Light-induced retinal degeneration causes a transient downregulation of melanopsin in the rat retina

Effect of hydrogen-rich saline on melanopsin after acute blue light-induced retinal damage in rats

Excessive exposure to blue light can cause retinal damage. Hydrogen-rich saline (HRS), one of the hydrogen therapies, has been demonstrated to be effective in eye photodamage, but the effect on the expression of melanopsin in intrinsically photosensitive retinal ganglion cells (ipRGCs) is unknown. In this study, we used a rat model of light-induced retinal injury to observe the expression of melanopsin after HRS treatment and to determine the effect of HRS on retinal ganglion cell protection. Adult SD rats were exposed to blue light (48 h) and treated with HRS for 0, 3, 7, and 14 days. Real-time polymerase chain reaction (qRT-PCR) and Western blotting (WB) were performed to find the expression of genes and proteins, respectively. The function of retinal ipRGCs was measured by pattern-evoked electroretinography (pERG). The number and morphological changes of melanopsin-positive ganglion cells in the retina were observed by immunofluorescence (IF). Acute blue light exposure caused a decrease in ipRGC function, decreased expression of melanopsin protein and the melanopsin-positive RGCs, and diminished immunoreactivity in dendrites. However, over time, melanopsin showed a tendency to self-recovery, with an increase in melanopsin protein expression and the number of melanopsin-positive RGCs, with incomplete recovery of function within two weeks. HRS treatment accelerated the recovery process, with a significant increase in melanopsin expression and the number of melanopsin-positive RGCs, and an improvement in the pERG waveform within two weeks.

Dose-Related Side Effects of Intravitreal Injections of Humanized Anti-Vascular Endothelial Growth Factor in Rats: Glial Cell Reactivity and Retinal Ganglion Cell Loss

Purpose

In a previous study, we documented that the Intravitreal injections (IVIs) of bevacizumab in rats caused a retinal inflammatory response. We now study whether the IVI of other humanized anti-VEGF: ranibizumab and aflibercept also cause an inflammatory reaction in the rat retina and if it depends on the dose administered. Finally, we study whether this reaction affects retinal ganglion cell (RGC) survival.

Methods

Albino Sprague-Dawley rats received a single IVI of 5 µL of PBS or ranibizumab or aflibercept at the concentration used in clinical practice (10 µg/µL or 40 µg/µL) or at a lower concentration (0.38 µg/µL and 1.5 µg/µL) calculated to obtain within the rat eye the same concentration as in the human eye in clinical practice. Others received a single 5 µL IVI of a polyclonal goat anti-rat VEGF (0.015 µg/µL) or of vehicle (PBS). Animals were processed 7 days or 1 month later. Retinal whole mounts were immunolabeled for the detection of microglial, macroglial, RGCs, and intrinsically photosensitive RGCs (ipRGCs). Fluorescence and confocal microscopy were used to examine retinal changes, and RGCs and ipRGCs were quantified automatically or semiautomatically, respectively.

Results

All the injected substances including the PBS induced detectable side effects, namely, retinal microglial cell activation and retinal astrocyte hypertrophy. However, there was a greater microglial and macroglial response when the higher concentrations of ranibizumab and aflibercept were injected than when PBS, the antibody anti-rat VEGF and the lower concentrations of ranibizumab or aflibercept were injected. The higher concentration of ranibizumab and aflibercept resulted also in significant RGC death, but did not cause appreciable ipRGC death.

Conclusions

The IVI of all the substances had some retinal inflammatory effects. The IVI of humanized anti-VEGF to rats at high doses cause important side effects: severe inflammation and RGC death, but not ipRGC death.

Evaluation of the neuroprotective efficacy of the gramine derivative ITH12657 against NMDA-induced excitotoxicity in the rat retina

Purpose

The aim of this study was to investigate, the neuroprotective effects of a new Gramine derivative named: ITH12657, in a model of retinal excitotoxicity induced by intravitreal injection of NMDA.

Methods

Adult Sprague Dawley rats received an intravitreal injection of 100 mM NMDA in their left eye and were treated daily with subcutaneous injections of ITH12657 or vehicle. The best dose-response, therapeutic window study, and optimal treatment duration of ITH12657 were studied. Based on the best survival of Brn3a + RGCs obtained from the above-mentioned studies, the protective effects of ITH12657 were studied in vivo (retinal thickness and full-field Electroretinography), and ex vivo by quantifying the surviving population of Brn3a + RGCs, αRGCs and their subtypes α-ONsRGCs, α-ONtRGCs, and α-OFFRGCs.

