin or WEB2086, respectively. PAR2 blockade impaired C-PAF-induced neutrophil rolling and adhesion, lung inflammation, and production of MPO, NAG, CXCL1, and CXCL2 production in lungs of mice. PAFR activation reduced PAR2 expression and physical interaction of PAR2 and PAFR; co-activation is required for PAFR/PAR2 physical interaction. PAR2 blockade impaired C-PAF-induced calcium signal and NF-κB p65 translocation in RAW 264.7 murine macrophages. This study provides the first evidence for a cooperation between PAFR and PAR2 mediating neutrophil recruitment, lung inflammation, and macrophage activation.

Bronchial Asthma, Airway Remodeling and Lung Fibrosis as Successive Steps of One Process

Bronchial asthma is a heterogeneous disease characterized by persistent respiratory system inflammation, airway hyperreactivity, and airflow obstruction. Airway remodeling, defined as changes in airway wall structure such as extensive epithelial damage, airway smooth muscle hypertrophy, collagen deposition, and subepithelial fibrosis, is a key feature of asthma. Lung fibrosis is a common occurrence in the pathogenesis of fatal and long-term asthma, and it is associated with disease severity and resistance to therapy. It can thus be regarded as an irreversible consequence of asthma-induced airway inflammation and remodeling. Asthma heterogeneity presents several diagnostic challenges, particularly in distinguishing between chronic asthma and other pulmonary diseases characterized by disruption of normal lung architecture and functions, such as chronic obstructive pulmonary disease. The search for instruments that can predict the development of irreversible structural changes in the lungs, such as chronic components of airway remodeling and fibrosis, is particularly difficult. To overcome these challenges, significant efforts are being directed toward the discovery and investigation of molecular characteristics and biomarkers capable of distinguishing between different types of asthma as well as between asthma and other pulmonary disorders with similar structural characteristics. The main features of bronchial asthma etiology, pathogenesis, and morphological characteristics as well as asthma-associated airway remodeling and lung fibrosis as successive stages of one process will be discussed in this review. The most common murine models and biomarkers of asthma progression and post-asthmatic fibrosis will also be covered. The molecular mechanisms and key cellular players of the asthmatic process described and systematized in this review are intended to help in the search for new molecular markers and promising therapeutic targets for asthma prediction and therapy.

BALB/c and C57BL/6 mice differ in oxidant and antioxidant responses in innate and adaptive immune cells in an asthma model induced by cockroach allergens

Asthma is a complex and heterogenous disease affected by a multitude of factors. Several phenotypes of asthma exist which are influenced by various molecular mechanisms that include presence of antioxidant and oxidant enzymes in different immune cells such as dendritic cells (DCs), alveolar macrophages (AMs), neutrophils, and T cells. Close interaction between epithelial cells and dendritic cells initiates complex pathogenesis of asthma followed by involvement of other innate and adaptive immune cells. In chronic phase of the disease, these immune cells support each other in amplification of airway inflammation where oxidant-antioxidant balance is known to be an important contributing factor. Genetic variability in antioxidant response may influence the development of airway inflammation, however it has not been studied in mice yet. The two most studied mice strains, i.e. BALB/c and C57BL/6 are reported to have dissimilar airway responses to the same allergens due to their genetic makeup. In this investigation, we explored whether these strains had any differences in pulmonary oxidant-antioxidant system (Nrf2, SOD2, iNOS, HO-1, nitrotyrosine) in different immune cells (DCs, AMs, neutrophils, T cells), airway inflammation (presence of eosinophils and/or neutrophils) and mucus production in response to repeated cockroach allergen extract (CE) mouse model of asthma. Our data show that C57BL/6 mice had better induction of antioxidant system than BALB/c mice. Consequently, iNOS/nitrotyrosine levels were much exaggerated in BALB/c than C57BL/6 mice. As a result, BALB/c mice developed mixed granulocytic airway inflammation, whereas C57BL/6 developed mostly eosinophilic airway inflammation. Our data suggest that an exaggerated oxidant generation along with a weak antioxidant induction in response to a natural allergen on a susceptible genetic background may determine development of severe asthma phenotype such as mixed granulocyte inflammation.

Role of the protease-activated receptor-2 (PAR2) in the exacerbation of house dust mite-induced murine allergic lung disease by multi-walled carbon nanotubes

BACKGROUND

Pulmonary exposure to multi-walled carbon nanotubes (MWCNTs) has been reported to exert strong pro-inflammatory and pro-fibrotic adjuvant effects in mouse models of allergic lung disease. However, the molecular mechanisms through which MWCNTs exacerbate allergen-induced lung disease remain to be elucidated. We hypothesized that protease-activated receptor 2 (PAR2), a G-protein coupled receptor previously implicated in the pathogenesis of various diseases including pulmonary fibrosis and asthma, may play an important role in the exacerbation of house dust mite (HDM) allergen-induced lung disease by MWCNTs.

METHODS

Wildtype (WT) male C57BL6 mice and Par2 KO mice were exposed to vehicle, MWCNTs, HDM extract, or both via oropharyngeal aspiration 6 times over a period of 3 weeks and were sacrificed 3-days after the final exposure (day 22). Bronchoalveolar lavage fluid (BALF) was harvested to measure changes in inflammatory cells, total protein, and lactate dehydrogenase (LDH). Lung protein and RNA were assayed for pro-inflammatory or profibrotic mediators, and formalin-fixed lung sections were evaluated for histopathology.

RESULTS

In both WT and Par2 KO mice, co-exposure to MWCNTs synergistically increased lung inflammation assessed by histopathology, and increased BALF cellularity, primarily eosinophils, as well as BALF total protein and LDH in the presence of relatively low doses of HDM extract that alone produced little, if any, lung inflammation. In addition, both WT and par2 KO mice displayed a similar increase in lung Cc1-11 mRNA, which encodes the eosinophil chemokine CCL-11, after co-exposure to MWCNTs and HDM extract. However, Par2 KO mice displayed significantly less airway fibrosis as determined by quantitative morphometry compared to WT mice after co-exposure to MWCNTs and HDM extract. Accordingly, at both protein and mRNA levels, the pro-fibrotic mediator arginase 1 (ARG-1), was downregulated in Par2 KO mice exposed to MWCNTs and HDM. In contrast, phosphorylation of the pro-inflammatory transcription factor NF-κB and the pro-inflammatory cytokine CXCL-1 was increased in Par2 KO mice exposed to MWCNTs and HDM.

CONCLUSIONS

Our study indicates that PAR2 mediates airway fibrosis but not eosinophilic lung inflammation induced by co-exposure to MWCNTs and HDM allergens.

