IL-33 drives airway hyper-responsiveness through IL-13-mediated mast cell: airway smooth muscle crosstalk

Mast cells contribute to T-cell accumulation in the bronchoalveolar space in mice with IL-33-induced airway inflammation

Interleukin (IL)-33 released from airway epithelial cells plays a vital role in shaping type 2 immune responses by binding to the ST2 receptor present in many immune cells, including mast cells (MCs). Intranasal administration of IL-33 in mice induces type 2 lung inflammation, an increase in lung MC progenitors, and transepithelial migration of leukocytes to the bronchoalveolar space. The aim of this study was to determine the contribution of MCs in IL-33-induced lung pathology. Four daily intranasal administrations of IL-33 reduced spirometry-like lung function parameters, induced airway hyperresponsiveness, and increased leukocytes in bronchoalveolar lavage fluid (BAL) in an ST2-dependent manner. MC-deficient (Cpa3cre/+) mice, which lack MCs, had intact spirometry-like lung function but slightly reduced airway hyperresponsiveness, possibly related to reduced IL-33 or serotonin. Strikingly, Cpa3cre/+ mice exposed to IL-33 had 50% reduction in BAL T-cells, and CXCL1 and IL-33 were reduced in the lung. Intranasal IL-33 induced CXCR2 expression in T-cells in a MC-independent fashion. Furthermore, IL-33-induced lung MCs were immunopositive for CXCL1 and localized in the epithelium of wild-type mice. These results suggest that MCs are required to sustain intact lung IL-33 and CXCL1 levels in mice with IL-33-induced airway inflammation, thereby facilitating T-cell accumulation in the bronchoalveolar space.

Multiarray screening identifies plasma proteins associated with Th17 cell differentiation and viral defense in coincident asthma and obesity

BACKGROUND

The immunological mechanisms behind the clinical association between asthma and obesity in adolescence are not fully understood. This study aimed to find new plasma protein biomarkers associated specifically with coincident asthma and obesity in adolescents.

METHODS

This was a cross-sectional study in children and adolescents 10-19 years old (N = 390). Relative plasma concentrations of 113 protein biomarkers related to inflammation and immune response were determined by proximity extension assay (Target 96; Olink, Uppsala, Sweden). Differences in protein concentrations between healthy controls (n = 84), subjects with asthma (n = 138), subjects with obesity (n = 107), and subjects with both asthma and obesity (AO; n = 58) were analyzed by ANCOVA, adjusting for age and sex, and in a separate model adjusting also for the sum of specific IgE antibody concentrations to a mix of food allergens (fx5) and aeroallergens (Phadiatop). Proteins elevated in the AO group but not in the obesity or asthma groups were considered specifically elevated in asthma and obesity.

RESULTS

Five proteins were elevated specifically in the AO group compared to controls (here sorted from largest to smallest effect of asthma and obesity combined): CCL8, IL-33, IL-17C, FGF-23, and CLEC7A. The effects of adjusting also for specific IgE were small but IL-33, IL-17C, and FGF-23 were no longer statistically significant.

CONCLUSION

We identified several new potential plasma biomarkers specifically elevated in coincident asthma and obesity in adolescents. Four of the proteins, CCL8, IL-33, IL-17C, and CLEC7A, have previously been associated with viral mucosal host defense and Th17 cell differentiation.

Cutaneous Wound Healing and the Effects of Cannabidiol

Cutaneous wounds, both acute and chronic, begin with loss of the integrity, and thus barrier function, of the skin. Surgery and trauma produce acute wounds. There are 22 million surgical procedures per year in the United States alone, based on data from the American College of Surgeons, resulting in a prevalence of 6.67%. Acute traumatic wounds requiring repair total 8 million per year, 2.42% or 24.2 per 1000. The cost of wound care is increasing; it approached USD 100 billion for just Medicare in 2018. This burden for wound care will continue to rise with population aging, the increase in metabolic syndrome, and more elective surgeries. To heal a wound, an orchestrated, evolutionarily conserved, and complex series of events involving cellular and molecular agents at the local and systemic levels are necessary. The principal factors of this important function include elements from the neurological, cardiovascular, immune, nutritional, and endocrine systems. The objectives of this review are to provide clinicians engaged in wound care and basic science researchers interested in wound healing with an updated synopsis from recent publications. We also present data from our primary investigations, testing the hypothesis that cannabidiol can alter cutaneous wound healing and documenting their effects in wild type (C57/BL6) and db/db mice (Type 2 Diabetes Mellitus, T2DM). The focus is on the potential roles of the endocannabinoid system, cannabidiol, and the important immune-regulatory wound cytokine IL-33, a member of the IL-1 family, and connective tissue growth factor, CTGF, due to their roles in both normal and abnormal wound healing. We found an initial delay in the rate of wound closure in B6 mice with CBD, but this difference disappeared with time. CBD decreased IL-33 + cells in B6 by 70% while nearly increasing CTGF + cells in db/db mice by two folds from 18.6% to 38.8% (p < 0.05) using a dorsal wound model. We review the current literature on normal and abnormal wound healing, and document effects of CBD in B6 and db/db dorsal cutaneous wounds. CBD may have some beneficial effects in diabetic wounds. We applied 6-mm circular punch to create standard size full-thickness dorsal wounds in B6 and db/db mice. The experimental group received CBD while the control group got only vehicle. The outcome measures were rate of wound closure, wound cells expressing IL-33 and CTGF, and ILC profiles. In B6, the initial rate of wound closure was slower but there was no delay in the time to final closure, and cells expressing IL-33 was significantly reduced. CTGF + cells were higher in db/bd wounds treated with CBD. These data support the potential use of CBD to improve diabetic cutaneous wound healing.

Airway hyperresponsiveness in asthma: The role of the epithelium

Airway hyperresponsiveness (AHR) is a key clinical feature of asthma. The presence of AHR in people with asthma provides the substrate for bronchoconstriction in response to numerous diverse stimuli, contributing to airflow limitation and symptoms including breathlessness, wheeze, and chest tightness. Dysfunctional airway smooth muscle significantly contributes to AHR and is displayed as increased sensitivity to direct pharmacologic bronchoconstrictor stimuli, such as inhaled histamine and methacholine (direct AHR), or to endogenous mediators released by activated airway cells such as mast cells (indirect AHR). Research in in vivo human models has shown that the disrupted airway epithelium plays an important role in driving inflammation that mediates indirect AHR in asthma through the release of cytokines such as thymic stromal lymphopoietin and IL-33. These cytokines upregulate type 2 cytokines promoting airway eosinophilia and induce the release of bronchoconstrictor mediators from mast cells such as histamine, prostaglandin D2, and cysteinyl leukotrienes. While bronchoconstriction is largely due to airway smooth muscle contraction, airway structural changes known as remodeling, likely mediated in part by epithelial-derived mediators, also lead to airflow obstruction and may enhance AHR. In this review, we outline the current knowledge of the role of the airway epithelium in AHR in asthma and its implications on the wider disease. Increased understanding of airway epithelial biology may contribute to better treatment options, particularly in precision medicine.

IL-10 Differentially Promotes Mast Cell Responsiveness to IL-33, Resulting in Enhancement of Type 2 Inflammation and Suppression of Neutrophilia

Mast cells (MCs) play critical roles in the establishment of allergic diseases. We recently demonstrated an unexpected, proinflammatory role for IL-10 in regulating MC responses. IL-10 enhanced MC activation and promoted IgE-dependent responses during food allergy. However, whether these effects extend to IgE-independent stimuli is not clear. In this article, we demonstrate that IL-10 plays a critical role in driving IL-33-mediated MC responses. IL-10 stimulation enhanced MC expansion and degranulation, ST2 expression, IL-13 production, and phospho-relA upregulation in IL-33-treated cells while suppressing TNF-α. These effects were partly dependent on endogenous IL-10 and further amplified in MCs coactivated with both IL-33 and IgE/Ag. IL-10's divergent effects also extended in vivo. In a MC-dependent model of IL-33-induced neutrophilia, IL-10 treatment enhanced MC responsiveness, leading to suppression of neutrophils and decreased TNF-α. In contrast, during IL-33-induced type 2 inflammation, IL-10 priming exacerbated MC activity, resulting in MC recruitment to various tissues, enhanced ST2 expression, induction of hypothermia, recruitment of eosinophils, and increased MCPT-1 and IL-13 levels. Our data elucidate an important role for IL-10 as an augmenter of IL-33-mediated MC responses, with implications during both allergic diseases and other MC-dependent disorders. IL-10 induction is routinely used as a prognostic marker of disease improvement. Our data suggest instead that IL-10 can enhance ST2 responsiveness in IL-33-activated MCs, with the potential to both aggravate or suppress disease severity depending on the inflammatory context.

