title: High dosage of Exendin-4 increased early insulin secretion in differentiated beta cells from mouse embryonic stem cells.
abstract: OBJECTIVE
  To investigate early insulin release (EIR) and late insulin release (LIR) upon glucose challenge as well as important insulin signaling factors in differentiated insulin-producing cells from embryonic stem cells(ESCs).
  
  
  METHODS
  A recently published protocol was modified by increasing the concentration of Exendin-4 (from 0.1 nmol/L to 10 nmol/L) together with an additional 5-day culture in low glucose (5.5 mmol/L) medium after differentiation. Gene expression profile, insulin content, C-peptide, EIR and LIR were determined.
  
  
  RESULTS
  Compared to a lower concentration of Exendin-4 (0.1 nmol/L), a higher concentration of Exendin-4 (10 nmol/L) increased glucose-responsive insulin secretion, especially EIR. Moreover, 10 nmol/L Exendin-4 increased the expression of the following genes: insulin 1, Pdx-1 (an important transcription factor, newly recognized insulin signaling factors), Epac1 and Epac2 (exchange proteins directly activated by cAMP 1 and 2), and sulfonylurea receptor 1 (SUR1, the subunit of the K(ATP) channel).
  
  
  CONCLUSIONS
  According to current knowledge, our modified protocol with a higher concentration of Exendin-4 (10 nmol/L) together with an additional 5-day 5.5 mmol/L glucose culture after differentiation improved the efficiency of differentiation toward the beta cell phenotype, which was possibly the result of stimulated expression of Pdx-1, Epac 1, and Epac 2, which in turn inhibited the K(ATP) channel through combination with SUR1, leading to increased EIR upon glucose challenge.
authors.affiliation: Department of Anatomy, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong SAR, China.
authors.forename: Hua
authors.initials: H
authors.lastname: Li
authors.forename: Amy
authors.initials: A
authors.lastname: Lam
authors.forename: Ai-min
authors.initials: AM
authors.lastname: Xu
authors.forename: Karen Sl
authors.initials: KS
authors.lastname: Lam
authors.forename: Sookja Kim
authors.initials: SK
authors.lastname: Chung
mesh_terms: D000818:Animals; D002096:C-Peptide / Q000378:metabolism; D002454:Cell Differentiation; D002478:Cells, Cultured; D053595:Embryonic Stem Cells / Q000166:cytology*; D000077270:Exenatide; D020869:Gene Expression Profiling; D005947:Glucose / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D051379:Mice; D010455:Peptides / Q000494:pharmacology*; D010641:Phenotype; D014688:Venoms / Q000494:pharmacology*
chemical_list: D002096:C-Peptide; D007004:Hypoglycemic Agents; D007328:Insulin; D010455:Peptides; D014688:Venoms; D000077270:Exenatide; D005947:Glucose