Dickkopf-1 may regulate bone coupling by attenuating wnt/beta-catenin signaling in chronic apical periodontitis.

OBJECTIVE: Alveolar bone loss is a common outcome of chronic apical periodontitis. In this study, we investigated the involvement of the Dickkopf-1-Wnt/beta-catenin signaling pathway in the attenuation of osteogenic differentiation induced by Escherichia coli lipopolysaccharide, and we evaluated the use of Dickkopf-1 inhibitor and Dickkopf-1 recombinant protein to reverse bone loss in different phases of osteogenic differentiation. METHODS: MC3T3-E1 cells grown in osteogenic medium were treated with Escherichia coli lipopolysaccharide for 24h during osteogenic induction on days 0, 1, 7, 14 and 21. Dickkopf-1 siRNA was added on days 0 and 1, and Dickkopf-1 recombinant was added on days 7, 14, and 21. Quantitative real-time PCR, Western blotting and alkaline phosphatase activity assays were performed to measure osteogenic marker expression and Wnt/beta-catenin signaling. A rat apical periodontitis model was used to further evaluate the function of Dickkopf-1 in relation to bone loss. RESULTS: MC3T3-E1 cells treated with Escherichia coli lipopolysaccharide showed decreased mRNA expression of osteogenic markers. Wnt/beta-catenin signaling was also inhibited, and Dickkopf-1 showed corresponding variations as quantified by Western blotting. Using Dickkopf-1 inhibitor or Dickkopf-1 recombinant protein at different phases of osteogenic differentiation in vitro partially reversed the decrease in osteogenic marker expression. The rat apical periodontitis model indicated that the Dickkopf-1 inhibitor could restore bone loss in the periapical area in vivo. CONCLUSIONS: Dickkopf-1 may play a key regulatory role in determining the outcome for bone in inflammatory environments, and modulating the Wnt/beta-catenin signaling pathway via Dickkopf-1 inhibitor or recombinant protein may provide a potential therapeutic option to prevent bone destruction in endodontic disease.