Dual CRALBP isoforms unveiled: iPSC-derived retinal modeling and AAV2/5-RLBP1 gene transfer raise considerations for effective therapy.

Inherited retinal diseases (IRDs) are characterized by progressive vision loss. There are over 270 causative IRD genes, and variants within the same gene can cause clinically distinct disorders. One example is RLBP1, which encodes CRALBP. CRALBP is an essential protein in the rod and cone visual cycles that take place primarily in the retinal pigment epithelium (RPE) but also in Müller cells of the neuroretina. RLBP1 variants lead to three clinical subtypes: Bothnia dystrophy, retinitis punctata albescens, and Newfoundland rod-cone dystrophy. We modeled RLBP1-IRD subtypes using patient-specific induced pluripotent stem cell (iPSC)-derived RPE and identified pathophysiological markers that served as pertinent therapeutic read-outs. We developed an AAV2/5-mediated gene-supplementation strategy and performed a proof-of-concept study in the human models, which was validated in vivo in an Rlbp1-/- murine model. Most importantly, we identified a previously unsuspected smaller CRALBP isoform that is naturally and differentially expressed both in the human and murine retina. This previously unidentified isoform is produced from an alternative methionine initiation site. This work provides further insights into CRALBP expression and RLBP1-associated pathophysiology and raises important considerations for successful gene-supplementation therapy.

A novel lipophenol quercetin derivative to prevent macular degeneration: Intravenous and oral formulations for preclinical pharmacological evaluation.

Drugs with properties against oxidative and carbonyl stresses are potential candidates to prevent dry age-related macular degeneration (Dry-AMD) and inherited Stargardt disease (STGD1). Previous studies have demonstrated the capacity of a new lipophenol drug: 3-O-DHA-7-O-isopropyl-quercetin (Q-IP-DHA) to protect ARPE19 and primary rat RPE cells respectively from A2E toxicity and under oxidative and carbonyl stress conditions. In this study, first, a new methodology has been developed to access gram scale of Q-IP-DHA. After classification of the lipophenol as BCS Class IV according to physico-chemical and biopharmaceutical properties, an intravenous formulation with micelles (M) and an oral formulation using lipid nanocapsules (LNC) were developed. M were formed with Kolliphor® HS 15 and saline solution 0.9 % (mean size of 16 nm, drug loading of 95 %). The oral formulation was optimized and successfully allowed the formation of LNC (25 nm, 96 %). The evaluation of the therapeutic potency of Q-IP-DHA was performed after IV administration of micelles loaded with Q-IP-DHA (M-Q-IP-DHA) at 30 mg/kg and after oral administration of LNC loaded with Q-IP-DHA (LNC-Q-IP-DHA) at 100 mg/kg in mice. Results demonstrated photoreceptor protection after induction of retinal degeneration by acute light stress making Q-IP-DHA a promising preventive candidate against dry-AMD and STGD1.

Hydrogen Peroxide Affects the Electroretinogram of Isolated Perfused Rat Retina.

PURPOSE: To evaluate the effects of H2O2 as an oxidant on the electroretinogram (ERG) in isolated rat retina. METHODS: Retinas were isolated from rat eyes and perfused with a nutrient solution. ERGs were recorded every 3 min. Once the signal was at a steady state, H2O2 was added to the perfusion solution. RESULTS: H2O2 caused instantaneous and transient changes in amplitudes and implicit times of the ERG, followed by changes in retinal survival curves. H2O2 0.2 mM produced a rapid increase in b-wave amplitude, followed by a return to the initial value and a survival curve above the control (without H2O2). A slight increase in a-wave was observed, followed by a decrease and a recovery above the control. The slow PIII decreased and then recovered to the initial value. H2O2 0.6 mM induced a small increase in b-wave amplitude, followed by a rapid decrease without recovery. The a-wave and slow PIII decreased rapidly without recovery. The implicit times of the a-wave and b-wave increased moderately with a low dose of H2O2, whereas they significantly increased with a high dose. Whatever the dose, the slow PIII implicit time increased significantly, followed by a return to the initial value. Barium increased the a-wave and b-wave, and then H2O2 reduced the two waves with a stronger effect on the a-wave. Aspartate and barium isolated the fast PIII, which decreased after H2O2 application. CONCLUSIONS: H2O2 affects retinal function as shown by ERGs in isolated rat retina. The response differs with the dose of H2O2, suggesting that mechanisms underlying the action at low doses might be different from those at high doses. Our results also suggest an effect of H2O2 on ionic currents and/or neurotransmitter releases involved in the generation of the ERG and indicate a more pronounced effect on photoreceptors than on postsynaptic cells.

