The cGAS-STING pathway drives type I IFN immunopathology in COVID-19

Effect of VBIT-4 on the functional activity of isolated mitochondria and cell viability

VBIT-4 is a new inhibitor of the oligomerization of VDAC proteins of the outer mitochondrial membrane preventing the development of oxidative stress, mitochondrial dysfunction, and cell death in various pathologies. However, as a VDAC inhibitor, VBIT-4 may itself cause mitochondrial dysfunction in healthy cells. The article examines the effect of VBIT-4 on the functional activity of rat liver mitochondria and cell cultures. We have demonstrated that high concentrations of VBIT-4 (15-30 μM) suppressed mitochondrial respiration in state 3 and 3UDNP driven by substrates of complex I and II. VBIT-4 induced depolarization of organelles fueled by substrates of complex I but not complex II of the respiratory chain. VBIT-4 has been found to inhibit the activity of complexes I, III, and IV of the respiratory chain. Molecular docking demonstrated that VBIT-4 interacts with the rotenone-binding site in complex I with similar affinity. 15-30 μM VBIT-4 caused an increase in H2O2 production in mitochondria, decreased the Ca2+ retention capacity, but increased the time of Ca2+-dependent mitochondrial swelling. We have found that the incubation of breast adenocarcinoma (MCF-7) with 30 μM VBIT-4 for 48 h led to the decrease of the mitochondrial membrane potential, an increase in ROS production and death of MCF-7 cells. The mechanism of action of VBIT-4 on mitochondria and cells is discussed.

Potential convergence of olfactory dysfunction in Parkinson's disease and COVID-19: The role of neuroinflammation

Parkinson's disease (PD) is a prevalent neurodegenerative disorder that affects 7-10 million individuals worldwide. A common early symptom of PD is olfactory dysfunction (OD), and more than 90% of PD patients suffer from OD. Recent studies have highlighted a high incidence of OD in patients with SARS-CoV-2 infection. This review investigates the potential convergence of OD in PD and COVID-19, particularly focusing on the mechanisms by which neuroinflammation contributes to OD and neurological events. Starting from our fundamental understanding of the olfactory bulb, we summarize the clinical features of OD and pathological features of the olfactory bulb from clinical cases and autopsy reports in PD patients. We then examine SARS-CoV-2-induced olfactory bulb neuropathology and OD and emphasize the SARS-CoV-2-induced neuroinflammatory cascades potentially leading to PD manifestations. By activating microglia and astrocytes, as well as facilitating the aggregation of α-synuclein, SARS-CoV-2 could contribute to the onset or exacerbation of PD. We also discuss the possible contributions of NF-κB, the NLRP3 inflammasome, and the JAK/STAT, p38 MAPK, TLR4, IL-6/JAK2/STAT3 and cGAS-STING signaling pathways. Although olfactory dysfunction in patients with COVID-19 may be reversible, it is challenging to restore OD in patients with PD. With the emergence of new SARS-CoV-2 variants and the recurrence of infections, we call for continued attention to the intersection between PD and SARS-CoV-2 infection, especially from the perspective of OD.

Fangchinoline induces antiviral response by suppressing STING degradation

The stimulator of interferon genes (STING), an integral adaptor protein in the DNA-sensing pathway, plays a pivotal role in the innate immune response against infections. Additionally, it presents a valuable therapeutic target for infectious diseases and cancer. We observed that fangchinoline (Fan), a bis-benzylisoquinoline alkaloid (BBA), effectively impedes the replication of vesicular stomatitis virus (VSV), encephalomyocarditis virus (EMCV), influenza A virus (H1N1), and herpes simplex virus-1 (HSV-1) in vitro. Fan treatment significantly reduced the viral load, attenuated tissue inflammation, and improved survival in a viral sepsis mouse model. Mechanistically, Fan activates the antiviral response in a STING-dependent manner, leading to increased expression of interferon (IFN) and interferon-stimulated genes (ISGs) for potent antiviral effects in vivo and in vitro. Notably, Fan interacts with STING, preventing its degradation and thereby extending the activation of IFN-based antiviral responses. Collectively, our findings highlight the potential of Fan, which elicits antiviral immunity by suppressing STING degradation, as a promising candidate for antiviral therapy.

The dual function of cGAS-STING signaling axis in liver diseases

Numerous liver diseases, such as nonalcoholic fatty liver disease, hepatitis, hepatocellular carcinoma, and hepatic ischemia-reperfusion injury, have been increasingly prevalent, posing significant threats to global health. In recent decades, there has been increasing evidence linking the dysregulation of cyclic-GMP-AMP synthase (cGAS)-stimulator of interferon gene (STING)-related immune signaling to liver disorders. Both hyperactivation and deletion of STING can disrupt the immune microenvironment dysfunction, exacerbating liver disorders. Consequently, there has been a surge in research investigating medical agents or mediators targeting cGAS-STING signaling. Interestingly, therapeutic manipulation of the cGAS-STING pathway has yielded inconsistent and even contradictory effects on different liver diseases due to the distinct physiological characteristics of intrahepatic cells that express and respond to STING. In this review, we comprehensively summarize recent advancements in understanding the dual roles of the STING pathway, highlighting that the benefits of targeting STING signaling depend on the specific types of target cells and stages of liver injury. Additionally, we offer a novel perspective on the suitability of STING agonists and antagonists for clinical assessment. In conclusion, STING signaling remains a highly promising therapeutic target, and the development of STING pathway modulators holds great potential for the treatment of liver diseases.

Innate Immunity in Protection and Pathogenesis During Coronavirus Infections and COVID-19

The COVID-19 pandemic was caused by the recently emerged β-coronavirus SARS-CoV-2. SARS-CoV-2 has had a catastrophic impact, resulting in nearly 7 million fatalities worldwide to date. The innate immune system is the first line of defense against infections, including the detection and response to SARS-CoV-2. Here, we discuss the innate immune mechanisms that sense coronaviruses, with a focus on SARS-CoV-2 infection and how these protective responses can become detrimental in severe cases of COVID-19, contributing to cytokine storm, inflammation, long-COVID, and other complications. We also highlight the complex cross talk among cytokines and the cellular components of the innate immune system, which can aid in viral clearance but also contribute to inflammatory cell death, cytokine storm, and organ damage in severe COVID-19 pathogenesis. Furthermore, we discuss how SARS-CoV-2 evades key protective innate immune mechanisms to enhance its virulence and pathogenicity, as well as how innate immunity can be therapeutically targeted as part of the vaccination and treatment strategy. Overall, we highlight how a comprehensive understanding of innate immune mechanisms has been crucial in the fight against SARS-CoV-2 infections and the development of novel host-directed immunotherapeutic strategies for various diseases.

Update on Omicron variant and its threat to vulnerable populations

Objective

To reduce the incidence of severe illness and fatalities, and promote the awareness of protection and precaution, increased vaccination, strengthen the physical fitness, frequent ventilation, and health education should be enhanced among vulnerable populations as essential measures for the future control of COVID-19.

Study design

Systematic review.

Method

The search was done using PubMed, EMBASE and Web of Science for studies without language restrictions, published up through March 2023, since their authoritative and comprehensive literature search database. Eighty articles were included. Extraction of articles and quality assessment of included reviews was performed independently by two authors using the AMSTAR 2 score.

Results

The articles in the final data set included research on epidemiological characteristics, pathogenicity, available vaccines, treatments and epidemiological features in special populations including the elders, pregnant women, kids, people with chronic diseases concerning Omicron.

