[Acoustic density of sclera as a prognostic factor of peripheral vitreochorioretinal degenerations in myopia: results of 10-years follow-up]

Prognostic value of acoustic density of sclera (ADS) is studied in development of peripheral vitreochorioretinal degenerations (PVCRD) in myopia. Children aged 8-10 years old with noncomplicated high and moderate myopia were divided into two groups after ADS measurement: 1 with ADS < or = 39dB - unfavorable prognosis, 2 with ADS >39dB - favorable prognosis. Follow-up during 10 years with examinations twice a year confirmed prognosis accuracy: in the 1st group PVCRD developed 2.5 times as often as in the 2nd group (64.6 and 25.6% respectively).

Light damage as a model of retinal degeneration

The induction of retinal degeneration by light exposure is widely used to study mechanisms of cell death. The advantage of such light-induced lesions over genetically determined degenerations is that light exposures can be manipulated according to the needs of the experimenter. Bright white light exposure can induce a synchronized burst of apoptosis in photoreceptors in a large retinal area which permits to study cellular and molecular events in a controlled fashion. Blue light of high energy induces a hot spot of high retinal irradiance within very short exposure durations (seconds to minutes) and may help to unravel the initial events after light absorption which may be similar for all damage regimens. These initial events may then induce various molecular signaling pathways and secondary effects such as lipid and protein oxidation, which may be varying in different light damage setups and different strains or species, respectively. Blue light lesions also allow to study cellular responses in a circumscribed retinal area (hot spot) in comparison with the surrounding tissue.Here we describe the methods for short-term exposures (within the hours range) to bright full-spectrum white light and for short exposures (seconds to minutes) to high-energy monochromatic blue or green light.

NAD(+) maintenance attenuates light induced photoreceptor degeneration

Light-induced retinal damage (LD) occurs after surgery or sun exposure. We previously showed that zinc (Zn(2+)) accumulated in photoreceptors and RPE cells after LD but prior to cell death, and pyruvate or nicotinamide attenuated the resultant death perhaps by restoring nicotinamide adenine dinucleotide (NAD(+)) levels. We first examined the levels of NAD(+) and the efficacy of pyruvate or nicotinamide in oxidative toxicities using primary retinal cultures. We next manipulated NAD(+) levels in vivo and tested the affect on LD to photoreceptors and RPE. NAD(+) levels cycle with a 24-h rhythm in mammals, which is affected by the feeding schedule. Therefore, we tested the affect of increasing NAD(+) levels on LD by giving nicotinamide, inverting the feeding schedule, or using transgenic mice which overexpress cytoplasmic nicotinamide mononucleotide adenyl-transferase-1 (cytNMNAT1), an NAD(+) synthetic enzyme. Zn(2+) accumulation was also assessed in culture and in retinal sections. Retinas of light damaged animals were examined by OCT and plastic sectioning, and retinal NAD(+) levels were measured. Day fed, or nicotinamide treated rats showed less NAD(+) loss, and LD compared to night fed rats or untreated rats without changing the Zn(2+) staining pattern. CytNMNAT1 showed less Zn(2+) staining, NAD(+) loss, and cell death after LD. In conclusion, intense light, Zn(2+) and oxidative toxicities caused an increase in Zn(2+), NAD(+) loss, and cell death which were attenuated by NAD(+) restoration. Therefore, NAD(+) levels play a protective role in LD-induced death of photoreceptors and RPE cells.

Retinal neurodegeneration in Wilson's disease revealed by spectral domain optical coherence tomography

Background/Objective

In addition to cirrhosis of the liver, Wilson’s disease leads to copper accumulation and widespread degeneration of the nervous system. Delayed visual evoked potentials (VEPs) suggest changes to the visual system and potential structural changes of the retina.

Methods

We used the latest generation of spectral domain optical coherence tomography to assess the retinal morphology of 42 patients with Wilson’s disease and 76 age- and sex-matched controls. We measured peripapillary retinal nerve fiber layer (RNFL) thickness and total macular thickness and manually segmented all retinal layers in foveal scans of 42 patients with Wilson’s disease and 76 age- and sex-matched controls. The results were compared with VEPs and clinical parameters.

Results

The mean thickness of the RNFL, paramacular region, retinal ganglion cell/inner plexiform layer and inner nuclear layer was reduced in Wilson’s disease. VEPs were altered with delayed N75 and P100 latencies, but the N140 latency and amplitude was unchanged. An analysis of the laboratory parameters indicated that the serum concentrations of copper and caeruloplasmin positively correlated with the thickness of the outer plexiform layer and with N75 and P100 VEP latencies.

Conclusion

Neuronal degeneration in Wilson’s disease involves the retina and changes can be quantified by optical coherence tomography. While the VEPs and the thickness of the outer plexiform layer appear to reflect the current copper metabolism, the thicknesses of the RNFL, ganglion cell/inner plexiform layer, inner nuclear layer and the total paramacular thickness may be the best indicators of chronic neuronal degeneration.

Neurodegeneration of the retina in type 1 diabetic patients

INTRODUCTION

The degeneration of retinal neurons and glial cells has recently been postulated in the pathogenesis of diabetic retinopathy. Optical coherence tomography (OCT) allows to perform qualitative and quantitative measurements of retinal thickness (RT) with identification of individual retinal layers.

OBJECTIVES

We compared RT, retinal nerve fiber layer (RNFL) thickness, and ganglion cell layer (GCL) thickness obtained by OCT in type 1 diabetic patients with and without clinically diagnosed retinopathy.

PATIENTS AND METHODS

The study included 77 consecutive patients with type 1 diabetes (39 men, 38 women; median age, 35 years [interquartile range (IQR), 29-42]; median disease duration, 10 years [IQR, 9-14]) and 31 age- and sex-matched controls. We measured RT in the fovea, parafovea, and perifovea, as well as RNFL and GCL thickness. We divided diabetic patients into 2 subgroups, i.e., those with diabetic retinopathy and without retinopathy.

