193 - Antioxidant activity of calcium-independent phospholipase A2γ in brain mitochondria

Abstract

Mitochondrial calcium-independent phospholipase A2γ (iPLA2γ) belongs to a family of enzymes that participate in cellular signaling by simultaneously producing free fatty acids and lysophospholipids. We have shown previously that the activity of iPLA2γ is increased following the addition of oxidants, such as tert-butyl hydroperoxide (tBHP) or H2O2. We have also shown that iPLA2γ-liberated fatty acids induce H+ transport mediated by mitochondrial uncoupling proteins and mitochondrial adenine nucleotide translocase (ANT) in heart, lung and spleen mitochondria, leading to a decrease in the mitochondrial protonmotive force and subsequent decrease in mitochondrial superoxide production [1,2]. Here we tested the hypothesis that iPLA2γ serves similar antioxidant function in brain. Using brain mitochondria isolated from wild-type (WT) mice, we found that low micromolar concentrations of tBHP induced increase in respiration and a parallel decrease in mitochondrial superoxide and H2O2 production. These effects of tBHP were fully prevented by bovine serum albumin and inhibited by R-bromoenol lactone, a selective inhibitor of iPLA2γ, and were absent in brain mitochondria isolated from iPLA2γ-KO mice. Moreover, the tBHP-induced effects were fully inhibited by carboxyatractyloside, indicating the participation of ANT. In addition, we observed decrease in mRNA levels of selected antioxidant enzymes and increase in lipid peroxidation products in brain tissues homogenates of iPLA2γ-KO mice compared to the WT controls. Our results support the hypothesis of an antioxidant role of iPLA2γ in brain, consistent with iPLA2γ-dependent, ANT-mediated attenuation of mitochondrial superoxide production. Supported by LTAUSA17174