SPACR Encoded by IMPG1 Is Essential for Photoreceptor Survival by Interplaying between the Interphotoreceptor Matrix and the Retinal Pigment Epithelium.

Several pathogenic variants have been reported in the IMPG1 gene associated with the inherited retinal disorders vitelliform macular dystrophy (VMD) and retinitis pigmentosa (RP). IMPG1 and its paralog IMPG2 encode for two proteoglycans, SPACR and SPACRCAN, respectively, which are the main components of the interphotoreceptor matrix (IPM), the extracellular matrix surrounding the photoreceptor cells. To determine the role of SPACR in the pathological mechanisms leading to RP and VMD, we generated a knockout mouse model lacking Impg1, the mouse ortholog. Impg1-deficient mice show abnormal accumulation of autofluorescent deposits visible by fundus imaging and spectral-domain optical coherence tomography (SD-OCT) and attenuated electroretinogram responses from 9 months of age. Furthermore, SD-OCT of Impg1-/- mice shows a degeneration of the photoreceptor layer, and transmission electron microscopy shows a disruption of the IPM and the retinal pigment epithelial cells. The decrease in the concentration of the chromophore 11-cis-retinal supports this loss of photoreceptors. In conclusion, our results demonstrate the essential role of SPACR in maintaining photoreceptors. Impg1-/- mice provide a novel model for mechanistic investigations and the development of therapies for VMD and RP caused by IMPG1 pathogenic variants.

Formulation and Evaluation of SNEDDS Loaded with Original Lipophenol for the Oral Route to Prevent Dry AMD and Stragardt's Disease.

Dry age-related macular degeneration (Dry AMD) and Stargardt's disease (STGD1) are common eye diseases, characterized by oxidative and carbonyl stress (COS)-inducing photoreceptor degeneration and vision loss. Previous studies have demonstrated the protective effect of photoreceptors after the intravenous administration of a new lipophenol drug, phloroglucinol-isopropyl-DHA (IP-DHA). In this study, we developed an oral formulation of IP-DHA (BCS Class IV) relying on a self-nanoemulsifying drug delivery system (SNEDDS). SNEDDS, composed of Phosal® 53 MCT, Labrasol®, and Transcutol HP® at a ratio of 25/60/15 (w/w/w), led to a homogeneous nanoemulsion (NE) with a mean size of 53.5 ± 4.5 nm. The loading of IP-DHA in SNEDDS (SNEDDS-IP-DHA) was successful, with a percentage of IP-DHA of 99.7% in nanoemulsions. The in vivo study of the therapeutic potency of SNEDDS-IP-DHA after oral administration on mice demonstrated photoreceptor protection after the induction of retinal degeneration with acute light stress (73-80%) or chronic light stress (52-69%). Thus, SNEDDS formulation proved to increase the solubility of IP-DHA, improving its stability in intestinal media and allowing its passage through the intestinal barrier after oral force-fed administration, while maintaining its biological activity. Therefore, SNEDDS-IP-DHA is a promising future preventive treatment for dry AMD and STGD1.

Endogenous Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Plays a Protective Effect Against Noise-Induced Hearing Loss.

Pituitary adenylyl cyclase-activating polypeptide (PACAP) is a member of the vasoactive intestinal polypeptide (VIP)-the secretin-glucagon family of neuropeptides. They act through two classes of receptors: PACAP type 1 (PAC1) and type 2 (VPAC1 and VPAC2). Among their pleiotropic effects throughout the body, PACAP functions as neuromodulators and neuroprotectors, rescuing neurons from apoptosis, mostly through the PAC1 receptor. To explore the potential protective effect of endogenous PACAP against Noise-induced hearing loss (NIHL), we used a knockout mouse model lacking PAC1 receptor expression (PACR1-/-) and a transgenic humanized mouse model expressing the human PAC1 receptor (TgHPAC1R). Based on complementary approaches combining electrophysiological, histochemical, and molecular biological evaluations, we show PAC1R expression in spiral ganglion neurons and in cochlear apical cells of the organ of Corti. Wild-type (WT), PAC1R-/-, and TgHPAC1R mice exhibit similar auditory thresholds. For most of the frequencies tested after acute noise damage, however, PAC1R-/- mice showed a larger elevation of the auditory threshold than did their WT counterparts. By contrast, in a transgene copy number-dependent fashion, TgHPAC1R mice showed smaller noise-induced elevations of auditory thresholds compared to their WT counterparts. Together, these findings suggest that PACAP could be a candidate for endogenous protection against noise-induced hearing loss.

