Eye drop delivery of pigment epithelium-derived factor-34 promotes retinal ganglion cell neuroprotection and axon regeneration

PEDF-34 attenuates neurological deficit and suppresses astrocyte-dependent neuroinflammation by modulating astrocyte polarization via 67LR/JNK/STAT1 signaling pathway after subarachnoid hemorrhage in rats

BACKGROUND

Reactive astrocytes participate in various pathophysiology after subarachnoid hemorrhage (SAH), including neuroinflammation, glymphatic-lymphatic system dysfunction, brain edema, BBB disruption, and cell death. Astrocytes transform into two new reactive phenotypes with changed morphology, altered gene expression, and secretion profiles, termed detrimental A1 and beneficial A2. This study investigates the effect of 67LR activation by PEDF-34, a PEDF peptide, on neuroinflammation and astrocyte polarization after the experimental SAH.

METHODS

A total of 318 male adult Sprague-Dawley rats were used in experiments in vivo, of which 272 rats were subjected to the endovascular perforation model of SAH and 46 rats underwent sham surgery. 67LR agonist (PEDF-34) was administrated intranasally 1 h after SAH. 67LR-specific inhibitor (NSC-47924) and STAT1 transcriptional activator (2-NP) were injected intracerebroventricularly 48 h before SAH. Short- and long-term neurological tests, brain water content, immunostaining, Nissl staining, western blot, and ELISA assay were performed. In experiments in vitro, primary astrocyte culture with hemoglobin (Hb) stimulation was used to mimic SAH. The expression of the PEDF-34/67LR signaling pathway and neuro-inflammatory cytokines were assessed using Western blot, ELISA, and immunohistochemistry assays both in vivo and in vitro.

RESULTS

Endogenous PEDF and 67LR expressions were significantly reduced at 6 h after SAH. 67LR was expressed in astrocytes and neurons. Intranasal administration of PEDF-34 significantly reduced brain water content, pro-inflammatory cytokines, and short-term and long-term neurological deficits after SAH. The ratio of p-JNK/JNK and p-STAT1/STAT1 and the expression of CFB and C3 (A1 astrocytes marker), significantly decreased after PEDF-34 treatment, along with fewer expression of TNF-α and IL-1β at 24 h after SAH. However, 2-NP (STAT1 transcriptional activator) and NSC-47924 (67LR inhibitor) reversed the protective effects of PEDF-34 in vivo and in vitro by promoting A1 astrocyte polarization with increased inflammatory cytokines.

CONCLUSION

PEDF-34 activated 67LR, attenuating neuroinflammation and inhibiting astrocyte A1 polarization partly via the JNK/STAT1 pathway, suggesting that PEDF-34 might be a potential treatment for SAH patients.

Suppressor of cytokine signaling 3-derived peptide as a therapeutic for inflammatory and oxidative stress-induced damage to the retina

Purpose

Inflammation and oxidative stress contribute to age-related macular degeneration (AMD) and other retinal diseases. We tested a cell-penetrating peptide from the kinase inhibitory region of an intracellular checkpoint inhibitor suppressor of cytokine signaling 3 (R9-SOCS3-KIR) peptide for its ability to blunt the inflammatory or oxidative pathways leading to AMD.

Methods

We used anaphylatoxin C5a to mimic the effect of activated complement, lipopolysaccharide (LPS), and tumor necrosis factor alpha (TNFα) to stimulate inflammation and paraquat to induce mitochondrial oxidative stress. We used a human retinal pigment epithelium (RPE) cell line (ARPE-19) as proliferating cells and a mouse macrophage cell line (J774A.1) to follow cell propagation using microscopy or cell titer assays. We evaluated inflammatory pathways by monitoring the nuclear translocation of NF-κB p65 and mitogen-activated protein kinase p38. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) and Western blot were used to evaluate the induction of inflammatory markers. In differentiated ARPE-19 monolayers, we evaluated the integrity of tight junction proteins through microscopy and the measurement of transepithelial electrical resistance (TEER). We used intraperitoneal injection of sodium iodate in mice to test the ability of R9-SOC3-KIR to prevent RPE and retinal injury, as assessed by fundoscopy, optical coherence tomography, and histology.

Results

R9-SOCS3-KIR treatment suppressed C5a-induced nuclear translocation of the NF-kB activation domain p65 in undifferentiated ARPE-19 cells. TNF-mediated damage to tight junction proteins in RPE, and the loss of TEER was prevented in the presence of R9-SOCS3-KIR. Treatment with the R9-SOCS3-KIR peptide blocked the C5a-induced expression of inflammatory genes. The R9-SOCS3-KIR treatment also blocked the LPS-induced expression of interleukin-6, MCP1, cyclooxygenase 2, and interleukin-1 beta. R9-SOCS3-KIR prevented paraquat-mediated cell death and enhanced the levels of antioxidant effectors. Daily eye drop treatment with R9-SOCS3-KIR protected against retinal injury caused by i.p. administration of sodium iodate.

Conclusions

R9-SOCS3-KIR blocks the induction of inflammatory signaling in cell culture and reduces retinal damage in a widely used RPE/retinal oxidative injury model. As this peptide can be administered through corneal instillation, this treatment may offer a convenient way to slow down the progression of ocular diseases arising from inflammation and chronic oxidative stress.

