Infiltration of proinflammatory m1 macrophages into the outer retina precedes damage in a mouse model of age-related macular degeneration

Splenic monocytes drive pathogenic subretinal inflammation in age-related macular degeneration

Age-related macular degeneration (AMD) is invariably associated with the chronic accumulation of activated mononuclear phagocytes in the subretinal space. The mononuclear phagocytes are composed of microglial cells but also of monocyte-derived cells, which promote photoreceptor degeneration and choroidal neovascularization. Infiltrating blood monocytes can originate directly from bone marrow, but also from a splenic reservoir, where bone marrow monocytes develop into angiotensin II receptor (ATR1)+ splenic monocytes. The involvement of splenic monocytes in neurodegenerative diseases such as AMD is not well understood. Using acute inflammatory and well-phenotyped AMD models, we demonstrate that angiotensin II mobilizes ATR1+ splenic monocytes, which we show are defined by a transcriptional signature using single-cell RNA sequencing and differ functionally from bone marrow monocytes. Splenic monocytes participate in the chorio-retinal infiltration and their inhibition by ATR1 antagonist and splenectomy reduces the subretinal mononuclear phagocyte accumulation and pathological choroidal neovascularization formation. In aged AMD-risk ApoE2-expressing mice, a chronic AMD model, ATR1 antagonist and splenectomy also inhibit the chronic retinal inflammation and associated cone degeneration that characterizes these mice. Our observation of elevated levels of plasma angiotensin II in AMD patients, suggests that similar events take place in clinical disease and argue for the therapeutic potential of ATR1 antagonists to inhibit splenic monocytes for the treatment of blinding AMD.

PolySialic acid-nanoparticles inhibit macrophage mediated inflammation through Siglec agonism: a potential treatment for age related macular degeneration

Age-related macular degeneration (AMD) is a chronic, progressive retinal disease characterized by an inflammatory response mediated by activated macrophages and microglia infiltrating the inner layer of the retina. In this study, we demonstrate that inhibition of macrophages through Siglec binding in the AMD eye can generate therapeutically useful effects. We show that Siglecs-7, -9 and -11 are upregulated in AMD associated M0 and M1 macrophages, and that these can be selectively targeted using polysialic acid (PolySia)-nanoparticles (NPs) to control dampen AMD-associated inflammation. In vitro studies showed that PolySia-NPs bind to macrophages through human Siglecs-7, -9, -11 as well as murine ortholog Siglec-E. Following treatment with PolySia-NPs, we observed that the PolySia-NPs bound and agonized the macrophage Siglecs resulting in a significant decrease in the secretion of IL-6, IL-1β, TNF-α and VEGF, and an increased secretion of IL-10. In vivo intravitreal (IVT) injection of PolySia-NPs was found to be well-tolerated and safe making it effective in preventing thinning of the retinal outer nuclear layer (ONL), inhibiting macrophage infiltration, and restoring electrophysiological retinal function in a model of bright light-induced retinal degeneration. In a clinically validated, laser-induced choroidal neovascularization (CNV) model of exudative AMD, PolySia-NPs reduced the size of neovascular lesions with associated reduction in macrophages. The PolySia-NPs described herein are therefore a promising therapeutic strategy for repolarizing pro-inflammatory macrophages to a more anti-inflammatory, non-angiogenic phenotype, which play a key role in the pathophysiology of non-exudative AMD.

CCR1 mediates Müller cell activation and photoreceptor cell death in macular and retinal degeneration

Mononuclear cells are involved in the pathogenesis of retinal diseases, including age-related macular degeneration (AMD). Here, we examined the mechanisms that underlie macrophage-driven retinal cell death. Monocytes were extracted from patients with AMD and differentiated into macrophages (hMdɸs), which were characterized based on proteomics, gene expression, and ex vivo and in vivo properties. Using bioinformatics, we identified the signaling pathway involved in macrophage-driven retinal cell death, and we assessed the therapeutic potential of targeting this pathway. We found that M2a hMdɸs were associated with retinal cell death in retinal explants and following adoptive transfer in a photic injury model. Moreover, M2a hMdɸs express several CCRI (C-C chemokine receptor type 1) ligands. Importantly, CCR1 was upregulated in Müller cells in models of retinal injury and aging, and CCR1 expression was correlated with retinal damage. Lastly, inhibiting CCR1 reduced photic-induced retinal damage, photoreceptor cell apoptosis, and retinal inflammation. These data suggest that hMdɸs, CCR1, and Müller cells work together to drive retinal and macular degeneration, suggesting that CCR1 may serve as a target for treating these sight-threatening conditions.

Excessive Thyroid Hormone Signaling Induces Photoreceptor Degeneration in Mice

Rod and cone photoreceptors degenerate in inherited and age-related retinal degenerative diseases, ultimately leading to loss of vision. Thyroid hormone (TH) signaling regulates cell proliferation, differentiation, and metabolism. Recent studies have shown a link between TH signaling and retinal degeneration. This work investigates the effects of excessive TH signaling on photoreceptor function and survival in mice. C57BL/6, Thra1 -/-, Thrb2 -/-, Thrb -/-, and the cone dominant Nrl -/- mice received triiodothyronine (T3) treatment (5-20 μg/ml in drinking water) for 30 d, followed by evaluations of retinal function, photoreceptor survival/death, and retinal stress/damage. Treatment with T3 reduced light responses of rods and cones by 50-60%, compared with untreated controls. Outer nuclear layer thickness and cone density were reduced by ∼18% and 75%, respectively, after T3 treatment. Retinal sections prepared from T3-treated mice showed significantly increased numbers of TUNEL-positive, p-γH2AX-positive, and 8-OHdG-positive cells, and activation of Müller glial cells. Gene expression analysis revealed upregulation of the genes involved in oxidative stress, necroptosis, and inflammation after T3 treatment. Deletion of Thra1 prevented T3-induced degeneration of rods but not cones, whereas deletion of Thrb2 preserved both rods and cones. Treatment with an antioxidant partially preserved photoreceptors and reduced retinal stress responses. This study demonstrates that excessive TH signaling induces oxidative stress/damage and necroptosis, induces photoreceptor degeneration, and impairs retinal function. The findings provide insights into the role of TH signaling in retinal degeneration and support the view of targeting TH signaling for photoreceptor protection.

Myeloid masquerade: Microglial transcriptional signatures in retinal development and disease

Microglia are dynamic guardians of neural tissue and the resident immune cells of the central nervous system (CNS). The disease-associated microglial signature (DAM), also known as the microglial neurodegenerative phenotype (MGnD), has gained significant attention in recent years as a fundamental microglial response common to various neurodegenerative disease pathologies. Interestingly, this signature shares many features in common with developmental microglia, suggesting the existence of recycled gene programs which play a role both in early neural circuit formation as well as in response to aging and disease. In addition, recent advances in single cell RNA sequencing have revealed significant heterogeneity within the original DAM signature, with contributions from both yolk sac-derived microglia as well as bone marrow-derived macrophages. In this review, we examine the role of the DAM signature in retinal development and disease, highlighting crosstalk between resident microglia and infiltrating monocytes which may critically contribute to the underlying mechanisms of age-related neurodegeneration.

Influence of Light-EmittingDiode-Derived Blue Light Overexposure on Rat Ocular Surface

We aim to investigate the effect of overexposure to blue light on the rat ocular surface and explore the potential mechanisms. 450 nm light-emitting diode (LED) derived light at 1000 lux was used to irradiate SD rats, 12 hours a day, for consecutive 28 days. Rats in the control group were exposed to 400 lux white light at the same time (in an indoor environment). Tear film breakup time (TBUT), tear volume, and corneal fluorescein staining scores were used to measure the changes to the ocular surface. Expressions of nuclear factor-κB (NF-κB), inhibitor-κB (I-κB), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) were measured by real-time PCR, and the activation of the NF-κB pathway was detected by Western blotting, respectively. Cornea ultrastructure was examined by TEM and optical microscope on day 28. Pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-κB signaling pathway, was used to measure the inhibition of blue light injury. The above indexes were detected again when compared with the solvent-treated group. On day 28, compared with day 0, the TBUT of the blue light group was significantly shorter, and the score was significantly higher. The amount of tear secretion changed slightly with time. HE and PAS staining revealed significantly decreased corneal epithelial cell layers and increased goblet cells after 28-day irradiation of blue light. Disarranged stromal cells, vacuoles in the basal nuclei, and decreased desmosomes were also found in the blue light group. Significantly increased levels of NF-κB, IL-6, TNF-α, and the ratio of phosphorylated NF-κB p65 (pNF-κB p65) to total NF-κB p65 implied blue light-induced damage and pathway activation. In addition, PDTC significantly reduced the phosphorylation of NF-κB activated in blue light-treated corneas and alleviated the ocular surface changes caused by blue light. Finally, our results demonstrated that long-term blue light exposure in rats could cause ocular surface changes and manifest as dry eye. Inflammation and activation of the NF-κB pathway may play a role in the pathogenesis.

