Aquaculture is essential to cover fish-product demands, providing seafood in high quantities, and covering the half amount of fish consumed worldwide. Greece is one of the leading producers of sea bream (Sparus aurata) and European sea bass (D. labrax ) in the Mediterranean. As fish health and welfare is a prerequisite for sustainable and profitable production in the Mediterranean area, combating diseases is highlighted as priority for the development and improvement of aquaculture sector. The most significant disease in terms of severity, economic impact and spread, is viral nervous necrosis (VNN). VNN is a devastating disease, which induces cell necrosis accompanied by vacuolation in fish retina and brain. The disease is caused by nervous necrosis virus (NNV), affecting more than 30 different fish species, worldwide. The first step to move forward on the battle against the NVV disease is to fully understand its progression and its effect on the host. Aim of the present study is to identify which cell brain population is attacked by the NNV and how it affects the neuronal and astroglial gene expression during the disease progression.
Hence, we studied the gene expression of neuronal and astroglial markers in brain tissues of experimentally infected D. labrax upon 0 and 3 hours of infection, 2 and 14 days of infection and upon 7 days following re-infection of the fishes that survived. Two different families of D. labrax were included in the current study : a sea bass family which exhibits resistance to NNV and an NNV-susceptible family. Comparison of the brain cell types’ gene expression in these two families upon infection with NNV, showed different expression patterns for neuronal (rbfox3, map), astroglial (coro1a, gfap) and whole brain markers (cart1, pomc1) between the two families, highlighting probable molecular mechanisms that are triggered in the brain for managing the infection more effectively.
Moreover, in brain primary cell cultures derived from uninfected D. labrax , we evaluated the expression of neuronal and astroglial markers using specific antibodies in an immunofluorescence before and after NNV infection of the primary cell cultures . Both neuronal and astroglial expressing cells were developed in the cultures and upon NNV infection, glial fibrillary acidic protein (GFAP- a stroglial marker) became condensed while vacuoles and disrupted structures were observed in Tuj- expressing cells (neuronal marker).
Overall, the results of the present study will provide a better understanding of the impact of NNV in the fish brain cell populations and it will give us the tools to further investigate potential signaling pathways involved in the progression of a nervous necrosis infection.
Funding: The research project was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Faculty Members & Researchers” (Project Number: 03990)