Elevated extracellular Ca2+ induces fibroblast growth factor-2 mRNA in cementoblasts

Objectives: G protein coupled receptors, such as calcium-sensing receptor, play an important role in calcium homeostasis, predominantly through effects on parathyroid glands. Such receptors are known to be expressed in osteoblastic cell lines and involved in osteoblastic differentiation. In contrast, little is know with regard to the response of cementoblasts to changes in extracellular Ca²⁺ concentration. Cementoblasts, cells lining the root surface expressing genes/proteins similar to osteoblasts, are considered to be pivotal for development and regeneration of cementum and a functional periodontal ligament. We investigated the effects of elevated levels of extracellular Ca²⁺ on gene expression of periodontal regeneration-associated growth factors in cementoblasts, in vitro. Methods: Mouse cementoblasts (OCCM-30) were stimulated with various concentrations of CaCl₂ in DMEM in the absence of FBS over a 24-hr period and gene expressions were analyzed using real-time quantitative RT-PCR. Phosphorylation of extracellular signal-regulated kinases (ERK1/2) was assessed by Western blot analyses. Results: Elevated extracellular Ca²⁺ (normally 1.8 mM in culture media) induced fibroblast growth factor (FGF)-2 mRNA (6-fold) at a peak point of 3 hrs in a dose dependent manner with plateau concentration of 10 mM, assessed by qRT-PCR. Other growth factors such as platelet derived growth factor (PDGF)-A and PDGF-B were not significantly changed. Calcium-sensing receptor agonists, spermine, neomycin and gadlinium showed a similar effect to CaCl₂. Elevated extracellular Ca²⁺ induced phosphorylation of ERK1/2 with a peak at 10 min, and, in addition, pretreatment of OCCM-30 with PD98059 (ERK1/2 inhibitor) abrogated the induction of FGF-2 mRNA expression. Conclusion: These results suggest that elevated extracellular Ca²⁺ induced FGF2 in mouse cementoblasts via MAPK pathway. These findings may be useful to consider for devising new strategies for use in periodontal regenerative therapy. Supported by the Tohoku University interface-science foundation.