The pivotal role of the complement system in aging and age-related macular degeneration: hypothesis re-visited

Microglia Contribution to the Regulation of the Retinal and Choroidal Vasculature in Age-Related Macular Degeneration

The retina is a highly metabolically active tissue with high-level consumption of nutrients and oxygen. This high metabolic demand requires a properly developed and maintained vascular system. The retina is nourished by two systems: the central retinal artery that supplies the inner retina and the choriocapillaris that supplies the outer retina and retinal pigment epithelium (RPE). Pathological neovascularization, characterized by endothelial cell proliferation and new vessel formation, is a common hallmark in several retinal degenerative diseases, including age-related macular degeneration (AMD). A limited number of studies have suggested that microglia, the resident immune cells of the retina, have an important role not only in the pathology but also in the formation and physiology of the retinal vascular system. Here, we review the current knowledge on microglial interaction with the retinal vascular system under physiological and pathological conditions. To do so, we first highlight the role of microglial cells in the formation and maintenance of the retinal vasculature system. Thereafter, we discuss the molecular signaling mechanisms through which microglial cells contribute to the alterations in retinal and choroidal vasculatures and to the neovascularization in AMD.

Age-related macular degeneration therapy: a review

PURPOSE OF REVIEW

The purpose of this review is to describe the current clinical landscape of potential future therapies for both nonexudative (dry) and exudative (wet) age-related macular degeneration (AMD). We highlight some of the more promising treatments that are furthest along in development.

RECENT FINDINGS

Patients with dry AMD have long been hoping for a highly efficacious treatment that may slow disease progression or even help regain vision. Patients with wet AMD have many effective treatment options but still there are those who have suboptimal responses or are burdened by the high frequency of treatment. We detail exciting new concepts and targets for novel medications. Specifically, for dry AMD we discuss research looking at complement inhibition, neuroprotection, visual cycle modulators, cell-based therapies, and anti-inflammatory agents. For wet AMD we summarize new, potentially more durable anti-vascular endothelial growth factor agents, extended release options, and gene therapy.

SUMMARY

There are promising new strategies for AMD. Many of the potential new treatments are in or have recently completed phase 2 or phase 3 clinical trials with promising results thus far, including some that have received US Food and Drug Administration approval. Additional therapeutic breakthroughs will likely continue to occur thanks to the number of clinical trials that are nearing the finish line.

Age-Related Macular Degeneration in Primary Osteoarthritis Egyptian Patients

Introduction

Both primary osteoarthritis (OA) and age-related macular degeneration (AMD) cause disability in old people. This study aimed to detect the relation between primary osteoarthritis and age-related macular degeneration in a sample of geriatric Egyptian population.

Methods

This cross-sectional study included 222 primary OA patients. Medical history, musculoskeletal examination, body mass index (BMI) calculation, and ophthalmological examination, radiographs of anteroposterior view and weight-bearing position for both hips and both knees and posteroanterior view for hands, Kellgren and Lawrence grading score for radiological severity of OA, optical coherence tomography (OCT), and fundus fluorescence angiography FFA for evaluation of the macula were done. AMD was classified into early, intermediate, and late. The collected data were analyzed using SPSS version 25.0.

Results

Forty-six OA patients had AMD [19 cases had early, 15 cases had intermediate and 12 cases with late (7 neovascular (NV) and 5 geographic atrophy (GA))]. There was a significant correlation between AMD stages and OA grading score. There were significant differences between OA patient with AMD and those without AMD regarding age, disease duration, disease severity, family history of OA, daily mild exercise and calcium, and vitamin D intake. Multivariable analysis revealed that older age, more severe OA, low exercise and less calcium and vitamin D intake were considered independent risk factors for AMD development in primary OA.

Conclusion

Primary OA patients are more liable to AMD due to common risk factors and related pathogenesis. Ophthalmological follow up of those patients is recommended.

Unstimulated, Serum-free Cultures of Retinal Pigment Epithelium Excrete Large Mounds of Drusen-like Deposits

Purpose: A hallmark of age-related macular degeneration is the accumulation of deposits of lipids and proteins, called drusen, in Bruch's membrane. Several culture models of retinal pigment epithelia (RPE) develop drusen-like deposits. We examined whether prolonged culture of RPE with a retina-like tissue affected the number or size of these deposits. Methods: RPE and retinal progenitor cells (RPC) were differentiated from induced pluripotent stem cells derived from fetal tissue and maintained in serum-free medium containing the B27 supplement. RPE was cultured on Transwell filter inserts, and RPC were cultured on a planar matrix composed of gelatin, hyaluronic acid, and chondroitin sulfate. After seeding the filter, RPC were layered on top of the RPE. RPE ± RPC were cultured for six months. The function of RPE tight junctions was assessed by the transepithelial electrical resistance. Cultures were stained for actin, neutral lipids, APOE, TIMP3, vitronectin, and calcium deposits. Morphometric analysis was used to determine the number and volume of the "druse". Results: After six months, the TER was greater for the co-cultures (304 ± 11 Ω× cm² vs 243 ± 7 Ω× cm², p < .01). RPE formed mounds of druse-like deposits that contained, vitronectin, APOE, TIMP3 and calcium deposits, but lipids were undetected. The mounds overlay areas of the filter where no lipid was detected in the pores, and the RPE overlying the mounds was often thin. The number of "druse"/100,000 μm² was 5.0 ± 0.4 (co-cultures) vs 2.3 ± 0.1 (monocultures) (p < .05). The total volume of "drusen"/100,000 μm³ was 15,133 ± 1544 (co-cultures) vs 5,993 ± 872 (monocultures) (p < .05). There was no statistical difference between the size-distribution of druse-like particles formed by each culture. Conclusions: Covering the apical membrane of RPE with a thick tissue increased the number of druse-like deposits. The apparent size limitation of the deposits may reflect the apparent interruption of the of lipid cycle found at the basal membrane of the RPE.

Complement factor B knockdown by short hairpin RNA inhibits laser-induced choroidal neovascularization in rats

AIM

To evaluate whether recombinant complement factor B (CFB) short hairpin RNA (shRNA) reduces laser-induced choroidal neovascularization (CNV) in rats.

METHODS

Laser-induced rat CNV model was established, and then the animals underwent fundus fluorescence angiography (FFA) and hematoxylin and eosin (HE) staining. On day 3 and 7 after photocoagulation, the expression of CFB and membrane attack complex (MAC) was detected by immunhischemistry. A recombinant CFB-shRNA plasmid was constructed. CFB and scrambled shRNA plasmids were intravenous injected into rats via the tail vein on the day of laser treatment, respectively. On day 7, the incidence of CNV was determined by FFA, and the expression of CFB and vascular endothelial growth factor (VEGF) in retinal pigment epithelium (RPE)/choroidal tissues was detected by immunhischemistry, Western blot and/or semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) in CFB and scrambled shRNA groups. The possible adverse effects of CFB-shRNA injection were assessed by transmission electron microscopy and electroretinography.

RESULTS

FFA and HE results indicated that a laser-induced rat CNV model was successfully established on day 7 after photocoagulation. The expression of CFB and MAC was extremely weak in normal retina and choroid, and increased on day 3 after photocoagulation. However, it started to reduce on day 7. CFB shRNA plasmid was successfully constructed and induced CFB knockdown in the retinal and choroidal tissues. FFA showed CFB knockdown significantly inhibited incidence of CNV in rats. Moreover, CFB knockdown significantly inhibited the expression of VEGF in RPE/choroidal tissues. CFB shRNA caused no obvious side effects in eyes.

CONCLUSION

CFB knockdown significantly inhibits the formation and development of CNV in vivo through reducing the expression of VEGF, which is a potential therapy target. The alternative pathway of complement activation plays an important role in CNV formation.

Cones in ageing and harsh environments: the neural economy hypothesis

PURPOSE

Cones are at great risk in a wide variety of retinal diseases, especially when there is a harsh microenvironment and retinal pigment epithelium is damaged. We provide established and new methods for assessing cones and retinal pigment epithelium, together with new results. We investigated conditions under which cones can be imaged and could guide light, despite the proximity of less than ideal retinal pigment epithelium.

