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The purpose of this study was to evaluate rod and cone function and outer retinal structure within macular lesions, and surrounding extralesional areas of patients with autosomal dominant Best vitelliform macular dystrophy caused by BEST1 mutations.Seventeen patients from seven families were examined with dark- and light-adapted chromatic perimetry and optical coherence tomography. Subsets of patients had long-term follow-up (14-22 years, n = 6) and dark-adaptation kinetics measured (n = 5).Within central lesions with large serous retinal detachments, rod sensitivity was severely reduced but visual acuity and cone sensitivity were relatively retained. In surrounding extralesional areas, there was a mild but detectable widening of the subretinal space in some patients and some retinal areas. Available evidence was consistent with subretinal widening causing slower dark-adaptation kinetics. Over long-term follow-up, some eyes showed formation of de novo satellite lesions at retinal locations that years previously demonstrated subretinal widening. A subclinical abnormality consisting of a retina-wide mild thickening of the outer nuclear layer was evident in many patients and thickening increased in the subset of patients with long-term follow-up.Outcome measures for future clinical trials should include evaluations of rod sensitivity within central lesions and quantitative measures of outer retinal structure in normal-appearing regions surrounding the lesions.

To characterize the progression of vascular changes that occur in each retinal plexus, in three canine models of inherited retinal degeneration.In this retrospective cohort study, we examined the retinal imaging records of 44 dogs from a research colony that had undergone optical coherence tomography angiography (OCTA) imaging. Animals enrolled included crd2/NPHP5 and xlpra2/RPGR mutant dogs imaged at different stages of photoreceptor loss, as well as RHOT4R/+ dogs after acute light-induced rod degeneration. Also included were normal controls imaged at similar ages. OCT angiograms of the superficial vascular plexus combined with the intermediate capillary plexus (SVP + ICP), and the deep capillary plexus (DCP) were analyzed using the AngioTool software to calculate vessel density and other vascular parameters.A reduction in vessel density was seen over time in both the SVP + ICP and DCP in all mutant dogs but was more pronounced in the DCP. Scans were subclassified based on outer nuclear layer (ONL) thinning compared to age-matched normal controls. When ONL loss was 0% to 50%, vessel density in the DCP was significantly lower than in age-matched controls. In all cases, when ONL loss exceeded 87.5%, vessel density in the SVP + ICP was significantly reduced as well. In the acute light-induced rod degeneration model, the vascular regression changes were observed mainly in the DCP.Vessel density reduction in dogs undergoing retinal degeneration is first detected by OCTA in the DCP, and only at later stages in the SVP + ICP.

Purpose To identify the causative mutations in two early-onset canine retinal degenerations, crd1 and crd2, segregating in the American Staffordshire terrier and the Pit Bull Terrier breeds, respectively. Methods Retinal morphology of crd1- and crd2-affected dogs was evaluated by light microscopy. DNA was extracted from affected and related unaffected controls. Association analysis was undertaken using the Illumina Canine SNP array and PLINK (crd1 study), or the Affymetrix Version 2 Canine array, the "MAGIC" genotype algorithm, and Fisher's Exact test for association (crd2 study). Positional candidate genes were evaluated for each disease. Results Structural photoreceptor abnormalities were observed in crd1-affected dogs as young as 11-weeks old. Rod and cone inner segment (IS) and outer segments (OS) were abnormal in size, shape, and number. In crd2-affected dogs, rod and cone IS and OS were abnormal as early as 3 weeks of age, progressing with age to severe loss of the OS, and thinning of the outer nuclear layer (ONL) by 12 weeks of age. Genome-wide association study (GWAS) identified association at the telomeric end of CFA3 in crd1-affected dogs and on CFA33 in crd2-affected dogs. Candidate gene evaluation identified a three bases deletion in exon 21 of PDE6B in crd1-affected dogs, and a cytosine insertion in exon 10 of IQCB1 in crd2-affected dogs. Conclusions Identification of the mutations responsible for these two early-onset retinal degenerations provides new large animal models for comparative disease studies and evaluation of potential therapeutic approaches for the homologous human diseases.

The cAMP response element binding protein 1 (CREB1), activating transcription factor 1 (ATF1) and cAMP response element modulator (CREM) are closely related members of the CREB/ATF family. This family belongs to the basic leucine zipper (bZIP) superfamily of transcription factors, which include mammalian c-Fos, c-Jun, and c-Myc.1 When activated by phosphorylation, these transcription factors bind as homo- or heterodimers to a palindromic consensus sequence known as the cAMP-response element (CRE).1–3 CREB1/ATF1 are activated by a wide array of physiological stimuli including peptide hormones, growth factors, intracellular Ca2+,1 and cellular stress.4–7 In adult mammalian retina, p-CREB1 is normally limited to the ganglion cell and inner nuclear layers.8–11 It appears that as in other parts of the nervous system,12–14 stressful stimuli can induce phosphorylation of CREB1 in retinal neurons.8–10,15 In photoreceptors, expression is noted in cat and rabbit after retinal injury by detachment10 and in rat photoreceptors after penetrating trauma.8 In vitro, increased expression of pCREB in mouse photoreceptor-derived 661W cells in response to FGF suggests that CREB1 may be associated with a neuroprotective outcome in photoreceptors.16 The present study was conducted to determine whether CREB1/ATF1 can be phosphorylated in dog and human photoreceptors and whether this occurs in response to degenerative or protective stimuli. We describe the distribution of phosphorylated CREB1/ATF1 in canine models of retinitis pigmentosa (RP) and in human retinas with age-related macular degeneration (AMD). The association between CREB1/ATF1 phosphorylation and photoreceptor protection induced by ciliary neurotrophic factor (CNTF) was evaluated to assess whether CREB1/ATF1 is influenced by this neuroprotective stimulus.

