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Title: Expression and activity of the 5'-AMP-activated protein kinase pathway in selected tissues during chicken embryonic development.

Author
item Proszkowiec-Weglarz, Monika
item Richards, Mark

Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2008
Publication Date: 1/1/2009
Citation: Proszkowiec Weglarz, M., Richards, M.P. 2009. Expression and activity of the 5'-adenosine monophosphate-activated protein kinase pathway in selected tissues during chicken embryonic development. Poultry Science. 88(1):159-178.

Interpretive Summary: Cellular energy levels must be carefully regulated to meet the metabolic demands of growth and development. This is especially true during embryonic development when nutrient demand is high and when an insufficient supply of energy can lead to developmental defects culminating in embryo mortality. Thus, it is essential that important functions such as growth and development be regulated commensurate with the availability of energy supplies needed to support such activities. Animals have developed a complex network of regulatory mechanisms that work together to adjust energy acquisition via food intake and internal metabolic activity to achieve a state of energy balance in response to changing environmental and nutritional conditions. A key component of this regulatory network involves 5’-AMP-activated protein kinase (AMPK), an enzyme that serves both as an energy sensor and as a regulator of metabolism. Although we have recently identified and characterized AMPK in young growing chickens, as of yet nothing is known about this important metabolic regulator in the developing embryo. A major shift in metabolism occurs as the embryo transitions from utilizing high fat yolk stores in the egg to a high carbohydrate diet immediately after hatching. Therefore, it is important to understand how energy metabolism is regulated during this critical phase of production and what role AMPK plays in this process. The objective of this study was to investigate AMPK in chicken embryos during the last half of incubation and at hatch. We found significant changes in AMPK as well as in the proteins that activate AMPK or are regulated by it in different organs that play key roles in metabolic regulation as the embryo progresses towards hatching. By understanding how AMPK functions in the embryo and in the hatched chick, we will be better able to discern the practical implications of this metabolic regulator in poultry production. Such information is also useful to researchers studying the control of energy balance and growth in poultry and to poultry producers in devising new genetic selection and management strategies for commercial poultry flocks.

Technical Abstract: The 5’-AMP-activated protein kinase (AMPK) is a highly conserved serine/threonine protein kinase and a key part of a kinase signaling cascade that senses cellular energy status (AMP/ATP ratio) and acts to maintain energy homeostasis by coordinately regulating energy-consuming and energy-generating metabolic pathways. The objective of this study was to investigate aspects of the AMPK pathway in liver, brain, breast muscle and heart from day 12 of incubation (e12) through hatch (H) in chickens. We first determined mRNA and protein expression profiles for a major upstream AMPK kinase, LKB1 that is known to activate (phosphorylate) AMPK in response to increases in the AMP/ATP ratio. Expression of LKB1 protein was highest in brain which demonstrated tissue-specific patterns for phosphorylation. Next, AMPK subunit mRNA and protein expression profiles were determined. Significant changes in AMPK subunit mRNA expression occurred in all tissues from e12 to hatch. Differences in the levels of active (phosphorylated) AMPK, as well as the alpha and beta subunit proteins were observed in all four tissues during embryonic development. Finally, we determined the protein level and phosphorylation status of an important downstream target for AMPK, acetyl-CoA carboxylase (ACC). The expression levels of ACC and pACC were higher in brain than liver, but were undetectable by Western blotting in breast muscle and heart throughout the period of study. Together, our results are the first to demonstrate the expression and activity of the AMPK pathway in key tissues during transition from embryonic to post-hatch development in chickens.