Ghrelin modulates fatty acid synthase and related transcription factor mRNA levels in a tissue-specific manner in neonatal broiler chicks

Abstract

The endogenous ligand for the growth hormone (GH) secretagogue receptor ghrelin is a peptide secreted by the stomach of mammals and stimulates food intake and enhances adiposity. In avian species, ghrelin is mainly produced by the proventriculus but reduces food intake whereas its effect on lipogenesis in different tissues is unknown. We therefore investigated the effects of a single intravenous injection of 2.8 microg (1 nmol per chick) recombinant chicken ghrelin in neonatal broiler chicks. Besides food intake and plasma corticosterone levels, mRNA levels of the key lipogenic enzyme fatty acid synthase (FAS) and its related transcription factors sterol regulatory element binding protein-1 (SREBP-1) and peroxisome proliferator-activated receptor-gamma (PPARgamma) were determined in diencephalon, liver and quadriceps femoris muscle before, and 15, 30, and 60 min after injection. Chicken ghrelin administration induced a significant short-term (<30 min) reduction in food intake and markedly elevated plasma corticosterone levels. In diencephalon, FAS, SREBP-1 and PPARgamma mRNA levels were significantly increased within 15 min after ghrelin injection. These observations suggest that central fatty acid metabolism is involved in the anorectic effects of ghrelin. In contrast, hepatic mRNA levels of FAS and both transcription factors were significantly reduced within 30 min after ghrelin injection. In muscle, FAS and transcription factor gene expression was very low and not affected by ghrelin. Overall, our results indicate that ghrelin has opposite effects on FAS and transcription factor mRNA amounts with increased levels in diencephalon (central anorectic effect) and decreased levels in liver (peripheral anti-lipogenic effect) in chickens.