IFN-γ directly controls IL-33 protein level through a STAT1- and LMP2-dependent mechanism

Keloids and inflammation: the crucial role of IL-33 in epidermal changes

Introduction

Keloids are benign fibroproliferative disorders characterized by excessive collagen deposition and inflammation that extend beyond the original wound boundaries. IL-33 is an alarmin cytokine released upon cellular damage or stress. Dysregulation of IL-33 in epidermal keratinocytes compromises the skin barrier and triggers chronic inflammation.

Method

In this study, we first noticed an increased expression of IL-33 in the keratinocytes of keloid epidermis through histological staining. Then, an increased expression of IL-33 receptor (ST2) in the lymphocytes infiltrating the superficial dermis of keloid scars were identified through histological staining and flow cytometry analysis. The IFN-γ-IL-33 loop between lymphocytes and keratinocytes were further revealed by flow cytometry and Western blotting analysis. The abnormal keratinocyte differentiation in epiderm is mediated by IFN-γ-IL-33 loop were confirmed by in vitro studies in HaCaT cells via Western blotting analysis and immunofluorescence staining. Finally, the IFN-γ-IL-33 loop were also verified in cocultured peripheral blood mononuclear cells and HaCaT through ELISA analysis.

Results

Our results demonstrate that IL-33 levels are significantly elevated in the epidermis of keloid tissues, where it functions as an alarmin, promoting a chronic inflammatory response. We further reveal a feedback loop between IL-33 and interferon-gamma (IFN-γ), whereby IL-33 induces IFN-g production in lymphocytes, which in turn stimulates keratinocytes to produce more IL-33. This loop contributes to impaired keratinocyte differentiation and skin barrier dysfunction, exacerbating the inflammatory environment.

Discussion

By elucidating the role of the IL-33/ST2 axis in keloid formation, this research provides valuable insights into potential therapeutic targets for managing this challenging condition.

Therapeutic targeting of full-length interleukin-33 protein levels with cell-permeable decoy peptides attenuates fibrosis in the bleomycin model in vivo

Interleukin (IL)-33 has been shown to centrally regulate, among other processes, inflammation and fibrosis. Both intracellular full-length (FLIL33) precursor and extracellular mature cytokine (MIL33) forms exert such regulation, albeit differentially. Drug development efforts to target the IL-33 pathway have focused mostly on MIL33 and its specific cell-surface receptor, ST2, with limited attempts to negotiate the pathophysiological contributions from FLIL33. Furthermore, even a successful strategy for targeting MIL33 effects would arguably benefit from a simultaneous attenuation of the levels of FLIL33, which remains the continuous source of MIL33 supply. We therefore sought to develop an approach to depleting FLIL33 protein levels. We previously reported that the steady-state levels of FLIL33 are controlled in part through its proteasomal degradation and that such regulation can be mapped to a segment in the N-terminal portion of FLIL33. We hypothesized that disruption of this regulation would lead to a decrease in FLIL33 levels, thus inducing a beneficial therapeutic effect in an IL-33-dependent pathology. To test this hypothesis, we designed and tested cell-permeable decoy peptides, which mimic the target N-terminal FLIL33 region. We argued that such mimic peptides would compete with FLIL33 for the components of the native FLIL33 production and maintenance molecular machinery. Administered in the therapeutic regimen to bleomycin-challenged mice, the tested cell-permeable decoy peptides alleviated the overall severity of the disease by restoring body weight loss and attenuating accumulation of collagen in the lungs. This proof-of-principle study lays the foundation for future work toward the development of this prospective therapeutic approach. SIGNIFICANCE STATEMENT: An antifibrotic therapeutic approach is proposed and preclinically tested in mice in vivo based on targeting the full-length IL-33 precursor protein. Peptide fusion constructs consisted of a cell-permeable sequence fused with a sequence mimicking an N-terminal segment of IL-33 precursor that is responsible for this protein's stability. Systemic administration of such peptides to mice in either the acute intratracheal or chronic systemic bleomycin challenge models leads to a decrease in the bleomycin-induced elevations of pulmonary IL-33 and collagen.

Wild-type S100A3 and S100A13 restore calcium homeostasis and mitigate mitochondrial dysregulation in pulmonary fibrosis patient-derived cells

Patients with digenic S100A3 and S100A13 mutations exhibited an atypical and progressive interstitial pulmonary fibrosis, with impaired intracellular calcium homeostasis and mitochondrial dysfunction. Here we provide direct evidence of a causative effect of the mutation on receptor mediated calcium signaling and calcium store responses in control cells transfected with mutant S100A3 and mutant S100A13. We demonstrate that the mutations lead to increased mitochondrial mass and hyperpolarization, both of which were reversed by transfecting patient-derived cells with the wild type S100A3 and S100A13, or extracellular treatment with the recombinant proteins. In addition, we demonstrate increased secretion of inflammatory mediators in patient-derived cells and in control cells transfected with the mutant-encoding constructs. These findings indicate that treatment of patients' cells with recombinant S100A3 and S100A13 proteins is sufficient to normalize most of cellular responses, and may therefore suggest the use of these recombinant proteins in the treatment of this devastating disease.

COVID-19 and autoimmune diseases: is there a connection?

PURPOSE OF REVIEW

This review summarizes current evidence on the potential link between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and autoimmunity.

RECENT FINDINGS

Several viral infections are potential triggers of reactive and autoimmune diseases by inducing type II and type IV hypersensitivity reactions. Recent evidence demonstrated that SARS-CoV-2 infection is not an exception, triggering the production of tissue-specific autoantibodies during the acute phase of coronavirus disease 2019 (COVID-19) and leading to autoimmune diseases development as long-term complication. The significant immune dysregulation with cytokine storm and organ damage observed in patients with severe to critical COVID-19 is considered the main mechanism explaining the high levels of autoantibodies, which are also implicated in disease severity and the need for an intensive care assessment. Multisystem inflammatory syndrome in children (MIS-C) is an immune-mediated disease where the recent viral infection leads to systemic inflammation, as already observed in other reactive and autoimmune diseases.

