Oral Presentation The Annual Scientific Meeting of the Endocrine Society of Australia and the Society for Reproductive Biology 2013

High concentrations of glucose induce ER and oxidative stress and activate the intrinsic apoptosis pathway but not the NLRP3 inflammasome in pancreatic islets. (#168)

Jibran Wali 1 2 , Lorraine Elkerbout 1 , Thomas Kay 1 , Seth Masters 3 , Helen Thomas 1 2
  1. St Vincent's Institute, Melbourne, Victoria, Australia
  2. Department of Medicine, University of Melbourne, Melbourne, Victoria, Australia
  3. Walter and Eliza Hall Institute, Melbourne, Victoria, Australia
Type-2 diabetes is caused by insulin resistance, together with apoptosis of beta-cells. High glucose concentrations induce apoptosis of islet cells in vitro, requiring the pro-apoptotic BH3-only proteins Bim and Puma. Glucose-induced reactive oxygen species may also activate the NLRP3-inflammasome leading to IL-1b production. We studied apoptosis activation in response to ER and oxidative stress. Culture of islets in 33.3 mM glucose or 50 mM ribose (a reducing sugar similar to glucose) increased CHOP gene and protein expression, JNK phosphorylation and XBP1 splicing but did not increase ER chaperones (BiP, Pdia4, P58) in wild type (B6) islets, indicating activation of pro-apoptotic ER stress signaling. CHOP deficiency partially protected islets from glucotoxicity. The ER stress inhibitor TUDCA prevented ribose-induced upregulation of CHOP, ATF4 and Puma mRNA. Inhibition of ER stress partially protected B6 islets, and further protected Bim-/- or Puma-/- islets from glucotoxicity. Bim-/- or Puma-/- islets were partially protected from thapsigargin and tunicamycin. These data indicate that ER stress is the major pathway activated by glucotoxicity, and Bim and Puma are downstream of ER stress. The antioxidant NAC partially protected B6 islets from glucose-induced apoptosis, but no additional protection was seen in Bim-/- or Puma-/- islets. Islets deficient in either Bim or Puma were not protected from killing induced by the mitochondrial ROS donor rotenone, but Bim/Puma double knockout islets were partially protected, indicating that both Bim and Puma are required for apoptosis activated by mitochondrial oxidative stress. Deficiency of NLRP3, caspase1 or IL-1 receptors did not protect islets from ribose, thapsigargin or rotenonetoxicity, suggesting that there is no role for NLRP3 inflammasome activation. Our data suggest that high concentrations of glucose induce ER stress and mitochondrial ROS resulting in intrinsic pathway apoptosis. We observed no role for the NLRP3 inflammasome in glucose induced ER or oxidative stress in pancreatic islets.