Aicardi-Goutières syndrome

Protein-protein interactions in cGAS-STING pathway: a medicinal chemistry perspective

Protein-protein interactions (PPIs) play pivotal roles in biological processes and are closely linked with human diseases. Research on small molecule inhibitors targeting PPIs provides valuable insights and guidance for novel drug development. The cGAS-STING pathway plays a crucial role in regulating human innate immunity and is implicated in various pathological conditions. Therefore, modulators of the cGAS-STING pathway have garnered extensive attention. Given that this pathway involves multiple PPIs, modulating PPIs associated with the cGAS-STING pathway has emerged as a promising strategy for modulating this pathway. In this review, we summarize an overview of recent advancements in medicinal chemistry insights into cGAS-STING PPI-based modulators and propose alternative strategies for further drug discovery based on the cGAS-STING pathway.

Vasculitis and vasculopathy associated with inborn errors of immunity: an overview

Systemic autoinflammatory diseases (SAIDs) are disorders of innate immunity, which are characterized by unprovoked recurrent flares of systemic inflammation often characterized by fever associated with clinical manifestations mainly involving the musculoskeletal, mucocutaneous, gastrointestinal, and nervous systems. Several conditions also present with varied, sometimes prominent, involvement of the vascular system, with features of vasculitis characterized by variable target vessel involvement and organ damage. Here, we report a systematic review of vasculitis and vasculopathy associated with inborn errors of immunity.

Antiviral Defence Mechanisms during Early Mammalian Development

The type-I interferon (IFN) response constitutes the major innate immune pathway against viruses in mammals. Despite its critical importance for antiviral defence, this pathway is inactive during early embryonic development. There seems to be an incompatibility between the IFN response and pluripotency, the ability of embryonic cells to develop into any cell type of an adult organism. Instead, pluripotent cells employ alternative ways to defend against viruses that are typically associated with safeguard mechanisms against transposable elements. The absence of an inducible IFN response in pluripotent cells and the constitutive activation of the alternative antiviral pathways have led to the hypothesis that embryonic cells are highly resistant to viruses. However, some findings challenge this interpretation. We have performed a meta-analysis that suggests that the susceptibility of pluripotent cells to viruses is directly correlated with the presence of receptors or co-receptors for viral adhesion and entry. These results challenge the current view of pluripotent cells as intrinsically resistant to infections and raise the fundamental question of why these cells have sacrificed the major antiviral defence pathway if this renders them susceptible to viruses.

Aicardi-Goutières Syndrome with Congenital Glaucoma Caused by Novel TREX1 Mutation

BACKGROUND

Aicardi-Goutières syndrome (AGS) is a rare genetic disorder characterized by microcephaly, white matter lesions, numerous intracranial calcifications, chilblain skin lesions and high levels of interferon-α (IFN-α) in the cerebrospinal fluid (CSF). However, ocular involvement is reported significantly less frequently.

CASE PRESENTATION

We present a case of a neonate with hypotrophy, microcephaly, frostbite-like skin lesions, thrombocytopenia, elevated liver enzymes and hepatosplenomegaly. Magnetic resonance imaging (MRI) of the brain showed multiple foci of calcification, white matter changes, cerebral atrophy, and atrophic dilatation of the ventricular system. The inflammatory parameters were not elevated, and the infectious etiology was excluded. Instead, elevated levels of IFN-α in the serum were detected. Based on the related clinical symptoms, imaging and test findings, the diagnosis of AGS was suspected. Genetic testing revealed two pathogenic mutations, c.490C>T and c.222del (novel mutation), in the three prime repair exonuclease 1 (TREX1) gene, confirming AGS type 1 (AGS1). An ophthalmologic examination of the child at 10 months of age revealed an impaired pupillary response to light, a corneal haze with Haab lines in the right eye (RE), pale optic nerve discs and neuropathy in both eyes (OU). The intraocular pressure (IOP) was 51 mmHg in the RE and 49 in the left eye (LE). The flash visual evoked potential (FVEP) showed prolonged P2 latencies of up to 125% in the LE and reduced amplitudes of up to approximately 10% OU. This girl was diagnosed with congenital glaucoma, and it was managed with a trabeculectomy with a basal iridectomy of OU, resulting in a reduction and stabilization in the IOP to 12 mmHg in the RE and 10 mmHg in the LE without any hypotensive eyedrops.

CONCLUSIONS

We present the clinical characteristics, electrophysiological and imaging findings, as well as the genetic test results of a patient with AGS1. Our case contributes to the extended ophthalmic involvement of the pathogenic c.490C>T and c.222del mutations in TREX1.

Recent trends in STING modulators: Structures, mechanisms, and therapeutic potential

The cyclic GMP-AMP synthase stimulator (cGAS)-stimulator of interferon gene (STING) signaling pathway has an integral role in the host immune response through DNA sensing followed by inducing a robust innate immune defense program. STING has become a promising therapeutic target associated with multiple diseases, including various inflammatory diseases, cancer, and infectious diseases, among others. Thus, modulators of STING are regarded as emerging therapeutic agents. Recent progress has been made in STING research, including recently identified STING-mediated regulatory pathways, the development of a new STING modulator, and the new association of STING with disease. In this review, we focus on recent trends in the development of STING modulators, including structures, mechanisms, and clinical application.

SP1/RNASEH2A accelerates the development of hepatocellular carcinoma by regulating EMT

Background

The expression level of Ribonuclease H2, subunit A (RNASEH2A) in hepatocellular carcinoma (HCC) has been reported, but the function of RNASEH2A on HCC cells development and the related molecular mechanisms remain unclear. Herein, we intend to explore the upstream regulator of RNASEH2A and its role in the HCC progression.

Methods

GEPIA website was employed to determine the level of RNASEH2A in HCC tissues and get a survival analysis. After reducing RNASEH2A expression by RNA interference, cell counting kit-8, colony formation, Western blot, Transwell and wound healing assays were performed to estimate the malignant properties of HCC cells. The transcriptional factor of RNASEH2A was predicted by UCSC and JASPAR database and confirmed by dual luciferase assay and Ch-IP assay. The expression level of EMT pathway related molecules was determined by western blotting.

