Integrative cell and tissue dynamics


We aim at understanding how physical forces and molecular control modules cooperate to drive biological function.

Super-stretched cells surrounded by only slightly deformed ones. The cell nuleus is shown in blue, actin filaments in red and keratin filaments in green.

We develop new technologies to map and perturb the main physical properties that determine how cells and tissues grow, move, invade and remodel. By combining this physical information with systematic molecular perturbations and computational models we explore the principles that govern the interplay between chemical and physical cues in living tissues.

We study how these principles are regulated in physiology and development, and how they are derailed in cancer and aging.

Making cellular forces visible

To study cell and tissue dynamics we develop new technologies to measure physical forces at the cell-cell and cell-matrix interface. By combining these technologies with computational analysis of cell shape and velocity we obtain a full experimental characterization of epithelial dynamics during tissue growth, wound healing and cancer cell invasion.

Breast cancer cells attached to a surface rich in collagen. The actin cytoskeleton can be seen in green, coated with active myosin (ppMLC) in red, and the cell-cell junctions (E-cadherin) in blue.

Tumour invasion by stromal forces

Cancer cell invasion and metastasis remain the leading cause of death in patients with cancer. Both processes are the result of a complex interaction between tumor cells and their microenvironment. One of our main lines of research is to study how tumours exploit the functions non-cancer cells in their microenvironment to invade and metasize. We focus on the interaction between epithelial cancer cells and Cancer Associated Fibroblasts (CAFs), the most abundant cell type in the tumour stroma. In a recent study we were able to demonstrate that CAFs guide the collective invasion of cancer cells through a physical force. This force enables CAFs to physically drag cancer cells into the surrounding tissue. Force transmission is mediated by a heterotypic interaction between two different proteins, one located on the surface of cancer cells called E-cadherin, and another expressed on the surface of fibroblasts, called N-cadherin.

Optogenetics to control cell mechanics

The recent development of optogenetic technologies offers promising possibilities to control signalling pathways with high spatiotemporal resolution. By expressing genetically encoded light-sensitive proteins, optogenetic technology enables the reversible perturbation of intracellular biochemistry with subcellular resolution. We have developed optogenetic tools based on controlling the activity of endogenous RhoA to upregulate or downregulate cell contractility. We have shown that these tools enable rapid, local and reversible changes in traction forces, cell–cell forces, and tissue compaction. We have shown, further, that changes in cellular forces are paralleled by translocation of the transcriptional regulator YAP, indicating that our tools can be used to control mechanotransductory pathways.

In the image, an epithelium of cells of the MDCK line with the marked nuclei: the color ranges from red to green depending on the phase of the cell cycle; red for phase G1, green for phases S, G2 and M.

Collective durotaxis: a mechanism for cellular guidance by mechanical cues

Directed cell migration is one of the earliest observations in cell biology, dating back to the late XIX century. Also known as taxis, directed cell migration has been commonly associated with chemotaxis, i.e. the ability of a broad variety of cell types to migrate following gradients of chemical factors. We recently demonstrated a new mode of collective cell guidance by mechanical cues, called collective durotaxis. This new migration mode emerges only in cell collectives and, strikingly, does not require isolated cells to exhibit gradient sensing. To study the mechanisms behind this phenomenon, we developed new tools to measure the forces that propel cells during durotaxis at the cell-matrix and cell-cell levels. Upon combining this new experimental technique with biochemical approaches and theoretical modelling, we concluded that collective durotaxis originates from long-range transmission of contractile intercellular forces. This mechanism is unique in that the very same machinery that senses the attractant -the actomyosin cytoskeleton- is responsible for propulsion towards it. As such, collective durotaxis appears to be the simplest and perhaps most primitive mechanism by which a collective system responds to a gradient.

Microfabrication and wound healing

Using microfabrication technologies, we designed new ways to decipher the mechanisms of wound healing. By doing so we uncovered a new understanding of how cells move and work together to close a gap in a tissue. We showed that a new mechanism applies in which cells assemble supracellular contractile arcs that compress the tissue under the wound. By combining experiments and computational modeling, we showed that contractions arising from these arcs make the wound heal in a quicker and more robust way.

Stretching epithelial tissues

Epithelial tissues are fundamental to life, as they protect the body from radiation, pollutants and pathogens. They’re also responsible for gas exchange in the lungs, absorption of nutrients in the gut, and excretion of urine in the kidneys. We developed a new approach to subject epithelial tissues to very large deformations, up to four times their original size. Most materials are ‘unhappy’ during stretching. As they become progressively deformed, they want to go back to their unstretched state, like a rubber band, or may even break as the tension increases. We found that epithelial sheets have a different and unusual mechanical behavior. To our surprise, tissues did not break during stretching, and they were able to recover their initial size in a fully reversible way when unstretched. Even more surprisingly, some cells in the tissue barely stretched, while others became ‘superstretched’, increasing their area more than ten times. We identified the molecular mechanisms that explain this physical behavior, which we call ‘active superelasticity’ as an analogy with the behavior of some high-tech metal alloys used in medical technologies. Understanding this surprising mechanical behavior in epithelial tissues could help us build better artificial organs or new bionic technologies such as organs-on-a-chip.


Xavier Trepat | Group Leader / ICREA Research Professor
Dobryna Julia Valeria Zalvidea | Senior Researcher
Juan Francisco Abenza Martínez | Postdoctoral Researcher
Tom Golde | Postdoctoral Researcher
Manuel Gómez González | Postdoctoral Researcher
Anna Labernadie | Postdoctoral Researcher
Andrea Malandrino | Postdoctoral Researcher
Marija Matejcic | Postdoctoral Researcher
Leone Rossetti | Postdoctoral Researcher
Raimon Sunyer Borrell | Postdoctoral Researcher
Gerardo Ceada Torres | PhD Student
Nimesh Ramesh Chahare | PhD Student
Sefora Conti | PhD Student
Ariadna Marin Llaurado | PhD Student
Macià Esteve Pallares Pallares | PhD Student
Isabela Corina Santos Fortunato | PhD Student
Anghara Menéndez Montes | Laboratory Technician
Miquel Bosch Padrós | Masters Student
Nerea Montedeoca Vázquez | Masters Student
Alice Perucca | Masters Student
Oriol Mañé Benach | Laboratory Assistant
Jonel Trebicka | Visiting Researcher




EU-funded projects
TensionControl Multiscale regulation of epithelial tension (2015-2020) European Commission, ERC – CoG Xavier Trepat
Mechano·Control Mechanical control of biological function (2017-2021) European Commission, FET Proactive Xavier Trepat
EpiFold Engineering epithelial shape and mechanics: from synthetic morphogenesis to biohybrid devices (2020-2025) European Commission, ERC-AdG Xavier Trepat
National projects
mGRADIENTMecanobiología de la migración colectiva durante la haptotaxis y la durotaxis: aplicación a los organoides intestinales (2019-2021) MICIU Generación Conocimiento: Proyectos I+D Xavier Trepat
DYNAGELHidrogeles biocompatibles con rigidez dinámicamente ajustable para estudiar la mecanobiología de células y tejidos (2019-2022) MICIU Retos investigación: Proyectos I+D Raimon Sunyer
Privately-funded projects
Joint Programme Healthy Ageing Obra Social La Caixa Xavier Trepat
Understanding and measuring mechanical tumor properties to improve cancer diagnosis, treatment, and survival: Application to liquid biopsies (2017-2020) Obra Social La Caixa Xavier Trepat
Finished projects


El mecanoma de la adhesión epitelial: mecanismos de detección, resistencia y transmisión de fuerzas intercelulares MINECO, I+D-Investigación fundamental no orientada Xavier Trepat
MICROGRADIENTPAGE Micro Gradient Polyacrylamide Gels for High Throughput Electrophoresis Analysis European Commission, ERC-PoC Xavier Trepat
GENESFORCEMOTION Physical Forces Driving Collective Cell Migration: from Genes to Mechanism European Commission, ERC-StG Xavier Trepat
CAMVAS Coordination and migration of cells during 3D Vasculogenesis (2014-2017) European Commission, MARIE CURIE – IOF Xavier Trepat
DUROTAXIS Mecanobiología de la durotaxis: de las células aisladas a los tejidos MINECO, Proyectos I+D Excelencia Xavier Trepat


Park, D., Wershof, E., Boeing, S., Labernadie, A., Jenkins, R. P., George, S., Trepat, X., Bates, P. A., Sahai, E., (2020). Extracellular matrix anisotropy is determined by TFAP2C-dependent regulation of cell collisions Nature Materials Article in Press

The isotropic or anisotropic organization of biological extracellular matrices has important consequences for tissue function. We study emergent anisotropy using fibroblasts that generate varying degrees of matrix alignment from uniform starting conditions. This reveals that the early migratory paths of fibroblasts are correlated with subsequent matrix organization. Combined experimentation and adaptation of Vicsek modelling demonstrates that the reorientation of cells relative to each other following collision plays a role in generating matrix anisotropy. We term this behaviour ‘cell collision guidance’. The transcription factor TFAP2C regulates cell collision guidance in part by controlling the expression of RND3. RND3 localizes to cell–cell collision zones where it downregulates actomyosin activity. Cell collision guidance fails without this mechanism in place, leading to isotropic matrix generation. The cross-referencing of alignment and TFAP2C gene expression signatures against existing datasets enables the identification and validation of several classes of pharmacological agents that disrupt matrix anisotropy.

Keywords: Biomaterials – cells, Cell migration, Self-assembly, Tissues

Malandrino, Andrea, Trepat, Xavier, Kamm, Roger D., Mak, Michael, (2019). Dynamic filopodial forces induce accumulation, damage, and plastic remodeling of 3D extracellular matrices PLoS Computational Biology 15, (4), e1006684

The mechanical properties of the extracellular matrix (ECM)–a complex, 3D, fibrillar scaffold of cells in physiological environments–modulate cell behavior and can drive tissue morphogenesis, regeneration, and disease progression. For simplicity, it is often convenient to assume these properties to be time-invariant. In living systems, however, cells dynamically remodel the ECM and create time-dependent local microenvironments. Here, we show how cell-generated contractile forces produce substantial irreversible changes to the density and architecture of physiologically relevant ECMs–collagen I and fibrin–in a matter of minutes. We measure the 3D deformation profiles of the ECM surrounding cancer and endothelial cells during stages when force generation is active or inactive. We further correlate these ECM measurements to both discrete fiber simulations that incorporate fiber crosslink unbinding kinetics and continuum-scale simulations that account for viscoplastic and damage features. Our findings further confirm that plasticity, as a mechanical law to capture remodeling in these networks, is fundamentally tied to material damage via force-driven unbinding of fiber crosslinks. These results characterize in a multiscale manner the dynamic nature of the mechanical environment of physiologically mimicking cell-in-gel systems.

Keywords: Collagens, Fibrin, Extracellular matrix, Cross-linking, Cell physiology, Deformation, Fluorescence imaging, Cell biology

Arroyo, M., Trepat, X., (2019). Embryonic self-fracking Science 365, (6452), 442-443

From a broken bone to a major earthquake, the fracture of a material usually means trouble. However, in some practical applications engineers have learned how to harness the mechanisms of fracture. This is illustrated by the well-known process of hydraulic fracturing, or “fracking,” in which injection of pressurized fluid in shale rocks opens cracks to extract oil or gas (1). On page 465 of this issue, Dumortier et al. (2) show that the developing mouse embryo uses this same principle to transiently disrupt its shape and sculpt a more complex one. Fracking is the key mechanism that enables the early embryo to develop its first symmetry axis, a key stage in fetal morphogenesis.

Garreta, Elena, Prado, Patricia, Tarantino, Carolina, Oria, Roger, Fanlo, Lucia, Martí, Elisa, Zalvidea, Dobryna, Trepat, Xavier, Roca-Cusachs, Pere, Gavaldà -Navarro, Aleix, Cozzuto, Luca, Campistol, Josep M., Izpisúa Belmonte, Juan Carlos, Hurtado del Pozo, Carmen, Montserrat, Nuria, (2019). Fine tuning the extracellular environment accelerates the derivation of kidney organoids from human pluripotent stem cells Nature Materials 18, 397-405

The generation of organoids is one of the biggest scientific advances in regenerative medicine. Here, by lengthening the time that human pluripotent stem cells (hPSCs) were exposed to a three-dimensional microenvironment, and by applying defined renal inductive signals, we generated kidney organoids that transcriptomically matched second-trimester human fetal kidneys. We validated these results using ex vivo and in vitro assays that model renal development. Furthermore, we developed a transplantation method that utilizes the chick chorioallantoic membrane. This approach created a soft in vivo microenvironment that promoted the growth and differentiation of implanted kidney organoids, as well as providing a vascular component. The stiffness of the in ovo chorioallantoic membrane microenvironment was recapitulated in vitro by fabricating compliant hydrogels. These biomaterials promoted the efficient generation of renal vesicles and nephron structures, demonstrating that a soft environment accelerates the differentiation of hPSC-derived kidney organoids.

Pérez-González, Carlos, Alert, Ricard, Blanch-Mercader, Carles, Gómez-González, Manuel, Kolodziej, Tomasz, Bazellieres, Elsa, Casademunt, Jaume, Trepat, Xavier, (2019). Active wetting of epithelial tissues Nature Physics 15, 79-88

Development, regeneration and cancer involve drastic transitions in tissue morphology. In analogy with the behaviour of inert fluids, some of these transitions have been interpreted as wetting transitions. The validity and scope of this analogy are unclear, however, because the active cellular forces that drive tissue wetting have been neither measured nor theoretically accounted for. Here we show that the transition between two-dimensional epithelial monolayers and three-dimensional spheroidal aggregates can be understood as an active wetting transition whose physics differs fundamentally from that of passive wetting phenomena. By combining an active polar fluid model with measurements of physical forces as a function of tissue size, contractility, cell–cell and cell–substrate adhesion, and substrate stiffness, we show that the wetting transition results from the competition between traction forces and contractile intercellular stresses. This competition defines a new intrinsic length scale that gives rise to a critical size for the wetting transition in tissues, a striking feature that has no counterpart in classical wetting. Finally, we show that active shape fluctuations are dynamically amplified during tissue dewetting. Overall, we conclude that tissue spreading constitutes a prominent example of active wetting—a novel physical scenario that may explain morphological transitions during tissue morphogenesis and tumour progression.

