Structural and molecular changes in the aging choroid: implications for age-related macular degeneration

Detection of choroidal vascular features in diabetic patients without clinically visible diabetic retinopathy by optical coherence tomography angiography: A systemic review and meta-analysis

Researchers have explored choroidal features in the eyes of diabetic patients without clinically visible diabetic retinopathy (DM-NoDR) employing optical coherence tomography angiography (OCTA); however, the results are controversial. We systematically searched PubMed, Embase, and Ovid databases for OCTA studies comparing choroidal parameters between DM-NoDR eyes and healthy controls or non-proliferative diabetic retinopathy (NPDR) eyes. Outcomes included choriocapillaris (CC) perfusion density (PD), flow area (FA), and flow deficits (FD). 36 studies were finally included in the quantitative meta-analysis, involving 1,908 DM-NoDR eyes, 792 NPDR eyes, and 1,391 healthy control eyes. DM-NoDR eyes had significantly lower CC PD in the foveal region (P=0.0005) and superior parafoveal region (P=0.003) than healthy control eyes, but no significant difference was found in other parafoveal subregions (P>0.05). DM-NoDR eyes were also associated with increased CC FD (P<0.00001) and decreased CC FA (P<0.0001) in whole OCTA images with a 3×3 mm2 field of view (FOV). Compared with all-stage NPDR eyes, DM-NoDR eyes had higher CC PD in the foveal region (P<0.0001), parafoveal region (P<0.00001), and the whole OCTA images with a 6×6 mm2 FOV (P<0.00001). Early choroidal microvascular changes may precede clinically visible DR and can be detected early using OCTA in DM-NoDR eyes.

In vivo multi-contrast depth-resolved choroidal imaging of a mouse using polarization-diversity optical coherence tomography

The results of depth-resolved multi-contrast in vivo mouse choroidal imaging using a polarization-diversity optical coherence tomography (PD-OCT) system are presented. A selectively chosen depth of focus that was fine-tuned with a sensorless adaptive optics technique and a simple segmentation based on the degree of polarization uniformity signal visualizes the detailed features of a mouse choroid from the OCT angiography images. A comprehensive image analysis of the choroid revealed the distinctive pathological characteristics of the laser-induced choroidal neovascularization mouse.

Association Between Quantitative and Qualitative Imaging Biomarkers and Geographic Atrophy Growth Rate

PURPOSE

Investigate associations between geographic atrophy (GA) growth rate and multimodal imaging biomarkers and patient demographics in patients with advanced non-neovascular age-related macular degeneration (nnAMD).

DESIGN

Prospective cohort study.

METHODS

One hundred twenty-one eyes of 66 patients with advanced nnAMD with GA enrolled in the University of Colorado AMD Registry from August 2014 to June 2021, with follow-up through June 2023. Multimodal images were reviewed by two graders for imaging biomarkers at enrollment. GA growth rate and square-root transformed (SQRT) GA growth rate were measured between enrollment and final visit. Associations between the outcome SQRT GA growth rate and imaging biomarkers, baseline GA lesions characteristics, and patient demographics were evaluated.

RESULTS

Average GA growth rate was 1.430 mm2/year and SQRT GA growth rate was 0.268 mm/year over a mean of 3.7 years. SQRT GA growth rate was positively associated with patient age (P = .010) and female sex (0.035), and negatively associated with body mass index (0.041). After adjustment for these demographic factors, SQRT GA growth rate was positively associated with presence of non-exudative subretinal fluid (P < .001), non-exudative subretinal hyperreflective material (P = .037), and incomplete retinal pigment epithelium and outer retina atrophy (P = .022), and negatively associated with subfoveal choroidal thickness (P = .031) and presence of retinal pseudocysts (P = .030). Larger baseline GA size at enrollment was associated with faster GA growth rate (P = .002) but not SQRT GA growth rate.

CONCLUSIONS

Select patient demographic factors and basic clinically-relevant imaging biomarkers were associated with GA growth rate. These biomarkers may guide patient selection when considering treating GA patients with novel therapeutics.

Spatial Distribution of Hyperreflective Choroidal Foci in the Macula of Normal Eyes

Purpose

To investigate variations in the spatial distribution of hyperreflective foci in the choroid of the macula in normal eyes.

Methods

We included eyes with a normal fundus from patients who had undergone optical coherence tomography angiography, covering a 6-mm × 6-mm area centered on the fovea. The macular area was divided into nine sectors according to the modified Early Treatment of Diabetic Retinopathy Study grid. Hyperreflective choroidal foci (HCF) distribution, choriocapillaris vascular density, and choroidal stromal density were determined on en face images of the choroid in each sector.

Results

We included 35 eyes from 35 participants, with a mean age of 52.7 ± 16.8 years. The mean number and area fraction of HCF at the 5-mm macular area were 35.6 ± 7.8 foci/mm2 and 3.0% ± 0.7%, respectively. The number of HCF in the central circle (50.7 ± 20.9 foci/mm2) was greater than that in the inner (35.1 ± 13.0 foci/mm2) or outer rings (35.6 ± 6.5 foci/mm2) (P < 0.001, P < 0.001, respectively). The area fraction of HCF in the central circle (4.84% ± 3.36%) was greater than that in the inner (2.62% ± 1.17%; P < 0.001) or outer rings (3.12% ± 0.67%; P = 0.004). The HCF distribution did not significantly correlate with the choriocapillaris vascular density or choroidal stromal density in each sector.

Conclusions

HCF were more densely distributed in the macular center than in the pericentral or peripheral macular areas.

Translational Relevance

HCF measurement and spatial distribution could provide additional information for evaluating choroidal stromal characteristics.

Challenges and opportunities of developing small-molecule therapies for age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of vision loss in senior adults. The disease can be categorized into two types: wet AMD and dry AMD. Wet AMD, also known as exudative or neovascular AMD, is less common but more severe than dry AMD and is responsible for 90% of the visual impairment caused by AMD and affects 20 million people worldwide. Current treatment options mainly involve biologics that inhibit the vascular endothelial growth factor or complement pathways. However, these treatments have limitations such as high cost, injection-related risks, and limited efficacy. Therefore, new therapeutic targets and strategies have been explored to improve the outcomes of patients with AMD. A promising approach is the use of small-molecule drugs that modulate different factors involved in AMD pathogenesis, such as tyrosine kinases and integrins. Small-molecule drugs offer advantages, such as oral administration, low cost, good penetration, and increased specificity for the treatment of wet and dry AMD. This review summarizes the current status and prospects of small-molecule drugs for the treatment of wet AMD. These advances are expected to support the development of effective and targeted treatments for patients with AMD.

Evaluation of choroid vascular layer thickness in wet age-related macular degeneration using artificial intelligence

PURPOSE

To facilitate the assessment of choroid vascular layer thickness in patients with wet age-related macular degeneration (AMD) using artificial intelligence (AI).

METHODS

We included 194 patients with wet AMD and 225 healthy participants. Choroid images were obtained using swept-source optical coherence tomography. The average Sattler layer-choriocapillaris complex thickness (SLCCT), Haller layer thickness (HLT), and choroidal thickness (CT) were auto-measured at 7 regions centered around the foveola using AI and subsequently compared between the 2 groups.

RESULTS

The SLCCT was lower in the AMD group than in the control group (P < 0.05). The HLT was significantly higher in the AMD group than in the control group at the Tparafovea and T-perifovea in the total population (P < 0.05) and in the ≤70-year subgroup (P < 0.05). The CT was higher in the AMD group than in the control group, particularly at the N-perifovea, T-perifovea, and T-parafovea in the ≤70-year subgroup; Interestingly, it was lower in the AMD group than in the control group at the Nparafovea, N-fovea, foveola, and T-fovea in the >70-year subgroup (P < 0.05).

CONCLUSION

This novel AI-based auto-measurement was more accurate, efficient, and detailed than manual measurements. SLCCT thinning was observed in wet AMD; however, CT changes depended on the interaction between HLT compensatory thickening and SLCCT thinning.

From theory to therapy: a bibliometric and visual study of stem cell advancements in age-related macular degeneration

BACKGROUND AIMS

Human pluripotent stem cells, including embryonic stem cells and induced pluripotent stem cells, offer groundbreaking therapeutic potential for degenerative diseases and cellular repair. Despite their significance, a comprehensive bibliometric analysis in this field, particularly in relation to age-related macular degeneration (AMD), is yet to be conducted. This study aims to map the foundational and emerging areas in stem cell and AMD research through bibliometric analysis.

METHODS

This study analyzed articles and reviews on stem cells and AMD from 2000 to 2022, sourced from the Web of Science Core Collection. We used VOSviewer and CiteSpace for analysis and visualization of data pertaining to countries, institutions, authors, journals, references and key words. Statistical analyses were conducted using R language and Microsoft Excel 365.

