C-reactive protein and complement factor H in aged human eyes and eyes with age-related macular degeneration

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

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

Potential Causal Association between C-Reactive Protein Levels in Age-Related Macular Degeneration: A Two-Sample Mendelian Randomization Study

Researchers have proposed a possible correlation between age-related macular degeneration (AMD) and inflammation or C-reactive protein (CRP) levels. We investigated the potential causal relationship between CRP levels and AMD. Single-nucleotide polymorphisms (SNPs) associated with CRP exposure were selected as the instrumental variables (IVs) with significance (p < 5 × 10-8) from the genome-wide association study (GWAS) meta-analysis data of Biobank Japan and the UK Biobank. GWAS data for AMD were obtained from 11 International AMD Genomics Consortium studies. An evaluation of causal estimates, utilizing the inverse-variance-weighted (IVW), weighted-median, MR-Egger, MR-Pleiotropy-Residual-Sum, and Outlier tests, was conducted in a two-sample Mendelian randomization (MR) study. We observed significant causal associations between CRP levels and AMD (odds ratio [OR] = 1.13, 95% CI = [1.02-1.24], and p = 0.014 in IVW; OR = 1.18, 95% CI = [1.00-1.38], and p = 0.044 in weight median; OR = 1.31, 95% CI = [1.13-1.52], and p < 0.001 in MR-Egger). The causal relationship between CRP and AMD warrants further research to address the significance of inflammation as a risk factor for AMD.

CFH Haploinsufficiency and Complement Alterations in Early-Onset Macular Degeneration

Purpose

Complement dysregulation is a key component in the pathogenesis of age-related macular degeneration (AMD) and related diseases such as early-onset macular drusen (EOMD). Although genetic variants of complement factor H (CFH) are associated with AMD risk, the impact of CFH and factor H-like protein 1 (FHL-1) expression on local complement activity in human retinal pigment epithelium (RPE) remains unclear.

Methods

We identified a novel CFH variant in a family with EOMD and generated patient induced pluripotent stem cell (iPSC)-derived RPE cells. We assessed CFH and FHL-1 co-factor activity through C3b breakdown assays and measured complement activation by immunostaining for membrane attack complex (MAC) formation. Expression of CFH, FHL-1, local alternative pathway (AP) components, and regulators of complement activation (RCA) in EOMD RPE cells was determined by quantitative PCR, western blot, and immunostaining. Isogenic EOMD (cEOMD) RPE was generated using CRISPR/Cas9 gene editing.

Results

The CFH variant (c.351-2A>G) resulted in loss of CFH and FHL-1 expression and significantly reduced CFH and FHL-1 protein expression (∼50%) in EOMD iPSC RPE cells. These cells exhibited increased MAC deposition upon exposure to normal human serum. Under inflammatory or oxidative stress conditions, CFH and FHL-1 expression in EOMD RPE cells paralleled that of controls, whereas RCA expression, including MAC formation inhibitors, was elevated. CRISPR/Cas9 correction restored CFH/FHL-1 expression and mitigated alternative pathway complement activity in cEOMD RPE cells.

Conclusions

Identification of a novel CFH variant in patients with EOMD resulting in reduced CFH and FHL-1 and increased local complement activity in EOMD iPSC RPE supports the involvement of CFH haploinsufficiency in EOMD pathogenesis.

Mitochondrial damage and clearance in retinal pigment epithelial cells

Age-related macular degeneration (AMD) is a devastating eye disease that causes permanent vision loss in the central part of the retina, known as the macula. Patients with such severe visual loss face a reduced quality of life and are at a 1.5 times greater risk of death compared to the general population. Currently, there is no cure for or effective treatment for dry AMD. There are several mechanisms thought to underlie the disease, for example, ageing-associated chronic oxidative stress, mitochondrial damage, harmful protein aggregation and inflammation. As a way of gaining a better understanding of the molecular mechanisms behind AMD and thus developing new therapies, we have created a peroxisome proliferator-activated receptor gamma coactivator 1-alpha and nuclear factor erythroid 2-related factor 2 (PGC1α/NFE2L2) double-knockout (dKO) mouse model that mimics many of the clinical features of dry AMD, including elevated levels of oxidative stress markers, damaged mitochondria, accumulating lysosomal lipofuscin and extracellular drusen-like structures in retinal pigment epithelial cells (RPE). In addition, a human RPE cell-based model was established to examine the impact of non-functional intracellular clearance systems on inflammasome activation. In this study, we found that there was a disturbance in the autolysosomal machinery responsible for clearing mitochondria in the RPE cells of one-year-old PGC1α/NFE2L2-deficient mice. The confocal immunohistochemical analysis revealed an increase in autophagosome marker microtubule-associated proteins 1A/1B light chain 3B (LC3B) as well as multiple mitophagy markers such as PTE-induced putative kinase 1 (PINK1) and E3 ubiquitin ligase (PARKIN), along with signs of damaged mitochondria. However, no increase in autolysosome formation was detected, nor was there a colocalization of the lysosomal marker LAMP2 or the mitochondrial marker, ATP synthase β. There was an upregulation of late autolysosomal fusion Ras-related protein (Rab7) in the perinuclear space of RPE cells, together with autofluorescent aggregates. Additionally, we observed an increase in the numbers of Toll-like receptors 3 and 9, while those of NOD-like receptor 3 were decreased in PGC1α/NFE2L2 dKO retinal specimens compared to wild-type animals. There was a trend towards increased complement component C5a and increased involvement of the serine protease enzyme, thrombin, in enhancing the terminal pathway producing C5a, independent of C3. The levels of primary acute phase C-reactive protein and receptor for advanced glycation end products were also increased in the PGC1α/NFE2L2 dKO retina. Furthermore, selective proteasome inhibition with epoxomicin promoted both nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and mitochondrial-mediated oxidative stress, leading to the release of mitochondrial DNA to the cytosol, resulting in potassium efflux-dependent activation of the absent in melanoma 2 (AIM2) inflammasome and the subsequent secretion of interleukin-1β in ARPE-19 cells. In conclusion, the data suggest that there is at least a relative decrease in mitophagy, increases in the amounts of C5 and thrombin and decreased C3 levels in this dry AMD-like model. Moreover, selective proteasome inhibition evoked mitochondrial damage and AIM2 inflammasome activation in ARPE-19 cells.

Central macular choriocapillaris impairment as a manifestation of microvascular disease in eyes with subretinal drusenoid deposits

BACKGROUND/OBJECTIVES

Microvascular alterations and choroidal impairment are emerging as a pathologic pathway in age-related macular degeneration (AMD). This study aimed to evaluate the central macular choriocapillaris (CC) in eyes with subretinal drusenoid deposits (SDD) and the retinal microvasculature in patients with early AMD phenotypes.

SUBJECTS/METHODS

This was an institutional, multicentric observational cross-sectional study. Ninety-nine eyes of 99 subjects; 33 eyes with SDD only, 33 eyes with conventional drusen (CD) only, and 33 eyes of healthy age-matched subjects were included. Comprehensive ophthalmologic examination and optical coherence tomography angiography (OCTA) was performed. The central macular flow area of the CC was analysed in the SDD group and the vessel density of the retinal superficial capillary plexus (SCP) and deep capillary plexus (DCP) was analysed in the SDD and CD groups using automated OCTA output parameters.

RESULTS

The flow area of the CC in the SDD group was significantly reduced (p ≤ 0.001) with respect to the healthy control group. There was a trend of reduction of vessel density of the SCP and the DCP in the SDD and CD group with respect to controls, although this did not reach statistical significance.

CONCLUSIONS

OCTA data in the present report corroborate the role of vascular damage in early AMD with CC impairment in the central macular area in eyes with SDD.

Rethinking the potential and necessity of drug delivery systems in neovascular age-related macular degeneration therapy

Age-related macular degeneration (AMD) is the predominant threat to human vision and ultimately results in blindness. With the increase in the aging population, it has become a more crucial issue to human health. AMD is a multifactorial disease with the unique feature of uncontrollable angiogenesis during initiation and progression. Although increasing evidence indicates that AMD is largely hereditary, the predominant efficient treatment is antiangiogenesis, which mainly involves VEGF and HIF-α as therapeutic targets. The repeated administration of this treatment over the long term, generally through intravitreal injection, has called for the introduction of long-term drug delivery systems, which are expected to be achieved by biomaterials. However, the clinical results of the port delivery system indicate that the optimization of medical devices toward prolonging the activities of therapeutic biologics in AMD therapy seems more promising. These results indicate that we should rethink the possibility and potential of biomaterials as drug delivery systems in achieving long-term, sustained inhibition of angiogenesis in AMD therapy. In this review, the etiology, categorization, risk factors, pathogenesis, and current clinical treatments of AMD are briefly introduced. Next, the development status of long-term drug delivery systems is discussed, and the drawbacks and shortages of these systems are emphasized. By comprehensively considering the pathological aspect and the recent application of drug delivery systems in AMD therapy, we hope to find a better solution for the further development of long-term therapeutic strategies for AMD.

