Variants of the IFI16 gene affecting the levels of expression of mRNA are associated with susceptibility to Behçet disease

PLK1-activating IFI16-STING-TBK1 pathway induces apoptosis of intestinal epithelial cells in patients with intestinal Behçet's syndrome

Inflammatory signals from immunological cells may cause damage to intestinal epithelial cells (IECs), resulting in intestinal inflammation and tissue impairment. Interferon-γ-inducible protein 16 (IFI16) was reported to be involved in the pathogenesis of Behçet's syndrome (BS). This study aimed to investigate how inflammatory cytokines released by immunological cells and IFI16 participate in the pathogenesis of intestinal BS. RNA sequencing and real-time quantitative PCR (qPCR) showed that the positive regulation of tumor necrosis factor-α (TNF-α) production in peripheral blood mononuclear cells (PBMCs) of intestinal BS patients may be related to the upregulation of polo like kinase 1 (PLK1) in PBMCs (P = 0.012). The plasma TNF-α protein level in intestinal BS was significantly higher than in healthy controls (HCs; P = 0.009). PBMCs of intestinal BS patients and HCs were co-cultured with human normal IECs (NCM460) to explore the interaction between immunological cells and IECs. Using IFI16 knockdown, PBMC-NCM460 co-culture, TNF-α neutralizing monoclonal antibody (mAb), stimulator of interferon genes (STING) agonist 2'3'-cGAMP, and the PLK1 inhibitor SBE 13 HCL, we found that PLK1 promotes the secretion of TNF-α from PBMCs of intestinal BS patients, which causes overexpression of IFI16 and induces apoptosis of IECs via the STING-TBK1 pathway. The expressions of IFI16, TNF-α, cleaved caspase 3, phosphorylated STING (pSTING) and phosphorylated tank binding kinase 1 (pTBK1) in the intestinal ulcer tissue of BS patients were significantly higher than that of HCs (all P < 0.05). PLK1 in PBMCs of intestinal BS patients increased TNF-α secretion, inducing IEC apoptosis via activation of the IFI16-STING-TBK1 pathway. PLK1 and the IFI16-STING-TBK1 pathway may be new therapeutic targets for intestinal BS.

Innate immune inflammatory cell death: PANoptosis and PANoptosomes in host defense and disease

Regulated cell death (RCD) triggered by innate immune activation is an important strategy for host survival during pathogen invasion and perturbations of cellular homeostasis. There are two main categories of RCD, including nonlytic and lytic pathways. Apoptosis is the most well-characterized nonlytic RCD, and the inflammatory pyroptosis and necroptosis pathways are among the best known lytic forms. While these were historically viewed as independent RCD pathways, extensive evidence of cross-talk among their molecular components created a knowledge gap in our mechanistic understanding of RCD and innate immune pathway components, which led to the identification of PANoptosis. PANoptosis is a unique innate immune inflammatory RCD pathway that is regulated by PANoptosome complexes upon sensing pathogens, pathogen-associated molecular patterns (PAMPs), damage-associated molecular patterns (DAMPs) or the cytokines produced downstream. Cytosolic innate immune sensors and regulators, such as ZBP1, AIM2 and RIPK1, promote the assembly of PANoptosomes to drive PANoptosis. In this review, we discuss the molecular components of the known PANoptosomes and highlight the mechanisms of PANoptosome assembly, activation and regulation identified to date. We also discuss how PANoptosomes and mutations in PANoptosome components are linked to diseases. Given the impact of RCD, and PANoptosis specifically, across the disease spectrum, improved understanding of PANoptosomes and their regulation will be critical for identifying new therapeutic targets and strategies.

