Time Course of Neurotrophic Factor Upregulation and Retinal Protection against Light-Induced Damage after Optic Nerve Section

Platinum Nanozymes Counteract Photoreceptor Degeneration and Retina Inflammation in a Light-Damage Model of Age-Related Macular Degeneration

Degeneration of photoreceptors in age-related macular degeneration (AMD) is associated with oxidative stress due to the intense aerobic metabolism of rods and cones that if not properly counterbalanced by endogenous antioxidant mechanisms can precipitate photoreceptor degeneration. In spite of being a priority eye disease for its high incidence in the elderly, no effective treatments for AMD exist. While systemic administration of antioxidants has been unsuccessful in slowing down degeneration, locally administered rare-earth nanoparticles were shown to be effective in preventing retinal photo-oxidative damage. However, because of inherent problems of dispersion in biological media, limited antioxidant power, and short lifetimes, these NPs are still confined to the preclinical stage. Here we propose platinum nanoparticles (PtNPs), potent antioxidant nanozymes, as a therapeutic tool for AMD. PtNPs exhibit high catalytic activity at minimal concentrations and protect primary neurons against oxidative insults and the ensuing apoptosis. We tested the efficacy of intravitreally injected PtNPs in preventing or mitigating light damage produced in dark-reared albino Sprague-Dawley rats by in vivo electroretinography (ERG) and ex vivo retina morphology and electrophysiology. We found that both preventive and postlesional treatments with PtNPs increased the amplitude of ERG responses to light stimuli. Ex vivo recordings demonstrated the selective preservation of ON retinal ganglion cell responses to light stimulation in lesioned retinas treated with PtNPs. PtNPs administered after light damage significantly preserved the number of photoreceptors and inhibited the inflammatory response to degeneration, while the preventive treatment had a milder effect. The data indicate that PtNPs can effectively break the vicious cycle linking oxidative stress, degeneration, and inflammation by exerting antioxidant and anti-inflammatory actions. The increased photoreceptor survival and visual performances in degenerated retinas, together with their high biocompatibility, make PtNPs a potential strategy to cure AMD.

Retinal ganglion cell loss in an ex vivo mouse model of optic nerve cut is prevented by curcumin treatment

Retinal ganglion cell (RGC) loss is a pathologic feature common to several retinopathies associated to optic nerve damage, leading to visual loss and blindness. Although several scientific efforts have been spent to understand the molecular and cellular changes occurring in retinal degeneration, an effective therapy to counteract the retinal damage is still not available. Here we show that eyeballs, enucleated with the concomitant optic nerve cut (ONC), when kept in PBS for 24 h showed retinal and optic nerve degeneration. Examining retinas and optic nerves at different time points in a temporal window of 24 h, we found a thinning of some retinal layers especially RGC's layer, observing a powerful RGC loss after 24 h correlated with an apoptotic, MAPKs and degradative pathways dysfunctions. Specifically, we detected a time-dependent increase of Caspase-3, -9 and pro-apoptotic marker levels, associated with a strong reduction of BRN3A and NeuN levels. Importantly, a powerful activation of JNK, c-Jun, and ERK signaling (MAPKs) were observed, correlated with a significant augmented SUMO-1 and UBC9 protein levels. The degradation signaling pathways was also altered, causing a significant decrease of ubiquitination level and an increased LC3B activation. Notably, it was also detected an augmented Tau protein level. Curcumin, a powerful antioxidant natural compound, prevented the alterations of apoptotic cascade, MAPKs, and SUMO-1 pathways and the degradation system, preserving the RGC survival and the retinal layer thickness. This ex vivo retinal degeneration model could be a useful method to study, in a short time window, the effect of neuroprotective tools like curcumin that could represent a potential treatment to contrast retinal cell death.

Risk Factors for Retinal Ganglion Cell Distress in Glaucoma and Neuroprotective Potential Intervention

Retinal ganglion cells (RGCs) are a population of neurons of the central nervous system (CNS) extending with their soma to the inner retina and with their axons to the optic nerve. Glaucoma represents a group of neurodegenerative diseases where the slow progressive death of RGCs results in a permanent loss of vision. To date, although Intra Ocular Pressure (IOP) is considered the main therapeutic target, the precise mechanisms by which RGCs die in glaucoma have not yet been clarified. In fact, Primary Open Angle Glaucoma (POAG), which is the most common glaucoma form, also occurs without elevated IOP. This present review provides a summary of some pathological conditions, i.e., axonal transport blockade, glutamate excitotoxicity and changes in pro-inflammatory cytokines along the RGC projection, all involved in the glaucoma cascade. Moreover, neuro-protective therapeutic approaches, which aim to improve RGC degeneration, have also been taken into consideration.

The Timecourses of Functional, Morphological, and Molecular Changes Triggered by Light Exposure in Sprague-Dawley Rat Retinas

Retinal neurodegeneration can impair visual perception at different levels, involving not only photoreceptors, which are the most metabolically active cells, but also the inner retina. Compensatory mechanisms may hide the first signs of these impairments and reduce the likelihood of receiving timely treatments. Therefore, it is essential to characterize the early critical steps in the neurodegenerative progression to design adequate therapies. This paper describes and correlates early morphological and biochemical changes in the degenerating retina with in vivo functional analysis of retinal activity and investigates the progression of neurodegenerative stages for up to 7 months. For these purposes, Sprague-Dawley rats were exposed to 1000 lux light either for different durations (12 h to 24 h) and examined seven days afterward (7d) or for a fixed duration (24 h) and monitored at various time points following the exposure (up to 210d). Flash electroretinogram (fERG) recordings were correlated with morphological and histological analyses to evaluate outer and inner retinal disruptions, gliosis, trophic factor release, and microglial activation. Twelve hours or fifteen hours of exposure to constant light led to a severe retinal dysfunction with only minor morphological changes. Therefore, early pathological signs might be hidden by compensatory mechanisms that silence retinal dysfunction, accounting for the discrepancy between photoreceptor loss and retinal functional output. The long-term analysis showed a transient functional recovery, maximum at 45 days, despite a progressive loss of photoreceptors and coincident increases in glial fibrillary acidic protein (GFAP) and basic fibroblast growth factor-2 (bFGF-2) expression. Interestingly, the progression of the disease presented different patterns in the dorsal and ventral retina. The information acquired gives us the potential to develop a specific diagnostic tool to monitor the disease's progression and treatment efficacy.

