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

Abstract

Macrophages accumulate in blood vessels during hypertension. However, their contribution to vessel remodeling is unknown. In the present study, 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 ANG II (0.7 mg·kg(-1)·day(-1), 14 days) had elevated systolic BP (158 ± 3 mmHg) compared with saline-treated animals (122 ± 3 mmHg). Flow cytometry revealed that ANG II infusion increased numbers of CD45(+)CD11b(+)Ly6C(hi) monocytes and CD45(+)CD11b(+)F4/80(+) macrophages by 10- and 2-fold, respectively. The majority of macrophages were positive for the M2 marker CD206 but negative for the M1 marker inducible nitric oxide synthase. Expression of other M2 genes (arginase-1, Fc receptor-like S scavenger receptor, and receptor-1) was elevated in aortas from ANG II-treated mice, whereas M1 genes [TNF and chemokine (C-X-C motif) ligand 2] were unaltered. A PCR array to identify chemokine receptor targets for intervention revealed chemokine (C-C motif) receptor 2 (CCR2) to be upregulated in aortas from ANG II-treated mice, while flow cytometry identified Ly6C(hi) monocytes as the main CCR2-expressing cell type. Intervention with a CCR2 antagonist (INCB3344; 30 mg·kg(-1)·day(-1)), 7 days after the commencement of ANG II infusion, reduced aortic macrophage numbers. INCB334 also reduced aortic collagen deposition, elastin loss, and BP in ANG II-treated mice. Thus, ANG II-dependent hypertension in mice is associated with Ly6C(hi) monocyte and M2 macrophage accumulation in the aorta. Inhibition of macrophage accumulation with a CCR2 antagonist prevents ANG II-induced vessel fibrosis and elevated BP, highlighting this as a promising approach for the future treatment of vessel remodeling/stiffening in hypertension.

Keywords: angiotensin II; blood pressure; chemokine (C-C motif) receptor 2; hypertension; macrophage polarization; vessel remodeling.