Mitochondrial Antiviral Signaling Protein Research Articles

Targeting PRMT7-mediated monomethylation of MAVS enhances antiviral innate immune responses and inhibits RNA virus replication

RIG-I-like receptors (RLRs)-mitochondrial antiviral signaling protein (MAVS) are crucial for type I interferon (IFN) signaling pathway and innate immune responses triggered by RNA viruses. However, the regulatory molecular mechanisms underlying RNA virus-activated type I IFN signaling pathway remain incompletely understood. Here, we found that protein arginine methyltransferase 7 (PRMT7) serves as a negative regulator of the type I IFN signaling pathway by interacting with MAVS and catalyzing monomethylation of arginine 232 (R232me1) in MAVS. RNA virus infection leads to the downregulation and dissociation of PRMT7 from MAVS as well as the decrease of R232me1 methylation, enhancing MAVS/RIG-I interaction, MAVS aggregation, type I IFN signaling activation, and antiviral immune responses. Knock-in mice with MAVS R232 substituted with lysine (MavsR232K-KI) are more resistant to Vesicular Stomatitis Virus infection due to enhanced antiviral immune responses. PiPRMT7-MAVS, a short peptide inhibitor designed to interrupt the interaction between PRMT7 and MAVS, inhibits R232me1 methylation, thereby enhancing MAVS/RIG-I interaction, promoting MAVS aggregation, activating type I IFN signaling, and bolstering antiviral immune responses to suppress RNA virus replication. Moreover, the clinical relevance of PRMT7 is highlighted that it is significantly downregulated in RNA virus-infected clinical samples, such as blood samples from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and Ebola virus, as well as H1N1-infected bronchial epithelial cells. Our findings uncovered that PRMT7-mediated arginine methylation plays critical roles in regulating MAVS-mediated antiviral innate immune responses, and targeting arginine methylation might represent a therapeutic avenue for treating RNA viral infection.

Avian TRIM13 attenuates antiviral innate immunity by targeting MAVS for autophagic degradation

ABSTRACT MAVS (mitochondrial antiviral signaling protein) is a crucial adaptor in antiviral innate immunity that must be tightly regulated to maintain immune homeostasis. In this study, we identified the duck Anas platyrhynchos domesticus TRIM13 (ApdTRIM13) as a novel negative regulator of duck MAVS (ApdMAVS) that mediates the antiviral innate immune response. Upon infection with RNA viruses, ApdTRIM13 expression increased, and it specifically binds to ApdMAVS through its TM domain, facilitating the degradation of ApdMAVS in a manner independent of E3 ligase activity. Furthermore, ApdTRIM13 recruits the autophagic cargo receptor duck SQSTM1 (ApdSQSTM1), which facilitates its interaction with ApdMAVS independent of ubiquitin signaling, and subsequently delivers ApdMAVS to phagophores for degradation. Depletion of ApdSQSTM1 reduces ApdTRIM13-mediated autophagic degradation of ApdMAVS, thereby enhancing the antiviral immune response. Collectively, our findings reveal a novel mechanism by which ApdTRIM13 regulates type I interferon production by targeting ApdMAVS for selective autophagic degradation mediated by ApdSQSTM1, providing insights into the crosstalk between selective autophagy and innate immune responses in avian species.

An NLR family member X1 mutation (p.Arg707Cys) suppresses hepatitis B virus infection in hepatocytes and favors the interaction of retinoic acid-inducible gene 1 with mitochondrial antiviral signaling protein.

