High magnitude, in vitro, biaxial, cyclic tensile strain induces actin depolymerization in tendon cells.
BACKGROUND
the cytoskeleton is a dynamic arrangement of actin filaments that maintain cell shape and are vital in mediating the mechanobiological response of the cell.


METHODS
to determine the cytoskeletal response to varying in vitro, biaxial stretch amplitudes, rat-tail tendon cells were paired into control and cyclically strained groups of 4.75, 9.5, or 12% strain at 1 Hz for 2 hours and the actin cytoskeleton stained. The cells were analyzed for actin staining intensity as a measure of relative depolymerization and for cell shape. Collagenase gene expression was measured in cells undergoing 12% cyclic strain at 1 Hz for 24 hours.


RESULTS
there was no significant difference in the degree of actin staining intensity between the control group and cells strained at either 4.75 or 9.5%. However, cells strained at 12% demonstrated a significant decrease in actin staining intensity (depolymerization) compared to control cells, increased collagenase expression by 81%, and a clear shift towards a more rounded cell shape.


CONCLUSIONS
the results of this study demonstrate that the previously reported induction of collagenase activity associated with the application of high magnitude, in vitro, tensile strains may actually be a result of cytoskeletal depolymerization, which causes loss of tensional homeostasis and alteration of cell shape.
Laboratory for Comparative Orthopaedic Research, Michigan State University, USA.
Michael
M
Lavagnino
Laboratory for Comparative Orthopaedic Research, Michigan State University, USA.
Keri L
KL
Gardner
Laboratory for Comparative Orthopaedic Research, Michigan State University, USA.
Steven P
SP
Arnoczky
actin intensity; cell shape; collagenase; mechanobiology; tendinopathy; under-stimulation