DNA sensor cGAS-mediated immune recognition

The cGAS-STING-mediated ROS and ferroptosis are involved in manganese neurotoxicity

Manganese (Mn) has been characterized as an environmental pollutant. Excessive releases of Mn due to human activities have increased Mn levels in the environment over the years, posing a threat to human health and the environment. Long-term exposure to high concentrations of Mn can induce neurotoxicity. Therefore, toxicological studies on Mn are of paramount importance. Mn induces oxidative stress through affecting the level of reactive oxygen species (ROS), and the overabundance of ROS further triggers ferroptosis. Additionally, Mn2+ was found to be a novel activator of the cyclic guanosine-adenosine synthase (cGAS)-stimulator of interferon genes (STING) pathway in the innate immune system. Thus, we speculate that Mn exposure may promote ROS production by activating the cGAS-STING pathway, which further induces oxidative stress and ferroptosis, and ultimately triggers Mn neurotoxicity. This review discusses the mechanism between Mn-induced oxidative stress and ferroptosis via activation of the cGAS-STING pathway, which may offer a prospective direction for future in-depth studies on the mechanism of Mn neurotoxicity.

Dual-tDCS Ameliorates Cerebral Injury and Promotes Motor Function Recovery via cGAS-STING Signaling Pathway in a Rat Model of Ischemic Stroke

Ischemic stroke is one of the leading causes of death and disability. Dual transcranial direct current stimulation (dual-tDCS) is a promising intervention to treat ischemic stroke, but its efficacy and underlying mechanism remain to be verified. Cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway has recently emerged as a key mediator in cerebral injury. However, little is known about the effect of cGAS-STING on neuronal damage in ischemic stroke, and it remains to be studied whether the cGAS-STING pathway is involved in tDCS intervention for ischemic stroke. Therefore, we aimed to investigate whether dual-tDCS can alleviate ischemic brain injury in a rat model of ischemic stroke and if so, whether via cGAS-STING pathway. Middle cerebral artery occlusion (MCAO) was employed to induce a rat model of ischemic stroke. Male SD rats weighing 250-280 g were randomly assigned to the Sham, MCAO, Dual-tDCS, Dual-tDCS + RU.521, and Dual-tDCS + 2'3'-cGAMP groups, with 10 rats in each group completing the experiment. Behavioral, morphological, MRI, and molecular biological methods were performed. We found that the cGAS-STING pathway was activated and expressed in neurons after MCAO. Dual-tDCS improved motor function and infarct volume, inhibited neuronal apoptosis, promoted the expression of neurotrophins (BDNF and NGF), CD31, and VEGF, and suppressed inflammation reaction after MCAO via the cGAS-STING pathway. Taken together, dual-tDCS may improve MCAO-induced brain injury and promote the recovery of motor function, resulting from the inhibition of neuronal apoptosis and inflammation reaction, as well as promotion of the expression of nerve plasticity- and angiogenesis-related proteins, via cGAS-STING pathway.

Marek's disease virus protein kinase US3 inhibits DNA-sensing antiviral innate immunity via abrogating activation of NF-κB

Marek's disease virus (MDV) is an avian alphaherpesvirus associated with Marek's disease, an immunosuppressive and lymphoproliferative disease in chickens. The DNA sensing pathway mediates innate immune defense against infection by many DNA-containing pathogens, while viruses have evolved multiple strategies to evade the host immune response to survive in host cells. This study found that ectopic expression of MDV protein kinase US3 inhibited beta interferon (IFN-β) and interleukin-6 (IL-6) production induced by interferon-stimulatory and viral DNA. US3 was further shown to abolish the nuclear factor κB (NF-κB) activation. The US3 kinase activity was indispensable for its inhibitory function, as the kinase-dead US3 mutant (US3K220A) did not inhibit NF-κB activation. Further studies showed that US3 interacted with the Rel homology domains of the NF-κB subunits p65 and p50, which phosphorylated these transcription factors and blocked their nuclear translocation. Finally, US3 deficiency promoted IFN-β and IL-6 production, resulting in reduced viral replication and lower MDV-specific lesion incidence during MDV infection in chickens. Altogether, these findings reveal a novel mechanism for MDV to evade host antiviral immunity.IMPORTANCEMarek's disease virus (MDV) is an oncogenic avian alphaherpesvirus that causes an economically important disease affecting the health and welfare of poultry worldwide. Whereas human herpesviruses have been shown to evolve various strategies to inhibit the DNA sensing signaling for the evasion of the host's innate immunity, little is known regarding the mechanism for MDV to regulate this pathway. In this study, MDV US3 protein kinase was demonstrated to inhibit the activation of NF-κB in the DNA sensing pathway via binding to the Rel homology domains of the NF-κB subunits p65 and p50, which hyperphosphorylated these transcription factors and abolished their nuclear translocation. This is an important finding toward a better understanding of the functions of avian alphaherpesviruses encoded US3 protein kinase.

The neuroimmune nexus: unraveling the role of the mtDNA-cGAS-STING signal pathway in Alzheimer's disease

The relationship between Alzheimer's disease (AD) and neuroimmunity has gradually begun to be unveiled. Emerging evidence indicates that cyclic GMP-AMP synthase (cGAS) acts as a cytosolic DNA sensor, recognizing cytosolic damage-associated molecular patterns (DAMPs), and inducing the innate immune response by activating stimulator of interferon genes (STING). Dysregulation of this pathway culminates in AD-related neuroinflammation and neurodegeneration. A substantial body of evidence indicates that mitochondria are involved in the critical pathogenic mechanisms of AD, whose damage leads to the release of mitochondrial DNA (mtDNA) into the extramitochondrial space. This leaked mtDNA serves as a DAMP, activating various pattern recognition receptors and immune defense networks in the brain, including the cGAS-STING pathway, ultimately leading to an imbalance in immune homeostasis. Therefore, modulation of the mtDNA-cGAS-STING pathway to restore neuroimmune homeostasis may offer promising prospects for improving AD treatment outcomes. In this review, we focus on the mechanisms of mtDNA release during stress and the activation of the cGAS-STING pathway. Additionally, we delve into the research progress on this pathway in AD, and further discuss the primary directions and potential hurdles in developing targeted therapeutic drugs, to gain a deeper understanding of the pathogenesis of AD and provide new approaches for its therapy.

Bidirectional regulation of the cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon gene pathway and its impact on hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) ranks as the fourth leading cause of cancer-related deaths in China, and the treatment options are limited. The cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) activates the stimulator of interferon gene (STING) signaling pathway as a crucial immune response pathway in the cytoplasm, which detects cytoplasmic DNA to regulate innate and adaptive immune responses. As a potential therapeutic target, cGAS-STING pathway markedly inhibits tumor cell proliferation and metastasis, with its activation being particularly relevant in HCC. However, prolonged pathway activation may lead to an immunosuppressive tumor microenvironment, which fostering the invasion or metastasis of liver tumor cells.

AIM

To investigate the dual-regulation mechanism of cGAS-STING in HCC.

METHODS

This review was conducted according to the PRISMA guidelines. The study conducted a comprehensive search for articles related to HCC on PubMed and Web of Science databases. Through rigorous screening and meticulous analysis of the retrieved literature, the research aimed to summarize and elucidate the impact of the cGAS-STING pathway on HCC tumors.

RESULTS

All authors collaboratively selected studies for inclusion, extracted data, and the initial search of online databases yielded 1445 studies. After removing duplicates, the remaining 964 records were screened. Ultimately, 55 articles met the inclusion criteria and were included in this review.

CONCLUSION

Acute inflammation can have a few inhibitory effects on cancer, while chronic inflammation generally promotes its progression. Extended cGAS-STING pathway activation will result in a suppressive tumor microenvironment.

Cyclic GMP-AMP synthase recognizes the physical features of DNA

Cyclic GMP-AMP synthase (cGAS) is a major cytosolic DNA sensor that plays a significant role in innate immunity. Upon binding to double stranded DNA (dsDNA), cGAS utilizes GTP and ATP to synthesize the second messenger cyclic GMP-AMP (cGAMP). The cGAMP then binds to the adapter protein stimulator of interferon genes (STING) in the endoplasmic reticulum, resulting in the activation of the transcription factor interferon regulatory factor 3 (IRF3) and subsequent induction of type I interferon. An important question is how cGAS distinguishes between self and non-self DNA. While cGAS binds to the phosphate backbone of DNA without discrimination, its activation is influenced by physical features such as DNA length, inter-DNA distance, and mechanical flexibility. This suggests that the recognition of DNA by cGAS may depend on these physical features. In this article we summarize the recent progress in research on cGAS-STING pathway involved in antiviral defense, cellular senescence and anti-tumor response, and focus on DNA recognition mechanisms based on the physical features.

