The retinal pigment epithelium: An important player of retinal disorders and regeneration

Tricetin suppresses the cell migration and BMP-6 expression through p38 signaling pathways in human retinal pigment epithelium cells

Proliferative vitreoretinopathy (PVR) is a visual-threatening disease, which cause from the migration of retinal pigment epithelium (RPE). Tricetin, a family of flavonoids, can inhibit the metastasis of several cancers. Herein, we aim to evaluate the possible effect of tricetin on inhibiting ARPE-19 cells migration. The Boyden chamber assay, wound healing assay, RNA sequencing, and Western blot analysis were applied in our experiment. The results revealed that tricetin inhibited the cell migration abilities of ARPE-19 cells. Moreover, using RNA sequencing technology, we revealed that tricetin repressed bone morphogenetic protein-6 (BMP-6) gene expressions in ARPE-19 cells. Overexpression of BMP-6 resulted in significant restoration of cell migration capabilities of tricetin-treated ARPE-19 cells. Furthermore, tricetin suppressed the phosphorylation of the p38 signaling pathway. Moreover, blocking the p38 pathway also inhibits BMP-6 expression and migration in the ARPE-19 cells. In conclusion, this study revealed that tricetin inhibits the ARPE-19 cell migration mainly via the suppression of BMP-6 expression and p38 signaling pathway.

Regeneration from three cellular sources and ectopic mini-retina formation upon neurotoxic retinal degeneration in Xenopus

Regenerative abilities are not evenly distributed across the animal kingdom. The underlying modalities are also highly variable. Retinal repair can involve the mobilization of different cellular sources, including ciliary marginal zone (CMZ) stem cells, the retinal pigmented epithelium (RPE), or Müller glia. To investigate whether the magnitude of retinal damage influences the regeneration modality of the Xenopus retina, we developed a model based on cobalt chloride (CoCl2 ) intraocular injection, allowing for a dose-dependent control of cell death extent. Analyses in Xenopus laevis revealed that limited CoCl2 -mediated neurotoxicity only triggers cone loss and results in a few Müller cells reentering the cell cycle. Severe CoCl2 -induced retinal degeneration not only potentializes Müller cell proliferation but also enhances CMZ activity and unexpectedly triggers RPE reprogramming. Surprisingly, reprogrammed RPE self-organizes into an ectopic mini-retina-like structure laid on top of the original retina. It is thus likely that the injury paradigm determines the awakening of different stem-like cell populations. We further show that these cellular sources exhibit distinct neurogenic capacities without any bias towards lost cells. This is particularly striking for Müller glia, which regenerates several types of neurons, but not cones, the most affected cell type. Finally, we found that X. tropicalis also has the ability to recruit Müller cells and reprogram its RPE following CoCl2 -induced damage, whereas only CMZ involvement was reported in previously examined degenerative models. Altogether, these findings highlight the critical role of the injury paradigm and reveal that three cellular sources can be reactivated in the very same degenerative model.

Bone morphogenetic protein 6 (BMP6) antagonises experimental proliferative vitreoretinopathy established by TGF-β2 stimulation in retinal pigment epithelial cells through modulation of the p38 and JNK MAPK pathways

The formation of the epiretinal fibrotic membrane by retinal pigment epithelial (RPE) cells is a primary pathological change for proliferative vitreoretinopathy (PVR). Bone morphogenetic protein 6 (BMP6) is an antifibrogenic factor in various cells. To date, it is still unknown whether BMP6 can interfere with the fibrogenesis of RPE cells during the progression of PVR. This work aimed to address the relationship between BMP6 and transforming growth factor-β2 (TGF-β2)-elicited fibrogenesis of RPE cells, an experimental model for studying PVR in vitro. The BMP6 level was down-regulated, while the TGF-β2 level was up-regulated in the vitreous humor of PVR patients. The BMP6 level was down-regulated in human RPE cells challenged with TGF-β2. The treatment of RPE cells with TGF-β2 resulted in significant increases in proliferation, migration, epithelial-to-mesenchymal transition (EMT), and extracellular matrix (ECM) remodelling. These effects were found to be inhibited by the overexpression of BMP6 or exacerbated by the knockdown of BMP6. BMP6 overexpression reduced the phosphorylation of p38 and JNK in TGF-β2-stimulated RPE cells, while BMP6 knockdown showed the opposite effects. The inhibition of p38 or JNK partially reversed the BMP6-silencing-induced promoting effects on TGF-β2-elicited fibrogenesis in RPE cells. Taken together, BMP6 demonstrates the ability to counteract the proliferation, migration, EMT, and ECM remodelling of RPE cells induced by TGF-β2. This is achieved through the regulation of the p38 and JNK MAPK pathways. These findings imply a potential connection between BMP6 and PVR, and highlight the potential application of BMP6 in therapeutic interventions for PVR.

Proliferative vitreoretinopathy: an update on the current and emerging treatment options

Proliferative vitreoretinopathy (PVR) remains the main cause of failure in retinal detachment (RD) surgery and a demanding challenge for vitreoretinal surgeons. Despite the large improvements in surgical techniques and a better understanding of PVR pathogenesis in the last years, satisfactory anatomical and visual outcomes have not been provided yet. For this reason, several different adjunctive pharmacological agents have been investigated in combination with surgery. In this review, we analyze the current and emerging adjunctive treatment options for the management of PVR and we discuss their possible clinical application and beneficial role in this subgroup of patients.

Targeting non-muscle myosin II inhibits proliferative vitreoretinopathy through regulating epithelial-mesenchymal transition

Proliferative vitreoretinopathy (PVR) is a common complication of rhegmatogenous retinal detachment, eventually leading to vision loss. To date, there are no effective drugs for the treatment of this disease. In this study, we investigated the effect of blebbistatin, a non-muscle myosin II inhibitor, on the ARPE-19 cell line and in a rabbit model of proliferative vitreoretinopathy. In vitro, we found that blebbistatin inhibited the epithelial-mesenchymal transition of retinal pigment epithelial (RPE) cells and inhibited the ability of RPE cells to migrate, proliferate, generate extracellular matrix, and affect contractility. In vivo the PVR model showed that blebbistatin significantly delayed PVR progression. It also partially prevents the loss of retinal function caused by PVR. Our results suggest that blebbistatin is a potential drug with clinical applications for the treatment of PVR.

Intrinsic and Induced Neuronal Regeneration in the Mammalian Retina

Significance: Retinal neurons are vulnerable to disease and injury, which can result in neuronal death and degeneration leading to irreversible vision loss. The human retina does not regenerate to replace neurons lost to disease or injury. However, cells within the retina of other animals are capable of regenerating neurons, and homologous cells within the mammalian retina could potentially be prompted to do the same. Activating evolutionarily silenced intrinsic regenerative capacity of the mammalian retina could slow, or even reverse, vision loss, leading to an improved quality of life for millions of people. Recent Advances: During development, neurons in the retina are generated progressively by retinal progenitor cells, with distinct neuron types born over developmental time. Many genes function in this process to specify the identity of newly generated neuron types, and these appropriate states of gene expression inform recent regenerative work. When regeneration is initiated in other vertebrates, including birds and fish, specific signaling pathways control the efficiency of regeneration, and these conserved pathways are likely to be important in mammals as well. Critical Issues: Using insights from development and from other animals, limited regeneration from intrinsic cell types has been demonstrated in the mammalian retina, but it is able only to generate a subset of partially differentiated retinal neuron types. Future Directions: Future studies should aim at increasing the efficiency of regeneration, activating regeneration in a targeted fashion across the retina, and improving the ability to generate specific types of retinal neurons to replace those lost to disease or injury. Antioxid. Redox Signal. 39, 1039-1052.

Molecular Signatures Integral to Natural Reprogramming in the Pigment Epithelium Cells after Retinal Detachment in Pleurodeles waltl

The reprogramming of retinal pigment epithelium (RPE) cells into retinal cells (transdifferentiation) lies in the bases of retinal regeneration in several Urodela. The identification of the key genes involved in this process helps with looking for approaches to the prevention and treatment of RPE-related degenerative diseases of the human retina. The purpose of our study was to examine the transcriptome changes at initial stages of RPE cell reprogramming in adult newt Pleurodeles waltl. RPE was isolated from the eye samples of day 0, 4, and 7 after experimental surgical detachment of the neural retina and was used for a de novo transcriptome assembly through the RNA-Seq method. A total of 1019 transcripts corresponding to the differently expressed genes have been revealed in silico: the 83 increased the expression at an early stage, and 168 increased the expression at a late stage of RPE reprogramming. We have identified up-regulation of classical early response genes, chaperones and co-chaperones, genes involved in the regulation of protein biosynthesis, suppressors of oncogenes, and EMT-related genes. We revealed the growth in the proportion of down-regulated ribosomal and translation-associated genes. Our findings contribute to revealing the molecular mechanism of RPE reprogramming in Urodela.