Protease allergens as initiators-regulators of allergic inflammation

Tremendous progress in the last few years has been made to explain how seemingly harmless environmental proteins from different origins can induce potent Th2-biased inflammatory responses. Convergent findings have shown the key roles of allergens displaying proteolytic activity in the initiation and progression of the allergic response. Through their propensity to activate IgE-independent inflammatory pathways, certain allergenic proteases are now considered as initiators for sensitization to themselves and to non-protease allergens. The protease allergens degrade junctional proteins of keratinocytes or airway epithelium to facilitate allergen delivery across the epithelial barrier and their subsequent uptake by antigen-presenting cells. Epithelial injuries mediated by these proteases together with their sensing by protease-activated receptors (PARs) elicit potent inflammatory responses resulting in the release of pro-Th2 cytokines (IL-6, IL-25, IL-1β, TSLP) and danger-associated molecular patterns (DAMPs; IL-33, ATP, uric acid). Recently, protease allergens were shown to cleave the protease sensor domain of IL-33 to produce a super-active form of the alarmin. At the same time, proteolytic cleavage of fibrinogen can trigger TLR4 signaling, and cleavage of various cell surface receptors further shape the Th2 polarization. Remarkably, the sensing of protease allergens by nociceptive neurons can represent a primary step in the development of the allergic response. The goal of this review is to highlight the multiple innate immune mechanisms triggered by protease allergens that converge to initiate the allergic response.

C781, a β-Arrestin Biased Antagonist at Protease-Activated Receptor-2 (PAR2), Displays in vivo Efficacy Against Protease-Induced Pain in Mice

Given the limited options and often harmful side effects of current analgesics and the suffering caused by the opioid crisis, new classes of pain therapeutics are needed. Protease-activated receptors (PARs), particularly PAR2, are implicated in a variety of pathologies, including pain. Since the discovery of the role of PAR2 in pain, development of potent and specific antagonists has been slow. In this study, we describe the in vivo characterization of a novel small molecule/peptidomimetic hybrid compound, C781, as a β-arrestin-biased PAR2 antagonist. In vivo behavioral studies were done in mice using von Frey filaments and the Mouse Grimace Scale. Pharmacokinetic studies were done to assess pharmacokinetic/pharmacodynamic relationship in vivo. We used both prevention and reversal paradigms with protease treatment to determine whether C781 could attenuate protease-evoked pain. C781 effectively prevented and reversed mechanical and spontaneous nociceptive behaviors in response to small molecule PAR2 agonists, mast cell activators, and neutrophil elastase. The ED50 of C781 (intraperitoneal dosing) for inhibition of PAR2 agonist (20.9 ng 2-AT)-evoked nociception was 6.3 mg/kg. C781 was not efficacious in the carrageenan inflammation model. Pharmacokinetic studies indicated limited long-term systemic bioavailability for C781 suggesting that optimizing pharmacokinetic properties could improve in vivo efficacy. Our work demonstrates in vivo efficacy of a biased PAR2 antagonist that selectively inhibits β-arrestin/MAPK signaling downstream of PAR2. Given the importance of this signaling pathway in PAR2-evoked nociception, C781 exemplifies a key pharmacophore for PAR2 that can be optimized for clinical development. PERSPECTIVE: Our work provides evidence that PAR2 antagonists that only block certain aspects of signaling by the receptor can be effective for blocking protease-evoked pain in mice. This is important because it creates a rationale for developing safer PAR2-targeting approaches for pain treatment.

β-Arrestin-biased proteinase-activated receptor-2 antagonist C781 limits allergen-induced airway hyperresponsiveness and inflammation

BACKGROUND AND PURPOSE

Asthma is a heterogenous disease strongly associated with inflammation that has many different causes and triggers. Current asthma treatments target symptoms such as bronchoconstriction and airway inflammation. Despite recent advances in biological therapies, there remains a need for new classes of therapeutic agents with novel, upstream targets. The proteinase-activated receptor-2 (PAR2) has long been implicated in allergic airway inflammation and asthma and it remains an intriguing target for novel therapies. Here, we describe the actions of C781, a newly developed low MW PAR2 biased antagonist, in vitro and in vivo in the context of acute allergen exposure.

EXPERIMENTAL APPROACH

A human bronchial epithelial cell line expressing PAR2 (16HBE14o- cells) was used to evaluate the modulation in vitro, by C781, of physiological responses to PAR2 activation and downstream β-arrestin/MAPK and Gq/Ca2+ signalling. Acute Alternaria alternata sensitized and challenged mice were used to evaluate C781 as a prophylactically administered modulator of airway hyperresponsiveness, inflammation and mucus overproduction in vivo.

KEY RESULTS

C781 reduced in vitro physiological signalling in response to ligand and proteinase activation. C781 effectively antagonized β-arrestin/MAPK signalling without significant effect on Gq/Ca2+ signalling in vitro. Given prophylactically, C781 modulated airway hyperresponsiveness, airway inflammation and mucus overproduction of the small airways in an acute allergen-challenged mouse model.

CONCLUSION AND IMPLICATIONS

Our work demonstrates the first biased PAR2 antagonist for β-arrestin/MAPK signalling. C781 is efficacious as a prophylactic treatment for allergen-induced airway hyperresponsiveness and inflammation in mice. It exemplifies a key pharmacophore for PAR2 that can be optimized for clinical development.

Bruton's tyrosine kinase inhibition suppresses neutrophilic inflammation and restores histone deacetylase 2 expression in myeloid and structural cells in a mixed granulocytic mouse model of asthma

Asthmatic inflammation is not a single homogenous inflammation but may be categorized into several phenotypes/endotypes. Severe asthma is characterized by mixed granulocytic inflammation in which there is increased presence of neutrophilic numbers and unresponsiveness to corticosteroids. Neutrophilic oxidative stress and histone deacetylase 2 (HDAC2) dysregulation in the pulmonary compartment are thought to lead to corticosteroid insensitivity in severe asthma with mixed granulocytic inflammation. Bruton's tyrosine kinase (BTK) is a no-receptor tyrosine kinase which is expressed in innate immune cells such as neutrophils and dendritic cells (DCs) where it is incriminated in balancing of inflammatory signaling. We hypothesized in this study that BTK inhibition strategy could be utilized to restore corticosteroid responsiveness in mixed granulocytic asthma. Therefore, combined therapy of BTK inhibitor (ibrutinib) and corticosteroid, dexamethasone was administered in cockroach allergen extract (CE)-induced mixed granulocyte airway inflammation model in mice. Our data show that CE-induced neutrophilic inflammation was concomitant with HDAC2 expression and upregulation of p-NFkB expression in airway epithelial cells (AECs), myeloid cells and pulmonary tissue. Further, there were increased expression/release of inflammatory and oxidative mediators such as MUC5AC, TNF-α, GM-CSF, MCP-1, iNOS, nitrotyrosine, MPO, lipid peroxides in AECs/myeloid cells/pulmonary tissue. Dexamethasone alone significantly attenuated eosinophilic inflammation and inflammatory cytokines but was not able to control oxidative inflammation. Ibrutinib alone markedly reduced neutrophilic infiltration and oxidative inflammation, and restored HDAC2 without having any significant effect on eosinophilic inflammation. These data suggest that BTK inhibition strategy may be used in conjunction with dexamethasone to treat both neutrophilic and eosinophilic inflammation, i.e. mixed granulocytic asthma.

