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Dietary leucine supplementation improves growth performance, metabolic responses of liver via GCN2/ATF4, and insulin signaling pathways in largemouth bass (Micropterus salmoides)

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Abstract

An 8-week growth experiment was conducted to investigate the effects of dietary leucine on growth performance, body composition, and gene expression of hepatic nutrient metabolism in the largemouth bass (Micropterus salmoides). Six isonitrogenous (49.87%) diets with graded leucine levels (2.62, 3.07, 3.60, 3.87, 4.20, 4.71% of dry diet) were fed to triplicate groups with 20 juvenile fish (20.00 ± 0.13 g). The results revealed that the specific growth rate (SGR) and weight gain (WG) increased significantly with increasing dietary leucine levels, reached their maximal value in the Leu-4.20% groups, and then decreased slightly. Although the feed conversion ratio (FCR) showed decreasing trends, no significant difference was detected. Leucine supplementation significantly improved the content of body protein and total plasma protein (TP). Additionally, a higher expression level of target of rapamycin (TOR) and ribosomal protein S6 (S6) mRNA was observed in the Leu-3.87% and Leu-4.20% diets, whereas the GCN2 (general control nonderepressible2 kinase) and AFT4 (activating transcription factor 4) mRNA expression levels were suppressed. The lipid content of the body was not influenced by leucine levels, whereas the content of total triglyceride (TG) first decreased significantly with increasing dietary leucine levels from 2.62 to 3.87% and then increased with increasing leucine levels (4.20% to 4.71%). The total cholesterol (TC) and low-density lipoproteins (LDL) trended in a similar direction but did not achieve statistical significance (P > 0.05). The expression of insulin receptor substrate 1 (IRS-1) was significantly elevated by dietary leucine levels, while protein kinase B (AKT) and phosphatidylinositol 3-kinase (PI3K) expression was inconsistently upregulated. Furthermore, leucine supplementation decreased plasma glucose and hepatic glycogen contents, and the expression levels of glucokinase (GK), phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase (G6pase) were significantly inhibited at 4.20% and 4.71% leucine diets. Analyses of the change in SGR and FCR using the quadratic regression model estimated that the optimum dietary leucine requirement of juvenile largemouth bass was 4.42% and 4.63% of the dry diet (8.86% and 9.28% of dietary protein), respectively.

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The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

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Funding

This study was financially supported by the National Key Research and Development Program of China (2018YFD0900400), the earmarked fund for CARS (CARS-46).

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Ming Shao: Investigation, data curation, writing—original draft. Hualiang Liang: data curation, project administration. Gangchun Xu: investigation, data curation. Jian Zhu: investigation, data curation. Songlin Li: investigation, data curation. Mingchun Ren: supervision, resources, writing—review and editing, project administration.

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Correspondence to Mingchun Ren.

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All experimental protocols were followed by the Institutional Animal Care and Ethics Committee of Nanjing Agricultural University, Nanjing, China. [Permit number: SYXK (Su) 2011–0036]; and carefully considering the welfare of the fishes.

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All authors agreed with the content, and all gave explicit consent to submit this manuscript in Fish Physiology and Biochemistry.

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Shao, M., Liang, H., Xu, G. et al. Dietary leucine supplementation improves growth performance, metabolic responses of liver via GCN2/ATF4, and insulin signaling pathways in largemouth bass (Micropterus salmoides). Fish Physiol Biochem 50, 331–347 (2024). https://doi.org/10.1007/s10695-022-01126-9

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