Cellular and Molecular Triggers of Retinal Regeneration in Amphibians

Understanding the mechanisms triggering the initiation of retinal regeneration in amphibians may advance the quest for prevention and treatment options for degenerating human retina diseases. Natural retinal regeneration in amphibians requires two cell sources, namely retinal pigment epithelium (RPE) and ciliary marginal zone. The disruption of RPE interaction with photoreceptors through surgery or injury triggers local and systemic responses for retinal protection. In mammals, disease-induced damage to the retina results in the shutdown of the function, cellular or oxidative stress, pronounced immune response, cell death and retinal degeneration. In contrast to retinal pathology in mammals, regenerative responses in amphibians have taxon-specific features ensuring efficient regeneration. These include rapid hemostasis, the recruitment of cells and factors of endogenous defense systems, activities of the immature immune system, high cell viability, and the efficiency of the extracellular matrix, cytoskeleton, and cell surface remodeling. These reactions are controlled by specific signaling pathways, transcription factors, and the epigenome, which are insufficiently studied. This review provides a summary of the mechanisms initiating retinal regeneration in amphibians and reveals its features collectively directed at recruiting universal responses to trauma to activate the cell sources of retinal regeneration. This study of the integrated molecular network of these processes is a prospect for future research in demand biomedicine.

DISTINCT METABOLIC STATES DIRECT RETINAL PIGMENT EPITHELIUM CELL FATE DECISIONS

During tissue regeneration, proliferation, dedifferentiation, and reprogramming are necessary to restore lost structures. However, it is not fully understood how metabolism intersects with these processes. Chicken embryos can regenerate their retina through retinal pigment epithelium (RPE) reprogramming when treated with fibroblast factor 2 (FGF2). Using transcriptome profiling, we uncovered extensive regulation of gene sets pertaining to proliferation, neurogenesis, and glycolysis throughout RPE-to-neural retina reprogramming. By manipulating cell media composition, we determined that glucose, glutamine, or pyruvate are sufficient to support RPE reprogramming identifying glycolysis as a requisite. Conversely, the induction of oxidative metabolism by activation of pyruvate dehydrogenase induces Epithelial-to-mesenchymal transition (EMT), while simultaneously blocking the activation of neural retina fate. We also identify that EMT is partially driven by an oxidative environment. Our findings provide evidence that metabolism controls RPE cell fate decisions and provide insights into the metabolic state of RPE cells, which are prone to fate changes in regeneration and pathologies, such as proliferative vitreoretinopathy.

Interleukin-6 in retinal diseases: From pathogenesis to therapy

Interleukin-6 (IL-6) is a pleiotropic cytokine that participates in immunomodulation, inflammation, increases vascular permeability, hematopoiesis, and stimulates cell proliferation, among other biological processes. It exerts effects primarily through the classic and trans-signaling pathways. Many studies have demonstrated that IL-6 plays a critical role in the development of retinal diseases including diabetic retinopathy, uveitis, age-related macular degeneration, glaucoma, retinal vein occlusion, central serous chorioretinopathy and proliferative vitreoretinopathy. Thus, the progressive development of drugs targeting IL-6 and IL-6 receptor may play a role in the treatment of multiple retinal diseases. In this article, we comprehensively review the IL-6's biological functions of and its mechanisms in the pathogenesis of various retinal diseases. Furthermore, we summarize the drugs targeting IL-6 and its receptor and prospect their potential application in retinal diseases, hoping to provide new ideas for the treatment of retinal diseases.

Non-viral gene therapy using RNA interference with PDGFR-α mediated epithelial-mesenchymal transformation for proliferative vitreoretinopathy

Fibrotic eye diseases, a series of severe oculopathy, that will destroy normal ocular refractive media and imaging structures. It is characterized by the transformation of the epithelial cells into mesenchyme cells. Proliferative vitreoretinopathy (PVR) is one of these representative diseases. In this investigation, polyethylene glycol grafted branched Polyethyleneimine (PEI-g-PEG) was used as a non-viral gene vector in gene therapy of PVR to achieve anti-fibroblastic effects in vitro and in vivo by interfering with platelet-derived growth factor alpha receptor (PDGFR-α) in the epithelial-mesenchymal transition (EMT) of retinal pigment epithelium (RPE) cells. The plasmid was wrapped by electrostatic conjugation. Physical characterization of the complexes indicated that the gene complexes were successfully prepared. In vitro, cellular experiments showed excellent biocompatibility of PEI-g-PEG, efficient cellular uptake of the gene complexes, and successful expression of the corresponding fragments. Through gene silencing technique, PEI-g-PEG/PDGFR-α shRNA successfully inhibited the process of EMT in vitro. Furthermore, in vivo animal experiments suggested that this method could effectively inhibit the progression of fibroproliferative membranes of PVR. Herein, a feasible and promising clinical idea was provided for developing non-viral gene vectors and preventing fibroblastic eye diseases by RNA interference (RNAi) technology.

Human Wharton's Jelly Mesenchymal Stem Cell Secretome Modifies the Processes of Neuroprotection and Epithelial-Mesenchymal Transition in Retinal Pigment Epithelium at Transcriptional Level

BACKGROUND

Retinal pigment epithelium (RPE) cells are potential targets for treating retinal detachment (RD) and proliferative vitreoretinopathy (PVR), considering the importance of neuroprotection and epithelial-mesenchymal transition (EMT) of RPE in these conditions. This study investigated the effect of human Wharton's jelly mesenchymal stem cell secretome (WJMSC-S) on the expression of genes involved in both neuroprotection and EMT in RPE cells in vitro (TRKB, MAPK, PI3K, BDNF, and NGF).

METHODS

RPE cells from passages 5-7 were treated with WJMSC-S (or the vehicle culture medium as control) for 24 h at 37◦C and subsequently subjected to RNA extraction and cDNA synthesis. Gene expression level was evaluated using real-time PCR in the treated versus control cells.

RESULTS

The results of our study showed that WJMSC-S led to a significant downregulation in three out of five studied gene expression (MAPK, TRKB, and NGF), and simultaneously, remarkably upregulated the expression of the BDNF gene.

CONCLUSIONS

According to the present data, WJMSC-S can affect the EMT and neuroprotection processes at the mRNA level by suppressing EMT and promoting neuroprotection in RPE cells. This finding may have positive clinical implications in the context of RD and PVR.

DAPL1 prevents epithelial-mesenchymal transition in the retinal pigment epithelium and experimental proliferative vitreoretinopathy

Epithelial-mesenchymal transition (EMT) of the retinal pigment epithelium (RPE) is a hallmark of the pathogenesis of proliferative vitreoretinopathy (PVR) that can lead to severe vision loss. Nevertheless, the precise regulatory mechanisms underlying the pathogenesis of PVR remain largely unknown. Here, we show that the expression of death-associated protein-like 1 (DAPL1) is downregulated in PVR membranes and that DAPL1 deficiency promotes EMT in RPE cells in mice. In fact, adeno-associated virus (AAV)-mediated DAPL1 overexpression in RPE cells of Dapl1-deficient mice inhibited EMT in physiological and retinal-detachment states. In a rabbit model of PVR, ARPE-19 cells overexpressing DAPL1 showed reduced ability to induce experimental PVR, and AAV-mediated DAPL1 delivery attenuated the severity of experimental PVR. Furthermore, a mechanistic study revealed that DAPL1 promotes P21 phosphorylation and its stabilization partially through NFκB (RelA) in RPE cells, whereas the knockdown of P21 led to neutralizing effects on DAPL1-dependent EMT inhibition and enhanced the severity of experimental PVR. These results suggest that DAPL1 acts as a novel suppressor of RPE-EMT and has an important role in antagonizing the pathogenesis of experimental PVR. Hence, this finding has implications for understanding the mechanism of and potential therapeutic applications for PVR.

