Inflammation in dry age-related macular degeneration

Age-Related Macular Degeneration in Patients with Androgenetic Alopecia: Could the Monocyte/HDL Ratio Be the Link?

INTRODUCTION

Both Androgenetic alopecia (AGA) and age-related macular degeneration (AMD) shared the microinflammatory milieu and increased oxidative stress as important criteria in their pathogenesis. The monocyte/high density lipoprotein (HDL) ratio (MHR) seems to be an easy-to-calculate prognostic marker of microinflammation.

OBJECTIVES

To assess MHR in patients with AGA and its correlation to AMD in these patients, if any.

METHODS

Forty patients with AGA aged 40 years or more of both sexes and 40 control subjects participated in this case-control study. General, dermatological, and ophthalmologic examination, MHR evaluation and optical coherence tomography (OCT) were performed.

RESULTS

The mean MHR was significantly higher in AGA patients (6.98 ± 2.21) than in controls (3.82 ± 0.68) (P < 0.001). AMD was significantly higher in patients than controls (P < 0.001). Eighty percent of AGA patients were diagnosed with AMD versus 20% of control subjects. The presence of AMD in AGA was significantly related to the degree of severity of AGA in male patients (P = 0.02). The MHR was significantly higher in AGA patients found to have AMD (9.37 ± 1.1 and 7.01 ± 1.42 in the wet and dry type respectively) than those without AMD (P < 0.001).

CONCLUSIONS

AMD may develop more frequently in those with AGA. The MHR seems to be a missing link between both conditions, and could be utilized as a potential biomarker for predicting AMD in AGA patients.

Retinal protection by fungal product theissenolactone B in a sodium iodate-induced AMD model through targeting retinal pigment epithelial matrix metalloproteinase-9 and microglia activity

Age-related macular degeneration (AMD) is the leading cause of low vision and blindness for which there is currently no cure. Increased matrix metalloproteinase-9 (MMP-9) was found in AMD and potently contributes to its pathogenesis. Resident microglia also promote the processes of chronic neuroinflammation, accelerating the progression of AMD. The present study investigates the effects and mechanisms of the natural compound theissenolactone B (LB53), isolated from Theissenia cinerea, on the effects of RPE dysregulation and microglia hyperactivation and its retinal protective ability in a sodium iodate (NaIO₃)-induced retinal degeneration model of AMD. The fungal component LB53 significantly reduces MMP-9 gelatinolysis in TNF-α-stimulated human RPE cells (ARPE-19). Similarly, LB53 abolishes MMP-9 protein and mRNA expression in ARPE-19 cells. Moreover, LB53 efficiently suppresses nitric oxide (NO) production, iNOS expression, and intracellular ROS levels in LPS-stimulated TLR 4-activated microglial BV-2 cells. According to signaling studies, LB53 specifically targets canonical NF-κB signaling in both ARPE-19 and BV-2 microglia. In an RPE-BV-2 interaction assay, LB53 ameliorates LPS-activated BV-2 conditioned medium-induced MMP-9 activation and expression in the RPE. In NaIO₃-induced AMD mouse model, LB53 restores photoreceptor and bipolar cell dysfunction as assessed by electroretinography (ERG). Additionally, LB53 prevents retinal thinning, primarily the photoreceptor, and reduces retinal blood flow from NaIO₃ damage evaluated by optic coherence tomography (OCT) and laser speckle flowgraphy (LSFG), respectively. Our results demonstrate that LB53 exerts neuroprotection in a mouse model of AMD, which can be attributed to its anti-retinal inflammatory effects by impeding RPE-mediated MMP-9 activation and anti-microglia.

Nanotechnology for Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a degenerative eye disease that is the leading cause of irreversible vision loss in people 50 years and older. Today, the most common treatment for AMD involves repeated intravitreal injections of anti-vascular endothelial growth factor (VEGF) drugs. However, the existing expensive therapies not only cannot cure this disease, they also produce a variety of side effects. For example, the number of injections increases the cumulative risk of endophthalmitis and other complications. Today, a single intravitreal injection of gene therapy products can greatly reduce the burden of treatment and improve visual effects. In addition, the latest innovations in nanotherapy provide the best drug delivery alternative for the treatment of AMD. In this review, we discuss the development of nano-drug delivery systems and gene therapy strategies for AMD in recent years. In addition, we discuss some novel targeting strategies and the potential application of these delivery methods in the treatment of AMD. Finally, we also propose that the combination of CRISPR/Cas9 technology with a new non-viral delivery system may be promising as a therapeutic strategy for the treatment of AMD.

Immunological aspects of RPE cell transplantation

Retinal pigment epithelial (RPE) cells have several functions, including support of the neural retina and choroid in the eye and immunosuppression. Cultured human RPE cells directly suppress inflammatory immune cells. For instance, they directly suppress the activation of T cells in vitro. In contrast, transplanted allogeneic human RPE cells are rejected by bystander immune cells such as T cells in vivo. Recently, human embryonic stem cell-derived RPE cells have been used in several clinical trials, and human induced pluripotent stem cell (iPSC)-RPE cells have also been tested in our clinical study in patients with retinal degeneration. Major safety concerns after stem cell-based transplantation surgery include hyper-proliferation, tumorigenicity, or ectopic tissue formation, but these events have currently not been seen in any of these patients. However, if RPE cells are allogeneic, there are concerns about immune rejection issues that have been raised in previous clinical trials. We therefore performed a preclinical study of allogeneic iPSC-RPE cell transplantation in animal rejection models. We then conducted autogenic or allogeneic iPSC-RPE cell transplantation in clinical studies of patients with age-related macular degeneration. In this review, we focus on immunological studies of RPE cells, including iPSC-derived cells. iPSC-RPE cells have unique inflammatory (immunosuppressive and immunogenic) characteristics like primary cultured RPE cells. The purpose of this review is to summarize the current findings obtained from preclinical (basic research) and clinical studies in iPSC-RPE cell transplantation, especially the immunological aspects.

Quercetin Inhibits the Production of IL-1β-Induced Inflammatory Cytokines and Chemokines in ARPE-19 Cells via the MAPK and NF-κB Signaling Pathways

Quercetin, a bioflavonoid derived from vegetables and fruits, exerts anti-inflammatory effects in various diseases. Our previous study revealed that quercetin could suppress the expression of matrix metalloprotease-9 (MMP-9) and intercellular adhesion molecule-1 (ICAM-1) to achieve anti-inflammatory effects in tumor necrosis factor-α (TNF-α)-stimulated human retinal pigment epithelial (ARPE-19) cells. The present study explored whether quercetin can inhibit the interleukin-1β (IL-1β)-induced production of inflammatory cytokines and chemokines in ARPE-19 cells. Prior to stimulation by IL-1β, ARPE-19 cells were pretreated with quercetin at various concentrations (2.5–20 µM). The results showed that quercetin could dose-dependently decrease the mRNA and protein levels of ICAM-1, IL-6, IL-8 and monocyte chemoattractant protein-1 (MCP-1). It also attenuated the adherence of the human monocytic leukemia cell line THP-1 to IL-1β-stimulated ARPE-19 cells. We also demonstrated that quercetin inhibited signaling pathways related to the inflammatory process, including phosphorylation of mitogen-activated protein kinases (MAPKs), inhibitor of nuclear factor κ-B kinase (IKK)α/β, c-Jun, cAMP response element-binding protein (CREB), activating transcription factor 2 (ATF2) and nuclear factor (NF)-κB p65, and blocked the translocation of NF-κB p65 into the nucleus. Furthermore, MAPK inhibitors including an extracellular signal-regulated kinase (ERK) 1/2 inhibitor (U0126), a p38 inhibitor (SB202190) and a c-Jun N-terminal kinase (JNK) inhibitor (SP600125) decreased the expression of soluble ICAM-1 (sICAM-1), but not ICAM-1. U0126 and SB202190 could inhibit the expression of IL-6, IL-8 and MCP-1, but SP600125 could not. An NF-κB inhibitor (Bay 11-7082) also reduced the expression of ICAM-1, sICAM-1, IL-6, IL-8 and MCP-1. Taken together, these results provide evidence that quercetin protects ARPE-19 cells from the IL-1β-stimulated increase in ICAM-1, sICAM-1, IL-6, IL-8 and MCP-1 production by blocking the activation of MAPK and NF-κB signaling pathways to ameliorate the inflammatory response.