Chen, Tianchi, Callan-Jones, Andrew, Fedorov, Eduard, Ravasio, Andrea, Brugués, Agustí, Ong, Hui Ting, Toyama, Yusuke, Low, Boon Chuan, Trepat, Xavier, Shemesh, Tom, Voituriez, Raphaël, Ladoux, Benoît, (2019). Large-scale curvature sensing by directional actin flow drives cellular migration mode switching Nature Physics 15, (4), 393-402

Cell migration over heterogeneous substrates during wound healing or morphogenetic processes leads to shape changes driven by different organizations of the actin cytoskeleton and by functional changes including lamellipodial protrusions and contractile actin cables. Cells distinguish between cell-sized positive and negative curvatures in their physical environment by forming protrusions at positive curvatures and actin cables at negative curvatures; however, the cellular mechanisms remain unclear. Here, we report that concave edges promote polarized actin structures with actin flow directed towards the cell edge, in contrast to well-documented retrograde flow at convex edges. Anterograde flow and contractility induce a tension anisotropy gradient. A polarized actin network is formed, accompanied by a local polymerization–depolymerization gradient, together with leading-edge contractile actin cables in the front. These cables extend onto non-adherent regions while still maintaining contact with the substrate through focal adhesions. The contraction and dynamic reorganization of this actin structure allows forward movements enabling cell migration over non-adherent regions on the substrate. These versatile functional structures may help cells sense and navigate their environment by adapting to external geometric and mechanical cues.

Keywords: Biopolymers in vivo, Cellular motility

Uroz, Marina, Garcia-Puig, Anna, Tekeli, Isil, Elosegui-Artola, Alberto, Abenza, Juan F., Marín-Llauradó, Ariadna, Pujals, Silvia, Conte, Vito, Albertazzi, Lorenzo, Roca-Cusachs, Pere, Raya, Ángel, Trepat, Xavier, (2019). Traction forces at the cytokinetic ring regulate cell division and polyploidy in the migrating zebrafish epicardium Nature Materials 18, 1015-1023

Epithelial repair and regeneration are driven by collective cell migration and division. Both cellular functions involve tightly controlled mechanical events, but how physical forces regulate cell division in migrating epithelia is largely unknown. Here we show that cells dividing in the migrating zebrafish epicardium exert large cell–extracellular matrix (ECM) forces during cytokinesis. These forces point towards the division axis and are exerted through focal adhesions that connect the cytokinetic ring to the underlying ECM. When subjected to high loading rates, these cytokinetic focal adhesions prevent closure of the contractile ring, leading to multi-nucleation through cytokinetic failure. By combining a clutch model with experiments on substrates of different rigidity, ECM composition and ligand density, we show that failed cytokinesis is triggered by adhesion reinforcement downstream of increased myosin density. The mechanical interaction between the cytokinetic ring and the ECM thus provides a mechanism for the regulation of cell division and polyploidy that may have implications in regeneration and cancer.

Zalvidea, D., Trepat, X., Rebollo, E., (2019). Fast multiphoton microscope based on polymer ulenses array using a 3D printed mold CL Poster session 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference , IEEE (Munich, Germany) OSA Technical Digest (Optical Society of America, 2019), paper cl_p_22

Multiphoton microscopy is a well-established technique for in vivo tissue imaging at high resolution and long penetration depth. As it uses a single point detector and a single scanning beam, image generation is slow. Several competitive solutions have been proposed during the last years, e.g. resonant scanning, that can reach 30 fps at 2048×2048 scanning resolution but relying on a fixed speed but it does not grant enough time for efficient collection of photons, or multiplexing beams, which show poor efficiency. Here, we propose a multiplexed beam solution that uses a rotating ulenses array for excitation and a camera for detection. The array of ulenses was built in polydimethilsiloxane (PDMS; > 90% transmission in the near IR wavelengths typically used in multiphoton microscopy), using a 3D-printed mold designed following a Nipkow disc pattern slightly modified to increase the lenses efficiency.

Zalvidea, D., Castano, O., Baker, S., Castro, N., Engel, E., Trepat, X., (2019). Time-lapse intravital imaging of biomaterials integration in tissues using a multicolor multiphoton microscope Novel lasers, instruments and technology 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference , IEEE (Munich, Germany) OSA Technical Digest (Optical Society of America, 2019), paper cl_3_1

Different mechanisms are triggered when tissue is exposed to a biomaterial. The success of the biomaterial targeted process, like the release of chemicals, promoted angiogenesis, tissue regeneration, etc. depends on its integration in the tissue [1]. Studying this interaction in vivo requires the ability to image simultaneously deep immersed proteins and biomaterials with high resolution and low damage. Several methods offer solutions but only multiphoton microscopy (MM) has the ability to image with high resolution deep inside the sample. Why is not MM more extensively applied as a platform for investigating biomaterial integration in vivo? The high cost of the typical source for multiphoton microscopy is a clear limitation. Furthermore, imaging several channels simultaneously becomes out of reach for most of the labs.

Timmers, H., Kowligy, A., Lind, A. J., Nader, N., Shaw, J., Zalvidea, D., Biegert, J., Diddams, S. A., (2019). Hyperspectral microscopy with broadband infrared frequency combs Ultrafast Applications (SF1E) 2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference , IEEE (Munich, Germany) OSA Technical Digest (Optical Society of America, 2019), paper SF1E.4

We present a new modality for infrared, hyperspectral microscopy using dual-comb, electro-optic sampling of octave-spanning infrared frequency combs. We obtain hyperspectral images of SU8 test patterns on Si wafers with a spatial resolution of 12 µm.

Latorre, Ernest, Kale, Sohan, Casares, Laura, Gómez-González, Manuel, Uroz, Marina, Valon, Léo, Nair, Roshna V., Garreta, Elena, Montserrat, Nuria, del Campo, Aránzazu, Ladoux, Benoit, Arroyo, Marino, Trepat, Xavier, (2018). Active superelasticity in three-dimensional epithelia of controlled shape Nature 563, (7730), 203-208

Fundamental biological processes are carried out by curved epithelial sheets that enclose a pressurized lumen. How these sheets develop and withstand three-dimensional deformations has remained unclear. Here we combine measurements of epithelial tension and shape with theoretical modelling to show that epithelial sheets are active superelastic materials. We produce arrays of epithelial domes with controlled geometry. Quantification of luminal pressure and epithelial tension reveals a tensional plateau over several-fold areal strains. These extreme strains in the tissue are accommodated by highly heterogeneous strains at a cellular level, in seeming contradiction to the measured tensional uniformity. This phenomenon is reminiscent of superelasticity, a behaviour that is generally attributed to microscopic material instabilities in metal alloys. We show that in epithelial cells this instability is triggered by a stretch-induced dilution of the actin cortex, and is rescued by the intermediate filament network. Our study reveals a type of mechanical behaviour—which we term active superelasticity—that enables epithelial sheets to sustain extreme stretching under constant tension.

Good, M., Trepat, X., (2018). Cell parts to complex processes, from the bottom up Nature 563, (7730), 188-189

Engineering approaches allow biological structures and behaviours to be reconstituted in vitro. A biologist and a physicist discuss the potential and limitations of this bottom-up philosophy in providing insights into complex biological processes.

Keywords: Biophysics, Complexity, Engineering

Shellard, Adam, Szabó, A., Trepat, Xavier, Mayor, Roberto, (2018). Supracellular contraction at the rear of neural crest cell groups drives collective chemotaxis Science 362, (6412), 339-343

Collective cell chemotaxis, the directed migration of cell groups along gradients of soluble chemical cues, underlies various developmental and pathological processes. We use neural crest cells, a migratory embryonic stem cell population whose behavior has been likened to malignant invasion, to study collective chemotaxis in vivo. Studying Xenopus and zebrafish, we have shown that the neural crest exhibits a tensile actomyosin ring at the edge of the migratory cell group that contracts in a supracellular fashion. This contractility is polarized during collective cell chemotaxis: It is inhibited at the front but persists at the rear of the cell cluster. The differential contractility drives directed collective cell migration ex vivo and in vivo through the intercalation of rear cells. Thus, in neural crest cells, collective chemotaxis works by rear-wheel drive.

Trepat, Xavier, Sahai, Erik, (2018). Mesoscale physical principles of collective cell organization Nature Physics 14, (7), 671-682

We review recent evidence showing that cell and tissue dynamics are governed by mesoscale physical principles. These principles can be understood in terms of simple state diagrams in which control variables include force, density, shape, adhesion and self-propulsion. An appropriate combination of these physical quantities gives rise to emergent phenomena such as cell jamming, topological defects and underdamped waves. Mesoscale physical properties of cell assemblies are found to precede and instruct biological functions such as cell division, extrusion, invasion and gradient sensing. These properties are related to properties of biomolecules, but cannot be predicted from biochemical principles. Thus, biological function is governed by emergent mesoscale states that can be predicted by a simple set of physical properties.

Uroz, Marina, Wistorf, Sabrina, Serra-Picamal, Xavier, Conte, Vito, Sales-Pardo, Marta, Roca-Cusachs, Pere, Guimerà, Roger, Trepat, Xavier, (2018). Regulation of cell cycle progression by cell–cell and cell–matrix forces Nature Cell Biology 20, (6), 646-654

It has long been proposed that the cell cycle is regulated by physical forces at the cell–cell and cell–extracellular matrix (ECM) interfaces. However, the evolution of these forces during the cycle has never been measured in a tissue, and whether this evolution affects cell cycle progression is unknown. Here, we quantified cell–cell tension and cell–ECM traction throughout the complete cycle of a large cell population in a growing epithelium. These measurements unveil temporal mechanical patterns that span the entire cell cycle and regulate its duration, the G1–S transition and mitotic rounding. Cells subjected to higher intercellular tension exhibit a higher probability to transition from G1 to S, as well as shorter G1 and S–G2–M phases. Moreover, we show that tension and mechanical energy are better predictors of the duration of G1 than measured geometric properties. Tension increases during the cell cycle but decreases 3 hours before mitosis. Using optogenetic control of contractility, we show that this tension drop favours mitotic rounding. Our results establish that cell cycle progression is regulated cooperatively by forces between the dividing cell and its neighbours.

Elosegui-Artola, Alberto, Trepat, Xavier, Roca-Cusachs, Pere, (2018). Control of mechanotransduction by molecular clutch dynamics Trends in Cell Biology 28, (5), 356-367

The linkage of cells to their microenvironment is mediated by a series of bonds that dynamically engage and disengage, in what has been conceptualized as the molecular clutch model. Whereas this model has long been employed to describe actin cytoskeleton and cell migration dynamics, it has recently been proposed to also explain mechanotransduction (i.e., the process by which cells convert mechanical signals from their environment into biochemical signals). Here we review the current understanding on how cell dynamics and mechanotransduction are driven by molecular clutch dynamics and its master regulator, the force loading rate. Throughout this Review, we place a specific emphasis on the quantitative prediction of cell response enabled by combined experimental and theoretical approaches.

Thottacherry, Joseph Jose, Kosmalska, Anita Joanna, Elosegui-Artola, Alberto, Pradhan, Susav, Sharma, Sumit, Singh, Parvinder P., Guadamillas, Marta C., Chaudhary, Natasha, Vishwakarma, Ram, Trepat, Xavier, del Pozo, Miguel A., Parton, Robert G., Pullarkat, Pramod, Roca-Cusachs, Pere, Mayor, Satyajit, (2018). Mechanochemical feedback and control of endocytosis and membrane tension Nature Communications 9, 4217

Plasma membrane tension is an important factor that regulates many key cellular processes. Membrane trafficking is tightly coupled to membrane tension and can modulate the latter by addition or removal of the membrane. However, the cellular pathway(s) involved in these processes are poorly understood. Although a number of endocytic processes function simultaneously at the cell surface, we find that a dynamin and clathrin-independent pathway, the CLIC/GEEC (CG) pathway, is rapidly and specifically upregulated upon reduction of tension. On the other hand, inhibition of the CG pathway results in lower membrane tension, while up regulation significantly enhances membrane tension. We find that vinculin, a well-studied mechanotransducer, mediates the tension-dependent regulation of the CG pathway. Vinculin negatively regulates a key CG pathway regulator, GBF1, at the plasma membrane in a tension dependent manner. Thus, the CG pathway operates in a negative feedback loop with membrane tension which leads to a homeostatic regulation of membrane tension.

Pardo-Pastor, Carlos, Rubio-Moscardo, Fanny, Vogel-González, Marina, Serra, Selma A., Afthinos, Alexandros, Mrkonjic, Sanela, Destaing, Olivier, Abenza, Juan F., Fernández-Fernández, José M., Trepat, Xavier, Albiges-Rizo, Corinne, Konstantopoulos, Konstantinos, Valverde, Miguel A., (2018). Piezo2 channel regulates RhoA and actin cytoskeleton to promote cell mechanobiological responses Proceedings of the National Academy of Sciences of the United States of America 115, (8), 1925-1930

The actin cytoskeleton is central to many cellular processes involving changes in cell shape, migration, and adhesiveness. Therefore, there is a great interest in the identification of the signaling pathways leading to the regulation of actin polymerization and assembly into stress fibers (SFs). However, to date it is not well understood how the mechanical interactions between cells and their environment activate the assembly of SFs. Here, we demonstrate that the mechanosensitive Piezo2 channel is required to sense physical cues from the environment to generate a calcium signal that maintains RhoA active and the formation and orientation of SFs and focal adhesions. Besides, this Piezo2-initiated signaling pathway has implications for different hallmarks of cancer invasion and metastasis.

