Characterization of the AMP-activated protein kinase pathway in chickens

Abstract

In mammals, AMP-activated protein kinase (AMPK) is involved in the regulation of cellular energy homeostasis and, on the whole animal level, in regulating energy balance and food intake. Because the chicken is a valuable experimental animal model and considering that a first draft of the chicken genome sequence has recently been completed, we were interested in verifying the genetic basis for the LKB1/AMPK pathway in chickens. We identified distinct gene homologues for AMPK alpha, beta and gamma subunits and for LKB1, MO25 and STRAD. Analysis of gene expression by RT-PCR showed that liver, brain, kidney, spleen, pancreas, duodenum, abdominal fat and hypothalamus from 3 wk-old broiler chickens preferentially expressed AMPK alpha-1, beta-2 and gamma-1 subunit isoforms. Heart predominantly expressed alpha-2, beta-2 and gamma-1, whereas skeletal muscle expressed alpha-2, beta-2 and gamma-3 preferentially. Moreover, the AMPK gamma-3 gene was only expressed in heart and skeletal muscle. Genes encoding LKB1, MO25 alpha, MO25 beta, and STRAD beta were expressed in all examined tissues, whereas STRAD alpha was expressed exclusively in brain, hypothalamus, heart and skeletal muscle. Alterations in energy status (fasting and refeeding) produced little significant change in AMPK subunit gene transcription. We also determined the level of phosphorylated (active) AMPK in different tissues and in different states of energy balance. Immunocytochemical analysis of the chicken hypothalamus showed that activated AMPK was present in hypothalamic nuclei involved in regulation of food intake and energy balance. Together, these findings suggest a functional LKB1/AMPK pathway exists in chickens similar to that observed in mammals.