NLRP3 inflammasome blockade inhibits VEGF-A-induced age-related macular degeneration

Vascular endothelial growth factor signaling in health and disease: from molecular mechanisms to therapeutic perspectives

Vascular endothelial growth factor (VEGF) signaling is a critical regulator of vasculogenesis, angiogenesis, and lymphangiogenesis, processes that are vital for the development of vascular and lymphatic systems, tissue repair, and the maintenance of homeostasis. VEGF ligands and their receptors orchestrate endothelial cell proliferation, migration, and survival, playing a pivotal role in dynamic vascular remodeling. Dysregulated VEGF signaling drives diverse pathological conditions, including tumor angiogenesis, cardiovascular diseases, and ocular disorders. Excessive VEGF activity promotes tumor growth, invasion, and metastasis, while insufficient signaling contributes to impaired wound healing and ischemic diseases. VEGF-targeted therapies, such as monoclonal antibodies and tyrosine kinase inhibitors, have revolutionized the treatment of diseases involving pathological angiogenesis, offering significant clinical benefits in oncology and ophthalmology. These therapies inhibit angiogenesis and slow disease progression, but they often face challenges such as therapeutic resistance, suboptimal efficacy, and adverse effects. To further explore these issues, this review provides a comprehensive overview of VEGF ligands and receptors, elucidating their molecular mechanisms and regulatory networks. It evaluates the latest progress in VEGF-targeted therapies and examines strategies to address current challenges, such as resistance mechanisms. Moreover, the discussion includes emerging therapeutic strategies such as innovative drug delivery systems and combination therapies, highlighting the continuous efforts to improve the effectiveness and safety of VEGF-targeted treatments. This review highlights the translational potential of recent discoveries in VEGF biology for improving patient outcomes.

Glucagon-Like Peptide 1 Receptor Agonist Stimulation Inhibits Laser-Induced Choroidal Neovascularization by Suppressing Intraocular Inflammation

Purpose

The glucagon-like peptide-1 receptor (GLP-1R), a diabetes therapy target, is expressed in multiple organs and is associated with neuroprotective, anti-inflammatory, and antitumor effects, particularly in cardiac and cerebral tissues. Although GLP-1's role in diabetic and ischemic retinopathies is well-studied, its influence on choroidal neovascularization (CNV) in exudative age-related macular degeneration (AMD) remains unclear. This study explored the effects of GLP-1 on CNV using a laser-induced mouse model.

Methods

The anti-angiogenic effects of GLP-1 were tested using ex vivo sprouting assays in 3-week-old C57BL/6J mice. In 6-week-old mice, GLP-1R localization in laser-induced CNV lesions was analyzed via immunohistochemistry. Liraglutide, a GLP-1R agonist, was administered subcutaneously for 7 days or by single intravitreal injection post-laser. Eyeballs collected on days 1 to 7 post-laser were analyzed using RT-qPCR for GLP-1R expression and inflammatory cytokines.

Results

GLP-1R-positive cells were detected in CNV lesions and were expressed in Iba-1-positive activated microglia or macrophages. They also expressed in abnormal retinal pigment epithelial cells and surrounding normal endothelial cells. NOD-like receptor protein 3 (NLRP3) inflammasome signaling was observed near CNV. Liraglutide inhibited angiogenesis in ex vivo assays and significantly reduced CNV formation with both subcutaneous and intravitreal administration. Additionally, Liraglutide inhibited expression of NLRP3, IL-1β, IL-6, and TNF expression compared with healthy controls. Intravitreal GLP-1R antagonist reduced subcutaneous effects.

Conclusions

Liraglutide suppresses CNV formation, likely via NLRP3 inflammasome inhibition. Intraocular GLP-1R appears to mediate anti-CNV effects, supporting GLP-1R agonists as potential adjunctive therapy for exudative AMD and warranting further investigation into its safety and clinical feasibility.

Inflammasome activation aggravates choroidal neovascularization

Inflammasome activation is implicated in diseases of aberrant angiogenesis such as age-related macular degeneration (AMD), though its precise role in choroidal neovascularization (CNV), a characteristic pathology of advanced AMD, is ill-defined. Reports on inhibition of inflammasome constituents on CNV are variable and the precise role of inflammasome in mediating pathological angiogenesis is unclear. Historically, subretinal injection of inflammasome agonists alone has been used to investigate retinal pigmented epithelium (RPE) degeneration, while the laser photocoagulation model has been used to study pathological angiogenesis in a model of CNV. Here, we report that the simultaneous introduction of any of several disease-relevant inflammasome agonists (Alu or B2 RNA, Alu cDNA, or oligomerized amyloid β (1-40)) exacerbates laser-induced CNV. These activities were diminished or abrogated by genetic or pharmacological targeting of inflammasome signaling constituents including P2rx7, Nlrp3, caspase-1, caspase-11, and Myd88, as well as in myeloid-specific caspase-1 knockout mice. Alu RNA treatment induced inflammasome activation in macrophages within the CNV lesion, and increased accumulation of macrophages in an inflammasome-dependent manner. Finally, IL-1β neutralization prevented inflammasome agonist-induced chemotaxis, macrophage trafficking, and angiogenesis. Collectively, these observations support a model wherein inflammasome stimulation promotes and exacerbates CNV and may be a therapeutic target for diseases of angiogenesis such as neovascular AMD.

The Scavenging Activity of Coenzyme Q10 Plus a Nutritional Complex on Human Retinal Pigment Epithelial Cells

Age-related macular degeneration (AMD) and diabetic retinopathy (DR) are common retinal diseases responsible for most blindness in working-age and elderly populations. Oxidative stress and mitochondrial dysfunction play roles in these pathogenesis, and new therapies counteracting these contributors could be of great interest. Some molecules, like coenzyme Q10 (CoQ10), are considered beneficial to maintain mitochondrial homeostasis and contribute to the prevention of cellular apoptosis. We investigated the impact of adding CoQ10 (Q) to a nutritional antioxidant complex (Nutrof Total®; N) on the mitochondrial status and apoptosis in an in vitro hydrogen peroxide (H2O2)-induced oxidative stress model in human retinal pigment epithelium (RPE) cells. H2O2 significantly increased 8-OHdG levels (p < 0.05), caspase-3 (p < 0.0001) and TUNEL intensity (p < 0.01), and RANTES (p < 0.05), caspase-1 (p < 0.05), superoxide (p < 0.05), and DRP-1 (p < 0.05) levels, and also decreased IL1β, SOD2, and CAT gene expression (p < 0.05) vs. control. Remarkably, Q showed a significant recovery in IL1β gene expression, TUNEL, TNFα, caspase-1, and JC-1 (p < 0.05) vs. H2O2, and NQ showed a synergist effect in caspase-3 (p < 0.01), TUNEL (p < 0.0001), mtDNA, and DRP-1 (p < 0.05). Our results showed that CoQ10 supplementation is effective in restoring/preventing apoptosis and mitochondrial stress-related damage, suggesting that it could be a valid strategy in degenerative processes such as AMD or DR.

Metabolic Regulation of Endothelial Cells: A New Era for Treating Wet Age-Related Macular Degeneration

Wet age-related macular degeneration (wet AMD) is a primary contributor to visual impairment and severe vision loss globally, but the prevailing treatments are often unsatisfactory. The development of conventional treatment strategies has largely been based on the understanding that the angiogenic switch of endothelial cells (ECs) is mainly dictated by angiogenic growth factors. Even though treatments targeting vascular endothelial growth factor (VEGF), like ranibizumab, are widely administered, more than half of patients still exhibit inadequate or null responses, suggesting the involvement of other pathogenic mechanisms. With advances in research in recent years, it has become well recognized that EC metabolic regulation plays an active rather than merely passive responsive role in angiogenesis. Disturbances of these metabolic pathways may lead to excessive neovascularization in angiogenic diseases such as wet AMD, therefore targeted modulation of EC metabolism represents a promising therapeutic strategy for wet AMD. In this review, we comprehensively discuss the potential applications of EC metabolic regulation in wet AMD treatment from multiple perspectives, including the involvement of ECs in wet AMD pathogenesis, the major endothelial metabolic pathways, and novel therapeutic approaches targeting metabolism for wet AMD.

