Cellular Response to Substrate Rigidity Is Governed by Either Stress or Strain

Abstract

Cells sense the rigidity of their substrate; however, little is known about the physical variables that determine their response to this rigidity. Here, we report traction stress measurements carried out using fibroblasts on polyacrylamide gels with Young's moduli ranging from 6 to 110 kPa. We prepared the substrates by employing a modified method that involves N-acryloyl-6-aminocaproic acid (ACA). ACA allows for covalent binding between proteins and elastomers and thus introduces a more stable immobilization of collagen onto the substrate when compared to the conventional method of using sulfo-succinimidyl-6-(4-azido-2-nitrophenyl-amino) hexanoate (sulfo-SANPAH). Cells remove extracellular matrix proteins off the surface of gels coated using sulfo-SANPAH, which corresponds to lower values of traction stress and substrate deformation compared to gels coated using ACA. On soft ACA gels (Young's modulus <20 kPa), cell-exerted substrate deformation remains constant, independent of the substrate Young's modulus. In contrast, on stiff substrates (Young's modulus >20 kPa), traction stress plateaus at a limiting value and the substrate deformation decreases with increasing substrate rigidity. Sustained substrate strain on soft substrates and sustained traction stress on stiff substrates suggest these may be factors governing cellular responses to substrate rigidity.

Mechanical stimulation induces formin-dependent assembly of a perinuclear actin rim

“…1A). The magnitude of force was estimated to be 100-200 nN by calibration using a variant of traction force microscopy (19). On force application, EGFP-Lifeact-labeled F-actin (20) was found to transiently accumulate at the perinuclear region (Fig.…”

“…Live-cell imaging was captured using Zeiss 710 Confocal Microscopy during force application. Calibration of force was done in the same setup using a 3-kPa Acrylamide gel embedded with fluorescent beads (19). The force applied by the AFM tip, calculated by the displacement of the fluorescent beads and elastic modulus of the gel, was estimated to be 100-200 nN.…”

Topography Design Concept of a Tissue Engineering Scaffold for Controlling Cell Function and Fate Through Actin Cytoskeletal Modulation

“…108 The decreased stress reduces the integrin clustering for normal maturation of focal adhesions, and as shown in Figure 4A, the actin cytoskeleton is weakly assembled in the cytoplasm, being concentrated predominantly in the cortex under the cell membrane. 106,110,112 On the other hand, in cells on a stiff substrate, mechanical tension is sufficient to facilitate 113 the recruitment and stable association of focal adhesion proteins to mature focal adhesions.…”

“…A wide variety of cell types, such as human MSCs, 61,105,106 mouse ES cells, 107 fibroblasts, 18,108,109 and glioma cells, 110 have been reported to respond to the ECM elasticity within the range of in vivo tissue elastic modulus from 0.1 kPa in the brain to 100 kPa in pre-calcified bone. 111 This property of cells can be used to specify strength of the cytoplasm-ECM link (Fig.…”

Mechanical Regulation and Maintenance of Organismal Homeostasis - Scientific Basis for Health Promotion by Physical Motility and Exercise

“…Using the technique called traction force microscopy, we previously demonstrated that traction stress increased with substrate rigidity up to 20 kPa ( Figure-3) 1) . Considering that the tissue rigidity is typically below 20 kPa except for bones 2) , higher force generation on stiffer substrates appears to be a physiological cell response or function.…”