NLR family member X1 (NLRX1) is an important member of the NOD-like receptor (NLR) family and plays unique roles in immune system regulation. Patients with hepatitis B virus (HBV) infection are more likely to have the NLRX1 mutation p.Arg707Cys than healthy individuals. It has been reported that NLRX1 increases the infection rate of HBV in HepG2 cells expressing sodium taurocholate cotransporting polypeptide (NTCP). However, the role of NLRX1 mutation (p.Arg707Cys) in hepatitis remains unclear. We constructed Huh7 cells that stably overexpressed NTCP, using LV003 lentivirus. First, wild-type (WT) and mutant (MT) NLRX1 overexpression plasmids were constructed. The MT plasmid contained a point mutation at position 707 of the WT overexpression plasmid. Then, Huh7-NTCP cells were transfected with the WT or MT NLRX1 overexpression plasmid, and subsequent NLRX1 expression was analyzed using real-time quantitative polymerase chain reaction (RT-qPCR) and western blot. HBV RNA levels were determined using RT-qPCR. HBsAg and HBcAg levels were confirmed immunohistochemically. Interferon alpha (IFN-α), interleukin 6 (IL-6), and type I interferon beta (IFN-β) levels were determined using enzyme-linked immunosorbent assay kits. p-p65, p-interferon regulatory factor (IRF) 3, and p-IRF7 expression levels were examined using western blot. The interaction of NLRX1 and retinoic acid-inducible gene (RIG)-1/mitochondrial antiviral signaling (MAVS) protein was confirmed by coimmunoprecipitation. The interaction of NLRX1 with IFN-α, IL-6, or IFN-β was analyzed by dual luciferase reporter gene assay. The levels of HBV RNA, HBsAg, and HBcAg in infected cells transfected with the WT NLRX1 or MT NLRX1 expression plasmid were higher than those in the untransfected control group; and these levels were lower in the cells transfected with MT NLRX1 than in those transfected with WT NLRX1. The levels of IFN-α, IFN-β, IL-6, p-p65, p-IRF3, and p-IRF7 were lower in cells transfected with WT NLRX1 or MT NLRX1 than in control cells. The levels of IFN-β, p-p65, p-IRF3, and p-IRF7 were higher in cells transfected with MT NLRX1 than in those transfected with WT NLRX1. Moreover, NLRX1 competitively inhibited RIG1 binding to MAVS, but the mutation in MT NLRX1 reduced this inhibitory effect. In addition, NLRX1 decreased the promoter activity of IFN-α, IFN-β, and IL-6. Our findings revealed that NLRX1 is a regulatory factor that inhibits the anti-HBV ability of hepatocytes and that the mutation p.Arg707Cys in NLRX1 suppresses HBV infection and activates the IFN/nuclear factor κB pathway.

Molecular depiction and functional delineation of E3 ubiquitin ligase MARCH5 in yellowtail clownfish (Amphiprion clarkii)

Membrane-associated Ring-CH 5 (MARCH5) is a mitochondrial E3 ubiquitin ligase playing a key role in the regulation of mitochondrial dynamics. In mammals, MARCH5 negatively regulates mitochondrial antiviral signaling (MAVS) protein aggregation during viral infection and hampers downstream type I interferon signaling to prevent excessive immune activation. However, its precise functional role in the teleost immune system remains unclear. This study investigated the molecular characteristics and immune response of the MARCH5 ortholog in Amphiprion clarkii (A. clarkii; AcMARCH5). The predicted AcMARCH5 protein sequence consists of 287 amino acids with a molecular weight of 32.02 kDa and a theoretical isoelectric point of 9.11. It contains four C-terminal transmembrane (TM) domains and an N-terminal RING cysteine-histidine (CH) domain, which directly regulates ubiquitin transfer. Multiple sequence alignment revealed a high level of conservation between AcMARCH5 and its orthologs in other vertebrate species. Under normal physiological conditions, AcMARCH5 showed the highest mRNA expression in the muscle, brain, and kidney tissues of A. clarkii. Upon stimulation with polyinosinic:polycytidylic acid (Poly I:C), lipopolysaccharide (LPS), and Vibrio harveyi, AcMARCH5 expression was drastically modulated. Functional assays showed that overexpression of AcMARCH5 in fathead minnow (FHM) cells downregulated antiviral gene expression, accompanied by enhanced viral hemorrhagic septicemia virus (VHSV) replication. In murine macrophages, AcMARCH5 overexpression markedly reduced the production of pro-inflammatory cytokines in response to poly I:C treatment. Additionally, AcMARCH5 exhibited an anti-apoptotic effect in H2O2-treated FHM cells. Collectively, these results suggest that AcMARCH5 may play a role in maintaining cellular homeostasis under disease and stress conditions in A. clarkii.