RESULTS

In total, 539 publications were included, indicating an increase in global literature on stem cells and AMD from 2000 to 2022. The USA was the leading contributor, with 239 papers and the highest H-index, also the USA had the highest average citation rate per article (59.82). Notably, 50% of the top 10 institutions were from the USA, with the University of California system being the most productive. Key authors included Masayo Takahashi, Michiko Mandai, Dennis Clegg, Pete J. Coffey, Boris Stanzel, and Budd A. Tucker. Investigative Ophthalmology & Visual Science published the majority of relevant papers (n = 27). Key words like "clinical trial," "stem cell therapy," "retinal organoid," and "retinal progenitor cells" were predominant.

CONCLUSIONS

Research on stem cells and AMD has grown significantly, highlighting the need for increased global cooperation. Current research prioritizes the relationship between "ipsc," "induced pluripotent stem cell," "cell culture," and "human embryonic stem cell." As stem cell culture and safety have advanced, focus has shifted to prognosis and complications post-transplantation, signifying the movement of stem cell research from labs to clinical settings.

Metabolic Regulation of Endothelial Cells: A New Era for Treating Wet Age-Related Macular Degeneration

Wet age-related macular degeneration (wet AMD) is a primary contributor to visual impairment and severe vision loss globally, but the prevailing treatments are often unsatisfactory. The development of conventional treatment strategies has largely been based on the understanding that the angiogenic switch of endothelial cells (ECs) is mainly dictated by angiogenic growth factors. Even though treatments targeting vascular endothelial growth factor (VEGF), like ranibizumab, are widely administered, more than half of patients still exhibit inadequate or null responses, suggesting the involvement of other pathogenic mechanisms. With advances in research in recent years, it has become well recognized that EC metabolic regulation plays an active rather than merely passive responsive role in angiogenesis. Disturbances of these metabolic pathways may lead to excessive neovascularization in angiogenic diseases such as wet AMD, therefore targeted modulation of EC metabolism represents a promising therapeutic strategy for wet AMD. In this review, we comprehensively discuss the potential applications of EC metabolic regulation in wet AMD treatment from multiple perspectives, including the involvement of ECs in wet AMD pathogenesis, the major endothelial metabolic pathways, and novel therapeutic approaches targeting metabolism for wet AMD.

Pachyvitelliform maculopathy: an optical coherence tomography analysis of a novel entity

PURPOSE

To describe the optical coherence tomography features of pachyvitelliform maculopathy (PVM), an acquired vitelliform lesion (AVL) associated with pachychoroid disease.

METHODS

This study was a retrospective, multicentre, observational analysis.Medical records and multimodal imaging were reviewed in all patients with pachychoroid disease and AVL. Visual acuity, central choroidal thickness (CCT), AVL dimensions, total choroidal area, luminal choroidal area, stromal choroidal area and choroidal vascular index were measured in all eyes with PVM and compared with normal age-matched control eyes.

RESULTS

Mean age of the PVM group (17 eyes of 17 patients) was 71.41 years. Average follow-up was 33.15 months. Baseline VA was 20/40 in the PVM group and declined to 20/100 (p=0.006). AVLs were all detected overlying pachyvessels with optical coherence tomography and were all hyperautofluorescent with fundus autofluorescent imaging. Mean CCT in the PVM group was significantly greater (352.35 µm) than the CCT in the control group (226.88 µm, p<0.001). Retinal pigment epithelium (RPE) disruption was present in 64.71% of eyes with PVM at baseline and 41.18% developed macular atrophy at the end of follow-up.

CONCLUSIONS

PVM, defined by the presence of AVL associated with pachychoroid features, is a distinct novel entity of the pachychoroid disease spectrum. This study suggests a possible pathogenesis of RPE dysfunction secondary to a thick choroid, leading to accumulation of undigested photoreceptor outer segments and AVL. Clinicians should be aware of this common cause of vitelliform lesions and the poor visual prognosis due to the high risk of atrophy development.

Complement regulation in the eye: implications for age-related macular degeneration

Careful regulation of the complement system is critical for enabling complement proteins to titrate immune defense while also preventing collateral tissue damage from poorly controlled inflammation. In the eye, this balance between complement activity and inhibition is crucial, as a low level of basal complement activity is necessary to support ocular immune privilege, a prerequisite for maintaining vision. Dysregulated complement activation contributes to parainflammation, a low level of inflammation triggered by cellular damage that functions to reestablish homeostasis, or outright inflammation that disrupts the visual axis. Complement dysregulation has been implicated in many ocular diseases, including glaucoma, diabetic retinopathy, and age-related macular degeneration (AMD). In the last two decades, complement activity has been the focus of intense investigation in AMD pathogenesis, leading to the development of novel therapeutics for the treatment of atrophic AMD. This Review outlines recent advances and challenges, highlighting therapeutic approaches that have advanced to clinical trials, as well as providing a general overview of the complement system in the posterior segment of the eye and selected ocular diseases.

Dynamics of Wnt/β-catenin reporter activity throughout whole life in a naturally short-lived vertebrate

Wnt/β-catenin signaling plays a major role in regulation of embryogenesis, organogenesis, and adult tissue homeostasis and regeneration. However, the roles played by Wnt/β-catenin and the spatiotemporal regulation of its activity throughout life, including during aging, are not fully understood. To address these issues, we introduced a Wnt/β-catenin signaling sensitive reporter into African turquoise killifish (Nothobranchius furzeri), a naturally ultra-short-lived fish that allows for the analysis of its whole life within a short period of time. Using this reporter killifish, we unraveled the previously unidentified dynamics of Wnt/β-catenin signaling during development and aging. Using the reporter strain, we detected Wnt/β-catenin activity in actively developing tissues as reported in previous reports, but also observed activation and attenuation of Wnt/β-catenin activity during embryonic reaggregation and diapause, respectively. During the aging process, the reporter was activated in the choroidal layer and liver, but its expression decreased in the kidneys. In addition, the reporter also revealed that aging disrupts the spatial regulation and intensity control of Wnt/β-catenin activity seen during fin regeneration, which interferes with precise regeneration. Thus, the employed reporter killifish is a highly useful model for investigating the dynamics of Wnt/β-catenin signaling during both the developmental and aging process.

Microglial repopulation restricts ocular inflammation and choroidal neovascularization in mice

Introduction

Age-related macular degeneration (AMD) is a prevalent, chronic and progressive retinal degenerative disease characterized by an inflammatory response mediated by activated microglia accumulating in the retina. In this study, we demonstrate the therapeutically effects and the underlying mechanisms of microglial repopulation in the laser-induced choroidal neovascularization (CNV) model of exudative AMD.

Methods

The CSF1R inhibitor PLX3397 was used to establish a treatment paradigm for microglial repopulation in the retina. Neovascular leakage and neovascular area were examined by fundus fluorescein angiography (FFA) and immunostaining of whole-mount RPE-choroid-sclera complexes in CNV mice receiving PLX3397. Altered cellular senescence was measured by beta-galactosidase (SA-β-gal) activity and p16INK4a expression. The effect and mechanisms of repopulated microglia on leukocyte infiltration and the inflammatory response in CNV lesions were analyzed.

Results

We showed that ten days of the CSF1R inhibitor PLX3397 treatment followed by 11 days of drug withdrawal was sufficient to stimulate rapid repopulation of the retina with new microglia. Microglial repopulation attenuated pathological choroid neovascularization and dampened cellular senescence in CNV lesions. Repopulating microglia exhibited lower levels of activation markers, enhanced phagocytic function and produced fewer cytokines involved in the immune response, thereby ameliorating leukocyte infiltration and attenuating the inflammatory response in CNV lesions.

Discussion

The microglial repopulation described herein are therefore a promising strategy for restricting inflammation and choroidal neovascularization, which are important players in the pathophysiology of AMD.

Aging in Ocular Blood Vessels: Molecular Insights and the Role of Oxidative Stress

Acknowledged as a significant pathogenetic driver for numerous diseases, aging has become a focal point in addressing the profound changes associated with increasing human life expectancy, posing a critical concern for global public health. Emerging evidence suggests that factors influencing vascular aging extend their impact to choroidal and retinal blood vessels. The objective of this work is to provide a comprehensive overview of the impact of vascular aging on ocular blood vessels and related diseases. Additionally, this study aims to illuminate molecular insights contributing to vascular cell aging, with a particular emphasis on the choroid and retina. Moreover, innovative molecular targets operating within the domain of ocular vascular aging are presented and discussed.

