Three-year results of phase I retinal gene therapy trial for CNGA3-mutated achromatopsia: results of a non randomised controlled trial

AIMS

To determine long-term safety and efficacy outcomes of a subretinal gene therapy for CNGA3-associated achromatopsia. We present data from an open-label, nonrandomised controlled trial (NCT02610582).

METHODS

Details of the study design have been previously described. Briefly, nine patients were treated in three escalating dose groups with subretinal AAV8.CNGA3 gene therapy between November 2015 and October 2016. After the first year, patients were seen on a yearly basis. Safety assessment constituted the primary endpoint. On a secondary level, multiple functional tests were carried out to determine efficacy of the therapy.

RESULTS

No adverse or serious adverse events deemed related to the study drug occurred after year 1. Safety of the therapy, as the primary endpoint of this trial, can, therefore, be confirmed. The functional benefits that were noted in the treated eye at year 1 were persistent throughout the following visits at years 2 and 3. While functional improvement in the treated eye reached statistical significance for some secondary endpoints, for most endpoints, this was not the case when the treated eye was compared with the untreated fellow eye.

CONCLUSION

The results demonstrate a very good safety profile of the therapy even at the highest dose administered. The small sample size limits the statistical power of efficacy analyses. However, trial results inform on the most promising design and endpoints for future clinical trials. Such trials have to determine whether treatment of younger patients results in greater functional gains by avoiding amblyopia as a potential limiting factor.

Mural Cell SRF Controls Pericyte Migration, Vessel Patterning and Blood Flow

Pericytes and vascular smooth muscle cells, collectively known as mural cells, are recruited through PDGFB (platelet-derived growth factor B)-PDGFRB (platelet-derived growth factor receptor beta) signaling. MCs are essential for vascular integrity, and their loss has been associated with numerous diseases. Most of this knowledge is based on studies in which MCs are insufficiently recruited or fully absent upon inducible ablation. In contrast, little is known about the physiological consequences that result from impairment of specific MC functions. Here, we characterize the role of the transcription factor SRF (serum response factor) in MCs and study its function in developmental and pathological contexts.

Safety and Vision Outcomes of Subretinal Gene Therapy Targeting Cone Photoreceptors in Achromatopsia: A Nonrandomized Controlled Trial

Question

What are the safety and vision outcomes associated with gene therapy for achromatopsia?

Findings

In this nonrandomized controlled trial of 9 patients with confirmed CNGA3-linked achromatopsia, gene therapy applying an adeno-associated viral vector encoding CNGA3, was not associated with substantial safety concerns and was associated with improvements of vision in patients.

Meaning

This study provides clinical proof of concept for viral vector–mediated gene supplementation therapy of inherited day blindness caused by pathogenic variants in the cone photoreceptor-specific gene CNGA3.

Importance

Achromatopsia linked to variations in the CNGA3 gene is associated with day blindness, poor visual acuity, photophobia, and involuntary eye movements owing to lack of cone photoreceptor function. No treatment is currently available.

Objective

To assess safety and vision outcomes of supplemental gene therapy with adeno-associated virus (AAV) encoding CNGA3 (AAV8.CNGA3) in patients with CNGA3-linked achromatopsia.

Design, Setting, and Participants

This open-label, exploratory nonrandomized controlled trial tested safety and vision outcomes of gene therapy vector AAV8.CNGA3 administered by subretinal injection at a single center. Nine patients (3 per dose group) with a clinical diagnosis of achromatopsia and confirmed biallelic disease-linked variants in CNGA3 were enrolled between November 5, 2015, and September 22, 2016. Data analysis was performed from June 6, 2017, to March 12, 2018.

Intervention

Patients received a single unilateral injection of 1.0 × 10¹⁰, 5.0 × 10¹⁰, or 1.0 × 10¹¹ total vector genomes of AAV8.CNGA3 and were followed up for a period of 12 months (November 11, 2015, to October 10, 2017).

Main Outcomes and Measures

Safety as the primary end point was assessed by clinical examination of ocular inflammation. Systemic safety was assessed by vital signs, routine clinical chemistry testing, and full and differential blood cell counts. Secondary outcomes were change in visual function from baseline in terms of spatial and temporal resolution and chromatic, luminance, and contrast sensitivity throughout a period of 12 months after treatment.

Results

Nine patients (mean [SD] age, 39.6 [11.9] years; age range, 24-59 years; 8 [89%] male) were included in the study. Baseline visual acuity letter score (approximate Snellen equivalent) ranged from 34 (20/200) to 49 (20/100), whereas baseline contrast sensitivity log scores ranged from 0.1 to 0.9. All 9 patients underwent surgery and subretinal injection of AAV8.CNGA3 without complications. No substantial safety problems were observed during the 12-month follow-up period. Despite the congenital deprivation of cone photoreceptor–mediated vision in achromatopsia, all 9 treated eyes demonstrated some level of improvement in secondary end points regarding cone function, including mean change in visual acuity of 2.9 letters (95% CI, 1.65-4.13; P = .006, 2-sided t test paired samples). Contrast sensitivity improved by a mean of 0.33 log (95% CI, 0.14-0.51 log; P = .003, 2-sided t test paired samples).

Conclusions and Relevance

Subretinal gene therapy with AAV8.CNGA3 was not associated with substantial safety problems and was associated with cone photoreceptor activation in adult patients, as reflected by visual acuity and contrast sensitivity gains.

