Macrophage-derived matrix metalloproteinase-1 enhances aortic aneurysm formation in transgenic rabbits

Increased expression of matrix metalloproteinase-1 (MMP-1) has been observed in the lesions of atherosclerosis and aneurysms; however, it is not fully understood whether macrophage-derived MMP-1 affects these diseases. To investigate whether macrophage-derived MMP-1 participates in the development of vascular diseases, we generated transgenic (Tg) rabbits expressing human MMP-1 in the monocyte/macrophage lineage under the control of the human scavenger receptor enhancer/promoter. Tg rabbits exhibited no visible abnormalities throughout their bodies. Western blotting analysis revealed that the amount of MMP-1 proteins in the conditioned media secreted from peritoneal macrophages of Tg rabbits was up to 3-fold higher than that in non-Tg rabbits. For the first experiment, Tg and non-Tg rabbits were fed a cholesterol diet for 16 weeks, and aortic and coronary atherosclerosis were evaluated. The gross lesion area of aortic atherosclerosis in Tg rabbits was not significantly different from that in non-Tg rabbits, but Tg rabbits had marked destruction of the medial elastic lamina of the aortic lesions on microscopic examination. For the second experiment, we generated aortic aneurysms by incubating with elastase. Compared with non-Tg rabbits, Tg rabbits exhibited a significantly greater aortic dilation. Increased macrophage-derived MMP-1 led to increased medial destruction in both aortic atherosclerosis and aneurysms. These results demonstrate that MMP-1 plays a different role in the pathogenesis of atherosclerosis and aneurysms.