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After integrating classic and cutting-edge research, we proposed a unified model that attempts to explain the key steps of mammalian retinal neurogenesis. We proposed that the Notch signaling-induced lateral inhibition mechanism promotes oscillatory expression of Hes1. Oscillating Hes1 inhibitory activity as a result leads to oscillatory expression of Notch signaling inhibitors, activators/inhibitors of retinal neuronal phenotypes, and cell cycle-promoting genes all within a retinal progenitor cell (RPC). We provided a mechanism explaining not only how oscillatory expression prevents the progenitor-to-precursor transition, but also how this transition happens. Our proposal of the mechanism posits that the levels of the above factors not only oscillate but also rise (with the exception of Hes1) as the factors accumulate within a progenitor. Depending on which factors accumulate fastest and reach the required supra-threshold levels (cell cycle activators or Notch signaling inhibitors), the progenitor either proliferates or begins to differentiate without any further proliferation when Notch signaling ceases. Thus, oscillatory gene expression may regulate an RPC's decision to proliferate or differentiate. Meanwhile, a post-mitotic precursor's selection of one retinal neuronal phenotype over many others depends on the expression level of key transcription factors (activators) required for each of these retinal neuronal phenotypes. Because the events described above are stochastic due to oscillatory gene expression and gene product inheritance from a mother RPC after its division, an RPC or precursor's decision requires the assignment of probabilities to specific outcomes in the selection process. While low and sustained (non-oscillatory) Notch signaling activity is required to promote the transition of retinal progenitors into various retinal neuronal phenotypes, we propose that the lateral inhibition mechanism, combined with high expression of the BMP signaling-induced Inhibitor of Differentiation (ID) protein family, promotes high and sustained (non-oscillatory) Hes1 and Hes5 expression. These events facilitate the transition of an RPC into the Müller glia (MG) phenotype at the late stage of retinal development.

Background Choroideremia is an X-linked chorioretinal dystrophy with well-characterized progression in affected males but variable phenotypes in female carriers. Understanding the phenotypic spectrum in female carriers is important for prognosis, monitoring, and trial design. This study aims to delineate the natural history of retinal phenotypes and visual function loss in female choroideremia carriers and establish an improved fundus grading system for disease stratification and prognostic prediction. Methods This single-center, longitudinal and cross-sectional, retrospective study included 64 genetically confirmed female choroideremia carriers. Clinical data included genotype, age, best-corrected visual acuity, color fundus photography, fundus autofluorescence, visual field testing, and full-field electroretinography. A novel fundus phenotypic grading system was proposed based on fundus autofluorescence and fundus color photographs, which included four types: granular (merged fine/coarse patterns), severe peripapillary atrophy (highlighting severe peripapillary atrophy as a crucial feature), localized atrophy, and widespread atrophy. The agreement between measurement-based grading and visual grading was assessed. Results Visual acuity and fundus phenotypes showed moderate interocular symmetry, while visual field and electroretinography metrics showed high interocular symmetry. At baseline, phenotypes included granular (76.3%), severe peripapillary atrophy (7.5%), localized atrophy (10.8%), and widespread atrophy (5.4%). Longitudinally, the granular type remained stable, while other types progressed, with a mean atrophy expansion rate of 3.1 mm 2 /year. Age did not correlate with visual function decline, and neither age nor genotype was linked to the severe fundus phenotype. Baseline phenotype was the strongest predictor of prognosis. Excellent agreement (weighted κ = 0.93) was observed between the measurement-based and visual grading methods. Conclusions We proposed a novel fundus grading system for choroideremia carriers and demonstrated its strong clinical utility and prognostic value. The granular type confers a favorable prognosis, whereas the other three types exhibit progressive deterioration. Baseline phenotypic grading is the best indicator of long-term outcomes, underscoring its value in clinical monitoring and therapeutic trial design.

We sought to delineate the retinal features associated with the high-fat diet (HFD) mouse, a widely used model of obesity. C57BL/6 mice were fed either a high-fat (60% fat; HFD) or low-fat (10% fat; LFD) diet for up to 12 months. The effect of HFD on body weight and insulin resistance were measured. The retina was assessed by electroretinogram (ERG), fundus photography, permeability studies, and trypsin digests for enumeration of acellular capillaries. The HFD cohort experienced hypercholesterolemia when compared to the LFD cohort, but not hyperglycemia. HFD mice developed a higher body weight (60.33 g vs. 30.17g, p < 0.0001) as well as a reduced insulin sensitivity index (9.418 vs. 62.01, p = 0.0002) compared to LFD controls. At 6 months, retinal functional testing demonstrated a reduction in a-wave and b-wave amplitudes. At 12 months, mice on HFD showed evidence of increased retinal nerve infarcts and vascular leakage, reduced vascular density, but no increase in number of acellular capillaries compared to LFD mice. In conclusion, the HFD mouse is a useful model for examining the effect of prediabetes and hypercholesterolemia on the retina. The HFD-induced changes appear to occur slower than those observed in type 2 diabetes (T2D) models but are consistent with other retinopathy models, showing neural damage prior to vascular changes.