Keywords: Mechanotransduction, Calcium signaling, RhoA, Actin stress fibers, Cancer

Dix, Christina L., Matthews, Helen K., Uroz, Marina, McLaren, Susannah, Wolf, Lucie, Heatley, Nicholas, Win, Zaw, Almada, Pedro, Henriques, Ricardo, Boutros, Michael, Trepat, Xavier, Baum, Buzz, (2018). The role of mitotic cell-substrate adhesion re-modeling in animal cell division Developmental Cell 45, (1), 132-145

Animal cells undergo a dramatic series of shape changes as they divide, which depend on re-modeling of cell-substrate adhesions. Here, we show that while focal adhesion complexes are disassembled during mitotic rounding, integrins remain in place. These integrin-rich contacts connect mitotic cells to the underlying substrate throughout mitosis, guide polarized cell migration following mitotic exit, and are functionally important, since adherent cells undergo division failure when removed from the substrate. Further, the ability of cells to re-spread along pre-existing adhesive contacts is essential for division in cells compromised in their ability to construct a RhoGEF-dependent (Ect2) actomyosin ring. As a result, following Ect2 depletion, cells fail to divide on small adhesive islands but successfully divide on larger patterns, as the connection between daughter cells narrows and severs as they migrate away from one another. In this way, regulated re-modeling of cell-substrate adhesions during mitotic rounding aids division in animal cells.

Keywords: Division, Mitotic-rounding, Integrin-based adhesion, Cytokinesis

De Pascalis, Chiara, Pérez-González, Carlos, Seetharaman, Shailaja, Boëda, Batiste, Vianay, Benoit, Burute, Mithila, Leduc, Cécile, Borghi, Nicolas, Trepat, Xavier, Etienne-Manneville, Sandrine, (2018). Intermediate filaments control collective migration by restricting traction forces and sustaining cell–cell contacts The Journal of Cell Biology 217, (9), 3031-3044

Mesenchymal cell migration relies on the coordinated regulation of the actin and microtubule networks that participate in polarized cell protrusion, adhesion, and contraction. During collective migration, most of the traction forces are generated by the acto-myosin network linked to focal adhesions at the front of leader cells, which transmit these pulling forces to the followers. Here, using an in vitro wound healing assay to induce polarization and collective directed migration of primary astrocytes, we show that the intermediate filament (IF) network composed of vimentin, glial fibrillary acidic protein, and nestin contributes to directed collective movement by controlling the distribution of forces in the migrating cell monolayer. Together with the cytoskeletal linker plectin, these IFs control the organization and dynamics of the acto-myosin network, promoting the actin-driven treadmilling of adherens junctions, thereby facilitating the polarization of leader cells. Independently of their effect on adherens junctions, IFs influence the dynamics and localization of focal adhesions and limit their mechanical coupling to the acto-myosin network. We thus conclude that IFs promote collective directed migration in astrocytes by restricting the generation of traction forces to the front of leader cells, preventing aberrant tractions in the followers, and by contributing to the maintenance of lateral cell–cell interactions.

Labernadie, Anna, Trepat, Xavier, (2018). Sticking, steering, squeezing and shearing: cell movements driven by heterotypic mechanical forces Current Opinion in Cell Biology 54, 57-65

During development, the immune response and cancer, cells of different types interact mechanically. Here we review how such heterotypic mechanical interactions enable cell movements. We begin by analyzing the heterotypic forces that single cells use to adhere and squeeze through tight barriers, as in the case of leucocyte extravasation and cancer metastasis. We next focus on the different mechanisms by which adjacent tissues influence each other's movements, with particular emphasis on dragging forces during dorsal closure in Drosophila and shearing forces during gastrulation in zebrafish. Finally, we discuss the mechanotransduction feedback loops that enable different cell types to steer each other's migration during development and cancer. We illustrate these migration modes focusing on the combination of attractive and repulsive cues during co-migration of neural crest cells and placodes in Xenopus, and of fibroblasts and cancer cells during invasion. Throughout the review, we discuss the nature of the heterotypic contact, which may involve both homophilic and heterophilic interactions between adhesion receptors.

Sehgal, Poonam, Kong, Xinyu, Wu, Jun, Sunyer, Raimon, Trepat, Xavier, Leckband, Deborah, (2018). Epidermal growth factor receptor and integrins control force-dependent vinculin recruitment to E-cadherin junctions Journal of Cell Science 131, (6), jcs206656

This study reports novel findings that link E-cadherin (also known as CDH1)-mediated force-transduction signaling to vinculin targeting to intercellular junctions via epidermal growth factor receptor (EGFR) and integrins. These results build on previous findings that demonstrated that mechanically perturbed E-cadherin receptors activate phosphoinositide 3-kinase and downstream integrins in an EGFR-dependent manner. Results of this study show that this EGFR-mediated kinase cascade controls the force-dependent recruitment of vinculin to stressed E-cadherin complexes – a key early signature of cadherin-based mechanotransduction. Vinculin targeting requires its phosphorylation at tyrosine 822 by Abl family kinases (hereafter Abl), but the origin of force-dependent Abl activation had not been identified. We now present evidence that integrin activation, which is downstream of EGFR signaling, controls Abl activation, thus linking E-cadherin to Abl through a mechanosensitive signaling network. These findings place EGFR and integrins at the center of a positive-feedback loop, through which force-activated E-cadherin signals regulate vinculin recruitment to cadherin complexes in response to increased intercellular tension.This article has an associated First Person interview with the first author of the paper.

Keywords: Cadherin, Epidermal growth factor receptor, Force transduction, Magnetic twisting cytometry, Vinculin, Integrin

Kuipers, Arthur J., Middelbeek, Jeroen, Vrenken, Kirsten, Pérez-González, Carlos, Poelmans, Geert, Klarenbeek, Jeffrey, Jalink, Kees, Trepat, Xavier, van Leeuwen, Frank N., (2018). TRPM7 controls mesenchymal features of breast cancer cells by tensional regulation of SOX4 Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease 1864, (7), 2409-2419

Mechanically induced signaling pathways are important drivers of tumor progression. However, if and how mechanical signals affect metastasis or therapy response remains poorly understood. We previously found that the channel-kinase TRPM7, a regulator of cellular tension implicated in mechano-sensory processes, is required for breast cancer metastasis in vitro and in vivo. Here, we show that TRPM7 contributes to maintaining a mesenchymal phenotype in breast cancer cells by tensional regulation of the EMT transcription factor SOX4. The functional consequences of SOX4 knockdown closely mirror those produced by TRPM7 knockdown. By traction force measurements, we demonstrate that TRPM7 reduces cytoskeletal tension through inhibition of myosin II activity. Moreover, we show that SOX4 expression and downstream mesenchymal markers are inversely regulated by cytoskeletal tension and matrix rigidity. Overall, our results identify SOX4 as a transcription factor that is uniquely sensitive to cellular tension and indicate that TRPM7 may contribute to breast cancer progression by tensional regulation of SOX4.

Keywords: TRPM7, SOX4, Epithelial-mesenchymal transition, Cytoskeleton, Mechanotransduction

Escribano, Jorge, Sunyer, Raimon, Sánchez, María Teresa, Trepat, Xavier, Roca-Cusachs, Pere, García-Aznar, José Manuel, (2018). A hybrid computational model for collective cell durotaxis Biomechanics and Modeling in Mechanobiology 17, (4), 1037-1052

Collective cell migration is regulated by a complex set of mechanical interactions and cellular mechanisms. Collective migration emerges from mechanisms occurring at single cell level, involving processes like contraction, polymerization and depolymerization, of cell–cell interactions and of cell–substrate adhesion. Here, we present a computational framework which simulates the dynamics of this emergent behavior conditioned by substrates with stiffness gradients. The computational model reproduces the cell’s ability to move toward the stiffer part of the substrate, process known as durotaxis. It combines the continuous formulation of truss elements and a particle-based approach to simulate the dynamics of cell–matrix adhesions and cell–cell interactions. Using this hybrid approach, researchers can quickly create a quantitative model to understand the regulatory role of different mechanical conditions on the dynamics of collective cell migration. Our model shows that durotaxis occurs due to the ability of cells to deform the substrate more in the part of lower stiffness than in the stiffer part. This effect explains why cell collective movement is more effective than single cell movement in stiffness gradient conditions. In addition, we numerically evaluate how gradient stiffness properties, cell monolayer size and force transmission between cells and extracellular matrix are crucial in regulating durotaxis.

Oria, Roger, Wiegand, Tina, Escribano, Jorge, Elosegui-Artola, Alberto, Uriarte, Juan Jose, Moreno-Pulido, Cristian, Platzman, Ilia, Delcanale, Pietro, Albertazzi, Lorenzo, Navajas, Daniel, Trepat, Xavier, García-Aznar, José Manuel, Cavalcanti-Adam, Elisabetta Ada, Roca-Cusachs, Pere, (2017). Force loading explains spatial sensing of ligands by cells Nature 552, 219-224

Cells can sense the density and distribution of extracellular matrix (ECM) molecules by means of individual integrin proteins and larger, integrin-containing adhesion complexes within the cell membrane. This spatial sensing drives cellular activity in a variety of normal and pathological contexts1,2. Previous studies of cells on rigid glass surfaces have shown that spatial sensing of ECM ligands takes place at the nanometre scale, with integrin clustering and subsequent formation of focal adhesions impaired when single integrin–ligand bonds are separated by more than a few tens of nanometres3,4,5,6. It has thus been suggested that a crosslinking ‘adaptor’ protein of this size might connect integrins to the actin cytoskeleton, acting as a molecular ruler that senses ligand spacing directly3,7,8,9. Here, we develop gels whose rigidity and nanometre-scale distribution of ECM ligands can be controlled and altered. We find that increasing the spacing between ligands promotes the growth of focal adhesions on low-rigidity substrates, but leads to adhesion collapse on more-rigid substrates. Furthermore, disordering the ligand distribution drastically increases adhesion growth, but reduces the rigidity threshold for adhesion collapse. The growth and collapse of focal adhesions are mirrored by, respectively, the nuclear or cytosolic localization of the transcriptional regulator protein YAP. We explain these findings not through direct sensing of ligand spacing, but by using an expanded computational molecular-clutch model10,11, in which individual integrin–ECM bonds—the molecular clutches—respond to force loading by recruiting extra integrins, up to a maximum value. This generates more clutches, redistributing the overall force among them, and reducing the force loading per clutch. At high rigidity and high ligand spacing, maximum recruitment is reached, preventing further force redistribution and leading to adhesion collapse. Measurements of cellular traction forces and actin flow speeds support our model. Our results provide a general framework for how cells sense spatial and physical information at the nanoscale, precisely tuning the range of conditions at which they form adhesions and activate transcriptional regulation.

Malinverno, C., Corallino, S., Giavazzi, F., Bergert, M., Li, Q., Leoni, M., Disanza, A., Frittoli, E., Oldani, A., Martini, E., Lendenmann, T., Deflorian, G., Beznoussenko, G. V., Poulikakos, D., Ong, K. H., Uroz, M., Trepat, X., Parazzoli, D., Maiuri, P., Yu, W., Ferrari, A., Cerbino, R., Scita, G., (2017). Endocytic reawakening of motility in jammed epithelia Nature Materials 16, 587–596

Dynamics of epithelial monolayers has recently been interpreted in terms of a jamming or rigidity transition. How cells control such phase transitions is, however, unknown. Here we show that RAB5A, a key endocytic protein, is sufficient to induce large-scale, coordinated motility over tens of cells, and ballistic motion in otherwise kinetically arrested monolayers. This is linked to increased traction forces and to the extension of cell protrusions, which align with local velocity. Molecularly, impairing endocytosis, macropinocytosis or increasing fluid efflux abrogates RAB5A-induced collective motility. A simple model based on mechanical junctional tension and an active cell reorientation mechanism for the velocity of self-propelled cells identifies regimes of monolayer dynamics that explain endocytic reawakening of locomotion in terms of a combination of large-scale directed migration and local unjamming. These changes in multicellular dynamics enable collectives to migrate under physical constraints and may be exploited by tumours for interstitial dissemination.

Rodriguez-Franco, P., Brugués, A., Marin-Llaurado, A., Conte, V., Solanas, G., Batlle, E., Fredberg, J. J., Roca-Cusachs, P., Sunyer, R., Trepat, X., (2017). Long-lived force patterns and deformation waves at repulsive epithelial boundaries Nature Materials 16, (10), 1029-1036

For an organism to develop and maintain homeostasis, cell types with distinct functions must often be separated by physical boundaries. The formation and maintenance of such boundaries are commonly attributed to mechanisms restricted to the cells lining the boundary. Here we show that, besides these local subcellular mechanisms, the formation and maintenance of tissue boundaries involves long-lived, long-ranged mechanical events. Following contact between two epithelial monolayers expressing, respectively, EphB2 and its ligand ephrinB1, both monolayers exhibit oscillatory patterns of traction forces and intercellular stresses that tend to pull cell-matrix adhesions away from the boundary. With time, monolayers jam, accompanied by the emergence of deformation waves that propagate away from the boundary. This phenomenon is not specific to EphB2/ephrinB1 repulsion but is also present during the formation of boundaries with an inert interface and during fusion of homotypic epithelial layers. Our findings thus unveil a global physical mechanism that sustains tissue separation independently of the biochemical and mechanical features of the local tissue boundary.

Keywords: Biological physics, Cellular motility

Elosegui-Artola, A., Andreu, I., Beedle, A. E. M., Lezamiz, A., Uroz, M., Kosmalska, A. J., Oria, R., Kechagia, J. Z., Rico-Lastres, P., Le Roux, A. L., Shanahan, C. M., Trepat, X., Navajas, D., Garcia-Manyes, S., Roca-Cusachs, P., (2017). Force triggers YAP nuclear entry by regulating transport across nuclear pores Cell 171, (6), 1397-1410

YAP is a mechanosensitive transcriptional activator with a critical role in cancer, regeneration, and organ size control. Here, we show that force applied to the nucleus directly drives YAP nuclear translocation by decreasing the mechanical restriction of nuclear pores to molecular transport. Exposure to a stiff environment leads cells to establish a mechanical connection between the nucleus and the cytoskeleton, allowing forces exerted through focal adhesions to reach the nucleus. Force transmission then leads to nuclear flattening, which stretches nuclear pores, reduces their mechanical resistance to molecular transport, and increases YAP nuclear import. The restriction to transport is further regulated by the mechanical stability of the transported protein, which determines both active nuclear transport of YAP and passive transport of small proteins. Our results unveil a mechanosensing mechanism mediated directly by nuclear pores, demonstrated for YAP but with potential general applicability in transcriptional regulation. Force-dependent changes in nuclear pores control protein access to the nucleus.

