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).
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.
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.
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.