The regulation of PEPCK isoforms is the potential reason for the discrepancy in glucose utilization among fishes with different food habits

Abstract

Regulation of gluconeogenesis rate-limiting enzymes is a novel approach to improve fish glucose utilization. Phosphoenolpyruvate carboxykinase (PEPCK), one of important gluconeogenesis rate-limiting enzymes, exists a cytosolic isoform (PEPCK-C) and a mitochondrial isoform (PEPCK-M) encoded by pck1 and pck2, respectively. Here, we first investigated the PEPCK-C/PEPCK-M activity ratio in the livers of six fishes with three different food habits. No direct relevance between food habit and the two enzymes proportion was observed among the fishes. To further explore the role of fish PEPCK isoforms regulation in response to energy change, we detected the enzyme activities and gene expressions of the isoforms in the livers of three representative fishes with different food habits after preprandial and postprandial administration. The decreased enzyme activities and increased gene expressions of two PEPCK isoforms in herbivorous grass carp were observed after postprandial administration compared with preprandial administration. Significantly decreased gene expressions and enzyme activities of these two isoforms of omnivorous crucian carp were induced by postprandial administration. In carnivorous mandarin fish, only the pck2 gene expression was down-regulated by the postprandial administration, no significant difference was seen in the enzyme activities of the two PEPCK isoforms. Therefore, the regulation of PEPCK isoforms might be one of the reasons for the discrepancy in glucose utilization among fishes with different food habits.