Mechanical stresses are ever present in the cellular environment, whether through external forces that are applied to tissues or endogenous forces that are generated within the active cytoskeleton. ...Despite the wide array of studies demonstrating that such forces affect cellular signaling and function, it remains unclear whether mechanotransduction in different contexts shares common mechanisms. Here, I discuss possible mechanisms by which applied forces, cell-generated forces and changes in substrate mechanics could exert changes in cell function through common mechanotransduction machinery. I draw from examples that are primarily focused on the role of adhesions in transducing mechanical forces. Based on this discussion, emerging themes arise that connect these different areas of inquiry and suggest multiple avenues for future studies.
Much of our understanding of the biological mechanisms that underlie cellular functions, such as migration, differentiation and force-sensing has been garnered from studying cells cultured on ...two-dimensional (2D) glass or plastic surfaces. However, more recently the cell biology field has come to appreciate the dissimilarity between these flat surfaces and the topographically complex, three-dimensional (3D) extracellular environments in which cells routinely operate in vivo. This has spurred substantial efforts towards the development of in vitro 3D biomimetic environments and has encouraged much cross-disciplinary work among biologists, material scientists and tissue engineers. As we move towards more-physiological culture systems for studying fundamental cellular processes, it is crucial to define exactly which factors are operative in 3D microenvironments. Thus, the focus of this Commentary will be on identifying and describing the fundamental features of 3D cell culture systems that influence cell structure, adhesion, mechanotransduction and signaling in response to soluble factors, which - in turn - regulate overall cellular function in ways that depart dramatically from traditional 2D culture formats. Additionally, we will describe experimental scenarios in which 3D culture is particularly relevant, highlight recent advances in materials engineering for studying cell biology, and discuss examples where studying cells in a 3D context provided insights that would not have been observed in traditional 2D systems.
Fluid shear stress (FSS) from blood flow acting on the endothelium critically regulates vascular morphogenesis, blood pressure, and atherosclerosis 1. FSS applied to endothelial cells (ECs) triggers ...signaling events including opening of ion channels, activation of signaling pathways, and changes in gene expression. Elucidating how ECs sense flow is important for understanding both normal vascular function and disease. EC responses to FSS are mediated in part by a junctional mechanosensory complex consisting of VE-cadherin, PECAM-1, and VEGFR2 2. Previous work suggested that flow increases force on PECAM-1, which initiates signaling 2–4. Deletion of PECAM-1 blocks responses to flow in vitro and flow-dependent vascular remodeling in vivo 2, 5. To understand this process, we developed and validated FRET-based tension sensors for VE-cadherin and PECAM-1 using our previously developed FRET tension biosensor 6. FRET measurements showed that in static culture, VE-cadherin in cell-cell junctions bears significant myosin-dependent tension, whereas there was no detectable tension on VE-cadherin outside of junctions. Onset of shear stress triggered a rapid (<30 s) decrease in tension across VE-cadherin, which paralleled a decrease in total cell-cell junctional tension. Flow triggered a simultaneous increase in tension across junctional PECAM-1, while nonjunctional PECAM-1 was unaffected. Tension on PECAM-1 was mediated by flow-stimulated association with vimentin. These data confirm the prediction that shear increases force on PECAM-1. However, they also argue against the current model of passive transfer of force through the cytoskeleton to the junctions 7, showing instead that flow triggers cytoskeletal remodeling, which alters forces across the junctional receptors.
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•VE-cadherin is under myosin-dependent tension•Flow triggers decreased tension on VE-cadherin by reducing overall contractility•Flow triggers increased tension on PECAM-1 through attachment to vimentin•The data suggest that an unidentified upstream mechanosensor initiates signaling
Biomaterials engineered with specific bioactive ligands, tunable mechanical properties, and complex architectural features have emerged as powerful tools to probe how cells sense and respond to the ...physical properties of their material surroundings, and ultimately provide designer approaches to control cell function.
