Neutrophil rolling at high shear: Flattening, catch bond behavior, tethers and slings

Abstract

Neutrophil recruitment to sites of inflammation involves neutrophil rolling along the inflamed endothelium in the presence of shear stress imposed by blood flow. Neutrophil rolling in post-capillary venules in vivo is primarily mediated by P-selectin on the endothelium binding to P-selectin glycoprotein ligand-1 (PSGL-1) constitutively expressed on neutrophils. Blood flow exerts a hydrodynamic drag on the rolling neutrophil which is partially or fully balanced by the adhesive forces generated in the P-selectin-PSGL-1 bonds. Rolling is the result of rapid formation and dissociation of P-selectin-PSGL-1 bonds at the center and rear of the rolling cell, respectively. Neutrophils roll stably on P-selectin in post-capillary venules in vivo and flow chambers in vitro at wall shear stresses greater than 6 dyn cm−2. However, the mechanisms that enable neutrophils to roll at such high shear stress are not completely understood. In vitro and in vivo studies have led to the discovery of four potential mechanisms, viz. cell flattening, catch bond behavior, membrane tethers, and slings. Rolling neutrophils undergo flattening at high shear stress, which not only increases the size of the cell footprint but also reduces the hydrodynamic drag experienced by the rolling cell. P-selectin-PSGL-1 bonds behave as catch bonds at small detachment forces and thus become stronger with increasing force. Neutrophils rolling at high shear stress form membrane tethers which can be longer than the cell diameter and promote the survival of P-selectin-PSGL-1 bonds. Finally, neutrophils rolling at high shear stress form slings, which act as cell autonomous adhesive substrates and support step-wise peeling. Tethers and slings act together and contribute to the forces balancing the hydrodynamic drag. How the synergy between the four mechanisms leads to stable rolling at high shear stress is an area that needs further investigation.

Not just a marker: CD34 on human hematopoietic stem/progenitor cells dominates vascular selectin binding along with CD44

“…18,59,61,62 Interestingly, many studies suggest that microvilli protrusions are critical for mediating interactions between KG1a cells in flow and selectins (or endothelial cells). The microvilli undergo extensions and may form tethers, [63][64][65][66][67][68][69] so if these structures are eliminated by the knockdown of CD34, this would likely explain the effect on cell rolling. Furthermore, these data are in agreement with previous flow-based studies that showed that CD34 isolated from lysates of KG1a cells bound CHO-E cells 17 and that mouse thymocytes ectopically expressing CD34 specifically bound to human BM endothelial cells where control thymocytes not expressing CD34 did not.…”

The class II PI 3-kinase, PI3KC2α, links platelet internal membrane structure to shear-dependent adhesive function

“…Furthermore, a growing body of evidence has accumulated from the study of shear-dependent adhesion of other haematopoietic cells, particularly neutrophils 40,41 , that dynamic changes in the plasma membrane, some of which involves membrane reserves, have a profound impact on cell adhesion.…”

Mapping Cell Surface Adhesion by Rotation Tracking and Adhesion Footprinting

“…At the molecular level, this adhesion is mediated by catch-bond-like interactions 12,13 between P- 14 and E-selectins 15 expressed on endothelial cells lining blood vessels and P-selectin glycoprotein ligand-1 (PSGL-1) found at microvilli tips of leukocytes 16 . Despite our understanding of the individual components, how the molecular details of adhesion bonds scale to cell-surface adhesion and rolling behavior remains poorly understood 2,17,18 . Here, we developed a label-free method that maps the functional adhesion sites and strengths on a cell surface as it rolls across a surface coated uniformly with adhesion receptors.…”