The role of phospho-adenosine monophosphate-activated protein kinase and vascular endothelial growth factor in a model of chronic heart failure.

We established a stable and reproducible animal model of chronic heart failure (CHF) in sheep to investigate biomolecular changes. Therefore, two biomarkers, adenosine monophosphate-activated protein kinase (AMPK) and vascular endothelial growth factor-A (VEGF-A) were examined to reveal their role during chronic ischemic conditions of the heart. AMPK was studied because it plays an important role in cellular energy homeostasis and its upregulation is associated with myocardial ischemia, whereas VEGF-A was studied because it acts as an important signaling protein for neoangiogenesis. We examined 15 juvenile sheep (mean weight, 78±4kg; control, n=3; ShamOP, n=2; coronary microembolization [CME], n=10). CHF was induced under fluoroscopic guidance by multiple sequential microembolizations (MEs) through bolus injection of polysterol microspheres (90µm, n=25.000) into the left main coronary artery. CME was repeated up to three times at 2- to 3-week intervals until animals started to develop stable signs of CHF. All animals were followed for 3 months. Phosphorylation of AMPK, marking the activated protein form, was detected by Western blotting. VEGF-A and vascular endothelial growth factor-receptor 2 (VEGF-R2) mRNA were detected by real-time polymerase chain reaction. Glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) was used as a reference housekeeping gene. All 10 CHF animals developed clinical signs of CHF as indicated by a significant decrease of cardiac output, decreased ejection fraction, as well as occurrence of tachycardia and tachypnoea. Western blots showed significant phosphorylation of AMPK in CME animals compared to the control group (phospho-adenosine monophosphate-activated protein kinase α) (GAPDH control: 0.0, CME left ventricle [LV]: 0.39±0.20, CME right ventricle [RV]: 0.53±0.30; P<0.05). VEGF-A and VEGF-R2 expression in CME animal myocardium was within the range of the control group, but this data did not reach statistical significance due to the small size of this group. While microinjection was performed into the left main coronary artery, phosphorylation of AMPK and expression of VEGF-A and VEGF-R2 were significantly higher in the RV than in the LV. Multiple sequential intracoronary MEs can effectively induce myocardial dysfunction with clinical and biomolecular signs of chronic ischemic cardiomyopathy. Quantitative analysis of biomolecular markers showed a significantly higher phosphorylation of AMPK in CHF animals compared with control myocardium.

AMPK - Activated Protein Kinase and its Role in Energy Metabolism of the Heart.

Adenosine monophosphate - activated kinase (AMPK) plays a key role in the coordination of the heart's anabolic and catabolic pathways. It induces a cellular cascade at the center of maintaining energy homeostasis in the cardiomyocytes.. The activated AMPK is a heterotrimeric protein, separated into a catalytic α - subunit (63kDa), a regulating ß - subunit (38kDa) and a γ - subunit (38kDa), which is allosterically adjusted by adenosine triphosphate (ATP) and adenosine monophosphate (AMP). The actual binding of AMP to the γ - subunit is the step which activates AMPK. AMPK serves also as a protein kinase in several metabolic pathways of the heart, including cellular energy sensoring or cardiovascular protection. The AMPK cascade represents a sensitive system, activated by cellular stresses that deplete ATP and acts as an indicator of intracellular ATP/AMP. In the context of cellular stressors (i.e. hypoxia, pressure overload, hypertrophy or ATP deficiency) the increasing levels of AMP promote allosteric activation and phosphorylation of AMPK. As the concentration of AMP begins to increase, ATP competitively inhibits further phosphorylation of AMPK. The increase of AMP may also be induced either from an iatrogenic emboli, percutaneous coronary intervention, or from atherosclerotic plaque rupture leading to an ischemia in the microcirculation. To modulate energy metabolism by phosphorylation and dephosphorylation is vital in terms of ATP usage, maintaining transmembrane transporters and preserving membrane potential. In this article, we review AMPK and its role as an important regulatory enzyme during periods of myocardial stress, regulating energy metabolism, protein synthesis and cardiovascular protection.

Hemodynamic changes in a model of chronic heart failure induced by multiple sequential coronary microembolization in sheep.

Although a large variety of animal models for acute ischemia and acute heart failure exist, valuable models for studies on the effect of ventricular assist devices in chronic heart failure are scarce. We established a stable and reproducible animal model of chronic heart failure in sheep and aimed to investigate the hemodynamic changes of this animal model of chronic heart failure in sheep. In five sheep (n = 5, 77 +/- 2 kg), chronic heart failure was induced under fluoroscopic guidance by multiple sequential microembolization through bolus injection of polysterol microspheres (90 microm, n = 25.000) into the left main coronary artery. Coronary microembolization (CME) was repeated up to three times in 2 to 3-week intervals until animals started to develop stable signs of heart failure. During each operation, hemodynamic monitoring was performed through implantation of central venous catheter (central venous pressure [CVP]), arterial pressure line (mean arterial pressure [MAP]), implantation of a right heart catheter {Swan-Ganz catheter (mean pulmonary arterial pressure [PAP mean])}, pulmonary capillary wedge pressure (PCWP), and cardiac output [CO]) as well as pre- and postoperative clinical investigations. All animals were followed for 3 months after first microembolization and then sacrificed for histological examination. All animals developed clinical signs of heart failure as indicated by increased heart rate (HR) at rest (68 +/- 4 bpm [base] to 93 +/- 5 bpm [3 mo][P < 0.05]), increased respiratory rate (RR) at rest (28 +/- 5 [base] to 38 +/- 7 [3 mo][P < 0.05]), and increased body weight 77 +/- 2 kg to 81 +/- 2 kg (P < 0.05) due to pleural effusion, peripheral edema, and ascites. Hemodynamic signs of heart failure were revealed as indicated by increase of HR, RR, CVP, PAP, and PCWP as well as a decrease of CO, stroke volume, and MAP 3 months after the first CME. Multiple sequential intracoronary microembolization can effectively induce myocardial dysfunction with clinical and hemodynamic signs of chronic ischemic cardiomyopathy. The present model may be suitable in experimental work on heart failure and left ventricular assist devices, for example, for studying the impact of mechanical unloading, mechanisms of recovery, and reverse remodeling.