Critical Roles of Macrophages in the Formation of Intracranial Aneurysm

abnormal vascular remodeling triggered by hemodynamic stresses and inflammation is believed to be a key process in the pathophysiology of intracranial aneurysms. Numerous studies have shown infiltration of inflammatory cells, especially macrophages, into intracranial aneurysmal walls in humans. Using a mouse model of intracranial aneurysms, we tested whether macrophages play critical roles in the formation of intracranial aneurysms. intracranial aneurysms were induced in adult male mice using a combination of a single injection of elastase into the cerebrospinal fluid and angiotensin II-induced hypertension. Aneurysm formation was assessed 3 weeks later. Roles of macrophages were assessed using clodronate liposome-induced macrophage depletion. In addition, the incidence of aneurysms was assessed in mice lacking monocyte chemotactic protein-1 (CCL2) and mice lacking matrix metalloproteinase-12 (macrophage elastase). intracranial aneurysms in this model showed leukocyte infiltration into the aneurysmal wall, the majority of the leukocytes being macrophages. Mice with macrophage depletion had a significantly reduced incidence of aneurysms compared with control mice (1 of 10 versus 6 of 10; P