Airway remodelling in asthma and the epithelium: on the edge of a new era

Asthma is a chronic, heterogeneous disease of the airways, often characterised by structural changes known collectively as airway remodelling. In response to environmental insults, including pathogens, allergens and pollutants, the epithelium can initiate remodelling via an inflammatory cascade involving a variety of mediators that have downstream effects on both structural and immune cells. These mediators include the epithelial cytokines thymic stromal lymphopoietin, interleukin (IL)-33 and IL-25, which facilitate airway remodelling through cross-talk between epithelial cells and fibroblasts, and between mast cells and airway smooth muscle cells, as well as through signalling with immune cells such as macrophages. The epithelium can also initiate airway remodelling independently of inflammation in response to the mechanical stress present during bronchoconstriction. Furthermore, genetic and epigenetic alterations to epithelial components are believed to influence remodelling. Here, we review recent advances in our understanding of the roles of the epithelium and epithelial cytokines in driving airway remodelling, facilitated by developments in genetic sequencing and imaging techniques. We also explore how new and existing therapeutics that target the epithelium and epithelial cytokines could modify airway remodelling.

Mast cells in the autonomic nervous system and potential role in disorders with dysautonomia and neuroinflammation

Mast cells (MC) are ubiquitous in the body, and they are critical for not only in allergic diseases but also in immunity and inflammation, including having potential involvement in the pathophysiology of dysautonomias and neuroinflammatory disorders. MC are located perivascularly close to nerve endings and sites such as the carotid bodies, heart, hypothalamus, the pineal gland, and the adrenal gland that would allow them not only to regulate but also to be affected by the autonomic nervous system (ANS). MC are stimulated not only by allergens but also many other triggers including some from the ANS that can affect MC release of neurosensitizing, proinflammatory, and vasoactive mediators. Hence, MC may be able to regulate homeostatic functions that seem to be dysfunctional in many conditions, such as postural orthostatic tachycardia syndrome, autism spectrum disorder, myalgic encephalomyelitis/chronic fatigue syndrome, and Long-COVID syndrome. The evidence indicates that there is a possible association between these conditions and diseases associated with MC activation. There is no effective treatment for any form of these conditions other than minimizing symptoms. Given the many ways MC could be activated and the numerous mediators released, it would be important to develop ways to inhibit stimulation of MC and the release of ANS-relevant mediators.

The airway epithelium: an orchestrator of inflammation, a key structural barrier and a therapeutic target in severe asthma

Asthma is a disease of heterogeneous pathology, typically characterised by excessive inflammatory and bronchoconstrictor responses to the environment. The clinical expression of the disease is a consequence of the interaction between environmental factors and host factors over time, including genetic susceptibility, immune dysregulation and airway remodelling. As a critical interface between the host and the environment, the airway epithelium plays an important role in maintaining homeostasis in the face of environmental challenges. Disruption of epithelial integrity is a key factor contributing to multiple processes underlying asthma pathology. In this review, we first discuss the unmet need in asthma management and provide an overview of the structure and function of the airway epithelium. We then focus on key pathophysiological changes that occur in the airway epithelium, including epithelial barrier disruption, immune hyperreactivity, remodelling, mucus hypersecretion and mucus plugging, highlighting how these processes manifest clinically and how they might be targeted by current and novel therapeutics.

Tezepelumab: patient selection and place in therapy in severe asthma

Asthma is a disease characterised by heterogeneous and multifaceted airway inflammation. Despite the availability of effective treatments, a substantial percentage of patients with the type 2 (T2)-high, but mainly the T2-low, phenotype complain of persistent symptoms, airflow limitation, and poor response to treatments. Currently available biologicals target T2 cytokines, but no monoclonal antibodies or other specific therapeutic options are available for non-T2 asthma. However, targeted therapy against alarmins is radically changing this perspective. The development of alarmin-targeted therapies, of which tezepelumab (TZP) is the first example, may offer broad action on inflammatory pathways as well as an enhanced therapeutic effect on epithelial dysfunction. In this regard, TZP demonstrated positive results not only in patients with severe T2 asthma but also those with non-allergic, non-eosinophilic disease. Therefore, it is necessary to identify clinical features of patients who can benefit from an upstream targeted therapy such as anti-thymic stromal lymphopoietin. The aims of this narrative review are to understand the role of alarmins in asthma pathogenesis and epithelial dysfunction, examine the rationale underlying the indication of TZP treatment in severe asthma, summarise the results of clinical studies, and recognise the specific characteristics of patients potentially eligible for TZP treatment.

Personalized Medicine in Severe Asthma: From Biomarkers to Biologics

Severe asthma is a complex and heterogeneous clinical condition presented as chronic inflammation of the airways. Conventional treatments are mainly focused on symptom control; however, there has been a shift towards personalized medicine. Identification of different phenotypes driven by complex pathobiological mechanisms (endotypes), especially those driven by type-2 (T2) inflammation, has led to improved treatment outcomes. Combining biomarkers with T2-targeting monoclonal antibodies is crucial for developing personalized treatment strategies. Several biological agents, including anti-immunoglobulin E, anti-interleukin-5, and anti-thymic stromal lymphopoietin/interleukin-4, have been approved for the treatment of severe asthma. These biological therapies have demonstrated efficacy in reducing asthma exacerbations, lowering eosinophil count, improving lung function, diminishing oral corticosteroid use, and improving the quality of life in selected patients. Severe asthma management is undergoing a profound transformation with the introduction of ongoing and future biological therapies. The availability of novel treatment options has facilitated the adoption of phenotype/endotype-specific approaches and disappearance of generic interventions. The transition towards precision medicine plays a crucial role in meticulously addressing the individual traits of asthma pathobiology. An era of tailored strategies has emerged, allowing for the successful targeting of immune-inflammatory responses that underlie uncontrolled T2-high asthma. These personalized approaches hold great promise for improving the overall efficacy and outcomes in the management of severe asthma. This article comprehensively reviews currently available biological agents and biomarkers for treating severe asthma. With the expanding repertoire of therapeutic options, it is becoming increasingly crucial to comprehend the influencing factors, understand the pathogenesis, and track treatment progress in severe asthma.

ATP functions as a primary alarmin in allergen-induced type 2 immunity

Environmental allergens that interact with the airway epithelium can activate cellular stress pathways that lead to the release of danger signals known as alarmins. The mechanisms of alarmin release are distinct from damage-associated molecular patterns (DAMPs), which typically escape from cells after loss of plasma membrane integrity. Oxidative stress represents a form of allergen-induced cellular stress that stimulates oxidant-sensing mechanisms coupled to pathways, which facilitate alarmin mobilization and efflux across the plasma membrane. In this review, we highlight examples of alarmin release and discuss their roles in the initiation of type 2 immunity and allergic airway inflammation. In addition, we discuss the concept of alarmin amplification, where "primary" alarmins, which are directly released in response to a specific cellular stress, stimulate additional signaling pathways that lead to secretion of "secondary" alarmins that include proinflammatory cytokines, such as IL-33, as well as genomic and mitochondrial DNA that coordinate or amplify type 2 immunity. Accordingly, allergen-evoked cellular stress can elicit a hierarchy of alarmin signaling responses from the airway epithelium that trigger local innate immune reactions, impact adaptive immunity, and exacerbate diseases including asthma and other chronic inflammatory conditions that affect airway function.

Tissue-resident innate lymphoid cells in asthma

Asthma is a chronic airway inflammatory disease whose global incidence increases annually. The role of innate lymphoid cells (ILCs) is a crucial aspect of asthma research with respect to different endotypes of asthma. Based on its pathological and inflammatory features, asthma is divided into type 2 high and type 2 low endotypes. Type-2 high asthma is distinguished by the activation of type 2 immune cells, including T helper 2 (Th2) cells and ILC2s; the production of cytokines interleukin (IL)-4, IL-5 and IL-13; eosinophilic aggregation; and bronchial hyper-responsiveness. Type-2 low asthma represents a variety of endotypes other than type 2 high endotype such as the IL-1β/ILC3/neutrophil endotype and a paucigranulocytic asthma, which may be insensitive to corticosteroid treatment and/or associated with obesity. The complexity of asthma is due to the involvement of multiple cell types, including tissue-resident ILCs and other innate immune cells including bronchial epithelial cells, dendritic cells, macrophages and eosinophils, which provide immediate defence against viruses, pathogens and allergens. On this basis, innate immune cells and adaptive immune cells combine to induce the pathological condition of asthma. In addition, the plasticity of ILCs increases the heterogeneity of asthma. This review focuses on the phenotypes of tissue-resident ILCs and their roles in the different endotypes of asthma, as well as the mechanisms of tissue-resident ILCs and other immune cells. Based on the phenotypes, roles and mechanisms of immune cells, the therapeutic strategies for asthma are reviewed.

