TGFβ inhibition during expansion phase increases the chondrogenic re-differentiation capacity of human articular chondrocytes

summary Objective: Autologous chondrocyte implantation is a cell-based treatment to repair articular cartilage defects, relying on the availability of expanded (de-differentiated) chondrocytes. Unfortunately, the expansion process causes several phenotypical changes, requiring re-establishment of the native chondrogenic phenotype to sustain proper repair. Among other proteins, transforming growth factor-b (TGFb) is known to influence the chondrogenic re-differentiation of human articular chondrocytes (HACs) and their matrix deposition. Thus we investigated the effects of TGFb-depletion during the expansion phase. Design: HACs were isolated from articular cartilage and expanded in the canonical serum-supplemented medium [fetal calf serum (FCS)] or in a chemically-defined (CD) medium, with or without anti-TGFb antibody administration. The re-differentiation potential of the cells was assessed by pellet cultures, gene expression analysis and histology. Results: Cell proliferation proceeded more rapidly in CD-medium than in FCS-medium; it was not affected by the use of anti-TGFb antibody but was further increased by addition of exogenous TGFb1, via increased p-Smad1/5/8. Conversely, in FCS-medium, addition of anti-TGFb antibody decreased both proliferation and p-Smad1/5/8 level. Challenging either FCS- or CD-medium with anti-TGFb antibody during expansion enhanced chondrogenesis in the subsequent pellet cultures. Moreover, TGFb-depletion during expansion in CD-medium inhibited mRNA expression of hypertrophic markers, collagen type-X (COL10) and matrix metalloproteinase-13 (MMP-13). Interestingly, the TGFb1 level detected by enzymelinked immunosorbent sandwich assay (ELISA) during cell expansion was correlated with COL10 mRNA expression after re-differentiation. Conclusion: TGFb-depletion during expansion improves the re-differentiation capacity of chondrocytes and inhibits hypertrophy. These results indicate the importance of the expansion medium composition to improve chondrogenic re-differentiation and to inhibit hypertrophy.