Gene therapy restores vision in rd1 mice after removal of a confounding mutation in Gpr179

Chronic sleep deprivation impairs retinal circadian transcriptome and visual function

Sleep loss is common in modern society and is increasingly associated with eye diseases. However, the precise effects of sleep loss on retinal structure and function, particularly on the retinal circadian system, remain largely unexplored. This study investigates these effects using a chronic sleep deprivation (CSD) model in mice. Our investigation reveals that CSD significantly alters the retinal circadian transcriptome, leading to remarkable changes in the temporal patterns of enriched pathways. This perturbation extends to metabolic and immune-related transcriptomes, coupled with an accumulation of reactive oxygen species in the retina. Notably, CSD rhythmically affects the thickness of the ganglion cell complex, along with diurnal shifts in microglial migration and morphology within the retina. Most critically, we observe a marked decrease in both scotopic and photopic retinal function under CSD conditions. These findings underscore the broad impact of sleep deprivation on retinal health, highlighting its role in altering circadian gene expression, metabolism, immune response, and structural integrity. Our study provides new insights into the broader impact of sleep loss on retinal health.

Mice with deficiency in Pcdh15, a gene associated with bipolar disorders, exhibit significantly elevated diurnal amplitudes of locomotion and body temperature

Genetic factors significantly affect the pathogenesis of psychiatric disorders. However, the specific pathogenic mechanisms underlying these effects are not fully understood. Recent extensive genomic studies have implicated the protocadherin-related 15 (PCDH15) gene in the onset of psychiatric disorders, such as bipolar disorder (BD). To further investigate the pathogenesis of these psychiatric disorders, we developed a mouse model lacking Pcdh15. Notably, although PCDH15 is primarily identified as the causative gene of Usher syndrome, which presents with visual and auditory impairments, our mice with Pcdh15 homozygous deletion (Pcdh15-null) did not exhibit observable structural abnormalities in either the retina or the inner ear. The Pcdh15-null mice showed very high levels of spontaneous motor activity which was too disturbed to perform standard behavioral testing. However, the Pcdh15 heterozygous deletion mice (Pcdh15-het) exhibited enhanced spontaneous locomotor activity, reduced prepulse inhibition, and diminished cliff avoidance behavior. These observations agreed with the symptoms observed in patients with various psychiatric disorders and several mouse models of psychiatric diseases. Specifically, the hyperactivity may mirror the manic episodes in BD. To obtain a more physiological, long-term quantification of the hyperactive phenotype, we implanted nano tag® sensor chips in the animals, to enable the continuous monitoring of both activity and body temperature. During the light-off period, Pcdh15-null exhibited elevated activity and body temperature compared with wild-type (WT) mice. However, we observed a decreased body temperature during the light-on period. Comprehensive brain activity was visualized using c-Fos mapping, which was assessed during the activity and temperature peak and trough. There was a stark contrast between the distribution of c-Fos expression in Pcdh15-null and WT brains during both the light-on and light-off periods. These results provide valuable insights into the neural basis of the behavioral and thermal characteristics of Pcdh15-deletion mice. Therefore, Pcdh15-deletion mice can be a novel model for BD with mania and other psychiatric disorders, with a strong genetic component that satisfies both construct and surface validity.

Effect of molecular hydrogen, a novelly-established antioxidant, on the retinal degeneration of hereditary retinitis pigmentosa: an in-vivo study

Objective Our research was performed in order to explore the effects of molecular hydrogen (H2), a novelly-established antioxidant, on the retinal degeneration in rd1 mice, an animal model of inherited retinitis pigmentosa (RP). Methods The rd1 mice were divided randomly into control and H2 intervention groups. Mice from other groups received H2 intervention in three modes, two modes of the hydrogen gas (HG) and one model of hydrogen-rich saline (HRS). At 14 days post born (P14) and P21, various indicators were detected in all mice, including eletroretinogram (ERG), fundus phography, optical coherence tomography (OCT), and retinal immunotaining of microglia cells' marker, Iba1. Results The ERG amplitude in mice from the control and H2 intervention groups showed no statistical differences (p > 0.05). At P14 and P21, no significant difference in the distance from the retinal pigment epithelium to the outer plexiform layer on OCT from mice of the above two groups was found (p > 0.05). The thickness of the outer nuclear layer (ONL) in mice at P14 and P21 showed no statistical differences between the control group and the H2 intervention group (p > 0.05). In the aspect of the number of Iba1-positive cells, we did not found any significant differences between the two groups (p > 0.05). Conclusion Different forms of H2 intervention (hydrogen-rich saline and hydrogen gas) had no obvious effects on the course of retinal degeneration in rd1 mice. The specific mechanism of photoreceptor degeneration in the hereditary RP mouse model may be different, requiring different medical interventions.

Fine-tuning FAM161A gene augmentation therapy to restore retinal function

For 15 years, gene therapy has been viewed as a beacon of hope for inherited retinal diseases. Many preclinical investigations have centered around vectors with maximal gene expression capabilities, yet despite efficient gene transfer, minimal physiological improvements have been observed in various ciliopathies. Retinitis pigmentosa-type 28 (RP28) is the consequence of bi-allelic null mutations in the FAM161A, an essential protein for the structure of the photoreceptor connecting cilium (CC). In its absence, cilia become disorganized, leading to outer segment collapses and vision impairment. Within the human retina, FAM161A has two isoforms: the long one with exon 4, and the short one without it. To restore CC in Fam161a-deficient mice shortly after the onset of cilium disorganization, we compared AAV vectors with varying promoter activities, doses, and human isoforms. While all vectors improved cell survival, only the combination of both isoforms using the weak FCBR1-F0.4 promoter enabled precise FAM161A expression in the CC and enhanced retinal function. Our investigation into FAM161A gene replacement for RP28 emphasizes the importance of precise therapeutic gene regulation, appropriate vector dosing, and delivery of both isoforms. This precision is pivotal for secure gene therapy involving structural proteins like FAM161A.

A clinically viable approach to restoring visual function using optogenetic gene therapy

Optogenetic gene therapies offer a promising strategy for restoring vision to patients with retinal degenerative diseases, such as retinitis pigmentosa (RP). Several clinical trials have begun in this area using different vectors and optogenetic proteins (Clinical Identifiers: NCT02556736, NCT03326336, NCT04945772, and NCT04278131). Here we present preclinical efficacy and safety data for the NCT04278131 trial, which uses an AAV2 vector and Chronos as the optogenetic protein. Efficacy was assessed in mice in a dose-dependent manner using electroretinograms (ERGs). Safety was assessed in rats, nonhuman primates, and mice, using several tests, including immunohistochemical analyses and cell counts (rats), electroretinograms (nonhuman primates), and ocular toxicology assays (mice). The results showed that Chronos-expressing vectors were efficacious over a broad range of vector doses and stimulating light intensities, and were well tolerated: no test article-related findings were observed in the anatomical and electrophysiological assays performed.

Nonselective Expression of Short-Wavelength Cone Opsin Improves Learning in Mice with Retinal Degeneration in a Visually Guided Task

The study explored the potential of an animal opsin nonselectively expressed in various neuronal elements of the degenerative retina to restore the impaired visual function. A knockout murine model of inherited retinal dystrophy was used. Mice were injected intravitreally with either a virus carrying the gene of short-wavelength cone opsin associated with a reporter fluorescent protein or a control virus carrying the sequence of a modified fluorescent protein with enhanced membrane tropism. Viral transduction induced pronounced opsin expression in ganglion, bipolar, and horizontal retinal neurons. Behavioral testing included the visually guided task in the trapezoid Morris water maze and showed a partial recovery of the learning ability in the mice whose retinas had been transduced with cone opsin.

Optogenetic Prosthetization of Retinal Bipolar Cells

Abstract

Although the experience of optogenetic retinal prosthetics in animal models dates back to more than 16 years, the first results obtained on humans have only been reported in the last year. Over this period, the main challenges of prosthetics became clear and the approaches to their solution were proposed. In this review, we aim to present the achievements in the field of optogenetic prosthetization of retinal bipolar cells with a focus mainly on relatively recent publications. The review addresses the advantages and disadvantages of bipolar cell prosthetics as compared to the alternative target, retinal ganglion cells, and provides a comparative analysis of the effectiveness of ionotropic light-sensitive proteins (channelrhodopsins) or metabotropic receptors (rhodopsins) as prosthetic tools.

