The oil spill in ageing Bruch membrane

Prenatally derived macrophages support choroidal health and decline in age-related macular degeneration

Hallmark findings in age-related macular degeneration (AMD) include the accumulation of extracellular lipid and vasodegeneration of the choriocapillaris. Choroidal inflammation has long been associated with AMD, but little is known about the immune landscape of the human choroid. Using 3D multiplex immunofluorescence, single-cell RNA sequencing, and flow cytometry, we unravel the cellular composition and spatial organization of the human choroid and the immune cells within it. We identify two populations of choroidal macrophages with distinct FOLR2 expression that account for the majority of myeloid cells. FOLR2+ macrophages predominate in the nondiseased eye, express lipid-handling machinery, uptake lipoprotein particles, and contain high amounts of lipid. In AMD, FOLR2+ macrophages are decreased in number and exhibit dysfunctional lipoprotein metabolism. In mice, FOLR2+ macrophages are negative for the postnatal fate-reporter Ms4a3, and their depletion causes an accelerated AMD-like phenotype. Our results show that prenatally derived resident macrophages decline in AMD and are implicated in multiple hallmark functions known to be compromised in the disease.

Characterizing Bruch's membrane: State-of-the-art imaging, computational segmentation, and biologic models in retinal disease and health

The Bruch's membrane (BM) is an acellular, extracellular matrix that lies between the choroid and retinal pigment epithelium (RPE). The BM plays a critical role in retinal health, performing various functions including biomolecule diffusion and RPE support. The BM is also involved in many retinal diseases, and insights into BM dysfunction allow for further understanding of the pathophysiology of various chorioretinal pathologies. Thus, characterization of the BM serves as an important area of research to further understand its involvement in retinal disease. In this article, we provide a review of various advancements in characterizing and visualizing the BM. We provide an overview of the BM in retinal health, as well as changes observed in aging and disease. We then describe current state-of-the-art imaging modalities and advances to further visualize the BM including various types of optical coherence tomography imaging, near-infrared reflectance (NIR), and autofluorescence imaging and tissue matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS). Following advances in imaging of the BM, we describe animal, cellular, and synthetic models that have been developed to further visualize the BM. Following this section, we provide an overview of deep learning in retinal imaging and describe advances in computational and artificial intelligence (AI) techniques to provide automated segmentation of the BM and BM opening. We conclude this section considering the clinical implications of these segmentation techniques. Ultimately, the diverse advances aimed to further characterize the BM may allow for deeper insights into the involvement of this critical structure in retinal health and disease.

Age-Related Macular Degeneration Pathophysiology and Therapeutic Potential of Tocotrienols: An Update

Age-related macular degeneration (AMD) poses a significant threat to visual health among the elderly, necessitating urgent preventive measures as the global population ages. Extensive research has implicated oxidative stress (OS)-induced retinal damage as a primary contributor to AMD pathogenesis, prompting investigations into potential therapeutic interventions. Among the various nutrients studied for their potential in AMD risk reduction, antioxidants have shown promise, with initial findings from the Age-Related Eye Disease Study suggesting a correlation between antioxidant supplementation and decreased AMD progression. This article explores the scientific foundation supporting the therapeutic efficacy of tocotrienol-rich fraction (TRF) as a viable candidate for slowing AMD progression, based on interventional studies. AMD is characterized by OS, inflammation, dysregulated lipid metabolism, and angiogenesis, all of which TRF purportedly addresses through its potent anti-inflammatory, lipid-lowering, antiangiogenic, and antioxidant properties. The review underscores TRF's promising attributes, aiming to deepen understanding of AMD pathogenesis and advocate for TRF-based pharmacological interventions to enhance therapeutic outcomes. Given the pressing need for effective AMD treatments, TRF represents a promising avenue for intervention, offering hope for improved vision outcomes and enhanced quality of life for individuals affected by this debilitating condition.

Review of type 3 macular neovascularization in age-related macular degeneration: no DRAMA (Deep Retinal Age-related Microvascular Anomalies)

Type 3 macular neovascularization (MNV) is a unique form of neovascular age-related macular degeneration (AMD) that presents distinct pathogenetic features, clinical manifestations, and prognostic considerations when compared to types 1 and 2 MNV. Insights gained from clinicopathological correlations, bridging in vivo examination techniques with ex vivo histological analysis, have significantly enhanced our comprehension of this MNV phenotype, shaped current management strategies and influenced future directions for therapeutics. The particularities of type 3 MNV, which may largely stem from its origin from the retinal vasculature, are critically important for predicting the disease course. Our current understanding suggests that type 3 MNV occurs in response to retinal pigment epithelium (RPE) disruption and photoreceptor loss when neovessels originating from the deep capillary plexus are accompanied by activated Müller glia as they infiltrate sub-retinal pigment epithelium basal laminar deposits. Dysregulation of angiogenic and angiostatic factors are thought to play a key role in its pathogenesis. The prognosis for type 3 MNV is likely bilateral involvement and progression towards macular atrophy. It may be imperative for practitioners to distinguish type 3 MNV from other mimicking pathologies such as intraretinal microvascular anomalies, which are also part of the type 3 disease spectrum. For instance, deep retinal age-related microvascular anomalies (DRAMA) may present with similar features on multimodal imaging yet may necessitate distinct management protocols. Distinguishing between these conditions may be vital for implementing tailored treatment regimens and improving patient outcomes in the diverse landscape of AMD phenotypes in the future.

Relationship Between Chronic Stress Measured by Allostatic Load and Age-Related Macular Degeneration in the All of Us Research Program

PURPOSE

To assess the longitudinal relationship between age-related macular degeneration (AMD) and allostatic load (AL), an established framework for quantifying the physiologic effects of chronic stress through measurements of systemic biomarkers.

DESIGN

Retrospective case-control study.

METHODS

Participants of the National Institutes of Health All of Us (AoU) Research Program with complete AL biomarker data between February 1985 to May 2022 and with (cases) or without (controls) AMD were identified. AL scores were calculated using the adapted Seeman AL scale consisting of 10 systemic biomarkers: body mass index, systolic blood pressure, diastolic blood pressure, total cholesterol, triglycerides, glomerular filtration rate, albumin, C-reactive protein, and homocysteine. AL score was defined as the number of biomarkers with measurements in the highest risk quartiles. Age was calculated as the median age at time of earliest or latest biomarker measurements. The main outcome was AMD status (AMD or non-AMD). Logistic regression models assessed the association between AL score and AMD after standardization of age and sex and adjustment for race/ethnicity and pack-years of cigarette smoking. Mediation analysis estimated the relationship between race/ethnicity and AMD as mediated by AL score.

RESULTS

Among 1530 participants (221 cases, 1309 controls) with complete biomarker data, there were 44.6% males, 76.1% non-Hispanic Whites (NHWs), 18.6% other specified race/ethnicity (Asian, Black, or Hispanic race/ethnicity), and 5.3% unspecified race/ethnicity. AL scores measured a median of 9.0 (IQR=5.0-14.0) years prior to diagnosis were higher among cases compared to controls (Median [IQR] = 2 [2-4] versus 2 [1-3]; P = .02). On multivariable analysis, higher baseline AL score (OR=1.11) and greater pack-years (OR=1.15 per 10 pack-years) conferred higher risk of AMD (P ≤ .02). Mediation analysis revealed a significant indirect effect that increased risk of AMD among other specified race/ethnicity participants compared to NHW participants through higher AL score (OR=1.07 per unit [1.01-1.15]).

CONCLUSION

All of Us participants diagnosed with AMD had greater AL score 9.0 years prior to AMD diagnosis. Chronic stress appears to increase risk for AMD and may contribute to racial/ethnic differences in disease prevalence.

Dietary effects on the retina of hamsters

The retina is a sensory tissue in the back of the eye, which captures visual information and relays it to the brain. The retinal pigment epithelium separates the neural retina from the choroidal (systemic) circulation and is thereby exposed to circulating lipoprotein particles. Herein, we used hamsters and conducted various retinal evaluations of animals fed either a normal diet or a Western-type diet (WTD). Prior to evaluations, hamsters were injected with indocyanine green (ICG), a fluorescent dye that binds to various proteins and lipids in the systemic circulation. The WTD increased plasma levels of total and HDL cholesterol 1.8- and 2.1-fold, respectively, and led to additional HDL2 and HDL3 subpopulations. The diet also increased the ICG fluorescence in the retinal pigment epithelium and the underlying choroidal circulation on histological tracking and altered retinal protein abundance as assessed by proteomics. Functional enrichments were found in the retinal gene expression, energy production, intracellular transport, cytoskeleton- and synapse-related processes, and protein ubiquitination. The biochemical basis linking the WTD, retinal energy production, and retinal neurotransmission was suggested as well. The data obtained were then compared with those from our previous investigations of hamsters and different mouse genotypes. We identified common retinal processes that can be affected by circulating lipoprotein particles regardless of the mechanism by which their levels and subpopulations were altered (through diet or genetic modification). Thus, we obtained novel mechanistic insights into how lipids in the systemic circulation can affect the retina.

Characterization of drusen formation in a primary porcine tissue culture model of dry AMD

Age-related macular degeneration (AMD) affects millions of individuals worldwide and is a leading cause of blindness in the elderly. In dry AMD, lipoproteinaceous deposits called drusen accumulate between the retinal pigment epithelium (RPE) and Bruch's membrane, leading to impairment of oxygen and nutrient trafficking to the neural retina, and degeneration of the overlying photoreceptor cells. Owing to key differences in human and animal ocular anatomy and the slowly progressing nature of the disease, AMD is not easily modeled in vivo. In this study, we further characterize a "drusen-in-a-dish" primary porcine RPE model system by employing vital lipid staining to monitor sub-RPE deposition over time in monolayers of cells cultured on porous transwell membranes. We demonstrate for the first time using a semi-automated image analysis pipeline that the number and size of sub-RPE deposits increases gradually but significantly over time and confirm that sub-RPE deposits grown in culture immunostain positive for multiple known components found in human drusen. As a result, we propose that drusen-in-a-dish cell culture models represent a high-throughput and cost-scalable alternative to animal models in which to study the pathobiology of drusen accumulation and may serve as useful tools for screening novel therapeutics aimed at treating dry AMD.

