Early MT-1 MMP expression following elastase exposure is associated with increased cleaved MMP-2 activity in experimental rodent aortic aneurysms

The objective of this study was to determine the significance of membrane type 1 matrix metalloproteinase (MT1-MMP) activation of MMP-2 in experimental abdominal aortic aneurysms. Rat aortas were perfused with either saline as a control or elastase, and harvested on 2, 4, or 7 days after perfusion (n=5 per treatment group/day). Aortic MT1-MMP and MMP-2 expression and protein were determined by real time polymerase chain reaction and Western blotting, respectively. Aortic explants were used to measure MMP-2 activity by zymography. Rat aortic smooth muscle cells in vitro were exposed to increasing doses of elastase and analyzed for MT-1 MMP expression. Aneurysms formed in 80% of the elastase-perfused aortas at 7 days, whereas none formed in the saline-perfused aortas. Significantly increased MT1-MMP expression was observed only on day 4, when levels were 6.5-fold higher in elastase-perfused aortas compared with saline-perfused aortas (P < .01). By day 7, MT1-MMP protein was present only in the elastase-perfused aortas (P=.02). By immunohistochemistry, MT1-MMP was detectable only in the elastase-perfused group at day 7. Cleaved MMP-2 activity (P=.045) was increased in elastase-perfused aortas compared with saline perfused aortas at day 7. In rat aortic smooth muscle cells, MT-1 MMP expression increased in response to elastase (P=.02). The rodent aortic aneurysm model exhibits upregulation of MT1-MMP expression and protein with subsequent increased conversion of MMP-2 from the latent to the cleaved form.