Biglycan modulates angiogenesis and bone formation during fracture healing

Abstract

Matrix proteoglycans such as biglycan (Bgn) dominate skeletal tissue and yet its exact role in regulating bone function is still unclear. In this paper we describe the potential role of (Bgn) in the fracture healing process. We hypothesized that Bgn could regulate fracture healing because of previous work showing that it can affect normal bone formation. To test this hypothesis, we created fractures in femurs of 6-week-old male wild type (WT or Bgn+/0) and Bgn-deficient (Bgn-KO or Bgn−/0) mice using a custom-made standardized fracture device, and analyzed the process of healing over time. The formation of a callus around the fracture site was observed at both 7 and 14 days post-fracture in WT and Bgn-deficient mice and immunohistochemistry revealed that Bgn was highly expressed in the fracture callus of WT mice, localizing within woven bone and cartilage. Micro-computed tomography (μCT) analysis of the region surrounding the fracture line showed that the Bgn-deficient mice had a smaller callus than WT mice. Histology of the same region also showed the presence of less cartilage and woven bone in the Bgn-deficient mice compared to WT mice. Picrosirius red staining of the callus visualized under polarized light showed that there was less fibrillar collagen in the Bgn-deficient mice, a finding confirmed by immunohistochemistry using antibodies to type I collagen. Interestingly, real time RT-PCR of the callus at 7 days post-fracture showed a significant decrease in relative vascular endothelial growth factor A (VEGF) gene expression by Bgn-deficient mice as compared to WT. Moreover, VEGF was shown to bind directly to Bgn through a solid-phase binding assay. The inability of Bgn to directly enhance VEGF-induced signaling suggests that Bgn has a unique role in regulating vessel formation, potentially related to VEGF storage or stabilization in the matrix. Taken together, these results suggest that Bgn has a regulatory role in the process of bone formation during fracture healing, and further, that reduced angiogenesis could be the molecular basis.

Biglycan up-regulated vascular endothelial growth factor (VEGF) expression and promoted angiogenesis in colon cancer

“…Our results revealed that biglycan is involved in regulating malignant transformation by up-regulation of VEGF. The results were consistent with previous findings, which reported that the VEGF expression is reduced in biglycan knockout mice [27].…”

Biglycan is a novel binding partner of fibroblast growth factor receptor 3c (FGFR3c) in the human testis

“…We show here that FGFR3 and BGN are expressed in the fetal bone tissue in neighboring cellular compartments in analogy to the testis, supporting a possibility of an interaction. The fact that both proteins have been described in relation to bone growth, albeit with opposing effects; FGFR3 as a growth inhibitor and BGN as a growth inducer (Berendsen et al, 2013;Chen et al, 2004;Colvin et al, 1996;Miguez et al, 2011;Parisuthiman et al, 2005;Qi et al, 2014;Xu et al, 1998), underlines the potential importance of these binding partners in relation to bone development as well.…”

Biglycan enhances the ability of migration and invasion in endometrial cancer

“…BGN, constitutively expressed in normal endothelial cells, becomes significantly overexpressed in tumor tissues and promotes the migration of endothelial cell and neovascularization of cancer [28]. With similar mechanisms, BGN is able to triggering VEGF synthesis in tumor cells, and it has been shown to bind and sequester (VEGFA) in the ECM, thus generating a reservoir of VEGF that can be released during ECM degradation that associated with tumor, capacitating angiogenesis [29]. Moreover, neovascularization is closely related with ROS and TLR2 signaling.…”