Molecular characterization of three peroxisome proliferator-activated receptors from the sea bass (Dicentrarchus labrax)

Peroxisome proliferator-activated receptors (PPAR) are nuclear hormone receptors that control the expression of genes involved in lipid homeostasis in mammals. We searched for PPAR in sea bass, a marine fish of particular interest to aquaculture, after hypothesizing that the physiological and molecular processes that regulate lipid metabolism in fish are similar to those in mammals. Here, we report the identification of complementary DNA and corresponding genomic sequences that encode three distinct PPAR from sea bass. The sea bass PPAR are the structural homologs of the mammalian PPARalpha, beta/delta, and gamma isotypes. As revealed by RNase protection, the tissue expression profile of the fish PPAR appears to be very similar to that of the mammalian PPAR homologs. Thus, PPARalpha is mainly expressed in the liver, PPARgamma in adipose tissue, and PPARbeta in all tissues tested, with its highest levels in the liver, where it is also the dominant isotype expressed. Like mammalian PPAR, the sea bass isotypes recognize and bind to PPAR response elements of both mammalian and piscine origin, as heterodimers with the 9-cis retinoic acid receptor. Through the coactivator-dependent receptor ligand assay, we also demonstrated that natural FA and synthetic hypolipidemic compounds can act as ligands of the sea bass PPARalpha and beta isotypes. This suggests that the sea bass PPAR act through similar mechanisms and perform the same critical lipid metabolism functions as mammalian PPAR.