Primate Retina Research Articles

Is Angiostatin Involved in Physiological Foveal Avascularity?

The primate central retina is characterized by an avascular fovea and well-defined perifoveal capillary plexus. Neither blood vessels nor their accompanying astrocytes enter the fovea during any stage of retinal development; a balance of angiogenic and angiostatic factors probably maintains foveal avascularity throughout life. The aim of this study was to identify potentially angiorepulsive factors involved in the development of the avascular primate retinal fovea. Retinas of newborn, juvenile, and adult Callithrix jacchus and Macaca fascicularis monkeys and control human retinas were studied to determine the localization of angiostatin relative to III β-tubulin, glial fibrillary acidic protein, vascular endothelial growth factor (VEGF), platelet endothelial cell adhesion molecule-1 (PECAM), and the angiostatin receptor αvβ3-integrin in the foveal, macular, and peripheral retina. Expression studies were performed using immunohistochemistry (IHC) on retinal whole-mount and paraffin sections, and Western blotting on frozen material. The complex network of the main retinal cell types was identified by IHC of retinal whole mounts. In general, lifetime expression of angiostatin was found in all retinas. Colabeling with different markers revealed retinal ganglion cells as the main source of angiostatin expression in the primate retina, whereas PECAM-immunopositive blood capillaries expressed the angiostatin receptor αvβ3-integrin, and capillary-associated astrocytes expressed VEGF. This study provides the first evidence of angiostatin expression in the primate retina; the expression of angiostatin in the avascular foveal region and the peripheral retina suggests that angiostatin may play a role in the regulation of retinal vascularization, providing a possible explanation for the development and persistence of an avascular fovea.

Wide-field diffuse amacrine cells in the monkey retina contain immunoreactive Cocaine- and Amphetamine-Regulated Transcript (CART)

The goals of this study were to localize the neuropeptide Cocaine- and Amphetamine-Regulated Transcript (CART) in primate retinas and to describe the morphology, neurotransmitter content and synaptic connections of the neurons that contain it. Using in situ hybridization, light and electron microscopic immunolabeling, CART was localized to GABAergic amacrine cells in baboon retinas. The CART-positive cells had thin, varicose dendrites that gradually descended through the inner plexiform layer and ramified extensively in the innermost stratum. They resembled two types of wide-field diffuse amacrine cells that had been described previously in macaque retinas using the Golgi method and also A17, serotonin-accumulating and waterfall cells of other mammals. The CART-positive cells received synapses from rod bipolar cell axons and made synapses onto the axons in a reciprocal configuration. The CART-positive cells also received synapses from other amacrine cells. Some of these were located on their primary dendrites, and the presynaptic cells there included dopaminergic amacrine cells. Although some CART-positive somas were localized in the ganglion cell layer, they did not contain the ganglion cell marker RNA binding protein with multiple splicing (RBPMS). Based on these results and electrophysiological studies in other mammals, the CART-positive amacrine cells would be expected to play a major role in the primary rod pathway of primates, providing feedback inhibition to rod bipolar cells.

Highly Efficient Delivery of Adeno-Associated Viral Vectors to the Primate Retina.

Adeno-associated virus (AAV) has emerged as the preferred vector for targeting gene expression to the retina. Subretinally injected AAV can efficiently transduce retinal pigment epithelium and photoreceptors in primate retina. Inner and middle primate retina can be transduced by intravitreally delivered AAV, but with low efficiency. This is due to dilution of vector, potential neutralization of capsid because it is not confined to the immune-privileged retinal compartment, and the presence of the inner limiting membrane (ILM), a barrier separating the vitreous from the neural retina. We here describe a novel "subILM" injection method that addresses all three issues. Specifically, vector is placed in a surgically induced, hydrodissected space between the ILM and neural retina. In an initial experiment, we injected viscoelastic (Healon(®)), a substance we confirmed was biocompatible with AAV, to create a subILM bleb and subsequently injected AAV2-GFP into the bleb after irrigation with basic salt solution. For later experiments, we used a Healon-AAV mixture to place single, subILM injections. In all cases, subILM delivery of AAV was well tolerated-no inflammation or gross structural changes were observed by ophthalmological examination or optical coherence tomography. In-life fluorescence imaging revealed profound transgene expression within the area of the subILM injection bleb that persisted for the study duration. Uniform and extensive transduction of retinal ganglion cells (RGCs) was achieved in the areas beneath the subILM bleb. Transduction of Müller glia, ON bipolar cells, and photoreceptors was also observed. Robust central labeling from green fluorescent protein-expressing RGCs confirmed their continued survival, and was observed in the lateral geniculate nucleus, the superior colliculus, and the pretectum. Our results confirm that the ILM is a major barrier to transduction by AAV in primate retina and that, when it is circumvented, the efficiency and depth to which AAV2 promotes transduction of multiple retinal cell classes are greatly enhanced.