SUMMARY

Autoimmunity may be a complication of SAR-CoV-2 infection. Understanding the pathogenesis of autoimmune manifestations in COVID-19 might help prevent the incidence or exacerbation of autoimmune disorders and design better and more efficient treatment strategies in children and adult populations.

Age-dependent Pdgfrβ signaling drives adipocyte progenitor dysfunction to alter the beige adipogenic niche in male mice

Perivascular adipocyte progenitor cells (APCs) can generate cold temperature-induced thermogenic beige adipocytes within white adipose tissue (WAT), an effect that could counteract excess fat mass and metabolic pathologies. Yet, the ability to generate beige adipocytes declines with age, creating a key challenge for their therapeutic potential. Here we show that ageing beige APCs overexpress platelet derived growth factor receptor beta (Pdgfrβ) to prevent beige adipogenesis. We show that genetically deleting Pdgfrβ, in adult male mice, restores beige adipocyte generation whereas activating Pdgfrβ in juvenile mice blocks beige fat formation. Mechanistically, we find that Stat1 phosphorylation mediates Pdgfrβ beige APC signaling to suppress IL-33 induction, which dampens immunological genes such as IL-13 and IL-5. Moreover, pharmacologically targeting Pdgfrβ signaling restores beige adipocyte development by rejuvenating the immunological niche. Thus, targeting Pdgfrβ signaling could be a strategy to restore WAT immune cell function to stimulate beige fat in adult mammals.

Full-length IL-33 augments pulmonary fibrosis in an ST2- and Th2-independent, non-transcriptomic fashion

Mature IL-33 (MIL33) acting through its receptor, ST2, is known to regulate fibrosis. The precursor, full-length IL-33 (FLIL33), may function differently from MIL33 and independently of ST2. Here we report that genetic deletion of either IL-33 or ST2 attenuates pulmonary fibrosis in the bleomycin model, as does Cre-induced IL-33 deficiency in response to either acute or chronic bleomycin challenge. However, adenovirus-mediated gene delivery of FLIL33, but not MIL33, to the lungs of either wild-type or ST2-deficient mice potentiates the profibrotic effect of bleomycin without inducing a Th2 phenotype. In cultured mouse lung cells, FLIL33 overexpression induces moderate and distinct transcriptomic changes compared with a robust response induced by MIL33, whereas ST2 deletion abrogates the effects of both IL-33 forms. Thus, FLIL33 may contribute to fibrosis in an ST2-independent, Th2-independent, non-transcriptomic fashion, suggesting that pharmacological targeting of both FLIL33 and MIL33 may prove efficacious in patients with pulmonary fibrosis.

Interleukin (IL)-33 immunobiology in asthma and airway inflammatory diseases

OBJECTIVE

Identify key features of IL-33 immunobiology important in allergic and nonallergic airway inflammatory diseases and potential therapeutic strategies to reduce disease burden.

DATA SOURCES

PubMed, clinicaltrials.gov.

STUDY SELECTIONS

A systematic and focused literature search was conducted of PubMed from March 2021 to December 2021 using keywords to either PubMed or BioMed Explorer including IL-33/ST2, genetic polymorphisms, transcription, translation, post-translation modification, nuclear protein, allergy, asthma, and lung disease. Clinical trial information on IL-33 was extracted from clinicaltrials.gov in August 2021.

RESULTS

In total, 72 publications with relevance to IL-33 immunobiology and/or clinical lung disease were identified (allergic airway inflammation/allergic asthma n = 26, non-allergic airway inflammation n = 9, COPD n = 8, lung fibrosis n = 10). IL-33 levels were higher in serum, BALF and/or lungs across inflammatory lung diseases. Eight studies described viral infections and IL-33 and 4 studies related to COVID-19. Mechanistic studies (n = 39) including transcript variants and post-translational modifications related to the immunobiology of IL-33. Single nucleotide polymorphism in IL-33 or ST2 were described in 9 studies (asthma n = 5, inflammatory bowel disease n = 1, mycosis fungoides n = 1, ankylosing spondylitis n = 1, coronary artery disease n = 1). Clinicaltrials.gov search yielded 84 studies of which 17 were related to therapeutic or biomarker relevance in lung disease.

CONCLUSION

An integral role of IL-33 in the pathogenesis of allergic and nonallergic airway inflammatory disease is evident with several emerging clinical trials investigating therapeutic approaches. Current data support a critical role of IL-33 in damage signaling, repair and regeneration of lungs.

Dual Immune Regulatory Roles of Interleukin-33 in Pathological Conditions

Interleukin-33 (IL-33), a member of the IL-1 cytokine family and a multifunctional cytokine, plays critical roles in maintaining host homeostasis and in pathological conditions, such as allergy, infectious diseases, and cancer, by acting on multiple types of immune cells and promoting type 1 and 2 immune responses. IL-33 is rapidly released by immune and non-immune cells upon stimulation by stress, acting as an “alarmin” by binding to its receptor, suppression of tumorigenicity 2 (ST2), to trigger downstream signaling pathways and activate inflammatory and immune responses. It has been recognized that IL-33 displays dual-functioning immune regulatory effects in many diseases and has both pro- and anti-tumorigenic effects, likely depending on its primary target cells, IL-33/sST2 expression levels, cellular context, and the cytokine microenvironment. Herein, we summarize our current understanding of the biological functions of IL-33 and its roles in the pathogenesis of various conditions, including inflammatory and autoimmune diseases, infections, cancers, and cases of organ transplantation. We emphasize the nature of context-dependent dual immune regulatory functions of IL-33 in many cells and diseases and review systemic studies to understand the distinct roles of IL-33 in different cells, which is essential to the development of more effective diagnoses and therapeutic approaches for IL-33-related diseases.