PAR2: The Cornerstone of Pancreatic Diseases

It has been 30 years since the first member of the protease-activated receptor (PAR) family was discovered. This was followed by the discovery of three other receptors, including PAR2. PAR2 is a G protein-coupled receptor activated by trypsin site-specific proteolysis. The process starts with serine proteases acting between arginine and serine, creating an N-terminus that functions as a tethered ligand that binds, after a conformational change, to the second extracellular loop of the receptor, leading to activation of G-proteins. The physiological and pathological functions of this ubiquitous receptor are still elusive. This review focuses on PAR2 activation and its distribution under physiological and pathological conditions, with a particular focus on the pancreas, a significant producer of trypsin, which is the prototype activator of the receptor. The role in acute or chronic pancreatitis, pancreatic cancer, and diabetes mellitus will be highlighted.

Protease-activated receptor-2: Role in asthma pathogenesis and utility as a biomarker of disease severity

PAR₂, a receptor activated by serine proteases, has primarily pro-inflammatory roles in the airways and may play a role in asthma pathogenesis. PAR₂ exerts its effects in the lungs through activation of a variety of airway cells, but also activation of circulating immune cells. There is evidence that PAR₂ expression increases in asthma and other inflammatory diseases, although the regulation of PAR₂ expression is not fully understood. Here we review the available literature on the potential role of PAR₂ in asthma pathogenesis and propose a model of PAR₂-mediated development of allergic sensitization. We also propose, based on our previous work, that PAR₂ expression on peripheral blood monocyte subsets has the potential to serve as a biomarker of asthma severity and/or control.

Proteinase-activated receptor-2 antagonist C391 inhibits Alternaria-induced airway epithelial signalling and asthma indicators in acute exposure mouse models

BACKGROUND AND PURPOSE

Despite the availability of a variety of treatment options, many asthma patients have poorly controlled disease with frequent exacerbations. Proteinase-activated receptor-2 (PAR2) has been identified in preclinical animal models as important to asthma initiation and progression following allergen exposure. Proteinase activation of PAR2 raises intracellular Ca²⁺ , inducing MAPK and β-arrestin signalling in the airway, leading to inflammatory and protective effects. We have developed C391, a potent PAR2 antagonist effective in blocking peptidomimetic- and trypsin-induced PAR2 signalling in vitro as well as reducing inflammatory PAR2-associated pain in vivo. We hypothesized that PAR2 antagonism by C391 would attenuate allergen-induced acutely expressed asthma indicators in murine models.

EXPERIMENTAL APPROACH

We evaluated the ability of C391 to alter Alternaria alternata-induced PAR2 signalling pathways in vitro using a human airway epithelial cell line that naturally expresses PAR2 (16HBE14o-) and a transfected embryonic cell line (HEK 293). We next evaluated the ability for C391 to reduce A. alternata-induced acutely expressed asthma indicators in vivo in two murine strains.

KEY RESULTS

C391 blocked A. alternata-induced, PAR2-dependent Ca²⁺ and MAPK signalling in 16HBE14o- cells, as well as β-arrestin recruitment in HEK 293 cells. C391 effectively attenuated A. alternata-induced inflammation, mucus production, mucus cell hyperplasia and airway hyperresponsiveness in acute allergen-challenged murine models.

CONCLUSIONS AND IMPLICATIONS

To our best knowledge, this is the first demonstration of pharmacological intervention of PAR2 to reduce allergen-induced asthma indicators in vivo. These data support further development of PAR2 antagonists as potential first-in-class allergic asthma drugs.

Myeloid Protease-Activated Receptor-2 Contributes to Influenza A Virus Pathology in Mice

Background

Innate immune responses to influenza A virus (IAV) infection are initiated in part by toll-like receptor 3 (TLR3). TLR3-dependent signaling induces an antiviral immune response and an NFκB-dependent inflammatory response. Protease-activated receptor 2 (PAR2) inhibits the antiviral response and enhances the inflammatory response. PAR2 deficiency protected mice during IAV infection. However, the PAR2 expressing cell-types contributing to IAV pathology in mice and the mechanism by which PAR2 contributes to IAV infection is unknown.

Methods

IAV infection was analyzed in global (Par2-/-), myeloid (Par2fl/fl;LysMCre+) and lung epithelial cell (EpC) Par2 deficient (Par2fl/fl;SPCCre+) mice and their respective controls (Par2+/+ and Par2fl/fl). In addition, the effect of PAR2 activation on polyinosinic-polycytidylic acid (poly I:C) activation of TLR3 was analyzed in bone marrow-derived macrophages (BMDM). Lastly, we determined the effect of PAR2 inhibition in wild-type (WT) mice.

Results

After IAV infection, Par2-/- and mice with myeloid Par2 deficiency exhibited increased survival compared to infected controls. The improved survival was associated with reduced proinflammatory mediators and reduced cellular infiltration in bronchoalveolar lavage fluid (BALF) of Par2-/- and Par2fl/fl;LysMCre+ 3 days post infection (dpi) compared to infected control mice. Interestingly, Par2fl/fl;SPCCre+ mice showed no survival benefit compared to Par2fl/fl. In vitro studies showed that Par2-/- BMDM produced less IL6 and IL12p40 than Par2+/+ BMDM after poly I:C stimulation. In addition, activation of PAR2 on Par2+/+ BMDM increased poly I:C induction of IL6 and IL12p40 compared to poly I:C stimulation alone. Importantly, PAR2 inhibition prior to IAV infection protect WT mice.

Conclusion

Global Par2 or myeloid cell but not lung EpC Par2 deficiency was associated with reduced BALF inflammatory markers and reduced IAV-induced mortality. Our study suggests that PAR2 may be a therapeutic target to reduce IAV pathology.

Lipopeptide Pepducins as Therapeutic Agents

Pepducins are lipidated peptides that target the intracellular loops of G protein-coupled receptors (GPCRs) in order to modulate transmembrane signaling to internally located effectors. With a wide array of potential activities ranging from partial, biased, or full agonism to antagonism, pepducins represent a versatile class of compounds that can be used to potentially treat diverse human diseases or be employed as novel tools to probe complex mechanisms of receptor activation and signaling in cells and in animals. Here, we describe a number of different pepducins including an advanced compound, PZ-128, that has successfully progressed through phase 2 clinical trials in cardiac patients demonstrating safety and efficacy in suppressing myonecrosis and arterial thrombosis.