DNA PAMPs as Molecular Tools for the cGAS-STING Signaling Pathways

Beyond its role as the bearer of genetic material, DNA also plays a crucial role in the activation phase of innate immunity. Pathogen recognition receptors (PRRs) and their homologs, pathogen-associated molecular patterns (PAMPs), form the foundation for driving innate immune activation and the induction of immune responses during infection. In the context of DNA viruses or bacterial infections, specific DNA sequences are recognized and bound by DNA sensors, marking the DNA as a PAMP for host recognition and subsequent activation of innate immunity. The primary DNA sensor pathway known to date is cGAS-STING, which can induce Type I interferons (IFN) and innate immune responses against viruses and bacteria. Additionally, the cGAS-STING pathway has been identified to mediate functions in autophagy and senescence. Herein, we introduce methods for using DNA PAMPs as molecular tools to study the role of cGAS-STING and its signaling pathway in regulating innate immunity, both in vitro and in vivo.

Small molecule innate immune modulators in cancer therapy

Immunotherapy has proved to be a breakthrough in cancer treatment. So far, a bulk of the approved/late-stage cancer immunotherapy are antibody-based. Although these antibody-based drugs have demonstrated great promise, a majority of them are limited due to their access to extracellular targets, lack of oral bioavailability, tumor microenvironment penetration, induction of antibody dependent cytotoxicity etc. In recent times, there has been an increased research focus on the development of small molecule immunomodulators since they have the potential to overcome the aforementioned limitations posed by antibodies. Furthermore, while most biologics based therapeutics that are in clinical use are limited to modulating the adaptive immune system, very few clinically approved therapeutic modalities exist that modulate the innate immune system. The innate immune system, which is the body's first line of defense, has the ability to turn cold tumors hot and synergize strongly with existing adaptive immune modulators. In preclinical studies, small molecule innate immune modulators have demonstrated synergistic efficacy as combination modalities with current standard-of-care immune checkpoint antibodies. In this review, we highlight the recent advances made by small molecule innate immunomodulators in cancer immunotherapy.

Multifaceted activation of STING axis upon Nipah and measles virus-induced syncytia formation

Activation of the DNA-sensing STING axis by RNA viruses plays a role in antiviral response through mechanisms that remain poorly understood. Here, we show that the STING pathway regulates Nipah virus (NiV) replication in vivo in mice. Moreover, we demonstrate that following both NiV and measles virus (MeV) infection, IFNγ-inducible protein 16 (IFI16), an alternative DNA sensor in addition to cGAS, induces the activation of STING, leading to the phosphorylation of NF-κB p65 and the production of IFNβ and interleukin 6. Finally, we found that paramyxovirus-induced syncytia formation is responsible for loss of mitochondrial membrane potential and leakage of mitochondrial DNA in the cytoplasm, the latter of which is further detected by both cGAS and IFI16. These results contribute to improve our understanding about NiV and MeV immunopathogenesis and provide potential paths for alternative therapeutic strategies.

Identification of new benzofuran derivatives as STING agonists with broad-spectrum antiviral activity

The Stimulator of Interferon Genes (STING) is involved in cytosolic DNA sensing and type I Interferons (IFN-I) induction. Aiming to identify new STING agonists with antiviral activity and given the known biological activity of benzothiazole and benzimidazole derivatives, a series of benzofuran derivatives were tested for their ability to act as STING agonists, induce IFN-I and inhibit viral replication. Compounds were firstly evaluated in a gene reporter assay measuring luciferase activity driven by the human IFN-β promoter in cells expressing exogenous STING (HEK293T). Seven of them were able to induce IFN-β transcription while no induction of the IFN promoter was observed in the presence of a mutated and inactive STING, showing specific protein-ligand interaction. Docking studies were performed to predict their putative binding mode. The best hit compounds were then tested on human coronavirus 229E replication in BEAS-2B and MRC-5 cells and three derivatives showed EC50 values in the μM range. Such compounds were also tested on SARS-CoV-2 replication in BEAS-2B cells and in Calu-3 showing they can inhibit SARS-CoV-2 replication at nanomolar concentrations. To further confirm their IFN-dependent antiviral activity, compounds were tested to verify their effect on phospho-IRF3 nuclear localization, that was found to be induced by benzofuran derivatives, and SARS-CoV-2 replication in Vero E6 cells, lacking IFN production, founding them to be inactive. In conclusion, we identified benzofurans as STING-dependent immunostimulatory compounds and host-targeting inhibitors of coronaviruses representing a novel chemical scaffold for the development of broad-spectrum antivirals.

TBK1 is paradoxical in tumor development: a focus on the pathway mediating IFN-I expression

TANK-binding kinase 1 (TBK1) is a member of the IKK family and plays a crucial role in the activation of non-canonical NF-κB signaling and type I interferon responses. The aberrant activation of TBK1 contributes to the proliferation and survival of various types of tumor cells, particularly in specific mutational or tumorous contexts. Inhibitors targeting TBK1 are under development and application in both in vivo and in vitro settings, yet their clinical efficacy remains limited. Numerous literatures have shown that TBK1 can exhibit both tumor promoting and tumor inhibiting effects. TBK1 acts as a pivotal node within the innate immune pathway, mediating anti-tumor immunity through the activation of innate immune responses. Facilitating interferon-I (IFN-I) production represents a critical mechanism through which TBK1 bridges these processes. IFN has been shown to exert both beneficial and detrimental effects on tumor progression. Hence, the paradoxical role of TBK1 in tumor development may necessitate acknowledgment in light of its downstream IFN-I signaling cascade. In this paper, we review the signaling pathways mediated by TBK1 in various tumor contexts and summarize the dual roles of TBK1 and the TBK1-IFN pathways in both promoting and inhibiting tumor progression. Additionally, we highlight the significance of the TBK1-IFN pathway in clinical therapy, particularly in the context of immune response. We anticipate further advancements in the development of TBK1 inhibitors as part of novel cancer treatment strategies.

cGAS suppresses β-cell proliferation by a STING-independent but CEBPβ-dependent mechanism

AIMS/HYPOTHESIS

cGAS (cyclic GMP-AMP synthase) has been implicated in various cellular processes, but its role in β-cell proliferation and diabetes is not fully understood. This study investigates the impact of cGAS on β-cell proliferation, particularly in the context of diabetes.

METHODS

Utilizing mouse models, including cGAS and STING (stimulator of interferon genes) knockout mice, we explored the role of cGAS in β-cell function. This involved β-cell-specific cGAS knockout (cGASβKO) mice, created by breeding cGAS floxed mice with transgenic mice expressing Cre recombinase under the insulin II promoter. We analyzed cGAS expression in diabetic mouse models, evaluated the effects of cGAS deficiency on glucose tolerance, and investigated the molecular mechanisms underlying these effects through RNA sequencing.

RESULTS

cGAS expression is upregulated in the islets of diabetic mice and by high glucose treatment in MIN6 cells. Both global cGAS deficiency and β-cell-specific cGAS knockout mice lead to improved glucose tolerance by promoting β-cell mass. Interestingly, STING knockout did not affect pancreatic β-cell mass, suggesting a STING-independent mechanism for cGAS's role in β-cells. Further analyses revealed that cGAS- but not STING-deficiency leads to reduced expression of CEBPβ, a known suppressor of β-cell proliferation, concurrently with increased β-cell proliferation. Moreover, overexpression of CEBPβ reverses the upregulation of Cyclin D1 and D2 induced by cGAS deficiency, thereby regulating β-cell proliferation. These results confirm that cGAS regulation of β-cell proliferation via a CEBPβ-dependent but STING-independent mechanism.

CONCLUSIONS/INTERPRETATION

Our findings highlight the pivotal role of cGAS in promoting β-cell proliferation and maintaining glucose homeostasis, potentially by regulating CEBPβ expression in a STING-independent manner. This study uncovers the significance of cGAS in controlling β-cell mass and identifies a potential therapeutic target for enhancing β-cell proliferation in the treatment of diabetes.

