DICER1 deficit induces Alu RNA toxicity in age-related macular degeneration

Geographic atrophy (GA), an untreatable advanced form of age-related macular degeneration, results from retinal pigmented epithelium (RPE) cell degeneration. Here we show that the microRNA (miRNA)-processing enzyme DICER1 is reduced in the RPE of humans with GA, and that conditional ablation of Dicer1, but not seven other miRNA-processing enzymes, induces RPE degeneration in mice. DICER1 knockdown induces accumulation of Alu RNA in human RPE cells and Alu-like B1 and B2 RNAs in mouse RPE. Alu RNA is increased in the RPE of humans with GA, and this pathogenic RNA induces human RPE cytotoxicity and RPE degeneration in mice. Antisense oligonucleotides targeting Alu/B1/B2 RNAs prevent DICER1 depletion-induced RPE degeneration despite global miRNA downregulation. DICER1 degrades Alu RNA, and this digested Alu RNA cannot induce RPE degeneration in mice. These findings reveal a miRNA-independent cell survival function for DICER1 involving retrotransposon transcript degradation, show that Alu RNA can directly cause human pathology, and identify new targets for a major cause of blindness.

Nicotinic acetylcholine receptor subunits in rhesus monkey retina

PURPOSE

The purpose of this study was to detect and establish the cellular localizations of nicotinic acetylcholine receptor (nAChR) subunits in Rhesus monkey retina.

METHODS

Retinas were dissected from the eyes of monkeys killed after unrelated experiments. RNA was extracted and analyzed by RT-PCR, using primers designed against human sequences of alpha3-alpha7, alpha9, and beta2-beta4 nAChR subunits. The RT-PCR products were separated by gel electrophoresis and sequenced. Frozen sections of postmortem fixed monkey eyes were immunolabeled with well-characterized and specific monoclonal antibodies against the alpha3, alpha4, alpha6, alpha7, beta2, or beta4 nAChR subunits and visualized with fluorescence labeling.

RESULTS

Products of the predicted size for the alpha3-alpha7, alpha9, and beta2-beta4 nAChR subunits were detected by RT-PCR in Rhesus monkey retina. Homology between transcripts from monkey retina and human nucleotide sequences ranged from 93 to 99%. Immunohistochemical studies demonstrated that neurons in various cell layers of monkey retina expressed alpha3, alpha4, alpha7, or beta2 nAChR subunits and cells with the morphology of microglia were immunoreactive for the alpha6 or beta4 nAChR subunits.

CONCLUSIONS

nAChR subunits are expressed in the monkey retina and localize to diverse retinal neurons as well as putative microglia. Besides mediating visual processing, retinal nAChRs may influence refractive development and ocular pathologies such as neovascularization.

Cone photoreceptor function loss-3, a novel mouse model of achromatopsia due to a mutation in Gnat2

PURPOSE

To report a novel mouse model of achromatopsia with a cpfl3 mutation found in the ALS/LtJ strain.

METHODS

The effects of a cpfl3 mutation were documented using fundus photography, electroretinography (ERG), and histopathology. Genetic analysis was performed using linkage studies and PCR gene identification.

RESULTS

Homozygous cpfl3 mice had poor cone-mediated responses on ERG at 3 weeks that became undetectable by 9 months. Rod-mediated waveforms were initially normal, but declined with age. Microscopy of the retinas revealed progressive vacuolization of the photoreceptor outer segments. Immunocytochemistry with cone-specific markers showed progressive loss of labeling for alpha-transducin, but the cone outer segments in the oldest mice examined remained intact and positive with peanut agglutinin (PNA). The cpfl3 mapped to mouse chromosome 3 at the same location as human GNAT2, known to cause achromatopsia. Sequence analysis revealed a missense mutation due to a single base pair substitution in exon 6 in cpfl3.

CONCLUSIONS

The Gnat2(cpfl3) mutation leads to cone dysfunction and the progressive loss of cone alpha-transducin immunolabeling. Despite a poor cone ERG signal and loss of cone alpha-transducin label, the cones survive at 14 weeks as demonstrated by PNA staining. This mouse model of achromatopsia will be useful in the study of the development, pathophysiology, and treatment of achromatopsia and other cone degenerations. The gene symbol for the cpfl3 mutation has been changed to Gnat2(cpfl3).

ABCA4-associated retinal degenerations spare structure and function of the human parapapillary retina

PURPOSE

To study the parapapillary retinal region in patients with ABCA4-associated retinal degenerations.

METHODS

Patients with Stargardt disease or cone-rod dystrophy and disease-causing variants in the ABCA4 gene were included. Fixation location was determined under fundus visualization, and central cone-mediated vision was measured. Intensity and texture abnormalities of autofluorescence (AF) images were quantified. Parapapillary retina of an eye donor with ungenotyped Stargardt disease was examined microscopically.

RESULTS

AF images ranged from normal, to spatially homogenous abnormal increase of intensity, to a spatially heterogenous speckled pattern, to variably sized patches of low intensity. A parapapillary ring of normal-appearing AF was visible at all disease stages. Quantitative analysis of the intensity and texture properties of AF images showed the preserved region to be an annulus, at least 0.6 mm wide, surrounding the optic nerve head. A similar region of relatively preserved photoreceptor nuclei was apparent in the donor retina. In patients with foveal fixation, there was better cone sensitivity at a parapapillary locus in the nasal retina than at the same eccentricity in the temporal retina. In patients with eccentric fixation, approximately 30% had a preferred retinal locus in the parapapillary retina.

CONCLUSIONS

Human retinal degenerations caused by ABCA4 mutations spare the structure of retina and RPE in a circular parapapillary region that commonly serves as the preferred fixation locus when central vision is lost. The retina between fovea and optic nerve head could serve as a convenient, accessible, and informative region for structural and functional studies to determine natural history or outcome of therapy in ABCA4-associated disease.

Identifying photoreceptors in blind eyes caused by RPE65 mutations: Prerequisite for human gene therapy success

Mutations in RPE65, a gene essential to normal operation of the visual (retinoid) cycle, cause the childhood blindness known as Leber congenital amaurosis (LCA). Retinal gene therapy restores vision to blind canine and murine models of LCA. Gene therapy in blind humans with LCA from RPE65 mutations may also have potential for success but only if the retinal photoreceptor layer is intact, as in the early-disease stage-treated animals. Here, we use high-resolution in vivo microscopy to quantify photoreceptor layer thickness in the human disease to define the relationship of retinal structure to vision and determine the potential for gene therapy success. The normally cone photoreceptor-rich central retina and rod-rich regions were studied. Despite severely reduced cone vision, many RPE65-mutant retinas had near-normal central microstructure. Absent rod vision was associated with a detectable but thinned photoreceptor layer. We asked whether abnormally thinned RPE65-mutant retina with photoreceptor loss would respond to treatment. Gene therapy in Rpe65(-/-) mice at advanced-disease stages, a more faithful mimic of the humans we studied, showed success but only in animals with better-preserved photoreceptor structure. The results indicate that identifying and then targeting retinal locations with retained photoreceptors will be a prerequisite for successful gene therapy in humans with RPE65 mutations and in other retinal degenerative disorders now moving from proof-of-concept studies toward clinical trials.

Histopathologic study of X-linked cone-rod dystrophy (CORDX1) caused by a mutation in the RPGR exon ORF15

PURPOSE

To evaluate the donor retina of a patient with X-linked cone-rod dystrophy caused by an RPGR exon ORF15 mutation.

DESIGN

Histopathologic study of the retina.

METHODS

The eye of a 69-year-old man was fixed at 1.6 hours postmortem and processed for histopathology and immunocytochemistry.

RESULTS

Grossly, the macula was atrophic with a bull's-eye appearance. The remaining retina showed postmortem edema but no intraretinal pigment. Microscopically, the macular retinal pigment epithelium was absent focally and had pigmentary changes elsewhere. Cones and rods were absent from the perifovea and reduced with shortened outer segments elsewhere in the macula. In the remainder of the retina, cones but not rods were reduced and all photoreceptor outer segments were shortened.

CONCLUSIONS

The abnormalities in both cone and rod photoreceptors confirm the importance of RPGR in both cell types but leaves unresolved how various exon ORF15 mutations lead to different clinical phenotypes.

Cone Damage in Patients Receiving High-Dose Irofulven Treatment

OBJECTIVES

To describe the clinical, perimetric, and electroretinographic (ERG) results of 4 patients with cone dysfunction following irofulven treatment including the histopathologic and immunocytochemical features of one patient's retinas.

DESIGN

Observational case series.

