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.