Changes in the endogenous BMP expression during redifferentiation of chondrocytes in 3D cultures

Engineering cartilage tissue is challenging, mainly because chondrocytes lose their differentiated phenotype when cultured in monolayer. The aim of this study was to analyse the influence of 3D-culture conditions on the redifferentiation of chondrocytes, devoting special attention to BMPs. Dedifferentiated chondrocytes were seeded onto two different scaffolds (Bio-Gide and HYAFF-11) and were then cultured for 38 days. Every week, samples were taken for gene expression analysis and immunohistochemistry. In both scaffolds an increasing differentiation was observed caused by an increase in Col2 and a reduction in Col1 expression. The various BMPs were regulated, albeit differently by the changing culture conditions. While GDF-5 and BMP-4 expression increased in the monolayer culture in comparison with native cartilage and decreased again in the 3D culture, the BMP-2 and BMP-6 expression decreased dramatically in the monolayer as well as in the 3D culture. BMP-7 was not detectable in any probe. Scaffold cultivation appears to stimulate the induction of redifferentiation, but is not sufficient to induce expression of BMP-2 -6 or -7. Since, in comparison to cartilage development, there is a lack of surrounding signal centres, external stimuli seem to be required to obtain complete redifferentiation. Our data indicate that a combination of BMP-2, -6 and -7 may be promising for this purpose.