METHODS

The patients were examined clinically, including perimetric and ERG evaluations. Eyes from patient 1 and healthy postmortem eyes were processed for histopathologic and immunocytochemistry studies with antibodies specific for cones, rods, and reactive Müller cells.

MAIN OUTCOME MEASURES

Clinical signs and symptoms, perimetry, ERG, retinal histopathologic and immunocytochemistry study results.

RESULTS

All 4 patients had ERG changes consistent with abnormal cone responses and relatively normal rod responses. Compared with control eyes, the retina of patient 1 had approximately half the normal numbers of macular cones and fewer peripheral cones. The number of rods were normal but all rod and cone outer segments were shortened.

CONCLUSION

High-dose irofulven treatment causes cone-specific damage with relative sparing of rods.

Electroretinographic and clinicopathologic correlations of retinal dysfunction in infantile neuronal ceroid lipofuscinosis (infantile Batten disease)

Infantile neuronal ceroid lipofuscinosis (INCL) is an autosomal recessive disease that results from deficiency of palmitoyl-protein thioesterase-1 (PPT1). INCL leads to retinal blindness, neurodegeneration, and early death. We studied the clinical features and electroretinogram (ERG) in three patients and histopathologic and immunofluorescence analyses of the retina in the third patient, who died at 3 years 2 months of age. The ERGs for the 2 youngest patients (ages 1.7 and 2.3 years) showed normal scotopic bright flash a-wave amplitudes with severe loss of b-wave (electronegative ERG), indicating dysfunction at or proximal to the photoreceptor inner segments. The third patient at 2.9 years of age showed subnormal a-wave amplitudes and even greater loss of b-wave amplitudes. Histopathology revealed reduced cell numbers in all retinal layers, including the inner nuclear layer (INL), and a central epiretinal membrane. Autofluorescent lipofuscin granules were present in all neuronal cell types in the retina. Cones and rods in the parafoveal area were labeled with a cone cytoplasmic marker, mAb 7G6, and anti-rhodopsin, respectively, and had extremely short outer segments. The periphery showed better preservation but photoreceptor outer segments were short. Immunofluorescence revealed degenerate rods and cones throughout the retina with better preservation in the periphery. Autofluorescent lipofuscin was found in all cell types, including cone inner segments, to a greater degree than seen in normal ageing. The ERG findings support the existence early in the disease of a relative pre- or post-synaptic block of effective neurotransmission from photoreceptor inner segments to the second order bipolar neurons.

Mutation in a short-chain collagen gene, CTRP5, results in extracellular deposit formation in late-onset retinal degeneration: a genetic model for age-related macular degeneration

A primary feature of age-related macular degeneration (AMD) is the presence of extracellular deposits between the retinal pigment epithelium (RPE) and underlying Bruch's membrane, leading to RPE dysfunction, photoreceptor death and severe visual loss. AMD accounts for about 50% of blind registrations in Western countries and is a common, genetically complex disorder. Very little is known regarding its molecular basis. Late-onset retinal degeneration (L-ORD) is an autosomal dominant disorder with striking clinical and pathological similarity to AMD. Here we show that L-ORD is genetically heterogeneous and that a proposed founder mutation in the CTRP5 (C1QTNF5) gene, which encodes a novel short-chain collagen, changes a highly conserved serine to arginine (Ser163Arg) in 7/14 L-ORD families and 0/1000 control individuals. The mutation occurs in the gC1q domain of CTRP5 and results in abnormal high molecular weight aggregate formation which may alter its higher-order structure and interactions. These results indicate a novel disease mechanism involving abnormal adhesion between RPE and Bruch's membrane.

Retinal remodeling triggered by photoreceptor degenerations

Many photoreceptor degenerations initially affect rods, secondarily leading to cone death. It has long been assumed that the surviving neural retina is largely resistant to this sensory deafferentation. New evidence from fast retinal degenerations reveals that subtle plasticities in neuronal form and connectivity emerge early in disease. By screening mature natural, transgenic, and knockout retinal degeneration models with computational molecular phenotyping, we have found an extended late phase of negative remodeling that radically changes retinal structure. Three major transformations emerge: 1) Müller cell hypertrophy and elaboration of a distal glial seal between retina and the choroid/retinal pigmented epithelium; 2) apparent neuronal migration along glial surfaces to ectopic sites; and 3) rewiring through evolution of complex neurite fascicles, new synaptic foci in the remnant inner nuclear layer, and new connections throughout the retina. Although some neurons die, survivors express molecular signatures characteristic of normal bipolar, amacrine, and ganglion cells. Remodeling in human and rodent retinas is independent of the initial molecular targets of retinal degenerations, including defects in the retinal pigmented epithelium, rhodopsin, or downstream phototransduction elements. Although remodeling may constrain therapeutic intervals for molecular, cellular, or bionic rescue, it suggests that the neural retina may be more plastic than previously believed.

Proapoptotic bcl-2 family members, Bax and Bak, are essential for developmental photoreceptor apoptosis

PURPOSE

Apoptosis has been implicated in retinal development and degeneration, but the specific apoptotic pathways used are incompletely understood. The purpose of this study was to characterize the roles in retinal development of the proapoptotic Bcl-2 family members Bax and Bak.

METHODS

Eyes from mice at postnatal day (P)7, during the peak of developmental apoptosis in the retina, were processed for TdT-dUTP terminal nick-end labeling (TUNEL) to determine whether Bax knockout or double Bax/Bak knockout causes a defect in developmental apoptosis. Adult (>2-month-old) eyes from wild-type, Bak(-/-), Bax(-/-), and Bax(-/-)Bak(-/-) mice were analyzed by histology and immunocytochemistry to identify persistent retinal cells.

RESULTS

Adult Bax(-/-)Bak(-/-) eyes showed significant increases in the number of inner retinal cells, with an almost complete absence of TUNEL-positive cell death at P7. Some of these persistent cells in the inner retina notably included rod photoreceptors that normally undergo apoptosis after failure to migrate to the outer retina. These inner nuclear layer (INL) rods contained markers of early rod differentiation: rod opsin, arrestin, and recoverin. However, they did not form ectopic outer segments or contain the associated markers ROM-1, peripherin-2, and RP1.

CONCLUSIONS

Bax and Bak are important for retinal development and are the first apoptotic factors identified as essential for developmental photoreceptor apoptosis. Future studies will investigate the potential role of Bax and Bak in mediating pathologic photoreceptor death.

Maculas affected by age-related macular degeneration contain increased chelatable iron in the retinal pigment epithelium and Bruch's membrane

OBJECTIVE

To investigate whether iron is involved in the pathogenesis of age-related macular degeneration (AMD).

METHODS

Postmortem AMD-affected (nonexudative or exudative) and healthy maculas were studied using the 3,3'-diaminobenzidine-enhanced Perls Prussian blue stain. The Perls Prussian blue stain was quantified by computer-assisted analysis of digital images. To determine whether the iron was chelatable, sections treated with the iron chelator deferoxamine were compared with adjacent, nonchelated sections.

RESULTS

Compared with healthy maculas, AMD-affected maculas had statistically significant increases in the total iron level. Some of this iron was chelatable. The iron was present in retinal pigment epithelium and Bruch's membrane in maculas from patients who had drusen only, geographic atrophy, and exudative AMD in pathologic areas and, occasionally, in relatively healthy areas.

CONCLUSIONS

Oxidative stress has been implicated in the pathogenesis of AMD by the Age-Related Eye Disease Study. Increased concentrations of iron, which generate highly reactive hydroxyl radicals via the Fenton reaction, may induce oxidative stress in the macula and lead to AMD. As the increased iron concentrations in AMD-affected eyes consist in part of a chelatable iron pool, treatment of patients who have AMD with iron chelators might be considered a potential therapy. While there are, as yet, no clinical data indicating that the treatment of patients who have AMD with iron chelators is beneficial, data presented herein indicate that further investigation of iron concentrations in postmortem tissues and the mechanisms of iron transport in the retina is warranted.

Amyloid-beta is found in drusen from some age-related macular degeneration retinas, but not in drusen from normal retinas

PURPOSE

Age-related macular degeneration (AMD) is the most common cause of irreversible vision loss in the elderly. Increased understanding of the pathogenesis is necessary. Amyloid-beta (Abeta), a major extracellular deposit in Alzheimer's disease plaques, has recently been found in drusen, the hallmark extracellular deposit in AMD. The goal of this study was to characterize the distribution and frequency of Abeta deposits in drusen from AMD and normal post mortem human retinas to gain additional insight about the potential role of Abeta in AMD patho genesis.

