| Alterations in myocardial metabolism are important determinants of functional recovery in the post-ischemic heart. 5'AMP-activated protein kinase (AMPK) is a pivotal regulator of key metabolic enzymes in the heart. While the mechanisms underlying the AMPK-dependent regulation of metabolism in the heart have been defined, the regulation of myocardial AMPK remains poorly understood. Thus, we conducted an in-depth characterization of the molecular and hormonal mechanisms that regulate AMPK in the heart.; In this thesis, stimulation of AMPK by ischemia is shown for the first time to be mediated by an AMPK kinase (AMPKK). Furthermore, a recently identified AMPKK, LKB1, is not activated by ischemia, supporting the existence of an LKB1-independent, ischemia-stimulated AMPKK. In efforts to identify an AMPKK that is distinct from LKB1, two rat heart AMPKKs were purified, neither of which co-purified with LKB1. Thus, LKB1 is but one of at least three AMPKKs expressed in mammalian cells.; In additional studies, the role of insulin-receptor signaling in the AMPKK-mediated regulation of AMPK was assessed. Since insulin inhibits AMPK activity and phosphorylation in aerobic and ischemic hearts, we investigated whether insulin also represses the activity of AMPKK and thus AMPK. However, insulin did not alter the activity of AMPKK in either aerobic or ischemic hearts perfused with clinically relevant levels of fatty acids.; Recently, AMPK was identified as an effector of signaling from the adiponectin/globular domain of adiponectin (gAd) receptor. Thus, we examined the signaling, metabolic and functional effects of adiponectin and gAd on the heart. Adiponectin promotes a shift from fatty acid oxidation towards glucose oxidation, while gAd elicits the converse effect. Although the metabolic effects of adiponectin and gAd are not associated with changes in AMPK activity, adiponectin and gAd increase and decrease Akt-dependent insulin signalling, respectively. Importantly, the metabolic actions of gAd do not alter cardiac function under aerobic conditions, but are associated with an impaired contractile recovery in reperfused-ischemic hearts.; In summary, this thesis delineates the molecular basis of myocardial AMPK regulation, in response to ischemia, insulin, adiponectin and gAd. Furthermore, two novel AMPKKs were purified that may play an integral role in coordinating AMPK signaling. |