Role of NLRP3 Inflammasomes in Monocyte and Microglial Recruitments in Choroidal Neovascularization

Although the pathogenesis of choroidal neovascularization (CNV) is largely unknown in age-related macular degeneration (AMD), inflammasomes may contribute to CNV development and progression. To understand the role NLRP3 inflammasomes in CNV, we used Ccr2RFPCx3cr1GFP dual-reporter mice and immunostaining techniques to confirm localization of NLRP3 inflammasomes in the laser-induced CNV (LCNV) lesions. Confocal microscopy was used to image and quantify LCNV volumes. MCC950 was used as NLRP3 inhibitor. ELISA and quantitative RT-PCR were used to confirm the activation of NLRP3 by monitoring the expression of IL-1β protein and mRNA in choroidal tissues from LCNV mice. In addition, NLRP3 (-/-) LCNV mice were used to investigate whether NLRP3 inflammasomes contribute to the development of LCNV lesions. We observed that red fluorescent protein (RFP)-positive monocyte-derived macrophages and GFP-positive microglia-derived macrophages, in addition to other cell types, were localized in LCNV lesions at day 7 post-laser injury. In addition, NLRP3 inflammasomes are associated with LCNV lesions. Inhibition of NLRP3 inflammasomes, using MCC950, caused an increased Ccr2RFP-positive macrophages, Cx3cr1GFP-positive microglia, and other cells, resulting in an increase in total lesion size. NLRP3 (-/-) LCNV mice showed significantly increased lesion size compared with age-matched controls. Inhibition of NLRP3 resulted in decreased IL-1β mRNA and protein expression in the choroidal tissues, suggesting that increased lesion size may not be directly related to IL-1β.

Association of Intermediate-Stage Age-Related Macular Degeneration with Plasma Inflammatory Biomarkers in Persons with AIDS

Purpose

To evaluate associations of plasma levels of inflammatory biomarkers with age-related macular degeneration (AMD) and cataract in persons with AIDS.

Design

Nested case-control study (analysis 1) and nested cohort study (analysis 2).

Participants

Analysis 1: persons with AIDS and incident intermediate-stage AMD (n = 26) and controls without AMD matched for age, race/ethnicity, and gender (n = 49) from The Longitudinal Study of Ocular Complications of AIDS. Analysis 2: 475 persons from LSOCA with baseline plasma biomarker levels followed prospectively for cataract.

Methods

In both analyses, cryopreserved plasma specimens obtained at baseline were assayed for monocyte chemoattractant protein (MCP)-1 (CC motif chemokine ligand [CCL] 2), macrophage inflammatory protein (MIP)-1β (CCL4), soluble tumor necrosis factor receptor (sTNFR) 2, interleukin (IL)-18, and fractalkine (CX3 motif chemokine ligand 1 [CX3CL1]).

Main Outcome Measures

Analysis 1: mean difference (cases - controls) in plasma biomarker levels. Analysis 2: incident cataract.

Results

After adjusting for plasma human immunodeficiency virus RNA level, CD4+ T-cell count, and smoking, elevated baseline plasma levels of sTNFR2 and IL-18 (mean differences [cases - controls] 0.11 log10[pg/mL]; 95% confidence interval [CI], 0.01-0.20; P = 0.024 and 0.13 log10[pg/mL]; 95% CI, 0.01-0.24; P = 0.037, respectively) each were associated with incident AMD. In a competing risk (with mortality) analysis, elevated baseline standardized log10 plasma levels of MCP-1, sTNFR2, IL-18, and fractalkine each were associated with a decreased cataract risk.

Conclusions

When combined with previous data suggesting that AMD is associated with elevated plasma levels of C-reactive protein, soluble CD14, and possibly IL-6, the association of elevated plasma levels of sTNFR2 and IL-18 with incident AMD, but not with incident cataract, suggests that innate immune system activation, and possibly NLRP3 inflammasome activation, may play a role in the pathogenesis of AMD in this population.

Financial Disclosures

The authors have no proprietary or commercial interest in any materials discussed in this article.

Ferroptosis as a potential therapeutic target for age-related macular degeneration

Cell death plays a crucial part in the process of age-related macular degeneration (AMD), but its mechanisms remain elusive. Accumulating evidence suggests that ferroptosis, a novel form of regulatory cell death characterized by iron-dependent accumulation of lipid hydroperoxides, has a crucial role in the pathogenesis of AMD. Numerous studies have suggested that ferroptosis participates in the degradation of retinal cells and accelerates the progression of AMD. Furthermore, inhibitors of ferroptosis exhibit notable protective effects in AMD, underscoring the significance of ferroptosis as a pivotal mechanism in the death of retinal cells during the process of AMD. This review aims to summarize the molecular mechanisms of ferroptosis in AMD, enumerate potential inhibitors and discuss the challenges and future opportunities associated with targeting ferroptosis as a therapeutic strategy, providing important information references and insights for the prevention and treatment of AMD.

Role of NLRP3 inflammasomes in monocyte and microglial recruitments in choroidal neovascularization

Though the pathogenesis of choroidal neovascularization (CNV) is largely unknown in age-related macular degeneration (AMD), inflammasomes may contribute to CNV development and progression. To understand the role NLRP3 inflammasomes in CNV, we used Ccr2RFPCx3cr1GFP dual-reporter mice to characterize migration of Ccr2RFP positive monocytes and Cx3cr1GFP positive microglial cells into CNV lesions after laser-induced rupture of Bruch's membrane. MCC950 was used as NLRP3 inhibitor. Immunostaining was used to confirm localization of NLRP3 inflammasomes in the LCNV lesions. Confocal microscopy was used to image and quantify LCNV volumes. ELISA and qRT-PCR were used to confirm the activation of NLRP3 by monitoring the expression of IL-1β protein and mRNA in choroidal tissues from LCNV mice. In addition, NLRP3 (-/-) LCNV mice were used to investigate whether NLRP3 inflammasomes contribute to the development of LCNV lesions. We observed that RFP positive monocyte-derived macrophages and GFP positive microglia-derived macrophages, in addition to other cell types, were localized in LCNV lesions at day 7 post-laser injury. In addition, NLRP3 inflammasomes are associated with LCNV lesions. Inhibition of NLRP3 inflammasomes, using MCC950, caused an increased Ccr2RFP positive macrophages, Cx3cr1GFP positive microglia, and other cells resulting in an increase in total lesion size. NLRP3 (-/-) LCNV mice, showed significantly increased lesion size compared to age-matched controls. Inhibition of NLRP3, resulted in decreased IL-1β mRNA and protein expression in the choroidal tissues, suggesting that increased lesion size may not be directly related to IL-1β.

IL-11 induces NLRP3 inflammasome activation in monocytes and inflammatory cell migration to the central nervous system

The objective of this study is to examine IL-11-induced mechanisms of inflammatory cell migration to the central nervous system (CNS). We report that IL-11 is produced at highest frequency by myeloid cells among the peripheral blood mononuclear cell (PBMC) subsets. Patients with relapsing-remitting multiple sclerosis (RRMS) have an increased frequency of IL-11+ monocytes, IL-11+ and IL-11R+ CD4+ lymphocytes, and IL-11R+ neutrophils in comparison to matched healthy controls. IL-11+ and granulocyte-macrophage colony-stimulating factor (GM-CSF)+ monocytes, CD4+ lymphocytes, and neutrophils accumulate in the cerebrospinal fluid (CSF). The effect of IL-11 in-vitro stimulation, examined using single-cell RNA sequencing, revealed the highest number of differentially expressed genes in classical monocytes, including up-regulated NFKB1, NLRP3, and IL1B. All CD4+ cell subsets had increased expression of S100A8/9 alarmin genes involved in NLRP3 inflammasome activation. In IL-11R+-sorted cells from the CSF, classical and intermediate monocytes significantly up-regulated the expression of multiple NLRP3 inflammasome-related genes, including complement, IL18, and migratory genes (VEGFA/B) in comparison to blood-derived cells. Therapeutic targeting of this pathway with αIL-11 mAb in mice with RR experimental autoimmune encephalomyelitis (EAE) decreased clinical scores, CNS inflammatory infiltrates, and demyelination. αIL-11 mAb treatment decreased the numbers of NFκBp65+, NLRP3+, and IL-1β+ monocytes in the CNS of mice with EAE. The results suggest that IL-11/IL-11R signaling in monocytes represents a therapeutic target in RRMS.

