Microglia Activation and Recruitment of Circulating Macrophages During Ischemic Experimental Branch Retinal Vein Occlusion

Abstract

METHODS. Experimental BRVO was induced in Balb/c mice and histologic changes were studied. Tissue hypoxia was visualized using pimonidazole hydrochloride. Monocyte-derived retinal cells were quantified using histology and flow cytometry. To investigate the dynamics of invading blood-borne macrophages, chimera mice were generated using bone marrow grafts from Cx3cr1 (gfp/gfp) mice to rescue lethally irradiated wild-type BALB/c mice. Longitudinal in vivo imaging was performed to monitor cell invasion. The levels of proinflammatory cytokines in the retina were quantified by quantitative real-time PCR.RESULTS. Histology showed disruption of tissue architecture and temporary swelling with marked hypoxia coinciding with increased VEGF-A and hypoxia inducible factor-1a (HIF-1a) expression and elevation of proinflammatory cytokines within 3 days after experimental BRVO, followed by thinning of the inner retinal layers at later time points. Proinflammatory cytokine levels were elevated. Activation of resident retinal microglia and recruitment of circulating macrophages in areas of hypoxic retina were evident early after the insult and peaked at day 7, remaining elevated for up to 28 days. Flow cytometry showed upregulation of CD68 and major histocompatibility complex class-II (MHC-II) expression at day 3, culminating at day 7.CONCLUSIONS. Experimental BRVO causes hypoxia and breakdown of the inner blood-retina barrier, followed by activation of microglia and invasion of macrophages from the systemic circulation. Consequently, treatments targeting microglia activation or macrophage recruitment might potentially mitigate the sequelae and attenuate degenerative changes induced by retinal vein occlusion.

Aldosterone Exposure Causes Increased Retinal Edema and Severe Retinopathy Following Laser-Induced Retinal Vein Occlusion in Mice

“…the previously reported finding by Ebneter and colleagues 13 showing maximal mononuclear phagocyte recruitment at day 7 after RVO. There was an apparent increase in density of Iba1positive cells in areas affected by vein occlusion but not in sham laser eyes or areas distant from vein occlusion.…”

“…This suggests that the effects of aldosterone at the tested dose and duration depend on an inciting vascular injury. Recently, Ebneter et al 13 reported that resident microglia become activated and that blood-derived macrophages are recruited following RVO. Increased mononuclear phagocyte infiltration is a feature of several other retinal disease models including laser-induced choroidal neovascularization 25 and oxygen-induced retinopathy.…”

“…Several groups have used laser induced vein occlusion in mouse and rat to characterize the response of various retinal cell types following vein occlusion. [11][12][13][14][15][16][17] Most have occluded half or all retinal veins, which leads to extensive ischemia and eventual retinal neovascularization. We altered this approach by occluding only a single vein and examining the tissue in the peripheral retina that is drained by the occluded vein.…”

Prospective study of aflibercept for the treatment of persistent macular oedema secondary to retinal vein occlusions in eyes not responsive to long‐term treatment with bevacizumab or ranibizumab

“…Recently, there has been interest in the presence of hyperreflective foci and microretinal changes observed on OCT. We assessed the possible interaction between this clinical feature and response to aflibercept treatment. The manifestation of stimulated microglia and influx of macrophages in the retina is prominent after RVO . These cells play a vital function in the inflammatory response within the ischaemic retina, usually isolated from the systemic immune system by the blood‐retina barrier .…”

Noninvasive Quantification of Retinal Microglia Using Widefield Autofluorescence Imaging

“…We have previously reported on the dynamics of activated microglia and macrophages in transgenic mice in the latter model. 19 Significant changes were found in the peripheral retina, which would have escaped our attention using conventional optics. Hence, widefield imaging tools are crucial for the assessment of experimental outcomes in such models.…”