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The Journal of Neuroscience : the... May 2024The canonical visual cycle employing RPE65 as the retinoid isomerase regenerates 11--retinal to support both rod- and cone-mediated vision. Mutations of are associated...
The canonical visual cycle employing RPE65 as the retinoid isomerase regenerates 11--retinal to support both rod- and cone-mediated vision. Mutations of are associated with Leber congenital amaurosis (LCA) that results in rod and cone photoreceptor degeneration and vision loss of affected patients at an early age. Dark-reared mouse has been known to form isorhodopsin that employs 9--retinal as the photosensitive chromophore. The mechanism regulating 9--retinal synthesis and the role of the endogenous 9--retinal in cone survival and function remain largely unknown. In the present study, we found that ablation of fatty acid transport protein-4 (FATP4), a negative regulator of 11--retinol synthesis catalyzed by RPE65, increased the formation of 9--retinal, but not 11--retinal, in a light-independent mechanism in both sexes of RPE65-null 12 mice. Both 12 and 12; mice contained a massive amount of all--retinyl esters in the eyes, exhibited comparable scotopic vision and rod degeneration. However, expression levels of M- and S-opsins as well as numbers of M- and S-cones surviving in the superior retinas of 12; mice were at least 2-fold greater than those in age-matched 12 mice. Moreover, FATP4-deficiency significantly shortened photopic -wave implicit time, improved M-cone visual function and substantially deaccelerated the progression of cone degeneration in 12 mice, whereas FATP4-deficiency in mice with wild-type alleles neither induced 9--retinal formation nor influenced cone survival and function. These results identify FATP4 as a new regulator of synthesis of 9--retinal, which is a "cone-tropic" chromophore supporting cone survival and function in the retinas with defective RPE65. Isorhodopsin, which employs 9--retinal as the light-sensitive chromophore, is known to support rod survival and function in dark-reared mouse model of LCA that exhibits early cone degeneration. The mechanism regulating 9--retinal formation and the role of 9--retinal in cone survival remain largely unknown. Here, we identified FATP4 as a new negative regulator of 9--retinal synthesis in RPE65-null mice. We further found that increased 9--retinal synthesis did not influence rod function and degeneration, but it significantly enhanced cone survival and function in mice lacking both RPE65 and FATP4. Our findings indicate that 9--retinal functions as a "cone-tropic" chromophore, providing 9--retinal and FATP4 as important therapeutic targets to alleviate cone degeneration and loss of daytime color vision in RPE65 mutation-associated LCA.
PubMed: 38811164
DOI: 10.1523/JNEUROSCI.1994-23.2024 -
Proceedings. Biological Sciences May 2024The ambient daylight variation is coded by melanopsin photoreceptors and their luxotonic activity increases towards midday when colour temperatures are cooler, and...
The ambient daylight variation is coded by melanopsin photoreceptors and their luxotonic activity increases towards midday when colour temperatures are cooler, and irradiances are higher. Although melanopsin and cone photoresponses can be mediated via separate pathways, the connectivity of melanopsin cells across all levels of the retina enables them to modify cone signals. The downstream effects of melanopsin-cone interactions on human vision are however, incompletely understood. Here, we determined how the change in daytime melanopsin activation affects the human cone pathway signals in the visual cortex. A 5-primary silent-substitution method was developed to evaluate the dependence of cone-mediated signals on melanopsin activation by spectrally tuning the lights and stabilizing the rhodopsin activation under a constant cone photometric luminance. The retinal (white noise electroretinogram) and cortical responses (visual evoked potential) were simultaneously recorded with the photoreceptor-directed lights in 10 observers. By increasing the melanopsin activation, a reverse response pattern was observed with cone signals being supressed in the retina by 27% ( = 0.03) and subsequently amplified by 16% ( = 0.01) as they reach the cortex. We infer that melanopsin activity can amplify cone signals at sites distal to retinal bipolar cells to cause a decrease in the psychophysical Weber fraction for cone vision.
Topics: Humans; Rod Opsins; Retinal Cone Photoreceptor Cells; Visual Cortex; Adult; Electroretinography; Evoked Potentials, Visual; Female; Male; Young Adult; Photic Stimulation
PubMed: 38808443
DOI: 10.1098/rspb.2023.2708 -
Cells May 2024Vision starts in retinal photoreceptors when specialized proteins (opsins) sense photons via their covalently bonded vitamin A derivative 11cis retinaldehyde...
