Analysis of autoantibodies against human retinal antigens in sera of patients with glaucoma and ocular hypertension

Damage-Associated Molecular Patterns (DAMPs) in Retinal Disorders

Damage-associated molecular patterns (DAMPs) are endogenous danger molecules released from the extracellular and intracellular space of damaged tissue or dead cells. Recent evidence indicates that DAMPs are associated with the sterile inflammation caused by aging, increased ocular pressure, high glucose, oxidative stress, ischemia, mechanical trauma, stress, or environmental conditions, in retinal diseases. DAMPs activate the innate immune system, suggesting their role to be protective, but may promote pathological inflammation and angiogenesis in response to the chronic insult or injury. DAMPs are recognized by specialized innate immune receptors, such as receptors for advanced glycation end products (RAGE), toll-like receptors (TLRs) and the NOD-like receptor family (NLRs), and purine receptor 7 (P2X7), in systemic diseases. However, studies describing the role of DAMPs in retinal disorders are meager. Here, we extensively reviewed the role of DAMPs in retinal disorders, including endophthalmitis, uveitis, glaucoma, ocular cancer, ischemic retinopathies, diabetic retinopathy, age-related macular degeneration, rhegmatogenous retinal detachment, proliferative vitreoretinopathy, and inherited retinal disorders. Finally, we discussed DAMPs as biomarkers, therapeutic targets, and therapeutic agents for retinal disorders.

Antibody and Protein Profiles in Glaucoma: Screening of Biomarkers and Identification of Signaling Pathways

Simple Summary

Glaucoma is a chronic eye disease that is one of the leading causes of blindness worldwide. Currently, the only therapeutic option is to lower intraocular pressure. The onset of the disease is often delayed because patients do not notice visual impairment until very late, which is why glaucoma is also known as “the silent thief of sight”. Therefore, early detection and definition of specific markers, the so-called biomarkers, are immensely important. For the methodical implementation, high-throughput methods and omic-based methods came more and more into focus. Thus, interesting targets for possible biomarkers were already suggested by clinical research and basic research, respectively. This review article aims to join the findings of the two disciplines by collecting overlaps as well as differences in various clinical studies and to shed light on promising candidates concerning findings from basic research, facilitating conclusions on possible therapy options.

Abstract

Glaucoma represents a group of chronic neurodegenerative diseases, constituting the second leading cause of blindness worldwide. To date, chronically elevated intraocular pressure has been identified as the main risk factor and the only treatable symptom. However, there is increasing evidence in the recent literature that IOP-independent molecular mechanisms also play an important role in the progression of the disease. In recent years, it has become increasingly clear that glaucoma has an autoimmune component. The main focus nowadays is elucidating glaucoma pathogenesis, finding early diagnostic options and new therapeutic approaches. This review article summarizes the impact of different antibodies and proteins associated with glaucoma that can be detected for example by microarray and mass spectrometric analyzes, which (i) provide information about expression profiles and associated molecular signaling pathways, (ii) can possibly be used as a diagnostic tool in future and, (iii) can identify possible targets for therapeutic approaches.

Serological Levels of Anti-clathrin Antibodies Are Decreased in Patients With Pseudoexfoliation Glaucoma

Evidence for immunologic contribution to glaucoma pathophysiology is steadily increasing in ophthalmic research. Particularly, an altered abundance of circulating autoantibodies to ocular antigens is frequently observed. Here, we report an analysis of autoantibody abundancies to selected antigens in sera of open-angle glaucoma patients, subdivided into normal-tension glaucoma (N = 31), primary open-angle glaucoma (N = 43) and pseudoexfoliation glaucoma (N = 45), vs. a non-glaucomatous control group (N = 46). Serum samples were analyzed by protein microarray, including 38 antigens. Differences in antibody levels were assessed by ANOVA. Five serological antibodies showed significantly altered levels among the four groups (P < 0.05), which can be used to cluster the subjects in groups consisting mainly of PEXG or POAG/NTG samples. Among the altered autoantibodies, anti-Clathrin antibodies were identified as most important subgroup predictors, enhancing prospective glaucoma subtype prediction. As a second aim, we wanted to gain further insights into the characteristics of previously identified glaucoma-related antigens and their role in glaucoma pathogenesis. To this end, we used the bioinformatics toolset of Metascape to construct protein-protein interaction networks and GO enrichment analysis. Glaucoma-related antigens were significantly enriched in 13 biological processes, including mRNA metabolism, protein folding, blood coagulation and apoptosis, proposing a link of glaucoma-associated pathways to changes in the autoantibody repertoire. In conclusion, our study provides new aspects of the involvement of natural autoimmunity in glaucoma pathomechanisms and promotes advanced opportunities toward new diagnostic approaches.

