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

Retina-directed gene therapy: Achievements and remaining challenges

Gene therapy is an innovative medical approach that offers new treatment options for congenital and acquired diseases by transferring, correcting, inactivating or regulating genes to supplement, replace or modify a gene function. The approval of voretigene neparvovec (Luxturna), a gene therapy for RPE65-associated retinopathy, has marked a milestone for the field of retinal gene therapy, but has also helped to accelerate the development of gene therapies for genetic diseases affecting other organs. Voretigene neparvovec is a vector based on adeno-associated virus (AAV) that delivers a functional copy of RPE65 to supplement the missing function of this gene. The AAV-based gene delivery has proven to be versatile and safe for the transfer of genetic material to retinal cells. However, challenges remain in treating additional inherited as well as acquired retinopathies with this technology. Despite the high level of activity in this field, no other AAV gene therapy for retinal diseases has been approved since voretigene neparvovec. Ongoing research focuses on overcoming the current restraints through innovative strategies like AAV capsid engineering, dual-AAV vector systems, or CRISPR/Cas-mediated genome editing. Additionally, AAV gene therapy is being explored for the treatment of complex acquired diseases like age-related macular degeneration (AMD) and diabetic retinopathy (DR) by targeting molecules involved in the pathobiology of the degenerative processes. This review outlines the current state of retinal gene therapy, highlighting ongoing challenges and future directions.

Differential Analysis of Core Complement Components Expression and Localization Across Rodent, Non-Human Primate, and Human Ocular Tissues

Age-related macular degeneration (AMD) is a leading cause of blindness. Genetic and pathophysiological studies have implicated that complement pathway dysfunction is a key contributor to progressive vision loss in AMD. Though the association between complement and AMD is recognized, numerous anti-complement therapeutics that had been tested in rodent model systems had limited success in clinical trials. Understanding complement factor production and site of action in ocular pathophysiology is critical for the development of efficacious therapeutics. However, our limited understanding of how these aspects of complement biology vary across species restricts our ability to predict clinical outcomes from studies using animal models. Here, we integrated transcriptomic and immunohistochemical assays to understand the expression and localization of core complement components (complement factor H (FH), complement 3 (C3), and complement 5 (C5)) between ocular tissues of rodent, non-human primate, and human species. We found that complement distribution varied significantly across the studied species, with the most striking differences observed in the FH. While rodents expressed Cfh, an alternative pathway inhibitor, mainly in the RPE, CFH expression in primate eyes was primarily confined to the choroid. These differences were consistent at the protein level, with rodent FH localized in the RPE and primate FH within the choriocapillaris, choroid and sclera. Regarding C5, a terminal complement pathway component, we observed minimal ocular mRNA levels in all three species. However, we observed detectable protein levels in the RPE in rodents and the choroid in humans. Next, C3 mRNA transcripts and C3 protein exhibited similar distribution in the choroid in both rodent and primate eyes. Together, our findings highlight key differences and similarities between rodent and primate complement biology that may offer insights into the translatability of animal models and inform the design of effective therapeutics.

Roles of MASP-1 and MASP-3 in the development of retinal degeneration in a murine model of dry age-related macular degeneration

Complement is activated through the three different pathways, which are the classical (CP), lectin (LP), and alternative pathways (AP). Complement activation functions to eliminate invading pathogens, whereas dysregulation of complement activation can induce inflammatory disorders such as age-related macular degeneration (AMD). In retinal degeneration induced by sodium iodate (NaIO3), a murine model of dry AMD (also called atrophic AMD), it has been suggested that the AP and CP are involved in the disease development. On the other hand, the role of the LP in the development of AMD remains unclear. In the current study, we generated murine dry AMD model with NaIO3 using mice deficient for mannose-binding lectin-associated serine protease (MASP)-1 and/or MASP-3, which are required for the LP and AP activation, respectively. Wild-type (WT) C57BL/6J mice showed retinal degeneration, including depigmentation and disruption of the retinal pigment epithelium (RPE), atrophy of the photoreceptor layer (PL), and thinning of the outer nuclear layer (ONL) after NaIO3 injection. In contrast, those pathological changes after NaIO3 injection were significantly attenuated in MASP-1-deficient (MASP-1-/-), MASP-3-deficient (MASP-3-/-), and MASP-1/3-double deficient (MASP-1/3-/-) mice. These results indicate that both MASP-1 and MASP-3 play a role in photoreceptor degeneration in the NaIO3-induced murine dry AMD model. In addition, photoreceptor cell death and retinal C3 activation were observed in NaIO3-injected WT mice, whereas those pathological changes were significantly attenuated in NaIO3-injected MASP-3-/- and MASP-1/3-/- mice. On the other hand, those pathological changes in NaIO3-injected MASP-1-/- mice were comparable to those in NaIO3-injected WT mice. Taken together, our results indicate that MASP-3 plays a pivotal role in C3 activation in the retina most likely via activation of the AP leading to the development of retinal degeneration in the NaIO3-induced murine dry AMD model. Our results also indicate that MASP-1 plays a role in the development of NaIO3-induced retinal degeneration in this murine model, although it remains unclear whether its role in the retinal degeneration is through the LP activation.

C3aR1-Deletion Delays Retinal Degeneration in a White-Light Damage Mouse Model

Purpose

In the aging retina, persistent activation of microglia is known to play a key role in retinal degenerative diseases like age-related macular degeneration (AMD). Furthermore, dysregulation of the alternative complement pathway is generally accepted as the main driver for AMD disease progression and microglia are important producers of local complement and are equipped with complement receptors themselves. Here, we investigate the involvement of anaphylatoxin signaling, predominantly on Iba1+ cell activity, in light-induced retinal degeneration as a model for dry AMD, using anaphylatoxin receptor knockout (KO) mice.

Methods

Bright white light with an intensity of 10,000 lux was applied for 30 minutes to complement component 3a receptor 1 (C3ar1) or complement component 5a receptor 1 (C5ar1) KO and wildtype (WT) mice. Analyses of transcriptome changes and migration activity of Iba1+ cells as well as retinal thickness were performed 4 days after light exposure.

Results

Full body KO mice of either C3aR1 or C5aR1 were tested, but none led to mitigated migration of Iba1+ cells to the subretinal space or decreased expression of complement factors after light damage compared to WT mice. However, a partial rescue of retinal thickness was shown in C3aR1 KO mice, which was mirrored by significant less membrane attack complex (MAC) occurrence in the outer retina.

Conclusions

We conclude that deletion of the anaphylatoxin receptor C3aR1 cannot modulate mononuclear phagocytes but diminishes retinal degeneration through interference with the complement pathway and thus decreased MAC assembling. C3aR1-targeted therapy may be considered for patients with dry AMD.

Cellular Senescence: An Emerging Player in the Pathogenesis of AMD

Age-related macular degeneration (AMD) is the leading cause of blindness in the aged population. The accumulation of abnormal extracellular drusen deposits between the retinal pigment epithelium (RPE) and Bruch's membrane is a significant driver of AMD pathology. Drusen deposition leads to the degeneration of RPE cells and, subsequently, photoreceptors, driving the disease to its advanced stages and ultimately resulting in complete vision loss. Although the exact mechanisms underlying the AMD pathogenesis are not fully understood, it is hypothesized that the disease begins with the dysfunction of the RPE, triggering the complement and pro-inflammatory cascade. Over the last decade, new findings have implicated the involvement of cellular senescence (CS) in the pathology of age-related disorders. Specifically for AMD, evidence suggests that the senescence of RPE cells may play a role in the pathogenesis of the disease. In this review, we discuss the potential role of senescence in the onset and progression of AMD and propose potential therapeutic interventions that could be developed by targeting senescence.