Therapeutic intervention in neuroinflammation for neovascular ocular diseases through targeting the cGAS-STING-necroptosis pathway

The microglia-mediated neuroinflammation have been shown to play a crucial role in the ocular pathological angiogenesis process, but specific immunotherapies for neovascular ocular diseases are still lacking. This study proposed that targeting GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) might be a novel immunotherapy for these angiogenesis diseases. We found a significant upregulation of CGAS and STING genes in the RNA-seq data derived from retinal tissues of the patients with proliferative diabetic retinopathy. In experimental models of ocular angiogenesis including laser-induced choroidal neovascularization (CNV) and oxygen-induced retinopathy (OIR), the cGAS-STING pathway was activated as angiogenesis progressed. Either genetic deletion or pharmacological inhibition of STING resulted in a remarkable suppression of neovascularization in both models. Furthermore, cGAS-STING signaling was specifically activated in myeloid cells, triggering the subsequent RIP1-RIP3-MLKL pathway activation and leading to necroptosis-mediated inflammation. Notably, targeted inhibition of the cGAS-STING pathway with C-176 or SN-011 could significantly suppress pathological angiogenesis in CNV and OIR. Additionally, the combination of C-176 or SN-011 with anti-VEGF therapy led to least angiogenesis, markedly enhancing the anti-angiogenic effectiveness. Together, our findings provide compelling evidence for the importance of the cGAS-STING-necroptosis axis in pathological angiogenesis, highlighting its potential as a promising immunotherapeutic target for treating neovascular ocular diseases.

Zeolite-iron oxide integrated interdigitated electrode sensor for diagnosing cervical cancer

Cervical cancer is caused by changes in the cervix that lead to precancerous cells and eventually progress to cancer. Human papillomavirus (HPV) infections are the primary cause of cervical cancer. Early detection of HPV is crucial in preventing cervical cancer, and regular screening for HPV infection can identify cell changes before they develop into cancer. While Pap smear tests are reliable for cervical cancer screening, they are critical, expensive, and labor-intensive. Therefore, researchers are focusing on identifying blood-based biomarkers using biosensors for cervical cancer screening. HPV strains 16, 45, and 18 are common culprits in cervical cancer. This study aimed to develop an HPV-16 DNA biosensor on a zeolite-iron oxide (zeolite-IO) modified interdigitated electrode (IDE) sensor. The DNA probe was immobilized on the IDE through amine-modified zeolite-IO, enhancing the hybridization of the target and DNA probe. The detection limit of the DNA-DNA duplex was found to be 7.5 pM with an R2 value of 0.9868. Additionally, control experiments with single and triple mismatched sequences showed no increase in current responses, and the identification of target DNA in a serum-spiked sample indicated specific and selective target identification.

Dysfunction of STING Autophagy Degradation in Senescent Nucleus Pulposus Cells Accelerates Intervertebral Disc Degeneration

The pathogenesis of Intervertebral Disc Degeneration (IDD) is complex and multifactorial, with cellular senescence of nucleus pulposus (NP) cells and inflammation playing major roles in the progression of IDD. The stimulator of interferon genes (STING) axis is a key mediator of inflammation during infection, cellular stress, and tissue damage. Here, we present a progressive increase in STING in senescent NP cells with the degradation disorder. The STING degradation function in normal NP cells can prevent IDD. However, the dysfunction of STING degradation through autophagy causes the accumulation and high expression of STING in senescent NP cells as well as inflammation continuous activation together significantly promotes IDD. In senescent NP cells and intervertebral discs (IVDs), we found that STING autophagy degradation was significantly lower than that of normal NP cells and IVDs when STING was activated by 2'3'-cGAMP. Also, the above phenomenon was found in STINGgt/gt, cGAS-/- mice with models of age-induced, lumbar instability-induced IDD as well as found in the rat caudal IVD puncture models. Taken together, we suggested that the promotion of STING autophagy degradation in senescent NP Cells demonstrated a potential therapeutic modality for the treatment of IDD.

Role of STING in the treatment of non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is a prevalent form of lung cancer. Patients with advanced NSCLC are currently being treated with various therapies, including traditional radiotherapy, chemotherapy, molecular targeted therapies and immunotherapy. However, a considerable proportion of advance patients who cannot benefit from them. Consequently, it is essential to identify a novel research target that offers an encouraging perspective. The stimulator of interferon genes (STING) has emerged as such a target. At present, it is confirmed that activating STING in NSCLC tumor cells can impede the proliferation and metastasis of dormant tumor cells. This review focuses on the role of STING in NSCLC treatment and the factors influencing its activation. Additionally, it explores the correlation between STING activation and diverse therapy modalities for NSCLC, such as radiotherapy, chemotherapy, molecular targeted therapies and immunotherapy. Furthermore, it proposes the prospect of innovative therapy methods involving nanoparticles, with the aim of using the features of STING to develop more strategies for NSCLC therapy.

How enzyme-centered approaches are advancing research on cyclic oligo-nucleotides

Cyclic nucleotides are the most diversified category of second messengers and are found in all organisms modulating diverse pathways. While cAMP and cGMP have been studied over 50 years, cyclic di-nucleotide signaling in eukaryotes emerged only recently with the anti-viral molecule 2´3´cGAMP. Recent breakthrough discoveries have revealed not only the astonishing chemical diversity of cyclic nucleotides but also surprisingly deep-rooted evolutionary origins of cyclic oligo-nucleotide signaling pathways and structural conservation of the proteins involved in their synthesis and signaling. Here we discuss how enzyme-centered approaches have paved the way for the identification of several cyclic nucleotide signals, focusing on the advantages and challenges associated with deciphering the activation mechanisms of such enzymes.

A conserved methyltransferase active site residue of Zika virus NS5 is required for the restriction of STING activation and interferon expression

Zika virus (ZIKV) is a re-emerging RNA virus and causes major public health events due to its link to severe neurological complications in foetuses and neonates. The cGAS-STING signalling pathway regulates innate immunity and plays an important role in the invasion of DNA and RNA viruses. This study reveals a distinct mechanism by which ZIKV restricts the cGAS-STING signalling to repress IFN-β expression. ZIKV attenuates IFN-β expression induced by DNA viruses (herpes simplex virus type 1, HSV-1) or two double-stranded DNAs (dsDNA90 and HSV120) in mouse embryonic fibroblasts (MEFs). Notably, ZIKV NS5, the viral RNA-dependent RNA polymerase, was responsible for the repression of IFN-β. NS5 interacts with STING in the cytoplasm, suppresses IRF3 phosphorylation and nucleus localization and promotes the cleavage of STING K48-linked polyubiquitination. Furthermore, the NS5 methyltransferase (MTase) domain interacts with STING to restrict STING-induced IFN-β expression. Interestingly, point mutation analyses of conserved methyltransferase active site residue D146 indicate that it is critical for repressing IFN-β expression induced by STING stimulation in cGAS-STING signalling.

GAS-STING: a classical DNA recognition pathways to tumor therapy

Cyclic GMP-AMP synthetase (cGAS), recognized as the primary DNA sensor within cells, possesses the capability to identify foreign DNA molecules along with free DNA fragments. This identification process facilitates the production of type I IFNs through the activator of the interferon gene (STING) which induces the phosphorylation of downstream transcription factors. This action characterizes the most archetypal biological functionality of the cGAS-STING pathway. When treated with anti-tumor agents, cells experience DNA damage that triggers activation of the cGAS-STING pathway, culminating in the expression of type I IFNs and associated downstream interferon-stimulated genes. cGAS-STING is one of the important innate immune pathways,the role of type I IFNs in the articulation between innate immunity and T-cell antitumour immunity.type I IFNs promote the recruitment and activation of inflammatory cells (including NK cells) at the tumor site.Type I IFNs also can promote the activation and maturation of dendritic cel(DC), improve the antigen presentation of CD4+T lymphocytes, and enhance the cross-presentation of CD8+T lymphocytes to upregulating anti-tumor responses. This review discussed the cGAS-STING signaling and its mechanism and biological function in traditional tumor therapy and immunotherapy.

Novel insight into cGAS-STING pathway in ischemic stroke: from pre- to post-disease

Ischemic stroke, a primary cause of disability and the second leading cause of mortality, has emerged as an urgent public health issue. Growing evidence suggests that the Cyclic GMP-AMP synthase (cGAS)- Stimulator of interferon genes (STING) pathway, a component of innate immunity, is closely associated with microglia activation, neuroinflammation, and regulated cell death in ischemic stroke. However, the mechanisms underlying this pathway remain inadequately understood. This article comprehensively reviews the existing literature on the cGAS-STING pathway and its multifaceted relationship with ischemic stroke. Initially, it examines how various risk factors and pre-disease mechanisms such as metabolic dysfunction and senescence (e.g., hypertension, hyperglycemia, hyperlipidemia) affect the cGAS-STING pathway in relation to ischemic stroke. Subsequently, we explore in depth the potential pathophysiological relationship between this pathway and oxidative stress, endoplasmic reticulum stress, neuroinflammation as well as regulated cell death including ferroptosis and PANoptosis following cerebral ischemia injury. Finally, it suggests that intervention targeting the cGAS-STING pathway may serve as promising therapeutic strategies for addressing neuroinflammation associated with ischemic stroke. Taken together, this review concludes that targeting the microglia cGAS-STING pathway may shed light on the exploration of new therapeutic strategies against ischemic stroke.