Lipopolysaccharide-Induced Autophagy Mediates Retinal Pigment Epithelium Cells Survival. Modulation by the Phospholipase D Pathway

Inflammation and oxidative stress are common factors involved in the pathogenesis of retinal diseases, such as aged-related macular degeneration (AMD) and diabetic retinopathy (DR). Autophagy is a catabolic process essential to cell survival in response to stress. This process is highly active in retinal pigment epithelium (RPE) cells. Our previous findings demonstrated that lipopolysaccharide (LPS) induces an inflammatory response of RPE cells that implies classical phospholipases D (PLD1 and 2) activation, cyclooxygenase-2 (COX-2) expression, prostaglandin E₂ (PGE₂) production and reduced cell viability. In this work, we studied the autophagic process and its modulation by the PLD pathway in D407 and ARPE-19 RPE cells exposed to LPS. LPS (10 μg/ml or 25 μg/ml) exposure for 24 h increased light chain 3B-II (LC3B-II) content (an autophagy marker) and LC3B-positive punctate structures in both RPE cell lines studied. Next, the drug bafilomycin A₁ (BAF, 50 nM) was used to block the autophagic flux. In cells pre-incubated with BAF, LC3B-II and sequestosome 1 (SQSTM1/p62) levels and autophagosome-like structures were increased by LPS, demonstrating that the inflammatory injury increases the autophagic process in RPE cells. To study the role of the PLD pathway, cells were pre-incubated for 1 h with selective PLD1 (VU0359595) or PLD2 (VU0285655-1) inhibitors prior to LPS addition. Under control condition, LC3B-positive punctate structures were increased in cells pre-incubated with PLD2 inhibitor while with PLD1 inhibitor were increased in cells exposed to LPS. MTT reduction assays showed that early autophagy inhibitors, 3-methyladenin (3-MA) or LY294002, enhanced the loss in cell viability induced by LPS exposure for 48 h. On the contrary, the inhibition of PLD1 and PLD2 prevented the loss in cell viability induced by LPS. In conclusion, our results show that even though LPS treatment promotes an inflammatory response in RPE cells, it also triggers the activation of the autophagic process which in turn may serve as a protective mechanism for the cells. In addition, we demonstrate that the PLD pathway modulates the autophagic process in RPE cells. Our findings contribute to the knowledge of the molecular basis of retinal inflammatory and degenerative diseases and open new avenues for potential therapeutic exploration.

Detection of Complement Activators in Immune Attack Eyes After iPS-Derived Retinal Pigment Epithelial Cell Transplantation

Purpose

To determine whether human induced pluripotent stem (iPS) cell-derived retinal pigment epithelial (RPE) cells (iPS-RPE) can express complement factors.

Methods

To confirm expression of complement factors in human iPS-RPE cells, we performed flow cytometry, immunohistochemistry, ELISA, and quantitative RT-PCR for the following: C3, C5, CFB (Factor B), C5b-9 (membrane attack complex [MAC]), CFH (Factor H), CFI (Factor I), CD46, CD55, CD59, clusterin, and vitronectin. We also prepared iPS-RPE cells in the presence of recombinant IFN-γ, recombinant TNF-α, lipopolysaccharide, supernatants of naïve T cells, and T helper 1 (Th1) cells. For the transplantation, after preparation of iPS-RPE cells from cynomolgus monkeys, the iPS-RPE cells (allografts) were transplanted into the subretinal space in monkeys. After surgery, monkeys were euthanized for IHC evaluation of the retinal section and determination of complement factors (C3, C5, CFB, MAC, and C1q), cytokines, and immunoglobulin G (IgG).

Results

Human iPS-RPE cells expressed complement activators and inhibitors. iPS-RPE cells highly expressed complement factors during inflammatory conditions, especially IFN-γ exposure including Th1 cell supernatants. In immune attack eyes after allogeneic iPS-RPE cell transplantation, complement activators such as C3, CFB, C5, and MAC were detected around the host RPE layer, grafted RPE cells, inflammatory retinal lesions, and transplanted subretinal space. In addition, we observed a large number of C1q and IgG double positive and IFN-γ positive inflammatory cells in the retinal sections.

Conclusions

iPS-derived RPE cells greatly expressed complement factors. Thus, RPE cells might be activated and produce complement factors after exposure to infiltrating inflammatory cells in the eye.

CFH Y402H polymorphism in Italian patients with age-related macular degeneration, retinitis pigmentosa, and Stargardt disease

BACKGROUND

The complement system has been implicated in the pathogenesis of age-related macular degeneration (AMD) and the CFH Y402H polymorphism has been suggested as a major risk factor for AMD. Recent evidences supported the role of inflammation in the pathogenesis of some retinal dystrophies. Aim of this study was to evaluate the prevalence of CFHY402H polymorphism in a group of Italian patients affected by atrophic AMD, Stargardt disease (STGD), or retinitis pigmentosa(RP).

MATERIALS AND METHODS

Our case-control association study included 116 patients with atrophic AMD, 77 with RP, 86 with STGD, and 100 healthy controls. All the patients were evaluated by a standard ophthalmologic examination and OCT. ERG was performed on STGD and RP patients. All the subjects underwent a blood drawing for genetic testing and the CFHY402H polymorphism was genotyped with the TaqMan real-time polymerase chain reaction single nucleotide polymorphism assay.

RESULTS

The prevalence of the risk genotype C/C was higher in the AMD group than in controls (p < 0.001). The risk allele C was more frequent in the AMD group than in controls (p < 0.001). The prevalence of the risk genotype was higher in the RP patients than in controls (p < 0.001) and similarly the risk allele C was more frequent in the RP group (p = 0.008). The CFHY402H genotype distribution was not different between patients with STGD and the controls, for the biallelic (p = 0.531) and for the monoallelic (p = 0.318) evaluation.

CONCLUSIONS

In our series of Italian patients, the CFHY402H genotype is associated with atrophic AMD and RP, but not with STGD. This result may support the hypothesis of a complement system dysregulation in the pathogenesis of AMD and RP.