Pseudorabies virus infection triggers mitophagy to dampen the interferon response and promote viral replication.

Pseudorabies virus (PRV) utilizes multiple strategies to inhibit type I interferon (IFN-I) production and signaling to achieve innate immune evasion. Among several other functions, mitochondria serve as a crucial immune hub in the initiation of innate antiviral responses. It is currently unknown whether PRV inhibits innate immune responses by manipulating mitochondria. In this study, we found that PRV infection damages mitochondrial structure and function, as shown by mitochondrial membrane potential depolarization, reduction in mitochondrial numbers, and an imbalance in mitochondrial dynamics. In addition, PRV infection triggered PINK1-Parkin-mediated mitophagy to eliminate the impaired mitochondria, which resulted in a suppression of IFN-I production, thereby promoting viral replication. Furthermore, we found that mitophagy resulted in the degradation of the mitochondrial antiviral signaling protein, which is located on the mitochondrial outer membrane. In conclusion, the data of the current study indicate that PRV-induced mitophagy represents a previously uncharacterized PRV evasion mechanism of the IFN-I response, thereby promoting virus replication.IMPORTANCEPseudorabies virus (PRV), a pathogen that induces different disease symptoms and is often fatal in domestic animals and wildlife, has caused great economic losses to the swine industry. Since 2011, different PRV variant strains have emerged in Asia, against which current commercial vaccines may not always provide optimal protection in pigs. In addition, there are indications that some of these PRV variant strains may sporadically infect people. In the current study, we found that PRV infection causes mitochondria injury. This is associated with the induction of mitophagy to eliminate the damaged mitochondria, which results in suppressed antiviral interferon production and signaling. Hence, our study reveals a novel mechanism that is used by PRV to antagonize the antiviral host immune response, providing a theoretical basis that may contribute to the research toward and development of new vaccines and antiviral drugs.

MAVS signaling shapes microglia responses to neurotropic virus infection

Viral encephalitis is characterized by a series of immunological reactions that can control virus infection in the brain, but dysregulated responses may cause excessive inflammation and brain damage. Microglia are brain-resident myeloid cells that are specialized in surveilling the local CNS environment and in case of viral brain infection they contribute to the control of the infection and to restriction of viral dissemination. Here, we report that after exposure to neurotropic vesicular stomatitis virus (VSV), murine in vitro microglia cultures showed rapid upregulation of a broad range of pro-inflammatory and antiviral genes, which were stably expressed over the entire 8 h infection period. Additionally, a set of immunomodulatory genes was upregulated between 6 and 8 h post infection. In microglia cultures, the induction of several immune response pathways including cytokine responses was dependent on mitochondrial antiviral-signaling protein (MAVS). Consequently, in Mavs-deficient microglia the control of virus propagation failed as indicated by augmented virus titers and the accumulation of viral transcripts. Thus, in the analyzed in vitro system, MAVS signaling is critically required to achieve full microglia activation and to mediate profound antiviral effects. In Mavs-deficient mice, intranasal VSV instillation caused higher disease severity than in WT mice and virus dissemination was noticed beyond the olfactory bulb. Virus spread to inner regions of the olfactory bulb, i.e., the granular cell layer, correlated with the recruitment of highly inflammatory non-microglia myeloid cells into the olfactory bulb in Mavs−/− mice. Furthermore, increased cytokine levels were detected in the nasal cavity, the olfactory bulb and in other brain regions. Thus, microglial MAVS signaling is critically needed for virus sensing, full microglia activation, and for orchestration of protective immunity in the virus-infected CNS.

Intra-tumoral delivery of 5'ppp-dsRNA induces robust anti-tumor response via RIG-I activation and Bcl-2 gene downregulation in murine model of prostate cancer.

