Abstract 2276: Degradation of Myosin Light Chains -1 and -2 in the Heart of Asphyxiated Neonatal Pigs Reoxygenated with 100% Oxygen
Background: Neonatal asphyxia is commonly associated with low cardiac output and myocardial dysfunction during recovery. Oxidative stress increases matrix metalloproteinase-2 activity in the heart subjected to ischemia-reperfusion, and triggers the degradation of contractile proteins (troponin I and myosin light chain (MLC)-1). Little is known about the molecular basis of the in vivo effect of neonatal hypoxia-reoxygenation (HR) on the cardiac mechanical function in intact animals. The impaired myocardial contractility triggered by HR could be related to the degradation of contractile proteins by matrix metalloproteinase-2.
Hypothesis: Neonatal HR would impair myocardial contractility with decreased MLC expression.
Methods: Piglets (1–3d, 1.4 –2.3kg) were acutely instrumented for hemodynamic measurements. After stabilization piglets were block-randomized to the sham-operated control group with no HR or the HR group which they were exposed to alveolar normocapnic hypoxia (FiO2=0.10 – 0.15) for 2h followed by reoxygenation with 100% oxygen (1h) then 21% (3h)(n=6/group). At the end of the experiment, animals were euthanized and the left ventricle of hearts was freeze-clamped for proteomic analysis. Protein level was analyzed by 2-D electrophoresis, mass spectrometry (MALD-TOF-TOF) was used for protein identification and analysis. ANOVA or Kruskal-Wallis test was used as appropriate with significance defined at p<0.05.
Results: After 2h hypoxia (PaO2 33± [SEM]1mmHg), HR piglets had shock, hypotension and metabolic acidosis (vs. controls, p<0.05). The hemodynamic measurements recovered immediately upon reoxygenation but gradually deteriorated over the following 4h (p<0.05 vs. controls). We found that in the left ventricular myocardial tissue, the expression of MLC-1 and MLC-2 was significantly lower in the HR piglets (30.5±6.6 and 10.3±1.9 vs. 111.7±7.1 and 70.6±1.79 AU/100 ug protein of controls, respectively, p<0.05). This was associated with poor myocardial contractile function.
Conclusions: Lower expression of MLC-1 and MLC-2 due to HR injury could suggest that myocardial stress leads to the downregulation of myosin, the major protein of the thick filaments. This in turn could result in compromised myocardial contractility.