Loss of Extracellular Signal-Regulated Kinase 1/2 in the Retinal Pigment Epithelium Leads to RPE65 Decrease and Retinal Degeneration

Recent work suggested that the activity of extracellular signal-regulated kinase 1/2 (ERK1/2) is increased in the retinal pigment epithelium (RPE) of age-related macular degeneration (ARMD) patients and therefore could be an attractive therapeutic target. Notably, ERK1/2 pathway inhibitors are used in cancer therapy, with severe and noncharacterized ocular side effects. To decipher the role of ERK1/2 in RPE cells, we conditionally disrupted the Erk1 and Erk2 genes in mouse RPE. The loss of ERK1/2 activity resulted in a significant decrease in the level of RPE65 expression, a decrease in ocular retinoid levels concomitant with low visual function, and a rapid disorganization of RPE cells, ultimately leading to retinal degeneration. Our results identify the ERK1/2 pathway as a direct regulator of the visual cycle and a critical component of the viability of RPE and photoreceptor cells. Moreover, our results caution about the need for a very fine adjustment of kinase inhibition in cancer or ARMD treatment in order to avoid ocular side effects.

A randomized clinical trial of salivary substitute as an adjunct to scaling and root planing for management of periodontal inflammation in mouth breathing patients

We investigated the outcome of conventional periodontal treatment in mouth breathing patients with chronic periodontitis, and compared the efficacy of applying salivary substitute to the anterior sextants as an adjunct to conventional treatment in such patients. In this randomized, investigator-blind, clinical study involving parallel groups, 40 mouth breathing patients were divided into two groups: a control group (CG, n = 20) comprising patients who received scaling and root planing (SRP), and a test group (TG, n = 20) who received salivary substitute as an adjunct to SRP for treatment of chronic periodontitis. The patients were followed up at various time intervals, and improvement of the gingival index (GI) was examined as the primary outcome. Student's t-test, repeated-measures ANOVA and Mann-Whitney U test were applied for statistical analysis. Although periodontal parameters were improved in both groups after 8 weeks of follow-up, the test group showed better improvement in terms of GI and percentage bleeding on probing. Within the limits of this study, our results suggest that the use of salivary substitute has a beneficial adjunctive effect for improvement of periodontal parameters in mouth breathing patients with chronic periodontitis.

The Relationship between Neutrophil-to-lymphocyte Ratio and Age-related Macular Degeneration

PURPOSE

To investigate the possible associations of neutrophil-to-lymphocyte ratio (NLR) and high sensitivity C-reactive protein (hs-CRP) level with age-related macular degeneration (ARMD).

METHODS

Patients were divided to three groups of 40 patients with non-neovascular ARMD (group 1), 40 patients with neovascular ARMD (group 2), and 40 healthy control subjects (group 3). The neutrophil and lymphocyte counts were evaluated using an ABX Pentra DF120/USA biochemical analyzer, and hs-CRP levels were measured using a Beckman Coulter Immage 800. The NLR was measured by dividing neutrophil count by lymphocyte count.

RESULTS

The patients in group 2 were older and more often diabetic than the patients in groups 1 and 3 (p < 0.001 and p < 0.001, respectively). The NLR level was 1.65 ± 0.71 in group 1, 1.98 ± 0.84 in group 2, and 1.46 ± 0.44 in group 3. The hs-CRP value was 1.98 ± 0.251 mg/L in group 1, 3.242 ± 0.211 mg/L in group 2, and 1.145 ± 0.193 mg/L in group 3. Both NLR and hs-CRP values were significantly higher in group 2 compared to group 3 (p = 0.002 and p = 0.002, respectively). In multivariate analysis, NLR remained an independent predictor of neovascular ARMD (odds ratio, 3.882; 95% confidence interval, 1.574 to 9.576; p = 0.003) together with age (p < 0.001), diabetes mellitus (p = 0.041), and hs-CRP (p = 0.018).

CONCLUSIONS

Our study suggests that increased NLR value is independently associated with neovascular ARMD.

Elevated neutrophil-to-lymphocyte ratio in pseudoexfoliation syndrome

PurposeTo investigate the relationship between serum neutrophil/lymphocyte ratio and pseudoexfoliation syndrome.Materials and methodsThis study was designed as a retrospective analysis. Patients were divided into three groups: 55 patients with pseudoexfoliation syndrome (group 1), 19 patients with pseudoexfoliation glaucoma (group 2), and 48 control subjects without pseudoexfoliation syndrome or pseudoexfoliation glaucoma (group 3). The levels of neutrophils and lymphocytes were measured by ABX Pentra DF120/USA biochemical analyzer. The neutrophil/lymphocyte ratio was measured by dividing neutrophil count by lymphocyte count.ResultsThe mean ages of patients were 67.9±8.1 in group 1, 70.6±7.4 in group 2, and 67.3±7.6 in group 3 (P=0.172). Baseline clinical characteristics, such as diabetes and hypertension, were similar among groups. The mean neutrophil/lymphocyte ratio values were 2.08±0.61 in group 1, 2.20±0.58 in group 2, and 1.51±0.57 in group 3. The neutrophil/lymphocyte ratio was significantly higher in group 1 and 2 than the group 3 (P<0.001). In receiver operating characteristics analysis, the area under the curve for neutrophil/lymphocyte ratio was 0.776, and a neutrophil/lymphocyte ratio of >1.72 predicted pseudoexfoliation syndrome with a sensitivity of 77% and specificity of 71%.ConclusionThe elevated neutrophil/lymphocyte ratio is significantly associated with pseudoexfoliation syndrome. This novel and low-cost parameter can provide useful information for the relevant risk evaluation in these patients.

Aged complement factor H knockout mice kept in a clean barriered environment have reduced retinal pathology

Age-related macular degeneration (AMD) is the largest cause of visual loss in those over 60 years in the West and is a condition increasing in prevalence. Many diseases result from genetic/environmental interactions and 50% of AMD cases have an association with polymorphisms of the complement system including complement factor H. Here we explore interactions between genetic predisposition and environmental conditions in triggering retinal pathology in two groups of aged complement factor H knock out (Cfh(-/-)) mice. Mice were maintained over 9 months in either a conventional open environment or a barriered pathogen free environment. Open environment Cfh(-/-) mice had significant increases in subretinal macrophage numbers, inflammatory and stress responses and reduced photoreceptor numbers over mice kept in a pathogen free environment. Hence, environmental factors can drive retinal disease in these mice when linked to complement deficits impairing immune function. Both groups of mice had similar levels of retinal amyloid beta accumulation. Consequently there is no direct link between this and inflammation in Cfh(-/-) mice.

Age-related Defects in Ocular and Nasal Mucosal Immune System and the Immunopathology of Dry Eye Disease

Dry eye disease (DED) is a prevalent public health concern that affects up to 30% of adults and is particularly chronic and severe in the elderly. Two interconnected mechanisms cause DED: (1) an age-related dysfunction of lacrimal and meibomian glands, which leads to decreased tear production and/or an increase in tear evaporation; and (2) an age-related uncontrolled inflammation of the surface of the eye triggered by yet-to-be-determined internal immunopathological mechanisms, independent of tear deficiency and evaporation. In this review we summarize current knowledge on animal models that mimic both the severity and chronicity of inflammatory DED and that have been reliably used to provide insights into the immunopathological mechanisms of DED, and we provide an overview of the opportunities and limitations of the rabbit model in investigating the role of both ocular and nasal mucosal immune systems in the immunopathology of inflammatory DED and in testing novel immunotherapies aimed at delaying or reversing the uncontrolled age-related inflammatory DED.