Vitreal Concentrations of Vascular Endothelial Growth Factor in Patients with Rhegmatogenous Retinal Detachment

The purpose of this study is to evaluate the concentration of vascular endothelial growth factor (VEGF) in the vitreous humor of patients with primary rhegmatogenous retinal detachment (RRD). This is a prospective case control study. Eighteen patients with primary RRD without proliferative vitreoretinopathy C (PVR C) were enrolled as cases, and twenty-two non-diabetic retinopathy patients who were candidates for complete pars plana vitrectomy due to Macular Hole or Epiretinal Membrane were included as the control group. Undiluted vitreal samples were collected during the initiation of Pars Plana Vitrectomy (PPV) prior to any infusion into the posterior cavity. Vitreous samples were also collected from 21 fresh cadaveric globes. The vitreous concentration of VEGF was measured by enzyme-linked immunosorbent assay (ELISA) technique and compared between these two groups. The vitreal concentration of VEGF was 0.643 ± 0.088 ng/mL in the RRD group. Measured concentrations of VEGF in controls were 0.043 ± 0.104 ng/mL, and in cadaveric eyes they were 0.033 ± 0.058 ng/mL. The mean VEGF concentration in the RRD group was statistically higher than in the control group (p < 0.0001) and cadaveric eyes (p < 0.0001). Our study shows that vitreal VEGF concentrations significantly increase in patients with RRD.

Applications of Human Amniotic Membrane Patching Assisted Vitrectomy in the Management of Postoperative PVR in Complex Retinal Detachments

Human amniotic membranes (hAMs) are extraembryonic tissues currently employed in the treatment of many ocular and systemic diseases. Several reports indicate that hAMs can suppress the signaling pathway of tissue growth factor beta (TGF-β), a cytokine that plays a major role in the pathogenesis of proliferative vitreoretinopathy (PVR) through the induction of epithelial-mesenchymal transition (EMT) in exposed retinal pigmented epithelium (RPE) cells. The present study was conducted to evaluate the efficacy of a modified vitrectomy procedure (hAMP-V) involving the extensive coverage of exposed RPE with hAM patches to prevent postoperative PVR in a series of 15 cases of retinal detachment complicated by severe preoperatory PVR. The primary outcome was to assess the rate of successful retinal reattachment of a single hAMP-V procedure at 6 months from silicone oil removal. Secondary outcomes included the collection of intraoperative data concerning the quantity, size, and scope of hAM patches, and the assessment of postoperative improvements in mean LogMar BCVA at 3 and 6 months. Successful retinal reattachment was obtained in 14 out of 15 eyes (93.3%). Surgical failure due to major recurrence of PVR occurred in 1 out of 15 eyes (6.7%). Postoperative improvements in mean LogMar BCVA were statistically significant (p < 0.05, paired t-test). No intraoperative and postoperative adverse effects were reported. The study helped to refine the surgical technique while also offering cues for future improvements.

Newtic1 Is a Component of Globular Structures That Accumulate along the Marginal Band of Erythrocytes in the Limb Blastema of Adult Newt, Cynops pyrrhogaster

In adult newts, when a limb is amputated, a mesenchymal cell mass called the blastema is formed on the stump, where blood vessels filled with premature erythrocytes, named polychromatic normoblasts (PcNobs), elongate. We previously demonstrated that PcNobs in the blastema express an orphan gene, Newtic1, and that they secrete growth factors such as BMP2 and TGFβ1 into the surrounding tissues. However, the relationship between Newtic1 expression and growth factor secretion was not clear since Newtic1 was thought to encode a membrane protein. In this study, we addressed this issue using morphological techniques and found that the Newtic1 protein is a component of globular structures that accumulate at the marginal band in the cytoplasm along the equator of PcNobs. Newtic1-positive (Newtic1(+)) globular structures along the equator were found only in PcNobs with a well-developed marginal band in the blastema. Newtic1(+) globular structures were associated with microtubules and potentially incorporated TGFβ1. Based on these observations, we propose a hypothesis that the Newtic1 protein localizes to the membrane of secretory vesicles that primarily carry TGFβ1 and binds to microtubules, thereby tethering secretory vesicles to microtubules and transporting them to the cell periphery as the marginal band develops.

3D printing in Ophthalmology: From medical implants to personalised medicine

3D printing was invented thirty years ago. However, its application in healthcare became prominent only in recent years to provide solutions for drug delivery and clinical challenges, and is constantly evolving. This cost-efficient technique utilises biocompatible materials and is used to develop model implants to provide a greater understanding of human anatomy and diseases, and can be used for organ transplants, surgical planning and for the manufacturing of advanced drug delivery systems. In addition, 3D printed medical devices and implants can be customised for each patient to provide a more tailored treatment approach. The advantages and applications of 3D printing can be used to treat patients with different eye conditions, with advances in 3D bioprinting offering novel therapy applications in ophthalmology. The purpose of this review paper is to provide an in-depth understanding of the applications and advantages of 3D printing in treating different ocular conditions in the cornea, glaucoma, retina, lids and orbits.

Transcriptome Changes in Retinal Pigment Epithelium Post-PNU-282987 Treatment Associated with Adult Retinal Neurogenesis in Mice

PNU-282987, a selective alpha7 nicotinic acetylcholine receptor agonist, has previously been shown to have both neurogenic and broad regenerative effects in the adult murine retina. The objective of this study was to assay the molecular mechanism by which PNU-282987 promotes the production of Muller-derived progenitor cells through signaling via the resident retinal pigment epithelium. These Muller-derived progenitor cells generate a myriad of differentiated neurons throughout the retina that have previously been characterized by morphology. Herein, we demonstrate that topical application of PNU-282987 stimulates production of functional neurons as measured by electroretinograms. Further, we examine the mechanism of how this phenomenon occurs through activation of this atypical receptor using a transcriptomic approach isolated retinal pigment epithelium activated by PNU-282987 and in whole retina. We provide evidence that PNU-282987 causes a bi-modal signaling event in which early activation primes the retina with an inflammatory response and developmental signaling cues, followed by an inhibition of gliotic mechanisms and a decrease in the immune response, ending with upregulation of genes associated with specific retinal neuron generation. Taken together, these data provide evidence that PNU-282987 activates the retinal pigment epithelium to signal to Muller glia to produce Muller-derived progenitor cells, which can differentiate into new, functional neurons in adult mice. These data not only increase our understanding of how adult mammalian retinal regeneration can occur, but also provide therapeutic promise for treating functional vision loss.

MicroRNA-4516 suppresses proliferative vitreoretinopathy development via negatively regulating OTX1

Proliferative vitreoretinopathy (PVR) progression is associated with TGF-β2-induced epithelial–mesenchymal transition (EMT) in retinal pigment epithelial (RPE) cells. In cancer cells, miR-4516 downregulates orthodenticle homeobox 1 (OTX1)-mediated cell invasion. Moreover, OTX1 is shown to be involved in invasion and EMT. The purpose of this study was to assess whether microRNA (miR-4516) suppresses EMT in RPE cells. EMT features were assessed using Western blotting, immunocytochemical staining, scratch-wound healing, modified Boyden chamber assay, and collagen gel contraction assay. For in vivo testing, a rabbit model was used, which involved induction of PVR by injection of transfected spontaneously arising RPE (ARPE) cells into the vitreous chamber. The putative target of miR-4516 was identified by luciferase reporter assay. Results showed that TGF-β2-induced transdifferentiation and migration of RPE cells was inhibited by miR-4516 delivery. Overexpression of miR-4516 led to upregulation of zonula occludens-1, downregulation of α-smooth muscle actin and vimentin, and cell contractility—all EMT features—in the TGF-β2-treated ARPE-19 cells. MiR-4516 regulated OTX1 expression negatively by binding to its 3’-UTR. TGF-β2-induced phosphorylated ERK was inhibited in miR-4516-overexpressing ARPE-19 cells. MiR-4516 suppressed experimental PVR in vitro and in vivo. In conclusion, the overexpression of miR-4516 suppresses TGF-β2-induced EMT in a PVR model, and its role in PVR depends on OTX1/ERK. Further research is needed to develop a feasible treatment method to prevent and treat PVR.

