Topography of retinal damage in light-exposed albino rats

The deubiquitinase Otud7b suppresses cone photoreceptor degeneration in mouse models of retinal degenerative diseases

Primary and secondary cone photoreceptor death in retinal degenerative diseases, including age-related macular degeneration (AMD) and retinitis pigmentosa (RP), leads to severe visual impairment and blindness. Although the cone photoreceptor protection in retinal degenerative diseases is crucial for maintaining vision, the underlying molecular mechanisms are unclear. Here, we found that the deubiquitinase Otud7b/Cezanne is predominantly expressed in photoreceptor cells in the retina. We analyzed Otud7b-/- mice, which were subjected to light-induced damage, a dry AMD model, or were mated with an RP mouse model, and observed increased cone photoreceptor degeneration. Using RNA-sequencing and bioinformatics analysis followed by a luciferase reporter assay, we found that Otud7b downregulates NF-κB activity. Furthermore, inhibition of NF-κB attenuated cone photoreceptor degeneration in the light-exposed Otud7b-/- retina and stress-induced neuronal cell death resulting from Otud7b deficiency. Together, our findings suggest that Otud7b protects cone photoreceptors in retinal degenerative diseases by modulating NF-κB activity.

Ilex paraguariensis Extracts Prevent Oxidative Damage in a Mouse Model of Age-Related Macular Degeneration

Age-related macular degeneration (AMD), a chronic disease of the retina, leads to severe visual loss. AMD affects the retinal pigment epithelium (RPE) and the visual cells (photoreceptors). RPE failure, the first step of this disease, is associated with oxidative stress. Since antioxidants can slow down AMD progression, the intake of foods and drinks rich in antioxidant compounds may reduce retinal damage. Ilex paraguariensis (yerba mate, YM) extracts reduce oxidative damage of RPE cells in vitro as shown in previous study. Here, the effects of YM drinking on RPE and photoreceptor survival after oxidative damage with sodium iodate (NaIO3; SI) in a murine AMD model are described. Funduscopy and histology show that YM treatment prevents RPE and photoreceptor damage. YM also increases the expression of NRF2, the master antioxidant gene, and its effectors HO-1 and SOD2. In mice receiving YM and SI, the antioxidant response is larger than in mice receiving YM or SI alone. The YM drink also increases expression of RPE65, a gene that is involved in the functionality and survival of photoreceptors and RPE cells. The results suggest YM can play an important role in the prevention of retinal damage associated with oxidative stress, such as AMD.

Structural and Functional Change in Albino Rat Retina Induced by Various Visible Light Wavelengths

The effects of visible light, from short to long wavelengths, on the retina were investigated functionally and histologically. The left eyes of Sprague-Dawley albino rats (6-weeks old, n = 6 for each wavelength) were exposed to seven narrow-band wavelengths (central wavelengths, 421, 441, 459, 501, 541, 581, and 615 nm) with bandwidths of 16 to 29 nm (half bandwidth, ±8-14.5 nm) using a xenon lamp source with bandpass filters at the retinal radiant exposures of 340 and 680 J/cm2. The right unexposed eyes served as controls. Seven days after exposure, flash electroretinograms (ERGs) were recorded, and the outer nuclear layer (ONL) thickness was measured. Compared to the unexposed eyes, significant reductions in the a- and b-wave ERG amplitudes were seen in eyes exposed to 460-nm or shorter wavelengths of light. The ONL thickness near the optic nerve head also tended to decrease with exposure to shorter wavelengths. The decreased ERG amplitudes and ONL thicknesses were most prominent in eyes exposed to 420-nm light at both radiant exposures. When the wavelengths were the same, the higher the amount of radiant exposure and the stronger the damage. Compared to the unexposed eyes, the a- and b-waves did not decrease significantly in eyes exposed to 500-nm or longer wavelength light. The results indicate that the retinal damage induced by visible light observed in albino rats depends on the wavelength and energy level of the exposed light.

Beyond Sector Retinitis Pigmentosa: Expanding the Phenotype and Natural History of the Rhodopsin Gene Codon 106 Mutation (Gly-to-Arg) in Autosomal Dominant Retinitis Pigmentosa

Sector and pericentral are two rare, regional forms of retinitis pigmentosa (RP). While usually defined as stable or only very slowly progressing, the available literature to support this claim is limited. Additionally, few studies have analyzed the spectrum of disease within a particular genotype. We identified all cases (9 patients) with an autosomal dominant Rhodopsin variant previously associated with sector RP (RHO c.316G > A, p.Gly106Arg) at our institution. Clinical histories were reviewed, and testing included visual fields, multimodal imaging, and electroretinography. Patients demonstrated a broad phenotypic spectrum that spanned regional phenotypes from sector-like to pericentral RP, as well as generalized disease. We also present evidence of significant intrafamilial variability in regional phenotypes. Finally, we present the longest-reported follow-up for a patient with RHO-associated sector-like RP, showing progression from sectoral to pericentral disease over three decades. In the absence of comorbid macular disease, the long-term prognosis for central visual acuity is good. However, we found that significant progression of RHO p.Gly106Arg disease can occur over protracted periods, with impact on peripheral vision. Longitudinal widefield imaging and periodic ERG reassessment are likely to aid in monitoring disease progression.

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.

Dorsal-Ventral Differences in Retinal Structure in the Pigmented Royal College of Surgeons Model of Retinal Degeneration

Retinitis pigmentosa is a family of inherited retinal degenerations associated with gradual loss of photoreceptors, that ultimately leads to irreversible vision loss. The Royal College of Surgeon's (RCS) rat carries a recessive mutation affecting mer proto-oncogene tyrosine kinase (merTK), that models autosomal recessive disease. The aim of this study was to understand the glial, microglial, and photoreceptor changes that occur in different retinal locations with advancing disease. Pigmented RCS rats (RCS-p^+/LAV) and age-matched isogenic control rdy (RCS-rdy ⁺p⁺/LAV) rats aged postnatal day 18 to 6 months were evaluated for in vivo retinal structure and function using optical coherence tomography and electroretinography. Retinal tissues were assessed using high resolution immunohistochemistry to evaluate changes in photoreceptors, glia and microglia in the dorsal, and ventral retina. Photoreceptor dysfunction and death occurred from 1 month of age. There was a striking difference in loss of photoreceptors between the dorsal and ventral retina, with a greater number of photoreceptors surviving in the dorsal retina, despite being adjacent a layer of photoreceptor debris within the subretinal space. Loss of photoreceptors in the ventral retina was associated with fragmentation of the outer limiting membrane, extension of glial processes into the subretinal space that was accompanied by possible adhesion and migration of mononuclear phagocytes in the subretinal space. Overall, these findings highlight that breakdown of the outer limiting membrane could play an important role in exacerbating photoreceptor loss in the ventral retina. Our results also highlight the value of using the RCS rat to model sectorial retinitis pigmentosa, a disease known to predominantly effect the inferior retina.

Transferrin Non-Viral Gene Therapy for Treatment of Retinal Degeneration

Dysregulation of iron metabolism is observed in animal models of retinitis pigmentosa (RP) and in patients with age-related macular degeneration (AMD), possibly contributing to oxidative damage of the retina. Transferrin (TF), an endogenous iron chelator, was proposed as a therapeutic candidate. Here, the efficacy of TF non-viral gene therapy based on the electrotransfection of pEYS611, a plasmid encoding human TF, into the ciliary muscle was evaluated in several rat models of retinal degeneration. pEYS611 administration allowed for the sustained intraocular production of TF for at least 3 and 6 months in rats and rabbits, respectively. In the photo-oxidative damage model, pEYS611 protected both retinal structure and function more efficiently than carnosic acid, a natural antioxidant, reduced microglial infiltration in the outer retina and preserved the integrity of the outer retinal barrier. pEYS611 also protected photoreceptors from N-methyl-N-nitrosourea-induced apoptosis. Finally, pEYS611 delayed structural and functional degeneration in the RCS rat model of RP while malondialdehyde (MDA) ocular content, a biomarker of oxidative stress, was decreased. The neuroprotective benefits of TF non-viral gene delivery in retinal degenerative disease models further validates iron overload as a therapeutic target and supports the continued development of pEY611 for treatment of RP and dry AMD.