Different Therapeutic Approaches for Dry and Wet AMD

Age-related macular degeneration (AMD) is the most common cause of irreversible loss of central vision in elderly subjects, affecting men and women equally. It is a degenerative pathology that causes progressive damage to the macula, the central and most vital part of the retina. There are two forms of AMD depending on how the macula is damaged, dry AMD and wet or neovascular AMD. Dry AMD is the most common form; waste materials accumulate under the retina as old cells die, not being replaced. Wet AMD is less common, but can lead to vision loss much more quickly. Wet AMD is characterized by new abnormal blood vessels developing under the macula, where they do not normally grow. This frequently occurs in patients who already have dry AMD, as new blood vessels are developed to try to solve the problem. It is not known what causes AMD to develop; however, certain risk factors (i.e., age, smoking, genetic factors) can increase the risk of developing AMD. There are currently no treatments for dry AMD. There is evidence that not smoking, exercising regularly, eating nutritious food, and taking certain supplements can reduce the risk of acquiring AMD or slow its development. The main treatment for wet AMD is inhibitors of VEGF (vascular endothelial growth factor), a protein that stimulates the growth of new blood vessels. VEGF inhibitors can stop the growth of new blood vessels, preventing further damage to the macula and vision loss. In most patients, VEGF inhibitors can improve vision if macular degeneration is diagnosed early and treated accordingly. However, VEGF inhibitors cannot repair damage that has already occurred. Current AMD research is trying to find treatments for dry AMD and other options for wet AMD. This review provides a summary of the current evidence regarding the different treatments aimed at both forms of AMD with particular and greater attention to the dry form.

Applying low levels of strain to model nascent phenomenon of retinal pathologies

Age-related macular degeneration (AMD) is a leading cause of vision loss in aging populations. A better understanding of the mechanisms of the disease, especially at early stages, could elucidate new treatment targets. One characteristic of AMD is strain on the retinal pigment epithelium (RPE), a crucial layer of the retina. This strain can be caused by physical phenomena like waste aggregation underneath the RPE, drusen formation, or leaky blood vessels that infiltrate the retina during choroidal neovascularization (CNV). It is not well understood how strain affects RPE cell function. Most models generate equibiaxial strain or higher levels of strain that are not representative of early stages of AMD. To overcome these issues, we engineered a device to cause controlled, low amounts of localized, radial strain (maximum ∼1.4%). This strain level is more mimetic to what occurs during aging or at the beginning of physical disruptions experienced during AMD. To evaluate how RPE cells respond to this physical stimulus, primary porcine RPE cells were exposed to low levels of strain applied by our custom-made device. Cell secretions and genetic expression were analyzed to determine how proteins linked to drusen and CNV are affected. The results indicate that this low amount of strain does not immediately initiate angiogenesis but causes changes in mRNA expression of amyloid precursor protein (APP), which plays a role in retinal health and drusen accumulation. This research offers insight into AMD progression as well as the health of other organs, including the brain.

The role of immune modulators in age-related macular degeneration

We provide an overview of the expanding literature on the role of cytokines and immune mediators in pathophysiology of age-related macular degeneration (AMD). Although many immunological mediators have been linked to AMD pathophysiology, the broader mechanistic picture remains unclear with substantial variations in the levels of evidence supporting these mediators. Therefore, we reviewed the literature considering the varying levels of supporting evidence. A Medical Subject Headings (MeSH) term-based literature research was conducted in September, 2023, consisting of the MeSH terms "cytokine" and "Age-related macular degeneration" connected by the operator "AND". After screening the publications by title, abstract, and full text, a total of 146 publications were included. The proinflammatory cytokines IL-1β (especially in basic research studies), IL-6, IL-8, IL-18, TNF-α, and MCP-1 are the most extensively characterised cytokines/chemokines, highlighting the role of local inflammasome activation and altered macrophage function in the AMD pathophysiology. Among the antiinflammatory mediators IL-4, IL-10, and TGF-β were found to be the most extensively characterised, with IL-4 driving and IL-10 and TGF-β suppressing disease progression. Despite the extensive literature on this topic, a profound understanding of AMD pathophysiology has not yet been achieved. Therefore, further studies are needed to identify potential therapeutic targets, followed by clinical studies.

NATURAL COURSE OF AGE-RELATED RETENTIONAL AVASCULAR PIGMENT EPITHELIAL DETACHMENT: Support For The Lipid Barrier Hypothesis

PURPOSE

Retentional pigment epithelial detachment (PED) associated with age-related scattered hypofluorescent spots on late-phase indocyanine green angiography (ASHS-LIA) is hypothesized to be caused by Bruch membrane's lipid barrier. This study aimed to report the natural course of retentional PED and evaluate the relationship between retentional PED evolution and ASHS-LIA.

METHODS

Patients with treatment-naïve retentional PED were enrolled and observed every 3 months for at least 12 months. Treatment was not performed except for secondary macular neovascularization.

RESULTS

In 55 studied eyes with a median follow-up of 18.0 (range: 12-36) months, 87.3% (48/55) of the retentional PEDs persisted, 7.3% (4/55) resolved, and 5.5% (3/55) progressed to polypoidal choroidal vasculopathy. The mean PED area significantly increased during the follow-up ( P < 0.001) and with the ASHS-LIA grade at each follow-up point (all P <0.05), especially during the first 6 months before approaching the edge of confluent ASHS-LIA. Persistent PEDs were mostly stable (52.1%) or enlarged (45.8%) but reduced in only 1 case (2.1%) because of retinal pigment epithelium microrip at the edge of PED. The persistent PEDs were all within the ASHS-LIA region, especially the macular confluence region. The resolved PEDs all had grade 1 ASHS-LIA and resolved after gradual expansion of PED beyond the confluent ASHS-LIA region. Pigment epithelial detachments that progressed to macular neovascularization all had confluent grade 2 or 3 ASHS-LIA. Retinal pigment epithelium microrips or apertures within PED did not affect the progression of the PED.

CONCLUSION

The natural course of retentional PED is closely related to the features of ASHS-LIA and supports its lipid-barrier hypothesis.

Age-Related Changes in the Glycolytic Enzymes of M2-Isoform of Pyruvate Kinase and Fructose-1,6-Bisphosphate Aldolase: Implications to Age-Related Macular Degeneration

Prior studies have emphasized a bioenergetic crisis in the retinal pigment epithelium (RPE) as a critical factor in the development of age-related macular degeneration (AMD). The isoforms Fructose-1,6-bisphosphate aldolase C (ALDOC) and pyruvate kinase M2 (PKM2) have been proposed to play a role in AMD pathogenesis. While PKM2 and ALDOC are crucial for aerobic glycolysis in the neural retina, they are not as essential for the RPE. In this study, we examined the expression and activity of PKM2 and ALDOC in both young and aged RPE cells, as well as in the retina and RPE tissue of mice, including an experimentally induced AMD mouse model. Our findings reveal an upregulation in PKM2 and ALDOC expression, accompanied by increased pyruvate kinase activity, in the aged and AMD mouse RPE. Conversely, there is a decrease in ALDOC expression but an increase in PKM2 expression and pyruvate kinase activity in the aged and AMD retina. Overall, our study indicates that aged and AMD RPE cells tend to favor aerobic glycolysis, while this tendency is diminished in the aged and AMD retina. These results underscore the significance of targeting PKM2 and ALDOC in the RPE as a promising therapeutic approach to address the bioenergetic crisis and prevent vision loss in AMD.

A distributed integral control mechanism for regulation of cholesterol concentration in the human retina

Tight homeostatic control of cholesterol concentration within the complex tissue microenvironment of the retina is the hallmark of a healthy eye. By contrast, dysregulation of biochemical mechanisms governing retinal cholesterol homeostasis likely contributes to the aetiology and progression of age-related macular degeneration (AMD). While the signalling mechanisms maintaining cellular cholesterol homeostasis are well-studied, a systems-level description of molecular interactions regulating cholesterol balance within the human retina remains elusive. Here, we provide a comprehensive overview of all currently-known molecular-level interactions involved in cholesterol regulation across the major compartments of the human retina, encompassing the retinal pigment epithelium (RPE), photoreceptor cell layer, Müller cell layer and Bruch's membrane. We develop a comprehensive chemical reaction network (CRN) of these interactions, involving 71 molecular species, partitioned into 10 independent subnetworks. These subnetworks collectively ensure robust homeostasis of 14 forms of cholesterol across distinct retinal cellular compartments. We provide mathematical evidence that three independent antithetic integral feedback controllers tightly regulate ER cholesterol in retinal cells, with additional independent mechanisms extending this regulation to other forms of cholesterol throughout the retina. Our novel mathematical model of retinal cholesterol regulation provides a framework for understanding the mechanisms of cholesterol dysregulation in diseased eyes and for exploring potential therapeutic strategies.