Retinal Proteomics of a Mouse Model of Dystroglycanopathies Reveals Molecular Alterations in Photoreceptors

Mutations in the POMT1 gene, encoding a protein O-mannosyltransferase essential for α-dystroglycan (α-DG) glycosylation, are frequently observed in a group of rare congenital muscular dystrophies, collectively known as dystroglycanopathies. However, it is hitherto unclear whether the effects seen in affected patients can be fully ascribed to α-DG hypoglycosylation. To study this, here we used comparative mass spectrometry-based proteomics and immunofluorescence microscopy and investigated the changes in the retina of mice in which Pomt1 is specifically knocked out in photoreceptor cells. Our results demonstrate significant proteomic changes and associated structural alteration in photoreceptor cells of Pomt1 cKO mice. In addition to the effects related to impaired α-DG O-mannosylation, we observed morphological alterations in the outer segment that are associated with dysregulation of a relatively understudied POMT1 substrate (KIAA1549), BBSome proteins, and retinal stress markers. In conclusion, our study provides new hypotheses to explain the phenotypic changes that are observed in the retina of patients with dystroglycanopathies.

Neurotrophic Factors in Glaucoma and Innovative Delivery Systems

Glaucoma is a neurodegenerative disease and a worldwide leading cause of irreversible vision loss. In the last decades, high efforts have been made to develop novel treatments effective in inducing protection and/or recovery of neural function in glaucoma, including neurotrophic factors (NTFs). These approaches have shown encouraging data in preclinical setting; however, the challenge of sustained, targeted delivery to the retina and optic nerve still prevents the clinical translation. In this paper, the authors review and discuss the most recent advances for the use of NTFs treatment in glaucoma, including intraocular delivery. Novel strategies in drug and gene delivery technology for NTFs are proving effective in promoting long-term retinal ganglion cells (RGCs) survival and related functional improvements. Results of experimental and clinical studies evaluating the efficacy and safety of biodegradable slow-release NTF-loaded microparticle devices, encapsulated NTF-secreting cells implants, mimetic ligands for NTF receptors, and viral and non-viral NTF gene vehicles are discussed. NTFs are able to prevent and even reverse apoptotic ganglion cell death. Nevertheless, neuroprotection in glaucoma remains an open issue due to the unmet need of sustained delivery to the posterior segment of the eye. The recent advances in intraocular delivery systems pave the way for possible future use of NTFs in clinical practice for the treatment of glaucoma.

Biocompatibility of a Conjugated Polymer Retinal Prosthesis in the Domestic Pig

The progressive degeneration of retinal photoreceptors is one of the most significant causes of blindness in humans. Conjugated polymers represent an attractive solution to the field of retinal prostheses, and a multi-layer fully organic prosthesis implanted subretinally in dystrophic Royal College of Surgeons (RCS) rats was able to rescue visual functions. As a step toward human translation, we report here the fabrication and in vivo testing of a similar device engineered to adapt to the human-like size of the eye of the domestic pig, an excellent animal paradigm to test therapeutic strategies for photoreceptors degeneration. The active conjugated polymers were layered onto two distinct passive substrates, namely electro-spun silk fibroin (ESF) and polyethylene terephthalate (PET). Naive pigs were implanted subretinally with the active device in one eye, while the contralateral eye was sham implanted with substrate only. Retinal morphology and functionality were assessed before and after surgery by means of in vivo optical coherence tomography and full-field electroretinogram (ff-ERG) analysis. After the sacrifice, the retina morphology and inflammatory markers were analyzed by immunohistochemistry of the excised retinas. Surprisingly, ESF-based prostheses caused a proliferative vitreoretinopathy with disappearance of the ff-ERG b-wave in the implanted eyes. In contrast, PET-based active devices did not evoke significant inflammatory responses. As expected, the subretinal implantation of both PET only and the PET-based prosthesis locally decreased the thickness of the outer nuclear layer due to local photoreceptor loss. However, while the implantation of the PET only substrate decreased the ff-ERG b-wave amplitude with respect to the pre-implant ERG, the eyes implanted with the active device fully preserved the ERG responses, indicating an active compensation of the surgery-induced photoreceptor loss. Our findings highlight the possibility of developing a new generation of conjugated polymer/PET-based prosthetic devices that are highly biocompatible and potentially suitable for subretinal implantation in patients suffering from degenerative blindness.

Cord Blood Serum (CBS)-Based Eye Drops Modulate Light-Induced Neurodegeneration in Albino Rat Retinas

Age-related macular degeneration (AMD) is one of the leading causes of visual loss in western countries, it has no cure, and its incidence will grow in the future, for the overall population aging. Albino rats with retinal degeneration induced by exposure to high-intensity light (light-damage, LD) have been extensively used as a model of AMD to test neuroprotective agents. Among them, trophic factors (NGF and BDNF) have been shown to play a significant role in photoreceptors' survival. Interestingly, cord blood serum (CBS) is an extract full of chemokines and trophic factors; we, therefore, hypothesized that CBS could be an excellent candidate for neuroprotection. Here, we investigate whether CBS-based eye drops might mitigate the effects of light-induced retinal degeneration in albino rats. CBS treatment significantly preserved flash-electroretinogram (f-ERG) response after LD and reduced the "hot-spot" extension. Besides, CBS-treated animals better preserved the morphology of the outer nuclear layer, together with a reduction in microglia migration and activation. Interestingly, the treatment did not modulate reactive gliosis and activation of the self-protective mechanism (FGF2). In conclusion, our results suggest that CBS-based eye drops might be successfully used to mitigate retinal neurodegenerative processes such as AMD.

670nm light treatment following retinal injury modulates Müller cell gliosis: Evidence from in vivo and in vitro stress models

Photobiomodulation (PBM) with 670 nm light has been shown to accelerate wound healing in soft tissue injuries, and also to protect neuronal tissues. However, little data exist on its effects on the non-neuronal components of the retina, such as Müller cells (MCs), which are the principal macroglia of the retina that play a role in maintaining retinal homeostasis. The aim of this study was to explore the effects of 670 nm light on activated MCs using in vivo and in vitro stress models. Adult Sprague-Dawley rats were exposed to photo-oxidative damage (PD) for 24 h and treated with 670 nm light at 0, 3 and 14 days after PD. Tissue was collected at 30 days post-PD for analysis. Using the in vitro scratch model with a human MC line (MIO-M1), area coverage and cellular stress were analysed following treatment with 670 nm light. We showed that early treatment with 670 nm light after PD reduced MC activation, lowering the retinal expression of GFAP and FGF-2. 670 nm light treatment mitigated the production of MC-related pro-inflammatory cytokines (including IL-1β), and reduced microglia/macrophage (MG/MΦ) recruitment into the outer retina following PD. This subsequently decreased photoreceptor loss, slowing the progression of retinal degeneration. In vitro, we showed that 670 nm light directly modulated MC activation, reducing rates of area coverage by suppressing cellular proliferation and spreading. This study indicates that 670 nm light treatment post-injury may have therapeutic benefit when administered shortly after retinal damage, and could be useful for retinal degenerations where MC gliosis is a feature of disease progression.

