46 research outputs found
Endurance ou force dans le réentrainement à l'effort chez des patients atteints d'artériopathie oblitérante des membres inférieurs: revue de la littérature : travail de Bachelor
Introduction : Les modalitĂ©s dâun rĂ©entrainement Ă lâeffort chez les patients atteints dâartĂ©riopathie oblitĂ©rante des membres infĂ©rieurs (AOMI) sont dĂ©crites de façon prĂ©cises et structurĂ©es concernant la marche, mais restent controversĂ©es pour le renforcement. Lâobjectif de cette revue de la littĂ©rature est de comparer un entrainement de force et dâendurance chez les patients atteints dâAOMI au stade dâischĂ©mie dâeffort symptomatique ou non sur la distance totale de marche. MĂ©thode : Nous avons effectuĂ© nos recherches sur les bases de donnĂ©es Medline, PEDro, Cochrane, CINHAL, embase BDSP et KinĂ©doc. Nos mots clĂ©s regroupaient 3 catĂ©gories ; les patients atteints dâAOMI au stade dâischĂ©mie dâeffort, lâentrainement de force et celui dâendurance. Lâoutcome Ă©tudiĂ© Ă©tait centrĂ© sur la distance totale de marche. LâĂ©valuation de la qualitĂ© des articles sâest faite avec lâĂ©chelle PEDro. RĂ©sultats : Une de nos trois Ă©tudes a montrĂ© une amĂ©lioration cliniquement significative de la distance totale de marche (DTM) en faveur dâun entrainement de force Ă haute intensitĂ© progressive comparĂ© Ă un entrainement de marche. Les deux autres Ă©tudes ont dĂ©montrĂ© une amĂ©lioration similaire de la DTM Ă©valuĂ©e sur tapis quelles que soient les modalitĂ©s dâentrainement (marche ou force). Conclusion : Les Ă©tudes montrent que les bĂ©nĂ©fices dâun entrainement de marche et dâun renforcement sont similaires. Cependant, une Ă©tude rĂ©cente a montrĂ© quâun entrainement de force Ă haute intensitĂ© permettrait dâamĂ©liorer aussi la DTM. Ce type dâentrainement apporte un intĂ©rĂȘt supplĂ©mentaire puisquâil ne dĂ©clenche pas de douleur de claudication par rapport Ă lâentrainement de marche. De futures Ă©tudes apporteront sĂ»rement une rĂ©ponse dĂ©finitive quant aux bĂ©nĂ©fices du renforcement
Nesprins are mechanotransducers that discriminate epithelial-mesenchymal transition programs
© 2020 DĂ©jardin et al. This article is distributed under the terms of an AttributionâNoncommercialâShare AlikeâNo Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms/). After six months it is available under a Creative Commons License (AttributionâNoncommercialâShare Alike 4.0 International license, as described at https://creativecommons.org/licenses/by-nc-sa/4.0/).LINC complexes are transmembrane protein assemblies that physically connect the nucleoskeleton and cytoskeleton through the nuclear envelope. Dysfunctions of LINC complexes are associated with pathologies such as cancer and muscular disorders. The mechanical roles of LINC complexes are poorly understood. To address this, we used genetically encoded FRET biosensors of molecular tension in a nesprin protein of the LINC complex of fibroblastic and epithelial cells in culture. We exposed cells to mechanical, genetic, and pharmacological perturbations, mimicking a range of physiological and pathological situations. We show that nesprin experiences tension generated by the cytoskeleton and acts as a mechanical sensor of cell packing. Moreover, nesprin discriminates between inductions of partial and complete epithelial-mesenchymal transitions. We identify the implicated mechanisms, which involve α-catenin capture at the nuclear envelope by nesprin upon its relaxation, thereby regulating ÎČ-catenin transcription. Our data thus implicate LINC complex proteins as mechanotransducers that fine-tune ÎČ-catenin signaling in a manner dependent on the epithelial-mesenchymal transition program.This material is based on work supported by the Centre national de la recherche scientifique (CNRS), Agence nationale de la recherche (ANR; grants ANR-13-JSV5-0007 and ANR-14-CE09-0006), France BioImaging (ANR-10-INBS-04), la Ligue contre le Cancer (REMX17751 to P.M. Davidson), and the Fondation ARC pour la Recherche sur le Cancer (PDF20161205227 to P.M. Davidson). P.S. Carollo has received funding from the European Unionâs Horizon 2020 Framework Programme for Research and Innovation (Marie SkĆodowska-Curie grant agreement 665850-INSPIRE) and acknowledges the Ecole Doctorale FrontiĂšres de l'Innovation en Recherche et Ăducation (FIRE) Programme Bettencourt. E.R. Gomes was supported by a European Research Council consolidator grant (617676).info:eu-repo/semantics/publishedVersio
