Eyeballing cholesterol efflux and macrophage function in disease pathogenesis

LXR/CD38 activation drives cholesterol-induced macrophage senescence and neurodegeneration via NAD+ depletion

Although dysregulated cholesterol metabolism predisposes aging tissues to inflammation and a plethora of diseases, the underlying molecular mechanism remains poorly defined. Here, we show that metabolic and genotoxic stresses, convergently acting through liver X nuclear receptor, upregulate CD38 to promote lysosomal cholesterol efflux, leading to nicotinamide adenine dinucleotide (NAD+) depletion in macrophages. Cholesterol-mediated NAD+ depletion induces macrophage senescence, promoting key features of age-related macular degeneration (AMD), including subretinal lipid deposition and neurodegeneration. NAD+ augmentation reverses cellular senescence and macrophage dysfunction, preventing the development of AMD phenotype. Genetic and pharmacological senolysis protect against the development of AMD and neurodegeneration. Subretinal administration of healthy macrophages promotes the clearance of senescent macrophages, reversing the AMD disease burden. Thus, NAD+ deficit induced by excess intracellular cholesterol is the converging mechanism of macrophage senescence and a causal process underlying age-related neurodegeneration.

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.

Drusen in AMD from the Perspective of Cholesterol Metabolism and Hypoxic Response

Drusen are one of the most characteristic pathologies of precursor lesion of age-related macular degeneration (AMD). Drusen comprise a yellowish white substance that accumulates typically under the retinal pigment epithelium (RPE), and their constituents are lipids, complement, amyloid, crystallin, and others. In the past, many researchers have focused on drusen and tried to elucidate the pathophysiology of AMD because they believed that disease progression from early AMD to advanced AMD might be based on drusen or drusen might cause AMD. In fact, it is well established that drusen are the hallmark of precursor lesion of AMD and a major risk factor for AMD progression mainly based on their size and number. However, the existence of advanced AMD without drusen has long been recognized. For example, polypoidal choroidal vasculopathy (PCV), which comprises the majority of AMD cases in Asians, often lacks drusen. Thus, there is the possibility that drusen might be no more than a biomarker of AMD and not a cause of AMD. Now is the time to reconsider the relationship between AMD and drusen. In this review, we focus on early AMD pathogenesis based on basic research from the perspective of cholesterol metabolism and hypoxic response in the retina, and we discuss the role of drusen.

Cell-specific Systemic Immune Signatures Associated with Treatment Burden in Neovascular Age-related Macular Degeneration

Purpose

Choroidal neovascularization (CNV) accounts for the majority of severe vision loss in neovascular age-related macular degeneration (AMD). Despite therapies that target VEGF, patients are often under-responsive, require frequent eye injections to control disease, and eventually lose some vision despite chronic therapy implicating a multifactorial etiology in treatment response. Genetic studies implicate systemic immunity in AMD and systemic immune cells accumulate within CNV lesions, yet a role for these cells in anti-VEGF response remains undetermined. The purpose of this study was to identify transcriptional signatures of circulating immune cells that are associated with high anti-VEGF treatment burden.

Design

Experimental pilot study.

Participants

Patients with neovascular AMD seen at Washington University School of Medicine in St. Louis and BJC Health System.

Methods

We profiled by single cell RNA sequencing the peripheral blood mononuclear cells of 27 treatment-experienced patients with wet AMD. We stratified this cohort into 2 groups with low and high treatment burden (≤ 5 or ≥ 6 injections in the past 12 months, respectively).

Main Outcome Measures

Identification of immune cells associated with high treatment burden.

Results

Gene expression signature of CD16+ monocytes may be associated with high treatment burden.

Conclusions

These studies delineate potential signatures of circulating immune cells that may be associated with high treatment burden in neovascular AMD, potentially informing the development of diagnostic predictors of anti-VEGF response and new precision medicine-based approaches to complement anti-VEGF therapies.

Financial Disclosures

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

Targeting cell-type-specific, choroid-peripheral immune signaling to treat age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness featuring pathogenic neovascularization of the choroidal vasculature (CNV). Although systemic immunity plays a role in AMD, the ocular signals that recruit and activate immune cells remain poorly defined. Using single-cell RNA sequencing, we prospectively profile peripheral blood mononuclear cells from 65 individuals including AMD and controls, which we integrate with existing choroid data. We generate a network of choroid-peripheral immune interactions dysregulated in AMD, including known AMD-relevant gene vascular endothelial growth factor (VEGF) receptor 2. Additionally, we find CYR61 is upregulated in choroidal veins and may signal to circulating monocytes. In mice, we validate that CYR61 is abundant in endothelial cells within CNV lesions neighboring monocyte-derived macrophages. Mechanistically, CYR61 activates macrophage anti-angiogenic gene expression, and ocular Cyr61 knockdown increases murine CNV size, indicating CYR61 inhibits CNV. This study highlights the potential of multi-tissue human datasets to identify disease-relevant and potentially therapeutically modifiable targets.

Macrophage Sult2b1 promotes pathological neovascularization in age-related macular degeneration

Disordered immune responses and cholesterol metabolism have been implicated in age-related macular degeneration (AMD), the leading cause of blindness in elderly individuals. SULT2B1, the key enzyme of sterol sulfonation, plays important roles in inflammation and cholesterol metabolism. However, the role and underlying mechanism of SULT2B1 in AMD have not been investigated thus far. Here, we report that SULT2B1 is specifically expressed in macrophages in choroidal neovascularization lesions. Sutl2b1 deficiency significantly reduced leakage areas and inhibited pathological angiogenesis by inhibiting M2 macrophage activation in vivo and in vitro. Mechanistically, loss of Sult2b1 activated LXRs and subsequently increased ABCA1 and ABCG1 (ABCA1/G1)-mediated cholesterol efflux from M2 macrophages. LXR inhibition (GSK2033 treatment) in Sult2b1 -/- macrophages reversed M2 polarization and decreased intracellular cholesterol capacity to promote pathological angiogenesis. In contrast to SULT2B1, STS, an enzyme of sterol desulfonation, protected against choroidal neovascularization development by activating LXR-ABCA1/G1 signalling to block M2 polarization. Collectively, these data reveal a cholesterol metabolism axis related to macrophage polarization in neovascular AMD.

Dynamic changes in macrophage morphology during the progression of choroidal neovascularization in a laser-induced choroidal neovascularization mouse model

BACKGROUND

Neovascular age-related macular degeneration (AMD) is responsible for the majority of severe vision loss cases and is mainly caused by choroidal neovascularization (CNV). This condition persists or recurs in a subset of patients and regresses after 5 or more years of anti-vascular endothelial growth factor (VEGF) treatment. The precise mechanisms of CNV continue to be elucidated. According to our previous studies, macrophages play a critical role in CNV. Herein, we aimed to determine the morphological changes in macrophages in CNV to help us understand the dynamic changes.

