Molecular response of chorioretinal endothelial cells to complement injury: implications for macular degeneration

Terminal complement complex deposition on chondrocytes promotes premature senescence in age- and trauma-related osteoarthritis

Background

The complement system is locally activated after joint injuries and leads to the deposition of the terminal complement complex (TCC). Sublytic TCC deposition is associated with phenotypical alterations of human articular chondrocytes (hAC) and enhanced release of inflammatory cytokines. Chronic inflammation is a known driver of chondrosenescence in osteoarthritis (OA). Therefore, we investigated whether TCC deposition contributes to stress-induced premature senescence (SIPS) during aging in vivo and after ex vivo cartilage injury.

Methods

Femoral condyles of male 13-week-old and 72-week-old CD59-ko (higher TCC deposition), C6-deficient (insufficient TCC formation), and C57BL/6 (WT) mice were collected to assess age-related OA. Furthermore, macroscopically intact human and porcine cartilage explants were traumatized and cultured with/without 30% human serum (HS) to activate the complement system. Explants were additionally treated with clusterin (CLU, TCC inhibitor), N-acetylcysteine (NAC, antioxidant), Sarilumab (IL-6 receptor inhibitor), STAT3-IN-1 (STAT3 inhibitor), or IL-1 receptor antagonist (IL-1RA) in order to investigate the consequences of TCC deposition. Gene and protein expression of senescence-associated markers such as CDKN1A and CDKN2A was determined.

Results

In the murine aging model, CD59-ko mice developed after 72 weeks more severe OA compared to C6-deficient and WT mice. mRNA analysis revealed that the expression of Cdkn1a, Cdkn2a, Tp53, Il1b, and Il6 was significantly increased in the cartilage of CD59-ko mice. In human cartilage, trauma and subsequent stimulation with HS increased mRNA levels of CDKN1A, CDKN2A, and IL6, while inhibition of TCC formation by CLU reduced the expression. Antioxidative therapy with NAC had no anti-senescent effect. In porcine tissue, HS exposure and trauma had additive effects on the number of CDKN2A-positive cells, while Sarilumab, STAT-IN-1, and IL-1RA reduced CDKN2A expression by trend.

Conclusion

Our results demonstrate that complement activation and consequent TCC deposition is associated with chondrosenescence in age-related and trauma-induced OA. We provided evidence that the SIPS-like phenotype is more likely induced by TCC-mediated cytokine release rather than oxidative stress. Overall, targeting TCC formation could be a future approach to attenuate OA progression.

Ref-1 is overexpressed in neovascular eye disease and targetable with a novel inhibitor

Reduction-oxidation factor-1 or apurinic/apyrimidinic endonuclease 1 (Ref-1/APE1) is a crucial redox-sensitive activator of transcription factors such as NF-κB, HIF-1α, STAT-3 and others. It could contribute to key features of ocular neovascularization including inflammation and angiogenesis; these underlie diseases like neovascular age-related macular degeneration (nAMD). We previously revealed a role for Ref-1 in the growth of ocular endothelial cells and in choroidal neovascularization (CNV). Here, we set out to further explore Ref-1 in neovascular eye disease. Ref-1 was highly expressed in human nAMD, murine laser-induced CNV and Vldlr-/- mouse subretinal neovascularization (SRN). Ref-1's interaction with a redox-specific small molecule inhibitor, APX2009, was shown by NMR and docking. This compound blocks crucial angiogenic features in multiple endothelial cell types. APX2009 also ameliorated murine laser-induced choroidal neovascularization (L-CNV) when delivered intravitreally. Moreover, systemic APX2009 reduced murine SRN and downregulated the expression of Ref-1 redox regulated HIF-1α target carbonic anhydrase 9 (CA9) in the Vldlr-/- mouse model. Our data validate the redox function of Ref-1 as a critical regulator of ocular angiogenesis, indicating that inhibition of Ref-1 holds therapeutic potential for treating nAMD.

Complement factor H in molecular regulation of angiogenesis

Angiogenesis, the process of formation of new capillaries from existing blood vessels, is required for multiple physiological and pathological processes. Complement factor H (CFH) is a plasma protein that inhibits the alternative pathway of the complement system. Loss of CFH enhances the alternative pathway and increases complement activation fragments with pro-angiogenic capacity, including complement 3a, complement 5a, and membrane attack complex. CFH protein contains binding sites for C-reactive protein, malondialdehyde, and endothelial heparan sulfates. Dysfunction of CFH prevents its interaction with these molecules and initiates pro-angiogenic events. Mutations in the CFH gene have been found in patients with age-related macular degeneration characterized by choroidal neovascularization. The Cfh-deficient mice show an increase in angiogenesis, which is decreased by administration of recombinant CFH protein. In this review, we summarize the molecular mechanisms of the anti-angiogenic effects of CFH and the regulatory mechanisms of CFH expression. The therapeutic potential of recombinant CFH protein in angiogenesis-related diseases has also been discussed.

Stable inhibition of choroidal neovascularization by adeno-associated virus 2/8-vectored bispecific molecules

Neovascular age-related macular degeneration (nAMD) causes severe visual impairment. Pigment epithelium-derived factor (PEDF), soluble CD59 (sCD59), and soluble fms-like tyrosine kinase-1 (sFLT-1) are potential therapeutic agents for nAMD, which target angiogenesis and the complement system. Using the AAV2/8 vector, two bi-target gene therapy agents, AAV2/8-PEDF-P2A-sCD59 and AAV2/8-sFLT-1-P2A-sCD59, were generated, and their therapeutic efficacy was investigated in laser-induced choroidal neovascularization (CNV) and Vldlr-/- mouse models. After a single injection, AAV2/8-mediated gene expression was maintained at high levels in the retina for two months. Both AAV2/8-PEDF-P2A-sCD59 and AAV2/8-sFLT-1-P2A-sCD59 significantly reduced CNV development for an extended period without side effects and provided efficacy similar to two injections of current anti-vascular endothelial growth factor monotherapy. Mechanistically, these agents suppressed the extracellular signal-regulated kinase and nuclear factor-κB pathways, resulting in anti-angiogenic activity. This study demonstrated the safety and long-lasting effects of AAV2/8-PEDF-P2A-sCD59 and AAV2/8-sFLT-1-P2A-sCD59 in CNV treatment, providing a promising therapeutic strategy for nAMD.

Evaluation of choroid vascular layer thickness in wet age-related macular degeneration using artificial intelligence

PURPOSE

To facilitate the assessment of choroid vascular layer thickness in patients with wet age-related macular degeneration (AMD) using artificial intelligence (AI).

METHODS

We included 194 patients with wet AMD and 225 healthy participants. Choroid images were obtained using swept-source optical coherence tomography. The average Sattler layer-choriocapillaris complex thickness (SLCCT), Haller layer thickness (HLT), and choroidal thickness (CT) were auto-measured at 7 regions centered around the foveola using AI and subsequently compared between the 2 groups.

RESULTS

The SLCCT was lower in the AMD group than in the control group (P < 0.05). The HLT was significantly higher in the AMD group than in the control group at the Tparafovea and T-perifovea in the total population (P < 0.05) and in the ≤70-year subgroup (P < 0.05). The CT was higher in the AMD group than in the control group, particularly at the N-perifovea, T-perifovea, and T-parafovea in the ≤70-year subgroup; Interestingly, it was lower in the AMD group than in the control group at the Nparafovea, N-fovea, foveola, and T-fovea in the >70-year subgroup (P < 0.05).

