Protection of pattern electroretinogram and retinal ganglion cells by oncostatin M after optic nerve injury

Establishment of a minimally invasive distal traumatic optic neuropathy model in mice to investigate cascade reactions of retinal glial cells

Traumatic optic neuropathy (TON) is a complication of craniocerebral, orbital and facial injuries, leading to irreversible vision loss. At present, there is no reliable, widely used animal model, although it has been confirmed that TON can cause the loss of retinal ganglion cells (RGC). However, the cascade reaction of retinal glial cells underlying TON is unclear. Therefore, the establishment of an animal model to explore the pathological mechanism of TON would be of great interest to the scientific community. In this study, we propose a novel mouse model utilizing a 3D stereotaxic apparatus combined with a 27G needle to evaluate damage to the optic nerve by micro-CT, anatomy, SD-OCT and F-VEP. Immunofluorescence, western blotting, qPCR experiments were conducted to investigate the loss of RGCs and activation or inactivation of microglia, astrocytes and Müller glial cells in the retina from the first week to the fourth week after modeling. The results showed that this minimally invasive method caused damage to the distal optic nerve and loss of RGC after optic nerve injury. Microglia cells were found to be activated from the first week to the third week; however, they were inactivated at the fourth week; astrocytes were activated at the second week of injury, while Müller glial cells were gradually inactivated following injury. In conclusion, this method can be used as a novel animal model of distal TON, that results in a series of cascade reactions of retinal glial cells, which will provide a basis for future studies aimed at exploring the mechanism of TON and the search for effective treatment methods.

Oncostatin M: Risks and Benefits of a Novel Therapeutic Target for Atherosclerosis

BACKGROUND

Cardiovascular disease (CVD) is a leading cause of death worldwide. It is predicted that approximately 23.6 million people will die from CVDs annually by 2030. Therefore, there is a great need for an effective therapeutic approach to combat this disease. The European Cardiovascular Target Discovery (CarTarDis) consortium identified Oncostatin M (OSM) as a potential therapeutic target for atherosclerosis. The benefits of modulating OSM - an interleukin (IL)-6 family cytokine - have since been studied for multiple indications. However, as decades of high attrition rates have stressed, the success of a drug target is determined by the fine balance between benefits and the risk of adverse events. Safety issues should therefore not be overlooked.

OBJECTIVE

In this review, a risk/benefit analysis is performed on OSM inhibition in the context of atherosclerosis treatment. First, OSM signaling characteristics and its role in atherosclerosis are described. Next, an overview of in vitro, in vivo, and clinical findings relating to both the benefits and risks of modulating OSM in major organ systems is provided. Based on OSM's biological function and expression profile as well as drug intervention studies, safety concerns of inhibiting this target have been identified, assessed, and ranked for the target population.

CONCLUSION

While OSM may be of therapeutic value in atherosclerosis, drug development should also focus on de-risking the herein identified major safety concerns: tissue remodeling, angiogenesis, bleeding, anemia, and NMDA- and glutamate-induced neurotoxicity. Close monitoring and/or exclusion of patients with various comorbidities may be required for optimal therapeutic benefit.

Retinal Protection by Sustained Nanoparticle Delivery of Oncostatin M and Ciliary Neurotrophic Factor Into Rodent Models of Retinal Degeneration

Purpose

Retinitis pigmentosa (RP) is caused by mutations in more than 60 genes. Mutation-independent approaches to its treatment by exogeneous administration of neurotrophic factors that will preserve existing retinal anatomy and visual function are a rational strategy. Ciliary neurotrophic factor (CNTF) and oncostatin M (OSM) are two potent survival factors for neurons. However, growth factors degrade rapidly if administered directly. A sustained delivery of growth factors is required for translating their potential therapeutic benefit into patients.

Methods

Stable and biocompatible nanoparticles (NP) that incorporated with CNTF and OSM (CNTF- and OSM-NP) were formulated. Both NP-trophic factors were tested in vitro using photoreceptor progenitor cells (PPC) and retinal ganglion progenitor cells (RGPC) derived from induced pluripotent stem cells and in vivo using an optic nerve crush model for glaucoma and the Royal College of Surgeons rat, model of RP (n = 8/treatment) by intravitreal delivery. Efficacy was evaluated by electroretinography and optokinetic response. Retinal histology and a whole mount analysis were performed at the end of experiments.