METHODS

Mice were subjected to laser injury to induce CNV, and lesion expansion and macrophage transformation were examined by immunofluorescence and confocal analysis. Several strategies were used to verify the dynamic changes in macrophages. Immunofluorescence and confocal assays were performed on choroidal flat mounts to evaluate the morphology and phenotype of macrophages in different CNV phases, and the results were further verified by western blotting and RT-PCR.

RESULTS

The location of infiltrated macrophages changed after laser injury in the CNV mouse model, and macrophage morphology also dynamically changed. Branching macrophages gradually shifted to become round with the progression of CNV, which was certified to be an M2 phenotypic shift.

CONCLUSIONS

Dynamic changes in macrophage morphology were observed during CNV formation, and the round-shaped M2 phenotype could promote neovascularization. In general, the changes in morphology we observed in this study can help us to understand the critical role of macrophages in CNV progression and exploit a potential treatment option for CNV indicated by a shift in macrophage polarity.

Age-Related Macular Degeneration in Patients with Androgenetic Alopecia: Could the Monocyte/HDL Ratio Be the Link?

INTRODUCTION

Both Androgenetic alopecia (AGA) and age-related macular degeneration (AMD) shared the microinflammatory milieu and increased oxidative stress as important criteria in their pathogenesis. The monocyte/high density lipoprotein (HDL) ratio (MHR) seems to be an easy-to-calculate prognostic marker of microinflammation.

OBJECTIVES

To assess MHR in patients with AGA and its correlation to AMD in these patients, if any.

METHODS

Forty patients with AGA aged 40 years or more of both sexes and 40 control subjects participated in this case-control study. General, dermatological, and ophthalmologic examination, MHR evaluation and optical coherence tomography (OCT) were performed.

RESULTS

The mean MHR was significantly higher in AGA patients (6.98 ± 2.21) than in controls (3.82 ± 0.68) (P < 0.001). AMD was significantly higher in patients than controls (P < 0.001). Eighty percent of AGA patients were diagnosed with AMD versus 20% of control subjects. The presence of AMD in AGA was significantly related to the degree of severity of AGA in male patients (P = 0.02). The MHR was significantly higher in AGA patients found to have AMD (9.37 ± 1.1 and 7.01 ± 1.42 in the wet and dry type respectively) than those without AMD (P < 0.001).

CONCLUSIONS

AMD may develop more frequently in those with AGA. The MHR seems to be a missing link between both conditions, and could be utilized as a potential biomarker for predicting AMD in AGA patients.

Causal effects of serum lipid biomarkers on early age-related macular degeneration using Mendelian randomization

BACKGROUND

Age-related macular degeneration (AMD) is one of the major causes of vision loss. Early AMD needs to be taken seriously, but the causal effects of lipid biomarkers on early AMD remain unclear.

METHODS

In this study, two-sample Mendelian randomization (MR) analysis was performed to systematically assess the causal relationships between seven serum lipid biomarkers (apolipoprotein A (ApoA), apolipoprotein B (ApoB), total cholesterol (CHOL), high-density lipoprotein cholesterol (HDL-C), direct low-density lipoprotein cholesterol (LDL-C), lipoprotein A [Lp(a)], and triglycerides (TG)) and risk of early AMD. In total, 14,034 cases and 91,214 controls of European ancestry were included in the analysis (number of SNPs = 11,304,110).

RESULTS

MR estimates revealed that a higher HDL-C level is strongly associated with increased risk of early AMD (OR = 1.25, 95% CI: 1.15-1.35, P = 2.61 × 10^-8). In addition, level of ApoA is also positively associated with risk of early AMD (OR = 2.04, 95% CI: 1.50-2.77, P = 6.27 × 10^-6). Conversely, higher levels of TG significantly decrease the risk of early AMD (OR = 0.77, 95% CI: 0.71-0.84, P = 5.02 × 10^-10). Sensitivity analyses further supported these associations. Moreover, multivariable MR analyses, adjusted for the effects of correlated lipid biomarkers, yielded similar results.

CONCLUSION

This study identifies causal relationships between elevated circulating HDL-C/ApoA levels and increased risk of early AMD, in addition to finding that TG specifically reduces the risk of early AMD. These findings contribute to a better understanding of the role of lipid metabolism in drusen formation, particularly in early AMD development.

Association of Plasma Vitamins and Carotenoids, DNA Methylation of LCAT, and Risk of Age-Related Macular Degeneration

Dysregulation of lipid metabolism has been implicated in age-related macular degeneration (AMD), the leading cause of blindness among the elderly. Lecithin cholesterol acyltransferase (LCAT) is an important enzyme responsible for lipid metabolism, which could be regulated by DNA methylation during the development of various age-related diseases. This study aimed to assess the association between LCAT DNA methylation and the risk of AMD, and to examine whether plasma vitamin and carotenoid concentrations modified this association. A total of 126 cases of AMD and 174 controls were included in the present analysis. LCAT DNA methylation was detected by quantitative real-time methylation-1specific PCR (qMSP). Circulating vitamins and carotenoids were measured using reversed-phase high-performance liquid chromatography (RP-HPLC). DNA methylation of LCAT was significantly higher in patients with AMD than those in the control subjects. After multivariable adjustment, participants in the highest tertile of LCAT DNA methylation had a 5.37-fold higher risk (95% CI: 2.56, 11.28) of AMD compared with those in the lowest tertile. Each standard deviation (SD) increment of LCAT DNA methylation was associated with a 2.23-fold (95% CI: 1.58, 3.13) increased risk of AMD. There was a J-shaped association between LCAT DNA methylation and AMD risk (P_{non-linearity} = 0.03). Higher concentrations of plasma retinol and β-cryptoxanthin were significantly associated with decreased levels of LCAT DNA methylation, with the multivariate-adjusted β coefficient being -0.05 (95% CI: -0.08, -0.01) and -0.25 (95% CI: -0.42, -0.08), respectively. In joint analyses of LCAT DNA methylation and plasma vitamin and carotenoid concentrations, the inverse association between increased LCAT DNA methylation and AMD risk was more pronounced among participants who had a lower concentration of plasma retinol and β-cryptoxanthin. These findings highlight the importance of comprehensively assessing LCAT DNA methylation and increasing vitamin and carotenoid status for the prevention of AMD.

