Differences between long- and short-wavelength light-induced retinal damage and the role of PARP-1 in retinal injury induced by blue light.

Photobiomodulation (PBM) therapy uses light of different wavelengths to treat various retinal degeneration diseases, but the potential damage to the retina caused by long-term light irradiation is still unclear. This study were designed to detect the difference between long- and short-wavelength light (650-nm red light and 450-nm blue light, 2.55 mW/cm2, reference intensity in PBM)-induced injury. In addition, a comparative study was conducted to investigate the differences in retinal light damage induced by different irradiation protocols (short periods of repeated irradiation and a long period of constant irradiation). Furthermore, the protective role of PARP-1 inhibition on the molecular mechanism of blue light-induced injury was confirmed by a gene knockdown technique or a specific inhibitor through in vitro and in vivo experiments. The results showed that the susceptibility to retinal damage caused by irradiation with long- and short-wavelength light is different. Shorter wavelength lights, such as blue light, induce more severe retinal damage, while the retina exhibits better resistance to longer wavelength lights, such as red light. In addition, repeated irradiation for short periods induces less retinal damage than constant exposure over a long period. PARP-1 plays a critical role in the molecular mechanism of blue light-induced damage in photoreceptors and retina, and inhibiting PARP-1 can significantly protect the retina against blue light damage. This study lays an experimental foundation for assessing the safety of phototherapy products and for developing target drugs to protect the retina from light damage.

Reduced light exposure mitigates streptozotocin-induced vascular changes and gliosis in diabetic retina by an anti-inflammatory effect and increased retinal cholesterol turnover.

Diabetic retinopathy is not cured efficiently and changes of lifestyle measures may delay early retinal injury in diabetes. The aim of our study was to investigate the effects of reduced daily light exposure on retinal vascular changes in streptozotocin (STZ)-induced model of DM with emphasis on inflammation, Aqp4 expression, visual cycle and cholesterol metabolism-related gene expression in rat retina and RPE. Male Wistar rats were divided into the following groups: 1. control; 2. diabetic group (DM) treated with streptozotocin (100 mg/kg); 3. group exposed to light/dark cycle 6/18 h (6/18); 4. diabetic group exposed to light/dark cycle 6/18 h (DM+6/18). Retinal vascular abnormalities were estimated based on lectin staining, while the expression of genes involved in the visual cycle, cholesterol metabolism, and inflammation was determined by qRT-PCR. Reduced light exposure alleviated vasculopathy, gliosis and the expression of IL-1 and TNF-α in the retina with increased perivascular Aqp4 expression. The expression of genes involved in visual cycle and cholesterol metabolism was significantly up-regulated in RPE in DM+6/18 vs. DM group. In the retina only the expression of APOE was significantly higher in DM+6/18 vs. DM group. Reduced light exposure mitigates vascular changes and gliosis in DM via its anti-inflammatory effect, increased retinal cholesterol turnover and perivascular Aqp4 expression.

Morphological Biomarkers Related to Visual Acuity in Patients With Radiation Retinopathy Treated With Intravitreal Ranibizumab.

BACKGROUND AND OBJECTIVE: Our objective was to monitor variables via spectral-domain optical coherence tomography (SD-OCT) and identify the most relevant biomarkers related to best-corrected visual acuity (BCVA) in radiation retinopathy (RR). PATIENTS AND METHODS: A post-hoc analysis of the two-year Ranibizumab for Radiation Retinopathy (RRR) trial analyzed vision and OCT parameters including intraretinal fluid, ellipsoid zone (EZ) disruption, retinal pigment epithelium atrophy, hard exudates, retinal hemorrhage, retinal neovascularization, and subfoveal fluid. BCVA and SD-OCT parameters were evaluated by univariate analysis and a mixed-effects model. RESULTS: Forty eyes from the RRR trial were included. Intraretinal cyst vertical size (week 24: P = 0.032; week 48: P = 0.021), neovascularization (week 48: P = 0.028; week 72: P = 0.025), and EZ disruption (week 72: P = 0.029; week 104: P = 0.019) were the clinical parameters most relevant to BCVA by univariate analysis in at least two time points. The mixed-effects model confirmed the relevance of intraretinal cyst vertical size (P = 0.001) and neovascularization (P = 0.001) but not EZ disruption (P = 0.119) over the course of the study. CONCLUSIONS: This study characterizes the course of visual loss in RR by identifying intraretinal cyst vertical size, neovascularization, and EZ disruption as biomarkers of poor BCVA over a span of two years. Larger multicenter studies are needed to confirm these findings. [Ophthalmic Surg Lasers Imaging Retina 2024;55:255-262.].