Vision starts in retinal photoreceptors when specialized proteins (opsins) sense photons via their covalently bonded vitamin A derivative 11cis retinaldehyde (11cis-RAL). The reaction of non-enzymatic aldehydes with amino groups lacks specificity, and the reaction products may trigger cell damage. However, the reduced synthesis of 11cis-RAL results in photoreceptor demise and suggests the need for careful control over 11cis-RAL handling by retinal cells. This perspective focuses on retinoid(s) synthesis, their control in the adult retina, and their role during retina development. It also explores the potential importance of 9cis vitamin A derivatives in regulating retinoid synthesis and their impact on photoreceptor development and survival. Additionally, recent advancements suggesting the pivotal nature of retinoid synthesis regulation for cone cell viability are discussed.
Topics: Animals; Humans; Retina; Retinal Diseases; Retinaldehyde; Retinoids; Vitamin A
PubMed: 38786093
DOI: 10.3390/cells13100871 -
BioRxiv : the Preprint Server For... Apr 2024Many inherited retinal diseases target photoreceptors, which transduce light into a neural signal that is processed by the downstream visual system. As photoreceptors...
Many inherited retinal diseases target photoreceptors, which transduce light into a neural signal that is processed by the downstream visual system. As photoreceptors degenerate, physiological and morphological changes to retinal synapses and circuitry reduce sensitivity and increase noise, degrading visual signal fidelity. Here, we pharmacologically targeted the first synapse in the retina in an effort to reduce circuit noise without sacrificing visual sensitivity. We tested a strategy to partially replace the neurotransmitter lost when photoreceptors die with an agonist of receptors that ON bipolars cells use to detect glutamate released from photoreceptors. In mice, which express a photoreceptor mutation that causes retinitis pigmentosa (RP), we found that a low dose of the mGluR6 agonist l-2-amino-4-phosphonobutyric acid (L-AP4) reduced pathological noise induced by photoreceptor degeneration. After making electroretinogram recordings in mice to characterize the developmental time course of visual signal degeneration, we examined effects of L-AP4 on sensitivity and circuit noise by recording light-evoked responses from individual retinal ganglion cells (RGCs). L-AP4 decreased circuit noise evident in RGC recordings without significantly reducing response amplitudes, an effect that persisted over the entire time course of rod photoreceptor degeneration. Subsequent recordings from rod bipolar cells (RBCs) showed that RBCs are more depolarized in retinas, likely contributing to downstream circuit noise and reduced synaptic gain, both of which appear to be ameliorated by hyperpolarizing RBCs with L-AP4. These beneficial effects may reduce pathological circuit remodeling and preserve the efficacy of therapies designed to restore vision.
PubMed: 38746092
DOI: 10.1101/2024.04.30.591881 -
Proceedings of the National Academy of... May 2024Congenital stationary night blindness (CSNB) is an inherited retinal disease that causes a profound loss of rod sensitivity without severe retinal degeneration. One...
Congenital stationary night blindness (CSNB) is an inherited retinal disease that causes a profound loss of rod sensitivity without severe retinal degeneration. One well-studied rhodopsin point mutant, G90D-Rho, is thought to cause CSNB because of its constitutive activity in darkness causing rod desensitization. However, the nature of this constitutive activity and its precise molecular source have not been resolved for almost 30 y. In this study, we made a knock-in (KI) mouse line with a very low expression of G90D-Rho (equal in amount to ~0.1% of normal rhodopsin, WT-Rho, in WT rods), with the remaining WT-Rho replaced by REY-Rho, a mutant with a very low efficiency of activating transducin due to a charge reversal of the highly conserved ERY motif to REY. We observed two kinds of constitutive noise: one being spontaneous isomerization (R*) of G90D-Rho at a molecular rate (R* s) 175-fold higher than WT-Rho and the other being G90D-Rho-generated dark continuous noise comprising low-amplitude unitary events occurring at a very high molecular rate equivalent in effect to ~40,000-fold of R* s from WT-Rho. Neither noise type originated from G90D-Opsin because exogenous 11--retinal had no effect. Extrapolating the above observations at low (0.1%) expression of G90D-Rho to normal disease exhibited by a KI mouse model with and genotypes predicts the disease condition very well quantitatively. Overall, the continuous noise from G90D-Rho therefore predominates, constituting the major equivalent background light causing rod desensitization in CSNB.
Topics: Animals; Night Blindness; Eye Diseases, Hereditary; Mice; Rhodopsin; Genetic Diseases, X-Linked; Myopia; Retinal Rod Photoreceptor Cells; Darkness; Transducin; Gene Knock-In Techniques; Disease Models, Animal
PubMed: 38743626
DOI: 10.1073/pnas.2404763121 -
ELife May 2024The retina consumes massive amounts of energy, yet its metabolism and substrate exploitation remain poorly understood. Here, we used a murine explant model to manipulate...