Heterogenous thinning of peripapillary tissues occurs early during high myopia development in juvenile tree shrews

Myopia is an independent risk factor for glaucoma, but the link between both conditions remains unknown. Both conditions induce connective tissue remodeling at the optic nerve head (ONH), including the peripapillary tissues. The purpose of this study was to investigate the thickness changes of the peripapillary tissues during experimental high myopia development in juvenile tree shrews. Six juvenile tree shrews experienced binocular normal vision, while nine received monocular -10D lens treatment starting at 24 days of visual experience (DVE) to induce high myopia in one eye and the other eye served as control. Daily refractive and biometric measurements and weekly optical coherence tomography scans of the ONH were obtained for five weeks. Peripapillary sclera (Scl), choroid-retinal pigment epithelium complex (Ch-RPE), retinal nerve fiber layer (RNFL), and remaining retinal layers (RRL) were auto-segmented using a deep learning algorithm after nonlinear distortion correction. Peripapillary thickness values were quantified from 3D reconstructed segmentations. All lens-treated eyes developed high myopia (-9.8 ± 1.5 D), significantly different (P < 0.001) from normal (0.69 ± 0.45 D) and control eyes (0.76 ± 1.44 D). Myopic eyes showed significant thinning of all peripapillary tissues compared to both, normal and control eyes (P < 0.001). At the experimental end point, the relative thinning from baseline was heterogeneous across tissues and significantly more pronounced in the Scl (-8.95 ± 3.1%) and Ch-RPE (-16.8 ± 5.8%) when compared to the RNFL (-5.5 ± 1.6%) and RRL (-6.7 ± 1.8%). Furthermore, while axial length increased significantly throughout the five weeks of lens wear, significant peripapillary tissue thinning occurred only during the first week of the experiment (until a refraction of -2.5 ± 1.9 D was reached) and ceased thereafter. A sectorial analysis revealed no clear pattern. In conclusion, our data show that in juvenile tree shrews, experimental high myopia induces significant and heterogeneous thinning of the peripapillary tissues, where the retina seems to be protected from profound thickness changes as seen in Ch-RPE and Scl. Peripapillary tissue thinning occurs early during high myopia development despite continued progression of axial elongation. The observed heterogeneous thinning may contribute to the increased risk for pathological optic nerve head remodeling and glaucoma later in life.

Racial Differences in Choroidal Vascularity Index in Healthy Patients: Novel Insights

BACKGROUND AND OBJECTIVE

Choroidal vascularity index (CVI) measures the ratio of blood vessels in the choroid to the total choroidal area. We aimed to compare CVI between young Black and White patients without a history of ocular or systemic disease.

PATIENTS AND METHODS

We used a previously validated algorithm for shadow compensation and choroidal vessel binarization to measure CVI across the Early Treatment of Diabetic Retinopathy Study grid.

RESULTS

Black patients had a lower CVI (ß = -0.05, P < 0.001) compared to White patients. Choroidal volume or luminal volume did not significantly differ with respect to race, whereas there was a trend for Black patients to have a greater stromal volume (ß = 3.08, P = 0.01).

CONCLUSIONS

Black patients have a lower CVI than do White patients, likely due to a greater proportion of stromal volume. Further study of this parameter is warranted to validate the findings of this exploratory study. [Ophthalmic Surg Lasers Imaging Retina 2024;55:30-38.].

Acute, Treatment-Naïve Branch Retinal Vein Occlusion in Younger Individuals: Risk Factors and Clinical Outcomes

Purpose: To compare the risk factors and clinical outcomes in patients younger than 50 years with acute, treatment-naïve branch retinal vein occlusion (BRVO) with outcomes in patients 50 years or older. Methods: Patients diagnosed with acute, treatment-naïve BRVO at Duke Eye Center over a 9.5-year period who had BRVO with onset 3 months or less before presentation, BRVO with macular involvement, and 12 months or more of follow-up were included. Demographic data, presenting clinical features, risk factors, treatment patterns, and clinical outcomes were extracted during a retrospective review of medical records. Results: Of 302 patients identified, 23 were younger than 50 years (younger group) and 279 were 50 years or older (older group). Compared with older patients, younger patients had similar rates of hypertension (P = .275), diabetes mellitus (P = 1.000), smokers (P = .787), and open-angle glaucoma (P = .628). The younger group had a lower rate of hyperlipidemia than the older group (35% vs 59%) (P = .028). The 2 groups had similar presenting logMAR visual acuities (VAs) in the BRVO eye (P = .131). At the final follow-up, younger patients had significantly better logMAR VA in the BRVO-affected eye than older patients (mean 0.51 ± 0.65 vs 1.01 ± 1.20) (P = .016). The 2 groups had similar treatment burdens at 1 year (P = .516) and at the final follow-up (P = .782). Conclusions: Younger patients with acute, treatment-naïve BRVO have similar risk factors and treatment patterns as older patients, except for a lower rate of hyperlipidemia. Younger patients with BRVO may have similar presenting VA as older BRVO patients but better final VA, suggesting that age may be a potential prognostic factor.

Effects of Humanin G (HNG) on angiogenesis and neurodegeneration markers in Age-related Macular Degeneration (AMD)

Advanced stages of Age-related Macular Degeneration (AMD) are characterized by retinal neurodegeneration and aberrant angiogenesis, and mitochondrial dysfunction contributes to the pathogenesis of AMD. In this study, we tested the hypothesis that Humanin G (HNG), a cytoprotective mitochondrial-derived peptide, positively regulates cell proliferation, cell death, and the protein levels of angiogenesis and neurodegeneration markers, in normal (control) and AMD RPE transmitochondrial cybrid cell lines. These normal and AMD RPE transmitochondrial cybrid cell lines had identical nuclei derived from mitochondria-deficient ARPE-19 cell line, but differed in mitochondrial DNA (mtDNA) content that was derived from clinically characterized AMD patients and normal (control) subjects. Cell lysates were extracted from untreated and HNG-treated AMD and normal (control) cybrid cell lines, and the Luminex XMAP multiplex assay was used to examine the protein levels of angiogenesis and neurodegeneration markers. Humanin G reduced Caspase-3/7-mediated apoptosis, improved cell proliferation, and normalized the protein levels of angiogenesis and neurodegeneration markers in AMD RPE cybrid cell lines, thereby suggesting Humanin G's positive regulatory role in AMD.

Immune System, Inflammation and Autoantigens in Wet Age-Related Macular Degeneration: Pathological Significance and Therapeutic Importance

Wet age-related macular degeneration (wAMD) is a chronic inflammation-associated neurodegenerative disease affecting the posterior part of the eye in the aging population. Aging results in the reduced functionality of cells and tissues, including the cells of the retina. Initiators of a chronic inflammatory and pathologic state in wAMD may be a result of the accumulation of inevitable metabolic injuries associated with the maintenance of tissue homeostasis from a young age to over 50. Apart from this, risk factors like smoking, genetic predisposition, and failure to repair the injuries that occur, alongside attempts to rescue the hypoxic outer retina may also contribute to the pathogenesis. Aging of the immune system (immunosenescence) and a compromised outer blood retinal barrier (BRB) result in the exposure of the privileged milieu of the retina to the systemic immune system, further increasing the severity of the disease. When immune-privileged sites like the retina are under pathological stress, certain age- and disease-related conditions may necessitate assistance from cells distant from the resident ones to help restore the functionality of the tissue. As a necessary part of tissue repair, inflammation is a major response to disease and recruits immune cells to the site of damage. We suspect that the specific reparative inflammatory responses are controlled by an autoantigen-T cell-mediated mechanism, a process that may be hindered in wAMD.

Endothelial Notch Signaling Regulates the Function of the Retinal Pigment Epithelial Barrier via EC Angiocrine Signaling

The outer blood-retina barrier (oBRB), comprises tightly connected retinal pigment epithelium (RPE) cells, Bruch's membrane, and choroid blood vessels, and is essential for retinal health and normal visual function. Disruption of the RPE barrier and its dysfunction can lead to retinal disorders such as age-related macular degeneration (AMD). In the present study, we investigated the essential role of choroid endothelial cells (ECs) in the RPE barrier formation process and its dysfunction. We discovered that ECs promoted RPE barrier formation through angiocrine signaling. Through blocking or activating endothelial Notch signaling and conducting experiments in vitro and in vivo, we confirmed that endothelial Notch signaling regulated the expression of heparin-binding epidermal growth factor (HBEGF) and consequently impacted the expression and activity of matrix metalloproteinases (MMP)-9 in RPE cells. This modulation influenced the RPE extracellular matrix deposition, tight junctions and RPE barrier function. In in vivo experiments, the intravitreal administration of recombinant HBEGF (r-HBEGF) alleviated the RPE barrier disruption induced by subretinal injection (SI) or laser treatment and also rescued RPE barrier disruption in endothelial Notch-deficient mice. Our results showed that the endothelial Notch signaling drove HBEGF expression through angiocrine signaling and effectively improved RPE barrier function by regulating the MMP-9 expression in RPE cells. It suggests that the modulation of Notch signaling in the choroidal endothelium may offer a novel therapeutic strategy for retinal degenerative diseases.

Construction of an Exudative Age-Related Macular Degeneration Diagnostic and Therapeutic Molecular Network Using Multi-Layer Network Analysis, a Fuzzy Logic Model, and Deep Learning Techniques: Are Retinal and Brain Neurodegenerative Disorders Related?