Brain-derived neurotrophic factor - a key player in the gastrointestinal system

Brain-derived neurotrophic factor (BDNF) is highly expressed throughout the gastrointestinal (GI) tract and plays a critical role in the regulation of intestinal motility, secretion, sensation, immunity, and mucosal integrity. Dysregulation of BDNF signalling has been implicated in the pathophysiology of various GI disorders including inflammatory bowel disease, irritable bowel syndrome, functional dyspepsia, and diabetic gastroenteropathy. This review provides a comprehensive overview of BDNF localization, synthesis, receptors, and signalling mechanisms in the gut. In addition, current evidence on the diverse physiologic and pathophysiologic roles of BDNF in the control of intestinal peristalsis, mucosal transport processes, visceral sensation, neuroimmune interactions, gastrointestinal mucosal healing, and enteric nervous system homeostasis are discussed. Finally, the therapeutic potential of targeting BDNF for the treatment of functional GI diseases is explored. Advancing knowledge of BDNF biology and mechanisms of action may lead to new therapies based on harnessing the gut trophic effects of this neurotrophin.

Neurovascular Unit: A New Target for Treating Early Stages of Diabetic Retinopathy

The concept of diabetic retinopathy as a microvascular disease has evolved and is now considered a more complex diabetic complication in which neurovascular unit impairment plays an essential role and, therefore, can be considered as a main therapeutic target in the early stages of the disease. However, neurodegeneration is not always the apparent primary event in the natural story of diabetic retinopathy, and a phenotyping characterization is recommendable to identify those patients in whom neuroprotective treatment might be of benefit. In recent years, a myriad of treatments based on neuroprotection have been tested in experimental models, but more interestingly, there are drugs with a dual activity (neuroprotective and vasculotropic). In this review, the recent evidence concerning the therapeutic approaches targeting neurovascular unit impairment will be presented, along with a critical review of the scientific gaps and problems which remain to be overcome before our knowledge can be transferred to clinical practice.

Rpsa Signaling Regulates Cortical Neuronal Morphogenesis via Its Ligand, PEDF, and Plasma Membrane Interaction Partner, Itga6

Neuromorphological defects underlie neurodevelopmental disorders and functional defects. We identified a function for Rpsa in regulating neuromorphogenesis using in utero electroporation to knockdown Rpsa, resulting in apical dendrite misorientation, fewer/shorter extensions, and decreased spine density with altered spine morphology in upper neuronal layers and decreased arborization in upper/lower cortical layers. Rpsa knockdown disrupts multiple aspects of cortical development, including radial glial cell fiber morphology and neuronal layering. We investigated Rpsa's ligand, PEDF, and interacting partner on the plasma membrane, Itga6. Rpsa, PEDF, and Itga6 knockdown cause similar phenotypes, with Rpsa and Itga6 overexpression rescuing morphological defects in PEDF-deficient neurons in vivo. Additionally, Itga6 overexpression increases and stabilizes Rpsa expression on the plasma membrane. GCaMP6s was used to functionally analyze Rpsa knockdown via ex vivo calcium imaging. Rpsa-deficient neurons showed less fluctuation in fluorescence intensity, suggesting defective subthreshold calcium signaling. The Serpinf1 gene coding for PEDF is localized at chromosome 17p13.3, which is deleted in patients with the neurodevelopmental disorder Miller-Dieker syndrome. Our study identifies a role for Rpsa in early cortical development and for PEDF-Rpsa-Itga6 signaling in neuromorphogenesis, thus implicating these molecules in the etiology of neurodevelopmental disorders like Miller-Dieker syndrome and identifying them as potential therapeutics.

Corneal Application of R9-SOCS1-KIR Peptide Alleviates Endotoxin-Induced Uveitis

Purpose

Uveitis is an ocular inflammation that can affect individuals of all ages and is a major cause of blindness. We have tested the therapeutic efficacy of a cell penetrating peptide from the kinase inhibitory region of suppressor of cytokine signaling 1, denoted as R9-SOCS1-KIR.

Methods

We stimulated J774A.1 cells with lipopolysaccharide (LPS) in the presence of R9-SOCS1-KIR or its inactive control peptide. Effect on inflammatory pathways was followed by the nuclear translocation of nuclear factor κB p65 subunit and phosphorylated-p38. Synthesis of inflammatory markers induced by LPS was tested by reverse transcriptase polymerase chain reaction, Western blot analysis, and ELISA of cell supernatants. We monitored effects on the barrier properties of a differentiated ARPE-19 monolayer treated with LPS. We treated C57BL/6 mice topically with either R9-SOCS1-KIR or vehicle and injected their eyes intravitreally with LPS. Eyes were analyzed by fundoscopy, fluorescein angiography, optical coherence tomography, histology, Western blotting, multiplex enzyme-linked immunosorbent assay, and flow cytometry.

Results

Treatment with R9-SOCS1-KIR resulted in suppression of signaling through nuclear factor κB and p-p38 pathways. R9-SOCS1-KIR suppressed the expression of inflammatory genes, the secretion of inflammatory makers such as nitric oxide, and IL-1β induced by LPS. Increased permeability of retinal pigment epithelial cell monolayers was prevented. Corneal administration of R9-SOCS1-KIR blocked the acute inflammation observed in LPS-injected mouse eyes.

