Abstract 5136: Reduction in Myocardial Ischemia-reperfusion Injury in Group IV Cytosolic Phospholipase A2-deficient Mice Partly Due to Inhibition of TNFα-mediated Pathway to Cell Injury
Type IV cytosolic phospholipase A2 (cPLA2), which preferentially cleaves arachidonic acid from phospholipids, plays an important role in tissue injury. The downstream signal in response to TNFα, a key mediator of myocardial ischemia reperfusion (I/R) injury, involves cPLA2 activation. This study examined a pathogenic role of cPLA2 and its mechanistic link with TNFα in myocardial I/R injury using cPLA2α knockout mice (cPLA2−/− mice).
Methods and Results: The cPLA2−/− mice with C57BL/6 background used in this study had comparable heart size, heart rate and blood pressure with the littermate cPLA2+/+ (wild-type; WT) mice (male at 10 weeks). In vivo myocardial I/R was created in 10-week-old male mice by 1-hr ligation of the left anterior descending coronary artery, followed by 24 hrs of reperfusion. Expression levels of mRNA and protein of TNFα in the ischemic myocardium were increased from baseline by 5-fold similarly in both cPLA2−/− and WT mice. Expression of TNFα receptors was unchanged after I/R in both genotypes. cPLA2−/− mice had a 45% reduction in myocardial infarct size and a preservation of LV fractional shortening (25% vs. 15%, respectively) after I/R compared with WT mice. The contents of thromboxane B2 and leukotriene B4, arachidonic acid-derived proinflammatory mediators, in injured myocardium were 40% ~ 50% lower in cPLA2−/− mice than WT mice. cPLA2−/− mice had a 30% decrease in caspase-3 activity and a 40% decrease in TUNEL-positive apoptotic cells in injured myocardium compared with WT mice. In cultured cardiomyocytes from WT mice, hypoxia-reoxygenation (H/R) induced cPLA2 activation that was suppressed by preincubation with the TNFα-neutralizing antibody. Incubation of cardiomyocytes with TNFα induced apoptosis, cell damage (MTT assay) and production of thromboxane B2 and leukotriene B4 that were attenuated in cPLA2−/− cardiomyocytes compared with WT cardiomyocytes. H/R exhibited similar results obtained from TNFα. Preincubation with the TNFα antibody significantly inhibited H/R-induced apoptosis and cell damage in WT cardiomyocytes, while it did not in cPLA2−/− cardiomyocytes.
Conclusions: Disruption of cPLA2 attenuated myocardial I/R injury partly through inhibition of TNFα-mediated pathway to cell injury and apoptosis.