CONCLUSION

This novel AI-based auto-measurement was more accurate, efficient, and detailed than manual measurements. SLCCT thinning was observed in wet AMD; however, CT changes depended on the interaction between HLT compensatory thickening and SLCCT thinning.

Novel Drug Delivery Methods and Approaches for the Treatment of Retinal Diseases

This review discusses emerging approaches to ocular drug delivery for retinal diseases. Intravitreal injections have proven to be an effective, safe, and commonly used drug delivery method. However, the optimal management of chronic retinal diseases requires frequent intravitreal injections over extended periods of time. Although this can be achieved in a clinical trial environment, it is difficult to replicate in routine clinical practice. In addition, frequent treatment increases the risk of complications, incurs more costs, and increases the treatment burden for patients and caregivers. Given the aging global population and diabetes pandemic, there is an urgent need for drug delivery methods that support more durable retinal therapy while maintaining the efficacy and safety of currently available intravitreal therapies. Several innovative drug delivery methods are currently being investigated. These include sustained-release implants and depots using prodrugs, microparticles, and hydrogels, surgically implanted reservoirs, gene therapy via submacular injections or suprachoroidal injections, as well as topical and systemic therapies.

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.

PRMT5 is a therapeutic target in choroidal neovascularization

Ocular neovascular diseases including neovascular age-related macular degeneration (nvAMD) are widespread causes of blindness. Patients' non-responsiveness to currently used biologics that target vascular endothelial growth factor (VEGF) poses an unmet need for novel therapies. Here, we identify protein arginine methyltransferase 5 (PRMT5) as a novel therapeutic target for nvAMD. PRMT5 is a well-known epigenetic enzyme. We previously showed that PRMT5 methylates and activates a proangiogenic and proinflammatory transcription factor, the nuclear factor kappa B (NF-κB), which has a master role in tumor progression, notably in pancreatic ductal adenocarcinoma and colorectal cancer. We identified a potent and specific small molecule inhibitor of PRMT5, PR5-LL-CM01, that dampens the methylation and activation of NF-κB. Here for the first time, we assessed the antiangiogenic activity of PR5-LL-CM01 in ocular cells. Immunostaining of human nvAMD sections revealed that PRMT5 is highly expressed in the retinal pigment epithelium (RPE)/choroid where neovascularization occurs, while mouse eyes with laser induced choroidal neovascularization (L-CNV) showed PRMT5 is overexpressed in the retinal ganglion cell layer and in the RPE/choroid. Importantly, inhibition of PRMT5 by PR5-LL-CM01 or shRNA knockdown of PRMT5 in human retinal endothelial cells (HRECs) and induced pluripotent stem cell (iPSC)-derived choroidal endothelial cells (iCEC2) reduced NF-κB activity and the expression of its target genes, such as tumor necrosis factor α (TNF-α) and VEGF-A. In addition to inhibiting angiogenic properties of proliferation and tube formation, PR5-LL-CM01 blocked cell cycle progression at G1/S-phase in a dose-dependent manner in these cells. Thus, we provide the first evidence that inhibition of PRMT5 impedes angiogenesis in ocular endothelial cells, suggesting PRMT5 as a potential therapeutic target to ameliorate ocular neovascularization.

High-Fat Diet Alters the Retinal Pigment Epithelium and Choroidal Transcriptome in the Absence of Gut Microbiota

Relationships between retinal disease, diet, and the gut microbiome have started to emerge. In particular, high-fat diets (HFDs) are associated with the prevalence and progression of several retinal diseases, including age-related macular degeneration (AMD) and diabetic retinopathy (DR). These effects are thought to be partly mediated by the gut microbiome, which modulates interactions between diet and host homeostasis. Nevertheless, the effects of HFDs on the retina and adjacent retinal pigment epithelium (RPE) and choroid at the transcriptional level, independent of gut microbiota, are not well-understood. In this study, we performed the high-throughput RNA-sequencing of germ-free (GF) mice to explore the transcriptional changes induced by HFD in the RPE/choroid. After filtering and cleaning the data, 649 differentially expressed genes (DEGs) were identified, with 616 genes transcriptionally upregulated and 33 genes downregulated by HFD compared to a normal diet (ND). Enrichment analysis for gene ontology (GO) using the DEGs was performed to analyze over-represented biological processes in the RPE/choroid of GF-HFD mice relative to GF-ND mice. GO analysis revealed the upregulation of processes related to angiogenesis, immune response, and the inflammatory response. Additionally, molecular functions that were altered involved extracellular matrix (ECM) binding, ECM structural constituents, and heparin binding. This study demonstrates novel data showing that HFDs can alter RPE/choroid tissue transcription in the absence of the gut microbiome.

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

Activation of the alternative complement pathway is an initiating event in the pathology of age-related macular degeneration (AMD). Unchecked complement activation leads to the formation of a pro-lytic pore, the membrane attack complex (MAC). MAC deposition is observed on the choriocapillaris of AMD patients and likely causes lysis of choroidal endothelial cells (CECs). Complement factor H (FH, encoded by the gene CFH) is an inhibitor of complement. Both loss of function of FH and reduced choroidal levels of FH have been reported in AMD. It is plausible that reduced local FH availability promotes MAC deposition on CECs. FH is produced primarily in the liver; however, cells including the retinal pigment epithelium can produce FH locally. We hypothesized that CECs produce FH locally to protect against MAC deposition. We aimed to investigate the effect of reduced FH levels in the choroid to determine whether increasing local FH could protect CECs from MAC deposition. We demonstrated that siRNA knockdown of FH (CFH) in human immortalized CECs results in increased MAC deposition. We generated AMD iPSC-derived CECs and found that overexpression of FH protects against MAC deposition. These results suggest that local CEC-produced FH protects against MAC deposition, and that increasing local FH protein may be beneficial in limiting MAC deposition in AMD. © 2022 The Pathological Society of Great Britain and Ireland.

The Role of Metalloproteinases and Their Tissue Inhibitors on Ocular Diseases: Focusing on Potential Mechanisms

Eye diseases are associated with visual impairment, reduced quality of life, and may even lead to vision loss. The efficacy of available treatment of eye diseases is not satisfactory. The unique environment of the eye related to anatomical and physiological barriers and constraints limits the bioavailability of existing agents. In turn, complex ethiopathogenesis of ocular disorders that used drugs generally are non-disease specific and do not act causally. Therefore, there is a need for the development of a new therapeutic and preventive approach. It seems that matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) have a significant role in the development and progression of eye diseases and could be used in the therapy of these disorders as pharmacological targets. MMPs and TIMPs play an important role in the angiogenesis, epithelial-mesenchymal transition, cell invasion, and migration, which occur in ocular diseases. In this review, we aim to describe the participation of MMPs and TIMPs in the eye diseases, such as age-related macular degeneration, cataract, diabetic retinopathy, dry eye syndrome, glaucoma, and ocular cancers, posterior capsule opacification focusing on potential mechanisms.

