DNase-active TREX1 frame-shift mutants induce serologic autoimmunity in mice

Inherited C-terminal TREX1 variants disrupt homology-directed repair to cause senescence and DNA damage phenotypes in Drosophila, mice, and humans

Age-related microangiopathy, also known as small vessel disease (SVD), causes damage to the brain, retina, liver, and kidney. Based on the DNA damage theory of aging, we reasoned that genomic instability may underlie an SVD caused by dominant C-terminal variants in TREX1, the most abundant 3'-5' DNA exonuclease in mammals. C-terminal TREX1 variants cause an adult-onset SVD known as retinal vasculopathy with cerebral leukoencephalopathy (RVCL or RVCL-S). In RVCL, an aberrant, C-terminally truncated TREX1 mislocalizes to the nucleus due to deletion of its ER-anchoring domain. Since RVCL pathology mimics that of radiation injury, we reasoned that nuclear TREX1 would cause DNA damage. Here, we show that RVCL-associated TREX1 variants trigger DNA damage in humans, mice, and Drosophila, and that cells expressing RVCL mutant TREX1 are more vulnerable to DNA damage induced by chemotherapy and cytokines that up-regulate TREX1, leading to depletion of TREX1-high cells in RVCL mice. RVCL-associated TREX1 mutants inhibit homology-directed repair (HDR), causing DNA deletions and vulnerablility to PARP inhibitors. In women with RVCL, we observe early-onset breast cancer, similar to patients with BRCA1/2 variants. Our results provide a mechanistic basis linking aberrant TREX1 activity to the DNA damage theory of aging, premature senescence, and microvascular disease.

Modeling of age-related neurological disease: utility of zebrafish

Many age-related neurological diseases still lack effective treatments, making their understanding a critical and urgent issue in the globally aging society. To overcome this challenge, an animal model that accurately mimics these diseases is essential. To date, many mouse models have been developed to induce age-related neurological diseases through genetic manipulation or drug administration. These models help in understanding disease mechanisms and finding potential therapeutic targets. However, some age-related neurological diseases cannot be fully replicated in human pathology due to the different aspects between humans and mice. Although zebrafish has recently come into focus as a promising model for studying aging, there are few genetic zebrafish models of the age-related neurological disease. This review compares the aging phenotypes of humans, mice, and zebrafish, and provides an overview of age-related neurological diseases that can be mimicked in mouse models and those that cannot. We presented the possibility that reproducing human cerebral small vessel diseases during aging might be difficult in mice, and zebrafish has potential to be another animal model of such diseases due to their similarity of aging phenotype to humans.

Disulfiram ameliorates STING/MITA-dependent inflammation and autoimmunity by targeting RNF115

STING (also known as MITA) is an adaptor protein that mediates cytoplasmic DNA-triggered signaling, and aberrant activation of STING/MITA by cytosolic self-DNA or gain-of-function mutations causes severe inflammation. Here, we show that STING-mediated inflammation and autoimmunity are promoted by RNF115 and alleviated by the RNF115 inhibitor disulfiram (DSF). Knockout of RNF115 or treatment with DSF significantly inhibit systemic inflammation and autoimmune lethality and restore immune cell development in Trex1-/- mice and STINGN153S/WT bone marrow chimeric mice. In addition, knockdown or pharmacological inhibition of RNF115 substantially downregulate the expression of IFN-α, IFN-γ and proinflammatory cytokines in PBMCs from patients with systemic lupus erythematosus (SLE) who exhibit high concentrations of dsDNA in peripheral blood. Mechanistically, knockout or inhibition of RNF115 impair the oligomerization and Golgi localization of STING in various types of cells transfected with cGAMP and in organs and cells from Trex1-/- mice. Interestingly, knockout of RNF115 inhibits the activation and Golgi localization of STINGN153S as well as the expression of proinflammatory cytokines in myeloid cells but not in endothelial cells or fibroblasts. Taken together, these findings highlight the RNF115-mediated cell type-specific regulation of STING and STINGN153S and provide potential targeted intervention strategies for STING-related autoimmune diseases.