Systemic and Ocular Long Pentraxin 3 in Patients with Age-Related Macular Degeneration

Age-related macular degeneration (AMD) has been associated with both systemic and ocular alterations of the immune system. In particular dysfunction of complement factor H (CFH), a soluble regulator of the alternative pathway of the complement system, has been implicated in AMD pathogenesis. One of the ligands for CFH is long pentraxin 3 (PTX3), which is produced locally in the retinal pigment epithelium (RPE). To test the hypothesis that PTX3 is relevant to retinal immunohomeostasis and may be associated with AMD pathogenesis, we measured plasma PTX3 protein concentration and analyzed the RPE/choroid PTX3 gene expression in patients with AMD. To measure the ability of RPE cells to secrete PTX3 in vitro, polarized ARPE-19 cells were treated with activated T cells or cytokines (interferon (IFN)-gamma and/or tumor necrosis factor (TNF)-alpha) from the basolateral side; then PTX3 protein concentration in supernatants and PTX3 gene expression in tissue lysates were quantified. Plasma levels of PTX3 were generally low and did not significantly differ between patients and controls (P=0.307). No statistically significant difference was observed between dry and exudative AMD nor was there any correlation with hsCRP or CFH genotype. The gene expression of PTX3 increased in RPE/choroid with age (P=0.0098 macular; P=0.003 extramacular), but did not differ between aged controls and AMD patients. In vitro, ARPE-19 cells increased expression of the PTX3 gene as well PTX3 apical secretions after stimulation with TNF-alpha or activated T cells (P<0.01). These findings indicate that PTX3 expressed in the eye cannot be detected systemically and systemic PTX3 may have little or no impact on disease progression, but our findings do not exclude that locally produced PTX3 produced in the posterior segment of the eye may be part of the AMD immunopathogenesis.

Intravitreal sirolimus for the treatment of geographic atrophy: results of a phase I/II clinical trial

PURPOSE

To investigate the safety and effects of intravitreal sirolimus for the potential treatment of geographic atrophy (GA).

METHODS

The study was a single-center, open-label, phase I/II trial enrolling six participants with bilateral GA treated with intravitreal sirolimus in only one randomly assigned eye, with the fellow eye as control. The primary efficacy outcome measure was the change in total GA area from baseline on color fundus photography (CFP); secondary outcomes included changes in GA area on fundus autofluorescence (FAF), visual acuity, central retinal thickness (CRT), and macular sensitivity from baseline.

RESULTS

Although no systemic adverse events were attributed to treatment, two of six participants had ocular adverse events that were possibly associated. The treated eye of one participant developed abnormal paralesional changes on FAF that were associated with accelerated retinal thinning. This accelerated retinal thinning was also seen in the treated eye of a second participant. Because of concern that these events were associated with treatment, treatment was suspended. Comparisons of treated and fellow eyes for change in visual acuity, change in GA area, and change in CRT showed no evidence of treatment benefit and generally favored the untreated fellow eye.

CONCLUSIONS

While paralesional FAF changes and rapid retinal thinning observed are potentially part of the natural course of GA, they may possibly be related to treatment. No general evidence of anatomical or functional benefit was detected in treated eyes. Further data on intravitreal sirolimus for GA treatment will be available from a larger phase II trial. (ClinicalTrials.gov number, NCT01445548.).

Morphological and physiological retinal degeneration induced by intravenous delivery of vitamin A dimers in rabbits

The eye uses vitamin A as a cofactor to sense light and, during this process, some vitamin A molecules dimerize, forming vitamin A dimers. A striking chemical signature of retinas undergoing degeneration in major eye diseases such as age-related macular degeneration (AMD) and Stargardt disease is the accumulation of these dimers in the retinal pigment epithelium (RPE) and Bruch's membrane (BM). However, it is not known whether dimers of vitamin A are secondary symptoms or primary insults that drive degeneration. Here, we present a chromatography-free method to prepare gram quantities of the vitamin A dimer, A2E, and show that intravenous administration of A2E to the rabbit results in retinal degeneration. A2E-damaged photoreceptors and RPE cells triggered inflammation, induced remolding of the choroidal vasculature and triggered a decline in the retina's response to light. Data suggest that vitamin A dimers are not bystanders, but can be primary drivers of retinal degeneration. Thus, preventing dimer formation could be a preemptive strategy to address serious forms of blindness.

Age-related macular degeneration in the aspect of chronic low-grade inflammation (pathophysiological parainflammation)

The products of oxidative stress trigger chronic low-grade inflammation (pathophysiological parainflammation) process in AMD patients. In early AMD, soft drusen contain many mediators of chronic low-grade inflammation such as C-reactive protein, adducts of the carboxyethylpyrrole protein, immunoglobulins, and acute phase molecules, as well as the complement-related proteins C3a, C5a, C5, C5b-9, CFH, CD35, and CD46. The complement system, mainly alternative pathway, mediates chronic autologous pathophysiological parainflammation in dry and exudative AMD, especially in the Y402H gene polymorphism, which causes hypofunction/lack of the protective complement factor H (CFH) and facilitates chronic inflammation mediated by C-reactive protein (CRP). Microglial activation induces photoreceptor cells injury and leads to the development of dry AMD. Many autoantibodies (antibodies against alpha beta crystallin, alpha-actinin, amyloid, C1q, chondroitin, collagen I, collagen III, collagen IV, elastin, fibronectin, heparan sulfate, histone H2A, histone H2B, hyaluronic acid, laminin, proteoglycan, vimentin, vitronectin, and aldolase C and pyruvate kinase M2) and overexpression of Fcc receptors play role in immune-mediated inflammation in AMD patients and in animal model. Macrophages infiltration of retinal/choroidal interface acts as protective factor in early AMD (M2 phenotype macrophages); however it acts as proinflammatory and proangiogenic factor in advanced AMD (M1 and M2 phenotype macrophages).

Proteasome inhibitors activate autophagy involving inhibition of PI3K-Akt-mTOR pathway as an anti-oxidation defense in human RPE cells

The two major intracellular protein degradation systems, the ubiquitin-proteasome system (UPS) and autophagy, work collaboratively in many biological processes including development, apoptosis, aging, and countering oxidative injuries. We report here that, in human retinal pigment epithelial cells (RPE), ARPE-19 cells, proteasome inhibitors, clasto-lactacystinβ-lactone (LA) or epoxomicin (Epo), at non-lethal doses, increased the protein levels of autophagy-specific genes Atg5 and Atg7 and enhanced the conversion of microtubule-associated protein light chain (LC3) from LC3-I to its lipidative form, LC3-II, which was enhanced by co-addition of the saturated concentration of Bafilomycin A1 (Baf). Detection of co-localization for LC3 staining and labeled-lysosome further confirmed autophagic flux induced by LA or Epo. LA or Epo reduced the phosphorylation of the protein kinase B (Akt), a downstream target of phosphatidylinositol-3-kinases (PI3K), and mammalian target of rapamycin (mTOR) in ARPE-19 cells; by contrast, the induced changes of autophagy substrate, p62, showed biphasic pattern. The autophagy inhibitor, Baf, attenuated the reduction in oxidative injury conferred by treatment with low doses of LA and Epo in ARPE-19 cells exposed to menadione (VK3) or 4-hydroxynonenal (4-HNE). Knockdown of Atg7 with siRNA in ARPE-19 cells reduced the protective effects of LA or Epo against VK3. Overall, our results suggest that treatment with low levels of proteasome inhibitors confers resistance to oxidative injury by a pathway involving inhibition of the PI3K-Akt-mTOR pathway and activation of autophagy.