Characterization and identification of measurable endpoints in a mouse model featuring age-related retinal pathologies: a platform to test therapies

Apolipoprotein B100 (apoB100) is the structural protein of cholesterol carriers including low-density lipoproteins. It is a constituent of sub-retinal pigment epithelial (sub-RPE) deposits and pro-atherogenic plaques, hallmarks of early dry age-related macular degeneration (AMD), an ocular neurodegenerative blinding disease, and cardiovascular disease, respectively. Herein, we characterized the retinal pathology of transgenic mice expressing mouse apoB100 in order to catalog their functional and morphological ocular phenotypes as a function of age and establish measurable endpoints for their use as a mouse model to test potential therapies. ApoB100 mice were found to exhibit an age-related decline in retinal function, as measured by electroretinogram (ERG) recordings of their scotopic a-wave, scotopic b-wave; and c-wave amplitudes. ApoB100 mice also displayed a buildup of the cholesterol carrier, apolipoprotein E (apoE) within and below the supporting extracellular matrix, Bruch's membrane (BrM), along with BrM thickening, and accumulation of thin diffuse electron-dense sub-RPE deposits, the severity of which increased with age. Moreover, the combination of apoB100 and advanced age were found to be associated with RPE morphological changes and the presence of sub-retinal immune cells as visualized in RPE-choroid flatmounts. Finally, aged apoB100 mice showed higher levels of circulating and ocular pro-inflammatory cytokines, supporting a link between age and increased local and systemic inflammation. Collectively, the data support the use of aged apoB100 mice as a platform to evaluate potential therapies for retinal degeneration, specifically drugs intended to target removal of lipids from Bruch's membrane and/or alleviate ocular inflammation.

The OSE complotype and its clinical potential

Cellular death, aging, and tissue damage trigger inflammation that leads to enzymatic and non-enzymatic lipid peroxidation of polyunsaturated fatty acids present on cellular membranes and lipoproteins. This results in the generation of highly reactive degradation products, such as malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE), that covalently modify free amino groups of proteins and lipids in their vicinity. These newly generated neoepitopes represent a unique set of damage-associated molecular patterns (DAMPs) associated with oxidative stress termed oxidation-specific epitopes (OSEs). OSEs are enriched on oxidized lipoproteins, microvesicles, and dying cells, and can trigger sterile inflammation. Therefore, prompt recognition and removal of OSEs is required to maintain the homeostatic balance. This is partially achieved by various humoral components of the innate immune system, such as natural IgM antibodies, pentraxins and complement components that not only bind OSEs but in some cases modulate their pro-inflammatory potential. Natural IgM antibodies are potent complement activators, and 30% of them recognize OSEs such as oxidized phosphocholine (OxPC-), 4-HNE-, and MDA-epitopes. Furthermore, OxPC-epitopes can bind the complement-activating pentraxin C-reactive protein, while MDA-epitopes are bound by C1q, C3a, complement factor H (CFH), and complement factor H-related proteins 1, 3, 5 (FHR-1, FHR-3, FHR-5). In addition, CFH and FHR-3 are recruited to 2-(ω-carboxyethyl)pyrrole (CEP), and full-length CFH also possesses the ability to attenuate 4-HNE-induced oxidative stress. Consequently, alterations in the innate humoral defense against OSEs predispose to the development of diseases associated with oxidative stress, as shown for the prototypical OSE, MDA-epitopes. In this mini-review, we focus on the mechanisms of the accumulation of OSEs, the pathophysiological consequences, and the interactions between different OSEs and complement components. Additionally, we will discuss the clinical potential of genetic variants in OSE-recognizing complement proteins – the OSE complotype - in the risk estimation of diseases associated with oxidative stress.

Investigational drugs in clinical trials for macular degeneration

INTRODUCTION

Intravitreal anti-vascular endothelial growth factor (VEGF) injections for exudative age-related macular degeneration (eAMD) are effective and safe but require frequent injections and have nonresponding patients. Geographic atrophy/dry AMD (gaAMD) remains an unmet medical need . New therapies are needed to address this leading cause of blindness in the increasing aged population.

AREAS COVERED

This paper reviews the pathogenesis of macular degeneration, current and failed therapeutics, therapies undergoing clinical trials and a rationale for why certain AMD therapies may succeed or fail .

EXPERT OPINION

VEGF- inhibitors reduce both vascular leakage and neovascularization. Experimental therapies that only address neovascularization or leakage will unlikely supplant anti-VEGF therapies. The most promising future therapies for eAMD, are those that target, more potently inhibit and have a more sustained effect on the VEGF pathway such as KSI-301, RGX-314, CLS-AX, EYEP-1901, OTX-TKI.

GaAMD is a phenotype of phagocytic retinal cell loss. Inhibiting phagocytic activity of retinal microglial/macrophages at the border of GA and reducing complement derived activators of microglial/macrophage is the most promising strategy. Complement inhibitors (Pegcetacoplan and Avacincaptad pegol) will likely obtain FDA approval but will serve to pave the way for combined complement and direct phagocytic inhibitors such as AVD-104.

Ovarian recovery via autologous platelet-rich plasma: New benchmarks for condensed cytokine applications to reverse reproductive aging

Health and life expectancy gains have pushed the overall number of menopausal patients to record levels. Because maternal age at first pregnancy also continues to rise, it is unsurprising that reduced birth rates are consistently reported across many populations. Both trends severely strain national demographics and present a socioeconomic challenge for which no satisfactory solution currently exists. Symptomatic menopause and infertility/miscarriage are met with standard therapies like hormone replacement therapy (HRT) and in vitro fertilization, respectively. Although these accepted interventions do supply some cover, both are expensive, low yield, and not without controversy. Meanwhile, ovarian steroid output and competent oocyte availability approach unrecoverable loss beyond age ~35 years, irrespective of treatment. Received wisdom holds that postnatal oogenesis in humans is impossible, a tenet which until recently encountered little serious confrontation. Reassessing this paradigm is overdue given proof‐of‐concept work on native sex steroid rejuvenation, de novo euploid oogenesis, ovulation, blastocyst development, fetal growth, and healthy term livebirths—all apparently possible with intraovarian insertion of platelet‐rich plasma (PRP). Discrete functional analysis of the full platelet‐derived cytokine array carried with PRP unfortunately for now, is incomplete. Here, selected platelet releasate constituents and measured effects are framed to address advances in wellness and women’s health. Emphasis is on cytokines best positioned to enable recovery of senescent ovarian function sufficient to suspend synthetic HRT dependency and/or permit egg retrieval and pregnancy. Whereas the chronicle of progress in other clinical fields does invite generalization of fresh platelet applications to reproductive endocrinology, basic mechanistic questions remain open.

Bim Expression Promotes the Clearance of Mononuclear Phagocytes during Choroidal Neovascularization, Mitigating Scar Formation in Mice

Inflammation is increasingly recognized as an important modulator in the pathogenesis of neovascular age-related macular degeneration (nAMD). Although significant progress has been made in delineating the pathways that contribute to the recruitment of inflammatory cells and their contribution to nAMD, we know little about what drives the resolution of these inflammatory responses. Gaining a better understanding of how immune cells are cleared in the choroid will give a novel insight into how sustained inflammation could influence the pathogenesis of nAMD. The pro-apoptotic Bcl-2 family member Bim is a master regulator of immune cell homeostasis. In its absence, immune cell lifespan and numbers increase. Most therapeutic regimes that squelch inflammation do so by enhancing immune cell apoptosis through enhanced Bim expression and activity. To test the hypothesis that Bim expression tempers inflammation during the pathogenesis of nAMD, we used the mouse laser-induced choroidal neovascularization (CNV) model in which inflammation acts as a facilitator of CNV. Here, we showed minimal to no change in the recruitment of F4/80-, CD80-, CD11b-, and Iba1-positive myeloid-derived mononuclear phagocytes to the site of laser photocoagulation in the absence of Bim expression. However, the resolution of these cells from the choroid of Bim-deficient (Bim -/-) mice was significantly diminished following laser photocoagulation. With time, we noted increased scar formation, demonstrated by collagen I staining, in Bim -/- mice with no change in the resolution of neovascularization compared to wild-type littermates. We also noted that mice lacking Bim expression in mononuclear phagocytes (Bim^Flox/Flox; Lyz2-Cre (Bim^MP) mice) had delayed resolution of F4/80-, CD80-, CD11b-, and Iba1-positive cells, while those lacking Bim expression in endothelial cells (Bim^Flox/Flox; Cad5-Cre (Bim^EC) mice) had delayed resolution of only CD11b- and Iba1-positive cells. Both Bim^MP and Bim^EC mice demonstrated increased scar formation, albeit to differing degrees. Thus, our studies show that resolving inflammation plays an important role in moderating scar formation in nAMD, and it is impacted by Bim expression in both the endothelium and mononuclear phagocyte lineages.

