N-acetylcysteine suppresses retinal detachment in an experimental model of proliferative vitreoretinopathy

Comprehensive exploration of hub genes involved in oxidative stress in rhegmatogenous retinal detachment based on bioinformatics analysis

Rhegmatogenous retinal detachment (RRD) is a type of ophthalmologic emergency, if left untreated, the blindness rate approaches 100 %. The RRD patient postoperative recovery of visual function is unsatisfactory, most notably due to photoreceptor death. We conducted to identify the key genes for oxidative stress (OS) in RRD through bioinformatics analysis and clinical validation, thus providing new ideas for the recovery of visual function in RRD patients after surgery. A gene database for RRD was obtained from the Gene Expression Omnibus (GEO) database (GSE28133). Then we screened differentially expressed OS genes (DEOSGs) from the database and assessed the critical pathways in RRD with Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway. Protein-protein interaction (PPI) networks and hub genes among the common DEOSGs were identified. In addition, we collected general information and vitreous fluid from 42 patients with RRD and 22 controls [11 each of epiretinal membrane (EM) and macular hole (MH)], examined the expression levels of proteins encoded by hub genes in vitreous fluid by enzyme-linked immunosorbent assay (ELISA) to further assess the relationship between the ELISA data and the clinical characteristics of patients with RRD. Ten hub genes (CCL2, ICAM1, STAT3, CD4, ITGAM, PTPRC, CCL5, IL18, TLR2, VCAM1) were finally screened out from the dataset. The ELISA results showed that, compared with the control group, patients with RRD: TLR2 and ICAM-1 were significantly elevated, and CCL2 had a tendency to be elevated, but no statistically significant; RRD patients and MH patients compared with EM patients: STAT3 and VCAM-1 were significantly elevated. We found affected eyes of RRD patients compared with healthy eyes: temporal and nasal retinal nerve fiber layer (RNFL) were significantly thickened. By correlation analysis, we found that: STAT3 was negatively correlated with ocular perfusion pressure (OPP); temporal RNFL was not only significantly positively correlated with CCL2, but also negatively correlated with Scotopic b-wave amplitude. These findings help us to further explore the mechanism of RRD development and provide new ideas for finding postoperative visual function recovery.

Proliferative Vitreoretinopathy: A Reappraisal

Proliferative vitreoretinopathy (PVR) remains the main cause of failure after retinal detachment (RD) surgery. Despite the development of modern technologies and sophisticated techniques for the management of RD, the growth of fibrocellular membranes within the vitreous cavity and on both sides of the retinal surface, as well as intraretinal fibrosis, can compromise surgical outcomes. Since 1983, when the term PVR was coined by the Retina Society, a lot of knowledge has been obtained about the physiopathology and risk factors of PVR, but, despite the proposal of a lot of therapeutic challenges, surgical skills seem to be the only effective way to manage PVR complications.

Ligand-independent activation of platelet-derived growth factor receptor β promotes vitreous-induced contraction of retinal pigment epithelial cells

BACKGROUND

Epiretinal membranes in patients with proliferative vitreoretinopathy (PVR) consist of extracellular matrix and a number of cell types including retinal pigment epithelial (RPE) cells and fibroblasts, whose contraction causes retinal detachment. In RPE cells depletion of platelet-derived growth factor (PDGF) receptor (PDGFR)β suppresses vitreous-induced Akt activation, whereas in fibroblasts Akt activation through indirect activation of PDGFRα by growth factors outside the PDGF family (non-PDGFs) plays an essential role in experimental PVR. Whether non-PDGFs in the vitreous, however, were also able to activate PDGFRβ in RPE cells remained elusive.

METHODS

The CRISPR/Cas9 technology was utilized to edit a genomic PDGFRB locus in RPE cells derived from an epiretinal membrane (RPEM) from a patient with PVR, and a retroviral vector was used to express a truncated PDGFRβ short of a PDGF-binding domain in the RPEM cells lacking PDGFRβ. Western blot was employed to analyze expression of PDGFRβ and α-smooth muscle actin, and signaling events (p-PDGFRβ and p-Akt). Cellular assays (proliferation, migration and contraction) were also applied in this study.

RESULTS

Expression of a truncated PDGFRβ lacking a PDGF-binding domain in the RPEM cells whose PDGFRB gene has been silent using the CRISPR/Cas9 technology restores vitreous-induced Akt activation as well as cell proliferation, epithelial-mesenchymal transition, migration and contraction. In addition, we show that scavenging reactive oxygen species (ROS) with N-acetyl-cysteine and inhibiting Src family kinases (SFKs) with their specific inhibitor SU6656 blunt the vitreous-induced activation of the truncated PDGFRβ and Akt as well as the cellular events related to the PVR pathogenesis. These discoveries suggest that in RPE cells PDGFRβ can be activated indirectly by non-PDGFs in the vitreous via an intracellular pathway of ROS/SFKs to facilitate the development of PVR, thereby providing novel opportunities for PVR therapeutics.

CONCLUSION

The data shown here will improve our understanding of the mechanism by which PDGFRβ can be activated by non-PDGFs in the vitreous via an intracellular route of ROS/SFKs and provide a conceptual foundation for preventing PVR by inhibiting PDGFRβ transactivation (ligand-independent activation).

Using Advanced Bioinformatics Tools to Identify Novel Therapeutic Candidates for Proliferative Vitreoretinopathy

Purpose

Proliferative vitreoretinopathy (PVR) is the dreaded cause of failure following retinal detachment repair; however, no cures or preventative therapies exist to date. The purpose of this study was to use bioinformatics tools to identify drugs or compounds that interact with biomarkers and pathways involved in PVR pathogenesis that could be eligible for further testing for the prevention and treatment of PVR.

Methods

We queried PubMed to compile a comprehensive list of genes described in PVR to date from human studies, animal models, and genomic studies found in the National Center for Biotechnology Information database. Gene enrichment analysis was performed using ToppGene on PVR-related genes against drug-gene interaction databases to construct a pharmacome and estimate the statistical significance of overrepresented compounds. Compounds with no clinical indications were filtered out from the resulting drug lists.

Results

Our query identified 34 unique genes associated with PVR. Out of 77,146 candidate drugs or compounds in the drug databases, our analysis revealed multiple drugs and compounds that have significant interactions with genes involved in PVR, including antiproliferatives, corticosteroids, cardiovascular agents, antioxidants, statins, and micronutrients. Top compounds, including curcumin, statins, and cardiovascular agents such as carvedilol and enalapril, have well-established safety profiles and potentially could be readily repurposed for PVR. Other significant compounds such as prednisone and methotrexate have shown promising results in ongoing clinical trials for PVR.

Conclusions

This bioinformatics approach of studying drug-gene interactions can identify drugs that may affect genes and pathways implicated in PVR. Predicted bioinformatics studies require further validation by preclinical or clinical studies; however, this unbiased approach could identify potential candidates among existing drugs and compounds that could be repurposed for PVR and guide future investigations.

Translational Relevance

Novel repurposable drug therapies for PVR can be found using advanced bioinformatics models.

