A Potential Role of Runx2 in Odontoblast Differentiation

Runx2 plays a central role in skeletal development as demonstrated by the complete absence of osteoblasts/bone in mice with targeted disruption of Runx2 gene. Despite the biochemical similarities between the matrices of bone and dentin, the molecular basis underlying odontoblast cell-lineage specification is poorly understood. The objectives: of the present study were to elucidate the role of Runx2 in odontoblast differentiation using both in vivo and in vitro approaches. Phenotypic analysis of Runx2 null mice showed an arrest of molar tooth organ development at the early bell stage and lack of normal dentin formation. In situ hybridization studies indicated a differential regulation of type I collagen gene expression in bone and dentin. Transient transfections followed by quantitative RT-PCR were methods: used to study the role of Runx2 in regulating dentin matrix gene expression. Three cell lines: the MDPC-23, RPC-C2A and ROS17/2.8 were utilized for our in vitro studies. Results: indicate that forced expression of Runx2 caused a downregulation of DSPP gene expression in MDPC-23 cells and an upregulation in RPC-C2A cells. Interestingly, the expression of type I collagen was minimally upregualted in MDPC-23 cells and remained unaltered in RPC-C2A and ROS17/2.8 cells. In conclusion:, there is a differential regulation of ECM gene expression by Runx2 in odontoblasts and osteoblasts. We propose a role for Runx2 in the delineation of the osteoblast and odontoblast lineages. This research was supported by a grant from NIDCR/NIH DE 13368 to RDS.