Gene expression of matrix metalloproteinases 1, 3, and 9 by chondrocytes in osteoarthritic human knee articular cartilage is zone and grade specific

Abstract

Objectives: Matrix metalloproteinases (MMPs) are thought to be major mediators of cartilage destruction. Osteoarthritis (OA) is characterised by cartilage degradation. This study explores gene expression of three MMPs in articular chondrocytes during the histological development of the cartilage lesion of OA.

Methods: Biopsy specimens of human normal and OA cartilage, classified into four grades on the basis of histology, were probed for MMPs 1, 3, and 9 using 35S-labelled cDNA probes. The signal was measured at four different depths (zones) using an automated image analyser and compared with signal from sections probed with lambda DNA. Rheumatoid synovium was used as a positive control for MMP gene expression.

Results: Rheumatoid tissue contained mRNA for all three MMPs. Expression in chondrocytes varied with the depth of the chondrocyte in the cartilage and the histomorphological extent of the OA changes. There was no detectable mRNA signal for these three MMPs in normal cartilage. In general, in OA, MMP-1 gene expression was greatest in the superficial cartilage in established disease. By contrast mRNAs for MMP-3 and 9 were expressed deeper in the cartilage, MMP-9 early in disease and MMP-3 with a biphasic pattern in early and late stage disease, most pronounced in the latter. This was a consequence of differential expression in single cells and chondrocyte clusters in late disease.

Conclusion: The data indicate that expression of genes for MMPs 1, 3, and 9 is differentially regulated in human articular chondrocytes and, in individual cells, is related to the depth of the chondrocyte below the cartilage surface and the nature and extent of the cartilage lesion.

Figure 1

Each diagram shows the distribution and amount of a metalloproteinase mRNA signal in articular cartilage in the various zones and grades of cartilage damage. The (S−N)/N ratio is represented by the density of shading of the box and by the numbers within the box. The numbers represent the mean (SD) ratio for all the sections of all the biopsy specimens in that grade. The shading has been arbitrarily divided into five as shown in the key. It is intended that the figure should aid visual comparison between the different MMPs in terms of signal and distribution.

Figure 2

Examples of ISH reaction in articular cartilage. (A) Low power light photomicrograph of zones 2, 3, and 4 grade 3 reacted for MMP-1. The subchondral bone is in the bottom right and the articular surface bearing a small fissure is just visible in the top left. Zones 2 and 4 contain very little reaction product whereas reaction product is visible within zone 3. ISH × 50. (B) Light field photomicrograph of zones 2 and 3 grade 3 reacted for MMP-3. The majority of lacunae containing single cells have little or no overlying reaction product (arrow heads). Almost all the lacunae containing multiple cells (chondrocyte clusters), such as that arrowed, have high signal levels. ISH × 150. (C) Light field photomicrograph of zones 1 and 2 of grade 1 articular changes reacted for MMP-9. There are no grains over the cells in zone 1 and a high grain count over cells in zone 2. ISH × 200. (D) RNase treated section reacted for MMP-1. ISH × 150.