LicochalconeB inhibits cGAS-STING signaling pathway and prevents autoimmunity diseases

Cytosolic DNA activates the STING (stimulator of interferon genes) signaling pathway to trigger interferon and inflammatory responses that protect against microbial infections and cancer. However, Aicardi-Goutières syndrome (AGS) persistently activates the STING signaling pathway, which can lead to severe autoimmune diseases. We demonstrate herein that Licochalcone B (LicoB), the main component of traditional licorice, is an inhibitor of the STING signaling pathway. We observed that LicoB inhibited the activation of the STING signaling pathway in macrophages. Mechanically, LicoB affected the STING-TBK1-IRF3 signal axis and inhibited the activation of the STING downstream signaling pathway. Furthermore, LicoB inhibited the increase in type I interferon levels in mice induced by the STING agonist CMA. LicoB significantly reduced systemic inflammation in Trex1-/- mice. Our results show that LicoB, a STING signaling pathway inhibitor, is a promising candidate for the treatment of diseases related to STING signaling pathway activation.

Stereoselective synthesis of photoactivatable Man(β1,4)GlcNAc-based bioorthogonal probes

We report an operationally facile protocol to prepare photoactivatable probes of the bioactive mammalian disaccharide, Man(β1,4)GlcNAc. Using conformationally restricted mannosyl hemi-acetal donors in a one-pot chlorination, iodination and glycosylation sequence, β-mannosides were generated in excellent diastereoselectivities and yields. Upon accessing the disaccharide, we generated the corresponding photoactivatable probes by appending a diazirine-alkyne equipped linker via a condensation reaction between a diazirine-containing linker and C-1 and C-2 derivatized mannosylamines to furnish the desired C-1 and C-2 modified Man(β1,4)GlcNAc-based probes. This new synthetic protocol greatly simplifies the preparation of this important bioactive disaccharide to enable future work to identify its protein binding partners in cells.

A path towards personalized medicine for autoinflammatory and related diseases

The human genome project led to the advancement of genetic technologies and genomic medicine for a variety of human diseases, including monogenic autoimmune and autoinflammatory diseases. As a result, the genome of an individual can now be rapidly sequenced at a low cost, and this technology is beginning to change the practice of rheumatology. In this Perspective, we describe how new sequencing technologies combined with careful clinical phenotyping have led to the discovery of rare rheumatic diseases and their corresponding disease-causing mutations. Additionally, we explore ways in which single-gene mutations, including somatic mutations, are creating opportunities to develop personalized medicines. To illustrate this idea, we focus on diseases affecting the TREX1-cGAS-STING pathway, which is associated with monogenic autoinflammatory diseases and vasculopathies. For many of the affected patients and families, there is an urgent, unmet need for the development of personalized therapies. New innovations related to small molecular inhibitors and gene therapies have the potential to benefit these families, and might help drive further innovations that could prove useful for patients with more common forms of autoimmunity and autoinflammation.

Case report: JAK inhibition as promising treatment option of fatal RVCLS due to TREX1 mutation (pVAL235Glyfs*6)

Introduction

Autosomal dominant mutations in the C-terminal part of TREX1 (pVAL235Glyfs^*6) result in fatal retinal vasculopathy with cerebral leukoencephalopathy and systemic manifestations (RVCLS) without any treatment options. Here, we report on a treatment of a RVCLS patient with anti-retroviral drugs and the janus kinase (JAK) inhibitor ruxolitinib.

Methods

We collected clinical data of an extended family with RVCLS (TREX1 pVAL235Glyfs^*6). Within this family we identified a 45-year-old woman as index patient that we treated experimentally for 5 years and prospectively collected clinical, laboratory and imaging data.

Results

We report clinical details from 29 family members with 17 of them showing RVCLS symptoms. Treatment of the index patient with ruxolitinib for >4 years was well-tolerated and clinically stabilized RVCLS activity. Moreover, we noticed normalization of initially elevated CXCL10 mRNA in peripheral blood monocular cells (PBMCs) and a reduction of antinuclear autoantibodies.

