Lipopolysaccharide-induced TNF-α factor in grass carp (Ctenopharyngodon idella): evidence for its involvement in antiviral innate immunity

Lipopolysaccharide-induced TNFα factor (LITAF) promotes inflammatory responses and activates apoptosis in zebrafish Danio rerio

Lipopolysaccharide-induced TNFα factor (LITAF) is an important transcription factor which activates the transcription of TNFα and regulates cell apoptosis and inflammatory response. In the present study, a LITAF gene homologue was identified in zebrafish (Danio rerio) and was shown to be well conserved in the protein sequence, genomic organization and synteny with human LITAF. DrLITAF was constitutively expressed in tissues, with the highest expression detected in the gills. Its expression could be modulated by LPS, poly(I:C), and infection with Edwardsiella tarda, Aeromonus hydrophila and septicemia viremia of carp virus (SVCV). DrLITAF, when overexpressed, was shown to be located on the cellular membrane and nuclear membrane of HEK293T and ZF4 cells and was associated with the endoplasmic reticulum. Stimulation with LPS resulted in rapid translocation of DrLITAF into the nucleus. In addition, DrLITAF was able to induce cell apoptosis and the expression of caspase 3. The results demonstrate that DrLITAF is involved in the immune defence against bacterial and viral infection and plays a role in regulating inflammation and apoptosis.

Molecular cloning and functional characterisation of NLRX1 in grass carp (Ctenopharyngodon idella)

The nucleotide-binding domain and leucine-rich-repeat-containing (NLR) proteins regulate innate immunity. Although the positive regulatory impact of NLRs is clear, their inhibitory roles are not well defined. In the present study, the NLR family gene NLRX1 from grass carp (Ctenopharyngodon idella) was cloned and characterised. NLRX1 was widely expressed in all tissues examined, albeit at varying levels. After exposure to the grass carp reovirus (GCRV), NLRX1 mRNA expression levels were altered in immune organs, and dramatically altered in liver. Subcellular localisation indicated that NLRX1 protein co-localised with the mitochondria in the transfected cells. Additionally, the bimolecular fluorescence complementation (BiFC) system was introduced to detect the interaction between tumour necrosis factor (TNF) receptor associated factor 6 (TRAF6) and NLRX1. Moreover, deficient of NLRX1 in CIK cells with small interference RNA (siRNA) promoted polyinosinic:polycytidylic acid (poly (I:C))-induced IFN-related genes production, including IRF3, IRF7, and IFN-I, which reveals that NLRX1 is a negative regulator of IFN. Taken together, our results demonstrate that NLRX1 gene plays an important role in innate immune regulation and provide new insights into understanding the functional characteristics of the NLRX1 in teleosts.

Orthoreovirus outer-fiber proteins are substrates for SUMO-conjugating enzyme Ubc9

Reoviruses are potential anticancer agents due to their ability to induce cell death in tumor cells. Grass carp reovirus (GCRV) is one of the best characterized models on reovirus pathogenesis in vitro. However, there is little known about how SUMOylation affects reovirus pathogenesis. The SUMO conjugating enzyme 9 (Ubc9) determines the targets of SUMOylation. Here, the protein interactions between reovirus outer fiber proteins, specifically GCRV-104 VP55, and Ubc9 were probed using a yeast two-hybrid system. The N-terminal coiled-coil domain of VP55, containing a single lysine residue, was responsible for the interaction between VP55 and Ubc9 in yeast. In solid phase binding assays, a single amino acid mutation (K87R) prevented Ubc9 from binding to VP55. Overexpression of Ubc9 enhanced GCRV-104 infection efficiency, and knockdown of Ubc9 in CIK cells inhibited viral replication, which suggested that Ubc9 was a proviral factor. Furthermore, Ubc9 was shown to bind outer fiber proteins from type II GCRV, avian reovirus and mammalian reovirus in yeast. To our knowledge, this is the first study to show that Ubc9 binds to reovirus outer-fiber proteins and likely contributes to efficient orthoreovirus replication. These results suggest that SUMOylation modifications could be targeted to improve the therapeutic efficacy of oncolytic reovirus.

