title: Chronic exposure to GLP-1 increases GLP-1 synthesis and release in a pancreatic alpha cell line (α-TC1): evidence of a direct effect of GLP-1 on pancreatic alpha cells.
abstract: OBJECTIVE
  Incretin therapies, which are used to treat diabetic patients, cause a chronic supra-physiological increase in GLP-1 circulating levels. It is still unclear how the resulting high hormone concentrations may affect pancreatic alpha cells. The present study was designed to investigate the effects of chronic exposure to high GLP-1 levels on a cultured pancreatic alpha cell line.
  
  
  METHODS
  α-TC1-6 cell line was cultured in the presence or absence of GLP-1 (100 nmol/l) for up to 72 h. In our model GLP-1 receptor (GLP-1R) was measured. After the cells were exposed to GLP-1 the levels of glucagon secretion were measured. Because GLP-1 acts on intracellular cAMP production, the function of GLP-1R was studied. We also investigated the effects of chronic GLP-1 exposure on the cAMP/MAPK pathway, Pax6 levels, the expression of prohormone convertases (PCs), glucagon gene (Gcg) and protein expression, glucagon and GLP-1 production.
  
  
  RESULTS
  In our model, we were able to detect GLP-1R. After GLP-1 exposure we found a reduction in glucagon secretion. During further investigation of the function of GLP-1R, we found an activation of the cAMP/MAPK/Pax6 pathway and an increase of Gcg gene and protein expression. Furthermore we observed a significant increase in PC1/3 protein expression, GLP-1 intracellular content and GLP-1 secretion.
  
  
  CONCLUSIONS
  Our data indicate that the chronic exposure of pancreatic alpha cells to GLP-1 increases the ability of these cells to produce and release GLP-1. This phenomenon occurs through the stimulation of the transcription factor Pax6 and the increased expression of the protein convertase PC1/3.
authors.affiliation: Department of Clinical and Molecular BioMedicine, University of Catania, Garibaldi-Nesima Hospital, Catania, Italy.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Piro
authors.affiliation: Department of Clinical and Molecular BioMedicine, University of Catania, Garibaldi-Nesima Hospital, Catania, Italy.
authors.forename: Loriana G
authors.initials: LG
authors.lastname: Mascali
authors.affiliation: Department of Clinical and Molecular BioMedicine, University of Catania, Garibaldi-Nesima Hospital, Catania, Italy.
authors.forename: Francesca
authors.initials: F
authors.lastname: Urbano
authors.affiliation: Department of Clinical and Molecular BioMedicine, University of Catania, Garibaldi-Nesima Hospital, Catania, Italy.
authors.forename: Agnese
authors.initials: A
authors.lastname: Filippello
authors.affiliation: Endocrinology, Department of Health Sciences, University Magna Graecia of Catanzaro, Catanzaro, Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Malaguarnera
authors.affiliation: Department of Clinical and Molecular BioMedicine, University of Catania, Garibaldi-Nesima Hospital, Catania, Italy.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Calanna
authors.affiliation: Department of Clinical and Molecular BioMedicine, University of Catania, Garibaldi-Nesima Hospital, Catania, Italy.
authors.forename: Agata M
authors.initials: AM
authors.lastname: Rabuazzo
authors.affiliation: Department of Clinical and Molecular BioMedicine, University of Catania, Garibaldi-Nesima Hospital, Catania, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Purrello
mesh_terms: D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000378:metabolism; D005136:Eye Proteins / Q000819:agonists / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D052216:Glucagon-Like Peptide 1 / Q000096:biosynthesis / Q000378:metabolism / Q000494:pharmacology*; D000067757:Glucagon-Like Peptide-1 Receptor; D050416:Glucagon-Secreting Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D018398:Homeodomain Proteins / Q000819:agonists / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors / Q000819:agonists / Q000235:genetics* / Q000378:metabolism; D045664:Proprotein Convertase 1 / Q000235:genetics* / Q000378:metabolism; D018027:Receptors, Glucagon / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000819:agonists / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D005136:Eye Proteins; C000593833:GLP1R protein, human; D000067757:Glucagon-Like Peptide-1 Receptor; D018398:Homeodomain Proteins; D000071841:PAX6 Transcription Factor; C000605730:PAX6 protein, human; D051761:Paired Box Transcription Factors; D018027:Receptors, Glucagon; D012097:Repressor Proteins; D052216:Glucagon-Like Peptide 1; D000242:Cyclic AMP; D020928:Mitogen-Activated Protein Kinases; D045664:Proprotein Convertase 1