The differentiated photoreceptor is elegantly organized to have an external light-capturing outer segment optimized for efficient quantal absorption. Internally, the inner segment has the protein synthetic and energy-generating organelles, and on the vitreal aspect is the synaptic terminal that connects to the second-order neurons that ultimately transfer information to higher visual centers. Each rod photoreceptor can be 120 μm or longer, and such exquisite compartmentalization efficiently separates multiple specialized functions. Not surprisingly, the photoreceptors' complexity, together with the specific signal transduction and “housekeeping” functions performed, renders them susceptible to degenerative diseases, either genetic or acquired, that result from damage to genes or pathways critical for their function or viability. Of the 190 retinal disease loci mapped to date, the genes and mutations have been identified for ∼135 (RetNet available at http://www.sph.uth.tmc.edu/RetNet/ provided in the public domain by the University of Texas Health Science Center, Houston, TX). In many cases, different mutations in the same gene result in a broad range of differing phenotypes, thus emphasizing the broad genetic and allelic heterogeneity of these degenerative retinal disorders. Of particular interest has been the interaction between light and the death of photoreceptors. After Noell et al.1,2 made the seminal finding that visible light may damage mammalian photoreceptors at intensities that are ordinarily encountered, many investigators in subsequent studies have examined this interaction, especially in normal albino rodents, and have begun to identify the pathways and molecular events that link exposure to light to photoreceptor degeneration.3,4 Two different pathways, the bright- and low-light pathways, mediate light-induced visual cell death, but only the bright-light pathway is accompanied by activation of the AP-1 transcription factor.5 This critical intermediary has been proposed to link damaging exposure to lights with photoreceptor apoptosis by activation of the c-Fos/AP-1 molecular pathway.5 Photoreceptor degeneration also results from exposure to light in retinas having mutations in the rhodopsin gene (RHO) that renders them especially sensitive to light. The naturally occurring T4R6 and transgenic T17M7 RHO mutations in dogs and mice, respectively, represent models for homologous diseases in humans with autosomal dominant retinitis pigmentosa (adRP).8,9 Although these mutations affect the first- and second-consensus glycosylation sequences,10 a possible indication of the enhanced light-damage susceptibility, other RHO mutations in humans also show marked delays in visual pigment regeneration with bleaching,11-13 a feature that raises concern as to the possible modulatory effect that exposure to light can have on the disease process.6,14 Although light-induced damage in both normal mice, and RHO mutant dogs or mice is mediated by RHO, the major difference between normal and mutant subjects is that, in the latter, photoreceptors degenerate with light intensities that cause no damage to normal retinas. Very short exposures to light, such as those used in routine clinical eye examinations of humans, result in severe outer retinal degeneration.14,15 Previous studies in albino rodents using genetic or pharmacologic approaches have demonstrated an association between AP-1 inhibition and prevention of photoreceptor degeneration.16-18 Although there are some questions as to the specificity of this inhibition and the role of AP-1 as a cell death or cell survival signal,19 it is clear that high-dose administration of corticosteroids before exposure to light is associated with no photoreceptor degeneration.18 In this study, we examined the effect of systemic or ocular corticosteroid administration on AP-1 induction and photoreceptor degeneration. We found that only systemic steroids inhibit AP-1 activation, but in neither case do steroids prevent or modulate photoreceptor damage. This supports prior findings that, at least in the T4R RHO mutant canine retina, AP-1 is not the critical player in the cell death signaling pathway that links exposure to light and photoreceptor degeneration.19

The T4R RHO mutant dog retina shows retinal degeneration with exposures to light comparable to those used in clinical eye examinations of patients. To define the molecular mechanisms of the degeneration, AP-1 DNA-binding activity, composition, posttranslational modification of the protein complex, and modulation of ERK/MAPK signaling pathways were examined in light-exposed mutant retinas.Dark-adapted retinas were exposed to short-duration light flashes from a retinal camera used clinically for retinal photography and were collected at different time points after exposure. Electrophoretic mobility shift assay (EMSA), supershift EMSA, Western blot analysis, and immunocytochemistry were used to examine AP-1 signaling.Exposure to light of mutant retinas significantly increased AP-1 DNA-binding activity by 1 hour after exposure, and levels remained elevated for 6 hours. Shielded mutant retinas had similar AP-1 levels to shielded or exposed wild-type retinas. The parallel phosphorylation of c-Fos and activation of ERK1/2 was detected only in exposed mutant retinas. Exposure to light changed the composition of the AP-1 protein complex in the mutant retina from c-Jun/Fra-1/c-Fos to JunB/c-Fos. Immunohistochemistry showed that the components of activated AP-1 (JunB, and phosphorylated c-Fos, and phosphorylated ERK1/2 isoforms) were localized in Müller cells.The inner nuclear layer/Müller cell localization of the key proteins induced by light exposure raises the question of the direct involvement of AP-1 in mediating photoreceptor cell death in this model of autosomal dominant retinitis pigmentosa.

