Activated STING in a vascular and pulmonary syndrome

Radiation-Induced Immunity and Toxicities: The Versatility of the cGAS-STING Pathway

In the past decade, radiation therapy (RT) entered the era of personalized medicine, following the striking improvements in radiation delivery and treatment planning optimization, and in the understanding of the cancer response, including the immunological response. The next challenge is to identify the optimal radiation regimen(s) to induce a clinically relevant anti-tumor immunity response. Organs at risks and the tumor microenvironment (e.g. endothelial cells, macrophages and fibroblasts) often limit the radiation regimen effects due to adverse toxicities. Here, we reviewed how RT can modulate the immune response involved in the tumor control and side effects associated with inflammatory processes. Moreover, we discussed the versatile roles of tumor microenvironment components during RT, how the innate immune sensing of RT-induced genotoxicity, through the cGAS-STING pathway, might link the anti-tumor immune response, radiation-induced necrosis and radiation-induced fibrosis, and how a better understanding of the switch between favorable and deleterious events might help to define innovative approaches to increase RT benefits in patients with cancer.

Augmentation of STING-induced type I interferon production in COPA syndrome

OBJECTIVES

COPA syndrome, also known as an autoinflammatory interstitial lung, joint, and kidney (AILJK) disease, is caused by heterozygous mutations in the coatomer subunit alpha (COPA) gene. We found a novel COPA variant in four patients in one family. We aimed to elucidate whether and how the variant causes manifestations of COPA syndrome by studying these four patients and in a gene-targeted mouse model.

METHOD

We performed whole exome sequencing in seven family members and measured type I interferon (IFN) signature of the peripheral blood cells. We analyzed the effects of COPA variants in in vitro experiments and Copa mutant mice we generated.

RESULTS

We identified a heterozygous variant of COPA gene in the four affected members of the family (c.725T>G, p.Val242Gly). IFN score was high in the members carrying the variant. In vitro analysis revealed that COPA V242G as well as the previously reported disease-causing variants augmented the stimulator of interferon genes (STING)-induced type I IFN promoter activities. Copa^V242G/+ mice manifested interstitial lung disease and STING-dependent elevation of IFN-stimulated genes (ISGs) expression. In Copa^V242G/+ dendritic cells, the STING pathway was not constitutively activated, but hyperactivated upon stimulation and led to increased type I IFN production.

CONCLUSION

V242G, a novel COPA variant, was found in four patients from one family. The gene-targeted mice with V242G variant recapitulated the interstitial lung disease and showed augmented responses of the STING pathway leading to increase of type I IFN production.

Small molecule approaches to treat autoimmune and inflammatory diseases (Part II): Nucleic acid sensing antagonists and inhibitors

Nucleic acid sensing pathways play an important role in the innate immune system, protecting hosts against infections. However, a large body of evidence supports a close association between aberrant activation of those pathways and autoimmune and inflammatory diseases. Part II of the digest series on small molecule approaches to autoimmune and inflammatory diseases concentrates on recent advances with respect to small molecule antagonists or inhibitors of the nucleic acid sensing pathways, including endosomal TLRs, NLRP3 inflammasome and cGAS-STING.

STING Operation at the ER/Golgi Interface

DNA is present in the nucleus and mitochondria of eukaryotic cells. There are, however, certain instances in which DNA emerges in the cytosol. The two major sources of cytosolic DNA are self DNA that is leaked out from the nucleus or mitochondria, and non-self DNA from DNA viruses. The cytosolic DNA triggers the host immune response. Recent studies have identified two key molecules, cyclic GMP-AMP (cGAMP) synthase (cGAS) and stimulator of interferon genes (STING) in this immune response. STING is an endoplasmic reticulum (ER) protein. After STING binding to cGAMP, STING exits the ER and translocates to the Golgi, where STING triggers the type I interferon- and proinflammatory responses through the activation of interferon regulatory factor 3 (IRF3) and nuclear factor-kappa B (NF-κB). STING also activates other cellular responses including cell senescence, autophagy, and cell death. In this review, we focus on emerging issues regarding the regulation of STING by membrane traffic, with a particular focus on the retrograde membrane traffic from the Golgi to the ER. The retrograde membrane traffic is recently shown by us and others to be critical for silencing the STING signaling pathway and the defect in this traffic underlies the pathogenesis of the COPA syndrome, a monogenic autoinflammatory disease caused by missense mutations of coatomer protein complex subunit α (COP-α).

The role of interferons type I, II and III in myositis: A review

The classification of idiopathic inflammatory myopathies (IIM) is based on clinical, serological and histological criteria. The identification of myositis-specific antibodies has helped to define more homogeneous groups of myositis into four dominant subsets: dermatomyositis (DM), antisynthetase syndrome (ASyS), sporadic inclusion body myositis (sIBM) and immune-mediated necrotising myopathy (IMNM). sIBM and IMNM patients present predominantly with muscle involvement, whereas DM and ASyS patients present additionally with other extramuscular features, such as skin, lung and joints manifestations. Moreover, the pathophysiological mechanisms are distinct between each myositis subsets. Recently, interferon (IFN) pathways have been identified as key players implicated in the pathophysiology of myositis. In DM, the key role of IFN, especially type I IFN, has been supported by the identification of an IFN signature in muscle, blood and skin of DM patients. In addition, DM-specific antibodies are targeting antigens involved in the IFN signalling pathways. The pathogenicity of type I IFN has been demonstrated by the identification of mutations in the IFN pathways leading to genetic diseases, the monogenic interferonopathies. This constitutive activation of IFN signalling pathways induces systemic manifestations such as interstitial lung disease, myositis and skin rashes. Since DM patients share similar features in the context of an acquired activation of the IFN signalling pathways, we may extend underlying concepts of monogenic diseases to acquired interferonopathy such as DM. Conversely, in ASyS, available data suggest a role of type II IFN in blood, muscle and lung. Indeed, transcriptomic analyses highlighted a type II IFN gene expression in ASyS muscle tissue. In sIBM, type II IFN appears to be an important cytokine involved in muscle inflammation mechanisms and potentially linked to myodegenerative features. For IMNM, currently published data are scarce, suggesting a minor implication of type II IFN. This review highlights the involvement of different IFN subtypes and their specific molecular mechanisms in each myositis subset.

Transferrable protection by gut microbes against STING-associated lung disease

STING modulates immunity by responding to bacterial and endogenous cyclic dinucleotides (CDNs). Humans and mice with STING gain-of-function mutations develop a syndrome known as STING-associated vasculopathy with onset in infancy (SAVI), which is characterized by inflammatory or fibrosing lung disease. We hypothesized that hyperresponsiveness of gain-of-function STING to bacterial CDNs might explain autoinflammatory lung disease in SAVI mice. We report that depletion of gut microbes with oral antibiotics (vancomycin, neomycin, and ampicillin [VNA]) nearly eliminates lung disease in SAVI mice, implying that gut microbes might promote STING-associated autoinflammation. However, we show that germ-free SAVI mice still develop severe autoinflammatory disease and that transferring gut microbiota from antibiotics-treated mice to germ-free animals eliminates lung inflammation. Depletion of anaerobes with metronidazole abolishes the protective effect of the VNA antibiotics cocktail, and recolonization with the metronidazole-sensitive anaerobe Bacteroides thetaiotaomicron prevents disease, confirming a protective role of a metronidazole-sensitive microbe in a model of SAVI.