The retina consumes massive amounts of energy, yet its metabolism and substrate exploitation remain poorly understood. Here, we used a murine explant model to manipulate retinal energy metabolism under entirely controlled conditions and utilised H-NMR spectroscopy-based metabolomics, in situ enzyme detection, and cell viability readouts to uncover the pathways of retinal energy production. Our experimental manipulations resulted in varying degrees of photoreceptor degeneration, while the inner retina and retinal pigment epithelium were essentially unaffected. This selective vulnerability of photoreceptors suggested very specific adaptations in their energy metabolism. Rod photoreceptors were found to rely strongly on oxidative phosphorylation, but only mildly on glycolysis. Conversely, cone photoreceptors were dependent on glycolysis but insensitive to electron transport chain decoupling. Importantly, photoreceptors appeared to uncouple glycolytic and Krebs-cycle metabolism via three different pathways: (1) the mini-Krebs-cycle, fuelled by glutamine and branched chain amino acids, generating -acetylaspartate; (2) the alanine-generating Cahill-cycle; (3) the lactate-releasing Cori-cycle. Moreover, the metabolomics data indicated a shuttling of taurine and hypotaurine between the retinal pigment epithelium and photoreceptors, likely resulting in an additional net transfer of reducing power to photoreceptors. These findings expand our understanding of retinal physiology and pathology and shed new light on neuronal energy homeostasis and the pathogenesis of neurodegenerative diseases.
Topics: Animals; Glycolysis; Oxidative Phosphorylation; Mice; Citric Acid Cycle; Retina; Energy Metabolism; Metabolomics; Retinal Pigment Epithelium; Retinal Rod Photoreceptor Cells; Mice, Inbred C57BL; Retinal Cone Photoreceptor Cells
PubMed: 38739438
DOI: 10.7554/eLife.91141 -
Scientific Reports May 2024Prominin 1 (PROM1) is a pentaspan transmembrane glycoprotein localized on the nascent photoreceptor discs. Mutations in PROM1 are linked to various retinal diseases. In...
Prominin 1 (PROM1) is a pentaspan transmembrane glycoprotein localized on the nascent photoreceptor discs. Mutations in PROM1 are linked to various retinal diseases. In this study, we assessed the role of PROM1 in photoreceptor biology and physiology using the PROM1 knockout murine model (rd19). Our study found that PROM1 is essential for vision and photoreceptor development. We found an early reduction in photoreceptor response beginning at post-natal day 12 (P12) before eye opening in the absence of PROM1 with no apparent loss in photoreceptor cells. However, at this stage, we observed an increased glial cell activation, indicative of cell damage. Contrary to our expectations, dark rearing did not mitigate photoreceptor degeneration or vision loss in PROM1 knockout mice. In addition to physiological defects seen in PROM1 knockout mice, ultrastructural analysis revealed malformed outer segments characterized by whorl-like continuous membranes instead of stacked disks. In parallel to the reduced rod response at P12, proteomics revealed a significant reduction in the levels of protocadherin, a known interactor of PROM1, and rod photoreceptor outer segment proteins, including rhodopsin. Overall, our results underscore the indispensable role of PROM1 in photoreceptor development and maintenance of healthy vision.
Topics: Animals; Mice; AC133 Antigen; Mice, Knockout; Photoreceptor Cells, Vertebrate; Retinal Degeneration; Retinal Photoreceptor Cell Outer Segment; Retinal Rod Photoreceptor Cells; Rhodopsin
PubMed: 38714794
DOI: 10.1038/s41598-024-60989-5 -
PloS One 2024Though rod and cone photoreceptors use similar phototransduction mechanisms, previous model calculations have indicated that the most important differences in their...
Though rod and cone photoreceptors use similar phototransduction mechanisms, previous model calculations have indicated that the most important differences in their light responses are likely to be differences in amplification of the G-protein cascade, different decay rates of phosphodiesterase (PDE) and pigment phosphorylation, and different rates of turnover of cGMP in darkness. To test this hypothesis, we constructed TrUx;GapOx rods by crossing mice with decreased transduction gain from decreased transducin expression, with mice displaying an increased rate of PDE decay from increased expression of GTPase-activating proteins (GAPs). These two manipulations brought the sensitivity of TrUx;GapOx rods to within a factor of 2 of WT cone sensitivity, after correcting for outer-segment dimensions. These alterations did not, however, change photoreceptor adaptation: rods continued to show increment saturation though at a higher background intensity. These experiments confirm model calculations that rod responses can mimic some (though not all) of the features of cone responses after only a few changes in the properties of transduction proteins.
