Clinical studies have indicated that high plasma levels of
fibrinogen, or decreased fibrinolytic potential, are conducive to an increased risk of
cardiovascular disease. Other investigations have shown that insoluble
fibrin promotes atherosclerotic lesion formation by affecting smooth muscle cell proliferation,
collagen deposition, and
cholesterol accumulation. To directly assess the physiological impact of an imbalanced fibrinolytic system on both early and late stages of this disease, mice deficient for
plasminogen activator inhibitor-1 (PAI-1(-/-)) were used in a model of
vascular injury/repair, and the resulting phenotype compared to that of wild-type (WT) mice. A
copper-induced arterial injury was found to generate a lesion with characteristics similar to many of the clinical features of
atherosclerosis.
Fibrin deposition in the injured arterial wall at early (7 days) and late (21 days) times after
copper cuff placement was prevalent in WT mice, but was greatly diminished in PAI-1(-/-) mice. A multilayered
neointima with enhanced
collagen deposition was evident at day 21 in WT mice. In contrast, only diffuse
fibrin was identified in the adventitial compartments of arteries from PAI-1(-/-) mice, with no evidence of a
neointima. Neovascularization was observed in the adventitia and was more extensive in WT arteries, relative to PAI-1(-/-) arteries. Additionally, enhanced
PAI-1 expression and fat deposition were seen only in the arterial walls of WT mice. The results of this study emphasize the involvement of the fibrinolytic system in vascular repair processes after injury and indicate that alterations in the fibrinolytic balance in the vessel wall have a profound effect on the development and progression of vascular lesion formation.