Results

Significant prosurvival and pro-proliferation effects of both complexes were observed in both photoreceptor progenitor cells and RGPC in vitro. Importantly, significant RGC survival and preservation of vision and photoreceptors in both complex-treated animals were observed compared with control groups.

Conclusions

These results demonstrate that NP-trophic factors are neuroprotective both in vitro and in vivo. A single intravitreal delivery of both NP-trophic factors offered neuroprotection in animal models of retinal degeneration.

Translational Relevance

Sustained nanoparticle delivery of neurotrophic factors may offer beneficial effects in slowing down progressive retinal degenerative conditions, including retinitis pigmentosa, age-related macular degeneration, and glaucoma.

Retinal and cortical visual acuity in a common inbred albino mouse

While albino mice are widely used in research which includes the use of visually guided behavioral tests, information on their visual capability is scarce. We compared the spatial resolution (acuity) of albino mice (BALB/c) with that of pigmented mice (C57BL/6J). We used a high-throughput pattern electroretinogram (PERG) and pattern visual evoked potential (PVEP) method for objective assessment of retinal and cortical acuity, as well as optomotor head-tracking response/ reflex (OMR). We found that PERG, PVEP, and OMR acuities of C57BL/6J mice were all in the range of 0.5-0.6 cycles/degree (cyc/deg). BALB/c mice had PERG and PVEP acuities in the range of 0.1-0.2 cyc/deg but were unresponsive to OMR stimulus. Results indicate that retinal and cortical acuity can be reliably determined with electrophysiological methods in BALB/c mice, although PERG/PVEP acuities are lower than those of C57BL/6J mice. The reduced acuity of BALB/c mice appears to be primarily determined at retinal level.

A novel retinal ganglion cell quantification tool based on deep learning

Glaucoma is a disease associated with the loss of retinal ganglion cells (RGCs), and remains one of the primary causes of blindness worldwide. Major research efforts are presently directed towards the understanding of disease pathogenesis and the development of new therapies, with the help of rodent models as an important preclinical research tool. The ultimate goal is reaching neuroprotection of the RGCs, which requires a tool to reliably quantify RGC survival. Hence, we demonstrate a novel deep learning pipeline that enables fully automated RGC quantification in the entire murine retina. This software, called RGCode (Retinal Ganglion Cell quantification based On DEep learning), provides a user-friendly interface that requires the input of RBPMS-immunostained flatmounts and returns the total RGC count, retinal area and density, together with output images showing the computed counts and isodensity maps. The counting model was trained on RBPMS-stained healthy and glaucomatous retinas, obtained from mice subjected to microbead-induced ocular hypertension and optic nerve crush injury paradigms. RGCode demonstrates excellent performance in RGC quantification as compared to manual counts. Furthermore, we convincingly show that RGCode has potential for wider application, by retraining the model with a minimal set of training data to count FluoroGold-traced RGCs.

Mining the proliferative diabetic retinopathy-associated genes and pathways by integrated bioinformatic analysis

PURPOSE

Diabetic retinopathy (DR) especially proliferative diabetic retinopathy (PDR) is a serious eye disease. We aimed to identify key pathway and hub genes associated with PDR by analyzing the expression of retinal fibrovascular tissue in PDR patients.

METHODS

First raw data were downloaded from the Gene Expression Omnibus database. Median normalization was subsequently applied to preprocess. Differentially expressed genes (DEGs) analyzed with the Limma package. Weighted correlation network analysis (WGCNA) was utilized to build the co-expression network for all genes. Then, we compared the DEGs and modules filtered out by WGCNA. A protein-protein interaction network based on the STRING web site and the Cytoscape software was constructed by the overlapping DEGs. Next, the Gene Ontology term and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were performed. Finally, we used the Comparative Toxicogenomics Database to identify some important pathways and hub genes tightly related to PDR.