Increased cell stiffness contributes to complement-mediated injury of choroidal endothelial cells in a monkey model of early age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in the aging population. Yet, no therapies exist for approximately 85% of all AMD patients who have the dry form that is marked by degeneration of the retinal pigmented epithelium (RPE) and underlying choroidal vasculature. As the choroidal vessels are crucial for RPE development and maintenance, understanding how they degenerate may lead to effective therapies for dry AMD. One likely causative factor for choroidal vascular loss is the cytolytic membrane attack complex (MAC) of the complement pathway that is abundant on choroidal vessels of humans with early dry AMD. To examine this possibility, we studied the effect of complement activation on choroidal endothelial cells (ECs) isolated from a rhesus monkey model of early AMD that, we report, exhibits MAC deposition and choriocapillaris endothelial loss similar to that seen in human early AMD. Treatment of choroidal ECs from AMD eyes with complement-competent normal human serum caused extensive actin cytoskeletal injury that was significantly less pronounced in choroidal ECs from young normal monkey eyes. We further show that ECs from AMD eyes are significantly stiffer than their younger counterparts and exhibit peripheral actin organization that is distinct from the longitudinal stress fibers in young ECs. Finally, these differences in complement susceptibility and mechanostructural properties were found to be regulated by the differential activity of the small GTPases Rac and Rho, because Rac inhibition in AMD cells led to simultaneous reduction in stiffness and complement susceptibility while Rho inhibition in young cells exacerbated complement injury. Thus, by identifying cell stiffness and cytoskeletal regulators Rac and Rho as important determinants of complement susceptibility, the current findings offer a new mechanistic insight into choroidal vascular loss in early AMD that warrants further investigation for assessment of translational potential. This article is protected by copyright. All rights reserved.

Fibroblast growth factor-21 alleviates phenotypic characteristics of dry age-related macular degeneration in mice

Age-related macular degeneration (AMD) is the main cause of blindness in elderly individuals. As a metabolic regulator, fibroblast growth factor 21 (FGF-21) has been proven indicated to have an effect on wet AMD, but whether this cytokine has a therapeutic effect on dry AMD is unclear. The current study aimed to evaluate the preventive effects of FGF-21 against retinal degeneration in mice and provide mechanistic insights. FGF-21-/- mice were raised to 10 months of age. Then, the morphological changes in the retinal pigment epithelium (RPE)/choroid of the mice were observed by transmission electron microscopy (TEM), and iTRAQ was used to detect the variations in the protein profile. Next, FGF-21-/- and wild-type mice of the same age were fed hydroquinone to generate a dry AMD mouse model to examine whether exogenous FGF-21 can interfere with the occurrence and development of dry AMD. In vivo studies revealed that following FGF-21 knockout, there was an increase in the expression of complement in the RPE/choroid concomitant with the occurrence of dry AMD-like pathological changes. Furthermore, exogenous FGF-21 administration effectively reversed this phenomenon. FGF-21 also demonstrated strong anti-inflammatory effects in the RPE/choroid by inhibiting the NF-κB pathway. In conclusion, the present study demonstrates that FGF-21 treatment presents a novel therapeutic approach for the prevention and development of dry AMD by reducing complement.

Aging of the human choriocapillaris: Evidence that early pericyte damage can trigger endothelial changes

The choriocapillaris (CC), the capillary bed in the choroid, essentially nourishes the photoreceptor cells. Its damage in aging and age-related diseases significantly influences the survival of the photoreceptor cells. Earlier reports implicated endothelial loss in aged and diseased CC; however, age-related pericyte changes and their contribution in CC death remain unknown. We examined human donor eyes (age: 56-94 years; N = 24), and found that CC pericyte damage preceded endothelial changes. With aging (>70 years), the sub-macular choroid accumulated debris in Bruch's membrane (BM). Of the debris content, the long-spaced collagens had a tendency to settle over the capillary basal lamina (BL), and this often resulted in endothelial projection into capillary lumen. Between 75 and 83 years, pericytes contained dark mitochondria, and their processes facing the BM debris showed partial loss of BL and intermediate filaments (IFs), when the endothelium remained unaltered. The endothelial changes appeared beyond 83 years, the abundance of IFs and autophagy reinforced their survival until late aging. TUNEL⁺ pericytes, and immunoreactivity to carboxymethyl lysine and 4-hydroxy 2-nonenal, but no nitro-tyrosine, was detected in aged CC walls. Iba-1⁺ dystrophic microglia were present in the vicinity of the CC. Our data indicate that (1) BM debris exerts pressure on the CC, leading to the damage of the capillary BL and pericyte processes (2) loss of IFs results in early pericyte destabilization (3) capillary wall undergoes lipid peroxidative and glycative damage, and (4) pericyte damage leads to late endothelial changes and ultimately CC loss. Future research should explore the normal ways of pericyte maintenance in the aging nervous system.

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

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

Meteorin Is a Novel Therapeutic Target for Wet Age-Related Macular Degeneration

The aim of this study was to evaluate the potential anti-angiogenic effect of MTRN (meteorin) in the laser-induced CNV rat model and explore its mechanisms of action. MTRN, thrompospondin-1, glial cell markers (GFAP, vimentin), and phalloidin were immuno-stained in non-human primate flat-mounted retinas and human retina cross sections. The effect of MTRN at different doses and time points was evaluated on laser-induced CNV at 14 days using in vivo fluorescein angiography and ex vivo quantification of CNV. A pan transcriptomic analysis of the retina and the RPE/choroid complex was used to explore MTRN effects mechanisms. In human retina, MTRN is enriched in the macula, expressed in and secreted by glial cells, and located in photoreceptor cells, including in nuclear bodies. Intravitreal MTRN administered preventively reduced CNV angiographic scores and CNV size in a dose-dependent manner. The highest dose, administered at day 7, also reduced CNV. MTRN, which is regulated by mineralocorticoid receptor modulators in the rat retina, regulates pathways associated with angiogenesis, oxidative stress, and neuroprotection. MTRN is a potential novel therapeutic candidate protein for wet AMD.

The rare C9 P167S risk variant for age-related macular degeneration increases polymerization of the terminal component of the complement cascade

Age-related macular degeneration (AMD) is a complex neurodegenerative eye disease with behavioral and genetic etiology and is the leading cause of irreversible vision loss among elderly Caucasians. Functionally significant genetic variants in the alternative pathway of complement have been strongly linked to disease. More recently, a rare variant in the terminal pathway of complement has been associated with increased risk, Complement component 9 (C9) P167S. To assess the functional consequence of this variant, C9 levels were measured in two independent cohorts of AMD patients. In both cohorts, it was demonstrated that the P167S variant was associated with low C9 plasma levels. Further analysis showed that patients with advanced AMD had elevated sC5b-9 compared to those with non-advanced AMD, although this was not associated with the P167S polymorphism. Electron microscopy of membrane attack complexes (MACs) generated using recombinantly produced wild type or P167S C9 demonstrated identical MAC ring structures. In functional assays, the P167S variant displayed a higher propensity to polymerize and a small increase in its ability to induce hemolysis of sheep erythrocytes when added to C9-depleted serum. The demonstration that this C9 P167S AMD risk polymorphism displays increased polymerization and functional activity provides a rationale for the gene therapy trials of sCD59 to inhibit the terminal pathway of complement in AMD that are underway.

CHOROIDAL THICKNESS AND VASCULARITY VARY WITH DISEASE SEVERITY AND SUBRETINAL DRUSENOID DEPOSIT PRESENCE IN NONADVANCED AGE-RELATED MACULAR DEGENERATION

PURPOSE

To investigate how choroidal features vary with age-related macular degeneration (AMD) severity in early-intermediate disease.

METHODS

One hundred fifty-one eyes of 151 participants >50 years with no to intermediate AMD were analyzed with enhanced depth imaging optical coherence tomography. Mean macular choroidal thickness (CT), choroidal vascular thickness (CV), and choroidal vascularity index (CVI) were determined, and statistical associations were calculated.

