Age-related macular degeneration: activation of innate immunity system via pattern recognition receptors

The contribution of pattern recognition receptor signalling in the development of age related macular degeneration: the role of toll-like-receptors and the NLRP3-inflammasome

Age-related macular degeneration (AMD) is a leading cause of irreversible vision loss, characterised by the dysfunction and death of the photoreceptors and retinal pigment epithelium (RPE). Innate immune cell activation and accompanying para-inflammation have been suggested to contribute to the pathogenesis of AMD, although the exact mechanism(s) and signalling pathways remain elusive. Pattern recognition receptors (PRRs) are essential activators of the innate immune system and drivers of para-inflammation. Of these PRRs, the two most prominent are (1) Toll-like receptors (TLR) and (2) NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3)-inflammasome have been found to modulate the progression of AMD. Mutations in TLR2 have been found to be associated with an increased risk of developing AMD. In animal models of AMD, inhibition of TLR and NLRP3 has been shown to reduce RPE cell death, inflammation and angiogenesis signalling, offering potential novel treatments for advanced AMD. Here, we examine the evidence for PRRs, TLRs2/3/4, and NLRP3-inflammasome pathways in macular degeneration pathogenesis.

Resveratrol and quercetin protect from Benzo(a)pyrene-induced autophagy in retinal pigment epithelial cells

PURPOSE

This study aims to investigate the role of Resveratrol (RES) and quercetin (QR) treatments against Benzo(a)pyrene (B(a)p)-induced autophagy in retinal pigment epithelial cells.

METHODS

The IC50 doses of B(a)p, RES and QR in retinal pigment epithelial cells were determined by MTT assay and the relevant agents were administered singly or in combinations to ARPE-19 cells for 24 h. Occurrence of autophagy in the cells was verified by detection of autophagosomes using fluorescence microscope. Also, the mRNA expression levels of LC3 and Beclin 1 genes were analyzed by RT-PCR to collect further data on autophagy. Caspase-3 and IL-1β levels in lysed cells were analyzed by ELISA.

RESULTS

Autophagosomes were detected in B(a)p-treated ARPE-19 cell lines, as well as a 1.787-fold increase in LC3 mRNA expression levels. No autophagosome occurred in RES and QR treatments, and a significant decrease in their percentage amounts were observed in B(a)p + RES and B(a)p + QR. The mRNA expression levels of LC3 and Beclin 1 also supported these findings. B(a)p had no effect on Caspase-3 levels in ARPE-19 cells, but combined with RES and QR, it increased Caspase-3 levels significantly.IL-1β levels were higher in B(a)p, B(a)p + QR, B(a)p + RES, RES and QR than control group. This rise in IL-1β levels was correlated with suppression of mRNA expression levels of Beclin 1.

CONCLUSION

B(a)p exposure caused autophagy in ARPE-19 cells, but did not induce apoptosis. RES and QR treatments prevented B(a)p-induced autophagy. Therefore, RES and QR treatments showed protective effect against potential degenerative diseases caused by chronic exposure to B(a)p.

Association of NLRPs with pathogenesis of dry age-related macular degeneration

BACKGROUND

Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly population, and Dry AMD is the most common clinical subtype. However, effective measures for the early diagnosis and treatment of dry AMD have not been proposed. In recent years, NOD-like receptors (NLRs) have received attention in the study of AMD as an important class of pattern recognition receptors. We attempted to elucidate the pathogenesis of NLRs in dry AMD from the perspective of chronic inflammation.

METHODS

This study involved 13 patients with dry AMD, 10 age- and sex-matched normal population without any history of disease and 8 patients with wet AMD as controls. Using RT-qPCR, the mRNA expression levels of NLRs in peripheral blood peripheral blood mononuclear cells (PBMCs) were compared to analyze the statistical differences in the expression contents among the three populations.

RESULTS

The relative RNA expression of nucleotide-binding oligomerization-like receptor protein 12 (NLRP12) with negative regulation of inflammation was significantly lower in dry AMD patients than in normal people and wet AMD patients. And NLRX1, which also has an anti-inflammatory effect, was lower in dry AMD patients than in wet AMD patients. However, NLRP3 with proinflammatory effect was significantly expressed in wet AMD.

CONCLUSION

The significant decrease in NLRP12 in dry AMD may become a breakthrough in the study of dry AMD and systemic chronic inflammatory response. However, NLRP3 may have a more important role in wet AMD.

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

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

MicroRNA-27a Promotes Oxidative-Induced RPE Cell Death through Targeting FOXO1

Age-related macular degeneration (AMD) is a multifactor disease, which is primarily characterized by retinal pigment epithelium (RPE) cell loss. Since the retina is the most metabolically active tissue, RPE cells are exposed to consistent oxidative environment. So, oxidation-induced RPE cell death has long been considered a contributor to the onset of AMD. Here, we applied a retinal degeneration (RD) rat model induced by blue light-emitting diode (LED) and a cell model constructed by H₂O₂ stimulus to mimic the prooxidant environment of the retina. We detected that the expression of miR-27a was upregulated and the expression of FOXO1 was downregulated in both models. So, we furtherly investigated the role of miR-27a-FOXO1 axis in RPE in protesting against oxidants. Lentivirus-mediated RNA was injected intravitreally into rats to modulate the miR-27a-FOXO1 axis. Retinal function and histopathological changes were evaluated by electroretinography (ERG) analysis and hematoxylin and eosin (H&E) staining, respectively. Massive photoreceptor and RPE cell death were examined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). The damage to the retina was aggravated in the FOXO1 gene-knockdown and miR-27a-overexpression groups after exposure to LED but was alleviated in the FOXO1 gene-overexpression or miR-27a-knockdown groups. Dual luciferase assay was used to detect the binding site of miR-27a and FOXO1. Upregulated miR-27a inhibited the expression of FOXO1 by directly binding to the FOXO1 mRNA 3′UTR and decreased the autophagy activity of ARPE-19 cells, resulting in the accumulation of reactive oxygen species (ROS) and decrease of cell viability. The results suggest that miR-27a is a negative regulator of FOXO1. Also, our data emphasize the prominent role of miR-27a/FOXO1 axis in modulating ROS accumulation and cell death in RPE cell model under oxidative stress and influencing the retinal function in the LED-induced RD rat model.

Pro-inflammatory activation changes intracellular transport of bevacizumab in the retinal pigment epithelium in vitro

Purpose

Bevacizumab is taken up and transported through the retinal pigment epithelium. Inflammatory signaling may influence this interaction. In the present study, we have investigated the effect of pro-inflammatory stimuli on the uptake, intracellular localization, and transepithelial transport of bevacizumab.

Methods

ARPE-19 cell line or primary porcine RPE cells were treated with clinical relevant concentrations of bevacizumab (250 µg/ml). Pro-inflammatory signaling was induced by TLR-3 agonist polyinosinic:polycytidylic acid (Poly I:C). Viability was investigated with MTT and trypan-blue exclusion assay, and cell number, uptake, and intracellular localization were investigated with immunofluorescence, investigating also actin filaments, the motor protein myosin 7a and lysosomes. Immunofluorescence signals were quantified. Intracellular bevacizumab was additionally detected in Western blot. Barrier function was investigated with transepithelial resistant measurements (TER). The transepithelial transport of bevacizumab and its influence on cytokine (IL-6, IL-8, IL-1β, TNFα) secretion was investigated with ELISA.

Results

Poly I:C in combination with bevacizumab reduced the viability of the cells. Treatment with Poly I:C reduced the uptake of bevacizumab, changed the intensity of the actin filaments, and reduced the colocalization with myosin 7a. In addition, Poly I:C reduced the capacity of RPE cells to transport bevacizumab over the barrier. In addition, bevacizumab reduced the secretion of IL-8 and TNFα after Poly I:C stimulation at selected time points.

Conclusions

Pro-inflammatory activation of RPE cells with TLR-3 agonist Poly I:C changes the interaction of RPE cells with the anti-VEGF compound bevacizumab, reducing its uptake and transport. On the other hand, bevacizumab might influence pro-inflammatory cytokine release. Our data indicate that inflammation may influence the pharmacokinetic of bevacizumab in the retina.

