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

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.

Pluripotent stem cell-derived models of retinal disease: Elucidating pathogenesis, evaluating novel treatments, and estimating toxicity

Blindness poses a growing global challenge, with approximately 26% of cases attributed to degenerative retinal diseases. While gene therapy, optogenetic tools, photosensitive switches, and retinal prostheses offer hope for vision restoration, these high-cost therapies will benefit few patients. Understanding retinal diseases is therefore key to advance effective treatments, requiring in vitro models replicating pathology and allowing quantitative assessments for drug discovery. Pluripotent stem cells (PSCs) provide a unique solution given their limitless supply and ability to differentiate into light-responsive retinal tissues encompassing all cell types. This review focuses on the history and current state of photoreceptor and retinal pigment epithelium (RPE) cell generation from PSCs. We explore the applications of this technology in disease modelling, experimental therapy testing, biomarker identification, and toxicity studies. We consider challenges in scalability, standardisation, and reproducibility, and stress the importance of incorporating vasculature and immune cells into retinal organoids. We advocate for high-throughput automation in data acquisition and analyses and underscore the value of advanced micro-physiological systems that fully capture the interactions between the neural retina, RPE, and choriocapillaris.

CFH Haploinsufficiency and Complement Alterations in Early-Onset Macular Degeneration

Purpose

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

Methods

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

Results

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

Conclusions

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

Transcriptomic and Chromatin Accessibility Analysis of the Human Macular and Peripheral Retinal Pigment Epithelium at the Single-Cell Level

Some human retinal diseases are characterized by pathology that is restricted to specific cell types and to specific regions of the eye. Several disease entities either selectively affect or spare the macula, the retina region at the center of the posterior pole. Photoreceptor cells in the macula are involved in high-acuity vision and require metabolic support from non-neuronal cell types. Some macular diseases involve the retinal pigment epithelium (RPE), an epithelial cell layer with several metabolic-support functions essential for the overlying photoreceptors. In the current study, the ways in which RPE confers region-specific disease susceptibility were determined by examining heterogeneity within RPE tissue from human donors. RPE nuclei from the macular and peripheral retina were profiled using joint single-nucleus RNA and ATAC sequencing. The expression of several genes differed between macular and peripheral RPE. Region-specific ATAC peaks were found, suggesting regulatory elements used exclusively by macular or peripheral RPE. Across anatomic regions, subpopulations of RPE were identified that appeared to have differential levels of expression of visual cycle genes. Finally, loci associated with age-related macular degeneration were examined for a better understanding of RPE-specific disease phenotypes. These findings showed variations in the regulation of gene expression in the human RPE by region and subpopulation, and provide a source for a better understanding of the molecular basis of macular disease.

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.

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.

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

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

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

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

Functional characterization of complement factor H in host defense against bacterial pathogen in Nile tilapia (Oreochromis niloticus)

Complement factor H (CFH), a multifunctional soluble complement regulatory protein, can bind to a variety of pathogens and play a crucial role in host innate immune defense. To explore the functional characteristics of CFH (OnCFH) in Nile tilapia (Oreochromis niloticus), we cloned and characterized the open reading frame (ORF) of OnCFH in this study. The full-length of OnCFH ORF is 1359 bp, encoding 452 aa for a 48.85 kDa peptide, and its predicted structure containing six short complement-like repeats (SCRs). The analysis of tissue distribution showed that OnCFH was constitutively expressed in all tested tissues, with the highest in the liver. Upon Streptococcus agalactiae and Aeromonas hydrophila stimuli in vivo and in vitro, OnCFH mRNA transcript was significantly upregulated in head kidney tissue as well as head kidney monocytes/macrophages. Further, the recombinant OnCFH protein ((r)OnCFH) could bind to pathogenic bacteria in a dose-dependent. Moreover, it got involved in the regulation of inflammation as well as phagocytosis of monocytes/macrophages. The knockdown of OnCFH remarkably decreased the amount of bacteria in the head kidney. In summary, our data demonstrated that OnCFH could participate in the immune response of Nile tilapia against bacterial infection.