Trial Registration

ClinicalTrials.gov Identifier: NCT02610582

Abstract P1-08-12: p53 status and 17q21.3 amplicon formation in HER2-positive breast cancer

Breast cancers that overexpress HER2/neu are associated with poor clinical outcome. Treatment of HER2-positive breast cancers with trastuzumab, a monoclonal antibody that antagonizes HER2 receptor signaling, increases patient overall and disease-free survival. While targeted therapy is reasonably effective, resistance to trastuzumab remains a problem, particularly in the case of metastatic disease. Tumor suppressor p53 is the most commonly mutated gene in human cancer and mutations that lead to the stabilization and accumulation of p53 in HER2-positive breast cancers are associated with worse clinical outcome. Another feature of HER2-enriched breast cancers are amplifications of the HER2 locus on chromosome 17q21.3.

Table 1 Wildtype p53Mutated p53No amplification12.8%63.9%17q21.3 amplification13.1%8.7%Table 1: Among 58 cases, Her2-positive tumors with mutated p53 (n=37, 63.9%) occurred at a 4.9-fold higher frequency than amplification of the 17q21.3 gene set (n=8, 13.1%), with significant mutual exclusivity (p=0.005), The patient genomic data set was obtained from the Breast Invasive Carcinoma Study conducted by the TCGA Network (Nature, 2012) and visualized using cBioPortal (MSKCC), Copy alterations of genes were assessed using GISTIC2.0 (Broad Institute) via cBioPortal.

We studied the genomic profiles of 58 HER2-positive breast tumor samples using cBioPortal to determine p53 mutation status. 74.1% of samples expressed mutant p53 and a large fraction of mutations occurred in the key DNA binding domain. We assessed the amplification status of 24 genes within the chromosome 17q21.3 locus as an indicator of amplicon formation, and found that 21.8% of breast tumors demonstrated copy number amplification (Table 2). Mutant p53 tumors with no amplicon formation occurred 5 times more frequently than tumors with only 17q21.3 amplicon formation. These alterations tended to occur exclusive of one another (p=0.005, Table 1). Separately, using gene expression data from Kaplan-Meier Plotter, we observed that alterations in gene expression within the 17q21.3 amplicon can have differential effects on the survival of HER2-positive breast cancer patients (Table 2).

Table 217q21.3 Gene SetHazard RatioP-valueCOL1A11.760.01MBTD10.530.01SPATA200.650.04UBE2Z0.680.07EME10.650.08Table 2: List of relevant genes within the chromosome 17q21.3 amplicon. Genes in this amplicon can influence both beneficial and hazardous survival outcomes in HER2-positive breast cancer patients (n=208). Hazard ratios (HR) were determined from gene expression data available through Kaplan-Meier Plotter (Gyorffy, 2010).

Our data shows that HER2-positive breast cancers can be divided into p53 mutant and non-mutant subsets with p53 mutations relatively exclusive to 17q21.3 gene amplification. However, p53 mutation status and 17q21.3 copy number have a variety of effects on patient outcome. We are interested in understanding the interaction between these two genetic alterations and whether subdividing HER2-positive breast cancer into these subtypes will improve our ability to provide effective therapy to patients.

Citation Format: Tan G, Seeliger M, Cohen J. p53 status and 17q21.3 amplicon formation in HER2-positive breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-08-12.

miRNAs 182 and 183 are necessary to maintain adult cone photoreceptor outer segments and visual function

The outer segments of cones serve as light detectors for daylight color vision, and their dysfunction leads to human blindness conditions. We show that the cone-specific disruption of DGCR8 in adult mice led to the loss of miRNAs and the loss of outer segments, resulting in photoreceptors with significantly reduced light responses. However, the number of cones remained unchanged. The loss of the outer segments occurred gradually over 1 month, and during this time the genetic signature of cones decreased. Reexpression of the sensory-cell-specific miR-182 and miR-183 prevented outer segment loss. These miRNAs were also necessary and sufficient for the formation of inner segments, connecting cilia and short outer segments, as well as light responses in stem-cell-derived retinal cultures. Our results show that miR-182- and miR-183-regulated pathways are necessary for cone outer segment maintenance in vivo and functional outer segment formation in vitro.

Cav1.4 IT mouse as model for vision impairment in human congenital stationary night blindness type 2

Mutations in the CACNA1F gene encoding the Cav1.4 Ca (2+) channel are associated with X-linked congenital stationary night blindness type 2 (CSNB2). Despite the increasing knowledge about the functional behavior of mutated channels in heterologous systems, the pathophysiological mechanisms that result in vision impairment remain to be elucidated. This work provides a thorough functional characterization of the novel IT mouse line that harbors the gain-of-function mutation I745T reported in a New Zealand CSNB2 family. (1) Electroretinographic recordings in IT mice permitted a direct comparison with human data. Our data supported the hypothesis that a hyperpolarizing shift in the voltage-dependence of channel activation-as seen in the IT gain-of-function mutant (2)-may reduce the dynamic range of photoreceptor activity. Morphologically, the retinal outer nuclear layer in adult IT mutants was reduced in size and cone outer segments appeared shorter. The organization of the outer plexiform layer was disrupted, and synaptic structures of photoreceptors had a variable, partly immature, appearance. The associated visual deficiency was substantiated in behavioral paradigms. The IT mouse line serves as a specific model for the functional phenotype of human CSNB2 patients with gain-of-function mutations and may help to further understand the dysfunction in CSNB.

