Glucose-induced insulin secretion is defective in type II diabetes mellitus, and the molecular events coupling glucose recognition to insulin secretion by pancreatic islets beta-cells are incompletely understood. Glucose induces hydrolysis of islet membrane phospholipids and accumulation of nonesterified arachidonic acid and its 12- lipoxygenase products by a process that requires glucose metabolism and is mediated in part by an ATP-stimulated, Ca2+-independent phospholipase A2 enzyme (ASCl-PLA2), which may be a component of the beta-cell fuel sensor. ASCl-PLA2 blockade with a specific suicide substrate suppresses arachidonate release, the rise in beta-cell [(Ca2+], and insulin secretion induced by glucose. Further studies of the role of this enzyme in beta-cells will include: A.) Characterizing beta-cell ASCl-PLA2 activity in islets from 3 species and insulinoma cells. Activation by ATP, modulation of this response (by factors including ADP and glycolytic intermediates which influence ASCl-PLA2 chromatographic behavior), ASCl- PLA2 membrane translocation, and ASCl-PLA2 expression in models of perturbed islet function will be examined. B.) Isolation of beta-cell ASCl-PLA2 and its distinct catalytic and regulatory proteins will be achieved by ATP-affinity chromatography, gel filtration, and FPLC. Relationships between catalytic and regulatory proteins from islets and insulinoma cells will be studied by cross-complementation. ASCl-PLA2 cellular and subcellular distribution and changes enzyme mass in perturbed-islet models will be studied with antibodies to the purified proteins. C.) Molecular characterization of islet phospholipids by HPLC and GC/MS will determine the islet content of plasmalogen substrates preferred by ASCl-PLA2; the phospholipid composition of islet subcellular membranes; the influence of insulin secretagogues on phospholipid arachidonate mass; and the depletion of critical beta-cell arachdionate pools in glucose-desensitized islets. D.) The influence of arachidonate on Ca2+ entry into beta-cells will be examined in studies of the effects of arachidonate on beta-cell voltage-operated Ca2+ channels (VOCC) and of effects of arachidonate and omega3 polyunsaturated fatty acids on the rise in beta-cell [Ca2+] induced by glucose and depolarization and the participation of omega-conotoxin-sensitive VOCC in these events. The major islet arachidonate-metabolizing enzyme is a 12-lipoxygenase (12-LO) selectively expressed by beta-cells which is not found in other islet cells or in a pancreatic acini, and 12-LO blockade suppresses insulin secretion. E.) The role of 12-LO in beta-cells will be studied by examining: 12-LO membrane tran-location in glucose-stimulated islets; islet conversion of the primary 12-LO product 12-HPETE and of linoleate to active products; effects of 12-LO products on beta-cell membrane potential and K+ permeability; and esterification of 12-LO products in islet plasma membrane and secretory granule phospholipids.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Method to Extend Research in Time (MERIT) Award (R37)
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Metabolism Study Section (MET)
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Washington University
Schools of Medicine
Saint Louis
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Turk, John; White, Tayleur D; Nelson, Alexander J et al. (2018) iPLA2? and its role in male fertility, neurological disorders, metabolic disorders, and inflammation. Biochim Biophys Acta Mol Cell Biol Lipids :
Thimgan, Matthew S; Seugnet, Laurent; Turk, John et al. (2015) Identification of genes associated with resilience/vulnerability to sleep deprivation and starvation in Drosophila. Sleep 38:801-14
Tan, Chunyan; Day, Robert; Bao, Shunzhong et al. (2014) Group VIA phospholipase A2 mediates enhanced macrophage migration in diabetes mellitus by increasing expression of nicotinamide adenine dinucleotide phosphate oxidase 4. Arterioscler Thromb Vasc Biol 34:768-78
Blanchard, Helene; Taha, Ameer Y; Cheon, Yewon et al. (2014) iPLA2? knockout mouse, a genetic model for progressive human motor disorders, develops age-related neuropathology. Neurochem Res 39:1522-32
Lei, Xiaoyong; Bone, Robert N; Ali, Tomader et al. (2014) Evidence of contribution of iPLA2?-mediated events during islet ?-cell apoptosis due to proinflammatory cytokines suggests a role for iPLA2? in T1D development. Endocrinology 155:3352-64
Song, Haowei; Wohltmann, Mary; Tan, Min et al. (2014) Group VIA phospholipase A2 mitigates palmitate-induced ?-cell mitochondrial injury and apoptosis. J Biol Chem 289:14194-210
Lei, Xiaoyong; Bone, Robert N; Ali, Tomader et al. (2013) Genetic modulation of islet ?-cell iPLA?? expression provides evidence for its impact on ?-cell apoptosis and autophagy. Islets 5:29-44
Tatituri, Raju V V; Watts, Gerald F M; Bhowruth, Veemal et al. (2013) Recognition of microbial and mammalian phospholipid antigens by NKT cells with diverse TCRs. Proc Natl Acad Sci U S A 110:1827-32
Tatituri, Raju Venkata Veera; Brenner, Michael B; Turk, John et al. (2012) Structural elucidation of diglycosyl diacylglycerol and monoglycosyl diacylglycerol from Streptococcus pneumoniae by multiple-stage linear ion-trap mass spectrometry with electrospray ionization. J Mass Spectrom 47:115-23
Lodhi, Irfan J; Yin, Li; Jensen-Urstad, Anne P L et al. (2012) Inhibiting adipose tissue lipogenesis reprograms thermogenesis and PPAR? activation to decrease diet-induced obesity. Cell Metab 16:189-201

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