Synthetic high-density lipoprotein nanoparticles delivering rapamycin for the treatment of age-related macular degeneration

Synthetic high-density lipoprotein (sHDL) and rapamycin (Rap) have both been shown to be potential treatments for age-related macular degeneration (AMD). The low aqueous solubility of Rap, however, limits its therapeutic utility. Here we used an Apolipoprotein A-I mimetic peptide and phospholipid-based sHDL for the intravitreal delivery of Rap. By incorporation of Rap in sHDL nanoparticles (sHDL-Rap), we achieve 125-fold increase in drug aqueous concentration. When applied in vitro to retinal pigment epithelium cells, sHDL-Rap exhibited the abilities to efflux cholesterol, neutralize endotoxin, and suppress NF-κB activation. As an mTOR inhibitor, Rap induced autophagy and inhibited NF-κB-mediated pro-inflammatory signaling. Additionally, a greater reduction in lipofuscin accumulation and increased anti-inflammatory effects were achieved by sHDL-Rap relative to free drug or sHDL alone. In vivo studies demonstrated that sHDL reached the target retina pigment epithelium (RPE) layer following intravitreal administration in rats. These results suggest that sHDL-Rap holds potential as a treatment for AMD.

Analysis of the aqueous humor lipid profile in patients with polypoidal choroidal vasculopathy

This study aimed to investigate the lipid profiles of aqueous humor from polypoidal choroidal vasculopathy (PCV) patients and identify potential biomarkers to increase the understanding of PCV pathomechanism. An ultra-high performance liquid chromatography-tandem mass spectrometry based untargeted lipidomic analysis was performed to acquire lipid profiles of aqueous humor of PCV patients and control subjects. Differentially expressed lipids were identified by univariate and multivariate analyses. A receiver operator characteristic curve (ROC) analysis was conducted to confirm the potential of identified lipids as biomarkers. Sixteen PCV patients and twenty-eight control subjects were enrolled in this study. In total, we identified 33 lipid classes and 639 lipid species in aqueous humor using the LipidSearch software. Of them, 50 differential lipids were obtained by combining univariate and multivariate statistical analyses (VIP>1 and P < 0.05), and 19 potential lipid biomarkers were identified by ROC analysis. In addition, significant alterations were found in several metabolic pathways, including glycerophospholipid, glycerolipid, and glycosylphosphatidylinositol-anchor biosynthesis. This study is the first to systematically characterize the alterations in lipid profiles in aqueous humor of PCV patients and screen for the potential lipid biomarkers for PCV diagnosis and treatment intervention. The results of this study are likely to broaden our understanding of the pathogenesis of PCV and contribute to improvements in the diagnosis and treatment of the disease.

Serum Cholesterol Efflux Capacity in Age-Related Macular Degeneration and Polypoidal Choroidal Vasculopathy

Purpose

To investigate serum cholesterol efflux capacity (the ability of the serum to accept cholesterol) and factors that regulate it using nuclear magnetic resonance-quantified measures of lipoprotein particle composition and size and apolipoproteins metrics in patients with age-related macular degeneration (AMD).

Design

Case-control study.

Participants

Four hundred two serum samples from 80 patients with early AMD (eAMD), and 212 patients with neovascular AMD (nAMD), including 80 with typical nAMD (tAMD) and 132 with polypoidal choroidal vasculopathy (PCV), and 110 age- and gender matched control participants.

Methods

Serum from participants showed cholesterol efflux capacity measured using in vitro cell assays and lipoprotein subfractions measured using nuclear magnetic resonance (Nightingale, Ltd). Associations between cholesterol efflux capacity (measured in percentage) and lipid subfractions were investigated in the patients and control participants.

Main Outcome Measures

Cholesterol efflux capacity and lipid subfractions in control, eAMD, and nAMD. Associations between HDL subfractions and cholesterol efflux capacity.

Results

Cholesterol efflux capacity was higher in patients with eAMD (68.0 ± 11.3% [mean ± standard deviation]) and nAMD (75.9 ± 27.7%) than in the control participants (56.9 ± 16.7%) after adjusting for age, gender, and use of lipid-lowering drug (P < 0.0001). Nuclear magnetic resonance lipidomics demonstrated that the mean diameter of HDL was larger both in eAMD (9.96 ± 0.27 mm [mean ± standard deviation]) and PCV (9.97 ± 0.23 mm) compared with that of the control participants (9.84 ± 0.24 mm; P = 0.0001 for both). Among the 28 HDL subfractions, most of the small, medium, and large HDLs, but none of the 7 extra large HDLs fractions, were associated moderately with cholesterol efflux capacity in eAMD and PCV (R = 0.149-0.277).

Conclusions

Serum cholesterol efflux capacity was increased in eAMD and PCV, but not tAMD, possibly reflecting differential underlying pathophysiologic features of lipid dysregulation in tAMD and PCV. Further studies should be directed toward investigating the diverse biological activities of HDL in AMD, including macular pigment transport, regulation of inflammation, and local cholesterol transport system.

Loss of Mir146b with aging contributes to inflammation and mitochondrial dysfunction in thioglycollate-elicited peritoneal macrophages

Macrophages undergo programmatic changes with age, leading to altered cytokine polarization and immune dysfunction, shifting these critical immune cells from protective sentinels to disease promoters. The molecular mechanisms underlying macrophage inflammaging are poorly understood. Using an unbiased RNA sequencing (RNA-seq) approach, we identified Mir146b as a microRNA whose expression progressively and unidirectionally declined with age in thioglycollate-elicited murine macrophages. Mir146b deficiency led to altered macrophage cytokine expression and reduced mitochondrial metabolic activity, two hallmarks of cellular aging. Single-cell RNA-seq identified patterns of altered inflammation and interferon gamma signaling in Mir146b-deficient macrophages. Identification of Mir146b as a potential regulator of macrophage aging provides novel insights into immune dysfunction associated with aging.

Age-Related Macular Degeneration

A 78-year-old woman presents with vision changes in the right eye for one week. Specifically, she describes central blurring in her vision and bending or waviness in straight lines. She also reports increasing difficulty reading print and often feels that there are blind spots in her vision. How would you diagnose and treat this patient?

Fasting and fasting-mimicking treatment activate SIRT1/LXRα and alleviate diabetes-induced systemic and microvascular dysfunction

AIMS/HYPOTHESIS

Homo sapiens evolved under conditions of intermittent food availability and prolonged fasting between meals. Periods of fasting are important for recovery from meal-induced oxidative and metabolic stress, and tissue repair. Constant high energy-density food availability in present-day society contributes to the pathogenesis of chronic diseases, including diabetes and its complications, with intermittent fasting (IF) and energy restriction shown to improve metabolic health. We have previously demonstrated that IF prevents the development of diabetic retinopathy in a mouse model of type 2 diabetes (db/db); however the mechanisms of fasting-induced health benefits and fasting-induced risks for individuals with diabetes remain largely unknown. Sirtuin 1 (SIRT1), a nutrient-sensing deacetylase, is downregulated in diabetes. In this study, the effect of SIRT1 stimulation by IF, fasting-mimicking cell culture conditions (FMC) or pharmacological treatment using SRT1720 was evaluated on systemic and retinal metabolism, systemic and retinal inflammation and vascular and bone marrow damage.

