Mutations in RNU7-1 Weaken Secondary RNA Structure, Induce MCP-1 and CXCL10 in CSF, and Result in Aicardi-Goutières Syndrome with Severe End-Organ Involvement

Emerging concepts and treatments in autoinflammatory interferonopathies and monogenic systemic lupus erythematosus

Over the past two decades, the number of genetically defined autoinflammatory interferonopathies has steadily increased. Aicardi-Goutières syndrome and proteasome-associated autoinflammatory syndromes (PRAAS, also known as CANDLE) are caused by genetic defects that impair homeostatic intracellular nucleic acid and protein processing respectively. Research into these genetic defects revealed intracellular sensors that activate type I interferon production. In SAVI and COPA syndrome, genetic defects that cause chronic activation of the dinucleotide sensor stimulator of interferon genes (STING) share features of lung inflammation and fibrosis; and selected mutations that amplify interferon-α/β receptor signalling cause central nervous system manifestations resembling Aicardi-Goutières syndrome. Research into the monogenic causes of childhood-onset systemic lupus erythematosus (SLE) demonstrates the pathogenic role of autoantibodies to particle-bound extracellular nucleic acids that distinguishes monogenic SLE from the autoinflammatory interferonopathies. This Review introduces a classification for autoinflammatory interferonopathies and discusses the divergent and shared pathomechanisms of interferon production and signalling in these diseases. Early success with drugs that block type I interferon signalling, new insights into the roles of cytoplasmic DNA or RNA sensors, pathways in type I interferon production and organ-specific pathology of the autoinflammatory interferonopathies and monogenic SLE, reveal novel drug targets that could personalize treatment approaches.

The prototypical interferonopathy: Aicardi-Goutières syndrome from bedside to bench

Aicardi-Goutières syndrome (AGS) is a progressive genetic encephalopathy caused by pathogenic mutations in genes controlling cellular anti-viral responses and nucleic acid metabolism. The mutations initiate autoinflammatory processes in the brain and systemically that are triggered by chronic overproduction of type I interferon (IFN), including IFN-alpha. Emerging disease-directed therapies aim to dampen autoinflammation and block cellular responses to IFN production, creating an urgent and unmet need to understand better which cells, compartments, and mechanisms underlying disease pathogenesis. In this review, we highlight existing pre-clinical models of AGS and our current understanding of how causative genetic mutations promote disease in AGS, to promote new model development and a continued focus on improving and directing future therapies.

A zebrafish model of Ifih1-driven Aicardi-Goutières syndrome reproduces the interferon signature and the exacerbated inflammation of patients

Type I interferonopathies are a heterogenic group of rare diseases associated with an increase in type I interferon (IFN). The main challenge for the study of Type I interferonopathies is the lack of a well-founded animal model to better characterize the phenotype as well as to perform fast and large drug screenings to offer the best treatment options. In this study, we report the development of a transgenic zebrafish model of Type I interferonopathy overexpressing ifih1 carrying the mutation p.Arg742His (Tg(ifih1_mut)), corresponding to the human mutation p.Arg779His. RNA sequence analysis from Tg(ifih1_mut) larvae revealed a systemic inflammation and IFN signature upon a suboptimal poly I:C induction compared with wild-type larvae, confirming the phenotype observed in patients suffering from Type I interferonopathies. More interestingly, the phenotype was manifested in the zebrafish inflammation and Type I IFN reporters nfkb:eGFP and isg15:eGFP, respectively, making this zebrafish model suitable for future high-throughput chemical screening (HTS). Using the unique advantages of the zebrafish model for gene editing, we have generated Tg(ifih1_mut) knocked down for mavs and ikbke, which completely abrogated the Poly I:C induction and activation of the GFP of the reporters. Finally, we used an FDA-approved drug, Baricitinib (Jak1/Jak2 inhibitor), which was able to reduce the inflammation and the ISG expression. Our results demonstrate the potential of this model to further understand AGS pathological mechanisms and to identify novel therapeutic drugs by HTS.