RESULTS

Functional enrichment analysis showed that the pathway of cytokine-cytokine receptor interaction was significantly related to PDR eight hub genes which were associated with pathway including tumor necrosis factor (TNF), tumor necrosis factor receptor superfamily member 12A (TNFRSF12A), C-C chemokine 20 (CCL20), chemokine (C-X-C motif) ligand 2 (CXCL2), oncostatin M (OSM) interleukin 10 (IL10), interleukin 15 (IL 15), and interleukin 1B (IL1B).

CONCLUSIONS

We identified one pathway and eight hub genes, which were associated with PDR. The pathway provided references that will advance the understanding of mechanisms of PDR. Moreover, the hub genes may serve as therapeutic targets for precise diagnosis and treatment of PDR in the future.

Hybrid Compound SA-2 is Neuroprotective in Animal Models of Retinal Ganglion Cell Death

Purpose

Determine the toxicity, bioavailability in the retina, and neuroprotective effects of a hybrid antioxidant-nitric oxide donor compound SA-2 against oxidative stress-induced retinal ganglion cell (RGC) death in neurodegenerative animal models.

Methods

Optic nerve crush (ONC) and ischemia reperfusion (I/R) injury models were used in 12-week-old C57BL/6J mice to mimic conditions of glaucomatous neurodegeneration. Mice were treated intravitreally with either vehicle or SA-2. Retinal thickness was measured by spectral-domain optical coherence tomography (SD-OCT). The electroretinogram and pattern ERG (PERG) were used to assess retinal function. RGC survival was determined by counting RBPMS-positive RGCs and immunohistochemical analysis of superoxide dismutase 1 (SOD1) levels was carried out in the retina sections. Concentrations of SA-2 in the retina and choroid were determined using HPLC and MS. In addition, the direct effect of SA-2 treatment on RGC survival was assessed in ex vivo rat retinal explants under hypoxic (0.5% O2) conditions.

Results

Compound SA-2 did not induce any appreciable change in retinal thickness, or in a- or b-wave amplitude in naive animals. SA-2 was found to be bioavailable in both the retina and choroid after a single intravitreal injection (2% wt/vol). An increase in SOD1 levels in the retina of mice subjected to ONC and SA-2 treatment, suggests an enhancement in antioxidant activity. SA-2 provided significant (P < 0.05) RGC protection in all three of the tested RGC injury models in rodents. PERG amplitudes were significantly higher in both I/R and ONC mouse eyes following SA-2 treatment (P ≤ 0.001) in comparison with the vehicle and control groups.

Conclusions

Compound SA-2 was effective in preventing RGC death and loss of function in three different rodent models of acute RGC injury: ONC, I/R, and hypoxia.

The role of insulin resistance in experimental diabetic retinopathy-Genetic and molecular aspects

BACKGROUND

Diabetic retinopathy is characterized by defects in the retinal neurovascular unit. The underlying mechanisms of impairment-including reactive intermediates and growth-factor dependent signalling pathways and their possible interplay are incompletely understood. This study aims to assess the relative role of hyperglycemia and hyperinsulinemia alone or in combination on the gene expression patterning in the retina of animal models of diabetes.

MATERIAL AND METHODS

As insulinopenic, hyperglycemic model reflecting type 1 diabetes, male STZ-Wistar rats (60mg/kg BW; i.p. injection at life age week 7) were used. Male obese ZDF rats (fa/fa) were used as type-2 diabetes model characterized by persisting hyperglycemia and transient hyperinsulinemia. Male obese ZF rats (fa/fa) were used reflecting euglycemia and severe insulin resistance. All groups were kept till an age of 20 weeks on respective conditions together with appropriate age-matched controls. Unbiased gene expression analysis was performed per group using Affymetrix gene arrays. Bioinformatics analysis included analysis for clustering and differential gene expression, and pathway and upstream activator analysis. Gene expression differences were confirmed by microfluidic card PCR technology.

