Biomechanics of Neutrophil Tethers

Leukocytes, including neutrophils, which are propelled by blood flow, can roll on inflamed endothelium using transient bonds between selectins and their ligands, and integrins and their ligands. When such receptor–ligand bonds last long enough, the leukocyte microvilli become extended and eventually form thin, 20 m long tethers. Tether formation can be observed in blood vessels in vivo and in microfluidic flow chambers. Tethers can also be extracted using micropipette aspiration, biomembrane force probe, optical trap, or atomic force microscopy approaches. Here, we review the biomechanical properties of leukocyte tethers as gleaned from such measurements and discuss the advantages and disadvantages of each approach. We also review and discuss viscoelastic models that describe the dependence of tether formation on time, force, rate of loading, and cell activation. We close by emphasizing the need to combine experimental observations with quantitative models and computer simulations to understand how tether formation is affected by membrane tension, membrane reservoir, and interactions of the membrane with the cytoskeleton.

Specific interaction of Penetratin with cell surface partners measured with biomembrane force probe

ABSTRACTPenetratin is a Cell Penetrating Peptide able to cross the cell plasma membrane possibly bound to a cargo molecule to be delivered into the cell. The mechanism of its entry is poorly known. A key to a molecular description of this mechanism is to identify the partners of Penetratin at the cell surface during its adhesion and internalization. We used the Biomembrane Force Probe to identify the partners during the first second of adhesion of Penetratin on the cell plasma membrane. We evidenced that heparan sulfates are the first partners after contact as well as unknown partners hidden by sialic acids. Experiments of binding of Penetratin on vesicles bearing charged or sulfated lipids showed no adhesion pointing that a negatively charged partner is not enough and there is a specificity for certain chemical groups bearing the charges. A model of the measured forces of interaction enabled to determine the adhesion energy of a Penetratin with heparan sulfates on a cell to be in the range 18 to 22 kBT.