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Séminaire de Félix Rico

Probing adhesion and mechanics with atomic force microscopy : from cells to single molecules

Felix Rico

Institut Curie, U1006 INSERM-UMR168 CNRS
26 rue d’Ulm, 75005 Paris, France

Cell adhesion is essential for the formation and the functional and structural integrity of multicellular organisms. Cells adhere to each other and to the extracellular matrix through cell adhesion molecules. I will talk about two different examples of cell adhesion molecules, integrins and gap junctions, studied using atomic force microscopy (AFM).
A paradigmatic example of cell adhesion modulation is found in white blood cells. During the so-called leukocyte adhesion cascade, different types of complexes are formed and disrupted at precise rates while continuously subjected to mechanical stresses. Thus, the mechanical state of the cell may play a crucial role during leukocyte adhesion modulation. A number of studies have shown that cell adhesion is dramatically reduced at temperatures lower than physiological temperature. However, the underlying mechanism of this modulation by temperature is still unclear. We investigated integrin-mediated cell adhesion of leukocytes as a function of temperature through whole cell and single molecule force measurements on cells using AFM. Force measurements revealed an increase of the work of de-adhesion with temperature that was coupled to a gradual decrease in cellular stiffness, while single-molecule rupture forces decreased with temperature. A detailed analysis of the force curves indicated that temperature-modulated cell adhesion was mainly due to the enhanced ability of cells to deform and to form a great number of long membrane tethers at physiological temperatures. These results emphasize the importance of cell mechanics and membrane-cytoskeleton interaction on the modulation of cell adhesion.
Another example of cell adhesion complex is the gap junction. Gap junction plaques are present in virtually every tissue and are formed by clusters of connexons or hemichannels. Each connexon is a hexamer of connexin proteins that dock between neighboring cells to form an intercellular channel, the gap junction. Although the channeling activity of gap junctions under various stimuli have been extensively studied, their function as adhesion complexes has only recently been explored. Using AFM we have characterized the two-dimensional binding kinetics and adhesion strength of the individual inter-connexin interaction. Our results suggest gap junctions as force-bearing complexes capable of withstanding important pulling forces.