Background Posterior cortical atrophy (PCA) is the most common atypical variant of Alzheimer's disease (AD). Changes associated with PCA in the brain affect the visual cortex, but little is known about retinal changes in PCA. In this study, we explored retinal phenotypic variations in typical AD (tAD) and PCA. Methods Retinal phenotyping was carried out on ultra‐widefield (UWF) images of 69 control, 24 tAD, and 25 PCA participants. Results Individuals with tAD (odds ratio [OR] = 2.76 [confidence interval (CI):1.24 to 6.10], P = .012) and PCA (OR = 3.40 [CI:1.25 to 9.22], P = .016) were more likely phenotyped as hard drusen. tAD (OR = 0.34 [CI:0.12 to 0.92], P = .035) were less likely to have soft drusen compared to control. Almost 3‐fold increase in reticular pseudodrusen formation in tAD (OR = 2.93 [CI:1.10 to 7.76], P = .030) compared to control was estimated. Discussion Studying the peripheral retina may contribute to a better understanding of differences in retinal phenotypes of different AD variants. Workflow for the Retinal phenotyping of variants of Alzheimer's disease using ultra widefield retinal images study.

Purpose: To describe the genotype and phenotype in a 9-year-old boy with bilateral retinopathy. Methods: The patient, his healthy (by history) nonconsanguineous parents and his sister were examined by best-corrected visual acuity, matrix frequency doubling technology, monocular static field analysis, fundus autofluorescence imaging, optical coherence tomography, Ganzfeld electroretinography (ERG), pattern ERG, multifocal ERG, electro-oculography and genotyping of the BEST1 gene. Results: The patient presented with an Arden ratio of 1.25, an unremarkable ERG and fluorescent yellow deposits distributed throughout the fundus suggestive of autosomal recessive bestrophinopathy (ARB). Genotyping revealed a homozygous nonsense mutation in BEST1 (p.R200X). The parents and the sister, who were heterozygous mutation carriers, presented with normal ophthalmological function. Conclusions: ARB is a rare retinal disorder. We contribute a novel patient report indicative of ARB, assessed by clinical examination and confirmed by genotyping of BEST1, to the short list of ARB cases in the literature.

The majority of inherited retinal degenerations converge on the phenotype of photoreceptor cell death. Second- and third-order neurons are spared in these diseases, making it possible to restore retinal light responses using optogenetics. Viral expression of channelrhodopsin in the third-order neurons under ubiquitous promoters was previously shown to restore visual function, albeit at light intensities above illumination safety thresholds. Here, we report (to our knowledge, for the first time) activation of macaque retinas, up to 6 months post-injection, using channelrhodopsin-Ca2+-permeable channelrhodopsin (CatCh) at safe light intensities. High-level CatCh expression was achieved due to a new promoter based on the regulatory region of the gamma-synuclein gene (SNCG) allowing strong expression in ganglion cells across species. Our promoter, in combination with clinically proven adeno-associated virus 2 (AAV2), provides CatCh expression in peri-foveolar ganglion cells responding robustly to light under the illumination safety thresholds for the human eye. On the contrary, the threshold of activation and the proportion of unresponsive cells were much higher when a ubiquitous promoter (cytomegalovirus [CMV]) was used to express CatCh. The results of our study suggest that the inclusion of optimized promoters is key in the path to clinical translation of optogenetics. Vision restoration using microbial opsins has substantial clinical potential; however, it requires high-level expression of a foreign protein in the patient’s eyes. Our study shows the feasibility of obtaining safe and functional expression in primates using a cell-specific promoter and provides the basis for further clinical development of this optogenetic strategy.

The rd6 mouse model, characterized by retinal degeneration due to an Mfrp mutation, has been widely studied. However, we identified a subset of rd6 mice that developed severe non-rhegmatogenous retinal detachment (rd6-RD), suggesting the presence of additional genetic factors. This study aimed to characterize the retinal phenotype of rd6-RD mice and identify potential causative genetic mutations. We performed optical coherence tomography, fundus imaging, electroretinography, and histological analysis to compare retinal structures and functions between rd6, rd6-RD, and C57BL/6J mice. Whole-genome sequencing was conducted to identify potential mutations associated with the retinal detachment phenotype. Optical coherence tomography revealed retinal detachment in rd6-RD mice as early as 4 weeks old, with complete loss of the outer nuclear layer by 6 weeks. Fundus examination at 11 weeks showed pale fundi and narrowed, whitened retinal vessels in rd6-RD mice, distinct from rd6 mice. On electroretinography, rd6-RD mice displayed significantly diminished a- and b-wave amplitudes, with no detectable responses by 10 weeks. Histological analysis confirmed severe outer retinal degeneration and disappearance of the outer layers in rd6-RD mice. Whole-genome sequencing identified a missense R560C mutation in Pde6b, corresponding to the Pde6brd10 mutation, in rd6-RD mice. A subset of rd6 mice exhibited severe retinal detachment and outer retinal degeneration, distinct from the previously characterized Mfrp-related phenotype. The identification of the Pde6brd10 mutation suggests that these mice possess a dual-mutant genotype (Mfrprd6 and Pde6brd10), exacerbating retinal degeneration. These findings highlight the importance of genetic verification in commercially available mouse models and provide new insights into the genetic complexity of inherited retinal degenerations.