Acetyl-CoA carboxylase inhibition increases retinal pigment epithelial cell fatty acid flux and restricts apolipoprotein efflux

Lipid-rich deposits called drusen accumulate under the retinal pigment epithelium (RPE) in the eyes of patients with age-related macular degeneration and Sorsby's fundus dystrophy (SFD). Drusen may contribute to photoreceptor degeneration in these blinding diseases. Stimulating β-oxidation of fatty acids could decrease the availability of lipid with which RPE cells generate drusen. Inhibitors of acetyl-CoA carboxylase (ACC) stimulate β-oxidation and diminish lipid accumulation in fatty liver disease. In this report, we test the hypothesis that an ACC inhibitor, Firsocostat, can diminish lipid deposition by RPE cells. We probed metabolism and cellular function in mouse RPE-choroid tissue and human RPE cells. We used 13C6-glucose, 13C16-palmitate, and gas chromatography-linked mass spectrometry to monitor effects of Firsocostat on glycolytic, Krebs cycle, and fatty acid metabolism. We quantified lipid abundance, apolipoprotein E levels, and vascular endothelial growth factor release using liquid chromatography-mass spectrometry, ELISAs, and immunostaining. RPE barrier function was assessed by trans-epithelial electrical resistance (TEER). Firsocostat-mediated ACC inhibition increases β-oxidation, decreases intracellular lipid levels, diminishes lipoprotein release, and increases TEER. When human serum or outer segments are used to stimulate lipoprotein release, fewer lipoproteins are released in the presence of Firsocostat. In a culture model of SFD, Firsocostat stimulates fatty acid oxidation, increases TEER, and decreases apolipoprotein E release. We conclude that Firsocostat remodels RPE metabolism and can limit lipid deposition. This suggests that ACC inhibition could be an effective strategy for diminishing pathologic drusen in the eyes of patients with age-related macular degeneration or SFD.

Aberrant Lipid Metabolism and Complement Activation in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) stands as a leading cause of severe visual impairment and blindness among the elderly globally. As a multifactorial disease, AMD's pathogenesis is influenced by genetic, environmental, and age-related factors, with lipid metabolism abnormalities and complement system dysregulation playing critical roles. This review delves into recent advancements in understanding the intricate interaction between these two crucial pathways, highlighting their contribution to the disease's progression through chronic inflammation, drusen formation, and retinal pigment epithelium dysfunction. Importantly, emerging evidence points to dysregulated lipid profiles, particularly alterations in high-density lipoprotein levels, oxidized lipid deposits, and intracellular lipofuscin accumulation, as exacerbating factors that enhance complement activation and subsequently amplify tissue damage in AMD. Furthermore, genetic studies have revealed significant associations between AMD and specific genes involved in lipid transport and complement regulation, shedding light on disease susceptibility and underlying mechanisms. The review further explores the clinical implications of these findings, advocating for a novel therapeutic approach that integrates lipid metabolism modulators with complement inhibitors. By concurrently targeting these pathways, the dual-targeted approach holds promise in significantly improving outcomes for AMD patients, heralding a new horizon in AMD management and treatment.

Serum-deprivation response of ARPE-19 cells; expression patterns relevant to age-related macular degeneration

ARPE-19 cells are derived from adult human retinal pigment epithelium (RPE). The response of these cells to the stress of serum deprivation mimics some important processes relevant to age-related macular degeneration (AMD). Here we extend the characterization of this response using RNASeq and EGSEA gene set analysis of ARPE-19 cells over nine days of serum deprivation. This experiment confirmed the up-regulation of cholesterol and lipid-associated pathways that increase cholesterol levels in these cells. The gene expression analysis also identified other pathways relevant to AMD progression. There were significant changes in extracellular matrix gene expression, notably a switch from expression of collagen IV, a key component of Bruch's membrane (part of the blood-retina barrier), to expression of a fibrosis-like collagen type I matrix. Changes in the expression profile of the extracellular matrix led to the discovery that amelotin is induced in AMD and is associated with the development of the calcium deposits seen in late-stage geographic atrophy. The transcriptional profiles of other pathways, including inflammation, complement, and coagulation, were also modified, consistent with immune response patterns seen in AMD. As previously noted, the cells resist apoptosis and autophagy but instead initiate a gene expression pattern characteristic of senescence, consistent with the maintenance of barrier function even as other aspects of RPE function are compromised. Other differentially regulated genes were identified that open new avenues for investigation. Our results suggest that ARPE-19 cells maintain significant stress responses characteristic of native RPE that are informative for AMD. As such, they provide a convenient system for discovery and for testing potential therapeutic interventions.

Association of Retinal Nerve Fiber Layer Thinning With Elevated High Density Lipoprotein Cholesterol in UK Biobank

Purpose

The purpose of this study was to investigate the association between retinal nerve fiber layer (RNFL) thickness and high-density lipoprotein cholesterol (HDL-C) in a healthy population.

Methods

This cross-sectional study included 31,738 UK Biobank participants with high quality optical coherence tomography (OCT) images, excluding those with neurological or ocular diseases. The locally estimated scatterplot smoothing (LOESS) curve and multivariable piecewise linear regression models were applied to assess the association between HDL-C and RNFL thickness, and HDL-C subclasses were further analyzed using nuclear magnetic resonance (NMR) spectroscopy.

Results

Multivariate piecewise linear regression revealed that high HDL-C levels (>1.7 mmol/L in women or > 1.5 mmol/L in men) were associated with thinner RNFL thickness (women: β = -0.13, 95% confidence interval [CI] = -0.23 to -0.02, P = 0.017; male: β = -0.23, 95% CI = -0.37 to -0.10, P = 0.001). Conversely, a significant positive association between HDL-C and RNFL thickness was observed when HDL-C was between 1.4 and 1.7 mmol/L for female participants (β = 0.13, 95% CI = 0.02 to 0.24, P = 0.025). NMR analysis showed that these associations are potentially driven by distinct HDL-C subclasses.

Conclusions

This study revealed an association between HDL-C levels and retinal markers of neurodegenerative diseases, suggesting that elevated HDL-C may serve as a new risk factor for neurodegenerative conditions. These findings may contribute to the implementation of preventive interventions and improved patient outcomes.

Decreased Circulating Very Small Low-Density Lipoprotein is Likely Causal for Age-Related Macular Degeneration

Objective

Abnormal changes in metabolite levels in serum or plasma have been highlighted in several studies in age-related macular degeneration (AMD), the leading cause of irreversible vision loss. Specific changes in lipid profiles are associated with an increased risk of AMD. Metabolites could thus be used to investigate AMD disease mechanisms or incorporated into AMD risk prediction models. However, whether particular metabolites causally affect the disease has yet to be established.

Design

A 3-tiered analysis of blood metabolites in the United Kingdom (UK) Biobank cohort to identify metabolites that differ in AMD patients with evidence for a putatively causal role in AMD.

Participants

A total of 72 376 donors from the UK Biobank cohort including participants with AMD (N = 1353) and non-AMD controls (N = 71 023).

Methods

We analyzed 325 directly measured or derived blood metabolites from the UK Biobank for 72 376 donors to identify AMD-associated metabolites. Genome-wide association studies for 325 metabolites in 98 316 European participants from the UK Biobank were performed. The causal effects of these metabolites in AMD were tested using a 2-sample Mendelian randomization approach. The predictive value of these measurements together with sex and age was assessed by developing a machine learning classifier.

Main Outcome Measures

Evaluating metabolic biomarkers associated with AMD susceptibility and investigating their potential causal contribution to the development of the disease.

Results

This study noted age to be the prominent risk factor associated with AMD development. While accounting for age and sex, we identified 84 metabolic markers as significantly (false discovery rate-adjusted P value < 0.05) associated with AMD. Lipoprotein subclasses comprised the majority of the AMD-associated metabolites (39%) followed by several lipoprotein to lipid ratios. Nineteen metabolites showed a likely causative role in AMD etiology. Of these, 6 lipoproteins contain very small, very low-density lipoprotein (VLDL), and phospholipids to total lipid ratio in medium VLDL. Based on this we postulate that depletion of circulating very small VLDLs is likely causal for AMD. The risk prediction model constructed from the metabolites, age and sex, identified age as the primary predictive factor with a much smaller contribution by metabolites to AMD risk prediction.

Conclusions

This study underscores the pronounced role of lipids in AMD susceptibility and the likely causal contribution of particular subclasses of lipoproteins to AMD. Our study provides valuable insights into the metabopathological mechanisms of AMD disease development and progression.

Basal Linear Deposit: Normal Physiological Ageing or a Defining Lesion of Age-Related Macular Degeneration?

Objective: To determine if basal linear deposit (BLinD) is a specific lesion of age-related macular degeneration (AMD). Methods: The cohort was selected from a clinically and histopathologically validated archive (Sarks Archive) and consisted of 10 normal eyes (age 55-80 years) without any macular basal laminar deposit (BLamD) (Sarks Group I) and 16 normal aged eyes (age 57-88 years) with patchy BLamD (Sarks Group II). Only eyes with in vivo fundus assessment and corresponding high-resolution transmission electron microscopy (TEM) micrographs of the macula were included. Semithin sections and fellow-eye paraffin sections were additionally examined. BLinD was defined as a diffuse layer of electron-lucent vesicles external to the retinal pigment epithelium (RPE) basement membrane by TEM and was graded as follows: (i) Grade 0, absence of a continuous layer; (ii) Grade 1, a continuous layer up to three times the thickness of the RPE basement membrane (0.9 µm); (iii) Grade 2, a continuous layer greater than 0.9 µm. Bruch's membrane (BrM) hyalinisation and RPE abnormalities were determined by light microscopic examination of corresponding semithin and paraffin sections. Results: BLinD was identified in both normal (30%) and normal aged (62.5%) eyes. BLinD was thicker in normal aged eyes (p = 0.045; 95% CI 0.04-3.4). BLinD thickness positively correlated with both the degree of BrM hyalinisation (p = 0.049; 95% CI 0.05-2.69) and increasing microscopic RPE abnormalities (p = 0.022; 95% CI 0.188-2.422). RPE abnormalities were more likely to be observed in eyes with increased BrM hyalinisation (p = 0.044; 95% CI 0.61-4.319). Conclusions: BLinD is most likely an age-related deposit rather than a specific lesion of AMD. Its accumulation is associated with increasing BrM hyalinisation and microscopic RPE abnormalities, suggesting a relationship with dysregulated RPE metabolism and/or transport.