Discussion

We provide evidence that JAK inhibition as RVCLS treatment appears safe and could slow clinical worsening in symptomatic adults. These results encourage further use of JAK inhibitors in affected individuals together with monitoring of CXCL10 transcripts in PBMCs as useful biomarker of disease activity.

Intracellular Sensing of DNA in Autoinflammation and Autoimmunity

Evidence has shown that DNA is a pathogen-associated molecular pattern, posing a unique challenge in the discrimination between endogenous and foreign DNA. This challenge is highlighted by certain autoinflammatory diseases that arise from monogenic mutations and result in periodic flares of inflammation, typically in the absence of autoantibodies or antigen-specific T lymphocytes. Several autoinflammatory diseases arise due to mutations in genes that normally prevent the accrual of endogenous DNA or are due to mutations that cause activation of intracellular DNA-sensing pathway components. Evidence from genetically modified murine models further support an ability of endogenous DNA and DNA sensing to drive disease pathogenesis, prompting the question of whether endogenous DNA can also induce inflammation in human autoimmune diseases. In this review, we discuss the current understanding of intracellular DNA sensing and downstream signaling pathways as they pertain to autoinflammatory disease, including the development of monogenic disorders such as Stimulator of interferon genes-associated vasculopathy with onset in infancy and Aicardi-Goutières syndrome. In addition, we discuss systemic rheumatic diseases, including certain forms of systemic lupus erythematosus, familial chilblain lupus, and other diseases with established links to intracellular DNA-sensing pathways, and highlight the lessons learned from these examples as they apply to the development of therapies targeting these pathways.

Exonucleases: Degrading DNA to Deal with Genome Damage, Cell Death, Inflammation and Cancer

Although DNA degradation might seem an unwanted event, it is essential in many cellular processes that are key to maintaining genomic stability and cell and organism homeostasis. The capacity to cut out nucleotides one at a time from the end of a DNA chain is present in enzymes called exonucleases. Exonuclease activity might come from enzymes with multiple other functions or specialized enzymes only dedicated to this function. Exonucleases are involved in central pathways of cell biology such as DNA replication, repair, and death, as well as tuning the immune response. Of note, malfunctioning of these enzymes is associated with immune disorders and cancer. In this review, we will dissect the impact of DNA degradation on the DNA damage response and its links with inflammation and cancer.

Retinal Vasculopathy with Cerebral Leukoencephalopathy and Systemic manifestations (RVCL-S): An update on basic science and clinical perspectives

Retinal vasculopathy with cerebral leukoencephalopathy and systemic manifestations (RVCL-S) is a rare, underrecognized, systemic small vessel disease caused by heterozygous C-terminal truncating TREX1 mutations. The disease is characterized by vascular retinopathy, focal neurological complaints, cognitive decline and a wide range of systemic manifestations, including Raynaud's phenomenon, anemia and liver and kidney disease. Eventually, RVCL-S leads to premature death. The underlying pathological finding in RVCL-S is a nonatherosclerotic, amyloid-negative angiopathy involving small arteries and capillaries. However, the exact mechanisms by which the truncated TREX1 protein causes angiopathy remains unknown. Timely recognition of this disease is important to slow down and treat complications of the disorder, but also to prevent unnecessary (invasive) diagnostic or therapeutic procedures. As we move forward, translational research combining basic science advances and clinical findings as well as studies focusing on natural history following RVCL-S patients at different disease stages, will be critical to help elucidate RVCL-S pathophysiology. These studies will also provide the tools to identify appropriate biomarkers and therapeutic agent options for RVCL-S patients.

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.

High clinical heterogeneity in a Chinese pedigree of retinal vasculopathy with cerebral leukoencephalopathy and systemic manifestations (RVCL-S)

Background

Being a newly defined disease, RVCL-S is underrecognized by clinicians globally. It is an autosomal dominantly inherited small vessel disease caused by the heterozygous C-terminal frameshift mutation in TREX1 gene. RVCL-S is featured by cerebral dysfunction, retinopathy, and vasculopathy in multiple internal organs. Misdiagnosis may cause devastating consequences in patients, such as iatrogenic PML caused by misuse of immunosuppressants. Thus, increasing awareness of this disease is in urgent need.

