EXPRESSION OF FIBRINOLYTIC GENES IN ATHEROSCLEROTIC ABDOMINAL AORTIC-ANEURYSM WALL - A POSSIBLE MECHANISM FOR ANEURYSM EXPANSION

Expansion of atherosclerotic abdominal aortic aneurysm (AAA) has been attributed to remodeling of the extracellular matrix by active proteol ysis. We used in situ hybridization to analyze the expression of fibri nolytic genes in aneurysm wall from eight AAA patients. All specimens exhibited specific areas of inflammatory infiltrates with macrophageli ke cells expressing urokinase-type plasminogen activator (u-PA) and ti ssue-type PA (t-PA) mRNA, Type 1 PA inhibitor (PAI-1) mRNA was express ed at the base of the necrotic atheroma of all specimens and also with in some of the inflammatory infiltrates where it frequently colocalize d in regions containing u-PA and t-PA mRNA expressing cells, However, in these areas, the cellular distribution of the transcripts for t-PA and u-PA extended far beyond the areas of PAI-1 expression, These obse rvations suggest a local ongoing proteolytic process, one which is onl y partially counteracted by the more restricted expression of PAI-1 mR NA, An abundance of capillaries was also obvious in all inflammatory i nfiltrates and may reflect local angiogenesis in response to active pe ricellular fibrinolysis. The increased fibrinolytic capacity in AAA wa ll may promote angiogenesis and contribute to local proteolytic degrad ation of the aortic wall leading to physical weakening and active expa nsion of the aneurysm.