Coordinated Intervention of Microglial and Müller Cells in Light-Induced Retinal Degeneration

Purpose

To analyze the role of microglial and Müller cells in the formation of rings of photoreceptor degeneration caused by phototoxicity.

Methods

Two-month-old Sprague-Dawley rats were exposed to light and processed 1, 2, or 3 months later. Retinas were dissected as whole-mounts, immunodetected for microglial cells, Müller cells, and S- and L/M-cones and analyzed using fluorescence, thunder imaging, and confocal microscopy. Cone populations were automatically counted and isodensity maps constructed to document cone topography.

Results

Phototoxicity causes a significant progressive loss of S- and L/M-cones of up to 68% and 44%, respectively, at 3 months after light exposure (ALE). One month ALE, we observed rings of cone degeneration in the photosensitive area of the superior retina. Two and 3 months ALE, these rings had extended to the central and inferior retina. Within the rings of cone degeneration, there were degenerating cones, often activated microglial cells, and numerous radially oriented processes of Müller cells that showed increased expression of intermediate filaments. Between 1 and 3 months ALE, the rings coalesced, and at the same time the microglial cells resumed a mosaic-like distribution, and there was a decrease of Müller cell gliosis at the areas devoid of cones.

Conclusions

Light-induced photoreceptor degeneration proceeds with rings of cone degeneration, as observed in inherited retinal degenerations in which cone death is secondary to rod degeneration. The spatiotemporal relationship of cone death microglial cell activation and Müller cell gliosis within the rings of cone degeneration suggests that, although both glial cells are involved in the formation of the rings, they may have coordinated actions and, while microglial cells may be more involved in photoreceptor phagocytosis, Müller cells may be more involved in cone and microglial cell migration, retinal remodeling and glial seal formation.

Small-Medium Extracellular Vesicles and Their miRNA Cargo in Retinal Health and Degeneration: Mediators of Homeostasis, and Vehicles for Targeted Gene Therapy

Photoreceptor cell death and inflammation are known to occur progressively in retinal degenerative diseases such as age-related macular degeneration (AMD). However, the molecular mechanisms underlying these biological processes are largely unknown. Extracellular vesicles (EV) are essential mediators of cell-to-cell communication with emerging roles in the modulation of immune responses. EVs, including exosomes, encapsulate and transfer microRNA (miRNA) to recipient cells and in this way can modulate the environment of recipient cells. Dysregulation of EVs however is correlated to a loss of cellular homeostasis and increased inflammation. In this work we investigated the role of isolated retinal small-medium sized EV (s-mEV) which includes exosomes in both the healthy and degenerating retina. Isolated s-mEV from normal retinas were characterized using dynamic light scattering, transmission electron microscopy and western blotting, and quantified across 5 days of photo-oxidative damage-induced degeneration using nanotracking analysis. Small RNAseq was used to characterize the miRNA cargo of retinal s-mEV isolated from healthy and damaged retinas. Finally, the effect of exosome inhibition on cell-to-cell miRNA transfer and immune modulation was conducted using systemic daily administration of exosome inhibitor GW4869 and in situ hybridization of s-mEV-abundant miRNA, miR-124-3p. Electroretinography and immunohistochemistry was performed to assess functional and morphological changes to the retina as a result of GW4869-induced exosome depletion. Results demonstrated an inverse correlation between s-mEV concentration and photoreceptor survivability, with a decrease in s-mEV numbers following degeneration. Small RNAseq revealed that s-mEVs contained uniquely enriched miRNAs in comparison to in whole retinal tissue, however, there was no differential change in the s-mEV miRNAnome following photo-oxidative damage. Exosome inhibition via the use of GW4869 was also found to exacerbate retinal degeneration, with reduced retinal function and increased levels of inflammation and cell death demonstrated following photo-oxidative damage in exosome-inhibited mice. Further, GW4869-treated mice displayed impaired translocation of photoreceptor-derived miR-124-3p to the inner retina during damage. Taken together, we propose that retinal s-mEV and their miRNA cargo play an essential role in maintaining retinal homeostasis through immune-modulation, and have the potential to be used in targeted gene therapy for retinal degenerative diseases.

Long-term Effects of 222-nm ultraviolet radiation C Sterilizing Lamps on Mice Susceptible to Ultraviolet Radiation

Germicidal lamps that emit primarily 254 nm ultraviolet radiation (UV) are routinely utilized for surface sterilization but cannot be used for human skin because they cause genotoxicity. As an alternative, 222‐nm UVC has been reported to exert sterilizing ability comparable to that of 254‐nm UVC without producing cyclobutane pyrimidine dimers (CPDs), the major DNA lesions caused by UV. However, there has been no clear evidence for safety in chronic exposure to skin, particularly with respect to carcinogenesis. We therefore investigated the long‐term effects of 222‐nm UVC on skin using a highly photocarcinogenic phenotype mice that lack xeroderma pigmentosum complementation group A (Xpa‐) gene, which is involved in repairing of CPDs. CPDs formation was recognized only uppermost layer of epidermis even with high dose of 222‐nm UVC exposure. No tumors were observed in Xpa‐knockout mice and wild‐type mice by repetitive irradiation with 222‐nm UVC, using a protocol which had shown to produce tumor in Xpa‐knockout mice irradiated with broad‐band UVB. Furthermore, erythema and ear swelling were not observed in both genotype mice following 222‐nm UVC exposure. Our data suggest that 222‐nm UVC lamps can be safely used for sterilizing human skin as far as the perspective of skin cancer development.

Glucocorticoid and progesterone mechanisms in photoreceptor survival

Death of retinal photoreceptors is the basis of prevalent blinding diseases. Since steroids might have a therapeutic role in retinal degenerations, we compared the protective effects of dexamethasone and progesterone on photoreceptor death induced by mifepristone and light exposure. Therefore, we studied the effective protection doses for each steroid in the two models. In addition, we analyzed changes in the levels of pro- and antiapoptotic molecules, glucocorticoid receptors α and β (GRα and GRβ), and rhodopsin under conditions of successful protection and photoreceptor survival. Mifepristone and light exposure selectively damaged photoreceptors. In light exposed retinas, photoreceptors mainly disappeared in the dorsotemporal region, while mifepristone produced a uniform damage. Dexamethasone and progesterone, at the same dose of 4 mg/kg/day for 2 days, preserved over 88% photoreceptor nuclei in both models. Assessment of cell death regulators showed that, in control retinas, both steroids activated BCL-X_L, a prosurvival molecule, and decreased BID, a proapoptotic regulator. After steroid treatment of damaged retinas, BCL-X_L, BCL2 and BAX showed characteristic patterns depending on the use of dexamethasone or progesterone on mifepristone or light exposed retinas. By contrast, BID decreased with any injury-steroid combination. Changes in GRα or GRβ levels did not correlate with survival but were consistent with a mechanism of ligand induced downregulation of receptor expression. GRβ might be upregulated by progesterone. Both dexamethasone and progesterone increased retinal rhodopsin stores, suggesting a link between photoreceptor protection and transduction pathways. Results show that dexamethasone and progesterone induced comparable but not identical protection responses in each model.