Characterization of a novel Pde6b-deficient rat model of retinal degeneration and treatment with adeno-associated virus (AAV) gene therapy

In humans, mutations in the beta subunit of cGMP-phosphodiesterase type 6 (PDE6B) cause autosomal recessive retinitis pigmentosa (RP), which typically has an aggressive clinical course of early-onset severe vision loss due to rapid photoreceptor degeneration. In this study, we describe the generation of a novel Pde6b-deficient rat model using CRISPR-Cas9 genome editing. We characterize the model at multiple time points using clinical imaging modalities as well as histology with immunohistochemistry to show rapid photoreceptor degeneration compared to wild-type and heterozygous animals. We describe the manufacture of two different adeno-associated viral (AAV) vectors (AAV2/1, AAV2/5) under current Good Manufacturing Practices (cGMP) and demonstrate their ability to drive human PDE6B expression in vivo. We further demonstrate the ability of AAV-mediated subretinal gene therapy to delay photoreceptor loss in Pde6b-deficient rats compared to untreated controls. However, severe progressive photoreceptor loss was noted even in treated eyes, likely due to the aggressive nature of the disease. These data provide useful preclinical data to guide the development of potential human gene therapy for PDE6B-associated RP. In addition, the rapid photoreceptor degeneration of the Pde6b-deficient rat with intact inner retina may provide a useful model for the study of cell replacement strategies.

Gene Therapy for Inherited Retinal Disease: Long-Term Durability of Effect

The recent approval of voretigene neparvovec (Luxturna®) for patients with biallelic RPE65 mutation-associated inherited retinal dystrophy with viable retinal cells represents an important step in the development of ocular gene therapies. Herein, we review studies investigating the episomal persistence of different recombinant adeno-associated virus (rAAV) vector genomes and the preclinical and clinical evidence of long-term effects of different RPE65 gene replacement therapies. A targeted review of articles published between 1974 and January 2021 in Medline®, Embase®, and other databases was conducted, followed by a descriptive longitudinal analysis of the clinical trial outcomes of voretigene neparvovec. Following an initial screening, 14 publications examining the episomal persistence of different rAAV genomes and 71 publications evaluating gene therapies in animal models were included. Viral genomes were found to persist for at least 22 months (longest study follow-up) as transcriptionally active episomes. Treatment effects lasting almost a decade were reported in canine disease models, with more pronounced effects the earlier the intervention. The clinical trial outcomes of voretigene neparvovec are consistent with preclinical findings and reveal sustained results for up to 7.5 years for the full-field light sensitivity threshold test and 5 years for the multi-luminance mobility test in the Phase I and Phase III trials, respectively. In conclusion, the therapeutic effect of voretigene neparvovec lasts for at least a decade in animal models and 7.5 years in human subjects. Since retinal cells can retain functionality over their lifetime after transduction, these effects may be expected to last even longer in patients with a sufficient number of outer retinal cells at the time of intervention.

mTORC1 regulates high levels of protein synthesis in retinal ganglion cells of adult mice

Mechanistic target of rapamycin (mTOR) and mTOR complex 1 (mTORC1), linchpins of the nutrient sensing and protein synthesis pathways, are present at relatively high levels in the ganglion cell layer (GCL) and retinal ganglion cells (RGCs) of rodent and human retinas. However, the role of mTORCs in the control of protein synthesis in RGC is unknown. Here, we applied the SUrface SEnsing of Translation (SUnSET) method of nascent protein labeling to localize and quantify protein synthesis in the retinas of adult mice. We also used intravitreal injection of an adeno-associated virus 2 vector encoding Cre recombinase in the eyes of mtor- or rptor-floxed mice to conditionally knockout either both mTORCs or only mTORC1, respectively, in cells within the GCL. A novel vector encoding an inactive Cre mutant (CreΔC) served as control. We found that retinal protein synthesis was highest in the GCL, particularly in RGC. Negation of both complexes or only mTORC1 significantly reduced protein synthesis in RGC. In addition, loss of mTORC1 function caused a significant reduction in the pan-RGC marker, RNA-binding protein with multiple splicing, with little decrease of the total number of cells in the RGC layer, even at 25 weeks after adeno-associated virus-Cre injection. These findings reveal that mTORC1 signaling is necessary for maintaining the high rate of protein synthesis in RGCs of adult rodents, but it may not be essential to maintain RGC viability. These findings may also be relevant to understanding the pathophysiology of RGC disorders, including glaucoma, diabetic retinopathy, and optic neuropathies.

A comprehensive atlas of Aggrecan, Versican, Neurocan and Phosphacan expression across time in wildtype retina and in retinal degeneration

As photoreceptor cells die during retinal degeneration, the surrounding microenvironment undergoes significant changes that are increasingly recognized to play a prominent role in determining the efficacy of therapeutic interventions. Chondroitin Sulphate Proteoglycans (CSPGs) are a major component of the extracellular matrix that have been shown to inhibit neuronal regrowth and regeneration in the brain and spinal cord, but comparatively little is known about their expression in retinal degeneration. Here we provide a comprehensive atlas of the expression patterns of four individual CSPGs in three models of inherited retinal degeneration and wildtype mice. In wildtype mice, Aggrecan presented a biphasic expression, while Neurocan and Phosphacan expression declined dramatically with time and Versican expression remained broadly constant. In degeneration, Aggrecan expression increased markedly in Aipl1-/- and Pde6brd1/rd1, while Versican showed regional increases in the periphery of Rho-/- mice. Conversely, Neurocan and Phosphacan broadly decrease with time in all models. Our data reveal significant heterogeneity in the expression of individual CSPGs. Moreover, there are striking differences in the expression patterns of specific CSPGs in the diseased retina, compared with those reported following injury elsewhere in the CNS. Better understanding of the distinct distributions of individual CSPGs will contribute to creating more permissive microenvironments for neuro-regeneration and repair.

Retinitis Pigmentosa: Progress in Molecular Pathology and Biotherapeutical Strategies

Retinitis pigmentosa (RP) is genetically heterogeneous retinopathy caused by photoreceptor cell death and retinal pigment epithelial atrophy that eventually results in blindness in bilateral eyes. Various photoreceptor cell death types and pathological phenotypic changes that have been disclosed in RP demand in-depth research of its pathogenic mechanism that may account for inter-patient heterogeneous responses to mainstream drug treatment. As the primary method for studying the genetic characteristics of RP, molecular biology has been widely used in disease diagnosis and clinical trials. Current technology iterations, such as gene therapy, stem cell therapy, and optogenetics, are advancing towards precise diagnosis and clinical applications. Specifically, technologies, such as effective delivery vectors, CRISPR/Cas9 technology, and iPSC-based cell transplantation, hasten the pace of personalized precision medicine in RP. The combination of conventional therapy and state-of-the-art medication is promising in revolutionizing RP treatment strategies. This article provides an overview of the latest research on the pathogenesis, diagnosis, and treatment of retinitis pigmentosa, aiming for a convenient reference of what has been achieved so far.

