Changes in messenger rna and protein levels of proteoglycans and link protein in human osteoarthritic cartilage samples

Abstract

Objective. To determine the steady‐state messenger RNA (mRNA) levels and corresponding protein contents of major matrix components in osteoarthritic (OA) cartilage. Methods. Steady‐state levels of gene‐specific mRNA (relative to GAPDH) were measured by quantitative polymerase chain reaction (PCR), and the relative levels of the corresponding proteins were determined by Western blotting. Results. All mRNA levels and corresponding protein contents of aggrecan and versican (hyaluronan‐binding large proteoglycans), decorin, biglycan, fibromodulin, and lumican (small proteoglycans), and link protein were higher in OA cartilage samples than in age‐matched normal samples. The ratio of increase, however, was different for each component. The mRNA and protein levels of biglycan, decorin, and fibromodulin increased synchronously, whereas message for link protein and lumican were several‐fold higher than expected by their measured protein contents. Versican was also detected in OA cartilage; however, the versican protein content was associated with a relatively low mRNA level. Conclusion. The expression of matrix components was increased in chondrocytes of OA cartilage, especially the expression of small proteoglycans, most likely due to the repair processes. A discoordinate gene expression accompanied with imbalanced accumulation of noncollagenous matrix components may contribute to the disorganization of the cartilage and the development of OA processes.