African Swine Fever Virus H240R Protein Inhibits the Production of Type I Interferon through Disrupting the Oligomerization of STING

African swine fever (ASF) is a highly contagious and acute hemorrhagic viral disease in domestic pigs and wild boars. Domestic pigs infected with virulent African swine fever virus (ASFV) isolates have a high mortality, approaching 100%. Identification of ASFV genes related to virulence/pathogenicity and deletion of them are considered to be key steps in the development of live attenuated vaccines, because the ability of ASFV to escape host innate immune responses is related to viral pathogenicity. However, the relationship between the host antiviral innate immune responses and the pathogenic genes of ASFV has not been fully understood. In this study, the ASFV H240R protein (pH240R), a capsid protein of ASFV, was found to inhibit type I interferon (IFN) production. Mechanistically, pH240R interacted with the N-terminal transmembrane domain of stimulator of interferon genes (STING) and inhibited its oligomerization and translocation from the endoplasmic reticulum to the Golgi apparatus. Additionally, pH240R inhibited the phosphorylation of interferon regulatory factor 3 (IRF3) and TANK binding kinase 1 (TBK1), leading to reduced production of type I IFN. Consistent with these results, infection with H240R-deficient ASFV (ASFV-ΔH240R) induced more type I IFN than infection with its parental strain, ASFV HLJ/18. We also found that pH240R may enhance viral replication via inhibition of type I IFN production and the antiviral effect of interferon alpha (IFN-α). Taken together, our findings provide a new explanation for the reduction of ASFV's replication ability by knockout of the H240R gene and a clue for the development of live attenuated ASFV vaccines. IMPORTANCE African swine fever (ASF), caused by African swine fever virus (ASFV), is a highly contagious and acute hemorrhagic viral disease with a high mortality, approaching 100% in domestic pigs. However, the relationship between viral pathogenicity and immune evasion of ASFV is not fully understood, which limits the development of safe and effective ASF vaccines, specifically, live attenuated vaccines. In this study, we found that pH240R, as a potent antagonist, inhibited type I IFN production by targeting STING and inhibiting its oligomerization and translocation from the endoplasmic reticulum to the Golgi apparatus. Furthermore, we also found that deletion of the H240R gene reduced viral pathogenicity by enhancing type I IFN production, which decreases ASFV replication. Taken together, our findings provide a clue for the development of an ASFV live attenuated vaccine via deleting the H240R gene.

Structure-based mechanisms of 2'3'-cGAMP intercellular transport in the cGAS-STING immune pathway

Upon activation by double-stranded DNA (dsDNA), the cytosolic dsDNA sensor cyclic GMP-AMP synthase (cGAS) synthesizes the diffusible cyclic dinucleotide 2'3'-cGAMP (cyclic GMP-AMP), which subsequently binds to the adaptor STING, triggering a cascade of events leading to an inflammatory response. Recent studies have highlighted the role of 2'3'-cGAMP as an 'immunotransmitter' between cells, a process facilitated by gap junctions as well as by specialized membrane-spanning importer and exporter channels. This review highlights recent advances from a structural perspective of intercellular trafficking of 2'3'-cGAMP, with particular emphasis on the binding of importer SLC19A1 to 2'3'-cGAMP, as well as the significance of associated folate nutrients and antifolate therapeutics. This provides a path forward for structure-guided understanding of the transport cycle in immunology, as well as for candidate targeting approaches towards therapeutic intervention in inflammation.

Unlocking STING as a Therapeutic Antiviral Strategy

Invading pathogens have developed weapons that subvert physiological conditions to weaken the host and permit the spread of infection. Cells, on their side, have thus developed countermeasures to maintain cellular physiology and counteract pathogenesis. The cyclic GMP-AMP (cGAMP) synthase (cGAS) is a pattern recognition receptor that recognizes viral DNA present in the cytosol, activating the stimulator of interferon genes (STING) protein and leading to the production of type I interferons (IFN-I). Given its role in innate immunity activation, STING is considered an interesting and innovative target for the development of broad-spectrum antivirals. In this review, we discuss the function of STING; its modulation by the cellular stimuli; the molecular mechanisms developed by viruses, through which they escape this defense system; and the therapeutical strategies that have been developed to date to inhibit viral replication restoring STING functionality.

Cytoplasmic DNAs: Sources, sensing, and roles in the development of lung inflammatory diseases and cancer

Cytoplasmic DNA is emerging as a pivotal contributor to the pathogenesis of inflammatory diseases and cancer, such as COVID-19 and lung carcinoma. However, the complexity of various cytoplasmic DNA-related pathways and their crosstalk remains challenging to distinguish their specific roles in many distinct inflammatory diseases, especially for the underlying mechanisms. Here, we reviewed the latest findings on cytoplasmic DNA and its signaling pathways in inflammatory lung conditions and lung cancer progression. We found that sustained activation of cytoplasmic DNA sensing pathways contributes to the development of common lung diseases, which may result from external factors or mutations of key genes in the organism. We further discussed the interplays between cytoplasmic DNA and anti-inflammatory or anti-tumor effects for potential immunotherapy. In sum, this review aids in understanding the roles of cytoplasmic DNAs and exploring more therapeutic strategies.

Interplay between RNA viruses and cGAS/STING axis in innate immunity

While the function of cGAS/STING signalling axis in the innate immune response to DNA viruses is well deciphered, increasing evidence demonstrates its significant contribution in the control of RNA virus infections. After the first evidence of cGAS/STING antagonism by flaviviruses, STING activation has been detected following infection by various enveloped RNA viruses. It has been discovered that numerous viral families have implemented advanced strategies to antagonize STING pathway through their evolutionary path. This review summarizes the characterized cGAS/STING escape strategies to date, together with the proposed mechanisms of STING signalling activation perpetrated by RNA viruses and discusses possible therapeutic approaches. Further studies regarding the interaction between RNA viruses and cGAS/STING-mediated immunity could lead to major discoveries important for the understanding of immunopathogenesis and for the treatment of RNA viral infections.

Targeting STING: From antiviral immunity to treat osteoporosis

The cGAS-STING signaling pathway can trigger innate immune responses by detecting dsDNA from outside or within the host. In addition, the cGAS-STING signaling pathway has emerged as a critical mediator of the inflammatory response and a new target for inflammatory diseases. STING activation leads to dimerization and translocation to the endoplasmic reticulum Golgi intermediate compartment or Golgi apparatus catalyzed by TBK1, triggers the production of IRF3 and NF-κB and translocates to the nucleus to induce a subsequent interferon response and pro-inflammatory factor production. Osteoporosis is a degenerative bone metabolic disease accompanied by chronic sterile inflammation. Activating the STING/IFN-β signaling pathway can reduce bone resorption by inhibiting osteoclast differentiation. Conversely, activation of STING/NF-κB leads to the formation of osteoporosis by increasing bone resorption and decreasing bone formation. In addition, activation of STING inhibits the generation of type H vessels with the capacity to osteogenesis, thereby inhibiting bone formation. Here, we outline the mechanism of action of STING and its downstream in osteoporosis and discuss the role of targeting STING in the treatment of osteoporosis, thus providing new ideas for the treatment of osteoporosis.

Targeting TBK1 attenuates ocular inflammation in uveitis by antagonizing NF-κB signaling

Uveitis with complex pathogenesis is a kind of eye emergency involving refractory and blinding inflammation. Dysregulation of TANK binding kinase 1 (TBK1), which plays an important role in innate immunity, often leads to inflammatory diseases in various organs. However, the role of TBK1 in uveitis remains elusive. In this study, we identified that the mRNA expression level of TBK1 and its phosphorylation level were significantly increased in peripheral blood mononuclear cells (PBMCs) of patients with uveitis. Consistent with this, the expression of Tbk1 was elevated in the ocular tissues of uveitis rats and primary peritoneal macrophages while its phosphorylation levels, which present activation forms, were upregulated as well, accompanied by an increase in the level of nuclear factor-κB (NF-κB) and proinflammatory cytokines. In addition, inhibition of TBK1 may effectively reduce the inflammatory response of uveitis rats by blocking NF-κB entry into the nucleus and impeding the initiation of NLRP3 inflammasome- and caspase-1-mediated pyroptosis pathways.

