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West Nile Virus (WNV), an emerging and re-emerging RNA virus, is the leading source of arboviral encephalitic morbidity and mortality in the United States. WNV infections are acutely controlled by innate immunity in peripheral tissues outside of the central nervous system (CNS) but WNV can evade the actions of interferon (IFN) to facilitate CNS invasion, causing encephalitis, encephalomyelitis, and death. Recent studies indicate that STimulator of INterferon Gene (STING), canonically known for initiating a type I IFN production and innate immune response to cytosolic DNA, is required for host defense against neurotropic RNA viruses. We evaluated the role of STING in host defense to control WNV infection and pathology in a murine model of infection. When challenged with WNV, STING knock out (-/-) mice displayed increased morbidity and mortality compared to wild type (WT) mice. Virologic analysis and assessment of STING activation revealed that STING signaling was not required for control of WNV in the spleen nor was WNV sufficient to mediate canonical STING activation in vitro. However, STING-/- mice exhibited a clear trend of increased viral load and virus dissemination in the CNS. We found that STING-/- mice exhibited increased and prolonged neurological signs compared to WT mice. Pathological examination revealed increased lesions, mononuclear cellular infiltration and neuronal death in the CNS of STING-/- mice, with sustained pathology after viral clearance. We found that STING was required in bone marrow derived macrophages for early control of WNV replication and innate immune activation. In vivo, STING-/- mice developed an aberrant T cell response in both the spleen and brain during WNV infection that linked with increased and sustained CNS pathology compared to WT mice. Our findings demonstrate that STING plays a critical role in immune programming for the control of neurotropic WNV infection and CNS disease. [ABSTRACT FROM AUTHOR]

Objective: Type I interferon (IFN) is strongly implicated in the pathogenesis of systemic lupus erythematosus (SLE) as well as rare monogenic interferonopathies such as Aicardi‐Goutières syndrome (AGS), a disease attributed to mutations in the DNA exonuclease TREX1. The DNA‐activated type I IFN pathway cyclic GMP‐AMP (cGAMP) synthase (cGAS) is linked to subsets of AGS and lupus. This study was undertaken to identify inhibitors of the DNA–cGAS interaction, and to test the lead candidate drug, X6, in a mouse model of AGS. Methods: Trex1−/− mice were treated orally from birth with either X6 or hydroxychloroquine (HCQ) for 8 weeks. Expression of IFN‐stimulated genes (ISGs) was quantified by quantitative polymerase chain reaction. Multiple reaction monitoring by ultra‐performance liquid chromatography coupled with tandem mass spectrometry was used to quantify the production of cGAMP and X6 drug concentrations in the serum and heart tissue of Trex1−/− mice. Results: On the basis of the efficacy‐to‐toxicity ratio established in vitro, drug X6 was selected as the lead candidate for treatment of Trex1−/− mice. X6 was significantly more effective than HCQ in attenuating ISG expression in mouse spleens (P < 0.01 for Isg15 and Isg20) and hearts (P < 0.05 for Isg15, Mx1, and Ifnb, and P < 0.01 for Cxcl10), and in reducing the production of cGAMP in mouse heart tissue (P < 0.05), thus demonstrating target engagement by the X6 compound. Of note, X6 was also more effective than HCQ in reducing ISG expression in vitro (P < 0.05 for IFI27 and MX1, and P < 0.01 for IFI44L and PKR) in human peripheral blood mononuclear cells from patients with SLE. Conclusion: This study demonstrates that X6 is superior to HCQ for the treatment of an experimental autoimmune myocarditis mediated in vivo by the cGAS/stimulator of IFN genes (cGAS/STING) pathway. The findings suggest that drug X6 could be developed as a novel treatment for AGS and/or lupus to inhibit activation of the cGAS/STING pathway. [ABSTRACT FROM AUTHOR]

