IL-37d Negatively Regulates NLRP3 Transcription via Receptor-mediated Pathway and Alleviates DSS-induced Colitis

IL-37d enhances COP1-mediated C/EBPβ degradation to suppress spontaneous neutrophil migration and tumor progression

The spontaneous migration of bone marrow neutrophils (BMNs) is typically induced by distant tumor cells during the early stage of the tumor and critically controls tumor progression and metastases. Therefore, identifying the key molecule that prevents this process is extremely important for suppressing tumors. Interleukin-37 (IL-37) can suppress pro-inflammatory cytokine generation via an IL-1R8- or Smad3-mediated pathway. Here, we demonstrate that human neutrophil IL-37 is responsively reduced by tumor cells and the recombinant IL-37 isoform d (IL-37d) significantly inhibits spontaneous BMN migration and tumor lesion formation in the lung by negatively modulating CCAAT/enhancer binding protein beta (C/EBPβ) in a Lewis lung carcinoma (LLC)-inducing lung cancer mouse model. Mechanistically, IL-37d promotes C/EBPβ ubiquitination degradation by facilitating ubiquitin ligase COP1 recruitment and disrupts C/EBPβ DNA binding abilities, thereby reducing neutrophil ATP generation and migration. Our work reveals an anti-tumor mechanism for IL-37 via destabilization of C/EBPβ to prevent spontaneous BMN migration and tumor progression.

Interleukin-37 ameliorates atherosclerosis by regulating autophagy-mediated endothelial cell apoptosis and inflammation

Atherosclerosis is a lipid-driven chronic inflammatory disease. Endothelial dysfunction is the initiating factor of atherosclerosis. Although much work has been done on the antiatherosclerotic effects of interleukin-37 (IL-37), the exact mechanism is still not fully understood. The aim of this study was to investigate whether IL-37 attenuates atherosclerosis by protecting endothelial cells and to confirm whether autophagy plays a role in this effect. In apolipoprotein E knockout (ApoE-/-) mice fed with a high fat diet, IL-37 treatment significantly attenuated progression of atherosclerotic plaques, reduced endothelial cell apoptosis and inflammasome activation. Human umbilical vein endothelial cells (HUVECs) were treated with oxidized low-density lipoprotein (ox-LDL) to establish an endothelial dysfunction model. We observed that IL-37 alleviated ox-LDL-induced endothelial cell inflammation and dysfunction, as evidenced by decreased nod-like receptor pyrin domain-containing 3 (NLRP3) inflammasome activation, ROS production, apoptosis rate and secretion of inflammatory cytokines IL-1β and TNF-α. Furthermore, IL-37 could activate autophagy in endothelial cells, which is characterized by the upregulation of LC3II/LC3I, the downregulation of p62 and an increase in autophagosomes. The autophagy inhibitor 3-Methyladenine (3-MA) dramatically reversed the promotion of autophagy and the protective effect of IL-37 against endothelial injury. Our data illustrate that IL-37 alleviated inflammation and apoptosis of atherosclerotic endothelial cells by enhancing autophagy. The current study provides new insights and promising therapeutic strategies for atherosclerosis.

IL-37 alleviates TNF-α-induced pyroptosis of rheumatoid arthritis fibroblast-like synoviocytes by inhibiting the NF-κB/GSDMD signaling pathway

OBJECTIVE

Pyroptosis is crucial to rheumatoid arthritis (RA) by inducing and aggravating inflammation. TNF-α is abundant in fibroblast-like synoviocytes of RA (RA-FLSs) and plays a key role in pyroptosis by inducing nuclear factor (NF)-κB activation. Additionally, interleukin (IL)-37 is involved in autoimmune diseases as an anti-inflammatory cytokine and innate and acquired immune response inhibitor. However, the effect of IL-37 on pyroptosis in RA-FLSs remains unclear. Therefore, this study investigated the effects and mechanism of IL-37 on RA-FLS pyroptosis induced by TNF-α.

METHODS

In this study, the serum cytokines in patients with RA and healthy controls were detected using ELISA. The RA-FLSs were then cultured with TNF-α, with or without various IL-37 concentrations, to test the cytokine levels in the cell supernatant. 5-Ethynyl-2'-Deoxyuridine (EdU) assay assessed the effects of IL-37 on RA FLS proliferation. RA-FLS apoptosis was assessed using flow cytometry and mitochondrial membrane potential (MMP) measurement. In addition, transmission electron microscopy (TEM) was used to examine cell pyroptosis. We selected the optimal concentration for the following experiments and detected the signal pathway of IL-37 on pyroptosis of RA FLSs by quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and Western blotting. Finally, we validated the therapeutic effects of IL-37 on CIA rat model in vivo.

