Evidence for a Novel Antiviral Mechanism of Teleost Fish: Serum-Derived Exosomes Inhibit Virus Replication through Incorporating Mx1 Protein

Exosomes are associated with cancer progression, pregnancy, cardiovascular diseases, central nervous system-related diseases, immune responses and viral pathogenicity. However, study on the role of exosomes in the immune response of teleost fish, especially antiviral immunity, is limited. Herein, serum-derived exosomes from mandarin fish were used to investigate the antiviral effect on the exosomes of teleost fish. Exosomes isolated from mandarin fish serum by ultra-centrifugation were internalized by mandarin fish fry cells and were able to inhibit Infectious spleen and kidney necrosis virus (ISKNV) infection. To further investigate the underlying mechanisms of exosomes in inhibiting ISKNV infection, the protein composition of serum-derived exosomes was analyzed by mass spectrometry. It was found that myxovirus resistance 1 (Mx1) was incorporated by exosomes. Furthermore, the mandarin fish Mx1 protein was proven to be transferred into the recipient cells though exosomes. Our results showed that the serum-derived exosomes from mandarin fish could inhibit ISKNV replication, which suggested an underlying mechanism of the exosome antivirus in that it incorporates Mx1 protein and delivery into recipient cells. This study provided evidence for the important antiviral role of exosomes in the immune system of teleost fish.

Characterization and Expression Profiling of Glutathione Peroxidase 1 gene (GPX1) and Activity of GPX in Onychostoma macrolepis suffered from Thermal Stress

In this study, full-length cDNA of glutathione peroxidases 1 (GPX1) of Onychostoma macrolepis was cloned by RACE, and expression of GPX1 and activity of GPX in O. macrolepis suffered from heat stress were analyzed. Compared with the control group (24°C), the experimental fish were stressed for 0, 1, 3, 6, 12, 24, and 48 hours at the heated water (30°C). Liver had highest level and response speed in GPX1 expression among various tissues after heat stress, indicated that liver was the highest sensitive tissue to heat stress. When the water was raised to the heating temperature (30°C), the GPX activity decreased in fish serum, and the consumption of GPX eliminated the increase of ROS caused by heat stress within 3h. However, after 6h and 12h stress at 30°C, GPX activity was significantly higher than that at 0h (P<0.05), which is due to the rapid response of GPX to heat stress. In summary, fish showed a transient stress response and was acclimated to the new temperature after 24 h according to the overall expression of the GPX1 and the serum GPX activity, and both GPX1 and GPX play crucial roles in this process.

An Evidence for a Novel Antiviral Mechanism of Teleost Fish: Serum-Derived Exosomes Inhibit Virus Replication Through Incorporating Mx1 Protein

Exosomes are associated with cancer progression, pregnancy, cardiovascular diseases, central nervous system&ndash;related diseases, immune responses and viral pathogenicity. However, study on the role of exosomes in the immune response of teleost fish, especially antiviral immunity, is limited. Herein, serum-derived exosomes from mandarin fish were used to investigate antiviral effect for the exosomes of teleost fish. Exosomes were isolated from mandarin fish serum by ultracentrifugation could internalize into Mandarin fish fry (MFF-1) cells and inhibited Infectious spleen and kidney necrosis virus (ISKNV) infection. To further investigated the underlying mechanisms of exosomes in inhibiting ISKNV infection. The protein composition of serum-derived exosomes was by analysis mass spectrometry and found that myxovirus resistance 1 (Mx1) was incorporated in the exosomes. Furthermore, the scMx1 protein was proved transferred to the recipient cells though the exosomes. Our results found that the serum-derived exosomes from mandarin fish could inhibit ISKNV replication and suggested an underlying mechanism of the serum-derived exosomes antivirus is that serum-derived exosomes incorporation of the Mx1 protein into exosomes and delivery into recipient cells. This study provided an evidence for the important antiviral role of exosomes in the immune system of teleost fish.

Hamp Type-1 Promotes Antimicrobial Defense via Direct Microbial Killing and Regulating Iron Metabolism in Grass Carp (Ctenopharyngodon idella)

Hepcidin is an antimicrobial peptide and regulator of iron homeostasis which has two isoforms in most fishes and some mammals. Previous studies have reported that the two hepcidin isoforms have different roles. Hamp type-1 plays a regulatory role in iron metabolism and hamp type-2 mostly performs an antimicrobial role. In this study, we found that Ctenopharyngodon idella (C. idella) have only one hepcidin isoform (hamp type-1), which showed both broad-spectrum antibacterial and iron regulatory functions. C. idella hepcidin mature peptide (hepcidin-25) and truncated peptide (hepcidin-20) exhibited bactericidal activities against both Gram-positive and Gram-negative bacteria in a dose-dependent manner in part through membrane rupture and binding to bacterial genomic DNA. The data from challenge tests demonstrated that the administration of hepcidin-25 significantly reduced mortality rates of C. idella by A. hydrophila infection, probably due to direct bactericidal activities of the peptide and a reduction of iron content in the fish serum. In addition, a comparison between hepcidin-20 and -25 suggests that the N terminal 5 amino acids play a critical role in reducing iron content in fish serum. Our findings revealed an important role of hamp type-1 in maintaining iron homeostasis and fighting against bacterial infections, suggesting the hepcidin has implications for the prevention and control of bacterial infection in aquaculture.