High lipid and high carbohydrate diets affect muscle growth of blunt snout bream (Megalobrama amblycephala) through different signaling pathways

Abstract

The study was carried out to explore the effect of high lipid/carbohydrate diet on muscle growth of Megalobrama amblycephala. In vivo, three experimental diets, a control diet (6% lipid and 28.13% carbohydrate, CD), a high lipid diet (11%lipid，HLD) and a high carbohydrate diet (39.6% carbohydrate, HCD), were formulated and randomly fed to Megalobrama amblycephala (average initial weight 19.80 ± 0.15 g) for 12 weeks. The results showed that there was no significant difference in specific growth rate (SGR) and weight gain rate (WGR) between the control diet group and the high energy diets group (P > 0.05). The springiness, gumminess, chewiness and muscle fiber density were significantly up-regulated in the high energy diets group than control diet group (P < 0.05). HLD, compared with HCD, significantly increased the muscle fiber cross-sectional area (CSA) and muscle fiber diameter in the white muscle (P < 0.05). High energy diets significantly elevate the transcriptional levels of Myf5, Myog and Mrf4, and reduce the transcriptional levels of MSTNa and MSTNb (P < 0.05). The transcriptional levels and protein expressions of AMPK and Sirt1 were significantly elevated in the HLD group (P < 0.05). The CAMK and CAN protein levels were significantly increased in the HCD group (P < 0.05). In vitro, the isolated primary hepatocytes from Megalobrama amblycephala were coincubated with 0.4 mM oleic acid (OA) and 40 mM d-glucose respectively. The results clearly state that 0.4 mM OA significantly increased the transcriptional levels of AMPKα1, AMPKα2 and Sirt1, the protein level of AMPK, p-AMPK, p-AMPK/AMPK and Sirt1 (P < 0.05). The protein expression of CAMK and CAN in hepatocytes treated with 40 mM d-glucose were significantly higher than that in the other two treatments (P < 0.05). In summary, high energy diets promoted the muscle fiber hyperplasia in Megalobrama amblycephala while high lipid and high carbohydrate diets may affect muscle growth through AMPK/Sirt1 pathway and Ca2+-dependent pathway, respectively.