3D artificial sebocyte glands from inertial focusing effect for facile and flexible analysis of light damage and drug screening

The sebaceous gland is a neuro-immuno-endocrine organ responsible for maintaining regular skin functions. Overdose exposure of UV and visible light (e.g., blue light) can cause sebocyte gland function disorders or even different diseases (e.g., chronic actinic dermatitis). Studying the mechanism of light-induced damage in sebaceous glands has been challenging, since ex vivo culture of sebaceous glands is difficult due to its short life in culture medium. To address this issue, a versatile 3D artificial sebocyte gland model was established using the inertial focusing effect for studying the impact of light damage and screening potential drugs. The artificial sebocyte gland exhibited specific biological function and structure similar to natural sebocyte glands. Using this artificial sebocyte gland, the interactions between the artificial organ and blue light or UV were studied. The results indicated that UV and blue light upregulated lipid secretion and downregulated cell viability within the sebocytes. Light damage intensified oxidative stress and promoted pro-inflammation cytokines (i.e., IL-1β and TNF-α) production in the artificial sebocytes. Additionally, the therapeutic effects of cannabidiol, a clinically tested drug for treating acne, was also indicated on restoring light damaged sebaceous gland functions. These results indicate that the 3D artificial sebocyte gland could be a versatile, fast, and low-cost platform for skincare studies or drug screening.

The Absence of FAIM Leads to a Delay in Dark Adaptation and Hampers Arrestin-1 Translocation upon Light Reception in the Retina

The short and long isoforms of FAIM (FAIM-S and FAIM-L) hold important functions in the central nervous system, and their expression levels are specifically enriched in the retina. We previously described that Faim knockout (KO) mice present structural and molecular alterations in the retina compatible with a neurodegenerative phenotype. Here, we aimed to study Faim KO retinal functions and molecular mechanisms leading to its alterations. Electroretinographic recordings showed that aged Faim KO mice present functional loss of rod photoreceptor and ganglion cells. Additionally, we found a significant delay in dark adaptation from early adult ages. This functional deficit is exacerbated by luminic stress, which also caused histopathological alterations. Interestingly, Faim KO mice present abnormal Arrestin-1 redistribution upon light reception, and we show that Arrestin-1 is ubiquitinated, a process that is abrogated by either FAIM-S or FAIM-L in vitro. Our results suggest that FAIM assists Arrestin-1 light-dependent translocation by a process that likely involves ubiquitination. In the absence of FAIM, this impairment could be the cause of dark adaptation delay and increased light sensitivity. Multiple retinal diseases are linked to deficits in photoresponse termination, and hence, investigating the role of FAIM could shed light onto the underlying mechanisms of their pathophysiology.

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.

ERG and Behavioral CFF in Light-Damaged Albino Rats

The full-field ERG is useful for index rod- or cone-mediated retinal function in rodent models of retinal degeneration. However, the relationship between the ERG response amplitudes and visually guided behavior, such as flicker detection, is not well understood. A comparison of ERG to behavioral responses in a light-damage model of retinal degeneration allows us to better understand the functional implications of electrophysiological changes. Flicker-ERG and behavioral responses to flicker were used to determine critical flicker frequency (CFF) under scotopic and photopic conditions before and up to 90 d after a 10-day period of low-intensity light damage. Dark- and light-adapted ERG flash responses were significantly reduced after light damage. The a-wave was permanently reduced, while the b-wave amplitude recovered over three weeks after light damage. There was a small, but significant dip in scotopic ERG CFF. Photopic behavioral CFF was slightly lower following light damage. The recovery of the b-wave amplitude and flicker sensitivity demonstrates the plasticity of retinal circuits following photopic injury.

Phototoxicities Caused by Continuous Light Exposure Were Not Induced in Retinal Ganglion Cells Transduced by an Optogenetic Gene

The death of photoreceptor cells is induced by continuous light exposure. However, it is unclear whether light damage was induced in retinal ganglion cells with photosensitivity by transduction of optogenetic genes. In this study, we evaluated the phototoxicities of continuous light exposure on retinal ganglion cells after transduction of the optogenetic gene mVChR1 using an adeno-associated virus vector. Rats were exposed to continuous light for a week, and visually evoked potentials (VEPs) were recorded. The intensities of continuous light (500, 1000, 3000, and 5000 lx) increased substantially after VEP recordings. After the final recording of VEPs, retinal ganglion cells (RGCs) were retrogradely labeled with a fluorescein tracer, FluoroGold, and the number of retinal ganglion cells was counted under a fluorescent microscope. There was no significant reduction in the amplitudes of VEPs and the number of RGCs after exposure to any light intensity. These results indicated that RGCs were photosensitive after the transduction of optogenetic genes and did not induce any phototoxicity by continuous light exposure.

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

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

Ginkgo biloba delays light-induced photoreceptor degeneration through antioxidant and antiapoptotic properties

Intense exposure to artificial bright light increases the risk of retinal damage resulting in blurred vision and blindness. Long-term exposure to bright light elevates oxidative stress-induced apoptosis, which results in photoreceptor cell degeneration. However, to the best of our knowledge, the molecular mechanism associated with light-induced retinopathy remains unclear. In the present study, the mechanisms involved in light-induced oxidative stress and apoptosis were investigated along with the protective effects of Ginkgo biloba (EGb 761) in photoreceptor cell degeneration. EGb 761 was administered to mice at a dose of 50 or 100 mg/kg for 7 days prior to exposure to bright light (5,000 lux for 24 h). Furthermore, photoreceptor cell disorders were evaluated using electroretinogram (ERG) and H&E staining analyses. The expression levels of antioxidant genes and proteins ERK, thioredoxin (Trx) and nuclear factor erythroid 2-related factor 2 (Nrf-2) and the induction of apoptosis cytochrome c (Cyc), cleaved caspase-3 and Bax, were determined by reverse transcription-quantitative PCR and western blotting. ERG and histological analysis revealed that exposure to bright light induced functional and morphological changes to the photoreceptor cells. Exposure to bright light increased the levels of Cyc, cleaved caspase-3 and Bax, and decreased the levels of phosphorylated (p-) Erk, Nrf-2 and thioredoxin (Trx). However, treatment of mice with EGb 761 increased the expression levels of antiapoptotic (Bcl-2) and antioxidant (p-Erk, Trx and Nrf-2) proteins and decreased the expression levels of the apoptotic genes (Cyc, cleaved caspase-3 and Bax). Based on these findings, the present study suggested that prolonged exposure to light induces photoreceptor cell degeneration, where EGb 761 treatment may serve a therapeutic effect on the development of photoreceptor cell degeneration.

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.

