In Vitro Movement and Chondrogenesis/ Osteogenesis in Mandibular Condylar Cartilage

In vivo experiments have shown the importance of movement and/or articulation for the maintenance of secondary cartilage. Recently, Buxton and colleagues (2004) demonstrated that the switch from chondrogenesis to osteogenesis in chick secondary cartilage in vitro can be regulated by artificially-applied movements. Objective: This study was designed to evaluate the role of movement in regulating bone/ cartilage formation in mouse mandibular condylar cartilage (MCC) explants. Methods: Heads from E17 mice pups were harvested, sectioned in the mid-sagittal plane, divested of skin and most overlying muscle, and placed in serum-free explant culture. Joints in half of the explants were taken through an opening movement 10 times every hour, while the other half experienced no movement. After 6 h of this regime, the MCC was dissected from the adjacent bone and the RNA extracted for real-time RT-PCR. Results: Collagen type I gene expression was increased 3-fold in non-movement MCC compared to movement MCC and ex vivo (non-cultured) MCC. Collagen type II gene expression was increased 2-fold in MCC from joints that had been moved compared to both non-movement and ex vivo MCC. There was no difference in collagen type X expression between movement and non-movement groups. Conclusions: These results suggest that a relatively small number of movements delivered at hourly intervals can effect a transition between osteogenesis and chondrogenesis in MCC. This study was supported by NIDCR grant DE015401 to RJH.