Suppressing Inflammation for the Treatment of Diabetic Retinopathy and Age-Related Macular Degeneration: Dazdotuftide as a Potential New Multitarget Therapeutic Candidate

Diabetic retinopathy (DR) and age-related macular degeneration (AMD) are major causes of blindness globally. The primary treatment option for DME and neovascular AMD (nAMD) is anti-vascular endothelial growth factor (VEGF) compounds, but this treatment modality often yields insufficient results, and monthly injections can place a burden on the health system and patients. Although various inflammatory pathways and mediators have been recognized as key players in the development of DR and AMD, there are limited treatment options targeting these pathways. Molecular pathways that are interlinked, or triggers of multiple inflammatory pathways, could be promising targets for drug development. This review focuses on the role of inflammation in the pathogenesis of DME and AMD and presents current anti-inflammatory compounds, as well as a potential multitarget anti-inflammatory compound (dazdotuftide) that could be a candidate treatment option for the management of DME and AMD.

Short exposure to photo-oxidative damage triggers molecular signals indicative of early retinal degeneration

Introduction

Age-related macular degeneration (AMD) is the leading cause of blindness in the developed world, currently affecting over 350 billion people globally. For the most prevalent late-stage form of this disease, atrophic AMD, there are no available prevention strategies or treatments, in part due to inherent difficulties in early-stage diagnosis. Photo-oxidative damage is a well-established model for studying inflammatory and cell death features that occur in late-stage atrophic AMD, however to date has not been investigated as a potential model for studying early features of disease onset. Therefore, in this study we aimed to determine if short exposure to photo-oxidative damage could be used to induce early retinal molecular changes and advance this as a potential model for studying early-stage AMD.

Methods

C57BL/6J mice were exposed to 1, 3, 6, 12, or 24h photo-oxidative damage (PD) using 100k lux bright white light. Mice were compared to dim-reared (DR) healthy controls as well as mice which had undergone long periods of photo-oxidative damage (3d and 5d-PD) as known timepoints for inducing late-stage retinal degeneration pathologies. Cell death and retinal inflammation were measured using immunohistochemistry and qRT-PCR. To identify retinal molecular changes, retinal lysates were sent for RNA sequencing, following which bioinformatics analyses including differential expression and pathway analyses were performed. Finally, to investigate modulations in gene regulation as a consequence of degeneration, microRNA (miRNA) expression patterns were quantified using qRT-PCR and visualized using in situ hybridization.

Results

Short exposure to photo-oxidative damage (1-24h-PD) induced early molecular changes in the retina, with progressive downregulation of homeostatic pathways including metabolism, transport and phototransduction observed across this time-course. Inflammatory pathway upregulation was observed from 3h-PD, preceding observable levels of microglia/macrophage activation which was noted from 6h-PD, as well as significant photoreceptor row loss from 24h-PD. Further rapid and dynamic movement of inflammatory regulator miRNA, miR-124-3p and miR-155-5p, was visualized in the retina in response to degeneration.

Conclusion

These results support the use of short exposure to photo-oxidative damage as a model of early AMD and suggest that early inflammatory changes in the retina may contribute to pathological features of AMD progression including immune cell activation and photoreceptor cell death. We suggest that early intervention of these inflammatory pathways by targeting miRNA such as miR-124-3p and miR-155-5p or their target genes may prevent progression into late-stage pathology.

Orally Delivered Connexin43 Hemichannel Blocker, Tonabersat, Inhibits Vascular Breakdown and Inflammasome Activation in a Mouse Model of Diabetic Retinopathy

Diabetic retinopathy (DR), a microvascular complication of diabetes, is associated with pronounced inflammation arising from the activation of a nucleotide-binding and oligomerization domain-like receptor (NLR) protein 3 (NLRP3) inflammasome. Cell culture models have shown that a connexin43 hemichannel blocker can prevent inflammasome activation in DR. The aim of this study was to evaluate the ocular safety and efficacy of tonabersat, an orally bioavailable connexin43 hemichannel blocker, to protect against DR signs in an inflammatory non-obese diabetic (NOD) DR mouse model. For retina safety studies, tonabersat was applied to retinal pigment epithelial (ARPE-19) cells or given orally to control NOD mice in the absence of any other stimuli. For efficacy studies, either tonabersat or a vehicle was given orally to the inflammatory NOD mouse model two hours before an intravitreal injection of pro-inflammatory cytokines, interleukin-1 beta, and tumour necrosis factor-alpha. Fundus and optical coherence tomography images were acquired at the baseline as well as at 2- and 7-day timepoints to assess microvascular abnormalities and sub-retinal fluid accumulation. Retinal inflammation and inflammasome activation were also assessed using immunohistochemistry. Tonabersat did not have any effect on ARPE-19 cells or control NOD mouse retinas in the absence of other stimuli. However, the tonabersat treatment in the inflammatory NOD mice significantly reduced macrovascular abnormalities, hyperreflective foci, sub-retinal fluid accumulation, vascular leak, inflammation, and inflammasome activation. These findings suggest that tonabersat may be a safe and effective treatment for DR.

Network Pharmacology-Based Identification of Key Targets of Ziyin Mingmu Pills Acting on Age-Related Macular Degeneration

Objective

This study is designed to find out the molecular targets of effective Chinese medicine Ziyin Mingmu pills (ZMPs) in treating age-related macular degeneration (AMD) based on network pharmacology and experimental data.

Methods

A comprehensive network pharmacology strategy that consists of three sequential modules (drug-disease target molecular docking, enrichment analysis, and external verification) was carried out to identify potential targets of ZMPs acting on AMD.

Results

The active ingredients of ZMPs targeting 66 genes have effects on the process of AMD. GO and KEGG pathway enrichment analyses suggested that response to oxidative stress, regulation of angiogenesis, and lipid and atherosclerosis might serve as the most important signaling pathways in ZMPs for AMD treatment. Combined with the GSE29801 dataset for further analysis, two key genes, EGFR and VEGFA, were identified. Immune infiltration analysis showed that there was a strong association between EGFR and immune cell content. In addition, images were acquired following 24 h in the scratch experiment showed that ZMPs can reduce the percentage of wound healing distance. The Western blot assay found that ZMPs increased the expression of EGFR and decreased the expression of VEGFA.

Conclusion

This study sheds light on some mechanisms of ZMP therapy for AMD, particularly the effect of ZMP on the oxidative stress in RPE and cell survival and angiogenesis in AMD. We propound ZMPs as a promising strategy to intervene in the process of AMD.

Role of inflammasome activation in neovascular age-related macular degeneration

Current anti-VEGF-A therapies inhibit choroidal neovascularization (CNV) in a subset of patients with neovascular age-related macular degeneration (NV-AMD). However, long-term treatment with such anti-VEGF-A therapies may impair physiological functions of the choriocapillaris and retina for which VEGF-A is needed. Moreover, disease progression can occur despite continuous anti-VEGF-A treatment. Thus, novel therapies for NV-AMD are urgently needed that target specifically disease-associated mechanisms without impairing growth factors and cellular pathways that are required for homeostatic functions of the retina and choroid. Inhibiting the inflammatory pathways that promote CNV would be such a promising novel approach that would likely not interfere with the normal functions of healthy retinal and choroidal cells. In this context, the inflammasome, a proinflammatory protein complex that promotes pathologic angiogenesis largely through generation of IL-1β and which has been reported to be activated in AMD, has become an area of much interest in the AMD field. However, most studies have focused mainly on the NLRP3 inflammasome in retinal pigment epithelial cells (RPE), and conflicting findings have resulted in an unclear picture of the role of the inflammasome for AMD pathogenesis. Recent data suggest that inflammasome activation in activated macrophages and retinal microglia but not in RPE cells promotes CNV. Furthermore, inflammasome activation can occur in CNV macrophages and microglia despite lack of NLRP3. Thus, activation of both NLRP3 inflammasomes as well as non-NLRP3 inflammasomes in macrophages/microglia at sites of CNV formation likely promote NV-AMD.

More than meets the eye: The role of microglia in healthy and diseased retina

Microglia are the main resident immune cells of the nervous system and as such they are involved in multiple roles ranging from tissue homeostasis to response to insults and circuit refinement. While most knowledge about microglia comes from brain studies, some mechanisms have been confirmed for microglia cells in the retina, the light-sensing compartment of the eye responsible for initial processing of visual information. However, several key pieces of this puzzle are still unaccounted for, as the characterization of retinal microglia has long been hindered by the reduced population size within the retina as well as the previous lack of technologies enabling single-cell analyses. Accumulating evidence indicates that the same cell type may harbor a high degree of transcriptional, morphological and functional differences depending on its location within the central nervous system. Thus, studying the roles and signatures adopted specifically by microglia in the retina has become increasingly important. Here, we review the current understanding of retinal microglia cells in physiology and in disease, with particular emphasis on newly discovered mechanisms and future research directions.

