Effects of a broad-spectrum caspase inhibitor, Z-VAD(OMe)-FMK, on viral hemorrhagic septicemia virus (VHSV) infection-mediated apoptosis and viral replication

Antiviral effects of umbelliferone against viral hemorrhagic septicemia virus in olive flounder (Paralichthys olivaceus)

Viral hemorrhagic septicemia virus (VHSV) poses a significant threat to global aquaculture, prompting ongoing efforts to identify potential drug candidates for disease prevention. Coumarin derivatives have recently emerged as a promising class of compounds effective against rhabdoviruses, which severely impact the aquaculture industry. In this study, we assessed the anti-VHSV activity of umbelliferone (7-hydroxycoumarin) in fathead minnow (FHM) cells and olive flounder Paralichthys olivaceus. Umbelliferone exhibited an EC50 of 100 μg/mL by reducing cytopathic effect, with a maximum cytotoxicity of 30.9 % at 750 μg/mL. Mechanistic analyses via a time-course plaque reduction assay revealed that direct incubation with the virus for 1 h resulted in 97.0 ± 1.8 % plaque reduction, showing excellent direct virucidal activity. Pretreatment for 4 h resulted in a 33.5 ± 7.8 % plaque reduction, which increased with longer incubation times. Cotreatment led to a 33.5 ± 2.9 % plaque reduction, suggesting interference with viral binding, whereas postinfection treatment proved less effective. Umbelliferone was prophylactically administered to the olive flounder through short-term (3 days) and long-term (14 days) medicated feeding, followed by a 4-day postinfection period. Short-term administration at 100 mg/kg body weight (bw)/day resulted in the highest relative percent survival (RPS) of 56 %, whereas long-term administration achieved a maximum RPS of 44 % at 30 mg/kg bw/day. Umbelliferone administration delayed mortality at these doses. Additionally, umbelliferone significantly inhibited the expression of the VHSV N gene during viral challenge, with no observed toxic effects in fish up to an administration dose of 30 mg/kg bw/day for 28 days. Our findings suggest that the protective mechanism of short-term administration of 100 mg umbelliferone against VHSV infection may involve the overexpression of TLR2, MDA5, STAT1, and NF-κB at 24 h postinfection (hpi). IL-8 and IFN II expression was upregulated, whereas TNF-α, IL-1β, and IFN I expression was suppressed at 24 hpi. The upregulation of ISG15 at 48 hpi may contribute to the inhibition of VHSV replication, whereas the downregulation of Caspase 3 expression at 96 hpi suggests a possible inhibition of virus-induced apoptosis at later infection stages. Overall, umbelliferone exhibited anti-VHSV activity through multiple mechanisms, with the added advantage of convenient administration via medicated feed.

Effect of the Viral Hemorrhagic Septicemia Virus Nonvirion Protein on Translation via PERK-eIF2α Pathway

Viral hemorrhagic septicemia virus (VHSV) is one of the most deadly infectious fish pathogens, posing a serious threat to the aquaculture industry and freshwater ecosystems worldwide. Previous work showed that VHSV sub-genotype IVb suppresses host innate immune responses, but the exact mechanism by which VHSV IVb inhibits antiviral response remains incompletely characterized. As with other novirhabdoviruses, VHSV IVb contains a unique and highly variable nonvirion (NV) gene, which is implicated in viral replication, virus-induced apoptosis and regulating interferon (IFN) production. However, the molecular mechanisms underlying the role of IVb NV gene in regulating viral or cellular processes is poorly understood. Compared to the wild-type recombinant (rWT) VHSV, mutant VHSV lacking a functional IVb NV reduced IFN expression and compromised innate immune response of the host cells by inhibiting translation. VHSV IVb infection increased phosphorylated eukaryotic initiation factor 2α (p-eIF2α), resulting in host translation shutoff. However, VHSV IVb protein synthesis proceeds despite increasing phosphorylation of eIF2α. During VHSV IVb infection, eIF2α phosphorylation was mediated via PKR-like endoplasmic reticulum kinase (PERK) and was required for efficient viral protein synthesis, but shutoff of host translation and IFN signaling was independent of p-eIF2α. Similarly, IVb NV null VHSV infection induced less p-eIF2α, but exhibited decreased viral protein synthesis despite increased levels of viral mRNA. These findings show a role for IVb NV in VHSV pathogenesis by utilizing the PERK-eIF2α pathway for viral-mediated host shutoff and interferon signaling to regulate host cell response.