Keywords: Atomic force microscopy, Hippo pathway, Mechanosensing, Mechanotransduction, Molecular mechanical stability, Nuclear mechanics, Nuclear pores, Nuclear transport, Rigidity sensing, Transcription regulation

Labernadie, A., Kato, T., Brugués, A., Serra-Picamal, X., Derzsi, S., Arwert, E., Weston, A., González-Tarragó, V., Elosegui-Artola, A., Albertazzi, L., Alcaraz, J., Roca-Cusachs, P., Sahai, E., Trepat, X., (2017). A mechanically active heterotypic E-cadherin/N-cadherin adhesion enables fibroblasts to drive cancer cell invasion Nature Cell Biology 19, (3), 224-237

Cancer-associated fibroblasts (CAFs) promote tumour invasion and metastasis. We show that CAFs exert a physical force on cancer cells that enables their collective invasion. Force transmission is mediated by a heterophilic adhesion involving N-cadherin at the CAF membrane and E-cadherin at the cancer cell membrane. This adhesion is mechanically active; when subjected to force it triggers β-catenin recruitment and adhesion reinforcement dependent on α-catenin/vinculin interaction. Impairment of E-cadherin/N-cadherin adhesion abrogates the ability of CAFs to guide collective cell migration and blocks cancer cell invasion. N-cadherin also mediates repolarization of the CAFs away from the cancer cells. In parallel, nectins and afadin are recruited to the cancer cell/CAF interface and CAF repolarization is afadin dependent. Heterotypic junctions between CAFs and cancer cells are observed in patient-derived material. Together, our findings show that a mechanically active heterophilic adhesion between CAFs and cancer cells enables cooperative tumour invasion.

Roca-Cusachs, Pere, Conte, Vito, Trepat, Xavier, (2017). Quantifying forces in cell biology Nature Cell Biology 19, (7), 742-751

Cells exert, sense, and respond to physical forces through an astounding diversity of mechanisms. Here we review recently developed tools to quantify the forces generated by cells. We first review technologies based on sensors of known or assumed mechanical properties, and discuss their applicability and limitations. We then proceed to draw an analogy between these human-made sensors and force sensing in the cell. As mechanics is increasingly revealed to play a fundamental role in cell function we envisage that tools to quantify physical forces may soon become widely applied in life-sciences laboratories.

Valon, L., Marín-Llauradó, A., Wyatt, T., Charras, G., Trepat, X., (2017). Optogenetic control of cellular forces and mechanotransduction Nature Communications 8, 14396

Contractile forces are the end effectors of cell migration, division, morphogenesis, wound healing and cancer invasion. Here we report optogenetic tools to upregulate and downregulate such forces with high spatiotemporal accuracy. The technology relies on controlling the subcellular activation of RhoA using the CRY2/CIBN light-gated dimerizer system. We fused the catalytic domain (DHPH domain) of the RhoA activator ARHGEF11 to CRY2-mCherry (optoGEF-RhoA) and engineered its binding partner CIBN to bind either to the plasma membrane or to the mitochondrial membrane. Translocation of optoGEF-RhoA to the plasma membrane causes a rapid and local increase in cellular traction, intercellular tension and tissue compaction. By contrast, translocation of optoGEF-RhoA to mitochondria results in opposite changes in these physical properties. Cellular changes in contractility are paralleled by modifications in the nuclear localization of the transcriptional regulator YAP, thus showing the ability of our approach to control mechanotransductory signalling pathways in time and space.

Arroyo, M., Trepat, X., (2017). Hydraulic fracturing in cells and tissues: fracking meets cell biology Current Opinion in Cell Biology 44, 1-6

The animal body is largely made of water. A small fraction of body water is freely flowing in blood and lymph, but most of it is trapped in hydrogels such as the extracellular matrix (ECM), the cytoskeleton, and chromatin. Besides providing a medium for biological molecules to diffuse, water trapped in hydrogels plays a fundamental mechanical role. This role is well captured by the theory of poroelasticity, which explains how any deformation applied to a hydrogel causes pressure gradients and water flows, much like compressing a sponge squeezes water out of it. Here we review recent evidence that poroelastic pressures and flows can fracture essential biological barriers such as the nuclear envelope, the cellular cortex, and epithelial layers. This type of fracture is known in engineering literature as hydraulic fracturing or ‘fracking’.

Castellanos, M. I., Mas-Moruno, C., Grau, A., Serra-Picamal, X., Trepat, X., Albericio, F., Joner, M., Gil, F. J., Ginebra, M. P., Manero, J. M., Pegueroles, M., (2017). Functionalization of CoCr surfaces with cell adhesive peptides to promote HUVECs adhesion and proliferation Applied Surface Science , 393, 82-92

Biomimetic surface modification with peptides that have specific cell-binding moieties is a promising approach to improve endothelialization of metal-based stents. In this study, we functionalized CoCr surfaces with RGDS, REDV, YIGSR peptides and their combinations to promote endothelial cells (ECs) adhesion and proliferation. An extensive characterization of the functionalized surfaces was performed by XPS analysis, surface charge and quartz crystal microbalance with dissipation monitoring (QCM-D), which demonstrated the successful immobilization of the peptides to the surface. Cell studies demonstrated that the covalent functionalization of CoCr surfaces with an equimolar combination of RGDS and YIGSR represents the most powerful strategy to enhance the early stages of ECs adhesion and proliferation, indicating a positive synergistic effect between the two peptide motifs. Although these peptide sequences slightly increased smooth muscle cells (SMCs) adhesion, these values were ten times lower than those observed for ECs. The combination of RGDS with the REDV sequence did not show synergistic effects in promoting the adhesion or proliferation of ECs. The strategy presented in this study holds great potential to overcome clinical limitations of current metal stents by enhancing their capacity to support surface endothelialization.

Keywords: Cell adhesive peptides, CoCr alloy, Endothelialization, HUVEC proliferation, SMCs adhesion, Surface functionalization

Li, Haiyue, Xu, Bin, Zhou, Enhua H., Sunyer, Raimon, Zhang, Yanhang, (2017). Multiscale measurements of the mechanical properties of collagen matrix ACS Biomaterials Science & Engineering 3, (11), 2815-2824

The underlying mechanisms by which extracellular matrix (ECM) mechanics influences cell and tissue function remain to be elucidated because the events associated with this process span size scales from tissue to molecular level. Furthermore, ECM has an extremely complex hierarchical 3D structure and the load distribution is highly dependent on the architecture and mechanical properties of ECM. In the present study, the macro- and microscale mechanical properties of collagen gel were studied. Dynamic rheological testing was performed to study the macroscale mechanical properties of collagen gel. The microscale mechanical properties of collagen gel were measured using optical magnetic twisting cytometry (OMTC). Ferromagnetic beads embedded in the matrix were used as mechanical probes. Our study on the multiscale mechanical properties of collage matrix suggests several interesting differences between macro and microscale mechanical properties originated from the scales of measurements. At the macroscopic scale, storage and loss modulus increase with collagen concentrations. Nonaffine collagen fibril structural network deformation plays an important role in determining the macroscopic mechanical properties of the collagen matrix. At the microscopic scale, however, the local mechanical properties are less sensitive to changes in collagen concentration because of the more immediate/direct deformation of collagen fibrils in the OMTC measurements through forces exerted by locally attached ferromagnetic beads. The loss modulus is more affected by the local interstitial fluid environment, leading to a rather dramatic increase in viscosity with frequency, especially at higher frequencies (>10 Hz). A finite element model was developed to study the geometric factors in the OMTC measurements when the collagen matrix was considered to be hyperelastic. Our results show that the geometric factors are dependent on collagen concentration, or the stiffness of matrix, when nonlinear material properties of the matrix are considered, and thus interpretation of the apparent modulus from OMTC measurements should be conducted carefully.

Keywords: Keywords: collagen, Extracellular matrix, Geometric factor, Nonaffine deformation, Optical magnetic twisting cytometry

Blanch-Mercader, C., Vincent, R., Bazellières, E., Serra-Picamal, X., Trepat, X., Casademunt, J., (2017). Effective viscosity and dynamics of spreading epithelia: a solvable model Soft Matter 13, (6), 1235-1243

Collective cell migration in spreading epithelia in controlled environments has become a landmark in our current understanding of fundamental biophysical processes in development, regeneration, wound healing or cancer. Epithelial monolayers are treated as thin layers of a viscous fluid that exert active traction forces on the substrate. The model is exactly solvable and shows a broad range of applicabilities for the quantitative analysis and interpretation of force microscopy data of monolayers from a variety of experiments and cell lines. In addition, the proposed model provides physical insights into how the biological regulation of the tissue is encoded in a reduced set of time-dependent physical parameters. In particular the temporal evolution of the effective viscosity entails a mechanosensitive regulation of adhesion. Besides, the observation of an effective elastic tensile modulus can be interpreted as an emergent phenomenon in an active fluid.

Sunyer, R., Conte, V., Escribano, J., Elosegui-Artola, A., Labernadie, A., Valon, L., Navajas, D., García-Aznar, J. M., Muñoz, J. J., Roca-Cusachs, P., Trepat, X., (2016). Collective cell durotaxis emerges from long-range intercellular force transmission Science 353, (6304), 1157-1161

The ability of cells to follow gradients of extracellular matrix stiffness-durotaxis-has been implicated in development, fibrosis, and cancer. Here, we found multicellular clusters that exhibited durotaxis even if isolated constituent cells did not. This emergent mode of directed collective cell migration applied to a variety of epithelial cell types, required the action of myosin motors, and originated from supracellular transmission of contractile physical forces. To explain the observed phenomenology, we developed a generalized clutch model in which local stick-slip dynamics of cell-matrix adhesions was integrated to the tissue level through cell-cell junctions. Collective durotaxis is far more efficient than single-cell durotaxis; it thus emerges as a robust mechanism to direct cell migration during development, wound healing, and collective cancer cell invasion.

Ladoux, B., Mège, R. M., Trepat, X., (2016). Front-rear polarization by mechanical cues: From single cells to tissues Trends in Cell Biology 26, (6), 420-433

Directed cell migration is a complex process that involves front-rear polarization, characterized by cell adhesion and cytoskeleton-based protrusion, retraction, and contraction of either a single cell or a cell collective. Single cell polarization depends on a variety of mechanochemical signals including external adhesive cues, substrate stiffness, and confinement. In cell ensembles, coordinated polarization of migrating tissues results not only from the application of traction forces on the extracellular matrix but also from the transmission of mechanical stress through intercellular junctions. We focus here on the impact of mechanical cues on the establishment and maintenance of front-rear polarization from single cell to collective cell behaviors through local or large-scale mechanisms.

Keywords: Cell forces, Cell polarity, Collective cell migration, Mechanobiology, Micropatterning, Substrate stiffness

Tekeli, I., Aujard, I., Trepat, X., Jullien, L., Raya, A., Zalvidea, D., (2016). Long-term in vivo single-cell lineage tracing of deep structures using three-photon activation Light: Science and Applications , 5, (6), e16084

Genetic labeling techniques allow for noninvasive lineage tracing of cells in vivo. Two-photon inducible activators provide spatial resolution for superficial cells, but labeling cells located deep within tissues is precluded by scattering of the far-red illumination required for two-photon photolysis. Three-photon illumination has been shown to overcome the limitations of two-photon microscopy for in vivo imaging of deep structures, but whether it can be used for photoactivation remains to be tested. Here we show, both theoretically and experimentally, that three-photon illumination overcomes scattering problems by combining longer wavelength excitation with high uncaging three-photon cross-section molecules. We prospectively labeled heart muscle cells in zebrafish embryos and found permanent labeling in their progeny in adult animals with negligible tissue damage. This technique allows for a noninvasive genetic manipulation in vivo with spatial, temporal and cell-type specificity, and may have wide applicability in experimental biology.

Keywords: Multi-photon microscopy, Photoactivation, Three-photon microscopy, Zebrafish

Plutoni, C., Bazellieres, E., Le Borgne-Rochet, M., Comunale, F., Brugues, A., Séveno, M., Planchon, D., Thuault, S., Morin, N., Bodin, S., Trepat, X., Gauthier-Rouvière, C., (2016). P-cadherin promotes collective cell migration via a Cdc42-mediated increase in mechanical forces Journal of Cell Biology , 212, (2), 199-217

Collective cell migration (CCM) is essential for organism development, wound healing, and metastatic transition, the primary cause of cancer-related death, and it involves cell-cell adhesion molecules of the cadherin family. Increased P-cadherin expression levels are correlated with tumor aggressiveness in carcinoma and aggressive sarcoma; however, how P-cadherin promotes tumor malignancy remains unknown. Here, using integrated cell biology and biophysical approaches, we determined that P-cadherin specifically induces polarization and CCM through an increase in the strength and anisotropy of mechanical forces. We show that this mechanical regulation is mediated by the P-cadherin/Î’-PIX/Cdc42 axis; P-cadherin specifically activates Cdc42 through Î’-PIX, which is specifically recruited at cell-cell contacts upon CCM. This mechanism of cell polarization and migration is absent in cells expressing E-or R-cadherin. Thus, we identify a specific role of P-cadherin through Î’-PIX-mediated Cdc42 activation in the regulation of cell polarity and force anisotropy that drives CCM.

Asadipour, N., Trepat, X., Muñoz, J. J., (2016). Porous-based rheological model for tissue fluidisation Journal of the Mechanics and Physics of Solids 96, 535-549

It has been experimentally observed that cells exhibit a fluidisation process when subjected to a transient stretch, with an eventual recovery of the mechanical properties upon removal of the applied deformation. This fluidisation process is characterised by a decrease of the storage modulus and an increase of the phase angle. We propose a rheological model which is able to reproduce this combined mechanical response. The model is described in the context of continua and adapted to a cell-centred particle system that simulates cell–cell interactions. Mechanical equilibrium is coupled with two evolution laws: (i) one for the reference configuration, and (ii) another for the porosity or polymer density. The first law depends on the actual strain of the tissue, while the second assumes different remodelling rates during porosity increase and decrease. The theory is implemented on a particle based model and tested on a stretching experiment. The numerical results agree with the experimental measurements for different stretching magnitudes.

