Muscle Nutritive Metabolism Changes after Dietary Fishmeal Replaced by Cottonseed Meal in Golden Pompano (Trachinotus ovatus)

Abstract

Our previous study demonstrated that based on growth performance and feed utilization, cottonseed meal (CSM) could substitute 20% fishmeal (FM) without adverse effect on golden pompano (Trachinotus ovatus). Muscle deposition was also an important indicator to evaluate the efficiency of alternative protein sources. Therefore, the present study was conducted to explore the changes of physiobiochemical and nutrient metabolism in muscle after FM replaced by CSM. Four isonitrogenous and isolipidic experimental diets (42.5% crude protein, 14.0% crude lipid) were formulated to replace 0% (CSM0 diet), 20% (CSM20 diet), 40% (CSM40 diet), and 60% (CSM60 diet) of FM with CSM. Juvenile fish (24.8 ± 0.02 g) were fed each diet for 6 weeks. The results presented, which, compared with the CSM0 diet, CSM20 and CSM40 diets, had no effect on changing the muscle proximate composition and free essential amino acid (EAA) concentration. For glycolipid metabolism, the CSM20 diet did not change the mRNA expression of hexokinase (hk), glucose transport protein 4 (glut4), glucagon-like peptide 1 receptor (glp-1r), while over 20% replacement impaired glucose metabolism. However, CSM20 and CSM40 diets had no effect on altering lipid metabolism. Mechanistically, compared with the CSM0 diet, the CSM20 diet did not change muscle nutritive metabolism through keeping the activities of the nutrient sensing signaling pathways stable. Higher replacement would break this balance and lead to muscle nutritive metabolism disorders. Based on the results, CSM could substitute 20-40% FM without affecting the muscle nutritive deposition. All data supplemented the powerful support for our previous conclusion that CSM could successfully replace 20% FM based on growth performance.

Keywords: cottonseed meal; fish nutrition; marine aquaculture; nutrient; physiobiochemical; replacement.

Figure 1

Diagrammatic representation of the gene expression pattern of (a) the key enzyme and transporters involved in glucose metabolism and (b) hormone receptors involved in insulin signaling pathway and glp-1r signaling in muscle after golden pompano (Trachinotus ovatus) were fed CSM0, CSM20, CSM40 and CSN60. Data were represented as mean ± SEM. Different letters above the bars denote significant differences between diet groups at the p < 0.05 level. Note: g6pdh, glucose-6-phosphate; hk, hexokinase; pk, pyruvate kinase; pfk-1, phosphofructokinase-1; pepck, phosphoenolpyruvate carboxykinase; glut2, glucose transport protein 2; glut4, glucose transport protein 4; irs1, insulin receptor substrate 1; igf-1r, insulin-like growth factor-1 receptor; glp-1r, glucagon-like peptide 1 receptor.

Figure 2

Effects of different experimental diets on the mRNA expression levels of (a) lipid anabolism, (b) lipid catabolism and (c) lipid transporters in muscle after the golden pompano (Trachinotus ovatus) were fed different diets. Data were represented as mean ± SEM. Different letters above the bars denote significant differences between diet groups at the p < 0.05 level. Note: FAS, fatty acid synthetase; ACC, acetyl-CoA carboxylase; AGPAT3, 1-acylglycerol-3-phosphate acyltransferase 3; FAD, fatty acyl desaturase; elovl5, elongase of very long-chain fatty acids 5; SREBP1, sterol regulatory element binding protein-1; PPARα, peroxisome proliferator activated receptors-alpha; PPARγ, peroxisome proliferator-activated receptors gamma; LPL, lipoprotein lipase; HSL, hormone-sensitive lipase; CPT1, carnitine palmitoyl transferase 1; FABP1, fatty acid binding protein 1; APROB100, apolipoprotein b 100.

Figure 3

LAT2, SNAT2 and PEPT1 expression in muscle of juvenile golden pompano (Trachinotus ovatus) after fed test diets for 6 weeks. Data were represented as mean ± SEM. Different letters above the bars denote significant differences between diet groups at the p < 0.05 level. Note: LAT2, L-type amino acid transporter 2; SNAT2, sodium-coupled neutral amino acid transporter 2; PEPT1, oligopeptide transporter1.

Figure 4

Different diets affected the relative gene expression of the key regulators of GH-IGF-1 axis in muscle of juvenile golden pompano (Trachinotus ovatus). Data were represented as mean ± SEM. Different letters above the bars denote significant differences between diet groups at the p < 0.05 level. Note: GH, growth hormone; IGF-1, insulin-like growth factor-1; IGF-2, insulin-like growth factor-2.

Figure 5

The mRNA expression and protein phosphorylation level of key regulators related to target of rapamycin (TOR) and amino acid response (AAR) signaling pathways in muscle. (a) mRNA expression level of TOR signaling pathway; (b) mRNA expression of AAR signaling pathway; (c) protein phosphorylation level of TOR and AAR signaling pathways. Data were represented as mean ± SEM. Different letters above the bars denote significant differences between diet groups at the p < 0.05 level. Note: TOR, target of rapamycin; S6, S6 Ribosomal Protein. 4E-BP1, eukaryotic initiation factor 4E-binding protein 1; eIF2α, initiation elongation factor alpha; ATF4, activating transcription factor 4; CHOP, channelopsin2; REDD1, regulated in development and DNA damage responses 1; AKT, protein kinase B.