Glial cell response to constant low light exposure in rat retina.

To study the macroglia and microglia and the immune role in long-time light exposure in rat eyes, we performed glial cell characterization along the time-course of retinal degeneration induced by chronic exposure to low-intensity light. Animals were exposed to light for periods of 2, 4, 6, or 8 days, and the retinal glial response was evaluated by immunohistochemistry, western blot and real-time reverse transcription polymerase chain reaction. Retinal cells presented an increased expression of the macroglia marker GFAP, as well as increased mRNA levels of microglia markers Iba1 and CD68 after 6 days. Also, at this time-point, we found a higher number of Iba1-positive cells in the outer nuclear layer area; moreover, these cells showed the characteristic activated-microglia morphology. The expression levels of immune mediators TNF, IL-6, and chemokines CX3CR1 and CCL2 were also significantly increased after 6 days. All the events of glial activation occurred after 5-6 days of constant light exposure, when the number of photoreceptor cells has already decreased significantly. Herein, we demonstrated that glial and immune activation are secondary to neurodegeneration; in this scenario, our results suggest that photoreceptor death is an early event that occurs independently of glial-derived immune responses.

The effect of a chrysanthemum water extract in protecting the retina of mice from light damage.

BACKGROUND: Oxidative stress can induce age-related diseases. Age-related retinal diseases, such as age-related macular degeneration (AMD), are difficult to cure owing to their complicated mechanisms. Although anti-neovascular therapeutics are used to treat wet AMD, vision cannot always be completely restored, and disease progression cannot always be inhibited. Therefore, determining a method to prevent or slow retinal damage is important. This study aimed to investigate the protective effect of a chrysanthemum water extract rich in flavone on the oxidatively stressed retina of mice. METHODS: Light damage was induced to establish oxidative stress mouse models. For in vitro experiments, ARPE-19 cells were cultured and divided into four groups: control, light-damaged, and low- and high-dose chrysanthemum extract. No treatment was administered in the control group. The light-damaged and low- and high-dose chrysanthemum extract groups were exposed to a similar white light level. The chrysanthemum extract was added at a low dose of 0.4 mg/mL or a high dose of 1.0 mg/mL before cell exposure to 2500-lx white light. Reactive oxygen species (ROS) level and cellular viability were measured using MTT and immunofluorescence staining. For in vivo experiments, C57BL/6 J mice were divided into the same four groups. Low- (0.23 g/kg/day) and high-dose (0.38 g/kg/day) chrysanthemum extracts were continuously intragastrically administered for 8 weeks before mouse exposure to 10,000-lx white light. Retinal function was evaluated using electroretinography. In vivo optical coherence tomography and in vitro haematoxylin and eosin staining were performed to observe the pathological retinal changes in each group after light damage. Fluorescein fundus angiography of the arteriovenous vessel was performed, and the findings were analysed using the AngioTool software. TUNEL immunofluorescence staining was used to assess isolated retinal apoptosis. RESULTS: In vitro, increased ROS production and decreased ARPE-19 cell viability were found in the light-damaged group. Improved ARPE-19 cell viability and reduced ROS levels were observed in the chrysanthemum extract treatment groups. In vivo, dysfunctional retinas and abnormal retinal structures were found in the light-damaged group, as well as increased apoptosis in the retinal ganglion cells (RGCs) and inner and outer nuclear layers. The apoptosis rate in the same layers was lower in the chrysanthemum extract treatment groups than in the light-damaged group. The production of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px), increased in the treatment groups. NF-κB in the nucleus and TNF-α were more highly expressed in the light-damaged group than in the low- and high-dose chrysanthemum extract groups. CONCLUSIONS: Light damage-induced retinal oxidative stress can lead to ROS accumulation in the retinal tissues. Herein, RGC and photoreceptor layer apoptosis was triggered, and NF-κB in the nucleus and TNF-α were highly expressed in the light-damaged group. Preventive chrysanthemum extract administration decreased ROS production by increasing SOD, CAT, and GSH-Px activities and reversing the negative changes, demonstrating a potential protective effect on the retina.