METHODS

The effects of IF were modelled in vivo using db/db mice and in vitro using bovine retinal endothelial cells or rat retinal neuroglial/precursor R28 cell line serum starved for 24 h. mRNA expression was analysed by quantitative PCR (qPCR). SIRT1 activity was measured via histone deacetylase activity assay. NR1H3 (also known as liver X receptor alpha [LXRα]) acetylation was measured via western blot analysis.

RESULTS

IF increased Sirt1 mRNA expression in mouse liver and retina when compared with non-fasted animals. IF also increased SIRT1 activity eightfold in mouse retina while FMC increased SIRT1 activity and expression in retinal endothelial cells when compared with control. Sirt1 expression was also increased twofold in neuronal retina progenitor cells (R28) after FMC treatment. Moreover, FMC led to SIRT1-mediated LXRα deacetylation and subsequent 2.4-fold increase in activity, as measured by increased mRNA expression of the genes encoding ATP-binding cassette transporter (Abca1 and Abcg1). These changes were reduced when retinal endothelial cells expressing a constitutively acetylated LXRα mutant were tested. Increased SIRT1/LXR/ABC-mediated cholesterol export resulted in decreased retinal endothelial cell cholesterol levels. Direct activation of SIRT1 by SRT1720 in db/db mice led to a twofold reduction of diabetes-induced inflammation in the retina and improved diabetes-induced visual function impairment, as measured by electroretinogram and optokinetic response. In the bone marrow, there was prevention of diabetes-induced myeloidosis and decreased inflammatory cytokine expression.

CONCLUSIONS/INTERPRETATION

Taken together, activation of SIRT1 signalling by IF or through pharmacological activation represents an effective therapeutic strategy that provides a mechanistic link between the advantageous effects associated with fasting regimens and prevention of microvascular and bone marrow dysfunction in diabetes.

The Role of the ATP-Binding Cassette A1 (ABCA1) in Human Disease

Cholesterol homeostasis is essential in normal physiology of all cells. One of several proteins involved in cholesterol homeostasis is the ATP-binding cassette transporter A1 (ABCA1), a transmembrane protein widely expressed in many tissues. One of its main functions is the efflux of intracellular free cholesterol and phospholipids across the plasma membrane to combine with apolipoproteins, mainly apolipoprotein A-I (Apo A-I), forming nascent high-density lipoprotein-cholesterol (HDL-C) particles, the first step of reverse cholesterol transport (RCT). In addition, ABCA1 regulates cholesterol and phospholipid content in the plasma membrane affecting lipid rafts, microparticle (MP) formation and cell signaling. Thus, it is not surprising that impaired ABCA1 function and altered cholesterol homeostasis may affect many different organs and is involved in the pathophysiology of a broad array of diseases. This review describes evidence obtained from animal models, human studies and genetic variation explaining how ABCA1 is involved in dyslipidemia, coronary heart disease (CHD), type 2 diabetes (T2D), thrombosis, neurological disorders, age-related macular degeneration (AMD), glaucoma, viral infections and in cancer progression.

Innate Immunity in Age-Related Macular Degeneration

Multiple lines of investigation have demonstrated that inflammation plays significant roles in etiology of age-related macular degeneration (AMD). Although interventional trials in AMD therapy targeting inflammatory pathways have been conducted, they have not yet been successful and a detailed understanding as to why some have failed is still elusive. One limitation is the relative dearth of information on how immune cells interact with retinal cells to generate AMD phenotypes at each disease stage. Here, we summarize current research evidence and hypotheses regarding potential pathogenic roles of innate immune cells in the eye, which include resident retinal microglia, macrophages derived from infiltrating systemic monocytes, and macrophages resident in the choroid. We relate recent findings regarding the physiology, function, and cellular interactions involving innate immune cells in the retina and choroid to AMD-related processes, including: (1) drusen formation and regression, (2) the onset and spread of degeneration in late atrophic AMD, and (3) the initiation, growth, and exudation of neovascular vessels in late "wet" AMD. Understanding how innate immune cells contribute to specific AMD phenotypes can assist in generating a comprehensive view on the inflammatory etiology of AMD and aid in identifying anti-inflammatory therapeutic strategies and selecting appropriate clinical outcomes for the planned interventions.

Drusen and pachydrusen: the definition, pathogenesis, and clinical significance

The pachychoroid disease spectrum encompasses seven major retinal conditions including central serous chorioretinopathy (CSC), polypoidal choroidal vasculopathy (PCV), and pachychoroid neovasculopathy or type I macular neovascularisation (MNV) secondary to chronic persistent thickening and dysfunction of the choroidal vasculature. Drusen are focal yellow-white deposits of extracellular debris, which consist of complement proteins, esterified and nonesterified cholesterol, apolipoproteins, carbohydrates, and trace elements, above the retinal pigment epithelium (RPE) or between the RPE and Bruch's membrane. Although drusen are an essential disease precursor of advanced age-related macular degeneration (AMD), a new entity "pachydrusen" has been identified to be associated with some of the enitites that constitute the pachychoroid spectrum. It remains to be determined what the exact differences are between soft drusen, pseudodrusen, and pachydrusen in terms of phenotype, genotype, and pathogenesis. Improving our knowledge in these areas will inevitably improve our understanding of their clinical significance especially as in disease prediction in AMD and the pachychroid spectrum disorders. It remains controversial whether PCV is a subtype of AMD. Understanding the pathogenesis of different types of drusen may also help in addressing if phenotype and/or genotype of type 1 MNV associated with pachychoroid are similar to type 1 MNV related to AMD. Furthermore, because pachydrusen links two pachychoroid diseases, CSC and PCV, it is also of great interest to investigate if CSC is an early stage or a predictor of PCV in future research. In this review, we share our experience in clinical practice and the latest published evidence-based literature to emphasize the differences and similarities in morphology, pathogenesis, and clinical significance of drusen and pachydrusen, a new member of the pachychoroid spectrum disorders.

