Chondrocyte isolation and culture
Primary chondrocytes were obtained from 5-day-old C57BL/6 mice as previously described 12. Briefly, the articular cartilage from the knee joint of mice was cut into 1 mm3 particles and then was digested with DMEM containing 1% penicillin/streptomycin, 0.5% trypsin, and 1% Collagenase type II for 2 h. After filtered through a 40 μm cell strainer, the digestive suspensions were placed in a centrifuge at 1500 rpm. The centrifuged cell deposits were resuspended and grown in DMEM supplemented with 10% FBS and 1% penicillin/streptomycin at 37 °C with 5% CO2. The cells were passaged to passage 3 and then used for the following experiments.