Genetically engineered viral hemorrhagic septicemia virus (VHSV) vaccines

Viral hemorrhagic septicemia virus (VHSV) has been one of the major causes of mortality in a wide range of freshwater and marine fishes worldwide. Although various types of vaccines have been tried to prevent VHSV disease in cultured fishes, there are still no commercial vaccines. Reverse genetics have made it possible to change a certain regions on viral genome in accordance with the requirements of a research. Various types of VHSV mutants have been generated through the reverse genetic method, and most of them were recovered to investigate the virulence mechanisms of VHSV. In the reverse genetically generated VHSV mutants-based vaccines, high protective efficacies of attenuated VHSVs and single-cycle VHSV particles have been reported. Furthermore, the application of VHSV for the delivery tools of heterologous antigens including not only fish pathogens but also mammalian pathogens has been studied. As not much research has been conducted on VHSV mutants-based vaccines, more studies on the enhancement of immunogenicity, vaccine administration routes, safety to environments are needed for the practical use in aquaculture farms.

A new meroterpenoid functions as an anti-tumor agent in hepatoma cells by downregulating mTOR activation and inhibiting EMT

Liver cancer, also known as primary liver cancer, is cancer that starts in the liver. JNU-144, a new meroterpenoid purified from Lithospermum erythrorhizon, has exhibited promising anticancer activity; however, the molecular mechanisms of action of JNU-144 on malignant cells remain unclear. Our studies revealed that JNU-144 suppressed cell viability and proliferation in hepatoma cells by downregulating mTOR activation. Meanwhile, JNU-144 activated the intrinsic apoptosis pathway and subsequently triggered apoptotic cell death in SMMC-7721 cells. We also found that JNU-144 inhibited the epithelial–mesenchymal transition in both SMMC-7721 and HepG2 cells through reprogramming of epithelial–mesenchymal transition (EMT)-related gene expression or regulating protein instability. These findings indicate that JNU-144 exerts potent anticancer activity in hepatoma cells and may be developed as a potential therapeutic drug.

Micropterus salmoides rhabdovirus (MSRV) infection induced apoptosis and activated interferon signaling pathway in largemouth bass skin cells

Largemouth bass (Micropterus salmoides) rhabdovirus (MSRV) was isolated from infected juveniles of largemouth bass, and the infected fish exhibited corkscrew, irregular swimming, and crooked body. To our knowledge, the potential molecular mechanisms underlying the pathogenesis of MSRV infection remain largely unknown. In the current study, we found that MSRV infection in largemouth bass skin (LBS) cells induced typical apoptosis, evidenced by the presence of apoptotic bodies and caspase-3 activation. To further analyze the host factors involved in MSRV infection in LBS cells, the transcriptomic profiles during MSRV infection were uncovered using deep RNA sequencing technique, and several differentially expressed genes (DEGs) were validated by quantitative PCR. Our results showed that a total of 124483 unigenes were assembled. Among them, 34465 and 27273 had significant hits to those in the NR and SwissProt databases. After MSRV infection, a total of 2432 and 2480 genes which involved in multiples pathways including TNF signaling, NF-κB signaling, Toll-like receptor signaling and RIG-I signaling pathway were differentially expressed in MSRV infected LBS cells compared to mock-infected cells at 12 h, respectively. Furthermore, quantitative PCR showed that the expression levels of 9 differentially expressed genes (DEGs) related to apoptosis and interferon signaling pathway was consistent with that from transcriptomic profiles. Together, our results not only demonstrated that interferon signaling pathway and apoptosis pathway might exerted crucial roles during MSRV infection, but also provided a useful resource for subsequent investigation of other immune-related genes related to virus infection.

Zebra Fish Lacking Adaptive Immunity Acquire an Antiviral Alert State Characterized by Upregulated Gene Expression of Apoptosis, Multigene Families, and Interferon-Related Genes

