Regulation by Fibrinogen and Its Products of Intercellular Adhesion Molecule-1 Expression in Human Saphenous Vein Endothelial Cells

Abstract

Abstract —It has been reported that fibrinogen may act as a bridging ligand, binding to intercellular adhesion molecule-1 (ICAM-1) on human umbilical vein endothelial cells and to Mac-1 on THP-1 cells (a monocytic cell line) to increase adhesion. In this study, we investigated whether fibrinogen altered the expression of ICAM-1 and, thus, increased the adhesion of THP-1 cells to cultured human saphenous vein endothelial cells (HSVECs). Incubation of HSVECs with 0.3 to 4 μmol/L fibrinogen caused a time- and concentration-dependent increase in ICAM-1, as determined by ELISA. The 4- to 5-fold increase in ICAM-1 protein concentration in HSVECs stimulated by 4 μmol/L fibrinogen for 6 hours was concomitant with a 4- to 5-fold increase in ICAM-1 mRNA. This fibrinogen-stimulated ICAM-1 upregulation was associated with a 2-fold increase in THP-1 cell adhesion to HSVECs. The fibrinogen-derived peptide Bβ15-42 bound to HSVECs ( K d 0.18 μmol/L). Preincubation of HSVECs with Bβ15-42, a neutralizing antibody to urokinase plasminogen activator (uPA), or the F(ab) 1 fragment of a monoclonal antibody to vascular endothelial cadherin significantly attenuated the increase in ICAM-1 stimulated by fibrinogen. Capillary electrophoretic analysis indicated that anti-uPA prevented the release of any fibrinopeptide B (Bβ1-14) in cultures of HSVECs incubated with 4 μmol/L fibrinogen for 6 hours. Moreover, incubation of HSVECs with either fibrin monomer (1 μmol/L) or monoclonal antibodies to vascular endothelial cadherin (25 μg/mL) increased ICAM-1 protein concentration 3- to 4-fold. These findings indicate that cleavage of fibrinopeptide B from fibrinogen by endothelial uPA permits the exposed Bβ15-42 sequence of fibrinogen to bind to vascular endothelial cadherin on HSVECs and to upregulate the expression of ICAM-1.