Increased oxygen radical formation and mitochondrial dysfunction mediate beta cell apoptosis under conditions of AMP-activated protein kinase stimulation.
AMP-activated protein kinase influences cellular metabolism, glucose-regulated gene expression, and insulin secretion of pancreatic beta cells. Its sustained activation by culture at low glucose concentrations or in the presence of 5-aminoimidazole-4-carboxamide riboside (AICAR) was shown to trigger apoptosis in beta cells. This study shows that both low glucose- and AICAR-induced apoptosis are associated with increased formation of mitochondrial superoxide-derived radicals and decreased mitochondrial activity. Mitochondrial dysfunction was reflected by an increased oxidized state of the mitochondrial flavins (FMN/FAD) but not of NAD(P)H. It was accompanied by suppression of glucose oxidation and glucose-induced insulin secretion, while palmitate oxidation appeared unaffected. When the cellular accumulation of superoxide-derived radicals was quenched by the ROS scavengers vitamin E, N-acetylcysteine, or the SOD-mimetic compound MnTBAP, apoptosis was significantly inhibited. Both low glucose and AICAR also elevated the expression of BH3-domain-only Bcl-2 antagonists, and induced caspase-3 activation, causing caspase-dependent truncation of Bcl-2. Overexpression of recombinant human Bcl-2 prevented caspase-3 activation, endogenous Bcl-2 processing, and apoptosis, but did not attenuate oxygen radical formation, AMPK activation, or JNK phosphorylation. We conclude that apoptosis by prolonged AMPK activation in beta cells results from enhanced production of mitochondria-derived oxygen radicals and onset of the intrinsic mitochondrial apoptosis pathway, followed by caspase activation and Bcl-2 cleavage which may amplify the death signal.
Cai
Ying
Y
Martens
Geert A
GA
Hinke
Simon A
SA
Heimberg
Harry
H
Pipeleers
Daniel
D
Van de Casteele
Mark
M
D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism; D002460:Cell Line; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D051379:Mice; D008928:Mitochondria / Q000378:metabolism* / Q000473:pathology; D009097:Multienzyme Complexes / Q000378:metabolism*; D010168:Palmitates / Q000494:pharmacology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012265:Ribonucleotides / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007004:Hypoglycemic Agents; D007328:Insulin; D009097:Multienzyme Complexes; D010168:Palmitates; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D012265:Ribonucleotides; D000620:Aminoimidazole Carboxamide; D006861:Hydrogen Peroxide; D017346:Protein Serine-Threonine Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D055372:AMP-Activated Protein Kinases; C505409:Casp3 protein, mouse; C505410:Casp3 protein, rat; D053148:Caspase 3; C031143:AICA ribonucleotide; D005947:Glucose