Expression of odontogenic ameloblast-associated protein in the dental follicle and its role in osteogenic differentiation of dental follicle stem cells.

OBJECTIVE: Odontogenic Ameloblast-Associated Protein (ODAM) is encoded by a secretory calcium-binding phosphoprotein cluster gene, which generally plays an important role for mineralization. Dental follicle (DF) is essential in regulating bone formation for tooth eruption. This study aims to reveal ODAM expression in the DFs of developing and erupting molars, and to determine the possible role of ODAM.

DESIGN: DFs were collected from human third molars and rat mandibular molars for gene expression assessment and for establishment of cell cultures. RT-PCR and western blot were conducted to determine ODAM expression. Over- or silencing expression of ODAM in the dental follicle stem cells (DFSCs) was done by transfecting the cells with ODAM plasmid or siRNA to evaluate ODAM effects on osteogenesis.

RESULTS: Rat DFs weakly expressed ODAM at early-postnatal days, but a chronological increment of ODAM expression from days 1 to 11 was observed. Differences in expression of ODAM were seen in the human DFs of different individuals. In vitro, ODAM was expressed in DFSCs, but almost no expression in DF-derived fibroblast-like cells. Forcing the DFSCs to overexpress ODAM accelerated osteogenesis, whereas continuously silencing the ODAM in the DFSCs reduced osteogenesis only at 2 weeks of osteogenic induction.

CONCLUSIONS: ODAM is differentially expressed in the DFs of different age molars. Its expression is coincident with the increased bone formation of tooth crypt during tooth eruption in rat DFs. Increase of ODAM expression may accelerate osteogenic differentiation of DFSCs. Thus, ODAM expression in the DF may regulate bone formation for timely tooth eruption.