The RNA deaminase ADAR1 is an essential negative regulator of the RNA sensor MDA5, and loss of ADAR1 function triggers inappropriate activation of MDA5 by self-RNAs. Mutations in ADAR , the gene that encodes ADAR1, cause human immune diseases, including Aicardi-Goutières syndrome (AGS). However, the mechanisms of MDA5-dependent disease pathogenesis in vivo remain unknown. Here we generated mice with a single amino acid change in ADAR1 that models the most common human ADAR AGS mutation. These Adar mutant mice developed lethal disease that required MDA5, the RIG-I-like receptor LGP2, type I interferons, and the eIF2α kinase PKR. A small-molecule inhibitor of the integrated stress response (ISR) that acts downstream of eIF2α phosphorylation prevented immunopathology and rescued the mice from mortality. These findings place PKR and the ISR as central components of immunopathology in vivo and identify therapeutic targets for treatment of human diseases associated with the ADAR1-MDA5 axis. [Display omitted] • Adar P195A/p150- mice model ADAR1 mutations found in human Aicardi-Goutières syndrome • Disease in Adar P195A/p150- mice requires MDA5, LGP2, the type I IFN receptor, and PKR • Adar P195A/p150 - mice develop PKR-dependent activation of integrated stress response (ISR) • Pharmacological inhibition of the ISR in vivo prevents all aspects of disease Mutations in ADAR1 cause human immune diseases, including Aicardi-Goutières syndrome (AGS), but the mechanisms of disease pathogenesis remain unknown. Using a mouse model of ADAR1 mutation, Maurano et al. define a pathway linking MDA5 and LGP2 to PKR and the integrated stress response (ISR). Pharmacological inhibition of the ISR prevents disease, establishing its role in immunopathology caused by ADAR1 mutations. [ABSTRACT FROM AUTHOR]

Summary Detection of intracellular DNA triggers activation of the STING-dependent interferon-stimulatory DNA (ISD) pathway, which is essential for antiviral responses. Multiple DNA sensors have been proposed to activate this pathway, including AIM2-like receptors (ALRs). Whether the ALRs are essential for activation of this pathway remains unknown. To rigorously explore the function of ALRs, we generated mice lacking all 13 ALR genes. We found that ALRs are dispensable for the type I interferon (IFN) response to transfected DNA ligands, DNA virus infection, and lentivirus infection. We also found that ALRs do not contribute to autoimmune disease in the Trex1 −/− mouse model of Aicardi-Goutières Syndrome. Finally, CRISPR-mediated disruption of the human AIM2-like receptor IFI16 in primary fibroblasts revealed that IFI16 is not essential for the IFN response to human cytomegalovirus infection. Our findings indicate that ALRs are dispensable for the ISD response and suggest that alternative functions for these receptors should be explored. [ABSTRACT FROM AUTHOR]

The DNA sensor cyclic GMP-AMP synthase (cGAS) is important for antiviral and anti-tumor immunity. cGAS generates cyclic GMP-AMP (cGAMP), a diffusible cyclic dinucleotide that activates the antiviral response through the adaptor protein stimulator of interferon genes (STING). cGAMP cannot passively cross cell membranes, but recent advances have established a role for extracellular cGAMP as an "immunotransmitter" that can be imported into cells. However, the mechanism by which cGAMP exits cells remains unknown. Here, we identifed ABCC1 as a direct, ATP-dependent cGAMP exporter in mouse and human cells. We show that ABCC1 overexpression enhanced cGAMP export and limited STING signaling and that loss of ABCC1 reduced cGAMP export and potentiated STING signaling. We demonstrate that ABCC1 deficiency exacerbated cGAS-dependent autoimmunity in the Trex1 −/− mouse model of Aicardi-Goutières syndrome. Thus, ABCC1-mediated cGAMP export is a key regulatory mechanism that limits cell-intrinsic activation of STING and ameliorates STING-dependent autoimmune disease. • The immunostimulatory molecule cGAMP is actively exported from live cells • ABCC1 mediates active, ATP-dependent cGAMP export • ABCC1-mediated cGAMP export limits activation of the STING-interferon pathway • ABCC1 limits cGAS-dependent autoimmunity in vivo Cyclic GMP-AMP (cGAMP) is an "immunotransmitter" that can be imported into cells to activate antiviral responses, but how cGAMP exits cells is currently unknown. Maltbaek et al. identify ABCC1 as an active cGAMP exporter that modulates STING-dependent immunity. [ABSTRACT FROM AUTHOR]