NUTRARET: Effect of 2-Year Nutraceutical Supplementation on Redox Status and Visual Function of Patients With Retinitis Pigmentosa: A Randomized, Double-Blind, Placebo-Controlled Trial

Oxidative stress plays a major role in the pathogenesis of retinitis pigmentosa (RP). The main goal of this study was to evaluate the effect of 2-year nutritional intervention with antioxidant nutraceuticals on the visual function of RP patients. Secondly, we assessed how nutritional intervention affected ocular and systemic redox status. We carried out a randomized, double-blind, placebo-controlled study. Thirty-one patients with RP participated in the study. RP patients randomly received either a mixture of nutraceuticals (NUT) containing folic acid, vitamin B6, vitamin A, zinc, copper, selenium, lutein, and zeaxanthin or placebo daily for 2 years. At baseline and after 2-year of the nutritional supplementation, visual function, dietetic-nutritional evaluations, serum concentration of nutraceuticals, plasma and aqueous humor concentration of several markers of redox status and inflammation were assessed. Retinal function and structure were assessed by multifocal electroretinogram (mfERG), spectral domain-optical coherence tomography (SD-OCT) and automated visual field (VF) tests. Nutritional status was estimated with validated questionnaires. Total antioxidant capacity, extracellular superoxide dismutase (SOD3), catalase (CAT), and glutathione peroxidase (GPx) activities, protein carbonyl adducts (CAR) content, thiobarbituric acid reactive substances (TBARS) formation (as indicator of lipid peroxidation), metabolites of the nitric oxide (NOX) and cytokine (interleukin 6 and tumor necrosis factor alpha) concentrations were assessed by biochemical and immunological techniques in aqueous humor or/and blood. Bayesian approach was performed to determine the probability of an effect. Region of practical equivalence (ROPE) was used. At baseline, Bayesian analysis revealed a high probability of an altered ocular redox status and to a lesser extent systemic redox status in RP patients compared to controls. Twenty-five patients (10 in the treated arm and 15 in the placebo arm) completed the nutritional intervention. After 2 years of supplementation, patients who received NUT presented better retinal responses (mfERG responses) compared to patients who received placebo. Besides, patients who received NUT showed better ocular antioxidant response (SOD3 activity) and lower oxidative damage (CAR) than those who received placebo. This study suggested that long-term NUT supplementation could slow down visual impairment and ameliorate ocular oxidative stress.

Sleep Deprivation Does not Change the Flash Electroretinogram in Wild-type and Opn4-/-Gnat1-/- Mice

Sleep deprivation reduces the response of neuronal activity in the suprachiasmatic nucleus (SCN) and the phase shift in circadian behaviour to phase shifting light pulses, and thus seems to impair the adaptation of the circadian clock to the external light-dark cycle. The question remains where in the pathway of light input to the SCN the response is reduced. We therefore investigated whether the electroretinogram (ERG) changes after sleep deprivation in wild-type mice and in Opn4^−/−Gnat1^−/− mutant male mice. We found that the ERG is clearly affected by the Opn4^−/−Gnat1^−/− mutations, but that the ERG after sleep deprivation does not differ from the baseline response. The difference between wild-type and mutant is in accordance with the lack of functional rod and melanopsin in the retina of the mutant mice. We conclude that the decrease in light responsiveness of the SCN after sleep deprivation is probably not caused by changes at the retinal level, but rather at the postsynaptic site within the SCN, reflecting affected neurotransmitter signalling.

Gene Therapy for Rdh12-Associated Retinal Diseases Helps to Delay Retinal Degeneration and Vision Loss

Purpose

The aim of study was to establish Rdh12-associated inherited retinal disease (Rdh12-IRD) mouse model and to identify the best timepoint for gene therapy.

Methods

We induced retinal degeneration in Rdh12^-/- mice using a bright light. We clarified the establishment of Rdh12-IRD mouse model by analyzing the thickness of retinal layers and electroretinography (ERG). Rdh12-IRD mice received a subretinal injection of adeno-associated virus 2/8-packaged Rdh12 cDNA for treatment. We evaluated the visual function and retinal structure in the treated and untreated eyes to identify the best timepoint for gene therapy.

Results

Rdh12-IRD mice showed significant differences in ERG amplitudes and photoreceptor survival compared to Rdh12^+/+ mice. Preventive gene therapy not only maintained normal visual function but also prevented photoreceptor loss. Salvage gene therapy could not reverse the retinal degeneration phenotype of Rdh12-IRD mice, but it could slow down the loss of visual function.

Conclusion

The light-induced retinal degeneration in our Rdh12^-/- mice indicated that a defect in Rdh12 alone was sufficient to cause visual dysfunction and photoreceptor degeneration, which reproduced the phenotypes observed in RDH12-IRD patients. This model is suitable for gene therapy studies. Early treatment of the primary Rdh12 defect helps to delay the later onset of photoreceptor degeneration and maintains visual function in Rdh12-IRD mice.

Retinal neovascularization induced by mutant Vldlr gene inhibited in an inherited retinitis pigmentosa mouse model: an in-vivo study

AIM

To explore whether the retinal neovascularization (NV) in a genetic mutant mice model could be ameliorated in an inherited retinitis pigmentosa (RP) mouse, which would help to elucidate the possible mechanism and prevention of retinal NV diseases in clinic.

METHODS

The Vldlr ^-/- mice, the genetic mutant mouse model of retinal NV caused by the homozygous mutation of Vldlr gene, with the rd1 mice, the inherited RP mouse caused by homozygous mutation of Pde6b gene were bred. Intercrossing of the above two mice led to the birth of the F1 hybrids, further inbreeding of which gave birth to the F2 offspring. The ocular genotypes and phenotypes of the mice from all generations were examined, with the F2 offspring grouped according to the genotypes.

RESULTS

The rd1 mice exhibited the RP phenotype of outer retinal degeneration and loss of retinal function. The Vldlr ^-/- mice exhibited the phenotype of retinal NV obviously shown by the fundus fluorescein angiography. The F1 hydrides, with the heterozygote genotype, exhibited no phenotypes of RP or retinal NV. The F2 offspring with homozygous genotypes were grouped into four subgroups. They were the F2-I mice with the wild-type Pde6b and Vldlr genes (Pde6b^+/+ -Vldlr^+/+ ), which had normal ocular phenotypes; the F2-II mice with homozygous mutant Vldlr gene (Pde6b^+/+ -Vldlr^-/- ), which exhibited the retinal NV phenotype; the F2-III mice with homozygous mutant Pde6b gene (Pde6b^-/- -Vldlr^+/+ ), which exhibited the RP phenotype. Specifically, the F2-IV mice with homozygous mutant Vldlr and Pde6b gene (Pde6b^-/- -Vldlr^-/- ) showed only the RP phenotype, without the signs of retinal NV.

CONCLUSION

The retinal NV can be inhibited by the RP phenotype, which implies the role of a hyperoxic state in treating retinal NV diseases.

Animals Models of Inherited Retinal Disease

Inherited retinal diseases (IRDs) are an important cause of blindness worldwide. Over 270 genes have been associated with IRD. Genetic testing can determine the cause of the clinical disease in the majority of patients. However, at least 25-50% of patients with clinical diagnosis of IRD remain unsolved even after whole genome sequencing. Animal models of IRD can be useful for expanding the set of established IRD genes, to gain biological understanding of the function of these genes in the retina, and to test advanced therapeutics prior to human clinical trials. In this chapter some small and large animal models of IRD are discussed including some of the advantages and limitations of each for various forms of retinopathy.

Nutraceutical Supplementation Ameliorates Visual Function, Retinal Degeneration, and Redox Status in rd10 Mice

Retinitis pigmentosa (RP) is a group of inherited retinal dystrophies characterized by progressive degeneration of photoreceptor cells. Ocular redox status is altered in RP suggesting oxidative stress could contribute to their progression. In this study, we investigated the effect of a mixture of nutraceuticals with antioxidant properties (NUT) on retinal degeneration in rd10 mice, a model of RP. NUT was orally administered to rd10 mice from postnatal day (PD) 9 to PD18. At PD18 retinal function and morphology were examined by electroretinography (ERG) and histology including TUNEL assay, immunolabeling of microglia, Müller cells, and poly ADP ribose polymers. Retinal redox status was determined by measuring the activity of antioxidant enzymes and some oxidative stress markers. Gene expression of the cytokines IL-6, TNFα, and IL-1β was assessed by real-time PCR. NUT treatment delayed the loss of photoreceptors in rd10 mice partially preserving their electrical responses to light stimuli. Moreover, it ameliorated redox status and reduced inflammation including microglia activation, upregulation of cytokines, reactive gliosis, and PARP overactivation. NUT ameliorated retinal functionality and morphology at early stages of RP in rd10 mice. This formulation could be useful as a neuroprotective approach for patients with RP in the future.

