Enhanced abdominal aortic aneurysm (AAA) formation in timp-1-deficient (timp-1-/-) mice after local elastase perfusion

Abstract

Background: Matrix metalloproteinases (MMPs) are known elastolytic mediators of abdominal aortic aneurysm (AAA) degeneration, and their activity is tightly regulated by the presence of tissue inhibitors of MMPs (TIMPs). TIMPs act as a negative regulator of MMPs. Imbalances in this system may be instrumental in compromising arterial wall integrity. The aim of this study is to show that, in an elastase-induced murine model of aneurysm formation, TIMP-1 has a protective effect. Methods: 24 wild-type (TIMP-1+/+) and 22 knockout (TIMP-1−/−) mice underwent laparotomy and isolation of the infrarenal aorta. A polyethylene catheter was inserted into the aorta and dilute pancreatic elastase (0.39 Units/ml) was infused over 5 minutes using a perfusion pump. Pre- and postperfusion maximal aortic diameters were obtained in triplicate for each animal using NIH Image. Final aortic measurements were obtained 14 days later, prior to perfusion fixation with 10% buffered-formalin. Aortic specimens were sectioned and stained with Verhoeff-van Giessen and H&E. Statistical analysis was performed using the Student’s t-test; data are presented as mean ± SEM. Results: Mean aortic diameter change was not significantly different between groups immediately following perfusion: 84 ± 4% (TIMP-1+/+) vs. 92 ± 5% (TIMP-1−/−). However, 14 days later, TIMP-1−/− mice showed a two-fold increase in maximal aortic diameter relative to postperfusion measurements, as compared to TIMP-1+/+ mice (108 ± 13% vs. 54 ± 9%, p = 0.001). A significant difference in mean aortic diameter between TIMP-1+/+ and TIMP-1−/− mice was also observed when comparing size change from preperfusion to time of sacrifice (p = 0.001). Histologically, TIMP-1−/− mice had a pronounced inflammatory infiltrate and extensive elastin fragmentation, whereas TIMP-1+/+ mice maintained an intact elastic lamellar structure and absence of inflammatory cells. Conclusions: TIMP-1−/− mice developed significantly larger aneurysms compared to TIMP-1+/+ mice. This study demonstrates the protective effects of TIMP-1 by inhibiting the effects of MMPs in an experimental AAA model and may provide a means for pharmacologically controlling the progressive growth in aneurysms.