Risk factors, clinical features and treatment of Behçet's disease uveitis

Behçet's disease is a systemic vasculitis frequently associated with intraocular inflammation. Recent findings identified independent clinical clusters in Behçet's disease, each involving distinct combinations of affected organs. Ocular Behçet's disease, mainly manifested as uveitis, is characterized as an independent cluster with a low likelihood of association with other system involvements, such as intestinal, cardiovascular, or central nervous system. A prevailing theory suggests that the pathogenesis of the disease is multifactorial, where a variety of genetic and infectious agents may interact with each other to cause the disease. Among sporadic cases, the human leukocyte antigen (HLA) genes, including HLA-B51, HLA-A26, HLA-B15, and HLA-B5701, have been found to be a key component conferring genetic susceptibility. Outside the HLA region, a set of susceptibility variants are identified, closely related to interleukin (IL)-23/IL-17 pathway, tumor necrosis factor (TNF) signaling, and pattern recognition receptor systems. Microbial infections, such as Streptococcus sanguinis, Mycobacterium tuberculosis, and Herpes simplex virus (HSV), are linked to play the triggering of disease in immunogenetically predisposed individuals. Clinically, due to the notable relapsing-remitting course of ocular Behçet's disease, the prevention of recurrent attack would be the primary treatment goal. Combination of corticosteroids and immunomodulatory drugs, such as anti-TNF agents, interferon, and conventional immunosuppressants (e.g. cyclosporine, azathioprine), have been the mainstream regimen for the disease. Future research may focus on comparing the effectiveness of immunomodulatory drugs and identifying the most suitable subgroups for a specific drug on the basis of the knowledge of the molecular heterogeneity of the disease.

Interferon activated gene 204 protects against bone loss in experimental periodontitis

BACKGROUND

Periodontal destruction can be the result of different known and yet-to-be-discovered biological pathways. Recent human genetic association studies have implicated interferon-gamma inducible protein 16 (IFI16) and absent in melanoma 2 (AIM2) with high periodontal interleukin (IL)-1β levels and more destructive disease, but mechanistic evidence is lacking. Here, we sought to experimentally validate these observational associations and better understand IFI16 and AIM2's roles in periodontitis.

METHODS

Periodontitis was induced in Ifi204-/- (IFI16 murine homolog) and Aim2-/- mice using the ligature model. Chimeric mice were created to identify the main source cells of Ifi204 in the periodontium. IFI16-silenced human endothelial cells were treated with periodontal pathogens in vitro. Periodontal tissues from Ifi204-/- mice were evaluated for alveolar bone (micro-CT), cell inflammatory infiltration (MPO+ staining), Il1b (qRT-PCR), and osteoclast numbers (cathepsin K+ staining).

RESULTS

Ifi204-deficient mice> exhibited >20% higher alveolar bone loss than wild-type (WT) (P < 0.05), while no significant difference was found in Aim2-/- mice. Ifi204's effect on bone loss was primarily mediated by a nonbone marrow source and was independent of Aim2. Ifi204-deficient mice had greater neutrophil/macrophage trafficking into gingival tissues regardless of periodontitis development compared to WT. In human endothelial cells, IFI16 decreased the chemokine response to periodontal pathogens. In murine periodontitis, Ifi204 depletion elevated gingival Il1b and increased osteoclast numbers at diseased sites (P < 0.05).

CONCLUSIONS

These findings support IFI16's role as a novel regulator of inflammatory cell trafficking to the periodontium that protects against bone loss and offers potential targets for the development of new periodontal disease biomarkers and therapeutics.

Genetics in Behcet's Disease: An Update Review

Behcet's disease (BD) is one of the most vision-threatening clinical entities of uveitis. Although the etiopathogenesis of BD remains obscure, accumulating evidence has demonstrated that both genetic and environmental factors may contribute to the development of BD. Genome-wide association studies (GWAS) and candidate association studies have identified several genetic variants strongly associated with BD, including variants in human leukocyte antigen (HLA) -A02, -A03, -A24, -A26, -A31, -B15, -B27, -B35, -B49, -B51, -B57, -B58, -C0704, CIITA, ERAP1, MICA, IL1A-IL1B, IL10, IL12, IL23R, IL-23R/IL-12RB2, IL1RL1-IL18R1, STAT4, TFCP2L1, TRAF5, TNFAIP3, CCR1/CCR3, RIPK2, ADO-ZNF365-EGR2, KLRC4, LACC1, MEFV, IRF8, FUT2, CEBPB-PTPN1, ZMIZ1, RPS6KA4, IL10RA, SIPA1-FIBP-FOSL1, VAMP1, JRKL/CTCN5, IFNGR1 and miRNA-146a. Epigenetic modifications are also reported to play essential roles in the development of BD, including DNA methylation and histone modification. We review here the recent advances in the genetic and epigenetic factors associated with the BD pathogenesis.