RESULTS

We observed thicker perifoveal retina (P = 0.05), mean RNFL (P = 0.002), inferior RNFL (P <0.0001), and superior and inferior GCL (P = 0.05 and P = 0.04, respectively) in diabetic subjects compared with the control group. We detected retinopathy in 23 diabetic patients (29%). Compared with patients without retinopathy, subjects with retinopathy had thinner parafoveal retina (P = 0.05), mean RNFL (P = 0.002), inferior and nasal RNFL (P = 0.002, P = 0.03), superior (P = 0.05) and inferior GCL (P = 0.006). Significant correlations were found between duration of diabetes and nasal RNFL thickness (r = -0.32, P = 0.004) and parafoveal RT (r = -0.47, P <0.001).

CONCLUSIONS

The results might suggest the loss of intraretinal neural tissue in type 1 diabetic patients with retinopathy. Neurodegeneration in diabetic retinopathy is closly associated with disease duration.

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.

Large-scale phenotyping of an accurate genetic mouse model of JNCL identifies novel early pathology outside the central nervous system

Cln3^Δex7/8 mice harbor the most common genetic defect causing juvenile neuronal ceroid lipofuscinosis (JNCL), an autosomal recessive disease involving seizures, visual, motor and cognitive decline, and premature death. Here, to more thoroughly investigate the manifestations of the common JNCL mutation, we performed a broad phenotyping study of Cln3^Δex7/8 mice. Homozygous Cln3^Δex7/8 mice, congenic on a C57BL/6N background, displayed subtle deficits in sensory and motor tasks at 10–14 weeks of age. Homozygous Cln3^Δex7/8 mice also displayed electroretinographic changes reflecting cone function deficits past 5 months of age and a progressive decline of retinal post-receptoral function. Metabolic analysis revealed increases in rectal body temperature and minimum oxygen consumption in 12–13 week old homozygous Cln3^Δex7/8mice, which were also seen to a lesser extent in heterozygous Cln3^Δex7/8 mice. Heart weight was slightly increased at 20 weeks of age, but no significant differences were observed in cardiac function in young adults. In a comprehensive blood analysis at 15–16 weeks of age, serum ferritin concentrations, mean corpuscular volume of red blood cells (MCV), and reticulocyte counts were reproducibly increased in homozygous Cln3^Δex7/8 mice, and male homozygotes had a relative T-cell deficiency, suggesting alterations in hematopoiesis. Finally, consistent with findings in JNCL patients, vacuolated peripheral blood lymphocytes were observed in homozygous Cln3^Δex7/8 neonates, and to a greater extent in older animals. Early onset, severe vacuolation in clear cells of the epididymis of male homozygous Cln3^Δex7/8 mice was also observed. These data highlight additional organ systems in which to study CLN3 function, and early phenotypes have been established in homozygous Cln3^Δex7/8 mice that merit further study for JNCL biomarker development.

Neurodegeneration of the retina in mouse models of Alzheimer's disease: what can we learn from the retina?

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disease commonly found among elderly. In addition to cognitive and behavioral deficits, vision abnormalities are prevalent in AD patients. Recent studies investigating retinal changes in AD double-transgenic mice have shown altered processing of amyloid precursor protein and accumulation of β-amyloid peptides in neurons of retinal ganglion cell layer (RGCL) and inner nuclear layer (INL). Apoptotic cells were also detected in the RGCL. Thus, the pathophysiological changes of retinas in AD patients are possibly resembled by AD transgenic models. The retina is a simple model of the brain in the sense that some pathological changes and therapeutic strategies from the retina may be observed or applicable to the brain. Furthermore, it is also possible to advance our understanding of pathological mechanisms in other retinal degenerative diseases. Therefore, studying AD-related retinal degeneration is a promising way for the investigation on (1) AD pathologies and therapies that would eventually benefit the brain and (2) cellular mechanisms in other retinal degenerations such as glaucoma and age-related macular degeneration. This review will highlight the efforts on retinal degenerative research using AD transgenic mouse models.

Inhibition of poly(ADP-ribose) polymerase inhibits ischemia/reperfusion induced neurodegeneration in retina via suppression of endoplasmic reticulum stress

Poly(ADP-ribose) polymerase (PARP) inhibitors have neuroprotective effects after retinal ischemia and reperfusion (I/R) injury, but mechanisms of this action are not clear. A second generation PARP inhibitor, GPI 15427, was administrated to mice to investigate the possible mechanisms underlying its neuroprotective effects after retinal I/R injury. Ischemia was induced by increasing intraocular pressure to 80-90 mm Hg for 60 min followed by reperfusion, and mice were treated with GPI 15427 (40 mg/kg(-1) day(-1), orally) 2 days before or 1 day after injury. Histopathology caused by the retinal I/R injury was estimated by TUNEL assay and histological analyses. Relative gene expressions were evaluated by RT-PCR, Western blotting and immunohistological studies. GPI 15427 inhibited the retinal I/R-induced PARP activation and glial cell activation. GPI 15427 also significantly inhibited the I/R-induced neurodegeneration, as well as increase in TUNEL-positive cells. I/R-induced PERK-eIF2α-CHOP activation and Bip over-expression were inhibited by GPI 15427, while it did not suppress I/R-induced CHOP over-expression and degeneration of retinal capillaries. Our results suggest that GPI 15427 inhibited retinal I/R-induced neurodegeneration and glial cell activation, and this was associated with an effect of the drug to suppress PERK-eIF2α-CHOP activation and Bip over-expression. These results provide evidence that GPI 15427 inhibits retinal I/R injury at least in part via inhibition of endoplasmic reticulum stress.

Effects of combined ketamine/xylazine anesthesia on light induced retinal degeneration in rats

Objectives

To explore the effect of ketamine-xylazine anesthesia on light-induced retinal degeneration in rats.

Methods

Rats were anesthetized with ketamine and xylazine (100 and 5 mg, respectively) for 1 h, followed by a recovery phase of 2 h before exposure to 16,000 lux of environmental illumination for 2 h. Functional assessment by electroretinography (ERG) and morphological assessment by in vivo imaging (optical coherence tomography), histology (hematoxylin/eosin staining, TUNEL assay) and immunohistochemistry (GFAP and rhodopsin staining) were performed at baseline (ERG), 36 h, 7 d and 14 d post-treatment. Non-anesthetized animals treated with light damage served as controls.