Conclusion

Although less pathogenic potential is found in Omicron, highly mutated forms have enhanced the ability of immune evasion and resistance to existing vaccines compared with former variants. Severe complications and outcomes may occur in vulnerable populations. Infected pregnant women are more likely to give birth prematurely, and fatal implications in children infected with Omicron are hyperimmune response and severe neurological disorders. In immunocompromised patients, there is a greater reported mortality and complication compared to patients with normal immune systems. Therefore, maintain social distancing, wear masks, and receive vaccinations are effective long-term measures.

ISGylation by HERCs facilitates STING activation

Optimal activation of stimulator of interferon genes (STING) protein is crucial for host defenses against pathogens and avoiding detrimental effects. Various post-translational modifications control STING activity. However, the function of interferon (IFN)-stimulated gene (ISG) 15 modification (ISGylation) in controlling STING stability and activation is unclear. Here, we show that the E3 ISGylation ligases HECT domain- and RCC1-like domain-containing proteins (HERCs; HERC5 in humans and HERC6 in mice) facilitate STING activation by mediating ISGylation of STING at K150, preventing its K48-linked ubiquitination and degradation. Concordantly, Herc6 deficiency suppresses herpes simplex virus 1 infection-induced type I IFN responses and facilitates viral replication both in vitro and in vivo. Notably, severe acute respiratory syndrome coronavirus 2 protein papain-like protease cleaves HERC5-mediated ISGylation of STING, suppressing host antiviral responses. These data identify a mechanism by which HERCs-mediated ISGylation controls STING stability and activation and uncover the correlations and interactions of ISGylation and ubiquitination during STING activation.

Multifaceted mitochondria in innate immunity

The ability of mitochondria to transform the energy we obtain from food into cell phosphorylation potential has long been appreciated. However, recent decades have seen an evolution in our understanding of mitochondria, highlighting their significance as key signal-transducing organelles with essential roles in immunity that extend beyond their bioenergetic function. Importantly, mitochondria retain bacterial motifs as a remnant of their endosymbiotic origin that are recognised by innate immune cells to trigger inflammation and participate in anti-microbial defence. This review aims to explore how mitochondrial physiology, spanning from oxidative phosphorylation (OxPhos) to signalling of mitochondrial nucleic acids, metabolites, and lipids, influences the effector functions of phagocytes. These myriad effector functions include macrophage polarisation, efferocytosis, anti-bactericidal activity, antigen presentation, immune signalling, and cytokine regulation. Strict regulation of these processes is critical for organismal homeostasis that when disrupted may cause injury or contribute to disease. Thus, the expanding body of literature, which continues to highlight the central role of mitochondria in the innate immune system, may provide insights for the development of the next generation of therapies for inflammatory diseases.

Extracellular vesicles alter trophoblast function in pregnancies complicated by COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and resulting coronavirus disease (COVID-19) causes placental dysfunction, which increases the risk of adverse pregnancy outcomes. While abnormal placental pathology resulting from COVID-19 is common, direct infection of the placenta is rare. This suggests that pathophysiology associated with maternal COVID-19, rather than direct placental infection, is responsible for placental dysfunction and alteration of the placental transcriptome. We hypothesized that maternal circulating extracellular vesicles (EVs), altered by COVID-19 during pregnancy, contribute to placental dysfunction. To examine this hypothesis, we characterized maternal circulating EVs from pregnancies complicated by COVID-19 and tested their effects on trophoblast cell physiology in vitro . We found that the gestational timing of COVID-19 is a major determinant of circulating EV function and cargo. In vitro trophoblast exposure to EVs isolated from patients with an active infection at the time of delivery, but not EVs isolated from Controls, altered key trophoblast functions including hormone production and invasion. Thus, circulating EVs from participants with an active infection, both symptomatic and asymptomatic cases, can disrupt vital trophoblast functions. EV cargo differed between participants with COVID-19 and Controls, which may contribute to the disruption of the placental transcriptome and morphology. Our findings show that COVID-19 can have effects throughout pregnancy on circulating EVs and circulating EVs are likely to participate in placental dysfunction induced by COVID-19.

Mitochondrial DNA release and sensing in innate immune responses

Mitochondria are pleiotropic organelles central to an array of cellular pathways including metabolism, signal transduction, and programmed cell death. Mitochondria are also key drivers of mammalian immune responses, functioning as scaffolds for innate immune signaling, governing metabolic switches required for immune cell activation, and releasing agonists that promote inflammation. Mitochondrial DNA (mtDNA) is a potent immunostimulatory agonist, triggering pro-inflammatory and type I interferon responses in a host of mammalian cell types. Here we review recent advances in how mtDNA is detected by nucleic acid sensors of the innate immune system upon release into the cytoplasm and extracellular space. We also discuss how the interplay between mtDNA release and sensing impacts cellular innate immune endpoints relevant to health and disease.

In vitro immunity: an overview of immunocompetent organ-on-chip models

Impressive advances have been made to replicate human physiology in vitro over the last few years due to the growth of the organ-on-chip (OoC) field in both industrial and academic settings. OoCs are a type of microphysiological system (MPS) that imitates functional and dynamic aspects of native human organ biology on a microfluidic device. Organoids and organotypic models, ranging in their complexity from simple single-cell to complex multi-cell type constructs, are being incorporated into OoC microfluidic devices to better mimic human physiology. OoC technology has now progressed to the stage at which it has received official recognition by the Food and Drug Administration (FDA) for use as an alternative to standard procedures in drug development, such as animal studies and traditional in vitro assays. However, an area that is still lagging behind is the incorporation of the immune system, which is a critical element required to investigate human health and disease. In this review, we summarise the progress made to integrate human immunology into various OoC systems, specifically focusing on models related to organ barriers and lymphoid organs. These models utilise microfluidic devices that are either commercially available or custom-made. This review explores the difference between the use of innate and adaptive immune cells and their role for modelling organ-specific diseases in OoCs. Immunocompetent multi-OoC models are also highlighted and the extent to which they recapitulate systemic physiology is discussed. Together, the aim of this review is to describe the current state of immune-OoCs, the limitations and the future perspectives needed to improve the field.

Sustained IFN signaling is associated with delayed development of SARS-CoV-2-specific immunity

Plasma RNAemia, delayed antibody responses and inflammation predict COVID-19 outcomes, but the mechanisms underlying these immunovirological patterns are poorly understood. We profile 782 longitudinal plasma samples from 318 hospitalized patients with COVID-19. Integrated analysis using k-means reveals four patient clusters in a discovery cohort: mechanically ventilated critically-ill cases are subdivided into good prognosis and high-fatality clusters (reproduced in a validation cohort), while non-critical survivors segregate into high and low early antibody responders. Only the high-fatality cluster is enriched for transcriptomic signatures associated with COVID-19 severity, and each cluster has distinct RBD-specific antibody elicitation kinetics. Both critical and non-critical clusters with delayed antibody responses exhibit sustained IFN signatures, which negatively correlate with contemporaneous RBD-specific IgG levels and absolute SARS-CoV-2-specific B and CD4+ T cell frequencies. These data suggest that the "Interferon paradox" previously described in murine LCMV models is operative in COVID-19, with excessive IFN signaling delaying development of adaptive virus-specific immunity.