Conclusions

Treatment with R9-SOCS1-KIR alleviated the inflammatory responses in cell culture. Topical delivery of this peptide on mouse eyes protected against LPS-induced damage.

Translational Relevance

Topical delivery of R9-SOCS1-KIR peptide allows the patient to self-administer the drug, while preventing any systemic effects on unrelated organs.

Neuroprotective Factors of the Retina and Their Role in Promoting Survival of Retinal Ganglion Cells: A Review

Retinal ganglion cells (RGCs) play a crucial role in the visual pathway. As their axons form the optic nerve, apoptosis of these cells causes neurodegenerative vision loss. RGC death could be triggered by increased intraocular pressure, advanced glycation end products, or mitochondrial dysfunction. In this review, we summarize the role of some neuroprotective factors in RGC injury: ciliary neurotrophic factor (CNTF), nerve growth factor (NGF), brain-derived neurotrophic factor, vascular endothelial growth factor, pigment epithelium-derived factor, glial cell line-derived neurotrophic factor, and Norrin. Each, in their own unique way, prevents RGC damage caused by glaucoma, ocular hypertension, ischemic neuropathy, and even oxygen-induced retinopathy. These factors are produced mainly by neurons, leukocytes, glial cells, and epithelial cells. Neuroprotective factors act via various signaling pathways, including JAK/STAT, MAPK, TrkA, and TrkB, which promotes RGC survival. Many attempts have been made to develop therapeutic strategies using these factors. There are ongoing clinical trials with CNTF and NGF, but they have not yet been accepted for clinical use.

Polarity and epithelial-mesenchymal transition of retinal pigment epithelial cells in proliferative vitreoretinopathy

Under physiological conditions, retinal pigment epithelium (RPE) is a cellular monolayer composed of mitotically quiescent cells. Tight junctions and adherens junctions maintain the polarity of RPE cells, and are required for cellular functions. In proliferative vitreoretinopathy (PVR), upon retinal tear, RPE cells lose cell-cell contact, undergo epithelial-mesenchymal transition (EMT), and ultimately transform into myofibroblasts, leading to the formation of fibrocellular membranes on both surfaces of the detached retina and on the posterior hyaloids, which causes tractional retinal detachment. In PVR, RPE cells are crucial contributors, and multiple signaling pathways, including the SMAD-dependent pathway, Rho pathway, MAPK pathways, Jagged/Notch pathway, and the Wnt/β-catenin pathway are activated. These pathways mediate the EMT of RPE cells, which play a key role in the pathogenesis of PVR. This review summarizes the current body of knowledge on the polarized phenotype of RPE, the role of cell-cell contact, and the molecular mechanisms underlying the RPE EMT in PVR, emphasizing key insights into potential approaches to prevent PVR.

Strategies to Promote Long-Distance Optic Nerve Regeneration

Mammalian retinal ganglion cells (RGCs) in the central nervous system (CNS) often die after optic nerve injury and surviving RGCs fail to regenerate their axons, eventually resulting in irreversible vision loss. Manipulation of a diverse group of genes can significantly boost optic nerve regeneration of mature RGCs by reactivating developmental-like growth programs or suppressing growth inhibitory pathways. By injury of the vision pathway near their brain targets, a few studies have shown that regenerated RGC axons could form functional synapses with targeted neurons but exhibited poor neural conduction or partial functional recovery. Therefore, the functional restoration of eye-to-brain pathways remains a greatly challenging issue. Here, we review recent advances in long-distance optic nerve regeneration and the subsequent reconnecting to central targets. By summarizing our current strategies for promoting functional recovery, we hope to provide potential insights into future exploration in vision reformation after neural injuries.

Inherited Eye Diseases with Retinal Manifestations through the Eyes of Homeobox Genes

Retinal development is under the coordinated control of overlapping networks of signaling pathways and transcription factors. The paper was conceived as a review of the data and ideas that have been formed to date on homeobox genes mutations that lead to the disruption of eye organogenesis and result in inherited eye/retinal diseases. Many of these diseases are part of the same clinical spectrum and have high genetic heterogeneity with already identified associated genes. We summarize the known key regulators of eye development, with a focus on the homeobox genes associated with monogenic eye diseases showing retinal manifestations. Recent advances in the field of genetics and high-throughput next-generation sequencing technologies, including single-cell transcriptome analysis have allowed for deepening of knowledge of the genetic basis of inherited retinal diseases (IRDs), as well as improve their diagnostics. We highlight some promising avenues of research involving molecular-genetic and cell-technology approaches that can be effective for IRDs therapy. The most promising neuroprotective strategies are aimed at mobilizing the endogenous cellular reserve of the retina.