Neovascular age-related macular degeneration (nAMD) is a leading cause of irreversible visual impairment in the elderly. The current management of nAMD is limited and involves regular intravitreal administration of anti-vascular endothelial growth factor (anti-VEGF). However, the effectiveness of these treatments is limited by overlapping and compensatory pathways leading to unresponsiveness to anti-VEGF treatments in a significant portion of nAMD patients. Therefore, a system view of pathways involved in pathophysiology of nAMD will have significant clinical value. The aim of this study was to identify proteins, miRNAs, long non-coding RNAs (lncRNAs), various metabolites, and single-nucleotide polymorphisms (SNPs) with a significant role in the pathogenesis of nAMD. To accomplish this goal, we conducted a multi-layer network analysis, which identified 30 key genes, six miRNAs, and four lncRNAs. We also found three key metabolites that are common with AMD, Alzheimer's disease (AD) and schizophrenia. Moreover, we identified nine key SNPs and their related genes that are common among AMD, AD, schizophrenia, multiple sclerosis (MS), and Parkinson's disease (PD). Thus, our findings suggest that there exists a connection between nAMD and the aforementioned neurodegenerative disorders. In addition, our study also demonstrates the effectiveness of using artificial intelligence, specifically the LSTM network, a fuzzy logic model, and genetic algorithms, to identify important metabolites in complex metabolic pathways to open new avenues for the design and/or repurposing of drugs for nAMD treatment.

Proteopathy Linked to Exon-Skipping Isoform of RGR-Opsin Contributes to the Pathogenesis of Age-Related Macular Degeneration

Purpose

Proteopathy is believed to contribute to age-related macular degeneration (AMD). Much research indicates that AMD begins in the retinal pigment epithelium (RPE), which is associated with formation of extracellular drusen, a clinical hallmark of AMD. Human RPE produces a drusen-associated abnormal protein, the exon Ⅵ-skipping splice isoform of retinal G protein-coupled receptor (RGR-d). In this study, we investigate the detrimental effects of RGR-d on cultured cells and mouse retina.

Methods

ARPE-19 cells were stably infected by lentivirus overexpressing RGR or RGR-d and were treated with MG132, sometimes combined with or without endoplasmic reticulum (ER) stress inducer, tunicamycin. RGR and RGR-d protein expression, degeneration pathway, and potential cytotoxicity were explored. Homozygous RGR-d mice aged 8 or 14 months were fed with a high-fat diet for 3 months and then subjected to ocular examination and histopathology experiments.

Results

We confirm that RGR-d is proteotoxic under various conditions. In ARPE-19 cells, RGR-d is misfolded and almost completely degraded via the ubiquitin-proteasome system. Unlike normal RGR, RGR-d increases ER stress, triggers the unfolded protein response, and exerts potent cytotoxicity. Aged RGR-d mice manifest disrupted RPE cell integrity, apoptotic photoreceptors, choroidal deposition of complement C3, and CD86+CD32+ proinflammatory cell infiltration into retina and RPE-choroid. Furthermore, the AMD-like phenotype of RGR-d mice can be aggravated by a high-fat diet.

Conclusions

Our study confirmed the pathogenicity of the RGR splice isoform and corroborated a significant role of proteopathy in AMD. These findings may contribute to greater comprehension of the multifactorial causes of AMD.

10q26 - The enigma in age-related macular degeneration

Despite comprehensive research efforts over the last decades, the pathomechanisms of age-related macular degeneration (AMD) remain far from being understood. Large-scale genome wide association studies (GWAS) were able to provide a defined set of genetic aberrations which contribute to disease risk, with the strongest contributors mapping to distinct regions on chromosome 1 and 10. While the chromosome 1 locus comprises factors of the complement system with well-known functions, the role of the 10q26-locus in AMD-pathophysiology remains enigmatic. 10q26 harbors a cluster of three functional genes, namely PLEKHA1, ARMS2 and HTRA1, with most of the AMD-associated genetic variants mapping to the latter two genes. High linkage disequilibrium between ARMS2 and HTRA1 has kept association studies from reliably defining the risk-causing gene for long and only very recently the genetic risk region has been narrowed to ARMS2, suggesting that this is the true AMD gene at this locus. However, genetic associations alone do not suffice to prove causality and one or more of the 14 SNPs on this haplotype may be involved in long-range control of gene expression, leaving HTRA1 and PLEKHA1 still suspects in the pathogenic pathway. Both, ARMS2 and HTRA1 have been linked to extracellular matrix homeostasis, yet their exact molecular function as well as their role in AMD pathogenesis remains to be uncovered. The transcriptional regulation of the 10q26 locus adds an additional level of complexity, given, that gene-regulatory as well as epigenetic alterations may influence expression levels from 10q26 in diseased individuals. Here, we provide a comprehensive overview on the 10q26 locus and its three gene products on various levels of biological complexity and discuss current and future research strategies to shed light on one of the remaining enigmatic spots in the AMD landscape.

Engineering a Biomimetic In Vitro Model of Bruch's Membrane Using Hagfish Slime Intermediate Filament Proteins

Bruch's membrane resides in the subretinal tissue and regulates the flow of nutrients and waste between the retinal pigment epithelial (RPE) and vascular layers of the eye. With age, Bruch's membrane becomes thicker, stiffer, and less permeable, which impedes its function as a boundary layer in the subretina. These changes contribute to pathologies such as age-related macular degeneration (AMD). To better understand how aging in Bruch's membrane affects surrounding tissues and to determine the relationship between aging and disease, an in vitro model of Bruch's membrane is needed. An accurate model of Bruch's membrane must be a proteinaceous, semipermeable, and nonporous biomaterial with similar mechanical properties to in vivo conditions. Additionally, this model must support RPE cell growth. While models of subretinal tissue exist, they typically differ from in vivo Bruch's membrane in one or more of these properties. This study evaluates the capability of membranes created from recombinant hagfish intermediate filament (rHIF) proteins to accurately replicate Bruch's membrane in an in vitro model of the subretinal tissue. The physical characteristics of these rHIF membranes were evaluated using mechanical testing, permeability assays, brightfield microscopy, and scanning electron microscopy. The capacity of the membranes to support RPE cell culture was determined using brightfield and fluorescent microscopy, as well as immunocytochemical staining. This study demonstrates that rHIF protein membranes are an appropriate biomaterial to accurately mimic both healthy and aged Bruch's membrane for in vitro modeling of the subretinal tissue.

Retro-mode: a newer insight into dry age-related macular degeneration (AMD)

The purpose of this study is to study the role of retro-mode (RM) in early detection and to compare it with other preexisting available modalities on multimodal imaging system in dry AMD. A prospective observational cross-sectional study was done between November 2020 and October 2021 which included 409 eyes of 207 patients. For study purpose, eyes were divided into 3 groups according to the size and number of the drusen, viz, group 1: No AMD, group 2: early AMD and group 3: intermediate AMD which was further divided into 2 subgroups, viz, subgroup A: eyes with drusen size 63-125 μm and subgroup B: eyes with drusen size 125-250 μm. Patients with active or treated wet AMD, scarred choroidal neovascular membrane (CNVM), other maculopathies, other retinopathies, high myopia, trauma and glaucoma were excluded from the study. In cases of No AMD and early AMD, a number of drusens detected on RM were statistically not significant compared to fundus autofluorescence (FAF) and color photo (CF), but in intermediate AMD cases, it was statistically significant. While the area involved by drusens calculated by RM was statistically significant compared to both other modalities. When all modalities were compared with enhanced depth imaging-optical coherence tomography (EDI-OCT) at the choroid and chorio-capillary (CC) level and vessel density (VD) on optical coherence tomography angiography (OCTA) at the choroid, capillaries, deep retinal and superficial retinal plexus level; it was only RM which was found to be in sync with these proven modalities in terms of pattern and trend. In the present scenario, RM is found to be a better diagnostic modality in detecting early and a greater number of drusens with area of involvement than other existing modalities. Though superior, as found in this study, this mode cannot replace other modalities at present but only acts as a complementary investigation in early detection of this disease.

Optical Coherence Tomography Angiography Is a Useful Tool for Distinguishing Primary Raynaud's Phenomenon from Systemic Sclerosis and/or Very Early Disease of Systemic Sclerosis

This cross-sectional study aimed to compare optical coherence tomography angiography (OCT-A) findings in patients with primary Raynaud's phenomenon (PRP; n = 22), very early disease of systemic sclerosis (VEDOSS; n = 19), and systemic sclerosis (SSc; 25 patients with limited cutaneous SSc (lcSSc) and 13 patients with diffuse cutaneous SSc (dcSSc)). Whole, parafoveal, and perifoveal superficial capillary plexus (SCP) vessel densities (VDs), deep capillary plexus VDs, and whole, inside, and peripapillary VDs were significantly higher in the PRP group (p < 0.001). In the lcSSc group, the FAZ perimeter was significantly higher than that in the VEDOSS group (p = 0.017). Retinal nerve fiber layer VDs were significantly lower in the lcSSc group than in the PRP and VEDOSS groups (p < 0.001). The whole and peripapillary optic disc VDs of the VEDOSS group were significantly higher than in the lcSSc group (p < 0.001). Whole SCP VDs (94.74% sensitivity, 100.00% specificity) and parafoveal SCP VDs (89.47% sensitivity, 100.00% specificity) showed the best performance in distinguishing patients with SSc from those with PRP. OCT-A seems to have potential diagnostic value in differentiating patients with PRP from patients with SSc and VEDOSS, and there is potential value in assessing prognostic roles, since findings from OCT-A images could be early indicators of retinal vascular injury long before overt SSc symptoms develop.

