Mechanisms of FH Protection Against Neovascular AMD.

A common allele (402H) of the complement factor H (FH) gene is the major risk factor for age-related macular degeneration (AMD), the leading cause of blindness in the elderly population. Development and progression of AMD involves vascular and inflammatory components partly by deregulation of the alternative pathway of the complement system (AP). The loss of central vision results from atrophy and/or from abnormal neovascularization arising from the choroid. The functional link between FH, the main inhibitor of AP, and choroidal neovascularization (CNV) in AMD remains unclear. In a murine model of CNV used as a model for neovascular AMD (nAMD), intraocular human recombinant FH (recFH) reduced CNV as efficiently as currently used anti-VEGF (vascular endothelial growth factor) antibody, decreasing deposition of C3 cleavage fragments, membrane attack complex (MAC), and microglia/macrophage recruitment markers in the CNV lesion site. In sharp contrast, recFH carrying the H402 risk variant had no effect on CNV indicating a causal link to disease etiology. Only the recFH NT <sup>al</sup> region (recFH1-7), containing the CCPs1-4 C3-convertase inhibition domains and the CCP7 binding domain, exerted all differential biological effects. The CT <sup>al</sup> region (recFH7-20) containing the CCP7 and CCPs19-20 binding domains was antiangiogenic but did not reduce the microglia/macrophage recruitment. The antiangiogenic effect of both recFH1-20 and recFH-CCP7-20 resulted from thrombospondin-1 (TSP-1) upregulation independently of the C3 cleavage fragments generation. This study provides insight on the mechanistic role of FH in nAMD and invites to reconsider its therapeutic potential

Optical phase contrast imaging of human retinal cells by changing the tissue refractive index

Purpose : Based on oblique partially coherent illumination of transparent samples, we developed a simple custom Optical Phase Imaging (OPI) microscope providing a label-free, semi-quantitative phase contrast imaging. The aim of this study was to explore this ex-vivo modality for retinal imaging and correlate it with standard clinical images and fluorescence microscopy. Methods : Multimodal macular imaging was performed on the flat-mounted retina of an eye presenting an epiretinal membrane with cystoid macular edema, enucleated for a peripheral melanoma. After glial fibrillary acidic protein (GFAP) - aquaporin (AQP)-4 – collagen (Col)-IV co-immuno-labeling and nuclei staining, the retina was cleared by index matching in a medium of refractive index (RI) 1.46 to decrease scattering for high-resolution deep-tissue ex vivo imaging. We performed a comparison of the clinical examinations obtained by Optical Coherence Tomography-Angiography and fluorescein angiography before enucleation, with the images obtained with confocal microscopy and OPI microscopy. Ex-vivo imaging of the retina mounted in a medium with a lower RI (1.40), close to the mean RI of Muller glial cell (MGC), was then repeated to better view the latter cells. Results : The retinal vessels were used as landmarks for correlating all imaging modalities. OPI microscopy allowed for different contrast imaging depending on the RI of the mounting medium. With the high RI medium (1.46), deep contrast imaging of nuclei and intraretinal cysts was obtained. The solution with a RI of 1.4 provided an improvement in the contrast of the retinal structures, from the inner layer (AQP4-positive MGC, epi-retinal membrane, nerve fibers surrounded by GFAP-positive astrocytes) to the photoreceptor segments. No AQP4 labeling was observed inside the cyst. AQP4-positive, GFAP-negative cells were visualized on the ColIV-labeled epi-retinal membrane, demonstrating that the membrane is made of retinal Muller glial cells. Conclusions : This morphological correlative imaging study demonstrated OPI on numerous cellular structures of a human retina by tuning the tissue RI. This label-free in-depth imaging modality offers a new research tool to study the cellular origin of retinal diseases

Meteorin Is a Novel Therapeutic Target for Wet Age-Related Macular Degeneration.

The aim of this study was to evaluate the potential anti-angiogenic effect of MTRN (meteorin) in the laser-induced CNV rat model and explore its mechanisms of action. MTRN, thrompospondin-1, glial cell markers (GFAP, vimentin), and phalloidin were immuno-stained in non-human primate flat-mounted retinas and human retina cross sections. The effect of MTRN at different doses and time points was evaluated on laser-induced CNV at 14 days using in vivo fluorescein angiography and ex vivo quantification of CNV. A pan transcriptomic analysis of the retina and the RPE/choroid complex was used to explore MTRN effects mechanisms. In human retina, MTRN is enriched in the macula, expressed in and secreted by glial cells, and located in photoreceptor cells, including in nuclear bodies. Intravitreal MTRN administered preventively reduced CNV angiographic scores and CNV size in a dose-dependent manner. The highest dose, administered at day 7, also reduced CNV. MTRN, which is regulated by mineralocorticoid receptor modulators in the rat retina, regulates pathways associated with angiogenesis, oxidative stress, and neuroprotection. MTRN is a potential novel therapeutic candidate protein for wet AMD

Mineralocorticoid Receptor Pathway and Its Antagonism in a Model of Diabetic Retinopathy.

Diabetic retinopathy remains a major cause of vision loss worldwide. Mineralocorticoid receptor (MR) pathway activation contributes to diabetic nephropathy, but its role in retinopathy is unknown. In this study, we show that MR is overexpressed in the retina of type 2 diabetic Goto-Kakizaki (GK) rats and humans and that cortisol is the MR ligand in human eyes. Lipocalin 2 and galectin 3, two biomarkers of diabetes complications regulated by MR, are increased in GK and human retina. The sustained intraocular delivery of spironolactone, a steroidal mineralocorticoid antagonist, decreased the early and late pathogenic features of retinopathy in GK rats, such as retinal inflammation, vascular leakage, and retinal edema, through the upregulation of genes encoding proteins known to intervene in vascular permeability such as Hey1, Vldlr, Pten, Slc7a1, Tjp1, Dlg1, and Sesn2 but did not decrease VEGF. Spironolactone also normalized the distribution of ion and water channels in macroglial cells. These results indicate that MR is activated in GK and human diabetic retina and that local MR antagonism could be a novel therapeutic option for diabetic retinopathy