Ablation of IL-33 Suppresses Th2 Responses but Is Accompanied by Sustained Mucus Obstruction in the Scnn1b Transgenic Mouse Model

Airspaces-derived exosomes contain disease-relevant protein signatures in a mouse model of cystic fibrosis (CF)-like mucoinflammatory lung disease

Exosomes, membrane-bound extracellular vesicles, ranging from approximately 30-200 nm in diameter, are released by almost all cell types and play critical roles in intercellular communication. In response to the prevailing stress, the exosome-bound protein signatures vary in abundance and composition. To identify the bronchoalveolar lavage fluid (BALF) exosome-bound proteins associated with mucoinflammatory lung disease and to gain insights into their functional implications, we compared BALF exosomes-derived proteins from adult Scnn1b transgenic (Scnn1b-Tg+) and wild type (WT) mice. A total of 3,144 and 3,119 proteins were identified in BALF exosomes from Scnn1b-Tg+ and WT mice, respectively. Using cutoff criteria (Log2 fold-change > 1 and adjusted p-value < 0.05), the comparison of identified proteins revealed 127 and 30 proteins that were significantly upregulated and downregulated, respectively, in Scnn1b-Tg+ versus WT mice. In addition, 52 and 27 proteins were exclusively enriched in Scnn1b-Tg+ and WT mice, respectively. The identified exosome-bound proteins from the homeostatic airspaces of WT mice were mostly relevant to the normal physiological processes. The protein signatures enriched in the BALF exosomes of Scnn1b-Tg+ mice were relevant to macrophage activation and mucoinflammatory processes. Ingenuity pathway analyses revealed that the enriched proteins in Scnn1b-Tg+ mice contributed to the inflammatory responses and antimicrobial defense pathways. Selective proteins including, RETNLA/FIZZ1, LGALS3/Galectin-3, S100A8/MRP8, and CHIL3/YM1 were immunolocalized to specific cell types. The comparative analysis between enriched BALF exosome proteins and previously identified differentially upregulated genes in Scnn1b-Tg+ versus WT mice suggested that the compartment-/cell-specific upregulation in gene expression dictates the enrichment of their respective proteins in the lung airspaces. Taken together, this study demonstrates that the BALF exosome-bound protein signatures reflect disease-relevant disturbances. Our findings suggest that the exosomes carry disease-relevant protein signatures that can be used as a diagnostic as well as predictive biomarkers for mucoinflammatory lung disease.

The production, function, and clinical applications of IL-33 in type 2 inflammation-related respiratory diseases

Epithelial-derived IL-33 (Interleukin-33), as a member of alarm signals, is a chemical substance produced under harmful stimuli that can promote innate immunity and activate adaptive immune responses. Type 2 inflammation refers to inflammation primarily mediated by Type 2 helper T cells (Th2), Type 2 innate lymphoid cells (ILC2), and related cytokines. Type 2 inflammation manifests in various forms in the lungs, with diseases such as asthma and chronic obstructive pulmonary disease chronic obstructive pulmonary disease (COPD) closely associated with Type 2 inflammation. Recent research suggests that IL-33 has a promoting effect on Type 2 inflammation in the lungs and can be regarded as an alarm signal for Type 2 inflammation. This article provides an overview of the mechanisms and related targets of IL-33 in the development of lung diseases caused by Type 2 inflammation, and summarizes the associated treatment methods. Analyzing lung diseases from a new perspective through the alarm of Type 2 inflammation helps to gain a deeper understanding of the pathogenesis of these related lung diseases. This, in turn, facilitates a better understanding of the latest treatment methods and potential therapeutic targets for diseases, with the expectation that targeting lL-33 can propose new strategies for disease prevention.

Epigenetic regulation of macrophage activation in chronic obstructive pulmonary disease

Macrophages in the innate immune system play a vital role in various lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), acute lung injury and pulmonary fibrosis. Macrophages involved in the process of immunity need to go through a process of activation, including changes in gene expression and cell metabolism. Epigenetic modifications are key factors of macrophage activation including DNA methylation, histone modification and non-coding RNA regulation. Understanding the role and mechanisms of epigenetic regulation of macrophage activation can provide insights into the function of macrophages in lung diseases and help identification of potential therapeutic targets. This review summarizes the latest progress in the epigenetic changes and regulation of macrophages in their development process and in normal physiological states, and the epigenetic regulation of macrophages in COPD as well as the influence of macrophage activation on COPD development.