Spontaneous migration of cellular aggregates from giant keratocytes to running spheroids
Despite extensive knowledge on the mechanisms that drive singlecell migration, those governing the migration of cell clusters, as occurring during embryonic development and cancer metastasis,remain poorly understood. Here, we investigate the collective migration of cell on adhesive gels with variable rigidity, using 3D cellular aggregates as a model system. After initial adhesion to the substrate, aggregates spread by expanding outward a cell monolayer, whose dynamics is optimal in a narrowrange of rigidities. Fast expansion gives rise to the accumulation of mechanical tension that leads to the rupture of cellâcell contacts and the nucleation of holes within the monolayer, which becomes unstable and undergoes dewetting like a liquid film. This leads to a symmetry breaking and causes the entire aggregate to move as a single entity. Varying the substrate rigidity modulates the extent of dewetting and induces different modes of aggregate motion: âgiant keratocytes,â where the lamellipodium is a cell monolayer that expands at the front and retracts at the back; âpenguins,â characterized by bipedal locomotion; and ârunning spheroids,â for nonspreading aggregates. We characterize these diverse
modes of collectivemigration by quantifying the flows and forces that drive them, andwe unveil the fundamental physical principles that govern these behaviors, which underscore the biological predisposition of living material to migrate, independent of length scale
Compressive forces stabilize microtubules in living cells
Microtubules are cytoskeleton components with unique mechanical and dynamic properties. They are rigid polymers that alternate phases of growth and shrinkage. Nonetheless, the cells can display a subset of stable microtubules, but it is unclear whether microtubule dynamics and mechanical properties are related. Recent in vitro studies suggest that microtubules have mechano-responsive properties, being able to stabilize their lattice by self-repair on physical damage. Here we study how microtubules respond to cycles of compressive forces in living cells and find that microtubules become distorted, less dynamic and more stable. This mechano-stabilization depends on CLASP2, which relocates from the end to the deformed shaft of microtubules. This process seems to be instrumental for cell migration in confined spaces. Overall, these results demonstrate that microtubules in living cells have mechano-responsive properties that allow them to resist and even counteract the forces to which they are subjected, being a central mediator of cellular mechano-responses
Adhésion cellulaire et tubes de membrane : Quelques aspects dynamiques, mécaniques et rhéologiques
In the "adhesion" section, we have shown that the dynamics of vesicleadhesion induced by specific stickers was either governed by the diffusion of ligandsin the membrane or by the reaction time between immobilized receptors and ligands,depending on the chemical preparation of the decorated substrate. In contrast, theearly stages of living cell adhesion seem to be controlled by the viscous dissipationinside the cell.In the "tubes" section, we have studied the formation and the elongation ofmembrane tethers. First, by pulling long tubes from firmly adhered vesicles, wedemonstrated that the resulting unusual force-extension trace was the signature ofan elastic stretching of the lipid membrane. Second, by analyzing both experimentallyand theoretically the interaction and coalescence of two tethers, we proposed a novelmethod to determine the bending rigidity of phospholipid vesicles. Third, we haverevisited the mechanical and rheological