Inflammation and Oxidative Stress Gene Variability in Retinal Detachment Patients with and without Proliferative Vitreoretinopathy

This study investigated the association between certain genetic variations and the risk of developing proliferative vitreoretinopathy (PVR) after surgery. The study was conducted on 192 patients with primary rhegmatogenous retinal detachment (RRD) who underwent 3-port pars plana vitrectomy (PPV). The distribution of single nucleotide polymorphisms (SNPs) located in genes involved in inflammation and oxidative stress associated with PVR pathways were analyzed among patients with and without postoperative PVR grade C1 or higher. A total of 7 defined SNPs of 5 genes were selected for genotyping: rs4880 (SOD2); rs1001179 (CAT); rs1050450 (GPX1); rs1143623, rs16944, rs1071676 (IL1B); rs2910164 (MIR146A) using competitive allele-specific polymerase chain reaction. The association of SNPs with PVR risk was evaluated using logistic regression. Furthermore, the possible association of SNPs with postoperative clinical parameters was evaluated using non-parametric tests. The difference between two genotype frequencies between patients with or without PVR grade C1 or higher was found to be statistically significant: SOD2 rs4880 and IL1B rs1071676. Carriers of at least one polymorphic IL1B rs1071676 GG allele appeared to have better postoperative best-corrected visual acuity only in patients without PVR (p = 0.070). Our study suggests that certain genetic variations may play a role in the development of PVR after surgery. These findings may have important implications for identifying patients at higher risk for PVR and developing new treatments.

Experimental Models to Study Epithelial-Mesenchymal Transition in Proliferative Vitreoretinopathy

Proliferative vitreoretinal diseases (PVDs) encompass proliferative vitreoretinopathy (PVR), epiretinal membranes, and proliferative diabetic retinopathy. These vision-threatening diseases are characterized by the development of proliferative membranes above, within and/or below the retina following epithelial-mesenchymal transition (EMT) of the retinal pigment epithelium (RPE) and/or endothelial-mesenchymal transition of endothelial cells. As surgical peeling of PVD membranes remains the sole therapeutic option for patients, development of in vitro and in vivo models has become essential to better understand PVD pathogenesis and identify potential therapeutic targets. The in vitro models range from immortalized cell lines to human pluripotent stem-cell-derived RPE and primary cells subjected to various treatments to induce EMT and mimic PVD. In vivo PVR animal models using rabbit, mouse, rat, and swine have mainly been obtained through surgical means to mimic ocular trauma and retinal detachment, and through intravitreal injection of cells or enzymes to induce EMT and investigate cell proliferation and invasion. This review offers a comprehensive overview of the usefulness, advantages, and limitations of the current models available to investigate EMT in PVD.

Vitreous humor proteome: unraveling the molecular mechanisms underlying proliferative and neovascular vitreoretinal diseases

Proliferative diabetic retinopathy (PDR), proliferative vitreoretinopathy (PVR), and neovascular age-related macular degeneration (nAMD) are among the leading causes of blindness. Due to the multifactorial nature of these vitreoretinal diseases, omics approaches are essential for a deeper understanding of the pathophysiologic processes underlying the evolution to a proliferative or neovascular etiology, in which patients suffer from an abrupt loss of vision. For many years, it was thought that the function of the vitreous was merely structural, supporting and protecting the surrounding ocular tissues. Proteomics studies proved that vitreous is more complex and biologically active than initially thought, and its changes reflect the physiological and pathological state of the eye. The vitreous is the scenario of a complex interplay between inflammation, fibrosis, oxidative stress, neurodegeneration, and extracellular matrix remodeling. Vitreous proteome not only reflects the pathological events that occur in the retina, but the changes in the vitreous itself play a central role in the onset and progression of vitreoretinal diseases. Therefore, this review offers an overview of the studies on the vitreous proteome that could help to elucidate some of the pathological mechanisms underlying proliferative and/or neovascular vitreoretinal diseases and to find new potential pharmaceutical targets.

Idelalisib inhibits experimental proliferative vitroretinopathy

Proliferative vitreoretinopathy (PVR) is a fibrotic eye disease that develops after rhegmatogenous retinal detachment surgery and open-globe traumatic injury. Idelalisib is a specific inhibitor of phosphoinositide 3-kinase (PI3K) δ. While PI3Kδ is primarily expressed in leukocytes, its expression is also considerably high in retinal pigment epithelial (RPE) cells, which play a crucial part in the PVR pathogenesis. Herein we show that GeoMx Digital Spatial Profiling uncovered strong expression of fibronectin in RPE cells within epiretinal membranes from patients with PVR, and that idelalisib (10 μM) inhibited Akt activation, fibronectin expression and collagen gel contraction induced by transforming growth factor (TGF)-β2 in human RPE cells. Furthermore, we discovered that idelalisib at a vitreal concentration of 10 μM, a non-toxic dose to the retina, prevented experimental PVR induced by intravitreally injected RPE cells in rabbits assessed by experienced ophthalmologists using an indirect ophthalmoscope plus a + 30 D fundus lens, electroretinography, optical coherence tomography and histological analysis. These data suggested idelalisib could be harnessed for preventing patients from PVR.

A Novel Role of IL13Rα2 in the Pathogenesis of Proliferative Vitreoretinopathy

Proliferative vitreoretinopathy (PVR), an inflammatory and fibrotic blinding disease, is still a therapeutic challenge. Retinal pigment epithelial (RPE) cells dislodged in the vitreous play a central role in the PVR pathogenesis. To identify potential novel contributors to the pathogenesis of PVR, we investigated a profile of vitreous-induced changes in ARPE-19 cells by RNA sequencing. Bioinformatics analysis of the sequencing data showed that there were 258 genes up-regulated and 835 genes down-regulated in the ARPE-19 cells treated with human vitreous. Among these genes, there were three genes related to eye disease with more than threefold changes. In particular, quantitative PCR and western blot results showed that interleukin 13 receptor (IL13R)α2 that is over-expressed in a variety of cancers was up-regulated more than three times in the vitreous-treated ARPE-19 cells. Immunofluorescence analysis indicated that interleukin-13 receptor subunit α2 (IL13Rα2) was highly expressed in ARPE-19 cells within epiretinal membranes from patients with PVR. Importantly, blocking IL13Rα2 with its neutralizing antibody significantly inhibited vitreous-induced contraction of ARPE-19 cells, suggesting a novel role of IL13Rα2 in the PVR pathogenesis. These findings will improve our understanding of the molecular mechanisms by which PVR develops and provides potential targets for PVR therapeutics.

Vitreous Humor Proteome: Targeting Oxidative Stress, Inflammation, and Neurodegeneration in Vitreoretinal Diseases

Oxidative stress is defined as an unbalance between pro-oxidants and antioxidants, as evidenced by an increase in reactive oxygen and reactive nitrogen species production over time. It is important in the pathophysiology of retinal disorders such as diabetic retinopathy, age-related macular degeneration, retinal detachment, and proliferative vitreoretinopathy, which are the focus of this article. Although the human organism’s defense mechanisms correct autoxidation caused by endogenous or exogenous factors, this may be insufficient, causing an imbalance in favor of excessive ROS production or a weakening of the endogenous antioxidant system, resulting in molecular and cellular damage. Furthermore, modern lifestyles and environmental factors contribute to increased chemical exposure and stress induction, resulting in oxidative stress. In this review, we discuss the current information about oxidative stress and the vitreous proteome with a special focus on vitreoretinal diseases. Additionally, we explore therapies using antioxidants in an attempt to rescue the body from oxidation, restore balance, and maximize healthy body function, as well as new investigational therapies that have shown significant therapeutic potential in preclinical studies and clinical trial outcomes, along with their goals and strategic approaches to combat oxidative stress.