METHODS

Immunocytochemistry was performed with three Abeta antibodies on sections from 9 normal and 9 AMD (3 early, 3 geographic atrophy, 3 exudative AMD) retinas. Five sections from each eye were evaluated. Abeta positive deposits in drusen were identified using epifluorescence and confocal microscopy. Antibodies were pre-adsorbed with Abeta peptide to verify specificity. Some sections were stained with PAS-hematoxylin to aid in evaluation of morphology.

RESULTS

To test and optimize immunocytochemistry, Abeta was detected in amyloid plaques from Alzheimer's brains. Abeta label was blocked by pre-adsorption of antibody with Abeta peptide, verifying specificity. Four of the 9 AMD retinas and none of the 9 normal retinas had Abeta positive drusen. Two of the early AMD eyes had a few A[beta] positive drusen, each with a few Abeta-containing vesicles, and 2 of the geographic atrophy (GA) eyes had many Abeta positive drusen with many Abeta containing vesicles.

CONCLUSIONS

Abeta was present in 4 of 9 AMD eyes. Within these eyes, Abeta localized to a subset of drusen. None of the 9 normal eyes surveyed, some of which had small drusen, were A beta positive. Abetapositive vesicles were most numerous in GA eyes at the edges of atrophy, the region at risk for further degeneration. These results suggest that Abeta in drusen correlates with the location of degenerating photoreceptors and retinal pigment epithelium (RPE) cells. Further work will be necessary to determine whether Abeta deposition in drusen may contribute to or result from retinal degeneration.

Crumbs homolog 1 (CRB1) mutations result in a thick human retina with abnormal lamination

Mutations in CRB1, the human homolog of Drosophila Crumbs, cause autosomal recessive blinding disorders of the retina. Whereas Crumbs is implicated in apical-basal epithelial polarity and photoreceptor morphogenesis, the role of CRB1 in normal or diseased retina remains unclear. We characterized the retinal organization in vivo of patients with CRB1 mutations and found that, unlike other inherited retinal degenerations studied to date, the CRB1 mutant retinas are remarkably thick in cross-section and lack the distinct layers of normal adult retina. There are coarse outer and inner zones and a thick surface layer around the optic nerve. The abnormal retinal architecture in CRB1 mutations resembles that of immature normal retina. The results suggest that the CRB1 disease pathway disturbs the development of normal human retinal organization by interrupting naturally occurring apoptosis.

Activated microglia in human retinitis pigmentosa, late-onset retinal degeneration, and age-related macular degeneration

Many gaps exist in our knowledge of human retinal microglia in health and disease. We address the hypothesis that primary death of rod photoreceptors leads to activation of resident microglia in human retinas with retinitis pigmentosa (RP), late-onset retinal degeneration (L-ORD), or age-related macular degeneration (AMD). Regions of ongoing photoreceptor cell death were studied by immunocytochemistry with microglia- and other retinal cell-specific markers. In normal human retinas, quiescent microglia were small, stellate cells associated with inner retinal blood vessels. In retinas with RP, L-ORD, or AMD, numerous activated microglia were present in the outer nuclear layer in regions of ongoing rod cell death. These microglia were enlarged, amoeboid cells that contained rhodopsin-positive cytoplasmic inclusions. We conclude that activated microglia migrate to the outer nuclear layer and remove rod cell debris. In other central nervous system diseases such as stroke, activated microglia phagocytose debris from the primary injury and also secrete molecules that kill nearby normal neurons. By analogy with these diseases, we suggest that microglia activated by primary rod cell death may kill adjacent photoreceptors. Activated microglia may be a missing link in understanding why initial rod cell death in the human diseases RP, L-ORD, and AMD leads to death of the cones that are critical for high acuity daytime vision.

Cone deactivation kinetics and GRK1/GRK7 expression in enhanced S cone syndrome caused by mutations in NR2E3

PURPOSE

To determine the relationship between cone deactivation kinetics in patients with the enhanced S cone syndrome (ESCS) caused by mutations in NR2E3 and the immunoreactivity to G-protein-coupled receptor kinase 1 (GRK1) and GRK7.

METHODS

Electroretinogram (ERG) photoresponses were used to investigate activation kinetics of cones with a model of cone phototransduction. Deactivation kinetics of cones after bright flashes was quantified with a paired-flash ERG paradigm. Immunocytochemistry was performed with antibodies against cone opsins and kinases GRK1 and GRK7 in postmortem normal and ESCS retinal tissue.

RESULTS

Activation kinetics of long/middle-wavelength-sensitive (L/M) cone-mediated responses in patients with ESCS were similar to those of normal L/M cones. Activation kinetics of ESCS short-wavelength-sensitive (S) cones, when compared with normal L/M cone responses evoked by the same stimulus, were slower by an amount consistent with the expected differences in spectral sensitivities. After bright flashes chosen to evoke identical activation kinetics, ESCS S cones deactivated much more slowly than ESCS or normal L/M cones. Normal human retina revealed strongly labeled cone outer segments with anti-GRK1 and anti-GRK7. In an ESCS retina, outer segments positive for L/M opsin were strongly labeled with anti-GRK1, whereas outer segments positive for S opsin showed no detectable GRK1 reactivity. GRK7 labeling was absent in all photoreceptors of the ESCS retina.

CONCLUSIONS

The cone-dominant human retina resulting from NR2E3 mutations affords greater understanding of the physiological roles of GRK1 and GRK7 in human cone photoreceptors. Normal deactivation kinetics in human L/M cones can occur without GRK7 when GRK1 is present in ESCS, but does not occur when GRK7 is present but GRK1 is deficient in Oguchi disease. Lack of both GRK1 and GRK7 in S cones of patients with ESCS results in a more pronounced abnormality in deactivation kinetics and suggests the existence of partial compensation by either GRK when the other is deficient.

Clinicopathologic effects of mutant GUCY2D in Leber congenital amaurosis

PURPOSE

To study the retinal degeneration in an 11 -year-old patient with Leber congenital amaurosis (LCA) caused by mutation in GUCY2D.

STUDY DESIGN

Comparative human tissue study.

PARTICIPANTS

Two subjects with LCA; postmortem eye from one LCA patient and three normal donors.

METHODS

Clinical and visual function studies were performed between the ages of 6 and 10 years in the LCA eye donor and at age 6 in an affected sibling. Genomic DNA was screened for mutations in known LCA genes. The retina of the 11 -year-old subject with LCA was compared with normal retinas from donors age 3 days, 18 years, and 53 years. The tissues were processed for histopathologic studies and immunofluorescence with retinal cell-specific antibodies.

RESULTS

Vision in both siblings at the ages examined was limited to severely impaired cone function. Mutation in the GUCY2D gene was identified in both siblings. Histopathologic study revealed rods and cones without outer segments in the macula and far periphery. The cones formed a monolayer of cell bodies, but the rods were clustered and had sprouted neurites in the periphery. Rods and cones were not identified in the midperipheral retina. The inner nuclear layer appeared normal in thickness throughout the retina, but ganglion cells were reduced in number.

CONCLUSIONS

An 11-year-old subject with LCA caused by mutant GUCY2D had only light perception but retained substantial numbers of cones and rods in the macula and far periphery. The finding of numerous photoreceptors at this age may portend well for therapies designed to restore vision at the photoreceptor level.

The role of apoptosis in age-related macular degeneration

OBJECTIVE

To investigate apoptosis in human age-related macular degeneration (AMD).

METHODS

Postmortem retinas with AMD and normal retinas were studied by terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) to identify dying cells, and by immunocytochemistry with cell-specific antibodies to identify rods and cones. Sections were also labeled for Fas, a cell surface receptor that triggers apoptosis in other cell types. The maculas with AMD had geographic atrophy (GA) or exudative AMD.

RESULTS

Maculas with AMD had statistically significant increases in TUNEL-positive cells in the inner choroid, retinal pigment epithelium (RPE), photoreceptors, and inner nuclear layers compared with normal retinas. In eyes with GA, TUNEL-positive rod and RPE cell nuclei were present near edges of RPE atrophy. Photoreceptors in the maculas of eyes with AMD were strongly Fas-positive, while normal photoreceptors were only weakly labeled.

CONCLUSIONS

Evidence in this study suggests that in human AMD, RPE, photoreceptors, and inner nuclear layer cells die by apoptosis. Most TUNEL-positive RPE and photoreceptor cells were at edges of atrophy, correlating with clinically observed expansion of atrophic areas with vision loss in patients with GA. Increased Fas labeling in AMD photoreceptors indicates that the Fas/Fas ligand system may be involved in photoreceptor apoptosis. This information is essential for developing rational therapy for AMD.