Retinopathy of prematurity shows alterations in Vegfa164 isoform expression

BACKGROUND

Pathologic ocular neovascularization in retinopathy of prematurity (ROP) and other proliferative retinopathies are characterized by dysregulation of vascular endothelial growth factor-A (VEGF-A). A study of Vegfa isoform expression during oxygen-induced ischemic retinopathy (OIR) may enhance our understanding of Vegf dysregulation.

METHODS

Following induction of OIR, immunohistochemistry and polymerase chain reaction (PCR) was performed on room air (RA) and OIR mice.

RESULTS

Total Vegfa messenger RNA (mRNA) expression was stable in RA mice, but increased in OIR mice with a peak at postnatal day 17 (P17), before returning to RA levels. Vegfa_164a expression was similar in both OIR and RA mice at P10 (Phase 1 OIR), but 2.4-fold higher in OIR mice compared to RA mice at P16 (Phase 2 OIR). At P10, Vegfa_164b mRNA was similar in OIR vs RA mice, but was expressed 2.5-fold higher in OIR mice compared to RA mice at P16. At P10 and P16, Vegfr2/Vegfr1 expression was increased in OIR mice compared to RA mice. Increased activation of microglia was seen in OIR mice.

CONCLUSIONS

Vegfa_164a, Vegfa_164b, and Vegfr1 were overexpressed in OIR mice, leading to abnormal signaling and angiogenesis. Further studies of mechanisms of Vegf dysregulation may lead to novel therapies for ROP and other proliferative retinopathies.

IMPACT

Vegfa₁₆₄ has two major isoforms, a proangiogenic, Vegfa_164a, and an antiangiogenic, Vegfa_164b, with opposing receptors, inhibitory Vegfr1, and stimulatory Vegfr2, but their role in OIR is unclear. In Phase 1 OIR, both isoforms and receptors are expressed similarly. In Phase 2 OIR, both isoforms are overexpressed, with an increased ratio of inhibitory Vegfr1. Modulation of angiogenesis by Vegf regulation enables pruning of excess angiogenesis during physiology, but results in ineffective angiogenesis during OIR. Knowledge of VEGF dysregulation may have novel therapeutic implications in the management of ROP and retinal proliferative diseases.

Inflammation-dependent oxidative stress metabolites as a hallmark of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease, with poor prognosis and no cure. Substantial evidence implicates inflammation and associated oxidative stress as a potential mechanism for ALS, especially in patients carrying the SOD1 mutation and, therefore, lacking anti-oxidant defense. The brain is particularly vulnerable to oxidation due to the abundance of polyunsaturated fatty acids, such as docosahexaenoic acid (DHA), which can give rise to several oxidized metabolites. Accumulation of a DHA peroxidation product, CarboxyEthylPyrrole (CEP) is dependent on activated inflammatory cells and myeloperoxidase (MPO), and thus marks areas of inflammation-associated oxidative stress. At the same time, generation of an alternative inactive DHA peroxidation product, ethylpyrrole, does not require cell activation and MPO activity. While absent in normal brain tissues, CEP is accumulated in the central nervous system (CNS) of ALS patients, reaching particularly high levels in individuals carrying a SOD1 mutation. ALS brains are characterized by high levels of MPO and lowered anti-oxidant activity (due to the SOD1 mutation), thereby aiding CEP generation and accumulation. Due to DHA oxidation within the membranes, CEP marks cells with the highest oxidative damage. In all ALS cases CEP is present in nearly all astrocytes and microglia, however, only in individuals carrying a SOD1 mutation CEP marks >90% of neurons, thereby emphasizing an importance of CEP accumulation as a potential hallmark of oxidative damage in neurodegenerative diseases.

Targeting Lipid Metabolism for the Treatment of Age-Related Macular Degeneration: Insights from Preclinical Mouse Models

Age-related macular degeneration (AMD) is a major leading cause of irreversible visual impairment in the world with limited therapeutic interventions. Histological, biochemical, genetic, and epidemiological studies strongly implicate dysregulated lipid metabolism in the retinal pigmented epithelium (RPE) in AMD pathobiology. However, effective therapies targeting lipid metabolism still need to be identified and developed for this blinding disease. To test lipid metabolism-targeting therapies, preclinical AMD mouse models are needed to establish therapeutic efficacy and the role of lipid metabolism in the development of AMD-like pathology. In this review, we provide a comprehensive overview of current AMD mouse models available to researchers that could be used to provide preclinical evidence supporting therapies targeting lipid metabolism for AMD. Based on previous studies of AMD mouse models, we discuss strategies to modulate lipid metabolism as well as examples of studies evaluating lipid-targeting therapeutics to restore lipid processing in the RPE. The use of AMD mouse models may lead to worthy lipid-targeting candidate therapies for clinical trials to prevent the blindness caused by AMD.

VEGFR1 signaling in retinal angiogenesis and microinflammation

Five vascular endothelial growth factor receptor (VEGFR) ligands (VEGF-A, -B, -C, -D, and placental growth factor [PlGF]) constitute the VEGF family. VEGF-A binds VEGF receptors 1 and 2 (VEGFR1/2), whereas VEGF-B and PlGF only bind VEGFR1. Although much research has been conducted on VEGFR2 to elucidate its key role in retinal diseases, recent efforts have shown the importance and involvement of VEGFR1 and its family of ligands in angiogenesis, vascular permeability, and microinflammatory cascades within the retina. Expression of VEGFR1 depends on the microenvironment, is differentially regulated under hypoxic and inflammatory conditions, and it has been detected in retinal and choroidal endothelial cells, pericytes, retinal and choroidal mononuclear phagocytes (including microglia), Müller cells, photoreceptor cells, and the retinal pigment epithelium. Whilst the VEGF-A decoy function of VEGFR1 is well established, consequences of its direct signaling are less clear. VEGFR1 activation can affect vascular permeability and induce macrophage and microglia production of proinflammatory and proangiogenic mediators. However the ability of the VEGFR1 ligands (VEGF-A, PlGF, and VEGF-B) to compete against each other for receptor binding and to heterodimerize complicates our understanding of the relative contribution of VEGFR1 signaling alone toward the pathologic processes seen in diabetic retinopathy, retinal vascular occlusions, retinopathy of prematurity, and age-related macular degeneration. Clinically, anti-VEGF drugs have proven transformational in these pathologies and their impact on modulation of VEGFR1 signaling is still an opportunity-rich field for further research.

Systemic Inflammation by Collagen-Induced Arthritis Affects the Progression of Age-Related Macular Degeneration Differently in Two Mouse Models of the Disease

Purpose

Age-related macular degeneration (AMD) shares similar risk factors and inflammatory responses with rheumatoid arthritis (RA). Previously, we identified increased risk for dry AMD among patients with RA compared to control subjects, using retrospective data analysis. In this current study, we investigate the role of systemic inflammation triggered in a murine model of arthritis on choroidal neovascularization and retinal pigment epithelium (RPE) degeneration mouse models.

Methods

Collagen-induced arthritis (CIA) was induced in C57BL/6J mice prior to laser-induced choroidal neovascularization (CNV; wet AMD model) or sodium iodate-induced retinal degeneration (NaIO3; dry AMD model). CNV lesion size and retinal thickness were quantified by optical coherence photography (OCT), visual function was analyzed using optokinetic response and electroretinography, RPE morphology was examined by immunohistochemistry, and inflammatory gene expression was analyzed by quantitative PCR.

Results

CIA mice demonstrated decreased spatial acuity and contrast sensitivity, whereas no difference was observed in the RPE-generated c-wave. CNV lesion size was decreased in CIA mice. NaIO3 decreased c-wave amplitude, as well as retinal thickness, which was augmented by CIA. NaIO3 treatment resulted in loss of normal RPE hexagonal shape, which was further aggravated by CIA. Increased Cxcl9 expression was observed in the presence of CIA and CIA combined with AMD. Disease severity differences were observed between sexes.