Cystic Fibrosis Reprograms Airway Epithelial IL-33 Release and Licenses IL-33-Dependent Inflammation

Rationale: Type 2 inflammation has been described in people with cystic fibrosis (CF). Whether loss of CFTR (cystic fibrosis transmembrane conductance regulator) function contributes directly to a type 2 inflammatory response has not been fully defined. Objectives: The potent alarmin IL-33 has emerged as a critical regulator of type 2 inflammation. We tested the hypothesis that CFTR deficiency increases IL-33 expression and/or release and deletion of IL-33 reduces allergen-induced inflammation in the CF lung. Methods: Human airway epithelial cells (AECs) grown from non-CF and CF cell lines and Cftr+/+ and Cftr-/- mice were used in this study. Pulmonary inflammation in Cftr+/+ and Cftr-/- mice with and without IL-33 or ST2 (IL-1 receptor-like 1) germline deletion was determined by histological analysis, BAL, and cytokine analysis. Measurements and Main Results: After allergen challenge, both CF human AECs and Cftr-/- mice had increased IL-33 expression compared with control AECs and Cftr+/+ mice, respectively. DUOX1 (dual oxidase 1) expression was increased in CF human AECs and Cftr-/- mouse lungs compared with control AECs and lungs from Cftr+/+ mice and was necessary for the increased IL-33 release in Cftr-/- mice compared with Cftr+/+ mice. IL-33 stimulation of Cftr-/- CD4+ T cells resulted in increased type 2 cytokine production compared with Cftr+/+ CD4+ T cells. Deletion of IL-33 or ST2 decreased both type 2 inflammation and neutrophil recruitment in Cftr-/- mice compared with Cftr+/+ mice. Conclusions: Absence of CFTR reprograms airway epithelial IL-33 release and licenses IL-33-dependent inflammation. Modulation of the IL-33/ST2 axis represents a novel therapeutic target in CF type 2-high and neutrophilic inflammation.

Airway epithelial cell-specific deletion of HMGB1 exaggerates inflammatory responses in mice with muco-obstructive airway disease

High mobility group box 1 (HMGB1), a ubiquitous chromatin-binding protein required for gene transcription regulation, is released into the extracellular microenvironment by various structural and immune cells, where it is known to act as an alarmin. Here, we investigated the role of airway epithelium-specific HMGB1 in the pathogenesis of muco-obstructive lung disease in Scnn1b-transgenic (Tg+) mouse, a model of human cystic fibrosis (CF)-like lung disease. We hypothesized that airway epithelium-derived HMGB1 modulates muco-inflammatory lung responses in the Tg+ mice. The airway epithelium-specific HMGB1-deficient mice were generated and the effects of HMGB1 deletion on immune cell recruitment, airway epithelial cell composition, mucous cell metaplasia, and bacterial clearance were determined. The airway epithelium-specific deletion of HMGB1 in wild-type (WT) mice did not result in any morphological alterations in the airway epithelium. The deficiency of HMGB1 in airway epithelial cells in the Tg+ mice, however, resulted in significantly increased infiltration of macrophages, neutrophils, and eosinophils which was associated with significantly higher levels of inflammatory mediators, including G-CSF, KC, MIP-2, MCP-1, MIP-1α, MIP-1β, IP-10, and TNF-α in the airspaces. Furthermore, as compared to the HMGB1-sufficient Tg+ mice, the airway epithelial cell-specific HMGB1-deficient Tg+ mice exhibited poor resolution of spontaneous bacterial infection. The HMGB1 deficiency in the airway epithelial cells of Tg+ mice did not alter airway epithelial cell-specific responses including epithelial cell proliferation, mucous cell metaplasia, and mucus obstruction. Collectively, our findings provide novel insights into the role of airway epithelial cell-derived HMGB1 in the pathogenesis of CF-like lung disease in Tg+ mice.

