Evaluation of osteochondral-like tissues using human freeze-dried cancellous bone and chondrocyte sheets to treat osteochondral defects in rabbits

Human freeze-dried cancellous bone combined with human chondrocyte sheets have recently been used to construct an osteochondral-like tissue, which resembled a cartilage layer on a subchondral bone layer. Nevertheless, the efficacy of these human tissues in a xenogeneic model has been rarely reported. Therefore, this study aimed to evaluate the potential of human freeze-dried cancellous bones combined with human chondrocyte sheets for the treatment of osteochondral defects in rabbits. The key roles of the extracellular matrix (ECM) and released cytokines in these tissues in osteochondral repair were also assessed. Triple-layered chondrocyte sheets were constructed using a temperature-responsive culture surface. Then, they were placed onto cancellous bone to form chondrocyte sheet–cancellous bone tissues. The immunostaining of collagen type II (COL2) and the proteomic analysis of the human tissues were carried out before the transplantation. In our in vitro study, the triple-layered chondrocyte sheets adhered well on the cancellous bone, and the COL2 expression was apparent throughout the tissue structures. From the proteomic analysis results, it was found that the major function of the secreted proteins found in these tissues was protein binding. The distinct pathways were focal adhesion and the ECM–receptor interaction pathways. Among the highly expressed proteins, laminin-alpha 5 (LAMA5) and fibronectin (FN) not only played roles in the protein binding and ECM–receptor interaction, but also were involved in the cytokine-mediated signaling pathway. At 12 weeks after xenogeneic transplantation, compared to the control group, the defects treated with the chondrocyte sheets showed more hyaline-like cartilage tissue, as indicated by the abundance of safranin-O and COL2 with a partial collagen type I (COL1) expression. At 4, 8, and 12 weeks, compared to the defects treated with the cancellous bone, the staining of safranin-O and COL2 was more apparent in the defects treated with the chondrocyte sheet–cancellous bone tissues. Therefore, the human chondrocyte sheets and chondrocyte sheet–cancellous bone tissues provide a potential treatment for rabbit femoral condyle defect. LAMA5 and FN found in these human xenografts and their culture media might play key roles in the ECM–receptor interaction and might be involved in the cytokine-mediated signaling pathway during tissue repair.