Retinitis Pigmentosa Research Articles

Phenotypic variability of RP1-related inherited retinal dystrophy associated with the c.5797 C > T (p.Arg1933*) variant in the Japanese population

The phenotypes of RP1-related inherited retinal dystrophies (RP1-IRD), causing autosomal dominant (AD) and autosomal recessive (AR) diseases, vary depending on specific RP1 variants. A common nonsense mutation near the C-terminus, c.5797 C > T (p.Arg1933*), is associated with RP1-IRD, but the exact role of this mutation in genotype-phenotype correlation remains unclear. In this study, we retrospectively analyzed patients with RP1-IRD (N = 42) from a single center in Japan. AR RP1-IRD patients with the c.5797 C > T mutation (N = 14) mostly displayed macular dystrophy but rarely retinitis pigmentosa or cone-rod dystrophy. Conversely, AR RP1-IRD patients without the c.5797 C > T mutation, including those with other pathogenic RP1 variants, were mostly diagnosed with severe retinitis pigmentosa. Full-field electroretinograms were significantly better in patients homozygous or compound heterozygous for the c.5797 C > T mutation than in those without this mutation, corresponding to their milder phenotypes. Clinical tests also revealed a slower onset of age and a better mean deviation value with the static visual field in AR RP1-IRD patients with the c.5797 C > T mutation compared to those without. Therefore, the presence of c.5797 C > T may partly account for the phenotypic variety of RP1-IRD and may yield milder phenotypes. These findings may be useful for predicting the prognosis of RP1-IRD patients.

Retinitis Pigmentosa Associated With EYS Gene Mutations in Puerto Rico: A Case Series

Retinitis Pigmentosa Associated With EYS Gene Mutations in Puerto Rico: A Case Series

Dynamics of clinical and immunological parameters in retinal pigment epithelium transplantation in the context of combined immunosuppressive therapy in the rabbit model of retinal degeneration

Progressive damage of the retinal pigment epithelium (RPE) underlies the pathogenesis of degenerative retinal diseases such as: age-related macular degeneration (AMD), Stargardt’s disease, retinitis pigmentosa, Best’s disease and others. This group of diseases led by AMD leads to irreversible loss of visual functions, blindness and disability. The possibilities of therapy of late stages of AMD are extremely limited. The most promising approach to replace the damaged retinal pigment epithelium appears to be transplantation of RPE cells derived from induced pluripotent stem cells (iPSC-RPE) into the subretinal space (SRS). Despite immune privilege in the SRS, transplantation of xenogeneic cellular material causes severe inflammation in the posterior segment of the eye and leads to graft rejection in an in vivo experiment in the absence of immunosuppression. The solution to the problem of tissue incompatibility in this case can be the use of combined immunosuppressive therapy (CIT), aimed, on the one hand, at suppression of local inflammation (in the eye) and, on the other hand, at suppression of the systemic transplantation immune response. The aim of the study: clinical and immunological analysis of the results of transplantation of IPSC-RPE suspension on the background of CIT, including single intravitreal intraoperative administration of kenalog and further systemic application of mycophenolate mofetil (MMF), in the model of RPE atrophy in rabbits. Standard and specialized ophthalmological examination was performed at early and distant terms after the intervention in order to clinically assess the posttransplantation process. To analyze the immune status, vitreous humor (VH) and blood serum (BS) of rabbits of the experimental groups were collected. The concentrations of TGF-β1, TGF-β2, and IL-2 were determined in the biomaterial using solid-phase enzyme immunoassay. According to the results of the study, subretinal transplantation of IPSC-RPE, performed against the background of combination of single intravitreal intraoperative administration of kenalog and systemic application of MMF, is a safe method, which provides preservation of the retina and other adjacent structures of the eye and allows to prevent rejection of xenogenic material during its transplantation both in a healthy eye and with pre-formed RPE atrophy, which opens perspectives for full testing of biological effects realized by IPSC-RPE.

