Responsiveness of bovine chondrocytes to growth factors in medium with different serum concentrations

Autologous transplantation of chondrocytes is currently under investigation as a potential therapy to stimulate intrinsic repair in articular cartilage defects. The quality of the repair tissue may benefit from the preservation of the characteristic chondrocytic phenotype of the transplanted cells together with the production of a new extracellular matrix composed of collagen type II and larger proteoglycans. A number of growth factors are believed to play an important role in the process of generating new cartilage repair tissue. In this study, the dose-dependent response of bovine chondrocytes to recombinant human insulin-like growth factor-1, recombinant human transforming growth factor-beta2, and recombinant human bone morphogenetic protein-2 was studied in an alginate culture system under different culture conditions. The chondrocytes were cultured in medium with increasing concentrations of fetal calf serum. The cultures were assessed by the total amount of DNA, quantitative and qualitative synthesis of proteoglycan, production of nitric oxide, and histology. Cells cultured in the presence of each growth factor had an equal, nonsignificant stimulation of DNA synthesis compared with those cultured in basal medium alone. Recombinant human insulin-like growth factor-1 and recombinant human transforming growth factor-beta2 stimulated proteoglycan synthesis in a dose-dependent and reversed dose-dependent fashion, respectively. Recombinant human bone morphogenetic protein-2 stimulated proteoglycan synthesis significantly only in the absence of fetal calf serum or in the presence of small amounts of the serum. Overall, proteoglycan synthesis dramatically decreased with the addition of each growth factor as the concentration of fetal calf serum in the medium decreased, and the dose-dependent stimulation pattern, as observed for recombinant human insulin-like growth factor-1 and recombinant human transforming growth factor-beta2, disappeared. Apart from a moderate increase in mRNA for aggrecan and decorin, the growth factors did not greatly affect the type of proteoglycans synthesized. Histological examination confirmed the presence of a dense pericellular matrix deposition, especially when the chondrocytes were cultured in the presence of recombinant human insulin-like growth factor-1 or recombinant human transforming growth factor-beta2. The results indicate that these growth factors can stimulate qualitatively superior matrix production and that the responsiveness of the chondrocytes to the growth factors changes with the culture conditions. Further knowledge about the interaction between chondrocytes, growth factors, and the external environment is important to stimulate chondrocytes to produce adequate repair tissue in cartilage defects in vivo. Insulin-like growth factor-1 especially seems capable of stimulating, in the most consistent and predictable fashion, qualitatively superior proteoglycan synthesis by differentiated chondrocytes. Additional in vivo studies are needed to evaluate the potential of these growth factors as stimulators in cartilage repair.