Engineering hyaline cartilage from mesenchymal stem cells with low hypertrophy potential via modulation of culture conditions and Wnt/β-catenin pathway

Mesenchymal stem cells (MSCs) represent a promising cell source to regenerate articular cartilage, but current chondroinduction protocols, commonly using transforming growth factor-beta (TGF beta), lead to concomitant chondrocytic hypertrophy with ossification risk. Here, we showed that a 14-day culture of MSC-laden hyaluronic acid hydrogel in the presence of TGF beta, followed by 7 days culture in TGF beta-free medium, with the supplement of Wnt/beta-catenin inhibitor XAV939 from day 10-21, resulted in significantly reduced hypertrophy phenotype. The stability of the hyaline phenotype of the MSC-derived cartilage, generated with a standard protocol (Control) or the optimized (Optimized) method developed in this study, was further examined through intramuscular implantation in nude mice. After 4 weeks, constructs from the Control group showed obvious mineralization; in contrast, the Optimized group displayed no signs of mineralization, and maintained cartilaginous histology. Further analysis showed that TGF beta treatment time affected p38 expression, while exposure to XAV939 significantly inhibited P-Smad 1/5 level, which together resulted in decreased level of Runx2. These findings suggest a novel treatment regimen to generate hyaline cartilage from human MSCs-loaded scaffolds, which have a minimal risk of eliciting endochondral ossification.