Local Agouti Signaling Protein/Melanocortin Signaling System that Possibly Regulates Lipid Metabolism in Adipose Tissues of Chickens

The agouti signaling protein (ASIP)/melanocortin signaling system regulates lipid metabolism in humans but not in mice. To examine whether the system is present in adipose tissues in chickens, we performed reverse transcription-polymerase chain reaction (RT-PCR) analysis using mRNAs extracted from subcutaneous and visceral adipose tissues. This revealed that mRNAs for melanocortin 1 receptor (MC1R), MC5R, ASIP, pro-opiomelanocortin (POMC), prohormone convertase 1 (PC1) and PC2 were expressed in both adipose tissues, suggesting the presence of a local ASIP/melanocortin signaling system in these tissues in chickens. To investigate the potential biological role of this system, the adipose tissue mRNA expression of ASIP and POMC was examined under food-deprived conditions. Forty-eight-hour fasting significantly decreased body weight and reduced the cell size in adipose tissues. In addition, the plasma levels of free fatty acids were increased while those of glucose, triacylglycerols and insulin were decreased, suggesting the activation of lipolysis and gluconeogenesis in the fasted chickens. Under this condition, the mRNA expression of ASIP and POMC was decreased and increased, respectively, in subcutaneous and visceral adipose tissues. ASIP and melanocortins are lipogenic and lipolytic hormones, respectively. Therefore, these findings suggest that lipid metabolism in the adipose tissues is regulated by a local ASIP/melanocortin signaling system in chickens. This is the first report demonstrating changes in the expression of ASIP mRNA in adipose tissues in the negative-energy state in vertebrates.