Zebrafish Crb1, Localizing Uniquely to the Cell Membranes around Cone Photoreceptor Axonemes, Alleviates Light Damage to Photoreceptors and Modulates Cones' Light Responsiveness

The crumbs (crb) apical polarity genes are essential for the development and functions of epithelia. Adult zebrafish retinal neuroepithelium expresses three crb genes (crb1, crb2a, and crb2b); however, it is unknown whether and how Crb1 differs from other Crb proteins in expression, localization, and functions. Here, we show that, unlike zebrafish Crb2a and Crb2b as well as mammalian Crb1 and Crb2, zebrafish Crb1 does not localize to the subapical regions of photoreceptors and Müller glial cells; rather, it localizes to a small region of cone outer segments: the cell membranes surrounding the axonemes. Moreover, zebrafish Crb1 is not required for retinal morphogenesis and photoreceptor patterning. Interestingly, Crb1 promotes rod survival under strong white light irradiation in a previously unreported non--cell-autonomous fashion; in addition, Crb1 delays UV and blue cones' chromatin condensation caused by UV light irradiation. Finally, Crb1 plays a role in cones' responsiveness to light through an arrestin-translocation-independent mechanism. The localization of Crb1 and its functions do not differ between male and female fish. We conclude that zebrafish Crb1 has diverged from other vertebrate Crb proteins, representing a neofunctionalization in Crb biology during evolution.SIGNIFICANCE STATEMENT Apicobasal polarity of epithelia is an important property that underlies the morphogenesis and functions of epithelial tissues. Epithelial apicobasal polarity is controlled by many polarity genes, including the crb genes. In vertebrates, multiple crb genes have been identified, but the differences in their expression patterns and functions are not fully understood. Here, we report a novel subcellular localization of zebrafish Crb1 in retinal cone photoreceptors and evidence for its new functions in photoreceptor maintenance and light responsiveness. This study expands our understanding of the biology of the crb genes in epithelia, including retinal neuroepithelium.

Establishment and Characterization of a Unilateral UV-Induced Photoreceptor Degeneration Model in the C57Bl/6J Mouse

Purpose

To investigate whether UV irradiation of the mouse eye can induce photoreceptor degeneration, producing a phenotype reminiscent of the rd10 mouse, left eyes of female C57Bl/6J mice were irradiated with a UV LED array (370 nm). A lens was placed between the cornea and LED, allowing illumination of about one-third of the retina. The short-term and long-term effects on the retina were evaluated.

Methods

First, a dose escalation study, in which corneal dosages between 2.8 and 9.3 J/cm² were tested, was performed. A dosage of 7.5 J/cm² was chosen for the following characterization study. Before and after irradiation slit-lamp examinations, full-field electroretinography, spectral domain optical coherence tomography and macroscopy were performed. After different time spans (5 days to 12 weeks) the animals were sacrificed and the retinae used for immunohistochemistry or multielectrode array testing. Right eyes served as untreated controls.

Results

In treated eyes, spectral domain optical coherence tomography revealed a decrease in retinal thickness to 53%. Full-field electroretinography responses decreased significantly from day 5 on in treated eyes. Multielectrode array recordings revealed oscillatory potentials with a mean frequency of 5.2 ± 0.6 Hz in the illuminated area. Structural changes in the retina were observed in immunohistochemical staining.

Conclusions

UV irradiation proved to be efficient in inducing photoreceptor degeneration in the mouse retina, while leaving the other retinal layers largely intact. The irradiated area of treated eyes can be identified easily in spectral domain optical coherence tomography and in explanted retinae.

Translational Relevance

This study provides information on anatomic and functional changes in UV-treated retina, enabling the use of this model for retinitis pigmentosa-like diseases in animals suited for experimental retinal surgery.

Nanoceria Particles Are an Eligible Candidate to Prevent Age-Related Macular Degeneration by Inhibiting Retinal Pigment Epithelium Cell Death and Autophagy Alterations

Retinal pigment epithelium (RPE) dysfunction and degeneration underlie the development of age-related macular degeneration (AMD), which is the leading cause of blindness worldwide. In this study, we investigated whether cerium oxide nanoparticles (CeO₂-NPs or nanoceria), which are anti-oxidant agents with auto-regenerative properties, are able to preserve the RPE. On ARPE-19 cells, we found that CeO₂-NPs promoted cell viability against H₂O₂-induced cellular damage. For the in vivo studies, we used a rat model of acute light damage (LD), which mimics many features of AMD. CeO₂-NPs intravitreally injected three days before LD prevented RPE cell death and degeneration and nanoceria labelled with fluorescein were found localized in the cytoplasm of RPE cells. CeO₂-NPs inhibited epithelial-mesenchymal transition of RPE cells and modulated autophagy by the down-regulation of LC3B-II and p62. Moreover, the treatment inhibited nuclear localization of LC3B. Taken together, our study demonstrates that CeO₂-NPs represent an eligible candidate to counteract RPE degeneration and, therefore, a powerful therapy for AMD.

Suppression of Light-Induced Retinal Degeneration by Quercetin via the AP-1 Pathway in Rats

We examined the cytoprotective effect of quercetin via activator protein (AP-1) and the heat shock protein 70 (Hsp70) pathway against light-induced retinal degeneration in rats. Quercetin was administered intraperitoneally to Sprague-Dawley rats for seven days before light exposure to intense white fluorescent light (3000 lux) for 24 h. Light-induced retinal damage was determined by the number of rows of photoreceptor cell nuclei, the microstructures of the rod outer segments and retinal pigment epithelium, and terminal deoxynucleotidyl transferase (TdT)-mediated 2′-Deoxyuridine-5′-triphosphate (dUTP) nick end labeling. To elucidate the cytoprotective mechanism of quercetin, expression levels were measured in the rat retinas of 8-hydroxy-deoxyguanosine (8-OHdG), a marker of oxidative stress; Hsp70; and transcription factor AP-1 transcription activity. Pretreatment with quercetin inhibited light-induced photoreceptor cellular apoptosis and subsequent retinal degeneration in rats. 8-OHdG and Hsp70 protein expressions were up-regulated markedly by light exposure and suppressed by quercetin pretreatment. The results of an electrophoretic mobility shift assay showed that AP-1-binding activity was activated by light exposure, and binding of c-Fos and c-Jun, but not JunB, mediated the binding activity. Intraperitoneal administration of quercetin decreases photooxidative damage in the retina and mediates cytoprotection against light-induced photoreceptor cell degeneration in rats. Suppression of the heterodimeric combination of c-Jun and c-Fos proteins at the AP-1 binding site is highly involved in quercetin-mediated cytoprotection.

Selective S Cone Damage and Retinal Remodeling Following Intense Ultrashort Pulse Laser Exposures in the Near-Infrared

Purpose

Infrared ultrashort pulse lasers are becoming increasingly popular for applications in the living eye. However, safety standards are not yet well established. Here we investigate retinal damage close to threshold for this pulse regime in the living macaque eye.

Methods

Retinal radiant exposures between 214 and 856 J/cm2 were delivered to the photoreceptor layer with an ultrashort pulse laser (730 nm, 55 fs, 80 MHz) through a two-photon adaptive optics scanning light ophthalmoscope. Retinal exposures were followed up immediately after and over several weeks with high-resolution reflectance and two-photon excited fluorescence ophthalmoscopy, providing structural and functional information.

