EcVig, a novel grouper immune-gene associated with antiviral activity against NNV infection

Fas/FasL of pacific cod mediated apoptosis

Fas and Fas ligand (FasL) pathway plays important roles in virus defense and cell apoptosis. In our previous work, nervous necrosis virus (NNV) was discovered in Pacific cod (Gadus macrocephalus), and the Fas ligand (PcFasL) was up-regulated when NNV outbreak, however, signal transmission of Fas/FasL in fish are still unclear. In the present study, Pacific cod Fas (PcFas), PcFasL and Fas-associating protein with a novel death domain (PcFADD) were characterized. The predicted protein of PcFas, PcFasL and PcFADD includes 333 aa, 90 aa and 93 aa, separately. 3-D models of PcFas, PcFasL and PcFADD were well constructed based on reported templates, respectively, even though the sequence homology with other fish is very low. The transcript levels of PcFas increased gradually from 15 day-post hatching (dph) to 75dph. PcFas was significantly up-regulated when cod larvae had NNV symptoms at 24dph, 37dph, 46dph, 69dph, and 77dph. Subcellular localization revealed that PcFasL was located in the cytoplasm, while PcFas was mainly located in the cell membrane. Exogenous expressed PcFasL of 900 μg/mL could kill the Epithelioma papulosum cyprinid (EPC) cells by MTT test, but low concentration has no effect on the cells. qPCR analysis showed that overexpression of PcFas could significantly up-regulate the expression of genes related to Fas/FasL signaling pathway, including bcl-2, bax, and RIP3, while overexpression of PcFasL significantly up-regulate the expression of caspase-3, caspase-9, and MLKL. Overexpression of PcFas or PcFasL could induce EPC apoptosis significantly by flow cytometry, which was consistent with the results of caspase-3 mRNA level increasing. The results indicated that NNV could induce apoptosis through Fas/FasL signal pathway.

The microbiota profile and transcriptome analysis of immune response during metamorphosis stages in orange spotted grouper (Epinephelus coioides)

Metamorphosis is a transformation process in larval development associated with changes in morphological and physiological features, including the immune system. The gastrointestinal tract harbors a plethora of bacteria, which might affect the digestion and absorption of nutrients, immunity, and gut-brain crosstalk in the host. In this study, we have performed metagenomic and transcriptomic analyses on the intestines of grouper at the pre-, mid- and post-metamorphosis stages. The sequencing data of 16S rRNA gene showed drastic changes in the microbial communities at different developmental stages. The transcriptomic data revealed that the leukocyte transendothelial migration and the phagosome pathways might play important roles in mediating immunity in grouper at the three developmental stages. This information will increase our understanding of the metamorphosis process in grouper larvae, and shed light on the development of antimicrobial strategy during larval development.

Interferon regulatory factor 3 from sea perch (Lateolabrax japonicus) exerts antiviral function against nervous necrosis virus infection

Interferon (IFN) regulatory factor 3 (IRF3) is a major regulator contributing to the host away from viral infection. Here, an IRF3 gene from sea perch (LjIRF3) was identified and its role in regulating early apoptosis signaling and IFN response was investigated during red spotted grouper nervous necrosis virus (RGNNV) infection. The cDNA of LjIRF3 encoded a putative 465 amino acids protein, containing a DNA binding domain, an IRF association domain and a serine-rich domain. Phylogenetic analysis suggested that LjIRF3 shared the closest genetic relationship with Epinephelus coioides IRF3. LjIRF3 was constitutively expressed in all examined tissues with the highest expression level in the liver. Upon RGNNV infection, mRNA transcript level of LjIRF3 was significantly up-regulated in vivo and in vitro, indicating the involvement of LjIRF3 in immune response to RGNNV infection. Furthermore, overexpression of LjIRF3 significantly suppressed RGNNV replication in vitro, meanwhile significantly up-regulating the expression of IFNI and IFN stimulated genes and resulting in the activation of caspase 3 and 9 proteases in the early stage of RGNNV infection. In short, these results demonstrated that LjIRF3 exerted antiviral function against RGNNV infection via triggering early apoptotic cell death and inducing IRF3-dependent IFN immune response.

Functional characterization of tumor necrosis factor receptor-associated factor 3 of sea perch (Lateolabrax japonicas) in innate immune

