title: Increased hexosamine biosynthetic pathway flux dedifferentiates INS-1E cells and murine islets by an extracellular signal-regulated kinase (ERK)1/2-mediated signal transmission pathway.
abstract: OBJECTIVE
  Beta cell failure is caused by loss of cell mass, mostly by apoptosis, but also by simple dysfunction (decline of glucose-stimulated insulin secretion, downregulation of specific gene expression). Apoptosis and dysfunction are caused, at least in part, by lipoglucotoxicity. The mechanisms implicated are oxidative stress, increase in the hexosamine biosynthetic pathway (HBP) flux and endoplasmic reticulum (ER) stress. Oxidative stress plays a role in glucotoxicity-induced beta cell dedifferentiation, while glucotoxicity-induced ER stress has been mostly linked to beta cell apoptosis. We sought to clarify whether ER stress caused by increased HBP flux participates in a dedifferentiating response of beta cells, in the absence of relevant apoptosis.
  
  
  METHODS
  We used INS-1E cells and murine islets. We analysed the unfolded protein response and the expression profile of beta cells by real-time RT-PCR and western blot. The signal transmission pathway elicited by ER stress was investigated by real-time RT-PCR and immunofluorescence.
  
  
  RESULTS
  Glucosamine and high glucose induced ER stress, but did not decrease cell viability in INS-1E cells. ER stress caused dedifferentiation of beta cells, as shown by downregulation of beta cell markers and of the transcription factor, pancreatic and duodenal homeobox 1. Glucose-stimulated insulin secretion was inhibited. These effects were prevented by the chemical chaperone, 4-phenyl butyric acid. The extracellular signal-regulated kinase (ERK) signal transmission pathway was implicated, since its inhibition prevented the effects induced by glucosamine and high glucose.
  
  
  CONCLUSIONS
  Glucotoxic ER stress dedifferentiates beta cells, in the absence of apoptosis, through a transcriptional response. These effects are mediated by the activation of ERK1/2.
authors: Dipartimento di Scienze e Tecnologie Biologiche e Ambientali, Università degli Studi del Salento, 73100 Lecce, Italy.
authors: A
authors: A
authors: Lombardi
authors: L
authors: L
authors: Ulianich
authors: A S
authors: AS
authors: Treglia
authors: C
authors: C
authors: Nigro
authors: L
authors: L
authors: Parrillo
authors: D D
authors: DD
authors: Lofrumento
authors: G
authors: G
authors: Nicolardi
authors: C
authors: C
authors: Garbi
authors: F
authors: F
authors: Beguinot
authors: C
authors: C
authors: Miele
authors: B
authors: B
authors: Di Jeso
mesh_terms: D000818:Animals; D054337:Cell Dedifferentiation / Q000187:drug effects; D002460:Cell Line; D002999:Clone Cells; D015536:Down-Regulation / Q000187:drug effects; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D005944:Glucosamine / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D010654:Phenylbutyrates / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D056811:Unfolded Protein Response / Q000187:drug effects
chemical_list: D018398:Homeodomain Proteins; D007328:Insulin; D010654:Phenylbutyrates; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; C075773:4-phenylbutyric acid; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D005944:Glucosamine