Retinal degeneration from oxidative damage

Replenishing IRAK-M expression in retinal pigment epithelium attenuates outer retinal degeneration

Chronic inflammation is a constitutive component of many age-related diseases, including age-related macular degeneration (AMD). Here, we identified interleukin-1 receptor-associated kinase M (IRAK-M) as a key immunoregulator in retinal pigment epithelium (RPE) that declines during the aging process. Rare genetic variants of IRAK3, which encodes IRAK-M, were associated with an increased likelihood of developing AMD. In human samples and mouse models, IRAK-M abundance in the RPE declined with advancing age or exposure to oxidative stress and was further reduced in AMD. Irak3-knockout mice exhibited an increased incidence of outer retinal degeneration at earlier ages, which was further exacerbated by oxidative stressors. The absence of IRAK-M led to a disruption in RPE cell homeostasis, characterized by compromised mitochondrial function, cellular senescence, and aberrant cytokine production. IRAK-M overexpression protected RPE cells against oxidative or immune stressors. Subretinal delivery of adeno-associated virus (AAV)-expressing human IRAK3 rescued light-induced outer retinal degeneration in wild-type mice and attenuated age-related spontaneous retinal degeneration in Irak3-knockout mice. Our data show that replenishment of IRAK-M in the RPE may redress dysregulated pro-inflammatory processes in AMD, suggesting a potential treatment for retinal degeneration.

Replenishing Age-Related Decline of IRAK-M Expression in Retinal Pigment Epithelium Attenuates Outer Retinal Degeneration

Unchecked, chronic inflammation is a constitutive component of age-related diseases, including age-related macular degeneration (AMD). Here we identified interleukin-1 receptor-associated kinase (IRAK)-M as a key immunoregulator in retinal pigment epithelium (RPE) that declines with age. Rare genetic variants of IRAK-M increased the likelihood of AMD. IRAK-M expression in RPE declined with age or oxidative stress and was further reduced in AMD. IRAK-M-deficient mice exhibited increased incidence of outer retinal degeneration at earlier ages, which was further exacerbated by oxidative stressors. The absence of IRAK-M disrupted RPE cell homeostasis, including compromised mitochondrial function, cellular senescence, and aberrant cytokine production. IRAK-M overexpression protected RPE cells against oxidative or immune stressors. Subretinal delivery of AAV-expressing IRAK-M rescued light-induced outer retinal degeneration in wild-type mice and attenuated age-related spontaneous retinal degeneration in IRAK-M-deficient mice. Our data support that replenishment of IRAK-M expression may redress dysregulated pro-inflammatory processes in AMD, thereby treating degeneration.

Environmental influences on ophthalmic conditions: A scoping review

BACKGROUND

Environmental factors have been implicated in various eye pathologies. The purpose of this review is to synthesise the published research on environmental effects on eye disease.

METHODS

Four databases were searched for terms relating to environmental exposures and ophthalmic disease. Titles and abstracts were screened followed by full-text review. Data was extracted from 118 included studies. Quality assessment was conducted for each study.

RESULTS

Air pollutants, including nitrogen dioxide, nitrites, sulphur dioxide, particulate matter, carbon monoxide, ozone and hydrocarbons are associated with ocular conditions ranging from corneal damage to various retinopathies, including central retinal artery occlusion. Certain chemicals and metals, such as cadmium, are associated with increased risk of age-related macular degeneration. Climate factors, such as sun exposure, have been associated with the development of cataracts. Living in rural areas was associated with various age-related eye diseases whereas people living in urban settings had higher risk for dry eye disease and uveitis.

CONCLUSION

Environmental exposures in every domain are associated with various ophthalmic conditions. These findings underscore the importance of continued research on the interplay between the environment and eye health.

Impact of Microgravity and Other Spaceflight Factors on Retina of Vertebrates and Humans In Vivo and In Vitro

Spaceflight (SF) increases the risk of developmental, regenerative, and physiological disorders in animals and humans. Astronauts, besides bone loss, muscle atrophy, and cardiovascular and immune system alterations, undergo ocular disorders affecting posterior eye tissues, including the retina. Few studies revealed abnormalities in the development and changes in the regeneration of eye tissues in lower vertebrates after SF and simulated microgravity. Under microgravity conditions, mammals show disturbances in the retinal vascular system and increased risk of oxidative stress that can lead to cell death in the retina. Animal studies provided evidence of gene expression changes associated with cellular stress, inflammation, and aberrant signaling pathways. Experiments using retinal cells in microgravity-modeling systems in vitro additionally indicated micro-g-induced changes at the molecular level. Here, we provide an overview of the literature and the authors' own data to assess the predictive value of structural and functional alterations for developing countermeasures and mitigating the SF effects on the human retina. Further emphasis is given to the importance of animal studies on the retina and other eye tissues in vivo and retinal cells in vitro aboard spacecraft for understanding alterations in the vertebrate visual system in response to stress caused by gravity variations.

Nutraceutical Molecules Slow Down Retinal Degeneration, in Tvrm4 Mice a Model of Retinitis Pigmentosa, by Genetic Modulation of Anti-oxidant Pathway

Rhodopsin (RHO) mutations are responsible for 25–40% of the dominant cases of retinitis pigmentosa (RP) with different severity and progression rates. The Tvrm4 mice, heterozygous for an I307N dominant mutation of RHO, display a normal retinal phenotype when raised in ambient light conditions, but undergo photoreceptor degeneration when briefly exposed to strong white light. Here, The Tvrm4 mice is pre-treated with naringenin 100 mg/kg/die, quercetin 100 mg/kg/die, naringenin 50 + quercercetin 100 mg/kg/die or vehicle dimethyl sulfoxide (DMSO 0.025%) in the drinking water for 35 days. On the 30th day, retinal degeneration was induced by exposure for 1 min to the white light of 12,000 lux intensity, and the treatment was repeated for another 5 days. At the end of the protocol retinal functionality was tested by recording an electroretinogram (ERG). The retinal tissue was collected and was used for further analyses, including immunohistochemically, biochemical, and molecular biology assays. The data obtained show that treatment with nutraceutical molecules is effective in counteracting retinal degeneration by preserving the functionality of photoreceptors and increasing the antioxidant and anti-apoptotic pathways of retinal cells. The present data confirm that nutraceutical molecules are effective in slowing photoreceptor degeneration in a mutation-independent way by modulating the antioxidant response of the retina at the gene expression level.

Oxidative stress-induced alterations in retinal glucose metabolism in Retinitis Pigmentosa

Retinitis pigmentosa occurs due to mutations that cause rod photoreceptor degeneration. Once most rods are lost, gradual degeneration of cone photoreceptors occurs. Oxidative damage and abnormal glucose metabolism have been implicated as contributors to cone photoreceptor death. Herein, we show increased phosphorylation of key enzymes of glucose metabolism in the retinas of rd10 mice, a model of RP, and retinas of wild type mice with paraquat-induced oxidative stress, thereby inhibiting these key enzymes. Dietary supplementation with glucose and pyruvate failed to overcome the inhibition, but increased reducing equivalents in the retina and improved cone function and survival. Dichloroacetate reversed the increased phosphorylation of pyruvate dehydrogenase in rd10 retina and increased histone acetylation and levels of TP53-induced glycolysis and apoptosis regulator (TIGAR), which redirected glucose metabolism toward the pentose phosphate pathway. These data indicate that oxidative stress induced damage can be reversed by shifting glycolytic intermediates toward the pentose phosphate pathway which increases reducing equivalents and provides photoreceptor protection.

Targeting Lipid Metabolism for the Treatment of Age-Related Macular Degeneration: Insights from Preclinical Mouse Models

Age-related macular degeneration (AMD) is a major leading cause of irreversible visual impairment in the world with limited therapeutic interventions. Histological, biochemical, genetic, and epidemiological studies strongly implicate dysregulated lipid metabolism in the retinal pigmented epithelium (RPE) in AMD pathobiology. However, effective therapies targeting lipid metabolism still need to be identified and developed for this blinding disease. To test lipid metabolism-targeting therapies, preclinical AMD mouse models are needed to establish therapeutic efficacy and the role of lipid metabolism in the development of AMD-like pathology. In this review, we provide a comprehensive overview of current AMD mouse models available to researchers that could be used to provide preclinical evidence supporting therapies targeting lipid metabolism for AMD. Based on previous studies of AMD mouse models, we discuss strategies to modulate lipid metabolism as well as examples of studies evaluating lipid-targeting therapeutics to restore lipid processing in the RPE. The use of AMD mouse models may lead to worthy lipid-targeting candidate therapies for clinical trials to prevent the blindness caused by AMD.