Lung Inflammatory Response to Environmental Dust Exposure in Mice Suggests a Link to Regional Respiratory Disease Risk

PURPOSE

The Salton Sea, California's largest lake, is designated as an agricultural drainage reservoir. In recent years, the lake has experienced shrinkage due to reduced water sources, increasing levels of aerosolized dusts in surrounding regions. Communities surrounding the Salton Sea have increased asthma prevalence versus the rest of California; however, a connection between dust inhalation and lung health impacts has not been defined.

METHODS

We used an established intranasal dust exposure murine model to study the lung inflammatory response following single or repetitive (7-day) exposure to extracts of dusts collected in regions surrounding the Salton Sea (SSDE), complemented with in vitro investigations assessing SSDE impacts on the airway epithelium.

RESULTS

In these investigations, single or repetitive SSDE exposure induced significant lung inflammatory cytokine release concomitant with neutrophil influx. Repetitive SSDE exposure led to significant lung eosinophil recruitment and altered expression of genes associated with allergen-mediated immune response, including Clec4e. SSDE treatment of human bronchial epithelial cells (BEAS-2B) induced inflammatory cytokine production at 5- and 24-hours post-treatment. When BEAS-2B were exposed to protease activity-depleted SSDE (PDSSDE) or treated with SSDE in the context of protease-activated receptor-1 and -2 antagonism, inflammatory cytokine release was decreased. Furthermore, repetitive exposure to PDSSDE led to decreased neutrophil and eosinophilic influx and IL-6 release in mice compared to SSDE-challenged mice.

CONCLUSION

These investigations demonstrate potent lung inflammatory responses and tissue remodeling in response to SSDE, in part due to environmental proteases found within the dusts. These studies provide the first evidence supporting a link between environmental dust exposure, protease-mediated immune activation, and respiratory disease in the Salton Sea region.

The development of proteinase-activated receptor-2 modulators and the challenges involved

Protease-activated receptor-2 (PAR2) has been extensively studied since its discovery in the mid-1990. Despite the advances in understanding PAR2 pharmacology, it has taken almost 25 years for the first inhibitor to reach clinical trials, and so far, no PAR2 antagonist has been approved for human use. Research has employed classical approaches to develop a wide array of PAR2 agonists and antagonists, consisting of peptides, peptoids and antibodies to name a few, with a surge in patent applications over this period. Recent breakthroughs in PAR2 structure determination has provided a unique insight into proposed PAR2 ligand binding sites. Publication of the first crystal structures of PAR2 resolved in complex with two novel non-peptide small molecule antagonists (AZ8838 and AZ3451) revealed two distinct binding pockets, originally presumed to be allosteric sites, with a PAR2 antibody (Fab3949) used to block tethered ligand engagement with the peptide-binding domain of the receptor. Further studies have proposed orthosteric site occupancy for AZ8838 as a competitive antagonist. One company has taken the first PAR2 antibody (MEDI0618) into phase I clinical trial (NCT04198558). While this first-in-human trial is at the early stages of the assessment of safety, other research into the structural characterisation of PAR2 is still ongoing in an attempt to identify new ways to target receptor activity. This review will focus on the development of novel PAR2 modulators developed to date, with an emphasis placed upon the advances made in the pharmacological targeting of PAR2 activity as a strategy to limit chronic inflammatory disease.

Japanese cedar pollen upregulates the effector functions of eosinophils

Background

Symptoms of rhinitis and asthma can be exacerbated during Japanese cedar pollen (JCP)-scattering season, even in subjects who are not sensitized to JCP, suggesting that innate immune responses may contribute to this process. We previously reported that house dust mite directly activates the effector functions of eosinophils. Similar mechanisms may play roles in the JCP-related aggravation of allergic diseases.

Objective

To investigate whether JCP or Cry j 1, a major allergen of JCP, can modify the effector functions of eosinophils.

Methods

Eosinophils isolated from the peripheral blood of healthy donors were stimulated with either JCP or Cry j 1, and their adhesion to human intercellular adhesion molecule-1 was measured using eosinophil peroxidase assays. The generation of eosinophil superoxide anion (O₂⁻) was measured based on the superoxide dismutase-inhibitable reduction of cytochrome C. Concentrations of eosinophil-derived neurotoxin in the cell media were measured by enzyme-linked immunosorbent assay as a marker of degranulation.

Results

Both JCP and Cry j 1 directly induced eosinophil adhesiveness, generation of O₂⁻, and release of eosinophil-derived neurotoxin. Both anti-αM and anti-β2 integrin antibodies blocked all of these eosinophil functions induced by JCP and Cry j 1. Similarly, PAR-2 antagonists also partially suppressed all of these effector functions induced by JCP and Cry j 1.

Conclusion

JCP and Cry j 1 directly activate the functions of eosinophils, and both αMβ2 integrin and partly PAR-2 are contributed to this activation. Therefore, JCP-induced eosinophil activation may play a role in the aggravation of allergic airway diseases in nonsensitized patients as well as in JCP-sensitized patients.

Can GPCRs Be Targeted to Control Inflammation in Asthma?

Historically, the drugs used to manage obstructive lung diseases (OLDs), asthma, and chronic obstructive pulmonary disease (COPD) either (1) directly regulate airway contraction by blocking or relaxing airway smooth muscle (ASM) contraction or (2) indirectly regulate ASM contraction by inhibiting the principal cause of ASM contraction/bronchoconstriction and airway inflammation. To date, these tasks have been respectively assigned to two diverse drug types: agonists/antagonists of G protein-coupled receptors (GPCRs) and inhaled or systemic steroids. These two types of drugs "stay in their lane" with respect to their actions and consequently require the addition of the other drug to effectively manage both inflammation and bronchoconstriction in OLDs. Indeed, it has been speculated that safety issues historically associated with beta-agonist use (beta-agonists activate the beta-2-adrenoceptor (β₂AR) on airway smooth muscle (ASM) to provide bronchoprotection/bronchorelaxation) are a function of pro-inflammatory actions of β₂AR agonism. Recently, however, previously unappreciated roles of various GPCRs on ASM contractility and on airway inflammation have been elucidated, raising the possibility that novel GPCR ligands targeting these GPCRs can be developed as anti-inflammatory therapeutics. Moreover, we now know that many GPCRs can be "tuned" and not just turned "off" or "on" to specifically activate the beneficial therapeutic signaling a receptor can transduce while avoiding detrimental signaling. Thus, the fledging field of biased agonism pharmacology has the potential to turn the β₂AR into an anti-inflammatory facilitator in asthma, possibly reducing or eliminating the need for steroids.

A role for mast cells and mast cell tryptase in driving neutrophil recruitment in LPS-induced lung inflammation via protease-activated receptor 2 in mice

OBJECTIVE

This study aims to investigate the role of protease-activated receptor (PAR) 2 and mast cell (MC) tryptase in LPS-induced lung inflammation and neutrophil recruitment in the lungs of C57BL/6 mice.