Axl Is Essential for in-vitro Angiogenesis Induced by Vitreous From Patients With Proliferative Diabetic Retinopathy

Proliferative diabetic retinopathy (PDR), characterized mainly with abnormal epiretinal angiogenesis forming fibrovascular membranes (FVMs), threatens vision of people with diabetes; FVMs consist of extracellular matrix and a variety of cell types including vascular endothelial cells. Axl, one of receptor tyrosine kinases, can be activated indirectly by vascular endothelial growth factor-A (VEGF-A) via an intracellular route for promoting angiogenesis. In this study, we revealed that growth arrest-specific protein 6 (Gas6), a specific ligand of Axl, was elevated in vitreous from patients with PDR and that Axl was activated in FVMs from patients with PDR. In addition, we demonstrated that in cultured human retinal microvascular endothelial cells (HRECs), Axl inhibition via suppression of Axl expression with Clustered Regularly Interspaced Short Palindromic Repeats/ CRISPR-associated protein 9 or through inactivation with its specific inhibitor R428 blocked PDR vitreous-induced Akt activation and proliferation of HRECs. Furthermore, PDR vitreous-heightened migration and tube formation of HRECs were also blunted by restraining Axl. These results indicate that in the pathogenesis of PDR, Axl can be activated by Gas6 binding directly and by VEGF-A via an intracellular route indirectly, suggesting that Axl plays a pivotal role in the development of PDR and that Axl inhibition shows a bright promise for PDR therapy.

Chalcomoracin prevents vitreous-induced activation of AKT and migration of retinal pigment epithelial cells

Retinal pigment epithelial (RPE) cells are the major cell type in the epi‐ or sub‐retinal membranes in the pathogenesis of proliferative vitreoretinopathy (PVR), which is a blinding fibrotic eye disease and still short of effective medicine. The purpose of this study is to demonstrate whether Chalocomoracin (CMR), a novel purified compound from fungus‐infected mulberry leaves, is able to inhibit vitreous‐induced signalling events and cellular responses intrinsic to PVR. Our studies have revealed that the CMR IC50 for ARPE‐19 cells is 35.5 μmol/L at 72 hours, and that 5 μmol/L CMR inhibits vitreous‐induced Akt activation and p53 suppression; in addition, we have discovered that this chemical effectively blocks vitreous‐stimulated proliferation, migration and contraction of ARPE‐19 cells, suggesting that CMR is a promising PVR prophylactic.

Experimental models and examination methods of retinal detachment

Retinal detachment refers to the separation of the retinal neuroepithelium and pigment epithelium, usually involving the death of photoreceptor cells. Severe detachment may lead to permanent visual impairment if not treated properly and promptly. According to the underlying causes, retinal detachment falls into one of three categories: exudative retinal detachment, traction detachment, and rhegmatogenous retinal detachment. Like many other diseases, it is difficult to study the pathophysiology of retinal detachment directly in humans, because the human retinal tissues are precious, scarce and non-regenerative; thus, establishing experimental models that better mimic the disease is necessary. In this review, we summarize the existing models of the three categories of retinal detachment both in vivo and in vitro, along with an overview of their examination methods and the major strengths and weaknesses of each model.

Normal vitreous promotes angiogenesis via activation of Axl

Vitreous has been reported to prevent tumor angiogenesis, but our previous findings indicate that vitreous activate the signaling pathway of phosphoinositide 3-kinase (PI3K)/Akt, which plays a critical role in angiogenesis. The goal of this research is to determine which role of vitreous plays in angiogenesis-related cellular responses in vitro. We found that in human retinal microvascular endothelial cells (HRECs) vitreous activates a number of receptor tyrosine kinases including Anexelekto (Axl), which plays an important role in angiogenesis. Subsequently, we discovered that depletion of Axl using CRISPR/Cas9 and an Axl-specific inhibitor R428 suppress vitreous-induced Akt activation and cell proliferation, migration, and tuber formation of HRECs. Therefore, this line of research not only demonstrate that vitreous promotes angiogenesis in vitro, but also reveal that Axl is one of receptor tyrosine kinases to mediate vitreous-induced angiogenesis in vitro, thereby providing a molecular basis for removal of vitreous as cleanly as possible when vitrectomy is performed in treating patients with proliferative diabetic retinopathy.

Nutritional and medical food therapies for diabetic retinopathy

Diabetic retinopathy (DR) is a form of microangiopathy. Reducing oxidative stress in the mitochondria and cell membranes decreases ischemic injury and end-organ damage to the retina. New approaches are needed, which reduce the risk and improve the outcomes of DR while complementing current therapeutic approaches. Homocysteine (Hcy) elevation and oxidative stress are potential therapeutic targets in DR. Common genetic polymorphisms such as those of methylenetetrahydrofolate reductase (MTHFR), increase Hcy and DR risk and severity. Patients with DR have high incidences of deficiencies of crucial vitamins, minerals, and related compounds, which also lead to elevation of Hcy and oxidative stress. Addressing the effects of the MTHFR polymorphism and addressing comorbid deficiencies and insufficiencies reduce the impact and severity of the disease. This approach provides safe and simple strategies that support conventional care and improve outcomes. Suboptimal vitamin co-factor availability also impairs the release of neurotrophic and neuroprotective growth factors. Collectively, this accounts for variability in presentation and response of DR to conventional therapy. Fortunately, there are straightforward recommendations for addressing these issues and supporting traditional treatment plans. We have reviewed the literature for nutritional interventions that support conventional therapies to reduce disease risk and severity. Optimal combinations of vitamins B1, B2, B6, L-methylfolate, methylcobalamin (B12), C, D, natural vitamin E complex, lutein, zeaxanthin, alpha-lipoic acid, and n-acetylcysteine are identified for protecting the retina and choroid. Certain medical foods have been successfully used as therapy for retinopathy. Recommendations based on this review and our clinical experience are developed for clinicians to use to support conventional therapy for DR. DR from both type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) have similar retinal findings and responses to nutritional therapies.

PDGFRβ plays an essential role in patient vitreous-stimulated contraction of retinal pigment epithelial cells from epiretinal membranes

Platelet-derived growth factor (PDGF) is associated with clinical proliferative vitreoretinopathy (PVR), which is characterized by formation of sub- or epi-retinal membranes that consist of cells including retinal pigment epithelial （RPE） cells and extracellular matrix. RPE cells play an important role in PVR pathogenesis. Previous findings indicated that PDGF receptor (PDGFR)α was essential in experimental PVR induced by fibroblasts. In RPE cells derived from epiretinal membranes from patients with PVR (RPEMs)， Akt was activated by PDGF-B but not PDGF-A, which suggested that PDGFRβ was the predominant PDGFR isoform expressed in RPEMs. Indeed, CRISPR/Cas9-mediated depletion of PDGFRβ in RPEMs attenuated patient vitreous-induced Akt activation and cellular responses intrinsic to PVR including cell proliferation, migration, and contraction. We conclude that PDGFRβ appears to be the PVR relevant PDGFR isoform in RPEMs.

Idelalisib inhibits vitreous-induced Akt activation and proliferation of retinal pigment epithelial cells from epiretinal membranes

Proliferative vitreoretinopathy (PVR) is a blinding fibrotic eye disease that develops in 8-10% of patients who undergo primary retinal detachment-reparative surgery and in 40-60% of patients with open-globe injury. At present, there is no pharmacological treatment for this devastating disease. Vitreal growth factors activate their respective receptors of cells in the vitreous, trigger their downstream signaling transduction (e.g. phosphoinositide 3 kinases (PI3Ks)/Akt), and drive cellular responses intrinsic to the pathogenesis of PVR. PI3Ks play a central role in experimental PVR. However, which isoform(s) are involved in PVR pathogenesis remain unknown. Herein, we show that p110δ, a catalytic subunit of receptor-regulated PI3K isoform δ, is highly expressed in epiretinal membranes from patients with PVR, and that idelalisib, a specific inhibitor of PI3Kδ, effectively inhibits vitreous-induced Akt activation, proliferation, migration and contraction of retinal pigment epithelial cells derived from an epiretinal membrane of a PVR patient. Small molecules of kinase inhibitors have shown great promise as a class of therapeutics for a variety of human diseases. The data herein suggest that idelalisib is a promising PVR prophylactic.