PURPOSE. Canine multifocal retinopathy (cmr) is an autosomal recessive disorder of multiple dog breeds. The disease shares a number of clinical and pathologic similarities with Best macular dystrophy (BMD), and cmr is proposed as a new large animal model for Best disease. METHODS. cmr was characterized by ophthalmoscopy and histopathology and compared with BMD-affected patients. BEST1 (alias VMD2), the bestrophin gene causally associated with BMD, was evaluated in the dog. Canine ortholog cDNA sequence was cloned and verified using RPE/choroid 5- and 3-RACE. Expression of the canine gene transcripts and protein was analyzed by Northern and Western blotting and immunocytochemistry. All exons and the flanking splice junctions were screened by direct sequencing. RESULTS. The clinical phenotype and pathology of cmr closely resemble lesions of BMD. Canine VMD2 spans 13.7 kb of genomic DNA on CFA18 and shows a high level of conservation among eukaryotes. The transcript is predominantly expressed in RPE/choroid and encodes bestrophin, a 580-amino acid protein of 66 kDa. Immunocytochemistry of normal canine retina demonstrated specific localization of protein to the RPE basolateral plasma membranes. Two disease-specific sequence alterations were identified in the canine VMD2 gene: a C73T stop mutation in cmr1 and aG 482A missense mutation in cmr2. CONCLUSIONS. The authors propose these two spontaneous mutations in the canine VMD2 gene, which cause cmr, as the first naturally occurring animal model of BMD. Further development of the cmr models will permit elucidation of the complex molecular mechanism of these retinopathies and the development of potential therapies. (Invest Ophthalmol Vis Sci. 2007; 48:1959‐1967) DOI:10.1167/iovs.06-1374

Purpose To characterize the course of retinal disease in X-linked progressive retinal atrophy 2 (XLPRA2), a canine model of early onset X-linked retinitis pigmentosa (XLRP) caused by a two-nucleotide microdeletion in RPGR ORF15. Methods The retinas of 25 XLPRA2-affected dogs (age range, 2-40.6 weeks) and age-matched control subjects were collected, fixed, and embedded in epoxy resin for morphologic evaluation or in optimal cutting temperature (OCT) medium for TUNEL assay and immunohistochemistry. Cell-specific antibodies were used to examine changes in rods and cones and to evaluate the effects of the primary photoreceptor degeneration on inner retinal cells. Results Abnormal development of photoreceptors was recognizable as early as 3.9 weeks of age. Outer segment (OS) misalignment was followed by their disorganization and fragmentation. Reduction in length and broadening of rod and cone inner segments (IS) was next observed, followed by the focal loss of rod and cone IS at later time points. The proportion of dying photoreceptors peaked at approximately 6 to 7 weeks of age and was significantly reduced after 12 weeks. In addition to rod and cone opsin mislocalization, there was early rod neurite sprouting, retraction of rod bipolar cell dendrites, and increased Muller cell reactivity. Later in the course of the disease, changes were also noted in horizontal cells and amacrine cells. Conclusions XLPRA2 is an early-onset model of XLRP that is morphologically characterized by abnormal photoreceptor maturation followed by progressive rod-cone degeneration and early inner retina remodeling. The results suggest that therapeutic strategies for this retinal degeneration should target not solely photoreceptor cells but also inner retinal neurons.

PURPOSE: To map the canine rcd2 retinal degeneration locus. Rod-cone dysplasia type 2 (rcd2), an early-onset autosomal recessive form of progressive retinal atrophy (PRA), is phenotypically similar to early-onset forms of retinitis pigmentosa collectively termed Leber congenital amaurosis and segregates naturally in the collie breed of dog. Multiple genes have previously been evaluated as candidates for rcd2, but all have been excluded. METHODS: A set of informative experimental pedigrees segregating the rcd2 phenotype was produced. A genome-wide scan of these pedigrees using a set of 241 markers was undertaken. To refine the localized homology between canine and human maps, an RH map of the identified rcd2 region was built using a 3000 cR panel. A positional candidate gene strategy was then undertaken to begin to evaluate potentially causative genes. RESULTS: A locus responsible for the rcd2 phenotype was mapped to CFA7 in a region corresponding to human chromosome 1, region q32.1-q32.2. Maximum linkage was observed between rcd2 and marker FH3972 (theta = 0.02; lod = 25.53), and the critical region was flanked by markers FH2226 and FH3972. As CRB1 is the closest gene on human chromosome 1q known to cause retinal degeneration, canine gene-specific markers for CRB1 were developed, and this gene was excluded as a positional candidate for rcd2. CONCLUSIONS: The rcd2 locus represents a novel retinal degeneration gene. It is anticipated that when identified, this gene will offer new insights into retinal developmental and degenerative processes, and new opportunities for exploring experimental therapies.