Genotype-Phenotype Correlations and Genetic Risk Assessment in Age-Related Macular Degeneration

Age-related macular degeneration (AMD), the leading cause of irreversible vision loss in the elderly, presents researchers and clinicians with a complex challenge due to its multifaceted etiology and phenotype. The difficulty in developing effective treatments, especially for atrophic AMD, is an ongoing concern. Genetics plays a significant role in AMD's pathogenesis, with 52 variants in 34 loci linked to AMD based on a genome-wide association study. The association of genetic burden to the phenotypic and progression features of AMD is a current focus in the field. This perspective presents available information on phenotype-genotype correlations in AMD and on future directions in AMD genetic research which may be further corroborated with specific phenotypes and progression patterns to eventually develop personalized follow-up and therapeutic strategies.

Detection of Geographic Atrophy Guided by Optical Coherence Tomography Sub-RPE Illumination Analysis in Patients With Intermediate Age-Related Macular Degeneration

Purpose: To evaluate the prevalence of geographic atrophy (GA) lesions in patients with a diagnosis of intermediate age-related macular degeneration (iAMD). Methods: A retrospective cross-sectional study was performed of patients with an International Classification of Diseases, 10th Revision, diagnosis of iAMD. The primary outcome was the percentage of eyes diagnosed with iAMD with an undocumented GA lesion identified on imaging. Multiple logistic regression was used to assess risk factors for atrophic lesions in patients with iAMD. Results: The study included 690 eyes of 428 patients with a diagnosis of iAMD. The mean age was 79.4 ± 8.4 years, and 66.3% of patients were women. Forty-nine eyes (7.1%) were graded as having GA lesions, and 34% of these eyes had foveal involvement. The mean visual acuity (VA) was better in patients without GA lesions than in patients with GA lesions (72.9 ± 12.9 letters vs 66.4 ± 13.8 letters; P = .001). No systemic comorbidity was associated with an increased risk of GA lesions in this cohort. Conclusions: A notable proportion of eyes diagnosed with iAMD by eye care providers had underlying GA lesions in this real-world cohort. The use of optical coherence tomography as an adjunctive tool helped increase the detection of early GA in these patients.

Complement-targeted therapeutics: Are we there yet, or just getting started?

Therapeutic interventions in the complement system, a key immune-inflammatory mediator and contributor to a broad range of clinical conditions, have long been considered important yet challenging or even unfeasible to achieve. Almost 20 years ago, a spark was lit demonstrating the clinical and commercial viability of complement-targeted therapies. Since then, the field has experienced an impressive expansion of targeted indications and available treatment modalities. Currently, a dozen distinct complement-specific therapeutics covering several intervention points are available in the clinic, benefiting patients suffering from eight disorders, not counting numerous clinical trials and off-label uses. Observing this rapid rise of complement-targeted therapy from obscurity to mainstream with amazement, one might ask whether the peak of this development has now been reached or whether the field will continue marching on to new heights. This review looks at the milestones of complement drug discovery and development achieved so far, surveys the currently approved drug entities and indications, and ventures a glimpse into the future advancements yet to come.

Intraocular complement activation is independent of systemic complement activation and is related to macular vascular remodelling in retinal vein occlusion

BACKGROUND

Retinal vein occlusion (RVO) is a major cause of vision loss. The pathogenesis remains poorly defined although inflammation is known to play a critical role. In this study, we investigated the levels of complement proteins in the aqueous humour and plasma of RVO participants and the relationship between complement levels and retinal pathologies.

METHODS

The plasma and aqueous humour were collected from 20 treatment-naive RVO and 20 cataract patients. Retinal lesions were examined by fundus stereoscopy and optical coherence tomography angiography. The levels of C1q, C2, C4, C4b, C3, C3b/iC3b, C5, C5a, CFB, CFD, CFI, CFH, and MBL in the plasma and aqueous humour were measured using the Luminex® x MAP® multiplex assay.

RESULTS

RVO patients had significantly higher levels of C4, C4b, C3b/iC3b, CFB, and CFH in the plasma and aqueous humour compared to controls. The aqueous levels of C1q, C2, C5, C5a, and MBL were also significantly higher in RVO patients than in controls. CRVO patients had higher intraocular levels of C1q, C4, C5, CFI, CFH, and MBL than BRVO patients. C5a was below the detectable limit in the plasma in 18 cataracts and 16 RVO participants. The intraocular levels of C5a positively correlated with C1q, C2, C4, C3, C5, CFB, CFH, and MBL. The intraocular levels of CFD, CFI and MBL positively correlated with CRT, and the levels of C2, C3, C5, CFB, and MBL negatively correlated with the size of the foveal avascular zone. The plasma levels of C4b, C3b/iC3b, and CFD positively correlated with their counterparts in the aqueous humour in cataracts but not in RVO patients. The ratios of aqueous humour/plasma of C1q, C4, C4b, C3b/iC3b, C5, CFB, CFD, CFI, and CFH in the RVO patients were significantly higher than those in the cataract patients.

DISCUSSION AND CONCLUSIONS

The intraocular complement activation in RVO is mediated by the classical and the alternative pathways and is largely independent of systemic complement activation. Intraocular complement activation may be related to retinal oedema and vascular remodeling in RVO patients.

Efficacy and safety of complement inhibitors in patients with geographic atrophy associated with age-related macular degeneration: a network meta-analysis of randomized controlled trials

Importance

Clinical trials in recent years have shown significant effectiveness of complement inhibitors for geographic atrophy (GA) treatment. Two complement inhibitor drugs have been approved by the Food and Drug Administration (FDA).

Objective

to compare and rank the different complement inhibitors in the treatment of GA secondary to age-related macular degeneration (AMD).

Data sources

A systematic literature search was conducted in the Cochrane Central, Web of Science Core Collection, PubMed, LWW Medical Journals, ClinicalTrials.gov, and WHO ICTRP from inception to October 2023.

Study selection

All randomized clinical trials evaluating the effectiveness of complement inhibitors in patients diagnosed with secondary GA in AMD were identified.

Data extraction and synthesis

This study followed Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) network meta-analysis Checklist of Items and the Cochrane Risk of Bias Assessment Tool for assessing the study quality. Multiple authors independently coded all titles and abstracts, reviewed full-text articles against the inclusion and exclusion criteria, and resolved all discrepancies by consensus. Random-effects network meta-analyses were applied. Bayesian network meta-analysis was performed using the BUGSnet package in R (4.2.0).

Main outcomes and measures

The primary efficacy outcome was the change in GA lesion size (mm2) from baseline to month 12. The secondary efficacy outcome was the mean change in best-corrected visual acuity (BCVA) from baseline to month 12. Safety outcome measures included the number of subjects with serious adverse events (SAEs) and macular neovascularization (MNV).

Results

Ten randomized controlled trials including 4,405 participants and five complement inhibitors were identified. Comparison with sham and SUCRA analysis showed that avacincaptad pegol 2 mg (MD: -0.58, 95% CrI: -0.97 to -0.18, SUCRA: 93.55), pegcetacoplan monthly (MD: -0.38, 95% CrI: -0.57 to -0.20, SUCRA: 81.37), and pegcetacoplan every other month (MD: -0.30, 95% CrI: -0.49 to -0.11, SUCRA: 70.16) have significant changes in GA lesion reduction. No treatments showed significant changes in BCVA and SAE compared with sham. Pegcetacoplan monthly (OR: 4.30, 95% CrI: 1.48-16.72) increased the risk of MNV. Avacincaptad pegol 2 mg demonstrated favorable outcomes in terms of SAE and MNV.

Conclusion and relevance

Avacincaptad pegol 2 mg is the most effective complement inhibitor with better safety for the treatment of GA secondary to AMD.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022351515, Identifier PROSPERO CRD42022351515.