description of tethers extracted from redblood cells and we evidenced a shear-thinning behavior of the membrane during theelongation, which indicates the significant influence of the underlying spectrinnetwork.Dans la partie "adhĂ©sion", nous avons montrĂ© que la dynamique d'adhĂ©sionde vĂ©sicules induite par des ligands spĂ©cifiques Ă©tait gouvernĂ©e soit par la diffusionde ligands dans la membrane, soit par le temps de rĂ©action entre le ligand et lerĂ©cepteur, dĂ©pendant de la prĂ©paration chimique des surfaces. Au contraire, lespremiĂšres Ă©tapes de l'adhĂ©sion de cellules semblent ĂȘtre contrĂŽlĂ©es par ladissipation visqueuse Ă l'intĂ©rieur de la cellule.Dans la partie "tubes de membrane", nous avons Ă©tudiĂ© la formation etl'Ă©longation de tubes de membrane. Tout d'abord, en formant des tubes Ă partir devĂ©sicules adhĂ©rĂ©es, nous avons montrĂ© que l'Ă©longation des tubes s'accompagned'un Ă©tirement Ă©lastique de la membrane. Ensuite, en analysant expĂ©rimentalementet thĂ©oriquement l'interaction et la coalescence de deux tubes membranaires, nousavons proposĂ© une mĂ©thode pour dĂ©terminer la rigiditĂ© de courbure de vĂ©siculeslipidiques. Enfin, nous avons revisitĂ© la description mĂ©canique de tubes extraits deglobules rouges et nous avons mis en Ă©vidence un comportement rhĂ©ofluidifiant dela membrane durant l'Ă©longation, indiquant l'influence du squelette de spectrine
Adhésion cellulaire et tubes de membrane (quelques aspects dynamiques, mécaniques et rhéologiques)
PARIS-BIUSJ-ThĂšses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF
Bilayer curling and winding in a viscous fluid
International audienceInduced spontaneous curvature is a new mechanism of microcapsules bursting by nucleation and growth of a hole surrounded by a curling rim. Here we study the dynamics of curling on a macroscopic scale induced by the elastic curvature of a bilayer of tracing paper and tape after soaking by water. The ribbon which is fully stretched at time t = 0 is immersed in a viscous oil. We observe the winding from the free end and find two regimes: rolling at constant velocity at short times, and a slowdown at long times. We interpret these two regimes by a balance of the elastic driving force and the friction force on the roll
Detachment and fracture of cellular aggregates
International audienceThe dynamics of cellular adhesion and deadhesion, which play key roles in many cellular processes, have most often been studied at the scale of single bonds or single cells. However, multicellular adhesion and deadhesion are also central processes in tissue mechanics, morphogenesis, and pathophysiology, where collective tissue phenomena may introduce additional effects that are absent at the single-cell level. In this paper we present experiments on the adhesion of cellular aggregates and a laboratory model system to study tissue mechanics. We introduce a technique to measure the forces and energies involved in the detachment of an aggregate from a substrate (which can be viewed as a cellular tack assay) and in the fracture between two partially fused aggregates, as a function of the adhesion time, the pulling speed, and the cadherin density at the cell surface. We develop a model based on polymer physics to interpret the observations. We identify a significant contribution to the adhesion energy of viscous dissipation mechanisms present at the tissue scale that are absent at the single-cell level, as well as a significant effect of the speed at which the separation force is applied
Curling instability induced by swelling
We study the spontaneous curving observed when a strip of tracing paper is deposited on a water surface. The differential swelling across the ribbon thickness leads to a curling of the sheet, with the curvature increasing to a maximum and then relaxing as the sheet becomes completely wet. We develop a theoretical model, in good agreement with our experimental observations and relevant to the understanding of curling instabilities induced by asymmetric swelling of natural or synthetic shells. © 2011 The Royal Society of Chemistry