FGF-2 abolishes the chondrogenic effect of combined BMP-6 and TGF-β in human adipose derived stem cells

In this study, we investigated the influence of transforming growth factor beta 3 (TGF-β3), bone morphogenetic protein 6 (BMP-6) and basic fibroblast growth factor (FGF-2) on chondrogenesis in adipose derived stem cells (ASC). Cells were isolated from liposuction material, expanded and subjected to chondrogenic differentiation. Micromass pellets were cultured in chondrogenic medium containing 10 ng/mL TGF-β3 which was additionally supplemented with 10 ng/mL BMP-6, 10 ng/mL FGF-2 or a combination of both. We quantitatively evaluated the cartilage specific gene expression after 14 days of culture. The end point measurements on day 35 included glycosaminoglycan (GAG) quantification, histological staining for chondrogenic markers, and transmission electron microscopy (TEM). In comparison to cultures induced with TGF-β3/FGF-2, the presence of TGF-β3/BMP-6 demonstrated strong induction of collagen type II, collagen type IX and aggrecan mRNA expression. This was corroborated by quanti-fication and histological staining for GAGs and immunohistological staining for collagen II. However, when a combination of BMP-6 and FGF-2 in addition to TGF-β3 was added, FGF-2 counteracted BMP-6, as indicated by reduced marker gene expression and weak to absent staining for GAGs. In conclusion, this study demonstrates that BMP-6 combined with TGF-β3 is a potent inducer of chondrogenesis in human ASC. In contrast, FGF-2 does not contribute to differentiation, but rather suppresses the chondrogenic potential of BMP-6.