A C-terminal peptide from type I interferon protects the retina in a mouse model of autoimmune uveitis

Experimental autoimmune uveitis (EAU) in rodents recapitulates many features of the disease in humans and has served as a useful tool for the development of therapeutics. A peptide from C-terminus of interferon α1, conjugated to palmitoyl-lysine for cell penetration, denoted as IFNα-C, was tested for its anti-inflammatory properties in ARPE-19 cells, followed by testing in a mouse model of EAU. Treatment with IFNα-C and evaluation by RT-qPCR showed the induction of anti-inflammatory cytokines and chemokine. Inflammatory markers induced by treatment with TNFα were suppressed when IFNα-C was simultaneously present. TNF-α mediated induction of NF-κB and signaling by IL-17A were attenuated by IFNα-C. Differentiated ARPE-19 cells were treated with TNFα in the presence or absence IFNα-C and analyzed by immmunhistochemistry. IFNα-C protected against the disruption integrity of tight junction proteins. Similarly, loss of transepithelial resistance caused by TNFα was prevented by IFNα-C. B10.RIII mice were immunized with a peptide from interphotoreceptor binding protein (IRBP) and treated by gavage with IFNα-C. Development of uveitis was monitored by histology, fundoscopy, SD-OCT, and ERG. Treatment with IFNα-C prevented uveitis in mice immunized with the IRBP peptide. Splenocytes isolated from mice with ongoing EAU exhibited antigen-specific T cell proliferation that was inhibited in the presence of IFNα-C. IFNα-C peptide exhibits anti-inflammatory properties and protects mice against damage to retinal structure and function suggesting that it has therapeutic potential for the treatment of autoimmune uveitis.

δ Opioid Receptor Agonism Preserves the Retinal Pigmented Epithelial Cell Tight Junctions and Ameliorates the Retinopathy in Experimental Diabetes

Purpose

Outer blood retinal barrier breakdown is a neglected feature of diabetic retinopathy (DR). We demonstrated that the agonism of the δ opioid receptor (DOR) by epicatechin preserves the tight junction proteins in ARPE-19 cells under diabetic conditions. Presently, we aimed to evaluate the possible role of the DOR on the maintenance of tight junction of RPE layer and on the early markers of experimental DR.

Methods

DR markers and external retinal tight junction proteins were evaluated in CL57B diabetic mice submitted to intravitreous injection of short hairpin RNA (shRNA)-DOR (108 transducing units [TU]/mL) treated or not with DOR agonist (0.05 g/animal/d of epicatechin in drinking water) for 16 weeks. The presence of DOR in human retina from postmortem eyes from diabetic and nondiabetic donors were also performed.

Results

DOR is present in RPE layer and in neuro retina. The treatment with DOR agonist prevented the upregulation of the early markers of retinopathy (glial fibrillary acidic protein, VEGF) and the downregulation of pigment epithelium-derived factor, occludin, claudin-1, and zonula occludens-1 tight junction expressions. The silencing of DOR in retina of diabetic mice partially abolished the protective effects of epicatechin. In human retina specimens, DOR is present throughout the retina, similarly in nondiabetic and diabetic donors.

Conclusions

This set of experiments strongly indicates that the DOR agonism preserves RPE tight junctions and reduces the early markers of retinopathy in model of diabetes. These novel findings designate DOR as a potential therapeutic tool to treat DR with preservation of the RPE tight junction proteins.

Pigment Epithelium-Derived Factor Promotes Axon Regeneration and Functional Recovery After Spinal Cord Injury

Although neurons in the adult mammalian CNS are inherently incapable of regeneration after injury, we previously showed that exogenous delivery of pigment epithelium-derived factor (PEDF), a 50-kDa neurotrophic factor (NTF), promoted adult retinal ganglion cell neuroprotection and axon regeneration. Here, we show that PEDF and other elements of the PEDF pathway are highly upregulated in dorsal root ganglion neurons (DRGN) from regenerating dorsal column (DC) injury paradigms when compared with non-regenerating DC injury models. Exogenous PEDF was neuroprotective to adult DRGN and disinhibited neurite outgrowth, whilst overexpression of PEDF after DC injury in vivo promoted significant DC axon regeneration with enhanced electrophysiological, sensory, and locomotor function. Our findings reveal that PEDF is a novel NTF for adult DRGN and may represent a therapeutically useful factor to promote functional recovery after spinal cord injury.

JIP1 Deficiency Protects Retinal Ganglion Cells From Apoptosis in a Rotenone-Induced Injury Model

Retinal ganglion cells (RGCs) undergo apoptosis after injury. c-Jun N-terminal kinase (JNK)-interacting protein 1 (JIP1) is a scaffold protein that is relevant to JNK activation and a key molecule known to regulate neuronal apoptosis. However, the specific role of JIP1 in the apoptosis of RGCs is currently undefined. Here, we used JIP1 gene knockout (KO) mice to investigate the importance of JIP1-JNK signaling in the apoptosis of RGCs in a rotenone-induced injury model. In adult JIP1 KO mice, the number and electrophysiological functions of RGCs were not different from those of wild-type (WT) mice. Ablation of JIP1 attenuated the activation of JNK and the cleavage of caspase-3 in the retina after rotenone injury and contributed to a lower number of TUNEL-positive RGCs, a greater percentage of surviving RGCs, and a significant reduction in the electrophysiological functional loss of RGCs when compared to those in WT controls. We also found that JIP1 was located in the neurites of primary RGCs, but accumulated in soma in response to rotenone treatment. Moreover, the number of TUNEL-positive RGCs, the level of activation of JNK and the rate of cleavage of caspase-3 were reduced in primary JIP1-deficient RGCs after rotenone injury than in WT controls. Together, our results demonstrate that the JIP1-mediated activation of JNK contributes to the apoptosis of RGCs in a rotenone-induced injury model in vitro and in vivo, suggesting that JIP1 may be a potential therapeutic target for RGC degeneration.