Fallopia japonica Root Extract Ameliorates Ovalbumin-Induced Airway Inflammation in a CARAS Mouse Model by Modulating the IL-33/TSLP/NF-κB Signaling Pathway

Fallopia japonica (Asian knotweed) is a medicinal herb traditionally used to treat inflammation, among other conditions. However, the effects of F. japonica root extract (FJE) on airway inflammation associated with combined allergic rhinitis and asthma (CARAS) and the related mechanisms have not been investigated. This study examined the effect of FJE against CARAS in an ovalbumin (OVA)-induced CARAS mouse model. Six-week-old male BALB/c mice were randomly segregated into six groups. Mice were sensitized intraperitoneally with OVA on days 1, 8, and 15, and administered saline, Dexamethasone (1.5 mg/kg), or FJE (50, 100, or 200 mg/kg) once a day for 16 days. Nasal symptoms, inflammatory cells, OVA-specific immunoglobulins, cytokine production, mast cell activation, and nasal histopathology were assessed. Administration of FJE down-regulated OVA-specific IgE and up-regulated OVA-specific IgG2a in serum. FJE reduced the production of T helper (Th) type 2 cytokines, and the Th1 cytokine levels were enhanced in nasal and bronchoalveolar lavage fluid. Moreover, FJE positively regulated allergic responses by reducing the accumulation of inflammatory cells, improving nasal and lung histopathological characteristics, and inhibiting inflammation-associated cytokines. FJE positively modulated the IL-33/TSLP/NF-B signaling pathway, which is involved in regulating inflammatory cells, immunoglobulin levels, and pro-inflammatory cytokines at the molecular level.

Potential Role of Moesin in Regulating Mast Cell Secretion

Mast cells have existed for millions of years in species that never suffer from allergic reactions. Hence, in addition to allergies, mast cells can play a critical role in homeostasis and inflammation via secretion of numerous vasoactive, pro-inflammatory and neuro-sensitizing mediators. Secretion may utilize different modes that involve the cytoskeleton, but our understanding of the molecular mechanisms regulating secretion is still not well understood. The Ezrin/Radixin/Moesin (ERM) family of proteins is involved in linking cell surface-initiated signaling to the actin cytoskeleton. However, how ERMs may regulate secretion from mast cells is still poorly understood. ERMs contain two functional domains connected through a long α-helix region, the N-terminal FERM (band 4.1 protein-ERM) domain and the C-terminal ERM association domain (C-ERMAD). The FERM domain and the C-ERMAD can bind to each other in a head-to-tail manner, leading to a closed/inactive conformation. Typically, phosphorylation on the C-terminus Thr has been associated with the activation of ERMs, including secretion from macrophages and platelets. It has previously been shown that the ability of the so-called mast cell "stabilizer" disodium cromoglycate (cromolyn) to inhibit secretion from rat mast cells closely paralleled the phosphorylation of a 78 kDa protein, which was subsequently shown to be moesin, a member of ERMs. Interestingly, the phosphorylation of moesin during the inhibition of mast cell secretion was on the N-terminal Ser56/74 and Thr66 residues. This phosphorylation pattern could lock moesin in its inactive state and render it inaccessible to binding to the Soluble NSF attachment protein receptors (SNAREs) and synaptosomal-associated proteins (SNAPs) critical for exocytosis. Using confocal microscopic imaging, we showed moesin was found to colocalize with actin and cluster around secretory granules during inhibition of secretion. In conclusion, the phosphorylation pattern and localization of moesin may be important in the regulation of mast cell secretion and could be targeted for the development of effective inhibitors of secretion of allergic and inflammatory mediators from mast cells.

A20 is a master switch of IL-33 signaling in macrophages and determines IL-33-induced lung immunity

BACKGROUND

IL-33 plays a major role in the pathogenesis of allergic diseases such as asthma and atopic dermatitis. On its release from lung epithelial cells, IL-33 primarily drives type 2 immune responses, accompanied by eosinophilia and robust production of IL-4, IL-5, and IL-13. However, several studies show that IL-33 can also drive a type 1 immune response.

OBJECTIVE

We sought to determine the role of A20 in the regulation of IL-33 signaling in macrophages and IL-33-induced lung immunity.

METHODS

We studied the immunologic response in lungs of IL-33-treated mice that specifically lack A20 in myeloid cells. We also analyzed IL-33 signaling in A20-deficient bone marrow-derived macrophages.

RESULTS

IL-33-induced lung innate lymphoid cell type 2 expansion, type 2 cytokine production, and eosinophilia were drastically reduced in the absence of macrophage A20 expression, whereas neutrophils and interstitial macrophages in lungs were increased. In vitro, IL-33-mediated nuclear factor kappa B activation was only weakly affected in A20-deficient macrophages. However, in the absence of A20, IL-33 gained the ability to activate signal transducer and activator of transcription 1 (STAT1) signaling and STAT1-dependent gene expression. Surprisingly, A20-deficient macrophages produced IFN-γ in response to IL-33, which was fully STAT1-dependent. Furthermore, STAT1 deficiency partially restored the ability of IL-33 to induce ILC2 expansion and eosinophilia in myeloid cell-specific A20 knockout mice.

CONCLUSIONS

We reveal a novel role for A20 as a negative regulator of IL-33-induced STAT1 signaling and IFN-γ production in macrophages, which determines lung immune responses.

Epithelial alarmins: a new target to treat chronic respiratory diseases

INTRODUCTION

In response to injury, epithelial cells release alarmins including thymic stromal lymphopoietin (TSLP), high mobility group-box-1 (HMGB1), interleukin (IL)-33 and -25 that can initiate innate immune responses. These alarmins are recognized as activators of T2-immune responses characteristic for asthma, but recent evidence highlighted their role in non-T2 inflammation, airway remodeling, and pulmonary fibrosis making them an attractive therapeutic target for chronic respiratory diseases (CRD).

AREAS COVERED

In this review, firstly we discuss the role of TSLP, IL-33, IL-25, and HMGB1 in the pathogenesis of asthma, COPD, idiopathic pulmonary fibrosis, and cystic fibrosis according to the published data. In the second part, we summarize the current evidence concerning the efficacy of the antialarmin therapies in CRD. Recent clinical trials showed that anti-TSLP and IL-33/R antibodies can improve severe asthma outcomes. Blocking the IL-33-mediated pathway decreased the exacerbation rate in COPD patients with more important benefit for former-smokers.

EXPERT OPINION

Despite progress in the understanding of the alarmins' role in the pathogenesis of CRD, all their mechanisms of action are not yet identified. Blocking IL-33 and TSLP pathways offers an interesting option to treat severe asthma and COPD, but future investigations are needed to establish their place in the treatment strategies.

Severe Asthmatic Responses: The Impact of TSLP

Asthma is a chronic inflammatory disease that affects the lower respiratory system and includes several categories of patients with varying features or phenotypes. Patients with severe asthma (SA) represent a group of asthmatics that are poorly responsive to medium-to-high doses of inhaled corticosteroids and additional controllers, thus leading in some cases to life-threatening disease exacerbations. To elaborate on SA heterogeneity, the concept of asthma endotypes has been developed, with the latter being characterized as T2-high or low, depending on the type of inflammation implicated in disease pathogenesis. As SA patients exhibit curtailed responses to standard-of-care treatment, biologic therapies are prescribed as adjunctive treatments. To date, several biologics that target specific downstream effector molecules involved in disease pathophysiology have displayed superior efficacy only in patients with T2-high, eosinophilic inflammation, suggesting that upstream mediators of the inflammatory cascade could constitute an attractive therapeutic approach for difficult-to-treat asthma. One such appealing therapeutic target is thymic stromal lymphopoietin (TSLP), an epithelial-derived cytokine with critical functions in allergic diseases, including asthma. Numerous studies in both humans and mice have provided major insights pertinent to the role of TSLP in the initiation and propagation of asthmatic responses. Undoubtedly, the magnitude of TSLP in asthma pathogenesis is highlighted by the fact that the FDA recently approved tezepelumab (Tezspire), a human monoclonal antibody that targets TSLP, for SA treatment. Nevertheless, further research focusing on the biology and mode of function of TSLP in SA will considerably advance disease management.

Interleukin-33 Mediates Cardiomyopathy After Acute Kidney Injury by Signaling to Cardiomyocytes

BACKGROUND

Acute kidney injury (AKI) is a short-term life-threatening condition that, if survived, can lead to renal insufficiency and development of chronic kidney disease. The pathogenesis of AKI and chronic kidney disease involves direct effects on the heart and the development of hypertrophy and cardiomyopathy.

METHODS

We used mouse models of ischemia/reperfusion AKI and unilateral ureteral obstruction to investigate the role of IL-33 (interleukin-33) and its receptor-encoding gene Il1rl1 (also called ST2L [suppression of tumorigenicity 2]) in cardiac remodeling after AKI. Mice with cell type-specific genetic disruption of the IL-33/ST2L axis were used, and IL-33 monoclonal antibody, adeno-associated virus encoding IL-33 or ST2L, and recombinant IL-33, as well.