Results

Retinal radiant exposures of 856 J/cm2 resulted in permanent S cone damage. Immediately after the exposure, the affected cones emitted about 2.6 times less two-photon excited fluorescence (TPEF) and showed an altered TPEF time course. Several weeks after the initial exposure, S cone outer and inner segments had disappeared. The space was filled by rods in the peripheral retina and cones near the fovea.

Conclusion

Interestingly, S cones are the receptor class with the lowest sensitivity in the near-infrared but are known to be particularly susceptible to ultraviolet and blue light. This effect of selective S cone damage after intense infrared ultrashort pulse laser exposure may be due to nonlinear absorption and distinct from pure thermal and mechanical mechanisms often associated with ultrashort pulse lasers.

Protective effects of autophagy against blue light-induced retinal degeneration in aged mice

The aim of this study was to explore the role of autophagy in response to blue light damage in aged mice and in human retinal pigmented epithelium (hRPE) cells. Blue light damage to the retina was induced in 10-month-old (10 mo) C57 mice and hRPE cells. Flash electroretinography was used to assess retinal function. Retinal structure changes were observed by electron microscopy. Western blot was conducted to determine the expression levels of the following proteins: cleaved caspase-3, p38 mitogen-activated protein kinases, protein kinase R-like endoplasmic reticulum kinase (PERK), autophagy marker light chain 3 (LC3), P62, and Beclin-1. On day 1 after light damage to the 10 mo mice, retinal function was changed. The latent periods of a-wave and b-wave were delayed, and amplitude was reduced. The electron microscopy results revealed mitochondria damage in the retinal pigmented epithelium and a disorganized photoreceptor outer segment (OS). PERK, LC3, and Beclin-1 were upregulated, whereas P62 was not. On day 5 after the blue light damage, restoration of electroretinography and OS was observed. PERK, LC3, and Beclin-1 were downregulated, whereas P62 was not. Protein changes in vitro were consistent with in vivo. The present study provided structural and functional evidence that autophagy plays an important role in the response to blue lightinduced retinal damage.

Macular phototoxicity after corneal cross-linking

Purpose

To assess potential vascular, structural, and functional changes to the macula in patients with keratoconus that underwent ultraviolet A (UVA)–riboflavin-mediated corneal collagen cross-linking (CXL) therapy.

Patients and methods

Seventeen eyes from 17 patients of age 16 years or older with keratoconus undergoing CXL treatment were studied. The same eye served as its own control (before CXL vs after CXL). Eyes were evaluated in terms of best-corrected visual acuity (BCVA), refractive error, intraocular pressure, Amsler grid, retinography, fluorescein angiography, autofluorescence, and spectral domain optical coherence tomography (SD-OCT) prior to CXL and 7 and 30 days after treatment. Multifocal electroretinography (mfERG) was recorded prior to and 7 days after CXL.

Results

Mean (SD) BCVA by logMAR chart was 0.47 (±0.12) pre-CXL, 0.55 (±0.15) 7 days post-CXL (P=0.57), and 0.46 (±0.10) 30 days post-CXL (P=0.87). Mean (SD) SD-OCT central macular thickness (µm) was 253.62 (±20.9) pre-CXL, 260.5 (±18.7) 7 days post-CXL (P=0.48), and 256.44 (±21.6) 30 days post-CXL (P=0.69). In 12 eyes, mfERG revealed a statistically significant increase (P=0.0353) in P1 latency (ms) of ring four from the pre-CXL period (39.45±2.05) to 7 days post-CXL (41.04±1.28) period. Regression analysis showed that the increase in P1 latency was correlated with the increase in central macular thickness (P=0.027). Furthermore, nine patients experienced a significant decrease in P1 amplitudes of rings 1 (P=0.0014), 2 (P=0.0029), 3 (P=0.0037), 4 (P=0.0014), and 5 (P=0.0012) from pre-CXL to 7 days post-CXL. Conclusion: In this pilot study, most of the patients exhibited slight changes in their mfERG parameters and OCT thickness, despite a lack of vascular abnormalities observed on fluorescein angiography/autofluorescence imaging, no alteration in BCVA, and no reports of symptoms. These changes could, therefore, be categorized as a mild subclinical effect of the corneal cross-linking procedure.

Lutein and Zeaxanthin Isomers Protect against Light-Induced Retinopathy via Decreasing Oxidative and Endoplasmic Reticulum Stress in BALB/cJ Mice

Oxidative stress (OS) and endoplasmic reticulum stress (ERS) are the major factors underlying photoreceptor degeneration. Lutein, RR-zeaxanthin (3R,3’R-zeaxanthin) and RS (meso)-zeaxanthin (3R,3’S-RS- zeaxanthin) (L/Zi) could protect against cell damage by ameliorating OS in retina. In this study, we examined the effect of L/Zi supplementation in a mouse model of photoreceptor degeneration and investigated whether the treatment of L/Zi ameliorated OS and ERS. BALB/cJ mice after light exposure were used as the animal model. The protective effects of L/Zi were observed by electroretinography (ERG) and terminal deoxyuridine triphosphate nick-end labeling (TUNEL) analysis. The underlying mechanisms related to OS and ERS were explored by Western blotting. After L/Zi treatment, the ERG amplitudes were significantly higher, and the number of TUNEL-positive cells was significantly reduced compared to that of the vehicle group. Western blotting results revealed that OS was ameliorated according to the significant downregulation of phosphorylated c-Jun N-terminal kinase (p-JNK), and significant upregulation of nuclear factor erythroid 2-related factor 2 (Nrf2). In addition, ERS was reduced according to the significant downregulation of 78 kDa glucose-regulated protein (GRP78), phosphorylated protein kinase RNA-like endoplasmic reticulum kinase (p-PERK), activating transcription factor 4 (ATF4) and activating transcription factor (ATF6). Our data shows that L/Zi provided functional and morphological preservation of photoreceptors against light damage, which is probably related to its mitigation of oxidative and endoplasmic reticulum stress.

Protective role of carotenoids in the visual cycle

Exposure to light and accumulation of aberrant visual cycle by-products causes stress in the retina. The physical and chemical properties of carotenoids may provide protection against such scenario. These pigments exist in retinas of many vertebrates, including humans. However, the absence of carotenoids in mice, the preferred ophthalmologic animal model, hindered molecular and biochemical examination of the pigments' role in vision. We established a mouse model that accumulates significant amounts of carotenoids in the retina due to inactivating mutations in the Isx and Bco2 genes. We introduced a robust light damage protocol for the mouse retina using green (532 nm) and blue (405 nm) low-energy lasers. We observed that blue but not green laser light treatment triggered the formation of aberrant retinaldehyde isomers in the retina. The production of these visual cycle by-products was accompanied by morphologic damage in inferior parts of the mouse retina. Zeaxanthin supplementation of mice shielded retinoids from these photochemical modifications. These pigments also reduced the extent of the damage to the retina after the blue laser light insult. Thus, our study discovered a novel role of carotenoids in the visual cycle and indicated that vertebrates accumulate carotenoids to shield photoreceptors from short-wavelength light-induced damage.-Widjaja-Adhi, M. A. K., Ramkumar, S., von Lintig, J. Protective role of carotenoids in the visual cycle.

