Single-Molecule Imaging and Microfluidic Platform Reveal Molecular Mechanisms of Leukemic Cell Rolling

Abstract

Hematopoietic stem/progenitor cell (HSPC) homing is initiated by tethering and rolling of the cells on endothelium through selectin-ligand interactions. Although multiple factors that affect the rolling behaviour of the cells have been identified, molecular mechanisms that enable slow and stable cell rolling remain elusive. Here, using a microfluidics-based single-molecule live cell fluorescence imaging, we reveal that unique spatiotemporal dynamics of selectin ligands on the membrane tethers and slings, which are distinct from that on the cell body, play an essential role in the rolling of the cell. Our results suggest that the spatial confinement of the selectin ligands to the tethers and slings together with the rapid scanning of a large area by the selectin ligands increases the efficiency of selectinligand interactions during cell rolling, resulting in slow and stable rolling of the cell on the selectins. Our findings provide novel insights and contribute significantly to the molecularlevel understanding of the initial and essential step of the homing.

The role of galectins in mediating the adhesion of circulating cells to vascular endothelium

“…SLe A is predominantly found on CTCs of epithelial origin (42), whereas sLe X expression is observed on a variety of circulating cells, including CTCs (43), granulocytes (44, 45), lymphocytes (46,47), monocytes (46), dendritic cells (48), and hematopoietic stem cells (49). SLe X and sLe A can interact with E-selectin to mediate the initial first step of vascular cell adhesion, "tethering and rolling," for circulating cells on the vascular endothelium that prompts firm adhesion and eventually transendothelial migration (2,(50)(51)(52)(53)(54). Similarly, SLe X -bearing surface glycoproteins, primarily P-selectin glycoprotein ligand-1 (PSGL-1) on leukocytes, for example, are crucial for vascular cell adhesion through their interaction with Pselectin, requiring tyrosine sulfation adjacent to these glycoproteins at the PSGL-1 terminus for effective binding (30,55,56).…”