RESULTS

Mice deficient in Il33 were refractory to cardiomyopathy associated with 2 models of kidney injury. Treatment of mice with monoclonal IL-33 antibody also protected the heart after AKI. Moreover, overexpression of IL-33 or injection of recombinant IL-33 induced cardiac hypertrophy or cardiomyopathy, but not in mice lacking Il1rl1. AKI-induced cardiomyopathy was also reduced in mice with cardiac myocyte-specific deletion of Il1rl1 but not in endothelial cell- or fibroblast-specific deletion of Il1rl1. Last, overexpression of the ST2L receptor in cardiac myocytes recapitulated induction of cardiac hypertrophy.

CONCLUSIONS

These results indicate that IL-33 released from the kidney during AKI underlies cardiorenal syndrome by directly signaling to cardiac myocytes, suggesting that antagonism of IL-33/ST2 axis would be cardioprotective in patients with kidney disease.

Role of SARS-CoV-2 Spike-Protein-Induced Activation of Microglia and Mast Cells in the Pathogenesis of Neuro-COVID

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19). About 45% of COVID-19 patients experience several symptoms a few months after the initial infection and develop post-acute sequelae of SARS-CoV-2 (PASC), referred to as "Long-COVID," characterized by persistent physical and mental fatigue. However, the exact pathogenetic mechanisms affecting the brain are still not well-understood. There is increasing evidence of neurovascular inflammation in the brain. However, the precise role of the neuroinflammatory response that contributes to the disease severity of COVID-19 and long COVID pathogenesis is not clearly understood. Here, we review the reports that the SARS-CoV-2 spike protein can cause blood-brain barrier (BBB) dysfunction and damage neurons either directly, or via activation of brain mast cells and microglia and the release of various neuroinflammatory molecules. Moreover, we provide recent evidence that the novel flavanol eriodictyol is particularly suited for development as an effective treatment alone or together with oleuropein and sulforaphane (ViralProtek®), all of which have potent anti-viral and anti-inflammatory actions.

Sounding the alarmins-The role of alarmin cytokines in asthma

The alarmin cytokines thymic stromal lymphopoietin (TSLP), interleukin (IL)-33, and IL-25 are epithelial cell-derived mediators that contribute to the pathobiology and pathophysiology of asthma. Released from airway epithelial cells exposed to environmental triggers, the alarmins drive airway inflammation through the release of predominantly T2 cytokines from multiple effector cells. The upstream positioning of the alarmins is an attractive pharmacological target to block multiple T2 pathways important in asthma. Blocking the function of TSLP inhibits allergen-induced responses including bronchoconstriction, airway hyperresponsiveness, and inflammation, and subsequent clinical trials of an anti-TSLP monoclonal antibody, tezepelumab, in asthma patients demonstrated improvements in lung function, airway responsiveness, inflammation, and importantly, a reduction in the rate of exacerbations. Notably, these improvements were observed in patients with T2-high and with T2-low asthma. Clinical trials blocking IL-33 and its receptor ST2 have also shown improvements in lung function and exacerbation rates; however, the impact of blocking the IL-33/ST2 axis in T2-high versus T2-low asthma is unclear. To date, there is no evidence that IL-25 blockade is beneficial in asthma. Despite the considerable overlap in the cellular functions of IL-25, IL-33, and TSLP, they appear to have distinct roles in the immunopathology of asthma.

Targeting interleukin-33 and thymic stromal lymphopoietin pathways for novel pulmonary therapeutics in asthma and COPD

Interleukin-33 (IL-33) and thymic stromal lymphopoietin (TSLP) are alarmins that are released upon airway epithelial injury from insults such as viruses and cigarette smoke, and play critical roles in the activation of immune cell populations such as mast cells, eosinophils and group 2 innate lymphoid cells. Both cytokines were previously understood to primarily drive type 2 (T2) inflammation, but there is emerging evidence for a role for these alarmins to additionally mediate non-T2 inflammation, with recent clinical trial data in asthma and COPD cohorts with non-T2 inflammation providing support. Currently available treatments for both COPD and asthma provide symptomatic relief with disease control, improving lung function and reducing exacerbation rates; however, there still remains an unmet need for further improving lung function and reducing exacerbations, particularly for those not responsive to currently available treatments. The epithelial cytokines/alarmins are involved in exacerbations; biologics targeting TSLP and IL-33 have been shown to reduce exacerbations in moderate-to-severe asthma, either in a broad population or in specific subgroups, respectively. For COPD, while there is clinical evidence for IL-33 blockade impacting exacerbations in COPD, clinical data from anti-TSLP therapies is awaited. Clinical data to date support an acceptable safety profile for patients with airway diseases for both anti-IL-33 and anti-TSLP antibodies in development. We examine the roles of IL-33 and TSLP, their potential use as drug targets, and the evidence for target patient populations for COPD and asthma, together with ongoing and future trials focused on these targets.

Human Lung Mast Cells: Therapeutic Implications in Asthma

Mast cells are strategically located in different compartments of the lung in asthmatic patients. These cells are widely recognized as central effectors and immunomodulators in different asthma phenotypes. Mast cell mediators activate a wide spectrum of cells of the innate and adaptive immune system during airway inflammation. Moreover, these cells modulate the activities of several structural cells (i.e., fibroblasts, airway smooth muscle cells, bronchial epithelial and goblet cells, and endothelial cells) in the human lung. These findings indicate that lung mast cells and their mediators significantly contribute to the immune induction of airway remodeling in severe asthma. Therapies targeting mast cell mediators and/or their receptors, including monoclonal antibodies targeting IgE, IL-4/IL-13, IL-5/IL-5Rα, IL-4Rα, TSLP, and IL-33, have been found safe and effective in the treatment of different phenotypes of asthma. Moreover, agonists of inhibitory receptors expressed by human mast cells (Siglec-8, Siglec-6) are under investigation for asthma treatment. Increasing evidence suggests that different approaches to depleting mast cells show promising results in severe asthma treatment. Novel treatments targeting mast cells can presumably change the course of the disease and induce drug-free remission in bronchial asthma. Here, we provide an overview of current and promising treatments for asthma that directly or indirectly target lung mast cells.

Cilia-Mediated Insulin/Akt and ST2/JNK Signaling Pathways Regulate the Recovery of Muscle Injury

Following injury, skeletal muscle regenerates but fatty tissue accumulation is seen in aged muscle or muscular dystrophies. Fibro/adipogenic progenitors (FAPs) are key players in these events; however, the effect of primary cilia on FAPs remains unclear. Here, it is reported that genetic ablation of trichoplein (TCHP), a ciliary regulator, induces ciliary elongation on FAPs after injury, which promotes muscle regeneration while inhibiting adipogenesis. The defective adipogenic differentiation of FAPs is attributed to dysfunction of cilia-dependent lipid raft dynamics, which is critical for insulin/Akt signaling. It is also found that interleukin (IL) 13 is substantially produced by intramuscular FAPs, which are upregulated by ciliary elongation and contribute to regeneration. Mechanistically, upon injury, long cilia excessively activate the IL33/ST2/JNK axis to enhance IL13 production, facilitating myoblast proliferation and M2 macrophage polarization. The results indicate that FAPs organize the regenerative responses to skeletal muscle injury via cilia-mediated insulin/Akt and ST2/JNK signaling pathways.

Mast Cell Cytokines in Acute and Chronic Gingival Tissue Inflammation: Role of IL-33 and IL-37

Much evidence suggests autoimmunity in the etiopathogenesis of periodontal disease. In fact, in periodontitis, there is antibody production against collagen, DNA, and IgG, as well as increased IgA expression, T cell dysfunction, high expression of class II MHC molecules on the surface of gingival epithelial cells in inflamed tissues, activation of NK cells, and the generation of antibodies against the azurophil granules of polymorphonuclear leukocytes. In general, direct activation of autoreactive immune cells and production of TNF can activate neutrophils to release pro-inflammatory enzymes with tissue damage in the gingiva. Gingival inflammation and, in the most serious cases, periodontitis, are mainly due to the dysbiosis of the commensal oral microbiota that triggers the immune system. This inflammatory pathological state can affect the periodontal ligament, bone, and the entire gingival tissue. Oral tolerance can be abrogated by some cytokines produced by epithelial cells and activated immune cells, including mast cells (MCs). Periodontal cells and inflammatory-immune cells, including mast cells (MCs), produce cytokines and chemokines, mediating local inflammation of the gingival, along with destruction of the periodontal ligament and alveolar bone. Immune-cell activation and recruitment can be induced by inflammatory cytokines, such as IL-1, TNF, IL-33, and bacterial products, including lipopolysaccharide (LPS). IL-1 and IL-33 are pleiotropic cytokines from members of the IL-1 family, which mediate inflammation of MCs and contribute to many key features of periodontitis and other inflammatory disorders. IL-33 activates several immune cells, including lymphocytes, Th2 cells, and MCs in both innate and acquired immunological diseases. The classic therapies for periodontitis include non-surgical periodontal treatment, surgery, antibiotics, anti-inflammatory drugs, and surgery, which have been only partially effective. Recently, a natural cytokine, IL-37, a member of the IL-1 family and a suppressor of IL-1b, has received considerable attention for the treatment of inflammatory diseases. In this article, we report that IL-37 may be an important and effective therapeutic cytokine that may inhibit periodontal inflammation. The purpose of this paper is to study the relationship between MCs, IL-1, IL-33, and IL-37 inhibition in acute and chronic inflamed gingival tissue.

