Mo-derived perivascular macrophage recruitment protects against endothelial cell death in retinal vein occlusion

BackgroundTo decipher the role of monocyte-derived macrophages (Ms) in vascular remodeling of the occluded vein following experimental branch retinal vein occlusion (BRVO).MethodsThe inflammation induced by laser-induced BRVO on mice retina was evaluated at different time points by RT-PCR looking at inflammatory markers mRNA level expression, Icam-1, Cd11b, F4/80, Ccl2, and Ccr2 and by quantification of Iba1-positive macrophage (M) density on Iba1-stained retinal flatmount. Repeated intraperitoneal EdU injection combined with liposome clodronate-induced monocyte (Mo) depletion in wildtype mice was used to differentiate Mo-derived M phi s from resident M phi s. Liposome clodronate Mo-depleted wildtype mice and Ccr2-deficient mice were used to evaluate the role of all CCR2(+) and CCR2(neg) Mo-derived M phi s on EC apoptosis in the occluded vein.Results cd11b, ICAM-1, F4/80, Ccl2, and Ccr2 mRNA expression were increased 1, 3, and 7days after vein occlusion. The number of parenchymal (parM phi s) and perivascular (vasM phi s) macrophages was increased 3 and 7days after BRVO. The systemic depletion of all circulating Mos decreased significantly the BRVO-induced parM phi s and vasM phi s macrophage accumulation, while the deletion of CCR2(+)-inflammatory Mo only diminished the accumulation of parM phi s, but not vasM phi s. Finally, apoptotic ECs of the vein were more numerous in fully depleted, liposome clodronate-treated mice, than in Ccr2(-/-) mice that only lack the recruitment of CCR2(+) inflammatory Mos.Conclusions BRVO triggers the recruitment of blood-derived parM phi s and vasM phi s. Interestingly, vasM phi s accumulation was independent of CCR2. The observation that the inhibition of the recruitment of all infiltrating M phi s increases the vein EC apoptosis, while CCR2 deficiency does not, demonstrates that CCR2(neg) Mo-derived vasM phi s protect the ECs against apoptosis in the occluded vein.