Animal Models Of Retinitis Pigmentosa Research Articles

Retinoic acid-dependent loss of synaptic output from bipolar cells impairs visual information processing in inherited retinal degeneration.

In retinitis pigmentosa (RP), rod and cone photoreceptors degenerate, depriving downstream neurons of light-sensitive input, leading to vision impairment or blindness. Although downstream neurons survive, some undergo morphological and physiological remodeling. Bipolar cells (BCs) link photoreceptors, which sense light, to retinal ganglion cells (RGCs), which send information to the brain. While photoreceptor loss disrupts input synapses to BCs, whether BC output synapses remodel has remained unknown. Here we report that synaptic output from BCs plummets in RP mouse models of both sexes owing to loss of voltage-gated Ca2+ channels. Remodeling reduces the reliability of synaptic output to repeated optogenetic stimuli, causing RGC firing to fail at high stimulus frequencies. Fortunately, functional remodeling of BCs can be reversed by inhibiting the retinoic acid receptor (RAR). RAR inhibitors targeted to BCs present a new therapeutic opportunity for mitigating detrimental effects of remodeling on signals initiated either by surviving photoreceptors or by vision-restoring tools.Significance Statement Photoreceptor degenerative disorders such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD) lead to vision impairment or blindness. Vision mediated by surviving photoreceptors or artificial vision restoration technologies, rely on bipolar cells retaining normal function despite photoreceptor death. We find that in two animal models of RP, synaptic transmission from both rod and cone bipolar cells is severely impaired owing to diminished voltage-gated calcium current, preventing postsynaptic amacrine cells and retinal ganglion cells from properly receiving and encoding visual information. We find that an inhibitor of the retinoic acid receptor restores both the calcium current and synaptic release from bipolar cells. These discoveries about bipolar cells reveal a new functional deficit in blindness and a potential therapeutically important solution.

Resilience and neuroprotection: The efficacy of saffron Repron® in counteracting the progression of inherited retinal degeneration

E‐mail: ilaria.piano@unipi.it.Retinal diseases can be induced by several factors, including genetic mutations, environmental stresses, and dysmetabolic processes. The result is a progressive loss of visual function, that can leading to total blindness. Among the diseases still orphaned of an effective therapy for slowing retinal degeneration is Retinitis Pigmentosa (RP). RP is one of the inherited retinal degenerative diseases (IRDs) whose cause is attributed to genetic mutations mainly at the level of rod‐specific genes. To date, about 150 mutations out of 60 different genes have been identified.Several therapeutic strategies are being investigated, although the results are still mostly unsatisfactory and limited to specific diseases, particularly in the case of gene therapy, which is applicable only to specific mutations and therefore not applicable on a large scale. Most of the proposed treatments have been tested in animal models, but few have progressed to human clinical trials. An important approach is to identify targets at the level of those mechanisms that are in common in all forms of RP and that drive disease progression, such as stress‐oxidative and inflammation that all together are known as oxinflammation. Here we provide data showing that in RP natural compounds are effective in slowing down the progression of the disease mainly counteracting oxinflammation. Specifically, saffron “Repron” was proved to be effective in AMD and Stargardt patients as well as in pre‐clinical models both “in vitro” and “in vivo.” We tested this treatment in a IRD model. Preliminary obtained in an animal model of RP (rd10 mice) where saffron treatment was able to slow down even the degeneration of rod due to a genetic mutation. In this study, the treatment began in rd10 pregnant females and continued throughout the weaning phase and then in pups that had become autonomous. Functional, immunohistochemical, molecular biology and biochemical analyses were performed at multiple time points from P20 to P120. The results obtained show a protective effect of saffron on both retinal function and morphology, opening a prospect of preventive treatment for those inherited diseases whose progression is known.

The light-dependent pseudo-capacitive charging of conjugated polymer nanoparticles coupled with the depolarization of the neuronal membrane.

