Role of peroxisome proliferator-activated receptor beta/delta ...

The adipocyte differentiation process involves a cascade of transcriptional events that culminates in the expression of peroxisome proliferator-activated receptor (PPAR)gamma. The present study was undertaken to identify the role of PPARbeta/delta in chicken adipocyte differentiation, with experiments performed using a PPARgamma agonist, a PPARbeta/delta agonist, a PPARgamma antagonist and fatty acid (oleate). Preadipocyte cells cultured in a differentiation medium (DMEM containing 500nM dexamethasone, 0.5mM 3-isobutyl-1-methylxanthine, 20mug/mL bovine insulin and 10% fetal bovine serum) supplemented with 200muM oleate resulted in a significant increase in adipocyte fatty acid binding protein (aP2) mRNA expression after 24h and 7d of culture compared to cells cultured in a differentiation medium alone, while supplementation of the differentiation medium with GW501516 (a PPARbeta/delta agonist) did not affect aP2 mRNA expression levels. Supplementation of the differentiation medium with troglitazone (a PPARgamma agonist) and GW501516 induced preadipocyte differentiation; a significant increase of aP2 mRNA expression was observed in cells after incubation for 7d, but not after 24h of incubation. These results suggest that PPARbeta/delta does not play a key role in adipocyte differentiation, but it does enhance the transformation of immature into mature adipocytes in chickens. In addition, oleate functions not only as an activator of PPARs but also induces PPARgamma gene expression via alternative pathway of PPARs activation. These results establish the importance of exogenous fatty acid in the processes of adipogenesis and fat accumulation in chickens.