Objective: To understand changes in gene expression levels that occur during osteoarthritic (OA) cartilage degeneration, using complementary DNA (cDNA)-array technology.
Methods: Nine normal, 6 early degenerated, and 6 late-stage OA cartilage samples of human knee joints were analyzed using the Human Cancer 1.2 cDNA array and TaqMan analysis.
Results: In addition to a large variability of expression levels between different patients, significant expression patterns were detectable for many genes. Cartilage types II and VI collagen were strongly expressed in late-stage specimens, reflecting the high matrix-remodeling activity of advanced OA cartilage. The increase in fibronectin expression in early degeneration suggests that fibronectin is a crucial regulator of matrix turnover activity of chondrocytes during early disease development. Of the matrix metalloproteinases (MMPs), MMP-3 appeared to be strongly expressed in normal and early degenerative cartilage and down-regulated in the late stages of disease. This indicates that other degradation pathways might be more important in late stages of cartilage degeneration, involving other enzymes, such as MMP-2 and MMP-11, both of which were up-regulated in late-stage disease. MMP-11 was up-regulated in OA chondrocytes and, interestingly, also in the early-stage samples. Neither MMP-1 nor MMP-8 was detectable, and MMP-13 and MMP-2 were significantly detectable only in late-stage specimens, suggesting that early stages are characterized more by degradation of other matrix components, such as aggrecan and other noncollagenous molecules, than by degradation of type II collagen fibers.
Conclusion: This investigation allowed us to identify gene expression profiles of the disease process and to get new insights into disease mechanisms, for example, to develop a picture of matrix proteinases that are differentially involved in different phases of the disease process.