The role of the inflammasomes in the pathogenesis of uveitis

Uveitis is a diverse group of sight-threatening intraocular inflammatory diseases usually causing eye redness, pain, blurred vision, and sometimes blindness. Although the exact pathogenesis of uveitis is not yet clear, accumulating evidences have shown that an imbalanced regulation of immune responses caused by a combination of genetic and environmental factors are implicated in the pathogenesis of this disease. As critical regulators of inflammation, inflammasomes have been assumed to play a role in the pathogenesis of uveitis. Recent studies have reported the association between a number of genetic variants in inflammasome related genes (such as NLRP3, NLRP1, NLRC4 and AIM2) with increased risk to uveitis. Mounting evidence have shown an aberrant activation of the NLRP3 inflammasome in both uveitis patients and murine models of uveitis. Some studies explored the intervention of uveitis via modulating inflammasome activity in the eye. This review aims at summarizing the main findings of these studies, proposing the possible mechanism whereby inflammasomes affect the susceptibility to develop uveitis, and giving a perspective for future studies, which may further improve our understanding about the role of inflammasomes and related cytokines in the pathogenesis of uveitis, and may hopefully lead to new therapeutics by targeting inflammasomes.

Behçet disease: From pathogenesis to novel therapeutic options

Behçet disease (BD) is a complex, multi-systemic inflammatory condition mainly hallmarked by oral and genital ulcers which can also affect the vessels, gastrointestinal tract, central nervous system and even the axial skeleton. Without a clear classification among autoimmune or autoinflammatory conditions, BD has been recently classified as a MHC-I-opathy. BD aetiology is still obscure, but it is thought that certain microorganisms can elicit an aberrant adaptive immune response in the presence of a permissive genetic background. Altered T-cell homeostasis, mostly Th1/Th17 expansion and Treg impairment, could lead to an overactivation of the innate immunity, which underlies tissue damage and thus, signs and symptoms. Immunosuppression and/or immunomodulation are central to the BD management. A complex armamentarium ranging from classical synthetic disease-modifying antirrheumatic drugs to new-era biologic agents or small molecules is available in BD, with different therapeutic outcomes depending on disease manifestations. However, the precise disease mechanisms that underlie BD symptoms are not fully deciphered, which may limit their therapeutic potential and add a significant layer of complexity to the treatment decision-making process. The aim of the present review is to provide an exhaustive overview of the latest breakthroughs in BD pathogenesis and therapeutic options.

The Trinity of cGAS, TLR9, and ALRs Guardians of the Cellular Galaxy Against Host-Derived Self-DNA

The immune system has evolved to protect the host from the pathogens and allergens surrounding their environment. The immune system develops in such a way to recognize self and non-self and develops self-tolerance against self-proteins, nucleic acids, and other larger molecules. However, the broken immunological self-tolerance leads to the development of autoimmune or autoinflammatory diseases. Pattern-recognition receptors (PRRs) are expressed by immunological cells on their cell membrane and in the cytosol. Different Toll-like receptors (TLRs), Nod-like receptors (NLRs) and absent in melanoma-2 (AIM-2)-like receptors (ALRs) forming inflammasomes in the cytosol, RIG (retinoic acid-inducible gene)-1-like receptors (RLRs), and C-type lectin receptors (CLRs) are some of the PRRs. The DNA-sensing receptor cyclic GMP–AMP synthase (cGAS) is another PRR present in the cytosol and the nucleus. The present review describes the role of ALRs (AIM2), TLR9, and cGAS in recognizing the host cell DNA as a potent damage/danger-associated molecular pattern (DAMP), which moves out to the cytosol from its housing organelles (nucleus and mitochondria). The introduction opens with the concept that the immune system has evolved to recognize pathogens, the idea of horror autotoxicus, and its failure due to the emergence of autoimmune diseases (ADs), and the discovery of PRRs revolutionizing immunology. The second section describes the cGAS-STING signaling pathway mediated cytosolic self-DNA recognition, its evolution, characteristics of self-DNAs activating it, and its role in different inflammatory conditions. The third section describes the role of TLR9 in recognizing self-DNA in the endolysosomes during infections depending on the self-DNA characteristics and various inflammatory diseases. The fourth section discusses about AIM2 (an ALR), which also binds cytosolic self-DNA (with 80–300 base pairs or bp) that inhibits cGAS-STING-dependent type 1 IFN generation but induces inflammation and pyroptosis during different inflammatory conditions. Hence, this trinity of PRRs has evolved to recognize self-DNA as a potential DAMP and comes into action to guard the cellular galaxy. However, their dysregulation proves dangerous to the host and leads to several inflammatory conditions, including sterile-inflammatory conditions autoinflammatory and ADs.