Ischemia reperfusion injury facilitates lung allograft acceptance through IL-33-mediated activation of donor-derived IL-5 producing group 2 innate lymphoid cells

Pathways regulating lung alloimmune responses differ from most other solid organs and remain poorly explored. Based on our recent work identifying the unique role of eosinophils in downregulating lung alloimmunity, we sought to define pathways contributing to eosinophil migration and homeostasis. Using a murine lung transplant model, we have uncovered that immunosuppression increases eosinophil infiltration into the allograft in an IL-5-dependent manner. IL-5 production depends on immunosuppression-mediated preservation of donor-derived group 2 innate lymphoid cells (ILC2). We further describe that ischemia reperfusion injury upregulates the expression of IL-33, which functions as the dominant and nonredundant mediator of IL-5 production by graft-resident ILC2. Our work thus identifies unique cellular mechanisms that contribute to lung allograft acceptance. Notably, ischemia reperfusion injury, widely considered to be solely deleterious to allograft survival, can also downregulate alloimmune responses by initiating unique pathways that promote IL-33/IL-5/eosinophil-mediated tolerance.

Natural Compounds Tapinarof and Galactomyces Ferment Filtrate Downregulate IL-33 Expression via the AHR/IL-37 Axis in Human Keratinocytes

Interleukin (IL)-37 suppresses systemic and local inflammation. It is expressed in the epidermis, the external layer of the skin, and is decreased in inflammatory skin diseases including atopic dermatitis (AD) and psoriasis. Therefore, an agent applied topically on the skin that can increase IL-37 could be promising for treating AD and psoriasis; however, the mechanism regulating IL-37 remains largely unknown. Given that IL-37 expression is induced in differentiated keratinocytes, a major component of the epidermis, and that activation of aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor, promotes keratinocyte differentiation, we hypothesized that AHR might be involved in the IL-37 expression in human keratinocytes. We analyzed normal epidermal human keratinocytes (NHEKs) treated with tapinarof and Galactomyces ferment filtrate (GFF), which are potent AHR modulators. We found that tapinarof and GFF upregulated IL-37 in NHEKs, which was canceled by the knockdown of AHR using siRNA transfection, indicating that AHR mediates IL-37 expression in NHEKs. Furthermore, we found that the knockdown of IL-37 resulted in the upregulation of IL-33, an alarmin cytokine with crucial roles in the pathogenesis of AD and psoriasis. These findings suggest that IL-37 negatively regulates IL-33 expression in NHEKs. Finally, we examined whether tapinarof and GFF treatment modulates IL-33 expression in NHEKs. Such treatment inhibited IL-33 expression, which was partially reversed by the knockdown of either AHR or IL-37. Taken together, our findings provide the first evidence that tapinarof and GFF could have potential to prevent IL-33-overexpressing disorders such as AD and psoriasis via the AHR/IL-37 axis.

Immunopathological signatures in multisystem inflammatory syndrome in children and pediatric COVID-19

Pediatric Coronavirus Disease 2019 (pCOVID-19) is rarely severe; however, a minority of children infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) might develop multisystem inflammatory syndrome in children (MIS-C), with substantial morbidity. In this longitudinal multi-institutional study, we applied multi-omics (analysis of soluble biomarkers, proteomics, single-cell gene expression and immune repertoire analysis) to profile children with COVID-19 (n = 110) and MIS-C (n = 76), along with pediatric healthy controls (pHCs; n = 76). pCOVID-19 was characterized by robust type I interferon (IFN) responses, whereas prominent type II IFN-dependent and NF-κB-dependent signatures, matrisome activation and increased levels of circulating spike protein were detected in MIS-C, with no correlation with SARS-CoV-2 PCR status around the time of admission. Transient expansion of TRBV11-2 T cell clonotypes in MIS-C was associated with signatures of inflammation and T cell activation. The association of MIS-C with the combination of HLA A*02, B*35 and C*04 alleles suggests genetic susceptibility. MIS-C B cells showed higher mutation load than pCOVID-19 and pHC. These results identify distinct immunopathological signatures in pCOVID-19 and MIS-C that might help better define the pathophysiology of these disorders and guide therapy.

A Pilot Clinical Study of Hyperacute Serum Treatment in Osteoarthritic Knee Joint: Cytokine Changes and Clinical Effects

The serum fraction of platelet-rich fibrin (hyperacute serum) has been shown to improve cartilage cell proliferation in in vitro osteoarthritic knee joint models. We hypothesize that hyperacute serum may be a potential regenerative therapeutic for osteoarthritic knees. In this study, the cytokine milieu at the synovial fluid of osteoarthritic knee joints exposed to hyperacute serum intraarticular injections was investigated. Patients with knee osteoarthritis received three injections of autologous hyperacute serum; synovial fluid was harvested before each injection and clinical monitoring was followed-up for 6 months. Forty osteoarthritic-related cytokines, growth factors and structural proteins from synovial fluid were quantified and analysed by Multivariate Factor Analysis. Hyperacute serum provided symptomatic relief regarding pain and joint stability for OA patients. Both patients "with" and "without effusion knees" had improved VAS, KOOS and Lysholm-Tegner scores 6 months after of hyperacute serum treatment. Synovial fluid analysis revealed two main clusters of proteins reacting together as a group, showing strong and significant correlations with their fluctuation patterns after hyperacute serum treatment. In conclusion, hyperacute serum has a positive effect in alleviating symptoms of osteoarthritic knees. Moreover, identified protein clusters may allow the prediction of protein expression, reducing the number of investigated proteins in future studies.

The blockade of interleukin-33 released by hepatectomy would be a promising treatment option for cholangiocarcinoma

Interleukin-33 (IL-33), an alarmin released during tissue injury, facilitates the development of cholangiocarcinoma (CCA) in a murine model. However, it is unclear whether IL-33 is associated with human CCA. The aim of this study was to support the following hypothesis: IL-33 is released during hepatectomy for CCA, subsequently facilitating the development of subclinical CCA and eventually leading to recurrent disease. IL-33 expression was assessed in various samples from both humans and mice including resected liver and paired plasma samples collected at hepatectomy and after surgery, and its influences on recurrent disease and patient prognosis were determined. Homogenized human liver samples with high or low IL-33 expression were added to the culture medium of human CCA cells, and the changes in proliferation and migration were evaluated. To examine the effects of inhibiting the IL-33 release induced by hepatectomy, syngraft transplantation of murine CCA cells was performed in C57BL/6J mice with or without IL-33 blockade. The amount of IL-33 released into the plasma during hepatectomy correlated with the background liver expression. High expression of IL-33 in the liver was an independent risk factor for recurrence. Homogenized liver tissue strongly expressing IL-33 increased both the proliferation and migration of tumor cells. Mice who underwent hepatectomy exhibited CCA progression in the remnant liver, whereas blockade of IL-33 during hepatectomy inhibited tumor progression. Thus, we concluded that surgery for CCA with curative intent paradoxically induced IL-33 release, which facilitated CCA recurrence, and anti-IL-33 therapy during hepatectomy might reduce the risk of CCA recurrence.