Keywords: Cell remodelling, Cell rheology, Fluidisation, Softening, Viscoelasticity

Alencar, A. M., Ferraz, M. S. A., Park, C. Y., Millet, E., Trepat, X., Fredberg, J. J., Butler, J. P., (2016). Non-equilibrium cytoquake dynamics in cytoskeletal remodeling and stabilization Soft Matter 12, (41), 8506-8511

The cytoskeleton (CSK) is a tensed fiber framework that supports, shapes and stabilizes the cell. The CSK is in a constant state of remodeling, moreover, which is an active non-equilibrium thermodynamic process. We report here that cytoskeletal remodeling involves reconfigurations that are not only sudden but also are transmitted to great distances within the cell in a fashion reminiscent of quakes in the Earth's crust. Remarkably, these events in the cell conform both qualitatively and quantitatively to empirical laws typical of earthquakes, including hierarchical fault structures, cumulative energy distributions following the Gutenberg-Richter law, and rate of after-shocks following Omori's law. While it is well-established that remodeling and stabilization of the cytoskeleton are non-equilibrium process, these new unanticipated observations establish that these processes are also remarkably non-local and strongly cooperative.

Przybyla, L., Lakins, J. N., Sunyer, R., Trepat, X., Weaver, V. M., (2016). Monitoring developmental force distributions in reconstituted embryonic epithelia Methods , 94, 101-113

The way cells are organized within a tissue dictates how they sense and respond to extracellular signals, as cues are received and interpreted based on expression and organization of receptors, downstream signaling proteins, and transcription factors. Part of this microenvironmental context is the result of forces acting on the cell, including forces from other cells or from the cellular substrate or basement membrane. However, measuring forces exerted on and by cells is difficult, particularly in an in vivo context, and interpreting how forces affect downstream cellular processes poses an even greater challenge. Here, we present a simple method for monitoring and analyzing forces generated from cell collectives. We demonstrate the ability to generate traction force data from human embryonic stem cells grown in large organized epithelial sheets to determine the magnitude and organization of cell-ECM and cell-cell forces within a self-renewing colony. We show that this method can be used to measure forces in a dynamic hESC system and demonstrate the ability to map intracolony protein localization to force organization.

Keywords: Epiblast, Human embryonic stem cells, Mechanotransduction, Monolayer stress microscopy, Self-organization, Traction force

Blanchard, R., Morin, C., Malandrino, A., Vella, A., Sant, Z., Hellmich, C., (2016). Patient-specific fracture risk assessment of vertebrae: A multiscale approach coupling X-ray physics and continuum micromechanics International Journal for Numerical Methods in Biomedical Engineering , 32, (9), e02760

Summary: While in clinical settings, bone mineral density measured by computed tomography (CT) remains the key indicator for bone fracture risk, there is an ongoing quest for more engineering mechanics-based approaches for safety analyses of the skeleton. This calls for determination of suitable material properties from respective CT data, where the traditional approach consists of regression analyses between attenuation-related grey values and mechanical properties. We here present a physics-oriented approach, considering that elasticity and strength of bone tissue originate from the material microstructure and the mechanical properties of its elementary components. Firstly, we reconstruct the linear relation between the clinically accessible grey values making up a CT, and the X-ray attenuation coefficients quantifying the intensity losses from which the image is actually reconstructed. Therefore, we combine X-ray attenuation averaging at different length scales and over different tissues, with recently identified 'universal' composition characteristics of the latter. This gives access to both the normally non-disclosed X-ray energy employed in the CT-device and to in vivo patient-specific and location-specific bone composition variables, such as voxel-specific mass density, as well as collagen and mineral contents. The latter feed an experimentally validated multiscale elastoplastic model based on the hierarchical organization of bone. Corresponding elasticity maps across the organ enter a finite element simulation of a typical load case, and the resulting stress states are increased in a proportional fashion, so as to check the safety against ultimate material failure. In the young patient investigated, even normal physiological loading is probable to already imply plastic events associated with the hydrated mineral crystals in the bone ultrastructure, while the safety factor against failure is still as high as five.

Keywords: Bone, Bone mass density, Continuum micromechanics, Elastoplasticity, Spine, Strength, X-ray physics

Casares, L., Vincent, R., Zalvidea, D., Campillo, N., Navajas, D., Arroyo, M., Trepat, X., (2015). Hydraulic fracture during epithelial stretching Nature Materials 14, (3), 343-351

The origin of fracture in epithelial cell sheets subject to stretch is commonly attributed to excess tension in the cells’ cytoskeleton, in the plasma membrane, or in cell–cell contacts. Here, we demonstrate that for a variety of synthetic and physiological hydrogel substrates the formation of epithelial cracks is caused by tissue stretching independently of epithelial tension. We show that the origin of the cracks is hydraulic; they result from a transient pressure build-up in the substrate during stretch and compression manoeuvres. After pressure equilibration, cracks heal readily through actomyosin-dependent mechanisms. The observed phenomenology is captured by the theory of poroelasticity, which predicts the size and healing dynamics of epithelial cracks as a function of the stiffness, geometry and composition of the hydrogel substrate. Our findings demonstrate that epithelial integrity is determined in a tension-independent manner by the coupling between tissue stretching and matrix hydraulics.

Bazellières, Elsa, Conte, Vito, Elosegui, Alberto, Serra-Picamal, Xavier, Bintanel-Morcillo, María, Roca-Cusachs, Pere, Muñoz, José J., Sales-Pardo, Marta, Guimerà, Roger, Trepat, Xavier, (2015). Control of cell-cell forces and collective cell dynamics by the intercellular adhesome Nature Cell Biology 17, (4), 409-420

Dynamics of epithelial tissues determine key processes in development, tissue healing and cancer invasion. These processes are critically influenced by cell–cell adhesion forces. However, the identity of the proteins that resist and transmit forces at cell–cell junctions remains unclear, and how these proteins control tissue dynamics is largely unknown. Here we provide a systematic study of the interplay between cell–cell adhesion proteins, intercellular forces and epithelial tissue dynamics. We show that collective cellular responses to selective perturbations of the intercellular adhesome conform to three mechanical phenotypes. These phenotypes are controlled by different molecular modules and characterized by distinct relationships between cellular kinematics and intercellular forces. We show that these forces and their rates can be predicted by the concentrations of cadherins and catenins. Unexpectedly, we identified different mechanical roles for P-cadherin and E-cadherin; whereas P-cadherin predicts levels of intercellular force, E-cadherin predicts the rate at which intercellular force builds up.

Ravasio, Andrea, Cheddadi, Ibrahim, Chen, Tianchi, Pereira, Telmo, Ong, Hui Ting, Bertocchi, Cristina, Brugues, Agusti, Jacinto, Antonio, Kabla, Alexandre J., Toyama, Yusuke, Trepat, Xavier, Gov, Nir, Neves de Almeida, Luis, Ladoux, Benoit, (2015). Gap geometry dictates epithelial closure efficiency Nature Communications 6, 7683

Closure of wounds and gaps in tissues is fundamental for the correct development and physiology of multicellular organisms and, when misregulated, may lead to inflammation and tumorigenesis. To re-establish tissue integrity, epithelial cells exhibit coordinated motion into the void by active crawling on the substrate and by constricting a supracellular actomyosin cable. Coexistence of these two mechanisms strongly depends on the environment. However, the nature of their coupling remains elusive because of the complexity of the overall process. Here we demonstrate that epithelial gap geometry in both in vitro and in vivo regulates these collective mechanisms. In addition, the mechanical coupling between actomyosin cable contraction and cell crawling acts as a large-scale regulator to control the dynamics of gap closure. Finally, our computational modelling clarifies the respective roles of the two mechanisms during this process, providing a robust and universal mechanism to explain how epithelial tissues restore their integrity.

Vedula, Sri Ram Krishna, Peyret, Grégoire, Cheddadi, Ibrahim, Chen, Tianchi, Brugués, Agustí, Hirata, Hiroaki, Lopez-Menendez, Horacio, Toyama, Yusuke, Neves de Almeida, Luis, Trepat, Xavier, Lim, Chwee Teck, Ladoux, Benoit, (2015). Mechanics of epithelial closure over non-adherent environments Nature Communications 6, 6111

The closure of gaps within epithelia is crucial to maintain its integrity during biological processes such as wound healing and gastrulation. Depending on the distribution of extracellular matrix, gap closure occurs through assembly of multicellular actin-based contractile cables or protrusive activity of border cells into the gap. Here we show that the supracellular actomyosin contractility of cells near the gap edge exerts sufficient tension on the surrounding tissue to promote closure of non-adherent gaps. Using traction force microscopy, we observe that cell-generated forces on the substrate at the gap edge first point away from the centre of the gap and then increase in the radial direction pointing into the gap as closure proceeds. Combining with numerical simulations, we show that the increase in force relies less on localized purse-string contractility and more on large-scale remodelling of the suspended tissue around the gap. Our results provide a framework for understanding the assembly and the mechanics of cellular contractility at the tissue level.

Kosmalska, A. J., Casares, L., Elosegui, A., Thottacherry, J. J., Moreno-Vicente, R., González-Tarragó, V., Del Pozo, M. Á, Mayor, S., Arroyo, M., Navajas, D., Trepat, X., Gauthier, N. C., Roca-Cusachs, P., (2015). Physical principles of membrane remodelling during cell mechanoadaptation Nature Communications 6, 7292

Biological processes in any physiological environment involve changes in cell shape, which must be accommodated by their physical envelope - the bilayer membrane. However, the fundamental biophysical principles by which the cell membrane allows for and responds to shape changes remain unclear. Here we show that the 3D remodelling of the membrane in response to a broad diversity of physiological perturbations can be explained by a purely mechanical process. This process is passive, local, almost instantaneous, before any active remodelling and generates different types of membrane invaginations that can repeatedly store and release large fractions of the cell membrane. We further demonstrate that the shape of those invaginations is determined by the minimum elastic and adhesive energy required to store both membrane area and liquid volume at the cell-substrate interface. Once formed, cells reabsorb the invaginations through an active process with duration of the order of minutes.

Vincent, Romaric, Bazellières, Elsa, Pérez-González, Carlos, Uroz, Marina, Serra-Picamal, Xavier, Trepat, Xavier, (2015). Active tensile modulus of an epithelial monolayer Physical Review Letters 115, (24), 248103

A general trait of cell monolayers is their ability to exert contractile stresses on their surroundings. The scaling laws that link such contractile stresses with the size and geometry of constituent cells remain largely unknown. In this Letter, we show that the active tension of an epithelial monolayer scales linearly with the size of the constituent cells, a surprisingly simple relationship. The slope of this relationship defines an active tensile modulus, which depends on the concentration of myosin and spans more than 2 orders of magnitude across cell types and molecular perturbations.

Lucantonio, Alessandro, Noselli, Giovanni, Trepat, Xavier, DeSimone, Antonio, Arroyo, Marino, (2015). Hydraulic fracture and toughening of a brittle layer bonded to a hydrogel Physical Review Letters 115, (18), 188105

Brittle materials propagate opening cracks under tension. When stress increases beyond a critical magnitude, then quasistatic crack propagation becomes unstable. In the presence of several precracks, a brittle material always propagates only the weakest crack, leading to catastrophic failure. Here, we show that all these features of brittle fracture are fundamentally modified when the material susceptible to cracking is bonded to a hydrogel, a common situation in biological tissues. In the presence of the hydrogel, the brittle material can fracture in compression and can hydraulically resist cracking in tension. Furthermore, the poroelastic coupling regularizes the crack dynamics and enhances material toughness by promoting multiple cracking.

Brask, J. B., Singla-Buxarrais, G., Uroz, M., Vincent, R., Trepat, X., (2015). Compressed sensing traction force microscopy Acta Biomaterialia 26, 286-294

Adherent cells exert traction forces on their substrate, and these forces play important roles in biological functions such as mechanosensing, cell differentiation and cancer invasion. The method of choice to assess these active forces is traction force microscopy (TFM). Despite recent advances, TFM remains highly sensitive to measurement noise and exhibits limited spatial resolution. To improve the resolution and noise robustness of TFM, here we adapt techniques from compressed sensing (CS) to the reconstruction of the traction field from the substrate displacement field. CS enables the recovery of sparse signals at higher resolution from lower resolution data. Focal adhesions (FAs) of adherent cells are spatially sparse implying that traction fields are also sparse. Here we show, by simulation and by experiment, that the CS approach enables circumventing the Nyquist-Shannon sampling theorem to faithfully reconstruct the traction field at a higher resolution than that of the displacement field. This allows reaching state-of-the-art resolution using only a medium magnification objective. We also find that CS improves reconstruction quality in the presence of noise. Statement of Significance A great scientific advance of the past decade is the recognition that physical forces determine an increasing list of biological processes. Traction force microscopy which measures the forces that cells exert on their surroundings has seen significant recent improvements, however the technique remains sensitive to measurement noise and severely limited in spatial resolution. We exploit the fact that the force fields are sparse to boost the spatial resolution and noise robustness by applying ideas from compressed sensing. The novel method allows high resolution on a larger field of view. This may in turn allow better understanding of the cell forces at the multicellular level, which are known to be important in wound healing and cancer invasion.

Keywords: Compressed sensing, High resolution, Traction force microscopy

Reginensi, Diego, Carulla, Patricia, Nocentini, Sara, Seira, Oscar, Serra-Picamal, Xavier, Torres-Espín, Abel, Matamoros-Angles, Andreu, Gavín, Rosalina, Moreno-Flores, María Teresa, Wandosell, Francisco, Samitier, Josep, Trepat, Xavier, Navarro, Xavier, del Río, José Antonio, (2015). Increased migration of olfactory ensheathing cells secreting the Nogo receptor ectodomain over inhibitory substrates and lesioned spinal cord Cellular and Molecular Life Sciences , 72, (14), 2719-2737

Olfactory ensheathing cell (OEC) transplantation emerged some years ago as a promising therapeutic strategy to repair injured spinal cord. However, inhibitory molecules are present for long periods of time in lesioned spinal cord, inhibiting both OEC migration and axonal regrowth. Two families of these molecules, chondroitin sulphate proteoglycans (CSPG) and myelin-derived inhibitors (MAIs), are able to trigger inhibitory responses in lesioned axons. Mounting evidence suggests that OEC migration is inhibited by myelin. Here we demonstrate that OEC migration is largely inhibited by CSPGs and that inhibition can be overcome by the bacterial enzyme Chondroitinase ABC. In parallel, we have generated a stable OEC cell line overexpressing the Nogo receptor (NgR) ectodomain to reduce MAI-associated inhibition in vitro and in vivo. Results indicate that engineered cells migrate longer distances than unmodified OECs over myelin or oligodendrocyte-myelin glycoprotein (OMgp)-coated substrates. In addition, they also show improved migration in lesioned spinal cord. Our results provide new insights toward the improvement of the mechanisms of action and optimization of OEC-based cell therapy for spinal cord lesion.