Mice lacking Period 1 and Period 2 circadian clock genes exhibit blue cone photoreceptor defects

Many aspects of retinal physiology are modulated by circadian clocks, but it is unclear whether clock malfunction impinges directly on photoreceptor survival, differentiation or function. Eyes from wild-type (WT) and Period1 (Per1) and Period2 (Per2) mutant mice (Per1(Brdm1) Per2(Brdm1) ) were examined for structural (histology, in vivo imaging), phenotypical (RNA expression, immunohistochemistry) and functional characteristics. Transcriptional levels of selected cone genes [red/green opsin (Opn1mw), blue cone opsin (Opn1sw) and cone arrestin (Arr3)] and one circadian clock gene (RORb) were quantified by real-time polymerase chain reaction. Although there were no changes in general retinal histology or visual responses (electroretinograms) between WT and Per1(Brdm1) Per2(Brdm1) mice, compared with age-matched controls, Per1(Brdm1) Per2(Brdm1) mice showed scattered retinal deformations by fundus inspection. Also, mRNA expression levels and immunostaining of blue cone opsin were significantly reduced in mutant mice. Especially, there was an alteration in the dorsal-ventral patterning of blue cones. Decreased blue cone opsin immunoreactivity was present by early postnatal stages, and remained throughout maturation. General photoreceptor differentiation was retarded in young mutant mice. In conclusion, deletion of both Per1 and Per2 clock genes leads to multiple discrete changes in retina, notably patchy tissue disorganization, reductions in cone opsin mRNA and protein levels, and altered distribution. These data represent the first direct link between Per1 and Per2 clock genes, and cone photoreceptor differentiation and function.

Pharmacological modulation of the retinal unfolded protein response in Bardet-Biedl syndrome reduces apoptosis and preserves light detection ability

Ciliopathies, a class of rare genetic disorders, present often with retinal degeneration caused by protein transport defects between the inner segment and the outer segment of the photoreceptors. Bardet-Biedl syndrome is one such ciliopathy, genetically heterogeneous with 17 BBS genes identified to date, presenting early onset retinitis pigmentosa. By investigating BBS12-deprived retinal explants and the Bbs12(-/-) murine model, we show that the impaired intraciliary transport results in protein retention in the endoplasmic reticulum. The protein overload activates a proapoptotic unfolded protein response leading to a specific Caspase12-mediated death of the photoreceptors. Having identified a therapeutic window in the early postnatal retinal development and through optimized pharmacological modulation of the unfolded protein response, combining three specific compounds, namely valproic acid, guanabenz, and a specific Caspase12 inhibitor, achieved efficient photoreceptor protection, thereby maintaining light detection ability in vivo.

Characterization of feline hereditary retinal dystrophies using clinical, functional, structural and molecular genetic studies

Only in recent years have specific mutations been elucidated for feline hereditary retinal dystrophies. Molecular genetic characterization of feline diseases has so far been a slow process but with a full genome sequence for the cat recently completed and the development of a feline single nucleotide polymorphism chip, the characterization of feline monogenic disorders will be significantly simplified. This review summarizes current knowledge with regard to specific hereditary retinal dystrophies in cats and gives an overview of how cats can be used as models in translational research.

PARP1 gene knock-out increases resistance to retinal degeneration without affecting retinal function

Retinitis pigmentosa (RP) is a group of inherited neurodegenerative diseases affecting photoreceptors and causing blindness in humans. Previously, excessive activation of enzymes belonging to the poly-ADP-ribose polymerase (PARP) group was shown to be involved in photoreceptor degeneration in the human homologous rd1 mouse model for RP. Since there are at least 16 different PARP isoforms, we investigated the exact relevance of the predominant isoform - PARP1 - for photoreceptor cell death using PARP1 knock-out (KO) mice. In vivo and ex vivo morphological analysis using optic coherence tomography (OCT) and conventional histology revealed no major alterations of retinal phenotype when compared to wild-type (wt). Likewise, retinal function as assessed by electroretinography (ERG) was normal in PARP1 KO animals. We then used retinal explant cultures derived from wt, rd1, and PARP1 KO animals to test their susceptibility to chemically induced photoreceptor degeneration. Since photoreceptor degeneration in the rd1 retina is triggered by a loss-of-function in phosphodiesterase-6 (PDE6), we used selective PDE6 inhibition to emulate the rd1 situation on non-rd1 genotypes. While wt retina subjected to PDE6 inhibition showed massive photoreceptor degeneration comparable to rd1 retina, in the PARP1 KO situation, cell death was robustly reduced. Together, these findings demonstrate that PARP1 activity is in principle dispensable for normal retinal function, but is of major importance for photoreceptor degeneration under pathological conditions. Moreover, our results suggest that PARP dependent cell death or PARthanatos may play a major role in retinal degeneration and highlight the possibility to use specific PARP inhibitors for the treatment of RP.

Genetic reactivation of cone photoreceptors restores visual responses in retinitis pigmentosa

Retinitis pigmentosa refers to a diverse group of hereditary diseases that lead to incurable blindness, affecting two million people worldwide. As a common pathology, rod photoreceptors die early, whereas light-insensitive, morphologically altered cone photoreceptors persist longer. It is unknown if these cones are accessible for therapeutic intervention. Here, we show that expression of archaebacterial halorhodopsin in light-insensitive cones can substitute for the native phototransduction cascade and restore light sensitivity in mouse models of retinitis pigmentosa. Resensitized photoreceptors activate all retinal cone pathways, drive sophisticated retinal circuit functions (including directional selectivity), activate cortical circuits, and mediate visually guided behaviors. Using human ex vivo retinas, we show that halorhodopsin can reactivate light-insensitive human photoreceptors. Finally, we identified blind patients with persisting, light-insensitive cones for potential halorhodopsin-based therapy.