RESULTS

IL-37 inhibited inflammation in vitro and in vivo and reduced pyroptosis-related protein expression in RA FLSs. Furthermore, we determined that nuclear factor κB (NF-κB) signaling is required for GSDMD-mediated pyroptosis in RA FLSs.

CONCLUSION

IL-37 alleviates TNF-α-induced pyroptosis of RA FLSs by inhibiting NF-κB/GSDMD signaling. Additionally, our data revealed a novel mechanism for IL-37 in RA FLSs, suggesting a new potential therapy for IL-37 to treat RA.

IL-1R8: A molecular brake of anti-tumor and anti-viral activity of NK cells and ILC

Interleukin-1 receptor family members (ILRs) and Toll-Like Receptors (TLRs) play pivotal role in immunity and inflammation and are expressed by most cell types including cells of both the innate and adaptive immune system. In this context, IL-1 superfamily members are also important players in regulating function and differentiation of adaptive and innate lymphoid cells. This system is tightly regulated in order to avoid uncontrolled activation, which may lead to detrimental inflammation contributing to autoimmune or allergic responses. IL-1R8 (also known as TIR8 or SIGIRR) is a member of the IL-1R family that acts as a negative regulator dampening ILR and TLR signaling and as a co-receptor for human IL-37. Human and mouse NK cells, that are key players in immune surveillance of tumors and infections, express high level of IL-1R8. In this review, we will summarize our current understanding on the structure, expression and function of IL-1R8 and we will also discuss the emerging role of IL-1R8 as an important checkpoint regulating NK cells function in pathological conditions including cancer and viral infections.

IL-37 alleviates alveolar bone resorption and inflammatory response through the NF-κB/NLRP3 signaling pathway in male mice with periodontitis

OBJECTIVE

Periodontitis is an inflammatory disease, characterized by periodontal pocket formation and alveolar bone resorption, is one of the most common oral diseases. Interleukin-37 (IL-37) is a novel inflammatory suppressor that plays an important role in many inflammatory diseases. This study aimed to investigate the role of IL-37 in periodontitis DESIGN: A mouse model of periodontitis was established by Porphyromonas gingivalis. After four weeks treatment of recombinant human IL-37 (rhIL-37), the effects of IL-37 on the gingival index and tooth loosening degree of periodontitis mice were observed. H&E staining and micro-CT scanning were used to analyze the bone resorption of the maxillary. The number of osteoclasts was counted by TRAP staining and the differentiation of osteoclasts was evaluated by immunohistochemistry. The expression of inflammatory cytokines was detected by ELISA, and the protein expressions of the NF-κB/NLRP3 pathway were analyzed by WB.

RESULTS

RhIL-37 significantly decreased the gingival index and tooth mobility degree, inhibited maxillary bone resorption, decreased the number of osteoclasts and the expression of calcitonin receptor (CTR), periodontal cathepsin K (CTSK) and receptor activator of NF-κB ligand (RANKL), and increased the expression of osteoprotegerin (OPG) in periodontitis mice. At the same time, rhIL-37 significantly decreased the expression of IL-1β, IL-6 and TNF-α, and increased the expression of IL-10 in the gingival tissue of periodontitis mice. In addition, rhIL-37 significantly inhibited the protein expressions of p-p65, NLRP3, ASC, caspase-1 and IL-1β in periodontitis mice.

CONCLUSION

IL-37 may alleviate alveolar bone resorption and inflammation response in periodontitis through the NF-κB/NLRP3 pathway.