Results

Ketamine-xylazine pre-treatment preserved retinal function and protected against light-induced retinal degeneration. In vivo retinal imaging demonstrated a significant increase of outer nuclear layer (ONL) thickness in the non-anesthetized group at 36 h (p<0.01) and significant reduction one week (p<0.01) after light damage. In contrast, ketamine-xylazine pre-treated animals showed no significant alteration of total retinal or ONL thickness at either time point (p>0.05), indicating a stabilizing and/or protective effect with regard to phototoxicity. Histology confirmed light-induced photoreceptor cell death and Müller cells gliosis in non-anesthetized rats, especially in the superior hemiretina, while ketamine-xylazine treated rats showed reduced photoreceptor cell death (TUNEL staining: p<0.001 after 7 d), thicker ONL and longer IS/OS. Fourteen days after light damage, a reduction of standard flash induced a-wave amplitudes and a-wave slopes (p = 0.01) and significant alterations in parameters of the scotopic sensitivity function (e.g. Vmax of the Naka Rushton fit p = 0.03) were observed in non-treated vs. ketamine-xylazine treated animals.

Conclusions

Our results suggest that pre-treatment with ketamine-xylazine anesthesia protects retinas against light damage, reducing photoreceptor cell death. These data support the notion that anesthesia with ketamine-xylazine provides neuroprotective effects in light-induced cell damage.

Role of fractalkine/CX3CR1 interaction in light-induced photoreceptor degeneration through regulating retinal microglial activation and migration

Background

Excessive exposure to light enhances the progression and severity of some human retinal degenerative diseases. While retinal microglia are likely to be important in neuron damage associated with these diseases, the relationship between photoreceptor damage and microglial activation remains poorly understood. Some recent studies have indicated that the chemokine fractalkine is involved in the pathogenesis of many neurodegenerative diseases. The present study was performed to investigate the cross-talk between injured photoreceptors and activated retinal microglia, focusing on the role of fractalkine and its receptor CX3CR1 in light-induced photoreceptor degeneration.

Methodology/Principal Findings

Both in vivo and in vitro experiments were involved in the research. In vivo, Sprague–Dawley rats were exposed to blue light for 24 hours. In vitro, the co-culture of primary retinal microglia and a photoreceptor cell line (661W cell) was exposed to blue light for five hours. Some cultures were pretreated by the addition of anti-CX3CR1 neutralizing antibody or recombinant fractalkine. Expression of fractalkine/CX3CR1 and inflammatory cytokines was detected by immunofluorescence, real-time PCR, Western immunoblot analysis, and ELISA assay. TUNEL method was used to detect cell apoptosis. In addition, chemotaxis assay was performed to evaluate the impact of soluble fractalkine on microglial migration. Our results showed that the expression of fractalkine that was significantly upregulated after exposure to light, located mainly at the photoreceptors. The extent of photoreceptor degeneration and microglial migration paralleled the increased level of fractalkine/CX3CR1. Compared with the control, the expression of inflammatory cytokines was significantly downregulated in the anti-CX3CR1 neutralizing antibody-treated group, and the number of photoreceptors was also well preserved. The addition of recombinant full-length fractalkine or soluble fractalkine resulted in fewer TUNEL-positive photoreceptors and an increased number of migratory microglia respectively.

Conclusions/Significance

These findings demonstrate that fractalkine/CX3CR1 interaction may play an important role in the photoreceptor-microglia cross-talk in light-induced photoreceptor degeneration.

Retinal degenerative diseases--mechanisms and perspectives of treatment

Retinal degenerative diseases are an extensive group of ocular diseases, leading to vision disorders and finally irreversible vision loss. They are an significant problem, because degenerative processes exist in common ocular disorders like glaucoma or age-related macular degeneration and many other less frequently occurring disorders. In this article, we present mechanisms leading to retinal degeneration like excitotoxicity, oxidative stress, inflammation and summarize the latest reports concerning neuroprotection in the treatment of retina degenerative diseases.

Vision deficits precede structural losses in a mouse model of mitochondrial dysfunction and progressive retinal degeneration

Current animal models of retinal disease often involve the rapid development of a retinal disease phenotype; however, this is at odds with age-related diseases that take many years to manifest clinical symptoms. The present study was performed to examine an apoptosis-inducing factor (Aif)-deficient model, the harlequin carrier mouse (X(hq)X), and determine how mitochondrial dysfunction and subsequent accelerated aging affect the function and structure of the mouse retina. Vision and eye structure for cohorts of 6 X(hq)X and 6 wild type mice at 3, 11, and 15 months of age were studied using in vivo electroretinography (ERG), and optical coherence tomography (OCT). Retinal superoxide levels were determined in situ using dihydroethidium (DHE) histochemistry. Retinal cell counts were quantified post mortem using hematoxylin and eosin (H&E) staining. ERG analysis of X(hq)X retinal function indicated a reduction in b-wave amplitude significant at 3 months of age (p < 0.05), declining further with age. However, retinal neuron counts demonstrated the absence of physical degeneration at 3 and 11 months of age despite significant reduction in ERG b-wave amplitude. Superoxide anion levels were elevated in the ganglion cell, inner nuclear and outer nuclear layers of the retina (p < 0.01, p < 0.01, and p < 0.001, respectively) of 11-month-old X(hq)X mice in comparison to wild type, preceding the structural losses observed at 15 mos. Early onset of retinal function deficits occurred independently of neuron loss. Changes in neurotransmitter localization in the stressed retina may account for the early and significant reduction in retinal function. This remodeling of retinal neurochemistry in response to stress may be a relevant mechanism in the progression of normal retinal aging and early stages of some retinal degenerative diseases.

Defective photoreceptor phagocytosis in a mouse model of enhanced S-cone syndrome causes progressive retinal degeneration

Enhanced S-cone syndrome (ESCS), featuring an excess number of S cones, manifests as a progressive retinal degeneration that leads to blindness. Here, through optical imaging, we identified an abnormal interface between photoreceptors and the retinal pigment epithelium (RPE) in 9 patients with ESCS. The neural retina leucine zipper transcription factor-knockout (Nrl(-/-)) mouse model demonstrates many phenotypic features of human ESCS, including unstable S-cone-positive photoreceptors. Using massively parallel RNA sequencing, we identified 6203 differentially expressed transcripts between wild-type (Wt) and Nrl(-/-) mouse retinas, with 6 highly significant differentially expressed genes of the Pax, Notch, and Wnt canonical pathways. Changes were also obvious in expression of 30 genes involved in the visual cycle and 3 key genes in photoreceptor phagocytosis. Novel high-resolution (100 nm) imaging and reconstruction of Nrl(-/-) retinas revealed an abnormal packing of photoreceptors that contributed to buildup of photoreceptor deposits. Furthermore, lack of phagosomes in the RPE layer of Nrl(-/-) retina revealed impairment in phagocytosis. Cultured RPE cells from Wt and Nrl(-/-) mice illustrated that the phagocytotic defect was attributable to the aberrant interface between ESCS photoreceptors and the RPE. Overcoming the retinal phagocytosis defect could arrest the progressive degenerative component of this disease.