A novel iridoid glycoside leonuride (ajugol) attenuates airway inflammation and remodeling through inhibiting type-2 high cytokine/chemokine activity in OVA-induced asthmatic mice

BACKGROUND

Asthma is a chronic airway disorder with a hallmark feature of airflow obstruction that associated with the remodeling and inflammation in the airway wall. Effective therapy for controlling both remodeling and inflammation is still urgently needed. Leonuride is the main pharmacological component identified from Bu-Shen-Yi-Qi-Tang (BSYQT) which has been traditionally used in treatment of lung diseases. However, no pharmacological effects of leonuride in asthma were reported.

PURPOSE

Here we aimed to investigated whether leonuride provided a therapeutic efficacy in reversing asthma airway remodeling and inflammation and uncover the underlying mechanisms.

STUDY DESIGN AND METHODS

Mouse models of chronic asthma were developed with ovalbumin (OVA) exposure for 8 weeks. Respiratory mechanics, lung histopathology and asthma-related cytokines were examined. Lung tissues were analyzed using RNA sequencing to reveal the transcriptional profiling changes.

RESULTS

After oral administration with leonuride (15 mg/kg or 30 mg/kg), mice exhibited a lower airway hyperresponsiveness in comparison to asthmatic mice. Leonuride suppressed airway inflammation evidenced by the significant reductions in accumulation of inflammatory cells around bronchi and vessels, leukocyte population counts and the abundance of type 2 inflammatory mediators (OVA specific IgE, IL-4, IL-5 and IL-13) in bronchoalveolar lavage fluid (BALF). On the other hand, leonuride slowed down the process of active remodeling as demonstrated by weaker goblet cell metaplasia and subepithelial fibrosis in lung histopathology and lower transforming growth factor (TGF)-β1 levels in serum and BALF in comparison to mice treated with OVA only. Furthermore, we uncovered transcriptional profiling alternations in lung tissue of mice after OVA exposure and leonuride treatment. Gene sets belonging to type-2 cytokine/chemokine activity stood out in leonuride target transcripts. Those upregulated (Bmp10, Ccl12, Ccl22, Ccl8, Ccl9, Cxcl15, Il13, Il33, Tnfrsf9, Il31ra, Il5ra, Il13ra2 and Ccl24) or downregulated (Acvr1c and Il18) genes in asthmatic mice, were all reversely regulated by leonuride treatment.

CONCLUSIONS

Our results revealed the therapeutic efficacy of leonuride in experimental chronic asthma for the first time, and implied that its anti-inflammatory and antifibrotic properties might be mediated by regulation of type-2 high cytokine/chemokines responses.

Current Understanding of Asthma Pathogenesis and Biomarkers

Asthma is a heterogeneous lung disease with variable phenotypes (clinical presentations) and distinctive endotypes (mechanisms). Over the last decade, considerable efforts have been made to dissect the cellular and molecular mechanisms of asthma. Aberrant T helper type 2 (Th2) inflammation is the most important pathological process for asthma, which is mediated by Th2 cytokines, such as interleukin (IL)-5, IL-4, and IL-13. Approximately 50% of mild-to-moderate asthma and a large portion of severe asthma is induced by Th2-dependent inflammation. Th2-low asthma can be mediated by non-Th2 cytokines, including IL-17 and tumor necrosis factor-α. There is emerging evidence to demonstrate that inflammation-independent processes also contribute to asthma pathogenesis. Protein kinases, adapter protein, microRNAs, ORMDL3, and gasdermin B are newly identified molecules that drive asthma progression, independent of inflammation. Eosinophils, IgE, fractional exhaled nitric oxide, and periostin are practical biomarkers for Th2-high asthma. Sputum neutrophils are easily used to diagnose Th2-low asthma. Despite progress, more studies are needed to delineate complex endotypes of asthma and to identify new and practical biomarkers for better diagnosis, classification, and treatment.

Interleukin-33 regulates the endoplasmic reticulum stress of human myometrium via an influx of calcium during initiation of labor

Background:

Inflammation is currently recognized as one of the major causes of premature delivery. As a member of the interleukin-1β (IL-1β) family, interleukin-33 (IL-33) has been shown to be involved in normal pregnancy as well as a variety of pregnancy-related disorder. This study aims to investigate the potential function of IL-33 in uterine smooth muscle cells during labor.

Methods:

Myometrium samples from term pregnant (≥37 weeks gestation) women were either frozen or cells were isolated and cultured. Immunohistochemistry and western blotting were used to assess the distribution of IL-33. Cultured cells were incubated with lipopolysaccharide (LPS) to mimic inflammation as well as in the presence of 4μ8C (IRE1 inhibitor III) to block endoplasmic reticulum (ER) stress and BAPTA-AM, a calcium chelator.

Results:

LPS reduced the expression of nuclear IL-33 in a time-limited manner and induced ER stress. However, knockdown of IL-33 increased LPS-induced calcium concentration, ER stress and phosphorylation of nuclear factor kappa-B (NF-κB), and P38 mitogen-activated protein kinase (P38 MAPK). In addition, siRNA IL-33 further stimulates LPS enhanced cyclooxygenase-2 (COX-2) expression via NF-κB and p38 pathways. IL-33 expression was decreased in the nucleus with the onset of labor. LPS-induced ER stress and increased expression of the labor-associated gene, COX-2, as well as IL-6 and IL-8 in cultured myometrial cells. IL-33 also increased COX-2 expression, but after it was knocked down, the stimulating effect of LPS on calcium was enhanced. 4μ8C also inhibited the expression of COX-2 markedly. The expression of calcium channels on the membrane and intracellular free calcium ion were both increased which was accompanied by phosphorylated NF-κB and p38.

Conclusions:

These data suggest that IL-33 may be involved in the initiation of labor by leading to stress of the ER via an influx of calcium ions in human uterine smooth muscle cells.

Funding:

This study was supported by grants from the National Natural Science Foundation of China (No. 81300507).

Signaling and functions of interleukin-33 in immune regulation and diseases

Interleukin-33 (IL-33) which belongs to the interleukin-1 (IL-1) family is an alarmin cytokine with critical roles in tissue homeostasis, pathogenic infection, inflammation, allergy and type 2 immunity. IL-33 transmits signals through its receptor IL-33R (also called ST2) which is expressed on the surface of T helper 2 (Th2) cells and group 2 innate lymphoid cells (ILC2s), thus inducing transcription of Th2-associated cytokine genes and host defense against pathogens. Moreover, the IL-33/IL-33R axis is also involved in development of multiple types of immune-related diseases. In this review, we focus on current progress on IL-33-trigggered signaling events, the important functions of IL-33/IL-33R axis in health and diseases as well as the promising therapeutic implications of these findings.

Sex Steroids Effects on Asthma: A Network Perspective of Immune and Airway Cells

A multitude of evidence has suggested the differential incidence, prevalence and severity of asthma between males and females. A compilation of recent literature recognized sex differences as a significant non-modifiable risk factor in asthma pathogenesis. Understanding the cellular and mechanistic basis of sex differences remains complex and the pivotal point of this ever elusive quest, which remains to be clarified in the current scenario. Sex steroids are an integral part of human development and evolution while also playing a critical role in the conditioning of the immune system and thereby influencing the function of peripheral organs. Classical perspectives suggest a pre-defined effect of sex steroids, generalizing estrogens popularly under the “estrogen paradox” due to conflicting reports associating estrogen with a pro- and anti-inflammatory role. On the other hand, androgens are classified as “anti-inflammatory,” serving a protective role in mitigating inflammation. Although considered mainstream and simplistic, this observation remains valid for numerous reasons, as elaborated in the current review. Women appear immune-favored with stronger and more responsive immune elements than men. However, the remarkable female predominance of diverse autoimmune and allergic diseases contradicts this observation suggesting that hormonal differences between the sexes might modulate the normal and dysfunctional regulation of the immune system. This review illustrates the potential relationship between key elements of the immune cell system and their interplay with sex steroids, relevant to structural cells in the pathophysiology of asthma and many other lung diseases. Here, we discuss established and emerging paradigms in the clarification of observed sex differences in asthma in the context of the immune system, which will deepen our understanding of asthma etiopathology.

