Abstract 264: Group X Secretory Phospholipase A2 has a Critical Role in Neutrophils Activation and Myocardial Ischemia-reperfusion Injury in Mice
Secretory phospholipase A2 (sPLA2) plays a critical role in the pathophysiology of cardiovascular diseases. Among several types of sPLA2, group X sPLA2 (sPLA2-X) has the most potent hydrolyzing activity on phosphatidylcholine. sPLA2-X is expressed in neutrophils, suggesting a potential role of neutrophil sPLA2-X in cardiovascular diseases. Thus, we generated mice that lack sPLA2-X and studied a role of sPLA2-X in neutrophil activities and myocardial ischemia-reperfusion injury.
Methods and Results: Neutrophils isolated from sPLA2-X−/− mice had a lower respiratory burst (50 ∼60% of sPLA2-X+/+ neutrophils) and reduced migration (55 ∼ 65%) in response to C5a and fMLP and less elastase release (56%) in response to opsonized zymosan than sPLA2-X+/+ neutrophils. However, neutrophil function in response to arachidonic acid and phorbol-12-myristate-13-acetate, which are capable of directly stimulating respiratory burst and migration, was comparable between sPLA2-X+/+ mice and sPLA2-X−/− mice Expression levels of NADPH oxidase p47phox and p67phox, elastase, CD11b/18, and cyclooxygenase-2 were comparable between neutrophils and sPLA2-X−/−neutro-phils.sPLA2-X+/+ Thus, the machinery for respiratory burst and migration is preserved in sPLA2-X−/− neutrophils. In sPLA2-X+/+ mice, immunoreactivity of sPLA2-X was detected in neutrophils and in the myocardial area, where neutrophils accumulated, in the injured myocardium that was made by 1 hr ligation of left coronary artery, followed by 24 hrs reperfusion. sPLA2-X was also detectable in extracellular supernatant of the isolated sPLA2-X+/+ neutrophils after activation, while no detectable in the sham-operated myocardium of sPLA2-X+/+ mice, suggesting that sPLA2-X in the injured myocardium was derived mainly from neutrophils. The sPLA2-X−/− mice had a 33% reduction in myocardial infarct size and 43% decrease in myocardial myeloperoxidase activity, a marker of neutrophils accumulation, in the ischemia-reperfusion model compared with sPLA2-X mice.
Conclusions:sPLA2-X is required for neutrophil cytotoxic activities in response to the external stimuli. sPLA2-X might have a pathogenetic role in the neutrophil-mediated tissue injury and inflammation in cardiovascular diseases.