Platt et al. report that oral antibiotics but not germ-free conditions prevent autoinflammatory lung disease in a mouse model of STING-associated vasculopathy with onset in infancy (SAVI). Recolonization of SAVI mice with either Bacteroidales-enriched stool or Bacteroides thetaiotaomicron is protective in this model of STING-associated autoinflammatory lung disease.

Pulmonary granulomatosis of genetic origin

Granulomatous inflammation of the lung can be a manifestation of different conditions and can be caused by endogenous inflammation or external triggers. A multitude of different genetic mutations can either predispose patients to infections with granuloma-forming pathogens or cause autoinflammatory disorders, both leading to the phenotype of pulmonary granulomatosis. Based on a detailed patient history, physical examination and a diagnostic approach including laboratory workup, pulmonary function tests (PFTs), computed tomography (CT) scans, bronchoscopy with bronchoalveolar lavage (BAL), lung biopsies and specialised microbiological and immunological diagnostics, a correct diagnosis of an underlying cause of pulmonary granulomatosis of genetic origin can be made and appropriate therapy can be initiated. Depending on the underlying disorder, treatment approaches can include antimicrobial therapy, immunosuppression and even haematopoietic stem cell transplantation (HSCT). Patients with immunodeficiencies and autoinflammatory conditions are at the highest risk of developing pulmonary granulomatosis of genetic origin. Here we provide a review on these disorders and discuss pathogenesis, clinical presentation, diagnostic approach and treatment.

Pulmonary granulomatosis of genetic origin mostly occurs in immunodeficiency disorders and autoinflammatory conditions. In addition to specific approaches in this regard, the diagnostic workup needs to cover environmental and occupational aspects.https://bit.ly/31SqdHW

Pinpointing cysteine oxidation sites by high-resolution proteomics reveals a mechanism of redox-dependent inhibition of human STING

Protein function is regulated by posttranslational modifications (PTMs), among which reversible oxidation of cysteine residues has emerged as a key regulatory mechanism of cellular responses. Given the redox regulation of virus-host interactions, the identification of oxidized cysteine sites in cells is essential to understand the underlying mechanisms involved. Here, we present a proteome-wide identification of reversibly oxidized cysteine sites in oxidant-treated cells using a maleimide-based bioswitch method coupled to mass spectrometry analysis. We identified 2720 unique oxidized cysteine sites within 1473 proteins with distinct abundances, locations, and functions. Oxidized cysteine sites were found in numerous signaling pathways, many relevant to virus-host interactions. We focused on the oxidation of STING, the central adaptor of the innate immune type I interferon pathway, which is stimulated in response to the detection of cytosolic DNA by cGAS. We demonstrated the reversible oxidation of Cys¹⁴⁸ and Cys²⁰⁶ of STING in cells. Molecular analyses led us to establish a model in which Cys¹⁴⁸ oxidation is constitutive, whereas Cys²⁰⁶ oxidation is inducible by oxidative stress or by the natural ligand of STING, 2'3'-cGAMP. Our data suggest that the oxidation of Cys²⁰⁶ prevented hyperactivation of STING by causing a conformational change associated with the formation of inactive polymers containing intermolecular disulfide bonds. This finding should aid the design of therapies targeting STING that are relevant to autoinflammatory disorders, immunotherapies, and vaccines.

Balasubramide derivative 3C attenuates atherosclerosis in apolipoprotein E-deficient mice: role of AMPK-STAT1-STING signaling pathway

We previously reported the neuroprotective effects of (+)-balasubramide derived compound 3C, but its action on atherosclerosis in vivo remains unknown. The study was designed to investigate the potential effects of 3C on atherogenesis and explore the possible underlying mechanisms. 3C ameliorated high-fat diet-induced body weight gain, hyperlipidemia, and atherosclerotic plaque burden in apolipoprotein E-deficient (ApoE^-/-) mice after 10 weeks of treatment. 3C suppressed the expression of genes involved in triglyceride synthesis in liver. 3C prevented aortic inflammation as evidenced by reduction of adhesive molecule levels and macrophage infiltration. Mechanistic studies revealed that activation of AMP-activated protein kinase (AMPK) is central to the athero-protective effects of 3C. Increased AMPK activity by 3C resulted in suppressing interferon-γ (IFN-γ) induced activation of signal transducer and activator of transcription-1 (STAT1) and stimulator of interferon genes (STING) signaling pathways and downstream pro-inflammatory markers. Moreover, 3C inhibited ox-LDL triggered lipid accumulation and IFN-γ induced phenotypic switch toward M1 macrophage in RAW 264.7 cells. Our present data suggest that 3C prevents atherosclerosis via pleiotropic effects, including amelioration of lipid profiles, vascular inflammation and macrophage pro-inflammatory phenotype. 3C has the potential to be developed as a promising drug for atherosclerosis and related cardiovascular disease.

Emerging mechanisms of immunocoagulation in sepsis and septic shock

Sepsis and septic shock driven by microbial infections are still among the most challenging health problems, causing 11 million deaths worldwide every year. How does the host's response to pathogen infections effectively restore homeostasis instead of precipitating pathogenic and potentially fatal feedforward reactions? Recently, there have been significant new advances in our understanding of the interface between mammalian immunity and coagulation ('immunocoagulation') and its impact on sepsis. In particular, the release and activation of F3 (the main initiator of coagulation) from and on myeloid or epithelial cells is facilitated by activating inflammasomes and consequent gasdermin D (GSDMD)-mediated pyroptosis, coupled to signaling via high mobility group box 1 (HMGB1), stimulator of interferon response CGAMP interactor 1 (STING1), or sequestosome 1 (SQSTM1). Pharmacological modulation of the immunocoagulation pathways emerge as novel and potential therapeutic strategies for sepsis.

UNC93B1 curbs cytosolic DNA signaling by promoting STING degradation

UNC93B1 is a trafficking chaperone of endosomal Toll-like receptors (TLRs) and plays an essential role in the TLR-mediated innate signaling. However, whether it is also involved in other innate immune sensing or cellular pathways remains largely unexplored. Here we investigated the role of UNC93B1 in cytosolic DNA-triggered cGAS-STING signaling in mouse and human cell lines. We showed that while UNC93B1 deficiency blunts the signal transduction by TLR3, it augments innate immune responses to cytosolic DNA stimulation and DNA virus infection. Mechanistic study reveals a distinct action of UNC93B1 upon STING, but not other parts along the cGAS-STING-TBK1 axis, through regulating the protein level of STING at both resting and cytosolic DNA-stimulated conditions. UNC93B1 can directly interact and traffic along with STING, and the disruption of this interaction causes accumulation of STING that subsequently leads to augmented signaling responses upon its activation. These findings reveal a new function of UNC93B1 in negatively regulating STING-mediated signaling responses.

