title: Proinflammatory cytokines activate the intrinsic apoptotic pathway in beta-cells.
abstract: OBJECTIVE
  Proinflammatory cytokines are cytotoxic to beta-cells and have been implicated in the pathogenesis of type 1 diabetes and islet graft failure. The importance of the intrinsic mitochondrial apoptotic pathway in cytokine-induced beta-cell death is unclear. Here, cytokine activation of the intrinsic apoptotic pathway and the role of the two proapoptotic Bcl-2 proteins, Bad and Bax, were examined in beta-cells.
  
  
  METHODS
  Human and rat islets and INS-1 cells were exposed to a combination of proinflammatory cytokines (interleukin-1beta, interferon-gamma, and/or tumor necrosis factor-alpha). Activation of Bad was determined by Ser136 dephosphorylation, mitochondrial stress by changes in mitochondrial metabolic activity and cytochrome c release, downstream apoptotic signaling by activation of caspase-9 and -3, and DNA fragmentation. The inhibitors FK506 and V5 were used to investigate the role of Bad and Bax activation, respectively.
  
  
  RESULTS
  We found that proinflammatory cytokines induced calcineurin-dependent dephosphorylation of Bad Ser136, mitochondrial stress, cytochrome c release, activation of caspase-9 and -3, and DNA fragmentation. Inhibition of Bad Ser136 dephosphorylation or Bax was found to inhibit cytokine-induced intrinsic proapoptotic signaling.
  
  
  CONCLUSIONS
  Our findings demonstrate that the intrinsic mitochondrial apoptotic pathway contributes significantly to cytokine-induced beta-cell death and suggest a functional role of calcineurin-mediated Bad Ser136 dephosphorylation and Bax activity in cytokine-induced apoptosis.
authors.affiliation: Department of Translational Diabetology, Steno Diabetes Center, Gentofte, Denmark.
authors.forename: Lars G
authors.initials: LG
authors.lastname: Grunnet
authors.forename: Reid
authors.initials: R
authors.lastname: Aikin
authors.forename: Morten F
authors.initials: MF
authors.lastname: Tonnesen
authors.forename: Steven
authors.initials: S
authors.lastname: Paraskevas
authors.forename: Lykke
authors.initials: L
authors.lastname: Blaabjerg
authors.forename: Joachim
authors.initials: J
authors.lastname: Størling
authors.forename: Lawrence
authors.initials: L
authors.lastname: Rosenberg
authors.forename: Nils
authors.initials: N
authors.lastname: Billestrup
authors.forename: Dusica
authors.initials: D
authors.lastname: Maysinger
authors.forename: Thomas
authors.initials: T
authors.lastname: Mandrup-Poulsen
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002102:Cadaver; D053453:Caspase 9 / Q000378:metabolism; D016923:Cell Death; D016207:Cytokines / Q000494:pharmacology*; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D007371:Interferon-gamma / Q000494:pharmacology*; D053583:Interleukin-1beta / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D014019:Tissue Donors; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D016207:Cytokines; D053583:Interleukin-1beta; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; D053453:Caspase 9