Pravastatin prevents steroid-induced osteonecrosis in rats by suppressing PPARγ expression and activating Wnt signaling pathway

Steroid-induced osteonecrosis of the femoral head (steroid-induced ONFH) is characterized by increase of intraosseous pressure because of lipid metabolism disturbance such as elevation of adipogenesis and fat cell hypertrophy in the bone marrow, subsequently leading to disturbances of coagulation-fibrinolysis system in the femoral head and finally resulting in bone ischemia. Pravastatin has been demonstrated to be useful in preventing steroid-induced ONFH in animal models. However, its exact mechanisms acting on this disease have not been fully elucidated. To address this problem, steroid-induced ONFH rat model was constructed to evaluate the effects of pravastatin treatment on the osteonecrotic changes and repair processes. Then, Micro-CT-based micro-angiography was performed to assess the effects of pravastatin treatment on vascularization. In addition, serum lipid levels were detected by haematological examination. After that, the expression of peroxisome proliferator-activated receptor gamma (PPAR gamma), Wnt3a, low density lipoprotein receptor-related protein 5 (LRP5), beta-catenin and runt-related transcription factor 2 (RUNX2) at both mRNA and protein levels were further detected by immunohistochemistry, real-time quantitative PCR, and Western blot analyses. The results, the ratio of empty lacuna, adipose tissue area, and adipocyte perimeter in the bone marrow were dramatically lower in the pravastatin treatment groups than in the model group (all P < 0.05). Moreover, by micro-CT quantification, pravastatin treatment dose-dependently increased vessel volume, vessel surface, percentage of vessel volume, and vessel thickness of the femoral heads of steroid-induced ONFH rats. Importantly, pravastatin treatment could prevent steroid-induced ONFH by suppressing the expression of PPAR gamma, and increasing the expression of Wnt3a, LRP5, beta-catenin, and RUNX2, at both mRNA and protein levels, in the femoral heads of steroid-induced ONFH rats. In conclusion, Pravastatin may prevent steroid-induced ONFH by suppressing PPAR gamma expression and activating Wnt signaling pathway.