Comparative analysis of In vivo endothelial cell translatomes across central nervous system vascular beds

Endothelial cells (ECs) display organ- and tissue-specific heterogeneity. In the eye, the retinal and choroidal vascular beds are distinct networks with different molecular and morphological properties that serve location-specific functions, i.e., the former maintaining a tight barrier and the latter, a permeable fenestrated vasculature. Given that retinal health critically relies on the function of these vascular beds and that their dysfunction is implicated in a variety of retinal diseases, a molecular understanding of both physiological and pathophysiological characteristics of these distinct vasculatures is critical. Given their interspersed anatomic distribution among parenchymal cells, the study of EC gene expression, in vivo, has been hampered by the challenge of isolating pure populations of ocular ECs in sufficient quantities for large-scale transcriptomics. To address this challenge, we present a methodological and analytical workflow to facilitate inter-tissue comparisons of the in vivo EC translatome isolated from choroid, retina, and brain using the Cre-inducible NuTRAP flox construct and two widely-used endothelial Cre mouse lines: constitutive Tie2-Cre and tamoxifen-inducible Cdh5-CreERT2. For each Cre line, inter-tissue comparison of TRAP-RNAseq enrichment (TRAP-isolated translatome vs input transcriptome) showed tissue-specific gene enrichments with differential pathway representation. For each mouse model, inter-tissue comparison of the EC translatome (choroid vs brain, choroid vs retina, and brain vs retina) showed over 50% overlap of differentially expressed genes (DEGs) between the three paired comparisons, with differential pathway representation for each tissue. Pathway analysis of DEGs in the Cdh5-NuTRAP vs Tie2-NuTRAP comparison for retina, choroid, and brain predicted inhibition of processes related to myeloid cell function and activation, consistent with more specific targeting of ECs in the Cdh5-NuTRAP than in the Tie2-NuTRAP model which also targets hematopoietic progenitors giving rise to immune cells. Indeed, while TRAP enriches for EC transcripts in both models, myeloid transcripts were also captured in the Tie2-NuTRAP model which was confirmed using cell sorting. We suggest experimental/analytical considerations should be taken when selecting Cre-lines to target ECs.

Ophthalmic Use of Targeted Biologics in the Management of Intraocular Diseases: Current and Emerging Therapies

BACKGROUND

Monoclonal antibodies (mAbs) have demonstrated substantial potential in the treatment of intraocular diseases. This review aimed to comprehensively evaluate the applications, efficacy, and safety of mAbs in the management of intraocular conditions.

METHODS

A comprehensive literature search was conducted in major medical databases through July 2024. Relevant studies on monoclonal antibodies for intraocular diseases were included. Two independent researchers screened the literature, extracted data, and assessed study quality. Cost-effectiveness analyses were also reviewed.

RESULTS

Anti-vascular endothelial growth factor (VEGF) antibodies, such as bevacizumab, ranibizumab, and aflibercept, showed significant therapeutic effects in neovascular age-related macular degeneration (NVAMD), diabetic macular edema (DME), and retinal vein occlusion (RVO). Tumor necrosis factor-alpha (TNF-α) inhibitors demonstrated promising results in treating noninfectious uveitis. Complement system-targeted therapies like pegcetacoplan offered new options for geographic atrophy. Anti-VEGF antibodies showed potential in managing retinopathy of prematurity (ROP). However, challenges persist, including high costs, potential drug resistance, and limited long-term safety data in certain scenarios.

CONCLUSIONS

Monoclonal antibodies are vital for treating intraocular diseases, but continuous innovation and rigorous clinical evaluation are essential. Future research should focus on developing novel delivery systems, exploring combination therapies, conducting long-term follow-up studies, and investigating personalized treatment strategies to provide safer, more effective, and cost-effective therapeutic solutions.

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

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

JR5558 mice are a reliable model to investigate subretinal fibrosis

Subretinal fibrosis is a major untreatable cause of poor outcomes in neovascular age-related macular degeneration. Mouse models of subretinal fibrosis all possess a degree of invasiveness and tissue damage not typical of fibrosis progression. This project characterises JR5558 mice as a model to study subretinal fibrosis. Fundus and optical coherence tomography (OCT) imaging was used to non-invasively track lesions. Lesion number and area were quantified with ImageJ. Retinal sections, wholemounts and Western blots were used to characterise alterations. Subretinal lesions expand between 4 and 8 weeks and become established in size and location around 12 weeks. Subretinal lesions were confirmed to be fibrotic, including various cell populations involved in fibrosis development. Müller cell processes extended from superficial retina into subretinal lesions at 8 weeks. Western blotting revealed increases in fibronectin (4 wk and 8 wk, p < 0.001), CTGF (20 wks, p < 0.001), MMP2 (12 wks and 20 wks p < 0.05), αSMA (12 wks and 20 wks p < 0.05) and GFAP (8 wk and 12 wk, p ≤ 0.01), consistent with our immunofluorescence results. Intravitreal injection of Aflibercept reduced subretinal lesion growth. Our study provides evidence JR5558 mice have subretinal fibrotic lesions that grow between 4 and 8 weeks and confirms this line to be a good model to study subretinal fibrosis development and assess treatment options.

Genome-wide sequencing identified extrachromosomal circular DNA as a transcription factor-binding motif of the senescence genes that govern replicative senescence in human mesenchymal stem cells

Introduction

Mesenchymal stem cells (MSCs) have long been postulated as an important source cell in regenerative medicine. During subculture expansion, mesenchymal stem cell (MSC) senescence diminishes their multi-differentiation capabilities, leading to a loss of therapeutic potential. Up to date, the extrachromosomal circular DNAs (eccDNAs) have been demonstrated to be involved in senescence but the roles of eccDNAs during MSC.

Methods

Here we explored eccDNA profiles in human bone marrow MSCs (BM-MSCs). EccDNA and mRNA was purified and sequenced, followed by quantification and functional annotation. Moreover, we mapped our datasets with the downloading enhancer and transcription factor-regulated genes to explore the potential role of eccDNAs.

Results

Sequentially, gene annotation analysis revealed that the majority of eccDNA were mapped in the intron regions with limited BM-MSC enhancer overlaps. We discovered that these eccDNA motifs in senescent BMSCs acted as motifs for binding transcription factors (TFs) of senescence-related genes.

Discussion

These findings are highly significant for identifying biomarkers of senescence and therapeutic targets in mesenchymal stem cells (MSCs) for future clinical applications. The potential of eccDNA as a stable therapeutic target for senescence-related disorders warrants further investigation, particularly exploring chemically synthesized eccDNAs as transcription factor regulatory elements to reverse cellular senescence.

Potential role of CTSS in AMDImmune modulatory and anti-angiogenic effects of cathepsin S knockdown in ARPE-19 cells

We aimed to determine the role of cathepsin S (CTSS) in modulating oxidative stress-induced immune and inflammatory reactions and angiogenesis in age-related macular degeneration. Human retinal pigment epithelium cells line ARPE-19 (immature) were maintained and treated with H2O2. The expression of CTSS, inflammatory cytokines, and complement factors induced by oxidative stress was compared between cells incubated without (control) and with CTSS knockdown (using small interfering ribonucleic acid; siRNA). To evaluate the role of CTSS in angiogenesis, we assayed tube formation using human umbilical vein endothelial cells and conditioned medium from ARPE-19 cells. We also used a mouse model of laser-induced choroidal neovascularization. CTSS levels were higher in ARPE-19 cells treated with H2O2 than in control cells. Oxidative stress-induced CTSS resulted in significantly elevated transcription of nuclear factor kappa B-dependent inflammatory cytokines, complement factors C3a and C5a, membrane attack complex (C5b-9), and C3a and C5a receptors. siRNA-mediated knockdown of CTSS reduced the number of inflammatory signals. Furthermore, oxidative stress-induced CTSS regulated the expression of peroxisome proliferator-activated receptor γ and vascular endothelial growth factor A/Akt serine/threonine kinase family signaling, which led to angiogenesis. Tube formation assays and mouse models of choroidal neovascularization revealed that CTSS knockdown ameliorated angiogenesis in vitro and in vivo. The present findings suggest that CTSS modulates the complement pathway, inflammatory reactions, and neovascularization, and that CTSS knockdown induces potent immunomodulatory effects. Hence, it could be a promising target for the prevention and treatment of early- and late-stage age-related macular degeneration.

