RIG-I-like Receptors Research Articles

The Impact of Pathogens on Sepsis Prevalence and Outcome.

Sepsis, a severe global healthcare challenge, is characterized by significant morbidity and mortality. The 2016 redefinition by the Third International Consensus Definitions Task Force emphasizes its complexity as a "life-threatening organ dysfunction caused by a dysregulated host response to infection". Bacterial pathogens, historically dominant, exhibit geographic variations, influencing healthcare strategies. The intricate dynamics of bacterial immunity involve recognizing pathogen-associated molecular patterns, triggering innate immune responses and inflammatory cascades. Dysregulation leads to immunothrombosis, disseminated intravascular coagulation, and mitochondrial dysfunction, contributing to the septic state. Viral sepsis, historically less prevalent, saw a paradigm shift during the COVID-19 pandemic, underscoring the need to understand the immunological response. Retinoic acid-inducible gene I-like receptors and Toll-like receptors play pivotal roles, and the cytokine storm in COVID-19 differs from bacterial sepsis. Latent viruses like human cytomegalovirus impact sepsis by reactivating during the immunosuppressive phases. Challenges in sepsis management include rapid pathogen identification, antibiotic resistance monitoring, and balancing therapy beyond antibiotics. This review highlights the evolving sepsis landscape, emphasizing the need for pathogen-specific therapeutic developments in a dynamic and heterogeneous clinical setting.

The LxIS motif is the language between virus and host RLRs: From fish to mammalian viruses

Regulation of host interferon (IFN) production is a crucial strategy for viral immune escape. We propose that the LxIS motif language, a marker for exogenous viral proteins, interacts with host retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) factors. In this study, the viral proteins containing the LxIS motif of grass carp reovirus (GCRV), and cyprinid herpesvirus 3 (CyHV-3), which belong to the fish RNA and DNA viruses, were found to interact with RLRs, and the general functions of these proteins were negative regulation of IFN activation. Terrestrial animal viruses with this motif language, such as SARS-CoV-2 and so on, are also examined. Several viral proteins that were not reported previously were found to be associated with the RLR pathway. Taken together, the LxIS motif language elucidates a straightforward and efficient method for identifying viral proteins that target host RLRs to regulate IFN expression, and is conserved in both lower and higher vertebrates.

USP13 Cooperates with MARCH8 to Inhibit Antiviral Signaling by Targeting MAVS for Autophagic Degradation in Teleost.

Mitochondrial antiviral signaling protein (MAVS), as a central adapter protein in retinoic acid-inducible gene I-like receptor signaling, is indispensable for innate antiviral immunity. Yet, the molecular mechanisms modulating the stability of MAVS are not fully understood in low vertebrates. In this study, we report that the deubiquitinase ubiquitin-specific protease 13 (USP13) acts as a negative regulator of antiviral immunity by targeting MAVS for selective autophagic degradation in teleost fish. USP13 is induced by RNA virus or polyinosinic:polycytidylic acid stimulation and acts as a negative regulator to potentiate viral replication in fish cells. Mechanistically, USP13 functions as a scaffold to enhance the interaction between MAVS and the E3 ubiquitin ligase MARCH8, thus promoting MARCH8 to catalyze MAVS through K27-linked polyubiquitination for selective autophagic degradation. Taken together, to our knowledge, our study demonstrates a novel mechanism by which viruses evade host antiviral immunity via USP13 in fish and provides a new idea for mammalian innate antiviral immunity.

The aldehyde dehydrogenase ALDH1B1 exerts antiviral effects through the aggregation of the adaptor MAVS.