The 15-deoxy-δ12,14-prostaglandin J2 inhibits LPS‑stimulated inflammation via enhancement of the platelet‑activating factor acetylhydrolase activity in human retinal pigment epithelial cells

A well-recognized natural ligand of PPARγ, 15-deoxy-δ(12,14)-prostaglandin J(2) (15d-PGJ(2)) possesses immunomodulatory properties. The aim of this study was to elucidate whether 15d-PGJ(2) was able to attenuate lipopolysaccharide (LPS)-induced inflammatory responses in human retinal pigment epithelial (RPE) cells, which are involved in ocular immune responses. In addition, we examined whether the platelet activating factor (PAF) is associated with the anti-inflammatory activity of 15d-PGJ(2). ARPE19 cells treated with varying concentrations of 15d-PGJ(2) and a PAF antagonist (CV3988) were used in this study. The activity of PAF-acetylhydrolase (PAF-AH) was assayed by treatment with 15d-PGJ(2) and CV3988 in the presence of LPS. 15d-PGJ(2) and CV3988 inhibited the LPS-induced mRNA expression and protein production of interleukin-6 (IL-6), monocyte chemoattractant protein-1 (MCP-1), and intercellular adhesion molecule-1 (ICAM-1) in ARPE19 cells. These effects resulting from 15d-PGJ(2) were not abrogated by the PPARγ antagonist, indicating that the actions were PPARγ-independent. Furthermore, 15d-PGJ(2) and CV3988 enhanced the PAF-AH activity. Additionally, 15d-PGJ(2) inhibited the phosphorylation of the extracellular signal-regulated kinase (ERK) and the activation of nuclear transcription factor-κB (NF-κB). These results demonstrated that 15d-PGJ(2) reduced LPS-stimulated inflammatory responses in ARPE19 cells by enhancing the PAH-AH activity. These results suggest that 15d-PGJ(2) may have potent anti-inflammatory activity against ocular inflammation.

Systemic administration of Abeta mAb reduces retinal deposition of Abeta and activated complement C3 in age-related macular degeneration mouse model

Age-related macular degeneration (AMD) is a leading cause of legal blindness in the Western world. There are effective treatments for the vascular complications of neo-vascular AMD, but no effective therapies are available for the dry/atrophic form of the disease. A previously described transgenic CFH-gene deficient mouse model, (cfh−/−), shows hallmarks of early AMD. The ocular phenotype has been further analysed to demonstrate amyloid beta (Aβ) rich basement membrane deposits associated with activated complement C3. Cfh−/− mice were treated systemically in both prophylactic and therapeutic regimes with an anti-Aβ monoclonal antibody (mAb), 6F6, to determine the effect on the cfh−/− retinal phenotype. Prophylactic treatment with 6F6 demonstrated a dose dependent reduction in the accumulation of both Aβ and activated C3 deposition. A similar reduction in the retinal endpoints could be seen after therapeutic treatment. Serum Aβ levels after systemic administration of 6F6 show accumulation of Aβ in the periphery suggestive of a peripheral sink mechanism. In summary, anti-Aβ mAb treatment can partially prevent or reverse ocular phenotypes of the cfh−/− mouse. The data support this therapeutic approach in humans potentially modulating two key elements in the pathogenesis of AMD – Aβ and activated, complement C3.

Inflammatory cytokines protect retinal pigment epithelial cells from oxidative stress-induced death

Purpose

To investigate the effects of inflammatory factors and oxidative stress on cell survival of the human retinal pigment epithelial (RPE) cell line, ARPE-19.

Methods

Confluent RPE cells were treated with peripheral blood mononuclear cells-conditioned medium (PCM), H₂O₂, NaIO₃, interferon (IFN)-γ, tumor necrosis factor (TNF)-α, or combinations of these. Cell viability was determined by viability assays and by light microscopy. Effector molecules of cell death were investigated by immunofluorescence microscopy and flow cytometry. Microarrays were performed to screen for differential expression of anti-oxidative enzymes, and protein expression was validated by immunoblotting.

Results

Viability of RPE cells was reduced by exposure to inflammatory agents (PCM, IFNγ+/-TNFα) or to oxidative agents (H₂O₂ or NaIO₃). Unexpectedly, cells treated with either H₂O₂ or NaIO₃ were partially protected from cell death by the addition of PCM. This protection was conferred, at least in part, by IFNγ and TNFα. Cell death induced by H₂O₂ or NaIO₃ was preceded by mitochondrial dysfunction and by p62 upregulation, both of which were attenuated by PCM and/or by IFNγ+TNFα. RPE cells co-cultured with activated T cells, or treated with cytokines showed increased expression of anti-oxidative genes, with upregulation of superoxide dismutase 2 protein following PCM treatment.

Conclusion

Oxidative stress-induced cell death was reduced by concomitant inflammatory stress. This is likely due to the cytokine-mediated induction of the anti-oxidative stress response, upregulating protective anti-oxidant pathway(s). These findings suggest caution for the clinical use of anti-inflammatory agents in the management of immune-associated eye diseases such as age-related macular degeneration.

Acute phase proteins are major clients for the chaperone action of α₂-macroglobulin in human plasma

Extracellular protein misfolding is implicated in many age-related diseases including Alzheimer's disease, macular degeneration and arthritis. In this study, putative endogenous clients for the chaperone activity of α₂-macroglobulin (α₂M) were identified after human plasma was subjected to physiologically relevant sheer stress at 37 °C for 10 days. Western blot analysis showed that four major acute phase proteins: ceruloplasmin, fibrinogen, α₁-acid glycoprotein and complement component 3, preferentially co-purified with α₂M after plasma was stressed. Furthermore, the formation of complexes between α₂M and these putative chaperone clients, detected by sandwich ELISA, was shown to be enhanced in response to stress. These results support the hypothesis that α₂M plays an important role in extracellular proteostasis by sequestering misfolded proteins and targeting them for disposal, particularly during acute phase reactions.

IL-33 is induced by amyloid-β stimulation and regulates inflammatory cytokine production in retinal pigment epithelium cells

Age-related macular degeneration (AMD) is the predominant cause of irreversible blindness in the elderly population. Despite intensive basic and clinical research, its pathogenesis remains unclear. However, evidence suggests that immunological and inflammatory factors contribute to the pathogenesis of AMD. A newly identified cytokine, IL-33, appears to be an important pro-inflammatory cytokine promoting tissue inflammation. In this study, IL-33 was increased through amyloid-beta(1-40) (Aβ(1-40)) stimulation and regulated inflammatory cytokines including IL-6, IL-8, IL-1β, and TNF-α secretion using different signaling pathways in retinal pigment epithelium (RPE) cells. Furthermore, ST2L, the important component of the IL-33 receptor, was significantly increased following recombinant human IL-33 stimulation in RPE cells. These findings suggest that IL-33-mediated inflammatory responses in RPE cells are involved in the pathogenesis of AMD. Greater understanding of the inflammatory effect of IL-33 and its role in RPE cells should aid the development of future clinical therapeutics and enable novel pharmacological approaches towards the prevention of AMD.

CFB/C2 gene polymorphisms and risk of age-related macular degeneration: a systematic review and meta-analysis

PURPOSE

To investigate whether the polymorphisms of CFB/C2 gene are associated with age-related macular degeneration (AMD), and to evaluate the magnitude of gene effect.