IL-37 alleviates Coxsackievirus B3-induced viral myocarditis via inhibiting NLRP3 inflammasome-mediated pyroptosis

Our study aims to verify the potential effects and underlying mechanisms of IL-37 in Coxsackievirus B3 (CVB3)-induced viral myocarditis (VMC). VMC model was established by intraperitoneal injection of CVB3 into 6-week-old male balb-c mice on day 0. Each mouse of the IL-37-control group and IL-37-VMC CVB3 groups was intraperitoneally injected with IL-37 on day 4 and day 7. The cardiac function was evaluated by transthoracic echocardiography including LVEF, LVFE, IVSs and IVSd. Myocardial injury was measured by Elisa for serum cTnI. The inflammation infiltration and fibrosis were evaluated by hematoxylin and eosin (HE) staining and Masson staining. The expression levels of NLRP3 inflammasome components in pyroptosis were determined by western blot, Elisa, and immunofluorescent analysis. We also detected the expression of IL-37-IL-1R8 in PBMCs by immunofluorescence after injection with CVB3 and IL-37. Compared with the VMC group, mice received CVB3 and IL-37 have improved cardiac function, reduced inflammation infiltration and fibrosis, and with lower expression of cTnI, IL-1β, IL-18 and NLRP3 inflammasome component. IL-37 weakened the upregulation of GSDMD and phosphorylation of NF-κB p65 induced by CVB3. Exogenous addition of IL-37 with CVB3 further increases the production of IL-37-IL-1R8 -IL-18RA complex in vitro. Our findings indicate that IL-37 alleviates CVB3-induced VMC, which may be produced by inhibiting NLRP3 inflammasome-mediated pyroptosis, NF-κB signaling pathway, and IL-37-IL-1R8 -IL-18RA complex.

High-fat diet alleviates colitis by inhibiting ferroptosis via solute carrier family 7 member 11

A high-fat diet (HFD) is reported to exacerbate ulcerative colitis by inducing obesity, which conceals the effect of the diet itself. Ferroptosis, a type of regulated cell death induced by lipid hydroperoxides, has recently been reported in colitis. Here, we aimed to determine whether HFD affects ferroptosis and colitis progression in an obesity-independent manner. We subjected male C57BL/6J mice to either an HFD (60% fat diet) or isocaloric control diet (10% fat diet) for 4 weeks, followed by inducing colitis with 2.5% dextran sulfate sodium (DSS). Compared with the isocaloric control diet, non-obesogenic HFD reduced DSS-induced colonic mucosal injury, as shown by disease activity index, colon thickness, inflammatory infiltrations, and mucosal damage index; however, there were no differences in body weight, Lee's index, and omental fat weight between the two groups. HFD mice exhibited decreased lipid peroxidation and ferroptosis marker expression in colon tissues. Furthermore, a lipid mixture protected gut organoids and normal colonic epithelial cells from RSL3-induced ferroptosis. Mechanistically, the lipid mixture prevented glutathione deficiency by upregulating the cysteine transporter, solute carrier family 7 member 11. Collectively, these findings suggest that an HFD ameliorates DSS-induced colitis through ferroptosis repression in an obesity-independent manner and provide new evidence to evaluate the effects of an HFD on colitis.

Interleukin-37 exacerbates experimental colitis in an intestinal microbiome-dependent fashion

Background: Inflammatory bowel disease (IBD) involves complicated crosstalk between host immunity and the gut microbiome, whereas the mechanics of how they govern intestinal inflammation remain poorly understood. In this study, we investigated the contribution of environmental factors to shaping gut microbiota composition in colitis mice that were transgenic for human IL-37, a natural anti-inflammatory cytokine possessing pathogenic and protective functions related to microbiota alterations. Methods: Mice transgenic expressing human IL-37 (IL-37tg) were housed under conventional and specific pathogen-free (SPF) conditions to develop a mouse model of dextran sulfate sodium (DSS)-induced colitis. 16S ribosomal RNA sequencing was used for analyzing fecal microbial communities. The efficacy of microbiota in the development of colitis in IL-37tg mice was investigated after antibiotic treatment and fecal microbiota transplantation (FMT). The mechanism by which IL-37 worsened colitis was studied by evaluating intestinal epithelial barrier function, immune cell infiltration, the expression of diverse cytokines and chemokines, as well as activated signaling pathways. Results: We found that IL-37 overexpression aggravated DSS-induced colitis in conventional mice but protected against colitis in SPF mice. These conflicting results from IL-37tg colitis mice are ascribed to a dysbiosis of the gut microbiota in which detrimental bacteria increased in IL-37tg conventional mice. We further identified that the outcome of IL-37-caused colon inflammation is strongly related to intestinal epithelial barrier impairment caused by pathogenic bacteria, neutrophils, and NK cells recruitment in colon lamina propria and mesenteric lymph node to enhance inflammatory responses in IL-37tg conventional mice. Conclusions: The immunoregulatory properties of IL-37 are detrimental in the face of dysbiosis of the intestinal microbiota, which contributes to exacerbated IBD occurrences that are uncontrollable by the immune system, suggesting that depleting gut pathogenic bacteria or maintaining intestinal microbial and immune homeostasis could be a promising therapeutic strategy for IBD.