A bio-functional polymer that prevents retinal scarring through modulation of NRF2 signalling pathway

One common cause of vision loss after retinal detachment surgery is the formation of proliferative and contractile fibrocellular membranes. This aberrant wound healing process is mediated by epithelial-mesenchymal transition (EMT) and hyper-proliferation of retinal pigment epithelial (RPE) cells. Current treatment relies primarily on surgical removal of these membranes. Here, we demonstrate that a bio-functional polymer by itself is able to prevent retinal scarring in an experimental rabbit model of proliferative vitreoretinopathy. This is mediated primarily via clathrin-dependent internalisation of polymeric micelles, downstream suppression of canonical EMT transcription factors, reduction of RPE cell hyper-proliferation and migration. Nuclear factor erythroid 2-related factor 2 signalling pathway was identified in a genome-wide transcriptomic profiling as a key sensor and effector. This study highlights the potential of using synthetic bio-functional polymer to modulate RPE cellular behaviour and offers a potential therapy for retinal scarring prevention.

Retinal pigment epithelium melanin imaging using polarization-sensitive optical coherence tomography for patients with retinitis pigmentosa

This study aimed to evaluate the distribution of retinal pigment epithelium (RPE) melanin in patients with retinitis pigmentosa (RP) using entropy measurements by custom-made polarization-sensitive optical coherence tomography (PS-OCT) images, and compare entropy with the intensity of short-wavelength (SW) and near-infrared (NIR) autofluorescence (AF). We retrospectively reviewed the retinal images, including PS-OCT, SW-AF, and NIR-AF of patients with RP who had a hyperautofluorescent ring on AF. A total of 12 eyes of 12 patients (8 women and 4 men; mean age: 37.9 years) were included. There was a strong positive correlation between entropy value and NIR-AF intensity (r = 0.626, p < 0.001), and there was a very weak negative correlation between entropy value and SW-AF (r = − 0.197, p = 0.001). The mean values of the entropy in the foveal, temporal (2 mm from the fovea), and nasal (2 mm from the fovea) sections were 0.41 (± 0.09), 0.29 (± 0.08), and 0.26 (± 0.08), respectively. The entropy was significantly higher in the foveal section than in the temporal and nasal sections (p = 0.002 and p = 0.003, respectively). There was no significant difference between the entropies values for the temporal and nasal sections (p = 0.157). Age, logMAR best-corrected visual acuity, ellipsoid zone width, and central retinal thickness were not correlated with foveal entropy. We presented RPE melanin imaging in patients with RP using PS-OCT for the first time. PS-OCT can be a useful tool for monitoring patients with RP.

Translational and clinical advancements in management of proliferative vitreoretinopathy

PURPOSE OF REVIEW

Despite advancement in the surgical instrumentation and techniques, proliferative vitreoretinopathy (PVR) remains the most common cause for failure of rhegmatogenous retinal detachment (RRD) repair. This review discusses ongoing translational and clinical advancements in PVR.

RECENT FINDINGS

PVR represents an exaggerated and protracted scarring process that can occur after RRD. The primary cell types involved are retinal pigment epithelium, glial, and inflammatory cells. They interact with growth factors and cytokines derived from the breakdown of the blood-retinal barrier that trigger a cascade of cellular processes, such as epithelial-mesenchymal transition, cell migration, chemotaxis, proliferation, elaboration of basement membrane and collagen and cellular contraction, leading to overt retinal pathology. Although there are currently no medical therapies proven to be effective against PVR in humans, increased understanding of the risks factors and pathophysiology have helped guide investigations for molecular targets of PVR. The leading therapeutic candidates are drugs that mitigate growth factors, inflammation, and proliferation are the leading therapeutic candidates.

SUMMARY

Although multiple molecular targets have been investigated to prevent and treat PVR, none have yet demonstrated substantial evidence of clinical benefit in humans though some show promise. Advancements in our understanding of the pathophysiology of PVR may help develop a multipronged approach for this condition.

A Stage-Specific OTX2 Regulatory Network and Maturation-Associated Gene Programs Are Inherent Barriers to RPE Neural Competency

The retinal pigment epithelium (RPE) exhibits a diverse range of plasticity across vertebrates and is a potential source of cells for the regeneration of retinal neurons. Embryonic amniotes possess a transitory ability to regenerate neural retina through the reprogramming of RPE cells in an FGF-dependent manner. Chicken RPE can regenerate neural retina at embryonic day 4 (E4), but RPE neural competence is lost by embryonic day 5 (E5). To identify mechanisms that underlie loss of regenerative competence, we performed RNA and ATAC sequencing using E4 and E5 chicken RPE, as well as at both stages following retinectomy and FGF2 treatment. We find that genes associated with neural retina fate remain FGF2-inducible in the non-regenerative E5 RPE. Coinciding with fate restriction, RPE cells stably exit the cell cycle and dampen the expression of cell cycle progression genes normally expressed during regeneration, including E2F1. E5 RPE exhibits progressive activation of gene pathways associated with mature function independently of retinectomy or FGF2 treatment, including retinal metabolism, pigmentation synthesis, and ion transport. Moreover, the E5 RPE fails to efficiently repress OTX2 expression in response to FGF2. Predicted OTX2 binding motifs undergo robust accessibility increases in E5 RPE, many of which coincide with putative regulatory elements for genes known to facilitate RPE differentiation and maturation. Together, these results uncover widespread alterations in gene regulation that culminate in the loss of RPE neural competence and implicate OTX2 as a key determinant in solidifying the RPE fate. These results yield valuable insight to the basis of RPE lineage restriction during early development and will be of importance in understanding the varying capacities for RPE-derived retinal regeneration observed among vertebrates.

Blood-retina barrier dysfunction in experimental autoimmune uveitis: the pathogenesis and therapeutic targets

Experimental autoimmune uveitis (EAU), an animal model of human uveitis, is characterized by infiltration of autoimmune T cells in the uvea as well as in the retina of susceptible animals. EAU is induced by the immunization of uveitogenic antigens, including either retinal soluble-antigen or interphotoreceptor retinoid-binding proteins, in Lewis rats. The pathogenesis of EAU in rats involves the proliferation of autoimmune T cells in peripheral lymphoid tissues and breakdown of the blood-retinal barrier, primarily in the uvea and retina, finally inducing visual dysfunction. In this review, we describe recent EAU studies to facilitate the design of a therapeutic strategy through the interruption of uveitogenic factors during the course of EAU, which will be helpful for controlling human uveitis.

The MDM2 Single-Nucleotide Polymorphism T309G Is Associated With the Development of Epimacular Membranes

Purpose: To investigate the role of the mouse double minute 2 (MDM2) gene single-nucleotide polymorphism (SNP) T309G in the development of epimacular membranes (EMMs) by analyzing the genotype distribution and consistency of the polymorphism in paired membrane-blood samples.

Methods: This was a cross–sectional genetic association study of patients with proliferative vitreoretinopathy (PVR) or EMMs. PVR membranes (PVRMs), internal limiting membranes (ILMs) (PVR-ILMs) and blood samples (PVR-blood) from patients with PVR, and EMMs, EMM-ILMs and EMM-blood from patients with EMMs were collected. The genotype of all samples was determined by Sanger sequencing. Sex composition, mean age, the genotype distribution of MDM2 T309G, the allelic frequency of the MDM2 SNP309 G allele (% G) and the somatic mutation rate at the MDM2 T309G locus (% M) were analyzed and compared. The PVR and healthy Chinese donor groups were used as controls for different comparisons.

Results: The EMM group of 62 patients was older than the PVR group of 61 patients by an average of 8.87 years (p < 0.0001), but the two groups were statistically similar in the sex composition (p = 0.1754). Importantly, G allele carriers were at a higher risk of developing EMMs than non-G allele carriers (p = 0.0479; OR = 2.047). Moreover, EMM-blood exhibited a significantly higher % G than blood samples from healthy Chinese donors (EMM-blood: 56.78%, donors: 45.61%; p = 0.0256; OR = 1.567). Regarding membrane-blood consistency, % M was significantly different between PVRMs and EMMs (PVRMs: 2.63%, EMMs: 21.57%; p = 0.0097; OR = 10.18) but not between different types of ILMs (PVR-ILMs: 18.18%, EMM-ILMs: 29.17%; p = 0.6855). Furthermore, EMMs (p = 0.0053; OR = 8.250) and EMM-ILMs (p = 0.0233; OR = 14.40) from patients with preoperative macular holes were more predisposed toward somatic mutations at the MDM2 T309G locus than those from patients without preoperative macular holes.

