Objective: To determine the mechanism of MMP-13 upregulation in osteoarthritic synovial fibroblasts (OASF) in response to stimulation with basic calcium phosphate (BCP) crystals and to investigate the effect of PGE2 on BCP crystal-stimulated MMP expression.
Methods: Primary OASF were stimulated with BCP crystals; mRNA expression was measured by real-time RT-PCR and protein levels were assessed by western blotting.
Results: BCP crystals upregulated MMP-13 mRNA expression over 20-fold and increased MMP-13 protein production in OASF. BCP crystal-stimulated MMP-13 mRNA expression was blocked by inhibition of the extracellular regulated kinase (ERK1/2) and p38 mitogen activated protein kinase (MAPK) pathways and inhibition of activation of nuclear factor kB. Addition of exogenous PGE2 downregulated BCP crystal-stimulated MMP-13 expression. In contrast, PGE2 upregulated, and had no effect, on BCP crystal stimulated MMP-3 and MMP-1 mRNA expression, respectively. These effects of PGE2 were diminished by L-161,982, a selective EP4 receptor antagonist, and mimicked by CAY10399, a selective EP2 receptor agonist, and forskolin, an adenylate cyclase activator.
Conclusions: These data suggest that BCP crystal induction of MMP-13 expression may involve the ERK1/2 and p38 MAPK pathways and activation of NFkB; this upregulation of MMP-13 may contribute to the accelerated cartilage breakdown in BCP crystal-associated OA. PGE2 had contrasting effects on BCP crystal-stimulated MMP-3 and MMP-13 mRNA expression, mediated in an EP2/EP4/cAMP dependent manner, suggesting that PGE2 may have beneficial as well as deleterious effects in BCP crystal-associated OA.
- basic calcium phosphate crystals
- matrix metalloproteinase-13
- prostaglandin E2
- synovial fibroblasts