Multiple Unfolded Protein Response pathways cooperate to link cytosolic dsDNA release to Stimulator of Interferon Gene (STING) activation

The double-stranded DNA (dsDNA) sensor STING has been increasingly implicated in responses to "sterile" endogenous threats and pathogens without nominal DNA or cyclic di-nucleotide stimuli. Previous work showed an endoplasmic reticulum (ER) stress response, known as the unfolded protein response (UPR), activates STING. Herein, we sought to determine if ER stress generated a STING ligand, and to identify the UPR pathways involved. Induction of IFN-β expression following stimulation with the UPR inducer thapsigargin (TPG) or oxygen glucose deprivation required both STING and the dsDNA-sensing cyclic GMP-AMP synthase (cGAS). Furthermore, TPG increased cytosolic mitochondrial DNA, and immunofluorescence visualized dsDNA punctae in murine and human cells, providing a cGAS stimulus. N-acetylcysteine decreased IFN-β induction by TPG, implicating reactive oxygen species (ROS). However, mitoTEMPO, a mitochondrial oxidative stress inhibitor did not impact TPG-induced IFN. On the other hand, inhibiting the inositol requiring enzyme 1 (IRE1) ER stress sensor and its target transcription factor XBP1 decreased the generation of cytosolic dsDNA. iNOS upregulation was XBP1-dependent, and an iNOS inhibitor decreased cytosolic dsDNA and IFN-β, implicating ROS downstream of the IRE1-XBP1 pathway. Inhibition of the PKR-like ER kinase (PERK) pathway also attenuated cytoplasmic dsDNA release. The PERK-regulated apoptotic factor Bim was required for both dsDNA release and IFN-β mRNA induction. Finally, XBP1 and PERK pathways contributed to cytosolic dsDNA release and IFN-induction by the RNA virus, Vesicular Stomatitis Virus (VSV). Together, our findings suggest that ER stressors, including viral pathogens without nominal STING or cGAS ligands such as RNA viruses, trigger multiple canonical UPR pathways that cooperate to activate STING and downstream IFN-β via mitochondrial dsDNA release.

Harnessing the power of IFN for therapeutic approaches to COVID-19

Interferons (IFNs) are essential for defense against viral infections but also drive recruitment of inflammatory cells to sites of infection, a key feature of severe COVID-19. Here, we explore the complexity of the IFN response in COVID-19, examine the effects of manipulating IFN on SARS-CoV-2 viral replication and pathogenesis, and highlight pre-clinical and clinical studies evaluating the therapeutic efficacy of IFN in limiting COVID-19 severity.

SARS-CoV-2-Induced Type I Interferon Signaling Dysregulation in Olfactory Networks Implications for Alzheimer's Disease

Type I interferon signaling (IFN-I) perturbations are major drivers of COVID-19. Dysregulated IFN-I in the brain, however, has been linked to both reduced cognitive resilience and neurodegenerative diseases such as Alzheimer's. Previous works from our group have proposed a model where peripheral induction of IFN-I may be relayed to the CNS, even in the absence of fulminant infection. The aim of our study was to identify significantly enriched IFN-I signatures and genes along the transolfactory route, utilizing published datasets of the nasal mucosa and olfactory bulb amygdala transcriptomes of COVID-19 patients. We furthermore sought to identify these IFN-I signature gene networks associated with Alzheimer's disease pathology and risk. Gene expression data involving the nasal epithelium, olfactory bulb, and amygdala of COVID-19 patients and transcriptomic data from Alzheimer's disease patients were scrutinized for enriched Type I interferon pathways. Gene set enrichment analyses and gene-Venn approaches were used to determine genes in IFN-I enriched signatures. The Agora web resource was used to identify genes in IFN-I signatures associated with Alzheimer's disease risk based on its aggregated multi-omic data. For all analyses, false discovery rates (FDR) <0.05 were considered statistically significant. Pathways associated with type I interferon signaling were found in all samples tested. Each type I interferon signature was enriched by IFITM and OAS family genes. A 14-gene signature was associated with COVID-19 CNS and the response to Alzheimer's disease pathology, whereas nine genes were associated with increased risk for Alzheimer's disease based on Agora. Our study provides further support to a type I interferon signaling dysregulation along the extended olfactory network as reconstructed herein, ranging from the nasal epithelium and extending to the amygdala. We furthermore identify the 14 genes implicated in this dysregulated pathway with Alzheimer's disease pathology, among which HLA-C, HLA-B, HLA-A, PSMB8, IFITM3, HLA-E, IFITM1, OAS2, and MX1 as genes with associated conferring increased risk for the latter. Further research into its druggability by IFNb therapeutics may be warranted.

Interleukin-1β promotes human metapneumovirus replication via activating the cGAS-STING pathway

BACKGROUND

Human metapneumovirus(hMPV) is one of the most common viruses that cause acute lower respiratory tract infections. Interleukin-1β (IL-1β) has been reported to play an important role in multiple virus replication. Patients with hMPV infection have increased levels of IL-1β which reminds IL-1β is associated with hMPV infection. However, the mechanism by which IL-1β affects hMPV replication remains unclear. In this study, we explore the effect of IL-1β on hMPV replication and investigate its specific mechanism of action.

METHODS

We established an hMPV infection model through Human bronchial epithelial cells (16HBE). qRT-PCR and Western Blot were used to detect the expression levels of IL-1β, cyclic GMP-AMP synthase (cGAS), and interferon stimulating factor (STING). Regulating IL-1β expression by small interfering RNA (siRNA) or exogenous supplementary to study the influence of hMPV replication. The selective cGAS inhibitor RU.521, G150, and STING inhibitor H-151 were utilized to detect hMPV replication in 16HBE cells.

RESULTS

The level of IL-1β protein increased in a time-dependent and dose-dependent manner after hMPV infection. The mRNA and protein levels of cGAS and STING were significantly up-regulated. Knockdown of IL-1β could contribute to the decreased viral loads of hMPV. While the exogenous supplement of recombinant human IL-1β in cells, replication of hMPV was significantly increased. Additionally, the level of cGAS-STING protein expression would be affected by regulating IL-1β expression. Inhibitors of the cGAS-STING pathway led to a lower level of hMPV replication.

CONCLUSION

This study found that IL-1β could promote hMPV replication through the cGAS-STING pathway, which has the potential to serve as a candidate to fight against hMPV infection, targeting IL-1β may be an effective new strategy to restrain virus replication.

The regulation of cGAS-STING signaling by RNA virus-derived components

The Cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) serves as a key innate immune signaling axis involved in the regulation of various human diseases. It has been found that cGAS-STING pathway can recognize a variety of cytosolic double-stranded DNA (dsDNA), contributing to cause a robust type I interferon response thereby affecting the occurrence and progression of viral infection. Accumulating evidence indicates RNA virus-derived components play an important role in regulating cGAS-STING signaling, either as protective or pathogenic factors in the pathogenesis of diseases. Thus, a comprehensive understanding of the function of RNA virus-derived components in regulating cGAS-STING signaling will provide insights into developing novel therapies. Here, we review the existing literature on cGAS-STING pathway regulated by RNA virus-derived components to propose insights into pharmacologic strategies targeting the cGAS-STING pathway.

