VEGFA From Early Osteoblast Lineage Cells (Osterix+) Is Required in Mice for Fracture Healing

Abstract

Bone formation via intramembranous and endochondral ossification is necessary for successful healing after a wide range of bone injuries. The pleiotropic cytokine, vascular endothelial growth factor A (VEGFA) has been shown, via nonspecific pharmacologic inhibition, to be indispensable for angiogenesis and ossification following bone fracture and cortical defect repair. However, the importance of VEGFA expression by different cell types during bone healing is not well understood. We sought to determine the role of VEGFA from different osteoblast cell subsets following clinically relevant models of bone fracture and cortical defect. Ubiquitin C (UBC), Osterix (Osx), or Dentin matrix protein 1 (Dmp1) Cre‐ERT2 mice (male and female) containing floxed VEGFA alleles (VEGFAfl/fl) were either given a femur full fracture, ulna stress fracture, or tibia cortical defect at 12 weeks of age. All mice received tamoxifen continuously starting 2 weeks before bone injury and throughout healing. UBC Cre‐ERT2 VEGFAfl/fl (UBC cKO) mice, which were used to mimic nonspecific inhibition, had minimal bone formation and impaired angiogenesis across all bone injury models. UBC cKO mice also exhibited impaired periosteal cell proliferation during full fracture, but not stress fracture repair. Osx Cre‐ERT2 VEGFAfl/fl (Osx cKO) mice, but not Dmp1 Cre‐ERT2 VEGFAfl/fl (Dmp1 cKO) mice, showed impaired periosteal bone formation and angiogenesis in models of full fracture and stress fracture. Neither Osx cKO nor Dmp1 cKO mice demonstrated significant impairments in intramedullary bone formation and angiogenesis following cortical defect. These data suggest that VEGFA from early osteolineage cells (Osx+), but not mature osteoblasts/osteocytes (Dmp1+), is critical at the time of bone injury for rapid periosteal angiogenesis and woven bone formation during fracture repair. Whereas VEGFA from another cell source, not from the osteoblast cell lineage, is necessary at the time of injury for maximum cortical defect intramedullary angiogenesis and osteogenesis. © 2019 American Society for Bone and Mineral Research.

TGFβ Inhibition Stimulates Collagen Maturation to Enhance Bone Repair and Fracture Resistance in a Murine Myeloma Model

“…This suggests lesion repair occurred via a process reminiscent of intramembranous fracture repair (as in drill‐hole repair models) rather than typical cortical remodeling or endochondral ossification. Supportive of this, we observed an increase in VEGFA, which plays a critical role in coupling of angiogenesis and osteogenesis during intramembranous repair . In myeloma patients, healing of bone lesions has been observed in flat bones of the pelvis, which form via intramembranous ossification.…”

“…Supportive of this, we observed an increase in VEGFA, which plays a critical role in coupling of angiogenesis and osteogenesis during intramembranous repair. (63,64) In myeloma patients, healing of bone lesions has been observed in flat bones of the pelvis, (25) which form via intramembranous ossification. As such, it is plausible that this could be the mechanism of repair in patients.…”

Exosomal miRNA-128-3p from mesenchymal stem cells of aged rats regulates osteogenesis and bone fracture healing by targeting Smad5

“…Bone tissue regeneration requires coordinated enrollment of osteoblasts and osteoclasts that are terminally differentiated from MSCs. In particular, the osteoblast, of mesenchymal origin, is pivotal during bone remodeling and skeletal development [10]. Transplantation of MSCs into target tissues has been proven effective in many disease models, including the promotion of osteogenesis in fractures [11,12].…”

Spatial Distribution of Macrophages During Callus Formation and Maturation Reveals Close Crosstalk Between Macrophages and Newly Forming Vessels

“…Osteoprogenitor cells also produce VEGF as a consequence of the hypoxic environment, leading to enhanced transcriptional activity of hypoxia-inducible factor 1-alpha (HIF-1α) (14,15). Buettmann et al most recently showed that especially the release of VEGFA by Osterix (Osx) + osteoprogenitors/pre-osteoblasts is critical for vessel formation during fracture healing (16). It is well-known that the crosstalk between endothelium and bone cells is essential for the integrity and formation of bone.…”