Associations of drusen location with risk factors and incidence of late age-related macular degeneration in the Alienor study

PURPOSE

To test the hypothesis that central drusen location is strongly linked with known Age-related Macular Degeneration (AMD) risk factors and risk of incident late AMD.

METHODS

The Alienor study is a prospective population-based cohort study of residents of Bordeaux, France, followed from 2009 to 2017. On retinal photographs, we defined central drusen as at least one soft drusen (>63 μm) within 500 μm from fovea and pericentral drusen as at least one drusen 500-3000 μm from fovea, in the absence of any central drusen. Late AMD (atrophic and/or neovascular) was diagnosed using multimodal imaging. In total, 481 eyes were included in the analysis: 160 central and 321 pericentral. We investigated associations with systemic (age, sex, smoking, medical prescriptions, plasma concentrations of lipids and nutrients, UV exposure, blood pressure), ocular (retinal thickness, cataract extraction) and genetic risk scores (GRS).

RESULTS

In multivariate logistic regression central drusen were associated with smoking (OR, 2.95 for smoking more than 20 pack-years, p = 0.02), HDL-cholesterol (OR, 1.57 for 1 standard deviation (SD) increase, p = 0.0048), pulse pressure (OR, 0.77 for 1 SD increase, p = 0.04), Age-Related Maculopathy Susceptibility 2 (ARMS2) GRS (OR, 1.42; 95% CI, 1.11-1.83) and complement GRS (OR, 1.55; 95% CI, 1.15-2.10). In Cox modelling, the central location of drusen (at baseline or during the follow-up) was associated with a 4.41-fold increased risk (95% CI,1.98-9.81) for an incident late AMD.

CONCLUSION

Central drusen were strongly associated with AMD risk factors and incident late AMD, suggesting that it represents a key marker for AMD progression.

Retinal debris triggers cytotoxic damage in cocultivated primary porcine RPE cells

Introduction

One of the most common causes of vision loss in the elderly population worldwide is age-related macular degeneration (AMD). Subsequently, the number of people affected by AMD is estimated to reach approximately 288 million by the year 2040. The aim of this study was to develop an ex vivo model that simulates various aspects of the complex AMD pathogenesis.

Methods

For this purpose, primary porcine retinal pigment epithelial cells (ppRPE) were isolated and cultured. One group was exposed to medium containing sodium iodate (NaIO3) to induce degeneration. The others were exposed to different supplemented media, such as bovine serum albumin (BSA), homogenized porcine retinas (HPR), or rod outer segments (ROOS) for eight days to promote retinal deposits. Then, these ppRPE cells were cocultured with porcine neuroretina explants for another eight days. To assess the viability of ppRPE cells, live/dead assay was performed at the end of the study. The positive RPE65 and ZO1 area was evaluated by immunocytochemistry and the expression of RLBP1, RPE65, and TJP1 was analyzed by RT-qPCR. Additionally, drusen (APOE), inflammation (ITGAM, IL6, IL8, NLRP3, TNF), oxidative stress (NFE2L2, SOD1, SOD2), and hypoxia (HIF1A) markers were investigated. The concentration of the inflammatory cytokines IL-6 and IL-8 was determined in medium supernatants from day 16 and 24 via ELISA.

Results

Live/dead assay suggests that especially exposure to NaIO3 and HPR induced damage to ppRPE cells, leading in a significant ppRPE cell loss. All supplemented media resulted in decreased RPE-characteristic markers (RPE65; ZO-1) and gene expression like RLBP1 and RPE65 in the cultured ppRPE cells. Besides, some inflammatory, oxidative as well as hypoxic stress markers were altered in ppRPE cells cultivated with NaIO3. The application of HPR induced an enhanced APOE expression. Pre-exposure of the ppRPE cells led to a diminished number of cones in all supplemented media groups compared to controls.

Discussion

Overall, this novel coculture model represents an interesting initial approach to incorporating deposits into coculture to mimic AMD pathogenesis. Nevertheless, the effects of the media used need to be investigated in further studies.

Genetic Insights into Age-Related Macular Degeneration

One of the major causes of vision impairment among elderly people in developed nations is age-related macular degeneration (AMD). The distinctive features of AMD are the accumulation of extracellular deposits called drusen and the gradual deterioration of photoreceptors and nearby tissues in the macula. AMD is a complex and multifaceted disease influenced by several factors such as aging, environmental risk factors, and a person's genetic susceptibility to the condition. The interaction among these factors leads to the initiation and advancement of AMD, where genetic predisposition plays a crucial role. With the advent of high-throughput genotyping technologies, many novel genetic loci associated with AMD have been identified, enhancing our knowledge of its genetic architecture. The common genetic variants linked to AMD are found on chromosome 1q32 (in the complement factor H gene) and 10q26 (age-related maculopathy susceptibility 2 and high-temperature requirement A serine peptidase 1 genes) loci, along with several other risk variants. This review summarizes the common genetic variants of complement pathways, lipid metabolism, and extracellular matrix proteins associated with AMD risk, highlighting the intricate pathways contributing to AMD pathogenesis. Knowledge of the genetic underpinnings of AMD will allow for the future development of personalized diagnostics and targeted therapeutic interventions, paving the way for more effective management of AMD and improved outcomes for affected individuals.

ApoB, non-HDL-C, and LDL-C Are More Prominent in Retinal Artery Occlusion Compared to Retinal Vein Occlusion

PURPOSE

To evaluate and compare the blood lipid profile in retinal artery occlusion (RAO) and retinal vein occlusion (RVO).

METHODS

We included 82 RAO patients and 95 RVO patients in this retrospective case-control study. Controls were matched to RAO or RVO patients at a 1:1 ratio, respectively. Associated lipid variates were analyzed in multivariable logistic regression models.

RESULTS

LDL-C (OR = 1.69), non-HDL-C (OR = 1.87), and ApoB (OR = 11.72) individually significantly increased the risk of RAO. ApoA1 was associated with RVO (OR = 0.02), and with 75.8% sensitivity and 67.4% specificity. TG (OR = 1.61), LDL-C (OR = 1.69), non-HDL-C (OR = 1.91), and ApoB (OR = 12.12) each significantly increased the risk of RAO when compared with RVO.

CONCLUSIONS

ApoB, non-HDL-C, and LDL-C may be potential biomarkers in RAO patients. Low ApoA1 is an independent risk factor for the development of RVO.

The Complement System as a Therapeutic Target in Retinal Disease

The complement cascade is a vital system in the human body's defense against pathogens. During the natural aging process, it has been observed that this system is imperative for ensuring the integrity and homeostasis of the retina. While this system is critical for proper host defense and retinal integrity, it has also been found that dysregulation of this system may lead to certain retinal pathologies, including geographic atrophy and diabetic retinopathy. Targeting components of the complement system for retinal diseases has been an area of interest, and in vivo, ex vivo, and clinical trials have been conducted in this area. Following clinical trials, medications targeting the complement system for retinal disease have also become available. In this manuscript, we discuss the pathophysiology of complement dysfunction in the retina and specific pathologies. We then describe the results of cellular, animal, and clinical studies targeting the complement system for retinal diseases. We then provide an overview of complement inhibitors that have been approved by the Food and Drug Administration (FDA) for geographic atrophy. The complement system in retinal diseases continues to serve as an emerging therapeutic target, and further research in this field will provide additional insights into the mechanisms and considerations for treatment of retinal pathologies.

Correlations Between the Neutrophil-Lymphocyte Ratio, Platelet-Lymphocyte Ratio, and Serum Lipid Fractions With Neovascular Age-Related Macular Degeneration

Introduction Age-related macular degeneration, a chronic and progressive disease, is one of the leading causes of vision loss globally among the elderly population. Multiple hypotheses have been proposed regarding its pathogenesis, including the presence of lipid metabolism alteration. Dysfunctional lipid handling within retinal pigment epithelial cells has been implicated in the accumulation of lipofuscin and subsequent induction of oxidative stress and inflammation, all contributing to retinal degeneration. The present study aims to comparatively analyze the serum lipid fraction distributions in patients with neovascular age-related macular degeneration (AMD) and controls. Materials and methods A retrospective study was carried out between January 2021 and December 2023 on 91 naïve patients with neovascular AMD and 90 controls admitted for routine cataract surgery. All subjects underwent a comprehensive ophthalmological exam, including ophthalmoscopy and optical coherence tomography (OCT) with central macular thickness (CMT) measurement. A complete blood count with differential and lipid fractions values was analyzed. The neutrophil-lymphocyte ratio (NLR), platelet-lymphocyte ratio (PLR), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglycerides (TG) were comparatively analyzed between the control group and the test group. Results The groups were comparable in terms of age (73.84 ±7.52 years for the neovascular AMD group vs 72.1±10.92 years in controls; p=0.8) and gender distribution (p=0.243). The mean NLR and PLR values were slightly higher in the AMD group but not statistically significant (p=0.51, p>0.99, respectively). Comparative analysis of lipid profile fractions showed significantly higher HDL-C values in the exudative AMD group compared to normal subjects (61.27±19.4 mg/dL vs 50.99±7.86 mg/dL, p=0.006). Also, the proportion of subjects with HDL-C>60 mg/dL was higher in the exudative AMD group (p=0.014). There were no significant differences in total cholesterol (189.77±53.39 mg/dL vs 190.43±37.84 mg/dL, p=0.681), LDL-C, and TG. Logistic regression analysis showed that serum HDL-C and HDL-C values >60 mg/dL are significantly associated factors with neovascular AMD. However, there is no statistical correlation between the values of these biochemical parameters and visual acuity or CMT in the neovascular AMD patient group. Conclusions There were no correlations between NLR and PLR with neovascular AMD in the study group. Higher HDL-C values exceeding 60 mg/dL were associated with neovascular age-related macular degeneration and could represent a possible therapeutic target in neovascular AMD.

