Identification and immunolocalization of type X collagen at the ligament-bone interface.

In some ligaments, ligamentous collagen fibrils attach to bone by first passing through non-mineralized and mineralized fibrocartilage present at the ligament-bone interface. To understand better the function of these fibrocartilages, collagens present at the femoral insertion of the bovine medial collateral ligament were isolated and characterized. Types II and IX collagens were identified in pepsin digests of the tissue in addition to type X collagen originally thought to be associated with the cartilages undergoing endochondral bone formation. Presence of type X collagen was confirmed by immunoblotting and by immunofluorescence localization using laser confocal microscopy. Type X collagen was localized predominantly in the mineralized zone of the ligament insertion. These data indicated that type X collagen may play a role in ligament attachment to bone.