METHODS

C57BL/6 mice were pretreated with the PAR2 antagonist ENMD-1068, compound 48/80 or aprotinin prior to intranasal instillation of MC tryptase or LPS. Blood leukocytes, C-X-C motif chemokine ligand (CXCL) 1 production leukocytes recovered from bronchoalveolar lavage fluid (BALF), and histopathological analysis of the lung were evaluated 4 h later. Furthermore, we performed experiments to determine intracellular calcium signaling in RAW 264.7 cells stimulated with LPS in the presence or absence of a protease inhibitor cocktail or ENMD-1068 and evaluated PAR2 expression in the lungs of LPS-treated mice.

RESULTS

Pharmacological blockade of PAR2 or inhibition of proteases reduced neutrophils recovered in BALF and LPS-induced calcium signaling. PAR2 blockade impaired LPS-induced lung inflammation, PAR2 expression in the lung and CXCL1 release in BALF, and increased circulating blood neutrophils. Intranasal instillation of MC tryptase increased the number of neutrophils recovered in BALF, and MC depletion with compound 48/80 impaired LPS-induced neutrophil migration.

CONCLUSION

Our study provides, for the first time, evidence of a pivotal role for MCs and MC tryptase in neutrophil migration, lung inflammation and macrophage activation triggered by LPS, by a mechanism dependent on PAR2 activation.

Protease-activated receptor 2 (PAR-2) antagonist AZ3451 as a novel therapeutic agent for osteoarthritis

Osteoarthritis (OA) is a highly prevalent joint disorder blamed for pain and disability in older individuals. It's commonly accepted that inflammation, apoptosis, autophagy and cellular senescence participate in the progress of OA. Protease activated receptor 2 (PAR2), a member of the G-protein coupled receptors, is involved in the regulation of various inflammation diseases. Previous studies have identified PAR2 as a potential therapeutic target for the treatment of OA. Here, we investigated the role of PAR2 antagonist AZ3451 in inflammation response, apoptosis, autophagy and cellular senescence during OA. We confirmed that PAR2 expression was significantly up-regulated in OA articular cartilage tissues as well as in interleukin 1β (IL-1β) stimulated chondrocytes. We demonstrated AZ3451 could prevent the IL-1β-induced inflammation response, cartilage degradation and premature senescence in chondrocytes. Further study showed that AZ3451 attenuated chondrocytes apoptosis by activating autophagy in vitro. The P38/MAPK, NF-κB and PI3K/AKT/mTOR pathways were involved in the protective effect of AZ3451. In vivo, we found that intra-articular injection of AZ3451 could ameliorate the surgery induced cartilage degradation in rat OA model. Our work provided a better understanding of the mechanism of PAR2 in OA, and indicated that PAR2 antagonist AZ3451 might serve as a promising strategy for OA treatment.

Effects of the serine protease inhibitor rBmTI-A in an experimental mouse model of chronic allergic pulmonary inflammation

To evaluate whether a recombinant serine protease inhibitor (rBmTI-A) modulates inflammation in an experimental model of chronic allergic lung inflammation. Balb/c mice were divided into four groups: SAL (saline), OVA (sensitized with ovalbumin), SAL + rBmTI-A (control treated with rBmTI-A) and OVA + rBmTI-A (sensitized with ovalbumin and treated with rBmTI-A). The animals received an intraperitoneal injection of saline or ovalbumin, according to the group. The groups received inhalation with saline or ovalbumin and were treated with rBmTI-A or saline by nasal instillation. After 29 days, we evaluated the respiratory mechanics; bronchoalveolar lavage fluid (BALF); cytokines; MMP-9, TIMP-1; eosinophils; collagen and elastic fibre expression in the airways; and the trypsin-like, MMP-1, and MMP-9 lung tissue proteolytic activity. Treatment with rBmTI-A reduced the trypsin-like proteolytic activity, the elastance and resistance maximum response, the polymorphonuclear cells, IL-5, IL-10, IL-13 and IL-17A in the BALF, the expression of IL-5, IL-13, IL-17, CD4+, MMP-9, TIMP-1, eosinophils, collagen and elastic fibres in the airways of the OVA + rBmTI-A group compared to the OVA group (p < 0.05). rBmTI-A attenuated bronchial hyperresponsiveness, inflammation and remodelling in this experimental model of chronic allergic pulmonary inflammation. This inhibitor may serve as a potential therapeutic tool for asthma treatment.

Mast cell tryptase - Marker and maker of cardiovascular diseases

Mast cells are tissue-resident cells, which have been proposed to participate in various inflammatory diseases, among them the cardiovascular diseases (CVDs). For mast cells to be able to contribute to an inflammatory process, they need to be activated to exocytose their cytoplasmic secretory granules. The granules contain a vast array of highly bioactive effector molecules, the neutral protease tryptase being the most abundant protein among them. The released tryptase may act locally in the inflamed cardiac or vascular tissue, so contributing directly to the pathogenesis of CVDs. Moreover, a fraction of the released tryptase reaches the systemic circulation, thereby serving as a biomarker of mast cell activation. Actually, increased levels of circulating tryptase have been found to associate with CVDs. Here we review the biological relevance of the circulating tryptase as a biomarker of mast cell activity in CVDs, with special emphasis on the relationship between activation of mast cells in their tissue microenvironments and the pathophysiological pathways of CVDs. Based on the available in vitro and in vivo studies, we highlight the potential molecular mechanisms by which tryptase may contribute to the pathogenesis of CVDs. Finally, the synthetic and natural inhibitors of tryptase are reviewed for their potential utility as therapeutic agents in CVDs.

Protease-activated receptors (PARs): mechanisms of action and potential therapeutic modulators in PAR-driven inflammatory diseases

Inflammatory diseases have become increasingly prevalent with industrialization. To address this, numerous anti-inflammatory agents and molecular targets have been considered in clinical trials. Among molecular targets, protease-activated receptors (PARs) are abundantly recognized for their roles in the development of chronic inflammatory diseases. In particular, several inflammatory effects are directly mediated by the sensing of proteolytic activity by PARs.

PARs belong to the seven transmembrane domain G protein-coupled receptor family, but are unique in their lack of physiologically soluble ligands. In contrast with classical receptors, PARs are activated by N-terminal proteolytic cleavage. Upon removal of specific N-terminal peptides, the resulting N-termini serve as tethered activation ligands that interact with the extracellular loop 2 domain and initiate receptor signaling. In the classical pathway, activated receptors mediate signaling by recruiting G proteins. However, activation of PARs alternatively lead to the transactivation of and signaling through receptors such as co-localized PARs, ion channels, and toll-like receptors.

In this review we consider PARs and their modulators as potential therapeutic agents, and summarize the current understanding of PAR functions from clinical and in vitro studies of PAR-related inflammation.