Neuroscience: Peeking Under the Sombrero

A recent study has introduced a new analytical approach to understanding neural circuits which has revealed previously hidden neural interactions in a large population of cells in the primate retina. The neural circuit described likely contributes to encoding visual motion.

Structure of the lutein-binding domain of human StARD3 at 1.74 Å resolution and model of a complex with lutein.

A crystal structure of the lutein-binding domain of human StARD3 (StAR-related lipid-transfer protein 3; also known as MLN64) has been refined to 1.74 Å resolution. A previous structure of the same protein determined to 2.2 Å resolution highlighted homology with StARD1 and shared cholesterol-binding character. StARD3 has since been recognized as a carotenoid-binding protein in the primate retina, where its biochemical function of binding lutein with specificity appears to be well suited to recruit this photoprotective molecule. The current and previous structures correspond closely to each other (r.m.s.d. of 0.25 Å), especially in terms of the helix-grip fold constructed around a solvent-filled cavity. Regions of interest were defined with alternate conformations in the current higher-resolution structure, including Arg351 found within the cavity and Ω1, a loop of four residues found just outside the cavity entrance. Models of the complex with lutein generated by rigid-body docking indicate that one of the ionone rings must protrude outside the cavity, and this insight has implications for molecular interactions with transport proteins and enzymes that act on lutein. Interestingly, models with the ℇ-ionone ring characteristic of lutein pointing towards the bottom of the cavity were associated with fewer steric clashes, suggesting that steric complementarity and ligand asymmetry may play a role in discriminating lutein from the other ocular carotenoids zeaxanthin and meso-zeaxanthin, which only have β-ionone rings.

Characterization of C-terminal Splice Variants of Cav1.4 Ca2+ Channels in Human Retina

Voltage-gated Ca(2+) channels (Cav) undergo extensive alternative splicing that greatly enhances their functional diversity in excitable cells. Here, we characterized novel splice variants of the cytoplasmic C-terminal domain of Cav1.4 Ca(2+) channels that regulate neurotransmitter release in photoreceptors in the retina. These variants lack a portion of exon 45 and/or the entire exon 47 (Cav1.4Δex p45, Cav1.4Δex 47, Cav1.4Δex p45,47) and are expressed in the retina of primates but not mice. Although the electrophysiological properties of Cav1.4Δex p45 are similar to those of full-length channels (Cav1.4FL), skipping of exon 47 dramatically alters Cav1.4 function. Deletion of exon 47 removes part of a C-terminal automodulatory domain (CTM) previously shown to suppress Ca(2+)-dependent inactivation (CDI) and to cause a positive shift in the voltage dependence of channel activation. Exon 47 is crucial for these effects of the CTM because variants lacking this exon show intense CDI and activate at more hyperpolarized voltages than Cav1.4FL The robust CDI of Cav1.4Δex 47 is suppressed by CaBP4, a regulator of Cav1.4 channels in photoreceptors. Although CaBP4 enhances activation of Cav1.4FL, Cav1.4Δex 47 shows similar voltage-dependent activation in the presence and absence of CaBP4. We conclude that exon 47 encodes structural determinants that regulate CDI and voltage-dependent activation of Cav1.4, and is necessary for modulation of channel activation by CaBP4.

