Spontaneous development of endoplasmic reticulum stress that can lead to diabetes mellitus is associated with higher calcium-independent phospholipase A2 expression: A role for regulation by SREBP-1

Academic Article

Abstract

  • Our recent studies indicate that endoplasmic reticulum (ER) stress causes INS-1 cell apoptosis by a Ca2+-independent phospholipase A 2 (iPLA2β)-mediated mechanism that promotes ceramide generation via sphingomyelin hydrolysis and subsequent activation of the intrinsic pathway. To elucidate the association between iPLA2β and ER stress, we compared β-cell lines generated from wild type (WT) and Akita mice. The Akita mouse is a spontaneous model of ER stress that develops hyperglycemia/diabetes due to ER stress-induced β-cell apoptosis. Consistent with a predisposition to developing ER stress, basal phosphorylated PERK and activated caspase-3 are higher in the Akita cells than WT cells. Interestingly, basal iPLA2β, mature SREBP-1 (mSREBP-1), phosphorylated Akt, and neutral sphingomyelinase (NSMase) are higher, relative abundances of sphingomyelins are lower, and mitochondrial membrane potential (ΔΨ) is compromised in Akita cells, in comparison with WT cells. Exposure to thapsigargin accelerates ΔΨ loss and apoptosis of Akita cells and is associated with increases in iPLA2β, mSREBP-1, and NSMase in both WT and Akita cells. Transfection of Akita cells with iPLA 2β small interfering RNA, however, suppresses NSMase message, ΔΨ loss, and apoptosis. The iPLA2β gene contains a sterol-regulatory element, and transfection with a dominant negative SREBP-1 reduces basal mSREBP-1 and iPLA2β in the Akita cells and suppresses increases in mSREBP-1 and iPLA2β due to thapsigargin. These findings suggest that ER stress leads to generation of mSREBP-1, which can bind to the sterol-regulatory element in the iPLA2β gene to promote its transcription. Consistent with this, SREBP-1, iPLA 2β, and NSMase messages in Akita mouse islets are higher than in WT islets. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.
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    Digital Object Identifier (doi)

    Author List

  • Lei X; Zhang S; Barbour SE; Bohrer A; Ford EL; Koizumi A; Papa FR; Ramanadham S
  • Start Page

  • 6693
  • End Page

  • 6705
  • Volume

  • 285
  • Issue

  • 9