CD73 controls ocular adenosine levels and protects retina from light-induced phototoxicity.

ATP and adenosine have emerged as important signaling molecules involved in vascular remodeling, retinal functioning and neurovascular coupling in the mammalian eye. However, little is known about the regulatory mechanisms of purinergic signaling in the eye. Here, we used three-dimensional multiplexed imaging, in situ enzyme histochemistry, flow cytometric analysis, and single cell transcriptomics to characterize the whole pattern of purine metabolism in mouse and human eyes. This study identified ecto-nucleoside triphosphate diphosphohydrolase-1 (NTPDase1/CD39), NTPDase2, and ecto-5'-nucleotidase/CD73 as major ocular ecto-nucleotidases, which are selectively expressed in the photoreceptor layer (CD73), optic nerve head, retinal vasculature and microglia (CD39), as well as in neuronal processes and cornea (CD39, NTPDase2). Specifically, microglial cells can create a spatially arranged network in the retinal parenchyma by extending and retracting their branched CD39high/CD73low processes and forming local "purinergic junctions" with CD39low/CD73- neuronal cell bodies and CD39high/CD73- retinal blood vessels. The relevance of the CD73-adenosine pathway was confirmed by flash electroretinography showing that pharmacological inhibition of adenosine production by injection of highly selective CD73 inhibitor PSB-12489 in the vitreous cavity of dark-adapted mouse eyes rendered the animals hypersensitive to prolonged bright light, manifested as decreased a-wave and b-wave amplitudes. The impaired electrical responses of retinal cells in PSB-12489-treated mice were not accompanied by decrease in total thickness of the retina or death of photoreceptors and retinal ganglion cells. Our study thus defines ocular adenosine metabolism as a complex and spatially integrated network and further characterizes the critical role of CD73 in maintaining the functional activity of retinal cells.

BRAIN AND EYE AS POTENTIAL TARGETS FOR IONIZING RADIATION IMPACT. PART III / FEATURES MORPHOMETRIC RETINAL PARAMETERS, AMPLITUDE AND LATENCY COMPONENTS OF VISUAL EVOKED POTENTIAL IN RADIATION EXPOSED IN UTERO. / GOLOVNYI MOZOK TA ORGAN ZORU IaK POTENTsIINI MIShENI DLIa VPLYVU IONIZUIuChOGO VYPROMINIuVANNIa: ChASTYNA III ­ OSOBLYVOSTI MORFOMETRYChNYKh PARAMETRIV SITChASTOÏ OBOLONKY TA AMPLITUDA I LATENTNIST' KOMPONENTIV ZOROVYKh VYKLYKANYKh POTENTsIALIV U OPROMINENYKh VNUTRIShN'OUTROBNO OSIB.

