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Dampened STING-Dependent Interferon Activation in Bats
Abstract
Compared with terrestrial mammals, bats have a longer lifespan and greater capacity to co-exist with a variety of viruses. In addition to cytosolic DNA generated by these viral infections, the metabolic demands of flight cause DNA damage and the release of self-DNA into the cytoplasm. However, whether bats have an altered DNA sensing/defense system to balance high cytosolic DNA levels remains an open question. We demonstrate that bats have a dampened interferon response due to the replacement of the highly conserved serine residue (S358) in STING, an essential adaptor protein in multiple DNA sensing pathways. Reversing this mutation by introducing S358 restored STING functionality, resulting in interferon activation and virus inhibition. Combined with previous reports on bat-specific changes of other DNA sensors such as TLR9, IFI16, and AIM2, our findings shed light on bat adaptation to flight, their long lifespan, and their unique capacity to serve as a virus reservoir.
... Flight is highly metabolic demanding and generates harmful free-radical byproducts that damage biologically relevant molecules s u c h a s D N A ( 1 4 ) . T o r e d u c e s e l f -D N Am e d i a t e d immunopathology, bats have evolved DNA repair mechanisms (9) and dampened endogenous DNA-sensing pathways (15,16). In addition, genome-wide comparisons across bat species have revealed unique gene losses in bats that downregulate inflammasome pathways in three main areas: the natural killer (NK) gene complex, epithelial defense receptors, and the interferon (IFN)-g-induced pathway (9,15,17,18). ...
... However, most research on the bat immune response to intracellular pathogens has focused on RNA viruses, whereas DNA viruses remain poorly understood. Although sensing mechanisms for DNA viruses may be dampened in bats [PYHIN family (15) and STING (16)], bats must evolve new ways of detecting exogenous and endogenous DNA, as DNA viruses have been detected and isolated in many bat species (26, 27). Additionally, bat immune responses against other intracellular pathogens (e.g., many bacteria) and extracellular pathogens (e.g., many protozoa) are even less studied. ...
... Interestingly, herpesvirus infections, but not a-CoV infections, also elicited downregulation of leukocyte-mediated immunity and upregulation of mitogen-activated protein kinase (MAPK) cascades and the inflammatory and humoral response. Besides the particularity of herpesviruses to persist in the host as latent infections (80), studies suggest that bat responses to DNA viruses are dampened in contrast to RNA viruses (15,16,104), potentially explaining our observed patterns. DNA viruses are known to usurp the MAPK signaling pathway to exploit DNA replication machinery, induce cell proliferation, and prevent cell death in response to pathogen recognition (105). ...
Bats carry many zoonotic pathogens without showing pronounced pathology, with a few exceptions. The underlying immune tolerance mechanisms in bats remain poorly understood, although information-rich omics tools hold promise for identifying a wide range of immune markers and their relationship with infection. To evaluate the generality of immune responses to infection, we assessed the differences and similarities in serum proteomes of wild vampire bats (Desmodus rotundus) across infection status with five taxonomically distinct pathogens: bacteria (Bartonella spp., hemoplasmas), protozoa (Trypanosoma cruzi), and DNA (herpesviruses) and RNA (alphacoronaviruses) viruses. From 19 bats sampled in 2019 in Belize, we evaluated the up- and downregulated immune responses of infected versus uninfected individuals for each pathogen. Using a high-quality genome annotation for vampire bats, we identified 586 serum proteins but found no evidence for differential abundance nor differences in composition between infected and uninfected bats. However, using receiver operating characteristic curves, we identified four to 48 candidate biomarkers of infection depending on the pathogen, including seven overlapping biomarkers (DSG2, PCBP1, MGAM, APOA4, DPEP1, GOT1, and IGFALS). Enrichment analysis of these proteins revealed that our viral pathogens, but not the bacteria or protozoa studied, were associated with upregulation of extracellular and cytoplasmatic secretory vesicles (indicative of viral replication) and downregulation of complement activation and coagulation cascades. Additionally, herpesvirus infection elicited a downregulation of leukocyte-mediated immunity and defense response but an upregulation of an inflammatory and humoral immune response. In contrast to our two viral infections, we found downregulation of lipid and cholesterol homeostasis and metabolism with Bartonella spp. infection, of platelet-dense and secretory granules with hemoplasma infection, and of blood coagulation pathways with T. cruzi infection. Despite the small sample size, our results suggest that vampire bats have a similar suite of immune mechanisms for viruses distinct from responses to the other pathogen taxa, and we identify potential biomarkers that can expand our understanding of pathogenesis of these infections in bats. By applying a proteomic approach to a multi-pathogen system in wild animals, our study provides a distinct framework that could be expanded across bat species to increase our understanding of how bats tolerate pathogens.
... A potential repressor binding motif (c-Rel) was identified in E. fuscus that limits the levels of bat TNFa transcripts and thus inhibits inflammatory pathologies (Banerjee et al., 2017). Other observations to match this include the absence of PYHIN proteins (Ahn et al., 2016), sometimes linked to IFN cascade (Xie et al., 2018), and suppression of a central inflammasome sensor, NLR family pyrin domain containing 3 (NLRP3), via a novel splice variant and alterations in the leucine-rich repeat domain leading to suppressed function of NLRP3 in addition to repressed transcription . ...
... In most human cells, the cyclic GMP-AMP receptor stimulator of interferon genes (cGAS-STING) signaling pathway detects the cytoplasmic DNA from pathogens to upregulate ISGs and drive inflammation (Hopfner and Hornung, 2020). Loss of S358 in bat STING results in a diminished ability to induce interferon and therefore ISGs (Xie et al., 2018). High-speed flight in bats and flight-induced hyperthermia may potentially cause more cellular damage in bats, producing an increase in cytosolic DNA (Hock, 1951;Banerjee et al., 2020b). ...
... All other mammals have at least one gene member of the PYHIN family, with only bats having lost the entire family of genes (Ahn et al., 2016). This absence of the PYHIN family in bats, still observed with newly released genomes, limits the activation of inflammatory responses from DNA damage, in addition to minimizing ISG induction from cytosolic DNA, as observed in other species via IFI16/IFI207 and related family members (Xie et al., 2018;Baran et al., 2023). A large-scale genomic screen of bats further confirmed that these genes are deleted in bats (Moreno Santillań et al., 2021). ...
The interferon pathway is the first line of defense in viral infection in all mammals, and its induction stimulates broad expression of interferon-stimulated genes (ISGs). In mice and also humans, the antiviral function of ISGs has been extensively studied. As an important viral reservoir in nature, bats can coexist with a variety of pathogenic viruses without overt signs of disease, yet only limited data are available for the role of ISGs in bats. There are multiple species of bats and work has begun deciphering the differences and similarities between ISG function of human/mouse and different bat species. This review summarizes the current knowledge of conserved and bat-specific-ISGs and their known antiviral effector functions.
... This means that the host usually carries a low viral load and is able to tolerate some viral replication. Studies have shown that bats have unique immunological approaches to enable coexistence with viral infections, causing no disease, while allowing enough viral replication for transmission (30)(31)(32). Screening the virome for over 4000 healthy bats from 40 different species of both Yangochiroptera and Yinpterochiroptera suborders, revealed an array of viruses belonging to diverse families, the most prevalent being Herpesviridae, Papillomaviridae, Retroviridae, Adenoviridae and Astroviridae, but also Coronaviridae, Caliciviridae, Polyomaviridae, Rhabdoviridae, among others (33), confirming bats as reservoirs of various virus. The unique ability of bats to act as reservoirs is thought to be mediated by a dampening of pro-inflammatory responses (30,32,34) as well as an increased resistance to infection mediated by special features of the antiviral type I interferon (IFN) system [reviewed in (35)]. ...
... Screening the virome for over 4000 healthy bats from 40 different species of both Yangochiroptera and Yinpterochiroptera suborders, revealed an array of viruses belonging to diverse families, the most prevalent being Herpesviridae, Papillomaviridae, Retroviridae, Adenoviridae and Astroviridae, but also Coronaviridae, Caliciviridae, Polyomaviridae, Rhabdoviridae, among others (33), confirming bats as reservoirs of various virus. The unique ability of bats to act as reservoirs is thought to be mediated by a dampening of pro-inflammatory responses (30,32,34) as well as an increased resistance to infection mediated by special features of the antiviral type I interferon (IFN) system [reviewed in (35)]. GBPs are IFN-induced GTPases that have been shown to have vital roles in host immunity to infection and inflammation. ...
Background
GBPs (guanylate binding proteins), an evolutionary ancient protein family, play a key role in the host’s innate immune response against bacterial, parasitic and viral infections. In Humans, seven GBP genes have been described (GBP1-7). Despite the interest these proteins have received over the last years, evolutionary studies have only been performed in primates, Tupaia and rodents. These have shown a pattern of gene gain and loss in each family, indicative of the birth-and-death evolution process.
Results
In this study, we analysed the evolution of this gene cluster in several bat species, belonging to the Yangochiroptera and Yinpterochiroptera sub-orders. Detailed analysis shows a conserved synteny and a gene expansion and loss history. Phylogenetic analysis showed that bats have GBPs 1,2 and 4-6. GBP2 has been lost in several bat families, being present only in Hipposideidae and Pteropodidae. GBPs1, 4 and 5 are present mostly as single-copy genes in all families but have suffered duplication events, particularly in Myotis myotis and Eptesicus fuscus. Most interestingly, we demonstrate that GBP6 duplicated in a Chiroptera ancestor species originating two genes, which we named GBP6a and GBP6b, with different subsequent evolutionary histories. GBP6a underwent several duplication events in all families while GBP6b is present as a single copy gene and has been lost in Pteropodidae, Miniopteridae and Desmodus rotundus, a Phyllostomidae. With 14 and 15 GBP genes, Myotis myotis and Eptesicus fuscus stand out as having far more copies than all other studied bat species. Antagonistically, Pteropodidae have the lowest number of GBP genes in bats.
Conclusion
Bats are important reservoirs of viruses, many of which have become zoonotic diseases in the last decades. Further functional studies on bats GBPs will help elucidate their function, evolutionary history, and the role of bats as virus reservoirs.
... There are data indicating that bats, as the only flight-adapted mammals, have developed methods for reducing inflammation incurred during flight. These include reducing inflammatory cytokines such as TNF 18 , loss of the PYHIN gene family 19 , reduced activation of the NLRP3 inflammasome 20 , downregulation of caspase-1-mediated inflammasome activation 21 , dampened interferon activation as a result of STING mutation 22 , and increased expression of inflammasome-suppressing ASC2 23 . There is also evidence supporting the constitutive expression of innate immune genes, such as interferon-stimulated genes 24,25 , to reduce flight-induced oxidative metabolism and DNA damage 22,26 in bats. ...
... These include reducing inflammatory cytokines such as TNF 18 , loss of the PYHIN gene family 19 , reduced activation of the NLRP3 inflammasome 20 , downregulation of caspase-1-mediated inflammasome activation 21 , dampened interferon activation as a result of STING mutation 22 , and increased expression of inflammasome-suppressing ASC2 23 . There is also evidence supporting the constitutive expression of innate immune genes, such as interferon-stimulated genes 24,25 , to reduce flight-induced oxidative metabolism and DNA damage 22,26 in bats. ...
The intestinal microbiome plays an important role in mammalian health, disease, and immune function. In light of this function, recent studies have aimed to characterize the microbiomes of various bat species, which are noteworthy for their roles as reservoir hosts for several viruses known to be highly pathogenic in other mammals. Despite ongoing bat microbiome research, its role in immune function and disease, especially the effects of changes in the microbiome on host health, remains nebulous. Here, we describe a novel methodology to investigate the intestinal microbiome of captive Jamaican fruit bats (Artibeus jamaicensis). We observed a high degree of individual variation in addition to sex- and cohort-linked differences. The intestinal microbiome was correlated with intestinal metabolite composition, possibly contributing to differences in immune status. This work provides a basis for future infection and field studies to examine in detail the role of the intestinal microbiome in antiviral immunity.
... It is a conserved protein found in various vertebrates and is expressed at various levels in different tissues [15], with higher expression observed in the spleen, pancreas, and lymph nodes in rats [16] and in the lung, spleen, bone marrow, and appendix in humans [17]. Single nucleotide polymorphisms in STING can affect its activity and innate immune responses in humans and bats [18]. ...
... STING is an endoplasmic reticulum membrane protein consisting of 379 amino acids with a molecular weight of 42 kDa. It consists of an N-terminal tail; four transmembrane domains (TMDs), namely, transmembrane (TM1) (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34), TM2 , TM3 (92)(93)(94)(95)(96)(97)(98)(99)(100)(101)(102)(103)(104)(105)(106) and TM4 (117)(118)(119)(120)(121)(122)(123)(124)(125)(126)(127)(128)(129)(130)(131)(132)(133)(134); a ligand-binding domain (LBD); and a CTT [24] ( Figure 1A). The LBD is responsible for binding to cGAMP, which activates STING, and the CTT contains the site of phosphorylation by TBK1 and the binding site for IRF3. ...
