Role of β1 and β3 integrins in human: Smooth muscle cell adhesion to and contraction of fibrin clots in vitro

Abstract

The degree of lumen narrowing in advanced lesions correlates poorly with the amount of intimal mass accumulated in the atherosclerotic plaque. As an alternate mechanism of stenosis, we propose that human smooth muscle cells bind to fibrin deposited in the matrix and exert contractile forces to cause a narrowing of the lumen. In the present study we demonstrated in vitro that human newborn aortic smooth muscle cell lines can contract and adhere to fibrin clots composed of either fibronectin-depleted plasma ('plasma') or recombinant fibrin. By using neutralizing antibodies and RGD peptides, we showed that members of the integrin family mediated the interaction between human newborn smooth muscle cells and fibrin. Neutralizing antibodies against the integrin αvβ3 (c7E3 Fab and LM609) did not inhibit either plasma clot contraction or recombinant fibrin clot contraction by human newborn smooth muscle cells. In contrast, antibodies against α5, β1, and α5βl inhibited contraction of clots composed of either plasma or recombinant fibrin. Anti- αvβ3, anti-αv, anti-α5, anti-β1, and anti-α5β1 antibodies inhibited human newborn smooth muscle cell adhesion to plasma clots; however, only anti-α5, anti-β1, and anti-α5β1 antibodies significantly inhibited adhesion to recombinant fibrin. While the linear RGD peptides had no effect, the cyclic peptide penRGD inhibited adhesion to plasma clots and recombinant fibrin. However, it did not block contraction of recombinant fibrin clots. These results suggest that during the interaction of human newborn smooth muscle cell lines with fibrin, α5βl plays a significant role. This interaction is of potential interest as a target for efforts to block vascular contraction.