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

Biomaterial engineering strategies for modeling the Bruch's membrane in age-related macular degeneration

Age-related macular degeneration, a multifactorial inflammatory degenerative retinal disease, ranks as the leading cause of blindness in the elderly. Strikingly, there is a scarcity of curative therapies, especially for the atrophic advanced form of age-related macular degeneration, likely due to the lack of models able to fully recapitulate the native structure of the outer blood retinal barrier, the prime target tissue of age-related macular degeneration. Standard in vitro systems rely on 2D monocultures unable to adequately reproduce the structure and function of the outer blood retinal barrier, integrated by the dynamic interaction of the retinal pigment epithelium, the Bruch's membrane, and the underlying choriocapillaris. The Bruch's membrane provides structural and mechanical support and regulates the molecular trafficking in the outer blood retinal barrier, and therefore adequate Bruch's membrane-mimics are key for the development of physiologically relevant models of the outer blood retinal barrier. In the last years, advances in the field of biomaterial engineering have provided novel approaches to mimic the Bruch's membrane from a variety of materials. This review provides a discussion of the integrated properties and function of outer blood retinal barrier components in healthy and age-related macular degeneration status to understand the requirements to adequately fabricate Bruch's membrane biomimetic systems. Then, we discuss novel materials and techniques to fabricate Bruch's membrane-like scaffolds for age-related macular degeneration in vitro modeling, discussing their advantages and challenges with a special focus on the potential of Bruch's membrane-like mimics based on decellularized tissue.

The impact of NF-κB on inflammatory and angiogenic processes in age-related macular degeneration

Age-related macular degeneration (AMD) is a prominent cause of vision loss, characterized by two different types, dry (atrophic) and wet (neovascular). Dry AMD is distinguished by the progressive deterioration of retinal cells, which ultimately causes a decline in vision. In contrast, wet AMD is defined by the abnormal development of blood vessels underneath the retina, leading to a sudden and severe vision impairment. The course of AMD is primarily driven by chronic inflammation and pathological angiogenesis, in which the NF-κB signaling pathway plays a crucial role. The activation of NF-κB results in the generation of pro-inflammatory cytokines, chemokines, and angiogenic factors like VEGF, which contribute to inflammation and the formation of new blood vessels in AMD. This review analyzes the intricate relationship between NF-κB signaling, inflammation, and angiogenesis in AMD and assesses the possibility of using NF-κB as a target for therapy. The evaluation involves a comprehensive examination of preclinical and clinical evidence that substantiates the effectiveness of NF-κB inhibitors in treating AMD by diminishing inflammation and pathological angiogenesis.

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.

Aging of the eye: Lessons from cataracts and age-related macular degeneration

Aging is the greatest risk factor for chronic human diseases, including many eye diseases. Geroscience aims to understand the effects of the aging process on these diseases, including the genetic, molecular, and cellular mechanisms that underlie the increased risk of disease over the lifetime. Understanding of the aging eye increases general knowledge of the cellular physiology impacted by aging processes at various biological extremes. Two major diseases, age-related cataract and age-related macular degeneration (AMD) are caused by dysfunction of the lens and retina, respectively. Lens transparency and light refraction are mediated by lens fiber cells lacking nuclei and other organelles, which provides a unique opportunity to study a single aging hallmark, i.e., loss of proteostasis, within an environment of limited metabolism. In AMD, local dysfunction of the photoreceptors/retinal pigmented epithelium/Bruch's membrane/choriocapillaris complex in the macula leads to the loss of photoreceptors and eventually loss of central vision, and is driven by nearly all the hallmarks of aging and shares features with Alzheimer's disease, Parkinson's disease, cardiovascular disease, and diabetes. The aging eye can function as a model for studying basic mechanisms of aging and, vice versa, well-defined hallmarks of aging can be used as tools to understand age-related eye disease.

Comprehensive functional characterization of complement factor I rare variant genotypes identified in the SCOPE geographic atrophy cohort

Rare variants (RVs) in the gene encoding the regulatory enzyme complement factor I (CFI; FI) that reduce protein function or levels increase age-related macular degeneration risk. A total of 3357 subjects underwent screening in the SCOPE natural history study for geographic atrophy secondary to age-related macular degeneration, including CFI sequencing and serum FI measurement. Eleven CFI RV genotypes that were challenging to categorize as type I (low serum level) or type II (normal serum level, reduced enzymatic function) were characterized in the context of pure FI protein in C3b and C4b fluid phase cleavage assays and a novel bead-based functional assay (BBFA) of C3b cleavage. Four variants predicted or previously characterized as benign were analyzed by BBFA for comparison. In all, three variants (W51S, C67R, and I370T) resulted in low expression. Furthermore, four variants (P64L, R339Q, G527V, and P528T) were identified as being highly deleterious with IC50s for C3b breakdown >1 log increased versus the WT protein, while two variants (K476E and R474Q) were ∼1 log reduced in function. Meanwhile, six variants (P50A, T203I, K441R, E548Q, P553S, and S570T) had IC50s similar to WT. Odds ratios and BBFA IC50s were positively correlated (r = 0.76, p < 0.01), while odds ratios versus combined annotation dependent depletion (CADD) scores were not (r = 0.43, p = 0.16). Overall, 15 CFI RVs were functionally characterized which may aid future patient stratification for complement-targeted therapies. Pure protein in vitro analysis remains the gold standard for determining the functional consequence of CFI RVs.