Conclusions:MDM2 T309G is associated with the development of EMMs. Herein, the MDM2 SNP309 G allele is first reported as an associated factor of EMMs in a Chinese population. In addition, EMMs and ILMs are genetically unstable at the MDM2 T309G locus, especially when complicated with preoperative macular holes.

CRISPR/Cas9-Mediated Models of Retinitis Pigmentosa Reveal Differential Proliferative Response of Müller Cells between Xenopus laevis and Xenopus tropicalis

Retinitis pigmentosa is an inherited retinal dystrophy that ultimately leads to blindness due to the progressive degeneration of rod photoreceptors and the subsequent non-cell autonomous death of cones. Rhodopsin is the most frequently mutated gene in this disease. We here developed rhodopsin gene editing-based models of retinitis pigmentosa in two Xenopus species, Xenopus laevis and Xenopus tropicalis, by using CRISPR/Cas9 technology. In both of them, loss of rhodopsin function results in massive rod cell degeneration characterized by progressive shortening of outer segments and occasional cell death. This is followed by cone morphology deterioration. Despite these apparently similar degenerative environments, we found that Müller glial cells behave differently in Xenopus laevis and Xenopus tropicalis. While a significant proportion of Müller cells re-enter into the cell cycle in Xenopus laevis, their proliferation remains extremely limited in Xenopus tropicalis. This work thus reveals divergent responses to retinal injury in closely related species. These models should help in the future to deepen our understanding of the mechanisms that have shaped regeneration during evolution, with tremendous differences across vertebrates.

The roles of mouse double minute 2 (MDM2) oncoprotein in ocular diseases: A review

Mouse double minute 2 (MDM2), an E3 ubiquitin ligase and the primary negative regulator of the tumor suppressor p53, cooperates with its structural homolog MDM4/MDMX to control intracellular p53 level. In turn, overexpression of p53 upregulates and forms an autoregulatory feedback loop with MDM2. The MDM2-p53 axis plays a pivotal role in modulating cell cycle control and apoptosis. MDM2 itself is regulated by the PI3K-AKT and RB-E2F-ARF pathways. While amplification of the MDM2 gene or overexpression of MDM2 (due to MDM2 SNP T309G, for instance) is associated with various malignancies, numerous studies have shown that MDM2/p53 alterations may also play a part in the pathogenetic process of certain ocular disorders (Fig. 1). These include cancers (retinoblastoma, uveal melanoma), fibrocellular proliferative diseases (proliferative vitreoretinopathy, pterygium), neovascular diseases, degenerative diseases (cataract, primary open-angle glaucoma, age-related macular degeneration) and infectious/inflammatory diseases (trachoma, uveitis). In addition, MDM2 is implicated in retinogenesis and regeneration after optic nerve injury. Anti-MDM2 therapy has shown potential as a novel approach to treating these diseases. Despite major safety concerns, there are high expectations for the clinical value of reformative MDM2 inhibitors. This review summarizes important findings about the role of MDM2 in ocular pathologies and provides an overview of recent advances in treating these diseases with anti-MDM2 therapies.

Skin Wound Healing of the Adult Newt, Cynops pyrrhogaster: A Unique Re-Epithelialization and Scarless Model

In surgical and cosmetic studies, scarless regeneration is an ideal method to heal skin wounds. To study the technologies that enable scarless skin wound healing in medicine, animal models are useful. However, four-limbed vertebrates, including humans, generally lose their competency of scarless regeneration as they transit to their terrestrial life-stages through metamorphosis, hatching or birth. Therefore, animals that serve as a model for postnatal humans must be an exception to this rule, such as the newt. Here, we evaluated the adult newt in detail for the first time. Using a Japanese fire-bellied newt, Cynops pyrrhogaster, we excised the full-thickness skin at various locations on the body, and surveyed their re-epithelialization, granulation or dermal fibrosis, and recovery of texture and appendages as well as color (hue, tone and pattern) for more than two years. We found that the skin of adult newts eventually regenerated exceptionally well through unique processes of re-epithelialization and the absence of fibrotic scar formation, except for the dorsal-lateral to ventral skin whose unique color patterns never recovered. Color pattern is species-specific. Consequently, the adult C. pyrrhogaster provides an ideal model system for studies aimed at perfect skin wound healing and regeneration in postnatal humans.

LncRNA NEAT1 Recruits SFPQ to Regulate MITF Splicing and Control RPE Cell Proliferation

Purpose

Retinal pigment epithelium (RPE) cell proliferation is precisely regulated to maintain retinal homoeostasis. Microphthalmia-associated transcription factor (MITF), a critical transcription factor in RPE cells, has two alternatively spliced isoforms: (+)MITF and (-)MITF. Previous work has shown that (-)MITF but not (+)MITF inhibits RPE cell proliferation. This study aims to investigate the role of long non-coding RNA (lncRNA) nuclear-enriched abundant transcript 1 (NEAT1) in regulating MITF splicing and hence proliferation of RPE cells.

Methods

Mouse RPE, primary cultured mouse RPE cells, and different proliferative human embryonic stem cell (hESC)-RPE cells were used to evaluate the expression of (+)MITF, (-)MITF, and NEAT1 by reverse-transcription PCR (RT-PCR) or quantitative RT-PCR. NEAT1 was knocked down using specific small interfering RNAs (siRNAs). Splicing factor proline- and glutamine-rich (SFPQ) was overexpressed with the use of lentivirus infection. Cell proliferation was analyzed by cell number counting and Ki67 immunostaining. RNA immunoprecipitation (RIP) was used to analyze the co-binding between the SFPQ and MITF or NEAT1.

Results

NEAT1 was highly expressed in proliferative RPE cells, which had low expression of (-)MITF. Knockdown of NEAT1 in RPE cells switched the MITF splicing pattern to produce higher levels of (-)MITF and inhibited cell proliferation. Mechanistically, NEAT1 recruited SFPQ to bind directly with MITF mRNA to regulate its alternative splicing. Overexpression of SFPQ in ARPE-19 cells enhanced the binding enrichment of SFPQ to MITF and increased the splicing efficiency of (+)MITF. The binding affinity between SFPQ and MITF was decreased after NEAT1 knockdown.

Conclusions

NEAT1 acts as a scaffold to recruit SFPQ to MITF mRNA and promote its binding affinity, which plays an important role in regulating the alternative splicing of MITF and RPE cell proliferation.

Exosomal miR-4488 and miR-1273g-5p inhibit the epithelial-mesenchymal transition of transforming growth factor β2-mediated retinal pigment epithelial cells by targeting ATP-binding cassette A4

Exosomal microRNAs (miRNAs) have been shown to be involved in the regulation of many disease progression, including proliferative vitreoretinopathy (PVR). However, the roles of exosomal miR-4488 and miR-1273g-5p in PVR progression have not been demonstrated. Transforming growth factor β2 (TGF-β2)-induced ARPE-19 cells were used to stimulate the epithelial-mesenchymal transition (EMT) of cells. Exosomes derived from TGF-β2-induced ARPE-19 cells were identified by transmission electron microscopy and nanoparticle tracking analysis. The expression levels of miR-4488, miR-1273g-5p and ATP-binding cassette A4 (ABCA4) were measured by quantitative real-time PCR. The promotion levels of exosomes markers, EMT markers, apoptosis markers and ABCA4 were determined by western blot analysis. The migration, invasion and apoptosis of cells were determined by transwell assay, wound healing assay and flow cytometry. Our data showed that miR-4488 and miR-1273g-5p were lowly expressed in TGF-β2-induced ARPE-19 cells. Overexpressed exosomal miR-4488 and miR-1273g-5p could inhibit the EMT, migration, invasion, and promote apoptosis in TGF-β2-induced ARPE-19 cells. In addition, ABCA4 was a target of miR-4488 and miR-1273g-5p. Overexpressed ABCA4 also could reverse the negatively regulation of exosomal miR-4488 and miR-1273g-5p on the EMT, migration, and invasion of TGF-β2-induced ARPE-19 cells. In conclusion, our data showed that exosomal miR-4488 and miR-1273g-5p could inhibit TGF-β2-stimulated EMT in ARPE-19 cells through targeting ABCA4.