RECENT FINDINGS

We used a variety of imaging methods to detect and localise damage to the retinal pigment epithelium. As age-related macular degeneration is a particularly widespread disease, we imaged clinical hallmarks: drusen and hyperpigmentation. Using near infrared light provided improved imaging of the deeper fundus layers. We compared confocal and multiply scattered light images, using both the variation of detection apertures and polarisation analysis. We used optical coherence tomography to examine distances between structures and thickness of retinal layers, as well as identifying damage to the retinal pigment epithelium. We counted cones using adaptive optics scanning laser ophthalmoscopy. We compared the results of five subjects with geographic atrophy to data from a previous normative ageing study. Using near infrared imaging and layer analysis of optical coherence tomography, the widespread aspect of drusen became evident. Both multiply scattered light imaging and analysis of the volume in the retinal pigment epithelial layer from the optical coherence tomography were effective in localising drusen and hyperpigmentation beneath the photoreceptors. Cone photoreceptors in normal older eyes were shorter than in younger eyes. Cone photoreceptors survived in regions of atrophy, but with greatly reduced and highly variable density. Regular arrays of cones were found in some locations, despite abnormal retinal pigment epithelium. For some subjects, the cone density was significantly greater than normative values in some retinal locations outside the atrophy.

SUMMARY

The survival of cones within atrophy is remarkable. The unusually dense packing of cones at some retinal locations outside the atrophy indicates more fluidity in cone distribution than typically thought. Together these findings suggest strategies for therapy that includes preserving cones.

A method for gene knockdown in the retina using a lipid-based carrier

Purpose

The use of small non-coding nucleic acids, such as siRNA and miRNA, has allowed for a deeper understanding of gene functions, as well as for development of gene therapies for complex neurodegenerative diseases, including retinal degeneration. For effective delivery into the eye and transfection of the retina, suitable transfection methods are required. We investigated the use of a lipid-based transfection agent, Invivofectamine^® 3.0 (Thermo Fisher Scientific), as a potential method for delivery of nucleic acids to the retina.

Methods

Rodents were injected intravitreally with formulations of Invivofectamine 3.0 containing scrambled, Gapdh, Il-1β, and C3 siRNAs, or sterile PBS (control) using a modified protocol for encapsulation of nucleic acids. TdT-mediated dUTP nick-end labeling (TUNEL) and IBA1 immunohistochemistry was used to determine histological cell death and inflammation. qPCR were used to determine the stress and inflammatory profile of the retina. Electroretinography (ERG) and optical coherence tomography (OCT) were employed as clinical indicators of retinal health.

Results

We showed that macrophage recruitment, retinal stress, and photoreceptor cell death in animals receiving Invivofectamine 3.0 were comparable to those in negative controls. Following delivery of Invivofectamine 3.0 alone, no statistically significant changes in expression were found in a suite of inflammatory and stress genes, and ERG and OCT analyses revealed no changes in retinal function or morphology. Injections with siRNAs for proinflammatory genes (C3 and Il-1β) and Gapdh, in combination with Invivofectamine 3.0, resulted in statistically significant targeted gene knockdown in the retina for up to 4 days following injection. Using a fluorescent Block-It siRNA, transfection was visualized throughout the neural retina with evidence of transfection observed in cells of the ganglion cell layer, inner nuclear layer, and outer nuclear layer.

Conclusions

This work supports the use of Invivofectamine 3.0 as a transfection agent for effective delivery of nucleic acids to the retina for gene function studies and as potential therapeutics.

Discovery of 4-((2S,4S)-4-Ethoxy-1-((5-methoxy-7-methyl-1H-indol-4-yl)methyl)piperidin-2-yl)benzoic Acid (LNP023), a Factor B Inhibitor Specifically Designed To Be Applicable to Treating a Diverse Array of Complement Mediated Diseases

The alternative pathway (AP) of the complement system is a key contributor to the pathogenesis of several human diseases including age-related macular degeneration, paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS), and various glomerular diseases. The serine protease factor B (FB) is a key node in the AP and is integral to the formation of C3 and C5 convertase. Despite the prominent role of FB in the AP, selective orally bioavailable inhibitors, beyond our own efforts, have not been reported previously. Herein we describe in more detail our efforts to identify FB inhibitors by high-throughput screening (HTS) and leveraging insights from several X-ray cocrystal structures during optimization efforts. This work culminated in the discovery of LNP023 (41), which is currently being evaluated clinically in several diverse AP mediated indications.

Mathematical Modelling of Alternative Pathway of Complement System

The complement system (CS) is an integral part of innate immunity and can be activated via three different pathways. The alternative pathway (AP) has a central role in the function of the CS. The AP of complement system is implicated in several human disease pathologies. In the absence of triggers, the AP exists in a time-invariant resting state (physiological steady state). It is capable of rapid, potent and transient activation response upon challenge with a trigger. Previous models of AP have focused on the activation response. In order to understand the molecular machinery necessary for AP activation and regulation of a physiological steady state, we built parsimonious AP models using experimentally supported kinetic parameters. The models further allowed us to test quantitative roles played by negative and positive regulators of the pathway in order to test hypotheses regarding their mechanisms of action, thus providing more insight into the complex regulation of AP.

Visual Function Decline Resulting from Geographic Atrophy: Results from the Chroma and Spectri Phase 3 Trials

PURPOSE

To assess visual function outcomes to 48 weeks in patients with bilateral geographic atrophy (GA) secondary to age-related macular degeneration included in 2 interventional clinical trials: relationship to baseline lesion size, outcomes by baseline lesion characteristic subgroups, and correlation of visual function outcomes with GA area.

DESIGN

The Chroma and Spectri studies (ClinicalTrials.gov identifiers, NCT02247479 and NCT02247531, respectively) were identically designed phase 3, double-masked, multicenter, randomized, sham injection-controlled clinical trials that evaluated intravitreal lampalizumab in GA.

PARTICIPANTS

Eligible patients were 50 years of age or older with well-demarcated bilateral GA (lesion size, 1-7 disc areas) without evidence of or previous treatment for choroidal neovascularization in either eye and best-corrected visual acuity (BCVA) letter score of 49 letters or more (≥1 GA lesion within 250 μm of foveal center if BCVA ≥79 letters).

METHODS

Patients (pooled n = 1881) were randomized 2:1:2:1 to lampalizumab every 4 weeks, sham every 4 weeks, lampalizumab every 6 weeks, or sham every 6 weeks. Sham arms were pooled for analysis.

MAIN OUTCOME MEASURES

Functional end points included change in BCVA from baseline to week 48, low-luminance visual acuity, mesopic microperimetry (number of absolute scotomatous points, mean macular sensitivity), binocular and monocular maximum reading speed, and 2 validated patient-reported outcome measures: Functional Reading Independence Index and 25-item National Eye Institute Visual Function Questionnaire.

RESULTS

Enlargement of GA area, approximately 2 mm²/year on average across all treatment groups in each study, was accompanied by overall deterioration in all functional end points. No statistically significant differences were found between lampalizumab or sham arms for changes from baseline in functional assessment scores. Of visual function tests, only microperimetry outcomes were correlated moderately with GA lesion area when assessed cross-sectionally at baseline and week 48.

CONCLUSIONS

Chroma and Spectri provide a unique data set of functional end points in GA that are relevant for future clinical trials. Patients with bilateral GA experienced a consistent decline in visual function over 48 weeks, but measures of visual function were not correlated strongly with GA lesion area. It is not possible to predict visual function outcomes from GA lesion size.

Dengue virus and the complement alternative pathway

Dengue disease is an inflammatory-driven pathology, and complement overactivation is linked to disease severity and vascular leakage. Additionally, dysregulation of complement alternative pathway (AP) components has been described, such as upregulation of complement factor D and downregulation of complement factor H (FH), which activate and inhibit the AP, respectively. Thus, the pathology of severe dengue could in part result from AP dysfunction, even though complement and AP activation usually provide protection against viral infections. In dengue virus-infected macrophages and endothelial cells (ECs), the site of replication and target for vascular pathology, respectively, the AP is activated. The AP activation, reduced FH and vascular leakage seen in dengue disease in part parallels other complement AP pathologies associated with FH deficiency, such as atypical haemolytic uraemic syndrome (aHUS). aHUS can be therapeutically targeted with inhibitors of complement terminal activity, raising the idea that strategies such as inhibition of complement or delivery of FH or other complement regulatory components to EC may be beneficial to combat the vascular leakage seen in severe dengue.