Bruch's Membrane: A Key Consideration with Complement-Based Therapies for Age-Related Macular Degeneration

The complement system is crucial for immune surveillance, providing the body's first line of defence against pathogens. However, an imbalance in its regulators can lead to inappropriate overactivation, resulting in diseases such as age-related macular degeneration (AMD), a leading cause of irreversible blindness globally affecting around 200 million people. Complement activation in AMD is believed to begin in the choriocapillaris, but it also plays a critical role in the subretinal and retinal pigment epithelium (RPE) spaces. Bruch's membrane (BrM) acts as a barrier between the retina/RPE and choroid, hindering complement protein diffusion. This impediment increases with age and AMD, leading to compartmentalisation of complement activation. In this review, we comprehensively examine the structure and function of BrM, including its age-related changes visible through in vivo imaging, and the consequences of complement dysfunction on AMD pathogenesis. We also explore the potential and limitations of various delivery routes (systemic, intravitreal, subretinal, and suprachoroidal) for safe and effective delivery of conventional and gene therapy-based complement inhibitors to treat AMD. Further research is needed to understand the diffusion of complement proteins across BrM and optimise therapeutic delivery to the retina.

Inflammation and retinal degenerative diseases

Vision is an ability that depends on the precise structure and functioning of the retina. Any kind of stress or injury can disrupt the retinal architecture and leads to vision impairment, vision loss, and blindness. Immune system and immune response function maintain homeostasis in the microenvironment. Several genetic, metabolic, and environmental factors may alter retinal homeostasis, and these events may initiate various inflammatory cascades. The prolonged inflammatory state may contribute to the initiation and development of retinal disorders such as glaucoma, age-related macular degeneration, diabetic retinopathy, and retinitis pigmentosa, which pose a threat to vision. In the current review, we attempted to provide sufficient evidence on the role of inflammation in these retinal disorders. Moreover, this review paves the way to focus on therapeutic targets of the disease, which are found to be promising.

Clinicopathologic Findings in Three Siblings With Geographic Atrophy

Purpose

Age-related macular degeneration (AMD) is a leading cause of blindness among the elderly worldwide. Clinical imaging and histopathologic studies are crucial to understanding disease pathology. This study combined clinical observations of three brothers with geographic atrophy (GA), followed for 20 years, with histopathologic analysis.

Methods

For two of the three brothers, clinical images were taken in 2016, 2 years prior to death. Immunohistochemistry, on both flat-mounts and cross sections, histology, and transmission electron microscopy were used to compare the choroid and retina in GA eyes to those of age-matched controls.

Results

Ulex europaeus agglutinin (UEA) lectin staining of the choroid demonstrated a significant reduction in the percent vascular area and vessel diameter. In one donor, histopathologic analysis demonstrated two separate areas with choroidal neovascularization (CNV). Reevaluation of swept-source optical coherence tomography angiography (SS-OCTA) images revealed CNV in two of the brothers. UEA lectin also revealed a significant reduction in retinal vasculature in the atrophic area. A subretinal glial membrane, composed of processes positive for glial fibrillary acidic protein and/or vimentin, occupied areas identical to those of retinal pigment epithelium (RPE) and choroidal atrophy in all three AMD donors. SS-OCTA also demonstrated presumed calcific drusen in the two donors imaged in 2016. Immunohistochemical analysis and alizarin red S staining verified calcium within drusen, which was ensheathed by glial processes.

Conclusions

This study demonstrates the importance of clinicohistopathologic correlation studies. It emphasizes the need to better understand how the symbiotic relationship between choriocapillaris and RPE, glial response, and calcified drusen impact GA progression.

Age-related macular degeneration: A disease of extracellular complement amplification

Age-related macular degeneration (AMD) is a major cause of vision impairment in the Western World, and with the aging world population, its incidence is increasing. As of today, for the majority of patients, no treatment exists. Multiple genetic and biochemical studies have shown a strong association with components in the complement system and AMD, and evidence suggests a major role of remodeling of the extracellular matrix underlying the outer blood/retinal barrier. As part of the innate immune system, the complement cascade acts as a first-line defense against pathogens, and upon activation, its amplification loop ensures a strong, rapid, and sustained response. Excessive activation, however, can lead to host tissue damage and cause complement-associated diseases like AMD. AMD patients present with aberrant activation of the alternative pathway, especially in ocular tissues but also on a systemic level. Here, we review the latest findings of complement activation in AMD, and we will discuss in vivo observations made in human tissue, cellular models, the potential synergy of different AMD-associated pathways, and conclude on current clinical trials and the future outlook.

C1q and the classical complement cascade in geographic atrophy secondary to age-related macular degeneration

Geographic atrophy (GA) secondary to age-related macular degeneration (AMD) is a retinal neurodegenerative disorder. Human genetic data support the complement system as a key component of pathogenesis in AMD, which has been further supported by pre-clinical and recent clinical studies. However, the involvement of the different complement pathways (classical, lectin, alternative), and thus the optimal complement inhibition target, has yet to be fully defined. There is evidence that C1q, the initiating molecule of the classical pathway, is a key driver of complement activity in AMD. C1q is expressed locally by infiltrating phagocytic cells and C1q-activating ligands are present at disease onset and continue to accumulate with disease progression. The accumulation of C1q on photoreceptor synapses with age and disease is consistent with its role in synapse elimination and neurodegeneration that has been observed in other neurodegenerative disorders. Furthermore, genetic deletion of C1q, local pharmacologic inhibition within the eye, or genetic deletion of downstream C4 prevents photoreceptor cell damage in mouse models. Hence, targeting the classical pathway in GA could provide a more specific therapeutic approach with potential for favorable efficacy and safety.

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

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

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

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

Advancements in ocular gene therapy delivery: vectors and subretinal, intravitreal, and suprachoroidal techniques

INTRODUCTION

: Ocular gene therapy represents fertile ground for rapid innovation, with ever-expanding therapeutic strategies, molecular targets, and indications.

AREAS COVERED

: Potential indications for ocular gene therapy have classically focused on inherited retinal disease (IRD), but more recently include acquired retinal diseases, such as neovascular age-related macular degeneration, geographic atrophy and diabetic retinopathy. Ocular gene therapy strategies have proliferated recently, and include gene augmentation, gene inactivation, gene editing, RNA modulation, and gene-independent gene augmentation. Viral vector therapeutic constructs include adeno-associated virus and lentivirus and continue to evolve through directed evolution and rationale design. Ocular gene therapy administration techniques have expanded beyond pars plana vitrectomy with subretinal injection to intravitreal injection and suprachoroidal injection.

EXPERT OPINION

: The success of treatment for IRD, paired with the promise of clinical research in acquired retinal diseases and in administration techniques, has raised the possibility of in-office gene therapy for common retinal disorders within the next five to ten years.

Genetic Variants of Complement Factor H Y402H (rs1061170), C2 R102G (rs2230199), and C3 E318D (rs9332739) and Response to Intravitreal Anti-VEGF Treatment in Patients with Exudative Age-Related Macular Degeneration

Background and Objectives: To assess the association between the single nucleotide polymorphisms (SNPs) in the genes encoding complement factors CFH, C2, and C3 (Y402H rs1061170, R102G rs2230199, and E318D rs9332739, respectively) and response to intravitreal anti-vascular endothelial growth factor (VEGF) therapy in patients with exudative age-related macular degeneration (AMD). Materials and Methods: The study included 111 patients with exudative AMD treated with intravitreal bevacizumab or ranibizumab injections. Response to therapy was assessed on the basis of best-corrected visual acuity (BCVA) and central retinal thickness (CRT) measured every 4 weeks for 12 months. The control group included 58 individuals without AMD. The SNPs were genotyped by a real-time polymerase chain reaction in genomic DNA isolated from peripheral blood samples. Results: The CC genotype in SNP rs1061170 of the CFH gene was more frequent in patients with AMD than in controls (p = 0.0058). It was also more common among the 28 patients (25.2%) with poor response to therapy compared with good responders (p = 0.0002). Poor responders, especially those without this genotype, benefited from switching to another anti-VEGF drug. At the last follow-up assessment, carriers of this genotype had significantly worse BCVA (p = 0.0350) and greater CRT (p = 0.0168) than noncarriers. TT genotype carriers showed improved BCVA (p = 0.0467) and reduced CRT compared with CC and CT genotype carriers (p = 0.0194). No associations with AMD or anti-VEGF therapy outcomes for SNP rs9332739 in the C2 gene and SNP rs2230199 in the C3 gene were found. Conclusions: The CC genotype for SNP rs1061170 in the CFH gene was associated with AMD in our population. Additionally, it promoted a poor response to anti-VEGF therapy. On the other hand, TT genotype carriers showed better functional and anatomical response to anti-VEGF therapy at 12 months than carriers of the other genotypes for this SNP.