Topics: Animals; Retinal Cone Photoreceptor Cells; Retinal Rod Photoreceptor Cells; Mice; Transducin; Retina; Phosphoric Diester Hydrolases
PubMed: 38709779
DOI: 10.1371/journal.pone.0300584 -
Ophthalmic Research 2024Retinitis pigmentosa (RP), a heterogeneous inherited retinal disorder causing gradual vision loss, affects over 1 million people worldwide. Pathogenic variants in CNGA1...
INTRODUCTION
Retinitis pigmentosa (RP), a heterogeneous inherited retinal disorder causing gradual vision loss, affects over 1 million people worldwide. Pathogenic variants in CNGA1 and CNGB1 genes, respectively, accounting for 1% and 4% of cases, impact the cyclic nucleotide-gated channel in rod photoreceptor cells. The aim of this study was to describe and compare genotypic and clinical characteristics of a cohort of patients with CNGA1- or CNGB1-related RP and to explore potential genotype-phenotype correlations.
METHODS
The following data from patients with CNGA1- or CNGB1-related RP, followed in five Italian inherited retinal degenerations services, were retrospectively collected: genetic variants in CNGA1 and CNGB1, best-corrected visual acuity (BCVA), ellipsoid zone (EZ) width, fundus photographs, and short-wavelength fundus autofluorescence (SW-AF) images. Comparisons and correlation analyses were performed by first dividing the cohort in two groups according to the gene responsible for the disease (CNGA1 and CNGB1 groups). In parallel, the whole cohort of RP patients was divided into two other groups, according to the expected impact of the variants at protein level (low and high group).
RESULTS
In total, 29 patients were recruited, 11 with CNGA1- and 18 with CNGB1-related RP. In both CNGA1 and CNGB1, 5 novel variants in CNGA1 and 5 in CNGB1 were found. BCVA was comparable between CNGA1 and CNGB1 groups, as well as between low and high groups. CNGA1 group had a larger mean EZ width compared to CNGB1 group, albeit not statistically significant, while EZ width did not differ between low and high groups A statistically significant correlation between EZ width and BCVA as well as between EZ width and age were observed in the whole cohort of RP patients. Fundus photographs of all patients in the cohort showed classic RP pattern, and in SW-AF images an hyperautofluorescent ring was observed in 14/21 patients.
CONCLUSION
Rod CNG channel-associated RP was demonstrated to be a slowly progressive disease in both CNGA1- and CNGB1-related forms, making it an ideal candidate for gene augmentation therapies.
Topics: Humans; Retinitis Pigmentosa; Male; Female; Cyclic Nucleotide-Gated Cation Channels; Retrospective Studies; Middle Aged; Adult; Visual Acuity; Phenotype; Genotype; Young Adult; Adolescent; Electroretinography; Tomography, Optical Coherence; Aged; Mutation; Child; Retinal Rod Photoreceptor Cells; Fluorescein Angiography; Genetic Association Studies; DNA Mutational Analysis; Pedigree; DNA
PubMed: 38705136
DOI: 10.1159/000538746 -
Brain Structure & Function Jun 2024β-synuclein, a member of the synuclein family, is frequently co-expressed with α-synuclein in the neural system, where it serves to inhibit abnormal aggregation of...
β-synuclein, a member of the synuclein family, is frequently co-expressed with α-synuclein in the neural system, where it serves to inhibit abnormal aggregation of α-synuclein in neurodegenerative diseases. Beyond its role in pathological conditions, β-synuclein plays various functions independently of α-synuclein. In our investigation, we discovered a broader expression of β-synuclein in the mouse retina compared to α-synuclein. This widespread pattern implies its potential significance in the retina. Through detailed examination via light- and electron-microscopic immunocytochemistry, we identified β-synuclein expression from the inner segment (IS) and outer segment (OS) of photoreceptor cells to the ganglion cell layer (GCL). Our findings unveiled unique features, including β-synuclein immunoreactive IS and OS of cones, higher expression in cone pedicles than in rod spherules, absence in horizontal cells, limited expression in cone bipolar dendrites and somas, higher expression in cone bipolar terminals, presence in most amacrine cells, and expression in almost majority of somas in GCL with an absence in intrinsically photosensitive retinal ganglion cell (ipRGCs) processes. Notably, all cholinergic amacrine cells express high β- but not α-synuclein, while dopaminergic amacrine cells express α-synuclein exclusively. These distinctive expression patterns offer valuable insights for further exploration into the functions of β-synuclein and its potential role in synuclein pathology within the retina.
Topics: Animals; Male; Mice; alpha-Synuclein; Amacrine Cells; beta-Synuclein; Mice, Inbred C57BL; Retina; Retinal Bipolar Cells; Retinal Ganglion Cells
PubMed: 38703218
DOI: 10.1007/s00429-024-02799-z