RESULTS

The most complex genetic regulation in the retina was observed in ZDF rats with a strong overlap to STZ-Wistar rats. Surprisingly, systemic insulin resistance alone in ZF rats without concomitant hyperglycemia did not induce any significant change in retinal gene expression pattern. Pathway analysis indicate an overlap between ZDF rats and STZ-treated rats in pathways like complement system activation, acute phase response signalling, and oncostatin-M signalling. Major array gene expression changes could be confirmed by subsequent PCR. An analysis of upstream transcriptional regulators revealed interferon-γ, interleukin-6 and oncostatin-M in STZ and ZDF rats. CONCLUSIONS: Systemic hyperinsulinaemia without hyperglycemia does not result in significant gene expression changes in retina. In contrast, persistent systemic hyperglycemia boosts much stronger expression changes with a limited number of known and new key regulators.

Evaluating retinal ganglion cell loss and dysfunction

Retinal ganglion cells (RGC) bear the sole responsibility of propagating visual stimuli to the brain. Their axons, which make up the optic nerve, project from the retina to the brain through the lamina cribrosa and in rodents, decussate almost entirely at the optic chiasm before synapsing at the superior colliculus. For many traumatic and degenerative ocular conditions, the dysfunction and/or loss of RGC is the primary determinant of visual loss and are the measurable endpoints in current research into experimental therapies. To actually measure these endpoints in rodent models, techniques must ascertain both the quantity of surviving RGC and their functional capacity. Quantification techniques include phenotypic markers of RGC, retrogradely transported fluorophores and morphological measurements of retinal thickness whereas functional assessments include electroretinography (flash and pattern) and visual evoked potential. The importance of the accuracy and reliability of these techniques cannot be understated, nor can the relationship between RGC death and dysfunction. The existence of up to 30 types of RGC complicates the measuring process, particularly as these may respond differently to disease and treatment. Since the above techniques may selectively identify and ignore particular subpopulations, their appropriateness as measures of RGC survival and function may be further limited. This review discusses the above techniques in the context of their subtype specificity.

Interleukin-6: A Constitutive Modulator of Glycoprotein 130, Neuroinflammatory and Cell Survival Signaling in Retina

Objective

The interleukin-6 (IL-6) family of cytokines and their signal transducer glycoprotein (gp130) are implicated in inflammatory and cell survival functions in glaucoma. There are several avenues for interdependent modulation of IL-6 family members and gp130 signaling. Here we investigated whether IL-6 modulates gp130 and related neuroinflammatory, cell survival and regulatory signaling in both healthy and glaucomatous retina.

Methods

In naïve and glaucomatous (Microbead Occlusion Model), wildtype (WT) and IL-6 knockout (IL-6−/−) mice, we examined gp130 protein expression and localization, using western blot and immunohistochemistry. Gene targets related to IL-6 and gp130 signaling and pertinent to neuroinflammation (TNFα, IL-1β), cell health (Bax, Bcl-xl) and STAT3 regulation (Socs3) were quantified using qRTPCR.

Results

In the naïve retina, IL-6−/− retina contained significantly less gp130 compared to WT retina. This IL-6-related decrease in gp130 was accompanied by a reduction in mRNA expression of TNFα, Socs3 and Bax. After 4 weeks of microbead-induced ocular hypertension, both microbead- and saline-injected (control) eyes of IL-6−/− mice exhibited higher expression of TNFα, compared to WT mice. IL-1β expression was also reduced specifically in IL-6−/− retina with microbead-induced glaucoma. While saline and microbead injection increased Bcl-xl and Socs3 mRNA in both WT and IL-6−/− mice, IL-6−/− deficiency led to smaller increases for both Bcl-xl and Socs3.

Conclusions

Our findings support a role for IL-6 in setting baseline parameters for neuroinflammatory, cell health and gp130 regulatory signaling that can impact the nature and magnitude of retinal responses to glaucoma-related stressors.

