Chondrocyte number and proteoglycan synthesis in the ageing and osteoarthritic human articular cartilage

Objective

To correlate the number of chondrocytes in healthy and osteoarthritic human articular cartilage with age and to evaluate the influence of senescence on total proteoglycan synthesis.

Methods

Chondrocytes were isolated from human articular cartilage derived from hip joints with and without osteoarthritic lesions. Cell number was assessed by light microscopy and normalized to cartilage sample wet weight. Chondrocytes were grown as monolayer cultures for 7 days in a chemically defined serum-free basal medium. Total proteoglycan synthesis was measured by [³⁵S]sulfate incorporation into newly synthesized macromolecules.

Results

Chondrocyte numbers in healthy cartilage decreased significantly with advancing age (r = -0.69, P < 0.0001). In contrast to healthy specimens, chondrocyte numbers were decreased in OA cartilage irrespective of and unrelated to age and differed markedly, by an average of 38%, from the cell numbers found in healthy cartilaginous tissue (P < 0.0001). Regarding proteoglycan synthesis, no dependence on patient's age, either in healthy or in OA specimens, were observed in our culture settings.

Conclusions

Chondrocytes from healthy and OA joints synthesized comparable amounts of PG, independent of age or underlying OA disease. As the cell count in our monolayer cultures was constant, we conclude that the decreased chondrocyte number found in the ageing and OA joints could be a crucial factor in limiting tissue replenishment in vivo.