Postprandial molecular responses in the liver of the barramundi, Lates calcarifer

The regulation of gene expression by nutrients is an important mechanism governing energy storage and growth in most animals, including fish. At present, very few genes that regulate intermediary metabolism have been identified in barramundi, nor is there any understanding of their nutritional regulation. In this study, a partial barramundi liver transcriptome was assembled from next-generation sequencing data and published barramundi EST sequences. A large number of putative metabolism genes were identified in barramundi, and the changes in the expression of 24 key metabolic regulators of nutritional pathways were investigated in barramundi liver over a time series immediately after a meal of a nutritionally optimised diet for this species. Plasma glucose and free amino acid levels showed a mild postprandial elevation which peaked 2 h after feeding, and had returned to basal levels within 4 or 8 h, respectively. Significant activation or repression of metabolic nuclear receptor regulator genes were observed, in combination with activation of glycolytic and lipogenic pathways, repression of the final step of gluconeogenesis and activation of the Akt-mTOR pathway. Strong correlations were identified between a number of different metabolic genes, and the coordinated co-regulation of these genes may underlie the ability of this fish to utilise dietary nutrients. Overall, these data clearly demonstrate a number of unique postprandial responses in barramundi compared with other fish species and provide a critical step in defining the response to different dietary nutrient sources

Dietary starch promotes hepatic lipogenesis in barramundi (Lates calcarifer)

Barramundi (Lates calcarifer) are a highly valued aquaculture species, and, as obligate carnivores, they have a demonstrated preference for dietary protein over lipid or starch to fuel energetic growth demands. In order to investigate how carnivorous fish regulate nutritional cues, we examined the metabolic effects of feeding two isoenergetic diets that contained different proportions of digestible protein or starch energy. Fish fed a high proportion of dietary starch energy had a higher proportion of liver SFA, but showed no change in plasma glucose levels, and few changes in the expression of genes regulating key hepatic metabolic pathways. Decreased activation of the mammalian target of rapamycin growth signalling cascade was consistent with decreased growth performance values. The fractional synthetic rate (lipogenesis), measured by TAG 2H-enrichment using 2H NMR, was significantly higher in barramundi fed with the starch diet compared with the protein diet (0·6 (se 0·1) v. 0·4 (se 0·1) % per d, respectively). Hepatic TAG-bound glycerol synthetic rates were much higher than other closely related fish such as sea bass, but were not significantly different (starch, 2·8 (se 0·3) v. protein, 3·4 (se 0·3) % per d), highlighting the role of glycerol as a metabolic intermediary and high TAG-FA cycling in barramundi. Overall, dietary starch significantly increased hepatic TAG through increased lipogenesis. Compared with other fish, barramundi possess a unique mechanism to metabolise dietary carbohydrates and this knowledge may define ways to improve performance of advanced formulated feeds

Early Hypothalamic FTO Overexpression in Response to Maternal Obesity – Potential Contribution to Postweaning Hyperphagia

Intrauterine and postnatal overnutrition program hyperphagia, adiposity and glucose intolerance in offspring. Single-nucleotide polymorphisms (SNPs) of the fat mass and obesity associated (FTO) gene have been linked to increased risk of obesity. FTO is highly expressed in hypothalamic regions critical for energy balance and hyperphagic phenotypes were linked with FTO SNPs. As nutrition during fetal development can influence the expression of genes involved in metabolic function, we investigated the impact of maternal obesity on FTO.Female Sprague Dawley rats were exposed to chow or high fat diet (HFD) for 5 weeks before mating, throughout gestation and lactation. On postnatal day 1 (PND1), some litters were adjusted to 3 pups (vs. 12 control) to induce postnatal overnutrition. At PND20, rats were weaned onto chow or HFD for 15 weeks. FTO mRNA expression in the hypothalamus and liver, as well as hepatic markers of lipid metabolism were measured.At weaning, hypothalamic FTO mRNA expression was increased significantly in offspring of obese mothers and FTO was correlated with both visceral and epididymal fat mass (P<0.05); body weight approached significance (P = 0.07). Hepatic FTO and Fatty Acid Synthase mRNA expression were decreased by maternal obesity. At 18 weeks, FTO mRNA expression did not differ between groups; however body weight was significantly correlated with hypothalamic FTO. Postnatal HFD feeding significantly reduced hepatic Carnitine Palmitoyltransferase-1a but did not affect the expression of other hepatic markers investigated. FTO was not affected by chronic HFD feeding.Maternal obesity significantly impacted FTO expression in both hypothalamus and liver at weaning. Early overexpression of hypothalamic FTO correlated with increased adiposity and later food intake of siblings exposed to HFD suggesting upregulation of FTO may contribute to subsequent hyperphagia, in line with some human data. No effect of maternal obesity was observed on FTO in adulthood

Intérêt des microalgues en alimentation des poissons

WebinaireNational audienc

Nutrition animale

International audienc

Ontogenetic expression of metabolic genes and microRNAs in rainbow trout alevins during the transition from the endogenous to the exogenous feeding period

International audienceAs oviparous fish, rainbow trout change their nutritional strategy during ontogenesis. This change is divided into the exclusive utilization of yolk-sac reserves (endogenous feeding), the concurrent utilization of yolk reserves and exogenous feeds (mixed feeding) and the complete dependence on external feeds (exogenous feeding). The change in food source is accompanied by well-characterized morphological changes, including the development of adipose tissue as an energy storage site, and continuous muscle development to improve foraging. The aim of this study was to investigate underlying molecular mechanisms that contribute to these ontogenetic changes between the nutritional phenotypes in rainbow trout alevins. We therefore analyzed the expression of marker genes of metabolic pathways and microRNAs (miRNAs) important in the differentiation and/or maintenance of metabolic tissues. In exogenously feeding alevins, the last enzyme involved in glucose production (g6pca and g6pcb) and lipolytic gene expression (cpt1a and cpt1b) decreased, while that of gk, involved in hepatic glucose use, was induced. This pattern is consistent with a progressive switch from the utilization of stored (gluconeogenic) amino acids and lipids in endogenously feeding alevins to a utilization of exogenous feeds via the glycolytic pathway. A shift towards the utilization of external feeds is further evidenced by the increased expression of omy-miRNA-143, a homologue of the mammalian marker of adipogenesis. The expression of its predicted target gene abhd5, a factor in triglyceride hydrolysis, decreased concurrently, suggesting a potential mechanism in the onset of lipid deposition. Muscle-specific omy-miRNA-1/133 and myod1 expression decreased in exogenously feeding alevins, a molecular signature consistent with muscle hypertrophy, which may be linked to nutritional cues or increased foragin

La prolactine, ses récepteurs et ses actions biologiques

chap. 6National audienc