Oxidative Stress and Mitochondrial Damage in Dry Age-Related Macular Degeneration Like NFE2L2/PGC-1α -/- Mouse Model Evoke Complement Component C5a Independent of C3

Aging-associated chronic oxidative stress and inflammation are known to be involved in various diseases, e.g., age-related macular degeneration (AMD). Previously, we reported the presence of dry AMD-like signs, such as elevated oxidative stress, dysfunctional mitophagy and the accumulation of detrimental oxidized materials in the retinal pigment epithelial (RPE) cells of nuclear factor erythroid 2-related factor 2, and a peroxisome proliferator-activated receptor gamma coactivator 1-alpha (NFE2L2/PGC1α) double knockout (dKO) mouse model. Here, we investigated the dynamics of inflammatory markers in one-year-old NFE2L2/PGC1α dKO mice. Immunohistochemical analysis revealed an increase in levels of Toll-like receptors 3 and 9, while those of NOD-like receptor 3 were decreased in NFE2L2/PGC1α dKO retinal specimens as compared to wild type animals. Further analysis showed a trend towards an increase in complement component C5a independent of component C3, observed to be tightly regulated by complement factor H. Interestingly, we found that thrombin, a serine protease enzyme, was involved in enhancing the terminal pathway producing C5a, independent of C3. We also detected an increase in primary acute phase C-reactive protein and receptor for advanced glycation end products in NFE2L2/PGC1α dKO retina. Our main data show C5 and thrombin upregulation together with decreased C3 levels in this dry AMD-like model. In general, the retina strives to mount an orchestrated inflammatory response while attempting to maintain tissue homeostasis and resolve inflammation.

Oxidative and Nitrosative Stress in Age-Related Macular Degeneration: A Review of Their Role in Different Stages of Disease

Although the exact pathogenetic mechanisms leading to age-related macular degeneration (AMD) have not been clearly identified, oxidative damage in the retina and choroid due to an imbalance between local oxidants/anti-oxidant systems leading to chronic inflammation could represent the trigger event. Different in vitro and in vivo models have demonstrated the involvement of reactive oxygen species generated in a highly oxidative environment in the development of drusen and retinal pigment epithelium (RPE) changes in the initial pathologic processes of AMD; moreover, recent evidence has highlighted the possible association of oxidative stress and neovascular AMD. Nitric oxide (NO), which is known to play a key role in retinal physiological processes and in the regulation of choroidal blood flow, under pathologic conditions could lead to RPE/photoreceptor degeneration due to the generation of peroxynitrite, a potentially cytotoxic tyrosine-nitrating molecule. Furthermore, the altered expression of the different isoforms of NO synthases could be involved in choroidal microvascular changes leading to neovascularization. The purpose of this review was to investigate the different pathways activated by oxidative/nitrosative stress in the pathogenesis of AMD, focusing on the mechanisms leading to neovascularization and on the possible protective role of anti-vascular endothelial growth factor agents in this context.

The Role of Inflammation and Infection in Age-Related Neurodegenerative Diseases: Lessons From Bacterial Meningitis Applied to Alzheimer Disease and Age-Related Macular Degeneration

Age-related neurodegenerative diseases, such as Alzheimer disease (AD) and age-related macular degeneration (AMD), are multifactorial and have diverse genetic and environmental risk factors. Despite the complex nature of the diseases, there is long-standing, and growing, evidence linking microbial infection to the development of AD dementia, which we summarize in this article. Also, we highlight emerging research findings that support a role for parainfection in the pathophysiology of AMD, a disease of the neurosensory retina that has been shown to share risk factors and pathological features with AD. Acute neurological infections, such as Bacterial Meningitis (BM), trigger inflammatory events that permanently change how the brain functions, leading to lasting cognitive impairment. Neuroinflammation likewise is a known pathological event that occurs in the early stages of chronic age-related neurodegenerative diseases AD and AMD and might be triggered as a parainfectious event. To date, at least 16 microbial pathogens have been linked to the development of AD; on the other hand, investigation of a microbe-AMD relationship is in its infancy. This mini-review article provides a synthesis of existing evidence indicating a contribution of parainfection in the aetiology of AD and of emerging findings that support a similar process in AMD. Subsequently, it describes the major immunopathological mechanisms that are common to BM and AD/AMD. Together, this evidence leads to our proposal that both AD and AMD may have an infectious aetiology that operates through a dysregulated inflammatory response, leading to deleterious outcomes. Last, it draws fresh insights from the existing literature about potential therapeutic options for BM that might alleviate neurological disruption associated with infections, and which could, by extension, be explored in the context of AD and AMD.

Immunological biomarkers of the vitreous responsible for proliferative alteration in the different forms of retinal detachment

Background

The purpose of the study was to explore the immunological components that are responsible for the proliferative alterations in the different forms of retinal detachment (RD).

Methods

Vitreous fluids were collected during 23G pars plana vitrectomy from 54 eyes of 54 patients with different RD types, such as rhegmatogenous RD (RRD) without proliferative vitreoretinopathy (PVR) (n = 30), PVR (n = 16) and proliferative diabetic retinopathy (PDR) with tractional RD (n = 8). Vitreous fluids were obtained from 19 eyes with epiretinal membrane (ERM), which were used as control samples. A multiplex chemiluminescent immunoassay was performed to evaluate the concentrations of 48 cytokines, chemokines and growth factors.

Results

The expression levels of eotaxin, IFN-gamma, IL-6, IL-8, IL-16, MCP-1, MIF and MIP-1 beta were significantly higher in all RD groups than in the ERM group. The levels of CTACK, IP-10, SCGF-beta, and SDF-1 alpha were significantly higher in patients with diabetic tractional RD and PVR than in other patients. The upregulation of VEGF and IL-18 was detected in PDR.

Conclusions

Our results indicate that complex and significant immunological mechanisms are associated with the pathogenesis of different forms of RD: selected cytokines, chemokines and growth factors are upregulated in the vitreous of eyes with RD. The detected proteins are present in different concentrations both in RRD and PVR. In the presence of PVR and PDR, the majority of cytokines are upregulated; thus, they may serve as biomarkers to estimate the progression or severity level of proliferation and later to develop personalized therapeutic strategies to slow down or prevent pathological changes.

Thyroid and Eye: Where They Meet in Clinical Practice

OBJECTIVE

Thyroid Hormones (TH) are essential for normal growth, development and continued optimal function of most of the body organs including the eye. TH signaling plays a central role in the regulation of retinal development and maturation. Deficiency in TH during fetal and early postnatal development impairs growth of the eye and proliferation of all retinal cell types. The present article reviews the most important topics of the different derangements in thyroid function and structure and its relation with eye diseases.

METHODS

A literature search strategy was conducted for all English-language literature.

RESULTS

From a clinical practice viewpoint, it should be mentioned that both hypothyroidism and hyperthyroidism are accompanied by ocular diseases i.e. thyroid-associated ophthalmopathy, diabetic retinopathy and age-related macular degeneration. Although the orbit and globe are not common sites for metastatic thyroid cancers, orbital metastasis may be the primary clinical manifestation of thyroid carcinoma. Finally, some medications as amiodarone may be accompanied by both thyroid dysfunction and adverse ocular events.

CONCLUSION

Thyroid disorders and eye diseases are interrelated through several mechanisms thus, awareness of this relation has a great impact on early diagnosis and treatment.

The role of reactive oxygen species in the pathogenesis and treatment of retinal diseases

Reactive oxygen species (ROS) normally play an important physiological role in health regulating cellular processes and signal transduction. The amount of ROS is usually kept in fine balance with the generation of ROS largely being offset by the body's antioxidants. A tipping of this balance has increasingly been recognised as a contributor to human disease. The retina, as a result of its cellular anatomy and physical location, is a potent generator of ROS that has been linked to several major retinal diseases. This review will provide a summary of the role of oxidative stress in the pathogenesis of diabetic retinopathy, age-related macular degeneration, myopia, retinal vein occlusion, retinitis pigmentosa and retinopathy of prematurity. Therapies aimed at controlling oxidative stress in these diseases are also examined.

Effect of long-term inflammation on viability and function of RPE cells

PURPOSE

Degenerative ocular disorders like age-related macular degeneration (AMD) are associated with long-term pro-inflammatory signals on retinal pigment epithelial (RPE) cells. In this study, we investigated the effect of long term treatment of RPE cells with agonists of toll-like receptor (TLR) -3 (Polyinosinic:polycytidylic acid, Poly I:C), TLR-4 (lipopolysaccharide, LPS) and the pro-inflammatory cytokine TNFα.