Identification of Age-Related Characteristic Genes Involved in Severe COVID-19 Infection Among Elderly Patients Using Machine Learning and Immune Cell Infiltration Analysis

Elderly patients infected with severe acute respiratory syndrome coronavirus 2 are at higher risk of severe clinical manifestation, extended hospitalization, and increased mortality. Those patients are more likely to experience persistent symptoms and exacerbate the condition of basic diseases with long COVID-19 syndrome. However, the molecular mechanisms underlying severe COVID-19 in the elderly patients remain unclear. Our study aims to investigate the function of the interaction between disease-characteristic genes and immune cell infiltration in patients with severe COVID-19 infection. COVID-19 datasets (GSE164805 and GSE180594) and aging dataset (GSE69832) were obtained from the Gene Expression Omnibus database. The combined different expression genes (DEGs) were subjected to Gene Ontology (GO) functional enrichment analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and Diseases Ontology functional enrichment analysis, Gene Set Enrichment Analysis, machine learning, and immune cell infiltration analysis. GO and KEGG enrichment analyses revealed that the eight DEGs (IL23A, PTGER4, PLCB1, IL1B, CXCR1, C1QB, MX2, ALOX12) were mainly involved in inflammatory mediator regulation of TRP channels, coronavirus disease-COVID-19, and cytokine activity signaling pathways. Three-degree algorithm (LASSO, SVM-RFE, KNN) and correlation analysis showed that the five DEGs up-regulated the immune cells of macrophages M0/M1, memory B cells, gamma delta T cell, dendritic cell resting, and master cell resisting. Our study identified five hallmark genes that can serve as disease-characteristic genes and target immune cells infiltrated in severe COVID-19 patients among the elderly population, which may contribute to the study of pathogenesis and the evaluation of diagnosis and prognosis in aging patients infected with severe COVID-19.

Endothelial cell expression of a STING gain-of-function mutation initiates pulmonary lymphocytic infiltration

Patients afflicted with Stimulator of interferon gene (STING) gain-of-function mutations frequently present with debilitating interstitial lung disease (ILD) that is recapitulated in mice expressing the STINGV154M mutation (VM). Prior radiation chimera studies revealed an unexpected and critical role for non-hematopoietic cells in initiating ILD. To identify STING-expressing non-hematopoietic cell types required for the development of ILD, we use a conditional knockin (CKI) model and direct expression of the VM allele to hematopoietic cells, fibroblasts, epithelial cells, or endothelial cells. Only endothelial cell-targeted VM expression results in enhanced recruitment of immune cells to the lung associated with elevated chemokine expression and the formation of bronchus-associated lymphoid tissue, as seen in the parental VM strain. These findings reveal the importance of endothelial cells as instigators of STING-driven lung disease and suggest that therapeutic targeting of STING inhibitors to endothelial cells could potentially mitigate inflammation in the lungs of STING-associated vasculopathy with onset in infancy (SAVI) patients or patients afflicted with other ILD-related disorders.

RNA m5C methylation modification: a potential therapeutic target for SARS-CoV-2-associated myocarditis

The Corona Virus Disease (COVID-19), caused by the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), has quickly spread worldwide and resulted in significant morbidity and mortality. Although most infections are mild, some patients can also develop severe and fatal myocarditis. In eukaryotic RNAs, 5-methylcytosine (m5C) is a common kind of post-transcriptional modification, which is involved in regulating various biological processes (such as RNA export, translation, and stability maintenance). With the rapid development of m5C modification detection technology, studies related to viral m5C modification are ever-increasing. These studies have revealed that m5C modification plays an important role in various stages of viral replication, including transcription and translation. According to recent studies, m5C methylation modification can regulate SARS-CoV-2 infection by modulating innate immune signaling pathways. However, the specific role of m5C modification in SARS-CoV-2-induced myocarditis remains unclear. Therefore, this review aims to provide insights into the molecular mechanisms of m5C methylation in SARS-CoV-2 infection. Moreover, the regulatory role of NSUN2 in viral infection and host innate immune response was also highlighted. This review may provide new directions for developing therapeutic strategies for SARS-CoV-2-associated myocarditis.

New frontiers in the cGAS-STING intracellular DNA-sensing pathway

The cGAS-STING intracellular DNA-sensing pathway has emerged as a key element of innate antiviral immunity and a promising therapeutic target. The existence of an innate immune sensor that can be activated by any double-stranded DNA (dsDNA) of any origin raises fundamental questions about how cGAS is regulated and how it responds to "foreign" DNA while maintaining tolerance to ubiquitous self-DNA. In this review, we summarize recent evidence implicating important roles for cGAS in the detection of foreign and self-DNA. We describe two recent and surprising insights into cGAS-STING biology: that cGAS is tightly tethered to the nucleosome and that the cGAMP product of cGAS is an immunotransmitter acting at a distance to control innate immunity. We consider how these advances influence our understanding of the emerging roles of cGAS in the DNA damage response (DDR), senescence, aging, and cancer biology. Finally, we describe emerging approaches to harness cGAS-STING biology for therapeutic benefit.

Chloride Homeostasis Regulates cGAS-STING Signaling

The cGAS-STING signaling pathway has emerged as a key mediator of inflammation. However, the roles of chloride homeostasis on this pathway are unclear. Here, we uncovered a correlation between chloride homeostasis and cGAS-STING signaling. We found that dysregulation of chloride homeostasis attenuates cGAS-STING signaling in a lysosome-independent manner. Treating immune cells with chloride channel inhibitors attenuated 2'3'-cGAMP production by cGAS and also suppressed STING polymerization, leading to reduced cytokine production. We also demonstrate that non-selective chloride channel blockers can suppress the NPC1 deficiency-induced, hyper-activated STING signaling in skin fibroblasts derived from Niemann Pick disease type C (NPC) patients. Our findings reveal that chloride homeostasis majorly affects cGAS-STING pathway and suggest a provocative strategy to dampen STING-mediated inflammation via targeting chloride channels.

Regulation of type I and type III interferon induction in response to pathogen sensing

Type I and III interferons (IFN-I and IFN-III) have a central role in the early antimicrobial response against invading pathogens. Induction of IFN-Is and IFN-IIIs arises due to the sensing by pattern recognition receptors of pathogen-associated molecular patterns (from micro-organisms) or of damage-associated molecular patterns (DAMPs; produced by host cells). Here, we review recent developments on how IFN-I and IFN-III expression is stimulated by different pathogens and how the signalling pathways leading to IFN induction are tightly regulated. We also summarise the growing knowledge of the sensing pathways that lead to IFN-I and IFN-III induction in response to severe acute respiratory syndrome coronavirus 2.

Organ-on-chip models for infectious disease research

Research on microbial pathogens has traditionally relied on animal and cell culture models to mimic infection processes in the host. Over recent years, developments in microfluidics and bioengineering have led to organ-on-chip (OoC) technologies. These microfluidic systems create conditions that are more physiologically relevant and can be considered humanized in vitro models. Here we review various OoC models and how they have been applied for infectious disease research. We outline the properties that make them valuable tools in microbiology, such as dynamic microenvironments, vascularization, near-physiological tissue constitutions and partial integration of functional immune cells, as well as their limitations. Finally, we discuss the prospects for OoCs and their potential role in future infectious disease research.

Palmitoylation of KSHV pORF55 is required for Golgi localization and efficient progeny virion production

Kaposi's sarcoma-associated herpesvirus (KSHV) is a double-stranded DNA virus etiologically associated with multiple malignancies. Both latency and sporadic lytic reactivation contribute to KSHV-associated malignancies, however, the specific roles of many KSHV lytic gene products in KSHV replication remain elusive. In this study, we report that ablation of ORF55, a late gene encoding a tegument protein, does not impact KSHV lytic reactivation but significantly reduces the production of progeny virions. We found that cysteine 10 and 11 (C10 and C11) of pORF55 are palmitoylated, and the palmytoilation is essential for its Golgi localization and secondary envelope formation. Palmitoylation-defective pORF55 mutants are unstable and undergo proteasomal degradation. Notably, introduction of a putative Golgi localization sequence to these palmitoylation-defective pORF55 mutants restores Golgi localization and fully reinstates KSHV progeny virion production. Together, our study provides new insight into the critical role of pORF55 palmitoylation in KSHV progeny virion production and offers potential therapeutic targets for the treatment of related malignancies.

