Diabetes mellitus is the most prevalent metabolic disease, and -cell apoptosis contributes to decreases in -cell mass and function during the evolution of diabetes. However, the mechanism(s) that contribute to -cell apoptosis are not well-understood. Our hypothesis in the 1st grant period was that the Group VIA Ca2+- independent phospholipase A2 (iPLA2?) participates in ER stress-induced -cell apoptosis. We find that (a) ER stress induces iPLA2? activation, ceramide generation via neutral sphingomyelinase (NSMase), and -cell apoptosis, (b) these outcomes are suppressed by inhibition of iPLA2 or NSmase, (c) iPLA2 -null islets are less and iPLA2 -tansgenic (Tg) islets more sensitive to ER stress-induced apoptosis;that ER stress (d) increases iPLA2 protein/activity in the ER and mitochondria, and (e) activates the mitochondrial apoptotic pathway via the iPLA2 -ceramide axis;and (f) ER stress-prone Akita -cells and islets from pre-diabetic NOD mice express higher levels of iPLA2 than WT cells and islets, (g) STZ-induced hyperglycemia is accelerated in iPLA2 -Tg mice, and (h) cytokines induce ceramide generation, loss in ?, and apoptosis in islet-cells that are all suppressed by iPLA2 inactivation. During the 2nd grant period, we propose to examine the mechanism of involvement of iPLA2 and iPLA2 -derived lipid mediators in -cell apoptosis under the following Aims:
Aim 1 will examine iPLA2 activation and lipid changes in -cells undergoing apoptosis. Hyperglycemia and cytokines promote -cell apoptosis, in part, by inducing ER stress and the dependence of this process on iPLA2 will be assessed.
Aim 2 will examine the mechanism of iPLA2 and ceramide-generating pathway induction. The roles of lipid mediators, SREBPs, ROS, and GSH on iPLA2 and NSMase expression and the affects of mutating the lipase sequence in iPLA2 on ceramide generation will be examined.
Aim 3 will examine the role of iPLA2 in ER-mitochondria crosstalk. The affects of genetic modulation of iPLA2 expression, ROS and GSH levels, NSMase expression, mutations in iPLA2 , and organelle-specific iPLA2 expression on activation of the mitochondrial apoptotic pathway will be examined.
Aim 4 will examine if in vivo modulation of iPLA2 expression alters islet -cell sensitivity to ER stress. iPLA2 -null mice will be crossed with Akita mice and iPLA2 -Tg mice with CHOP-null mice and the development of ER stress monitored.
Aim 5 will determine if iPLA2 contributes to -cell apoptosis during the evolution of autoimmune DM. The dependence of cytokine-induced -cell apoptosis on iPLA2 and nitric oxide pathway and of STZ-induced -cell apoptosis and hyperglycemia on iPLA2 expression will be determined. Apoptosis, flow cytometry, immunoblotting, real time-PCR, enzymatic activity, confocal microscopy, molecular biology, and mass spectrometry protocols will be utilized in these studies.

Public Health Relevance

-cell apoptosis contributes to loss in -cell mass and function during the evolution of diabetes mellitus and is therefore important to understand the mechanisms underlying -cell apoptosis if this process is to be prevented or delayed. Our findings of iPLA2 participation in this process and of stimuli, that contribute to the development of diabetes, activating iPLA2 raises the possibility that iPLA2 contributes to -cell apoptosis during the evolution of diabetes mellitus. Our findings will reveal factors that adversely affect -cell health and identify targets for future therapeutic interventions to prevent -cell death.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK069455-09
Application #
8248593
Study Section
Cellular Aspects of Diabetes and Obesity Study Section (CADO)
Program Officer
Silva, Corinne M
Project Start
2004-09-30
Project End
2014-03-31
Budget Start
2012-04-01
Budget End
2013-03-31
Support Year
9
Fiscal Year
2012
Total Cost
$289,346
Indirect Cost
$91,840
Name
University of Alabama Birmingham
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
063690705
City
Birmingham
State
AL
Country
United States
Zip Code
35294
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
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
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
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

Showing the most recent 10 out of 21 publications