Retinal histopathology of an XLRP carrier with a mutation in the RPGR exon ORF15

X-linked retinitis pigmentosa comprises the severe forms of RP, with early onset of night blindness, rapid constriction of visual fields and eventual loss of central acuity. Of the five distinct XLRP loci identified on the X chromosome, mutations have been found only in the RP2 and RPGR genes. Of these, mutations in RPGR are more common, particularly in a mutational hot spot that was identified in the newly discovered exon ORF15. We report on an extended family with a microdeletion in RPGR exon ORF15 and the retinal histopathology of a female carrier of this mutation. We found a 1bp deletion at position 632 in exon ORF15 in affected members of family XLRP-319. This mutation alters the reading frame of the predicted RPGR protein, resulting in a premature stop codon. The mutation segregated with disease in three generations of the family and was associated with severe early onset retinal disease in affected men. The retina from a 75 year old carrier female donor had slight photoreceptor loss in the less diseased areas. More severe atrophy with retinal pigment epithelium (RPE) migration was present in areas of the mid- and far periphery. By immunocytochemistry, loss of rhodopsin labelling in rods was found in the areas of focal atrophy and loss of uniform cone spacing was apparent even in well preserved regions. Small multifocal areas of outer retinal degeneration were present in the better preserved regions of the eye. In these foci, rod and cone loss did not coincide. The dissociation of rod and cone degeneration in areas of focal disease is consistent with random X-inactivation early in embryonic development and the occurrence of distinct patterns of radial (rod) and tangential (cone) dispersion during clonal expansion early in photoreceptor differentiation.

Nature of the cone ON-pathway dysfunction in melanoma-associated retinopathy

PURPOSE

To establish the basis for an ON-pathway abnormality of the cone system in melanoma-associated retinopathy (MAR) through analysis of the electroretinogram (ERG) and visual evoked potential (VEP).

METHODS

Two patients with MAR syndrome whose sera produced immunolabeling of retinal bipolar cells participated in the study. Full-field ERGs were recorded in response to brief flashes, to rapid-on and rapid-off sawtooth stimuli at a temporal frequency of 8 Hz, and to sine-wave stimuli at temporal frequencies ranging from 8 to 96 Hz. Fundamental responses to the sine-wave stimuli were evaluated within the context of a vector-summation model of the depolarizing bipolar cell (DBC) and hyperpolarizing bipolar cell (HBC) contributions to the response fundamental. VEPs were recorded to the onset of luminance increments and decrements that had contrasts of 10%, 20%, and 50%. The patients' results were compared with those of age-similar control subjects.

RESULTS

The patients with MAR showed abnormal ERG responses to luminance increments, consisting of a marked attenuation of the initial portion of the b-wave, but their ERG responses to luminance decrements were normal in amplitude and timing. The ERG temporal response functions of the patients with MAR had normal amplitudes at frequencies of 32 Hz and higher, with a constant phase lag across these frequencies, but larger-than-normal amplitudes at frequencies below 32 Hz, and a phase lead at 8 Hz. Their VEP responses showed a marked delay to increments but only a minimal delay to decrements.

CONCLUSIONS

Within the context of the vector-summation model, the ERG findings in the patients with MAR are more consistent with an attenuation of the DBC contribution to the ERG response than with a DBC response delay. The delayed VEP responses of the patients with MAR to luminance increments may represent a late response of the OFF system to increment onset.

The nuclear receptor NR2E3 plays a role in human retinal photoreceptor differentiation and degeneration

Normal human retinal development involves orderly generation of rods and cones by complex mechanisms. Cell-fate specification involves progenitor cell lineage and external signals such as soluble factors and cell-cell interactions. In most inherited human retinal degenerations, including retinitis pigmentosa, a mutant gene causes loss of visual function, death of mature rods, and eventually death of all cone subtypes. Only one inherited retinal disorder, the enhanced S cone syndrome (ESCS), shows increased visual function, involving the minority S (blue) cones, and decreased rod and L/M (red/green) cone function. This autosomal recessive disease is caused by mutations in NR2E3, a photoreceptor nuclear receptor transcription factor, and may result from abnormal cell-fate determination, leading to excess S cones at the expense of other photoreceptor subtypes. In 16 ESCS patients with the most common NR2E3 mutation, R311Q, we documented an abnormal ratio of S to L/M cone function and progressive retinal degeneration. We studied the postmortem retina of an ESCS patient homozygous for NR2E3 R311Q. No rods were identified, but cones were increased approximately 2-fold, and 92% were S cones. Only 15% of the cones expressed L/M cone opsin, and some coexpressed S cone opsin. The retina was disorganized, with densely packed cones intermixed with inner retinal neurons. The retina was also degenerate, retaining photoreceptors in only the central and far peripheral regions. These observations suggest a key role for NR2E3 in regulation of human photoreceptor development. Degeneration of the NR2E3 retina may result from defective development, known S cone fragility, or abnormal maintenance of mature photoreceptors.

Identification and subcellular localization of the RP1 protein in human and mouse photoreceptors

PURPOSE

Mutations in the RP1 gene account for 6% to 10% of autosomal dominant retinitis pigmentosa (adRP). Previous studies have shown that the RP1 gene is expressed specifically in photoreceptor cells. So far, little is known about the RP1 protein or how mutations in RP1 lead to photoreceptor cell death. The goal of this study was to identify the RP1 protein and investigate its location in photoreceptor cells.

METHODS

A combination of RT-PCR and rapid amplification of cDNA ends (RACE) was used to isolate the full-length mouse Rp1 cDNA. Antibodies against different regions of the predicted mouse Rp1 protein were generated. Western blot analyses were used to identify the RP1/Rp1 proteins. The subcellular location of RP1 in human and mouse retinas was determined by immunostaining retinal sections.

RESULTS

The full-length mouse Rp1 cDNA is 6944 bp, encoding a predicted protein of 2095 amino acids. Rp1 was found to be a soluble protein of approximately 240 kDa, consistent with predictions based on the cDNA sequence. Immunofluorescence analyses revealed that both the human RP1 and mouse Rp1 proteins are specifically localized in the connecting cilia of rod and cone photoreceptors.

CONCLUSIONS

The presence of RP1/Rp1 in connecting cilia suggests that it may participate in transport of proteins between the inner and outer segments of photoreceptors or in maintenance of cilial structure. This study forms the basis for further investigation of the function of RP1 in retina and the mechanism by which mutations in RP1 lead to photoreceptor cell death.

Concentric retinitis pigmentosa: clinicopathologic correlations

Progressive concentric (centripetal) loss of vision is one pattern of visual field loss in retinitis pigmentosa. This study provides the first clinicopathologic correlations for this form of retinitis pigmentosa. A family with autosomal dominant concentric retinitis pigmentosa was examined clinically and with visual function tests. A post-mortem eye of an affected 94 year old family member was processed for histopathology and immunocytochemistry with retinal cell specific antibodies. Unrelated simplex/multiplex patients with concentric retinitis pigmentosa were also examined. Affected family members of the eye donor and patients from the other families had prominent peripheral pigmentary retinopathy with more normal appearing central retina, good visual acuity, concentric field loss, normal or near normal rod and cone sensitivity within the preserved visual field, and reduced rod and cone electroretinograms. The eye donor, at age 90, had good acuity and function in a central island. Grossly, the central region of the donor retina appeared thinned but otherwise normal, while the far periphery contained heavy bone spicule pigment. Microscopically the central retina showed photoreceptor outer segment shortening and some photoreceptor cell loss. The mid periphery had a sharp line of demarcation where more central photoreceptors were near normal except for very short outer segments and peripheral photoreceptors were absent. Rods and cones showed abrupt loss of outer segments and cell death at this interface. It is concluded that concentric retinitis pigmentosa is a rare but recognizable phenotype with slowly progressive photoreceptor death from the far periphery toward the central retina. The disease is retina-wide but shows regional variation in severity of degeneration; photoreceptor death is severe in the peripheral retina with an abrupt edge between viable and degenerate photoreceptors. Peripheral to central gradients of unknown retinal molecule(s) may be defective or modify photoreceptor degeneration in concentric retinitis pigmentosa.

Multiple phosphorylated isoforms of NRL are expressed in rod photoreceptors

NRL, a bZIP transcription factor of the Maf subfamily, interacts with the homeodomain protein CRX and synergistically regulates rhodopsin expression. Here we report that six isoforms of NRL (29-35 kDa) are generated by phosphorylation and expressed specifically in the mammalian retina. The anti-NRL antibody also cross-reacts with a cytosolic 45-kDa protein, which is detected in neuronal tissues but is not encoded by the NRL gene. In both human retinal cell cultures and sections of fetal and adult human retina, NRL is present in the nuclei of developing and mature rods but not cones. We propose that NRL regulates rod photoreceptor-specific gene expression and is involved in rod differentiation.

