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Calcium-independent phospholipases (iPLA2s) are a family of enzymes participating in cellular signaling by simultaneously producing free fatty acids and lysophospholipids. Phospholipase iPLA2γ (PNPLA8) is targeted to mitochondria and has been shown to augment GPR40-dependent insulin secretion in β-cell model insulinoma INS1-E cells [1]. Here, we investigated the participation of iPLA2γ on the blood glucose homeostasis and pancreatic β-cell insulin secretion using iPLA2γ-KO mice. Wild type (wt) controls and iPLA2γ-KO mice showed similar cholesterol, triglyceride and basal glucose levels after 6 hours of starving. However, the uric acid levels were increased in iPLA2γ-KOmice. Following the intraperitoneal injection of Intralipid, iPLA2γ-KO mice exhibited a prolonged hyperglycemic state compared to wt mice. Glucose-stimulated insulin release in isolated pancreatic islets (PI) was moderately decreased in iPLA2γ-KO PI. Physiologically relevant concentrations of palmitic acid stimulated insulin secretion in PI from wt mice, and this stimulation was absent in iPLA2γ-KO PI. In conclusion, the data are consistent with iPLA2γ ablation causing impairment of GPR40-dependent insulin secretion, resulting in prolonged glycemia. Thus, our results support the role of iPLA2γ in regulating insulin secretion in vivo.

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