Modification of Cysteine 179 in IKKβ by Ursolic Acid Inhibits Titanium-Wear-Particle-Induced Inflammation, Osteoclastogenesis, and Hydroxylapatite Resorption

Aseptic loosening of artificial joints mainly accounts for the failure of arthroplasty. We previously reported that ursolic acid (UA) inhibited osteolysis caused by titanium (Ti) wear particles via suppression of NF-kB signaling. In the present study, that the suppressive effect of UA on Ti-particle-induced inflammation and osteoclastogenesis targets on IKKβ cys-179 was demonstrated. A retrovirus packaged IKKβC179A plasmid with a Cys-179 mutation replaced by Ala was constructed. qRT-PCR, immunoblot, and immunofluorescence were used to evaluate the gene expressions. Secreted inflammatory cytokines were detected by ELISA. Formation and function of osteoclastogenesis were evaluated by TRAP stain and hydroxylapatite resorption assays. As a result, a mutation of IKKβC179A rescued the therapeutic effect of UA on Ti-particle-induced inflammation, including morphological transforms, upregulation of iNOS and COX-2, increased secretions of TNF-α, IL-1β, and IL-6, and decreased secretion of IL-10. Meanwhile, inhibition of osteoclastogenesis and hydroxylapatite resorptions were restored by transfection of IKKβC179A. Phosphorylations of p65 and the IKKα/β complex and translocation of p65 into the nucleus were suppressed by UA but rescued by a mutation of IKKβC179A. Conclusively, UA inhibits Ti-wear-particle-induced inflammation, osteoclastogenesis, and hydroxylapatite resorption via modifying cysteine 179 of IKKβ.