Transcriptomic profiling of Tibetan highland fish (Gymnocypris przewalskii) in response to the infection of parasite ciliate Ichthyophthirius multifiliis

Gymnocypris przewalskii is a native cyprinid in the Lake Qinghai of the Qinghai-Tibetan Plateau. G. przewalskii is highly susceptible to the infection of a parasite, Ichthyophthirius multifiliis, in the artificial propagation and breeding. To better understand the host immune reaction to I. multifiliis infection, we characterize the gene expression profiles in the spleen of healthy and I. multifiliis infected G. przewalskii by RNA-seq. Totally, the transcriptomic analysis produces 463,031,110 high quality reads, which are assembled to 213,538 genes with N50 of 1918 bp and the average length of 1205 bp. Of assembled genes, 90.52% are annotated by public databases. The expression analysis shows 744 genes are significantly changed by the infection of I. multifiliis, which are validated by qRT-PCR with the correlation coefficient of 0.896. The differentially expressed genes are classified into 689 GO terms and 230 KEGG pathways, highlighting the promoted innate immunity in I. multifiliis infected G. przewalskii at 2 days post infection. Our results pinpoint that the up-regulated genes are enriched in TLR signaling pathway, inflammatory response and activation of immune cell migration. On the contrary, complement genes are down-regulated, indicating the evasion of host complement cascades by I. multifiliis. The repressed genes are also enriched in the pathways related to metabolism and endocrine, suggesting the metabolic disturbance in I. multifiliis treated G. przewalskii. In summary, the present study profiles the gene expression signature of G. przewalskii in the responses to I. multifiliis infection, and improves our understanding on molecular mechanisms of host-parasite interaction in G. przewalskii, which focuses the crucial function of TLRs, cytokines and complement components in the host defense against I. multifiliis.

Repression of SUMOylation pathway by grass carp reovirus contributes to the upregulation of PKR in an IFN-independent manner

SUMOylation, a post-translational modification, is involved in interaction between hosts and viruses, and participates in diverse cellular processes including inflammatory responses and innate immunity. Here, we investigated the interaction between reovirus infection and the cellular SUMOylation machinery using grass carp reovirus (GCRV) as a model. Full-length cDNAs of grass carp SUMO-1 and SUMO-2 were obtained and phylogenetic analysis indicated that they shared high homology with those of higher vertebrates. The two modifiers and SUMO conjugating enzyme 9 (Ubc9) were ubiquitously expressed in all tested tissues of grass carp. During GCRV infection in CIK cells, transcriptional expressions of SUMO1/2 and Ubc9 were significantly inhibited; while UV-inactivated GCRV failed to inhibit the expression of the three molecules, which suggested that SUMOylation system was suppressed during viral replication. In CIK cells treated with inhibitor 2-D08 for SUMOylation, GCRV replication was not interfered; however, transcriptional analysis of immune genes involved in anti-viral interferon (IFN) response indicated that IRF2 and PKR were significantly up-regulated in CIK cells treated with inhibitor in contrast to IRF1, IRF7 and IFNI. Furthermore, 2-D08 treatment coupled with GCRV challenge resulted in higher IRF2 and PKR level during infection in comparison to those of CIK cells infected with GCRV only. These results indicated that inhibition of SUMOylation should result in the induction of PKR via IFN-independent manner, and both IFN-signaling and IFN-independent signaling seemed to involve in the upregulation of PKR during the process of GCRV infection. Repression of SUMOylation by GCRV might represent a cellular antiviral mechanism.

Magnolol and honokiol from Magnolia officinalis enhanced antiviral immune responses against grass carp reovirus in Ctenopharyngodon idella kidney cells

Medicinal plants have been widely used for a long history. Exploration of pharmacologically active compounds from medicinal plants present a broad prevalent of application. By examining viral mRNA expression in GCRV-infected Ctenopharyngodon idella kidney (CIK) cells treated with thirty kinds of plant extracts, we identified Magnolia officinalis Rehd et Wils. was able to preferably suppress viral replication. Further studies demonstrated that the main ingredients of magnolia bark, namely, magnolol and honokiol presented protective pharmacological function when treated GCRV-infected CIK cells with a concentration of 2.00 μg/ml and 1.25 μg/ml, respectively. Furthermore, reverse transcript quantitative polymerase chain reaction (RT-qPCR) and western blot showed that both magnolol and honokiol were efficient to restrain the replication of GCRV in CIK cells at non-toxic concentration (2.51 ± 0.51 μg/ml for magnolol, and 3.18 ± 0.61 μg/ml for honokiol). Moreover, it was found that magnolol and honokiol promoted the expression of immune-related genes. Magnolol obviously significantly increased the expression of interferon (IFN) regulatory factor (IRF)7 rather than that of IRF3 in the GCRV-infected cells, leading to the activation of type I IFN (IFN-I). Simultaneously, magnolol drastically facilitated the expression of interleukin (IL)-1β, but failed to induce the molecules in nuclear factor (NF)-κB pathways. Differently, honokiol strikingly motivated not only the expression of IL-1β, but also those of tumor necrosis factor α (TNFα) and NF-κB. Interestingly, though honokiol motivated the expression of IFN-β promoter stimulator 1 (IPS-1), IRF3 and IRF7, it failed to up-regulate the expression of IFN-I, indicating that honokiol enhanced the host innate antiviral response to GCRV infection via NF-κB pathways. Collectively, the present study revealed that magnolol and honokiol facilitated the expression of innate immune-related genes to strengthen the innate immune signaling responses to resist GCRV infection, which contributed to understanding the mechanisms by which small-molecule drugs possessed antiviral activities. In addition, these results lay a foundation for the development of broad-spectrum antiviral compounds in aquaculture industry.