Phosphoinositide 3-kinase δ inactivation prevents vitreous-induced activation of AKT/MDM2/p53 and migration of retinal pigment epithelial cells

Phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases that play a critical role in transmitting signals from cell-surface molecules to intracellular protein effectors. Key PI3Ks include PI3Kα, PI3Kβ, and PI3Kδ, which are regulated by receptors. The signaling pathway comprising the PI3Ks, along with a Ser/Thr kinase (AKT), a proto-oncogene product (mouse double minute (MDM)2), and a tumor suppressor protein (p53), plays an essential role in experimental proliferative vitreoretinopathy (PVR), which is a fibrotic blinding eye disorder. However, which PI3K isoforms are involved in PVR is unknown. A major characteristic of PVR is the formation of epi (or sub)-retinal membranes that consist of extracellular matrix and cells, including retinal pigment epithelium (RPE) cells, glial cells, and macrophages. RPE cells are considered key players in PVR pathogenesis. Using immunoblotting and immunofluorescence analyses, we herein provide the evidence that PI3Kδ is highly expressed in human RPEs when it is primarily expressed in leukocytes. We also found that PI3Kδ inactivation through two approaches, CRISPR/Cas9-mediated depletion and a PI3Kδ-specific inhibitor (idelalisib), not only blocks vitreous-induced activation of AKT and MDM2 but also abrogates a vitreous-stimulated decrease in p53. Furthermore, we demonstrate that PI3Kδ inactivation prevents vitreous-induced proliferation, migration, and contraction of human RPEs. These results suggest that PI3Kδ may represent a potential therapeutic target for RPE-related eye diseases, including PVR.

Utility of Induced Pluripotent Stem Cell-Derived Retinal Pigment Epithelium for an In Vitro Model of Proliferative Vitreoretinopathy

The advent of stem cell technology, including the technology to induce pluripotency in somatic cells, and direct differentiation of stem cells into specific somatic cell types, has created an exciting new field of scientific research. Much of the work with pluripotent stem (PS) cells has been focused on the exploration and exploitation of their potential as cells/tissue replacement therapies for personalized medicine. However, PS and stem cell-derived somatic cells are also proving to be valuable tools to study disease pathology and tissue-specific responses to injury. High-throughput drug screening assays using tissue-specific injury models have the potential to identify specific and effective treatments that will promote wound healing. Retinal pigment epithelium (RPE) derived from induced pluripotent stem cells (iPS-RPE) are well characterized cells that exhibit the phenotype and functions of in vivo RPE. In addition to their role as a source of cells to replace damaged or diseased RPE, iPS-RPE provide a robust platform for in vitro drug screening to identify novel therapeutics to promote healing and repair of ocular tissues after injury. Proliferative vitreoretinopathy (PVR) is an abnormal wound healing process that occurs after retinal tears or detachments. In this chapter, the role of iPS-RPE in the development of an in vitro model of PVR is described. Comprehensive analyses of the iPS-RPE response to injury suggests that these cells provide a physiologically relevant tool to investigate the cellular mechanisms of the three phases of PVR pathology: migration, proliferation, and contraction. This in vitro model will provide valuable information regarding cellular wound healing responses specific to RPE and enable the identification of effective therapeutics.

Proliferative Vitreoretinopathy: A Review

Proliferative vitreoretinopathy (PVR) is the most common cause for failure of rhegmatogenous retinal detachment repair and is characterized by the growth and contraction of cellular membranes within the vitreous cavity and on both sides of the retinal surface as well as intraretinal fibrosis. Currently, PVR is thought to be an abnormal wound healing response that is primarily driven by inflammatory, retinal, and RPE cells. At this time, surgery is the only management option for PVR as there is no proven pharmacologic agent for the treatment or prevention of PVR. Laboratory research to better understand PVR pathophysiology and clinical trials of various agents to prevent PVR formation are ongoing.

Determining the effect of low-dose isotretinoin on proliferative vitreoretinopathy: the DELIVER trial

PURPOSE

To examine the effect of low-dose, oral isotretinoin in lowering the risk of proliferative vitreoretinopathy (PVR) following rhegmatogenous retinal detachment (RRD) repair.

METHODS

Prospective, open label, dual-cohort study with pathology-matched historical controls. The prospective experimental arms included two cohorts, composed of 51 eyes with recurrent PVR-related RRD and 58 eyes with primary RRD associated with high-risk features for developing PVR. Eyes in the experimental arms received 20 mg of isotretinoin by mouth once daily for 12 weeks starting the day after surgical repair. The primary outcome measure was single surgery anatomical success rate at 3 months following the study surgery.

RESULTS

The single surgery anatomic success rate was 78.4% versus 70.0% (p=0.358) in eyes with recurrent PVR-related retinal detachment exposed to isotretinoin versus historical controls, respectively. In eyes with RRD at high risk for developing PVR, the single surgery success rate was 84.5% versus 61.1% (p=0.005) for eyes exposed to isotretinoin versus historical controls, respectively. For eyes enrolled in the experimental arms, the most common isotretinoin-related side effects were dry skin/mucus membranes in 106 patients (97.2%), abnormal sleep/dreams in 4 patients (3.7%) and fatigue in 3 patients (2.8%).

CONCLUSION

The management and prevention of PVR is challenging and complex. At the dose and duration given in this study, oral istotretinoin may reduce the risk of PVR-associated recurrent retinal detachment in eyes with primary RRD at high risk of developing PVR.

Inhibitory Effects of Plumbagin on Retinal Pigment Epithelial Cell Epithelial-Mesenchymal Transition In Vitro and In Vivo

Background

This study aimed to explore the effects of plumbagin (PLB) on epithelial-to-mesenchymal transition in retinal pigment epithelial (RPE) cells and in proliferative vitreoretinopathy (PVR) rabbit models.

Material/Methods

Rabbit RPE cells were exposed to various concentrations (0, 5, 15, and 25 μM) of PLB. Motility, migration, and invasion of PLB-treated cells were determined in vitro using Transwell chamber assays and scratch wound assays. The contractile ability was evaluated by cell contraction assay. Expression of matrix metalloproteinases (MMPs) and epithelial-mesenchymal transition (EMT) markers were assessed by western blotting. Furthermore, PLB was injected in rabbit eyes along with RPE cells after gas compression of the vitreous. The presence of PVR was determined by indirect ophthalmoscopy on days 1, 7, 14, and 21 after injection. Also, optical coherence tomography (OCT), ultrasound images, electroretinograms (ERG), and histopathology were used to assess efficacy and toxicity.

Results

PLB significantly inhibited the migration and invasion of RPE cells. The agent also markedly reduced cell contractive ability. Furthermore, PLB treatment resulted in the decreased expression of MMP-1, MMP2, α-SMA, and the protection of ZO-1. In addition, the PLB-treated eyes showed lower PVR grades than the untreated eyes in rabbit models. PLB exhibited a wide safety margin, indicating no evidence of causing retinal toxicity.

Conclusions

PLB effectively inhibited the EMT of rabbit RPE cells in vitro and in the experimental PVR models. The results open new avenues for the use of PLB in prevention and treatment of PVR.