Pigment epithelium-derived factor inhibits adipogenesis in 3T3-L1 adipocytes and protects against high-fat diet-induced obesity and metabolic disorders in mice

Obesity is a major cause of metabolic syndrome and type II diabetes, and it presents with metabolic disorders, such as hyperglycemia, hyperlipidemia, and insulin resistance. Pigment epithelium-derived factor (PEDF), a protein isolated from retinal pigment epithelial cells, has multiple functions, including neuronal protection, antineoplastic effects, and anti-inflammatory activity. The aim of this study is to investigate the antiobesity effects of PEDF. The antiobesity effects of PEDF on fat accumulation, inflammation, energy expenditure, insulin resistance, and obesity-related physiological parameters and protein levels were assessed in high-fat diet (HFD)-induced obese mice in vivo and in 3T3-L1 adipocytes, palmitate (PA)-treated HepG2 cells, and C2C12 myotubes in vitro. In an in vivo assay, PEDF effectively decreased body weight gain, white adipose tissue mass, and inflammation and improved insulin resistance, dyslipidemia, and hyperglycemia in HFD-induced mice. In liver tissue, PEDF decreased lipid accumulation and fibrosis. In an in vitro assay, PEDF diminished the differentiation of 3T3-L1 preadipocytes. We also determined that PEDF promoted lipolysis and prolonged cell cycle progression, through the mTOR-S6K pathway and downstream transcription factors, such as peroxisome proliferator-activated receptor gamma, CCAAT/enhancer-binding protein α (CEBP-α), and CEBP-β. In addition, PEDF decreased reactive oxygen species production in PA-induced HepG2 cells and improved glucose uptake ability in PA-induced HepG2 cells and C2C12 myotubes. In the present study, PEDF protected against HFD-induced obesity and metabolic disorders in mice, inhibited adipogenesis, and improved insulin resistance. These results provide a new potential treatment for obesity in the future.

Effects of a combinatorial treatment with gene and cell therapy on retinal ganglion cell survival and axonal outgrowth after optic nerve injury

After an injury, axons in the central nervous system do not regenerate over large distances and permanently lose their connections to the brain. Two promising approaches to correct this condition are cell and gene therapies. In the present work, we evaluated the neuroprotective and neuroregenerative potential of pigment epithelium-derived factor (PEDF) gene therapy alone and combined with human mesenchymal stem cell (hMSC) therapy after optic nerve injury by analysis of retinal ganglion cell survival and axonal outgrowth. Overexpression of PEDF by intravitreal delivery of AAV2 vector significantly increased Tuj1-positive cells survival and modulated FGF-2, IL-1ß, Iba-1, and GFAP immunostaining in the ganglion cell layer (GCL) at 4 weeks after optic nerve crush, although it could not promote axonal outgrowth. The combination of AAV2.PEDF and hMSC therapy showed a higher number of Tuj1-positive cells and a pronounced axonal outgrowth than unimodal therapy after optic nerve crush. In summary, our results highlight a synergistic effect of combined gene and cell therapy relevant for future therapeutic interventions regarding optic nerve injury.

Type I pig collagen enhances the efficacy of PEDF 34-mer peptide in a mouse model of laser-induced choroidal neovascularization

BACKGROUND

Pigment epithelium-derived factor (PEDF)-derived 34-mer peptide (PEDF34, Asp⁴⁴-Asn⁷⁷) has anti-angiogenic activity but has limitations in clinical application because of an inverted bell-shaped dose-effect relationship and a short half-life. In this study, we attempted to mitigate these problems by mixing PEDF34 with type I collagen.

METHODS

The anti-angiogenic activity of the PEDF34/atelocollagen mixture was evaluated by HUVEC tube formation assay and in a laser-induced choroidal neovascular (CNV) mouse model. PEDF34 and/or collagen were administrated using intravitreal injections or eye drops. CNV lesion size was quantified using FITC-dextran-perfused retinal whole mounts. Western blot analysis and inhibitor assays were used to define the action mechanisms of PEDF34 and the mixture.

RESULTS

Collagen broadened the effective dose range of PEDF34 in the tube formation assay by > 250 times (from 0.2 to 50 nM). In the CNV model, five intravitreal injections of PEDF34 were required for therapeutic effect, whereas the mixture had a significant therapeutic effect following a single injection. Eye drops of the mixture showed significantly stronger CNV-suppressive effects than drops of PEDF34 alone. The anti-angiogenic activity of PEDF34 might be mediated by inhibition of ERK and JNK activation by VEGF, and collagen potentiated these effects.

CONCLUSIONS

Collagen can serve as a carrier and reservoir of PEDF34. PEDF peptide/collagen mixture is easy to prepare than conventional methods for maintaining the therapeutic effect of PEDF peptide.