Retinitis Punctata Albescens and RLBP1-Allied Phenotypes: Phenotype-Genotype Correlation and Natural History in the Aim of Gene Therapy.

Purpose: To identify relevant criteria for gene therapy based on clinical and genetic characteristics of rod-cone dystrophy associated with RLBP1 pathogenic variants in a large cohort comprising children and adults. Design: Retrospective cohort study. Participants: Patients with pathogenic variants in RLBP1 registered in a single French reference center specialized in inherited retinal dystrophies. Methods: Clinical, multimodal imaging, and genetic findings were reviewed. Main Outcome Measures: Age of onset; visual acuity; ellipsoid line length; nasal, temporal, and foveal retinal thickness; and pathogenic variants and related phenotypes, including Newfoundland rod-cone and Bothnia dystrophies (NFRCDs), were reappraised. Results: Twenty-one patients (15 families) were included. The most frequent form was NFRCD with 12 patients (8 families) homozygous for the recurrent deletion of exons 7 through 9 in RLBP1 and 5 patients (4 families) with biallelic protein-truncating variants (2 novel: p.Gln16∗ and p.Tyr251∗). A novel combination of the p.Arg234Trp Bothnia variant with a nonsense variant in trans led to Bothnia dystrophy in 2 sisters. One proband carrying the p.Met266Lys Bothnia variant and in trans p.Arg121Trp and a second, with the p.Arg9Cys and p.Tyr111∗ combination, both demonstrated mild retinitis punctata albescens. Independently of genotype, all patients showed a visual acuity of worse than 20/200, an ellipsoid line width of less than 1000 µm, and a mean foveal thickness of less than 130 to 150 µm, with loss of both the interdigitation and ellipsoid lines. Conclusions: The eligibility for RLBP1 gene therapy first should be determined according to the biallelic variant combination using a robust classification as proposed herein. An ellipsoid line width of more than 1200 µm and a central thickness of more than 130 to 150 µm with detectable ellipsoid and interdigitation lines should be 2 prerequisite imaging indicators for gene therapy.

New lipophenols prevent carbonyl and oxidative stresses involved in macular degeneration.

Dry age-related macular degeneration and Stargardt disease undergo a known toxic mechanism caused by carbonyl and oxidative stresses (COS). This is responsible for accumulation in the retinal pigment epithelium (RPE) of A2E, a main toxic pyridinium bis-retinoid lipofuscin component. Previous studies have shown that carbonyl stress in retinal cells could be reduced by an alkyl-phloroglucinol-DHA conjugate (lipophenol). Here, we performed a rational design of different families of lipophenols to conserve anti-carbonyl stress activities and improve antioxidant properties. Five synthetic pathways leading to alkyl-(poly)phenol derivatives, with phloroglucinol, resveratrol, catechin and quercetin as the main backbone, linked to poly-unsaturated fatty acid, are presented. These lipophenols were evaluated in ARPE-19 cell line for their anti-COS properties and a structure-activity relationship study is proposed. Protection of ARPE-19 cells against A2E toxicity was assessed for the four best candidates. Finally, interesting anti-COS properties of the most promising quercetin lipophenol were confirmed in primary RPE cells.

Preclinical pharmacology of a lipophenol in a mouse model of light-induced retinopathy.

Environmental light has deleterious effects on the outer retina in human retinopathies, such as ABCA4-related Stargardt's disease and dry age-related macular degeneration. These effects involve carbonyl and oxidative stress, which contribute to retinal cell death and vision loss. Here, we used an albino Abca4-/- mouse model, the outer retina of which shows susceptibility to acute photodamage, to test the protective efficacy of a new polyunsaturated fatty acid lipophenol derivative. Anatomical and functional analyses demonstrated that a single intravenous injection of isopropyl-phloroglucinol-DHA, termed IP-DHA, dose-dependently decreased light-induced photoreceptor degeneration and preserved visual sensitivity. This protective effect persisted for 3 months. IP-DHA did not affect the kinetics of the visual cycle in vivo or the activity of the RPE65 isomerase in vitro. Moreover, IP-DHA administered by oral gavage showed significant protection of photoreceptors against acute light damage. In conclusion, short-term tests in Abca4-deficient mice, following single-dose administration and light exposure, identify IP-DHA as a therapeutic agent for the prevention of retinal degeneration.