Innate Immunity in Diabetic Wound Healing: Focus on the Mastermind Hidden in Chronic Inflammatory

A growing body of evidence suggests that the interaction between immune and metabolic responses is essential for maintaining tissue and organ homeostasis. These interacting disorders contribute to the development of chronic diseases associated with immune-aging such as diabetes, obesity, atherosclerosis, and nonalcoholic fatty liver disease. In Diabetic wound (DW), innate immune cells respond to the Pathogen-associated molecular patterns (PAMAs) and/or Damage-associated molecular patterns (DAMPs), changes from resting to an active phenotype, and play an important role in the triggering and maintenance of inflammation. Furthermore, the abnormal activation of innate immune pathways secondary to immune-aging also plays a key role in DW healing. Here, we review studies of innate immune cellular molecular events that identify metabolic disorders in the local microenvironment of DW and provide a historical perspective. At the same time, we describe some of the recent progress, such as TLR receptor-mediated intracellular signaling pathways that lead to the activation of NF-κB and the production of various pro-inflammatory mediators, NLRP3 inflammatory via pyroptosis, induction of IL-1β and IL-18, cGAS-STING responds to mitochondrial injury and endoplasmic reticulum stress, links sensing of metabolic stress to activation of pro-inflammatory cascades. Besides, JAK-STAT is also involved in DW healing by mediating the action of various innate immune effectors. Finally, we discuss the great potential of targeting these innate immune pathways and reprogramming innate immune cell phenotypes in DW therapy.

Genetic Mosaicism as a Cause of Inborn Errors of Immunity

Inborn errors of immunity (IEIs) are a heterogeneous group of disorders due to genetic defects in the immune response that have a broad clinical spectrum. Diagnosis of the precise genetic cause of IEI has led to improved care and treatment of patients; however, genetic diagnosis using standard approaches is only successful in ~40% of patients and is particularly challenging in “sporadic” cases without a family history. Standard genetic testing for IEI evaluates for germline changes in genes encoding proteins important for the immune response. It is now clear that IEI can also arise from de novo mutations leading to genetic variants present in germ cells and/or somatic cells. In particular, somatic mosaicism, i.e., post-zygotic genetic changes in DNA sequence, is emerging as a significant contributor to IEI. Testing for somatic mosaicism can be challenging, and both older sequencing techniques such as Sanger sequencing and newer next-generation sequencing may not be sensitive enough to detect variants depending on the platform and analysis tools used. Investigation of multiple tissue samples and specifically targeting sequence technologies to detect low frequency variants is important for detection of variants. This review examines the role and functional consequences of genetic mosaicism in IEI. We emphasize the need to refine the current exome and genome analysis pipeline to efficiently identify mosaic variants and recommend considering somatic mosaicism in disease discovery and in the first-tier of genetic analysis.

Golgi apparatus-synthesized sulfated glycosaminoglycans mediate polymerization and activation of the cGAMP sensor STING

Activation of the cyclic guanosine monophosphate (GMP)-AMP (cGAMP) sensor STING requires its translocation from the endoplasmic reticulum to the Golgi apparatus and subsequent polymerization. Using a genome-wide CRISPR-Cas9 screen to define factors critical for STING activation in cells, we identified proteins critical for biosynthesis of sulfated glycosaminoglycans (sGAGs) in the Golgi apparatus. Binding of sGAGs promoted STING polymerization through luminal, positively charged, polar residues. These residues are evolutionarily conserved, and selective mutation of specific residues inhibited STING activation. Purified or chemically synthesized sGAGs induced STING polymerization and activation of the kinase TBK1. The chain length and O-linked sulfation of sGAGs directly affected the level of STING polymerization and, therefore, its activation. Reducing the expression of Slc35b2 to inhibit GAG sulfation in mice impaired responses to vaccinia virus infection. Thus, sGAGs in the Golgi apparatus are necessary and sufficient to drive STING polymerization, providing a mechanistic understanding of the requirement for endoplasmic reticulum (ER)-to-Golgi apparatus translocation for STING activation.

A STING antagonist modulating the interaction with STIM1 blocks ER-to-Golgi trafficking and inhibits lupus pathology

BACKGROUND

Nucleic acids are potent stimulators of type I interferon (IFN-I) and antiviral defense, but may also promote pathological inflammation. A range of diseases are characterized by elevated IFN-I, including systemic lupus erythematosus (lupus). The DNA-activated cGAS-STING pathway is a major IFN-I-inducing pathway, and activation of signaling is dependent on trafficking of STING from the ER to the Golgi.

METHODS

Here we used cell culture systems, a mouse lupus model, and material from lupus patients, to explore the mode of action of a STING antagonistic peptide, and its ability to modulate disease processes.

FINDINGS

We report that the peptide ISD017 selectively inhibits all known down-stream activities of STING, including IFN-I, inflammatory cytokines, autophagy, and apoptosis. ISD017 blocks the essential trafficking of STING from the ER to Golgi through a mechanism dependent on the STING ER retention factor STIM1. Importantly, ISD017 blocks STING activity in vivo and ameliorates disease development in a mouse model for lupus. Finally, ISD017 treatment blocks pathological cytokine responses in cells from lupus patients with elevated IFN-I levels.

INTERPRETATION

These data hold promise for beneficial use of STING-targeting therapy in lupus.

FUNDING

The Novo Nordisk Foundation, The European Research Council, The Lundbeck Foundation, European Union under the Horizon 2020 Research, Deutsche Forschungsgemeinschaft, Chulalongkorn University.

The STING phase-separator suppresses innate immune signalling

Biomolecular condensates (biocondensates) formed via liquid-liquid phase-separation of soluble proteins have been studied extensively. However, neither the phase-separation of endoplasmic reticulum (ER) transmembrane protein nor a biocondensate with organized membranous structures has been reported. Here, we have discovered a spherical ER membranous biocondensate with puzzle-like structures caused by condensation of the ER-resident stimulator of interferon genes (STING) in DNA virus-infected or 2'3'-cGAMP (cyclic GMP-AMP)-treated cells, which required STING transmembrane domains, an intrinsically disordered region (IDR) and a dimerization domain. Intracellular 2'3'-cGAMP concentrations determined STING translocation or condensation. STING biocondensates constrained STING and TBK1 (TANK binding protein 1) to prevent innate immunity from overactivation, presumably acting like a 'STING-TBK1-cGAMP sponge'. Cells expressing STING-E³³⁶G/E³³⁷G showed notably enhanced innate immune responses due to impaired STING condensation after viral infection at later stages. Microtubule inhibitors impeded the STING condensate gel-like transition and augmented type I-interferon production in DNA virus-infected cells. This membranous biocondensate was therefore named the STING phase-separator.

Stimulator of Interferon Genes-associated Vasculopathy with an Onset in Infancy Diagnosed after the Development of Atypical Pulmonary Lesions During Treatment as Juvenile Idiopathic Arthritis

An 18-year-old man showed swelling, pain, and limited motion of the hand, knee, and foot joints without X-ray abnormalities at 2 years old (X-16). In X-12, interstitial pneumonia was observed. He was diagnosed with juvenile idiopathic arthritis associated with interstitial pneumonia and received immunosuppressive therapy. However, interstitial pneumonia progressed, and in X-2, he was referred to our hospital. Whole-exome sequencing and an in silico analysis revealed a gain-of-function mutation in TMEM173 (p.R281Q), and he was diagnosed with stimulator of interferon genes (STING)-associated vasculopathy with onset in infancy (SAVI). We encountered the first SAVI case in Japan.

