Putative roles of Ca2+-independent phospholipase A(2) in respiratory chain-associated ROS production in brain mitochondria: influence of docosahexaenoic acid and bromoenol lactone

摘要

Ca2+-independent phospholipase A(2) (iPLA(2)) is hypothesized to control mitochondrial reactive oxygen species (ROS) generation. Here, we modulated the influence of iPLA(2)-induced liberation of non-esterified free fatty acids on ROS generation associated with the electron transport chain. We demonstrate enzymatic activity of membrane-associated iPLA(2) in native, energized rat brain mitochondria (RBM). Theoretically, enhanced liberation of free fatty acids by iPLA(2) modulates mitochondrial ROS generation, either attenuating the reversed electron transport (RET) or deregulating the forward electron transport of electron transport chain. For mimicking such conditions, we probed the effect of docosahexaenoic acid (DHA), a major iPLA(2) product on ROS generation. We demonstrate that the adenine nucleotide translocase partly mediates DHA-induced uncoupling, and that low micromolar DHA concentrations diminish RET-dependent ROS generation. Uncoupling proteins have no effect, but the adenine nucleotide translocase inhibitor carboxyatractyloside attenuates DHA-linked uncoupling effect on RET-dependent ROS generation. Under physiological conditions of forward electron transport, low micromolar DHA stimulates ROS generation. Finally, exposure of RBM to the iPLA(2) inhibitor bromoenol lactone (BEL) enhanced ROS generation. BEL diminished RBM glutathione content. BEL-treated RBM exhibits reduced Ca2+ retention capacity and partial depolarization. Thus, we rebut the view that iPLA(2) attenuates oxidative stress in brain mitochondria. However, the iPLA(2) inhibitor BEL has detrimental activities on energy-dependent mitochondrial functionsThe Ca2+-independent phospholipase A(2) (iPLA(2)), a FFA (free fatty acids)-generating membrane-attached mitochondrial phospholipase, is potential to regulate ROS (reactive oxygen species) generation by mitochondria. FFA can either decrease reversed electron transport (RET)-linked or enhance forward electron transport (FET)-linked ROS generation. In the physiological mode of FET, iPLA(2) activity increases ROS generation. The iPLA(2) inhibitor BEL exerts detrimental effects on energy-dependent mitochondrial functions.