Results

An increased expression of RNASEH2A was presented in HCC and predicted worse prognosis of HCC patients. Functionally, the results demonstrated that depletion of RNASEH2A suppressed HCC cell proliferation, cell cycle, migration and invasion. Moreover, we illustrated that SP1 targeted to the promoter of RNASEH2A and modulated its expression in HCC cell lines. RNASEH2A knockdown counteracted the function of SP1 overexpression in modulating HCC cell growth, cell cycle, and mobility. Then, our data showed that the SP1/RNASEH2A axis affected the malignant behaviors of HCC cells by regulating EMT process.

Conclusions

In summary, these results demonstrated that RNASEH2A promoted HCC cells development through regulating EMT process and was transcriptionally modulated by SP1.

A Case Report and Literature Review of Pseudo-TORCH Syndrome Type 2 (PTORCH2)

A pseudo-TORCH syndrome is a rare autosomal recessive disease characterized by intracranial calcification and microcephaly, leading to spasticity and seizures, but the serology of TORCH infection is negative. We present a 4-day-old female patient with jaundice, abnormal movement, and convulsions who was found to be homozygous for the missense USP18 gene mutation that causes pseudo-TORCH syndrome 2 (PTORCH2). The patient was managed with conservative measures.

Emerging cellular themes in leukodystrophies

Leukodystrophies are a broad spectrum of neurological disorders that are characterized primarily by deficiencies in myelin formation. Clinical manifestations of leukodystrophies usually appear during childhood and common symptoms include lack of motor coordination, difficulty with or loss of ambulation, issues with vision and/or hearing, cognitive decline, regression in speech skills, and even seizures. Many cases of leukodystrophy can be attributed to genetic mutations, but they have diverse inheritance patterns (e.g., autosomal recessive, autosomal dominant, or X-linked) and some arise from de novo mutations. In this review, we provide an updated overview of 35 types of leukodystrophies and focus on cellular mechanisms that may underlie these disorders. We find common themes in specialized functions in oligodendrocytes, which are specialized producers of membranes and myelin lipids. These mechanisms include myelin protein defects, lipid processing and peroxisome dysfunction, transcriptional and translational dysregulation, disruptions in cytoskeletal organization, and cell junction defects. In addition, non-cell-autonomous factors in astrocytes and microglia, such as autoimmune reactivity, and intercellular communication, may also play a role in leukodystrophy onset. We hope that highlighting these themes in cellular dysfunction in leukodystrophies may yield conceptual insights on future therapeutic approaches.

P2RY8 variants in lupus patients uncover a role for the receptor in immunological tolerance

B cell self-tolerance is maintained through multiple checkpoints, including restraints on intracellular signaling and cell trafficking. P2RY8 is a receptor with established roles in germinal center (GC) B cell migration inhibition and growth regulation. Somatic P2RY8 variants are common in GC-derived B cell lymphomas. Here, we identify germline novel or rare P2RY8 missense variants in lupus kindreds or the related antiphospholipid syndrome, including a "de novo" variant in a child with severe nephritis. All variants decreased protein expression, F-actin abundance, and GPCR-RhoA signaling, and those with stronger effects increased AKT and ERK activity and cell migration. Remarkably, P2RY8 was reduced in B cell subsets from some SLE patients lacking P2RY8 gene variants. Low P2RY8 correlated with lupus nephritis and increased age-associated B cells and plasma cells. By contrast, P2RY8 overexpression in cells and mice restrained plasma cell development and reinforced negative selection of DNA-reactive developing B cells. These findings uncover a role of P2RY8 in immunological tolerance and lupus pathogenesis.

Human iPSC-Derived Astrocytes: A Powerful Tool to Study Primary Astrocyte Dysfunction in the Pathogenesis of Rare Leukodystrophies

Astrocytes are very versatile cells, endowed with multitasking capacities to ensure brain homeostasis maintenance from brain development to adult life. It has become increasingly evident that astrocytes play a central role in many central nervous system pathologies, not only as regulators of defensive responses against brain insults but also as primary culprits of the disease onset and progression. This is particularly evident in some rare leukodystrophies (LDs) where white matter/myelin deterioration is due to primary astrocyte dysfunctions. Understanding the molecular defects causing these LDs may help clarify astrocyte contribution to myelin formation/maintenance and favor the identification of possible therapeutic targets for LDs and other CNS demyelinating diseases. To date, the pathogenic mechanisms of these LDs are poorly known due to the rarity of the pathological tissue and the failure of the animal models to fully recapitulate the human diseases. Thus, the development of human induced pluripotent stem cells (hiPSC) from patient fibroblasts and their differentiation into astrocytes is a promising approach to overcome these issues. In this review, we discuss the primary role of astrocytes in LD pathogenesis, the experimental models currently available and the advantages, future evolutions, perspectives, and limitations of hiPSC to study pathologies implying astrocyte dysfunctions.

The c-Rel transcription factor limits early interferon and neuroinflammatory responses to prevent herpes simplex encephalitis onset in mice

Herpes simplex virus type 1 (HSV-1) is the predominant cause of herpes simplex encephalitis (HSE), a condition characterized by acute inflammation and viral replication in the brain. Host genetics contribute to HSE onset, including monogenic defects in type I interferon signaling in cases of childhood HSE. Mouse models suggest a further contribution of immune cell-mediated inflammation to HSE pathogenesis. We have previously described a truncating mutation in the c-Rel transcription factor (Rel^C307X) that drives lethal HSE in 60% of HSV-1-infected Rel^C307X mice. In this study, we combined dual host-virus RNA sequencing with flow cytometry to explore cell populations and mechanisms involved in Rel^C307X-driven HSE. At day 5 postinfection, prior to HSE clinical symptom onset, elevated HSV-1 transcription was detected together with augmented host interferon-stimulated and inflammatory gene expression in the brainstems of high-responding Rel^C307X mice, predictive of HSE development. This early induction of host gene expression preceded pathological infiltration of myeloid and T cells in Rel^C307X mice at HSE onset by day 7. Thus, we establish c-Rel as an early regulator of viral and host responses during mouse HSE. These data further highlight the importance of achieving a balanced immune response and avoiding excess interferon-driven inflammation to promote HSE resistance.