lhCLIP reveals the in vivo RNA-RNA interactions recognized by hnRNPK

RNA-RNA interactions play a crucial role in regulating gene expression and various biological processes, but identifying these interactions on a transcriptomic scale remains a challenge. To address this, we have developed a new biochemical technique called pCp-biotin labelled RNA hybrid and ultraviolet crosslinking and immunoprecipitation (lhCLIP) that enables the transcriptome-wide identification of intra- and intermolecular RNA-RNA interactions mediated by a specific RNA-binding protein (RBP). Using lhCLIP, we have uncovered a diverse landscape of intermolecular RNA interactions recognized by hnRNPK in human cells, involving all major classes of noncoding RNAs (ncRNAs) and mRNA. Notably, hnRNPK selectively binds with snRNA U4, U11, and U12, and shapes the secondary structure of these snRNAs, which may impact RNA splicing. Our study demonstrates the potential of lhCLIP as a user-friendly and widely applicable method for discovering RNA-RNA interactions mediated by a particular protein of interest and provides a valuable tool for further investigating the role of RBPs in gene expression and biological processes.

Aicardi-Goutières syndrome: A monogenic type I interferonopathy

Aicardi-Goutières syndrome (AGS) is a rare monogenic autoimmune disease that primarily affects the brains of children patients. Its main clinical features include encephalatrophy, basal ganglia calcification, leukoencephalopathy, lymphocytosis and increased interferon-α (IFN-α) levels in the patient's cerebrospinal fluid (CSF) and serum. AGS may be caused by mutations in any one of nine genes (TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, ADAR1, IFIH1, LSM11 and RNU7-1) that result in accumulation of self-nucleic acids in the cytoplasm or aberrant sensing of self-nucleic acids. This triggers overproduction of type I interferons (IFNs) and subsequently causes AGS, the prototype of type I interferonopathies. This review describes the discovery history of AGS with various genotypes and provides the latest knowledge of clinical manifestations and causative genes of AGS. The relationship between AGS and type I interferonopathy and potential therapeutic methods for AGS are also discussed in this review.

Significance of the cGAS-STING Pathway in Health and Disease

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway plays a significant role in health and disease. In this pathway, cGAS, one of the major cytosolic DNA sensors in mammalian cells, regulates innate immunity and the STING-dependent production of pro-inflammatory cytokines, including type-I interferon. Moreover, the cGAS-STING pathway is integral to other cellular processes, such as cell death, cell senescence, and autophagy. Activation of the cGAS-STING pathway by "self" DNA is also attributed to various infectious diseases and autoimmune or inflammatory conditions. In addition, the cGAS-STING pathway activation functions as a link between innate and adaptive immunity, leading to the inhibition or facilitation of tumorigenesis; therefore, research targeting this pathway can provide novel clues for clinical applications to treat infectious, inflammatory, and autoimmune diseases and even cancer. In this review, we focus on the cGAS-STING pathway and its corresponding cellular and molecular mechanisms in health and disease.

Understanding the role of cGAS-STING signaling in ischemic stroke: a new avenue for drug discovery

INTRODUCTION

Ischemic stroke is a significant global health challenge with limited treatment options. Neuroinflammation, driven by microglial activation, plays a critical role in stroke pathophysiology. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has emerged as a key player in microglial activation, sterile neuroinflammation, and cell death following stroke. Understanding the interplay between this pathway and stroke pathophysiology is crucial for exploring newer therapeutics for stroke patients.

AREAS COVERED

This review discusses the pivotal role of the cGAS-STING pathway in ischemic stroke. It explores the interplay between cGAS-STING activation, neuroinflammation, microglia activation, M2 polarization, neutrophil infiltration, and cytokine release. Additionally, the authors examine its contributions to various cell death programs (pyroptosis, apoptosis, necroptosis, lysosomal cell death, autophagy, and ferroptosis). The review summarizes recent studies on targeting cGAS-STING signaling in stroke, highlighting the therapeutic potential of small molecule inhibitors and RNA-based approaches in mitigating neuroinflammation, preventing cell death, and improving patient outcomes.