Tumor necrosis factor receptor-associated factor 3 (TRAF3) is a multifunctional regulator implicated in both bacterial defense and antiviral immunity. Here, a TRAF3 gene from the seawater fish sea perch, designated as LjTRAF3, was characterized. The full-length cDNA of LjTRAF3 was 2972 bp including a 5' untranslated region (UTR) of 243 bp, a 3'UTR of 941 bp and a putative open reading frame of 1608 bp encoding a putative protein of 536 amino acid. The deduced LjTRAF3 protein contained a RING finger, two zinc fingers, a coiled-coil, and a meprin and TRAF-C homology domain. Phylogenetic analysis showed that LjTRAF3 shared the closest genetic relationship with Larimichthys crocea TRAF3. Gene expression analyses suggested that LjTRAF3 mRNA was ubiquitously expressed in all the tissues tested, and was up-regulated post red spotted grouper nervous necrosis virus (RGNNV) infection in vivo and in vitro. Reporter gene assay showed that LjTRAF3 significantly activated zebrafish type I interferon (IFN) promoter in vitro. During RGNNV infection, ectopic expression of LjTRAF3 significantly reduced the RNA dependent RNA polymerase transcription of RGNNV, and enhanced the expression of RIG-I-like receptors (RLR), janus kinase-signal transducers and activators of transcription (JAK-STAT) signaling pathway related genes and IFN stimulated genes (ISGs), including ISG15, PKR, VIG and TRIM39. Taken together, our results suggested that LjTRAF3 might trigger the expression of various ISGs to counter RGNNV infection by regulating the RLR-induced IFN and JAK-STAT signaling pathways.

Characterization of microRNAs in orange-spotted grouper (Epinephelus coioides) fin cells upon red-spotted grouper nervous necrosis virus infection

Nervous necrosis virus (NNV), one of the most prevalent fish pathogens, has caused fatal disease of viral nervous necrosis (VNN) in many marine and freshwater fishes, and resulted in heavy economic losses in aquaculture industry worldwide. However, the molecular mechanisms underlying the pathogenicity of NNV remain elusive. In this study, the expression profiles of microRNA (miRNA) were investigated in grouper fin (GF-1) cells infected with red-spotted grouper nervous necrosis virus (RGNNV) via deep sequencing technique. The results showed that a total of 220 miRNAs were identified by aligning the small RNA sequences with the miRNA database of zebrafish, and 18 novel miRNAs were predicted using miRDeep2 software. Compared with the non-infected groups, 51 and 16 differentially expressed miRNAs (DE-miRNAs) were identified in the samples infected with RGNNV at 3 and 24 h, respectively. Six DE-miRNAs were randomly selected to validate their expressions using quantitative reverse transcription polymerase chain reaction (qRT-PCR), the results showed that their expression profiles were consistent with those obtained by deep sequencing. The target genes of the DE-miRNAs covered a wide range of functions, such as regulation of transcription, oxidation-reduction process, proteolysis, regulation of apoptotic process, and immune response. In addition, the effects of four DE-miRNAs including miR-1, miR-30b, miR-150, and miR-184 on RGNNV replication were evaluated, and the results showed that over-expression of each of the four miRNAs promoted the replication of RGNNV. These data provide insight into the molecular mechanism of RGNNV infection, and will benefit for the development of effective strategies to control RGNNV infection.

Fish interferon-stimulated genes: The antiviral effectors

Type I interferons (IFN) are the cornerstone cytokine of innate antiviral immunity. In response to a viral infection, IFN signaling results in the expression of a diverse group of genes known as interferon-stimulated genes (ISGs). These ISGs are responsible for interfering with viral replication and infectivity, helping to limit viral infection within a cell. In mammals, many antiviral effector ISGs have been identified and the antiviral mechanisms are at least partially elucidated. In fish fewer ISGs have been identified and while there is evidence they limit viral infection, almost nothing is known of their respective antiviral mechanisms. This review discusses seven ISGs common to mammals and fish and three ISGs that are unique to fish. The lack of understanding regarding fish ISG's antiviral effector functions is highlighted and draws attention to the need for research in this aspect of aquatic innate immunity.

A member of the immunoglobulin superfamily, orange-spotted grouper novel immune gene EcVig, is induced by immune stimulants and type I interferon

A novel grouper immune gene, EcVig was identified in orange-spotted grouper (Epinephelus coioides). We recently determined that EcVig expression can be induced by infection with nervous necrosis virus (NNV, an RNA virus), whereas NNV replication may be suppressed when EcVig was overexpressed. Although EcVig appeared to be involved in grouper antiviral activity, its immune effects have not been well characterized. In the present study, two PAMPs (pathogen-associated molecular patterns; lipopolysaccharides [LPS] and synthetic double-stranded RNA polyriboinosinic-polyribocytidylic acid [poly(I:C)]), as well as fish DNA virus (red sea bream iridovirus, RSIV; grouper iridovirus, GIV), were used to study EcVig responses in orange-spotted grouper. In addition, groupers were given recombinant type I interferon to determine whether EcVig expression was induced. Poly(I:C) rapidly induced substantial expression of EcVig, whereas LPS stimulation did not appear to have any effect in grouper intestine. Expression levels of total EcVig and other IFN-stimulated genes (ISGs) were all significantly increased after RSIV and GIV infection. Furthermore, stimulation of recombinant type I IFN also increased EcVig expression. We conclude that EcVig may be a novel IFN-stimulated gene that demonstrates an antiviral immune response.

