TBK1 regulates the induction of innate immune response against GCRV by phosphorylating IRF3 in rare minnow (Gobiocypris rarus)

TBK1 upregulates the interferon response against virus by the TBK1-IRF3/7 axis in yellow catfish (Pelteobagrus fulvidraco)

Yellow catfish (Pelteobagrus fulvidraco) is an important economic species of freshwater fish, widely distributed in China. Recently, viral diseases of yellow catfish have been identified in Chian (Hubei province), arising more attention to the viral immunity in P. fulvidraco. Tumor necrosis factor (TNF) receptor-associated factor NF-κB activator (TANK)-binding kinase 1 (TBK1) plays an essential role in IFN production and innate antiviral immunity. In the present study, we characterized the P. fulvidraco TBK1 (PfTBK1) and reported its function in interferon response. The full-length open reading frame (ORF) is 2184 bp encoding a protein with 727 amino acids, which is composed of four conserved domains, including KD, ULD, CCD1, and CCD2, similar to TBK1 in other species. Pftbk1 was widely expressed in all detected tissues by qPCR and was not inducible by the spring viremia of carp virus (SVCV), a single-strand RNA virus. In addition, the cellular distribution indicated that PfTBK1 was only located in the cytoplasm. Moreover, PfTBK1 induced strong IFN promoter activities through the Jak-stat pathway, and PfTBK1 interacted with and significantly phosphorylated IFN regulatory factor 3/7 (IRF3/7) in P. fulvidraco, promoting the nuclear translocation of pfIRF3 and PfIRF7, and PfTBK1 upregulated IFN response by PfTBK1-PfIRF3/7 axis. Above all, PfTBK1 triggered IFN response and strongly inhibited the replication of SVCV in EPC cells through induction of IFN downstream IFN-stimulated genes (ISGs). Summarily, this work reveals that PfTBK1 plays a positive regulatory role in IFN induction through the TBK1-IRF3/7 axis, laying a foundation for further exploring the molecular mechanism of the antiviral process in P. fulvidraco.

Molecular and functional characterization of golden pompano (Trachinotus blochii) TBK1 on IFN regulation

The golden pompano (Trachinotus blochii), a pivotal commercial marine species in China, has gained significant popularity worldwide. However, accompanied with rapid growth and high density aquaculture, golden pompano has been seriously threatened by Nervous necrosis virus (NNV), while its molecular biology research regarding the innate immune system remains unexplored, which is crucial for understanding the activation of interferon (IFN) production and antiviral responses. In this study, we aimed to identify the characterization and function of golden pompano TANK-binding kinase 1 (gpTBK1), thereby providing evidence of the conservation of this classical factor in the RLR pathway among marine fish. Initially, we found the expression of gpTBK1 upregulation in diseased golden pompano with NNV infection and we successfully cloned the full-length open reading frame (ORF) of gpTBK1, consisting of 2172 nucleotides encoding 723 amino acids, from the head kidney. Subsequent analysis of the amino acid sequence revealed homology between gpTBK1 and other fish TBK1 proteins, with conserved N-terminal Serine/Threonine protein kinases catalytic domain (S_TKc) and C-terminal coiled coil domain (CCD). Moreover, the expression pattern showed that gpTBK1 exhibited ubiquitous expression across all evaluated tissues. Furthermore, functional identification experiments indicated that gpTBK1 activated interferon promoters' activity in golden pompano and induced the expression of downstream IFN-stimulated genes (ISGs). Notably, gpTBK1 was found to co-localize and interact with gpIRF3 in the cytoplasm. Collectively, these data provide a comprehensive analysis of the characterization and functional role of gpTBK1 in promoting interferon production. This research may facilitate the further study of the innate antiviral response, particularly the anti-NNV mechanisms, in golden pompano.

march2 negatively regulates antiviral immune response by targeting tbk1 in grass carp (Ctenopharyngodon idella)