Advanced late-onset retinitis pigmentosa with dominant-acting D477G RPE65 mutation is responsive to oral synthetic retinoid therapy.

OBJECTIVES: No therapeutic interventions are currently available for autosomal dominant retinitis pigmentosa (adRP). An RPE65 Asp477Gly transition associates with late-onset adRP, reduced RPE65 enzymatic activity being one feature associated with this dominant variant. Our objective: to assess whether in a proof-of-concept study, oral synthetic 9 cis-retinyl acetate therapy improves vision in such advanced disease. METHODS AND ANALYSIS: A phase 1b proof-of-concept clinical trial was conducted involving five patients with advanced disease, aged 41-68 years. Goldmann visual fields (GVF) and visual acuities (VA) were assessed for 6-12 months after 7-day treatment, patients receiving consecutive oral doses (40 mg/m2) of 9-cis-retinyl acetate, a synthetic retinoid replacement. RESULTS: Pathological effects of D477G variant were preliminarily assessed by electroretinography in mice expressing AAV-delivered D477G RPE65, by MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxyme- thoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] assays on RPE viability and enzyme activity in cultured cells. In addition to a mild dominant effect reflected in reduced electroretinographics in mice, and reduced cellular function in vitro, D477G exhibited reduced enzymatic RPE65 activity in vitro. In patients, significant improvements were observed in GVF from baseline ranging from 70% to 200% in three of five subjects aged 67-68 years, with largest improvements at 7-10 months. Of two GVF non-responders, one had significant visual acuity improvement (5-15 letters) from baseline after 6 months. CONCLUSION: Families with D477G variant have been identified in Ireland, the UK, France, the USA and Canada. Effects of single 7-day oral retinoid supplementation lasted at least 6 months, possibly giving visual benefit throughout remaining life in patients with advanced disease, where gene therapy is unlikely to prove beneficial.

Isopropyl-phloroglucinol-DHA protects outer retinal cells against lethal dose of all-trans-retinal.

All-trans-retinal (atRAL) is a highly reactive carbonyl specie, known for its reactivity on cellular phosphatidylethanolamine in photoreceptor. It is generated by photoisomerization of 11-cis-retinal chromophore linked to opsin by the Schiff's base reaction. In ABCA4-associated autosomal recessive Stargardt macular dystrophy, atRAL results in carbonyl and oxidative stress, which leads to bisretinoid A2E, accumulation in the retinal pigment epithelium (RPE). This A2E-accumulation presents as lipofuscin fluorescent pigment, and its photooxidation causes subsequent damage. Here we describe protection against a lethal dose of atRAL in both photoreceptors and RPE in primary cultures by a lipidic polyphenol derivative, an isopropyl-phloroglucinol linked to DHA, referred to as IP-DHA. Next, we addressed the cellular and molecular defence mechanisms in commonly used human ARPE-19 cells. We determined that both polyunsaturated fatty acid and isopropyl substituents bond to phloroglucinol are essential to confer the highest protection. IP-DHA responds rapidly against the toxicity of atRAL and its protective effect persists. This healthy effect of IP-DHA applies to the mitochondrial respiration. IP-DHA also rescues RPE cells subjected to the toxic effects of A2E after blue light exposure. Together, our findings suggest that the beneficial role of IP-DHA in retinal cells involves both anti-carbonyl and anti-oxidative capacities.

Bis-allylic Deuterated DHA Alleviates Oxidative Stress in Retinal Epithelial Cells.