The Possible Link Between Vitamin D Levels and Exudative Age-related Macular Degeneration

Objectives

We sought to evaluate the possible correlation between serum vitamin D levels and exudative age-related macular degeneration (AMD).

Methods

We conducted a cross-sectional study including 95 patients with exudative AMD and 95 healthy age- and sex-matched controls. The participants’ serum 25-hydroxyvitamin D3 (25(OH)D3) levels were measured, and the results were classified into three categories: deficient (< 20.0 ng/mL), insufficient (20.1–29.9 ng/mL), and sufficient (>30.0 ng/mL). We compared serum 25(OH)D3 levels between the two study groups and the AMD ratio between the patients with deficient serum 25(OH)D3 levels and those with levels in the sufficient and insufficient ranges.

Results

The median 25(OH)D3 levels were significantly lower in patients with AMD compared to the control subjects (p = 0.042). The frequencies of patients with AMD among the vitamin D categories were statistically significant (p = 0.043). Subgroup analysis showed that the frequency of patients with AMD and deficient vitamin D levels was significantly higher than that found in the patients who had sufficient and/or insufficient ranges of vitamin D levels (55.0% vs. 36.0%, p = 0.043, respectively).

Conclusions

Serum 25(OH)D3 levels may have an impact on the neovascular type of AMD. As 25(OH)D3 levels decrease, the frequency of AMD increases.

Age-related macular degeneration: A two-level model hypothesis

Age-related diseases, including age-related macular degeneration (AMD), are of growing importance in a world where population ageing has become a dominant global trend. Although a wide variety of risk factors for AMD have been identified, age itself remains by far the most important risk factor, making it an urgent priority to understand the connections between underlying ageing mechanisms and pathophysiology of AMD. Ageing is both multicausal and variable, so that differences between individuals in biological ageing processes are the focus of a growing number of pathophysiological studies seeking to explain how ageing contributes to chronic, age-related conditions. The aim of this review is to integrate the available knowledge on the pathophysiology of AMD within the framework of the biology of ageing. One highly significant feature of biological ageing is systemic inflammation, which arises as a second-level response to a first level of molecular damage involving oxidative stress, mutations etc. Combining these insights, the various co-existing pathophysiological explanations in AMD arrange themselves according to a two-level hypothesis. Accordingly, we describe how AMD can be considered the consequence of age-related random accumulation of molecular damage at the ocular level and the subsequent systemic inflammatory host response thereof. We summarize evidence and provide original data to enlighten where evidence is lacking. Finally, we discuss how this two-level hypothesis provides a foundation for thoughts and future studies in prevention, prognosis, and intervention.

Complement Receptor 1 (CR1/CD35)-expressing retinal pigment epithelial cells as a potential therapy for age-related macular degeneration

The purpose of this study was to identify a membrane-bound complement inhibitor that could be overexpressed on retinal pigment epithelial cells (RPE) providing a potential therapy for age-related macular degeneration (AMD). This type of therapy may allow replacement of damaged RPE with cells that are able to limit complement activation in the retina. Complement Receptor 1 (CR1) is a membrane-bound complement inhibitor commonly found on erythrocytes and immune cells. In this study, QPCR and flow cytometry data demonstrated that CR1 is not well-expressed by RPE, indicating that its overexpression may provide extra protection from complement activation. To screen CR1 for this ability, a stable CR1-expressing ARPE19 line was created using a combination of antibiotic selection and FACS. Cell-based assays were used to demonstrate that addition of CR1 inhibited deposition of complement proteins C3b and C6 on the transfected line. In the end, this study identifies CR1 as a complement inhibitor that may be overexpressed on stem cell-derived RPE to create a potential "enhanced" cell therapy for AMD. A combination cell/complement therapy may create transplantable RPE better suited to avoid complement-mediated lysis and limit chronic inflammation in the retina.

Fluorescence Lifetime Imaging Ophthalmoscopy (FLIO) in Eyes With Pigment Epithelial Detachments Due to Age-Related Macular Degeneration

Purpose

To investigate fluorescence lifetime imaging ophthalmoscopy (FLIO) in neovascular AMD and pigment epithelial detachments (PEDs).

Methods

A total of 46 eyes with PEDs (>350 μm) as well as age-matched healthy controls were included in this study. We found 28 eyes showed neovascular AMD (nvAMD), and 17 had nonneovascular (dry) AMD (dAMD). The Heidelberg Engineering FLIO excited fluorescence at 473 nm. Fluorescence decays were detected in two spectral channels (498–560 nm; 560–720 nm) to determine fluorescence lifetimes of endogenous fluorophores in their specific spectral emission ranges. Mean fluorescence lifetimes (τ_m) were investigated. Multimodal imaging was reviewed by two ophthalmologists who circumscribed and classified PEDs as either serous (n = 4), hemorrhagic (n = 4), fibrovascular (n = 16), drusenoid (n = 17), or mixed (n = 5). Blood samples from a healthy subject and a patient with PED were investigated in a quartz cuvette.

Results

Eyes with nvAMD show similar FLIO patterns to dAMD: ring-shaped prolongations of τ_m 3 to 6 mm from the fovea. Different PED-forms show characteristic τ_m, while serous and hemorrhagic PEDs exhibit shortened τ_m, drusenoid PEDs show prolonged τ_m, and τ_m in fibrovascular PEDs is variable. Areas corresponding to sub-/intraretinal fluid display shortened τ_m. Ex vivo studies of blood also show short τ_m.

Conclusions

The previously described dAMD-related FLIO pattern is also present in nvAMD. Short τ_m in serous, fibrovascular, and hemorrhagic PEDs as well as sub/intraretinal fluid may disrupt this pattern. FLIO appears to differentiate between PEDs, hemorrhage, and fluid. Additionally, ex vivo studies of human blood help to better interpret FLIO images.

Cell-Type-Specific Complement Expression in the Healthy and Diseased Retina

Complement dysregulation is a feature of many retinal diseases, yet mechanistic understanding at the cellular level is limited. Given this knowledge gap about which retinal cells express complement, we performed single-cell RNA sequencing on ~92,000 mouse retinal cells and validated our results in five major purified retinal cell types. We found evidence for a distributed cell-type-specific complement expression across 11 cell types. Notably, Müller cells are the major contributor of complement activators c1s, c3, c4, and cfb. Retinal pigment epithelium (RPE) mainly expresses cfh and the terminal complement components, whereas cfi and cfp transcripts are most abundant in neurons. Aging enhances c1s, cfb, cfp, and cfi expression, while cfh expression decreases. Transient retinal ischemia increases complement expression in microglia, Müller cells, and RPE. In summary, we report a unique complement expression signature for murine retinal cell types suggesting a well-orchestrated regulation of local complement expression in the retinal microenvironment.

Overshooting complement activity contributes to retinal degeneration. Pauly et al. demonstrate a distinct complement expression profile of retinal cell types that changes with aging and during retinal degeneration. This prompts the intriguing concept of a local retinal complement activation possibly independent of the systemic components typically produced by the liver.

Oxidative Stress Increases Endogenous Complement-Dependent Inflammatory and Angiogenic Responses in Retinal Pigment Epithelial Cells Independently of Exogenous Complement Sources

Oxidative stress-induced damage of the retinal pigment epithelium (RPE) and chronic inflammation have been suggested as major contributors to a range of retinal diseases. Here, we examined the effects of oxidative stress on endogenous complement components and proinflammatory and angiogenic responses in RPE cells. ARPE-19 cells exposed for 1–48 h to H₂O₂ had reduced cell–cell contact and increased markers for epithelial–mesenchymal transition but showed insignificant cell death. Stressed ARPE-19 cells increased the expression of complement receptors CR3 (subunit CD11b) and C5aR1. CD11b was colocalized with cell-derived complement protein C3, which was present in its activated form in ARPE-19 cells. C3, as well as its regulators complement factor H (CFH) and properdin, accumulated in the ARPE-19 cells after oxidative stress independently of external complement sources. This cell-associated complement accumulation was accompanied by increased nlrp3 and foxp3 expression and the subsequently enhanced secretion of proinflammatory and proangiogenic factors. The complement-associated ARPE-19 reaction to oxidative stress, which was independent of exogenous complement sources, was further augmented by the poly(ADP-ribose) polymerase (PARP) inhibitor olaparib. Our results indicate that ARPE-19 cell-derived complement proteins and receptors are involved in ARPE-19 cell homeostasis following oxidative stress and should be considered as targets for treatment development for retinal degeneration.

