Apoptosis associated with Wnt/β-catenin pathway leads to steroid-induced avascular necrosis of femoral head

Background: The objective of the current study was to establish a rat model to investigate apoptosis in steroid-induced femoral head osteonecrosis occurring via the Wnt/beta-catenin pathway. Methods: Male Sprague-Dawley (SD) rats were randomly divided into a control group (group A), model group (group B) and sFRP1 group (group C), each consisting of 24 rats, and the rats were intravenously injected with LPS (10 mu g/kg body weight). After 24 h, three injections of MPS (20 mg/kg body weight) were administered intramuscularly at 24-h intervals. The rats in group C were injected intramuscularly with 1 mu g/kg sFRP1 protein per day for 30 days, beginning at the time of the first MPS administration. The group A rats were fed and housed under identical conditions but received saline injection. All animals were sacrificed at weeks 2, 4 and 8 from the first MPS injection. Histopathological staining was preformed to evaluated osteonecrosis. Apoptosis was detected via quantitative terminal deoxynucleotidyl transferase (TdT) deoxyuridine triphosphate nick-end labelling (TUNEL) staining, caspase-3 activity assay, and detection of Bcl-2 and Bax protein expression by immunohistochemistry and Western blotting. Wnt/beta-catenin pathway signalling molecules, including activated beta-catenin and c-Myc, were detected by immunohistochemistry and Western blotting. Results: Typical osteonecrosis was observed in groups B and C. Apoptosis gradually increased with increasing time in both groups B and C. More severe osteonecrosis and apoptosis were observed in group C compared with group B. The expression levels of caspase-3 and Bax were higher while that of Bcl-2 was lower in group C compared with group B. The expression levels of activated beta-catenin and c-Myc gradually decreased with increasing time in both groups B and C, and they were lower in group C compared with group B. Conclusions: The Wnt/beta-catenin pathway is involved in the pathogenesis of early stage SANFH, as we have demonstrated in an SANFH rat model, and it may act through the regulation of c-Myc, which affects the cell cycle and cell apoptosis.