Type I interferons (IFNs) are produced by almost all cell types and play a vital role in host defense against viral infection. Infection with an RNA virus activates receptors such as RIG-I, resulting in the recruitment of the adaptor protein MAVS to the RIG-I-like receptor (RLR) signalosome and the formation of prion-like functional aggregates of MAVS, which leads to IFN-β production. Here, we identified the aldehyde dehydrogenase 1B1 (ALDH1B1) as a previously uncharacterized IFN-stimulated gene (ISG) product with critical roles in the antiviral response. Knockout of ALDH1B1 increased, whereas overexpression of ALDH1B1 restricted, the replication of RNA viruses, such as vesicular stomatitis virus (VSV), Zika virus (ZIKV), dengue virus (DENV), and influenza A virus (IAV). We found that ALDH1B1 localized to mitochondria, where it interacted with the transmembrane domain of MAVS to promote MAVS aggregation. ALDH1B1 was recruited to MAVS aggregates. In addition, ALDH1B1 also enhanced the interaction between activated RIG-I and MAVS, thus increasing IFN-β production and the antiviral response. Furthermore, Aldh1b1-/- mice developed more severe symptoms than did wild-type mice upon IAV infection. Together, these data identify an aldehyde dehydrogenase in mitochondria that functionally regulates MAVS-mediated signaling and the antiviral response.

H5N1 avian influenza virus PB2 antagonizes duck IFN-β signaling pathway by targeting mitochondrial antiviral signaling protein1

Type I interferon (IFN)-mediated innate immune responses represent the first line of host defense against viral infection. However, the molecular mechanisms by which avian influenza virus (AIV) inhibits type I IFN production in ducks are not well understood. Here, we first found that the polymerase basic 2 (PB2) protein of H5N1 subtype AIV inhibited the type I IFN responses by targeting duck mitochondrial antiviral signaling protein (MAVS). We further demonstrated that H5N1-PB2 bound to the △transmembrane (△TM) domain of duck MAVS, and the polymerase basic 1 (PB1) binding domain (PBD) and RNA binding nuclear import domain (RND) of H5N1-PB2 interacted with MAVS to inhibit type I IFN expression in ducks. Collectively, our findings contribute to understanding the molecular mechanism by which AIV proteins regulate the retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) signaling pathway to evade host antiviral immune responses in ducks.

Research progress on the pattern recognition receptors involved in porcine reproductive and respiratory syndrome virus infection.

Porcine reproductive and respiratory syndrome (PRRS) is one of the most economically devastating infectious diseases of pigs globally. The pathogen, porcine reproductive and respiratory syndrome virus (PRRSV), is an enveloped positive-stranded RNA virus, which is considered to be the key triggers for the activation of effective innate immunity through pattern recognition receptor (PRR)-dependent signaling pathways. Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), C-type lectin receptors (CLRs), NOD-like receptors (NLRs) and Cytoplasmic DNA receptors (CDRs) are used as PRRs to identify distinct but overlapping microbial components. The innate immune system has evolved to recognize RNA or DNA molecules from microbes through pattern recognition receptors (PRRs) and to induce defense response against infections, including the production of type I interferon (IFN-I) and inflammatory cytokines. However, PRRSV is capable of continuous evolution through gene mutation and recombination to evade host immune defenses and exploit host cell mechanisms to synthesize and transport its components, thereby facilitating successful infection and replication. This review presents the research progress made in recent years in the study of these PRRs and their associated adapters during PRRSV infection.

Orange-spotted grouper nervous necrosis virus-encoded protein A induces interferon expression via RIG-I/MDA5-MAVS-TBK1-IRF3 signaling in fish cells.

As a major pathogen, nervous necrosis virus (NNV) infects more than 120 fish species worldwide and is virulent to larvae and juvenile fish, hampering the development of the fish fry industry. Understanding virus-host interaction and underlying mechanisms is an important but largely unknown issue in fish virus studies. Here, using channel catfish ovary and fathead minnow cells as models for the study of innate immunity signaling, we found that NNV-encoded ProA activated interferon signaling via the retinoic acid-inducible gene I (RIG-I)-like receptor (RLR) pathway which was still suppressed by the infection of wild-type NNV. This finding has important implications for the comprehension of NNV protein function and the immune response from different cells. First, RIG-I is the key node for anti-NNV innate immunity. Second, the response intensity of RLR signaling determines the degree of NNV proliferation. This study expands our knowledge regarding the overview of signal pathways affected by NNV-encoded protein and also highlights potential directions for the control of aquatic viruses.

