Physical Properties of Fibrinogen Substrates Control Integrin Mediated Cell Adhesion

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The physical properties of substrates are known to control cell adhesion via integrin-mediated signaling. Recently, we have shown that binding of fibrinogen to the surface of fibrin gel prevents integrin αMβ2-mediated leukocyte adhesion by creating an anti-adhesive layer. Furthermore, fibrinogen immobilized on various surfaces at high density supports weak cell adhesion whereas at low density it is highly adhesive.To gain an understanding of the mechanism underlying differential cell adhesion, we extended the cell adhesion assays to platelets carrying integrin αIIbβ3. The results showed a similar behavior indicating that the process is independent of the type of integrins. In order to quantify the adhesion forces, we applied single cell force spectroscopy (SCFS). In this assay, a single cell is attached to a tipless cantilever of an atomic force microscope (AFM) and force-distance curves for different surfaces are acquired. For cells carrying αMβ2-integrins we found significant lower adhesion forces for high- compared to low-density fibrinogen substrates.Furthermore, we analyzed the adhesive behavior of fibrinogen surfaces using force spectroscopy with a silicon nitride AFM tip. These experiments, unrelated to the cells and integrins, show similar behaviors as the cell adhesion assays. AFM images of the different substrates indicate that fibrinogen deposition at high density results in an aggregated multilayered material characterized by low adhesion forces. However, low-density fibrinogen produces a single layer in which molecules are directly attached to the solid surface resulting in higher adhesion forces.The data suggest that deposition of a multilayered fibrinogen matrix prevents stable cell adhesion by modifying the physical properties of surfaces resulting in reduced force generation with implications for hemostasis and biomaterial applications.