RESULTS

Decreased CT and CV were associated with increased axial length (+30 and +14 µm/mm, respectively; P < 0.0001 each), whereas decreased CVI was associated with increased age (+0.1%/year; P = 0.004). Compared with eyes with no/early AMD (Group 0), eyes with large drusen without late AMD in the fellow eye (Group 1) showed increased CV and CVI (+22 µm, P = 0.03 and +2.2%, P = 0.02, respectively). However, eyes with large drusen and late AMD in the fellow eye (Group 2) resembled Group 0. Eyes with subretinal drusenoid deposits demonstrated lower mean CT/CV/CVI than Group 0 (-57 µm, P = 0.02; -31 µm, P = 0.02; -3.6%, P = 0.007).

CONCLUSION

Early AMD progression seems associated with biphasic alterations in choroidal dimensions, increasing during early drusen formation but decreasing thereafter. Subretinal drusenoid deposits are independently associated with marked reductions in all choroidal parameters. Changes in choroidal vascular anatomy may drive or reflect the pathobiology of AMD progression.

Changes in complement activation products after anti-VEGF injection for choroidal neovascularization in age-related macular degeneration and pachychoroid disease

We evaluated changes in the complement system resulting from anti-vascular endothelial growth factor (VEGF) in eyes with age-related choroidal neovascularization (CNV) including neovascular age-related macular degeneration, pachychoroid neovasculopathy, and polypoidal choroidal neovasculopathy. We measured the concentrations of the complement activation products (C3a, C4a), VEGF, and monocyte chemotactic protein-1 in the aqueous humor during intravitreal anti-VEGF injections for CNV. The VEGF level decreased significantly (P < 0.001), while the C3a and C4a levels increased significantly (P < 0.001 for both comparisons) 1 month after two monthly anti-VEGF injections. The VEGF level was correlated with the C3a (R = 0.328, P = 0.007) and C4a (R = − 0.237, P = 0.055) levels at baseline, but the correlation between the VEGF and C3a levels (R = − 0.148, P = 0.242) changed significantly (P = 0.028 by analysis of covariance) after anti-VEGF treatment. The C3a increase after anti-VEGF therapy did not change the visual outcomes in eyes with CNV for 1 year. Dysregulation of the complement system can be induced after anti-VEGF therapy.

Cell-Matrix Interactions in the Eye: From Cornea to Choroid

The extracellular matrix (ECM) plays a crucial role in all parts of the eye, from maintaining clarity and hydration of the cornea and vitreous to regulating angiogenesis, intraocular pressure maintenance, and vascular signaling. This review focuses on the interactions of the ECM for homeostasis of normal physiologic functions of the cornea, vitreous, retina, retinal pigment epithelium, Bruch's membrane, and choroid as well as trabecular meshwork, optic nerve, conjunctiva and tenon's layer as it relates to glaucoma. A variety of pathways and key factors related to ECM in the eye are discussed, including but not limited to those related to transforming growth factor-β, vascular endothelial growth factor, basic-fibroblastic growth factor, connective tissue growth factor, matrix metalloproteinases (including MMP-2 and MMP-9, and MMP-14), collagen IV, fibronectin, elastin, canonical signaling, integrins, and endothelial morphogenesis consistent of cellular activation-tubulogenesis and cellular differentiation-stabilization. Alterations contributing to disease states such as wound healing, diabetes-related complications, Fuchs endothelial corneal dystrophy, angiogenesis, fibrosis, age-related macular degeneration, retinal detachment, and posteriorly inserted vitreous base are also reviewed.

Treatments for dry age-related macular degeneration: therapeutic avenues, clinical trials and future directions

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in the developed world. The identification of the central role of vascular endothelial growth factor (VEGF) in the pathogenesis of neovascular AMD and the introduction of anti-VEGF agents as gold-standard treatment, have drastically changed its prognosis-something yet to be seen in dry AMD. Several therapeutic avenues with a wide variability of targets are currently being investigated in dry AMD. The approaches being investigated to reduce the rate of disease progression include, (1) drugs with antioxidative properties, (2) inhibitors of the complement cascade, (3) neuroprotective agents, (4) visual cycle inhibitors, (5) gene therapy and (6) cell-based therapies. A number of early phase clinical trials have provided promising results, with many more ongoing and anticipated in the near future. In this review, we aim to provide an update of the interventional trials to date and future prospects for the treatment of dry AMD.

Toll-like Receptor 2 Facilitates Oxidative Damage-Induced Retinal Degeneration

Retinal degeneration is a form of neurodegenerative disease and is the leading cause of vision loss globally. The Toll-like receptors (TLRs) are primary components of the innate immune system involved in signal transduction. Here we show that TLR2 induces complement factors C3 and CFB, the common and rate-limiting factors of the alternative pathway in both retinal pigment epithelial (RPE) cells and mononuclear phagocytes. Neutralization of TLR2 reduces opsonizing fragments of C3 in the outer retina and protects photoreceptor neurons from oxidative stress-induced degeneration. TLR2 deficiency also preserves tight junction expression and promotes RPE resistance to fragmentation. Finally, oxidative stress-induced formation of the terminal complement membrane attack complex and Iba1+ cell infiltration are strikingly inhibited in the TLR2-deficient retina. Our data directly implicate TLR2 as a mediator of retinal degeneration in response to oxidative stress and present TLR2 as a bridge between oxidative damage and complement-mediated retinal pathology.

Oxidative stress and complement deposition are common to many retinal degenerative diseases. Mulfaul et al. demonstrate that TLR2 blockade protects against photoreceptor neuronal cell death and RPE fragmentation in experimental models of oxidative stress-induced retinal degeneration and present TLR2 as a bridge between oxidative damage and complement-mediated retinal pathology.

The Relationship between Age-Related Macular Degeneration and Cardiovascular Disease: A Meta-Analysis

Background:

Age-related macular degeneration (AMD) and cardiovascular disease (CVD) share pathogenic mechanisms, and their lead-lag relationship remains unclear. We performed a meta-analysis of data from longitudinal studies to evaluate the interactive association between age-related macular degeneration (AMD) and cardiovascular disease (CVD).

Methods:

A literature search was performed in PubMed, Embase, and Cochrane Library up to Feb 2019. Estimates were pooled by study quality and type of AMD and CVD. Publication bias was assessed by Begg’s test.

Results:

We identified nine studies for the risk of AMD in CVD and ten studies for the risk of CVD in AMD. Overall, evidence for the risk of CVD in AMD patients was most robust. Both early and late AMD preceded CVD, but more solid significance existed in late AMD. Among the types of CVD, stroke was more tightly associated with AMD than coronary heart disease. Publication bias was not significant in either direction.

Conclusion:

AMD is a risk factor for CVD, which is primarily driven by the increased risk of stroke in patients with late AMD. Moreover, these results suggested that AMD treatment and screening for CVD in AMD patients may have unexplored clinical benefits.

Immunological Aspects of Age-Related Macular Degeneration

Increasing evidence over the past two decades points to a pivotal role for immune mechanisms in age-related macular degeneration (AMD) pathobiology. In this chapter, we will explore immunological aspects of AMD, with a specific focus on how immune mechanisms modulate clinical phenotypes of disease and severity and how components of the immune system may serve as triggers for disease progression in both dry and neovascular AMD. We will briefly review the biology of the immune system, defining the role of immune mechanisms in chronic degenerative disease and differentiating from immune responses to acute injury or infection. We will explore current understanding of the roles of innate immunity (especially macrophages), antigen-specific immunity (T cells, B cells, and autoimmunity), immune amplifications systems, especially complement activity and the NLRP3 inflammasome, in the pathogenesis of both dry and neovascular AMD, reviewing data from pathology, experimental animal models, and clinical studies of AMD patients. We will also assess how interactions between the immune system and infectious pathogens could potentially modulate AMD pathobiology via alterations in in immune effector mechanisms. We will conclude by reviewing the paradigm of "response to injury," which provides a means to integrate various immunologic mechanisms along with nonimmune mechanisms of tissue injury and repair as a model to understand the pathobiology of AMD.