One of the current problems of modern radiobiology is determine the characteristics of the manifestation of radiation-induced effects not only at different dose loads, but also at different stages of development of the organism. In previous reports, we have summarized available evidence that at certain ages there is a comparative acceleration of radiation-induced pathological changes in the eye and brain, and the study and assessment of the risk of possible ophthalmic and neurological pathology in remote periods after contamination of radioactive areas. Data of irradiated in utero individuals are possible on the basis of observation of the state of the visual analyzer in persons who underwent intrauterine irradiation in 1986. Therefore, a parallel study of retinal morphometric parameters, amplitude and latency of components of evoked visual potentials in irradiated in utero individuals was performed. OBJECTIVE: to evaluate the retinal morphometric parameters, amplitude and latency components of the evoked visual potentials in intrauterine irradiated persons. MATERIALS AND METHODS: The results of surveys of 16 people irradiated in utero in the aftermath of the Chornobyl disaster were used; the comparison group were residents of Kyiv of the corresponding age (25 people). Optical coherence tomography was performed on a Cirrus HD-OCT, Macular Cube 512x128 study technique was used. At the same time, the study of visual evoked potentials on the inverted pattern was performed, and occipital leads wereanalyzed. Visual evoked potentials were recorded on a reversible chess pattern (VEP) - an electrophysiological test, which is a visual response to a sharp change in image contrast when presenting a reversible image of a chessboard. RESULTS: In those irradiated in utero at the age of 22-25 years, there was a probable increase in retinal thickness in the fovea, there was a tendency to increase the thickness of the retina in the areas around the fovea. When recording visual evoked potentials on a reversible chess pattern in this group, there was a tendency to decrease the amplitudes of components (N75, P100, N145, P200) in the right and left parieto-occipital areas and asymmetric changes in latency of these components. CONCLUSIONS: Early changes of fovea recorded in OCT and decreasing amplitudes of components of visual evoked potentials on the reversible chess pattern at the age of 22 25 years may indicate a risk of development in patients irradiated in utero, early age-related macular degeneration, as well as increased risk and increased risk structures of the visual analyzer.

Retinal Protection from LED-Backlit Screen Lights by Short Wavelength Absorption Filters.

(1) Background: Ocular exposure to intense light or long-time exposure to low-intensity short-wavelength lights may cause eye injury. Excessive levels of blue light induce photochemical damage to the retinal pigment and degeneration of photoreceptors of the outer segments. Currently, people spend a lot of time watching LED screens that emit high proportions of blue light. This study aims to assess the effects of light emitted by LED tablet screens on pigmented rat retinas with and without optical filters. (2) Methods: Commercially available tablets were used for exposure experiments on three groups of rats. One was exposed to tablet screens, the other was exposed to the tablet screens with a selective filter and the other was a control group. Structure, gene expression (including life/death, extracellular matrix degradation, growth factors, and oxidative stress related genes), and immunohistochemistry in the retina were compared among groups. (3) Results: There was a reduction of the thickness of the external nuclear layer and changes in the genes involved in cell survival and death, extracellular matrix turnover, growth factors, inflammation, and oxidative stress, leading decrease in cell density and retinal damage in the first group. Modulation of gene changes was observed when the LED light of screens was modified with an optical filter. (4) Conclusions: The use of short-wavelength selective filters on the screens contribute to reduce LED light-induced damage in the rat retina.

Effects of water-filtered infrared A and visible light (wIRA/VIS) radiation on heat- and stress-responsive proteins in the retina and cornea of guinea pigs.

Water-filtered infrared A and visible light (wIRA/VIS), shown to reduce chlamydial infections in vitro and in vivo, might represent an innovative therapeutic approach against trachoma, a neglected tropical disease caused by ocular infection with the bacterium C. trachomatis. In this in vivo study, we assessed the impact of wIRA radiation in combination with VIS (wavelength range 595-1400 nm, intensity 2100 W/m2) on the retina and cornea in a guinea pig animal model of inclusion conjunctivitis. We investigated the effects 19 days after wIRA/VIS irradiation by comparing a single and double wIRA/VIS treatment with a sham control. By immunolabeling and western blot analyses of critical heat- and stress-responsive proteins, we could not detect wIRA/VIS-induced changes in their expression pattern. Also, immunolabeling of specific retinal marker proteins revealed no changes in their expression pattern caused by the treatment. Our preclinical study suggests wIRA/VIS as a promising and safe therapeutic tool to treat ocular chlamydial infections.

