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

IHNV induced miR-19-3p modulates immune response of rainbow trout (Oncorhynchus mykiss) by targeting DHX58-dependent RLR signaling pathway

miR-19-3p has been implicated in various pathological and physiological processes, including immune response, inflammation, oncogenesis and cell damage. However, its function in rainbow trout (Oncorhynchus mykiss) has not been well elucidated. In this study, the expression patterns of miR-19-3p and target gene DExH-Box helicase 58 (DHX58) in rainbow trout infected with infectious hematopoietic necrosis virus (IHNV) were detected, and regulatory mechanism and function of miR-19-3p were investigated by overexpression and inhibition experiment in vitro and in vivo. Expression patterns showed that miR-19-3p and DHX58 displayed significant time-dependent changes in IHNV-infected rainbow trout intestines, skins, gills, and liver cells, and their expression were negatively correlated at multiple time points. In vitro, the targeting relationship between miR-19-3p and DHX58 was confirmed by dual-luciferase reporter assay and RNA immunoprecipitation assay, and overexpression of miR-19-3p significantly suppressed the expression of DHX58 and downstream genes interferon regulatory factor 3 (IRF3), interferon regulatory factor 7 (IRF7), interferon (IFN), myxovirus 1 (MX1), interferon-stimulated gene 15 (ISG15), nuclear factor kappa-B (NF-κB), and interleukin-1 beta (IL-1β), whereas the expression levels of DHX58 and downstream genes were significantly increased after transfecting miR-19-3p inhibitor. In vivo, agomiR-19-3p significantly inhibited the expression of DHX58, and then reduced the expression levels of IRF3, IRF7, IFN, MX1, NF-κB, IL-1β, tumor necrosis factor-α (TNFα), and ISG15. Additionally, overexpression of miR-19-3p significantly increased IHNV copies and cell proliferation number, and suppressed apoptosis, while the opposite results were obtained after miR-19-3p repressing. This study confirmed that miR-19-3p regulates rainbow trout antiviral immune by DHX58-mediated interferon pathway in vitro and in vivo, which provides potential for using miRNAs as anti-viral target drugs.

Fish Brain Cell Lines Can Be Infected with Adenoviral Vectors and Support Transgene Expression-An In Vitro Approach

Host-pathogen interactions and the design of vaccines for aquaculture fish viruses are challenging and call for innovative approaches. This study explores the potential of adenoviral (Ad) vectors Ad5 and chimeric Ad5/40 as gene delivery tools for fish brain cells susceptible to neurotropic viruses. For this purpose, European sea bass (Dicentrarchus labrax) DLB-1 and gilthead seabream (Sparus aurata) SaB-1 brain cell lines were infected with Ad5 or Ad5/40 vectors expressing GFP, and we evaluated their capacity for infection by fluorescence microscopy and flow cytometry, as well as their antiviral innate immune response by the transcription of gene markers (irf3 and mx). We found that both vectors are able to infect DLB-1 and SaB-1 brain cell lines to similar levels, as demonstrated by fluorescence microscopy and flow cytometry, though the infection efficiency was low. In addition, infection with Ad vectors regulated the transcription of genes related to the interferon-mediated antiviral immune response. Our results indicate that the Ad5/40 vector achieves better infection and consistent cellular distribution. These findings suggest that these vectors may offer targeted gene delivery and local immune responses.

Orange-spotted grouper IFNh response to NNV or MSRV and its potential antiviral activities

Type I interferon (IFN) plays a crucial role in the antiviral immune response. Nervous necrosis virus (NNV) and Micropterus salmoides rhabdovirus (MSRV) are the most important viruses in cultured larvae and juveniles, causing great economic losses to fish farming. To better understand the antiviral activities and immunoregulatory role of IFN from orange-spotted grouper (Epinephelus coioides), EcIFNh was cloned from NNV infected sample. EcIFNh has an open reading frame (ORF) of 552 bp and encodes a polypeptide of 183 amino acids. Phylogenetic tree analysis showed that EcIFNh was clustered into the IFNh branch. The tissue distribution analysis revealed that EcIFNh was highly expressed in the liver and brain of healthy orange-spotted grouper. The mRNA levels of EcIFNh were significantly upregulated after poly (I:C) stimulation and NNV or MSRV infection. Furthermore, the promoter of EcIFNh was characterized and significantly activated by EcMDA5, EcMAVS, EcSTING, EcIRF3, and EcIRF7 in the luciferase activity assays. We found that EcIFNh overexpression resisted the replication of NNV and MSRV, while EcIFNh silencing facilitated NNV replication in GB cells. In addition, EcIFNh recombinant protein (rEcIFNh) enhanced the immune response by inducing the expression of ISGs in vivo and in vitro, suggesting the potential application of rEcIFNh for anti-NNV and anti-MSRV. Taken together, our research may offer the foundation for virus-IFN system interaction in orange-spotted grouper.