Integrative cell and tissue dynamics

Xavier Trepat | Group Leader / ICREA Research Professor
Dobryna Julia Valeria Zalvidea | Senior Researcher
Juan Francisco Abenza Martínez | Postdoctoral Researcher
Manuel Gómez González | Postdoctoral Researcher
Anna Labernadie | Postdoctoral Researcher
Andrea Malandrino | Postdoctoral Researcher
Raimon Sunyer Borrell | Postdoctoral Researcher
Ernest Latorre Ibars | PhD Student
Ariadna Marin Llaurado | PhD Student
Macià Esteve Pallares Pallares | PhD Student
Carlos Pérez González | PhD Student
Marina Uroz Marimon | PhD Student
Sabrina Wistorf | PhD Student
Nimesh Ramesh Chahare | Research Assistant
Sefora Conti | Research Assistant
Maria Eleni Naoum | Research Assistant
Leone Rossetti | Research Assistant
Natalia Castro Morán | Laboratory Technician
Mohammad Zadehkamand | Masters Student
Jonel Trebicka | Visiting Researcher


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

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.

A group of human mammary epithelial cells expands asymmetrically on a surface of increasing rigidity (towards the right of the image). Colored lines correspond to the tracks followed by each cell (gray dots) for 10h.

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.

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.

Our lab has developed techniques to simultaneously map cell velocities, cytoskeletal structure, intercellular stresses, and cell-substrate tractions (from top to bottom).

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.

Fracking epithelial layers
Epithelial sheets must be malleable enough to adopt functional shapes during morphogenesis and to quickly self-repair after damage. Yet, they must be resilient enough to ensure organ compartmentalization and to protect organisms against environmental pathogens. To study the mechanisms that regulate this fine balance between malleability and integrity we develop tools to map epithelial tension during tissue stretching. By combining these tools with computational modeling we determined the mechanisms of epithelial fracture. Intriguingly, one of such mechanisms is hydraulic fracturing or “fracking”.



A video produced by Fundación Banco Sabadell of Xavier Trepat, 2015 winner of the Banco Sabadell Award for Biomedical Research, appears on their YouTube channel.

How tumor cells hijack healthy cells to promote metastasis

In a study published today in Nature Cell Biology and supported by Obra Social “la Caixa”, researchers at IBEC have identified an interaction between two proteins that enables cancerous cells to use the physical forces of healthy cells to start tumor metastasis.

An optogenetic tool that directs cellular contractility using light

Researchers at IBEC have controlled the contractility of a group of epithelial cells using an optogenetic switch activated by light.

Cells move en masse towards rigid tissues

A new phenomenon, collective durotaxis, opens new avenues to control tumor growth and improve wound healing

IBEC’s Xavier Trepat a guest star at Big Vang’s first anniversary

Xavier Trepat, ICREA professor and group leader at IBEC, was the guest star at the first anniversary celebration of Big Vang, La Vanguardia’s online science section.

Reaching new depths: a non-invasive solution for the activation of proteins in deep tissues

Researchers at IBEC and their collaborators at the Centre of Regenerative Medicine of Barcelona (CMR[B]) have developed a revolutionary new technique based on photoactivation (light activation), by which cells in deep tissue can activated and tracked in vivo without causing any damage.

Xavier a runner-up in the La Vanguardia Science Award

IBEC group leader and ICREA research professor Xavier Trepat has come third in the La Vanguardia Science Award.

Cells are liquids – but behave like solids

Scientists at the Institute for Bioengineering of Catalonia (IBEC) have revealed that, counter to previous understanding, the living cells in our bodies behave like solids rather than the liquids they are made of.

How cells cope with stress and strain

A study by the Institute for Bioengineering of Catalonia (IBEC) reveals how cells withstand breakage during the constant changes in shape and volume experienced in most biological processes.

Xavier Trepat winner of the 10th Banc Sabadell Award for Biomedical Research

IBEC group leader and ICREA research professor Xavier Trepat is this year’s winner of the Banc Sabadell Award for Biomedical Research for his work on understanding the fundamental biophysical mechanisms underlying cell interaction and communication.