A Leaky Deep Intronic Splice Variant in CLRN1 Is Associated with Non-Syndromic Retinitis Pigmentosa

Background: Inherited retinal diseases (IRDs) are clinically complex and genetically heterogeneous visual impairment disorders with varying penetrance and severity. Disease-causing variants in at least 289 nuclear and mitochondrial genes have been implicated in their pathogenesis. Methods: Whole exome sequencing results were analyzed using established pipelines and the results were further confirmed by Sanger sequencing and minigene splicing assay. Results: Exome sequencing in a 51-year-old Ashkenazi Jewish patient with non-syndromic retinitis pigmentosa (RP) identified compound heterozygous variants in the CLRN1 gene: a known pathogenic missense [p.(N48K)] and a novel deep intronic variant c.254-643G>T. A minigene splicing assay that was performed aiming to study the effect of the c.254-643G>T variant on CLRN1 pre-mRNA splicing revealed the inclusion of a pseudo-exon that was also reported to be included in the transcript due to an adjacent variant, c.254-649T>G. However, unlike the reported c.254-649T>G variant, c.254-643G>T showed aberrant splicing in a leaky manner, implying that the identified variant is not totally penetrant. Conclusion: We report on a novel deep intronic variant in CLRN1 causing non-syndromic RP. The non-syndromic phenotype observed in this index case may be attributed to the leaky nature of this variant, which is causing some normal transcripts to be produced.

Infantile Nystagmus Syndrome—Associated Inherited Retinal Diseases: Perspectives from Gene Therapy Clinical Trials

Inherited retinal diseases (IRDs) are a clinically and genetically diverse group of progressive degenerative disorders that can result in severe visual impairment or complete blindness. Despite their predominantly monogenic inheritance patterns, the genetic complexity of over 300 identified disease-causing genes presents a significant challenge in correlating clinical phenotypes with genotypes. Achieving a molecular diagnosis is crucial for providing patients with definitive diagnostic clarity and facilitating access to emerging gene-based therapies and ongoing clinical trials. Recent advances in next-generation sequencing technologies have markedly enhanced our ability to identify genes and genetic defects leading to IRDs, thereby propelling the development of gene-based therapies. The clinical success of voretigene neparvovec (Luxturna), the first approved retinal gene therapy for RPE65-associated Leber congenital amaurosis (LCA), has spurred considerable research and development in gene-based therapies, highlighting the importance of reviewing the current status of gene therapy for IRDs, particularly those utilizing adeno-associated virus (AAV)-based therapies. As novel disease-causing mutations continue to be discovered and more targeted gene therapies are developed, integrating these treatment opportunities into the standard care for IRD patients becomes increasingly critical. This review provides an update on the diverse phenotypic–genotypic landscape of IRDs, with a specific focus on recent advances in the understanding of IRDs in children with infantile nystagmus syndrome (INS). We highlight the complexities of the genotypic–phenotypic landscape of INS-associated IRDs, including conditions such as achromatopsia, LCA, congenital stationary night blindness, and subtypes of retinitis pigmentosa. Additionally, we provide an updated overview of AAV-based gene therapies for these diseases and discuss the potential of gene-based therapies for underlying IRDs that lead to INS, offering a valuable resource for pediatric patients potentially eligible for ongoing clinical trials.

Identification of novel 3D-genome altering and complex structural variants underlying retinitis pigmentosa type 17 through a multistep and high-throughput approach

IntroductionAutosomal dominant retinitis pigmentosa type 17 (adRP, type RP17) is caused by complex structural variants (SVs) affecting a locus on chromosome 17 (chr17q22). The SVs disrupt the 3D regulatory landscape by altering the topologically associating domain (TAD) structure of the locus, creating novel TAD structures (neo-TADs) and ectopic enhancer-gene contacts. Currently, screening for RP17-associated SVs is not included in routine diagnostics given the complexity of the variants and a lack of cost-effective detection methods. The aim of this study was to accurately detect novel RP17-SVs by establishing a systematic and efficient workflow.MethodsGenetically unexplained probands diagnosed with adRP (n = 509) from an international cohort were screened using a smMIPs or genomic qPCR-based approach tailored for the RP17 locus. Suspected copy number changes were validated using high-density SNP-array genotyping, and SV breakpoint characterization was performed by mutation-specific breakpoint PCR, genome sequencing and, if required, optical genome mapping. In silico modeling of novel SVs was performed to predict the formation of neo-TADs and whether ectopic contacts between the retinal enhancers and the GDPD1-promoter could be formed.ResultsUsing this workflow, potential RP17-SVs were detected in eight probands of which seven were confirmed. Two novel SVs were identified that are predicted to cause TAD rearrangement and retinal enhancer-GDPD1 contact, one from Germany (DE-SV9) and three with the same SV from the United States (US-SV10). Previously reported RP17-SVs were also identified in three Australian probands, one with UK-SV2 and two with SA-SV3.DiscussionIn summary, we describe a validated multi-step pipeline for reliable and efficient RP17-SV discovery and expand the range of disease-associated SVs. Based on these data, RP17-SVs can be considered a frequent cause of adRP which warrants the inclusion of RP17-screening as a standard diagnostic test for this disease.