Results

We uncovered a large Chinese origin RVCL-S pedigree bearing the TREX1 mutation. A comprehensive characterization combining clinical, genetic, and neuropathological analysis was performed. The Intrafamilial comparison showed highly heterogeneous clinical phenotypes. Mutation carriers in our pedigree presented with retinopathy (8/13), seizures (2/13), increased intracranial pressure (1/13), mild cognitive impairment (3/13), stroke-like episode (3/13), mesenteric ischemia (1/13), nephropathy (9/13), ascites (3/13), hypertension (9/13), hyperlipidemia (3/8), hypoalbuminemia (3/8), normocytic anemia (3/8), subclinical hypothyroidism (1/8), hyperfibrinogenemia (1/8), hyperparathyroidism (2/8), and abnormal inflammatory markers (4/8). The constellation of symptoms is highly varied, making RVCL-S a challenging diagnosis. Comparison with reported RVCL-S pedigrees further revealed that the mesenteric ischemia is a novel clinical finding and the MRS pattern of brain lesions is emulating neoplasm and tumefactive demyelination.

Conclusion

Our reports characterize a highly heterogeneous RVCL-S pedigree, highlight the probability of misdiagnosis in clinical practice, and broaden the clinical spectrum of RVCL-S.

Aicardi-Goutières syndrome-like encephalitis in mutant mice with constitutively active MDA5

MDA5 is a cytoplasmic sensor of viral RNA, triggering type I interferon (IFN-I) production. Constitutively active MDA5 has been linked to autoimmune diseases such as systemic lupus erythematosus, Singleton-Merten syndrome (SMS) and Aicardi-Goutières syndrome (AGS), a genetically determined inflammatory encephalopathy. However, AGS research is challenging due to the lack of animal models. We previously reported lupus-like nephritis and SMS-like bone abnormalities in adult mice with constitutively active MDA5 (Ifih1G821S/+), and herein demonstrate that these mice also exhibit high lethality and spontaneous encephalitis with high IFN-I production during the early postnatal period. Increases in the number of microglia were observed in MDA5/MAVS signaling- and IFN-I-dependent manners. Furthermore, microglia showed an activated state with an increased phagocytic capability and reduced expression of neurotrophic factors. Although multiple auto-antibodies including lupus-related ones were detected in the sera of the mice as well as AGS patients, Ifih1G821S/+Rag2-/- mice also exhibited up-regulation of IFN-I, astrogliosis and microgliosis, indicating that auto-antibodies or lymphocytes are not required for the development of the encephalitis. The IFN-I signature without lymphocytic infiltration observed in Ifih1G821S/+ mice is a typical feature of AGS. Collectively, our results suggest that the Ifih1G821S/+ mice are a model recapitulating AGS and that microglia are a potential target for AGS therapy.

A Novel Mutation in Aicardi–Goutières' Syndrome: A Case Report

Aicardi–Goutières' syndrome (AGS) is a rare heterogeneous genetic disorder characterized by encephalopathy and may bear resemblance to congenital infections. The prevalence of AGS is estimated at more than 4,000 worldwide. Mutations in TREX1 gene are present in ∼22% of patients. We present the case of a 2-year-old boy who came to the Biogene laboratory (Tehran, Iran) with a constellation of congenital disorders but no clear diagnosis. His clinical phenotype consisted of neonatal jaundice, relative microcephaly with diffuse cerebral atrophy in both hemispheres, developmental delay, hypotonia, and nystagmus. There was history of parental consanguineous marriage and prematurity. In our study, a homozygous potentially pathogenic mutation in TREX1 gene associated with AGS1 was detected. This mutation has not been reported in the other patients with AGS. A novel frameshift homozygous potentially pathogenic mutation in TREX1 is postulated to be the cause of disease in our patient.

Lesion evolution and neurodegeneration in RVCL-S: A monogenic microvasculopathy

Objective

To characterize lesion evolution and neurodegeneration in retinal vasculopathy with cerebral leukoencephalopathy and systemic manifestations (RVCL-S) using multimodal MRI.