Measuring Ciliary Neurotrophic Factor (CNTF) in Lacrimal Fluid Using Optimized Commercial ELISA

The concentration of ciliary neurotrophic factor (CNTF) was measured in lacrimal fluid (LF) using Human CNTF Quantikine ELISA kit (“R&D Systems”, USA) on a ChemWell 2910 automatic analyzer (“Awareness Technology Inc.”, USA). We initially attempted to use commercial kits, designed for serum and plasma CNTF detection, to quantify lacrimal CNTF. The results, however, were rarely above the minimum detection level of the kits, most likely due to matrix complexity and low concentrations of CNTF in diluted LF (LF had to be diluted because of the small volume of collected samples). The optimal sensitivity and the lowest background for the best minimum quantifiable value were determined empirically. Phosphate buffer solution containing 1% bovine serum albumin was selected as an optimal diluent for CNTF measurements in small fluid samples. A standard curve was produced using the calibrating solutions 0-250 pg/ml. Acid treatment of LF samples before the analysis allowed to increase the detectable concentration of the CNTF two-fold. The 1:3 dilution was selected based on the available volume of collected LF and a reasonable variation coefficient. The described protocol allowed to develop a sandwich ELISA optimized for lacrimal CNTF.

Ciliary neurotrophic factor (CNTF) delivery to retina: an overview of current research advancements

The intraocular administration of the ciliary neurotrophic factor (CNTF) has been found to attenuate the photoreceptor degeneration and preserve retinal functions in the animal research models of the inherited or induced retinal disease. Studies with the aim of CNTF transfer to the posterior segment inside the eye have been directed to determine the best method for its administration. An ideal delivery method would overcome the eye drug elimination mechanisms or barriers and provide the sustained release of the CNTF into retina in the safest fashion with the minimum harm to the quality of life. This review focuses on the present state of CNTF delivery to retina, also provides an overview of available technologies and their challenges.

CNTF Attenuates Vasoproliferative Changes Through Upregulation of SOCS3 in a Mouse-Model of Oxygen-Induced Retinopathy

Purpose

Retinal vascular disease represents a major cause for vision loss in the Western world. Recent research has shown that neuronal and vascular damage are closely related in retinal disease. Ciliary neurotrophic factor (CNTF) is a well-studied neurotrophic factor that is currently being tested in clinical trials for the treatment of retinal degenerative diseases and macular telangiectasia. However, little is known about its effect on retinal vasculature. In this study, we investigate the effects of CNTF in retinal neovascular disease using the mouse model of oxygen-induced retinopathy (OIR).

Methods

Newborn pups were exposed to 75% oxygen from postnatal day (P)7 to P12 and subsequently returned to room air. Ciliary neurotrophic factor was injected intravitreally at OIR P12 and the vaso-obliterated and neovascular areas were quantified at OIR P17. Immunohistochemistry, RNA, and protein analysis were used to identify CNTF-responsive cells. In vitro experiments were performed to analyze the effect of CNTF on endothelial and astroglial cells.

Results

In the OIR model, CNTF facilitated capillary regrowth and attenuated preretinal neovascularization in a dose-dependent manner. The protective effect of CNTF was mediated via activation of the JAK/STAT3/SOCS3 signaling pathway. Immunohistochemical studies identified endothelial cells among others as CNTF-responsive cells in the retina. In vitro studies confirmed the anti-angiogenic effect of CNTF on endothelial cell sprouting.

Conclusions

This study provides evidence for a therapeutic potential of CNTF beyond degenerative retinal disease. Vasoproliferative retinopathies may benefit from a CNTF-dependent and SOCS3-mediated angiomodulatory effect.

Hypoxia-Inducible Factor-1α Target Genes Contribute to Retinal Neuroprotection

Hypoxia-inducible factor (HIF) is a transcription factor that facilitates cellular adaptation to hypoxia and ischemia. Long-standing evidence suggests that one isotype of HIF, HIF-1α, is involved in the pathogenesis of various solid tumors and cardiac diseases. However, the role of HIF-1α in retina remains poorly understood. HIF-1α has been recognized as neuroprotective in cerebral ischemia in the past two decades. Additionally, an increasing number of studies has shown that HIF-1α and its target genes contribute to retinal neuroprotection. This review will focus on recent advances in the studies of HIF-1α and its target genes that contribute to retinal neuroprotection. A thorough understanding of the function of HIF-1α and its target genes may lead to identification of novel therapeutic targets for treating degenerative retinal diseases including glaucoma, age-related macular degeneration, diabetic retinopathy, and retinal vein occlusions.

Alteration of Neurotrophic Factors After Transplantation of Bone Marrow Derived Lin-ve Stem Cell in NMDA-Induced Mouse Model of Retinal Degeneration

Retinal ganglion cell layer (RGCs) is one of the important layers of retina, depleted in Glaucoma. Loss of RGC neurons is a major cellular mechanism involved in its pathogenesis resulting in severe vision loss. Stem cell therapy has emerged as a potential strategy to arrest the apoptotic loss of RGCs and also replace the degenerative cells in damaged retina. Here, we have investigated the incorporation and survival of mouse bone marrow derived Lin-ve stem cells in N-methyl-d-aspartate (NMDA)-induced mouse model of retinal degeneration. Two days after intravitreal injection of NMDA (100 mM) showed significant decrease in ganglion cell number and increase in TUNEL positive apoptotic cells in retinal layers. The injury was further characterized by immunohistochemical expression of Brn3b, GFAP, Bcl2, pCREB, CNTF, GDNF, and BDNF in retinal layers. Lin-ve cells (100,000 dose) were intravitreally transplanted after 2 days of injury and evaluated after 7, 14, and 21 days of transplantation. Transplanted cells were found to have migrated from intravitreal space and incorporated into injured retina at 7, 14, and 21 days post-transplantation. At 21 days Brn3b, CNTF, and BDNF expression was found to be upregulated whereas GDNF was downregulated when compared to respective injury time points. Molecular data showed decrease in the expression of Brn3b, BDNF, CNTF, and GDNF post transplantation when compared with injury groups. This study reveals that Lin-ve stem cells may exert neuroprotective effect in damaged retina mediated by participation of neurotrophic factors induced by stem cell transplantation at the site of injury. J. Cell. Biochem. 118: 1699-1711, 2017. © 2016 Wiley Periodicals, Inc.