The mechanism underlying visual restoration in blind animal models of retinitis pigmentosa using a liquid retina prosthesis based on semiconductive polymeric nanoparticles is still being debated. Through the application of mathematical models and specific experiments, we developed a coherent understanding of abiotic/biotic coupling, capturing the essential mechanism of photostimulation responsible for nanoparticle-induced retina activation. Our modeling is based on the solution of drift-diffusion and Poisson-Nernst-Planck models in the multi-physics neuron-cleft-nanoparticle-extracellular space domain, accounting for the electro-chemical motion of all the relevant species following photoexcitation. Modeling was coupled with electron microscopy to estimate the size of the neuron-nanoparticle cleft and electrophysiology on retina explants acutely or chronically injected with nanoparticles. Overall, we present a consistent picture of electrostatic depolarization of the bipolar cell driven by the pseudo-capacitive charging of the nanoparticle. We demonstrate that the highly resistive cleft composition, due to filling by adhesion/extracellular matrix proteins, is a crucial ingredient for establishing functional electrostatic coupling. Additionally, we show that the photo-chemical generation of reactive oxygen species (ROS) becomes relevant only at very high light intensities, far exceeding the physiological ones, in agreement with the lack of phototoxicity shown in vivo.

Neuroprotective effects of syngeneic bone marrow‐derived mononuclear stem cell transplantation and intraperitoneal minocycline in the treatment of inherited photoreceptor retinal degeneration

Inherited retinal degenerations are diseases characterized by photoreceptor loss secondary to genetic defects and Retinitis Pigmentosa (RP) is the most frequent inherited retinal degeneration. This disease has a prevalence of around 1 in 4000 individuals and is caused by mutations in more than 300 genes. RP is characterized by progressive loss of photoreceptors (fist rods following by cones), activation of microglial cells and gliosis increases of macroglial cell.The Royal college of Surgeon (RCS) rat is a well characterized animal models of RP which suffer a mutation of the MERTK gene, that impedes the normal photoreceptor outer segment phagocytosis by RPE cells thus triggers the simultaneous degeneration of rods and cones. Recent studies have shown that microglial activation starts simultaneously with the beginning of photoreceptor death in the RCS retinas, suggesting that microglial cells play an important role in the retinal degeneration progression.Therapies for inherited photoreceptor degeneration aim to prevent or delay death of the photoreceptors, or in specific circumstances try to replace them.The Bone marrow derived‐mononuclear cells (BM‐MNCs) are a mononuclear CD34+ subpopulation of bone marrow‐derived cells that can be separated from the other cellular fractions of the bone marrow aspirate using a Ficoll density gradient‐based protocol. These cells have shown promising results in different animal models of neuronal degeneration, including inherited photoreceptor degenerations such us: improve the morphology of the photoreceptors outer segment, decrease synaptic degeneration in the outer plexiform layer and reduce glial fibrillary acidic protein expression in Müller cells.On the other hands minocycline is a broad‐spectrum tetracycline antibiotic, of which it has been demonstrated has antimicrobial, anti‐inflammatory, antiapoptotic, neuroprotective, and microglial inhibition effects in central nervous system diseases.In RCS rat retina the neuroprotective effect of minocycline against photoreceptor apoptosis is can be explained by mainly two different mechanisms: (1) a direct antiapoptotic effect on photoreceptors and/or (2) an effect through its anti‐inflammatory properties reducing microglial cells activation and migration.The question arises whether the combination of intravitreal BM‐MNCs transplantation with minocycline, substances that increase survival presumably through different mechanisms, could further increase photoreceptor survival and therefore be used for the treatment of retinal degenerations.Our results showed that intravitreal transplantation of BM‐MNCs increase photoreceptor survival, improved the morphology of the photoreceptors outer segment, and reduce retinal thinning (in vivo). On the other hands intraperitoneally minocycline treatment, and reduced activation and migration of microglia and produced a significant rescue of photoreceptors. Finally, our result show that combination both treatments had higher neuroprotective effects in the retina, increasing photoreceptor survival, than each of the treatments alone.In conclusion in RCS rat animal model of photoreceptor degeneration, minocycline reduces microglial activation and migration, and intravitreal transplantation of BM‐MNCs and minocycline increase photoreceptor survival. The combination of both treatments shows greater neuroprotective effects than their isolated effects, and therefore could be indicated for treatment of the early stages of photoreceptor degenerations.

Therapeutic Extracellular Vesicles from Tonsil-Derived Mesenchymal Stem Cells for the Treatment of Retinal Degenerative Disease.

