Dietary Lysine Regulates Body Growth Performance via the Nutrient-Sensing Signaling Pathways in Largemouth Bass (Micropterus salmoides)

Wenqiang Wang,Kangsen Mai,Yujue Xu,Fei Song,Peng Yang,Shuyan Chi

doi:10.3389/fmars.2020.595682

Abstract

Lysine is known to be a functional nutrient from yeast to human beings. However, the mechanisms for lysine to regulate body growth and metabolism in fish species are far from fully illuminated. In order to elucidate the molecular effects of lysine on growth performance and metabolism, largemouth bass (Micropterus salmoides), which is extremely sensitive to protein composition, was chosen as the experimental model. Juvenile largemouth bass (4.16 ± 0.02g) were fed with the lysine control diet (LC diet), the lysine supplementation diet (LS diet), and the low lysine diet (LL diet) for 8 weeks. The results showed that the LS diet group significantly increased fish growth, feed efficiency, and nutrient retention compared with those of the LL diet group in largemouth bass. Moreover, compared to the LL diet, lysine supplementation also elevated the plasma total protein, total EAA, total AA, and some individual AA concentrations. Mechanistically, lysine supplementation had a significant effect to decrease the mRNA expression levels of peptide and AA transporters induced by lysine restriction. Lysine supplementation also had an important impact on regulating the target of rapamycin (TOR) signaling pathway. More importantly, the key regulators in the amino acid response (AAR) signaling pathway were also down-regulated by lysine supplementation. Our results provide a clear elucidation of how dietary lysine affected growth performance, physiological and biochemical responses, and signaling responses and represent a sound foundation for using lysine to improve the nutrient utilization of poultry by-product meal in largemouth bass.

Highlights

Beyond acting as building blocks for proteins, amino acids (AA) have diverse physiological functions, such as regulating body growth and metabolism, cell signaling, immunity, appetite stimulation, stress responses, and reproduction (Li et al, 2009; Wu et al, 2014)
Consistent with the turbot study, the present study showed that largemouth bass fed the lysine diet (LL diet) for 8 weeks presented significantly lower concentration of total EAA, TAA, and individual AA than did fish fed the lysine supplementation diet (LS diet)
The present study showed that low lysine level diet activated the amino acid response (AAR) pathway and inhibited the activity of the target of rapamycin (TOR) signaling pathway

Summary

Introduction

Beyond acting as building blocks for proteins, amino acids (AA) have diverse physiological functions, such as regulating body growth and metabolism, cell signaling, immunity, appetite stimulation, stress responses, and reproduction (Li et al, 2009; Wu et al, 2014). As an important FAA in both human beings and other animals, lysine exerts extraordinary effects on body growth and metabolism (Li et al, 2009). Consistent with mammals, studies on fish revealed that lysine restriction caused growth restriction and metabolic obstruction (Marine et al, 2011) and scoliosis, lordosis, and immune problems (Khan and Abidi, 2015). A large number of studies have only explored the effect of dietary lysine on the phenotypic changes in the growth performance of fish species, but the underlying molecular mechanism by which lysine affects growth and metabolism still need to be fully revealed

Methods

Results

Discussion

Conclusion