VEGF improves, whereas sFlt1 inhibits, BMP2-induced bone formation and bone healing through modulation of angiogenesis

Introduction: Angiogenesis is closely associated with bone formation during normal bone development and is important for the bone formation elicited by BMP4. However, it remains unknown whether vascular endothelial growth factor (VEGF) also interacts with other BMPs, especially BMP2, in bone formation and bone healing. Materials and Methods: For this study, mouse muscle-derived stem cells were transduced to express BMP2, VEGF, or VEGF antagonist (sFlt1). We studied the angiogenic process during endochondral bone formation elicited by BMP2, a prototypical osteogenic BMP. Using radiographic and histologic analyses, we also evaluated the interaction between VEGF and BMP2 during bone formation and bone healing. Results: Our results indicate that BMP2-elicited bone formation comprises two phases of angiogenesis, with an early phase occurring before the appearance of hypertrophic cartilage, followed by a late phase coupled with the appearance of hypertrophic cartilage. Our finding that the administration of sFlt1, a specific antagonist of VEGF, significantly inhibited BMP2-induced bone formation and the associated angiogenesis indicates that endogenous VEGF activity is important for bone formation. Furthermore, we found that the delivery of exogenous VEGF enhanced BMP2-induced bone formation and bone healing by improving angiogenesis, which in turn led to accelerated cartilage resorption and enhanced mineralized bone formation. Our findings also indicate that the ratio between VEGF and BNP2 influences their synergistic interaction, with a higher proportion of VEGF leading to decreased synergism. Our study also revealed unique VEGF-BMP2 interactions that differ from the VEGF-BMP4 interactions that we have described previously. Conclusions: This study, along with previously published work, shows that VEGF interacts synergistically with both BMP4 and BMP2 but elicits substantially different effects with these two BMPs.