Retinal degenerative disease (RDD), one of the most common causes of blindness, is predominantly caused by the gradual death of retinal pigment epithelial cells (RPEs) and photoreceptors due to various causes. Cell-based therapies, such as stem cell implantation, have been developed for the treatment of RDD, but potential risks, including teratogenicity and immune reactions, have hampered their clinical application. Stem cell-derived extracellular vesicles (EVs) have recently emerged as a cell-free alternative therapeutic strategy; however, additional invasiveness and low yield of the stem cell extraction process is problematic. To overcome these limitations, we developed therapeutic EVs for the treatment of RDD which were extracted from tonsil-derived mesenchymal stem cells obtained from human tonsil tissue discarded as medical waste following tonsillectomy (T-MSC EVs). To verify the biocompatibility and cytoprotective effect of T-MSC EVs, we measured cell viability by co-culture with human RPE without or with toxic all-trans-retinal. To elucidate the cytoprotective mechanism of T-MSC EVs, we performed transcriptome sequencing using RNA extracted from RPEs. The in vivo protective effect of T-MSC EVs was evaluated using Pde6b gene knockout rats as an animal model of retinitis pigmentosa. T-MSC EVs showed high biocompatibility and the human pigment epithelial cells were significantly protected in the presence of T-MSC EVs from the toxic effect of all-trans-retinal. In addition, T-MSC EVs showed a dose-dependent cell death-delaying effect in real-time quantification of cell death. Transcriptome sequencing analysis revealed that the efficient ability of T-MSC EVs to regulate intracellular oxidative stress may be one of the reasons explaining their excellent cytoprotective effect. Additionally, intravitreally injected T-MSC EVs had an inhibitory effect on the destruction of the outer nuclear layer in the Pde6b gene knockout rat. Together, the results of this study indicate the preventive and therapeutic effects of T-MSC EVs during the initiation and development of retinal degeneration, which may be a beneficial alternative for the treatment of RDD.

Reduced inspired oxygen decreases retinal superoxide radicals and promotes cone function and survival in a model of retinitis pigmentosa.

Retinitis pigmentosa (RP) is caused by many different mutations that promote the degeneration of rod photoreceptors and have no direct effect on cones. After the majority of rods have died cone photoreceptors begin to slowly degenerate. Oxidative damage contributes to cone cell death and it has been hypothesized that tissue hyperoxia due to reduced oxygen consumption from the loss of rods is what initiates oxidative stress. Herein, we demonstrate in animal models of RP that reduction of retinal hyperoxia by reducing inspired oxygen to continuous breathing of 11% O2 reduced the generation of superoxide radicals in the retina and preserved cone structure and function. These data indicate that retinal hyperoxia is the initiating event that promotes oxidative damage, loss of cone function, and cone degeneration in the RP retina.

Advances in Ophthalmic Epigenetics and Implications for Epigenetic Therapies: A Review

The epigenome represents a vast molecular apparatus that writes, reads, and erases chemical modifications to the DNA and histone code without changing the DNA base-pair sequence itself. Recent advances in molecular sequencing technology have revealed that epigenetic chromatin marks directly mediate critical events in retinal development, aging, and degeneration. Epigenetic signaling regulates retinal progenitor (RPC) cell cycle exit during retinal laminar development, giving rise to retinal ganglion cells (RGCs), amacrine cells, horizontal cells, bipolar cells, photoreceptors, and Müller glia. Age-related epigenetic changes such as DNA methylation in the retina and optic nerve are accelerated in pathogenic conditions such as glaucoma and macular degeneration, but reversing these epigenetic marks may represent a novel therapeutic target. Epigenetic writers also integrate environmental signals such as hypoxia, inflammation, and hyperglycemia in complex retinal conditions such as diabetic retinopathy (DR) and choroidal neovascularization (CNV). Histone deacetylase (HDAC) inhibitors protect against apoptosis and photoreceptor degeneration in animal models of retinitis pigmentosa (RP). The epigenome represents an intriguing therapeutic target for age-, genetic-, and neovascular-related retinal diseases, though more work is needed before advancement to clinical trials.

Large Animal Models of Retinitis Pigmentosa in Therapy Development and Preclinical Testing.