Association Between Cilioretinal Arteries and Advanced Age-Related Macular Degeneration: Secondary Analysis of the Comparison of Age-Related Macular Degeneration Treatment Trials (CATT)

Importance

Recent reports suggest that cilioretinal arteries (CRAs) confer protection against developing advanced age-related macular degeneration (AMD).

Objective

To further characterize the association between the presence of a CRA and incidence of geographic atrophy (GA) or choroidal neovascularization (CNV).

Design

This cohort study constituted an ad hoc secondary analysis of data from the Comparison of Age-Related Macular Degeneration Treatments Trials (CATT) and was performed at 44 clinical centers in the United States among participants in CATT with CNV in the study eye and without advanced AMD in the fellow eye at baseline. The presence of a CRA was determined by 2 graders, masked to clinical data, using color fundus photographs, red-free fundus photographs, and fluorescein angiography. The proportion with CRAs at baseline between the study eye with CNV and fellow eye without CNV was first compared. The association of a CRA with incidence of CNV or GA at 5 years among fellow eyes and with incidence of GA among study (treated) eyes was then assessed. In addition, the association of CRAs with the Age-Related Eye Disease Study severity scale among the fellow eyes at baseline was assessed. Data were collected from February 1, 2008, through April 30, 2015, and analyzed from July 1, 2018, through April 30, 2019.

Exposures

Presence of a CRA.

Main Outcomes and Measures

The association between the presence of a CRA and incidence of CNV or GA at 5 years of follow-up.

Results

A total of 350 patients (700 eyes) (230 [65.7% women; mean [SD] age, 77 [7.2] years) were included in the analysis. Cilioretinal arteries were present in 67 of 345 (19.4%) fellow eyes without baseline CNV and 73 of 349 (20.9%) study eyes with baseline CNV (P = .60). Cilioretinal arteries in fellow eyes were not associated with incidence of CNV at 5 years (125 of 278 [45.0%] among eyes without CRAs and 30 of 67 [44.8%] among eyes with CRAs; P = .99) or with incidence of GA at 5 years (110 of 278 [39.6%] among eyes without CRAs and 25 of 67 [37.3%] among eyes with CRAs; P = .89). Cilioretinal arteries in study eyes were not associated with incidence of GA at 5 years (105 of 276 [38.0%] study eyes without CRAs and 26 of 73 [35.6%] study eyes with CRAs; P = .72).

Conclusions and Relevance

The analysis did not find a protective association between CRAs and incidence of CNV or GA among CATT participants who had unilateral exudative AMD. Why these findings were different from those of previous publications is unclear but may be partially explained by the different techniques used to detect CRAs or by the baseline advanced disease in CATT participants.

Trial Registration

ClinicalTrials.gov identifier: NCT00593450.

Molecular Mechanisms of Complement System Proteins and Matrix Metalloproteinases in the Pathogenesis of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is an eye disorder affecting predominantly the older people above the age of 50 years in which the macular region of the retina deteriorates, resulting in the loss of central vision. The key factors associated with the pathogenesis of AMD are age, smoking, dietary, and genetic risk factors. There are few associated and plausible genes involved in AMD pathogenesis. Common genetic variants (with a minor allele frequency of >5% in the population) near the complement genes explain 40-60% of the heritability of AMD. The complement system is a group of proteins that work together to destroy foreign invaders, trigger inflammation, and remove debris from cells and tissues. Genetic changes in and around several complement system genes, including the CFH, contribute to the formation of drusen and progression of AMD. Similarly, Matrix metalloproteinases (MMPs) that are normally involved in tissue remodeling also play a critical role in the pathogenesis of AMD. MMPs are involved in the degradation of cell debris and lipid deposits beneath retina but with age their functions get affected and result in the drusen formation, succeeding to macular degeneration. In this review, AMD pathology, existing knowledge about the normal and pathological role of complement system proteins and MMPs in the eye is reviewed. The scattered data of complement system proteins, MMPs, drusenogenesis, and lipofusogenesis have been gathered and discussed in detail. This might add new dimensions to the understanding of molecular mechanisms of AMD pathophysiology and might help in finding new therapeutic options for AMD.

Ocular manifestations of rheumatic diseases

PURPOSE

Our aim was to summarize key aspects of the pathomechanism and the ocular involvements of rheumatic and systemic autoimmune diseases.

METHODS

Apart from a paper in French (Morax V, Ann Oculist 109:368-370, 1893), all papers referred to in this article were published in English. All the materials were peer-reviewed full-text papers, letters, reviews, or book chapters obtained through a literature search of the PubMed database using the keywords ocular manifestations; pathogenesis; systemic inflammatory rheumatic diseases; rheumatoid arthritis; osteoarthritis; fibromyalgia; systemic lupus erythematosus; seronegative spondyloarthritis; ankylosing spondylitis; reactive arthritis; enteropathic arthritis; psoriatic arthritis; systemic sclerosis; polymyalgia rheumatica and covering all years available. Some statements articulated in this paper reflect the clinical experience of the authors in their tertiary-referral center.

RESULTS

Ophthalmic disorders are categorized by anatomical subgroups in all rheumatic diseases. The most common ocular manifestations are diverse types of inflammations of different tissues and dry eye disease (DED).

CONCLUSION

The eye could be a responsive marker for the onset or aggravation of an immune reactivation in many rheumatic diseases, furthermore, ocular findings can antedate the diagnosis of the underlying rheumatic disease. By recognizing ocular manifestations of systemic rheumatic diseases it might be possible to avoid or at least delay many long term sequelae.

CFH exerts anti-oxidant effects on retinal pigment epithelial cells independently from protecting against membrane attack complex

Age Related Macular Degeneration (AMD) is the first cause of social blindness in people aged over 65 leading to atrophy of retinal pigment epithelial cells (RPE), photoreceptors and choroids, eventually associated with choroidal neovascularization. Accumulation of undigested cellular debris within RPE cells or under the RPE (Drusen), oxidative stress and inflammatory mediators contribute to the RPE cell death. The major risk to develop AMD is the Y402H polymorphism of complement factor H (CFH). CFH interacting with oxidized phospholipids on the RPE membrane modulates the functions of these cells, but the exact role of CFH in RPE cell death and survival remain poorly understood. The aim of this study was to analyze the potential protective mechanism of CFH on RPE cells submitted to oxidative stress. Upon exposure to oxidized lipids 4-HNE (4-hydroxy-2-nonenal) derived from photoreceptors, both the human RPE cell line ARPE-19 and RPE cells derived from human induced pluripotent stem cells were protected from death only in the presence of the full length human recombinant CFH in the culture medium. This protective effect was independent from the membrane attack complex (MAC) formation. CFH maintained RPE cells tight junctions’ structure and regulated the caspase dependent apoptosis process. These results demonstrated the CFH anti-oxidative stress functions independently of its capacity to inhibit MAC formation.

Vascular Inflammation Risk Factors in Retinal Disease

Inflammation of the blood vessels that serve the central nervous system has been increasingly identified as an early and possibly initiating event among neurodegenerative conditions such as Alzheimer's disease and related dementias. However, the causal relevance of vascular inflammation to major retinal degenerative diseases is unresolved. Here, we describe how genetics, aging-associated changes, and environmental factors contribute to vascular inflammation in age-related macular degeneration, diabetic retinopathy, and glaucoma. We highlight the importance of mouse models in studying the underlying mechanisms and possible treatments for these diseases. We conclude that data support vascular inflammation playing a central if not primary role in retinal degenerative diseases, and this association should be a focus of future research.

Immunometabolic modulation of retinal inflammation by CD36 ligand

In subretinal inflammation, activated mononuclear phagocytes (MP) play a key role in the progression of retinopathies. Little is known about the mechanism involved in the loss of photoreceptors leading to vision impairment. Studying retinal damage induced by photo-oxidative stress, we observed that cluster of differentiation 36 (CD36)-deficient mice featured less subretinal MP accumulation and attenuated photoreceptor degeneration. Moreover, treatment with a CD36-selective azapeptide ligand (MPE-001) reduced subretinal activated MP accumulation in wild type mice and preserved photoreceptor layers and function as assessed by electroretinography in a CD36-dependent manner. The azapeptide modulated the transcriptome of subretinal activated MP by reducing pro-inflammatory markers. In isolated MP, MPE-001 induced dissociation of the CD36-Toll-like receptor 2 (TLR2) oligomeric complex, decreasing nuclear factor-kappa B (NF-κB) and NLR family pyrin domain containing 3 (NLRP3) inflammasome activation. In addition, MPE-001 caused an aerobic metabolic shift in activated MP, involving peroxisome proliferator-activated receptor-γ (PPAR-γ) activation, which in turn mitigated inflammation. Accordingly, PPAR-γ inhibition blocked the cytoprotective effect of MPE-001 on photoreceptor apoptosis elicited by activated MP. By altering activated MP metabolism, MPE-001 decreased immune responses to alleviate subsequent inflammation-dependent neuronal injury characteristic of various vision-threatening retinal disorders.

