M2 macrophage accumulation in the aortic wall during angiotensin II infusion in mice is associated with fibrosis, elastin loss, and elevated blood pressure

Macrophages accumulate in blood vessels during hypertension. However, their contribution to vessel remodeling is unknown. Here we examined the polarization state of macrophages (M1/M2) in aortas of mice during hypertension and investigated whether antagonism of chemokine receptors involved in macrophage accumulation reduces vessel remodeling and blood pressure (BP). Mice treated with angiotensin II (0.7 mg.kg-1.d-1, 14 d) had elevated systolic BP (158+/-3 mmHg) compared to saline-treated animals (122+/-3 mmHg). Flow cytometry revealed that angiotensin II infusion increased numbers of CD45+CD11b+Ly6Chi monocytes and CD45+CD11b+F4/80+ macrophages by 10-fold and 2-fold, respectively. The majority of macrophages were positive for the M2 marker, CD206, but negative for the M1 marker, iNOS. Expression of other M2 genes (arginase-1, Fc scavenger receptor-like, receptor-1) was elevated in aortas from angiotensin II-treated mice, whereas M1 genes (tumour necrosis factor, CXCL2) were unaltered. A PCR array to identify chemokine receptor targets for intervention revealed CCR2 to be upregulated in aortas from angiotensin II-treated mice, while flow cytometry identified Ly6Chi monocytes as the main CCR2-expressing cell type. Intervention with a CCR2 antagonist (INCB3344, 30 mg.kg-1.d-1), 7 days after commencing angiotensin II infusion, reduced aortic macrophage numbers. INCB334 also reduced aortic collagen deposition, elastin loss and BP in angiotensin II-treated mice. Thus, angiotensin II-dependent hypertension in mice is associated with Ly6Chi monocyte and M2 macrophage accumulation in the aorta. Inhibition of macrophage accumulation with a CCR2 antagonist prevents angiotensin II-induced vessel fibrosis and elevated BP, highlighting this as a promising approach for the future treatment of vessel remodeling/stiffening in hypertension.