To investigate fish innate immunity, we have conducted organ and cell immune-related transcriptomic as well as immunohistologic analysis in mutant zebra fish (Danio rerio) lacking adaptive immunity (rag1^−/−) at different developmental stages (egg, larvae, and adult), before and after infection with spring viremia carp virus (SVCV). The results revealed that, compared to immunocompetent zebra fish (rag1^+/+), rag1^−/− acquired increased resistance to SVCV with age, correlating with elevated transcript levels of immune genes in skin/fins and lymphoid organs (head kidney and spleen). Gene sets corresponding to apoptotic functions, immune-related multigene families, and interferon-related genes were constitutively upregulated in uninfected adult rag1^−/− zebra fish. Overexpression of activated CASPASE-3 in different tissues before and after infection with SVCV further confirmed increased apoptotic function in rag1^−/− zebra fish. Concurrently, staining of different tissue samples with a pan-leukocyte antibody marker showed abundant leukocyte infiltrations in SVCV-infected rag1^−/− fish, coinciding with increased transcript expression of genes related to NK-cells and macrophages, suggesting that these genes played a key role in the enhanced immune response of rag1^−/− zebra fish to SVCV lethal infection. Overall, we present evidence that indicates that rag1^−/− zebra fish acquire an antiviral alert state while they reach adulthood in the absence of adaptive immunity. This antiviral state was characterized by (i) a more rapid response to viral infection, which resulted in increased survival, (ii) the involvement of NK-cell- and macrophage-mediated transcript responses rather than B- and/or T-cell dependent cells, and (iii) enhanced apoptosis, described here for the first time, as well as the similar modulation of multigene family/interferon-related genes previously associated to fish that survived lethal viral infections. From this and other studies, it might be concluded that some of the characteristics of mammalian trained immunity are present in lower vertebrates.

Regulation of Viral Replication, Apoptosis and Pro-Inflammatory Responses by 17-AAG during Chikungunya Virus Infection in Macrophages

Chikungunya virus (CHIKV) infection has re-emerged as a major public health concern due to its recent worldwide epidemics and lack of control measures. Although CHIKV is known to infect macrophages, regulation of CHIKV replication, apoptosis and immune responses towards macrophages are not well understood. Accordingly, the Raw264.7 cells, a mouse macrophage cell line, were infected with CHIKV and viral replication as well as new viral progeny release was assessed by flow cytometry and plaque assay, respectively. Moreover, host immune modulation and apoptosis were studied through flow cytometry, Western blot and ELISA. Our current findings suggest that expression of CHIKV proteins were maximum at 8 hpi and the release of new viral progenies were remarkably increased around 12 hpi. The induction of Annexin V binding, cleaved caspase-3, cleaved caspase-9 and cleaved caspase-8 in CHIKV infected macrophages suggests activation of apoptosis through both intrinsic and extrinsic pathways. The pro-inflammatory mediators (TNF and IL-6) MHC-I/II and B7.2 (CD86) were also up-regulated during infection over time. Further, 17-AAG, a potential HSP90 inhibitor, was found to regulate CHIKV infection, apoptosis and pro-inflammatory cytokine/chemokine productions of host macrophages significantly. Hence, the present findings might bring new insight into the therapeutic implication in CHIKV disease biology.

Over-passage of epithelioma papulosum cyprini (EPC) cells increased viral hemorrhagic septicemia virus (VHSV) replication

Vaccines based on inactivated or attenuated viruses can be a way to prevent viral hemorrhagic septicemia virus (VHSV) disease, and the efficiency of viral production is a critical factor that can determine the practical use of developed vaccines in aquaculture farms. To know the effects of epithelioma papulosum cyprini (EPC) cells over-subculture on VHSV replication, the VHSV titer produced from high-passage EPC cells (subcultured more than 200 times in our laboratory) was compared to the titer produced from low-passage EPC cells (subcultured 5-15 times). Furthermore, to know whether immune factors are involved in VHSV titers, differences not only in the expression of Mx1 and ISG15 genes but also in the apoptosis progression by VHSV infection between high- and low-passage EPC cells were analyzed. The VHSV titers from high-passage EPC cells were significantly higher than titers from low-passage EPC cells, suggesting that the changed properties of EPC cells by over-subculture were favorable for VHSV proliferation. The DNA laddering of high-passage EPC cells by VHSV infection took a longer time than that of low-passage EPC cells, suggesting that over-subculture might delay apoptosis in VHSV infected EPC cells, and the delay of apoptosis by over-subculture can be thought as one of the factors that increased VHSV titers in high-passage EPC cells. The increased folds of Mx1 and ISG15 genes in high-passage EPC cells were significantly lower than those in low-passage EPC cells when exposed to either poly (I:C) or VHSV. However, the expression levels of Mx1 and ISG15 genes of high-passage EPC cells that were not stimulated with poly I:C or VHSV were almost equal to or higher than the expression levels of low-passage EPC cells that were exposed to poly (I:C) or VHSV. This result suggests that high-passage EPC cells were already in an excited state in type I interferon responses without any stimulants. The full open reading frame (ORF) sequences of Mx1 gene between high- and low-passage EPC cells were completely same. However, there were some differences in the amino acids sequences of ISG15 gene between high- and low-passage EPC cells, suggesting that ISG15-mediated pathways might be different between high- and low-passage EPC cells, which might influence on the replication of VHSV. The present results showed that the changed properties of EPC cells by over-subculture were favorable for VHSV proliferation.