Cellular Orientation Is Guided by Strain Gradients

Abstract

Cyclically stretched cells are known to exhibit a strain-induced reorientation response. In this study, we comprehensively analyse this behaviour for human fibroblasts subjected to a highly non-uniform strain field within a polymethylsiloxane microdevice. We demonstrate a strong correlation between the strain amplitude and the degree of cell alignment perpendicular to the principal strain direction (stretching avoidance). Analogously, our results indicate that the strain gradient amplitude and direction also regulate this reorientation through a coordinated gradient avoidance response. We stipulate that strain gradients are thus biologically relevant mechanical cues sensed by cells. To gain insight into the underlying mechanosensing processes, we also studied focal adhesion reorganization and the effect of modulating myosin-II contractility. The extracted focal adhesion orientation distributions are similar to those obtained for the cell bodies, and their density is increased by the presence of stretching forces. Moreover, it was found that the myosin-II activity promoter calyculin-A has little effect on the cellular response, while the inhibitor blebbistatin suppresses cell and focal adhesion alignment and reduces focal adhesion density.These results confirm that similar internal structures involved in sensing and responding to strain direction and amplitude are also key players in strain gradient mechanosensing and avoidance.

Time dependence of cellular responses to dynamic and complex strain fields

“…The strain gradient has recently been identified as a genuine mechanical cue involved in the reorientation response of fibroblasts 26 and it can indeed explain the trend observed in Fig. 4b.…”

“…In principle, they also have the potential to enable high-throughput screening experiments. An often-overlooked advantage of microstretchers over macrostretchers in certain studies is that they naturally produce non-uniform strain fields with biologically relevant strain gradients, while maintaining the strain magnitude to desirably low levels 26 (see Supporting Information). This enables the study of mechanical cues which better mimics the complexity of the cell microenvironment in vivo.…”

“…3a-f but the orientations are reported with respect to the local principal strain direction. Moreover, considering that lower strain amplitudes are inefficient at inducing reorientation 10,26 , regions of sub-5% strain amplitude were excluded in Fig. 3g-l. As a result of these two considerations, a systematic narrowing is observed in the angle distributions from Fig.…”

Mechanotransduction of strain regulates an invasive phenotype in newly transformed epithelial cells

“…To generate a biologically relevant strain field, we employed an all-PDMS pneumatic-based microfluidic stretcher which we reported previously [27]. Cells were cultured on a thin suspended membrane encased in a microchamber.…”

“…A detailed description of the microfluidic device fabrication and characterization can be found in previously reported work [27]. Briefly, the PDMS (Sylgard184, Ellsworth Adhesives Canada Corporation) microfluidic stretchers were prepared using standard microfabrication techniques, including UV photolithography and soft lithography.…”