Increased production of omega-3 fatty acids protects retinal ganglion cells after optic nerve injury in mice

Injury to the central nervous system causes progressive degeneration of injured axons, leading to loss of the neuronal bodies. Neuronal survival after injury is a prerequisite for successful regeneration of injured axons. In this study, we investigated the effects of increased production of omega-3 fatty acids and elevation of cAMP on retinal ganglion cell (RGC) survival and axonal regeneration after optic nerve (ON) crush injury in adult mice. We found that increased production of omega-3 fatty acids in mice enhanced RGC survival, but not axonal regeneration, over a period of 3 weeks after ON injury. cAMP elevation promoted RGC survival in wild type mice, but no significant difference in cell survival was seen in mice over-producing omega-3 fatty acids and receiving intravitreal injections of CPT-cAMP, suggesting that cAMP elevation protects RGCs after injury but does not potentiate the actions of the omega-3 fatty acids. The observed omega-3 fatty acid-mediated neuroprotection is likely achieved partially through ERK1/2 signaling as inhibition of this pathway by PD98059 hindered, but did not completely block, RGC protection. Our study thus enhances our current understanding of neural repair after CNS injury, including the visual system.

Integrative properties of retinal ganglion cell electrical responsiveness depend on neurotrophic support and genotype in the mouse

Early stages of glaucoma and optic neuropathies are thought to show inner retina remodeling and functional changes of retinal ganglion cells (RGCs) before they die. To assess RGC functional plasticity, we investigated the contrast-gain control properties of the pattern electroretinogram (PERG), a sensitive measure of RGC function, as an index of spatio-temporal integration occurring in the inner retina circuitry subserving PERG generators. We studied the integrative properties of the PERG in mice exposed to different conditions of neurotrophic support. We also investigated the effect of genotypic differences among mouse strains with different susceptibility to glaucoma (C57BL/6J, DBA/2J, DBA/2.Gpnmb(+)). Results show that the integrative properties of the PERG recorded in the standard C57BL/6J inbred mouse strain are impaired after deficit of neurotrophic support and partially restored after exogenous neurotrophic administration. Changes in PERG amplitude, latency, and contrast-dependent responses differ between mouse strains with different susceptibility to glaucoma. Results represent a proof of concept that the PERG could be used as a tool for in-vivo monitoring of RGC functional plasticity before RGC death, the effect of neuroactive treatments, as well as for high-throughput tool for phenotypic screening of different mouse genotypes.

Neuregulin-1 protects against acute optic nerve injury in rat model

OBJECTIVES

In this study, we employed a rat model and examined the expression pattern of neuregulin-1 (NRG-1) in optic nerve and retinal ganglion cells (RGCs) in response to optic nerve injury to understand the role of NRG-1 in conferring protection against acute optic nerve injury.

METHOD

Forty-eight male rats were randomly divided into two groups, the sham-operation group (n=24) and optic nerve injury group (n=24). Flash visual evoked potentials (FVEP) and fundography images were acquired at different time points following optic nerve injury (2h, 1d, 2d, 7d, 14d and 28d). Semi-quantitative analysis of NGR-1 expression pattern was performed by immunohistochemistry (IHC) staining. In a related experiment, 100 male rats were randomly divided into NGR-1 treatment group (n=60) (treated with increasing dose of NGR-1 at 0.5μg, 1μg and 3μg), normal saline (NS) group (n=20) and negative control group (n=20). Optic nerve injury was induced in all the animals and in situ cell death was measured by detecting the apoptosis rates using TUNEL assay.

RESULTS

Fundus photography results revealed no detectable differences between the sham-operation group and optic nerve injury group at 2h, 1d, 2d and 7d. However at 2weeks, the optic discs turned pale in all animals in the optic nerve injury group. NRG-1 expression increased significantly at all time points in the optic nerve injury group (P<0.05), compared to the sham-operation group, with NRG-1 expression peaking at 14d and gradually declining by 28d. Statistically significant differences in amplitude and latency of P100 wave were also detected between the optic nerve injury and sham-operation group (P<0.05). In related experiment, compared to NS group, treatment with 1μg and 3μg of recombinant human NRG-1 resulted in statistically significant FVEP-P100 amplitude values (all P<0.05). Further, compared to the NS group, ganglion cell apoptosis was dramatically reduced in the NRG-1 group at all time points and the reduction was statistically significant in 3μg NRG-1 treatment group at 7d, 14d and 28d (all P<0.05).

CONCLUSION

Our results strongly suggest that NRG-1 is highly effective in preserving normal optic nerve function and is essential for tissue repair following optic nerve injury. Thus, NRG-1 expression confers protection against acute optic nerve injury in a dose-dependent manner.

