Mitochondrial dysfunction and reduced prostaglandin synthesis in skeletal muscle of Group VIB Ca2+-independent phospholipase A2γ-deficient mice

Abstract

Supplementary key words cardiolipin • mitochondria • muscle • phospholipidsPhospholipase A 2 (PLA 2 ) enzymes catalyze the cleavage of the sn -2 ester bond of glycerophospholipids to yield free fatty acids and lysophospholipids, thereby playing critical roles in cellular lipid metabolisms linked to energy storage, membrane remodeling, and lipid mediator signaling. In the membrane remodeling reaction, fatty acyl groups are fi rst removed (deacylated) by PLA 2 and then replaced (reacylated) with different fatty acyl groups by acyltransferases, which allow membrane phospholipids to acquire a variation of molecular species. In the signaling reaction, polyunsaturated fatty acids [typically arachidonic acid (AA)] and lysophospholipids released by the action of PLA 2 s are metabolized to various lipid mediators, such as prostaglandins (PG), leukotrienes, and platelet-activating factor, which exert a variety of biological actions through their cognate receptors. Abstract Group VIB Ca2+ -independent phospholipase A 2 ␥ (iPLA 2 ␥ ) is a membrane-bound iPLA 2 enzyme with unique features, such as the utilization of distinct translation initiation sites and the presence of mitochondrial and peroxisomal localization signals. Here we investigated the physiological functions of iPLA 2 ␥ by disrupting its gene in mice. iPLA 2 ␥ -knockout (KO) mice were born with an expected Mendelian ratio and appeared normal and healthy at the age of one month but began to show growth retardation from the age of two months as well as kyphosis and significant muscle weakness at the age of four months. Electron microscopy revealed swelling and reduced numbers of mitochondria and atrophy of myofi laments in iPLA 2 ␥ -KO skeletal muscles. Increased lipid peroxidation and the induction of several oxidative stress-related genes were also found in the iPLA 2 ␥ -KO muscles. These results provide evidence that impairment of iPLA 2 ␥ causes mitochondrial dysfunction and increased oxidative stress, leading to the loss of skeletal muscle structure and function. We further found that the compositions of cardiolipin and other phospholipid subclasses were altered and that the levels of myoprotective prostanoids were reduced in iPLA 2 ␥ -KO skeletal muscle. Thus, in addition to maintenance of homeostasis of the mitochondrial membrane, iPLA 2 ␥ may contribute to modulation of lipid mediator production in vivo. -Yoda, E., K. Hachisu, Y. Taketomi, K. Yoshida, M. Nakamura, K. Ikeda, R. Taguchi, Y. Nakatani, H. Kuwata, M. Murakami, I. Kudo, and S. Hara. Mitochondrial dysfunction and reduced prostaglandin synthesis in skeletal muscle of Group VIB Ca 2+ -independent phospholipase A2 ␥ -defi cient mice. J. Lipid Res.

Genetic Ablation of Calcium-independent Phospholipase A2γ Induces Glomerular Injury in Mice

“…Excretion-General phenotypic features of mice null for iPLA 2 ␥ were described previously (7,11). In keeping with the earlier report, modest growth retardation was visible in KO mice after 2 months of age.…”

“…Our results in podocytes are in keeping with previous studies, where deletion of iPLA 2 ␥ in mice resulted in mitochondrial disruption. For example, deletion of iPLA 2 ␥ induced mitochondrial dysfunction in the heart, skeletal muscle, liver, and brain (7,8,10,11). iPLA 2 ␥ KO mice displayed cold intolerance, a defect in mitochondrial cytochrome oxidase, and multiple bioenergetic dysfunctional phenotypes at 4 -6 months of age (7).…”

“…In other cells, such as primary cultures of rabbit renal proximal tubules cells, knockdown of iPLA 2 ␥ expression increased lipid peroxidation and impaired mitochondrial function (22). Likewise, knockdown of iPLA 2 ␥ in C2C12 myoblasts also caused an elevation of lipid peroxidation and reduction of ATP synthesis (11). Thus, the function of iPLA 2 ␥ can be cytoprotective, and depending on the cellular context, it may involve ER stress or removal of peroxidized phospholipid from the mitochondrial membrane, thereby preserving membrane integrity.…”

“…Taken together, these reports confirm an obligatory role for iPLA 2 ␥ in mitochondrial lipid metabolism and membrane structure, perturbation of which may profoundly influence fatty acid ␤-oxidation, oxygen consumption, energy expenditure, and, thus, tissue homeostasis. Despite the recent advances in studying the pathophysiological role of iPLA 2 ␥ in the brain, liver, heart, and skeletal muscles (7,8,10,11), the pathophysiological roles of iPLA 2 ␥ in the kidney are poorly understood.…”

Cardiac Myocyte-specific Knock-out of Calcium-independent Phospholipase A2γ (iPLA2γ) Decreases Oxidized Fatty Acids during Ischemia/Reperfusion and Reduces Infarct Size

“…Mass Spectrometric Analysis of Myocardial Eicosanoids, Docosanoids, and Oxidized Linoleic Acids-Previous studies have demonstrated the important roles of iPLA 2 ␥ in releasing polyunsaturated fatty acids from mitochondria that are subsequently oxidized by a wide variety of downstream oxygenases (32)(33)(34)(35). To gain access to the extremely low abundance regime necessary for accurate identification and quantification of oxidized fatty acids in myocardium, we used charge-switch derivatization with multiple reaction monitoring (MRM) in conjunction with high mass accuracy analysis of signature product ions from diagnostic transitions (36).…”