Testing Visual Function by Assessment of the Optomotor Reflex in Glaucoma.

Optomotor response/reflex (OMR) is a fast and efficient first-in-line visual screening method, especially for rodents. It has the potential to evaluate both the scotopic and photopic visions of nonrestrained animals through tracking head movement, providing a quantitative estimate of visual functions. In restrained animals, optokinetic response (OKR), compensatory eye movements for visual shifts in the surroundings, is utilized. Both OMR and OKR capitalize on an individual's innate reflex to stabilize images for the purpose of capturing clear vision. The two reflexes have similar reliability when evaluating stimulus luminance, contrast, spatial frequency, and velocity. They have emerged as powerful tools to evaluate the efficacy of pharmacological treatments and phenotypes of subjects undergoing study. With OMR and OKR accurately assessing visual acuity (VA) as well as contrast sensitivity (CS), the gold standards for measuring clinical vision, they provide reliable and easily accessible results that further eye and brain research. These methods of sight evaluation have been used in multiple animal models, particularly mice and zebrafish. Through OMR assays, these animal models have been utilized to investigate retinal degenerative diseases, helping researchers differentiate between worsening stages. Alongside tests such as optical coherence tomography (OCT), OMR provides confirmation of visual status, where increased OMR function often correlates with improved visual status. OMR has continued to be used outside of glaucoma in various retinal diseases, such as retinitis pigmentosa (RP), diabetic retinopathy, and age-related macular degeneration.In this chapter, we will introduce the concept and application of visual stimulus-induced head or eye reflex movement in different animal species and experimental models of eye diseases, such as glaucoma and other neurodegenerative disorders, and in patients with glaucoma.

Lycium barbarum L. and Salvia miltiorrhiza Bunge extract ameliorates retinitis pigmentosa in rd10 mice by affecting endoplasmic reticulum stress

Ethnopharmacological relevanceLycium barbarum L. and Salvia miltiorrhiza Bunge (Gouqi and Danshen, LS) have led to their inclusion in the pharmacopoeia and healthcare systems of numerous countries globally. Traditional herbs known as LS are used in China to treat retinitis pigmentosa (RP). However, the mechanism is not clear. Aim of the studyThis study is to investigate the mechanism by which LS improves RP using rd10 mice as a model. Materials and methodsLS extract was used to treat the rd10 mice for four weeks. Fundus photographs, optical coherence tomography, electroretinography, histopathological examination, TUNEL apoptosis assay, digital PCR analysis, western blotting, and immunofluorescence double staining were performed. ResultsThe outer nuclear layer (ONL) thickness of the retina was significantly increased by the LS extract, improving atrophy, and both the ONL and the retinal pigment epithelium (RPE) layer were visible. Following treatment with LS extract, there was a notable increase in the magnitudes of ERG a- and b-waves in the retina, along with a significant reduction in the quantity of TUNEL-positive cells. Additionally, LS extract significantly reduced the levels of ER stress-related factors in rd10 mice. The results of immunofluorescence double staining further confirm that LS extract inhibits the GRP78/PERK/ATF4/CHOP pathway. ConclusionIn this study, the protective effects of LS extract on the retina were uncovered, suggesting that its mechanism could involve decreasing retinal cell apoptosis through the inhibition of the ER stress pathway.