Deficiency of the innate immune adaptor STING promotes autoreactive T cell expansion in NOD mice

AIMS/HYPOTHESIS

Stimulator of IFN genes (STING) is a central hub for cytosolic nucleic acid sensing and its activation results in upregulation of type I IFN production in innate immune cells. A type I IFN gene signature seen before the onset of type 1 diabetes has been suggested as a driver of disease initiation both in humans and in the NOD mouse model. A possible source of type I IFN is through activation of the STING pathway. Recent studies suggest that STING also has antiproliferative and proapoptotic functions in T cells that are independent of IFN. To investigate whether STING is involved in autoimmune diabetes, we examined the impact of genetic deletion of STING in NOD mice.

METHODS

CRISPR/Cas9 gene editing was used to generate STING-deficient NOD mice. Quantitative real-time PCR was used to assess the level of type I IFN-regulated genes in islets from wild-type and STING-deficient NOD mice. The number of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)206-214-specific CD8+ T cells was determined by magnetic bead-based MHC tetramer enrichment and flow cytometry. The incidence of spontaneous diabetes and diabetes after adoptive transfer of T cells was determined.

RESULTS

STING deficiency partially attenuated the type I IFN gene signature in islets but did not suppress insulitis. STING-deficient NOD mice accumulated an increased number of IGRP206-214-specific CD8+ T cells (2878 ± 642 cells in NOD.STING-/- mice and 728.8 ± 196 cells in wild-type NOD mice) in peripheral lymphoid tissue, associated with a higher incidence of spontaneous diabetes (95.5% in NOD.STING-/- mice and 86.2% in wild-type NOD mice). Splenocytes from STING-deficient mice rapidly induced diabetes after adoptive transfer into irradiated NOD recipients (median survival 75 days for NOD recipients of NOD.STING-/- mouse splenocytes and 121 days for NOD recipients of NOD mouse splenocytes).

CONCLUSIONS/INTERPRETATION

Data suggest that sensing of endogenous nucleic acids through the STING pathway may be partially responsible for the type I IFN gene signature but not autoimmunity in NOD mice. Our results show that the STING pathway may play an unexpected intrinsic role in suppressing the number of diabetogenic T cells.

Type I Interferonopathies in Children: An Overview

Notable advances in gene sequencing methods in recent years have permitted enormous progress in the phenotypic and genotypic characterization of autoinflammatory syndromes. Interferonopathies are a recent group of inherited autoinflammatory diseases, characterized by a dysregulation of the interferon pathway, leading to constitutive upregulation of its activation mechanisms or downregulation of negative regulatory systems. They are clinically heterogeneous, but some peculiar clinical features may lead to suspicion: a familial "idiopathic" juvenile arthritis resistant to conventional treatments, an early necrotizing vasculitis, a non-infectious interstitial lung disease, and a panniculitis associated or not with a lipodystrophy may represent the "interferon alarm bells." The awareness of this group of diseases represents a challenge for pediatricians because, despite being rare, a differential diagnosis with the most common childhood rheumatological and immunological disorders is mandatory. Furthermore, the characterization of interferonopathy molecular pathogenetic mechanisms is allowing important steps forward in other immune dysregulation diseases, such as systemic lupus erythematosus and inflammatory myositis, implementing the opportunity of a more effective target therapy.

cGAS-STING Pathway Does Not Promote Autoimmunity in Murine Models of SLE

Detection of DNA is an important determinant of host-defense but also a driver of autoinflammatory and autoimmune diseases. Failure to degrade self-DNA in DNAseII or III(TREX1)-deficient mice results in activation of the cGAS-STING pathway. Deficiency of cGAS or STING in these models ameliorates disease manifestations. However, the contribution of the cGAS-STING pathway, relative to endosomal TLRs, in systemic lupus erythematosus (SLE) is controversial. In fact, STING deficiency failed to rescue, and actually exacerbated, disease manifestations in Fas-deficient SLE-prone mice. We have now extended these observations to a chronic model of SLE induced by the i.p. injection of TMPD (pristane). We found that both cGAS- and STING-deficiency not only failed to rescue mice from TMPD-induced SLE, but resulted in increased autoantibody production and higher proteinuria levels compared to cGAS STING sufficient mice. Further, we generated cGAS^KOFas^lpr mice on a pure MRL/Fas^lpr background using Crispr/Cas9 and found slightly exacerbated, and not attenuated, disease. We hypothesized that the cGAS-STING pathway constrains TLR activation, and thereby limits autoimmune manifestations in these two models. Consistent with this premise, mice lacking cGAS and Unc93B1 or STING and Unc93B1 developed minimal systemic autoimmunity as compared to cGAS or STING single knock out animals. Nevertheless, TMPD-driven lupus in B6 mice was abrogated upon AAV-delivery of DNAse I, implicating a DNA trigger. Overall, this study demonstrated that the cGAS-STING pathway does not promote systemic autoimmunity in murine models of SLE. These data have important implications for cGAS-STING-directed therapies being developed for the treatment of systemic autoimmunity.

IFN Regulatory Factor 3 in Health and Disease

Immunity to viruses requires an array of critical cellular proteins that include IFN regulatory factor 3 (IRF3). Consequently, most viruses that infect vertebrates encode proteins that interfere with IRF3 activation. This review describes the cellular pathways linked to IRF3 activation and where those pathways are targeted by human viral pathogens. Moreover, key regulatory pathways that control IRF3 are discussed. Besides viral infections, IRF3 is also involved in resistance to some bacterial infections, in anticancer immunity, and in anticancer therapies involving DNA damage agents. A recent finding shows that IRF3 is needed for T cell effector functions that are involved in anticancer immunity and also in T cell autoimmune diseases. In contrast, unregulated IRF3 activity is clearly not beneficial, considering it is implicated in certain interferonopathies, in which heightened IRF3 activity leads to IFN-β-induced disease. Therefore, IRF3 is involved largely in maintaining health but sometimes contributing to disease.

Somatic Mutations in UBA1 Define a Distinct Subset of Relapsing Polychondritis Patients With VEXAS

OBJECTIVE

Somatic mutations in UBA1 cause a newly defined syndrome known as VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic syndrome). More than 50% of patients currently identified as having VEXAS met diagnostic criteria for relapsing polychondritis (RP), but clinical features that characterize VEXAS within a cohort of patients with RP have not been defined. We undertook this study to define the prevalence of somatic mutations in UBA1 in patients with RP and to create an algorithm to identify patients with genetically confirmed VEXAS among those with RP.

METHODS

Exome and targeted sequencing of UBA1 was performed in a prospective observational cohort of patients with RP. Clinical and immunologic characteristics of patients with RP were compared based on the presence or absence of UBA1 mutations. The random forest method was used to derive a clinical algorithm to identify patients with UBA1 mutations.

RESULTS

Seven of 92 patients with RP (7.6%) had UBA1 mutations (referred to here as VEXAS-RP). Patients with VEXAS-RP were all male, were on average ≥45 years of age at disease onset, and commonly had fever, ear chondritis, skin involvement, deep vein thrombosis, and pulmonary infiltrates. No patient with VEXAS-RP had chondritis of the airways or costochondritis. Mortality was greater in VEXAS-RP than in RP (23% versus 4%; P = 0.029). Elevated acute-phase reactants and hematologic abnormalities (e.g., macrocytic anemia, thrombocytopenia, lymphopenia, multiple myeloma, myelodysplastic syndrome) were prevalent in VEXAS-RP. A decision tree algorithm based on male sex, a mean corpuscular volume >100 fl, and a platelet count <200 ×10³ /μl differentiated VEXAS-RP from RP with 100% sensitivity and 96% specificity.