The absence of angiopoietin-2 leads to abnormal vascular maturation and persistent proliferative retinopathy

Angiopoietin-2 (Ang-2) antagonises the maturing effect of angiopoietin-1 (Ang-1) on blood vessels, and cooperates with VEGF to induce neovascularisation. In knockout mice, Ang-2 displayed a specific role in postnatal angiogenic remodelling. Here, we demonstrate that mice deficient in Ang-2 fail to form a proper spatial retinal vascular network. The retinal vasculature was characterised by reduced large vessel numbers and defects forming the superficial periphery mostly on the arteriolar site, and the secondary and tertiary deep capillary network. Hypoxia in the retinal periphery induced a four-fold VEGF upregulation and active endothelial proliferation for up to 60 days. Concomitantly, retinal digest preparations showed increased arteriolar (+33%) and capillary diameters (+90%), and fluorescein angiograms revealed leakiness of neovascular front. At one year of age, persistent preretinal vessels were non-leaky in accordance with a relative increase in the ratio of Ang-1 to VEGF. Taken together, the data suggest that Ang-2 has an important function in the spatial configuration of the three-dimensional retinal vasculature. Secondarily, prolonged VEGF activity results in a model of persistent proliferative retinopathy.

Rod and cone contributions to horizontal cell light responses in the mouse retina

Mammalian B-type horizontal cells make contact with both photoreceptor types: the dendrites contact cone photoreceptors, whereas the axon terminal processes contact rods. Despite their distinct synaptic contacts, horizontal cell somata and axon terminals receive a mixture of rod and cone inputs. Interaction of the two photoreceptor systems is essential for adaptation of photoreceptor sensitivity to different levels of background illumination, and horizontal cells play a key role in this adaptation. In this study, we used transgenic mouse lines to examine the contributions of rod and cone photoreceptor inputs to horizontal cell light responses in the mouse retina: rod signals were isolated by recording intracellularly from horizontal cells in a mouse lacking the cone cyclic nucleotide-gated channel, which lacks cone function, and cone signals were assessed using the rhodopsin knock-out mouse, which is a model for pure cone function. We found that both horizontal cell compartments receive a mixture of inputs from both photoreceptor types. To determine whether these inputs arrive via the long axon connecting the compartments or by way of rod-cone gap junctional coupling, we assessed the rod and cone contributions to horizontal cell somatic and axon terminal light responses in the connexin36-deficient mouse retina, which lacks rod-cone coupling. Our results confirm that rods and cones are coupled by connexin36, and suggest that signal transmission along the axon is unidirectional: signals are passed from horizontal cell soma to axon terminal but not from axon terminal to soma.

Abnormal vessel formation in the choroid of mice lacking tissue inhibitor of metalloprotease-3

PURPOSE

Tissue inhibitor of metalloprotease (TIMP)-3 is an inhibitor of matrix metalloprotease (MMP) and regulates angiogenesis. In the eye, TIMP3 is tightly associated with Bruch's membrane. In this study, the authors analyzed mice lacking TIMP3 for retinal abnormalities.

METHODS

Mice with targeted disruption of the Timp3 gene were generated (Timp3(-/-)) and bred into C57/Bl6 and CD1 backgrounds. Eyes were analyzed by light and electron microscopy. Vasculature was examined by scanning laser ophthalmoscopy, corrosion casts, and whole mount preparations. MMP activity was assessed by in situ zymography, angiogenic potential was evaluated by tube formation, and aortic ring assays and signaling pathways were studied by immunoblotting.

RESULTS

TIMP3-deficient mice develop abnormal vessels with dilated capillaries throughout the choroid. Enhanced MMP activity in the choroid region of Timp3(-/-) eyes was detected when compared with controls. Timp3(-/-)-derived tissue showed an increased angiogenic activity over wild-type, an effect that could specifically be inhibited by recombinant TIMP3. Moreover, the antiangiogenic property of TIMP3 was demonstrated to reside within the C-terminal domain. When VEGFR2 inhibitor was added to Timp3(-/-) aortic explants, endothelial sprout formation was markedly reduced, which provided evidence for an unbalanced VEGF-mediated angiogenesis in Timp3(-/-) animals. Finally, angiogenic signaling pathways are activated in Timp3(-/-)-derived cells.

CONCLUSIONS

These findings suggest that the distinct choroidal phenotype in mice lacking TIMP3 may be the result of a local disruption of extracellular matrix and angiogenic homeostasis, and they support an important role of TIMP3 in the regulation of choroidal vascularization.

