Lipid metabolism related gene expression in European sea bass (Dicentrarchus labrax): effects of fasting and refeeding.

European sea bass (Dicentrarchus labrax) is the second most cultured fish species in the Mediterranean area and there is a great interest to gain better knowledge on nutritional requirements for this species, by exploring not only new feed ingredients and feeding strategies, but also, by understanding in depth the molecular mechanisms regulating feed digestion, utilization and metabolism of nutrients. In this context, transcriptomic analysis represents a useful nutrigenomic discovery tool for identifying the molecular basis of biological responses to nutrition and novel nutritional biomarkers in fish. The objective of the present study was to evaluate how the transcriptional activity of genes controlling lipid metabolism in sea bass are modulated in a tissue-specific manner in response to 15 days of fasting, followed by refeeding. The study focused on liver, white skeletal muscle, brain and mesenteric adipose tissue and included a panel of 30 genes including desaturases, elongases, triacylglycerol lipases, fatty acid binding proteins, β-oxidation and oxidative phosphorylation enzymes, phospholipid-related enzymes and lipid transcription factors. Fasting increased the expression of lipolytic proteins, in particular that of LPL-like and adipose triglyceride lipase (ATGL) in liver and muscle of sea bass. Markers of lipogenesis, such as SCD1b, showed a down-regulation in liver and adipose tissue in response to fasting. Contrariwise, genes involved in synthesis and remodeling of phospholipids (LPCAT2, PEMT, PLA2G12B) were upregulated in liver and muscle of fasted sea bass. The up-regulation of CTP1A and SDHC in response to fasting in both, muscle and liver may indicate an increase mitochondrial β-oxidation of of fatty acids in order to provide energy during fasting. Ten days of refeeding were sufficient to reverse the expression of most part of key genes. In conclusion, the present study clearly showed in European sea bass a tissue- specific regulation of lipid-related genes according to the different metabolic capabilities of each tissue and their vital functions. Our data revealed that brain is highly refractory at the transcriptional level to changes in nutrient and energy availability. In contrast, liver is clearly the most reactive tissue, with changes in gene expression affecting not only the biosynthetic, but also the oxidative and lipolytic machinery