IL-33 Mediates Lung Inflammation by the IL-6-Type Cytokine Oncostatin M

The interleukin-1 family member IL-33 participates in both innate and adaptive T helper-2 immune cell responses in models of lung disease. The IL-6-type cytokine Oncostatin M (OSM) elevates lung inflammation, Th2-skewed cytokines, alternatively activated (M2) macrophages, and eosinophils in C57Bl/6 mice in vivo. Since OSM induces IL-33 expression, we here test the IL-33 function in OSM-mediated lung inflammation using IL-33-/- mice. Adenoviral OSM (AdOSM) markedly induced IL-33 mRNA and protein levels in wild-type animals while IL-33 was undetectable in IL-33-/- animals. AdOSM treatment showed recruitment of neutrophils, eosinophils, and elevated inflammatory chemokines (KC, eotaxin-1, MIP1a, and MIP1b), Th2 cytokines (IL-4/IL-5), and arginase-1 (M2 macrophage marker) whereas these responses were markedly diminished in IL-33-/- mice. AdOSM-induced IL-33 was unaffected by IL-6-/- deficiency. AdOSM also induced IL-33R+ ILC2 cells in the lung, while IL-6 (AdIL-6) overexpression did not. Flow-sorted ILC2 responded in vitro to IL-33 (but not OSM or IL-6 stimulation). Matrix remodelling genes col3A1, MMP-13, and TIMP-1 were also decreased in IL-33-/- mice. In vitro, IL-33 upregulated expression of OSM in the RAW264.7 macrophage cell line and in bone marrow-derived macrophages. Taken together, IL-33 is a critical mediator of OSM-driven, Th2-skewed, and M2-like responses in mouse lung inflammation and contributes in part through activation of ILC2 cells.

DAMPs in Unilateral Ureteral Obstruction

Damage-associated molecular patterns (DAMPs) are released from tubular and interstitial cells in the kidney after unilateral ureteral obstruction (UUO). DAMPs are recognized by pattern recognition receptors (PRRs), which mediate the initiation of an immune response and the release of inflammatory cytokines. The animal model of UUO is used for various purposes. UUO in adult mice serves as a model for accelerated renal fibrosis, which is a hallmark of progressive renal disease. UUO in adult mice enables to study cell death, inflammation, and extracellular matrix deposition in the kidney. Neonatal UUO is a model for congenital obstructive nephropathies. It studies inflammation, apoptosis, and interstitial fibrosis in the neonatal kidney, when nephrogenesis is still ongoing. Following UUO, several DAMPs as well as DAMP receptors are upregulated. In adult UUO, soluble uric acid is upregulated and activates the NOD-like receptor family, pyrin domain containing-3 (NLRP3) inflammasome, which promotes fibrosis, apoptosis, and reactive oxygen species (ROS) injury. Further DAMPs associated with UUO are uromodulin, members of the IL-1 family, and necrotic cell DNA, all of which promote sterile inflammation. In neonatal UUO, the receptor for advanced glycation endproducts (RAGE) is highly upregulated. RAGE is a ligand for several DAMPs, including high mobility group box 1 (HMGB1) and S100 proteins, which play an important role in renal fibrosis. Additionally, necroptosis is an important mechanism of cell death, besides apoptosis, in neonatal UUO. It is highly inflammatory due to release of cytokines and specific DAMPs. The release and recognition of DAMPs initiate sterile inflammation, which makes them good candidates to develop and improve diagnostic and therapeutic strategies in renal fibrosis and congenital obstructive nephropathies.

Contributions of IL-33 in Non-hematopoietic Lung Cells to Obstructive Lung Disease

Interleukin (IL)-33 plays important roles in pulmonary immune responses and lung diseases including asthma and chronic obstructive pulmonary disease (COPD). There is substantial interest in identifying and characterizing cellular sources vs. targets of IL-33, and downstream signaling pathways involved in disease pathophysiology. While epithelial and immune cells have largely been the focus, in this review, we summarize current knowledge of expression, induction, and function of IL-33 and its receptor ST2 in non-hematopoietic lung cells in the context of health and disease. Under basal conditions, epithelial cells and endothelial cells are thought to be the primary resident cell types that express high levels of IL-33 and serve as ligand sources compared to mesenchymal cells (smooth muscle cells and fibroblasts). Under inflammatory conditions, IL-33 expression is increased in most non-hematopoietic lung cells, including epithelial, endothelial, and mesenchymal cells. In comparison to its ligand, the receptor ST2 shows low expression levels at baseline but similar to IL-33, ST2 expression is upregulated by inflammation in these non-hematopoietic lung cells which may then participate in chronic inflammation both as sources and autocrine/paracrine targets of IL-33. Downstream effects of IL-33 may occur via direct receptor activation or indirect interactions with the immune system, overall contributing to lung inflammation, airway hyper-responsiveness and remodeling (proliferation and fibrosis). Accordingly from a therapeutic perspective, targeting IL-33 and/or its receptor in non-hematopoietic lung cells becomes relevant.

