Macrophage-derived matrix metalloproteinase-2 and-9 promote the progression of cerebral aneurysms in rats

Background and Purpose-Mechanisms of initiation, progression and rupture of cerebral aneurysms have not yet been fully understood despite its clinical significance. Matrix metalloproteinases (MMPs) are a family of proteinases which are involved in the remodeling of vascular walls. In the present study, we investigated the significance of MMPs in the progression of cerebral aneurysms. Methods-Cerebral aneurysms were experimentally induced in 7-week-old male Sprague-Dawley rats. MMP-2 and MMP-9 expression was examined by immunohistochemistry and RT-PCR. Gelatinase activity in aneurysmal walls was assessed by in situ zymography. A selective inhibitor for MMP-2, -9 and -12, tolylsam, was used to examine the effect of inhibition of MMP-2 and MMP-9. Results-Macrophages infiltrated in arterial walls of experimentally induced rat cerebral aneurysms and expressed MMP-2 and -9. Macrophage infiltration and MMP expression was increased with the progression of aneurysms. Gelatinase activity attributable to MMP-2 and MMP-9 increased in arterial walls of rat cerebral aneurysms. Furthermore, tolylsam reduced the ratio of advanced aneurysms in our rat model. Conclusions-These data suggest that macrophage-derived MMP-2 and -9 may play an important role in the progression of cerebral aneurysms. The findings of this study will shed a new light into the pathogenesis of cerebral aneurysms and highlight the importance of inflammatory response causing the degeneration of extracellular matrix in the process of this disease.