Characterization of a Polymer-Based, Fully Organic Prosthesis for Implantation into the Subretinal Space of the Rat

Replacement strategies arise as promising approaches in case of inherited retinal dystrophies leading to blindness. A fully organic retinal prosthesis made of conjugated polymers layered onto a silk fibroin substrate is engineered. First, the biophysical and surface properties are characterized; then, the long-term biocompatibility is assessed after implantation of the organic device in the subretinal space of 3-months-old rats for a period of five months. The results indicate a good stability of the subretinal implants over time, with preservation of the physical properties of the polymeric layer and a tight contact with the outer retina. Immunoinflammatory markers detect only a modest tissue reaction to the surgical insult and the foreign body that peaks shortly after surgery and progressively decreases with time to normal levels at five months after implantation. Importantly, the integrity of the polymeric layer in direct contact with the retinal tissue is preserved after five months of implantation. The recovery of the foreign-body tissue reaction is also associated with a normal b-wave in the electroretinographic response. The results demonstrate that the device implanted in nondystrophic eyes is well tolerated, highly biocompatible, and suitable as retinal prosthesis in case of photoreceptor degeneration.

Intravitreal Ciliary Neurotrophic Factor Transiently Improves Cone-Mediated Function in a CNGB3-/- Mouse Model of Achromatopsia

PURPOSE

Ciliary neurotrophic factor (CNTF) was recently shown to augment cone function in CNGB3 mutant achromat dogs. However, testing CNTF-releasing implant in human CNGB3 achromats failed to show benefit. We evaluated the effects of CNTF protein on the retinal function in an additional achromatopsia model, the CNGB3-/- mouse.

METHODS

Fifty-nine CNGB3-/- mice (postnatal day [PD] ± SD = 30 ± 7) received a unilateral intravitreal injection of 1 or 2 μg CNTF protein, and 15 wild-type (WT) mice (PD = 34 ± 3) received 1 μg CNTF. Retinal function was evaluated by flash ERG and photopic flicker ERG (fERG) at 7 and 14 days after treatment.

RESULTS

Seven days post CNTF, the photopic b-wave Vmax was significantly increased in CNGB3-/- mice (P < 0.01), whereas it was reduced in WT mice (P < 0.05). Ciliary neurotrophic factor significantly increased the amplitude of photopic fERG and the photopic oscillatory potentials (OPs) in CNGB3-/- mice. Ciliary neurotrophic factor did not alter the scotopic a-wave in either CNGB3-/- or WT mice, but it increased the scotopic b-wave k (P < 0.01) in CNGB3-/- mice, indicating diminished scotopic sensitivity, and reduced the scotopic b-wave Vmax in WT mice (P < 0.05). No difference was found in ERG parameters between 1 or 2 μg CNTF. Fourteen days after CNTF injection the ERG changes in CNGB3-/- mice were lost.

CONCLUSIONS

Intravitreal bolus CNTF protein caused a small and transient improvement of cone-mediated function in CNGB3-/- mice, whereas it reduced rod-mediated function. The increase in photopic OPs and the lack of changes in scotopic a-wave suggest a CNTF effect on the inner retina.

Light, lipids and photoreceptor survival: live or let die?

Due to its constant exposure to light and its high oxygen consumption the retina is highly sensitive to oxidative damage, which is a common factor in inducing the death of photoreceptors after light damage or in inherited retinal degenerations. The high content of docosahexaenoic acid (DHA), the major polyunsaturated fatty acid in the retina, has been suggested to contribute to this sensitivity. DHA is crucial for developing and preserving normal visual function. However, further roles of DHA in the retina are still controversial. Current data support that it can tilt the scale either towards degeneration or survival of retinal cells. DHA peroxidation products can be deleterious to the retina and might lead to retinal degeneration. However, DHA has also been shown to act as, or to be the source of, a survival molecule that protects photoreceptors and retinal pigment epithelium cells from oxidative damage. We have established that DHA protects photoreceptors from oxidative stress-induced apoptosis and promotes their differentiation in vitro. DHA activates the retinoid X receptor (RXR) and the ERK/MAPK pathway, thus regulating the expression of anti and pro-apoptotic proteins. It also orchestrates a diversity of signaling pathways, modulating enzymatic pathways that control the sphingolipid metabolism and activate antioxidant defense mechanisms to promote photoreceptor survival and development. A deeper comprehension of DHA signaling pathways and context-dependent behavior is required to understand its dual functions in retinal physiology.

CNTF-mediated protection of photoreceptors requires initial activation of the cytokine receptor gp130 in Müller glial cells

Ciliary neurotrophic factor (CNTF) acts as a potent neuroprotective agent in multiple retinal degeneration animal models. Recently, CNTF has been evaluated in clinical trials for the inherited degenerative disease retinitis pigmentosa (RP) and for dry age-related macular degeneration (AMD). Despite its potential as a broad-spectrum therapeutic treatment for blinding diseases, the target cells of exogenous CNTF and its mechanism of action remain poorly understood. We have shown previously that constitutive expression of CNTF prevents photoreceptor death but alters the retinal transcriptome and suppresses visual function. Here, we use a lentivirus to deliver the same secreted human CNTF used in clinical trials to a mouse model of RP. We found that low levels of CNTF halt photoreceptor death, improve photoreceptor morphology, and correct opsin mislocalization. However, we did not detect corresponding improvement of retinal function as measured by the electroretinogram. Disruption of the cytokine receptor gp130 gene in Müller glia reduces CNTF-dependent photoreceptor survival and prevents phosphorylation of STAT3 and ERK in Müller glia and the rest of the retina. Targeted deletion of gp130 in rods also demolishes neuroprotection by CNTF and prevents further activation of Müller glia. Moreover, CNTF elevates the expression of LIF and endothelin 2, thus positively promoting Müller and photoreceptor interactions. We propose that exogenous CNTF initially targets Müller glia, and subsequently induces cytokines acting through gp130 in photoreceptors to promote neuronal survival. These results elucidate a cellular mechanism for exogenous CNTF-triggered neuroprotection and provide insight into the complex cellular responses induced by CNTF in diseased retinas.