Methods

We prospectively performed MRI and cognitive testing in RVCL-S and healthy control cohorts. Gray and white matter volume and disruption of white matter microstructure were quantified. Asymmetric spin echo acquisition permitted voxel-wise oxygen extraction fraction (OEF) calculation as an in vivo marker of microvascular ischemia. The RVCL-S cohort was included in a longitudinal analysis of lesion subtypes in which hyperintense lesions on fluid-attenuated inversion recovery (FLAIR), T1-postgadolinium, and diffusion-weighted imaging were delineated and quantified volumetrically.

Results

Twenty individuals with RVCL-S and 26 controls were enrolled. White matter volume and microstructure declined faster in those with RVCL–S compared to controls. White matter atrophy in RVCL-S was highly linear (ρ = −0.908, p < 0.0001). Normalized OEF was elevated in RVCL-S and increased with disease duration. Multiple cognitive domains, specifically those measuring working memory and processing speed, were impaired in RVCL-S. Lesion volumes, regardless of subtype, progressed/regressed with high variability as a function of age, while FLAIR lesion burden increased near time to death (p < 0.001).

Conclusion

RVCL-S is a monogenic microvasculopathy affecting predominantly the white matter with regard to atrophy and cognitive impairment. White matter volumes in RVCL-S declined linearly, providing a potential metric against which to test the efficacy of future therapies. Progressive elevation of white matter OEF suggests that microvascular ischemia may underlie neurodegeneration in RVCL-S.

The cGAS-STING pathway: The role of self-DNA sensing in inflammatory lung disease

The presence of DNA in the cytosol is usually a sign of microbial infections, which alerts the host innate immune system to mount a defense response. Cyclic GMP-AMP synthase (cGAS) is a critical cytosolic DNA sensor that elicits robust innate immune responses through the production of the second messenger, cyclic GMP-AMP (cGAMP), which binds and activates stimulator of interferon genes (STING). However, cGAS binds to DNA irrespective of DNA sequence, therefore, self-DNA leaked from the nucleus or mitochondria can also serve as a cGAS ligand to activate this pathway and trigger extensive inflammatory responses. Dysregulation of the cGAS-STING pathway is responsible for a broad array of inflammatory and autoimmune diseases. Recently, evidence has shown that self-DNA release and cGAS-STING pathway over-activation can drive lung disease, making this pathway a promising therapeutic target for inflammatory lung disease. Here, we review recent advances on the cGAS-STING pathway governing self-DNA sensing, highlighting its role in pulmonary disease.

TREX1 As a Potential Therapeutic Target for Autoimmune and Inflammatory Diseases

BACKGROUND AND OBJECTIVES

The 3' repair exonuclease 1 (TREX1) gene is the major DNA-specific 3'-5 'exonuclease of mammalian cells which reduces single- and double-stranded DNA (ssDNA and dsDNA) to prevent undue immune activation mediated by the nucleic acid. TREX1 is also a crucial suppressor of selfrecognition that protects the host from inappropriate autoimmune activations. It has been revealed that TREX1 function is necessary to prevent host DNA accumulating after cell death which could actuate an autoimmune response. In the manuscript, we will discuss in detail the latest advancement to study the role of TREX1 in autoimmune disease.

METHODS

As a pivotal cytoprotective, antioxidant, anti-apoptotic, immunosuppressive, as well as an antiinflammatory molecule, the functional mechanisms of TREX1 were multifactorial. In this review, we will briefly summarize the latest advancement in studying the role of TREX1 in autoimmune disease, and discuss its potential as a therapeutic target for these diseases.

RESULTS

Deficiency of TREX1 in human patients and murine models is characterized by systemic inflammation and the disorder of TREX1 functions drives inflammatory responses leading to autoimmune disease. Moreover, much more studies revealed that mutations in TREX1 have been associated with a range of autoimmune disorders. But it is also unclear whether the mutations of TREX1 play a causal role in the disease progression, and whether manipulation of TREX1 has a beneficial effect in the treatment of autoimmune diseases.

CONCLUSION

Integration of functional TREX1 biology into autoimmune diseases may further deepen our understanding of the development and pathogenesis of autoimmune diseases and provide new clues and evidence for the treatment of autoimmune diseases.

