Red sea bream (Pagrosomus major) is one of the most popular farmed marine teleost fish species. Fish cell lines are becoming important research tool in the aquaculture field, and they are suitable models to study fish virology, immunology and toxicology. To obtain a Pagrosomus major cell line for biological studies, a continuous cell line from brain of red sea bream (designated as RSBB cell line) was established and has been successfully subcultured over 100 passages. The RSBB cell line predominantly consisted of fibroblast-like cells and multiplied well in M199 medium supplemented with 10% fetal bovine serum at 28 °C. Karyotyping analysis indicated that the modal chromosome numbers of RSBB cells was 48. After transfection with pEGFP-N1, RSBB cells showed bright green fluorescence with a transfection efficiency approaching 8%. For toxicology study, it was demonstrated that metal Cd could induce cytotoxic effects of RSBB cells, accompanied with a dose-dependent MTT conversion capacity. Morphologically, cells treated with metal Cd produced rounding, shrinking and detaching and induced both cell apoptosis and necrosis. For virology study, the RSBB cells were highly susceptible to Nervous necrosis virus (NNV) and Singapore grouper iridovirus (SGIV) with steady titers (i.e., 10^8.0~8.3 TCID₅₀ mL⁻¹ and 10^7.0~7.2 TCID₅₀ mL⁻¹ respectively). Furthermore, an obvious cytopathic effect (CPE) could be observed in RSBB cells infected with Infectious spleen and kidney necrosis virus (ISKNV) and Siniperca chuatsi rhabdoviruses (SCRV). Meanwhile, all the infections were confirmed by polymerase chain reaction. The new brain cell line developed and characterized from red sea bream in this study could be used as an in vitro model for fish studies in the fields of toxicology and virology.

The disease caused by Largemouth bass ranavirus (LMBV) is one of the most severe viral diseases in largemouth bass (Micropterus salmoides). It is crucial to evaluate the genetic resistance of largemouth bass to LMBV and develop markers for disease-resistance breeding. In this study, 100 individuals (45 resistant and 55 susceptible) were sequenced and evaluated for resistance to LMBV and a total of 2,579,770 variant sites (SNPs-single-nucleotide polymorphisms (SNPs) and insertions–deletions (InDels)) were identified. A total of 2348 SNPs-InDels and 1018 putative candidate genes associated with LMBV resistance were identified by genome-wide association analyses (GWAS). Furthermore, GO and KEGG analyses revealed that the 10 candidate genes (MHC II, p38 MAPK, AMPK, SGK1, FOXO3, FOXO6, S1PR1, IL7R, RBL2, and GADD45) were related to intestinal immune network for IgA production pathway and FoxO signaling pathway. The acquisition of candidate genes related to resistance will help to explore the molecular mechanism of resistance to LMBV in largemouth bass. The potential polymorphic markers identified in this study are important molecular markers for disease resistance breeding in largemouth bass.

Infectious spleen and kidney necrosis virus (ISKNV) has brought huge economic loss to the aquaculture industry. Through interfering with the viral replication and proliferation process that depends on host cells, its pathogenicity can be effectively reduced. In this study, we investigated the role of asparagine metabolites in ISKNV proliferation. The results showed that ISKNV infection up-regulated the expression of some key enzymes of the asparagine metabolic pathway in Chinese perch brain (CPB) cells. These key enzymes, including glutamic oxaloacetic transaminase 1/2 (GOT1/2) and malate dehydrogenase1/2 (MDH1/2) associated with the malate-aspartate shuttle (MAS) pathway and asparagine synthetase (ASNS) involved in the asparagine biosynthesis pathway, were up-regulated during ISKNV replication and release stages. In addition, results showed that the production of ISKNV was significantly reduced by inhibiting the MAS pathway or reducing the expression of ASNS by 1.3-fold and 0.6-fold, respectively, indicating that asparagine was a critical limiting metabolite for ISKNV protein synthesis. Furthermore, when asparagine was added to the medium without glutamine, ISKNV copy number was restored to 92% of that in the complete medium, indicating that ISKNV could be fully rescued from the absence of glutamine by supplementing asparagine. The above results indicated that asparagine was a critical factor in limiting the effective replication of ISKNV, which provided a new idea for the treatment of aquatic viral diseases.