Keywords: Olfactory ensheathing cells, Traction force microscopy, Chondroitin sulphate proteoglycans, Cell migration, Nogo receptor ectodomain

García, S., Sunyer, R., Olivares, A., Noailly, J., Atencia, J., Trepat, X., (2015). Generation of stable orthogonal gradients of chemical concentration and substrate stiffness in a microfluidic device Lab on a Chip 15, (12), 2606-2614

Cellular responses to chemical cues are at the core of a myriad of fundamental biological processes ranging from embryonic development to cancer metastasis. Most of these biological processes are also influenced by mechanical cues such as the stiffness of the extracellular matrix. How a biological function is influenced by a synergy between chemical concentration and extracellular matrix stiffness is largely unknown, however, because no current strategy enables the integration of both types of cues in a single experiment. Here we present a robust microfluidic device that generates a stable, linear and diffusive chemical gradient over a biocompatible hydrogel with a well-defined stiffness gradient. Device fabrication relies on patterned PSA (Pressure Sensitive Adhesive) stacks that can be implemented with minimal cost and lab equipment. This technique is suitable for long-term observation of cell migration and application of traction force microscopy. We validate our device by testing MDCK cell scattering in response to perpendicular gradients of hepatocyte growth factor (HGF) and substrate stiffness.

Vizoso, Miguel, Puig, Marta, Carmona, F. Javier, Maqueda, Maria, Velásquez, Adriana, Gomez, Antonio, Labernadie, Anna, Lugo, Roberto, Gabasa, Marta, Rigat-Brugarolas, Luis G., Trepat, Xavier, Ramírez, Jose, Reguart, Noemí, Moran, Sebastian, Vidal, Enrique, Perera, Alexandre, Esteller, Manel, Alcaraz, Jordi, (2015). Aberrant DNA methylation in Non Small Cell Lung Cancer associated fibroblasts Carcinogenesis , 32, (12), 1453-1463

Epigenetic changes through altered DNA methylation have been implicated in critical aspects of tumor progression, and have been extensively studied in a variety of cancer types. In contrast, our current knowledge of the aberrant genomic DNA methylation in tumor-associated fibroblasts (TAFs) or other stromal cells that act as critical co-conspirators of tumor progression is very scarce. To address this gap of knowledge, we conducted genome-wide DNA methylation profiling on lung TAFs and paired control fibroblasts (CFs) from non-small cell lung cancer patients using the HumanMethylation450 microarray. We found widespread DNA hypomethylation concomitant with focal gain of DNA methylation in TAFs compared to CFs. The aberrant DNA methylation landscape of TAFs had a global impact on gene expression and a selective impact on the TGF-β pathway. The latter included promoter hypermethylation-associated SMAD3 silencing, which was associated with hyperresponsiveness to exogenous TGF-β1 in terms of contractility and extracellular matrix deposition. In turn, activation of CFs with exogenous TGF-β1 partially mimicked the epigenetic alterations observed in TAFs, suggesting that TGF-β1 may be necessary but not sufficient to elicit such alterations. Moreover, integrated pathway-enrichment analyses of the DNA methylation alterations revealed that a fraction of TAFs may be bone marrow-derived fibrocytes. Finally, survival analyses using DNA methylation and gene expression datasets identified aberrant DNA methylation on the EDARADD promoter sequence as a prognostic factor in NSCLC patients. Our findings shed light on the unique origin and molecular alterations underlying the aberrant phenotype of lung TAFs, and identify a stromal biomarker with potential clinical relevance.

Mrkonji, Garcia-Elias, A., Pardo-Pastor, C., Bazellières, E., Trepat, X., Vriens, J., Ghosh, D., Voets, T., Vicente, R., Valverde, M. A., (2015). TRPV4 participates in the establishment of trailing adhesions and directional persistence of migrating cells Pflugers Archiv European Journal of Physiology , 467, (10), 2107-2119

Calcium signaling participates in different cellular processes leading to cell migration. TRPV4, a non-selective cation channel that responds to mechano-osmotic stimulation and heat, is also involved in cell migration. However, the mechanistic involvement of TRPV4 in cell migration is currently unknown. We now report that expression of the mutant channel TRPV4-121AAWAA (lacking the phosphoinositide-binding site 121KRWRK125 and the response to physiological stimuli) altered HEK293 cell migration. Altered migration patterns included periods of fast and persistent motion followed by periods of stalling and turning, and the extension of multiple long cellular protrusions. TRPV4-WT overexpressing cells showed almost complete loss of directionality with frequent turns, no progression, and absence of long protrusions. Traction microscopy revealed higher tractions forces in the tail of TRPV4-121AAWAA than in TRPV4-WT expressing cells. These results are consistent with a defective and augmented tail retraction in TRPV4-121AAWAA- and TRPV4-WT-expressing cells, respectively. The activity of calpain, a protease implicated in focal adhesion (FA) disassembly, was decreased in TRPV4-121AAWAA compared with TRPV4-WT-expressing cells. Consistently, larger focal adhesions were seen in TRPV4-121AAWAA compared with TRPV4-WT-expressing HEK293 cells, a result that was also reproduced in T47D and U87 cells. Similarly, overexpression of the pore-dead mutant TRPV4-M680D resumed the TRPV4-121AAWAA phenotype presenting larger FA. The migratory phenotype obtained in HEK293 cells overexpressing TRPV4-121AAWAA was mimicked by knocking-down TRPC1, a cationic channel that participates in cell migration. Together, our results point to the participation of TRPV4 in the dynamics of trailing adhesions, a function that may require the interplay of TRPV4 with other cation channels or proteins present at the FA sites.

Keywords: Calcium, Calpain, Focal adhesion, Migration, Traction forces, TRPV4

Zaritsky, Assaf, Welf, Erik S., Tseng, Yun-Yu, Angeles Rabadán, M., Serra-Picamal, Xavier, Trepat, Xavier, Danuser, Gaudenz, (2015). Seeds of locally aligned motion and stress coordinate a collective cell migration Biophysical Journal , 109, (12), 2492-2500

Abstract We find how collective migration emerges from mechanical information transfer between cells. Local alignment of cell velocity and mechanical stress orientation—a phenomenon dubbed “plithotaxis”—plays a crucial role in inducing coordinated migration. Leader cells at the monolayer edge better align velocity and stress to migrate faster toward the open space. Local seeds of enhanced motion then generate stress on neighboring cells to guide their migration. Stress-induced motion propagates into the monolayer as well as along the monolayer boundary to generate increasingly larger clusters of coordinately migrating cells that move faster with enhanced alignment of velocity and stress. Together, our analysis provides a model of long-range mechanical communication between cells, in which plithotaxis translates local mechanical fluctuations into globally collective migration of entire tissues.

Perrault, Cecile, Brugues, Agusti, Bazellieres, Elsa, Ricco, Pierre, Lacroix, Damien, Trepat, Xavier, (2015). Traction forces of endothelial cells under slow shear flow Biophysical Journal , 109, (8), 1533-1536

Endothelial cells are constantly exposed to fluid shear stresses that regulate vascular morphogenesis, homeostasis, and disease. The mechanical responses of endothelial cells to relatively high shear flow such as that characteristic of arterial circulation has been extensively studied. Much less is known about the responses of endothelial cells to slow shear flow such as that characteristic of venous circulation, early angiogenesis, atherosclerosis, intracranial aneurysm, or interstitial flow. Here we used a novel, to our knowledge, microfluidic technique to measure traction forces exerted by confluent vascular endothelial cell monolayers under slow shear flow. We found that cells respond to flow with rapid and pronounced increases in traction forces and cell-cell stresses. These responses are reversible in time and do not involve reorientation of the cell body. Traction maps reveal that local cell responses to slow shear flow are highly heterogeneous in magnitude and sign. Our findings unveil a low-flow regime in which endothelial cell mechanics is acutely responsive to shear stress. Endothelial cells are constantly exposed to fluid shear stresses that regulate vascular morphogenesis, homeostasis, and disease. The mechanical responses of endothelial cells to relatively high shear flow such as that characteristic of arterial circulation has been extensively studied. Much less is known about the responses of endothelial cells to slow shear flow such as that characteristic of venous circulation, early angiogenesis, atherosclerosis, intracranial aneurysm, or interstitial flow. Here we used a novel, to our knowledge, microfluidic technique to measure traction forces exerted by confluent vascular endothelial cell monolayers under slow shear flow. We found that cells respond to flow with rapid and pronounced increases in traction forces and cell-cell stresses. These responses are reversible in time and do not involve reorientation of the cell body. Traction maps reveal that local cell responses to slow shear flow are highly heterogeneous in magnitude and sign. Our findings unveil a low-flow regime in which endothelial cell mechanics is acutely responsive to shear stress.

Serra-Picamal, Xavier, Conte, Vito, Sunyer, Raimon, Muñoz, José J., Trepat, Xavier, (2015). Mapping forces and kinematics during collective cell migration Methods in Cell Biology - Biophysical Methods in Cell Biology (ed. Wilson, L., Tran, P.), Academic Press (Santa Barbara, USA) 125, 309-330

Abstract Fundamental biological processes including morphogenesis and tissue repair require cells to migrate collectively. In these processes, epithelial or endothelial cells move in a cooperative manner coupled by intercellular junctions. Ultimately, the movement of these multicellular systems occurs through the generation of cellular forces, exerted either on the substrate via focal adhesions (cell–substrate forces) or on neighboring cells through cell–cell junctions (cell–cell forces). Quantitative measurements of multicellular forces and kinematics with cellular or subcellular resolution have become possible only in recent years. In this chapter, we describe some of these techniques, which include particle image velocimetry to map cell velocities, traction force microscopy to map forces exerted by cells on the substrate, and monolayer stress microscopy to map forces within and between cells. We also describe experimental protocols to perform these measurements. The combination of these techniques with high-resolution imaging tools and molecular perturbations will lead to a better understanding of the mechanisms underlying collective cell migration in health and disease.

Keywords: Collective cell migration, Monolayer stress microscopy, Traction force microscopy

Vedula, S. R. K., Hirata, H., Nai, M. H., Brugués, A., Toyama, Y., Trepat, X., Lim, C. T., Ladoux, B., (2014). Epithelial bridges maintain tissue integrity during collective cell migration Nature Materials 13, (1), 87-96

The ability of skin to act as a barrier is primarily determined by the efficiency of skin cells to maintain and restore its continuity and integrity. In fact, during wound healing keratinocytes migrate collectively to maintain their cohesion despite heterogeneities in the extracellular matrix. Here, we show that monolayers of human keratinocytes migrating along functionalized micropatterned surfaces comprising alternating strips of extracellular matrix (fibronectin) and non-adherent polymer form suspended multicellular bridges over the non-adherent areas. The bridges are held together by intercellular adhesion and are subjected to considerable tension, as indicated by the presence of prominent actin bundles. We also show that a model based on force propagation through an elastic material reproduces the main features of bridge maintenance and tension distribution. Our findings suggest that multicellular bridges maintain tissue integrity during wound healing when cell-substrate interactions are weak and may prove helpful in the design of artificial scaffolds for skin regeneration.

Elosegui, A., Bazellières, E., Allen, M. D., Andreu, I., Oria, R., Sunyer, R., Gomm, J. J., Marshall, J. F., Jones, J. L., Trepat, X., Roca-Cusachs, P., (2014). Rigidity sensing and adaptation through regulation of integrin types Nature Materials 13, (6), 631-637

Tissue rigidity regulates processes in development, cancer and wound healing. However, how cells detect rigidity, and thereby modulate their behaviour, remains unknown. Here, we show that sensing and adaptation to matrix rigidity in breast myoepithelial cells is determined by the bond dynamics of different integrin types. Cell binding to fibronectin through either α5β1 integrins (constitutively expressed) or αvβ6 integrins (selectively expressed in cancer and development) adapts force generation, actin flow and integrin recruitment to rigidities associated with healthy or malignant tissue, respectively. In vitro experiments and theoretical modelling further demonstrate that this behaviour is explained by the different binding and unbinding rates of both integrin types to fibronectin. Moreover, rigidity sensing through differences in integrin bond dynamics applies both when integrins bind separately and when they compete for binding to fibronectin.

Brugués, A., Anon, E., Conte, V., Veldhuis, J. H., Gupta, M., Colombelli, J., Muñoz, J. J., Brodland, G. W., Ladoux, B., Trepat, X., (2014). Forces driving epithelial wound healing Nature Physics 10, (9), 683–690

A fundamental feature of multicellular organisms is their ability to self-repair wounds through the movement of epithelial cells into the damaged area. This collective cellular movement is commonly attributed to a combination of cell crawling and 'purse-string' contraction of a supracellular actomyosin ring. Here we show by direct experimental measurement that these two mechanisms are insufficient to explain force patterns observed during wound closure. At early stages of the process, leading actin protrusions generate traction forces that point away from the wound, showing that wound closure is initially driven by cell crawling. At later stages, we observed unanticipated patterns of traction forces pointing towards the wound. Such patterns have strong force components that are both radial and tangential to the wound. We show that these force components arise from tensions transmitted by a heterogeneous actomyosin ring to the underlying substrate through focal adhesions. The structural and mechanical organization reported here provides cells with a mechanism to close the wound by cooperatively compressing the underlying substrate.