Oxidative stress plays a crucial role in developing and accelerating retinal diseases including age-related macular degeneration (AMD). Docosahexaenoic acid (DHA, C22:6, n-3), the main lipid constituent of retinal epithelial cell membranes, is highly prone to radical and enzymatic oxidation leading to deleterious or beneficial metabolites for retinal tissue. To inhibit radical oxidation while preserving enzymatic metabolism, deuterium was incorporated at specific positions of DHA, resulting in D2-DHA when incorporated at position 6 and D4-DHA when incorporated at the 6,9 bis-allylic positions. Both derivatives were able to decrease DHAs' toxicity and free radical processes involved in lipid peroxidation, in ARPE-19 cells (Adult Retinal Pigment Epithelial cell line), under pro-oxidant conditions. Our positive results encouraged us to prepare lipophenolic-deuterated-DHA conjugates as possible drug candidates for AMD treatment. These novel derivatives proved efficient in limiting lipid peroxidation in ARPE-19 cells. Finally, we evaluated the underlying mechanisms and the enzymatic conversion of both deuterated DHA. While radical abstraction was affected at the deuterium incorporation sites, enzymatic conversion by the lipoxygenase 15s-LOX was not impacted. Our results suggest that site-specifically deuterated DHA could be used in the development of DHA conjugates for treatment of oxidative stress driven diseases, or as biological tools to study the roles, activities and mechanisms of DHA metabolites.

Natural models for retinitis pigmentosa: progressive retinal atrophy in dog breeds.

Retinitis pigmentosa (RP) is a heterogeneous group of inherited retinal disorders eventually leading to blindness with different ages of onset, progression and severity. Human RP, first characterized by the progressive degeneration of rod photoreceptor cells, shows high genetic heterogeneity with more than 90 genes identified. However, about one-third of patients have no known genetic causes. Interestingly, dogs are also severely affected by similar diseases, called progressive retinal atrophy (PRA). Indeed, RP and PRA have comparable clinical signs, physiopathology and outcomes, similar diagnosis methods and most often, orthologous genes are involved. The many different dog PRAs often segregate in specific breeds. Indeed, undesired alleles have been selected and amplified through drastic selection and excessive use of inbreeding. Out of the 400 breeds, nearly 100 have an inherited form of PRA, which are natural animal models that can be used to investigate the genetics, disease progression and therapies in dogs for the benefit of both dogs and humans. Recent knowledge on the canine genome and access to new genotyping and sequencing technologies now efficiently allows the identification of mutations involved in canine genetic diseases. To date, PRA genes identified in dog breeds correspond to the same genes in humans and represent relevant RP models, and new genes found in dogs represent good candidate for still unknown human RP. We present here a review of the main advantages of the dog models for human RP with the genes already identified and an X-linked PRA in the Border collie as a model for orphan X-linked RPs in human.

New Lipophenol Antioxidants Reduce Oxidative Damage in Retina Pigment Epithelial Cells.

Age-related macular degeneration (AMD) is a multifactorial pathology and its progression is exacerbated by oxidative stress. Oxidation and photo-oxidation reactions modify lipids in retinal cells, contribute to tissue injury, and lead to the formation of toxic adducts. In particular, autofluorescent pigments such as N-retinylidene-N-retinylethanolamine (A2E) accumulate as lipofuscin in retinal pigment epithelial cells, contribute to the production of additional reactive oxygen species (ROS), and lead to cell degeneration. In an effort to develop efficient antioxidants to reduce damage caused by lipid oxidation, various natural polyphenols were structurally modified to increase their lipophilicity (lipophenols). In this study, resveratrol, phloroglucinol, quercetin and catechin were selected and conjugated to various polyunsaturated fatty acids (PUFAs) using classical chemical strategies or enzymatic reactions. After screening for cytotoxicity, the capacity of the synthesized lipophenols to reduce ROS production was evaluated in ARPE-19 cells subjected to H2O2 treatment using a dichlorofluorescein diacetate probe. The positions of the PUFA on the polyphenol core appear to influence the antioxidant effect. In addition, two lipophenolic quercetin derivatives were evaluated to highlight their potency in protecting ARPE-19 cells against A2E photo-oxidation toxicity. Quercetin conjugated to linoleic or α-linolenic acid were promising lipophilic antioxidants, as they protected ARPE-19 cells from A2E-induced cell death more effectively than the parent polyphenol, quercetin.

Physiological and pathological roles of FATP-mediated lipid droplets in Drosophila and mice retina.