An insight on established retinal injury mechanisms and prevalent retinal stem cell activation pathways in vertebrate models

Implementing different tools and injury mechanisms in multiple animal models of retina regeneration, researchers have discovered the existence of retinal stem/progenitor cells. Although they appear to be distributed uniformly across the vertebrate lineage, the reparative potential of the retina is mainly restricted to lower vertebrates. Regenerative repair post-injury requires the creation of a proliferative niche, vital for proper stem cell activation, propagation, and lineage differentiation. This seems to be lacking in mammals. Hence, in this review, we first discuss the many forms of retinal injuries that have been generated using animal models. Next, we discuss how they are utilized to stimulate regeneration and mimic eye disease pathologies. The key to driving stem cell activation in mammals relies on the information we can gather from these models. Lastly, we present a brief update about the genes, growth factors, and signaling pathways that have been brought to light using these models.

A sustained dual drug delivery system for proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) is a significant threat for vision recovery from retinal detachment or ocular trauma. Currently, no approved pharmacological intervention to prevent PVR. Daunorubicin (DNR) and dexamethasone (DEX) were sequentially loaded into oxidized porous silicon (pSiO₂) particles by covalent conjugation. The DNR + DEX-loaded particles, and control particles loaded with DNR only and DEX only were incubated with RPE-populated collagen for daily gel surface quantitation. Toxicity was monitored by ophthalmic examinations and histological evaluation 21 days after injection. At 3rd week following intravitreal injection, a localized retinal detachment (RD) was created by subretinal injection of Healon in all pretreated eyes in addition to 3 non-interventional control eyes. 10 µg of bromodeoxyuridine (BrdU) was injected into the vitreous 4 h before sacrifice on day 3 after RD induction. Retinal sections were stained for glial fibrillary green protein (GFAP) and BrdU to identify activated glial cells and retinal cell proliferation. The studies demonstrated that all three pSiO₂ particle types were well tolerated in vivo. DNR alone and DNR + DEX combination formulations demonstrated equally strong suppression on gel contraction (least square mean area of the gel: control = 1.71 vs. 30DNR = 1.85 or 30/40Dual = 1.83, p < .05). Eyes pretreated with pSiO₂−DNR + DEX exhibited the least GFAP activation (least square mean intensity mm⁻²: Dual = 4.03, DNR = 7.76, Dex = 16.23, control = 29.11, p < .05) and BrdU expression (Mean number of BrdU positive cells per mm of retina: Dual = 2.77, DNR = 4.58, Dex = 4.01, control = 6.16, p < .05). The synergistic effect of a sustained release pSiO₂−DNR/DEX showed promise for the prevention of PVR development while reducing the necessary therapeutic concentration of each drug.

Inhibition of TGF-β2-induced migration and epithelial-mesenchymal transition in ARPE-19 by sulforaphane

AIM

To investigate the effects of sulforaphane (SFN) on transforming growth factor (TGF)-β2 stimulated migration and epithelial-mesenchymal transition (EMT) in ARPE-19 cells.

METHODS

ARPE-19 cells were cultured in the presence or absence of SFN or TGF-β2. SFN toxicity was assessed by performing a lactate dehydrogenase assay (LDH) and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assays, and cell migration was evaluated by Transwell migration assay. Actin stress fiber formation in ARPE-19 cells was determined using immunofluorescence analysis. Immunoblotting analysis was used to determine fibronectin and α-smooth muscle actin expressions along with the degree of Smad and Akt phosphorylation.

RESULTS

SFN inhibited ARPE-19 migration. Additionally, SFN attenuated TGF-β2-induced appearance of actin stress fibers as well as fibronectin and α-smooth muscle actin expressions in these cells. SFN also hindered the TGF-β2-stimulated phosphorylation of Smad2, Smad3, and Akt. SFN showed no cytotoxicity towards ARPE-19 cells.

CONCLUSION

SFN inhibits TGF-β2-stimulated migration and EMT in ARPE-19 cells, probably by preventing the establishment of actin stress fibers and Akt and Smad2/3 signaling.

Retinal Stem Cell 'Retirement Plans': Growth, Regulation and Species Adaptations in the Retinal Ciliary Marginal Zone

The vertebrate retina develops from a specified group of precursor cells that adopt distinct identities and generate lineages of either the neural retina, retinal pigmented epithelium, or ciliary body. In some species, including teleost fish and amphibians, proliferative cells with stem-cell-like properties capable of continuously supplying new retinal cells post-embryonically have been characterized and extensively studied. This region, termed the ciliary or circumferential marginal zone (CMZ), possibly represents a conserved retinal stem cell niche. In this review, we highlight the research characterizing similar CMZ-like regions, or stem-like cells located at the peripheral margin, across multiple different species. We discuss the proliferative parameters, multipotency and growth mechanisms of these cells to understand how they behave in vivo and how different molecular factors and signalling networks converge at the CMZ niche to regulate their activity. The evidence suggests that the mature retina may have a conserved propensity for homeostatic growth and plasticity and that dysfunction in the regulation of CMZ activity may partially account for dystrophic eye growth diseases such as myopia and hyperopia. A better understanding of the properties of CMZ cells will enable important insight into how an endogenous generative tissue compartment can adapt to altered retinal physiology and potentially even restore vision loss caused by retinal degenerative conditions.

Transcriptome Profiling of Embryonic Retinal Pigment Epithelium Reprogramming

The plasticity of human retinal pigment epithelium (RPE) has been observed during proliferative vitreoretinopathy, a defective repair process during which injured RPE gives rise to fibrosis. In contrast, following injury, the RPE of the embryonic chicken can be reprogrammed to regenerate neural retina in a fibroblast growth factor 2 (FGF2)-dependent manner. To better explore the mechanisms underlying embryonic RPE reprogramming, we used laser capture microdissection to isolate RNA from (1) intact RPE, (2) transiently reprogrammed RPE (t-rRPE) 6 h post-retinectomy, and (3) reprogrammed RPE (rRPE) 6 h post-retinectomy with FGF2 treatment. Using RNA-seq, we observed the acute repression of genes related to cell cycle progression in the injured t-rRPE, as well as up-regulation of genes associated with injury. In contrast, the rRPE was strongly enriched for mitogen-activated protein kinase (MAPK)-responsive genes and retina development factors, confirming that FGF2 and the downstream MAPK cascade are the main drivers of embryonic RPE reprogramming. Clustering and pathway enrichment analysis was used to create an integrated network of the core processes associated with RPE reprogramming, including key terms pertaining to injury response, migration, actin dynamics, and cell cycle progression. Finally, we employed gene set enrichment analysis to suggest a previously uncovered role for epithelial-mesenchymal transition (EMT) machinery in the initiation of embryonic chick RPE reprogramming. The EMT program is accompanied by extensive, coordinated regulation of extracellular matrix (ECM) associated factors, and these observations together suggest an early role for ECM and EMT-like dynamics during reprogramming. Our study provides for the first time an in-depth transcriptomic analysis of embryonic RPE reprogramming and will prove useful in guiding future efforts to understand proliferative disorders of the RPE and to promote retinal regeneration.

The immune response is a critical regulator of zebrafish retinal pigment epithelium regeneration

Loss of the retinal pigment epithelium (RPE) because of dysfunction or disease can lead to blindness in humans. Harnessing the intrinsic ability of the RPE to self-repair is an attractive therapeutic strategy; however, mammalian RPE is limited in its regenerative capacity. Zebrafish possess tremendous intrinsic regenerative potential in ocular tissues, including the RPE, but little is known about the mechanisms driving RPE regeneration. Here, utilizing transgenic and mutant zebrafish lines, pharmacological manipulations, transcriptomics, and imaging analyses, we identified elements of the immune response as critical mediators of intrinsic RPE regeneration. After genetic ablation, the RPE express immune-related genes, including leukocyte recruitment factors such as interleukin 34 We demonstrate that macrophage/microglia cells are responsive to RPE damage and that their function is required for the timely progression of the regenerative response. These data identify the molecular and cellular underpinnings of RPE regeneration and hold significant potential for translational approaches aimed toward promoting a pro-regenerative environment in mammalian RPE.

SINGLE NUCLEOTIDE POLYMORPHISMS IN RETINAL DETACHMENT PATIENTS WITH AND WITHOUT PROLIFERATIVE VITREORETINOPATHY

PURPOSE

To investigate differences in genotype distributions of single nucleotide polymorphisms within genes, encoding inflammatory mediators, among patients with rhegmatogenous retinal detachment (RRD) and patients with proliferative vitreoretinopathy (PVR).