Genetic Insights into Age-Related Macular Degeneration

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

Effect of Low-Dose Aspirin on the Course of Age-Related Macular Degeneration: A Secondary Analysis of the ASPREE Randomized Clinical Trial

Importance

Age-related macular degeneration (AMD) is the leading cause of irreversible vision loss in old age. There is no proven intervention to prevent AMD and, apart from lifestyle, nutritional, and supplement advice, there is no intervention to delay its progression.

Objective

To determine the impact of long-term low-dose aspirin on the incidence and progression of AMD.

Design, Setting and Participants

The Aspirin in Reducing Events in the Elderly-AMD (ASPREE-AMD) study was an Australian-based substudy of the ASPREE trial, a multicenter, international, randomized, double-masked, placebo-clinical trial investigating the efficacy of low-dose aspirin in prolonging disability-free survival among older individuals. Retinal photography was conducted at baseline from March 2010 to January 2015, then 3 and 5 years after randomization. AMD status was determined using color retinal images and treatment records. Australian participants in ASPREE aged 70 years and older without dementia, independence-limiting physical disability, cardiovascular disease, or chronic illness limiting 5-year survival and with gradable retinal images at baseline were included. Data were analyzed from December 2022 to December 2023.

Interventions

Aspirin (100 mg daily, enteric coated) or placebo.

Main Outcomes and Measures

Incidence of AMD and progression from early/intermediate to late AMD. Outcomes were analyzed by modified intention-to-treat analysis.

Results

A total of 4993 participants were enrolled in this substudy. Baseline characteristics were similar between groups. At the time of sponsor-determined trial termination, retinal follow-up data were available for 3208 participants, 3171 of whom were analyzed for AMD incidence and progression, with a median (IQR) age of 73.5 (71.5-76.4) years and even sex distribution (1619 [51%] female). Median (IQR) follow-up time was 3.1 (3.0-3.5) years. Cumulative AMD incidence was 195 of 1004 (19.4%) in the aspirin group and 187 of 979 (19.1%) in the placebo group (relative risk [RR], 1.02; 95% CI, 0.85-1.22; P = .86). Cumulative progression from early/intermediate AMD to late AMD was observed in 14 of 615 (2.3%) participants in the aspirin group and 18 of 573 (3.1%) in the placebo group (RR, 0.72; 95% CI, 0.36-1.44; P = .36).

Conclusions and Relevance

In this trial, low-dose aspirin administered for 3 years did not affect the incidence of AMD. The evidence was weaker for progression of AMD due to low number of progressed cases. Overall, these results do not support suggestion that low-dose daily aspirin prevents the development or progression of AMD.

Trial Registration

anzctr.org Identifier: ACTRN12613000755730.

The Complement System as a Therapeutic Target in Retinal Disease

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

The role of mannose-binding lectin (MBL) in diabetic retinopathy: A scoping review

Diabetes mellitus (DM) is a chronic systemic disease characterized by a multifactorial nature, which may lead to several macro and microvascular complications. Diabetic retinopathy (DR) is one of the most severe microvascular complications of DM, which can result in permanent blindness. The mechanisms involved in the pathogenesis of DR are multiple and still poorly understood. Factors such as dysregulation of vascular regeneration, oxidative and hyperosmolar stress in addition to inflammatory processes have been associated with the pathogenesis of DR. Furthermore, compelling evidence shows that components of the immune system, including the complement system, play a relevant role in the development of the disease. Studies suggest that high concentrations of mannose-binding lectin (MBL), an essential component of the complement lectin pathway, may contribute to the development of DR in patients with DM. This review provides an update on the possible role of the complement system, specifically the lectin pathway, in the pathogenesis of DR and discusses the potential of MBL as a non-invasive biomarker for both, the presence and severity of DR, in addition to its potential as a therapeutic target for intervention strategies.

The complement pathway as a therapeutic target for neovascular age-related macular degeneration-mediated subretinal fibrosis

Neovascular age-related macular degeneration (nAMD) is the leading cause of blindness in the elderly in developed countries. Intravitreal injection of VEGF inhibitors is the mainstream therapy for nAMD, although nearly 50% of the patients do not respond or respond poorly to the therapy. One of the main reasons for the poor outcome of the therapy is the development of subretinal macular fibrosis, a process of excessive deposition of extracellular matrix proteins around the diseased blood vessels. Currently, there is no medication to prevent or treat the condition. Here, we discussed recent advances in the pathogenesis of nAMD-mediated macular fibrosis, with a focus on the role of the complement system. We further proposed approaches to target the complement system for the management of macular fibrosis and highlighted the area of further research for future clinical applications of complement-based therapy.

Age-Related Macular Degeneration: A Disease of Cellular Senescence and Dysregulated Immune Homeostasis

Age-related macular degeneration (AMD) is a degenerative ocular disease primarily affecting central vision in the elderly. Its pathogenesis is complex, involving cellular senescence and immune homeostasis dysregulation. This review investigates the interaction between these two critical biological processes in AMD pathogenesis and their impact on disease progression. Initially, cellular senescence is analyzed, with particular emphasis on retinal damage induced by senescent retinal pigment epithelial cells. Subsequently, the occurrence of immune homeostasis dysregulation within the retina and its mechanistic role in AMD areis explored. Furthermore, the paper also discusses in detail the interplay between cellular senescence and immune responses, forming a vicious cycle that exacerbates retinal damage and may influence treatment outcomes. In summary, a deeper understanding of the interrelation between cellular senescence and immune dysregulation is vital for the developing innovative therapeutic strategies for AMD.

Crosstalk Between Microglia and Müller Glia in the Age-Related Macular Degeneration: Role and Therapeutic Value of Neuroinflammation

Age-related macular degeneration (AMD) is a progressive neurodegeneration disease that causes photoreceptor demise and vision impairments. In AMD pathogenesis, the primary death of retinal neurons always leads to the activation of resident microglia. The migration of activated microglia to the ongoing retinal lesion and their morphological transformation from branching to ameboid-like are recognized as hallmarks of AMD pathogenesis. Activated microglia send signals to Müller cells and promote them to react correspondingly to damaging stimulus. Müller cells are a type of neuroglia cells that maintain the normal function of retinal neurons, modulating innate inflammatory responses, and stabilize retinal structure. Activated Müller cells can accelerate the progression of AMD by damaging neurons and blood vessels. Therefore, the crosstalk between microglia and Müller cells plays a homeostatic role in maintaining the retinal environment, and this interaction is complicatedly modulated. In particular, the mechanism of mutual regulation between the two glia populations is complex under pathological conditions. This paper reviews recent findings on the crosstalk between microglia and Müller glia during AMD pathology process, with special emphasis on its therapeutic potentials.

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

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

Tumoral C2 Regulates the Tumor Microenvironment by Increasing the Ratio of M1/M2 Macrophages and Tertiary Lymphoid Structures to Improve Prognosis in Melanoma

Immunotherapy is an essential therapy for individuals with advanced melanoma. However, not all patients respond to such treatment due to individual differences. We conducted a multidimensional analysis using transcriptome data from our center, as well as publicly available databases. We found that effective nivolumab treatment led to an upregulation of C2 levels, and higher levels following treatment are indicative of a good outcome. Through bioinformatics analyses and immunofluorescence, we identified a correlation between C2 and M1 macrophages. To further investigate the role of C2 in melanoma, we constructed subcutaneous tumorigenic models in C57BL/6 mice. The tumors in the C2 overexpression group exhibited significantly smaller sizes. Flow cytometric analysis of the mouse tumors demonstrated enhanced recruitment of macrophages, particularly of the M1 subtype, in the overexpression group. Moreover, single-cell RNA sequencing analysis revealed that C2-positive tumor cells exhibited enhanced communication with immune cells. We co-cultured tumor cell supernatants with macrophages in vitro and observed the induction of M1 subtype polarization. In addition, we discovered a close correlation between C2 and tertiary lymphoid structures. C2 has been demonstrated to exert a protective effect, mediated by its ability to modulate the tumor microenvironment. C2 serves as a prognostic marker for melanoma and can be employed to monitor the efficacy of immunotherapy.