LTN1 promotes RLR degradation to inhibit immune response to RNA virus through the ESCRT pathway

ABSTRACT The excessive activation of immune responses will trigger autoimmune diseases or inflammatory injury. The endosomal sorting complexes required for transport (ESCRT) system can capture and mediate ubiquitinated protein degradation, which timely terminates signaling pathway hyperactivation. However, whether the ESCRT system participates in regulating RIGI-like receptor (RLR)-mediated antiviral responses remains unknown. In this study, we show that LTN1/listerin, a major component of RQC, can recruit E3 ubiquitin ligase TRIM27 to trigger K63-linked polyubiquitination of RIGI and IFIH1/MDA5. This K63-linked polyubiquitination facilitates the sorting and degradation of RIGI and IFIH1 proteins through the ESCRT-dependent pathway. Concordantly, LTN1 deficiency enhances the innate antiviral response to infection with RNA viruses. Thus, our work uncovers a new mechanism for RIGI and IFIH1 degradation and identifies the role of LTN1 in negatively regulating RLR-mediated antiviral innate immunity, which may provide new targets for the intervention of viral infection. Abbreviation: 5'-pppRNA: 5’ triphosphate double stranded RNA; ATG5: autophagy related 5; ATG7: autophagy related 7; BafA1: bafilomycin A1; ESCRT: endosomal sorting complexes required for transport; CHX: cycloheximide; IFIH1/MDA5: interferon induced with helicase C domain 1; IFN: interferon; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; RIGI: RNA sensor RIG-I; RLR: RIGI-like receptors; RQC: ribosome-associated protein quality control; SeV: Sendai virus; TRIM27: tripartite motif-containing 27; VSV: vesicular stomatitis virus; VPS4: vacuolar protein sorting 4.

A novel protein encoded by circVPS13D attenuates antiviral innate immunity by targeting MAVS in teleost fish.

The expression of circVPS13D was upregulated with SCRV invasion, which proved that circVPS13D was involved in the regulation of the antiviral immune response. Our study revealed that the existence of circVPS13D promoted the replication of SCRV. Functionally, circVPS13D negatively regulates the antiviral responses of fish. Mechanistically, we confirmed that circVPS13D inhibited RLRs antiviral signaling pathway via the encoded protein VPS13D-170aa by targeting MAVS. Our study provided novel insights into the roles of protein-coding circRNAs and supported VPS13D-170aa as a negative regulator in the antiviral immune responses of teleost fish.

Zebrafish spop promotes ubiquitination and degradation of mavs to suppress antiviral response via the lysosomal pathway

Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) signaling pathways are required to be tightly controlled to initiate host innate immune responses. Fish mitochondrial antiviral signaling (mavs) is a key determinant in the RLR pathway, and its ubiquitination is associated with mavs activation. Here, we identified the zebrafish E3 ubiquitin ligase Speckle-type BTB–POZ protein (spop) negatively regulates mavs-mediated the type I interferon (IFN) responses. Consistently, overexpression of zebrafish spop repressed the activity of IFN promoter and reduced host ifn transcription, whereas knockdown spop by small interfering RNA (siRNA) transfection had the opposite effects. Accordingly, overexpression of spop dampened the cellular antiviral responses triggered by spring viremia of carp virus (SVCV). A functional domain assay revealed that the N-terminal substrate-binding MATH domain regions of spop were necessary for IFN suppression. Further assays indicated that spop interacts with mavs through the C-terminal transmembrane (TM) domain of mavs. Moreover, zebrafish spop selectively promotes K48-linked polyubiquitination and degradation of mavs through the lysosomal pathway to suppress IFN expression. Our findings unearth a post-translational mechanism by which mavs is regulated and reveal a role for spop in inhibiting antiviral innate responses.