Conclusions

Our data suggest systemic inflammation by CIA results in increased pathology in a dry AMD model, whereas it reduces lesions in a wet AMD model. These findings highlight the need for additional investigation into the role of secondary inflammation and sex-based differences on AMD.

An allosteric interleukin-1 receptor modulator mitigates inflammation and photoreceptor toxicity in a model of retinal degeneration

BACKGROUND

Inflammation and particularly interleukin-1β (IL-1β), a pro-inflammatory cytokine highly secreted by activated immune cells during early AMD pathological events, contribute significantly to retinal neurodegeneration. Here, we identify specific cell types that generate IL-1β and harbor the IL-1 receptor (IL-1R) and pharmacologically validate IL-1β's contribution to neuro-retinal degeneration using the IL-1R allosteric modulator composed of the amino acid sequence rytvela (as well as the orthosteric antagonist, Kineret) in a model of blue light-induced retinal degeneration.

METHODS

Mice were exposed to blue light for 6 h and sacrificed 3 days later. Mice were intraperitoneally injected with rytvela, Kineret, or vehicle twice daily for 3 days. The inflammatory markers F4/80, NLRP3, caspase-1, and IL-1β were assessed in the retinas. Single-cell RNA sequencing was used to determine the cell-specific expression patterns of retinal Il1b and Il1r1. Macrophage-induced photoreceptor death was assessed ex vivo using retinal explants co-cultured with LPS-activated bone marrow-derived macrophages. Photoreceptor cell death was evaluated by the TUNEL assay. Retinal function was assessed by flash electroretinography.

RESULTS

Blue light markedly increased the mononuclear phagocyte recruitment and levels of inflammatory markers associated with photoreceptor death. Co-localization of NLRP3, caspase-1, and IL-1β with F4/80⁺ mononuclear phagocytes was clearly detected in the subretinal space, suggesting that these inflammatory cells are the main source of IL-1β. Single-cell RNA sequencing confirmed the immune-specific expression of Il1b and notably perivascular macrophages in light-challenged mice, while Il1r1 expression was found primarily in astrocytes, bipolar, and vascular cells. Retinal explants co-cultured with LPS/ATP-activated bone marrow-derived macrophages displayed a high number of TUNEL-positive photoreceptors, which was abrogated by rytvela treatment. IL-1R antagonism significantly mitigated the inflammatory response triggered in vivo by blue light exposure, and rytvela was superior to Kineret in preserving photoreceptor density and retinal function.

CONCLUSION

These findings substantiate the importance of IL-1β in neuro-retinal degeneration and revealed specific sources of Il1b from perivascular MPs, with its receptor Ilr1 being separately expressed on surrounding neuro-vascular and astroglial cells. They also validate the efficacy of rytvela-induced IL-1R modulation in suppressing detrimental inflammatory responses and preserving photoreceptor density and function in these conditions, reinforcing the rationale for clinical translation.

Ablation of C3 modulates macrophage reactivity in the outer retina during photo-oxidative damage

Purpose

Dysregulation of the complement cascade contributes to a variety of retinal dystrophies, including age-related macular degeneration (AMD). The central component of complement, C3, is expressed in abundance by macrophages in the outer retina, and its ablation suppresses photoreceptor death in experimental photo-oxidative damage. Whether this also influences macrophage reactivity in this model system, however, is unknown. We investigate the effect of C3 ablation on macrophage activity and phagocytosis by outer retinal macrophages during photo-oxidative damage.

Methods

Age-matched C3 knockout (KO) mice and wild-type (WT) C57/Bl6 mice were subjected to photo-oxidative damage. Measurements of the outer nuclear layer (ONL) thickness and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining were used to assess pathology and photoreceptor apoptosis, respectively. Macrophage abundance and phagocytosis were assessed with immunolabeling for pan-macrophage and phagocytic markers, in conjunction with TUNEL staining in cohorts of C3 KO and WT mice.

Results

The C3 KO mice exhibited protection against photoreceptor cell death following photo-oxidative damage, which was associated with a reduction in immunoreactivity for the stress-related factor GFAP. In conjunction, there was a reduction in IBA1-positive macrophages in the outer retina compared to the WT mice and a decrease in the number of CD68-positive cells in the outer nuclear layer and the subretinal space. In addition, the engulfment of TUNEL-positive and -negative photoreceptors by macrophages was significantly lower in the C3 KO mice cohort following photo-oxidative damage compared to the WT cohort.

Conclusions

The results show that the absence of C3 mitigates the phagocytosis of photoreceptors by macrophages in the outer retina, and the net impact of C3 depletion is neuroprotective in the context of photo-oxidative damage. These data improve our understanding of the impact of C3 inhibition in subretinal inflammation and inform the development of treatments for targeting complement activation in diseases such as AMD.

Human Fetal Pigmented Ciliary Epithelium Stem Cells have Regenerative Capacity in the Murine Retinal Degeneration Model of Laser Injury

BACKGROUND

Retinal degeneration and related eye disorders have limited treatment interventions. Since stem cell therapy has shown promising results, ciliary epithelium (CE) derived stem cells could be a better choice given the fact that cells from eye niche can better integrate with the degenerating retina, rewiring the synaptic damage.

OBJECTIVE

To test the effect of human fetal pigmented ciliary epithelium-derived neurospheres in the mouse model of laser-induced retinal degeneration.

METHODS

C57 male mice were subjected to retinal injury by Laser photocoagulation. Human fetal pigmented ciliary epithelium was obtained from post-aborted human eyeballs and cultured with epidermal growth factor (rhEGF) and fibroblast growth factor (rhFGF). The six day neurospheres were isolated, dissociated and transplanted into the subretinal space of the laser injured mice at the closest proximity to Laser shots. Mice were analyzed for functional vision through electroretinogram (ERG) and sacrificed at 1 week and 12 week time points. Retinal, Neurotropic, Apoptotic and proliferation markers were analysed using real-time polymerase chain reaction (PCR).

RESULTS

The CE neurospheres showed an increase in the expression of candidate genes analyzed in the study at 1 week time point, which sustained for longer time point of 12 weeks.

CONCLUSION

We showed the efficacy of human CE cells in the regeneration of retinal degeneration in murine model for the first time. CE cells need to be explored comprehensively both in disease and degeneration.

Correlation of Immunological Markers with Disease and Clinical Outcome Measures in Patients with Autoimmune Retinopathy

Purpose

To determine if immunological markers (1) are significantly different between autoimmune retinopathy (AIR) patients and controls and (2) correlate with disease progression in AIR patients.

Methods

We enrolled patients with a possible AIR diagnosis, as well as control participants without eye disease, autoimmunity, or cancer. Immunological markers were tested in all participants. In addition, AIR patients had up to three blood draws for testing over their disease course. For AIR patients, clinical measures, including visual acuity (VA) and Goldmann visual field (GVF) area, were recorded at each draw. We used the Mann-Whitney U test to compare the immunological markers between AIR patients and controls. We used multilevel mixed-effect regression to investigate the correlation between markers and clinical parameters over time in AIR patients.

Results

Seventeen patients with AIR and 14 controls were included. AIR patients had a higher percent of monocytes (Z = 3.076, P = 0.002). An increase in immunoglobulin G against recoverin was correlated with a VA decrease (β = 0.0044, P < 0.0001). An increase in monocyte proportion was correlated with a decrease in GVF area (β = -7.27, P = 0.0021). Several markers of B-cell depletion were correlated with GVF improvement.

Conclusions

Monocytes may play a role in AIR pathophysiology and be a disease activity marker. B-cell depletion markers correlated with clinical parameter improvement, particularly GVF.

Translational Relevance

This work elucidates immunologic markers that may improve the accuracy of diagnosis and treatment of AIR.

