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 SS5. Smooth Muscle Cells from Abdominal Aortic Aneurysms Are Unique and Can Independently and Synergistically Degrade Insoluble Elastin

Nathan D. Airhart, Bernard Brownstein, William Schierding, Perren Cobb, Batool Arif, Terri Ennis, Robert Thompson, John A. Curci
Surgery, Washington University School of Medicine, St Louis, MO
 
SVS Foundation Resident Research Prize Paper

OBJECTIVES: The purpose of this study was to further elucidate the role of the vascular smooth muscle cell (SMC) in abdominal aortic aneurysm (AAA) disease. Our hypothesis is that AAA-SMC are unique and actively participate in the process of degrading the aortic matrix.
 
METHODS: Using microarray, we compared whole-genome expression profiles of SMC from AAA, normal abdominal aorta (NAA) and carotid endarterectomy (CEA). 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.
 
RESULTS: Unique gene expression patterns were observed for each SMC type. Under basal conditions, AAA-SMC had much greater elastolytic activity than NAA (+68%, p<0.001) and CEA-SMC (+45%, p<0.001). Zymography showed a relative 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 activated U937 monocytes led to a synergistic increase in elastolytic activity by AAA-SMC (41%, p<0.001). This effect was not apparent in NAA or CEA co-cultures (p=0.99). Co-culture with U937 led to a large increase in MMP-9 mRNA in both AAA and NAA-SMC (p<0.001). MMP-2 mRNA expression was not affected. Western blots of conditioned media showed increased MMP-9 (92kD) protein secretion by AAA-SMC/U937 cultures which was approximately 4-fold greater than NAA-SMC / U937 (p<0.001). AAA-SMC/U937 co-cultures also exhibited a large increase in active-MMP2 (62kD) in conditioned media, an effect that was much less apparent in NAA/U937 media (p<0.01).
 
CONCLUSIONS: AAA-SMC exhibit a unique gene expression pattern and have a pro-elastolytic phenotype that is augmented by macrophages. This may occur via a failure of post-transcriptional control of MMP-9 protein synthesis, leading to increased production and activation of elastolytic MMPs.
 
AUTHOR DISCLOSURES: N. D. Airhart: Nothing to disclose; B. Arif: Nothing to disclose; B. Brownstein: Nothing to disclose; P. Cobb: Nothing to disclose; J. A. Curci: Nothing to disclose; T. Ennis: Nothing to disclose; W. Schierding: Nothing to disclose; R. Thompson: Nothing to disclose.
 
Posted April 2013

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