Early enterovirus translation deficits extend viral RNA replication and elicit sustained MDA5-directed innate signaling.

Multiple pattern recognition receptors sense vRNAs and initiate downstream innate signaling: endosomal Toll-like receptors (TLRs) 3, 7, and 8 and cytoplasmic RIG-I-like receptors (RLRs) RIG-I, and MDA5. They engage distinct signaling scaffolds: mitochondrial antiviral signaling protein (RLR), MyD88, and TLR-adaptor interacting with SLC15A4 on the lysosome (TLR7 and TLR8) and toll/IL-1R domain-containing adaptor inducing IFN (TLR3). By virtue of their unusual vRNA structure and direct host cell entry path, the innate response to EVs uniquely is orchestrated by MDA5. We reported that PVSRIPO's profound attenuation and loss of cytopathogenicity triggers MDA5-directed polar TBK1-IRF3 signaling that generates priming of polyfunctional antitumor CD8+ T-cell responses and durable antitumor surveillance in vivo. Here we unraveled EV-host relations that control suppression of host type-I IFN responses and show that PVSRIPO's deficient immediate host eIF4G cleavage generates unopposed MDA5-directed downstream signaling cascades resulting in sustained type-I IFN release.

Black carp LGP2 suppresses RIG-I mediated IFN signaling during the antiviral innate immunity

Laboratory of genetics and physiology 2 (LGP2), a member of retinoic acid-inducible gene (RIG)-I-like receptors (RLRs), has been reported to play different roles in IFN signaling in both mammals and teleost fish. In our previous study, black carp (Mylopharyngodon piceus) LGP2 (bcLGP2) has been characterized to positively regulate melanoma differentiation-associated gene 5 (MDA5). In this study, knockdown of bcLGP2 decreased the expression of host genes, including bcIFNb, bcPKR, bcMx1, and bcViperin, and also attenuated the antiviral capability of host cells. The relationship between bcLGP2 and black carp RIG-Ib (bcRIG-Ib) has been explored. Dual-luciferase reporter assay and qRT-PCR assay indicated that bcLGP2 dampened bcRIG-Ib induced transcription of type I interferons (IFNs) and interferon-stimulated genes (ISGs), including PKR, ISG15, and Viperin. Consistently, the plaque assay identified that bcLGP2 attenuated bcRIG-Ib mediated antiviral ability against spring viremia of carp virus (SVCV). Co-immunoprecipitation assay identified the interaction between bcLGP2 and bcRIG-Ib, as well as bcLGP2 and bcRIG-Ib-CARD. And bcRIG-Ib-CARD mediated antiviral ability was also attenuated by bcLGP2. Truncation mutation analysis showed DExD/H-box Helicase domain of bcLGP2 possessed a similar inhibitory effect on bcRIG-Ib to that of bcLGP2, while the C-terminus repressor domain (CTD) presented little impact on bcRIG-Ib. Furthermore, bcLGP2 enhanced the K48-linked ubiquitination of bcRIG-Ib, promoting proteasome-dependent degradation of bcRIG-Ib. Thus, our data supported the conclusion that bcLGP2 interacted with and induced degradation of bcRIG-Ib through proteasome, leading to the dampened antiviral signaling mediated by bcRIG-Ib.

The TRK-fused gene negatively regulates interferon signaling by inhibiting TBK1 phosphorylation during PPMV-1 infection

