Hallmarks of Life in Single Cell Contact Mechanics: Outstanding Challenges and Perspectives

Abstract

Cell mechanics is a fascinating subject that has witnessed a boost of scientific interest in the most diverse disciplines. Evidence of its biological relevance is continuously mounting, unveiling a real-life scenario ever more intricate and complex, and ever less universal. This review revisits the topic at the same time that appraises routine approaches and the synchronous combination of experimental methodologies to tackle cell mechanics in all its dimensionality and complexity. The focus is placed on cultured mammalian cells and on highly sensitive experimental techniques that rely on contact mechanics, namely scanning-probe and traction force microscopies. The importance of time as key variable in theory and experiment is particularly highlighted, together with the need to unambiguously identify the active and physiological contributions to cell behavior, and provide suitable mechanisms that dynamically interconnect relevant events, cellular structures and organelles to thoroughly understand the mechanobiology of cells. A special consideration is given to the role of friction and the importance of cell-cell interactions in scaling up the mechanical behavior from single cells to tissues. The topic is in constant demand of crossdisciplinarity, and in that sense, this review also serves the purpose of bringing the subject nearer to the mechanical physics and engineering community.

Quantitative Methodologies to Dissect Immune Cell Mechanobiology

“…For example, quantifying both cell mechanical properties and signalling events simultaneously might yield a more complete picture of how mechanics, force generation and biochemical signalling are coupled across scales, from single receptor–ligand interactions to cell morphological changes driven by the actin cytoskeleton, to the overall mechanical properties of the tissue environment. Recent efforts of combining AFM with TFM as well as with different fluorescence imaging approaches have already proven to be promising [ 36 , 87 , 90 , 91 , 92 , 93 ]. Quantifying the mechanobiology of the immune response utilizing methodologies with the appropriate sensitivity may thus be the route to enhancing our understanding of the role of mechanobiology in health and disease.…”

“…Thus, it is essential to differentiate between the macroscopic, or “bulk”, mechanical properties of cells and their microscopic subcellular mechanical properties. Moreover, both the macroscopic and microscopic mechanical properties of cells as well as the forces they generate are time dependent, because their dynamics rely on a constant re-arrangement and molecular turnover [ 10 , 36 , 37 ]. Some processes, for example, actin turnover, occur at the time scale of seconds [ 10 ], while others, such as the re-location of the nucleus of activating T cells, may take multiple hours [ 38 , 39 , 40 ].…”

“…Some of the most commonly used techniques to measure mechanical properties in biomechanics and mechanobiology that are based on a direct mechanical contact with the cells linked to the measured mechanical readout. [13,36,49,51,53] To quantify subcellular mechanics, passive and active particle-tracking microrheology (PTM) is commonly used, where the so-called tracer particles, which can vary in size, are injected into the cell, and their motion is then followed by an optical microscope. In passive PTM, the particles' dynamics are exclusively driven by thermal fluctuations, while in active PTM, an additional external (oscillating) magnetic force is applied to drive the particles' movement [57,58].…”

Possibilities of using T-cell biophysical biomarkers of ageing

“…Indeed, a biophysical point of departure for investigating the mechanical age-related changes in T cells is that changes in the mechanical properties of cells are hallmarks of ageing (Refs 88 , 89 ). Cell mechanical behaviour has been largely overlooked in the context of the immune system (Refs 90 , 91 ). Outside of the immune system, studies have demonstrated that there is a strong correlation between age and cell stiffness, in numerous diseases, including vascular degeneration, cardiac dysfunction and cancer (Ref.…”

What Is the Right Mechanical Readout for Understanding the Mechanobiology of the Immune Response?

“…We and others have spent significant efforts in evolving the sensitivity of traction force microscopy, probably the most widely applied force quantification methodology, which offers the simultaneous quantification of mechanical force production and the dynamics of cells (Colin-York and Fritzsche, 2018 ; Colin-York et al, 2019a ; Stubb et al, 2020 ; Vorselen et al, 2020 ). More recent efforts of combining different types of quantitative simultaneous measurements hold the promise to achieve a more complete understanding of how biomechanics feeds into immune cell physiology of the immune response (Skamrahl et al, 2019 ; Hobson et al, 2020 ; Moreno-Flores, 2020 ; Nelsen et al, 2020 ). Quantifying the mechanical settings of the immune response in full utilizing methodologies with the right sensitivity may thus be the route to enable broad recognition of mechanobiology in health and disease.…”