NATIVE ATHEROSCLEROSIS AND VEIN GRAFT ARTERIALIZATION - ASSOCIATION WITH INCREASED UROKINASE RECEPTOR EXPRESSION IN-VITRO AND IN-VIVO

Interaction of proteases with cell surface receptors may modulate cell adhesion, migration, invasion, and matric degradation. Since the plas minogen activator system has been hypothesized to play a role in intim al thickening after various types of vascular injury. We first studied the expression of urokinase receptor(u-PAR) protein and mRNA by smoot h muscle cells (SMC) grown in explant cultures from normal and disease d vessels. Using equilibrium binding studies with radiolabeled I-125-l abeled single chain urokinase-type plasminogen activator (scu-PA), we determined that SMC cultured from atherosclerotic arteries expressed a higher maximal number of binding sites/cell (3.6 +/- 0.4 x 10(5) site s/cell vs. 2.1 +/- 0.3 x 10(5), +/- SEM. p < 0.05) with a similar affi nity (Kd = 1.5 +/- 0.1 vs. 1.2 +/- 0.2 nM, p = ns). However, SMC subcu ltured from diseased saphenous vein grafts expressed the highest level s of u-PAR compared to SMC from normal saphenous vein (4.8 +/- 0.6 x 1 0(5) sites/cell vs. 1.6 +/- 0.9 x 10(5). +/- SEM p <0.05). Using bindi ng studies and Northern analysis, we demonstrated a dose and time depe ndent upregulation of u-PAR protein and mRNA expression respectively i n human SMC in response to serum stimulation. Using a rabbit specific u-PAR cDNA probe, we demonstrated a similar upregulation of u-PAR mRNA both in rabbit aortic SMC in culture in response to serum stimulation and up to a 20 fold increase in u-PAR mRNA in rabbit jugular veins in response to implantation as arterial grafts in vivo. Finally, to conf irm that u-PAR mRNA is upregulated in human vessels after injury, we p erformed immunohistochemistry and in situ hybridization studies on cor onary arteries. normal saphenous veins and saphenous veins from 10 wee ks to 13 years after implantation as grafts. u-PAR mRNA was found main ly in the periadventitial microcirculation in normal veins, but was fo und to be upregulated in the neointima and media of thickened veins in both macrophages and smooth muscle cells. SMC near the internal elast ic laminae in diseased coronary arteries appeared to express increased u-PAR mRNA. These data suggest that this increased expression of u-PA R may contribute to early lesion development.