Abstract
AIMS/HYPOTHESIS: Stromal cell-derived factor-1 (SDF-1) is a chemokine produced in stromal tissues in multiple organs. Earlier we reported on levels of SDF-1 and SDF-1 receptor (CXCR4) in the insulin-producing beta cells of the mouse pancreas and determined that the SDF-1/CXCR4 axis is important for beta cell survival through activation of the prosurvival kinase, protein kinase B (AKT). Since AKT is known to modulate the wingless-type MMTV integration site family (WNT) signalling cascade, we examined the effects of SDF-1/CXCR4 on WNT signalling in beta cells and whether this signalling is important for cell survival. METHODS: Activation of downstream WNT signalling (beta-catenin and transcription factor 7-like 2, [TCF7L2]) in response to SDF-1 was examined in the islets of WNT signalling reporter (Tcf-optimal promoter beta-galactosidase) mice and in INS-1 and MIN6 beta cells. Cytoprotection of beta cells by SDF-1 in response to the induction of apoptosis was assessed by caspase 3 and TUNEL assays. RESULTS: SDF-1 induced WNT signalling in beta cells of isolated islets and in INS-1 cells via CXCR4-mediated activation of Galphai/o-coupled signalling and the phosphatidylinositol 3-kinase/AKT signalling cascade resulting in the inhibition of glycogen synthase kinase 3-beta. The key WNT signalling regulators, beta-catenin and AKT, were activated by SDF-1 at the transcriptional and post-translational levels. Specific inhibition of beta-catenin in the WNT signalling cascade reversed the anti-apoptotic effects of SDF-1. CONCLUSIONS/INTERPRETATION: SDF-1 promotes pancreatic beta cell survival via activation of AKT and downstream WNT signalling via the stabilisation and activation of beta-catenin/TCF7L2 transcriptional activators. These findings suggest a mechanism for SDF-1 based glucose-lowering therapies by enhancing beta cell mass through increasing cell survival.