PURPOSE. To characterize CLUL1, a cone photoreceptor-specific gene. METHODS. A comparative genomics approach was used to analyze the gene organization and protein sequence of a retinal clusterin-like protein and to identify conserved elements between human and dog. Its expression was studied by Northern and Western analyses and its localization by in situ hybridization and immunocytochemistry. RESULTS. The CLULI sequences of the human and dog share 85% and 73% identity, respectively, at the nucleotide and deduced amino acid level. The gene is organized into nine exons and shows strong homology, not only in exonic but also in some intronic sequences between the species. The polypeptide homology of CLUL1 to CLU, a molecular chaperone, indicates structural similarity of the two proteins. However, these data demonstrated that they present different expression profiles in the tissues, in retinal development, and in retinal diseases. Finally, CLUL1 was localized to retinal cone photoreceptor cells and a different immunolabeling in light- and dark-adapted retinas was shown. CONCLUSIONS. CLULI represents a potentially important gene and a candidate locus for retinal disease, particularly those diseases that affect cones.

Purpose To clone, map, and determine the site of expression (mRNA and protein) of the alpha subunit of the receptor for ciliary neurotrophic factor (CNTFRalpha) in the normal adult canine retina. Methods The complete coding sequence of the canine CNTFRalpha cDNA was cloned, and radiation hybrid (RH) mapping was used to determine the chromosomal localization of the gene. CNTFRalpha mRNA expression in retina and other tissues was examined by reverse transcription-polymerase chain reaction. The cellular distribution of CNTFRalpha in the canine retina was studied by in situ hybridization and immunocytochemistry. Results Canine CNTFRalpha shares a high degree of homology with the human, mouse, and rat coding sequences, both at the nucleotide and amino acid level, but has lower homology with the chicken. CNTFRalpha was RH mapped to CFA 11 (Canis familiaris autosome 11) in the dog, a region showing homology to the short arm of human chromosome 9 (9p13). The gene is transcribed in retina, brain, spleen, lung, liver, and kidney. In the retina, CNTFRalpha was highly expressed by photoreceptors, but both the transcript and protein were also found in the RPE, inner nuclear layer, and ganglion cells. Conclusions These findings demonstrate that CNTFRalpha is expressed by rods and cones in the normal adult canine retina and suggest that ciliary neurotrophic factor (CNTF) could have a direct photoreceptor rescue effect by binding to CNTFRalpha in these cells. This could open novel pathways for the treatment of retinal degeneration in animal models and humans.

Canine X-linked progressive retinal atrophy (XLPRA) is a hereditary, progressive retinal degeneration that has been mapped previously to the canine X chromosome in a region flanked by the dystrophin (DMD) and tissue inhibitor of metalloproteinase 1 (TIMP1) genes, and is tightly linked to the gene RPGR. The comparable region of the human X chromosome includes the disease locus for RP3, an X-linked form of retinitis pigmentosa, although the current canine disease interval is much larger.To refine the map of the canine XLPRA disease interval, 11 X-linked markers were mapped, both meiotically, in two extensive canine pedigrees informative for XLPRA, and on a 3000-rad canine-hamster radiation hybrid (RH) panel. A 12th marker was mapped on the RH panel alone.The integrated map of this region of CFAX now covers approximately 47.3 centimorgans (cM) and 194 centirays (cR)(3000), and demonstrates strong conservation of synteny between humans and dogs. Genes defining the human RP3 zero-recombination interval (human homologue of mouse t complex [TCTE1L], sushi repeat-containing protein, X chromosome [SRPX], and retinitis pigmentosa guanosine triphosphatase [GTPase] regulator [RPGR]) are tightly linked to each other, to the XLPRA locus, and to the gene ornithine transcarbamylase (OTC) in dogs.Strong conservation of gene order was demonstrated in the short arm of the X chromosome between dogs and humans as was homology of the canine XLPRA and human RP3 intervals. These results create a valuable tool for investigating canine XLPRA and other X-linked eye diseases in dogs.

To describe the course of photoreceptor disease in canine X-linked retinal degeneration.Retinas from 55 dogs (44 males, 8 carrier females, 3 homozygous females) were obtained by enucleation under general anesthesia. After fixation and dehydration, tissues were embedded in epoxy resin, sectioned at 1 microm for light microscopy and stained with azure II/methylene blue and a paraphenylenediamine counterstain. For electron microscopy, regions identified by light microscopy were selected and cut at 60 nm. Sections were stained with uranyl acetate-lead citrate. Electroretinography from an additional group of normal males, affected males, and carrier females was performed and the rod and cone responses evaluated.The earliest lesion detectable by electron microscopy was vesiculation of rod discs, followed by disruption of outer segments and death of rods. Loss of cones and progressive atrophy of inner retinal layers followed. Lesions were most severe in the peripheral retina and advanced toward the optic disc with disease progression. Significant variation in disease severity was present in males despite the presence of the same disease allele in all affected dogs. Carrier females displayed generalized reduction in photoreceptor density as well as multifocal areas of complete rod loss. The electroretinogram (ERG) findings were compatible with the histopathologic abnormalities. Homozygous females had lesions similar to those seen in affected males.X-linked retinal degeneration is characterized by initial degeneration of rod photoreceptors, followed by loss of cones and progressive atrophy of the inner retina. Carrier females display a phenotype consistent with random X-chromosome inactivation. Variation in genetic background may alter expression of the disease allele in affected animals, thus accounting for variation in phenotypic expression of the disease.

