Dentin Matrix Protein 1 Compensates for Lack of Osteopontin in Regulating Odontoblastlike Cell Differentiation after Tooth Injury in Mice

Introduction: Although dentin matrix protein 1 (DMP1) and osteopontin (OPN) act as substrates and signaling molecules for odontoblastlike cell differentiation after tooth injury, the mutual interaction between these proteins in the mechanism of odontoblastlike cell differentiation remains to be clarified. This study aimed to elucidate the role of DMP1 and OPN in regulating odontoblastlike cell differentiation after tooth injury.

Methods: A groove-shaped cavity was prepared on the mesial surface of the upper first molars in wild-type and Opn knockout (KO) mice. The demineralized paraffin sections were processed for immunohistochemistry for nestin and DMP1 and in situ hybridization for Dmp1. For the in vitro assay, the experiments of organ culture for evaluating dentin-pulp complex regeneration using small interfering RNA treatment were performed.

Results: Once preexisting odontoblasts died, nestin-positive newly differentiated odontoblastlike cells were arranged along the pulp-dentin border and began to express DMP1/Dmp1. In Opn KO mice, the expression of DMP1/Dmp1 was up-regulated compared with that of wild-type mice. The in vitro assay showed that the gene suppression of Dmp1 by small interfering RNA showed a tendency to decrease the differentiation rate of odontoblastlike cells from 70.1% to 52.2% in wild-type teeth. In addition, the suppression of Dmp1 in Opn KO teeth tended to lead to the inhibition of odontoblastlike cell differentiation.

Conclusions: These results suggest that the expression of Dmp1 is up-regulated in Opn KO mice both in vivo and in vitro, and DMP1 compensates for the lack of OPN in regulating odontoblastlike cell differentiation after tooth injury.