Eye Drop Instillation of the Rac1 Modulator CNF1 Attenuates Retinal Gliosis and Ameliorates Visual Performance in a Rat Model of Hypertensive Retinopathy

In hypertensive retinopathy, the retinal damage due to high blood pressure is accompanied by increased expression of Glial Fibrillary Acidic Protein (GFAP), which indicates a role of neuroinflammatory processes in such a retinopathy. Proteins belonging to the Rho GTPase family, particularly Rac1, are involved in the activation of Müller glia and in the progression of photoreceptor degeneration, and may thus represent a novel candidate for therapeutic intervention following central nervous system inflammation. In this paper, we have observed that topical administration as eye drops of Cytotoxic Necrotizing Factor 1 (CNF1), a Rho GTPase modulator, surprisingly improves electrophysiological and behavioral visual performances in aged spontaneously hypertensive rats. Furthermore, such functional improvement is accompanied by a reduction of Rac1 activity and retinal GFAP expression. Our results suggest that Rac1 inhibition through CNF1 topical administration may represent a new strategy to target retinal gliosis.

Pigment epithelium-derived factor mediates retinal ganglion cell neuroprotection by suppression of caspase-2

Retinal ganglion cells (RGCs) undergo rapid cell death by apoptosis after injury but can be rescued by suppression of caspase-2 (CASP2) using an siRNA to CASP2 (siCASP2). Pigment epithelium-derived factor (PEDF), has neuroprotective and anti-angiogenic functions and protects RGC from death. The purpose of this study was to investigate if suppression of CASP2 is a possible mechanism of neuroprotection by PEDF in RGC. Adult rat retinal cells were treated in vitro with sub-optimal and optimal concentrations of siCASP2 and PEDF and levels of CASP2 mRNA and RGC survival were then quantified. Optic nerve crush (ONC) injury followed by intravitreal injections of siCASP2 or PEDF and eye drops of PEDF-34 were also used to determine CASP2 mRNA and protein reduction. Results showed that PEDF and PEDF-34 significantly suppressed CASP2 mRNA in culture, by 1.85- and 3.04-fold, respectively, and increased RGC survival by 63.2 ± 3.8% and 81.9 ± 6.6%, respectively compared to cells grown in Neurobasal-A alone. RGC survival was significantly reduced in glial proliferation inhibited and purified RGC cultures suggesting that some of the effects of PEDF were glia-mediated. In addition, intravitreal injection of PEDF and eye drops of PEDF-34 after ONC also suppressed CASP2 mRNA levels by 1.82- and 3.89-fold and cleaved caspase-2 (C-CASP2) protein levels by 4.98- and 8.93-fold compared to ONC + PBS vehicle groups, respectively, without affecting other executioner caspases. Treatment of retinal cultures with PEDF and PEDF-34 promoted the secretion of neurotrophic factors (NTF) into the culture media, of which brain-derived neurotrophic factor (BDNF) caused the greatest reduction in CASP2 mRNA and C-CASP2 protein. The neuroprotective effects of PEDF were blocked by a polyclonal antibody and PEDF suppressed key elements in the apoptotic pathway. In conclusion, this study shows that some of the RGC neuroprotective effects of PEDF is regulated through suppression of CASP2 and downstream apoptotic signalling molecules.

Photoreceptor degeneration in microphthalmia (Mitf) mice: partial rescue by pigment epithelium-derived factor

Dysfunction and loss of the retinal pigment epithelium (RPE) are hallmarks of retinal degeneration, but the underlying pathogenetic processes are only partially understood. Using mice with a null mutation in the transcription factor gene Mitf, in which RPE deficiencies are associated with retinal degeneration, we evaluated the role of trophic factors secreted by the RPE in retinal homeostasis. In such mice, the thickness of the outer nuclear layer (ONL) is as in wild type up to postnatal day 10, but then is progressively reduced, associated with a marked increase in the number of apoptotic cells and a decline in staining for rhodopsin. We show that retinal degeneration and decrease in rhodopsin staining can be prevented partially in three different ways: first, by recombining mutant-derived postnatal retina with postnatal wild-type RPE in tissue explant cultures; second, by adding to cultured mutant retina the trophic factor pigment epithelium-derived factor (PEDF; also known as SERPINF1), which is normally produced in RPE under the control of Mitf; and third, by treating the eyes of Mitf mutant mice in vivo with drops containing a bioactive PEDF 17-mer peptide. This latter treatment also led to marked increases in a number of rod and cone genes. The results indicate that RPE-derived trophic factors, in particular PEDF, are instrumental in retinal homeostasis, and suggest that PEDF or its bioactive fragments may have therapeutic potential in RPE deficiency-associated retinal degeneration.