A new mechanism in cell communication that promotes cancer metastasis

At a press conference at the Obra Social “la Caixa”’s Palau Macaya earlier today, Xavier Trepat, group leader at the Institute for Bioengineering of Catalonia (IBEC), Enric Banda, director of the department of Science and Environment of the Obra Social ”la Caixa”, and Josep Samitier, director of IBEC, described a study published in Nature Cell Biology which sheds new light on how to control metastasis.

A major step towards repairing the spinal cord

Researchers at the Institute for Bioengineering of Catalonia and their collaborators reveal that they’re a step closer to optimizing cells able to guide regeneration of the spine

‘Fracking’ found in living tissues

In an article published in the journal Nature Materials, researchers at the IBEC and the UPC describe their discovery that ‘fracking’takes place in the body at a cellular level.

Wounds heal using a cellular ‘tug-of-war’

Researchers at IBEC reveal in a Nature Communications paper some surprising mechanics that drive epithelial gap closure in the absence of underlying layers.

Ramon Margalef Prize for former IBEC PhD student

Xavier Serra Picamal, formerly a PhD student in IBEC’s Integrative Cell and Tissue Dynamics group, was awarded a prestigious Ramon Margalef Prize for the best paper derived from a doctoral thesis at a ceremony at the UB last night.

“Los científicos descubren cómo las células del cuerpo humano curan las heridas”

Today’s news about the Integrative Cell and Tissue Dynamics group’s paper in Nature Physics has been covered in La Vanguardia.

IBEC group uncovers new mechanism for wound healing 


When we think of wound healing, we normally think of wounds to our skin. But wounds happen inside the body in all sorts of tissues and organs, and can have implications in many chronic diseases such as diabetes and asthma. Wounds also favour cancer progression by providing a physical and chemical environment that promotes the invasion of malignant cells. Now, a group at the Institute for Bioengineering of Catalonia (IBEC) has found a new way to decipher the mechanisms of wound healing, and by doing so has uncovered a new understanding of how cells move and work together to close a gap in a tissue.

“El físico que innova en biología” 


Integrative cell and tissue dynamics group leader Xavier Trepat is profiled in El Mundo’s ‘Innovadores’ supplement today.

“El consejo europeo de investigación otorga dos nuevas distinciones a Cataluña” 


The news about Xavier Trepat’s Proof of Concept grant from the ERC appears in La Vanguardia today.

“Las células humanas construyen puentes colgantes para cicatrizar las heridas”

This week’s press release about the Integrative Cell and Tissue Dynamics group’s work published in Nature Materials has appeared online in La Vanguardia, ABC and El Diario.

A double dose of ERC success for IBEC researchers

The Integrative Cell and Tissue Dynamics group starts the year with good news from the European Research Council – they’ve been awarded both a new Consolidator Grant and a Proof of Concept award.

Skin forms ‘suspension bridges’ for wound healing

Results from IBEC researchers and their collaborators will pave the way for better and faster wound healing, as well opening new avenues for tissue engineering of skin

IBEC research on a journal cover again

The October cover of Current Opinion in Cell Biology (the reference opinion journal in cell biology, with impact factor 12) features research by IBEC’s Pere Roca and Xavier Trepat, who together with Raimon Sunyer from the UB have published a review paper in the issue, “Mechanical guidance of cell migration: lessons from chemotaxis”.

IBEC paper on the cover of Nature Materials

The latest cover of Nature Materials was designed by IBEC PhD student Xavier Serra and shows a real tissue segmented computationally to give the impression of a Gaudinian trencadís.

“La física ‘guía’ a las células”

Integrative Cell and Tissue Dynamics group leader Xavier Trepat and his recent paper in Nature Cell Biology are the subject of an article in El Périodico today.