An Altered Neurovascular System in Aging-Related Eye Diseases

The eye has a complex and metabolically active neurovascular system. Repeated light injuries induce aging and trigger age-dependent eye diseases. Damage to blood vessels is related to the disruption of the blood-retinal barrier (BRB), altered cellular communication, disrupted mitochondrial functions, and exacerbated aggregated protein accumulation. Vascular complications, such as insufficient blood supply and BRB disruption, have been suggested to play a role in glaucoma, age-related macular degeneration (AMD), and Alzheimer's disease (AD), resulting in neuronal cell death. Neuronal loss can induce vision loss. In this review, we discuss the importance of the neurovascular system in the eye, especially in aging-related diseases such as glaucoma, AMD, and AD. Beneficial molecular pathways to prevent or slow down retinal pathologic processes will also be discussed.

AIP1 suppresses neovascularization by inhibiting the NOX4-induced NLRP3/NLRP6 imbalance in a murine corneal alkali burn model

Background

Apoptosis signal-regulating kinase 1-interacting protein 1 (AIP1) participates in inflammatory neovascularization induction. NADPH oxidase 4 (NOX4) produces reactive oxygen species (ROS), leading to an imbalance in nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) and NLR family pyrin domain containing 6 (NLRP6) expression. The mechanisms of AIP1, NOX4, ROS and inflammasomes in corneal neovascularization were studied herein.

Methods

C57BL/6 and AIP1-knockout mice were used in this study. The alkali burn procedure was performed on the right eye. Adenovirus encoding AIP1 plus green fluorescence protein (GFP) (Ad-AIP1-GFP) or GFP alone was injected into the right anterior chamber, GLX351322 was applied as a NOX4 inhibitor, and then corneal neovascularization was scored. The expression of related genes was measured by quantitative real-time polymerase chain reaction, western blotting and immunofluorescence staining. 2′,7′-Dichlorofluorescin diacetate staining was used to determine the ROS levels.

Results

The expression of AIP1 was decreased, while that of cleaved interleukin-1β (clv-IL-1β) and vascular endothelial growth factor A (VEGFa) was increased after alkali burn injury. NOX4 expression was increased, the imbalance in NLRP3/NLRP6 was exacerbated, and corneal neovascularization was increased significantly in AIP1-knockout mice compared with those in C57BL/6 mice after alkali burns. These effects were reversed by AIP1 overexpression. NLRP3/NLRP6 expression was imbalanced after alkali burns. GLX351322 reversed the imbalance in NLRP3/NLRP6 by reducing the ROS levels. This treatment also reduced the expression of clv-IL-1β and VEGFa, suppressing neovascularization.

Conclusions

AIP1 and NOX4 can regulate corneal inflammation and neovascularization after alkali burn injury. Based on the pathogenesis of corneal neovascularization, these findings are expected to provide new therapeutic strategies for patients.

Plain English summary

Corneal alkali burn injury is a common type of ocular injury that is difficult to treat in the clinic. The cornea is a clear and avascular tissue. Corneal neovascularization after alkali burn injury is a serious complication; it not only seriously affects the patient’s vision but also is the main reason for failed corneal transplantation. Corneal neovascularization affects approximately 1.4 million patients a year. We show for the first time that AIP1 and NOX4 can regulate corneal inflammation and neovascularization after alkali burns. The expression of AIP1 was decreased, while that of clv-IL-1β and VEGFa was increased after alkali burns. We tried to elucidate the specific molecular mechanisms by which AIP1 regulates corneal neovascularization. NOX4 activation was due to decreased AIP1 expression in murine corneas with alkali burns. NOX4 expression was increased, the imbalance in NLRP3/NLRP6 was exacerbated, and corneal neovascularization was increased significantly in AIP1-knockout mice compared with those in C57BL/6 mice after alkali burns. These effects were reversed by AIP1 overexpression. Additionally, NLRP3/NLRP6 expression was unbalanced, with NLRP3 activation and NLRP6 suppression in the corneal alkali burn murine model. Eye drops containing GLX351322, a NOX4 inhibitor, reversed the imbalance in NLRP3/NLRP6 by reducing ROS expression. This treatment also reduced the expression of clv-IL-1β and VEGFa, reducing neovascularization. Therefore, we provide new gene therapeutic strategies for patients. With the development of neovascularization therapy, we believe that in addition to corneal transplantation, new drug or gene therapies can achieve better results.

Exudative versus Nonexudative Age-Related Macular Degeneration: Physiopathology and Treatment Options

Age-related macular degeneration (AMD) is an eye disease typically associated with the aging and can be classified into two types—namely, the exudative and the nonexudative AMD. Currently available treatments for exudative AMD use intravitreal injections, which are associated with high risk of infection that can lead to endophthalmitis, while no successful treatments yet exist for the nonexudative form of AMD. In addition to the pharmacologic therapies administered by intravitreal injection already approved by the Food and Drug Administration (FDA) in exudative AMD, there are some laser treatments approved that can be used in combination with the pharmacological therapies. In this review, we discuss the latest developments of treatment options for AMD. Relevant literature available from 1993 was used, which included original articles and reviews available in PubMed database and also information collected from Clinical Trials Gov website using “age-related macular degeneration” and “antiangiogenic therapies” as keywords. The clinical trials search was limited to ongoing trials from 2015 to date.

Targeting Pyroptotic Cell Death Pathways in Retinal Disease

Pyroptosis is a gasdermin-mediated, pro-inflammatory form of cell death distinct from apoptosis. In recent years, increasing attention has shifted toward pyroptosis as more studies demonstrate its involvement in diverse inflammatory disease states, including retinal diseases. This review discusses how currently known pyroptotic cell death pathways have been implicated in models of age-related macular degeneration, diabetic retinopathy, and glaucoma. We also identify potential future therapeutic strategies for these retinopathies that target drivers of pyroptotic cell death. Presently, the drivers of pyroptosis that have been studied the most in retinal cells are the nucleotide-binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, caspase-1, and gasdermin D (GSDMD). Targeting these proteins may help us develop new drug therapies, or supplement existing therapies, in the treatment of retinal diseases. As novel mechanisms of pyroptosis come to light, including those involving other inflammatory caspases and members of the gasdermin protein family, more targets for pyroptosis-mediated therapies in retinal disease can be explored.

The NLRP3 inflammasome in age-related eye disease: Evidence-based connexin hemichannel therapeutics

The inflammasome pathway is a fundamental component of the innate immune system, playing a key role especially in chronic age-related eye diseases (AREDs). The inflammasome is of particular interest because it is a common disease pathway that once instigated, can amplify and perpetuate itself leading to chronic inflammation. With aging, it becomes more difficult to shut down inflammation after an insult but the common pathway means that a shared solution may be feasible that could be effective across multiple disease indications. This review focusses on the NLRP3 inflammasome, the most studied and characterized inflammasome in the eye. It describes the two-step signalling required for NLRP3 inflammasome complex activation, and provides evidence for its role in AREDs. In the final section, the article gives an overview of potential NLRP3 inflammasome targeting therapies, before presenting evidence for connexin hemichannel regulators as upstream blockers of inflammasome activation. These have shown therapeutic efficacy in multiple ocular disease models.

Global characterization of macrophage polarization mechanisms and identification of M2-type polarization inhibitors

Macrophages undergoing M1- versus M2-type polarization differ significantly in their cell metabolism and cellular functions. Here, global quantitative time-course proteomics and phosphoproteomics paired with transcriptomics provide a comprehensive characterization of temporal changes in cell metabolism, cellular functions, and signaling pathways that occur during the induction phase of M1- versus M2-type polarization. Significant differences in, especially, metabolic pathways are observed, including changes in glucose metabolism, glycosaminoglycan metabolism, and retinoic acid signaling. Kinase-enrichment analysis shows activation patterns of specific kinases that are distinct in M1- versus M2-type polarization. M2-type polarization inhibitor drug screens identify drugs that selectively block M2- but not M1-type polarization, including mitogen-activated protein kinase kinase (MEK) and histone deacetylase (HDAC) inhibitors. These datasets provide a comprehensive resource to identify specific signaling and metabolic pathways that are critical for macrophage polarization. In a proof-of-principle approach, we use these datasets to show that MEK signaling is required for M2-type polarization by promoting peroxisome proliferator-activated receptor-γ (PPARγ)-induced retinoic acid signaling.