Restoration of visual function in advanced disease after transplantation of purified human pluripotent stem cell-derived cone photoreceptors

Age-related macular degeneration and other macular diseases result in the loss of light-sensing cone photoreceptors, causing irreversible sight impairment. Photoreceptor replacement may restore vision by transplanting healthy cells, which must form new synaptic connections with the recipient retina. Despite recent advances, convincing evidence of functional connectivity arising from transplanted human cone photoreceptors in advanced retinal degeneration is lacking. Here, we show restoration of visual function after transplantation of purified human pluripotent stem cell-derived cones into a mouse model of advanced degeneration. Transplanted human cones elaborate nascent outer segments and make putative synapses with recipient murine bipolar cells (BCs), which themselves undergo significant remodeling. Electrophysiological and behavioral assessments demonstrate restoration of surprisingly complex light-evoked retinal ganglion cell responses and improved light-evoked behaviors in treated animals. Stringent controls exclude alternative explanations, including material transfer and neuroprotection. These data provide crucial validation for photoreceptor replacement therapy and for the potential to rescue cone-mediated vision.

Defining Phenotype, Tropism, and Retinal Gene Therapy Using Adeno-Associated Viral Vectors (AAVs) in New-Born Brown Norway Rats with a Spontaneous Mutation in Crb1

Mutations in the Crumbs homologue 1 (CRB1) gene cause inherited retinal dystrophies, such as early-onset retinitis pigmentosa and Leber congenital amaurosis. A Brown Norway rat strain was reported with a spontaneous insertion-deletion (indel) mutation in exon 6 of Crb1. It has been reported that these Crb1 mutant rats show vascular abnormalities associated with retinal telangiectasia and possess an early-onset retinal degenerative phenotype with outer limiting membrane breaks and focal loss of retinal lamination at 2 months of age. Here, we further characterized the morphological phenotype of new-born and adult Crb1 mutant rats in comparison with age-matched Brown Norway rats without a mutation in Crb1. A significantly decreased retinal function and visual acuity was observed in Crb1 mutant rats at 1 and 3 months of age, respectively. Moreover, in control rats, the subcellular localization of canonical CRB1 was observed at the subapical region in Müller glial cells while CRB2 was observed at the subapical region in both photoreceptors and Müller glial cells by immuno-electron microscopy. CRB1 localization was lost in the Crb1 mutant rats, whereas CRB2 was still observed. In addition, we determined the tropism of subretinal or intravitreally administered AAV5-, AAV9- or AAV6-variant ShH10^Y445F vectors in new-born control and Crb1 mutant rat retinas. We showed that subretinal injection of AAV5 and AAV9 at postnatal days 5 (P5) or 8 (P8) predominantly infected the retinal pigment epithelium (RPE) and photoreceptor cells; while intravitreal injection of ShH10^Y445F at P5 or P8 resulted in efficient infection of mainly Müller glial cells. Using knowledge of the subcellular localization of CRB1 and the ability of ShH10^Y445F to infect Müller glial cells, canonical hCRB1 and hCRB2 AAV-mediated gene therapy were explored in new-born Crb1 mutant rats. Enhanced retinal function after gene therapy delivery in the Crb1 rat was not observed. No timely rescue of the retinal phenotype was observed using retinal function and visual acuity, suggesting the need for earlier onset of expression of recombinant hCRB proteins in Müller glial cells to rescue the severe retinal phenotype in Crb1 mutant rats.

Changes in Gene Expression Profiling and Phenotype in Aged Multidrug Resistance Protein 4-Deficient Mouse Retinas

Multidrug resistance protein 4 (MRP4) is an energy-dependent membrane transporter responsible for cellular efflux of a broad range of xenobiotics and physiological substrates. In this trial, we aimed to investigate the coeffects of aging and MRP4 deficiency using gene expression microarray and morphological and electrophysiological analyses of mouse retinas. Mrp4-knockout (null) mice and wild-type (WT) mice were reared in the same conditions to 8–12 weeks (young) or 45–55 weeks (aged). Microarray analysis identified 186 differently expressed genes from the retinas of aged Mrp4-null mice as compared to aged WT mice, and subsequent gene ontology and KEGG pathway analyses showed that differently expressed genes were related to lens, eye development, vision and transcellular barrier functions that are involved in metabolic pathways or viral infection pathways. No significant change in thickness was observed for each retinal layer among young/aged WT mice and young/aged Mrp4-null mice. Moreover, immunohistochemical analyses of retinal cell type did not exhibit an overt change in the cellular morphology or distribution among the four age/genotype groups, and the electroretinogram responses showed no significant differences in the amplitude or the latency between aged WT mice and aged Mrp4-null mice. Aging would be an insufficient stress to cause some damage to the retina in the presence of MRP4 deficiency.

Migration of pre-induced human peripheral blood mononuclear cells from the transplanted to contralateral eye in mice

Background

Retina diseases may lead to blindness as they often afflict both eyes. Stem cell transplantation into the affected eye(s) is a promising therapeutic strategy for certain retinal diseases. Human peripheral blood mononuclear cells (hPBMCs) are a good source of stem cells, but it is unclear whether pre-induced hPBMCs can migrate from the injected eye to the contralateral eye for bilateral treatment. We examine the possibility of bilateral cell transplantation from unilateral cell injection.

Methods

One hundred and sixty-one 3-month-old retinal degeneration 1 (rd1) mice were divided randomly into 3 groups: an untreated group (n = 45), a control group receiving serum-free Dulbecco’s modified Eagle’s medium (DMEM) injection into the right subretina (n = 45), and a treatment group receiving injection of pre-induced hPBMCs into the right subretina (n = 71). Both eyes were examined by full-field electroretinogram (ERG), immunofluorescence, flow cytometry, and quantitative real-time polymerase chain reaction (qRT-PCR) at 1 and 3 months post-injection.

Results

At both 1 and 3 months post-injection, labeled pre-induced hPBMCs were observed in the retinal inner nuclear layer of the contralateral (left untreated) eye as well as the treated eye as evidenced by immunofluorescence staining for a human antigen. Flow cytometry of fluorescently label cells and qRT-PCR of hPBMCs genes confirmed that transplanted hPBMCs migrated from the treated to the contralateral untreated eye and remained viable for up to 3 months. Further, full-field ERG showed clear light-evoked a and b waves in both treated and untreated eyes at 3 months post-transplantation. Labeled pre-induced hPBMCs were also observed in the contralateral optic nerve but not in the blood circulation, suggesting migration via the optic chiasm.

Conclusion

It may be possible to treat binocular eye diseases by unilateral stem cell injection.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02180-5.

Suppression of cGMP-Dependent Photoreceptor Cytotoxicity With Mycophenolate Is Neuroprotective in Murine Models of Retinitis Pigmentosa

Purpose

To determine the effect of mycophenolate mofetil (MMF) on retinal degeneration on two mouse models of retinitis pigmentosa.

Methods

Intraperitoneal injections of MMF were administered daily in rd10 and c57 mice starting at postoperative day 12 (P12) and rd1 mice starting at P8. The effect of MMF was assessed with optical coherence tomography, immunohistochemistry, electroretinography, and OptoMotry. Whole retinal cyclic guanosine monophosphate (cGMP) and mycophenolic acid levels were quantified with mass spectrometry. Photoreceptor cGMP cytotoxicity was evaluated with cell counts of cGMP immunostaining.

Results

MMF treatment significantly delays the onset of retinal degeneration and cGMP-dependent photoreceptor cytotoxicity in rd10 and rd1 mice, albeit a more modest effect in the latter. In rd10 mice, treatment with MMF showed robust preservation of the photoreceptors up to P22 with associated suppression of cGMP immunostaining and microglial activation; The neuroprotective effect diminished after P22, but outer retinal thickness was still significantly thicker by P35 and OptoMotry response was significantly better up to P60. Whereas cGMP immunostaining of the photoreceptors were present in rd10 and rd1 mice, hyperphysiological whole retinal cGMP levels were observed only in rd1 mice.

Conclusions

Early treatment with MMF confers potent neuroprotection in two animal models of RP by suppressing the cGMP-dependent common pathway for photoreceptor cell death. The neuroprotective effect of MMF on cGMP-dependent cytotoxicity occurs independently of the presence of hyperphysiological whole retinal cGMP levels. Thus our data suggest that MMF may be an important new class of neuroprotective agent that could be useful in the treatment of patients with RP.

ERG Responses in Mice with Deletion of the Synaptic Ribbon Component RIBEYE

Purpose

To determine the influence of RIBEYE deletion and the resulting absence of synaptic ribbons on retinal light signaling by electroretinography.