Unexpected discovery about the ways cells move could boost understanding of complex diseases

A new discovery about how cells move inside the body may provide scientists with crucial information about disease mechanisms such as the spread of cancer or the constriction of airways caused by asthma. Researchers at IBEC and Harvard School of Public Health have found that epithelial cells—the type that form a barrier between the inside and the outside of the body, such as skin cells—move in a group, propelled by forces both from within and from nearby cells to fill any spaces they encounter.

“Las células juegan al «pilla-pilla» en su desarrollo embrionario”

Monday’s news about the Nature Cell Biology paper ‘Chase-and-run between adjacent cell populations promotes directional collective migration’ was covered in several science and general news sites and magazines, including La Razón.

Cells play ‘tag’ to determine direction of movement

Researchers at IBEC, the University of Barcelona and their collaborators have found that cells in our bodies, when moving collectively, carry out something similar to a game of ‘tag’ to coordinate their movement in a particular direction.

Scientists discover a new type of wave in living tissues

Researchers have shed new light on how the cells in our bodies collectively migrate, a critical process in positive events such as embryonic development and wound healing, but which is also integral to the development of cancer.

“Una nueva técnica de control de las microheridas epiteliales”

The Integrative Cell and Tissue Dynamics group’s recent paper published in PNAS was covered in Diario Medico.

Plithotaxis: how crowds of cells find their way

First measurements of forces driving collective cell migration unveil new principle in biology

We’re made of glass, say scientists

People can be brittle, transparent, shattered, or have a heart of glass. Now these attributes seem all the more appropriate following a discovery by researchers that migrating cells in our bodies behave in a remarkably similar way to glass when it is heated and cooled.

Researcher at IBEC publishes in Nature Physics

An article by Dr. Xavier Trepat, senior researcher of IBEC´s Cellular and respiratory biomechanics group and the Department of Physiology Sciences of the University of Barcelona, contributes for the first time an experimental answer to the question of how cells move during biological processes as diverse as the development, metastasis, or regeneration of tissues.

Press coverage elsewhere

Cells flow like glass, study finds. Harvard Science Foundation

How do cells move: Cooperative forces boost collective mobility of cells. Science Daily

Cells guided on their journey. Nature Physics

Disorderly conduct. Harvard Medical School Focus

How growing cells move together. Harvard Science Foundation

A stretch in cells. Nature

More than lip service. Nature

In Catalan / Spanish:

“Xavier Trepat, investigador principal del Laboratori de Dinàmica Cel·lular i del Teixit de l’IBEC”. Destacamus

Estamos hechos de vidrio. El Mundo

L’observador. RTVE, Spanish National Radio

Europa premia vuit joves investigadors de Catalunya. Avui

Com actuen les forces físiques durant la migració cel·lular? Comunicacions UB

Journal covers



EU-funded projects
GENESFORCEMOTION Physical Forces Driving Collective Cell Migration: from Genes to Mechanism European Commission, ERC-StG Xavier Trepat
MICROGRADIENTPAGE Micro Gradient Polyacrylamide Gels for High Throughput Electrophoresis Analysis European Commission, ERC-PoC Xavier Trepat
TensionControl Multiscale regulation of epithelial tension (2015-2019) European Commission, ERC – CoG Xavier Trepat
CAMVAS Coordination and migration of cells during 3D Vasculogenesis (2014-2017) European Commission, MARIE CURIE – IOF Xavier Trepat
National 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
DUROTAXIS Mecanobiología de la durotaxis: de las células aisladas a los tejidos MINECO, Proyectos I+D Excelencia Xavier Trepat
Privately-funded projects
Joint Programme_Healthy Ageing Obra Social La Caixa Xavier Trepat


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.

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’.

Reiberger, T., Trebicka, J., (2017). New liver – Fresh microbiome: Implications on brain function Liver Transplantation 23, (7), 873-874

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.