The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) is a crucial innate defence mechanism against viral infection in the innate immune system, as it principally induces the production of type I interferons. Immune responses and metabolic control are inextricably linked, and chronic low-grade inflammation promotes the development of metabolic diseases. The cGAS-STING pathway activated by double-stranded DNA (dsDNA), cyclic dinucleotides (CDNs), endoplasmic reticulum stress (ER stress), mitochondrial stress, and energy imbalance in metabolic cells and immune cells triggers proinflammatory responses and metabolic disorders. Abnormal overactivation of the pathway is closely associated with metabolic diseases such as obesity, nonalcoholic fatty liver disease (NAFLD), insulin resistance and cardiovascular diseases (CVDs). The interaction of cGAS-STING with other pathways, such as the nuclear factor-kappa B (NF-κB), Jun N-terminal kinase (JNK), AMP-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), autophagy, pyroptosis and insulin signalling pathways, is considered an important mechanism by which cGAS-STING regulates inflammation and metabolism. This review focuses on the link between immune responses related to the cGAS-STING pathway and metabolic diseases and cGAS-STING interaction with other pathways for mediating signal input and affecting output. Moreover, potential inhibitors of the cGAS-STING pathway and therapeutic prospects against metabolic diseases are discussed. This review provides a comprehensive perspective on the involvement of STING in immune-related metabolic diseases.
... 17 A research group sequenced multiple bat species STING protein in comparison with different mammalian species like humans and mice's STING protein sequences. 55 Across all bat species included in the study, a serine 358 amino acid in the STING protein is substituted with N, H, F, Y, P, D, and R residues. 55 ...
... 55 Across all bat species included in the study, a serine 358 amino acid in the STING protein is substituted with N, H, F, Y, P, D, and R residues. 55 ...
Bat‐borne viruses have attracted considerable research, especially in relation to the Covid‐19 pandemic. Although bats can carry multiple zoonotic viruses that are lethal to many mammalian species, they appear to be asymptomatic to viral infection despite the high viral loads contained in their bodies. There are several differences between bats and other mammals. One of the major differences between bats and other mammals is the bats' ability to fly, which is believed to have induced evolutionary changes. It may have also favoured them as suitable hosts for viruses. This is related to their tolerance to viral infection. Innate immunity is the first line of defence against viral infection, but bats have metamorphosed the type of responses induced by innate immunity factors such as interferons. The expression patterns of interferons differ, as do those of interferon‐related genes such as interferon regulatory factors and interferon‐stimulated genes that contribute to the antiviral response of infected cells. In addition, the signalling pathways related to viral infection and immune responses have been subject to evolutionary changes, including mutations compared to their homologues in other mammals and gene selection. This article discusses the differences in the interferon‐mediated antiviral response in bats compared to that of other mammals and how these differences are correlated to viral tolerance in bats. The effect of bat interferons related genes on human antiviral response against bat‐borne viruses is also discussed.
... The vital role of the cGAS-STING axis in the innate immune response to RNA viruses in humans (Domizio et al., 2022), mice (Yu et al., 2021), pigs (Xu et al., 2021) and other mammals has been described. And homologs of STING have been confirmed in several bat species of Myotis davidii, Rhinolophus sinicus and Pteropus Alecto (Xie et al., 2018). Studies of them have shown that STING-dependent IFN activation is weakened in bats (Xie et al., Frontiers in Microbiology 03 frontiersin.org ...
... In addition, BatSTING-d1-17aa, BatSTING-d1-32aa, and BatSTING-33-43aa, with deletion of only 17, 32, and 10 amino acids at the N-terminal of BatSTING, respectively, also led to a strong decrease in TBK1 and IFN-β induction, which may be related to their problematic intracellular localization. Zhou et al. found that the inhibition of the IFN response in bats was due to the substitution of a highly conserved serine residue (S358) in STING (Xie et al., 2018). To verify whether amino acid at position 358 has the same effect on STING's ability to activate IFN in TB1 Lu cells, we mutated the histidine at position 358 in BatSTING to serine and examined the ability of the mutant to activate IFN-β. ...
The ability of stimulator of interferon genes (STING) to activate interferon (IFN) responses during RNA virus infection has been demonstrated in different mammalian cells. Despite being the host of numerous RNA viruses, the role of STING in bats during RNA virus infection has not been elucidated. In this study, we identified and cloned the STING gene of the Brazilian free-tailed bat Tadarida brasiliensis ( T. brasiliensis ) and tested its ability to induce IFN-β by overexpressing and knocking down bat STING (BatSTING) in T. brasiliensis 1 lung (TB1 Lu) cells. In addition, we used green fluorescent protein (GFP)-labeled vesicular stomatitis virus (VSV) VSV-GFP as a model to detect the antiviral activity of BatSTING. The results showed that overexpression of STING in TB1 Lu cells stimulated by cGAS significantly inhibited RNA virus replication, and the antiviral activities were associated with its ability to regulate basal expression of IFN-β and some IFN stimulated genes (ISGs). We also found that BatSTING was able to be activated after stimulation by diverse RNA viruses. The results of TB1 Lu cells with STING deficiency showed that knockdown of BatSTING severely hindered the IFN-β response triggered by VSV-GFP. Based on this, we confirm that BatSTING is required to induce IFN-β expression during RNA virus infection. In conclusion, our experimental data clearly show that STING in bat hosts plays an irreplaceable role in mediating IFN-β responses and anti-RNA virus infection.
... Molecular studies have also provided insights, shedding light on the potential genetic bases of bat immunity. For example, reduced activation of the stimulator of interferion genes (STING)dependent pathway has been attributed to specific amino acid residues in some bats (13), while constitutive expression of interferonα (IFN-α) in some pteropodids may help maintain a state of preparedness to control viral replication (14). ...
... Despite growing numbers of reports of putative molecular adaptations underlying immunity in bats, few studies have experimentally validated the phenotypic impacts of bat-specific variants (12,18,69). In a notable exception, Xie et al. (13) showed that dampened IFN activation in bats was attributable to the replacement of a conserved S358 residue in the bat STING protein, a key component of several DNA sensing pathways. STING has a role in regulating the NLRP3 inflammasome, and Ahn et al. (10) independently used cellbased assays to show that major bat isoforms of NLRP3 are associated with reduced induction by TLR stimuli. ...
Bats have been identified as natural reservoir hosts of several zoonotic viruses, prompting suggestions that they have unique immunological adaptations. Among bats, Old World fruit bats (Pteropodidae) have been linked to multiple spillovers. To test for lineage-specific molecular adaptations in these bats, we developed a new assembly pipeline to generate a reference-quality genome of the fruit bat Cynopterus sphinx and used this in comparative analyses of 12 bat species, including six pteropodids. Our results reveal that immunity-related genes have higher evolutionary rates in pteropodids than in other bats. Several lineage-specific genetic changes were shared across pteropodids, including the loss of NLRP1, duplications of PGLYRP1 and C5AR2, and amino acid replacements in MyD88. We introduced MyD88 transgenes containing Pteropodidae-specific residues into bat and human cell lines and found evidence of dampened inflammatory responses. By uncovering distinct immune adaptations, our results could help explain why pteropodids are frequently identified as viral hosts.
... Bats carry highly pathogenic viruses without symptoms, which should be attributed to their special innate and adaptive immune responses. The composition and function of Toll-like receptor (13,14), interferon (15), and a variety of innate immune response genes have been preliminary elaborated in bats, and the mechanism of interferon in bats and humans is different (16), suggesting that bats have a stronger innate antiviral response and can control viral replication early (17,18). However, it is not clear what role the adaptive immune response of bats plays in this process. ...
The emergence and re-emergence of abundant viruses from bats that impact human and animal health have resulted in a resurgence of interest in bat immunology. Characterizing the immune receptor repertoire is critical to understanding how bats coexist with viruses in the absence of disease and developing new therapeutics to target viruses in humans and susceptible livestock. In this study, IGH germline genes of Chiroptera including Rhinolophus ferrumequinum , Phyllostomus discolor, and Pipistrellus pipistrellus were annotated, and we profiled the characteristics of Rhinolophus affinis (RA) IGH CDR3 repertoire. The germline genes of Chiroptera are quite different from those of human, mouse, cow, and dog in evolution, but the three bat species have high homology. The CDR3 repertoire of RA is unique in many aspects including CDR3 subclass, V/J genes access and pairing, CDR3 clones, and somatic high-frequency mutation compared with that of human and mouse, which is an important point in understanding the asymptomatic nature of viral infection in bats. This study unveiled a detailed map of bat IGH germline genes on chromosome level and provided the first immune receptor repertoire of bat, which will stimulate new avenues of research that are directly relevant to human health and disease.
IMPORTANCE
The intricate relationship between bats and viruses has been a subject of study since the mid-20th century, with more than 100 viruses identified, including those affecting humans. While preliminary investigations have outlined the innate immune responses of bats, the role of adaptive immunity remains unclear. This study presents a pioneering contribution to bat immunology by unveiling, for the first time, a detailed map of bat IGH germline genes at the chromosome level. This breakthrough not only provides a foundation for B cell receptor research in bats but also contributes to primer design and sequencing of the CDR3 repertoire. Additionally, we offer the first comprehensive immune receptor repertoire of bats, serving as a crucial library for future comparative analyses. In summary, this research significantly advances the understanding of bats’ immune responses, providing essential resources for further investigations into viral tolerance and potential zoonotic threats.
... Bat cell lines have been pivotal for characterizing antiviral responses against virus infections and discovering how these responses differ from their human counterparts [26]. For example, loss of a conserved serine residue, S358 dampened, but did not fully diminish, the function of P. alecto STING; indeed, P. alecto STING induced interferon (IFN)-β (IFNB) transcripts in human kidney cells but comparatively, the effects were less than when using human STING [27]. Similarly, a recent study identified subdued NLRP3 inflammasome activity in MERS-CoV-infected P. alecto-derived primary immune cells, relative to human-derived immune cells (i.e., peripheral blood mononuclear cells); this resulted in less production of the proinflammatory cytokine, IL-1β [28]. ...
... Finally, several mammals, like bats and naked mole-rats, that possess an increased relative, to their size, longevity [172,173] do have important alterations in the axis mitochondria-autophagy-inflammation. For example, bats cells possess increased levels of autophagy [174] and dampened NLRP3 and STING immune responses [175,176], while naked mole-rats have higher levels of signaling activity of Nrf2 [177]. ...
In this manuscript, I discuss the direct link between abnormalities in inflammatory responses, mitochondrial metabolism and autophagy during the process of aging. It is focused on the cytosolic receptors nucleotide-binding domain, leucine-rich–containing family, pyrin domain–containing-3 (NLRP3) and cyclic GMP-AMP synthase (cGAS); myeloid-derived suppressor cells (MDSCs) expansion and their associated immunosuppressive metabolite, methyl-glyoxal, all of them negatively regulated by mitochondrial autophagy, biogenesis, metabolic pathways and its distinct metabolites.
... Similarly, bats also possess gene deficiencies in inflammation pathways like STING [10] and express high levels of special ASC2 which rather inhibits inflammasome activation [11]. These may reduce cytokine storms during infections therefore prolong their life-span. ...
Immune system aging (immune senescence) is an important factor contributing to the increased incidence and mortality rates among the elderly. Immune senescence, characterized by a decline in immune function, can also lead to aging and tissue dysfunction in organs as well as the lymphatic system. This suggests that aged immune cells may contribute to systemic aging. Conversely, transplantation of young immune cells into aged mice has been shown to improve systemic aging traits, indicating that immune system senescent cells could be a significant therapeutic target for promoting healthy aging. However, the molecular mechanisms behind immune senescence are not fully understood. Advances in unraveling these molecular processes are expected to lead to the discovery of new methods for preventing aging and extending lifespan.
... However, it has been found that a common serine deletion point mutation in bat species weakens the STING initiated immune response. [32][33][34][35] Multiple research has showed that bats can also tolerate the replication and infection of RNA viruses, like SARS-CoV-2. 31 In that, bat cells do not induce NFκB expression through p50 protein 31. Thus limiting the immune response to be initiated by Interferon regulatory factors 3 and 7. 31 Bats are known as the only mammals to fly. ...