Evidences Suggesting that Distinct Immunological and Cellular Responses to Light Damage Distinguishes Juvenile and Adult Rat Retinas

To unravel the mechanisms behind the higher resistance to light damage of juvenile (JR) versus adult (AR) rats, Sprague Dawley rats were exposed to a bright luminous environment of 10, 000 lux. The light-induced retinopathy (LIR) was assessed with histology, electroretinography and immunohistochemistry (IHC). In JR, 2 days of exposure induced the typical LIR, while >3 days added little LIR. IHC revealed a subtle migration of microglia (Iba1 marker) from the inner to the outer retina after 3 days of exposure in JR contrasting with the stronger reaction seen after 1 day in AR. Similarly, in JR, the Müller cells expressed less intense GFAP, CNTF and FGF2 staining compared to AR. Our results suggest that in JR the degree of retinal damage is not proportional to the duration of light exposure (i.e., dose-independent retinopathy), contrasting with the dose-dependent LIR reported in AR. The immature immune system in JR may explain the delayed and/or weaker inflammatory response compared to AR, a finding that would also point to the devastating contribution of the immune system in generating the LIR phenotype, a claim also advanced to explain the pathophysiology of other retinal degenerative disorders such as Age-related Macular Degeneration, Diabetic Retinopathy and Retinitis Pigmentosa.

Photoreceptor Survival Is Regulated by GSTO1-1 in the Degenerating Retina

Purpose

Glutathione-S-transferase omega 1-1 (GSTO1-1) is a cytosolic glutathione transferase enzyme, involved in glutathionylation, toll-like receptor signaling, and calcium channel regulation. GSTO1-1 dysregulation has been implicated in oxidative stress and inflammation, and contributes to the pathogenesis of several diseases and neurological disorders; however, its role in retinal degenerations is unknown. The aim of this study was to investigate the role of GSTO1-1 in modulating oxidative stress and consequent inflammation in the normal and degenerating retina.

Methods

The role of GSTO1-1 in retinal degenerations was explored by using Gsto1-/- mice in a model of retinal degeneration. The expression and localization of GSTO1-1 were investigated with immunohistochemistry and Western blot. Changes in the expression of inflammatory (Ccl2, Il-1β, and C3) and oxidative stress (Nox1, Sod2, Gpx3, Hmox1, Nrf2, and Nqo1) genes were investigated via quantitative real-time polymerase chain reaction. Retinal function in Gsto1-/- mice was investigated by using electroretinography.

Results

GSTO1-1 was localized to the inner segment of cone photoreceptors in the retina. Gsto1-/- photo-oxidative damage (PD) mice had decreased photoreceptor cell death as well as decreased expression of inflammatory (Ccl2, Il-1β, and C3) markers and oxidative stress marker Nqo1. Further, retinal function in the Gsto1-/- PD mice was increased as compared to wild-type PD mice.

Conclusions

These results indicate that GSTO1-1 is required for inflammatory-mediated photoreceptor death in retinal degenerations. Targeting GSTO1-1 may be a useful strategy to reduce oxidative stress and inflammation and ameliorate photoreceptor loss, slowing the progression of retinal degenerations.

Aberrant RNA splicing is the major pathogenic effect in a knock-in mouse model of the dominantly inherited c.1430A>G human RPE65 mutation

Human RPE65 mutations cause a spectrum of retinal dystrophies that result in blindness. While RPE65 mutations have been almost invariably recessively inherited, a c.1430A>G (p.(D477G)) mutation has been reported to cause autosomal dominant retinitis pigmentosa (adRP). To study the pathogenesis of this human mutation, we have replicated the mutation in a knock-in (KI) mouse model using CRISPR/Cas9-mediated genome editing. Significantly, in contrast to human patients, heterozygous KI mice do not exhibit any phenotypes in visual function tests. When raised in regular vivarium conditions, homozygous KI mice display relatively undisturbed visual functions with minimal retinal structural changes. However, KI/KI mouse retinae are more sensitive to light exposure and exhibit signs of degenerative features when subjected to light stress. We find that instead of merely producing a missense mutant protein, the A>G nucleotide substitution greatly affects appropriate splicing of Rpe65 mRNA by generating an ectopic splice site in comparable context to the canonical one, thereby disrupting RPE65 protein expression. Similar splicing defects were also confirmed for the human RPE65 c.1430G mutant in an in vitro Exontrap assay. Our data demonstrate that a splicing defect is associated with c.1430G pathogenesis, and therefore provide insights in the therapeutic strategy for human patients.

Carteolol hydrochloride reduces visible light-induced retinal damage in vivo and BSO/glutamate-induced oxidative stress in vitro

The purpose of this study was to determine whether carteolol eye drops, a β-adrenoceptor antagonist used as an intraocular hypotensive agent, has protective effects against the light-induced oxidative stress in retina. Dark-adapted pigmented rats were pre-treated with topical carteolol ophthalmic solution or saline and then exposed to visible light. The effects on electroretinogram (ERG), morphology, oxidative stress, and expression of mRNAs in the retinas were determined. The l-buthionine-(S,R)-sulfoximine (BSO)/glutamate-induced oxidative stress in 661 W cells, a murine photoreceptor cell line, was evaluated by cell death assays, production of reactive oxygen species (ROS), and activation of caspase. In vivo studies showed that exposure to light caused a decrease in the amplitudes of ERGs and the outer nuclear layer (ONL) thickness and an increase of the 8-hydroxy-2'-deoxyguanosine (8-OHdG)-positive cells in the ONL. These changes were significantly reduced by pre-treatment with carteolol. Carteolol also significantly up-regulated the mRNA levels of thioredoxin 1 and glutathione peroxidase 1 compared to saline-treated group. Moreover, carteolol and timolol, another β-adrenoceptor antagonist, significantly inhibited BSO/glutamate-induced cell death and reduced caspase-3/7 activity and ROS production in vitro. Therefore, carteolol could protect retina from light-induced damage with multiple effects such as enhancing the antioxidative potential and decreasing the intracellular ROS production.

Reduced Disc Shedding and Phagocytosis of Photoreceptor Outer Segment Contributes to Kava Kava Extract-induced Retinal Degeneration in F344/N Rats

There was a significant increase in the incidence of retinal degeneration in F344/N rats chronically exposed to Kava kava extract (KKE) in National Toxicology Program (NTP) bioassay. A retrospective evaluation of these rat retinas indicated a similar spatial and morphological alteration as seen in light-induced retinal degeneration in albino rats. Therefore, it was hypothesized that KKE has a potential to exacerbate the light-induced retinal degeneration. To investigate the early mechanism of retinal degeneration, we conducted a 90-day F344/N rat KKE gavage study at doses of 0 and 1.0 g/kg (dose which induced retinal degeneration in the 2-year NTP rat KKE bioassay). The morphological evaluation indicated reduced number of phagosomes in the retinal pigment epithelium (RPE) of the superior retina. Transcriptomic alterations related to retinal epithelial homeostasis and melatoninergic signaling were observed in microarray analysis. Phagocytosis of photoreceptor outer segment by the underlying RPE is essential to maintain the homeostasis of the photoreceptor layer and is regulated by melatonin signaling. Therefore, reduced photoreceptor outer segment disc shedding and subsequent lower number of phagosomes in the RPE and alterations in the melatonin pathway may have contributed to the increased incidences of retinal degeneration observed in F344/N rats in the 2-year KKE bioassay.

