Kinetic study of E-selectin-mediated adhesion under flow
Wayman, Annica M.
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During inflammation and thrombosis, leukocytes tether to and roll on vascular surfaces and platelets through selectin molecules under shear flow. This selectin family of cell adhesion molecules includes P-, E-, and L-selectin. The association and dissociation of two or more selectin-mediated bonds under mechanical load produce the rolling motion of the leukocytes. Although much has been uncovered about the properties of selectins, the complete story of the selectin-mediated adhesion process is yet to be told. The goal of this research is to gain a more quantitative understanding of this receptor-ligand binding through the study of the dissociation kinetics of E-selectin-mediated adhesion using flow chamber techniques. From transient tethering experiments, the dissociation rate of E-selectin-mediated adhesion was found to have a triphasic shear dependence at low shear stresses, where the bond transitioned from a slip to a catch then again to a slip bond. This trend was further supported by observations of the average rolling velocity of cells adhering to E-selectin at various shear stresses. A triphasic force dependence of the rolling velocity was revealed that showed that regions of increasing rolling velocity corresponded to the slip bond regime where tether lifetime decreased with increasing shear stress. Decreasing rolling velocity coincided with the catch bond regime, a regime of prolonged tether lifetime with increasing shear stress. An invertible flow chamber was used in hopes of directly quantifying the dissociation rate of rollingly adherent cells on E-selectin to compare it to the dissociation rate data obtained through transient tethering experiments. However, tether formation, which relates to the association rate, and its role in the stability of rolling seemed to be a key factor in the dissociation rate of rollingly adherent cells over the low shear stress range. Overall, these results provide supporting evidence of a shear threshold for E-selectin as well as data to suggest that tether formation, in coordination with off-rate, determine the rolling velocity behavior of cells on E-selectin substrates.