Summary
Urokinase plasminogen activator (uPA) is strongly expressed in atherosclerotic lesions,
but the overall effect of the protease on plaque composition and growth remains controversial.
In the present study, apolipoprotein E-deficient (apoE-/-) mice were intercrossed with mice which were lacking the uPA gene (doubleknockout;
DKO). In ferric chloride-induced carotid artery lesions in chow-fed mice, uPA deficiency
increased neointimal size (P=0.015) and luminal stenosis (P=0.014), while reducing
media thickness (P=0.002). A lack of uPA also increased the size of and the luminal
obstruction from atherosclerotic plaques at the coronary and brachiocephalic arteries
of apoE-/- mice. Plaques were characterised by a higher fibrinogen/fibrin content and a decrease
in cellularity and collagen content. When apoE-/- and DKO mice were analysed as a single group, a significant correlation was found
between the α-actin (smooth muscle cell) and collagen content of atherosclerotic lesions
(r = 0.554; P<0.05), and a negative correlation existed between the α-actin and fibrin/fibrinogen
immunopositive area (r = –0.791; P<0.001). Further analysis of brachiocephalic atherosclerosis,
a predilection site for plaque rupture in the apoE-/- mouse, revealed signs of plaque vulnerability, including a reduced cap-to-intima
ratio (0.21 ± 0.04 vs. 0.37 ± 0.05; P=0.03) and more frequent detection of intraplaque
haemorrhage (56% vs. 13%; P<0.01) and buried fibrous caps (1.8 ± 0.5 vs. 0.5 ± 0.2;
P=0.02) in DKO compared to apoE-/- mice. These results indicate that, at least at (patho)physiologic concentrations,
uPA is essential for maintaining the cellularity and collagen content and, possibly,
the stability of lesions, both by preventing excessive intramural fibrin accumulation
and by facilitating cell migration and invasion.
Keywords
Urokinase / receptor - arterial thrombosis - atherosclerosis - restenosis - animal
models