CONCLUSION

Mutations in UBA1 were causal for disease in a subset of patients with RP. This subset of patients was defined by disease onset in the fifth decade of life or later, male sex, ear/nose chondritis, and hematologic abnormalities. Early identification is important in VEXAS given the associated high mortality rate.

Nucleic Acid Sensors as Therapeutic Targets for Human Disease

Innate immune sensors that detect nucleic acids are attractive targets for therapeutic intervention because of their diverse roles in many disease processes. In detecting RNA and DNA from either self or non-self, nucleic acid sensors mediate the pathogenesis of many autoimmune and inflammatory conditions. Despite promising pre-clinical data and investigational use in the clinic, relatively few drugs targeting nucleic acid sensors are approved for therapeutic use. Nevertheless, there is growing appreciation for the untapped potential of nucleic acid sensors as therapeutic targets, driven by the need for better therapies for cancer, infectious diseases, and autoimmune disorders. This review highlights the diverse mechanisms by which nucleic acid sensors are activated and exert their biological effects in the context of various disease settings. We discuss current therapeutic strategies utilizing agonists and antagonists targeting nucleic acid sensors to treat infectious disease, cancer, and autoimmune and inflammatory disorders.

Case Report: Novel SAVI-Causing Variants in STING1 Expand the Clinical Disease Spectrum and Suggest a Refined Model of STING Activation

Gain-of-function mutations in STING1 cause the monogenic interferonopathy, SAVI, which presents with early-onset systemic inflammation, cold-induced vasculopathy and/or interstitial lung disease. We identified 5 patients (3 kindreds) with predominantly peripheral vascular disease who harbor 3 novel STING1 variants, p.H72N, p.F153V, and p.G158A. The latter two were predicted by a previous cryo-EM structure model to cause STING autoactivation. The p.H72N variant in exon 3, however, is the first SAVI-causing variant in the transmembrane linker region. Mutations of p.H72 into either charged residues or hydrophobic residues all led to dramatic loss of cGAMP response, while amino acid changes to residues with polar side chains were able to maintain the wild type status. Structural modeling of these novel mutations suggests a reconciled model of STING activation, which indicates that STING dimers can oligomerize in both open and closed states which would obliviate a high-energy 180° rotation of the ligand-binding head for STING activation, thus refining existing models of STING activation. Quantitative comparison showed that an overall lower autoactivating potential of the disease-causing mutations was associated with less severe lung disease, more severe peripheral vascular disease and the absence of a robust interferon signature in whole blood. Our findings are important in understanding genotype-phenotype correlation, designing targeted STING inhibitors and in dissecting differentially activated pathways downstream of different STING mutations.

Unique and complementary suppression of cGAS-STING and RNA sensing- triggered innate immune responses by SARS-CoV-2 proteins

The emergence of SARS-CoV-2 has resulted in the COVID-19 pandemic, leading to millions of infections and hundreds of thousands of human deaths. The efficient replication and population spread of SARS-CoV-2 indicates an effective evasion of human innate immune responses, although the viral proteins responsible for this immune evasion are not clear. In this study, we identified SARS-CoV-2 structural proteins, accessory proteins, and the main viral protease as potent inhibitors of host innate immune responses of distinct pathways. In particular, the main viral protease was a potent inhibitor of both the RLR and cGAS-STING pathways. Viral accessory protein ORF3a had the unique ability to inhibit STING, but not the RLR response. On the other hand, structural protein N was a unique RLR inhibitor. ORF3a bound STING in a unique fashion and blocked the nuclear accumulation of p65 to inhibit nuclear factor-κB signaling. 3CL of SARS-CoV-2 inhibited K63-ubiquitin modification of STING to disrupt the assembly of the STING functional complex and downstream signaling. Diverse vertebrate STINGs, including those from humans, mice, and chickens, could be inhibited by ORF3a and 3CL of SARS-CoV-2. The existence of more effective innate immune suppressors in pathogenic coronaviruses may allow them to replicate more efficiently in vivo. Since evasion of host innate immune responses is essential for the survival of all viruses, our study provides insights into the design of therapeutic agents against SARS-CoV-2.

Monogenic autoinflammatory disorders: Conceptual overview, phenotype, and clinical approach

Autoinflammatory diseases are conditions in which pathogenic inflammation arises primarily through antigen-independent hyperactivation of immune pathways. First recognized just over 2 decades ago, the autoinflammatory disease spectrum has expanded rapidly to include more than 40 distinct monogenic conditions. Related mechanisms contribute to common conditions such as gout and cardiovascular disease. Here, we review the basic concepts underlying the "autoinflammatory revolution" in the understanding of immune-mediated disease and introduce major categories of monogenic autoinflammatory disorders recognized to date, including inflammasomopathies and other IL-1-related conditions, interferonopathies, and disorders of nuclear factor kappa B and/or aberrant TNF activity. We highlight phenotypic presentation as a reflection of pathogenesis and outline a practical approach to the evaluation of patients with suspected autoinflammation.

Successful treatment of a novel type I interferonopathy due to a de novo PSMB9 gene mutation with a Janus kinase inhibitor

BACKGROUND

Type I interferonopathies are a recently established subgroup of autoinflammatory diseases caused by mutations in genes associated with proteasome degradation or cytoplasmic RNA- and DNA-sensing pathways.

OBJECTIVE

This study aimed to unveil the molecular pathogenesis of a patient with novel type I interferonopathy, for which no known genetic mutations have been identified.

METHODS

We performed the whole-exome sequencing of a 1-month-old boy with novel type I interferonopathy. We also investigated proteasome activities using patient-derived B lymphoblastoid cell lines (LCLs) and normal LCLs transduced with the mutant gene.

RESULTS

Whole-exome sequencing identified a de novo proteasome 20S subunit beta 9 (PSMB9) p.G156D mutation in the patient who developed fever, a chilblain-like skin rash, myositis, and severe pulmonary hypertension due to the hyperactivation of IFN-α. Patient-derived LCLs revealed reduced proteasome activities, and exogenous transduction of mutant PSMB9 p.G156D into normal LCLs significantly suppressed proteasome activities, and the endogenous PSMB9 protein was lost along with the reduction of other immunoproteasome subunits, PSMB8 and PSMB10 proteins. He responded to the administration of a Janus kinase inhibitor, tofacitinib, and he was successfully withdrawn from venoarterial extracorporeal membranous oxygenation. At age 7 months, he received an unrelated cord blood transplantation. At 2 years posttransplantation, he no longer required tofacitinib and experienced no disease recurrence.

CONCLUSIONS

We present the case of a patient with a novel type I interferonopathy caused by a de novo PSMB9 p.G156D mutation that suppressed the wild-type PSMB9 protein expression. Janus kinase inhibitor and stem cell transplantation could be curative therapies in patients with severe interferonopathies.

