Co-culture pellet of human Wharton's jelly mesenchymal stem cells and rat costal chondrocytes as a candidate for articular cartilage regeneration: in vitro and in vivo study.

Background: Seeding cells are key factors in cell-based cartilage tissue regeneration. Monoculture of either chondrocyte or mesenchymal stem cells has several limitations. In recent years, co-culture strategies have provided potential solutions. In this study, directly co-cultured rat costal chondrocytes (CCs) and human Wharton's jelly mesenchymal stem (hWJMSCs) cells were evaluated as a candidate to regenerate articular cartilage.

Methods: Rat CCs are directly co-cultured with hWJMSCs in a pellet model at different ratios (3:1, 1:1, 1:3) for 21 days. The monoculture pellets were used as controls. RT-qPCR, biochemical assays, histological staining and evaluations were performed to analyze the chondrogenic differentiation of each group. The 1:1 ratio co-culture pellet group together with monoculture controls were implanted into the osteochondral defects made on the femoral grooves of the rats for 4, 8, 12 weeks. Then, macroscopic and histological evaluations were performed.

Results: Compared to rat CCs pellet group, 3:1 and 1:1 ratio group demonstrated similar extracellular matrix production but less hypertrophy intendency. Immunochemistry staining found the consistent results. RT-PCR analysis indicated that chondrogenesis was promoted in co-cultured rat CCs, while expressions of hypertrophic genes were inhibited. However, hWJMSCs showed only slightly improved in chondrogenesis but not significantly different in hypertrophic expressions. In vivo experiments showed that all the pellets filled the defects but co-culture pellets demonstrated reduced hypertrophy, better surrounding cartilage integration and appropriate subchondral bone remodeling.

Conclusion: Co-culture of rat CCs and hWJMSCs demonstrated stable chondrogenic phenotype and decreased hypertrophic intendency in both vitro and vivo. These results suggest this co-culture combination as a promising candidate in articular cartilage regeneration.