CCL2/CCR2 and CX3CL1/CX3CR1 chemokine axes and their possible involvement in age-related macular degeneration

The causes of age-related macular degeneration (AMD) are not well understood. Due to demographic shifts in the industrialized world a growing number of people will develop AMD in the coming decades. To develop treatments it is essential to characterize the disease's pathogenic process. Over the past few years, numerous studies have focused on the role of chemotactic cytokines, also known as chemokines. Certain chemokines, such as CCL2 and CX3CL1, appear to be crucial in subretinal microglia and macrophage accumulation observed in AMD, and participate in the development of retinal degeneration as well as in choroidal neovascularization. This paper reviews the possible implications of CCL2 and CX3CL1 signaling in AMD. Expression patterns, single nucleotide polymorphisms (SNPs) association studies, chemokine and chemokine receptor knockout models are discussed. Future AMD treatments could target chemokines and/or their receptors

Thinning of the RPE and choroid associated with T lymphocyte recruitment in aged and light-challenged mice

International audienceThe choroidal vasculature is essential when it comes to bringing oxygen and nutrients to the functioning retina and evacuating debris resulting from the normal visual cycle. Choroidal thinning is a common feature in many human eye diseases, including high myopia [1,2] and retinitis pigmentosa [3,4], and has been reproducibly observed with age [5-7]. However, the association between choroidal thinning and age-related macular degeneration (AMD) remains controversial. Some authors have reported the loss of choriocapillaries in eyes with exudative AMD [8], and choroidal thinning has been detected in some studies [9-11]. Choroidal thinning has also been associated with geographic atrophy (GA), the dry form of late AMD [12-15]. A morphometric analysis by Ramrattan et al. more than two decades ago showed a decrease in choriocapillary density and diameter with age and in GA, but choroidal thinning was only significant with age [6]. Moreover, it has been reported that the choriocapillaries and choroid are thinner in areas where the RPE has degenerated [8]. However, all studies agree that aging is associated with significant choroidal thinning [16-18]. The exact mechanisms behind choroidal thinning with age or disease are not clear. The RPE is a monolayer of pigmented cells situated between photoreceptors and Bruch's membrane; its plays an essential role in the visual cycle. RPE65, which is also called 11-cis retinol isomerase and is strongly expressed in the RPE, participates in the production of 11-cis retinal [19], which is essential for photoreceptor function [20]. Mutations in the RPE65 gene cause progressive photoreceptor degeneration [21,22] and adult RPE65 −/

APOE Isoforms Control Pathogenic Subretinal Inflammation in Age-Related Macular Degeneration

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CD36 Deficiency Leads to Choroidal Involution via COX2 Down-Regulation in Rodents

Florian Sennelaub and colleagues show that CD36 deficiency leads to choroidal involution, a key feature of "dry" age-related macular degeneration, via COX-2 down-regulation in the retinal pigment epithelium

Delta-like 4 inhibits choroidal neovascularization despite opposing effects on vascular endothelium and macrophages.: DLL4's opposing effects in choroidal neovascularization

International audienceInflammatory neovascularization, such as choroidal neovascularization (CNV), occur in the presence of Notch expressing macrophages. DLL4s anti-angiogenic effect on endothelial cells (EC) has been widely recognized, but its influence on Notch signaling on macrophages and its overall effect in inflammatory neovascularization is not well understood. We identified macrophages and ECs as the main Notch 1 and Notch 4 expressing cells in CNV. A soluble fraction spanning Ser28-Pro525 of the murine extracellular DLL4 domain (sDLL4/28-525) activated the Notch pathway, as it induces Notch target genes in macrophages and ECs and inhibited EC proliferation and vascular sprouting in aortic rings. In contrast, sDLL4/28-525 increased pro-angiogenic VEGF, and IL-1β expression in macrophages responsible for increased vascular sprouting observed in aortic rings incubated in conditioned media from sDLL4/28-525 stimulated macrophages. In vivo, Dll4(+/-) mice developed significantly more CNV and sDLL4/28-525 injections inhibited CNV in Dll4(+/-) CD1 mice. Similarly, sDLL4/28-525 inhibited CNV in C57Bl6 and its effect was reversed by a γ-secretase inhibitor that blocks Notch signaling. The inhibition occurred despite increased VEGF, IL-1β expression in infiltrating inflammatory macrophages in sDLL4/28-525 treated mice and might be due to direct inhibition of EC proliferation in laser-induced CNV as demonstrated by EdU labelling in vivo. In conclusion, Notch activation on macrophages and ECs leads to opposing effects in inflammatory neovascularization in situations such as CNV

