title: Exendin-4 upregulates the expression of Wnt-4, a novel regulator of pancreatic β-cell proliferation.
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.
authors.affiliation: Department of Endocrinology, Diabetes, and Rheumatology, University Hospital Düsseldorf, Düsseldorf, Germany.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Heller
authors.forename: Markus C
authors.initials: MC
authors.lastname: Kühn
authors.forename: Birgit
authors.initials: B
authors.lastname: Mülders-Opgenoorth
authors.forename: Matthias
authors.initials: M
authors.lastname: Schott
authors.forename: Holger S
authors.initials: HS
authors.lastname: Willenberg
authors.forename: Werner A
authors.initials: WA
authors.lastname: Scherbaum
authors.forename: Sven
authors.initials: S
authors.lastname: Schinner
mesh_terms: D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D004353:Drug Evaluation, Preclinical; D000077270:Exenatide; D005786:Gene Expression Regulation / Q000187:drug effects; D000067757:Glucagon-Like Peptide-1 Receptor; D005947:Glucose / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000235:genetics / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D008687:Metformin / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D010455:Peptides / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D018027:Receptors, Glucagon / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology; D000077154:Rosiglitazone; D045162:Thiazolidinediones / Q000494:pharmacology; D014044:Tolbutamide / Q000494:pharmacology; D015854:Up-Regulation / Q000187:drug effects; D014688:Venoms / Q000494:pharmacology*; D060528:Wnt4 Protein / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism
chemical_list: C000593834:Glp1r protein, mouse; D000067757:Glucagon-Like Peptide-1 Receptor; D007004:Hypoglycemic Agents; D007328:Insulin; D010455:Peptides; D034741:RNA, Small Interfering; D018027:Receptors, Glucagon; D045162:Thiazolidinediones; D014688:Venoms; D060528:Wnt4 Protein; D000077154:Rosiglitazone; D008687:Metformin; D014044:Tolbutamide; D000077270:Exenatide; D005947:Glucose