Gliosis-dependent expression of complement factor H truncated variants attenuates retinal neurodegeneration following ischemic injury

Inherited, age-related, and acute retinal diseases are often exacerbated by an aberrant or excessive activity of the complement system. Consequently, cells not directly affected by an acute event or genetic variants may degenerate, resulting in enhanced visual impairment. The therapeutic potential of supplementation of complement factor H (FH), a key regulator of the complement cascade, is therefore particularly promising in the context of retinal diseases caused by complement activation. In this study, we engineered adeno-associated viruses (AAVs) containing sequences of two truncated human FH variants. The expression of these variants was regulated by the glial fibrillary acidic protein (GFAP) promoter, which is selectively active in gliotic Müller cells. Both FH variants consisted of FH domains 19-20, which were connected to domains 1-4 and 1-7, respectively, by a polyglycine linker. These AAVs were intravitreally injected following ischemic injury of C57BL/6J mouse retinas. We observed transgene expression in gliotic Müller cells and to some extent in astrocytes. The expression correlated directly with damage severity. Interventions resulted in decreased complement activation, accelerated normalization of microglia activity and morphological improvements. Reduced levels of C3 transcripts and C3d protein in conjunction with higher transcript levels of inhibitory regulators like Cfi and Cfh, hinted at attenuated complement activity. This study demonstrates the great potential of complement regulatory gene addition therapy. With further in vivo testing it could be applied to treat a wide range of retinal diseases where no causative therapies are available.

The Role of Complement Dysregulation in Glaucoma

Glaucoma is a progressive neurodegenerative disease characterized by damage to the optic nerve that results in irreversible vision loss. While the exact pathology of glaucoma is not well understood, emerging evidence suggests that dysregulation of the complement system, a key component of innate immunity, plays a crucial role. In glaucoma, dysregulation of the complement cascade and impaired regulation of complement factors contribute to chronic inflammation and neurodegeneration. Complement components such as C1Q, C3, and the membrane attack complex have been implicated in glaucomatous neuroinflammation and retinal ganglion cell death. This review will provide a summary of human and experimental studies that document the dysregulation of the complement system observed in glaucoma patients and animal models of glaucoma driving chronic inflammation and neurodegeneration. Understanding how complement-mediated damage contributes to glaucoma will provide opportunities for new therapies.

Seeing the Future: A Review of Ocular Therapy

Ocular diseases present a unique challenge and opportunity for therapeutic development. The eye has distinct advantages as a therapy target given its accessibility, compartmentalization, immune privilege, and size. Various methodologies for therapeutic delivery in ocular diseases are under investigation that impact long-term efficacy, toxicity, invasiveness, and delivery range. While gene, cell, and antibody therapy and nanoparticle delivery directly treat regions that have been damaged by disease, they can be limited in the duration of the therapeutic delivery and have a focal effect. In contrast, contact lenses and ocular implants can more effectively achieve sustained and widespread delivery of therapies; however, they can increase dilution of therapeutics, which may result in reduced effectiveness. Current therapies either offer a sustained release or a broad therapeutic effect, and future directions should aim toward achieving both. This review discusses current ocular therapy delivery systems and their applications, mechanisms for delivering therapeutic products to ocular tissues, advantages and challenges associated with each delivery system, current approved therapies, and clinical trials. Future directions for the improvement in existing ocular therapies include combination therapies, such as combined cell and gene therapies, as well as AI-driven devices, such as cortical implants that directly transmit visual information to the cortex.

Role of immune inflammation regulated by macrophage in the pathogenesis of age-related macular degeneration

Age-related macular degeneration (AMD) can lead to irreversible impairment of visual function, and the number of patients with AMD has been increasing globally. The immunoinflammatory theory is an important pathogenic mechanism of AMD, with macrophages serving as the primary inflammatory infiltrating cells in AMD lesions. Its powerful immunoinflammatory regulatory function has attracted considerable attention. Herein, we provide an overview of the involvement of macrophage-regulated immunoinflammation in different stages of AMD. Additionally, we summarize novel therapeutic approaches for AMD, focusing on targeting macrophages, such as macrophage/microglia modulators, reduction of macrophage aggregation in the subretinal space, modulation of macrophage effector function, macrophage phenotypic alterations, and novel biomimetic nanocomposites development based on macrophage-associated functional properties. We aimed to provide a basis and reference for the further exploration of AMD pathogenesis, developmental influences, and new therapeutic approaches.

Recent Advances in Our Understanding of Age-Related Macular Degeneration: Mitochondrial Dysfunction, Redox Signaling, and the Complement System

Age-related macular degeneration (AMD) is a prevalent degenerative disorder of the central retina, which holds global significance as the fourth leading cause of blindness. The condition is characterized by a multifaceted pathophysiology that involves aging, oxidative stress, inflammation, vascular dysfunction, and complement activation. The complex interplay of these factors contributes to the initiation and progression of AMD. Current treatments primarily address choroidal neovascularization (CNV) in neovascular AMD. However, the approval of novel drug therapies for the atrophic and more gradual variant, known as geographic atrophy (GA), has recently occurred. In light of the substantial impact of AMD on affected individuals' quality of life and the strain it places on healthcare systems, there is a pressing need for innovative medications. This paper aims to provide an updated and comprehensive overview of advancements in our understanding of the etiopathogenesis of AMD. Special attention will be given to the influence of aging and altered redox status on mitochondrial dynamics, cell death pathways, and the intricate interplay between oxidative stress and the complement system, specifically in the context of GA. Additionally, this review will shed light on newly approved therapies and explore emerging alternative treatment strategies in the field. The objective is to contribute to the ongoing dialogue surrounding AMD, offering insights into the latest developments that may pave the way for more effective management and intervention approaches.

AAV for Gene Therapy in Ocular Diseases: Progress and Prospects

Owing to the promising therapeutic effect and one-time treatment advantage, gene therapy may completely change the management of eye diseases, especially retinal diseases. Adeno-associated virus (AAV) is considered one of the most promising viral gene delivery tools because it can infect various types of tissues and is considered as a relatively safe gene delivery vector. The eye is one of the most popular organs for gene therapy, since its limited volume is suitable for small doses of AAV stably transduction. Recently, an increasing number of clinical trials of AAV-mediated gene therapy are underway. This review summarizes the biological functions of AAV and its application in the treatment of various ocular diseases, as well as the characteristics of different AAV delivery routes in clinical applications. Here, the latest research progresses in AAV-mediated gene editing and silencing strategies to modify that the genetic ocular diseases are systematically outlined, especially by base editing and prime editing. We discuss the progress of AAV in ocular optogenetic therapy. We also summarize the application of AAV-mediated gene therapy in animal models and the difficulties in its clinical transformation.

Lipofuscin, Its Origin, Properties, and Contribution to Retinal Fluorescence as a Potential Biomarker of Oxidative Damage to the Retina

Lipofuscin accumulates with age as intracellular fluorescent granules originating from incomplete lysosomal digestion of phagocytosed and autophagocytosed material. The purpose of this review is to provide an update on the current understanding of the role of oxidative stress and/or lysosomal dysfunction in lipofuscin accumulation and its consequences, particularly for retinal pigment epithelium (RPE). Next, the fluorescence of lipofuscin, spectral changes induced by oxidation, and its contribution to retinal fluorescence are discussed. This is followed by reviewing recent developments in fluorescence imaging of the retina and the current evidence on the prognostic value of retinal fluorescence for the progression of age-related macular degeneration (AMD), the major blinding disease affecting elderly people in developed countries. The evidence of lipofuscin oxidation in vivo and the evidence of increased oxidative damage in AMD retina ex vivo lead to the conclusion that imaging of spectral characteristics of lipofuscin fluorescence may serve as a useful biomarker of oxidative damage, which can be helpful in assessing the efficacy of potential antioxidant therapies in retinal degenerations associated with accumulation of lipofuscin and increased oxidative stress. Finally, amendments to currently used fluorescence imaging instruments are suggested to be more sensitive and specific for imaging spectral characteristics of lipofuscin fluorescence.