Neuro-consequences of the spaceflight environment

As human space exploration advances to establish a permanent presence beyond the Low Earth Orbit (LEO) with NASA's Artemis mission, researchers are striving to understand and address the health challenges of living and working in the spaceflight environment. Exposure to ionizing radiation, microgravity, isolation and other spaceflight hazards pose significant risks to astronauts. Determining neurobiological and neurobehavioral responses, understanding physiological responses under Central Nervous System (CNS) control, and identifying putative mechanisms to inform countermeasure development are critically important to ensuring brain and behavioral health of crew on long duration missions. Here we provide a detailed and comprehensive review of the effects of spaceflight and of ground-based spaceflight analogs, including simulated weightlessness, social isolation, and ionizing radiation on humans and animals. Further, we discuss dietary and non-dietary countermeasures including artificial gravity and antioxidants, among others. Significant future work is needed to ensure that neural, sensorimotor, cognitive and other physiological functions are maintained during extended deep space missions to avoid potentially catastrophic health and safety outcomes.

Quantitative Assessment of Experimental Ocular Inflammatory Disease

Ocular inflammation imposes a high medical burden on patients and substantial costs on the health-care systems that mange these often chronic and debilitating diseases. Many clinical phenotypes are recognized and classifying the severity of inflammation in an eye with uveitis is an ongoing challenge. With the widespread application of optical coherence tomography in the clinic has come the impetus for more robust methods to compare disease between different patients and different treatment centers. Models can recapitulate many of the features seen in the clinic, but until recently the quality of imaging available has lagged that applied in humans. In the model experimental autoimmune uveitis (EAU), we highlight three linked clinical states that produce retinal vulnerability to inflammation, all different from healthy tissue, but distinct from each other. Deploying longitudinal, multimodal imaging approaches can be coupled to analysis in the tissue of changes in architecture, cell content and function. This can enrich our understanding of pathology, increase the sensitivity with which the impacts of therapeutic interventions are assessed and address questions of tissue regeneration and repair. Modern image processing, including the application of artificial intelligence, in the context of such models of disease can lay a foundation for new approaches to monitoring tissue health.

An inadvertent issue of human retina exposure to endocrine disrupting chemicals: A safety assessment

Endocrine disrupting chemicals (EDCs) are a group of chemical compounds that present a considerable public health problem due to their pervasiveness and associations with chronic diseases. EDCs can interrupt the endocrine system and interfere with hormone homeostasis, leading to abnormalities in human physiology. Much attention has been focused on the adverse effects EDCs have on the reproductive system, neurogenesis, neuroendocrine system, and thyroid dysfunction. The eye is usually directly exposed to the surrounding environment; however, the influences of EDCs on the eye have received comparatively little attention. Ocular diseases, such as ocular surface diseases and retinal diseases, have been implicated in hormone deficiency or excess. Epidemiologic studies have shown that EDC exposure not only causes ocular surface disorders, such as dry eye, but also associates with visual deficits and retinopathy. EDCs can pass through the human blood-retinal barrier and enter the neural retina, and can then accumulate in the retina. The retina is an embryologic extension of the central nervous system, and is extremely sensitive and vulnerable to EDCs that could be passed across the placenta during critical periods of retinal development. Subtle alterations in the retinal development process usually result in profound immediate, long-term, and delayed effects late in life. This review, based on extensive literature survey, briefly summarizes the current knowledge about the impact of representative manufactured EDCs on retinal toxicity, including retinal structure alterations and dysfunction. We also highlight the potential mechanism of action of EDCs on the retina, and the predictive retinal models of EDC exposure.

Influence of Microgravity on Apoptosis in Cells, Tissues, and Other Systems In Vivo and In Vitro

All life forms have evolved under the constant force of gravity on Earth and developed ways to counterbalance acceleration load. In space, shear forces, buoyance-driven convection, and hydrostatic pressure are nullified or strongly reduced. When subjected to microgravity in space, the equilibrium between cell architecture and the external force is disturbed, resulting in changes at the cellular and sub-cellular levels (e.g., cytoskeleton, signal transduction, membrane permeability, etc.). Cosmic radiation also poses great health risks to astronauts because it has high linear energy transfer values that evoke complex DNA and other cellular damage. Space environmental conditions have been shown to influence apoptosis in various cell types. Apoptosis has important functions in morphogenesis, organ development, and wound healing. This review provides an overview of microgravity research platforms and apoptosis. The sections summarize the current knowledge of the impact of microgravity and cosmic radiation on cells with respect to apoptosis. Apoptosis-related microgravity experiments conducted with different mammalian model systems are presented. Recent findings in cells of the immune system, cardiovascular system, brain, eyes, cartilage, bone, gastrointestinal tract, liver, and pancreas, as well as cancer cells investigated under real and simulated microgravity conditions, are discussed. This comprehensive review indicates the potential of the space environment in biomedical research.

The Ocular Protective Effects of Nano/Submicron Particles Prepared from Lycium barbarum Fruits Against Oxidative Stress in an Animal Model

Purpose: To investigate the antioxidative properties of Lycium barbarum (LB) fruits in the eyes and to study whether LB fruits prepared with new nanotechnology have stronger antioxidative effects. Methods: Fourteen days post-supplementation with milled or blended LB fruits, intravitreal paraquat (PQ) was injected into Wistar rats to create oxidative stress. After an additional 14-day supplementation with LB fruits, the rats were sacrificed. An electroretinogram (ERG) was performed to evaluate retinal function before and after the PQ injection. Expression levels of antioxidative responders' mRNA in retina were detected by reverse transcription-polymerase chain reaction. Superoxide dismutase (SOD) and glutathione reductase activity in the aqueous humor (AqH) were analyzed by ELISA. Immunohistochemistry was conducted to evaluate the morphological changes of retina and the levels of oxidative biomarkers. The levels of cell apoptosis were assessed by the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The reactive oxygen species (ROS) levels in AqH were measured by chemiluminescence methods. Results: The murine eyes supplemented with LB fruits exhibited several changes compared with the control group. The ERGs revealed significant improvement in retinal function. The mRNA expression levels of oxidative responders were downregulated in the retinas. The ROS was significantly reduced in the retinas, but the SOD meaningfully increased in the AqH. Immunohistochemistry staining and TUNEL assays showed decreased incidences of oxidative biomarkers and apoptosis in the retinas. Milled LB fruits exhibited better antioxidative effects than blended fruits. Conclusions: Milled LB fruits demonstrated superior protection against oxidative threats than blended fruits. Thus, these fruits could be an inexpensive supplement for many oxidative stress-related ocular diseases.

Pathogenic Tau Protein Species: Promising Therapeutic Targets for Ocular Neurodegenerative Diseases

Tau is a microtubule-associated protein, which is highly expressed in the central nervous system as well as ocular neurons and stabilizes microtubule structure. It is a phospho-protein being moderately phosphorylated under physiological conditions but its abnormal hyperphosphorylation or some post-phosphorylation modifications would result in a pathogenic condition, microtubule dissociation, and aggregation. The aggregates can induce neuroinflammation and trigger some pathogenic cascades, leading to neurodegeneration. Taking these together, targeting pathogenic tau employing tau immunotherapy may be a promising therapeutic strategy in fighting with cerebral and ocular neurodegenerative disorders.

Mitochondrial Respiration in Outer Retina Contributes to Light-Evoked Increase in Hydration In Vivo

Purpose

To test the hypothesis that mitochondrial respiration contributes to local changes in hydration involved in phototransduction-driven expansion of outer retina, as measured by structural responses on optical coherence tomography (OCT) and diffusion magnetic resonance imaging (MRI).

Methods

Oxygen consumption rate and mitochondrial reserve capacity of freshly isolated C57BL/6 and 129S6/SvEvTac mouse retina were measured using a Seahorse Extracellular Flux Analyzer. Light-stimulated outer retina layer water content was determined by proton density MRI, structure and thickness by ultrahigh-resolution OCT, and water mobility by diffusion MRI.

Results

Compared with C57BL/6 mice, 129S6/SvEvTac retina demonstrated a less robust mitochondrial respiratory basal level, with a higher reserve capacity and lower oxygen consumption in the light, suggesting a relatively lower production of water. C57BL/6 mice showed a light-triggered surge in water content of outer retina in vivo as well as an increase in hyporeflective bands, thickness, and water mobility. In contrast, light did not evoke augmented hydration in this region or an increase in hyporeflective bands or water mobility in the 129S6/SvEvTac outer retina. Nonetheless, we observed a significant but small increase in outer retinal thickness.