TRK-fused gene (TFG, tropomyosin-receptor kinase fused gene) is known to negatively regulate the retinoic acid inducible gene (RIG)-I-like receptor (RLR)-mediated interferon (IFN)-I pathway in human cells, thereby participating in the paramyxovirus infection process. We showed that pigeon paramyxovirus type 1 (PPMV-1) infection significantly upregulates TFG expression in infected cells at an early stage. We speculated that PPMV-1 would inhibit IFN activation by upregulating a negative regulator of the IFN pathway. This hypothesis was proved when TFG protein expression was knocked down by RNAi and the replication level of PPMV-1 virus decreased, which indicated that TFG upregulation in the early infection stage benefit virus replication. We next used the IFN-β promoter reporter system to evaluate the role of the TFG in the IFN pathway. The results showed that the TFG inhibited the IFN-β expression stimulated by RIG-I, MAVS (mitochondrial antiviral signaling protein) and TANK-binding kinase 1 (TBK1), but did not inhibit IFN-β activated by the interferon regulatory transcription factor 3 (IRF3), indicating that TFG may affect the function of TBK1, which play an important role in phosphorylation of the IRF3. Further experiments showed that the TFG inhibited the phosphorylation of TBK1, resulting in IRF3 being unable to be phosphorylated. Subsequent experiments on IFN pathway activation confirmed that the IRF3 phosphorylation level was significantly downregulated after overexpression of TFG, while the IFN-β promoter reporting experiment showed that TFG did not directly inhibit the IFN response activated by IRF3. This confirmed that TFG protein negatively regulates the IFN-β pathway by inhibiting TBK1 phosphorylation.

The role of duck LGP2 in innate immune response of host anti-tembusu virus

Laboratory of Genetics and Physiology 2 (LGP2), along with Retinoic Acid Induced Gene-I (RIG-I) and Melanoma Differentiation Associated Gene 5, are members of the retinoic acid-inducible gene-I-like receptors (RLRs) in pattern recognition receptors, playing an important role in the host’s innate immunity. Due to lacking a caspase activation and recruitment domain, LGP2 is controversially regarded as a positive or negative regulator in the antiviral response. This study aimed to explore how duck LGP2 (duLGP2) participates in duck innate immunity and its role in countering the duck Tembusu virus (DTMUV). In duck embryo fibroblast cells, the overexpression of duLGP2 significantly reduced the cell’s antiviral capacity by inhibiting type I interferon (IFN) production and the expression of downstream IFN-stimulated genes. Conversely, duLGP2 knockdown had the opposite effect. For the first time, we introduced the LGP2 gene fragment into duck embryos using a lentiviral vector to ensure persistent expression and generated gene-edited ducks with LGP2 overexpression. We demonstrated that duLGP2 facilitates DTMUV replication in both in vitro and in vivo experiments, leading to robust inflammatory and antiviral responses. Interestingly, the repressive effects of duLGP2 on type I IFN production were only observed in the early stage of DTMUV infection, with type I IFN responses becoming enhanced as the viral load increased. These results indicate that duLGP2 acts as a negative regulator during the resting state and early stages of DTMUV infection. This study provides a theoretical basis for further research on duck RLRs and developing new anti-DTMUV drugs or vaccine adjuvants.

MDA5 RNA-sensing pathway activation by Mycobacterium tuberculosis promotes innate immune subversion and pathogen survival.

Host cytosolic sensing of Mycobacterium tuberculosis (M. tuberculosis) RNA by the RIG-I-like receptor (RLR) family perturbs innate immune control within macrophages; however, a distinct role of MDA5, a member of the RLR family, in M. tuberculosis pathogenesis has yet to be fully elucidated. To further define the role of MDA5 in M. tuberculosis pathogenesis, we evaluated M. tuberculosis intracellular growth and innate immune responses in WT and Mda5-/- macrophages. Transfection of M. tuberculosis RNA strongly induced proinflammatory cytokine production in WT macrophages, which was abrogated in Mda5-/- macrophages. M. tuberculosis infection in macrophages induced MDA5 protein expression, accompanied by an increase in MDA5 activation as assessed by multimer formation. IFN-γ-primed Mda5-/- macrophages effectively contained intracellular M. tuberculosis proliferation to a markedly greater degree than WT macrophages. Further comparisons of WT versus Mda5-/- macrophages revealed that during M. tuberculosis infection MDA5 contributed to IL-1β production and inflammasome activation and that loss of MDA5 led to a substantial increase in autophagy. In the mouse TB model, loss of MDA5 conferred host survival benefits with a concomitant reduction in M. tuberculosis bacillary burden. These data reveal that loss of MDA5 is host protective during M. tuberculosis infection in vitro and in vivo, suggesting that M. tuberculosis exploits MDA5 to subvert immune containment.

