When adherent cells are subjected to uniaxial sinusoidal stretch at frequencies close to physiological, their body and their contractile stress fibers realign nearly perpendicularly to the stretch axis. A common explanation for this phenomenon is that stress fibers reorient along the direction where they are unaffected by the applied cyclic stretch and thus can maintain optimal (homeostatic) tensile force. The ability of cells to achieve tensional homeostasis in response to external disturbances is important for normal physiological functions of cells and tissues and it provides protection against diseases, including cancer and atherosclerosis. However, quantitative experimental data that support the idea that stretch-induced reorientation is associated with tensional homeostasis are lacking. We observed previously that in response to uniaxial cyclic stretch of 10% strain amplitudes, traction forces of single endothelial cells reorient in the direction perpendicular to the stretch axis. Here we carried out a secondary analysis of those data to investigate whether this reorientation of traction forces is associated with tensional homeostasis. Our analysis showed that stretch-induced reorientation of traction forces was accompanied by attenuation of temporal variability of the traction field to the level that was observed in the absence of stretch. These findings represent a quantitative experimental evidence that stretch-induced reorientation of the cell’s traction forces is associated with the cell’s tendency to achieve tensional homeostasis.
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Time‐dependent combinatory effects of active mechanical loading and passive topographical cues on cell orientation
Mechanical stretching and topographical cues are both effective mechanical stimulations for regulating cell morphology, orientation, and behaviors. The competition of these two mechanical stimulations remains largely underexplored. Previous studies have suggested that a small cyclic mechanical strain is not able to reorient cells that have been pre‐aligned by relatively large linear microstructures, but can reorient those pre‐aligned by small linear micro/nanostructures if the characteristic dimension of these structures is below a certain threshold. Likewise, for micro/nanostructures with a given characteristic dimension, the strain must exceed a certain magnitude to overrule the topographic cues. There are however no in‐depth investigations of such “thresholds” due to the lack of close examination of dynamic cell orientation during and shortly after the mechanical loading. In this study, the time‐dependent combinatory effects of active and passive mechanical stimulations on cell orientation are investigated by developing a micromechanical stimulator. The results show that the cells pre‐aligned by linear micro/nanostructures can be altered by cyclic in‐plane strain, regardless of the structure size. During the loading, the micro/nanostructures can resist the reorientation effects by cyclic in‐plane strain while the resistive capability (measured by the mean orientation angle change and the reorientation speed) increases with the increasing characteristic dimension. The micro/nanostructures also can recover the cell orientation after the cessation of cyclic in‐plane strain, while the recovering capability increases with the characteristic dimension. The previously observed thresholds are largely dependent on the observation time points. In order to accurately evaluate the combinatory effects of the two mechanical stimulations, observations during the active loading with a short time interval or endpoint observations shortly after the loading are preferred. This study provides a microengineering solution to investigate the time‐dependent combinatory effects of the active and passive mechanical stimulations and is expected to enhance our understanding of cell responses to complex mechanical environments. Biotechnol. Bioeng. 2016;113: 2191–2201. © 2016 Wiley Periodicals, Inc.
- NSF-PAR ID:
- 10236564
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Biotechnology and Bioengineering
- Volume:
- 113
- Issue:
- 10
- ISSN:
- 0006-3592
- Format(s):
- Medium: X Size: p. 2191-2201
- Size(s):
- p. 2191-2201
- Sponsoring Org:
- National Science Foundation
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