Cytosolic DNA sensors in neurodegenerative diseases: from physiological defenders to pathological culprits

Cytosolic DNA sensors are a group of pattern recognition receptors (PRRs) that vary in structures, molecular mechanisms, and origins but share a common function to detect intracellular microbial DNA and trigger the innate immune response like type 1 interferon production and autophagy. Cytosolic DNA sensors have been proven as indispensable defenders against the invasion of many pathogens; however, growing evidence shows that self-DNA misplacement to cytoplasm also frequently occurs in non-infectious circumstances. Accumulation of cytosolic DNA causes improper activation of cytosolic DNA sensors and triggers an abnormal autoimmune response, that significantly promotes pathological progression. Neurodegenerative diseases are a group of neurological disorders characterized by neuron loss and still lack effective treatments due to a limited understanding of pathogenesis. But current research has found a solid relationship between neurodegenerative diseases and cytosolic DNA sensing pathways. This review summarizes profiles of several major cytosolic DNA sensors and their common adaptor protein STING. It also discusses both the beneficial and detrimental roles of cytosolic DNA sensors in the genesis and progression of neurodegenerative diseases.

Comparative single-cell RNA sequencing analysis of immune response to inactivated vaccine and natural SARS-CoV-2 infection

Uncovering the immune response to an inactivated SARS-CoV-2 vaccine (In-Vac) and natural infection is crucial for comprehending COVID-19 immunology. Here we conducted an integrated analysis of single-cell RNA sequencing (scRNA-seq) data from serial peripheral blood mononuclear cell (PBMC) samples derived from 12 individuals receiving In-Vac compared with those from COVID-19 patients. Our study reveals that In-Vac induces subtle immunological changes in PBMC, including cell proportions and transcriptomes, compared with profound changes for natural infection. In-Vac modestly upregulates IFN-α but downregulates NF-κB pathways, while natural infection triggers hyperactive IFN-α and NF-κB pathways. Both In-Vac and natural infection alter T/B cell receptor repertoires, but COVID-19 has more significant change in preferential VJ gene, indicating a vigorous immune response. Our study reveals distinct patterns of cellular communications, including a selective activation of IL-15RA/IL-15 receptor pathway after In-Vac boost, suggesting its potential role in enhancing In-Vac-induced immunity. Collectively, our study illuminates multifaceted immune responses to In-Vac and natural infection, providing insights for optimizing SARS-CoV-2 vaccine efficacy.

Exploring COVID-19 causal genes through disease-specific Cis-eQTLs

Genome-wide association study (GWAS) analysis has exposed that genetic factors play important roles in COVID-19. Whereas a deeper understanding of the underlying mechanism of COVID-19 was hindered by the lack of expression of quantitative trait loci (eQTL) data specific for disease. To this end, we identified COVID-19-specific cis-eQTLs by integrating nucleotide sequence variations and RNA-Seq data from COVID-19 samples. These identified eQTLs have different regulatory effect on genes between patients and controls, indicating that SARS-CoV-2 infection may cause alterations in the human body's internal environment. Individuals with the TT genotype in the rs1128320 region seemed more susceptible to SARS-CoV-2 infection and developed into severe COVID-19 due to the abnormal expression of IFITM1. We subsequently discovered potential causal genes, of the result, a total of 48 genes from six tissues were identified. siRNA-mediated depletion assays in SARS-CoV-2 infection proved that 14 causal genes were directly associated with SARS-CoV-2 infection. These results enriched existing research on COVID-19 causal genes and provided a new sight in the mechanism exploration for COVID-19.

Elossaily G, Ansari MN, Ali N. An Insight on Microfluidic Organ-on-a-Chip Models for PM2.5-Induced Pulmonary Complications

Pulmonary diseases like asthma, chronic obstructive pulmonary disorder, lung fibrosis, and lung cancer pose a significant burden to global human health. Many of these complications arise as a result of exposure to particulate matter (PM), which has been examined in several preclinical and clinical trials for its effect on several respiratory diseases. Particulate matter of size less than 2.5 μm (PM2.5) has been known to inflict unforeseen repercussions, although data from epidemiological studies to back this are pending. Conventionally utilized two-dimensional (2D) cell culture and preclinical animal models have provided insufficient benefits in emulating the in vivo physiological and pathological pulmonary conditions. Three-dimensional (3D) structural models, including organ-on-a-chip models, have experienced a developmental upsurge in recent times. Lung-on-a-chip models have the potential to simulate the specific features of the lungs. With the advancement of technology, an emerging and advanced technique termed microfluidic organ-on-a-chip has been developed with the aim of identifying the complexity of the respiratory cellular microenvironment of the body. In the present Review, the role of lung-on-a-chip modeling in reproducing pulmonary complications has been explored, with a specific emphasis on PM2.5-induced pulmonary complications.

Diabetes Mellitus, Energy Metabolism, and COVID-19

Obesity, diabetes mellitus (mostly type 2), and COVID-19 show mutual interactions because they are not only risk factors for both acute and chronic COVID-19 manifestations, but also because COVID-19 alters energy metabolism. Such metabolic alterations can lead to dysglycemia and long-lasting effects. Thus, the COVID-19 pandemic has the potential for a further rise of the diabetes pandemic. This review outlines how preexisting metabolic alterations spanning from excess visceral adipose tissue to hyperglycemia and overt diabetes may exacerbate COVID-19 severity. We also summarize the different effects of SARS-CoV-2 infection on the key organs and tissues orchestrating energy metabolism, including adipose tissue, liver, skeletal muscle, and pancreas. Last, we provide an integrative view of the metabolic derangements that occur during COVID-19. Altogether, this review allows for better understanding of the metabolic derangements occurring when a fire starts from a small flame, and thereby help reducing the impact of the COVID-19 pandemic.

ISGylation of DRP1 closely balances other post-translational modifications to mediate mitochondrial fission

Dynamin related protein 1 (DRP1), a pivotal mitochondrial fission protein, is post-translationally modified by multiple mechanisms. Here we identify a new post-translational modification of DRP1 by the ubiquitin-like protein, interferon-stimulated gene 15 (ISG15). DRP1 ISGylation is mediated by ISG15 E3 ligase, HERC5; this promotes mitochondrial fission. DeISGylation of DRP1 however leads to hyperfusion. Heterologous expression of SARS-CoV2 PLpro, a deISGylating enzyme, results in similar mitochondrial filamentation, significant decrease in total DRP1 protein levels and efflux of mtDNA. We report that deISGylated DRP1 gets ubiquitylated and degraded by TRIM25, instead of PARKIN and MITOL. While the cytosolic pool of DRP1 is primarily ISGylated, both mitochondrial and cytosolic fractions may be ubiquitylated. It is known that phosphorylation of DRP1 at S616 residue regulates its mitochondrial localisation; we show that ISGylation of phospho-DRP1 (S616) renders fission competence at mitochondria. This is significant because DRP1 ISGylation affects its functionality and mitochondrial dynamics in Alzheimer's disease pathophysiology.

