Bone Abstracts

Objectives: To define the role of bone morphogenetic proteins (BMP) in human osteochondromas. The expression of bone morphogenetic proteins and their corresponding receptors has not been clarified in osteochondromas. We determined immunohistochemically the localization and distribution of bone morphogenetic proteins 2, 4, 6 and 7, bone morphogenetic protein receptor types 1A, 1B and 2 and the functional effectors phosphorylated Smad proteins 1, 5 and 8 in the cartilaginous cap of human osteochondromas and compared with growth plate and articular cartilage of bovine knee joints.

Methods: The localization of antibodies against human BMP-2/-4, BMP-6, BMP-7, BMP receptor type 1A, 1B and 2 and phospho-Smads 1/5/8 on sections of solitary (n=6) and multiple hereditary (n=6) osteochondromas was examined using immunohistochemical localization methods.

Results: The distribution and localization of BMP-2/-4, BMP-7 and receptors BMPR-1A, BMPR-1B and BMPR-2 was observed uniformly in chondrocytes in osteochondromas and growth plate. A difference in the distribution of BMP-6 and phospho-Smads 1/5/8 was observed between osteochondroma and growth plate. BMP-6 was localized throughout the cartilaginous cap of osteochondromas while BMP-6 was mainly found in the hypertrophic zone of the growth plate. In osteochondromas phospho-Smads 1/5/8 was observed in hypertrophic chondrocytes undergoing calcification. In contrast, phospho-Smads 1/5/8 was observed throughout the growth plate with greater staining intensity in the resting zone. The expression of BMP-6, BMPR-1A, BMPR-1B and BMPR-2 varied among the cartilaginous cap of solitary and multiple hereditary osteochondromas, the difference is not significant (P>0.05).

Conclusion: The localization of BMP 2, 4, 6 and 7, BMP receptor types 1A, 1B and 2 and phosphorylated Smad proteins 1, 5 and 8 was analysed in human osteochondromas immunohistologically. Distributions of BMP-6 and phosphorylated Smad proteins 1, 5 and 8 in human osteochondromas were different from normal growth plate. Since bone morphogenetic proteins can stimulate proliferation and differentiation of chondrocytes, these findings suggests that there may be a dysregulation of chondrocyte proliferation and differentiation in the cartilaginous cap of human osteochondromas.