TNF-α Pretreatment Improves the Survival and Function of Transplanted Human Neural Progenitor Cells Following Hypoxic-Ischemic Brain Injury

Neural progenitor cells (NPCs) therapy offers great promise in hypoxic-ischemic (HI) brain injury. However, the poor survival of implanted NPCs in the HI host environment limits their therapeutic effects. Tumor necrosis factor-alpha (TNF-α) is a pleiotropic cytokine that is induced in response to a variety of pathological processes including inflammation and immunity. On the other hand, TNF-α has protective effects on cell apoptosis and death and affects the differentiation, proliferation, and survival of neural stem/progenitor cells in the brain. The present study investigated whether TNF-α pretreatment on human NPCs (hNPCs) enhances the effectiveness of cell transplantation therapy under ischemic brain. Fetal brain tissue-derived hNPCs were pretreated with TNF-α before being used in vitro experiments or transplantation. TNF-α significantly increased expression of cIAP2, and the use of short hairpin RNA-mediated knockdown of cIAP2 demonstrated that cIAP2 protected hNPCs against HI-induced cytotoxicity. In addition, pretreatment of hNPCs with TNF-α mediated neuroprotection by altering microglia polarization via increased expression of CX3CL1 and by enhancing expression of neurotrophic factors. Furthermore, transplantation of TNF-α-treated hNPCs reduced infarct volume and improved neurological functions in comparison with non-pretreated hNPCs or vehicle. These findings show that TNF-α pretreatment, which protects hNPCs from HI-injured brain-induced apoptosis and increases neuroprotection, is a simple and safe approach to improve the survival of transplanted hNPCs and the therapeutic efficacy of hNPCs in HI brain injury.

Transcriptomic Characterization of Human Choroidal Neovascular Membranes Identifies Calprotectin as a Novel Biomarker for Patients with Age-Related Macular Degeneration

Recent studies deciphering the transcriptional profile of choroidal neovascularization (CNV) in body donor eyes with neovascular age-related macular degeneration are limited by the time span from death to preservation and the associated 5'-RNA degradation. This study therefore used CNV and control specimens that were formalin-fixed and paraffin-embedded immediately after surgical extraction and analyzed them by a 3'-RNA sequencing approach. Transcriptome profiles were analyzed to estimate content of immune and stromal cells and to define disease-associated gene signatures by using statistical and bioinformatics methods. This study identified 158 differentially expressed genes (DEGs) that were significantly increased in CNV compared with control tissue. Cell type enrichment analysis revealed a diverse cellular landscape with an enrichment of endothelial cells, macrophages, T cells, and natural killer T cells in the CNV. Gene ontology enrichment analysis found that DEGs contributed to blood vessel development, extracellular structure organization, response to wounding, and several immune-related terms. The S100 calcium-binding proteins A8 (S100A8) and A9 (S100A9) emerged among the top DEGs, as confirmed by immunohistochemistry on CNV tissue and protein analysis of vitreous samples. This study provides a high-resolution RNA-sequencing-based transcriptional signature of human CNV, characterizes its compositional pattern of immune and stromal cells, and reveals S100A8/A9 to be a novel biomarker and promising target for therapeutics and diagnostics directed at age-related macular degeneration.

Microglia versus Monocytes: Distinct Roles in Degenerative Diseases of the Retina

Unlike in the healthy mammalian retina, macrophages in retinal degenerative states are not solely comprised of microglia but may include monocyte-derived recruits. Recent studies have applied transgenics, lineage-tracing, and transcriptomics to help decipher the distinct roles of these two cell types in the diseasesettings of inherited retinal degenerations and age-related macular degeneration.Literature discussed here focuses on the ectopic presence of both macrophage types in the extracellular site surrounding the outer aspect ofphotoreceptor cells (i.e.,the subretinal space), which is crucially involved in the pathobiology. From these studies we propose a working model in which perturbed photoreceptor states cause microglial dominant migration to the subretinal space as a protective response, whereas the abundant presence ofmonocyte-derived cells there instead drives and accelerates pathology. The latter, we propose, is underpinned by specific genetic and nongenetic determinants that lead to a maladaptive macrophage state.

Inflammaging is associated with shifted macrophage ontogeny and polarization in the aging mouse ovary

The fertility of women declines sharply after age 35 and is essentially lost upon menopause at age 51. The ovary plays an important part in aging-associated changes in women's physiology since it is an essential component of both the reproductive and endocrine systems. Several previous studies in mice have shown that the ovarian tissue goes through drastic changes over the course of aging and exhibits signs of aging-associated chronic inflammation (inflammaging), which may contribute to the marked decline of oocyte quality in aged individuals. To further examine aging-associated gene expression changes in the ovary and to characterize the development of inflammaging, we performed detailed transcriptomic analysis of whole ovaries from mice of six different age groups over the mouse reproductive lifespan and identified more than 5000 genes with significant expression change over the course of aging. Intriguingly, we found aging-associated changes in the expression of several markers that indicate alterations in the composition of ovarian macrophages, which are known to be central players of inflammaging. Using flow cytometry, we analyzed and compared macrophage populations and polarization in young and old ovaries and found a significant increase in monocyte recruitment and macrophage alternative activation (M2) in the old ovaries compared to those in young. Our results are consistent with previous findings of aging-associated increase of fibrosis in the ovarian stromal extracellular matrix, and they provide new clues about the development of inflammaging in the mammalian ovary.

The role of lymphocytes and phagocytes in age-related macular degeneration (AMD)

Age-related macular degeneration (AMD) is a leading cause of visual impairment of the elderly population. Since AMD is a multifactorial age-related disease with various genetic risk factors, the understanding of its complex pathophysiology is still limited. However, animal experiments, genome-wide association data and the molecular profiling of AMD patient samples have highlighted a key role of systemic and local immune processes that contribute to this chronic eye disease. In this overview article, we concentrate on the role of lymphocytes and mononuclear phagocytes and their interplay in triggering a persistent immune response in the AMD retina. We preferentially review findings from human immune cell analyses and complement these with related findings in experimental models. We conclude that both immune cell types as their signaling network may be a rich source to identify novel molecular targets for immunomodulation in AMD.

MANF delivery improves retinal homeostasis and cell replacement therapies in ageing mice

Ageing is a major risk factor for vision loss, and inflammation is an important contributor to retinal disease in the elderly. Regenerative medicine based on cell replacement strategies has emerged in recent years as a promising approach to restore vision. However, how the ageing process affects retinal homeostasis and inflammation in the retina and how this may impose a limitation to the success of such interventions remains unknown. Here we report that, in mice and humans, retinal ageing is associated with a reduction in MANF protein levels, specifically in the choroid, where increased densities of activated macrophages can be detected. We further show that the retina of old wild type mice, in the absence of any other genetic alteration, has limited homeostatic capacity after damage imposed by light exposure and reduced engraftment efficiency of exogenously supplied photoreceptors. Finally, we show that supplementation of MANF recombinant protein can improve retinal homeostasis and repair capacity in both settings, correlating with reduced numbers of activated macrophages in the old retina. Our work identifies age-related alterations in retinal homeostasis, independent of genetic alterations, leading to age-related retinal inflammation and damage susceptibility. We suggest that MANF therapy is a potential intervention to maintain retinal homeostasis in the elderly and improve the success of retinal regenerative therapies applied to aged individuals.

CD36 Deficiency Inhibits Retinal Inflammation and Retinal Degeneration in Cx3cr1 Knockout Mice

Background: CD36, a member of the class B scavenger receptor family, participates in Toll-like receptor signaling on mononuclear phagocytes (MP) and can promote sterile pathogenic inflammation. We here analyzed the effect of CD36 deficiency on retinal inflammation and photoreceptor degeneration, the hallmarks of age-related macular degeneration (AMD), that characterize Cx3cr1^−/−mice.

Methods: We analyzed subretinal MP accumulation, and cone- and rod-degeneration in light-challenged and aged, CD36 competent or deficient, hyper-inflammatory Cx3cr1^−/− mice, using histology and immune-stained retinal flatmounts. Monocytes (Mo) were subretinally adoptively transferred to evaluate their elimination rate from the subretinal space and Interleukin 6 (IL-6) secretion from cultured Mo-derived cells (MdCs) of the different mouse strains were analyzed.

Results: CD36 deficient Cx3cr1^−/− mice were protected against age- and light-induced subretinal inflammation and associated cone and rod degeneration. CD36 deficiency in Cx3cr1^−/− MPs inhibited their prolonged survival in the immune-suppressive subretinal space and reduced the exaggerated IL-6 secretion observed in Cx3cr1^−/− MPs that we previously showed leads to increased subretinal MP survival.

Conclusion:Cd36 deficiency significantly protected hyperinflammatory Cx3cr1^−/− mice against subretinal MP accumulation and associated photoreceptor degeneration. The observed CD36-dependent induction of pro-inflammatory IL-6 might be at least partially responsible for the prolonged MP survival in the immune-suppressive environment and its pathological consequences on photoreceptor homeostasis.

IL-1β induces rod degeneration through the disruption of retinal glutamate homeostasis

BACKGROUND

Age-related macular degeneration is characterized by the accumulation of subretinal macrophages and the degeneration of cones, but mainly of rods. We have previously shown that Mononuclear Phagocytes-derived IL-1β induces rod photoreceptor cell death during experimental subretinal inflammation and in retinal explants exposed to IL-1β but the mechanism is unknown.