Protective Effect of Highly Polymeric A-Type Proanthocyanidins from Seed Shells of Japanese Horse Chestnut (Aesculus turbinata BLUME) against Light-Induced Oxidative Damage in Rat Retina

Retinal tissue is exposed to oxidative stress caused by visible light. Light-damaged rat used in age-related macular degeneration (AMD) studies clarified that antioxidants decrease retinal light damage. Albino rats were exposed to 5000 Lux light for 12 h with oral administration of the polyphenolic compounds fraction (PF) from the seed shells of Japanese horse chestnut (30 mg/kg, 100 mg/kg, and 300 mg/kg body weight: BW). To evaluate the protective effects against light damage, electroretinograms (ERGs), the outer nuclear layer (ONL) thickness, the antioxidant activity of plasma, oxidized retinal lipids, and the detection of apoptosis were examined. To reveal their active compounds, PF were separated into an A-type proanthocyanidin (PAF) and a flavonol O-glycosides fraction. The protective effects of these fractions against light damage were compared by measuring the thickness of the ERGs and ONL. Compared with the negative control, the PF group (100 mg/kg and 300 mg/kg BW) significantly suppressed the decrease of the ERG amplitudes and ONL thickness. PF (300 mg/kg BW) induced the elevation of in vivo antioxidant activity, and the suppression of retinal lipid oxidation. PF administration also suppressed apoptotic cell death. The protective effects against light damage were attributable to the antioxidant activity of PAF. The light-induced damage of retinas was protected by oral administration of PF and PAF. Taken together, these compounds are potentially useful for the prevention of the disease caused by light exposure. Highlights: The protective effects of retinal damage by light exposure were evaluated using polyphenolic compounds from the seed shells of Japanese horse chestnut (Aesculus turbinata BLUME) as an antioxidant. Decreases in the electroretinographic amplitude and outer nuclear layer thickness were suppressed by the polyphenolic compounds of the seed shells. Polyphenolic compounds from the seed shells of Japanese horse chestnut inhibited the oxidation of retinal lipids. Highly polymeric A-type proanthocyanidin from the seed shells protected the rat retina from light exposure damage by inhibiting oxidative stress and apoptotic mechanisms.

Influences of photic stress on postsubicular head-directional processing

The stress response serves vital adaptive functions. However, acute stress episodes often negatively impact cognitive processing. Here, we aimed to elucidate whether stress detrimentally affects the head‐direction cells of the postsubiculum, which may in turn impair downstream spatial information processing. We recorded neurons in the rats’ postsubiculum during a pellet‐chasing task during baseline non‐stress conditions and after a 30‐min acute photic stress exposure. Based on their baseline firing rate, we identified a subpopulation of head‐direction cells that drastically decreased its firing rate as a response to stress while preserving their head directionality. The remaining population of head‐direction cells as well as other neurons recorded in the postsubiculum were unaffected. The observed altered activity in the subpopulation might be the basis for spatial processing deficits observed following acute stress episodes.

Effect of LED photobiomodulation on fluorescent light induced changes in cellular ATPases and Cytochrome c oxidase activity in Wistar rat

BACKGROUND

Fluorescent light exposure at night alters cellular enzyme activities resulting in health defects. Studies have demonstrated that light emitting diode photobiomodulation enhances cellular enzyme activities.

OBJECTIVE

The objectives of this study are to evaluate the effects of fluorescent light induced changes in cellular enzymes and to assess the protective role of pre exposure to 670 nm LED in rat model.

METHODS

Male Wistar albino rats were divided into 10 groups of 6 animals each based on duration of exposure (1, 15, and 30 days) and exposure regimen (cage control, exposure to fluorescent light [1800 lx], LED preexposure followed by fluorescent light exposure and only LED exposure). Na⁺-K⁺ ATPase, Ca²⁺ ATPase, and cytochrome c oxidase of the brain, heart, kidney, liver, and skeletal muscle were assayed.

RESULTS

Animals of the fluorescent light exposure group showed a significant reduction in Na⁺-K⁺ ATPase and Ca²⁺ ATPase activities in 1 and 15 days and their increase in animals of 30-day group in most of the regions studied. Cytochrome c oxidase showed increase in their level at all the time points assessed in most of the tissues. LED light preexposure showed a significant enhancement in the degree of increase in the enzyme activities in almost all the tissues and at all the time points assessed.

CONCLUSIONS

This study demonstrates the protective effect of 670 nm LED pre exposure on cellular enzymes against fluorescent light induced change.

Chemical Exacerbation of Light-induced Retinal Degeneration in F344/N Rats in National Toxicology Program Rodent Bioassays

Retinal degeneration due to chronic ambient light exposure is a common spontaneous age-related finding in albino rats, but it can also be related to exposures associated with environmental chemicals and drugs. Typically, light-induced retinal degeneration has a central/hemispherical localization whereas chemical-induced retinal degeneration has a diffuse localization. This study was conducted to identify and characterize treatment-related retinal degeneration in National Toxicology Program rodent bioassays. A total of 3 chronic bioassays in F344/N rats (but not in B6C3F1/N mice) were identified that had treatment-related increases in retinal degeneration (kava kava extract, acrylamide, and leucomalachite green). A retrospective light microscopic evaluation of the retinas from rats in these 3 studies showed a dose-related increase in the frequencies of retinal degeneration, beginning with the loss of photoreceptor cells, followed by the inner nuclear layer cells. These dose-related increased frequencies of degenerative retinal lesions localized within the central/hemispherical region are suggestive of exacerbation of light-induced retinal degeneration.

Assessment of visual function and retinal structure following acute light exposure in the light sensitive T4R rhodopsin mutant dog

The effect of acute exposure to various intensities of white light on visual behavior and retinal structure was evaluated in the T4R RHO dog, a naturally-occurring model of autosomal dominant retinitis pigmentosa due to a mutation in the Rhodopsin gene. A total of 14 dogs (ages: 4-5.5 months) were used in this study: 3 homozygous mutant RHO(T4R/T4R), 8 heterozygous mutant RHO(T4R/+), and 3 normal wild-type (WT) dogs. Following overnight dark adaptation, the left eyes were acutely exposed to bright white light with a monocular Ganzfeld dome, while the contralateral right eye was shielded. Each of the 3 homozygous (RHO(T4R/T4R)) mutant dogs had a single unilateral light exposure (LE) to a different (low, moderate, and high) dose of white light (corneal irradiance/illuminance: 0.1 mW/cm(2), 170 lux; 0.5 mW/cm(2), 820 lux; or 1 mW/cm(2), 1590 lux) for 1 min. All 8 heterozygous (RHO(T4R/+)) mutant dogs were exposed once to the same moderate dose of light. The 3 WT dogs had their left eyes exposed 1, 2, or 3 times to the same highest dose of light. Visual function prior to LE and at 2 weeks and 33 weeks after exposure was objectively assessed in the RHO(T4R/T4R) and WT dogs by using an obstacle-avoidance course. Transit time through the obstacle course was measured under different scotopic to photopic ambient illuminations. Morphological retinal changes were evaluated by non-invasive in vivo cSLO/sdOCT imaging and histology before and at several time-points (2-36 weeks) after light exposure. The analysis of the transit time through the obstacle course showed that no differences were observed in any of mutant or WT dogs at 2 weeks and 33 weeks post LE. The RHO(T4R/T4R) retina exposed to the lowest dose of white light showed no obvious changes in ONL thickness at 2 weeks, but mild decrease was noted 36 weeks after LE. The RHO(T4R/T4R) retina that received a moderate dose (showed an obvious decrease in ONL thickness along the superior and temporal meridians at 2 weeks post LE with more severe damage at 36 weeks post LE in all four meridians. The RHO(T4R/T4R) retina exposed to the high dose showed at 2 weeks after LE extensive ONL damage in all four meridians. This light intensity did not cause any retinal damage in WT dogs even after repeated (up to 3) LE. Analysis of ONL thickness in heterozygous mutant dogs exposed to the moderate dose of light confirmed the increased sensitivity to light damage of the superior/tapetal retina, and the occurrence of an ongoing cell death process several weeks after the acute LE. In conclusion, a short single exposure to a dose of white light that is not retinotoxic in WT dogs causes in the T4R RHO retina an acute loss of ONL in the central to mid peripheral region that keeps progressing over the course of several weeks. However, this severe retinal damage does not affect visual behavior presumably because of islands of surviving photoreceptors found in the area centralis including the newly discovered canine fovea-like area, and the lack of damage to peripheral photoreceptors.

