Cyclic Mechanical Loading of 3D-cultured Temporomandibular Fibrochondrocytes Induces MMP-13 Expression

Objectives: Mechanical loading can have both anabolic and catabolic effects on cartilagenous tissues, amongst others through stimulation of expression of catabolic factors by chondrocytes embedded within their matrix. Thus far it is unknown whether mechanical loads associated with chronic clenching are likely to lead to damage of condyle of the temporomandibular joint (TMJ). We hypothesized that overload cyclic strain of 3 dimensionally cultured fibrochondrocytes derived from TMJ condyle leads to an increased expression of catabolic factors, and decrease expression of matrix proteins.
The aim of this study was to use a 3D in vitro model to find out how TMJ fobrochondrocytes cells react to cyclic strain mechanical loading (mimicking a night sleep clenching) in various intensities.
Methods: Fibrochondrocytes from the condyle of juvenile porcine TMJs were isolated and embedded at a density of 1 x 10⁶ cells/ml in 3% agarose gel (n=8). After 7 days of culture, gels cointaining cells were subjected to 8 hours of mechanical loading by cyclic strain at 3% or 6% at 0.5HZ, 1 cycle of 10 seconds every 6 minutes. Gene expression of cartilage matrix molecules (collagen type I, IIA and IIB) and the catabolic factor matrix metalloproteinase 13 (MMP-13) were quantified by quantitative PCR.
Results: 6% strain slightly enhance gene expression of Col I, IIA and IIB compared to unloaded samples, however no statistical significance was reached. 6% strain enhance MMP-13 espression by 2-fold compared to unloaded samples, which was significantly higher response than elicited by 3%strain (p= 0.0122).
Conclusions: Cyclic mechanical loading for 8hr at 6%, but not at 3%, induces the expression of MMP-13, suggesting that higher clenching loading can induce collagen degradation in TMJ fibrochondrocytes. This may imply that a reduction of nighttime clenching might be important to prevent changes of the TMJ cartilage.