Grass carp is one of the most economically important fish species. Hemorrhagic diseases caused by grass carp reovirus (GCRV) can seriously damage the economic yield of grass carp. Therefore, antiviral research on grass carp is urgently needed. Membrane-associated RING-CH2 (MARCH2) negatively regulates the innate immune response in mice. However, little is known about the role of march2 in the antiviral innate immune response in teleost fish. Our present study showed that march2 has high homology in grass carp, its orthologs, and mammals, and has the same amino acid sequence in grass carp and crucian carp. Overexpression of Cimarch2 (Ctenopharyngodon idella march2) significantly inhibited interferon (IFN) activation induced by Polyinosinic-polycytidylic acid (poly I: C), spring viremia of carp virus (SVCV), and GCRV. However, knocking down Cimarch2 enhanced the activation of IFN induced by poly I: C, SVCV, and GCRV. Overexpression of Cimarch2 can promotes viral replication. Mechanistically, Cimarch2 tightly bound to TANK-binding kinase 1 (tbk1) and downregulated tbk1 through the proteasome pathway. Our results demonstrated the potential role of Cimarch2 in the antiviral breeding of grass carp.

Identification and analysis of long non-coding RNAs that are involved in response to GCRV infection in grass carp (Ctenopharyngodon idella)

Long noncoding RNAs (lncRNAs) play important roles in many biological processes including the immune response against virus infection. However, their roles in grass carp reovirus (GCRV) pathogenicity are largely unknown. In this study, the next-generation sequencing (NGS) technology was used to analyze the profiles of lncRNAs in GCRV-infected and mock-infected grass carp kidney (CIK) cells. Our results showed that 37 lncRNAs and 1039 mRNA transcripts exhibited differential expression in CIK cells after GCRV infection compared with the mock infection. Functional analysis through the gene ontology and Kyoto Encyclopedia of Genes and Genomes databases (KEGG) indicated that target genes of the differentially expressed lncRNAs were mainly enriched in the biological processes - biological regulation, cellular process, metabolic process and regulation of the biological process, such as MAPK signaling pathway and Notch signaling. Furthermore, we observed that the lncRNA3076 (ON693852) was markedly upregulated after the GCRV infection. In addition, silencing lncRNA3076 decreased the GCRV replication, which indicates that it might play an important role in the replication of GCRV.

Review of Medicinal Plants and Active Pharmaceutical Ingredients against Aquatic Pathogenic Viruses

Aquaculture offers a promising source of economic and healthy protein for human consumption, which can improve wellbeing. Viral diseases are the most serious type of diseases affecting aquatic animals and a major obstacle to the development of the aquaculture industry. In the background of antibiotic-free farming, the development and application of antibiotic alternatives has become one of the most important issues in aquaculture. In recent years, many medicinal plants and their active pharmaceutical ingredients have been found to be effective in the treatment and prevention of viral diseases in aquatic animals. Compared with chemical drugs and antibiotics, medicinal plants have fewer side-effects, produce little drug resistance, and exhibit low toxicity to the water environment. Most medicinal plants can effectively improve the growth performance of aquatic animals; thus, they are becoming increasingly valued and widely used in aquaculture. The present review summarizes the promising antiviral activities of medicinal plants and their active pharmaceutical ingredients against aquatic viruses. Furthermore, it also explains their possible mechanisms of action and possible implications in the prevention or treatment of viral diseases in aquaculture. This article could lay the foundation for the future development of harmless drugs for the prevention and control of viral disease outbreaks in aquaculture.

Establishment of a rare minnow (Gobiocypris rarus) model for evaluation of experimental vaccines against a disease induced by grass carp reovirus genotype II

Vaccination is the most effective way to control the grass carp haemorrhagic disease (GCHD) with the primary pathogen grass carp reovirus genotype II (GCRV-II). However, due to the large difference in breeding conditions and unclear genetic background of grass carp, the results of the experiment were not reliable, which further hinders the effective prevention and control of GCHD. The rare minnow (Gobiocypris rarus) is highly sensitive to GCRV. Its small size, easy feeding, transparent egg membrane, and annual spawning are in line with the necessary conditions for an experimental aquatic animals culture object. In this study, immunogenicity and protective effects of attenuated and inactivated viruses for grass carp and rare minnow were evaluated in parallel. The expression of immune-related genes increased statistically significant after immunization. With the rise of specific serum antibody titers, the results of rare minnow and grass carp were consistent. In addition, there was no significant residue of adjuvant observed in both fish species injected with an adjuvanted and inactivated virus. Challenge of immunized grass carp and rare minnow with the isolate HuNan1307 resulted in protection rates of 95.8% and 92.6% for attenuated virus, 81.4% and 77.7% for inactivated virus, respectively, as well as the viral load changed consistently. The results indicated that rare minnow can be used as a model for evaluation of experimental vaccines against GCHD.