Length-Dependent Modulation of B Cell Activating Factor Transcripts in Chicken Macrophage by Viral Double-Stranded RNA.

Viral double-stranded RNA (dsRNA) interacts with Retinoic-acid-inducible-gene-1 (RIG-1)-like receptors (RLRs) to induce type 1 interferons. Melanoma-derived-antigen-5 (MDA-5), an RLR, but not RIG-1, is found in chickens. Ducks express both RIG-1 and MDA-5, a possible cause of differences in susceptibility to influenza virus infection between chickens and ducks. Using the HD11 chicken macrophage cell line and an RT2 Profiler PCR-array system, we showed that high-molecular-weight poly(I:C), HMW-poly(I:C), upregulates CCL4, interferon-gamma, interleukin-1, and interleukin-6 mRNA transcripts. HMW-poly(I:C), an in vitro surrogate of long dsRNA species, also induces the upregulation of IL-12B and B cell activating factor (BAFF). Conversely, low-molecular-weight poly(I:C), LMW-poly(I:C) did not induce a distinct cytokine expression pattern. Nonetheless, co-transfection of LMW and HMW-poly(I:C) significantly reduced the upregulation of IL12B and BAFF by HMW-poly(I:C). These findings support previous studies that found no expression of RIG-1, a receptor for short dsRNA species, in chicken cells. Surprisingly, however, our data suggested that in the absence of RIG-1 in chicken macrophages, short dsRNA species may inhibit macrophage-mediated B cell development and survival by modulating the expression of BAFF without significantly reducing type 1 interferon response.

The RLR intrinsic antiviral system is expressed in neural retina and restricts lentiviral transduction of human Mueller cells

The retinoic acid-inducible gene I (RIG)-I-like receptor (RLR) family of RNA sensor proteins plays a key role in the innate immune response to viral nucleic acids, including viral gene delivery vectors, but little is known about the expression of RLR proteins in the retina. The purpose of this study was to characterize cell-specific expression patterns of RLR proteins in non-human primate (NHP) neural retina tissue and to examine if RLR pathway signaling restricts viral gene delivery transduction. Since RLR protein signaling converges at the mitochondrial antiviral signaling protein (MAVS), experiments were performed to determine if knockdown of MAVS affected FIVGFP transduction efficiency in the human Mueller cell line MIO-M1. Immunoblotting confirmed expression of RIG-I, melanoma differentiation-associated protein 5 (MDA5), laboratory of genetics and physiology 2 (LGP2), and MAVS proteins in MIO-M1 cells and NHP retina tissue. Double label immunofluorescence (IF) studies revealed RIG-I, LGP2, and MAVS were expressed in Mueller microglial cells in the NHP retina. In addition, LGP2 and MDA5 proteins were detected in cone and retinal ganglion cells (RGC). MDA5 was also present in a subset of calretinin positive amacrine cells, and in nuclei within the inner nuclear layer (INL). Knockdown of MAVS significantly increased the transduction efficiency of the lentiviral vector FIVGFP in MIO-M1 cells, compared to control cells. FIVGFP or AAVGFP challenge did not alter expression of the LGP2, MAVS, MDA5 or RIG-I genes in MIO-M1 cells or NHP retina tissue compared to media treated controls. Our data demonstrate that innate immune response proteins involved in viral RNA sensing, including MDA5, RIG-I, LGP2, and MAVS, are expressed in several cell types within the NHP neural retina. In addition, the MAVS protein restricts non-human lentiviral transduction efficiency in MIO-M1 cells.

MicroRNAs in the Regulation of RIG-I-like Receptor Signaling Pathway: Possible Strategy for Viral Infection and Cancer.

The retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) play a crucial role as pattern-recognition receptors within the innate immune system. These receptors, present in various cell and tissue types, serve as essential sensors for viral infections, enhancing the immune system's capacity to combat infections through the induction of type I interferons (IFN-I) and inflammatory cytokines. RLRs are involved in a variety of physiological and pathological processes, including viral infections, autoimmune disorders, and cancer. An increasing body of research has examined the possibility of RLRs or microRNAs as therapeutic targets for antiviral infections and malignancies, despite the fact that few studies have focused on the regulatory function of microRNAs on RLR signaling. Consequently, our main emphasis in this review is on elucidating the role of microRNAs in modulating the signaling pathways of RLRs in the context of cancer and viral infections. The aim is to establish a robust knowledge base that can serve as a basis for future comprehensive investigations into the interplay between microRNAs and RIG-I, while also facilitating the advancement of therapeutic drug development.

MAVS integrates glucose metabolism and RIG-I-like receptor signaling

MAVS is an adapter protein involved in RIG-I-like receptor (RLR) signaling in mitochondria, peroxisomes, and mitochondria-associated ER membranes (MAMs). However, the role of MAVS in glucose metabolism and RLR signaling cross-regulation and how these signaling pathways are coordinated among these organelles have not been defined. This study reports that RLR action drives a switch from glycolysis to the pentose phosphate pathway (PPP) and the hexosamine biosynthesis pathway (HBP) through MAVS. We show that peroxisomal MAVS is responsible for glucose flux shift into PPP and type III interferon (IFN) expression, whereas MAMs-located MAVS is responsible for glucose flux shift into HBP and type I IFN expression. Mechanistically, peroxisomal MAVS interacts with G6PD and the MAVS signalosome forms at peroxisomes by recruiting TNF receptor-associated factor 6 (TRAF6) and interferon regulatory factor 1 (IRF1). By contrast, MAMs-located MAVS interact with glutamine-fructose-6-phosphate transaminase, and the MAVS signalosome forms at MAMs by recruiting TRAF6 and TRAF2. Our findings suggest that MAVS mediates the interaction of RLR signaling and glucose metabolism.

Identification of long non-coding RNA MSTRG.5748.1 and MSTRG.7894.1 from Megalobrama amblycephala and their potential roles in innate immunity.

Megalobrama amblycephala is one of the most economically important freshwater fish in China, and the bacterial septicemia caused by Aeromonas hydrophila is a serious threat to the breeding industry of M. amblycephala. Unfortunately, the characterization of long noncoding RNA (lncRNA) in response to A. hydrophila infection has not been performed in M. amblycephala. To better understand the biological significance of lncRNA in the immune system, we identified two lncRNA, named MSTRG.5748.1 and MSTRG.7894.1, as playing critical roles in the antibacterial response of M. amblycephala. After separating the nucleus and cytoplasm of the hepatocytes from M. amblycephala, cellular localization of MSTRG.5748.1 and MSTRG.7894.1 was performed to predict their functions. The results showed that MSTRG.5748.1 was mainly expressed in the nucleus, suggesting that its functions are mostly to regulate the expression of downstream genes through epistasis and transcription. MSTRG.7894.1 existed in both the nucleus and cytoplasm, which indicated that it has many regulatory modes. qPCR analysis showed that MSTRG.5748.1 and MSTRG.7894.1 were expressed in the immune-related organs of M. amblycephala, and significantly changed in the liver after A. hydrophila infection. RNA-seq analysis revealed that differentially expressed genes (DEGs) were mainly enriched in antigen processing and presentation via MHC class I, RIG-I-like receptor (RLR) signaling pathway, and IFN-related pathway, and a large number of pathway-related genes were significantly regulated after lncRNA overexpression in muscle cell of M. amblycephala. Overexpression of MSTRG.5748.1 and MSTRG.7894.1 significantly inhibited the expression of STING and IFN, significantly upregulated muscle cell viability, and promoted cell proliferation by targeting STING and IFN.