Cell biological study on physiological root resorption of deciduous teeth ; potentiality to support odontoclast differentiation on periodontal ligament fibroblasts derived from of human deciduous teeth

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It was suggested that the fibroblasts derived from periodontal ligament of human permanent teeth (HPLF) and deciduous teeth (HPLF-Y) inhibit the formation of odontoclast (or osteoclast)-like cells using coculture system with mouse bone marrow cells (BMC), while the osteoblasts derived from human alveolar bone (hOB) has no effect on that compared to the culture of BMC alone. The inhibitory effects on the osteoclast-like cells (OC) formation in contact with HPLF or HPLF-Y were more significant than the coculture at non-contact condition between BMC and HPLF or HPLF-Y.On the other hand, pretreated HPLF and HPLF-Y with 1 α 25(OH)_2 vitaminD_3 (D_3) and dexamethasone (Dex) did not inhibited tartrate- resistant acid phosphatase (TRAP) positive multinucleated cells (MNC) formation in the coculture system. Then we performed RT-PCR to examine the mRNA level for macrophage colony stimulating factor (M-CSF), one of the essential factors for the differentiation of osteoclast precursor in early stage, on total RNA isolated from HPLF-Y, hOB and the fibroblasts derived from human gingival tissue (hGF) treated with D_3, Dex or both of them. As the result of semi-quantitative RT-PCR, the expression of mRNA for secreted form M-CSF (M-CSFs) was predominant over that for membrane-bound form M-CSF (M-CSFm) on hOB and hGF, however mRNA expression of both forms was same level on HPLF- Y.Moreover, the level of mRNA for M-CSFm increased by D_3 treatment and the effect was more remarkable in the presence of Dex while mRNA expression for M-CSFs was not affected by D_3 and Dex treatment. On the other hand, Dex treatment increased the ratio of M-CSFm mRNA level in total expression of both M-CSFs and M-CSFm on HPLF-Y and hGF, while it was reduced by D_3 treatment. These results suggest that the proportion of mRNA level of M-CSFm to that of M-CSFs on the fibroblast is different from osteoblast and that the ratio is altered by soluble factors related to bone metabolism such as D_3 and Dex.