Molecular characterization of peroxisome proliferator-activated receptors (PPARs) and their gene expression in the differentiating adipocytes of red sea bream Pagrus major

To investigate the molecular mechanism of fish adipocyte differentiation, the three subtypes of PPAR genes (α, β and γ) were characterized in a marine teleost red sea bream (Pagrus major). The primary structures of red sea bream PPARs exhibited high degrees of similarities to their mammalian counterparts, and their gene expression was detected in various tissues including adipose tissue, heart and hepatopancreas. During the differentiation of primary cultured red sea bream adipocytes, three PPARs showed distinct expression patterns: The α subtype showed a transient increase and the β gene expression tended to increase during adipocyte differentiation whereas the gene expression level of PPARγ did not change. These results suggest that they play distinct roles in adipocyte differentiation in red sea bream. In the differentiating red sea bream adipocytes, mammalian PPAR agonists, 15-deoxy-Δ12,14-prostaglandin J2, ciglitazone and fenofibrate did not show clear effects on the adipogenic gene expression. However, 2-bromopalmitate increased the PPARγ and related adipogenic gene expression levels, suggesting the γ subtype plays a central role in red sea bream adipocyte differentiation and in addition, fatty acid metabolites can be used as modulators of adipocyte function. Thus our study highlighted the roles of PPARs in fish adipocyte differentiation and provided information on the molecular mechanisms of fish adipocyte development.