Innate immune response in retinal homeostasis and inflammatory disorders

Innate immune cells such as neutrophils, monocyte-macrophages and microglial cells are pivotal for the health and disease of the retina. For the maintenance of retinal homeostasis, these cells and immunosuppressive molecules in the eye actively regulate the induction and the expression of inflammation in order to prevent excessive activation and subsequent tissue damage. In the disease context, these regulatory mechanisms are modulated genetically and/or by environmental stimuli such as damage-associated molecular patterns (DAMPs), and a chronic innate immune response regulates or contributes to the formation of diverse retinal disorders such as uveitis, retinitis pigmentosa, retinal vascular diseases and retinal fibrosis. Here we summarize the recent knowledge regarding the innate immune response in both ocular immune regulation and inflammatory retinal diseases, and we describe the potential of the innate immune response as a biomarker and therapeutic target.

Understanding the complexity of the matrix metalloproteinase system and its relevance to age-related diseases: Age-related macular degeneration and Alzheimer's disease

Extracellular matrices (ECMs) are maintained by tightly coupled processes of continuous synthesis and degradation. The degradative arm is mediated by a family of proteolytic enzymes called the matrix metalloproteinases (MMPs). These enzymes are released as latent proteins (pro-MMPs) and on activation are capable of degrading most components of an ECM. Activity of these enzymes is checked by the presence of tissue inhibitors of MMPs (TIMPs) and current opinion holds that the ratio of TIMPs/MMPs determines the relative rate of degradation. Thus, elevated ratios are thought to compromise degradation leading to the accumulation of abnormal ECM material, whilst diminished ratios are thought to lead to excessive ECM degradation (facilitating angiogenesis and the spread of cancer cells). Our recent work has shown this system to be far more complex. MMP species tend to undergo covalent modification leading to homo- and hetero-dimerization and aggregation resulting in the formation of very large macromolecular weight MMP complexes (LMMCs). In addition, the various MMP species also show a bound-free compartmentalisation. The net result of these changes is to reduce the availability of the latent forms of MMPs for the activation process. An assessment of the degradation potential of the MMP system in any tissue must therefore take into account the degree of sequestration of the latent MMP species, a protocol that has not previously been addressed. Taking into consideration the complexities already described, we will present an analysis of the MMP system in two common neurodegenerative disorders, namely age-related macular degeneration (AMD) and Alzheimer's disease (AD).

[Molecular and genetic aspects of age-related macular degeneration and glaucoma]

In most cases, age-related macular degeneration (AMD) and glaucoma are considered multi-factor diseases that lead to irreversible blindness in senior population of developed countries. Among different types of these diseases, around 5% are monogenic. Studying their molecular and genetic aspects can lay the basis for improvement of diagnostic methods, prognosis of the risks of development, manner of progression and treatment outcomes, as well as creation of new therapy methods. The article reviews modern understanding of the etiopathogenesis of AMD and glaucoma and describes their interrelations.

Promiscuous Chemokine Antagonist (BKT130) Suppresses Laser-Induced Choroidal Neovascularization by Inhibition of Monocyte Recruitment

Background

Age-related macular degeneration (AMD), the most common cause of blindness in the developed world, usually affects individuals older than 60 years of age. The majority of visual loss in this disease is attributable to the development of choroidal neovascularization (CNV). Mononuclear phagocytes, including monocytes and their tissue descendants, macrophages, have long been implicated in the pathogenesis of neovascular AMD (nvAMD). Current therapies for nvAMD are based on targeting vascular endothelial growth factor (VEGF). This study is aimed at assessing if perturbation of chemokine signaling and mononuclear cell recruitment may serve as novel complementary therapeutic targets for nvAMD.

Methods

A promiscuous chemokine antagonist (BKT130), aflibercept treatment, or combined BKT130+aflibercept treatment was tested in an in vivo laser-induced model of choroidal neovascularization (LI-CNV) and in an ex vivo choroidal sprouting assay (CSA). Quantification of CD11b+ cell in the CNV area was performed, and mRNA levels of genes implicated in CNV growth were measured in the retina and RPE-choroid.

Results

BKT130 reduced the CNV area and recruitment of CD11b+ cells by 30-35%. No effect of BKT130 on macrophages' proangiogenic phenotype was demonstrated ex vivo, but a lower VEGFA and CCR2 expression was found in the RPE-choroid and a lower expression of TNFα and NOS1 was found in both RPE-choroid and retinal tissues in the LI-CNV model under treatment with BKT130.

Conclusions

Targeting monocyte recruitment via perturbation of chemokine signaling can reduce the size of experimental CNV and should be evaluated as a potential novel therapeutic modality for nvAMD.

IL-1 Family Members Mediate Cell Death, Inflammation and Angiogenesis in Retinal Degenerative Diseases

Inflammation underpins and contributes to the pathogenesis of many retinal degenerative diseases. The recruitment and activation of both resident microglia and recruited macrophages, as well as the production of cytokines, are key contributing factors for progressive cell death in these diseases. In particular, the interleukin 1 (IL-1) family consisting of both pro- and anti-inflammatory cytokines has been shown to be pivotal in the mediation of innate immunity and contribute directly to a number of retinal degenerations, including Age-Related Macular Degeneration (AMD), diabetic retinopathy, retinitis pigmentosa, glaucoma, and retinopathy of prematurity (ROP). In this review, we will discuss the role of IL-1 family members and inflammasome signaling in retinal degenerative diseases, piecing together their contribution to retinal disease pathology, and identifying areas of research expansion required to further elucidate their function in the retina.

Complement C3 Inhibitor Pegcetacoplan for Geographic Atrophy Secondary to Age-Related Macular Degeneration: A Randomized Phase 2 Trial

PURPOSE

Geographic atrophy (GA), a late stage of age-related macular degeneration (AMD), is a major cause of blindness. Even while central visual acuity remains relatively well preserved, GA often causes considerable compromise of visual function and quality of life. No treatment currently exists. We evaluated the safety and efficacy of pegcetacoplan, a complement C3 inhibitor, for treatment of GA.

DESIGN

Prospective, multicenter, randomized, sham-controlled phase 2 study.

PARTICIPANTS

Two hundred forty-six patients with GA.

METHODS

Patients with GA were assigned randomly in a 2:2:1:1 ratio to receive intravitreal injections of 15 mg pegcetacoplan monthly or every other month (EOM) or sham intravitreal injections monthly or EOM for 12 months with follow-up at months 15 and 18. Area and growth of GA were measured using fundus autofluorescence imaging.

MAIN OUTCOME MEASURES

The primary efficacy end point was mean change in square root GA lesion area from baseline to month 12. Secondary outcome measures included mean change from baseline in GA lesion area without the square root transformation, distance of GA lesion from the fovea, best-corrected visual acuity (BCVA), low-luminance BCVA, and low-luminance visual acuity deficit. The primary safety end point was the number and severity of treatment-emergent adverse events.

RESULTS

In patients receiving pegcetacoplan monthly or EOM, the GA growth rate was reduced by 29% (95% confidence interval [CI], 9-49; P = 0.008) and 20% (95% CI, 0-40; P = 0.067) compared with the sham treatment group. Post hoc analysis showed that the effect was greater in the second 6 months of treatment, with observed reductions of 45% (P = 0.0004) and 33% (P = 0.009) for pegcetacoplan monthly and EOM, respectively. Two cases of culture-positive endophthalmitis and 1 case of culture-negative endophthalmitis occurred in the pegcetacoplan monthly group. New-onset investigator-determined exudative AMD was reported more frequently in pegcetacoplan-treated eyes (18/86 eyes [20.9%] and 7/79 eyes [8.9%] in monthly and EOM groups, respectively) than in sham-treated eyes (1/81 eyes [1.2%]).

