Adventitial recruitment of Lyve-1^- macrophages drives aortic aneurysm in an angiotensin-2-based murine model

Objective: Aortic macrophage accumulation is characteristic of the pathogenesis of abdominal aortic aneurysm (AAA) but the mechanisms of macrophage accumulation and their phenotype are poorly understood. Lymphatic vessel endothelial receptor-1 (Lyve-1(+)) resident aortic macrophages independently self-renew and are functionally distinct from monocyte-derived macrophages recruited during inflammation. We hypothesized that Lyve-1(+) and Lyve-1-macrophages differentially contribute to aortic aneurysm. Approach and results: Angiotensin-2 and beta-aminopropionitrile (AT2/BAPN) were administered to induce AAA in C57BL/6J mice. Using immunohistochemistry (IHC), we demonstrated primarily adventitial accumulation of aortic macrophages, and in association with areas of elastin fragmentation and aortic dissection. Compared with controls, AAA was associated with a relative percent depletion of Lyve-1(+) resident aortic macrophages and accumulation of Lyve-1-macrophages. Using CD45.1/CD45.2 parabiosis, we demonstrated aortic macrophage recruitment in AAA. Depletion of aortic macrophages in CCR2(-/-) mice was associated with reduced aortic dilatation indicating the functional role of recruitment from the bone marrow. Depletion of aortic macrophages using anti-macrophage colony-stimulating factor 1 receptor (MCSF1R)-neutralizing antibody (Ab) reduced the incidence of AAA. Conditional depletion of Lyve-1(+) aortic macrophages was achieved by generating Lyve-1(wt/cre) Csf1r(fl/fl) mice. Selective depletion of Lyve-1(+) aortic macrophages had no protective effects following AT2/BAPN administration and resulted in increased aortic dilatation in the suprarenal aorta. Conclusions: Aortic macrophage accumulation in AAA derives from adventitial recruitment of Lyve-1(-) macrophages, with relative percent depletion of Lyve-1(+) macrophages. Selective targeting of macrophage subtypes represents a potential novel therapeutic avenue for the medical treatment of AAA.