P-glycoprotein Overexpression in Bone Marrow-derived Multipotent Stromal Cells Decreases the Risk of Steroid-induced Osteonecrosis in the Femoral Head

P-glycoprotein (P-gp) plays a role in steroid-induced osteonecrosis of the femoral head (ONFH), but the underlying mechanism remains unknown. We hypothesized that P-gp overexpression can prevent ONFH by regulating bone marrow-derived multipotent stromal cell (BMSC) adipogenesis and osteogenesis. BMSCs from Sprague-Dawley rats were transfected with green fluorescent protein (GFP) or the multidrug resistance gene 1 (MDR1) encoding GFP and P-gp. Dexamethasone was used to induce BMSC differentiation. Adipogenesis was determined by measuring peroxisome proliferator-activated receptor (PPAR-γ) expression and the triglyceride level. Osteogenesis was determined by measuring runt-related transcription factor 2 (Runx2) expression and alkaline phosphatase activity. For in vivo experiments, rats were injected with saline, BMSCs expressing GFP (GFP-BMSCs) or BMSCs expressing GFP-P-gp (MDR1-GFP-BMSCs). After dexamethasone induction, adipogenesis was determined by measuring PPAR-γ expression and fatty marrow, whereas osteogenesis was detected by measuring Runx2 expression, trabecular parameters and the mineral apposition rate, followed by evaluation of the incidence of ONFH. Overexpression of P-gp in BMSCs resulted in markedly decreased expression of adipogenic markers and increased expression of osteogenic markers. Compared with rats injected with saline, rats injected with GFP-BMSCs showed reduced ONFH, and the injected GFP-positive BMSCs attached to trabecular surfaces and exhibited an osteoblast-like morphology. Compared with the rats injected with BMSCs expressing GFP alone, rats injected with BMSCs overexpressing GFP and P-gp showed lower adipocytic variables, higher osteogenic variables and lower incidence of ONFH. Overexpression of P-gp inhibited BMSC adipogenesis and promoted osteogenesis, which reduced the incidence of steroid-induced ONFH.