The excessive activation of Toll-like receptor 4 signaling pathway leads to steroid-induced femoral head osteonecrosis in rats

Objective: To establish a rat model to investigate Toll-like receptor 4 (TLR4) signaling pathway associated with the pathogenesis of steroid-induced femoral head osteonecrosis.

Methods: Adult male SD rats were randomly divided into model group and intervention group with 24 rats in each, and then were injected intramuscularly with 20 mg/kg methylprednisolone (MP) via bilateral gluteus maximus alternatively once a week for 8 weeks. The rats in intervention group were injected intravenously with 10 mg/kg TAK242 before each MP administration. A control group consisting of 12 rats received saline injection. All animals were sacrificed at week 8, 10 or 12 from the first MP injection, respectively. The analyses of histopathology and TRAP staining were performed and the concentration of tartrate-resistant acid phosphatase (TRAP) in serum was tested. The mRNA and protein expressions of TLR4, MyD88, NF-κB p65 and MCP-1 were detected by quantitative real-time PCR and Western blot.

Results: Femoral head osteonecrosis was observed in the model rats, and the concentration and positive staining of TRAP, the mRNA and protein expression levels of all the factors were enhanced significantly in model group compared with that in intervention group and control group (P<0.05). There was no significant difference in the tested factors between intervention group and control group (P>0.05).

Conclusion: Excessive dosage of corticosteroids can induce femoral head osteonecrosis via the abnormal activation of TLR4 signaling pathway.