[Comparative analysis of retinotomographic and histological examinations of retina in health and primary open-angle glaucoma]

Comparative analysis of retinal structure was performed in patients with POAG and control healthy group using spectral OCT and histology. An apparent similarity of tomographic and histological patterns of retinal changes was found in patients with POAG. These results make OCT potentially appropriate method for vital examination of retinal structure in glaucomatous eyes including early stages of the disease. Degeneration of all retinal layers is revealed. Blood flow deficiency due to sclerosis and hyalinosis of uveal vessels is considered to be an immediate cause of outer and intermediate retinal layers degeneration.

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

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

A Drosophila model for TDP-43 proteinopathy

Neuropathology involving TAR DNA binding protein-43 (TDP-43) has been identified in a wide spectrum of neurodegenerative diseases collectively named as TDP-43 proteinopathy, including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar dementia (FTLD). To test whether increased expression of wide-type human TDP-43 (hTDP-43) may cause neurotoxicity in vivo, we generated transgenic flies expressing hTDP-43 in various neuronal subpopulations. Expression in the fly eyes of the full-length hTDP-43, but not a mutant lacking its amino-terminal domain, led to progressive loss of ommatidia with remarkable signs of neurodegeneration. Expressing hTDP-43 in mushroom bodies (MBs) resulted in dramatic axon losses and neuronal death. Furthermore, hTDP-43 expression in motor neurons led to axon swelling, reduction in axon branches and bouton numbers, and motor neuron loss together with functional deficits. Thus, our transgenic flies expressing hTDP-43 recapitulate important neuropathological and clinical features of human TDP-43 proteinopathy, providing a powerful animal model for this group of devastating diseases. Our study indicates that simply increasing hTDP-43 expression is sufficient to cause neurotoxicity in vivo, suggesting that aberrant regulation of TDP-43 expression or decreased clearance of hTDP-43 may contribute to the pathogenesis of TDP-43 proteinopathy.

[Idiopatic parafoveolar telangiectasia associated with pseudoviteliform lesion, basal laminar drusen and optic nerve head drusen]

BACKGROUND

We present a case with bilateral optic disc drusen, associated in one eye with idiopathic parafoveal telangiectasis (Group 1B), basal laminar drusen, and foveal pseudovitelliform lesion.

PATIENT

A 45-years old female patient, which complained about a deterioration of vision at the right eye, was ophthalmologically examined.

RESULTS

The examination revealed a bilateral optic disc drusen, and on the right eye a macular haemorrhage. An examination after 2 months revealed a good vision, the resorption of the macular haemorrhage, idiopathic parafoveal telangiectasis, basal laminal drusen, and a foveal pseudovitelliform lesion.

CONCLUSIONS

The association is of importance because of the rarity of the haemorrhagic complication in the idiopathic parafoveal telangiectasis (Group IB), the possibility of a pathogenic correlation, and the difficulty of differential diagnosis with the optic disc drusen complicated with retinal haemorrhages. This association was not found in the literature we consulted.

Cancer-Induced, Immune-Mediated Ocular Degenerations

The means whereby vision can be lost from a disease located distant from the eye include autoimmunity, with sensitization resulting from extraocular stimuli, a process illustrated here by the immunologic confusion caused by cancers. The uncontrolled proliferation of malignancies commonly involves the expression of components of the central nervous system, but a damaging loss of tolerance is rare. When autoimmunity does develop, organ-specific antigens are more often involved than the more generalized and widely disseminated common neuronal components. A focus upon a single antigen is typical of the immune-mediated paraneoplasia, a collection of syndromes identified by unusual antibody reactions. This review provides an outline of the immunologic trail that led to the recognition of autoimmunity in paraneoplastic ocular degenerations, how specific antibody reactions aid in diagnosis, and the possibility of including antibodies in modes for sight-saving intervention. 'Those who do not know history are destined to repeat it'.

Nephronophthisis: disease mechanisms of a ciliopathy

Nephronophthisis (NPHP), a recessive cystic kidney disease, is the most frequent genetic cause of end-stage kidney disease in children and young adults. Positional cloning of nine genes (NPHP1 through 9) and functional characterization of their encoded proteins (nephrocystins) have contributed to a unifying theory that defines cystic kidney diseases as "ciliopathies." The theory is based on the finding that all proteins mutated in cystic kidney diseases of humans or animal models are expressed in primary cilia or centrosomes of renal epithelial cells. Primary cilia are sensory organelles that connect mechanosensory, visual, and other stimuli to mechanisms of epithelial cell polarity and cell-cycle control. Mutations in NPHP genes cause defects in signaling mechanisms that involve the noncanonical Wnt signaling pathway and the sonic hedgehog signaling pathway, resulting in defects of planar cell polarity and tissue maintenance. The ciliary theory explains the multiple organ involvement in NPHP, which includes retinal degeneration, cerebellar hypoplasia, liver fibrosis, situs inversus, and mental retardation. Positional cloning of dozens of unknown genes that cause NPHP will elucidate further signaling mechanisms involved. Nephrocystins are highly conserved in evolution, thereby allowing the use of animal models to develop future therapeutic approaches.