Retinotopic Distribution of Structural and Functional Damages following Bright Light Exposure of Juvenile Rats

In the present study, we aimed at better understanding the short (acute) and long term (chronic) degenerative processes characterizing the juvenile rat model of light-induced retinopathy. Electroretinograms, visual evoked potentials (VEP), retinal histology and western blots were obtained from juvenile albino Sprague-Dawley rats at preselected postnatal ages (from P30 to P400) following exposure to 10,000 lux from P14 to P28. Our results show that while immediately following the cessation of exposure, photoreceptor degeneration was concentrated within a well delineated area of the superior retina (i.e. the photoreceptor hole), with time, this hole continued to expand to form an almost photoreceptor-free region covering most of superior-inferior axis. By the end of the first year of life, only few photoreceptors remained in the far periphery of the superior hemiretina. Interestingly, despite a significant impairment of the outer retinal function, the retinal output (VEP) was maintained in the early phase of this retinopathy. Our findings thus suggest that postnatal exposure to a bright luminous environment triggers a degenerative process that continues to impair the retinal structure and function (mostly at the photoreceptor level) long after the cessation of the exposure regimen (more than 1 year documented herein). Given the slow degenerative process triggered following postnatal bright light exposure, we believe that our model represents an attractive alternative (to other more genetic models) to study the pathophysiology of photoreceptor-induced retinal degeneration as well as therapeutic strategies to counteract it.

Autophagy in light-induced retinal damage

Vision is reliant upon converting photon signals to electrical information which is interpreted by the brain and therefore allowing us to receive information about our surroundings. However, when exposed to excessive light, photoreceptors and other types of cells in the retina can undergo light-induced cell death, termed light-induced retinal damage. In this review, we summarize our current knowledge regarding molecular events in the retina after excessive light exposure and mechanisms of light-induced retinal damage. We also introduce works which investigate potential roles of autophagy, an essential cellular mechanism required for maintaining homeostasis under stress conditions, in the illuminated retina and animal models of light-induced retinal damage.

Preventive and therapeutic effects of SkQ1-containing Visomitin eye drops against light-induced retinal degeneration

The human retina is constantly affected by light of varying intensity, this being especially true for photoreceptor cells and retinal pigment epithelium. Traditionally, photoinduced damages of the retina are induced by visible light of high intensity in albino rats using the LIRD (light-induced retinal degeneration) model. This model allows study of pathological processes in the retina and the search for retinoprotectors preventing retinal photodamage. In addition, the etiology and mechanisms of retina damage in the LIRD model have much in common with the mechanisms of the development of age-related retinal disorders, in particular, with age-related macular degeneration (AMD). We have studied preventive and therapeutic effects of Visomitin eye drops (based on the mitochondria-targeted antioxidant SkQ1) on albino rat retinas damaged by bright light. In the first series of experiments, rats receiving Visomitin for two weeks prior to illumination demonstrated significantly less expressed atrophic and degenerative changes in the retina compared to animals receiving similar drops with no SkQ1. In the second series, the illuminated rats were treated for two weeks with Visomitin or similar drops without SkQ1. The damaged retinas of the experimental animals were repaired much more effectively than those of the control animals. Therefore, we conclude that Visomitin SkQ1-containing eye drops have pronounced preventive and therapeutic effects on the photodamaged retina and might be recommended as a photoprotector and a pharmaceutical preparation for the treatment of AMD in combination with conventional medicines.

Retinitis pigmentosa caused by mutations in the ciliary MAK gene is relatively mild and is not associated with apparent extra-ocular features

PURPOSE

Defects in MAK, encoding a protein localized to the photoreceptor connecting cilium, have recently been associated with autosomal recessive retinitis pigmentosa (RP). The aim of this study is to describe our detailed clinical observations in patients with MAK-associated RP, including an assessment of syndromic symptoms frequently observed in ciliopathies.

METHODS

In this international collaborative study, 11 patients carrying nonsense or missense mutations in MAK were clinically evaluated, including extensive assessment of the medical history, slit-lamp biomicroscopy, ophthalmoscopy, kinetic perimetry, electroretinography (ERG), spectral-domain optical coherence tomography (SD-OCT), autofluorescence imaging and fundus photography. Additionally, we used a questionnaire to evaluate the presence of syndromic features and tested the olfactory function.

RESULTS

MAK-associated RP is not associated with syndromic features, not even with subclinical dysfunction of the olfactory apparatus. All patients experienced typical RP symptoms of night blindness followed by visual field constriction. Symptoms initiated between childhood and the age of 43 (mean: 23 years). Although some patients experienced vision loss, the visual acuity remained normal in most patients. ERG and ophthalmoscopy revealed classic RP characteristics, and SD-OCT demonstrated thinning of the overall retina, outer nuclear layer and photoreceptor-pigment epithelium complex.

CONCLUSION

Nonsense and missense mutations in MAK give rise to a non-syndromic recessive RP phenotype without apparent extra-ocular features. When compared to other retinal ciliopathies, MAK-associated RP appears to be relatively mild and shows remarkable resemblance to RP1-associated RP, which could be explained by the close functional relation of these proteins.

A novel in vivo model of focal light emitting diode-induced cone-photoreceptor phototoxicity: neuroprotection afforded by brimonidine, BDNF, PEDF or bFGF

We have investigated the effects of light-emitting diode (LED)-induced phototoxicity (LIP) on cone-photoreceptors and their protection with brimonidine (BMD), brain-derived neurotrophic factor (BDNF), pigment epithelium-derived factor (PEDF), ciliary neurotrophic factor (CNTF) or basic fibroblast growth factor (bFGF). In anesthetized, dark adapted, adult albino rats a blue (400 nm) LED was placed perpendicular to the cornea (10 sec, 200 lux) and the effects were investigated using Spectral Domain Optical Coherence Tomography (SD-OCT) and/or analysing the retina in oriented cross-sections or wholemounts immune-labelled for L- and S-opsin and counterstained with the nuclear stain DAPI. The effects of topical BMD (1%) or, intravitreally injected BDNF (5 µg), PEDF (2 µg), CNTF (0.4 µg) or bFGF (1 µg) after LIP were examined on wholemounts at 7 days. SD-OCT showed damage in a circular region of the superotemporal retina, whose diameter varied from 1,842.4±84.5 µm (at 24 hours) to 1,407.7±52.8 µm (at 7 days). This region had a progressive thickness diminution from 183.4±5 µm (at 12 h) to 114.6±6 µm (at 7 d). Oriented cross-sections showed within the light-damaged region of the retina massive loss of rods and cone-photoreceptors. Wholemounts documented a circular region containing lower numbers of L- and S-cones. Within a circular area (1 mm or 1.3 mm radius, respectively) in the left and in its corresponding region of the contralateral-fellow-retina, total L- or S-cones were 7,118±842 or 661±125 for the LED exposed retinas (n = 7) and 14,040±1,860 or 2,255±193 for the fellow retinas (n = 7), respectively. BMD, BDNF, PEDF and bFGF but not CNTF showed significant neuroprotective effects on L- or S-cones. We conclude that LIP results in rod and cone-photoreceptor loss, and is a reliable, quantifiable model to study cone-photoreceptor degeneration. Intravitreal BDNF, PEDF or bFGF, or topical BMD afford significant cone neuroprotection in this model.

Parkinson's disease, lights and melanocytes: looking beyond the retina

Critical analysis of recent research suggesting that light pollution causes Parkinson's disease (PD) reveals that such a hypothesis is unsustainable in the context of therapeutic use of light in treating various neuropsychiatric conditions. Reinterpretation of their findings suggests that retinal damage caused by prolonged light exposure may have contributed to the observed enhancement of experimental PD. To test this hypothesis further, forty-two Sprague Dawley rats received microinjections of 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenyl-2, 4, 6-tetrahydropyridine (MPTP), paraquat or rotenone into the vitreal mass in doses so minute that the effects could not be attributed to diffusion into brain. Significant changes in five motor parameters consistent with symptoms of experimental PD were observed. These findings support the interpretation that the retina is involved in the control of motor function and in the aetiology of PD.

