Combined Angiogenic and Osteogenic Factor Delivery Enhances Bone Marrow Stromal Cell-Driven Bone Regeneration

Abstract

Bone formation is a coordinated process involving various biological factors. We have developed a scaffold system capable of sustained and localized presentation of osteogenic (BMP-4) and angiogenic (VEGF) growth factors and human bone marrow stromal cells to promote bone formation at an ectopic site. Combined delivery of these factors significantly enhanced bone formation compared with other conditions. Introduction: Tissue regeneration entails complex interactions between multiple signals and materials platforms. Orchestrating the presentation of these signals may greatly enhance the regeneration of lost tissue mass. Bone formation, for example, is dependent on the signaling of BMPs, molecules initiating vascularization (e.g., vascular endothelial growth factor [VEGF]), and osteogenic precursor cells capable of responding to these cues and forming bone tissue. It was hypothesized that combined and concerted delivery of these factors from biodegradable scaffolds would lead to enhanced bone formation. Materials and Methods: Poly(lactic-co-glycolic acid) scaffolds containing combinations of condensed plasmid DNA encoding for BMP-4, VEGF, and human bone marrow stromal cells (hBMSCs) were implanted into the subcutaneous tissue of SCID mice. Implants (n = 6) were retrieved at 3, 8, and 15 weeks after implantation. Bone and blood vessel formation was determined qualitatively and quantitatively by methods including histology, immmunostaining, and μCT. Results: Scaffolds delivering VEGF resulted in a prominent increase in blood vessel formation relative to the conditions without VEGF. BMP-4 expression in scaffolds encapsulating condensed DNA was also confirmed at the 15-week time-point, showing the characteristic of long-term delivery in this system. Combined delivery of all three types of factors resulted in a significant increase in the quantity of regenerated bone compared with any factor alone or any two factors combined, as measured with DXA, X-ray, and histomorphometric analysis. Furthermore, bone formed with all three factors had elastic moduli significantly higher than any other condition. Conclusions: Concerted delivery of BMP-4, VEGF, and hBMSCs promoted greater bone formation relative to any single factor or combination of two factors. Materials systems that allows multifactorial presentation more closely mimic natural developmental processes, and these results may have important implications for bone regeneration therapeutics.