Results

Administration of 10 mg/kg ITH12657, starting 12 h before NMDA injection and dispensed for 3 days, resulted in the best significant protection of Brn3a + RGCs against NMDA-induced excitotoxicity. In vivo, ITH12657-treated rats showed significant preservation of retinal thickness and functional protection against NMDA-induced retinal excitotoxicity. Ex vivo results showed that ITH12657 afforded a significant protection against NMDA-induced excitotoxicity for the populations of Brn3a + RGC, αRGC, and αONs-RGC, but not for the population of αOFF-RGC, while the population of α-ONtRGC was fully resistant to NMDA-induced excitotoxicity.

Conclusion

Subcutaneous administration of ITH12657 at 10 mg/kg, initiated 12 h before NMDA-induced retinal injury and continued for 3 days, resulted in the best protection of Brn3a + RGCs, αRGC, and αONs-RGC against excitotoxicity-induced RGC death. The population of αOFF-RGCs was extremely sensitive while α-ONtRGCs were fully resistant to NMDA-induced excitotoxicity.

Low-Intensity Blue Light Exposure Reduces Melanopsin Expression in Intrinsically Photosensitive Retinal Ganglion Cells and Damages Mitochondria in Retinal Ganglion Cells in Wistar Rats

This study investigated the effect of low-intensity blue light on the albino Wistar rat retina, including intrinsically photosensitive retinal ganglion cells (ipRGCs). Three groups of nine albino Wistar rats were used. One group was continuously exposed to blue light (150 lx) for 2 d (STE); one was exposed to 12 h of blue light and 12 h of darkness for 10 d (LTE); one was maintained in 12 h of white light (150 lx) and 12 h of darkness for 10 d (control). Melanopsin (Opn4) was immunolabelled on retinal whole-mounts. To count and measure Opn4-positive ipRGC somas and dendrites (including Sholl profiles), Neuron J was used. Retinal cryosections were immunolabeled for glial fibrillary acid protein (GFAP) and with terminal deoxynucleotidyl transferase dUTP nick-end labelling for apoptosis detection. LTE reduced the length of Opn4-positive ipRGC dendrites (p = 0.03) and decreased Opn4-immunoreactivity in ipRGC outer stratifying dendrites. LTE and STE decreased the complexity of dendritic arborization (Sholl profile; p < 0.001, p = 0.03, respectively), increased retinal GFAP immunoreactivity (p < 0.001, p = 0.002, respectively), and caused outer segment vesiculation and outer nuclear layer apoptosis. Ultrastructural analysis showed that LTE damaged mitochondria in retinal ganglion cells and in the inner plexiform layer. Thus, LTE to low-intensity blue light harms the retinas of albino Wistar rats.

Profiles of Rho, Opn4, c-Fos, and Birc5 mRNA expression in Wistar rat retinas exposed to white or monochromatic light

Despite concern over potential retinal damage linked to exposure to light-emitting-diode (LED) light (particularly blue light), it remains unknown how exposure to low-intensity monochromatic LED light affects the expression of rhodopsin (Rho, a photopigment that mediates light-induced retinal degeneration), melanopsin (Opn4, a blue-light sensitive photopigment), c-Fos (associated with retinal damage/degeneration), and Birc5 (anti-apoptotic). This study investigated the mRNA expression profiles of these genes under exposure to white and monochromatic light (blue, red, green) in the retinas of albino rats under a cycle of 12 h of light and 12 h of darkness. In each group, 32 Wistar rats were exposed to one type of monochromatic-LED or white-fluorescent light for 7 day (150 lx). Retinal samples were taken for qPCR analysis and light and electron microscopy. Blue and green light exposure markedly decreased expression of Rho and Opn4 mRNA and increased expression of Birc5 and c-Fos mRNA (P < 0.05). In retinas from the blue-light group, loss and vesiculation of photoreceptor outer segments were visible, but not in retinas from the red-light and control group. Measurements of the photoreceptor inner and outer segments length revealed, that this length was significantly decreased in the blue- and green-light exposure groups (P < 0.02), but not in the red-light exposure group. Increased expression of Birc5 and decreased expression of Rho and Opn4 after exposure to blue and green light may be early responses that help to reduce light-induced retinal damage.

Exposure to Blue Light Reduces Melanopsin Expression in Intrinsically Photoreceptive Retinal Ganglion Cells and Damages the Inner Retina in Rats

Purpose

The purpose of this study was to investigative the effects of blue light on intrinsically photoreceptive retinal ganglion cells (ipRGCs).