Methods

Full-field flash electroretinograms (ERGs) were recorded in RIBEYE knock-out (KO) and wild-type (WT) littermate mice under photopic and scotopic conditions, with oscillatory potentials (OPs) extracted by digital filtering. Flicker ERGs and ERGs following intravitreal injection of pharmacological agents were also obtained under scotopic conditions.

Results

The a-wave amplitudes were unchanged between RIBEYE KO and WT mice; however, the b-wave amplitudes were reduced in KOs under scotopic, but not photopic, conditions. Increasing stimulation frequency led to a greater reduction in RIBEYE KO b-wave amplitudes compared with WTs. Furthermore, we observed prominent, supernormal OPs in RIBEYE KO mice in comparison with WT mice. Following intravitreal injections with l-2 amino-4-phosphonobutyric acid and cis-2,3 piperidine dicarboxylic acid to block ON and OFF responses at photoreceptor synapses, OPs were completely abolished in both mice types, indicating a synaptic origin of the prominent OPs in the KOs. Conversely, tetrodotoxin treatment to block voltage-gated Na⁺ channels/spiking neurons did not differentially affect OPs in WT and KO mice.

Conclusions

The decreased scotopic b-wave and decreased responses to increased stimulation frequencies are consistent with signaling malfunctions at photoreceptor and inner retinal ribbon synapses. Because phototransduction in the photoreceptor outer segments is unaffected in the KOs, their supernormal OPs presumably result from a dysfunction in retinal synapses. The relatively mild ERG phenotype in KO mice, particularly in the photopic range, is probably caused by compensatory mechanisms in retinal signaling pathways.

Oxidative Stress and Microglial Response in Retinitis Pigmentosa

An imbalance between the production of reactive oxygen species (ROS) and anti-oxidant capacity results in oxidative injury to cellular components and molecules, which in turn disturbs the homeostasis of cells and organs. Although retinitis pigmentosa (RP) is a hereditary disease, non-genetic biological factors including oxidative stress also modulate or contribute to the disease progression. In animal models of RP, the degenerating retina exhibits marked oxidative damage in the nucleic acids, proteins, and lipids, and anti-oxidant treatments substantially suppress photoreceptor cell death and microgliosis. Although the mechanisms by which oxidative stress mediates retinal degeneration have not been fully elucidated, our group has shown that oxidative DNA damage and its defense system are key regulators of microglial activation and photoreceptor degeneration in RP. In this review, we summarize the current evidence regarding oxidative stress in animal models and patients with RP. The clinical efficacy of anti-oxidant treatments for RP has not been fully established. Nevertheless, elucidating key biological processes that underlie oxidative damage in RP will be pivotal to understanding the pathology and developing a potent anti-oxidant strategy that targets specific cell types or molecules under oxidative stress.

AAV-Delivered Tulp1 Supplementation Therapy Targeting Photoreceptors Provides Minimal Benefit in Tulp1-/- Retinas

With marketing approval of the first ocular gene therapy, and other gene therapies in clinical trial, treatments for inherited retinal degenerations (IRDs) have become a reality. Biallelic mutations in the tubby like protein 1 gene (TULP1) are causative of IRDs in humans; a mouse knock-out model (Tulp1−/−) is characterized by a similar disease phenotype. We developed a Tulp1 supplementation therapy for Tulp1−/− mice. Utilizing subretinal AAV2/5 delivery at postnatal day (p)2–3 and rhodopsin-kinase promoter (GRK1P) we targeted Tulp1 to photoreceptor cells exploring three doses, 2.2E9, 3.7E8, and 1.2E8 vgs. Tulp1 mRNA and TULP1 protein were assessed by RT-qPCR, western blot and immunocytochemistry, and visual function by electroretinography. Our results indicate that TULP1 was expressed in photoreceptors; achieved levels of Tulp1 mRNA and protein were similar to wild type levels at p20. However, the thickness of the outer nuclear layer (ONL) did not improve in treated Tulp1−/− mice. There was a small and transient electroretinography benefit in the treated retinas at 4 weeks of age (not observed by 6 weeks) when using 3.7E8 vg dose. Dark-adapted mixed rod and cone a- and b-wave amplitudes were 24.3 ± 13.5 μV and 52.2 ± 31.7 μV in treated Tulp1−/− mice, which were significantly different (p < 0.001, t-test), from those detected in untreated eyes (7.1 ± 7.0 μV and 9.4 ± 15.1 μV, respectively). Our results indicate that Tulp1 supplementation in photoreceptors may not be sufficient to provide robust benefit in Tulp1−/− mice. As such, further studies are required to fine tune the Tulp1 supplementation therapy, which, in principle, should rescue the Tulp1−/− phenotype.

Development of Stem Cell Therapies for Retinal Degeneration

Degenerative retinal disease is the major cause of sight loss in the developed world and currently there is a lack of effective treatments. As the loss of vision is directly the result of the loss of retinal cells, effective cell replacement through stem-cell-based therapies may have the potential to treat a great number of retinal diseases whatever their underlying etiology. The eye is an ideal organ to develop cell therapies as it is immune privileged, and modern surgical techniques enable precise delivery of cells to the retina. Furthermore, a range of noninvasive diagnostic tests and high-resolution imaging techniques facilitate the evaluation of any therapeutic intervention. In this review, we evaluate the progress to date of current cell therapy strategies for retinal repair, focusing on transplantation of pluripotent stem-cell-derived retinal pigment epithelium (RPE) and photoreceptor cells.

Gene Therapy Targeting the Inner Retina Rescues the Retinal Phenotype in a Mouse Model of CLN3 Batten Disease

The neuronal ceroid lipofuscinoses (NCLs), often referred to as Batten disease, are inherited lysosomal storage disorders that represent the most common neurodegeneration during childhood. Symptoms include seizures, vision loss, motor and cognitive decline, and premature death. The development of brain-directed treatments for NCLs has made noteworthy progress in recent years. Clinical trials are currently ongoing or planned for different forms of the disease. Despite these promising advances, it is unlikely that therapeutic interventions targeting the brain will prevent loss of vision in patients as retinal cells remain untreated and will continue to degenerate. Here, we demonstrate that Cln3^Δex7/8 mice, a mouse model of CLN3 Batten disease with juvenile onset, suffer from a decline in inner retinal function resulting from the death of rod bipolar cells, interneurons vital for signal transmission from photoreceptors to ganglion cells in the retina. We also show that this ocular phenotype can be treated by adeno-associated virus (AAV)-mediated expression of CLN3 in cells of the inner retina, leading to significant survival of bipolar cells and preserved retinal function. In contrast, the treatment of photoreceptors, which are lost in patients at late disease stages, was not therapeutic in Cln3^Δex7/8 mice, underlining the notion that CLN3 disease is primarily a disease of the inner retina with secondary changes in the outer retina. These data indicate that bipolar cells play a central role in this disease and identify this cell type as an important target for ocular AAV-based gene therapies for CLN3 disease.

AAV-mediated ERdj5 overexpression protects against P23H rhodopsin toxicity

Rhodopsin misfolding caused by the P23H mutation is a major cause of autosomal dominant retinitis pigmentosa (adRP). To date, there are no effective treatments for adRP. The BiP co-chaperone and reductase ERdj5 (DNAJC10) is part of the endoplasmic reticulum (ER) quality control machinery, and previous studies have shown that overexpression of ERdj5 in vitro enhanced the degradation of P23H rhodopsin, whereas knockdown of ERdj5 increased P23H rhodopsin ER retention and aggregation. Here, we investigated the role of ERdj5 in photoreceptor homeostasis in vivo by using an Erdj5 knockout mouse crossed with the P23H knock-in mouse and by adeno-associated viral (AAV) vector-mediated gene augmentation of ERdj5 in P23H-3 rats. Electroretinogram (ERG) and optical coherence tomography of Erdj5-/- and P23H+/-:Erdj5-/- mice showed no effect of ERdj5 ablation on retinal function or photoreceptor survival. Rhodopsin levels and localization were similar to those of control animals at a range of time points. By contrast, when AAV2/8-ERdj5-HA was subretinally injected into P23H-3 rats, analysis of the full-field ERG suggested that overexpression of ERdj5 reduced visual function loss 10 weeks post-injection (PI). This correlated with a significant preservation of photoreceptor cells at 4 and 10 weeks PI. Assessment of the outer nuclear layer (ONL) morphology showed preserved ONL thickness and reduced rhodopsin retention in the ONL in the injected superior retina. Overall, these data suggest that manipulation of the ER quality control and ER-associated degradation factors to promote mutant protein degradation could be beneficial for the treatment of adRP caused by mutant rhodopsin.