CRISPR-Mediated Gene Editing Tool Development for Patients with Usher Syndrome Type II

Usher syndrome, a rare genetic disease affecting hearing and vision, is an autosomal recessive condition affecting 4 to 17 per 100,000 people and accounting for about 50 percent of hereditary deaf-blindness cases. Usher syndrome type II is caused by mutations of the USH2A gene, a 15.7 kb gene encoding the protein usherin, which localizes to photoreceptor cilium and cochlear hair cells. This subtype of Usher syndrome includes hearing loss from birth and progressive loss of vision, prompting retinitis pigmentosa (RP). Prime editing is a viable option for addressing USH2A mutations and restoring usherin expression and function. To begin, a HEK293T cell line needs to be established for subsequent testing of prime editors. Since prime editing to make the cell line was unsuccessful, homology-directed repair was done and successfully created a cell population with the mutation of interest (single base-pair deletion). Now that this cell population has been created, prime editors will be tested and optimized to address the mutation in a HEK293T cell line and potentially patient-derived induced pluripotent stem cells that are differentiated into photoreceptor precursor cells.

Multi-Characteristic Opsin Therapy to Functionalize Retina, Attenuate Retinal Degeneration, and Restore Vision in Mouse Models of Retinitis Pigmentosa.

Retinal degeneration 1 and 10 (rd1 and rd10) mice are useful animal models of retinitis pigmentosa (RP) with rapidly and slowly progressive pathologies, respectively. Our study aims were to determine the effect of adeno-associated viral vector 2 (AAV2)-delivered multi-characteristic opsin (MCO-010; under the control of a metabotropic glutamate receptor-6 promoter enhancer) on the morphological and functional characteristics of vision in both rd1 and rd10 mice. Various retinal measures of MCO-010 transduction and electrophysiological, behavioral, and other routine blood analyses were performed in the rd1 and/or rd10 mice after intravitreal injection of 1µL of MCO-010 or AAV2 vehicle. Functional tests included electroretinogram, visually evoked potential, and behavior assay (optomotor and water maze). Retinal thickness, intraocular pressure, and plasma cytokine levels were also determined. Following intravitreal MCO-010 injection, approximately 80% of bipolar cells were transduced in the retina, and no alterations in retinal thickness were observed at 4months post-injection. However, retinal thickness significantly decreased in control mice. MCO-010 treatment increased head movements and induced faster navigation of mice to the platform in a water-maze test. The MCO-010 gene therapy helped preserve visually evoked electrical response in the retina and visual cortex. No ocular toxicity, immunotoxicity, or phototoxicity was observed in the MCO-010-treated mice, even under chronic intense light conditions. Intravitreal MCO-010 was well tolerated in rd1 and rd10 mice models of RP, and it appeared to attenuate retinal photoreceptor degeneration based on retinal structure and functional outcome measures. As reported here, optogenetic treatment of the inner retina attenuates further retinal degeneration in addition to photosensitizing higher order neurons, and this disease-modifying aspect should be evaluated in optogenetic clinical trials.

PCDH15 Dual-AAV Gene Therapy for Deafness and Blindness in Usher Syndrome Type 1F Models.

Usher syndrome type 1F (USH1F), resulting from mutations in the protocadherin-15 (PCDH15) gene, is characterized by congenital lack of hearing and balance, and progressive blindness in the form of retinitis pigmentosa. In this study, we explore an approach for USH1F gene therapy, exceeding the single AAV packaging limit by employing a dual adeno-associated virus (AAV) strategy to deliver the full-length PCDH15 coding sequence. We demonstrate the efficacy of this strategy in mouse USH1F models, effectively restoring hearing and balance in these mice. Importantly, our approach also proves successful in expressing PCDH15 protein in clinically relevant retinal models, including human retinal organoids and non-human primate retina, showing efficient targeting of photoreceptors and proper protein expression in the calyceal processes. This research represents a major step toward advancing gene therapy for USH1F and the multiple challenges of hearing, balance, and vision impairment.