Conclusions

These studies suggest that respiratory-controlled hydration in healthy retina is linked with a localized light-evoked expansion of the posterior retina in vivo and may serve as a useful biomarker of the function of photoreceptor/retinal pigment epithelium complex.

Outer Retinal Oxidative Stress Measured In Vivo Using QUEnch-assiSTed (QUEST) OCT

Purpose

To test the hypothesis that oxidative stress in the outer retina (OR = distance from external limiting membrane to the retinal pigment epithelium-choroid boundary) can be detected by using antioxidants (AOs) to correct an impaired light-evoked response as measured by optical coherence tomography (OCT).

Methods

C57BL/6J mice were maintained in the dark for ∼20 hours and studied by OCT before and after 1 hour of light exposure. OR thickness in dark or light was measured, and the light-dark difference (i.e., the photoresponse) was calculated. Subgroups of mice were given either saline or d-cis-diltiazem (an inducer of transient and nondamaging OR oxidative stress) ± methylene blue (24 hours before examination) and α-lipoic acid (1 hour before examination); one group was kept only in the dark and given only AOs.

Results

In uninjected or saline-injected control mice, the OR showed a similar and reproducible light-induced expansion; dark-adapted mice given AOs did not increase dark-adapted OR thickness. The d-cis-diltiazem-treated mice had no photoresponse (P > 0.05). The d-cis-diltiazem-treated mice given AOs corrected (P < 0.05) the suppressed OR photoresponse, indicating the presence of oxidative stress.

Conclusions

QUEnch-assiSTed (QUEST) OCT reproduced results from previous gold standard assays, showing that oxidative stress impairs the OR photoresponse and that d-cis-diltiazem produces OR oxidative stress. We envision future applications of QUEST OCT in a range of oxidative stress-based retinopathies.

D-cis-Diltiazem Can Produce Oxidative Stress in Healthy Depolarized Rods In Vivo

Purpose

New perspectives are needed to understand decades of contradictory reports on the neuroprotective effects of the Cav1.2 L-type calcium channel blocker d-cis-diltiazem in retinitis pigmentosa (RP) models. Here, we address, in vivo, the following two knowledge gaps regarding d-cis-diltiazem's actions in the murine outer retina: (1) do normal mouse rods contain d-cis-diltiazem-insensitive Cav1.2 L-type calcium channels? (2) Can d-cis-diltiazem modify the normal rod redox environment?

Methods

First, transretinal Cav1.2 L-type calcium channels were noninvasively mapped with manganese-enhanced magnetic resonance imaging (MRI) following agonist Bay K 8644 in C57BL/6 (B6) and in Cav1.2 L-type calcium channel BAY K 8644-insensitive mutant B6 mice. Second, d-cis-diltiazem-treated oxidative stress-vulnerable (B6) or -resistant [129S6 (S6)] mice were examined in vivo (QUEnch-assiSTed [QUEST] MRI) and in whole retina ex vivo (lucigenin). Retinal thickness was measured using MRI.

Results

The following results were observed: (1) manganese uptake patterns in BAY K 8644-treated controls and mutant mice identified in vivo Cav1.2 L-type calcium channels in inner and outer retina; and (2) d-cis-diltiazem induced rod oxidative stress in dark-adapted B6 mice but not in light-adapted B6 mice or dark-adapted S6 mice (QUEST MRI). Oxidative stress in vivo was limited to inferior outer retina in dark-adapted B6 mice approximately 1-hour post d-cis-diltiazem. By approximately 4 hours post, only superior outer retina oxidative stress was observed and whole retinal superoxide production was supernormal. All groups had unremarkable retinal thicknesses.

Conclusions

D-cis-diltiazem's unexpectedly complex spatiotemporal outer retinal oxidative stress pattern in vivo was dependent on genetic background and rod membrane depolarization, but not apparently dependent on Cav1.2 L-type calcium channels, providing a potential rationale for contradictory results in different RP models.

Ultrastructural alterations in the retinal pigment epithelium and photoreceptors of a Stargardt patient and three Stargardt mouse models: indication for the central role of RPE melanin in oxidative stress

Background

Stargardt disease (SD) is characterized by the accumulation of the age-pigment lipofuscin in the retinal pigment epithelium (RPE) and subsequent neuroretinal degeneration. The disease leads to vision loss early in life. Here, we investigate age-dependent ultrastructural changes in three SD mouse models: albino Abca4^-/- and pigmented Abca4^-/- and Abca4^-/-.Rdh8^-/- mice. Since we found indications for oxidative stress primarily in albino SD mice, we tested RPE melanin for its antioxidative capabilities.

Methods

SD mouse eyes were investigated by light, fluorescence and electron microscopy and were compared to the respective albino and pigmented wild type mice and to a human donor SD eye. To confirm the role of RPE melanin in scavenging oxidative stress, melanin from S. officinalis as a standard and porcine RPE were tested for their capability to quench superoxide anions.

Results

Histological alterations indicative of oxidative stress and/or lysosomal dysfunction were present in albino Abca4^-/- and Abca4^-/-.Rdh8^-/- mice. Retinal damage, such as inner segment rupture and pyknotic or free photoreceptor nuclei in the subretinal space and RPE vacuolization were exclusively found in albino Abca4^-/- mice. Shortened and disorganized photoreceptor outer segments and dead RPE cells were found in albino Abca4^-/- and Abca4^-/-.Rdh8^-/- mice, with earlier onset in albino Abca4^-/- mice. Undegraded phagosomes and lipofuscin accumulation were present in the RPE of all three SD strains, but numbers were highest in Abca4^-/-.Rdh8^-/- mice. Lipofuscin morphology differed between SD strains: (melano-)lipofuscin granules in pigmented Abca4^-/- mice had a homogenous electron density and sharp demarcations, while lipofuscin in albino Abca4^-/- mice had a flocculent electron density and often lacked a surrounding membrane, indicating loss of lysosomal integrity. Young Abca4^-/-.Rdh8^-/- mice showed (melano-)lipofuscin granules with homogenous electron density, while in aged animals granules with flocculent electron density predominated. Both strains of pigmented SD mice had melanolipofuscin clusters as found in the human SD eye. Like melanin from S. officinalis, porcine RPE melanin can also quench superoxide anions.

Discussion

The presented pathologies in albino Abca4^-/- and Abca4^-/-.Rdh8^-/- mice suggest oxidative stress and/or lysosomal dysfunction within the RPE. Since albino Abca4^-/- mice have the earliest onset and severest damage and as absence of melanin and also melanin turnover with age are known to diminish RPEs anti-oxidative properties, we assume that RPE melanin plays a role in SD related damages. A lack of pathology in pigmented Abca4^-/- mice due to lower stress levels as compared to the Abca4^-/-.Rdh8^-/- mice underlines this hypothesis. It is also supported by the finding that RPE melanin can quench superoxide anions. We therefore suppose that RPE melanin is important in retinal health and we discuss its role as an oxidative stress scavenger.

Deficiency of type 2 iodothyronine deiodinase reduces necroptosis activity and oxidative stress responses in retinas of Leber congenital amaurosis model mice

Thyroid hormone (TH) signaling has been shown to regulate cone photoreceptor viability. Suppression of TH signaling with antithyroid drug treatment or by targeting iodothyronine deiodinases and TH receptors preserves cones in mouse models of retinal degeneration, including the Leber congenital amaurosis Rpe65-deficient mice. This work investigates the cellular mechanisms underlying how suppressing TH signaling preserves cones in Rpe65-deficient mice, using mice deficient in type 2 iodothyronine deiodinase (Dio2), the enzyme that converts the prohormone thyroxine to the active hormone triiodothyronine (T3). Deficiency of Dio2 improved cone survival and function in Rpe65-/- and Rpe65-deficiency on a cone dominant background ( Rpe65-/-/ Nrl-/-) mice. Analysis of cell death pathways revealed that receptor-interacting serine/threonine-protein kinase (RIPK)/necroptosis activity was increased in Rpe65-/-/ Nrl-/- retinas, and Dio2 deficiency reversed the alterations. Cell-stress analysis showed that the cellular oxidative stress responses were increased in Rpe65-/-/ Nrl-/- retinas, and Dio2 deficiency abolished the elevations. Similarly, antithyroid drug treatment resulted in reduced RIPK/necroptosis activity and oxidative stress responses in Rpe65-/-/ Nrl-/- retinas. Moreover, treatment with T3 significantly induced RIPK/necroptosis activity and oxidative stress responses in the retina. This work shows that suppression of TH signaling reduces cellular RIPK/necroptosis activity and oxidative stress responses in degenerating retinas, suggesting a mechanism underlying the observed cone preservation.-Yang, F., Ma, H., Butler, M. R., Ding, X.-Q. Deficiency of type 2 iodothyronine deiodinase reduces necroptosis activity and oxidative stress responses in retinas of Leber congenital amaurosis model mice.

