Role of CX3CR1 Receptor in Monocyte/Macrophage Driven Neovascularization

Monocyte/Macrophages are implicated in initiation of angiogenesis, tissue/organ perfusion and atherosclerosis biology. We recently showed that chemokine receptor CX 3 CR1 is an essential regulator of monocyte/macrophage derived smooth muscle cell differentiation in the vessel wall after injury. Here we hypothesised the contribution of CX 3 CR1- CX 3 CL1 interaction to in vivo neovascularization and studied the functional consequences of genetic and pharmacologic targeting of CX 3 CR1 in formation, maturation and maintenance of microvascular integrity. Cells functionally deficient in CX 3 CR1 lacked matrix tunnelling and tubulation capacity in a 3D Matrigel assay. These morphogenic and cytokinetic responses were driven by CX 3 CL1-CX 3 CR1 interaction and totally abrogated by a Rho antagonist. To evaluate the role of CX 3 CR1 system in vivo, Matrigel plugs were implanted in competent CX 3 CR1 +/gfp and functionally deficient CX 3 CR1 gfp/gfp mice. Leaky microvessels (MV) were formed in the Matrigel implanted in CX 3 CR1 gfp/gfp but not in CX 3 CR1 +/gfp mice. In experimental plaque neovascularization immature MV phenotype was observed in CX 3 CR1 gfp/gfp mice, lacking CX 3 CR1 positive smooth muscle-like cells, extracellular collagen and basement membrane (BM) laminin compared to competent CX 3 CR1 +/gfp mice. This was associated with increased extravasation of platelets into the intima of CX 3 CR1 gfp/gfp but not functionally competent CX 3 CR1 mice. Pharmacologic targeting using CX 3 CR1 receptor antagonist in wild type mice resulted in formation of plaque MV with poor BM coverage and a leaky phenotype. Our data indicate a hitherto unrecognised role for functional CX 3 CR1 in Matrigel and experimental plaque neovascularization in vivo, which may buttress MV collectively in favour of a more stable non-leaky phenotype.