Dietary pyridoxine promoted muscle protein deposition relating to PI3K/AKT/TOR pathway and the ubiquitin proteasome system in grass carp (Ctenopharyngodon idella)

Abstract

Pyridoxine (PN) is essential for the normal growth and development of the body. The purpose of this study was to investigate the possible mechanism of pyridoxine in improving the meat quality of grass carp (Ctenopharyngodon idella). A total of 450 grass carp (746.08 ± 1.70 g) were randomly assigned to six treatments, each with three replicates, and fed diets containing pyridoxine 0.32, 1.60, 3.14, 4.59, 6.15 and 7.62 mg/kg, respectively, for 8 weeks. The results showed that the PWG, SGR and FE were increased, indicating that pyridoxine promoted the growth of grass carp. Appropriate pyridoxine increased the crude protein, crude lipid, hydrolyzed amino acids, amino acid score, resilience, hardness, and pH of muscles, indicating that pyridoxine elevated muscle quality. Optimal pyridoxine enhanced the levels of muscle SLC38A2, SLC7A1, IGF-1, PDK1 and AKT, p-S6K1, p-TOR, p-AKT and IRS1, and decreased the expression of SLC1A3, PTEN, 4EBP1 and GSK3β, revealing that pyridoxine may promote protein synthesis by activating the PI3K/AKT/TOR pathway. In addition, the levels of muscle FOXO1a, MuRF1, MAFbx, ULK1, ubiquitin, psmc1, psma2, nrdp1, chip, parkin, and p-FOXO3a were significantly reduced, suggesting that pyridoxine may inhibit protein degradation by preventing protein ubiquitination and autophagy. At last, the pyridoxine requirements of grass carp were determined to be 4.00, 5.09 and 4.96 mg/kg diet, respectively, based on PWG, liver PN content, and muscle GPT activity.