Innate Immunity in Age-Related Macular Degeneration

Multiple lines of investigation have demonstrated that inflammation plays significant roles in etiology of age-related macular degeneration (AMD). Although interventional trials in AMD therapy targeting inflammatory pathways have been conducted, they have not yet been successful and a detailed understanding as to why some have failed is still elusive. One limitation is the relative dearth of information on how immune cells interact with retinal cells to generate AMD phenotypes at each disease stage. Here, we summarize current research evidence and hypotheses regarding potential pathogenic roles of innate immune cells in the eye, which include resident retinal microglia, macrophages derived from infiltrating systemic monocytes, and macrophages resident in the choroid. We relate recent findings regarding the physiology, function, and cellular interactions involving innate immune cells in the retina and choroid to AMD-related processes, including: (1) drusen formation and regression, (2) the onset and spread of degeneration in late atrophic AMD, and (3) the initiation, growth, and exudation of neovascular vessels in late "wet" AMD. Understanding how innate immune cells contribute to specific AMD phenotypes can assist in generating a comprehensive view on the inflammatory etiology of AMD and aid in identifying anti-inflammatory therapeutic strategies and selecting appropriate clinical outcomes for the planned interventions.

Single-cell RNA sequencing in vision research: Insights into human retinal health and disease

Gene expression provides valuable insight into cell function. As such, vision researchers have frequently employed gene expression studies to better understand retinal physiology and disease. With the advent of single-cell RNA sequencing, expression experiments provide an unparalleled resolution of information. Instead of studying aggregated gene expression across all cells in a heterogenous tissue, single-cell technology maps RNA to an individual cell, which facilitates grouping of retinal and choroidal cell types for further study. Single-cell RNA sequencing has been quickly adopted by both basic and translational vision researchers, and single-cell level gene expression has been studied in the visual systems of animal models, retinal organoids, and primary human retina, RPE, and choroid. These experiments have generated detailed atlases of gene expression and identified new retinal cell types. Likewise, single-cell RNA sequencing investigations have characterized how gene expression changes in the setting of many retinal diseases, including how choroidal endothelial cells are altered in age-related macular degeneration. In addition, this technology has allowed vision researchers to discover drivers of retinal development and model rare retinal diseases with induced pluripotent stem cells. In this review, we will overview the growing number of single-cell RNA sequencing studies in the field of vision research. We will summarize experimental considerations for designing single-cell RNA sequencing experiments and highlight important advancements in retinal, RPE, choroidal, and retinal organoid biology driven by this technology. Finally, we generalize these findings to genes involved in retinal degeneration and outline the future of single-cell expression experiments in studying retinal disease.

Visualization of Mouse Choroidal and Retinal Vasculature Using Fluorescent Tomato Lectin Perfusion

Purpose

To develop a reliable and simplified method to assess choroid and retinal vasculature on whole mount and cross sections in mice using tomato lectin (TL; Lycopersicon esculentum).

Methods

Albino mice (n = 27) received 1 mg/mL of TL (conjugated to Dylight-594) intravascularly through the tail vein, jugular vein, or cardiac left ventricle. Whole mounts of the retina and choroid were evaluated using fluorescence microscopy. Perfusion with GSL-IB4 conjugated to Dylight-594 and fluorescein isothiocyanate was performed to compare against labeling with TL. Co-labeling of choroidal endothelial cells with perfused TL on cross-sections with antibodies directed against the choriocapillaris-restricted endothelial cell marker CA4 was performed. The percentage of perfused choroidal and retinal vessels was assessed semiquantitatively. One mouse was subjected to thermal laser damage before perfusion to cause retinal and choroidal vasculature ablation.

Results

Intravascular injection of TL led to consistent, robust labeling of retinal and choroidal vascular walls. On cross-sections, choriocapillaris was co-labeled with CA4 and TL. On flat mount, TL perfusion resulted in better labeling of choroidal vessels using tail/jugular vein injection compared with cardiac perfusion (P < .01). More consistent labeling of the choroidal and retinal vascular trees was observed with TL than with GSL-IB4. Vascular damage caused by laser ablation was detected readily using this method.

Conclusions

TL injection intravascularly can reliably label normal and ablated choroid and retinal vasculature in mouse in a quick, simple manner.

Translational Relevance

These data will help to facilitate modeling in rodents for diseases such as age-related macular degeneration, diabetes, and other ischemic/angiogenic processes that can also be used for treatment evaluation.

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

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

Single-cell transcriptomics of the human retinal pigment epithelium and choroid in health and macular degeneration

The retinal pigment epithelium and the choroid are complex tissues whose dysfunction can lead to irreversible visual loss. In this study, single-cell RNA sequencing of both of these tissues was performed to characterize gene expression patterns specific to the retinal pigment epithelium and all major choroidal cell populations. Unique gene expression signatures of arterial, venous, and choriocapillaris vascular beds within the choroid were identified. RGCC, a gene that responds to complement and has been shown to induce endothelial apoptosis, was specifically expressed in choriocapillaris endothelial cells. This study provides potential insight into the molecular mechanisms of choroidal vascular disease and its contribution to age-related macular degeneration.

The human retinal pigment epithelium (RPE) and choroid are complex tissues that provide crucial support to the retina. Disease affecting either of these supportive tissues can lead to irreversible blindness in the setting of age-related macular degeneration. In this study, single-cell RNA sequencing was performed on macular and peripheral regions of RPE-choroid from 7 human donor eyes in 2 independent experiments. In the first experiment, total RPE/choroid preparations were evaluated and expression profiles specific to RPE and major choroidal cell populations were identified. As choroidal endothelial cells represent a minority of the total RPE/choroidal cell population but are strongly implicated in age-related macular degeneration (AMD) pathogenesis, a second single-cell RNA-sequencing experiment was performed using endothelial cells enriched by magnetic separation. In this second study, we identified gene expression signatures along the choroidal vascular tree, classifying the transcriptome of human choriocapillaris, arterial, and venous endothelial cells. We found that the choriocapillaris highly and specifically expresses the regulator of cell cycle gene (RGCC), a gene that responds to complement activation and induces apoptosis in endothelial cells. In addition, RGCC was the most up-regulated choriocapillaris gene in a donor diagnosed with AMD. These results provide a characterization of the human RPE and choriocapillaris transcriptome, offering potential insight into the mechanisms of choriocapillaris response to complement injury and choroidal vascular disease in age-related macular degeneration.

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

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

Immunological Considerations for Retinal Stem Cell Therapy

There is an increasing effort toward generating replacement cells for neuronal application due to the nonregenerative nature of these tissues. While much progress has been made toward developing methodologies to generate these cells, there have been limited improvements in functional restoration. Some of these are linked to the degenerative and often nonreceptive microenvironment that the new cells need to integrate into. In this chapter, we will focus on the status and role of the immune microenvironment of the retina during homeostasis and disease states. We will review changes in both innate and adaptive immunity as well as the role of immune rejection in stem cell replacement therapies. The chapter will end with a discussion of immune-modulatory strategies that have helped to ameliorate these effects and could potentially improve functional outcome for cell replacement therapies for the eye.

