Antimicrobial peptides and proteins mediating viral defense in Atlantic salmon

Pancreatic disease causes great damage to farmed Atlantic salmon, and the causative agent is Salmonid alphavirus (SAV). It is necessary to detect the virus before the pandemic. This project studied the antimicrobial peptides that are capable of protecting Atlantic salmon from SAV3 virus, a subtype of SAV. The expression of antimicrobial peptide during SAV3 infection were profiled using quantitative PCR (genes) and shotgun proteomic (proteins) techniques. Mucosal immune responses of salmon were dependent on the route of infection. New molecular markers of SAV3 infection in Atlantic salmon skin mucus were identified and these could be used for early detection of the virus and to prevent the pandemic. AMP gene expression profile in SAV infected Atlantic salmon. This part of the project was undertaken in collaboration with the MitSAV project (NFR-funded) at IMR. In a virus (SAV3) challenge study on Atlantic salmon, AMP gene expression profiling (qPCR) was performed on skin tissues. The viral structural protein gene, AMP genes and viral infection marker genes were examined. In the intramuscular injection group, the peak of virus gene was observed at 7 days after injection. On the other hand, in the bath immersion group, the peak of expression was recorded at 4 weeks after exposure. Interestingly, the viral infection marker genes and AMP genes were not induced by the bath immersion at this time point. The metaproteomics using iTRAQ system suggested that some of the protein may useful as a novel molecular marker for early phase SAV3 infection.

Atlantic salmon farming industry in Norway registered mortality of 27 million in 2012 and viral diseases such as infectious salmon anaemia, pancreas disease, heart and skeletal muscle inflammation, cardiomyopathy syndrome and infectious pancreatic necrosi s continue to plague the industry. To combat diseases, new and sustainable solutions should be discovered. A possible choice could be to exploit the molecules of the innate immune system, including antimicrobial peptides and proteins (AMPs). Therefore, t he present project aims to understand the antiviral potential of selected AMPs of Atlantic salmon. Molecular and biochemical approaches will be employed to clarify the functions and structure of the chosen AMPs - defensin, cathelicidin and L-amino acid ox idase. Their action in naturally and experimentally infected Atlantic salmon would be investigated. The antiviral properties of the recombinant AMPs against a range of viruses will be assessed in vitro. The knowledge on the antiviral capabilities of the AMPs would be valuable in the future to develop them as disease control agents.