The Asthma Risk Gene, GSDMB, Promotes Mitochondrial DNA-induced ISGs Expression

Released mitochondrial DNA (mtDNA) in cells activates cGAS-STING pathway, which induces expression of interferon-stimulated genes (ISGs) and thereby promotes inflammation, as frequently seen in asthmatic airways. However, whether the genetic determinant, Gasdermin B (GSDMB), the most replicated asthma risk gene, regulates this pathway remains unknown. We set out to determine whether and how GSDMB regulates mtDNA-activated cGAS-STING pathway and subsequent ISGs induction in human airway epithelial cells. Using qPCR, ELISA, native polyacrylamide gel electrophoresis, co-immunoprecipitation and immunofluorescence assays, we evaluated the regulation of GSDMB on cGAS-STING pathway in both BEAS-2B cells and primary normal human bronchial epithelial cells (nHBEs). mtDNA was extracted in plasma samples from human asthmatics and the correlation between mtDNA levels and eosinophil counts was analyzed. GSDMB is significantly associated with RANTES expression in asthmatic nasal epithelial brushing samples from the Genes-environments and Admixture in Latino Americans (GALA) II study. Over-expression of GSDMB promotes DNA-induced IFN and ISGs expression in bronchial epithelial BEAS-2B cells and nHBEs. Conversely, knockout of GSDMB led to weakened induction of interferon (IFNs) and ISGs in BEAS-2B cells. Mechanistically, GSDMB interacts with the C-terminus of STING, promoting the translocation of STING to Golgi, leading to the phosphorylation of IRF3 and induction of IFNs and ISGs. mtDNA copy number in serum from asthmatics was significantly correlated with blood eosinophil counts especially in male subjects. GSDMB promotes the activation of mtDNA and poly (dA:dT)-induced activation of cGAS-STING pathway in airway epithelial cells, leading to enhanced induction of ISGs.

Interferon lambda in respiratory viral infection: immunomodulatory functions and antiviral effects in epithelium

Type III interferon (IFN-λ), a new member of the IFN family, was initially considered to possess antiviral functions similar to those of type I interferon, both of which are induced via the JAK/STAT pathway. Nevertheless, recent findings demonstrated that IFN-λ exerts a nonredundant antiviral function at the mucosal surface, preferentially produced in epithelial cells in contrast to type I interferon, and its function cannot be replaced by type I interferon. This review summarizes recent studies showing that IFN-λ inhibits the spread of viruses from the cell surface to the body. Further studies have found that the role of IFN-λ is not only limited to the abovementioned functions, but it can also can exert direct and/or indirect effects on immune cells in virus-induced inflammation. This review focuses on the antiviral activity of IFN-λ in the mucosal epithelial cells and its action on immune cells and summarizes the pathways by which IFN-λ exerts its action and differentiates it from other interferons in terms of mechanism. Finally, we conclude that IFN-λ is a potent epidermal antiviral factor that enhances the respiratory mucosal immune response and has excellent therapeutic potential in combating respiratory viral infections.

Neutrophil-plasmacytoid dendritic cell interaction leads to production of type I IFN in response to Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) can cause a latent infection that sometimes progresses to clinically active tuberculosis (TB). Type I interferons (IFN-I) have been implicated in initiating the progression from latency to active TB, in part because IFN-I stimulated genes are the earliest genes to be upregulated in patients as they advance to active TB. Plasmacytoid dendritic cells (pDCs) are major producers of IFN-I during viral infections and in response to autoimmune-induced neutrophil extracellular traps. pDCs have also been suggested to be the major producers of IFN-I during Mtb infection of mice and nonhuman primates, but direct evidence has been lacking. Here, we found that Mtb did not stimulate isolated human pDCs to produce IFN-I, but human neutrophils infected with Mtb-activated co-cultured pDCs to do so. Mtb-infected neutrophils produced neutrophil extracellular traps, whose exposed DNA is a well-known mechanism to activate pDCs to secrete IFN-I. We conclude that pDCs contribute to the IFN-I response during Mtb infection by interacting with infected neutrophils which may then promote Mtb pathogenesis.

Type I and type III interferons: From basic biology and genetics to clinical development for COVID-19 and beyond

Type I and type III interferons (IFNs) constitute a key antiviral defense systems of the body, inducing viral resistance to cells and mediating diverse innate and adaptive immune functions. Defective type I and type III IFN responses have recently emerged as the 'Achilles heel' in COVID-19, with such patients developing severe disease and exhibiting a high risk for critical pneumonia and death. Here, we review the biology of type I and type III IFNs, their similarities and important functional differences, and their roles in SARS-CoV-2 infection. We also appraise the various mechanisms proposed to drive defective IFN responses in COVID-19 with particular emphasis to the ability of SARS-CoV-2 to suppress IFN production and activities, the genetic factors involved and the presence of autoantibodies neutralizing IFNs and accounting for a large proportion of individuals with severe COVID-19. Finally, we discuss the long history of the type I IFN therapeutics for the treatment of viral diseases, cancer and multiple sclerosis, the various efforts to use them in respiratory infections, and the newly emerging type III IFN therapeutics, with emphasis to the more recent studies on COVID-19 and their potential use as broad spectrum antivirals for future epidemics or pandemics.

IUPHAR ECR review: The cGAS-STING pathway: Novel functions beyond innate immune and emerging therapeutic opportunities

Stimulator of interferon genes (STING) is a crucial innate immune sensor responsible for distinguishing pathogens and cytosolic DNA, mediating innate immune signaling pathways to defend the host. Recent studies have revealed additional regulatory functions of STING beyond its innate immune-related activities, including the regulation of cellular metabolism, DNA repair, cellular senescence, autophagy and various cell deaths. These findings highlight the broader implications of STING in cellular physiology beyond its role in innate immunity. Currently, approximately 10 STING agonists have entered the clinical stage. Unlike inhibitors, which have a maximum inhibition limit, agonists have the potential for infinite amplification. STING signaling is a complex process that requires precise regulation of STING to ensure balanced immune responses and prevent detrimental autoinflammation. Recent research on the structural mechanism of STING autoinhibition and its negative regulation by adaptor protein complex 1 (AP-1) provides valuable insights into its different effects under physiological and pathological conditions, offering a new perspective for developing immune regulatory drugs. Herein, we present a comprehensive overview of the regulatory functions and molecular mechanisms of STING beyond innate immune regulation, along with updated details of its structural mechanisms. We discuss the implications of these complex regulations in various diseases, emphasizing the importance and feasibility of targeting the immunity-dependent or immunity-independent functions of STING. Moreover, we highlight the current trend in drug development and key points for clinical research, basic research, and translational research related to STING.

Severe COVID-19 and long COVID are associated with high expression of STING, cGAS and IFN-α

The cGAS-STING pathway appears to contribute to dysregulated inflammation during coronavirus disease 2019 (COVID-19); however, inflammatory factors related to long COVID are still being investigated. In the present study, we evaluated the association of cGAS and STING gene expression levels and plasma IFN-α, TNF-α and IL-6 levels with COVID-19 severity in acute infection and long COVID, based on analysis of blood samples from 148 individuals, 87 with acute COVID-19 and 61 in the post-COVID-19 period. Quantification of gene expression was performed by real-time PCR, and cytokine levels were quantified by ELISA and flow cytometry. In acute COVID-19, cGAS, STING, IFN-α, TNF-α, and IL-6 levels were higher in patients with severe disease than in those with nonsevere manifestations (p < 0.05). Long COVID was associated with elevated cGAS, STING and IFN-α levels (p < 0.05). Activation of the cGAS-STING pathway may contribute to an intense systemic inflammatory state in severe COVID-19 and, after infection resolution, induce an autoinflammatory disease in some tissues, resulting in long COVID.