First insights into the expression of VAX2 in humans and its localization in the adult primate retina

VAX2 is a transcription factor specifically expressed in the ventral region of the prospective neural retina in vertebrates and is required for ventral eye specification. Despite its extensive analysis in vertebrates, the biological role of VAX2 in the human is presently unclear. This study was undertaken to investigate VAX2 in humans aiming to gain new knowledge into its involvement in retinal function. Here, we report VAX2 gene expression and protein localization in cultured cells and adult retina. RT-PCR experiments indicated that VAX2 is enriched in neuronal tissues. Moreover, we identified a novel isoform most abundantly expressed in the retina. We termed the known transcript (NM_012476) isoform-1, and the newly identified transcript as isoform-2. Analysis of protein localization in cultured cells revealed that isoform-1 localizes to the nucleus and isoform-2 is widely expressed within the cell; partial co-localization of isoform-2 and actin filaments was also observed. In nonhuman primate retina VAX2 was seen either in the nuclear or in the cytoplasmic compartment depending on the retinal cell type. In addition, a noteworthy enrichment of the signal was observed in the outer segment of cone photoreceptors.Overall, this study provides the first insights into the expression of VAX2 in humans and its localization in the adult primate retina. Moreover, preliminary characterization of alternative variants suggests an involvement of VAX2 in multiple cellular pathways. Our findings raise the interesting possibility for further investigation of VAX2 in the retina in health and disease.

Primate neural retina upregulates IL-6 and IL-10 in response to a herpes simplex vector suggesting the presence of a pro-/anti-inflammatory axis

Injection of herpes simplex virus vectors into the vitreous of primate eyes induces an acute, transient uveitis. The purpose of this study was to characterize innate immune responses of macaque neural retina tissue to the herpes simplex virus type 1-based gene delivery vector hrR3. PCR array analysis demonstrated the induction of the pro-inflammatory cytokine IL-6, as well as the anti-inflammatory cytokine IL-10, following hrR3 exposure. Secretion of IL-6 was detected by ELISA and cone photoreceptors and Muller cells were the predominant IL-6 positive cell types. RNA in situ hybridization confirmed that IL-6 was expressed in photoreceptor and Muller cells. The IL-10 positive cells in the inner nuclear layer were identified as amacrine cells by immunofluorescence staining with calretinin antibody. hrR3 challenge resulted in activation of NFκB (p65) in Muller glial cells, but not in cone photoreceptors, suggesting a novel regulatory mechanism for IL-6 expression in cone cells. hrR3 replication was not required for IL-6 induction or NFκB (p65) activation. These data suggest a pro-inflammatory (IL-6)/anti-inflammatory (IL-10) axis exists in neural retina and the severity of acute posterior uveitis may be determined by this interaction. Further studies are needed to identify the trigger for IL-6 and IL-10 induction and the mechanism of IL-6 induction in cone cells.

29. Novel Surgical Method for Intravitreal AAV Administration Overcomes Transduction Barriers in Non-Human Primates

Introduction For gene therapy applications in the primate retina, intravitreal injections (IVT) of adeno-associated virus (AAV) have been shown to target the retina inefficiently, mainly in retinal ganglion cells within a small perifoveal region. The internal limiting membrane (ILM) has been previously hypothesized to be a barrier to broader transduction. We further hypothesized that the local concentration and residence time of AAV at the vitreo-retinal interface was insufficient for efficient retinal transduction. Here, we investigate gene delivery to the retina in rhesus macaque with regular IVT injection as compared to a novel surgical technique “Peel and Puddle” aimed at overcoming these potential barriers. Methods Three eyes of rhesus macaques were injected with AAV-CMV-GFP via a traditional IVT at a concentration of 1E+11 particles (2/2 or Anc80 capsid). Another two eyes from different rhesus macaques had the ILM surgically removed followed by the concentrated application of AAV2 onto the peeled area, known as “Peel and Puddle” (PP), also at 1E+11 particles. The PP procedure consisted of a vitrectomy, posterior hyaloid separation, ILM staining and subsequent ILM peel over the majority of the macula. This was followed by fluid-air exchange, and deposition of the virus on the peeled area with 30 minutes of supine positioning generating a “puddle” onto the retina aimed at maximizing the AAV residence time at an undiluted concentration. Results GFP expression in the PP condition was dramatically greater than with a regular intravitreal injection, both in intensity and the region of transduction. In the PP eyes, fluorescence was noted in an area that matched the extent of the ILM peel and puddle, as shown by imaging and histology whereas traditional IVT demonstrated the expected parafoveal dim pattern of transduction. All eyes, irrespective of the type of IVT injection, presented clinically significant signs of inflammation, which was managed effectively by intravitreal steroid injections. Histological sections show increase microglia infiltration in both groups compared to un-injected controls. Conclusions The vitreous, ILM, and/or physical parameters of the vector delivery significantly limit gene transfer to the retina. Surgical minimization of these barriers demonstrated highly increased levels and distribution of transduction. Inflammation following intravitreal injection with a non-self transgene is of concern and requires further study.