Local Factor H production by human choroidal endothelial cells mitigates complement deposition: implications for macular degeneration

Activation of the alternative complement pathway is an initiating event in the pathology of Age-related Macular Degeneration (AMD). Unchecked complement activation leads to the formation of a pro-lytic pore, the Membrane Attack Complex (MAC). MAC deposition is observed on the choriocapillaris of AMD patients and likely causes lysis of choroidal endothelial cells (CECs). Complement factor H (FH, encoded by the gene CFH), is an inhibitor of complement. Both loss of function of FH and reduced choroidal levels of FH have been reported in AMD. It is plausible that reduced local FH availability promotes MAC deposition on CECs. FH is produced primarily in the liver; however, cells including the retinal pigment epithelium can produce FH locally. We hypothesized that CECs produce FH locally to protect against MAC deposition. We aimed to investigate the effect of reduced FH levels in the choroid to determine whether increasing local FH could protect CECs from MAC deposition. We demonstrated that siRNA knockdown of FH (CFH) in human immortalized CECs results in increased MAC deposition. We generated AMD iPSC-derived CECs and found that overexpression of FH protects against MAC deposition. These results suggest that local CEC-produced FH protects against MAC deposition, and that increasing local FH protein may be beneficial in limiting MAC deposition in AMD. This article is protected by copyright. All rights reserved.

Topical Ketotifen Fumarate Inhibits Choroidal Mast Cell Degranulation and Loss of Retinal Pigment Epithelial Cells in Rat Model for Geographic Atrophy

Purpose

This study evaluates whether topical ketotifen fumarate (KTF) can prevent geographic atrophy (GA)-like phenotypes in a rat model.

Methods

Pharmacokinetics (PKs) of KTF after topical administration twice daily for 5 days was analyzed in rat retina, retinal pigment epithelium (RPE)/choroid/sclera, and in plasma by an liquid chromatography tandem mass spectrometry (LC-MS/MS) method. Rats were then given hydrogel implants +/- 48/80 in the superior subconjunctival space and topically treated with 1% and 0.25% of KTF or phosphate buffer saline (PBS) twice daily. Rats were euthanized at 1, 2, 4, and 8 weeks postinjection. Choroidal mast cells (MCs) were stained with nonspecific esterase and the RPE monolayer was labeled with RPE65 and ZO-1 in whole mount choroids. Retinal and choroidal areas were determined in cryosections stained with picrosirius red. Dark-adapted electroretinogram (ERG) was also performed to evaluate retinal function.

Results

PK results showed the highest level of KTF (average 5.6 nM/mg) in the RPE/choroid/sclera in rats given topical 1% KTF. Topical 1% KTF significantly reduced choroidal MC degranulation at 1 week and 2 weeks (both P < 0.001) and RPE loss at 4 weeks (P < 0.001) as well as retinal and choroidal thinning (both P < 0.001) and reduction in ERG amplitude at 8 weeks (P < 0.05) compared to PBS. Similar results were obtained with 0.25% KTF.

Conclusions

Both 1% and 0.25% KTF eye drops effectively reduced MC degranulation, RPE loss, and retinal and choroidal thinning while preventing the decline of ERG amplitude in a GA-like rat model. These data suggest that topical KTF might be a new therapeutic drug for treating GA.

Translational Relevance

The results of this study demonstrate that topical KTF successfully reduced GA-like phenotypes in a rat model and may provide a novel therapy for GA.

Increased Systemic C-Reactive Protein Is Associated With Choroidal Thinning in Intermediate Age-Related Macular Degeneration

Purpose

C-reactive protein (CRP) and decreased choroidal thickness (CT) are risk factors for progression to advanced age-related macular degeneration (AMD). We examined the association between systemic levels of CRP and CT in patients with intermediate AMD (iAMD).

Methods

Patients with iAMD in the Colorado AMD Registry were included. Baseline serum samples and multimodal imaging including spectral domain–optical coherence tomography (SD-OCT), fundus photography, and autofluorescence were obtained. Medical and social histories were surveyed. CT was obtained by manual segmentation of OCT images. High-sensitivity CRP levels were quantified in serum samples. Univariate and multivariable linear regression models accounting for the intrasubject correlation of two eyes were fit using log-transformed CT as the outcome.

Results

The study included 213 eyes from 107 patients with a mean age of 76.8 years (SD, 6.8). Median CT was 200.5 µm (range, 86.5–447.0). Median CRP was 1.43 mg/L (range, 0.13–17.10). Higher CRP was associated with decreased CT in the univariate model (P = 0.01). Older age and presence of reticular pseudodrusen (RPD) were associated with decreased CT (P < 0.01), whereas gender, body mass index, and smoking were not associated with CT. Higher CRP remained significantly associated with decreased CT after adjustment for age and RPD (P = 0.01).

Conclusions

Increased CRP may damage the choroid, leading to choroidal thinning and increased risk of progression to advanced AMD. Alternatively, CRP may be a marker for inflammatory events that mediate ocular disease. The results of this study further strengthen the association between inflammation and AMD.

Translational Relevance

Increased CRP is associated with choroidal thinning, a clinical risk factor for AMD.

Exploring the choroidal vascular labyrinth and its molecular and structural roles in health and disease

The choroid is a key player in maintaining ocular homeostasis and plays a role in a variety of chorioretinal diseases, many of which are poorly understood. Recent advances in the field of single-cell RNA sequencing have yielded valuable insights into the properties of choroidal endothelial cells (CECs). Here, we review the role of the choroid in various physiological and pathophysiological mechanisms, focusing on the role of CECs. We also discuss new insights regarding the phenotypic properties of CECs, CEC subpopulations, and the value of measuring transcriptomics in primary CEC cultures derived from post-mortem eyes. In addition, we discuss key phenotypic, structural, and functional differences that distinguish CECs from other endothelial cells such as retinal vascular endothelial cells. Understanding the specific clinical and molecular properties of the choroid will shed new light on the pathogenesis of the broad clinical range of chorioretinal diseases such as age-related macular degeneration, central serous chorioretinopathy and other diseases within the pachychoroid spectrum, uveitis, and diabetic choroidopathy. Although our knowledge is still relatively limited with respect to the clinical features and molecular pathways that underlie these chorioretinal diseases, we summarise new approaches and discuss future directions for gaining new insights into these sight-threatening diseases and highlight new therapeutic strategies such as pluripotent stem cell‒based technologies and gene therapy.

Oxidative Stress and Mitochondrial Damage in Dry Age-Related Macular Degeneration Like NFE2L2/PGC-1α -/- Mouse Model Evoke Complement Component C5a Independent of C3

Aging-associated chronic oxidative stress and inflammation are known to be involved in various diseases, e.g., age-related macular degeneration (AMD). Previously, we reported the presence of dry AMD-like signs, such as elevated oxidative stress, dysfunctional mitophagy and the accumulation of detrimental oxidized materials in the retinal pigment epithelial (RPE) cells of nuclear factor erythroid 2-related factor 2, and a peroxisome proliferator-activated receptor gamma coactivator 1-alpha (NFE2L2/PGC1α) double knockout (dKO) mouse model. Here, we investigated the dynamics of inflammatory markers in one-year-old NFE2L2/PGC1α dKO mice. Immunohistochemical analysis revealed an increase in levels of Toll-like receptors 3 and 9, while those of NOD-like receptor 3 were decreased in NFE2L2/PGC1α dKO retinal specimens as compared to wild type animals. Further analysis showed a trend towards an increase in complement component C5a independent of component C3, observed to be tightly regulated by complement factor H. Interestingly, we found that thrombin, a serine protease enzyme, was involved in enhancing the terminal pathway producing C5a, independent of C3. We also detected an increase in primary acute phase C-reactive protein and receptor for advanced glycation end products in NFE2L2/PGC1α dKO retina. Our main data show C5 and thrombin upregulation together with decreased C3 levels in this dry AMD-like model. In general, the retina strives to mount an orchestrated inflammatory response while attempting to maintain tissue homeostasis and resolve inflammation.