670 nm light mitigates oxygen-induced degeneration in C57BL/6J mouse retina

Background

Irradiation with light wavelengths from the far red (FR) to the near infrared (NIR) spectrum (600 nm -1000 nm) has been shown to have beneficial effects in several disease models. In this study, we aim to examine whether 670 nm red light pretreatment can provide protection against hyperoxia-induced damage in the C57BL/6J mouse retina. Adult mice (90–110 days) were pretreated with 9 J/cm² of 670 nm light once daily for 5 consecutive days prior to being placed in hyperoxic environment (75% oxygen). Control groups were exposed to hyperoxia, but received no 670 nm light pretreatment. Retinas were collected after 0, 3, 7, 10 or 14 days of hyperoxia exposure (n = 12/group) and prepared either for histological analysis, or RNA extraction and quantitative polymerase chain reaction (qPCR). Photoreceptor damage and loss were quantified by counting photoreceptors undergoing cell death and measuring photoreceptor layer thickness. Localization of acrolein, and cytochrome c oxidase subunit Va (Cox Va) were identified through immunohistochemistry. Expression of heme oxygenase-1 (Hmox-1), complement component 3 (C3) and fibroblast growth factor 2 (Fgf-2) genes were quantified using qPCR.

Results

The hyperoxia-induced photoreceptor loss was accompanied by reduction of metabolic marker, Cox Va, and increased expression of oxidative stress indicator, acrolein and Hmox-1. Pretreatment with 670 nm red light reduced expression of markers of oxidative stress and C3, and slowed, but did not prevent, photoreceptor loss over the time course of hyperoxia exposure.

Conclusion

The damaging effects of hyperoxia on photoreceptors were ameliorated following pretreatment with 670 nm light in hyperoxic mouse retinas. These results suggest that pretreatment with 670 nm light may provide stability to photoreceptors in conditions of oxidative stress.

Basic fibroblast growth factor expression is implicated in mesenchymal stem cells response to light-induced retinal injury

Neurotrophic factors are involved in neuroprotection and its expression in mesenchymal stem cells (MSCs) may change during light-induced retinal injury. In this study, neurotrophic factor expression in MSCs was investigated after stimulation by supernatants of homogenized retina (SHR) from normal and light-injured rats. Conditioned media from control MSCs (CM-MSCs), MSCs stimulated by normal SHR (CM-NSHR), and MSCs stimulated by light-injured SHR (CM-ISHR) were examined regarding their ability to prevent degeneration of retinal explants. Basic fibroblast growth factor (bFGF) in MSCs was knockdown by lentivirus-mediated mRNA interference. Transfected MSCs were stimulated by SHR, and retinal preservation was reevaluated in the resultant conditioned media. We detected significant up-regulation of bFGF in CM-ISHR, accompanied by superior retinal neurotrophic effects in CM-ISHR over CM-NSHR and CM-MSCs. Down-regulation of bFGF in MSCs effectively inhibited this protective effect. Adding neutralizing antibody against bFGF to CM-ISHR also induced a similar effect. It is thus concluded that retinal injury may enhance neurotrophic factor expression in MSCs and promote the repair process. bFGF may play a critical role in MSCs' response to retinal injury.

A polymer optoelectronic interface restores light sensitivity in blind rat retinas

Interfacing organic electronics with biological substrates offers new possibilities for biotechnology due to the beneficial properties exhibited by organic conducting polymers. These polymers have been used for cellular interfaces in several fashions, including cellular scaffolds, neural probes, biosensors and actuators for drug release. Recently, an organic photovoltaic blend has been exploited for neuronal stimulation via a photo-excitation process. Here, we document the use of a single-component organic film of poly(3-hexylthiophene) (P3HT) to trigger neuronal firing upon illumination. Moreover, we demonstrate that this bio-organic interface restored light sensitivity in explants of rat retinas with light-induced photoreceptor degeneration. These findings suggest that all-organic devices may play an important future role in sub-retinal prosthetic implants.

Endothelin-2-mediated protection of mutant photoreceptors in inherited photoreceptor degeneration

Expression of the Endothelin-2 (Edn2) mRNA is greatly increased in the photoreceptors (PRs) of mouse models of inherited PR degeneration (IPD). To examine the role of Edn2 in mutant PR survival, we generated Edn2^−/− mice carrying homozygous Pde6b^rd1 alleles or the Tg(RHO P347S) transgene. In the Edn2^−/− background, PR survival increased 110% in Pde6b^rd1/rd1 mice at post-natal (PN) day 15, and 60% in Tg(RHO P347S) mice at PN40. In contrast, PR survival was not increased in retinal explants of Pde6b^rd1/rd1; Edn2^−/− mice. This finding, together with systemic abnormalities in Edn2^−/− mice, suggested that the increased survival of mutant PRs in the Edn2^−/− background resulted at least partly from the systemic EDN2 loss of function. To examine directly the role of EDN2 in mutant PRs, we used a scAAV5-Edn2 cDNA vector to restore Edn2 expression in Pde6b^rd1/rd1; Edn2^−/− PRs and observed an 18% increase in PR survival at PN14. Importantly, PR survival was also increased after injection of scAAV5-Edn2 into Pde6b^rd1/rd1 retinas, by 31% at PN15. Together, these findings suggest that increased Edn2 expression is protective to mutant PRs. To begin to elucidate Edn2-mediated mechanisms that contribute to PR survival, we used microarray analysis and identified a cohort of 20 genes with >4-fold increased expression in Tg(RHO P347S) retinas, including Fgf2. Notably, increased expression of the FGF2 protein in Tg(RHO P347S) PRs was ablated in Tg(RHO P347S); Edn2^−/− retinas. Our findings indicate that the increased expression of PR Edn2 increases PR survival, and suggest that the Edn2-dependent increase in PR expression of FGF2 may contribute to the augmented survival.

