Preparation of Scaffold-Free Tissue-Engineered Constructs Derived from Human Synovial Mesenchymal Stem Cells under Low Oxygen Tension Enhances Their Chondrogenic Differentiation Capacity

Low oxygen tension (LOT) has been reported to promote chondrogenic differentiation and prevent cellular senescence of stem cells. Therefore, the introduction of LOT conditions into conventional tissue engineering processes could further improve the potential of the constructs generated for cartilage repair. The purpose of this study was to elucidate the feasibility of LOT preparation on the chondrogenic differentiation of a scaffold-free tissue-engineered construct (TEC) derived from synovial mesenchymal stem cells (MSCs), construct whose feasibility for cartilage repair has been demonstrated in previous preclinical and clinical studies. Culture of MSCs under LOT conditions prevented cellular senescence and promoted the proliferative capacity of human synovial MSCs. In addition, TEC prepared from human synovial MSCs under LOT conditions (5% O₂; LOT-TEC) showed superior in vitro chondrogenic differentiation capacity compared to that prepared under the usual 20% O₂ (normal oxygen tension [NOT]; NOT-TEC), with elevated glycosaminoglycan production and elevated levels of chondrogenic marker gene expression. Notably, LOT-TEC differentiated into a hyaline-like cartilaginous tissue of approximately 1 cm in diameter without the detectable presence of fibrous tissue, while conventional NOT-TEC differentiated into a mixture of hyaline-like and fibrocartilaginous tissues. This is the first demonstration of in vitro development of a hyaline-like cartilaginous tissue of an implantable size to chondral lesion that was derived from human MSCs without the use of an exogenous scaffold. The manipulation of oxygen tension is a safe procedure with low cost and, thus, may be a clinically relevant option to improve the quality of TEC-mediated cartilage repair.