TREX1 - Apex predator of cytosolic DNA metabolism

The cytosolic Three prime Repair EXonuclease 1 (TREX1) is a powerful DNA-degrading enzyme required for clearing cytosolic DNA to prevent aberrant inflammation and autoimmunity. In the absence of TREX1 activity, cytosolic DNA pattern recognition receptors of the innate immune system are constitutively activated by undegraded TREX1 substrates. This triggers a chronic inflammatory response in humans expressing mutant TREX1 alleles, eliciting a spectrum of rare autoimmune diseases dependent on the nature of the mutation. The precise origins of cytosolic DNA targeted by TREX1 continue to emerge, but DNA emerging from the nucleus or taken up by the cell could represent potential sources. In this Review, we explore the biochemical and immunological data supporting the role of TREX1 in suppressing cytosolic DNA sensing, and discuss the possibility that TREX1 may contribute to maintenance of genome integrity.

T Cells Produce IFN-α in the TREX1 D18N Model of Lupus-like Autoimmunity

Autoimmunity can result when cells fail to properly dispose of DNA. Mutations in the three-prime repair exonuclease 1 (TREX1) cause a spectrum of human autoimmune diseases resembling systemic lupus erythematosus. The cytosolic dsDNA sensor, cyclic GMP-AMP synthase (cGAS), and the stimulator of IFN genes (STING) are required for pathogenesis, but specific cells in which DNA sensing and subsequent type I IFN (IFN-I) production occur remain elusive. In this study, we demonstrate that TREX1 D18N catalytic deficiency causes dysregulated IFN-I signaling and autoimmunity in mice. Moreover, we show that bone marrow-derived cells drive this process. We identify both innate immune and, surprisingly, activated T cells as sources of pathological IFN-α production. These findings demonstrate that TREX1 enzymatic activity is crucial to prevent inappropriate DNA sensing and IFN-I production in immune cells, including normally low-level IFN-α-producing cells. These results expand our understanding of DNA sensing and innate immunity in T cells and may have relevance to the pathogenesis of human disease caused by TREX1 mutation.

Increased Mortality and Vascular Phenotype in a Knock-In Mouse Model of Retinal Vasculopathy With Cerebral Leukoencephalopathy and Systemic Manifestations

Background and Purpose—

Retinal vasculopathy with cerebral leukoencephalopathy and systemic manifestations (RVCL-S) is an autosomal dominant small vessel disease caused by C-terminal frameshift mutations in the TREX1 gene that encodes the major mammalian 3′ to 5′ DNA exonuclease. RVCL-S is characterized by vasculopathy, especially in densely vascularized organs, progressive retinopathy, cerebral microvascular disease, white matter lesions, and migraine, but the underlying mechanisms are unknown.

Methods—

Homozygous transgenic RVCL-S knock-in mice expressing a truncated Trex1 (three prime repair exonuclease 1) protein (similar to what is seen in patients) and wild-type littermates, of various age groups, were subjected to (1) a survival analysis, (2) in vivo postocclusive reactive hyperemia and ex vivo Mulvany myograph studies to characterize the microvascular and macrovascular reactivity, and (3) experimental stroke after transient middle cerebral artery occlusion with neurological deficit assessment.

Results—

The mutant mice show increased mortality starting at midlife ( P =0.03 with hazard ratio, 3.14 [95% CI, 1.05–9.39]). The mutants also show a vascular phenotype as evidenced by attenuated postocclusive reactive hyperemia responses (across all age groups; F[1, 65]=5.7, P =0.02) and lower acetylcholine-induced relaxations in aortae (in 20- to 24-month-old mice; RVCL-S knock-in: E max : 37±8% versus WT: E max : 65±6%, P =0.01). A vascular phenotype is also suggested by the increased infarct volume seen in 12- to 14-month-old mutant mice at 24 hours after infarct onset (RVCL-S knock-in: 75.4±2.7 mm 3 versus WT: 52.9±5.6 mm 3 , P =0.01).