SMOKING IS A RISK FACTOR FOR PROLIFERATIVE VITREORETINOPATHY AFTER TRAUMATIC RETINAL DETACHMENT

PURPOSE

To determine the incidence of retinal redetachment due to proliferative vitreoretinopathy after open-globe trauma in smokers and nonsmokers.

METHODS

A total of 892 patients comprising 893 open-globe injuries, in whom 255 eyes were diagnosed with a retinal detachment, and 138 underwent surgical repair were analyzed in a retrospective case-control study. Time to redetachment was examined using the Kaplan-Meier method and analysis of risk factors was analyzed using Cox proportional hazards modeling.

RESULTS

Within one year after retinal detachment surgery, 47% (95% CI, 39-56%) of all 138 repaired retinas redetached because of proliferative vitreoretinopathy. Being a smoker was associated with a higher rate of detachment (adjusted hazard ratio 1.96, P = 0.01). As shown in previous studies, the presence of proliferative vitreoretinopathy at the time of surgery was also an independent risk factor for failure (adjusted hazard ratio 2.13, P = 0.005). Treatment with vitrectomy-buckle compared favorably to vitrectomy alone (adjusted hazard ratio 0.58, P = 0.04). Only 8% of eyes that redetached achieved a best-corrected visual acuity of 20/200 or better, in comparison to 44% of eyes that did not redetach (P < 0.001).

CONCLUSION

Proliferative vitreoretinopathy is a common complication after the repair of retinal detachment associated with open-globe trauma, and being a smoker is a risk factor for redetachment. Further study is needed to understand the pathophysiologic mechanisms underlying this correlation.

AAV-CRISPR/Cas9-Mediated Depletion of VEGFR2 Blocks Angiogenesis In Vitro

Purpose

Pathologic angiogenesis is a component of many diseases, including neovascular age-related macular degeneration, proliferation diabetic retinopathy, as well as tumor growth and metastasis. The purpose of this project was to examine whether the system of adeno-associated viral (AAV)–mediated CRISPR (clustered regularly interspaced short palindromic repeats)–associated endonuclease (Cas)9 can be used to deplete expression of VEGF receptor 2 (VEGFR2) in human vascular endothelial cells in vitro and thus suppress its downstream signaling events.

Methods

The dual AAV system of CRISPR/Cas9 from Streptococcus pyogenes (AAV-SpGuide and -SpCas9) was adapted to edit genomic VEGFR2 in primary human retinal microvascular endothelial cells (HRECs). In this system, the endothelial-specific promoter for intercellular adhesion molecule 2 (ICAM2) was cloned into the dual AAV vectors of SpGuide and SpCas9 for driving expression of green fluorescence protein (GFP) and SpCas9, respectively. These two AAV vectors were applied to production of recombinant AAV serotype 5 (rAAV5), which were used to infect HRECs for depletion of VEGFR2. Protein expression was determined by Western blot; and cell proliferation, migration, as well as tube formation were examined.

Results

AAV5 effectively infected vascular endothelial cells (ECs) and retinal pigment epithelial (RPE) cells; the ICAM2 promoter drove expression of GFP and SpCas9 in HRECs, but not in RPE cells. The results showed that the rAAV5-CRISPR/Cas9 depleted VEGFR2 by 80% and completely blocked VEGF-induced activation of Akt, and proliferation, migration as well as tube formation of HRECs.

Conclusions

AAV-CRISRP/Cas9–mediated depletion of VEGFR2 is a potential therapeutic strategy for pathologic angiogenesis.

[The significance of fibroblasts in experimental modeling of proliferative vitreoretinopathy]

AIM

to investigate the role of heterogeneous fibroblasts in the development of epiretinal membrane in eyes with modeled proliferative vitreoretinopathy.

MATERIAL AND METHODS

The material for investigation were 6 eyes of 3 Chinchilla rabbits. Suspended fibroblasts (fibroblasts of the human skin - 200000 cells in 0.1 ml) were injected into the vitreous cavity via the pars plana. The animals were followed up for 1 month and then made out of the experiment. The eyes were enucleated and fixed in 10% neutral buffered formalin for routine histological examination. Microscopy was performed on the Leica system.

RESULTS

The main clinical and morphological criteria for a rabbit model of PVR induced by intravitreal injection of heterogenic fibroblasts have been established: epiretinal membrane formation, changes in intraocular structures (the retinal pigment epithelium and retina), and inflammation (due to transplantation immunity). Particularities of the epiretinal membrane development and the role of different intraocular structures have been described.

CONCLUSION

The experimental fibroblastic model of PVR reproduces the final, fibrous, stage of PVR, which is significant for efficacy evaluation of antiproliferative drugs.

Introduction of the MDM2 T309G Mutation in Primary Human Retinal Epithelial Cells Enhances Experimental Proliferative Vitreoretinopathy

Purpose

The murine double minute (MDM)2 is a critical negative regulator of the p53 tumor suppressor, and MDM2 SNP309G is associated with a higher risk of proliferative vitreoretinopathy (PVR); in addition, the MDM2 T309G created using clustered regularly interspaced short palindromic repeats (CRISPR)/associated endonuclease (Cas)9 enhances normal rabbit vitreous-induced expression of MDM2 and survival of primary human retinal pigment epithelial (hRPE) cells in vitro. The goal of this study was to determine whether this MDM2 T309G contributes to the development of experimental PVR.

Methods

hRPE cells expressing MDM2 T309G or T309T only were treated with vitreous from human PVR donors (HV). The expression of MDM2 and p53 in the treated cells was examined by Western blot. The in vitro vitreous-induced cellular responses, such as contraction were assessed, and PVR was induced by intravitreal injection of the hRPE cells with MDM2 T309G or T309T only into rabbit eyes.

Results

Western blot analyses indicated that treatment of hRPE cells with HV led to a significant increase (1.7 ± 0.2-fold) in the expression of MDM2 and a significant decrease in p53 in the cells expressing MDM2 T309G compared with those with MDM2 T309T. In addition, HV promoted contraction of the hRPE cells expressing MDM2 T309G significantly more than those with MDM2 T309T only. Furthermore, MDM2 T309G in the hRPE cells enhanced the development of PVR in a rabbit model.

Conclusions

The MDM2 SNP309 in RPE cells enhances their potential of PVR pathogenesis.

Editing VEGFR2 Blocks VEGF-Induced Activation of Akt and Tube Formation

Purpose

Vascular endothelial growth factor receptor 2 (VEGFR2) plays a key role in VEGF-induced angiogenesis. The goal of this project was to test the hypothesis that editing genomic VEGFR2 loci using the technology of clustered regularly interspaced palindromic repeats (CRISPR)-associated DNA endonuclease (Cas)9 in Streptococcus pyogenes (SpCas9) was able to block VEGF-induced activation of Akt and tube formation.

Methods

Four 20 nucleotides for synthesizing single-guide RNAs based on human genomic VEGFR2 exon 3 loci were selected and cloned into a lentiCRISPR v2 vector, respectively. The DNA fragments from the genomic VEGFR2 exon 3 of transduced primary human retinal microvascular endothelial cells (HRECs) were analyzed by Sanger DNA sequencing, surveyor nuclease assay, and next-generation sequencing (NGS). In the transduced cells, expression of VEGFR2 and VEGF-stimulated signaling events (e.g., Akt phosphorylation) were determined by Western blot analyses; VEGF-induced cellular responses (proliferation, migration, and tube formation) were examined.