Therapeutic Benefit of Melatonin in Choroidal Neovascularization During Aging Through the Regulation of Senescent Macrophage/Microglia Polarization

Purpose

This study aimed to investigate the age-dependent anti-angiogenic capability of melatonin in choroidal neovascularization (CNV) and to explore the underlying molecular mechanisms.

Methods

In the present study, a laser-induced CNV model was established in both young (three months of age) and old (18 months of age) mice, and the size of CNV lesions and vascular leakage was detected by morphological and imaging examination. Next, Western blot and immunostaining were used to observe the levels of M2 markers, senescence-related markers, and molecules involved in IL-10/STAT3 pathway. Additionally, colivelin was used to study the effect of IL-10/STAT3 pathway activation on the expression of M2 markers and senescence-related markers by Western blot and immunostaining. Finally, the effects of colivelin on melatonin-induced reduction of CNV size and vascular leakage in mice at different ages were assessed using morphological and imaging examination.

Results

Our results revealed that aging promoted M2 macrophage/microglia polarization, and aggravated CNV and vascular leakage. Melatonin significantly inhibited the M2 polarization of senescent macrophage/microglia and reduced the CNV area and vascular leakage. Moreover, melatonin markedly suppressed IL-10/STAT3 pathway activation in the macrophage/microglia of old mice, and STAT3 activator colivelin reversed the suppressive effect of melatonin on M2 polarization of senescent macrophage/microglia and laser-induced CNV in old mice.

Conclusions

Our data demonstrated that melatonin significantly prevented the M2 polarization of senescent macrophage/microglia by inhibiting the IL-10/STAT3 pathway, and eventually attenuated senescence-associated CNV. These findings suggested that melatonin could serve as a promising therapeutic agent to treat CNV and other age-related ocular diseases.

SUBRETINAL FLUID ASSOCIATED WITH DRUSENOID PIGMENT EPITHELIAL DETACHMENT

PURPOSE

To analyze the clinical characteristics of drusenoid pigment epithelial detachment (PED) with subretinal fluid (SRF) and to evaluate the impact of SRF on the long-term visual and anatomical outcomes.

METHODS

Forty-seven eyes with drusenoid PED (47 patients) who completed >24 months of follow-up were retrospectively analyzed. Intergroup comparisons of the visual and anatomical outcomes with and without SRF were made.

RESULTS

The mean duration of follow-up was 32.9 ± 18.7 months. The group with drusenoid PED with SRF (14 eyes) showed significantly higher PED height (468 ± 130 µ m vs. 313 ± 88 µ m, P < 0.001), larger PED diameter (2,328 ± 953 µ m vs. 1,227 ± 882 µ m, P < 0.001), and larger PED volume (1.88 ± 1.73 mm 3 vs. 1.12 ± 1.35 mm 3 , P = 0.021) than that in the group with drusenoid PED without SRF (33 eyes) at baseline. No significant intergroup difference was found regarding the best-corrected visual acuity at the final visit. In addition, the incidence of complete retinal pigment epithelial and outer retinal atrophy (cRORA; 21.4%) and the development of macular neovascularization (MNV; 7.1%) for the group with drusenoid PED with SRF showed no difference compared with those (39.4% for cRORA development and 9.1% for MNV development) with drusenoid PED without SRF.

CONCLUSION

The size, height, and volume of drusenoid PED were associated with the development of SRF. The SRF in drusenoid PED did not affect the visual prognosis or the development of macular atrophy during long-term follow-up.

Oxidative Stress and Antioxidants in Age-Related Macular Degeneration

Oxidative stress plays a crucial role in aging-related eye diseases, including age-related macular degeneration (AMD), cataracts, and glaucoma. With age, antioxidant reparative capacity decreases, and excess levels of reactive oxygen species produce oxidative damage in many ocular cell types underling age-related pathologies. In AMD, loss of central vision in the elderly is caused primarily by retinal pigment epithelium (RPE) dysfunction and degeneration and/or choroidal neovascularization that trigger malfunction and loss of photo-sensing photoreceptor cells. Along with various genetic and environmental factors that contribute to AMD, aging and age-related oxidative damage have critical involvement in AMD pathogenesis. To this end, dietary intake of antioxidants is a proven way to scavenge free radicals and to prevent or slow AMD progression. This review focuses on AMD and highlights the pathogenic role of oxidative stress in AMD from both clinical and experimental studies. The beneficial roles of antioxidants and dietary micronutrients in AMD are also summarized.

Longitudinal Changes in Choroidal Structure Following Repeated Low-Level Red-Light Therapy for Myopia Control: Secondary Analysis of a Randomized Controlled Trial

PURPOSE

Repeated low-level red-light (RLRL) therapy has been confirmed as a novel intervention for myopia control in children. This study aims to investigate longitudinal changes in choroidal structure in myopic children following 12-month RLRL treatment.

MATERIALS AND METHODS

The current study is a secondary analysis from a multicenter, randomized controlled trial (NCT04073238). Choroidal parameters were derived from baseline and follow-up swept-source optical coherence tomography scans taken at 1, 3, 6, and 12 months. These parameters included the luminal area (LA), stromal area (SA), total choroidal area (TCA; a combination of LA and SA), and choroidal vascularity index (CVI; ratio of LA to TCA), which were automatically measured by a validated custom choroidal structure assessment tool.

RESULTS

A total of 143 children (88.3% of all participants) with sufficient image quality were included in the analysis (n=67 in the RLRL and n=76 in the control groups). At the 12-month visit, all choroidal parameters increased in the RLRL group, with changes from baseline of 11.70×10 3  μm 2 (95% CI: 4.14-19.26×10 3  μm 2 ), 3.92×10 3  μm 2 (95% CI: 0.56-7.27×10 3  μm 2 ), 15.61×10 3  μm 2 (95% CI: 5.02-26.20×10 3  μm 2 ), and 0.21% (95% CI: -0.09% to 0.51%) for LA, SA, TCA, and CVI, respectively, whereas these parameters reduced in the control group.

CONCLUSIONS

Following RLRL therapy, the choroidal thickening was found to be accompanied by increases in both the vessel LA and SA, with the increase in LA being greater than that of SA. In the control group, with myopia progression, both the LA and SA decreased over time.

The Role of Diabetic Choroidopathy in the Pathogenesis and Progression of Diabetic Retinopathy

Diabetic choroidopathy was first described on histopathological specimens of diabetic eyes. This alteration was characterized by the accumulation of PAS-positive material within the intracapillary stroma. Inflammation and polymorphonuclear neutrophils (PMNs) activation are crucial elements in choriocapillaris impairment. The evidence of diabetic choroidopathy in vivo was confirmed with multimodal imaging, which provides key quantitative and qualitative features to characterize the choroidal involvement. The choroid can be virtually affected in each vascular layer, from Haller's layer to the choriocapillaris. However, the damage on the outer retina and photoreceptor cells is essentially driven by a choriocapillaris deficiency, which can be assessed through optical coherence tomography angiography (OCTA). The identification of characteristic features of diabetic choroidopathy can be significant for understanding the potential pathogenic and prognostic implications in diabetic retinopathy.

Evidence of vascular involvement in myopia: a review

The benign public perception of myopia (nearsightedness) as a visual inconvenience masks the severity of its sight-threatening consequences. Myopia is a significant risk factor for posterior pole conditions such as maculopathy, choroidal neovascularization and glaucoma, all of which have a vascular component. These associations strongly suggest that myopic eyes might experience vascular alterations prior to the development of complications. Myopic eyes are out of focus because they are larger in size, which in turn affects their overall structure and function, including those of the vascular beds. By reviewing the vascular changes that characterize myopia, this review aims to provide an understanding of the gross, cellular and molecular alterations identified at the structural and functional levels with the goal to provide an understanding of the latest evidence in the field of experimental and clinical myopia vascular research. From the evidence presented, we hypothesize that the interaction between excessive myopic eye growth and vascular alterations are tipping-points for the development of sight-threatening changes.

Subretinal drusenoid deposits as a biomarker of age-related macular degeneration progression via reduction of the choroidal vascularity index

BACKGROUND/OBJECTIVES

This study aimed to analyse the role of the choroid in early age-related macular degeneration (AMD) by analysing choroidal vascularity index (CVI) in pure cohorts of patients with subretinal drusenoid deposits (SDD) or conventional drusen (CD).

SUBJECTS/METHODS

This was an observational cross-sectional study. Comprehensive ophthalmologic examination and multimodal imaging including fundus photography, autofluorescence, near infrared reflectance, and spectral domain optical coherence tomography (SDOCT) was performed. CVI processing was performed on a foveal horizontal SDOCT scan with binarization using Image J Image software and calculated as the ratio between luminal area (LA) and total area (TA).