Chapter 8. Evolution and development in the cavefish Astyanax

The teleost Astyanax mexicanus is a single species consisting of two radically different forms: a sighted pigmented surface-dwelling form (surface fish) and a blind depigmented cave-dwelling form (cavefish). The two forms of Astyanax have favorable attributes, including descent from a common ancestor, ease of laboratory culture, and the ability to perform genetic analysis, permitting their use as a model system to explore questions in evolution and development. Here, we review current research on the molecular, cellular, and developmental mechanisms underlying the loss of eyes and pigmentation in Astyanax cavefish. Although functional eyes are lacking in adults, cavefish embryos begin to develop eye primordia, which subsequently degenerate. The major cause of eye degeneration appears to be apoptotic cell death of the lens, which prevents the growth of other optic tissues, including the retina. Ultimately, the loss of the eye is the cause of craniofacial differences between cavefish and surface fish. Lens apoptosis is induced by enhanced activity of the Hedgehog signaling system along the cavefish embryonic midline. The absence of melanin pigmentation in cavefish is due to a block in the ability of undifferentiated melanoblasts to accumulate L-tyrosine, the precursor of L-DOPA and melanin, in melanosomes. Genetic analysis has shown that this defect is caused by a hypomorphic mutation in the p/oca2 gene encoding an integral melanosomal membrane protein. We discuss how current studies of eye and pigment regression have revealed some of the mechanisms in which cavefish development has been changed during evolution.

[Activation of endoplasmic reticulum stress proteins in light-induced retinal degeneration]

OBJECTIVE

To investigate the expression of endoplasmic reticulum stress proteins in photoreceptor apoptosis in light-induced retinal degeneration.

METHODS

Exposure to excessive levels of light induced photoreceptor apoptosis and had been previously used as a model for the study of retinal degeneration. Photoreceptor apoptosis was detected by terminal dUTP transferase nick end labeling (TUNEL). The protein expression levels of ER stress sensors including glucosejregulated protein-78 (GRP78/BiP), caspase-12, phospho-eukaryotic initiation factor 2alpha (eIF2alpha) and phospho- double-stranded RNA-activated protein kinase-like endoplasmic reticulum kinase (PERK) were examined by immunojfluorescence and Western blot analysis.

RESULTS

Following light exposure, the protein expression levels of GRP78/BiP, caspase-12, phospho-eIF2alpha and phospho-PERK were up-regulated in a time dependent manner. The up-regulation of these proteins coincided with or preceded the photoreceptor apoptosis. At the peak of their expression, they were mainly located in the photoreceptor inner segments and/or outer nuclear layers (ONL).

CONCLUSION

Activation of endoplasmic reticulum stress proteins appears to play an important role in light-induced retinal degeneration. Therefore endoplasmic reticulum stress modulators could become a strong candidate for a therapeutic agent in treatment of these diseases.

5-Lipoxygenase, but not 12/15-lipoxygenase, contributes to degeneration of retinal capillaries in a mouse model of diabetic retinopathy

OBJECTIVE

Lipoxygenases are regulators of chronic inflammation and oxidative stress generation. We evaluated the role of 5- and 12-lipoxygenases in the development of diabetic retinopathy.

RESEARCH DESIGN AND METHODS

Wild-type mice, 5-lipoxygenase-deficient mice, and 12/15-lipoxygenase-deficient mice were assessed 1) after 9 months of diabetes for retinal histopathology and leukotriene receptor expression and 2) after 3 months of diabetes for leukostasis and retinal superoxide generation.

RESULTS

Diabetic wild-type mice developed the expected degeneration of retinal capillaries and pericytes and increases in both leukostasis and superoxide production (P < 0.006). We found no evidence of diabetes-induced degeneration of retinal ganglion cells in these animals. The vascular histopathology was significantly inhibited in 5-lipoxygenase-deficient mice, but not in 12/15-lipoxygenase-deficient mice. Retinas from diabetic 5-lipoxygenase-deficient mice also had significantly less leukostasis, superoxide production, and nuclear factor-kappaB (NF-kappaB) expression (all P < 0.006), whereas retinas from diabetic 12/15-lipoxygenase-deficient mice had significantly less leukostasis (P < 0.005) but not superoxide production or NF- kappaB expression. Retinas from diabetic wild-type mice were enriched with receptors for the 5-lipoxygenase metabolite leukotriene B(4). Diabetes-induced histological and biochemical alterations were significantly reduced in 5-lipoxygenase-deficient mice, but not 12/15-lipoxygenase-deficient mice.

CONCLUSIONS

5-Lipoxygenase represents a novel pathway for therapeutic intervention of diabetic retinopathy.

Developmental mechanisms for retinal degeneration in the blind cavefish Astyanax mexicanus

The sighted surface-dwelling (surface fish, SF) and the blind cave-living (cavefish, CF) forms of Astyanax mexicanus offer a unique opportunity to study the evolutionary changes in developmental mechanisms that lead to retinal degeneration. Previous data have shown the role of increased midline Sonic Hedgehog (Shh) signalling in cavefish eye degeneration (Yamamoto et al. [2004] Nature 431:844-847). Here, we have compared the major steps of eye development in SF and CF between 14 hours and 5 days of development. We have analyzed cell proliferation through PCNA and phospho-histone H3 staining and apoptosis through TUNEL and live LysoTracker analysis. We have assessed the expression of the major eye development signalling factors Shh and Fgf8, and the eye patterning genes Pax6, Lhx2, Lhx9, and Vax1, together with the differentiation marker GAD65. We show that eye development is retarded in CF and that cell proliferation in CF retina is proportionately similar to SF during early development, yet the retina degenerates after massive apoptosis in the lens and widespread cell death throughout the neuroretina. Moreover, and surprisingly, the signalling, patterning, and differentiation processes leading to the establishment of retinal layers and cell types happen almost normally in CF, although some signs of disorganization, slight heterochronies, and a lack of expression gradients are observable. Our data demonstrate that the evolutionary process of eye degeneration in the blind CF does not occur because of patterning defects of the retina and are consistent with the proposed scenario in which the trigger for eye degeneration in CF is lens apoptosis.

Experimental coronavirus retinopathy (ECOR): retinal degeneration susceptible mice have an augmented interferon and chemokine (CXCL9, CXCL10) response early after virus infection

Mouse hepatitis virus induces a biphasic disease in BALB/c mice that consists of an acute retinitis followed by progression to a chronic retinal degeneration with autoimmune reactivity. Retinal degeneration resistant CD-1 mice do not develop the late phase. What host factors contribute to the distinct responses to the virus are unknown. Herein, we show that IFN-α, IFN-β and IFN-γ act in concert as part of the innate immune response to the retinal infection. At day 2, high serum levels of IFN-γ, CXCL9 and CXCL10, were detected in BALB/c mice. Moreover, elevated levels of CXCL9 and CXCL10 gene expression were detected in retinal tissue. Although IFN-γ and the chemokines were detected in CD-1 mice, they were at significantly lower levels compared to BALB/c mice. These augmented innate responses observed correlated with the development of autoimmune reactivity and retinal degeneration and thus may contribute to the pathogenic processes.