Changes in fibroblast growth factor-2 and FGF receptors in the frog visual system during optic nerve regeneration

We have previously shown that application of fibroblast growth factor-2 (FGF-2) to cut optic nerve axons enhances retinal ganglion cell (RGC) survival in the adult frog visual system. These actions are mediated via activation of its high affinity receptor FGFR1, enhanced BDNF and TrkB expression, increased CREB phosphorylation, and by promoting MAPK and PKA signaling pathways. The role of endogenous FGF-2 in this system is less well understood. In this study, we determine the distribution of FGF-2 and its receptors in normal animals and in animals at different times after optic nerve cut. Immunohistochemistry and Western blot analysis were conducted using specific antibodies against FGF-2 and its receptors in control retinas and optic tecta, and after one, three, and six weeks post nerve injury. FGF-2 was transiently increased in the retina while it was reduced in the optic tectum just one week after optic nerve transection. Axotomy induced a prolonged upregulation of FGFR1 and FGFR3 in both retina and tectum. FGFR4 levels decreased in the retina shortly after axotomy, whereas a significant increase was detected in the optic tectum. FGFR2 distribution was not affected by the optic nerve lesion. Changes in the presence of these proteins after axotomy suggest a potential role during regeneration.

Neurotrophic factors and the regeneration of adult retinal ganglion cell axons

The adult central nervous system (CNS) has only a limited capacity to regenerate axons after injury. This is due to a number of factors including the presence of extrinsic inhibitory factors that limit plasticity, lack of effective trophic support, and intrinsic changes in neuronal responsiveness. In this review, we describe the expression and role of neurotrophins in retinal ganglion cells (RGCs) during development and adulthood, and the receptors and miscellaneous signaling systems that influence axonal regeneration after injury. The impact of exogenous neurotrophic factors on adult RGCs injured at different sites in the visual pathway is described for several modes of delivery, including recombinant factors, viral vectors, cell transplantation, as well as combinatorial treatments involving other pharmacotherapeutic agents. Indirect, off-target effects of neurotrophic factors on RGC axonal regeneration are also considered. There remain unresolved issues relating to optimal delivery of neurotrophic factors, and we emphasize the need to develop safe, reliable methods for the regulation of exogenous supply of these factors to the injured CNS.

Neurotrophic factor delivery as a protective treatment for glaucoma

Glaucoma is a progressive optic neuropathy and a major cause of visual impairment worldwide. Neuroprotective therapies for glaucoma aim to ameliorate retinal ganglion cell degeneration through direct or indirect action on these neurons. Neurotrophic factor (NTF) delivery is a key target for the development of potential neuroprotective glaucoma treatments. This article will critically summarize the evidence that NTF deprivation and/or dysfunction plays a role in the pathogenesis of glaucoma. Experimental support for the neuroprotective potential of NTF supplementation in animal models of glaucoma will be reviewed, in particular for brain-derived neurotrophic factor, ciliary neurotrophic factor, and glial cell line-derived neurotrophic factor. Finally, the challenges of clinical translation will be considered with an emphasis on the most promising NTF delivery strategies including slow-release drug delivery, gene therapy, and cell transplantation.

Cellular signaling and factors involved in Müller cell gliosis: neuroprotective and detrimental effects

Müller cells are active players in normal retinal function and in virtually all forms of retinal injury and disease. Reactive Müller cells protect the tissue from further damage and preserve tissue function by the release of antioxidants and neurotrophic factors, and may contribute to retinal regeneration by the generation of neural progenitor/stem cells. However, Müller cell gliosis can also contribute to neurodegeneration and impedes regenerative processes in the retinal tissue by the formation of glial scars. This article provides an overview of the neuroprotective and detrimental effects of Müller cell gliosis, with accounts on the cellular signal transduction mechanisms and factors which are implicated in Müller cell-mediated neuroprotection, immunomodulation, regulation of Müller cell proliferation, upregulation of intermediate filaments, glial scar formation, and the generation of neural progenitor/stem cells. A proper understanding of the signaling mechanisms implicated in gliotic alterations of Müller cells is essential for the development of efficient therapeutic strategies that increase the supportive/protective and decrease the destructive roles of gliosis.

Selective regulation of growth factor expression in cultured cortical astrocytes by neuro-pathological toxins

Astrocytes are integrated in the complex regulation of neurodegeneration and neuronal damage in the CNS. It is well-known that astroglia produces a plethora of growth factors which might be protective for neurons. Growth factors prevent neurons from cell death and promote proliferation and differentiation of precursor cells. Previous data suggest that astrocytes may respond to toxic stimuli by a selective mobilization of guarding molecules. In the present study, we have investigated the potency of different pathological stimuli such as lipopolysaccharides, tumor necrosis factor alpha, glutamate, and hydrogen peroxide to activate cultured cortical astroglia and stimulate growth factor expression. Astroglial cultures were exposed to the above factors for 24h at non-toxic concentrations for astrocytes. Growth factor expression was analyzed by real-time PCR, oligo-microarray technique, and ELISA. Insulin-like growth factor-1 was selectively down-regulated by lipopolysaccharides and tumor necrosis factor alpha, bone morphogenetic protein 6 by all stimuli. In contrast, lipopolysaccharides, tumor necrosis factor alpha, and glutamate increased leukemia inhibitory factor. Fibroblast growth factor 2 was up-regulated by lipopolysaccharides and tumor necrosis factor alpha and down-regulated by hydrogen peroxide. Besides hydrogen peroxide, all other stimuli promoted vascular epithelial growth factor A mRNA and protein expression. It appears that lipopolysaccharides but not tumor necrosis factor alpha effects on vascular epithelial growth factor A depend on the classic NFkappaB pathway. Our data clearly demonstrate that astroglia actively responses to diverse pathological compounds by a selective expression pattern of growth factors. These findings make astrocytes likely candidates to participate in disease-specific characteristics of neuronal support or damage.