R91W mutation in Rpe65 leads to milder early-onset retinal dystrophy due to the generation of low levels of 11-cis-retinal

RPE65 is a retinal pigment epithelial protein essential for the regeneration of 11-cis-retinal, the chromophore of cone and rod visual pigments. Mutations in RPE65 lead to a spectrum of retinal dystrophies ranging from Leber's congenital amaurosis to autosomal recessive retinitis pigmentosa. One of the most frequent missense mutations is an amino acid substitution at position 91 (R91W). Affected patients have useful cone vision in the first decade of life, but progressively lose sight during adolescence. We generated R91W knock-in mice to understand the mechanism of retinal degeneration caused by this aberrant Rpe65 variant. We found that in contrast to Rpe65 null mice, low but substantial levels of both RPE65 and 11-cis-retinal were present. Whereas rod function was impaired already in young animals, cone function was less affected. Rhodopsin metabolism and photoreceptor morphology were disturbed, leading to a progressive loss of photoreceptor cells and retinal function. Thus, the consequences of the R91W mutation are clearly distinguishable from an Rpe65 null mutation as evidenced by the production of 11-cis-retinal and rhodopsin as well as by less severe morphological and functional disturbances at early age. Taken together, the pathology in R91W knock-in mice mimics many aspects of the corresponding human blinding disease. Therefore, this mouse mutant provides a valuable animal model to test therapeutic concepts for patients affected by RPE65 missense mutations.

Assessment of Structure and Function Over a 3-year Period after Gene Transfer in RPE65−/− dogs

AIM

To assess retinal structure and function over a 3-year period in a group of five RPE65-/- dogs treated by unilateral rAAV- mediated subretinal gene transfer.

METHODS

Post-operative functional follow-ups were performed using simultaneous, bilateral, full-field ERGs. Structure was evaluated by SLO using FL and ICG angiography and by EM.

RESULTS

Significant improvement of retinal function was observed through ERGs approximately 4 weeks following surgery. Scotopic b-wave amplitudes peaked 3 months after surgery. Then there was a successive reduction, although greater amplitudes than base-line values were observed at all post-operative time points. A-wave amplitudes increased at a later time than b-wave amplitudes and were sustained throughout the follow-up period. The increased cone function was preserved longer than the rod function. Angiography showed structural changes at the site of injection, corroborated by photoreceptor destruction observed ultrastructurally. Immediately adjacent to the subretinal injection area photoreceptor outer segments appeared normal.

CONCLUSION

Despite local structural alterations at the subretinal injection site, subretinal gene transfer in the RPE65 null mutation dog effectively increases retinal function for at least 3 years after surgery.

Hypoxic Preconditioning and Erythropoietin Protect Retinal Neurons from Degeneration

Reduced tissue oxygenation stabilizes the alpha-subunit of the transcription factor hypoxia-inducible factor-1 (HIF-1). This leads to the induction of a number of hypoxia responsive genes. One of the best known HIF-1 targets is erythropoietin that exerts neuroprotective effects on ischemia-related injury in the brain. Thus, pre-exposure to low environmental oxygen concentrations might be exploited as a preconditioning procedure to protect tissues against a variety of harmful conditions. We present recent work on neuroprotection of retinal photoreceptors induced by hypoxic preconditioning or by systemically elevated levels of Epo in mouse plasma.

Impaired channel targeting and retinal degeneration in mice lacking the cyclic nucleotide-gated channel subunit CNGB1

Cyclic nucleotide-gated (CNG) channels are important mediators in the transduction pathways of rod and cone photoreceptors. Native CNG channels are heterotetramers composed of homologous A and B subunits. In heterologous expression systems, B subunits alone cannot form functional CNG channels, but they confer a number of channel properties when coexpressed with A subunits. To investigate the importance of the CNGB subunits in vivo, we deleted the CNGB1 gene in mice. In the absence of CNGB1, only trace amounts of the CNGA1 subunit were found on the rod outer segment. As a consequence, the vast majority of isolated rod photoreceptors in mice lacking CNGB1 (CNGB1-/-) failed to respond to light. In electroretinograms (ERGs), CNGB1-/- mice showed no rod-mediated responses. The rods also showed a slow-progressing degeneration caused by apoptotic death and concurred by retinal gliosis. Cones were primarily unaffected and showed normal ERG responses up to 6 months, but they started to degenerate in later stages. At the age of approximately 1 year, CNGB1-/- animals were devoid of both rods and cones. Our results show that CNGB1 is a crucial determinant of native CNG channel targeting. As a result of the lack of rod CNG channels, CNGB1-/- mice develop a retinal degeneration that resembles human retinitis pigmentosa.

Grating acuity at different luminances in wild-type mice and in mice lacking rod or cone function

PURPOSE

The mouse eye has become an important model in vision research. However, it is not known how visual acuity changes with luminance. Therefore, grating acuity of mice was measured at different luminances in an automated optomotor paradigm. Furthermore, mutant mice lacking either rods (RHO-/- and CNGB1-/-) or cones (CNGA3-/-), or both, were studied to determine the rod and cone contribution to visual acuity.

METHODS

Freely ranging individual mice were automatically tracked at a 25-Hz sampling rate with a self-programmed video system in a large rotating optomotor drum. The drum had a square-wave grating inside with adjustable spatial frequency. The angular speed of the mice with respect to the center of the drum and the angular orientation of the snout-tail body axis were analyzed. In addition, the motor activity of the wild-type mice was recorded at different luminances.

RESULTS

The optomotor drum provided reliable data on visual input to the mouse's behavior and was convenient to use, since the experimenter's had only to place the mice individually in a Perspex cylinder. Optomotor grating acuity of the wild-type mice was limited to 0.3 to 0.4 cyc/deg. Maximum optomotor responses were obtained at 0.1 to 0.2 cyc/deg. The importance of visual input declined monotonically with decreasing luminance (30 cd/m2, 100%; 0.1 cd/m2, 76.4%; 0.005 cd/m2, 45.9%; and darkness, -9%). Mice lacking functional rods were able to resolve gratings up to 0.1 cyc/deg at 30 cd/m2. Surprisingly, mice lacking functional cones had an optomotor acuity that was similar to the wild-type. Double-knockout mice without rods and cones had no detectable grating acuity.