Hidden etiology of cerebral palsy: genetic and clinical heterogeneity and efficient diagnosis by next-generation sequencing

Cerebral palsy (CP) is a heterogeneous neurodevelopmental disorder that causes movement and postural disabilities. Recent research studies focused on genetic diagnosis in patients with CP of unknown etiology. The present study was carried out in 20 families with one family member affected with idiopathic CP. Chromosomal microarray and exome sequencing techniques were performed in all patients. Chromosomal microarray analysis did not show any pathological or probable pathological structural variant. However, the next-generation sequencing study showed a high diagnostic yield. We report 11/20 patients (55%) with different pathogenic or potentially pathogenic variants detected by exome sequencing analysis: five patients with mutations in genes related to hereditary spastic paraplegia, two with mutations in genes related to Aicardi-Goutières syndrome, three with mutations in genes related to developmental/epileptic encephalopathies, and one with a mutation in the PGK1 gene. The accurate and precise patients' selection, the use of a high-throughput genetic platform, the selection of adequate target genes, and the application of rigorous criteria for the clinical interpretation are the most important elements for a good diagnostic performance. Based on our findings, next-generation sequencing should be considered in patients with cryptogenic CP as the first line of genetic workup. IMPACT: Sequencing techniques in CP of uncertain etiology provides a diagnostic yield of 55%. The appropriate selection of cases optimizes the diagnostic yield. NGS facilitate better understanding of new phenotypes of certain genetic diseases.

Vasculitis, Autoimmunity, and Cytokines: How the Immune System Can Harm the Brain

More and more findings suggest that neurological disorders could have an immunopathological cause. Thus, immune-targeted therapies are increasingly proposed in neurology (even if often controversial), as anakinra, inhibiting IL-1 for febrile inflammatory illnesses, and JAK inhibitors for anti-interferons treatment. Precision medicine in neurology could be fostered by a better understanding of the disease machinery, to develop a rational use of immuno-modulators in clinical trials. In this review, we focus on monogenic disorders with neurological hyper-inflammation/autoimmunity as simplified "models" to correlate immune pathology and targeted treatments. The study of monogenic models yields great advantages for the elucidation of the pathogenic mechanisms that can be reproduced in cellular/animal models, overcoming the limitations of biological samples to study. Moreover, monogenic disorders provide a unique tool to study the mechanisms of neuroinflammatory and autoimmune brain damage, in all their manifestations. The insight of clinical, pathological, and therapeutic aspects of the considered monogenic models can impact knowledge about brain inflammation and can provide useful hints to better understand and cure some neurologic multifactorial disorders.

Systemic Type I IFN Inflammation in Human ISG15 Deficiency Leads to Necrotizing Skin Lesions

Most monogenic disorders have a primary clinical presentation. Inherited ISG15 deficiency, however, has manifested with two distinct presentations to date: susceptibility to mycobacterial disease and intracranial calcifications from hypomorphic interferon-II (IFN-II) production and excessive IFN-I response, respectively. Accordingly, these patients were managed for their infectious and neurologic complications. Herein, we describe five new patients with six novel ISG15 mutations presenting with skin lesions who were managed for dermatologic disease. Cellularly, we denote striking specificity to the IFN-I response, which was previously assumed to be universal. In peripheral blood, myeloid cells display the most robust IFN-I signatures. In the affected skin, IFN-I signaling is observed in the keratinocytes of the epidermis, endothelia, and the monocytes and macrophages of the dermis. These findings define the specific cells causing circulating and dermatologic inflammation and expand the clinical spectrum of ISG15 deficiency to dermatologic presentations as a third phenotype co-dominant to the infectious and neurologic manifestations.

Martin-Fernandez et al. report on five patients with inherited ISG15 deficiency, a recently discovered syndrome of type I IFN autoinflammation and mycobacterial susceptibility. This study defines an expanded clinical spectrum that now includes dermatologic disease and pinpoints the specific cell types driving inflammation.

SAMHD1 as the Potential Link Between SARS-CoV-2 Infection and Neurological Complications

The recent pandemic of coronavirus infectious illness 2019 (COVID19) triggered by SARS-CoV-2 has rapidly spread around the globe, generating in severe events an acute, highly lethal pneumonia and death. In the past two hitherto similar CoVs, the severe acute respiratory syndrome CoV (SARS-CoV-1) and Middle East respiratory syndrome CoV (MERS-CoV) also gained universal attention as they produced clinical symptoms similar to those of SARS-CoV-2 utilizing angiotensin-converting enzyme 2 (ACE2) receptor and dipeptidyl peptidase 4 (DPP4) to go into the cells. COVID-19 may also present with overtly neurological symptoms. The proper understanding of the expression and dissemination of ACE2 in central and peripheral nerve systems is crucial to understand better the neurological morbidity caused by COVID-19. Using the STRING bioinformatic tool and references through text mining tools associated to Coronaviruses, we identified SAMHD1 as the probable link to neurological symptoms. Paralleled to the response to influenza A virus and, specifically, respiratory syncytial virus, SARS-CoV-2 evokes a response that needs robust induction of a subclass of cytokines, including the Type I and, obviously, Type III interferons as well as a few chemokines. We correlate ACE2 to the pathogenesis and neurologic complications of COVID-19 and found that SAMHD1 links to NF-κB pathway. No correlation was found with other molecules associated with Coronavirus infection, including ADAR, BST2, IRF3, IFITM3, ISG15, MX1, MX2, RNASEL, RSAD2, and VPRBP. We suggest that SAMHD1 is the molecule that may be behind the mechanisms of the neurological complications associated with COVID-19.

Development of a neurologic severity scale for Aicardi Goutières Syndrome

BACKGROUND AND PURPOSE

Aicardi Goutières Syndrome (AGS) is a severe, autoinflammatory leukodystrophy characterized by global neurologic dysfunction. Our goal was to create an easy-to-apply scale relevant to the unique developmental challenges associated with AGS.

METHODS

All individuals were recruited through our natural history study. Individuals were classified by AGS severity as mild, moderate, or severe, and clinical encounters were assigned a composite score for neurologic function calculated from the sum of three functional classification scales. Through expert consensus, we identified 11 key items to reflect the severity of AGS across gross motor, fine motor, and cognitive skills to create the AGS Scale. There was strong interrater reliability. The AGS scale was applied across available medical records to evaluate neurologic function over time. The AGS scale was compared to performance on a standard measure of gross motor function (Gross Motor Function Measure-88, GMFM-88) and a putative diagnostic biomarker of disease, the interferon signaling gene expression score (ISG).

RESULTS

The AGS scale score correlated with severity classifications and the composite neurologic function scores. When retrospectively applied across our natural history study, the majority of individuals demonstrated an initial decline in function followed by stable scores. Within the first 6 months of disease, the AGS score was the most dynamic. The AGS scale correlated with performance by the GMFM-88, but did not correlate with ISG levels.

