Sensing of cytoplasmic chromatin by cGAS activates innate immune response in SARS-CoV-2 infection

Porcine deltacoronavirus nonstructural protein 2 inhibits type I and III IFN production by targeting STING for degradation

Porcine deltacoronavirus (PDCoV) is an enteropathogenic coronavirus that has been reported to use various strategies to counter the host antiviral innate immune response. The cGAS-STING signalling pathway plays an important role in antiviral innate immunity. However, it remains unclear whether PDCoV achieves immune evasion by regulating the cGAS-STING pathway. Here, we demonstrated that the nonstructural protein 2 (nsp2) encoded by PDCoV inhibits cGAS-STING-mediated type I and III interferon (IFN) responses via the regulation of porcine STING (pSTING) stability. Mechanistically, ectopically expressed PDCoV nsp2 was found to interact with the N-terminal region of pSTING. Consequently, pSTING was degraded through K48-linked ubiquitination and the proteasomal pathway, leading to the disruption of cGAS-STING signalling. Furthermore, K150 and K236 of pSTING were identified as crucial residues for nsp2-mediated ubiquitination and degradation. In summary, our findings provide a basis for elucidating the immune evasion mechanism of PDCoV and will contribute to the development of targets for anti-coronavirus drugs.

SFTSV nucleoprotein mediates DNA sensor cGAS degradation to suppress cGAS-dependent antiviral responses

Cyclic GMP-AMP synthase (cGAS) is an important DNA pattern recognition receptor that senses double-stranded DNA derived from invading pathogens or self DNA in cytoplasm, leading to an antiviral interferon response. A tick-borne Bunyavirus, severe fever with thrombocytopenia syndrome virus (SFTSV), is an RNA virus that causes a severe emerging viral hemorrhagic fever in Asia with a high case fatality rate of up to 30%. However, it is unclear whether cGAS interacts with SFTSV infection. In this study, we found that SFTSV infection upregulated cGAS RNA transcription and protein expression, indicating that cGAS is an important innate immune response against SFTSV infection. The mechanism of cGAS recognizing SFTSV is by cGAS interacting with misplaced mitochondrial DNA in the cytoplasm. Depletion of mitochondrial DNA significantly inhibited cGAS activation under SFTSV infection. Strikingly, we found that SFTSV nucleoprotein (N) induced cGAS degradation in a dose-dependent manner. Mechanically, N interacted with the 161-382 domain of cGAS and linked the cGAS to LC3. The cGAS-N-LC3 trimer was targeted to N-induced autophagy, and the cGAS was degraded in autolysosome. Taken together, our study discovered a novel antagonistic mechanism of RNA viruses, SFTSV is able to suppress the cGAS-dependent antiviral innate immune responses through N-hijacking cGAS into N-induced autophagy. Our results indicated that SFTSV N is an important virulence factor of SFTSV in mediating host antiviral immune responses.

IMPORTANCE

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a tick-borne RNA virus that is widespread in East and Southeast Asian countries with a high fatality rate of up to 30%. Up to now, many cytoplasmic pattern recognition receptors, such as RIG-I, MDA5, and SAFA, have been reported to recognize SFTSV genomic RNA and trigger interferon-dependent antiviral responses. However, current knowledge is not clear whether SFTSV can be recognized by DNA sensor cyclic GMP-AMP synthase (cGAS). Our study demonstrated that cGAS could recognize SFTSV infection via ectopic mitochondrial DNA, and the activated cGAS-stimulator of interferon genes signaling pathway could significantly inhibit SFTSV replication. Importantly, we further uncovered a novel mechanism of SFTSV to inhibit innate immune responses by the degradation of cGAS. cGAS was degraded in N-induced autophagy. Collectively, this study illustrated a novel virulence factor of SFTSV to suppress innate immune responses through autophagy-dependent cGAS degradation.

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.

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.

cGAS-STING, an important signaling pathway in diseases and their therapy

Since cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway was discovered in 2013, great progress has been made to elucidate the origin, function, and regulating mechanism of cGAS-STING signaling pathway in the past decade. Meanwhile, the triggering and transduction mechanisms have been continuously illuminated. cGAS-STING plays a key role in human diseases, particularly DNA-triggered inflammatory diseases, making it a potentially effective therapeutic target for inflammation-related diseases. Here, we aim to summarize the ancient origin of the cGAS-STING defense mechanism, as well as the triggers, transduction, and regulating mechanisms of the cGAS-STING. We will also focus on the important roles of cGAS-STING signal under pathological conditions, such as infections, cancers, autoimmune diseases, neurological diseases, and visceral inflammations, and review the progress in drug development targeting cGAS-STING signaling pathway. The main directions and potential obstacles in the regulating mechanism research and therapeutic drug development of the cGAS-STING signaling pathway for inflammatory diseases and cancers will be discussed. These research advancements expand our understanding of cGAS-STING, provide a theoretical basis for further exploration of the roles of cGAS-STING in diseases, and open up new strategies for targeting cGAS-STING as a promising therapeutic intervention in multiple diseases.

In situ bio-mineralized Mn nanoadjuvant enhances anti-influenza immunity of recombinant virus-like particle vaccines

Virus like particles (VLPs) have been well recognized as one of the most important vaccine platforms due to their structural similarity to natural viruses to induce effective humoral and cellular immune responses. Nevertheless, lack of viral nucleic acids in VLPs usually leads the vaccine candidates less efficient in provoking innate immune against viral infection. Here, we constructed a biomimetic dual antigen hybrid influenza nanovaccines THM-HA@Mn with robust immunogenicity via in situ synthesizing a stimulator of interferon genes (STING) agonist Mn3O4 inside the cavity of a recombinant Hepatitis B core antigen VLP (HBc VLP) having fused SpyTag and influenza M2e antigen peptides (Tag-HBc-M2e, THM for short), followed by conjugating a recombinant hemagglutinin (rHA) antigen on the surface of the nanoparticles through SpyTag/SpyCatcher ligating. Such inside Mn3O4 immunostimulator-outside rHA antigen design, together with the chimeric M2e antigen on the HBc skeleton, enabled the synthesized hybrid nanovaccines THM-HA@Mn to well imitate the spatial distribution of M2e/HA antigens and immunostimulant in natural influenza virus. In vitro cellular experiments indicated that compared with the THM-HA antigen without Mn3O4 and a mixture vaccine consisting of THM-HA + MnOx, the THM-HA@Mn hybrid nanovaccines showed the highest efficacies in dendritic cells uptake and in promoting BMDC maturation, as well as inducing expression of TNF-α and type I interferon IFN-β. The THM-HA@Mn also displayed the most sustained antigen release at the injection site, the highest efficacies in promoting the DC maturation in lymph nodes and germinal center B cells activation in the spleen of the immunized mice. The co-delivery of immunostimulant and antigens enabled the THM-HA@Mn nanovaccines to induce the highest systemic antigen-specific antibody responses and cellular immunogenicity in mice. Together with the excellent colloid dispersion stability, low cytotoxicity, as well as good biosafety, the synthetic hybrid nanovaccines presented in this study offers a promising strategy to design VLP-based vaccine with robust natural and adaptive immunogenicity against emerging viral pathogens.