(3R)-5,6,7-trihydroxy-3-isopropyl-3-methylisochroman-1-one ameliorates retinal degeneration in Pde6brd10 mice

As a severe photoreceptor-degenerative disease, retinitis pigmentosa (RP) is currently incurable and eventually leads to partial or complete blindness. (3R)-5,6,7-trihydroxy-3-isopropyl-3-methylisochroman-1-one (TIM) is a novel antioxidant isolated from the plant of Alpinia katsumadai Hayata, with protective effects on photoreceptor cells against lipoteichoic acid-induced damage through inhibiting oxidative stress. The present study was to further demonstrate whether TIM could ameliorate retinal degeneration of Pde6b^rd10 (rd10) mice, a mouse model of RP. rd10 mice were treated with TIM by intraperitoneal injection daily from postnatal Day 10 (P10) to P26. Retinal function was tested by electroretinography. Histology was evaluated by toluidine blue staining and TUNEL assay. Oxidative stress markers were measured by ELISA. Immunohistochemistry, real-time PCR, and western blotting were applied to explore the protective mechanism. Results showed TIM significantly improved the retinal function and decreased photoreceptor cell apoptosis in rd10 mice through reducing oxidative stress. For the first time, this study demonstrated the protective effects of TIM against retinal degeneration in rd10 mice, providing scientific rationale to use TIM treating the RP.

Pesticide Use and Age-Related Macular Degeneration in the Agricultural Health Study

BACKGROUND

Age-related macular degeneration (AMD) is a leading cause of blindness in developed countries. Few studies have investigated its relationship to environmental neurotoxicants. In previous cross-sectional studies, we found an association between pesticide use and self-reported retinal degeneration.

OBJECTIVE

We evaluated the association of pesticide use with physician-confirmed incident AMD.

METHODS

The Agricultural Health Study (AHS) is a prospective cohort of pesticide applicators and their spouses enrolled from 1993-1997 in Iowa and North Carolina. Cohort members reported lifetime use of 50 specific pesticides at enrollment. Self-reports of incident AMD during follow-up through 2007 were confirmed by reports from participants' physicians and by independent evaluation of retinal photographs provided by the physicians. Confirmed cases (n=161) were compared with AHS cohort members without AMD (n=39,108). We estimated odds ratios (ORs) and 95% confidence intervals (CIs) by logistic regression with adjustment for age, gender, and smoking.

RESULTS

AMD was associated with ever use of organochlorine [OR=2.7 (95% CI: 1.8, 4.0)] and organophosphate [OR=2.0 (95% CI: 1.3, 3.0)] insecticides and phenoxyacetate herbicides [OR=1.9 (95% CI: 1.2, 2.8)]. Specific pesticides consistently associated with AMD included chlordane, dichlorodiphenyltrichloroethane (DDT), malathion, and captan; others with notable but slightly less consistent associations were heptachlor, diazinon, phorate, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and 2,4-dichlorophenoxyacetic acid (2,4-D). Results were similar for men and women. Some specific pesticides were associated with both early- and late-stage AMD, but others were associated with only one stage.

CONCLUSIONS

Exposures to specific pesticides may be modifiable risk factors for AMD. https://doi.org/10.1289/EHP793.

Sodium Iodate Produces a Strain-Dependent Retinal Oxidative Stress Response Measured In Vivo Using QUEST MRI

Purpose

We identify noninvasive biomarkers that measure the severity of oxidative stress within retina layers in sodium iodate (SI)-atrophy vulnerable (C57BL/6 [B6]) and SI-atrophy resistant (129S6/SvEvTac [S6]) mice.

Methods

At 24 hours after administering systemic SI to B6 and S6 mice we measured: (1) superoxide production in whole retina ex vivo, (2) excessive free radical production in vivo based on layer-specific 1/T1 values before and after α-lipoic acid (ALA) administration while the animal was inside the magnet (QUEnch-assiSTed MRI [QUEST MRI]), and (3) visual performance (optokinetic tracking) ± antioxidants; control mice were similarly assessed. Retinal layer spacing and thickness in vivo also were evaluated (optical coherence tomography, MRI).

Results

SI-treated B6 mice retina had a significantly higher superoxide production than SI-treated S6 mice. ALA-injected SI-treated B6 mice had reduced 1/T1 in more retinal layers in vivo than in SI-treated S6 mice. Uninjected and saline-injected SI-treated B6 mice had similar transretinal 1/T1 profiles. Notably, the inner segment layer 1/T1 of SI-treated B6 mice was responsive to ALA but was unresponsive in SI-treated S6 mice. In both SI-treated strains, antioxidants improved contrast sensitivity to similar extents; antioxidants did not change acuity in either group. Retinal thicknesses were normal in both SI-treated strains at 24 hours after treatment.

Conclusions

QUEST MRI uniquely measured severity of excessive free radical production within retinal layers of the same subject. Identifying the mechanisms underlying genetic vulnerabilities to oxidative stress is expected to help in understanding the pathogenesis of retinal degeneration.

(2R, 3S)-Pinobanksin-3-cinnamate ameliorates photoreceptor degeneration in Pde6rd10 mice

As an inherited disorder caused by initial death of rod photoreceptors, retinitis pigmentosa is currently untreatable and usually leads to partial or complete blindness. (2R, 3S)-Pinobanksin-3-cinnamate (PC) is a new flavonone isolated from the seed of Alpinia galanga Willd, and has been reported to exert neuroprotective effects by upregulating endogenous antioxidant enzymes. In this study, the anti-oxidative and neuroprotective activity of PC against photoreceptor apoptosis in rd10 mouse model of retinitis pigmentosa was explored. PC showed to produce significant improvement in histology and function in rd10 mice through reducing oxidative stress. For the first time, the protective effects of PC were demonstrated against retina degeneration in rd10 mice and our study provides scientific rationale on using PC as the supplementary treatment to the outer retina diseases, including retinitis pigmentosa, in which oxidative stress is thought to contribute to disease progression.

Mouse Tmem135 mutation reveals a mechanism involving mitochondrial dynamics that leads to age-dependent retinal pathologies

While the aging process is central to the pathogenesis of age-dependent diseases, it is poorly understood at the molecular level. We identified a mouse mutant with accelerated aging in the retina as well as pathologies observed in age-dependent retinal diseases, suggesting that the responsible gene regulates retinal aging, and its impairment results in age-dependent disease. We determined that a mutation in the transmembrane 135 (Tmem135) is responsible for these phenotypes. We observed localization of TMEM135 on mitochondria, and imbalance of mitochondrial fission and fusion in mutant Tmem135 as well as Tmem135 overexpressing cells, indicating that TMEM135 is involved in the regulation of mitochondrial dynamics. Additionally, mutant retina showed higher sensitivity to oxidative stress. These results suggest that the regulation of mitochondrial dynamics through TMEM135 is critical for protection from environmental stress and controlling the progression of retinal aging. Our study identified TMEM135 as a critical link between aging and age-dependent diseases.

Interphotoreceptor Retinoid-Binding Protein Mitigates Cellular Oxidative Stress and Mitochondrial Dysfunction Induced by All-trans-Retinal

Purpose

Point and null mutations in interphotoreceptor retinoid-binding protein (IRBP) cause retinal dystrophy in affected patients and IRBP-deficient mice with unknown mechanism. This study investigated whether IRBP protects cells from damages induced by all-trans-retinal (atRAL), which was increased in the Irbp^−/− retina.

Methods

Wild-type and Irbp^−/− mice retinal explants in buffer with or without purified IBRP were exposed to 800 lux light for different times and subjected to retinoid analysis by high-performance liquid chromatography. Purity of IRBP was determined by Coomassie Brilliant Blue staining and immunoblot analysis. Cellular damages induced by atRAL in the presence or absence of IRBP were evaluated in the mouse photoreceptor-derived 661W cells. Cell viability and death were measured by 3-(4,5-dimethyl-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) and TUNEL assays. Expression and modification levels of retinal proteins were determined by immunoblot analysis. Intracellular reactive oxygen species (ROS) and nitric oxide (NO) were detected with fluorogenic dyes and confocal microscopy. Mitochondrial membrane potential was analyzed by using JC-1 fluorescent probe and a flow cytometer.

