Effects of feed deprivation on the AMPK signaling pathway in skeletal muscle of broiler chickens

Abstract

The 5'-adenosine monophosphate-activated protein kinase (AMPK) plays a key role in rapid metabolic adaptations to maintain energy homeostasis in poultry. It remains unclear if AMPK is involved in muscular energy metabolism in broiler chickens. Hence, in the present study, seven-day-old male broilers were equally divided into three groups: fed ad libitum (control); feed-deprived for 24h (S24); feed-deprived for 24h and then refed for 24h (S24R24). Compared to the control group, the plasma levels of glucose, insulin, T3 and triglycerides in the S24 group were significantly lower (P<0.05), whereas the uric acid levels were significantly higher (P<0.01). Except for glucose, refeeding for 24h reversed the fasting-induced alterations in plasma metabolite. Fasting decreased the liver kinase B1 (LKB1), AMPK alpha 2 subunit (AMPKα2), and fatty acid synthase (FAS) mRNA levels (P<0.05) in M. pectoralis major (PM). Feed deprivation did not affect the phosphorylated AKT, mammalian target of rapamycin (mTOR) and ribosomal protein S6 kinase (p70S6K) in PM (P>0.05), but upregulated carnitine palmitoyltransferase 1 (CPT1) gene expression and increased phosphorylated LKB1 (0.05<P<0.1) and AMPKα (P<0.05) levels. AMPKα2, FAS, and CPT1 mRNA levels and the protein levels of phosphorylated AMPK and LKB1 of the PM muscle returned to control group levels after 24h refeeding. In M. biceps femoris (BF), the AMPKα2 and FAS mRNA levels were decreased by fasting compared to control (P<0.05), whereas CPT1 mRNA and phosphorylated LKB1 and AMPK protein levels were increased. Refeeding for 24h reversed the changes in AMPKα2 and CPT1 gene expression and phosphorylated AMPKα2 subunit. Fasting did not affect the AKT, mTOR and p70S6K in both PM and BF muscles (P>0.05). However, refeeding after 24h of fasting increased the phosphorylated mTOR level in BF muscle which was in parallel with increased plasma insulin concentration. It was likely that increased phospho-mTOR level in the BF muscle was due to the higher sensitivity of BF to insulin. Together, the results suggested that the AMPK signaling pathway might be involved in the energy metabolism alterations in the skeletal muscles of broiler chickens and was also dependent upon the muscle fiber type. Furthermore, the regulatory effects of AMPK on energy metabolism in muscles of broiler chickens might be mediated by the AMPK/FAS pathway.

Keywords: AMPK; Broiler; Fasting; Skeletal muscle; mTOR.