A cell penetrating peptide from SOCS-1 prevents ocular damage in experimental autoimmune uveitis

We describe an immunosuppressive peptide corresponding to the kinase inhibitory region (KIR) of the intracellular checkpoint protein suppressor of cytokine signaling 1 (SOCS-1) that binds to the phospho-tyrosine containing regions of the tyrosine kinases JAK2 and TYK2 and the adaptor protein MAL, and thereby inhibits signaling downstream from these signaling mediators. The peptide, SOCS1-KIR, is thus capable of downregulating overactive JAK/STAT or NF-kB signaling in somatic cells, including those in many compartments of the eye. Attachment of poly-arginine to this peptide (R9-SOCS1-KIR) allows it to penetrate the plasma membrane in aqueous media. R9-SOCS1-KIR was tested in ARPE-19 cells and was found to attenuate mediators of inflammation by blocking the inflammatory effects of IFNγ, TNFα, or IL-17A. R9-SOCS1-KIR and also protected against TNFα or IL-17A mediated damage to the barrier properties of ARPE-19 cells, as evidenced by immunostaining with the tight junction protein, zona occludin 1 (ZO-1), and measurement of transepithelial electrical resistance (TEER). Experimental autoimmune uveitis (EAU) was generated in B10. RIII mice using a peptide of interphotoreceptor retinal binding protein (IRBP^161-180) as immunogen. Topical administration of R9-SOCS1-KIR, 2 days before (prophylactic), or 7 days after immunization (therapeutic) protected ocular structure and function as seen by fundoscopy, optical coherence tomography (OCT), and electroretinography (ERG). The ability R9-SOCS1-KIR to suppress ocular inflammation and preserve barrier properties of retinal pigment epithelium makes it a potential candidate for treatment of autoimmune uveitis.

Reconnecting Eye to Brain

Although much is known about the regenerative capacity of retinal ganglion cells, very significant barriers remain in our ability to restore visual function following traumatic injury or disease-induced degeneration. Here we summarize our current understanding of the factors regulating axon guidance and target engagement in regenerating axons, and review the state of the field of neural regeneration, focusing on the visual system and highlighting studies using other model systems that can inform analysis of visual system regeneration. This overview is motivated by a Society for Neuroscience Satellite meeting, "Reconnecting Neurons in the Visual System," held in October 2015 sponsored by the National Eye Institute as part of their "Audacious Goals Initiative" and co-organized by Carol Mason (Columbia University) and Michael Crair (Yale University). The collective wisdom of the conference participants pointed to important gaps in our knowledge and barriers to progress in promoting the restoration of visual system function. This article is thus a summary of our existing understanding of visual system regeneration and provides a blueprint for future progress in the field.

Retinal pigment epithelium-secretome: A diabetic retinopathy perspective

Diabetic retinopathy is a major complication of diabetes mellitus that can lead to retinal vascular abnormalities and visual impairment. While retinal endothelial pathology is well studied, retinal pigment epithelium (RPE) layer modifications and the patho-physiological regulations are not widely understood. The RPE is a highly specialized pigmented layer regulating not only physiological functions such as transport of nutrients, ions, absorption of light, phagocytosis of photoreceptor membranes, but also secretion of a number of cytokines, chemokines, angiogenic and anti-angiogenic factors. The RPE secretome, though crucial in health and disease, remains elusive in diabetic retinopathy. A knowledge of these secreted factors would help explain and correlate the clinical phase of the disease aiding in improved disease management. A comprehensive knowledge of the secreted factors of the RPE is a potential tool for understanding the differential treatment regime of early diabetic retinopathy, diabetic proliferative retinopathy and diabetic macular edema. In this review, we have delineated the importance of factors secreted by the retinal pigment epithelium and its regulation in the pathogenesis of diabetic retinopathy.

3D culture of human pluripotent stem cells in RGD-alginate hydrogel improves retinal tissue development

No treatments exist to effectively treat many retinal diseases. Retinal pigmented epithelium (RPE) and neural retina can be generated from human embryonic stem cells/induced pluripotent stem cells (hESCs/hiPSCs). The efficacy of current protocols is, however, limited. It was hypothesised that generation of laminated neural retina and/or RPE from hiPSCs/hESCs could be enhanced by three dimensional (3D) culture in hydrogels. hiPSC- and hESC-derived embryoid bodies (EBs) were encapsulated in 0.5% RGD-alginate; 1% RGD-alginate; hyaluronic acid (HA) or HA/gelatin hydrogels and maintained until day 45. Compared with controls (no gel), 0.5% RGD-alginate increased: the percentage of EBs with pigmented RPE foci; the percentage EBs with optic vesicles (OVs) and pigmented RPE simultaneously; the area covered by RPE; frequency of RPE cells (CRALBP+); expression of RPE markers (TYR and RPE65) and the retinal ganglion cell marker, MATH5. Furthermore, 0.5% RGD-alginate hydrogel encapsulation did not adversely affect the expression of other neural retina markers (PROX1, CRX, RCVRN, AP2α or VSX2) as determined by qRT-PCR, or the percentage of VSX2 positive cells as determined by flow cytometry. 1% RGD-alginate increased the percentage of EBs with OVs and/or RPE, but did not significantly influence any other measures of retinal differentiation. HA-based hydrogels had no significant effect on retinal tissue development. The results indicated that derivation of retinal tissue from hESCs/hiPSCs can be enhanced by culture in 0.5% RGD-alginate hydrogel. This RGD-alginate scaffold may be useful for derivation, transport and transplantation of neural retina and RPE, and may also enhance formation of other pigmented, neural or epithelial tissue.