Bat borne disease have attracted many researchers for years. The ability of the bat to host several exogenous viruses has been a focal point in research lately. The latest pandemic shifted the focus of scholars towards understanding the difference in response to viral infection between humans and bats. In a way to understand the basis of the interaction and behaviour between SARS-CoV-2 and the environment, a conflict between different researchers across the globe arose. This conflict asked many questions about the truth of virus-host integration, whether an interaction between RNA viruses and human genomes has ever been reported, the possible route and mechanism that could lead to genomic integration of viral sequences and the methods used to detect integration. This article highlights those questions and will discuss the diverse opinions of the controversy and provide examples on reported integration mechanisms and possible detection techniques. K E Y W O R D S integration, LINE-1, retrotransposition, SARS-CoV-2
... The interspecies transmission of SARS-CoV-2 poses a significant threat to global public health. Once SARS-CoV-2 circulates among bats, the suppressed innate immune response and special adaptive immune system of bats may facilitate the SARS-CoV-2 evolution [38][39][40]. In particular, recombination between different lineages in the same reservoir host has been proved as an important virus evolution method, which might give birth to new variants or even new viruses [41,42]. ...
Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has caused a global pandemic. Intermediate horseshoe bats (Rhinolophus affinis) are hosts of RaTG13, the second most phylogenetically related viruses to SARS-CoV-2. We report the binding between intermediate horseshoe bat ACE2 (bACE2-Ra) and SARS-CoV-2 receptor-binding domain (RBD), supporting the pseudotyped SARS-CoV-2 viral infection. A 3.3 Å resolution crystal structure of the bACE2-Ra/SARS-CoV-2 RBD complex was determined. The interaction networks of Patch 1 showed differences in R34 and E35 of bACE2-Ra compared to hACE2 and big-eared horseshoe bat ACE2 (bACE2-Rm). The E35K substitution, existing in other species, significantly enhanced the binding affinity owing to its electrostatic attraction with E484 of SARS-CoV-2 RBD. Furthermore, bACE2-Ra showed extensive support for the SARS-CoV-2 variants. These results broaden our knowledge of the ACE2/RBD interaction mechanism and emphasize the importance of continued surveillance of intermediate horseshoe bats to prevent spillover risk.
... D'autres adaptations existent dans la voie de reconnaissance des ADN cytoplasmiques impliquant la protéine STING (stimulator of interferon genes), dont l'activation entraîne la production d'IFN-β. Chez les trente espèces de chauves-souris pour lesquelles la séquence de STING est disponible, une mutation de cette protéine qui induit une diminution de son activité antivirale a été décrite [38]. La présence de nombreuses adaptations des voies de reconnaissance des ADN cytoplasmiques pourrait être liée à l'évolution du vol actif chez les chauves-souris. ...
Durant les dernières décennies, les chauves-souris ont été associées à de nombreuses pandémies virales. Ces animaux hébergent en effet une diversité importante de virus, certains à potentiel zoonotique pour l’homme. Alors que ces virus peuvent être mortels chez d’autres mammifères, les chauves-souris sont souvent infectées de façon asymptomatique. La mise en place d’une réponse immunitaire équilibrée leur permettrait de maintenir l’homéostasie lors de l’infection, en limitant la réplication virale tout en évitant l’impact d’une inflammation trop importante. Le décryptage de ces mécanismes, à l’aide de modèles in vitro adaptés, devrait contribuer à évaluer et à éviter le risque zoonotique potentiel de ces animaux, tout en ouvrant la voie au développement de thérapeutiques pour les maladies infectieuses et inflammatoires.
... Upon DNA binding within the cytoplasm cGAS (Cyclic GMP-AMP synthase) is able to generate the second messenger cyclic cGAMP necessary to activate Sting (Stimulator of INF Genes) with eventual transcriptional induction of type I interferons 11 . Paradoxically, the activation of cGAS/Sting is able to effectively block the viral infection, but its activation is the main driver of the cytokine storm in severe disease [12][13][14][15] . These findings suggest that the activation of innate immunity may be relevant in viral clearance in healthy people, but is a severe pathogenic driver in predisposed individuals. ...
Even if the SARS-CoV-2 pandemic has been declared over, several risks and clinical problems remain to be faced, including long-COVID sequelae and possible outbreaks of pathogenic variants. Intense research on COVID-19 has provided in these few years a striking amount of data covering different fields and disciplines, which can help to provide a knowledge shield against new potential infective spreads, and may also potentially be applied to other fields of medicine, including oncology and neurology. Nevertheless, areas of uncertainty still remain regarding the pathogenic mechanisms that subtend the multifaceted manifestations of the disease. To better clarify the pathogenesis of the disease, a systematic multidisciplinary evaluation of the many mechanisms involved in COVID-19 is mandatory, including clinical, physiological, radiological, immunological and pathological studies. In COVID-19 syndrome the pathological studies have been mainly performed on autopsy cases, and only a few studies are available on biopsies. Nevertheless, these studies have provided relevant information that can substantially contribute to decipher the complex scenario characterizing the different forms of COVID-19 and long-COVID-19. In this review the data provided by pathological investigations are recapitulated and discussed, in the light of different hypothesis and data provided by clinical, physiological and immunological data. Keep reading
... 并介导炎症反应的受体在蝙蝠基因组中缺失 [112] . 多个 活化抗病毒信号通路的接头分子也发生了适应性突 变, 包括蝙蝠ASC2(apoptosis-associated speck-like protein containing CARD 2)中的四个突变(E10K, R37E, C61Y和G77R)与抗病毒反应的负调控相关 [113] ; STING 中高度保守的丝氨酸残基(S358)在蝙蝠中也发生突变, 该位点的突变削弱了病毒感染后的炎症反应水平 [114] . ...
... It is known that 2 DNA-sensing pathways mediated by the cGAS-STING pathway [ 16 ] and PYHIN proteins, including AIM2 and IFI16 [ 17 ], are dampened in bats, including Egyptian fruit bats. In addition, a pr e vious stud y using a cell line deri v ed fr om big brown bats ( Eptesicus fuscus ) suggested that the TLR9-mediated DN A-sensing pathw ay is also w eakened in bats [ 27 ]. ...
Background
Bats harbor various viruses without severe symptoms and act as their natural reservoirs. The tolerance of bats against viral infections is assumed to originate from the uniqueness of their immune system. However, how immune responses vary between primates and bats remains unclear. Here, we characterized differences in the immune responses by peripheral blood mononuclear cells to various pathogenic stimuli between primates (humans, chimpanzees, and macaques) and bats (Egyptian fruit bats) using single-cell RNA sequencing.
Results
We show that the induction patterns of key cytosolic DNA/RNA sensors and antiviral genes differed between primates and bats. A novel subset of monocytes induced by pathogenic stimuli specifically in bats was identified. Furthermore, bats robustly respond to DNA virus infection even though major DNA sensors are dampened in bats.
Conclusions
Overall, our data suggest that immune responses are substantially different between primates and bats, presumably underlying the difference in viral pathogenicity among the mammalian species tested.
... Conversely, gene expression of type I IFNs in multiple tissues from Egyptian fruit bats (R. aegyptiacus) was low at baseline, but was inducible upon viral infection 34 . Other studies have reported dampened activation of stimulator of IFN genes (STING), a nucleic acid sensor involved in the regulation of IFN expression upon viral infection 35,36 . These reports highlight that the mechanisms of IFN expression, regulation, and signaling appear to be unique to individual bat species, pointing to a need for more detailed analyses. ...
Bats are natural reservoirs for several zoonotic viruses, potentially due to an enhanced capacity to control viral infection. However, the mechanisms of antiviral responses in bats are poorly defined. Here we established a Jamaican fruit bat (JFB, Artibeus jamaicensis ) intestinal organoid model of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection. Upon infection with SARS-CoV-2, increased viral RNA and subgenomic RNA was detected, but no infectious virus was released, indicating that JFB organoids support only limited viral replication but not viral reproduction. SARS-CoV-2 replication was associated with significantly increased gene expression of type I interferons and inflammatory cytokines. Interestingly, SARS-CoV-2 also caused enhanced formation and growth of JFB organoids. Proteomics revealed an increase in inflammatory signaling, cell turnover, cell repair, and SARS-CoV-2 infection pathways. Collectively, our findings suggest that primary JFB intestinal epithelial cells mount successful antiviral interferon responses and that SARS-CoV-2 infection in JFB cells induces protective regenerative pathways.
... The IFN-stimulated genes (ISGs) basally expressed, due to constant IFNα expression, are predicted to be involved in antiviral and DNA repair functions but not in pro-inflammatory responses [22]. Reduced pro-inflammatory signaling in bats after virus recognition may limit the immunopathogenic side effects observed in other mammalian species [23][24][25]. Other hypotheses include the co-evolution of bats and viruses to allow viral persistence and shedding without causing death or overt disease, and the evolution of powered flight in bats selected for an immune system with unique immunosuppressive mechanisms that impair virus clearance as a trade-off [26][27][28][29][30]. ...
Nipah virus (NiV; genus: Henipavirus; family: Paramyxoviridae) naturally infects Old World fruit bats (family Pteropodidae) without causing overt disease. Conversely, NiV infection in humans and other mammals can be lethal. Comparing bat antiviral responses with those of humans may illuminate the mechanisms that facilitate bats’ tolerance. Tripartite motif proteins (TRIMs), a large family of E3-ubiquitin ligases, fine-tune innate antiviral immune responses, and two human TRIMs interact with Henipavirus proteins. We hypothesize that NiV infection induces the expression of an immunosuppressive TRIM in bat, but not human cells, to promote tolerance. Here, we show that TRIM40 is an interferon-stimulated gene (ISG) in pteropodid but not human cells. Knockdown of bat TRIM40 increases gene expression of IFNβ, ISGs, and pro-inflammatory cytokines following poly(I:C) transfection. In Pteropus vampyrus, but not human cells, NiV induces TRIM40 expression within 16 h after infection, and knockdown of TRIM40 correlates with reduced NiV titers as compared to control cells. Bats may have evolved to express TRIM40 in response to viral infections to control immunopathogenesis.
... Bats are the reservoir hosts of viruses in several families, including Filoviridae, Paramyxoviridae, and Coronaviridae, that can cause severe disease in humans 10-12 . There are data indicating that bats, as the only ight-adapted mammals, have developed methods for reducing in ammatory cytokines, such as TNF 13 , while constitutively expressing innate immune genes, such as interferon-stimulated genes 14 , to reduce ight-induced oxidative metabolism and DNA damage 15,16 . Flight has also been implicated in the unique signatures of bat intestinal microbiomes 17,18 . ...
Although the intestinal microbiome plays an important role in mammalian health, disease, and immune function, it has not been well characterized in bats, the reservoir hosts of several highly pathogenic viruses. Here, we describe a pipeline to investigate the intestinal microbiome of captive Jamaican fruit bats ( Artibeus jamaicensis ). We observed a high degree of individual variation in addition to sex- and cohort-linked differences. The intestinal microbiome drove intestinal metabolite composition, possibly contributing to differences in immune status. This work provides a basis for future infection and field studies to examine in detail the role of the intestinal microbiome in antiviral immunity.
... Se conoce que la respuesta de IFN I dependiente de STING (stimulator of interferon genes), una proteína adaptadora citoplásmica esencial en múltiples vías sensoras de ADN, está disminuida en varias especies de murciélagos debido a una mutación puntual de un residuo de serina (S358) altamente conservado de STING (Xie et al., 2018). La reversión de esta mutación restauró funcionalmente el STING, con activación de IFN e inhibición viral. ...
Los murciélagos o quirópteros (orden Chiroptera) representan el 20 % de los mamíferos vivientes. Se han adaptado a todos los nichos ecológicos existentes (exceptuando la Antártida y el Ártico) como producto de procesos evolutivos que les permiten sobrevivir y reproducirse en condiciones muy diferentes. Además, los murciélagos son los únicos mamíferos voladores, lo que exige una alta carga metabólica y lleva a la liberación de moléculas genotóxicas y proinflamatorias. Sin embargo, los Chiroptera han desarrollado mecanismos para contrarrestar estos efectos dañinos que, paralelamente, se asocian con una vida prolongada, baja incidencia de cáncer y tolerancia a las infecciones virales. Los murciélagos son reservorios de una gran variedad de virus sin presentar enfermedad. Su resistencia a las infecciones virales se ha explicado por una tolerancia inmunitaria que permite que los virus permanezcan en estos hospederos sin causar daño tisular o enfermedad. La tolerancia se rompe cuando los murciélagos sufren estrés por alteración de los ecosistemas donde habitan o por reducción de sus fuentes de alimento, situaciones que ocurren generalmente por efecto antrópico. Los principales mecanismos de la tolerancia inmunitaria a las infecciones virales en los quirópteros son la activación constitutiva de los genes estimulados por interferón tipo I con actividad antiviral y la disminución de la activación del inflamasoma, lo que permite controlar la replicación viral sin inducir respuestas inflamatorias que causen daño tisular. El estudio de la tolerancia a las infecciones en los quirópteros puede conducir al desarrollo de nuevas formas de prevención y tratamiento de las infecciones epizoóticas.