Results

In the VEGFR2-sgRNA/SpCas9–transduced HRECs, Sanger DNA sequencing indicated that there were mutations, and NGS demonstrated that there were 83.57% insertion and deletions in the genomic VEGFR2 locus; expression of VEGFR2 was depleted in the VEGFR2-sgRNA/SpCas9–transduced HRECs. In addition, there were lower levels of Akt phosphorylation in HRECs with VEGFR2-sgRNA/SpCas9 than those with LacZ-sgRNA/SpCas9, and there was less VEGF-stimulated Akt activation, proliferation, migration, or tube formation in the VEGFR2-depleted HRECs than those treated with aflibercept or ranibizumab.

Conclusions

The CRISPR-SpCas9 technology is a potential novel approach to prevention of pathologic angiogenesis.

Prevention of Proliferative Vitreoretinopathy by Suppression of Phosphatidylinositol 5-Phosphate 4-Kinases

Purpose

Previous studies have shown that vitreous stimulates degradation of the tumor suppressor protein p53 and that knockdown of phosphatidylinositol 5-phosphate 4-kinases (PI5P4Kα and -β) abrogates proliferation of p53-deficient cells. The purpose of this study was to determine whether vitreous stimulated expression of PI5P4Kα and -β and whether suppression of PI5P4Kα and -β would inhibit vitreous-induced cellular responses and experimental proliferative vitreoretinopathy (PVR).

Methods

PI5P4Kα and -β encoded by PIP4K2A and 2B, respectively, in human ARPE-19 cells were knocked down by stably expressing short hairpin (sh)RNA directed at human PIP4K2A and -2B. In addition, we rescued expression of PI5P4Kα and -β by re-expressing mouse PIP4K2A and -2B in the PI5P4Kα and -β knocked-down ARPE-19 cells. Expression of PI5P4Kα and -β was determined by Western blot and immunofluorescence. The following cellular responses were monitored: cell proliferation, survival, migration, and contraction. Moreover, the cell potential of inducing PVR was examined in a rabbit model of PVR effected by intravitreal cell injection.

Results

We found that vitreous enhanced expression of PI5P4Kα and -β in RPE cells and that knocking down PI5P4Kα and -β abrogated vitreous-stimulated cell proliferation, survival, migration, and contraction. Re-expression of mouse PIP4Kα and -β in the human PI5P4Kα and -β knocked-down cells recovered the loss of vitreous-induced cell contraction. Importantly, suppression of PI5P4Kα and -β abrogated the pathogenesis of PVR induced by intravitreal cell injection in rabbits. Moreover, we revealed that expression of PI5P4Kα and -β was abundant in epiretinal membranes from PVR grade C patients.

Conclusions

The findings from this study indicate that PI5P4Kα and -β could be novel therapeutic targets for the treatment of PVR.

Inhibition of Proliferation and Epithelial Mesenchymal Transition in Retinal Pigment Epithelial Cells by Heavy Chain-Hyaluronan/Pentraxin 3

Proliferative vitreoretinopathy (PVR) is mediated by proliferation and epithelial mesenchymal transition (EMT) of retinal pigment epithelium (RPE). Because heavy chain-hyaluronic acid/pentraxin 3 (HC-HA/PTX3) purified from human amniotic membrane exerts anti-inflammatory and anti-scarring actions, we hypothesized that HC-HA/PTX3 could inhibit these PVR-related processes in vitro. In this study, we first optimized an ARPE-19 cell culture model to mimic PVR by defining cell density, growth factors, and cultivation time. Using this low cell density culture model and HA as a control, we tested effects of HC-HA/PTX3 on the cell viability (cytotoxicity), proliferation (EGF + FGF-2) and EMT (TGF-β1). Furthermore, we determined effects of HC-HA/PTX3 on cell migration (EGF + FGF-2 + TGF-β1) and collagen gel contraction (TGF-β1). We found both HA and HC-HA/PTX3 were not toxic to unstimulated RPE cells. Only HC-HA/PTX3 dose-dependently inhibited proliferation and EMT of stimulated RPE cells by down-regulating Wnt (β-catenin, LEF1) and TGF-β (Smad2/3, collagen type I, α-SMA) signaling, respectively. Additionally, HA and HC-HA/PTX3 inhibited migration but only HC-HA/PTX3 inhibited collagen gel contraction. These results suggest HC-HA/PTX3 is a non-toxic, potent inhibitor of proliferation and EMT of RPE in vitro, and HC-HA/PTX3’s ability to inhibit PVR formation warrants evaluation in an animal model.

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.

Proliferative vitreoretinopathy: A new concept of disease pathogenesis and practical consequences

During the last four decades, proliferative vitreoretinopathy (PVR) has defied the efforts of many researchers to prevent its occurrence or development. Thus, PVR is still the major complication following retinal detachment (RD) surgery and a bottle-neck for advances in cell therapy that require intraocular surgery. In this review we tried to combine basic and clinical knowledge, as an example of translational research, providing new and practical information for clinicians. PVR was defined as the proliferation of cells after RD. This idea was used for classifying PVR and also for designing experimental models used for testing many drugs, none of which were successful in humans. We summarize current information regarding the pathogenic events that follow any RD because this information may be the key for understanding and treating the earliest stages of PVR. A major focus is made on the intraretinal changes derived mainly from retinal glial cell reactivity. These responses can lead to intraretinal PVR, an entity that has not been clearly recognized. Inflammation is one of the major components of PVR, and we describe new genetic biomarkers that have the potential to predict its development. New treatment approaches are analyzed, especially those directed towards neuroprotection, which can also be useful for preventing visual loss after any RD. We also summarize the results of different surgical techniques and clinical information that is oriented toward the identification of high risk patients. Finally, we provide some recommendations for future classification of PVR and for designing comparable protocols for testing new drugs or techniques.

The roles of signaling pathways in epithelial-to-mesenchymal transition of PVR

Proliferative vitreoretinopathy (PVR) is the major cause of failure in patients undergoing surgery for rhegmatogenous retinal detachment (RRD). Characterized by the formation of an abnormal contractile membrane within the eye, PVR can cause tractional retinal redetachment. Epithelial-to-mesenchymal transition (EMT), in which epithelial cells morphologically and phenotypically transdifferentiate into mesenchymal cells, is the major pathological process implicated in PVR. Among the various cell types involved in the process, retinal pigment epithelium cells are primary contributors although, after decades of research, the mechanisms underlying EMT have remained elusive. Recently, signaling pathways, some involving growth factors, have been demonstrated to contribute to EMT. In this article, we review research to date about the roles of such signaling, including including transforming growth factor-beta-, hepatocyte growth factor-, platelet-derived growth factor-, and Notch-, Wnt/β-catenin-, and Hippo-signaling pathways, in the EMT of PVR.

RasGAP Promotes Autophagy and Thereby Suppresses Platelet-Derived Growth Factor Receptor-Mediated Signaling Events, Cellular Responses, and Pathology

Platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) make profound contributions to both physiology and pathology. While it is widely believed that direct (PDGF-mediated) activation is the primary mode of activating PDGFRs, the discovery that they can also be activated indirectly begs the question of the relevance of the indirect mode of activating PDGFRs. In the context of a blinding eye disease, indirect activation of PDGFRα results in persistent signaling, which suppresses the level of p53 and thereby promotes viability of cells that drive pathogenesis. Under the same conditions, PDGFRβ fails to undergo indirect activation. In this paper, we report that RasGAP (GTPase-activating protein of Ras) prevented indirect activation of PDGFRβ. RasGAP, which associates with PDGFRβ but not PDGFRα, reduced the level of mitochondrion-derived reactive oxygen species, which are required for enduring activation of PDGFRs. Furthermore, preventing PDGFRβ from associating with RasGAP allowed it to signal enduringly and drive pathogenesis of a blinding eye disease. These results indicate a previously unappreciated role of RasGAP in antagonizing indirect activation of PDGFRβ, define the underlying mechanism, and raise the possibility that PDGFRβ-mediated diseases involve indirect activation of PDGFRβ.