Localization of pigment epithelium derived factor (PEDF) in developing and adult human ocular tissues

PURPOSE

To localize pigment epithelium-derived factor (PEDF) in developing and adult human ocular tissues.

METHODS

PEDF was localized in fetal and adult eyes by immunofluorescence with a polyclonal antibody (pAb) against amino acids 327-343 of PEDF, or a monoclonal antibody (mAb) against the C-terminal 155 amino acids of PEDF. Specificity of the antibodies was documented by Western blotting. PEDF mRNA was localized in adult retina by in situ hybridization.

RESULTS

In developing retinas (7.4 to 21.5 fetal weeks, Fwks), pAb anti-PEDF labeled retinal pigment epithelium (RPE) granules, developing cones, some neuroblasts and many cells in the ganglion cell layer (GCL). In adult retinas, pAb anti-PEDF labeled rod and cone cytoplasm and nuclei of rods but not cones. Cells in the INL and GCL, choroid, corneal epithelium and endothelium, and ciliary body were also pAb PEDF-positive. Preadsorption of pAb anti-PEDF with the immunizing peptide blocked specific labeling in retina and other tissues, except for photoreceptor outer segments. In agreement with the immunolocalization with pAb anti-PEDF, in situ hybridization revealed PEDF mRNA in the RPE, photoreceptors, inner nuclear layer cells and ganglion cells in adult retina. In developing retinas 18 Fwks and older, and in adult retinas, mAb anti-PEDF labeled the interphotoreceptor matrix (IPM). Western blots of retina, cornea, and ciliary body/iris with pAb anti-PEDF produced several bands at about 46 kDa. With mAb anti-PEDF, retina produced one band at about 46 kDa; cornea and ciliary body/iris had several bands at about 46 kDa.

CONCLUSIONS

PEDF, originally reported as a product of RPE cells, is present in photoreceptors and inner retinal cell types in developing and adult human eyes. Photoreceptors and RPE may secrete PEDF into the IPM.

Evaluation of retinal photoreceptors and pigment epithelium in a female carrier of choroideremia

PURPOSE

To clarify the pathogenesis of choroideremia.

STUDY DESIGN

Human tissue study. TISSUES: Eyes of an 88-year-old symptomatic female carrier of choroideremia (CHM) and six normal, age-matched donors.

METHODS

The eyes were processed for histopathologic examination, including immunocytochemistry with an antibody against the CHM gene product, REP-1, and retinal cell-specific markers.

RESULTS

The CHM carrier retina showed patchy degeneration, but the photoreceptor and retinal pigment epithelium (RPE) loss appeared to be independent. The choriocapillaris was normal except where retinal areas were severely degenerate. The CHM gene product, REP-1, was localized to the cytoplasm of rods but not cones.

CONCLUSIONS

It has generally been considered that photoreceptor degeneration in CHM is secondary to loss of the choriocapillaris or RPE. This study suggests that the rod photoreceptors are a primary site of disease in CHM.

Immunocytochemical characterization of macular hole opercula

OBJECTIVES

To immunocytochemically characterize the neural and glial elements of idiopathic full-thickness macular hole (FTMH) opercula excised during vitrectomy, and to correlate them with the outcome of surgery.

METHODS

Opercula were collected from eyes undergoing vitrectomy for stage 3 FTMH and processed for transmission electron microscopy, light epifluorescence, and laser scanning confocal microscopy. Glia were identified using anti-glial fibrillary acid protein (GFAP), antivimentin, and anti-cellular retinaldehyde binding protein antibodies. Anti-phosphodiesterase gamma and antirhodopsin were used for cone and rod photoreceptors, and anticytokeratin was used for retinal pigment epithelium. The findings were correlated with the clinical data before and after surgery. For statistical analysis, data were combined with those of a previous study by the authors of 18 opercula.

RESULTS

Opercula from 12 consecutive eyes of 12 patients were studied. In all opercula, GFAP, vimentin, and cellular retinaldehyde binding protein-positive glia were present. Six (50%) of 12 opercula contained more than 5 photoreceptors with somata and internal photoreceptor fibres, but lacking outer segments, demonstrating strong immunoreactivity to anti-phosphodiesterase gamma without antirhodopsin reactivity consistent with cones. Further, 2 (17%) of 12 opercula showed few cones (1-5 cones), and 4 (33%) of 12 contained only glia. Clinicopathologic correlation of the 30 opercula from the 2 studies showed that eyes with opercula containing more than 5 photoreceptors were associated with a worse anatomical closure rate after initial surgery, compared with those with fewer than 5 photoreceptors (P =.004). Once closure had been achieved with reoperation, median postoperative vision was similar in both groups (20/40 and 20/60, respectively).

CONCLUSIONS

A spectrum of opercula occur in FTMH ranging from those containing only glia to those containing numerous cones. The extent of foveal neuroretinal tissue loss may affect the outcome of surgery.

Dominant late-onset retinal degeneration with regional variation of sub-retinal pigment epithelium deposits, retinal function, and photoreceptor degeneration

PURPOSE

To clarify the pathogenesis of late-onset retinal degeneration (L-ORD), an autosomal dominant disorder characterized by thick deposits of lipid-rich material between the retinal pigment epithelium (RPE) and Bruch's membrane.

STUDY DESIGN

Comparative clinicopathologic case report and case series. TISSUES: Eyes of an 82-year-old L-ORD eye donor and an age-matched control.

SUBJECTS

Five descendants of the eye donor and his affected sister.

METHODS

The eyes were processed for histopathologic examination, including electron microscopy and immunohistochemistry. Family members were examined clinically and with retinal function tests.

RESULTS

The L-ORD eye had sub-RPE deposits that were positive for lipid, including esterified and unesterified cholesterol. The deposits were thinnest in the macula, which retained the highest percentage of photoreceptors. In the periphery, RPE thinning and photoreceptor loss correlated with thickness of the sub-RPE deposits. The eye donor was asymptomatic until his late 50s, when he developed problems with adapting to darkness. At age 68, the eye donor had normal acuity but a midperipheral scotoma and subnormal electroretinograms (ERGs); visual loss was progressive. The five descendants (at the time of examination ages 44-58) of the eye donor and his affected sister, who were at 50/50 risk of inheriting L-ORD, had normal ERGs, but four showed defects in dark adaptation. The dark adaptation abnormalities had a distribution similar to the thickness of the sub-RPE deposits in the eye donor, with slow kinetics in the midperiphery and normal kinetics centrally.

CONCLUSIONS

The L-ORD donor eye differed from a previous case in the regional distribution of sub-RPE deposits and photoreceptors. In the next generation of this L-ORD family, the first expression of disease, abnormal dark adaptation, mirrored the regional distribution of the deposits in the donor eye. The fine structure and staining characteristics of the sub-RPE deposits in L-ORD resemble those in age-related macular degeneration and Sorsby fundus dystrophy.

Loss of cone molecular markers in rhodopsin-mutant human retinas with retinitis pigmentosa

PURPOSE

To examine the effect of rhodopsin mutations on cone photoreceptors in human retinas with retinitis pigmentosa (RP).

METHODS

Four RP retinas with rhodopsin mutations and four normal retinas were examined by immunofluorescence with a battery of cell-specific antibodies against cone and rod cytoplasmic and outer segment membrane proteins. Areas of the retinas were studied that showed maximal preservation of photoreceptor structure.

RESULTS

All four RP retinas showed loss of rods, ranging from mild (T-17-M), to more severe (P-23-H), to advanced degeneration (Q-64-ter and G-106-R). The majority of cones in the T-17-M and P-23-H retinas were cytologically normal but showed loss of immunoreactivity for the cytoplasmic proteins 7G6, calbindin, and X-arrestin. The cone outer segments (OS) remained positive for cone opsins and peripherin-2 (rds/peripherin). All remaining cones in the Q-64-ter and G-106-R retinas were degenerate, with short to absent OS, but had strong reactivity for these cytoplasmic and OS membrane markers. Cones in the maculas of the RP retinas were degenerate, with short to absent OS, but retained strong labeling for the cytoplasmic and OS proteins.

CONCLUSIONS

Even before cones show cytologic changes in response to rod cell degeneration, they lose immunoreactivity for certain cytoplasmic proteins. These cones later show shortening and loss of OS, although their OS membrane proteins remain well labeled. Cones may down regulate expression of both cytoplasmic and outer segment membrane proteins in response to mutant rod cell dysfunction and/or cell death in human RP retinas. Such cytologic and immunocytochemical changes in the cones may presage death of these critical cells in the later stages of RP.