CONCLUSIONS

Local C3 inhibition with pegcetacoplan resulted in statistically significant reductions in the growth of GA compared with sham treatment. Phase 3 studies will define the efficacy and safety profile further.

Early local activation of complement in aqueous humour of patients with age-related macular degeneration

OBJECTIVE

To investigate complement activation in aqueous humour of patients with early, intermediate and neovascular age-related macular degeneration (AMD).

PATIENTS AND METHODS

Aqueous humour of 79 AMD patients (early, intermediate and neovascular) and 77 age-matched controls was prospectively collected. The levels of the complement protein 3 (C3), activation products complement factor 3a (C3a) and Ba, C3b/iC3b, complement factors B, H and I (CFB, CFH and CFI), and total protein concentration were measured. Data were modelled using covariate analysis to assess the impact of age and glaucoma status of patients and total protein concentration of samples on complement protein concentration across groups.

RESULTS

C3a concentration was significantly increased in the aqueous humour of early (p = 0.016), intermediate (p = 0.003) and neovascular (p = 0.018) AMD patients, whilst C3 concentration was significantly increased in early AMD patients only (p = 0.019). Levels of CFB and CFH were significantly increased in the aqueous humour of neovascular AMD patients (p = 0.023 and p = 0.018, respectively).

CONCLUSIONS

Our findings provide evidence for early local complement dysregulation in AMD patients, suggesting that complement pathway inhibition may be a clinically relevant intervention for early stages of AMD.

Chemokine Expression in Murine RPE/Choroid in Response to Systemic Viral Infection and Elevated Levels of Circulating Interferon-γ

Purpose

To examine how circulating immune mediators in vivo may affect gene and protein expression at the RPE/choroid interface.

Methods

Young mice were systemically infected with lymphocytic choriomeningitis virus (LCMV) or continuously infused with IFN-γ. RPE/choroid was isolated and analyzed with whole-transcriptome gene expression microarrays. Selected gene expression findings were validated at the protein level.

Results

Both the systemic immune activation from virus infection and the sterile systemically increased level of IFN-γ resulted in increased expression of chemokine ligands, chemokine receptors, and early complement components in isolates of RPE/choroid. These findings were largely absent from LCMV-infected mice deficient in either the interferon α/β receptor or IFN-γ.

Conclusions

Together, these findings demonstrate that acute systemic immune activation results in a local response at the RPE/choroid interface that may include chemokine-dependent recruitment of inflammatory cells and engagement of the complement system. This may represent a link between the systemic low-grade inflammation and the retinal pathology observed in several multifactorial entities such as aging, AMD, and diabetes.

Effects of Fish n-3 PUFAs on Intestinal Microbiota and Immune System

Studies over several decades have documented the beneficial actions of n-3 polyunsaturated fatty acids (PUFAs), which are plentiful in fish oil, in different disease states. Mechanisms responsible for the efficacy of n-3 PUFAs include: (1) Reduction of triglyceride levels; (2) anti-arrhythmic and antithrombotic effects, and (3) resolution of inflammatory processes. The human microbiota project and subsequent studies using next-generation sequencing technology have highlighted that thousands of different microbial species are present in the human gut, and that there has been a significant variability of taxa in the microbiota composition among people. Several factors (gestational age, mode of delivery, diet, sanitation and antibiotic treatment) influence the bacterial community in the human gastrointestinal tract, and among these diet habits play a crucial role. The disturbances in the gut microbiota composition, i.e., gut dysbiosis, have been associated with diseases ranging from localized gastrointestinal disorders to neurologic, respiratory, metabolic, ocular, and cardiovascular illnesses. Many studies have been published about the effects of probiotics and prebiotics on the gut microbiota/microbioma. On the contrary, PUFAs in the gut microbiota have been less well defined. However, experimental studies suggested that gut microbiota, n-3 PUFAs, and host immune cells work together to ensure the intestinal wall integrity. This review discussed current evidence concerning the links among gut microbiota, n-3 PUFAs intake, and human inflammatory disease.

Systemic activation of the complement system in patients with advanced age-related macular degeneration

Purpose:

To examine the role of systemic activation of the complement system (assessed by levels of circulating C3a, Ba, and sC5b-9) in patients (n = 122) with advanced age-related macular degeneration, geographic atrophy, and neovascular age-related macular degeneration, compared with cataract controls (n = 27).

Methods:

Plasma complement factors were measured using enzyme-linked immunosorbent assays. Statistical analysis included univariate and multivariate logistic regression (p < 0.05).

Results:

Adjusted for age, the odds ratios of C3a and sC5b-9 for any advanced age-related macular degeneration were 1.78 (95% confidence interval = 1.16–2.73, p < 0.01) and 1.20 (95% confidence interval = 1.04–1.39, p = 0.01), respectively. We found a significantly elevated adjusted odds ratio of C3a (adjusted odds ratio = 1.71, 95% confidence interval = 1.12–2.60, p = 0.01) and sC5b-9 (adjusted odds ratio = 1.22, 95% confidence interval = 1.04–1.43, p = 0.01) for neovascular age-related macular degeneration. Adjusted for age, neither C3a, sC5b-9, nor Ba were associated with geographic atrophy.

Conclusion:

We suggest a role for elevated plasma levels of C3a and sC5b-9 in patients with neovascular age-related macular degeneration. The study’s results reinforce the need for more investigation to assess the impact of therapeutic interventions targeted at the complement signaling pathways in age-related macular degeneration.

A chronic hypoxic response in photoreceptors alters the vitreous proteome in mice

Reduced oxygenation of the outer retina in the aging eye may activate a chronic hypoxic response in RPE and photoreceptor cells and is considered as a risk factor for the development of age-related macular degeneration (AMD). In mice, a chronically active hypoxic response in the retinal pigment epithelium (RPE) or photoreceptors leads to age-dependent retinal degeneration. To identify proteins that may serve as accessible markers for a chronic hypoxic insult to photoreceptors, we used proteomics to determine the protein composition of the vitreous humor in genetically engineered mice that lack the von Hippel-Lindau tumor suppressor (Vhl) specifically in rods (rod^ΔVhl) or cones (all-cone^ΔVhl). Absence of VHL leads to constitutively active hypoxia-inducible transcription factors (HIFs) and thus to a molecular response to hypoxia even in normal room air. To discriminate between the consequences of a local response in photoreceptors and systemic hypoxic effects, we also evaluated the vitreous proteome of wild type mice after exposure to acute hypoxia. 1'043 of the identified proteins were common to all three hypoxia models. 257, 258 and 356 proteins were significantly regulated after systemic hypoxia, in rod^ΔVhl and in all-cone^ΔVhl mice, respectively, at least at one of the analyzed time points. Only few of the regulated proteins were shared by the models indicating that the vitreous proteome is differentially affected by systemic hypoxia and the rod or cone-specific hypoxic response. Similarly, the distinct protein compositions in the individual genetic models at early and late time points suggest regulated, cell-specific and time-dependent processes. Among the proteins commonly regulated in the genetic models, guanylate binding protein 2 (GBP2) showed elevated levels in the vitreous that were accompanied by increased mRNA expression in the retina of both rod^ΔVhl and all-cone^ΔVhl mice. We hypothesize that some of the differentially regulated proteins at early time points may potentially be used as markers for the detection of a chronic hypoxic response of photoreceptors.

Ocular gene therapies in clinical practice: viral vectors and nonviral alternatives

Ocular gene therapy has entered into clinical practice. Although viral vectors are currently the best option to replace and/or correct genes, the optimal method to deliver these treatments to the retinal pigment epithelial (RPE) cells and/or photoreceptor cells remains to be improved to increase transduction efficacy and reduce iatrogenic risks. Beyond viral-mediated gene replacement therapies, nonviral gene delivery approaches offer the promise of sustained fine-tuned expression of secreted therapeutic proteins that can be adapted to the evolving stage of the disease course and can address more common nongenetic retinal diseases, such as age-related macular degeneration (AMD). Here, we review current gene therapy strategies for ocular diseases, with a focus on clinical stage products.

