Biglycan in Bone Angiogenesis During Fracture Healing

Objectives: Small leucine-rich proteoglycans (SLRPs) are abundant in different types of extracellular matrices including teeth, bone, and cartilage. Biglycan (Bgn), one member of the SLRP family, is implicated in bone growth and healing. We previously showed Bgn-knock out (KO) mice have less vessel formation during fracture healing. The goal of this study was to determine the spatial and temporal expression patterns of angiogenesis markers during fracture healing by comparing fracture healing in wild type (WT) and Bgn-KO mice.
Methods: In this study, we used 6-8 weeks old WT and Bgn-KO mice. Prior to fracturing the right femur, the bone was stabilized by inserting a thin needle into the marrow cavity. The right femur was then fractured with a fracturing device. Tissue from the healing callus was harvested 7 days post-fracture and used for mRNA analysis and histology. To isolate mRNA, harvested tissues were frozen, pulverized, and RNA was extracted using TriPure. cDNA was made and used for qPCR with primer sets designed to measure the relative expression of various angiogenic genes including HIF-1-α, VEGFα and PECAM (CD31). Immunohistochemistry was performed to assess the location and level of HIF-1-α.
Results: Our study showed that callus tissue from Bgn-KO bones had reduced levels of HIF-1-α and VEGFα compared to WT controls. The endothelial cell marker PECAM (CD31) that is abundant in vessels and considered a marker of angiogenesis was also reduced in Bgn-KO healing bones. Interestingly, immunohistochemistry analysis showed that HIF-1-α expression was reduced in the Bgn-KO tissues compared to WT controls.
Conclusions: Bgn depletion leads to reduced angiogenesis and altered expression of numerous angiogenic genes during fracture healing. Future work needs to be done to assess whether stimulating Bgn production could be a beneficial intervention to facilitate the bone healing process.