Cyclical strain modulates metalloprotease and matrix gene expression in human tenocytes via activation of TGFβ

Tendinopathies are a range of diseases characterised by degeneration and chronic tendon pain and represent a significant cause of morbidity. Relatively little is known about the underlying mechanisms; however onset is often associated with physical activity. A number of molecular changes have been documented in tendinopathy such as a decrease in overall collagen content, increased extracellular matrix turnover and protease activity. Metalloproteinases are involved in the homeostasis of the extracellular matrix and expression is regulated by mechanical strain. The aims of this study were to determine the effects of strain upon matrix turnover by measuring metalloproteinase and matrix gene expression and to elucidate the mechanism of action. Primary Human Achilles tenocytes were seeded in type I rat tail collagen gels in a Flexcell (TM) tissue train system and subjected to 5% cyclic uniaxial strain at 1 Hz for 48 h. TGF beta l and TGF beta RI inhibitor were added to selected cultures. RNA was measured using qRT-PCR and TGF beta protein levels were determined using a cell based luciferase assay. We observed that mechanical strain regulated the mRNA levels of multiple protease and matrix genes anabolically, and this regulation mirrored that seen with TGF beta stimulation alone. We have also demonstrated that the inhibition of the TGF beta signalling pathway abrogated the strain induced changes in mRNA and that TGF beta activation, rather than gene expression, was increased with mechanical strain. We concluded that TGF beta activation plays an important role in mechanotransduction. Targeting this pathway may have its place in the treatment of tendinopathy. (c) 2013 The Authors. Published by Elsevier B.V. All rights reserved.