Antioxidant Role and Cardiolipin Remodeling by Redox-Activated Mitochondrial Ca 2+ -Independent Phospholipase A 2 γ in the Brain.

Mitochondrial Ca 2+ -independent phospholipase A 2 γ (iPLA 2 γ/PNPLA8) was previously shown to be directly activated by H 2 O 2 and release free fatty acids (FAs) for FA-dependent H + transport mediated by the adenine nucleotide translocase (ANT) or uncoupling protein 2 (UCP2). The resulting mild mitochondrial uncoupling and consequent partial attenuation of mitochondrial superoxide production lead to an antioxidant effect. However, the antioxidant role of iPLA 2 γ in the brain is not completely understood. Here, using wild-type and iPLA 2 γ-KO mice, we demonstrate the ability of tert -butylhydroperoxide (TBHP) to activate iPLA 2 γ in isolated brain mitochondria, with consequent liberation of FAs and lysophospholipids. The liberated FA caused an increase in respiratory rate, which was fully inhibited by carboxyatractyloside (CATR), a specific inhibitor of ANT. Employing detailed lipidomic analysis, we also demonstrate a typical cleavage pattern for TBHP-activated iPLA 2 γ, reflecting cleavage of glycerophospholipids from both sn -1 and sn -2 positions releasing saturated FAs, monoenoic FAs, and predominant polyunsaturated FAs. The acute antioxidant role of iPLA 2 γ-released FAs is supported by monitoring both intramitochondrial superoxide and extramitochondrial H 2 O 2 release. We also show that iPLA 2 γ-KO mice were more sensitive to stimulation by pro-inflammatory lipopolysaccharide, as reflected by the concomitant increase in protein carbonyls in the brain and pro-inflammatory IL-6 release in the serum. These data support the antioxidant and anti-inflammatory role of iPLA 2 γ in vivo. Our data also reveal a substantial decrease of several high molecular weight cardiolipin (CL) species and accumulation of low molecular weight CL species in brain mitochondria of iPLA 2 γ-KO mice. Collectively, our results support a key role of iPLA 2 γ in the remodeling of lower molecular weight immature cardiolipins with predominantly saturated acyl chains to high molecular weight mature cardiolipins with highly unsaturated PUFA acyl chains, typical for the brain.