Collagen IX in weight-bearing areas of human articular cartilage in late stages of osteoarthritis.

Aim: To determine if the amounts of collagen IX mRNA and protein are higher in osteoarthritic cartilage from weight-bearing areas of the knee joint compared to non-weight bearing areas in patients with stage IV osteoarthritis (OA).

Methods: Normal and OA cartilage samples were obtained from 15 patients undergoing total knee replacement or necropsies. mRNA was measured by real time RT-PCR and proteins were detected by Western blot and localized at the light and ultrastructural level.

Results: Collagen IX was found throughout all cartilage layers in healthy and OA tissue. Cells deposited collagen IX in the pericellular and interterritorial matrix and a 66% higher amount of collagen IX was detected in the pericellular matrix of the weight-bearing areas adjacent to the main defect in comparison to the macroscopically intact areas. This is in line with a 3.72 times higher amount of the respective mRNA.

Conclusion: The increased levels of collagen IX protein and its mRNAs found in the weight-bearing areas adjacent to the main cartilage defect might reflect an attempt on the part of the diseased cartilage tissue to stabilize and protect the remaining matrix of late-stage osteoarthritic cartilage from further destruction.