Modulation of type I interferon signaling by natural products in the treatment of immune-related diseases

Type I interferon (IFN) is considered as a bridge between innate and adaptive immunity. Proper activation or inhibition of type I IFN signaling is essential for host defense against pathogen invasion, tumor cell proliferation, and overactive immune responses. Due to intricate and diverse chemical structures, natural products and their derivatives have become an invaluable source inspiring innovative drug discovery. In addition, some natural products have been applied in clinical practice for infection, cancer, and autoimmunity over thousands of years and their promising curative effects and safety have been well-accepted. However, whether these natural products are primarily targeting type I IFN signaling and specific molecular targets involved are not fully elucidated. In the current review, we thoroughly summarize recent advances in the pharmacology researches of natural products for their type I IFN activity, including both agonism/activation and antagonism/inhibition, and their potential application as therapies. Furthermore, the source and chemical nature of natural products with type I IFN activity are highlighted and their specific molecular targets in the type I IFN pathway and mode of action are classified. In conclusion, natural products possessing type I IFN activity represent promising therapeutic strategies and have a bright prospect in the treatment of infection, cancer, and autoimmune diseases.

Duck Enteritis Virus Protein Kinase US3 Inhibits DNA Sensing Signaling by Phosphorylating Interferon Regulatory Factor 7

The cytosolic DNA sensing pathway mediates innate immune defense against infection by many DNA viruses; however, viruses have evolved multiple strategies to evade the host immune response. Duck enteritis virus (DEV) causes an acute and contagious disease with high mortality in waterfowl. The mechanisms employed by DEV to block the DNA sensing pathway are not well understood. Here, we sought to investigate the role of DEV US3, a serine/threonine protein kinase, in the inhibition of DNA sensing. We found that ectopic expression of DEV US3 significantly inhibited the production of IFN-β and expression of interferon-stimulated genes induced by interferon-stimulatory DNA and poly(dA-dT). US3 also inhibited viral DNA-triggered IFN-β activation and promoted DEV replication in duck embryo fibroblasts, while knockdown of US3 during DEV infection enhances the IFN-β response and suppresses viral replication. US3 inhibited the DNA-sensing signaling pathway by targeting interferon regulatory factor 7 (IRF7), and the kinase activity of US3 was indispensable for its inhibitory function. Furthermore, we found that US3 interacts with the activation domain of IRF7, phosphorylating IRF7, blocking its dimerization and nuclear translocation, and finally leading to the inhibition of IFN-β production. These findings expand our knowledge on DNA sensing in ducks and reveal a novel mechanism whereby DEV evades host antiviral immunity. IMPORTANCE Duck enteritis virus (DEV) is a duck alphaherpesvirus that causes an acute and contagious disease with high mortality, resulting in substantial economic losses in the commercial waterfowl industry. The evasion of DNA-sensing pathway-mediated antiviral innate immunity is essential for the persistent infection and replication for many DNA viruses. However, the strategies used by DEV to block the DNA-sensing pathway are not well understood. In this study, DEV US3 protein kinase was demonstrated to inhibit the DNA-sensing signaling via binding to the activation domain of interferon regulatory factor 7 (IRF7), which induced the hyperphosphorylation of IRF7 and abolished IRF7 dimerization and nuclear translocation. Our findings provide insights into how duck herpesviral kinase counteracts host antiviral innate immunity to ensure viral replication and spread.

Duck Enteritis Virus Inhibits the cGAS-STING DNA-Sensing Pathway To Evade the Innate Immune Response

Cyclic GMP-AMP synthase (cGAS), a key DNA sensor, detects cytosolic viral DNA and activates the adaptor protein stimulator of interferon genes (STING) to initiate interferon (IFN) production and host innate antiviral responses. Duck enteritis virus (DEV) is a duck alphaherpesvirus that causes an acute and contagious disease with high mortality in waterfowl. In the present study, we found that DEV inhibits host innate immune responses during the late phase of viral infection. Furthermore, we screened DEV proteins for their ability to inhibit the cGAS-STING DNA-sensing pathway and identified multiple viral proteins, including UL41, US3, UL28, UL53, and UL24, which block IFN-β activation through this pathway. The DEV tegument protein UL41, which exhibited the strongest inhibitory effect, selectively downregulated the expression of interferon regulatory factor 7 (IRF7) by reducing its mRNA accumulation, thereby inhibiting the DNA-sensing pathway. Ectopic expression of UL41 markedly reduced viral DNA-triggered IFN-β production and promoted viral replication, whereas deficiency of UL41 in the context of DEV infection increased the IFN-β response to DEV and suppressed viral replication. In addition, ectopic expression of IRF7 inhibited the replication of the UL41-deficient virus, whereas IRF7 knockdown facilitated its replication. This study is the first report identifying multiple viral proteins encoded by a duck DNA virus, which inhibit the cGAS-STING DNA-sensing pathway. These findings expand our knowledge of DNA sensing in ducks and reveal a mechanism through which DEV antagonizes the host innate immune response. IMPORTANCE Duck enteritis virus (DEV) is a duck alphaherpesvirus that causes an acute and contagious disease with high mortality, resulting in substantial economic losses in the commercial waterfowl industry. The evasion of DNA-sensing pathway-mediated antiviral innate immunity is essential for the persistent infection and replication of many DNA viruses. However, the mechanisms used by DEV to modulate the DNA-sensing pathway remain poorly understood. In the present study, we found that DEV encodes multiple viral proteins to inhibit the cGAS-STING DNA-sensing pathway. The DEV tegument protein UL41 selectively diminished the accumulation of interferon regulatory factor 7 (IRF7) mRNA, thereby inhibiting the DNA-sensing pathway. Loss of UL41 potently enhanced the IFN-β response to DEV and impaired viral replication in ducks. These findings provide insights into the host-virus interaction during DEV infection and help develop new live attenuated vaccines against DEV.

cGAS deficiency enhances inflammasome activation in macrophages and inflammatory pathology in pristane-induced lupus

Introduction

Type I interferon (IFN) plays a vital role in the pathogenesis of systemic lupus erythematosus. Cyclic GMP AMP synthase (cGAS) is a cytosolic DNA sensor that recognizes dsDNA and creates cGAMP to activate STING-mediated type I IFN production. The activation of STING induces lupus disease in Fcgr2b deficient mice through the differentiation of dendritic cells. In contrast, Cgas-deficient mice could be generated more autoantibody production and proteinuria in pristane-induced lupus (PIL). These data suggested that the other dsDNA sensors could be involved in lupus development mechanisms.

Methods

This study aimed to identify the cGAS-mediated mechanisms contributing to lupus pathogenesis in PIL. The Cgas-deficient and WT mice were induced lupus disease with pristane and subsequently analyzed autoantibody, histopathology, and immunophenotypes. The lung tissues were analyzed with the expression profiles by RT-PCR and western blot. The bone marrow-derived macrophages were stimulated with inflammasome activators and observed pyroptosis.

Results

The Cgas-/- mice developed more severe pulmonary hemorrhage and autoantibody production than WT mice. The activated dendritic cells, IFN-g-, and IL-17a-producing T helper cells, and infiltrated macrophages in the lung were detected in Cgas-/- mice higher than in WT mice. We observed an increase in expression of Aim2, Casp11, and Ifi16 in the lung and serum IL-1a but IL-1b in pristane-injected Cgas-/- mice. The rise of Caspase-11 in the lung of pristane-injected Cgas-/- mice suggested noncanonical inflammasome activation. The activation of AIM2 and NLRP3 inflammasomes in bone marrow-derived macrophages (BMDMs) enhanced the number of dead cells in Cgas-/- mice compared with WT mice. Activation of the inflammasome significantly induced pyroptosis in Cgas-/- BMDMs. The dsDNA level, but not mitochondrial DNA, increased dramatically in pristane-injected Cgas-/- mice suggesting the dsDNA could be a ligand activating inflammasomes. The cGAS agonist-induced BMDM activation in the Cgas-/- mice indicated that the activation of DNA sensors other than cGAS enhanced activated macrophages.

Conclusion

These findings suggested that cGAS hampers the unusual noncanonical inflammasome activation through other DNA sensors.