Dogs affected with progressive rod-cone degeneration (prcd) have reduced levels of docosahexaenoic acid (DHA, 22:6n-3) in their plasma and rod photoreceptor outer segments (ROS). Dietary supplementation of DHA has failed to increase the ROS DHA levels to that of unaffected control dogs. The present study was undertaken to test the hypothesis that prcd-affected dogs have a reduced capacity for the synthesis and/or release of DHA in retinal pigment epithelial (RPE) cells.RPE cells (first passage cultures) from prcd-affected and normal dogs were incubated with [3H]eicosapentaenoic acid (EPA, 20:5n-3) for 24 and 72 hours. After incubation, the radiolabeled fatty acids in the cells and media were analyzed.DHA and all its metabolic intermediates were detected in RPE cells from prcd-affected and normal dogs. No significant difference was found in the amount of products (including DHA) synthesized between normal and affected RPE cells at either time point. In the culture media, RPE cells from prcd-affected dogs released significantly more DHA than cells from normal dogs after 72-hour incubation, but not after 24-hour incubation.RPE cells from prcd-affected dogs can synthesize and release DHA at least as efficiently as cells from normal dogs. Therefore, synthesis of DHA from its precursor and its release from RPE cells does not appear to contribute to the reduction in ROS DHA levels found in prcd-affected animals.

Progressive rod-cone degeneration (prcd) is an autosomal recessive retinal degeneration of dogs characterized by abnormalities in lipid metabolism. It has recently been mapped to the centromeric region of canine chromosome 9, homologous to human 17q, which contains the apolipoprotein H (apoH, protein; APOH, gene) gene involved in lipid metabolism and regulation of triglycerides. The present study was undertaken to evaluate APOH as a positional candidate for prcd.Expression of APOH in the retina was examined by reverse transcription-polymerase chain reaction (RT-PCR) and by immunocytochemistry in normal and prcd-affected dogs. The level of apoH in the plasma was determined by western blot analysis. Intragenic polymorphic markers were identified and typed in the prcd pedigree. Canine-rodent hybrid cell lines were analyzed to detect canine APOH.ApoH has been localized to the photoreceptor outer segment layer by immunocytochemistry. Its expression in the retina of normal and prcd-affected dogs was confirmed by RT-PCR. The levels of antihuman apoH cross-reacting material in plasma were similar in all dogs, regardless of disease status. Finally, linkage analysis of the APOH gene with the disease locus in the prcd pedigree detected 3 recombinants among 70 informative offsprings (lod score 15.09 at 0 = 4.3 centimorgan [cM]).APOH is expressed in the retina and tightly linked to the prcd locus. However, despite its potential role in phenotypes of abnormal lipid metabolism associated with prcd, the gene has been excluded as a primary candidate for prcd by linkage analysis.

To characterize the cDNA and the organization of the gene encoding the cone-specific gamma subunit of transducin (Tgamma c) and to examine this gene as a candidate for the recessively inherited cone photoreceptor degeneration in the cd dog.Canine Tgamma c cDNA was cloned and sequenced. Polymerase chain reaction (PCR) was used to define the Tgamma c gene structure, northern blot analysis to examine the level of expression of Tgamma c mRNA in control and cd-affected retinas, and immunocytochemistry to determine the presence and localization of Tgamma c in normal and cd retinas.Immunocytochemical results showed Tgamma c localized to cone photoreceptor outer segments in the normal retina, whereas no Tgamma c immunoreactivity was observed in the cd retinas. However, the level of transcription and the primary structure of the cloned cDNA coding for the 69-amino acid protein were identical in retinas from wild-type and affected dogs.Although Tgamma c immunoreactivity was specifically absent in the cd dog retina, no differences were detected between normal and cd retinas in the nucleotide sequence of Tgamma c mRNA or in its synthesis. These results indicate that a mutation in the Tgamma c gene may not be causally associated with the cd dog disease. These findings suggest that possible abnormalities in posttranslational modification of Tgamma c or defective assembly of the transducin alphabetagamma complex could lead to rapid degradation of Tgamma c.

To determine the versatility of retroviral vector-mediated rat beta-glucuronidase cDNA expression in the normal retinal pigment epithelium (RPE) of eyes of various species and in RPE of eyes with three types of mucopolysaccharidosis (MPS types I, VI, and VII) and to evaluate the effect of multiple transductions and long-term stable expression in the RPE.A retroviral construct containing a rat beta-glucuronidase cDNA (NTK-BGEO) was used to infect RPE cells at subconfluence. The transduced cells were selected in G418, an antibiotic toxic to normal mammalian cells. Beta-glucuronidase activity was measured in transduced cells and media, using a fluorogenic substrate. Glycosaminoglycan profiles were examined by metabolically labeling RPE with Na2(35)SO4.Transduced RPE cells, regardless of species or disease status, expressed rat beta-glucuronidase. The expressed enzyme restored normal levels of glycosaminoglycans in the RPE cells of homozygous MPS VII-affected dogs by metabolizing stored glycosaminoglycans. The expressed enzyme failed to metabolize stored glycosaminoglycans of MPS I and MPS VI, indicating that overexpression could not bypass the exoglycosidase restriction. Multiple transductions increased beta-glucuronidase activity several times in the cell layer and in the media. The expression was stable in vitro for at least 12 weeks.A retroviral vector can mediate transfer of beta-glucuronidase in various species of normal and MPS-affected RPE. The expression is stable in vitro. The metabolism of stored glycosaminoglycans in MPS needs replacement of only the deficient enzyme to reverse the storage.

