C9orf72 in myeloid cells suppresses STING-induced inflammation

Immune modulation to treat Alzheimer's disease

Immune mechanisms play a fundamental role in Alzheimer's disease (AD) pathogenesis, suggesting that approaches which target immune cells and immunologically relevant molecules can offer therapeutic opportunities beyond the recently approved amyloid beta monoclonal therapies. In this review, we provide an overview of immunomodulatory therapeutics in development, including their preclinical evidence and clinical trial results. Along with detailing immune processes involved in AD pathogenesis and highlighting how these mechanisms can be therapeutically targeted to modify disease progression, we summarize knowledge gained from previous trials of immune-based interventions, and provide a series of recommendations for the development of future immunomodulatory therapeutics to treat AD.

Recurrent patterns of widespread neuronal genomic damage shared by major neurodegenerative disorders

Amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Alzheimer's disease (AD) are common neurodegenerative disorders for which the mechanisms driving neuronal death remain unclear. Single-cell whole-genome sequencing of 429 neurons from three C9ORF72 ALS, six C9ORF72 FTD, seven AD, and twenty-three neurotypical control brains revealed significantly increased burdens in somatic single nucleotide variant (sSNV) and insertion/deletion (sIndel) in all three disease conditions. Mutational signature analysis identified a disease-associated sSNV signature suggestive of oxidative damage and an sIndel process, affecting 28% of ALS, 79% of FTD, and 65% of AD neurons but only 5% of control neurons (diseased vs. control: OR=31.20, p = 2.35×10-10). Disease-associated sIndels were primarily two-basepair deletions resembling signature ID4, which was previously linked to topoisomerase 1 (TOP1)-mediated mutagenesis. Duplex sequencing confirmed the presence of sIndels and identified similar single-strand events as potential precursor lesions. TOP1-associated sIndel mutagenesis and resulting genome instability may thus represent a common mechanism of neurodegeneration.

Origin and cell type specificity of mitochondrial DNA mutations in C9ORF72 ALS-FTLD human brain organoids

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are primarily genetic in ~20% of patients. Mutations in C9ORF72 are the most frequent cause, but it is not understood why there is notable regional pathology. An increased burden of mitochondrial DNA (mtDNA) mutations in ALS-FTLD brains implicates mitochondrial mechanisms; however, it remains unclear how and when these mutations arise. To address this, we generated cerebral organoids derived from human-induced pluripotent stem cells (hiPSCs) of patients with ALS-FTLD harboring the C9ORF72 hexanucleotide repeat expansion alongside CRISPR-corrected isogenic and healthy controls. Here, we show a higher mtDNA single-nucleotide variant (mtSNV) burden in astroglia derived from C9ORF72-mutant organoids, with some de novo mtSNVs likely due to the C9ORF72 repeat and others evading selection to reach higher heteroplasmy levels. Thus, the functional consequences of the regional accumulation of mtSNVs in C9ORF72 ALS-FTLD brains are likely to manifest through astroglial mitochondrial dysfunction.

Dynamic STING repression orchestrates immune cell development and function

STING is an essential component of the innate immune system, yet homeostatic STING expression patterns and regulation are unknown. Using Sting1IRES-EGFP reporter and conditional Sting1 transgenic mice, we found that regulation of STING expression is critical for immune cell development and functionality. STING expression was repressed in neutrophils, and forced STING expression or signaling drove systemic inflammatory disease. During T lymphocyte development, STING expression was restricted at the double-positive stage via epigenetic silencing by DNA methyltransferase 1. Forced STING expression or signaling impaired T lymphocyte development independent of type I interferon and promoted lineage commitment to innate-like γδ T cells over adaptive αβ T cells. In the tumor microenvironment, CD8+ T lymphocytes repressed STING expression, correlating with features of T cell exhaustion in syngeneic mouse tumors and human colorectal cancer. Our data demonstrate the necessity of controlled, rather than ubiquitous, STING expression, uncovering a previously unappreciated dimension of STING pathobiology.

Phenotypical Characterization of C9ALS Patients from the Emilia Romagna Registry of ALS: A Retrospective Case-Control Study

BACKGROUND/OBJECTIVES

C9ORF72 expansion is associated with significant phenotypic heterogeneity. This study aimed to characterize the clinical features of C9ALS patients from the Emilia Romagna ALS registry (ERRALS) and compare them with non-mutated ALS (nmALS) patients matched for sex, age at onset, and diagnostic delay, sourced from the same register.

METHODS

In total, 67 C9ALS patients were compared to 201 nmALS. Clinical data, phenotype, and prognostic factors were analyzed in the two groups and within the C9ALS group after stratification by sex.

RESULTS

C9ALS patients displayed a higher disease progression rate and shorter times to gastrostomy and invasive ventilation, despite no differences in overall survival. Female C9ALS had a more severe bulbar and upper motor neuron involvement compared to males. Cognitive and behavioral symptoms were more common in the C9ALS group, and the former was an independent prognostic factor. Prevalences of, autoimmune diseases, and dyslipidemia were significantly higher among C9ALS patients.

CONCLUSIONS

In our dataset, we show an overall increased disease progression rate in C9ALS patients and hint at sex-specific discrepancies in some phenotypical characteristics. We also suggest a possible clinically relevant involvement of C9ORF72 expansion in metabolism and autoimmunity.

Integrated transcriptomic profiling reveals a STING-mediated Type II Interferon signature in SOD1-mutant amyotrophic lateral sclerosis models

Inflammation is a hallmark of amyotrophic lateral sclerosis (ALS), particularly in cases with SOD1 mutations. Using integrative transcriptomics, we analyzed gene expression changes in mouse models throughout progression, human induced-pluripotent stem cells (hiPSCs), and post-mortem spinal cord tissue from ALS patients. We identified a conserved upregulation of interferon (IFN) genes and IFN-stimulating genes (ISGs) in both mouse models and human ALS, with a predominance Type I IFNs (IFN-α/β) in mice and Type II IFNs (IFN-γ) in humans. In mouse models, we observed robust and sustained upregulation of Type I and II ISGs, including ATF3, beginning at disease onset stage and persisting throughout disease progression. Single-cell transcriptomics further pinpointed vascular endothelial cells as a major source of ISGs. Furthermore, we found that the STING-TBK1 axis is essential for the induction of Type II ISGs in ALS, as its deletion impaired their expression. Our study uncovers a conserved ISGs signature across ALS models and patients, highlighting the potential role of innate immune activation in ALS pathogenesis. These findings suggest that ISGs may serve as potential biomarkers and therapeutic targets for ALS.