Unraveling the Role of RNase L Knockout in Alleviating Immune Response Activation in Mice Bone Marrow after Irradiation

Ionizing radiation (IR) induces severe hematopoietic injury by causing DNA and RNA damage as well as activating the immune responses, necessitating the development of effective therapeutic strategies. Ribonuclease L (RNase L) as an innate immune response pathway is triggered by exogenous and endogenous abnormal dsRNA under viral infection and dyshomeostasis, thereby activating the immune responses. Thus, we investigated the effect of RNase L on irradiation-induced bone marrow damage using RNase L knockout (RNase L-/-) mice. Phenotypic analysis revealed that RNase L knockout mitigates irradiation-induced injury in the bone marrow. Further investigation into the mechanism of RNase L by RNA-seq, qRT-PCR, and CBA analysis demonstrated that RNase L deficiency counteracts the upregulation of genes related to immune responses induced by irradiation, including cytokines and interferon-stimulated genes. Moreover, RNase L deficiency inhibits the increased levels of immunoglobulins in serum induced by irradiation. These findings indicate that RNase L plays a role in the immune response induced by irradiation in the bone marrow. This study further enhances our understanding of the biological functions of RNase L in the immune response induced by irradiation and offers a novel approach for managing irradiation-induced bone marrow injury through the regulation of RNase L activation.

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.

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 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 basally active cGAS-STING pathway limits SARS-CoV-2 replication in a subset of ACE2 positive airway cell models

Host factors that define the cellular tropism of SARS-CoV-2 beyond the cognate ACE2 receptor are poorly defined. From a screen of human airway derived cell lines that express varying levels of ACE2/TMPRSS2, we found a subset that express comparably high endogenous levels of ACE2 but surprisingly did not support SARS-CoV-2 replication. Here we report that this resistance is mediated by a basally active cGAS-STING pathway culminating in interferon (IFN)-mediated restriction of SARS-CoV-2 replication at a post-entry step. Pharmacological inhibition of JAK1/2, depletion of the IFN-α receptor and cGAS-STING pathway effectors substantially increased SARS-CoV-2 replication in these cell models. While depletion of cGAS or STING was sufficient to reduce the preexisting levels of IFN-stimulated genes (ISGs), SARS-CoV-2 infection in STING knockout cells independently induced ISG expression. Remarkably, SARS-CoV-2-induced ISG expression in STING knockout cell as well as in primary human airway cultures was limited to uninfected bystander cells, demonstrating efficient antagonism of the type I/III IFN-pathway, but not viral sensing or IFN production, in productively infected cells. Of note, SARS-CoV-2-infected primary human airway cells also displayed markedly lower levels of STING expression, raising the possibility that SARS-CoV-2 can target STING expression or preferentially infect cells that express low levels of STING. Finally, ectopic ACE2 overexpression overcame the IFN-mediated blocks, suggesting the ability of SARS-CoV-2 to overcome these possibly saturable blocks to infection. Our study highlights that in addition to viral receptors, basal activation of the cGAS-STING pathway and innate immune defenses may contribute to defining SARS-CoV-2 cellular tropism.

Sting mutation attenuates acetaminophen-induced acute liver injury by limiting NLRP3 activation

Acetaminophen (N-acetyl-p-aminophenol; APAP), a widely used effective nonsteroidal anti-inflammatory drug, leads to acute liver injury at overdose worldwide. Evidence showed that the severity of liver injury associated with the subsequent involvement of inflammatory mediators and immune cells. The innate immune stimulator of interferon genes protein (STING) pathway was critical in modulating inflammation. Here, we show that STING was activated and inflammation was enhanced in the liver in APAP-overdosed C57BL/6J mice, and Sting mutation (Stinggt/gt) mice exhibited less liver damage. Multiplexing flow cytometry displayed that Sting mutation changed hepatic recruitment and replacement of macrophages/monocytes in APAP-overdosed mice, which was inclined to anti-inflammation. In addition, Sting mutation limited NLRP3 activation in the liver in APAP-overdosed mice, and inhibited the expression of inflammatory cytokines. Finally, MCC950, a potent and selective NLRP3 inhibitor, significantly ameliorated APAP-induced liver injury and inflammation. Besides, pretreatment of MCC950 in C57 mice resulted in changes of immune cells infiltration in the liver similar to Stinggt/gt mice. Our study revealed that STING played a crucial role in APAP-induced acute liver injury, possibly by maintaining liver immune cells homeostasis and inhibiting NLRP3 inflammasome activation, suggesting that inhibiting STING-NLRP3 pathway might be a potential therapeutic strategy for acute liver injury.

STING is redundant for host defense and pathology of COVID-19-like disease in mice

Critical COVID-19 is characterized by lack of early type I interferon-mediated host defense and subsequent hyper-inflammation in the lungs. Aberrant activation of macrophages and neutrophils has been reported to lead to excessive activation of innate immunological pathways. It has recently been suggested that the DNA-sensing cGAS-STING pathway drives pathology in the SARS-CoV-2-infected lungs, but mechanistic understanding from in vivo models is needed. Here, we tested whether STING is involved in COVID-19-like disease using the K18-hACE2 mouse model. We report that disease development after SARS-CoV-2 infection is unaltered in STING-deficient K18-hACE2 mice. In agreement with this, STING deficiency did not affect control of viral replication or production of interferons and inflammatory cytokines. This was accompanied by comparable profiles of infiltrating immune cells into the lungs of infected mice. These data do not support a role for STING in COVID-19 pathology and calls for further investigation into the pathogenesis of critical COVID-19.