31. AAV Gene Therapy for Choroideremia: Dose Determination Analyses

Choroideremia (CHM) is a degenerative, X-linked retinal disease characterized by deletions or mutations in the choroideremia (CHM) gene, resulting in defective or absent Rab escort protein-1 (REP-1). In normal retinas, the CHM gene is expressed in multiple cell types, including retinal pigment epithelium, photoreceptors, and choroidal cells, though there is evidence that the RPE cell is the primary disease-causing cell type. Absence or deficiency of REP-1 leads to cellular apoptosis and degeneration of the retinal pigment epithelium (RPE), choroid, and retinal photoreceptors. Choroideremia is an excellent disease candidate for gene transfer as it shares several key features with other inherited retinal degenerative diseases that are also candidates for AAV-mediated vector delivery. These features include: a) the small and localized nature of the target area, namely the retina; b) the tissue boundaries surrounding the area to be injected, which minimizes exposure of other cells to the vector and facilitates treatment with a relatively small vector dose; and c) the favorable immune status of the eye with respect to viral vector-mediated gene transfer. We are conducting a Phase 1 clinical trial to treat CHM subjects using either 5×1010 or 1×1011 vg/eye of an AAV2-hRep1 vector, and delivering the vector via a subretinal injection. Due to the lack of suitable animal models that mimic CHM disease in humans, we took a different approach to assess the potential therapeutic dose. A molecular analysis of non-human primate retinas was performed following subretinal injection of AAV2-hCHM to determine the relative amount of human Rep1 compared to endogenous monkey Rep1. Cynomolgus monkey eyes were injected subretinally with either 5×1011, 7.5×1011 or 2×1012 vg of AAV2-hRep1. Fundus images were taken following the injection of 300 ul of vector, and these images were used at the time of sacrifice to dissect the tissue associated with the injection bleb. The remaining retina was also collected and analyzed separately. RNA was isolated and absolute quantitative RT-PCR was performed using both cynomolgus monkey-specific Rep1 primers/probe and human Rep1-specific primers/probe. No human Rep1 mRNA was observed in non-injected eyes, and the amount of human Rep1 mRNA in the bleb area was determined to be at least 50 fold higher than cynomolgus Rep1 mRNA following a dose of 5×1011 vg/eye. At the two higher doses, similar levels of hRep1 mRNA, ranging from 270-380 times more than cynomolgus Rep1 mRNA, were observed. These data suggest that in the Phase 1 clinical trial, the low dose subjects (5×1010 vg/eye) will express hRep1 at a level approximately five fold higher than normal and the high dose subjects will express at least 10 fold higher levels of hRep1 than normal. Ongoing studies are evaluating the level of hRep1 in normal human retinas to confirm these ratios. Thus, the results from this non-conventional pharmacology model provide an estimate of the potential therapeutic dose of AAV2-hCHM for use in clinical studies.

Elevated Fundus Autofluorescence in Monkeys Deficient in Lutein, Zeaxanthin, and Omega-3 Fatty Acids.