Histopathologic and immunocytochemical analysis of the retina and ocular tissues in Batten disease

PURPOSE

To describe the pathophysiologic features of retinal degeneration in Batten disease (juvenile neuronal ceroid lipofuscinosis [JNCL]) caused by mutations in the CLN3 gene.

STUDY DESIGN

Comparative human tissue study.

MATERIALS

The retina and other ocular tissues of a 22-year-old man with JNCL were compared with the same tissues of a healthy 30-year-old man. DNA from whole blood and RNA from retina were used for genotype analysis.

METHODS

The retinas, corneas, conjunctiva, and ciliary body were processed for histopathologic and immunofluorescence analysis. Genomic DNA was subjected to polymerase chain reaction (PCR) and nucleotide sequence analyses. Reverse transcriptase/PCR and sequence analysis were performed on retinal RNA.

RESULTS

The JNCL donor was heterozygous for a approximately 1 kb deletion in CLN3, as found in most JNCL patients. The other allele had a single base pair deletion in exon 6 that resulted in a frame shift. Gross pathology of the JNCL retina resembled that in retinitis pigmentosa, including deposits of bone spicule pigment. Histopathologic studies revealed loss of neurons from all retinal layers. Immunofluorescence labeling with antibodies to rhodopsin, recoverin, and cone opsin demonstrated degenerate rods and cones with short outer segments in the far periphery. Autofluorescent lipopigment granules were prominent in ganglion cells and some cells of the inner nuclear layer, but not in the photoreceptors. The retinal pigment epithelium (RPE) had fewer lipofuscin granules than the control specimen. Increased numbers of lipofuscin granules were found in the epithelia of the ciliary body and conjunctiva, but not in the cornea of the JNCL eye.

CONCLUSIONS

Immunofluorescence studies revealed degenerate rods and cones in the far periphery. Lipofuscin granules were decreased in the RPE, consistent with loss of photoreceptor outer segments. The novel finding that degenerate photoreceptors did not contain autofluorescent inclusions suggests that granule accumulation may not precede photoreceptor degeneration in JNCL. The presence of normal photoreceptor proteins in the degenerate rods and cones suggests that these cells may be capable of functional regeneration if a therapy for Batten disease is developed.

Localization of tubby-like protein 1 in developing and adult human retinas

PURPOSE

To localize tubby-like protein 1 (TULP1) in developing and adult human retinas.

METHODS

TULP1 was localized by immunofluorescence microscopy in human retinas, aged 8.4 fetal weeks to adult. TULP1-positive cells were identified by double labeling with antibodies specific for cones, rods, and astrocytes.

RESULTS

In adult retinas, anti-TULP1 labels cone and rod inner segments, somata, and synapses; outer segments are TULP1-negative. A few inner nuclear and ganglion cells are weakly TULP1-positive. In fetal retinas, cells at the outer retinal border are TULP1-positive at 8.4 weeks. At 11 weeks, the differentiating central cones are strongly TULP1-reactive and some are positive for blue cone opsin. At 15.4 weeks, all central cones are strongly positive for TULP1 and many are reactive for red/green cone opsin. At 17.4 weeks, central rods are weakly TULP-reactive. In peripheral retina at 15.4 weeks to 1 month after birth, displaced cones in the nerve fiber layer are positive for TULP1, recoverin, and blue cone opsin. Some ganglion cells are weakly reactive for TULP1 at 11 weeks and later, but astrocytes and the optic nerve are TULP1-negative at all ages examined.

CONCLUSIONS

The finding of TULP1 labeling of cones before they are reactive for blue or red/green cone opsin suggests an important role for TULP1 in development. TULP1 expression in both developing and mature cones and rods is consistent with a primary photoreceptor defect in retinitis pigmentosa (RP) caused by TULP1 mutations. Weak TULP1-immunolabeling of some inner retinal neurons in developing and adult retinas suggests that optic disc changes in patients with RP who have TULP1 mutations may be primary as well as secondary to photoreceptor degeneration.

Correction of ornithine accumulation prevents retinal degeneration in a mouse model of gyrate atrophy of the choroid and retina

Deficiency of ornithine-delta-aminotransferase (OAT) in humans results in gyrate atrophy of the choroid and retina (GA), an autosomal recessive disorder characterized by ornithine accumulation and a progressive chorioretinal degeneration of unknown pathogenesis. To determine whether chronic, systemic reduction of ornithine can prevent this form of retinal degeneration, we used an arginine-restricted diet to maintain long term reduction of ornithine in a mouse model of OAT-deficiency (Oat(-/-)) produced by gene targeting. We evaluated the mice over a 12-month period by measurement of plasma amino acids, electroretinograms, and retinal histologic and ultrastructural studies. We found that an arginine-restricted diet substantially reduces plasma ornithine levels and completely prevents retinal degeneration in Oat(-/-). This result indicates that ornithine accumulation is a necessary factor in the pathophysiology of the retinal degeneration in GA and that restoration of OAT activity in retina is not required for effective treatment of GA.

Abnormalities in rod photoreceptors, amacrine cells, and horizontal cells in human retinas with retinitis pigmentosa

PURPOSE

To evaluate changes in the rods and amacrine cells and horizontal cells in human retinas with retinitis pigmentosa.

METHODS

Seven retinas from patient donors with retinitis pigmentosa and 14 age- and postmortem-matched normal human retinas were processed for immunocytochemistry and confocal microscopy. The following cell-specific antibodies were used: anti-rhodopsin (rods), anti-gamma-aminobutyric acid (amacrine cells), anticalbindin (cones and horizontal cells), anti-glial fibrillary acidic protein (astrocytes and reactive Müller cells), and anti-synaptophysin and anti-SV2 (synaptic vesicles).

RESULTS

In retinal regions with significant photoreceptor loss, the rods, gamma-aminobutyric acid-positive amacrine cells, and calbindin-positive horizontal cells had undergone neurite sprouting. The rod, amacrine and horizontal cell neurites were associated with the surfaces of glial fibrillary acidic protein-immunoreactive Müller cells. Most rod neurites that projected into the inner retina contacted the somata of gamma-aminobutyric acid-positive amacrine cells.

CONCLUSIONS

Rods, amacrine and horizontal cells undergo neurite sprouting in human retinas with retinitis pigmentosa. These changes in the retinal neurons may contribute to the electroretinographic abnormalities and progressive decline in vision noted by patients with retinitis pigmentosa. These alterations may also complicate strategies for treatment of retinitis pigmentosa.

Human melanoma-associated retinopathy (MAR) antibodies alter the retinal ON-response of the monkey ERG in vivo

PURPOSE

Melanoma-associated retinopathy (MAR) is a paraneoplastic condition that causes visual symptoms of night-blindness and photopsias. The electroretinogram (ERG) of MAR patients is characteristically abnormal in a way that implicates retinal depolarizing bipolar cell (DBC) dysfunction. Whether an injection of IgG from MAR patients into the vitreous of monkeys would alter the ERG acutely as a demonstration of a functional basis for patients' visual symptoms was explored.

METHODS

MAR IgG was isolated from three visually symptomatic melanoma patients. Control IgG was from melanoma patients with no vision problems. The ERG was monitored after intravitreal injections into monkey eyes. One eye was injected with 2-amino-4-phosphonobutyric acid (APB), which is known to block DBC ON-pathway responses. Retinal immunocytochemistry was performed using fluorescein isothiocyanate-labeled goat anti-human IgG.

RESULTS

Within 1 to 3 hours after MAR IgG injection, the ERG photopic b-wave was diminished, with far less effect on the a- and d-waves. These changes are characteristic of DBC dysfunction and were similar to the effects of APB. The scotopic ERG b-wave, which reflects activity of rod-driven DBCs, showed a loss of amplitude and threshold sensitivity after MAR IgG. Retinal immunocytochemistry with anti-IgG antibody showed IgG penetration throughout the retinal layers, but staining was not specific for a single type of retinal neuron.

CONCLUSIONS

Intravitreal injection of human MAR IgG altered the monkey ERG acutely in ways that implicate functional disruption of retinal DBC signaling. These results support the hypothesis that MAR IgG circulating antibodies are responsible for the reported visual symptoms. Bipolar cells in the ON-pathway appear to be affected more than OFF-pathway bipolar cells of the cone pathway in this acute preparation.

Cancer-associated retinopathy

Patients with systemic cancer may have a variety of ocular complaints. Most commonly these are metastases or adverse effects of therapy. Paraneoplastic syndromes, like cancer-associated retinopathy, rarely cause ophthalmic symptoms. We describe a patient with a malignant mixed mullerian tumor and cancer-associated retinopathy who had circulating serum antibodies to recoverin and cells positive for recoverin in the tumor. We discuss the typical clinical symptoms as well as the pathophysiology of this uncommon disorder.