METHODS

All tests were conducted with primary porcine RPE. Cells were stimulated with Poly I:C (1, 10, 100 μg/ml), LPS (0.1, 1, 10 μg/ml) or TNFα (12.5, 25 or 50 ng/ml) for 1 day, 7 days or 4 weeks. Cell viability tests (MTT) were additionally tested in ARPE-19 cells. Cytokine secretion (IL-6, IL-1β, IL-8, TNFα, TGF-β) was tested in ELISA, phagocytosis in a microscopic assay, and expression of RPE65 in Western blot. Barrier function was tested in transwell-cultured cells by measuring transepithelial resistance for up to 3 days.

RESULTS

LPS and TNFα significantly reduce cell viability after 1 day and 7 days, Poly I:C after 7 days and 4 weeks. LPS, Poly I:C and TNFα significantly induce the secretion of IL-6 and IL-8 at all tested time points. IL-1β is increased by LPS and Poly I:C after 1 day, but not by TNFα. TNFα secretion is increased by Poly I:C and LPS after 1 day but not at later time points. TGF-β secretion is not influenced by any stimulus. Concerning RPE function, LPS decreased phagocytosis after 7 days, while Poly I:C and TNFα showed no effect. RPE65 expression was strongly reduced by TNFα and LPS after 4 weeks. Wound healing capacity was reduced by Poly I:C but induced by LPS after 7 d and 4 w. Barrier function was not affected by Poly I:C or LPS, while TNFα reduced barrier function after 1 h, 4 h and 3 days.

CONCLUSION

Long term pro-inflammatory stimuli reduce RPE viability, barrier properties and cellular function and induce pro-inflammatory cytokines and therefore may contribute directly to atrophic changes in AMD.

Association study of toll-like receptors 4 polymorphisms and the risk of age-related macular degeneration: a meta-analysis

BACKGROUND

Toll-like receptor 4 (rs4986790, rs4986791) single nucleotide polymorphisms (SNPs) have been shown to be associated with age-related macular degeneration (AMD), but the results are still inconclusive. The present meta-analysis was conducted to evaluate the association between SNPs of TLR4 gene and AMD susceptibility.

METHODS

Relevant articles were obtained through computer retrieval of Pubmed, Embase, Chinese National Knowledge Infrastructure and China wanfang database. Eligible articles were selected according to the inclusion and exclusion criteria, and quality scores were made for them by NOS-scale. Relevant data were extracted for meta-analysis. The combined OR value and 95% confidence interval were used to evaluate the strength of the correlation. Funnel plot and Egger's regression were used to evaluate publication bias. All analyses were performed using STATA 11.0 software.

RESULTS

A total of nine case-control studies were included in this meta-analysis. After combination, an significant association was found between rs4986790 polymorphism and AMD susceptibility in heterozygote model (AG vs. AA, OR = 1.400, 95%CI = 1.049-1.867, P = .022) and dominant model (GG+AG vs. AA, OR = 1.365, 95%CI = 1.028-1.813, P = .032). There was no association found between rs4986791 polymorphism and AMD susceptibility in all genetic models (all P > .05). Funnel plot and Egger's regression analysis showed no publication bias existed in this study.

CONCLUSIONS

Meta-analysis suggested that there is an association between TLR4 gene rs4986790 polymorphism and AMD susceptibility, while no association between rs4986791 polymorphism and AMD susceptibility.

Identification of Novel Serum MicroRNAs in Age-Related Macular Degeneration

Purpose

To identify circulating microRNAs (miRNA) associated with age-related macular degeneration (AMD). Thus differentially expressed serum miRNA could be used as AMD biomarkers.

Methods

This study involved total RNA isolation from sera from patients with atrophic AMD (n = 10), neovascular AMD (n = 10), and age- and sex-matched controls (n = 10). A total of 377 miRNAs were coanalyzed using array technologies, and differentially regulated miRNAs were determined. Extensive validation studies (n = 90) of serum from AMD patients and controls confirmed initial results. Total RNA isolation was carried out from sera from patients with atrophic AMD (n = 30), neovascular AMD (n = 30), and controls (n = 30). Fourteen miRNAs from the discovery dataset were coanalyzed using quantitative real-time polymerase chain reaction (qRT-PCR) to validate their presence.

Results

Unsupervised hierarchical clustering indicated that AMD serum specimens have a different miRNA profile to healthy controls. We successfully identified and validated the differentially regulated miRNAs in serum from AMD patients versus controls. The biomarker potential of three miRNAs (miR-126, miR-19a, and miR-410) was confirmed by qRT-PCR, with significantly increased quantities in serum of AMD patients compared with healthy controls.

Conclusions

Increased quantities of miR-126, miR-410, and miR-19a in serum from AMD patients indicate that these miRNAs could potentially serve as diagnostic AMD biomarkers. All three miRNAs significantly correlated with AMD pathogenesis.

Translational Relevance

The discovery of new AMD miRNA may act as biomarkers in evaluating AMD diagnosis and prognosis.

Repeat exposure to polyinosinic:polycytidylic acid induces TLR3 expression via JAK-STAT signaling and synergistically potentiates NFκB-RelA signaling in ARPE-19 cells

Dry age-related macular degeneration (AMD), accounting for approximately 90% of AMD cases, is characterized by photoreceptor death, retinal pigment epithelium (RPE) dysfunction and, ultimately, geographic atrophy - the localized death of RPE leading to loss of the center of the visual field. The pathological etiology of AMD is multifactorial, but innate immune signaling and inflammation are involved in early stages of the disease. Although numerous single-nucleotide polymorphisms in innate immune genes are associated with dry AMD, no single gene appears to cause dry AMD. Here, we hypothesized that activation of TLR3 potentiates expression of TLR3 itself and the NFκB-p65 (RelA) subunit as part of pro-inflammatory RPE signaling. Furthermore, we hypothesized that TLR3 activation can 'prime' cells to future RelA stimulation, leading to enhanced, persistent RelA expression and signaling following a second TLR3 activation. We used the human RPE-derived cell line ARPE-19 as a model system for RPE signaling and measured NFκB expression and activity in response to TLR3 stimulation with its ligand, polyinosinic:polycytidylic acid (pI:C). Activation of TLR3 with pI:C led to increased TLR3 and RelA expression that was sustained for at least 24 h. Cells exposed for a second time to pI:C after an initial pI:C exposure displayed elevated RelA expression and RelA nuclear translocation above the level generated by individual primary or secondary exposures alone. Such an elevated response could also not be generated by a single application of higher concentrations of the agonist pI:C. Additionally, we determined the mechanism for TLR3 mediated TLR3 and RelA expression by using inhibitors of canonical TLR3-TBK1-IKKε and JAK-STAT signaling pathways. These data suggest that initial exposure of ARPE-19 cells to pI:C upregulates TLR3 and RelA signaling, leading to potentiated and persistent RelA signaling potentially generated by a positive feedback loop that may cause exacerbated inflammation in AMD. Furthermore, inhibition of JAK-STAT signaling may be a possible therapeutic treatment to prevent induction of TLR3 expression subsequent to pI:C exposure. Our results identify possible therapeutic targets to reduce the TLR3 positive feedback loop and subsequent overproduction of pro-inflammatory cytokines in RPE cells.

Effect of Inhibition of Colony-Stimulating Factor 1 Receptor on Choroidal Neovascularization in Mice

Neovascular age-related macular degeneration is one of the leading causes of blindness. Microglia and macrophages play a critical role in choroidal neovascularization (CNV) and may, therefore, be potential targets to modulate the disease course. This study evaluated the effect of the colony-stimulating factor-1 receptor inhibitor PLX5622 on experimental laser-induced CNV. A 98% reduction of retinal microglia cells was observed in the retina 1 week after initiation of PLX5622 treatment, preventing accumulation of macrophages within the laser site and leading to a reduction of leukocytes within the choroid after CNV induction. Mice treated with PLX5622 had a significantly faster decrease of the CNV lesion size, as revealed by in vivo imaging and immunohistochemistry from day 3 to day 14 compared with untreated mice. Several inflammatory modulators, such as chemokine (C-C motif) ligand 9, granulocyte-macrophage colony-stimulating factor, soluble tumor necrosis factor receptor-I, IL-1α, and matrix metallopeptidase-2, were elevated in the acute phase of the disease when microglia were ablated with PLX5622, whereas other cytokines (eg, interferon-γ, IL-4, and IL-10) were reduced. Our results suggest that colony-stimulating factor-1 receptor inhibition may be a novel therapeutic target in patients with neovascular age-related macular degeneration.