Phase-separated nucleocapsid protein of SARS-CoV-2 suppresses cGAS-DNA recognition by disrupting cGAS-G3BP1 complex

Currently, the incidence and fatality rate of SARS-CoV-2 remain continually high worldwide. COVID-19 patients infected with SARS-CoV-2 exhibited decreased type I interferon (IFN-I) signal, along with limited activation of antiviral immune responses as well as enhanced viral infectivity. Dramatic progresses have been made in revealing the multiple strategies employed by SARS-CoV-2 in impairing canonical RNA sensing pathways. However, it remains to be determined about the SARS-CoV-2 antagonism of cGAS-mediated activation of IFN responses during infection. In the current study, we figure out that SARS-CoV-2 infection leads to the accumulation of released mitochondria DNA (mtDNA), which in turn triggers cGAS to activate IFN-I signaling. As countermeasures, SARS-CoV-2 nucleocapsid (N) protein restricts the DNA recognition capacity of cGAS to impair cGAS-induced IFN-I signaling. Mechanically, N protein disrupts the assembly of cGAS with its co-factor G3BP1 by undergoing DNA-induced liquid-liquid phase separation (LLPS), subsequently impairs the double-strand DNA (dsDNA) detection ability of cGAS. Taken together, our findings unravel a novel antagonistic strategy by which SARS-CoV-2 reduces DNA-triggered IFN-I pathway through interfering with cGAS-DNA phase separation.

Autophagy and SARS-CoV-2-Old Players in New Games

At present it is well-defined that autophagy is a fundamental process essential for cell life but its pro-viral and anti-viral role has been stated out with the COVID pandemic. However, viruses in turn have evolved diverse adaptive strategies to cope with autophagy driven host defense, either by blocking or hijacking the autophagy machinery for their own benefit. The mechanisms underlying autophagy modulation are presented in the current review which summarizes the accumulated knowledge on the crosstalk between autophagy and viral infections, with a particular emphasizes on SARS-CoV-2. The different types of autophagy related to infections and their molecular mechanisms are focused in the context of inflammation. In particular, SARS-CoV-2 entry, replication and disease pathogenesis are discussed. Models to study autophagy and to formulate novel treatment approaches and pharmacological modulation to fight COVID-19 are debated. The SARS-CoV-2-autophagy interplay is presented, revealing the complex dynamics and the molecular machinery of autophagy. The new molecular targets and strategies to treat COVID-19 effectively are envisaged. In conclusion, our finding underline the importance of development new treatment strategies and pharmacological modulation of autophagy to fight COVID-19.

SARS-CoV-2 infection induces DNA damage, through CHK1 degradation and impaired 53BP1 recruitment, and cellular senescence

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the RNA virus responsible for the coronavirus disease 2019 (COVID-19) pandemic. Although SARS-CoV-2 was reported to alter several cellular pathways, its impact on DNA integrity and the mechanisms involved remain unknown. Here we show that SARS-CoV-2 causes DNA damage and elicits an altered DNA damage response. Mechanistically, SARS-CoV-2 proteins ORF6 and NSP13 cause degradation of the DNA damage response kinase CHK1 through proteasome and autophagy, respectively. CHK1 loss leads to deoxynucleoside triphosphate (dNTP) shortage, causing impaired S-phase progression, DNA damage, pro-inflammatory pathways activation and cellular senescence. Supplementation of deoxynucleosides reduces that. Furthermore, SARS-CoV-2 N-protein impairs 53BP1 focal recruitment by interfering with damage-induced long non-coding RNAs, thus reducing DNA repair. Key observations are recapitulated in SARS-CoV-2-infected mice and patients with COVID-19. We propose that SARS-CoV-2, by boosting ribonucleoside triphosphate levels to promote its replication at the expense of dNTPs and by hijacking damage-induced long non-coding RNAs' biology, threatens genome integrity and causes altered DNA damage response activation, induction of inflammation and cellular senescence.

TRAF3 activates STING-mediated suppression of EV-A71 and target of viral evasion

Innate immunity represents one of the main host responses to viral infection.^1-3 STING (Stimulator of interferon genes), a crucial immune adapter functioning in host cells, mediates cGAS (Cyclic GMP-AMP Synthase) sensing of exogenous and endogenous DNA fragments and generates innate immune responses.⁴ Whether STING activation was involved in infection and replication of enterovirus remains largely unknown. In the present study, we discovered that human enterovirus A71 (EV-A71) infection triggered STING activation in a cGAS dependent manner. EV-A71 infection caused mitochondrial damage and the discharge of mitochondrial DNA into the cytosol of infected cells. However, during EV-A71 infection, cGAS-STING activation was attenuated. EV-A71 proteins were screened and the viral protease 2A^pro had the greatest capacity to inhibit cGAS-STING activation. We identified TRAF3 as an important factor during STING activation and as a target of 2A^pro. Supplement of TRAF3 rescued cGAS-STING activation suppression by 2A^pro. TRAF3 supported STING activation mediated TBK1 phosphorylation. Moreover, we found that 2A^pro protease activity was essential for inhibiting STING activation. Furthermore, EV-D68 and CV-A16 infection also triggered STING activation. The viral protease 2A^pro from EV-D68 and CV-A16 also had the ability to inhibit STING activation. As STING activation prior to EV-A71 infection generated cellular resistance to EV-A71 replication, blocking EV-A71-mediated STING suppression represents a new anti-viral target.

Function and regulation of cGAS-STING signaling in infectious diseases

The efficacious detection of pathogens and prompt induction of innate immune signaling serve as a crucial component of immune defense against infectious pathogens. Over the past decade, DNA-sensing receptor cyclic GMP-AMP synthase (cGAS) and its downstream signaling adaptor stimulator of interferon genes (STING) have emerged as key mediators of type I interferon (IFN) and nuclear factor-κB (NF-κB) responses in health and infection diseases. Moreover, both cGAS-STING pathway and pathogens have developed delicate strategies to resist each other for their survival. The mechanistic and functional comprehension of the interplay between cGAS-STING pathway and pathogens is opening the way for the development and application of pharmacological agonists and antagonists in the treatment of infectious diseases. Here, we briefly review the current knowledge of DNA sensing through the cGAS-STING pathway, and emphatically highlight the potent undertaking of cGAS-STING signaling pathway in the host against infectious pathogenic organisms.