Conclusions—

Homozygous RVCL-S knock-in mice show increased mortality, signs of abnormal vascular function, and increased sensitivity to experimental stroke and can be instrumental to investigate the pathology seen in patients with RVCL-S.

Monogenic lupus: Dissecting heterogeneity

Systemic lupus erythematosus (SLE) is a severe lifelong multisystem autoimmune disease characterized by the presence of autoantibodies targeting nuclear autoantigens, increased production of type I interferon and B cell abnormalities. Clinical presentation of SLE is extremely heterogeneous and different groups of disease are likely to exist. Recently, childhood-onset SLE (cSLE) cases have been linked to single gene mutations, defining the concept of monogenic or Mendelian lupus. Genes associated with Mendelian lupus can be grouped in at least three functional categories. First, complement deficiencies represent the main cause of monogenic lupus and its components are involved in the clearance of dying cells, a mechanism also called efferocytosis. Mutations in extracellular DNASE have been also identified in cSLE patients and represent additional causes leading to defective clearance of nucleic acids and apoptotic bodies. Second, the study of Aicardi-Goutières syndromes has introduced the concept of type-I interferonopathies. Bona fide lupus syndromes have been associated to this genetic condition, driven by defective nucleic acids metabolism or innate sensors overactivity. Interferon signalling anomalies can be detected and monitored during therapies, such as Janus-kinase (JAK) inhibitors. Third, tolerance breakdown can occur following genetic mutations in B and/or T cell expressing key immunoregulatory molecules. Biallelic mutations in PRKCD are associated to lupus and lymphoproliferative diseases as PKC-δ displays proapoptotic activity and is crucial to eliminate self-reactive transitional B cells. Here we review the literature of the emerging field of Mendelian lupus and discuss the physiopathological learning from these inborn errors of immunity. In addition, clinical and biological features are highlighted as well as specific therapies that have been tested in these genetic contexts.

Systemic Lupus Erythematosus and DNA Degradation and Elimination Defects

Introduction: Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that is characterized by the production of autoantibodies specific for components of the cell nucleus and that causes damage to body tissues and organs. The pathogenesis of SLE remains unclear, with numerous studies pointing to a combination of genetic and environmental factors. A critical stage in SLE development is cell necrosis, in which undegraded chromatin and nucleoproteins are released into the blood, resulting in circulating cell-free DNA and serum nucleoproteins that trigger anti-dsDNA autoantibody production. This systematic literature review aimed to examine whether SLE stems from a DNA degradation and elimination defect. Materials and Methods: An advanced literature search was conducted in PubMed using the following keywords: [("SLE" OR "Systemic Lupus Erythematosus" OR "Lupus")] AND [("DNA" OR "DNA Degradation")] AND [("Defect Elimination")]. More articles were obtained from the references of the identified articles and basic Google searches. Twenty-five peer-reviewed articles published within the past 10 years (2007-2018) were included for review. Results: The findings of each study are summarized in Tables 1, 2. Discussion and Conclusion: The etiopathogenesis of SLE remains controversial, which limits therapeutic inventions for this disease. However, SLE is a DNA degradation and elimination disorder caused by uncleared histones and nuclear material that leak into the extracellular space and form cell-free DNA, triggering an immune response that destroys tissues and organs. Under normal conditions, apoptosis allows DNA and other nuclear material to be efficiently cleared through degradation and additional complex mechanisms such that this material does not trigger the immune system to produce nuclear autoantibodies.

Measuring TREX1 and TREX2 exonuclease activities

Three-prime Repair Exonuclease (TREX1) degrades ssDNA and dsDNA. TREX1 localizes to the perinuclear space in cells and degrades cytosolic DNA to prevent aberrant nucleic acid sensing and immune activation in humans and mice. Mutations in the TREX1 gene cause a spectrum of human autoimmune diseases including Aicardi-Goutières syndrome, familial chilblain lupus, retinal vasculopathy with cerebral leukodystrophy, and are associated with systemic lupus erythematosus. More than 60 disease-causing TREX1 variants have been identified including dominant and recessive, missense, and frameshift mutations that map to the catalytic core region and to the C-terminal cell localization region. The TREX1-disease causing mutations affect exonuclease activity at varied levels. In this chapter, we describe methods to purify variant recombinant TREX1 enzymes and measure the exonuclease activity using ssDNA and dsDNA substrates. The relationships between TREX1 activities, types of TREX1 mutations, and TREX1-associated autoimmune diseases are considered.