Association of rs10490924 in ARMS2/HTRA1 with age-related macular degeneration in the Pakistani population

Age-related macular degeneration (AMD) is a disease of the elderly in which central vision is lost because of degenerative changes of the macula. The current study investigated the association of single-nucleotide polymorphisms (SNPs) with AMD in the Pakistani population. Four SNPs were analyzed in this study: rs1061170 in the CFH, rs429608 near CFB, rs2230199 in the C3, and rs10490924 in ARMS2/HTRA1. This case-control association study was conducted on 300 AMD patients (125 wet AMD and 175 dry AMD) and 200 unaffected age- and gender-matched control individuals. The association of the SNP genotypes and allele frequency distributions were compared between patients and healthy controls, keeping age, gender, and smoking status as covariates. A significant genotype and variant allele association was found of rs10490924 in ARMS2/HTRA1 with wet AMD, while the SNPs in CFH, CFB, and C3 were not associated with AMD in the current Pakistani cohort. The lack of association of CFH, CFB, and C3 may be attributed to limited sample size. This study demonstrates that genetic causative factors of AMD differ among populations and supports the need for genetic association studies among cohorts from various populations to increase our global understanding of the disease pathogenesis.

17β-estradiol ameliorates oxidative stress and blue light-emitting diode-induced retinal degeneration by decreasing apoptosis and enhancing autophagy

Purpose

This study aimed to assess the effects of 17β-estradiol (βE₂) on blue light-emitting diode (LED)-induced retinal degeneration (RD) in rats and hydrogen peroxide (H₂O₂)-induced retinal pigment epithelium cell injury in humans and elucidate the protective mechanism of βE₂ underlying these processes.

Methods

Female ovariectomized (OVX) rats were intravitreally injected with βE2 before blue LED exposure (3,000 lux, 2 hours). Retinal function and morphology were assayed via electroretinogram (ERG) and H&E, respectively. Cell viability was assayed using the Cell Counting Kit-8. Cell ROS were measured using dichlorofluorescein fluorescence. Apoptosis was evaluated by TUNEL and Annexin V/propidium iodide staining. Gene expression and protein expression were quantified using quantitative real-time RT-PCR, Western blotting, and immunohistochemistry. Autophagosomes were examined by electron microscopy.

Results

Female OVX rats were exposed to blue LED, inducing RD. βE₂ significantly prevented the reduction in the a- and b-wave ERG amplitudes and the disruption of retinal structure, the loss of photoreceptor cells, and the decrease in the thickness of the outer nuclear layer caused by blue LED exposure. βE₂ also decreased cell apoptosis in the retina in blue LED-induced RD. Additionally, βE₂ reduced ROS levels and apoptosis in H₂O₂-treated human retinal pigment epithelial (ARPE-19) cells. Furthermore, βE₂ increased the protein expression of p-Akt and Bcl-2 and decreased the protein expression of cleaved caspase-3 and Bax during blue LED-induced retinal damage and in H₂O₂-treated ARPE-19 cells. βE₂ also increased the number of autopha-gosomes and upregulated the expression of LC3-II/LC3-I and Beclin 1 in these processes.

Conclusion

βE₂ protects against blue LED-induced RD and H₂O₂-induced oxidative stress by acting as an antioxidant, and its protective mechanism might occur by reducing apoptosis and enhancing autophagy; βE₂ may be a novel and effective therapy for age-related macular degeneration.

Evidence for an Association between Macular Degeneration and Thyroid Cancer in the Aged Population

Direct evidence of whether thyroid cancer patients have a higher risk of age-related macular degeneration (AMD) has yet to be investigated. Patients older than 50 years-old and newly diagnosed with thyroid cancer between 2000 and 2008 were identified from the national health insurance research database (NHIRD). We applied time-varying Cox proportional hazard models to assess the association between thyroid cancer and AMD. The multivariable models included conventional cardiovascular risk factors, myopia, vitreous floaters, hypothyroidism, hyperthyroidism, and treatment modality of thyroid cancer. The analysis process was stratified by age, gender, and comorbidity. In this study, 5253 patients were included in a thyroid cancer cohort (men 24.5%; median age 59.1 years (53.7–67.4 years), and 21,012 matched controls were included in a non-thyroid cancer cohort. The AMD incidence was 40.7 per 10,000 person/year in the thyroid cancer cohort. The thyroid cancer cohort had a higher risk (adjusted hazard ratio (aHR) = 1.38, 95% confidence interval, CI = 1.09–1.75) of AMD than the non-thyroid cohort. Thyroid cancer patients had a higher risk of AMD, especially the male patients (aHR = 1.92, 95% CI = 1.38–3.14) and the patients with comorbidities (aHR = 1.38, 95% CI = 1.09–1.74). In conclusion, thyroid cancer patients older than 50 years-old have increased risk of AMD.

Human stem cell-derived retinal epithelial cells activate complement via collectin 11 in response to stress

Age-related macular degeneration (AMD) is a major cause of blindness and is associated with complement dysregulation. The disease is a potential target for stem cell therapy but success is likely to be limited by the inflammatory response. We investigated the innate immune properties of human induced-pluripotent stem cell (iPSC)-derived RPE cells, particularly with regard to the complement pathway. We focused on collectin-11 (CL-11), a pattern recognition molecule that can trigger complement activation in renal epithelial tissue. We found evidence of constitutive and hypoxia-induced expression of CL-11 in iPS-RPE cells, and in the extracellular fluid. Complement activation on the cell surface occurred in conjunction with CL-11 binding. CL-11 has been shown to activate inflammatory responses through recognition of L-fucose, which we confirmed by showing that fucosidase-treated cells, largely, failed to activate complement. The presence of CL-11 in healthy murine and human retinal tissues confirmed the biological relevance of CL-11. Our data describe a new trigger mechanism of complement activation that could be important in disease pathogenesis and therapeutic interventions.

A Proinflammatory Function of Toll-Like Receptor 2 in the Retinal Pigment Epithelium as a Novel Target for Reducing Choroidal Neovascularization in Age-Related Macular Degeneration

Current treatments for choroidal neovascularization, a major cause of blindness for patients with age-related macular degeneration, treat symptoms but not the underlying causes of the disease. Inflammation has been strongly implicated in the pathogenesis of choroidal neovascularization. We examined the inflammatory role of Toll-like receptor 2 (TLR2) in age-related macular degeneration. TLR2 was robustly expressed by the retinal pigment epithelium in mouse and human eyes, both normal and with macular degeneration/choroidal neovascularization. Nuclear localization of NF-κB, a major downstream target of TLR2 signaling, was detected in the retinal pigment epithelium of human eyes, particularly in eyes with advanced stages of age-related macular degeneration. TLR2 antagonism effectively suppressed initiation and growth of spontaneous choroidal neovascularization in a mouse model, and the combination of anti-TLR2 and antivascular endothelial growth factor receptor 2 yielded an additive therapeutic effect on both area and number of spontaneous choroidal neovascularization lesions. Finally, in primary human fetal retinal pigment epithelium cells, ligand binding to TLR2 induced robust expression of proinflammatory cytokines, and end products of lipid oxidation had a synergistic effect on TLR2 activation. Our data illustrate a functional role for TLR2 in the pathogenesis of choroidal neovascularization, likely by promoting inflammation of the retinal pigment epithelium, and validate TLR2 as a novel therapeutic target for reducing choroidal neovascularization.

T-helper-associated cytokines expression by peripheral blood mononuclear cells in patients with polypoidal choroidal vasculopathy and age-related macular degeneration

Background

Immune responses play a key role in the pathogenesis and progression of polypoidal choroidal vasculopath (PCV) and age-related macular degeneration (AMD). In this study, we determined the Th cell-associated immune responses by measuring the cytokine expression of peripheral blood mononuclear cells (PBMC) in both PCV and neovascular AMD (nAMD) patients.

Methods

Twenty-seven nAMD patients, 33 PCV patients and a gender- and age-matched group of 18 healthy individuals were involved in this study. The Th-cell cytokine profiles including levels of interferon-gamma (INF-γ), interleukin (IL)-17A and IL-4 in cultures of PBMCs were determined by enzyme-linked immunosorbent assay (ELISA).

Results

IFN-γ,IL-17A and IL-4 production was significantly increased after stimulation with PHA. The levels of IFN-γ and IL-4 in PHA-stimulated cultures were higher in PCV and nAMD patients than that in healthy controls (P = 0.038,P = 0.014), while no difference was found between PCV and nAMD (all P > 0.05). No significant difference in IL-17A level in PHA-stimulated cultures was found among PCV, nAMD and control groups (P > 0.05).

Conclusions

These findings suggest that circulating IFN-γ and IL-4 producing Th1 and Th2 cells may involve in the pathogenesis of PCV and nAMD. PCV may have the similar immune responses with nAMD.