CONCLUSIONS

This study demonstrates the utility of the AGS scale as a multimodal tool for the assessment of neurologic function in AGS. The AGS scale correlates with clinical severity and with a more labor-intensive tool, GMFM-88. This study underscores the limitations of the ISG score as a marker of disease severity. With the AGS scale, we found that AGS neurologic severity is the most dynamic early in disease. This novel AGS scale is a promising tool to longitudinally follow neurologic function in this unique population.

Diagnosis of Aicardi-Goutières Syndrome in Adults: A Case Series

Introduction

Aicardi-Goutières syndrome (AGS) is a genetic disease presenting with early-onset encephalopathy, generalized dystonia, spasticity, and cognitive disability. Diagnosis may be difficult in adults, as the clinical course seems static from infancy.

Methods

AGS patients from an adult movement disorders outpatient clinic were retrospectively analyzed.

Results

A total of 5 patients and 1 asymptomatic carrier from 3 different families were identified. All had a homozygous c.529G>A,p.A177T mutation in exon 7 of the RNASEH2B gene. Two patients had neonatal-onset AGS, 2 had later onset forms, and 1 was slightly symptomatic. All were diagnosed in adulthood after chilblains, and basal ganglia calcifications were identified on computed tomography scans.

Discussion

AGS patients have marked phenotypic variability regarding psychomotor development and morbidity. The present series included 1 asymptomatic carrier and 1 slightly symptomatic patient, both with homozygous RNASEH2B mutations. Chilblains and basal ganglia calcifications identified on computed tomography scan (but not on magnetic resonance imaging) are important clues for late diagnosis.

Novel RNASEH2C mutation in multiple members of a large family: insights into phenotypic spectrum of Aicardi-Goutières Syndrome

Background

Aicardi-Goutières syndrome (AGS) is a genetic inflammatory disorder that presents with early infantile encephalopathy. We report the clinical and molecular details of multiple members of a family with AGS secondary to a novel RNASEH2C mutation, highlighting the evolution of phenotypic abnormalities in AGS.

Methods

Between February 2018 and June 2019, a pedigree tree was constructed for 141 members of a family. The clinical and radiological details of 14 symptomatic children were chronicled and compared with the asymptomatic family members. Genetic analysis was performed on 23 individuals (six symptomatic). This involved whole exome sequencing for one patient and confirmation of the identified indel variant in other family members.

Results

The symptomatic children were diagnosed as AGS secondary to a novel indel variation in exon 2 of the RNASEH2C gene (chr11:65487843_65487846delinsGCCA). Clinically, between the ages of 2 and 6 months, the symptomatic children developed irritability (14/14), unexplained fever (9/14), chill blains (12/14), sleep irregularities (14/14) and developmental delay (14/14), with deterioration to vegetative state at a median (IQR) age of 10.5 months (9.25–11). In addition, chill blains were observed in 5/17 (29.4%) carrier individuals. Neuroimaging demonstrated a gradual progression of calcification involving basal ganglia, periventricular white matter and dentate nucleus. Three patients also demonstrated presence of subependymal germinolytic cysts.

Conclusion

This report highlights a novel founder RNASEH2C mutation and the phenotypic evolution of AGS. In addition, we report chill blains in one-third of RNASEH2C mutation carriers. Neuroradiologically, the report illustrates novel MRI findings and demonstrates a progression pattern of disease. These findings will aid in earlier suspicion and diagnosis of AGS.

Developmental Outcomes of Aicardi Goutières Syndrome

Aicardi Goutières syndrome is a monogenic interferonopathy caused by abnormalities in the intracellular nucleic acid sensing machinery (TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, ADAR1, or IFIH1). Most individuals affected by Aicardi Goutières syndrome exhibit some degree of neurologic impairment, from spastic paraparesis with relatively preserved cognition to tetraparesis and severe intellectual disability. Because of this heterogeneity, it is important to fully characterize the developmental trajectory in Aicardi Goutières syndrome. To characterize the clinical presentation in Aicardi Goutières syndrome, early features were collected from an international cohort of children (n = 100) with genetically confirmed Aicardi Goutières syndrome. There was a heterogeneous age of onset, with overlapping clusters of presenting symptoms: altered mental status, systemic inflammatory symptoms, and acute neurologic disability. Next, we created genotype-specific developmental milestone acquisition curves. Individuals with microcephaly or TREX1-related Aicardi Goutières syndrome secondary were the most severely affected and less likely to reach milestones, including head control, sitting, and nonspecific mama/dada. Individuals affected by SAMHD1, IFIH1, and ADAR attained the most advanced milestones, with 44% achieving verbal communication and 31% independently ambulating. Retrospective function scales (Gross Motor Function Classification System, Manual Ability Classification System, and Communication Function Classification System) demonstrated that two-thirds of the Aicardi Goutières syndrome population are severely affected. Our results suggest multifactorial influences on developmental trajectory, including a strong contribution from genotype. Further studies are needed to identify the additional factors that influence overall outcomes to better counsel families and to design clinical trials with appropriate clinical endpoints.

Astroglia in Leukodystrophies

Leukodystrophies are genetically determined disorders affecting the white matter of the central nervous system. The combination of MRI pattern recognition and next-generation sequencing for the definition of novel disease entities has recently demonstrated that many leukodystrophies are due to the primary involvement and/or mutations in genes selectively expressed by cell types other than the oligodendrocytes, the myelin-forming cells in the brain. This has led to a new definition of leukodystrophies as genetic white matter disorders resulting from the involvement of any white matter structural component. As a result, the research has shifted its main focus from oligodendrocytes to other types of neuroglia. Astrocytes are the housekeeping cells of the nervous system, responsible for maintaining homeostasis and normal brain physiology and to orchestrate repair upon injury. Several lines of evidence show that astrocytic interactions with the other white matter cellular constituents play a primary pathophysiologic role in many leukodystrophies. These are thus now classified as astrocytopathies. This chapter addresses how the crosstalk between astrocytes, other glial cells, axons and non-neural cells are essential for the integrity and maintenance of the white matter in health. It also addresses the current knowledge of the cellular pathomechanisms of astrocytic leukodystrophies, and specifically Alexander disease, vanishing white matter, megalencephalic leukoencephalopathy with subcortical cysts and Aicardi-Goutière Syndrome.

