Functional analysis of osteocyte-specific acidic phosphoprotein by gene transfection

点击翻译按钮获取中文摘要

Dentin matrix protein 1 (DMP1) is one of the acidic phosphoproteins originally identified from a rat incisor cDNA library. DMP1 has abundant acidic domains and a large number of phosphorylation consensus sites for casein kinase I and II, which are negatively charged at physiological pH. Therefore, DMP1 likely binds with calcium and may regulate matrix mineralization.We demonstrated that DMP1 mRNA was predominantly expressed in osteocytes but not in osteoblasts and that DMP1 protein was in the pericellular bone matrix of osteocytes, while other bone matrix proteins including osteohalcin, osteopontin and bone sialoprotein were expressed in osteoblasts. We determined the precise expression pattern of DMP1 mRNA and localization of its protein in dentin and cementum. The localization of DMP1 mRNA and DMP1 protein in bone and tooth was closely related to their mineralization, suggesting that DMP1 plays an important role in mineraliztion.To elucidate the function of DMPI in vivo, we generated transenic mice that overexpressed DMP1 in osteoblasts and odontoblasts using type I collagen promoter. In DMP1 transgenic mice, trabecular bone the metaphysis was dramatically decrease. However, the number of osteoclasts was not increased, although the functional level of osteoclasts was not studied. The bone density of cortical bone near the metaphysis was increased. Northern blot analysis demonstrated no change of the production of the bone matrix. These findings suggested that DMP1 promotes the rate of bone mineralization process, although the significance of DMP1 expression specific for osteocytes was not yet known.