Transplanted olfactory ensheathing cells restore retinal function in a rat model of light-induced retinal damage by inhibiting oxidative stress

There is still not an effective treatment for continuous retinal light exposure and subsequent photoreceptor degeneration. Olfactory ensheathing cell (OEC) transplantation has been shown to be neuroprotective in spinal cord, and optic nerve injury and retinitis pigmentosa. However, whether OECs protect rat photoreceptors against light-induced damage and how this may work is unclear. Thus, to elucidate this mechanism, purified rat OECs were grafted into the subretinal space of a Long-Evans rat model with light-induced photoreceptor damage. Light exposure decreased a- and b- wave amplitudes and outer nuclear layer (ONL) thickness, whereas the ONL of rats exposed to light for 24 h after having received OEC transplants in their subretinal space was thicker than the PBS control and untreated groups. A- and b- wave amplitudes from electroretinogram of OEC-transplanted rats were maintained until 8 weeks post OEC transplantation. Also, transplanted OECs inhibited formation of reactive oxygen species in retinas exposed to light. In vitro experiments showed that OECs had more total antioxidant capacity in a co-cultured 661W photoreceptor cell line, and cells were protected from damage induced by hydrogen-peroxide. Thus, transplanted OECs preserved retinal structure and function in a rat model of light-induced degeneration by suppressing retinal oxidative stress reactions.

Protective effect of resveratrol against light-induced retinal degeneration in aged SAMP8 mice

Purpose

The purpose of this study was to determine the protective effects of Resveratrol (RESV) on acute bright light-induced retinal degeneration in aged senescence accelerated mouse strain.

Methods

Ten three-month-old male SAMP8 mice (prone to aging) were randomly assigned to two experimental dietary groups: one untreated group and one RESV treatment group (n=20 eyes for each group). After 30 days of treatment, mice were exposed to intense bright light. Ten male SAMR1 mice (resistant to aging) served as control (n=20 eyes). The protective effects of RESV administration on light-induced retinal degeneration in SAMP8 strain as well as the effect of bright light damage in the retinas of SAMP8 mice were analyzed by electroretinography (ERG), retinal histology, mRNA, protein and lipid profile.

Results

68%-85% of a-wave amplitude and 72%-92% of b-wave amplitude were persevered by RESV in SAMP8 mice that were exposed to light damage. Also, RESV preserved their photoreceptor nuclei. mRNA expression of neuroprotective factors leukemia inhibitory factor (LIF), brain derived neurotrophic factor (BDNF), oncostatin M (OSM), cardiotrophin 1(CT-1) and cardiotrophin-like cytokine (CLC) were up-regulated 28, 8, 7, 5 and 9-fold in SAMP8 mice after RESV treatment. In addition, RESV could suppress the NF-κB pathway by down-regulating the expression of pIκB. Light damage led to increase of saturated FA, monoenoic FA, n6 PUFA and n6/n3 ratio and decrease of Docosahexaenoic acid (DHA). There was no significant difference on DHA and the ratio of n6/n3-FA between the untreated and RESV treated SAMP8 mice.

Conclusions

Collectively, our study provides evidence that RESV prevents light-induced retinal damage associated with aging.

Light Modulates Ocular Complications in an Albino Rat Model of Type 1 Diabetes Mellitus

PURPOSE

The purpose of the study was to assess potential interactions of light exposure and hyperglycemia upon ocular complications in diabetic rats.

METHODS

Streptozotocin-induced (STZ-induced) diabetic rats (N = 39) and non-diabetic rats (N = 9) were distributed into eight groups according to the irradiance and color of the light phase during the 12/12-hour light/dark regime. Follow-up lasted 90 days and included assessment of cataract development and electroretinogram (ERG) recordings. Stress to the retina was also assessed by glial fibrillary acidic protein immunocytochemistry.

RESULTS

Cataract development was fast in diabetic rats that were exposed to unattenuated white light or to bright colored lights during the light phase. Diabetic rats that were kept under attenuated brown or yellow light during the light phase exhibited slower rate of cataract development. Electroretinogram responses indicated very severe retinal damage in diabetic rats kept under bright colored lights in the blue-yellow range or bright white light during the light phase. Electroretinogram damage was milder in rats kept under bright red light or attenuated yellow or brown light during the light phase. Glial fibrillary acidic protein expression in retinal Müller cells was consistent with ERG assessment of retinal damage.

CONCLUSIONS

Attenuating white light and filtering out short wavelengths have a protective effect on the eyes of diabetic rats as evident by slower rate of cataract formation and a smaller degree of retinal damage.

TRANSLATIONAL RELEVANCE

Our findings suggest that special glasses attenuating light exposure and filtering out short wavelengths (400-530 nm) may be beneficial for diabetic patients.

AAV-Nrf2 Promotes Protection and Recovery in Animal Models of Oxidative Stress

NRF2 is a transcription factor that drives antioxidant gene expression in multiple organ systems. We hypothesized that Nrf2 overexpression could be therapeutically applied toward diseases in which redox homeostasis is disrupted. In this study, adeno-associated virus (AAV)-Nrf2 was tested in a mouse model of acute acetaminophen-induced liver toxicity and successfully conferred protection from hepatotoxicity, validating the vector design and early onset of NRF2-mediated protection. Furthermore, therapeutic potential of AAV-Nrf2 in chronic disease also was tested in a light-induced mouse model of age-related macular degeneration. Adult BALB/c mice were intravitreally injected with AAV-Nrf2 and subject to light damage following injection. Retinal thickness and function were monitored following light damage using optical coherence tomography and electroretinography, respectively. By 3 months post-damage, injected eyes had greater retinal thickness compared to uninjected controls. At 1 month post-damage, AAV-Nrf2 injection facilitated full functional recovery from light damage. Our results suggest a therapeutic potential for Nrf2 overexpression in acute and long-term capacities in multiple organ systems, opening up doors for combination gene therapy where replacement gene therapy requires additional therapeutic support to prevent further degeneration.

CCR3 Is Associated with the Death of a Photoreceptor Cell-line Induced by Light Exposure

The C-C chemokine receptor type 3 (CCR3) is the receptor for eotaxins (CCL-11, 24, 26), RANTES (CCL-5) and MCP-3 (CCL-7). It was reported that an inhibition of CCR3 by antagonists or antibodies reduces the degree of laser-induced choroidal neovascularization in mice, a model for wet age-related macular degeneration (AMD). Although several chemokine receptors have the potential of reducing the degree of the chronic inflammation in experimental dry AMD, the association of CCR3 remains unknown. The purpose of this study was to determine the role played by CCR3 in the death of 661W cells which are cells of a murine photoreceptor-derived cell line as an in vitro model of dry AMD. The expression of CCR3 was increased in the 661W cells after light exposure. Inhibition of CCR3 reduced the rate of cell death induced by light exposure. A blockade of CCR3 signaling by CCR3 silencing and two kinds of CCR3 antagonists, SB 328437 and SB 297006, reduced the rate of light-induced cell death. In addition, CCR3 inhibition decreased the level of reactive oxygen species and the activation of caspase-3/7 induced by light exposure. These findings indicated that the CCR3 blockade should be considered for the treatment of the dry AMD.

