Pellet coculture of osteoarthritic chondrocytes and infrapatellar fat pad-derived mesenchymal stem cells with chitosan/hyaluronic acid nanoparticles promotes chondrogenic differentiation.

Cell source plays a key role in cell-based cartilage repair and regeneration. Recent efforts in cell coculture have attempted to combine the advantages and negate the drawbacks of the constituent cell types. The aim of this study was to evaluate the chondrogenic outcome of articular chondrocytes (ACs) and infrapatellar fat pad (IPFP)-derived mesenchymal stem cells (MSCs) in direct coculture. ACs and IPFP MSCs from the same patients with knee osteoarthritis (OA) were cocultured in monolayer and in pellets. The monocultures of each cell type were also used as controls. Morphological and histologic analysis, immunofluorescence staining, reverse transcription-polymerase chain reaction, and enzyme-linked immunosorbent assay were performed to characterize the chondrogenic differentiation of cocultures. Furthermore, the effects of chitosan/hyaluronic acid (CS/HA) nanoparticle exposure on the chondrogenesis of cocultures were examined. In both monolayer and pellet coculture, the hypertrophy of MSCs and the inflammatory activities of ACs were inhibited, although the chondrogenic production in coculture was not promoted compared with that in monoculture. In addition, the exposure of CS/HA nanoparticles to pellet coculture improved the production of type II collagen and aggrecan. We demonstrate for the first time that pellet coculture of ACs and IPFP MSCs with CS/HA nanoparticles could promote chondrogenic outcome while preventing the inflammatory status of ACs and the hypertrophic differentiation of MSCs. These findings suggest that the combination of ACs, IPFP MSCs, and CS/HA might be useful in cartilage repair in knee OA.