... Since bats are a major reservoir of many different coronaviruses, they have been proposed as the primary host, but their exact role is not clear. Bats can host a huge number of different viruses without themselves becoming sick [12], but it is not known how bats, while naturally maintaining a high burden of viruses and the oxidative stressors of their fast flight, are able to regulate the immunological response and avoid hyperactivation of immune proinflammatory pathways [13]. Bats do not have many natural enemies, but in recent years, a fungus generating 'white nose syndrome' has killed millions of bats. ...
It has been suggested that it would be more appropriate to term the COVID-19 pandemic a syndemic, as the infection interacts synergistically with pre-existing chronic conditions such as obesity. Both conditions occur with steep socio-economic inequalities, and Brazil is suffering a heavy burden from both. What and who drives the clustering and interaction of these disorders? In this commentary, we examine the pathways leading to the COVID-19 syndemic. Deforestation, declining biodiversity and factory farming are promoting the emergence of new pathogens. Widespread use of pesticides influences immune, endocrine and metabolic systems. The ingestion of ultra-processed food promotes malnutrition and obesity in a country where at the same time poverty and food insecurity is rising. Brazilian agribusiness is focused on the production and global export of agricultural commodities, mainly for animal food and meat production. It is made possible through a combination of expanded land use, with deforestation in Amazonas and other Brazilian biomes, and the intensification of land use and cultivation of genetically modified crops with fertilizers and pesticides. This development is not sustainable for either population health or the environment.
... Interferon regulatory factors directly influence inflammation following viral infection [12,16] and the interferon (IFN) type I expression is unusually high without viral stimulation, in contrast to other mammals [17] (but see [18]). Adaptations in innate interferon regulators have been shown to diminish the immune response to viruses in bats [19]. These adaptations can be found in functional consensus at the level of immune genes expression regulation [17,20], enabling bats to maintain immune homeostasis to thrive in changing environmental conditions. ...
Background
Coevolution between pathogens and their hosts decreases host morbidity and mortality. Bats host and can tolerate viruses which can be lethal to other vertebrate orders, including humans. Bat adaptations to infection include localized immune response, early pathogen sensing, high interferon expression without pathogen stimulation, and regulated inflammatory response. The immune reaction is costly, and bats suppress high-cost metabolism during torpor. In the temperate zone, bats hibernate in winter, utilizing a specific behavioural adaptation to survive detrimental environmental conditions and lack of energy resources. Hibernation torpor involves major physiological changes that pose an additional challenge to bat-pathogen coexistence. Here, we compared bat cellular reaction to viral challenge under conditions simulating hibernation, evaluating the changes between torpor and euthermia.
Results
We infected the olfactory nerve-derived cell culture of Myotis myotis with an endemic bat pathogen, European bat lyssavirus 1 (EBLV-1). After infection, the bat cells were cultivated at two different temperatures, 37 °C and 5 °C, to examine the cell response during conditions simulating euthermia and torpor, respectively. The mRNA isolated from the cells was sequenced and analysed for differential gene expression attributable to the temperature and/or infection treatment. In conditions simulating euthermia, infected bat cells produce an excess signalling by multitude of pathways involved in apoptosis and immune regulation influencing proliferation of regulatory cell types which can, in synergy with other produced cytokines, contribute to viral tolerance. We found no up- or down-regulated genes expressed in infected cells cultivated at conditions simulating torpor compared to non-infected cells cultivated under the same conditions. When studying the reaction of uninfected cells to the temperature treatment, bat cells show an increased production of heat shock proteins (HSPs) with chaperone activity, improving the bat’s ability to repair molecular structures damaged due to the stress related to the temperature change.
Conclusions
The lack of bat cell reaction to infection in conditions simulating hibernation may contribute to the virus tolerance or persistence in bats. Together with the cell damage repair mechanisms induced in response to hibernation, the immune regulation may promote bats’ ability to act as reservoirs of zoonotic viruses such as lyssaviruses.
... cGAS/STING activation has been characterized during SARS-CoV-2 infection and may play a central role in the pathogenesis of COVID-19 (Berthelot et al., 2020;Rui et al., 2021;Domizio et al., 2022). The involvement of STING signalling in Coronaviridae infections has been suggested initially by the fact that bats expressing a STING protein defective for anti-viral response induction do not display any disease manifestation, despite their capacity to harbour several coronaviruses (Xie et al., 2018;Berthelot et al., 2020;Mougari et al., 2022). One of the hallmarks of severe COVID-19 is an unbalanced immune response, with reduced IFN-I expression and overproduction of inflammatory cytokines causing systemic inflammatory symptoms (Cevik et al., 2020). ...
While the function of cGAS/STING signalling axis in the innate immune response to DNA viruses is well deciphered, increasing evidence demonstrates its significant contribution in the control of RNA virus infections. After the first evidence of cGAS/STING antagonism by flaviviruses, STING activation has been detected following infection by various enveloped RNA viruses. It has been discovered that numerous viral families have implemented advanced strategies to antagonize STING pathway through their evolutionary path. This review summarizes the characterized cGAS/STING escape strategies to date, together with the proposed mechanisms of STING signalling activation perpetrated by RNA viruses and discusses possible therapeutic approaches. Further studies regarding the interaction between RNA viruses and cGAS/STING-mediated immunity could lead to major discoveries important for the understanding of immunopathogenesis and for the treatment of RNA viral infections.
... Bat1K, an initiative aimed at sequencing the genomes of all living bat species, will promote an understanding of unique bat adaptations [7]. Furthermore, there are growing comparative studies related to bat antiviral immunity, such as the discoveries of constitutively expressed IFN-α, dampened STING-dependent interferon response and NLRP3 inflammasome activation in bats [8][9][10]. However, studies related to the regulation of immune response in bats remain rare. ...
Bats have received increasing attention because of some unique biological features they possess. TRIM is a large family of proteins that participate in diverse cellular functions, such as antiviral immunity, DNA damage repair, tumor suppression, and aging. These functional areas appear to be highly consistent with the special characteristics of bats, such as tolerance to viruses and DNA damage generated in flight, low cancer incidence, and longevity. However, there is still a lack of systematic study of the TRIM family in bats. Here, we explored the TRIM family of bats using the genomes of 16 representative species. The results showed that the bat TRIM family contains 70 members, with 24 under positive selection and 7 duplicated. Additional transcriptomic analysis revealed the tissue-specific expressions of TRIM9, 46, 54, 55, 63, and 72. Additionally, following interferon or viral stimulation, TRIM orthologs associated with antiviral immunity reported in humans were also upregulated in bat cells. The present study systematically analyzed the composition, evolution, and expression of bat TRIM genes. It may provide a theoretical basis for studies of bat TRIM in the fields of antiviral immunity, longevity, and tolerance to DNA damage.
... In contrast, bats inhibit the transcriptional initiation of NLRP3, leading to reduced functionality of interferon-inducible proteins AIM2 and IFI-16 (6)(7)(8)(9), This, in turn, leads to lower caspase-1 activity and IL-1b cleavage, resulting in overall reduced inflammation. A recent study also found that deletion of the 358th serine site of the bat STING protein inhibits interferon secretion (10). Moreover, Pavlovich et al. reported a "high amplification and non-classical distribution of genes" at MHC-I loci in bats, suggesting that the combination of these abundant nonclassically distributed MHC-I type genes with highly expressed NKG2, which contain inhibitory interaction motifs, increases the activation threshold of NK cells and reduces their response (11,12). ...
Introduction
Bats are recognized as natural reservoirs for many viruses, and their unique immune system enables them to coexist with these viruses without frequently exhibiting disease symptoms. However, the current understanding of the bat adaptive immune system is limited due to the lack of a database or tool capable of processing T-cell receptor (TCR) sequences for bats.
Methods
We performed germline gene annotation in three bat species using homologous genes and RSSs (Recombinational Signal Sequences) scanning method. Then we used the conserved C gene to construct the TCRβ chain receptor library of the Intermediate Horseshoe Bat. Bats' TCRβ data will be analyzed using MiXCR and constructed reference library.
Results
Regarding the annotation results, we found that the Pale Spear-nosed Bat has 37 members in the TRBV12 family, which is more than the total number of TRBV genes in the Greater Horseshoe Bat. The average number of unique TCRβ chain receptor sequences in each Intermediate Horseshoe Bat sample reached 24,904.
Discussion
The distinct variations in the distribution of TRBV genes among the three types of bats could have a direct impact on the diversity of the TCR repertoire, as evidenced by the presence of conserved amino acids that indicate the T-cell recognition of antigens in bats is MHC-restricted. The bats’ TCRβ repertoire is formed through the rearrangement of the V-D-J-C genes, with D-J/V-D deletions and insertions resulting in high diversity.
... 29,30 Furthermore, a wide survey of bat species that serve as important natural hosts for coronaviruses and many other virus types revealed that these animals all expressed a hypofunctional STING allele. 31 Importantly, it was also recently reported by Domizio et al. 32 that the cGAS-STING pathway was a vital component involved in the generation of pathologic type I IFN responses during COVID-19. ...
Excessive levels of circulating proinflammatory mediators, known as "hypercytokinemia," that are generated by overwhelming immune system activation can lead to death due to critical organ failure and thrombotic events. Hypercytokinemia has been frequently associated with a variety of infectious and autoimmune diseases, with severe acute respiratory syndrome coronavirus 2 infection currently being the commonest cause, of what has been termed the cytokine storm. Among its various functions within the host, STING (stimulator of interferon genes) is critical in the defense against certain viruses and other pathogens. STING activation, particularly within cells of the innate immune system, triggers potent type I interferon and proinflammatory cytokine production. We thus hypothesized that generalized expression of a constitutively active STING mutant in mice would lead to hypercytokinemia. To test this, a Cre-loxP-based system was used to cause the inducible expression of a constitutively active hSTING mutant (hSTING-N154S) in any tissue or cell type. Herein, we employed a tamoxifen-inducible ubiquitin C-CreERT2 transgenic to obtain generalized expression of the hSTING-N154S protein, thereby triggering the production of IFN-β and multiple proinflammatory cytokines. This required euthanizing the mice within 3 to 4 d after tamoxifen administration. This preclinical model will allow for the rapid identification of compounds aimed at either preventing or ameliorating the lethal effects of hypercytokinemia.
Jamaican fruit bats (Artibeus jamaicensis) naturally harbor a wide range of viruses of human relevance. These infections are typically mild in bats, suggesting unique features of their immune system. To better understand the immune response to viral infections in bats, we infected male Jamaican fruit bats with the bat-derived influenza A virus (IAV) H18N11. Using comparative single-cell RNA sequencing, we generated single-cell atlases of the Jamaican fruit bat intestine and mesentery. Gene expression profiling showed that H18N11 infection resulted in a moderate induction of interferon-stimulated genes and transcriptional activation of immune cells. H18N11 infection was predominant in various leukocytes, including macrophages, B cells, and NK/T cells. Confirming these findings, human leukocytes, particularly macrophages, were also susceptible to H18N11, highlighting the zoonotic potential of this bat-derived IAV. Our study provides insight into a natural virus-host relationship and thus serves as a fundamental resource for future in-depth characterization of bat immunology.
Bats are considered unique in their ability to harbor large numbers of viruses and serve as reservoirs for zoonotic viruses that have the potential to spill over into humans. However, these animals appear relatively resistant to the pathogenic effects of many viruses. Mounting evidence suggests that bats may tolerate viral infections due to unique immune features. These include evolutionary innovations in inflammatory pathways and in the molecules involved in viral sensing, interferon induction, and downstream interferon-induced antiviral effectors. We sought to determine whether interferon-stimulated genes (ISGs) from the black flying fox ( Pteropus alecto ) encoded proteins with unique antiviral activity relative to their human orthologs. Accordingly, we compared the antiviral activity of over 50 ISG human-bat ortholog pairs to identify differences in individual effector functions. We identified IRF7 from Pteropus alecto (Pa.IRF7) as a potent and broad-acting antiviral molecule that provides robust antiviral protection without prior activation. We show that Pa.IRF7 uniquely induces a subset of protective ISGs independent of canonical IFN signaling, which leads to protection from alphaviruses, a flavivirus, a rhabdovirus, and a paramyxovirus. In uninfected cells, Pa.IRF7 partially localizes to the nucleus and can directly bind interferon-sensitive regulatory elements (ISREs). Compared to human IRF7, Pa.IRF7 also has additional serines in its C terminal domain that contribute to antiviral activity and may serve as unique phosphorylation hubs for activation. These properties constitute major differences between bat and human IRF7 that offer additional insight into the potential uniqueness of the black flying fox immune system.
