Exendin-4 upregulates the expression of Wnt-4, a novel regulator of pancreatic β-cell proliferation

Am J Physiol Endocrinol Metab. 2011 Nov;301(5):E864-72. doi: 10.1152/ajpendo.00144.2011. Epub 2011 Jul 19.

Abstract

The Wnt-signaling pathway regulates β-cell functions. It is not known how the expression of endogenous Wnt-signaling molecules is regulated in β-cells. Therefore, we investigated the effect of antidiabetic drugs and glucose on the expression of Wnt-signaling molecules in β-cells. Primary islets were isolated and cultured. The expression of Wnt-signaling molecules (Wnt-4, Wnt-10b, Frizzled-4, LRP5, TCF7L2) and TNFα was analyzed by semiquantitative PCR and Western blotting. Transient transfections were carried out and proliferation assays of INS-1 β-cells performed using [(3)H]thymidine uptake and BrdU ELISA. Insulin secretion was quantified. A knockdown (siRNA) of Wnt-4 in β-cells was carried out. Exendin-4 significantly increased the expression of Wnt-4 in β-cells on the mRNA level (2.8-fold) and the protein level (3-fold) (P < 0.001). The effect was dose dependent, with strongest stimulation at 10 nM, and it was maintained after long-term stimulation over 4 wk. Addition of exd-(9-39), a GLP-1 receptor antagonist, abolished the effect of exendin-4. Treatment with glucose, insulin, or other antidiabetic drugs had no effect on the expression of any of the examined Wnt-signaling molecules. Functionally, Wnt-4 antagonized the activation of canonical Wnt-signaling in β-cells. Wnt-4 had no effect on glucose-stimulated insulin secretion or insulin gene expression. Knocking down Wnt-4 decreased β-cell proliferation to 45% of controls (P < 0.05). In addition, Wnt-4 and exendin-4 treatment decreased the expression of TNFaα mRNA in primary β-cells. These data demonstrate that stimulation with exendin-4 increases the expression of Wnt-4 in β-cells. Wnt-4 modulates canonical Wnt signaling and acts as regulator of β-cell proliferation and inflammatory cytokine release. This suggests a novel mechanism through which GLP-1 can regulate β-cell proliferation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Proliferation / drug effects*
  • Cells, Cultured
  • Drug Evaluation, Preclinical
  • Exenatide
  • Gene Expression Regulation / drug effects
  • Glucagon-Like Peptide-1 Receptor
  • Glucose / pharmacology
  • Hypoglycemic Agents / pharmacology
  • Insulin / genetics
  • Insulin / metabolism
  • Insulin Secretion
  • Insulin-Secreting Cells / drug effects*
  • Insulin-Secreting Cells / metabolism
  • Insulin-Secreting Cells / physiology
  • Metformin / pharmacology
  • Mice
  • Mice, Inbred C57BL
  • Peptides / pharmacology*
  • RNA, Small Interfering / pharmacology
  • Receptors, Glucagon / antagonists & inhibitors
  • Receptors, Glucagon / metabolism
  • Receptors, Glucagon / physiology
  • Rosiglitazone
  • Thiazolidinediones / pharmacology
  • Tolbutamide / pharmacology
  • Up-Regulation / drug effects
  • Venoms / pharmacology*
  • Wnt4 Protein / antagonists & inhibitors
  • Wnt4 Protein / genetics*
  • Wnt4 Protein / metabolism

Substances

  • Glp1r protein, mouse
  • Glucagon-Like Peptide-1 Receptor
  • Hypoglycemic Agents
  • Insulin
  • Peptides
  • RNA, Small Interfering
  • Receptors, Glucagon
  • Thiazolidinediones
  • Venoms
  • Wnt4 Protein
  • Rosiglitazone
  • Metformin
  • Tolbutamide
  • Exenatide
  • Glucose