Trepat, Xavier, (2014). Discussion of “Cytoskeletal Mechanics Regulating Amoeboid Cell Locomotion” (Álvarez-González, B., Bastounis, E., Meili, R., del Alamo, J. C., Firtel, R. A., and Lasheras, J. C., 2014, ASME Appl. Mech. Rev., 66(5), p. 050804) Applied Mechanics Reviews , 66, (5), 055502

A virtually universal feature of adherent cells is their ability to exert traction forces. To measure these forces, several methods have been developed over the past 15 years. In this issue of Applied Mechanics Reviews, Álvarez-González and co-workers review their own traction force microscopy approach and its application to the study of amoeboid cell locomotion. They show that the cycle of cell motility is exquisitely synchronized by a cycle of traction forces. In addition, they show how traction forces and cell cycle synchronization are affected by myosin and SCAR/WAVE mutants. Here, I discuss some open questions that derive from the work of the authors and other laboratories as regards the relationship between cell motility and traction forces.

Vedula, Sri Ram Krishna, Ravasio, Andrea, Anon, Ester, Chen, Tianchi, Peyret, G., Ashraf, Mohammed, Ladoux, Benoit, (2014). Microfabricated environments to study collective cell behaviors Methods in Cell Biology (ed. Piel, M., Théry, M.), Academic Press 120, 235-252

Abstract Coordinated cell movements in epithelial layers are essential for proper tissue morphogenesis and homeostasis. Microfabrication techniques have proven to be very useful for studies of collective cell migration in vitro. In this chapter, we briefly review the use of microfabricated substrates in providing new insights into collective cell behaviors. We first describe the development of micropatterned substrates to study the influence of geometrical constraints on cell migration and coordinated movements. Then, we present an alternative method based on microfabricated pillar substrates to create well-defined gaps within cell sheets and study gap closure. We also provide a discussion that presents possible pitfalls and sheds light onto the important parameters that allow the study of long-term cell culture on substrates of well-defined geometries.

Keywords: Microfabricated substrates, Microcontact printing, Collective cell behavior, Geometrical constraints, Epithelial gap closure

Kim, Jae Hun, Serra-Picamal, Xavier, Tambe, Dhananjay T., Zhou, Enhua H., Park, Chan Young, Sadati, Monirosadat, Park, Jin-Ah, Krishnan, Ramaswamy, Gweon, Bomi, Millet, Emil, Butler, James P., Trepat, Xavier, Fredberg, Jeffrey J., (2013). Propulsion and navigation within the advancing monolayer sheet Nature Materials 12, (9), 856-863

As a wound heals, or a body plan forms, or a tumour invades, observed cellular motions within the advancing cell swarm are thought to stem from yet to be observed physical stresses that act in some direct and causal mechanical fashion. Here we show that such a relationship between motion and stress is far from direct. Using monolayer stress microscopy, we probed migration velocities, cellular tractions and intercellular stresses in an epithelial cell sheet advancing towards an island on which cells cannot adhere. We found that cells located near the island exert tractions that pull systematically towards this island regardless of whether the cells approach the island, migrate tangentially along its edge, or paradoxically, recede from it. This unanticipated cell-patterning motif, which we call kenotaxis, represents the robust and systematic mechanical drive of the cellular collective to fill unfilled space.

Theveneau, E., Steventon, B., Scarpa, E., Garcia, S., Trepat, X., Streit, A., Mayor, R., (2013). Chase-and-run between adjacent cell populations promotes directional collective migration Nature Cell Biology 15, (7), 763-772

Collective cell migration in morphogenesis and cancer progression often involves the coordination of multiple cell types. How reciprocal interactions between adjacent cell populations lead to new emergent behaviours remains unknown. Here we studied the interaction between neural crest (NC) cells, a highly migratory cell population, and placodal cells, an epithelial tissue that contributes to sensory organs. We found that NC cells chase placodal cells by chemotaxis, and placodal cells run when contacted by NC. Chemotaxis to Sdf1 underlies the chase, and repulsion involving PCP and N-cadherin signalling is responsible for the run. This chase-and-run requires the generation of asymmetric forces, which depend on local inhibition of focal adhesions. The cell interactions described here are essential for correct NC migration and for segregation of placodes in vivo and are likely to represent a general mechanism of coordinated migration.

Roca-Cusachs, P., Sunyer, R., Trepat, X., (2013). Mechanical guidance of cell migration: lessons from chemotaxis Current Opinion in Cell Biology 25, (5), 543-549

For an organism to develop, for a wound to heal, or for a tumor to invade, cells must be able to migrate following directional cues. It is widely accepted that directed cell migration is enabled by cellular sensing of local gradients in the concentration of chemical factors. The main molecular players involved in this mode of cellular guidance - chemotaxis - have been identified and the combination of modeling and experimental approaches is progressively unveiling a clear picture of the underlying mechanisms. Evidence obtained over the past decade has shown that cells can also be guided by mechanical stimuli such as physical forces or gradients in extracellular matrix stiffness. Mechanical guidance, which we refer here globally as mechanotaxis, is also thought to drive processes in development, cancer, and wound healing, but experimental evidence is scattered and mechanisms remain largely unknown. Here we use the better understood process of chemotaxis as a reference to define the building blocks that are required for cell guidance, and then discuss how these building blocks might be organized in mechanotaxis. We show that both chemotaxis and mechanotaxis involve an exquisite interplay between physical and chemical mechanisms to sense gradients, establish polarization, and drive directed migration.

Chen, Zaozao, Lessey, Elizabeth, Berginski, Matthew E., Cao, Li, Li, Jonathan, Trepat, Xavier, Itano, Michelle, Gomez, Shawn M., Kapustina, Maryna, Huang, Cai, Burridge, Keith, Truskey, George, Jacobson, Ken, (2013). Gleevec, an Abl family inhibitor, produces a profound change in cell shape and migration PLoS ONE 8, (1), e52233

The issue of how contractility and adhesion are related to cell shape and migration pattern remains largely unresolved. In this paper we report that Gleevec (Imatinib), an Abl family kinase inhibitor, produces a profound change in the shape and migration of rat bladder tumor cells (NBTII) plated on collagen-coated substrates. Cells treated with Gleevec adopt a highly spread D-shape and migrate more rapidly with greater persistence. Accompanying this more spread state is an increase in integrin-mediated adhesion coupled with increases in the size and number of discrete adhesions. In addition, both total internal reflection fluorescence microscopy (TIRFM) and interference reflection microscopy (IRM) revealed a band of small punctate adhesions with rapid turnover near the cell leading margin. These changes led to an increase in global cell-substrate adhesion strength, as assessed by laminar flow experiments. Gleevec-treated cells have greater RhoA activity which, via myosin activation, led to an increase in the magnitude of total traction force applied to the substrate. These chemical and physical alterations upon Gleevec treatment produce the dramatic change in morphology and migration that is observed.

Tambe, D. T., Croutelle, U., Trepat, X., Park, C. Y., Kim, J. H., Millet, E., Butler, J. P., Fredberg, J. J., (2013). Monolayer stress microscopy: Limitations, artifacts, and accuracy of recovered intercellular stresses PLoS ONE 8, (2), e55172

In wound healing, tissue growth, and certain cancers, the epithelial or the endothelial monolayer sheet expands. Within the expanding monolayer sheet, migration of the individual cell is strongly guided by physical forces imposed by adjacent cells. This process is called plithotaxis and was discovered using Monolayer Stress Microscopy (MSM). MSM rests upon certain simplifying assumptions, however, concerning boundary conditions, cell material properties and system dimensionality. To assess the validity of these assumptions and to quantify associated errors, here we report new analytical, numerical, and experimental investigations. For several commonly used experimental monolayer systems, the simplifying assumptions used previously lead to errors that are shown to be quite small. Out-of-plane components of displacement and traction fields can be safely neglected, and characteristic features of intercellular stresses that underlie plithotaxis remain largely unaffected. Taken together, these findings validate Monolayer Stress Microscopy within broad but well-defined limits of applicability.

Muñoz, J. J., Conte, V., Asadipour, N., Miodownik, M., (2013). A truss element for modelling reversible softening in living tissues Mechanics Research Communications , 49, 44-49

We resort to non-linear viscoelasticity to develop a truss element able to model reversible softening in lung epithelial tissues undergoing transient stretch. Such a Maxwell truss element is built by resorting to a three-noded element whose mid-node is kinematically constrained to remain on the line connecting the end-nodes. The whole mechanical system undergoes an additive decomposition of the strains along the truss direction where the total contribution of the mid-node is accounted for by using a null-space projection and static condensation techniques. Assembling of such line-elements in 3D networks allows us to model extended regions of living tissues as well as their anisotropies.

Keywords: Maxwell, Null-space, Reversible softening, Truss, Viscoelasticity

Serra-Picamal, Xavier, Conte, Vito, Vincent, Romaric, Anon, Ester, Tambe, Dhananjay T., Bazellieres, Elsa, Butler, James P., Fredberg, Jeffrey J., Trepat, Xavier, (2012). Mechanical waves during tissue expansion Nature Physics Nature Publishing Group 8, (8), 628-634

The processes by which an organism develops its shape and heals wounds involve expansion of a monolayer sheet of cells. The mechanism underpinning this epithelial expansion remains obscure, despite the fact that its failure is known to contribute to several diseases, including carcinomas, which account for about 90% of all human cancers. Here, using the micropatterned epithelial monolayer as a model system, we report the discovery of a mechanical wave that propagates slowly to span the monolayer, traverses intercellular junctions in a cooperative manner and builds up differentials of mechanical stress. Essential features of this wave generation and propagation are captured by a minimal model based on sequential fronts of cytoskeletal reinforcement and fluidization. These findings establish a mechanism of long-range cell guidance, symmetry breaking and pattern formation during monolayer expansion.

Keywords: Biological physics

Anon, Ester, Serra-Picamal, Xavier, Hersen, Pascal, Gauthier, Nils C., Sheetz, Michael P., Trepat, Xavier, Ladoux, Benoît, (2012). Cell crawling mediates collective cell migration to close undamaged epithelial gaps Proceedings of the National Academy of Sciences of the United States of America 109, (27), 10891-10896

Fundamental biological processes such as morphogenesis and wound healing involve the closure of epithelial gaps. Epithelial gap closure is commonly attributed either to the purse-string contraction of an intercellular actomyosin cable or to active cell migration, but the relative contribution of these two mechanisms remains unknown. Here we present a model experiment to systematically study epithelial closure in the absence of cell injury. We developed a pillar stencil approach to create well-defined gaps in terms of size and shape within an epithelial cell monolayer. Upon pillar removal, cells actively respond to the newly accessible free space by extending lamellipodia and migrating into the gap. The decrease of gap area over time is strikingly linear and shows two different regimes depending on the size of the gap. In large gaps, closure is dominated by lamellipodium-mediated cell migration. By contrast, closure of gaps smaller than 20 μm was affected by cell density and progressed independently of Rac, myosin light chain kinase, and Rho kinase, suggesting a passive physical mechanism. By changing the shape of the gap, we observed that low-curvature areas favored the appearance of lamellipodia, promoting faster closure. Altogether, our results reveal that the closure of epithelial gaps in the absence of cell injury is governed by the collective migration of cells through the activation of lamellipodium protrusion.

Nocentini, S., Reginensi, D., Garcia, S., Carulla, P., Moreno-Flores, Wandosell, F., Trepat, X., Bribian, A., Del Rí, (2012). Myelin-associated proteins block the migration of olfactory ensheathing cells: an in vitro study using single-cell tracking and traction force microscopy Cellular and Molecular Life Sciences , 69, (10), 1689-1703

Newly generated olfactory receptor axons grow from the peripheral to the central nervous system aided by olfactory ensheathing cells (OECs). Thus, OEC transplantation has emerged as a promising therapy for spinal cord injuries and for other neural diseases. However, these cells do not present a uniform population, but instead a functionally heterogeneous population that exhibits a variety of responses including adhesion, repulsion, and crossover during cell–cell and cell–matrix interactions. Some studies report that the migratory properties of OECs are compromised by inhibitory molecules and potentiated by chemical gradients. Here, we demonstrated that rodent OECs express all the components of the Nogo receptor complex and that their migration is blocked by myelin. Next, we used cell tracking and traction force microscopy to analyze OEC migration and its mechanical properties over myelin. Our data relate the decrease of traction force of OEC with lower migratory capacity over myelin, which correlates with changes in the F-actin cytoskeleton and focal adhesion distribution. Lastly, OEC traction force and migratory capacity is enhanced after cell incubation with the Nogo receptor inhibitor NEP1-40.

Keywords: Ensheathing glia, Traction force, microscopy, Migration, Myelin-associated inhibitors

Conte, Vito, Ulrich, Florian, Baum, Buzz, Muñoz, Jose, Veldhuis, Jim, Brodland, Wayne, Miodownik, Mark, (2012). A biomechanical analysis of ventral furrow formation in the Drosophila Melanogaster Embryo PLoS ONE Public Library of Science 7, (4), e34473

The article provides a biomechanical analysis of ventral furrow formation in the Drosophila melanogaster embryo. Ventral furrow formation is the first large-scale morphogenetic movement in the fly embryo. It involves deformation of a uniform cellular monolayer formed following cellularisation, and has therefore long been used as a simple system in which to explore the role of mechanics in force generation. Here we use a quantitative framework to carry out a systematic perturbation analysis to determine the role of each of the active forces observed. The analysis confirms that ventral furrow invagination arises from a combination of apical constriction and apical–basal shortening forces in the mesoderm, together with a combination of ectodermal forces. We show that the mesodermal forces are crucial for invagination: the loss of apical constriction leads to a loss of the furrow, while the mesodermal radial shortening forces are the primary cause of the internalisation of the future mesoderm as the furrow rises. Ectodermal forces play a minor but significant role in furrow formation: without ectodermal forces the furrow is slower to form, does not close properly and has an aberrant morphology. Nevertheless, despite changes in the active mesodermal and ectodermal forces lead to changes in the timing and extent of furrow, invagination is eventually achieved in most cases, implying that the system is robust to perturbation and therefore over-determined.

