Role of peroxisome proliferator-activated receptor β/δ in chicken adipogenesis

The adipocyte differentiation process involves a cascade of transcriptional events that culminates in the expression of peroxisome proliferator-activated receptor (PPAR)γ. The present study was undertaken to identify the role of PPARβ/δ in chicken adipocyte differentiation, with experiments performed using a PPARγ agonist, a PPARβ/δ agonist, a PPARγ antagonist and fatty acid (oleate). Preadipocyte cells cultured in a differentiation medium (DMEM containing 500 nM dexamethasone, 0.5 mM 3-isobutyl-1-methylxanthine, 20 μg/mL bovine insulin and 10% fetal bovine serum) supplemented with 200 μM oleate resulted in a significant increase in adipocyte fatty acid binding protein (aP2) mRNA expression after 24 h and 7 d of culture compared to cells cultured in a differentiation medium alone, while supplementation of the differentiation medium with GW501516 (a PPARβ/δ agonist) did not affect aP2 mRNA expression levels. Supplementation of the differentiation medium with troglitazone (a PPARγ agonist) and GW501516 induced preadipocyte differentiation; a significant increase of aP2 mRNA expression was observed in cells after incubation for 7 d, but not after 24 h of incubation. These results suggest that PPARβ/δ 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 PPARγ 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.