Identification and Characterization of Lipopolysaccharide Induced TNFα Factor from Blunt Snout Bream, Megalobrama amblycephala

Lipopolysaccharide induced TNFα factor (LITAF) is an important transcription factor responsible for regulation of tumor necrosis factor α. In this study, a novel litaf gene (designated as Malitaf) was identified and characterized from blunt snout bream, Megalobrama amblycephala. The full-length cDNA of Malitaf was of 956 bp, encoding a polypeptide of 161 amino acids with high similarity to other known LITAFs. A phylogenetic tree also showed that Malitaf significantly clustered with those of other teleost, indicating that Malitaf was a new member of fish LITAF family. The putative maLITAF protein possessed a highly conserved LITAF domain with two CXXC motifs. The mRNA transcripts of Malitaf were detected in all examined tissues of healthy M. amblycephala, including kidney, head kidney, muscle, liver, spleen, gill, and heart, and with the highest expression in immune organs: spleen and head kidney. The expression level of Malitaf in spleen was rapidly up-regulated and peaked (1.29-fold, p < 0.05) at 2 h after lipopolysaccharide (LPS) stimulation. Followed the stimulation of Malitaf, Matnfα transcriptional level was also transiently induced to a high level (51.74-fold, p < 0.001) at 4 h after LPS stimulation. Taken together, we have identified a putative fish LITAF ortholog, which was a constitutive and inducible immune response gene involved in M. amblycephala innate immunity during the course of a pathogenic infection.

Identification and functional analysis of the toll-like receptor 20.2 gene in grass carp, Ctenopharyngodon idella

We characterized and identified the cDNA sequence of Toll-like receptor 20.2 in Ctenopharyngodon idella (gctlr20.2); it consisted of 3197 bp, with an open reading frame of 2835 bp that encoded a 944 amino acid polypeptide. Relatively, high expression levels of gctlr20.2 were observed in the spleen, head kidney, liver and brain tissues, with lower expression levels in the trunk kidney, intestine and heart tissues. In vivo and in vitro, after being challenged with Aeromonas hydrophila or grass carp reovirus (GCRV), gctlr20.2 expression was induced in C. idella kidney cells stimulated with lipopolysaccharide, flagellin or polyinosinic-polycytidylic acid. Overexpression of gctlr20.2 increased the expression of il1β, il8 and tnf-α, but not ifn, and also increased the activity of the nf-κB signal pathway. Silencing, via siRNA-tlr20.2, inhibited gctlr20.2 transcription by 65.7% and down-regulated the expression of inflammatory cytokine genes, but not tnf-α. This study increases understanding of the immune system in C. idella.

Cell mediated immune response of the Mediterranean sea urchin Paracentrotus lividus after PAMPs stimulation

The Mediterranean sea urchin (Paracentrotus lividus) is of great ecological and economic importance for the European aquaculture. Yet, most of the studies regarding echinoderm's immunological defense mechanisms reported so far have used the sea urchin Strongylocentrotus purpuratus as a model, and information on the immunological defense mechanisms of Paracentrotus lividus and other sea urchins, is scarce. To remedy this gap in information, in this study, flow cytometry was used to evaluate several cellular immune mechanisms, such as phagocytosis, cell cooperation, and ROS production in P. lividus coelomocytes after PAMP stimulation. Two cell populations were described. Of the two, the amoeboid-phagocytes were responsible for the phagocytosis and ROS production. Cooperation between amoeboid-phagocytes and non-adherent cells resulted in an increased phagocytic response. Stimulation with several PAMPs modified the phagocytic activity and the production of ROS. The premise that the coelomocytes were activated by the bacterial components was confirmed by the expression levels of two cell mediated immune genes: LPS-Induced TNF-alpha Factor (LITAF) and macrophage migration inhibitory factor (MIF). These results have helped us understand the cellular immune mechanisms in P. lividus and their modulation after PAMP stimulation.