Recent Developments in Gene Therapy for Neovascular Age-Related Macular Degeneration: A Review

Age-related macular degeneration (AMD) is a complex and multifactorial disease and a leading cause of irreversible blindness in the elderly population. The anti-vascular endothelial growth factor (anti-VEGF) therapy has revolutionized the management and prognosis of neovascular AMD (nAMD) and is currently the standard of care for this disease. However, patients are required to receive repeated injections, imposing substantial social and economic burdens. The implementation of gene therapy methods to achieve sustained delivery of various therapeutic proteins holds the promise of a single treatment that could ameliorate the treatment challenges associated with chronic intravitreal therapy, and potentially improve visual outcomes. Several early-phase trials are currently underway, evaluating the safety and efficacy of gene therapy for nAMD; however, areas of controversy persist, including the therapeutic target, route of administration, and potential safety issues. In this review, we assess the evolution of gene therapy for nAMD and summarize several preclinical and early-stage clinical trials, exploring challenges and future directions.

Avacincaptad pegol for geographic atrophy secondary to age-related macular degeneration: 18-month findings from the GATHER1 trial

BACKGROUND/OBJECTIVES

To assess the safety and efficacy of avacincaptad pegol (ACP), a C5 inhibitor, for geographic atrophy (GA) secondary to age-related macular degeneration (AMD) over an 18-month treatment course.

SUBJECTS/METHODS

This study was an international, prospective, randomized, double-masked, sham-controlled, phase 2/3 clinical trial that consisted of 2 parts. In part 1, 77 participants were randomized 1:1:1 to receive monthly intravitreal injections of ACP 1 mg, ACP 2 mg, or sham. In part 2, 209 participants were randomized 1:2:2 to receive monthly ACP 2 mg, ACP 4 mg, or sham. The mean rate of change of GA over 18 months was measured by fundus autofluorescence.

RESULTS

Compared with their respective sham cohorts, monthly ACP treatment reduced the mean GA growth (square root transformation) over 18 months by 28.1% (0.168 mm, 95% CI [0.066, 0.271]) for the 2 mg cohort and 30.0% (0.167 mm, 95% CI [0.062, 0.273]) for the 4 mg cohort. ACP treatment was generally well tolerated over 18 months, with most ocular adverse events (AEs) related to the injection procedure. Macular neovascularization (MNV) was more frequent in both 2 mg (11.9%) and 4 mg (15.7%) cohorts than their respective sham control groups (2.7% and 2.4%).

CONCLUSIONS

Over this 18-month study, ACP 2 mg and 4 mg showed continued reductions in the progression of GA growth compared to sham and continued to be generally well tolerated. A pivotal phase 3 GATHER2 trial is currently underway to support the efficacy and safety of ACP as a potential treatment for GA.

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

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

Treating patients with geographic atrophy: are we there yet?

Geographic atrophy (GA) is a progressive degenerative disease that significantly contributes to visual impairment in individuals aged 50 years and older. The development of GA is influenced by various modifiable and non-modifiable risk factors, including age, smoking, and specific genetic variants, particularly those related to the complement system regulators. Given the multifactorial and complex nature of GA, several treatment approaches have been explored, such as complement inhibition, gene therapy, and cell therapy. The recent approval by the Food and Drug Administration of pegcetacoplan, a complement C3 inhibitor, marks a significant breakthrough as the first approved treatment for GA. Furthermore, numerous interventions are currently in phase II or III trials, alongside this groundbreaking development. In light of these advancements, this review provides a comprehensive overview of GA, encompassing risk factors, prevalence, genetic associations, and imaging characteristics. Additionally, it delves into the current landscape of GA treatment, emphasizing the latest progress and future considerations. The goal of starting this discussion is to ultimately identify the most suitable candidates for each therapy, highlight the importance of tailoring treatments to individual cases, and continue monitoring the long-term implications of these emerging interventions.

Exploring the contribution of ARMS2 and HTRA1 genetic risk factors in age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of severe irreversible central vision loss in individuals over 65 years old. Genome-wide association studies (GWASs) have shown that the region at chromosome 10q26, where the age-related maculopathy susceptibility (ARMS2/LOC387715) and HtrA serine peptidase 1 (HTRA1) genes are located, represents one of the strongest associated loci for AMD. However, the underlying biological mechanism of this genetic association has remained elusive. In this article, we extensively review the literature by us and others regarding the ARMS2/HTRA1 risk alleles and their functional significance. We also review the literature regarding the presumed function of the ARMS2 protein and the molecular processes of the HTRA1 protein in AMD pathogenesis in vitro and in vivo, including those of transgenic mice overexpressing HtrA1/HTRA1 which developed Bruch's membrane (BM) damage, choroidal neovascularization (CNV), and polypoidal choroidal vasculopathy (PCV), similar to human AMD patients. The elucidation of the molecular mechanisms of the ARMS2 and HTRA1 susceptibility loci has begun to untangle the complex biological pathways underlying AMD pathophysiology, pointing to new testable paradigms for treatment.

Therapeutic targeting of the complement system in ocular disease

The complement system is involved in the pathogenesis of several ocular diseases, providing a rationale for the investigation of complement-targeting therapeutics for these conditions. Dry age-related macular degeneration, as characterised by geographic atrophy (GA), is currently the most active area of research for complement-targeting therapeutics, with a complement C3 inhibitor approved in the United States earlier this year marking the first approved therapy for GA. This review discusses the role of complement in ocular disease, provides an overview of the complement-targeting agents currently under development for ocular conditions, and reflects on the lessons that can be learned from the preclinical investigations and clinical trials conducted in this field to date.

Brain-wide genome-wide colocalization study for integrating genetics, transcriptomics and brain morphometry in Alzheimer's disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. However, the AD mechanism has not yet been fully elucidated to date, hindering the development of effective therapies. In our work, we perform a brain imaging genomics study to link genetics, single-cell gene expression data, tissue-specific gene expression data, brain imaging-derived volumetric endophenotypes, and disease diagnosis to discover potential underlying neurobiological pathways for AD. To do so, we perform brain-wide genome-wide colocalization analyses to integrate multidimensional imaging genomic biobank data. Specifically, we use (1) the individual-level imputed genotyping data and magnetic resonance imaging (MRI) data from the UK Biobank, (2) the summary statistics of the genome-wide association study (GWAS) from multiple European ancestry cohorts, and (3) the tissue-specific cis-expression quantitative trait loci (cis-eQTL) summary statistics from the GTEx project. We apply a Bayes factor colocalization framework and mediation analysis to these multi-modal imaging genomic data. As a result, we derive the brain regional level GWAS summary statistics for 145 brain regions with 482,831 single nucleotide polymorphisms (SNPs) followed by posthoc functional annotations. Our analysis yields the discovery of a potential AD causal pathway from a systems biology perspective: the SNP chr10:124165615:G>A (rs6585827) mutation upregulates the expression of BTBD16 gene in oligodendrocytes, a specialized glial cells, in the brain cortex, leading to a reduced risk of volumetric loss in the entorhinal cortex, resulting in the protective effect on AD. We substantiate our findings with multiple evidence from existing imaging, genetic and genomic studies in AD literature. Our study connects genetics, molecular and cellular signatures, regional brain morphologic endophenotypes, and AD diagnosis, providing new insights into the mechanistic understanding of the disease. Our findings can provide valuable guidance for subsequent therapeutic target identification and drug discovery in AD.

Hyperreflective foci distribution in eyes with dry age-related macular degeneration with subretinal drusenoid deposits

PURPOSE

To investigate the distribution of hyperreflective foci (HRF) in eyes with dry age-related macular degeneration (AMD).