Towards an integrated approach for understanding glia in Amyotrophic Lateral Sclerosis

Substantial advances in technology are permitting a high resolution understanding of the salience of glia, and have helped us to transcend decades of predominantly neuron-centric research. In particular, recent advances in 'omic' technologies have enabled unique insights into glial biology, shedding light on the cellular and molecular aspects of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Here, we review studies using omic techniques to attempt to understand the role of glia in ALS across different model systems and post mortem tissue. We also address caveats that should be considered when interpreting such studies, and how some of these may be mitigated through either using a multi-omic approach and/or careful low throughput, high fidelity orthogonal validation with particular emphasis on functional validation. Finally, we consider emerging technologies and their potential relevance in deepening our understanding of glia in ALS.

cGAS-STING targeting offers novel therapeutic opportunities in neurological diseases

Cyclic guanosine monophosphate (GMP)-adenosine monophosphate (AMP) (cGAMP) synthase (cGAS) is a cytosolic DNA sensor that produces the secondary messenger cGAMP. cGAMP activates the endoplasmic reticulum-associated adaptor stimulator of interferon genes (STING) and activates the innate immune system to produce a type I interferon response. Besides sensing microbial DNA, cGAS can also be activated by self-DNA or endogenous DNA, including that derived from genotoxic extranuclear chromatin and mitochondrially released DNA, indicating that cGAS-STING is an important mechanism in sterile inflammatory responses, autoimmunity, and cellular senescence. However, aberrant activation of the cGAS-STING pathway results in inflammatory and autoimmune diseases. cGAS-STING has emerged as a vital mechanism driving the pathogenesis of inflammation, implicating cGAS-STING signaling in neurological diseases. In this review, we first outline the principal elements of the cGAS-STING signaling cascade, summarizing recent research highlighting how cGAS-STING activation contributes to the pathogenesis of neurological diseases, including various autoimmune, autoinflammatory, and neurodegenerative diseases. Next, we outline selective small-molecule modulators that function as cGAS-STING inhibitors and summarize their mechanisms for treating multiple neurological diseases. Finally, we discuss key limitations of the current therapeutic paradigm and generate possible strategies to overcome them.

Amyotrophic lateral sclerosis caused by hexanucleotide repeat expansions in C9orf72: from genetics to therapeutics

GGGGCC repeat expansions in C9orf72 are a common genetic cause of amyotrophic lateral sclerosis in people of European ancestry; however, substantial variability in the penetrance of the mutation, age at disease onset, and clinical presentation can complicate diagnosis and prognosis. The repeat expansion is bidirectionally transcribed in the sense and antisense directions into repetitive RNAs and translated into dipeptide repeat proteins, and both accumulate in the cortex, cerebellum, and the spinal cord. Furthermore, neuropathological aggregates of phosphorylated TDP-43 are observed in motor cortex and other cortical regions, and in the spinal cord of patients at autopsy. C9orf72 repeat expansions can also cause frontotemporal dementia. The GGGGCC repeat induces a complex interplay of loss-of-function and gain-of-function pathological mechanisms. Clinical trials using antisense oligonucleotides to target the GGGGCC repeat RNA have not been successful, potentially because they only target a single gain-of-function mechanism. Novel therapeutic approaches targeting the DNA repeat expansion, multiple repeat-derived RNA species, or downstream targets of TDP-43 dysfunction are, however, on the horizon, together with the development of diagnostic and prognostic biomarkers.

Targeting common disease pathomechanisms to treat amyotrophic lateral sclerosis

The motor neuron disease amyotrophic lateral sclerosis (ALS) is a devastating condition with limited treatment options. The past few years have witnessed a ramping up of translational ALS research, offering the prospect of disease-modifying therapies. Although breakthroughs using gene-targeted approaches have shown potential to treat patients with specific disease-causing mutations, the applicability of such therapies remains restricted to a minority of individuals. Therapies targeting more general mechanisms that underlie motor neuron pathology in ALS are therefore of considerable interest. ALS pathology is associated with disruption to a complex array of key cellular pathways, including RNA processing, proteostasis, metabolism and inflammation. This Review details attempts to restore cellular homeostasis by targeting these pathways in order to develop effective, broadly-applicable ALS therapeutics.

Role of Microglial Mitophagy in Alleviating Postoperative Cognitive Dysfunction: a Mechanistic Study

Postoperative cognitive dysfunction (POCD), a common complication following anesthesia and surgery, is influenced by hippocampal neuroinflammation and microglial activation. Mitophagy, a process regulating inflammatory responses by limiting the accumulation of damaged mitochondria, plays a significant role. This study aimed to determine whether regulating microglial mitophagy and the cGAS-STING pathway could alleviate cognitive decline after surgery. Exploratory laparotomy was performed to establish a POCD model using mice. Western blotting, immunofluorescence staining, transmission electron microscopy, and mt-Keima assays were used to examine microglial mitophagy and the cGAS-STING pathway. Quantitative polymerase chain reaction (qPCR) was used to detect inflammatory mediators and cytosolic mitochondrial DNA (mtDNA) levels in BV2 cells. Exploratory laparotomy triggered mitophagy and enhanced the cGAS-STING pathway in mice hippocampi. Pharmacological treatment reduced microglial activation, neuroinflammation, and cognitive impairment after surgery. Mitophagy suppressed the cGAS-STING pathway in mice hippocampi. In vitro, microglia-induced inflammation was mediated by mitophagy and the cGAS-STING pathway. Small interfering RNA (siRNA) of PINK1 hindered mitophagy activation and facilitated the cytosolic release of mtDNA, resulting in the initiation of the cGAS-STING pathway and innate immune response. Microglial mitophagy inhibited inflammatory responses via the mtDNA-cGAS-STING pathway inducing microglial mitophagy and inhibiting the mtDNA-cGAS-STING pathway may be an effective therapeutic approach for patients with POCD.

Semen Strychni Pulveratum and vomicine alleviate neuroinflammation in amyotrophic lateral sclerosis through cGAS-STING-TBK1 pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Amyotrophic lateral sclerosis (ALS) is a fetal neuromuscular disorder characterized by the gradual deterioration of motor neurons. Semen Strychni pulveratum (SSP), a processed version of Semen Strychni (SS) powder, is widely used to treat ALS in China. Vomicine is one of the most primary components of SS. However, their pharmacological effects and mechanisms for ALS remain elusive.

AIM OF THE STUDY

This study aimed to evaluate the neuroprotective and anti-neuroinflammatory effects of SSP and vomicine, as well as to explore their protective roles in ALS and the underlying mechanisms.

MATERIALS AND METHODS

In vivo, 8-week-old hSOD1-WT mice and hSOD1-G93A mice were orally administered different concentrations of SSP (SSP-L = 5.46 mg/ml, SSP-M = 10.92 mg/ml or SSP-H = 16.38 mg/ml) once every other day for 8 weeks. A series of experiments, including body weight measurement, footprint tests, Hematoxylin & Eosin staining, and Nissl staining, were performed to evaluate the preventive effect of SSP. Immunofluorescence staining, western blotting, and RT-qPCR were subsequently performed to evaluate activation of the cGAS-STING-TBK1 pathway in the spinal cord. In vitro, hSOD1G93A NSC-34 cells were treated with vomicine to further explore the pharmacological mechanism of vomicine in the treatment of ALS via the cGAS-STING-TBK1 pathway.