RESULTS

Sixty-nine eyes of 69 participants were included; 23 eyes with SDD alone, 22 eyes with CD alone, and 24 control eyes of healthy age-matched subjects. CVI was significantly reduced in the SDD and CD group compared to controls (p = 0.0001). Post-hoc analysis revealed a significant reduction of CVI in the SDD versus the control group (p = 0.0002), in the CD versus the control group (p = 0.001), and in the SDD versus the CD group (p = 0.006). Covariance analysis showed a significant difference of LA (p = 0.033) but no significant difference of TA (p = 0.106) between the three groups. Direct comparison between CD and SDD showed a significant reduction of LA and TA in the SDD group.

CONCLUSIONS

CVI may have prognostic implications in early AMD. SDD is a biomarker of AMD progression and the mechanism for this could be via reduction of the CVI.

Does the Presence of the Cilioretinal Artery Affect the Incidence, Clinical Picture and Progression of Age-Related Macular Degeneration?

The aims of this study were to analyze the relationship between the presence of the cilioretinal artery (CRA) and the incidence, severity and progression of age-related macular degeneration (AMD) and to estimate the influence of the CRA on choroidal and retinal parameters. A total of 287 patients with AMD and 110 healthy controls were enrolled in the study. CRA occurrence was determined using color fundus images. AMD progression was assessed after 3 years. There was no difference in the incidence of CRA between the AMD and control groups (23.34% vs. 24.55%; p = 0.8). Lower-stage AMD was more frequently observed in eyes with the CRA than in eyes without the artery (p = 0.016). The CRA did not influence disease progression (p = 0.79). The CRA did not influence retinal and choroidal thickness and volume parameters or the retinal vessel caliber and functionality in either the AMD or control groups. There was no relationship between CRA presence and CFH Y402H and ARMS2 A69S risk variants. The results did not show a protective effect of the CRA on the incidence and progression of AMD. The CRA may affect the severity of AMD; however, the mechanism of this phenomenon is unclear.

Advanced Therapy Medicinal Products for Age-Related Macular Degeneration; Scaffold Fabrication and Delivery Methods

Retinal degenerative diseases such as age-related macular degeneration (AMD) represent a leading cause of blindness, resulting in permanent damage to retinal cells that are essential for maintaining normal vision. Around 12% of people over the age of 65 have some form of retinal degenerative disease. Whilst antibody-based drugs have revolutionised treatment of neovascular AMD, they are only effective at an early stage and cannot prevent eventual progression or allow recovery of previously lost vision. Hence, there is a clear unmet need to find innovative treatment strategies to develop a long-term cure. The replacement of damaged retinal cells is thought to be the best therapeutic strategy for the treatment of patients with retinal degeneration. Advanced therapy medicinal products (ATMPs) are a group of innovative and complex biological products including cell therapy medicinal products, gene therapy medicinal products, and tissue engineered products. Development of ATMPs for the treatment of retinal degeneration diseases has become a fast-growing field of research because it offers the potential to replace damaged retinal cells for long-term treatment of AMD. While gene therapy has shown encouraging results, its effectiveness for treatment of retinal disease may be hampered by the body's response and problems associated with inflammation in the eye. In this mini-review, we focus on describing ATMP approaches including cell- and gene-based therapies for treatment of AMD along with their applications. We also aim to provide a brief overview of biological substitutes, also known as scaffolds, that can be used for delivery of cells to the target tissue and describe biomechanical properties required for optimal delivery. We describe different fabrication methods for preparing cell-scaffolds and explain how the use of artificial intelligence (AI) can aid with the process. We predict that combining AI with 3D bioprinting for 3D cell-scaffold fabrication could potentially revolutionise retinal tissue engineering and open up new opportunities for developing innovative platforms to deliver therapeutic agents to the target tissues.

Quantitative Assessment of Choroidal Thickness and Choroidal Vascular Features in Healthy Eyes Based on Image Binarization of EDI-OCT: A Single-Center Cross-Sectional Analysis in Chinese Population

PURPOSE

To quantify the structural changes in choroidal vessels and to observe choroid microstructural changes in different age and sex groups in a healthy Chinese population.

METHODS

Enhanced depth imaging optical coherence tomography (EDI-OCT) was employed to analyze the luminal area, stromal area, total choroidal area, subfoveal choroidal thickness (SFCT), choroidal vascularity index (CVI), large choroidal vessel layer (LCVL), choriocapillaris-medium choroidal vessel layer, and LCVL/SFCT of the choroid in the subfoveal macular area within 1500 μm of the macula. We analyzed the age- and sex-related changes in the subfoveal choroidal structure.

RESULTS

A total of 1566 eyes from 1566 healthy individuals were included. The mean age of the participants was 43.62 ± 23.29 years, the mean SFCT of healthy individuals was 269.30 ± 66.43 μm, LCVL/SFCT percentage was 77.21 ± 5.84%, and the mean macular CVI was 68.39 ± 3.15%. CVI was maximum in the 0-10 years group, decreasing with age, and the lowest values occurred in the >80 years group; LCVL/SFCT was the lowest in the 0-10 years group, increasing with age and reaching a maximum in the >80 years group. CVI showed a significant negative correlation with age, and LCVL/SFCT showed a significant positive correlation with age. There was no statistically significant difference between males and females. Interrater and intrarater reliability was less variable with CVI than with SFCT.

CONCLUSIONS

The choroidal vascular area and CVI decreased with age in the healthy Chinese population, of which the age-related decrease in vascular components maybe dominated by the decrease in choriocapillaris and medium choroidal vessels. Sex had no effect on CVI. The CVI of healthy populations showed better consistency and reproducibility when compared with SFCT.

Oxidative stress and epigenetics in ocular vascular aging: an updated review

Vascular aging is an inevitable process with advancing age, which plays a crucial role in the pathogenesis of cardiovascular and microvascular diseases. Diabetic retinopathy (DR) and age-related macular degeneration (AMD), characterized by microvascular dysfunction, are the common causes of irreversible blindness worldwide, however there is still a lack of effective therapeutic strategies for rescuing the visual function. In order to develop novel treatments, it is essential to illuminate the pathological mechanisms underlying the vascular aging during DR and AMD progression. In this review, we have summarized the recent discoveries of the effects of oxidative stress and epigenetics on microvascular degeneration, which could provide potential therapeutic targets for DR and AMD.

Choriocapillaris Flow Signal Impairment in Patients With Pseudoxanthoma Elasticum

Purpose

To quantify choriocapillaris flow alterations in patients with pseudoxanthoma elasticum (PXE) in pre-atrophic stages and its association with structural changes of the choroid and outer retina.

Methods

Thirty-two eyes of 21 patients with PXE and 35 healthy eyes of 35 controls were included. The density of choriocapillaris flow signal deficits (FDs) was quantified on 6 × 6-mm optical coherence tomography angiography (OCTA) images. Spectral-domain optical coherence tomography (SD-OCT) images were analyzed for thicknesses of the choroid and outer retinal microstructure and correlated with choriocapillaris FDs in the respective Early Treatment Diabetic Retinopathy Study subfield.

Results

The multivariable mixed model analysis for choriocapillaris FDs revealed significantly higher FDs associated with the group (PXE patients vs. controls +13.6; 95% confidence interval [CI] 9.87-17.3; P < 0.001), with increasing age (+0.22% per year; 95% CI 0.12-0.33; P < 0.001), and with retinal location (significantly higher FDs in nasal compared to temporal subfields). Choroidal thickness (CT) did not differ significantly between both groups (P = 0.078). The CT and choriocapillaris FDs were inversely correlated (-1.92 µm per %FDs; interquartile range -2.81 to -1.03; P < 0.001). Larger values of the choriocapillaris FDs were associated with significant thinning of the overlying photoreceptor layers (outer segments: -0.21 µm per %FDs, P < 0.001; inner segments: -0.12 µm per %FDs, P = 0.001; outer nuclear layer: -0.72 µm per %FDs; P < 0.001).

Conclusions

Patients with PXE display significant alterations of the choriocapillaris on OCTA even in pre-atrophic stages and in the absence of significant choroidal thinning. The analysis favors choriocapillaris FDs over choroidal thickness as a potential early outcome measure for future interventional trials in PXE. Further, increased FDs in nasal compared to temporal locations mirror the centrifugal spread of Bruch's membrane calcification in PXE.