METHODS

A genetic association study was performed on 191 Slovenian patients, divided into 2 groups: 113 RRD patients with PVR and 78 RRD patients without PVR. Genotype distributions were investigated within the following 13 single nucleotide polymorphisms: rs3760396 (CCL2), rs9990554 (FGF2), rs17561 (IL1A), rs2069763 (IL2), rs1800795 (IL6), rs1800871 (IL10), rs3008 (JAK3), rs2229094 (LTA), rs1042522 (TP53), rs7656613 (PDGFRA), rs7226855 (SMAD7), rs1800471 (TGFB1), and rs1800629 (TNF).

RESULTS

Differences in genotype distributions between patients with RRD with or without PVR were detected in rs1800795 (IL6) (P = 0.04), rs1800871 (in the vicinity of the IL10) (P = 0.034), and rs1800471 (TGFB1) (P = 0.032). After adjustment none of the 13 analyzed single nucleotide polymorphisms showed statistically significant associations in single nucleotide polymorphism genotype distributions between patients with RRD with and without PVR.

CONCLUSION

Further research is needed, particularly expanded multicentric population-based studies, to clarify the issue of genetic contribution to PVR from different genetic, clinical, and population-based aspects.

Plumbagin Inhibits Proliferation, Migration, and Invasion of Retinal Pigment Epithelial Cells Induced by FGF-2

Proliferative vitreoretinopathy (PVR) is a serious ophthalmic disease and characterized by the formation of proliferative membranes by retinal pigment epithelial (RPE) cells. In PVR, the contraction and traction of the fibrocellular membranes cause retinal detachment, which can cause reduction surgery for retinal detachment to fail. Fibroblast growth factor-2 (FGF-2) causes RPE cells to form extracellular matrix (ECM), promotes chemotaxis, mitosis, and positively promotes the disease process of PVR. Plumbagin (PLB) is a plant small molecule naphthoquinone compound. It has the functions in anti-tumor, anti-inflammatory, inhibit proliferation. We tried to investigate the possible effects of PLB on the biological behavior of ARPE-19 cells induced by FGF-2 and its underlying mechanisms. Our study confirmed that proliferation, migration, and invasion of ARPE-19 cells induced by FGF-2 (10 ng/ml) were significantly inhibited by PLB. PLB also significantly inhibits the expression of MMP-2/-9, collagen I Alpha 1 (Col1A1), collagen IV Alpha 1 (Col4A1), collagen VI Alpha 1 (Col6A1), and the phosphorylation of FGF receptor (FGFR)-1, FGFR-2, ERK, p38, JNK of FGF-2-induced ARPE-19 cells. In summary, PLB inhibits FGF-2-stimulated proliferation, migration, and invasion of ARPE-19 cells, which may take place through inhibiting the expression of MMP-2/-9, Col1A1, Col4A1, Col6A1, and the mitogen-activated protein kinase (MAPK) pathway. PLB may have a preventive effect on proliferation, migration, and invasion of FGF-2-induced ARPE-19 cells.

The retinal pigment epithelium: Development, injury responses, and regenerative potential in mammalian and non-mammalian systems

Diseases that result in retinal pigment epithelium (RPE) degeneration, such as age-related macular degeneration (AMD), are among the leading causes of blindness worldwide. Atrophic (dry) AMD is the most prevalent form of AMD and there are currently no effective therapies to prevent RPE cell death or restore RPE cells lost from AMD. An intriguing approach to treat AMD and other RPE degenerative diseases is to develop therapies focused on stimulating endogenous RPE regeneration. For this to become feasible, a deeper understanding of the mechanisms underlying RPE development, injury responses and regenerative potential is needed. In mammals, RPE regeneration is extremely limited; small lesions can be repaired by the expansion of adjacent RPE cells, but large lesions cannot be repaired as remaining RPE cells are unable to functionally replace lost RPE tissue. In some injury paradigms, RPE cells proliferate but do not regenerate a morphologically normal monolayer, while in others, proliferation is pathogenic and results in further disruption to the retina. This is in contrast to non-mammalian vertebrates, which possess tremendous RPE regenerative potential. Here, we discuss what is known about RPE formation during development in mammalian and non-mammalian vertebrates, we detail the processes by which RPE cells respond to injury, and we describe examples of RPE-to-retina and RPE-to-RPE regeneration in non-mammalian vertebrates. Finally, we outline barriers to RPE-dependent regeneration in mammals that could potentially be overcome to stimulate a regenerative response from the RPE.

YM155 inhibits retinal pigment epithelium cell survival through EGFR/MAPK signaling pathway

AIM

To investigate YM155's effect on retinal pigment epithelium (RPE) cells' viability and the potential regulatory mechanisms.

METHODS

Human immortalized RPE cell lines (ARPE-19 cell line) were processed with YM155 and epidermal growth factor (EGF). ARPE-19 cell viability was detected by methyl thiazolyl tetrazolium assay, and apoptosis was tested by flow cytometry assay. ARPE-19 cell proliferation was assessed with bromodeoxyuridine tagged incorporation assay, and migration ability was evaluated via a wound-healing assay. Epidermal growth factor receptor (EGFR)/MAPK pathway proteins were tested via immunoblotting. EGFR localization was examined by immunofluorescence assay.

RESULTS

YM155 suppressed ARPE-19 cells' viability in a time and concentration-dependent manner. A high dose of YM155 caused a small amount of ARPE-19 cell death. YM155 significantly diminished the ARPE-19 cells' proliferative and migrative capacity. YM155 down-regulated total EGFR and phosphorylated external signal-regulated protein kinase (ERK), and it up-regulated the phosphorylation of P38MAPK and c-Jun N-terminal kinase (JNK). YM155 induced endocytosis of EGFR in ARPE-19 cell. YM155 also attenuated EGF-induced ARPE-19 cells' proliferative and migrative capacity. Moreover, YM155 significantly decreased the expression of phosphorylated EGFR and ERK after treated by EGF.

CONCLUSION

YM155 inhibits RPE cell survival, the cell proliferative and migrative capacity, and it effectuates a small amount of cell death through the EGFR/MAPK signaling pathway. YM155 might, therefore, be an agent to prevent and treat abnormal RPE cell survival in proliferative vitreoretinopathy.

The Role of Intravitreal Anti-VEGF Agents in Rabbit Eye Model of Open-Globe Injury

Purpose

To evaluate the effects of intravitreal anti-VEGF agents in a rabbit model of open-globe injury (OGI).

Methods

OGI was induced in the right eyes of 75 Belgian rabbits by making 5 mm circumferential incision placed 6 mm behind the limbus. The rabbits were divided into 4 groups: control (n = 5), OGI group (n = 40), and intravitreal Ranibizumab and Conbercept (n = 15 each). Ranibizumab or Conbercept was injected into the vitreous at 0.5 hours, 3 days, or 7 days. Vitreous fluid was collected, and levels of growth factors and cytokines were measured by enzyme-linked immunosorbent assay (ELISA). On day 28 after OGI, B scan examination and histological examination were performed to evaluate intravitreal proliferation and formation of epiretinal fibrosis.

Results

Vitreous levels of vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-β), and plasminogen activator inhibitor-1 (PAI-1) were significantly increased in rabbit eyes after OGI. Compared to eyes in OGI group, anti-VEGF treatments significantly reduced these growth factors and cytokines. Among the 7 eyes examined from each group for intravitreal proliferative changes, they were found in 7 of 7 (100%) in OGI group and were decreased by Ranibizumab and Conbercept to 5 of 7 (71.4%) and 4 of 7 (57.1%), respectively. Both Ranibizumab and Conbercept inhibited epiretinal scar formation at the wound site, with Conbercept showing the greatest effect (maximal length of scar (L), L_OGI = 503 ± 82.44 μm, L_Ranibizumab = 355 ± 43.66 μm, and L_Conbercept = 250.33 ± 36.02 μm).

Conclusion

Anti-VEGF treatments after OGI significantly attenuated the upregulation of growth factors and cytokines in the vitreous and prevented intravitreal proliferation and epiretinal scar formation and thus may protect against the development of posttraumatic complications such as proliferative vitreoretinopathy (PVR).