Oral 8-aminoguanine against age-related retinal degeneration

Visual decline in the elderly is often attributed to retinal aging, which predisposes the tissue to pathologies such as age-related macular degeneration. Currently, effective oral pharmacological interventions for retinal degeneration are limited. We present a novel oral intervention, 8-aminoguanine (8-AG), targeting age-related retinal degeneration, utilizing the aged Fischer 344 rat model. A low-dose 8-AG regimen (5 mg/kg body weight) via drinking water, beginning at 22 months for 8 weeks, demonstrated significant retinal preservation. This was evidenced by increased retinal thickness, improved photoreceptor integrity, and enhanced electroretinogram responses. 8-AG effectively reduced apoptosis, oxidative damage, and microglial/macrophage activation associated with aging retinae. Age-induced alterations in the retinal purine metabolome, characterized by elevated levels of inosine, hypoxanthine, and xanthine, were partially mitigated by 8-AG. Transcriptomics highlighted 8-AG's anti-inflammatory effects on innate and adaptive immune responses. Extended treatment to 17 weeks further amplified the retinal protective effects. Moreover, 8-AG showed temporary protective effects in the RhoP23H/+ mouse model of retinitis pigmentosa, reducing active microglia/macrophages. Our study positions 8-AG as a promising oral agent against retinal aging. Coupled with previous findings in diverse disease models, 8-AG emerges as a promising anti-aging compound with the capability to reverse common aging hallmarks.

Microsomal triglyceride transfer protein is necessary to maintain lipid homeostasis and retinal function

Lipid processing by the retinal pigment epithelium (RPE) is necessary to maintain retinal health and function. Dysregulation of retinal lipid homeostasis due to normal aging or age-related disease triggers lipid accumulation within the RPE, on Bruch's membrane (BrM), and in the subretinal space. In its role as a hub for lipid trafficking into and out of the neural retina, the RPE packages a significant amount of lipid into lipid droplets for storage and into apolipoprotein B (APOB)-containing lipoproteins (Blps) for export. Microsomal triglyceride transfer protein (MTP), encoded by the MTTP gene, is essential for Blp assembly. Herein we test the hypothesis that MTP expression in the RPE is essential to maintain lipid balance and retinal function using the newly generated RPEΔMttp mouse model. Using non-invasive ocular imaging, electroretinography, and histochemical and biochemical analyses we show that genetic depletion of Mttp from the RPE results in intracellular lipid accumulation, increased photoreceptor-associated cholesterol deposits, and photoreceptor cell death, and loss of rod but not cone function. RPE-specific reduction in Mttp had no significant effect on plasma lipids and lipoproteins. While APOB was decreased in the RPE, most ocular retinoids remained unchanged, with the exception of the storage form of retinoid, retinyl ester. Thus suggesting that RPE MTP is critical for Blp synthesis and assembly but is not directly involved in plasma lipoprotein metabolism. These studies demonstrate that RPE-specific MTP expression is necessary to establish and maintain retinal lipid homeostasis and visual function.

Bottlenecks in the Investigation of Retinal Sterol Homeostasis

Sterol homeostasis in mammalian cells and tissues involves balancing three fundamental processes: de novo sterol biosynthesis; sterol import (e.g., from blood-borne lipoproteins); and sterol export. In complex tissues, composed of multiple different cell types (such as the retina), import and export also may involve intratissue, intercellular sterol exchange. Disruption of any of these processes can result in pathologies that impact the normal structure and function of the retina. Here, we provide a brief overview of what is known currently about sterol homeostasis in the vertebrate retina and offer a proposed path for future experimental work to further our understanding of these processes, with relevance to the development of novel therapeutic interventions for human diseases involving defective sterol homeostasis.

Bruch's Membrane Calcification in Pseudoxanthoma Elasticum: Comparing Histopathology and Clinical Imaging

Purpose

To investigate the histology of Bruch's membrane (BM) calcification in pseudoxanthoma elasticum (PXE) and correlate this to clinical retinal imaging.

Design

Experimental study with clinicopathological correlation.

Subjects and Controls

Six postmortem eyes from 4 PXE patients and 1 comparison eye from an anonymous donor without PXE. One of the eyes had a multimodal clinical image set for comparison.

Methods

Calcification was labeled with OsteSense 680RD, a fluorescent dye specific for hydroxyapatite, and visualized with confocal microscopy. Scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy (SEM-EDX) and time-of-flight secondary ion mass spectrometry (TOF-SIMs) were used to analyze the elemental and ionic composition of different anatomical locations. Findings on cadaver tissues were compared with clinical imaging of 1 PXE patient.

Main Outcome Measures

The characteristics and topographical distribution of hydroxyapatite in BM in eyes with PXE were compared with the clinical manifestations of the disease.

Results

Analyses of whole-mount and sectioned PXE eyes revealed an extensive, confluent OsteoSense labeling in the central and midperipheral BM, transitioning to a speckled labeling in the midperiphery. These areas corresponded to hyperreflective and isoreflective zones on clinical imaging. Scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy and TOF-SIMs analyses identified these calcifications as hydroxyapatite in BM of PXE eyes. The confluent fluorescent appearance originates from heavily calcified fibrous structures of both the collagen and the elastic layers of BM. Calcification was also detected in an aged comparison eye, but this was markedly different from PXE eyes and presented as small snowflake-like deposits in the posterior pole.

Conclusions

Pseudoxanthoma elasticum eyes show extensive hydroxyapatite deposition in the inner and outer collagenous and elastic BM layers in the macula with a gradual change toward the midperiphery, which seems to correlate with the clinical phenotype. The snowflake-like calcification in BM of an aged comparison eye differed markedly from the extensive calcification in PXE.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Age-Related Macular Degeneration and Mitochondria-Associated Autoantibodies: A Review of the Specific Pathogenesis and Therapeutic Strategies

Age-related macular degeneration (AMD) is a severe retinal disease that causes irreversible visual loss and blindness in elderly populations worldwide. The pathological mechanism of AMD is complex, involving the interactions of multiple environmental and genetic factors. A poor understanding of the disease leads to limited treatment options and few effective prevention methods. The discovery of autoantibodies in AMD patients provides an opportunity to explore the pathogenesis and treatment direction of the disease. This review focuses on the mitochondria-associated autoantibodies and summarizes the functional roles of mitochondria under physiological conditions and their alterations during the pathological states. Additionally, it discusses the crosstalk between mitochondria and other organelles, as well as the mitochondria-related therapeutic strategies in AMD.

APOB100 transgenic mice exemplify how the systemic circulation content may affect the retina without altering retinal cholesterol input

Apolipoprotein B (APOB) is a constituent of unique lipoprotein particles (LPPs) produced in the retinal pigment epithelium (RPE), which separates the neural retina from Bruch's membrane (BrM) and choroidal circulation. These LPPs accumulate with age in BrM and contribute to the development of age-related macular degeneration, a major blinding disease. The APOB100 transgenic expression in mice, which unlike humans lack the full-length APOB100, leads to lipid deposits in BrM. Herein, we further characterized APOB100 transgenic mice. We imaged mouse retina in vivo and assessed chorioretinal lipid distribution, retinal sterol levels, retinal cholesterol input, and serum content as well as tracked indocyanine green-bound LPPs in mouse plasma and retina after an intraperitoneal injection. Retinal function and differentially expressed proteins were also investigated. APOB100 transgenic mice had increased serum LDL content and an additional higher density HDL subpopulation; their retinal cholesterol levels (initially decreased) became normal with age. The LPP cycling between the RPE and choroidal circulation was increased. Yet, LPP trafficking from the RPE to the neural retina was limited, and total retinal cholesterol input did not change. There were lipid deposits in the RPE and BrM, and retinal function was impaired. Retinal proteomics provided mechanistic insights. Collectively, our data suggested that the serum LDL/HDL ratio may not affect retinal pathways of cholesterol input as serum LPP load is mainly handled by the RPE, which offloads LPP excess to the choroidal circulation rather than neural retina. Different HDL subpopulations should be considered in studies linking serum LPPs and age-related macular degeneration.