Green Light-Triggered Intraocular Drug Release for Intravenous Chemotherapy of Retinoblastoma.

Retinoblastoma is one of the most severe ocular diseases, of which current chemotherapy is limited to the repetitive intravitreal injections of chemotherapeutics. Systemic drug administration is a less invasive route; however, it is also less efficient for ocular drug delivery because of the existence of blood-retinal barrier and systemic side effects. Here, a photoresponsive drug release system is reported, which is self-assembled from photocleavable trigonal small molecules, to achieve light-triggered intraocular drug accumulation. After intravenous injection of drug-loaded nanocarriers, green light can trigger the disassembly of the nanocarriers in retinal blood vessels, which leads to intraocular drug release and accumulation to suppress retinoblastoma growth. This proof-of-concept study would advance the development of light-triggered drug release systems for the intravenous treatment of eye diseases.

NF1 mutation drives neuronal activity-dependent initiation of optic glioma.

Neurons have recently emerged as essential cellular constituents of the tumour microenvironment, and their activity has been shown to increase the growth of a diverse number of solid tumours1. Although the role of neurons in tumour progression has previously been demonstrated2, the importance of neuronal activity to tumour initiation is less clear-particularly in the setting of cancer predisposition syndromes. Fifteen per cent of individuals with the neurofibromatosis 1 (NF1) cancer predisposition syndrome (in which tumours arise in close association with nerves) develop low-grade neoplasms of the optic pathway (known as optic pathway gliomas (OPGs)) during early childhood3,4, raising  the possibility that postnatal light-induced activity of the optic nerve drives tumour initiation. Here we use an authenticated mouse model of OPG driven by mutations in the neurofibromatosis 1 tumour suppressor gene (Nf1)5 to demonstrate that stimulation of optic nerve activity increases optic glioma growth, and that decreasing visual experience via light deprivation prevents tumour formation and maintenance. We show that the initiation of Nf1-driven OPGs (Nf1-OPGs) depends on visual experience during a developmental period in which Nf1-mutant mice are susceptible to tumorigenesis. Germline Nf1 mutation in retinal neurons results in aberrantly increased shedding of neuroligin 3 (NLGN3) within the optic nerve in response to retinal neuronal activity. Moreover, genetic Nlgn3 loss or pharmacological inhibition of NLGN3 shedding blocks the formation and progression of Nf1-OPGs. Collectively, our studies establish an obligate role for neuronal activity in the development of some types of brain tumours, elucidate a therapeutic strategy to reduce OPG incidence or mitigate tumour progression, and underscore the role of Nf1mutation-mediated dysregulation of neuronal signalling pathways in mouse models of the NF1 cancer predisposition syndrome.

Expression patterns of iron regulatory proteins after intense light exposure in a cone-dominated retina.

Iron is implicated in ocular diseases such as in age-related macular degeneration. Light is also considered as a pathological factor in this disease. Earlier, two studies reported the influence of constant light environment on the pattern of expressions of iron-handling proteins. Here, we aimed to see the influence of light in 12-h light-12-h dark (12L:12D) cycles on the expression of iron-handling proteins in chick retina. Chicks were exposed to 400 lx (control) and 5000 lx (experimental) light at 12L:12D cycles and sacrificed at variable timepoints. Retinal ferrous ion (Fe2+) level, ultrastructural changes, lipid peroxidation level, immunolocalization and expression patterns of iron-handling proteins were analysed after light exposure. Both total Fe2+ level (p = 0.0004) and lipid peroxidation (p = 0.002) significantly increased at 12-, 48- and 168-h timepoint (for Fe2+) and 48- and 168-h timepoint (for lipid peroxidation), and there were degenerative retinal changes after 168 h of light exposure. Intense light exposure led to an increase in the levels of transferrin and transferrin receptor-1 (at 168-h) and ferroportin-1, whereas the levels of ferritins, hephaestin, (at 24-, 48- and 168-h timepoint) and ceruloplasmin (at 168-h timepoint) were decreased. These changes in iron-handling proteins after light exposure are likely due to a disturbance in the iron storage pool evident from decreased ferritin levels, which would result in increased intracellular Fe2+ levels. To counteract this, Fe2+ is released into the extracellular space, an observation supported by increased expression of ferroportin-1. Ceruloplasmin was able to convert Fe2+ into Fe3+ until 48 h of light exposure, but its decreased expression with time (at 168-h timepoint) resulted in increased extracellular Fe2+ that might have caused oxidative stress and retinal cell damage.

