Abstract
Overwinter starvation is one of the environmental stress factors in grass carp Ctenopharyngodon idellus culture. During the overwinter starvation process, the energy mobilization mechanism of grass carp may be different from that under normal conditions. Although someone have studied the metabolism of protein and lipid in grass carp under starvation at a normal situation, the response of glucose, lipid and protein metabolism to overwinter starvation has not been reported. In order to explore the metabolic adaptation mechanism of energy utilization of grass carp during overwinter starvation, 45 fish with the initial body weight of (1053.33±16.11) g were randomly distributed into the three repetitions for natural overwinter starvation. When the water temperature naturally decreased to the point, the grass carp ceased ingestion (water temperature: 15℃), the experiment began. When the water temperature naturally rose to the point, the grass carp refeeding commenced (water temperature: 15℃), the overwinter starvation period, and thus our experiments, concluded. Samples were collected after 0, 1, 2, 4, 8, 12 and 16 weeks of natural overwinter starvation. The contents of muscle routine components, serum energy metabolites, tissue glycogen, triglyceride, and transcription levels of AMP activated protein kinase and glucose-lipid-protein metabolism related genes were detected. The results showed that the content of various conventional components in grass carp muscles changed significantly after overwinter starvation for 1 week (P<0.05); with the extension of overwinter starvation time, serum triglycerides (TG), glycerol, total protein (TP), total cholesterol (TCHO) and blood sugar (GLU) first decreased significantly (P<0.05), then remained stable, and the content of free fatty acids increased significantly (P<0.05); hepatopancreas glycogen and muscle glycogen and the content of TG in hepatopancreas, muscle and adipose tissue reduced significantly (P<0.05); the content of serum ATP, ADP and AMP reduced significantly, and the ratio of ADP+AMP/ATP increased significantly (P<0.05); the expression ofAMPKα1 and AMPKα2 genes in the hepatopancreas, muscle and adipose tissue increased significantly (P<0.05), and the transcription level of downstream glucose-lipid and protein metabolism related genes increased significantly (including ATGL, HSL, CPT1α, CD36 and other lipolysis related genes; GK, PFK, PK and other glycolysis related genes; GLDH, IGF-1 and other proteolysis-related genes) or significantly down-regulated (ACC, FAS and other lipid synthesis-related genes; CREB, FoxO1, PGC-1α, PEPCK, G6Pase, GLUT2 and other gluconeogenesis related genes; TOR, S6K and other related to protein synthesis genes) (P<0.05). The results revealed that grass carp utilized energy storage to maintain its energy homeostasis during the overwinter starvation period with significant changes in the biochemical composition of serum, hepatopancreas, muscle and adipose tissue of grass carp during the overwinter starvation period has undergone significant changes. At the same time, the overwinter starvation activates the AMPK pathway and promotes glycolysis, lipid decomposition, fatty acid β-oxidation, the process of fatty acid transport and protein decomposition inhibits the process of glycogen synthesis, lipid synthesis and protein synthesis, thereby maintaining the body’s energy homeostasis. This study showed that the changes of biochemical components and the regulation of transcription level of glucose-lipid-protein metabolism genes based on AMPK pathway in grass carp during overwinter starvation, and revealed the regulatory content and mechanism of adaptive changes of grass carp during overwinter starvation.
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