SPI1-mediated macrophage polarization aggravates age-related macular degeneration

Objective

This study revealed a core regulator and common upstream mechanisms for the multifaceted pathological processes of age-related macular degeneration (AMD) and provided proof-of-concept for this new therapeutic target.

Methods

Comprehensive gene expression analysis was performed using RNA sequencing of eye cup from old mice as well as laser-induced choroidal neovascularization (CNV) mouse model. Through integrative analysis and protein-protein interaction (PPI) analysis, common pathways and key transcription factor was identified simultaneously engaged in age-related retinal degeneration and CNV, the two typical pathological process of AMD. Subsequently, the expression changes of Spi1, the key regulator, as well as the alternation of the downstream mechanisms were validated in both models through qRT-PCR, Elisa, flow cytometry and immunofluorescence. Further, we assessed the impact of Spi1 knockdown in vitro and in vivo using gene intervention vectors carried by adeno-associated virus or lentivirus to test its potential as a therapeutic target.

Results

Compared to corresponding controls, we found 1,939 and 1,319 genes differentially expressed in eye cups of old and CNV mice respectively. The integrative analysis identified a total of 275 overlapping DEGs, of which 150 genes were co-upregulated. PPI analysis verified a central transcription factor, SPI1. The significant upregulation of Spi1 expression was then validated in both models, accompanied by macrophage polarization towards the M1 phenotype. Finally, SPI1 suppression significantly inhibited M1 polarization of BMDMs and attenuated neovascularization in CNV mice.

Conclusion

This study demonstrates that SPI1 exerts a pivotal role in AMD by regulation of macrophage polarization and innate immune response, offering promise as an innovative target for treating AMD.

Investing in vision: Innovation in retinal therapeutics and the influence on venture capital investment

Since the groundbreaking approval of the first anti-VEGF therapy in 2004, the retinal therapeutics field has undergone a remarkable transformation, witnessing a surge in novel, disease-modifying therapeutics for a broad spectrum of retinal diseases, extending beyond exudative VEGF-driven conditions. The surge in scientific advancement and the pressing, unmet, medical need have captured the attention of venture capital investors, who have collectively invested close to $10 billion in research and development of new retinal therapeutics between 2004 and 2023. Notably, the field of exudative diseases has gradually shifted away from trying to outcompete anti-VEGF therapeutics towards lowering the overall treatment burden by reducing injection frequency. Simultaneously, a new era has emerged in the non-exudative field, targeting prevalent conditions like dry AMD and rare indications such as Retinitis pigmentosa. This has led to promising drug candidates in development, culminating in the landmark approval of Luxturna for a rare form of Retinitis pigmentosa. The validation of new mechanisms, such as the complement pathway in dry AMD has paved the way for the approvals of Syvovre (Apellis) and Izervay (Iveric/Astellas), marking the first two therapies for this condition. In this comprehensive review, we share our view on the cumulative lessons from the past two decades in developing retinal therapeutics, covering both positive achievements and challenges. We also contextualize the investments, strategic partnering deals, and acquisitions of biotech companies, pharmaceutical companies venture capital investors in retinal therapeutics, respectively. Finally, we provide an outlook and potentially a forward-looking roadmap on novel retinal therapeutics, highlighting the emergence of potential new intervention strategies, such as cell-based therapies, gene editing, and combination therapies. We conclude that upcoming developments have the potential to further stimulate venture capital investments, which ultimately could facilitate the development and delivery of new therapies to patients in need.

The human factor H protein family - an update

Complement is an ancient and complex network of the immune system and, as such, it plays vital physiological roles, but it is also involved in numerous pathological processes. The proper regulation of the complement system is important to allow its sufficient and targeted activity without deleterious side-effects. Factor H is a major complement regulator, and together with its splice variant factor H-like protein 1 and the five human factor H-related (FHR) proteins, they have been linked to various diseases. The role of factor H in inhibiting complement activation is well studied, but the function of the FHRs is less characterized. Current evidence supports the main role of the FHRs as enhancers of complement activation and opsonization, i.e., counter-balancing the inhibitory effect of factor H. FHRs emerge as soluble pattern recognition molecules and positive regulators of the complement system. In addition, factor H and some of the FHR proteins were shown to modulate the activity of immune cells, a non-canonical function outside the complement cascade. Recent efforts have intensified to study factor H and the FHRs and develop new tools for the distinction, quantification and functional characterization of members of this protein family. Here, we provide an update and overview on the versatile roles of factor H family proteins, what we know about their biological functions in healthy conditions and in diseases.