Synapse and Receptor Alterations in Two Different S100B-Induced Glaucoma-Like Models

Glaucoma is identified by an irreversible retinal ganglion cell (RGC) loss and optic nerve damage. Over the past few years, the immune system gained importance in its genesis. In a glaucoma-like animal model with intraocular S100B injection, RGC death occurs at 14 days. In an experimental autoimmune glaucoma model with systemic S100B immunization, a loss of RGCs is accompanied by a decreased synaptic signal at 28 days. Here, we aimed to study synaptic alterations in these two models. In one group, rats received a systemic S100B immunization (n = 7/group), while in the other group, S100B was injected intraocularly (n = 6–7/group). Both groups were compared to appropriate controls and investigated after 14 days. While inhibitory post-synapses remained unchanged in both models, excitatory post-synapses degenerated in animals with intraocular S100B injection (p = 0.03). Excitatory pre-synapses tendentially increased in animals with systemic S100B immunization (p = 0.08) and significantly decreased in intraocular ones (p = 0.04). Significantly more N-methyl-d-aspartate (NMDA) receptors (both p ≤ 0.04) as well as gamma-aminobutyric acid (GABA) receptors (both p < 0.03) were observed in S100B animals in both models. We assume that an upregulation of these receptors causes the interacting synapse types to degenerate. Heightened levels of excitatory pre-synapses could be explained by remodeling followed by degeneration.

Intravitreal Therapy Against the Complement Factor C5 Prevents Retinal Degeneration in an Experimental Autoimmune Glaucoma Model

In glaucoma, studies revealed an involvement of the complement system. In an experimental autoimmune glaucoma model, immunization with an optic nerve homogenate antigen (ONA) led to retinal ganglion cell (RGC) loss, while intraocular pressure (IOP) remained unchanged. Here, we investigated the therapeutic effect of a complement system inhibition in this model. Hence, rats were immunized with ONA and compared to controls. In one eye of the ONA animals, an antibody against complement factor C5 was intravitreally injected (15 μmol: ONA+C5-I or 25 μmol: ONA+C5-II) before immunization and then every two weeks. IOP was measured weekly. After 6 weeks, spectral-domain optical coherence tomographies (SD-OCT), electroretinograms (ERG), immunohistochemistry, and quantitative real-time PCR analyses were performed. IOP and retinal thickness remained unchanged within all groups. The a-wave amplitudes were not altered in the ONA and ONA+C5-I groups, whereas a decrease was noted in ONA+C5-II animals (p < 0.05). ONA immunization provoked a significant decrease of the b-wave amplitude (p < 0.05), which could be preserved in ONA+C5-I, but not in ONA+C5-II animals. ONA animals showed a loss of RGCs (p = 0.001), while ONA+C5-I and ONA+C5-II retinae had similar cell counts as controls. A significant downregulation of apoptotic Bax/Bcl2 mRNA was noted in ONA+C5-I retinae (p = 0.02). Significantly more C3⁺ and MAC⁺ cells were observed in ONA animals (p < 0.001). The amount of C3⁺ cells in both treatment groups was significantly increased (p < 0.01), while the number of MAC⁺ cells in the treated retinas did not differ from controls. The number of activated microglia cells remained unchanged in ONA animals, but was increased in the treatment groups (p < 0.05). Recoverin⁺ cells were diminished in ONA animals (p = 0.049), but not in treated ones. Rho mRNA was downregulated in ONA and in ONA+C5-II retinas (both p = 0.014). Less opsin⁺ cones were observed in ONA animals (p = 0.009), but not in the treated groups. Our results indicate that the C5 antibody inhibits activation of the complement system, preventing the loss of retinal function as well as RGC, cone bipolar, and photoreceptor loss. Therefore, this approach might be a suitable new treatment for glaucoma patients, in which immune dysregulation plays an important factor for the development and progression of glaucoma.

Autoantibodies Activating the β2-Adrenergic Receptor Characterize Patients With Primary and Secondary Glaucoma

