A constant supply of oxygen is indispensable for cardiac viability and function. However, the role of oxygen and oxygen-associated processes in the heart is complex, and they and can be either beneficial or contribute to cardiac dysfunction and death. As oxygen is a major determinant of cardiac gene expression, and a critical participant in the formation of ROS and numerous other cellular processes, consideration of its role in the heart is essential in understanding the pathogenesis of cardiac dysfunction.The mammalian heart is an obligate aerobic organ. At a resting pulse rate, the heart consumes approximately 8-15 ml O 2 /min/100 g tissue. This is significantly more than that consumed by the brain (approximately 3 ml O 2 /min/100 g tissue) and can increase to more than 70 ml O 2 /min/100 g myocardial tissue during vigorous exercise (1, 2). Mammalian heart muscle cannot produce enough energy under anaerobic conditions to maintain essential cellular processes; thus, a constant supply of oxygen is indispensable to sustain cardiac function and viability. The story of oxygen in the heart is complex, however, and goes well beyond its role in energy metabolism.Oxygen is a major determinant of myocardial gene expression, and as myocardial O 2 levels decrease, either during isolated hypoxia or ischemia-associated hypoxia, gene expression patterns in the heart are significantly altered (3). Oxygen participates in the generation of NO, which plays a critical role in determining vascular tone, cardiac contractility, and a variety of additional parameters. Oxygen is also central in the generation of reactive oxygen species (ROS), which can participate as benevolent molecules in cell signaling processes or can induce irreversible cellular damage and death. Oxygen is thus both vital and deleterious (4). The role of oxygen in myocardial energetics and metabolismThe heart can utilize a variety of metabolic fuels, including fatty acids, glucose, lactate, ketones, and amino acids. In the fed state, fatty acids are the preferred fuel, accounting for up to 90% of the total acetyl-CoA provided to cardiac mitochondria (5). Fatty acids are metabolized by β-oxidation, producing acetyl-CoA, NADH, and FADH 2 . The acetyl-CoA enters the Krebs cycle, producing more NADH and FADH 2 . Glucose is metabolized initially via the glycolytic pathway, producing a relatively small amount of ATP and also pyruvate, which enters the Krebs cycle, producing NADH and FADH 2 . In the absence of oxygen, the total amount of energy produced by these processes is insufficient to meet cardiac needs. The cardiac energy requirement is met, however, by entry of the resultant NADH and FADH 2 into the electron transport chain, which generates ATP by oxidative phosphorylation in the mitochondria. Oxygen serves as the terminal electron acceptor in the electron transport chain, and in the absence of sufficient oxygen, electron transport ceases and cardiac energy demands are not met (Figure 1). Generation and counterbalancing of ROSROS can be formed in the heart by a ...

Background-After myocardial infarction (MI), bone marrow-derived cells (BMDCs) are found within the myocardium.The mechanisms determining BMDC recruitment to the heart remain unclear. We investigated the role of stromal cell-derived factor-1␣ (SDF-1) in this process. Methods and Results-MI produced in mice by coronary ligation induced SDF-1 mRNA and protein expression in the infarct and border zone and decreased serum SDF-1 levels. By quantitative polymerase chain reaction, 48 hours after intravenous infusion of donor-lineage BMDCs, there were 80.5Ϯ15.6% more BDMCs in infarcted hearts compared with sham-operated controls (PϽ0.01). Administration of AMD3100, which specifically blocks binding of SDF-1 to its endogenous receptor CXCR4, diminished BMDC recruitment after MI by 64.2Ϯ5.5% (PϽ0.05), strongly suggesting a requirement for SDF-1 in BMDC recruitment to the infarcted heart. Forced expression of SDF-1 in the heart by adenoviral gene delivery 48 hours after MI doubled BMDC recruitment over MI alone (PϽ0.001) but did not enhance recruitment in the absence of MI, suggesting that SDF-1 can augment, but is not singularly sufficient for, BDMC recruitment to the heart. Gene expression analysis after MI revealed increased levels of several genes in addition to SDF-1, including those for vascular endothelial growth factor, matrix metalloproteinase-9, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1, which might act in concert with SDF-1 to recruit BMDCs to the injured heart. Conclusion-SDF-1/CXCR4 interactions play a crucial role in the recruitment of BMDCs to the heart after MI and can further increase homing in the presence, but not in the absence,

