Cell response to substrate rigidity is regulated by active and passive cytoskeletal stress

Abstract

Morphogenesis, tumor formation, and wound healing are regulated by tissue rigidity. Focal adhesion behavior is locally regulated by stiffness; however, how cells globally adapt, detect, and respond to rigidity remains unknown. Here, we studied the interplay between the rheological properties of the cytoskeleton and matrix rigidity. We seeded fibroblasts onto flexible microfabricated pillar arrays with varying stiffness and simultaneously measured the cytoskeleton organization, traction forces, and cell-rigidity responses at both the adhesion and cell scale. Cells adopted a rigidity-dependent phenotype whereby the actin cytoskeleton polarized on stiff substrates but not on soft. We further showed a crucial role of active and passive cross-linkers in rigidity-sensing responses. By reducing myosin II activity or knocking down α-actinin, we found that both promoted cell polarization on soft substrates, whereas α-actinin overexpression prevented polarization on stiff substrates. Atomic force microscopy indentation experiments showed that this polarization response correlated with cell stiffness, whereby cell stiffness decreased when active or passive cross-linking was reduced and softer cells polarized on softer matrices. Theoretical modeling of the actin network as an active gel suggests that adaptation to matrix rigidity is controlled by internal mechanical properties of the cytoskeleton and puts forward a universal scaling between nematic order of the actin cytoskeleton and the substrate-to-cell elastic modulus ratio. Altogether, our study demonstrates the implication of cell-scale mechanosensing through the internal stress within the actomyosin cytoskeleton and its coupling with local rigidity sensing at focal adhesions in the regulation of cell shape changes and polarity.

Articular Chondrocyte Phenotype Regulation through the Cytoskeleton and the Signaling Processes That Originate from or Converge on the Cytoskeleton: Towards a Novel Understanding of the Intersection between Actin Dynamics and Chondrogenic Function

“…In a substrate stiffness-related context, the actin cytoskeleton acts like a rigidity sensor because it behaves on soft substrates like a fluid-like material and on stiffer substrates like a solid-like material, with the solid-like state characterized by a transition from an isotropic to a parallel, ordered filament organization, leading to long-lived SFs and higher tension on stiffer substrates [ 359 ]. Thus, some researchers [ 359 ] connected a polarized SF orientation with increased cytoskeletal tension, which is in general accordance with the findings in [ 360 ]. SF-induced increased cytoskeletal tension would affect the forces at individual FAs and activate FAK, as FAK localizes into FA complexes and is activated after force generation, likely through conformational changes [ 361 ].…”

Cancer-associated fibroblasts of the prostate promote a compliant and more invasive phenotype in benign prostate epithelial cells

“…In our co-cultures, the benign epithelial cells were likely sensitive to the mechanical properties of the fibroblast-derived matrix as well as the stiffness of the fibroblasts themselves. Cells respond to their mechanoenvironment by adapting their cytoskeletal and mechanical properties when exposed to mechanical cues [ 86 , 87 ], although opposed responses have been reported. For instance, PCa (PC-3) cells reduced their cellular elastic modulus in response to an increased substrate stiffness [ 88 ], while fibroblasts stiffened [ 89 ].…”

Mechanobiology of Autophagy: The Unexplored Side of Cancer

“…Cells have been reported to sense and respond to the a) physical status of the extracellular matrix (e.g. composition, stiffness, topography and density) by exerting traction forces on the substrate (112)(113)(114), b) geometrical cues (e.g. size, confinement, curvature) affecting cortical and membrane tension (115,116), c) presence of surrounding cells (e.g.…”