METHODS

Retinal explants were culture in the presence of human monocytes or IL-1β and photoreceptor cell survival was analyzed by TUNEL labeling. Glutamate concentration and transcription levels of gene involved in the homeostasis of glutamate were analyzed in cell fractions of explant cultured or not in the presence of IL-1β. Glutamate receptor antagonists were evaluated for their ability to reduce photoreceptor cell death in the presence of IL1-β or monocytes.

RESULTS

We here show that IL-1β does not induce death in isolated photoreceptors, suggesting an indirect effect. We demonstrate that IL-1β leads to glutamate-induced rod photoreceptor cell death as it increases the extracellular glutamate concentrations in the retina through the inhibition of its conversion to glutamine in Müller cells, increased release from Müller cells, and diminished reuptake. The inhibition of non-NMDA receptors completely and efficiently prevented rod apoptosis in retinal explants cultured in the presence of IL-1β or, more importantly, in vivo, in a model of subretinal inflammation.

CONCLUSIONS

Our study emphasizes the importance of inflammation in the deregulation of glutamate homeostasis and provides a comprehensive mechanism of action for IL-1β-induced rod degeneration.

Immunometabolic modulation of retinal inflammation by CD36 ligand

In subretinal inflammation, activated mononuclear phagocytes (MP) play a key role in the progression of retinopathies. Little is known about the mechanism involved in the loss of photoreceptors leading to vision impairment. Studying retinal damage induced by photo-oxidative stress, we observed that cluster of differentiation 36 (CD36)-deficient mice featured less subretinal MP accumulation and attenuated photoreceptor degeneration. Moreover, treatment with a CD36-selective azapeptide ligand (MPE-001) reduced subretinal activated MP accumulation in wild type mice and preserved photoreceptor layers and function as assessed by electroretinography in a CD36-dependent manner. The azapeptide modulated the transcriptome of subretinal activated MP by reducing pro-inflammatory markers. In isolated MP, MPE-001 induced dissociation of the CD36-Toll-like receptor 2 (TLR2) oligomeric complex, decreasing nuclear factor-kappa B (NF-κB) and NLR family pyrin domain containing 3 (NLRP3) inflammasome activation. In addition, MPE-001 caused an aerobic metabolic shift in activated MP, involving peroxisome proliferator-activated receptor-γ (PPAR-γ) activation, which in turn mitigated inflammation. Accordingly, PPAR-γ inhibition blocked the cytoprotective effect of MPE-001 on photoreceptor apoptosis elicited by activated MP. By altering activated MP metabolism, MPE-001 decreased immune responses to alleviate subsequent inflammation-dependent neuronal injury characteristic of various vision-threatening retinal disorders.

Evaluation of antioxidant treatments for the modulation of macrophage function in the context of retinal degeneration

Purpose

Oxidative stress and macrophages have been implicated in the pathogenesis of atrophic and neovascular age-related macular degeneration (aAMD and nvAMD). It is unclear whether oxidative injury mediates macrophage involvement in AMD. We aimed to investigate the effect of antioxidant treatments on human monocyte-derived macrophages (hMDMs) from patients with AMD in models for the disease.

Methods

Four antioxidant treatments were evaluated (G1: lutein + zeaxanthin, G2: lutein + zeaxanthin and zinc, G3: lutein + zeaxanthin, zinc, Lyc-O-Mato, and carnosic acid, G4: lutein + zeaxanthin, carnosic acid, and beta-carotene, G5: olive oil as vehicle control). The compounds were added to the culture medium of M1 (interferon-gamma [IFN-Ɣ] and lipopolysaccharide [LPS]) and M2a (interleukin-13 [IL-13] and IL-4) hMDMs from patients with AMD (n=7 and n=8, respectively). Mouse choroidal tissue was cultured with supernatants from treated M1/M2a hMDMs, to evaluate the effect of treatments on the angiogenic properties of macrophages with choroidal sprouting assay (CSA). Mouse retinal explants were cultured with treated hMDMs for 18 h, and evaluated for photoreceptor apoptosis using terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) labeling. Adult BALB/c mice (n=8) were exposed to 8,000 lux bright light for 3 h, and treated orally with antioxidant supplements for 7 days that preceded light injury and following it. Oxidative stress was assessed using an anti-4 hydroxynonenal (4-HNE) antibody. Retinal function and the thickness of the outer nuclear layer were evaluated with electroretinography (ERG) and histological analysis, respectively.

Results

The G3 treatment reduced M2a hMDMs-associated sprouting in the CSA compared to the untreated group (n=7, -1.52-fold, p=0.05). Conversely, the G2 treatment was associated with an increased neurotoxic effect of M2a hMDMs in the retinal explant assay compared to the control group (n=7, 1.37-fold, p=0.047), as well as compared to the G3 treatment group (1.46-fold, p=0.01). The G4 treatment was also associated with increased cytotoxicity compared to the control group (1.48-fold, p=0.004), and compared to the G3 treatment group (1.58-fold, p=0.001). In the in vivo light damage model, mice (n=8) supplemented with G2, G3, and G4 had decreased levels of oxidative injury assessed using 4-HNE labeling (-2.32-fold, -2.17-fold, and -2.18-fold, respectively, p<0.05 for all comparisons). None of the treatments were associated with reduced photoreceptor cell loss, as shown with histology and ERG.

Conclusions

Antioxidant treatment modulates M2a hMDMs at the functional level. In particular, we found that the G3 combination has a beneficial effect on M2a macrophages in reducing their angiogenic and neurotoxic capacity ex vivo. In addition, antioxidant treatments considerably reduced the oxidative stress level in light-damaged retinas. Further research is required to assess whether such therapies may curb macrophage-driven photoreceptor loss and neovascularization in AMD.

Macrophage Plasticity and Function in the Eye and Heart

Macrophages are important mediators of inflammation and tissue remodeling. Recent insights into the heterogeneity of macrophage subpopulations have renewed interest in their functional diversity in homeostasis and disease. In addition, their plasticity enables them to perform a variety of functions in response to changing tissue contexts, such as those imposed by aging. These qualities make macrophages particularly intriguing cells given their dichotomous role in protecting against, or accelerating, diseases of the cardiovascular system and the eye, two tissues that are particularly susceptible to the effects of aging. We review novel perspectives on macrophage biology, as informed by recent studies detailing the diversity of macrophage identity and function, as well as mechanisms influencing macrophage behavior that might offer opportunities for new therapeutic strategies.

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

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

Evidences Suggesting that Distinct Immunological and Cellular Responses to Light Damage Distinguishes Juvenile and Adult Rat Retinas

To unravel the mechanisms behind the higher resistance to light damage of juvenile (JR) versus adult (AR) rats, Sprague Dawley rats were exposed to a bright luminous environment of 10, 000 lux. The light-induced retinopathy (LIR) was assessed with histology, electroretinography and immunohistochemistry (IHC). In JR, 2 days of exposure induced the typical LIR, while >3 days added little LIR. IHC revealed a subtle migration of microglia (Iba1 marker) from the inner to the outer retina after 3 days of exposure in JR contrasting with the stronger reaction seen after 1 day in AR. Similarly, in JR, the Müller cells expressed less intense GFAP, CNTF and FGF2 staining compared to AR. Our results suggest that in JR the degree of retinal damage is not proportional to the duration of light exposure (i.e., dose-independent retinopathy), contrasting with the dose-dependent LIR reported in AR. The immature immune system in JR may explain the delayed and/or weaker inflammatory response compared to AR, a finding that would also point to the devastating contribution of the immune system in generating the LIR phenotype, a claim also advanced to explain the pathophysiology of other retinal degenerative disorders such as Age-related Macular Degeneration, Diabetic Retinopathy and Retinitis Pigmentosa.

Modulation of three key innate immune pathways for the most common retinal degenerative diseases

This review highlights the role of three key immune pathways in the pathophysiology of major retinal degenerative diseases including diabetic retinopathy, age‐related macular degeneration, and rare retinal dystrophies. We first discuss the mechanisms how loss of retinal homeostasis evokes an unbalanced retinal immune reaction involving responses of local microglia and recruited macrophages, activity of the alternative complement system, and inflammasome assembly in the retinal pigment epithelium. Presenting these key mechanisms as complementary targets, we specifically emphasize the concept of immunomodulation as potential treatment strategy to prevent or delay vision loss. Promising molecules are ligands for phagocyte receptors, specific inhibitors of complement activation products, and inflammasome inhibitors. We comprehensively summarize the scientific evidence for this strategy from preclinical animal models, human ocular tissue analyses, and clinical trials evolving in the last few years.