The Evolution of Single-Cell RNA Sequencing Technology and Application: Progress and Perspectives

As an emerging sequencing technology, single-cell RNA sequencing (scRNA-Seq) has become a powerful tool for describing cell subpopulation classification and cell heterogeneity by achieving high-throughput and multidimensional analysis of individual cells and circumventing the shortcomings of traditional sequencing for detecting the average transcript level of cell populations. It has been applied to life science and medicine research fields such as tracking dynamic cell differentiation, revealing sensitive effector cells, and key molecular events of diseases. This review focuses on the recent technological innovations in scRNA-Seq, highlighting the latest research results with scRNA-Seq as the core technology in frontier research areas such as embryology, histology, oncology, and immunology. In addition, this review outlines the prospects for its innovative application in traditional Chinese medicine (TCM) research and discusses the key issues currently being addressed by scRNA-Seq and its great potential for exploring disease diagnostic targets and uncovering drug therapeutic targets in combination with multiomics technologies.

Cellular Sensors and Viral Countermeasures: A Molecular Arms Race between Host and SARS-CoV-2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the coronavirus disease 2019 (COVID-19) pandemic that has caused disastrous effects on the society and human health globally. SARS-CoV-2 is a sarbecovirus in the Coronaviridae family with a positive-sense single-stranded RNA genome. It mainly replicates in the cytoplasm and viral components including RNAs and proteins can be sensed by pattern recognition receptors including toll-like receptors (TLRs), RIG-I-like receptors (RLRs), and NOD-like receptors (NLRs) that regulate the host innate and adaptive immune responses. On the other hand, the SARS-CoV-2 genome encodes multiple proteins that can antagonize the host immune response to facilitate viral replication. In this review, we discuss the current knowledge on host sensors and viral countermeasures against host innate immune response to provide insights on virus-host interactions and novel approaches to modulate host inflammation and antiviral responses.

Differential Cellular Sensing of Fusion from within and Fusion from without during Virus Infection

The physical entry of virus particles into cells triggers an innate immune response that is dependent on both calcium and nucleic acid sensors, with particles containing RNA or DNA genomes detected by RNA or DNA sensors, respectively. While membrane fusion in the absence of viral nucleic acid causes an innate immune response that is dependent on calcium, the involvement of nucleic acid sensors is poorly understood. Here, we used lipoplexes containing purified reovirus p14 fusion protein as a model of exogenous or fusion from without and a cell line expressing inducible p14 protein as a model of endogenous or fusion from within to examine cellular membrane fusion sensing events. We show that the cellular response to membrane fusion in both models is dependent on calcium, IRF3 and IFN. The method of sensing fusion, however, differs between fusion from without and fusion from within. Exogenous p14 lipoplexes are detected by RIG-I-like RNA sensors, whereas fusion by endogenous p14 requires both RIG-I and STING to trigger an IFN response. The source of nucleic acid that is sensed appears to be cellular in origin. Future studies will investigate the source of endogenous nucleic acids recognized following membrane fusion events.

Current understanding of the cGAS-STING signaling pathway: Structure, regulatory mechanisms, and related diseases

The innate immune system protects the host from external pathogens and internal damage in various ways. The cGAS-STING signaling pathway, comprised of cyclic GMP-AMP synthase (cGAS), stimulator of interferon genes (STING), and downstream signaling adaptors, plays an essential role in protective immune defense against microbial DNA and internal damaged-associated DNA and is responsible for various immune-related diseases. After binding with DNA, cytosolic cGAS undergoes conformational change and DNA-linked liquid-liquid phase separation to produce 2'3'-cGAMP for the activation of endoplasmic reticulum (ER)-localized STING. However, further studies revealed that cGAS is predominantly expressed in the nucleus and strictly tethered to chromatin to prevent binding with nuclear DNA, and functions differently from cytosolic-localized cGAS. Detailed delineation of this pathway, including its structure, signaling, and regulatory mechanisms, is of great significance to fully understand the diversity of cGAS-STING activation and signaling and will be of benefit for the treatment of inflammatory diseases and cancer. Here, we review recent progress on the above-mentioned perspectives of the cGAS-STING signaling pathway and discuss new avenues for further study.

Inosine: A broad-spectrum anti-inflammatory against SARS-CoV-2 infection-induced acute lung injury via suppressing TBK1 phosphorylation

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-induced cytokine storms constitute the primary cause of coronavirus disease 19 (COVID-19) progression, severity, criticality, and death. Glucocorticoid and anti-cytokine therapies are frequently administered to treat COVID-19, but have limited clinical efficacy in severe and critical cases. Nevertheless, the weaknesses of these treatment modalities have prompted the development of anti-inflammatory therapy against this infection. We found that the broad-spectrum anti-inflammatory agent inosine downregulated proinflammatory interleukin (IL)-6, upregulated anti-inflammatory IL-10, and ameliorated acute inflammatory lung injury caused by multiple infectious agents. Inosine significantly improved survival in mice infected with SARS-CoV-2. It indirectly impeded TANK-binding kinase 1 (TBK1) phosphorylation by binding stimulator of interferon genes (STING) and glycogen synthase kinase-3β (GSK3β), inhibited the activation and nuclear translocation of the downstream transcription factors interferon regulatory factor (IRF3) and nuclear factor kappa B (NF-κB), and downregulated IL-6 in the sera and lung tissues of mice infected with lipopolysaccharide (LPS), H1N1, or SARS-CoV-2. Thus, inosine administration is feasible for clinical anti-inflammatory therapy against severe and critical COVID-19. Moreover, targeting TBK1 is a promising strategy for inhibiting cytokine storms and mitigating acute inflammatory lung injury induced by SARS-CoV-2 and other infectious agents.

SARS-CoV-2, HIV, and HPV: Convergent evolution of selective regulation of cGAS-STING signaling

Recognizing aberrant cytoplasmic double-stranded DNA and stimulating innate immunity is essential for the host's defense against viruses and tumors. Cyclic GMP-AMP (cGAMP) synthase (cGAS) is a cytosolic DNA sensor that synthesizes the second messenger 2'3'-cGAMP and subsequently activates stimulator of interferon genes (STING)-mediated activation of TANK-binding kinase 1 (TBK1)/interferon regulatory factor 3 (IRF3) and the production of type I interferon (IFN-I). Both the cGAS-STING-mediated IFN-I antiviral defense and the countermeasures developed by diverse viruses have been extensively studied. However, recent studies have revealed a convergent evolutionary feature of severe acute respiratory syndrome coronavirus 2 and human immunodeficiency virus (HIV) viral proteins in terms of the selective regulation of cGAS-STING-mediated nuclear factor-κB (NF-κB) signaling without any effect on cGAS-STING-mediated TBK1/IRF3 activation and IFN production. The potential beneficial effect of this cGAS-STING-mediated, NF-κB-dependent antiviral effect, and the possible detrimental effect of IFN-I in the pathogenesis of coronavirus disease 2019 and HIV infection deserve more attention and future investigation.