Onco-immunotherapy via blocking checkpoint-inhibitors has revolutionized the treatment-landscape of several malignancies, though not in the metastatic castration-resistant prostate cancer (PCa) owing to immunosuppressive and poorly immunogenic "cold" tumor microenvironment (TME). Turning up the heat of such cold TME via triggering innate immunity is now of increasing interest to restore immune-surveillance. Retinoic acid-inducible gene- I (RIG-I)-like receptors (RLRs) are cytosolic innate-sensors that can detect exogenous RNAs and induce type-I interferons and other pro-inflammatory signaling. RIG-I activation is suggested to be a valuable addition to the treatment approaches for several cancers. However, the knowledge about RIG-I signaling in PCa remains elusive. The present study evaluated the expression of two important RLRs, RIG-I and melanoma differentiation-associated protein 5 (MDA5) along with their downstream partners, mitochondrial antiviral-signaling protein (MAVS) and ERA G-protein-like 1 (ERAL1) during PCa progression in the transgenic adenocarcinoma of mouse prostate (TRAMP) model. The early stage of PCa revealed a significant increment in the expression of RLRs, but not MAVS. However, the advanced stage showed downregulated RLR signaling. Further, the therapeutic implication of 5'ppp-dsRNA, a synthetic RIG-I agonist and Bcl2 gene silencer has been investigated in vitro and in vivo. Intra-tumoral delivery of 5'ppp-dsRNA regressed tumor growth via triggering tumor cells apoptosis, immunomodulation, and inducing phagocytic "eat me" signals. These findings highlight that, for the first time, RIG-I activation and Bcl-2 silencing with 5'ppp-dsRNA can serve as a potent tumor-suppressor strategy in PCa and has a significant clinical implication in transforming "cold" TME into immunogenic "hot" TME of PCa.

Macrophage migration inhibitory factor facilitates replication of Senecavirus A by enhancing the glycolysis via hypoxia inducible factor 1 alpha

Senecavirus A (SVA) induced porcine idiopathic vesicular disease (PIVD) has been spread worldwide due to persistent infection, causing economic losses in swine industry. Host factors play an important role in replication of SVA, while, the interaction of migration inhibitory factor (MIF) and the virus has not been verified. Here, MIF facilitates the replication of SVA by enhancing the glycolysis via hypoxia-inducible factor alpha (HIF-1α) was reported. SVA infection up-regulates the expression of MIF in 3D4/21 cells, and infection experiment of cells with overexpression and interference expression of MIF showed that MIF facilitates the replication of SVA. MIF promoted the glycolysis in SVA infection to facilitate its replication by enhancing the accumulation of lactate and decreasing the production of adenosine triphosphate (ATP) and inhibiting the expression of retinoic acid-inducible gene I (RIG-I), mitochondrial antiviral-signaling protein (MAVS), interferon regulatory factor 3 (IRF3), interferon-beta (IFN-β), IFN-α, interferon-stimulating gene 15 (ISG15), and ISG56. Meanwhile, specific inhibitor verified MIF facilitates the replication of SVA by enhancing glycolysis. Further results showed MIF induces the increased expression of HIF-1α, which enhances MIF-induced glycolysis. These results provide new data on host factors in replication of SVA, as well as better understanding the role of MIF in virus infection.

Bunyavirus SFTSV nucleoprotein exploits TUFM-mediated mitophagy to impair antiviral innate immunity