RNA interference of GADD153 protects photoreceptors from endoplasmic reticulum stress-mediated apoptosis after retinal detachment

BACKGROUND

Apoptosis of photoreceptors plays a critical role in the vision loss caused by retinal detachment (RD). Pharmacologic inhibition of photoreceptor cell death may prevent RD. This study investigated the role of GADD153 that participates in endoplasmic reticulum (ER) stress-mediated apoptosis of photoreceptor cells after RD.

METHODS

Retinal detachment was created in Wistar rats by subretinal injection of hyaluronic acid. The rats were then randomly divided into four groups: normal control group, RD group, GADD153 RNAi group and vehicle group. RNA interference of GADD153 was performed using short hairpin RNA (shRNA). Expressions of GADD153 mRNA and protein were examined by RT-PCR and Western blotting analysis, respectively. GADD153 protein distribution in the retinal cells was observed using immunofluorescence confocal laser scanning microscopy. Apoptosis of retinal cells was determined by TdT-mediated fluorescein-16-dUTP nick-end labeling (TUNEL) assay.

RESULTS

Lentivirus GADD153 shRNA with the most effective silencing effect was chosen for in vivo animal study and was successfully delivered into the retinal tissues. GADD153 mRNA and protein expressions in GADD153 RNAi group were significantly lower than those in the RD group. Silencing of GADD153 by RNAi protected photoreceptors from ER stress-induced apoptosis.

CONCLUSION

ER stress-mediated pathway is involved in photoreceptor cell apoptosis after RD. GADD153 is a key regulatory molecule regulating ER-stress pathways and plays a crucial role in the apoptosis of photoreceptor cells after RD.

Inhibition of de novo ceramide biosynthesis by FTY720 protects rat retina from light-induced degeneration

Light-induced retinal degeneration (LIRD) in albino rats causes apoptotic photoreceptor cell death. Ceramide is a second messenger for apoptosis. We tested whether increases in ceramide mediate photoreceptor apoptosis in LIRD and if inhibition of ceramide synthesis protects the retina. Sprague-Dawley rats were exposed to 2,700 lux white light for 6 h, and the retinal levels of ceramide and its intermediary metabolites were measured by GC-MS or electrospray ionization tandem mass spectrometry. Enzymes of the de novo biosynthetic and sphingomyelinase pathways of ceramide generation were assayed, and gene expression was measured. The dosage and temporal effect of the ceramide synthase inhibitor FTY720 on the LIRD retina were measured by histological and functional analyses. Retinal ceramide levels increased coincident with the increase of dihydroceramide at various time points after light stress. Light stress in retina induces ceramide generation predominantly through the de novo pathway, which was prevented by systemic administration of FTY720 (10 mg/kg) leading to the protection of retinal structure and function. The neuroprotection of FTY720 was independent of its immunosuppressive action. We conclude that ceramide increase by de novo biosynthesis mediates photoreceptor apoptosis in the LIRD model and that inhibition of ceramide production protects the retina against light stress.

Protective effect of carnosic acid, a pro-electrophilic compound, in models of oxidative stress and light-induced retinal degeneration

PURPOSE

The herb rosemary has been reported to have antioxidant and anti-inflammatory activity. We have previously shown that carnosic acid (CA), present in rosemary extract, crosses the blood-brain barrier to exert neuroprotective effects by upregulating endogenous antioxidant enzymes via the Nrf2 transcriptional pathway. Here we investigated the antioxidant and neuroprotective activity of CA in retinal cell lines exposed to oxidative stress and in a rat model of light-induced retinal degeneration (LIRD).

METHODS

Retina-derived cell lines ARPE-19 and 661W treated with hydrogen peroxide were used as in vitro models for testing the protective activity of CA. For in vivo testing, dark-adapted rats were given intraperitoneal injections of CA prior to exposure to white light to assess protection of the photoreceptor cells. Retinal damage was assessed by measuring outer nuclear layer thickness and by electroretinogram (ERG).

RESULTS

In vitro, CA significantly protected retina-derived cell lines (ARPE-19 and 661W) against H(2)O(2)-induced toxicity. CA induced antioxidant phase 2 enzymes and reduced formation of hyperoxidized peroxiredoxin (Prx)2. Similarly, we found that CA protected retinas in vivo from LIRD, producing significant improvement in outer nuclear layer thickness and ERG activity.

CONCLUSIONS

These findings suggest that CA may potentially have clinical application to diseases affecting the outer retina, including age-related macular degeneration and retinitis pigmentosa, in which oxidative stress is thought to contribute to disease progression.

Differential participation of phospholipase A2 isoforms during iron-induced retinal toxicity. Implications for age-related macular degeneration

Both elevated iron concentrations and the resulting oxidative stress condition are common signs in retinas of patients with age-related macular degeneration (AMD). The role of phospholipase A(2) (PLA(2)) during iron-induced retinal toxicity was investigated. To this end, isolated retinas were exposed to increasing Fe(2+) concentrations (25, 200 or 800 μM) or to the vehicle, and lipid peroxidation levels, mitochondrial function, and the activities of cytosolic PLA(2) (cPLA(2)) and calcium-independent PLA(2) (iPLA(2)) were studied. Incubation with Fe(2+) led to a time- and concentration-dependent increase in retinal lipid peroxidation levels whereas retinal cell viability was only affected after 60 min of oxidative injury. A differential release of arachidonic acid (AA) and palmitic acid (PAL) catalyzed by cPLA(2) and iPLA(2) activities, respectively, was also observed in microsomal and cytosolic fractions obtained from retinas incubated with iron. AA release diminished as the association of cyclooxygenase-2 increased in microsomes from retinas exposed to iron. Retinal lipid peroxidation and cell viability were also analyzed in the presence of cPLA(2) inhibitor, arachidonoyl trifluoromethyl ketone (ATK), and in the presence of iPLA(2) inhibitor, bromoenol lactone (BEL). ATK decreased lipid peroxidation levels and also ERK1/2 activation without affecting cell viability. BEL showed the opposite effect on lipid peroxidation. Our results demonstrate that iPLA(2) and cPLA(2) are differentially regulated and that they selectively participate in retinal signaling in an experimental model resembling AMD.

Autosomal recessive retinitis pigmentosa caused by mutations in the MAK gene

PURPOSE

To determine the disease expression in autosomal recessive (ar) retinitis pigmentosa (RP) caused by mutations in the MAK (male germ cell-associated kinase) gene.

METHODS

Patients with RP and MAK gene mutations (n = 24; age, 32-77 years at first visit) were studied by ocular examination, perimetry, and optical coherence tomography (OCT).

RESULTS

All but one MAK patient were homozygous for an identical truncating mutation in exon 9 and had Ashkenazi Jewish heritage. The carrier frequency of this mutation among 1207 unrelated Ashkenazi control subjects was 1 in 55, making it the most common cause of heritable retinal disease in this population and MAK-associated RP the sixth most common Mendelian disease overall in this group. Visual acuities could be normal into the eighth decade of life. Kinetic fields showed early loss in the superior-temporal quadrant. With more advanced disease, superior and midperipheral function was lost, but the nasal field remained. Only a central island was present at late stages. Pigmentary retinopathy was less prominent in the superior nasal quadrant. Rod-mediated vision was abnormal but detectable in the residual field; all patients had rod>cone dysfunction. Photoreceptor layer thickness was normal centrally but decreased with eccentricity. At the stages studied, there was no evidence of photoreceptor ciliary elongation.