Clinical and immunocytochemical findings in a case of melanoma-associated retinopathy

OBJECTIVE

To describe an unusual case of melanoma-associated retinopathy (MAR).

DESIGN

Retrospective, observational case report and experimental study.

PARTICIPANTS

A 61-year-old man with a history of cutaneous melanoma, acquired bilateral central scotomas, and night blindness.

INTERVENTION

Serial full-field electroretinography (ERG) and Goldmann perimetry were performed. Serum was screened for cancer-associated retinopathy (CAR) antibodies by Western blotting. Sections of human and rat retina were examined by immunofluorescence microscopy to determine whether retinal cells were reactive with this patient's serum. A metastatic workup was performed.

MAIN OUTCOME MEASURES

Electroretinography, Goldmann visual field testing, and immunocytochemistry were performed.

RESULTS

The results were as follows: (1) The ERG showed a profound loss of the b-wave amplitude and a "negative" b-wave characteristic of congenital stationary night blindness; (2) a central scotoma and peripheral constriction were identified on Goldmann visual field tests; (3) as in other patients with MAR, bipolar cells in human and rat retinas were immunolabeled with this patient's serum; and (4) a previously unsuspected focus of metastatic melanoma was discovered.

CONCLUSIONS

Recognition of this condition may help to identify an occult focus of metastatic melanoma.

Retinal rod photoreceptor-specific gene mutation perturbs cone pathway development

Rod-specific photoreceptor dystrophies are complicated by the delayed death of genetically normal neighboring cones. In transgenic (Tg) swine with a rod-specific (rhodopsin) gene mutation, cone photoreceptor physiology was normal for months but later declined, consistent with delayed cone cell death. Surprisingly, cone postreceptoral function was markedly abnormal when cone photoreceptor physiology was still normal. The defect was localized to hyperpolarizing cells postsynaptic to the middle wavelength-sensitive cones. Recordings throughout postnatal development indicated a failure of cone circuitry maturation, a novel mechanism of secondary cone abnormality in rod dystrophy. The results have implications for therapy for human retinal dystrophies and raise the possibility that rod afferent activity plays a role in the postnatal maturation of cone retinal circuitry.

Morphometric analysis of the extramacular retina from postmortem eyes with retinitis pigmentosa

PURPOSE

To evaluate the degree of inner retinal preservation in the extramacular regions of postmortem retinitis pigmentosa (RP) eyes.

METHODS

Eighteen RP retinas and 11 age-matched healthy retinas were sectioned for morphometric analysis by light microscopy. The 18 RP retinas were classified by disease severity and mode of inheritance. Cell nuclei in the outer nuclear layer (ONL), inner nuclear layer (INL), and ganglion cell layer (GCL) were counted in adjacent 125-microm segments from an area spanning the region between 4 mm and 10 mm from the fovea.

RESULTS

A mixed-effects model showed a decrease in mean cell counts for each of the cell layers when the severity groups and inheritance types compared with those of control retinas. There was no statistically significant difference in the number of nuclei preserved in the INL and GCL in the moderate group compared with the severe group. Results from the INL counts for the different inheritance types of RP showed a higher overall mean percentage of cells was preserved for the autosomal dominant RP (ADRP) group when compared with the X-linked (XLRP) and simplex RP groups. Analysis of the GCL counts revealed significantly more counts only in the ADRP group compared with the XLRP group; the other group comparisons were not significant.

CONCLUSIONS

Retinitis pigmentosa results in cell loss in all retinal layers, with the most profound loss in the ONL, followed by the GCL and then the INL. The preservation of the INL and GCL in the extramacular region is less than that previously reported for the macular region of the same retinas.

Abnormal cone synapses in human cone-rod dystrophy

OBJECTIVE

Little is known of the cytopathology of photoreceptors in human inherited retinal dystrophies that initially affect the central retina, including the macula. The current study sought to determine the cytologic features of dysfunctional cone and rod photoreceptors, as well as the pattern of degeneration of the cells in representative cases of central retinal dystrophy.

STUDY DESIGN

Comparative human tissue study.

MATERIALS

Four human donor eyes with the following forms of central retinal dystrophy: cone-rod dystrophy (CRD), central areolar choroidal dystrophy, Bardet-Biedl syndrome, and cone dystrophy-cerebellar ataxia. The cytologic features of retinal photoreceptors in these eyes were compared with those in an eye with retinitis pigmentosa and six normal human eyes.

METHODS AND OUTCOME MEASURES

Immunocytochemistry and electron microscopy were used to evaluate the retinal histopathology in the donor eyes.

RESULTS

Cone numbers were decreased in the case of CRD, particularly in the central and far peripheral retina, and both cone and rod outer segments were slightly shortened. Occasional degenerate cones had dense cytoplasm and pyknotic nuclei dislocated sclerad to the external-limiting membrane. The most prominent alteration in this retina was marked enlargement and distortion of the cone photoreceptor pedicles, which contained reduced numbers of synaptic vesicles. The retina with central areolar choroidal dystrophy contained a few cones with similarly abnormal synapses. However, comparable cone synapse abnormalities were not observed in the cases of Bardet-Biedl syndrome, cone dystrophy-cerebellar ataxia, retinitis pigmentosa, or in the normal retinas.

CONCLUSIONS

The functional consequences of the cone synapse abnormalities in CRD are not known but may correlate with the electroretinographic abnormalities documented in some cases of CRD. To our knowledge, comparable synapse changes have not been noted in either rods or cones in other forms of retinal dystrophy, including retinitis pigmentosa, suggesting that different cytopathologic mechanisms may be involved.

Accumulation of tissue inhibitor of metalloproteinases-3 in human eyes with Sorsby's fundus dystrophy or retinitis pigmentosa

BACKGROUND/AIMS

Tissue inhibitor of metalloproteinases-3 (TIMP-3) is normally synthesised by the retinal pigment epithelium (RPE) and deposited in Bruch's membrane. Mutations in the TIMP3 gene cause Sorsby's fundus dystrophy (SFD), which is characterised by thickening of Bruch's membrane, choroidal neovascularisation, and photoreceptor degeneration. To elucidate the role of TIMP-3 in human retinal degenerative diseases, we immunolocalised TIMP-3 in eyes with SFD caused by the Ser-181-Cys TIMP3 gene mutation or retinitis pigmentosa (RP; not caused by TIMP3 mutations).

METHODS

Standard light microscopic immunocytochemistry, including antigen retrieval, was used to localise TIMP-3 in paraffin sections of human eyes: two with SFD, three with different genetic forms of RP, and two normal.

RESULTS

In the SFD eyes, the thickened Bruch's membrane was strongly TIMP-3 positive except where RPE cells had degenerated. Similarly, in the RP eyes, Bruch's membrane was TIMP-3 positive except where RPE cells were lost, consistent with ongoing RPE mediated turnover of TIMP-3 in this region. In areas of total photoreceptor loss, migrated RPE cells formed cuffs around blood vessels in the RP retinas. Thick, TIMP-3 positive extracellular matrix (ECM) deposits associated with the migrated RPE cells occluded some vascular lumina, correlating with the observed loss of inner retinal neurons in RP.

CONCLUSIONS

TIMP-3 is a component of the increased ECM sequestered in Bruch's membrane in SFD. Further information is needed on normal TIMP-3/ECM interactions in Bruch's membrane and the effect of mutant TIMP-3 on this process. The finding of TIMP-3 accumulations in retinas with RP not caused by TIMP-3 mutations emphasises the importance of ECM remodelling in normal and diseased human eyes.

Relation of optical coherence tomography to microanatomy in normal and rd chickens

PURPOSE

To elucidate the relation between optical coherence tomography (OCT) scans and retinal histology in normal and retinal degeneration (rd) chickens.

METHODS

Retinas from adult normal and rd chickens were examined in vivo with OCT at 850 nm and compared quantitatively with stained cryosections of unfixed retinas from the same locations.

RESULTS

The nerve fiber layer (NFL) and inner plexiform layer (IPL) show homogeneous backscatter throughout their thicknesses. NFL reflectivity is approximately 0.6 log units higher than that of the IPL. The inner nuclear layer shows a low reflectivity; the properties of reflections from ganglion cell and outer nuclear layers are indeterminate. The outer retina and choroid form a large reflective complex. Photoreceptor inner segments produce the highest of these reflections in normal chicken retinas, approximately 1.5 log units higher than that of the IPL. The retinal pigment epithelium also has a relatively large backscatter coefficient and is the dominant reflector in rd retinas that lack photoreceptors. Choroidal pigment produces an intermediate level of backscatter and is the largest attenuator of signal at 850 nm.