STING signaling in the brain: Molecular threats, signaling activities, and therapeutic challenges

Stimulator of interferon genes (STING) is an innate immune signaling protein critical to infections, autoimmunity, and cancer. STING signaling is also emerging as an exciting and integral part of many neurological diseases. Here, we discuss recent advances in STING signaling in the brain. We summarize how molecular threats activate STING signaling in the diseased brain and how STING signaling activities in glial and neuronal cells cause neuropathology. We also review human studies of STING neurobiology and consider therapeutic challenges in targeting STING to treat neurological diseases.

Self-DNA driven inflammation in COVID-19 and after mRNA-based vaccination: lessons for non-COVID-19 pathologies

The coronavirus disease 2019 (COVID-19) pandemic triggered an unprecedented concentration of economic and research efforts to generate knowledge at unequalled speed on deregulated interferon type I signalling and nuclear factor kappa light chain enhancer in B-cells (NF-κB)-driven interleukin (IL)-1β, IL-6, IL-18 secretion causing cytokine storms. The translation of the knowledge on how the resulting systemic inflammation can lead to life-threatening complications into novel treatments and vaccine technologies is underway. Nevertheless, previously existing knowledge on the role of cytoplasmatic or circulating self-DNA as a pro-inflammatory damage-associated molecular pattern (DAMP) was largely ignored. Pathologies reported 'de novo' for patients infected with Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV)-2 to be outcomes of self-DNA-driven inflammation in fact had been linked earlier to self-DNA in different contexts, e.g., the infection with Human Immunodeficiency Virus (HIV)-1, sterile inflammation, and autoimmune diseases. I highlight particularly how synergies with other DAMPs can render immunogenic properties to normally non-immunogenic extracellular self-DNA, and I discuss the shared features of the gp41 unit of the HIV-1 envelope protein and the SARS-CoV 2 Spike protein that enable HIV-1 and SARS-CoV-2 to interact with cell or nuclear membranes, trigger syncytia formation, inflict damage to their host's DNA, and trigger inflammation - likely for their own benefit. These similarities motivate speculations that similar mechanisms to those driven by gp41 can explain how inflammatory self-DNA contributes to some of most frequent adverse events after vaccination with the BNT162b2 mRNA (Pfizer/BioNTech) or the mRNA-1273 (Moderna) vaccine, i.e., myocarditis, herpes zoster, rheumatoid arthritis, autoimmune nephritis or hepatitis, new-onset systemic lupus erythematosus, and flare-ups of psoriasis or lupus. The hope is to motivate a wider application of the lessons learned from the experiences with COVID-19 and the new mRNA vaccines to combat future non-COVID-19 diseases.

The cGAS-STING pathway in viral infections: a promising link between inflammation, oxidative stress and autophagy

The host defence responses play vital roles in viral infection and are regulated by complex interactive networks. The host immune system recognizes viral pathogens through the interaction of pattern-recognition receptors (PRRs) with pathogen-associated molecular patterns (PAMPs). As a PRR mainly in the cytoplasm, cyclic GMP-AMP synthase (cGAS) senses and binds virus DNA and subsequently activates stimulator of interferon genes (STING) to trigger a series of intracellular signalling cascades to defend against invading pathogenic microorganisms. Integrated omic and functional analyses identify the cGAS-STING pathway regulating various host cellular responses and controlling viral infections. Aside from its most common function in regulating inflammation and type I interferon, a growing body of evidence suggests that the cGAS-STING signalling axis is closely associated with a series of cellular responses, such as oxidative stress, autophagy, and endoplasmic reticulum stress, which have major impacts on physiological homeostasis. Interestingly, these host cellular responses play dual roles in the regulation of the cGAS-STING signalling axis and the clearance of viruses. Here, we outline recent insights into cGAS-STING in regulating type I interferon, inflammation, oxidative stress, autophagy and endoplasmic reticulum stress and discuss their interactions with viral infections. A detailed understanding of the cGAS-STING-mediated potential antiviral effects contributes to revealing the pathogenesis of certain viruses and sheds light on effective solutions for antiviral therapy.

SARS-CoV-2: A Glance at the Innate Immune Response Elicited by Infection and Vaccination

The COVID-19 pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has led to almost seven million deaths worldwide. SARS-CoV-2 causes infection through respiratory transmission and can occur either without any symptoms or with clinical manifestations which can be mild, severe or, in some cases, even fatal. Innate immunity provides the initial defense against the virus by sensing pathogen-associated molecular patterns and triggering signaling pathways that activate the antiviral and inflammatory responses, which limit viral replication and help the identification and removal of infected cells. However, temporally dysregulated and excessive activation of the innate immune response is deleterious for the host and associates with severe COVID-19. In addition to its defensive role, innate immunity is pivotal in priming the adaptive immune response and polarizing its effector function. This capacity is relevant in the context of both SARS-CoV-2 natural infection and COVID-19 vaccination. Here, we provide an overview of the current knowledge of the innate immune responses to SARS-CoV-2 infection and vaccination.

The cGAS-STING pathway: a therapeutic target in diabetes and its complications

Diabetic wound healing (DWH) represents a major complication of diabetes where inflammation is a key impediment to proper healing. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has emerged as a central mediator of inflammatory responses to cell stress and damage. However, the contribution of cGAS-STING activation to impaired healing in DWH remains understudied. In this review, we examine the evidence that cGAS-STING-driven inflammation is a critical factor underlying defective DWH. We summarize studies revealing upregulation of the cGAS-STING pathway in diabetic wounds and discuss how this exacerbates inflammation and senescence and disrupts cellular metabolism to block healing. Partial pharmaceutical inhibition of cGAS-STING has shown promise in damping inflammation and improving DWH in preclinical models. We highlight key knowledge gaps regarding cGAS-STING in DWH, including its relationships with endoplasmic reticulum stress and metal-ion signaling. Elucidating these mechanisms may unveil new therapeutic targets within the cGAS-STING pathway to improve healing outcomes in DWH. This review synthesizes current understanding of how cGAS-STING activation contributes to DWH pathology and proposes future research directions to exploit modulation of this pathway for therapeutic benefit.

Regulation of kynurenine metabolism by blood donor genetics and biology impacts red cell hemolysis in vitro and in vivo

ABSTRACT

In the field of transfusion medicine, the clinical relevance of the metabolic markers of the red blood cell (RBC) storage lesion is incompletely understood. Here, we performed metabolomics of RBC units from 643 donors enrolled in the Recipient Epidemiology and Donor Evaluation Study, REDS RBC Omics. These units were tested on storage days 10, 23, and 42 for a total of 1929 samples and also characterized for end-of-storage hemolytic propensity after oxidative and osmotic insults. Our results indicate that the metabolic markers of the storage lesion poorly correlated with hemolytic propensity. In contrast, kynurenine was not affected by storage duration and was identified as the top predictor of osmotic fragility. RBC kynurenine levels were affected by donor age and body mass index and were reproducible within the same donor across multiple donations from 2 to 12 months apart. To delve into the genetic underpinnings of kynurenine levels in stored RBCs, we thus tested kynurenine levels in stored RBCs on day 42 from 13 091 donors from the REDS RBC Omics study, a population that was also genotyped for 879 000 single nucleotide polymorphisms. Through a metabolite quantitative trait loci analysis, we identified polymorphisms in SLC7A5, ATXN2, and a series of rate-limiting enzymes (eg, kynurenine monooxygenase, indoleamine 2,3-dioxygenase, and tryptophan dioxygenase) in the kynurenine pathway as critical factors affecting RBC kynurenine levels. By interrogating a donor-recipient linkage vein-to-vein database, we then report that SLC7A5 polymorphisms are also associated with changes in hemoglobin and bilirubin levels, suggestive of in vivo hemolysis in 4470 individuals who were critically ill and receiving single-unit transfusions.