Duck cGAS inhibits DNA and RNA virus replication by activating IFNs and antiviral ISGs

Cyclic GMP-AMP Synthase (cGAS) is a pivotal adaptor of the signaling pathways involving the pattern recognition receptors and plays an important role in apoptosis and immune regulation. The cGAS function in mammals has been investigated extensively; however, the function of duck cGAS (du-cGAS) in response to viral infections is still unclear. This study aimed to clone the mallard (Anas platyrhynchos) cGAS homolog to investigate the function of duck cGAS (du-cGAS) in host antiviral innate immunity. The results showed that the open reading frame (ORF) region of the du-cGAS gene was 1296 bp, encoding 432 amino acids (aa) and exhibiting similar functional domains with its chicken counterpart. Knockdown of the endogenous du-cGAS by specific sgRNA strongly increased the replication of DNA viruses, including duck adenovirus B2 (DAdV B2) and duck short beak and dwarfism syndrome virus (SBDSV). However, the knockout did not impair the replication of novel duck reovirus (NDRV), an RNA virus. Furthermore, the mRNA expressions of type I interferon (IFNs) and vital interferon-stimulated genes (ISGs) were remarkably reduced in the du-cGAS knockout DEF cell line. Inversely, du-cGAS overexpression greatly activated the transcription of IFN-α, IFN-β, and vital ISGs, and impaired the replication of DAdV B2, SBDSV, and NDRV in the DEF cell line. Importantly, we found that a deletion of 68 aa in the N terminus didn't impair the antiviral function of du-cGAS. Overexpressing NTase Core, C-Domain (Mab21), or Zinc-Ribbon domain independently had no antiviral effects. Generally, these results reveal that du-cGAS is a vital component of the innate immune system of ducks, with a universal antiviral activity, and provides a useful strategy for the control of waterfowl viral diseases.

Emerging toolset of three-dimensional pulmonary cell culture models for simulating lung pathophysiology towards mechanistic elucidation and therapeutic treatment of SARS-COV-2 infection

The ongoing COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) poses a never before seen challenge to human health and the world economy. However, it is difficult to widely use conventional animal and cell culture models in understanding the underlying pathological mechanisms of COVID-19, which in turn hinders the development of relevant therapeutic treatments, including drugs. To overcome this challenge, various three-dimensional (3D) pulmonary cell culture models such as organoids are emerging as an innovative toolset for simulating the pathophysiology occurring in the respiratory system, including bronchial airways, alveoli, capillary network, and pulmonary interstitium, which provide a robust and powerful platform for studying the process and underlying mechanisms of SARS-CoV-2 infection among the potential primary targets in the lung. This review introduces the key features of some of these recently developed tools, including organoid, lung-on-a-chip, and 3D bioprinting, which can recapitulate different structural compartments of the lung and lung function, in particular, accurately resembling the human-relevant pathophysiology of SARS-CoV-2 infection in vivo. In addition, the recent progress in developing organoids for alveolar and airway disease modeling and their applications for discovering drugs against SARS-CoV-2 infection are highlighted. These innovative 3D cell culture models together may hold the promise to fully understand the pathogenesis and eventually eradicate the pandemic of COVID-19.

Involvement of the STING signaling in COVID-19

The coronavirus disease 2019 (COVID-19) pandemic caused by the infection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has cast a notorious damage to the public health and global economy. The Stimulator of Interferon Genes (STING) is a crucial element of the host antiviral pathway and plays a pivotal but complex role in the infection and development of COVID-19. Herein, we discussed the antagonistic mechanism of viral proteins to the STING pathway as well as its activation induced by host cells. Specifically, we highlighted that the persistent activation of STING by SARS-CoV-2 led to abnormal inflammation, and STING inhibitors could reduce the excessive inflammation. In addition, we also emphasized that STING agonists possessed antiviral potency against diverse coronavirus and showed adjuvant efficacy in SARS-CoV-2 vaccines by inducing IFN responses.

Progress of cGAS-STING signaling in response to SARS-CoV-2 infection

Coronavirus disease 2019 (COVID-19) is an epidemic respiratory disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that can cause infections in millions of individuals, who can develop lung injury, organ failure, and subsequent death. As the first line of host defense, the innate immune system is involved in initiating the immune response to SARS-CoV-2 infection and the hyperinflammatory phenotype of COVID-19. However, the interplay between SARS-CoV-2 and host innate immunity is not yet well understood. It had become known that the cGAS-STING pathway is involved in the detection of cytosolic DNA, which elicits an innate immune response involving a robust type I interferon response against viral and bacterial infections. Nevertheless, several lines of evidence indicate that SARS-CoV-2, a single-stranded positive-sense RNA virus, triggered the cGAS-STING signaling pathway. Therefore, understanding the molecular and cellular details of cGAS-STING signaling upon SARS-CoV-2 infection is of considerable biomedical importance. In this review, we discuss the role of cGAS-STING signaling in SARS-CoV-2 infection and summarize the potential therapeutics of STING agonists as virus vaccine adjuvants.

The effect of the cyclic GMP-AMP synthase-stimulator of interferon genes signaling pathway on organ inflammatory injury and fibrosis

The cyclic GMP-AMP synthase-stimulator of interferon genes signal transduction pathway is critical in innate immunity, infection, and inflammation. In response to pathogenic microbial infections and other conditions, cyclic GMP-AMP synthase (cGAS) recognizes abnormal DNA and initiates a downstream type I interferon response. This paper reviews the pathogenic mechanisms of stimulator of interferon genes (STING) in different organs, including changes in fibrosis-related biomarkers, intending to systematically investigate the effect of the cyclic GMP-AMP synthase-stimulator of interferon genes signal transduction in inflammation and fibrosis processes. The effects of stimulator of interferon genes in related auto-inflammatory and neurodegenerative diseases are described in this article, in addition to the application of stimulator of interferon genes-related drugs in treating fibrosis.

