Abstract 203: Smooth Muscle Cells from Abdominal Aortic Aneurysms are Unique and Can Independently and Synergistically Degrade Insoluble Elastin

Abstract

Background The purpose of this study was to further elucidate the role of the vascular smooth muscle cell (SMC) in abdominal aortic aneurysm (AAA) disease. We hypothesized that that AAA-SMC are unique and actively participate in the process of degrading the aortic matrix. Methods and Results Whole-genome expression profiles of SMC from AAA, normal abdominal aorta (NAA) and carotid endarterectomy (CEA) were compared. We quantified elastolytic activity by culturing SMC in [3H]elastin-coated plates and measuring solubilized tritium in the media after 7 days. MMP-2 and MMP-9 production was assessed using real-time PCR, zymography and western blotting. Each SMC type exhibited a unique gene expression pattern. AAA-SMC had greater elastolytic activity than NAA (+68%, p<0.001) and CEA-SMC (+45%, p<0.001). Zymography showed an increase of active-MMP-2 (62kD) in media from AAA-SMC. AAA-SMC demonstrated 2-fold greater expression of MMP-2 mRNA (p<0.05) and 7.3-fold greater MMP-9 expression (p<0.01) than NAA-SMC. Culture with U937 monocytes caused a synergistic increase of elastolysis by AAA-SMC (41%, p<0.001) but not NAA or CEA (p=0.99). Co-culture with U937 caused a large increase in MMP-9 mRNA in AAA and NAA-SMC (p<0.001). MMP-2 mRNA expression was not affected. Western blots of culture media showed a 4-fold increase of MMP-9 (92kD) protein in AAA-SMC/U937 compared to NAA-SMC/U937 (p<0.001) and a large increase in active-MMP2 (62kD) which was less apparent in NAA/U937 media (p<0.01). Conclusions AAA-SMC have a unique gene expression profile and a pro-elastolytic phenotype that is augmented by macrophages. This may occur via a failure of post-transcriptional control of MMP-9 synthesis.