To determine the ability of basic calcium phosphate (BCP) crystals to induce (a) mitogenesis, matrix metalloproteinase (MMP)-1, and MMP-13 in human osteoarthritic synovial fibroblasts (HOAS) and (b) MMP-13 in cultured porcine articular chondrocytes.
Mitogenesis of HOAS was measured by [3H]thymidine incorporation assay and counts of cells in monolayer culture. MMP messenger RNA (mRNA) accumulation was determined either by northern blot analysis or reverse transcriptase-polymerase chain reaction (RT-PCR) of RNA from chondrocytes or HOAS treated with BCP crystals. MMP-13 secretion was identified by immunoprecipitation and MMP-1 secretion by western blot of conditioned media.
BCP crystals caused a 4.5-fold increase in [3H]thymidine incorporation by HOAS within 20 hours compared with untreated control cultures (p< or =0.05). BCP crystals induced MMP-13 mRNA accumulation and MMP-13 protein secretion by articular chondrocytes. In contrast, in HOAS, MMP-13 mRNA induced by BCP crystals was detectable only by RT-PCR, and MMP-13 protein was undetectable. BCP crystals induced MMP-1 mRNA accumulation and MMP-1 protein secretion by HOAS. MMP-1 expression was further augmented when HOAS were co-incubated with either BCP and tumour necrosis factor alpha (TNFalpha; threefold) or BCP and interleukin 1alpha (IL1alpha; twofold).
These data confirm the ability of BCP crystals to activate HOAS, leading to the induction of mitogenesis and MMP-1 production. MMP-13 production in response to BCP crystals is substantially more detectable in porcine articular chondrocytes than in HOAS. These data support the active role of BCP crystals in osteoarthritis and suggest that BCP crystals act synergistically with IL1alpha and TNFalpha to promote MMP production and subsequent joint degeneration.