Methods

Brown Norway rats were used. Nine rats were continuously exposed to blue light (light emitting diodes [LEDs]: 463 nm; 1000 lx) for 2 days (acute exposure [AE]); 9 rats were exposed to 12 hours of blue light and 12 hours of darkness for 10 days (long-term exposure [LTE]); 6 control rats were exposed to 12 hours of white fluorescent light (1000 lx) and 12 hours of darkness for 10 days. Whole-mount retinas were immunolabelled with melanopsin antibodies; melanopsin-positive (MP) ipRGC somas and processes were counted and measured with Neuron J. To detect apoptosis, retinal cryo-sections were stained with terminal deoxynucleotidyl transferase dUTP nick-end labeling. Ultra-thin sections were visualized with transmission electron microscopy.

Results

The number of MP ipRGC somas was significantly lower in retinas from AE and LTE rats than in those from control rats (P < 0.001 and = 0.002, respectively). The mean length of MP areas of processes was significantly lower in AE rats (P < 0.001). AE rats had severe retinal damage and massive apoptosis in the outer nuclear layer; their mitochondria were damaged in the axons and dendrites of the nerve fiber layer and the inner plexiform layer. Retinal ganglion cells (RGCs) in AE rats appeared to have reduced amounts of free ribosomes and rough endoplasmic reticulum.

Conclusions

AE to blue light reduces melanopsin expression and damages RGCs, likely including ipRGCs. Changes in the axons and dendrites of RGCs suggest possible disruption of intraretinal and extraretinal signal transmission.

Glial Cell Activation and Oxidative Stress in Retinal Degeneration Induced by β-Alanine Caused Taurine Depletion and Light Exposure

We investigate glial cell activation and oxidative stress induced by taurine deficiency secondary to β-alanine administration and light exposure. Two months old Sprague-Dawley rats were divided into a control group and three experimental groups that were treated with 3% β-alanine in drinking water (taurine depleted) for two months, light exposed or both. Retinal and external thickness were measured in vivo at baseline and pre-processing with Spectral-Domain Optical Coherence Tomography (SD-OCT). Retinal cryostat cross sections were immunodetected with antibodies against various antigens to investigate microglial and macroglial cell reaction, photoreceptor outer segments, synaptic connections and oxidative stress. Taurine depletion caused a decrease in retinal thickness, shortening of photoreceptor outer segments, microglial cell activation, oxidative stress in the outer and inner nuclear layers and the ganglion cell layer and synaptic loss. These events were also observed in light exposed animals, which in addition showed photoreceptor death and macroglial cell reactivity. Light exposure under taurine depletion further increased glial cell reaction and oxidative stress. Finally, the retinal pigment epithelial cells were Fluorogold labeled and whole mounted, and we document that taurine depletion impairs their phagocytic capacity. We conclude that taurine depletion causes cell damage to various retinal layers including retinal pigment epithelial cells, photoreceptors and retinal ganglion cells, and increases the susceptibility of the photoreceptor outer segments to light damage. Thus, beta-alanine supplements should be used with caution.

Mechanisms implicated in the contralateral effect in the central nervous system after unilateral injury: focus on the visual system

The retina, as part of the central nervous system is an ideal model to study the response of neurons to injury and disease and to test new treatments. During the last decade is becoming clear that unilateral lesions in bilateral areas of the central nervous system trigger an inflammatory response in the contralateral uninjured site. This effect has been better studied in the visual system where, as a rule, one retina is used as experimental and the other as control. Contralateral retinas in unilateral models of retinal injury show neuronal degeneration and glial activation. The mechanisms by which this adverse response in the central nervous system occurs are discussed in this review, focusing primarily on the visual system.

7,8-Dihydroxiflavone Maintains Retinal Functionality and Protects Various Types of RGCs in Adult Rats with Optic Nerve Transection