METHODS

We retrospectively reviewed optical coherence tomography (OCT) images of 58 dry AMD eyes presenting HRF. The distribution of HRF according to the early treatment diabetic retinopathy study area was analyzed according to the presence of subretinal drusenoid deposits (SDDs).

RESULTS

We classified 32 eyes and 26 eyes into the dry AMD with SDD group (SDD group) and dry AMD without SDD group (non-SDD group), respectively. The non-SDD group had higher prevalence and density of HRF at the fovea (65.4% and 1.71 ± 1.48) than the SDD group (37.5% and 0.48 ± 0.63, P = 0.035 and P < 0.001, respectively). However, the prevalence and density of HRF in the outer circle area of the SDD group (81.3% and 0.11 ± 0.09) were greater than those of the non-SDD group (53.8% and 0.05 ± 0.06, p = 0.025 and p = 0.004, respectively). The SDD group showed higher prevalence and mean densities of HRF in the superior and temporal area than in the non-SDD group (all, p < 0.05).

CONCLUSION

HRF distributions in dry AMD varied according to the presence of SDDs. This might support that the degenerative features may be different between dry AMD eyes with and without SDDs.

ASCEND-Eye: Rationale, design and baseline characteristics for a sub-study of the ASCEND randomised trial, exploring the effects of aspirin and omega-3 fatty acids on diabetic retinopathy and age-related macular degeneration

Background

Aspirin and omega-3 fatty acids (FAs) have potential disease-modifying roles in diabetic retinopathy (DR) and age-related macular degeneration (AMD), but randomized evidence of these effects is limited. We present the rationale and baseline characteristics of ASCEND-Eye, a sub-study of the double-blind, 2x2 factorial design, randomized placebo-controlled ASCEND (A Study of Cardiovascular Events iN Diabetes) trial of 100 mg aspirin daily and, separately, 1g omega-3 FAs daily for the primary prevention of serious cardiovascular events, in 15,480 British adults, aged 40 years or older with diabetes.

Methods

Eye events will be derived from three sources: 1) participant follow-up questionnaires from ASCEND, 2) electronic NHS Diabetic Eye Screening Programme (DESP) data and 3) responses to the National Eye Institute's Visual Function Questionnaire-25 (NEI-VFQ-25) sent to a subset of participants after the main trial ended. Analytic cohorts and outcomes relevant to these data sources are described. The primary outcome is referable diabetic eye disease, a secondary outcome is incident AMD events.

Results

Participant-reported events were ascertained for the full cohort of randomized individuals who were followed up over 7.4 years in ASCEND (n = 15,480). Linked DESP data were available for 48% of those (n = 7360), and 57% completed the NEI-VFQ-25 (n = 8839). The baseline characteristics of these three cohorts are presented.

Discussion

Establishing the risks and benefits of drugs commonly taken by people with diabetes, the elderly, or both, and finding new treatments for DR and AMD is important. ASCEND-Eye provides the opportunity to evaluate the effect of aspirin and, separately, omega-3 FAs for both conditions.

Study registration

Eudract No. 2004-000991-15; Multicentre Research Ethics Committee Ref No. 03/8/087; ClinicalTrials.gov No. NCT00135226; ISRCTN No. ISRCTN60635500.

Stages, pathogenesis, clinical management and advancements in therapies of age-related macular degeneration

Age-related macular degeneration (AMD) is a retinal degenerative disorder prevalent in the elderly population, which leads to the loss of central vision. The disease progression can be managed, if not prevented, either by blocking neovascularization ("wet" form of AMD) or by preserving retinal pigment epithelium and photoreceptor cells ("dry" form of AMD). Although current therapeutic modalities are moderately successful in delaying the progression and management of the disease, advances over the past years in regenerative medicine using iPSC, embryonic stem cells, advanced materials (including nanomaterials) and organ bio-printing show great prospects in restoring vision and efficient management of either forms of AMD. This review focuses on the molecular mechanism of the disease, model systems (both cellular and animal) used in studying AMD, the list of various regenerative therapies and the current treatments available. The article also highlights on the recent clinical trials using regenerative therapies and management of the disease.

Complement factor I: Regulatory nexus, driver of immunopathology, and therapeutic

Complement factor I (FI) is the nexus for classical, lectin and alternative pathway complement regulation. FI is an 88 kDa plasma protein that circulates in an inactive configuration until it forms a trimolecular complex with its cofactor and substrate whereupon a structural reorganization allows the catalytic triad to cleave its substrates, C3b and C4b. In keeping with its role as the master complement regulatory enzyme, deficiency has been linked to immunopathology. In the setting of complete FI deficiency, a consumptive C3 deficiency results in recurrent infections with encapsulated microorganisms. Aseptic cerebral inflammation and vasculitic presentations are also less commonly observed. Heterozygous mutations in the factor I gene (CFI) have been demonstrated to be enriched in atypical haemolytic uraemic syndrome, albeit with a very low penetrance. Haploinsufficiency of CFI has also been associated with decreased retinal thickness and is a strong risk factor for the development of age-related macular degeneration. Supplementation of FI using plasma purified or recombinant protein has long been postulated, however, technical difficulties prevented progression into clinical trials. It is only using gene therapy that CFI supplementation has reached the clinic with GT005 in phase I/II clinical trials for geographic atrophy.

Geographic Atrophy in Age-Related Macular Degeneration: A Tale of Two Stages

Purpose

To examine disease progression in age-related macular degeneration (AMD) at 2 distinct stages, progression to geographic atrophy (GA) versus GA expansion, by comparison of the risk and protective factors at each stage.

Design

Perspective.

Subjects

Individuals at risk of GA or with GA.

Main Outcome Measures

Progression to GA and GA expansion rate.

Methods

Critical synthesis of the literature on risk and protective factors, both environmental and genetic, for progression to GA versus GA expansion in AMD.

Results

Comparison of the risk and protective factors demonstrates partially overlapping but partially distinct risk and protective factors for progression to GA versus GA expansion. Some factors are shared (i.e., operating in the same direction at both stages), others are not shared, and others seem to operate in different directions at each stage. Risk variants at ARMS2/HTRA1 increase both risk of progression to GA and GA expansion rate, presumably through the same mechanism. By contrast, risk and protective variants at CFH/CFHR alter risk of GA but not GA expansion rate. A risk variant at C3 increases risk of GA but is associated with slower GA expansion. In environmental factors, cigarette smoking is associated with increased risk of GA and faster GA expansion, whereas increased age is associated with the former but not the latter. The Mediterranean diet is associated with decreased progression at both stages, although the food components with the largest contributions seem to differ between the 2 stages. Some phenotypic features, such as reticular pseudodrusen and hyperreflective foci, are associated with increased progression at both stages.

Conclusions

Analysis of the risk and protective factors for progression to GA and GA expansion demonstrates partially overlapping but partially distinct elements at each stage: some are shared, some are relevant to 1 stage only, and some even seem active in opposite directions at each stage. Aside from ARMS2/HTRA1, the overlap between the genetic risk factors for the 2 stages is minimal. This suggests that the biologic mechanisms differ at least partially between the 2 disease stages. This has implications for therapeutic approaches and suggests that treatment aimed at the underlying disease processes may need to be tailored by stage.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

The complement system: a novel therapeutic target for age-related macular degeneration

INTRODUCTION

With the recent FDA approvals of pegcetacoplan (SYFOVRE, Apellis Pharmaceuticals) and avacincaptad pegol (IZERVAY, Astellas Pharmaceuticals), modulation of the complement system has emerged as a promising therapeutic approach for slowing progression of geographic atrophy (GA) in AMD.

AREAS COVERED

This article reviews the current understanding of the complement system, its role in AMD, and the various complement-targeting therapies in development for the treatment of GA, including monoclonal antibodies, aptamers, protein analogs, and gene therapies. Approved and investigational agents have largely focused on interfering with the activity of complement components 3 and 5, owing to their central roles in the classical, lectin, and alternative complement pathways. Other investigational therapies have targeted formation of membrane attack complex (a terminal step in the complement cascade which leads to cell lysis), complement factors H and I (which serve regulatory functions in the alternative pathway), complement factors B and D (within the alternative pathway), and complement component 1 (within the classical pathway). Clinical trials investigating these agents are summarized, and the potential benefits and limitations of these therapies are discussed.

