Abstract
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.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Apoptosis Regulatory Proteins
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Apoptosis* / drug effects
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Bcl-2-Like Protein 11
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Carrier Proteins / metabolism
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Caspase 3
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Caspases / metabolism
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Cell Survival / drug effects
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Cells, Cultured
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DNA-Binding Proteins / metabolism
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Enzyme Activation / drug effects
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Forkhead Box Protein O1
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Forkhead Transcription Factors
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Glucosamine / pharmacology
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Glucose / pharmacology
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Glycogen Synthase Kinase 3 / metabolism
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Glycosylation / drug effects
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Humans
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Insulin / genetics
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Insulin / pharmacology*
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Insulin Receptor Substrate Proteins
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Intracellular Signaling Peptides and Proteins
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Islets of Langerhans / cytology*
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Islets of Langerhans / drug effects*
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Membrane Proteins / metabolism
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Phosphatidylinositol 3-Kinases / metabolism
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Phosphoproteins / metabolism
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Phosphorylation / drug effects
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Protein Serine-Threonine Kinases / metabolism
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins c-akt
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Proto-Oncogene Proteins c-bcl-2 / metabolism
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Signal Transduction / drug effects*
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Transcription Factors / metabolism
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bcl-Associated Death Protein
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bcl-X Protein
Substances
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Apoptosis Regulatory Proteins
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BAD protein, human
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BCL2L1 protein, human
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BCL2L11 protein, human
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Bcl-2-Like Protein 11
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Bcl2l11 protein, rat
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Carrier Proteins
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DNA-Binding Proteins
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FOXO1 protein, human
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Forkhead Box Protein O1
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Forkhead Transcription Factors
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IRS1 protein, human
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IRS2 protein, human
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Insulin
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Insulin Receptor Substrate Proteins
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Intracellular Signaling Peptides and Proteins
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Irs1 protein, rat
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Irs2 protein, rat
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Membrane Proteins
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Phosphoproteins
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Proto-Oncogene Proteins
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Proto-Oncogene Proteins c-bcl-2
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Transcription Factors
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bcl-Associated Death Protein
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bcl-X Protein
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AKT1 protein, human
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Protein Serine-Threonine Kinases
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Proto-Oncogene Proteins c-akt
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Glycogen Synthase Kinase 3
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CASP3 protein, human
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Casp3 protein, rat
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Caspase 3
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Caspases
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Glucose
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Glucosamine