Identification of miRNAs in a Model of Retinal Degenerations

PURPOSE

We investigated the expression profile of and identify all microRNAs (miRNAs) that potentially regulate inflammation in a light-induced model of focal retinal degeneration.

METHODS

Sprague Dawley (SD) rats aged 90 to 140 postnatal days were exposed to 1000 lux white fluorescent light for 24 hours. At 24 hours, and 3 and 7 days after exposure, the animals were euthanized and retinas processed for RNA. Expression of 750 miRNAs at 24 hours of exposure was assessed using low density array analysis. Significantly modulated miRNAs and their target mRNAs were used to assess the potential biological effects. Expression of seven miRNAs, potentially modulating inflammation, was investigated across a protracted time course after light exposure using quantitative PCR. Photoreceptor cell death was analyzed using TUNEL.

RESULTS

Intense light exposure for 24 hours led to differential expression of a number of miRNAs, 37 of which were significantly modulated by 2-fold or more. Of those, 19 may potentially regulate the inflammatory immune response observed in the model. MicroRNAs -125-3p, -155, -207, -347, -449a, -351, and -542-3p are all upregulated at 24 hours of exposure along with peak photoreceptor cell death. The MiRNAs -542-3p and -351 reached maximum expression at 7 days after exposure, while -125-3p, -155, -207, -347, and -449 reached a peak expression at 3 days.

CONCLUSIONS

The results of the study show that miRNAs are modulated in response to light damage (LD). These miRNAs potentially regulate the inflammatory immune response, triggered as a result of the acute retinal damage, which is a key mediator of retinal degeneration in this model and age-related macular degeneration.

Rod photopigment kinetics after photodisruption of the retinal pigment epithelium

PURPOSE

Advances in retinal imaging have led to the discovery of long-lasting retinal changes caused by light exposures below published safety limits, including disruption of the RPE. To investigate the functional consequences of RPE disruption, we combined adaptive optics ophthalmoscopy with retinal densitometry.

METHODS

A modified adaptive optics scanning light ophthalmoscope (AOSLO) measured the apparent density and regeneration rate of rhodopsin in two macaques before and after four different 568-nm retinal radiant exposures (RREs; 400-3200 J/cm(2)). Optical coherence tomography (OCT) was used to measure the optical path length through the photoreceptor outer segments before and after RPE disruption.

RESULTS

All tested RREs caused visible RPE disruption. Apparent rhodopsin density was significantly reduced following 1600 (P = 0.01) and 3200 J/cm(2) (P = 0.007) exposures. No significant change in apparent density was observed in response to 800 J/cm(2). Surprisingly, exposure to 400 J/cm(2) showed a significant increase in apparent density (P = 0.047). Rhodopsin recovery rate was not significantly affected by these RREs. Optical coherence tomography measurements showed a significant decrease in the optical path length through the photoreceptor outer segments for RREs above 800 J/cm(2) (P < 0.001).

CONCLUSIONS

At higher RREs, optical path length through the outer segments was reduced. However, the rate of photopigment regeneration was unchanged. While some ambiguity remains as to the correlation between measured reflectivity and absolute rhodopsin density; at the lowest RREs, RPE disruption appears not to be accompanied by a loss of apparent rhodopsin density, which would have been indicative of functional loss.

Systemic administration of the antioxidant/iron chelator α-lipoic acid protects against light-induced photoreceptor degeneration in the mouse retina

PURPOSE

Oxidative stress and inflammation have key roles in the light damage (LD) model of retinal degeneration as well as in age-related macular degeneration (AMD). We sought to determine if lipoic acid (LA), an antioxidant and iron chelator, protects the retina against LD.

METHODS

Balb/c mice were treated with LA or control saline via intraperitoneal injection, and then were placed in constant cool white light-emitting diode (LED) light (10,000 lux) for 4 hours. Retinas were evaluated at several time points after LD. Photoreceptor apoptosis was assessed using the TUNEL assay. Retinal function was analyzed via electroretinography (ERG). Retinal degeneration was assessed after LD by optical coherence tomography (OCT), TUNEL analysis, and histology. The mRNAs of several oxidative stress, inflammation, and iron-related genes were quantified by quantitative PCR (qPCR).

RESULTS

The LD resulted in substantial photoreceptor-specific cell death. Dosing with LA protected photoreceptors, decreasing the numbers of TUNEL-positive photoreceptors and increasing the number of surviving photoreceptors. The retinal mRNA levels of genes indicating oxidative stress, inflammation, and iron accumulation were lower following LD in mice treated with LA than in control mice. The ERG analysis demonstrated functional protection by LA.

CONCLUSIONS

Systemic LA is protective against light-induced retinal degeneration. Since this agent already has proven protective in other retinal degeneration models, and is safe and protective against diabetic neuropathy in patients, it is worthy of consideration for a human clinical trial against retinal degeneration or AMD.

Long-term reduction in infrared autofluorescence caused by infrared light below the maximum permissible exposure

PURPOSE

Many retinal imaging instruments use infrared wavelengths to reduce the risk of light damage. However, we have discovered that exposure to infrared illumination causes a long-lasting reduction in infrared autofluorescence (IRAF). We have characterized the dependence of this effect on radiant exposure and investigated its origin.

METHODS

A scanning laser ophthalmoscope was used to obtain IRAF images from two macaques before and after exposure to 790-nm light (15-450 J/cm(2)). Exposures were performed with either raster-scanning or uniform illumination. Infrared autofluorescence images also were obtained in two humans exposed to 790-nm light in a separate study. Humans were assessed with direct ophthalmoscopy, Goldmann visual fields, multifocal ERG, and photopic microperimetry to determine whether these measures revealed any effects in the exposed locations.

RESULTS

A significant decrease in IRAF after exposure to infrared light was seen in both monkeys and humans. In monkeys, the magnitude of this reduction increased with retinal radiant exposure. Partial recovery was seen at 1 month, with full recovery within 21 months. Consistent with a photochemical origin, IRAF decreases caused by either raster-scanning or uniform illumination were not significantly different. We were unable to detect any effect of the light exposure with any measure other than IRAF imaging. We cannot exclude the possibility that changes could be detected with more sensitive tests or longer follow-up.

CONCLUSIONS

This long-lasting effect of infrared illumination in both humans and monkeys occurs at exposure levels four to five times below current safety limits. The photochemical basis for this phenomenon remains unknown.

Effect of EGb761 on light-damaged retinal pigment epithelial cells

AIM

To investigate the protective mechanism of Gingko Biloba extract (EGb761) on the ability of retinal pigment epithelial (RPE) cells to resist light-induced damage in a comparative proteomics study.

METHODS

Human RPE cells (ARPE-19) were randomly distributed to one of three groups: normal control (NC group) and light-damaged model without or with EGb761 group (M and ME groups, respectively). The light-damaged model was formed by exposing to white light (2 200±300)lx for 6h. The RPE cells in ME group were conducted with EGb 761 (100µg/mL) before light exposure. The soluble cellular proteins extracting from each groups were separated by two-dimensional electrophoresis and stained by silver staining. Different proteins in the profiles of the gels were analyzed by Image Master Software. Two-fold expressing protein spots were identified by Matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI-TOF/TOF) mass spectrometry.