Large animal models are valuable for developing and testing translational therapies for inherited retinal dystrophies such as retinitis pigmentosa (RP). Gene augmentation therapy has been developed utilizing such models. Adeno-associated viral (AAV) vectors have been frequently utilized and delivered by intravitreal or subretinal injection. In vivo longitudinal assessments of therapeutic outcomes are essential. These include regular ophthalmic examinations as well as detailed fundus assessments including confocal scanning laser ophthalmoscopy (cSLO) and high-resolution cross-sectional imaging of the retina by spectral domain-optical coherence tomography (SD-OCT). Retinal function assessment includes vision testing and electroretinography (ERG).

Microglial alterations as a possible treatment target in retinitis pigmentosa

AbstractPurpose: The term retinitis pigmentosa (RP) describes a group of hereditary retinopathies. The first clinical signs of RP are night blindness and loss of peripheral vision. Central vision remains preserved until advanced stages of the disease. At a cellular level, the rods are the first to degenerate. Subsequently, there is degeneration of the cones. Inflammation plays a fundamental role in RP. The microglia respond quickly to alterations, acquiring amoeboid morphology; migrating to damage focus; acquiring macrophages functions; phagocytosing cellular debris; secreting molecules that initiate tissue repair; and favouring neuroprotection. However, if the activation is excessive, the constant secretion of nitric oxide and proinflammatory cytokines lead to pathological side effects. The purpose of this work was to review published studies in order to know if the inhibition of micloglial activation may be a good option to increase photoreceptor protection.Methods: A systematic literature review was conducted, in accordance with PRISMA criteria, in different bibliographic databases: Medline, Embase, SCOPUS and Web of Science. We searched human and animal reviews, published in English in the past 10 years. Initial search terms were ‘retina’, ‘retinitis pigmentosa’, ‘retinal degeneration’ and ‘therapeutics. Duplicate studies were removed, and the remaining articles were assessed for eligibility by full‐text review.Results: Understanding the mechanisms leading to photoreceptor death is essential for the development of new treatments in RP. It has been shown increased retinal infiltration of activated microglia in many animal models of RP. Different works have studied the clinical efficacy of antioxidants, minocycline, transforming growth factor beta or tamoxifen. However, the complete efficacy in RP has not been fully established.Conclusions: Pharmacological inhibition of microglial activation may be a good therapeutic target to reduce photoreceptor cell death in RP.

A Modified Arrestin1 Increases Lactate Production in the Retina and Slows Retinal Degeneration.

Glucose metabolism in the retina is carefully orchestrated, with glucose being delivered to photoreceptors from the choroidal circulation through the retinal pigmented epithelium (RPE). In photoreceptors, glucose is processed principally by aerobic glycolysis, from which the lactate byproduct is provided to the RPE and Müller glia for their energetic needs. In this study, we utilize a modified arrestin1 protein to enhance the glycolytic output of lactate from rod photoreceptors through disinhibition of enolase1 activity with the goal being to use this increased lactate production as a gene-agnostic approach to slowing retinal degeneration. Mouse arrestin1 with E362G/D363G amino acid substitutions (referred to as “ArrGG”) was packaged into AAV and tested for safety and for efficacy in increasing retinal lactate production. Overexpression of ArrGG in C57BL/6J mice did not result in any detectable changes in either electroretinogram (ERG) function or photoreceptor survival as measured by outer nuclear layer (ONL) thickness. However, mouse retinas expressing ArrGG showed a ∼25% increase in the rate of lactate secretion.Therefore, AAV-ArrGG was delivered intravitreally to heterozygous P23H rhodopsin knockin mice (RhoP23H/+) to determine if enhancing glycolysis in photoreceptors can slow retinal degeneration in this animal model of retinitis pigmentosa. We found that the expression of ArrGG in these mice slowed the decline of both scotopic and photopic ERG function. Correspondingly, there was significant preservation of ONL thickness in RhoP23H/+ mice treated with ArrGG compared with controls. In conclusion, our studies show that expressing ArrGG in C57BL/6J mouse retina results in an increase in lactate production, consistent with an upregulation of glycolysis. In the P23H rhodopsin model of retinitis pigmentosa, the expression of ArrGG led to significant preservation of photoreceptor function and slowing of retinal degeneration. These findings suggest that enhancing glycolysis by targeting increased enolase1 activity with a modified arrestin1 in photoreceptors may offer a therapeutic approach to slowing retinal degeneration.