Role of inflammasomes in the pathogenesis of periodontal disease and therapeutics

Inflammasomes are a group of multimolecular intracellular complexes assembled around several innate immune proteins. Recognition of a diverse range of microbial, stress and damage signals by inflammasomes results in direct activation of caspase‐1, which subsequently induces the only known form of secretion of active interleukin‐1β and interleukin‐18. Although the importance of interleukin‐1β in the periodontium is not questioned, the impact of inflammasomes in periodontal disease and its potential for therapeutics in periodontology is still in its very early stages. Increasing evidence in preclinical models and human data strongly implicate the involvement of inflammasomes in a number of inflammatory, autoinflammatory and autoimmune disorders. Here we review: (a) the currently known inflammasome functions, (b) clinical/preclinical data supporting inflammasome involvement in the context of periodontal and comorbid diseases and (c) potential therapies targeting inflammasomes. To clarify further the inflammasome involvement in periodontitis, we present analyses of data from a large clinical study (n = 5809) that measured the gingival crevicular fluid‐interleukin‐1β and grouped the participants based on current periodontal disease classifications. We review data on 4910 European‐Americans that correlate 16 polymorphisms in the interleukin‐1B region with high gingival crevicular fluid‐interleukin‐1β levels. We show that inflammasome components are increased in diseased periodontal tissues and that the caspase‐1 inhibitor, VX‐765, inhibits ~50% of alveolar bone loss in experimental periodontitis. The literature review further supports that although patients clinically present with the same phenotype, the disease that develops probably has different underlying biological pathways. The current data indicate that inflammasomes have a role in periodontal disease pathogenesis. Understanding the contribution of different inflammasomes to disease development and distinct patient susceptibility will probably translate into improved, personalized therapies.

Identifying the culprits in neurological autoimmune diseases

The target organ of neurological autoimmune diseases (NADs) is the central or peripheral nervous system. Multiple sclerosis (MS) is the most common NAD, whereas Guillain-Barré syndrome (GBS), myasthenia gravis (MG), and neuromyelitis optica (NMO) are less common NADs, but the incidence of these diseases has increased exponentially in the last few years. The identification of a specific culprit in NADs is challenging since a myriad of triggering factors interplay with each other to cause an autoimmune response. Among the factors that have been associated with NADs are genetic susceptibility, epigenetic mechanisms, and environmental factors such as infection, microbiota, vitamins, etc. This review focuses on the most studied culprits as well as the mechanisms used by these to trigger NADs.

•

Neurological autoimmune diseases are caused by a complex interaction between genes, environmental factors, and epigenetic deregulation.

•

Infectious agents can cause an autoimmune reaction to myelin epitopes through molecular mimicry and/or bystander activation.

•

Gut microbiota dysbiosis contributes to neurological autoimmune diseases.

•

Smoking increases the risk of NADs through inflammatory signaling pathways, oxidative stress, and Th17 differentiation.

•

Deficiency in vitamin D favors NAD development through direct damage to the central and peripheral nervous system.