TNF-α is involved in apoptosis triggered by grass carp reovirus infection in vitro

Grass carp reovirus (GCRV) infection causes apoptosis in Ctenopharyngodon idella kidney cells (CIK). However, the cause of GCRV-induced apoptosis and its signaling pathways remain unknown. This study investigated the role of TNF-α-induced capase-8 pathways in mediating GCRV-induced apoptosis in the grass carp (Ctenopharyngodon idella). Recombinant TNF-α was expressed and purified from Escherichia. coli. The western blot assay indicated that TNF-α expression level in kidney and spleen was higher than that in liver. In apoptosis assay, recombinant TNF-α triggered significant apoptosis in CIK cells, which was characterized by increased mRNA levels of TNF-α, TRADD or caspase-8, and enhanced caspase-8 activity in CIK cells. To confirm the biological activity of TNF-α during GCRV infection, significant apoptosis in CIK cells was induced by GCRV correlating with enhanced caspase-8 activity, increased mRNA level of TNF-α, TRADD or caspase-8, increased protein level of TNF-α in CIK cells and cell supernatant, suggesting that TNF-α-induced capase-8 pathways might be involved in GCRV-triggered apoptosis. Furthermore, treatment with an anti-TNF-α polyclonal antibody significantly decreased the degree of apoptosis in infected CIK cells compared with cells treated with a control antibody, which confirmed that TNF-α was a key mediator involved in GCRV-induced apoptosis. Taken together, these results indicated that GCRV might trigger apoptosis via TNF-α induced capase-8 pathways in CIK cells.

Grass carp reovirus NS26 interacts with cellular lipopolysaccharide-induced tumor necrosis factor-alpha factor, LITAF

The nonstructural protein NS26 of grass carp reovirus (GCRV) is encoded by the 11th genomic dsRNA segment, homolog of which is not found in orthoreoviruses. The role of NS26 in GCRV pathogenesis is still unclear. Previously, grass carp LITAF/SIMPLE protein was identified as a putative binding partner for NS26 in a yeast two-hybrid screen. Here, we further characterized the association between NS26 and LITAF using in vivo and in vitro protein interaction assays. Soluble GST-NS26 and His₆-LITAF were expressed and purified from E. coli; recombinant NS26 tagged with myc and LITAF tagged with GFP were expressed in Ctenopharyngon idellus kidney cells (CIK) by transient transfection experiments. A GST pulldown assay demonstrated that GST-tagged NS26 efficiently bound to His₆-LITAF. Co-immunoprecipitation assays demonstrated that GCRV NS26 reciprocally precipitated endogenous LITAF in CIK cells. Double-immunofluorescent analyses revealed myc-NS26 colocalized with GFP-LITAF in CIK cells. Taken together, the current in vitro and in vivo data demonstrated the interaction between cellular LITAF and GCRV NS26.

Laminin receptor is an interacting partner for viral outer capsid protein VP5 in grass carp reovirus infection

Grass carp reovirus (GCRV) is responsible for viral hemorrhagic disease in cultured grass carp Ctenopharyngon idellus. Through yeast two-hybrid screen, laminin receptor (LamR) was identified as a potential interacting partner for the outer capsid protein VP5 of GCRV. We cloned and sequenced the gene encoding grass carp LamR. Viral attachment assay demonstrated the involvement of membrane-associated LamR in GCRV infection. Solid-phase overlay assays demonstrated that GCRV interacted with GST-tagged LamR in vitro. In contrast to VP7, GST-tagged VP5 was shown to associate with LamR in both pull-down and solid-phase blot overlay assays. With the reduction of LamR expression in CIK cells achieved by RNAi, remarkably reduced infection efficiency of GCRV was observed. CIK cells pretreated with polyclonal antibody against LamR resulted in dose-dependent inhibition of GCRV infection. These results collectively indicated that grass carp LamR was involved in GCRV infection by interacting with viral outer capsid protein VP5.

Identification of (-)-epigallocatechin-3-gallate as a potential agent for blocking infection by grass carp reovirus

Grass carp reovirus (GCRV), the representative strain of the species Aquareovirus C, serves as a model for studying the pathogenesis of aquareoviruses. Previously, epigallocatechin gallate (EGCG) was shown to inhibit orthoreovirus infection. The aim of this study was to test its potential in blocking infection by GCRV. We show that adhesion to the CIK (Ctenopharyngodon idellus kidney) cell surface by GCRV particles is inhibited in a dose-dependent manner by EGCG, as well as by a crude extract of green tea. We also evaluated the safety of EGCG and green tea extract using CIK cells, and the results suggest that EGCG is a promising compound that may be developed as a plant-derived small molecular therapeutic agent against grass carp hemorrhagic disease caused by GCRV infection. As the ligand for the 37/67-kDa laminin receptor (LamR), EGCG's blocking effect on GCRV attachment was associated with the binding potential of GCRV particles to LamR, which was inferred from a VOPBA assay.