Aicardi-Goutières syndrome gene Rnaseh2c is a metastasis susceptibility gene in breast cancer

Breast cancer is the second leading cause of cancer-related deaths in the United States, with the majority of these deaths due to metastatic lesions rather than the primary tumor. Thus, a better understanding of the etiology of metastatic disease is crucial for improving survival. Using a haplotype mapping strategy in mouse and shRNA-mediated gene knockdown, we identified Rnaseh2c, a scaffolding protein of the heterotrimeric RNase H2 endoribonuclease complex, as a novel metastasis susceptibility factor. We found that the role of Rnaseh2c in metastatic disease is independent of RNase H2 enzymatic activity, and immunophenotyping and RNA-sequencing analysis revealed engagement of the T cell-mediated adaptive immune response. Furthermore, the cGAS-Sting pathway was not activated in the metastatic cancer cells used in this study, suggesting that the mechanism of immune response in breast cancer is different from the mechanism proposed for Aicardi-Goutières Syndrome, a rare interferonopathy caused by RNase H2 mutation. These results suggest an important novel, non-enzymatic role for RNASEH2C during breast cancer progression and add Rnaseh2c to a panel of genes we have identified that together could determine patients with high risk for metastasis. These results also highlight a potential new target for combination with immunotherapies and may contribute to a better understanding of the etiology of Aicardi-Goutières Syndrome autoimmunity.

Adenosine-to-inosine RNA editing may be implicated in human pathogenesis

Adenosine-to-inosine (A-to-I) RNA editing is a common mechanism of post-transcriptional modification in many metazoans including vertebrates; the process is catalyzed by adenosine deaminases acting on RNA (ADARs). Using high-throughput sequencing technologies resulted in finding thousands of RNA editing sites throughout the human transcriptome however, their functions are still poorly understood. The aim of this brief review is to draw attention of clinicians and biomedical researchers to ADAR-mediated RNA editing phenomenon and its possible implication in development of neuropathologies, antiviral immune responses and cancer.

A STING to inflammation and autoimmunity

Various intracellular pattern recognition receptors (PRRs) recognize cytosolic pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Cyclic GMP-AMP synthase (cGAS), a cytosolic PRR, recognizes cytosolic nucleic acids including dsDNAs. The recognition of dsDNA by cGAS generates cyclic GMP-AMP (GAMP). The cGAMP is then recognized by STING generating type 1 IFNs and NF-κB-mediated generation of pro-inflammatory cytokines and molecules. Thus, cGAS-STING signaling mediated recognition of cytosolic dsDNA causing the induction of type 1 IFNs plays a crucial role in innate immunity against cytosolic pathogens, PAMPs, and DAMPs. The overactivation of this system may lead to the development of autoinflammation and autoimmune diseases. The article opens with the introduction of different PRRs involved in the intracellular recognition of dsDNA and gives a brief introduction of cGAS-STING signaling. The second section briefly describes cGAS as intracellular PRR required to recognize intracellular nucleic acids (dsDNA and CDNs) and the formation of cGAMP. The cGAMP acts as a second messenger to activate STING- and TANK-binding kinase 1-mediated generation of type 1 IFNs and the activation of NF-κB. The third section of the article describes the role of cGAS-STING signaling in the induction of autoinflammation and various autoimmune diseases. The subsequent fourth section describes both chemical compounds developed and the endogenous negative regulators of cGAS-STING signaling required for its regulation. Therapeutic targeting of cGAS-STING signaling could offer new ways to treat inflammatory and autoimmune diseases.

Neuropathological Findings in a Case of IFIH1-Related Aicardi-Goutières Syndrome

Aicardi-Goutières syndrome (AGS) is a rare syndrome characterized by calcification, diffuse demyelination, and variable degree of brain atrophy. The syndrome is genetically heterogeneous with mutations in 7 genes, including TREX1, RNASEH2A, RNASEH2B, RNASEH2C, SAMHD1, ADAR1, and IFIH1 (interferon-induced helicase c domain-containing protein 1) associated with the syndrome, so far. These mutations lead to the overproduction of α-interferon within the central nervous system. Mutations in IFIH1 have been recently described in a subset of AGS, with only 1 previous report of neuropathological findings. We report neuropathological findings in a second case of AGS with a known mutation in IFIH1 gene. The patient is a 16-year-old adolescent boy with early-onset symptoms that progressed to profound loss of cognitive and motor functions. The patient experienced sudden cardiopulmonary arrest at the age of 16 years. At autopsy, the cause of death was determined to be pulmonary thromboembolism. Neuropathological examination revealed microcephaly (brain weight: 916 g) with relatively mild brain atrophy on gross examination. Microscopic examination revealed multifocal calcifications limited to small to medium central nervous system arteries (no evidence of calcification in other organs), involving bilateral cerebral cortex, basal ganglia, thalamus, and cerebellum. Ultrastructural examination showed Calcospherules limited to the vessel walls and the perivasulcar area without evidence of neuronal ferrugination or tubuloreticular bodies. The extent of calcifications was variable across different brain regions, resembling findings in previously reported cases and correlated with the extent of IFIH1 protein expression (data derived from Allen Brain Institute). AGS is a rare cause of brain calcifications that can closely mimic congenital and neonatal infections such as Rubella and similar infections.

Brain microglia activation induced by intracranial administration of oligonucleotides and its pharmacological modulation

Oligonucleotide overloading results in type I interferonopathies such as the Aicardi-Goutiéres Syndrome, a progressive encephalopathy determined by an immune response against endogenous DNA/RNA molecules. No therapy targeting pathogenic mechanisms is available for affected patients. Accordingly, we set up an in vitro/in vivo experimental model aimed at reproducing the pathogenic mechanisms of type I interferonopathies, in order to develop an effective pharmacological modulation and toxicological alterations caused by intracranial delivery of encapsulated CpG. The in vitro model used Aicardi-Goutiéres Syndrome immortalized lymphocytes activated by interferon I and co-cultured with human astrocytes; lymphocyte neurotoxicity was attenuated by the calcineurin-inhibitor Tacrolimus and by the anti-interferon monoclonal antibody Sifalimumab. The in vivo model was set up in mice by subcutaneous injection of encapsulated CpG oligonucleotides; the immune-stimulating activity was demonstrated by cytometric analysis in the spleen. To mime pathogenesis of type I interferonopathies in the central nervous system, CpG oligonucleotides were administered intracranially in mice. In the brain, CpG overload induced a rapid activation of macrophage-like microglial cells and focal accumulation mononuclear cells. The subcutaneous administration of Tacrolimus and, more potently, Sifalimumab attenuated CpG-induced brain alterations. These findings shed light on molecular mechanisms triggered by oligonucleotides to induce brain damage. Monoclonal antibodies inhibiting interferon seem a promising therapeutic strategy to protect brain in type I interferonopathies.

