title: Exendin-4 protects pancreatic beta cells from human islet amyloid polypeptide-induced cell damage: potential involvement of AKT and mitochondria biogenesis.
abstract: OBJECTIVE
  Glucagon-like peptide-1 (GLP-1) stimulates beta-cell proliferation and enhances beta-cell survival, whereas oligomerization of human islet amyloid polypeptide (hIAPP) may induce beta-cell apoptosis and reduce beta-cell mass. Type 2 diabetes is associated with increased expression of IAPP. As GLP-1-based therapy is currently developed as a novel antidiabetic therapy, we examined the potential protective action of the GLP-1 receptor agonist exendin-4 on hIAPP-induced beta-cell apoptosis.
  
  
  METHODS
  The study was performed in clonal insulinoma (INS-1E) cells. Both method of transcriptional and translational and sulphorhodamine B (SRB) assays were used to evaluate cell viability and cell mass. Western blot analysis was applied to detect protein expression. Transfection of constitutively active protein kinase B (PKB/AKT) was performed to examine the role of AKT. Mitochondrial biogenesis was quantified by mitogreen staining and RT-PCR.
  
  
  RESULTS
  First, we confirmed that hIAPP induced cell apoptosis and growth inhibition in INS-1E cells. These effects were partially protected by exendin-4 in association with partial recovery of the hIAPP-mediated AKT inhibition. Furthermore, AKT constitutive activation attenuated hIAPP-induced apoptosis, whereas PI3K/AKT inhibition abrogated exendin-4-mediated effects. These findings suggest that the antiapoptotic and proliferative effects of exendin-4 in hIAPP-treated INS-1E cells were partially mediated through AKT pathway. Moreover, hIAPP induced FOXO1 but inhibited pdx-1 nucleus translocation. These effects were restored by exendin-4. Finally, mitogreen staining and RT-PCR revealed enhanced mitochondrial biogenesis by exendin-4 treatment.
  
  
  CONCLUSIONS
  Collectively, these results suggest that GLP-1 receptor agonist protects beta cells from hIAPP-induced cell death partially through the activation of AKT pathway and improved mitochondrial function.
authors.affiliation: Department of Medicine and Therapeutics, The Chinese University of Hong Kong, The Prince of Wales Hospital, Shatin, Hong Kong SAR, China.
authors.forename: R
authors.initials: R
authors.lastname: Fan
authors.forename: X
authors.initials: X
authors.lastname: Li
authors.forename: X
authors.initials: X
authors.lastname: Gu
authors.forename: J C N
authors.initials: JC
authors.lastname: Chan
authors.forename: G
authors.initials: G
authors.lastname: Xu
mesh_terms: D017209:Apoptosis / Q000502:physiology; D019610:Cytoprotection; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy* / Q000503:physiopathology; D000077270:Exenatide; D052216:Glucagon-Like Peptide 1 / Q000819:agonists / Q000494:pharmacology*; D000067757:Glucagon-Like Peptide-1 Receptor; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000502:physiology; D058228:Islet Amyloid Polypeptide / Q000037:antagonists & inhibitors* / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects* / Q000502:physiology; D010455:Peptides / Q000494:pharmacology*; D018027:Receptors, Glucagon; D015398:Signal Transduction / Q000502:physiology; D014688:Venoms / Q000494:pharmacology*
chemical_list: C000593833:GLP1R protein, human; D000067757:Glucagon-Like Peptide-1 Receptor; D007004:Hypoglycemic Agents; D058228:Islet Amyloid Polypeptide; D010455:Peptides; D018027:Receptors, Glucagon; D014688:Venoms; D052216:Glucagon-Like Peptide 1; D000077270:Exenatide