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

Abstract

It is not known how the expression of endogenous Wnt-signaling molecules is regulated in ␤-cells. Therefore, we investigated the effect of antidiabetic drugs and glucose on the expression of Wnt-signaling molecules in ␤-cells. Primary islets were isolated and cultured. The expression of Wnt-signaling molecules (Wnt-4, Wnt-10b, Frizzled-4, LRP5, TCF7L2) and TNF␣ was analyzed by semiquantitative PCR and Western blotting. Transient transfections were carried out and proliferation assays of INS-1 ␤-cells performed using [3 H]thymidine uptake and BrdU ELISA. Insulin secretion was quantified. A knockdown (siRNA) of Wnt-4 in ␤-cells was carried out. Exendin-4 significantly increased the expression of Wnt-4 in ␤-cells on the mRNA level (2.8-fold) and the protein level (3-fold) (P Ͻ 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 ␤-cells. Wnt-4 had no effect on glucosestimulated insulin secretion or insulin gene expression. Knocking down Wnt-4 decreased ␤-cell proliferation to 45% of controls (P Ͻ 0.05). In addition, Wnt-4 and exendin-4 treatment decreased the expression of TNFa␣ mRNA in primary ␤-cells. These data demonstrate that stimulation with exendin-4 increases the expression of Wnt-4 in ␤-cells. Wnt-4 modulates canonical Wnt signaling and acts as regulator of ␤-cell proliferation and inflammatory cytokine release. This suggests a novel mechanism through which GLP-1 can regulate ␤-cell proliferation.glucagon-like peptide-1; diabetes RECENT RESULTS FROM INDEPENDENT GROUPS identified the Wntsignaling pathway as a regulator of ␤-cell proliferation and insulin secretion (3,22,27,28). Interestingly, the Wnt-signaling pathway and the incretin system interact at different stages. On one hand, glucagon-like peptide-1 (GLP-1) receptor agonists activate the canonical Wnt-signaling pathway in ␤-cells and increase ␤-cell proliferation, at least partly, through canonical Wnt-signaling (12). On the other hand, canonical Wnt signaling regulates the expression of GLP-1 in intestinal L cells (16,30).The canonical Wnt-signaling pathway consists of extracellular ligands (Wnts), cell membrane receptors [Frizzled and LDL receptor-related protein (LRP)5/6], and intracellular signaling molecules. In the inactivated state, ␤-catenin is constitutively phosphorylated by GSK-3␤, which leads to the ubiquitin-mediated degradation of ␤-catenin in the cytoplasm. Ligand binding leads to the inhibition of GSK-3␤ and stabilization of ␤-catenin. ␤-Catenin is the central player in the canonical Wnt-signaling pathway; as a transcriptional coactivator it translocates to the nucleus and binds to transcription factors of the T cell-specific transcription factor (TC...

Effects of glucagon-like peptide-1 receptor agonists on non-alcoholic fatty liver disease and inflammation

“…Stimulation with exendin-4 increases the expression of Wnt-4 in β-cells [79] . In addition, the mechanism of the anti-inflammatory action of exendin-4 involved a decrease in signal transducer and activator of transcription-1 levels [68] .…”

Exendin-4 promotes proliferation and differentiation of MC3T3-E1 osteoblasts by MAPKs activation

“…We inferred that these effects are probably owing to the saturability of the receptor. Most studies report that the effective concentrations of GLP1 or exendin-4 for different cell lines are between 10 −9 and 10 −6 M (Sanz et al 2010, Heller et al 2011, Xie et al 2014 dosage range of exendin-4 for osteoblast proliferation, with a maximum effective dose of 10 −7 M. The optimum treatment time of 48 h may be attributable to a number of factors, including the half-life of exendin-4 and a corresponding decrease in bio-utilization of the drug, as well as increased cell apoptosis given the limited volume of the cell culture plates used in this study.…”

Wnt4 antagonises Wnt3a mediated increases in growth and glucose stimulated insulin secretion in the pancreatic beta-cell line, INS-1

“…The activation of the canonical Wnt pathway, by ligands such as Wnt3a, has been of particular interest as it can increase β-cell proliferation, decrease apoptosis and improve glucose stimulated insulin secretion [6][7][8][9][10][11][12]. However there is now increasing evidence that non-canonical Wnt ligands such as Wnt4 can antagonise the signalling mediated by Wnt3a and may play an equally important role in β-cell function [13][14][15].…”

“…In the nucleus β-catenin can act as a transcription factor (along with its cofactors TCF/LEF) to promote gene transcription of effectors of Wnt signalling, such as c-myc and cyclin D2. In contrast, the non-canonical pathways, such as those stimulated by Wnt4 are β-catenin independent and have been shown to antagonise the canonical Wnt pathway in several cell types [13,14,[19][20][21].…”