Role of SARS-CoV-2-induced Cytokine Storm in Multi-Organ Failure: Molecular Pathways and Potential Therapeutic Options

Coronavirus disease 2019 (COVID-19) outbreak has become a global public health emergency and has led to devastating results. Mounting evidence proposes that the disease causes severe pulmonary involvement and influences different organs, leading to a critical situation named multi-organ failure. It is yet to be fully clarified how the disease becomes so deadly in some patients. However, it is proven that a condition called “cytokine storm” is involved in the deterioration of COVID-19. Although beneficial, sustained production of cytokines and overabundance of inflammatory mediators causing cytokine storm can lead to collateral vital organ damages. Furthermore, cytokine storm can cause post-COVID-19 syndrome (PCS), an important cause of morbidity after the acute phase of COVID-19. Herein, we aim to explain the possible pathophysiology mechanisms involved in COVID-19-related cytokine storm and its association with multi-organ failure and PCS. We also discuss the latest advances in finding the potential therapeutic targets to control cytokine storm wishing to answer unmet clinical demands for treatment of COVID-19.

SARS-CoV-2 ORF10 antagonizes STING-dependent interferon activation and autophagy

A characteristic feature of COVID-19, the disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, is the dysregulated immune response with impaired type I and III interferon (IFN) expression and an overwhelming inflammatory cytokine storm. RIG-I-like receptors (RLRs) and cGAS-STING signaling pathways are responsible for sensing viral infection and inducing IFN production to combat invading viruses. Multiple proteins of SARS-CoV-2 have been reported to modulate the RLR signaling pathways to achieve immune evasion. Although SARS-CoV-2 infection also activates the cGAS-STING signaling by stimulating micronuclei formation during the process of syncytia, whether SARS-CoV-2 modulates the cGAS-STING pathway requires further investigation. Here, we screened 29 SARS-CoV-2-encoded viral proteins to explore the viral proteins that affect the cGAS-STING signaling pathway and found that SARS-CoV-2 open reading frame 10 (ORF10) targets STING to antagonize IFN activation. Overexpression of ORF10 inhibits cGAS-STING-induced interferon regulatory factor 3 phosphorylation, translocation, and subsequent IFN induction. Mechanistically, ORF10 interacts with STING, attenuates the STING-TBK1 association, and impairs STING oligomerization and aggregation and STING-mediated autophagy; ORF10 also prevents the endoplasmic reticulum (ER)-to-Golgi trafficking of STING by anchoring STING in the ER. Taken together, these findings suggest that SARS-CoV-2 ORF10 impairs the cGAS-STING signaling by blocking the translocation of STING and the interaction between STING and TBK1 to antagonize innate antiviral immunity.

Revisiting potential value of antitumor drugs in the treatment of COVID-19

Since an outbreak started in China in 2019, coronavirus disease 2019 (COVID-19) has rapidly become a worldwide epidemic with high contagiousness and caused mass mortalities of infected cases around the world. Currently, available treatments for COVID-19, including supportive care, respiratory support and antiviral therapy, have shown limited efficacy. Thus, more effective therapeutic modalities are highly warranted. Drug repurposing, as an efficient strategy to explore a potential broader scope of the application of approved drugs beyond their original indications, accelerates the process of discovering safe and effective agents for a given disease. Since the outbreak of COVID-19 pandemic, drug repurposing strategy has been widely used to discover potential antiviral agents, and some of these drugs have advanced into clinical trials. Antitumor drugs compromise a vast variety of compounds and exhibit extensive mechanism of action, showing promising properties in drug repurposing. In this review, we revisit the potential value of antitumor drugs in the treatment of COVID-19 and systematically discuss their possible underlying mechanisms of the antiviral actions.

SARS-CoV-2 ORF3a inhibits cGAS-STING-mediated autophagy flux and antiviral function

Recognizing aberrant cytoplasmic dsDNA and stimulating cGAS-STING-mediated innate immunity is essential for the host defense against viruses. Recent studies have reported that SARS-CoV-2 infection, responsible for the COVID-19 pandemic, triggers cGAS-STING activation. cGAS-STING activation can trigger IRF3-Type I interferon (IFN) and autophagy-mediated antiviral activity. Although viral evasion of STING-triggered IFN-mediated antiviral function has been well studied, studies concerning viral evasion of STING-triggered autophagy-mediated antiviral function are scarce. In the present study, we have discovered that SARS-CoV-2 ORF3a is a unique viral protein that can interact with STING and disrupt the STING-LC3 interaction, thus blocking cGAS-STING-induced autophagy but not IRF3-Type I IFN induction. This novel function of ORF3a, distinct from targeting autophagosome-lysosome fusion, is a selective inhibition of STING-triggered autophagy to facilitate viral replication. We have also found that activation of bat STING can induce autophagy and antiviral activity despite its defect in IFN induction. Furthermore, ORF3a from bat coronaviruses can block bat STING-triggered autophagy and antiviral function. Interestingly, the ability to inhibit STING-induced autophagy appears to be an acquired function of SARS-CoV-2 ORF3a, since SARS-CoV ORF3a lacks this function. Taken together, these discoveries identify ORF3a as a potential target for intervention against COVID-19.

Regulation of cGAS/STING signaling and corresponding immune escape strategies of viruses

Innate immunity is the first line of defense against invading external pathogens, and pattern recognition receptors (PRRs) are the key receptors that mediate the innate immune response. Nowadays, there are various PRRs in cells that can activate the innate immune response by recognizing pathogen-related molecular patterns (PAMPs). The DNA sensor cGAS, which belongs to the PRRs, plays a crucial role in innate immunity. cGAS detects both foreign and host DNA and generates a second-messenger cGAMP to mediate stimulator of interferon gene (STING)-dependent antiviral responses, thereby exerting an antiviral immune response. However, the process of cGAS/STING signaling is regulated by a wide range of factors. Multiple studies have shown that viruses directly target signal transduction proteins in the cGAS/STING signaling through viral surface proteins to impede innate immunity. It is noteworthy that the virus utilizes these cGAS/STING signaling regulators to evade immune surveillance. Thus, this paper mainly summarized the regulatory mechanism of the cGAS/STING signaling pathway and the immune escape mechanism of the corresponding virus, intending to provide targeted immunotherapy ideas for dealing with specific viral infections in the future.