EXPERT OPINION

Targeting the complement system is a promising therapeutic approach for slowing the progression of GA in AMD, potentially improving visual outcomes. However, increased risk of exudative conversion must be considered, and further research is required to identify clinical criteria and best practices for initiating complement inhibitor therapy for GA.

Complement Inhibitors for Advanced Dry Age-Related Macular Degeneration (Geographic Atrophy): Some Light at the End of the Tunnel?

Geographic atrophy (GA) affects around 5 million individuals worldwide. Genome-wide, histopathologic, in vitro and animal studies have implicated the activation of the complement system and chronic local inflammation in the pathogenesis of GA. Recently, clinical trials have demonstrated that an intravitreal injection of pegcetacoplan, a C3 inhibitor, and avacincaptad pegol, a C5 inhibitor, both statistically significantly reduce the growth of GA up to 20% in a dose-dependent fashion. Furthermore, the protective effect of both pegcetacoplan and avacincaptad appear to increase with time. However, despite these anatomic outcomes, visual function has not improved as these drugs appear to only slow down the degenerative process. Unexpected adverse events included conversion to exudative NV-AMD with both drugs. Occlusive retinal vasculitis and anterior ischemic optic neuropathy have been reported in pegcetacoplan-treated eyes.

Anaphylatoxin C5a receptor signaling induces mitochondrial fusion and sensitizes retinal pigment epithelial cells to oxidative stress

Mitochondrial dynamics is a morphological balance between fragmented and elongated shapes, reflecting mitochondrial metabolic status, cellular damage, and mitochondrial dysfunction. The anaphylatoxin C5a derived from complement component 5 cleavage, enhances cellular responses involved in pathological stimulation, innate immune responses, and host defense. However, the specific response of C5a and its receptor, C5a receptor (C5aR), in mitochondria is unclear. Here, we tested whether the C5a/C5aR signaling axis affects mitochondrial morphology in human-derived retinal pigment epithelial cell monolayers (ARPE-19). C5aR activation with the C5a polypeptide induced mitochondrial elongation. In contrast, oxidatively stressed cells (H2O2) responded to C5a with an enhancement of mitochondrial fragmentation and an increase in the number of pyknotic nuclei. C5a/C5aR signaling increased the expression of mitochondrial fusion-related protein, mitofusin-1 (MFN1) and - 2 (MFN2), as well as enhanced optic atrophy-1 (Opa1) cleavage, which are required for mitochondrial fusion events, whereas the mitochondrial fission protein, dynamin-related protein-1 (Drp1), and mitogen-activated protein kinase (MAPK)-dependent extracellular signal-regulated protein kinase (Erk1/2) phosphorylation were not affected. Moreover, C5aR activation increased the frequency of endoplasmic reticulum (ER)-mitochondria contacts. Finally, oxidative stress induced in a single cell within an RPE monolayer (488 nm blue laser spot stimulation) induced a bystander effect of mitochondrial fragmentation in adjacent surrounding cells only in C5a-treated monolayers. These results suggest that C5a/C5aR signaling produced an intermediate state, characterized by increased mitochondrial fusion and ER-mitochondrial contacts, that sensitizes cells to oxidative stress, leading to mitochondrial fragmentation and cell death.

PET imaging of retinal inflammation in mice exposed to blue light using [18F]-DPA-714

Purpose

Positron emission tomography (PET) is widely used in high-precision imaging, which may provide a simple and noninvasive method for the detection of pathology and therapeutic effects. [18F]-DPA-714 is a second-generation translocator protein (TSPO) positron emission tomography radiotracer that shows great promise in a model of neuroinflammation. In this study, [18F]-DPA-714 micro-PET imaging was used to evaluate retinal inflammation in mice exposed to blue light, a well-established model of age-related macular degeneration (AMD) for molecular mechanism research and drug screening.

Methods

C57BL/6J melanized mice were subjected to 10,000, 15,000, and 20,000 lux blue light for 5 days (8 h/day) to develop the retinal injury model, and the structure and function of the retina were assessed using hematoxylin-eosin (HE) staining, electroretinography (ERG), and terminal-deoxynucleotidyl transferase (TdT)-mediated nick-end labeling (TUNEL) immunostaining. Then, [18F]-DPA-714 was injected approximately 100 μCi through each tail vein, and static imaging was performed 1 h after injection. Finally, the mice eyeballs were collected for biodistribution and immune analysis.

Results

The blue light exposure significantly destroyed the structure and function of the retina, and the uptake of [18F]-DPA-714 in the retinas of the mice exposed to blue light were the most significantly upregulated, which was consistent with the biodistribution data. In addition, the immunohistochemical, western blot, and immunofluorescence data showed an increase in microglial TSPO expression.

Conclusions

[18F]-DPA-714 micro-PET imaging might be a good method for evaluating early inflammatory status during retinal pathology.

Soluble Collectin 11 (CL-11) Acts as an Immunosuppressive Molecule Potentially Used by Stem Cell-Derived Retinal Epithelial Cells to Modulate T Cell Response

Retinal pigment epithelium (RPE) cell allotransplantation is seen as a possible solution to retinal diseases. However, the RPE-complement system triggered by the binding of collectin-11 (CL-11) is a potential barrier for RPE transplantation as the complement-mediated inflammatory response may promote T cell recognition. To address this, we investigated the role of CL-11 on T cell immuno-response. We confirmed that RPE cells up-regulated MHC class I and expressed MHC class II molecules in an inflammatory setting. Co-cultures of RPE cells with T cells led to the inhibition of T cell proliferation. We found that CL-11 was partially responsible for this effect as T cell binding of CL-11 inhibited T cell proliferation in association with the downregulation of CD28. We also found that the suppressive action of CL-11 was abrogated in the presence of the RGD peptide given to block the T cell binding of CL-11 by its collagen-like domain. Because RPE cells can bind and secrete CL-11 under stress conditions, we postulate that soluble CL-11 contributes to the immunosuppressive properties of RPE cells. The investigation of this dual biological activity of CL-11, namely as a trigger of the complement cascade and a modulator of T cell responses, may provide additional clues about the mechanisms that orchestrate the immunogenic properties of RPE cells.

AAV Gene Augmentation of Truncated Complement Factor H Differentially Rescues Ocular Complement Dysregulation in a Mouse Model

Purpose

Complement dysregulation in the eye has been implicated in the pathogenesis of age-related macular degeneration (AMD), and genetic variants of complement factor H (CFH) are strongly associated with AMD risk. We therefore aimed to untangle the role of CFH and its splice variant, factor H-like 1 (FHL-1), in ocular complement regulation derived from local versus circulating sources. We assessed the therapeutic efficacy of adeno-associated viruses (AAVs) expressing human FHL-1 and a truncated version of CFH (tCFH), which retains the functional N- and C-terminal ends of the CFH protein, in restoring the alternative complement pathway in Cfh-/- mouse eyes and plasma.

Methods

Using Cfh-/- mice as a model of complement dysregulation, AAV vectors expressing tCFH or FHL-1 were injected subretinally or via tail vein, and the efficacy of the constructs was evaluated.

Results

Following subretinal injections, tCFH expression rescued factor B (FB) retention in the eye, but FHL-1 expression did not. By contrast, both constructs restored FB detection in plasma following tail vein injections. Both tCFH and FHL-1 proteins accumulated in the posterior eyecup from the circulation following liver transduction; however, neither was able to significantly regulate local ocular complement.

Conclusions

Our findings demonstrate that the C-terminus of human CFH is necessary for complement regulation in the murine eye. Furthermore, exogenous CFH must be synthesized locally to maximize complement regulation in the retina. These findings establish a critical foundation for development of CFH augmentation-based gene therapies for the eye.