Results

Content of atRAL in Irbp^−/− retinal explants exposed to light for 40 minutes was significantly higher than that in wild-type retinas under the same light conditions. All-trans-retinal caused increase in cell death, tumor necrosis factor activation, and Adam17 upregulation in 661W cells. NADPH oxidase-1 (NOX1) upregulation, ROS generation, NO-mediated protein S-nitrosylation, and mitochondrial dysfunction were also observed in 661W cells treated with atRAL. These cytotoxic effects were significantly attenuated in the presence of IRBP.

Conclusions

Interphotoreceptor retinoid-binding protein is required for preventing accumulation of retinal atRAL, which causes inflammation, oxidative stress, and mitochondrial dysfunction of the cells.

Alterations in glutamate cysteine ligase content in the retina of two retinitis pigmentosa animal models

Retinitis Pigmentosa (RP) comprises a group of rare genetic retinal disorders in which one of several different mutations induces photoreceptor death. Oxidative stress and glutathione (GSH) alterations may be related to the pathogenesis of RP. GSH has been shown to be present in high concentrations in the retina. In addition, the retina has the capability to synthesize GSH. In this study, we tested whether the two subunits of glutamate cysteine ligase, the rate-limiting enzyme in GSH synthesis, and the concentrations of retinal GSH, oxidized glutathione (GSSG), cysteine (Cys) and glutamate are altered in the retina of two different RP mice models. Retinas from C3H and rd1 mice at different postnatal days (P7, P11, P15, P19, P21 and P28) and from C57BL/6 and rd10 mice at P21 were obtained. Western blot analysis was performed to determine the protein content of catalytic and modulatory subunits from glutamate cysteine ligase (GCLC and GCLM, respectively). In another set of experiments, control and rd1 mice were administered buthinine sulfoximine, a glutathione synthase inhibitor, or paraquat. GSH, GSSG, glutamate and Cys concentrations were determined, by HPLC. A decrease in retinal GCLC content was observed in C3H and rd1 mice with age, nevertheless, there was an increase in retinal GCLC in rd1 mice compared to control retinas at P19. No modifications in GCLM content with age and no difference between GCLM content in rd1 and control retinas were observed. The GSH concentration decreased in the rd1 retinas compared with control ones at P15, it increased at P19, and was again similar at P21 and P28. No changes in GSSG concentration in control retinas with age were observed; the GSSG levels in rd1 retinas were similar from P7 to P19 and then increased significantly at P21 and P28. Glutamate concentration was increased in the rd1 retinas compared to control mice from P7 to P15 and were comparable at P21 and P28. The Cys concentrations was measured in control and rd1 retinas, but no significant changes were observed between them. BSO administration decreases GSH retinal concentration in control and rd1 mice, while paraquat administration induced an increase in GSH retinal concentration in control mice and a decrease in GSH in rd1 mice retina. Retinal GCLC was significantly increased in rd10 mice at P21 as well as GSSG. Our results suggest alterations in retinal GCLC content and GSH and/or its precursors in these two RP animal models. Regulation of the enzymes related to GSH metabolism and the retinal concentration of glutamate may be a possible target to delay especially cone death in RP.

Measuring In Vivo Free Radical Production by the Outer Retina

PURPOSE

Excessive and continuously produced free radicals in the outer retina are implicated in retinal aging and the pathogenesis of sight-threatening retinopathies, yet measuring outer retinal oxidative stress in vivo remains a challenge. Here, we test the hypothesis that continuously produced paramagnetic free radicals from the outer retina can be measured in vivo using high-resolution (22-μm axial resolution) 1/T1magnetic resonance imaging (MRI) without and with a confirmatory quench (quench-assisted MRI).

METHODS

Low-dose sodium iodate-treated and diabetic C57Bl6/J mice (and their controls), and rod-dominated (129S6) or cone-only R91W;Nrl-/- mice were studied. In dark-adapted groups, 1/T1 was mapped transretinally in vivo without or with (1) the antioxidant combination of methylene blue (MB) and α-lipoic acid (LPA), or (2) light exposure; in subgroups, retinal superoxide production was measured ex vivo (lucigenin).

RESULTS

In the sodium iodate model, retinal superoxide production and outer retina-specific 1/T1 values were both significantly greater than normal and corrected to baseline with MB+LPA therapy. Nondiabetic mice at two ages and 1.2-month diabetic mice (before the appearance of oxidative stress) had similar transretinal 1/T1 profiles. By 2.3 months of diabetes, only outer retinal 1/T1 values were significantly greater than normal and were corrected to baseline with MB+LPA therapy. In mice with healthy photoreceptors, a light quench caused 1/T1 of rods, but not cones, to significantly decrease from their values in the dark.

CONCLUSIONS

Quench-assisted MRI is a feasible method for noninvasively measuring normal and pathologic production of free radicals in photoreceptors/RPE in vivo.

Carnosic acid slows photoreceptor degeneration in the Pde6b(rd10) mouse model of retinitis pigmentosa

The photoreceptor cell death associated with the various genetic forms of retinitis pigmentosa (RP) is currently untreatable and leads to partial or complete vision loss. Carnosic acid (CA) upregulates endogenous antioxidant enzymes and has proven neuroprotective in studies of neurodegenerative models affecting the brain. In this study, we examined the potential effect of CA on photoreceptor death in the Pde6b^rd10 mouse model of RP. Our data shows that CA provided morphological and functional preservation of photoreceptors. CA appears to exert its neuroprotective effects through inhibition of oxidative stress and endoplasmic reticulum stress.

Defining the Relationships Among Retinal Function, Layer Thickness and Visual Behavior During Oxidative Stress-Induced Retinal Degeneration

PURPOSE

The purpose of this study was to identify how changes in retinal structure and function correlate with visual deficits during increasing amounts of retinal degeneration.

MATERIALS AND METHODS

Retinal degeneration was induced in adult mice by subretinal injections of paraquat (PQ) (0.2-1 mM). Retinal anatomy and photoreceptor layer thickness were quantified by histology and optical coherence tomography (OCT), retinal function was measured using electroretinography (ERG), and visual behavior were measured by optokinetic tracking, at 1 to 3 week post-injury.

RESULTS

Photoreceptor layer structure, function and visual behavior declined at a linear rate over time following PQ-induced degeneration, with the correlations between outcome measures being lowest at mild injury levels and increasing with injury severity. Overall reductions in visual acuity were highly correlated with declines in retinal thickness (r(2) = 0.78) and function (r(2) = 0.67) and retinal thickness correlated with photoreceptor function (r(2) = 0.72). ERG a-wave scotopic amplitudes showed a stronger correspondence to retinal structure and visual behavior than b-waves.

CONCLUSIONS

Measurements of photoreceptor loss at the structural and functional levels showed good correspondence with degeneration-associated changes in visual behavior after oxidative stress injury. The results provide new insight about the relative kinetics of measurements of retinal degeneration induced by oxidative stress, which could guide the choice of optimal outcome measurements for other retinal diseases.

Protective effects of a grape-supplemented diet in a mouse model of retinal degeneration

OBJECTIVE

Retinal degenerations are a class of devastating blinding diseases that are characterized by photoreceptor dysfunction and death. In this study, we tested whether grape consumption, in the form of freeze-dried grape powder (FDGP), improves photoreceptor survival in a mouse model of retinal degeneration.

METHODS

Retinal degeneration was induced in mice by acute oxidative stress using subretinal injection of paraquat. The grape-supplemented diet was made by formulating base mouse chow with FDGP, corresponding to three daily human servings of grapes, and a control diet was formulated with equivalent sugar composition as FDGP (0.68% glucose-0.68% fructose mixture). Mice were placed on the diets at weaning for 5 wk before oxidative stress injury until analysis at 2 wk post-injection. Retinal function was measured using electroretinography, thickness of the photoreceptor layer was measured using optical coherence tomography, and rows of photoreceptor nuclei were counted on histologic sections.

RESULTS

In mice fed the control diet, oxidative stress significantly reduced photoreceptor layer thickness and photoreceptor numbers. In contrast, retinal thickness and photoreceptor numbers were not reduced by oxidative stress in mice on the grape-supplemented diet, indicating significantly higher photoreceptor survival after injury than mice on the control diet. Furthermore, mice on the grape diet showed preservation of retinal function after oxidative stress injury compared with mice on the control diet.