Results of a previous study show abnormal plasma lipids in progressive rod-cone degeneration (prcd)-affected dogs, with lower docosahexaenoic acid (DHA; 22:6n-3) and cholesterol levels but no differences in other plasma fatty acids, lipids, triglycerides, and fat-soluble vitamins. There is also an increase of the DHA precursor 22:5n-3, so that the ratio of 22:5n-3 to 22:6n-3 is higher in affected than in normal dogs. Because DHA is the predominant esterified fatty acid in rod outer segment (ROS) phospholipids, these findings suggest a possible causal association between abnormal plasma lipid levels and retinal degeneration. In the current study, dietary supplements rich in 22:6n-3 were used to determine whether plasma, liver, and rod outer segment phospholipid composition can be altered to modify the prcd disease phenotype.prcd-affected and normal control dogs were given DHA-enriched supplements for short (7- and 25-day) and long (21-week) periods, and the fatty acid composition of plasma, liver, and rod outer segment phospholipids were examined. In the long-term study, electroretinography and morphology were used to assess modification of the retinal degeneration phenotype.Administration of DHA-enriched supplements resulted in increases in plasma DHA and n-3 polyunsaturated fatty acids and in decreases in some n-6 fatty acids in normal and prcd-affected dogs. Similar increases in DHA and n-3 fatty acids were observed in the liver, but affected dogs had significantly higher levels at all supplementation time points examined. In contrast, the ROS of affected dogs had statistically lower (approximately 20%) DHA levels, and these levels could not be increased with dietary supplementation. The disease phenotype could not be modified by DHA-enriched supplements.Regardless of the sustained three- to fourfold elevation in plasma and liver DHA that occurs as the result of supplementation, the ROS DHA levels remain unchanged, and the prcd disease phenotype is not modified by the dietary manipulation. These findings could be the result of a reduction in the synthesis of DHA-containing phospholipids in the retinas of affected dogs; or, alternatively, there could be a reduction in DHA uptake, transport, or storage within the retinal pigment epithelium-photoreceptor complex.

To determine whether early retinal degeneration (erd) and progressive rod cone degeneration (prcd), two canine hereditary retinal degenerations, are caused by allelic mutations; to determine the cDNA sequence of the canine RDS/peripherin homolog (CFRDSP); and to test whether mutations(s) in CFRDSP cause(s) either erd or prcd.Three erd-affected dogs were crossbred to three prcd-affected dogs, and their progeny were tested by electroretinography and retinal morphology for evidence of retinal degeneration. Canine RDS/peripherin cDNA was cloned and sequenced after reverse-transcription-polymerase chain reaction (RT-PCR) of total retinal RNA. A set of overlapping fragments of CFRDSP cDNA amplified from normal and prcd-affected retinal RNA was examined by double-stranded conformational polymorphism analysis for evidence of any mutation in prcd-affected dogs. RDS/peripherin-specific restriction fragment length polymorphism (RFLP) allelic differences within informative prcd and erd pedigrees were sought by digestion of amplified regions of the CFRDSP gene with different restriction enzymes. A Hinf I RFLP was identified with alleles segregating in a set of prcd and erd informative pedigrees. Linkage of CFRDSP to either prcd or erd was tested using the LINKAGE analysis package.All progeny from the erd x prcd cross were phenotypically normal at ages beyond the age of diagnosis for both parental disorders. The sequence of CFRDSP cDNA is reported (Genbank accession U27349). It is, overall, 79% identical at the nucleotide level with the corresponding human sequence. The coding region shares 89% and 93% nucleotide identity with the corresponding human and feline sequences, respectively. No mutation has been identified in the coding region of CFRDSP in prcd-affected dogs. In prcd pedigrees informative for both prcd and the CFRDSP Hinf I RFLP, a minimum of six obligate recombinants were identified. Similarly, in erd pedigrees, 14 of 29 progeny informative for both erd and this RFLP were obligate recombinants.The canine erd and prcd mutations are nonallelic. The canine RDS/peripherin gene (CFRDSP) has been excluded as a candidate for both prcd and erd. The demonstrated informativeness of the canine pedigrees on which these studies were based will enable testing other candidate genes for prcd and erd. Sequence information of CFRDSP will enable testing this locus as a candidate in other canine hereditary retinal degenerations.

