Cartilage destruction in osteoarthritis (OA) is associated with increased levels of several matrix metalloproteinases (MMPs), including the gelatinases MMP-2 and MMP-9. While increases in some MMPs may be destructive, up-regulation of others may result from increases in normal tissue turnover. The production of MMP-2 and MMP-9 by the anabolic transforming growth factor beta-1 (TGF-beta1) in normal equine chondrocytes was investigated.
Equine chondrocytes from clinically normal femoropatellar joints were maintained in alginate beads. After serum deprivation, cells were exposed to TGF-beta1 at several concentrations for varying times. Activities of MMP-2 and MMP-9 were estimated by gelatin zymography, while mRNA for MMP-2, MMP-9 and collagen type II were detected using reverse transcription-polymerase chain reaction.
Stimulation with TGF-beta1 differentially regulated MMP-2 and MMP-9, with strong up-regulation of both MMP-9 mRNA and enzyme. Increases in MMP-9 enzyme were dose-dependent (0-49 h). There is some evidence suggesting a slight reduction in MMP-2 release following stimulation. Collagen type II mRNA was transiently increased following stimulation.
The different effects of TGF-beta1 on MMP-2 and MMP-9 production by normal chondrocytes suggests different roles for these enzymes. The increases in both MMP-9 and collagen type II mRNA following stimulation may suggest a role for MMP-9 in tissue maintenance. Therefore, increased MMP-9 may be secondary to, as distinct from a cause of, cartilage damage.