CRISPR/Cas9-mediated generation of a human induced pluripotent stem cell line with PRPF6 c.2699 G > A mutation to model retinitis pigmentosa

PRPF6, located on chromosome 20, is required for the formation of the spliceosome. Mutations in the PRPF6 gene can lead to retinitis pigmentosa (RP), a common inherited retinal disease characterized by progressive degeneration of retinal pigment epithelium and photoreceptors. Here, we generated an induced pluripotent stem cell (iPSC) line carrying the PRPF6 c.2699 G > A mutation using CRISPR/Cas9 technology, which will provide a valuable resource for RP pathogenesis and treatment research.

Retinal oxygen metabolic function in choroideremia and retinitis pigmentosa.

To measure the retinal oxygen metabolic function with retinal oximetry (RO) in patients with choroideremia (CHM) and compare these findings with retinitis pigmentosa (RP) patients and controls. Prospective observational study including 18 eyes of 9 molecularly confirmed CHM patients (9♂; 40.2 ± 21.2years (mean ± SD), 77 eyes from 39 patients with RP (15♀ 24♂; 45.6 ± 14.7years) and 100 eyes from 53 controls (31♀ 22♂; 40.2 ± 13.4years). Main outcome parameters were the mean arterial (A-SO2; %), venular (V-SO2; %) oxygen saturation, and their difference (A-V SO2; %) recorded with the oxygen saturation tool of the Retinal Vessel Analyzer (IMEDOS Systems UG, Germany). Statistical analyses were performed with linear mixed-effects models. Eyes suffering from CHM differed significantly from both RP and control eyes, when the retinal oxygen metabolic parameters were taken into account. While RP showed significantly higher A-SO2 and V-SO2 values when compared to controls, CHM showed opposite findings with significantly lower values when compared to both RP and controls (P < 0.001). The A-V SO2, which represents the retinal oxygen metabolic consumption, showed significantly lower values in CHM compared to controls. The retina in CHM is a relatively hypoxic environment. The decrease in oxygen levels may be due to the profound choroidal degeneration, leading to decreased oxygen flux to the retina. RO measurements may help understand the pathogenesis of CHM and RP. These findings may provide useful details to inform the planning of clinical trials of emerging therapies for CHM. What was known before? Retinal oxygen metabolic function measured with retinal oximetry (RO) shows significant alterations in patients with retinitis pigmentosa. RO function in choroideremia is significantly altered when compared to controls. Furthermore, RO in choroideremia shows opposing findings within different oxygen metabolic parameters to those that were so far known for retinitis pigmentosa. By providing insights into the retinal oxygen metabolic mechanisms, RO can help understand the underlying pathophysiology in choroideremia.

Delivering large genes using adeno-associated virus and the CRE-lox DNA recombination system.

Adeno-associated virus (AAV) is a safe and efficient gene delivery vehicle for gene therapies. However, its relatively small packaging capacity limits its use as a gene transfer vector. Here, we describe a strategy to deliver large genes that exceed the AAV's packaging capacity using up to four AAV vectors and the CRE-lox DNA recombination system. We devised novel lox sites by combining non-compatible and reaction equilibrium-modifying lox site variants. These lox sites facilitate sequence-specific and near-unidirectional recombination of AAV vector genomes, enabling efficient reconstitution of up to 16kb of therapeutic genes in a pre-determined configuration. Using this strategy, we have developed AAV gene therapy vectors to deliver IFT140, PCDH15, CEP290, and CDH23 and demonstrate efficient production of full-length proteins in cultured mammalian cells and mouse retinas. Notably, AAV-IFT140 gene therapy vectors ameliorated retinal degeneration and preserved visual functions in an IFT140-associated retinitis pigmentosa mouse model. The CRE-lox approach described here provides a simple, flexible, and effective platform for generating AAV gene therapy vectors beyond AAV's packaging capacity.

Hyperreflective ganglion cell layer band in a large cohort of non-syndromic retinitis pigmentosa: Frequency and clinical correlations.

