Enhanced bone regeneration through combined delivery of rhPDGF-BB and BMP-2 gene transfected BMSCs

Abstract

Background: Recombinant human platelet derived growth factor-BB (rhPDGF-BB) influences the cell proliferation and recruitment in early stage of wound healing as well as the bone regeneration indirectly. Bone morphogenetic protein-2 (BMP-2), a potent osteogenic differentiation inducer, has been widely reported in bone regeneration therapy. This study was aimed to investigate the effect of combined delivery of rhPDGF-BB and BMP-2 gene transfected bone marrow stromal cells (BMSCs) on bone regeneration in rat calvarial model.

Materials and methods: Rat BMSCs was transfected with adenoviral vector containing BMP-2 gene (AdBMP-2 BMSCs). The expression of BMP-2 was measured by enzyme-linked immunosorbent assay. Cell proliferation and osteogenic differentiation were examined for the AdBMP-2 BMSCs. In animal studies, critical size calvarial defect (8 mm in diameter) was formed in 60 Sprague– Dawley rats and collagen gel containing autologous AdBMP-2 BMSC and/or rhPDGF-BB was delivered into the defect. After 2 and 4 weeks, animals were sacrificed and their histomorphometric analysis and micro-CT evaluation were performed.

Results: In in vitro experiments, AdBMP-2 BMSCs overexpressed BMP-2 until 21 days and rhPDGF-BB treatment did not affect the expression of BMP-2. Proliferation of BMSCs was not influenced by BMP-2 gene delivery. rhPDGF-BB treatment on AdBMP-2 BMSCs significantly increased cell proliferation. Osteogenic differentiation of AdBMP-2 BMSCs was significantly increased compared to normal BMSCs. However, rhPDGF-BB treatment on AdBMP-2 BMSCs suppressed alkaline phosphatase activity and mineralization at day 7. In in vivo experiment, both AdBMP-2 BMSC group and AdBMP-2 BMSC/rhPDGF-BB group showed extensive new bone formation at 2 weeks without significant difference between the 2 groups. At 4 weeks, AdBMP-2 BMSC/rhPDGF-BB group showed significantly enhanced bone regeneration and bone mineral density compared with AdBMP-2 BMSCs group.

Conclusion: BMP-2 gene transfected BMSCs produced BMP-2 in long-term period up to 21 days under rhPDGF-BB treatment. rhPDGF-BB increased cell population and capacitated to differentiate the various cells needed in the bone tissue healing. Combined delivery of AdBMP-2 BMSC and rhPDGF-BB induced excellent new bone formation in rat calvarial defect compared with single application of AdBMP-2 BMSC. The combined delivery distinctively enhanced bone regeneration process and might be a potential modality in bone regenerative therapy.