Essential amino acids exhibit variable effects on protein degradation in rainbow trout (Oncorhynchus mykiss) primary myocytes

Authors: Cleveland, Beth; Radler, Lisa

Submitted to: Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2018
Publication Date: 11/29/2018
Citation: Cleveland, B.M., Radler, L.M. 2018. Essential amino acids exhibit variable effects on protein degradation in rainbow trout (Oncorhynchus mykiss) primary myocytes. Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology. doi:10.1016/j.cbpa.2018.11.019.
DOI: https://doi.org/10.1016/j.cbpa.2018.11.019

Interpretive Summary: Dietary protein is composed of amino acids that are essential nutrients for sustaining growth and building muscle mass. Amino acids directly regulate growth by promoting muscle protein accretion, both by increasing protein synthesis and decreasing protein degradation. However, it is unknown if certain amino acids play a greater role than others as regulators of these processes. To determine the functional roles of amino acids as regulators of protein accretion, rainbow trout muscle cells were exposed to individual or combinations of amino acids and the protein degradation response was analyzed. Results indicate that amino acids exhibit variable effects on protein turnover; leucine and phenylalanine reduced protein degradation, indicating that a dietary deficiency of these amino acids will reduce muscle growth. In contrast, an excess of lysine or valine increased protein degradation, supporting that a diet too rich in these amino acids will inhibit muscle protein accretion. Collectively, these findings provide information important for developing diets with amino acid profiles that optimize growth performance and muscle/fillet yield.

Technical Abstract: The functional role of amino acids as regulators of protein degradation was investigated using primary myogenic precursor cell culture as in vitro model of rainbow trout white muscle. Seven-day old myocytes were starved of amino acids for two hours then exposed to media that contained amino acid treatments, during which protein degradation rates were analyzed over five hours by measuring cellular release of 3H-tyrosine. Increasing concentrations of essential amino acids (EAA) reduced protein degradation rates; this effect was dose-dependent within the physiological range found in plasma. Addition of leucine or phenylalanine at 5 mM and 2.5 mM, respectively, decreased rates of protein degradation compared to media without amino acid supplementation, suggesting that these amino acids directly regulate muscle proteolysis. Protein degradation rates were similar in cells exposed to media without EAA and media lacking only leucine, further supporting a role for leucine as a central regulator of protein turnover. Addition of 5 mM lysine or valine to media without amino acids increased protein degradation; this response was attenuated as EAA were added back into media, supporting that a lysine or valine imbalance is costly for muscle protein retention. In summary, there is evidence for amino acids as both positive and negative regulators of protein turnover in rainbow trout muscle. These findings suggest that there may be an optimal plasma amino acid profile that minimizes protein turnover and that this could be achieved through diet formulation.