The emergence of highly zoonotic viral infections has propelled bat research forward. The viral outbreaks including Hendra virus, Nipah virus, Marburg virus, Ebola virus, Rabies virus, Middle East respiratory syndrome coronavirus, SARS-CoV and the latest SARS-CoV-2 have been epidemiologically linked to various bat species. Bats possess unique immunological characteristics that allow them to serve as a potential viral reservoir. Bats are also known to protect themselves against viruses and maintain their immunity. Therefore, there is a need for in-depth understanding into bat-virus biology to unravel the major factors contributing to the coexistence and spread of viruses.
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.
Stimulatorof interferon genes (STING) is an intracellular sensor of cyclic dinucleotides involved in the innate immune response against pathogen‐ or self‐derived DNA. For years, interferon (IFN) induction of cyclic GMP–AMP synthase (cGAS)–STING has been considered as a canonical pattern defending the host from viral invasion. The mechanism of the cGAS–STING–IFN pathway has been well‐illustrated. However, other signalling cascades driven by cGAS–STING have emerged in recent years and some of them have been found to possess antiviral ability independent of IFN. Here, we summarize the current progress on cGAS–STING‐mediated nonclassic antiviral activities with an emphasis on the nuclear factor‐κB and autophagy pathways, which are the most‐studied pathways. In addition, we briefly present the primordial function of the cGAS–STING pathway in primitive species to show the importance of IFN‐unrelated antiviral activity from an evolutionary angle. Finally, we discuss open questions that need to be solved for further exploitation of this field.
Activation of the DNA-sensing STING axis by RNA viruses plays a role in antiviral response through mechanisms that remain poorly understood. Here, we show that the STING pathway regulates Nipah virus (NiV) replication in vivo in mice. Moreover, we demonstrate that following both NiV and measles virus (MeV) infection, IFNγ-inducible protein 16 (IFI16), an alternative DNA sensor in addition to cGAS, induces the activation of STING, leading to the phosphorylation of NF-κB p65 and the production of IFNβ and interleukin 6. Finally, we found that paramyxovirus-induced syncytia formation is responsible for loss of mitochondrial membrane potential and leakage of mitochondrial DNA in the cytoplasm, the latter of which is further detected by both cGAS and IFI16. These results contribute to improve our understanding about NiV and MeV immunopathogenesis and provide potential paths for alternative therapeutic strategies.
Several filoviruses, including Marburg virus (MARV), cause severe disease in humans and nonhuman primates (NHPs). However, the Egyptian rousette bat (ERB, Rousettus aegyptiacus), the only known MARV reservoir, shows no overt illness upon natural or experimental infection, which, like other bat hosts of zoonoses, is due to well-adapted, likely species-specific immune features. Despite advances in understanding reservoir immune responses to filoviruses, ERB peripheral blood responses to MARV and how they compare to those of diseased filovirus-infected spillover hosts remain ill-defined. We thus conducted a longitudinal analysis of ERB blood gene responses during acute MARV infection. These data were then contrasted with a compilation of published primate blood response studies to elucidate gene correlates of filovirus protection versus disease. Our work expands on previous findings in MARV-infected ERBs by supporting both host resistance and disease tolerance mechanisms, offers insight into the peripheral immunocellular repertoire during infection, and provides the most direct known cross-examination between reservoir and spillover hosts of the most prevalently-regulated response genes, pathways and activities associated with differences in filovirus pathogenesis and pathogenicity.
Broad‐spectrum antivirals (BSAs) have the advantageous property of being effective against a wide range of viruses with a single drug, offering a promising therapeutic solution for the largely unmet need in treating both existing and emerging viral infections. In this review, we summarize the current strategies for the development of novel BSAs, focusing on either targeting the commonalities during the replication of multiple viruses or the systemic immunity of humans. In comparison to BSAs that target viral replication, these immuno‐modulatory agents possess an expanded spectrum of antiviral activity. However, antiviral immunity is a double‐edged sword, and maintaining immune homeostasis ultimately dictates the health status of hosts during viral infections. Therefore, establishing an ideal goal for immuno‐modulation in antiviral interventions is crucial. Herein we propose a bionic approach for immuno‐modulation inspired by mimicking bats, which possess a more robust immune system for combating viral invasions, compared to humans. In addition, we discuss an empirical approach to treat diverse viral infections using traditional Chinese medicines (TCMs), mainly through bidirectional immuno‐modulation to restore the disrupted homeostasis. Advancing our understanding of both the immune system of bats and the mechanisms underlying antiviral TCMs will significantly contribute to the future development of novel BSAs.
This comprehensive reference explores medicinal plants, phytomedicines, and traditional herbal remedies as potential sources for the prevention and treatment of COVID-19. It features 9 chapters authored and edited by renowned experts. The book specifically highlights the promising drug discovery opportunities grounded in bioactive compounds from medicinal plants and herbal medicines, offering insights into combatting SARS-CoV-2 infections and respiratory complications.
Key Highlights:
Drug Discovery Potential: Explores the vast potential of medicinal plants, phytomedicine, and traditional remedies against COVID-19, shedding light on groundbreaking drug discovery avenues.
Cutting-Edge Insights: Provides up-to-date insights into the use of medicinal plants, herbal drugs, and traditional medicines in the fight against COVID-19.
Natural Immune Boosters: Details the use of indigenous herbs, spices, functional foods, and herbal drugs for boosting immunity and preventing SARS-CoV-2 infections.
Drug Repurposing: Highlights innovative drug repurposing strategies using phytomedicine-derived bioactive compounds and phytochemical databases for COVID-19 drug development.
Additional features of the book include a reader-friendly introduction to each topic and a list of references for advanced readers. This timely reference is an informative resource for a broad range of readers interested in strategies to control COVID-19, including postgraduate researchers, and pharmaceutical R&D experts. It also serves as a handbook for professionals in clinical and herbal medicine.
Background
SARS-CoV-2 emerged in Wuhan in December 2019, and after that, it spread quickly around the world. The virus could spread to millions of individuals since there were no particular treatments or preventative measures. The COVID-19 infection is often treated with current drugs such as Remdesivir, steroids, tocilizumab, favipiravir, and ivermectin. However, the immunosuppressive effects of these medicines might worsen COVID-19 symptoms and put the lives of immunocompromised individuals in peril. Thus, it is important to sustain a robust immune system when undergoing therapy for COVID-19. Herbal treatment has the potential to accomplish this objective.
Objective
The current investigation involves the preparation of polyherbal syrup containing various medicinal plants such as ephedra, diascorea, ginger, echinacea, garlic, rhubarb, and glycyrrhiza for the effective control of the COVID-19 infection.
Methods
All varieties of the individual plant powders (200 g) were treated to a 7 day maceration in aqueous ethanol (70:30) in a percolator at room temperature with intermittent vigorous shaking at room temperature and storage of the extract in a dark room. The mixture was run through a muslin cloth and then a Whatman qualitative grade 1 filter paper to produce the filtrate. The filtrate was evaporated to a thick paste-like consistency at 370 °C under decreased pressure in a rota evaporator connected to a vacuum pump. After that, each individual extract was collected and kept in airtight jars at 4°C. According to the Indian Pharmacopoeia, simple syrup (66.67% w/v) of polyherbal extract was prepared. The oral administration of polyherbal syrup was carried out at varied doses of 0.5 ml, 1 ml, and 1.5 ml to infected golden Syrian hamsters from the 7th day for one week after infection reached its peak.
Results
When compared to the infection control group, the results revealed that the viral load was significantly reduced by 79.1% when treated with polyherbal syrup. A histological examination of the infected hamster lung on days 7, 10, and 13 demonstrated that polyherbal syrup significantly decreased viral load in a dose-dependent manner.
Conclusion
It is inferred that the polyherbal syrup formulation demonstrates efficacy in the prevention of COVID-19 infection during its first stages and may serve as a potential contender for SARSCoV- 2 due to its immunomodulatory properties.
COVID-19 is a global pandemic caused by severe acute respiratory syndrome (SARS) coronavirus- 2 (SARS-CoV-2). The three main receptors used by SARS-CoV-2 to bind and gain entry into human cells are ACE, TMPRSS2, and CD147. These molecular factors have crucial roles in human metabolism and homeostasis, but the upregulation of these factors causes severe diseases such as myocarditis, prostate cancer, and other endocrine-related cancers. Studies have found that once humans come into contact with SARS-CoV-2, the chances of being affected by such disorders increase; indeed, infection with the virus is associated with increased morbidity and mortality from heart attacks and pulmonary inflammation. Notably, exposure to some pesticides, such as chlorpyrifos, cypermethrin, and imidacloprid, which are identified as potential endocrine disruptors, causes such disorders by interfering with hormonal signaling pathways, such as the insulinglucagon pathway and the thyroid pathway. This review focuses on the potential role of pesticides in exacerbating the comorbidities linked with SARS-CoV-2 and their effect on the molecular factors associated with SARS-CoV-2. Understanding the potential therapeutic implications of this link between SARS-CoV-2 severity and pesticides requires further clinical trials and investigations.
Bats are exceptional among mammals for their powered flight, extended lifespans, and robust immune systems and therefore have been of particular interest in comparative genomics. Using the Oxford Nanopore Technologies long-read platform, we sequenced the genomes of two bat species with key phylogenetic positions, the Jamaican fruit bat (Artibeus jamaicensis) and the Mesoamerican mustached bat (Pteronotus mesoamericanus), and carried out a comprehensive comparative genomic analysis with a diverse collection of bats and other mammals. The high-quality, long-read genome assemblies revealed a contraction of interferon (IFN)-α at the immunity-related type I IFN locus in bats, resulting in a shift in relative IFN-ω and IFN-α copy numbers. Contradicting previous hypotheses of constitutive expression of IFN-α being a feature of the bat immune system, three bat species lost all IFN-α genes. This shift to IFN-ω could contribute to the increased viral tolerance that has made bats a common reservoir for viruses that can be transmitted to humans. Antiviral genes stimulated by type I IFNs also showed evidence of rapid evolution, including a lineage-specific duplication of IFN-induced transmembrane genes and positive selection in IFIT2. In addition, 33 tumor suppressors and 6 DNA-repair genes showed signs of positive selection, perhaps contributing to increased longevity and reduced cancer rates in bats. The robust immune systems of bats rely on both bat-wide and lineage-specific evolution in the immune gene repertoire, suggesting diverse immune strategies. Our study provides new genomic resources for bats and sheds new light on the extraordinary molecular evolution in this critically important group of mammals.
Bats (order Chiroptera ) are a major reservoir for emerging and re-emerging zoonotic viruses. Their tolerance toward highly pathogenic human viruses led to the hypothesis that bats may possess an especially active antiviral interferon (IFN) system. Here, we cloned and functionally characterized the virus RNA sensor, retinoic acid-inducible gene-I (RIG-I), from the “microbat” Myotis daubentonii (suborder Yangochiroptera ) and the “megabat” Rousettus aegyptiacus (suborder Yinpterochiroptera) and compared them to the human ortholog. Our data show that the overall sequence and domain organization are highly conserved and that all three RIG-I orthologs can mediate a similar IFN induction in response to viral RNA at 37° and 39°C but not at 30°C. Like human RIG-I, bat RIG-Is were optimally activated by double stranded RNA containing a 5’-triphosphate end and required mitochondrial antiviral-signaling protein (MAVS) for antiviral signaling. Moreover, the RIG-I orthologs of humans and of R. aegyptiacus , but not of M. daubentonii , enable innate immune sensing of SARS-CoV-2 infection. Our results thus show that microbats and megabats express a RIG-I that is not substantially different from the human counterpart with respect to function, temperature dependency, antiviral signaling, and RNA ligand properties, and that human and megabat RIG-I are able to sense SARS-CoV-2 infection.
IMPORTANCE
A common hypothesis holds that bats (order Chiroptera ) are outstanding reservoirs for zoonotic viruses because of a special antiviral interferon (IFN) system. However, functional studies about key components of the bat IFN system are rare. RIG-I is a cellular sensor for viral RNA signatures that activates the antiviral signaling chain to induce IFN. We cloned and functionally characterized RIG-I genes from two species of the suborders Yangochiroptera and Yinpterochiroptera . The bat RIG-Is were conserved in their sequence and domain organization, and similar to human RIG-I in (i) mediating virus- and IFN-activated gene expression, (ii) antiviral signaling, (iii) temperature dependence, and (iv) recognition of RNA ligands. Moreover, RIG-I of Rousettus aegyptiacus (suborder Yinpterochiroptera ) and of humans were found to recognize SARS-CoV-2 infection. Thus, members of both bat suborders encode RIG-Is that are comparable to their human counterpart. The ability of bats to harbor zoonotic viruses therefore seems due to other features.