CONCLUSIONS

A diet supplemented with grapes rescued retinal structure and function in an oxidative stress-induced mouse model of retinal degeneration, which demonstrates the beneficial effect of grapes on photoreceptors.

MRI of rod cell compartment-specific function in disease and treatment in vivo

Rod cell oxidative stress is a major pathogenic factor in retinal disease, such as diabetic retinopathy (DR) and retinitis pigmentosa (RP). Personalized, non-destructive, and targeted treatment for these diseases remains elusive since current imaging methods cannot analytically measure treatment efficacy against rod cell compartment-specific oxidative stress in vivo. Over the last decade, novel MRI-based approaches that address this technology gap have been developed. This review summarizes progress in the development of MRI since 2006 that enables earlier evaluation of the impact of disease on rod cell compartment-specific function and the efficacy of anti-oxidant treatment than is currently possible with other methods. Most of the new assays of rod cell compartment-specific function are based on endogenous contrast mechanisms, and this is expected to facilitate their translation into patients with DR and RP, and other oxidative stress-based retinal diseases.

Pharmacological approaches to retinitis pigmentosa: A laboratory perspective

Retinal photoreceptors are highly specialized and performing neurons. Their cellular architecture is exquisitely designed to host a high concentration of molecules involved in light capture, phototransduction, electric and chemical signaling, membrane and molecular turnover, light and dark adaption, network activities etc. Such high efficiency and molecular complexity require a great metabolic demand, altogether conferring to photoreceptors particular susceptibility to external and internal insults, whose occurrence usually precipitate into degeneration of these cells and blindness. In Retinitis Pigmentosa, an impressive number of mutations in genes expressed in the retina and coding for a large varieties of proteins leads to the progressive death of photoreceptors and blindness. Recent advances in molecular tools have greatly facilitated the identification of the underlying genetics and molecular bases of RP leading to the successful implementation of gene therapy for some types of mutations, with visual restoration in human patients. Yet, genetic heterogeneity of RP makes mutation-independent approaches highly desirable, although many obstacles pave the way to general strategies for treating this complex disease, which remains orphan. The review will focus on treatments for RP based on pharmacological tools, choosing, among the many ongoing studies, approaches which rely on strong experimental evidence or rationale. For perspective treatments, new concepts are foreseen to emerge from basic studies elucidating the pathways connecting the primary mutations to photoreceptor death, possibly revealing common molecular targets for drug intervention.

Transcriptional regulation of nucleoredoxin-like genes takes place on a daily basis in the retina and pineal gland of rats

The nucleoredoxin-like gene Nxnl1 (Txnl6) and its paralogue Nxnl2 encode the rod-derived cone viability factors (RdCVF and RdCVF2), which increase the resistance to photooxidative damage and have therapeutic potential for the survival of cones in retinitis pigmentosa. In this study, the transcription of Nxnl genes was investigated as a function of the day/night cycle in rats. The transcript levels of Nxnl1 and Nxnl2 were seen to display daily rhythms with steadily increasing values during the light phase and peak expression around dark onset in preparations of whole retina, photoreceptor cells and—but only in regard to Nxnl1—in photoreceptor-related pinealocytes. The cycling of Nxnl1 but not that of Nxnl2 persisted in constant darkness in the retina. This suggests that daily regulation of Nxnl1 is driven by a circadian clock, whereas that of Nxnl2 is promoted by environmental light. The present data indicate clock- and light-dependent regulations of nucleoredoxin-like genes that may be part of a protective shield against photooxidative damage.

Yttrium oxide nanoparticles prevent photoreceptor death in a light-damage model of retinal degeneration

Photoreceptor (PR) cells are prone to accumulation of reactive oxygen species (ROS) and oxidative stress. An imbalance between the production of ROS and cellular antioxidant defenses contributes to PR degeneration and blindness in many different ocular disease states. Yttrium oxide (Y2O3) nanoparticles (NPs) are excellent free radical scavengers owing to their nonstoichiometric crystal defects. Here we utilize a murine light-stress model to test the efficacy of Y2O3 NPs (~10-14nm in diameter) in ameliorating retinal oxidative stress-associated degeneration. Our studies demonstrate that intravitreal injections of these NPs at doses ranging from 0.1 to 5.0µM 2 weeks before acute light stress protect PRs from degeneration. This protection is reflected both structurally (i.e., decreased light-associated thinning of the outer nuclear layer) and functionally (i.e., preservation of scotopic and photopic electroretinogram amplitudes). We also observe preservation of structure and function when NPs are delivered immediately after acute light stress, although the magnitude of the preservation is smaller, and only doses ranging from 1.0 to 5.0µM were effective. We show that the Y2O3 NPs are nontoxic and well tolerated after intravitreal delivery. Our results suggest that Y2O3 NPs have astonishing antioxidant benefits and, with further exploration, may be an excellent strategy for the treatment of oxidative stress associated with multiple forms of retinal degeneration.

A novel protective role for the innate immunity Toll-Like Receptor 3 (TLR3) in the retina via Stat3

The innate immune system and inflammatory pathways play key roles in numerous diseases of the central nervous system (CNS). Recent evidence indicates that innate immunity induces both pathogenesis and protection during neuronal injury. To test the possibility that the conflicting roles of innate immunity in the CNS depends on the cellular environment in which innate immunity is stimulated, we analyzed the effect of Toll-Like Receptor 3 (TLR3) activation on neuronal survival in the presence and absence of oxidative injury in a mouse model system. We demonstrated that activation of TLR3 by the double stranded RNA activator, Poly (I:C), during paraquat induced oxidative stress, significantly protected mouse photoreceptors, as measured by increased retinal structure, function, and improved visual acuity. In contrast, TLR3 activation without concurrent oxidative injury was neurotoxic. The neurotoxic and protective effects of Poly (I:C) stimulation were absent in TLR3 knockout animals, which indicates that protection by Poly (I:C) is dependent on the TLR3 signaling pathway. Furthermore, we identified the pro-survival transcription factor Stat3 as a necessary mechanism for protection. Knockdown of Stat3 using lentivirally delivered shRNA abolished the protective effects of TLR3 signaling in the retina during oxidative stress. Therefore, TLR3 activation in the context of oxidative stress triggers protective instead of pathogenic signaling, suggesting that TLR3 is a potential therapeutic target for neurodegeneration where oxidative stress is a significant contributor.

Induced pluripotent stem cells without c-Myc ameliorate retinal oxidative damage via paracrine effects and reduced oxidative stress in rats

PURPOSE

To investigate the efficacy and mechanisms of non-c-Myc induced pluripotent stem cell (iPSC) transplantation in a rat model of retinal oxidative damage.

METHODS

Paraquat was intravitreously injected into Sprague-Dawley rats. After non-c-Myc iPSC transplantation, retinal function was evaluated by electroretinograms (ERGs). The generation of reactive oxygen species (ROS) was determined by lucigenin- and luminol-enhanced chemiluminescence. The expression of brain-derived neurotrophic factor, ciliary neurotrophic factor, basic fibroblast growth factor (bFGF), stromal cell-derived factor (SDF)-1α, and CXCR4 was measured by immunohistochemistry and ELISA. An in vitro study using SH-SY5Y cells was performed to verify the protective effects of SDF-1α.

RESULTS

Transplantation of non-c-Myc iPSCs effectively promoted the recovery of the b-wave ratio in ERGs and significantly ameliorated retinal damage. Non-c-Myc iPSC transplantation decreased ROS production and increased the activities of superoxide dismutase and catalase, thereby reducing retinal oxidative damage and apoptotic cells. Moreover, non-c-Myc iPSC transplantation resulted in significant upregulation of SDF-1α, followed by bFGF, accompanied by a significant improvement in the ERG. In vitro studies confirmed that treatment with SDF-1α significantly reduced apoptosis in a dose-dependent manner in SH-SY5Y cells. Most transplanted cells remained in the subretinal space, with spare cells expressing neurofilament M markers at day 28. Six months after transplantation, no tumor formation was seen in animals with non-c-Myc iPSC grafts.

CONCLUSIONS

We demonstrated the potential benefits of non-c-Myc iPSC transplantation for treating oxidative-damage-induced retinal diseases. SDF-1α and bFGF play important roles in facilitating the amelioration of retinal oxidative damage after non-c-Myc iPSC transplantation.

