Abstract

Endoplasmic reticulum (ER) stress leads to beta-cell apoptosis that is suppressed by inhibition of the Group VIA Ca2+-independent phospholipase A2 (iPLA2beta), and our hypothesis is that iPLA2beta participates in ER stress-induced beta-cell apoptosis. In both type 1 and type 2 diabetes mellitus (DM), beta-cell apoptosis contributes to the loss of beta-cells and decreases in beta-cell function. It is therefore important to understand the mechanisms underlying beta-cell apoptosis if this process is to be prevented or delayed. The secretory nature of beta-cells endows them with a highly developed ER making them susceptible to ER stress. This process is suggested to promote beta-cell apoptosis and, in part, contribute to the decreases in beta-cell mass and beta-cell dysfunction in T2DM. The iPLA2beta catalyzes hydrolysis of arachidonic acid from membrane phospholipids and has a signal transduction role in beta-cells. We observed that ER stress-induced beta-cell apoptosis is related to the levels of iPLA2beta expression, is associated with perinuclear accumulation of a caspase-3-cleaved iPLA2beta isoform and increased generation of arachidonic acid and ceramides, and is suppressed by iPLA2beta inhibition. ER stress-induced apoptosis of pancreatic islets is also attenuated by inactivation of iPLA2beta and iPLA2beta -KO islets are less susceptible to ER stress. We propose to further examine the role of iPLA2a in a-cell apoptosis using pancreatic islets (wild type and iPLA2beta -KO) and INS-1 cells (parental, iPLA2beta over expressing, and iPLA2beta -KO) through the following Aims:
Aim 1 is to characterize participation of iPLA2beta in beta-cell apoptosis using stimuli that induce both a-cell apoptosis and ER stress.
Aim 2 is to examine the roles and subcellular localization of iPLA2beta isoforms in beta-cell apoptosis by expressing truncated and mutated iPLA2beta isoforms in a-cells.
Aim 3 is to identify beta-cell subcellular phospholipid substrates for iPLA2beta during ER stress using ESI/MS/MS protocols.
Aim 4 is to examine involvement of iPLA2beta phosphorylation and iPLA2beta -derived arachidonic acid in beta-cell apoptosis using LC/ESI/MS/MS and biochemical analyses.

  Funding Agency

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
1R01DK069455-01
Application #
6854097
Study Section
Cellular Aspects of Diabetes and Obesity Study Section (CADO)
Program Officer
Blondel, Olivier
Project Start
2004-09-30
Project End
2009-07-31
Budget Start
2004-09-30
Budget End
2005-07-31
Support Year
1
Fiscal Year
2004
Total Cost
$302,940
Indirect Cost

  Institution

Name
Washington University
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
068552207
City
Saint Louis
State
MO
Country
United States
Zip Code
63130

  Publications

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 :
Barbour, S E; Ramanadham, S (2017) Analyses of Calcium-Independent Phospholipase A2beta (iPLA2?) in Biological Systems. Methods Enzymol 583:119-141
Ashley, Jason W; Hancock, William D; Nelson, Alexander J et al. (2016) Polarization of Macrophages toward M2 Phenotype Is Favored by Reduction in iPLA2? (Group VIA Phospholipase A2). J Biol Chem 291:23268-23281
Barbour, Suzanne E; Nguyen, Phuong T; Park, Margaret et al. (2015) Group VIA Phospholipase A2 (iPLA2?) Modulates Bcl-x 5'-Splice Site Selection and Suppresses Anti-apoptotic Bcl-x(L) in ?-Cells. J Biol Chem 290:11021-31
Bone, Robert N; Gai, Ying; Magrioti, Victoria et al. (2015) Inhibition of Ca2+-independent phospholipase A2? (iPLA2?) ameliorates islet infiltration and incidence of diabetes in NOD mice. Diabetes 64:541-54
Ramanadham, Sasanka; Ali, Tomader; Ashley, Jason W et al. (2015) Calcium-independent phospholipases A2 and their roles in biological processes and diseases. J Lipid Res 56:1643-68
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
Arora, Daleep K; Machhadieh, Baker; Matti, Andrea et al. (2014) High glucose exposure promotes activation of protein phosphatase 2A in rodent islets and INS-1 832/13 ?-cells by increasing the posttranslational carboxylmethylation of its catalytic subunit. Endocrinology 155:380-91
Mitchell, Tanecia; Johnson, Michelle S; Ouyang, Xiaosen et al. (2013) Dysfunctional mitochondrial bioenergetics and oxidative stress in Akita(+/Ins2)-derived ?-cells. Am J Physiol Endocrinol Metab 305:E585-99
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

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