The management of future pandemic risk requires a better understanding of the mechanisms that determine the virulence of emerging zoonotic viruses. Meta-analyses suggest that the virulence of emerging zoonoses is correlated with but not completely predictable from reservoir host phylogeny, indicating that specific characteristics of reservoir host immunology and life history may drive the evolution of viral traits responsible for cross-species virulence. In particular, bats host viruses that cause higher case fatality rates upon spillover to humans than those derived from any other mammal, a phenomenon that cannot be explained by phylogenetic distance alone. In order to disentangle the fundamental drivers of these patterns, we develop a nested modeling framework that highlights mechanisms that underpin the evolution of viral traits in reservoir hosts that cause virulence following cross-species emergence. We apply this framework to generate virulence predictions for viral zoonoses derived from diverse mammalian reservoirs, recapturing trends in virus-induced human mortality rates reported in the literature. Notably, our work offers a mechanistic hypothesis to explain the extreme virulence of bat-borne zoonoses and, more generally, demonstrates how key differences in reservoir host longevity, viral tolerance, and constitutive immunity impact the evolution of viral traits that cause virulence following spillover to humans. Our theoretical framework offers a series of testable questions and predictions designed to stimulate future work comparing cross-species virulence evolution in zoonotic viruses derived from diverse mammalian hosts.
COVID-19 emerged as a public health emergency of international concern in 2019 and spread globally. The spectrum of the diseases varied from asymptomatic to severe, even resulting in mortality. Gender and pre-existing co-morbidities were identifiable risk factors. Diabetes, hypertension, and chronic respiratory and cardiovascular diseases pose a risk of severe infections and manifestations. The vulnerability was due to ACE 2 receptors, thereby enhancing the entry and subsequent multiplication of the virus. Immune responses acted as the two-way sword, with cytokine storms posing a risk of severe complications. COVID-19 is also associated with long-term effects varying from neuropsychiatric to other complications. Mutations are expected to pose a challenge in the future. The second wave was also related to fungal infections due to varied causes like side effects of treatment and opportunistic infection due to immune suppression from using steroids. Naturopathy is also expected to work wonders. However, scientific and evidence-based results are required. COVID combat requires a multi-level approach. Nutrition and strict adherence to health and hygiene are essential preventive strategies.
Normally, the host immunological response to viral infection is coordinated to restore homeostasis and protect the individual from possible tissue damage. The two major approaches are adopted by the host to deal with the pathogen: resistance or tolerance. The nature of the responses often differs between species and between individuals of the same species. Resistance includes innate and adaptive immune responses to control virus replication. Disease tolerance relies on the immune response allowing the coexistence of infections in the host with minimal or no clinical signs, while maintaining sufficient viral replication for transmission. Here, we compared the virome of bats, rodents and migratory birds and the molecular mechanisms underlying symptomatic and asymptomatic disease progression. We also explore the influence of the host physiology and environmental influences on RNA virus expression and how it impacts on the whole brain transcriptome of seemingly healthy semipalmated sandpiper (Calidris pusilla) and spotted sandpiper (Actitis macularius). Three time points throughout the year were selected to understand the importance of longitudinal surveys in the characterization of the virome. We finally revisited evidence that upstream and downstream regulation of the inflammatory response is, respectively, associated with resistance and tolerance to viral infections.
Bats are special in their ability to live long and host many emerging viruses. Our previous studies showed that bats have altered inflammasomes, which are central players in aging and infection. However, the role of inflammasome signaling in combating inflammatory diseases remains poorly understood. Here, we report bat ASC2 as a potent negative regulator of inflammasomes. Bat ASC2 is highly expressed at both the mRNA and protein levels and is highly potent in inhibiting human and mouse inflammasomes. Transgenic expression of bat ASC2 in mice reduced the severity of peritonitis induced by gout crystals and ASC particles. Bat ASC2 also dampened inflammation induced by multiple viruses and reduced mortality of influenza A virus infection. Importantly, it also suppressed SARS-CoV-2-immune-complex-induced inflammasome activation. Four key residues were identified for the gain of function of bat ASC2. Our results demonstrate that bat ASC2 is an important negative regulator of inflammasomes with therapeutic potential in inflammatory diseases.
Mitochondrial antiviral signaling protein (MAVS) is an essential articulatory protein in immune responses against most RNA viruses. Whether bats, the natural hosts of numerous zoonotic RNA viruses, utilize conserved signaling pathways involving MAVS-mediated interferon (IFN) responses remains elusive. In this study, we performed the cloning and functional analysis of bat MAVS (BatMAVS). Amino acid sequence analysis revealed that BatMAVS was poorly conserved among species and evolutionarily closer to other mammals. Overexpression of BatMAVS significantly inhibited the replication of green fluorescent protein (GFP)-tagged VSV (VSV-GFP) and GFP-tagged Newcastle disease virus (NDV) (NDV-GFP) by activating the type I IFN pathway, and its expression at the transcriptional level was upregulated at the late stage of VSV-GFP infection. We further demonstrated that the CARD_2 and TM domains occupy a large proportion in the ability of BatMAVS to activate IFN-β. These results suggest that BatMAVS acts as an important regulatory molecule in IFN-induction and anti-RNA viruses in bats.
The majority of human emerging infectious diseases are zoonotic, with viruses that originate in wild mammals of particular concern (for example, HIV, Ebola and SARS). Understanding patterns of viral diversity in wildlife and determinants of successful cross-species transmission, or spillover, are therefore key goals for pandemic surveillance programs. However, few analytical tools exist to identify which host species are likely to harbour the next human virus, or which viruses can cross species boundaries. Here we conduct a comprehensive analysis of mammalian host-virus relationships and show that both the total number of viruses that infect a given species and the proportion likely to be zoonotic are predictable. After controlling for research effort, the proportion of zoonotic viruses per species is predicted by phylogenetic relatedness to humans, host taxonomy and human population within a species range-which may reflect human-wildlife contact. We demonstrate that bats harbour a significantly higher proportion of zoonotic viruses than all other mammalian orders. We also identify the taxa and geographic regions with the largest estimated number of 'missing viruses' and 'missing zoonoses' and therefore of highest value for future surveillance. We then show that phylogenetic host breadth and other viral traits are significant predictors of zoonotic potential, providing a novel framework to assess if a newly discovered mammalian virus could infect people.
Immune-mediated autoinflammatory diseases are occupying an increasingly prominent position among the pantheon of debilitating conditions that afflict mankind. This review focuses on some of the key developments which have occurred since the original description of autoinflammatory disease in 1999, and focuses on underlying mechanisms that trigger autoinflammation. The monogenic autoinflammatory disease range has expanded considerably during that time, and now includes a broad spectrum of disorders, including relatively common conditions such as cystic fibrosis and subsets of systemic lupus erythematosus. The innate immune system also plays a key role in the pathogenesis of complex inflammatory disorders. We have proposed a new nomenclature to accommodate the rapidly increasing number of monogenic disorders, which predispose to either autoinflammation or autoimmunity or, indeed, combinations of both. This new terminology also encompasses a wide spectrum of genetically determined autoinflammatory diseases, with variable clinical manifestations of immunodeficiency and immune dysregulation/autoimmunity. We also explore some of the ramifications of the breakthrough discovery of the physiologic role of pyrin and the search for identifiable factors that may serve to trigger attacks of autoinflammation. The evidence that pyrin, as part of the pyrin inflammasome, acts as a sensor of different inactivating bacterial modification Rho GTPases, rather than interacting directly with these microbial products, sets the stage for a better understanding of the role of micro-organisms and infections in the autoinflammatory disorders. Finally, we discuss some of the triggers of autoinflammation as well as potential therapeutic interventions aimed at enhancing autophagy and proteasome degradation pathways.
Recent genomic analysis of two bat species (Pteropus alecto and Myotis davidii) revealed the absence of the PYHIN gene family. This family is recognized as important immune sensors of intracellular self and foreign DNA and activators of the inflammasome and/or interferon pathways. Further assessment of a wider range of bat genomes was necessary to determine if this is a universal pattern for this large mammalian group. Here we expanded genomic analysis of this gene family to include ten bat species. We confirmed the complete loss of this gene family, with only a truncated AIM2 remaining in one species (Pteronotus parnellii). Divergence of the PYHIN gene loci between the bat lineages infers different loss-of-function histories during bat evolution. While all other major groups of placental mammals have at least one gene member, only bats have lost the entire family. This removal of inflammasome DNA sensors may indicate an important adaptation that is flight-induced and related, at least in part, to pathogen-host co-existence.
Significance
Here we provide what is, to our knowledge, the first gene map of the type I IFN region of any bat species with the sequence of the type I IFN locus of the Australian black flying fox, Pteropus alecto. The bat IFN locus contains fewer IFN genes compared with any other mammal sequenced to date, including only three IFN-α genes. We also demonstrate that bat IFN-α genes are constitutively expressed in unstimulated bat tissues and cells and that their expression is unaffected by viral infection. This unusual pattern of IFN-α expression has not been described in any other species to our knowledge and has important implications for the role of innate immunity in the ability of bats to coexist with viruses in the absence of disease.
RNA viruses are a genetically diverse group of pathogens that are responsible for some of the most prevalent and lethal human diseases. Numerous viruses introduce DNA damage and genetic instability in host cells during their lifecycles and some species also manipulate components of the DNA damage response (DDR), a complex and sophisticated series of cellular pathways that have evolved to detect and repair DNA lesions. Activation and manipulation of the DDR by DNA viruses has been extensively studied. It is apparent, however, that many RNA viruses can also induce significant DNA damage, even in cases where viral replication takes place exclusively in the cytoplasm. DNA damage can contribute to the pathogenesis of RNA viruses through the triggering of apoptosis, stimulation of inflammatory immune responses and the introduction of deleterious mutations that can increase the risk of tumorigenesis. In addition, activation of DDR pathways can contribute positively to replication of viral RNA genomes. Elucidation of the interactions between RNA viruses and the DDR has provided important insights into modulation of host cell functions by these pathogens. This review summarises the current literature regarding activation and manipulation of the DDR by several medically important RNA viruses.
We characterized the nucleic acid sensing Toll-like receptors (TLR) of a New World bat species, the common vampire bat (Desmodus rotundus), and through a comparative molecular evolutionary approach searched for general adaptation patterns among the nucleic acid sensing TLRs of eight different bats species belonging to three families (Pteropodidae, Vespertilionidae and Phyllostomidae). We found that the bat TLRs are evolving slowly and mostly under purifying selection and that the divergence pattern of such receptors is overall congruent with the species tree, consistent with the evolution of many other mammalian nuclear genes. However, the chiropteran TLRs exhibited unique mutations fixed in ligand binding sites, some of which involved non-conservative amino acid changes and/or targets of positive selection. Such changes could potentially modify protein function and ligand biding properties, as some changes were predicted to alter nucleic acid binding motifs in TLR 9. Moreover, evidence for episodic diversifying selection acting specifically upon the bat lineage and sub lineages was detected. Thus, the long-term adaptation of chiropterans to a wide variety of environments and ecological niches with different pathogen profiles is likely to have shaped the evolution of the bat TLRs in an order-specific manner. The observed evolutionary patterns provide evidence for potential functional differences between bat and other mammalian TLRs in terms of resistance to specific pathogens or recognition of nucleic acids in general. This article is protected by copyright. All rights reserved.
During virus infection, the adaptor proteins MAVS and STING transduce signals from the cytosolic nucleic acid sensors RIG-I and cyclic guanosine monophosphate-adenosine monophosphate synthase, respectively, to induce type I interferons (IFNs) and other antiviral molecules. Here, we show that MAVS and STING harbor two conserved serine and threonine clusters that are phosphorylated by the kinases inhibitor of nuclear factor κB subunit IKK and/or TBK1 in response to stimulation. Phosphorylated MAVS and STING then bind to a positively charged surface of interferon regulatory factor 3 (IRF3) and thereby recruit IRF3 for its phosphorylation and activation by TBK1. We further show that TRIF, an adaptor protein in Toll-like receptor signaling, activates IRF3 through a similar phosphorylation-dependent mechanism. These results reveal that phosphorylation of innate adaptor proteins is an essential and conserved mechanism that selectively recruits IRF3 to activate the type I IFN pathway.
Copyright © 2015, American Association for the Advancement of Science.