The protective effects of NE 52-QQ57 against interleukin-33-induced inflammatory response in activated synovial mast cells

Cytokines-mediated immunity is essential for the pathological development of rheumatoid arthritis (RA). Inhibition of signaling has suggested a potential remedial approach to RA. G protein-coupled receptor 4 (GPR4) has been proven to possess a broad range of physiological functions, but its function in synovial mast cells and RA is less reported. In this study, the protective effects of NE 52-QQ57, a GPR4 antagonist, against interleukin (IL)-33-challenged inflammatory response in activated synovial mast cells were investigated. We report that IL-33 amplified GPR4 expression in HMC-1 mast cells. The GPR4 antagonist NE 52-QQ57 alleviated IL-33-caused secretions of IL-17, interferon-γ, and tumor necrosis factor-α in HMC-1 mast cells. Furthermore, we note that NE 52-QQ57 reduced IL-33-induced expressions of matrix metalloproteinase-2 (MMP-2) and MMP-9. Also, NE 52-QQ57 inhibited cyclooxygenase 2 and prostaglandin E2 expression in IL-33-challenged cells. Also, NE 52-QQ57 ameliorated IL-33-induced oxidative stress by reducing mitochondrial reactive oxygen species and 4-hydroxynonenal. Mechanistically, NE 52-QQ57 mitigated IL-33-induced activation of the p38/nuclear factor-κB signaling pathway. We conclude that targeting GPR4 might be a promising strategy for RA treatment.

IL-33 Enhances ACE2 Expression on Epidermal Keratinocytes in Atopic Dermatitis: A Plausible Issue for SARS-CoV-2 Transmission in Inflamed Atopic Skin

Background: Interleukin-33 (IL-33) is an important cytokine in the pathophysiology of atopic dermatitis (AD) and in the progression of COVID-19. Angiotensin converting enzyme 2 (ACE2), the entry receptor for SARS-CoV-2, is expressed in epidermal keratinocytes. Whether IL-33 could regulate the expression of ACE2 mechanistically in keratinocytes warrants investigation. Objective: We questioned whether the ACE2 expression is increased in AD skin. We also questioned whether ACE2 is expressed in keratinocytes; if so, would its expression be enhanced mechanistically by IL-33. Methods: We measured and compared the expression of ACE2 in skin from patients with AD, patients with psoriasis, and healthy controls using immunohistochemistry. Flow cytometry, immunofluorescent exam, and quantitative RT-PCR were used for measuring the ACE2 expression in cultured keratinocytes treated with IL-33 and IL-17. Blocking antibodies were utilized to study the intracellular signaling pathways governing the ACE2 expression using cytokines. Results: The results showed that the ACE2 expression is increased in AD compared with that in healthy skin and psoriasis. In primary epidermal keratinocytes, ACE2 is constitutively expressed. IL-33 induces a time-dependent increase in ACE2 expression in cultured keratinocytes through quantitative PCR, flow cytometry, and immunofluorescent examinations. Furthermore, pretreatment of an ERK inhibitor, but not a STAT3 inhibitor, eliminated the increases in ACE2 by IL-33 in keratinocytes, indicating that IL-33 enhances ACE2 expression through ERK on epidermal keratinocytes. Conclusion: This is the first study to reveal that IL-33 enhances ACE2 expression on keratinocytes via ERK. Although further mechanistic studies are required, the increased ACE2 expression in IL-33 might have a biological implication on the transmission of SARS-CoV-2 in patients with AD.

Interaction Between CD34+ Fibrocytes and Airway Smooth Muscle Promotes IL-8 Production and Akt/PRAS40/mTOR Signaling in Asthma

Background

The circulating progenitor cells of fibroblasts (fibrocytes) have been shown to infiltrate the airway smooth muscle compartment of asthma patients; however, the pathological significance of this discovery has yet to be elucidated. This study established a co-culture model of airway smooth muscle cells (ASMCs) and fibrocytes from asthmatic or normal subjects to evaluate innate cytokine production, corticosteroid responses, and signaling in ASMCs.

Methods

CD34⁺ fibrocytes were purified from peripheral blood of asthmatic (Global Initiative for Asthma treatment step 4–5) and normal subjects and cultured for 5∼7 days. In a transwell plate, ASMCs were co-cultured with fibrocytes at a ratio of 2:1, ASMCs were cultured alone (control condition), and fibrocytes were cultured alone for 48 h. Measurements were obtained of interleukin-8 (IL-8), IL-6, IL-17, thymic stromal lymphopoietin, and IL-33 levels in the supernatant and IL-33 levels in the cell lysate of the co-culture. Screening for intracellular signaling in the ASMCs after stimulation was performed using condition medium from the patients’ co-culture (PtCM) or IL-8. mRNA and western blot analysis were used to analyze AKT/mTOR signaling in ASMCs stimulated via treatment with PtCM or IL-8.

Results

Compared with ASMCs cultured alone, IL-8 levels in the supernatant and IL-33 levels in the ASMCs lysate were significantly higher in samples co-cultured from asthmatics, but not in those co-cultured from normal subjects. Corticosteroid-induced suppression of IL-8 production was less pronounced in ASMCs co-cultured with fibrocytes from asthma patients than in ASMCs co-cultured from normal subjects. ASMCs stimulated using PtCM and IL-8 presented elevating activated AKT substrate PRAS40. Treatment with IL-8 and PtCM increased mRNA expression of mTOR and P70S6 kinases in ASMCs. Treatment with IL-8 and PtCM also significantly increased phosphorylation of AKT and mTOR subtract S6 ribosomal protein in ASMCs.

Conclusion

The interaction between ASMCs and fibrocytes from asthmatic patients was shown to increase IL-8 and IL-33 production and promote AKT/mTOR signaling in ASMCs. IL-8 production in the co-culture from asthmatic patients was less affected by corticosteroid than was that in the co-culture from normal subjects. Our results elucidate the novel role of fibrocytes and ASMCs in the pathogenesis of asthma.

Elastase- and LPS-Exposed Cpa3Cre/+ and ST2-/- Mice Develop Unimpaired Obstructive Pulmonary Disease

IL-33 and its receptor ST2, as well as mast cells and their mediators, have been implicated in the development of chronic obstructive pulmonary disease (COPD). However, whether mast cells and the ST2 receptor play a critical role in COPD pathophysiology remains unclear. Here, we performed repeated intranasal administrations of porcine pancreatic elastase and LPS for four weeks to study COPD-like disease in wildtype, ST2-deficient, and Cpa3^Cre/+ mice, which lack mast cells and have a partial reduction in basophils. Alveolar enlargement and changes in spirometry-like parameters, e.g. increased dynamic compliance and decreased expiratory capacity, were evident one day after the final LPS challenge and worsened over time. The elastase/LPS model also induced mild COPD-like airway inflammation, which encompassed a transient increase in lung mast cell progenitors, but not in mature mast cells. While ST2-deficient and Cpa3^Cre/+ mice developed reduced pulmonary function uninterruptedly, they had a defective inflammatory response. Importantly, both ST2-deficient and Cpa3^Cre/+ mice had fewer alveolar macrophages, known effector cells in COPD. Elastase/LPS instillation in vivo also caused increased bronchiole contraction in precision cut lung slices challenged with methacholine ex vivo, which occurred in a mast cell-independent fashion. Taken together, our data suggest that the ST2 receptor and mast cells play a minor role in COPD pathophysiology by sustaining alveolar macrophages.

PM2.5 Exposure and Asthma Development: The Key Role of Oxidative Stress

Oxidative stress is defined as the imbalance between reactive oxygen species (ROS) production and the endogenous antioxidant defense system, leading to cellular damage. Asthma is a common chronic inflammatory airway disease. The presence of asthma tends to increase the production of reactive oxygen species (ROS), and the antioxidant system in the lungs is insufficient to mitigate it. Therefore, asthma can lead to an exacerbation of airway hyperresponsiveness and airway inflammation. PM2.5 exposure increases ROS levels. Meanwhile, the accumulation of ROS will further enhance the oxidative stress response, resulting in DNA, protein, lipid, and other cellular and molecular damage, leading to respiratory diseases. An in-depth study on the relationship between oxidative stress and PM2.5-related asthma is helpful to understand the pathogenesis and progression of the disease and provides a new direction for the treatment of the disease. This paper reviews the research progress of oxidative stress in PM2.5-induced asthma as well as highlights the therapeutic potentials of antioxidant approaches in treatment of asthma.

The Role of Airway Epithelial Cell Alarmins in Asthma

The airway epithelium is the first line of defense for the lungs, detecting inhaled environmental threats through pattern recognition receptors expressed transmembrane or intracellularly. Activation of pattern recognition receptors triggers the release of alarmin cytokines IL-25, IL-33, and TSLP. These alarmins are important mediators of inflammation, with receptors widely expressed in structural cells as well as innate and adaptive immune cells. Many of the key effector cells in the allergic cascade also produce alarmins, thereby contributing to the airways disease by driving downstream type 2 inflammatory processes. Randomized controlled clinical trials have demonstrated benefit when blockade of TSLP and IL-33 were added to standard of care medications, suggesting these are important new targets for treatment of asthma. With genome-wide association studies demonstrating associations between single-nucleotide polymorphisms of the TSLP and IL-33 gene and risk of asthma, it will be important to understand which subsets of asthma patients will benefit most from anti-alarmin therapy.