The role of cGAS/STING in intestinal immunity

The gastrointestinal tract is a highly complex microenvironment under constant interaction with potentially harmful pathogens. Inflammatory bowel disease (IBD) is an archetypical inflammatory disease, in which the intestinal epithelium, defective autophagy, endoplasmic reticulum stress and dysbiosis play a key role. Although no risk-mediating gene variants of STING (TMEM173) have been identified so far, several seminal findings have elucidated a novel understanding of STING in the context of acute and chronic inflammation. STING, an endoplasmic reticulum resident adaptor protein binding cyclic dinucleotides, is a main inducer of type I interferons and canonically involved in antiviral and antibacterial immunity. Recent research has shed light on additional features of STING signaling involved in regulating the microbiota, facilitating autophagy, cell death or ER stress. Importantly, an increasing amount of studies suggests a considerable overlap of IBD pathophysiology and features of STING signaling. Since compelling evidence shows dysregulated type I IFNs in IBD, it is prompting to speculate on the hypothetical role of cGAS/STING/type I IFN signaling in IBD. Here, we summarize recent findings about the origin and function of STING signaling in the gastrointestinal tract and evolve the hypothesis that disturbed STING signaling might be profoundly interconnected with the pathophysiology of IBD.

Genetic Testing for Neonatal Respiratory Disease

Genetic mechanisms are now recognized as rare causes of neonatal lung disease. Genes potentially responsible for neonatal lung disease include those encoding proteins important in surfactant function and metabolism, transcription factors important in lung development, proteins involved in ciliary assembly and function, and various other structural and immune regulation genes. The phenotypes of infants with genetic causes of neonatal lung disease may have some features that are difficult to distinguish clinically from more common, reversible causes of lung disease, and from each other. Multigene panels are now available that can allow for a specific diagnosis, providing important information for treatment and prognosis. This review discusses genes in which abnormalities are known to cause neonatal lung disease and their associated phenotypes, and advantages and limitations of genetic testing.

Type I interferon activation and endothelial dysfunction in caveolin-1 insufficiency-associated pulmonary arterial hypertension

Interferonopathies, interferon (IFN)-α/β therapy, and caveolin-1 (CAV1) loss-of-function have all been associated with pulmonary arterial hypertension (PAH). Here, CAV1-silenced primary human pulmonary artery endothelial cells (PAECs) were proliferative and hypermigratory, with reduced cytoskeletal stress fibers. Signal transducers and activators of transcription (STAT) and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) were both constitutively activated in these cells, resulting in a type I IFN-biased inflammatory signature. Cav1 ^-/- mice that spontaneously develop pulmonary hypertension were found to have STAT1 and AKT activation in lung homogenates and increased circulating levels of CXCL10, a hallmark of IFN-mediated inflammation. PAH patients with CAV1 mutations also had elevated serum CXCL10 levels and their fibroblasts mirrored phenotypic and molecular features of CAV1-deficient PAECs. Moreover, immunofluorescence staining revealed endothelial CAV1 loss and STAT1 activation in the pulmonary arterioles of patients with idiopathic PAH, suggesting that this paradigm might not be limited to rare CAV1 frameshift mutations. While blocking JAK/STAT or AKT rescued aspects of CAV1 loss, only AKT inhibitors suppressed activation of both signaling pathways simultaneously. Silencing endothelial nitric oxide synthase (NOS3) prevented STAT1 and AKT activation induced by CAV1 loss, implicating CAV1/NOS3 uncoupling and NOS3 dysregulation in the inflammatory phenotype. Exogenous IFN reduced CAV1 expression, activated STAT1 and AKT, and altered the cytoskeleton of PAECs, implicating these mechanisms in PAH associated with autoimmune and autoinflammatory diseases, as well as IFN therapy. CAV1 insufficiency elicits an IFN inflammatory response that results in a dysfunctional endothelial cell phenotype and targeting this pathway may reduce pathologic vascular remodeling in PAH.

mRNA-encoded, constitutively active STINGV155M is a potent genetic adjuvant of antigen-specific CD8+ T cell response

mRNA vaccines induce potent immune responses in preclinical models and clinical studies. Adjuvants are used to stimulate specific components of the immune system to increase immunogenicity of vaccines. We utilized a constitutively active mutation (V155M) of the stimulator of interferon (IFN) genes (STING), which had been described in a patient with STING-associated vasculopathy with onset in infancy (SAVI), to act as a genetic adjuvant for use with our lipid nanoparticle (LNP)-encapsulated mRNA vaccines. mRNA-encoded constitutively active STING^V155M was most effective at maximizing CD8⁺ T cell responses at an antigen/adjuvant mass ratio of 5:1. STING^V155M appears to enhance development of antigen-specific T cells by activating type I IFN responses via the nuclear factor κB (NF-κB) and IFN-stimulated response element (ISRE) pathways. mRNA-encoded STING^V155M increased the efficacy of mRNA vaccines encoding the E6 and E7 oncoproteins of human papillomavirus (HPV), leading to reduced HPV⁺ TC-1 tumor growth and prolonged survival in vaccinated mice. This proof-of-concept study demonstrated the utility of an mRNA-encoded genetic adjuvant.

cGAS phase separation inhibits TREX1-mediated DNA degradation and enhances cytosolic DNA sensing

Cyclic GMP-AMP synthase (cGAS) recognition of cytosolic DNA is critical for the immune response to cancer and pathogen infection. Here, we discover that cGAS-DNA phase separation is required to resist negative regulation and allow efficient sensing of immunostimulatory DNA. We map the molecular determinants of cGAS condensate formation and demonstrate that phase separation functions to limit activity of the cytosolic exonuclease TREX1. Mechanistically, phase separation forms a selective environment that suppresses TREX1 catalytic function and restricts DNA degradation to an outer shell at the droplet periphery. We identify a TREX1 mutation associated with the severe autoimmune disease Aicardi-Goutières syndrome that increases penetration of TREX1 into the repressive droplet interior and specifically impairs degradation of phase-separated DNA. Our results define a critical function of cGAS-DNA phase separation and reveal a molecular mechanism that balances cytosolic DNA degradation and innate immune activation.

Immune Regulation of the cGAS-STING Signaling Pathway in the Tumor Microenvironment and Its Clinical Application

As a DNA receptor in the cytoplasm, cyclic GMP-AMP synthase (cGAS) contributes to the recognition of abnormal DNA in the cytoplasm and contributes to the stimulator of interferon genes (STING) signaling pathway. cGAS could mediate the expression of interferon-related genes, inflammatory-related factors, and downstream chemokines, thus initiating the immune response. The STING protein is a key effector downstream of the DNA receptor pathway. It is widely expressed across cell types such as immune cells, tumor cells, and stromal cells and plays a role in signal transduction for cytoplasmic DNA sensing and immunity. STING agonists, as novel agonists, are used in preclinical research and in the treatment of various tumors via clinical trials and have displayed attractive application prospects. Studying the cGAS-STING signaling pathway will deepen our understanding of tumor immunity and provide a basis for the research and development of antitumor drugs.