Interlink between Inflammation and Oxidative Stress in Age-Related Macular Degeneration: Role of Complement Factor H

Age-related macular degeneration (AMD) heads the list of legal blindness among the elderly population in developed countries. Due to the complex nature of the retina and the variety of risk factors and mechanisms involved, the molecular pathways underlying AMD are not yet fully defined. Persistent low-grade inflammation and oxidative stress eventually lead to retinal pigment epithelium dysfunction and outer blood-retinal barrier (oBRB) breakdown. The identification of AMD susceptibility genes encoding complement factors, and the presence of inflammatory mediators in drusen, the hallmark deposits of AMD, supports the notion that immune-mediated processes are major drivers of AMD pathobiology. Complement factor H (FH), the main regulator of the alternative pathway of the complement system, may have a key contribution in the pathogenesis of AMD as it is able to regulate both inflammatory and oxidative stress responses in the oBRB. Indeed, genetic variants in the CFH gene account for the strongest genetic risk factors for AMD. In this review, we focus on the roles of inflammation and oxidative stress and their connection with FH and related proteins as regulators of both phenomena in the context of AMD.

Targeted Gene Candidates for Treatment and Early Diagnosis of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is an eye disease that impairs the sharp and central vision need for daily activities. Recent advances in molecular biology research not only lead to a better understanding of the genetics and pathophysiology of AMD but also to the development of applications based on targeted gene expressions to treat the disease. Clarification of molecular pathways that causing to development and progression in dry and wet types of AMD needs comprehensive and comparative investigations in particular precious biopsies involving peripheral blood samples from the patients. Therefore, in this investigation, dry and wet types of AMD patients and healthy individuals were aimed at investigating in regard to targeted gene candidates by using gene expression analysis for the first time. 13 most potent candidate genes involved in neurodegeneration were selected via in silico approach and investigated through gene expression analysis to suggest new targets for disease therapy. For the analyses, 30 individuals (10 dry and 10 wet types AMD patients and 10 healthy people) were involved in the study. SYBR-Green based Real-Time PCR analysis was performed on isolated peripheral blood mononuclear cells (PBMCs) to analyze differentially expressed genes related to these cases. According to the investigations, only the CRP gene was found to be upregulated for both dry and wet disease types. When the downregulated genes were analyzed, it was found that 11 genes were commonly decreased for both dry and wet types in the aspect of expression pattern. From these genes, CFH, CX3CR1, FLT1, and TIMP3 were found to have the most downregulated gene expression properties for both diseases. From these results, it might be concluded that these common upregulated and downregulated genes could be used as targets for early diagnosis and treatment for AMD.

Bruch's Membrane and the Choroid in Age-Related Macular Degeneration

A healthy choroidal vasculature is necessary to support the retinal pigment epithelium (RPE) and photoreceptors, because there is a mutualistic symbiotic relationship between the components of the photoreceptor/retinal pigment epithelium (RPE)/Bruch's membrane (BrMb)/choriocapillaris (CC) complex. This relationship is compromised in age-related macular degeneration (AMD) by the dysfunction or death of the choroidal vasculature. This chapter will provide a basic description of the human Bruch's membrane and choroidal anatomy and physiology and how they change in AMD.The choriocapillaris is the lobular, fenestrated capillary system of choroid. It lies immediately posterior to the pentalaminar Bruch's membrane (BrMb). The blood supply for this system is the intermediate blood vessels of Sattler's layer and the large blood vessels in Haller's layer.In geographic atrophy (GA), an advanced form of dry AMD, large confluent drusen form on BrMb, and hyperpigmentation (presumably dysfunction in RPE) appears to be the initial insult. The resorption of these drusen and loss of RPE (hypopigmentation) can be predictive for progression of GA. The death and dysfunction of CC and photoreceptors appear to be secondary events to loss in RPE. The loss of choroidal vasculature may be the initial insult in neovascular AMD (nAMD). We have observed a loss of CC with an intact RPE monolayer in nAMD, by making RPE hypoxic. These hypoxic cells then produce angiogenic substances like vascular endothelial growth factor (VEGF), which stimulate growth of new vessels from CC, resulting in choroidal neovascularization (CNV). Reduction in blood supply to the CC, often stenosis of intermediate and large blood vessels, is associated with CC loss.The polymorphisms in the complement system components are associated with AMD. In addition, the environment of the CC, basement membrane and intercapillary septa, is a proinflammatory milieu with accumulation of proinflammatory molecules like CRP and complement components during AMD. In this toxic milieu, CC die or become dysfunctional even early in AMD. The loss of CC might be a stimulus for drusen formation since the disposal system for retinal debris and exocytosed material from RPE would be limited. Ultimately, the photoreceptors die of lack of nutrients, leakage of serum components from the neovascularization, and scar formation.Therefore, the mutualistic symbiotic relationship of the photoreceptor/RPE/BrMb/CC complex is lost in both forms of AMD. Loss of this functionally integrated relationship results in death and dysfunction of all of the components in the complex.

Associations between the Complement System and Choroidal Neovascularization in Wet Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness affecting the elderly in the Western world. The most severe form of AMD, wet AMD (wAMD), is characterized by choroidal neovascularization (CNV) and acute vision loss. The current treatment for these patients comprises monthly intravitreal injections of anti-vascular endothelial growth factor (VEGF) antibodies, but this treatment is expensive, uncomfortable for the patient, and only effective in some individuals. AMD is a complex disease that has strong associations with the complement system. All three initiating complement pathways may be relevant in CNV formation, but most evidence indicates a major role for the alternative pathway (AP) and for the terminal complement complex, as well as certain complement peptides generated upon complement activation. Since the complement system is associated with AMD and CNV, a complement inhibitor may be a therapeutic option for patients with wAMD. The aim of this review is to (i) reflect on the possible complement targets in the context of wAMD pathology, (ii) investigate the results of prior clinical trials with complement inhibitors for wAMD patients, and (iii) outline important considerations when developing a future strategy for the treatment of wAMD.

Tuning the Functionality by Splicing: Factor H and Its Alternative Splice Variant FHL-1 Share a Gene but Not All Functions

The alternative pathway regulator Factor H-like protein 1 (FHL-1) is composed of the first 7 N-terminal complement control protein domains of Factor H (FH) and protects host surfaces from uncontrolled complement attack. Although FHL-1 shares the N-terminal regulatory domains with FH, it was thought to be a weaker regulator. Recently, the regulatory activity of FHL-1 was shown to be comparable to FH. Nonetheless, the question remained whether FHL-1 is an indispensable, unique regulator. The discovery that FHL-1 is the predominant regulator on Bruch’s membrane, a critical site for the onset and progression of age-related-macular degeneration (AMD), showed that FHL-1 is essential for complement regulation. A common single nucleotide polymorphism in FH/FHL-1 that predisposes for AMD underlines the important role of FHL-1 in this context. Reports that some cancer tissues specifically upregulate FHL-1 expression, thereby evading immune surveillance, suggests a pronounced regulatory activity of the splice variant. Several microorganisms specifically recruit FHL-1 to evade complement attack. From a phylogenetic point of view, FHL-1 appears much later than other complement regulators, which could imply a specific role that is possibly not systemic but rather tissue specific. This review focuses on the current knowledge of FHL-1 and its physiological and pathophysiological roles.