Ocular growth and metabolomics are dependent upon the spectral content of ambient white light.

Myopia results from an excessive axial growth of the eye, causing abnormal projection of remote images in front of the retina. Without adequate interventions, myopia is forecasted to affect 50% of the world population by 2050. Exposure to outdoor light plays a critical role in preventing myopia in children, possibly through the brightness and blue-shifted spectral composition of sunlight, which lacks in artificial indoor lighting. Here, we evaluated the impact of moderate levels of ambient standard white (SW: 233.1 lux, 3900 K) and blue-enriched white (BEW: 223.8 lux, 9700 K) lights on ocular growth and metabolomics in a chicken-model of form-deprivation myopia. Compared to SW light, BEW light decreased aberrant ocular axial elongation and accelerated recovery from form-deprivation. Furthermore, the metabolomic profiles in the vitreous and retinas of recovering form-deprived eyes were distinct from control eyes and were dependent on the spectral content of ambient light. For instance, exposure to BEW light was associated with deep lipid remodeling and metabolic changes related to energy production, cell proliferation, collagen turnover and nitric oxide metabolism. This study provides new insight on light-dependent modulations in ocular growth and metabolomics. If replicable in humans, our findings open new potential avenues for spectrally-tailored light-therapy strategies for myopia.

Different Doses of ß-Cryptoxanthin May Secure the Retina from Photooxidative Injury Resulted from Common LED Sources.

Retinal damage associated with loss of photoreceptors is a hallmark of eye diseases such as age-related macular degeneration (AMD) and diabetic retinopathy. Potent nutritional antioxidants were previously shown to abate the degenerative process in AMD. ß-Cryptoxanthin (BCX) is an essential dietary carotenoid with antioxidant, anti-inflammatory, and provitamin A activity. It is a potential candidate for developing intervention strategies to delay the development/progression of AMD. In the current study, the effect of a novel, highly purified BCX oral formulation on the rat retinal damage model was evaluated. Rats were fed with BCX for four weeks at the doses of 2 and 4 mg/kg body weight in the form of highly bioavailable oil suspension, followed by retinal damage by exposing to the bright light-emitting diode (LED) light (750 lux) for 48 hrs. Animals were sacrificed after 48 hours, and eyes and blood samples were collected and analyzed. BCX supplementations (2 and 4 mg/kg) showed improvements in the visual condition as demonstrated by histopathology of the retina and measured parameters such as total retinal thickness and outer nuclear layer thickness. BCX supplementation helped reduce the burden of oxidative stress as seen by decreased serum and retinal tissue levels of malondialdehyde (MDA) and restored the antioxidant enzyme activities in BCX groups. Further, BCX supplementation modulated inflammatory markers (IL-1ß, IL-6, and NF-κB), apoptotic proteins (Bax, Bcl-2, caspase 3), growth proteins and factors (GAP43, VEGF), glial and neuronal proteins (GFAP, NCAM), and heme oxygenase-1 (HO-1), along with the mitochondrial stress markers (ATF4, ATF6, Grp78, Grp94) in the rat retinal tissue. This study indicates that oral supplementation of BCX exerts a protective effect on light-induced retinal damage in the rats via reducing oxidative stress and inflammation, also protected against mitochondrial DNA damage and cellular death.