Molecular dynamics characterization of the SAMHD1 Aicardi-Goutières Arg145Gln mutant: structural determinants for the impaired tetramerization

Aicardi-Goutières syndrome, a rare genetic disorder characterized by calcification of basal ganglia, results in psychomotor delays and epilepsy states from the early months of children life. This disease is caused by mutations in seven different genes encoding proteins implicated in the metabolism of nucleic acids, including SAMHD1. Twenty SAMHD1 gene variants have been discovered and in this work, a structural characterization of the SAMHD1 Aicardi-Goutières Arg145Gln mutant is reported by classical molecular dynamics simulation. Four simulations have been carried out and compared. Two concerning the wild-type SAMHD1 form in presence and absence of cofactors, in order to explain the role of cofactors in the SAMHD1 assembly/disassembly process and, two concerning the Arg145Gln mutant, also in presence and absence of cofactors, in order to have an accurate comparison with the corresponding native forms. Results show the importance of native residue Arg145 in maintaining the tetramer, interacting with GTP cofactor inside allosteric sites. Replacement of arginine in glutamine gives rise to a loosening of GTP-protein interactions, when cofactors are present in allosteric sites, whilst in absence of cofactors, the occurrence of intra and inter-chain interactions is observed in the mutant, not seen in the native enzyme, making energetically unfavourable the tetramerization process.

The Dynamic Interplay between HIV-1, SAMHD1, and the Innate Antiviral Response

The innate immune response constitutes the first cellular line of defense against initial HIV-1 infection. Immune cells sense invading virus and trigger signaling cascades that induce antiviral defenses to control or eliminate infection. Professional antigen-presenting cells located in mucosal tissues, including dendritic cells and macrophages, are critical for recognizing HIV-1 at the site of initial exposure. These cells are less permissive to HIV-1 infection compared to activated CD4⁺ T-cells, which is mainly due to host restriction factors that serve an immediate role in controlling the establishment or spread of viral infection. However, HIV-1 can exploit innate immune cells and their cellular factors to avoid detection and clearance by the host immune system. Sterile alpha motif and HD-domain containing protein 1 (SAMHD1) is the mammalian deoxynucleoside triphosphate triphosphohydrolase responsible for regulating intracellular dNTP pools and restricting the replication of HIV-1 in non-dividing myeloid cells and quiescent CD4⁺ T-cells. Here, we review and analyze the latest literature on the antiviral function of SAMHD1, including the mechanism of HIV-1 restriction and the ability of SAMHD1 to regulate the innate immune response to viral infection. We also provide an overview of the dynamic interplay between HIV-1, SAMHD1, and the cell-intrinsic antiviral response to elucidate how SAMHD1 modulates HIV-1 infection in non-dividing immune cells. A more complete understanding of SAMHD1’s role in the innate immune response to HIV-1 infection may help develop stratagems to enhance its antiviral effects and to more efficiently block HIV-1 replication and avoid the pathogenic result of viral infection.

Restricting retrotransposons: ADAR1 is another guardian of the human genome

ADAR1 is an enzyme that belongs to the Adenosine Deaminases Acting on RNA (ADARs) family. These enzymes deaminate adenosines to inosines (RNA editing A-to-I) within double-stranded RNA regions in transcripts. Since inosines are recognized as guanosines by the cellular machinery, RNA editing mediated by ADARs can either lead to the formation of an altered protein (recoding) or affect different aspects of RNA metabolism. Recently, a proteomic analysis led to the identification of novel ADAR1-associated factors and found that a good fraction of them is shared with the Long Interspersed Element 1 (LINE-1 or L1) ribonucleoparticles (RNPs). This evidence suggested a possible role of ADAR1 in regulating the L1 life cycle. By taking advantage of the use of cell culture retrotransposition assays, a novel function of this deaminase as an inhibitor of L1 retrotransposition was demonstrated. These results pave the way toward a better comprehension of the mechanisms of restriction of retrotransposons.

RIG-I-Like Receptors and Type I Interferonopathies

Type I interferon (IFN) production by the proper activation of nucleic acid sensors is essential for hosts to eliminate invading viruses. Among these sensors, RIG-I-like receptors (RLRs) are well-known viral RNA sensors in the cytoplasm that recognize the nonself signatures of viral RNAs to trigger IFN responses. Recent accumulating evidence has clarified that some specific and atypical self-RNAs also cause activation of RLRs independently of virus infection. Importantly, when RLR-activation by these RNAs or a conformational change via missense mutations is sustained, the resulting continuous production of type I IFN will lead to autoimmune disorders. We, herein, focus on autoimmune diseases caused by chronic activation of RLRs and discuss possible mechanisms of their onset.

STAT2 is an essential adaptor in USP18-mediated suppression of type I interferon signaling

Type I interferons (IFNs) are multifunctional cytokines that regulate immune responses and cellular functions but also can have detrimental effects on human health. A tight regulatory network therefore controls IFN signaling, which in turn may interfere with medical interventions. The JAK-STAT signaling pathway transmits the IFN extracellular signal to the nucleus, thus resulting in alterations in gene expression. STAT2 is a well-known essential and specific positive effector of type I IFN signaling. Here, we report that STAT2 is also a previously unrecognized, crucial component of the USP18-mediated negative-feedback control in both human and mouse cells. We found that STAT2 recruits USP18 to the type I IFN receptor subunit IFNAR2 via its constitutive membrane-distal STAT2-binding site. This mechanistic coupling of effector and negative-feedback functions of STAT2 may provide novel strategies for treatment of IFN-signaling-related human diseases.

Immune-Mediated Diseases of the Central Nervous System: A Specificity-Focused Diagnostic Paradigm

Immune-mediated diseases of the central nervous system show wide variability both symptomatically and with respect to underlying pathophysiology. Recognizing aberrant immunologic activity as the cause of neurologic dysfunction requires establishing as precise a neuroanatomic and functional phenotype as possible, and a diagnostic and therapeutic strategy that stabilizes the patient, excludes broad categories of disease via rapidly available diagnostic assays, and maintains a broad differential diagnosis that includes immune-mediated conditions. This process is aided by recognizing the appropriate clinical circumstances under which immune-mediated disease should be suspected, and how to differentiate these conditions from other causes of similar neurologic dysfunction.