Schierwagen, R., Uschner, F. E., Magdaleno, F., Klein, S., Trebicka, J., (2017). Rationale for the use of statins in liver disease American Journal of Physiology - Gastrointestinal and Liver Physiology 312, (5), G407-G412

The evolution of chronic liver injuries from benign and manageable dysfunction to life threatening end-stage liver disease with severe complications renders chronic liver disease a global health burden. Because of the lack of effective medication, transplantation remains the only and final curative option for end-stage liver disease. Since the demand for organ transplants by far exceeds the supply, other treatment options are urgently required to prevent progression and improve end-stage liver disease. Statins are primarily cholesterol-lowering drugs used for primary or secondary prevention of cardiovascular diseases. In addition to the primary effect, statins act beneficially through different pleiotropic mechanisms on inflammation, fibrosis, endothelial function, thrombosis, and coagulation to improve chronic liver diseases. However, concerns remain about the efficacy and safety of statin treatment because of their potential hepatotoxic risks, and as of now, these risks impede broader use of statins in the treatment of chronic liver diseases. The aim of this review is to comprehensively describe the mechanisms by which statins improve prospects for different chronic liver diseases with special focus on the pathophysiological rationale and the clinical experience of statin use in the treatment of liver diseases.

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

Beiert, T., Tiyerili, V., Knappe, V., Effelsberg, V., Linhart, M., Stöckigt, F., Klein, S., Schierwagen, R., Trebicka, J., Nickenig, G., Schrickel, J. W., Andrié, R. P., (2017). Relaxin reduces susceptibility to post-infarct atrial fibrillation in mice due to anti-fibrotic and anti-inflammatory properties Biochemical and Biophysical Research Communications 490, (3), 643-649

Background Relaxin-2 (RLX) is a peptide hormone that exerts beneficial anti-fibrotic and anti-inflammatory effects in diverse models of cardiovascular disease. The goal of this study was to determine the effects of RLX treatment on the susceptibility to atrial fibrillation (AF) after myocardial infarction (MI). Methods Mice with cryoinfarction of the left anterior ventricular wall were treated for two weeks with either RLX (75

Keywords: Atrial fibrillation, Atrial fibrosis, Myocardial infarction, Relaxin-2

Schwab, S., Lehmann, J., Lutz, P., Jansen, C., Appenrodt, B., Lammert, F., Strassburg, C. P., Spengler, U., Nischalke, H. D., Trebicka, J., (2017). Influence of genetic variations in the SOD1 gene on the development of ascites and spontaneous bacterial peritonitis in decompensated liver cirrhosis European Journal of Gastroenterology and Hepatology 29, (7), 800-804

Background The balance between generation and elimination of reactive oxygen species by superoxide dismutase (SOD) is crucially involved in the pathophysiology of liver cirrhosis. Reactive oxygen species damage cells and induce inflammation/fibrosis, but also play a critical role in immune defense from pathogens. As both processes are involved in the development of liver cirrhosis and its complications, genetic variation of the SOD1 gene was investigated. Patients and methods Two SOD1 single nucleotide polymorphisms (rs1041740 and rs3844942) were analyzed in 49 cirrhotic patients undergoing liver transplantation. In addition, 344 cirrhotic patients with ascites were analyzed in a cohort of 521 individuals in terms of the relationship of these polymorphisms with spontaneous bacterial peritonitis (SBP). Results Although rs3844942 showed no associations with complications of cirrhosis, we observed a significant association between rs1041740 and the presence of ascites and SBP in the discovery cohort of patients with cirrhosis. Importantly, the association with SBP was not confirmed in the validation cohort of patients with ascites. By contrast, a trend toward lower SBP rates was observed in carriers of rs1041740. In this cohort, rs1041740 was not associated with survival. Conclusion These data suggest a complex role of SOD1 in different processes leading to complications of liver cirrhosis. rs1041740 might be associated with the development of ascites and possibly plays a role in SBP once ascites has developed.

Keywords: Ascites, Genetic polymorphism, Liver cirrhosis, Reactive oxygen stress, Spontaneous bacterial peritonitis, Superoxide dismutases

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

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.

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 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

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