RESULTS

SSP improved motor function, body weight loss, gastrocnemius muscle atrophy, and motor neuron loss in the spine and cortex of hSOD1-G93A mice. Furthermore, the cGAS-STING-TBK1 pathway was activated in the spinal cord of hSOD1-G93A mice, with activation predominantly observed in neurons and microglia. However, the levels of cGAS, STING, and pTBK1 proteins and cGAS, IRF3, IL-6, and IL-1β mRNA were reversed following intervention with SSP. Vomicine not only downregulated the levels of cGAS, TBK1, IL-6 and IFN-β mRNA, but also the levels of cGAS and STING protein in hSOD1G93A NSC-34 cells.

CONCLUSION

This study demonstrated that SSP and vomicine exert neuroprotective and anti-neuroinflammatory effects in the treatment of ALS. SSP and vomicine may reduce neuroinflammation by regulating the cGAS-STING-TBK1 pathway, and could thereby play a role in ALS treatment.

Regulation of cGAS-STING signalling and its diversity of cellular outcomes

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signalling pathway, which recognizes both pathogen DNA and host-derived DNA, has emerged as a crucial component of the innate immune system, having important roles in antimicrobial defence, inflammatory disease, ageing, autoimmunity and cancer. Recent work suggests that the regulation of cGAS-STING signalling is complex and sophisticated. In this Review, we describe recent insights from structural studies that have helped to elucidate the molecular mechanisms of the cGAS-STING signalling cascade and we discuss how the cGAS-STING pathway is regulated by both activating and inhibitory factors. Furthermore, we summarize the newly emerging understanding of crosstalk between cGAS-STING signalling and other signalling pathways and provide examples to highlight the wide variety of cellular processes in which cGAS-STING signalling is involved, including autophagy, metabolism, ageing, inflammation and tumorigenesis.

C9orf72 Alleviates DSS‑Induced Ulcerative Colitis via the cGAS-STING Pathway

PURPOSE

C9orf72 deficiency contributes to severe inflammation in mice. Ulcerative colitis (UC) is a chronic inflammatory disorder with the shortage of clinical success. However, whether C9orf72 is involved in the progression of UC is not fully understood. This study investigated whether C9orf72 could alleviate dextran sulfate sodium (DSS)-induced colitis in mice and lipopolysaccharide (LPS)-induced colitis in Caco-2 cells.

METHODS

Mice were injected AAV9-C9orf72 lentivirus through tail vein and fed 3% DSS for a week. Caco-2 cells were cultured to establish C9orf723 overexpressed model. Histopathological examination, level of inflammation, cGAS-STING pathway, and gut barrier function were detected in mice and cells.

RESULTS

C9orf72 overexpression in mice attenuated DSS-induced colitis and intestinal epithelial barrier damage by stimulating ZO-1 and Occludin expression. In LPS-induced Caco-2 cells, C9orf72 overexpression increased cell viability and the expression of ZO-1 and Occludin. C9orf72 overexpression alleviated inflammation by inhibiting the cGAS-STING pathway in colonic tissue and Caco-2 cells.

CONCLUSION

C9orf72 overexpression attenuated DSS-induced colitis and intestinal epithelial barrier damage by inhibiting the cGAS-STING pathway. C9orf72 may present a target for mitigating UC.

Emerging therapeutic strategies for optic nerve regeneration

The optic nerve, comprising axons from retinal ganglion cells (RGCs), is a component of the central nervous system (CNS) that generally exhibits a limited regeneration capacity following injury in mature mammals, resulting in permanent vision loss. Here, we summarize recent advances in interventions targeting cell-intrinsic and cell-extrinsic mechanisms to enhance RGC axon regeneration. Additionally, we summarize strategies for guiding the reconnection of regenerating axons with brain visual targets, aiming to restore partial visual function. Given the advent of high-throughput screening techniques and multiomics analyses, we discuss how these emerging methodologies deepen our understanding of regenerative mechanisms and expedite the development of innovative therapeutic approaches. Lastly, we explore the translational potential of these strategies in achieving clinically meaningful vision recovery.

Endosomal traffic disorders: a driving force behind neurodegenerative diseases

Endosomes are crucial sites for intracellular material sorting and transportation. Endosomal transport is a critical process involved in the selective uptake, processing, and intracellular transport of substances. The equilibrium between endocytosis and circulation mediated by the endosome-centered transport pathway plays a significant role in cell homeostasis, signal transduction, and immune response. In recent years, there have been hints linking endosomal transport abnormalities to neurodegenerative diseases, including Alzheimer's disease. Nonetheless, the related mechanisms remain unclear. Here, we provide an overview of endosomal-centered transport pathways and highlight potential physiological processes regulated by these pathways, with a particular focus on the correlation of endosomal trafficking disorders with common pathological features of neurodegenerative diseases. Additionally, we summarize potential therapeutic agents targeting endosomal trafficking for the treatment of neurodegenerative diseases.

Classification and functional characterization of regulators of intracellular STING trafficking identified by genome-wide optical pooled screening

Stimulator of interferon genes (STING) traffics across intracellular compartments to trigger innate responses. Mutations in factors regulating this process lead to inflammatory disorders. To systematically identify factors involved in STING trafficking, we performed a genome-wide optical pooled screen (OPS). Based on the subcellular localization of STING in 45 million cells, we defined 464 clusters of gene perturbations based on their cellular phenotypes. A secondary, higher-dimensional OPS identified 73 finer clusters. We show that the loss of the gene of unknown function C19orf25, which clustered with USE1, a protein involved in Golgi-to-endoplasmic reticulum (ER) transport, enhances STING signaling. Additionally, HOPS deficiency delayed STING degradation and consequently increased signaling. Similarly, GARP/RIC1-RGP1 loss increased STING signaling by delaying STING Golgi exit. Our findings demonstrate that genome-wide genotype-phenotype maps based on high-content cell imaging outperform other screening approaches and provide a community resource for mining factors that impact STING trafficking and other cellular processes.

The Underestimated Role of Iron in Frontotemporal Dementia: A Narrative Review

The term frontotemporal dementia (FTD) comprises a group of neurodegenerative disorders characterized by the progressive degeneration of the frontal and temporal lobes of the brain with language impairment and changes in cognitive, behavioral and executive functions, and in some cases motor manifestations. A high proportion of FTD cases are due to genetic mutations and inherited in an autosomal-dominant manner with variable penetrance depending on the implicated gene. Iron is a crucial microelement that is involved in several cellular essential functions in the whole body and plays additional specialized roles in the central nervous system (CNS) mainly through its redox-cycling properties. Such a feature may be harmful under aerobic conditions, since it may lead to the generation of highly reactive hydroxyl radicals. Dysfunctions of iron homeostasis in the CNS are indeed involved in several neurodegenerative disorders, although it is still challenging to determine whether the dyshomeostasis of this essential but harmful metal is a direct cause of neurodegeneration, a contributor factor or simply a consequence of other neurodegenerative mechanisms. Unlike many other neurodegenerative disorders, evidence of the dysfunction in brain iron homeostasis in FTD is still scarce; nonetheless, the recent literature intriguingly suggests its possible involvement. The present review aims to summarize what is currently known about the contribution of iron dyshomeostasis in FTD based on clinical, imaging, histological, biochemical and molecular studies, further suggesting new perspectives and offering new insights for future investigations on this underexplored field of research.

