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Zhumabayeva, Bakhyt D.,Lin, Wen-Lang,Choung, Pill-Hoon,Chien, Hua-Hong,Jaro Sodek,Sampath, Kuber T.,Cho, Moon-Il Korean Academy of Oral Biology and the UCLA Dental 1998 International Journal of Oral Biology Vol.23 No.2
Both osteogenic protein-1 (OP-1) and dexamethasone (Dex) are known to promote osteogenic cell differentiation and mineralized nodule formation in cultures of fetal rat calvarial cells and MC3T3-EI (MC3T3) cells. However, only Dex induces mineralized nodule formation by rat bone marrow stromal cells and periodontal ligament (PDL) cells. To determine the differential effects of OP-1, the synthesis of matrix components and the mineralization of nodules in cultures of PDL were investigated and compared with those of MC3T3 cells using electron microscopy, Northern blot, immunoprecipitation and immunogold labeling. Rat PDL cells derived from coagulum in the sockets at two days after tooth extrction, and MC3T3 cells were cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with 10% FBS, β-glycerophosphate (GP), and ascorbic acid (AA). When cultured for 21 days with Dex, PDL cells underwent sequential defferentiation and formed mineralized nodules. the mineral deposit was first observed on densely-stained globular patches located primarily in the upper cell layers of nodules. As mineralization progressed, the deposits fused together and increased in size, forming a continuous mineral deposit that extended into the lower cell layers of the nodule. High levels of mRNA expression for secreted protein, acidic and rich in cysteine (SPARC) and type I collagen (Col I) were observed, together with a time-dependent induction of alkaline phosphatase (ALP). osteopontin (OPN), bone sialoprotein (BSP) and osteocalcin (OC) mRNAs, and the synthesis of BSP shown by immunoprecipitation, A comparable expression pattern of matrix protein mRNAs was observed when PDL cells were treted gor 21 day with OP-1. However, OP-1 failed to induce the expression of BSP m RNA and the mineralization of nodules. Although globular patches were formed, they were neither fused together nor associated with mineral deposits. In contrast, OP-1 not only drmatically increased expression levels of mRNA for the matrix components including BSP in MC3T3 cells, but also increased the number of mineralized areas. These results demonstrate that there are marked differences in the ability of OP-1 to induce BSP gene expression depending on cell types, and also indicate that BSP is required for the mineralization of extracellular matrix.