Type II collagen deposition in cruciate ligament precedes osteoarthritis in the guinea pig knee

Objective: To examine the collagens in cruciate ligaments of young Dunkin-Hartley guinea pigs, to determine whether a change in specific collagen types is an early feature of the spontaneous osteoarthritis (OA), which consistently develops in the medial compartment of the knee in this strain. Design: Collagen types I, II, III, IX, and XI were detected by immunofluorescence microscopy in the anterior and posterior cruciate ligaments of animals at 3, 4–5 and 12 weeks of age. Type II collagen in PCL was further analysed by confocal microscopy or biochemical assay after cyanogen bromide digestion, SDS-PAGE and immunoblotting. Interfibrillar proteoglycans were visualized by transmission electron microscopy. Results: Collagen types I and III formed the bulk of fibrous mid-ligament tissue in all animals. Typical cartilage collagens, types II, IX and XI, were identified by immunolabeling where ligaments attached to tibial bone. Type II collagen, normally restricted to the fibrocartilage attachment sites, was also found at separate foci in anterior fiber bundles of the posterior cruciate ligament in 12-week-old animals. Biochemical data confirmed these observations which, together with electron microscopy showing large atypical proteoglycan structures, suggested the deposition of fibrocartilage within the fibrous mid-ligament. Conclusions: Cruciate ligaments, especially posterior cruciate ligament in Dunkin-Hartley guinea pigs synthesize cartilage-like matrix in mid-ligament prior to the appearance of classical signs of OA