Pharmacologic fibroblast reprogramming into photoreceptors restores vision

Photoreceptor loss is the final common endpoint in most retinopathies that lead to irreversible blindness, and there are no effective treatments to restore vision1,2. Chemical reprogramming of fibroblasts offers an opportunity to reverse vision loss; however, the generation of sensory neuronal subtypes such as photoreceptors remains a challenge. Here we report that the administration of a set of five small molecules can chemically induce the transformation of fibroblasts into rod photoreceptor-like cells. The transplantation of these chemically induced photoreceptor-like cells (CiPCs) into the subretinal space of rod degeneration mice (homozygous for rd1, also known as Pde6b) leads to partial restoration of the pupil reflex and visual function. We show that mitonuclear communication is a key determining factor for the reprogramming of fibroblasts into CiPCs. Specifically, treatment with these five compounds leads to the translocation of AXIN2 to the mitochondria, which results in the production of reactive oxygen species, the activation of NF-κB and the upregulation of Ascl1. We anticipate that CiPCs could have therapeutic potential for restoring vision.

Single AAV-mediated mutation replacement genome editing in limited number of photoreceptors restores vision in mice

Supplementing wildtype copies of functionally defective genes with adeno-associated virus (AAV) is a strategy being explored clinically for various retinal dystrophies. However, the low cargo limit of this vector allows its use in only a fraction of patients with mutations in relatively small pathogenic genes. To overcome this issue, we developed a single AAV platform that allows local replacement of a mutated sequence with its wildtype counterpart, based on combined CRISPR-Cas9 and micro-homology-mediated end-joining (MMEJ). In blind mice, the mutation replacement rescued approximately 10% of photoreceptors, resulting in an improvement in light sensitivity and an increase in visual acuity. These effects were comparable to restoration mediated by gene supplementation, which targets a greater number of photoreceptors. This strategy may be applied for the treatment of inherited disorders caused by mutations in larger genes, for which conventional gene supplementation therapy is not currently feasible.

Replacing mutant genes with wildtype copies using adeno-associated virus (AAV) has been explored for the treatment of inherited retinopathies, but the low cargo limit restricts its use. Here the authors describe a single AAV platform that allows local replacement of a mutated sequence with its wildtype counterpart, based on combined CRISPR-Cas9 and micro-homology-mediated end joining.

In vivo imaging of the light response in mouse retinal ganglion cells based on a neuronal activity-dependent promoter

Diseases of the retinal ganglion cells (RGCs) are an important cause of blindness, yet the light response of individual RGCs is difficult to assess in vivo, particularly in mammals, due to a lack of effective methods. We report a simple in vivo platform for imaging the light response of mouse RGCs based on a fluorescent reporter-tagged enhanced synaptic activity-responsive element (E-SARE) that mediates neuronal activity-dependent gene transcription. When E-SARE-driven d2Venus, packaged into an AAV vector, was injected intravitreally, light-responsive retinal neurons expressing d2Venus were visible at single-cell resolution using confocal ophthalmoscopy. Immunohistological assessment identified the majority of these cells as RGCs. In a murine model of RGC injury, the number of d2Venus-positive cells was correlated with the amplitude of light-induced responses and with visual acuity, measured electrophysiologically at the visual cortex, indicating that the vector can be used as a tool to assess visual function in RGCs. The platform described herein allows a simple in vivo assessment of RGC function, which should help basic research into the mechanisms of RGC death and the development of treatments for diseases involving the RGCs.

Effect of MMP-9 gene knockout on retinal vascular form and function

Retinal degeneration from inherited gene mutation(s) is a common cause of blindness because of structural and functional alterations in photoreceptors. Accordingly, various approaches are being tested to ameliorate or even cure neuroretinal blinding conditions in susceptible patients by employing neuroprotective agents, gene therapeutics, optogenetics, regenerative therapies, and retinal prostheses. The FVB/NJ mouse strain inherently has a common Pde6b rd1 homozygous allele that renders its progeny blind by the time pups reach weaning age. To study the role matrix metalloproteinase-9 (MMP-9) in retinal structure and function, we examined a global MMP-9 knockout (KO) mouse model that has been engineered on the same FVB/NJ background to test the hypothesis whether lack of MMP-9 activity diminishes neuroretinal degenerative changes and thus helps improve the vision. We compared side-by-side various aspects of the ocular physiology in the wild-type (WT) C57BL/6J, FVB/NJ, and MMP-9 KO strains of mice. The results suggest that MMP-9 KO mice display subdued changes in their retinae as reflected by both structural and functional enhancement in the overall ocular neurophysiological parameters. Altogether, the findings appear to have clinical relevance for targeting conditions wherein MMPs and their overactivities are suspected to play dominant pathophysiological roles in advancing neurodegenerative retinal diseases.

CRB2 Loss in Rod Photoreceptors Is Associated with Progressive Loss of Retinal Contrast Sensitivity

Variations in the Crumbs homolog-1 (CRB1) gene are associated with a wide variety of autosomal recessive retinal dystrophies, including early onset retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA). CRB1 belongs to the Crumbs family, which in mammals includes CRB2 and CRB3. Here, we studied the specific roles of CRB2 in rod photoreceptor cells and whether ablation of CRB2 in rods exacerbates the Crb1-disease. Therefore, we assessed the morphological, retinal, and visual functional consequences of specific ablation of CRB2 from rods with or without concomitant loss of CRB1. Our data demonstrated that loss of CRB2 in mature rods resulted in RP. The retina showed gliosis and disruption of the subapical region and adherens junctions at the outer limiting membrane. Rods were lost at the peripheral and central superior retina, while gross retinal lamination was preserved. Rod function as measured by electroretinography was impaired in adult mice. Additional loss of CRB1 exacerbated the retinal phenotype leading to an early reduction of the dark-adapted rod photoreceptor a-wave and reduced contrast sensitivity from 3-months-of-age, as measured by optokinetic tracking reflex (OKT) behavior testing. The data suggest that CRB2 present in rods is required to prevent photoreceptor degeneration and vision loss.

Development of a Gene Therapy Vector for RDH12-Associated Retinal Dystrophy

Early-onset severe retinal dystrophy (EOSRD) is a genetically heterogeneous group of diseases resulting in serious visual disability in children. A significant number of EOSRD cases, often diagnosed as Leber congenital amaurosis (LCA13), are associated with mutations in the gene encoding retinol dehydrogenase 12 (RDH12). RDH12 is a member of the enzyme family of short-chain dehydrogenases/reductases. In the retina, RDH12 plays a critical role in reducing toxic retinaldehydes generated by visual cycle activity that is required for the light response of the photoreceptor cells. Individuals with RDH12 deficiency exhibit widespread retinal degeneration impacting both rods and cones. Although Rdh12-deficient (Rdh12^-/-) mice do not exhibit retinal degeneration, functional deficits relevant to visual cycle function can be demonstrated. In the present study, we describe the development and preclinical testing of a recombinant adeno-associated viral (rAAV) vector that has the potential for use in treating EOSRD due to RDH12 mutations. Wild-type and Rdh12^-/- mice that received a subretinal injection of rAAV2/5 carrying a human RDH12 cDNA driven by a human rhodopsin-kinase promoter exhibited transgene expression that was stable, correctly localized, and did not cause retinal toxicity. In addition, administration of the vector reconstituted retinal reductase activity in the retinas of Rdh12^-/- mice and decreased susceptibility to light damage associated with Rdh12 deficiency, thus demonstrating potential therapeutic efficacy in an animal model that does not exhibit a retinal degeneration phenotype. These findings support further efforts to develop gene replacement therapy for individuals with RDH12 mutations.