PurposeWe quantified fundus autofluorescence (FAF) in the nonhuman primate retina as a function of age and diets lacking lutein and zeaxanthin (L/Z) and omega-3 fatty acids.MethodsQuantitative FAF was measured in a cross-sectional study of rhesus macaques fed a standard diet across the lifespan, and in aged rhesus macaques fed lifelong diets lacking L/Z and providing either adequate or deficient levels of omega-3 fatty acids. Macular FAF images were segmented into multiple regions of interest, and mean gray values for each region were calculated using ImageJ. The resulting FAF values were compared across ages within the standard diet animals, and among diet groups and regions.ResultsFundus autofluorescence increased with age in the standard diet animals, and was highest in the perifovea. Monkeys fed L/Z-free diets with either adequate or deficient omega-3 fatty acids had significantly higher FAF overall than age-matched standard diet monkeys. Examined by region, those with adequate omega-3 fatty acids had higher FAF in the fovea and superior regions, while monkeys fed the diet lacking L/Z and omega-3 fatty acids had higher FAF in all regions.ConclusionsDiets devoid of L/Z resulted in increased retinal autofluorescence, with the highest values in animals also lacking omega-3 fatty acids. The increase was equivalent to a 12- to 20-year acceleration in lipofuscin accumulation compared to animals fed a standard diet. Together these data add support for the role of these nutrients as important factors in lipofuscin accumulation, retinal aging, and progression of macular disease.

Two-Photon Autofluorescence Imaging Reveals Cellular Structures Throughout the Retina of the Living Primate Eye.

PurposeAlthough extrinsic fluorophores can be introduced to label specific cell types in the retina, endogenous fluorophores, such as NAD(P)H, FAD, collagen, and others, are present in all retinal layers. These molecules are a potential source of optical contrast and can enable noninvasive visualization of all cellular layers. We used a two-photon fluorescence adaptive optics scanning light ophthalmoscope (TPF-AOSLO) to explore the native autofluorescence of various cell classes spanning several layers in the unlabeled retina of a living primate eye.MethodsThree macaques were imaged on separate occasions using a custom TPF-AOSLO. Two-photon fluorescence was evoked by pulsed light at 730 and 920 nm excitation wavelengths, while fluorescence emission was collected in the visible range from several retinal layers and different locations. Backscattered light was recorded simultaneously in confocal modality and images were postprocessed to remove eye motion.ResultsAll retinal layers yielded two-photon signals and the heterogeneous distribution of fluorophores provided optical contrast. Several structural features were observed, such as autofluorescence from vessel walls, Müller cell processes in the nerve fibers, mosaics of cells in the ganglion cell and other nuclear layers of the inner retina, as well as photoreceptor and RPE layers in the outer retina.ConclusionsThis in vivo survey of two-photon autofluorescence throughout the primate retina demonstrates a wider variety of structural detail in the living eye than is available through conventional imaging methods, and broadens the use of two-photon imaging of normal and diseased eyes.

Prevalence and clinical impact of antiretinal antibodies in uveitis.

To determine the prevalence of serum antiretinal antibodies (ARAs) among patients with uveitis and establish their clinical relevance. This prospective study assessed the presence of ARAs by indirect immunofluorescence (IIF) using primate retina in 126 patients with uveitis and 60 healthy controls. Clinical data of uveitis patients were collected from medical charts and included the classification of uveitis, cause of uveitis or its association with systemic disease, stage and activity of uveitis and specific retinal features. Correlations between the presence of specific ARAs and various clinical characteristics were analysed. The presence of ARAs was observed in 49 of 104 (47%) of patients with uveitis and in 10 of 59 (17%) of healthy controls (p < 0.001). Staining of the nuclear layers or the photoreceptors were both more often observed in patients with uveitis compared to healthy controls (p = 0.002 and p = 0.018, respectively). No specific associations were found between the presence of serum ARAs and various clinical characteristics. Serum ARAs were more frequent in patients with uveitis compared to healthy controls, but their clinical role remains elusive. The assessment of intraocular production of specific ARAs may provide further insight into the role of ocular autoantibodies in diverse uveitis entities.

Mapping nonlinear receptive field structure in primate retina at single cone resolution.