Multiplex bioimaging of proteins-related to neurodegenerative diseases in eye sections by laser ablation - Inductively coupled plasma - Mass spectrometry using metal nanoclusters as labels

Simultaneous determination of proteins with micrometric resolution is a significant challenge. In this study, laser ablation (LA) inductively coupled plasma - mass spectrometry (ICP-MS) was employed to quantify the distribution of proteins associated to the eye disease age-related macular degeneration (AMD) using antibodies labelled with three different metal nanoclusters (MNCs). PtNCs, AuNCs and AgNCs contain hundreds of metal atoms and were used to detect metallothionein 1/2 (MT1/2), complement factor H (CFH) and amyloid precursor protein (APP) in retina, ciliary body, retinal pigment epithelium (RPE), choroid and sclera from human cadaveric eye sections. First, the labelling of MNCs bioconjugated primary antibodies (Ab) was optimised following an immunolabelling protocol to avoid the non-specific interaction of MNCs with the tissue. Then, the LA and ICP-MS conditions were studied to obtain high-resolution images for the simultaneous detection of the three labels at the same tissue section. A significant signal amplification was found when using AuNCs, AgNCs and PtNCs labelled Ab of 310, 723 and 1194 respectively. After the characterisation of MNCs labelled immunoprobes, the Ab labelling was used for determination of MT1/2, CFH and APP in the RPE-choroid-sclera, where accumulation of extracellular deposits related to AMD was observed. Experimental results suggest that this method is fully suitable for the simultaneous detection of at least three different proteins.

Activation of C-reactive protein proinflammatory phenotype in the blood retinal barrier in vitro: implications for age-related macular degeneration

The retinal pigment epithelium (RPE) is considered one of the main targets of age-related macular degeneration (AMD), the leading cause of irreversible vision loss among the ageing population worldwide. Persistent low grade inflammation and oxidative stress eventually lead to RPE dysfunction and disruption of the outer blood-retinal barrier (oBRB). Increased levels of circulating pentameric C-reactive protein (pCRP) are associated with higher risk of AMD. The monomeric form (mCRP) has been detected in drusen, the hallmark deposits associated with AMD, and we have found that mCRP induces oBRB disruption. However, it is unknown how mCRP is generated in the subretinal space. Using a Transwell model we found that both pCRP and mCRP can cross choroidal endothelial cells and reach the RPE in vitro and that mCRP, but not pCRP, is able to cross the RPE monolayer in ARPE-19 cells. Alternatively, mCRP can originate from the dissociation of pCRP in the surface of lipopolysaccharide-damaged RPE in both ARPE-19 and primary porcine RPE lines. In addition, we found that the proinflammatory phenotype of mCRP in the RPE depends on its topological localization. Together, our findings further support mCRP contribution to AMD progression enhancing oBRB disruption.

Characteristics of Pachychoroid Diseases and Age-Related Macular Degeneration: Multimodal Imaging and Genetic Backgrounds

The emergence of pachychoroid disease is changing the concept of age-related macular degeneration (AMD). The concept of pachychoroid diseases was developed through clinical observation of multimodal images of eyes with AMD and central serous chorioretinopathy; however, recent genetic studies have provided a proof of concept for pachychoroid spectrum disease, which should be differentiated from drusen-driven AMD. The genetic confirmation of pachychoroid concept further provides novel viewpoints to decode previously reported findings, which facilitates an understanding of the true nature of pachychoroid diseases and AMD. The purpose of this review was to elucidate the relationship between pachychoroid diseases and AMD by interpreting previous findings on pachychoroid diseases and AMD from the novel viewpoints of genetic associations. We confirmed that previous genetic studies supported the concept of pachychoroid diseases. From a genetic viewpoint, the presence of thick choroid and the presence of choroidal vascular hyperpermeability were important characteristics of pachychoroid spectrum diseases. Previous studies have also suggested the classification of polypoidal choroidal vasculopathy (PCV) into two subtypes, pachychoroid neovasculopathy and drusen-driven PCV. Genetic viewpoints will be beneficial to rearrange subtypes of drusen-driven AMD and pachychoroid spectrum diseases. Further genetic studies are needed to investigate pachyvessels, pachydrusen and the significance of polypoidal lesions in pachychoroid neovasculopathy and drusen-driven AMD/PCV.

A role for mast cells in geographic atrophy

Mast cells (MCs) are the initial responders of innate immunity and their degranulation contribute to various etiologies. While the abundance of MCs in the choroid implies their fundamental importance in the eye, little is known about the significance of MCs and their degranulation in choroid. The cause of geographic atrophy (GA), a progressive dry form of age-related macular degeneration is elusive and there is currently no therapy for this blinding disorder. Here we demonstrate in both human GA and a rat model for GA, that MC degranulation and MC-derived tryptase are central to disease progression. Retinal pigment epithelium degeneration followed by retinal and choroidal thinning, characteristic phenotypes of GA, were driven by continuous choroidal MC stimulation and activation in a slow release fashion in the rat. Genetic manipulation of MCs, pharmacological intervention targeting MC degranulation with ketotifen fumarate or inhibition of MC-derived tryptase with APC 366 prevented all of GA-like phenotypes following MC degranulation in the rat model. Our results demonstrate the fundamental role of choroidal MC involvement in GA disease etiology, and will provide new opportunities for understanding GA pathology and identifying novel therapies targeting MCs.

Functionally validated imaging endpoints in the Alabama study on early age-related macular degeneration 2 (ALSTAR2): design and methods

Background

Age-related macular degeneration (AMD), a leading cause of irreversible vision impairment in the United States and globally, is a disease of the photoreceptor support system involving the retinal pigment epithelium (RPE), Bruch’s membrane, and the choriocapillaris in the setting of characteristic extracellular deposits between outer retinal cells and their blood supply. Research has clearly documented the selective vulnerability of rod photoreceptors and rod-mediated (scotopic) vision in early AMD, including delayed rod-mediated dark adaptation (RMDA) and impaired rod-mediated light and pattern sensitivity. The unifying hypothesis of the Alabama Study on Early Macular Degeneration (ALSTAR2) is that early AMD is a disease of micronutrient deficiency and vascular insufficiency, due to detectable structural changes in the retinoid re-supply route from the choriocapillaris to the photoreceptors. Functionally this is manifest as delayed rod-mediated dark adaptation and eventually as rod-mediated visual dysfunction in general.

Methods

A cohort of 480 older adults either in normal macular health or with early AMD will be enrolled and followed for 3 years to examine cross-sectional and longitudinal associations between structural and functional characteristics of AMD. Using spectral domain optical coherence tomography, the association between (1) subretinal drusenoid deposits and drusen, (2) RPE cell bodies, and (3) the choriocapillaris’ vascular density and rod- and cone-mediated vision will be examined. An accurate map and timeline of structure-function relationships in aging and early AMD gained from ALSTAR2, especially the critical transition from aging to disease, will identify major characteristics relevant to future treatments and preventative measures.

Discussion

A major barrier to developing treatments and prevention strategies for early AMD is a limited understanding of the temporal interrelationships among structural and functional characteristics while transitioning from aging to early AMD. ALSTAR2 will enable the development of functionally valid, structural biomarkers for early AMD, suitable for use in forthcoming clinical trials as endpoint/outcome measures. The comprehensive dataset will also allow hypothesis-testing for mechanisms that underlie the transition from aging to AMD, one of which is a newly developed Center-Surround model of cone resilience and rod vulnerability.

Trial registration

ClinicalTrials.gov Identifier NCT04112667, October 7, 2019.

Microvascular contributions to age-related macular degeneration (AMD): from mechanisms of choriocapillaris aging to novel interventions

Aging of the microcirculatory network plays a central role in the pathogenesis of a wide range of age-related diseases, from heart failure to Alzheimer's disease. In the eye, changes in the choroid and choroidal microcirculation (choriocapillaris) also occur with age, and these changes can play a critical role in the pathogenesis of age-related macular degeneration (AMD). In order to develop novel treatments for amelioration of choriocapillaris aging and prevention of AMD, it is essential to understand the cellular and functional changes that occur in the choroid and choriocapillaris during aging. In this review, recent advances in in vivo analysis of choroidal structure and function in AMD patients and patients at risk for AMD are discussed. The pathophysiological roles of fundamental cellular and molecular mechanisms of aging including oxidative stress, mitochondrial dysfunction, and impaired resistance to molecular stressors in the choriocapillaris are also considered in terms of their contribution to the pathogenesis of AMD. The pathogenic roles of cardiovascular risk factors that exacerbate microvascular aging processes, such as smoking, hypertension, and obesity as they relate to AMD and choroid and choriocapillaris changes in patients with these cardiovascular risk factors, are also discussed. Finally, future directions and opportunities to develop novel interventions to prevent/delay AMD by targeting fundamental cellular and molecular aging processes are presented.