Inherited retinal dystrophies (IRDs) are a group of clinically and genetically heterogeneous degenerative disorders. To date, mutations have been associated with IRDs in over 270 disease genes, but molecular diagnosis still remains elusive in about a third of cases. The methodologic developments in genome sequencing techniques that we have witnessed in this last decade have represented a turning point not only in diagnosis and prognosis but, above all, in the identification of new therapeutic perspectives. The discovery of new disease genes and pathogenetic mechanisms underlying IRDs has laid the groundwork for gene therapy approaches. Several clinical trials are ongoing, and the recent approval of Luxturna, the first gene therapy product for Leber congenital amaurosis, marks the beginning of a new era. Due to its anatomical and functional characteristics, the retina is the organ of choice for gene therapy, although there are quite a few difficulties in the translational approaches from preclinical models to humans. In the first part of this review, an overview of the current knowledge on methodological issues and future perspectives of gene therapy applied to IRDs is discussed; in the second part, the state of the art of clinical trials on the gene therapy approach in IRDs is illustrated.

Retinal disease and loss of vision can result from any disruption of the complex pathways controlling retinal development and homeostasis. Forward genetics provides an excellent tool to find, in an unbiased manner, genes that are essential to these processes. Using N-ethyl-N-nitrosourea mutagenesis in mice in combination with a screening protocol using optical coherence tomography (OCT) and automated meiotic mapping, we identified 11 mutations presumably causative of retinal phenotypes in genes previously known to be essential for retinal integrity. In addition, we found multiple statistically significant gene-phenotype associations that have not been reported previously and decided to target one of these genes, Sfxn3 (encoding sideroflexin-3), using CRISPR/Cas9 technology. We demonstrate, using OCT, light microscopy, and electroretinography, that two Sfxn3−/− mouse lines developed progressive and severe outer retinal degeneration. Electron microscopy showed thinning of the retinal pigment epithelium and disruption of the external limiting membrane. Using single-cell RNA sequencing of retinal cells isolated from C57BL/6J mice, we demonstrate that Sfxn3 is expressed in several bipolar cell subtypes, retinal ganglion cells, and some amacrine cell subtypes but not significantly in Müller cells or photoreceptors. In situ hybridization confirmed these findings. Furthermore, pathway analysis suggests that Sfxn3 may be associated with synaptic homeostasis. Importantly, electron microscopy analysis showed disruption of synapses and synaptic ribbons in the outer plexiform layer of Sfxn3−/− mice. Our work describes a previously unknown requirement for Sfxn3 in retinal function.

Senescent cells contribute to degenerative processes in multiple tissues, including the retina. In the retinal pigment epithelium (RPE), their accumulation is closely associated with retinal aging and disease progression. Eliminating senescent RPE cells has shown therapeutic potential, but conventional senolytics often lack the specificity required to spare non-senescent cells, raising safety concerns. To overcome this, we performed integrated transcriptomic analyses of male mouse-derived RPE cells under natural aging and chemically induced senescence conditions. These analyses identified Bst2 as a membrane-localized marker selectively upregulated in senescent RPE cells, with minimal expression in young controls. Based on this discovery, we developed a modular, antibody-pluggable drug delivery platform–B-Z-PON–comprising mesoporous silica nanoparticles functionalized with a recombinant Fc-binding domain and conjugated with anti-Bst2 antibodies. This nanocarrier selectively accumulates in Bst2-expressing senescent RPE cells, enabling targeted drug delivery and sparing healthy retinal cells. In vivo administration of ABT-263-loaded B-Z-PON in aged and senescence-induced retinal degeneration models resulted in the selective ablation of senescent cells, restoration of RPE function, and improved visual outcomes. Together, our study integrates senescence-specific marker discovery with precision nanomedicine, establishing a versatile platform for targeted senotherapy. These findings offer a promising therapeutic approach for retinal aging disorders, such as age-related macular degeneration. Accumulation of senescent retinal pigment epithelial (RPE) cells is associated with retinal aging and disease. Here, authors identify Bst2 as a membrane-localized marker upregulated in senescent RPE cells and develop an antibody-pluggable drug delivery platform targeting Bst2-expressing cells for targeted senotherapy.