Adult body height and age-related macular degeneration in healthy individuals: A nationwide population-based survey from Korea

We sought to evaluate the relationship between adult body height and risk of age-related macular degeneration (AMD) among healthy Koreans using nationwide population-based data. We analyzed data derived from the Korea National Health and Nutrition Examination Survey 2008–2011. Participants over 40 years of age were included in the sample after excluding individuals with systemic comorbidities or missing relevant data. The presence and severity of AMD were graded using fundus photographs. The relationship between body height and risk of AMD was determined using multiple logistic regression analyses. Among a total of 8,435 participants, 544 (6.45%) had AMD: 502 (5.95%) with early AMD and 42 (0.5%) with late AMD. In multivariate-adjusted analyses, taller body height was significantly associated with a lower prevalence of AMD (odds ratio [OR], 0.89; 95% confidence interval [CI], 0.81–0.99), while body mass index (BMI) was not associated with AMD. An inverse association between body height and risk of AMD was observed most frequently in participants under 65 years of age (OR, 0.81; 95% CI, 0.70–0.94). Furthermore, body height showed an inverse association with risk of AMD among obese participants (BMI ≥25.0 kg/m²) (OR, 0.75; 95% CI, 0.60–0.93). Subgroup analysis by AMD type disclosed a significant inverse association between body height and early AMD (OR, 0.87; 95% CI, 0.79–0.97) but not late AMD. Our results suggest that shorter body height is independently associated with increased risk of AMD, especially early AMD, in a dose-response manner in people who are obese or under 65 years of age.

VEGF in Signaling and Disease: Beyond Discovery and Development

The discovery of vascular endothelial-derived growth factor (VEGF) has revolutionized our understanding of vasculogenesis and angiogenesis during development and physiological homeostasis. Over a short span of two decades, our understanding of the molecular mechanisms by which VEGF coordinates neurovascular homeostasis has become more sophisticated. The central role of VEGF in the pathogenesis of diverse cancers and blinding eye diseases has also become evident. Elucidation of the molecular regulation of VEGF and the transformative development of multiple therapeutic pathways targeting VEGF directly or indirectly is a powerful case study of how fundamental research can guide innovation and translation. It is also an elegant example of how agnostic discovery and can transform our understanding of human disease. This review will highlight critical nodal points in VEGF biology, including recent developments in immunotherapy for cancer and multitarget approaches in neovascular eye disease.

FGF2-induced STAT3 activation regulates pathologic neovascularization

Cell-autonomous endothelial cell (EC) fibroblast growth factor receptor (FGFR) signaling through FGFR1/2 is essential for injury-induced wound vascularization and pathologic neovascularization as in blinding eye diseases such as age-related macular degeneration. Which FGF ligand(s) is critical in regulating angiogenesis is unknown. Utilizing ex vivo models of choroidal endothelial sprouting and in vivo models of choroidal neovascularization (CNV), we demonstrate here that only FGF2 is the essential ligand. Though FGF-FGFR signaling can activate multiple intracellular signaling pathways, we show that FGF2 regulates pathogenic angiogenesis via STAT3 activation. The identification of FGF2 as a critical mediator in aberrant neovascularization provides a new opportunity for developing multi-target therapies in blinding eye diseases especially given the limitations of anti-VEGF monotherapy.

Macrophage Plasticity and Function in the Eye and Heart

Macrophages are important mediators of inflammation and tissue remodeling. Recent insights into the heterogeneity of macrophage subpopulations have renewed interest in their functional diversity in homeostasis and disease. In addition, their plasticity enables them to perform a variety of functions in response to changing tissue contexts, such as those imposed by aging. These qualities make macrophages particularly intriguing cells given their dichotomous role in protecting against, or accelerating, diseases of the cardiovascular system and the eye, two tissues that are particularly susceptible to the effects of aging. We review novel perspectives on macrophage biology, as informed by recent studies detailing the diversity of macrophage identity and function, as well as mechanisms influencing macrophage behavior that might offer opportunities for new therapeutic strategies.

Impaired monocyte cholesterol clearance initiates age-related retinal degeneration and vision loss

Advanced age-related macular degeneration (AMD), the leading cause of blindness among people over 50 years of age, is characterized by atrophic neurodegeneration or pathologic angiogenesis. Early AMD is characterized by extracellular cholesterol-rich deposits underneath the retinal pigment epithelium (RPE) called drusen or in the subretinal space called subretinal drusenoid deposits (SDD) that drive disease progression. However, mechanisms of drusen and SDD biogenesis remain poorly understood. Although human AMD is characterized by abnormalities in cholesterol homeostasis and shares phenotypic features with atherosclerosis, it is unclear whether systemic immunity or local tissue metabolism regulates this homeostasis. Here, we demonstrate that targeted deletion of macrophage cholesterol ABC transporters A1 (ABCA1) and -G1 (ABCG1) leads to age-associated extracellular cholesterol-rich deposits underneath the neurosensory retina similar to SDD seen in early human AMD. These mice also develop impaired dark adaptation, a cardinal feature of RPE cell dysfunction seen in human AMD patients even before central vision is affected. Subretinal deposits in these mice progressively worsen with age, with concomitant accumulation of cholesterol metabolites including several oxysterols and cholesterol esters causing lipotoxicity that manifests as photoreceptor dysfunction and neurodegeneration. These findings suggest that impaired macrophage cholesterol transport initiates several key elements of early human AMD, demonstrating the importance of systemic immunity and aging in promoting disease manifestation. Polymorphisms in genes involved with cholesterol transport and homeostasis are associated with a significantly higher risk of developing AMD, thus making these studies translationally relevant by identifying potential targets for therapy.

HDL-cholesterol levels and risk of age-related macular degeneration: a multiethnic genetic study using Mendelian randomization

Background

Dyslipidemia, particularly high-density lipoprotein cholesterol (HDL-C), has recently been implicated in the pathogenesis of age-related macular degeneration (AMD), the leading cause of vision loss. However, epidemiological studies have yielded conflicting results.

Methods

We investigated the causal role of plasma lipid levels in AMD in multiethnic populations comprising 16 144 advanced AMD cases and 17 832 controls of European descent, together with 2219 cases and 5275 controls of Asian descent, using Mendelian randomization in three models. Model 1 is a conventional meta-analysis which does not account for pleiotropy of instrumental variable (IV) effects. Model 2 is a univariate, inverse variance weighted regression analysis that accounts for potential unbalanced pleiotropy using MR-Egger method. Finally, Model 3 is a multivariate regression analysis that addresses pleiotropy by MR-Egger method and by adjusting for effects on other lipid traits.

Results

A 1 standard deviation (SD) higher HDL-cholesterol level was associated with an odds ratio (OR) for AMD of 1.17 (95% confidence interval: 1.07–1.29) in Europeans (P = 6.88 × 10^–4) and of 1.58 (1.24–2.00) in Asians (P = 2.92 × 10^–4) in Model 3. The corresponding OR estimates were 1.30 (1.09–1.55) in Europeans (P = 3.18 × 10^–3) and 1.42 (1.11—1.80) in Asians (P = 4.42 × 10^–3) in Model 1, and 1.21 (1.11–1.31) in Europeans (P = 3.12 × 10^–5) and 1.51 (1.20–1.91) in Asians (P = 7.61 × 10^–4) in Model 2. Conversely, neither LDL-C (Europeans: OR = 0.96, P = 0.272; Asians: OR = 1.02, P = 0.874; Model 3) nor triglyceride levels (Europeans: OR = 0.91, P = 0.102; Asians: OR = 1.06, P = 0.613) were associated with AMD. We also assessed the association between lipid levels and polypoidal choroidal vasculopathy (PCV) in Asians, a subtype of AMD, and found a similar trend for association of PCV with HDL-C levels.

