Molecular characterization and expression analysis of glucose transporter 1 and hepatic glycolytic enzymes activities from herbivorous fish Ctenopharyngodon idellus in respond to a glucose load after the adaptation to dietary carbohydrate levels

摘要

In the present study, we test the hypothesis that the ability of Ctenopharyngodon idellu to clear a glucose load is related to nutrient history of different dietary carbohydrate through the transport and glycolysis of glucose. Firstly, we obtained the complete coding sequence from C. idellus GLUT1 (ciGLUT1), composed by 2364 bp with an open reading frame of 1473 bp encoding 490 amino acids. Sequence alignment and phylogenetic analysis revealed a high degree of conservation (80-97%) among most fish and higher vertebrates. The analysis of the 5' and 3' UTRs showed the presence of several post-transcriptional regulatory elements. The highest ciGLUT1 expression was observed in the heart followed by brain, whereas relatively low values were detected in the muscle, gill, intestine, kidney, spleen and liver. Then, hepatic and intestine ciGLUT1 expressions and hepatic glycolytic enzymes activities were determined in fish subjected to a glucose load after being fed different dietary carbohydrate levels (20%, 40% and 60%) for 8 weeks. And the result showed that different dietary carbohydrate had no effect on ciGLUT1 mRNA of hepatic and intestine after 8 weeks trail. However, after the adaptation of carbohydrate levels, glucose administration caused a prompt increase of hepatic ciGLUT1 mRNA expressions in all treatments whereas it either had no effect or a negative effect on intestine ciGLUT1 mRNA. In terms of dietary carbohydrate levels, the ciGLUT1 expressions of fish fed high carbohydrate diet (60%) were significantly higher than the other groups after the glucose load. In additon, after the glucose administration, hepatic low Km hexokinases (HK) activities of fish fed high carbohydrate diets increased significantly and was also significantly higher than the other groups. The results indicated that the GLUT1 gene of C. idellus showed a typical structure of the glucose transporters family, supporting the concept that ciGLUT1 functions as a ubiquitous and constitutive basal level glucose transporter. Consistent with the function of the GLUT1 as a constitutive glucose transporter, ciGLUT1 expressions of hepatic and intestine were hardly affected by the changes in dietary carbohydrate. Furthermore, after the glucose load, the fish after a long-term high dietary carbohydrate adaptation showed a more efficient clearance of glucose through the more remarkable enhancements of hepatic ciGLUT1 expressions and HK activities.