Bioprinted 3D outer retina barrier uncovers RPE-dependent choroidal phenotype in advanced macular degeneration

Age-related macular degeneration (AMD), a leading cause of blindness, initiates in the outer-blood-retina-barrier (oBRB) formed by the retinal pigment epithelium (RPE), Bruch's membrane, and choriocapillaris. The mechanisms of AMD initiation and progression remain poorly understood owing to the lack of physiologically relevant human oBRB models. To this end, we engineered a native-like three-dimensional (3D) oBRB tissue (3D-oBRB) by bioprinting endothelial cells, pericytes, and fibroblasts on the basal side of a biodegradable scaffold and establishing an RPE monolayer on top. In this 3D-oBRB model, a fully-polarized RPE monolayer provides barrier resistance, induces choriocapillaris fenestration, and supports the formation of Bruch's-membrane-like structure by inducing changes in gene expression in cells of the choroid. Complement activation in the 3D-oBRB triggers dry AMD phenotypes (including subRPE lipid-rich deposits called drusen and choriocapillaris degeneration), and HIF-α stabilization or STAT3 overactivation induce choriocapillaris neovascularization and type-I wet AMD phenotype. The 3D-oBRB provides a physiologically relevant model to studying RPE-choriocapillaris interactions under healthy and diseased conditions.

CHOROIDAL VASCULAR ALTERATIONS IN AGE-RELATED MACULAR DEGENERATION AND POLYPOIDAL CHOROIDAL VASCULOPATHY

PURPOSE

To evaluate morphologic alterations in choroidal veins in eyes with typical neovascular age-related macular degeneration (nAMD) and polypoidal choroidal vasculopathy (PCV).

METHODS

A retrospective review of baseline indocyanine green angiography in eyes with typical nAMD and PCV. We evaluated Haller layer veins in the early-phase indocyanine green angiography (before 2 minutes) for 1) macular anastomosis, 2) dilated Haller veins, and 3) focal variation in vessel caliber by at least 50% from the narrowest to largest diameters.

RESULTS

We included 70 patients with gradable indocyanine green angiography for the prespecified features in the study eye (36 typical nAMD and 34 PCV) and 59 fellow eyes. The median subfoveal choroidal thickness was 167 µm versus 219 µm, P = 0.08, in the presenting eyes in typical nAMD and PCV, respectively. Macular anastomosis was common in both typical nAMD and PCV (presenting eyes 58.3% vs. 58.8%. P = 0.97; fellow eyes 65.5% vs. 63.3%, P = 0.86). Dilated Haller veins were numerically less common in typical nAMD than PCV (presenting eyes 52.8% vs. 67.6%, P = 0.21; fellow eyes 65.5% vs. 70.0%, P = 0.71), while vascular caliber variation was numerically more common in typical nAMD than PCV (presenting eyes 72.2% vs. 63.8%, P = 0.45; fellow eyes 69.0% vs. 56.7%, P = 0.33). The presence of all three features was more common in the presenting eyes with PCV compared with typical nAMD (35.3% vs. 13.9%, P = 0.03). In a multivariable analysis, every increase of 100 µm of CT conferred a 2.75 risk of having all three features present.

CONCLUSION

Choroidal vascular remodeling is common in both tAMD and PCV but may be driven by different stimuli.

Cell Sources for Retinal Regeneration: Implication for Data Translation in Biomedicine of the Eye

The main degenerative diseases of the retina include macular degeneration, proliferative vitreoretinopathy, retinitis pigmentosa, and glaucoma. Novel approaches for treating retinal diseases are based on cell replacement therapy using a variety of exogenous stem cells. An alternative and complementary approach is the potential use of retinal regeneration cell sources (RRCSs) containing retinal pigment epithelium, ciliary body, Müller glia, and retinal ciliary region. RRCSs in lower vertebrates in vivo and in mammals mostly in vitro are able to proliferate and exhibit gene expression and epigenetic characteristics typical for neural/retinal cell progenitors. Here, we review research on the factors controlling the RRCSs' properties, such as the cell microenvironment, growth factors, cytokines, hormones, etc., that determine the regenerative responses and alterations underlying the RRCS-associated pathologies. We also discuss how the current data on molecular features and regulatory mechanisms of RRCSs could be translated in retinal biomedicine with a special focus on (1) attempts to obtain retinal neurons de novo both in vivo and in vitro to replace damaged retinal cells; and (2) investigations of the key molecular networks stimulating regenerative responses and preventing RRCS-related pathologies.

Single-Cell Transcriptome of Wet AMD Patient-Derived Endothelial Cells in Angiogenic Sprouting

Age-related macular degeneration (AMD) is a global leading cause of visual impairment in older populations. ‘Wet’ AMD, the most common subtype of this disease, occurs when pathological angiogenesis infiltrates the subretinal space (choroidal neovascularization), causing hemorrhage and retinal damage. Gold standard anti-vascular endothelial growth factor (VEGF) treatment is an effective therapy, but the long-term prevention of visual decline has not been as successful. This warrants the need to elucidate potential VEGF-independent pathways. We generated blood out-growth endothelial cells (BOECs) from wet AMD and normal control subjects, then induced angiogenic sprouting of BOECs using a fibrin gel bead assay. To deconvolute endothelial heterogeneity, we performed single-cell transcriptomic analysis on the sprouting BOECs, revealing a spectrum of cell states. Our wet AMD BOECs share common pathways with choroidal neovascularization such as extracellular matrix remodeling that promoted proangiogenic phenotype, and our ‘activated’ BOEC subpopulation demonstrated proinflammatory hallmarks, resembling the tip-like cells in vivo. We uncovered new molecular insights that pathological angiogenesis in wet AMD BOECs could also be driven by interleukin signaling and amino acid metabolism. A web-based visualization of the sprouting BOEC single-cell transcriptome has been created to facilitate further discovery research.

Choroidal Vasculature Changes in Age-Related Macular Degeneration: From a Molecular to a Clinical Perspective

The contribution of choroidal vasculature to the pathogenesis of age-related macular degeneration (AMD) has been long debated. The present narrative review aims to discuss the primary molecular and choroidal structural changes occurring with aging and AMD with a brief overview of the principal multimodal imaging modalities and techniques that enable the optimal in vivo visualization of choroidal modifications. The molecular aspects that target the choroid in AMD mainly involve human leukocyte antigen (HLA) expression, complement dysregulation, leukocyte interaction at Bruch’s membrane, and mast cell infiltration of the choroid. A mechanistic link between high-risk genetic loci for AMD and mast cell recruitment has also been recently demonstrated. Recent advances in multimodal imaging allow more detailed visualization of choroidal structure, identifying alterations that may expand our comprehension of aging and AMD development.

Secretory autophagy: a turn key for understanding AMD pathology and developing new therapeutic targets?

INTRODUCTION

Age-related macular degeneration (AMD) is an eye disease leading to vision loss with poorly known pathogenesis and limited therapeutic options. Degradative autophagy (DA) is impaired in AMD, but emerging evidence points to secretary autophagy (SA) as a key element in AMD pathogenesis.

AREAS COVERED

SA may cause the release of proteins and protein aggregates, lipofuscin, beta amyloid, faulty mitochondria, pro-inflammatory and pro-angiogenic factors from the retinal pigment epithelium (RPE) that may contribute to drusen formation and choroidal neovascularization. SA may replace DA, when formation of autolysosome is impaired, and then a harmful cargo, instead of being degraded, is extruded from the RPE contributing to drusen and/or angiogenic environment. Therefore, the interplay between DA and SA may be critical for drusen formation and choroidal neovascularization, so it can be a turn key to understand AMD pathogenesis.

EXPERT OPINION

Although SA fulfills some beneficial functions, it is detrimental for the retina in many cases. Therefore, inhibiting SA may be a therapeutic strategy in AMD, but it is challenged by the development of selective SA inhibitors that would not affect DA. The TRIM16, SEC22B and RAB8A proteins, specific for secretory autophagosome, may be primary candidates as therapeutic targets, but their action is not limited to autophagy and therefore requires further studies.

The Essential Role of the Choriocapillaris in Vision: Novel Insights from Imaging and Molecular Biology

The choriocapillaris, a dense capillary network located at the posterior pole of the eye, is essential for supporting normal vision, supplying nutrients, and removing waste products from photoreceptor cells and the retinal pigment epithelium. The anatomical location, heterogeneity, and homeostatic interactions with surrounding cell types make the choroid complex to study both in vivo and in vitro. Recent advances in single-cell RNA sequencing, in vivo imaging, and in vitro cell modeling are vastly improving our knowledge of the choroid and its role in normal health and in age-related macular degeneration (AMD). Histologically, loss of endothelial cells (ECs) of the choriocapillaris occurs early in AMD concomitant with elevated formation of the membrane attack complex of complement. Advanced imaging has allowed us to visualize early choroidal blood flow changes in AMD in living patients, supporting histological findings of loss of choroidal ECs. Single-cell RNA sequencing is being used to characterize choroidal cell types transcriptionally and discover their altered patterns of gene expression in aging and disease. Advances in induced pluripotent stem cell protocols and 3D cultures will allow us to closely mimic the in vivo microenvironment of the choroid in vitro to better understand the mechanism leading to choriocapillaris loss in AMD.