ABSTRACT Severe fever with thrombocytopenia syndrome is an emerging viral hemorrhagic fever caused by a tick-borne bunyavirus, severe fever with thrombocytopenia syndrome virus (SFTSV), with a high case fatality. We previously found that SFTSV nucleoprotein (NP) induces macroautophagy/autophagy to facilitate virus replication. However, the role of NP in antagonizing host innate immunity remains unclear. Mitophagy, a selected form of autophagy, eliminates damaged mitochondria to maintain mitochondrial homeostasis. Here, we demonstrate that SFTSV NP triggers mitophagy to degrade MAVS (mitochondrial antiviral signaling protein), thereby blocking MAVS-mediated antiviral signaling to escape the host immune response. Mechanistically, SFTSV NP translocates to mitochondria by interacting with TUFM (Tu translation elongation factor, mitochondrial), and mediates mitochondrial sequestration into phagophores through interacting with LC3, thus inducing mitophagy. Notably, the N-terminal LC3-interacting region (LIR) motif of NP is essential for mitophagy induction. Collectively, our results demonstrated that SFTSV NP serves as a novel virulence factor, inducing TUFM-mediated mitophagy to degrade MAVS and evade the host immune response. Abbreviation: 3-MA: 3-methyladenine; ACTB: actin beta; co-IP: co-immunoprecipitation; CQ: chloroquine; DAPI: 4ʹ,6-diamidino-2-phenylindole, dihydrochloride; DMSO: dimethyl sulfoxide; FCCP: carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone; GFP: green fluorescent protein; HTNV: Hantan virus; IAV: influenza A virus; IFN: interferon; LAMP1: lysosomal associated membraneprotein 1; LIR: LC3-interacting region; MAP1LC3B/LC3B: microtubule associatedprotein 1 light chain 3 beta; MAVS: mitochondrial antiviral signaling protein; Mdivi-1: mitochondrial division inhibitor 1; MOI: multiplicity of infection; MT-CO2/COXII: mitochondrially encoded cytochrome C oxidase II; NP: nucleoprotein; NSs: nonstructural proteins; poly(I:C): polyinosinic:polycytidylic acid; RIGI: RNA sensor RIG-I; RLR: RIGI-like receptor; SFTSV: severe fever withthrombocytopenia syndrome virus; TCID50: 50% tissue culture infectiousdose; TIMM23: translocase of inner mitochondrial membrane 23; TOMM20:translocase of outer mitochondrial membrane 20; TUFM: Tu translation elongationfactor, mitochondrial.

TGFβ primes alveolar-like macrophages to induce type I IFN following TLR2 activation.

Alveolar macrophages (AMs) are key mediators of lung function and are potential targets for therapies during respiratory infections. TGFβ is an important regulator of AM differentiation and maintenance, but how TGFβ directly modulates the innate immune responses of AMs remains unclear. This shortcoming prevents effective targeting of AMs to improve lung function in health and disease. Here we leveraged an optimized ex vivo AM model system, fetal-liver derived alveolar-like macrophages (FLAMs), to dissect the role of TGFβ in AMs. Using transcriptional analysis, we first globally defined how TGFβ regulates gene expression of resting FLAMs. We found that TGFβ maintains the baseline metabolic state of AMs by driving lipid metabolism through oxidative phosphorylation and restricting inflammation. To better understand inflammatory regulation in FLAMs, we next directly tested how TGFβ alters the response to TLR2 agonists. While both TGFβ (+) and TGFβ (-) FLAMs robustly responded to TLR2 agonists, we found an unexpected activation of type I interferon (IFN) responses in FLAMs and primary AMs in a TGFβ-dependent manner. Surprisingly, mitochondrial antiviral signaling protein and the interferon regulator factors 3 and 7 were required for IFN production by TLR2 agonists. Together, these data suggest that TGFβ modulates AM metabolic networks and innate immune signaling cascades to control inflammatory pathways in AMs.

Targeting APT2 improves MAVS palmitoylation and antiviral innate immunity

Innate immunity serves as the primary defense against viral and microbial infections in humans. The precise influence of cellular metabolites, especially fatty acids, on antiviral innate immunity remains largely elusive. Here, through screening a metabolite library, palmitic acid (PA) has been identified as a key modulator of antiviral infections in human cells. Mechanistically, PA induces mitochondrial antiviral signaling protein (MAVS) palmitoylation, aggregation, and subsequent activation, thereby enhancing the innate immune response. The palmitoyl-transferase ZDHHC24 catalyzes MAVS palmitoylation, thereby boosting the TBK1-IRF3-interferon (IFN) pathway, particularly under conditions of PA stimulation or high-fat-diet-fed mouse models, leading to antiviral immune responses. Additionally, APT2 de-palmitoylates MAVS, thus inhibiting antiviral signaling, suggesting that its inhibitors, such as ML349, effectively reverse MAVS activation in response to antiviral infections. These findings underscore the critical role of PA in regulating antiviral innate immunity through MAVS palmitoylation and provide strategies for enhancing PA intake or targeting APT2 for combating viral infections.