Activation of cGAS-STING suppresses coxsackievirus replication via interferon-dependent signaling

Coxsackievirus B3 (CVB3) is a non-enveloped, single-stranded, positive RNA virus known for its role in provoking inflammatory diseases that affect the heart, pancreas, and brain, leading to conditions such as myocarditis, pancreatitis, and meningitis. Currently, there are no FDA-approved drugs treating CVB3 infection; therefore, identifying potential molecular targets for antiviral drug development is imperative. In this study, we examined the possibility of activating the cyclic GMP-AMP (cGAMP) synthase (cGAS)-stimulator of interferon genes (STING) pathway, a cytosolic DNA-sensing pathway that triggers a type-I interferon (IFN) response, in inhibiting CVB3 infection. We found that activation of the cGAS-STING pathway through the application of cGAS (poly dA:dT and herring testes DNA) or STING agonists (2'3'-cGAMP and diamidobenzimidazole), or the overexpression of STING, significantly suppresses CVB3 replication. Conversely, gene-silencing of STING enhances viral replication. Mechanistically, we demonstrated that cGAS-STING activation combats CVB3 infection by inducing IFN response. Notably, we discovered that knockdown of IFN-α/β receptor, a key membrane receptor in type-I IFN signaling, or inhibition of the downstream JAK1/2 signaling with ruxolitinib, mitigates the effects of STING activation, resulting in increased viral protein production. Furthermore, we investigated the interplay between CVB3 and the cGAS-STING pathway. We showed that CVB3 does not trigger cGAS-STING activation; instead, it antagonizes STING and the downstream TBK1 activation induced by cGAMP. In summary, our results provide insights into the interaction of an RNA virus and the DNA-sensing pathway, highlighting the potential for agonist activation of the cGAS-STING pathway in the development of anti-CVB3 drugs.

SARS-CoV-2-Induced Vasculitic Skin Lesions Are Associated with Massive Spike Protein Depositions in Autophagosomes

In patients infected with severe acute respiratory syndrome coronavirus 2, vasculopathic changes of the skin are associated with a severe prognosis. However, the pathogenesis of this vasculopathy is not conclusively clarified. In this study, 25 prospectively collected skin samples from patients with COVID-19-related skin lesions were examined for vasculopathic changes and, in case of vasculitis, were further analyzed with electron microscopy and immunohistochemistry. Vasculopathy was observed in 76% of all COVID-19-related inflammatory skin lesions. Visual endothelial changes without manifest leukocytoclastic vasculitis were found in 60% of the COVID-19-related skin lesions, whereas leukocytoclastic vasculitis was diagnosed in 16%. In the cases of vasculitis, there were extensive spike protein depositions in microvascular endothelial cells that colocalized with the autophagosome proteins LC3B and LC3C. The autophagy protein complex LC3-associated endocytosis in microvascular endothelial cells seems to be an important pathogenic factor for severe acute respiratory syndrome coronavirus 2-related vasculitis in the skin. On ultrastructural morphology, the vasculitic process was dominated by intracellular vesicle formation and endothelial cell disruption. Direct presence of severe acute respiratory syndrome coronavirus 2 particles in the skin was not observed. Therefore, our results suggest that instead of direct viral infection, dermal vasculitic lesions in COVID-19 are caused by severe acute respiratory syndrome coronavirus 2 spike protein deposition followed by endothelial damage with activation of autophagy.

Megakaryocytes possess a STING pathway that is transferred to platelets to potentiate activation

Platelets display unexpected roles in immune and coagulation responses. Emerging evidence suggests that STING is implicated in hypercoagulation. STING is an adaptor protein downstream of the DNA sensor cyclic GMP-AMP synthase (cGAS) that is activated by cytosolic microbial and self-DNA during infections, and in the context of loss of cellular integrity, to instigate the production of type-I IFN and pro-inflammatory cytokines. To date, whether the cGAS-STING pathway is present in platelets and contributes to platelet functions is not defined. Using a combination of pharmacological and genetic approaches, we demonstrate here that megakaryocytes and platelets possess a functional cGAS-STING pathway. Our results suggest that in megakaryocytes, STING stimulation activates a type-I IFN response, and during thrombopoiesis, cGAS and STING are transferred to proplatelets. Finally, we show that both murine and human platelets contain cGAS and STING proteins, and the cGAS-STING pathway contributes to potentiation of platelet activation and aggregation. Taken together, these observations establish for the first time a novel role of the cGAS-STING DNA sensing axis in the megakaryocyte and platelet lineage.

SARS-CoV-2 and innate immunity: the good, the bad, and the "goldilocks"

An ancient conflict between hosts and pathogens has driven the innate and adaptive arms of immunity. Knowledge about this interplay can not only help us identify biological mechanisms but also reveal pathogen vulnerabilities that can be leveraged therapeutically. The humoral response to SARS-CoV-2 infection has been the focus of intense research, and the role of the innate immune system has received significantly less attention. Here, we review current knowledge of the innate immune response to SARS-CoV-2 infection and the various means SARS-CoV-2 employs to evade innate defense systems. We also consider the role of innate immunity in SARS-CoV-2 vaccines and in the phenomenon of long COVID.

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.

Longitudinal single cell atlas identifies complex temporal relationship between type I interferon response and COVID-19 severity

Due to the paucity of longitudinal molecular studies of COVID-19, particularly those covering the early stages of infection (Days 1-8 symptom onset), our understanding of host response over the disease course is limited. We perform longitudinal single cell RNA-seq on 286 blood samples from 108 age- and sex-matched COVID-19 patients, including 73 with early samples. We examine discrete cell subtypes and continuous cell states longitudinally, and we identify upregulation of type I IFN-stimulated genes (ISGs) as the predominant early signature of subsequent worsening of symptoms, which we validate in an independent cohort and corroborate by plasma markers. However, ISG expression is dynamic in progressors, spiking early and then rapidly receding to the level of severity-matched non-progressors. In contrast, cross-sectional analysis shows that ISG expression is deficient and IFN suppressors such as SOCS3 are upregulated in severe and critical COVID-19. We validate the latter in four independent cohorts, and SOCS3 inhibition reduces SARS-CoV-2 replication in vitro. In summary, we identify complexity in type I IFN response to COVID-19, as well as a potential avenue for host-directed therapy.

M335, a novel small-molecule STING agonist activates the immune response and exerts antitumor effects

In the context of antitumor immune responses, the activation of the stimulator of interferon genes (STING) assumes a critical role and imparts enhanced immunogenicity. An effective strategy for exogenously activating the immune system involves the utilization of STING agonists, and prior investigations primarily concentrated on modifying endogenous cyclic dinucleotides (CDNs) to achieve this. Nevertheless, the practical utility of CDNs was restricted due to limitations associated with their physicochemical attributes and administration protocols. In this article, we present the discovery of a novel small-molecule agonist denoted as M335, identified through high-throughput screening using surface plasmon resonance (SPR). M335 demonstrates the ability to activate the TBK1-IRF3-IFN axis in a STING-dependent manner in vitro. Through experimentation on mouse models bearing tumors, we observed that the administration of M335 resulted in the activation of immune cells. Notably, significant antitumor effects were achieved with both intratumoral and intraperitoneal administration of M335. These findings suggest the potential of M335 as a promising agent for cancer immunotherapy, which will promote the development of STING agonists in anti-tumor applications.