Role of the cGAS-STING pathway in systemic and organ-specific diseases

Cells are equipped with numerous sensors that recognize nucleic acids, which probably evolved for defence against viruses. Once triggered, these sensors stimulate the production of type I interferons and other cytokines that activate immune cells and promote an antiviral state. The evolutionary conserved enzyme cyclic GMP-AMP synthase (cGAS) is one of the most recently identified DNA sensors. Upon ligand engagement, cGAS dimerizes and synthesizes the dinucleotide second messenger 2',3'-cyclic GMP-AMP (cGAMP), which binds to the endoplasmic reticulum protein stimulator of interferon genes (STING) with high affinity, thereby unleashing an inflammatory response. cGAS-binding DNA is not restricted by sequence and must only be >45 nucleotides in length; therefore, cGAS can also be stimulated by self genomic or mitochondrial DNA. This broad specificity probably explains why the cGAS-STING pathway has been implicated in a number of autoinflammatory, autoimmune and neurodegenerative diseases; this pathway might also be activated during acute and chronic kidney injury. Therapeutic manipulation of the cGAS-STING pathway, using synthetic cyclic dinucleotides or inhibitors of cGAMP metabolism, promises to enhance immune responses in cancer or viral infections. By contrast, inhibitors of cGAS or STING might be useful in diseases in which this pro-inflammatory pathway is chronically activated.

SARS-CoV-2 and the Nucleus

The ongoing COVID-19 pandemic is caused by an RNA virus, SARS-CoV-2. The genome of SARS-CoV-2 lacks a nuclear phase in its life cycle and is replicated in the cytoplasm. However, interfering with nuclear trafficking using pharmacological inhibitors greatly reduces virus infection and virus replication of other coronaviruses is blocked in enucleated cells, suggesting a critical role of the nucleus in virus infection. Here, we summarize the alternations of nuclear pathways caused by SARS-CoV-2, including nuclear translocation pathways, innate immune responses, mRNA metabolism, epigenetic mechanisms, DNA damage response, cytoskeleton regulation, and nuclear rupture. We consider how these alternations contribute to virus replication and discuss therapeutic treatments that target these pathways, focusing on small molecule drugs that are being used in clinical studies.

Roles of RNA Sensors in Host Innate Response to Influenza Virus and Coronavirus Infections

Influenza virus and coronavirus are two important respiratory viruses, which often cause serious respiratory diseases in humans and animals after infection. In recent years, highly pathogenic avian influenza virus (HPAIV) and SARS-CoV-2 have become major pathogens causing respiratory diseases in humans. Thus, an in-depth understanding of the relationship between viral infection and host innate immunity is particularly important to the stipulation of effective control strategies. As the first line of defense against pathogens infection, innate immunity not only acts as a natural physiological barrier, but also eliminates pathogens through the production of interferon (IFN), the formation of inflammasomes, and the production of pro-inflammatory cytokines. In this process, the recognition of viral pathogen-associated molecular patterns (PAMPs) by host pattern recognition receptors (PRRs) is the initiation and the most important part of the innate immune response. In this review, we summarize the roles of RNA sensors in the host innate immune response to influenza virus and coronavirus infections in different species, with a particular focus on innate immune recognition of viral nucleic acids in host cells, which will help to develop an effective strategy for the control of respiratory infectious diseases.

Additional Evidence for Commonalities between COVID-19 and Radiation Injury: Novel Insight into COVID-19 Candidate Drugs

COVID-19 is a challenge to biosecurity and public health. The speed of vaccine development lags behind that of virus evolution and mutation. To date, no agent has been demonstrated to be fully effective against COVID-19. Therefore, it remains of great urgency to rapidly develop promising therapeutic and diagnostic candidates. Intriguingly, mounting evidence hints at parallel etiologies between SARS-CoV-2 infection and radiation injury. Herein, from the perspectives of immunogenic pathway activation and metabolic alterations, we provide novel evidence of commonalities between these two pathological conditions based on the most recent findings. Since numerous agents have been developed to prevent or reverse radiation injury in the past 70 years to ensure nuclear safety, we also advocate investigating the promising function of radioprotectors and radiomitigators against COVID-19 in clinical settings.

SARS-CoV-2 spike and nucleocapsid proteins fail to activate human dendritic cells or γδ T cells

γδ T cells are thought to contribute to immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but the mechanisms by which they are activated by the virus are unknown. Using flow cytometry, we investigated if the two most abundant viral structural proteins, spike and nucleocapsid, can activate human γδ T cell subsets, directly or in the presence of dendritic cells (DC). Both proteins failed to induce interferon-γ production by Vδ1 or Vδ2 T cells within fresh mononuclear cells or lines of expanded γδ T cells generated from healthy donors, but the same proteins stimulated CD3⁺ cells from COVID-19 patients. The nucleocapsid protein stimulated interleukin-12 production by DC and downstream interferon-γ production by co-cultured Vδ1 and Vδ2 T cells, but protease digestion and use of an alternative nucleocapsid preparation indicated that this activity was due to contaminating non-protein material. Thus, SARS-CoV-2 spike and nucleocapsid proteins do not have stimulatory activity for DC or γδ T cells. We propose that γδ T cell activation in COVID-19 patients is mediated by immune recognition of viral RNA or other structural proteins by γδ T cells, or by other immune cells, such as DC, that produce γδ T cell-stimulatory ligands or cytokines.

Interplay of cGAS with micronuclei: Regulation and diseases

In higher eukaryotes, sophisticate regulation of genome function requires all chromosomes to be packed into a single nucleus. Micronucleus (MN), the dissociative nucleus-like structure frequently observed in aging and multiple disease settings, has critical, yet under-recognized, pathophysiological functions. Micronuclei (MNi) have recently emerged as major sources of cytosolic DNA that can activate the cGAS-STING axis in a cell-intrinsic manner. However, MNi induced from different genotoxic stressors display great heterogeneity in binding or activating cGAS and the signaling responses downstream of the MN-induced cGAS-STING axis have divergent outcomes including autoimmunity, autoinflammation, metastasis, or cell death. Thus, full characterization of molecular network underpinning the interplay of cGAS and MN is important to elucidate the pathophysiological roles of immunogenic MN and design improved drugs that selectively target cancer via boosting the MN-derived cGAS-STING axis. Here, we summarize our current understanding of the mechanisms for self-DNA discrimination by cGAS. We focus on discussing how MN immunogencity is dictated by multiple mechanisms including integrity of micronuclear envelope, state of nucleosome and DNA, competitive factors, damaged mitochondrial DNA and micronucleophagy. We also describe emerging links between immunogenic MN and human diseases including cancer, neurodegenerative diseases and COVID-19. Particularly, we explore the exciting concept of inducing immunogenic MN as a therapeutic approach in treating cancer. We propose a new theoretical framework to describe immunogenic MN as a biological sensor to modulate cellular processes in response to genotoxic stress and provide perspectives on developing novel experimental approaches to unravel the complexity of MN immunogenicity regulation and immunogenic MN pathophysiology.