Grass carp Ctenopharyngodon idella Fibulin-4 as a potential interacting partner for grass carp reovirus outer capsid proteins

Mammalian EGF containing fibulin-like extracellular matrix protein 2 (Fibulin-4/EFEMP2), an extracellular matrix(ECM) protein and a member of the fibulin family, is involved in elastic fiber formation, connective tissue development and some human diseases. In a yeast-two hybrid screening of host proteins interacting with outer capsid protein of grass carp reovirus (GCRV), a grass carp homologue of Fibulin-4 (designated as GcFibulin-4) is suggested to hold the potential to bind VP7, VP56 and VP55, the outer capsid protein encoded by type I, II, III GCRV, respectively. GcFibulin-4 gene of grass carp was cloned and sequenced from the cDNA library constructed for the yeast two-hybrid screening. Full-length cDNA of GcFibulin-4 contains an open reading frame (ORF) of 1323 bp encoding a putative protein of 440 amino acids. Phylogenetic analysis of GcFibulin-4 indicated that it shared a high homology with zebra fish Fibulin-4 protein. Transcriptional distribution analysis of GcFibulin-4 in various tissues of healthy grass carp showed that GcFibulin-4 was highly expressed in muscle, moderately expressed in the intestine and brain, and slightly expressed in other examined tissues; the expression pattern is consistent with tissue tropism of GCRV resulting in hemorrhage symptom in the corresponding tissues. Our results suggested that Fibulin-4 might enable free GCRV particles, the pathogen for grass carp hemorrhagic disease, to target fish tissues more efficiently by interacting with viral outer capsid proteins.

Fish reovirus GCReV-109 VP33 protein elicits protective immunity in rare minnows

Grass carp reovirus strain 109 (GCReV-109) was previously isolated from a grass carp (Ctenopharyngodon idellus) with hemorrhagic disease, and its complete genome has been sequenced. However, the infectivity of GCReV-109 has not been studied, and the viral protein VP33, encoded on genome segment S11, had no detectable sequence homology to other known reovirus proteins. In this study, we characterized GCReV-109 infections in vivo and in vitro, as well as the VP33 protein. Infectivity analysis showed that GCReV-109 caused severe hemorrhagic disease and 100% mortality at dilutions up to 10(-4) in rare minnows (Gobiocypris rarus) by 8 days postinfection, but no visible cytopathic effect was observed in GCReV-109-infected subcultured grass carp muscle (GCM) cells. To confirm that GCReV-109 could be propagated in GCM cells, three virus genome segments were detected by RT-PCR, and large numbers of virus particles were observed by transmission electron microscopy in samples from the infected GCM cells. The suspension of GCReV-109-infected GCM cells was pathogenic to rare minnows. VP33 protein was expressed and purified for generation of an anti-VP33 antiserum. In western blot analysis of purified GCReV-109 particles, the antiserum specifically recognized a protein band (approximately 33 kDa). This revealed that VP33 is a major structural protein of GCReV-109 that might have immunogenic properties. The protective efficacy of the anti-VP33 antiserum against GCReV-109 infection was tested. The death of infected fish was delayed and the mortality fell to 10% when fish were treated with the anti-VP33 antiserum, suggesting that it might be useful for the prevention and control of fish reoviral disease.

Proteomic analysis of cellular protein expression profiles in response to grass carp reovirus infection

Grass carp (Ctenopharyngodon idella) hemorrhagic disease, caused by grass carp reovirus (GCRV), is emerging as a serious problem in grass carp aquaculture. To better understand the molecular responses to GCRV infection, two-dimensional electrophoresis (2-DE) and matrix-assisted laser desorption/ionization tandem mass spectroscopy were performed to investigate altered proteins in C. idella kidney (CIK) cells. Differentially expressed proteins in mock infected CIK cells and GCRV-infected CIK cells were compared. Twenty-three differentially expressed spots were identified (22 upregulated spots and 1 downregulated spot), which included cytoskeleton proteins, macromolecular biosynthesis-associated proteins, stress response proteins, signal transduction proteins, energy metabolism-associated proteins and ubiquitin proteasome pathway-associated proteins. Moreover, 10 of the corresponding genes of the differentially expressed proteins were quantified by real-time reverse transcription polymerase chain reaction to examine their transcriptional profiles. The T cell internal antigen 1 (TIA1) and Ras-GTPase-activating SH3-domain-binding protein1 (G3BP1) of the cellular stress granule pathway from grass carp C. idella (designated as CiTIA1 and CiG3BP1) were upregulated and downregulated during GCRV infection, respectively. The full-length cDNA of CiTIA1 was 2753 bp, with an open reading frame (ORF) of 1155bp, which encodes a putative 385-amino acid protein. The 2271 bp full-length cDNA of CiG3BP1 comprised an ORF of 1455 bp that encodes a putative 485-amino acid protein. Phylogenetic analysis revealed that the complete ORFs of CiTIA1 and CiG3BP1 were very similar to zebrafish and well-characterized mammalian homologs. The expressions of the cellular proteins CiTIA1 and CiG3BP1 in response to GCRV were validated by western blotting, which indicated that the GCRV should unlink TIA1 aggregation and stress granule formation. This study provides useful information on the proteomic and cellular stress granule pathway's responses to GCRV infection, which adds to our understanding of viral pathogenesis.

