Methods: Immunocytochemistry, immunogold electron microscopy and flow cytometry were used to examine the relative expression of BMPR-IA, IB and II in human alveolar osteoblasts, periodontal ligament cells and the osteosarcoma cell lines MG63 and HOS. Human gingival fibroblasts and oral epithelial cells were used to compare the cellular specificities of receptor expression.
Results: Immunocytochemical analysis demonstrated that a number of cell types, particularly the osteoblast-like cells and periodontal ligament cells, showed readily detectable expression of BMPR-IB. In contrast, the fibroblasts and epithelial cells appeared to be only weakly positive. Much lower bone cell staining profiles were observed for the BMPR-IA and II antigens, which were not detected in the fibroblasts and epithelial cells. In addition, in all of the receptor-positive cells the staining of all three types of BMPR was localised mainly on the cell surface. Immunogold electron microscopy confirmed these findings but also revealed the presence of some intracellular antigens, while flow cytometry analysis also showed that there was differential expression of the BMPR on these different types of oral cells.
Conclusion: These results show that the different BMPR are differentially regulated in different types of cell, suggesting that, like TGF-b, the BMP are likely to also have a major and selective impact on the growth and function of these oral cells. Studies are currently in progress to determine the precise intracellular localization of the BMPR and the post-transcriptional processes which regulate their expression and activity.