Abnormal expression of plasminogen activators in aortic aneurysmal and occlusive disease

Aortic aneurysms are characterized by the destruction of the extracellular matrix of the media, whereas occlusive disease involves excess matrix accumulation within the intima. Plasmin degrades extracellular matrix directly and indirectly by activation of latent metalloenzymes. To determine the expression of tissue- and urokinase-type plasminogen activators, immunoassay, fibrin autography, Northern analysis, and immunohistochemistry were performed on specimens of aneurysmal (n = 12), occlusive (n = 8), and healthy (n = 6) aorta.

Immunoassay of tissue-type plasminogen activator revealed 8.7 +/- 0.9 ng tissue-type plasminogen activator/mg extracted protein in aneurysmal aorta, 5.7 +/- 0.3 ng/mg in normal aorta, and 2.5 +/- 0.3 ng/mg in occlusive aorta (p < 0.05 for comparisons between all groups). No urokinase-type plasminogen activator antigen was detected by urokinase-type plasminogen activator immunoassay. Fibrin autography exhibited lytic activity at 64 kDa and 54 kDa attributable to tissue-type plasminogen activator and urokinase-type plasminogen activator. The vast majority of fibrinolysis was secondary to free tissue-type plasminogen activator and was greatest in aneurysmal disease and least in occlusive disease. There was only a small amount of lysis secondary to urokinase-type plasminogen activator. Expression of tissue-type plasminogen activator and urokinase-type plasminogen activators mRNA was comparable in aneurysmal and occlusive aortas. In contrast to occlusive disease, aneurysms had an inflammatory cell infiltrate characterized by the expression of urokinase-type plasminogen activator by specific mononuclear cells. Tissue-type plasminogen activator expression was evident in the intima of normal and diseased aorta and in the media of diseased aorta.

Differential expression of plasminogen activators within the arterial wall may contribute to the unique pathogenesis of aneurysmal and occlusive aortic disease.