The function of a neural circuit is shaped by the computations performed by its interneurons, which in many cases are not easily accessible to experimental investigation. Here, we elucidate the transformation of visual signals flowing from the input to the output of the primate retina, using a combination of large-scale multi-electrode recordings from an identified ganglion cell type, visual stimulation targeted at individual cone photoreceptors, and a hierarchical computational model. The results reveal nonlinear subunits in the circuity of OFF midget ganglion cells, which subserve high-resolution vision. The model explains light responses to a variety of stimuli more accurately than a linear model, including stimuli targeted to cones within and across subunits. The recovered model components are consistent with known anatomical organization of midget bipolar interneurons. These results reveal the spatial structure of linear and nonlinear encoding, at the resolution of single cells and at the scale of complete circuits.

Expression and distribution of peroxiredoxins in the retina and optic nerve.

Oxidative stress is implicated in various pathological conditions of the retina and optic nerve. Peroxiredoxins (Prdxs) comprise a recently characterized family of antioxidant enzymes. To date, little information exists regarding the distribution of Prdxs in the eye. Herein, we employed a combination of qRT-PCR, immunohistochemistry and Western blotting to determine the level of expression and distribution of the six Prdx isoforms in the retina and optic nerve of the rat. In addition, we performed some parallel analyses on the common marmoset (Callithrix Jacchus). In the rat, all of the Prdx transcripts were expressed in relatively high amounts in both retina and optic nerve, with abundances ranging from approximately 3–50 % of the level of the housekeeping gene cyclophilin. With regard to protein expression, each isoform was detected in the retina and optic nerve by either Western blotting and/or immunohistochemistry. Excepting Prdx4, there was a good correspondence between the rodent and primate results. In the retina, Prdx1 and Prdx2 were principally localized to neurons in the inner nuclear layer and cone photoreceptors, Prdx3 and Prdx5 displayed characteristic mitochondrial immunolabeling, while Prdx6 was associated with astrocytes and Müller cells. In the optic nerve, Prdx1 was robustly expressed by oligodendrocytes, Prdx3 and Prdx5 were observed in axons, and Prdx6 was restricted to astrocytes. The present findings augment our understanding of the distribution and expression of the Prdxs in the retina and optic nerve of rodents and primates and lay the foundation for subsequent analysis of their involvement in relevant blinding diseases.

Lutein and Brain Function.

Lutein is one of the most prevalent carotenoids in nature and in the human diet. Together with zeaxanthin, it is highly concentrated as macular pigment in the foveal retina of primates, attenuating blue light exposure, providing protection from photo-oxidation and enhancing visual performance. Recently, interest in lutein has expanded beyond the retina to its possible contributions to brain development and function. Only primates accumulate lutein within the brain, but little is known about its distribution or physiological role. Our team has begun to utilize the rhesus macaque (Macaca mulatta) model to study the uptake and bio-localization of lutein in the brain. Our overall goal has been to assess the association of lutein localization with brain function. In this review, we will first cover the evolution of the non-human primate model for lutein and brain studies, discuss prior association studies of lutein with retina and brain function, and review approaches that can be used to localize brain lutein. We also describe our approach to the biosynthesis of 13C-lutein, which will allow investigation of lutein flux, localization, metabolism and pharmacokinetics. Lastly, we describe potential future research opportunities.

Characterization of the Role of β-Carotene 9,10-Dioxygenase in Macular Pigment Metabolism

A family of enzymes collectively referred to as carotenoid cleavage oxygenases is responsible for oxidative conversion of carotenoids into apocarotenoids, including retinoids (vitamin A and its derivatives). A member of this family, the β-carotene 9,10-dioxygenase (BCO2), converts xanthophylls to rosafluene and ionones. Animals deficient in BCO2 highlight the critical role of the enzyme in carotenoid clearance as accumulation of these compounds occur in tissues. Inactivation of the enzyme by a four-amino acid-long insertion has recently been proposed to underlie xanthophyll concentration in the macula of the primate retina. Here, we focused on comparing the properties of primate and murine BCO2s. We demonstrate that the enzymes display a conserved structural fold and subcellular localization. Low temperature expression and detergent choice significantly affected binding and turnover rates of the recombinant enzymes with various xanthophyll substrates, including the unique macula pigment meso-zeaxanthin. Mice with genetically disrupted carotenoid cleavage oxygenases displayed adipose tissue rather than eye-specific accumulation of supplemented carotenoids. Studies in a human hepatic cell line revealed that BCO2 is expressed as an oxidative stress-induced gene. Our studies provide evidence that the enzymatic function of BCO2 is conserved in primates and link regulation of BCO2 gene expression with oxidative stress that can be caused by excessive carotenoid supplementation.

