The ectopic study of tissue-engineered bone with hBMP-4 gene modified bone marrow stromal cells in rabbits

Background Tissue-engineering techniques combined with gene therapy have been recently reported to improve osteogenesis. In this study, tissue-engineered bone constructed by human Bone Morphogenetic Protein 4 (hBMP-4) gene-modified bone marrow stromal cells (bMSCs) was explored in an ectopic bone formation model in rabbits. Methods A pEGFP-hBMP-4 mammalian plasmid ( EGFP: Enhanced Green Fluorescent Protein) was constructed by subcloning techniques. bMSCs obtained from rabbits were cultured and transfected with either pEGFP-hBMP-4, pEGFP or left uninfected in vitro. Transfer efficiency was detected through the expression of EGFP. Transcription of the target gene was detected by RT-PCR. Alkaline phosphatase (ALP) and Von Kossa tests were also conducted to explore the phenotypes of osteoblasts. The autologous bMSCs of the 3 groups were then combined with Natural Non-organic Bone (NNB), a porous hydroxyapatite implant with a dimension of 6 mm x 6 mm x 3 mm, at a concentration of 5 x 10(7) cells/ml. They were subsequently implanted into 6 rabbits subcutaneously using NNB alone as a blank control (6 implants per group). Four weeks after surgery, the implants were evaluated with histological staining and computerized analysis of new bone formation. Results pEGFP-hBMP-4 expression plasmid was constructed. Under optimal conditions, gene transfer efficiency reached more than 30%. Target gene transfer could strengthen the transcription of BMP-4, and increase the expression of ALP as well as the number of calcium nodules. In the ectopic animal model, NNB alone could not induce new bone formation. The new bone area formed in the bMSCs group was ( 17.2 +/- 7.1) %, and pEGFP group was ( 14.7 +/- 6.1) %, while pEGFP-hBMP-4 group was (29.5 +/- 8.2) %, which was the highest among the groups ( F = 7.295, P < 0.01). Conclusions The mammalian hBMP-4 expression plasmid was successfully constructed and a comparatively high transfer efficiency was achieved. The gene transfer technique enhanced the expression of BMP-4 and promoted differentiation from bMSCs to osteoblasts. These in vivo results suggested that transfection of bMSCs with hBMP-4 might be a suitable method to enhance their inherent osteogenic capacity for bone tissue engineering applications.