Geographic atrophy: pathophysiology and current therapeutic strategies

Geographic atrophy (GA) is an advanced stage of age-related macular degeneration (AMD) that leads to gradual and permanent vision loss. GA is characterized by the loss of photoreceptor cells and retinal pigment epithelium (RPE), leading to distinct atrophic patches in the macula, which tends to increase with time. Patients with geographic atrophy often experience a gradual and painless loss of central vision, resulting in difficulty reading, recognizing faces, or performing activities that require detailed vision. The primary risk factor for the development of geographic atrophy is advanced age; however, other risk factors, such as family history, smoking, and certain genetic variations, are also associated with AMD. Diagnosis is usually based on a comprehensive eye examination, including imaging tests such as fundus photography, optical coherence tomography (OCT), and fluorescein angiography. Numerous clinical trials are underway, targeting identified molecular pathways associated with GA that are promising. Recent approvals of Syfovre and Izervay by the FDA for the treatment of GA provide hope to affected patients. Administration of these drugs resulted in slowing the rate of progression of the disease. Though these products provide treatment benefits to the patients, they do not offer a cure for geographic atrophy and are limited in efficacy. Considering these safety concerns and limited treatment benefits, there is still a significant need for therapeutics with improved efficacy, safety profiles, and better patient compliance. This comprehensive review discusses pathophysiology, currently approved products, their limitations, and potential future treatment strategies for GA.

Complement factor H Y402H polymorphism results in diminishing CD4+ T cells and increasing C-reactive protein in plasma

Age-related macular degeneration (AMD) is a common cause of visual loss among the elderly. Genetic variants in the gene encoding complement factor H (CFH) have been identified as an AMD susceptibility gene, however, the mechanistic link is debated. Here, we investigated the link between the CFH Y402H genotype and low-grade inflammation. We recruited 153 healthy individuals, 84 participants with dry stages of AMD, and 148 participants with neovascular AMD. All participants were subjected to detailed retinal examination, and interview regarding comorbidities and lifestyle. Blood samples were analyzed for level of C-Reactive Protein (CRP), white blood cell differential count, and stained with fluorescent antibodies to differentiate CD4+ and CD8+ T cells. CFH Y402H genotyping was performed using an allele-specific polymerase chain reaction genotyping assay. Splenocytes from young and aged wild type and Cfh null mutant C57BL/6J mice were examined for CD4+ and CD8+ T cells. Healthy individuals with the CFH Y402H at-risk polymorphism HH had higher levels of CRP and lower proportions of CD4+ T cells compared to persons with the YH or YY polymorphism (P = 0.037, Chi-square). Healthy individuals with the HH polymorphism displayed lower proportions of CD4+ T cells with ageing (P < 0.01, one-way ANOVA), whereas both young and aged Cfh null mutant mice displayed lower proportions of CD4+ T cells (P < 0.001 and P < 0.05; unpaired t test). Participants with dry AMD and the HH polymorphism had similarly lower proportions of CD4+ T cells (P = 0.024, one-way ANOVA), but no difference in CRP-levels. In the neovascular stage of AMD, there was no difference in proportion of CD4+ cells or CRP levels according to genotype. The risk-associated CFH genotype is associated with an age-related decrease in proportion of CD4+ T cells and increased levels of CRP in healthy individuals. This indicates that decreased complement regulation results in extensive changes in innate and adaptive immune compartments that precede development of AMD.

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.

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.

Recent Advances of Ocular Drug Delivery Systems: Prominence of Ocular Implants for Chronic Eye Diseases

Chronic ocular diseases can seriously impact the eyes and could potentially result in blindness or serious vision loss. According to the most recent data from the WHO, there are more than 2 billion visually impaired people in the world. Therefore, it is pivotal to develop more sophisticated, long-acting drug delivery systems/devices to treat chronic eye conditions. This review covers several drug delivery nanocarriers that can control chronic eye disorders non-invasively. However, most of the developed nanocarriers are still in preclinical or clinical stages. Long-acting drug delivery systems, such as inserts and implants, constitute the majority of the clinically used methods for the treatment of chronic eye diseases due to their steady state release, persistent therapeutic activity, and ability to bypass most ocular barriers. However, implants are considered invasive drug delivery technologies, especially those that are nonbiodegradable. Furthermore, in vitro characterization approaches, although useful, are limited in mimicking or truly representing the in vivo environment. This review focuses on long-acting drug delivery systems (LADDS), particularly implantable drug delivery systems (IDDS), their formulation, methods of characterization, and clinical application for the treatment of eye diseases.