Targeting of cathepsin S reduces cystic fibrosis-like lung disease

Cathepsin S (CatS) is upregulated in the lungs of patients with cystic fibrosis (CF). However, its role in CF lung disease pathogenesis remains unclear.In this study, β-epithelial Na⁺ channel-overexpressing transgenic (βENaC-Tg) mice, a model of CF-like lung disease, were crossed with CatS null (CatS^-/-) mice or treated with the CatS inhibitor VBY-999.Levels of active CatS were elevated in the lungs of βENaC-Tg mice compared with wild-type (WT) littermates. CatS^-/-βENaC-Tg mice exhibited decreased pulmonary inflammation, mucus obstruction and structural lung damage compared with βENaC-Tg mice. Pharmacological inhibition of CatS resulted in a significant decrease in pulmonary inflammation, lung damage and mucus plugging in the lungs of βENaC-Tg mice. In addition, instillation of CatS into the lungs of WT mice resulted in inflammation, lung remodelling and upregulation of mucin expression. Inhibition of the CatS target, protease-activated receptor 2 (PAR2), in βENaC-Tg mice resulted in a reduction in airway inflammation and mucin expression, indicating a role for this receptor in CatS-induced lung pathology.Our data indicate an important role for CatS in the pathogenesis of CF-like lung disease mediated in part by PAR2 and highlight CatS as a therapeutic target.

Dermatophagoides farinae Upregulates the Effector Functions of Eosinophils through αMβ2-Integrin and Protease-Activated Receptor-2

BACKGROUND

Even in subjects who are not sensitized to house dust mite (HDM), allergic symptoms can be aggravated by exposure to dust, suggesting that innate immune responses may be involved in these processes. Since eosinophils express pattern recognition receptors, HDM may directly upregulate eosinophil functions through these re ceptors. The objective of this study was to examine whether Dermatophagoides farinae (Df), a representative HDM, or Der f 1, a major allergen of Df, modifies the effector functions of eosinophils.

METHODS

Eosinophils isolated from the blood of healthy donors or allergic patients were stimulated with Df extract or Der f 1, and their adhesion to recombinant human intercellular adhesion molecule (ICAM)-1 was measured using eosinophil peroxidase assays. Generation of the eosinophil superoxide anion (O2-) was examined based on the superoxide dismutase-inhibitable reduction of cytochrome C. Eosinophil-derived neurotoxin (EDN) concentrations in cell media were measured by ELISA as a marker of degranulation.

RESULTS

Df extract or Der f 1 directly induced eosinophil adhesion to ICAM-1, O2- generation, and EDN release. Anti-αM- or anti-β2-integrin antibodies or protease-activated receptor (PAR)-2 antagonists suppressed the eosinophil adhesion, O2- generation, and EDN release induced by Df extract or Der f 1. Eosinophils from allergic patients showed higher adhesion to ICAM-1 than those from healthy donors.

CONCLUSIONS

These findings suggested that Df extract and Der f 1 directly activate eosinophil functions through αMβ2-integrin and PAR-2. Eosinophil activation by HDM may play roles in the aggravation of allergic symptoms, not only in HDM-sensitized patients, but also in nonsensitized patients.

Protease-activated receptor-2 signaling through β-arrestin-2 mediates Alternaria alkaline serine protease-induced airway inflammation

Alternaria alternata is a fungal allergen associated with severe asthma and asthma exacerbations. Similarly to other asthma-associated allergens, Alternaria secretes a serine-like trypsin protease(s) that is thought to act through the G protein-coupled receptor protease-activated receptor-2 (PAR2) to induce asthma symptoms. However, specific mechanisms underlying Alternaria-induced PAR2 activation and signaling remain ill-defined. We sought to determine whether Alternaria-induced PAR2 signaling contributed to asthma symptoms via a PAR2/β-arrestin signaling axis, identify the protease activity responsible for PAR2 signaling, and determine whether protease activity was sufficient for Alternaria-induced asthma symptoms in animal models. We initially used in vitro models to demonstrate Alternaria-induced PAR2/β-arrestin-2 signaling. Alternaria filtrates were then used to sensitize and challenge wild-type, PAR2-/- and β-arrestin-2-/- mice in vivo. Intranasal administration of Alternaria filtrate resulted in a protease-dependent increase of airway inflammation and mucin production in wild-type but not PAR2-/- or β-arrestin-2-/- mice. Protease was isolated from Alternaria preparations, and select in vitro and in vivo experiments were repeated to evaluate sufficiency of the isolated Alternaria protease to induce asthma phenotype. Administration of a single isolated serine protease from Alternaria, Alternaria alkaline serine protease (AASP), was sufficient to fully activate PAR2 signaling and induce β-arrestin-2-/--dependent eosinophil and lymphocyte recruitment in vivo. In conclusion, Alternaria filtrates induce airway inflammation and mucus hyperplasia largely via AASP using the PAR2/β-arrestin signaling axis. Thus, β-arrestin-biased PAR2 antagonists represent novel therapeutic targets for treating aeroallergen-induced asthma.

Cigarette smoke extract enhances neutrophil elastase-induced IL-8 production via proteinase-activated receptor-2 upregulation in human bronchial epithelial cells

Although inflammation, oxidative stress, and protease-antiprotease imbalance have been referred to as a pathogenic triad in chronic obstructive pulmonary disease (COPD), little is known about how they interact. The objectives of this study were to elucidate the effect of cigarette smoke extract (CSE) on the neutrophil elastase (NE)-induced inflammatory response and its molecular mechanism in bronchial epithelial cells. We observed that NE activated extracellular signal-regulated kinase (ERK) and induced IL-8 production. Blocking ERK activation using a MEK inhibitor (U0126) suppressed NE-induced IL-8 secretion and knockdown of proteinase-activated receptor 2 (PAR2) using siRNAs inhibited both NE-induced ERK activation and subsequent IL-8 release, suggesting that NE-induced IL-8 production is dependent on PAR2-mediated ERK activation. Interestingly, pre-exposure to CSE markedly enhanced NE-induced IL-8 production. As PAR2 acts as a receptor for NE, we next investigated the effect of CSE on PAR2 expression as a molecular mechanism for the increased IL-8 production induced by NE in CSE exposed cells. CSE, but not NE, increased the expression of PAR2 mRNA and surface membrane protein. Inhibition of p38 MAPK reduced PAR2 expression induced by CSE while inhibition of the ERK and Akt pathway had no effect. Consequently, p38 inhibition significantly abrogated CSE-induced enhancement of IL-8 production in NE-treated cells. Of note, we observed increased PAR2 levels in lung homogenates and lung epithelial cells from CSE-treated mice and from both smokers and patients with COPD. Taken together, these results suggest that CSE upregulates PAR2 in normal human bronchial epithelial cells, thereby enhancing the inflammatory response to NE.

