Inhibition of mitochondrial calcium-independent phospholipase A2 (iPLA2) attenuates mitochondrial phospholipid loss and is cardioprotective

摘要

pCalcium-independent phospholipase Asub2/sub (iPLAsub2/sub) is the predominant phospholipase Asub2/sub present in myocardium, and its pathophysiological role in acute myocardial infarction has been suggested by the rapid increase in membrane-associated iPLAsub2/sub activity during myocardial ischaemia and reperfusion (I/R). We therefore examined iPLAsub2/sub in mitochondrial fractions prepared from Langendorff-perfused adult rabbit hearts. Our studies indicate that iPLAsub2/subβ is present in rabbit heart mitochondrial inner membranes with no apparent translocation during ischaemia, I/R or preconditioning. Mitochondrion-associated iPLAsub2/sub was catalytically competent and exhibited 2-, 3- and 2.5-fold increases in measured iPLAsub2/sub activity following ischaemia, I/R and preconditioning, respectively, when compared with the activity of iPLAsub2/sub measured in mitochondria from control hearts. Mitochondrial phospholipids are essential for maintaining the ordered structure and function of the organelle. I/R resulted in a rapid overall decrease in phosphatidylcholine and phosphatidylethanolamine glycerophospholipid species, as determined by electrospray ionization MS, that was partially alleviated by pretreatment of hearts with the iPLAsub2/sub-specific inhibitor, bromoenol lactone (BEL). Pretreatment of I/R hearts with 10iμ/iM BEL significantly reduced the infarct size almost to that of continuously perfused hearts and was cardioprotective only when administered prior to ischaemia. Cardioprotection by BEL was reversed by the simultaneous perfusion of 100iμ/iM 5-hydroxydecanoate, implicating the mitochondrial KsubATP/sub channel in BEL-mediated protection from I/R. Preconditioning also significantly reduced the infarct size in response to I/R but protection was lost by concurrent perfusion of 10iμ/iM arachidonic acid. Taken together, these data strongly implicate mitochondria-associated iPLAsub2/sub in the signal transduction of myocardial I/R injury./p