British Journal of Nutrition

Full Papers

Molecular Nutrition

Hepatic protein kinase B (Akt)–target of rapamycin (TOR)-signalling pathways and intermediary metabolism in rainbow trout (Oncorhynchus mykiss) are not significantly affected by feeding plant-based diets

Marine Lansarda1a2a3, Stéphane Panserata1a2a3, Iban Seilieza1a2a3, Sergio Polakofa1a2a3a4, Elisabeth Plagnes-Juana1a2a3a4, Inge Geurdena1a2a3, Françoise Médalea1a2a3, Sadasivam Kaushika1a2a3, Geneviève Corrazea1a2a3 and Sandrine Skiba-Cassya1a2a3 c1

a1 INRA, UMR1067 Nutrition Aquaculture et Génomique, Pôle d'hydrobiologie, CD918, F-64310 St-Pée-sur-Nivelle, France

a2 IFREMER, UMR1067 Nutrition Aquaculture et Génomique, F-29280 Plouzané, France

a3 Université Bordeaux 1, UMR 1067 Nutrition Aquaculture et Génomique, F-33405 Talence, France

a4 Laboratorio de Fisioloxía Animal, Departamento de Bioloxía Funcional Ciencias da saúde, Facultade de Bioloxía, Universidade de Vigo, Vigo, Spain

Abstract

The aim of the present study was to analyse the effects of partial or total replacement of fish meal (FM) and fish oil (FO) by a mixture of plant protein (PP) and a mixture of vegetable oils (VO) on the hepatic insulin–nutrient-signalling pathway and intermediary metabolism-related gene expression in rainbow trout (Oncorhynchus mykiss). Triplicate groups of fish were fed four practical diets containing graded levels of replacement of FM and FO by PP and VO for 12 weeks: diet 0/0 (100 % FM, 100 % FO); diet 50/50 (50 % FM and 50 % PP, 50 % FO and 50 % VO); diet 50/100 (50 % FM and 50 % PP, 100 % VO); diet 100/100 (100 % PP, 100 % VO). Samplings were performed on trout starved for 5 d then refed with their allocated diet. In contrast to partial substitution (diet 50/50), total substitution of FM and FO (diet 100/100) led to significantly lower growth compared with diet 0/0. The insulin–nutrient-signalling pathway (protein kinase B (Akt), target of rapamycin (TOR), S6 protein kinase 1 (S6K1) and S6) was characterised in trout liver and found to be activated by refeeding. However, changes in diet compositions did not differentially affect the Akt–TOR-signalling pathway. Moreover, expression of genes encoding fructose-1,6-biphosphatase, mitochondrial phosphoenolpyruvate carboxykinase, glucokinase, pyruvate kinase and carnitine palmitoyl transferase 1 were not affected by refeeding or by dietary changes. Refeeding down- and up-regulated the expression of gluconeogenic glucose-6-phosphatase isoform 1 and lipogenic fatty acid synthase genes, respectively. Expression of both genes was also increased with partial replacement of FM and total replacement of FO (diet 50/100). These findings indicate that plant-based diets barely affect glucose and lipid metabolism in trout.

(Received March 09 2009)

(Revised June 11 2009)

(Accepted June 12 2009)

(Online publication August 10 2009)

Correspondence:

c1 Corresponding author: Dr Sandrine Skiba-Cassy, fax +33 5 59 54 51 52, email skiba@st-pee.inra.fr

Footnotes

Abbreviations: Akt, protein kinase B; CPT1, carnitine palmitoyl transferase 1; diet 0/0, fish meal and fish oil as the main protein and fat sources; diet 50/50, 50 % supply of proteins by a mixture of plant protein sources and 50 % of fish oil substituted by a mixture of vegetable oil; diet 50/100, 50 % supply of proteins by a mixture of plant protein sources and all fish oil substituted by vegetable oil; diet 100/100, total replacement of both fish meal and fish oil by plant protein and vegetable oil; EF1α, elongation factor 1α; FAS, fatty acid synthase; FBPase, fructose-1,6-biphosphatase; FM, fish meal; FO, fish oil; GK, glucokinase; G6Pase, glucose-6-phosphatase; PEPCK, phosphoenolpyruvate carboxykinase; PK, pyruvate kinase; PP, plant protein; TOR, target of rapamycin; VO, vegetable oil

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