AMP-activated protein kinase (AMPK)is an important regulator of diverse cellular pathways in the setting of energetic stress. Whether AMPK plays a critical role in the metabolic and functional responses to myocardial ischemia and reperfusion remains uncertain. We examined the cardiac consequences of long-term inhibition of AMPK activity in transgenic mice expressing a kinase dead (KD) form of the enzyme. The KD mice had normal fractional shortening and no heart failure, cardiac hypertrophy, or fibrosis, although the in vivo left ventricular (LV) dP/dt was lower than that in WT hearts. During low-flow ischemia and postischemic reperfusion in vitro, KD hearts failed to augment glucose uptake and glycolysis, although glucose transporter content and insulin-stimulated glucose uptake were normal. KD hearts also failed to increase fatty acid oxidation during reperfusion. Furthermore, KD hearts demonstrated significantly impaired recovery of LV contractile function during postischemic reperfusion that was associated with a lower ATP content and increased injury compared with WT hearts. Caspase-3 activity and TUNEL-staining were increased in KD hearts after ischemia and reperfusion. Thus, AMPK is responsible for activation of glucose uptake and glycolysis during low-flow ischemia and plays an important protective role in limiting damage and apoptotic activity associated with ischemia and reperfusion in the heart.

We deleted the hypoxia-responsive transcription factor HIF-1alpha in endothelial cells (EC) to determine its role during neovascularization. We found that loss of HIF-1alpha inhibits a number of important parameters of EC behavior during angiogenesis: these include proliferation, chemotaxis, extracellular matrix penetration, and wound healing. Most strikingly, loss of HIF-1alpha in EC results in a profound inhibition of blood vessel growth in solid tumors. These phenomena are all linked to a decreased level of VEGF expression and loss of autocrine response of VEGFR-2 in HIF-1alpha null EC. We thus show that a HIF-1alpha-driven, VEGF-mediated autocrine loop in EC is an essential component of solid tumor angiogenesis.

A constant supply of oxygen is indispensable for cardiac viability and function. However, the role of oxygen and oxygen-associated processes in the heart is complex, and they and can be either beneficial or contribute to cardiac dysfunction and death. As oxygen is a major determinant of cardiac gene expression, and a critical participant in the formation of ROS and numerous other cellular processes, consideration of its role in the heart is essential in understanding the pathogenesis of cardiac dysfunction.The mammalian heart is an obligate aerobic organ. At a resting pulse rate, the heart consumes approximately 8-15 ml O 2 /min/100 g tissue. This is significantly more than that consumed by the brain (approximately 3 ml O 2 /min/100 g tissue) and can increase to more than 70 ml O 2 /min/100 g myocardial tissue during vigorous exercise (1, 2). Mammalian heart muscle cannot produce enough energy under anaerobic conditions to maintain essential cellular processes; thus, a constant supply of oxygen is indispensable to sustain cardiac function and viability. The story of oxygen in the heart is complex, however, and goes well beyond its role in energy metabolism.Oxygen is a major determinant of myocardial gene expression, and as myocardial O 2 levels decrease, either during isolated hypoxia or ischemia-associated hypoxia, gene expression patterns in the heart are significantly altered (3). Oxygen participates in the generation of NO, which plays a critical role in determining vascular tone, cardiac contractility, and a variety of additional parameters. Oxygen is also central in the generation of reactive oxygen species (ROS), which can participate as benevolent molecules in cell signaling processes or can induce irreversible cellular damage and death. Oxygen is thus both vital and deleterious (4). The role of oxygen in myocardial energetics and metabolismThe heart can utilize a variety of metabolic fuels, including fatty acids, glucose, lactate, ketones, and amino acids. In the fed state, fatty acids are the preferred fuel, accounting for up to 90% of the total acetyl-CoA provided to cardiac mitochondria (5). Fatty acids are metabolized by β-oxidation, producing acetyl-CoA, NADH, and FADH 2 . The acetyl-CoA enters the Krebs cycle, producing more NADH and FADH 2 . Glucose is metabolized initially via the glycolytic pathway, producing a relatively small amount of ATP and also pyruvate, which enters the Krebs cycle, producing NADH and FADH 2 . In the absence of oxygen, the total amount of energy produced by these processes is insufficient to meet cardiac needs. The cardiac energy requirement is met, however, by entry of the resultant NADH and FADH 2 into the electron transport chain, which generates ATP by oxidative phosphorylation in the mitochondria. Oxygen serves as the terminal electron acceptor in the electron transport chain, and in the absence of sufficient oxygen, electron transport ceases and cardiac energy demands are not met (Figure 1). Generation and counterbalancing of ROSROS can be formed in the heart by a ...