Neonatal obstructive nephropathy induces necroptosis and necroinflammation

Urinary tract obstruction during kidney development causes tubular apoptosis, tubular necrosis, and interstitial inflammation. Necroptosis is a subtype of programmed necrosis mediated by the receptor-interacting serine/threonine-protein kinase-3 (RIPK3) and the pseudokinase mixed lineage kinase domain-like (MLKL). Necrosis induces inflammation and stimulates cell death in an autoamplification loop named necroinflammation. Here, we studied necroptosis and necroinflammation in obstructive nephropathy induced by unilateral ureteral obstruction (UUO) in neonatal C57Bl/6J mice. Ureteral obstruction induced tubular dilatation, tubular basement membrane thickening, cast formation, and increased expression of kidney injury molecule-1 (KIM-1). Morphological investigations showed either apoptotic or necrotic cells in the tubular compartment. Biochemical analysis revealed increased caspase-8 activity and upregulation of RIPK3 as well as phosphorylated-MLKL in UUO-kidneys. Pro-inflammatory cytokines (IL-1α, INF-γ, TNF-α) were upregulated following UUO. Taken together we show that necroptosis and necroinflammation are accompanied phenomena in neonatal kidneys with obstruction. These findings may help to develop novel strategies to treat congenital obstructive nephropathy.

Pleiotropic Effects of IL-33 on CD4+ T Cell Differentiation and Effector Functions

IL-33, a member of the IL-1 family of cytokines, was originally described in 2005 as a promoter of type 2 immune responses. However, recent evidence reveals a more complex picture. This cytokine is released locally as an alarmin upon cellular damage where innate cell types respond to IL-33 by modulating their differentiation and influencing the polarizing signals they provide to T cells at the time of antigen presentation. Moreover, the prominent expression of the IL-33 receptor, ST2, on GATA3+ T helper 2 cells (TH2) demonstrated that IL-33 could have a direct impact on T cells. Recent observations reveal that T-bet+ TH1 cells and Foxp3+ regulatory T (TREG) cells can also express the ST2 receptor, either transiently or permanently. As such, IL-33 can have a direct effect on the dynamics of T cell populations. As IL-33 release was shown to play both an inflammatory and a suppressive role, understanding the complex effect of this cytokine on T cell homeostasis is paramount. In this review, we will focus on the factors that modulate ST2 expression on T cells, the effect of IL-33 on helper T cell responses and the role of IL-33 on TREG cell function.

Identification of the IL-33 protein segment that controls subcellular localization, extracellular secretion, and functional maturation

Proteolytic activation of the IL-33 precursor, full-length interleukin-33 (FLIL33), at multiple sites within the sensor domain (aa 95-109) yields several functionally mature (MIL33) forms. Unlike nuclear FLIL33, intracellular MIL33 occurs in the cytoplasm, is secreted from source cells, and exerts biological effects by activating the ST2 receptor on target cells. Previous studies and our findings in this report indicated that IL-33 forms that are substantially longer than those produced by cleavage within the sensor domain are biologically indistinguishable from classical MIL33. We utilized a series of human and mouse N-terminal FLIL33 mutants to narrow down the boundaries of the nuclear localization sequence to aa 46-67, a segment known to include a portion of the chromatin-binding motif as well as another site controlling intracellular stability of FLIL33 in an importin-5-dependent fashion. The N-terminal FLIL33 deletion mutants starting prior to this region were intranuclear, non-secreted in cell culture, and manifested modest functional activity in vivo, similar to FLIL33. By contrast, the mutants starting after this region were cytoplasmic, secreted from cells in culture, and overtly biologically active in vivo, similar to MIL33. The deletion mutants starting within this region manifested an intermediate phenotype between FLIL33 and MIL33. Thus, this segment of IL-33 molecule controls multiple aspects of its biology, including subcellular localization, extracellular secretion, and functional maturation into the longest possible form of mature IL-33 cytokine. Future anti-IL-33 therapies may be based on interfering with this segment, thus restraining extracellular release and maturation of IL-33 into the active cytokine.

BLT1 signaling in epithelial cells mediates allergic sensitization via promotion of IL-33 production

BACKGROUND

Epithelial cells (ECs) play a crucial role in allergic sensitization to inhaled protease allergens by instructing type 2 innate lymphoid cells (ILC2) and dendritic cells (DCs) via release of pro-type 2 cytokines, particularly interleukin-33 (IL-33). Leukotriene B4 (LTB4) is a well-known leukocyte chemoattractant via engagement of its receptor 1 (BLT1). However, the role of LTB4-BLT1 axis in allergic sensitization via activation of ECs is still unknown.

METHODS

We evaluated the effect of LTB4-BLT1 axis on IL-33 expression and ILC2 activation in vivo and in vitro. Chimeric mice were established to evaluate the contribution of BLT1 expression in nonimmune cell to allergic sensitization.

RESULTS

Genetical or pharmacological interruption of LTB4-BLT1 axis during sensitization phase markedly reduced papain-induced IL-33 expression, decreased ILC2 activation and DC migration, thereby impairing the priming of allergic Th2 responses. Furthermore, papain inhalation induced a rapid release of LTB4 preceding IL-33, and intranasal administration of LTB4 to naïve WT mice significantly increased IL-33 expression and ILC2 activation in lung, which was absent in Il33^-/- or Ltb4r1^-/- mice. Furthermore, BLT1 was expressed in primary mouse ECs or normal human bronchial ECs (NHBE), and papain induced LTB4 release by NHBE, which in turn amplified IL-33 production dependent on Akt activation via BLT1. Consequently, bone marrow chimeric mice lacking BLT1 in radio-resistant structural cells failed to develop allergic lung inflammation to papain.

CONCLUSION

Our study reveals a functional role of LTB4-BLT1 axis in nonimmune cells, most likely lung ECs, in controlling allergic sensitization as an upstream regulator of IL-33.