CONCLUSIONS

Quantified OCT signals have a predictable relationship to histology and pathology in chicken retinas. The results from rd retinas represent a first step toward in vivo quantitation of retinal structure in retinal degenerative disease.

Recoverin-associated retinopathy: a clinically and immunologically distinctive disease

PURPOSE

To compare the immune response to retinal antigens in a patient with a clinical condition resembling cancer-associated retinopathy with the immune responses of patients with other retinal degenerations or uveitis.

METHODS

Cellular and humoral immune responses to retinal S-antigen and recoverin were determined in one patient with disease resembling cancer-associated retinopathy, three patients with other retinal degenerations, and eight patients with uveitis.

RESULTS

A cellular immune response against recoverin was found only in the patient with the condition resembling cancer-associated retinopathy. Elevated levels of antibody against recoverin were found in this patient and in one of the three patients with a retinal degeneration, but in none of the eight patients with uveitis. In contrast, moderate lymphocyte responses to retinal S-antigen were found in most of the patients studied, and this response did not distinguish among the patient groups. Levels of serum antibodies against retinal S-antigen were also similar in all patients tested. Serum from the patient with disease resembling cancer-associated retinopathy produced strong immunostaining of the rods, cones, outer plexiform layer, and some cone bipolar cells, but serum from the patients with uveitis or other retinal degenerations did not show specific reactivity with the retina.

CONCLUSIONS

We propose that this immunologically and clinically distinctive condition be termed recoverin-associated retinopathy, and we suggest that a cellular immune response against recoverin may be a distinguishing feature of the disorder.

Disease sequence from mutant rhodopsin allele to rod and cone photoreceptor degeneration in man

Mutations in the gene encoding rhodopsin, the visual pigment in rod photoreceptors, lead to retinal degeneration in species from Drosophila to man. The pathogenic sequence from rod cell-specific mutation to degeneration of rods and cones remains unclear. To understand the disease process in man, we studied heterozygotes with 18 different rhodopsin gene mutations by using noninvasive tests of rod and cone function and retinal histopathology. Two classes of disease expression were found, and there was allele-specificity. Class A mutants lead to severely abnormal rod function across the retina early in life; topography of residual cone function parallels cone cell density. Class B mutants are compatible with normal rods in adult life in some retinal regions or throughout the retina, and there is a slow stereotypical disease sequence. Disease manifests as a loss of rod photoreceptor outer segments, not singly but in microscopic patches that coalesce into larger irregular areas of degeneration. Cone outer segment function remains normal until >75% of rod outer segments are lost. The topography of cone loss coincides with that of rod loss. Most class B mutants show an inferior-nasal to superior-temporal retinal gradient of disease vulnerability associated with visual cycle abnormalities. Class A mutant alleles behave as if cytotoxic; class B mutants can be relatively innocuous and epigenetic factors may play a major role in the retinal degeneration.

Rhodopsin transgenic pigs as a model for human retinitis pigmentosa

PURPOSE

To further characterize the retinas of Pro3471Leu rhodopsin transgenic pigs, a model for human retinitis pigmentosa.

METHODS

Retinas from normal and transgenic pigs, newborn to 20 months old, were processed for light and electron microscopic immunocytochemical examination.

RESULTS

At birth, rod numbers were normal in the transgenic retinas, but their outer segments were short and disorganized and their inner segments contained stacks of rhodopsin-positive membranes. The newborn rod synapses lacked synaptic vesicles and ribbons and had numerous rhodopsin-positive, filopodia-like processes that extended past the cone synapses into the outer plexiform layer. Rod cell death was apparent by 2 weeks and was pronounced in the mid periphery and central regions by 6 weeks. Far peripheral rods were initially better preserved, but by 9 months virtually all rods had degenerated. Cones degenerated more slowly than rods, but by 4 weeks the cone synapses were shrunken and some mid peripheral cones had lost their immunoreactivity for phosphodiesterase-gamma, arrestin, and recoverin. From 9 months to 20 months, the cone outer segments shortened progressively, and more cones lost immunoreactivity for these proteins.

CONCLUSIONS

The rhodopsin transgenic pig retina shares many cytologic features with human retinas with retinitis pigmentosa and provides an opportunity to examine the earliest stages in photoreceptor degeneration, about which little is known in humans. The finding of abnormal rhodopsin localization in newborn rods is consistent with misrouting of mutant rhodopsin as an early process leading to rod cell death. Novel changes in the photoreceptor synapses may correlate with early electrophysiological abnormalities in these retinas.

Histopathology of the human retina in retinitis pigmentosa

The term, 'retinitis pigmentosa', refers to a heterogeneous group of inherited diseases that cause degeneration of rod and cone photoreceptors in the human retina. Loss of photoreceptor cells is usually followed by alterations in the retinal pigment epithelium and retinal glia. Ultimately, degenerative changes occur in the inner retinal neurons, blood vessels, and optic nerve head. This chapter provides background information on the genetics of retinitis pigmentosa and a summary of the histopathologic alterations in human retinas caused by this disease. Detailed information is provided on the effects of the primary disease process on the rod photoreceptors and changes in the other retinal components, all of which are important considerations for understanding and developing therapies for retinitis pigmentosa.

Guanylate-cyclase-inhibitory protein is a frog retinal Ca2+-binding protein related to mammalian guanylate-cyclase-activating proteins

Two guanylate-cyclase-activating proteins (GCAP) encoded by a tail-to-tail gene array have been characterized in the mammalian retina. Using frog retina as a model, we obtained evidence for the presence of a photoreceptor Ca2+-binding protein closely related to GCAP. This protein (206 amino acids) does not stimulate guanylate cyclase (GC) in low [Ca2+], but inhibits GC in high [Ca2+], and is therefore termed guanylate-cyclase-inhibitory protein (GCIP). Sequence analysis indicates that GCIP and GCAP1 and GCAP2 have diverged substantially, but conserved domains present in all vertebrate GCAP are present in GCIP. Moreover, partial characterization of the GCIP gene showed that the positions of two introns in the GCIP gene are identical to positions of corresponding introns of the mammalian GCAP gene array. As to the major differences between GCIP and GCAP, the fourth EF hand Ca2+-binding motif of GCIP is disabled for Ca2+ binding, and GCIP does not stimulate GC. Monoclonal and polyclonal antibodies raised against recombinant GCIP identified high levels of GCIP in the inner segments, somata and synaptic terminals of frog cone photoreceptors. The results suggest that GCIP is a Ca2+-binding protein of the GCAP/recoverin subfamily. Its localization in frog cones closely resembles that of GC in mammalian cones. GCIP inhibits GC at high free [Ca2+], competing with GCAP1 and GCAP2 for GC regulatory sites.

Effects of retinal laser photocoagulation on photoreceptor basic fibroblast growth factor and survival

PURPOSE

In an unpublished study, the authors found that immunoreactivity for basic fibroblast growth factor (bFGF) is increased in rod photoreceptors adjacent to long-standing laser burns in human diabetic retinas. The goal of this study was to determine whether laser photocoagulation produces a similar increase in photoreceptor bFGF and promotes survival of these cells in dystrophic rodent retinas.

METHODS

Threshold (whitening) and subthreshold (nonwhitening) laser burns were made in retinas of normal and Royal College of Surgeons (RCS) rats and normal and rds mice. The retinas were processed for immunocytochemical and morphometric analyses.

RESULTS

In nonlasered normal rat and mouse retinas, bFGF immunoreactivity was prominent in the nuclei of Müller cells and astrocytes. Photoreceptors were bFGF negative except for a zone of bFGF-immunoreactive rods near the ora serrata. Some photoreceptors in nonlasered retinas of RCS rats and rds mice became bFGF immunoreactive. After laser treatment, bFGF immunoreactivity was markedly increased in all photoreceptors flanking the threshold burns and within the subthreshold burns in normal and mutant rats and mice. In RCS rat retinas, photoreceptor bFGF immunoreactivity remained elevated within subthreshold burns and flanking the threshold burns, and photoreceptor survival was prolonged. In rds mouse retinas, increased bFGF immunoreactivity in photoreceptors was not sustained and their degeneration was not retarded.

CONCLUSIONS

Laser treatment of RCS rat retinas produced a sustained increase in bFGF immunoreactivity in photoreceptors and prolonged their survival, but laser treatment of rds mouse retinas did not have a long-term effect on photoreceptor bFGF immunoreactivity or survival. Although species differences in laser effects on photoreceptor bFGF and survival are apparent, the finding that rods flanking laser burns in human retinas have sustained increases in bFGF immunoreactivity suggests that laser treatment may be useful for prolonging survival of mutant photoreceptors in retinas of patients with retinitis pigmentosa.