Proteomic identification and characterization of Ctenopharyngodon idella tumor necrosis factor receptor-associated protein 1 (CiTrap1): an anti-apoptosis factor upregulated by grass carp reovirus infection

Human tumor necrosis factor receptor-associated protein 1 (Trap1) is a mitochondrial protein identical to heat shock protein 75 (HSP75) that plays an important role in protecting cells from oxidative stress and apoptosis. In this study, grass carp (Ctenopharyngodon idella) tumor necrosis factor receptor-associated protein 1 (designated as CiTrap1) was identified through two-dimensional electrophoresis (2-DE) analysis and its pattern of expression was investigated in grass carp kidney (CIK) cells infected with grass carp reovirus (GCRV). The full length cDNA of CiTrap1 contained an opening reading frame of 2157 bp that encoded a peptide of 718 amino acids. Phylogenetic analyses indicated that the CiTrap1 shared 87% identity with its homologue from zebrafish (Danio rerio). The transcriptional level of CiTrap1 in CIK cells was upregulated post virus infection as well as poly (I: C) stimulation. Following virus infection, grass carp PTEN-induced putative kinase 1 (PINK1) and Sorcin, whose coding proteins interact with Trap1 in human, were simultaneously upregulated with CiTrap1. Typical characteristics of apoptosis were observed in CIK cells infected with GCRV by DAPI staining, DNA ladder electrophoresis, TUNEL assay and Annexin Ⅴ labeling. RNAi-mediated silencing of CiTrap1 in CIK cells resulted in the increased rate of virus-induced apoptotic cells. The results of this study suggest that CiTrap1 is involved in the host's innate immune response to viral infection possibly through protecting infected cells from apoptosis.

Insights into the antiviral immunity against grass carp (Ctenopharyngodon idella) reovirus (GCRV) in grass carp

Global fish production from aquaculture has rapidly grown over the past decades, and grass carp shares the largest portion. However, hemorrhagic disease caused by grass carp reovirus (GCRV) results in tremendous loss of grass carp (Ctenopharyngodon idella) industry. During the past years, development of molecular biology and cellular biology technologies has promoted significant advances in the understanding of the pathogen and the immune system. Immunoprophylaxis based on stimulation of the immune system of fish has also got some achievements. In this review, authors summarize the recent progresses in basic researches on GCRV; viral nucleic acid sensors, high-mobility group box proteins (HMGBs); pattern recognition receptors (PRRs), Toll-like receptors (TLRs) and retinoic acid inducible gene I- (RIG-I-) like receptors (RLRs); antiviral immune responses induced by PRRs-mediated signaling cascades of type I interferon (IFN-I) and IFN-stimulated genes (ISGs) activation. The present review also notices the potential applications of molecule genetic markers. Additionally, authors discuss the current preventive and therapeutic strategies (vaccines, RNAi, and prevention medicine) and highlight the importance of innate immunity in long term control for grass carp hemorrhagic disease.

Molecular cloning and expression analysis of the Ajuba gene of grass carp (Ctenopharyngodon idella) involved in cellular response to viral infection

Ajuba belongs to the LIM domain proteins, which are involved in the assembly of the extracellular matrix and, along with associated proteins, regulate target genes that connect the extracellular matrix and the cytoskeleton. In the present study, we characterized the entire cDNA sequence of the Ajuba gene from grass carp (gcAjuba). The gcAjuba cDNA contained an open reading frame (ORF) of 2121 bp encoding a polypeptide of 706 amino acids with an estimated molecular mass of 75.966 kDa and three LIM domains in the C-terminal. The transcriptional level of gcAjuba was significantly up-regulated following the stimulation of virus in vitro. Sub-cellular location of gcAjuba and GCRV-JX01 NS26 proteins did not overlap in the cytoplasm and no direct interaction between gcAjuba and the protein NS26 was detected by co-immunoprecipitation (CO-IP) test in grass carp kidney cells. Based on these results, the gcAjuba is determined to be an immediately inducible gene responding to viral infection and in vivo association of gcAjuba with NS26 could not be confirmed, which has been suggested by yeast two-hybrid assay in previous report.