Inflammation and its role in age-related macular degeneration

Inflammation is a cellular response to factors that challenge the homeostasis of cells and tissues. Cell-associated and soluble pattern-recognition receptors, e.g. Toll-like receptors, inflammasome receptors, and complement components initiate complex cellular cascades by recognizing or sensing different pathogen and damage-associated molecular patterns, respectively. Cytokines and chemokines represent alarm messages for leukocytes and once activated, these cells travel long distances to targeted inflamed tissues. Although it is a crucial survival mechanism, prolonged inflammation is detrimental and participates in numerous chronic age-related diseases. This article will review the onset of inflammation and link its functions to the pathogenesis of age-related macular degeneration (AMD), which is the leading cause of severe vision loss in aged individuals in the developed countries. In this progressive disease, degeneration of the retinal pigment epithelium (RPE) results in the death of photoreceptors, leading to a loss of central vision. The RPE is prone to oxidative stress, a factor that together with deteriorating functionality, e.g. decreased intracellular recycling and degradation due to attenuated heterophagy/autophagy, induces inflammation. In the early phases, accumulation of intracellular lipofuscin in the RPE and extracellular drusen between RPE cells and Bruch's membrane can be clinically detected. Subsequently, in dry (atrophic) AMD there is geographic atrophy with discrete areas of RPE loss whereas in the wet (exudative) form there is neovascularization penetrating from the choroid to retinal layers. Elevations in levels of local and systemic biomarkers indicate that chronic inflammation is involved in the pathogenesis of both disease forms.

Circulating Autoantibodies in Age-Related Macular Degeneration Recognize Human Macular Tissue Antigens Implicated in Autophagy, Immunomodulation, and Protection from Oxidative Stress and Apoptosis

BACKGROUND

We investigated sera from elderly subjects with and without age-related macular degeneration (AMD) for presence of autoantibodies (AAbs) against human macular antigens and characterized their identity.

METHODS

Sera were collected from participants in the Age-Related Maculopathy Ancillary (ARMA) Study, a cross-sectional investigation ancillary to the Health ABC Study, enriched with participants from the general population. The resulting sample (mean age: 79.2±3.9 years old) included subjects with early to advanced AMD (n = 131) and controls (n = 231). Sera were tested by Western blots for immunoreactive bands against human donor macular tissue homogenates. Immunoreactive bands were identified and graded, and odds ratios (OR) calculated. Based on these findings, sera were immunoprecipitated, and subjected to 2D gel electrophoresis (GE). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to identify the targets recognized by circulating AAbs seen on 2D-GE, followed by ELISAs with recombinant proteins to confirm LC-MS/MS results, and quantify autoreactivities.

RESULTS

In AMD, 11 immunoreactive bands were significantly more frequent and 13 were significantly stronger than in controls. Nine of the more frequent bands also showed stronger reactivity. OR estimates ranged between 4.06 and 1.93, and all clearly excluded the null value. Following immunoprecipitation, 2D-GE and LC-MS/MS, five of the possible autoreactivity targets were conclusively identified: two members of the heat shock protein 70 (HSP70) family, HSPA8 and HSPA9; another member of the HSP family, HSPB4, also known as alpha-crystallin A chain (CRYAA); Annexin A5 (ANXA5); and Protein S100-A9, also known as calgranulin B that, when complexed with S100A8, forms calprotectin. ELISA testing with recombinant proteins confirmed, on average, significantly higher reactivities against all targets in AMD samples compared to controls.

CONCLUSIONS

Consistent with other evidence supporting the role of inflammation and the immune system in AMD pathogenesis, AAbs were identified in AMD sera, including early-stage disease. Identified targets may be mechanistically linked to AMD pathogenesis because the identified proteins are implicated in autophagy, immunomodulation, and protection from oxidative stress and apoptosis. In particular, a role in autophagy activation is shared by all five autoantigens, raising the possibility that the detected AAbs may play a role in AMD via autophagy compromise and downstream activation of the inflammasome. Thus, we propose that the detected AAbs provide further insight into AMD pathogenesis and have the potential to contribute to disease biogenesis and progression.

Defects in retinal pigment epithelial cell proteolysis and the pathology associated with age-related macular degeneration

Maintenance of protein homeostasis, also referred to as "Proteostasis", integrates multiple pathways that regulate protein synthesis, folding, translocation, and degradation. Failure in proteostasis may be one of the underlying mechanisms responsible for the cascade of events leading to age-related macular degeneration (AMD). This review covers the major degradative pathways (ubiquitin-proteasome and lysosomal involvement in phagocytosis and autophagy) in the retinal pigment epithelium (RPE) and summarizes evidence of their involvement in AMD. Degradation of damaged and misfolded proteins via the proteasome occurs in coordination with heat shock proteins. Evidence of increased content of proteasome and heat shock proteins in retinas from human donors with AMD is consistent with increased oxidative stress and extensive protein damage with AMD. Phagocytosis and autophagy share key molecules in phagosome maturation as well as degradation of their cargo following fusion with lysosomes. Phagocytosis and degradation of photoreceptor outer segments ensures functional integrity of the neural retina. Autophagy rids the cell of toxic protein aggregates and defective mitochondria. Evidence suggesting a decline in autophagic flux includes the accumulation of autophagic substrates and damaged mitochondria in RPE from AMD donors. An age-related decrease in lysosomal enzymatic activity inhibits autophagic clearance of outer segments, mitochondria, and protein aggregates, thereby accelerating the accumulation of lipofuscin. This cumulative damage over a person's lifetime tips the balance in RPE from a state of para-inflammation, which strives to restore cell homeostasis, to the chronic inflammation associated with AMD.

Beneficial protective effect of pramipexole on light-induced retinal damage in mice

We investigated the effects of pramipexole, a potent dopamine receptor D2/D3 agonist, on light-induced retinal damage in mice, H2O2-induced retinal pigment epithelium ARPE-19 cell injury in humans, and hydroxyl radical scavenging activity in a cell-free system. Pramipexole (0.1 and 1 mg/kg body weight) was orally administered to mice 1 h before light exposure (5000 lux, 2 h). Electrophysiological and morphologic studies were performed to evaluate the effects of the pramipexole on light-induced retinal damage in mice. Pramipexole significantly prevented the reduction of the a- and b-wave electroretinogram (ERG) amplitudes caused by light exposure in a dose-dependent manner. In parallel, damage to the inner and outer segments (IS/OS) of the photoreceptors, loss of photoreceptor nuclei, and the number of Tdt-mediated dUTP nick-end labeling (TUNEL)-positive cells in the outer nuclear layer (ONL) caused by light exposure were notably ameliorated by pramipexole. Additionally, pramipexole suppressed H2O2-induced ARPE-19 cell death in vitro in a concentration-dependent manner. The effect of pramipexole was significant at concentrations of 10(-6) M or higher. Pramipexole also significantly prevented H2O2-induced activation of caspases-3/7 and the intracellular accumulation of reactive oxygen species (ROS) in a concentration-dependent manner ranging from 10(-5) to 10(-3) M. Furthermore, pramipexole increased the scavenging activity toward a hydroxyl radical generated from H2O2 in a Fenton reaction. Our results suggest that pramipexole protects against light-induced retinal damage as an antioxidant and that it may be a novel and effective therapy for retinal degenerative disorders, such as dry age-related macular degeneration.

Interleukin-1β Level Is Increased in Vitreous of Patients with Neovascular Age-Related Macular Degeneration (nAMD) and Polypoidal Choroidal Vasculopathy (PCV)

Purpose

To examine the expression of pro-interleukin-1β (pro-IL-1β) and interleukin-1β (IL-1β) in the vitreous body of patients with neovascular age-related macular degeneration(nAMD), polypoidal choroidal vasculopathy (PCV), proliferative diabetic retinopathy (PDR), retinal vein occlusion (RVO) or Eales’ disease to further elucidate the role of IL-1β and inflammation in the pathogenesis of neovascular retinal disease.

Design

Prospective clinical laboratory investigation study.

Methods

All patients enrolled had vitreous hemorrhage due to nAMD, PCV, PDR, RVO or Eales’ disease that required vitrectomy. Patients were excluded for any history of active intraocular inflammation, or other ophthalmic surgery besides vitrectomy. Control samples were obtained from patients with idiopathic macular epiretinal membrane. A total of fifty vitreous samples were collected from patient during vitrectomy. Pro-IL-1β and IL-1β expression were measured by enzyme-linked immunosorbent assay (ELISA). Results were analyzed statistically using nonparametric tests.