Elevated expression of TREK-TRAAK K2P channels in the retina of adult rd1 mice

AIM

To examine the expression of Twik-related K⁺ channel 1 (TREK-1), Twik-related K⁺ channel 2 (TREK-2), and Twik-related arachidonic acid-stimulated K⁺ channel (TRAAK) in the retina of adult rd1 mice and to detect the protective roles of TREK-TRAAK two-pore-domain K⁺ (K_2P) channels against retinal degeneration.

METHODS

Twenty-eight-day-old C57BL/6J mice and 28-day-old rd1 mice were used in this study. Retinal protein, retinal RNA, and embedded eyeballs were prepared from these two groups of mice. Real-time quantitative polymerase chain reaction and Western blot analyses were used to assess the gene transcription and protein levels, respectively. Retinal structures were observed using hematoxylin and eosin (H&E) staining. Immunohistochemistry was utilized to observe the retinal localization of TREK-TRAAK channels. Current changes in retinal ganglion cells (RGCs) after activation of TREK-TRAAK channels were examined using a patch-clamp technique.

RESULTS

Compared with C57BL/6J mice, rd1 mice exhibited significantly higher retinal mRNA and protein expression levels of TREK-1, TREK-2, and TRAAK channels. In both groups, immunohistochemistry showed expression of TREK-TRAAK channels in retinal layers. After addition of the TREK-TRAAK channel agonist arachidonic acid (AA), whole-cell voltage step evoked currents were significantly higher in RGCs from rd1 mice than in RGCs from control C57BL/6J mice, suggesting that TREK-TRAAK channels were opened in RGCs from rd1 mice.

CONCLUSION

TREK-TRAAK K_2P channels' expression is increased in adult rd1 mice. AA induced the opening of TREK-TRAAK K_2P channels in adult rd1 mice and may thus counterbalance depolarization of RGCs and protect the retina from excitotoxicity. TREK-TRAAK channels may play a protective role against retinal degeneration.

Loss of CRB2 in Müller glial cells modifies a CRB1-associated retinitis pigmentosa phenotype into a Leber congenital amaurosis phenotype

Variations in the human Crumbs homolog-1 (CRB1) gene lead to an array of retinal dystrophies including early onset of retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA) in children. To investigate the physiological roles of CRB1 and CRB2 in retinal Müller glial cells (MGCs), we analysed mouse retinas lacking both proteins in MGC. The peripheral retina showed a faster progression of dystrophy than the central retina. The central retina showed retinal folds, disruptions at the outer limiting membrane, protrusion of photoreceptor nuclei into the inner and outer segment layers and ingression of photoreceptor nuclei into the photoreceptor synaptic layer. The peripheral retina showed a complete loss of the photoreceptor synapse layer, intermingling of photoreceptor nuclei within the inner nuclear layer and ectopic photoreceptor cells in the ganglion cell layer. Electroretinography showed severe attenuation of the scotopic a-wave at 1 month of age with responses below detection levels at 3 months of age. The double knockout mouse retinas mimicked a phenotype equivalent to a clinical LCA phenotype due to loss of CRB1. Localization of CRB1 and CRB2 in non-human primate (NHP) retinas was analyzed at the ultrastructural level. We found that NHP CRB1 and CRB2 proteins localized to the subapical region adjacent to adherens junctions at the outer limiting membrane in MGC and photoreceptors. Our data suggest that loss of CRB2 in MGC aggravates the CRB1-associated RP-like phenotype towards an LCA-like phenotype.

In vivo genome editing rescues photoreceptor degeneration via a Cas9/RecA-mediated homology-directed repair pathway

Although Cas9-mediated genome editing has been widely used to engineer alleles in animal models of human inherited diseases, very few homology-directed repair (HDR)-based genetic editing systems have been established in postnatal mouse models for effective and lasting phenotypic rescue. Here, we developed an HDR-based Cas9/RecA system to precisely correct Pde6b mutation with increased HDR efficiency in postnatal rodless (rd1) mice, a retinitis pigmentosa (RP) mutant model characterized by photoreceptor degeneration and loss of vision. The Cas9/RecA system incorporated Cas9 endonuclease enzyme to generate double-strand breaks (DSBs) and bacterial recombinase A (RecA) to increase homologous recombination. Our data revealed that Cas9/RecA treatment significantly promoted the survival of both rod and cone photoreceptors, restored the expression of PDE6B in rod photoreceptors, and enhanced the visual functions of rd1 mice. Thus, this study provides a precise therapeutic strategy for RP and other genetic diseases.

CRB2 in immature photoreceptors determines the superior-inferior symmetry of the developing retina to maintain retinal structure and function

The mammalian apical-basal determinant Crumbs homolog-1 (CRB1) plays a crucial role in retinal structure and function by the maintenance of adherens junctions between photoreceptors and Müller glial cells. Patients with mutations in the CRB1 gene develop retinal dystrophies, including early-onset retinitis pigmentosa and Leber congenital amaurosis. Previously, we showed that Crb1 knockout mice developed a slow-progressing retinal phenotype at foci in the inferior retina, although specific ablation of Crb2 in immature photoreceptors leads to an early-onset phenotype throughout the retina. Here, we conditionally disrupted one or both alleles of Crb2 in immature photoreceptors, on a genetic background lacking Crb1, and studied the retinal dystrophies thereof. Our data showed that disruption of one allele of Crb2 in immature photoreceptors caused a substantial aggravation of the Crb1 phenotype in the entire inferior retina. The photoreceptor layer showed early-onset progressive thinning limited to the inferior retina, although the superior retina maintained intact. Surprisingly, disruption of both alleles of Crb2 in immature photoreceptors further aggravated the phenotype. Throughout the retina, photoreceptor synapses were disrupted and photoreceptor nuclei intermingled with nuclei of the inner nuclear layer. In the superior retina, the ganglion cell layer appeared thicker because of ectopic nuclei of photoreceptors. In conclusion, the data suggest that CRB2 is required to maintain retinal progenitor and photoreceptor cell adhesion and prevent photoreceptor ingression into the immature inner retina. We hypothesize, from these animal models, that decreased levels of CRB2 in immature photoreceptors adjust retinitis pigmentosa because of the loss of CRB1 into Leber congenital amaurosis phenotype.

Testing for Known Retinal Degeneration Mutants in Mouse Strains

Approximately 93 years ago at the zoological laboratories of Harvard University, Keeler, a medical geneticist, discovered a retina from a male albino mouse that was completely devoid of visual cells (rods). This rodless mouse was to be the first ever reported murine model of retinal degeneration. Over the years, naturally occurring retinal degeneration mouse mutants have been identified in several common laboratory inbred lines including FVB/NJ (Pde6b^rd1) and C57BL/6N (Crb1^rd8). It is therefore imperative that vision researchers employing other genetically induced retinal degeneration models and experimental models such as laser-induced choroidal neovascularization (CNV) or bright white-light exposure screen for such naturally occurring mutations to prevent costly misinterpretations. In this regard, we describe herein simple molecular-based techniques for screening the presence of some commonly encountered rd mutations (Pde6b^rd1, Crb1^rd8, Pde6b^rd10, and Rpe65^rd12).

Reliable detection of low visual acuity in mice with pattern visually evoked potentials

Measuring the optokinetic response (OKR) to rotating sinusoidal gratings is becoming an increasingly common method to determine visual function thresholds in mice. This is possible also through direct electrophysiological recording of the response of the neurons in the visual cortex to the presentation of reversing patterned stimuli, i.e. the pattern visually evoked potential (pVEP). Herein, we optimized the conditions for recording pVEPs in wild-type mice: we investigated the optimal depth (1, 2, or 3 mm) of the inserted electrode and the optimal stimulus pattern (vertical, horizontal, or oblique black and white stripes, or a checkerboard pattern). Visual acuity was higher when measured with the optimal pVEP recording conditions, i.e., with the electrode at 2 mm and a vertical-stripe stimulus (0.530 ± 0.021 cycle/degree), than with OKR (0.455 ± 0.006 cycle/degree). Moreover, in murine eyes with optic nerve crush-induced low vision, OKR could not measure any visual acuity, while pVEPs allowed the reliable quantification of residual vision (0.064 ± 0.004 cycle/degree). Our results show that pVEPs allow more sensitive measurement of visual function than the OKR-based method. This technique should be particularly useful in mouse models of ocular disease and low vision.

