Increased O-glycosylation of insulin signaling proteins results in their impaired activation and enhanced susceptibility to apoptosis in pancreatic beta-cells.
Because adverse effects of glucose were attributed to its increased routing through the hexosamine pathway (HBP), we inquired whether HBP activation affects pancreatic beta-cell survival. Exposure of human islets to high glucose resulted in increased apoptosis of beta-cells upon serum deprivation that was reversed by azaserine. Also, glucosamine, a direct precursor of the downstream product of the HBP, increased human beta-cells apoptosis upon serum deprivation, which was reversed by benzyl-2-acetamido-2-deoxy-alpha-d-galactopyranoside (BADGP), an inhibitor of protein O-glycosylation. These results were reproduced in RIN rat beta-cells. Glucosamine treatment resulted in inhibition of tyrosine-phosphorylation of the insulin receptor (IR), IRS-1, and IRS-2, which was associated with increased O-glycosylation. These changes caused impaired activation of the PI 3-kinase/Akt survival signaling that resulted in reduced GSK-3 and FOXO1a inactivation. BADGP reversed the glucosamine-induced reduction in insulin-stimulated phosphorylation of IR, IRS-1, IRS-2, Akt, GSK-3, and FOXO1a. Impaired FOXO1a inactivation sustained expression of the pro-apoptotic protein Bim, without affecting Bad, Bcl-XL, or Bcl-2 expression. These results indicate that hyperglycemia may increase susceptibility to apoptosis of human and rat beta-cell through activation of the HBP. Increased routing of glucose through this metabolic pathway results in impaired activation of the IR/IRSs/PI3-kinase/Akt survival pathway by induction of O-glycosylation of signaling molecules.
D'Alessandris
Cristina
C
Laboratory of Molecular Medicine, Department of Internal Medicine, University of Rome-Tor Vergata, Rome, Italy.
Andreozzi
Francesco
F
Federici
Massimo
M
Cardellini
Marina
M
Brunetti
Antonio
A
Ranalli
Marco
M
Del Guerra
Silvia
S
Lauro
Davide
D
Del Prato
Stefano
S
Marchetti
Piero
P
Lauro
Renato
R
Sesti
Giorgio
G
D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D005944:Glucosamine / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D006031:Glycosylation / Q000187:drug effects; D006801:Humans; D007328:Insulin / Q000235:genetics / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007515:Islets of Langerhans / Q000166:cytology* / Q000187:drug effects*; D008565:Membrane Proteins / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D014157:Transcription Factors / Q000378:metabolism; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein
D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; D002352:Carrier Proteins; D053148:Caspase 3; D020169:Caspases; D004268:DNA-Binding Proteins; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D005944:Glucosamine; D005947:Glucose; D038362:Glycogen Synthase Kinase 3; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D014157:Transcription Factors; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein; C494819:BAD protein, human; C494811:BCL2L1 protein, human; C000606775:BCL2L11 protein, human; C000606778:Bcl2l11 protein, rat; C085126:FOXO1 protein, human; C526292:IRS1 protein, human; C526297:IRS2 protein, human; C526296:Irs1 protein, rat; C526299:Irs2 protein, rat; C494918:AKT1 protein, human; C505407:CASP3 protein, human; C505410:Casp3 protein, rat