Stromal-Cell-Derived Factor (SDF) 1-Alpha Overexpression Promotes Bone Regeneration by Osteogenesis and Angiogenesis in Osteonecrosis of the Femoral Head

Background/Aims: Osteonecrosis of the femoral head (ONFH) is a devastating orthopedic disease. Previous studies suggested that stromal-cell-derived factor (SDF)-1 was involved in osteogenesis and angiogenesis. However, whether SDF-1 potentiates the angiogenesis and osteogenesis of bone marrow-derived stromal stem cells (BMSCs) in ONFH is not clear. Methods: BMSCs were transfected with green fluorescent protein (GFP) or the fusion gene encoding GFP and SDF-1α, and transgenic efficacy was monitored by immunofluorescence. The expression of SDF-1α, runt-related transcription factor 2 (Runx2, osteocalcin (OCN), and alkaline phosphatase (ALP) at the mRNA level was measured by real-time polymerase chain reactions (RT-PCR). The expression of SDF-1α, Runx2, OCN, and p-Smad1/5 were measured at the protein level by Western blot. Transwell migration assay and tube formation assay were utilized to detect the angiogenesis in vitro, whereas the in vivo angiogenesis was monitored by angiography. Immunohistological staining and micro-CT scanning were conducted to assess the histological changes in morphology. Results: In vitro, SDF-1α overexpression in BMSCs promoted osteogenic differentiation and upregulated the expression of osteogenic-related proteins, such as ALP, Runx2, OCN, and p-Smadl/5. In the methylprednisolone induced ONFH rat model used in our investigation, the overexpression of SDF-1α in BMSCs promoted significantly more bone regeneration and the expression of OCN and Runx2 as compared with the effect of vehicle overexpression. Moreover, the morphology of ONFH was ameliorated after the transplantation of BMSCs with SDF-1α overexpression. Furthermore, SDF-1α overexpression in BMSCs significantly increased osteoblastic angiogenesis as indicated by the increased tube formation ability, CD31 expression, and vessel volume. Conclusion: SDF-1α overexpression in BMSCs promotes bone generation as indicated by osteogenesis and angiogenesis, suggesting SDF-1α may serve as a therapeutic drug target for ONFH treatment.