Molecular Genetic Mechanisms in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is among the leading causes of irreversible blindness worldwide. In addition to environmental risk factors, such as tobacco use and diet, genetic background has long been established as a major risk factor for the development of AMD. However, our ability to predict disease risk and personalize treatment remains limited by our nascent understanding of the molecular mechanisms underlying AMD pathogenesis. Research into the molecular genetics of AMD over the past two decades has uncovered 52 independent gene variants and 34 independent loci that are implicated in the development of AMD, accounting for over half of the genetic risk. This research has helped delineate at least five major pathways that may be disrupted in the pathogenesis of AMD: the complement system, extracellular matrix remodeling, lipid metabolism, angiogenesis, and oxidative stress response. This review surveys our current understanding of each of these disease mechanisms, in turn, along with their associated pathogenic gene variants. Continued research into the molecular genetics of AMD holds great promise for the development of precision-targeted, personalized therapies that bring us closer to a cure for this debilitating disease.

A Novel Full-Length Recombinant Human Complement Factor H (CFH; GEM103) for the Treatment of Age-Related Macular Degeneration Shows Similar In Vitro Functional Activity to Native CFH

PURPOSE

GEM103 is a recombinantly produced full-length version of the human complement factor H (CFH) under clinical investigation for treatment of age-related macular degeneration (AMD) in individuals carrying an AMD risk-associated genetic variant of CFH. This study aimed to investigate the complement pathway-related functions of GEM103 in comparison with those of native human CFH.

METHODS

Key biological activities of GEM103 and human serum-derived CFH (sdCFH) were compared using four independent functional assays. Assays of C3b binding and C3 convertase decay-accelerating activity (DAA) were performed by surface plasmon resonance (SPR). Cofactor activity (CA) was measured using 8-anilinonaphthalene-1-sulfonic acid as a fluorescent probe of C3b integrity. The abilities of GEM103 and sdCFH to protect sheep erythrocytes from hemolysis by CFH-depleted normal human serum were assessed colorimetrically.

RESULTS

In multiple SPR-based assays of C3b binding and DAA, the performance of GEM103 was consistently comparable to that of sdCFH across a range of matching concentrations. The EC50 ± SD in the fluorescence-based fluid-phase CA assay was 0.21 ± 0.06 µM for GEM103 compared to 0.20 ± 0.09 µM for sdCFH. In hemolysis assays, the EC50 value of 0.33 ± 0.16 µM for GEM103 versus 0.46 ± 0.06 µM for sdCFH were not significantly different (p = 0.81).

CONCLUSIONS

GEM103, a recombinant CFH developed by Gemini Therapeutics, shows activity profiles comparable to sdCFH in all complement-related assays employed in this study, suggesting that GEM103 is equivalent to the native glycoprotein in terms of its in vitro functional activity. These results support further study of GEM103 as a potential therapy for AMD.

Mast cell infiltration of the choroid and protease release are early events in age-related macular degeneration associated with genetic risk at both chromosomes 1q32 and 10q26

Age-related macular degeneration (AMD) is a leading cause of visual loss. It has a strong genetic basis, and common haplotypes on chromosome (Chr) 1 (CFH Y402H variant) and on Chr10 (near HTRA1/ARMS2) contribute the most risk. Little is known about the early molecular and cellular processes in AMD, and we hypothesized that analyzing submacular tissue from older donors with genetic risk but without clinical features of AMD would provide biological insights. Therefore, we used mass spectrometry–based quantitative proteomics to compare the proteins in human submacular stromal tissue punches from donors who were homozygous for high-risk alleles at either Chr1 or Chr10 with those from donors who had protective haplotypes at these loci, all without clinical features of AMD. Additional comparisons were made with tissue from donors who were homozygous for high-risk Chr1 alleles and had early AMD. The Chr1 and Chr10 risk groups shared common changes compared with the low-risk group, particularly increased levels of mast cell–specific proteases, including tryptase, chymase, and carboxypeptidase A3. Histological analyses of submacular tissue from donors with genetic risk of AMD but without clinical features of AMD and from donors with Chr1 risk and AMD demonstrated increased mast cells, particularly the tryptase-positive/chymase-negative cells variety, along with increased levels of denatured collagen compared with tissue from low–genetic risk donors. We conclude that increased mast cell infiltration of the inner choroid, degranulation, and subsequent extracellular matrix remodeling are early events in AMD pathogenesis and represent a unifying mechanistic link between Chr1- and Chr10-mediated AMD.