Increasing evidence suggests that dysregulation of lipid metabolism is associated with neurodegeneration in retinal diseases such as age-related macular degeneration and in brain disorders such as Alzheimer's and Parkinson's diseases. Lipid storage organelles (lipid droplets, LDs), accumulate in many cell types in response to stress, and it is now clear that LDs function not only as lipid stores but also as dynamic regulators of the stress response. However, whether these LDs are always protective or can also be deleterious to the cell is unknown. Here, we investigated the consequences of LD accumulation on retinal cell homeostasis under physiological and stress conditions in Drosophila and in mice. In wild-type Drosophila, we show that dFatp is required and sufficient for expansion of LD size in retinal pigment cells (RPCs) and that LDs in RPCs are required for photoreceptor survival during aging. Similarly, in mice, LD accumulation induced by RPC-specific expression of human FATP1 was non-toxic and promoted mitochondrial energy metabolism in RPCs and non-autonomously in photoreceptor cells. In contrast, the inhibition of LD accumulation by dFatp knockdown suppressed neurodegeneration in Aats-metFB Drosophila mutants, which carry elevated levels of reactive oxygen species (ROS). This suggests that abnormal turnover of LD may be toxic for photoreceptors cells of the retina under oxidative stress. Collectively, these findings indicate that FATP-mediated LD formation in RPCs promotes RPC and neuronal homeostasis under physiological conditions but could be deleterious for the photoreceptors under pathological conditions.

Fatty acid transport protein 1 regulates retinoid metabolism and photoreceptor development in mouse retina.

In retinal pigment epithelium (RPE), RPE65 catalyzes the isomerization of all-trans-retinyl fatty acid esters to 11-cis-retinol in the visual cycle and controls the rhodopsin regeneration rate. However, the mechanisms by which these processes are regulated are still unclear. Fatty Acid Transport Protein 1 (FATP1) is involved in fatty acid uptake and lipid metabolism in a variety of cell types. FATP1 co-localizes with RPE65 in RPE and inhibits its isomerase activity in vitro. Here, we further investigated the role of FATP1 in the visual cycle using transgenic mice that overexpress human FATP1 specifically in the RPE (hFATP1TG mice). The mice displayed no delay in the kinetics of regeneration of the visual chromophore 11-cis-retinal after photobleaching and had no defects in light sensitivity. However, the total retinoid content was higher in the hFATP1TG mice than in wild type mice, and the transgenic mice also displayed an age-related accumulation (up to 40%) of all-trans-retinal and retinyl esters that was not observed in control mice. Consistent with these results, hFATP1TG mice were more susceptible to light-induced photoreceptor degeneration. hFATP1 overexpression also induced an ~3.5-fold increase in retinosome autofluorescence, as measured by two-photon microscopy. Interestingly, hFATP1TG retina contained ~25% more photoreceptor cells and ~35% longer outer segments than wild type mice, revealing a non-cell-autonomous effect of hFATP1 expressed in the RPE. These data are the first to show that FATP1-mediated fatty acid uptake in the RPE controls both retinoid metabolism in the outer retina and photoreceptor development.

Phloroglucinol protects retinal pigment epithelium and photoreceptor against all-trans-retinal-induced toxicity and inhibits A2E formation.

Among retinal macular diseases, the juvenile recessive Stargardt disease and the age-related degenerative disease arise from carbonyl and oxidative stresses (COS). Both stresses originate from an accumulation of all-trans-retinal (atRAL) and are involved in bisretinoid formation by condensation of atRAL with phosphatidylethanolamine (carbonyl stress) in the photoreceptor and its transformation into lipofuscin bisretinoids (oxidative stress) in the retinal pigment epithelium (RPE). As atRAL and bisretinoid accumulation contribute to RPE and photoreceptor cell death, our goal is to select powerful chemical inhibitors of COS. Here, we describe that phloroglucinol, a natural phenolic compound having anti-COS properties, protects both rat RPE and mouse photoreceptor primary cultures from atRAL-induced cell death and reduces hydrogen peroxide (H2 O2 )-induced damage in RPE in a dose-dependent manner. Mechanistic analyses demonstrate that the protective effect encompasses decrease in atRAL-induced intracellular reactive oxygen species and free atRAL levels. Moreover, we show that phloroglucinol reacts with atRAL to form a chromene adduct which prevents bisretinoid A2E synthesis in vitro. Taken together, these data show that the protective effect of phloroglucinol correlates with its ability to trap atRAL and to prevent its further transformation into deleterious bisretinoids. Phloroglucinol might be a good basis to develop efficient therapeutic derivatives in the treatment of retinal macular diseases.