The Relationship between Reactive Oxygen Species and the cGAS/STING Signaling Pathway in the Inflammaging Process

During Inflammaging, a dysregulation of the immune cell functions is generated, and these cells acquire a senescent phenotype with an increase in pro-inflammatory cytokines and ROS. This increase in pro-inflammatory molecules contributes to the chronic inflammation and oxidative damage of biomolecules, classically observed in the Inflammaging process. One of the most critical oxidative damages is generated to the host DNA. Damaged DNA is located out of the natural compartments, such as the nucleus and mitochondria, and is present in the cell's cytoplasm. This DNA localization activates some DNA sensors, such as the cGAS/STING signaling pathway, that induce transcriptional factors involved in increasing inflammatory molecules. Some of the targets of this signaling pathway are the SASPs. SASPs are secreted pro-inflammatory molecules characteristic of the senescent cells and inducers of ROS production. It has been suggested that oxidative damage to nuclear and mitochondrial DNA generates activation of the cGAS/STING pathway, increasing ROS levels induced by SASPs. These additional ROS increase oxidative DNA damage, causing a loop during the Inflammaging. However, the relationship between the cGAS/STING pathway and the increase in ROS during Inflammaging has not been clarified. This review attempt to describe the potential connection between the cGAS/STING pathway and ROS during the Inflammaging process, based on the current literature, as a contribution to the knowledge of the molecular mechanisms that occur and contribute to the development of the considered adaptative Inflammaging process during aging.

Measles Virus-Induced Host Immunity and Mechanisms of Viral Evasion

The immune system deploys a complex network of cells and signaling pathways to protect host integrity against exogenous threats, including measles virus (MeV). However, throughout its evolutionary path, MeV developed various mechanisms to disrupt and evade immune responses. Despite an available vaccine, MeV remains an important re-emerging pathogen with a continuous increase in prevalence worldwide during the last decade. Considerable knowledge has been accumulated regarding MeV interactions with the innate immune system through two antagonistic aspects: recognition of the virus by cellular sensors and viral ability to inhibit the induction of the interferon cascade. Indeed, while the host could use several innate adaptors to sense MeV infection, the virus is adapted to unsettle defenses by obstructing host cell signaling pathways. Recent works have highlighted a novel aspect of innate immune response directed against MeV unexpectedly involving DNA-related sensing through activation of the cGAS/STING axis, even in the absence of any viral DNA intermediate. In addition, while MeV infection most often causes a mild disease and triggers a lifelong immunity, its tropism for invariant T-cells and memory T and B-cells provokes the elimination of one primary shield and the pre-existing immunity against previously encountered pathogens, known as "immune amnesia".

Manganese enhances DNA- or RNA-mediated innate immune response by inducing phosphorylation of TANK-binding kinase 1

Trace metals are essential for various physiological processes, but their roles in innate immunity have not been fully explored. Here, we found that manganese (Mn) significantly enhanced DNA-mediated IFN-α, IFN-β, and IFN-λ1 production. Microarray analysis demonstrated Mn highly upregulated 351 genes, which were involved in multiple biological functions related to innate immune response. Moreover, we found that Mn2+ alone activates phosphorylation of TANK-binding kinase 1 (TBK1). Inhibiting ataxia telangiectasia mutated (ATM) kinase using ATM inhibitor or siRNA suppressed Mn-enhanced DNA-mediated immune response with decreasing phosphorylation of TBK-1, suggesting that ATM involves in Mn-dependent phosphorylation of TBK1. Given that TBK1 is an essential mediator in DNA- or RNA-mediated signaling pathways, we further demonstrated that Mn2+ suppressed infection of HSV-1 (DNA virus) or Sendai virus (RNA virus) into human macrophages by enhancing antiviral immunity. Our finding highlights a beneficial role of Mn in nucleic-acid-based preventive or therapeutic reagents against infectious diseases.

Singapore Grouper Iridovirus VP131 Drives Degradation of STING-TBK1 Pathway Proteins and Negatively Regulates Antiviral Innate Immunity

Iridoviruses are large DNA viruses which cause great economic losses to the aquaculture industry and serious threats to ecological diversity worldwide. Singapore grouper iridovirus (SGIV), a novel member of the genus Ranavirus, causes high mortality in grouper aquaculture. Previous work on genome annotation demonstrated that SGIV contained numerous uncharacterized or hypothetical open reading frames (ORFs), whose functions remained largely unknown. Here, we reported that the protein encoded by SGIV ORF131R (VP131) was localized predominantly within the endoplasmic reticulum (ER). Ectopic expression of GFP-VP131 significantly enhanced SGIV replication, while VP131 knockdown decreased viral infection in vitro, suggesting that VP131 functioned as a proviral factor during SGIV infection. Overexpression of GFP-VP131 inhibited the interferon (IFN)-1 promoter activity and mRNA level of IFN-related genes induced by poly(I:C), Epinephelus coioides cyclic GMP/AMP synthase (EccGAS)/stimulator of IFN genes (EcSTING), TANK-binding kinase 1 (EcTBK1), or melanoma differentiation-associated gene 5 (EcMDA5), whereas such activation induced by mitochondrial antiviral signaling protein (EcMAVS) was not affected. Moreover, VP131 interacted with EcSTING and degraded EcSTING through both the autophagy-lysosome pathway and ubiquitin-proteasome pathway, and targeted for the K63-linked ubiquitination. Of note, we also found that EcSTING significantly accelerated the formation of GFP-VP131 aggregates in co-transfected cells. Finally, GFP-VP131 inhibited EcSTING- or EcTBK1-induced antiviral activity upon red-spotted grouper nervous necrosis virus (RGNNV) infection. Together, our results demonstrated that the SGIV VP131 negatively regulated the IFN response by inhibiting EcSTING-EcTBK1 signaling for viral evasion. IMPORTANCE STING has been identified as a critical factor participating in the innate immune response which recruits and phosphorylates TBK1 and IFN regulatory factor 3 (IRF3) to induce IFN production and defend against viral infection. However, viruses also distort the STING-TBK1 pathway to negatively regulate the IFN response and facilitate viral replication. Here, we reported that SGIV VP131 interacted with EcSTING within the ER and degraded EcSTING, leading to the suppression of IFN production and the promotion of SGIV infection. These results for the first time demonstrated that fish iridovirus evaded the host antiviral response via abrogating the STING-TBK1 signaling pathway.

Chicken anemia virus VP1 negatively regulates type I interferon via targeting interferon regulatory factor 7 of the DNA-sensing pathway

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway plays a vital role in sensing viral DNA in the cytosol, stimulating type I interferon (IFN) production and triggering the innate immune response against DNA virus infection. However, viruses have evolved effective inhibitors to impede this sensing pathway. Chicken anemia virus (CAV), a nonenveloped ssDNA virus, is a ubiquitous pathogen causing great economic losses to the poultry industry globally. CAV infection is reported to downregulate type I IFN induction. However, whether the cGAS-STING signal axis is used by CAV to regulate type I IFN remains unclear. Our results demonstrate that CAV infection significantly elevates the expression of cGAS and STING at the mRNA level, whereas IFN-β levels are reduced. Furthermore, IFN-β activation was completely blocked by the structural protein VP1 of CAV in interferon stimulatory DNA (ISD) or STING-stimulated cells. VP1 was further confirmed as an inhibitor by interacting with interferon regulatory factor 7 (IRF7) by binding its C-terminal 143-492 aa region. IRF7 dimerization induced by TANK binding kinase 1 (TBK1) could be inhibited by VP1 in a dose-dependent manner. Together, our study demonstrates that CAV VP1 is an effective inhibitor that interacts with IRF7 and antagonizes cGAS-STING pathway-mediated IFN-β activation. These findings reveal a new mechanism of immune evasion by CAV.

Role of alarmins in poststroke inflammation and neuronal repair

Severe loss of cerebral blood flow causes hypoxia and glucose deprivation in the brain tissue, resulting in necrotic cell death in the ischemic brain. Several endogenous molecules, called alarmins or damage-associated molecular patterns (DAMPs), are extracellularly released from the dead cells to activate pattern recognition receptors (PRRs) in immune cells that infiltrate into ischemic brain tissue following the disruption of the blood-brain barrier (BBB) after stroke onset. The activated immune cells produce various inflammatory cytokines and chemokines, triggering sterile cerebral inflammation in the ischemic brain that causes further neuronal cell death. Poststroke inflammation is resolved within several days after stroke onset, and neurological functions are restored to some extent as neural repair occurs around peri-infarct neurons. Clearance of DAMPs from the injured brain is necessary for the resolution of poststroke inflammation. Neurons and glial cells also express PRRs and receive DAMP signaling. Although the role of PRRs in neural cells in the ischemic brain has not yet been clarified, the signaling pathway is likely to be contribute to stroke pathology and neural repair after ischemic stroke. This review describes the molecular dynamics, signaling pathways, and functions of DAMPs in poststroke inflammation and its resolution.

