Expression of type VI collagen in normal and osteoarthritic human cartilage

OBJECTIVE: This study was undertaken in order to study the expression of type VI collagen in normal and osteoarthritic human knee cartilage. METHODS: Seventy-two osteoarthritic cartilage/bone samples were obtained form 29 patients with primary OA undergoing surgery for a total knee replacement. Normal cartilage was collected from five human knees at the time of autopsy. Type VI collagen protein was localized using a polyclonal anti human type VI collagen antibody, the corresponding mRNA was detected with an 310 base antisense probe, specific for the alpha2(VI) collagen chain. RESULTS: In normal cartilage, type VI collagen protein is concentrated pericellularly around the chondrocytes of all cartilage zones. In the middle and deep zones, type VI collagen was also found in the interterritorial matrix. Type VI collagen mRNA expression was detected in chondrocytes of all cartilage zones. In moderately affected osteoarthritic cartilage, type VI collagen expression was increased. An intensive immunohistological interterritorial staining for type VI collagen was observed in the middle and deep cartilage zones. Specific mRNA signals were also increased especially in the middle and deep cartilage zone. In the superficial zone and calcified cartilage of these samples, type VI collagen mRNA expression was restricted to focal areas. In severe osteoarthritic cartilage, an intensive staining for type VI collagen mRNA was found in clusters of proliferating chondrocytes and in the deep cartilage zone. Type VI collagen was localized pericellularly and in the matrix of chondrocyte clusters. Furthermore, chondrocytes from the deep zone showed a territorial distribution of type VI collagen. CONCLUSIONS: These results demonstrate that in normal and osteoarthritic cartilage, type VI collagen is expressed in a zone specific pattern. The observed increase of type VI collagen expression in osteoarthritis suggests a potential role in the disease process.