Regulation of the Complement System by Pentraxins

The functions of pentraxins, like C-reactive protein (CRP), serum amyloid protein P (SAP) and pentraxin-3 (PTX3), are to coordinate spatially and temporally targeted clearance of injured tissue components, to protect against infections and to regulate related inflammation together with the complement system. For this, pentraxins have a dual relationship with the complement system. Initially, after a focused binding to their targets, e.g., exposed phospholipids or cholesterol in the injured tissue area, or microbial components, the pentraxins activate complement by binding its first component C1q. However, the emerging inflammation needs to be limited to the target area. Therefore, pentraxins inhibit complement at the C3b stage to prevent excessive damage. The complement inhibitory functions of pentraxins are based on their ability to interact with complement inhibitors C4bp or factor H (FH). C4bp binds to SAP, while FH binds to both CRP and PTX3. FH promotes opsonophagocytosis through inactivation of C3b to iC3b, and inhibits AP activity thus preventing formation of the C5a anaphylatoxin and the complement membrane attack complex (MAC). Monitoring CRP levels gives important clinical information about the extent of tissue damage and severity of infections. CRP is a valuable marker for distinguishing bacterial infections from viral infections. Disturbances in the functions and interactions of pentraxins and complement are also involved in a number of human diseases. This review will summarize what is currently known about the FH family proteins and pentraxins that interact with FH. Furthermore, we will discuss diseases, where interactions between these molecules may play a role.

Systemic Levels of Interleukin-6 Correlate With Progression Rate of Geographic Atrophy Secondary to Age-Related Macular Degeneration

Purpose

Geographic atrophy (GA) is a clinical phenotype of late age-related macular degeneration (AMD) with no current treatment available. In this study, we investigated markers of chronic inflammation in plasma of patients with GA and how these relate to progression rate.

Methods

We prospectively included 42 patients with GA, 41 patients with neovascular AMD, and 27 healthy controls. We quantified levels of interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor (TNF) receptor 2, and C-reactive protein (CRP). We adapted an inflammation summary score to cluster conceptually related markers of chronic inflammation. Enlargement rate of the atrophic lesion was measured from fundus autofluorescence images performed at baseline and after 1 year.

Results

Patients with GA showed an increase in proinflammatory markers of IL-6 (P = 0.009), TNF receptor 2 (P = 0.013), and CRP (P = 0.017) compared to healthy controls. We found that IL-8 levels were markedly higher in patients with GA when compared to patients with neovascular AMD (P = 0.013). The inflammation summary score was high in patients with neovascular AMD (P = 0.024), but even higher in patients with GA (<0.001), when compared to healthy controls. GA enlargement was measured in 36 patients, who completed follow-up. Plasma levels of IL-6 had a moderate but significant correlation with GA enlargement rate (R2 = 0.23, P = 0.0035).

Conclusions

Markers of chronic inflammation strongly associates with presence of GA secondary to AMD. Plasma IL-6 possesses predictive ability of progression and constitutes the first known plasma biomarker of disease activity in GA. These findings shed light into a poorly understood clinical phenotype of AMD and highlights the important role of chronic inflammation in GA.

The role of complement membrane attack complex in dry and wet AMD - From hypothesis to clinical trials

Data from human dry and wet age-related macular degeneration (AMD) eyes support the hypothesis that constant 'tickover' of the alternative complement pathway results in chronic deposition of the complement membrane attack complex (MAC) on the choriocapillaris and the retinal pigment epithelium (RPE). Sub-lytic levels of MAC lead to cell signaling associated with tissue remodeling and the production of cytokines and inflammatory molecules. Lytic levels of MAC lead to cell death. CD59 is a naturally occurring inhibitor of the assembly of MAC. CD59 may thus be therapeutically efficacious against the pathophysiology of dry and wet AMD. The first gene therapy clinical trial for geographic atrophy - the advanced form of dry AMD has recently completed recruitment. This trial is studying the safety and tolerability of expressing CD59 from an adeno-associated virus (AAV) vector injected once into the vitreous. A second clinical trial assessing the efficacy of CD59 in wet AMD patients is also under way. Herein, the evidence for the role of MAC in the pathophysiology of dry as well as wet AMD and the scientific rationale underlying the use of AAV- delivered CD59 for the treatment of dry and wet AMD is discussed.

Increased serum levels of soluble CD146 and vascular endothelial growth factor receptor 2 in patients with exudative age-related macular degeneration

AIM

To investigate serum levels of soluble CD146 (sCD146) and vascular endothelial growth factor receptor 2 (VEGFR2) in patients with age-related macular degeneration (AMD).

METHODS

Eighty-eight patients with exudative AMD and 45 sex- and age-matched healthy controls were enrolled in this study conducted in China. Serum samples was obtained from the patients with exudative AMD and from the controls. Serum sCD146 and VEGFR2 protein levels were measured using an enzyme-linked immunosorbent assay.

RESULTS

We found that serum sCD146 and VEGFR2 protein levels were significantly higher in the patients with exudative AMD group than in the controls (t=3.859, P<0.001 and t=3.829, P<0.001, respectively). Serum sCD146 levels were significantly higher in patients with classic choroidal neovascularization (CNV) than in those with occult CNV (t=9.899, P<0.001). There was a significant difference in the trend for exudative AMD in the highest versus lowest quartile of circulating sCD146 levels (χ ²=10.29, P=0.001). The receiver operating characteristic curve analysis showed that the area under the curve was 0.696 for sCD146 (95%CI: 0.601-0.791) with an optimum diagnostic cut-off value of 157.16 ng/mL, a sensitivity of 55.7%, and a specificity of 82.2%.

CONCLUSION

The serum sCD146 level increases and may be a biomarker for exudative AMD.

Ultrastructural analysis of submacular choriocapillaris and its transport systems in AMD and aged control eyes

The choriocapillaris is the source of nutrients and oxygen for photoreceptors, which consume more oxygen per gram of tissue than any other cell in the body. The purpose of this study was to evaluate and compare the ultrastructure of the choriocapillaris and its transport systems in patients with and without age-related macular degeneration (AMD). Ultrastructural changes were also evaluated in subjects that were homozygous for polymorphisms in high risk CFH alleles (Pure 1) only or homozygous only for high risk ARMS2/HTRA1 (Pure 10) alleles. Tissue samples were obtained from the macular region of forty male (n = 24) and female (n = 16) donor eyes and prepared for ultrastructural studies with transmission electron microscopy (TEM). The average age of the aged donors was 74 ± 7.2 (n = 30) and the young donors 31.7 ± 11.25 (n = 10). There was no significant difference in average ages between the adult groups. TEM images of the capillaries in the choriocapillaris (CC) were taken at 4,000X and 25,000X and used to measure the area of endothelial cell somas, the number of fenestrations, and area of caveolae within the endothelial cells per length of Bruchs membrane (BrMb). The Student t-test and Wilcoxon sum rank test were used to determine significant differences. There was no significant difference between young subjects and aged controls in any of the morphological criteria assessed. There was a significant decrease in the number of fenestrations/mm of BrMb in atrophic areas of GA eyes (p = 0.007) when compared with aged control eyes. A significant increase was found in the caveolae area as a percent of the endothelial cell soma of capillaries from GA subjects as compared with the controls (p = 0.03). Loss of capillary segments in choriocapillaris was also evident, especially in areas of geographic atrophy and CNV. In eyes from patients with sequence variations, the capillary endothelial cells often appeared degenerative and exhibited atypical fenestrations and pericytes covering the blood vessels. Subjects that were homozygous for polymorphisms in high risk CFH alleles only had more fenestrations/mm of BrMb than subjects that were homozygous only for high risk ARMS2/HTRA1 alleles (p = 0.04), while the latter had greater caveolae area/endothelial cell area than the former (p = 0.007). This study demonstrated an attenuation of CC and a significant decline in the two major transport systems in CC endothelial cells in AMD. This may contribute to drusen deposition, nutrient transport, and vision loss in AMD subjects.

Increased soluble urokinase plasminogen activator receptor (suPAR) levels in neovascular age-related macular degeneration: a role for inflammation in the pathogenesis of the disease?

PURPOSE

To evaluate the plasma concentration of the soluble form of the urokinase-type plasminogen activator receptor ((s)uPAR), an established biomarker of chronic inflammation, in patients affected by neovascular age-related macular degeneration.

METHODS

Forty consecutive patients affected by age-related macular degeneration and 52 subjects with no history of the disease were included in this case-control study. The two groups of individuals considered for the study were matched for age, sex, and class of medications taken. Plasma concentration of suPAR was measured using a specific ELISA assay (suPARnostic, Birkeroed, Denmark).

