Regulation of insulin on lipid metabolism in freshly isolated hepatocytes from yellow catfish (Pelteobagrus fulvidraco)

Although the metabolic actions of insulin in fish have been investigated widely in the past years, the regulatory effect of insulin on lipid metabolism has received little attention, especially in primary hepatocytes of fish. In the present study, freshly hepatocytes were isolated from yellow catfish, cultured and subjected to different insulin levels (0, 10, 100 and 1000 nM) for 0 h, 24 h and 48 h. Triglyceride (TG) content, activity and expression of several key enzymes involved in lipid metabolism, as well as mRNA levels of key transcription factors related to lipid metabolism, were assessed at 0 h, 24 h and 48 h, respectively. Insulin incubation tended to increase the activities and expression of several lipogenic enzymes (such as FAS, G6PD, 6PGD). However, reduced CPT I gene expression was observed in hepatocytes following incubation treatment. Insulin administration also tended to up-regulate SREBP-1 expression but down-regulate PPARα mRNA levels. Insulin incubation enhanced lipogenesis and reduced lipolysis of freshly isolated hepatocytes of yellow catfish, in coincidence with increased TG content. Pearson correlations between expression of SREBP-1 and PPARα, and expression and activity of several enzymes were also observed, especially at 48-h insulin incubation. To the best of our knowledge, this is the first to study the effects of insulin on lipogenesis and lipolysis at both transcriptional and enzymatic levels using primary hepatocytes culture model in fish, which will help to understand the regulation of lipid metabolism by insulin in vivo, and will give us new insight into the insulin role in nutrient metabolism in fish.