To analyze the neuroprotective effects of 7,8-Dihydroxyflavone (DHF) in vivo and ex vivo, adult albino Sprague-Dawley rats were given a left intraorbital optic nerve transection (IONT) and were divided in two groups: One was treated daily with intraperitoneal (ip) DHF (5 mg/kg) (n = 24) and the other (n = 18) received ip vehicle (1% DMSO in 0.9% NaCl) from one day before IONT until processing. At 5, 7, 10, 12, 14, and 21 days (d) after IONT, full field electroretinograms (ERG) were recorded from both experimental and one additional naïve-control group (n = 6). Treated rats were analyzed 7 (n = 14), 14 (n = 14) or 21 d (n = 14) after IONT, and the retinas immune stained against Brn3a, Osteopontin (OPN) and the T-box transcription factor T-brain 2 (Tbr2) to identify surviving retinal ganglion cells (RGCs) (Brn3a⁺), α-like (OPN⁺), α-OFF like (OPN⁺Brn3a⁺) or M4-like/α-ON sustained RGCs (OPN⁺Tbr⁺). Naïve and right treated retinas showed normal ERG recordings. Left vehicle-treated retinas showed decreased amplitudes of the scotopic threshold response (pSTR) (as early as 5 d), the rod b-wave, the mixed response and the cone response (as early as 10 d), which did not recover with time. In these retinas, by day 7 the total numbers of Brn3a⁺RGCs, OPN⁺RGCs and OPN⁺Tbr2⁺RGCs decreased to less than one half and OPN⁺Brn3a⁺RGCs decreased to approximately 0.5%, and Brn3a⁺RGCs showed a progressive loss with time, while OPN⁺RGCs and OPN⁺Tbr2⁺RGCs did not diminish after seven days. Compared to vehicle-treated, the left DHF-treated retinas showed significantly greater amplitudes of the pSTR, normal b-wave values and significantly greater numbers of OPN⁺RGCs and OPN⁺Tbr2⁺RGCs for up to 14 d and of Brn3a⁺RGCs for up to 21 days. DHF affords significant rescue of Brn3a⁺RGCs, OPN⁺RGCs and OPN⁺Tbr2⁺RGCs, but not OPN⁺Brn3a⁺RGCs, and preserves functional ERG responses after IONT.

Animal Models of LED-Induced Phototoxicity. Short- and Long-Term In Vivo and Ex Vivo Retinal Alterations

Phototoxicity animal models have been largely studied due to their degenerative communalities with human pathologies, e.g., age-related macular degeneration (AMD). Studies have documented not only the effects of white light exposure, but also other wavelengths using LEDs, such as blue or green light. Recently, a blue LED-induced phototoxicity (LIP) model has been developed that causes focal damage in the outer layers of the superior-temporal region of the retina in rodents. In vivo studies described a progressive reduction in retinal thickness that affected the most extensively the photoreceptor layer. Functionally, a transient reduction in a- and b-wave amplitude of the ERG response was observed. Ex vivo studies showed a progressive reduction of cones and an involvement of retinal pigment epithelium cells in the area of the lesion and, in parallel, an activation of microglial cells that perfectly circumscribe the damage in the outer retinal layer. The use of neuroprotective strategies such as intravitreal administration of trophic factors, e.g., basic fibroblast growth factor (bFGF), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF) or pigment epithelium-derived factor (PEDF) and topical administration of the selective alpha-2 agonist (Brimonidine) have demonstrated to increase the survival of the cone population after LIP.

An in vivo model of focal light emitting diode-induced cone photoreceptor phototoxicity in adult pigmented mice: Protection with bFGF

PURPOSE

To develop a model of focal injury by blue light-emitting diode (LED)-induced phototoxicity (LIP) in pigmented mouse retinas and to study the effects on cone, Iba-1⁺ cells and retinal pigment epithelium (RPE) cell populations after administration of basic fibroblast growth factor (bFGF) and minocycline, alone or combined.

METHODS

In anesthetized dark-adapted adult female pigmented C57BL/6 mice, left pupils were dilated and the eye exposed to LIP (500 lux, 45 s). The retina was monitored longitudinally in vivo with SD-OCT for 7 days (d). Ex vivo, the effects of LIP and its protection with bFGF (0.5 μg) administered alone or combined with minocycline (45 mg/kg) were studied in immunolabeled arrestin-cone outer segments (a⁺OS) and quantified within a predetermined fixed-size circular area (PCA) centered on the lesion in flattened retinas at 1, 3, 5 or 7d. Moreover, Iba-1⁺ cells and RPE cell morphology were analysed with Iba-1 and ZO-1 antibodies, respectively.

RESULTS

LIP caused a focal lesion within the superior-temporal retina with retinal thinning, particularly the outer retinal layers (116.5 ± 2.9 μm to 36.8 ± 6.3 μm at 7d), and with progressive diminution of a⁺OS within the PCA reaching minimum values at 7d (6218 ± 342 to 3966 ± 311). Administration of bFGF alone (4519 ± 320) or in combination with minocycline (4882 ± 446) had a significant effect on a⁺OS survival at 7d and Iba-1⁺ cell activation was attenuated in the groups treated with minocycline. In parallel, the RPE cell integrity was progressively altered after LIP and administration of neuroprotective components had no restorative effect at 7d.

CONCLUSIONS

LIP resulted in progressive outer retinal damage affecting the OS cone population and RPE. Administration of bFGF increased a⁺OS survival but did not prevent RPE deterioration.