CONCLUSIONS

Because the visual system of the mouse is more responsive at bright luminances, experiments in which visual input is important should be performed in photopic conditions (30 cd/m2 or even more). Apparently, spatial vision is governed by the rod system, which is not saturated in the mesopic or low photopic range. Mice lacking both rods and cones have no detectable grating acuity, indicating that the retinal melanopsin system does not contribute to spatial vision.

Morphological characterization of the retina of the CNGA3(-/-)Rho(-/-) mutant mouse lacking functional cones and rods

PURPOSE

To assess the structural changes in the retina caused by a functional blockade of rods and cones and to document the time course of their degeneration.

METHODS

Double knockout mice were generated by cross-breeding CNGA3(-/-) mice with Rho(-/-) mice. Retinas of mutant and wild-type mice from 3 weeks up to 12 months of age were studied by confocal light and electron microscopy. The retinas were immunostained with cell-type-specific markers and with antibodies against synapse-associated proteins and transmitter receptors.

RESULTS

In 3-week-old CNGA3(-/-)Rho(-/-) mice, retinal layers showed normal structural organization, and photoreceptors established normal synaptic contacts. Until postnatal week (Pw)7, presynaptic markers and postsynaptic glutamate receptors were well expressed at the photoreceptor terminals. Photoreceptor degeneration started at Pw4, progressing to an almost complete loss by 3 months. Rod spherules showed an increase in the number of synaptic ribbons and postsynaptic elements during this early stage of degeneration, and horizontal cell processes grew into the outer nuclear layer. At later stages of retinal degeneration, the inner plexiform layer (IPL) was also affected. Rod bipolar cell axon terminals showed morphologic alterations, but the stratification pattern of cone bipolar cell axons and amacrine cell processes appeared unaffected. Transmitter receptors (GlyRalpha3, GABA(A) alpha2, GluR2/3) showed no obvious changes in the distribution and density of their synaptic clusters throughout the IPL at postnatal month 12.

CONCLUSIONS

The normal structural and synaptic organization of the mutant retina at Pw3 suggests that photoreceptor light responses are not essential for the development of the retinal circuitry. However, functional photoreceptors are necessary for the maintenance of rods and cones and their contacts in the OPL, because they degenerate almost completely by 3 months after birth. Degenerative changes can also be observed in the IPL; however, they appear to have a slower time course and by 12 months of age the IPL circuitry appears to be surprisingly intact.

Functional and structural recovery of the retina after gene therapy in the RPE65 null mutation dog

PURPOSE

To assess the efficacy of AAV-mediated gene therapy to restore vision in a large number of RPE65(-/-) dogs and to determine whether systemic and local side effects are caused by the treatment.

METHODS

Normal RPE65 dog cDNA was subcloned into an rAAV vector under control of a cytomegalovirus promoter, and an AAV.GFP control vector was also produced with the titers 2 x 10(12) particles/mL and 2 x 10(10) transducing U/mL, respectively. RPE65(-/-) dogs, aged 4 to 30 months were treated with subretinal injections of the AAV.RPE65 and control vectors, respectively, in each eye, and three 24- to 30-month-old normal control dogs with the latter. Baseline and postoperative systemic and ophthalmic examinations, blood screenings, vision testing, and electroretinography (ERG) were performed. Two RPE65(-/-) dogs were killed at 3 and 6 months after treatment for morphologic examination of the retinas.

RESULTS

RPE65(-/-) dogs were practically blind from birth with nonrecordable or low-amplitude ERGs. Construct injections or sham surgeries were performed in 28 eyes; 11 were injected subretinally with the AAV.RPE65 construct. ERGs at 3 months after surgery showed that in the latter eyes, dark-adapted b-wave amplitudes recovered to an average of 28% of normal, and light adapted b-wave amplitudes to 32% of normal. ERG amplitudes were not reduced during a 6- to 9-month follow-up. No systemic side effects were observed, but uveitis developed in nine AAV.RPE65-treated eyes. No uveitis was observed in the eyes treated with the control vector. Immunocytochemistry showed expression of RPE65 in the retinal pigment epithelium (RPE) of AAV.RPE65-treated eyes. Fluorescence microscopy showed expression of green fluorescent protein (GFP) in the RPE and, to a lesser extent, in the neural retinas of AAV.GFP-treated eyes. Ultrastructurally, a reversal of RPE lipid droplet accumulation was observed at the AAV.RPE65 transgene injection site, but not at the site of injection of the control vector.

CONCLUSIONS

In 10 of 11 treated RPE65(-/-) eyes, gene transfer resulted in development of vision, both subjectively apparent by loss of nystagmus, and objectively recorded by ERG. Structurally, there was reversal of lipid droplet accumulation in the RPE. Uveitis developed in 75% of the transgene-treated eyes, a complication possibly due to an immunopathogenic response to the RPE65 molecule.