Ancestry-specific gene expression in peripheral monocytes mediates risk of neurodegenerative disease

It is hypothesised that peripheral immune states responding to regional environmental triggers contribute to central neurodegeneration. Region-specific genetic selection pressures require this hypothesis to be assessed in an ancestry specific manner. Here we utilise genome-wide association studies and expression quantitative trait loci from African, East Asian and European ancestries to show that genes causing neurodegeneration are preferentially expressed in innate rather than adaptive immune cells, and that expression of these genes mediates the risk of neurodegenerative disease in monocytes in an ancestry-specific manner.

Single-cell transcriptomic landscape of the neuroimmune compartment in amyotrophic lateral sclerosis brain and spinal cord

Development of therapeutic approaches that target specific microglia responses in amyotrophic lateral sclerosis (ALS) is crucial due to the involvement of microglia in ALS progression. Our study identifies the predominant microglia subset in human ALS primary motor cortex and spinal cord as an undifferentiated phenotype with dysregulated respiratory electron transport. Moreover, we find that the interferon response microglia subset is enriched in donors with aggressive disease progression, while a previously described potentially protective microglia phenotype is depleted in ALS. Additionally, we observe an enrichment of non-microglial immune cell, mainly NK/T cells, in ALS central nervous system, primarily in the spinal cord. These findings pave the way for the development of microglia subset-specific therapeutic interventions to slow or even stop ALS progression.

The cGAS-STING pathway drives neuroinflammation and neurodegeneration via cellular and molecular mechanisms in neurodegenerative diseases

Neurodegenerative diseases (NDs) are a type of common chronic progressive disorders characterized by progressive damage to specific cell populations in the nervous system, ultimately leading to disability or death. Effective treatments for these diseases are still lacking, due to a limited understanding of their pathogeneses, which involve multiple cellular and molecular pathways. The triggering of an immune response is a common feature in neurodegenerative disorders. A critical challenge is the intricate interplay between neuroinflammation, neurodegeneration, and immune responses, which are not yet fully characterized. In recent years, the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon gene (STING) pathway, a crucial immune response for intracellular DNA sensing, has gradually gained attention. However, the specific roles of this pathway within cellular types such as immune cells, glial and neuronal cells, and its contribution to ND pathogenesis, remain not fully elucidated. In this review, we systematically explore how the cGAS-STING signaling links various cell types with related cellular effector pathways under the context of NDs for multifaceted therapeutic directions. We emphasize the discovery of condition-dependent cellular heterogeneity in the cGAS-STING pathway, which is integral for understanding the diverse cellular responses and potential therapeutic targets. Additionally, we review the pathogenic role of cGAS-STING activation in Parkinson's disease, ataxia-telangiectasia, and amyotrophic lateral sclerosis. We focus on the complex bidirectional roles of the cGAS-STING pathway in Alzheimer's disease, Huntington's disease, and multiple sclerosis, revealing their double-edged nature in disease progression. The objective of this review is to elucidate the pivotal role of the cGAS-STING pathway in ND pathogenesis and catalyze new insights for facilitating the development of novel therapeutic strategies.

CNS disease associated with enhanced type I interferon signalling

The ability to mount an interferon-mediated innate immune response is essential in protection against neurotropic viruses, but antiviral type I interferons also have neurotoxic potential. The production of type I interferons can be triggered by self-derived nucleic acids, and the brain can be susceptible to inappropriate upregulation of type I interferon signalling. Homoeostatic dysregulation of type I interferons has been implicated in rare inborn errors of immunity (referred to as type I interferonopathies) and more common neurodegenerative disorders (eg, Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis). Recent developments include new insights into the pathogenesis of these disorders that involve dysregulated type I interferon signalling, as well as advances in their diagnosis and management. The role of type I interferons in brain cellular health suggests the future therapeutic potential of approaches that target these interferons and their signalling.

C9orf72 expansion creates the unstable folate-sensitive fragile site FRA9A

The hyper-unstable Chr9p21 locus, harbouring the interferon gene cluster, oncogenes and C9orf72, is linked to multiple diseases. C9orf72 (GGGGCC)n expansions ( C9orf72 Exp) are associated with incompletely penetrant amyotrophic lateral sclerosis, frontotemporal dementia and autoimmune disorders. C9orf72 Exp patients display hyperactive cGAS-STING-linked interferon immune and DNA damage responses, but the source of immuno-stimulatory or damaged DNA is unknown. Here, we show C9orf72 Exp in pre-symptomatic and ALS-FTD patient cells and brains cause the folate-sensitive chromosomal fragile site, FRA9A. FRA9A centers on >33kb of C9orf72 as highly-compacted chromatin embedded in an 8.2Mb fragility zone spanning 9p21, encompassing 46 genes, making FRA9A one of the largest fragile sites. C9orf72 Exp cells show chromosomal instability, heightened global- and Chr9p-enriched sister-chromatid exchanges, truncated-Chr9s, acentric-Chr9s and Chr9-containing micronuclei, providing endogenous sources of damaged and immunostimulatory DNA. Cells from one C9orf72 Exp patient contained highly-rearranged FRA9A-expressing Chr9 with Chr9-wide dysregulated gene expression. Somatic C9orf72 Exp repeat instability and chromosomal fragility are sensitive to folate-deficiency. Age-dependent repeat instability, chromosomal fragility, and chromosomal instability can be transferred to CNS and peripheral tissues of transgenic C9orf72 Exp mice, implicating C9orf72 Exp as the source. Our results highlight unappreciated effects of C9orf72 expansions that trigger vitamin-sensitive chromosome fragility, adding structural variations to the disease-enriched 9p21 locus, and likely elsewhere.

The role of interferon signaling in neurodegeneration and neuropsychiatric disorders

Recent advances in transcriptomics research have uncovered heightened interferon (IFN) responses in neurodegenerative diseases including Alzheimer's disease, primary tauopathy, Parkinson's disease, TDP-43 proteinopathy, and related mouse models. Augmented IFN signaling is now relatively well established for microglia in these contexts, but emerging work has highlighted a novel role for IFN-responsive T cells in the brain and peripheral blood in some types of neurodegeneration. These findings complement a body of literature implicating dysregulated IFN signaling in neuropsychiatric disorders including major depression and post-traumatic stress disorder. In this review, we will characterize and integrate advances in our understanding of IFN responses in neurodegenerative and neuropsychiatric disease, discuss how sex and ancestry modulate the IFN response, and examine potential mechanistic explanations for the upregulation of antiviral-like IFN signaling pathways in these seemingly non-viral neurological and psychiatric disorders.