Results

Expression of pro-IL-1β protein was increased by 2.83-fold and 9.19-fold in PCV and nAMD vitreous samples relative to control, respectively. Expression of IL-β protein was increased by 10-fold and 4.83-fold in PCV and nAMD vitreous samples relative to control, respectively.

Conclusions

Our results demonstrate that expression of pro-IL-1β and IL-1β proteins is higher in PCV and nAMD. The roles of pro-IL-1β and IL-1β as inflammatory mediators in the development of PCV and nAMD may be associated with photoreceptor degeneration and neovascularization which necessitates further study.

Reduced photoreceptor death and improved retinal function during retinal degeneration in mice lacking innate immunity adaptor protein MyD88

The injury inflammatory response mediated by the innate immune system is an important contributor to neurodegeneration in the central nervous system (CNS) and retina. A major branch of the innate immune system is regulated by the Toll-like receptors (TLRs), which are receptors for endogenous damage associated molecules released from injured cells as well as pathogen-derived molecules, and interleukin-1 receptors (IL-1R), which are activated by IL-1α, IL-1β and IL-18 cytokines. TLRs and IL-1R are expressed on immune and non-immune cell types and act as first responders to cell damage, which results in tissue repair, or inflammation and apoptosis. Both TLR and IL-1R require the adaptor protein myeloid differentiation primary response gene 88 (MyD88) for signaling. Although inflammation is implicated in neuronal death in the retina, the role of MyD88-dependent TLR and IL-1R signaling in retinal degeneration is unknown. Therefore, the purpose of this study was to investigate the role of MyD88-mediated signaling in neuronal degeneration in the retinal degeneration 1 (rd1) mouse model, which exhibits a phenotype of rapid photoreceptor death and inflammation. To generate rd1 mice lacking the MyD88 gene, rd1 were bred with MyD88 knockout mice (MyD88(-/-)) for several generations to produce rd1/MyD88(+/+) and rd1/MyD88(-/-) genotypes. Chemokine mRNA expression levels were analyzed by qRT-PCR, and recruitment of activated microglia was quantified by immunodetection of the IBA-1 protein. Retinal outer nuclear layer cell counts were performed to quantify photoreceptor degeneration, and retinal function was assessed using electroretinograms (ERG). Our results revealed that retinal expression of Ccl2, Ccl4, Ccl7 and Cxcl10 was reduced by 2 to 8-fold in rd1/MyD88(-/-) mice compared with rd1/MyD88(+/+) mice (p<0.05), which coincided with attenuated microglial activation, higher numbers of photoreceptors and higher retina responses to photopic and scotopic stimuli. At later ages, rd1/MyD88(-/-) had reduced chemokine expression and higher photopic responses but no change in microglial recruitment compared with rd1 mice with functional MyD88. In conclusion, lack of MyD88-mediated signaling increased photoreceptor survival and retina function in rd1 mice, which implicates MyD88-mediated innate immunity pathways as an important pathogenic factor during retinal degeneration.

Decline in cellular clearance systems induces inflammasome signaling in human ARPE-19 cells

Retinal pigment epithelium (RPE) plays a major role in the maintenance of photoreceptors, and degeneration of RPE results in the development of age-related macular degeneration (AMD). Accumulation of intracellular protein aggregates, increased oxidative stress, and chronic inflammation are all factors damaging the functionality of aged RPE cells. Here, we report that inhibition of proteasomal degradation with MG-132 and autophagy with bafilomycin A1 resulted in the release of IL-1β but not that of IL-18 in human ARPE-19 cells. NLRP3 receptor became upregulated, and caspase-1, the functional component of an inflammasome complex, was activated. In addition to accumulating intracellular protein aggregates, inhibition of degradation systems induced oxidative stress which was demonstrated by elevated amounts of intracellular 4-hydroxynonenal (HNE)-protein adducts. Along with IL-1β, exposure to MG-132 and bafilomycin A1 resulted in the secretion of IL-8. A low concentration (1pg/ml) of IL-1β was capable of triggering significant IL-8 production which also became attenuated by treatment with a specific caspase-1 inhibitor. These results suggest that decline in intracellular degradation systems results not only in increased amounts of intracellular protein aggregates and oxidative stress but also in the activation of NLRP3 inflammasomes, arisen as a result of elevated production of biologically active IL-1β.

The role of proteases and inflammatory molecules in triggering neovascular age-related macular degeneration: basic science to clinical relevance

Age-related macular degeneration (AMD) causes severe vision impairment in aged individuals. The health impact and cost of the disease will dramatically increase over the years, with the increase in the aging population. Currently, antivascular endothelial growth factor agents are routinely used for managing late-stage AMD, and recent data have shown that up to 15%-33% of patients do not respond to this treatment. Henceforth, there is a need to develop better treatment options. One avenue is to investigate the role proteases and inflammatory molecules might have in regulating and being regulated by vascular endothelial growth factor. Moreover, emerging data indicate that proteases and inflammatory molecules might be critical in the development and progression of AMD. This article reviews recent literature that investigates proteases and inflammatory molecules involved in the development of AMD. Gaining insights into the proteolytic and inflammatory pathways associated with the pathophysiology of AMD could enable the development of additional or alternative drug strategies for the treatment of AMD.

The retinal pigment epithelium (RPE) induces FasL and reduces iNOS and Cox2 in primary monocytes

PURPOSE

Retinal pigment epithelium (RPE) cells may alter the phenotype of monocytes by soluble factors that may be influenced by stimulation of the RPE. Since RPE cells carry the toll-like receptor-3 (TLR3) that detects and reacts to viral infection through binding of dsRNA we investigated the effects of RPE cells with or without TLR3 stimulation on blood-derived monocytes with respect to regulation of pro-/anti-inflammatory cytokines, anti-angiogenic factors and migratory properties.

METHODS

Primary RPE cells were prepared from porcine eyes; monocytes were prepared from porcine blood. TLR3 activation was induced by polyinosinic:polycytidylic acid (Poly I:C). RPE cells were stimulated with Poly I:C in different concentrations for 24 hours and a cell culture supernatant was applied to the monocytes. Expression of CD14 and Fas ligand (FasL) was determined via flow cytometry. The expression of IL-6, IL-1ß, TNFα, Cox2, iNOS and IL-10 was determined via quantitative RT-PCR. Migration was determined using Boyden chamber experiments.

RESULTS

The supernatant of RPE cells, irrespective of TLR3 activation, induced FasL expression in the monocytes. Expression of iNOS and Cox2 was reduced by RPE cells and the reduction of Cox2 but not if iNOS was lost under TLR3 activation. No induction of IL-6, IL-1ß, IL-10 or TNFα by the RPE was seen. TLR3-activated RPE cells induced monocyte migration.

CONCLUSION

RPE cells induce an upregulation of FasL and a downregulation of iNOS and Cox2 without upregulating inflammatory cytokines, possibly inducing an anti-angiogenic phenotype in the monocytes. This phenotype is still upheld after challenging RPE cells with dsRNA, mimicking a viral infection.

AprioriGWAS, a new pattern mining strategy for detecting genetic variants associated with disease through interaction effects

Identifying gene-gene interaction is a hot topic in genome wide association studies. Two fundamental challenges are: (1) how to smartly identify combinations of variants that may be associated with the trait from astronomical number of all possible combinations; and (2) how to test epistatic interaction when all potential combinations are available. We developed AprioriGWAS, which brings two innovations. (1) Based on Apriori, a successful method in field of Frequent Itemset Mining (FIM) in which a pattern growth strategy is leveraged to effectively and accurately reduce search space, AprioriGWAS can efficiently identify genetically associated genotype patterns. (2) To test the hypotheses of epistasis, we adopt a new conditional permutation procedure to obtain reliable statistical inference of Pearson's chi-square test for the contingency table generated by associated variants. By applying AprioriGWAS to age-related macular degeneration (AMD) data, we found that: (1) angiopoietin 1 (ANGPT1) and four retinal genes interact with Complement Factor H (CFH). (2) GO term “glycosaminoglycan biosynthetic process” was enriched in AMD interacting genes. The epistatic interactions newly found by AprioriGWAS on AMD data are likely true interactions, since genes interacting with CFH are retinal genes, and GO term enrichment also verified that interaction between glycosaminoglycans (GAGs) and CFH plays an important role in disease pathology of AMD. By applying AprioriGWAS on Bipolar disorder in WTCCC data, we found variants without marginal effect show significant interactions. For example, multiple-SNP genotype patterns inside gene GABRB2 and GRIA1 (AMPA subunit 1 receptor gene). AMPARs are found in many parts of the brain and are the most commonly found receptor in the nervous system. The GABRB2 mediates the fastest inhibitory synaptic transmission in the central nervous system. GRIA1 and GABRB2 are relevant to mental disorders supported by multiple evidences.