RESULTS

NC, M and ME groups displayed 1 892±71, 2 145±23 and 2 216±85 protein spots, respectively. We identified 33 proteins with different expression levels between the NC and M groups, 25 proteins between the M and ME groups, and 11 proteins between the NC and ME groups. MALDI-TOF/TOF mass spectrometry successfully identified 16 proteins, including metabolic enzymes, cytoskeletal proteins, anti-oxidation proteins, and others.

CONCLUSION

Differences in some important proteins, such as cathepsin B, heat shock protein, and cytochrome c reductase, indicated that multiple pathways may be induced in light-damaged RPE cells and the protective effect of EGb761.

Focal damage to macaque photoreceptors produces persistent visual loss

Insertion of light-gated channels into inner retina neurons restores neural light responses, light evoked potentials, visual optomotor responses and visually-guided maze behavior in mice blinded by retinal degeneration. This method of vision restoration bypasses damaged outer retina, providing stimulation directly to retinal ganglion cells in inner retina. The approach is similar to that of electronic visual protheses, but may offer some advantages, such as avoidance of complex surgery and direct targeting of many thousands of neurons. However, the promise of this technique for restoring human vision remains uncertain because rodent animal models, in which it has been largely developed, are not ideal for evaluating visual perception. On the other hand, psychophysical vision studies in macaque can be used to evaluate different approaches to vision restoration in humans. Furthermore, it has not been possible to test vision restoration in macaques, the optimal model for human-like vision, because there has been no macaque model of outer retina degeneration. In this study, we describe development of a macaque model of photoreceptor degeneration that can in future studies be used to test restoration of perception by visual prostheses. Our results show that perceptual deficits caused by focal light damage are restricted to locations at which photoreceptors are damaged, that optical coherence tomography (OCT) can be used to track such lesions, and that adaptive optics retinal imaging, which we recently used for in vivo recording of ganglion cell function, can be used in future studies to examine these lesions.

Enhancing performance while avoiding damage: a contribution of macular pigment

PURPOSE

To compare action spectra for visual discomfort in the fovea and the parafovea and to determine the effect of macular pigment (MP).

METHODS

Visual discomfort thresholds to lights from 440 to 600 nm were obtained for six young (<35 y), visually normal subjects with a wide range of MP densities (0.10-0.71 at 30' eccentricity). Foveal and parafoveal conditions were assessed. Discomfort thresholds were also obtained for xenon-white light (partially absorbed by MP), and a broadband yellow (outside the absorption band of MP). MP was measured psychophysically using heterochromatic flicker photometry (HFP).

RESULTS

For the parafovea, discomfort sensitivity (1/threshold) increased sharply with decreasing wavelength for all subjects. Commensurate with a subject's MP level, MP significantly reduced visual discomfort to short wavelengths (including xenon-white light) for central viewing.

CONCLUSIONS

MP simultaneously reduces visual discomfort and protects from light damage at short wavelengths. As a result, MP increases the range of safe and comfortable light levels. Because higher light levels enable improved visual sensitivity for fine detail, these findings indicate that the spectral absorption properties and spatial distribution of MP combine to protect the retina while enhancing visual performance. The action spectrum for visual discomfort closely matches the risk for acute light damage to the retinal pigment epithelium, and it is consistent with a major influence from the intrinsically photosensitive retinal ganglion cells containing melanopsin. We suggest that MP interacts with nonimage-forming retinal input to achieve the dual outcomes of visual discomfort reduction and protection from light damage.

The time course of action of two neuroprotectants, dietary saffron and photobiomodulation, assessed in the rat retina

BACKGROUND

Dietary saffron and photobiomodulation (low-level infrared radiation, PBM) are emerging as therapeutically promising protectants for neurodegenerative conditions, such as the retinal dystrophies. In animal models, saffron and PBM, given in limited daily doses, protect retina and brain from toxin- or light-induced stress. This study addresses the rate at which saffron and PBM, given in daily doses, induce neuroprotection, using a light damage model of photoreceptor degeneration in Sprague Dawley (SD) rats.

RESULTS

Rats were raised in dim cyclic (12 h 5 lux, 12 h dark) illumination, treated with saffron or PBM for 2-10 d, and then exposed to bright damaging light (1,000 lux for 24 h). After 1 week survival, the retina was assessed for photoreceptor death (using the TUNEL reaction), for surviving photoreceptor damage (thickness of the outer nuclear layer) and for the expression of a stress-related protein GFAP, using immunohistochemistry. Preconditioning the retina with saffron or PBM reduced photoreceptor death, preserved the population of surviving photoreceptors and reduced the upregulation of GFAP in Müller cells. At the daily dose of saffron used (1 mg/kg), protection was detectable at 2 d, increasing to 10 d. At the daily dose of PBM used (5 J/cm(2) at 670 nm) protection was detectable at 5 d, increasing to 7-10 d.

CONCLUSIONS

The results provide time parameters for exploration of the mechanisms and durability of the protection provided by saffron and PBM.

Entrance pupil size predicts retinal illumination in darkly pigmented eyes, but not lightly pigmented eyes

PURPOSE

We determined the effect of entrance pupil size on retinal illumination. The influence of unilateral miosis on the magnitude of the pupil light reflex was studied to ascertain how a clinically significant anisocoria influences the relative afferent pupil defect (RAPD).

METHODS

Miosis was induced by topical 1% pilocarpine in the right eye of 14 healthy subjects with normal eyes. The interocular difference in retinal illumination was assessed by computerized pupillometry from the stimulus response curve of the right and left eyes. The main outcome measure was the RAPD, determined by computerized pupillography, at baseline and after pilocarpine-induced anisocoria.

RESULTS

Induced anisocoria produced a significant change in RAPD from baseline (mean = 1.60 dB in the miotic eye, P = 0.007). However, anisocoria correlated with RAPD only in subjects with darkly pigmented irides (Pearson correlation coefficient 0.793, P = 0.05).

CONCLUSIONS

In darkly pigmented eyes, entrance pupil size significantly influenced the retinal illumination. However, retinal illumination of lightly pigmented eyes is relatively independent of entrance pupil size, presumably due to extrapupillary transmission of light through the iris and sclera. This has important implications in understanding the potential influence of anisocoria on the RAPD and also greater susceptibility of lightly pigmented eyes to light toxicity.

Disruption of cell-cell junctions and induction of pathological cytokines in the retinal pigment epithelium of light-exposed mice

PURPOSE

To elucidate the influences of light exposure on the retinal pigment epithelium (RPE) in vivo that may be involved in the pathogenesis of AMD.

