P Jeanene Willcox | PubMed Health

PubMed2005

Dynamic heterodimer-functionalized surfaces for endothelial cell adhesion.

The functionalization of hydrogels for receptor-mediated cell adhesion is one approach for targeted cell and tissue engineering applications. In this study, polyacrylamide gel surfaces were functionalized with specific cell adhesion ligands via the self-assembly of a peptide-based heterodimer. The system was comprised of a cysteine-terminated monomer, A (MW approximately 5400), grafted to the polyacrylamide gels and a complementary ligand presenting monomer, B(X) (MW approximately 5800) that was designed to heterodimerize with A. Two ligand presenting monomers were synthesized: one presenting the RGDS ligand, B(D), for receptor-mediated cell adhesion, and the other, a control monomer presenting the nonadhesive RGES ligand, B(E). Assembly of the peptide pair A-B(X) by association of the monomers into a coiled coil was verified by circular dichroism in solution. Binding studies were conducted to determine the dissociation constant of the pair A-B(X), which was found to be K(D) approximately 10(-8) m. Polyacrylamide gels functionalized with A-B(X) heterodimers were evaluated for cell adhesion using bovine aortic endothelial cells (BAECs). Endothelial cells cultured on the A-B(D) functionalized surfaces demonstrated typical cell morphologies and expected spreading behavior as a function of the density of RGDS ligand, calculated as the amount of B(D) associated with grafted A on the surface of the gels. In contrast, A-B(E) linked surfaces supported no cell adhesion. The adhesion of the substrate was dynamically altered through the reassembly of A-B(X) dimers as B(D) molecules in the solution replaced B(E) molecules at the substrate. The molecular constructs described here demonstrate the potential to design a broad family of switchable peptides that impart the dynamic control of biofunctionality at an interface, which would be useful for precise manipulation of cell physiology.

Adsorption↗

PubMed2003

Interplay between rolling and firm adhesion elucidated with a cell-free system engineered with two distinct receptor-ligand pairs.

The firm arrest of leukocytes to the endothelium during inflammation is known to be mediated by endothelial intercellular adhesion molecules (ICAMs) binding to activated integrins displayed on leukocyte surface. Selectin-ligand interactions, which mediate rolling, are believed to be important for facilitating firm adhesion, either by activating integrins or by facilitating the transition to firm adhesion by making it easier for integrins to bind. Although leukocytes employ two distinct adhesion molecules that mediate different states of adhesion, the fundamental biophysical mechanisms by which two pairs of adhesion molecules facilitate cell adhesion is not well understood. In this work, we attempt to understand the interaction between two molecular systems using a cell-free system in which polystyrene microspheres functionalized with the selectin ligand, sialyl Lewis(X) (sLe(X)), and an antibody against ICAM-1, aICAM-1, are perfused over P-selectin/ICAM-1 coated surfaces in a parallel plate flow chamber. Separately, sLe(X)/P-selectin interactions support rolling and aICAM-1/ICAM-1 interactions mediate firm adhesion. Our results show that sLe(X)/aICAM-1 microspheres will firmly adhere to P-selectin/ICAM-1 coated surfaces, and that the extent of firm adhesion of microspheres is dependent on wall shear stress within the flow chamber, sLe(X)/aICAM-1 microsphere site density, and P-selectin/ICAM-1 surface density ratio. We show that P-selectin's interaction with sLe(X) mechanistically facilitates firm adhesion mediated by antibody binding to ICAM-1: the extent of firm adhesion for the same concentration of aICAM-1/ICAM-1 interaction is greater when sLe(X)/P-selectin interactions are present. aICAM-1/ICAM-1 interactions also stabilize rolling by increasing pause times and decreasing average rolling velocities. Although aICAM-1 is a surrogate for beta(2)-integrin, the kinetics of association between aICAM-1 and ICAM-1 is within a factor of 1.5 of activated integrin binding ICAM-1, suggesting the findings from this model system may be insightful to the mechanism of leukocyte firm adhesion. In particular, these experimental results show how two molecule systems can interact to produce an effect not achievable by either system alone, a fundamental mechanism that may pervade leukocyte adhesion biology.

Antigen-Antibody Complex↗