Role of the Choroid in Age-related Macular Degeneration: A Current Review

Age-related macular degeneration (AMD) is a major cause of vision loss in the developed world and its pathogenesis is a topic of active research. To date, much study has been focused on the role of the retinal pigment epithelium (RPE) and Bruch's membrane (BrM) in AMD pathogenesis, but the role of the choroid has also been investigated. In this review, we focus on recent advancements in research in the role of the choroid in AMD, beginning with an exploration of the histopathologic, cellular and molecular changes that occur in the choroid in AMD and concluding by discussing new choroidal imaging techniques and patterns seen on fluorescein angiography, indocyanine green angiography, spectral-domain optical coherence tomography and optical coherence tomography angiography. Exploring these domains will lead to a better understanding of the factors at play beyond the outer retina in this important disease.

Generation of an immortalized human choroid endothelial cell line (iChEC-1) using an endothelial cell specific promoter

Age-related macular degeneration (AMD) is a common cause of blindness worldwide. While recent studies have revealed that the loss of choroidal endothelial cells (ChECs) is critical to the disease pathogenesis of dry AMD, in vitro studies are needed to fully elucidate the disease mechanism. However, these studies remain hindered due to the lack of publically available human ChEC lines. To address this need, ChECs were harvested form donor tissue and enriched for by using magnetic cell separation using anti-CD31 conjugated microbeads. Next, lenti-viral vectors with endothelial-specific promoters driving genes necessary for immortalization, CDH5p-hTERT and CDH5p TAg, were generated. Stable integration of both gene cassettes allowed cells to maintain their proliferative state and yielded an immortalized cell line (iChEC-1). Immunocytochemical analysis of iChEC-1 confirmed the expression of important ChEC markers such as CA4, a marker of choriocapillaris endothelial cells, CDH5, and CD34, pan-endothelial cell markers. qRT-PCR analysis of expanded clones from iChEC-1 further showed that the line maintained expression of other important endothelial markers, vWF, PECAM1, and PLVAP, similar to primary cells. Functional responses were characterized by tube-forming assays and repopulation of decellularized choroid with the immortalized cell line. In conclusion, the iChEC-1 line presents a suitable immortalized human ChEC line for future in vitro studies of AMD.

RF/6A Chorioretinal Cells Do Not Display Key Endothelial Phenotypes

Purpose

The misuse of inauthentic cell lines is widely recognized as a major threat to the integrity of biomedical science. Whereas the majority of efforts to address this have focused on DNA profiling, we sought to anatomically, transcriptionally, and functionally authenticate the RF/6A chorioretinal cell line, which is widely used as an endothelial cell line to model retinal and choroidal angiogenesis.

Methods

Multiple vials of RF/6A cells obtained from different commercial distributors were studied to validate their genetic, transcriptomic, anatomic, and functional fidelity to bona fide endothelial cells.

Results

Transcriptomic profiles of RF/6A cells obtained either de novo or from a public data repository did not correspond to endothelial gene expression signatures. Expression of established endothelial markers were very low or undetectable in RF/6A compared to primary human endothelial cells. Importantly, RF/6A cells also did not display functional characteristics of endothelial cells such as uptake of acetylated LDL, expression of E-selectin in response to TNF-α exposure, alignment in the direction of shear stress, and AKT and ERK1/2 phosphorylation following VEGFA stimulation.

Conclusions

Multiple independent sources of RF/6A do not exhibit key endothelial cell phenotypes. Therefore, these cells appear unsuitable as surrogates for choroidal or retinal endothelial cells. Further, cell line authentication methods should extend beyond genomic profiling to include anatomic, transcriptional, and functional assessments.

The ARMS2 A69S Polymorphism Is Associated with Delayed Rod-Mediated Dark Adaptation in Eyes at Risk for Incident Age-Related Macular Degeneration

PURPOSE

To examine the association between sequence variants in genetic risk factors for age-related macular degeneration (AMD) and delayed rod-mediated dark adaptation (RMDA), the first functional biomarker for incident AMD, in older adults with normal macular health and early AMD.

DESIGN

Cross-sectional.

PARTICIPANTS

Adults 60 years of age or older showing normal macular health (defined as both eyes at step 1 on the Age-Related Eye Disease Study 9-step AMD classification system) and those with AMD in one or both eyes (defined as steps 2-9).

METHODS

Single nucleotide polymorphisms were genotyped in the complement factor H (CFH) and ARMS2 genes using a Taqman assay. Rod-mediated dark adaptation was assessed in 1 eye after photobleach with targets centered at 5° on the inferior vertical meridian. Rate of dark adaptation was defined by rod intercept time (RIT), duration (in minutes) required for sensitivity to reach a criterion sensitivity level in the latter half of the second component of rod recovery. Associations between CFH and ARMS2 polymorphisms and RMDA were adjusted for age and smoking.

MAIN OUTCOME MEASURE

Rod intercept time.

RESULTS

The sample consisted of 543 participants having both genotype and RIT determination; 408 showed normal macular health and 135 demonstrated AMD, most having early AMD (124 of 135). For the combined sample, higher RIT (slower RMDA) was observed for both the A69S variant in ARMS2 and the Y402H variant in CFH (adjusted P = 0.0001 and P = 0.0023, respectively). For healthy participants, the A69S variant in ARMS2 was associated with higher RIT (adjusted P = 0.0011), whereas the Y402H variant in CFH was not (adjusted P = 0.2175). For AMD patients, the A69S variant of ARMS2 and the Y402H variant of CFH were associated with higher RIT (adjusted P = 0.0182 and P = 0.0222, respectively). Those with a larger number of high-risk ARMS2 and CFH alleles showed higher RIT, in both healthy and AMD groups (adjusted P = 0.0002 and P < 0.0001, respectively).

CONCLUSIONS

We report a novel association wherein older adults with high-risk ARMS2 and CFH genotypes are more likely to demonstrate delayed RMDA, the first functional biomarker for incident early AMD. Before the AMD clinical phenotype is present, those showing normal macular health with the ARMS2 A69S allele demonstrate delayed RMDA. Understanding ARMS2 function is a research priority.

Choriocapillaris changes in dry age-related macular degeneration and geographic atrophy: a review

Age-related macular degeneration (AMD) is a leading cause of central vision loss worldwide. The progression of dry AMD from early to intermediate stages is primarily characterized by increasing drusen formation and adverse impact on outer retinal cells. Late stage AMD consists of either geographic atrophy (GA), the non-exudative (dry) AMD subtype, or choroidal neovascularization, the exudative (wet) AMD subtype. GA is characterized by outer retinal and choroidal atrophy, specifically the photoreceptor layer, RPE, and choriocapillaris. Much remains to be discovered regarding the pathogenesis of AMD progression and subsequent development of GA. As the functionality of all three layers is closely linked, the temporal sequence of events that end up in atrophy is important in the understanding of the pathogenic pathway of the disease. The advent of OCTA, and particularly of swept-source technology, has allowed for depth-resolved imaging of retinal vasculature and the choriocapillaris. With the use of OCTA, recent studies demonstrate that choriocapillaris flow alterations are closely associated with the development and progression of AMD. Such changes may even possibly offer predictive value in determining progression of GA. This article reviews studies demonstrating choriocapillaris changes in dry AMD and summarizes the existing literature on the potential role of the choriocapillaris as a key factor in the pathogenesis of AMD.

