Role of calcium-independent phospholipase A(2)? in human pancreatic islet ?-cell apoptosis.
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ABSTRACT: Death of ?-cells due to apoptosis is an important contributor to ?-cell dysfunction in both type 1 and type 2 diabetes mellitus. Previously, we described participation of the Group VIA Ca(2+)-independent phospholipase A(2) (iPLA(2)?) in apoptosis of insulinoma cells due to ER stress. To examine whether islet ?-cells are similarly susceptible to ER stress and undergo iPLA(2)?-mediated apoptosis, we assessed the ER stress response in human pancreatic islets. Here, we report that the iPLA(2)? protein is expressed predominantly in the ?-cells of human islets and that thapsigargin-induced ER stress promotes ?-cell apoptosis, as reflected by increases in activated caspase-3 in the ?-cells. Furthermore, we demonstrate that ER stress is associated with increases in islet iPLA(2)? message, protein, and activity, iPLA(2)?-dependent induction of neutral sphingomyelinase and ceramide accumulation, and subsequent loss of mitochondrial membrane potential. We also observe that basal activated caspase-3 increases with age, raising the possibility that ?-cells in older human subjects have a greater susceptibility to undergo apoptotic cell death. These findings reveal for the first time expression of iPLA(2)? protein in human islet ?-cells and that induction of iPLA(2)? during ER stress contributes to human islet ?-cell apoptosis. We hypothesize that modulation of iPLA(2)? activity might reduce ?-cell apoptosis and this would be beneficial in delaying or preventing ?-cell dysfunction associated with diabetes.
SUBMITTER: Lei X
PROVIDER: S-EPMC3774083 | biostudies-literature | 2012 Dec
REPOSITORIES: biostudies-literature
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