Effect of steady and pulsatile laminar shear stress on extracellular matrix and focal contact-associated proteins of endothelial cells

Ph.D.Peggy R. Girar

Control of Cellular Morphology by Mechanical Factors

This short review deals with the influence of mechanical factors on eucaryotic cell morphology and structure. We classify these factors into two types: i) external forces (e.g. gravitational forces or hemodynamic stresses), which when applied experimentally allow characterization of passive mechanical properties; and ii) internal forces, e.g. generated by molecular motors or polymerization processes. Perturbation of one or more of these forces induces significant changes in cell shape, cytoskeleton and pericellular matrix organization. We describe these phenomena in view of current models.Cette brève revue traite de l'influence des facteurs mécaniques sur la morphologie et la structure des cellules eucaryotes. Nous classifions ces facteurs en deux catégories : i) les forces externes (par exemple les forces de gravitation et les contraintes hèmodynamiques) qui, imposées in vitro, permettent de caractériser les propriétés mécaniques passives ; et ii) les forces internes, par exemple celles générées par les moteurs moléculaires ou les processus de polymérisation. La perturbation de l'une ou de l'autre de ces forces provoque des changements significatifs de la morphologie cellulaire ainsi que l'organisation du cytosquelette et de la matrice péricellulaire. Nous décrivons ces phénomènes en fonction de modèles existants

A Triad of Crystals Sheds Light on MDGA Interference with Neuroligation

International audienceNeurexins and neuroligins form trans-synaptic complexes that promote synapse development. In this issue of Neuron, Aricescu and colleagues (Elegheert et al., 2017) complement and strengthen two recent reports by the Kim and Rudenko teams (Kim et al., 2017; Gangwar et al., 2017) to dissect the molecular determinants by which MDGAs challenge the neurexin-neuroligin partnership

Etude de la dynamique des adhésions neuronales N-cadhérine et L1 dans la croissance axonale et la synaptogenèse

Lors des processus développementaux d'élongation axonale et de synaptogenèse, les protéines d'adhésion telles cadhérines ou Ig-CAM jouent des rôles fondamentaux en permettant la formation de contacts entre neurones. Pour étudier la dynamique de ces contacts et leurs rôles dans ces processus, nous avons mis en oeuvre des techniques d'imagerie sur neurones primaires d'hippocampe (clivage thrombine, FRAP, pinces optiques, quantum-dots) associés à un système semi-artificiel de microsphères recouvertes d'adhésion purifiées (N-cadhérine et L1). Dans ce travail, j'ai précisé l'implication des processus de diffusion membranaire et d'exo-endocytose dans la dynamique des contacts L1-dépendants. J'ai également contribué à caractériser la liaison extracellulaire entre N-cadhérine et GluR2, sous unité des récepteurs AMPA, et l'influence de l'expression de la N-cadhérine sur la mobilité de GluR2.BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

Differential role of pre-and postsynaptic neurons in the activity-dependent control of synaptic strengths across dendrites

International audienceNeurons receive a large number of active synaptic inputs from their many presynaptic partners across their dendritic tree. However, little is known about how the strengths of individual synapses are controlled in balance with other synapses to effectively encode information while maintaining network homeostasis. This is in part due to the difficulty in assessing the activity of individual synapses with identified afferent and efferent connections for a synapse population in the brain. Here, to gain insights into the basic cellular rules that drive the activity-dependent spatial distribution of pre- and postsynaptic strengths across incoming axons and dendrites, we combine patch-clamp recordings with live-cell imaging of hippocampal pyramidal neurons in dissociated cultures and organotypic slices. Under basal conditions, both pre- and postsynaptic strengths cluster on single dendritic branches according to the identity of the presynaptic neurons, thus highlighting the ability of single dendritic branches to exhibit input specificity. Stimulating a single presynaptic neuron induces input-specific and dendritic branchwise spatial clustering of presynaptic strengths, which accompanies a widespread multiplicative scaling of postsynaptic strengths in dissociated cultures and heterosynaptic plasticity at distant synapses in organotypic slices. Our study provides evidence for a potential homeostatic mechanism by which the rapid changes in global or distant postsynaptic strengths compensate for input-specific presynaptic plasticity

Regulation of N-Cadherin Dynamics at Neuronal Contacts by Ligand Binding and Cytoskeletal Coupling

N-cadherin plays a key role in axonal outgrowth and synaptogenesis, but how neurons initiate and remodel N-cadherin-based adhesions remains unclear. We addressed this issue with a semiartificial system consisting of N-cadherin coated microspheres adhering to cultured neurons transfected for N-cadherin-GFP. Using optical tweezers, we show that growth cones are particularly reactive to N-cadherin coated microspheres, which they capture in a few seconds and drag rearward. Such strong coupling requires an intact connection between N-cadherin receptors and catenins. As they move to the basis of growth cones, microspheres slow down while gradually accumulating N-cadherin-GFP, demonstrating a clear delay between bead coupling to the actin flow and receptor recruitment. Using FRAP and photoactivation, N-cadherin receptors at bead-to-cell contacts were found to continuously recycle, consistently with a model of ligand-receptor reaction not limited by membrane diffusion. The use of N-cadherin-GFP receptors truncated or mutated in specific cytoplasmic regions show that N-cadherin turnover is exquisitely regulated by catenin partners. Turnover rates are considerably lower than those obtained previously in single molecule studies, demonstrating an active regulation of cadherin bond kinetics in intact cells. Finally, spontaneous neuronal contacts enriched in N-cadherin exhibited similar turnover rates, suggesting that such dynamics of N-cadherin may represent an intrinsic mechanism underlying the plasticity of neuronal adhesions

Contribution of the nucleus to the mechanical properties of endothelial cells

The cell nucleus plays a central role in the response of the endothelium to mechanical forces, possibly by deforming during cellular adaptation. The goal of this work was to precisely quantify the mechanical properties of the nucleus. Individual endothelial cells were subjected to compression between glass microplates. This technique allows measurement of the uniaxial force applied to the cell and the resulting deformation. Measurements were made on round and spread cells to rule out the influence of cell morphology on the nucleus mechanical properties. Tests were also carried out with nuclei isolated from cell cultures by a chemical treatment. The non-linear force-deformation curves indicate that round cells deform at lower forces than spread cells and nuclei. Finite-element models were also built with geometries adapted to actual morphometric measurements of round cells, spread cells and isolated nuclei. The nucleus and the cytoplasm were modeled as separate homogeneous hyperelastic materials. The models simulate the compression and yield the force-deformation curve for a given set of elastic moduli. These parameters are varied to obtain a best fit between the theoretical and experimental data. The elastic modulus of the cytoplasm is found to be on the order of 500N/m(2) for spread and round cells. The elastic modulus of the endothelial nucleus is on the order of 5000N/m(2) for nuclei in the cell and on the order of 8000N/m(2) for isolated nuclei. These results represent an unambiguous measurement of the nucleus mechanical properties and will be important in understanding how cells perceive mechanical forces and respond to them

miRNA-Dependent Control of Homeostatic Plasticity in Neurons

International audienc