IDENTIFICATION OF TYPE-II, TYPE-IX AND TYPE-X COLLAGENS AT THE INSERTION SITE OF THE BOVINE ACHILLES-TENDON

Achilles tendinous collagen fibrils insert into the calcaneus by first passing through a zone that is defined histologically as fibrocartila ginous. This zone consists of four regions: tendon proper, non-mineral ized and mineralized fibrocartilage and bone. The function of this zon e has not yet been clearly defined. To gain more insight into the role of this fibrocartilaginous zone, collagens present in the zone of the Achilles tendon-calcaneus interface were isolated and characterized. Types II, IX and X collagens were identified in the pepsin digests of the tissue harvested from the bovine Achilles tendon-calcaneus interfa ce. Western blotting using specific antisera to types IT, IX and X col lagens confirmed the identity of these collagens. Immunofluorescence l ocalization placed type X collagen predominantly in the mineralized zo ne of the tendon-calcaneus junction, while type IX collagen was distri buted throught the the insertion site. The presence of the cartilage-s pecific collagens at the Achilles tendon-calcaneus-interface suggests that this zone is cartilaginous in nature. The presence of type X coll agen at this junction is not clear, but our present findings go along with the previous report which showed that type X collagen is present in the mineralized zone of the medial collateral ligament femoral inse rtion site. These data suggest that type X collagen may be a resident of mineralized fibrocartilaginous zones of tendon or ligament-bone jun ctions and may participate in anchoring ligament or tendon to bone.