Retained Plasticity and Substantial Recovery of Rod-Mediated Visual Acuity at the Visual Cortex in Blind Adult Mice with Retinal Dystrophy

In patients born blind with retinal dystrophies, understanding the critical periods of cortical plasticity is important for successful visual restoration. In this study, we sought to model childhood blindness and investigate the plasticity of visual pathways. To this end, we generated double-mutant (Pde6c^cpfl1/cpfl1Gnat1^IRD2/IRD2) mice with absent rod and cone photoreceptor function, and we evaluated their response for restoring rod (GNAT1) function through gene therapy. Despite the limited effectiveness of gene therapy in restoring visual acuity in patients with retinal dystrophy, visual acuity was, unexpectedly, successfully restored in the mice at the level of the primary visual cortex in this study. This success in visual restoration, defined by changes in the quantified optokinetic response and pattern visually evoked potential, was achieved regardless of the age at treatment (up to 16 months). In the contralateral visual cortex, cortical plasticity, tagged with light-triggered transcription of Arc, was also restored after the treatment in blind mice carrying an Arc promoter-driven reporter gene, dVenus. Our results demonstrate the remarkable plasticity of visual circuits for one of the two photoreceptor mechanisms in older as well as younger mice with congenital blindness due to retinal dystrophies.

Assessment of AAV Vector Tropisms for Mouse and Human Pluripotent Stem Cell-Derived RPE and Photoreceptor Cells

Adeno-associated viral vectors are showing great promise as gene therapy vectors for a wide range of retinal disorders. To date, evaluation of therapeutic approaches has depended almost exclusively on the use of animal models. With recent advances in human stem cell technology, stem cell-derived retina now offers the possibility to assess efficacy in human organoids in vitro. Here we test six adeno-associated virus (AAV) serotypes [AAV2/2, AAV2/9, AAV2/8, AAV2/8T(Y733F), AAV2/5, and ShH10] to determine their efficiency in transducing mouse and human pluripotent stem cell-derived retinal pigment epithelium (RPE) and photoreceptor cells in vitro. All the serotypes tested were capable of transducing RPE and photoreceptor cells in vitro. AAV ShH10 and AAV2/5 are the most efficient vectors at transducing both mouse and human RPE, while AAV2/8 and ShH10 achieved similarly robust transduction of human embryonic stem cell-derived cone photoreceptors. Furthermore, we show that human embryonic stem cell-derived photoreceptors can be used to establish promoter specificity in human cells in vitro. The results of this study will aid capsid selection and vector design for preclinical evaluation of gene therapy approaches, such as gene editing, that require the use of human cells and tissues.

Tissue inhibitor of metalloproteinases 1 enhances rod survival in the rd1 mouse retina

Retinitis pigmentosa (RP), an inherited retinal degenerative disease, is characterized by a progressive loss of rod photoreceptors followed by loss of cone photoreceptors. Previously, when tissue inhibitor of metalloproteinase 1 (TIMP1), a key extracellular matrix (ECM) regulator that binds to and inhibits activation of Matrix metallopeptidase 9 (MMP9) was intravitreal injected into eyes of a transgenic rhodopsin rat model of RP, S334ter-line3, we discovered cone outer segments are partially protected. In parallel, we reported that a specific MMP9 and MMP2 inhibitor, SB-3CT, interferes with mechanisms leading to rod photoreceptor cell death in an MMP9 dependent manner. Here, we extend our initial rat studies to examine the potential of TIMP1 as a treatment in retinal degeneration by investigating neuroprotective effects in a classic mouse retinal degeneration model, rdPde6b-/- (rd1). The results clearly demonstrate that intravitreal injections of TIMP1 produce extended protection to delay rod photoreceptor cell death. The mean total number of rods in whole-mount retinas was significantly greater in TIMP-treated rd1 retinas (postnatal (P) 30, P35 (P<0.0001) and P45 (P<0.05) than in saline-treated rd1 retinas. In contrast, SB-3CT did not delay rod cell death, leading us to further investigate alternative pathways that do not involve MMPs. In addition to inducing phosphorylated ERK1/2, TIMP1 significantly reduces BAX activity and delays attenuation of the outer nuclear layer (ONL). Physiological responses using scotopic electroretinograms (ERG) reveal b-wave amplitudes from TIMP1-treated retinas are significantly greater than from saline-treated rd1 retinas (P<0.05). In later degenerative stages of rd1 retinas, photopic b-wave amplitudes from TIMP1-treated rd1 retinas are significantly larger than from saline-treated rd1 retinas (P<0.05). Our findings demonstrate that TIMP1 delays photoreceptor cell death. Furthermore, this study provides new insights into how TIMP1 works in the mouse animal model of RP.

Prevention of Photoreceptor Cell Loss in a Cln6nclf Mouse Model of Batten Disease Requires CLN6 Gene Transfer to Bipolar Cells

The neuronal ceroid lipofuscinoses (NCLs) are inherited lysosomal storage disorders characterized by general neurodegeneration and premature death. Sight loss is also a major symptom in NCLs, severely affecting the quality of life of patients, but it is not targeted effectively by brain-directed therapies. Here we set out to explore the therapeutic potential of an ocular gene therapy to treat sight loss in NCL due to a deficiency in the transmembrane protein CLN6. We found that, although Cln6^nclf mice presented mainly with photoreceptor degeneration, supplementation of CLN6 in photoreceptors was not beneficial. Because the level of CLN6 is low in photoreceptors but high in bipolar cells (retinal interneurons that are only lost in Cln6-deficient mice at late disease stages), we explored the therapeutic effects of delivering CLN6 to bipolar cells using adeno-associated virus (AAV) serotype 7m8. Bipolar cell-specific expression of CLN6 slowed significantly the loss of photoreceptor function and photoreceptor cells. This study shows that the deficiency of a gene normally expressed in bipolar cells can cause the loss of photoreceptors and that this can be prevented by bipolar cell-directed treatment.

Emerging therapies for inherited retinal degeneration

Inherited retinal degenerative diseases, a genetically and phenotypically heterogeneous group of disorders, affect the function of photoreceptor cells and are among the leading causes of blindness. Recent advances in molecular genetics and cell biology are elucidating the pathophysiological mechanisms underlying these disorders and are helping to identify new therapeutic approaches, such as gene therapy, stem cell therapy, and optogenetics. Several of these approaches have entered the clinical phase of development. Artificial replacement of dying photoreceptor cells using retinal prostheses has received regulatory approval. Precise retinal imaging and testing of visual function are facilitating more efficient clinical trial design. In individual patients, disease stage will determine whether the therapeutic strategy should comprise photoreceptor cell rescue to delay or arrest vision loss or retinal replacement for vision restoration.

Progressive loss of retinal blood vessels in a live model of retinitis pigmentosa

OBJECTIVE

To assess retinal blood vessels in a live retinitis pigmentosa (RP) model with rd1 mutation and green fluorescent protein (GFP) expressed in vascular endothelium.

METHODS

Homozygous (hm) Tie2-GFP mice with rd1 mutation and known retinal degeneration were crossed with wild-type CD1 mice to generate control heterozygous (ht) Tie2-GFP mice. The retinas of 16 live hm mice were evaluated at 2 weeks and 3, 5, and 8 months of age, and compared with age-matched control ht and CD1 mice by optical coherence tomography (OCT) and confocal scanning laser ophthalmoscopy (cSLO). Fluorescence intensity was measured and compared between strains at 3, 5, and 8 months. In vivo findings were validated by immunostaining with collagen IV and isolectin histopathology.

RESULTS

All hm Tie2-GFP mice showed progressive outer retinal degeneration by OCT. Loss of small branches of blood vessels and then larger main vessels was seen by cSLO. Retinal tissue and vessels were preserved in control ht mice. At all ages, measurements of fluorescence intensity were reduced in hm compared with ht mice (p < 0.001). In all strains, intensity at 8 months was reduced compared with 3 months (p < 0.001) and 5 months (p = 0.021). Histopathological studies confirmed in vivo findings and revealed a pattern of blood vessel regression in the deep plexus, followed by intermediate and superficial retinal plexuses.

CONCLUSIONS

This is the first evidence of progressive loss of retinal blood vessels in a live mouse model of RP. These findings may be highly relevant to understanding retinal degeneration in RP to prevent blindness.