Effects of aluminium and bacterial lipopolysaccharide on oxidative stress and immune parameters in roach, Rutilus rutilus L

Aluminium is used in diverse anthropogenic processes at the origin of pollution events in aquatic ecosystems. In the Champagne region (France), high concentrations of aluminium (Al) are detected due to vine-growing practices. In fish, little is known about the possible immune-related effects at relevant environmental concentrations. The present study analyzes the simultaneous effects of aluminium and bacterial lipopolysaccharide (LPS), alone and in combination, on toxicological biomarkers in the freshwater fish species Rutilus rutilus. For this purpose, roach treated or not with LPS were exposed to environmental concentrations of aluminium (100 μg/L) under laboratory-controlled conditions for 2, 7, 14 and 21 days. After each exposure time, we assessed hepatic lipoperoxidation, catalase activity, glutathione reductase activity and total glutathione content. We also analyzed cellular components related to the LPS-induced inflammatory response in possible target tissues, i.e. head kidney and spleen. Our results revealed a significant prooxidant effect in the liver cells and head kidney leukocytes of roach exposed to 100 μg of Al/L for 2 days. In liver, we observed more lipoperoxidation products and lower endogenous antioxidant activity levels such as glutathione reductase activity and total glutathione content. These prooxidant effects were associated with a higher oxidative burst in head kidney leukocytes, and they were all the more important in fish stimulated by LPS injection. These findings demonstrate that environmental concentrations of Al induce oxidative and immunotoxic effects in fish and are associated to an immunomodulatory process related to the inflammatory response.

Identification and expression analysis of lipopolysaccharide-induced TNF-alpha factor gene in Chinese mitten crab Eriocheir sinensis

Lipopolysaccharide-induced TNF-alpha factor (LITAF) is an important transcription factor in transcriptional regulation of TNF-alpha and other cytokines. Here we identified a full-length LITAF homolog cDNA, termed EsLITAF, that contains a 71 bp 5'-untranslated sequence, an open reading frame consisting of 381 bp, and a 208 bp 3'-untranslated sequence in Chinese mitten crab (Eriocheir sinensis), an economically important freshwater crustacean species in China. EsLITAF protein possesses a conserved C-terminal LITAF-like domain with two CXXC motifs and is comprised of 126 amino acids with a theoretical molecular mass of 13.1 kDa and an isoelectric point of 6.36. Blast search against GenBank database revealed that EsLITAF protein shared the highest sequence identity (84%) with the counterpart of Pacific white shrimp (Litopenaeus vannamei). EsLITAF mRNA transcript expresses ubiquitously in all examined tissues with the highest expression in hepatopancreas and lowest expression in haemocytes. Furthermore, EsLITAF mRNA expression could be significantly and rapidly induced in haemocytes by LPS and Poly(I:C) stimulations in vitro. Moreover, EsLITAF gene expression was up-regulated in haemocytes, gill and hepatopancreas after Edwardsiella tarda and Vibrio anguillarum challenges. Taken together, we have identified and characterized a new crustacean LITAF homolog from the Chinese mitten crab.

Molecular cloning and expression analysis of two lipopolysaccharide-induced TNF-α factors (LITAFs) from rock bream, Oplegnathus fasciatus

Lipopolysaccharide (LPS)-induced tumor necrosis factor (TNF)-α factor (LITAF) plays an important role controlling the expression of TNF-α and the other cytokine genes in the presence of LPS. However, two LITAF homologues have not been characterized in fish. In this study, we cloned two distinct LITAF (RbLITAF1 and RbLITAF2) cDNAs from rock bream (Oplegnathus fasciatus) and characterized their expression profiles after infection with Edwardsiella tarda, Streptococcus iniae or red seabream iridovirus (RSIV). The coding regions of RbLITAF1 and RbLITAF2 cDNAs were 492 bp and 417 bp, encoding 153 and 138 amino acid residues, respectively. The genes consisted of a LITAF domain. RbLITAF1 was highly expressed in the spleen and heart of healthy rock bream, whereas RbLITAF2 was highly expressed in the gill, intestine and stomach. In spleen, the gene expression of RbLITAF1 and RbLITAF2 were increased until 5 days post-infection (dpi), and then decreased at 7 dpi. In kidney, E. tarda and RSIV infection led to induction of the RbLITAF1 gene at 1 dpi, RbLITAF2 gene was down-regulated after pathogen infection. These results suggest that RbLITAFs may be involved in the LITAF-mediated immune response and regulate systemic immune responses against pathogen infection.