Plasma-activated medium suppresses choroidal neovascularization in mice: a new therapeutic concept for age-related macular degeneration

Choroidal neovascularization (CNV) is the main pathogenesis of age-related macular degeneration (AMD), which leads to severe vision loss in many aged patients in most advanced country. CNV compromises vision via hemorrhage and retinal detachment on account of pathological neovascularization penetrating the retina. Plasma medicine represents the medical application of ionized gas “plasma” that is typically studied in the field of physical science. Here we examined the therapeutic ability of plasma-activated medium (PAM) to suppress CNV. The effect of PAM on vascularization was assessed on the basis of human retinal endothelial cell (HREC) tube formation. In mice, laser photocoagulation was performed to induce CNV (laser-CNV), followed by intravitreal injection of PAM. N-Acetylcysteine was used to examine the role of reactive oxygen species in PAM-induced CNV suppression. Fundus imaging, retinal histology examination, and electroretinography (ERG) were also performed to evaluate PAM-induced retinal toxicity. Interestingly, HREC tube formation and laser-CNV were both reduced by treatment with PAM. N-acetylcysteine only partly neutralized the PAM-induced reduction in laser-CNV. In addition, PAM injection had no effect on regular retinal vessels, nor did it show retinal toxicity in vivo. Our findings indicate the potential of PAM as a novel therapeutic agent for suppressing CNV.

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.

A reactive oxygen species-mediated, self-perpetuating loop persistently activates platelet-derived growth factor receptor α

The platelet-derived growth factor (PDGF) receptors (PDGFRs) are central to a spectrum of human diseases. When PDGFRs are activated by PDGF, reactive oxygen species (ROS) and Src family kinases (SFKs) act downstream of PDGFRs to enhance PDGF-mediated tyrosine phosphorylation of various signaling intermediates. In contrast to these firmly established principles of signal transduction, much less is known regarding the recently appreciated ability of ROS and SFKs to indirectly and chronically activate monomeric PDGF receptor α (PDGFRα) in the setting of a blinding condition called proliferative vitreoretinopathy (PVR). In this context, we made a series of discoveries that substantially expands our appreciation of epigenetic-based mechanisms to chronically activate PDGFRα. Vitreous, which contains growth factors outside the PDGF family but little or no PDGFs, promoted formation of a unique SFK-PDGFRα complex that was dependent on SFK-mediated phosphorylation of PDGFRα and activated the receptor's kinase activity. While vitreous engaged a total of five receptor tyrosine kinases, PDGFRα was the only one that was activated persistently (at least 16 h). Prolonged activation of PDGFRα involved mTOR-mediated inhibition of autophagy and accumulation of mitochondrial ROS. These findings reveal that growth factor-containing biological fluids, such as vitreous, are able to tirelessly activate PDGFRα by engaging a ROS-mediated, self-perpetuating loop.

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.

Fibrotic remodeling of the extracellular matrix through a novel (engineered, dual-function) antibody reactive to a cryptic epitope on the N-terminal 30 kDa fragment of fibronectin

Fibrosis is characterized by excessive accumulation of scar tissue as a result of exaggerated deposition of extracellular matrix (ECM), leading to tissue contraction and impaired function of the organ. Fibronectin (Fn) is an essential component of the ECM, and plays an important role in fibrosis. One such fibrotic pathology is that of proliferative vitreoretinopathy (PVR), a sight-threatening complication which develops as a consequence of failure of surgical repair of retinal detachment. Such patients often require repeated surgeries for retinal re-attachment; therefore, a preventive measure for PVR is of utmost importance. The contractile membranes formed in PVR, are composed of various cell types including the retinal pigment epithelial cells (RPE); fibronectin is an important constituent of the ECM surrounding these cells. Together with the vitreous, fibronectin creates microenvironments in which RPE cells proliferate. We have successfully developed a dual-action, fully human, fibronectin-specific single chain variable fragment antibody (scFv) termed Fn52RGDS, which acts in two ways: i) binds to cryptic sites in fibronectin, and thereby prevents its self polymerization/fibrillogenesis, and ii) interacts with the cell surface receptors, ie., integrins (through an attached “RGD” sequence tag), and thereby blocks the downstream cell signaling events. We demonstrate the ability of this antibody to effectively reduce some of the hallmark features of fibrosis - migration, adhesion, fibronectin polymerization, matrix metalloprotease (MMP) expression, as well as reduction of collagen gel contraction (a model of fibrotic tissue remodeling). The data suggests that the antibody can be used as a rational, novel anti-fibrotic candidate.

Ranibizumab is a potential prophylaxis for proliferative vitreoretinopathy, a nonangiogenic blinding disease

Proliferative vitreoretinopathy (PVR) exemplifies a disease that is difficult to predict, lacks effective treatment options, and substantially reduces the quality of life of an individual. Surgery to correct a rhegmatogenous retinal detachment fails primarily because of PVR. Likely mediators of PVR are growth factors in vitreous, which stimulate cells within and behind the retina as an inevitable consequence of a breached retina. Three classes of growth factors [vascular endothelial growth factor A (VEGF-A), platelet-derived growth factors (PDGFs), and non-PDGFs (growth factors outside of the PDGF family)] are relevant to PVR pathogenesis because they act on PDGF receptor α, which is required for experimental PVR and is associated with this disease in humans. We discovered that ranibizumab (a clinically approved agent that neutralizes VEGF-A) reduced the bioactivity of vitreous from patients and experimental animals with PVR, and protected rabbits from developing disease. The apparent mechanism of ranibizumab action involved derepressing PDGFs, which, at the concentrations present in PVR vitreous, inhibited non-PDGF-mediated activation of PDGF receptor α. These preclinical findings suggest that available approaches to neutralize VEGF-A are prophylactic for PVR, and that anti-VEGF-based therapies may be effective for managing more than angiogenesis- and edema-driven pathological conditions.

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

PURPOSE

Proliferative vitreoretinopathy (PVR) is a complication of retinal detachment that can lead to surgical failure and vision loss. Previous studies suggest that a variety of retinal cells, including RPE and Müller glia, may be responsible. Platelet-derived growth factor receptor alpha (PDGFRα) has been strongly implicated in the pathogenesis, and found to be intrinsic to the development of PVR in rabbit models. We examine whether SU9518, a tyrosine kinase inhibitor with PDGFRα specificity, can inhibit the development of PVR in fibroblast and Müller cell rabbit models of PVR.

METHODS

SU9518 was injected in rabbit eyes along with fibroblasts, Müller cells (MIO-M1), or Müller cells transfected to increase their expression of PDGFRα (MIO-M1α). Indirect ophthalmoscopy and histopathology were used to assess efficacy and toxicity.

RESULTS

SU9518 was an effective inhibitor of PVR in both fibroblast and Müller cell models of PVR. No toxic effects were identified by indirect ophthalmoscopy or histopathology.

CONCLUSIONS

SU9518 is an effective and safe inhibitor of PVR in rabbit models, and could potentially be used in humans for the treatment of this and other proliferative diseases of the retina involving fibrosis and gliosis. Further animal studies need to be performed to examine retinal toxicity and sustained delivery mechanisms.