CONCLUSIONS

The patterns of disease expression in the MAK form of arRP showed some resemblance to patterns described in autosomal dominant RP, especially the form caused by RP1 mutations. The similarity in phenotypes is of interest, considering that there is experimental evidence of interaction between Mak and RP1 in the photoreceptor cilium.

Cellular and 3D optical coherence tomography assessment during the initiation and progression of retinal degeneration in the Ccl2/Cx3cr1-deficient mouse

Retinal pathologies common to human eye diseases, including abnormal retinal pigment epithelial (RPE) cells, drusen-like accumulation, photoreceptor atrophy, and choroidal neovascularization, have been reported in the Ccl2/Cx3cr1-deficient mouse. The Ccl2 gene encodes the pro-inflammatory chemokine CCL2 (MCP-1), which is responsible for chemotactic recruitment of monocyte-derived macrophages to sites of inflammation. The Cx3cr1 gene encodes the fractalkine receptor, CX3CR1, and is required for accumulation of monocytes and microglia recruited via CCL2. Chemokine-mediated inflammation is implicated in retinal degenerative diseases such as diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, and uveoretinitis, and proper chemokine signaling from the RPE, Müller glia, and astrocytes is necessary to regulate leukocyte trafficking. Therefore, this mouse, possessing aberrant chemokine signaling coupled with retinal degenerative pathologies, presents an ideal opportunity to investigate the effect of altered signaling on retinal homeostasis and photoreceptor degeneration. Since this mouse is a recent development, more data covering the onset, location, and progression rate of pathologies is needed. In the present study we establish these parameters and show two photoreceptor cell death processes. Our observations of decreased glutamine synthetase and increased glial fibrillary acidic protein suggest that Müller cells respond very early within regions where lesions are forming. Finally, we suggest that retinal angiomatous proliferation contributes to pathological angiogenesis in this Ccl2/Cx3cr1-deficient mouse.

Retinal nerve fibre layer attenuation: clinical indicator for vigabatrin toxicity

PURPOSE

To investigate whether persistent visual field defects among patients exposed once to the antiepileptic drug vigabatrin (VGB) were associated with peripapillary retinal nerve fibre layer thickness (RNFLT) attenuation.

METHODS

Nine individuals with partial epilepsy and VGB-attributed visual field loss (group 1; 18 eyes) and seven age- and gender-matched individuals with epilepsy and no previous VGB exposure (group 2; 14 eyes) were included in the study. Full-field 120 point screening perimetry out to 60 degrees from central fixation using the Humphrey Field Analyzer was performed. RNFLT was quantified by optical coherence tomography (OCT) using Fast RNFLT protocol, Stratus OCT (3.0) after pupillary dilation. The results from the right eye are presented in this article.

RESULTS

Among the patients with VGB-attributed visual field loss, five patients had only peripheral field defect (group 1a) and the remaining four had advanced field defects both in the periphery and within 30° from central fixation (group 1b). None of the patients in the control group had manifest visual field loss. The mean RNFLT among the patients with VGB-attributed visual field loss was significantly attenuated compared to the controls [mean total RNFLT: group 1: 75.6 ± 12.7 μm, group 2: 103.5 ± 9.7 μm, mean difference 27.9 μm, (CI 15.9-39.9; p < 0.001)]. RNFLT values classified as borderline according to normative database (Stratus OCT) occurred more frequently among individuals with VGB-attributed visual field loss than in controls (frequency in group 1: 6/9; group 2: 0/7, p = 0.011). The nasal, superior and inferior quadrants of RNFLT in individuals with VGB-attributed visual field loss were significantly attenuated, while no difference was detected in temporal quadrants compared to controls. Both individuals with peripheral and those with advanced visual field losses in the VGB group had attenuated mean total RNFLT compared to controls (p = 0.006, p = 0.002, respectively). Occurrence of borderline classification of total RNFLT ≤5th percentile was more frequent among individuals with advanced visual field loss than among controls (p = 0.048).

CONCLUSION

Persistent visual field loss attributed to VGB is associated with reduced peripapillary RNFLT and was detected both among patients with advanced and among patients with only peripheral visual field defects. Measurements of RNFLT with OCT might be considered as a diagnostic supplement in the follow-up of patients exposed to vigabatrin.

Sponge transgenic mouse model reveals important roles for the microRNA-183 (miR-183)/96/182 cluster in postmitotic photoreceptors of the retina

MicroRNA-183 (miR-183), miR-96, and miR-182 comprising the miR-183/96/182 cluster are highly expressed in photoreceptor cells. Although in vitro data have indicated an important role for this cluster in the retina, details of its in vivo biological activity are still unknown. To observe the impact of the miR-183/96/182 cluster on retinal maintenance and light adaptation, we generated a sponge transgenic mouse model that disrupted the activities of the three-component microRNAs simultaneously and selectively in the retina. Although our morphological and functional studies showed no differences between transgenic and wild type mice under normal laboratory lighting conditions, sponge transgenic mice displayed severe retinal degeneration after 30 min of exposure to 10,000 lux light. Histological studies showed that the outer nuclear layer thickness was dramatically reduced in the superior retina of transgenic mice. Real time PCR experiments in both the sponge transgenic mouse model and different microRNA stable cell lines identified Arrdc3, Neurod4, and caspase-2 (Casp2) as probable downstream targets of this cluster, a result also supported by luciferase assay and immunoblotting analyses. Further studies indicated that expression of both the cluster and Casp2 increased in response to light exposure. Importantly, Casp2 expression was enhanced in transgenic mice, and inhibition of Casp2 partially rescued their light-induced retinal degeneration. By connecting the microRNA and apoptotic pathways, these findings imply an important role for the miR-183/96/182 cluster in acute light-induced retinal degeneration of mice. This study demonstrates a clear involvement of miRs in the physiology of postmitotic cells in vivo.

Early focal expression of the chemokine Ccl2 by Müller cells during exposure to damage-inducing bright continuous light

PURPOSE

To investigate the time course and localization of Ccl2 expression and recruitment of inflammatory cells associated with light-induced photoreceptor degeneration.

METHODS

Sprague-Dawley (SD) rats were exposed to 1000 lux light for up to 24 hours, after which some animals were allowed to recover in dim light (5 lux) for 3 or 7 days. During and after exposure to light, the animals were euthanatized and the retinas processed. Ccl2 expression was assessed by qPCR, immunohistochemistry, and in situ hybridization at each time point. Counts were made of perivascular monocytes/microglia immunolabeled with ED1, and photoreceptor apoptosis was assessed with TUNEL.

RESULTS

Upregulation of Ccl2 expression was evident in the retina by 12 hours of exposure and correlated with increased photoreceptor death. Ccl2 expression reached its maximum at 24 hours, coinciding with peak cell death. Immunohistochemistry and in situ hybridization showed that Ccl2 is expressed by Müller cells from 12 hours of exposure, most intensely in the superior retina, in the region of the incipient light-induced lesion. After the Müller cell-driven expression of Ccl2, there was a substantial recruitment of monocytes to the local retina and choroidal vasculature. This coincided spatially with the expression of Ccl2 in the superior retina. Peak monocyte infiltration followed maximum Ccl2 expression by up to 3 days. Furthermore, Ccl2 immunoreactivity was observed in many infiltrating monocytes after a 24-hour exposure.

CONCLUSIONS

The data indicate that photoreceptor death promotes region-specific expression of Ccl2 by Müller cells, which facilitates targeting of monocytes to sites of injury. The data suggest that recruitment of monocytes to developing lesions is secondary to signaling events in the retina.

Brief exposure to damaging light causes focal recruitment of macrophages, and long-term destabilization of photoreceptors in the albino rat retina

PURPOSE

To characterize the long-term spatiotemporal features of light-mediated retinal degeneration.

