Effects of transforming growth factor βs and basic fibroblast growth factor on articular chondrocytes obtained from immobilised rabbit knees

Abstract

Objective - To clarify the effects of transforming growth factor β1 (TGFβ1), TGFβ2, and basic fibroblast growth factor (bFGF) on cell proliferation and proteoglycan (PG) synthesis in articular chondrocytes obtained from immobilised rabbit knees. Methods - The right knees of rabbits were immobilised in full extension for up to 42 days using fibreglass casts. Specimens for histology were stained with safranin O. Chondrocytes were isolated from the weight bearing regions of the femur and tibia of the immobilised knees and cultured with combinations of growth factors. Cell proliferation and PG synthesis were determined by 3H-thymidine and 35S-sulphate incorporations. Results - Histological study revealed loss of metachromasia in the articular cartilage at seven days, fissuring and cell clusters at 28 days, and loss of cartilage layers 42 days after immobilisation; Radioisotope assay of the chondrocytes revealed no remarkable change in DNA synthesis in the presence of either TGFβ1 or TGFβ2 alone. bFGF markedly stimulated cell proliferation in specimens obtained 0 to seven days after immobilisation. The combination of either TGFβ1 or TGFβ2 with bFGF had a synergistic effect, inducing significant increases in DNA synthesis four, seven, and 14 days after immobilisation. PG synthesis by chondrocytes from immobilised joints was not significantly altered by these agents. Conclusion - TGFβ1 or TGFβ2 in combination with bFGF exert synergistic effects on cell proliferation in articular chondrocytes obtained from the rabbit knee during the early days after immobilisation by a cast. These results suggest a critical role of cytokine combinations in the development of articular cartilage degeneration after immobilisation.