Dietary carbohydrate-to-protein ratio affects TOR signaling and metabolism-related gene expression in the liver and muscle of rainbow trout after a single meal

Abstract

Most teleost fish are known to require high levels of dietary proteins. Such high-protein intake could have significant effects, particularly on insulin-regulated gene expression. We therefore analyzed the effects of an increase in the ratio of dietary carbohydrates/proteins on the refeeding activation of the Akt-target of rapamycin (TOR) signaling pathways in rainbow trout and the effects on the expression of several genes related to hepatic and muscle metabolism and known to be regulated by insulin, amino acids, and/or glucose. Fish were fed once one of three experimental diets containing high (H), medium (M), or low (L) protein (P) or carbohydrate (C) levels after 48 h of feed deprivation. Activation of the Akt/TOR signaling pathway by refeeding was severely impaired by decreasing the proteins-to-carbohydrates ratio. Similarly, postprandial regulation of several genes related to glucose (Glut4, glucose-6-phosphatase isoform 1), lipid (fatty acid synthase, ATP-citrate lyase, sterol responsive element binding protein, carnitine palmitoyltransferase 1, and 3-hydroxyacyl-CoA dehydrogenase), and amino acid metabolism (serine dehydratase and branched-chain α-keto acid dehydrogenase E2 subunit) only occurred when fish were fed the high-protein diet. On the other hand, diet composition had a low impact on the expression of genes related to muscle protein degradation. Interestingly, glucokinase was the only gene of those monitored whose expression was significantly upregulated by increased carbohydrate intake. In conclusion, this study demonstrated that macro-nutrient composition of the diet strongly affected the insulin/amino acids signaling pathway and expression pattern of genes related to metabolism.

Nutritional regulation of glucokinase: a cross-species story

“…Moreover, this induction of activity is mainly linked to the induction of GK gene expression in the liver. The increased GK gene expression in the liver of carnivorous fish appears after long-term feeding with carbohydrates but also after a single meal with carbohydrates, as shown in rainbow trout (204,209,210) ( Figs. 3 and 4).…”

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

“…Recent studies performed in mammals and fish indicate that TOR signalling pathway controls de novo lipogenesis by regulating the expression and processing of sterol regulatory element-binding protein 1c (SREBP1c), a master regulator of sterol-and lipogenic gene transcription (Dentin et al 2005;Duvel et al 2010;Eberle et al 2004;Lansard et al, 2010;Seiliez et al 2011). Genes that code the enzymes glucokinase (GK), ATP-citrate lyase (acyl), acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS) have been thus identified as targets of the transcription factor SREBP-1c (Girard et al 1997;Kim 2004;Portsmann et al 2008;Sato 2000;.…”

“…As such, our data confirm the link between the mTOR pathway and SREBP-1c as the master regulator of fatty acid and triglyceride synthesis in barramundi, resulting in increased expression of glycolytic and lipogenic genes. Whereas Akt phosphorylation is mainly controlled by insulin in trout, in vivo activation of the mTOR pathway seems to require both insulin and amino acids (Avruch et al, 2009;Lansard et al 2010 and2011;Seiliez et al 2011). We observed a small increase in circulating free amino acids in the plasma that coincided with the activation of the mTOR pathway, but this was not significantly correlated.…”

Looking at the metabolic consequences of the colchicine-based in vivo autophagic flux assay

“…The primer sequences used in the quantitative real-time PCR, as well as the protocol conditions of the assays, have been previously published. 47,48 Primers of the Plin2/Adrp, Plin3/Tip47, Atp6v1a and Ddit3 genes were newly designed using Primer3 software, as previously described. 49 To confirm specificity of the newly developed RT-PCR assay, the amplicon was purified and sequenced (Beckman-Coulter Genomics, Takeley, UK).…”