The extracellular concentration of osteocalcin decreased in dental follicle cell cultures during biomineralization.

The secretion of osteocalcin (OCN) is an excellent differentiation marker for the osteogenic differentiation. This study investigated the secretion of OCN during the osteogenic differentiation of DFCs. During the differentiation of DFCs the extracellular concentrations of OCN were higher in standard cell culture medium than in osteogenic differentiation medium. However, after 4 weeks in the osteogenic differentiation medium the extracellular OCN concentration decreased strongly, whereas the concentration remains high in the control medium. At this point in time DFCs formed connective tissue like structures with mineralized clusters and OCN. Real-time RT-PCR analyses and western-blot analyses proved that OCN was expressed in both cell culture media. However, the expression of the mRNA was inhibited in the osteogenic differentiation medium. These results suggest that DFCs secrete constitutively OCN into the cell culture medium and that the osteogenic differentiation medium suppresses the gene expression of OCN. Moreover, OCN imbeds into the extracellular matrix after the formation of connective tissue like structures, and the soluble OCN in the cell culture medium disappears. Hence, extracellular OCN in the cell culture medium is not a marker for the osteogenic differentiation of DFCs.