Molecular characterization of AMP-activated protein kinase α2 from herbivorous fish Megalobrama amblycephala and responsiveness to glucose loading and dietary carbohydrate levels

This study aimed to characterize the full-length cDNA of AMPKα2 in Megalobrama amblycephala, and evaluate its potential role in glucose homeostasis and carbohydrate metabolism. The cDNA obtained covered 1942 bp with an open reading frame of 1635 bp encoding 545 amino acids. Multiple alignments and phylogenetic analysis revealed a high homology (91-100%) among most fish and higher vertebrates. This AMPKα2 mRNA predominantly expressed in muscle, liver and brain, while little in gill and intestine. Then, the AMPKα2 expressions were determined in the muscle, liver and brain of fish subjected to a glucose load (injected intraperitoneally with 0, 1.67 and 3.34 g glucose per kg body weight) and after a 12-week feeding trial (fed two dietary carbohydrate levels: 30% and 43%), respectively. After the glucose load, plasma glycemia peaked at 1 h in fish. Thereafter, it decreased significantly to the basal level at 8 h. However, AMPKα2 expression in muscle, liver and brain all decreased significantly during the first 2 h, then returned to the basal value at 24 h. Unlikely, tissue AMPKα2 expression of fish receiving saline solution increased significantly during the whole sampling period. Additionally, high-carbohydrate diet enhanced its expression in liver and muscle, but not that in brain. These findings indicated that the AMPKα2 gene shared a high degree of conservation with that of the other vertebrates. Muscle, liver and brain AMPKα2 expressions were highly induced by glucose administration. Furthermore, high dietary carbohydrate modified its expressions in these tissues.