Collateral artery growth (arteriogenesis) after experimental arterial occlusion is impaired in mice lacking CC-chemokine receptor-2

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.