Interleukin-33/ Suppression of Tumorigenicity 2 in Renal Fibrosis: Emerging Roles in Prognosis and Treatment

Chronic kidney disease (CKD) is a major public health problem that affects more than 10% of the population worldwide and has a high mortality rate. Therefore, it is necessary to identify novel treatment strategies for CKD. Incidentally, renal fibrosis plays a central role in the progression of CKD to end-stage renal disease (ESRD). The activation of inflammatory pathways leads to the development of renal fibrosis. In fact, interleukin-33 (IL-33), a newly discovered member of the interleukin 1 (IL-1) cytokine family, is a crucial regulator of the inflammatory process. It exerts pro-inflammatory and pro-fibrotic effects via the suppression of tumorigenicity 2 (ST2) receptor, which, in turn, activates other inflammatory pathways. Although the role of this pathway in cardiac, pulmonary, and hepatic fibrotic diseases has been extensively studied, its precise role in renal fibrosis has not yet been completely elucidated. Recent studies have shown that a sustained activation of IL-33/ST2 pathway promotes the development of renal fibrosis. However, with prolonged research in this field, it is expected that the IL-33/ST2 pathway will be used as a diagnostic and prognostic tool for renal diseases. In addition, the IL-33/ST2 pathway seems to be a new target for the future treatment of CKD. Here, we review the mechanisms and potential applications of the IL-33/ST2 pathway in renal fibrosis; such that it can help clinicians and researchers to explore effective treatment options and develop novel medicines for CKD patients.

Temporal Quantitative Phosphoproteomics Profiling of Interleukin-33 Signaling Network Reveals Unique Modulators of Monocyte Activation

Interleukin-33 (IL-33), a member of the IL-1 superfamily cytokines, is an endogenous danger signal and a nuclear-associated cytokine. It is one of the essential mediators of both innate and adaptive immune responses. Aberrant IL-33 signaling has been demonstrated to play a defensive role against various infectious and inflammatory diseases. Although the signaling responses mediated by IL-33 have been previously reported, the temporal signaling dynamics are yet to be explored. To this end, we applied quantitative temporal phosphoproteomics analysis to elucidate pathways and proteins induced by IL-33 in THP-1 monocytes. Employing a TMT labeling-based quantitation and titanium dioxide (TiO₂)-based phosphopeptide enrichment strategy followed by mass spectrometry analysis, we identified and quantified 9448 unique phosphopeptides corresponding to 3392 proteins that showed differential regulation. Of these, 171 protein kinases, 60 phosphatases and 178 transcription factors were regulated at different phases of IL-33 signaling. In addition to the confirmed activation of canonical signaling modules including MAPK, NFκB, PI3K/AKT modules, pathway analysis of the time-dependent phosphorylation dynamics revealed enrichment of several cellular processes, including leukocyte adhesion, response to reactive oxygen species, cell cycle checkpoints, DNA damage and repair pathways. The detailed quantitative phosphoproteomic map of IL-33 signaling will serve as a potentially useful resource to study its function in the context of inflammatory and pathological conditions.

Advances and Challenges of Antibody Therapeutics for Severe Bronchial Asthma

Asthma is a disease that consists of three main components: airway inflammation, airway hyperresponsiveness, and airway remodeling. Persistent airway inflammation leads to the destruction and degeneration of normal airway tissues, resulting in thickening of the airway wall, decreased reversibility, and increased airway hyperresponsiveness. The progression of irreversible airway narrowing and the associated increase in airway hyperresponsiveness are major factors in severe asthma. This has led to the identification of effective pharmacological targets and the recognition of several biomarkers that enable a more personalized approach to asthma. However, the efficacies of current antibody therapeutics and biomarkers are still unsatisfactory in clinical practice. The establishment of an ideal phenotype classification that will predict the response of antibody treatment is urgently needed. Here, we review recent advancements in antibody therapeutics and novel findings related to the disease process for severe asthma.

Beclomethasone dipropionate and sodium cromoglycate protect against airway hyperresponsiveness in a human ex vivo model of cow's milk aspiration

Background

Recurrent cow's milk (CM) aspiration is often associated with gastroesophageal reflux in infants and toddlers and it seems to be implicated in the etiology of different inflammatory lung disorders. This study aimed to investigate ex vivo the impact of CM aspiration on human airways and whether treatment with beclomethasone dipropionate (BDP) or sodium cromoglycate (SCG) may prevent the potential CM-induced airway hyperresponsiveness (AHR).

Methods

Human isolated bronchi were contracted by electrical field stimulation (EFS_10Hz) to mimic the contractile tone induced by the parasympathetic activity and challenged with CM, fat/lactose-free CM, or human breast milk (HM). The effect of pre-treatment with beclomethasone dipropionate (BDP) and sodium cromoglycate (SCG) was also investigated on the AHR induced by CM.

Results

After a 60 min-challenge with CM 1:10 v/v and fat/lactose-free CM 1:10 v/v, ASM significantly (P ​< ​0.05) increased compared to control (+67.04 ​± ​17.08% and +77.91 ​± ​1.34%, respectively), a condition that remained stable for 150 ​min post-treatment, whereas HM did not alter ASM contractility. BDP 1 ​μM and 10 ​μM significantly (P ​< ​0.05) reduced the AHR elicited by CM (−52.49 ​± ​10.97% and −66.98 ​± ​7.90%, respectively vs. control). At the same manner, SCG 1 ​μM and 10 ​μM significantly (P ​< ​0.05) inhibited the CM-induced AHR (−59.03 ​± ​9.24% and −73.52 ​± ​7.41%, respectively vs. control).

Conclusion

CM induces AHR in human ASM by eliciting an increased parasympathetic contractile response. Preventive treatment with nebulized SCG may be indicated in infants or toddlers fed with CM, rather than with BDP due to a superior safety profile.

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Cow's milk aspiration seems to be associated with some inflammatory lung diseases.

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Cow's milk aspiration induces human airway hyperresponsiveness.

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Beclomethasone and sodium cromoglycate protect against cow's milk hyperresponsiveness in vitro.

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Inhaled sodium cromoglycate might be suitable in children at risk of cow's milk aspiration.

Dysregulated Notch Signaling in the Airway Epithelium of Children with Wheeze

The airway epithelium of children with wheeze is characterized by defective repair that contributes to disease pathobiology. Dysregulation of developmental processes controlled by Notch has been identified in chronic asthma. However, its role in airway epithelial cells of young children with wheeze, particularly during repair, is yet to be determined. We hypothesized that Notch is dysregulated in primary airway epithelial cells (pAEC) of children with wheeze contributing to defective repair. This study investigated transcriptional and protein expression and function of Notch in pAEC isolated from children with and without wheeze. Primary AEC of children with and without wheeze were found to express all known Notch receptors and ligands, although pAEC from children with wheeze expressed significantly lower NOTCH2 (10-fold, p = 0.004) and higher JAG1 (3.5-fold, p = 0.002) mRNA levels. These dysregulations were maintained in vitro and cultures from children with wheeze displayed altered kinetics of both NOTCH2 and JAG1 expression during repair. Following Notch signaling inhibition, pAEC from children without wheeze failed to repair (wound closure rate of 76.9 ± 3.2%). Overexpression of NOTCH2 in pAEC from children with wheeze failed to rescue epithelial repair following wounding. This study illustrates the involvement of the Notch pathway in airway epithelial wound repair in health and disease, where its dysregulation may contribute to asthma development.

Airway Wall Remodeling in Childhood Asthma-A Personalized Perspective from Cell Type-Specific Biology

Airway wall remodeling is a pathology occurring in chronic inflammatory lung diseases including asthma, chronic obstructive pulmonary disease, and fibrosis. In 2017, the American Thoracic Society released a research statement highlighting the gaps in knowledge and understanding of airway wall remodeling. The four major challenges addressed in this statement were: (i) the lack of consensus to define “airway wall remodeling” in different diseases, (ii) methodologic limitations and inappropriate models, (iii) the lack of anti-remodeling therapies, and (iv) the difficulty to define endpoints and outcomes in relevant studies. This review focuses on the importance of cell-cell interaction, especially the bronchial epithelium, in asthma-associated airway wall remodeling. The pathology of “airway wall remodeling” summarizes all structural changes of the airway wall without differentiating between different pheno- or endo-types of asthma. Indicators of airway wall remodeling have been reported in childhood asthma in the absence of any sign of inflammation; thus, the initiation event remains unknown. Recent studies have implied that the interaction between the epithelium with immune cells and sub-epithelial mesenchymal cells is modified in asthma by a yet unknown epigenetic mechanism during early childhood.

