Abstract
The endogenous mechanisms contributing to tissue survival following myocardial infarction are not fully understood. We investigated the alterations in the mitochondrial proteome after ischemia-reperfusion (I/R) and its possible implications on cell survival. Mitochondrial proteomic analysis of cardiac tissue from an in vivo porcine I/R model found that surviving tissue in the peri-infarct border zone showed increased expression of several proteins. Notably, these included subunits of the mitochondrial pyruvate carrier (MPC), namely MPC1 and MPC2. Western blot, immunohistochemistry, and mRNA analysis corroborated the elevated expression of MPC in the surviving tissue. Furthermore, MPC1 and MPC2 protein levels were found to be markedly elevated in the myocardium of ischemic cardiomyopathy patients. These findings led to the hypothesis that increased MPC expression is cardioprotective due to enhancement of mitochondrial pyruvate uptake in the energy-starved heart following I/R. To test this, isolated mouse hearts perfused with a modified Krebs buffer (containing glucose, pyruvate, and octanoate as metabolic substrates) were subjected to I/R with or without the MPC transport inhibitor UK5099. UK5099 increased myocardial infarction and attenuated post-ischemic recovery of left ventricular end-diastolic pressure. However, aerobically perfused control hearts that were exposed to UK5099 did not modulate contractile function, although pyruvate uptake was blocked as evidenced by increased cytosolic lactate and pyruvate levels. Our findings indicate that increased expression of MPC leads to enhanced uptake and utilization of pyruvate during I/R. We propose this as a putative endogenous mechanism that promotes myocardial survival to limit infarct size.
Highlights
From the ‡Cardiovascular Division, King’s College London, The Rayne Institute, and St
Samples of surviving myocardium were taken 1 cm away from the infarct zone. Histological analysis of this tissue by staining with hematoxylin and eosin as well as Masson’s trichrome verified the absence of fibrosis in all groups (Fig. 1C). Samples of this surviving myocardium were taken for proteomic analyses in which protein expression was compared with control samples collected from the same anatomical location in control hearts
Mitochondrial function and energetics are important determinants of myocardial viability after I/R that can lead to infarction and progress to heart failure
Summary
Porcine Model of I/R Injury—Seventeen 3-month-old pigs were randomly assigned into one of three groups, which included healthy controls (n ϭ 6), ischemia followed by 3 days of reperfusion (3/R, n ϭ 5), or ischemia followed by 15 days of reperfusion (15 I/R, n ϭ 6). Ischemia was induced by inserting an inflatable catheter and occluding the left anterior descending coronary artery for 120 min. This involved sedation using an intramuscular injection of ketamine (15 mg/kg) and azaperone (2 mg/kg), after which a 6 French sheath was inserted (via the femoral artery and using a Judkins Right 6 French guiding catheter) to the ascending aorta, so to selectively engage the left coronary artery. A 0.014-inch intracoronary guide wire was advanced up to the distal left anterior descending coronary artery, and a balloon catheter was inflated in the medial left anterior descending coronary artery for 120 min. All procedures followed the European Agreement of Vertebrate Animal Protection for Experimental Use (86/609)
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