Infectious spleen and kidney necrosis virus (ISKNV) resulted in severe systemic diseases with high morbidity and mortality in Siniperca chuatsi. Vaccination is the primary method for effective prevention and control of these diseases. The development of inactivated ISKNV vaccines made some progress, but the technique of quality evaluation is scarce. Herein, a measurement of the MCP (major capsid protein) antigen concentration for the inactivated ISKNV vaccine was developed by double-antibody sandwich ELISA. Firstly, mouse monoclonal antibodies against ISKNV particles and MCP were generated. Then, a double-antibody sandwich ELISA was developed using the monoclonal antibody 1C8 1B9 as the capture antibody and Biotin-3B12 6B3 as the detection antibody. A standard curve was generated using the MCP concentration versus OD value with the linear range of concentration of 4.69~300 ng/mL. The assay sensitivity was 0.9 ng/mL. The antigen content of three batches of inactivated ISKNV vaccines was quantitatively detected using the double-antibody sandwich ELISA. The results showed that MCP antigen contents of inactivated ISKNV vaccines were positively correlated with the viral titers. The newly established double-antibody sandwich ELISA provided a useful tool for the detection of antigen quality for ISKNV inactivated vaccines.

The role of ferroptosis—a novel iron-dependent programmed cell death pathway—in infectious spleen and kidney necrosis virus (ISKNV) infection remains poorly understood. Here, we demonstrate that ISKNV infection induces ferroptosis in CPB cells. Following ISKNV challenge, CPB cells exhibited hallmark morphological alterations including mitochondrial shrinkage, increased membrane density, and cristae reduction. Biochemical assays confirmed significant time-dependent elevations in ferroptosis markers: malondialdehyde (MDA, 1.7-fold), reactive oxygen species (ROS, 3.14-fold), and ferrous iron (Fe²⁺, 1.42-fold) compared to controls (p < 0.05). Mechanistic studies revealed that ISKNV downregulated glutathione peroxidase 4 (GPx4) while upregulating acyl-CoA synthetase long-chain family member 4 (ACSL4), as validated by quantitative real-time PCR (qRT-PCR) and immunoblotting. Ferroptosis induction with erastin enhanced ISKNV replication, whereas inhibition with liproxstatin-1 suppressed viral yield. These findings establish that ISKNV exploits ferroptosis to facilitate its replication, and pharmacological blockade of this pathway significantly suppresses viral propagation, providing a new strategy and intervention approach for controlling ISKNV infection.

Tripartite Motif-Containing 44 (TRIM44) is responsible for cancers, neurodegenerative diseases, and viral infections. However, the role of Siniperca chuatsi TRIM44 (scTRIM44) during viral infection remains unclear. In the present study, we analyzed the molecular characteristics of scTRIM44 and its role in infectious spleen and kidney necrosis virus (ISKNV), largemouth bass virus (LMBV), and Siniperca chuatsi rhabdovirus (SCRV) infection. ScTRIM44 contained one B-box domain (B, 166–207 aa) and a coiled-coil domain (CC, 279–309 aa), but lacked the canonical RING domain of E3 ubiquitin ligases. The scTRIM44 mRNA was expressed relatively high in immune-related tissues. The mRNA expression of scTRIM44 significantly decreased in vivo and vitro post-ISKNV and -LMBV infection. However, the expression of scTRIM44 mRNA showed significant up-regulation post-SCRV infection. ScTRIM44 positively regulated SCRV infection in CPB cells, but copies of ISKNV and LMBV showed no significant alteration in over-expressed or knocked-down scTRIM44 cells. Moreover, scTRIM44 positively regulated RIG-I- and MDA5-mediated interferon molecule signaling. These data suggested that scTRIM44 promoted SCRV infection by positively regulating RIG-I- and MDA5-mediated interferon molecule signaling, but didn’t regulate ISKNV and LMBV infection. This research provided a comprehensive insight into the antiviral activity of scTRIM44.