Genes do not operate in vacuum. They interact with each other in many ways. Therefore, to figure out genetic causes of disease by case-control association studies, it is important to take interactions into account. There are two fundamental challenges in interaction-focused analysis. The first is the number of possible combinations of genetic variants easily goes to astronomic which is beyond current computational facility, which is referred as “the curse of dimensionality” in field of computer science. The other is, even if all potential combinations could be exhaustively checked, genuine signals are likely to be buried by false positives that are composed of single variant with large main effect and some other irrelevant variant. In this work, we propose AprioriGWAS that employees Apriori, an algorithm that pioneers the branch of “Frequent Itemset Mining” in computer science to cope with daunting numbers of combinations, and conditional permutation, to enable real signals standing out. By applying AprioriGWAS to age-related macular degeneration (AMD) data and bipolar disorder (BD) in WTCCC data, we found interesting interactions between sensible genes in terms of disease. Consequently, AprioriGWAS could be a good tool to find epistasis interaction from GWA data.

Oxidative stress, hypoxia, and autophagy in the neovascular processes of age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of severe and irreversible loss of vision in the elderly in developed countries. AMD is a complex chronic neurodegenerative disease associated with many environmental, lifestyle, and genetic factors. Oxidative stress and the production of reactive oxygen species (ROS) seem to play a pivotal role in AMD pathogenesis. It is known that the macula receives the highest blood flow of any tissue in the body when related to size, and anything that can reduce the rich blood supply can cause hypoxia, malfunction, or disease. Oxidative stress can affect both the lipid rich retinal outer segment structure and the light processing in the macula. The response to oxidative stress involves several cellular defense reactions, for example, increases in antioxidant production and proteolysis of damaged proteins. The imbalance between production of damaged cellular components and degradation leads to the accumulation of detrimental products, for example, intracellular lipofuscin and extracellular drusen. Autophagy is a central lysosomal clearance system that may play an important role in AMD development. There are many anatomical changes in retinal pigment epithelium (RPE), Bruch's membrane, and choriocapillaris in response to chronic oxidative stress, hypoxia, and disturbed autophagy and these are estimated to be crucial components in the pathology of neovascular processes in AMD.

A2E induces IL-1ß production in retinal pigment epithelial cells via the NLRP3 inflammasome

AIMS

With ageing extracellular material is deposited in Bruch's membrane, as drusen. Lipofuscin is deposited in retinal pigment epithelial cells. Both of these changes are associated with age related macular degeneration, a disease now believed to involve chronic inflammation at the retinal-choroidal interface. We hypothesise that these molecules may act as danger signals, causing the production of inflammatory chemokines and cytokines by the retinal pigment epithelium, via activation of pattern recognition receptors.

METHODS

ARPE-19 cells were stimulated in vitro with the following reported components of drusen: amyloid-ß (1-42), Carboxyethylpyrrole (CEP) modified proteins (CEP-HSA), Nε-(Carboxymethyl)lysine (CML) modified proteins and aggregated vitronectin. The cells were also stimulated with the major fluorophore of lipofuscin: N-retinylidene-N-retinylethanolamine (A2E). Inflammatory chemokine and cytokine production was assessed using Multiplex assays and ELISA. The mechanistic evaluation of the NLRP3 inflammasome pathway was assessed in a stepwise fashion.

RESULTS

Of all the molecules tested only A2E induced inflammatory chemokine and cytokine production. 25 µM A2E induced the production of significantly increased levels of the chemokines IL-8, MCP-1, MCG and MIP-1α, the cytokines IL-1ß, IL-2, IL-6, and TNF-α, and the protein VEGF-A. The release of IL-1ß was studied further, and was determined to be due to NLRP3 inflammasome activation. The pathway of activation involved endocytosis of A2E, and the three inflammasome components NLRP3, ASC and activated caspase-1. Immunohistochemical staining of ABCA4 knockout mice, which show progressive accumulation of A2E levels with age, showed increased amounts of IL-1ß proximal to the retinal pigment epithelium.

CONCLUSIONS

A2E has the ability to stimulate inflammatory chemokine and cytokine production by RPE cells. The pattern recognition receptor NLRP3 is involved in this process. This provides further evidence for the link between A2E, inflammation, and the pathogenesis of AMD. It also supports the recent discovery of NLRP3 inflammasome activation in AMD.

Retinal pigment epithelium (RPE) exosomes contain signaling phosphoproteins affected by oxidative stress

Age-related macular degeneration (AMD) is a leading cause of vision loss and blindness among the elderly population in the industrialized world. One of the typical features of this pathology is the gradual death of retinal pigment epithelial (RPE) cells, which are essential for maintaining photoreceptor functions and survival. The etiology is multifactorial, and oxidative stress is clearly one of the key factors involved in disease pathogenesis (Plafker, Adv. Exp. Med. Biol. 664 (2010) 447-56; Qin, Drug Dev. Res. 68 (2007) 213-225). Recent work has revealed the presence of phosphorylated signaling proteins in the vitreous humour of patients affected by AMD or other retinal diseases. While the location of these signaling proteins is typically the cell membrane or intracellular compartments, vitreous samples were proven to be cell-free (Davuluri et al., Arch. Ophthalmol. 127 (2009) 613-21). To gain a better understanding of how these proteins can be shed into the vitreous, we used reverse phase protein arrays (RPMA) to analyze the protein and phosphoprotein content of exosomes shed by cultured ARPE-19 cells under oxidative stress conditions. Seventy two proteins were shown to be released by ARPE-19 cells and compartmentalized within exosomes. Forty one of them were selectively detected in their post-translationally modified form (i.e., phosphorylated or cleaved) for the first time in exosomes. Sets of these proteins were linked together reflecting activation of pathway units within exosomes. A subset of (phospho)proteins were altered in exosomes secreted by ARPE-19 cells subjected to oxidative stress, compared to that secreted by control/non stressed cells. Stress-altered exosome proteins were found to be involved in pathways regulating apoptosis/survival (i.e, Bak, Smac/Diablo, PDK1 (S241), Akt (T308), Src (Y416), Elk1 (S383), ERK 1/2 (T202/Y204)) and cell metabolism (i.e., AMPKα1 (S485), acetyl-CoA carboxylase (S79), LDHA). Exosomes may thus represent the conduit through which membrane and intracellular signaling proteins are released into the vitreous. Changes in their (phospho)protein content upon stress conditions suggest their possible role in mediating cell-cell signaling during physio-pathological events; furthermore, exosomes may represent a potential source of biomarkers.

Autophagy regulating kinases as potential therapeutic targets for age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of central vision loss in the elderly in the developed countries. The number of AMD patients will double during the next decades due to increasing number of aged people. Chronic oxidative stress, inflammation and accumulation of protein-rich deposits both in the retinal pigment epithelium lysosomes and under the retinal pigment epithelium herald the onset of AMD. The disease can be divided into dry and wet AMD forms. The dry form of the disease is more prevalent accounting for up to 90% of all cases. Continued intraocular injections are the current treatment strategy to prevent progression of wet AMD. It is a major challenge to develop new drugs that could prevent or at least ease the symptoms of the increasing population of AMD patients. Since AMD pathology is clearly associated with accumulated protein deposits, the autophagy clearance system might represent a potential future therapeutic target for AMD as is thoroughly discussed here.

NLRP3 inflammasome activation in retinal pigment epithelial cells by lysosomal destabilization: implications for age-related macular degeneration

PURPOSE

To evaluate the effect of lysosomal destabilization on NLRP3 inflammasome activation in RPE cells and to investigate the mechanisms by which inflammasome activation may contribute to the pathogenesis of age-related macular degeneration (AMD).

METHODS

Human ocular tissue sections from patients with geographic atrophy or neovascular AMD were stained for NLRP3 and compared to tissues from age-matched controls. Expression of the IL-1β precursor, pro-IL-1β, was induced in ARPE-19 cells by IL-1α treatment. Immunoblotting was performed to assess expression of NLRP3 inflammasome components (NLRP3, ASC, and procaspase-1) and pro-IL-1β in ARPE-19 cells. Lysosomes were destabilized using the lysosomotropic agent L-leucyl-L-leucine methyl ester (Leu-Leu-OMe). Active caspase-1 was detected using FAM-YVAD-FMK, a fluorescent-labeled inhibitor of caspases (FLICA) specific for caspase-1. IL-1β was detected by immunoblotting and ELISA, and cytotoxicity was evaluated by LDH quantification.

