Free Amino Acid Profile and Expression of Genes Implicated in Protein Metabolism in Skeletal Muscle of Growing Pigs Fed Low-Protein Diets Supplemented with Branched-Chain Amino Acids

Abstract

Revealing the expression patterns of genes involved in protein metabolism as affected by diets would be useful for further clarifying the importance of the balance among the branched-chain amino acids (BCAAs), which include leucine (Leu), isoleucine (Ile), and valine (Val). Therefore, we used growing pigs to explore the effects of different dietary BCAA ratios on muscle protein metabolism. The Leu:Ile:Val ratio was 1:0.51:0.63 (20% crude protein, CP), 1:1:1 (17% CP), 1:0.75:0.75 (17% CP), 1:0.51:0.63 (17% CP), and 1:0.25:0.25 (17% CP), respectively. Results showed that compared with the control group, low-protein diets with the BCAA ratio ranging from 1:0.75:0.75 to 1:0.25:0.25 elevated muscle free amino acid (AA) concentrations and AA transporter expression, significantly activated the mammalian target of rapamycin complex 1 pathway, and decreased serum urea nitrogen content and the mRNA expression of genes related to muscle protein degradation (P < 0.05). In conclusion, these results indicated that maintaining the dietary Leu:Ile:Val ratio within 1:0.25:0.25-1:0.75:0.75 in low-protein diets (17% CP) would facilitate the absorption and utilization of free AA and result in improved protein metabolism and muscle growth.

Leucine alone or in combination with glutamic acid, but not with arginine, increases biceps femoris muscle and alters muscle AA transport and concentrations in fattening pigs

“…In the present study, the concentrations of Lys, Met, Tau and total EAAs in the LD muscle were higher in the LG group than those in the L group, suggesting the FAA concentrations in the LD muscle were increased by dietary Leu and Glu supplementation. Interestingly, dietary supplementation with Leu had no effects on branch‐chain AA concentration in LD and BF muscle, which is in line with an earlier report where it was stated dietary Leu concentration increased from 1.65% to 2.35% did not impact branch‐chain AA concentration in LD muscle (Duan et al, ). Very unfortunate, the LD muscle weight was not available in the present study to elucidate the relevance between intracellular muscle FAA profile and muscle weight.…”

“…For instance, reduced semitendinosus mass was associated with changes in the concentrations of Leu, Thr, Val, Met, Orn, Lys and serine (Sales, Pacheco, Blair, Kenyon, & McCoard, ). In addition, the roles of FAAs in protein synthesis in muscle were associated with changes in muscular FAA concentration (Duan et al, ), suggesting muscular FAA pools are critical to muscle protein synthesis. In the present study, the concentrations of Lys, Met, Tau and total EAAs in the LD muscle were higher in the LG group than those in the L group, suggesting the FAA concentrations in the LD muscle were increased by dietary Leu and Glu supplementation.…”

“…In addition, increases in EAA availability can up‐regulate AA transporter expression in muscle (Drummond et al, ). Available evidence shows that dietary supplementation with branched‐chain AA increased transceptor (including SNAT 2 and LAT 1) expression levels in the LD and BF muscles (Duan et al, ), suggesting the transceptor expression levels in muscle could be regulated by dietary AA treatment. Here, the LG group showed the highest mRNA expression levels of LAT 1, PAT2 and SNAT 2 in the LD muscle, and the LA group showed the lowest mRNA expression levels of LAT 1 and PAT 2 in the LD and BF muscles.…”

Chronic feeding with protein-restricted diets affect ileal amino acid digestibility and the expression of nutrient-sensing, hormone secretion, gastrointestinal digestive enzyme, and nutrient transporter genes in young weaned pigs

“…Many studies have shown that a protein-restricted diet can regulate muscle and serum free AA concentrations in pigs [34][35][36]. In the present study, weaned pigs fed the 20% CP diet exhibited a significant difference in the serum free AA concentrations of Arg (P < 0.05), His (P < 0.05), Leu (P < 0.01), Val (P < 0.01), and Tyr (P < 0.05) compared with the concentrations in those fed the 14% CP diet, while Ser (P < 0.05) was significantly different between the 14% CP and 17% CP groups ( Table 2).…”

Taurine is Involved in Energy Metabolism in Muscles, Adipose Tissue, and the Liver

“…Branched‐chain amino acids (BCAAs) are abundant in the skeletal muscle and help to inhibit protein breakdown . Combined supplementation of taurine (2.0 g)–BCAA (3.2 g) attenuate eccentric elbow flexor exercise‐induced DOMS and muscle damage, which is a sign of lower LDH levels .…”