Comparison of response to mechanical loading between two articular cartilages

The functional role of mandibular condylar cartilage (MNC) is essentially similar to ankle articular cartilage (ANC), both provides lubrication to resist friction and offers protection against external mechanical loading. However, the effect of tension loadings on these two articular cartilages remains unclear. Objectives: The purpose of this study was to compare the in vitro mechanical response of the chondrocytes isolated from porcine MNC and ANC in relation to the syntheses of DNA and proteoglycan (PTG). Methods: The synthesis variety of cartilaginous matrix during chondrocyte differentiation (from 3 to 12 days) were estimated by the expression of type II collagen and aggrecan mRNA using a quantitative real-time PCR analysis. The chondrocytes were submitted to tensile mechanical strains of 2 kPa (3% elongation), 5 kPa (7% elongation) and 10 kPa (12% elongation), with a frequency of 30 cycles/min for 12 and 24 hours. Results: The results showed that the type II collagen and aggrecan mRNA in MNC were highly expressed in proliferating chondrocytes and decreased progressively in matrix-forming chondrocytes; conversely in ANC, these mRNAs increased chronologically with the differentiation of the chondrocytes. The condrocytes from MNC, when submitted to tension forces of 2 kPa and 5 kPa, demonstrated a statistically significant enhancement of DNA and PTG, in 12 h. and in 24 h. The force of 10 kPa caused a statistically significant decrease of DNA and PTG syntheses on the condrocytes of MNC, in both periods of mechanical stimulation. On the other side, the condrocytes of ANC showed a statistically significant increase of DNA and PTG syntheses when subjected to all the magnitudes of tension forces. Conclusions: In conclusion, the chondrocytes from MNC and ANC showed different response to mechanical loading and distinct chondrocyte metabolism, which may be the possible reason why the MNC must be a fibrocartilage.