A bioactive mammalian disaccharide associated with autoimmunity activates STING-TBK1-dependent immune response

Glycans from microbial pathogens are well known pathogen-associated molecular patterns that are recognized by the host immunity; however, little is known about whether and how mammalian self-glycans activate the host immune response, especially in the context of autoimmune disease. Using biochemical fractionation and two-dimensional HPLC, we identify an abundant and bioactive free glycan, the Manβ1-4GlcNAc disaccharide in TREX1-associated autoimmune diseases. We report that both monosaccharide residues and the β1-4 linkage are critical for bioactivity of this disaccharide. We also show that Manβ1-4GlcNAc is produced by oligosaccharyltransferase hydrolysis of lipid-linked oligosaccharides in the ER lumen, followed by ENGase and mannosidase processing in the cytosol and lysosomes. Furthermore, synthetic Manβ1-4GlcNAc disaccharide stimulates a broad immune response in vitro, which is in part dependent on the STING-TBK1 pathway, and enhances antibody response in vivo. Together, our data identify Manβ1-4GlcNAc as a novel innate immune modulator associated with chronic autoimmune diseases.

cGAS activation causes lupus-like autoimmune disorders in a TREX1 mutant mouse model

TREX1 encodes a major cellular DNA exonuclease. Mutations of this gene in human cause cellular accumulation of DNA that triggers autoimmune diseases including Aicardi-Goutieres Syndrome (AGS) and systemic lupus erythematosus (SLE). We created a lupus mouse model by engineering a D18 N mutation in the Trex1 gene which inactivates the enzyme and has been found in human patients with lupus-like disorders. The Trex1^D18N/D18N mice exhibited systemic inflammation that consistently recapitulates many characteristics of human AGS and SLE. Importantly, ablation of cGas gene in the Trex1^D18N/D18N mice rescued the lethality and all detectable pathological phenotypes, including multi-organ inflammation, interferon stimulated gene induction, autoantibody production and aberrant T-cell activation. These results indicate that cGAS is a key mediator in the autoimmune disease associated with defective TREX1 function, providing additional insights into disease pathogenesis and guidance to the development of therapeutics for human systemic autoimmune disorders.

Retinal vasculopathy with cerebral leukoencephalopathy (RVCL): A rare mimic of tumefactive MS

OBJECTIVE

We report a series of 2 brothers who each developed tumefactive brain lesions, initially thought to have brain tumors or tumefactive multiple sclerosis (MS), but who were ultimately diagnosed with a rare autosomal dominant condition known as retinal vasculopathy with cerebral leukoencephalopathy (RVCL).

METHODS

Case series and literature review.

RESULTS

We present 2 brothers who developed tumefactive right frontal brain lesions leading to gait disturbances and cognitive changes. Both brothers also had nonspecific brain calcifications and T2-hyperintense lesions, and both had ophthalmic and liver disease of unclear etiology. The first brother had been extensively evaluated by various specialists, underwent inconclusive brain and liver biopsies, and was ultimately unsuccessfully treated for a diagnosis of tumefactive MS. The second brother also underwent unrevealing evaluation with CSF analysis and brain biopsy. Further family history revealed that the patients' father developed a tumefactive brain lesion in the 1980s and had been diagnosed with CNS vasculitis. Given the familial link, RVCL was suspected, and genetic analysis confirmed the diagnosis with a 3-prime repair exonuclease 1 (TREX1) C-terminal mutation.

CONCLUSION

The presence of tumefactive brain lesions, nonspecific brain calcifications, liver disease, and retinal vasculopathy, coupled with suggestive family history, led to the RVCL diagnosis. This report contributes to the limited understanding of RVCL, which can cause brain lesions that mimic gliomas or tumefactive MS. Recognition of this entity may prevent unnecessary invasive procedures and inappropriate therapeutic interventions, and would allow for proper counseling of family members.