Overview of the rarest causes of fever in newborns: handy hints for the neonatologist

Neonatal causes of fever are a major source of concern for clinicians. If fever is combined with organ-specific sterile inflammatory manifestations the suspicion of autoinflammatory disorders should be considered, and the list of such conditions starting in the neonatal period includes chronic infantile neurological cutaneous articular syndrome, mevalonate kinase deficiency, deficiency of the interleukin-1 receptor antagonist, otulipenia, STING-associated vasculopathy with onset in infancy and Blau syndrome. Other causes of noninfectious fever that can rarely occur in newborns are Kawasaki disease, Behçet's disease, and hemophagocytic lymphohistiocytosis. Diagnosis of these exceptionally rare disorders is challenging for neonatologists. An early recognition of these complex diseases might lead to use more specific or rational drugs preventing permanent consequences. This review focuses on the rarest causes of fever occurring in the neonatal age with the aim of portraying many protean clinical pictures associated with fever and reviewing the potential available treatments.

STING negatively regulates allogeneic T-cell responses by constraining antigen-presenting cell function

Stimulator of interferon genes (STING)-mediated innate immune activation plays a key role in tumor- and self-DNA-elicited antitumor immunity and autoimmunity. However, STING can also suppress tumor immunity and autoimmunity. STING signaling in host nonhematopoietic cells was reported to either protect against or promote graft-versus-host disease (GVHD), a major complication of allogeneic hematopoietic cell transplantation (allo-HCT). Host hematopoietic antigen-presenting cells (APCs) play key roles in donor T-cell priming during GVHD initiation. However, how STING regulates host hematopoietic APCs after allo-HCT remains unknown. We utilized murine models of allo-HCT to assess the role of STING in hematopoietic APCs. STING-deficient recipients developed more severe GVHD after major histocompatibility complex-mismatched allo-HCT. Using bone marrow chimeras, we found that STING deficiency in host hematopoietic cells was primarily responsible for exacerbating the disease. Furthermore, STING on host CD11c⁺ cells played a dominant role in suppressing allogeneic T-cell responses. Mechanistically, STING deficiency resulted in increased survival, activation, and function of APCs, including macrophages and dendritic cells. Consistently, constitutive activation of STING attenuated the survival, activation, and function of APCs isolated from STING V154M knock-in mice. STING-deficient APCs augmented donor T-cell expansion, chemokine receptor expression, and migration into intestinal tissues, resulting in accelerated/exacerbated GVHD. Using pharmacologic approaches, we demonstrated that systemic administration of a STING agonist (bis-(3'-5')-cyclic dimeric guanosine monophosphate) to recipient mice before transplantation significantly reduced GVHD mortality. In conclusion, we revealed a novel role of STING in APC activity that dictates T-cell allogeneic responses and validated STING as a potential therapeutic target for controlling GVHD after allo-HCT.

Mitochondrial Damage-Induced Innate Immune Activation in Vascular Smooth Muscle Cells Promotes Chronic Kidney Disease-Associated Plaque Vulnerability

Chronic kidney disease (CKD) is associated with accelerated atherosclerosis progression and high incidence of cardiovascular events, hinting that atherosclerotic plaques in CKD may be vulnerable. However, its cause and mechanism remain obscure. Here, it is shown that apolipoprotein E-deficient (ApoE-/-) mouse with CKD (CKD/ApoE-/- mouse) is a useful model for investigating the pathogenesis of plaque vulnerability, and premature senescence and phenotypic switching of vascular smooth muscle cells (VSMCs) contributes to CKD-associated plaque vulnerability. Subsequently, VSMC phenotypes in patients with CKD and CKD/ApoE-/- mice are comprehensively investigated. Using multi-omics analysis and targeted and VSMC-specific gene knockout mice, VSMCs are identified as both type-I-interferon (IFN-I)-responsive and IFN-I-productive cells. Mechanistically, mitochondrial damage resulting from CKD-induced oxidative stress primes the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway to trigger IFN-I response in VSMCs. Enhanced IFN-I response then induces VSMC premature senescence and phenotypic switching in an autocrine/paracrine manner, resulting in the loss of fibrous cap VSMCs and fibrous cap thinning. Conversely, blocking IFN-I response remarkably attenuates CKD-associated plaque vulnerability. These findings reveal that IFN-I response in VSMCs through immune sensing of mitochondrial damage is essential for the pathogenesis of CKD-associated plaque vulnerability. Mitigating IFN-I response may hold promise for the treatment of CKD-associated cardiovascular diseases.

Autoinflammatory syndromes

Autoinflammatory syndromes are a steadily growing group of inflammatory diseases caused by abnormal regulations of the innate immune system. The clinical presentation is multifaceted, but recurrent fever, skin involvement, joint inflammation and other systemic symptoms of inflammation are characteristic. In contrast to classic autoimmune diseases, autoantibodies or specific T cells are not involved in the pathogenesis. In fact, innate immunity plays the most important role in autoinflammation. While activation of the innate immune system is usually self-limiting in healthy individuals, mutations and dysregulation can lead to chronic and excessive activation of innate immune responses and to the development of autoinflammatory diseases.

Cyclic Guanosine Monophosphate-Adenosine Monophosphate Synthase (cGAS), a Multifaceted Platform of Intracellular DNA Sensing

Innate immune pathways are the first line of cellular defense against pathogen infections ranging from bacteria to Metazoa. These pathways are activated following the recognition of pathogen associated molecular patterns (PAMPs) by membrane and cytosolic pattern recognition receptors. In addition, some of these cellular sensors can also recognize endogenous danger-associated molecular patterns (DAMPs) arising from damaged or dying cells and triggering innate immune responses. Among the cytosolic nucleic acid sensors, the cyclic guanosine monophosphate–adenosine monophosphate (cGAMP) synthase (cGAS) plays an essential role in the activation of the type I interferon (IFNs) response and the production of pro-inflammatory cytokines. Indeed, upon nucleic acid binding, cGAS synthesizes cGAMP, a second messenger mediating the activation of the STING signaling pathway. The functional conservation of the cGAS-STING pathway during evolution highlights its importance in host cellular surveillance against pathogen infections. Apart from their functions in immunity, cGAS and STING also play major roles in nuclear functions and tumor development. Therefore, cGAS-STING is now considered as an attractive target to identify novel biomarkers and design therapeutics for auto-inflammatory and autoimmune disorders as well as infectious diseases and cancer. Here, we review the current knowledge about the structure of cGAS and the evolution from bacteria to Metazoa and present its main functions in defense against pathogens and cancer, in connection with STING. The advantages and limitations of in vivo models relevant for studying the cGAS-STING pathway will be discussed for the notion of species specificity and in the context of their integration into therapeutic screening assays targeting cGAG and/or STING.

Cellular Metabolites Regulate Central Nucleic Acid Sensing Pathways

Detection of pathogen-derived DNA or RNA species by cellular nucleic acid sensors prompts release of anti-microbial interferons and cytokines. In contrast to their protective anti-microbial functions, inappropriate or excessive activation of nucleic acid sensors can cause inflammatory diseases. Nucleic acid sensing is therefore tightly controlled by regulatory factors acting through both transcriptional and post-transcriptional mechanisms. Recently, it has become clearer that metabolic pathways-previously thought to be unconnected with immune responses-can influence nucleic acid sensing. This regulation can be observed when immune system cells undergo metabolic reprogramming in response to stimulation with pathogen-associated molecular patterns such as lipopolysaccharide from gram negative bacteria. Metabolic reprogramming leads to accumulation and secretion of metabolites, which have been mostly viewed as end-products of processes providing cellular energy and building blocks. However, metabolites have now been identified as important regulators of nucleic acid sensing. This mini-review aims to outline current knowledge on regulation of central nucleic acid sensing pathways by metabolites during metabolic reprogramming.