Plasticizer, di(2-ethylhexyl)phthalate (DEHP) enhances cockroach allergen extract-driven airway inflammation by enhancing pulmonary Th2 as well as Th17 immune responses in mice

In recent decades, there has been a gradual increase in the prevalence of asthma. Various factors including environmental pollutants have contributed to this phenomenon. Plasticizer, di(2-ethylhexyl)phthalate (DEHP) is one of the commonest environmental pollutants due to its association with plastic products. DEHP gets released from plastic products easily leading to respiratory exposure in humans. As a consequence, DEHP is associated with allergic asthma in humans and animals. DEHP is reported to act as an adjuvant in ovalbumin-induced mouse models of asthma at high doses. However, these studies mostly looked into the role of DEHP on Th2 cytokines/eosinophilic inflammation without investigating the role of airway epithelial cells (AECs)/dendritic cells (DCs)/Th17 cells. Its adjuvant activity with natural allergens such as cockroach allergens at tolerable daily intake needs to be explored. Cockroach allergens and DEHP may be inhaled together due to their coexistence in work place as well as household environments. Therefore, effect of DEHP was assessed in cockroach allergens extract (CE)-induced mouse model of asthma. Airway inflammation, histopathology, mucus secretion, and immune responses related to Th2/Th17/DCs and AECs were assessed in mice with DEHP exposure alone and in combination with CE. Our study shows that DEHP converts CE-induced eosinophilic inflammation into mixed granulocytic inflammation by promoting Th2 as well as Th17 immune responses. This was probably due to downregulation of E-cadherin in AECs, and enhancement of costimulatory molecules (MHCII/CD86/CD40)/pro-inflammatory cytokines (IL-6/MCP-1) in DCs by DEHP. This suggests that DEHP facilitates development of mixed granulocytic airway inflammation in the presence of a natural allergen.

Inhibition of BET bromodomains restores corticosteroid responsiveness in a mixed granulocytic mouse model of asthma

Asthma is a heterogeneous disease characterized by different endotypes/phenotypes. Th2/Th17 driven mixed granulocytic asthma is one of them and shows resistance to corticosteroid therapy. Bromodomain and extra-terminal (BET) proteins are required for differentiation of Th17 cells which play a pivotal role in neutrophilic inflammation. Therefore, we sought to characterize the differential effects of BET inhibitor versus corticosteroids, and their potential synergism in cockroach allergen extract (CE)-induced mixed granulocytic (eosinophilic and neutrophilic) mouse model of asthma having Th2/Th17 endotype. Effects of BET inhibitor, (+)JQ-1 alone and in combination with dexamethasone (Dexa) were assessed on airway inflammation as well as Th2/Th17 related airway immune responses in CE-induced mixed granulocytic asthma. Markers of steroid resistance [histone deacetylase 2 (HDAC2), and oxidative stress] were also assessed in the lungs of mice and primary human bronchial epithelial cells (HBECs). BET inhibitor, (+)JQ-1 abolished Th17 driven neutrophilic inflammation in CE-induced mixed granulocytic asthma. Dexa had limited effect on overall airway inflammation despite having significant reductions in Th2 driven immune responses. However, combination of (+)JQ-1 with Dexa completely blocked both Th2 and /Th17 driven immune responses in the lung which led to significant reductions in eosinophils, neutrophils, and mucin secretion. (+)JQ-1 also reversed CE- and IL-17A-induced decrease in HDAC2 expression in murine and human airway epithelial cells respectively.

Serine protease allergen favours Th2 responses via PAR-2 and STAT3 activation in murine model

BACKGROUND

Protease activity of Per a 10 favours Th2 responses by differential regulation of IL-12p70 and IL-23 cytokine subunits. This study aimed to elucidate the underlying mechanism of differential regulation of IL-12p70 and IL-23.

METHODS

PAR-2 activation was blocked in murine model by administering SAM11 before each sensitization. CD11c⁺ p-STAT3⁺ cells were measured in lungs by flow cytometry. BMDCs were pretreated with SAM11 or isotype control or stattic and stimulated with Per a 10. p-STAT3 levels were measured using Western blot. Transcript levels of IL-12p35, IL-12/23p40 and IL-23p19 were measured using RT-PCR. Cytokine levels were analysed using ELISA.

RESULTS

Protease activity of Per a 10 increased p-STAT3 levels in mouse lungs, which was reduced upon PAR-2 blockage. Percentage of p-STAT3⁺ CD11c⁺ cells was higher in Per a 10-administered mice and was reduced upon PAR-2 blockage. IL-12p35 and IL-12p70 levels were higher, and IL-23p19 and IL-23 levels were lower in both SAM11-treated mice and BMDCs indicating a role of PAR-2-mediated signalling. IL-4, TSLP, IL-17A, EPO activity, total cell count and specific IgE and IgG1 levels were lower in SAM11-administered mice. Inhibiting STAT3 activation via stattic also leads to lower levels of IL-23p19 and IL-23 and higher levels of IL-12p35.

CONCLUSIONS

Per a 10 leads to PAR-2 activation on BMDCs resulting in downstream activation of STAT3 to regulate the balance between IL-12/IL-23 subunits causing a cytokine milieu rich in IL-23 to favour Th2 polarization.

Proteinase-activated receptor-2 blockade inhibits changes seen in a chronic murine asthma model

BACKGROUND

Proteinase-Activated Receptor-2 (PAR₂ ) is a G protein-coupled receptor activated by serine proteinases. We have shown that PAR₂ activation in the airways is involved in the development of allergic inflammation and airway hyperresponsiveness (AHR) in acute murine models. We hypothesized that functional inhibition of PAR₂ prevents allergic inflammation, AHR and airway remodeling in chronic allergic airway inflammation models.

MATERIAL AND METHODS

We developed and used a 12 week model of cockroach extract (CE)-mediated AHR, airway inflammation and remodeling in BALB/c mice.

RESULTS

Mice sensitized and challenged with CE for 12 weeks exhibit AHR, increased numbers of eosinophils in bronchoalveolar lavage (BAL) and increased collagen content in the lung tissue compared to saline controls. Administration of an anti-PAR₂ antibody, SAM-11, after the initial development of airway inflammation significantly inhibited all these parameters.

CONCLUSIONS

Our data demonstrate that PAR₂ signaling plays a key role in CE-induced AHR and airway inflammation/remodeling in long term models of allergic airway inflammation. Targeting PAR₂ activation may be a successful therapeutic strategy for allergic asthma.