Characterization of LPS-induced TNFα factor (LITAF) from orange-spotted grouper, Epinephelus coioides

Lipopolysaccharide-induced TNFα factor (LITAF) is an important transcription factor that mediates cell apoptosis and inflammatory response. In the present study, we cloned and characterized a LITAF gene from orange-spotted grouper (Epinephelus coioides) (Ec-LITAF). Ec-LITAF encoded a predicted 142 amino acid protein which shared 74% identity to sablefish (Anoplopoma fimbria) LITAF homolog. Multiple amino acid alignment showed that Ec-LITAF contained a typical LITAF domain with two CXXC motifs. Phylogenetic analysis indicated that Ec-LITAF was closely related to that of sablefish. Ec-LITAF mRNA was widely expressed in different tissues and its expression level in spleen was up-regulated after Singapore grouper iridovirus (SGIV) infection. Subcellular localization analysis revealed that the distribution of Ec-LITAF showed diffuse and aggregated patterns in cytoplasm. Interestingly, the distribution of Ec-LITAF overlayed with a viral LITAF homolog (vLITAF) encoded by SGIV. Overexpression of Ec-LITAF in vitro up-regulated the expression of tumor necrosis factors (TNF1 and TNF2) and TNF receptors (TNFR1 and TNFR2), and the expression of itself initiated apoptosis in fish cells. In addition, overexpression of Ec-LITAF not only accelerated SGIV infection induced CPE and cell death, but also increased viral gene transcription. Taken together, our data suggested that Ec-LITAF might play crucial roles during SGIV replication.

Identification and characterization of lipopolysaccharide-induced TNF-alpha factor gene from Japanese flounder Paralichthys olivaceus

Lipopolysaccharide-induced TNF-α factor (LITAF) is an important transcription factor participating in innate immunity through regulating TNF-α and other inflammatory cytokines expression. However, the expression and biological relevance of LITAF in fish is still very limited. In this study, a full-length LITAF cDNA, termed PoLITAF, was identified from Japanese flounder Paralichthys olivaceus. PoLITAF contains a 67 bp 5'-untranslated sequence, a 435 bp open reading frame, and a 647 bp 3'-untranslated sequence. PoLITAF protein is comprised of 144 amino acids with a conserved C-terminal LITAF-like domain and shows 51-76% sequence similarity and 40-65% sequence identity with other LITAF homologues. Characterization of this new gene revealed that PoLITAF mRNA was detected in all examined tissues with the highest expression in gill. In head kidney primary culture, the expression of Japanese flounder PoLITAF and TNF-α was significantly up-regulated in response to Poly(I:C) and bacterial endotoxin LPS stimulation. Further in vivo experiments demonstrated that PoLITAF expression was up-regulated in head kidney, gill and spleen post bacterial challenge with Edwardsiella tarda. Moreover, the up-regulated expression of Japanese flounder TNF-α following the enhanced expression of PoLITAF was detected as early as 4h in both gill and head kidney tissues and 12h in spleen after the bacterial infection in vivo. Our findings suggest that PoLITAF is a novel inducible gene possibly involved in Japanese flounder innate immunity.

Molecular cloning, characterization and expression analysis of coagulation factor VII gene in grass carp (Ctenopharyngodon idella)

Coagulation factor VII has been studied in several species but, to date, not in grass carp (Ctenopharyngodon idella), a commercially important freshwater fish found in China. In this study, the full-length cDNA of grass carp coagulation factor VII (GcCFVII) was cloned using a RACE-Ready cDNA Kit, grass carp were challenged with a hemorrhagic virus, and temporal expression profiles of GcCFVII in the thymus, gills, liver, spleen, and head kidney were examined at 0 h, 24 h, 48 h, 72 h, 96 h, and 138 h using fluorescence quantitative PCR. The results showed the 1480 bp GcCFVII to contain three conservative motifs: Gla, EGF-CA, and Tryp-SPc, similar to other species. Phylogenetic analysis showed the evolution of GcCFVII gene to be consistent with the evolution of the species. After viral challenge, GcCFVII expression in five tissues of grass carp showed different patterns of fluctuation. These results provide a solid basis for further investigation of GcCFVII and its relationship with grass carp hemorrhage.