Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2005
Publication Date: 1/1/2006
Citation: Proszkowiec-Weglarz, M., Richards, M.P., Ramachandran, R., McMurtry, J.P. 2006. Characterization of the AMP-activated protein kinase pathway in chickens. Comparative Biochemistry and Physiology Part B. 143:92-106. Interpretive Summary: Poultry producers are faced with a number of challenges related to regulation of energy balance in commercial lines of birds that have been subjected to intensive selection for rapid growth and increased meat production. For example, modern broiler chickens do not adequately regulate voluntary feed intake to achieve energy balance and constant body weight. When given free access to food, birds will overeat and thus be prone to a variety of health-related problems stemming from the development of excessive fattening (obesity). In mammalian species, a cellular enzyme designated AMP-activated protein kinase (AMPK) is known to play a pivotal role in the regulation of food intake and energy metabolism. AMPK functions as a “fuel gauge” that responds to fluctuations in cellular energy level, as well as, to the levels of specific extracellular nutrients and hormones. In general, AMPK acts to increase cellular energy levels by reducing the activity of energy (ATP)-utilizing metabolic pathways and increasing those that generate ATP. Since there has been no prior investigation of AMPK in chickens, the aim of this study was to identify and characterize the AMPK pathway in broiler chickens. This is the first report to identify and characterize AMPK at the molecular (gene/protein) level in different chicken tissues. We found that the chicken AMPK enzyme is activated in the same way as it is in mammals. In addition, we determined the level of active AMPK in different tissues and during alterations in energy status. We also localized the active form of AMPK in chicken brain to specific regions that are known to regulate food intake and energy balance. Together, these findings clearly demonstrate for the first time that an active AMPK pathway exists in chickens. Moreover, AMPK most likely is an important component of the mechanisms that regulate food intake and energy balance in poultry. This work provides new information to researchers that will be useful in studying the regulation of food intake and energy balance.
Technical 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.