カルシウムが破骨細胞に及ぼす影響

概要

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Though it has been reported that osteoblasts perceive extracellular calcium levels and regulate the differentiation and function of osteoclasts, the details of its mechanism of calcium perception or of its genetic expression system mostly remains unclear. In the present study, therefore, the influence of a high-calcium environment on osteoblasts was examined from the expressions of RANKL and CaSR mRNAs as well as from the formation of osteoclasts following cocultures. The identification of CaSR was made by the immunohistochemical staining method using rat alveolar bones with experimental tooth movement. On the third and seventh days after manipulation, both osteoclasts and osteoblasts showed CaSR positive reaction on the compressed side of the alveolar bones. On the other hand, CaSR positive reaction was observed only for osteoblasts on the tension side of the alveolar bones, though the reaction was weak. In the subsequent experiment using an osteoblast-like cell line (SaOS-2 ), PT-PCR was performed by changing the calcium concentration in the cultured solution from 1.8 to 2.5, 10 and 40 mM and further by treating with 0.1 and 1.0 μM of ionomycin. The PCR products of RANKL and CaSR mRNAs were then analyzed. The expressions of RANKL and CaSR mRNAs decreased in a calcium concentration dependent manner. When SaOS-2 cells were treated with ionomycin, RANKL mRNA expression increased in a dose dependent manner. However, CaSR mRNA expression increased at 0.1 μM ionomycin but showed almost no difference at 1.0 μM as compared with the untreated level. In order to examine the effect of calcium on the differentiation of osteoclasts, SaOS-2 cells were cocultured with a human myeloid leukemia cell line (HL-60). Total RNAs were extracted after SaOS- 2 cells pretreated with calcium were cocultured with HL-60 and after SaOS-2 cells pretreated with lα,25(OH)_2D_3 were cocultured with HL-60 under the presence of calcium, and the amount of tartrate-resistant acid phosphatase (TRAP) mRNA expression was examined by RT-PCR, Simultaneously, the number of osteoclasts that appeared was counted. As a result, the expression of TRAP mRNA increased in a dose dependent manner up to the calcium level of 2.5 mM but decreased at levels above it. The number of osteoclast-like cells showed a similar pattern to the expression of TRAP mRNA. In the case of SaOS-2 cells pretreated with 1α,25(OH)_2D_3, the TRAP mRNA expression increased in a dose dependent manner up to a calcium level of 10 mM but the expression at a calcium level of 40 mM decreased to a similar level observed at 1.8 mM. From the results mentioned above, it was suggested that a high extracellular calcium level in osteoblasts suppresses the expression of RANKL through CaSR which exists in the cell membrane and further suppresses the differentiation of osteoclastic precursors to osteoclasts.
岩手医科大学歯学会の論文
2004-04-26

著者

三條晃
岩手医科大学歯学部口腔保健育成学講座歯科矯正学分野

カルシウムが破骨細胞に及ぼす影響

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