Trepat, Xavier, Chen, Zaozao, Jacobson, Ken, (2012). Cell Migration Comprehensive Physiology (ed. Terjung, Ron), John Wiley & Sons, Inc. (Hoboken, USA) 2, 2369–2392

Cell migration is fundamental to establishing and maintaining the proper organization of multicellular organisms. Morphogenesis can be viewed as a consequence, in part, of cell locomotion, from large-scale migrations of epithelial sheets during gastrulation, to the movement of individual cells during development of the nervous system. In an adult organism, cell migration is essential for proper immune response, wound repair, and tissue homeostasis, while aberrant cell migration is found in various pathologies. Indeed, as our knowledge of migration increases, we can look forward to, for example, abating the spread of highly malignant cancer cells, retarding the invasion of white cells in the inflammatory process, or enhancing the healing of wounds. This article is organized in two main sections. The first section is devoted to the single-cell migrating in isolation such as occurs when leukocytes migrate during the immune response or when fibroblasts squeeze through connective tissue. The second section is devoted to cells collectively migrating as part of multicellular clusters or sheets. This second type of migration is prevalent in development, wound healing, and in some forms of cancer metastasis.

Trepat, X., (2011). Forcing tumor arrest Physics , 4, 85


Keywords: -----

Tambe, Dhananjay T., Corey Hardin, C., Angelini, Thomas E., Rajendran, Kavitha, Park, Chan Young, Serra-Picamal, Xavier, Zhou, Enhua H., Zaman, Muhammad H., Butler, James P., Weitz, David A., Fredberg, Jeffrey J., Trepat, X., (2011). Collective cell guidance by cooperative intercellular forces Nature Materials 10, (6), 469-475

Cells comprising a tissue migrate as part of a collective. How collective processes are coordinated over large multi-cellular assemblies has remained unclear, however, because mechanical stresses exerted at cell–cell junctions have not been accessible experimentally. We report here maps of these stresses within and between cells comprising a monolayer. Within the cell sheet there arise unanticipated fluctuations of mechanical stress that are severe, emerge spontaneously, and ripple across the monolayer. Within that stress landscape, local cellular migrations follow local orientations of maximal principal stress. Migrations of both endothelial and epithelial monolayers conform to this behaviour, as do breast cancer cell lines before but not after the epithelial–mesenchymal transition. Collective migration in these diverse systems is seen to be governed by a simple but unifying physiological principle: neighbouring cells join forces to transmit appreciable normal stress across the cell–cell junction, but migrate along orientations of minimal intercellular shear stress.

Keywords: Biological materials, Mechanical properties

Trepat, X., Fredberg, J. J., (2011). Plithotaxis and emergent dynamics in collective cellular migration Trends in Cell Biology 21, (11), 638-646

For a monolayer sheet to migrate cohesively, it has long been suspected that each constituent cell must exert physical forces not only upon its extracellular matrix but also upon neighboring cells. The first comprehensive maps of these distinct force components reveal an unexpected physical picture. Rather than showing smooth and systematic variation within the monolayer, the distribution of physical forces is dominated by heterogeneity, both in space and in time, which emerges spontaneously, propagates over great distances, and cooperates over the span of many cell bodies. To explain the severe ruggedness of this force landscape and its role in collective cell guidance, the well known mechanisms of chemotaxis, durotaxis, haptotaxis are clearly insufficient. In a broad range of epithelial and endothelial cell sheets, collective cell migration is governed instead by a newly discovered emergent mechanism of innately collective cell guidance - plithotaxis.

Keywords: Positional information, Drosophila embryo, Sheet migration, Dpp gradient, Cells, Force, Morphogenesis, Transition, Identification, Proliferation

Angelini, Thomas E., Hannezo, Edouard, Trepat, Xavier, Marquez, Manuel, Fredberg, Jeffrey J., Weitz, David A., (2011). Glass-like dynamics of collective cell migration Proceedings of the National Academy of Sciences of the United States of America 108, (12), 4714-4719

Collective cell migration in tissues occurs throughout embryonic development, during wound healing, and in cancerous tumor invasion, yet most detailed knowledge of cell migration comes from single-cell studies. As single cells migrate, the shape of the cell body fluctuates dramatically through cyclic processes of extension, adhesion, and retraction, accompanied by erratic changes in migration direction. Within confluent cell layers, such subcellular motions must be coupled between neighbors, yet the influence of these subcellular motions on collective migration is not known. Here we study motion within a confluent epithelial cell sheet, simultaneously measuring collective migration and subcellular motions, covering a broad range of length scales, time scales, and cell densities. At large length scales and time scales collective migration slows as cell density rises, yet the fastest cells move in large, multicell groups whose scale grows with increasing cell density. This behavior has an intriguing analogy to dynamic heterogeneities found in particulate systems as they become more crowded and approach a glass transition. In addition we find a diminishing self-diffusivity of short-wavelength motions within the cell layer, and growing peaks in the vibrational density of states associated with cooperative cell-shape fluctuations. Both of these observations are also intriguingly reminiscent of a glass transition. Thus, these results provide a broad and suggestive analogy between cell motion within a confluent layer and the dynamics of supercooled colloidal and molecular fluids approaching a glass transition.

Keywords: Active matter, Cell mechanics, Jamming, Collective cell dynamics, Nonequilibrium

Krishnan, Ramaswamy, Klumpers, Darinka D., Park, Chan Y., Rajendran, Kavitha, Trepat, Xavier, van Bezu, Jan, van Hinsbergh, Victor W. M., Carman, Christopher V., Brain, Joseph D., Fredberg, Jeffrey J., Butler, James P., van Nieuw Amerongen, Geerten P., (2011). Substrate stiffening promotes endothelial monolayer disruption through enhanced physical forces American Journal of Physiology - Cell Physiology , 300, (1), C146-C154

A hallmark of many, sometimes life-threatening, inflammatory diseases and disorders is vascular leakage. The extent and severity of vascular leakage is broadly mediated by the integrity of the endothelial cell (EC) monolayer, which is in turn governed by three major interactions: cell-cell and cell-substrate contacts, soluble mediators, and biomechanical forces. A potentially critical but essentially uninvestigated component mediating these interactions is the stiffness of the substrate to which the endothelial monolayer is adherent. Accordingly, we investigated the extent to which substrate stiffening influences endothelial monolayer disruption and the role of cell-cell and cell-substrate contacts, soluble mediators, and physical forces in that process. Traction force microscopy showed that forces between cell and cell and between cell and substrate were greater on stiffer substrates. On stiffer substrates, these forces were substantially enhanced by a hyperpermeability stimulus (thrombin, 1 U/ml), and gaps formed between cells. On softer substrates, by contrast, these forces were increased far less by thrombin, and gaps did not form between cells. This stiffness-dependent force enhancement was associated with increased Rho kinase activity, whereas inhibition of Rho kinase attenuated baseline forces and lessened thrombin-induced inter-EC gap formation. Our findings demonstrate a central role of physical forces in EC gap formation and highlight a novel physiological mechanism. Integrity of the endothelial monolayer is governed by its physical microenvironment, which in normal circumstances is compliant but during pathology becomes stiffer.

Keywords: Contraction, Human umbilical vein endothelial cells, Permeability, Traction force, Cell-cell contact, Cell-substrate contact, Substrate stiffness, Rho kinase, Vascular endothelial cadherin, Thrombin


  • Soft Lithography
  • Micro/Nano fabrication
  • Cell stretching
  • Live Confocal Microcopy
  • Magnetic Tweezers
  • Magnetic Twisting Cytometry
  • Monolayer stress microscopy
  • Traction microscopy


  • Julien Colombelli / Eduard Batlle
    Institute for Research in Biomedicine (IRB) Barcelona
  • Marino Arroyo
    Universitat Politècnica de Catalunya, Barcelona
  • Guillaume Charras / Roberto Mayor
    University College London, UK
  • Erik Sahai
    Cancer Research, UK
  • Benoit Ladoux
    Université Paris 7, France
  • Jim Butler & Jeff Fredberg
    Harvard University, Boston
  • Danijela Vignjevic
    Institut Curie, Paris



Com es mesura l’estrès mecànic en teixits vius?

Un equip d’experts de l’Institut de Bioenginyeria de Catalunya (IBEC) publica a la revista Nature Reviews Physics una revisió detallada de les diferents tècniques que s’utilitzen per calcular l’estrès mecànic en teixits, tant en cultius cel·lulars, com in vivo. Determinar aquests mecanismes d’estrès mecànic és clau per estudiar els processos vinculats a la morfogènesi, l’homeòstasi i a malalties com el càncer.

Els teixits vius són materials que, per funcionar adequadament, necessiten moure’s, dividir-se, remodelar-se i percebre el seu microambient en tot moment. És a dir, necessiten suportar cert estrès mecànic derivat del contacte.

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Investigadors de l’IBEC expliquen la “durotaxis”, un mecanisme de migració cel·lular amb un paper potencial en diverses malalties

Xavier Trepat, líder del grup de “Dinàmica integrativa de cèl·lules i teixits” a l’IBEC juntament amb Raimon Sunyer, investigador sènior en el laboratori de Trepat, han escrit un Primer a la revista Current Biology sobre la “Durotaxis”, un mecanisme de migració cel·lular que podria tenir un paper en diverses malalties que impliquin l’enduriment dels teixits.

El desenvolupament embrionari, la progressió tumoral o la resposta immunològica contra patògens requereix la migració cel·lular.

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L’EMBL-IBEC Winter Conference es clausura amb un gran èxit de participació

La conferència organitzada per l’Institut de Bioingeniería de Catalunya (IBEC) i el Laboratori Europeu de Biologia Molecular (EMBL) va reunir aquesta setmana a la Pedrera de Barcelona a un total de 200 experts internacionals en el camp de la bioingeniería.

En la inauguració de l’esdeveniment, que va ser a càrrec de l’alcaldessa de Barcelona Ada Colau, es va destacar la consolidació de Barcelona com a centre internacional de recerca i coneixement.

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Les cèl·lules amb dos nuclis podrien ser clau en la regeneració del cor

Un equip d’investigadors de l’IBEC liderat per Xavier Trepat, en col·laboració amb el CMR[B], ha descobert un mecanisme que genera cèl·lules de dos nuclis. Aquest mecanisme s’ha identificat durant la regeneració del cor del peix zebra, i podria estar associat a l’extraordinari poder regeneratiu d’aquest animal.

Després d’una lesió aguda, com un infart de miocardi, el cor humà és incapaç de regenerar-se. Les cèl·lules cardíaques adultes no poden créixer i dividir-se per substituir les danyades, i la lesió esdevé irreversible. Però això no passa en tots els animals. Un peix d’aigua dolça originari del Sud-est d’Àsia, conegut com a peix zebra, pot regenerar per complet el seu cor fins i tot després de l’amputació del 20% del seu ventricle.

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L’enfocament ascendent és suficient per entendre tot un sistema?

El responsable del grup de l’IBEC, Xavier Trepat, ha publicat un article d’opinió a la secció News and Views (Notícies i Opinió) del darrer número de la revista Nature, dedicat a la «Biologia ascendent».

En el seu article «Bottom does not explain top» («El nivell inferior no explica el nivell superior»), Xavier argumenta que entendre com es construeixen les estructures biològiques complexes —o fins i tot les cèl·lules com un tot—, només aporta una certa idea de com funcionen els sistemes biològics en nivells superiors d’organització. Hi ha moltes variables, com ara la densitat, o fins i tot les patologies que pot patir un subjecte, que afecten el comportament cel·lular a nivell de mesoescala, és a dir, a més llarg termini, a una escala més sistèmica que la dels components individuals d’un organisme.

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Investigadors descobreixen cèl·lules superdeformables

Una de les habilitats més envejables dels superherois és la seva capacitat per estirar els seus cossos més enllà dels límits imaginables.

En un estudi publicat avui a la revista Nature, científics han descobert el mecanisme que explica com les nostres cèl·lules poden fer precisament això: deformar-se de forma extrema sense trencar-se.

La investigació de l’IBEC, impulsada per la Fundació Bancària “la Caixa”, i la UPC presenten una nova propietat física de les cèl·lules, que denominen superelasticitat activa, que explica la seva capacitat inusual per suportar deformacions extremes.

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La teva cara prové de la part posterior del teu cap

Les cèl·lules mare embrionàries que donen forma a la cara (cèl·lules de la cresta neural) utilitzen un mecanisme inesperat per desenvolupar les característiques facials, segons revela un nou estudi dirigit per la UCL que involucra a investigadors de l’IBEC.

Els investigadors han desxifrat com es mouen aquestes cèl·lules, podent ajudar a comprendre com ocorren els defectes facials, com el paladar fes i la paràlisi facial.

El mecanisme recentment descrit podria ser rellevant per al desenvolupament de noves teràpies, atès que podria estar darrere d’altres processos de migració cel·lular, com la invasió del càncer durant la metàstasi o la cicatrització de ferides.

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L’expansió de cèl·lules tumorals desafia la física actual

• Investigadors de l’IBEC i la UB descobreixen que l’expansió de cèl·lules tumorals no obeeix les lleis de la física tal com estan formulades actualment. Aquesta descoberta ha estat impulsada per la Fundació Bancària “la Caixa”.

• En un article publicat avui a la revista Nature Physics, els investigadors reformulen aquestes lleis i desenvolupen un nou marc que pot contribuir a predir les condicions en què els tumors inicien la metàstasi.

Un tumor maligne es caracteritza per la seva capacitat de disseminar-se pel seu entorn. Per fer-ho, les cèl·lules del tumor han d’adherir-se al teixit que les envolta (principalment col·lagen) i exercir-hi forces per propulsar-se.

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Les forces físiques regulen la divisió cel·lular

Investigadors de l’IBEC ha descobert que la divisió cel·lular que es produeix en teixits epitelials està regulada per forces mecàniques

Aquest descobriment obre la porta a una major comprensió de la proliferació descontrolada de les cèl·lules canceroses en els tumors, i a la seva possible regulació per mitjà de forces físiques.

El resultat de la recerca, que s’ha publicat a la revista Nature Cell Biology, ha estat duta a terme pel grup de recerca del Xavier Trepat, professor ICREA a l’IBEC i professor associat a la UB, i en ella es relaciona l’estat mecànic del teixit amb la progressió al llarg del cicle cel·lular i divisió de les seves cèl·lules.

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