Ozone exposure upregulates the expression of host susceptibility protein TMPRSS2 to SARS-CoV-2

SARS-CoV-2, a novel coronavirus and an etiologic agent for the current global health emergency, causes acute infection of the respiratory tract leading to severe disease and significant mortality. Ever since the start of SARS-CoV-2, also known as the COVID-19 pandemic, countless uncertainties have been revolving around the pathogenesis and epidemiology of the SARS-CoV-2 infection. While air pollution has been shown to be strongly correlated to increased SARS-CoV-2 morbidity and mortality, whether environmental pollutants such as ground-level ozone affects the susceptibility of individuals to SARS-CoV-2 is not yet established. To investigate the impact of ozone inhalation on the expression levels of signatures associated with host susceptibility to SARS-CoV-2, we analyzed lung tissues collected from mice that were sub-chronically exposed to air or 0.8 ppm ozone for three weeks (4 h/night, 5 nights/week), and analyzed the expression of signatures associated with host susceptibility to SARS-CoV-2. SARS-CoV-2 entry into the host cells is dependent on the binding of the virus to the host cellular receptor, angiotensin-converting enzyme (ACE2), and its subsequent proteolytic priming by the host-derived protease, transmembrane protease serine 2 (TMPRSS2). The Ace2 transcripts were significantly elevated in the parenchyma, but not in the extrapulmonary airways and alveolar macrophages, from ozone-exposed mice. The TMPRSS2 protein and Tmprss2 transcripts were significantly elevated in the extrapulmonary airways, parenchyma, and alveolar macrophages from ozone-exposed mice. A significant proportion of additional known SARS-CoV-2 host susceptibility genes were upregulated in alveolar macrophages and parenchyma from ozone-exposed mice. Our data indicate that the unhealthy levels of ozone in the environment may predispose individuals to severe SARS-CoV-2 infection. Given the severity of this pandemic and the challenges associated with direct testing of host-environment interactions in clinical settings, we believe that this ozone exposure-based study informs the scientific community of the potentially detrimental effects of the ambient ozone levels in determining the host susceptibility to SARS-CoV-2.

Vesicular and extravesicular protein analyses from the airspaces of ozone-exposed mice revealed signatures associated with mucoinflammatory lung disease

Lung epithelial lining fluid (ELF) harbors a variety of proteins that influence homeostatic and stress responses in the airspaces. Exosomes, nano-sized extracellular vesicles, contain many proteins that vary in abundance and composition based on the prevailing conditions. Ozone causes inflammatory responses in the airspaces of experimental animals and humans. However, the exosomal protein signatures contained within the ELF from ozone-exposed lung airspaces remain poorly characterized. To explore this, we hypothesized that ozone triggers the release of exosome-bound inflammatory proteins from various cells that reflect mucoobstructive lung disease. Accordingly, we repetitively exposed adult male and female C57BL/6 mice to HEPA-filtered air (air) or 0.8 ppm ozone (4 h per day) for 14 days (five consecutive days of exposure, 2 days of rest, five consecutive days of exposure, 2 days of rest, four consecutive days of exposure). Exosome-bound proteomic signatures, as well as the levels of soluble inflammatory mediators in the bronchoalveolar lavage fluid (BALF), were determined 12-16 h after the last exposure. Principal component analyses of the exosome-bound proteome revealed a clear distinction between air-exposed and ozone-exposed mice, as well as between ozone-exposed males and ozone-exposed females. In addition to 575 proteins that were enriched in both sexes upon ozone exposure, 243 and 326 proteins were enriched uniquely in ozone-exposed males and females, respectively. Ingenuity pathway analyses on enriched proteins between ozone- and air-exposed mice revealed enrichment of pro-inflammatory pathways. More specifically, macrophage activation-related proteins were enriched in exosomes from ozone-exposed mice. Cytokine analyses on the BALF revealed elevated levels of G-CSF, KC, IP-10, IL-6, and IL-5 in ozone-exposed mice. Finally, the histopathological assessment revealed significantly enhanced intracellular localization of mucoinflammatory proteins including MUC5B and FIZZ1 in ozone-exposed mice in a cell-specific manner indicating the cellular sources of the proteins that are ferried in the exosomes upon ozone-induced lung injury. Collectively, this study identified exosomal, secretory, and cell-specific proteins and biological pathways following repetitive exposure of mice to ozone.

Epigenetic reprogramming of airway macrophages promotes polarization and inflammation in muco-obstructive lung disease

Lung diseases, such as cystic fibrosis and COPD, are characterized by mucus obstruction and chronic airway inflammation, but their mechanistic link remains poorly understood. Here, we focus on the function of the mucostatic airway microenvironment on epigenetic reprogramming of airway macrophages (AM) and resulting transcriptomic and phenotypical changes. Using a mouse model of muco-obstructive lung disease (Scnn1b-transgenic), we identify epigenetically controlled, differentially regulated pathways and transcription factors involved in inflammatory responses and macrophage polarization. Functionally, AMs from Scnn1b-transgenic mice have reduced efferocytosis and phagocytosis, and excessive inflammatory responses upon lipopolysaccharide challenge, mediated through enhanced Irf1 function and expression. Ex vivo stimulation of wild-type AMs with native mucus impairs efferocytosis and phagocytosis capacities. In addition, mucus induces gene expression changes, comparable with those observed in AMs from Scnn1b-transgenic mice. Our data show that mucostasis induces epigenetic reprogramming of AMs, leading to changes favoring tissue damage and disease progression. Targeting these altered AMs may support therapeutic approaches in patients with muco-obstructive lung diseases.