Morphometrics in three dimensional choroidal vessel models constructed from swept-source optical coherence tomography images

We created three types of vessel models: vessel volume, surface, and line models from swept-source optical coherence tomography images and tested experimentally calculated three-dimensional (3D) biomarkers. The choroidal volume (CVolume), surface area (VSurface), and vessel length-associated index (VLI) were measured. The calculated 3D parameters were the mean choroidal thickness, choroidal vascularity index (CVI), vessel length density index (VLDI), vessel length to the stromal (VL–S) ratio, surface-to-volume ratio (S–V ratio), and vessel diameter index (VDI). Cluster analysis showed that the parameters were classified into two clusters: one was represented by the VVolume including the CVolume, VSurface, CVI, S–V ratio, VLI, VDI, and subfoveal choroidal thickness and the other by the VL–S ratio including the VLDI. Regarding the regional distribution, the VVolume, CVolume, VSurface, CVI, VLI, VL–S ratio, and VDI at the foveal center were higher than at the parafovea (P < 0.01). Although the VVolume decreased with age and axial length (AL) elongation, the association of the 3D parameters with age and AL elongation differed. The VLI, VLDI, VL–S ratio, and CVI decreased with age (P < 0.01) but not with AL elongation. The results suggested a structural difference in the choroidal vessel volume reduction between aging and AL elongation. The 3D parameters may provide additional information about the choroidal vasculature.

Age and Sex-Related Changes in Retinal Function in the Vervet Monkey

Among the deficits in visual processing that accompany healthy aging, the earliest originate in the retina. Moreover, sex-related differences in retinal function have been increasingly recognized. To better understand the dynamics of the retinal aging trajectory, we used the light-adapted flicker electroretinogram (ERG) to functionally assess the state of the neuroretina in a large cohort of age- and sex-matched vervet monkeys (N = 35), aged 9 to 28 years old, with no signs of obvious ocular pathology. We primarily isolated the cone–bipolar axis by stimulating the retina with a standard intensity light flash (2.57 cd/s/m²) at eight different frequencies, ranging from 5 to 40 Hz. Sex-specific changes in the voltage and temporal characteristics of the flicker waveform were found in older individuals (21–28 years-old, N = 16), when compared to younger monkeys (9–20 years-old, N = 19), across all stimulus frequencies tested. Specifically, significantly prolonged implicit times were observed in older monkeys (p < 0.05), but a significant reduction of the amplitude of the response was only found in old male monkeys (p < 0.05). These changes might reflect ongoing degenerative processes targeting the retinal circuitry and the cone subsystem in particular. Altogether, our findings corroborate the existing literature in humans and other species, where aging detrimentally affects photopic retinal responses, and draw attention to the potential contribution of different hormonal environments.

Microbiota mitochondria disorders as hubs for early age-related macular degeneration

Age-related macular degeneration (AMD) is a progressive neurodegenerative disease affecting the central area (macula lutea) of the retina. Research on the pathogenic mechanism of AMD showed complex cellular contribution governed by such risk factors as aging, genetic predisposition, diet, and lifestyle. Recent studies suggested that microbiota is a transducer and a modifier of risk factors for neurodegenerative diseases, and mitochondria may be one of the intracellular targets of microbial signaling molecules. This review explores studies supporting a new concept on the contribution of microbiota-mitochondria disorders to AMD. We discuss metabolic, vascular, immune, and neuronal mechanism in AMD as well as key alterations of photoreceptor cells, retinal pigment epithelium (RPE), Bruch's membrane, choriocapillaris endothelial, immune, and neuronal cells. Special attention was paid to alterations of mitochondria contact sites (MCSs), an organelle network of mitochondria, endoplasmic reticulum, lipid droplets (LDs), and peroxisomes being documented based on our own electron microscopic findings from surgically removed human eyes. Morphometry of Bruch's membrane lipids and proteoglycans has also been performed in early AMD and aged controls. Microbial metabolites (short-chain fatty acids, polyphenols, and secondary bile acids) and microbial compounds (lipopolysaccharide, peptidoglycan, and bacterial DNA)-now called postbiotics-in addition to local effects on resident microbiota and mucous membrane, regulate systemic metabolic, vascular, immune, and neuronal mechanisms in normal conditions and in various common diseases. We also discuss their antioxidant, anti-inflammatory, and metabolic effects as well as experimental and clinical observations on regulating the main processes of photoreceptor renewal, mitophagy, and autophagy in early AMD. These findings support an emerging concept that microbiota-mitochondria disorders may be a crucial pathogenic mechanism of early AMD; and similarly, to other age-related neurodegenerative diseases, new treatment approaches should be targeted at these disorders.

Nuclear Receptor Atlases of Choroidal Tissues Reveal Candidate Receptors Associated with Age-Related Macular Degeneration

The choroid is a vulnerable tissue site in the eye, impacted in several blinding diseases including age related macular degeneration (AMD), which is the leading cause of central vision loss in the aging population. Choroidal thinning and choriocapillary dropout are features of the early form of AMD, and endothelial dysfunction and vascular changes are primary characteristics of the neovascular clinical sub-type of AMD. Given the importance, the choroidal endothelium and outer vasculature play in supporting visual function, a better understanding of baseline choroidal signaling pathways engaged in tissue and cellular homeostasis is needed. Nuclear receptors are a large family of transcription factors responsible for maintaining various cellular processes during development, aging and disease. Herein we developed a comprehensive nuclear receptor atlas of human choroidal endothelial cells and freshly isolated choroidal tissue by examining the expression levels of all members of this transcription family using quantitative real time PCR. Given the close relationship between the choroid and retinal pigment epithelium (RPE), this data was cross-referenced with the expression profile of nuclear receptors in human RPE cells, to discover potential overlap versus cell-specific nuclear receptor expression. Finally, to identify candidate receptors that may participate in the pathobiology of AMD, we cataloged nuclear receptor expression in a murine model of wet AMD, from which we discovered a subset of nuclear receptors differentially regulated following neovascularization. Overall, these databases serve as useful resources establishing the influence of nuclear receptor signaling pathways on the outer vascular tissue of the eye, while providing a list of receptors, for more focused investigations in the future, to determine their suitability as potential therapeutic targets for diseases, in which the choroid is affected.

Bioengineering approaches for modelling retinal pathologies of the outer blood-retinal barrier

Alterations of the junctional complex of the outer blood-retinal barrier (oBRB), which is integrated by the close interaction of the retinal pigment epithelium, the Bruch's membrane, and the choriocapillaris, contribute to the loss of neuronal signalling and subsequent vision impairment in several retinal inflammatory disorders such as age-related macular degeneration and diabetic retinopathy. Reductionist approaches into the mechanisms that underlie such diseases have been hindered by the absence of adequate in vitro models using human cells to provide the 3D dynamic architecture that enables expression of the in vivo phenotype of the oBRB. Conventional in vitro cell models are based on 2D monolayer cellular cultures, unable to properly recapitulate the complexity of living systems. The main drawbacks of conventional oBRB models also emerge from the cell sourcing, the lack of an appropriate Bruch's membrane analogue, and the lack of choroidal microvasculature with flow. In the last years, the advent of organ-on-a-chip, bioengineering, and stem cell technologies is providing more advanced 3D models with flow, multicellularity, and external control over microenvironmental properties. By incorporating additional biological complexity, organ-on-a-chip devices can mirror physiologically relevant properties of the native tissue while offering additional set ups to model and study disease. In this review we first examine the current understanding of oBRB biology as a functional unit, highlighting the coordinated contribution of the different components to barrier function in health and disease. Then we describe recent advances in the use of pluripotent stem cells-derived retinal cells, Bruch's membrane analogues, and co-culture techniques to recapitulate the oBRB. We finally discuss current advances and challenges of oBRB-on-a-chip technologies for disease modelling.

High-Fat Diet Alters the Retinal Pigment Epithelium and Choroidal Transcriptome in the Absence of Gut Microbiota

Relationships between retinal disease, diet, and the gut microbiome have started to emerge. In particular, high-fat diets (HFDs) are associated with the prevalence and progression of several retinal diseases, including age-related macular degeneration (AMD) and diabetic retinopathy (DR). These effects are thought to be partly mediated by the gut microbiome, which modulates interactions between diet and host homeostasis. Nevertheless, the effects of HFDs on the retina and adjacent retinal pigment epithelium (RPE) and choroid at the transcriptional level, independent of gut microbiota, are not well-understood. In this study, we performed the high-throughput RNA-sequencing of germ-free (GF) mice to explore the transcriptional changes induced by HFD in the RPE/choroid. After filtering and cleaning the data, 649 differentially expressed genes (DEGs) were identified, with 616 genes transcriptionally upregulated and 33 genes downregulated by HFD compared to a normal diet (ND). Enrichment analysis for gene ontology (GO) using the DEGs was performed to analyze over-represented biological processes in the RPE/choroid of GF-HFD mice relative to GF-ND mice. GO analysis revealed the upregulation of processes related to angiogenesis, immune response, and the inflammatory response. Additionally, molecular functions that were altered involved extracellular matrix (ECM) binding, ECM structural constituents, and heparin binding. This study demonstrates novel data showing that HFDs can alter RPE/choroid tissue transcription in the absence of the gut microbiome.