Iron, Ferritin, Transferrin, and Transferrin Receptor in the Adult Rat Retina

PURPOSE. The retina and other tissues need iron to survive. However, the normal iron metabolism in rodent retinas had not been characterized. This study was intended to investigate iron and iron homeostasis protein (ferritin, transferrin [Tf] and transferrin receptor [Tf-R]) distribution in 20-to 55-day-old rat retinas. METHODS. Iron was revealed on retinal sections directly by proton-induced x-ray emission (PIXE) and indirectly by electron microscopy (EM). Ferritin, Tf, and Tf-R proteins were localized by immunohistochemistry. Transferrin expression was localized by in situ hybridization (ISH). Transferrin and ferritin proteins and mRNA were analyzed by Western blot analysis and reverse transcription-polymerase chain reaction (RT-PCR), respectively. RESULTS. Iron is widely and unevenly distributed throughout the adult rat retina. The highest concentration was observed by PIXE in the choroid and the retinal pigmented epithelial cell (RPE) layer, and in inner segments of photoreceptors (IS). Outer segments of photoreceptors (OS) also contain iron. EM studies suggested the presence of iron inclusions inside the photoreceptor discs. Choroid, RPE, and IS showed a strong immunoreactivity for ferritin. Transferrin accumulated mainly in the IS and OS areas and in RPE cells but can also be detected slightly in retinal capillaries. Western blot analysis for Tf and ferritin confirmed their presence in the adult neural retina. By RT-PCR, H-and L-chains of ferritin and Tf mRNAs were expressed in neural retina, but the main sites of Tf synthesis observed by ISH were the RPE and choroid cell layers. Tf-R immunoreactivity was detected in the ganglion cell layer, inner nuclear layer, outer plexiform layer, IS, RPE, and choroid. These results were similar for all stages studied. CONCLUSIONS. For the first time, the present study characterized both iron and iron homeostasis proteins in rodent retinas. In the outer retina, iron and ferritin shared the same distribution patterns. In contrast, Tf, mainly synthesized by RPE cells and detected in OS and IS areas, probably helps to transport iron to photoreceptors through their Tf-R. This is a likely pathway for filling iron needs in the outer retina. (Invest Ophthalmol Vis Sci. 2000;41:2343-235

Apolipoprotein E promotes subretinal mononuclear phagocyte survival and chronic inflammation in age-related macular degeneration

International audiencePhysiologically, the retinal pigment epithelium (RPE) expresses immunosuppressive signals such as FAS ligand (FASL), which prevents the accumulation of leukocytes in the subretinal space. Age-related macular degeneration (AMD) is associated with a breakdown of the subretinal immunosuppressive environment and chronic accumulation of mononuclear phagocytes (MPs). We show that subretinal MPs in AMD patients accumulate on the RPE and express high levels of APOE. MPs of Cx3cr1 À/À mice that develop MP accumulation on the RPE, photoreceptor degeneration, and increased choroidal neovascularization similarly express high levels of APOE. ApoE deletion in Cx3cr1 À/À mice prevents patho-genic age-and stress-induced subretinal MP accumulation. We demonstrate that increased APOE levels induce IL-6 in MPs via the activation of the TLR2-CD14-dependent innate immunity receptor cluster. IL-6 in turn represses RPE FasL expression and prolongs subretinal MP survival. This mechanism may account, in part, for the MP accumulation observed in Cx3cr1 À/À mice. Our results underline the inflammatory role of APOE in sterile inflammation in the immunosuppressive subretinal space. They provide rationale for the implication of IL-6 in AMD and open avenues toward therapies inhibiting pathogenic chronic inflammation in late AMD