Inhibition of cGAS in Paraventricular Nucleus Attenuates Hypertensive Heart Injury Via Regulating Microglial Autophagy

Neuroinflammation in the cardiovascular center plays a critical role in the progression of hypertensive heart disease. And microglial autophagy is involved in the regulation of neuroinflammation. Cyclic GMP-AMP synthase (cGAS), a cytosolic DNA sensor, senses mitochondrial DNA (mtDNA) and regulates autophagy. The detailed mechanisms of central cGAS affects neuroinflammatory response in hypertensive heart disease via regulating autophagy remain unknown. Angiotensin II (Ang II, 1.5 mg·kg⁻¹·12 h⁻¹, 2 weeks) was intraperitoneally injected to induce hypertension in mice. The cGAS-STING pathway was activated in the paraventricular nucleus (PVN) of Ang II-induced hypertensive mice. The contractile dysfunction of heart was alleviated in Ang II-induced hypertensive cGAS^−/− mice. To observe the central effects of cGAS on regulating hypertensive heart disease, the RU.521 (a cGAS inhibitor) was intracisternally infused in hypertensive mice. Intracisternal infusion of the RU.521-alleviated myocardial interstitial fibrosis, cardiomyocyte hypertrophy, and the contractile dysfunction in Ang II-induced hypertensive mice. Intracisternal infusion of RU.521 attenuated the microglial activation, neuroinflammation, sympathetic/parasympathetic activity ratio, and lowered blood pressure. The autophagic flux in the PVN cells was blocked, while intracisternal infusion of RU.521 alleviated this effect in the Ang II-induced hypertensive mice. In vitro, it was found that cGAS-STING activation-induced autophagic flux blockage, while when the impaired autophagic flux was facilitated by rapamycin, an autophagy inducer, the microglial M1 polarization was decreased correspondingly. In conclusion, cGAS induces the inflammatory phenotype of microglia via impairing autophagic flux, thereby participating in neuroinflammation, which leads to sympathetic overactivation in hypertension and further caused hypertensive myocardial injury.

HSP27 Attenuates cGAS-Mediated IFN-β Signaling through Ubiquitination of cGAS and Promotes PRV Infection

Pseudorabies (PR) is a domestic and wild animal infectious disease caused by the pseudorabies virus (PRV) and is one of the major infectious diseases that endanger the global swine industry. Studies have reported that PRV may achieve cross-species transmission from pigs to humans in recent years. Therefore, in-depth exploration of the relationship between PRV and host proteins is of great significance for elucidating the pathogenic mechanism of PRV and anti-PRV infection. Here, we report that heat shock protein 27 (HSP27) ubiquitinates and degrades cyclic GMP-AMP synthase (cGAS) and attenuates cGAS-mediated antiviral responses, thereby promoting PRV infection. Overexpression of HSP27 promoted PRV proliferation in vitro, while knockdown of HSP27 inhibited PRV infection. Importantly, we found that HSP27 inhibited PRV infection or poly(dA:dT)-activated IFN-β expression. Further studies found that HSP27 may inhibit cGAS-STING-mediated IFN-β expression through targeting cGAS. In addition, we found that HSP27 can suppress the expression of endogenous cGAS in different cells at both gene transcription and protein expression levels, and that HSP27 interacts with and ubiquitinates cGAS. In conclusion, we reveal for the first time that HSP27 is a novel negative regulator of the cGAS-STING signaling pathway induced by PRV infection or poly(dA:dT) activation and demonstrate that HSP27 plays a crucial role in PRV infection.

DDX56 inhibits PRV replication through regulation of IFN-β signaling pathway by targeting cGAS

Pseudorabies virus (PRV) is an agent of Aujeszky's disease, and causes great economic losses to pig farming. Re-outburst of pseudorabies implies that new control measures are urgently needed. We show here that DDX56 possesses the ability to inhibit PRV replication in vitro, which may be an important factor for PRV infection. Overexpression of DDX56 inhibited PRV genomic DNA transcription and lower titers of PRV infection in PK15 cells, whereas down-regulation of the DDX56 expression had a promotion role on virus replication. Further study demonstrated that DDX56 exerted its proliferation-inhibitory effects of PRV through up-regulating cGAS-STING-induced IFN-β expression. Moreover, we found that DDX56 could promote cGAS expression and direct interaction also existed between DDX56 and cGAS. Based on this, DDX56-regulated IFN-β pathway may be targeted at cGAS. To verify this, down-regulated cGAS expression in DDX56 over-expression cells was performed. Results indicated that knockdown of cGAS expression could abrogate the inhibition role of DDX56 on PRV proliferation and weaken the effect of DDX56 on IFN-β expression. In addition, DDX56 played a promotion role in IRF3 phosphorylation and nucleus translocation. Altogether, our results highlight DDX56's antiviral role in PRV infection, and our findings contribute to a better understanding of host factors controlling PRV replication.

E3 ligase RNF5 inhibits type I interferon response in herpes simplex virus keratitis through the STING/IRF3 signaling pathway

Herpes simplex keratitis (HSK), caused by the herpes simplex virus 1 (HSV-1), is a major blinding disease in developed countries. HSV-1 can remain latent in the host for life and cannot be eradicated. The infection causes the secretion of various cytokines and aggregation of inflammatory cells. In the early stage of inflammation, mainly neutrophils infiltrate the cornea, and CD4⁺ T cells mediate the immunopathological changes in herpetic stromal keratitis in the subsequent progression. The STING/IRF3-mediated type I interferon (IFN) response can effectively inhibit viral replication and control infection, but the activity of STING is affected by various ubiquitination modifications. In this study, we found that the expression of RNF5 was elevated in corneal tissues and corneal epithelial cells after infection with HSV-1. Immunofluorescence staining confirmed that RNF5 was mainly expressed in the corneal epithelial layer. We silenced and overexpressed RNF5 expression in corneal epithelial cells and then inoculated them with HSV-1. We found that the expressions of STING, p-IRF3, p-TBK1, and IFN-β mRNA increased after RNF5 silencing. The opposite results were obtained after RNF5 overexpression. We also used siRNA to silence RNF5 in the mouse cornea and then established the HSK model. Compared with the siRNA-control group, the siRNA-RNF5 group showed significantly improved corneal inflammation, reduced clinical scores and tear virus titers, and significantly increased corneal IFN-β expression. In addition, the expressions of the proinflammatory cytokines IL-6 and TNF-α in the corneal tissue were significantly decreased, indicating that RNF5 silencing could effectively promote IFN-I expression, inhibit virus replication, alleviate inflammation, and reduce corneal inflammatory damage. In summary, our results suggest that RNF5 limits the type I IFN antiviral response in HSV corneal epithelitis by inhibiting STING/IRF3 signaling.

In vitro and in vivo correlation of skin and cellular responses to nucleic acid delivery

Skin, the largest organ in the body, provides a passive physical barrier against infection and contains elements of the innate and adaptive immune systems. Skin consists of various cells, including keratinocytes, fibroblasts, endothelial cells and immune cells. This diversity of cell types could be important to gene therapies because DNA transfection could elicit different responses in different cell types. Previously, we observed the upregulation and activation of cytosolic DNA sensing pathways in several non-tumor and tumor cell types as well in tumors after the electroporation (electrotransfer) of plasmid DNA (pDNA). Based on this research and the innate immunogenicity of skin, we correlated the effects of pDNA electrotransfer to fibroblasts and keratinocytes to mouse skin using reverse transcription real-time PCR (RT-qPCR) and several types of protein quantification. After pDNA electrotransfer, the mRNAs of the putative DNA sensors DEAD (AspGlu-Ala-Asp) box polypeptide 60 (Ddx60), absent in melanoma 2 (Aim2), Z-DNA binding protein 1 (Zbp1), interferon activated gene 202 (Ifi202), and interferon-inducible protein 204 (Ifi204) were upregulated in keratinocytes, while Ddx60, Zbp1 and Ifi204 were upregulated in fibroblasts. Increased levels of the mRNAs and proteins of several cytokines and chemokines were detected and varied based on cell type. Mouse skin experiments in vivo confirmed our in vitro results with increased expression of putative DNA sensor mRNAs and of the mRNAs and proteins of several cytokines and chemokines. Finally, with immunofluorescent staining, we demonstrated that skin keratinocytes, fibroblasts and macrophages contribute to the immune response observed after pDNA electrotransfer.