Recharging mitochondrial batteries in old eyes. Near infra-red increases ATP

Progressive accumulation of age related mitochondrial DNA mutations reduce ATP production and increase reactive oxygen species output, leading to oxidative stress, inflammation and degradation. The pace of this is linked to metabolic demand. The retina has the greatest metabolic demand and mitochondrial density in the body and displays progressive age related inflammation and marked cell loss. Near infra-red (670 nm) is thought to be absorbed by cytochrome c oxidase (COX), a key element in mitochondrial respiration and it has been demonstrated that it improves mitochondrial membrane potentials in aged eyes. It also significantly reduces the impact of experimental pathology and ameliorates age related retinal inflammation. We show ATP decline with ageing in mouse retina and brain. Also, in these tissues that ATP is significantly increased by 670 nm exposure in old mice. In the retina this was associated with increased COX and reduced acrolein expression. Acrolein, being a free radical marker of retinal oxidative stress, is up regulated in Alzheimer's and retinal degeneration. This is the first demonstration of ATP manipulation in vivo and may provide a simple non-invasive route to combating age related tissue decline.

Degeneration modulates retinal response to transient exogenous oxidative injury

Purpose

Oxidative injury is involved in retinal and macular degeneration. We aim to assess if retinal degeneration associated with genetic defect modulates the retinal threshold for encountering additional oxidative challenges.

Methods

Retinal oxidative injury was induced in degenerating retinas (rd10) and in control mice (WT) by intravitreal injections of paraquat (PQ). Retinal function and structure was evaluated by electroretinogram (ERG) and histology, respectively. Oxidative injury was assessed by immunohistochemistry for 4-Hydroxy-2-nonenal (HNE), and by Thiobarbituric Acid Reactive Substances (TBARS) and protein carbonyl content (PCC) assays. Anti-oxidant mechanism was assessed by quantitative real time PCR (QPCR) for mRNA of antioxidant genes and genes related to iron metabolism, and by catalase activity assay.

Results

Three days following PQ injections (1 µl of 0.25, 0.75, and 2 mM) the average ERG amplitudes decreased more in the WT mice compared with the rd10 mice. For example, following 2 mM PQ injection, ERG amplitudes reduced 1.84-fold more in WT compared with rd10 mice (p = 0.02). Injection of 4 mM PQ resulted in retinal destruction. Altered retina morphology associated with PQ was substantially more severe in WT eyes compared with rd10 eyes. Oxidative injury according to HNE staining and TBARS assay increased 1.3-fold and 2.1-fold more, respectively, in WT compared with rd10 mice. At baseline, prior to PQ injection, mRNA levels of antioxidant genes (Superoxide Dismutase1, Glutathione Peroxidase1, Catalase) and of Transferrin measured by quantitative PCR were 2.1–7.8-fold higher in rd10 compared with WT mice (p<0.01 each), and catalase activity was 1.7-fold higher in rd10 (p = 0.0006).

Conclusions

This data suggests that degenerating rd10 retinas encounter a relatively lower degree of damage in response to oxidative injury compared with normal retinas. Constitutive up-regulation of the oxidative defense mechanism in degenerating retinas may confer such relative protection from oxidative injury.

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.

A high content screening approach to identify molecules neuroprotective for photoreceptor cells

PURPOSE

Retinal degenerations are a heterogeneous group of diseases in which there is slow but progressive loss of photoreceptors (PR). There are currently no approved therapies for treating retinal degenerations. In an effort to identify novel small molecules that are (1) neuroprotective and (2) promote PR differentiation, we have developed microscale (1,536 well) cell culture assays using primary retinal neurons.

METHODS

Primary murine retinal cells are isolated, seeded, treated with a 1,280 compound chemical library in a 7 point titration and then cultured under conditions developed to assay protection against an introduced stress or enhance PR differentiation. In the protection assays a chemical insult is introduced and viability assessed after 72 h using CellTiterGlo, a single-step chemiluminescent reagent. In the differentiation assay, cells are isolated from the rhodopsin-GFP knock-in mouse and PR differentiation is assessed by fixing cells after 21 days in culture and imaging with the Acumen plate-based laser cytometer (TTP Labtech) to determine number and intensity of GFP-expressing cells. Positive wells are re-imaged at higher resolution with an INCell2000 automated microscope (GE). Concentration-response curves are generated to pharmacologically profile each compound and hits identified by xx.

RESULTS

We have developed PR differentiation and neuroprotection assays with a signal to background (S/B) ratios of 11 and 3, and a coefficient of variation (CV) of 20 and 9 %, suitable for chemical screening. Staurosporine has been shown in our differentiation assay to simultaneously increase the number of rhodopsin positive objects while decreasing the mean rhodopsin intensity and punctate rhodopsin fluorescent objects.

CONCLUSIONS

Using primary murine retinal cells, we developed high throughput assays to identify small molecules that influence PR development and survival. By screening multiple compound concentrations, dose-response curves can be generated, and the false negative rate minimized. It is hoped that this work will identify both potential preclinical candidates as well as molecular probes that will be useful for analysis of the molecular mechanisms that promote PR differentiation and survival.

Chitosan oligosaccharides attenuates oxidative-stress related retinal degeneration in rats

This study investigated the therapeutic potential and mechanisms of chitosan oligosaccharides (COS) for oxidative stress-induced retinal diseases. Retinal oxidative damage was induced in Sprague-Dawley rats by intravitreal injection of paraquat (PQ). Low-dose (5 mg/kg) or high-dose (10 mg/kg) COS or PBS was intragastrically given for 14 days after PQ injection. Electroretinograms were performed to determine the functionality of the retinas. The surviving neurons in the retinal ganglion cell layer and retinal apoptosis were determined by counting Neu N-positive cells in whole-mounted retinas and TUNEL staining, respectively. The generation of reactive oxygen species (ROS) was determined by lucigenin- and luminol-enhanced chemiluminescence. Retinal oxidative damages were assessed by staining with nitrotyrosine, acrolein, and 8-hydroxy-2'-deoxyguanosine (8-OHdG). Immunohistochemical studies were used to demonstrate the expression of nuclear factor-kappa B (NF-κB) p65 in retinas. An in vitro study using RGC-5 cells was performed to verify the results. We demonstrated COS significantly enhanced the recovery of retinal function, preserved inner retinal thickness, and decreased retinal neurons loss in a dose-dependent manner. COS administration demonstrated anti-oxidative effects by reducing luminol- and lucigenin-dependent chemiluminenscense levels and activating superoxide dismutase and catalase, leading to decreased retinal apoptosis. COS markedly reduced retinal NF-κB p65. An in vitro study demonstrated COS increased IκB expression, attenuated the increase of p65 and thus decreased NF-κB/DNA binding activity in PQ-stimulated RGC-5 cells. In conclusion, COS attenuates oxidative stress-induced retinal damages, probably by decreasing free radicals, maintaining the activities of anti-oxidative enzymes, and inhibiting the activation of NF-κB.

Spaceflight environment induces mitochondrial oxidative damage in ocular tissue

A recent report shows that more than 30% of the astronauts returning from Space Shuttle missions or the International Space Station (ISS) were diagnosed with eye problems that can cause reduced visual acuity. We investigate here whether spaceflight environment-associated retinal damage might be related to oxidative stress-induced mitochondrial apoptosis. Female C57BL/6 mice were flown in the space shuttle Atlantis (STS-135), and within 3-5 h of landing, the spaceflight and ground-control mice, similarly housed in animal enclosure modules (AEMs) were euthanized and their eyes were removed for analysis. Changes in expression of genes involved in oxidative stress, mitochondrial and endothelial cell biology were examined. Apoptosis in the retina was analyzed by caspase-3 immunocytochemical analysis and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay. Levels of 4-hydroxynonenal (4-HNE) protein, an oxidative specific marker for lipid peroxidation were also measured. Evaluation of spaceflight mice and AEM ground-control mice showed that expression of several genes playing central roles in regulating the mitochondria-associated apoptotic pathway were significantly altered in mouse ocular tissue after spaceflight compared to AEM ground-control mice. In addition, the mRNA levels of several genes, which are responsible for regulating the production of reactive oxygen species were also significantly up-regulated in spaceflight samples compared to AEM ground-control mice. Further more, the level of HNE protein was significantly elevated in the retina after spaceflight compared to controls. Our results also revealed that spaceflight conditions induced significant apoptosis in the retina especially inner nuclear layer (INL) and ganglion cell layer (GCL) compared to AEM ground controls. The data provided the first evidence that spaceflight conditions induce oxidative damage that results in mitochondrial apoptosis in the retina. This data suggest that astronauts may be at increased risk for late retinal degeneration.