METHODS

We performed a meta-analysis of the association between four SNPs in CFB/C2 gene (rs9332739, rs547154, rs4151667, and rs641153) and risk of AMD using data from 15 case-control studies involving 8905 subjects. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using fixed- and random-effects models. The Q and I(2) statistics were used to evaluate between-study heterogeneity. Harbord's modified test was used to detect small study effects. Sensitivity analysis, cumulative meta-analysis, and meta-regression were also performed.

RESULTS

For rs9332739, rs547154, rs4151667, and rs641153, the pooled ORs in a dominant genetic model were 0.474 (fixed effects, P < 0.001, 95% CI 0.378-0.596), 0.399 (random effects, 95% CI 0.289-0.551, P < 0.001), 0.496 (fixed effects, 95% CI 0.390-0.632, P < 0.001), and 0.557 (random effects, P = 0.008, 95% CI 0.362-0.856), respectively. These results suggested that variant alleles of all the four SNPs has significant protective effect against AMD. Contour-enhanced funnel plots and Harbord's test showed moderate small study effects for rs9332739 and rs4151667. Heterogeneity were found for rs547154 and rs641153, subgroup analysis suggested that ethnicity was the main source for heterogeneity. Stratification by ethnicity indicated stronger protective effects of rare alleles in Caucasians. Genotype distribution analysis also suggested that frequencies of rare homozygous genotype were higher in Caucasian group.

CONCLUSIONS

Our meta-analysis indicated strong protective effects of the variant alleles of four SNPs in CFB/C2 gene (rs9332739, rs547154, rs4151667, and rs641153) against AMD. The disease risk descended to nearly one half for individuals carrying at least one copy of the rare alleles. The protective effects seemed to be stronger in Caucasians, of which the genotype frequencies were also higher.

Treatment of dry age-related macular degeneration with dobesilate

The authors present anatomical and functional evidences of dry age-macular degeneration improvement, after intravitreal treatment with dobesilate. Main outcomes measures were normalisation of retinal structure and function, assessed by optical coherence tomography, fundus-monitored microperimetry, electrophysiology and visual acuity. The effect might be related to the normalisation of the outer retinal architecture.

Neurodegeneration of the retina in mouse models of Alzheimer's disease: what can we learn from the retina?

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disease commonly found among elderly. In addition to cognitive and behavioral deficits, vision abnormalities are prevalent in AD patients. Recent studies investigating retinal changes in AD double-transgenic mice have shown altered processing of amyloid precursor protein and accumulation of β-amyloid peptides in neurons of retinal ganglion cell layer (RGCL) and inner nuclear layer (INL). Apoptotic cells were also detected in the RGCL. Thus, the pathophysiological changes of retinas in AD patients are possibly resembled by AD transgenic models. The retina is a simple model of the brain in the sense that some pathological changes and therapeutic strategies from the retina may be observed or applicable to the brain. Furthermore, it is also possible to advance our understanding of pathological mechanisms in other retinal degenerative diseases. Therefore, studying AD-related retinal degeneration is a promising way for the investigation on (1) AD pathologies and therapies that would eventually benefit the brain and (2) cellular mechanisms in other retinal degenerations such as glaucoma and age-related macular degeneration. This review will highlight the efforts on retinal degenerative research using AD transgenic mouse models.

Neovascular age-related macular degeneration: opportunities for development of first-in-class biopharmaceuticals

Age-related macular degeneration (AMD) is a condition that may cause blindness. The prevalence of the disease in the Western world is estimated at 1-2% of the population. Over the past decade, treatment of neovascular AMD has been shifting from destruction of newly formed blood vessels towards inhibitors that silence the vascular endothelial growth factor (VEGF) pathway. Such agents are often first-in-class biopharmaceuticals that benefit from the fact that they can be locally administered in an immune-privileged environment with slow clearance. These new VEGF pathway inhibitors have improved therapeutic effects over conventional treatment and have promoted the identification of novel targets for inhibition of AMD angiogenesis. This review describes the rationale behind the shift from conventional to current treatment options and discusses investigational, most notably biopharmaceutical, drugs that are in clinical trials. It also provides possible points for improvement of these treatments, specifically regarding their delivery.

Documentation of intraretinal retinal pigment epithelium migration via high-speed ultrahigh-resolution optical coherence tomography

PURPOSE

To describe the features of intraretinal retinal pigment epithelium (RPE) migration documented on a prototype spectral-domain, high-speed, ultrahigh-resolution optical coherence tomography (OCT) device in a group of patients with early to intermediate dry age-related macular degeneration (AMD) and to correlate intraretinal RPE migration on OCT to RPE pigment clumping on fundus photographs.

DESIGN

Retrospective, noncomparative, noninterventional case series.

PARTICIPANTS

Fifty-five eyes of 44 patients seen at the New England Eye Center between December 2007 and June 2008 with early to intermediate dry AMD.

METHODS

Three-dimensional OCT scan sets from all patients were analyzed for the presence of intraretinal RPE migration, defined as small discreet hyperreflective and highly backscattering lesions within the neurosensory retina. Fundus photographs also were analyzed to determine the presence of RPE pigment clumping, defined as black, often spiculated, areas of pigment clumping within the macula. The en face OCT images were correlated with fundus photographs to demonstrate correspondence of intraretinal RPE migration on OCT and RPE clumping on fundus photography.

MAIN OUTCOME MEASURES

Drusen, dry AMD, intraretinal RPE migration, and RPE pigment clumping.

RESULTS

On OCT scans, 54.5% of eyes (61.4% of patients) demonstrated intraretinal RPE migration. Of the fundus photographs, 56.4% demonstrated RPE pigment clumping. All eyes with intraretinal RPE migration on OCT had corresponding RPE pigment clumping on fundus photographs. The RPE pigment migrated most frequently into the outer nuclear layer (66.7% of eyes) and less frequently into more anterior retinal layers. Intraretinal RPE migration mainly occurred above areas of drusen (73.3% of eyes).

CONCLUSIONS

The appearance of intraretinal RPE migration on OCT is a common occurrence in early to intermediate dry AMD, occurring in 54.5% of eyes, or 61.4% of patients. The area of intraretinal RPE migration on OCT always correlated to areas of pigment clumping on fundus photography. Conversely, all but 1 eye with RPE pigment clumping on fundus photography also had areas of intraretinal RPE migration on OCT. The high incidence of intraretinal RPE migration observed above areas of drusen suggests that drusen may play physical and catalytic roles in facilitating intraretinal RPE migration in dry AMD patients.

Ketorolac inhibits choroidal neovascularization by suppression of retinal VEGF

We assessed the effect of topical ketorolac on laser-induced choroidal neovascularization (CNV), measured retinal PGE(2) and VEGF levels after laser treatment, and determined the effect of ketorolac on PGE(2) and VEGF production. Six laser burns were placed in eyes of rats which then received topical ketorolac 0.4% or artificial tears four times daily until sacrifice. Fluorescein angiography (FA) was performed at 2 and 3 weeks and retinal pigment epithelium-choroid-sclera flat mounts were prepared. The retina and vitreous were isolated at 1, 3, 5, 7, and 14 days after laser treatment and tested for VEGF and PGE(2). Additional animals were lasered and treated with topical ketorolac or artificial tears and tested at 3 and 7 days for retinal and vitreous VEGF and PGE(2.) Ketorolac reduced CNV on FA by 27% at 2 weeks (P<0.001) and 25% at 3 weeks (P<0.001). Baseline retina and vitreous PGE(2) levels were 29.4 μg/g and 16.5 μg/g respectively, and reached 51.2 μg/g and 26.9 μg/g respectively, 24h after laser treatment (P<0.05). Retinal VEGF level was 781pg/g 24h after laser treatment and reached 931pg/g by 7 days (P<0.01). Ketorolac reduced retinal PGE(2) by 35% at 3 days (P<0.05) and 29% at 7 days (P<0.001) and retinal VEGF by 31% at 3 days (P=0.10) and 19% at 7 days (P<0.001). Topical ketorolac inhibited CNV and suppressed retinal PGE(2) and VEGF production.