METHODS

Six- to 7-week-old BALB/c mice were exposed to light at 2000 lux for 3 hours. Flat-mount RPE samples were immunostained with anti-ZO-1 antibody for evaluating tight junction, anti-N-cadherin, and anti-β-catenin antibodies for adherens junction, and stained with phalloidin for actin cytoskeleton. The reactive oxygen species (ROS) level was measured using DCFH-DA; Rho-associated coiled-coil forming kinase (ROCK) activity was by ELISA. Cytokine expression was analyzed by real-time RT-PCR and/or ELISA in the RPE-choroid, and macrophage recruitment was by real-time RT-PCR and immunohistochemistry. Either an antioxidant, N-Acetyl-L-cysteine (NAC), or a ROCK inhibitor, Y-27632, were administered to analyze the roles of ROS and ROCK activation, respectively.

RESULTS

Light exposure disrupted staining patterns of tight junctions, adherens junctions, and actin cytoskeleton in the RPE, where ROS was elevated. However, NAC treatment avoided the RPE changes, reducing ROS. ROCK activity increased after light exposure was suppressed by NAC, and the structural disruptions were suppressed by Y-27632. The levels of MCP-1, CCL11, and IL-6 increased after light exposure were suppressed by NAC. Light-induced MCP-1 and IL-6 were suppressed by Y-27632. Macrophage recruitment after light exposure was also suppressed either by NAC or Y-27632.

CONCLUSIONS

Light exposure induced ROS and Rho/ROCK activation, which caused disruption of cell-cell junctions (tight junctions and adherens junctions) and actin cytoskeleton, the RPE's barrier structure, and induced AMD-associated pathological changes in the RPE-choroid.

Autophagy protects the retina from light-induced degeneration

Autophagy is a conserved feature of lysosome-mediated intracellular degradation. Dysregulated autophagy is implicated as a contributor in neurodegenerative diseases; however, the role of autophagy in retinal degeneration remains largely unknown. Here, we report that the photo-activated visual chromophore, all-trans-retinal, modulated autophagosome formation in ARPE19 retinal cells. Increased formation of autophagosomes in these cells was observed when incubated with 2.5 μM all-trans-retinal, a condition that did not cause cell death after 24 h in culture. However, autophagosome formation was decreased at concentrations, which caused cell death. Increased expression of activating transcription factor 4 (Atf4), which indicates the activation of oxidative stress, was recorded in response to light illumination in retinas of Abca4(-/-)Rdh8(-/-) mice, which showed delayed clearance of all-trans-retinal after light exposure. Expression of autophagosome marker LC3B-II and mitochondria-specific autophagy, mitophagy, regulator Park2, were significantly increased in the retinas of Abca4(-/-)Rdh8(-/-) mice after light exposure, suggesting involvement of autophagy and mitophagy in the pathogenesis of light-induced retinal degeneration. Deletion of essential genes required for autophagy, including Beclin1 systemically or Atg7 in only rod photoreceptors resulted in increased susceptibility to light-induced retinal damage. Increased photoreceptor cell death was observed when retinas lacking the rod photoreceptor-specific Atg7 gene were coincubated with 20 μM all-trans-retinal. Park2(-/-) mice also displayed light-induced retinal degeneration. Ultra-structural analyses showed mitochondrial and endoplasmic reticulum impairment in retinas of these model animals after light exposure. Taken together, these observations provide novel evidence implicating an important role of autophagy and mitophagy in protecting the retina from all-trans-retinal- and light-induced degeneration.

Systemic administration of the iron chelator deferiprone protects against light-induced photoreceptor degeneration in the mouse retina

Oxidative stress plays a key role in a light-damage (LD) model of retinal degeneration as well as in age-related macular degeneration (AMD). Since iron can promote oxidative stress, the iron chelator deferiprone (DFP) was tested for protection against light-induced retinal degeneration. To accomplish this, A/J mice were treated with or without oral DFP and then were placed in constant bright white fluorescent light (10,000 lx) for 20 h. Retinas were evaluated at several time points after light exposure. Photoreceptor apoptosis was assessed using the TUNEL assay. Retinal degeneration was assessed by histology 10 days after exposure to damaging white light. Two genes upregulated by oxidative stress, heme oxygenase 1 (Hmox1) and ceruloplasmin (Cp), as well as complement component 3 (C3) were quantified by RT-qPCR. Cryosections were immunolabeled for an oxidative stress marker (nitrotyrosine), a microglial marker (Iba1), as well as both heavy (H) and light (L) ferritin. Light exposure resulted in substantial photoreceptor-specific cell death. Dosing with DFP protected photoreceptors, decreasing the numbers of TUNEL-positive photoreceptors and increasing the number of surviving photoreceptors. The retinal mRNA levels of oxidative stress-related genes and C3 were upregulated following light exposure and diminished by DFP treatment. Immunostaining for nitrotyrosine indicated that DFP reduced the nitrative stress caused by light exposure. Robust H/L-ferritin-containing microglial activation and migration to the outer retina occurred after light exposure and DFP treatment reduced microglial invasion. DFP is protective against light-induced retinal degeneration and has the potential to diminish oxidative stress in the retina.

Light distributions on the retina: relevance to macular pigment photoprotection

Light exposure has been implicated in age-related macular degeneration (AMD). This study was designed to measure cumulative light distribution on the retina to determine whether it peaked in the macula. An eye-tracker recorded the subject's field of view and pupil size, and superimposed the gaze position. Fifteen naïve subjects formed a test group; 5 formed a control group. In phase 1, all subjects viewed a sequence of photographic images. In phase 2, the naïve subjects observed a video; in phase 3, they performed computer tasks; in phase 4, the subjects walked around freely. In phase 1, control subjects were instructed to gaze at bright features in the field of view and, in a second test, at dark features. Test group subjects were allowed to gaze freely for all phases. Using the subject's gaze coordinates, we calculated the cumulative light distribution on the retina. As expected for control subjects, cumulative retinal light distributions peaked and dipped in the fovea when they gazed at bright or dark features respectively in the field of view. The light distribution maps obtained from the test group showed a consistent tendency to peak in the macula in phase 3, a variable tendency in phase 4, but little tendency in phases 1 and 2. We conclude that a tendency for light to peak in the macula is a characteristic of some individuals and of certain tasks. In these situations, risk of AMD could be increased but, at the same time, mitigated by the presence of macular carotenoids.

Alpha-phenyl-N-tert-butylnitrone (PBN) prevents light-induced degeneration of the retina by inhibiting RPE65 protein isomerohydrolase activity

α-Phenyl-N-tert-butylnitrone (PBN), a free radical spin trap, has been shown previously to protect retinas against light-induced neurodegeneration, but the mechanism of protection is not known. Here we report that PBN-mediated retinal protection probably occurs by slowing down the rate of rhodopsin regeneration by inhibiting RPE65 activity. PBN (50 mg/kg) protected albino Sprague-Dawley rat retinas when injected 0.5-12 h before exposure to damaging light at 2,700 lux intensity for 6 h but had no effect when administered after the exposure. PBN injection significantly inhibited in vivo recovery of rod photoresponses and the rate of recovery of functional rhodopsin photopigment. Assays for visual cycle enzyme activities indicated that PBN inhibited one of the key enzymes of the visual cycle, RPE65, with an IC(50) = 0.1 mm. The inhibition type for RPE65 was found to be uncompetitive with K(i) = 53 μm. PBN had no effect on the activity of other visual cycle enzymes, lecithin retinol acyltransferase and retinol dehydrogenases. Interestingly, a more soluble form of PBN, N-tert-butyl-α-(2-sulfophenyl) nitrone, which has similar free radical trapping activity, did not protect the retina or inhibit RPE65 activity, providing some insight into the mechanism of PBN specificity and action. Slowing down the visual cycle is considered a treatment strategy for retinal diseases, such as Stargardt disease and dry age-related macular degeneration, in which toxic byproducts of the visual cycle accumulate in retinal cells. Thus, PBN inhibition of RPE65 catalytic action may provide therapeutic benefit for such retinal diseases.