Advances and highlights in asthma in 2021

Last year brought a significant advance in asthma management, unyielding to the pressure of the pandemics. Novel key findings in asthma pathogenesis focus on the resident cell compartment, epigenetics and the innate immune system. The precision immunology unbiased approach was supplemented with novel tools and greatly facilitated by the use of artificial intelligence. Several randomised clinical trials and good quality real-world evidence shed new light on asthma treatment and supported the revision of several asthma guidelines (GINA, Expert Panel Report 3, ERS/ATS guidelines on severe asthma) and the conception of new ones (EAACI Guidelines for the use of biologicals in severe asthma). Integrating asthma management within the broader context of Planetary Health has been put forward. In this review, recently published articles and clinical trials are summarised and discussed with the goal to provide clinicians and researchers with a concise update on asthma research from a translational perspective.

Monoclonal Antibodies Targeting Alarmins: A New Perspective for Biological Therapies of Severe Asthma

Alarmins are innate cytokines, including thymic stromal lymphopoietin (TSLP), interleukin-33 (IL-33), and interleukin-25 (IL-25), which are mainly produced by airway epithelium and exert a prominent role in asthma pathobiology. In particular, several environmental factors such as allergens, cigarette smoking, airborne pollutants, and infectious agents trigger the release of alarmins, which in turn act as upstream activators of pro-inflammatory pathways underlying type 2 (T2-high) asthma. Indeed, alarmins directly activate group 2 innate lymphoid cells (ILC2), eosinophils, basophils, and mast cells and also stimulate dendritic cells to drive the commitment of naïve T helper (Th) cells towards the Th2 immunophenotype. Therefore, TSLP, IL-33, and IL-25 represent suitable targets for add-on therapies of severe asthma. Within this context, the fully human anti-TSLP monoclonal antibody tezepelumab has been evaluated in very promising randomized clinical trials. Tezepelumab and other anti-alarmins are thus likely to become, in the near future, valuable therapeutic options for the biological treatment of uncontrolled severe asthma.

Interleukin-18, IL-18 binding protein and IL-18 receptor expression in asthma: a hypothesis showing IL-18 promotes epithelial cell differentiation

Objective

In asthma, genome‐wide association studies have shown that interleukin‐18 (IL‐18) receptor 1 gene (IL‐18R1) and sputum IL‐18 are increased during exacerbations. However, the role of the IL‐18 axis in bronchial epithelial function is unclear. To investigate IL‐18, IL‐18 binding protein (BP) and IL‐18R expression in bronchial biopsies and sputum samples from patients with asthma, and to determine its functional role using in vitro bronchial epithelial cells.

Methods

The expression of IL‐18, IL‐18BP and IL‐18Rα was examined in subjects with asthma and healthy controls in bronchial biopsies by immunohistochemistry and IL‐18 and IL‐18BP release in sputum. In epithelial cells, the mRNA and protein expression of IL‐18, IL‐18BP, IL‐18Rα and IL‐18Rβ was assessed by qPCR, flow cytometry, Western blotting and immunofluorescence respectively. IL‐18 function in epithelial cells was examined by intracellular calcium, wound repair, synthetic activation and epithelial differentiation changes.

Results

In biopsies from subjects with asthma, the IL‐18 expression was not different in the lamina propria compared with controls but was decreased in the epithelium. In contrast, the IL‐18BP was decreased in the lamina propria in asthma and was absent in the bronchial epithelium. IL‐18 was released in sputum with IL‐18BP elevated in patients with asthma. The IL‐18Rα expression was not different between health and disease. In vitro, IL‐18‐stimulated bronchial epithelial cells increased intracellular calcium, wound repair, metabolic activity, morphological changes and epithelial cellular differentiation.

Conclusion

In asthma, the dynamic interaction between IL‐18, its cognate receptor and natural inhibitor is complex, with differences between airway compartments. Upregulation of IL‐18 can promote epithelial activation and cellular differentiation.

Mechanisms and biomarkers of airway epithelial cell damage in asthma: A review

Bronchial asthma is a heterogeneous disease with complex pathological mechanisms representing different phenotypes, including severe asthma. The airway epithelium is a major site of complex pathological changes in severe asthma due, in part, to activation of inflammatory and immune mechanisms in response to noxious agents. Current imaging procedures are unable to accurately measure epithelial and airway remodeling. Damage of airway epithelial cells occurs is linked to specific phenotypes and endotypes which provides an opportunity for the identification of biomarkers reflecting epithelial, and airway, remodeling. Identification of patients with more severe epithelial disruption using biomarkers may also provide personalised therapeutic opportunities and/or markers of successful therapeutic intervention. Here, we review the evidence for ongoing epithelial cell dysregulation in the pathogenesis of asthma, the sentinel role of the airway epithelium and how understanding these molecular mechanisms provides the basis for the identification of candidate biomarkers for asthma prediction, prevention, diagnosis, treatment and monitoring.

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.

Nicotinic α7 acetylcholine receptor (α7nAChR) in human airway smooth muscle

Diseases such as asthma are exacerbated by inflammation, cigarette smoke and even nicotine delivery devices such as e-cigarettes. However, there is currently little information on how nicotine affects airways, particularly in humans, and changes in the context of inflammation or asthma. Here, a longstanding assumption is that airway smooth muscle (ASM) that is key to bronchoconstriction has muscarinic receptors while nicotinic receptors (nAChRs) are only on airway neurons. In this study, we tested the hypothesis that human ASM expresses α7nAChR and explored its profile in inflammation and asthma using ASM of non-asthmatics vs. mild-moderate asthmatics. mRNA and western analysis showed the α7 subunit is most expressed in ASM cells and further increased in asthmatics and smokers, or by exposure to nicotine, cigarette smoke or pro-inflammatory cytokines TNFα and IL-13. In these effects, signaling pathways relevant to asthma such as NFκB, AP-1 and CREB are involved. These novel data demonstrate the expression of α7nAChR in human ASM and suggest their potential role in asthma pathophysiology in the context of nicotine exposure.

Astegolimab (anti-ST2) efficacy and safety in adults with severe asthma: A randomized clinical trial

BACKGROUND

The IL-33/ST2 pathway is linked with asthma susceptibility. Inhaled allergens, pollutants, and respiratory viruses, which trigger asthma exacerbations, induce release of IL-33, an epithelial-derived "alarmin." Astegolimab, a human IgG₂ mAb, selectively inhibits the IL-33 receptor, ST2. Approved biologic therapies for severe asthma mainly benefit patients with elevated blood eosinophils (type 2-high), but limited options are available for patients with low blood eosinophils (type 2-low). Inhibiting IL-33 signaling may target pathogenic pathways in a wider spectrum of asthmatics.

OBJECTIVES

This study evaluated astegolimab efficacy and safety in patients with severe asthma.

METHODS

This double-blind, placebo-controlled, dose-ranging study (ZENYATTA [A Study to Assess the Efficacy and Safety of MSTT1041A in Participants With Uncontrolled Severe Asthma]) randomized 502 adults with severe asthma to subcutaneous placebo or 70-mg, 210-mg, or 490-mg doses of astegolimab every 4 weeks. The primary endpoint was the annualized asthma exacerbation rate (AER) at week 54. Enrollment caps ensured ∼30 patients who were eosinophil-high (≥300 cells/μL) and ∼95 patients who were eosinophil-low (<300 cells/μL) per arm.

RESULTS

Overall, adjusted AER reductions relative to placebo were 43% (P = .005), 22% (P = .18), and 37% (P = .01) for 490-mg, 210-mg, and 70-mg doses of astegolimab, respectively. Adjusted AER reductions for patients who were eosinophil-low were comparable to reductions in the overall population: 54% (P = .002), 14% (P = .48), and 35% (P = .05) for 490-mg, 210-mg, and 70-mg doses of astegolimab. Adverse events were similar in astegolimab- and placebo-treated groups.

CONCLUSIONS

Astegolimab reduced AER in a broad population of patients, including those who were eosinophil-low, with inadequately controlled, severe asthma. Astegolimab was safe and well tolerated.

The central role of IL-33/IL-1RL1 pathway in asthma: From pathogenesis to intervention

Interleukin-33 (IL-33), a member of the IL-1 family, and its cognate receptor, Interleukin-1 receptor like-1 (IL-1RL1 or ST2), are susceptibility genes for childhood asthma. In response to cellular damage, IL-33 is released from barrier tissues as an 'alarmin' to activate the innate immune response. IL-33 drives type 2 responses by inducing signalling through its receptor IL-1RL1 in several immune and structural cells, thereby leading to type 2 cytokine and chemokine production. IL-1RL1 gene transcript encodes different isoforms generated through alternative splicing. Its soluble isoform, IL-1RL1-a or sST2, acts as a decoy receptor by sequestering IL-33, thereby inhibiting IL1RL1-b/IL-33 signalling. IL-33 and its receptor IL-1RL1 are therefore considered as putative biomarkers or targets for pharmacological intervention in asthma. This review will provide an overview of the genetics and biology of the IL-33/IL-1RL1 pathway in the context of asthma pathogenesis. It will discuss the potential and complexities of targeting the cytokine or its receptor, how genetics or biomarkers may inform precision medicine for asthma targeting this pathway, and the possible positioning of therapeutics targeting IL-33 or its receptor in the expanding landscape of novel biologicals applied in asthma management.