Immunity to nervous necrosis virus infections of orange-spotted grouper (Epinephelus coioides) by vaccination with virus-like particles

Nervous necrosis virus (NNV) is a kind of the betanodaviruses, which can cause viral nervous necrosis (VNN) and massive mortality in larval and juvenile stages of orange-spotted grouper (Epinephelus coioides). Due to the lack of viral genomes, virus-like particles (VLPs) are considered as one of the most promising candidates in vaccine study to control this disease. In this study, a type of VLPs, which was engineered on the basis of orange-spotted grouper nervous necrosis virus (OGNNV), was produced from prokaryotes. They possessed the similar structure and size to the native NNV. In addition, synthetic oligodeoxynucleotide (ODN) containing CpG motif was added in vaccines, and the expression patterns of several genes were analyzed after injecting with VLP and VLP with adjuvant (VA) to assess the regulation effect of vaccine for inducing immune responses. RT-PCR assays showed that six related genes in healthy tissues were ubiquitously expressed in all nine tested tissues. The vaccine alone was able to enhance the expression of genes, including MHCIa, MyD88, TLR3, TLR9 and TLR22 after vaccination, indicating that the vaccine was able to induce immune response in grouper. In liver, spleen and kidney, the gene expressions of VA group were all significantly higher than that of VLP group at 72 h post-stimulation, showing that the fish of VA challenge group obtained the longer-lasting protective immunity and resistance to pathogen challenge than that of VLP group. The data indicated that the efficacy of vaccine could be further enhanced by CpG ODN after vaccination and provided the reference for the development of future viral vaccine in grouper.

JNK1 Derived from Orange-Spotted Grouper, Epinephelus coioides, Involving in the Evasion and Infection of Singapore Grouper Iridovirus (SGIV)

c-Jun N-terminal kinase (JNK) regulates cellular responses to various extracellular stimuli, environmental stresses, pathogen infections, and apoptotic agents. Here, a JNK1, Ec-JNK1, was identified from orange-spotted grouper, Epinephelus coioides. Ec-JNK1 has been found involving in the immune response to pathogen challenges in vivo, and the infection of Singapore grouper iridovirus (SGIV) and SGIV-induced apoptosis in vitro. SGIV infection activated Ec-JNK1, of which phosphorylation of motif TPY is crucial for its activity. Over-expressing Ec-JNK1 phosphorylated transcription factors c-Jun and promoted the infection and replication of SGIV, while partial inhibition of the phosphorylation of Ec-JNK1 showed the opposite effects by over-expressing the dominant-negative EcJNK1-Δ183-185 mutant. Interestingly, SGIV enhanced the viral infectivity by activating Ec-JNK1 which in turn drastically inhibited the antiviral responses of type 1 IFN, indicating that Ec-JNK1 could be involved in blocking IFN signaling during SGIV infection. In addition, Ec-JNK1 enhanced the activation of AP-1, p53, and NF-κB, and resulted in increasing the levels of SGIV-induced cell death. The caspase 3-dependent activation correlated with the phosphorylation of Ec-JNK1 and contributed to SGIV-induced apoptosis. Taken together, SGIV modulated the phosphorylation of Ec-JNK1 to inactivate the antiviral signaling, enhance the SGIV-induced apoptosis and activate transcription factors for efficient infection and replication. The “positive cooperativity” molecular mechanism mediated by Ec-JNK1 contributes to the successful evasion and infection of iridovirus pathogenesis.

Transcriptome analysis of medaka following epinecidin-1 and TH1-5 treatment of NNV infection

Nervous necrosis virus (NNV) infects a wide range of larval and juvenile fish species, thereby causing enormous economic losses in the aquaculture industry. Possible solutions to this problem include the use of antimicrobial peptides (AMPs), which directly inhibit bacterial growth, and also modulate host signaling mechanisms. The AMPs epinecidin (Epi)-1 and Tilapia hepcidin (TH) 1-5 have been demonstrated to be effective against Nervous necrosis virus infection in medaka (Oryzias latipes). However, the underlying molecular mechanisms are yet to be explored. Here, microarray analyses were performed to examine how NNV infection and/or epinecidin-1 or TH1-5 treatment affects gene expression in medaka; such analyses enabled the prediction of host signaling pathways affected by virus infection and/or regulated by epinecidin-1 and TH1-5. Transcriptome analysis revealed altered expression of genes involved in B cell activation, T cell activation, adipocytokine signaling, and mast cell activation. We subsequently used real-time PCR to analyze expression of key genes involved in these signaling mechanisms. Medaka infected with NNV exhibited up-regulation of PVALB, CEBPA, IFIM, IFN, IL-6ST, NF-kB2, SOC3, SP1, and TGFB1, and such increases were prevented by pre-treatment with epinecidin-1 or TH1-5. Immunohistochemistry using the anti-NNV antibody to stain brain and eye sections revealed that epinecidin-1 treatment during or after infection clears viral load, while TH1-5 treatment only reduces viral numbers if applied during infection. These observations demonstrate that epinecidin-1 and TH1-5 modulate NNV-induced host signaling mechanisms, thereby preventing viral multiplication in host organisms.