The effect of stress-deprivation and cyclic loading on the TIMP/MMP ratio in tendon cells: An in vitro experimental study

Purpose. To determine the effect of stress deprivation and cyclic loading on TIMP-1/MMP-13 mRNA expression ratio in rat tail tendon (RTT) cells. Method. Adult RTTs were stress-deprived for 0, 24, 48, or 72 hours in the presence or absence of a MMP inhibitor (ilomastat), or subjected to 1%, 3%, or 6% strain for 24h under tissue culture conditions. TIMP-1 and MMP-13 (rat interstitial collagenase) mRNA expression were measured using quantitative PCR and TIMP/MMP ratios were calculated for each group. Results. The ratio of TIMP-1 to MMP-13 in control RTTs was 3.73:10.73. Stress deprivation for 24h significantly decreased the TIMP-1/MMP-13 ratio (0.25:10.04) and MMP-13 expression continued to increase significantly with time of stress deprivation. Inhibition of MMP-13 mRNA expression with ilomastat in stress-deprived samples did not alter TIMP-1 expression when compared to normal controls. Cyclic loading significantly increased TIMP-1/MMP-13 expression at all strain levels examined. Conclusions. RTTs normally have a positive TIMP-1/MMP-13 expression ratio. While cyclic loading increased the TIMP-1/MMP-13 ratio, loss of cellular homeostatic tension inversed this ratio through a significant increase in MMP-13 mRNA expression rather than a decrease in TIMP expression. A negative TIMP/MMP ratio has been implicated in the pathogenesis of tendinopathy. Increasing the TIMP/MMP ratios in these patients through exercise may be beneficial in the management of tendinopathy.