IL-1R8 as Pathoimmunological Marker for Severity of Canine Chronic Enteropathy

Chronic enteropathy (CE) is a severe multifactorial gastrointestinal disease that affects dogs and is driven by poorly characterized inflammatory pathways. Imbalance of pro-inflammatory response regulators, including IL-1R8, may be due to different factors, among which the infection with Helicobacteraceae is known to lead to a vicious circle in which excessive pro-inflammatory signaling and gastrointestinal injury reinforce each other and boost the disease. We investigated the expression of IL-1R8 in large intestine biopsies of dogs with or without clinical signs of CE and with previously assessed enterohepatic Helicobacter spp. colonization status by mean of quantitative real-time PCR. Our study revealed that IL-1R8 is downregulated in both acutely (p = 0.0074) and chronically (p = 0.0159) CE affected dogs compared to healthy controls. The data also showed that IL-1R8 expression tends to decrease with colonization by Helicobacter spp. Interestingly, a negative correlation was detected between the level of expression of IL-1R8 and the severity of macroscopic lesions identified by endoscopy and the crypt hyperplasia score. We further compared the expression levels between males and females and found no statistically significant difference between the two groups. No significant difference was observed in IL-1R8 expression profiles with the age of the animals either. Interestingly, an association was uncovered between IL-1R8 expression level and dog breed. Together, our data advance knowledge on gastrointestinal pathoimmunology in dogs and highlight the potential utilization of IL-1R8 as a diagnostic, prognostic and therapeutic biomarker for canine chronic enteropathy.

IL-37 isoform D acts as an inhibitor of soluble ST2 to boost type 2 immune homeostasis in white adipose tissue

White adipose tissue (WAT) homeostasis substantiated by type 2 immunity is indispensable to counteract obesity and metabolic disorders. IL-33/suppression of tumorigenicity (ST) 2 signaling promotes type 2 response in WAT, while potential regulators remain to be discovered. We identified human IL-37 isoform D (IL-37D) as an effective trigger for ST2-mediated type 2 immune homeostasis in WAT. IL-37D transgene amplified ST2⁺ immune cells, promoted M2 macrophage polarization and type 2 cytokine secretion in WAT that mediate beiging and inflammation resolution, thereby increasing energy expenditure, reducing obesity and insulin resistance in high-fat diet (HFD)-fed mice. Mechanistically, either endogenous or exogenous IL-37D inhibited soluble ST2 (sST2) production from WAT challenged with HFD or TNF-α. Recombinant sST2 impaired the beneficial effects of IL-37D transgene in HFD-fed mice, characterized by damaged weight loss, insulin action, and type 2 cytokine secretion from WAT. In adipose-derived stem cells, IL-37D inhibited TNF-α-stimulated sST2 expression through IL-1 receptor 8 (IL-1R8)-dependent NF-κB inactivation. Collectively, human IL-37D suppresses sST2 to boost type 2 immune homeostasis in WAT, which may be a promising therapy target for obesity and metabolic disorders.

Negative Regulation of the IL-1 System by IL-1R2 and IL-1R8: Relevance in Pathophysiology and Disease

Interleukin-1 (IL-1) is a primary cytokine of innate immunity and inflammation. IL-1 belongs to a complex family including ligands with agonist activity, receptor antagonists, and an anti-inflammatory cytokine. The receptors for these ligands, the IL-1 Receptor (IL-1R) family, include signaling receptor complexes, decoy receptors, and negative regulators. Agonists and regulatory molecules co-evolved, suggesting the evolutionary relevance of a tight control of inflammatory responses, which ensures a balance between amplification of innate immunity and uncontrolled inflammation. IL-1 family members interact with innate immunity cells promoting innate immunity, as well as with innate and adaptive lymphoid cells, contributing to their differentiation and functional polarization and plasticity. Here we will review the properties of two key regulatory receptors of the IL-1 system, IL-1R2, the first decoy receptor identified, and IL-1R8, a pleiotropic regulator of different IL-1 family members and co-receptor for IL-37, the anti-inflammatory member of the IL-1 family. Their complex impact in pathology, ranging from infections and inflammatory responses, to cancer and neurologic disorders, as well as clinical implications and potential therapeutic exploitation will be presented.

