Effect of Differentially Crosslinked Collagenous Matrix on Osteoblast and Osteoclast Activities.

Objectives: Collagen crosslinks, which covalently connect collagen molecules and provide 3D template of bone architecture is one of the key elements of bone quality. The mechanical properties of bone is known to be affected by the amount and composition of collagen crosslinks. At the same time, collagen crosslinks might be a key factor to regulate bone metabolism controlling osteoblast and osteoclast activities. The purpose of this study was to investigate the effect of differentially crosslinked collagenous matrix on osteoblast and osteoclast activities.
Methods: MC3T3-E1 osteoblastic cells were cultured under the presence of β-aminopropionitrile (BAPN), an inhibitor of collagen crosslinking. After 2 weeks, cultured cell/matrices were abraded and then either osteoblasts or osteoclasts (RAW264.7) were seeded. Cellular actives were analyzed by respective activity assay and gene expression assay. C57BL/6J mice were assigned with BAPN containing diet for 8 weeks and diet was changed to normal diet thereafter. Mice were sacrificed at 8, 9, 10, 12 and 16 weeks. Femur and whole blood were collected and were analyzed by micro-CT and ELISA respectively.
Results: In the presence of BAPN, matrices synthesized by osteoblasts showed significantly lower collagen crosslinks. The osteoblasts cultured on the inferior crosslinked matrices showed higher ALP activity and gene expression of Alpl. On the other hand, TRAP staining and gene expression of Ctsk showed that osteoclast differentiation was down-regulated on the inferior crosslinked matrices. In animal model, assignment of BAPN decreased the collagen crosslinks but did not significantly affect the bone volume of femur epiphysis. The serum bone metabolic marker was increased at 2-4 weeks on TRACP-5b and 8 weeks on osteocalcin.
Conclusions: These results indicate that the collagen crosslinks of bone matrix may affect bone metabolism, possibly by controlling osteoblast and osteoclast activities.