Postnatal Ozone Exposure Disrupts Alveolar Development, Exaggerates Mucoinflammatory Responses, and Suppresses Bacterial Clearance in Developing Scnn1b-Tg+ Mice Lungs

Increased levels of ambient ozone, one of the six criteria air pollutants, result in respiratory tract injury and worsening of ongoing lung diseases. However, the effect of ozone exposure on the respiratory tract undergoing active lung development and simultaneously experiencing mucoinflammatory lung diseases, such as cystic fibrosis, remains unclear. To address these questions, we exposed Scnn1b transgenic (Scnn1b-Tg⁺) mice, a mouse model of cystic fibrosis-like lung disease, and littermate wild-type (WT) mice to ozone from postnatal days (PND) 3-20 and examined the lung phenotypes at PND21. As compared with filtered air (FA)-exposed WT mice, the ozone-exposed WT mice exhibited marked alveolar space enlargement, in addition to significant eosinophilic infiltration, type 2 inflammation, and mucous cell metaplasia. Ozone-exposed Scnn1b-Tg⁺ mice also exhibited significantly increased alveolar space enlargement, which was also accompanied by exaggerated granulocytic infiltration, type 2 inflammation, and a greater degree of mucus obstruction. The alveolar space enlargement in ozone-exposed WT, FA-exposed Scnn1b-Tg⁺, and ozone-exposed Scnn1b-Tg⁺ mice was accompanied by elevated levels of MMP12 protein in macrophages and Mmp12 mRNA in the lung homogenates. Finally, although bacterial burden was largely resolved by PND21 in FA-exposed Scnn1b-Tg⁺ mice, ozone-exposed Scnn1b-Tg⁺ mice exhibited compromised bacterial clearance, which was also associated with increased levels of IL-10, an immunosuppressive cytokine, and marked mucus obstruction. Taken together, our data show that ozone exposure results in alveolar space remodeling during active phases of lung development and markedly exaggerates the mucoinflammatory outcomes of pediatric-onset lung disease, including bacterial infections, granulocytic inflammation, mucus obstruction, and alveolar space enlargement.

Myeloid-IL4Rα is an indispensable link in IL-33-ILCs-IL-13-IL4Rα axis of eosinophil recruitment in murine lungs

Increased eosinophil recruitment is a hallmark feature of eosinophilic disorders. Here, we delineated the key molecular and cellular players involved in physiological eosinophilic recruitment during normal postnatal lung development in mice. Physiological eosinophilic recruitment was consistently present in 7-, 10-, and 15-day-old neonatal mice, but not in 42-day-old mice. This feature was completely abolished in interleukin 33 (IL-33)-, interleukin 2 receptor gamma chain (IL2rγ)-, and interleukin 4 receptor alpha (IL4Rα)-knockout mice, but not in recombination activating gene 1 (Rag1)-knockout mice demonstrating an indispensable role for IL-33, innate lymphoid cells (ILCs), and IL4Rα in eosinophil recruitment. Interestingly, myeloid-specific IL4Rα-deficient (mye-IL4Rα^−/−) mice had significantly reduced eosinophilia in the airspaces that was associated with reduced levels of IL-4 and IL-5 in the bronchoalveolar lavage fluid (BALF). Further, we tested the effect of myeloid-specific IL4Rα deficiency on IL-13-induced eosinophil recruitment into adult lung airspaces. Eosinophil recruitment into the airspaces was elevated in IL-13-treated WT mice but not in IL-13-treated mye-IL4Rα^−/− mice. Consistent with the degree of eosinophilia, the BALF levels of eosinophil recruitment-associated cytokines were significantly elevated in IL-13-treated WT but not in IL-13-treated mye-IL4Rα^−/− mice. These data establish that myeloid-IL4Rα is an indispensable component of the IL-33-ILCsIL-13-IL4Rα axis of eosinophil recruitment.