RESULTS

RPE of eyes affected by geographic atrophy or neovascular AMD exhibited NLRP3 staining at lesion sites. ARPE-19 cells were found to express NLRP3, ASC, and procaspase-1. IL-1α dose-dependently induced pro-IL-1β expression in ARPE-19 cells. Lysosomal destabilization induced by Leu-Leu-OMe triggered caspase-1 activation, IL-1β secretion, and ARPE-19 cell death. Blocking Leu-Leu-OMe-induced lysosomal disruption with the compound Gly-Phe-CHN(2) or inhibiting caspase-1 with Z-YVAD-FMK abrogated IL-1β release and ARPE-19 cytotoxicity.

CONCLUSIONS

NLRP3 upregulation occurs in the RPE during the pathogenesis of advanced AMD, in both geographic atrophy and neovascular AMD. Destabilization of RPE lysosomes induces NLRP3 inflammasome activation, which may contribute to AMD pathology through the release of the proinflammatory cytokine IL-1β and through caspase-1-mediated cell death, known as "pyroptosis."

Molecular mechanisms of retinal pigment epithelium damage and development of age-related macular degeneration

Age-related macular degeneration (AMD) is attributed to a complex interaction of genetic and environmental factors. It is characterized by degeneration involving the retinal photoreceptors, retinal pigment epithelium (RPE) and Bruch's membrane, as well as alterations in choroidal capillaries. AMD pathogenesis is strongly associated with chronic oxidative stress and inflammation that ultimately lead to protein damage, aggregation and degeneration of RPE. Specific degenerative findings for AMD are accumulation of intracellular lysosomal lipofuscin and extracellular drusens. In this review, we discuss thoroughly RPE-derived mechanisms in AMD pathology.

Novel role for the innate immune receptor Toll-like receptor 4 (TLR4) in the regulation of the Wnt signaling pathway and photoreceptor apoptosis

Recent evidence has implicated innate immunity in regulating neuronal survival in the brain during stroke and other neurodegenerations. Photoreceptors are specialized light-detecting neurons in the retina that are essential for vision. In this study, we investigated the role of the innate immunity receptor TLR4 in photoreceptors. TLR4 activation by lipopolysaccharide (LPS) significantly reduced the survival of cultured mouse photoreceptors exposed to oxidative stress. With respect to mechanism, TLR4 suppressed Wnt signaling, decreased phosphorylation and activation of the Wnt receptor LRP6, and blocked the protective effect of the Wnt3a ligand. Paradoxically, TLR4 activation prior to oxidative injury protected photoreceptors, in a phenomenon known as preconditioning. Expression of TNFα and its receptors TNFR1 and TNFR2 decreased during preconditioning, and preconditioning was mimicked by TNFα antagonists, but was independent of Wnt signaling. Therefore, TLR4 is a novel regulator of photoreceptor survival that acts through the Wnt and TNFα pathways.

Inhibition of RPE cell sterile inflammatory responses and endotoxin-induced uveitis by a cell-impermeable HSP90 inhibitor

Dying cells release pro-inflammatory molecules, functioning as cytokines to trigger cell/tissue inflammation that is relevant to disease pathology. Heat-shock protein 90 (HSP90) is believed to act as a danger signal for tissue damage once released extracellularly. Potential roles of HSP90 were explored in retinal pigment epithelial (RPE) inflammatory responses to necrosis. Cellular extracts can trigger ARPE-19 cell inflammatory responses, producing cytokines that lead to an increase in ARPE-19 cell monolayer permeability. Addition of recombinant HSP90β mimics the induction of chemokines IL-8 and MCP-1 in cultured RPE cells, suggesting that released HSP90 can incite RPE cell sterile inflammatory responses. Consistent with this, classical HSP90 inhibitors were shown to substantially reduce necrosis-induced cytokine production and permeability increases in ARPE-19 cells. Moreover, a cell-impermeable inhibitor, 17-N,N-dimethylaminoethylamino-17-demethoxy-geldanamycin-N-oxide, also efficiently inhibited necrosis-induced cytokine production and TNF-α/IL-1β-induced increase in ARPE-19 cell permeability in vitro and endotoxin-induced development of uveitis in vivo, suggesting that HSP90 can contribute to necrosis-induced RPE inflammatory responses. Collectively, our data identify HSP90 as a pro-inflammatory molecule in RPE cell sterile inflammatory responses.

Advances in assay of complement function and activation

The main function of the complement system is pattern recognition of danger. Typical exogenous danger signals are pathogen associated molecular patterns inducing a protective inflammatory response. Other examples are exposure to foreign surfaces of biomedical materials including nanoparticles, which principally induce the same inflammatory response. If a surface is "foreign" to the host, it induces complement activation. Development of monoclonal antibodies to neoepitopes on complement activation products introduced an entirely new set of methods for assay of complement activation. Activation of complement by a surface occurs by impairment of the fine balance of the control system, e.g. by preferred binding of factor B at the expense of factor H. Sensitive methods to detect complement activation on surfaces and in the fluid phase are a prerequisite for investigation of the biocompatibility of artificial materials. This information can be used to develop new materials with enhanced biocompatibility. Here we review available methods to study human and animal complement function and activation in vitro and in vivo.

The A Allele of the -576G>A polymorphism of the transferrin gene is associated with the increased risk of age-related macular degeneration in smokers

Age-related macular degeneration (AMD) is the leading cause of blindness among the elderly in developed countries, and its pathogenesis is underlined by genetic and environmental factors. Oxidative stress is a major environmental risk factor of AMD; namely, AMD is associated with the increased level of reactive oxygen species, which may be produced in reactions catalyzed by iron present in the retina. Therefore, variability of the genes of iron metabolism may be important in the AMD risk. In the present study, we analyzed the association between AMD and the -576G>A polymorphism of the transferrin gene or the 1892C>T polymorphism of the transferrin receptor 2 (TFR2) gene in 278 patients with AMD and 105 controls. The former polymorphism is located in the promoter region of the transferrin gene and may affect the level of its transcription, while the latter is a synonymous mutation in the exon 16, which may affect the efficiency of translation of TFR2 mRNA. Transferrin and TFR2 are important in iron homeostasis. The A allele of the -576A>G polymorphism was significantly associated with the increased risk of AMD in tobacco smokers, whereas the 1892C>T polymorphism did not influence the risk of AMD related to smoking. Moreover, each polymorphism does not influence the risk of AMD associated with age, sex or the family history of the disease. In conclusion, the A allele of the -576A>G polymorphism of the transferrin gene may increase the risk of AMD in smokers.

Celastrol regulates innate immunity response via NF-κB and Hsp70 in human retinal pigment epithelial cells

Elevated nuclear factor kappa B (NF-κB) activity and interleukin-6 (IL-6) secretion participates in the pathology of several age and inflammatory-related diseases, including age-related macular degeneration (AMD), in which retinal pigment epithelial cells are the key target. Recent findings reveal that heat shock protein 70 (Hsp70) may affect regulation of NF-κB. In the current study, effects of Hsp70 expression on NF-κB RelA/p65 activity were evaluated in human retinal pigment epithelial cells (ARPE-19) by using celastrol, a novel anti-inflammatory compound. Anti-inflammatory properties of celastrol were determined by measuring expression levels of IL-6 and endogenous NF-κB levels during lipopolysaccharide (LPS) exposure by using enzyme-linked immunosorbent assays (ELISA). Cell viability was measured by MTT and LDH assay, and Hsp70 expression levels were analyzed by Western blotting. ARPE-19 cells were transfected with hsp70 small interfering RNA (siRNA) in order to attenuate Hsp70 expression and activity of NF-κB RelA/p65 was measured using NF-κB consensus bound ELISA. Simultaneous exposures to LPS and celastrol reduced IL-6 expression levels as well as activity of phosphorylated NF-κB at serine 536 (Ser536) in ARPE-19 cells when compared to LPS exposure alone. In addition, inhibition of NF-κB RelA/p65 activity by celastrol was attenuated when Hsp70 response was silenced by siRNA. Favorable anti-inflammatory concentrations of celastrol showed no signs of cytotoxic response. Our findings reveal that celastrol is a novel plant compound which suppresses innate immunity response in human retinal pigment epithelial cells via NF-κB and Hsp70 regulation, and that Hsp70 is a critical regulator of NF-κB.