RESULTS

The case and control groups were similar for age, gender distribution, weight, height, and systolic and diastolic blood pressure, as well as for dyslipidemia and high blood pressure medication (P > 0.28). The plasma concentrations of suPAR were significantly increased in patients with neovascular age-related macular degeneration when compared to controls (6.19 ± 2.2 ng/ml, vs 5.21 ± 1.5, respectively, mean ± SD P = 0.01).

CONCLUSIONS

Patients with neovascular age-related macular degeneration display increased plasma levels of suPAR, suggesting that chronic inflammation may be involved in the pathogenesis of the disease.

Asian age-related macular degeneration: from basic science research perspective

In Asian populations, polypoidal choroidal vasculopathy (PCV), a distinct phenotype of neovascular age-related macular degeneration (AMD), is more prevalent than Caucasians. Recently, there has been significant focus on how PCV differs from typical AMD. Although typical AMD and PCV share a variety of mechanisms by which abnormal angiogenic process occurs at the retinochoroidal interface, PCV has different clinical characteristics such as aneurysm-like dilation at the terminal of choroidal neovascular membranes, less frequent drusen and inner choroidal degeneration due to the thickened choroid. Recent studies support an important role for inflammation, angiogenesis molecules and lipid metabolism in the pathogenesis of neovascular AMD. Furthermore, although less attention has been paid to the role of the choroid in AMD, accumulating evidence suggests that the choriocapillaris and choroid also play a pivotal role in drusenogenesis, typical AMD and PCV. This review discusses the basic pathogenic mechanisms of AMD and explores the difference between typical AMD and PCV.

Pentraxins in Complement Activation and Regulation

The complement is the first line of immune defense system involved in elimination of invading pathogens and dying host cells. Its activation is mainly triggered by immune complexes or pattern recognition molecules (PRMs) upon recognition against non-self or altered self-cells, such as C1q, collectins, ficolins, and properdin. Recent findings have interestingly shown that the pentraxins (C-reactive protein, CRP; serum-amyloid P component, SAP; long pentraxin 3, PTX3) are involved in complement activation and amplification via communication with complement initiation PRMs, but also complement regulation via recruitment of complement regulators, for instance C4b binding protein (C4BP) and factor H (fH). This review addresses the potential roles of the pentraxins in the complement system during infection and inflammation, and emphasizes the underlining implications of the pentraxins in the context of complement activation and regulation both under physiological and pathological conditions.

Quantitative proteomic analysis of aqueous humor from patients with drusen and reticular pseudodrusen in age-related macular degeneration

Background

To identify novel biomarkers related to the pathogenesis of dry age-related macular degeneration (AMD), we adopted a human retinal pigment epithelial (RPE) cell culture model that mimics some features of dry AMD including the accumulation of intra- and sub-RPE deposits. Then, we investigated the aqueous humor (AH) proteome using a data-independent acquisition method (sequential window acquisition of all theoretical fragment ion mass spectrometry) for dry AMD patients and controls.

Methods

After uniformly pigmented polarized monolayers of human fetal primary RPE (hfRPE) cells were established, the cells were exposed to 4-hydroxy-2-nonenal (4-HNE), followed by Western blotting, immunofluorescence analysis and ELISA of cells or conditioned media for several proteins of interest. Data-dependent acquisition for identification of the AH proteome and SWATH-based mass spectrometry were performed for 11 dry AMD patients according to their phenotypes (including soft drusen and reticular pseudodrusen [RPD]) and 2 controls (3 groups).

Results

Increased intra- and sub-RPE deposits were observed in 4-HNE-treated hfRPE cells compared with control cultures based on APOA1, cathepsin D, and clusterin immunoreactivity. Additionally, the differential abundance of proteins in apical and basal chambers with or without 4-HNE treatment confirmed the polarized secretion of proteins from hfRPE cells. A total of 119 proteins were quantified in dry AMD patients and controls by SWATH-MS. Sixty-five proteins exhibited significantly altered abundance among the three groups. A two-dimensional principal component analysis plot was generated to identify typical proteins related to the pathogenesis of dry AMD. Among the identified proteins, eight proteins, including APOA1, CFHR2, and CLUS, were previously considered major components or regulators of drusen. Three proteins (SERPINA4, LUM, and KERA proteins) have not been previously described as components of drusen or as being related to dry AMD. Interestingly, the LUM and KERA proteins, which are related to extracellular matrix organization, were upregulated in both RPD and soft drusen.

Conclusions

Differential protein expression in the AH between patients with drusen and RPD was quantified using SWATH-MS in the present study. Detailed proteomic analyses of dry AMD patients might provide insights into the in vivo biology of drusen and RPD.

Electronic supplementary material

The online version of this article (10.1186/s12886-018-0941-9) contains supplementary material, which is available to authorized users.

Novel Association of High C-Reactive Protein Levels and A69S at Risk Alleles in Wet Age-Related Macular Degeneration Women

Purpose

To explore the relationship between plasma C-reactive protein (CRP) levels, the main ARMS2 gene single nucleotide polymorphism (SNP), and gender in patients with neovascular age-related macular degeneration (wet AMD).

Methods

Our study included 131 patients with wetAMD [age-related eye disease study (AREDS) category 4] and 153 control participants (AREDS category 1) from two Spanish retinal units. CRP levels were determined on blood samples by high-sensitivity ELISA assay. According to their CRP level, subjects were categorized into three well-established CRP categories: low (<1.00 mg/L, L-CRP), moderate (1–2.99 mg/L, M-CRP), and high (>3.00 mg/L, H-CRP). Genomic DNA was extracted from oral swabs using QIAcube (Qiagen, Hilden, Germany) and the A69S; rs10490924 of ARMS2 gene was genotyped by allelic discrimination with validated TaqMan assays (Applied Biosystems, Foster City, CA, USA). Univariate and multivariate logistic regression adjusted for age was used to analyze the genomic frequencies and to calculate odds ratio (OR) using SNPStats software.

Results

Considering CRP risk categories, H-CRP group showed a significant [OR 4.0 (1.9–8.3)] association with wetAMD compared to L-CRP group. The risk genotypes of A69S (TT) SNPs showed an association with wetAMD risk [OR 14.0 (4.8–40.8)]. Interestingly, the gender stratification of the CRP categories showed a significant increase in CRP levels in wetAMD women compared with control women [OR 6.9 (2.2–22.3)] and with wetAMD men [OR 4.6 (1.3–16.9)]. In addition, the subgroup analysis of CRP within A69S genotype and gender showed a link in women between the A69S and CRP levels in the AMD group compared to controls [OR 4.2 (1.4–12.6)].

Conclusion

Our study shows, for the first time, that a different genetic association related with gender could contribute to AMD risk. As a consequence, the risk of female gender in the different CRP levels and A69S SNP frequencies could be taken into consideration to the established risk relationship of high levels of CRP and its association with risk A69S genotype.

Evaluation of serum and ocular levels of membrane attack complex and C-reactive protein in CFH-genotyped human donors

BACKGROUND

There is a considerable body of evidence demonstrating a link between the membrane attack complex (MAC) and age-related macular degeneration (AMD), and between C-reactive protein (CRP) and AMD. Both the MAC and the monomeric form of CRP (mCRP) accumulate within the choriocapillaris in AMD. However, the precise contribution of these species to AMD pathophysiology has not been fully elucidated.

METHODS

We sought to directly assess CRP and MAC levels between human serum and ocular tissues from the same CFH Y402H genotyped donors using ELISA of serum and RPE/choroid proteins.

RESULTS

The Y402H polymorphism was associated with significantly increased MAC in RPE/choroid samples, but not in the serum, in a previously unstudied cohort. While MAC levels in the choroid were independent of circulating levels, choroidal CRP was correlated to serum levels.

CONCLUSIONS

These data provide further evidence for local activation of complement within the choriocapillaris in AMD.

The Clinical Significance and Potential Role of C-Reactive Protein in Chronic Inflammatory and Neurodegenerative Diseases

C-reactive protein (CRP) is an acute-phase protein synthesized by hepatocytes in response to pro-inflammatory cytokines during inflammatory/infectious processes. CRP exists in conformationally distinct forms such as the native pentameric CRP and monomeric CRP (mCRP) and may bind to distinct receptors and lipid rafts and exhibit different functional properties. It is known as a biomarker of acute inflammation, but many large-scale prospective studies demonstrate that CRP is also known to be associated with chronic inflammation. This review is focused on discussing the clinical significance of CRP in chronic inflammatory and neurodegenerative diseases, such as cardiovascular disease, type 2 diabetes mellitus, age-related macular degeneration, hemorrhagic stroke, Alzheimer’s disease, and Parkinson’s disease, including recent advances on the implication of CRP and its forms specifically on the pathogenesis of these diseases. Overall, we highlight the advances in these areas that may be translated into promising measures for the diagnosis and treatment of inflammatory diseases.

