Genetic Ablation of Calcium-independent Phospholipase A2γ Leads to Alterations in Mitochondrial Lipid Metabolism and Function Resulting in a Deficient Mitochondrial Bioenergetic Phenotype

Abstract

Previously, we identified a novel calcium-independent phospholipase, designated calcium-independent phospholipase A 2 ␥ (iPLA 2 ␥), which possesses dual mitochondrial and peroxisomal subcellular localization signals. To identify the roles of iPLA 2 ␥ in cellular bioenergetics, we generated mice null for the iPLA 2 ␥ gene by eliminating the active site of the enzyme through homologous recombination. Mice null for iPLA 2 ␥ display multiple bioenergetic dysfunctional phenotypes, including 1) growth retardation, 2) cold intolerance, 3) reduced exercise endurance, 4) greatly increased mortality from cardiac stress after transverse aortic constriction, 5) abnormal mitochondrial function with a 65% decrease in ascorbate-induced Complex IVmediated oxygen consumption, and 6) a reduction in myocardial cardiolipin content accompanied by an altered cardiolipin molecular species composition. We conclude that iPLA 2 ␥ is essential for maintaining efficient bioenergetic mitochondrial function through tailoring mitochondrial membrane lipid metabolism and composition.Mitochondria transduce chemical energy from multiple dietary substrates into ATP and heat and are important participants in cellular lipid metabolism and signaling (1, 2). Through the precisely regulated partitioning of energy derived from substrates between ATP synthesis and heat production, a finely tuned dynamic balance is maintained to promote organism survival. In addition, excess energy derived from substrates, not immediately needed to fulfill chemical or thermodynamic demands, is directed into the production of lipid synthetic intermediates for energy storage (e.g. mitochondrial synthesis of lysophosphatidic acid, a precursor of triglycerides). Moreover, mitochondria generate diverse chemical signals that reflect the bioenergetic status of the cell (e.g. NO and cytochrome c) and thus integrate multiple energetic, metabolic, and signaling cascades (1-5).Mitochondrial phospholipases are important participants in the regulation of mitochondrial function and signaling (6 -11). Mitochondrial phospholipases catalyze the production of nonesterified fatty acids that regulate UCP function, release lipid second messengers, such as 2-arachidonoyl lysophosphatidylcholine (LPC), 2 and modulate membrane molecular dynamics (12). Maladaptive activation of phospholipases has deleterious metabolic effects in many systems, and previous studies have implicated calcium-independent phospholipases A 2 (iPLA 2 s) as the enzymic mediators of membrane dysfunction in diabetic cardiomyopathy (13-16). Metabolic flexibility is dependent on the efficient coordinated transitions of substrate flux that occur during alterations in energy sources (e.g. glucose versus fatty acid) or energy demand (e.g. exercise). Obesity and type II diabetes are thought to result from disruption of these transitions (17). Diabetic cardiomyopathy is characterized by altered lipid metabolism (i.e. greatly increased utilization of fatty acids) that results in changes in the chemical composition of cardiac membran...

Genetic Ablation of Calcium-independent Phospholipase A2γ Leads to Alterations in Hippocampal Cardiolipin Content and Molecular Species Distribution, Mitochondrial Degeneration, Autophagy, and Cognitive Dysfunction

“…The observed increase in hippocampal cardiolipin content and increases in shorter aliphatic chain molecular species are likely direct consequences of decreased hydrolysis and remodeling of nascent cardiolipin, which appears to be a direct result of iPLA 2 ␥ loss of function. We point out that myocardium from iPLA 2 ␥ Ϫ/Ϫ mice contains reduced cardiolipin levels containing an increased relative proportion of molecular species with arachidonic and docosahexenoic acids (33). This is most likely due to the profound differences in brain and heart cardiolipin-remodeling enzymes, including alterations in transacylation and acyl transferase activity.…”

“…Generation of the iPLA 2 ␥ Ϫ/Ϫ Mouse-The iPLA 2 ␥ Ϫ/Ϫ mice used in this study were generated as previously described (33). Interbreeding of heterozygous offspring was used to generate homozygous knockouts and wild-type (WT) littermates used in all studies.…”

“…Cardiac myocyte-specific overexpression of iPLA 2 ␥ in mice results in alterations in mitochondrial ultrastructure that is accompanied by organelle dysfunction (32). Genetic ablation of iPLA 2 ␥ resulted in the generation of viable progeny that demonstrated decreased growth and cold intolerance and possessed defects in ascorbate-stimulated Complex IV function (33).…”

Les protéines à domaine patatine

“…Elle s'avère capable d'hydrolyser les phospholipides saturés ou mono-insaturés, qu'ils soient en position sn-1 ou bien sn-2 [13]. L'importance de cette enzyme dans l'homéostasie phospholipidique des cellules cardiaques ainsi que dans la fonction mitochondriale a été mise en évidence par des études de perte et de gain de fonction chez la souris [21,22]. Notamment, le contenu en cardiolipines (phospholipides spécifiques des membranes mitochondriales des cellules du myocarde) s'avère très perturbé chez les souris knock-out pour l'iPLA 2 γ entraînant des défauts de fonctionnement de la chaîne respiratoire, ce qui indique son implication dans le remodelage des membranes phospholipidiques mitochondriales [21].…”

“…L'importance de cette enzyme dans l'homéostasie phospholipidique des cellules cardiaques ainsi que dans la fonction mitochondriale a été mise en évidence par des études de perte et de gain de fonction chez la souris [21,22]. Notamment, le contenu en cardiolipines (phospholipides spécifiques des membranes mitochondriales des cellules du myocarde) s'avère très perturbé chez les souris knock-out pour l'iPLA 2 γ entraînant des défauts de fonctionnement de la chaîne respiratoire, ce qui indique son implication dans le remodelage des membranes phospholipidiques mitochondriales [21]. La neuropathy target esterase (NTE ou PNPLA6) est majoritairement exprimée dans le système nerveux central chez la souris [23] où elle est localisée dans le réticulum endoplasmique et l'appareil de Golgi des cellules [24].…”