The induction of osteopontin by osteoprotegerin in HPDL cells

Methods: Cultured HPDL cells were treated with recombinant human OPG (0-100 ng/ml) for 24-48 h. The expression of OPN mRNA and protein were analyzed by reverse transcription polymerase chain reaction and Western blot analysis, respectively. Phosphoinositol 3-kinase (PI3K) inhibitor, Akt inhibitor, heparinase, neutralizing antibody against RANKL and syndecan-1 and small interfering RNA (siRNA) against syndecan-1 were used to determine the mechanism involved.

Results: OPG (100 ng/ml) up-regulated the mRNA and protein expression of OPN in HPDL cells. Upon the induction, Akt was activated. The inductive effect by OPG was abolished by PI3K and Akt inhibitors as well as by the neutralizing antibody against syndecan-1 or syndecan-1 small interfering RNA (siRNA). All the inhibitors had no effect on the background expression of OPN.

Conclusion: Endogenous OPG does not alter the OPN expression. Interestingly, exogenous OPG significantly increases OPN expression in HPDL cells. The increased OPG may play a significant role in alveolar bone remodeling by modulating the expression of OPN via syndecan-1/PI3K/Akt signaling pathway in HPDL cells.

This work was supported by Research Fund of Faculty of Dentistry and Research Unit of Mineralized Tissue, Chulalongkorn University