Increased serum proteins in non-exudative AMD retinas

The blood retinal barrier (BRB) closely regulates the retinal microenvironment. Its compromise leads to the accumulation of retinal fluid containing potentially harmful plasma components. While eyes with non-exudative age-related macular degeneration (AMD) were previously felt to have an intact BRB, we propose that the BRB in non-exudative AMD eyes may be subclinically compromised, allowing entry of retina-toxic plasma proteins. We test this hypothesis by measuring retinal levels of abundant plasma proteins that should not cross the intact BRB. Two cohorts of frozen, post mortem neurosensory retinas were studied by Western analysis. One cohort from Alabama had 4 normal controls and 4 eyes with various forms of AMD. Another cohort from Minnesota had 5 intermediate AMD eyes and 5 normals. Both cohorts were age/post mortem interval (PMI) matched. The non-exudative AMD retinas in the Alabama cohort had significantly higher levels of albumin and complement component 9 (C9) than normal controls. The positive control exudative AMD donor retina had higher levels of all but one serum protein. In both macular and peripheral neurosensory retina samples, intermediate AMD retinas in the Minnesota cohort had significantly higher levels of albumin, fibrinogen, IgG, and C9 than controls. Our results suggest that there may be moderate subclinical BRB leakage in non-exudative AMD. Potentially harmful plasma components including complement or iron could enter the neurosensory retina in AMD patients prior to advanced disease. Thus, therapies aiming to stabilize the BRB might have a role in the management of non-exudative AMD.

Modulation of three key innate immune pathways for the most common retinal degenerative diseases

This review highlights the role of three key immune pathways in the pathophysiology of major retinal degenerative diseases including diabetic retinopathy, age‐related macular degeneration, and rare retinal dystrophies. We first discuss the mechanisms how loss of retinal homeostasis evokes an unbalanced retinal immune reaction involving responses of local microglia and recruited macrophages, activity of the alternative complement system, and inflammasome assembly in the retinal pigment epithelium. Presenting these key mechanisms as complementary targets, we specifically emphasize the concept of immunomodulation as potential treatment strategy to prevent or delay vision loss. Promising molecules are ligands for phagocyte receptors, specific inhibitors of complement activation products, and inflammasome inhibitors. We comprehensively summarize the scientific evidence for this strategy from preclinical animal models, human ocular tissue analyses, and clinical trials evolving in the last few years.

The Challenges and Promise of Complement Therapeutics for Ocular Diseases

Ocular inflammation is a defining feature of sight threating diseases and its dysregulation can catalyze and or propagate ocular neurodegenerative maladies such as age-related macular degeneration (AMD). The complement system, an intrinsic component of the innate immunity, has an integral role in maintaining immune-surveillance and homeostasis in the ocular microenvironment; however, overstimulation can drive ocular inflammatory diseases. The mechanism for complement disease propagation in AMD is not fully understood, although there is accumulating evidence showing that targeted modulation of complement-specific proteins has the potential to become a viable therapeutic approach. To date, a major focus of complement therapeutics has been on targeting the alternative complement system in AMD. Recent studies have outlined potential complement cascade inhibitors that might mitigate AMD disease progression. First-in-class complement inhibitors target the modulation of complement proteins C3, C5, factor B, factor D, and properdin. Herein, we will summarize ocular inflammation in the context of AMD disease progression, current clinical outcomes and complications of complement-mediated therapeutics. Given the need for additional therapeutic approaches for ocular inflammatory diseases, targeted complement modulation has emerged as a leading candidate for eliminating inflammation-driven ocular maladies.

Treatments for dry age-related macular degeneration and Stargardt disease: a systematic review

BACKGROUND

Age-related macular degeneration (AMD) is the leading cause of visual loss in older people. Advanced AMD takes two forms, neovascular (wet) and atrophic (dry). Stargardt disease (STGD) is the commonest form of inherited macular dystrophy.

OBJECTIVE

To carry out a systematic review of treatments for dry AMD and STGD, and to identify emerging treatments where future NIHR research might be commissioned.

DESIGN

Systematic review.

METHODS

We searched MEDLINE, EMBASE, Web of Science and The Cochrane Library from 2005 to 13 July 2017 for reviews, journal articles and meeting abstracts. We looked for studies of interventions that aim to preserve or restore vision in people with dry AMD or STGD. The most important outcomes are those that matter to patients: visual acuity (VA), contrast sensitivity, reading speed, ability to drive, adverse effects of treatment, quality of life, progression of disease and patient preference. However, visual loss is a late event and intermediate predictors of future decline were accepted if there was good evidence that they are strong predictors of subsequent visual outcomes. These include changes detectable by investigation, but not necessarily noticed by people with AMD or STGD. ClinicalTrials.gov, the World Health Organization search portal and the UK Clinical Trials gateway were searched for ongoing and recently completed clinical trials.

RESULTS

The titles and abstracts of 7948 articles were screened for inclusion. The full text of 398 articles were obtained for further screening and checking of references and 112 articles were included in the final report. Overall, there were disappointingly few good-quality studies (including of sufficient size and duration) reporting useful outcomes, particularly in STGD. However we did identify a number of promising research topics, including drug treatments, stem cells, new forms of laser treatment, and implantable intraocular lens telescopes. In many cases, research is already under way, funded by industry or governments.

LIMITATIONS

In AMD, the main limitation came from the poor quality of much of the evidence. Many studies used VA as their main outcome despite not having sufficient duration to observe changes. The evidence on treatments for STGD is sparse. Most studies tested interventions with no comparison group, were far too short term, and the quality of some studies was poor.

FUTURE WORK

We think that the topics on which the Health Technology Assessment (HTA) and Efficacy Mechanism and Evaluation (EME) programmes might consider commissioning primary research are in STGD, a HTA trial of fenretinide (ReVision Therapeutics, San Diego, CA, USA), a visual cycle inhibitor, and EME research into the value of lutein and zeaxanthin supplements, using short-term measures of retinal function. In AMD, we suggest trials of fenretinide and of a potent statin. There is epidemiological evidence from the USA that the drug, levodopa, used for treating Parkinson's disease, may reduce the incidence of AMD. We suggest that similar research should be carried out using the large general practice databases in the UK. Ideally, future research should be at earlier stages in both diseases, before vision is impaired, using sensitive measures of macular function. This may require early detection of AMD by screening.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42016038708.

FUNDING

The National Institute for Health Research HTA programme.

MORPHOLOGIC FEATURES OF THE RETINAL PIGMENT EPITHELIUM AND ASSOCIATED CHORIORETINAL CHARACTERISTICS IN EYES WITH EARLY AGE-RELATED MACULAR DEGENERATION AND SUBRETINAL DRUSENOID DEPOSITS

PURPOSE

To investigate the features of the retinal pigment epithelium (RPE) on optical coherence tomography in eyes with early age-related macular degeneration with subretinal drusenoid deposit.

METHODS

We classified the eyes into three types: nonundulating RPE, undulating RPE, and wedge-shaped RPE. We compared the retinal vessel densities, retinal thickness, and choroidal thickness of a 3-mm-diameter zone.

RESULTS

We classified 33, 27, and 20 as nonundulating RPE, undulating RPE, and wedge-shaped RPE eyes, respectively. The vascular densities of the superficial and deep capillary plexus showed differences; nonundulating RPE group (23.93 ± 2.26% and 23.54 ± 1.78%), undulating RPE group (22.29 ± 2.80% and 21.94 ± 2.42%), and wedge-shaped RPE group (21.93 ± 2.70% and 20.63 ± 2.42%, P = 0.010 and P < 0.001). The mean retinal thickness and choroidal thickness were also different, nonundulating RPE group (298.26 ± 13.81 µm and 180.08 ± 55.49 µm), undulating RPE group (285.29 ± 21.88 µm and 148.45 ± 55.08 µm), and wedge-shaped RPE group (274.86 ± 20.62 µm and 135.75 ± 39.77 µm) (P = 0.001 and P = 0.007).

CONCLUSION

Altered features of the RPE on optical coherence tomography may indicate advancement in disease and be part of an overall degeneration process in these eyes.

Transcriptome-wide analysis of differentially expressed chemokine receptors, SNPs, and SSRs in the age-related macular degeneration

Background

Age-related macular degeneration (AMD) is the most common, progressive, and polygenic cause of irreversible visual impairment in the world. The molecular pathogenesis of the primary events of AMD is poorly understood. We have investigated a transcriptome-wide analysis of differential gene expression, single-nucleotide polymorphisms (SNPs), indels, and simple sequence repeats (SSRs) in datasets of the human peripheral retina and RPE-choroid-sclera control and AMD.