Crosstalk Between RPE Cells and Choroidal Endothelial Cells via the ANXA1/FPR2/SHP2/NLRP3 Inflammasome/Pyroptosis Axis Promotes Choroidal Neovascularization

One type of age-related macular degeneration (AMD), neovascular (nAMD), characterized by choroidal neovascularization (CNV), accounts for the majority of the severe central vision impairment associated with AMD. Endothelial cells (ECs) in direct contact with retinal pigment epithelial (RPE) cells are more prone to the pathological angiogenesis involved in CNV. Herein, we investigated the effect of crosstalk between RPE cells and choroidal endothelial cells (CECs) via the ANXA1/FPR2/NLRP3 inflammasome/pyroptosis axis on the development of choroidal neovascularization (CNV) in vitro and in vivo. ANXA1 expression and secretion from ARPE-19 cells were upregulated by hypoxia. FPR2 expression, especially on the plasma membrane, in HCECs was upregulated under hypoxic conditions. ANXA1 secreted from ARPE-19 cells inhibited NLRP3 inflammasome activation and NLRP3 inflammasome-mediated pyroptosis in HCECs by activating the FPR2/SHP2 axis. Moreover, ANXA1 secreted by ARPE-19 cells promoted behaviors of HCECs, including proliferation, migration, and tube formation, by activating the FPR2/SHP2 axis and inhibiting NLRP3 inflammasome-mediated pyroptosis. Inhibiting the upregulated ANXA1/FPR2/SHP2/NLRP3 inflammasome/pyroptosis axis decreased the volume of CNV. Our data suggest that the crosstalk between RPE cells and CECs via the ANXA1/FPR2/NLRP3 inflammasome/pyroptosis axis promotes CNV. This finding could identify a potential target for the prevention and treatment of CNV.

P2X7 Receptor Antagonist Attenuates Retinal Inflammation and Neovascularization Induced by Oxidized Low-Density Lipoprotein

Age-related macular degeneration (AMD) is a common and severe blinding disease among people worldwide. Retinal inflammation and neovascularization are two fundamental pathological processes in AMD. Recent studies showed that P2X7 receptor was closely involved in the inflammatory response. Here, we aim to investigate whether A740003, a P2X7 receptor antagonist, could prevent retinal inflammation and neovascularization induced by oxidized low-density lipoprotein (ox-LDL) and explore the underlying mechanisms. ARPE-19 cells and C57BL/6 mice were treated with ox-LDL and A740003 successively for in vitro and in vivo studies. In this research, we found that A740003 suppressed reactive oxygen species (ROS) generation and inhibited the activation of Nod-like receptor pyrin-domain protein 3 (NLRP3) inflammasome and nuclear factor-κB (NF-κB) pathway. A740003 also inhibited the generation of angiogenic factors in ARPE-19 cells and angiogenesis in mice. The inflammatory cytokines and phosphorylation of inhibitor of nuclear factor-κB alpha (IKBα) were repressed by A740003. Besides, ERG assessment showed that retinal functions were remarkably preserved in A740003-treated mice. In summary, our results revealed that the P2X7 receptor antagonist reduced retinal inflammation and neovascularization and protected retinal function. The protective effects were associated with regulation of NLRP3 inflammasome and the NF-κB pathway, as well as inhibition of angiogenic factors.

Iron Accumulation and Lipid Peroxidation in the Aging Retina: Implication of Ferroptosis in Age-Related Macular Degeneration

Iron is an essential component in many biological processes in the human body. It is critical for the visual phototransduction cascade in the retina. However, excess iron can be toxic. Iron accumulation and reduced efficiency of intracellular antioxidative defense systems predispose the aging retina to oxidative stress-induced cell death. Age-related macular degeneration (AMD) is characterized by retinal iron accumulation and lipid peroxidation. The mechanisms underlying AMD include oxidative stress-mediated death of retinal pigment epithelium (RPE) cells and subsequent death of retinal photoreceptors. Understanding the mechanism of the disruption of iron and redox homeostasis in the aging retina and AMD is crucial to decipher these mechanisms of cell death and AMD pathogenesis. The mechanisms of retinal cell death in AMD are an area of active investigation; previous studies have proposed several types of cell death as major mechanisms. Ferroptosis, a newly discovered programmed cell death pathway, has been associated with the pathogenesis of several neurodegenerative diseases. Ferroptosis is initiated by lipid peroxidation and is characterized by iron-dependent accumulation. In this review, we provide an overview of the mechanisms of iron accumulation and lipid peroxidation in the aging retina and AMD, with an emphasis on ferroptosis.

Emerging therapies and their delivery for treating age-related macular degeneration

Age-related macular degeneration (AMD) is the most common cause of blindness in the Western world and is characterised in its latter stages by retinal cell death and neovascularisation and earlier stages with the loss of parainflammatory homeostasis. Patients with neovascular AMD (nAMD) are treated with frequent intraocular injections of anti-vascular endothelial growth factor (VEGF) therapies, which are not only unpopular with patients but carry risks of sight-threatening complications. A minority of patients are unresponsive with no alternative treatment available, and some patients who respond initially eventually develop a tolerance to treatment. New therapeutics with improved delivery methods and sustainability of clinical effects are required, in particular for non-neovascular AMD (90% of cases and no current approved treatments). There are age-related and disease-related changes that occur which can affect ocular drug delivery. Here, we review the latest emerging therapies for AMD, their delivery routes and implications for translating to clinical practice.

Neovascular Macular Degeneration: A Review of Etiology, Risk Factors, and Recent Advances in Research and Therapy

Neovascular age-related macular degeneration (exudative or wet AMD) is a prevalent, progressive retinal degenerative macular disease that is characterized by neovascularization of the choroid, mainly affecting the elderly population causing gradual vision impairment. Risk factors such as age, race, genetics, iris color, smoking, drinking, BMI, and diet all play a part in nvAMD's progression, with anti-vascular endothelial growth factor (anti-VEGF) therapy being the mainstay of treatment. Current therapeutic advancements slow the progression of the disease but do not cure or reverse its course. Newer therapies such as gene therapies, Rho-kinase inhibitors, and levodopa offer potential new targets for treatment.

Effects of Resvega on Inflammasome Activation in Conjunction with Dysfunctional Intracellular Clearance in Retinal Pigment Epithelial (RPE) Cells

Age-related macular degeneration (AMD) is an eye disease in which retinal pigment epithelium (RPE) cells play a crucial role in maintaining retinal homeostasis and photoreceptors’ functionality. During disease progression, there is increased inflammation with nucleotide-binding domain, leucine-rich repeat, and Pyrin domain 3 (NLRP3) inflammasome activation, oxidative stress, and impaired autophagy in RPE cells. Previously, we have shown that the dietary supplement Resvega reduces reactive oxygen species (ROS) production and induces autophagy in RPE cells. Here, we investigated the ability of Resvega to prevent NLRP3 inflammasome activation with impaired protein clearance in human RPE cells. Cell viability was measured using the lactate dehydrogenase (LDH) and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Enzyme-linked immunosorbent assays (ELISA) were utilized to determine the secretion of cytokines, NLRP3, and vascular endothelial growth factor (VEGF). Caspase-1 activity was measured with a fluorescent labeled inhibitor of caspase-1 (FLICA; FAM-YVAD-FMK) and detected microscopically. Resvega improved the cell membrane integrity, which was evident as reduced LDH leakage from cells. In addition, the caspase-1 activity and NLRP3 release were reduced, as was the secretion of two inflammatory cytokines, interleukin (IL)-1β and IL-8, in IL-1α-primed ARPE-19 cells. According to our results, Resvega can potentially reduce NLRP3 inflammasome-mediated inflammation in RPE cells with impaired protein clearance.

Inflammasome Proteins as Inflammatory Biomarkers of Age-Related Macular Degeneration

Purpose

Age-related macular degeneration (AMD) can result in severe vision loss and blurriness in the older population. The early and intermediate stages of AMD typically start without noticeable symptoms and can only be detected with a comprehensive eye exam. Because of the quiet onset of the disease, it is necessary to identify potential biomarkers to aid in the diagnosis, staging, and association with disease onset. Inflammasome signaling proteins are prominent biomarkers in the central nervous system, and the inflammasome has been shown to play a role in the innate inflammatory response in aging and AMD.

