title: The effect of stress-deprivation and cyclic loading on the TIMP/MMP ratio in tendon cells: an in vitro experimental study.
abstract: OBJECTIVE
  To determine the effect of stress deprivation and cyclic loading on TIMP-1/MMP-13 mRNA expression ratio in rat tail tendon (RTT) cells.
  
  
  METHODS
  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 24 h 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 3.73:1 +/- 0.73. Stress deprivation for 24 h significantly decreased the TIMP-1/MMP-13 ratio (0.25:1 +/- 0.04) 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.
authors.affiliation: The Laboratory for Comparative Orthopaedic Research, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, USA.
authors.forename: Keri
authors.initials: K
authors.lastname: Gardner
authors.forename: Steven P
authors.initials: SP
authors.lastname: Arnoczky
authors.forename: Oscar
authors.initials: O
authors.lastname: Caballero
authors.forename: Michael
authors.initials: M
authors.lastname: Lavagnino
mesh_terms: D000818:Animals; D006877:Hydroxamic Acids; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D053509:Matrix Metalloproteinase 13 / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013312:Stress, Physiological; D013710:Tendons / Q000166:cytology / Q000378:metabolism*; D013997:Time Factors; D019715:Tissue Inhibitor of Metalloproteinase-1 / Q000378:metabolism*; D016474:Weight-Bearing
chemical_list: D006877:Hydroxamic Acids; D007211:Indoles; D012333:RNA, Messenger; D019715:Tissue Inhibitor of Metalloproteinase-1; D053509:Matrix Metalloproteinase 13; C119203:ilomastat