Cholesterol and oxysterols in retinal neuron-glia interactions: relevance for glaucoma

Cholesterol is an essential component of cellular membranes, crucial for maintaining their structural and functional integrity. It is especially important for nervous tissues, including the retina, which rely on high amounts of plasma membranes for the transmission of the nervous signal. While cholesterol is by far the most abundant sterol, the retina also contains cholesterol precursors and metabolites, especially oxysterols, which are bioactive molecules. Cholesterol lack or excess is deleterious and some oxysterols are known for their effect on neuron survival. Cholesterol homeostasis must therefore be maintained. Retinal glial cells, especially Müller cells, the principal glial cells of the vertebrate retina, provide mechanical, nutritional, and metabolic support for the neighboring neurons. Several pieces of evidence indicate that Müller cells are major actors of cholesterol homeostasis in the retina, as it is known for other glial cells in the brain. This process is based on a close cooperation with neurons, and sterols can be signaling molecules participating in glia-neuron interactions. While some implication of cholesterol in age-related macular degeneration is now recognized, based on epidemiological and laboratory data, evidence for its role in glaucoma is still scarce. The association between cholesterolemia and glaucoma is controversial, but experimental data suggest that sterols could take part in the pathological processes. It has been demonstrated that Müller glial cells are implicated in the development of glaucoma through an ambivalent reactive retinal gliosis process. The early steps contribute to maintaining retinal homeostasis and favor the survival of ganglion cells, which are targeted during glaucoma. If gliosis persists, dysregulation of the neuroprotective functions, cytotoxic effects of gliotic Müller cells and disruption of glia-neuron interactions lead to an acceleration of ganglion cell death. Sterols could play a role in the glial cell response to glaucomatous injury. This represents an understudied but attractive topic to better understand glaucoma and conceive novel preventive or curative strategies. The present review describes the current knowledge on i) sterol metabolism in retinal glial cells, ii) the potential role of cholesterol in glaucoma, and iii) the possible relationships between cholesterol and oxysterols, glial cells and glaucoma. Focus is put on glia-neuron interactions.

The Relationship between Complements and Age-Related Macular Degeneration and Its Pathogenesis

Age-related macular degeneration is a retinal disease that causes permanent loss of central vision in people over the age of 65. Its pathogenesis may be related to mitochondrial dysfunction, inflammation, apoptosis, autophagy, complement, intestinal flora, and lipid disorders. In addition, the patient's genes, age, gender, cardiovascular disease, unhealthy diet, and living habits may also be risk factors for this disease. Complement proteins are widely distributed in serum and tissue fluid. In the early 21st century, a connection was found between the complement cascade and age-related macular degeneration. However, little is known about the effect of complement factors on the pathogenesis of age-related macular degeneration. This article reviews the factors associated with age-related macular degeneration, the relationship between each factor and complement, the related functions, and variants and provides new ideas for the treatment of this disease.

Microsomal triglyceride transfer protein is necessary to maintain lipid homeostasis and retinal function

Lipid processing by the retinal pigment epithelium (RPE) is necessary to maintain retinal health and function. Dysregulation of retinal lipid homeostasis due to normal aging or to age-related disease triggers lipid accumulation within the RPE, on Bruch's membrane (BrM), and in the subretinal space. In its role as a hub for lipid trafficking into and out of the neural retina, the RPE packages a significant amount of lipid into lipid droplets for storage and into apolipoprotein B (apoB)-containing lipoproteins (Blps) for export. Microsomal triglyceride transfer protein (MTP), encoded by the MTTP gene, is essential for Blp assembly. Herein we test the hypothesis that MTP expression in the RPE is essential to maintain lipid balance and retinal function using the newly generated RPEΔMttp mouse model. Using non-invasive ocular imaging, electroretinography, and histochemical and biochemical analyses we show that genetic deletion of Mttp from the RPE results in intracellular lipid accumulation, increased photoreceptor -associated cholesterol deposits and photoreceptor cell death, and loss of rod but not cone function. RPE-specific ablation of Mttp had no significant effect on plasma lipids and lipoproteins. While, apoB was decreased in the RPE, ocular retinoid concentrations remained unchanged. Thus suggesting that RPE MTP is critical for Blp synthesis and assembly but not directly involved in ocular retinoid and plasma lipoprotein metabolism. These studies demonstrate that RPE-specific MTP expression is necessary to establish and maintain retinal lipid homeostasis and visual function.

Lysolipids are prominent in subretinal drusenoid deposits, a high-risk phenotype in age-related macular degeneration

Introduction

Age related macular degeneration (AMD) causes legal blindness worldwide, with few therapeutic targets in early disease and no treatments for 80% of cases. Extracellular deposits, including drusen and subretinal drusenoid deposits (SDD; also called reticular pseudodrusen), disrupt cone and rod photoreceptor functions and strongly confer risk for advanced disease. Due to the differential cholesterol composition of drusen and SDD, lipid transfer and cycling between photoreceptors and support cells are candidate dysregulated pathways leading to deposit formation. The current study explores this hypothesis through a comprehensive lipid compositional analysis of SDD.

Methods

Histology and transmission electron microscopy were used to characterize the morphology of SDD. Highly sensitive tools of imaging mass spectrometry (IMS) and nano liquid chromatography tandem mass spectrometry (nLC-MS/MS) in positive and negative ion modes were used to spatially map and identify SDD lipids, respectively. An interpretable supervised machine learning approach was utilized to compare the lipid composition of SDD to regions of uninvolved retina across 1873 IMS features and to automatically discern candidate markers for SDD. Immunohistochemistry (IHC) was used to localize secretory phospholipase A2 group 5 (PLA2G5).

Results

Among the 1873 detected features in IMS data, three lipid classes, including lysophosphatidylcholine (LysoPC), lysophosphatidylethanolamine (LysoPE) and lysophosphatidic acid (LysoPA) were observed nearly exclusively in SDD while presumed precursors, including phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidic acid (PA) lipids were detected in SDD and adjacent photoreceptor outer segments. Molecular signals specific to SDD were found in central retina and elsewhere. IHC results indicated abundant PLA2G5 in photoreceptors and retinal pigment epithelium (RPE).

Discussion

The abundance of lysolipids in SDD implicates lipid remodeling or degradation in deposit formation, consistent with ultrastructural evidence of electron dense lipid-containing structures distinct from photoreceptor outer segment disks and immunolocalization of secretory PLA2G5 in photoreceptors and RPE. Further studies are required to understand the role of lipid signals observed in and around SDD.

Patterns of Gene Expression, Splicing, and Allele-Specific Expression Vary among Macular Tissues and Clinical Stages of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness, and elucidating its underlying disease mechanisms is vital to the development of appropriate therapeutics. We identified differentially expressed genes (DEGs) and differentially spliced genes (DSGs) across the clinical stages of AMD in disease-affected tissue, the macular retina pigment epithelium (RPE)/choroid and the macular neural retina within the same eye. We utilized 27 deeply phenotyped donor eyes (recovered within a 6 h postmortem interval time) from Caucasian donors (60-94 years) using a standardized published protocol. Significant findings were then validated in an independent set of well-characterized donor eyes (n = 85). There was limited overlap between DEGs and DSGs, suggesting distinct mechanisms at play in AMD pathophysiology. A greater number of previously reported AMD loci overlapped with DSGs compared to DEGs between disease states, and no DEG overlap with previously reported loci was found in the macular retina between disease states. Additionally, we explored allele-specific expression (ASE) in coding regions of previously reported AMD risk loci, uncovering a significant imbalance in C3 rs2230199 and CFH rs1061170 in the macular RPE/choroid for normal eyes and intermediate AMD (iAMD), and for CFH rs1061147 in the macular RPE/choroid for normal eyes and iAMD, and separately neovascular AMD (NEO). Only significant DEGs/DSGs from the macular RPE/choroid were found to overlap between disease states. STAT1, validated between the iAMD vs. normal comparison, and AGTPBP1, BBS5, CERKL, FGFBP2, KIFC3, RORα, and ZNF292, validated between the NEO vs. normal comparison, revealed an intricate regulatory network with transcription factors and miRNAs identifying potential upstream and downstream regulators. Findings regarding the complement genes C3 and CFH suggest that coding variants at these loci may influence AMD development via an imbalance of gene expression in a tissue-specific manner. Our study provides crucial insights into the multifaceted genomic underpinnings of AMD (i.e., tissue-specific gene expression changes, potential splice variation, and allelic imbalance), which may open new avenues for AMD diagnostics and therapies specific to iAMD and NEO.

Acetyl-CoA carboxylase Inhibition increases RPE cell fatty acid oxidation and limits apolipoprotein efflux

Purpose

In age-related macular degeneration (AMD) and Sorsby's fundus dystrophy (SFD), lipid-rich deposits known as drusen accumulate under the retinal pigment epithelium (RPE). Drusen may contribute to photoreceptor and RPE degeneration in AMD and SFD. We hypothesize that stimulating β-oxidation in RPE will reduce drusen accumulation. Inhibitors of acetyl-CoA carboxylase (ACC) stimulate β-oxidation and diminish lipid accumulation in fatty liver disease. In this report we test the hypothesis that an ACC inhibitor, Firsocostat, limits the accumulation of lipid deposits in cultured RPE cells.

Methods

We probed metabolism and cellular function in mouse RPE-choroid, human fetal- derived RPE cells, and induced pluripotent stem cell-derived RPE cells. We used 13 C6-glucose and 13 C16-palmitate to determine the effects of Firsocostat on glycolytic, Krebs cycle, and fatty acid metabolism. 13 C labeling of metabolites in these pathways were analyzed using gas chromatography-linked mass spectrometry. We quantified ApoE and VEGF release using enzyme-linked immunosorbent assays. Immunostaining of sectioned RPE was used to visualize ApoE deposits. RPE function was assessed by measuring the trans-epithelial electrical resistance (TEER).

Results

ACC inhibition with Firsocostat increases fatty acid oxidation and remodels lipid composition, glycolytic metabolism, lipoprotein release, and enhances TEER. When human serum is used to induce sub-RPE lipoprotein accumulation, fewer lipoproteins accumulate with Firsocostat. In a culture model of Sorsby's fundus dystrophy, Firsocostat also stimulates fatty acid oxidation, improves morphology, and increases TEER.

Conclusions

Firsocostat remodels intracellular metabolism and improves RPE resilience to serum-induced lipid deposition. This effect of ACC inhibition suggests that it could be an effective strategy for diminishing drusen accumulation in the eyes of patients with AMD.