MicroRNA-181 contributes to downregulation of SAMHD1 expression in CD4+ T-cells derived from Sèzary syndrome patients

Sézary syndrome (SS) is a rare subtype of cutaneous T-cell lymphoma (CTCL) that is characterized by aggressive spread of neoplastic CD4+ T-cells from the skin into the bloodstream with metastasis to visceral organs. The deoxynucleoside triphosphohydrolase SAMHD1 is highly expressed in normal CD4+ T-cells, while its expression is down-regulated in CD4+ T-cells from SS patients. MicroRNA (miR) dysregulation is an important epigenetic mechanism in the pathogenesis and progression of SS. MiR-181 has been shown to inhibit SAMHD1 expression in cell lines and was identified as an important prognostic biomarker in CTCL. However, whether SAMHD1 is down-regulated by miR-181 in primary CD4+ T-cells of SS patients is unknown. Compared to normal CD4+ T-cells, SAMHD1 protein expression is significantly reduced in transformed CD4+ T-cell lines and CD4+ T-cells from SS patients, which inversely correlates with increased miR-181 levels in these cells. Over-expression of miR-181b in primary CD4+ T-cells from healthy donors significantly decreased SAMHD1 protein level, but not mRNA level. In contrast, inhibition of miR-181 in a CD4+ T-cell line significantly increased the level of SAMHD1 protein expression. Our results demonstrate that miR-181 is an important regulator of SAMHD1 protein expression in neoplastic CD4+ T-cells, likely through a mechanism of translational inhibition.

The proteasome - victim or culprit in autoimmunity

The ubiquitin proteasome system is closely connected to apoptosis, autophagy, signaling of inflammatory cytokines and generation of ligands for MHC class I antigen presentation. Proteasome function in the innate immune response becomes particularly evident in patients with proteasome-associated autoinflammatory syndromes (PRAAS), where disease causing mutations result in reduced proteasome activity. PRAAS can be classified as a novel type of interferonopathy, however the molecular mechanism and signaling pathways leading from impaired proteasome capacity, the accumulation of damaged proteins, and the induction of type I IFN-genes remain to be determined. In contrast, several studies have confirmed an up-regulation of inducible subunits of the proteasome in systemic autoimmune diseases. Since proteasome inhibition was shown to be efficacious in several in-vitro studies and animal models of autoimmune diseases, it is justified to investigate the application of proteasome inhibitors in human disease. In this context, a number of available proteasome inhibitors has been characterized as potent immune-suppressants. The mode of action of proteasome inhibition interferes with the quality control of the huge amounts of synthetized antibodies causing an unfolded protein response. Further effects of proteasome inhibition includes inhibition of NFκB activation as well as direct activation of intrinsic and extrinsic pathways of apoptosis. The preliminary clinical work on proteasome inhibition in autoimmune diseases comprises only few studies in small cohorts with promising effects, which needs to be confirmed in controlled clinical trials.

RNaseH2A is involved in human gliomagenesis through the regulation of cell proliferation and apoptosis

Mutations in the RNaseH2A gene are involved in Aicardi‑Goutieres syndrome, an autosomal recessive neurological dysfunction; however, studies assessing RNaseH2A in relation to glioma are scarce. This study aimed to assess the role of RNaseH2A in glioma and to unveil the underlying mechanisms. RNaseH2A was silenced in glioblastoma cell lines U87 and U251. Gene expression was assessed in the cells transfected with RNaseH2A shRNA or scramble shRNA by microarrays, validated by quantitative real time PCR. Protein expression was evaluated by western blot analysis. Cell proliferation was assessed by the MTT assay; cell cycle distribution and apoptosis were analyzed by flow cytometry. Finally, the effects of RNaseH2A on colony formation and tumorigenicity were assessed in vitro and in a mouse xenograft model, respectively. RNaseH2A was successively knocked down in U87 and U251 cells. Notably, RNaseH2A silencing resulted in impaired cell proliferation, with 70.7 and 57.8% reduction in the U87 and U251 cells, respectively, with the cell cycle being blocked in the G0/G1 phase in vitro. Meanwhile, clone formation was significantly reduced by RNaseH2A knockdown, which also increased cell apoptosis by approximately 4.5-fold. In nude mice, tumor size was significantly decreased after RNaseH2A knockdown: 219.29±246.43 vs. 1160.26±222.61 mm3 for the control group; similar findings were obtained for tumor weight (0.261±0.245 and 1.127±0.232 g) in the shRNA and control groups, respectively). In the microarray data, RNaseH2A was shown to modulate several signaling pathways responsible for cell proliferation and apoptosis, such as IL-6 and FAS pathways. RNaseH2A may be involved in human gliomagenesis, likely by regulating signaling pathways responsible for cell proliferation and apoptosis.

Endogenized viral sequences in mammals

Reverse-transcribed RNA molecules compose a significant portion of the human genome. Many of these RNA molecules were retrovirus genomes either infecting germline cells or having done so in a previous generation but retaining transcriptional activity. This mechanism itself accounts for a quarter of the genomic sequence information of mammals for which there is data. We understand relatively little about the causes and consequences of retroviral endogenization. This review highlights functions ascribed to sequences of viral origin endogenized into mammalian genomes and suggests some of the most pressing questions raised by these observations.

The Influence of LINE-1 and SINE Retrotransposons on Mammalian Genomes

Transposable elements have had a profound impact on the structure and function of mammalian genomes. The retrotransposon Long INterspersed Element-1 (LINE-1 or L1), by virtue of its replicative mobilization mechanism, comprises ∼17% of the human genome. Although the vast majority of human LINE-1 sequences are inactive molecular fossils, an estimated 80-100 copies per individual retain the ability to mobilize by a process termed retrotransposition. Indeed, LINE-1 is the only active, autonomous retrotransposon in humans and its retrotransposition continues to generate both intra-individual and inter-individual genetic diversity. Here, we briefly review the types of transposable elements that reside in mammalian genomes. We will focus our discussion on LINE-1 retrotransposons and the non-autonomous Short INterspersed Elements (SINEs) that rely on the proteins encoded by LINE-1 for their mobilization. We review cases where LINE-1-mediated retrotransposition events have resulted in genetic disease and discuss how the characterization of these mutagenic insertions led to the identification of retrotransposition-competent LINE-1s in the human and mouse genomes. We then discuss how the integration of molecular genetic, biochemical, and modern genomic technologies have yielded insight into the mechanism of LINE-1 retrotransposition, the impact of LINE-1-mediated retrotransposition events on mammalian genomes, and the host cellular mechanisms that protect the genome from unabated LINE-1-mediated retrotransposition events. Throughout this review, we highlight unanswered questions in LINE-1 biology that provide exciting opportunities for future research. Clearly, much has been learned about LINE-1 and SINE biology since the publication of Mobile DNA II thirteen years ago. Future studies should continue to yield exciting discoveries about how these retrotransposons contribute to genetic diversity in mammalian genomes.

