SU9518 inhibits proliferative vitreoretinopathy in fibroblast and genetically modified Müller cell-induced rabbit models

Transition to Chronic Fibrosis in an Animal Model of Retinal Detachment With Features of Proliferative Vitreoretinopathy

Purpose

Proliferative vitreoretinopathy (PVR) is the most common cause of failure of surgically repaired rhegmatogenous retinal detachment (RRD). Chemically induced and cell injection PVR models do not fully simulate the clinical characteristics of PVR in the post-RRD context. There is an unmet need for translational models in which to study mechanisms and treatments specific to RRD-PVR.

Methods

RRD was induced in adult Dutch Belted rabbits. Posterior segments were fixed or processed for RNA sequencing at 6 hours and 2, 7, 14, and 35 days after induction. Histochemical staining and immunolabeling for glial fibrillary acidic protein, alpha smooth muscle actin, vascular endothelial growth factor receptor 2, CD68, and RPE 65 kDa protein were performed, and labeling intensity was scored. Single cell RNA sequencing was performed.

Results

Acute histopathological changes included intravitreal and intraretinal hemorrhage, leukocytic vitritis, chorioretinitis, and retinal rarefaction. Chronic lesions showed retinal atrophy, gliosis, fibrotic subretinal membranes, and epiretinal fibrovascular proliferation. Fibrillar collagen was present in the fibrocellular and fibrovascular membranes in chronic lesions. Moderate to strong labeling of glia and vasculature was detected in chronic lesions. At day 14, most cells profiled by single cell sequencing were identified as Mϋller glia and microglia, consistent with immunolabeling. Expression of several fibrillar collagen genes was upregulated in chronic lesions.

Conclusions

Histological and transcriptional features of this rabbit model simulate important features of human RRD-PVR, including the transition to chronic intraretinal and periretinal fibrosis. This animal model of RRD with features of PVR will enable further research on targeted treatment interventions.

Postoperative Macular Proliferative Vitreoretinopathy: A Case Series and Literature Review

Premacular membranes developing following pars plana vitrectomy (PPV) can cause significant anatomical and functional deficits to the macula. Recent reports showed that postoperative premacular membranes are a localized presentation of macular proliferative vitreoretinopathy (mPVR). Here, we report retrospectively a case series of 5 patients with severe mPVR which developed following uneventful PPV and were followed up to 32 months in the Department of Ophthalmology, Hadassah-Hebrew University Medical Center, Jerusalem, between October 2016 and February 2020. All patients underwent primary repair of rhegmatogenous retinal detachment (RRD) before mPVR developed. Mean best-corrected visual acuity (BCVA) at presentation was 20/76 Snellen (0.58 LogMAR). Median duration of the retinal detachment time until surgery was 1.5 days (range 1–21 days). Mean interval time from last normal follow-up exam to diagnosis of mPVR was 19 days (range 10–28). BCVA dropped from a mean of 20/38 Snellen (0.28 LogMAR) prior to mPVR development to 20/166 Snellen (0.92 LogMAR) following its development, recovering to 20/57 Snellen (0.45 LogMAR) after peeling of membranes. Mean central macular thickness measured by optical coherence tomography decreased from 711 to 354 μm postsurgery. In conclusion, short-term mPVR is a different entity from macular pucker in terms of rapid development, structural distortion, and visual compromise. Surgical treatment significantly restores macular function and anatomy.

Arsenic trioxide inhibits proliferation of retinal pigment epithelium by downregulating expression of extracellular matrix and p27

The present study aimed to investigate the effect of arsenic trioxide (ATO) on the proliferation of retinal pigment epithelium (RPE) and its mechanism. RPE cells were cultivated with 0.5-11 μmol/L ATO for 24, 48, and 72 h and their survival and growth were measured by MTT assay. The expression of p27 and proliferating cell nuclear antigen (PCNA) in RPE cells was detected using cell immunofluorescence and western blotting. Dose-dependency was evident in both the experimental and control groups. The 50% inhibitory concentration was obtained at a concentration of 6 mol/L with cells treated for 3 days. The optimum concentration of ATO was 6 μmol/L based on the result of MTT. After the third day of ATO treatment, the number of cells was significantly lower in the experimental group compared with the control group. The expression of extracellular matrix (ECM) components decreased relative to the control group. The expression of p27 and PCNA declined gradually in cells treated for 72 h at 6 μmol/L ATO compared with the control group. The difference between the experimental and control groups was significant (P=0.005). ATO has the ability to inhibit the growth and proliferation of RPE cells by regulating the expression of the ECM components' p27 and PCNA, in a time- and dose-dependent manner. Thus, ATO may lead to an innovative method for the treatment of proliferative retinopathy.