Color Doppler imaging of the retrobulbar circulation and plasmatic biomarkers of vascular risk in age-related macular degeneration: A pilot study

PURPOSE

To evaluate preliminarily and compare the level of plasmatic biomarkers of vascular risk in patients with and without exudative age-related macular degeneration (ARMD) and to relate it to vascular resistance alterations in the ophthalmic artery (OA), central retinal artery (CRA), posterior temporal ciliary artery (PTCA), and posterior nasal ciliary artery (PNCA).

METHODS

Color Doppler imaging of the OA, CRA, PTCA, and PNCA was performed in 30 eyes of 30 cataract patients (control group) as well as in 30 eyes of 30 patients with naive exudative ARMD (study group), measuring the peak systolic velocity, end-diastolic velocity (EDV), and Pourcelot resistive index (RI). Likewise, in both groups, a blood test was performed to determine the plasmatic levels of homocysteine, C-reactive protein (CRP), B12 vitamin, and folic acid.

RESULTS

A positive and significant correlation was found between the level of CRP and RI of the OA in the ARMD group (r = 0.498, P = 0.005), with an increased RI in all arteries compared to controls, although differences only reached statistical significance for the PTCA (P = 0.035). Likewise, a significantly lower EDV for the CRA was found in ARMD eyes compared to controls (P = 0.041). In the study group, significantly higher plasmatic levels of homocysteine (P = 0.042) and CRP (P = 0.046) were found. In contrast, no significant differences were found between groups in the levels of folic acid (P = 0.265) and B12 vitamin (P = 0.520).

CONCLUSION

The decrease of the choroidal perfusion related to hyperhomocysteinemia, and increase in the CRP plasmatic levels may play an etiological role on the exudative ARMD. This should be investigated in future studies with larger samples of patients.

C-Reactive Protein as a Therapeutic Target in Age-Related Macular Degeneration

Age-related macular degeneration (AMD), a retinal degenerative disease, is the leading cause of central vision loss among the elderly population in developed countries and an increasing global burden. The major risk is aging, compounded by other environmental factors and association with genetic variants for risk of progression. Although the etiology of AMD is not yet clearly understood, several pathogenic pathways have been proposed, including dysfunction of the retinal pigment epithelium, inflammation, and oxidative stress. The identification of AMD susceptibility genes encoding complement factors and the presence of complement and other inflammatory mediators in drusen, the hallmark deposits of AMD, support the concept that local inflammation and immune-mediated processes play a key role in AMD pathogenesis that may be accelerated through systemic immune activation. In this regard, increased levels of circulating C-reactive protein (CRP) have been associated with higher risk of AMD. Besides being a risk marker for AMD, CRP may also play a role in the progression of the disease as it has been identified in drusen, and we have recently found that its monomeric form (mCRP) induces blood retinal barrier disruption in vitro. In this review, we will address recent evidence that links CRP and AMD pathogenesis, which may open new therapeutic opportunities to prevent the progression of AMD.

C-Reactive Protein As a Mediator of Complement Activation and Inflammatory Signaling in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a devastating neurodegenerative disease affecting millions worldwide. Complement activation, inflammation, and the loss of choroidal endothelial cells have been established as key factors in both normal aging and AMD; however, the exact mechanisms for these events have yet to be fully uncovered. Herein, we provide evidence that the prototypic acute phase reactant, C-reactive protein (CRP), contributes to AMD pathogenesis. We discuss serum CRP levels as a risk factor for disease, immunolocalization of distinct forms of CRP in the at-risk and diseased retina, and direct effects of CRP on ocular tissue. Furthermore, we discuss the complement system as it relates to AMD pathophysiology, provide a model for the role of CRP in this disease, and outline current therapies being developed and tested to treat AMD patients.

C-reactive protein and pentraxin-3 binding of factor H-like protein 1 differs from complement factor H: implications for retinal inflammation

Retinal inflammation plays a key role in the progression of age-related macular degeneration (AMD), a condition that leads to loss of central vision. The deposition of the acute phase pentraxin C-reactive protein (CRP) in the macula activates the complement system, thereby contributing to dysregulated inflammation. The complement protein factor H (FH) can bind CRP and down-regulate an inflammatory response. However, it is not known whether a truncated form of FH, called factor H-like protein 1 (FHL-1), which plays a significant regulatory role in the eye, also interacts with CRP. Here, we compare the binding properties of FHL-1 and FH to both CRP and the related protein pentraxin-3 (PTX3). We find that, unlike FH, FHL-1 can bind pro-inflammatory monomeric CRP (mCRP) as well as the circulating pentameric form. Furthermore, the four-amino acid C-terminal tail of FHL-1 (not present in FH) plays a role in mediating its binding to mCRP. PTX3 was found to be present in the macula of donor eyes and the AMD-associated Y402H polymorphism altered the binding of FHL-1 to PTX3. Our findings reveal that the binding characteristics of FHL-1 differ from those of FH, likely underpinning independent immune regulatory functions in the context of the human retina.

Mast Cell-Derived Tryptase in Geographic Atrophy

Purpose

Our previous study demonstrated significantly more degranulating mast cells (MCs) in choroids from subjects with age-related macular degeneration compared to aged controls. This study examined the immunolocalization of tryptase, the most abundant MC secretory granule-derived serine protease, in aged control eyes and eyes with geographic atrophy (GA).

Methods

Postmortem human eyes with and without GA were obtained from the National Disease Research Interchange. Tissue was fixed, cryopreserved, sectioned, and immunostained with a monoclonal antibody against tryptase. Sections were imaged on a Zeiss 710 Confocal Microscope.

Results

In the posterior pole of all aged control eyes, tryptase was confined to choroidal MCs, which were located primarily in Sattler's layer. In eyes with GA, many MCs were located in the inner choroid near choriocapillaris and Bruch's membrane (BM). Tryptase was found not only in MCs but also diffusely around them in stroma, suggesting they had degranulated. In contrast with aged control eyes, eyes with GA also had strong tryptase staining in BM. Tryptase was observed within BM in regions of RPE atrophy, at the border of atrophy, and extending well into the nonatrophic region.

Conclusions

Our results demonstrate that tryptase, released during choroidal MC degranulation, binds to BM in GA in advance of RPE atrophy. Tryptase activates MMPs that can degrade extracellular matrix (ECM) and basement membrane components found in BM. ECM modifications are likely to have a profound effect on the function and health of RPE and choroidal thinning in GA.

A novel, multiplexed targeted mass spectrometry assay for quantification of complement factor H (CFH) variants and CFH-related proteins 1-5 in human plasma

Age-related macular degeneration (AMD) is a leading cause of visual loss among older adults. Two variants in the complement factor H (CFH) gene, Y402H and I62V, are strongly associated with risk of AMD. CFH is encoded in regulator of complement activation gene cluster in chromosome 1q32, which includes complement factor related (CFHR) proteins, CFHR1 to CFHR5, with high amino acid sequence homology to CFH. Our goal was to build a SRM assay to measure plasma concentrations of CFH variants Y402, H402, I62, and V62, and CFHR1-5. The final assay consisted of 24 peptides and 72 interference-free SRM transition ion pairs. Most peptides showed good linearity over 0.3-200 fmol/μL concentration range. Plasma concentrations of CFH variants and CFHR1-5 were measured using the SRM assay in 344 adults. Plasma CFH concentrations (mean, SE in μg/mL) by inferred genotype were: YY402, II62 (170.1, 31.4), YY402, VV62 (188.8, 38.5), HH402, VV62 (144.0, 37.0), HY402, VV62 (164.2, 42.3), YY402, IV62 (194.8, 36.8), HY402, IV62 (181.3, 44.7). Mean (SE) plasma concentrations of CFHR1-5 were 1.63 (0.04), 3.64 (1.20), 0.020 (0.001), 2.42 (0.18), and 5.49 (1.55) μg/mL, respectively. This SRM assay should facilitate the study of the role of systemic complement and risk of AMD.