Targeting 7KCh-Induced Cell Death Response Mediated by p38, P2X7 and GSDME in Retinal Pigment Epithelium Cells with Sterculic Acid

Age-related macular degeneration (AMD) is the main cause of blindness in developed countries. AMD is characterized by the formation of drusen, which are lipidic deposits, between retinal pigment epithelium (RPE) and the choroid. One of the main molecules accumulated in drusen is 7-Ketocholesterol (7KCh), an oxidized-cholesterol derivative. It is known that 7KCh induces inflammatory and cytotoxic responses in different cell types and the study of its mechanism of action is interesting in order to understand the development of AMD. Sterculic acid (SA) counteracts 7KCh response in RPE cells and could represent an alternative to improve currently used AMD treatments, which are not efficient enough. In the present study, we determine that 7KCh induces a complex cell death signaling characterized by the activation of necrosis and an alternative pyroptosis mediated by P2X7, p38 and GSDME, a new mechanism not yet related to the response to 7KCh until now. On the other hand, SA treatment can successfully attenuate the activation of both necrosis and pyroptosis, highlighting its therapeutic potential for the treatment of AMD.

High-Fat Diet Alters Acylcarnitine Metabolism of the Retina and Retinal Pigment Epithelium/Choroidal Tissues in Laser-Induced Choroidal Neovascularization Rat Models

SCOPE

Choroidal neovascularization (CNV) is age-related macular degeneration's (AMD) main pathological change. High-fat diet (HFD) is associated with a form of CNV; however, the specific mechanism is unclear. Mitochondrial dysfunction, characterized by abnormal acylcarnitine, occurs during metabolic screening of serum or other body tissues in AMD. This study investigates HFD's role in retinal and retinal pigment epithelium (RPE)/choroidal acylcarnitine metabolism in CNV formation.

METHODS AND RESULTS

Chow diet and HFD-BN rats are laser-treated to induce CNV. Acylcarnitine species are quantitatively characterized by ultrahigh-performance liquid chromatography-tandem mass spectrometry. Optical coherence tomography and fundus fluorescein angiography evaluate CNV severity. HFD promotes weight gain, dyslipidemia, and CNV formation. In CNV rats, few medium-chain fatty acids (MCFAs) acylcarnitine in the RPE/choroid are initially affected. When an HFD is administered to these, even MCFA acylcarnitine in the RPE/choroid is found to decline. However, in the retina, odd acylcarnitines are increased, revealing "an opposite" change within the RPE/choroid, accompanied by influencing glycolytic key enzymes. The HFD+CNV group incorporated fewer long-chain acylcarnitines, like C18:2, into the retina than controls.

CONCLUSIONS

HFD hastens choroidal neovascularization. The study comprehensively documented acylcarnitine profiles in a CNV rat model. Acylcarnitine's odd-even and carbon-chain length properties may guide future therapeutics.

Robust homeostasis of cellular cholesterol is a consequence of endogenous antithetic integral control

Although cholesterol is essential for cellular viability and proliferation, it is highly toxic in excess. The concentration of cellular cholesterol must therefore be maintained within tight tolerances, and is thought to be subject to a stringent form of homeostasis known as Robust Perfect Adaptation (RPA). While much is known about the cellular signalling interactions involved in cholesterol regulation, the specific chemical reaction network structures that might be responsible for the robust homeostatic regulation of cellular cholesterol have been entirely unclear until now. In particular, the molecular mechanisms responsible for sensing excess whole-cell cholesterol levels have not been identified previously, and no mathematical models to date have been able to capture an integral control implementation that could impose RPA on cellular cholesterol. Here we provide a detailed mathematical description of cholesterol regulation pathways in terms of biochemical reactions, based on an extensive review of experimental and clinical literature. We are able to decompose the associated chemical reaction network structures into several independent subnetworks, one of which is responsible for conferring RPA on several intracellular forms of cholesterol. Remarkably, our analysis reveals that RPA in the cholesterol concentration in the endoplasmic reticulum (ER) is almost certainly due to a well-characterised control strategy known as antithetic integral control which, in this case, involves the high-affinity binding of a multi-molecular transcription factor complex with cholesterol molecules that are excluded from the ER membrane. Our model provides a detailed framework for exploring the necessary biochemical conditions for robust homeostatic control of essential and tightly regulated cellular molecules such as cholesterol.

Genetic variants in the adenosine triphosphate-binding cassette transporter A1 and risk of age-related macular degeneration

Genetic variants in ABCA1 are associated with higher concentrations of high-density lipoprotein (HDL) cholesterol. Higher HDL cholesterol concentrations are observationally and genetically associated with higher risk of age-related macular degeneration (AMD). However, whether amino acid-changing genetic variants in ABCA1 associated with high HDL cholesterol concentrations confer a higher risk of AMD in the general population is currently unknown. We tested this hypothesis. The study included 80,972 individuals (1,370 AMD cases) from the Copenhagen General Population Study (CGPS) and 9,584 individuals (142 AMD cases) from the Copenhagen City Heart Study (CCHS) with 10 to 18 years of follow-up. We created an HDL cholesterol weighted allele score based on amino acid-changing ABCA1 variants with a minor allele frequency above 0.001 and divided it into tertiles. The study included 55% women. Mean age was 58 years. The ABCA1 allele score for the third versus the first tertile was associated with HRs (95% confidence intervals (CIs)) of 1.30 (1.14-1.49) for all-cause AMD, 1.26 (1.06-1.50) for nonneovascular AMD, and 1.31 (1.12-1.53) for neovascular AMD in a multivariable adjusted model. On a continuous scale, higher concentrations of genetically determined HDL cholesterol were associated with higher risk of all-cause AMD, nonneovascular AMD, and neovascular AMD in an age- and sex adjusted model and in a multivariable adjusted model. In conclusion, amino acid-changing genetic variants in ABCA1 associated with higher HDL cholesterol concentrations were also associated with higher risk of AMD, suggesting a role for ABCA1 in AMD pathogenesis.

LOW-DOSE SUPPLEMENTATION WITH RETINOL IMPROVES RETINAL FUNCTION IN EYES WITH AGE-RELATED MACULAR DEGENERATION BUT WITHOUT RETICULAR PSEUDODRUSEN

PURPOSE

The aim of this study was to determine the functional impact of oral vitamin A supplementation in patients with intermediate age-related macular degeneration with and without reticular pseudodrusen (RPD) demonstrating dysfunction in dark adaptation.

METHODS

Five patients with intermediate age-related macular degeneration and without RPD (AMD group; mean ± SD age 78.0 ± 4.7 years) and seven with RPD (RPD group; age 74.1 ± 11.2 years) were supplemented with 16,000 IU of vitamin A palmitate for 8 weeks. Assessment at baseline, 4, 8, and 12 weeks included scotopic thresholds, dark adaptation, best-corrected and low luminance visual acuities, and the low-luminance quality of life questionnaire.

RESULTS

In the linear mixed model, rod intercept time improved significantly in the AMD group (mean [95% CI] change -1.1 minutes [-1.8; -0.5] after 4 weeks ( P < 0.001) and -2.2 min [-2.9 to -1.6] after 8 weeks of vitamin A supplementation ( P < 0.001). The dark adaptation cone plateau also significantly improved (i.e., more sensitive cone threshold) at 4 and 8 weeks ( P = 0.026 and P = 0.001). No other parameters improved in the AMD group, and there was no significant improvement in any parameter in the RPD group despite significantly elevated serum vitamin A levels measurable in both groups after supplementation ( P = 0.024 and P = 0.013).

CONCLUSION

Supplementation with 16,000 IU vitamin A, a lower dose than used in previous studies, partially overcomes the pathophysiologic functional changes in AMD eyes. The lack of improvement in the RPD group may indicate structural impediments to increasing vitamin A availability in these patients and/or may reflect the higher variability observed in the functional parameters for this group.

The Role of Inflammation in Age-Related Macular Degeneration-Therapeutic Landscapes in Geographic Atrophy

Age-related macular degeneration (AMD) is the leading cause of vision loss and visual impairment in people over 50 years of age. In the current therapeutic landscape, intravitreal anti-vascular endothelial growth factor (anti-VEGF) therapies have been central to the management of neovascular AMD (also known as wet AMD), whereas treatments for geographic atrophy have lagged behind. Several therapeutic approaches are being developed for geographic atrophy with the goal of either slowing down disease progression or reversing sight loss. Such strategies target the inflammatory pathways, complement cascade, visual cycle or neuroprotective mechanisms to slow down the degeneration. In addition, retinal implants have been tried for vision restoration and stem cell therapies for potentially a dual purpose of slowing down the degeneration and restoring visual function. In particular, therapies focusing on the complement pathway have shown promising results with the FDA approved pegcetacoplan, a complement C3 inhibitor, and avacincaptad pegol, a complement C5 inhibitor. In this review, we discuss the mechanisms of inflammation in AMD and outline the therapeutic landscapes of atrophy AMD. Improved understanding of the various pathway components and their interplay in this complex neuroinflammatory degeneration will guide the development of current and future therapeutic options, such as optogenetic therapy.

Effect of statins on the age of onset of age-related macular degeneration

BACKGROUND

This study evaluated the relationship between statin use and the age of onset of age-related macular degeneration (AMD).

METHODS

Electronic Health Records from 52,840 patients evaluated at University of California Los Angeles (UCLA) Ophthalmology Clinics and 9,977 patients evaluated at University of California San Francisco (UCSF) Ophthalmology Clinics were screened. Survival analysis was performed using Cox proportional hazards regression models and visualized using Kaplan Meier survival curves, with the following covariates-sex, ethnicity, smoking history, fluoxetine use, obesity, diabetes mellitus, and hypertension.

