Cloning and expression characterization of peroxisome proliferator-activated receptors (PPARs) with their agonists, dietary lipids, and ambient salinity in rabbitfish Siganus canaliculatus

Rabbitfish Siganus canaliculatus is the first marine teleost reported to have the ability of biosynthesizing C20-22 long-chain polyunsaturated fatty acids (LC-PUFA) from C-18 precursors, and thus provides a model for studying the regulatory mechanisms of LC-PUFA biosynthesis in teleosts. To investigate the possible roles of peroxisome proliferator-activated receptors (PPARs), critical transcription factors involved in the regulation of lipid metabolism, in the regulation of LC-PUFA biosynthesis in rabbitfish, the PPAR genes were cloned and their expression characterization with PPAR agonists, dietary lipid resource, and ambient salinity were examined. Three cDNA sequences respectively encoding 477,516 and 519 amino acids of PPARce, PPAR beta, and PPAR gamma isoforms were obtained. PPAR alpha, exhibited a wide tissue expression with its highest levels in the heart and brain: PPARS was predominantly expressed in the gills, while PPAR gamma was highly expressed in the intestine and gills. In rabbitfish primary hepatocytes, both the PPAR agonists 2-bromopalmitate (2-Bro) and fenofibrate (FF) increased the expression of PPAR gamma, SREBP1c and Elov15, whereas FF depressed the expression of Delta 6/Delta 5 Fad. Moreover, a higher hepatic PPAR beta expression was observed in fish fed diets with vegetable oils (VO) than that with fish oil (FO), in the former the expression of PPAR alpha, PPAR beta, and PPAR gamma were increased at the low ambient salinity (10 ppt), where an increasing expression of Delta 5/Delta 6 Fad, Delta 4 Fad and Elovl5 genes was previously reported. These results suggest that PPARs might be involved in the upregulation of LC-PUFA biosynthesis with dietary VO and low ambient salinity in rabbitfish. (C) 2017 Elsevier Inc. All rights reserved.