Cells from many different tissues sense the stiffness and spatial patterning of their microenvironment to modulate their shape and cortical stiffness. It is currently unknown how substrate stiffness, ...cell shape, and cell stiffness modulate or interact with one another. Here, we use microcontact printing and microfabricated arrays of elastomeric posts to independently and simultaneously control cell shape and substrate stiffness. Our experiments show that cell cortical stiffness increases as a function of both substrate stiffness and spread area. For soft substrates, the influence of substrate stiffness on cell cortical stiffness is more prominent than that of cell shape, since increasing adherent area does not lead to cell stiffening. On the other hand, for cells constrained to a small area, cell shape effects are more dominant than substrate stiffness, since increasing substrate stiffness no longer affects cell stiffness. These results suggest that cell size and substrate stiffness can interact in a complex fashion to either enhance or antagonize each other's effect on cell morphology and mechanics.
Forces generated by cells are critical regulators of cell adhesion, signaling, and function, and they are also essential drivers in the morphogenetic events of development. Over the past 20 years, ...several methods have been developed to measure these forces. However, despite recent substantial interest in understanding the contribution of these forces in biology, implementation and adoption of the developed methods by the broader biological community remain challenging because of the inherently multidisciplinary expertise required to conduct and interpret the measurements. In this review, we introduce the established methods and highlight the technical challenges associated with implementing each technique in a biological laboratory.
Cadherins and integrins are intrinsically linked through the actin cytoskeleton and share common signaling molecules. Although mechanosensing by the integrin-actin axis has long been appreciated, a ...growing body of literature now demonstrates that cadherins also transduce and respond to mechanical forces. Mounting evidence shows that mechanically driven crosstalk between integrins and cadherins regulates the spatial distribution of these receptors, their signaling intermediates, the actin cytoskeleton and intracellular forces. This interplay between integrins and cadherins can control fibronectin matrix assembly and signaling, and a fine balance between traction forces at focal adhesions and intercellular tension at adherens junctions is crucial for directional collective cell migration. In this Commentary, we discuss two central ideas: (1) how the dynamic interplay between integrins and cadherins regulates the spatial organization of intracellular signals and the extracellular matrix, and (2) the emerging consensus that intracellular force is a central mechanism that dictates cell behavior, guides tissue development and ultimately drives physiology.
More than a century ago, it was proposed that mechanical forces could drive tissue formation. However, only recently with the advent of enabling biophysical and molecular technologies are we ...beginning to understand how individual cells transduce mechanical force into biochemical signals. In turn, this knowledge of mechanotransduction at the cellular level is beginning to clarify the role of mechanics in patterning processes during embryonic development. In this perspective, we will discuss current mechanotransduction paradigms, along with the technologies that have shaped the field of mechanobiology.
Physical factors in the local cellular microenvironment, including cell shape and geometry, matrix mechanics, external mechanical forces, and nanotopographical features of the extracellular matrix, ...can all have strong influences on regulating stem cell fate. Stem cells sense and respond to these insoluble biophysical signals through integrin-mediated adhesions and the force balance between intracellular cytoskeletal contractility and the resistant forces originated from the extracellular matrix. Importantly, these mechanotransduction processes can couple with many other potent growth-factor-mediated signaling pathways to regulate stem cell fate. Different bioengineering tools and microscale/nanoscale devices have been successfully developed to engineer the physical aspects of the cellular microenvironment for stem cells, and these tools and devices have proven extremely powerful for identifying the extrinsic physical factors and their downstream intracellular signaling pathways that control stem cell functions.
Mechanotransduction research has focused historically on how externally applied forces can affect cell signalling and function. A growing body of evidence suggests that contractile forces that are ...generated internally by the actomyosin cytoskeleton are also important in regulating cell behaviour, and suggest a broader role for mechanotransduction in biology. Although the molecular basis for these cellular forces in mechanotransduction is being pursued in cell culture, researchers are also beginning to appreciate their contribution to in vivo developmental processes. Here, we examine the role for mechanical forces and contractility in regulating cell and tissue structure and function during development.
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