C9orf72 repeat expansion creates the unstable folate-sensitive fragile site FRA9A

The hyper-unstable Chr9p21 locus, harbouring the interferon gene cluster, oncogenes and C9orf72, is linked to multiple diseases. C9orf72 (GGGGCC)n expansions (C9orf72Exp) are associated with incompletely penetrant amyotrophic lateral sclerosis, frontotemporal dementia and autoimmune disorders. C9orf72Exp patients display hyperactive cGAS-STING-linked interferon immune and DNA damage responses, but the source of immunostimulatory or damaged DNA is unknown. Here, we show C9orf72Exp in pre-symptomatic and amyotrophic lateral sclerosis-frontotemporal dementia patient cells and brains cause the folate-sensitive chromosomal fragile site, FRA9A. FRA9A centers on >33 kb of C9orf72 as highly compacted chromatin embedded in an 8.2 Mb fragility zone spanning 9p21, encompassing 46 genes, making FRA9A one of the largest fragile sites. C9orf72Exp cells show chromosomal instability, heightened global- and Chr9p-enriched sister-chromatid exchanges, truncated-Chr9s, acentric-Chr9s and Chr9-containing micronuclei, providing endogenous sources of damaged and immunostimulatory DNA. Cells from one C9orf72Exp patient contained a highly rearranged FRA9A-expressing Chr9 with Chr9-wide dysregulated gene expression. Somatic C9orf72Exp repeat instability and chromosomal fragility are sensitive to folate deficiency. Age-dependent repeat instability, chromosomal fragility and chromosomal instability can be transferred to CNS and peripheral tissues of transgenic C9orf72Exp mice, implicating C9orf72Exp as the source. Our results highlight unappreciated effects of C9orf72 expansions that trigger vitamin-sensitive chromosome fragility, adding structural variations to the disease-enriched 9p21 locus, and likely elsewhere.

Nucleic acid sensing in the central nervous system: Implications for neural circuit development, function, and degeneration

Nucleic acids are a critical trigger for the innate immune response to infection, wherein pathogen-derived RNA and DNA are sensed by nucleic acid sensing receptors. This subsequently drives the production of type I interferon and other inflammatory cytokines to combat infection. While the system is designed such that these receptors should specifically recognize pathogen-derived nucleic acids, it is now clear that self-derived RNA and DNA can also stimulate these receptors to cause aberrant inflammation and autoimmune disease. Intriguingly, similar pathways are now emerging in the central nervous system in neurons and glial cells. As in the periphery, these signaling pathways are active in neurons and glia to present the spread of pathogens in the CNS. They further appear to be active even under steady conditions to regulate neuronal development and function, and they can become activated aberrantly during disease to propagate neuroinflammation and neurodegeneration. Here, we review the emerging new roles for nucleic acid sensing mechanisms in the CNS and raise open questions that we are poised to explore in the future.

Targeting EGLN2/PHD1 protects motor neurons and normalizes the astrocytic interferon response

Neuroinflammation and dysregulated energy metabolism are linked to motor neuron degeneration in amyotrophic lateral sclerosis (ALS). The egl-9 family hypoxia-inducible factor (EGLN) enzymes, also known as prolyl hydroxylase domain (PHD) enzymes, are metabolic sensors regulating cellular inflammation and metabolism. Using an oligonucleotide-based and a genetic approach, we showed that the downregulation of Egln2 protected motor neurons and mitigated the ALS phenotype in two zebrafish models and a mouse model of ALS. Single-nucleus RNA sequencing of the murine spinal cord revealed that the loss of EGLN2 induced an astrocyte-specific downregulation of interferon-stimulated genes, mediated via the stimulator of interferon genes (STING) protein. In addition, we found that the genetic deletion of EGLN2 restored this interferon response in patient induced pluripotent stem cell (iPSC)-derived astrocytes, confirming the link between EGLN2 and astrocytic interferon signaling. In conclusion, we identified EGLN2 as a motor neuron protective target normalizing the astrocytic interferon-dependent inflammatory axis in vivo, as well as in patient-derived cells.

Therapeutic targeting of RNA for neurological and neuromuscular disease

Neurological and neuromuscular diseases resulting from familial, sporadic, or de novo mutations have devasting personal, familial, and societal impacts. As the initial product of DNA transcription, RNA transcripts and their associated ribonucleoprotein complexes provide attractive targets for modulation by increasing wild-type or blocking mutant allele expression, thus relieving downstream pathological consequences. Therefore, it is unsurprising that many existing and under-development therapeutics have focused on targeting disease-associated RNA transcripts as a frontline drug strategy for these genetic disorders. This review focuses on the current range of RNA targeting modalities using examples of both dominant and recessive neurological and neuromuscular diseases.

Microglial cGAS-STING signaling underlies glaucoma pathogenesis

Characterized by progressive degeneration of retinal ganglion cells (RGCs) and vision loss, glaucoma is the primary cause of irreversible blindness, incurable and affecting over 78 million patients. However, pathogenic mechanisms leading to glaucoma-induced RGC loss are incompletely understood. Unexpectedly, we found that cGAS-STING (2'3'-cyclic GMP-AMP-stimulator of interferon genes) signaling, which surveils displaced double-stranded DNA (dsDNA) in the cytosol and initiates innate immune responses, was robustly activated during glaucoma in retinal microglia in distinct murine models. Global or microglial deletion of STING markedly relieved glaucoma symptoms and protected RGC degeneration and vision loss, while mice bearing genetic cGAS-STING supersensitivity aggravated retinal neuroinflammation and RGC loss. Mechanistically, dsDNA from tissue injury activated microglial cGAS-STING signaling, causing deleterious macroglia reactivity in retinas by cytokine-mediated microglia-macroglia interactions, progressively driving apoptotic death of RGCs. Remarkably, preclinical investigations of targeting cGAS-STING signaling by intraocular injection of TBK1i or anti-IFNAR1 antibody prevented glaucoma-induced losses of RGCs and vision. Therefore, we unravel an essential role of cGAS-STING signaling underlying glaucoma pathogenesis and suggest promising therapeutic strategies for treating this devastating disease.

Nucleotide metabolism, leukodystrophies, and CNS pathology

The balance between a protective and a destructive immune response can be precarious, as exemplified by inborn errors in nucleotide metabolism. This class of inherited disorders, which mimics infection, can result in systemic injury and severe neurologic outcomes. The most common of these disorders is Aicardi Goutières syndrome (AGS). AGS results in a phenotype similar to "TORCH" infections (Toxoplasma gondii, Other [Zika virus (ZIKV), human immunodeficiency virus (HIV)], Rubella virus, human Cytomegalovirus [HCMV], and Herpesviruses), but with sustained inflammation and ongoing potential for complications. AGS was first described in the early 1980s as familial clusters of "TORCH" infections, with severe neurology impairment, microcephaly, and basal ganglia calcifications (Aicardi & Goutières, Ann Neurol, 1984;15:49-54) and was associated with chronic cerebrospinal fluid (CSF) lymphocytosis and elevated type I interferon levels (Goutières et al., Ann Neurol, 1998;44:900-907). Since its first description, the clinical spectrum of AGS has dramatically expanded from the initial cohorts of children with severe impairment to including individuals with average intelligence and mild spastic paraparesis. This broad spectrum of potential clinical manifestations can result in a delayed diagnosis, which families cite as a major stressor. Additionally, a timely diagnosis is increasingly critical with emerging therapies targeting the interferon signaling pathway. Despite the many gains in understanding about AGS, there are still many gaps in our understanding of the cell-type drivers of pathology and characterization of modifying variables that influence clinical outcomes and achievement of timely diagnosis.