Bats are reservoir hosts of several high-impact viruses that cause significant human diseases, including Nipah virus, Marburg virus and rabies virus. They also harbor many other viruses that are thought to have caused disease in humans after spillover into intermediate hosts, including SARS and MERS coronaviruses. As is usual with reservoir hosts, these viruses apparently cause little or no pathology in bats. Despite the importance of bats as reservoir hosts of zoonotic and potentially zoonotic agents, virtually nothing is known about the host/virus relationships; principally because few colonies of bats are available for experimental infections, a lack of reagents, methods and expertise for studying bat antiviral responses and immunology, and the difficulty of conducting meaningful field work. These challenges can be addressed, in part, with new technologies that are species-independent that can provide insight into the interactions of bats and viruses, which should clarify how the viruses persist in nature, and what risk factors might facilitate transmission to humans and livestock.
The STING (stimulator of interferon genes) protein can bind cyclic dinucleotides to activate the production of type I interferons and inflammatory cytokines. The cyclic dinucleotides can be bacterial second messengers c-di-GMP and c-di-AMP, 3'5'-3'5' cyclic GMP-AMP (3'3' cGAMP) produced by Vibrio cholerae and metazoan second messenger 2'5'-3'5' Cyclic GMP-AMP (2'3' cGAMP). Analysis of single nucleotide polymorphism (SNP) data from the 1000 Genome Project revealed that R71H-G230A-R293Q (HAQ) occurs in 20.4%, R232H in 13.7%, G230A-R293Q (AQ) in 5.2%, and R293Q in 1.5% of human population. In the absence of exogenous ligands, the R232H, R293Q and AQ SNPs had only modest effect on the stimulation of IFN-β and NF-κB promoter activities in HEK293T cells, while HAQ had significantly lower intrinsic activity. The decrease was primarily due to the R71H substitution. The SNPs also affected the response to the cyclic dinucleotides. In the presence of c-di-GMP, the R232H variant partially decreased the ability to activate IFN-βsignaling, while it was defective for the response to c-di-AMP and 3'3' cGAMP. The R293Q dramatically decreased the stimulatory response to all bacterial ligands. Surprisingly, the AQ and HAQ variants maintained partial abilities to activate the IFN-β signaling in the presence of ligands due primarily to the G230A substitution. Biochemical analysis revealed that the recombinant G230A protein could affect the conformation of the C-terminal domain of STING and the binding to c-di-GMP. Comparison of G230A structure with that of WT revealed that the conformation of the lid region that clamps onto the c-di-GMP was significantly altered. These results suggest that hSTING variation can affect innate immune signaling and that the common HAQ haplotype expresses a STING protein with reduced intrinsic signaling activity but retained the ability to response to bacterial cyclic dinucleotides.
Emerging infectious diseases pose a significant threat to human and animal welfare. A high proportion of emerging and reemerging infectious diseases are zoonoses derived from wildlife [1]. Bats harbour more zoonotic viruses per species than rodents and are now recognised as a significant source of zoonotic agents [2]. Henipaviruses, coronaviruses, filoviruses, and the rabies-causing lyssaviruses have all been shown to be transmissible from bats to humans—often through an intermediate host—with fatal consequences (Figure 1). Despite the obvious risk bat viruses pose to human health, it must be acknowledged that most outbreaks of bat-borne zoonotic diseases are a consequence of human activities. From an ecological perspective, bats are a remarkable and ecologically important group with many unique biological features.
Figure 1
Bats are diverse, as are the viruses that infect them.
The 2002-3 pandemic caused by severe acute respiratory syndrome coronavirus (SARS-CoV) was one of the most significant public health events in recent history. An ongoing outbreak of Middle East respiratory syndrome coronavirus suggests that this group of viruses remains a key threat and that their distribution is wider than previously recognized. Although bats have been suggested to be the natural reservoirs of both viruses, attempts to isolate the progenitor virus of SARS-CoV from bats have been unsuccessful. Diverse SARS-like coronaviruses (SL-CoVs) have now been reported from bats in China, Europe and Africa, but none is considered a direct progenitor of SARS-CoV because of their phylogenetic disparity from this virus and the inability of their spike proteins to use the SARS-CoV cellular receptor molecule, the human angiotensin converting enzyme II (ACE2). Here we report whole-genome sequences of two novel bat coronaviruses from Chinese horseshoe bats (family: Rhinolophidae) in Yunnan, China: RsSHC014 and Rs3367. These viruses are far more closely related to SARS-CoV than any previously identified bat coronaviruses, particularly in the receptor binding domain of the spike protein. Most importantly, we report the first recorded isolation of a live SL-CoV (bat SL-CoV-WIV1) from bat faecal samples in Vero E6 cells, which has typical coronavirus morphology, 99.9% sequence identity to Rs3367 and uses ACE2 from humans, civets and Chinese horseshoe bats for cell entry. Preliminary in vitro testing indicates that WIV1 also has a broad species tropism. Our results provide the strongest evidence to date that Chinese horseshoe bats are natural reservoirs of SARS-CoV, and that intermediate hosts may not be necessary for direct human infection by some bat SL-CoVs. They also highlight the importance of pathogen-discovery programs targeting high-risk wildlife groups in emerging disease hotspots as a strategy for pandemic preparedness.
Bats are the natural reservoirs of a number of high-impact viral zoonoses. We present a quantitative analysis to address the hypothesis that bats are unique in their propensity to host zoonotic viruses based on a comparison with rodents, another important host order. We found that bats indeed host more zoonotic viruses per species than rodents, and we identified life-history and ecological factors that promote zoonotic viral richness. More zoonotic viruses are hosted by species whose distributions overlap with a greater number of other species in the same taxonomic order (sympatry). Specifically in bats, there was evidence for increased zoonotic viral richness in species with smaller litters (one young), greater longevity and more litters per year. Furthermore, our results point to a new hypothesis to explain in part why bats host more zoonotic viruses per species: the stronger effect of sympatry in bats and more viruses shared between bat species suggests that interspecific transmission is more prevalent among bats than among rodents. Although bats host more zoonotic viruses per species, the total number of zoonotic viruses identified in bats (61) was lower than in rodents (68), a result of there being approximately twice the number of rodent species as bat species. Therefore, rodents should still be a serious concern as reservoirs of emerging viruses. These findings shed light on disease emergence and perpetuation mechanisms and may help lead to a predictive framework for identifying future emerging infectious virus reservoirs.
The presence of DNA in the cytoplasm of mammalian cells is a danger signal that triggers host immune responses such as the
production of type I interferons. Cytosolic DNA induces interferons through the production of cyclic guanosine monophosphate–adenosine
monophosphate (cyclic GMP-AMP, or cGAMP), which binds to and activates the adaptor protein STING. Through biochemical fractionation
and quantitative mass spectrometry, we identified a cGAMP synthase (cGAS), which belongs to the nucleotidyltransferase family.
Overexpression of cGAS activated the transcription factor IRF3 and induced interferon-β in a STING-dependent manner. Knockdown
of cGAS inhibited IRF3 activation and interferon-β induction by DNA transfection or DNA virus infection. cGAS bound to DNA
in the cytoplasm and catalyzed cGAMP synthesis. These results indicate that cGAS is a cytosolic DNA sensor that induces interferons
by producing the second messenger cGAMP.
Recognition of viral nucleic acids by pattern recognition receptors initiates type I IFN induction and innate antiviral immune response. Here we show that LSm14A, a member of the LSm family involved in RNA processing in the processing bodies, binds to synthetic or viral RNA and DNA and mediates IRF3 activation and IFN-β induction. Knockdown of LSm14A inhibits cytosolic RNA- and DNA-trigger type I IFN production and cellular antiviral response. Moreover, LSm14A is essential for early-phase induction of IFN-β after either RNA or DNA virus infection. We further found that LSm14A-mediated IFN-β induction requires RIG-I-VISA or MITA after RNA or DNA virus infection, respectively, and viral infection causes translocation of LSm14A to peroxisomes, where RIG-I, VISA, and MITA are located. These findings suggest that LSm14A is a sensor for both viral RNA and DNA and plays an important role in initiating IFN-β induction in the early phase of viral infection.
Herpes simplex virus type 1 (HSV-1) is a ubiquitous human pathogen of skin and mucous membranes. In the present study, the genome of the HSV-1 F strain was cloned as an infectious bacterial artificial chromosome (BAC) clone without any deletions of the viral genes. Additionally, a firefly luciferase cassette was inserted to generate a novel luciferase-expressing HSV-1 BAC. Importantly, the resulting recombinant HSV-1 BAC Luc behaved indistinguishably from the wild-type virus in Vero cells, and the luciferase activity could be easily quantified in vitro. Thus, this novel HSV-1 BAC system would serve as a powerful tool for gene function profiling.
The recognition of pathogenic DNA is important to the initiation of antiviral responses. Here we report the identification of DDX41, a member of the DEXDc family of helicases, as an intracellular DNA sensor in myeloid dendritic cells (mDCs). Knockdown of DDX41 expression by short hairpin RNA blocked the ability of mDCs to mount type I interferon and cytokine responses to DNA and DNA viruses. Overexpression of both DDX41 and the membrane-associated adaptor STING together had a synergistic effect in promoting Ifnb promoter activity. DDX41 bound both DNA and STING and localized together with STING in the cytosol. Knockdown of DDX41 expression blocked activation of the mitogen-activated protein kinase TBK1 and the transcription factors NF-κB and IRF3 by B-form DNA. Our results suggest that DDX41 is an additional DNA sensor that depends on STING to sense pathogenic DNA.
Bats are known to harbor a number of emerging and re-emerging zoonotic viruses, many of which are highly pathogenic in other mammals but result in no clinical symptoms in bats. The ability of bats to coexist with viruses may be the result of rapid control of viral replication early in the immune response. IFNs provide the first line of defense against viral infection in vertebrates. Type III IFNs (IFN-λs) are a recently identified IFN family that share similar antiviral activities with type I IFNs. To our knowledge, we demonstrate the first functional analysis of type III IFNs from any species of bat, with the investigation of two IFN-λ genes from the pteropid bat, Pteropus alecto. Our results demonstrate that bat type III IFN has similar antiviral activity to type I and III IFNs from other mammals. In addition, the two bat type III IFNs are differentially induced relative to each other and to type I IFNs after treatment or transfection with synthetic dsRNA. Infection with the bat paramyxovirus, Tioman virus, resulted in no upregulation of type I IFN production in bat splenocytes but was capable of inducing a type III IFN response in three of the four bats tested. To our knowledge, this is the first report to describe the simultaneous suppression of type I IFN and induction of type III IFN after virus infection. These results may have important implications for the role of type III IFNs in the ability of bats to coexist with viruses.
The detection of intracellular microbial DNA is critical to appropriate innate immune responses; however, knowledge of how such DNA is sensed is limited. Here we identify IFI16, a PYHIN protein, as an intracellular DNA sensor that mediates the induction of interferon-β (IFN-β). IFI16 directly associated with IFN-β-inducing viral DNA motifs. STING, a critical mediator of IFN-β responses to DNA, was recruited to IFI16 after DNA stimulation. Lowering the expression of IFI16 or its mouse ortholog p204 by RNA-mediated interference inhibited gene induction and activation of the transcription factors IRF3 and NF-κB induced by DNA and herpes simplex virus type 1 (HSV-1). IFI16 (p204) is the first PYHIN protein to our knowledge shown to be involved in IFN-β induction. Thus, the PYHIN proteins IFI16 and AIM2 form a new family of innate DNA sensors we call 'AIM2-like receptors' (ALRs).
Bat flight poses intriguing questions about how flight independently developed in mammals. Flight is among the most energy-consuming activities. Thus, we deduced that changes in energy metabolism must be a primary factor in the origin of flight in bats. The respiratory chain of the mitochondrial produces 95% of the adenosine triphosphate (ATP) needed for locomotion. Because the respiratory chain has a dual genetic foundation, with genes encoded by both the mitochondrial and nuclear genomes, we examined both genomes to gain insights into the evolution of flight within mammals. Evidence for positive selection was detected in 23.08% of the mitochondrial-encoded and 4.90% of nuclear-encoded oxidative phosphorylation (OXPHOS) genes, but in only 2.25% of the nuclear-encoded nonrespiratory genes that function in mitochondria or 1.005% of other nuclear genes in bats. To address the caveat that the two available bat genomes are of only draft quality, we resequenced 77 OXPHOS genes from four species of bats. The analysis of the resequenced gene data are in agreement with our conclusion that a significantly higher proportion of genes involved in energy metabolism, compared with background genes, show evidence of adaptive evolution specific on the common ancestral bat lineage. Both mitochondrial and nuclear-encoded OXPHOS genes display evidence of adaptive evolution along the common ancestral branch of bats, supporting our hypothesis that genes involved in energy metabolism were targets of natural selection and allowed adaptation to the huge change in energy demand that were required during the origin of flight.