One Year of Glaucoma Research in Review-2013 to 2014

PURPOSE

The purpose of this study was to provide the practicing clinical ophthalmologist with an update on relevant glaucoma literature published from 2013 to 2014.

DESIGN

This study is a literature review.

METHODS

The authors conducted a 1-year (October 1, 2013, to September 30, 2014) English-language glaucoma literature search on PubMed of articles containing "glaucoma" or "glaucomatous" with title/abstract as a filter. Medical subject headings filtered searching was not performed because of the newness of the reviewed material.

RESULTS

Literature search yielded 2314 articles, after which we excluded reviews and letters to the editor. We highlighted articles featuring new or updated approaches to the pathophysiology, diagnosis, or treatment of glaucoma and gave preference to human research.

CONCLUSIONS

This review features literature that is of interest to ophthalmologists in practice and also highlights studies that may provide insight on future developments applicable to clinical ophthalmology.

Electrophysiological assessment of retinal ganglion cell function

The function of retinal ganglion cells (RGCs) can be non-invasively assessed in experimental and genetic models of glaucoma by means of variants of the ERG technique that emphasize the activity of inner retina neurons. The best understood technique is the Pattern Electroretinogram (PERG) in response to contrast-reversing gratings or checkerboards, which selectively depends on the presence of functional RGCs. In glaucoma models, the PERG can be altered before histological loss of RGCs; PERG alterations may be either reversed with moderate IOP lowering or exacerbated with moderate IOP elevation. Under particular luminance-stimulus conditions, the Flash-ERG displays components that may reflect electrical activity originating in the proximal retina and be altered in some experimental glaucoma models (positive Scotopic Threshold response, pSTR; negative Scotopic Threshold Response, nSTR; Photopic Negative Response, PhNR; Oscillatory Potentials, OPs; multifocal ERG, mfERG). It is not yet known which of these components is most sensitive to glaucomatous damage. Electrophysiological assessment of RGC function appears to be a necessary outcome measure in experimental glaucoma models, which complements structural assessment and may even predict it. Neuroprotective strategies could be tested based on enhancement of baseline electrophysiological function that results in improved RGC survival. The use of electrophysiology in glaucoma models may be facilitated by specifically designed instruments that allow high throughput, robust assessment of electrophysiological function.

Intravitreal inhibition of complement C5a reduces choroidal neovascularization in mice

PURPOSE

To investigate the influence of complement component C5a inhibition on laser-induced choroidal neovascularization (CNV) in mice using a C5a specific L-aptamer.

METHODS

In C57BL/6 J mice CNV was induced by argon-laser, C5a-inhibitor (NOX-D20) was intravitreally injected in three concentrations: 0.3, 3.0, and 30 mg/ml. The unPEGylated derivate (NOX-D20001) was applied at 3.0 mg/ml; the vehicle (5 % glucose) was injected in controls. Vascular leakage was evaluated using fluorescence angiography, CNV area was examined immunohistochemically. Activated immune cells surrounding the CNV lesion and potential cytotoxicity were analyzed.

RESULTS

Compared to controls, CNV areas were significantly reduced after NOX-D20 injection at a concentration of 0.3 and 3.0 mg/ml (p = 0.042; p = 0.016). NOX-D20001 significantly decreased CNV leakage but not the area (p = 0.007; p = 0.276). At a concentration of 30 mg/ml, NOX-D20 did not reveal significant effects on vascular leakage or CNV area (p = 0.624; p = 0.121). The amount of CD11b positive cells was significantly reduced after treatment with 0.3 and 3.0 mg/ml NOX-D20 (p = 0.027; p = 0.002). No adverse glial cell proliferation or increased apoptosis were observed at effective dosages.

CONCLUSIONS

Our findings demonstrate that the targeted inhibition of complement component C5a reduces vascular leakage and neovascular area in laser-induced CNV in mice. NOX-D20 was proven to be an effective and safe agent that might be considered as a therapeutic candidate for CNV treatment. The deficiency of activated immune cells highlights promising new aspects in the pathology of choroidal neovascularization, and warrants further investigations.