Tendon cells respond to mechanical loads. The character (anabolic or catabolic) and sensitivity of this response is determined
by the mechanostat set point of the cell, which is governed by the cytoskeleton and its interaction with the extracellular
matrix. To determine if loss of cytoskeletal tension following stress deprivation decreases the mechanoresponsiveness of tendon
cells, we cultured rat tail tendons under stress-deprived conditions for 48 hours and then cyclically loaded them for 24 hours
at 1%, 3%, or 6% strain at 0.17 Hz. Stress deprivation upregulated MMP-13 mRNA expression and caused progressive loss of cell-matrix
contact compared to fresh controls. The application of 1% strain to fresh tendons for 24 hours inhibited MMP-13 mRNA expression
compared to stress-deprived tendons over the same period. However, when tendons were stress-deprived for 48 hours and then
subjected to the same loading regime, the inhibition of MMP-13 mRNA expression was decreased. In stress-deprived tendons,
it was necessary to increase the strain magnitude to 3% to achieve the same level of MMP-13 mRNA inhibition seen in fresh
tendons exercised at 1% strain. The data suggest loss of cytoskeletal tension alters the mechanostat set point and decreases
the mechanoresponsiveness of tendon cells.
Each author certifies that he or she has no commercial associations (e.g., consultancies, stock ownership, equity interest,
patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.
Each author certifies that his or her institution has approved the animal protocol for this investigation and that all investigations
were conducted in conformity with ethical principles of research.