INCREASED SYNTHESIS OF MATRIX METALLOPROTEINASES BY AORTIC SMOOTH-MUSCLE CELLS IS IMPLICATED IN THE ETIOPATHOGENESIS OF ABDOMINAL AORTIC-ANEURYSMS

Purpose: The objective of this study was to identify the metalloprotei nases elaborated by medial smooth muscle cells (SMCs) isolated from ab dominal aortic aneurysm (AAA) and control arterial tissues and to asce rtain if the levels produced by AAA SMCs were elevated. Methods: SMC m onolayers cultured from the outgrowth cells of tunica media explants w ere established, and their identity was determined by fluorescent micr oscopy by using a fluorescein isothiocyanate conjugated anti-SMC alpha -actin antibody. Matrix metalloproteinases (MMPs) produced by SMC mono layers in serum-free culture were examined by gelatin zymography and W estern blotting with monoclonal antibodies to MMP-2, 3, and 9. Results : Serum-free media from AAA SMCs contained metal-dependent elastolytic activity that cleaved the synthetic substrate succinyl trialanyl 4-ni troanilide (pH optima 7.2) and also C-14-insoluble elastin. The level of proteolytic activity found in these cultures was significantly grea ter than from control SMC media. Zymography established that AAA SMC m edia samples contained metal-dependent gelatinases of 50 to 64 and 92 kDa, which were identified respectively as MMP-2 and 9 by Western blot ting by using monoclonal antibodies to these proteases. Conclusion: Me dial SMCs isolated from AAA tissue produce significantly higher levels of MMP-9 and 2 than SMCs from control arterial tissues. These protein ases have the capacity to degrade elastin and a range of extracellular matrix proteins. From these data, we suggest SMCs may be involved in the abnormal degradation of the aortic wall in AAA through the excessi ve metalloproteinase activity produced by SMCs.