Differential Action of Connexin Hemichannel and Pannexin Channel Therapeutics for Potential Treatment of Retinal Diseases.

Dysregulation of retinal function in the early stages of light-induced retinal degeneration involves pannexins and connexins. These two types of proteins may contribute to channels that release ATP, leading to activation of the inflammasome pathway, spread of inflammation and retinal dysfunction. However, the effect of pannexin channel block alone or block of both pannexin channels and connexin hemichannels in parallel on retinal activity in vivo is unknown. In this study, the pannexin channel blocker probenecid and the connexin hemichannel blocker tonabersat were used in the light-damaged rat retina. Retinal function was evaluated using electroretinography (ERG), retinal structure was analyzed using optical coherence tomography (OCT) imaging and the tissue response to light-induced injury was assessed immunohistochemically with antibodies against glial fibrillary acidic protein (GFAP), Ionized calcium binding adaptor molecule 1 (Iba-1) and Connexin43 (Cx43). Probenecid did not further enhance the therapeutic effect of connexin hemichannel block in this model, but on its own improved activity of certain inner retina neurons. The therapeutic benefit of blocking connexin hemichannels was further evaluated by comparing these data against results from our previously published studies that also used the light-damaged rat retina model. The analysis showed that treatment with tonabersat alone was better than probenecid alone at restoring retinal function in the light-damaged retina model. The results assist in the interpretation of the differential action of connexin hemichannel and pannexin channel therapeutics for potential treatment of retinal diseases.

Photoperiodic regulation of dopamine signaling regulates seasonal changes in retinal photosensitivity in mice.

At high latitudes, approximately 10% of people suffer from depression during the winter season, a phenomenon known as seasonal affective disorder (SAD). Shortened photoperiod and/or light intensity during winter season are risk factors for SAD, and bright light therapy is an effective treatment. Interestingly, reduced retinal photosensitivity along with the mood is observed in SAD patients in winter. However, the molecular basis underlying seasonal changes in retinal photosensitivity remains unclear, and pharmacological intervention is required. Here we show photoperiodic regulation of dopamine signaling and improvement of short day-attenuated photosensitivity by its pharmacological intervention in mice. Electroretinograms revealed dynamic seasonal changes in retinal photosensitivity. Transcriptome analysis identified short day-mediated suppression of the Th gene, which encodes tyrosine hydroxylase, a rate-limiting enzyme for dopamine biosynthesis. Furthermore, pharmacological intervention in dopamine signaling through activation of the cAMP signaling pathway rescued short day-attenuated photosensitivity, whereas dopamine receptor antagonists decreased photosensitivity under long-day conditions. Our results reveal molecular basis of seasonal changes in retinal photosensitivity in mammals. In addition, our findings provide important insights into the pathogenesis of SAD and offer potential therapeutic interventions.

A genome-wide microRNA screen identifies the microRNA-183/96/182 cluster as a modulator of circadian rhythms.

The regulatory mechanisms of circadian rhythms have been studied primarily at the level of the transcription-translation feedback loops of protein-coding genes. Regulatory modules involving noncoding RNAs are less thoroughly understood. In particular, emerging evidence has revealed the important role of microRNAs (miRNAs) in maintaining the robustness of the circadian system. To identify miRNAs that have the potential to modulate circadian rhythms, we conducted a genome-wide miRNA screen using U2OS luciferase reporter cells. Among 989 miRNAs in the library, 120 changed the period length in a dose-dependent manner. We further validated the circadian regulatory function of an miRNA cluster, miR-183/96/182, both in vitro and in vivo. We found that all three members of this miRNA cluster can modulate circadian rhythms. Particularly, miR-96 directly targeted a core circadian clock gene, PER2. The knockout of the miR-183/96/182 cluster in mice showed tissue-specific effects on circadian parameters and altered circadian rhythms at the behavioral level. This study identified a large number of miRNAs, including the miR-183/96/182 cluster, as circadian modulators. We provide a resource for further understanding the role of miRNAs in the circadian network and highlight the importance of miRNAs as a genome-wide layer of circadian clock regulation.