HIF-1-induced erythropoietin in the hypoxic retina protects against light-induced retinal degeneration

Erythropoietin (Epo) is upregulated by hypoxia and provides protection against apoptosis of erythroid progenitors in bone marrow and brain neurons. Here we show in the adult mouse retina that acute hypoxia dose-dependently stimulates expression of Epo, fibroblast growth factor 2 and vascular endothelial growth factor via hypoxia-inducible factor-1alpha (HIF-1alpha) stabilization. Hypoxic preconditioning protects retinal morphology and function against light-induced apoptosis by interfering with caspase-1 activation, a downstream event in the intracellular death cascade. In contrast, induction of activator protein-1, an early event in the light-stressed retina, is not affected by hypoxia. The Epo receptor required for Epo signaling localizes to photoreceptor cells. The protective effect of hypoxic preconditioning is mimicked by systemically applied Epo that crosses the blood retina barrier and prevents apoptosis even when given therapeutically after light insult. Application of Epo may, through the inhibition of apoptosis, be beneficial for the treatment of different forms of retinal disease.

[Vitamin A metabolism and retinal degeneration]

Vitamin A plays an important role in the pathogenesis and during the course of retinal degenerations. Following a brief overview of the metabolic pathway of Vitamin A from the entrance into the body to the arrival in retinal target structures, the most important retinal degenerations that are related to the Vitamin A-metabolism are presented. Ways of prevention or therapy of such diseases are discussed in the light of the still incomplete knowledge about basic mechanisms of retinol transport and metabolism.

Mutation of CDH23, encoding a new member of the cadherin gene family, causes Usher syndrome type 1D

Usher syndrome type I (USH1) is an autosomal recessive disorder characterized by congenital sensorineural hearing loss, vestibular dysfunction and visual impairment due to early onset retinitis pigmentosa (RP). So far, six loci (USH1A-USH1F) have been mapped, but only two USH1 genes have been identified: MYO7A for USH1B and the gene encoding harmonin for USH1C. We identified a Cuban pedigree linked to the locus for Usher syndrome type 1D (MIM 601067) within the q2 region of chromosome 10). Affected individuals present with congenital deafness and a highly variable degree of retinal degeneration. Using a positional candidate approach, we identified a new member of the cadherin gene superfamily, CDH23. It encodes a protein of 3,354 amino acids with a single transmembrane domain and 27 cadherin repeats. In the Cuban family, we detected two different mutations: a severe course of the retinal disease was observed in individuals homozygous for what is probably a truncating splice-site mutation (c.4488G-->C), whereas mild RP is present in individuals carrying the homozygous missense mutation R1746Q. A variable expression of the retinal phenotype was seen in patients with a combination of both mutations. In addition, we identified two mutations, Delta M1281 and IVS51+5G-->A, in a German USH1 patient. Our data show that different mutations in CDH23 result in USH1D with a variable retinal phenotype. In an accompanying paper, it is shown that mutations in the mouse ortholog cause disorganization of inner ear stereocilia and deafness in the waltzer mouse.

Oa1 knock-out: new insights on the pathogenesis of ocular albinism type 1

Ocular albinism type I (OA1) is an X-linked disorder characterized by severe reduction of visual acuity, strabismus, photophobia and nystagmus. Ophthalmologic examination reveals hypopigmentation of the retina, foveal hypoplasia and iris translucency. Microscopic examination of both retinal pigment epithelium (RPE) and skin melanocytes shows the presence of large pigment granules called giant melanosomes or macromelanosomes. In this study, we have generated and characterized Oa1-deficient mice by gene targeting (KO). The KO males are viable, fertile and phenotypically indistinguishable from the wild-type littermates. Ophthalmologic examination shows hypopigmentation of the ocular fundus in mutant animals compared with wild-type. Analysis of the retinofugal pathway reveals a reduction in the size of the uncrossed pathway, demonstrating a misrouting of the optic fibres at the chiasm, as observed in OA1 patients. Microscopic examination of the RPE shows the presence of giant melanosomes comparable with those described in OA1 patients. Ultrastructural analysis of the RPE cells, suggests that the giant melanosomes may form by abnormal growth of single melanosomes, rather than the fusion of several, shedding light on the pathogenesis of ocular albinism.

Selective loss of cone function in mice lacking the cyclic nucleotide-gated channel CNG3

Two types of photoreceptors, rods and cones, coexist in the vertebrate retina. An in-depth analysis of the retinal circuitry that transmits rod and cone signals has been hampered by the presence of intimate physical and functional connections between rod and cone pathways. By deleting the cyclic nucleotide-gated channel CNG3 we have generated a mouse lacking any cone-mediated photoresponse. In contrast, the rod pathway is completely intact in CNG3-deficient mice. The functional loss of cone function correlates with a progressive degeneration of cone photoreceptors but not of other retinal cell types. CNG3-deficient mice provide an animal model to dissect unequivocally the contribution of rod and cone pathways for normal retinal function.

Comparative study of visual, auditory, and olfactory function in Usher syndrome

BACKGROUND

Usher syndrome is a genotypically and phenotypically heterogeneous group of autosomal recessive diseases featuring retinitis pigmentosa (RP) and sensorineural hearing loss. A general ciliary dysfunction has been suspected following reports of a mutated cytoskeletal protein (myosin VIIA) in type IB, and preliminary data has suggested an olfactory deficit. The purpose of this study was to quantitatively assess olfactory function in Usher syndrome patients and to search for a correlation between the degree of impairment of the three sensory systems as indication of an underlying ciliary defect.

METHODS

39 patients with Usher syndrome (8 type I, 31 type II) were examined. The ophthalmologic protocol included patient history, visual acuity, eye morphology, Goldmann perimetry, and electroretinography. The ENT protocol included a thorough examination, speech-recognition test, pure-tone audiometry and an olfactory function test.

