Effects of stromal cell-derived factor-1 alpha gene therapy on bone regeneration and wound healing

Although dental implantation has been widely applied for the reconstruction of edentulous ridge, implant placement may not be feasible in cases with poor bone volume. For the severely atrophic ridge, the technique of guided bone regeneration (GBR), is commonly used for alveolar ridge augmentation. However, there are still technical difficulties remain to be resolved. Such difficulties include how to increase the regenerative potential of bone tissue in defect areas and the assurance of stable soft tissue healing. Past researches mainly focused on the use of growth factors for promoting bone regenerative capacity. However, obstacles still exist in the use of growth factors for alveolar ridge augmentation. How to assure the stable healing of soft tissue overlaying the defect area is another key point for increasing the success rate of GBR, but studies focusing on this subject are rare. Tissue regeneration requires the migration and differentiation of stem cells. Hence, recruitment of stem cells has become the main direction of development in the field of regenerative medicine. Stromal cell-derived factor-1α (SDF-1α), considered as an important stem cell chemokine, has been reported to have the capacity of attracting multipotent mesenchymal stem cells (MSCs). Studies have shown that SDF-1α is beneficial for soft tissue healing and bone regeneration, and most of the studies used SDF-1α protein as the research subject. However, protein has its limitations, such as rapid degradation leading to short lasting duration, safety concern and poor cost efficiency. Consequently, gene therapy has been the main strategy in the present study. We constructed a plasmid encoding mSDF-1α and investigated the therapeutic effect of mSDF-1α gene therapy. First, in our experiment, in-vitro transfection efficiency with polyethylenimine(PEI) was tested in order to determine the optimal ratio of PEI and plasmid DNA, which was adopted in the following animal study. Second, MSC transwell migration assay was performed to ascertain the production of SDF-1α protein by transfected mammalian cells and the protein can promote MSC migration. The third part of the experiment employed the rat calvarial defect model. Application of PEI/DNA condensates in combination with the use of collagen barrier membrane and bone substitutes was performed. The effects on soft tissue healing and bone regeneration were evaluated. Based on the results of the first part of experiment, when the ratio of PEI and DNA was 7.5(3uL PEI and 1ug DNA), the transfection efficiency can reached 55.68% after 48 hours. The data indicated that PEI and DNA should be maintained at a high ratio with low concentration. Therefore, an acceptable transfection rate can be obtained after sufficient time. The second part of experiment verified that the SDF-1α protein can be expressed normally by mammalian cell 293FT after gene transfection. In the MSC transwell migration assay, the SDF-1α protein-added group promoted 3.5 times more MSCs migration compared to the control group. In the third part of experiment, the rat calvarial defect model was used to evaluate the therapeutic effect of SDF-1α gene therapy on wound healing, including soft tissue healing and bone regeneration. In the aspect of assessing soft tissue healing, the SDF-1α-treated group showed an average 100% healed tissue after 14 days, while the control group was only 88.7%; In the use of micro-tomography, the data showed that SDF-1α-treated group had more new bone formation (12.9% ± 3.64) than the PEI-only group (7.07% ± 4.85) with statistically significant differences (P <0.05) ; In the histomorphometric analysis, the results demonstrated that more newly-formed bone can be detected in SDF-1α-treated group compared with the control group at four different time points. Results of the study suggest that SDF-1α gene therapy is beneficial for bone regeneration and soft tissue healing and may have the potential to improve the success rate of alveolar ridge augmentation.