Animals as models of age-related macular degeneration: an imperfect measure of the truth

Age-related macular degeneration (AMD) is a degenerative condition that begins in Bruch's membrane and progresses to involve the retinal pigment epithelium and ultimately the overlying photoreceptors. The only required etiologic factor is age, and AMD is regarded as the leading cause of blindness in individuals older than 65 years. AMD results from variable contributions of age, environment, and genetic predisposition. Many loci are linked to AMD; in the majority of cases, the disease is associated with polymorphisms within these genes, rather than mutations that ablate gene function. The etiologic complexity of AMD is reflected by the paucity of animal models that entirely replicate the human disease. This review compares the salient anatomy of the primate and rodent retina, particularly in the light of AMD pathology. It next discusses prevailing hypotheses explaining how AMD may develop. These include the role of complement activation and macrophage chemotaxis in AMD, molecular mechanisms of choroidal neovascularization, and the roles of oxidative damage and lipid metabolism. Finally, the article gives an overview of spontaneous and induced nonhuman primate models and describes relevant mouse models in the context of each pathogenetic mechanism.

Effects of vitrectomy on age-related macular degeneration

PURPOSE

To determine whether vitrectomy alters the long-term progression of age-related macular degeneration (AMD).

DESIGN

Retrospective case-control study.

PARTICIPANTS

Forty-four eyes of 22 patients with AMD who underwent vitrectomy in 1 eye were included in the study. The progression of AMD at follow-up in the 22 eyes that underwent vitrectomy was compared with the 22 fellow, nonvitrectomized eyes.

METHODS

The charts and photographs of subjects with Age-Related Eye Disease Study category 3 AMD in both eyes who previously underwent vitrectomy surgery for an epiretinal membrane or macular hole were reviewed. Subjects were excluded if they had had a vitrectomy in both eyes, had <2 years of follow-up, had previous choroidal neovascularization (CNV), retinal detachment, diabetic retinopathy, angioid streaks, high myopia, vascular occlusions, or extensive macular scarring in either eye, or insufficient hospital records or photographs to determine the extent of AMD. Clinical notes throughout the follow-up interval were reviewed. Two vitreoretinal specialists independently graded pre- and postvitrectomy fundus photographs of all eyes in a masked fashion.

MAIN OUTCOME MEASURES

The development or progression of geographic atrophy of the retinal pigment epithelium and the development of CNV.

RESULTS

Twenty-two patients were included. The average follow up interval was 5.5 years (range, 2-15). Choroidal neovascularization developed in 5 control eyes and in 2 vitrectomized eyes, and atrophy developed in 7 control and 4 vitrectomized eyes. The difference between vitrectomized eyes and fellow eyes for the combined end points of RPE geographic atrophy or CNV was significant (P = 0.02).

CONCLUSIONS

In this pilot study, we did not detect that vitrectomy increased the progression of AMD. In fact, it was associated with a reduced progression to geographic atrophy or CNV. Additional studies are needed to confirm or refute this association.

FINANCIAL DISCLOSURE(S)

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

Identification of human plasma proteins as major clients for the extracellular chaperone clusterin

Clusterin (CLU) is an extracellular chaperone that is likely to play an important role in protein folding quality control. This study identified three deposition disease-associated proteins as major plasma clients for clusterin by studying CLU-client complexes formed in response to physiologically relevant stress (shear stress, approximately 36 dynes/cm(2) at 37 degrees C). Analysis of plasma samples by size exclusion chromatography indicated that (i) relative to control plasma, stressed plasma contained proportionally more soluble protein species of high molecular weight, and (ii) high molecular weight species were far more abundant when proteins purified by anti-CLU immunoaffinity chromatography from stressed plasma were compared with those purified from control plasma. SDS-PAGE and Western blot analyses indicated that a variety of proteins co-purified with CLU from both stressed and control plasma; however, several proteins were uniquely present or much more abundant when plasma was stressed. These proteins were identified by mass spectrometry as ceruloplasmin, fibrinogen, and albumin. Immunodot blot analysis of size exclusion chromatography fractionated plasma suggested that CLU-client complexes generated in situ are very large and may reach >or=4 x 10(7) Da. Lastly, sandwich enzyme-linked immunosorbent assay detected complexes containing CLU and ceruloplasmin, fibrinogen, or albumin in stressed but not control plasma. We have previously proposed that CLU-client complexes serve as vehicles to dispose of damaged misfolded extracellular proteins in vivo via receptor-mediated endocytosis. A better understanding of these mechanisms is likely to ultimately lead to the identification of new therapies for extracellular protein deposition disorders.

Microglia in the mouse retina alter the structure and function of retinal pigmented epithelial cells: a potential cellular interaction relevant to AMD

BACKGROUND

Age-related macular degeneration (AMD) is a leading cause of legal blindness in the elderly in the industrialized word. While the immune system in the retina is likely to be important in AMD pathogenesis, the cell biology underlying the disease is incompletely understood. Clinical and basic science studies have implicated alterations in the retinal pigment epithelium (RPE) layer as a locus of early change. Also, retinal microglia, the resident immune cells of the retina, have been observed to translocate from their normal position in the inner retina to accumulate in the subretinal space close to the RPE layer in AMD eyes and in animal models of AMD.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we examined the effects of retinal microglia on RPE cells using 1) an in vitro model where activated retinal microglia are co-cultured with primary RPE cells, and 2) an in vivo mouse model where retinal microglia are transplanted into the subretinal space. We found that retinal microglia induced in RPE cells 1) changes in RPE structure and distribution, 2) increased expression and secretion of pro-inflammatory, chemotactic, and pro-angiogenic molecules, and 3) increased extent of in vivo choroidal neovascularization in the subretinal space.

CONCLUSIONS/SIGNIFICANCE

These findings share similarities with important pathological features found in AMD and suggest the relevance of microglia-RPE interactions in AMD pathogenesis. We speculate that the migration of retinal microglia into the subretinal space in early stages of the disease induces significant changes in RPE cells that perpetuate further microglial accumulation, increase inflammation in the outer retina, and fosters an environment conducive for the formation of neovascular changes responsible for much of vision loss in advanced AMD.

Inflammation and the pathogenesis of age-related macular degeneration

BACKGROUND

Age-related macular degeneration (AMD) is the leading cause of blindness in the Western world. Many changes occur in various areas of the eye as it ages. These include choroidal thinning, thickening of Bruch's membrane and drusen formation. Each of these is associated with the onset of AMD.

METHODS

Recent findings on how those changes contribute to the pathogenesis of AMD with a focus on inflammation are examined.

