title: Glucagon-like peptide-1 protects beta-cells against apoptosis by increasing the activity of an IGF-2/IGF-1 receptor autocrine loop.
abstract: OBJECTIVE
  The gluco-incretin hormones glucagon-like peptide (GLP)-1 and gastric inhibitory peptide (GIP) protect beta-cells against cytokine-induced apoptosis. Their action is initiated by binding to specific receptors that activate the cAMP signaling pathway, but the downstream events are not fully elucidated. Here we searched for mechanisms that may underlie this protective effect.
  
  
  METHODS
  We performed comparative transcriptomic analysis of islets from control and GipR(-/-);Glp-1-R(-/-) mice, which have increased sensitivity to cytokine-induced apoptosis. We found that IGF-1 receptor expression was markedly reduced in the mutant islets. Because the IGF-1 receptor signaling pathway is known for its antiapoptotic effect, we explored the relationship between gluco-incretin action, IGF-1 receptor expression and signaling, and apoptosis.
  
  
  RESULTS
  We found that GLP-1 robustly stimulated IGF-1 receptor expression and Akt phosphorylation and that increased Akt phosphorylation was dependent on IGF-1 but not insulin receptor expression. We demonstrated that GLP-1-induced Akt phosphorylation required active secretion, indicating the presence of an autocrine activation mechanism; we showed that activation of IGF-1 receptor signaling was dependent on the secretion of IGF-2. We demonstrated, both in MIN6 cell line and primary beta-cells, that reducing IGF-1 receptor or IGF-2 expression or neutralizing secreted IGF-2 suppressed GLP-1-induced protection against apoptosis.
  
  
  CONCLUSIONS
  An IGF-2/IGF-1 receptor autocrine loop operates in beta-cells. GLP-1 increases its activity by augmenting IGF-1 receptor expression and by stimulating secretion; this mechanism is required for GLP-1-induced protection against apoptosis. These findings may lead to novel ways of preventing beta-cell loss in the pathogenesis of diabetes.
authors.affiliation: Department of Physiology and Center for Integrative Genomics, University of Lausanne, Lausanne, Switzerland.
authors.forename: Marion
authors.initials: M
authors.lastname: Cornu
authors.forename: Jiang-Yan
authors.initials: JY
authors.lastname: Yang
authors.forename: Evrim
authors.initials: E
authors.lastname: Jaccard
authors.forename: Carine
authors.initials: C
authors.lastname: Poussin
authors.forename: Christian
authors.initials: C
authors.lastname: Widmann
authors.forename: Bernard
authors.initials: B
authors.lastname: Thorens
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D005786:Gene Expression Regulation / Q000187:drug effects; D052216:Glucagon-Like Peptide 1 / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017526:Receptor, IGF Type 1 / Q000172:deficiency / Q000187:drug effects / Q000235:genetics*; D017527:Receptor, IGF Type 2 / Q000172:deficiency / Q000187:drug effects / Q000235:genetics*
chemical_list: D007328:Insulin; D017527:Receptor, IGF Type 2; D052216:Glucagon-Like Peptide 1; D017526:Receptor, IGF Type 1