Methods

Serum from healthy controls and AMD patients were analyzed for the protein levels of Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), interleukin (IL)-18 and C-reactive protein (CRP) to determine cutoff points, positive and negative predictive values, and receiver operator characteristic curves, as well as univariate and multivariate linear and logistic regression models.

Results

ASC, IL-18, and CRP were elevated in the serum of AMD patients when compared to healthy controls. The area under the curve (AUC) for ASC was 0.98 with a cutoff point of 365.6 pg/mL, whereas IL-18 had an AUC of 0.73 and a cutoff point of 242.4 pg/mL, and the AUC for CRP was 0.67 with a cutoff point of 8,684,152 pg/mL. Levels of IL-18 had a statistically significant linear correlation with that of ASC with an adjusted R² of 0.1906, indicating that 19% of IL-18 could be explained by ASC protein levels in serum. Moreover, a logistic regression model for the diagnosis of AMD consists of ASC and having a diagnosis of hypertension, indicating that these two factors (elevated levels of ASC and a diagnosis of hypertension [HTN]) are associated with the diagnosis of AMD.

Conclusions

ASC, IL-18, and CRP are elevated in patients with AMD, and the protein levels of IL-18 are partially the result of ASC protein expression. Moreover, elevated protein levels of ASC in serum and a diagnosis of HTN increase the odds of patients having a diagnosis of AMD.

Translational Relevance

Biomarkers of AMD may be used to monitor disease risk, response to treatment and disease progression.

Distinct effects of complement and of NLRP3- and non-NLRP3 inflammasomes for choroidal neovascularization

NLRP3 inflammasome activation and complement-mediated inflammation have been implicated in promoting choroidal neovascularization (CNV) in age-related macular degeneration (AMD), but central questions regarding their contributions to AMD pathogenesis remain unanswered. Key open questions are (1) whether NLRP3 inflammasome activation mainly in retinal pigment epithelium (RPE) or rather in non-RPE cells promotes CNV, (2) whether inflammasome activation in CNV occurs via NLRP3 or also through NLRP3-independent mechanisms, and (3) whether complement activation induces inflammasome activation in CNV. Here we show in a neovascular AMD mouse model that NLRP3 inflammasome activation in non-RPE cells but not in RPE cells promotes CNV. We demonstrate that both NLRP3-dependent and NLRP3-independent inflammasome activation mechanisms induce CNV. Finally, we find that complement and inflammasomes promote CNV through independent mechanisms. Our findings uncover an unexpected role of non-NLRP3 inflammasomes for CNV and suggest that combination therapies targeting inflammasomes and complement may offer synergistic benefits to inhibit CNV.

Recent advances in the NEK7-licensed NLRP3 inflammasome activation: Mechanisms, role in diseases and related inhibitors

The nucleotide-binding oligomerization domain (NOD)-like receptor containing pyrin domain 3 (NLRP3) inflammasome is a high-molecular-weight complex mediated by the activation of pattern-recognition receptors (PRRs) seed in innate immunity. Once NLRP3 is activated, the following recruitment of the adapter apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD) (ASC) and procaspase-1 would be initiated. Cleavage of procaspase-1 into active caspase-1 then leads to the maturation of the precursor forms of interleukin (IL)-1β and IL-18 into biologically active IL-1β and IL-18. The activation of NLRP3 inflammasome is thought to be tightly associated with a regulator never in mitosis A (NIMA)-related kinase 7 (NEK7), apart from other signaling events such as K⁺ efflux and reactive oxygen species (ROS). Plus, the NLRP3 inflammasome has been linked to various metabolic disorders, chronic inflammation and other diseases. In this review, we firstly describe the cellular/molecular mechanisms of the NEK7-licensed NLRP3 inflammasome activation. Then we detail the potential inhibitors that can selectively and effectively modulate either the NEK7-NLRP3 complex itself or the related molecular/cellular events. Finally, we describe some inhibitors as promising therapeutic strategies for diverse diseases driven by NLRP3 inflammasome.

Ocular cytomegalovirus latency exacerbates the development of choroidal neovascularization

Age-related macular degeneration (AMD) is a complex, multifactorial, progressive disease which represents a leading cause of irreversible visual impairment and blindness in older individuals. Human cytomegalovirus (HCMV), which infects 50-80% of humans, is usually acquired during early life and persists in a latent state for the life of the individual. In view of its previously described pro-angiogenic properties, we hypothesized that cytomegalovirus might be a novel risk factor for progression to an advanced form, neovascular AMD, which is characterized by choroidal neovascularization (CNV). The purpose of this study was to investigate if latent ocular murine cytomegalovirus (MCMV) infection exacerbated the development of CNV in vascular endothelial growth factor (VEGF)-overexpressing VEGF-A^hyper mice. Here we show that neonatal infection with MCMV resulted in dissemination of virus to various organs throughout the body including the eye, where it localized principally to the choroid in both VEGF-overexpressingVEGF-A^hyper and wild-type(WT) 129 mice. By 6 months post-infection, no replicating virus was detected in eyes and extraocular tissues, although virus DNA was still present in all eyes and extraocular tissues of both VEGF-A^hyper and WT mice. Expression of MCMV immediate early (IE) 1 mRNA was detected only in latently infected eyes of VEGF-A^hyper mice, but not in eyes of WT mice. Significantly increased CNV was observed in eyes of MCMV-infected VEGF-A^hyper mice compared to eyes of uninfected VEGF-A^hyper mice, while no CNV lesions were observed in eyes of either infected or uninfected WT mice. Protein levels of several inflammatory/angiogenic factors, particularly VEGF and IL-6, were significantly higher in eyes of MCMV-infected VEGF-A^hyper mice, compared to uninfected controls. Initial studies of ocular tissue from human cadavers revealed that HCMV DNA was present in four choroid/retinal pigment epithelium samples from 24 cadavers. Taken together, our data suggest that ocular HCMV latency could be a significant risk factor for the development of AMD. © 2020 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

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

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

Caspase-1-dependent inflammasomes mediate photoreceptor cell death in photo-oxidative damage-induced retinal degeneration

Activation of the inflammasome is involved in the progression of retinal degenerative diseases, in particular, in the pathogenesis of Age-Related Macular Degeneration (AMD), with NLRP3 activation the focus of many investigations. In this study, we used genetic and pharmacological approaches to explore the role of the inflammasome in a mouse model of retinal degeneration. We identify that Casp1/11-/- mice have better-preserved retinal function, reduced inflammation and increased photoreceptor survivability. While Nlrp3-/- mice display some level of preservation of retinal function compared to controls, pharmacological inhibition of NLRP3 did not protect against photoreceptor cell death. Further, Aim2-/-, Nlrc4-/-, Asc-/-, and Casp11-/- mice show no substantial retinal protection. We propose that CASP-1-associated photoreceptor cell death occurs largely independently of NLRP3 and other established inflammasome sensor proteins, or that inhibition of a single sensor is not sufficient to repress the inflammatory cascade. Therapeutic targeting of CASP-1 may offer a more promising avenue to delay the progression of retinal degenerations.

NOD-like Receptors in the Eye: Uncovering Its Role in Diabetic Retinopathy

Diabetic retinopathy (DR) is an ocular complication of diabetes mellitus (DM). International Diabetic Federations (IDF) estimates up to 629 million people with DM by the year 2045 worldwide. Nearly 50% of DM patients will show evidence of diabetic-related eye problems. Therapeutic interventions for DR are limited and mostly involve surgical intervention at the late-stages of the disease. The lack of early-stage diagnostic tools and therapies, especially in DR, demands a better understanding of the biological processes involved in the etiology of disease progression. The recent surge in literature associated with NOD-like receptors (NLRs) has gained massive attraction due to their involvement in mediating the innate immune response and perpetuating inflammatory pathways, a central phenomenon found in the pathogenesis of ocular diseases including DR. The NLR family of receptors are expressed in different eye tissues during pathological conditions suggesting their potential roles in dry eye, ocular infection, retinal ischemia, cataract, glaucoma, age-related macular degeneration (AMD), diabetic macular edema (DME) and DR. Our group is interested in studying the critical early components involved in the immune cell infiltration and inflammatory pathways involved in the progression of DR. Recently, we reported that NLRP3 inflammasome might play a pivotal role in the pathogenesis of DR. This comprehensive review summarizes the findings of NLRs expression in the ocular tissues with special emphasis on its presence in the retinal microglia and DR pathogenesis.