IL-33 Is a Negative Regulator of Vaccine-Induced Antigen-Specific Cellular Immunity

The cytokine IL-33 is a well-established inducer of Th2 responses. However, roles for IL-33 in promoting CD8, Th1, and T regulatory cell responses have also emerged. In this study, the role of IL-33 as a regulator of particulate vaccine adjuvant-induced Ag-specific cellular immunity was investigated. We found that polymeric nanoparticles surpassed alum in their ability to enhance Ag-specific CD8 and Th1 responses. IL-33 was a potent negative regulator of both CD8⁺ T cell and Th1 responses following i.m. vaccination with Ag and nanoparticles, whereas the cytokine was required for the nanoparticle enhancement in Ag-specific IL-10. In contrast to the effect on cellular immunity, Ab responses were comparable between vaccinated wild-type and IL-33-deficient mice. IL-33 did not compromise alum-induced adaptive cellular immunity after i.m. vaccination. These data suggest that IL-33 attenuates the induction of cellular immune responses by nanoparticulate adjuvants and should be considered in the rational design of vaccines targeting enhanced CD8 and Th1 responses.

Interleukin-33 in Systemic Sclerosis: Expression and Pathogenesis

Interleukin-33 (IL-33), a member of the IL-1 superfamily, functions as a traditional cytokine and nuclear factor. It is proposed to have an “alarmin” role. IL-33 mediates biological effects by interacting with the ST2 receptor and IL-1 receptor accessory protein, particularly in innate immune cells and T helper 2 cells. Recent articles have described IL-33 as an emerging pro-fibrotic cytokine in the immune system as well as a novel potential target for systemic sclerosis. Here, we review the available information and focus on the pleiotropic expression and pathogenesis of IL-33 in systemic sclerosis, as well as the feasibility of using IL-33 in clinical applications.

IL-25 protects against high-fat diet-induced hepatic steatosis in mice by inducing IL-25 and M2a macrophage production

Interleukin (IL)-25 is a cytokine that has previously been shown to have a protective role against nonalcoholic fatty liver disease (NAFLD), which is associated with the induction of M2 macrophage differentiation. However, the direct relationships between IL-25 expression regulation, M2 induction and NAFLD remain unknown. In this study, we demonstrate that IL-25 promotes hepatic macrophage differentiation into M2a macrophages both in vivo and in vitro via the IL-13/STAT6 pathway. M2 macrophages that were differentiated in vitro were able to ameliorate high-fat diet HFD-induced hepatic steatosis. Furthermore, we found that IL-25 treatment, both in vitro and in vivo, promotes direct binding of STAT6 to the IL-25 gene promoter region. This binding of STAT6 in response to IL-25 treatment also resulted in the increase of IL-25 expression in hepatocytes. Together, these findings identify IL-25 as a protective factor against HFD-induced hepatic steatosis by inducing an increase of IL-25 expression in hepatocytes and through promotion of M2a macrophage production.

Conflicting vascular and metabolic impact of the IL-33/sST2 axis

Interleukin 33 (IL-33), which is expressed by several immune cell types, endothelial and epithelial cells, and fibroblasts, is a cytokine of the IL-1 family that acts both intra- and extracellularly to either enhance or resolve the inflammatory response. Intracellular IL-33 acts in the nucleus as a regulator of transcription. Once released from cells by mechanical stress, inflammatory cytokines, or necrosis, extracellular IL-33 is proteolytically processed to act in an autocrine/paracrine manner as an 'alarmin' on neighbouring or various immune cells expressing the ST2 receptor. Thus, IL-33 may serve an important role in tissue preservation and repair in response to injury; however, the actions of IL-33 are dampened by a soluble form of ST2 (sST2) that acts as a decoy receptor and is produced by endothelial and certain immune cells. Accumulating evidence supports the conclusion that sST2 is a biomarker of vascular health with diagnostic and/or prognostic value in various cardiovascular diseases, including coronary artery disease, myocardial infarction, atherosclerosis, giant-cell arteritis, acute aortic dissection, and ischaemic stroke, as well as obesity and diabetes. Although sST2 levels are positively associated with cardiovascular disease severity, the assumption that IL-33 is always beneficial is naïve. It is increasingly appreciated that the pathophysiological importance of IL-33 is highly dependent on cellular and temporal expression. Although IL-33 is atheroprotective and may prevent obesity and type 2 diabetes by regulating lipid metabolism, IL-33 appears to drive endothelial inflammation. Here, we review the current knowledge of the IL-33/ST2/sST2 signalling network and discuss its pathophysiological and translational implications in cardiovascular diseases.

Atopy-Dependent and Independent Immune Responses in the Heightened Severity of Atopics to Respiratory Viral Infections: Rat Model Studies

Allergic (Th2^high immunophenotype) asthmatics have a heightened susceptibility to common respiratory viral infections such as human rhinovirus. Evidence suggests that the innate interferon response is deficient in asthmatic/atopic individuals, while other studies show no differences in antiviral response pathways. Unsensitized and OVA-sensitized/challenged Th2^high (BN rats) and Th2^low immunophenotype (PVG rats) animals were inoculated intranasally with attenuated mengovirus (vMC₀). Sensitized animals were exposed/unexposed during the acute viral response phase. Cellular and transcriptomic profiling was performed on bronchoalveolar lavage cells. In unsensitized PVG rats, vMC₀ elicits a prototypical antiviral response (neutrophilic airways inflammation, upregulation of Th1/type I interferon-related pathways). In contrast, response to infection in the Th2^high BN rats was associated with a radically altered intrinsic host response to respiratory viral infection, characterized by macrophage influx/Th2-associated pathways. In sensitized animals, response to virus infection alone was not altered compared to unsensitized animals. However, allergen exposure of sensitized animals during viral infection unleashes a notably exaggerated airways inflammatory response profile orders of magnitude higher in BN versus PVG rats despite similar viral loads. The co-exposure responses in the Th2^high BN incorporated type I interferon/Th1, alternative macrophage activation/Th2 and Th17 signatures. Similar factors may underlie the hyper-susceptibility to infection-associated airways inflammation characteristic of the human Th2^high immunophenotype.