Imidazole Compounds for Protecting Choroidal Endothelial Cells from Complement Injury

Age-related macular degeneration (AMD) is a common, blinding disease associated with increased complement system activity. Eyes with AMD show elevated accumulation of the membrane attack complex (MAC) in the choriocapillaris and degeneration of macular choriocapillaris endothelial cells (ECs). Thus, one could reasonably conclude that the endothelial cell death that occurs in AMD is due to injury by the MAC. We therefore sought to identify strategies for protecting ECs against MAC lysis. RF/6A endothelial cells were pre-incubated with a library of FDA-approved small molecules, followed by incubation with complement intact human serum quantification of cell death. Two closely related molecules identified in the screen, econazole nitrate and miconazole nitrate, were followed in validation and mechanistic studies. Both compounds reduced lysis of choroidal ECs treated with complement-intact serum, across a range of doses from 1 to 100 µM. Cell rescue was confirmed in mouse primary choroidal ECs. Both exosome release and cell surface roughness (assessed using a Holomonitor system) were reduced by drug pretreatment in RF/6A cells, whereas endosome formation increased with both drugs, consistent with imidazole-mediated alterations of cell surface dynamics. The results in the current study provide further proof of principle that small molecules can protect choroidal ECs from MAC-induced cell death and suggest that FDA approved compounds may be beneficial in reducing vascular loss and progression of AMD.

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

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

Choriocapillaris Loss in Advanced Age-Related Macular Degeneration

The purpose of this review is to summarize the current knowledge on choriocapillaris loss in advanced age macular degeneration (AMD). Several histopathological studies in animal models and human eyes had showed that the choriocapillaris density decreases with age. However, the role of choriocapillaris loss is still unclear in AMD and its advanced forms, either choroidal neovascularization (CNV) or geographic atrophy (GA). Some authors have hypothesized that choriocapillaris loss might precede overt retinal pigment epithelium atrophy. Others have hypothesized that deposition of complement complexes on and around the choriocapillaris could be related to the tissue loss observed in early AMD. The development of imaging modalities, such as optical coherence tomography angiography (OCTA), have led to a better understanding of underlying physiopathological mechanisms in AMD. OCTA showed atrophy of choriocapillaris underneath and beyond the region of photoreceptors and RPE loss, in agreement with previous histopathologic studies. The evolution of OCTA technology suggests that CNV seems to originate from regions of severe choriocapillaris alteration. Significant progress has been made in the understanding of development and progression of GA and CNV. In vivo investigation of the choriocapillaris using OCTA may lead to new insights related to underlying disease mechanisms in AMD.

Induced neural stem cell-derived astrocytes modulate complement activation and mediate neuroprotection following closed head injury

The complement system is a crucial component of immunity, and its activation has critical roles in neuroinflammatory response and cellular damage following closed head injury (CHI). We previously demonstrated that systemically injected induced neural stem cells (iNSCs) could modulate complement activation to ameliorate neuronal apoptosis in mouse CHI models. However, it remains unknown whether iNSC derivatives can regulate complement activation. In the present study, after CHI mouse serum treatment, we found dramatic decreases in the cellular viabilities of differentiated iNSCs. Interestingly, following CHI mouse serum treatment, the death of astrocytes derived from iNSCs which were pre-treated with CHI mouse serum was significantly decreased. Meanwhile, the deposition of C3 (C3d) and C5b-9 in these astrocytes was substantially reduced. Remarkably, we detected increased expression of complement receptor type 1-related protein y (Crry) in these astrocytes. Moreover, these astrocytes could reduce the numbers of apoptotic neurons via Crry expression post-CHI mouse serum treatment. Additionally, intracerebral-transplanted iNSCs, pre-treated with CHI mouse serum, significantly increased the levels of Crry expression in astrocytes to reduce the accumulation of C3d and C9 and the death of neurons in the brains of CHI mice. In summary, iNSCs receiving CHI mouse serum pre-treatment could enhance the expression of Crry in iNSC-derived astrocytes to modulate complement activation and mediate neuroprotection following CHI.

From compliment to insult: genetics of the complement system in physiology and disease in the human retina

Age-related macular degeneration (AMD) is a major cause of visual impairment that affects the central retina. Genome wide association studies and candidate gene screens have identified members of the complement pathway as contributing to the risk of AMD. In this review, we discuss the complement system, its importance in retinal development and normal physiology, how its dysregulation may contribute to disease, and how it might be targeted to prevent damage to the aging choriocapillaris in AMD.

Risks of newly onset hemorrhagic stroke in patients with neovascular age-related macular degeneration

PURPOSE

Age-related macular degeneration (AMD) is an eye disease causing blindness in the elderly. It shares many common possible pathogenic mechanisms with cardiovascular diseases. Many studies have discussed the association between AMD and stroke, but the results were inconsistent. Our aim was to determine the associations between neovascular AMD and the risk of stroke in the Taiwanese population.

METHODS

This is a retrospective cohort study. We used claims data from National Health Insurance Research Database. Patients aged more than 45 years without stroke, myocardial infarction, or any AMD were selected from 2001 to 2008 and followed until 2010. The index date was defined as the date of nAMD diagnosis (ICD-9 code, 362.52). The comparison group was patients without an nAMD diagnosis with age- and sex-matched to nAMD subjects at a ratio of up to 10 to 1. Kaplan-Meier survival analysis and Cox regression analysis were used. The incidence of stroke events (ICD-9 codes, 430-434) and their subtypes (hemorrhagic and ischemic) were primary outcomes. Secondary outcomes included acute myocardial infarction (AMI), composite AMI/stroke, and all-cause mortality.

RESULTS

Patients with nAMD had a higher risk of developing stroke, with an adjusted HR of 1.30 (95% CI, 1.01-1.68). A higher risk for hemorrhagic stroke (HR, 1.70, 95% CI, 1.03-2.83) was also found. No significant differences were observed in ischemic stroke, the composite of AMI/stroke, and all-cause mortality.

CONCLUSIONS

Patients with nAMD had a significantly higher risk of developing stroke, which was driven mainly by the increased risk of developing the hemorrhagic subtype.

Connective Tissue Growth Factor Promotes Efficient Generation of Human Induced Pluripotent Stem Cell-Derived Choroidal Endothelium

Age‐related macular degeneration (AMD) is a leading cause of irreversible blindness in the Western world. Although, the majority of stem cell research to date has focused on production of retinal pigment epithelial (RPE) and photoreceptor cells for the purpose of evaluating disease pathophysiology and cell replacement, there is strong evidence that the choroidal endothelial cells (CECs) that form the choriocapillaris vessels are the first to be lost in this disease. As such, to accurately evaluate disease pathophysiology and develop an effective treatment, production of patient‐specific, stem cell‐derived CECs will be required. In this study, we report for the first time a stepwise differentiation protocol suitable for generating human iPSC‐derived CEC‐like cells. RNA‐seq analysis of the monkey CEC line, RF/6A, combined with two statistical screens allowed us to develop media comprised of various protein combinations. In both screens, connective tissue growth factor (CTGF) was identified as the key component required for driving CEC development. A second factor tumor necrosis factor (TNF)‐related weak inducer of apoptosis receptor was also found to promote iPSC to CEC differentiation by inducing endogenous CTGF secretion. CTGF‐driven iPSC‐derived CEC‐like cells formed capillary tube‐like vascular networks, and expressed the EC‐specific markers CD31, ICAM1, PLVAP, vWF, and the CEC‐restricted marker CA4. In combination with RPE and photoreceptor cells, patient‐specific iPSC derived CEC‐like cells will enable scientists to accurately evaluate AMD pathophysiology and develop effective cell replacement therapies. Stem Cells Translational Medicine2017;6:1533–1546