Systemic treatment with 7,8-Dihydroxiflavone activates TtkB and affords protection of two different retinal ganglion cell populations against axotomy in adult rats

PURPOSE

To analyze responses of different RGC populations to left intraorbital optic nerve transection (IONT) and intraperitoneal (i.p.) treatment with 7,8-Dihydroxyflavone (DHF), a potent selective TrkB agonist.

METHODS

Adult albino Sprague-Dawley rats received, following IONT, daily i.p. injections of vehicle (1%DMSO in 0.9%NaCl) or DHF. Group-1 (n = 58) assessed at 7days (d) the optimal DHF amount (1-25 mg/kg). Group-2, using freshly dissected naïve or treated retinas (n = 28), investigated if DHF treatment was associated with TrkB activation using Western-blotting at 1, 3 or 7d. Group-3 (n = 98) explored persistence of protection and was analyzed at survival intervals from 7 to 60d after IONT. Groups 2-3 received daily i.p. vehicle or DHF (5 mg/kg). Retinal wholemounts were immunolabelled for Brn3a and melanopsin to identify Brn3a⁺RGCs and m⁺RGCs, respectively.

RESULTS

Optimal neuroprotection was achieved with 5 mg/kg DHF and resulted in TrkB phosphorylation. The percentage of surviving Brn3a⁺RGCs in vehicle treated rats was 60, 28, 18, 13, 12 or 8% of the original value at 7, 10, 14, 21, 30 or 60d, respectively, while in DHF treated retinas was 94, 70, 64, 17, 10 or 9% at the same time intervals. The percentages of m⁺RGCs diminished by 7d-13%, and recovered by 14d-38% in vehicle-treated and to 48% in DHF-treated retinas, without further variations.

CONCLUSIONS

DHF neuroprotects Brn3a ⁺ RGCs and m ⁺ RGCs; its protective effects for Brn3a⁺RGCs are maximal at 7 days but still significant at 21d, whereas for m⁺RGCs neuroprotection was significant at 14d and permanent.

Modeling of Retinal Degeneration

We developed a model of retinal degeneration in rabbits based on exposure to light with a wavelength of 405 nm. This model allows reproducing structural and functional disorders in the central parts of the retina, including primarily degeneration of the outer layers of the retina (retinal pigment epithelium and layer of photoreceptor cells), and is designed to study the mechanisms of formation, progression and effectiveness of new drugs and methods of treatment of degenerative diseases of the retina.

Astragalus membranaceus Injection Protects Retinal Ganglion Cells by Regulating the Nerve Growth Factor Signaling Pathway in Experimental Rat Traumatic Optic Neuropathy

Activation of the nerve growth factor (NGF) signaling pathway is a potential method of treatment for retinal ganglion cell (RGC) loss due to traumatic optic neuropathy (TON). The present study aimed to explore the biological effects of injecting Astragalus membranaceus (A. mem) on RGCs in an experimental TON model. Adult male Wistar rats were randomly divided into three groups: sham-operated (SL), model (ML), and A. mem injection (AL). The left eyes of the rats were considered the experimental eyes, and the right eyes served as the controls. AL rats received daily intraperitoneal injections of A. mem (3 mL/kg), whereas ML and SL rats were administered the same volume of normal saline. The TON rat model was induced by optic nerve (ON) transverse quantitative traction. After two-week administration, the number of RGCs was determined using retrograde labeling with Fluoro-Gold. The protein levels of NGF, tyrosine kinase receptor A (TrkA), c-Jun N-terminal protein kinase (JNK), JNK phosphorylation (p-JNK), and nuclear factor kappa-B (NF-κB) were assessed using western blotting. The levels of p75 neurotrophin receptor (p75^NTR) and NF-κB DNA binding were examined using real-time PCR and an electrophoretic mobility shift assay. In addition, the concentrations of JNK and p-JNK were assessed using an enzyme-linked immunosorbent assay. Results. The number of RGCs in ML was found to be significantly decreased (P < 0.01) relative to both AL and SL, together with the downregulation of NGF (P < 0.01), TrkA (P < 0.05), and NF-κB (P < 0.01); upregulation of p75^NTR mRNA (P < 0.01); and increased protein levels of JNK (P < 0.05) and p-JNK (P < 0.05). Treatment using A. mem injection significantly preserved the density of RGCs in rats with experimental TON and markedly upregulated the proteins of NGF (P < 0.01), TrkA (P < 0.05), and NF-κB (P < 0.01) and downregulated the mRNA level of p75^NTR(P < 0.01), as well as the proteins of JNK (P < 0.05) and p-JNK (P < 0.01). Thus, A. mem injection could reduce RGC death in TON induced by ON transverse quantitative traction by stimulating the NGF signaling pathway.