Visual functional effects of constant blue light in a retinal degenerate rat model

Retinal degenerative conditions increase susceptibility to light damage, but rapid retinal degeneration (RD) models show less susceptibility to cyclic dim light. We investigated whether constant blue light (BL) exposure can eliminate the residual visual responses in a comparatively rapid RD rat model. Pigmented rhodopsin mutant S334ter line-3 rat pups (21 days old) were exposed for 5-6 consecutive days to constant BL. Visual behavior was evaluated with an optokinetic head tracking apparatus. Electrophysiological recordings were made from the superior colliculus (SC). S-antigen, red-green opsin and rhodopsin immunoreactive residual photoreceptors were counted. Following BL exposure, head tracking was significantly reduced at 0.25 cycles degree(-1) in 38-day-old line 3 rats. With a 0.125 cycles degree(-1) stimulus, the head tracking performance of 80-day-old BL rats were similar to that of 220-day-old no-BL-treated line-3 rats. SC recordings also revealed a significant decrease in the residual photoreceptor activity. Histological evaluation showed reduction of the rod population in the central area of the light-damaged retina. Exposure to constant BL considerably reduces the residual visual responses in a rapid degenerating RD rat model.

Perinatal hypoxia induces subsequent retinal degeneration in the offspring of ovoviviparous fish, Xiphophorous maculates

OBJECTIVE

This experiment evaluated the perinatal hypoxic effect on the retina of offspring of the ovoviviparous fish.

ANIMAL STUDIED

The ovoviviparous fish Xiphophorous maculates was used for the experiment.

PROCEDURE

The mothers were kept in a hypoxic environment of 3.5% oxygen for 6 h, starting 30 h before hatching. Subsequently, the retinae of the offspring were fixed, sectioned at 6 microm and evaluated microscopically from the age of 1 to 35 days.

RESULTS

Degeneration of the outer nuclear layer of the retina was noted on the 3rd day and severe retinal degeneration was observed on the 35th day. Immunocytochemistry confirmed apoptosis by TUNEL reaction. There was no difference in neovascularization, as revealed by vascular endothelial growth factor, between controls (group 1) and hypoxic fish (group 2).

CONCLUSIONS

Perinatal hypoxia could have long-lasting effects on the central nervous system in some species.

Bilateral Isolated Lateral Geniculate Body Lesions in a Patient with Pancreatitis and Microangiopathy

An 18-year-old woman developed pancreatitis and a thrombotic microangiopathy but no electrolyte abnormalities. She required intubation hours after admission and was not able to communicate for 8 days. Upon recovering consciousness, she reported severely impaired vision in both eyes, but ophthalmologic evaluation and neuroimaging were not obtained until several days later. Ophthalmologic examination documented retinal infarcts and profound binocular vision loss with hourglass bilateral homonymous hemianopic visual field loss. MRI showed signal abnormalities restricted to the area of the lateral geniculate bodies (LGBs) with characteristics most suggestive of hemorrhagic infarction. Very few cases of isolated bilateral LBG lesions have been reported. Damage has been attributed to myelinolysis from osmotic demyelination or to infarction from microvascular occlusion. This case conforms more to microvascular infarction. The vulnerability of the LGB to selective microvascular infarction may be based on a combination of its unique architecture and high metabolic demand.

Functional study in NSE-Hu-Bcl-2 transgenic mice: a model for retinal diseases starting in Müller cells

In NSE-Hu-Bcl-2 transgenic mice, line 71, retina undergoes early postnatal degeneration linked to the prior death of Müller cells. The purpose of this study was to complete the characterization of this retinal dysfunction by using electroretinographic (ERG) recordings in both scotopic and photopic conditions. Here, we showed that both rod and cone systems were profoundly affected in NSE-Hu-Bcl-2 transgenic mice as soon as 15 postnatal days in accordance with histological study performed previously.

Attenuated glial reactions and photoreceptor degeneration after retinal detachment in mice deficient in glial fibrillary acidic protein and vimentin

PURPOSE

To characterize the reactions of retinal glial cells (astrocytes and Müller cells) to retinal injury in mice that lack glial fibrillary acidic protein (GFAP) and vimentin (GFAP-/-Vim-/-) and to determine the role of glial cells in retinal detachment (RD)-induced photoreceptor degeneration.

METHODS

RD was induced by subretinal injection of sodium hyaluronate in adult wild-type (WT) and GFAP-/-Vim-/- mice. Astroglial reaction and subsequent monocyte recruitment were quantified by measuring extracellular signal-regulated kinase (Erk) and c-fos activation and the level of expression of chemokine monocyte chemoattractant protein (MCP)-1 and by counting monocytes/microglia in the detached retinas. Immunohistochemistry, immunoblotting, real-time quantitative polymerase chain reaction (PCR), and enzyme-linked immunosorbent assay (ELISA) were used. RD-induced photoreceptor degeneration was assessed by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) and measurement of outer nuclear layer (ONL) thickness.

RESULTS

RD-induced reactive gliosis, characterized by GFAP and vimentin upregulation, Erk and c-fos activation, MCP-1 induction, and increased monocyte recruitment in WT mice. Absence of GFAP and vimentin effectively attenuated reactive responses of retinal glial cells and monocyte infiltration. As a result, detached retinas of GFAP-/-Vim-/- mice exhibited significantly reduced numbers of TUNEL-positive photoreceptor cells and increased ONL thickness compared with those of WT mice.

CONCLUSIONS

The absence of GFAP and vimentin attenuates RD-induced reactive gliosis and, subsequently, limits photoreceptor degeneration. Results of this study indicate that reactive retinal glial cells contribute critically to retinal damage induced by RD and provide a new avenue for limiting photoreceptor degeneration associated with RD and other retinal diseases or damage.