A network map of IL-33 signaling pathway

Interleukin-33 (IL-33) is a member of the IL-1 family of cytokines that play a central role in the regulation of immune responses. Its release from epithelial and endothelial cells is mediated by pro-inflammatory cytokines, cell damage and by recognition of pathogen-associated molecular patterns (PAMPs). The activity of IL-33 is mediated by binding to the IL-33 receptor complex (IL-33R) and activation of NF-κB signaling via the classical MyD88/IRAK/TRAF6 module. IL-33 also induces the phosphorylation and activation of ERK1/2, JNK, p38 and PI3K/AKT signaling modules resulting in the production and release of pro-inflammatory cytokines. Aberrant signaling by IL-33 has been implicated in the pathogenesis of several acute and chronic inflammatory diseases, including asthma, atopic dermatitis, rheumatoid arthritis and ulcerative colitis among others. Considering the biomedical importance of IL-33, we developed a pathway resource of signaling events mediated by IL-33/IL-33R in this study. Using data mined from the published literature, we describe an integrated pathway reaction map of IL-33/IL-33R consisting of 681 proteins and 765 reactions. These include information pertaining to 19 physical interaction events, 740 enzyme catalysis events, 6 protein translocation events, 4 activation/inhibition events, 9 transcriptional regulators and 2492 gene regulation events. The pathway map is publicly available through NetPath ( http://www.netpath.org /), a resource of human signaling pathways developed previously by our group. This resource will provide a platform to the scientific community in facilitating identification of novel therapeutic targets for diseases associated with dysregulated IL-33 signaling. Database URL: http://www.netpath.org/pathways?path_id=NetPath_120 .

The full-length interleukin-33 (FLIL33)-importin-5 interaction does not regulate nuclear localization of FLIL33 but controls its intracellular degradation

Human mature IL-33 is a member of the IL-1 family and a potent regulator of immunity through its pro-T helper cell 2 activity. Its precursor form, full-length interleukin-33 (FLIL33), is an intranuclear protein in many cell types, including fibroblasts, and its intracellular levels can change in response to stimuli. However, the mechanisms controlling the nuclear localization of FLIL33 or its stability in cells are not understood. Here, we identified importin-5 (IPO5), a member of the importin family of nuclear transport proteins, as an intracellular binding partner of FLIL33. By overexpressing various FLIL33 protein segments and variants in primary human lung fibroblasts and HEK293T cells, we show that FLIL33, but not mature interleukin-33, physically interacts with IPO5 and that this interaction localizes to a cluster of charged amino acids (positions 46-56) but not to an adjacent segment (positions 61-67) in the FLIL33 N-terminal region. siRNA-mediated IPO5 knockdown in cell culture did not affect nuclear localization of FLIL33. However, the IPO5 knockdown significantly decreased the intracellular levels of overexpressed FLIL33, reversed by treatment with the 20S proteasome inhibitor bortezomib. Furthermore, FLIL33 variants deficient in IPO5 binding remained intranuclear and exhibited decreased levels, which were also restored by the bortezomib treatment. These results indicate that the interaction between FLIL33 and IPO5 is localized to a specific segment of the FLIL33 protein, is not required for nuclear localization of FLIL33, and protects FLIL33 from proteasome-dependent degradation.

STAT1 Represses Cytokine-Producing Group 2 and Group 3 Innate Lymphoid Cells during Viral Infection

The appropriate orchestration of different arms of the immune response is critical during viral infection to promote efficient viral clearance while limiting immunopathology. However, the signals and mechanisms that guide this coordination are not fully understood. IFNs are produced at high levels during viral infection and have convergent signaling through STAT1. We hypothesized that STAT1 signaling during viral infection regulates the balance of innate lymphoid cells (ILC), a diverse class of lymphocytes that are poised to respond to environmental insults including viral infections with the potential for both antiviral or immunopathologic functions. During infection with respiratory syncytial virus (RSV), STAT1-deficient mice had reduced numbers of antiviral IFN-γ+ ILC1 and increased numbers of immunopathologic IL-5+ and IL-13+ ILC2 and IL-17A+ ILC3 compared with RSV-infected wild-type mice. Using bone marrow chimeric mice, we found that both ILC-intrinsic and ILC-extrinsic factors were responsible for this ILC dysregulation during viral infection in STAT1-deficient mice. Regarding ILC-extrinsic mechanisms, we found that STAT1-deficient mice had significantly increased expression of IL-33 and IL-23, cytokines that promote ILC2 and ILC3, respectively, compared with wild-type mice during RSV infection. Moreover, disruption of IL-33 or IL-23 signaling attenuated cytokine-producing ILC2 and ILC3 responses in STAT1-deficient mice during RSV infection. Collectively, these data demonstrate that STAT1 is a key orchestrator of cytokine-producing ILC responses during viral infection via ILC-extrinsic regulation of IL-33 and IL-23.

Innate Immune Cytokines, Fibroblast Phenotypes, and Regulation of Extracellular Matrix in Lung

Chronic inflammation can be caused by adaptive immune responses in autoimmune and allergic conditions, driven by a T lymphocyte subset balance (TH1, TH2, Th17, Th22, and/or Treg) and skewed cellular profiles in an antigen-specific manner. However, several chronic inflammatory diseases have no clearly defined adaptive immune mechanisms that drive chronicity. These conditions include those that affect the lung such as nonatopic asthma or idiopathic pulmonary fibrosis comprising significant health problems. The remodeling of extracellular matrix (ECM) causes organ dysfunction, and it is largely generated by fibroblasts as the major cell controlling net ECM. As such, these are potential targets of treatment approaches in the context of ECM pathology. Fibroblast phenotypes contribute to ECM and inflammatory cell accumulation, and they are integrated into chronic disease mechanisms including cancer. Evidence suggests that innate cytokine responses may be critical in nonallergic/nonautoimmune disease, and they enable environmental agent exposure mechanisms that are independent of adaptive immunity. Innate immune cytokines derived from macrophage subsets (M1/M2) and innate lymphoid cell (ILC) subsets can directly regulate fibroblast function. We also suggest that STAT3-activating gp130 cytokines can sensitize fibroblasts to the innate cytokine milieu to drive phenotypes and exacerbate existing adaptive responses. Here, we review evidence exploring innate cytokine regulation of fibroblast behavior.