Quail egg homogenate alleviates food allergy induced eosinophilic esophagitis like disease through modulating PAR-2 transduction pathway in peanut sensitized mice

The present pharmacotherapy for eosinophilic esophagitis (EoE) fundamentally depend on inhaled corticosteroids. Despite the fact that oral intake of topical steroids can be successful in restricting EoE-related inflammation, there are concerns with respect to the long term utilization of steroids, especially in kids. In the current research, we assess the effect of quail egg, which is reportedly a known serine protease inhibitor, on symptomatology and immune responses in a peanut-sensitized mouse model of food allergy induced EoE. Daily oral treatment with quail egg attenuated mice symptomatology and immune response. Treatment with quail egg inhibited antigen-prompted increments in mouse tryptase and eosinophil cationic protein (ECP) in serum and eosinophil in inflamed tissues like oesophagus, lung, and digestive system. Quail egg treatment resulted in decreased antibody specific IgE and IgG1 and a variety of inflammatory genes that were abnormally expressed in EoE. Other effects included increased IL-10, decreased PAR-2 activation and NF-kB p65 in inflamed tissues. Our results suggest that quail egg treatment may have therapeutic potential in attenuating the symptoms of food allergy induced EoE like disease through regulating PAR-2 downstream pathway by blocking the activation of the transcription factor NF-kB p65 activity.

Developments in the field of allergy mechanisms in 2015 through the eyes of Clinical & Experimental Allergy

In the first of two papers we described the development in the field of allergy mechanisms as described by Clinical and Experimental Allergy in 2015. Experimental models of allergic disease, basic mechanisms, clinical mechanisms and allergens are all covered. A second paper will cover clinical aspects.

Monoclonal Antibodies for the Management of Severe Asthma

Asthma is a heterogeneous inflammatory disease. Most patients respond to current standard of care, i.e., bronchodilators, inhaled glucocorticosteroids and other anti-inflammatory drugs, but in some adequate asthma control cannot be achieved with standard treatments. These difficult-to-treat patients would be the target population for new biological therapies. At present, omalizumab is the only biological agent approved for the treatment of early-onset, severe IgE-dependent asthma. It is safe, effective, and well tolerated. Also, discovery of asthma subtypes suggests new treatments. Half of patients with severe asthma have T-helper type 2 (Th-2) inflammation and they are expected to benefit from monoclonal antibody-based treatments. The efficacy of the investigational monoclonal antibody mepolizumab which targets IL-5 has been well documented in late onset non-atopic asthma with persistent eosinophilic airway inflammation. Anti-IL-4 and IL-13 agents (dupilumab, lebrikizumab, and tralokinumab) which block different Th-2 inflammatory pathways and agents targeting the Th-17 inflammatory pathway in severe refractory asthma are under development. In clinical trials, these drugs reduce disease activity and improve lung function, asthma symptoms, and quality of life. However, studies on larger groups of patients are needed to confirm their safety and efficacy.

Psoriatic inflammation enhances allergic airway inflammation through IL-23/STAT3 signaling in a murine model

Psoriasis is an autoimmune inflammatory skin disease characterized by activated IL-23/STAT3/Th17 axis. Recently psoriatic inflammation has been shown to be associated with asthma. However, no study has previously explored how psoriatic inflammation affects airway inflammation. Therefore, this study investigated the effect of imiquimod (IMQ)-induced psoriatic inflammation on cockroach extract (CE)-induced airway inflammation in murine models. Mice were subjected to topical and intranasal administration of IMQ and CE to develop psoriatic and airway inflammation respectively. Various analyses in lung/spleen related to inflammation, Th17/Th2/Th1 cell immune responses, and their signature cytokines/transcription factors were carried out. Psoriatic inflammation in allergic mice was associated with increased airway inflammation with concurrent increase in Th2/Th17 cells/signature cytokines/transcription factors. Splenic CD4+ T and CD11c+ dendritic cells in psoriatic mice had increased STAT3/RORC and IL-23 mRNA expression respectively. This led us to explore the effect of systemic IL-23/STAT3 signaling on airway inflammation. Topical application of STA-21, a small molecule STAT3 inhibitor significantly reduced airway inflammation in allergic mice having psoriatic inflammation. On the other hand, adoptive transfer of IL-23-treated splenic CD4+ T cells from allergic mice into naive recipient mice produced mixed neutrophilic/eosinophilic airway inflammation similar to allergic mice with psoriatic inflammation. Our data suggest that systemic IL-23/STAT3 axis is responsible for enhanced airway inflammation during psoriasis. The current study also suggests that only anti-asthma therapy may not be sufficient to alleviate airway inflammatory burden in asthmatics with psoriasis.

Bronchoprotection and bronchorelaxation in asthma: New targets, and new ways to target the old ones

Despite over 50years of inhaled beta-agonists and corticosteroids as the default management or rescue drugs for asthma, recent research suggests that new therapeutic options are likely to emerge. This belief stems from both an improved understanding of what causes and regulates airway smooth muscle (ASM) contraction, and the identification of new targets whose inhibition or activation can relax ASM. In this review we discuss the recent findings that provide new insight into ASM contractile regulation, a revolution in pharmacology that identifies new ways to "tune" G protein-coupled receptors to improve therapeutic efficacy, and the discovery of several novel targets/approaches capable of effecting bronchoprotection or bronchodilation.

TLR-7 agonist attenuates airway reactivity and inflammation through Nrf2-mediated antioxidant protection in a murine model of allergic asthma

Toll-like receptors (TLRs) through innate immune system recognize pathogen associated molecular patterns and play an important role in host defense against bacteria, fungi and viruses. TLR-7 is responsible for sensing single stranded nucleic acids of viruses but its activation has been shown to be protective in mouse models of asthma. The NADPH oxidase (NOX) enzymes family mainly produces reactive oxygen species (ROS) in the lung and is involved in regulation of airway inflammation in response to TLRs activation. However, NOX-4 mediated signaling in response to TLR-7 activation in a mouse model of allergic asthma has not been explored previously. Therefore, this study investigated the role TLR-7 activation and downstream oxidant-antioxidant signaling in a murine model of asthma. Mice were sensitized with ovalbumin (OVA) intraperitoneally and treated with TLR-7 agonist, resiquimod (RSQ) intranasally before each OVA challenge from days 14 to 16. Mice were then assessed for airway reactivity, inflammation, and NOX-4 and nuclear factor E2-related factor 2 (Nrf2) related signaling [inducible nitric oxide synthase (iNOS), nitrotyrosine, lipid peroxides and copper/zinc superoxide dismutase (Cu/Zn SOD)]. Treatment with RSQ reduced allergen induced airway reactivity and inflammation. This was paralleled by a decrease in ROS which was due to induction of Nrf2 and Cu/Zn SOD in RSQ treated group. Inhibition of MyD88 reversed RSQ-mediated protective effects on airway reactivity/inflammation due to reduction in Nrf2 signaling. SOD inhibition produced effects similar to MyD88 inhibition. The current study suggests that TLR-7 agonist is beneficial and may be developed into a therapeutic option in allergic asthma.