Free radical trap phenyl-N-tert-butylnitrone protects against light damage but does not rescue P23H and S334ter rhodopsin transgenic rats from inherited retinal degeneration

Phenyl-N-tert-butylnitrone (PBN) protects rat retinas against light damage. Because the degenerative process involved in light damage and inherited retinal degeneration both lead to a common final cell death, apoptosis, we used transgenic rats with a P23H or S334ter rhodopsin mutation to test the effects of PBN on retinal degeneration and light damage and the susceptibility of the transgenic rats to light damage. In the first study, 3-week-old mutant and wild-type rats were given no drug, 0.25% PBN in drinking water, or 0.25% PBN in drinking water plus three daily intraperitoneal injections of PBN (100 mg/kg, i.p., every 8 hr). Electroretinograms were recorded at postnatal day 49, after which the rats were killed for morphometric analysis. There was no photoreceptor rescue by PBN in P23H or S334ter rats, as evidenced by equivalent loss of function and photoreceptor cells in the three treatment groups. In the second study, P23H, S334ter, and wild-type rats were exposed for 24 hr to 2700 lux light. The rats were untreated or treated with PBN (50 mg/kg per injection, every 6 hr, starting before exposure). ERGs were recorded before and 1 d after exposure. Animals were killed 6 d later for morphometric analysis. PBN protected wild-type and P23H but not S334ter retinas from light damage. S334ter retinas were relatively less susceptible to light damage than P23H and wild-type rats. The results suggest that the initiating event(s) that causes photoreceptor cell death in the mutated rats is different from that which occurs in light damage, although both ultimately undergo an apoptotic cell death.

The Rpe65 Leu450Met variation increases retinal resistance against light-induced degeneration by slowing rhodopsin regeneration

Excessive light can cause retinal degeneration and may be an environmental cofactor accelerating retinal dystrophies and age-related diseases. In rodent models, the light damage susceptibility (LDS) of the retina is determined genetically. In two mouse strains, with different degrees of LDS, a Leu450Met variation in the pigment epithelial protein RPE65 was shown recently to cosegregate with low LDS. Because light damage is rhodopsin-mediated, and RPE65 is essential for the regeneration of rhodopsin in the visual cycle, we analyzed this variation regarding rhodopsin metabolism and LDS in four mouse strains. We found that, in contrast to previous assertions, LDS does not correlate with the maximal retinal content of rhodopsin present after dark adaptation. Instead, LDS correlated positively with the kinetics of rhodopsin regeneration, which determine rhodopsin availability during light exposure. Light damage occurred after absorption of a threshold dose of photons and thus fast regeneration, as observed in those two strains having Leu at position 450 of RPE65, was correlated with the occurrence of photoreceptor apoptosis after short exposure. In contrast, mice with the Leu450Met variation of Rpe65 regenerated rhodopsin with slow kinetics and showed an increased resistance to light-induced retinal degeneration. In these mice, RPE65 protein levels were reduced by a post-transcriptional mechanism. F(1) hybrid mice, carrying one normal and one variant Rpe65 gene, had intermediate levels of the corresponding protein and showed intermediate rhodopsin regeneration kinetics and an intermediate LDS. Thus, none of the two variants of Rpe65 had a dominant effect.

c-fos controls the "private pathway" of light-induced apoptosis of retinal photoreceptors

White light (5 klux for 2 hr) induces apoptosis of rod photoreceptors in wild-type mice (c-fos(+/+)) within 24 hr, whereas rods of c-fos knock-out mice (c-fos(-/-)) are protected (). The range of this protection was tested by analyzing retinas of c-fos(+/+) and c-fos(-/-) mice up to 10 d after exposure to threefold increased light intensities (15 klux for 2 hr). In c-fos(-/-) mice, rods were unaffected, whereas they were destroyed in c-fos(+/+) mice. After light exposure, mitochondrial damage in rods was observed exclusively in c-fos(+/+) mice. Electroretinograms recorded 48 hr after exposure revealed a decrease of all components in c-fos(+/+) mice but indicated no light-induced loss of function in c-fos(-/-) mice. Thus, in c-fos(-/-) mice, light-induced apoptosis is blocked or its threshold is elevated more than threefold. Increased activity of the transcription factor activator protein-1 (AP-1) in retinas of light-exposed c-fos(+/+) mice indicated an acute contribution of AP-1 to apoptosis induction. AP-1 activity increased already during exposure and peaked approximately 6 hr thereafter, coinciding with the appearance of major morphological signs of apoptosis. Activated AP-1 mainly consisted of c-Fos/Jun heterodimers. In c-fos(-/-) mice, AP-1 activity remained unchanged, indicating that no other Jun- or Fos-family member could substitute for c-Fos. Like damaging light, N-methyl-N-nitrosourea (MNU) induced AP-1 containing c-Fos in c-fos(+/+) mice and did not induce AP-1 in c-fos(-/-) mice. In contrast to light, however, MNU induced apoptosis in rods of c-fos(-/-) mice. Thus, c-Fos is essential for a specific premitochondrial "private apoptotic pathway" induced by light but not for the execution of apoptosis induced by other stimuli.

Preconditioning with bright light evokes a protective response against light damage in the rat retina

Constant exposure to bright light induces photoreceptor degeneration and at the same time upregulates the expression of several neurotrophic factors in the retina. At issue is whether the induced neurotrophic factors protect photoreceptors. We used a preconditioning paradigm to show that animals preconditioned with bright light became resistant to subsequent light damage. The preconditioning consisted of a 12-48 hr preexposure, followed by a 48 hr "rest phase" of normal cyclic lighting. The greatest protection was achieved by a 12 hr preexposure. Preconditioning induces a prolonged increase in two endogenous neurotrophic factors: basic fibroblast growth factor (bFGF) and ciliary neurotrophic factor (CNTF). It also stimulates the phosphorylation of extracellular signal-regulated protein kinases (Erks) in both photoreceptors and Müller cells. These findings indicate that exposure to bright light initiates two opposing processes: a fast degenerative process that kills photoreceptors and a relatively slower process that leads to the protection of photoreceptors. The extent of light damage, therefore, depends on the interaction of the two processes. These results also suggest a role of endogenous bFGF and CNTF in photoreceptor protection and the importance of Erk activation in photoreceptor survival.