Transcriptomic response of skeletal muscle to lipopolysaccharide in the gilthead seabream (Sparus aurata)

The physiological consequences of an activation of the immune system in fish are not well understood. In particular, skeletal muscle, due to its essential role in locomotion and whole-animal energy homeostasis, is a potentially important target of inflammation. In this study, we have evaluated the in vivo effects of lipopolysaccharide (LPS) on the white and red skeletal muscle transcriptome of the gilthead seabream (Sparus aurata) by microarray analysis at 24 and 72 hours after injection. In white muscle, the transcriptomic response was characterized by an up-regulation of genes involved in carbohydrate catabolism and protein synthesis at 24 hours and a complete reversal of this pattern at 72 hours. In red muscle, an up-regulation of genes involved in carbohydrate catabolism and protein synthesis was observed only at 72 hours after LPS administration. Interestingly, both white and red muscles showed a similar consistent down-regulation of immune genes at 72 hours post-injection. However, genes involved in muscle contraction showed a general up-regulation in response to LPS in both types of muscle. In summary, LPS administration causes muscle type-specific responses regarding the expression of genes involved in carbohydrate and protein metabolism and a common decreased expression of immune genes in skeletal muscle, concomitant with increased expression of genes for contractile elements. Our results evidence a robust and tissue-specific transcriptomic response of the skeletal muscle to an acute inflammatory challenge. Total RNA from pooled control (n = 5) and LPS-treated (n = 5) sea bream white and red muscle tissues was labeled with Cy3-dUTP and Cy5-dUTP (GE Healthcare, Barcelona, Spain). We used a dye swap experimental design and each cDNA from a pooled RNA sample was hybridized to two microarrays. For the first slide, test and control cDNA were labeled with Cy5 and Cy3 respectively, and for the second array dye assignment was reversed. Therefore, samples from individual fish within each group were pooled and expression values shown represent the means of 6 × 2 = 12 technical replicates. A total of eight slides were used in this study.