Salamanders: The molecular basis of tissue regeneration and its relevance to human disease

Salamanders are recognized for their ability to regenerate a broad range of tissues. They have also have been used for hundreds of years for classical developmental biology studies because of their large accessible embryos. The range of tissues these animals can regenerate is fascinating, from full limbs to parts of the brain or heart, a potential that is missing in humans. Many promising research efforts are working to decipher the molecular blueprints shared across the organisms that naturally have the capacity to regenerate different tissues and organs. Salamanders are an excellent example of a vertebrate that can functionally regenerate a wide range of tissue types. In this review, we outline some of the significant insights that have been made that are aiding in understanding the cellular and molecular mechanisms of tissue regeneration in salamanders and discuss why salamanders are a worthy model in which to study regenerative biology and how this may benefit research fields like regenerative medicine to develop therapies for humans in the future.

Loss of Active Neurogenesis in the Adult Shark Retina

Neurogenesis is the process by which progenitor cells generate new neurons. As development progresses neurogenesis becomes restricted to discrete neurogenic niches, where it persists during postnatal life. The retina of teleost fishes is thought to proliferate and produce new cells throughout life. Whether this capacity may be an ancestral characteristic of gnathostome vertebrates is completely unknown. Cartilaginous fishes occupy a key phylogenetic position to infer ancestral states fixed prior to the gnathostome radiation. Previous work from our group revealed that the juvenile retina of the catshark Scyliorhinus canicula, a cartilaginous fish, shows active proliferation and neurogenesis. Here, we compared the morphology and proliferative status of the retina in catshark juveniles and adults. Histological and immunohistochemical analyses revealed an important reduction in the size of the peripheral retina (where progenitor cells are mainly located), a decrease in the thickness of the inner nuclear layer (INL), an increase in the thickness of the inner plexiform layer and a decrease in the cell density in the INL and in the ganglion cell layer in adults. Contrary to what has been reported in teleost fish, mitotic activity in the catshark retina was virtually absent after sexual maturation. Based on these results, we carried out RNA-Sequencing (RNA-Seq) analyses comparing the retinal transcriptome of juveniles and adults, which revealed a statistically significant decrease in the expression of many genes involved in cell proliferation and neurogenesis in adult catsharks. Our RNA-Seq data provides an excellent resource to identify new signaling pathways controlling neurogenesis in the vertebrate retina.

Obacunone protects retinal pigment epithelium cells from ultra-violet radiation-induced oxidative injury

Ultra-violet (UV) radiation (UVR) causes significant oxidative injury to retinal pigment epithelium (RPE) cells. Obacunone is a highly oxygenated triterpenoid limonoid compound with various pharmacological properties. Its potential effect in RPE cells has not been studied thus far. Here in ARPE-19 cells and primary murine RPE cells, obacunone potently inhibited UVR-induced reactive oxygen species accumulation, mitochondrial depolarization, lipid peroxidation and single strand DNA accumulation. UVR-induced RPE cell death and apoptosis were largely alleviated by obacunone. Obacunone activated Nrf2 signaling cascade in RPE cells, causing Keap1-Nrf2 disassociation, Nrf2 protein stabilization and nuclear translocation. It promoted transcription and expression of antioxidant responsive element-dependent genes. Nrf2 silencing or CRISPR/Cas9-induced Nrf2 knockout almost reversed obacunone-induced RPE cytoprotection against UVR. Forced activation of Nrf2 cascade, by Keap1 knockout, similarly protected RPE cells from UVR. Importantly, obacunone failed to offer further RPE cytoprotection against UVR in Keap1-knockout cells. In vivo, intravitreal injection of obacunone largely inhibited light-induced retinal damage. Collectively, obacunone protects RPE cells from UVR-induced oxidative injury through activation of Nrf2 signaling cascade.

Inhibition of PARP activity improves therapeutic effect of ARPE-19 transplantation in RCS rats through decreasing photoreceptor death

Photoreceptor (PR) dysfunction or death is the key pathological change in retinal degeneration (RD). The death of PRs might be due to a primary change in PRs themselves or secondary to the dysfunction of the retinal pigment epithelium (RPE). Poly(ADP-ribose) polymerase (PARP) was reported to be involved in primary PR death, but whether it plays a role in PR death secondary to RPE dysfunction has not been determined. To clarify this question and develop a new therapeutic approach, we studied the changes in PAR/PARP in the RCS rat, a RD model, and tested the effect of PARP intervention when given alone or in combination with RPE cell transplantation. The results showed that poly(ADP-ribosyl)ation of proteins was increased in PRs undergoing secondary death in RCS rats, and this result was confirmed by the observation of similar changes in sodium iodate (SI)-induced secondary RD in SD rats. The increase in PAR/PARP was highly associated with increased apoptotic PRs and decreased visual function, as represented by lowered b-wave amplitudes on electroretinogram (ERG). Then, as we expected, when the RCS rats were treated with subretinal injection of the PARP inhibitor PJ34, the RD process was delayed. Furthermore, when PJ34 was given simultaneously with subretinal ARPE-19 cell transplantation, the therapeutic effects were significantly improved and lasted longer than those of ARPE-19 or PJ34 treatment alone. These results provide a potential new approach for treating RD.

Effect of aflibercept on proliferative vitreoretinopathy: Proteomic analysis in an experimental animal model

PURPOSE

The aim of this study was to monitor inflammatory, proliferative and progressive effects of proliferative vitreoretinopathy (PVR) and aflibercept treatment in dispase induced PVR rat model by proteomic analysis.

MATERIAL AND METHODS

A total of 35 male Long Evans pigmented rats were divided into three groups, namely, PVR (dispase+saline), PVR+aflibercept (dispase+aflibercept) and control. The PVR group received 2 μl of 0.03 IU/μl dispase and 2 μl saline, the PVR+aflibercept group received 2 μl of 0.03 IU/μl and 2 μl of 40 mg/ml aflibercept at the first day of the experiment. At the end of the 6th week all retina and vitreous specimens were collected by evisceration and transferred to the proteomics laboratory for analysis. Proteomic analysis by 2D gel electrophoresis coupled with MALDI-TOF/TOF was performed.

RESULTS

In the PVR and PVR+aflibercept group 16 different proteins that were identified to be differentially regulated in comparison to the control group. In the PVR+aflibercept group, ENO1, ENO2, LDH-B, PEBP-1 and GS levels were higher than the PVR group. In addition, the association of proteins such as UCHL, PEBP1, PDHB and ENO1 with PVR has been demonstrated for the first time.

CONCLUSION

STRING analysis elucidated the functional protein-protein interaction among the differentially regulated proteins and highlighted that those proteins mainly played roles in carbon and nucleotide metabolisms. Functional analysis of the differentially regulated proteins indicated the presence of inflammation, gliosis and retinal damage in the PVR group. Aflibercept treatment had pronounced effect on prevention of inflammation and retinal damage while causing a slight increase in gliosis. However, aflibercept treatment was not effective enough to normalize the levels of differentially regulated proteins of the PVR group. Therefore, we predict that the treatment dose of aflibercept used in this study was below of its ideal concentration and should be increased in the future studies. The differential regulation of these structural proteins in this study should shed some light to the mechanism of glial wound formation in the retina and guide future treatment modalities.

Topical delivery of a small molecule RUNX1 transcription factor inhibitor for the treatment of proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) is the leading cause of retinal detachment surgery failure. Despite significant advances in vitreoretinal surgery, it still remains without an effective prophylactic or therapeutic medical treatment. After ocular injury or retinal detachment, misplaced retinal cells undergo epithelial to mesenchymal transition (EMT) to form contractile membranes within the eye. We identified Runt-related transcription factor 1 (RUNX1) as a gene highly expressed in surgically-removed human PVR specimens. RUNX1 upregulation was a hallmark of EMT in primary cultures derived from human PVR membranes (C-PVR). The inhibition of RUNX1 reduced proliferation of human C-PVR cells in vitro, and curbed growth of freshly isolated human PVR membranes in an explant assay. We formulated Ro5-3335, a lipophilic small molecule RUNX1 inhibitor, into a nanoemulsion that when administered topically curbed the progression of disease in a novel rabbit model of mild PVR developed using C-PVR cells. Mass spectrometry analysis detected 2.67 ng/mL of Ro5-3335 within the vitreous cavity after treatment. This work shows a critical role for RUNX1 in PVR and supports the feasibility of targeting RUNX1 within the eye for the treatment of an EMT-mediated condition using a topical ophthalmic agent.