Detection of Retinal Fibrosis in a Rabbit Model of Penetrating Eye Injury

INTRODUCTION

To establish a rabbit model of posterior penetrating eye injury as a platform to test potential therapeutics.

MATERIALS AND METHODS

Anesthetized rabbits received posterior penetrating eye injury in one eye, whereas contralateral eyes were maintained as uninjured controls. Rabbits were randomized into two experimental groups. Group A was euthanized on Day 14 postinjury to determine retinal fibrosis at an early phase of disease progression. Group B was euthanized on Day 28 postinjury to examine retinal fibrosis at a late phase of disease progression. We examined animals on postinjury Days 7, 14, 21, and 28 with indirect ophthalmoscope and fundus photography. After euthanasia, eyes were processed for histology and immunofluorescence labeling of fibrotic proteins α-smooth muscle actin and collagen I.

RESULTS

Early fibrosis was detected by Day 14, as indicated by indirect ophthalmoscopy and fundus imaging. Fibrotic membranes were visible at sites of injury. Immunofluorescence analysis detected α-smooth muscle actin and collagen I within the fibrotic membranes.

CONCLUSIONS

These data show that ocular fibrosis can be detected within 14 days after initial injury, with more severe fibrosis detected at 28 days postinjury. These results will be used to determine the optimal time points for later studies designed to test treatment strategies.

Proteome-wide Identification of Glycosylation-dependent Interactors of Galectin-1 and Galectin-3 on Mesenchymal Retinal Pigment Epithelial (RPE) Cells

Identification of interactors is a major goal in cell biology. Not only protein-protein but also protein-carbohydrate interactions are of high relevance for signal transduction in biological systems. Here, we aim to identify novel interacting binding partners for the β-galactoside-binding proteins galectin-1 (Gal-1) and galectin-3 (Gal-3) relevant in the context of the eye disease proliferative vitreoretinopathy (PVR). PVR is one of the most common failures after retinal detachment surgeries and is characterized by the migration, adhesion, and epithelial-to-mesenchymal transition of retinal pigment epithelial cells (RPE) and the subsequent formation of sub- and epiretinal fibrocellular membranes. Gal-1 and Gal-3 bind in a dose- and carbohydrate-dependent manner to mesenchymal RPE cells and inhibit cellular processes like attachment and spreading. Yet knowledge about glycan-dependent interactors of Gal-1 and Gal-3 on RPE cells is very limited, although this is a prerequisite for unraveling the influence of galectins on distinct cellular processes in RPE cells. We identify here 131 Gal-3 and 15 Gal-1 interactors by galectin pulldown experiments combined with quantitative proteomics. They mainly play a role in multiple binding processes and are mostly membrane proteins. We focused on two novel identified interactors of Gal-1 and Gal-3 in the context of PVR: the low-density lipoprotein receptor LRP1 and the platelet-derived growth factor receptor β PDGFRB. Addition of exogenous Gal-1 and Gal-3 induced cross-linking with LRP1/PDGFRB and integrin-β1 (ITGB1) on the cell surface of human RPE cells and induced ERK/MAPK and Akt signaling. Treatment with kifunensine, an inhibitor of complex-type N-glycosylation, weakened the binding of Gal-1 and Gal-3 to these interactors and prevented lattice formation. In conclusion, the identified specific glycoprotein ligands shed light into the highly specific binding of galectins to dedifferentiated RPE cells and the resulting prevention of PVR-associated cellular events.

Epithelial-to-Mesenchymal Transition of RPE Cells In Vitro Confers Increased β1,6-N-Glycosylation and Increased Susceptibility to Galectin-3 Binding

Epithelial-to-mesenchymal transition (EMT) of retinal pigment epithelial cells is a crucial event in the onset of proliferative vitreoretinopathy (PVR), the most common reason for treatment failure in retinal detachment surgery. We studied alterations in the cell surface glycan expression profile upon EMT of RPE cells and focused on its relevance for the interaction with galectin-3 (Gal-3), a carbohydrate binding protein, which can inhibit attachment and spreading of human RPE cells in a dose- and carbohydrate-dependent manner, and thus bares the potential to counteract PVR-associated cellular events. Lectin blot analysis revealed that EMT of RPE cells in vitro confers a glycomic shift towards an abundance of Thomsen-Friedenreich antigen, poly-N-acetyllactosamine chains, and complex-type branched N-glycans. Using inhibitors of glycosylation we found that both, binding of Gal-3 to the RPE cell surface and Gal-3-mediated inhibition of RPE attachment and spreading, strongly depend on the interaction of Gal-3 with tri- or tetra-antennary complex type N-glycans and sialylation of glycans but not on complex-type O-glycans. Importantly, we found that β1,6 N-acetylglucosaminyltransferase V (Mgat5), the key enzyme catalyzing the synthesis of tetra- or tri-antennary complex type N-glycans, is increased upon EMT of RPE cells. Silencing of Mgat5 by siRNA and CRISPR-Cas9 genome editing resulted in reduced Gal-3 binding. We conclude from these data that binding of recombinant Gal-3 to the RPE cell surface and inhibitory effects on RPE attachment and spreading largely dependent on interaction with Mgat5 modified N-glycans, which are more abundant on dedifferentiated than on the healthy, native RPE cells. Based on these findings we hypothesize that EMT of RPE cells in vitro confers glycomic changes, which account for high affinity binding of recombinant Gal-3, particularly to the cell surface of myofibroblastic RPE. From a future perspective recombinant Gal-3 may disclose a therapeutic option allowing for selectively targeting RPE cells with pathogenic relevance for development of PVR.