A novel function of p53: a gatekeeper of retinal detachment

Proliferative vitreoretinopathy (PVR) is a blinding disease associated with rhegmatogenous retinal detachment, for which there is no satisfactory treatment. Surgery helps in many cases, but, to our knowledge, there are no pharmacological approaches to reduce PVR risk. We report that suppressing expression of p53 was a required event in two assays of PVR (namely, platelet-derived growth factor receptor α-mediated contraction of cells in a collagen gel and retinal detachment in an animal model of PVR). Furthermore, preventing the decline in the level of p53 with agents such as Nutlin-3 protected from retinal detachment, which is the most vision-compromising component of PVR. Finally, Nutlin-3 may be effective in the clinical setting because it prevented human PVR vitreous-induced contraction of cells isolated from a patient PVR membrane. These studies identify Nutlin-3 as a potential PVR prophylaxis.

Mechanisms of inflammation in proliferative vitreoretinopathy: from bench to bedside

Proliferative vitreoretinopathy (PVR) is a vision-threatening disease and a common complication of surgery to correct rhegmatogenous retinal detachment (RRD). Several models of the pathogenesis of this disease have been described with some of these models focusing on the role of inflammatory cells and other models focusing on the role of growth factors and cytokines in the vitreous which come into contact with intraretinal and retinal pigment epithelial cells. New experiments have shed light on the pathogenesis of PVR and offer promising avenues for clinical intervention before PVR develops. One such target is the indirect pathway of activation of platelet-derived growth factor receptor alpha (PDGRα), which plays an important role in PVR. Clinical trials assessing the efficacy of 5-fluorouracil (5-FU) and low-molecular-weight heparin (LMWH), daunorubicin, and 13-cis-retinoic acid, among other therapies, have yielded mixed results. Here we review inflammatory and other mechanisms involved in the pathogenesis of PVR, we highlight important clinical trials, and we discuss how findings at the bench have the potential to be translated to the bedside.

Retinal Pigment Epithelium and Müller Progenitor Cell Interaction Increase Müller Progenitor Cell Expression of PDGFRα and Ability to Induce Proliferative Vitreoretinopathy in a Rabbit Model

Purpose. Proliferative vitreoretinopathy (PVR) is a complication of retinal detachment characterized by redetachment of the retina as a result of membrane formation and contraction. A variety of retinal cells, including retinal pigment epithelial (RPE) and Müller glia, and growth factors may be responsible. Platelet-derived growth factor receptor alpha (PDGFRα) is found in large quantities in PVR membranes, and is intrinsic to the development of PVR in rabbit models. This study explores the expression of PDGFR in cocultures of RPE and Müller cells over time to examine how these two cell types may collaborate in the development of PVR. We also examine how changes in PDGFRα expression alter Müller cell pathogenicity. Methods. Human MIO-M1 Müller progenitor (MPC) and ARPE19 cells were studied in a transmembrane coculture system. Immunocytochemistry and Western blot were used to look at PDGFRα, PDGFRβ, and GFAP expression. A transfected MPC line cell line expressing the PDGFRα (MIO-M1α) was generated, and tested in a rabbit model for its ability to induce PVR. Results. The expression of PDGFRα and PDGFRβ was upregulated in MIO-M1 MPCs cocultured with ARPE19 cells; GFAP was slightly decreased. Increased expression of PDGFRα in the MIO-M1 cell line resulted in increased pathogenicity and enhanced ability to induce PVR in a rabbit model. Conclusions. Müller and RPE cell interaction can lead to upregulation of PDGFRα and increased Müller cell pathogenicity. Müller cells may play a more active role than previously thought in the development of PVR membranes, particularly when stimulated by an RPE-cell-rich environment. Additional studies of human samples and in animal models are warranted.

Neuroprotective effects of lutein in a rat model of retinal detachment

Background

Retinal detachment (RD) is a leading cause of blindness, and although final surgical re-attachment rate has greatly improved, visual outcome in many macula-off detachments is disappointing, mainly because of photoreceptor cell death. We previously showed that lutein is anti-apoptotic in rodent models of ischemia/reperfusion injury. The objective of this study is to investigate lutein as a possible pharmacological adjunct to surgery.

Methods

Subretinal injections of 1.4 % sodium hyaluronate were used to induce RD in Sprague–Dawley rats until their retinae were approximately 70 % detached. Daily injections of corn oil (control group) or 0.5 mg/kg lutein in corn oil (treatment group) were given intraperitoneally starting 4 h after RD induction. Animals were euthanized 3 days and 30 days after RD and their retinae were analyzed for photoreceptor apoptosis and cell survival at the outer nuclear layer (ONL) using TUNEL staining and cell counting on retinal sections. Glial fibrillary acidic protein (GFAP) and rhodopsin (RHO) expression were evaluated with immunohistochemistry. Western blotting was done with antibodies against cleaved caspase-3, cleaved caspase-8 and cleaved caspase-9 to delineate lutein’s mechanism of action in the apoptotic cascade. To seek a possible therapeutic time window, the same set of experiments was repeated with treatment commencing 36 h after RD.

Results

When lutein was given 4 h after RD, there were significantly fewer TUNEL-positive cells in ONL 3 days after RD when compared with the vehicle group. Cell counting showed that there were significantly more nuclei in ONL in lutein-treated retinae by day 30. Treatment groups also showed significantly reduced GFAP immunoreactivity and preserved RHO expression. At day 3 after RD, Western blotting showed reduced expression of cleaved caspase-3 and cleaved caspase-8 in the treatment group. No difference was found for cleaved caspase-9. When lutein was given 36 h after RD similar results were observed.

Conclusions

Our results suggest that lutein is a potent neuroprotective agent that can salvage photoreceptors in rats with RD, with a therapeutic window of at least 36 h. The use of lutein in patients with RD may serve as an adjunct to surgery to improve visual outcomes.

Proliferative vitreoretinopathy: current and emerging treatments

Proliferative vitreoretinopathy is a disease process that follows the proliferation of ectopic cell sheets in the vitreous and/or periretinal area, causing periretinal membrane formation and traction, in patients with rhegmatogenous retinal detachments. Currently, vitreous surgery is the standard treatment; however, the results aren't satisfactory given the vision loss that ensues and that redetachment is relatively common. It is becoming clearer that there exists an interplay between various cytokines/growth factors, matrix proteins, and the different cell types that drive the undesirable formation of periretinal membranes. This fundamental understanding is aiding in identifying different adjunct agents that can block the cellular events intrinsic to proliferative vitreoretinopathy. In this review, we describe the current understanding on the pathogenesis and discuss how the fundamental understanding of the biochemical/molecular events is instrumental in developing the novel treatment strategies that are also highlighted.

Vascular endothelial growth factor A competitively inhibits platelet-derived growth factor (PDGF)-dependent activation of PDGF receptor and subsequent signaling events and cellular responses

Certain platelet-derived growth factor (PDGF) isoforms are associated with proliferative vitreoretinopathy (PVR), a sight-threatening complication that develops in a subset of patients recovering from retinal reattachment surgery. Although these PDGF isoforms are abundant in the vitreous of patients and experimental animals with PVR, they make only a minor contribution to activating PDGF receptor α (PDGFRα) and driving experimental PVR. Rather, growth factors outside of the PDGF family are the primary (and indirect) agonists of PDGFRα. These observations beg the question of why vitreal PDGFs fail to activate PDGFRα. We report here that vitreous contains an inhibitor of PDGF-dependent activation of PDGFRα and that a major portion of this inhibitory activity is due to vascular endothelial cell growth factor A (VEGF-A). Furthermore, recombinant VEGF-A competitively blocks PDGF-dependent binding and activation of PDGFR, signaling events, and cellular responses. These findings unveil a previously unappreciated relationship between distant members of the PDGF/VEGF family that may contribute to pathogenesis of a blinding eye disease.