To determine if a previously reported nonsense mutation (G to A transition at nucleotide position 2420) in the canine rod cyclic GMP (cGMP) phosphodiesterase beta (PDEB) subunit gene cosegregates with the rod-cone dysplasia 1 disease allele (rcd1) in the rcd1-dog reference colony; to establish the prevalence of this mutation among rcd1-affected Irish setters in the United States; and to screen for this mutation in other forms of canine hereditary progressive retinal atrophy (PRA).Exon 21 of canine PDEB, previously reported to contain a nonsense mutation in rcd1-affected dogs, was amplified by polymerase chain reaction from genomic DNA isolated from peripheral blood samples. The mutation was detected in amplified DNA by restriction enzyme digestion and double-stranded conformational polymorphism. Linkage between rcd1 and the PDEB mutation was tested using the computer program LIPED:Three different rcd1-informative canine pedigrees were tested for the PDEB nonsense mutation. The first was a multigenerational pedigree representing the rcd1 reference colony. The other two pedigrees represented purebred Irish setter breeding lines in which rcd1 was known to be segregating. In all three pedigrees, the same point mutation was present and segregated with no discordance with the rcd1 allele. Linkage analysis established a maximum logarithm of odds (LOD) score of 12.05 at a linkage distance (theta) of 0.0. In a representative sampling of Irish setters in the United States diagnosed clinically as affected with typical rcd1 phenotype, all dogs were demonstrated to have the same (codon 807) PDEB mutation. Three of four Irish setters affected with atypical, relatively slower disease also had this mutation, but one dog did not. This point mutation in the canine PDEB gene was absent in other forms of canine hereditary retinal degeneration.In three informative pedigrees, the codon 807 mutation in canine PDEB cosegregates with the rcd1 disease allele with zero discordance. A linkage distance (theta) of zero, with an LOD score of 12.05, indicates identity of this mutation and rcd1. This appears to be the only mutation causing rcd1 in the United States. In all other forms of canine hereditary retinal degeneration tested (cd, erd, prcd, rcd2, X-linked PRA, and in one Iris degeneration tested (cd, erd, prcd, rcd2, X-linked PRA, and in one Irish setter with late onset PRA), this PDEB point mutation was absent.

Docosahexaenoic acid (DHA, 22:6n-3) is the major fatty acid of photoreceptor membranes that is necessary for optimal retinal function. Miniature poodle dogs with progressive rod-cone degeneration have lower plasma levels of DHA than normal dogs and higher 22:5n-3/22:6n-3 ratios. The purpose of this study was to test the hypothesis that the metabolic defect in dogs affected with progressive rod-cone degeneration was a reduced capacity for ocular synthesis of DHA from its precursor 22:5n-3.The in vivo retinal conversion of [14C]22:5n-3 to [14C]22:6n-3 was investigated by injecting normal dogs and dogs affected with progressive rod-cone degeneration intravitreally with [14C]22:5n-3. After 72 hours, rod outer segments, remaining retina, and retinal pigment epithelium/choroid were analyzed for metabolic products.Using high-performance liquid chromatography, six radioactive peaks were detected in both normal and affected dogs: [14C]20:5n-3, [14C]22:6n-3, [14C]22:5n-3, [14C]24:6n-3, [14C]24:5n-3, and [14C]18:0. The majority of the label in each tissue was in 22:6n-3 and there was no difference in the dpm% of [14C]22:6n-3 in normal and affected animals in any of the three tissues. Voss et al (J Biol Chem 1991;266:19995-20000) proposed a new pathway for the synthesis of DHA that involves elongation of 22:5n-3 to 24:5n-3, desaturation to 24:6n-3, and beta-oxidation to 22:6n-3. Identification of the products [14C]24:5n-3 and [14C]24:6n-3 verified that these putative intermediates are present in the dog retina.The finding of large amounts of label in DHA shows that the normal and progressive rod-cone-degenerated retina and retinal pigment epithelium are capable of DHA synthesis from 22:5n-3. The presence of radioactivity in 24:5n-3 and 24:6n-3 suggests that the synthesis of DHA in the retina is similar to that described in the liver.

In the retinal disorder progressive rod-cone degeneration (prcd) in miniature poodle dogs, the photoreceptor layer degenerates slowly in the course of 5 to 7 years. Components of the interphotoreceptor matrix form a continuous extracellular lattice around photoreceptors. The purpose was to study the photoreceptor cell-matrix interactions during the disease and degeneration phases. Because degeneration rate was slower in cones, the authors also wanted to investigate whether there was a link between the degeneration and the photoreceptor-specific interphotoreceptor matrix domains.Rod- and cone-specific interphotoreceptor matrix domains were examined during two periods: before morphological signs of disease had appeared and during the degenerative stages. Two lectin probes were used; wheat germ agglutinin and peanut agglutinin. By their affinity for terminal carbohydrates, the lectins visually separated the two photoreceptor-specific domains and allowed follow-up of the fate of the rod and cone matrices separately.Before and during the course of disease, the lectin distribution in rod and cone domains remained normal, however, in the degenerative phase of the disease, there were structural changes in the matrix domains. The matrix connections between the individual domains was disrupted and single domains were formed. Cone domains and, to a lesser degree rod domains, were thickened around the inner and outer segments.The changes occurring in the photoreceptor-specific domains were indicative of structural adaptation to cell death and to degenerative conditions. There was no evidence of an active involvement of the interphotoreceptor matrix components studied in the disease process.

