Effect of transforming growth factor β on cell proliferation and glycosaminoglycan synthesis by rabbit growth-plate chondrocytes in culture

Abstract

The effects of the transforming growth factor β (TGF-β) on the growth and glycosaminoglycan synthesis of rabbit growth plate-chondrocytes in culture were studied. In serum-free medium, TGF-β caused dose-dependent inhibition of DNA synthesis by chondrocytes, measured as [ 3H]thymidine incorporation ( ED 50 = 0.1–0.3 ng/ml ). The inhibitory effect was maximal at a dose of 1 ng/ml, and extended for a duration of 16–42 h. In contrast, TGF-β potentiated the synthesis of DNA stimulated by fetal calf serum (FCS). Addition of TGF-β (1 ng/ml) to cultures containing 10% FCS increased [ 3H]thymidine incorporation to 1.6-times that in cultures with 10% FCS alone. Consistent with this finding, TGF-β potentiated DNA synthesis stimulated by the purified growth factors such as platelet-derived growth factor (PDGF), epidermal growth factor (EGF) and fibroblast growth factor (FGF). The maximal stimulation of DNA synthesis by FGF (0.4 ng/ml) was further potentiated dose dependently by TGF-β ( ED 50 = 0.1 ng/ml , maximum at 1 ng/ml). When the cultures were treated with the optimal concentrations of TGF-β (1 ng/ml) and FGF (0.4 ng/ml), [ 3H]thymidine incorporation was 3-times higher than that of cultures treated with FGF alone. This TGF-β-induced potentiation of DNA synthesis was associated with replication of chondrocytes, as shown by a marked increase in the amount of DNA during treatment of sparse cultures of the cells with the growth factors for 5 days. In contrast, TGF-β caused dose-dependent stimulation of glycosaminoglycan synthesis in confluent cultures of growth-plate chondrocytes ( ED 50 = 0.3 ng/ml , maximum at 1 ng/ml). This stimulatory effect of TGF-β was greater than that of insulin-like growth factor I (IGF-I) or PDGF. Furthermore, TGF-β stimulated glycosaminoglycan synthesis additively with IGF-I or PDGF. Recently, it has been suggested that bone and articular cartilage are rich sources of TGF-β, whereas epiphyseal growth cartilage is not. Thus, the present data indicate that TGF-β may be important in bone formation by modulating growth and phenotypic expression of chondrocytes in the growth plate, possibly via a paracrine mechanism.