E3 ubiquitin ligase ANKIB1 attenuates antiviral immune responses by promoting K48-linked polyubiquitination of MAVS

Upon sensing cytosolic viral RNA, retinoic acid-inducible gene-I-like receptors (RLRs) interact with mitochondrial antiviral signaling proteins (MAVSs) to activate IRF3 and nuclear factor κB (NF-κB) signaling, initiating innate immune responses. Thus, RLR activation plays a vital role in the removal of invasive RNA viruses while maintaining immune homeostasis. However, inadequate or excessive activation of immunity can cause harm and can even lead to lethal consequences. In this study, we identify an E3 ligase, ankyrin repeat and IBR domain containing 1 (ANKIB1), which suppresses RLR signaling via MAVS. ANKIB1 binds to MAVS to enhance K48-linked polyubiquitination with K311R, causing proteasomal degradation of MAVS. Deficiency of ANKIB1 significantly increases the RLR-mediated production of type I interferon (IFN) along with pro-inflammatory factors. Consequently, ANKIB1 deficiency remarkably increases antiviral immunity and decreases viral replication invivo. Therefore, we reveal that ANKIB1 restricts RLR-induced innate immune activation, indicating its potential role as a therapeutic target for viral infections.

MicroRNA 29a alleviates mitochondrial stress in diet-induced NAFLD by inhibiting the MAVS pathway

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder characterized by fat accumulation in the liver. This leads to aggravated hepatocyte inflammation due to impaired mitochondrial function, mitochondrial double-stranded RNA (mt-dsRNA) release, elevated oxidative stress, and reactive oxygen species (ROS) production.MicroRNA-29a (miR-29a) is used to reduce hepatic fibrosis in cases of cholestatic liver damage and lessen the severity of non-alcoholic steatohepatitis in animal studies by influencing mitochondrial protein balance. However, the effectiveness of miR-29a in diminishing mt-dsRNA-induced exacerbation of NAFLD remains poorly understood, particularly in the context of a Western diet (WD). Our results have found that mice with increased miR-29a levels and fed a WD showed notably decreased serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), total cholesterol, and low-density lipoprotein cholesterol levels. They also experienced less weight gain and lower final body and liver weights. In addition, overexpression of miR-29a reduced the severity of fibrosis, alleviated hepatic oxidative stress, misfolded protein aggregates, and the release of mt-dsRNA. Moreover, miR-29a attenuated the innate immune mitochondrial antiviral-signaling protein (MAVS) pathway response. In vitro, the research using HepG2 cells confirmed that miR-29a reduces MAVS expression and decreases the release of mt-dsRNA and superoxide initiated by palmitic acid (PA). Analysis of luciferase activity further established that the specific binding of miR-29a to the 3′UTR of MAVS led to a repression of its expression. In conclusion, these groundbreaking findings underscore the potential of miR-29a in improving the treatment of NAFLD and liver steatofibrosis by inhibiting the MAVS signaling pathway.

Modifications of Mitochondrial Network Morphology Affect the MAVS-Dependent Immune Response in L929 Murine Fibroblasts during Ectromelia Virus Infection.

Since smallpox vaccination was discontinued in 1980, there has been a resurgence of poxvirus infections, particularly the monkeypox virus. Without a global recommendation to use the smallpox vaccine, the population is not immune, posing a severe threat to public health. Given these circumstances, it is crucial to understand the relationship between poxviruses and their hosts. Therefore, this study focuses on the ectromelia virus, the causative agent of mousepox, which serves as an excellent model for studying poxvirus pathogenesis. Additionally, we investigated the role of mitochondria in innate antiviral immunity during ECTV infection, focusing specifically on mitochondrial antiviral signaling protein. The study used a Moscow strain of ECTV and L929 mouse fibroblasts. Cells were treated with ECTV and chemical modulators of mitochondrial network: Mdivi-1 and CCCP. Our investigation revealed that an elongated mitochondrial network attenuates the suppression of MAVS-dependent immunity by ECTV and reduces ECTV replication in L929 fibroblasts compared to cells with an unaltered mitochondrial network. Conversely, a fragmented mitochondrial network reduces the number of progeny virions while increasing the inhibition of the virus-induced immune response during infection. In conclusion, our study showed that modifications of mitochondrial network morphology alter MAVS-dependent immunity in ECTV-infected mouse L929 fibroblasts.