Conclusions

Our study shows that high levels of plasma HDL-C are causally associated with an increased risk for advanced AMD in European and Asian populations, implying that strategies reducing HDL-C levels may be useful to prevent and treat AMD.

Disrupted cholesterol metabolism promotes age-related photoreceptor neurodegeneration

Photoreceptors have high intrinsic metabolic demand and are exquisitely sensitive to metabolic perturbation. In addition, they shed a large portion of their outer segment lipid membranes in a circadian manner, increasing the metabolic burden on the outer retina associated with the resynthesis of cell membranes and disposal of the cellular cargo. Here, we demonstrate that deletion of both ABCA1 and ABCG1 in rod photoreceptors leads to age-related accumulation of cholesterol metabolites in the outer retina, photoreceptor dysfunction, degeneration of rod outer segments, and ultimately blindness. A high-fat diet significantly accelerates rod neurodegeneration and vision loss, further highlighting the role of lipid homeostasis in regulating photoreceptor neurodegeneration and vision.

Oxysterol Signatures Distinguish Age-Related Macular Degeneration from Physiologic Aging

Macrophage aging is pathogenic in numerous diseases, including age-related macular degeneration (AMD), a leading cause of blindness in older adults. Although prior studies have explored the functional consequences of macrophage aging, less is known about its cellular basis or what defines the transition from physiologic aging to disease. Here, we show that despite their frequent self-renewal, macrophages from old mice exhibited numerous signs of aging, such as impaired oxidative respiration. Transcriptomic profiling of aged murine macrophages revealed dysregulation of diverse cellular pathways, especially in cholesterol homeostasis, that manifested in altered oxysterol signatures. Although the levels of numerous oxysterols in human peripheral blood mononuclear cells and plasma exhibited age-associated changes, plasma 24-hydroxycholesterol levels were specifically associated with AMD. These novel findings demonstrate that oxysterol levels can discriminate disease from physiologic aging. Furthermore, modulation of cholesterol homeostasis may be a novel strategy for treating age-associated diseases in which macrophage aging is pathogenic.

A new perspective on lipid research in age-related macular degeneration

There is an urgency to find new treatment strategies that could prevent or delay the onset or progression of AMD. Different classes of lipids and lipoproteins metabolism genes have been associated with AMD in a multiple ways, but despite the ever-increasing knowledge base, we still do not understand fully how circulating lipids or local lipid metabolism contribute to AMD. It is essential to clarify whether dietary lipids, systemic or local lipoprotein metabolismtrafficking of lipids in the retina should be targeted in the disease. In this article, we critically evaluate what has been reported in the literature and identify new directions needed to bring about a significant advance in our understanding of the role for lipids in AMD. This may help to develop potential new treatment strategies through targeting the lipid homeostasis.

Macrophage microRNA-150 promotes pathological angiogenesis as seen in age-related macular degeneration

Macrophage aging is pathogenic in diseases of the elderly, including age-related macular degeneration (AMD), a leading cause of blindness in older adults. However, the role of microRNAs, which modulate immune processes, in regulating macrophage dysfunction and thereby promoting age-associated diseases is underexplored. Here, we report that microRNA-150 (miR-150) coordinates transcriptomic changes in aged murine macrophages, especially those associated with aberrant lipid trafficking and metabolism in AMD pathogenesis. Molecular profiling confirmed that aged murine macrophages exhibit dysregulated ceramide and phospholipid profiles compared with young macrophages. Of translational relevance, upregulation of miR-150 in human peripheral blood mononuclear cells was also significantly associated with increased odds of AMD, even after controlling for age. Mechanistically, miR-150 directly targets stearoyl-CoA desaturase-2, which coordinates macrophage-mediated inflammation and pathologic angiogenesis, as seen in AMD, in a VEGF-independent manner. Together, our results implicate miR-150 as pathogenic in AMD and provide potentially novel molecular insights into diseases of aging.

Macrophages and lipid metabolism

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The transcriptional signature of Kupffer cells & Alveolar macrophages are enriched for lipid metabolism genes.

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Lipid metabolism may control macrophage phenotype.

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Dysregulated lipid metabolism in macrophages contributes to disease pathology.

Distinct macrophage populations throughout the body display highly heterogeneous transcriptional and epigenetic programs. Recent research has highlighted that these profiles enable the different macrophage populations to perform distinct functions as required in their tissue of residence, in addition to the prototypical macrophage functions such as in innate immunity. These ‘extra’ tissue-specific functions have been termed accessory functions. One such putative accessory function is lipid metabolism, with macrophages in the lung and liver in particular being associated with this function. As it is now appreciated that cell metabolism not only provides energy but also greatly influences the phenotype and function of the cell, here we review how lipid metabolism affects macrophage phenotype and function and the specific roles played by macrophages in the pathogenesis of lipid-related diseases. In addition, we highlight the current questions limiting our understanding of the role of macrophages in lipid metabolism.

Understanding AMD by analogy: systematic review of lipid-related common pathogenic mechanisms in AMD, AD, AS and GN

RATIONALE

Age-related macular degeneration (AMD) is one of the leading causes of blindness among the elderly. Due to its complex etiology, current treatments have been insufficient. Previous studies reveal three systems closely involved in AMD pathogenesis: lipid metabolism, oxidation and inflammation. These systems are also involved in Alzheimer's disease, atherosclerosis and glomerulonephritis. Understanding commonalities of these four diseases may provide insight into AMD etiology.

OBJECTIVES

To understand AMD pathogenesis by analogy and suggest ideas for future research, this study summarizes main commonalities in disease pathogenesis of AMD, Alzheimer's disease, atherosclerosis and glomerulonephritis.

METHODS

Articles were identified through PubMed, Ovid Medline and Google Scholar. We summarized the common findings and synthesized critical differences.

RESULTS

Oxidation, lipid deposition, complement activation, and macrophage recruitment are involved in all four diseases shown by genetic, molecular, animal and human studies. Shared genetic variations further strengthen their connection. Potential areas for future research are suggested throughout the review.

CONCLUSIONS

The four diseases share many steps of an overall framework of pathogenesis. Various oxidative sources cause oxidative stress. Oxidized lipids and related molecules accumulate and lead to complement activation, macrophage recruitment and pathology. Investigations that arise under this structure may aid us to better understand AMD pathology.