A truncated form of rod photoreceptor PDE6 ß-subunit causes autosomal dominant congenital stationary night blindness by interfering with the inhibitory activity of the γ-subunit.

Autosomal dominant congenital stationary night blindness (adCSNB) is caused by mutations in three genes of the rod phototransduction cascade, rhodopsin (RHO), transducin α-subunit (GNAT1), and cGMP phosphodiesterase type 6 ß-subunit (PDE6B). In most cases, the constitutive activation of the phototransduction cascade is a prerequisite to cause adCSNB. The unique adCSNB-associated PDE6B mutation found in the Rambusch pedigree, the substitution p.His258Asn, leads to rod photoreceptors desensitization. Here, we report a three-generation French family with adCSNB harboring a novel PDE6B mutation, the duplication, c.928-9_940dup resulting in a tyrosine to cysteine substitution at codon 314, a frameshift, and a premature termination (p.Tyr314Cysfs*50). To understand the mechanism of the PDE6ß1-314fs*50 mutant, we examined the properties of its PDE6-specific portion, PDE6ß1-313. We found that PDE6ß1-313 maintains the ability to bind noncatalytic cGMP and the inhibitory γ-subunit (Pγ), and interferes with the inhibition of normal PDE6αß catalytic subunits by Pγ. Moreover, both truncated forms of the PDE6ß protein, PDE6ß1-313 and PDE6ß1-314fs*50 expressed in rods of transgenic X. laevis are targeted to the phototransduction compartment. We hypothesize that in affected family members the p.Tyr314Cysfs*50 change results in the production of the truncated protein, which binds Pγ and causes constitutive activation of the phototransduction thus leading to the absence of rod adaptation.

Mutations in IMPG1 cause vitelliform macular dystrophies.

Vitelliform macular dystrophies (VMD) are inherited retinal dystrophies characterized by yellow, round deposits visible upon fundus examination and encountered in individuals with juvenile Best macular dystrophy (BMD) or adult-onset vitelliform macular dystrophy (AVMD). Although many BMD and some AVMD cases harbor mutations in BEST1 or PRPH2, the underlying genetic cause remains unknown for many affected individuals. In a large family with autosomal-dominant VMD, gene mapping and whole-exome sequencing led to the identification of a c.713T>G (p.Leu238Arg) IMPG1 mutation, which was subsequently found in two other families with autosomal-dominant VMD and the same phenotype. IMPG1 encodes the SPACR protein, a component of the rod and cone photoreceptor extracellular matrix domains. Structural modeling indicates that the p.Leu238Arg substitution destabilizes the conserved SEA1 domain of SPACR. Screening of 144 probands who had various forms of macular dystrophy revealed three other IMPG1 mutations. Two individuals from one family affected by autosomal-recessive VMD were homozygous for the splice-site mutation c.807+1G>T, and two from another family were compound heterozygous for the mutations c.461T>C (p.Leu154Pro) and c.1519C>T (p.Arg507(∗)). Most cases had a normal or moderately decreased electrooculogram Arden ratio. We conclude that IMPG1 mutations cause both autosomal-dominant and -recessive forms of VMD, thus indicating that impairment of the interphotoreceptor matrix might be a general cause of VMD.

The human OPA1delTTAG mutation induces premature age-related systemic neurodegeneration in mouse.

Dominant optic atrophy is a rare inherited optic nerve degeneration caused by mutations in the mitochondrial fusion gene OPA1. Recently, the clinical spectrum of dominant optic atrophy has been extended to frequent syndromic forms, exhibiting various degrees of neurological and muscle impairments frequently found in mitochondrial diseases. Although characterized by a specific loss of retinal ganglion cells, the pathophysiology of dominant optic atrophy is still poorly understood. We generated an Opa1 mouse model carrying the recurrent Opa1(delTTAG) mutation, which is found in 30% of all patients with dominant optic atrophy. We show that this mouse displays a multi-systemic poly-degenerative phenotype, with a presentation associating signs of visual failure, deafness, encephalomyopathy, peripheral neuropathy, ataxia and cardiomyopathy. Moreover, we found premature age-related axonal and myelin degenerations, increased autophagy and mitophagy and mitochondrial supercomplex instability preceding degeneration and cell death. Thus, these results support the concept that Opa1 protects against neuronal degeneration and opens new perspectives for the exploration and the treatment of mitochondrial diseases.