Therapeutic Targets in Innate Immunity to Tackle Alzheimer's Disease

There is an urgent need for effective disease-modifying therapeutic interventions for Alzheimer's disease (AD)-the most prevalent cause of dementia with a profound socioeconomic burden. Most clinical trials targeting the classical hallmarks of this disease-β-amyloid plaques and neurofibrillary tangles-failed, showed discrete clinical effects, or were accompanied by concerning side effects. There has been an ongoing search for novel therapeutic targets. Neuroinflammation, now widely recognized as a hallmark of all neurodegenerative diseases, has been proven to be a major contributor to AD pathology. Here, we summarize the role of neuroinflammation in the pathogenesis and progression of AD and discuss potential targets such as microglia, TREM2, the complement system, inflammasomes, and cytosolic DNA sensors. We also present an overview of ongoing studies targeting specific innate immune system components, highlighting the progress in this field of drug research while bringing attention to the delicate nature of innate immune modulations in AD.

Mitophagy and cGAS-STING crosstalk in neuroinflammation

Mitophagy, essential for mitochondrial health, selectively degrades damaged mitochondria. It is intricately linked to the cGAS-STING pathway, which is crucial for innate immunity. This pathway responds to mitochondrial DNA and is associated with cellular stress response. Our review explores the molecular details and regulatory mechanisms of mitophagy and the cGAS-STING pathway. We critically evaluate the literature demonstrating how dysfunctional mitophagy leads to neuroinflammatory conditions, primarily through the accumulation of damaged mitochondria, which activates the cGAS-STING pathway. This activation prompts the production of pro-inflammatory cytokines, exacerbating neuroinflammation. This review emphasizes the interaction between mitophagy and the cGAS-STING pathways. Effective mitophagy may suppress the cGAS-STING pathway, offering protection against neuroinflammation. Conversely, impaired mitophagy may activate the cGAS-STING pathway, leading to chronic neuroinflammation. Additionally, we explored how this interaction influences neurodegenerative disorders, suggesting a common mechanism underlying these diseases. In conclusion, there is a need for additional targeted research to unravel the complexities of mitophagy-cGAS-STING interactions and their role in neurodegeneration. This review highlights potential therapies targeting these pathways, potentially leading to new treatments for neuroinflammatory and neurodegenerative conditions. This synthesis enhances our understanding of the cellular and molecular foundations of neuroinflammation and opens new therapeutic avenues for neurodegenerative disease research.

Aberrant protein aggregation in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal disease. As its pathological mechanisms are not well understood, there are no efficient therapeutics for it at present. While it is highly heterogenous both etiologically and clinically, it has a common salient hallmark, i.e., aberrant protein aggregation (APA). The upstream pathogenesis and the downstream effects of APA in ALS are sophisticated and the investigation of this pathology would be of consequence for understanding ALS. In this paper, the pathomechanism of APA in ALS and the candidate treatment strategies for it are discussed.

C9orf72 controls hepatic lipid metabolism by regulating SREBP1 transport

Sterol regulatory element binding transcription factors (SREBPs) play a crucial role in lipid homeostasis. They are processed and transported to the nucleus via COPII, where they induce the expression of lipogenic genes. COPII maintains the homeostasis of organelles and plays an essential role in the protein secretion pathways in eukaryotes. The formation of COPII begins at endoplasmic reticulum exit sites (ERES), and is regulated by SEC16A, which provides a platform for the assembly of COPII. However, there have been few studies on the changes in SEC16A protein levels. The repetitive expansion of the hexanucleotide sequence GGGGCC within the chromosome 9 open reading frame 72 (C9orf72) gene is a prevalent factor in the development of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here, we found that the absence of C9orf72 leads to a decrease in SEC16A protein levels, resulting in reduced localization of the guanine nucleotide exchange factor SEC12 at the ERES. Consequently, the small GTP binding protein SAR1 is unable to bind the endoplasmic reticulum normally, impairing the assembly of COPII. Ultimately, the disruption of SREBPs transport decreases de novo lipogenesis. These results suggest that C9orf72 acts as a novel role in regulating lipid homeostasis and may serve as a potential therapeutic target for obesity.

STING orchestrates the neuronal inflammatory stress response in multiple sclerosis

Inflammation-induced neurodegeneration is a defining feature of multiple sclerosis (MS), yet the underlying mechanisms remain unclear. By dissecting the neuronal inflammatory stress response, we discovered that neurons in MS and its mouse model induce the stimulator of interferon genes (STING). However, activation of neuronal STING requires its detachment from the stromal interaction molecule 1 (STIM1), a process triggered by glutamate excitotoxicity. This detachment initiates non-canonical STING signaling, which leads to autophagic degradation of glutathione peroxidase 4 (GPX4), essential for neuronal redox homeostasis and thereby inducing ferroptosis. Both genetic and pharmacological interventions that target STING in neurons protect against inflammation-induced neurodegeneration. Our findings position STING as a central regulator of the detrimental neuronal inflammatory stress response, integrating inflammation with glutamate signaling to cause neuronal cell death, and present it as a tractable target for treating neurodegeneration in MS.

Control of innate immunity and lipid biosynthesis in neurodegeneration

The cGAS-STING innate immunity pathway and the SREBP-activated cholesterol and fatty acid synthesis pathway are abnormally co-regulated in neurodegenerative disease. Activation of STING signaling occurs at the endoplasmic reticulum (ER) membrane with STING anchored by INSIG1 along with SREBP and the sterol-bound SREBP cleavage activating protein (SCAP) when sterols are in abundance. When sterols are low, the INSIG-dependent STING pathway is inactivated and the SREBP-SCAP complex is translocated to the Golgi where SREBP is cleaved and translocated to the nucleus to transactivate genes for cholesterol and fatty acid synthesis. Thus, there is inverse activation of STING vs. SREBP: when innate immunity is active, pathways for cholesterol and fatty acid synthesis are suppressed, and vice versa. The STING pathway is stimulated by foreign viral cytoplasmic nucleic acids interacting with the cyclic GMP-AMP synthase (cGAS) DNA sensor or RIG-I and MDA5 dsRNA sensors, but with neurodegeneration innate immunity is also activated by self-DNAs and double-stranded RNAs that accumulate with neuronal death. Downstream, activated STING recruits TBK1 and stimulates the transactivation of interferon stimulated genes and the autophagy pathway, which are both protective. However, chronic activation of innate immunity contributes to microglia activation, neuroinflammation and autophagy failure leading to neurodegeneration. STING is also a proton channel that when activated stimulates proton exit from STING vesicles leading to cell death. Here we review the salient features of the innate immunity and cholesterol and fatty acid synthesis pathways, observations of abnormal STING and SREBP signaling in neurodegenerative disease, and relevant therapeutic approaches.