Recently, an 'hyperreflective ganglion cell layer band' (HGB) has been described on spectral-domain optical coherence tomography (SD-OCT) in a subset of patients with retinitis pigmentosa (RP). This study aims to validate and describe the frequency of HGB in a large cohort of Portuguese patients with RP. This single-centre, cross-sectional cohort study included consecutive patients with a genetic diagnosis of RP. SD-OCT images were reviewed to identify the presence of the HGB and other retinal comorbidities. The HGB was defined as a continuous hyperreflective band within the thickness of the ganglion cell layer (GCL). We built mixed-effects regression models, accounting for inter-eye correlations, to investigate features predictive of visual acuity. Subsequently, a reduced model was fitted. A total of 398 eyes from 201 patients were included. HGB was identified in 69 (17.3%) eyes from 39 (19.4%) patients. Patients presenting with the HGB were significantly younger at diagnosis and at symptom onset. Median BCVA [ETDRS (IQR)] was 65 (29) letters in eyes with the HGB and 70 (21) letters in eyes without HGB (p < 0.001). In both the full and reduced mixed-effects models, the presence of HGB and macular hole (MH) was significantly associated with worse BCVA. This study validates the recent description of HGB within the GCL in a subset of patients with RP. Eyes with HGB demonstrated significantly worse BCVA compared to those without HGB, suggesting that the presence of HGB may serve as an SD-OCT biomarker of worse visual prognosis in these patients.

Risk and protective factors of late in-the-bag intraocular lens dislocations – a systematic review

Topic: This article aimed to identify and review published articles addressing risk and protective factors of late in-the-bag (ITB) intraocular lens (IOL) dislocations. Clinical relevance: Prevention of this complication is of great importance considering the great number of cataract cases and its vision threatening capacity. Methods: A structured search on PubMed (MEDLINE) using both Medical Subject Headings (MeSH) and key words was conducted. Additionally, the reference lists of the resulting articles were screened for further publications. Articles were eligible if they included 20 or more patients. Hazard and odds ratios were analyzed if they were calculated in the original study. The relative frequency of risk factors was recorded if hazard or odds ratios were not available. The threshold for clinical significance was set at 10%. Risk-of-bias in individual studies was evaluated using the revised Cochrane risk-of-bias tool in randomized trials (RoB 2.0) and the Cochrane risk-of-bias in non-randomized studies of interventions tool. Results: Database search identified 3474 records and no further records were obtained from the reference lists. After exclusion of records not related to the topic, 177 articles were assessed for eligibility. Of these, 39 were considered eligible and read in full. Three studies were prospective, while all other investigations were retrospective. In total, 18 614 cases of late ITB dislocations were analyzed across all studies. The risk of bias within studies was considerable, as only three studies were prospective and statistical significance of risk factors was assessed in only five studies. Conclusions: Typical patient age of this condition is between 70 and 85 years and there appears to be a slight male predominance. Risk factors with a good level of evidence include preoperative trauma and zonular dehiscence, previous vitrectomy, retinitis pigmentosa, pseudoexfoliation, high myopia, glaucoma/previous glaucoma surgery, corneal endothelial damage, and uveitis. Hydrophilic, quadripode and haptic-angulation IOLs are further risk factors. Capsular tension rings, Nd:YAG capsulotomy, three-piece IOLs and IOLs with large optic diameters protect from ITB dislocations. Typically, no risk factors can be identified in approximately one-fourth of patients.

Deprivation of visual input alters specific subset of inhibitory neurons and affect thalamic afferent terminals in V1 of rd1 mouse.

Retinitis Pigmentosa (RP) is a heterogenous group of inherited disorder, and its progression not only affects the retina but also the primary visual cortex. This manifests imbalances in the excitatory and inhibitory neurotransmission. Here, we investigated if changes in cortical functioning is linked to alterations in GABAergic population of neurons and its two important subsets, somatostatin (SST) and parvalbumin (PV) neuron in rd1 model of retinal degeneration (RD). We demonstrate marked decrease in the proportion of SST neurons in different layers of cortex whereas PV neurons were less affected. Moreover, we found reduced expression of glutamatergic thalamic afferents (VGLUT2) due to lack of visual activity. These results suggest PV neurons are likely recruited by the cortical circuitry to increase the inhibitory drive and compensate the disrupted inhibition-excitation balance. However, reduced SST expression perhaps results in weakening of stimulus selectivity. Delineating their functional role during RD will provide insights for acquisition of high-resolution vision thereby improving current state of vision restoration.