FoxJ1 inhibits African swine fever virus replication and viral S273R protein decreases the expression of FoxJ1 to impair its antiviral effect

African swine fever (ASF) is a highly pathogenic swine infectious disease that affects domestic pigs and wild boar, which is caused by the African swine fever virus (ASFV). ASF has caused huge economic losses to the pig industry and seriously threatens global food security and livestock health. To date, there is no safe and effective commercial vaccine against ASF. Unveiling the underlying mechanisms of ASFV-host interplay is critical for developing effective vaccines and drugs against ASFV. In the present study, RNA-sequencing, RT-qPCR and Western blotting analysis revealed that the transcriptional and protein levels of the host factor FoxJ1 were significantly down-regulated in primary porcine alveolar macrophages (PAMs) infected by ASFV. RT-qPCR analysis showed that overexpression of FoxJ1 upregulated the transcription of type I interferon and interferon stimulating genes (ISGs) induced by poly(dA:dT). FoxJ1 revealed a function to positively regulate innate immune response, therefore, suppressing the replication of ASFV. In addition, Western blotting analysis indicated that FoxJ1 degraded ASFV MGF505-2R and E165R proteins through autophagy pathway. Meanwhile, RT-qPCR and Western blotting analysis showed that ASFV S273R inhibited the expression of FoxJ1. Altogether, we determined that FoxJ1 plays an antiviral role against ASFV replication, and ASFV protein impairs FoxJ1-mediated antiviral effect by degradation of FoxJ1. Our findings provide new insights into the antiviral function of FoxJ1, which might help design antiviral drugs or vaccines against ASFV infection.

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FoxJ1 inhibits ASFV replication by degrading ASFV MGF505-2R and E165R proteins via autophagy.

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FoxJ1 enhances type I IFN response, showing an essential antiviral role.

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ASFV S273R protein inhibits FoxJ1 expression to impair its antiviral effect.

Deficient DNASE1L3 facilitates neutrophil extracellular traps-induced invasion via cyclic GMP-AMP synthase and the non-canonical NF-κB pathway in diabetic hepatocellular carcinoma

Objective

Diabetic hepatocellular carcinoma (HCC) patients have high mortality and metastasis rates. Diabetic conditions promote neutrophil extracellular traps (NETs) generation, which mediates HCC metastasis and invasion. However, whether and how diabetes-induced NETs trigger HCC invasion is largely unknown. Here, we aimed to observe the effects of diabetes-induced NETs on HCC invasion and investigate mechanisms relevant to a DNA sensor cyclic GMP-AMP synthase (cGAS).

Methods

Serum from diabetic patients and healthy individuals was collected. Human neutrophil-derived NETs were isolated for stimulating HCC cell invasion. Data from the SEER and TCGA databases were used for bioinformatics analysis. In HCC cells and allograft models, NETs-triggered invasion was observed.

Results

Diabetic HCC patients had poorer survival than non-diabetic ones. Either diabetic serum or extracted NETs caused HCC invasion. Induction of diabetes or NETosis elicited HCC allograft invasion in nude mice. HCC cell invasion was attenuated by the treatment with DNase1. In TCGA_LIHC, an extracellular DNase DNASE1L3 was downregulated in tumor tissues, while function terms (the endocytic vesicle membrane, the NF-κB pathway and extracellular matrix disassembly) were enriched. DNASE1L3 knockdown in LO2 hepatocytes or H22 cell-derived allografts facilitated HCC invasion in NETotic or diabetic nude mice. Moreover, exposure of HCC cells to NETs upregulated cGAS and the non-canonical NF-κB pathway and induced expression of metastasis genes (MMP9 and SPP1). Both cGAS inhibitor and NF-κB RELB knockdown diminished HCC invasion caused by NETs DNA. Also, cGAS inhibitor was able to retard translocation of NF-κB RELB.

Conclusion

Defective DNASE1L3 aggravates NETs DNA-triggered HCC invasion on diabetic conditions via cGAS and the non-canonical NF-κB pathway.

The role of TBK1 in cancer pathogenesis and anticancer immunity

The TANK-binding kinase 1 (TBK1) is a serine/threonine kinase belonging to the non-canonical inhibitor of nuclear factor-κB (IκB) kinase (IKK) family. TBK1 can be activated by pathogen-associated molecular patterns (PAMPs), inflammatory cytokines, and oncogenic kinases, including activated K-RAS/N-RAS mutants. TBK1 primarily mediates IRF3/7 activation and NF-κB signaling to regulate inflammatory cytokine production and the activation of innate immunity. TBK1 is also involved in the regulation of several other cellular activities, including autophagy, mitochondrial metabolism, and cellular proliferation. Although TBK1 mutations have not been reported in human cancers, aberrant TBK1 activation has been implicated in the oncogenesis of several types of cancer, including leukemia and solid tumors with KRAS-activating mutations. As such, TBK1 has been proposed to be a feasible target for pharmacological treatment of these types of cancer. Studies suggest that TBK1 inhibition suppresses cancer development not only by directly suppressing the proliferation and survival of cancer cells but also by activating antitumor T-cell immunity. Several small molecule inhibitors of TBK1 have been identified and interrogated. However, to this point, only momelotinib (MMB)/CYT387 has been evaluated as a cancer therapy in clinical trials, while amlexanox (AMX) has been evaluated clinically for treatment of type II diabetes, nonalcoholic fatty liver disease, and obesity. In this review, we summarize advances in research into TBK1 signaling pathways and regulation, as well as recent studies on TBK1 in cancer pathogenesis. We also discuss the potential molecular mechanisms of targeting TBK1 for cancer treatment. We hope that our effort can help to stimulate the development of novel strategies for targeting TBK1 signaling in future approaches to cancer therapy.

A Tug of War: Pseudorabies Virus and Host Antiviral Innate Immunity

The non-specific innate immunity can initiate host antiviral innate immune responses within minutes to hours after the invasion of pathogenic microorganisms. Therefore, the natural immune response is the first line of defense for the host to resist the invaders, including viruses, bacteria, fungi. Host pattern recognition receptors (PRRs) in the infected cells or bystander cells recognize pathogen-associated molecular patterns (PAMPs) of invading pathogens and initiate a series of signal cascades, resulting in the expression of type I interferons (IFN-I) and inflammatory cytokines to antagonize the infection of microorganisms. In contrast, the invading pathogens take a variety of mechanisms to inhibit the induction of IFN-I production from avoiding being cleared. Pseudorabies virus (PRV) belongs to the family Herpesviridae, subfamily Alphaherpesvirinae, genus Varicellovirus. PRV is the causative agent of Aujeszky’s disease (AD, pseudorabies). Although the natural host of PRV is swine, it can infect a wide variety of mammals, such as cattle, sheep, cats, and dogs. The disease is usually fatal to these hosts. PRV mainly infects the peripheral nervous system (PNS) in swine. For other species, PRV mainly invades the PNS first and then progresses to the central nervous system (CNS), which leads to acute death of the host with serious clinical and neurological symptoms. In recent years, new PRV variant strains have appeared in some areas, and sporadic cases of PRV infection in humans have also been reported, suggesting that PRV is still an important emerging and re-emerging infectious disease. This review summarizes the strategies of PRV evading host innate immunity and new targets for inhibition of PRV replication, which will provide more information for the development of effective inactivated vaccines and drugs for PRV.

Targeting innate immune system by nanoparticles for cancer immunotherapy

Various cancer therapies have advanced remarkably over the past decade. Unlike the direct therapeutic targeting of tumor cells, cancer immunotherapy is a new strategy that boosts the host's immune system...

Pseudorabies Virus US3 Protein Inhibits IFN-β Production by Interacting With IRF3 to Block Its Activation

Pseudorabies virus is a typical swine alphaherpesvirus, which can cause obvious neurological disorders and reproductive failure in pigs. It is capable of evading host antiviral immune response. However, the mechanism by which many PRV proteins assist the virus to evade innate immunity is not fully understood. This study identified PRV US3 protein as a crucial antagonistic viral factor that represses interferon beta (IFN-β) expression. A in-depth study showed that US3 protein restricted type I IFN production by targeting interferon regulatory factor 3 (IRF3), a key molecule required for type I IFN induction. Additionally, US3 protein interacted with IRF3, degraded its protein expression to block the phosphorylation of IRF3. These findings suggested a novel strategy utilized by PRV to inhibit IFN-β production and escape the host innate immunity.