METHODS

Sprague-Dawley rats were exposed to 1000 lux for 24 h, then kept in dim light (5 lux), for up to 56 days. Animals were killed at 0, 3, 7, 28, and 56 days post-exposure, and retinas were prepared for immunohistochemistry. Outer nuclear layer (ONL) thickness and TUNEL labeling were used to quantify photoreceptor death. Antibodies to opsins, glial fibrillary acidic protein (GFAP), fibroblast growth factor-2 (FGF-2), and ED1 were used to assess the retina.

RESULTS

At 0 days post-exposure, we detected photoreceptor death 2 mm superior to the optic disc (the "hotspot"), and ED1-positive macrophages in the retinal vasculature and underlying choroid. By 3 days, the ONL was thinner and there was gliosis in the outer retina, where ED1 positive macrophages were also present. Few ED1 positive cells remained at 28 days. At 56 days, there were TUNEL-positive nuclei in the penumbra, and increased FGF-2, and GFAP expression by Müller cells (MCs). In inferior retina, outer segment length was initially reduced, but recovered to near-normal by 28 days.

CONCLUSIONS

Short exposure to damaging light destabilizes the retina adjacent to a hotspot of degeneration, so that the damaged region expands in size over time. Recruitment of macrophages is associated with the early phase of damage, but not with the longer term photoreceptor loss in the penumbra. Features of the focal and progressive retinal damage in this model are reminiscent of the progression of age-related macular degeneration (AMD).

Effects of PACAP in UV-A radiation-induced retinal degeneration models in rats

The retina is constantly exposed to ultraviolet (UV) light with different wavelengths, which may lead to chronic UV-induced retinal injury. In our previous studies, we have shown the protective effects of pituitary adenylate cyclase activating polypeptide (PACAP) in toxic and ischemic retinal injuries. The aim of the present study was to investigate the effects of PACAP in UV-A-induced retinal lesion. We used diffuse UV-A radiation (315-400 nm) to induce acute retinal damage over a short period of exposure. Using standard histological (morphological and morphometrical) analysis, we assessed the actions of intravitreal PACAP (100 pmol/5 µl) treatment on acute UV-A-induced retinal damage. We measured the thickness of nuclear and plexiform layers as well as the number of cells in the outer nuclear and inner nuclear layers and in the ganglion cell layer. Outer limiting membrane-inner limiting membrane distances in the cross-section of the retina were also examined. Our results show that UV-A light-induced retinal damage led to severe degeneration in the photoreceptor layer, and in the outer and inner nuclear layers. Alteration in the plexiform layers was also observed. We found that post-irradiation PACAP treatment significantly attenuated the UV-A-induced retinal damage. Our results provide the basis for future clinical application of PACAP treatment in retinal degeneration and may have clinical implications in several ophthalmic diseases.

Protection of retinal pigment epithelium by OT-551 and its metabolite TEMPOL-H against light-induced damage in rats

OT-551 (1-hydroxy-4-cyclopropanecarbonyloxy-2,2,6,6-tetramethylpiperidine hydrochloride), is a novel small molecule with antioxidant and anti-inflammatory effects. Protective efficacy of OT-551 and its metabolite TEMPOL-H (TP-H) against light-induced degeneration of retinal pigment epithelium (RPE) was tested. Albino rats were intraperitoneally injected with OT-551, TP-H, or water approximately 30 min prior to a 6 h exposure to 2700 lux white fluorescent light. Retinal protection was evaluated histologically by counting the RPE cell nuclei and measuring the extent of RPE damage on the retinal sections as RPE damage index (%). Following light exposure, the number of RPE cell nuclei was significantly reduced in light-exposed eyes from water-treated animals, while the number was not significantly different between light-exposed and unexposed eyes from the animals treated with 100 mg/kg TP-H or with any dose of OT-551 in the inferior hemisphere, and with 100 mg/kg OT-551 in the superior hemisphere. RPE damage index was significantly lower in the animals treated with any dose of OT-551 compared to water-treated animals both in the inferior and superior hemispheres. Systemic administration of OT-551 and TP-H provides RPE cell protection against acute light damage, and the protection by OT-551 was greater than by TP-H.

The anatomy of the rat eye with oxygen-induced retinopathy

Prior studies have documented the intertwined developmental courses of retinal blood vessel tortuosity (in fundus photographs) and retinal dysfunction (in electroretinographs) in Sprague-Dawley rat models of retinopathy of prematurity (ROP). Two such models, the "50/10 model" and the "75 model," are named after the oxygen regimens used to induce retinopathy and are characterized by distinct neurovascular courses that span a range of disease severity. In this study of 50/10 and 75 model rats, retinal flatmounts were used to study the full vasculature at postnatal day (P) 15, P19 and P30. In addition, the layers of the neural retina were measured in toluidine blue-stained cross sections. Finally, gross anatomic features of the eye, including axial length, retinal surface area, and the ratio of anterior to posterior axial-lengths were evaluated. Both clock hours of neovascularization (NV) and percent avascular retina (AR) peaked at P19 and resolved by P30. Through P19, NV was found in every 50/10 model rat, but in only 60% of 75 model rats. AR was positively related to NV. All inner layers of the retina (outer plexiform layer through ganglion cell layer) were attenuated in 50/10 model rats but, in the 75 model, no layer differed significantly from that in controls. The eyes in both ROP models were smaller than those of age-matched controls. The ratio of anterior to posterior axial-lengths ranged from 0.45 in controls through 0.37 in the 75 model to 0.32 in the 50/10 model. Thus, eye growth is altered in these rat models of ROP.

Curcumin protects retinal cells from light-and oxidant stress-induced cell death

Age-related macular degeneration (AMD) is a complex disease that has potential involvement of inflammatory and oxidative stress-related pathways in its pathogenesis. In search of effective therapeutic agents, we tested curcumin, a naturally occurring compound with known anti-inflammatory and antioxidative properties, in a rat model of light-induced retinal degeneration (LIRD) and in retina-derived cell lines. We hypothesized that any compound effective against LIRD, which involves significant oxidative stress and inflammation, would be a candidate for further characterization for its potential application in AMD. We observed significant retinal neuroprotection in rats fed diets supplemented with curcumin (0.2% in diet) for 2 weeks. The mechanism of retinal protection from LIRD by curcumin involves inhibition of NF-kappaB activation and down-regulation of cellular inflammatory genes. When tested on retina-derived cell lines (661W and ARPE-19), pretreatment of curcumin protected these cells from H(2)O(2)-induced cell death by up-regulating cellular protective enzymes, such as HO-1, thioredoxin. Since, curcumin with its pleiotropic activities can modulate the expression and activation of many cellular regulatory proteins such as NF-kappaB, AKT, NRF2, and growth factors, which in turn inhibit cellular inflammatory responses and protect cells; we speculate that curcumin would be an effective nutraceutical compound for preventive and augmentative therapy of AMD.

Subsets of retinal neurons and glia express P2Y1 receptors

Recent evidence suggests that extracellular ATP modulates retinal processing and could play a role in modulating glial cells during retinal diseases. Here, we evaluated the localization of P2Y(1) receptors in the rat retina using indirect immunofluorescence immunocytochemistry. We observed labeling within defined populations of inner retinal neurons and Müller cell processes and end feet. Double labeling of P2Y(1) receptor with choline acetyltransferase revealed extensive colocalization indicating the expression of this receptor by cholinergic amacrine cells. Ganglion cell labeling for P2Y(1) receptors was also observed. Having established the normal pattern of immunolabeling within the retina, we next examined whether immunolabeling was altered by retinal disease. P2Y(1) receptor immunolabeling of Müller cells was of greater intensity following light-induced retinal degeneration, suggesting that Müller cell gliosis is accompanied by changes in P2Y(1) receptor expression. Overall, these data provide further evidence for a role of extracellular ATP in retinal signaling within subsets of retinal neurons as well as glia.