Pathology of damaging electrical stimulation in the retina

The goal of this study was to examine the characteristics of electrically induced retinal damage. A retinal prosthesis must be both effective and safe, but most research related to electrical stimulation of the retina has involved measures of efficacy (for example, stimulus threshold), while relatively little research has investigated the safety of electrical stimulation. In this study, a single platinum microelectrode was inserted into the vitreous cavity of normally-sighted adult Long Evans pigmented rats. In one group of animals, no contact was made between the electrode and the retina and current pulses of 0.05 (n=3) and 0.2 (n=6) microC/phase were applied. In a second group, visible contact (slight dimpling of the retina) was made between the electrode and the retina and current pulses of 0.09 (n=4) microC/phase were applied. In both cases, stimulus pulses (biphasic, cathodic first, 1 ms/phase) were applied for 1 h at 100 Hz. Also, control experiments were run with no electrical stimulation with retina contact (n=4) and with no retinal contact (n=3). After stimulation, the animal was survived for 2 weeks with ocular photography and electroretinography (ERG) to document changes. During the follow-up period, retinal changes were observed only when the electrode contacted the retina, with or without electrical stimulation. No difference was noted in ERG amplitude or latency comparing the test eye to the stimulated eye. Histological analysis was performed after sacrifice at 2 weeks. A semi-quantitative method for grading 18 features of retina/RPE/choroidal appearance was established and integer grades applied to both test and control eyes. Using this method and comparing the most severely affected area (highest grade), significant differences (p<0.05) were noted between experiments with retinal contact and without retinal contact in all features except inner nuclear layer thickness. No difference was noted within a group based on the intensity of electrical stimulus applied. The size of the affected area was significantly larger with both retinal contact and electrical stimulation compared to with retinal contact alone. We conclude that mechanical pressure alone and mechanical pressure with excessive electrical stimulation causes damage to the retina but that electrical stimulation coupled with mechanical pressure increases the area of the damage.

The Effect of intravitreal N-methyl-DL-aspartic acid on the electroretinogram in Royal College of surgeons rats

PURPOSE

To investigate how the third-order neuronal response contributes to shaping the electroretinogram (ERG) in the Royal College of Surgeons (RCS) rat.

METHODS

Full-field ERGs were recorded from dystrophic RCS rats (n = 30) at 4, 6, 8, 10, 12, or 14 weeks of age in response to different stimulus intensities (maximum intensity, 0.84 log cd-s/m(2)). N-methyl-DL: -aspartic acid (NMDA, 5 mM) was injected into the vitreous cavity of the right eyes to eliminate the third-order neuronal response. The left eyes received the vehicle and served as controls. The third-order neuronal response was isolated by digitally subtracting waveforms of the NMDA-injected eyes from those of the control eyes.

RESULTS

The ERG a- and b-waves deteriorated with the age of the rat. The third-order neuronal response was preserved to a greater degree than the b-wave despite progression of photoreceptor degeneration. Intravitreal injection of NMDA attenuated the a-wave and enhanced the b-wave across the stimulus range from low to middle intensities. This tendency became more pronounced with advancing rat age. In aged dystrophic RCS rats this phenomenon was seen even at maximum intensity. The difference between NMDA-injected and vehicle-injected eyes was larger for the threshold than for the maximum amplitude at each examined time point (P < 0.001). Intravitreal injection of NMDA decreased implicit times of the a- and b-waves after the rats reached 8 weeks of age (P < 0.005 for the a-wave).

CONCLUSION

With advancing photoreceptor degeneration, the third-order neuronal response made a greater contribution to shaping the a- and b-waves in dystrophic RCS rats.

Angiogênese e doenças da retina

Angiogenesis is the process involving the growth of new blood vessels from preexisting vessels which occurs in both physiologic and pathological settings. It is a complex process controlled by a large number of modulating factors, the pro-and antiangiogenic factors. The underlying cause of vision loss in proliferative retinal diseases, such as age-related macular degeneration and proliferative diabetic retinopathy, are increased vascular permeability and choroidal neovascularization, and vascular endothelial growth factor (VEGF) plays a central role in this process. VEGF is produced in the eye by retinal pigment epithelium (RPE) cells and is upregulated by hypoxia. There are four major biologically active human isoforms, of which VEGF165 is the predominant in the human eye and appears to be the responsible for pathological ocular neovascularization. Besides being a potent and specific mitogen for endothelial cells, VEGF increases vascular permeability, inhibits endothelial cells apoptosis, and is a chemoattractant for endothelial cell precursors. VEGF is not the only growth factor involved in ocular neovascularization. Basic fibroblast growth factor (bFGF), angiopoietins, pigment epithelium-derived factor (PEDF), and adhesion molecules also play a role in the pro- and antiangiogenic balance. Advances in the understanding of the bases of pathological ocular angiogenesis and identification of angiogenesis regulators have enabled the development of novel therapeutic agents. Anti-VEGF antibodies have been developed for intravitreal use, and other approaches are currently under investigation. These new drugs may be powerful tools for the treatment of the leading causes of irreversible blindness in people over age 65.

Neurotrophic rationale in glaucoma: A TrkA agonist, but not NGF or a p75 antagonist, protects retinal ganglion cellsin vivo

Glaucoma is a major cause of vision impairment, which arises from the sustained and progressive apoptosis of retinal ganglion cells (RGC), with ocular hypertension being a major risk or co-morbidity factor. Because RGC death often continues after normalization of ocular hypertension, growth factor-mediated protection of compromised neurons may be useful. However, the therapeutic use of nerve growth factor (NGF) has not proven effective at delaying RGC death in glaucoma. We postulated that one cause for the failure of NGF may be related to its binding to two receptors, TrkA and p75. These receptors have distinct cellular distribution in the retina and in neurons they induce complex and sometimes opposing activities. Here, we show in an in vivo therapeutic model of glaucoma that a selective agonist of the pro-survival TrkA receptor was effective at preventing RGC death. RGC loss was fully prevented by combining the selective agonist of TrkA with intraocular pressure-lowering drugs. In contrast, neither NGF nor an antagonist of the pro-apoptotic p75 receptor protected RGCs. These results further a neurotrophic rationale for glaucoma.

Abnormal retinal thickness in patients with mild cognitive impairment and Alzheimer's disease

In Alzheimer's disease (AD), brain lesions are marked by severe neuronal loss and retinal degeneration was previously mentioned in affected patients. Mild cognitive impairment (MCI) is a clinical syndrome that could be an early phase of AD. In this study, using optical coherence tomography (OCT), the retinal nerve fiber layer (RNFL) thickness was assessed in patients with mild AD, moderate to severe AD, amnestic MCI and control subjects. The results show that RNFL thickness is statistically reduced in patients with MCI, mild AD or moderate to severe AD compared to controls. In addition, no statistical difference was found between the results in MCI patients and mild AD patients. The RNFL seems to be involved early during the course of amnestic MCI and OCT tests could be carried out in patients with cognitive troubles.