STATEMENT OF SIGNIFICANCE

The burden of retinal disease is ever growing with the increasing age of the world-wide population. Transplantation of retinal tissue derived from human pluripotent stem cells (PSCs) is considered a promising treatment. However, derivation of retinal tissue from PSCs using defined media is a lengthy process and often variable between different cell lines. This study indicated that alginate hydrogels enhanced retinal tissue development from PSCs, whereas hyaluronic acid-based hydrogels did not. This is the first study to show that 3D culture with a biomaterial scaffold can improve retinal tissue derivation from PSCs. These findings indicate potential for the clinical application of alginate hydrogels for the derivation and subsequent transplantation retinal tissue. This work may also have implications for the derivation of other pigmented, neural or epithelial tissue.

Neural Stem Cell-based Intraocular Administration of Pigment Epithelium-derived Factor Promotes Retinal Ganglion Cell Survival and Axon Regeneration after Optic Nerve Crush Injury in Rat: An Experimental Study

BACKGROUND

Pigment epithelium-derived factor (PEDF) is regarded as a multifunctional protein possessing neurotrophic and neuroprotective properties. PEDF has a very short half-life, and it would require multiple injections to maintain a therapeutically relevant level without a delivery system. However, multiple injections are prone to cause local damage or infection. To overcome this, we chose a cell-based system that provided sustained delivery of PEDF and compared the effect of weekly injections of PEDF and neural stem cell (NSC)-based intraocular administration of PEDF on retinal ganglion cell (RGC) survival and axon regeneration after optic nerve injury.

METHODS

Seventy-two rats were randomly assigned to 3 groups: group with injections of phosphate buffered saline (PBS) (n=24), group with weekly injections of PEDF (n=24), and group with NSC-based administration of PEDF (n=24). Western blot was used to analyze the PEDF protein level 2 weeks after injection. Retinal flat mounts and immunohistochemistry were employed to analyze RGC survival and axon regeneration 2 weeks and 4 weeks after injection. The data were analyzed with one-way ANOVA in SPSS (version 19.0). A P<0.05 was considered significant.

RESULTS

The PEDF protein level in the group with NSC-based administration of PEDF increased compared with that in the groups with injections of PEDF and PBS (P<0.05). The PEDF-modified NSCs differentiated into GFAP-positive astrocytes andβ-tubulin-III-positive neurons. NSC-based administration of PEDF effectively increased RGC survival and improved the axon regeneration of the optic nerve compared with weekly injections of PEDF.

CONCLUSION

Subretinal space transplantation of PEDF-secreting NSCs sustained high concentrations of PEDF, differentiated into neurons and astrocytes, and significantly promoted RGC survival and axon regeneration after optic nerve injury.

Methods for culturing retinal pigment epithelial cells: a review of current protocols and future recommendations

The retinal pigment epithelium is an important part of the vertebrate eye, particularly in studying the causes and possible treatment of age-related macular degeneration. The retinal pigment epithelium is difficult to access in vivo due to its location at the back of the eye, making experimentation with age-related macular degeneration treatments problematic. An alternative to in vivo experimentation is cultivating the retinal pigment epithelium in vitro, a practice that has been going on since the 1970s, providing a wide range of retinal pigment epithelial culture protocols, each producing cells and tissue of varying degrees of similarity to natural retinal pigment epithelium. The purpose of this review is to provide researchers with a ready list of retinal pigment epithelial protocols, their effects on cultured tissue, and their specific possible applications. Protocols using human and animal retinal pigment epithelium cells, derived from tissue or cell lines, are discussed, and recommendations for future researchers included.

Indirect traumatic optic neuropathy

Indirect traumatic optic neuropathy (ITON) refers to optic nerve injury resulting from impact remote to the optic nerve. The mechanism of injury is not understood, and there are no confirmed protocols for prevention, mitigation or treatment. Most data concerning this condition comes from case series of civilian patients suffering blunt injury, such as from sports- or motor vehicle-related concussion, rather than military-related ballistic or blast damage. Research in this field will likely require the development of robust databases to identify patients with ITON and follow related outcomes, in addition to both in-vivo animal and virtual human models to study the mechanisms of damage and potential therapies.

Neuroprotection as a Therapeutic Target for Diabetic Retinopathy

Diabetic retinopathy (DR) is a multifactorial progressive disease of the retina and a leading cause of vision loss. DR has long been regarded as a vascular disorder, although neuronal death and visual impairment appear before vascular lesions, suggesting an important role played by neurodegeneration in DR and the appropriateness of neuroprotective strategies. Upregulation of vascular endothelial growth factor (VEGF), the main target of current therapies, is likely to be one of the first responses to retinal hyperglycemic stress and VEGF may represent an important survival factor in early phases of DR. Of central importance for clinical trials is the detection of retinal neurodegeneration in the clinical setting, and spectral domain optical coherence tomography seems the most indicated technique. Many substances have been tested in animal studies for their neuroprotective properties and for possible use in humans. Perhaps, the most intriguing perspective is the use of endogenous neuroprotective substances or nutraceuticals. Together, the data point to the central role of neurodegeneration in the pathogenesis of DR and indicate neuroprotection as an effective strategy for treating this disease. However, clinical trials to determine not only the effectiveness and safety but also the compliance of a noninvasive route of drug administration are needed.