Current Understanding of IL-37 in Human Health and Disease

IL-37 is a recently discovered cytokine in the IL-1 family exerting broad protective effects on inflammatory diseases, autoimmune diseases, and cancer. Immune and non-immune cells produce the IL-37 precursor upon pro-inflammatory stimuli. Intracellularly, caspase-1 cleaves and activates IL-37, and its mature form binds to Smad3; this complex translocates into the nucleus where it suppresses cytokine production, consequently reducing inflammation. Extracellularly, IL-37 forms a complex with IL-18Rα and IL-1R8 (formerly TIR8 or SIGIRR) that transduces anti-inflammatory signals by the suppression of NF-κB and MAPK and the activation of Mer-PTEN-DOK pathways. During inflammation, IL-37 suppresses the expression of several pro-inflammatory cytokine in favor to the expression of the anti-inflammatory ones by the regulation of macrophage polarization, lipid metabolism, inflammasome function, TSLP synthesis and miRNAs function. Moreover, IL-37 not only regulates the innate and acquired immunity, but also improves aging-associated immunosenescence. Furthermore, IL-37 exerts an inhibitory effect on tumor angiogenesis and metastasis, and progression. Finally, IL-37 may have a potential ability to reduce excessive inflammation since it is aberrantly expressed in patients with inflammatory diseases, autoimmune diseases, and cancer, thus, it may be used as a marker for different types of diseases. Therefore, this review provides an updated view of the role of IL-37 in human health and disease, and discusses the potential of IL-37 as a therapeutic target and biomarker in inflammatory diseases, autoimmune diseases, and cancer.

IL-37b alleviates endothelial cell apoptosis and inflammation in Kawasaki disease through IL-1R8 pathway

Kawasaki disease (KD) is an acute vasculitis of pediatric populations that may develop coronary artery aneurysms if untreated. It has been regarded as the principal cause of acquired heart disease in children of the developed countries. Interleukin (IL)-37, as one of the IL-1 family members, is a natural suppressor of inflammation that is caused by activation of innate and adaptive immunity. However, detailed roles of IL-37 in KD are largely unclear. Sera from patients with KD displayed that IL-37 level was significantly decreased compared with healthy controls (HCs). QRT-PCR and western blot analyses showed that the expression level of IL-37 variant, IL-37b, was remarkably downregulated in human umbilical vein endothelial cells (HUVECs) exposed to KD sera-treated THP1 cells. Therefore, we researched the role of IL-37b in the context of KD and hypothesized that IL-37b may have a powerful protective effect in KD patients. We first observed and substantiated the protective role of IL-37b in a mouse model of KD induced by Candida albicans cell wall extracts (CAWS). In vitro experiments demonstrated that IL-37b alleviated endothelial cell apoptosis and inflammation via IL-1R8 receptor by inhibiting ERK and NFκB activation, which were also recapitulated in the KD mouse model. Together, our findings suggest that IL-37b play an effective protective role in coronary endothelial damage in KD, providing new evidence that IL-37b is a potential candidate drug to treat KD.

An update on the regulatory mechanisms of NLRP3 inflammasome activation

The NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome is a multiprotein complex involved in the release of mature interleukin-1β and triggering of pyroptosis, which is of paramount importance in a variety of physiological and pathological conditions. Over the past decade, considerable advances have been made in elucidating the molecular mechanisms underlying the priming/licensing (Signal 1) and assembly (Signal 2) involved in NLRP3 inflammasome activation. Recently, a number of studies have indicated that the priming/licensing step is regulated by complicated mechanisms at both the transcriptional and posttranslational levels. In this review, we discuss the current understanding of the mechanistic details of NLRP3 inflammasome activation with a particular emphasis on protein-protein interactions, posttranslational modifications, and spatiotemporal regulation of the NLRP3 inflammasome machinery. We also present a detailed summary of multiple positive and/or negative regulatory pathways providing upstream signals that culminate in NLRP3 inflammasome complex assembly. A better understanding of the molecular mechanisms underlying NLRP3 inflammasome activation will provide opportunities for the development of methods for the prevention and treatment of NLRP3 inflammasome-related diseases.