RESULTS

5,498 of 52,840 patients at UCLA were diagnosed with AMD. Statin use was associated with a later AMD onset (HR = 0.8823, p < 0.0001), while female sex (HR = 1.0852, p= 00,035), obesity (HR = 1.4555, p < 0.0001), and fluoxetine (HR = 1.3797, p= 0.0003) were associated with an earlier AMD onset. Non-hispanic black (HR = 0.5687, p < 0.0001) and hispanic ethnicities (HR = 0.8269, p= 0.0028) were associated with a later AMD onset. When stratifying for ethnicity, statins, fluoxetine, sex, and obesity were significant only within non-hispanic white subjects. Statin use was significant among patients with dry AMD (HR = 0.8410, p= 0.0001) but not wet AMD (0.9188, p= 0.0351). In the replication cohort, 526 of 9,977 patients at UCSF had AMD. Associations between statins (HR = 0.7643, p= 0.0033), non-hispanic black ethnicity (HR = 0.5043, p= 0.0035), and obesity (HR = 1.9602, p < 0.0001) on AMD onset were confirmed.

CONCLUSIONS

In both cohorts, statin use and non-hispanic black ethnicity are associated with a later AMD onset, while obesity with an earlier AMD onset.

Age-related macular degeneration is associated with probable cerebral amyloid angiopathy: A case-control study

BACKGROUND

Age-related macular degeneration (AMD) is a common retinal degenerative disorder among older individuals. Amyloid deposits, a hallmark of cerebral amyloid angiopathy (CAA), may be involved in the pathogenesis of AMD. Since amyloid deposits may contribute to the development of both AMD and CAA, we hypothesized that patients with AMD have a higher prevalence of CAA.

OBJECTIVE

To compare the prevalence of CAA in patients with or without AMD matched for age.

METHODS

We conducted a cross-sectional, 1:1 age-matched, case-control study of patients ≥40 years of age at the Mayo Clinic who had undergone both retinal optical coherence tomography and brain MRI from 2011 to 2015. Primary dependent variables were probable CAA, superficial siderosis, and lobar and deep cerebral microbleeds (CMBs). The relationship between AMD and CAA was assessed using multivariable logistic regression and was compared across AMD severity (none vs early vs late AMD).

RESULTS

Our analysis included 256 age-matched pairs (AMD 126, no AMD 130). Of those with AMD, 79 (30.9%) had early AMD and 47 (19.4%) had late AMD. The mean age was 75±9 years, and there was no significant difference in vascular risk factors between groups. Patients with AMD had a higher prevalence of CAA (16.7% vs 10.0%, p=0.116) and superficial siderosis (15.1% vs 6.2%, p=0.020), but not deep CMB (5.2% vs 6.2%, p=0.426), compared to those without AMD. After adjusting for covariates, having late AMD was associated with increased odds of CAA (OR 2.83, 95% CI 1.10-7.27, p=0.031) and superficial siderosis (OR 3.40, 95%CI 1.20-9.65, p=0.022), but not deep CMB (OR 0.7, 95%CI 0.14-3.51, p=0.669).

CONCLUSIONS

AMD was associated with CAA and superficial siderosis but not deep CMB, consistent with the hypothesis that amyloid deposits play a role in the development of AMD. Prospective studies are needed to determine if features of AMD may serve as biomarkers for the early diagnosis of CAA.

The impact of early RPE cell junction loss on VEGF, Ang-2, and TIMP secretion in vitro

Purpose

The retinal pigment epithelium (RPE) is an important tissue for maintaining a healthy retina. Retinal pigment epithelial cells help regulate nutrient transport to photoreceptors and are heavily pigmented to prevent light scattering. These cells also have junction proteins to form monolayers. Monolayers are key players in pathologies such as age-related macular degeneration (AMD), a leading cause of vision loss in older adults. During AMD, RPE cell detachment can occur, resulting in a loss of junctions. Losing junctions can increase the expression of pro-angiogenic vascular endothelial growth factor (VEGF). This overexpression can cause abnormal blood vessel growth or angiogenesis in the retina. Age-related macular degeneration treatments target VEGF to slow angiogenesis progression. However, other proteins, such as angiopoietin-2 (Ang-2) and the tissue inhibitor of metalloproteinase-1 (TIMP-1), may also play important roles, making them potential targets for treatment. Controlling RPE junction formation will help elucidate the relationship between RPE cell detachment and additional angiogenic factor secretion, lead to more therapeutics, and increase the efficacy of current treatments.

Methods

Micropatterning was used to control the spatial arrangement of primary porcine RPE cells using polydimethylsiloxane (PDMS) stencils. Patterns were formed into PDMS stencils to mimic 10%, 25%, and 50% overall detachment of the RPE monolayer. Zonula-occludens-1 (ZO-1), Ang-2, and VEGF were visualized using immunocytochemical (ICC) staining. An enzyme-linked immunosorbent assay (ELISA) was used to quantify extracellular Ang-2, VEGF, TIMP-1, and TIMP-2 levels. A rod outer segment (OS) phagocytosis assay was performed to determine how RPE junction loss directly affects photoreceptor support.

Results

The growth of primary porcine RPE cells was successfully controlled using stencils. Morphological changes and a decrease in pigmentation were observed, showing a decline in barrier and light absorption functions as degeneration increased. One day after stencil removal, junction proteins were delocalized, and angiogenic factor secretions were correlated with increased levels of detachment. Secretion levels of Ang-2 and TIMP-1 were significantly increased, whereas VEGF and TIMP-2 concentrations were not as affected by varying levels of detachment. OS phagocytosis appeared lower in RPE cells when ZO-1 was affected.

Conclusions

These results suggest a correlation between loss of junctions, abnormal angiogenic protein secretion, and reduced OS phagocytosis. Furthermore, Ang-2 and TIMP-1 proteins might be beneficial targets for AMD treatments, and their roles in retinal diseases deserve further investigation.

Quantitative characterizations of the cholesterol-related pathways in the retina and brain of hamsters

The retina and brain are separated from the systemic circulation by the anatomical barriers, which are permeable (the outer blood-retinal barrier) and impermeable (the blood-brain and inner blood-retina barriers) to cholesterol. Herein we investigated whether the whole-body cholesterol maintenance affects cholesterol homeostasis in the retina and brain. We used hamsters, whose whole-body cholesterol handling is more similar to those in humans than in mice and conducted separate administrations of deuterated water and deuterated cholesterol. We assessed the quantitative significance of the retinal and brain pathways of cholesterol input and compared the results with those from our previous studies in mice. The utility of the measurements in the plasma of deuterated 24-hydroxycholesterol, the major cholesterol elimination product from the brain, was investigated as well. We established that despite a 7-fold higher serum LDL to HDL ratio and other cholesterol-related differences, in situ biosynthesis remained the major source of cholesterol for hamster retina, although its quantitative significance was reduced to 53% as compared to 72-78% in mouse retina. In the brain, the principal pathway of cholesterol input was also the same, in situ biosynthesis, accounting for 94% of the total brain cholesterol input (96% in mice); the interspecies differences pertained to the absolute rates of the total cholesterol input and turnover. We documented the correlations between deuterium enrichments of the brain 24-hydroxycholesterol, brain cholesterol, and plasma 24-hydroxycholesterol, which suggested that deuterium enrichment of plasma 24-hydroxycholesteol could be an in vivo marker of cholesterol elimination and turnover in the brain.

Repurposing medications for treatment of age-related macular degeneration: Insights from novel approaches to data mining

The economic and visual burdens associated with age-related macular degeneration (AMD) are expected to significantly increase in the coming years. As of now, interventions to delay or prevent AMD are limited. Hence, there is an urgent and unmet need to expand our therapeutic tools for AMD in a manner, that is, both efficient and cost-effective. In this review, we consider the idea of drug repurposing, in which existing medications with other indications can be re-imagined for treating AMD. We detail the results of several population-level studies that have shown associations between several candidates and decreased risk of AMD development or progression. Such candidates include the more extensively studied metformin and statins, in addition to recently identified candidates fluoxetine and l-DOPA (levodopa) that show promise. We then briefly explore results from an advanced bioinformatics study, which provides further evidence that existing medications are associated with AMD risk genes. Many of these candidates warrant further study in prospective, clinical trials, where their potential causal relationships with AMD can be thoroughly assessed.

Identification of 7-Ketocholesterol-Modulated Pathways and Sterculic Acid Protective Effect in Retinal Pigmented Epithelium Cells by Using Genome-Wide Transcriptomic Analysis

Age-related macular degeneration (AMD) is the leading cause of blindness in developed countries. AMD is characterized by the formation of lipidic deposits between the retinal pigment epithelium (RPE) and the choroid called drusen. 7-Ketocholesterol (7KCh), an oxidized-cholesterol derivative, is closely related to AMD as it is one of the main molecules accumulated in drusen. 7KCh induces inflammatory and cytotoxic responses in different cell types, and a better knowledge of the signaling pathways involved in its response would provide a new perspective on the molecular mechanisms that lead to the development of AMD. Furthermore, currently used therapies for AMD are not efficient enough. Sterculic acid (SA) attenuates the 7KCh response in RPE cells and is presented as an alternative to improve these therapies. By using genome-wide transcriptomic analysis in monkey RPE cells, we have provided new insight into 7KCh-induced signaling in RPE cells, as well as the protective capacity of SA. 7KCh modulates the expression of several genes associated with lipid metabolism, endoplasmic reticulum stress, inflammation and cell death and induces a complex response in RPE cells. The addition of SA successfully attenuates the deleterious effect of 7KCh and highlights its potential for the treatment of AMD.