Modulation of canonical Wnt signaling by the extracellular matrix component biglycan

Abstract

Although extracellular control of canonical Wnt signaling is crucial for tissue homeostasis, the role of the extracellular microenvironment in modulating this signaling pathway is largely unknown. In the present study, we show that a member of the small leucine-rich proteoglycan family, biglycan, enhances canonical Wnt signaling by mediating Wnt function via its core protein. Immunoprecipitation analysis revealed that biglycan interacts with both the canonical Wnt ligand Wnt3a and the Wnt coreceptor low-density lipoprotein receptor-related protein 6 (LRP6), possibly via the formation of a trimeric complex. Biglycan-deficient cells treated with exogenous Wnt3a had less Wnt3a retained in cell layers compared with WT cells. Furthermore, the Wnt-induced levels of LRP6 phosphorylation and expression of several Wnt target genes were blunted in biglycan-deficient cells. Both recombinant biglycan proteoglycan and biglycan core protein increased Wnt-induced β-catenin/T cell-specific factor–mediated transcriptional activity, and this activity was completely inhibited by Dickkopf 1. Interestingly, recombinant biglycan was able to rescue impaired Wnt signaling caused by a previously described missense mutation in the extracellular domain of human LRP6 (R611C). Furthermore, biglycan's modulation of canonical Wnt signaling affected the functional activities of osteoprogenitor cells, including the RUNX2-mediated transcriptional activity and calcium deposition. Use of a transplant system and a fracture healing model revealed that expression of Wnt-induced secreted protein 1 was decreased in bone formed by biglycan-deficient cells, further suggesting reduced Wnt signaling in vivo. We propose that biglycan may serve as a reservoir for Wnt in the pericellular space and modulate Wnt availability for activation of the canonical Wnt pathway.

Recombinant Biglycan Promotes Bone Morphogenetic Protein-induced Osteogenesis

“…Some studies showed that BMP-2 activates Wnt/β-catenin in C2C12, C3H10T1/2, and MC3T3-E1 cells (Rawadi et al, 2003;Zhang et al, 2009), while others reported the lack of such effect (Nakashima et al, 2005). In a recent bone fracture-healing model, the callus of BGN-deficient mice reduced gene expression levels of Wnt-induced secreted protein 1, indicating a role of BGN in Wnt signaling (Berendsen et al, 2011). The discrepancy between the current study and those reports could be due to the assay conditions, such as timing (1-hr incubation in this study), passage effect, and culture conditions, among others.…”

LDL particle core enrichment in cholesteryl oleate increases proteoglycan binding and promotes atherosclerosis

“…Each binding cycle began with the delivery of recombinant human BGN (24)(25)(26)(27), which had been purifi ed by ion exchange chromatography as described above and kindly provided by Dr. Rick Owens (LifeCell Corporation; Branchburg, NJ). The BGN was added to the sample channel at a concentration of 34 g/ml protein at a fl ow rate of 20 l/min for 180 s followed by a 300 s stabilization period to achieve ‫ف‬ 10% saturation of the mAb sample channel surface (1,239 ± 18 RU, n = 30) (see supplementary Fig.…”

Wnt-YAP interactions in the neural fate of human pluripotent stem cells and the implications for neural organoid formation

“…Extracellular matrix (ECM) components, such as biglycan, glypican, and heparan sulfate, are able to modulate the activation or the inhibition of Wnt/b-catenin signaling by binding Wnt to the frizzled receptor and its coreceptor LRP6. 28 It has been reported that biglycan directly interacts with Wnt3a at Cterminus, which enhances b-catenin/T cell factor mediated transcriptional activity. 28 Syndecan-4 was shown to inhibit Wnt/b-catenin signaling through regulation of LRP6 and R-spondin 3.…”

“…28 It has been reported that biglycan directly interacts with Wnt3a at Cterminus, which enhances b-catenin/T cell factor mediated transcriptional activity. 28 Syndecan-4 was shown to inhibit Wnt/b-catenin signaling through regulation of LRP6 and R-spondin 3. 29 The influence of acellular ECMs on b-catenin expression and the response to Wnt activator and inhibitor were demonstrated recently.…”

“…28 In this regard, proteoglycans and glycosaminoglycan chain components may affect Wnt/b-catenin pathway through the interactions with Wnt ligands or inhibitors. Extracellular matrix (ECM) components, such as biglycan, glypican, and heparan sulfate, are able to modulate the activation or the inhibition of Wnt/b-catenin signaling by binding Wnt to the frizzled receptor and its coreceptor LRP6.…”