The multidimensional nature of antiviral innate immunity

Viruses possess elaborate defensive mechanisms to evade host innate immune responses. In this issue of Cell Host & Microbe, Stavrou et al. (2015) reveal how the murine leukemia virus uses a sugar-protein shield to protect from inevitable destruction by cellular innate immune factors including the APOBEC3 DNA mutating enzyme.

RNA editing by ADAR1 marks dsRNA as "self"

A paper recently published in Science reports that adenosine deaminase acting on RNA 1-dependent adenosine-to-inosine editing marks endogenous double strand RNA as self and prevents their immune recognition by cytosolic RNA sensor MDA5.

Structural Insights into the High-efficiency Catalytic Mechanism of the Sterile α-Motif/Histidine-Aspartate Domain-containing Protein

Sterile α-motif/histidine-aspartate domain-containing protein (SAMHD1), a homo-tetrameric GTP/dGTP-dependent dNTP triphosphohydrolase, catalyzes the conversion of dNTP into deoxynucleoside and triphosphate. As the only characterized dNTP triphosphohydrolase in human cells, SAMHD1 plays an important role in human innate immunity, autoimmunity, and cell cycle control. Previous biochemical studies and crystal structures have revealed that SAMHD1 interconverts between an inactive monomeric or dimeric form and a dGTP/GTP-induced active tetrameric form. Here, we describe a novel state of SAMHD1 (109-626 amino acids, SAMHD1C) that is characterized by a rapid initial hydrolysis rate. Interestingly, the crystal structure showed that this novel SAMHD1 tetramer contains only GTP and has structural features distinct from the GTP/dNTP-bound SAMHD1 tetramer. Our work thus reveals structural features of SAMHD1 that may represent one of its biological assembly states in cells. The biochemical and structural information generated by the present study not only provides an ordered pathway for the assembly and activation of SAMHD1 but also provides insights into the potential mechanisms of the high-efficiency catalytic activity of this enzyme family in vivo.

New Insights into the Biological Role of Mammalian ADARs; the RNA Editing Proteins

The ADAR proteins deaminate adenosine to inosine in double-stranded RNA which is one of the most abundant modifications present in mammalian RNA. Inosine can have a profound effect on the RNAs that are edited, not only changing the base-pairing properties, but can also result in recoding, as inosine behaves as if it were guanosine. In mammals there are three ADAR proteins and two ADAR-related proteins (ADAD) expressed. All have a very similar modular structure; however, both their expression and biological function differ significantly. Only two of the ADAR proteins have enzymatic activity. However, both ADAR and ADAD proteins possess the ability to bind double-strand RNA. Mutations in ADARs have been associated with many diseases ranging from cancer, innate immunity to neurological disorders. Here, we will discuss in detail the domain structure of mammalian ADARs, the effects of RNA editing, and the role of ADARs in human diseases.

AIM2 Drives Joint Inflammation in a Self-DNA Triggered Model of Chronic Polyarthritis

Mice lacking DNase II display a polyarthritis-like disease phenotype that is driven by translocation of self-DNA into the cytoplasm of phagocytic cells, where it is sensed by pattern recognition receptors. While pro-inflammatory gene expression is non-redundantly linked to the presence of STING in these mice, the contribution of the inflammasome pathway has not been explored. To this end, we studied the role of the DNA-sensing inflammasome receptor AIM2 in this self-DNA driven disease model. Arthritis-prone mice lacking AIM2 displayed strongly decreased signs of joint inflammation and associated histopathological findings. This was paralleled with a reduction of caspase-1 activation and pro-inflammatory cytokine production in diseased joints. Interestingly, systemic signs of inflammation that are associated with the lack of DNase II were not dependent on AIM2. Taken together, these data suggest a tissue-specific role for the AIM2 inflammasome as a sensor for endogenous DNA species in the course of a ligand-dependent autoinflammatory condition.

Interferon-α and the calcifying microangiopathy in Aicardi-Goutières syndrome

Aicardi–Goutières syndrome is a leukoencephalopathy with calcifications and increased cerebrospinal fluid interferon-α. The relation between interferon-α and brain pathology is poorly understood. We report a patient with mutations in the disease-associated gene SAMHD1. Neuropathology showed an extensive microangiopathy with calcifications consistently associate with blood vessels. In an in vitro model of the microangiopathy, interferon-α enhanced vascular smooth muscle cell-derived calcifications. The noninfarcted white matter harbored apoptotic oligodendrocytes and increased numbers of oligodendrocyte progenitors. These findings better define the white matter pathology and provide evidence that interferon-α plays a direct pathogenetic role in the calcifying angiopathy typical of this disease.

Dysfunction in protein clearance by the proteasome: impact on autoinflammatory diseases

During innate immune responses, proteostasis is greatly impacted by synthesis of pathogen proteins as well as by inflammatory tissue damage through radicals or other damaging molecules released by phagocytes. An adequate adaptation of cellular clearance pathways to the increased burden of damaged proteins is thus of fundamental importance for cells and tissues to prevent protein aggregation, inclusion body formation, and ultimately cell death. We here review the current understanding of the pivotal role of the ubiquitin proteasome system (UPS) in this proteostasis network. The proteolytic capacity of the UPS can be adjusted by differential gene expression, the incorporation and maturation kinetics of alternative active sites, and the attachment of different regulators. Dysregulation of this fine-tuning is likely to induce cell death but seen more often to promote inflammation as well. The link between proteostasis impairment and inflammation may play a crucial role in autoinflammation as well as in age-related diseases and currently uncharacterized diseases. Recent studies on proteasome-associated autoinflammatory syndromes (PRAAS) discovered that IFN signaling drives the inflammation caused by reduction of degradation capacity. Elucidation of these syndromes will reveal further insights in the understanding of inadequate immune responses. Knowledge related to the diversity of this degradation system will raise the awareness of potential pitfalls in the molecular diagnostics of autoinflammatory syndromes and may help to identify novel drug targets.