Feline mucopolysaccharidosis VI (MPS VI) is a recessively inherited lysosomal storage disease resulting from a deficiency of arylsulfatase B (ASB). Previous histopathologic findings have indicated that the disease is expressed morphologically in non-pigmented retinal pigment epithelial cells (RPE) in the posterior pole and superior equatorial regions by the accumulation of vacuolated inclusions and eventual cellular hypertrophy, while pigmented regions in the periphery are minimally affected. To determine if the regional and age-dependent variations in disease severity result from differences in residual enzyme activity, primary cultures of feline MPS VI-affected RPE were initiated from defined regions of the eye and maintained in vitro for 14 days. Cultures initiated from nonpigmented areas of affected adult eyes (posterior pole, superior equatorial) were more diseased than those from pigmented (inferior-equatorial, peripheral) areas. In the nonpigmented cultures, the disease was expressed by the accumulation of single membrane-bound inclusions and cellular hypertrophy. These inclusions were indistinguishable in their morphologic appearance and distribution from those found in situ. In contrast, the cultures initiated from pigmented areas remained normal or minimally affected. The same spatial disease distribution was present in young affected eyes, but the expression of the disease was much less severe. It is apparent that temporal, spatial, and pigmentation factors were correlated with disease expression in vitro as well as in situ. Arylsulfatase B activity was measured biochemically, and found to be deficient in all regions of young and adult eyes. It was notable that there was no correlation between the level of residual enzyme activity, and the pigmentation or spatial position from which the cells were obtained.(ABSTRACT TRUNCATED AT 250 WORDS)

These studies show that onset of photoreceptor cell degeneration preceded the loss of taurine in retinas of Irish setters with rod-cone dysplasia. The numbers of photoreceptor cell nuclei were within the normal adult range in affected setters at 10 through 26 days of age but declined rapidly between 26 and 45 days and more gradually thereafter; their numbers became reduced to 50% of normal at 45 days and then to 12-20% and 3-10% of normal at 192 and 346 days, respectively. Taurine concentrations increased within the photoreceptor cell layer during normal development to peak values (50 mM) at a time (45 days of age) corresponding to the development of adult photoreceptor function. In the affected setters, taurine levels increased as in the normal until 26 days of age and then remained at that value until 40-50% of the photoreceptor cells had degenerated. Thereafter, taurine levels declined gradually throughout the period of photoreceptor cell degeneration and were reduced to 30-40% of the normal adult level at the time (346 days) when the thickness of the outer nuclear layer was reduced to less than one complete row of nuclei. These observations agree with findings in retinal degeneration (rd) mice and RCS rats and indicate that in all three of these animal models of hereditary retinal degenerations, reductions in retinal taurine levels occur secondary to the loss of photoreceptor cells.

The synthesis and turnover of glycosaminoglycans (GAGs) in different fractions of cultured feline retinal pigment epithelium (RPE) were characterized. In one method of fractionation, trypsin was used to separate the extracellular components (referred to as trypsin-soluble glycocalyx) from the intracellular components. As a second method, the basal extracellular matrix (basal ECM) was separated from the rest of the GAGs (cell-associated GAGs) by extracting the cell layer with NH4OH. The incorporation of 35SO4 into cetylpyridinium chloride-precipitable GAGs in the cell-associated and the intracellular fractions increased throughout the labeling period, while in the trypsin-soluble glycocalyx and the basal ECM incorporation approached a maximum. While heparan sulfate was the predominant GAG in all compartments, most was located extracellularly. The majority of dermatan sulfate was localized in the intracellular fraction. GAGs in the trypsin-soluble glycocalyx exhibited a rapid rate of turnover, while GAGs in the intracellular compartment and basal ECM turned over much more slowly. Ascorbic acid increased the incorporation of 35SO4 into ECM chondroitin sulfate/dermatan sulfate, but not heparan sulfate, on a per cell basis. Cycloheximide reduced incorporation of 35SO4-GAGs into both the cell-associated compartment and the basal ECM. In contrast, monensin caused a reduction in basal ECM GAGs while increasing the GAGs in the cell-associated compartment. The intracellular accumulation of GAGs and resultant pathology in alpha-L-iduronidase (alpha-L-id)-deficient RPE indicated that this pathway for the intracellular degradation of GAGs is important in normal RPE function. However, the turnover of GAGs in the trypsin-soluble glycocalyx was not affected by deficient alpha-L-id activity or by the subsequent intracellular accumulation of GAGs. Therefore, normal lysosomal activity in the RPE is not a prerequisite for maintaining the rate of extracellular GAG turnover within normal limits.

Electroretinographic studies of myctalopic Appaloosa horses demonstrated photopic and scotopic abnormalities similar to those in humans with congenital stationary night blindness (CSNB) of the Schubert-Bornschein type. The phototopic abnormalities consisted of reduced b-wave amplitudes and slower than normal b-wave implict time. The dark-adapted ERG's consisted of a simple negative potential; the scotopic b-wave was nonrecordable. However, a normal c-wave was present in the dark-adapted response. Histologic studies demonstrated no structural abnormalities that could explain the functional defect.

In a survey of 546 rhesus monkeys of various ages, 6.1% of the animals showed ophthalmoscopically visible hypopigmented spots in their maculas. There was a statistically significant correlation between the age of the animal and the degree of hypopigmentation. Electroretinographic responses and visually evoked potentials were evaluated in a selected group of monkeys with and without hypopigmented macular spots. No significant change in retinal function as a result of the macular abnormalities could be detected.