Extracellular matrix deposited by synovium-derived stem cells delays replicative senescent chondrocyte dedifferentiation and enhances redifferentiation

The aim of this study was to assess the effect of extracellular matrix (ECM) deposited by synovium-derived stem cells (SDSCs) on articular chondrocyte expansion and maintenance of differentiation status and redifferentiation capacity. Passage 0 (P0) pig articular chondrocytes were expanded for six passages on plastic flasks (Plastic), SDSC-derived ECM (ECM), or substrate switching from either Plastic to ECM (PtoE) or ECM to Plastic (EtoP). Cell morphology, gene expression profiles, and immunophenotypes at each passage were used to characterize differentiation status of expanded cells. Chondrocytes at P0, P2, and P6 were assessed for redifferentiation capacity in a pellet culture system treated with either TGF-β1- or serum-containing medium for 14 days, using histology, immunohistochemistry, biochemistry, Western blot, and real-time PCR. We found that ECM not only greatly enhanced chondrocyte expansion but also delayed dedifferentiation of expanded chondrocytes. Intriguingly, compared to a dramatic decrease in CD90+/CD105+ cells and CD90+ cells, CD105+ cells dramatically increased when chondrocytes were plated on Plastic; on the contrary, ECM expansion dramatically increased CD90+ cells and delayed the decrease of CD90+/CD105+ cells. Interestingly, expanded chondrocytes on ECM also acquired a strong redifferentiation capacity, particularly in the pellets treated with TGF-β1. In conclusion, the ratio of CD90 to CD105 may serve as a marker indicative of proliferation and redifferentiation capacity of dedifferentiated chondrocytes. ECM deposited by SDSCs provides a tissue-specific three-dimensional microenvironment for ex vivo expansion of articular chondrocytes while retaining redifferentiation capacity, suggesting that ECM may provide a novel approach for autologous chondrocyte-based cartilage repair.