Abstract
Purpose :
To investigate the role mononuclear phagocytes (MP) in vascular remodeling after branch retinal vein occlusion (BRVO)
Methods :
Occlusion of one branch of the retinal vein was performed by laser photocoagulation on C57Bl6 (WT), CCR2 KO (CCR2-/-), control liposome and liposome clodronate injected (CLO) mice. Liposome injected animals were repeatedly injected systemically with EdU to mark circulating but not resident MPs. Animals were injected with 100µl of 1% fluorescein and the proximal superior vein was occluded laser impacts (0.5s, 200mW, 50µm spot size, Laser Yag 532 Eyelite). The retina section from to the occluded area was dissected and analyzed by RT-PCR and flatmount immunohistochemistry (CollIV, IBA1, TUNEL) at day 1, 3 and 7 after BRVO. Total and perivascular IBA1+EdU+ and IBA1+EdU- cells and TUNEL+CollIV+ nuclei were counted in the area around the occluded vein of WT, CCR2-/- and liposome injected mice.
Results :
RT-PCR revealed elevated mRNA levels at d1,3 and 7 of cd11b, ICAM-1, F4/80, CCL2 and CCR2, mediators of leukocyte recruitment. Immunohistochemistry on flatmount retina showed a recruitment of recruited IBA1+EdU+ cells 3 days after BRVO around the occluded vein (perivascular macrophages) and within the retina in the occluded area. The deficiency of CCR2 did not affect the BRVO-induced perivascular IBA1+EdU+ macrophage recruitment, but inhibited the increase in retinal IBA1+EdU+ macrophages. The systemic depletion of circulating monocytes (liposome clodronate) inhibited the recruitment of both populations. Finally, the density of apoptotic vein endothelial cells was not different in CCR2-/- mice but increased in monocyte depleted mice in which perivascular macrophage recruitment was inhibited.
Conclusions :
BRVO triggers the recruitment of CCR2+ inflammatory macrophages to the occluded retina and CCR2negperivascular macrophages to the occluded vein. The inhibition of the perivascular macrophage recruitment, but not inflammatory macrophages, significantly increased vein endothelial cell apoptosis, suggesting that CCR2-independent perivascular macrophage recruitment are important mediators in BRVO remodeling.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.