Inflammation-Induced Photoreceptor Cell Death

Neuroinflammation is an important aspect of many diseases of the eye, and experimental animal models have been widely used to determine its impact on retinal homeostasis and neuron survival. Physical separation of the neurosensory retina from the underlying retinal pigment epithelium (RPE) results in activation and infiltration of macrophages. Numerous studies have shown the critical role of macrophages in retinal disease processes. In retinal detachment, accumulation of macrophages in the subretinal space is associated with changes in cytokine and chemokine profile which lead to photoreceptor cell death. Targeted disruption of macrophage chemotaxis significantly reduces retinal detachment-induced photoreceptor degeneration. Apoptosis is the predominant mechanism of cell death; however regulated necrosis is also a contributor of photoreceptor loss. Therefore, effective neuroprotective approaches could integrate combined inhibition of both apoptotic and regulated necrosis pathways.

NAMPT-Mediated NAD(+) Biosynthesis Is Essential for Vision In Mice

Photoreceptor death is the endpoint of many blinding diseases. Identifying unifying pathogenic mechanisms in these diseases may offer global approaches for facilitating photoreceptor survival. We found that rod or cone photoreceptor-specific deletion of nicotinamide phosphoribosyltransferase (Nampt), the rate-limiting enzyme in the major NAD(+) biosynthetic pathway beginning with nicotinamide, caused retinal degeneration. In both cases, we could rescue vision with nicotinamide mononucleotide (NMN). Significantly, retinal NAD(+) deficiency was an early feature of multiple mouse models of retinal dysfunction, including light-induced degeneration, streptozotocin-induced diabetic retinopathy, and age-associated dysfunction. Mechanistically, NAD(+) deficiency caused metabolic dysfunction and consequent photoreceptor death. We further demonstrate that the NAD(+)-dependent mitochondrial deacylases SIRT3 and SIRT5 play important roles in retinal homeostasis and that NAD(+) deficiency causes SIRT3 dysfunction. These findings demonstrate that NAD(+) biosynthesis is essential for vision, provide a foundation for future work to further clarify the mechanisms involved, and identify a unifying therapeutic target for diverse blinding diseases.

Plasma lipoprotein subfraction concentrations are associated with lipid metabolism and age-related macular degeneration

Disturbance in lipid metabolism has been suggested as a major pathogenic factor for age-related macular degeneration (AMD). Conventional lipid measures have been inconsistently associated with AMD. Other factors that can alter lipid metabolism include lipoprotein phenotype and genetic mutations. We performed a case-control study to examine the association between lipoprotein profile and neovascular AMD (nAMD) and whether the cholesterylester transfer protein (CETP) D442G mutation modulates these associations. Patients with nAMD had significantly higher concentrations of HDL and IDL compared with controls. The increase in HDL particles in nAMD patients was driven by an excess of medium-sized particles. Concurrently, patients with nAMD also had lower Apo A-1, lower VLDL and chylomicron lipoprotein. Many of these associations showed a dose-dependent association between controls, early AMD cases, and nAMD cases. Adjustment for the presence of the D442G mutation at the CETP locus did not significantly alter the increased AMD risk associated with HDL particle concentration. AMD is associated with variation in many lipoprotein subclasses, including increased HDL and IDL particles and decreased Apo A-1, VLDL, and chylomicron particles. These data suggest widespread systemic disturbance in lipid metabolism in the pathogenesis of AMD, including possible alterations in lipoprotein carrier capacity.

Activation of liver X receptor α protects amyloid β1-40 induced inflammatory and senescent responses in human retinal pigment epithelial cells

OBJECTIVE

To investigate whether activation of the liver X receptors (LXRs) inhibits amyloid β_1-40 (Aβ_1-40) induced inflammatory and senescent responses in human retinal pigment epithelial (RPE) cells.

MATERIALS AND METHODS

Confluent cultures of human primary RPE and ARPE-19 cells pretreated with 5 μΜ of TO901317 (TO90), a synthetic agonist of LXR, or vehicle were incubated with 1 μΜ of Aβ_1-40 or Aβ_40-1. The optimum concentrations of Aβ_1-40 and TO90 were determined by cell viability assay. Pro-inflammatory cytokines IL-6, IL-8, MCP-1 were detected by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). Expression and localization of an aging protein p16INK4a (p16) were analyzed by western blotting and immunofluorescence. Expressions of LXRs and one of their target genes ATP-binding cassette transporter A1 (ABCA1) were examined by real-time PCR and western blotting. Phosphorylated transcription inhibition factor-κB-α (p-IκB-α) was assessed by western blotting.

RESULTS

A negative linear relationship between the Aβ_1-40 concentration and the cell viability was evident, indicating Aβ_1-40 decreased ARPE-19 cell viability in a dose-dependent manner. Aβ_1-40 enhanced the expression of IL-6, IL-8, MCP-1 as well as p16 in both RPE cell lines at both mRNA and protein levels, whereas TO90 counteracted the detrimental effects. TO90 upregulated the expression of LXRα and its target gene ABCA1, but it did not affect the expression of LXRβ. Meanwhile, TO90 inhibited the phosphorylation of IκB-α mediated by Aβ_1-40 stimulation.

CONCLUSION

Activation of the LXRα-ABCA1 axis may alleviate Aβ_1-40 induced inflammatory and senescent responses in RPE cells. The beneficial effect appears associated with the inhibition of the NF-κB signaling pathway.

Regression of Some High-risk Features of Age-related Macular Degeneration (AMD) in Patients Receiving Intensive Statin Treatment

Importance

Age-related macular degeneration (AMD) remains the leading cause of blindness in developed countries, and affects more than 150 million worldwide. Despite effective anti-angiogenic therapies for the less prevalent neovascular form of AMD, treatments are lacking for the more prevalent dry form. Similarities in risk factors and pathogenesis between AMD and atherosclerosis have led investigators to study the effects of statins on AMD incidence and progression with mixed results. A limitation of these studies has been the heterogeneity of AMD disease and the lack of standardization in statin dosage.

Objective

We were interested in studying the effects of high-dose statins, similar to those showing regression of atherosclerotic plaques, in AMD.

Design

Pilot multicenter open-label prospective clinical study of 26 patients with diagnosis of AMD and the presence of many large, soft drusenoid deposits. Patients received 80 mg of atorvastatin daily and were monitored at baseline and every 3 months with complete ophthalmologic exam, best corrected visual acuity (VA), fundus photographs, optical coherence tomography (OCT), and blood work (AST, ALT, CPK, total cholesterol, TSH, creatinine, as well as a pregnancy test for premenopausal women).

Results

Twenty-three subjects completed a minimum follow-up of 12 months. High-dose atorvastatin resulted in regression of drusen deposits associated with vision gain (+ 3.3 letters, p = 0.06) in 10 patients. No subjects progressed to advanced neovascular AMD.

