[Immunocytochemistry of proteoglycan in dentin and odontoblasts]

To clarify the distribution of proteoglycan (PG) and matrix metalloproteinase-3 (MMP-3) in the molar tooth germ dentin of rats, immunohistochemical investigation was performed using a antibody 2-B-6 specific for chondroitin 4 sulfate (Ch4-S) and dermatan sulfate (DS) of PG, antibody 3-B-3 specific for chondroitin 6 sulfate (Ch6-S) and chondroitin (Ch) of PG and anti-human-MMP3 antibody. 2-B-6 reacted with the predentin and dentinal tubules. However, there were no reactions around the calcification front or in the calcified dentin matrix other than the dentinal tubules. 3-B-3 and anti-MMP3 antibodies reacted with only the predentin. These results showed that PG containing Ch4-S and DS was present in the dentinal tubules, while PG containing Ch4-S, DS, Ch6-S and Ch as well as MMP-3 was present in the predentin. It is suggested that PG of the predentin is degraded by MMP-3 at the calcification front. In undecalcified sections, the reaction of the dentinal tubules with 2-B-6 was localized in electron-dense sites corresponding to the peritubular dentin, suggesting that PG at this site binds to hydroxyapatite. Furthermore, in odontoblasts, the localization of 2-B-6 was noted in secretory granules distributed in the Golgi region and the odontoblastic process. This suggests that PG is transported from the Golgi region to the odontoblastic process in the form of secretory granules. Immunoreactive secretory granules were also noted in the cellular process of the calcified dentin. PG of the peritubular dentin may be secreted by these secretory granules in the process.