Comparison of Meniscal Cell-Mediated and Chondrocyte-Mediated Calcification

BACKGROUND: Chondrocytes have been traditionally thought to be responsible for calcium crystal deposits within osteoarthritic knees. Increasing recent experimental evidence suggests that menisci may also play a role. However, the calcifying potential of chondrocytes and meniscal cells derived from same OA patients, and the genes associated with meniscal calcification have never been fully examined. OBJECTIVE: Examine and compare the calcifying potential of articular chondrocytes and meniscal cells derived from same OA patients and identify the calcium crystal type(s) and selected gene expression in OA menisci. METHODS: Chondrocytes and meniscal cells were isolated from articular cartilage and menisci of OA patients undergoing total knee arthroplasty. Chondrocyte- and meniscal cell-mediated calcification was examined using both monolayer and micromass culture-based assays. Crustal types were examined with histological staining. Levels of Type X Collagen, MMP-13, and ANKH in OA menisci were examined using immunohistochemistry. RESULTS: Primary human OA meniscal cells produced calcified deposits at a similar rate compared to OA chondrocytes in-vitro. Histological examinations indicate that both BCP crystals and CPPD crystals are present in the meniscal tissue. Type X collagen, MMP-13, and ANKH were found in human OA menisci and their levels increased with OA severity. In addition, type X collagen was co-localized with calcium crystals. CONCLUSION: These findings suggest that OA meniscal cells have a similar calcifying potential as OA chondrocytes, supporting a pathogenic role of OA menisci in OA.