Regulation of IL-33 by Oncostatin M in Mouse Lung Epithelial Cells

IL-33 modulates both innate and adaptive immune responses at tissue sites including lung and may play critical roles in inflammatory lung disease. Although IL-33 expression can be altered upon NF-Kappa B activation, here we examine regulation by Oncostatin M, a gp130 cytokine family member, in mouse lung tissue. Responses were assessed in BALB/c mouse lung at day 7 of transient overexpression using endotracheally administered adenovirus encoding OSM (AdOSM) or empty vector (AdDel70). Whole lung extracts showed induction of IL-33 mRNA (>20-fold) and protein (10-fold increase in immunoblots) by AdOSM relative to AdDel70. Immunohistochemistry for IL-33 indicated a marked induction of nuclear staining in alveolar epithelial cells in vivo. Oncostatin M stimulated IL-33 mRNA and IL-33 full length protein in C10 mouse type 2 alveolar epithelial cells in culture in time-dependent and dose-dependent fashion, whereas IL-6, LIF, IL-31, IL-4, or IL-13 did not, and TGFβ repressed IL-33. IL-33 induction was associated with activation of STAT3, and pharmacological inhibition of STAT3 ameliorated IL-33 levels. These results indicate Oncostatin M as a potent inducer of IL-33 in mouse lung epithelial cells and suggest that an OSM/IL-33 axis may participate in innate immunity and inflammatory conditions in lung.

Elevated expression of NEU1 sialidase in idiopathic pulmonary fibrosis provokes pulmonary collagen deposition, lymphocytosis, and fibrosis

Idiopathic pulmonary fibrosis (IPF) poses challenges to understanding its underlying cellular and molecular mechanisms and the development of better therapies. Previous studies suggest a pathophysiological role for neuraminidase 1 (NEU1), an enzyme that removes terminal sialic acid from glycoproteins. We observed increased NEU1 expression in epithelial and endothelial cells, as well as fibroblasts, in the lungs of patients with IPF compared with healthy control lungs. Recombinant adenovirus-mediated gene delivery of NEU1 to cultured primary human cells elicited profound changes in cellular phenotypes. Small airway epithelial cell migration was impaired in wounding assays, whereas, in pulmonary microvascular endothelial cells, NEU1 overexpression strongly impacted global gene expression, increased T cell adhesion to endothelial monolayers, and disrupted endothelial capillary-like tube formation. NEU1 overexpression in fibroblasts provoked increased levels of collagen types I and III, substantial changes in global gene expression, and accelerated degradation of matrix metalloproteinase-14. Intratracheal instillation of NEU1 encoding, but not control adenovirus, induced lymphocyte accumulation in bronchoalveolar lavage samples and lung tissues and elevations of pulmonary transforming growth factor-β and collagen. The lymphocytes were predominantly T cells, with CD8(+) cells exceeding CD4(+) cells by nearly twofold. These combined data indicate that elevated NEU1 expression alters functional activities of distinct lung cell types in vitro and recapitulates lymphocytic infiltration and collagen accumulation in vivo, consistent with mechanisms implicated in lung fibrosis.

Pharmacological In Vivo Inhibition of S-Nitrosoglutathione Reductase Attenuates Bleomycin-Induced Inflammation and Fibrosis

Interstitial lung disease (ILD) characterized by pulmonary fibrosis and inflammation poses a substantial biomedical challenge due to often negative disease outcomes combined with the need to develop better, more effective therapies. We assessed the in vivo effect of administration of a pharmacological inhibitor of S-nitrosoglutathione reductase, SPL-334 (4-{[2-[(2-cyanobenzyl)thio]-4-oxothieno[3,2-d]pyrimidin-3(4H)-yl]methyl}benzoic acid), in a mouse model of ILD induced by intratracheal instillation of bleomycin (BLM). Daily i.p. administration of SPL-334 alone at 0.3, 1.0, or 3.0 mg/kg had no effect on animal body weight, appearance, behavior, total and differential bronchoalveolar lavage (BAL) cell counts, or collagen accumulation in the lungs, showing no toxicity of our investigational compound. Similar administration of SPL-334 for 7 days before and for an additional 14 days after BLM instillation resulted in a preventive protective effect on the BLM challenge-induced decline in total body weight and changes in total and differential BAL cellularity. In the therapeutic treatment regimen, SPL-334 was administered at days 7-21 after BLM challenge. Such treatment attenuated the BLM challenge-induced decline in total body weight, changes in total and differential BAL cellularity, and magnitudes of histologic changes and collagen accumulation in the lungs. These changes were accompanied by an attenuation of BLM-induced elevations in pulmonary levels of profibrotic cytokines interleukin-6, monocyte chemoattractant protein-1, and transforming growth factor-β (TGF-β). Experiments in cell cultures of primary normal human lung fibroblast have demonstrated attenuation of TGF-β-induced upregulation in collagen by SPL-334. It was concluded that SPL-334 is a potential therapeutic agent for ILD.

Regulation rewiring analysis reveals mutual regulation between STAT1 and miR-155-5p in tumor immunosurveillance in seven major cancers

Transcription factors (TFs) and microRNAs (miRNAs) form a gene regulatory network (GRN) at the transcriptional and post-transcriptional level in living cells. However, this network has not been well characterized, especially in regards to the mutual regulations between TFs and miRNAs in cancers. In this study, we collected those regulations inferred by ChIP-Seq or CLIP-Seq to construct the GRN formed by TFs, miRNAs, and target genes. To increase the reliability of the proposed network and examine the regulation activity of TFs and miRNAs, we further incorporated the mRNA and miRNA expression profiles in seven cancer types using The Cancer Genome Atlas data. We observed that regulation rewiring was prevalent during tumorigenesis and found that the rewired regulatory feedback loops formed by TFs and miRNAs were highly associated with cancer. Interestingly, we identified one regulatory feedback loop between STAT1 and miR-155-5p that is consistently activated in all seven cancer types with its function to regulate tumor-related biological processes. Our results provide insights on the losing equilibrium of the regulatory feedback loop between STAT1 and miR-155-5p influencing tumorigenesis.