Inflammasomes and autoimmune and rheumatic diseases: A comprehensive review

Inflammasomes are a multi-protein platform forming a part of the innate immune system. Inflammasomes are at standby status and can be activated when needed. Inflammasome activation is an important mechanism for the production of active interleukin (IL)-1β and IL-18, which have important roles to instruct adaptive immunity. Active forms of inflammasomes trigger a series of inflammatory cascades and lead to the differentiation and polarization of naïve T cells and secretion of various cytokines, which can induce various kinds of autoimmune and rheumatic diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), gout, Sjögren's syndrome, Behçet's disease, anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis and IgA vasculitis (former Henoch-Schönlein purpura ). In this review, we summarize studies published on inflammasomes and review their roles in various autoimmune diseases. Understanding of the role of inflammasomes may facilitate the diagnosis of autoimmune diseases and the development of tailored therapies in the future.

Cytosolic Nucleic Acid Sensors in Inflammatory and Autoimmune Disorders

Innate immunity employs germline-encoded pattern recognition receptors (PRRs) to sense microbial pattern molecules. Recognition of pathogen-associated molecular patterns (PAMPs) by various PPRs located on the cell membrane or in the cytosol leads to the activation of cell signaling pathways and production of inflammatory mediators. Nucleic acids including DNA, RNA, and their derivatives are potent PAMPs which can be recognized by multiple PRRs to induce inflammatory responses. While nucleic acid sensors can also sense endogenous nucleic acids, they are capable of discriminating self from non-self. However, defects in nucleic acid sensing PRRs or dysregulation of nucleic acid sensing signaling pathways may cause excessive activation of the immune system resulting in the development of inflammatory and autoimmune diseases. This review will discuss the major pathways for sensing intracellular nucleic acids and how defects in these nucleic acid sensing are associated with different kinds of autoimmune and inflammatory disorders.

The Absent in Melanoma 2-Like Receptor IFN-Inducible Protein 16 as an Inflammasome Regulator in Systemic Lupus Erythematosus: The Dark Side of Sensing Microbes

Absent in melanoma 2 (AIM2)-like receptors (ALRs) are a newly characterized class of pathogen recognition receptors (PRRs) involved in cytosolic and nuclear pathogen DNA recognition. In recent years, two ALR family members, the interferon (IFN)-inducible protein 16 (IFI16) and AIM2, have been linked to the pathogenesis of various autoimmune diseases, among which systemic lupus erythematosus (SLE) has recently gained increasing attention. SLE patients are indeed often characterized by constitutively high serum IFN levels and increased expression of IFN-stimulated genes due to an abnormal response to pathogens and/or incorrect self-DNA recognition process. Consistently, we and others have shown that IFI16 is overexpressed in a wide range of autoimmune diseases where it triggers production of specific autoantibodies. In addition, evidence from mouse models supports a model whereby ALRs are required for IFN-mediated host response to both exogenous and endogenous DNA. Following interaction with cytoplasmic or nuclear nucleic acids, ALRs can form a functional inflammasome through association with the adaptor ASC [apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD)] and with procaspase-1. Importantly, inflammasome-mediated upregulation of IL-1β and IL-18 production positively correlates with SLE disease severity. Therefore, targeting ALR sensors and their downstream pathways represents a promising alternative therapeutic approach for SLE and other systemic autoimmune diseases.

STING dependent sensing - Does HIV actually care?

Sensing of DNA is essential for the innate immune system to detect threats, like viruses, intracellular bacteria or cellular DNA damage. At the centre of this conserved mammalian mechanism stands the adaptor protein STING. STING is highly regulated and is part of a complex signalling network. This network depends on the sensors cGAS and IFI16 to detect misplaced DNA in the cytoplasm as well as on the kinase TBK1 and the transcription factor IRF3. The DNA sensing machinery has been implicated in many diseases, among others HIV. Here we present a comprehensive review of current status on the STING pathway with all its components and regulations related to HIV pathogenesis. By this, we try to answer the question if STING-mediated DNA sensing plays a role in HIV infections.