Molluscum contagiosum virus protein MC089 inhibits interferon regulatory factor 3 activation.

Molluscum contagiosum virus (MCV) is a human-specific poxvirus that causes a highly common but mild infection characterized by distinctive and persistent papular skin lesions. These lesions can persist for long periods without an effective clearance response from the host. MCV, like all poxviruses, encodes multiple known immunosuppressive proteins which target innate immune signalling pathways involved in viral nucleic acid sensing, interferon production and inflammation which should trigger antiviral immunity leading to clearance. Two major families of transcription factors responsible for driving the immune response to viruses are the NF-κB and the interferon regulatory factor (IRF) families. While NF-κB broadly drives pro-inflammatory gene expression and IRFs chiefly drive interferon induction, both collaborate in transactivating many of the same genes in a concerted immune response to viral infection. Here, we report that the MCV protein MC089 specifically inhibits IRF activation from both DNA- and RNA-sensing pathways, making it the first characterized MCV inhibitor to selectively target IRF activation to date. MC089 interacts with proteins required for IRF activation, namely IKKε, TBKBP1 and NAP1. Additionally, MC089 targets RNA sensing by associating with the RNA-sensing adaptor protein mitochondrial antiviral-signalling protein on mitochondria. MC089 displays specificity in its inhibition of IRF3 activation by suppressing immunostimulatory nucleic acid-induced serine 396 phosphorylation without affecting the phosphorylation of serine 386. The selective interaction of MC089 with IRF-regulatory proteins and site-specific inhibition of IRF3 phosphorylation may offer a tool to provide novel insights into the biology of IRF3 regulation.

The Hemagglutinin of Influenza A Virus Induces Ferroptosis to Facilitate Viral Replication.

Ferroptosis is a novel form of cell death caused by the accumulation of lipid peroxides in an iron-dependent manner. However, the precise mechanism underlying the exploitation of ferroptosis by influenza A viruses (IAV) remains unclear. The results demonstrate that IAV promotes its own replication through ferritinophagy by sensitizing cells to ferroptosis, with hemagglutinin identified as a key trigger in this process. Hemagglutinin interacts with autophagic receptors nuclear receptor coactivator 4 (NCOA4)and tax1-binding protein 1 (TAX1BP1), facilitating the formation of ferritin-NCOA4 condensates and inducing ferritinophagy. Further investigation shows that hemagglutinin-induced ferritinophagy causes cellular lipid peroxidation, inhibits aggregation of mitochondrial antiviral signaling protein (MAVS), and suppresses the type I interferon response, thereby contributing to viral replication. Collectively, a novel mechanism by which IAV hemagglutinin induces ferritinophagy resulting in cellular lipid peroxidation, consequently impairing MAVS-mediated antiviral immunity, is revealed.

Trim47 prevents hematopoietic stem cell exhaustion during stress by regulating MAVS-mediated innate immune pathway

The maintenance of hematopoietic stem cell (HSC) functional integrity is essential for effective hematopoietic regeneration when suffering from injuries. Studies have shown that the innate immune pathways play crucial roles in the stress response of HSCs, whereas how to precisely modulate these pathways is not well characterized. Here, we identify the E3 ubiquitin ligase tripartite motif-containing 47 (Trim47) as a negative regulator of the mitochondrial antiviral-signaling protein (MAVS)-mediated innate immune pathway in HSCs. We find that Trim47 is predominantly enriched in HSCs, and its deficiency impairs the function and survival of HSCs after exposure to 5-flurouracil (5-FU) and irradiation (IR). Mechanistically, Trim47 impedes the excessive activation of the innate immune signaling and inflammatory response via K48-linked ubiquitination and degradation of MAVS. Collectively, our findings demonstrate a role of Trim47 in preventing stress-induced hematopoietic failure and thus provide a promising avenue for treatment of related diseases in the clinic.

