Dietary isoleucine promoted myofiber hypertrophy associated with myonucleus input and protein deposition in fish

Abstract

Isoleucine (Ile) is an essential amino-acid, which also has important regulatory functions in animals. Thus, this study was for the first time to investigate effects of dietary Ile on the flesh quality and myofiber hypertrophy in fish. Four hundred and fifty healthy fish (initial weight 615.69 ± 0.03 g) were allotted in 6 experimental groups with 3 replicates each. The basal diet was added different concentrations to comprise six levels of 0.00, 3.00, 6.00, 9.00, 12.00 and 15.00 g/kg of Ile diet, and fed the fish with the experimental diet for 9 weeks. Our data showed that (1)10.81 g Ile/kg diet enhanced (P < 0.05) the Asp, Pro, Ile, Leu, Tyr, Lys, His and IMP contents of fish muscle; (2) Ile increased (P < 0.05) the mRNA and protein levels of MyoD, MyoG, Myf5 and MyHC; (3) Ile enhanced (P < 0.05) the proteins of fibronectin (FN), Integrin-α5 (IN-α5), focal adhesion kinase (FAK), non-receptor tyrosine kinase (Src), cell division cycle 42 (Cdc42), p-target of rapamycin (p-TOR) and p70 ribosomal protein S6 kinase 1 (p-S6K1); (4) Ile decreased (P < 0.05) the protein levels of general control nonderepressible 2 (GCN2), F-box only protein 22 (FBXO22), muscle atrophy F-box (MAFBX) and Muscle RING finger 1 (MURF1). The results conclude that dietary Ile (about 10.81 g/kg) enhanced muscle flavor (mainly including sweet, umami and savory tasting) and changed the fatty acid profile. In addition, we found for the first time that dietary Ile improved muscle myofiber hypertrophy in adult grass carp muscle by promoting myonucleus proliferation and protein deposition.