A phytomedicine extract exerts an anti-inflammatory response in the lungs by reducing STING-mediated type I interferon release

BACKGROUND

Acute respiratory distress syndrome (ARDS) is an acute respiratory disease characterized by bilateral chest radiolucency and severe hypoxemia. Quzhou Fructus Aurantii ethyl acetate extract (QFAEE), which is prepared from the traditional Chinese respiratory anti-inflammatory natural herb Quzhou Fructus Arantii, has the potential to alleviate ARDS. In this work, we aimed to investigate the potential and mechanism underlying the action of QFAEE on ARDS and how QFAEE modulates the STING pathway to reduce type I interferon release to alleviate the inflammatory response.

METHODS

Lipopolysaccharide (LPS), a potential proinflammatory stimulant capable of causing pulmonary inflammation with edema after nasal drops, was employed to model ARDS in vitro and in vivo. Under QFAEE intervention, the mechanism of action of QFAEE to alleviate ARDS was explored in this study. TREX1-/- mice were sued as a research model for the activation of the congenital STING signaling pathway. The effect of QFAEE on TREX1-/- mice could explain the STING-targeted effect of QFAEE on alleviating the inflammatory response. Our explorations covered several techniques, Western blot, histological assays, immunofluorescence staining, transcriptomic assays and qRT-PCR to determine the potential mechanism of action of QFAEE in antagonizing the inflammatory response in the lungs, as well as the mechanism of action of QFAEE in targeting the STING signaling pathway to regulate the release of type I interferon.

RESULTS

QFAEE effectively alleviates ARDS symptoms in LPS-induced ARDS. We revealed that the mechanism underlying LPS-induced ARDS is the STING-TBK1 signaling pathway and further elucidated the molecular mechanism of QFAEE in the prevention and treatment of ARDS. QFAEE reduced the release of type I interferons by inhibiting the STING-TBK1-IRF3 axis, thus alleviating LPS-induced pneumonia and lung cell death in mice. Another key finding is that activation of the STING pathway by activators or targeted knockdown of the TREX1 gene can also induce ARDS. As expected, QFAEE was found to be an effective protective agent in alleviating ARDS and the antagonistic effect of QFAEE on ARDS was achieved by inhibiting the STING signaling pathway.

CONCLUSIONS

The main anti-inflammatory effect of QFAEE was achieved by inhibiting the STING signaling pathway and reducing the release of type I interferons. According to this mechanism of effect, QFAEE can effectively alleviate ARDS and can be considered a potential therapeutic agent. In addition, the STING pathway plays an essential role in the development and progression of ARDS, and it is a potential target for ARDS therapy.

Copper toxicity and deficiency: the vicious cycle at the core of protein aggregation in ALS

The pathophysiology of ALS involves many signs of a disruption in copper homeostasis, with both excess free levels and functional deficiency likely occurring simultaneously. This is crucial, as many important physiological functions are performed by cuproenzymes. While it is unsurprising that many ALS symptoms are related to signs of copper deficiency, resulting in vascular, antioxidant system and mitochondrial oxidative respiration deficiencies, there are also signs of copper toxicity such as ROS generation and enhanced protein aggregation. We discuss how copper also plays a key role in proteostasis and interacts either directly or indirectly with many of the key aggregate-prone proteins implicated in ALS, such as TDP-43, C9ORF72, SOD1 and FUS as well as the effect of their aggregation on copper homeostasis. We suggest that loss of cuproprotein function is at the core of ALS pathology, a condition that is driven by a combination of unbound copper and ROS that can either initiate and/or accelerate protein aggregation. This could trigger a positive feedback cycle whereby protein aggregates trigger the aggregation of other proteins in a chain reaction that eventually captures elements of the proteostatic mechanisms in place to counteract them. The end result is an abundance of aggregated non-functional cuproproteins and chaperones alongside depleted intracellular copper stores, resulting in a general lack of cuproenzyme function. We then discuss the possible aetiology of ALS and illustrate how strong risk factors including environmental toxins such as BMAA and heavy metals can functionally behave to promote protein aggregation and disturb copper metabolism that likely drives this vicious cycle in sporadic ALS. From this synthesis, we propose restoration of copper balance using copper delivery agents in combination with chaperones/chaperone mimetics, perhaps in conjunction with the neuroprotective amino acid serine, as a promising strategy in the treatment of this incurable disease.

Lysosomal microautophagy: an emerging dimension in mammalian autophagy

Autophagy is a self-catabolic process through which cellular components are delivered to lysosomes for degradation. There are three types of autophagy, i.e., macroautophagy, chaperone-mediated autophagy (CMA), and microautophagy. In macroautophagy, a portion of the cytoplasm is wrapped by the autophagosome, which then fuses with lysosomes and delivers the engulfed cytoplasm for degradation. In CMA, the translocation of cytosolic substrates to the lysosomal lumen is directly across the limiting membrane of lysosomes. In microautophagy, lytic organelles, including endosomes or lysosomes, take up a portion of the cytoplasm directly. Although macroautophagy has been investigated extensively, microautophagy has received much less attention. Nonetheless, it has become evident that microautophagy plays a variety of cellular roles from yeast to mammals. Here we review the very recent updates of microautophagy. In particular, we focus on the feature of the degradative substrates and the molecular machinery that mediates microautophagy.

Single-nucleus sequencing reveals enriched expression of genetic risk factors in extratelencephalic neurons sensitive to degeneration in ALS

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder characterized by a progressive loss of motor function linked to degenerating extratelencephalic neurons/Betz cells (ETNs). The reasons why these neurons are selectively affected remain unclear. Here, to understand the unique molecular properties that may sensitize ETNs to ALS, we performed RNA sequencing of 79,169 single nuclei from cortices of patients and controls. In both patients and unaffected individuals, we found significantly higher expression of ALS risk genes in THY1+ ETNs, regardless of diagnosis. In patients, this was accompanied by the induction of genes involved in protein homeostasis and stress responses that were significantly induced in a wide collection of ETNs. Examination of oligodendroglial and microglial nuclei revealed patient-specific downregulation of myelinating genes in oligodendrocytes and upregulation of an endolysosomal reactive state in microglia. Our findings suggest that selective vulnerability of extratelencephalic neurons is partly connected to their intrinsic molecular properties sensitizing them to genetics and mechanisms of degeneration.

