Direct Coculture of Human Chondrocytes and Synovium-Derived Stem Cells Enhances In Vitro Chondrogenesis

OBJECTIVES Coculture of chondrocytes and mesenchymal stem cells (MSCs) has been developed as a strategy to overcome the dedifferentiation of chondrocytes during in vitro expansion in autologous chondrocyte transplantation. Synovium-derived stem cells (SDSCs) can be a promising cell source for coculture due to their superior chondrogenic potential compared to other MSCs and easy accessibility without donor site morbidity. However, studies on coculture of chondrocytes and SDSCs are very limited. The aim of this study was to investigate whether direct coculture of human chondrocytes and SDSCs could enhance chondrogenesis compared to monoculture of each cell. MATERIALS AND METHODS In this experimental study, passage 2 chondrocytes and SDSCs were directly cocultured using different ratios of chondrocytes to SDSCs (3:1, 1:1, or 1:3). glycosaminoglycan (GAG) synthetic activity was assessed using GAG assays and Safranin-O staining. Expression of chondrogenesis-related genes (collagen types I, II, X, Aggrecan, and Sox-9) were analyzed by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry staining. RESULTS GAG/DNA ratios in 1:1 and 1:3 coculture groups were significantly increased compared to those in the chondrocyte and SDSC monoculture groups. Type II collagen and SOX-9 were significantly upregulated in the 1:1 coculture group compared to those in the chondrocyte and SDSC monoculture groups. On the other hand, osteogenic marker (type I collagen) and hypertrophic marker (type X collagen) were significantly downregulated in the coculture groups compared to those in the SDSC monoculture group. CONCLUSIONS Direct coculture of human chondrocytes and SDSCs significantly enhanced chondrogenic potential, especially at a ratio of 1:1, compared to chondrocyte or SDSC monocultures.