Cytokine-induced SOCS expression is inhibited by cAMP analogue: impact on regeneration in injured retina

Injured adult retinal ganglion cells (RGCs) regrow axons into peripheral nerve (PN) grafted onto cut optic nerve. Survival and regeneration of RGCs is increased by intraocular injections of ciliary neurotrophic factor (CNTF) and axonal regeneration is further enhanced by co-injection of a cyclic AMP analogue (CPT-cAMP). Based on these data, and because cytokine signaling is negatively regulated by suppressor of cytokine signaling (SOCS) proteins, we set out to determine whether CNTF injections increase retinal SOCS expression and whether any changes are attenuated by co-injection with CPT-cAMP. Using quantitative PCR we found increased SOCS1, SOCS2 and SOCS3 mRNA levels at various times after a single CNTF injection. Expression remained high for many days. SOCS protein levels were also increased. In situ hybridization revealed that RGCs express SOCS3 mRNA, and SOCS expression in cultured RGCs was increased by CNTF. Co-injection of CPT-cAMP reduced CNTF induced expression of SOCS1 and SOCS3 mRNA and decreased SOCS3 protein expression. CNTF injection also transiently increased retinal leukemia inhibitory factor (LIF) expression, an effect that was also moderated by CPT-cAMP. We propose that, along with known reparative effects of elevated cAMP on neurons, reducing SOCS upregulation may be an additional way in which cyclic nucleotides augment cytokine-induced regenerative responses in the injured CNS.

Effect of CNTF on retinal ganglion cell survival in experimental glaucoma

PURPOSE

To assess the neuroprotective effect of virally mediated overexpression of ciliary-derived neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) in experimental rat glaucoma.

METHODS

Laser-induced glaucoma was produced in one eye of 224 Wistar rats after injection of adenoassociated viral vectors (type 2) containing either CNTF, BDNF, or both, with saline-injected eyes and noninjected glaucomatous eyes serving as the control. IOP was measured with a hand-held tonometer, and semiautomated optic nerve axon counts were performed by masked observers. IOP exposure over time was adjusted in multivariate regression analysis to calculate the effect of CNTF and BDNF.

RESULTS

By multivariate regression, CNTF had a significant protective effect, with 15% less RGC axon death (P < 0.01). Both combined CNTF-BDNF and BDNF overexpression alone had no statistically significant improvement in RGC axon survival. By Western blot, there was a quantitative increase in CNTF and BDNF expression in retinas exposed to single viral vectors carrying each gene, but no increase with sequential injection of both vectors.

CONCLUSIONS

These data confirm that CNTF can exert a protective effect in experimental glaucoma. The reason for the lack of observed effect in the BDNF overexpression groups is unclear, but it may be a function of the level of neurotrophin expression achieved.

Neurotrophins induce neuroprotective signaling in the retinal pigment epithelial cell by activating the synthesis of the anti-inflammatory and anti-apoptotic neuroprotectin D1

The integrity of retinal pigment epithelial cells is critical for photoreceptor cell survival and vision. The essential omega-3 fatty acid, docosahexaenoic acid, attains its highest concentration in the human body in photoreceptors. Docosahexaenoic acid is the essential precursor of neuroprotectin D1 (NPD1). NPD1 acts against apoptosis mediated by A2E, a byproduct of phototransduction that becomes toxic when it accumulates in aging retinal pigment epithelial (RPE) cells and in some inherited retinal degenerations. Here we also describe that neurotrophins, mainly pigment epithelium-derived factor, induce NPD1 synthesis and its polarized apical secretion, suggesting paracrine and autocrine bioactivity of this lipid mediator. In addition, DHA elicits a concentration-dependent and selective potentiation of pigment epithelial-derived factor-stimulated NPD1 synthesis and release through the apical RPE cell surface. The bioactivity of signaling activated by PEDF and DHA demonstrates synergistic cytoprotection when cells were challenged with oxidative stress, resulting in concomitant NPD1 synthesis. Also, DHA and PEDF synergistically activate anti-apoptotic protein expression and decreased pro-apoptotic Bcl-2 protein expression and caspase 3 activation during oxidative stress. Thus, DHA-derived NPD1 protects against RPE cell damage mediated by aging/disease-induced A2E accumulation. Also, neurotrophins are regulators of NPD1 synthesis and of its polarized apical efflux from RPE cells. Therefore, NPD1 may elicit autocrine and paracrine bioactivity in cells located in the proximity of the interphotoreceptor matrix.

Basic fibroblast growth factor-induced protection from light damage in the mouse retina in vivo

Basic fibroblast growth factor (bFGF) has proven neuroprotective efficacy in the rodent retina against a diverse array of injurious stimuli. However, there is no consensus to date as to the molecular mechanisms underlying this neuroprotection. The study presented herein demonstrates increased expression of endogenous bFGF in the albino mouse retina in response to acute exposure to sublethal levels of light stress. The increased expression correlates with significant photoreceptor protection from light damage. The neuroprotection is likely to be mediated by bFGF as we demonstrate that a shorter exposure to bright light stress that does not up-regulate bFGF fails to protect photoreceptors from light damage. Furthermore, intravitreal bFGF injection into the retina of mice 3 h prior to light damage affords almost complete photoreceptor protection from light-induced degeneration. In addition, injected bFGF induces the activation of protein kinase B and extracellular signal-regulated kinase 1/2 signalling which correlate directly with the pathways we find to be activated in response to light stress and up-regulated bFGF. Moreover, we demonstrate that both bright light pre-conditioning and intravitreal bFGF injection result in dramatic increases in levels of inactive glycogen synthase kinase 3beta and cyclic AMP response element binding protein phosphorylation indicating a potential mechanism by which bFGF promotes survival of photoreceptors in vivo.

Neurotrophins enhance retinal pigment epithelial cell survival through neuroprotectin D1 signaling

Integrity of retinal pigment epithelial cells is necessary for photoreceptor survival and vision. The essential omega-3 fatty acid, docosahexaenoic acid, attains its highest concentration in the human body in photoreceptors and is assumed to be a target for lipid peroxidation during cell damage. We have previously shown, in contrast, that docosahexaenoic acid is also the precursor of neuroprotectin D1 (NPD1), which now we demonstrate, acts against apoptosis mediated by A2E, a byproduct of phototransduction that becomes toxic when it accumulates in aging retinal pigment epithelial (RPE) cells and in some inherited retinal degenerations. Furthermore, we show that neurotrophins, particularly pigment epithelium-derived factor, induce NPD1 synthesis and its polarized apical secretion. Moreover, docosahexaenoic acid (DHA) elicits a concentration-dependent and selective potentiation of pigment epithelial-derived factor-stimulated NPD1 synthesis and release through the apical RPE cell surface. The bioactivity of signaling activated by pigment epithelium-derived factor and DHA uncovered synergistic cytoprotection with concomitant NPD1 synthesis when cells were challenged with oxidative stress. Also, DHA and pigment epithelium-derived factor synergistically modify the expression of Bcl-2 family members, activating antiapoptotic proteins and decreasing proapoptotic proteins, and by attenuating caspase 3 activation during oxidative stress. Thus, our findings demonstrate that DHA-derived NPD1 protects against RPE cell damage mediated by aging/disease-induced A2E accumulation. Also, our results identify neurotrophins as regulators of NPD1 and of its polarized apical efflux from RPE cells. Taken together, these findings imply NPD1 may elicit autocrine actions on RPE cells and paracrine bioactivity in cells located in the proximity of the interphotoreceptor matrix.