Lentiviral expression of calpain-1 C2-like domain peptide prevents glutamate-induced cell death in mouse hippocampal neuronal HT22 cells.

Glutamate neurotoxicity is involved in neurodegenerative diseases, including Alzheimer's and Parkinson's diseases. Excess glutamate causes caspase-independent programmed cell death via oxidative stress and calcium influx. Our previous study showed that calpain-1 localizes to both the cytoplasm and mitochondria, where apoptosis-inducing factor (AIF) is cleaved by calpain-1 and translocates to the nucleus to induce DNA fragmentation. The autoinhibitory region of calpain-1 conjugated with the cell-penetrating peptide HIV1-Tat (namely Tat-μCL) specifically prevents the activity of mitochondrial calpain-1 and attenuates neuronal cell death in animal models of retinitis pigmentosa, as well as glutamate-induced cell death in mouse hippocampal HT22 cells. In the present study, we constructed a lentiviral vector expressing the Tat-μCL peptide and evaluated its protective effect against glutamate-induced cell death in HT22 cells. Lentiviral transduction with Tat-μCL significantly suppressed glutamate-induced nuclear translocation of AIF and DNA fragmentation. The findings of the present study suggest that the stable expression of Tat-μCL may be a potential gene therapy modality for neurodegenerative diseases.

Topical Ocular Administration of Progesterone Decreases Photoreceptor Cell Death in Retinal Degeneration Slow (rds) Mice.

Retinitis pigmentosa (RP) is an inherited eye disorder which triggers a cascade of retinal disorders leading to photoreceptor cell death and for which there is currently no effective treatment. The purpose of this research was to study whether ocular administration of a solution of progesterone (PG) in β-cyclodextrins (CD) could delay photoreceptor cell death and counteract the gliosis process in an animal model of RP (rds mice). The possible effect of PG reaching the contralateral eye through the circulatory system was also evaluated. Finally, this research discusses and evaluates the diffusion of the drug from possible topical formulations for ocular administration of PG. A group of rds mice received one drop of a solution of PG in CD every 12 h for 10 days to the left eye, while the right eye was left untreated. Another group of rds mice (control) received the drug vehicle (PBS) on the left eye and, again, the right eye was left untreated. Once the treatment was finished on postnatal day 21, the animals were euthanized and histological immunofluorescence studies (TUNEL, GFAP, and DAPI staining) were carried out. Our results showed that the administration of a solution of PG in CD (CD-PG) as drops significantly decreased cell death and inflammation in the retina of the PG-treated eyes of rds mice. No effect was seen in the contralateral eye from PG that may have entered systemic circulation. In conclusion, CD-PG applied topically as drops to the eye decreases photoreceptor cell death in the early stages of RP, delaying vision loss and decreasing gliosis.

Retinitis Pigmentosa (RP): The Role of Oxidative Stress in the Degenerative Process Progression.

Purpose: Retinitis Pigmentosa is a term that includes a group of inherited bilateral and progressive retinal degenerations, with the involvement of rod photoreceptors, which frequently leads to blindness; oxidative stress may be involved in the degeneration progression as proposed by several recent studies. The goal of this study is to evaluate whether circulating free radicals taken from capillary blood are related to one of the most important features of Retinitis pigmentosa that can affect frequently patients: cystoid macular oedema (CME). Materials: A total of 186 patients with Retinitis Pigmentosa (range: 25–69 years) were enrolled; all patients completed an ophthalmologic examination and SD-OCT at baseline and were divided into three subgroups according to the SD-OCT features. ROS blood levels were determined using FORT with monitoring of free oxygen radicals. Results: Test levels of free oxygen radicals were significantly increased, almost twice, in RP patients showing cystoid macular oedema and significantly increased compared to the control group. (p < 0.001). Discussion: Our findings suggest that oxidative stress may speed cone photoreceptors’ morphological damage (CMT); because long lasting oxidative stress in the RP may cause oxidative damage, with animal models of RP suggesting this is a micromolecular mechanism of photoreceptors’ (cone) death, it can be similar to cone damage in human RP eyes. The limitations of this paper are the relatively small sample, the horizontal design of the study, and the lack of data about the levels of ROS in the vitreous body.

Effects of Daily Melatonin Supplementation on Visual Loss, Circadian Rhythms, and Hepatic Oxidative Damage in a Rodent Model of Retinitis Pigmentosa.