Choroidal Neovascularization: Mechanisms of Endothelial Dysfunction

Many conditions affecting the heart, brain, and even the eyes have their origins in blood vessel pathology, underscoring the role of vascular regulation. In age-related macular degeneration (AMD), there is excessive growth of abnormal blood vessels in the eye (choroidal neovascularization), eventually leading to vision loss due to detachment of retinal pigmented epithelium. As the advanced stage of this disease involves loss of retinal pigmented epithelium, much less attention has been given to early vascular events such as endothelial dysfunction. Although current gold standard therapy using inhibitors of vascular endothelial growth factor (VEGF) have achieved initial successes, some drawbacks include the lack of long-term restoration of visual acuity, as well as a subset of the patients being refractory to existing treatment, alluding us and others to hypothesize upon VEGF-independent mechanisms. Against this backdrop, we present here a nonexhaustive review on the vascular underpinnings of AMD, implications with genetic and systemic factors, experimental models for studying choroidal neovascularization, and interestingly, on both endothelial-centric pathways and noncell autonomous mechanisms. We hope to shed light on future research directions in improving vascular function in ocular disorders.

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

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

Osmotic induction of cyclooxygenase-2 in RPE cells: Stimulation of inflammasome activation

Purpose

Systemic hypertension is a risk factor of age-related macular degeneration, a disease associated with chronic retinal inflammation. The main cause of acute hypertension in the elderly is consumption of dietary salt (NaCl) resulting in increased extracellular osmolarity. The aim of the present study was to determine whether extracellular osmolarity regulates the expression of cyclooxygenase (COX) genes in cultured human retinal pigment epithelial (RPE) cells, and whether COX activity is involved in mediating the osmotic expression of key inflammatory (NLRP3 and IL1B) and angiogenic factor (VEGFA) genes.

Methods

Extracellular hyperosmolarity was induced by addition of NaCl or sucrose. Gene expression was determined with real-time reverse transcription (RT)-PCR. Cytosolic interleukin-1β (IL-1β) and extracellular vascular endothelial growth factor (VEGF) levels were evaluated with enzyme-linked immunosorbent assay (ELISA).

Results

Extracellular hyperosmolarity induced a dose-dependent increase in COX2 gene expression when >10 mM NaCl was added to the culture medium, while COX1 gene expression was increased at higher doses (>50 mM of added NaCl). Extracellular hypo-osmolarity decreased COX2 gene expression. High extracellular osmolarity also induced increases in the COX2 protein level. NaCl-induced expression of COX2 was mediated by various intracellular signal transduction molecules (p38 mitogen-activated protein kinase [p38 MAPK], extracellular signal-regulated kinases 1 and 2 [ERK1/2], and phosphatidylinositol-3 kinase [PI3K]), intracellular calcium signaling involving activation of phospholipase Cγ (PLCγ) and protein kinase Cα/β (PKCα/β), and the activity of nuclear factor of activated T cell 5 (NFAT5). Inhibition of fibroblast growth factor (FGF), transforming growth factor-β (TGF-β), and interleukin-1 (IL-1) receptor activities decreased NaCl-induced COX2 gene expression. Selective inhibition of COX2 activity decreased osmotic expression of the VEGFA, IL1B, and NLRP3 genes, and blocked the NaCl-induced increase in the cytosolic IL-1β level.

Conclusions

The expression of COX2 in RPE cells is osmoresponsive, and depends on NFAT5. COX2 activity stimulates hyperosmotic expression of angiogenic (VEGFA) and inflammatory factor (IL1B and NLRP3) genes, and activation of the NLRP3 inflammasome in RPE cells.

IL-1 Family Cytokine Regulation of Vascular Permeability and Angiogenesis

The IL-1 family of cytokines are well-known for their primary role in initiating inflammatory responses both in response to and acting as danger signals. It has long been established that IL-1 is capable of simultaneously regulating inflammation and angiogenesis, indeed one of IL-1's earliest names was haemopoeitn-1 due to its pro-angiogenic effects. Other IL-1 family cytokines are also known to have roles in mediating angiogenesis, either directly or indirectly via induction of proangiogenic factors such as VEGF. Of note, some of these family members appear to have directly opposing effects in different tissues and pathologies. Here we will review what is known about how the various IL-1 family members regulate vascular permeability and angiogenic function in a range of different tissues, and describe some of the mechanisms employed to achieve these effects.

VEGF-like protein from Apostichopus japonicus promotes cell proliferation and migration

Vascular endothelial growth factor (VEGF) is a key conservative regulator of inflammation response by promoting cell proliferation, migration, and vascular permeability. It also induces the release of inflammatory factors in vertebrates. We previously characterized NLR family pyrin domain containing 3 and HMGB3 homology in Apostichopus japonicus, providing the occurrence of inflammation in this species. However, to our knowledge, other inflammation-related molecules, such as VEGF, have rarely been investigated. In the present study, a novel VEGF homolog was identified from A. japonicus (designated as AjVEGF) by rapid amplification of cDNA ends. Full-length cDNA of AjVEGF was 3181 bp with a putative open reading frame of 1752 bp encoding 583 amino acid (aa) residue protein. Structural analysis revealed that AjVEGF processed characteristic VEGF domains of platelet-derived growth factor domain (132-232 aa) and CXC domain (223-270 aa). Multiple sequence alignment and phylogenetic analysis both supported that AjVEGF belongs to a new member of VEGF protein subfamily. Both Vibrio splendidus challenge in vivo and lipopolysaccharide stimulation in vitro could significantly upregulate mRNA expression of AjVEGF compared with the control group. Functional analysis indicated that recombinant AjVEGF promoted coelomocyte proliferation and migration not only in sea cucumber but also in human colorectal adenocarcinoma cells (HT29). This consistent function was also detected for human VEGFs. Taken together, these findings suggest that AjVEGF has a similar function of VEGF in higher animals and might serve as a candidate cytokine in sea cucumber inflammation.

Hypoxic expression of NLRP3 and VEGF in cultured retinal pigment epithelial cells: contribution of P2Y2 receptor signaling

Retinal hypoxia is a major condition of the chronic inflammatory disease age-related macular degeneration. Extracellular ATP is a danger signal which is known to activate the NLRP3 inflammasome in various cell systems. We investigated in cultured human retinal pigment epithelial (RPE) cells whether hypoxia alters the expression of inflammasome-associated genes and whether purinergic receptor signaling contributes to the hypoxic expression of key inflammatory (NLRP3) and angiogenic factor (VEGF) genes. Hypoxia and chemical hypoxia were induced by a 0.2%-O₂ atmosphere and addition of CoCl₂, respectively. Gene expression was determined with real-time RT-PCR. Cytosolic NLRP3 and (pro-) IL-1β levels, and the extracellular VEGF level, were evaluated with Western blot and ELISA analyses. Cell culture in 0.2% O₂ induced expression of NLRP3 and pro-IL-1β genes but not of the pro-IL-18 gene. Hypoxia also increased the cytosolic levels of NLRP3 and (pro-) IL-1β proteins. Inflammasome activation by lysosomal destabilization decreased the cell viability under hypoxic, but not control conditions. In addition to activation of IL-1 receptors, purinergic receptor signaling mediated by a pannexin-dependent release of ATP and a release of adenosine, and activation of P2Y₂ and adenosine A₁ receptors, was required for the full hypoxic expression of the NLRP3 gene. P2Y₂ (but not A₁) receptor signaling also contributed to the hypoxic expression and secretion of VEGF. The data indicate that hypoxia induces priming and activation of the NLRP3 inflammasome in cultured RPE cells. The hypoxic NLRP3 and VEGF gene expression and the secretion of VEGF are in part mediated by P2Y₂ receptor signaling.

Osmotic and hypoxic induction of the complement factor C9 in cultured human retinal pigment epithelial cells: Regulation of VEGF and NLRP3 expression

Purpose

Variants of complement factor genes, hypoxia and oxidative stress of the outer retina, and systemic hypertension affect the risk of age-related macular degeneration. Hypertension often results from the high intake of dietary salt that increases extracellular osmolarity. We determined the effects of extracellular hyperosmolarity, hypoxia, and oxidative stress on the expression of complement genes in cultured (dedifferentiated) human RPE cells and investigated the effects of C9 siRNA and C9 protein on RPE cells.