Role of Gonadal Steroid Hormones in the Eye: Therapeutic Implications.

Gonadal steroid hormones are critical regulatory substances involved in various developmental and physiological processes from fetal development through adulthood. These hormones, derived from cholesterol, are synthesized primarily by the gonads, adrenal cortex, and placenta. The synthesis of these hormones involves a series of enzymatic steps starting in the mitochondria and includes enzymes such as cytochrome P450 and aromatase. Beyond their genomic actions, which involve altering gene transcription over hours, gonadal steroids also exhibit rapid, nongenomic effects through receptors located on the cell membrane. Additionally, recent research has highlighted the role of these hormones in the central nervous system (CNS). However, the interactions between gonadal steroid hormones and the retina have received limited attention, though it has been suggested that they may play a protective role in retinal diseases. This review explores the synthesis of gonadal hormones, their mechanisms of action, and their potential implications in various retinal and optic nerve diseases, such as glaucoma, age-related macular degeneration (AMD), diabetic retinopathy (DR), or retinitis pigmentosa (RP), discussing both protective and risk factors associated with hormone levels and their therapeutic potential.

Therapeutic Effects of Metformin on Central Nervous System Diseases: A Focus on Protection of Neurovascular Unit.

Metformin is one of the most commonly used oral hypoglycemic drugs in clinical practice, with unique roles in neurodegeneration and vascular lesions. Neurodegeneration and vasculopathy coexist in many diseases and typically affect the neurovascular unit (NVU), a minimal structural and functional unit in the central nervous system. Its components interact with one another and are indispensable for maintaining tissue homeostasis. This review focuses on retinal (diabetic retinopathy, retinitis pigmentosa) and cerebral (ischemic stroke, Alzheimer's disease) diseases to explore the effects of metformin on the NVU. Metformin has a preliminarily confirmed therapeutic effect on the retinal NUV, affecting many of its components, such as photoreceptors (cones and rods), microglia, ganglion, Müller, and vascular endothelial cells. Since it rapidly penetrates the blood-brain barrier (BBB) and accumulates in the brain, metformin also has an extensively studied neuronal protective effect in neuronal diseases. Its mechanism affects various NVU components, including pericytes, astrocytes, microglia, and vascular endothelial cells, mainly serving to protect the BBB. Regulating the inflammatory response in NVU (especially neurons and microglia) may be the main mechanism of metformin in improving central nervous system related diseases. Metformin may be a potential drug for treating diseases associated with NVU deterioration, however, more trials are needed to validate its timing, duration, dose, clinical effects, and side effects.

Host-Graft Synapses Form Functional Microstructures and Shape the Host Light Responses After Stem Cell-Derived Retinal Sheet Transplantation.

Retinitis pigmentosa represents a leading cause of blindness in developed countries, yet effective treatments for the disease remain unestablished. Previous studies have demonstrated the potential of stem cell-derived retinal organoid (SC-RO) sheet transplantation to form host-graft synapses and to improve light responsiveness in animal models of retinal degeneration. However, the detailed microstructures of these de novo synapses and their functional contribution have not been well elucidated. This study aims to (1) elucidate the microstructures of the host-graft synapse, and (2) investigate the overall distribution and contribution of these synapses to host retinal light responses. We identified host-graft synapses using a reporter system in mouse SC-RO and rd1 mice, a well-established model of end-stage retinal degeneration. Correlative array tomography was used to reveal the microstructure of host-graft synapses. Furthermore, we developed a semi-automated algorithm that robustly detects the host-graft photoreceptor synapses in the overall grafted area using the same reporter system in flat-mount retinas. We then integrated the spatial distribution of the host-graft synapses with light responses detected by multi-electrode array recording. Correlative array tomography revealed that host-graft synapses recapitulate the developmental process of photoreceptor synapse formation involving horizontal cells first and then rod bipolar cells. By integrating the spatial distribution of host-graft synapse and multi-electrode array recording, we showed that the number of light-responsive host retinal ganglion cells is positively correlated with the local density of host-graft synapses. De novo host-graft synapses recapitulate the developmental microstructure of the photoreceptor synapse, and their formation contributes to the light responsiveness after SC-RO transplantation.