Transplantation of induced pluripotent stem cells without C-Myc attenuates retinal ischemia and reperfusion injury in rats

Induced pluripotent stem cells (iPSC) are novel stem cell populations, but the role of iPSC in retinal ischemia and reperfusion (I/R) injury remains unknown. Since oncogene c-Myc is substantially contributed to tumor formation, in this study, we investigated the effects, mechanisms and safety of subretinal transplantation of iPSC without c-Myc (non-c-Myc iPSC) in a rat model of retinal I/R injury. Retinal I/R injury was induced by raising the intraocular pressure of Sprague-Dawley rats to 110 mmHg for 60 min. A subretinal injection of non-c-Myc iPSC or murine epidermal fibroblast was given 2 h after I/R injury. Electroretinograms (ERG) were performed to determine the functionality of the retinas. The surviving retinal ganglion cells (RGCs) and retinal apoptosis following I/R injury were determined by counting NeuN-positive cells in whole-mounted retinas and TUNEL staining, respectively. The generation of reactive oxygen species (ROS) and the activities of superoxide dismutase (SOD) and catalase (CAT) in the retinal tissues were determined by lucigenin- and luminol-enhanced chemiluminescence and enzyme-linked immunosorbent assay (ELISA). The degree of retinal oxidative damage was assessed by nitrotyrosine, acrolein, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) staining. The expression of brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF) and basic fibroblast growth factor (bFGF) in retinas was measured by immunohistochemistry and ELISA. We found that subretinal transplantation of non-c-Myc iPSC significantly suppressed the I/R-induced reduction in the ERG a- and b-wave ratio, attenuated I/R-induced loss of RGCs and remarkably ameliorated retinal morphological changes. Non-c-Myc iPSC potentially increased the activities of SOD and CAT, decreased the levels of ROS, which may account for preventing retinal cells from apoptotic cell death. In addition, the levels of BDNF and CNTF in retina were significantly elevated in non-c-Myc iPSC-treated eyes. Track the non-c-Myc iPSC after transplantation, most transplanted cells are remained in the subretinal space, with spare cells express neurofilament M markers at day 28. Six months after transplantation in I/R injured rats, no tumor formation was seen in non-c-Myc iPSC graft. In conclusion, non-c-Myc iPSC effectively rescued I/R-induced retinal damages and diminished tumorigenicity. Non-c-Myc iPSC transplantation attenuated retinal I/R injury, possibly via a mechanism involving the regulation of oxidative parameters and paracrinal secretion of trophic factors.

Cone survival and preservation of visual acuity in an animal model of retinal degeneration

The prevention of cone loss during retinal degeneration is a major goal of most therapeutic strategies in retinal degenerative diseases. An intriguing issue in the current research in this field is to understand why a genetic mutation that affects rods eventually leads to cone death. The main objective of the present study was to investigate to what extent rescuing rods from degeneration affects the survival of cones and prevents functional impairment of the visual performance. To this purpose, we compared rod and cone viabilities by both ex vivo and in vivo determinations in the rd10 mutant mouse, a validated model of human retinitis pigmentosa. The ex vivo experiments included morphological and biochemical tests, whereas in vivo studies compared the rod-mediated scotopic with the cone-mediated photopic electroretinogram. We also determined the overall visual performance by behaviorally testing the visual acuity (VA). The electroretinogram measurements showed that the kinetics of the photopic response in rd10 mice was slowed down with respect to the age-paired wild-type at a very early stage of the disease, when rods were still present and responsive. We then tested cone viability and function under a pharmacological scheme previously shown to prolong rod survival. The treatment consisted of eye drop administration of myriocin, an inhibitor of the biosynthesis of ceramide, a powerful proapoptotic messenger. The results of biochemical, morphological and functional assays converged to show that, in treated rd10 mice cone photoreceptors, the inner retina and overall visual performance were preserved well after rod death.

Toll-like receptor 3 (TLR3) protects retinal pigmented epithelium (RPE) cells from oxidative stress through a STAT3-dependent mechanism

Toll-like receptors (TLRs) are essential receptors of the innate immune system and are first responders for protection against bacterial and viral pathogens. Recently, several TLRs have also been implicated in regulating cell death and survival in non-pathogen injuries such as stroke and oxidative stress. Investigating the role of TLRs during central nervous system damage is an important focus of research that may reveal new mechanisms underlying the cellular response to injury and survival. Retinal pigmented epithelium (RPE) cells form an epithelial layer underneath the neural retina that maintains the function of photoreceptors and are the primary cell type affected in the retinal disease age-related macular degeneration (AMD). Predicted loss of function polymorphisms in the TLR3 gene are associated with protection from AMD but the role of TLR3 in regulating RPE survival during AMD-like injury, such as high oxidative stress, is not known. Therefore the purpose of this study is to evaluate the effect of TLR3 signaling on RPE viability during oxidative stress. We demonstrated that TLR3 activation in the presence of oxidative stress injury significantly increased RPE cell viability, in contrast to TLR3 reducing cell viability in the absence of cellular injury. Furthermore, we show signal transducer and activator of transcription 3 (STAT3) signaling as an essential mediator of TLR3-regulated protection of RPE cells. STAT3 signaling was increased by TLR3 activation and knockdown of STAT3 transcripts using siRNA abolished the protective effect of TLR3 during oxidative stress. Together, these results demonstrate a novel pro-survival role for TLR3 signaling within the RPE during injury. These findings support the concept that dysregulation of TLR3 activity may contribute to the development of AMD, suggesting that precise regulation of the TLR3 pathway during AMD-associated injury could be of therapeutic interest.

CNGA3 deficiency affects cone synaptic terminal structure and function and leads to secondary rod dysfunction and degeneration

PURPOSE

To investigate rod function and survival after cone dysfunction and degeneration in a mouse model of cone cyclic nucleotide-gated (CNG) channel deficiency.

METHODS

Rod function and survival in mice with cone CNG channel subunit CNGA3 deficiency (CNGA3-/- mice) were evaluated by electroretinographic (ERG), morphometric, and Western blot analyses. The arrangement, integrity, and ultrastructure of photoreceptor terminals were investigated by immunohistochemistry and electron microscopy.

RESULTS

The authors found loss of cone function and cone death accompanied by impairment of rods and rod-driven signaling in CNGA3-/- mice. Scotopic ERG b-wave amplitudes were reduced by 15% at 1 month, 30% at 6 months, and 40% at 9 months and older, while scotopic a-wave amplitudes were decreased by 20% at 9 months, compared with ERGs of age-matched wild-type mice. Outer nuclear layer thickness in CNGA3-/- retina was reduced by 15% at 12 months compared with age-matched wild-type controls. This was accompanied by a 30%-40% reduction in expression of rod-specific proteins, including rhodopsin, rod transducin α-subunit, and glutamic acid-rich protein (GARP). Cone terminals in the CNGA3-/- retina showed a progressive loss of neurochemical and ultrastructural integrity. Abnormalities were observed as early as 1 month. Disorganized rod terminal ultrastructure was noted by 12 months.

CONCLUSIONS

These findings demonstrate secondary rod impairment and degeneration after cone degeneration in mice with cone CNG channel deficiency. Loss of cone phototransduction accompanies the compromised integrity of cone terminals. With time, rod synaptic structure, function, and viability also become compromised.

Zinc-desferrioxamine attenuates retinal degeneration in the rd10 mouse model of retinitis pigmentosa

Iron-associated oxidative injury plays a role in retinal degeneration such as age-related macular degeneration and retinitis pigmentosa. The metallo-complex zinc-desferrioxamine (Zn/DFO) may ameliorate such injury by chelation of labile iron in combination with release of zinc. We explored whether Zn/DFO can affect the course of retinal degeneration in the rd10 mouse model of retinitis pigmentosa. Zn/DFO-treated animals showed significantly higher electroretinographic responses at 3 and 4.5 weeks of age compared with saline-injected controls. Corresponding retinal (photoreceptor) structural rescue was observed by quantitative histological and immunohistochemical techniques. When administered alone, the components of the complex, Zn and DFO, showed a lesser, partial effect. TBARS, a marker of lipid peroxidation, and levels of oxidative DNA damage as quantified by 8-OHdG immunostaining were significantly lower in Zn/DFO-treated retinas compared with saline-injected controls. Reduced levels of retinal ferritin as well as reduced iron content within ferritin molecules were measured in Zn/DFO-treated retinas. The data, taken together, suggest that the protective effects of the Zn/DFO complex are mediated through modulation of iron bioavailability, leading to attenuation of oxidative injury. Reducing iron-associated oxidative stress using complexes such as Zn/DFO may serve as a "common pathway" therapeutic approach to attenuate injury in retinal degeneration.