Prevalence of anti-myelin oligodendrocyte glycoprotein antibodies across neuroinflammatory and neurodegenerative diseases

Inflammatory central nervous system (CNS) diseases, such as multiple sclerosis (MS) and myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD), are characterized by humoral immune abnormalities. Anti-MOG antibodies are not specific to MOGAD, with their presence described in MS. Autoantibodies may also be present and play a role in various neurodegenerative diseases. Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease driven by motor neuron dysfunction. While immune involvement in ALS has been recognized, the presence of antibodies targeting CNS myelin antigens has not been established. We aimed to establish a live cell-based assay for quantification of serum anti-MOG IgG1 in patients with CNS diseases, including MS and ALS. In total, 771 serum samples from the John L. Trotter MS Center and the Northeast ALS Consortium were examined using a live cell-based assay for detection of anti-MOG IgG1. Samples from three cohorts were tested in blinded fashion: healthy control (HC) subjects, patients with clinically diagnosed MOGAD, and an experimental group of ALS and MS patients. All samples from established MOGAD cases were positive for anti-MOG antibodies, while all HC samples were negative. Anti-MOG IgG1 was detected in 65 of 658 samples (9.9%) from MS subjects and 4 of 108 (3.7%) samples from ALS subjects. The presence of serum anti-MOG IgG1 in MS and ALS patients raises questions about the contribution of these antibodies to disease pathophysiology as well as accuracy of diagnostic approaches for CNS inflammatory diseases.

Liquid-liquid phase separation in innate immunity

Intrinsic and innate immune responses are essential lines of defense in the body's constant surveillance of pathogens. The discovery of liquid-liquid phase separation (LLPS) as a key regulator of this primal response to infection brings an updated perspective to our understanding of cellular defense mechanisms. Here, we review the emerging multifaceted role of LLPS in diverse aspects of mammalian innate immunity, including DNA and RNA sensing and inflammasome activity. We discuss the intricate regulation of LLPS by post-translational modifications (PTMs), and the subversive tactics used by viruses to antagonize LLPS. This Review, therefore, underscores the significance of LLPS as a regulatory node that offers rapid and plastic control over host immune signaling, representing a promising target for future therapeutic strategies.

Relationship between the cGAS-STING and NF-κB pathways-role in neurotoxicity

Neurotoxicity can cause a range of symptoms and disorders in humans, including neurodegenerative diseases, neurodevelopmental disorders, nerve conduction abnormalities, neuroinflammation, autoimmune disorders, and cognitive deficits. The cyclic guanosine-adenosine synthase (cGAS)-stimulator of interferon genes (STING) pathway and NF-κB pathway are two important signaling pathways involved in the innate immune response. The cGAS-STING pathway is activated by the recognition of intracellular DNA, which triggers the production of type I interferons and pro-inflammatory cytokines, such as tumor necrosis factor, IL-1β, and IL-6. These cytokines play a role in oxidative stress and mitochondrial dysfunction in neurons. The NF-κB pathway is activated by various stimuli, such as bacterial lipopolysaccharide, viral particle components, and neurotoxins. NF-κB activation may lead to the production of pro-inflammatory cytokines, which promote neuroinflammation and cause neuronal damage. A potential interaction exists between the cGAS-STING and NF-κB pathways, and NF-κB activation blocks STING degradation by inhibiting microtubule-mediated STING transport. This review examines the progress of research on the roles of these pathways in neurotoxicity and their interrelationships. Understanding the mechanisms of these pathways will provide valuable therapeutic insights for preventing and controlling neurotoxicity.

Pharmacological potential of cyclic nucleotide signaling in immunity

Cyclic nucleotides are important signaling molecules that play many critical physiological roles including controlling cell fate and development, regulation of metabolic processes, and responding to changes in the environment. Cyclic nucleotides are also pivotal regulators in immune signaling, orchestrating intricate processes that maintain homeostasis and defend against pathogenic threats. This review provides a comprehensive examination of the pharmacological potential of cyclic nucleotide signaling pathways within the realm of immunity. Beginning with an overview of the fundamental roles of cAMP and cGMP as ubiquitous second messengers, this review delves into the complexities of their involvement in immune responses. Special attention is given to the challenges associated with modulating these signaling pathways for therapeutic purposes, emphasizing the necessity for achieving cell-type specificity to avert unintended consequences. A major focus of the review is on the recent paradigm-shifting discoveries regarding specialized cyclic nucleotide signals in the innate immune system, notably the cGAS-STING pathway. The significance of cyclic dinucleotides, exemplified by 2'3'-cGAMP, in controlling immune responses against pathogens and cancer, is explored. The evolutionarily conserved nature of cyclic dinucleotides as antiviral agents, spanning across diverse organisms, underscores their potential as targets for innovative immunotherapies. Findings from the last several years have revealed a striking diversity of novel bacterial cyclic nucleotide second messengers which are involved in antiviral responses. Knowledge of the existence and precise identity of these molecules coupled with accurate descriptions of their associated immune defense pathways will be essential to the future development of novel antibacterial therapeutic strategies. The insights presented herein may help researchers navigate the evolving landscape of immunopharmacology as it pertains to cyclic nucleotides and point toward new avenues or lines of thinking about development of therapeutics against the pathways they regulate.

Gain-of-function mutations of TRPV4 acting in endothelial cells drive blood-CNS barrier breakdown and motor neuron degeneration in mice

Blood-CNS barrier disruption is a hallmark of numerous neurological disorders, yet whether barrier breakdown is sufficient to trigger neurodegenerative disease remains unresolved. Therapeutic strategies to mitigate barrier hyperpermeability are also limited. Dominant missense mutations of the cation channel transient receptor potential vanilloid 4 (TRPV4) cause forms of hereditary motor neuron disease. To gain insights into the cellular basis of these disorders, we generated knock-in mouse models of TRPV4 channelopathy by introducing two disease-causing mutations (R269C and R232C) into the endogenous mouse Trpv4 gene. TRPV4 mutant mice exhibited weakness, early lethality, and regional motor neuron loss. Genetic deletion of the mutant Trpv4 allele from endothelial cells (but not neurons, glia, or muscle) rescued these phenotypes. Symptomatic mutant mice exhibited focal disruptions of blood-spinal cord barrier (BSCB) integrity, associated with a gain of function of mutant TRPV4 channel activity in neural vascular endothelial cells (NVECs) and alterations of NVEC tight junction structure. Systemic administration of a TRPV4-specific antagonist abrogated channel-mediated BSCB impairments and provided a marked phenotypic rescue of symptomatic mutant mice. Together, our findings show that mutant TRPV4 channels can drive motor neuron degeneration in a non-cell autonomous manner by precipitating focal breakdown of the BSCB. Further, these data highlight the reversibility of TRPV4-mediated BSCB impairments and identify a potential therapeutic strategy for patients with TRPV4 mutations.

In sickness and in health-Type I interferon and the brain

Type I interferons (IFN-I) represent a group of pleiotropic cytokines renowned for their antiviral activity and immune regulatory functions. A multitude of studies have unveiled a critical role of IFN-I in the brain, influencing various neurological processes and diseases. In this mini-review, I highlight recent findings on IFN-I's effects on brain aging, Alzheimer's disease (AD) progression, and central nervous system (CNS) homeostasis. The multifaceted influence of IFN-I on brain health and disease sheds light on the complex interplay between immune responses and neurological processes. Of particular interest is the cGAS-STING-IFN-I axis, which extensively participates in brain aging and various forms of neurodegeneration. Understanding the intricate role of IFN-I and its associated pathways in the CNS not only advances our comprehension of brain health and disease but also presents opportunities for developing interventions to modify the process of neurodegeneration and prevent age-related cognitive decline.