Glucose Metabolism and Energy Homeostasis in Mouse Hearts Overexpressing Dominant Negative α2 Subunit of AMP-activated Protein Kinase

Abstract

AMP-activated protein kinase (AMPK) is an energysensing enzyme that plays a pivotal role in regulating cellular metabolism for sustaining energy homeostasis under stress conditions. Activation of AMPK has been observed in the heart during acute and chronic stresses, but its functional role has not been completely understood because of the lack of effective activators and inhibitors of this kinase in the heart. We generated transgenic mice (TG) with cardiac-specific overexpression of a dominant negative mutant of the AMPK ␣2 catalytic subunit to clarify the functional role of this kinase in myocardial ischemia. In isolated perfused hearts subjected to a 10-min ischemia, AMPK ␣2 activity in wild type (WT) increased substantially (by 4.5-fold), whereas AMPK ␣2 activity in TG was similar to the level of WT at base line. Basal AMPK ␣1 activity was unchanged in TG and increased normally during ischemia. Ischemia stimulated a 2.5-fold increase in 2-deoxyglucose uptake over base line in WT, whereas the inactivation of AMPK ␣2 in TG significantly blunted this response. Using 31 P NMR spectroscopy, we found that ATP depletion was accelerated in TG hearts during no-flow ischemia, and these hearts developed left ventricular dysfunction manifested by an early and more rapid increase in left ventricular end-diastolic pressure. The exacerbated ATP depletion could not be attributed to impaired glycolytic ATP synthesis because TG hearts consumed slightly more glycogen during this period of no-flow ischemia. Thus, AMPK ␣2 is necessary for maintaining myocardial energy homeostasis during ischemia. It is likely that the functional role of AMPK in myocardial energy metabolism resides both in energy supply and utilization.The AMP-activated protein kinase (AMPK) 1 functions as a fuel gauge, such that when the cell is exposed to stresses associated with energy depletion, it switches off ATP-utilizing pathways and switches on ATP-generating pathways to restore energy homeostasis (1, 2). This kinase is activated by decreases in ATP/AMP and in phosphocreatine (PCr)/creatine through Thr 172 phosphorylation by one or more upstream kinases (AMPK kinase) and through allosteric modification by AMP (1, 2). AMPK is a heterotrimeric protein consisting of a catalytic subunit (␣) and two regulatory subunits (␤ and ␥) (1, 3). Each subunit has two or more different isoforms; the ␣1 subunit is widely expressed, whereas the ␣2 subunit is expressed primarily in liver, heart, and skeletal muscle (2, 4, 5).It has been suggested that AMPK regulates glucose and fatty acid metabolism in striated muscles (6, 7). Studies from our groups and others showed increased AMPK activity during acute and chronic stresses, such as hypoxia and exercise in skeletal muscle and ischemia and pressure overload in the heart (8 -12). Activation of AMPK in the heart is associated with enhanced glucose uptake and glycolysis (10, 11, 13). As glycolysis is a major source of ATP during ischemia, stimulation of glucose uptake and glycolysis by AMPK in the ischemic heart is consistent ...

Anti-hypoxic effect of ginsenoside Rbl on neonatal rat cardiomyocytes is mediated through the specific activation of glucose transporter-4 ex vivo

“…A growing number of in-vivo [28][29][30][31] and in-vitro [32] studies have indicated that AMPK activation may directly regulate GLUT-4 expression [11,[28][29][30][31][32][33] and induce a significant increase in glucose uptake [9][10][11][28][29][30][31][32][33][34] in cultured skeletal muscle cells. In cardiomyocytes, hypoxia may increase AMPK-mediated glucose uptake and GLUT-4 translocation [35] , which is not sufficient to increase glucose uptake [36] .…”

“…Its facilitative uptake is dependent on the activity of glucose transporters (GLUT) on the cell surface, in particular, glucose transporter-4 (GLUT-4) [7,8] . The increase in glucose uptake is mainly dependent on GLUT-4 translocation via AMP-activated protein kinase (AMPK) [9][10][11] , phosphatidylinositol-3 kinase (PI3K) [12,13] , etc. The increased glucose uptake provides a substrate for glycolysis and then partly compensates for the energy deficit.…”

AMP-activated protein kinase control of energy metabolism in the ischemic heart

“…Studies in which hearts are exposed to ischemia in the presence of either no or low levels of fatty acids have suggested that hearts that have a decreased ischemiainduced activation of AMPK result in a decreased recovery of cardiac function. 6,42 However, a recent study in hearts from mice in which AMPKa2 was deleted showed that a decrease in AMPK activation results in no difference in functional recovery following ischemia. 43 We have also recently shown in hearts from AMPK dominate negative mutant of the a2 subunit (DNa2) of mice that if hearts were exposed to either low or high levels of fatty acids there was either no difference in functional recovery, or an actual increase in functional recovery (Folmes et al, unpublished data).…”

Régulation du métabolisme énergétique par l’AMPK

“…Celle-ci est le résultat d'une chute plus rapide d'ATP. La surexpression cardiaque d'une forme dominante négative de l'AMPK inhibe l'activation de l'AMPK, la stimulation de la glycolyse et la production de lactate au cours de l'ischémie et entraîne une aggravation des lésions ischémiques (mort cellulaire) [41,42]. Récemment, l'AMPK a été impliquée dans les effets cardioprotecteurs de l'adiponectine en inhibant l'apoptose des cardiomyocytes [43].…”