Caspase-Dependent Apoptosis in Light-Induced Retinal Degeneration

PURPOSE

To study the apoptotic mechanism involved in our model of light-induced retinal degeneration.

METHODS

Rats were injected intravitreally with PBS, 2% dimethyl sulfoxide (DMSO), caspase inhibitor Z-VAD-FMK (1.06 mM), Z-YVAD-FMK (0.16 mM), or Z-DEVD-FMK (2 mM) before they were placed in constant light (3400 lux) for 24 hours. Additional controls included rats that were uninjected or were punctured with a dry needle. Electroretinograms were recorded before injection and 1 day after the cessation of exposure to constant light. A group of rats was killed for apoptotic cell detection in the outer nuclear layer. Fifteen days later, the remaining rats were killed for histology, and the outer nuclear layer (ONL) thickness was measured. Caspase-1, caspase-3, and calpain activities were measured before and 1 day after exposure to the damaging light.

RESULTS

ZVAD, YVAD, and DEVD inhibited caspase-1 and -3 activities, but not calpain activity, from the beginning and up to 1 day after light exposure. In untreated, dry needle-punctured, PBS, DMSO, and YVAD groups, light exposure significantly reduced retinal function and ONL thickness and increased by 51-fold the number of apoptotic cells. ZVAD and DEVD preserved retinal function to 86% and 78%, respectively, and reduced by three times the number of apoptotic photoreceptors. ONL thickness was more preserved in ZVAD (to 72%) than in DEVD (to 56%).

CONCLUSIONS

In the authors' model of retinal degeneration, photoreceptor cells die through a caspase-dependent mechanism. However, the molecular events involved during and after light exposure seemed to implicate different proteases.

Retinal degenerations: from cell signaling to cell therapy; pre-clinical and clinical issues

Extracellular signaling molecules have been implicated in the progression of Retinal Degeneration (RD). Gene regulatory events linked to the maintenance of retinal structure and function incorporate signaling cascades that may serve as therapeutic targets for some forms of blindness. This review shall focus on the evidence for non-cell-autonomous mechanisms that affect the pattern of degeneration seen in retinal dystrophies, the types of signals that may influence the course of degeneration and finally with the related prospects for retinal-therapies.

Delayed loss of cone and remaining rod photoreceptor cells due to impairment of choroidal circulation after acute light exposure in rats

PURPOSE

To examine the long-term effects of acute photooxidative stress in the retina, retinal pigment epithelium (RPE), and choroid.

METHODS

Albino rats injected with either the protective antioxidant phenyl-N-tert-butylnitrone (PBN) or saline 30 minutes before exposure to 5 klx white fluorescent light for 6 hours were kept for up to 3 months in 5 lux cyclic light. Electroretinograms were recorded, and the outer nuclear layer (ONL) and the choroidal thickness and area were measured after hematoxylin-eosin (H&E) staining. The expression of rod, cone, and RPE cell markers was detected by Western blotting, and apoptosis was analyzed by TUNEL staining. Oxidative stress was analyzed by immunohistochemistry against 4-hydroxynonenal (4-HNE)-modified proteins. Retinal and choroidal ultrastructures were observed by transmission electron microscopy (TEM). Choroidal circulation was analyzed by in vivo staining of the choroidal layer by trypan blue.

RESULTS

In the saline-injected animals, TUNEL- and 4-HNE-labeling in the ONL, RPE, and choroid were higher 24 hours and 7 days after light exposure, and ERG amplitude, ONL and choroidal thickness and area, and rhodopsin and RPE65 expression were lower 7 or more days after light exposure than in phenyl-N-tert-butylnitrone (PBN)-injected animals. In the saline-injected animals, the expression of mid-wavelength opsin and the presence of cone cells in the ONL and the choroidal circulation were preserved for 7 days after light exposure but started to decrease by 1 month and continued to decrease for 3 months after light exposure. An increase in TUNEL-positive cells was observed in the ONL at the inferior peripheral retina, just behind the iris, by 3 months after light exposure. Delayed loss of cone cells, remaining rod cells, and choroidal circulation were counteracted by PBN treatment.

CONCLUSIONS

Although cone cells are resistant to cell damage induced by acute photooxidative stress, progressive loss of cone cells continued for up to 3 months after light exposure. Impaired choroidal circulation is likely to be involved in the mechanism of delayed photoreceptor cell death after light exposure. Preserving choroidal circulation may provide a novel target for preserving the cone and the remaining rod cells in patients with retinal degeneration such as retinitis pigmentosa.

Acute retinal ganglion cell injury caused by intraocular pressure spikes is mediated by endogenous extracellular ATP

Elevated intraocular pressure may lead to retinal ganglion cell injury and consequent visual deficits. Chronic intraocular pressure increase is a major risk factor for glaucoma, a leading blinding disease, and permanent visual deficits can also occur following acute pressure increments due to trauma, acute glaucoma or refractive surgery. How pressure affects retinal neurons is not firmly established. Mechanical damage at the optic nerve head, reduced blood supply, inflammation and cytotoxic factors have all been called into play. Reasoning that the analysis of retinal neurons soon after pressure elevation would provide useful cues, we imaged individual ganglion cells in isolated rat retinas before and after short hydrostatic pressure increments. We found that slowly rising pressure to peaks observed in trauma, acute glaucoma or refractive surgery (50-90 mmHg) did not damage ganglion cells, whereas a rapid 1 min pulse to 50 mmHg injured 30% of these cells within 1 h. The severity of damage and the number of affected cells increased with stronger or repeated insults. Degrading extracellular ATP or blocking the P2X receptors for ATP prevented acute pressure-induced damage in ganglion cells. Similar effects were observed in vivo. A short intraocular pressure transient increased extracellular ATP levels in the eye fluids and damaged ganglion cells within 1 h. Reducing extracellular ATP in the eye prevented damage to ganglion cells and accelerated recovery of their response to light. These data show that rapid pressure transients induce acute ganglion cell injury and unveil the causal role of extracellular ATP elevation in such injury.