Role of ß1 and ß3 Integrins in Human Smooth Muscle Cell Adhesion to and Contraction of Fibrin Clots In Vitro

From the Departments of Pathology (K.O.Y., C.M.G., S.M.S.) and Molecular and Cellular Biology (K.O.Y.), University of Washington, Seattle, and Departments of Chemistry (M.M.R., S.T.L.) and Pathology and Laboratory Medicine (S.T.L.), University of North Carolina at Chapel Hill.

Correspondence to Karen O Yee, University of Washington, Box 357335, Seattle, WA 98195. E-mail y66409d{at}u.washington.edu

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 vß3 (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 5, ß1, and 5ß1 inhibited contraction of clots composed of either plasma or recombinant fibrin. Anti-vß3, anti-v, anti-5, anti-ß1, and anti-5ß1 antibodies inhibited human newborn smooth muscle cell adhesion to plasma clots; however, only anti-5, anti-ß1, and anti-5ß1 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, 5ß1 plays a significant role. This interaction is of potential interest as a target for efforts to block vascular contraction.

Key Words: atherosclerosis • remodeling • stenosis • thrombosis

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