Collateral Artery Growth (Arteriogenesis) After Experimental Arterial Occlusion Is Impaired in Mice Lacking CC-Chemokine Receptor-2

Abstract

Arteriogenesis has been associated with the presence of monocytes/macrophages within the collateral vessel wall. Induced macrophage migration in vivo is driven by the binding of monocyte chemoattractant protein-1 (MCP-1, or CCL2 in the new nomenclature) to the CCR2-chemokine receptor on macrophages. To determine whether the CCL2-CCR2 signaling pathway is involved in the accumulation of macrophages in growing collateral vessels, we used mice that are deficient in CCR2 in a model of experimental arterial occlusion and collateral vessel growth. In an in vitro CCL2-driven chemotaxis assay, mononuclear cells isolated from wild-type BALB/c mice exhibited CCL2 concentration–dependent migration, whereas this migration was abolished in cells from CCR2 −/− mice on a BALB/c genetic background. In vivo, blood flow recovery as measured by laser Doppler (LDI) and MRI (MRI) was impaired in CCR2 −/− mice on either the BALB/c or C57BL/6 genetic backgrounds. Three weeks after femoral artery ligation, LDI perfusion ratio of operated versus nonoperated distal hindlimb in BALB/c wild-type mice increased to 0.45±0.06 and in CCR2 −/− animals only to 0.21±0.03 ( P <0.01). In C57BL/6 mice, ratio increased to 0.96±0.09 and 0.85±0.08 ( P <0.05), respectively. MRI at 3 weeks (0.76±0.06 versus 0.62±0.01; P <0.05) and hemoglobin oxygen saturation measurements confirmed these findings. Active foot movement score significantly decreased and gastrocnemius muscle atrophy was significantly greater in CCR2 −/− mice. Morphometric analysis showed a lesser increase in collateral vessel diameters in CCR2 −/− mice. Importantly, the number of invaded monocytes/macrophages in the perivascular space of collateral arteries of CCR2 −/− animals was dramatically reduced in comparison to wild-type mice. In conclusion, our results demonstrate that the CCR2 signaling pathway is essential for efficient collateral artery growth.