Ionising radiation causes vision impairment in neonatal B6C3F1 mice.

Ionising radiation interacts with lenses and retinae differently. In human lenses, posterior subcapsular cataracts are the predominant observation, whereas retinae of adults are comparably resistant to even relatively high doses. In this study, we demonstrate the effects of 2 Gy of low linear energy transfer ionising radiation on eyes of B6C3F1 mice aged postnatal day 2. Optical coherence tomography and Scheimpflug imaging were utilised for the first time to monitor murine lenses and retinae in vivo. The visual acuity of the mice was determined and histological analysis was conducted. Our results demonstrated that visual acuity was reduced by as much as 50 % approximately 9 months after irradiation in irradiated mice. Vision impairment was caused by retinal atrophy and inner cortical cataracts. These results help to further our understanding of the risk of ionising radiation for human foeti (∼ 8 mo), which follow the same eye development stages as neonatal mice.

Evaluation of Potential Optical Radiation Hazards from LED Flashlights.

We performed optical radiation safety evaluations of LED flashlights to determine if they pose potential ocular hazards. Six commercially available flashlight samples were randomly selected from various vendors online. They were evaluated in accordance with specifications provided in the American National Standards Institute/Illuminating Engineering Society of North America (ANSI/IESNA) Standards RP 27.1 and RP 27.3. Four of the flashlights were found to have relatively high blue-light-weighted radiance values with short times (40 to 50 s) to reach the exposure limit specified in RP 27.1. These flashlights are in Risk Group 2 and present a moderate risk for retinal damage. Two of the flashlights are in Risk Group 1 and present a low risk for retinal damage. None of the flashlights present an ultraviolet (UV) radiation hazard or a retinal thermal hazard. Cautionary labeling on the packaging as required by RP 27.3 and on the flashlight handle is recommended for flashlights and on other handheld light sources that are in Risk Group 2 or Risk Group 3.

Ablation of C3 modulates macrophage reactivity in the outer retina during photo-oxidative damage.

Purpose: Dysregulation of the complement cascade contributes to a variety of retinal dystrophies, including age-related macular degeneration (AMD). The central component of complement, C3, is expressed in abundance by macrophages in the outer retina, and its ablation suppresses photoreceptor death in experimental photo-oxidative damage. Whether this also influences macrophage reactivity in this model system, however, is unknown. We investigate the effect of C3 ablation on macrophage activity and phagocytosis by outer retinal macrophages during photo-oxidative damage. Methods: Age-matched C3 knockout (KO) mice and wild-type (WT) C57/Bl6 mice were subjected to photo-oxidative damage. Measurements of the outer nuclear layer (ONL) thickness and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were used to assess pathology and photoreceptor apoptosis, respectively. Macrophage abundance and phagocytosis were assessed with immunolabeling for pan-macrophage and phagocytic markers, in conjunction with TUNEL staining in cohorts of C3 KO and WT mice. Results: The C3 KO mice exhibited protection against photoreceptor cell death following photo-oxidative damage, which was associated with a reduction in immunoreactivity for the stress-related factor GFAP. In conjunction, there was a reduction in IBA1-positive macrophages in the outer retina compared to the WT mice and a decrease in the number of CD68-positive cells in the outer nuclear layer and the subretinal space. In addition, the engulfment of TUNEL-positive and -negative photoreceptors by macrophages was significantly lower in the C3 KO mice cohort following photo-oxidative damage compared to the WT cohort. Conclusions: The results show that the absence of C3 mitigates the phagocytosis of photoreceptors by macrophages in the outer retina, and the net impact of C3 depletion is neuroprotective in the context of photo-oxidative damage. These data improve our understanding of the impact of C3 inhibition in subretinal inflammation and inform the development of treatments for targeting complement activation in diseases such as AMD.