Photosensitive ganglion cells: A diminutive, yet essential population

Our visual system has evolved to provide us with an image of the scene that surrounds us, informing us of its texture, colour, movement, and depth with an enormous spatial and temporal resolution, and for this purpose, the image formation (IF) dedicates the vast majority of our retinal ganglion cell (RGC) population and much of our cerebral cortex. On the other hand, a minuscule proportion of RGCs, in addition to receiving information from classic cone and rod photoreceptors, express melanopsin and are intrinsically photosensitive (ipRGC). These ipRGC are dedicated to non-image-forming (NIF) visual functions, of which we are unaware, but which are essential for aspects related to our daily physiology, such as the timing of our circadian rhythms and our pupillary light reflex, among many others. Before the discovery of ipRGCs, it was thought that the IF and NIF functions were distinct compartments regulated by different RGCs, but this concept has evolved in recent years with the discovery of new types of ipRGCs that innervate subcortical IF regions, and therefore have IF visual functions. Six different types of ipRGCs are currently known. These are termed M1-M6, and differ in their morphological, functional, molecular properties, central projections, and visual behaviour responsibilities. A review is presented on the melanopsin visual system, the most active field of research in vision, for which knowledge has grown exponentially during the last two decades, when RGCs giving rise to this pathway were first discovered.

Pigment Epithelium-Derived Factor (PEDF) Fragments Prevent Mouse Cone Photoreceptor Cell Loss Induced by Focal Phototoxicity In Vivo

Here, we evaluated the effects of PEDF (pigment epithelium-derived factor) and PEDF peptides on cone-photoreceptor cell damage in a mouse model of focal LED-induced phototoxicity (LIP) in vivo. Swiss mice were dark-adapted overnight, anesthetized, and their left eyes were exposed to a blue LED placed over the cornea. Immediately after, intravitreal injection of PEDF, PEDF-peptide fragments 17-mer, 17-mer[H105A] or 17-mer[R99A] (all at 10 pmol) were administered into the left eye of each animal. BDNF (92 pmol) and bFGF (27 pmol) injections were positive controls, and vehicle negative control. After 7 days, LIP resulted in a consistent circular lesion located in the supratemporal quadrant and the number of S-cones were counted within an area centered on the lesion. Retinas treated with effectors had significantly greater S-cone numbers (PEDF (60%), 17-mer (56%), 17-mer [H105A] (57%), BDNF (64%) or bFGF (60%)) relative to their corresponding vehicle groups (≈42%). The 17-mer[R99A] with no PEDF receptor binding and no neurotrophic activity, PEDF combined with a molar excess of the PEDF receptor blocker P1 peptide, or with a PEDF-R enzymatic inhibitor had undetectable effects in S-cone survival. The findings demonstrated that the cone survival effects were mediated via interactions between the 17-mer region of the PEDF molecule and its PEDF-R receptor.

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

Purpose

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

Methods

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

Results

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

Conclusions

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

Light-Induced Retinal Ganglion Cell Damage and the Relevant Mechanisms

While light is the basic element for inducing vision and modulating circadian rhythms, excessive light has been reported to have a negative effect on the survival of various types of retinal cells. Among them photoreceptors and retinal pigment epithelial (RPE) cells degeneration after light exposure is widely observed, but light-induced retinal ganglion cell (RGC) damage achieves relatively little attention. The purpose of this article is to summarize the experimental evidence for the possible negative effects of excessive light on RGCs. By searching the database, twenty-six related articles have been included. Taken together, excessive light may insult RGCs through the three main ways: (i) directly action on RGC mitochondria, as well as DNA, resulting in an upregulation of reactive oxygen species (ROS) and subsequently caspase-dependent or -independent cell death; (ii) mediation in gliotransmitters or relevant receptors of retinal glial cells; and (iii) a secondary event to photoreceptors and RPE cells degeneration and subsequent retinal remodeling. So RGCs can certainly be injured by excessive light, especially when they are already energetically compromised in some diseases. And more attentions should be paid to this topic to take timely measures to protect these frail RGCs from being damaged by excessive light.

Topical Brimonidine or Intravitreal BDNF, CNTF, or bFGF Protect Cones Against Phototoxicity

Purpose

To develop a focal photoreceptor degeneration model by blue light-emitting diode (LED)-induced phototoxicity (LIP) and investigate the protective effects of topical brimonidine (BMD) or intravitreal brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), or basic fibroblast growth factor (bFGF).