RESULTS

In both groups, visual acuity was typically 20/40, the remaining visual field area was small, and the ERG responses were low to non-detectable. Average hearing loss was 100% in type I and 40% in type II. Olfactory thresholds were normal [median 9.7 (I) and 8.5 (II) vs. 8.5 in the control group]. There were multiple significant correlations between parameters of the same organ, but no relationship between parameters of different sensory systems.

CONCLUSION

Almost all Usher syndrome patients in this study had an advanced form of RP. In contrast, auditory function differed considerably between type I and type II. An impairment of the olfactory system could not be detected, and there was no correlation between parameters representing visual function, hearing ability, and olfactory sense.

Spatial cone activity distribution in diseases of the posterior pole determined by multifocal electroretinography

Thirty patients with a reduced central vision due to diseases of the posterior pole were examined with the VERIS system developed by Sutter and Tran (Vis Res 1992;32:433-446) to characterize the topography of electroretinographic (ERG) changes in comparison to the results in 30 normal volunteers. Diagnoses included Stargardt's macular dystrophy (SMD, n = 10), age-related macular degeneration (AMD, n = 5), cone dystrophy (CD, n = 5), central retinal vein occlusion (CRVO, n = 5), and autosomal dominant optic atrophy (ADOA, n = 5). The 61 local responses obtained from each subjects were grouped by eccentricity to form five concentric rings. The foveal ERG, originating from a central area of 2 degrees radius, was non-recordable or markedly diminished in all patients except those with optic atrophy, where amplitudes were found to be in the normal range. In patients with advanced stages of SMD, functional defects were larger and involved more peripheral areas than in patients with early stages of SMD or with AMD. A reduction of response amplitude even in the most peripheral ring (17-30.5 degrees eccentricity) was found in cone dystrophies and--moderately--in patients with advanced SMD and central retinal vein occlusion only. Prolonged implicit times were found in all but the patients in early stages of SMD and they were maximal in patients with CRVO. This study shows that the multifocal ERG (MFERG) can contribute to differential diagnosis of retinal diseases of the posterior pole especially in cases with a normal photopic Ganzfeld ERG.

Multifocal electroretinography in retinitis pigmentosa

PURPOSE

To investigate the diagnostic potential of multifocal electroretinography for the evaluation of retinal affection by retinitis pigmentosa in a clinical setting.

METHODS

For this prospective study, multifocal electroretinograms were obtained from 38 patients who matched the inclusion criteria of either a detectable photopic Ganzfeld response or visual fields of 10 degrees or more, and from 30 normal volunteers. Recordings were performed with the visual evoked response imaging system, using a resolution of 61 hexagonal elements within a 30-degree visual field. The results of the left eye of each patient and control subject were used for statistical evaluation by the Mann-Whitney U test.

RESULTS

The 38 eligible patients included those with Usher syndrome types I and II (one patient and six patients, respectively) and those with autosomal-recessive (18), X-recessive (two), and autosomal-dominant (11) forms of retinitis pigmentosa. In 27 (71%) of these 38 patients, at least a central response of the multifocal electroretinogram was detectable. Loss of multifocal electroretinogram response density in patients with retinitis pigmentosa was significant (P < .00001) in all five eccentricity groups (concentric rings), with a progression from center to periphery. Implicit time was significantly elevated in the third eccentricity group (P < .0038) and increased further toward the periphery (P < .00001). The results did not differ notably between retinitis pigmentosa subgroups.

CONCLUSIONS

Because the multifocal electroretinogram differentiates between affected and nonaffected retinal areas, eccentricity-dependent changes in both amplitude and implicit time were found. It can therefore add to the diagnostic information of many patients with retinitis pigmentosa.

[Juvenile neuronal ceroid lipofuscinosis (Batten-Mayou) disease. Ophthalmologic diagnosis and findings]

BACKGROUND

Juvenile neuronal ceroid lipofuscinosis (JNCL) is important to the ophthalmologist, since eye symptoms are usually the first evidence of the disease and permit establishment of an early diagnosis. The disorder usually begins with a dramatic loss of vision between age 4 and 10 due to bulls-eye maculopathy followed by rapid degeneration of the retina and pigment epithelium. Blindness results within 1 to 3 years after onset of symptoms. The further course of the disease is mainly determined by degradation of the CNS with motor and intellectual deficits. Most patients die before the age of 30.

METHODS

A case of two sisters is presented to demonstrate eye findings and diagnostic procedures, emphasizing electrophysiologic and morphologic tests (peripheral blood smear, histology).

RESULTS

Both sisters reported the first decrease in vision at the ages of 8 and 6 respectively; visual acuity at time of visit was light projection (20/400). Both had tapetoretinal degeneration with optic disc atrophy, narrowed vessels, pigment epitheliopathy and bullseye maculopathy. The ERG was almost extinguished in the older sister and greatly reduced in the younger one (scotopic more than photopic). Histologically, vacuolated lymphocytes were found in the peripheral blood smear, as were intracellular inclusions of the fingerprint and curvilinear type in the conjunctival biopsy.

CONCLUSION

During the course of JNCL, it is very common for the vision to be affected at the age of 6-7. The correct diagnosis, however, is often made years later when massive neurologic symptoms such as seizures appear. When there is sudden loss of vision in a child of this age combined with a tapetoretinal degeneration, a biopsy or at least a peripheral blood smear should be performed.