title: Biomechanics of P-selectin PSGL-1 bonds: shear threshold and integrin-independent cell adhesion.
abstract: Platelet-leukocyte adhesion may contribute to thrombosis and inflammation. We examined the heterotypic interaction between unactivated neutrophils and either thrombin receptor activating peptide (TRAP)-stimulated platelets or P-selectin-bearing beads (Ps-beads) in suspension. Cone-plate viscometers were used to apply controlled shear rates from 14 to 3000/s. Platelet-neutrophil and bead-neutrophil adhesion analysis was performed using both flow cytometry and high-speed videomicroscopy. We observed that although blocking antibodies against either P-selectin or P-selectin glycoprotein ligand-1 (PSGL-1) alone inhibited platelet-neutrophil adhesion by approximately 60% at 140/s, these reagents completely blocked adhesion at 3000/s. Anti-Mac-1 alone did not alter platelet-neutrophil adhesion rates at any shear rate, though in synergy with selectin antagonists it abrogated cell binding. Unstimulated neutrophils avidly bound Ps-beads and activated platelets in an integrin-independent manner, suggesting that purely selectin-dependent cell adhesion is possible. In support of this, antagonists against P-selectin or PSGL-1 caused dissociation of previously formed platelet-neutrophil and Ps-bead neutrophil aggregates under shear in a variety of experimental systems, including in assays performed with whole blood. In studies where medium viscosity and shear rate were varied, a shear threshold for P-selectin PSGL-1 binding was also noted at shear rates <100/s when Ps-beads collided with isolated neutrophils. Results are discussed in light of biophysical computations that characterize the collision between unequal-size particles in linear shear flow. Overall, our studies reveal an integrin-independent regime for cell adhesion and weak shear threshold for P-selectin PSGL-1 interactions that may be physiologically relevant.
authors.affiliation: Department of Chemical and Biological Engineering, State University of New York, Buffalo, New York, 14260, USA.
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Xiao
authors.forename: Harry L
authors.initials: HL
authors.lastname: Goldsmith
authors.forename: Fiona A
authors.initials: FA
authors.lastname: McIntosh
authors.forename: Harish
authors.initials: H
authors.lastname: Shankaran
authors.forename: Sriram
authors.initials: S
authors.lastname: Neelamegham
mesh_terms: D001665:Binding Sites; D001696:Biomechanical Phenomena / Q000379:methods; D001792:Blood Platelets / Q000502:physiology*; D048429:Cell Size; D002478:Cells, Cultured; D004056:Differential Threshold / Q000502:physiology; D006801:Humans; D016023:Integrins / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D019007:P-Selectin / Q000378:metabolism*; D010973:Platelet Adhesiveness / Q000502:physiology*; D011485:Protein Binding; D033081:Shear Strength
chemical_list: D016023:Integrins; D008562:Membrane Glycoproteins; D019007:P-Selectin; C084882:P-selectin ligand protein