[Osteocyte and DMP1].

Dentin matrix protein (DMP1) is a non-collagenous bone matrix protein produced specifically by osteocytes. Because of its highly acidic nature, DMP1 can participate in bone matrix mineralization through Ca(2 + ) binding capacity. Inactivating mutations in DMP1 have recently been shown to cause autosomal recessive hypophosphatemic rickets (ARHR) . In a murine model of ARHR, DMP1-null mice had increased fibroblast growth factor23 (FGF23) expression in osteocytes, indicating that DMP1 participates in the systemic phosphate regulation by restraining osteocytic FGF23 production. In addition, the DMP1 promoter has been used frequently as an osteocyte-specific promoter. However, DMP1 is not expressed in all osteocytes. DMP1 expression is seen in osteoblastic-, osteoid-, young osteocytes of the superficial bone layer, but is reduced remarkably in old osteocytes distributed over the bone inside. This pattern of DMP1 expression may influence the interpretation of DMP1 function and the studies that use the DMP1 promoter.