Sensing of endogenous nucleic acids by ZBP1 induces keratinocyte necroptosis and skin inflammation

Aberrant detection of endogenous nucleic acids by the immune system can cause inflammatory disease. The scaffold function of the signaling kinase RIPK1 limits spontaneous activation of the nucleic acid sensor ZBP1. Consequently, loss of RIPK1 in keratinocytes induces ZBP1-dependent necroptosis and skin inflammation. Whether nucleic acid sensing is required to activate ZBP1 in RIPK1-deficient conditions and which immune pathways are associated with skin disease remained open questions. Using knock-in mice with disrupted ZBP1 nucleic acid–binding activity, we report that sensing of endogenous nucleic acids by ZBP1 is critical in driving skin pathology characterized by antiviral and IL-17 immune responses. Inducing ZBP1 expression by interferons triggers necroptosis in RIPK1-deficient keratinocytes, and epidermis-specific deletion of MLKL prevents disease, demonstrating that cell-intrinsic events cause inflammation. These findings indicate that dysregulated sensing of endogenous nucleic acid by ZBP1 can drive inflammation and may contribute to the pathogenesis of IL-17–driven inflammatory skin conditions such as psoriasis.

Childhood vasculitis

Vasculitis is a challenging disease for paediatricians. Certain vasculitides are quite common in children whereas others are much rarer compared with adults. The most common vasculitides in childhood are IgA-associated vasculitis (Henoch-Schönlein purpura) and Kawasaki disease, which are usually self-limiting vasculitides although children do develop complications as a result. We now have much better knowledge of how to manage these patients and prevent the deleterious complications. This review provides an up-to-date discussion on childhood vasculitides, including diagnosis, treatment and follow-up strategies, together with a comparison with vasculitides in adults. It also discusses the newly defined monogenic vasculitides that often present during early childhood.

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.

The Complexity of the cGAS-STING Pathway in CNS Pathologies

Neuroinflammation driven by type-I interferons in the CNS is well established to exacerbate the progression of many CNS pathologies both acute and chronic. The role of adaptor protein Stimulator of Interferon Genes (STING) is increasingly appreciated to instigate type-I IFN-mediated neuroinflammation. As an upstream regulator of type-I IFNs, STING modulation presents a novel therapeutic opportunity to mediate inflammation in the CNS. This review will detail the current knowledge of protective and detrimental STING activity in acute and chronic CNS pathologies and the current therapeutic avenues being explored.

Severe Liver Disorder Following Liver Transplantation in STING-Associated Vasculopathy with Onset in Infancy

PURPOSE

STING-associated vasculopathy with onset in infancy (SAVI) is a type-I interferonopathy, characterized by systemic inflammation, peripheral vascular inflammation, and pulmonary manifestations. There are three reports of SAVI patients developing liver disease, but no report of a SAVI patient requiring liver transplantation. Therefore, the relevance of liver inflammation is unclear in SAVI. We report a SAVI patient who developed severe liver disorder following liver transplantation.

METHODS

SAVI was diagnosed in a 4-year-old girl based on genetic analysis by whole-exome sequencing. We demonstrated clinical features, laboratory findings, and pathological examination of her original and transplanted livers.

RESULTS

At 2 months of age, she developed bronchitis showing resistance to bronchodilators and antibiotics. At 10 months of age, she developed liver dysfunction with atypical cholangitis, which required liver transplantation at 1 year of age. At 2 years of age, multiple biliary cysts developed in the transplanted liver. At 3.9 years of age, SAVI was diagnosed by whole-exome sequencing. Inflammatory cells from the liver invaded the stomach wall directly, leading to fatal gastrointestinal bleeding unexpectedly at 4.6 years of age. In pathological findings, there were no typical findings of liver abscess, vasculitis, or graft rejection, but biliary cysts and infiltration of inflammatory cells, including plasmacytes around the bile duct area, in the transplanted liver were noted, which were findings similar to those of her original liver.

CONCLUSION

Although further studies to clarify the mechanisms of the various liver disorders described in SAVI patients are needed, inflammatory liver manifestations may be amplified in the context of SAVI.

STING-Mediated Lung Inflammation and Beyond

Mendelian autoinflammatory diseases characterized by constitutive activation of the type I interferon pathway, the so-called type I interferonopathies, constitute a rapidly expanding group of inborn errors of immunity. Among the type I interferonopathies, STING-associated vasculopathy with onset in infancy (SAVI) and COPA syndrome were described in the last 6 years, both manifesting a major inflammatory lung component associated with significant morbidity and increased mortality. There is striking clinical and histopathological overlap between SAVI and COPA syndrome, although distinct features are also present. Of note, there is a remarkably high frequency of clinical non-penetrance among individuals harboring pathogenic COPA mutations. SAVI is caused by, principally heterozygous, gain-of-function mutations in STING1 (previously referred to as TMEM173) encoding STING, a key adaptor of the interferon signaling pathway induced by DNA. COPA syndrome results from heterozygous dominant-negative mutations in the coatomer protein subunit alpha, forming part of a complex involved in intracellular cargo protein transport between the Golgi and the endoplasmic reticulum (ER). Of importance, a role for COPA in regulating the trafficking of STING, an ER-resident protein which translocates to the Golgi during the process of its activation, was recently defined, thereby possibly explaining some aspects of the phenotypic overlap between SAVI and COPA syndrome. Here, we review the expanding phenotype of these diseases, highlighting common as well as specific features, and recent advances in our understanding of STING biology that have informed therapeutic decision-making in both conditions. Beyond these rare Mendelian disorders, DNA sensing through STING is likely relevant to the pathology of several diseases associated with lung inflammation, including systemic lupus erythematosus, dermatomyositis, environmental toxin exposure, and viral infection.

Signaling Through Nucleic Acid Sensors and Their Roles in Inflammatory Diseases

Recognition of pathogen-derived nucleic acids by pattern-recognition receptors (PRRs) is essential for eliciting antiviral immune responses by inducing the production of type I interferons (IFNs) and proinflammatory cytokines. Such responses are a prerequisite for mounting innate and pathogen-specific adaptive immune responses. However, host cells also use nucleic acids as carriers of genetic information, and the aberrant recognition of self-nucleic acids by PRRs is associated with the onset of autoimmune or autoinflammatory diseases. In this review, we describe the mechanisms of nucleic acid sensing by PRRs, including Toll-like receptors, RIG-I-like receptors, and DNA sensor molecules, and their signaling pathways as well as the disorders caused by uncontrolled or unnecessary activation of these PRRs.

Monogenic autoinflammatory disorders: beyond the periodic fever

The past two decades have seen an exponential increase in the number of monogenic autoinflammatory disorders described, coinciding with improved genetic sequencing techniques. This group of disorders has evolved to be heterogeneous and certainly more complex than the original four 'periodic fever syndromes' caused by innate immune over-activation. This review aims to provide an update on the classic periodic fever syndromes as well as introducing the broadening spectrum of clinical features seen in more recently described conditions.