Retinitis pigmentosa (RP) is a group of inherited neurodegenerative diseases characterized by a progressive loss of visual function that primarily affect photoreceptors, resulting in the complete disorganization and remodeling of the retina. Progression of the disease is enhanced by increased oxidative stress in the retina, aqueous humor, plasma, and liver of RP animal models and patients. Melatonin has beneficial effects against age-related macular degeneration, glaucoma, and diabetic retinopathy, in which oxidative stress plays a key role. In the present study, we used the P23HxLE rat as an animal model of RP. Melatonin treatment (10 mg/kg b.w. daily in drinking water for 6 months) improved the parameters of visual function and decreased the rate of desynchronization of the circadian rhythm, both in P23HxLE and wild-type rats. Melatonin reduced oxidative stress and increased antioxidant defenses in P23HxLE animals. In wild-type animals, melatonin did not modify any of the oxidative stress markers analyzed and reduced the levels of total antioxidant defenses. Treatment with melatonin improved visual function, circadian synchronization, and hepatic oxidative stress in P23HxLE rats, an RP model, and had beneficial effects against age-related visual damage in wild-type rats.

Effect of Dual Endothelin Receptor Antagonist on a Retinal Degeneration Animal Model by Regulating Choroidal Microvascular Morphology.

Objective Clinical studies have found that increasing levels of plasma endothelin-1 (ET-1) might inhibit choroidal blood flow (BF) and promote choroidal vasoconstriction. This study was designed to investigate ET-1 levels and its effect on choroidal microvascular morphology in a retinitis pigmentosa (RP) animal model. Methods Mice with retinal degeneration (rd10) were intragastrically administered bosentan, a dual endothelin receptor antagonist. We detected plasma ET-1 levels using an enzyme-linked immunosorbent assay (ELISA) kit at P14, P21, and P28 and evaluated ET-1 expression in RPE/choroid/sclera complexes using western blot and whole mount immunofluorescence staining at P28. Retinal thickness was measured using hematoxylin and eosin (H&E) staining at P28. At the same time, we also estimated choroidal microvascular densities using vascular luminal casting with a scanning electron microscope (SEM). Results Plasma ET-1 levels were increased significantly in rd10 mice at P21 (65.48 ± 24.83 pg/ml) and P28 (85.89 ± 20.23 pg/ml) compared with C57BL/6J mice at P21 (33.52 ± 16.33 pg/ml) and P28 (42.38 ± 17.53 pg/ml); the expression of ET-1 was also upregulated in RPE/choroid/sclera complexes at P28. Bosentan inhibited ET-1 expression in plasma (P < 0.05) and RPE/choroid/sclera complexes at P28 in rd10 mice. Choroidal microvascular densities were decreased in rd10 mice, and bosentan could weaken these changes. Conclusion Plasma and local ET-1 was elevated in an animal model of RP, suggesting that it likely participates in the pathological progression of retinal degeneration and may thus provide a new intervention target. ET-1 blockade might exert its protective effect by elevating choroidal microvascular density via inhibition of ET-1.

A rat model for retinitis pigmentosa with rapid retinal degeneration enables drug evaluation in vivo

BackgroundAlthough retinitis pigmentosa (RP) is most frequently studied in mouse models, rats, rabbits, and pigs are also used as animal models of RP. However, no studies have reported postnatal photoreceptor cell loss before complete development in these models. Here, we generated a transgenic rat strain, named the P347L rat, in which proline at position 347 in the rhodopsin protein was replaced with leucine.ResultsA pathological analysis of photoreceptor cells in the P347L rat model was performed, and drugs with potential use as therapeutic agents against RP were investigated. The data clearly showed rapid degeneration and elimination of the outer nuclear layer even before the photoreceptor cells were fully established in P347L rats. To test the usefulness of the P347L rat in the search for new therapeutic agents against RP, the effects of rapamycin on RP were investigated in this rat strain. The findings suggest that rapamycin promotes autophagy and autophagosomal uptake of the rhodopsin that has accumulated abnormally in the cytoplasm, thereby alleviating stress and delaying photoreceptor cell death.ConclusionsIn this RP model, the time to onset of retinal degeneration was less than that of previously reported RP models with other rhodopsin mutations, enabling quicker in vivo evaluation of drug efficacy. Administration of rapamycin delayed the photoreceptor cell degeneration by approximately 1 day.

