RESUMEN
Focal adhesions (FAs) are important mediators of cell-substrate interactions. One of their key functions is the transmission of forces between the intracellular acto-myosin network and the substrate. However, the relationships between cell traction forces, FA architecture, and molecular forces within FAs are poorly understood. Here, by combining Förster resonance energy transfer (FRET)-based molecular force biosensors with micropillar-based traction force sensors and high-resolution fluorescence microscopy, we simultaneously map molecular tension across vinculin, a key protein in FAs, and traction forces at FAs. Our results reveal strong spatiotemporal correlations between vinculin tension and cell traction forces at FAs throughout a wide range of substrate stiffnesses. Furthermore, we find that molecular tension within individual FAs follows a biphasic distribution from the proximal (toward the cell nucleus) to distal end (toward the cell edge). Using super-resolution imaging, we show that such a distribution relates to that of FA proteins. On the basis of our experimental data, we propose a model in which FA dynamics results from tension changes along the FAs.
RESUMEN
Physical interactions between cells and micro/nanometer-sized architecture presented in an extracellular matrix (ECM) environment significantly influence cell adhesion and morphology, often facilitating the incidence of diseases, such as cancer invasion and metastasis. Sensing and responding to the topographical cues are deeply associated with a physical interplay between integrins, ligands, and mechanical force transmission, ultimately determining diverse cell behavior. Thus, how the tension applied to the integrin-ligand bonds controls cells' response to the topographical cues needs to be elucidated through quantitative analysis. Here, in this brief research report, we reported a novel platform, termed "topo-tension gauge tether (TGT)," to visualize single-molecule force applied to the integrin-ligand on the aligned anisotropic nanopatterns. Using the topo-TGT assay, first, topography-induced adhesion and morphology of cancerous and normal cells were compared with the pre-defined peak integrin tension. Next, spatial integrin tensions underneath cells were identified using reconstructed integrin tension maps. As a result, we characterized each cell's capability to comply with nanotopographies and the magnitude of the spatial integrin tension. Altogether, the quantitative information on integrin tension will be a valuable basis for understanding the biophysical mechanisms underlying the force balance influencing adhesion to the topographical cues.
RESUMEN
Motility of eukaryotic cells or pathogens within tissues is mediated by the turnover of specific interactions with other cells or with the extracellular matrix. Biophysical characterization of these ligand-receptor adhesions helps to unravel the molecular mechanisms driving migration. Traction force microscopy or optical tweezers are typically used to measure the cellular forces exerted by cells on a substrate. However, the spatial resolution of traction force microscopy is limited to ~2 µm and performing experiments with optical traps is very time-consuming. Here we present the production of biomimetic surfaces that enable specific cell adhesion via synthetic ligands and at the same time monitor the transmitted forces by using molecular tension sensors. The ligands were coupled to double-stranded DNA probes with defined force thresholds for DNA unzipping. Receptor-mediated forces in the pN range are thereby semi-quantitatively converted into fluorescence signals, which can be detected by standard fluorescence microscopy at the resolution limit (~0.2 µm). The modular design of the assay allows to vary the presented ligands and the mechanical strength of the DNA probes, which provides a number of possibilities to probe the adhesion of different eukaryotic cell types and pathogens and is exemplified here with osteosarcoma cells and Plasmodium berghei Sporozoites.