Methods

In anesthetized, dark-adapted, adult female Swiss mice, the left eye was dilated and exposed to blue light (10 seconds, 200 lux). After LIP, full-field electroretinograms (ERG) and spectral-domain optical coherence tomography (SD-OCT) were obtained longitudinally, and reactive-Iba-1⁺monocytic cells, TUNEL⁺ cells and S-opsin⁺ cone outer segments were examined up to 7 days. Left eyes were treated topically with BMD (1%) or vehicle, before or right after LIP, or intravitreally with BDNF (2.5 μg), CNTF (0.2 μg), bFGF (0.5 μg), or corresponding vehicle right after LIP. At 7 days, S-opsin⁺ cone outer segments were counted within predetermined fixed-size areas (PFA) centered on the lesion in both flattened retinas.

Results

SD-OCT showed a circular region in the superior-temporal left retina with progressive thinning (207.9 ± 5.6 μm to 160.7 ± 6.8 μm [7 days], n = 8), increasing TUNEL⁺ cells (peak at 3 days), decreasing S-opsin⁺ cone outer segments, and strong microglia activation. ERGs were normal by 3 days. Total S-opsin⁺ cones in the PFA for LIP-treated and fellow-retinas were 2330 ± 262 and 5601 ± 583 (n = 8), respectively. All neuroprotectants (n = 7–11), including topical BMD pre- or post-LIP, or intravitreal BDNF, CNTF, and bFGF, showed significantly greater S-opsin⁺ cone survival than their corresponding vehicle-treated groups.

Conclusions

LIP is a reliable, quantifiable focal photoreceptor degeneration model. Topical BMD or intravitreal BDNF, CNTF, or bFGF protect against LIP-induced cone-photoreceptor loss.

Translational Relevance

Topical BMD or intravitreal BDNF, CNTF, or bFGF protect cones against phototoxicity.

Retinal Ganglion Cell Death as a Late Remodeling Effect of Photoreceptor Degeneration

Inherited or acquired photoreceptor degenerations, one of the leading causes of irreversible blindness in the world, are a group of retinal disorders that initially affect rods and cones, situated in the outer retina. For many years it was assumed that these diseases did not spread to the inner retina. However, it is now known that photoreceptor loss leads to an unavoidable chain of events that cause neurovascular changes in the retina including migration of retinal pigment epithelium cells, formation of “subretinal vascular complexes”, vessel displacement, retinal ganglion cell (RGC) axonal strangulation by retinal vessels, axonal transport alteration and, ultimately, RGC death. These events are common to all photoreceptor degenerations regardless of the initial trigger and thus threaten the outcome of photoreceptor substitution as a therapeutic approach, because with a degenerating inner retina, the photoreceptor signal will not reach the brain. In conclusion, therapies should be applied early in the course of photoreceptor degeneration, before the remodeling process reaches the inner retina.

β-alanine supplementation induces taurine depletion and causes alterations of the retinal nerve fiber layer and axonal transport by retinal ganglion cells

To study the effect of taurine depletion induced by β-alanine supplementation in the retinal nerve fiber layer (RNFL), and retinal ganglion cell (RGC) survival and axonal transport. Albino Sprague-Dawley rats were divided into two groups: one group received β-alanine supplementation (3%) in the drinking water during 2 months to induce taurine depletion, and the other group received regular water. After one month, half of the rats from each group were exposed to light. Retinas were analyzed in-vivo using Spectral-Domain Optical Coherence Tomography (SD-OCT). Prior to processing, RGCs were retrogradely traced with fluorogold (FG) applied to both superior colliculi, to assess the state of their retrograde axonal transport. Retinas were dissected as wholemounts, surviving RGCs were immunoidentified with Brn3a, and the RNFL with phosphorylated high-molecular-weight subunit of the neurofilament triplet (pNFH) antibodies. β-alanine supplementation decreases significantly taurine plasma levels and causes a significant reduction of the RNFL thickness that is increased after light exposure. An abnormal pNFH immunoreactivity in some RGC bodies, their proximal dendrites and axons, and a further diminution of the mean number of FG-traced RGCs compared with Brn3a⁺RGCs, indicate that their retrograde axonal transport is affected. In conclusion, taurine depletion causes RGC loss and axonal transport impairment. Finally, our results suggest that care should be taken when ingesting β-alanine supplements due to the limited understanding of their potential adverse effects.