Methods

Hyperosmolarity was induced by adding 100 mM NaCl or sucrose to the culture medium. Hypoxia was induced by culturing cells in 1% O₂ or by adding the hypoxia mimetic CoCl₂. Oxidative stress was induced by adding H₂O₂. Gene and protein expression levels were determined with real-time RT-PCR, western blot, and ELISA analyses. The expression of the nuclear factor of activated T cell 5 (NFAT5) and complement factor (C9) was knocked down with siRNA.

Results

Extracellular hyperosmolarity, hypoxia, and oxidative stress strongly increased the transcription of the C9 gene, while the expression of the C3, C5, CFH, and CFB genes was moderately altered or not altered at all. Hyperosmolarity also induced a moderate increase in the cytosolic C9 protein level. The hyperosmotic C9 gene expression was reduced by inhibitors of the p38 MAPK, ERK1/2, JNK, and PI3K signal transduction pathways and of the transcription factors STAT3 and NFAT5. The hypoxic C9 gene expression was reduced by a STAT3 inhibitor. The knockdown of C9 with siRNA decreased the hypoxic vascular endothelial growth factor (VEGF) and NLRP3 gene expression, the hypoxic secretion of VEGF, and the hyperosmotic expression of the NLRP3 gene. Exogenous C9 protein inhibited the hyperosmotic expression of the C9 gene, the hypoxic and hyperosmotic VEGF gene expression, and the hyperosmotic expression of the NLRP3 gene. Both C9 siRNA and C9 protein inhibited inflammasome activation under hyperosmotic conditions, as indicated by the decrease in the cytosolic level of mature IL-1β.

Conclusions

The expression of the C9 gene in cultured RPE cells is highly induced by extracellular hyperosmolarity, hypoxia, and oxidative stress. The data may support the assumption that C9 gene expression may stimulate the expression of inflammatory (NLRP3) and angiogenic growth factors (VEGF) in RPE cells. Extracellular C9 protein may attenuate this effect, in part via negative regulation of the C9 mRNA level.

Inflammation and outer blood-retina barrier (BRB) compromise following choroidal murine cytomegalovirus (MCMV) infections

PURPOSE

The purpose of this study was to determine whether the blood-retina barrier is compromised by choroidal murine cytomegalovirus (MCMV) infection, using electron microscopy.

METHODS

BALB/c mice were immunosuppressed with methylprednisolone and monoclonal antibodies to CD4 and CD8. At several time points post-MCMV intraperitoneal inoculation, the eyes were removed and analyzed with western blotting and immunoelectron microscopy for the presence of MCMV early antigen (EA) and the host protein RIP3. Posterior eyecups from RIP3^-/- and RIP3^+/+ mice were cultured and inoculated with MCMV. At days 4, 7, and 11 post-infection, cultures were collected and analyzed with plaque assay, immunohistochemical staining, and real-time PCR (RT-PCR).

RESULTS

MCMV EA was observed in the nuclei of vascular endothelial cells and pericytes in the choriocapillaris. Disruption of Bruch's membrane was observed, especially at sites adjacent to activated platelets, and a few RPE cells containing some enlarged vesicles were found directly beneath disrupted Bruch's membrane. Some virus particles were also observed in the enlarged vesicles of RPE cells. Levels of the RIP3 protein, which was observed mainly in the RPE cells and the basement membrane of the choriocapillaris, were greatly increased following MCMV infection, while depletion of RIP3 resulted in greatly decreased inflammasome formation, as well as expression of downstream inflammation factors.

CONCLUSIONS

The results suggest that systemic MCMV spreads to the choroid and replicates in vascular endothelia and pericytes of the choriocapillaris during immunosuppression. Choroidal MCMV infection is associated with in situ inflammation and subsequent disruption of Bruch's membrane and the outer blood-retina barrier.

The rescue effect of mesenchymal stem cell on sodium iodate-induced retinal pigment epithelial cell death through deactivation of NF-κB-mediated NLRP3 inflammasome

Age-related macular degeneration (AMD) is a multifactorial disease resulting in the gradual loss of retinal pigment epithelium (RPE) and the permanent visual damage. Various risk factors, including oxidative stress, form a complex network at the confluence of inflammation. Mesenchymal stem cell (MSC) is a well-studied population of adult stem cell with strong neuroprotective and immunoregulatory properties. Here, we reported the protective effect of MSC on sodium iodate (NaIO3)-triggered RPE degeneration. Sodium iodate (NaIO3)-induced RPE cell death was remarkably reduced when cocultured with MSC. Inhibition of several cell death pathways mediated by mitochondrial instability and its subsequent caspase-1/3/8 activation was implicated in this process. In addition, NLRP3 inflammasome, the upstream of caspase-1 activation, was also found downregulated via suppressing its priming signal NF-κB pathway. Taken together, MSC protected against NaIO3-triggered RPE death via deactivating NF-κB-mediated NLRP3 inflammasome and maintaining mitochondrial integrity. This study highlights the significant role of MSC in modulating the proinflammatory environment of AMD, and suggests the clinical value of MSC in treating AMD as well as RPE replacement therapy.

Distinct CD40L receptors mediate inflammasome activation and secretion of IL-1β and MCP-1 in cultured human retinal pigment epithelial cells

CD40L signaling occurs in several diseases with inflammatory components, including ocular and retinal diseases. However, it has never been evaluated as a pathogenic mechanism in age-related macular degeneration (AMD) or as an inducer of inflammasome formation in any cell type. mRNA and protein levels of CD40, IL-1β, NALP1, NALP3, caspase-1, and caspase-5 were determined by RT-PCR, qPCR, and Western blot. CD40L receptor (CD40, α5β1, and CD11b) expression was determined by Western and immunofluorescent staining. IL-1β, IL-18, and MCP-1 secretions were determined by ELISA. NALP1 and NALP3 inflammasome formation were determined by Co-IP. Experiments were conducted on primary human retinal pigment epithelial (hRPE) cells from four different donors. Human umbilical vein endothelial (HUVEC) and monocytic leukemia (THP-1) cells demonstrated the general applicability of our findings. In hRPE cells, CD40L-induced NALP1 and NALP3 inflammasome activation, cleavage of caspase-1 and caspase-5, and IL-1β and IL-18 secretion. Interestingly, neutralizing CD11b and α5β1 antibodies, but not CD40, reduced CD40L-induced IL-1β secretion in hRPE cells. Similarly, CD40L treatment also induced HUVEC and THP-1 cells to secret IL-1β through CD11b and α5β1. Additionally, the CD40L-induced IL-1β secretion acted in an autocrine/paracrine manner to feed back and induce hRPE cells to secrete MCP-1. This study is the first to show that CD40L induces inflammasome activation in any cell type, including hRPE cells, and that this induction is through CD11b and α5β1 cell-surface receptors. These mechanisms likely play an important role in many retinal and non-retinal diseases and provide compelling drug targets that may help reduce pro-inflammatory processes.

Issues with the Specificity of Immunological Reagents for NLRP3: Implications for Age-related Macular Degeneration

Contradictory data have been presented regarding the implication of the NACHT, LRR and PYD domains-containing protein 3 (NLRP3) inflammasome in age-related macular degeneration (AMD), the leading cause of vision loss in the Western world. Recognizing that antibody specificity may explain this discrepancy and in line with recent National Institutes of Health (NIH) guidelines requiring authentication of key biological resources, the specificity of anti-NLRP3 antibodies was assessed to elucidate whether non-immune RPE cells express NLRP3. Using validated resources, NLRP3 was not detected in human primary or human established RPE cell lines under multiple inflammasome-priming conditions, including purported NLRP3 stimuli in RPE such as DICER1 deletion and Alu RNA transfection. Furthermore, NLRP3 was below detection limits in ex vivo macular RPE from AMD patients, as well as in human induced pluripotent stem cell (hiPSC)-derived RPE from patients with overactive NLRP3 syndrome (Chronic infantile neurologic cutaneous and articulate, CINCA syndrome). Evidence presented in this study provides new data regarding the interpretation of published results reporting NLRP3 expression and upregulation in RPE and addresses the role that this inflammasome plays in AMD pathogenesis.