MRNA Expression of Glycolytic Enzymes and Glucose Transporter Proteins in Ischemic Myocardium With and Without Reperfusion

Abstract

It is known that ischemia commonly increases exogenous glucose utilization by accelerating glucose uptake and flux rates through the Embden–Meyerhof pathway. Constitutive enzymes regulate the rate of glycolysis and in turn are regulated by product inhibition and allosteric controls. The purpose of this report was to test whether mRNA abundance for select glycolytic enzymes, and glucose transport proteins, is also modified. Six intact, working pig hearts with coronary flow controlled by extracorporeal perfusion were compared at the following conditions: (1) aerobic control perfusion; (2) ischemia affected by a 60% decrease in left anterior descending (LAD) coronary perfusion; (3) ischemia again affected by a 60% decrease in LAD flow followed by a 40-min interval of aerobic reflow; (4) an intermittent ischemia and reflow protocol including four cycles of similar LAD flow reductions (5 min per cycle) interspersed with 15–20 min of aerobic reperfusion; (5) a 4-day model designed to produce myocardial chronic hibernation; and (6) mild ischemia induced by a 40% decrease in LAD flow for 85 min to produce certain adaptations compatible with short-term hibernation. In each heart, mRNA abundance was measured from LAD and circumflex (LCF) perfused myocardium for hexokinase, phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase and the two glucose transporter isomers, GLUT 4 and GLUT 1. mRNA data from LAD myocardium in intervention hearts were normalized to those from LAD tissue in the control heart (LADc) and with LCF values in the same intervention hearts. Signal variance around unity in the LAD tissue, with respect to that of the LCF myocardium, in the control heart compared closely (44 and 41% in two separate runs, respectively). GLUT 1/GLUT 4 ratios in the LAD and LCF beds of this heart also agreed closely. LAD/LADc ratios were increased for hexokinase (1.69), phosphofructokinase (3.69), and glyceraldehyde-3-phosphate dehydrogenase (2.29) in the ischemia heart and for phosphofructokinase (3.90), glyceraldehyde-3-phosphate dehydrogenase (2.20), GLUT 4 (1.55) and GLUT 1 (2.20) in the ischemia/reflow heart. There was no evidence of excess signal in the intermittent ischemia/reflow, chronic hibernation, or mild ischemia hearts. Altered signal from LCF myocardium was also suggested. These data indicate that mRNA abundance for select glycolytic enzymes and transporter proteins is increased in ischemic myocardium with or without reperfusion and offers a possible mechanism for increased protein activity in settings of diminished regional coronary flow.