Abstract 102: The Detrimental Role Of iPLA2β In Ischemia/reperfusion Injury

Abstract

Background: Ca 2+ -independent phospholipase A2 (iPLA2) is crucial for a caspase-independent non-apoptotic cell death signaling pathway and involved in nuclear shrinkage induced by hypoxia. PLA2 family hydrolyzes the sn-2 ester bond in phospholipids to release free fatty acids and lysophospholipids. PLA2 inhibitors are known to prevent ischemic-reperfusion (I/R) injury. Here, we attempted to clarify the role of iPLA2β in myocardial I/R injury using cardiac-specific iPLA2β-deficient mice. Methods: Pla2g6 gene-targeting vector was constructed using mouse BAC genomic library. The ES clones with targeted homologous recombination were injected into blastocyst mouse embryos. Floxed iPLA2β mice were crossed with transgenic mice expressing Cre recombinase under the control of the α-myosin heavy chain ( αMHC ) promoter to generate cardiac-specific iPLA2β-deficient mice ( pla2g6 flox/flox αMHC-Cre + : CKO). We used pla2g6 flox/flox αMHC-Cre - littermates as controls (CTRL). We performed transthoracic M-mode echocardiographic analysis to examine the cardiac function of CKO and CTRL. Next, we subjected CKO and CTRL to I/R injury by using Langendorff-perfused mouse heart model. The heart was subjected to 30 minutes of global ischemia followed by 30 minutes of reperfusion. After the reperfusion, infarct area was determined with 1% triphenyltetrazolium chloride, and apoptotic cell death was detected by in situ TUNEL assay on heart sections. We exposed isolated adult cardiomyocytes from CKO and CTRL to various stimuli, such as Ca 2+ ionophore, H 2 O 2 and staurosporine, to examine the involvement of necrosis and apoptosis. Results: CKO and CTRL mice were born at the expected Mendelian ratio. There were no differences in cardiac function between CKO and CTRL. The functional recovery during reperfusion was significantly greater in CKO than in CTRL. CKO exhibited a significant decrease in the size of myocardial infarct. There were no significant differences in necrotic cell death induced by necrotic stimuli in vitro, while apoptotic cell death tended to decrease in CKO heart. Conclusions: These results suggest that iPLA2β exacerbates apoptotic cell death in I/R.