Melanopsin+RGCs Are fully Resistant to NMDA-Induced Excitotoxicity

We studied short- and long-term effects of intravitreal injection of N-methyl-d-aspartate (NMDA) on melanopsin-containing (m⁺) and non-melanopsin-containing (Brn3a⁺) retinal ganglion cells (RGCs). In adult SD-rats, the left eye received a single intravitreal injection of 5µL of 100nM NMDA. At 3 and 15 months, retinal thickness was measured in vivo using Spectral Domain-Optical Coherence Tomography (SD-OCT). Ex vivo analyses were done at 3, 7, or 14 days or 15 months after damage. Whole-mounted retinas were immunolabelled for brain-specific homeobox/POU domain protein 3A (Brn3a) and melanopsin (m), the total number of Brn3a⁺RGCs and m⁺RGCs were quantified, and their topography represented. In control retinas, the mean total numbers of Brn3a⁺RGCs and m⁺RGCs were 78,903 ± 3572 and 2358 ± 144 (mean ± SD; n = 10), respectively. In the NMDA injected retinas, Brn3a⁺RGCs numbers diminished to 49%, 28%, 24%, and 19%, at 3, 7, 14 days, and 15 months, respectively. There was no further loss between 7 days and 15 months. The number of immunoidentified m⁺RGCs decreased significantly at 3 days, recovered between 3 and 7 days, and were back to normal thereafter. OCT measurements revealed a significant thinning of the left retinas at 3 and 15 months. Intravitreal injections of NMDA induced within a week a rapid loss of 72% of Brn3a⁺RGCs, a transient downregulation of melanopsin expression (but not m⁺RGC death), and a thinning of the inner retinal layers.

Did you choose appropriate tracer for retrograde tracing of retinal ganglion cells? The differences between cholera toxin subunit B and Fluorogold

Cholera toxin subunit B (CTB) and Fluorogold(FG) are two widely utilized retrograde tracers to assess the number and function of retinal ganglion cells (RGCs). However, the relative advantages and disadvantages of these tracers remain unclear, which may lead to their inappropriate application. In this study, we compared these tracers by separately injecting the tracer into the superior Colliculi (SC) in rats, one or 2 weeks later, the rats were sacrificed, and their retinas, brains, and optic nerves were collected. From the first to second week, FG displayed a greater number of labeled RGCs and a larger diffusion area in the SC than CTB; The number of CTB labeled RGCs and the diffusion area of CTB in the SC increased significantly, but there was no distinction between FG; Furthermore, CTB exhibited more labeled RGC neurites and longer neurites than FG, but no difference was evident between the same trace; The optic nerves labeled using CTB were much clearer than those labeled using FG. In conclusion, both CTB and FG can be used for the retrograde labeling of RGCs in rats at 1 or 2 weeks. FG achieves retrograde labeling of a greater number of RGCs than CTB, whereas CTB better delineates the morphology of RGCs. Furthermore, CTB seems more suitable for retrograde labeling of some small, non-image forming nuclei in the brain to which certain RGC subtypes project their axons.

Non-Visual Photopigments Effects of Constant Light-Emitting Diode Light Exposure on the Inner Retina of Wistar Rats

The retina is part of the central nervous system specially adapted to capture light photons and transmit this information to the brain through photosensitive retinal cells involved in visual and non-visual activities. However, excessive light exposure may accelerate genetic retinal diseases or induce photoreceptor cell (PRC) death, finally leading to retinal degeneration (RD). Light pollution (LP) caused by the characteristic use of artificial light in modern day life may accelerate degenerative diseases or promote RD and circadian desynchrony. We have developed a working model to study RD mechanisms in a low light environment using light-emitting diode (LED) sources, at constant or long exposure times under LP conditions. The mechanism of PRC death is still not fully understood. Our main goal is to study the biochemical mechanisms of RD. We have previously demonstrated that constant light (LL) exposure to white LED produces a significant reduction in the outer nuclear layer (ONL) by classical PRC death after 7 days of LL exposure. The PRCs showed TUNEL-positive labeling and a caspase-3-independent mechanism of cell death. Here, we investigate whether constant LED exposure affects the inner-retinal organization and structure, cell survival and the expression of photopigments; in particular we look into whether constant LED exposure causes the death of retinal ganglion cells (RGCs), of intrinsically photosensitive RGCs (ipRGCs), or of other inner-retinal cells. Wistar rats exposed to 200 lx of LED for 2 to 8 days (LL 2 and LL 8) were processed for histological and protein. The results show no differences in the number of nucleus or TUNEL positive RGCs nor inner structural damage in any of LL groups studied, indicating that LL exposure affects ONL but does not produce RGC death. However, the photopigments melanopsin (OPN4) and neuropsin (OPN5) expressed in the inner retina were seen to modify their localization and expression during LL exposure. Our findings suggest that constant light during several days produces retinal remodeling and ONL cell death as well as significant changes in opsin expression in the inner nuclear layer.