Compartment-specific transcriptomics of ozone-exposed murine lungs reveals sex- and cell type-associated perturbations relevant to mucoinflammatory lung diseases

Ozone is known to cause lung injury, and resident cells of the respiratory tract (i.e., epithelial cells and macrophages) respond to inhaled ozone in a variety of ways that affect their survival, morphology, and functioning. However, a complete understanding of the sex-associated and the cell type-specific gene expression changes in response to ozone exposure is still limited. Through transcriptome profiling, we aimed to analyze gene expression alterations and associated enrichment of biological pathways in three distinct cell type-enriched compartments of ozone-exposed murine lungs. We subchronically exposed adult male and female mice to 0.8 ppm ozone or filtered air. RNA-Seq was performed on airway epithelium-enriched airways, parenchyma, and purified airspace macrophages. Differential gene expression and biological pathway analyses were performed and supported by cellular and immunohistochemical analyses. While a majority of differentially expressed genes (DEGs) in ozone-exposed versus air-exposed groups were common between both sexes, sex-specific DEGs were also identified in all of the three tissue compartments. As compared with ozone-exposed males, ozone-exposed females had significant alterations in gene expression in three compartments. Pathways relevant to cell division and DNA repair were enriched in the ozone-exposed airways, indicating ozone-induced airway injury and repair, which was further supported by immunohistochemical analyses. In addition to cell division and DNA repair pathways, inflammatory pathways were also enriched within the parenchyma, supporting contribution by both epithelial and immune cells. Further, immune response and cytokine-cytokine receptor interactions were enriched in macrophages, indicating ozone-induced macrophage activation. Finally, our analyses also revealed the overall upregulation of mucoinflammation- and mucous cell metaplasia-associated pathways following ozone exposure.

The Contradictory Role of Interleukin-33 in Immune Cells and Tumor Immunity

Interleukin (IL)-33 is a member of the IL-1 superfamily and is a crucial cytokine playing the role of a dual-function molecule. IL-33 mediates its function by interacting with its receptor suppression of tumorigenicity 2 (ST2), which is constitutively expressed on T helper (Th)1 cells, Th2 cells, and other immune cells. Previously, we summarized findings on IL-33 and performed an intensive study of the correlation between IL-33 and tumor. IL-33 enables anti-tumor immune responses through Th1 cells and natural killer (NK) cells and plays a role in tumor immune escape in cancers via Th2 cells and regulatory T cells. Herein, we discuss the contradictory role of IL-33 in immune cells in different cancer, and our summaries may be helpful for better understanding of the development of research on IL-33 and tumor immunity.

The Innate Lymphoid System Is a Critical Player in the Manifestation of Mucoinflammatory Airway Disease in Mice

Innate lymphoid and adaptive immune cells are known to regulate epithelial responses, including mucous cell metaplasia (MCM), but their roles in mucoinflammatory airway diseases, such as cystic fibrosis, remain unknown. Scnn1b transgenic (Scnn1b-Tg⁺) mice, which recapitulate cystic fibrosis-like mucoinflammatory airway disease, deficient in innate lymphoid (Il2rg knockout mice [Il2rg ^KO]), adaptive immune (Rag1 knockout mice [Rag1 ^KO]), or both systems (Il2rg ^KO/Rag1 ^KO), were employed to investigate their respective contributions in the pathogenesis of mucoinflammatory airway disease. As previously reported, immunocompetent Tg⁺ juveniles exhibited spontaneous neonatal bacterial infections with robust mucoinflammatory features, including elevated expression of Th2-associated markers accompanied by MCM, elevated MUC5B expression, and airway mucus obstruction. The bacterial burden was increased in Il2rg ^KO/Tg⁺ juveniles but returned to significantly lower levels in Il2rg ^KO/Rag1 ^KO/Tg⁺ juveniles. Mechanistically, this improvement reflected reduced production of adaptive immunity-derived IL-10 and, in turn, increased activation of macrophages. Although all the mucoinflammatory features were comparable between the immunocompetent Tg⁺ and Rag1 ^KO/Tg⁺ juveniles, the Il2rg ^KO/Tg⁺ and Il2rg ^KO/Rag1 ^KO/Tg⁺ juveniles exhibited suppressed expression levels of Th2 markers, diminished MCM, suppressed MUC5B expression, and reduced mucus obstruction. Collectively, these data indicate that, in the context of airway mucus obstruction, the adaptive immune system suppresses antibacterial macrophage activation, whereas the innate lymphoid system contributes to MCM, mucin production, and mucus obstruction.