Is Retinal Metabolic Dysfunction at the Center of the Pathogenesis of Age-related Macular Degeneration?

The retinal pigment epithelium (RPE) forms the outer blood⁻retina barrier and facilitates the transepithelial transport of glucose into the outer retina via GLUT1. Glucose is metabolized in photoreceptors via the tricarboxylic acid cycle (TCA) and oxidative phosphorylation (OXPHOS) but also by aerobic glycolysis to generate glycerol for the synthesis of phospholipids for the renewal of their outer segments. Aerobic glycolysis in the photoreceptors also leads to a high rate of production of lactate which is transported out of the subretinal space to the choroidal circulation by the RPE. Lactate taken up by the RPE is converted to pyruvate and metabolized via OXPHOS. Excess lactate in the RPE is transported across the basolateral membrane to the choroid. The uptake of glucose by cone photoreceptor cells is enhanced by rod-derived cone viability factor (RdCVF) secreted by rods and by insulin signaling. Together, the three cells act as symbiotes: the RPE supplies the glucose from the choroidal circulation to the photoreceptors, the rods help the cones, and both produce lactate to feed the RPE. In age-related macular degeneration this delicate ménage à trois is disturbed by the chronic infiltration of inflammatory macrophages. These immune cells also rely on aerobic glycolysis and compete for glucose and produce lactate. We here review the glucose metabolism in the homeostasis of the outer retina and in macrophages and hypothesize what happens when the metabolism of photoreceptors and the RPE is disturbed by chronic inflammation.

Changes in Retinal Glial Cells with Age and during Development of Age-Related Macular Degeneration

Age is the major risk factor in the age-related macular degeneration (AMD) which is a complex multifactor neurodegenerative disease of the retina and the main cause of irreversible vision loss in people over 60 years old. The major role in AMD pathogenesis belongs to structure-functional changes in the retinal pigment epithelium cells, while the onset and progression of AMD are commonly believed to be caused by the immune system dysfunctions. The role of retinal glial cells (Muller cells, astrocytes, and microglia) in AMD pathogenesis is studied much less. These cells maintain neurons and retinal vessels through the synthesis of neurotrophic and angiogenic factors, as well as perform supporting, separating, trophic, secretory, and immune functions. It is known that retinal glia experiences morphological and functional changes with age. Age-related impairments in the functional activity of glial cells are closely related to the changes in the expression of trophic factors that affect the status of all cell types in the retina. In this review, we summarized available literature data on the role of retinal macro- and microglia and on the contribution of these cells to AMD pathogenesis.

Exposure to excessive blue LED light damages retinal pigment epithelium and photoreceptors of pigmented mice

To determine the characteristics of the damages of the retinal pigment epithelium (RPE) and photoreceptors of pigmented mice induced by exposure to blue light emitting diode (LED) light, and to determine the mechanisms causing the damages. Exposure to blue LED light for 3 days induced retinal damage, and the characteristics of the damage differed from that induced by white fluorescent light exposure. Ophthalmoscopy showed that blue LED exposure for 3 days induced white spots on the retina, and histological examinations showed materials accumulated at the IS/OS junction of the photoreceptors. The accumulated materials were stained by ionized calcium binding adapter molecule-1 (Iba-1), a marker for macrophages. The debris was also positive for periodic acid-Schiff (PAS). An enlarging the area of RPE was detected just after the blue LED exposure especially around the optic nerve, and this led to a secondary degeneration of the photoreceptors. Exposure of pigmented mice to 3 consecutive days of blue LED light will cause RPE and photoreceptor damage. The damage led to an accumulation of macrophages and drusen-like materials around the outer segments of the photoreceptors. This blue light exposed model may be useful for investigating the pathogenesis of non-exudative age-related macular degeneration.

4-Hydroxy-7-oxo-5-heptenoic Acid Lactone Is a Potent Inducer of the Complement Pathway in Human Retinal Pigmented Epithelial Cells

We previously discovered that oxidative cleavage of docosahexaenoate (DHA), which is especially abundant in the retinal photoreceptor rod outer segments and retinal pigmented endothelial (RPE) cells, generates 4-hydroxy-7-oxo-5-heptenoate (HOHA) lactone, and that HOHA lactone can enter RPE cells that metabolize it through conjugation with glutathione (GSH). The consequent depletion of GSH results in oxidative stress. We now find that HOHA lactone induces upregulation of the antioxidant transcription factor Nrf2 in ARPE-19 cells. This leads to expression of GCLM, HO1, and NQO1, three known Nrf2-responsive antioxidant genes. Besides this protective response, HOHA lactone also triggers a countervailing inflammatory activation of innate immunity. Evidence for a contribution of the complement pathway to age-related macular degeneration (AMD) pathology includes the presence of complement proteins in drusen and Bruch's membrane from AMD donor eyes, and the identification of genetic susceptibility loci for AMD in the complement pathway. In eye tissues from a mouse model of AMD, accumulation of complement protein in Bruch's membrane below the RPE suggested that the complement pathway targets this interface, where lesions occur in the RPE and photoreceptor rod outer segments. In animal models of AMD, intravenous injection of NaIO₃ to induce oxidative injury selectively destroys the RPE and causes secretion of factor C3 from the RPE into areas directly adjacent to sites of RPE damage. However, a molecular-level link between oxidative injury and complement activation remained elusive. We now find that sub-micromolar concentrations of HOHA lactone foster expression of C3, CFB, and C5 in ARPE-19 cells and induce a countervailing upregulation of CD55, an inhibitor of C3 convertase production and complement cascade amplification. Ultimately, HOHA lactone causes membrane attack complex formation on the plasma membrane. Thus, HOHA lactone provides a molecular-level connection between free-radical-induced oxidative cleavage of DHA and activation of the complement pathway in AMD pathology.

Oxidative modifications of extracellular matrix promote the second wave of inflammation via β2 integrins

Early stages of inflammation are characterized by extensive oxidative insult by recruited and activated neutrophils. Secretion of peroxidases, including the main enzyme, myeloperoxidase, leads to the generation of reactive oxygen species. We show that this oxidative insult leads to polyunsaturated fatty acid (eg, docosahexaenoate), oxidation, and accumulation of its product 2-(ω-carboxyethyl)pyrrole (CEP), which, in turn, is capable of protein modifications. In vivo CEP is generated predominantly at the inflammatory sites in macrophage-rich areas. During thioglycollate-induced inflammation, neutralization of CEP adducts dramatically reduced macrophage accumulation in the inflamed peritoneal cavity while exhibiting no effect on the early recruitment of neutrophils, suggesting a role in the second wave of inflammation. CEP modifications were abundantly deposited along the path of neutrophils migrating through the 3-dimensional fibrin matrix in vitro. Neutrophil-mediated CEP formation was markedly inhibited by the myeloperoxidase inhibitor, 4-ABH, and significantly reduced in myeloperoxidase-deficient mice. On macrophages, CEP adducts were recognized by cell adhesion receptors, integrin αMβ2 and αDβ2 Macrophage migration through CEP-fibrin gel was dramatically augmented when compared with fibrin alone, and was reduced by β2-integrin deficiency. Thus, neutrophil-mediated oxidation of abundant polyunsaturated fatty acids leads to the transformation of existing proteins into stronger adhesive ligands for αMβ2- and αDβ2-dependent macrophage migration. The presence of a carboxyl group rather than a pyrrole moiety on these adducts, resembling characteristics of bacterial and/or immobilized ligands, is critical for recognition by macrophages. Therefore, specific oxidation-dependent modification of extracellular matrix, aided by neutrophils, promotes subsequent αMβ2- and αDβ2-mediated migration/retention of macrophages during inflammation.

Retinal microglia - A key player in healthy and diseased retina

Microglia, the resident immune cells of the brain and retina, are constantly engaged in the surveillance of their surrounding neural tissue. During embryonic development they infiltrate the retinal tissues and participate in the phagocytosis of redundant neurons. The contribution of microglia in maintaining the purposeful and functional histo-architecture of the adult retina is indispensable. Within the retinal microenvironment, robust microglial activation is elicited by subtle changes caused by extrinsic and intrinsic factors. When there is a disturbance in the cell-cell communication between microglia and other retinal cells, for example in retinal injury, the activated microglia can manifest actions that can be detrimental. This is evidenced by activated microglia secreting inflammatory mediators that can further aggravate the retinal injury. Microglial activation as a harbinger of a variety of retinal diseases is well documented by many studies. In addition, a change in the microglial phenotype which may be associated with aging, may predispose the retina to age-related diseases. In light of the above, the focus of this review is to highlight the role played by microglia in the healthy and diseased retina, based on findings of our own work and from that of others.