Systemic Administration of Induced Neural Stem Cells Regulates Complement Activation in Mouse Closed Head Injury Models

Complement activation plays important roles in the pathogenesis of central nervous system (CNS) diseases. Patients face neurological disorders due to the development of complement activation, which contributes to cell apoptosis, brain edema, blood-brain barrier dysfunction and inflammatory infiltration. We previously reported that induced neural stem cells (iNSCs) can promote neurological functional recovery in closed head injury (CHI) animals. Remarkably, we discovered that local iNSC grafts have the potential to modulate CNS inflammation post-CHI. In this study, we aimed to explore the role of systemically delivered iNSCs in complement activation following CNS injury. Our data showed that iNSC grafts decreased the levels of sera C3a and C5a and down-regulated the expression of C3d, C9, active Caspase-3 and Bax in the brain, kidney and lung tissues of CHI mice. Furthermore, iNSC grafts decreased the levels of C3d⁺/NeuN⁺, C5b-9⁺/NeuN⁺, C3d⁺/Map2⁺ and C5b-9⁺/Map2⁺ neurons in the injured cortices of CHI mice. Subsequently, we explored the mechanisms underlying these effects. With flow cytometry analysis, we observed a dramatic increase in complement receptor type 1-related protein y (Crry) expression in iNSCs after CHI mouse serum treatment. Moreover, both in vitro and in vivo loss-of-function studies revealed that iNSCs could modulate complement activation via Crry expression.

Potential protective function of the sterol regulatory element binding factor 1-fatty acid desaturase 1/2 axis in early-stage age-related macular degeneration

Age-related macular degeneration (AMD) is the most common cause of vision loss in elderly individuals throughout the developed world. Inhibitors of vascular endothelial growth factor have been successfully used to treat choroidal neovascularization in late-stage AMD. The pathogenesis of early-stage AMD, however, remains largely unknown, impairing efforts to develop effective therapies that prevent progression to late-stage AMD. To address this, we performed comparative transcriptomics of macular and extramacular retinal pigmented epithelium-choroid (RPE-choroid) tissue from early-stage AMD patients. We found that expression of fatty acid desaturase 1 (FADS1), FADS2, and acetyl-CoA acetyltransferase 2 (ACAT2) is increased in macular but not extramacular tissue, possibly through activation of sterol regulatory element binding factor 1 (SREBF1). Consistent with this, we also found that expression of Fads1 is increased in RPE-choroid in a mouse model of early-stage AMD. In zebrafish, deletion of fads2, which encodes a protein that functions as both Fads1 and Fads2 in other species, enhanced apoptosis in the retina upon exposure to intense light. Similarly, pharmacological inhibition of Srebf1 enhanced apoptosis and reduced fads2 expression in zebrafish exposed to intense light. These results suggest that the SREBF1-FADS1/2 axis may be activated in macular RPE-choroid as a protective response during early-stage AMD and could thus be a therapeutic target for early-stage AMD.

VEGF regulates local inhibitory complement proteins in the eye and kidney

Outer retinal and renal glomerular functions rely on specialized vasculature maintained by VEGF that is produced by neighboring epithelial cells, the retinal pigment epithelium (RPE) and podocytes, respectively. Dysregulation of RPE- and podocyte-derived VEGF is associated with neovascularization in wet age-related macular degeneration (ARMD), choriocapillaris degeneration, and glomerular thrombotic microangiopathy (TMA). Since complement activation and genetic variants in inhibitory complement factor H (CFH) are also features of both ARMD and TMA, we hypothesized that VEGF and CFH interact. Here, we demonstrated that VEGF inhibition decreases local CFH and other complement regulators in the eye and kidney through reduced VEGFR2/PKC-α/CREB signaling. Patient podocytes and RPE cells carrying disease-associated CFH genetic variants had more alternative complement pathway deposits than controls. These deposits were increased by VEGF antagonism, a common wet ARMD treatment, suggesting that VEGF inhibition could reduce cellular complement regulatory capacity. VEGF antagonism also increased markers of endothelial cell activation, which was partially reduced by genetic complement inhibition. Together, these results suggest that VEGF protects the retinal and glomerular microvasculature, not only through VEGFR2-mediated vasculotrophism, but also through modulation of local complement proteins that could protect against complement-mediated damage. Though further study is warranted, these findings could be relevant for patients receiving VEGF antagonists.

Structural and molecular changes in the aging choroid: implications for age-related macular degeneration

Age-related macular degeneration (AMD) is a devastating disease-causing vision loss in millions of people around the world. In advanced stages of disease, death of photoreceptor cells, retinal pigment epithelial cells, and choroidal endothelial cells (CECs) are common. Loss of endothelial cells of the choriocapillaris is one of the earliest detectable events in AMD, and, because the outer retina relies on the choriocapillaris for metabolic support, this loss may be the trigger for progression to more advanced stages. Here we highlight evidence for loss of CECs, including changes to vascular density within the choriocapillaris, altered abundance of CEC markers, and changes to overall thickness of the choroid. Furthermore, we review the key components and functions of the choroid, as well as Bruch's membrane, both of which are vital for healthy vision. We discuss changes to the structure and molecular composition of these tissues, many of which develop with age and may contribute to AMD pathogenesis. For example, a crucial event that occurs in the aging choriocapillaris is accumulation of the membrane attack complex, which may result in complement-mediated CEC lysis, and may be a primary cause for AMD-associated choriocapillaris degeneration. The actions of elevated monomeric C-reactive protein in the choriocapillaris in at-risk individuals may also contribute to the inflammatory environment in the choroid and promote disease progression. Finally, we discuss the progress that has been made in the development of AMD therapies, with a focus on cell replacement.

A Revised Hemodynamic Theory of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) afflicts one out of every 40 individuals worldwide, causing irreversible central blindness in millions. The transformation of various tissue layers within the macula in the retina has led to competing conceptual models of the molecular pathways, cell types, and tissues responsible for the onset and progression of AMD. A model that has persisted for over 6 decades is the hemodynamic, or vascular theory of AMD progression, which states that vascular dysfunction of the choroid underlies AMD pathogenesis. Here, we re-evaluate this hypothesis in light of recent advances on molecular, anatomic, and hemodynamic changes underlying choroidal dysfunction in AMD. We propose an updated, detailed model of hemodynamic dysfunction as a mechanism of AMD development and progression.

Dry Age-Related Macular Degeneration Pharmacology

Age-related macular degeneration (AMD), the most common form of irreversible blindness in the industrially developed world, can present years before a patient begins to lose vision. For most of these patients, AMD never progresses past its early stages to the advanced forms that are principally responsible for the vast majority of vision loss. Advanced AMD can manifest as either an advanced avascular form known as geographic atrophy (GA) marked by regional retinal pigment epithelium (RPE) cell death or as an advanced form known as neovascular AMD marked by the intrusion of fragile new blood vessels into the normally avascular retina. Physicians have several therapeutic interventions available to combat neovascular AMD, but GA has no approved effective therapies as of yet. In this chapter, we will discuss the current strategies for limiting dry AMD in patients. We will also discuss previous attempts at pharmacological intervention that were tested in a clinical setting and consider reasons why these putative therapeutics did not perform successfully in large-scale trials. Despite the number of unsuccessful past trials, new pharmacological interventions may succeed. These future therapies may aid millions of AMD patients worldwide.