Thioredoxin Delays Photoreceptor Degeneration, Oxidative and Inflammation Alterations in Retinitis Pigmentosa.

Retinitis pigmentosa (RP) is an inherited ocular disorder with no effective treatment. RP onset and progression trigger a cascade of retinal disorders that lead to the death of photoreceptors. After photoreceptors death, neuronal, glial and vascular remodeling can be observed in the retina. The purpose of this study was to study if thioredoxin (TRX) administration is able to decrease photoreceptor death in an animal model of RP (rd1 mouse), but also if it is able to modulate the retinal oxidative stress, glial and vascular changes that can be observed as the disease progresses. Wild type and rd1 mice received several doses of TRX. After treatment, animals were euthanized at postnatals days 11, 17, or 28. Glutathione (GSH) and other thiol compounds were determined by high performance liquid chromatography (HPLC). Glial fibrilary acidic protein (GFAP) and anti-ionized calcium binding adaptor molecule 1 (Iba1) were studied by immunohistochemistry. Vascular endothelial growth factor (VEGF) and hepatic growth factor (HGF) expression were determined by western blot. TRX administration significantly diminished cell death in rd1 mouse retinas and increased GSH retinal concentrations at postnatal day 11 (PN11). TRX was also able to reverse glial alterations at PN11 and PN17. No alterations were observed in retinal VEGF and HGF expression in rd1 mice. In conclusion, TRX treatment decreases photoreceptor death in the first stages of RP and this protective effect may be due in part to the GSH system activation and to a partially decrease in inflammation.

HDAC inhibition ameliorates cone survival in retinitis pigmentosa mice

Cone photoreceptor cell death in inherited retinal diseases, such as Retinitis Pigmentosa (RP), leads to the loss of high acuity and color vision and, ultimately to blindness. In RP, a vast number of mutations perturb the structure and function of rod photoreceptors, while cones remain initially unaffected. Extensive rod loss in advanced stages of the disease triggers cone death by a mechanism that is still largely unknown. Here, we show that secondary cone cell death in animal models for RP is associated with increased activity of histone deacetylates (HDACs). A single intravitreal injection of an HDAC inhibitor at late stages of the disease, when the majority of rods have already degenerated, was sufficient to delay cone death and support long-term cone survival in two mouse models for RP, affected by mutations in the phosphodiesterase 6b gene. Moreover, the surviving cones remained light-sensitive, leading to an improvement in visual function. RNA-seq analysis of protected cones demonstrated that HDAC inhibition initiated multi-level protection via regulation of different pro-survival pathways, including MAPK, PI3K-Akt, and autophagy. This study suggests a unique opportunity for targeted pharmacological protection of secondary dying cones by HDAC inhibition and creates hope to maintain vision in RP patients even in advanced disease stages.

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.

Transferrin Non-Viral Gene Therapy for Treatment of Retinal Degeneration.

Dysregulation of iron metabolism is observed in animal models of retinitis pigmentosa (RP) and in patients with age-related macular degeneration (AMD), possibly contributing to oxidative damage of the retina. Transferrin (TF), an endogenous iron chelator, was proposed as a therapeutic candidate. Here, the efficacy of TF non-viral gene therapy based on the electrotransfection of pEYS611, a plasmid encoding human TF, into the ciliary muscle was evaluated in several rat models of retinal degeneration. pEYS611 administration allowed for the sustained intraocular production of TF for at least 3 and 6 months in rats and rabbits, respectively. In the photo-oxidative damage model, pEYS611 protected both retinal structure and function more efficiently than carnosic acid, a natural antioxidant, reduced microglial infiltration in the outer retina and preserved the integrity of the outer retinal barrier. pEYS611 also protected photoreceptors from N-methyl-N-nitrosourea-induced apoptosis. Finally, pEYS611 delayed structural and functional degeneration in the RCS rat model of RP while malondialdehyde (MDA) ocular content, a biomarker of oxidative stress, was decreased. The neuroprotective benefits of TF non-viral gene delivery in retinal degenerative disease models further validates iron overload as a therapeutic target and supports the continued development of pEY611 for treatment of RP and dry AMD.