Immunohistochemical evidence for sclerostin during cementogenesis in mice.

The purpose of this study was to investigate systematically the expression of the glycoprotein sclerostin, the product of the SOST gene, in periodontal tissues, especially in the cementum of mice. Immunolocalization of sclerostin was performed in decalcified histological sections of the maxillary and mandibular jaws of 20 CB56BL/6 mice. For analysis, newborn mice as well as mice at the age of, 1, 2, 4 and 8 weeks were used to detect sclerostin in the cementum, periodontal ligament (PDL) and alveolar bone. For further characterization of the cells within the periodontium, antibodies for Runx2 and S100A4 were also applied. S100A4 as a marker for fibroblasts was used to characterize the fibroblasts, especially in the periodontal ligament. Runx2 as a marker for osteoblast-maturation was used to detect the osteoblasts in the alveolar bone. In addition to the detection in osteocytes, expression of sclerostin was observed in cementocytes of the cellular cementum. With regard to cementogenesis, positive identification of sclerostin could be verified in mice at the age of 4 and 8 weeks but not during the initial stages of cementogenesis. Positive immune reactions for Runx2 were observed in PDL cells, cementoblasts, cementocytes, osteoblasts and osteocytes. PDL cells generally showed positive immunoreactions for the S100A4 antibody. The main findings of this study were: (1) due to the fact that sclerostin was not identified in the initial stages of cementum development, its biological significance seems to be restricted to cementum homeostasis and possibly to regenerative processes; (2) verification of sclerostin only in cementocytes of cellular cementum points to biological similarity of cellular cementum and bone.