Abstract
The X-linked hypophosphatemic (Hyp) mouse is a model of human X-linked hypophosphatemic rickets(XLH) and is characterized by hypophosphatemia, growth retardation, and osteomalacia. A histological examination of Hyp mouse incisors revealed evidence of poor dentin mineralization such as interglobular dentin, widened predentin, and irregular dentinal tubules. Bone and dentin disorders in Hypmice are considered to be induced by low serum phosphate levels caused by impaired renal phosphate reabsorption. The purpose of this study was to examine the distribution of osteocalcin (OC), which is the major non-collagenous protein in dentin, in Hyp mice using an immunohistochemical method. In the labial region, which corresponds to the crown region in the molar, we found OC-like immunoreactivity (-LI) in dentin and predentin of wild type mice. On the other hand, the dentin and predentin of Hyp mice lacked OC-LI. In the palatal region, which corresponds to the root of the molar, OC-LI was observed in the dentin and cementum of wild type mice, whereas it was observed in the cementum, but not in the dentin of Hyp mice. These findings suggest that odontoblasts in Hypmice may have a defect in the secretion of OC, and that the hypominerarization of dentin seen in Hyp mice may not be caused by only hypophosphatemia but also by this defect.