The use of the vaccinia virus complement control protein (VCP) in the rat retina

The complement system is highly implicated in both the prevalence and progression of Age-Related Macular Degeneration (AMD). Complement system inhibitors therefore have potential therapeutic value in managing excessive activation of the complement pathways in retinal degenerations. The vaccinia virus complement control protein (VCP) has been shown to be effective as a complement inhibitor in neuroinflammatory models including traumatic brain injury and spinal cord injury. We aimed to investigate the potential of VCP as a therapeutic molecule for retinal degenerations. In this study, we investigated the effect, localisation and delivery of VCP to the rodent retina. Complement inhibition activity of VCP was tested using a hemolytic assay. Photoreceptor cell death, inflammation and retinal stress were assayed to determine if any retinal toxicity was induced by an intravitreal injection of VCP. The effect of VCP was investigated in a model of photo-oxidative retinal degeneration. Localisation of VCP after injection was determined using a fluorescein-tagged form of VCP, as well as immunohistochemistry. Finally, a copolymer resin (Elvax) was trialled for the slow-release delivery of VCP to the retina. We found that a dose equivalent to 20μg VCP when intravitreally injected into the rat eye did not cause any photoreceptor cell death or immune cell recruitment, but led to an increase in GFAP. In photo-oxidative damaged retinas, there were no differences in photoreceptor loss, retinal stress (Gfap) and inflammation (Ccl2 and C3) between VCP and saline-injected groups; however, Jun expression was reduced in VCP-treated retinas. After VCP was injected into the eye, it was taken up in all layers of the retina but was cleared within 1-3 hours of delivery. This study indicates that a method to sustain the delivery of VCP to the retina is necessary to further investigate the effect of VCP as a complement inhibitor for retinal degenerations.

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

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

Inflammation-Induced Photoreceptor Cell Death

Neuroinflammation is an important aspect of many diseases of the eye, and experimental animal models have been widely used to determine its impact on retinal homeostasis and neuron survival. Physical separation of the neurosensory retina from the underlying retinal pigment epithelium (RPE) results in activation and infiltration of macrophages. Numerous studies have shown the critical role of macrophages in retinal disease processes. In retinal detachment, accumulation of macrophages in the subretinal space is associated with changes in cytokine and chemokine profile which lead to photoreceptor cell death. Targeted disruption of macrophage chemotaxis significantly reduces retinal detachment-induced photoreceptor degeneration. Apoptosis is the predominant mechanism of cell death; however regulated necrosis is also a contributor of photoreceptor loss. Therefore, effective neuroprotective approaches could integrate combined inhibition of both apoptotic and regulated necrosis pathways.

Ischemic Retinopathies: Oxidative Stress and Inflammation

Ischemic retinopathies (IRs), such as retinopathy of prematurity (ROP), diabetic retinopathy (DR), and (in many cases) age-related macular degeneration (AMD), are ocular disorders characterized by an initial phase of microvascular changes that results in ischemia, followed by a second phase of abnormal neovascularization that may culminate into retinal detachment and blindness. IRs are complex retinal conditions in which several factors play a key role during the development of the different pathological stages of the disease. Increasing evidence reveals that oxidative stress and inflammatory processes are important contributors to the pathogenesis of IRs. Despite the beneficial effects of the photocoagulation and anti-VEGF therapy during neovascularization phase, the need to identify novel targets to prevent initial phases of these ocular pathologies is still needed. In this review, we provide an update on the involvement of oxidative stress and inflammation in the progression of IRs and address some therapeutic interventions by using antioxidants and anti-inflammatory agents.

Diverse roles of macrophages in intraocular neovascular diseases: a review

Macrophages are involved in angiogenesis, and might also contribute to the pathogenesis of intraocular neovascular diseases. Recent studies indicated that macrophages exert different functions in the process of intraocular neovascularization, and the polarization of M1 and M2 phenotypes plays extremely essential roles in the diverse functions of macrophages. Moreover, a large number of cytokines released by macrophages not only participate in macrophage polarization, but also associate with retinal and choroidal neovascular diseases. Therefore, macrophage might be considered as a novel therapeutic target to the treatment of pathological neovascularization in the eye. This review mainly summarizes diverse roles of macrophages and discusses the possible mechanisms in retinal and choroidal neovascularization.

Characterizing the effect of supplements on the phenotype of cultured macrophages from patients with age-related macular degeneration

Purpose

Oral vitamin and mineral supplements reduce the risk of visual loss in age-related macular degeneration (AMD). However, the pathways that mediate this beneficial effect are poorly understood. Macrophages may exert oxidative, inflammatory, and angiogenic effects in the context of AMD. We aim to assess if oral supplements can modulate the macrophage phenotype in this disease.

Methods

Monocytes were isolated from patients with neovascular AMD (nvAMD), cultured, matured to macrophages, and polarized to classical [M1 (stimulated by IFNγ and lipopolysaccharide (LPS))] and alternative [M2 (stimulated with IL-4 and IL-13)] phenotypes. Combinations of antioxidants including lutein+zeaxanthin (1 μM; 0.2 μM), zinc (10 µM), carnosic acid (2 µM), beta-carotene (2 µM), and standardized tomato extract containing lycopene and other tomato phytonutrients were added to the culture media. Levels of anti-inflammatory, antioxidant, and pro-angiogenic gene and protein expression were then evaluated.

Results

Combinations of lutein and carnosic acid with zinc and standardized tomato extract or with beta-carotene yielded an antioxidative, anti-inflammatory, and antiangiogenic effect in M1 and M2 macrophages. These effects manifested in the upregulation of antioxidative genes (HMOX1, SOD1) and the downregulation of pro-angiogenic genes and pro-inflammatory genes (SDF-1, TNF-alpha, IL-6, MCP-1). Lutein monotherapy or a combination of lutein and zinc had less effect on the expression of these genes.

Conclusions

Combinations of supplements can modify the expression of genes and proteins that may be relevant for the involvement of macrophages in the pathogenesis of AMD. Further studies are required to evaluate if the modulation of the macrophage phenotype partially accounts for the beneficial effect of oral supplements in AMD and if modification of the AREDS formula can improve its effect on macrophages.

The Oxygen Paradox, the French Paradox, and age-related diseases

A paradox is a seemingly absurd or impossible concept, proposition, or theory that is often difficult to understand or explain, sometimes apparently self-contradictory, and yet ultimately correct or true. How is it possible, for example, that oxygen "a toxic environmental poison" could be also indispensable for life (Beckman and Ames Physiol Rev 78(2):547-81, 1998; Stadtman and Berlett Chem Res Toxicol 10(5):485-94, 1997)?: the so-called Oxygen Paradox (Davies and Ursini 1995; Davies Biochem Soc Symp 61:1-31, 1995). How can French people apparently disregard the rule that high dietary intakes of cholesterol and saturated fats (e.g., cheese and paté) will result in an early death from cardiovascular diseases (Renaud and de Lorgeril Lancet 339(8808):1523-6, 1992; Catalgol et al. Front Pharmacol 3:141, 2012; Eisenberg et al. Nat Med 22(12):1428-1438, 2016)?: the so-called, French Paradox. Doubtless, the truth is not a duality and epistemological bias probably generates apparently self-contradictory conclusions. Perhaps nowhere in biology are there so many apparently contradictory views, and even experimental results, affecting human physiology and pathology as in the fields of free radicals and oxidative stress, antioxidants, foods and drinks, and dietary recommendations; this is particularly true when issues such as disease-susceptibility or avoidance, "healthspan," "lifespan," and ageing are involved. Consider, for example, the apparently paradoxical observation that treatment with low doses of a substance that is toxic at high concentrations may actually induce transient adaptations that protect against a subsequent exposure to the same (or similar) toxin. This particular paradox is now mechanistically explained as "Adaptive Homeostasis" (Davies Mol Asp Med 49:1-7, 2016; Pomatto et al. 2017a; Lomeli et al. Clin Sci (Lond) 131(21):2573-2599, 2017; Pomatto and Davies 2017); the non-damaging process by which an apparent toxicant can activate biological signal transduction pathways to increase expression of protective genes, by mechanisms that are completely different from those by which the same agent induces toxicity at high concentrations. In this review, we explore the influences and effects of paradoxes such as the Oxygen Paradox and the French Paradox on the etiology, progression, and outcomes of many of the major human age-related diseases, as well as the basic biological phenomenon of ageing itself.