Vascular endothelial growth factor acts primarily via platelet-derived growth factor receptor α to promote proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) is a nonneovascular blinding disease and the leading cause for failure in surgical repair of rhegmatogenous retinal detachments. Once formed, PVR is difficult to treat. Hence, there is an acute interest in developing approaches to prevent PVR. Of the many growth factors and cytokines that accumulate in vitreous as PVR develops, neutralizing vascular endothelial growth factor (VEGF) A has recently been found to prevent PVR in at least one animal model. The goal of this study was to test if Food and Drug Administration-approved agents could protect the eye from PVR in multiple animal models and to further investigate the underlying mechanisms. Neutralizing VEGF with aflibercept (VEGF Trap-Eye) safely and effectively protected rabbits from PVR in multiple models of disease. Furthermore, aflibercept reduced the bioactivity of both experimental and clinical PVR vitreous. Finally, although VEGF could promote some PVR-associated cellular responses via VEGF receptors expressed on the retinal pigment epithelial cells that drive this disease, VEGF's major contribution to vitreal bioactivity occurred via platelet-derived growth factor receptor α. Thus, VEGF promotes PVR by a noncanonical ability to engage platelet-derived growth factor receptor α. These findings indicate that VEGF contributes to nonangiogenic diseases and that anti-VEGF-based therapies may be effective on a wider spectrum of diseases than previously appreciated.

Is neutralizing vitreal growth factors a viable strategy to prevent proliferative vitreoretinopathy?

Proliferative vitreoretinopathy (PVR) is a blinding disorder that occurs in eyes with rhegmatogenous retinal detachment and in eyes that have recently undergone retinal detachment surgery. There are presently no treatment strategies to reduce the risk of developing PVR in eyes with retinal detachment, and surgical intervention is the only option for eyes with retinal detachment and established PVR. Given the poor visual outcome associated with the surgical treatment of PVR, considerable work has been done to identify pharmacologic agents that could antagonize the PVR process. Intensive efforts to identify molecular determinants of PVR implicate vitreal growth factors. A surprise that emerged in the course of testing the 'growth factor hypothesis' of PVR was the existence of a functional relationship amongst growth factors that engage platelet-derived growth factor (PDGF) receptor α (PDGFRα), a receptor tyrosine kinase that is key to pathogenesis of experimental PVR. Vascular endothelial cell growth factor A (VEGF), which is best known for its ability to activate VEGF receptors (VEGFRs) and induce permeability and/or angiogenesis, enables activation of PDGFRα by a wide spectrum of vitreal growth factors outside of the PDGF family (non-PDGFs) in a way that triggers signaling events that potently enhance the viability of cells displaced into vitreous. Targeting these growth factors or signaling events effectively neutralizes the bioactivity of PVR vitreous and prevents PVR in a number of preclinical models. In this review, we discuss recent conceptual advances in understanding the role of growth factors in PVR, and consider the tangible treatment strategies for clinical application.

Proliferative vitreoretinopathy after eye injuries: an overexpression of growth factors and cytokines leading to a retinal keloid

Eye injury is a significant disabling worldwide health problem. Proliferative Vitreoretinopathy (PVR) is a common complication that develops in up to 40–60% of patients with an open-globe injury. Our knowledge about the pathogenesis of PVR has improved in the last decades. It seems that the introduction of immune cells into the vitreous, like in penetrating ocular trauma, triggers the production of growth factors and cytokines that come in contact with intra-retinal cells, like Müller cells and RPE cells. Growth factors and cytokines drive the cellular responses leading to PVR's development. Knowledge of the pathobiological and pathophysiological mechanisms involved in posttraumatic PVR is increasing the possibilities of management, and it is hoped that in the future our treatment strategies will evolve, in particular adopting a multidrug approach, and become even more effective in vision recovery. This paper reviews the current literature and clinical trial data on the pathogenesis of PVR and its correlation with ocular trauma and describes the biochemical/molecular events that will be fundamental for the development of novel treatment strategies. This literature review included PubMed articles published from 1979 through 2013. Only studies written in English were included.