Type X collagen: covalent crosslinking to hypertrophic cartilage-collagen fibrils

Our previous studies suggest that the fibril-associated form of type X collagen occurs through the addition of type X of molecules, newly synthesized in the hypertrophic zone, to preexisting heterotypic cartilage-collagen fibrils, assembled at an earlier stage of development from collagen type II + IX + XI. Consistent with this, we recently observed in an in vitro model system that exogenous type X collagen rapidly enters non-hypertrophic cartilage, and there becomes associated with the preexisting fibrils within the tissues. Now we have further examined this association and have found that it probably involves stabilization by covalent, lysine-derived crosslinking.