Conclusions

High-dose statins may result in resolution of drusenoid pigment epithelial detachments (PEDs) and improvement in VA, without atrophy or neovascularization in a high-risk subgroup of AMD patients. Confirmation from larger studies is warranted.

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High dose lipophilic statin administration was associated with regression of large soft drusen and vision gain in 10/23 AMD patients.

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Duration of treatment before a positive response was observed was usually 1–1.5 years.

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Patients on high-dose statin appeared to be protected from progression to “wet” neovascular-AMD.

There is a lack of effective therapies for dry age-related macular degeneration (AMD), one of the leading causes of blindness affecting millions. Although AMD shares similarities with atherosclerosis, prior studies on statins and AMD have failed to show improvement. A limitation of these studies has been the heterogeneity of AMD disease and the lack of standardization in statin dosage. Here, we present for the first time evidence that treatment with high-dose atorvastatin (80 mg) is associated with regression of lipid deposits and improvement in visual acuity, without atrophy or neovascularization, in high-risk AMD patients.

Mitochondrial regulation of macrophage cholesterol homeostasis

This review explores the relationship between mitochondrial structure and function in the regulation of macrophage cholesterol metabolism and proposes that mitochondrial dysfunction contributes to loss of the elegant homeostatic mechanisms which normally maintain cellular sterol levels within defined limits. Mitochondrial sterol 27-hydroxylase (CYP27A1) can generate oxysterol activators of liver X receptors which heterodimerise with retinoid X receptors, enhancing the transcription of ATP binding cassette transporters (ABCA1, ABCG1, and ABCG4), that can remove excess cholesterol via efflux to apolipoproteins A-1, E, and high density lipoprotein, and inhibit inflammation. The activity of CYP27A1 is regulated by the rate of supply of cholesterol substrate to the inner mitochondrial membrane, mediated by a complex of proteins. The precise identity of this dynamic complex remains controversial, even in steroidogenic tissues, but may include steroidogenic acute regulatory protein and the 18 kDa translocator protein, together with voltage-dependent anion channels, ATPase AAA domain containing protein 3A, and optic atrophy type 1 proteins. Certainly, overexpression of StAR and TSPO proteins can enhance macrophage cholesterol efflux to apoA-I and/or HDL, while perturbations in mitochondrial function, or changes in the expression of mitochondrial fusion proteins, alter the efficiency of cholesterol efflux. Molecules which can sustain or improve mitochondrial function or increase the activity of the protein complex involved in cholesterol transfer may have utility in resolving the problem of dysregulated macrophage cholesterol homeostasis, a condition which may contribute to inflammation, atherosclerosis, nonalcoholic steatohepatitis, osteoblastic bone resorption, and some disorders of the central nervous system.

IL10-driven STAT3 signalling in senescent macrophages promotes pathological eye angiogenesis

Macrophage dysfunction plays a pivotal role during neovascular proliferation in diseases of ageing including cancers, atherosclerosis and blinding eye disease. In the eye, choroidal neovascularization (CNV) causes blindness in patients with age-related macular degeneration (AMD). Here we report that increased IL10, not IL4 or IL13, in senescent eyes activates STAT3 signalling that induces the alternative activation of macrophages and vascular proliferation. Targeted inhibition of both IL10 receptor-mediated signalling and STAT3 activation in macrophages reverses the ageing phenotype. In addition, adoptive transfer of STAT3-deficient macrophages into eyes of old mice significantly reduces the amount of CNV. Systemic and CD163⁺ eye macrophages obtained from AMD patients also demonstrate STAT3 activation. Our studies demonstrate that impaired SOCS3 feedback leads to permissive IL10/STAT3 signalling that promotes alternative macrophage activation and pathological neovascularization. These findings have significant implications for our understanding of the pathobiology of age-associated diseases and may guide targeted immunotherapy.

Pathological neovascularization causes blinding eye disease. Here the authors show that IL10 activates STAT3 signalling in the macrophages in the ageing eye, promoting their polarization towards a pro-angiogenic phenotype; interfering with this pathway reverses the pathology in a mouse model.

Transcriptional programming of human macrophages: on the way to systems immunology

Many of the major common diseases such as atherosclerosis, diabetes, obesity, numerous autoimmune diseases, as well as neurodegenerative diseases such as Alzheimer's disease and many cancer types are characterised by a chronic inflammatory component termed sterile inflammation. Myeloid cells, particularly macrophages, are an important cellular component of chronic inflammation in these diseases. For almost all of these disease conditions, previous reports suggested that macrophages can exert either so-called pro-inflammatory or anti-inflammatory functions, thereby either fighting or feeding the disease. This apparent dichotomy of reactions of macrophages led to a dichotomous definition of macrophage activation classified as macrophage polarisation. However, analysis of large transcriptomics data derived from human and murine macrophages show that macrophage functions are shaped in a very tissue- and signal-input specific manner, allowing these cells to develop extremely specific functional programmes. Integrating global views on macrophage activation on the transcriptome, the epigenome, the proteome or the metabolome will finally lead to a data-driven approach to understand macrophage biology in context of major diseases. We are indeed on the way to a systems immunology approach that integrates -omics data with mathematical and bioinformatical modelling as the pre-requisite to generate data-driven hypotheses. This approach opens completely new avenues for the development of tailored diagnostics and therapies targeting macrophages in sterile inflammations of the major common diseases. I will also discuss some of the next developments that will be necessary to reach these important goals.

Seeing through VEGF: innate and adaptive immunity in pathological angiogenesis in the eye

The central role of vascular endothelial growth factor (VEGF) signaling in regulating normal vascular development and pathological angiogenesis has been documented in multiple studies. Ocular anti-VEGF therapy is highly effective for treating a subset of patients with blinding eye disorders such as diabetic retinopathy and neovascular age-related macular degeneration (AMD). However, chronic VEGF suppression can lead to adverse effects associated with poor visual outcomes due to the loss of prosurvival and neurotrophic capacities of VEGF. In this review, we discuss emerging evidence for immune-related mechanisms that regulate ocular angiogenesis in a VEGF-independent manner. These novel molecular and cellular pathways may provide potential therapeutic avenues for a multitarget strategy, preserving the neuroprotective functions of VEGF in those patients whose disease is unresponsive to VEGF neutralization.

Genomic aspects of age-related macular degeneration

Age-related macular degeneration (AMD) is a major late-onset posterior eye disease that causes central vision to deteriorate among elderly populations. The predominant lesion of AMD is the macula, at the interface between the outer retina and the inner choroid. Recent advances in genetics have revealed that inflammatory and angiogenic pathways play critical roles in the pathophysiology of AMD. Genome-wide association studies have identified ARMS2/HTRA1 and CFH as major AMD susceptibility genes. Genetic studies for AMD will contribute to the prevention of central vision loss, the development of new treatment, and the maintenance of quality of vision for productive aging.