RESULTS

There is evidence suggesting that all changes identified so far as being involved in the pathogenesis of AMD are not able to cause AMD alone. Instead, susceptibility genes, and in particular a coding variant of a gene on chromosome 1 result in dysfunction of the immune system. This leads to an inappropriate inflammatory response, which then sets the stage for AMD onset.

CONCLUSIONS

It is now well-known that AMD is a multi-factorial disease, with environmental causes and genetics all playing a role.

Para-inflammation in the aging retina

Para-inflammation is a tissue adaptive response to noxious stress or malfunction and has characteristics that are intermediate between basal and inflammatory states (Medzhitov, 2008). The physiological purpose of para-inflammation is to restore tissue functionality and homeostasis. Para-inflammation may become chronic or turn into inflammation if tissue stress or malfunction persists for a sustained period. Chronic para-inflammation contributes to the initiation and progression of many human diseases including obesity, type 2 diabetes, atherosclerosis, and age-related neurodegenerative diseases. Evidence from our studies and the studies of some others suggests that para-inflammation also exists in the aging retina in physiological conditions and might contribute to age-related retinal pathologies. The purpose of this review is to introduce the notion of "para-inflammation" as a state between frank, overt destructive inflammation and the non-inflammatory removal of dead or dying cells by apoptosis, to the retinal community. In diabetes and atherosclerosis, leukocytes particularly monocytes and vascular endothelial cells are constantly under noxious stress due to glycaemic and/or lipidaemic dysregulation. These blood-borne stresses trigger para-inflammatory responses in leukocytes and endothelial cells by up-regulating the expression of adhesion molecules or releasing cytokines/chemokines, which in turn cause abnormal leukocyte-endothelial interactions and ultimately vascular damage. In the aging retina, on the other hand, oxidized lipoproteins and free radicals are considered to be major causes of tissue stress and serve as local triggers for retinal para-inflammation. Microarray analysis has revealed the up-regulation of a large number of inflammatory genes, including genes involved in complement activation and inflammatory cytokine/chemokine production, in the aging retina. Para-inflammatory responses in the neuroretina of aged mice are characterized by microglial activation and subretinal migration, and breakdown of blood-retinal barrier. At the retinal/choroidal interface para-inflammation is manifested by complement activation in Bruch's membrane and RPE cells, and microglia accumulation in subretinal space. With age, para-inflammatory changes have also been observed in the choroidal tissue, evidenced by 1) increased thickness of choroid; 2) increased number of CD45(+)CRIg(+) macrophages; 3) morphological abnormalities in choroidal melanocytes; and 4) fibrosis in choroidal tissue. An increased knowledge of contribution of retinal para-inflammation to various pathological conditions is essential for the better understanding of the pathogenesis of various age-related retinal diseases including diabetic retinopathy, glaucoma and age-related macular degeneration.

Biologically active fibronectin fragments stimulate release of MCP-1 and catabolic cytokines from murine retinal pigment epithelium

PURPOSE

High-temperature requirement serine protease (HTRA1) was identified as a candidate age-related macular degeneration gene in multiple genetic studies in humans. To date, no functional studies have shown a mechanism for HTRA1 to instigate ocular tissue abnormalities. In the present study, the authors focused on a substrate of HTRA1, fibronectin, because fibronectin fragments (Fnfs) stimulate biochemical events in other age-related degenerative diseases that are analogous to changes associated with age-related macular degeneration (AMD). The purpose of the study was to determine whether Fnfs stimulate the release of proinflammatory and catabolic cytokines from murine retinal pigment epithelium (RPE).

METHODS

Fibronectin was purified from murine serum by gelatin cross-linked agarose chromatography and subsequently was enzymatically digested with alpha-chymotrypsin. The bioactivity of Fnfs was verified by measuring levels of IL-6 and TNF-alpha in Fnf-exposed murine splenocytes. To analyze the effect of Fnfs on RPE, cytokine and chemokine levels in RPE culture supernatants were assayed by ELISA.

RESULTS

IL-6 and TNF-alpha proinflammatory cytokines were released from primary murine splenocytes in proportion to the dose and length of Fnf treatment, indicating that alpha-chymotryptic digests of fibronectin are biologically active. Fnf treatment of murine RPE cells stimulated the release of microgram and nanogram levels of IL-6, MMP-3, MMP-9, and MCP-1, whereas only picogram levels were detected in untreated cells.

CONCLUSIONS

Fnfs stimulate the release of proinflammatory cytokines, matrix metalloproteinases, and monocyte chemoattractant protein from murine RPE cells. This observation indicated that Fnfs could contribute to ocular abnormalities by promoting inflammation, catabolism, and monocyte chemoattraction.

Progress and perspectives on the role of RPE cell inflammatory responses in the development of age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in developed countries. The etiology of AMD remains poorly understood and no treatment is currently available for the atrophic form of AMD. Atrophic AMD has been proposed to involve abnormalities of the retinal pigment epithelium (RPE), which lies beneath the photoreceptor cells and normally provides critical metabolic support to these light-sensing cells. Cumulative oxidative stress and local inflammation are thought to represent pathological processes involved in the etiology of atrophic AMD. Studies of tissue culture and animal models reveal that oxidative stress-induced injury to the RPE results in a chronic inflammatory response, drusen formation, and RPE atrophy. RPE degeneration in turn causes a progressive degeneration of photoreceptors, leading to the irreversible loss of vision. This review describes some of the potential major molecular and cellular events contributing to RPE death and inflammatory responses. In addition, potential target areas for therapeutic intervention will be discussed and new experimental therapeutic strategies for atrophic AMD will be presented.

Vitreomacular traction and exudative age-related macular degeneration

Vitreomacular traction resulting from lacking, incomplete or anomalous posterior vitreous detachment is suspected to play a crucial role in the pathogenesis of different forms of age-related macular degeneration (AMD) along with the known mechanisms. It is probable that the fundamental pathomechanisms of AMD formation have already begun by the time tractional forces lead to a change for the worse. Vitreomacular traction alone is perhaps not able to induce AMD. It would seem sensible to consider vitreous changes when diagnosing and treating AMD patients because of the high coincidence of vitreomacular traction and choroidal neovascularization (CNV) and the often successful treatment of other diseases of the vitreoretinal interface by vitrectomy. The concept of the pathogenesis of AMD should therefore be extended to include the influence of the vitreous, especially where therapeutic concepts such as pharmacological vitreolysis and vitreous separation have been established as causative treatment of late forms of AMD.

Downregulation of p22phox in retinal pigment epithelial cells inhibits choroidal neovascularization in mice

Choroidal neovascularization (CNV) occurs in a variety of chorioretinal diseases including age-related macular degeneration (AMD), and is the major cause of severe visual loss in patients with AMD. Oxidative stress has been thought to play an important role in the development of CNV. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is one of the major intracellular sources of reactive oxygen species (ROS) in the vascular system. In this study, we examined the expression of p22phox, an integral subunit in the NADPH oxidase complex, in the mouse eye. We determined that p22phox is expressed in the retinal pigment epithelial (RPE) cells and inner retinal neurons. A small-interfering RNA (siRNA) designed against p22phox efficiently reduced the expression of the protein in the eye when delivered by means of recombinant adeno-associated virus (AAV) vector. Vector treatment inhibited CNV in the mouse when delivered into the subretinal space where RPE cells were transduced. These results suggest that NADPH oxidase-mediated ROS production in RPE cells may play an important role in the pathogenesis of neovascular AMD, and that this pathway may represent a new target for therapeutic intervention in AMD.