Inflammasomes and dermatology

Inflammasomes are intracellular multiprotein complexes that comprise part of the innate immune response. Since their definition, inflammasome disorders have been linked to an increasing number of diseases. Autoinflammatory diseases refer to disorders in which local factors lead to the activation of innate immune cells, causing tissue damage when in the absence of autoantigens and autoantibodies. Skin symptoms include the main features of monogenic inflammasomopathies, such as Cryopyrin-Associated Periodic Syndromes (CAPS), Familial Mediterranean Fever (FMF), Schnitzler Syndrome, Hyper-IgD Syndrome (HIDS), PAPA Syndrome, and Deficiency of IL-1 Receptor Antagonist (DIRA). Concepts from other pathologies have also been reviewed in recent years, such as psoriasis, after the recognition of a combined contribution of innate and adaptive immunity in its pathogenesis. Inflammasomes are also involved in the response to various infections, malignancies, such as melanoma, autoimmune diseases, including vitiligo and lupus erythematosus, atopic and contact dermatitis, acne, hidradenitis suppurativa, among others. Inhibition of the inflammasome pathway may be a target for future therapies, as already occurs in the handling of CAPS, through the introduction of IL-1 inhibitors. This study presents a literature review focusing on the participation of inflammasomes in skin diseases.

Common Polymorphisms in IFI16 and AIM2 Genes Are Associated With Periodontal Disease

BACKGROUND

The single nucleotide polymorphism (SNP) context of a previously identified periodontitis-associated locus is investigated, and its association with microbial, biologic, and periodontal disease clinical parameters is examined.

METHODS

A 200-kb spanning region of 1q12 previously highlighted in a genome-wide association scan among 4,766 European American individuals (SNP rs1633266) was annotated. Two haplotype blocks were selected. Association of these polymorphisms with data on microbial plaque composition, gingival crevicular fluid (GCF)-interleukin (IL)-1β levels, and clinical parameters of periodontal disease were examined. Descriptive analysis of IFI16 and AIM2 protein expression in gingival tissues from healthy individuals (n = 2) and individuals with chronic periodontitis (n = 2) was done via immunohistochemistry.

RESULTS

The highlighted locus is a 100-kb region containing the interferon γ-inducible protein 16 (IFI16) and absent in melanoma 2 (AIM2) genes. Two haplotype blocks, rs6940 and rs1057028, were significantly associated with increased extent bleeding on probing and levels of microorganisms Porphyromonas gingivalis, Tannerella forsythia, and Campylobacter rectus (P ≤0.05). Haplotype block rs1057028 was also significantly associated with pathogens Fusobacterium nucleatum and Aggregatibacter actinomycetemcomitans, increased GCF-IL-1β levels, and extent of probing depth ≥4 mm (P ≤0.05). Prevalence of severe periodontitis (biofilm-gingival interface P3 classification) was positively associated with haplotype block rs1057028. Similar trends were observed for haplotype block rs1057028. IFI16 and AIM2 protein expression was observed in multiple cell types of gingival tissues, including inflammatory cells.

CONCLUSION

This study found IFI16 and AIM2 SNPs associated with higher levels of periodontal microorganisms and an increased percentage of periodontal disease clinical parameters, suggesting the need for functional studies and additional fine-mapping of variants in the 1q12-locus.

The potential of genetically guided treatment in Behçet's disease

Continuous identification of specific targets and candidate genes together with novel approaches offers new promises for the future of gene therapy design in Behçet's disease (BD). Personalized medicine based on pharmacogenomics is being developed at the clinical stage to improve treatment response. Screening the whole gene and regulatory regions is important when searching for novel variants associated with such complex diseases. Different host genetic factors play significant roles in susceptibility to BD. Thus, identifying these genes responsible for susceptibility and resistance to BD may offer a notable contribution toward understanding its pathogenesis, and may lead to the development of novel prophylactic and treatment strategies. Evidenced-based treatment strategy is recommended for the management in BD patients. This review sheds light on the immunopathogenesis and pharmacogenetics of BD with special attention to the treatment targeting gene polymorphisms. In conclusion, the potential of genetically guided treatment in BD takes us back to the future for an accurate management strategy of this serious rheumatic disease. The ongoing discovery of pivotal genes related to the susceptibility, manifestations, disease activity and treatment options provide substantial hope to the reduced frequency of BD, effective control and improvement in the prognosis. Targeted gene therapy could be a leading option in the treatment armamentarium of BD.