Paradoxical role of BDNF: BDNF+/- retinas are protected against light damage-mediated stress

PURPOSE

Photoreceptors can be prevented from undergoing apoptosis in response to constant light by the application of exogenous neuroprotective agents, including brain-derived neurotrophic factor (BDNF). BDNF, however, cannot exert its effect directly on photoreceptors because they do not express receptors for BDNF. It has been proposed that BDNF released from Müller cells provides a feed-forward loop, increasing ciliary neurotrophic factor (CNTF) and basic fibroblast growth factor (bFGF) production in Müller cells, which may enhance photoreceptor survival. The authors hypothesized that retinas with reduced BDNF levels in which the BDNF-mediated release of neuroprotective signals is dampened are more susceptible to light-induced photoreceptor degeneration.

METHODS

Young adult BDNF+/+ and BDNF+/- littermates (B6.129-BDNF(tm1-LT)) were analyzed. Retinal neurotrophin and growth factor mRNA levels were determined by quantitative RT-PCR, photoreceptor function was assessed through electroretinography, and survival was documented in morphologic sections and in TUNEL assays. Oxidative stress was assayed by measuring glutathione peroxidase activity.

RESULTS

At baseline, BDNF+/- animals had significantly increased levels of glial-derived neurotrophic factor (GDNF) mRNA compared with their wild-type littermates. After light damage GDNF, CNTF, and BDNF mRNA levels dropped 14- to 16-fold in the BDNF+/+ mice but remained almost unchanged compared with baseline levels in the BDNF+/- mice. Preservation of neurotrophin levels in BDNF+/- mice correlated with photoreceptor cell survival, preservation of function, and reduced oxidative stress.

CONCLUSIONS

Contrary to the hypothesis, reducing BDNF levels resulted in photoreceptor protection against light damage. Survival was paralleled by a reduction in oxidative stress and the preservation of neurotrophin levels, suggesting that chronic reduction of BDNF in the retina provides a level of preconditioning against stress.

Differential role of Jak-STAT signaling in retinal degenerations

Retinal degeneration is a major cause of severe visual impairment or blindness. Understanding the underlying molecular mechanisms is a prerequisite to develop therapeutic approaches for human patients. We show in three mouse models that induced and inherited retinal degeneration induces LIF and CLC as members of the interleukin (IL)-6 family of proteins, activates proteins of the Jak-STAT signaling pathway, and up-regulates suppressors of cytokine signaling as a negative feedback loop. Inhibition of Jak2 leads to protection of photoreceptors in a model of induced but not in a model of inherited retinal degeneration. Differential activation of Akt suggests alternative pathways for cell death and/or survival in different models. Proteins induced during photoreceptor degeneration are not mainly expressed in photoreceptors but in cells of other retinal layers. This suggests a model in which photoreceptor injury is signaled to cells of the inner retina, which in turn initiate a response either to support viability or accelerate death of injured cells.

Docosahexaenoic acid prevents apoptosis of retina photoreceptors by activating the ERK/MAPK pathway

Identifying the trophic factors for retina photoreceptors and the intracellular pathways activated to promote cell survival is crucial for treating retina neurodegenerative diseases. Docosahexaenoic acid (DHA), the major retinal polyunsaturated fatty acid, prevents photoreceptor apoptosis during early development in vitro, and upon oxidative stress. However, the signaling mechanisms activated by DHA are still unclear. We investigated whether the extracellular signal regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) or the phosphatidylinositol-3-kinase (PI3K) pathway participated in DHA protection. 1,4-Diamino-2,3-dicyano-1,4-bis(2-aminophynyltio) butadiene (U0126), a specific MEK inhibitor, completely blocked the DHA anti-apoptotic effect. DHA rapidly increased ERK phosphorylation in photoreceptors, whereas U0126 blocked this increase. U0126 hindered DHA prevention of mitochondrial depolarization, and blocked the DHA-induced increase in opsin expression. On the contrary, PI3K inhibitors did not diminish the DHA protective effect. DHA promoted the early expression of Bcl-2, decreased Bax expression and reduced caspase-3 activation in photoreceptors. These results suggest that DHA exclusively activates the ERK/MAPK pathway to promote photoreceptor survival during early development in vitro and upon oxidative stress. This leads to the regulation of Bcl-2 and Bax expression, thus preserving mitochondrial membrane potential and inhibiting caspase activation. Hence, DHA, a lipid trophic factor, promotes photoreceptor survival and differentiation by activating the same signaling pathways triggered by peptidic trophic factors.

Transformation of adult retina from the regenerative to the axonogenesis state activates specific genes in various subsets of neurons and glial cells

The purpose of this study was to identify the gene expression profile of the regenerating retina in vitro. To achieve this goal, three experimental groups were studied: (1) an injury control group (OC-LI group) that underwent open crush (OC) of the optic nerve and lens injury (LI) in vivo; (2) an experimental group (OC-LI-R group) that comprised animals treated like those in the OC-LI group except that retinal axons were allowed to regenerate (R) in vitro; and (3) an experimental group (OC-LI-NR group) that comprised animals treated as those in the OC-LI group, except that the retinas were cultured in vitro with the retinal ganglion cell (RGC) layer facing upwards to prevent axonal regeneration (NR). Gene expression in each treatment group was compared to that of untreated controls. Immunohistochemistry was used to examine whether expression of differentially regulated genes also occurred at the protein level and to localize these proteins to the respective retinal cells. Genes that were regulated belonged to different functional categories such as antioxidants, antiapoptotic molecules, transcription factors, secreted signaling molecules, inflammation-related genes, and others. Comparison of changes in gene expression among the various treatment groups revealed a relatively small cohort of genes that was expressed in different subsets of cells only in the OC-LI-R group; these genes can be considered to be regeneration-specific. Our findings demonstrate that axonal regeneration of RGC involves an orchestrated response of all retinal neurons and glia, and could provide a platform for the development of therapeutic strategies for the regeneration of injured ganglion cells.