Effect and the related signaling pathways of insulin influencing lipid metabolism in yellow catfish Pelteobagrus fulvidraco

Abstract

The present study was conducted to investigate the effects and the related signaling pathways of insulin influencing lipid metabolism in yellow catfish Pelteobagrus fulvidraco. As a result, hepatic lipid and intracellular triglyceride (TG) content, the activities and expression levels of several enzymes (CPT I, 6PGD, G6PD, FAS, ME and ICDH) as well as the mRNA expression of transcription factors (PPARα and PPARγ) involved in lipid metabolism were determined. Troglitazone (specific PPARγ pathway activator), GW6471 and fenofibrate (specific PPARα pathway inhibitor and activator, respectively), and wortmannin (PI 3-kinase/Akt pathway blocker) were used to explore the signaling pathways of insulin influencing lipid metabolism. Insulin tended to increase hepatic lipid accumulation, activities of lipogenic enzymes (6PGD, G6PD, ME, ICDH and FAS) and mRNA levels of FAS, G6PD, 6PGD, CPT IA and PPARγ, but down-regulated PPARα mRNA level. Insulin-induced effect could be stimulated by specific PPARγ activator troglitazone or reversed by PI 3-kinase/Akt inhibitor wortmannin, demonstrating that signaling pathways of PPARγ and PI 3-kinase/Akt were involved in the insulin-induced alteration of lipid metabolism. Fenofibrate reduced insulin-induced TG accumulation, down-regulated the mRNA levels of FAS, G6PD and 6PGD, and up-regulated mRNA levels of CPT IA, PPARα and PPARγ. GW6471 reduced insulin-induced changes of all the tested genes' expression, indicating that PPARα mediated the insulin-induced changes of lipid metabolism. The present results contribute to gain new knowledge on the regulatory role of insulin in hepatic metabolism in fish.