Hypoxic Conditions Promote Cartilage Repair in an Animal Knee Osteochondral Defect Model via Hif-1α

Bone marrow stimulation is a treatment for articular cartilage injuries that promotes cartilage repair by creating small holes to induce mesenchymal stem cells (MSCs). However, most of the repair tissue is fibrocartilage, with poor mechanical durability and functionality. Recent studies have demonstrated that hypoxic conditions promote the chondrogenic differentiation of MSCs, but the effects of hypoxic conditions on cartilage repair in vivo remain unclear. Therefore, this study aimed to investigate the effect of hypoxic conditions on cartilage repair using a rat osteochondral defect model. Osteochondral defects, 1.0 mm in diameter, were created in the femoral trochlear groove. After surgery, rats were bred under hypoxic conditions (12%) for 4 weeks, and histological analysis was performed. Protein expression of hypoxia-inducible factor-1α (HIF-1α) and SRY-box transcription factor 9 (SOX9) in the repair tissue was evaluated at 1 week. As a result, Hypoxia group exhibited hyaline cartilage-like tissue structure and early expression of HIF-1α and SOX9 compared to Normoxia group. These findings suggest that hypoxic conditions promote SOX9 expression via HIF-1α during the early phase of MSC chondrogenic differentiation, and formation of hyaline cartilage-like repair tissue. In conclusion, bone marrow stimulation with hypoxic conditions may enhance the repair effect on articular cartilage injuries.