Introduction: Cementoblasts, the cells responsible for tooth root cementum formation, are especially sensitive to local phosphate and pyrophosphate during development, as evidenced by cementum phenotypes resulting from altered phosphate/pyrophosphate distribution. SIBLING family members BSP, OPN, and DMP-1 are regulated by phosphate in cementoblasts and have been shown to activate three specific matrix metalloproteinase (MMP) partners: MMP2, MMP3, and MMP9, respectively, in vitro. The aim of this study was to examine regulatory effects of phosphate on SIBLING and MMP expression in cementoblasts, in vitro.
Materials & Methods: Immortalized murine cementoblasts were treated with inorganic phosphate, in vitro, and effects on gene expression (by real time RT-PCR and mouse total genome microarray) were observed. Dose-response 80.1-10 mM phosphate) and time-course (1-48hr) assays were performed. A sodium-phosphate uptake inhibitor, foscarnet, was used to better define phosphate-mediated effects on cells.
Results: Three SIBLING family members were regulated by phosphate: OPN (increased over 3000f control), DMP-1 (increased over 3,00027777701060f control), and BSP (decreased). MMP3 was dramatically increased (4,00026651125000f control), paralleling regulation of its partner OPN. Both MMP2 and MMP9 were slightly down-regulated. Time-course experiments indicated a response for SIBLING and MMP genes within 24 hr. Use of foscarnet demonstrated that phosphate uptake was required for observed changes in gene expression.
Discussion: These results indicate an effect of phosphate on cementoblast SIBLING and MMP expression in vitro. During cementum formation, phosphate may be an important regulator of cementoblast activity, including modulation of biomineralization, attachment, and matrix modification
