Abstract: PURPOSE: To establish an in vitro mechanical stimulation model of cranial base synchondrosis chondrocytes, and to study the effect of cyclic tensile stress on the main extracellular matrix of rat cranial base synchondrosis. METHODS: Cyclic tensile stress was imposed to the second passage of cranial base synchondrosis chondrocytes for 3, 6, 12 and 24 hours respectively by using a Flexcell Strain Unit-5000T(10% surface elongation, 1 Hz). After mechanical loading, the total RNA of the cells harvested from six-well BioFlex was extracted. Real-time quantitative RT-PCR was performed to quantify the mRNA levels of type Ⅱ collagen and Sox9. The data were analyzed with SPSS 17.0 software package. RESULTS: Compared with the control group(0 h group), the mRNA expression of type Ⅱ collagen was decreased after 3 hours of loading, but not statistically significant; While the expression of Sox9 decreased significantly (P <0.05). In the 6 h group, the expression of Col-Ⅱ and Sox9 decreased significantly (P<0.01 and 0.05, respectively). The expression of Col-Ⅱ and Sox9 increased in the 12 h group. The 24 h group showed significant increase in both type Ⅱ collagen and Sox9 (P<0.05). CONCLUSIONS: The results illustrate that cyclic tensile stress can affect the synthesis of the main extracellular matrix of cranial base synchondrosis in vitro. Expression of type Ⅱ collagen and Sox9 can be inhibited during early stage of mechanical loading. However, when loading time extends, the mechanical stimuli greatly promotes the expression of type Ⅱ collagen and Sox9. The reaction of Sox9 in this in vitro mechanical stimulation model happens earlier than that of type Ⅱ collagen.

Key words: Cyclic tensile stress, Cranial base synchondrosis, Type Ⅱ collagen, Sox9