Is adding a new class of cones to the retina sufficient to cure color-blindness?

New genetic methods have made it possible to substitute cone pigments in the retinas of adult nonhuman primates. Doing so influences the animals' visual abilities, demonstrating that the gene therapy was effective. However, we argue that no studies conducted so far have unambiguously demonstrated that the experimental animals have also acquired the ability to make new color distinctions. Simply put, it has been shown that animals that underwent the gene treatment can now-in addition to finding a red ball on a grayish background-find a green ball on a grayish background. However, it has not been shown that the animals can distinguish a red ball from a green one. For most people, that essential ability would be the primary reason for wanting to undergo a treatment for color-blindness in the first place, for instance, because their color-blindness currently prevents them from pursuing a career as a pilot or firefighter. It is important to point out such possible limitations of gene therapy for color-blindness to avoid unwarranted expectations in both clinicians and patients. To explain the origin of our concerns, we simulate how replacing the pigment of some cones is expected to influence the outcomes on the behavioral test used so far. The simulations show that this test does not provide conclusive evidence that the animals acquired the ability to make new chromatic distinctions. In our view, it is therefore premature to claim that human color-blindness can be cured through gene therapy. We propose a test that would provide more conclusive evidence of fundamentally altered color vision after gene therapy.

Gene therapy in LHON

SummaryGene therapy is a promise for the treatment of Leber hereditary optic neuropathy (LHON). The techniques required for introducing genes into mitochondria have not yet been developed and allotopic expression is one means of circumventing this barrier. To ensure efficient mitochondrial uptake of the nuclear expressed mtDNA gene, the protein should have a mitochondrial targeting signal (MTS). We have optimized allotopic expression by targeting the mRNAs to the mitochondrial surface with a specific 3′UnTranslated Region (UTR) which can cooperate with the MTS for ensuring the localization of ND4 mRNA to the mitochondrial surface. After having collected data proving that an AAV2/2 vector carrying this therapeutic ND4 gene meets the criteria of robust, long‐duration gene expression, and safety in LHON rat model and non human primate retinas, we are leading a phase I/II, open‐label, prospective clinical trial with dose escalation, which intends to evaluate safety of this gene therapy administered in one single intravitreal (IVT) injection in humans with chronic ND4 LHON. Actually 9 patients were included and no SAE or treatment‐related systemic AE occurred. At last, we look forward to be successful in the generation of a treatment for patients suffering from ND4 LHON.

Neonatal aphakia is associated with altered levels of dopamine metabolites in the non-human primate retina

Neonatal aphakia is associated with retardation of the axial elongation of the neonatal eye. In contrast, form deprivation increases axial elongation, an effect that has been associated with decreased retinal dopamine metabolism. The present investigation was conducted to test the hypothesis that neonatal aphakia induces an effect on the levels of retinal dopamine opposite to form deprivation. Lensectomy and vitrectomy were performed on the right eyes of rhesus monkeys at approximately 1 week of age; their left eyes were unmanipulated. Axial length was measured by A-scan ultrasonography. Prior to surgery, mean axial length of the right and left eyes was identical. Following lens removal, both eyes continued to elongate, however the aphakic eyes elongated at a slower rate resulting in a significant shorter axial length compared to that of the unmanipulated eye. Removal of the crystalline lens had no effect on steady-state dopamine levels in either central or peripheral retina. However, levels of the dopamine metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid were significantly elevated in central retina, but not in the peripheral retina of aphakic eyes. Our results support the hypothesis that dopamine is a component of the retinal signaling pathways that are involved in the regulation of eye growth and emmetropization.