Methods and results

Adaptors and unbiased components were removed and checked to ensure the quality of the data sets. Molecular function, biological process, cellular component, and pathway analyses were performed on differentially expressed genes. Analysis of the gene expression datasets identified 5011 upregulated genes, 11,800 downregulated genes, 42,016 SNPs, 1141 indels, and 6668 SRRs between healthy controls and AMD donor material. Enrichment categories for gene ontology included chemokine activity, cytokine activity, cytokine receptor binding, immune system process, and signal transduction respectively. A functional pathways analysis identified that chemokine receptors bind chemokines, complement cascade genes, and create cytokine signaling in immune system pathway genes (p value < 0.001). Finally, allele-specific expression was found to be significant for Chemokine (C-C motif) ligand (CCL) 2, 3, 4, 13, 19, 21; C-C chemokine receptor (CCR) 1, 5; chemokine (C-X-C motif) ligand (CXCL) 9, 10, 16; C-X-C chemokine receptor type (CXCR) 6; as well as atypical chemokine receptor (ACKR) 3,4 and pro-platelet basic protein (PPBP).

Conclusions

Our results improve our overall understanding of the chemokine receptors’ signaling pathway in AMD conditions, which may lead to potential new diagnostic and therapeutic targets.

Electronic supplementary material

The online version of this article (10.1186/s40246-019-0199-1) contains supplementary material, which is available to authorized users.

Human complement factor H Y402H polymorphism causes an age-related macular degeneration phenotype and lipoprotein dysregulation in mice

The complement factor H (CFH) Y402H polymorphism (rs1061170) imparts the strongest risk for age-related macular degeneration (AMD), the leading cause of blindness in the elderly. Popular thinking holds that the CFH H402 variant increases complement activation in the eye, predisposing susceptibility to disease. However, clinical trials of complement inhibitors in AMD patients have failed. Here we provide an explanation, showing CFH variant-specific differences in the presentation of AMD-like pathologies. We show that aged mice expressing the human H402, but not Y402 variant, (i) develop AMD-like symptoms and (ii) display differences in their systemic and ocular lipoprotein levels, but not in their complement activation, after diet. These findings support targeting lipoproteins for the treatment of AMD.

One of the strongest susceptibility genes for age-related macular degeneration (AMD) is complement factor H (CFH); however, its impact on AMD pathobiology remains unresolved. Here, the effect of the principal AMD-risk–associated CFH variant (Y402H) on the development and progression of age-dependent AMD-like pathologies was determined in vivo. Transgenic mice expressing equal amounts of the full-length normal human CFH Y402 (CFH-Y/0) or the AMD-risk associated CFH H402 (CFH-H/H) variant on a Cfh^−/− background were aged to 90 weeks and switched from normal diet (ND) to a high fat, cholesterol-enriched (HFC) diet for 8 weeks. The resulting phenotype was compared with age-matched controls maintained on ND. Remarkably, an AMD-like phenotype consisting of vision loss, increased retinal pigmented epithelium (RPE) stress, and increased basal laminar deposits was detected only in aged CFH-H/H mice following the HFC diet. These changes were not observed in aged CFH-Y/0 mice or in younger (36- to 40-week-old) CFH mice of both genotypes fed either diet. Biochemical analyses of aged CFH mice after HFC diet revealed genotype-dependent changes in plasma and eyecup lipoproteins, but not complement activation, which correlated with the AMD-like phenotype in old CFH-H/H mice. Specifically, apolipoproteins B48 and A1 are elevated in the RPE/choroid of the aged CFH-H/H mice compared with age-matched control CFH-Y/0 fed a HFC diet. Hence, we demonstrate a functional consequence of the Y402H polymorphism in vivo, which promotes AMD-like pathology development and affects lipoprotein levels in aged mice. These findings support targeting lipoproteins as a viable therapeutic strategy for treating AMD.

Changes in extracellular matrix cause RPE cells to make basal deposits and activate the alternative complement pathway

The design of efficient therapies for age-related macular degeneration (AMD) is limited by our understanding of the pathogenesis of basal deposits, which form between retinal pigment epithelium (RPE) and Bruch's membrane (BrM) early in disease, and involve activation of the complement system. To investigate the roles of BrM, RPE and complement in an AMD, we generated abnormal extracellular matrix (ECM) using CRISPR-edited ARPE-19 cells. We introduced to these cells the p.R345W mutation in EFEMP1, which causes early-onset macular degeneration. The abnormal ECM binds active complement C3 and causes the formation of basal deposits by normal human fetal (hf)RPE cells. Human fetal RPE (hfRPE) cells grown on abnormal ECM or BrM explants from AMD donors show chronic activation of the alternative complement pathway by excessive deposition of C3b. This process is exacerbated by impaired ECM turnover via increased matrix metalloproteinase-2 activity. The local cleavage of C3 via convertase-independent mechanisms can be a new therapeutic target for early AMD.

Role of Bioactive Sphingolipids in Inflammation and Eye Diseases

Inflammation is a common underlying factor in a diversity of ocular diseases, ranging from macular degeneration, autoimmune uveitis, glaucoma, diabetic retinopathy and microbial infection. In addition to the variety of known cellular mediators of inflammation, such as cytokines, chemokines and lipid mediators, there is now considerable evidence that sphingolipid metabolites also play a central role in the regulation of inflammatory pathways. Various sphingolipid metabolites, such as ceramide (Cer), ceramide-1-phosphate (C1P), sphingosine-1-phosphate (S1P), and lactosylceramide (LacCer) can contribute to ocular inflammatory diseases through multiple pathways. For example, inflammation generates Cer from sphingomyelins (SM) in the plasma membrane, which induces death receptor ligand formation and leads to apoptosis of retinal pigment epithelial (RPE) and photoreceptor cells. Inflammatory stress by reactive oxygen species leads to LacCer accumulation and S1P secretion and induces proliferation of retinal endothelial cells and eventual formation of new vessels. In sphingolipid/lysosomal storage disorders, sphingolipid metabolites accumulate in lysosomes and can cause ocular disorders that have an inflammatory etiology. Sphingolipid metabolites activate complement factors in the immune-response mediated pathogenesis of macular degeneration. These examples highlight the integral association between sphingolipids and inflammation in ocular diseases.

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.

Developmental roles of microglia: A window into mechanisms of disease

Microglia are engineers of the central nervous system (CNS) both in health and disease. In addition to the canonical immunological roles of clearing damaging entities and limiting the spread of toxicity and death, microglia remodel the CNS throughout life. While they have been extensively studied in disease and injury, due to their highly variable functions, their precise role in these contexts still remains uncertain. Over the past decade, we have greatly expanded our understanding of microglial function, including their essential homeostatic roles during development. Here, we review these developmental roles, identify parallels in disease, and speculate whether developmental mechanisms re-emerge in disease and injury. Developmental Dynamics 248:98-117, 2019. © 2018 Wiley Periodicals, Inc.

On the origin of proteins in human drusen: The meet, greet and stick hypothesis

Retinal drusen formation is not only a clinical hallmark for the development of age-related macular degeneration (AMD) but also for other disorders, such as Alzheimer's disease and renal diseases. The initiation and growth of drusen is poorly understood. Attention has focused on lipids and minerals, but relatively little is known about the origin of drusen-associated proteins and how they are retained in the space between the basal lamina of the retinal pigment epithelium and the inner collagenous layer space (sub-RPE-BL space). While some authors suggested that drusen proteins are mainly derived from cellular debris from processed photoreceptor outer segments and the RPE, others suggest a choroidal cell or blood origin. Here, we reviewed and supplemented the existing literature on the molecular composition of the retina/choroid complex, to gain a more complete understanding of the sources of proteins in drusen. These "drusenomics" studies showed that a considerable proportion of currently identified drusen proteins is uniquely originating from the blood. A smaller, but still large fraction of drusen proteins comes from both blood and/or RPE. Only a small proportion of drusen proteins is uniquely derived from the photoreceptors or choroid. We next evaluated how drusen components may "meet, greet and stick" to each other and/or to structures like hydroxyapatite spherules to form macroscopic deposits in the sub-RPE-BL space. Finally, we discuss implications of our findings with respect to the previously proposed homology between drusenogenesis in AMD and plaque formation in atherosclerosis.