Suppression of cartilage matrix gene expression in upper zone chondrocytes of osteoarthritic cartilage

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Abstract
Objective. To evaluate the anabolic activity of osteoarthritic chondrocytes in situ by investigating the messenger RNA (mRNA) expression of 3 major cartilage components, type II collagen, aggrecan, and link protein. Methods. In situ hybridization experiments and histochemical analysis for proteoglycan content were performed on parallel sections of normal and osteoarthritic (OA) cartilage specimens. Results. Most chondrocytes in the deeper zones of OA cartilage showed an increase in mRNA expression, in particular, of type II collagen and to a lesser extent, aggrecan, compared with normal specimens. However, chondrocytes of the upper zone were largely negative for aggrecan or type II collagen mRNA. The expression of link protein mRNA was low in normal and OA specimens. Conclusion. These observations suggest that suppression of the anabolic activity of chondrocytes in the upper zones contributes to the metabolic imbalance observed in OA cartilage. Stimulation of matrix anabolism in superficial chondrocytes might be a suitable target for therapeutic intervention.

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