Tissue-specific Nutrient Metabolism in the Liver and Muscle of Juvenile Blunt Snout Bream (Megalobrama Amblycephala) in Response to Dietary Methionine Levels

Background: Methionine is an essential amino acid, that affects the metabolism of protein, lipid and glucose. However, the metabolic polytrophic response in the liver and muscle of juvenile Megalobrama amblycephala to dietary methionine levels is unclear.ResultsThe 0.84% methionine diet significantly improved the growth performance compared with the 0.40% diet. Dietary methionine levels had no marked effects on plasma parameters or whole body composition of juveniles. The protein levels of phospho-phosphatidylinositol 3-kinase, protein kinase B, phospho-eukaryotic initiation factor 4E binding protein-1 (p-4E-BP1), 4E-BP1 and ribosomal protein S6 kinase 1, in the liver of fish fed the 0.84% diet were higher than those in fish fed the 0.40% diet. While in muscle, these proteins showed the opposite trend. The mRNA levels of the muscular lipid synthesis associated genes: sterol regulatory element-binding protein 1 (SREBP1), fatty acid synthetase (FAS) and acetyl-CoA carboxylase (ACC), were significantly upregulated by the 1.28% methionine diet; while hepatic SREBP1, FAS and ACC mRNA expression levels were increased by 0.40% methionine. In addition, 1.28% dietary methionine significantly induced fatty acid β-oxidation and lipolysis of the liver and muscle via increased carnitine palmitoyl transferase 1, peroxisome proliferator activated receptor alpha, lipoprotein lipase and lipase expression levels. Compared with 0.40% dietary methionine, 1.28% methionine enhanced the mRNA levels of the hepatic gluconeogenesis related genes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase, and the muscular glycolysis related genes phosphofructokinase (PFK) and pyruvate kinase (PK). The mRNA expression levels of hepatic PFK, PK and glucokinase were markedly upregulated by the 0.84% methionine diet compared with the 1.28% diet. In addition, muscular PEPCK and glycogen synthase, and hepatic glucose transporters 2 mRNA levels were induced by 1.28% methionine. ConclusionThe study showed that optimal methionine levels could enhance the growth of juvenile Megalobrama amblycephala , and the nutrient metabolism response to dietary methionine in the liver and muscle was tissue-specific.