Effects of Isochlorogenic Acid A on Mitochondrial Dynamics Imbalance and RLR Damage in PAM Cells Induced by Combined Mycotoxins

Mycotoxins have strong immunotoxicity and can induce oxidative stress and mitochondrial dynamics imbalance. Mitochondrial antiviral signaling protein (MAVS) in the RIG-I like receptor (RLR) pathway of innate immunity is located on mitochondria, and whether it is affected by mycotoxins has not been reported yet. This experiment used porcine alveolar macrophages (PAM) to evaluate the antagonism of three isomers of chlorogenic acid (chlorogenic acid, isochlorogenic acid A, and neochlorogenic acid) against combined mycotoxins (Aflatoxin B1, Deoxynivalenol, and Ochratoxin A) induced mitochondrial damage and their effects on the RLR pathway, providing assistance for further elucidating the mechanism of mycotoxin immunotoxicity. Western blotting, enzyme linked immunosorbent assay (ELISA), and flow cytometry were used to detect relevant indicators. All three types of chlorogenic acid treatment can antagonize the cytotoxicity induced by combined mycotoxins, especially isochlorogenic acid A, which can protect cells from mycotoxins damage by maintaining mitochondrial dynamic homeostasis and improving innate immune function related to the RLR pathway.

Encephalomyocarditis Virus Structural Protein VP3 Interacts with MAVS and Promotes its Autophagic Degradation to Interfere with the Type I Interferon Signaling Pathway.

Understanding the mechanisms through which interferon (IFN) signaling is negatively regulated is crucial for preserving the equilibrium of innate immune reactions, as the innate immune system functions, such as the original barrier, combat threats to the host. Although the function of the encephalomyocarditis virus (EMCV) viral proteins in antagonizing innate immunity has been related to earlier studies, the precise mechanism underlying the role of viral protein 3 (VP3) in type I IFN has yet to be fully illuminated. VP3 expression and many other adaptor molecules belonging to type I IFN pathway expression levels were evaluated using Western blotting. The IFN and other antiviral genes, such as interferon-stimulated genes (ISGs) 15 and 56, were assessed by real-time quantitative polymerase chain reaction (RT-qPCR). A 50% tissue culture infectious dose (TCID50) assay was utilized to explore the effect of VP3 on EMCV proliferation in human embryonic kidney (HEK293) cells. Co-immunoprecipitation (Co-IP) assays and confocal microscope analysis were used to investigate the underlying mechanisms mediated by VP3. We discovered that the VP3 of EMCV acts as a suppressor of innate immune reactions. Increased levels of VP3 enhance viral reproduction through modulation of innate immune signaling pathways and suppression of antiviral responses. Additional information indicated that during viral infection, the VP3 of EMCV enhances autophagy and interacts specifically with mitochondrial antiviral signaling protein (MAVS), leading to its degradation in an autophagy pathway that relies on p62. Our findings showed that EMCV developed a tactic to combat host antiviral defenses by using autophagy to break down a protein that controls the innate immune response following a viral infection of the host. Notably, VP3 plays an important role in this process. Overall, these discoveries may provide a novel therapeutic target for EMCV.

Fetal MAVS and type I IFN signaling pathways control ZIKV infection in the placenta and maternal decidua.

The contribution of placental immune responses to congenital Zika virus (ZIKV) syndrome remains poorly understood. Here, we leveraged a mouse model of ZIKV infection to identify mechanisms of innate immune restriction exclusively in the fetal compartment of the placenta. ZIKV principally infected mononuclear trophoblasts in the junctional zone, which was limited by mitochondrial antiviral-signaling protein (MAVS) and type I interferon (IFN) signaling mechanisms. Single nuclear RNA sequencing revealed MAVS-dependent expression of IFN-stimulated genes (ISGs) in spongiotrophoblasts but not in other placental cells that use alternate pathways to induce ISGs. ZIKV infection of Ifnar1-/- or Mavs-/- placentas was associated with greater infection of the adjacent immunocompetent decidua, and heterozygous Mavs+/- or Ifnar1+/- dams carrying immunodeficient fetuses sustained greater maternal viremia and tissue infection than dams carrying wild-type fetuses. Thus, MAVS-IFN signaling in the fetus restricts ZIKV infection in junctional zone trophoblasts, which modulates dissemination and outcome for both the fetus and the pregnant mother.