Multidimensional traction force microscopy reveals out-of-plane rotational moments about focal adhesions

Abstract

Recent methods have revealed that cells on planar substrates exert both shear (in-plane) and normal (out-of-plane) tractions against the extracellular matrix (ECM). However, the location and origin of the normal tractions with respect to the adhesive and cytoskeletal elements of cells have not been elucidated. We developed a highspatiotemporal-resolution, multidimensional (2.5D) traction force microscopy to measure and model the full 3D nature of cellular forces on planar 2D surfaces. We show that shear tractions are centered under elongated focal adhesions whereas upward and downward normal tractions are detected on distal (toward the cell edge) and proximal (toward the cell body) ends of adhesions, respectively. Together, these forces produce significant rotational moments about focal adhesions in both protruding and retracting peripheral regions. Temporal 2.5D traction force microscopy analysis of migrating and spreading cells shows that these rotational moments are highly dynamic, propagating outward with the leading edge of the cell. Finally, we developed a finite element model to examine how rotational moments could be generated about focal adhesions in a thin lamella. Our model suggests that rotational moments can be generated largely via shear lag transfer to the underlying ECM from actomyosin contractility applied at the intracellular surface of a rigid adhesion of finite thickness. Together, these data demonstrate and probe the origin of a previously unappreciated multidimensional stress profile associated with adhesions and highlight the importance of new approaches to characterize cellular forces.cell mechanics | mechanotransduction | migration | actin U nderstanding how cells generate and respond to mechanical forces is critical in cell biology. In anchorage-dependent cells, myosin-II cross-links and contracts actin filaments to generate tension, which is transmitted to the extracellular matrix (ECM) via integrin-mediated adhesions (1-4). The traction stresses (force per area) exerted between adhesions and the ECM drive cell spreading and migration in morphogenesis (5, 6), wound healing (7), and tumor metastasis (8, 9). In addition, these stresses induce changes in adhesion signaling, cytoskeletal reorganization, and gene expression (4, 10-13), thereby regulating functions such as proliferation (14, 15) and differentiation (16,17).Measurements of cellular traction stresses have advanced our understanding of mechanotransduction and enabled quantitative modeling of cellular interactions with the ECM (18-20). These measurements reveal that cells exert inwardly oriented tractions at their periphery, where focal adhesions grow centripetally (3,4,21). However, the vast majority of methods (collectively termed traction force microscopy, TFM) have assumed that cells exert only shear forces (parallel to the plane of the substrate). Interestingly, recent studies have demonstrated that cells on planar substrata exert significant vertical (normal) tractions, indicating that patterns of cellular force generation...

Plectin-containing, centrally-localized focal adhesions exert traction forces in primary lung epithelial cells

“…Moreover, their formation is dependent on the latter. Indeed, they exhibit properties that make them exquisitely different from FAs located towards the cell interior in other cell types (Legant et al, 2013;Stricker et al, 2011). Furthermore, we observe no dynamic movement of the cFAs over time, indicating highly stable protein structures, and yet cFAs display significantly faster FRAP turnover rates of GFP-paxillin than pFAs or FAs in cells without the ring pattern.…”

“…FAs exert traction forces, with recent data indicating that FAs at the cell edge support more tension than matrix adhesions located towards the cell center (Legant et al, 2013;Stricker et al, 2011). Given the unique nature of the cFAs, we decided to compare central and peripheral traction forces in rAEC with and without rings as well as RLE-6TN cells expressing GFP-tagged paxillin (Fig.…”

Talin determines the nanoscale architecture of focal adhesions

“…Indeed, torque exertion by FAs has recently been documented by high-resolution 3D traction force microscopy (57). Together with recent studies suggesting that FA traction force is spatially and temporally heterogeneous across a given FA structure, this would imply that talin geometry may be variable across FAs as well (54,58).…”

Mechanotransduction of mesenchymal melanoma cell invasion into 3D collagen lattices: Filopod-mediated extension–relaxation cycles and force anisotropy

“…In both 2D and 3D environments, the forces exerted by cells on the substrate are anisotropic in space, with polarized traction by the leading edge, and oscillatory over time alternating between high and low forces [5,10]. For fibroblasts embedded in 3D fibrillar collagen, confocal reflectance microscopy has revealed cytoskeletal focalization and actomyosin mediated contractility as the basis of migration and structural remodeling of tissue [6,24,25].…”

“…Whereas many approaches have been developed to monitor the force fields underlying dynamic cell-substrate interactions and cell migration across 2D surfaces (reviewed in [10][11][12]), only few approaches allow to detect the cell mechanics within 3D tissue. As 3D environments for migration and traction analysis, cells are embedded in either synthetic substrate, typically elastic polyethylene glycol hydrogels [13,14], or scaffolds composed of physiological, in vivo-like polymers, such as fibrillar collagen matrices [15].…”