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Ferritin is a highly-conserved iron-storage protein that has also been identified as an acute phase protein within the innate immune system. The iron-storage function is mediated through complementary roles played by heavy (H)-chain subunit as well as the light (L) in mammals or middle (M)-chain in teleosts, respectively. In this study, we report the identification of five ferritin subunits (H1, H2, M1, M2, M3) in the Atlantic salmon that were supported by the presence of iron-regulatory regions, gene structure, conserved domains and phylogenetic analysis. Tissue distribution analysis across eight different tissues showed that each of these isoforms is differentially expressed. We also examined the expression of the ferritin isoforms in the liver and kidney of juvenile Atlantic salmon that was challenged with Aeromonas salmonicida as well as in muscle cell culture stimulated with interleukin-1β. We found that each isoform displayed unique expression profiles, and in certain conditions the expressions between the isoforms were completely diametrical to each other. Our study is the first report of multiple ferritin isoforms from both the H- and M-chains in a vertebrate species, as well as ferritin isoforms that showed decreased expression in response to infection. Taken together, the results of our study suggest the possibility of functional differences between the H- and M-chain isoforms in terms of tissue localisation, transcriptional response to bacterial exposure and stimulation by specific immune factors. [ABSTRACT FROM AUTHOR]

Background The relationship between fish health and muscle growth is critical for continued expansion of the aquaculture industry. The effect of immune stimulation on the expression of genes related to the energy balance of fish is poorly understood. In mammals immune stimulation results in major transcriptional changes in muscle, potentially to allow a reallocation of amino acids for use in the immune response and energy homeostasis. The aim of this study was to investigate the effects of immune stimulation on fish muscle gene expression. Results Atlantic salmon (Salmo salar) primary muscle cell cultures were stimulated with recombinant (r)IL-1β, a major proinflammatory cytokine, for 24 h in order to simulate an acute immune response. The transcriptomic response was determined by RNA hybridization to a 4 × 44 K Agilent Atlantic salmon microarray platform. The rIL-1β stimulation induced the expression of genes related to both the innate and adaptive immune systems. In addition there were highly significant changes in the expression of genes related to regulation of the cell cycle, growth/structural proteins, proteolysis and lipid metabolism. Of interest were a number of IGF binding proteins that were differentially expressed, which may demonstrate cross talk between the growth and immune systems. Conclusion We show rIL-1β modulates the expression of not only immune related genes, but also that of genes involved in processes related to growth and metabolism. Co-stimulation of muscle cells with both rIGF-I and rIL-1β demonstrates cross talk between these pathways providing potential avenues for further research. This study highlights the potential negative effects of inflammation on muscle protein deposition and growth in fish and extends our understanding of energy allocation in ectothermic animals. [ABSTRACT FROM AUTHOR]

Abstract: E3 ubiquitin ligases are central for the selection of proteins targeted for degradation by the ubiquitin proteasome pathway. In this study atrogin-1 (Fbox-32), a major E3 ligase in muscle, has been characterized in Atlantic salmon (Salmo salar). The protein sequence is highly conserved between teleosts and mammals and is characterized by the presence of five conserved motifs related to the identification of protein targets. The genomic structure is conserved between teleosts and mammals and contains 9 exon and 8 introns. The phylogenetic relationship between atrogin-1 and two other closely related ubiquitin E3 ligases FBXO25 and MuRF1 showed atrogin-1 and FBXO25 grouped together with MuRF1 being more distant. The mRNAs were expressed in multiple tissues, atrogin-1 and MuRF1 were most abundant in white muscle and heart whereas FBXO25 had greatest expression in brain, white muscle and heart. The transcriptional modulation of these E3 ligases was examined in starved fish and fish following different immune stimulations. Expression of atrogin-1 and MuRF1 was increased following food deprivation, implementing these two genes in degradation of muscle protein during starvation. During viral infection atrogin-1 expression was not altered, whereas it was increased following stimulation with LPS, indicating an onset of catabolic processes during inflammatory responses. [ABSTRACT FROM AUTHOR]