Little is known about Wnt signalling in dental tissues. Wnt-signalling has been suggested to play an important role in tooth development and the regulation of the dentine-pulp complex. In bone, Wnt signalling is upregulated in cells after mechanical loading. We hypothesised that ultrasound may exert biological effects on dental tissues that could involve the Wnt signalling pathway. In this study, the effects of ultrasound on Wnt/beta-catenin signalling were investigated using an odontoblastic cell line, MDPC-23.
Methods:
MDPC-23 cells in suspension were treated for 1 minute using incremental ultrasonic powers (P0, P3, P5 and P7) at 30 kHz ultrasound transmitted via a dental scaler probe (EMS, Nyon, Switzerland). Treated cells were then cultured in DMEM/10%FBS for 4 or 24 hours. Viability and numbers of adherent cells were measured using WST-1 assay (Roche). Immunocytochemical localisation of beta-catenin was carried out after fixing the cultured cells with an acetone:methanol mixture. In addition, the expression of the Wnt target gene, nkd1, was analysed by real-time PCR.
Results:
MDPC-23 cells showed a non-linear response to ultrasound inducing approximately 40% cell death at the highest ultrasound dose P7. MDPC-23 cells exhibited no significant beta-catenin staining at 4H after ultrasound treatment; however a dose-related response was evident in the 24h treated cells, which was characterised by the accumulation of beta-catenin within cell nuclei. Real-time PCR data showed a 1.9 fold and 2.8 fold increase in expression of nkd-1 at P3 and P5 respectively 24h after treatment relative to 4h cultures. At P7, nkd-1 expression was decreased.
Conclusion:
Data indicate that ultrasound may induce the Wnt signalling pathway in odontoblast-like cells. Further work is warranted to elucidate the mechanisms by which ultrasound may affect cellular Wnt signalling in cells of the dentine-pulp complex.