We report here the identification and characterization of a protein, ERIS, an endoplasmic reticulum (ER) IFN stimulator, which is a strong type I IFN stimulator and plays a pivotal role in response to both non-self-cytosolic RNA and dsDNA. ERIS (also known as STING or MITA) resided exclusively on ER membrane. The ER retention/retrieval sequence RIR was found to be critical to retain the protein on ER membrane and to maintain its integrity. ERIS was dimerized on innate immune challenges. Coumermycin-induced ERIS dimerization led to strong and fast IFN induction, suggesting that dimerization of ERIS was critical for self-activation and subsequent downstream signaling.
The innate immune system senses nucleic acids by germline-encoded pattern recognition receptors. RNA is sensed by Toll-like receptor members TLR3, TLR7 and TLR8, or by the RNA helicases RIG-I (also known as DDX58) and MDA-5 (IFIH1). Little is known about sensors for cytoplasmic DNA that trigger antiviral and/or inflammatory responses. The best characterized of these responses involves activation of the TANK-binding kinase (TBK1)-interferon regulatory factor 3 (IRF3) signalling axis to trigger transcriptional induction of type I interferon genes. A second, less well-defined pathway leads to the activation of an 'inflammasome' that, via caspase-1, controls the catalytic cleavage of the pro-forms of the cytokines IL1beta and IL18 (refs 6, 7). Using mouse and human cells, here we identify the PYHIN (pyrin and HIN domain-containing protein) family member absent in melanoma 2 (AIM2) as a receptor for cytosolic DNA, which regulates caspase-1. The HIN200 domain of AIM2 binds to DNA, whereas the pyrin domain (but not that of the other PYHIN family members) associates with the adaptor molecule ASC (apoptosis-associated speck-like protein containing a caspase activation and recruitment domain) to activate both NF-kappaB and caspase-1. Knockdown of Aim2 abrogates caspase-1 activation in response to cytoplasmic double-stranded DNA and the double-stranded DNA vaccinia virus. Collectively, these observations identify AIM2 as a new receptor for cytoplasmic DNA, which forms an inflammasome with the ligand and ASC to activate caspase-1.
Microbial DNA sequences containing unmethylated CpG dinucleotides activate Toll-like receptor 9 (TLR9). We have found that TLR9 is localized to the endoplasmic reticulum (ER) of dendritic cells (DCs) and macrophages. Because there is no precedent for immune receptor signaling in the ER, we investigated how TLR9 is activated. We show that CpG DNA binds directly to TLR9 in ligand-binding studies. CpG DNA moves into early endosomes and is subsequently transported to a tubular lysosomal compartment. Concurrent with the movement of CpG DNA in cells, TLR9 redistributes from the ER to CpG DNA-containing structures, which also accumulate MyD88. Our data indicate a previously unknown mechanism of cellular activation involving the recruitment of TLR9 from the ER to sites of CpG DNA uptake, where signal transduction is initiated.
Although the best-defined function of type II major histocompatibility complex (MHC-II) is presentation of antigenic peptides
to T lymphocytes, these molecules can also transduce signals leading alternatively to cell activation or apoptotic death.
MHC-II is a heterodimer of two transmembrane proteins, each containing a short cytoplasmic tail that is dispensable for transduction
of death signals. This suggests the function of an undefined MHC-II-associated transducer in signaling the death response.
Here we describe a novel plasma membrane tetraspanner (MPYS) that is associated with MHC-II and mediates its transduction
of death signals. MPYS is unusual among tetraspanners in containing an extended C-terminal cytoplasmic tail (∼140 amino acids)
with multiple embedded signaling motifs. MPYS is tyrosine phosphorylated upon MHC-II aggregation and associates with inositol
lipid and tyrosine phosphatases. Finally, MHC class II-mediated cell death signaling requires MPYS-dependent activation of
the extracellular signal-regulated kinase signaling pathway.
Recognition of human cytomegalovirus (HCMV) DNA by the cytosolic sensor cGAS initiates STING-dependent innate antiviral responses. HCMV can antagonize host immune responses to promote latency infection. However, it is unknown whether and how HCMV targets the cGAS-STING axis for immune evasion. Here we identified the HCMV tegument protein UL82 as a negative regulator of STING-dependent antiviral responses. UL82 interacted with STING and impaired STING-mediated signaling via two mechanisms. UL82 inhibited the translocation of STING from the ER to perinuclear microsomes by disrupting the STING-iRhom2-TRAPβ translocation complex. UL82 also impaired the recruitment of TBK1 and IRF3 to the STING complex. The levels of downstream antiviral genes induced by UL82-deficient HCMV were higher than those induced by wild-type HCMV. Conversely, wild-type HCMV replicated more efficiently than the UL82-deficient mutant. These findings reveal an important mechanism of immune evasion by HCMV.
Innate immunity against pathogens relies on an array of immune receptors to detect molecular patterns that are characteristic of the pathogens, including receptors that are specialized in the detection of foreign nucleic acids. In vertebrates, nucleic acid sensing is the dominant antiviral defence pathway. Stimulation of nucleic acid receptors results in antiviral immune responses with the production of type I interferon (IFN), as well as the expression of IFN-stimulated genes, which encode molecules such as cell-autonomous antiviral effector proteins. This Review summarizes the tremendous progress that has been made in understanding how this sophisticated immune sensory system discriminates self from non-self nucleic acids in order to reliably detect pathogenic viruses.
Highly pathogenic human respiratory coronaviruses cause acute lethal disease characterized by exuberant inflammatory responses and lung damage. However, the factors leading to lung pathology are not well understood. Using mice infected with SARS (severe acute respiratory syndrome)-CoV, we show that robust virus replication accompanied by delayed type I interferon (IFN-I) signaling orchestrates inflammatory responses and lung immunopathology with diminished survival. IFN-I remains detectable until after virus titers peak, but early IFN-I administration ameliorates immunopathology. This delayed IFN-I signaling promotes the accumulation of pathogenic inflammatory monocyte-macrophages (IMMs), resulting in elevated lung cytokine/chemokine levels, vascular leakage, and impaired virus-specific T cell responses. Genetic ablation of the IFN-αβ receptor (IFNAR) or IMM depletion protects mice from lethal infection, without affecting viral load. These results demonstrate that IFN-I and IMM promote lethal SARS-CoV infection and identify IFN-I and IMMs as potential therapeutic targets in patients infected with pathogenic coronavirus and perhaps other respiratory viruses.
The rapid detection of microbial agents is essential for the effective initiation of host defence mechanisms against infection. Understanding how cells detect cytosolic DNA to trigger innate immune gene transcription has important implications-not only for comprehending the immune response to pathogens but also for elucidating the causes of autoinflammatory disease involving the sensing of self-DNA and the generation of effective antitumour adaptive immunity. The discovery of the STING (stimulator of interferon genes)-controlled innate immune pathway, which mediates cytosolic DNA-induced signalling events, has recently provided important insights into these processes, opening the way for the development of novel immunization regimes, as well as therapies to treat autoinflammatory disease and cancer.
The ongoing West African Ebola epidemic highlights a recurring trend in the zoonotic emergence of virulent pathogens likely to come from bat reservoirs that has caused epidemiologists to ask 'Are bats special reservoirs for emerging zoonotic pathogens?' We collate evidence from the past decade to delineate mitochondrial mechanisms of bat physiology that have evolved to mitigate oxidative stress incurred during metabolically costly activities such as flight. We further describe how such mechanisms might have generated pleiotropic effects responsible for tumor mitigation and pathogen control in bat hosts. These synergisms may enable 'special' tolerance of intracellular pathogens in bat hosts; paradoxically, this may leave them more susceptible to immunopathological morbidity when attempting to clear extracellular infections such as 'white-nose syndrome' (WNS).
Copyright © 2014 Elsevier Ltd. All rights reserved.
Bat Genomes
Bats are of great interest because of their ability to fly and as hosts for infectious disease. Zhang et al. (p. 456 , published online 20 December) sequenced the genomes of two distantly related bat species, David's Myotis and Black flying fox. Analysis of the two genomes revealed likely changes that accompanied the evolution of bats, including selection for increased expression of genes involved in the oxidative phosphorylation pathway needed to generate the energy required for flight. Furthermore, while some immune genes have been lost, others are under positive selection, which may potentially explain bats' status as viral reservoirs.
Cytosolic double-stranded DNA (dsDNA) stimulates the production of type I interferon (IFN) through the endoplasmic reticulum (ER)-resident adaptor protein STING (stimulator of IFN genes), which activates the transcription factor interferon regulatory factor 3 (IRF3); however, how STING activates IRF3 is unclear. Here, we showed that STING stimulates phosphorylation of IRF3 by the kinase TBK1 (TANK-binding kinase 1) in an in vitro reconstitution system. With this system, we identified a carboxyl-terminal region of STING that was both necessary and sufficient to activate TBK1 and stimulate the phosphorylation of IRF3. We also found that STING interacted with both TBK1 and IRF3 and that mutations in STING that selectively disrupted its binding to IRF3 abrogated phosphorylation of IRF3 without impairing the activation of TBK1. These results suggest that STING functions as a scaffold protein to specify and promote the phosphorylation of IRF3 by TBK1. This scaffolding function of STING (and possibly of other adaptor proteins) may explain why IRF3 is activated in only a subset of signaling pathways that activate TBK1.
Inflammasomes are cytoplasmic sensors of foreign molecules, including pathogens, and function to induce caspase-1 activation and IL-1β cytokine maturation. Whether such a mechanism exists in the nucleus and is effective against nuclear replicating pathogens is unknown. Nuclear replicating herpesvirus KSHV is associated with Kaposi Sarcoma, an angioproliferative tumor characterized by an inflammatory microenvironment including IL-1β. We demonstrate that during KSHV infection of endothelial cells, interferon gamma-inducible protein 16 (IFI16) interacts with the adaptor molecule ASC and procaspase-1 to form a functional inflammasome. This complex was initially detected in the nucleus and subsequently in the perinuclear area. KSHV gene expression and/or latent KSHV genome is required for inflammasome activation and IFI16 colocalizes with the KSHV genome in the infected cell nucleus. Caspase-1 activation by KSHV was reduced by IFI16 and ASC silencing. Our studies reveal IFI16 as a nuclear pathogen sensor and demonstrate that the inflammasome also functions in the nucleus.
The innate immune system detects pathogen- and host-derived double-stranded DNA exposed to the cytosol and induces type I interferon (IFN) and other cytokines. Here, we identified interferon-inducible tripartite-motif (TRIM) 56 as a regulator of double-stranded DNA-mediated type I interferon induction. TRIM56 overexpression enhanced IFN-β promoter activation after double-stranded DNA stimulation whereas TRIM56 knockdown abrogated it. TRIM56 interacted with STING and targeted it for lysine 63-linked ubiquitination. This modification induced STING dimerization, which was a prerequisite for recruitment of the antiviral kinase TBK1 and subsequent induction of IFN-β. Taken together, these results indicate that TRIM56 is an interferon-inducible E3 ubiquitin ligase that modulates STING to confer double-stranded DNA-mediated innate immune responses.
Viral infection triggers activation of transcription factors such as NF-kappaB and IRF3, which collaborate to induce type I interferons (IFNs) and elicit innate antiviral response. Here, we identified MITA as a critical mediator of virus-triggered type I IFN signaling by expression cloning. Overexpression of MITA activated IRF3, whereas knockdown of MITA inhibited virus-triggered activation of IRF3, expression of type I IFNs, and cellular antiviral response. MITA was found to localize to the outer membrane of mitochondria and to be associated with VISA, a mitochondrial protein that acts as an adaptor in virus-triggered signaling. MITA also interacted with IRF3 and recruited the kinase TBK1 to the VISA-associated complex. MITA was phosphorylated by TBK1, which is required for MITA-mediated activation of IRF3. Our results suggest that MITA is a critical mediator of virus-triggered IRF3 activation and IFN expression and further demonstrate the importance of certain mitochondrial proteins in innate antiviral immunity.
ATM is one of the sentries at the gate of genome stability. This multifunctional protein kinase orchestrates the intricate array of cellular responses to DNA double-strand breaks. Absence or inactivation of ATM leads to the pleiotropic genetic disorder ataxia-telangiectasia (A-T), whose hallmarks are neuronal degeneration, immunodeficiency, genomic instability, premature aging and cancer predisposition. Several features of the complex clinical and cellular phenotype of A-T are reminiscent of other syndromes involving neurodegeneration, premature aging or genomic instability. A common denominator of many of these conditions is the perturbation of the cellular balance of reactive oxygen species, which leads to constant oxidative stress. Of these disorders, ATM deficiency is one of the most extensively studied with regard to the genome instability-oxidative stress connection. This connection may provide new insights into the phenotypes associated with genetic deficiencies of DNA damage responses, and point to new strategies to alleviate some of their clinical symptoms.