EXPERT OPINION

Understanding cGAS-STING signaling in ischemic stroke offers an exciting avenue for drug discovery. Targeting this pathway holds promise for developing novel therapeutics that effectively mitigate neuroinflammation, prevent cell death, and enhance patient outcomes. Further research and development of therapeutic strategies are warranted to fully exploit the potential of this pathway as a therapeutic target for stroke.

Exome Sequencing and Multigene Panel Testing in 1,411 Patients With Adult-Onset Neurologic Disorders

Background and Objectives

Owing to their extensive clinical and molecular heterogeneity, hereditary neurologic diseases in adults are difficult to diagnose. The current knowledge about the diagnostic yield and clinical utility of exome sequencing (ES) for neurologic diseases in adults is limited. This observational study assesses the diagnostic value of ES and multigene panel analysis in adult-onset neurologic disorders.

Methods

From January 2019 through April 2022, ES-based multigene panel testing was conducted in 1,411 patients with molecularly unexplained neurologic phenotypes at the Ghent University Hospital. Gene panels were developed for ataxia and spasticity, leukoencephalopathy, movement disorders, paroxysmal episodic disorders, neurodegeneration with brain iron accumulation, progressive myoclonic epilepsy, and amyotrophic lateral sclerosis. Single nucleotide variants, small indels, and copy number variants were analyzed. Across all panels, our analysis covered a total of 725 genes associated with Mendelian inheritance.

Results

A molecular diagnosis was established in 10% of the cases (144 of 1,411) representing 71 different monogenic disorders. The diagnostic yield depended significantly on the presenting phenotype with the highest yield seen in patients with ataxia or spastic paraparesis (19%). Most of the established diagnoses comprised disorders with an autosomal dominant inheritance (62%), and the most frequently mutated genes were NOTCH3 (13 patients), SPG7 (11 patients), and RFC1 (8 patients). 34% of the disease-causing variants were novel, including a unique likely pathogenic variant in APP (Ghent mutation, p.[Asn698Asp]) in a family presenting with stroke and severe cerebral white matter disease. 7% of the pathogenic variants comprised copy number variants detected in the ES data and confirmed by an independent technique.

Discussion

ES and multigene panel testing is a powerful and efficient tool to diagnose patients with unexplained, adult-onset neurologic disorders.

GTF3A mutations predispose to herpes simplex encephalitis by disrupting biogenesis of the host-derived RIG-I ligand RNA5SP141

Herpes simplex virus 1 (HSV-1) infects several billion people worldwide and can cause life-threatening herpes simplex encephalitis (HSE) in some patients. Monogenic defects in components of the type I interferon system have been identified in patients with HSE, emphasizing the role of inborn errors of immunity underlying HSE pathogenesis. Here, we identify compound heterozygous loss-of-function mutations in the gene GTF3A encoding for transcription factor IIIA (TFIIIA), a component of the RNA polymerase III complex, in a patient with common variable immunodeficiency and HSE. Patient fibroblasts and GTF3A gene-edited cells displayed impaired HSV-1-induced innate immune responses and enhanced HSV-1 replication. Chromatin immunoprecipitation sequencing analysis identified the 5S ribosomal RNA pseudogene 141 (RNA5SP141), an endogenous ligand of the RNA sensor RIG-I, as a transcriptional target of TFIIIA. GTF3A mutant cells exhibited diminished RNA5SP141 expression and abrogated RIG-I activation upon HSV-1 infection. Our work unveils a crucial role for TFIIIA in transcriptional regulation of a cellular RIG-I agonist and shows that GTF3A genetic defects lead to impaired cell-intrinsic anti-HSV-1 responses and can predispose to HSE.