Therapy Targets SARS-CoV-2 Infection-Induced Cell Death

Coronavirus Disease 2019 (COVID-19) caused by SARS-CoV-2 has become a global health issue. The clinical presentation of COVID-19 is highly variable, ranging from asymptomatic and mild disease to severe. However, the mechanisms for the high mortality induced by SARS-CoV-2 infection are still not well understood. Recent studies have indicated that the cytokine storm might play an essential role in the disease progression in patients with COVID-19, which is characterized by the uncontrolled release of cytokines and chemokines leading to acute respiratory distress syndrome (ARDS), multi-organ failure, and even death. Cell death, especially, inflammatory cell death, might be the initiation of a cytokine storm caused by SARS-CoV-2 infection. This review summarizes the forms of cell death caused by SARS-CoV-2 in vivo or in vitro and elaborates on the dedication of apoptosis, necroptosis, NETosis, pyroptosis of syncytia, and even SARS-CoV-2 E proteins forming channel induced cell death, providing insights into targets on the cell death pathway for the treatment of COVID-19.

Long-range enhancement of N501Y-endowed mouse infectivity of SARS-CoV-2 by the non-RBD mutations of Ins215KLRS and H655Y

Background

Rodents, such as mice, are vulnerable targets, and potential intermediate hosts, of SARS-CoV-2 variants of concern, including Alpha, Beta, Gamma, and Omicron. N501Y in the receptor-binding domain (RBD) of Spike protein is the key mutation dictating the mouse infectivity, on which the neighboring mutations within RBD have profound impacts. However, the impacts of mutations outside RBD on N501Y-mediated mouse infectivity remain to be explored.

Results

Herein, we report that two non-RBD mutations derived from mouse-adapted strain, Ins215KLRS in the N-terminal domain (NTD) and H655Y in the subdomain linking S1 to S2, enhance mouse infectivity in the presence of N501Y mutation, either alone or together. This is associated with increased interaction of Spike with mouse ACE2 and mutations-induced local conformation changes in Spike protein. Mechanistically, the H655Y mutation disrupts interaction with N657, resulting in a less tight loop that wraps the furin-cleavage finger; and the insertion of 215KLRS in NTD increases its intramolecular interaction with a peptide chain that interfaced with the RBD-proximal region of the neighboring protomer, leading to a more flexible RBD that facilitates receptor binding. Moreover, the Omicron Spike that contains Ins214EPE and H655Y mutations confer mouse infectivity > 50 times over the N501Y mutant, which could be effectively suppressed by mutating them back to wild type.

Conclusions

Collectively, our study sheds light on the cooperation between distant Spike mutations in promoting virus infectivity, which may undermine the high infectiousness of Omicron variants towards mice.

Supplementary information

The online version contains supplementary material available at 10.1186/s13062-022-00325-x.

Immune response in COVID-19: what is next?

The coronavirus disease 2019 (COVID-19) has been a global pandemic for more than 2 years and it still impacts our daily lifestyle and quality in unprecedented ways. A better understanding of immunity and its regulation in response to SARS-CoV-2 infection is urgently needed. Based on the current literature, we review here the various virus mutations and the evolving disease manifestations along with the alterations of immune responses with specific focuses on the innate immune response, neutrophil extracellular traps, humoral immunity, and cellular immunity. Different types of vaccines were compared and analyzed based on their unique properties to elicit specific immunity. Various therapeutic strategies such as antibody, anti-viral medications and inflammation control were discussed. We predict that with the available and continuously emerging new technologies, more powerful vaccines and administration schedules, more effective medications and better public health measures, the COVID-19 pandemic will be under control in the near future.

Post-Translational Modifications of STING: A Potential Therapeutic Target

Stimulator of interferon genes (STING) is an endoplasmic-reticulum resident protein, playing essential roles in immune responses against microbial infections. However, over-activation of STING is accompanied by excessive inflammation and results in various diseases, including autoinflammatory diseases and cancers. Therefore, precise regulation of STING activities is critical for adequate immune protection while limiting abnormal tissue damage. Numerous mechanisms regulate STING to maintain homeostasis, including protein-protein interaction and molecular modification. Among these, post-translational modifications (PTMs) are key to accurately orchestrating the activation and degradation of STING by temporarily changing the structure of STING. In this review, we focus on the emerging roles of PTMs that regulate activation and inhibition of STING, and provide insights into the roles of the PTMs of STING in disease pathogenesis and as potential targeted therapy.

SARS-CoV-2 Variants, Vaccines, and Host Immunity

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a new beta coronavirus that emerged at the end of 2019 in the Hubei province of China. SARS-CoV-2 causes coronavirus disease 2019 (COVID-19) and was declared a pandemic by the World Health Organization (WHO) on 11 March 2020. Herd or community immunity has been proposed as a strategy to protect the vulnerable, and can be established through immunity from past infection or vaccination. Whether SARS-CoV-2 infection results in the development of a reservoir of resilient memory cells is under investigation. Vaccines have been developed at an unprecedented rate and 7 408 870 760 vaccine doses have been administered worldwide. Recently emerged SARS-CoV-2 variants are more transmissible with a reduced sensitivity to immune mechanisms. This is due to the presence of amino acid substitutions in the spike protein, which confer a selective advantage. The emergence of variants therefore poses a risk for vaccine effectiveness and long-term immunity, and it is crucial therefore to determine the effectiveness of vaccines against currently circulating variants. Here we review both SARS-CoV-2-induced host immune activation and vaccine-induced immune responses, highlighting the responses of immune memory cells that are key indicators of host immunity. We further discuss how variants emerge and the currently circulating variants of concern (VOC), with particular focus on implications for vaccine effectiveness. Finally, we describe new antibody treatments and future vaccine approaches that will be important as we navigate through the COVID-19 pandemic.