Recently, agonistic autoantibodies (agAAb) activating the β2-adrenergic receptor were detected in primary open-angle glaucoma (POAG) or ocular hypertension (OHT) patients and were linked to intraocular pressure (IOP) (1). The aim of the present study was to quantify β2-agAAb in the sera of glaucoma suspects and patients with primary and secondary glaucoma. Patients with OHT (n = 33), pre-perimetric POAG (pre-POAG; n = 11), POAG (n = 28), and 11 secondary OAG (SOAG) underwent ophthalmological examinations including examinations with Octopus G1 perimetry and morphometry. Twenty-five healthy individuals served as controls. Serum-derived IgG samples were analyzed for β2-agAAb using a functional bioassay. The beat-rate-increase of spontaneously beating cultured neonatal rat cardiomyocytes was monitored with 1.6 beats/15 s as cut-off. None of the sera of normal subjects showed β2-agAAb. In POAG or OHT patients increased beating rates of 4.1 ± 2.2 beats/15 s, and 3.7 ± 2.8 beats/15 s were detected (p > 0.05). Glaucoma patients with (POAG) and without perimetric (pre-POAG) defects did not differ (pre-POAG 4.4 ± 2.6 beats/15 s, POAG 4.1 ± 2.0 beats/15 s, p > 0.05). Patients with SOAG yielded mean beating rates of 4.7 ± 1.7 beats/15 s (p > 0.05). β2-agAAb were seen in 73% of OHT, 82% of pre-POAG, 82% of POAG, and 91% SOAG patients (p < 0.001). Clinical data did not correlate with beating rate (p > 0.05). The robust β2-agAAb seropositivity in patients with OHT, pre-POAG, POAG, and SOAG suggest a primary common role for β2-agAAb starting early in glaucoma pathophysiology and turned out to be a novel marker identifying all patients with increased IOP independent of glaucoma stage and entity.

Is primary open-angle glaucoma an ocular manifestation of systemic disease?

Primary open-angle glaucoma is currently characterized by a pattern of progressive retinal ganglion cell loss that stems from a complex underlying pathophysiology that remains poorly elucidated. The roles of blood flow and intraocular pressure (IOP) in glaucoma pathogenesis have been extensively studied. Further, it has been established that lowering IOP can slow the progression of glaucoma. In addition, a number of influential factors have emerged and gained momentum over the years. Increasing evidence implicates the contributions of low cerebrospinal fluid pressure, autoimmunity, neurodegeneration, and impaired autoregulation towards glaucoma pathophysiology. We aggregate and explore these different camps of thought that have garnered attention over the last few decades, and, in doing so, aim to challenge the long-standing view of glaucoma as a primary disease of the eye. A shift in our perspective towards understanding glaucoma as an ocular manifestation of systemic dysregulation may lead ultimately to better clinical management of the disease.

Agonistic Autoantibodies to the β2-Adrenergic Receptor Involved in the Pathogenesis of Open-Angle Glaucoma

Glaucoma is a frequent ocular disease that may lead to blindness. Primary open-angle glaucoma (POAG) and ocular hypertension (OHT) are common diseases with increased intraocular pressure (IOP), which are mainly responsible for these disorders. Their pathogenesis is widely unknown. We screened the sera of patients with POAG and OHT for the prevalence of autoantibodies (AAb) against G protein-coupled receptors (GPCRs) in comparison to controls. Employing frequency modulation of spontaneously contracting neonatal rat cardiomyocytes in vitro, agonistic GPCR AAb were to be detected in roughly 75% of the patients with POAG and OHT, however, not in controls. Using inhibitory peptides the AAb’ target was identified as β2 adrenergic receptor (β2AR). The AAb interact with the second extracellular loop of β2AR. The peptides 181–187 and 186–192 were identified as binding sites of the AAb within the extracellular loop II. The binding of the AAb to β2ARs was verified by surface-plasmon-resonance analysis. The isotype of the AAb was (immunoglobulin) IgG3. In an additional pilot principal-of-proof study, including four patients with POAG, the removal of the AAb against the β2AR and other immunoglobulins G by immunoadsorption resulted in a transient reduction of IOP. These findings might indicate a possible role of agonistic AAb directed against β2ARs in the dynamics of aqueous humor and might support a contribution of adaptive autoimmunity in the etiopathogenesis of POAG and OHT.

Caspases in retinal ganglion cell death and axon regeneration

Retinal ganglion cells (RGC) are terminally differentiated CNS neurons that possess limited endogenous regenerative capacity after injury and thus RGC death causes permanent visual loss. RGC die by caspase-dependent mechanisms, including apoptosis, during development, after ocular injury and in progressive degenerative diseases of the eye and optic nerve, such as glaucoma, anterior ischemic optic neuropathy, diabetic retinopathy and multiple sclerosis. Inhibition of caspases through genetic or pharmacological approaches can arrest the apoptotic cascade and protect a proportion of RGC. Novel findings have also highlighted a pyroptotic role of inflammatory caspases in RGC death. In this review, we discuss the molecular signalling mechanisms of apoptotic and inflammatory caspase responses in RGC specifically, their involvement in RGC degeneration and explore their potential as therapeutic targets.

A prospective, randomised, placebo-controlled, double-masked, three-armed, multicentre phase II/III trial for the Study of a Topical Treatment of Ischaemic Central Retinal Vein Occlusion to Prevent Neovascular Glaucoma - the STRONG study: study protocol for a randomised controlled trial

Background

Neovascular glaucoma (NVG) is rare, comprising only 3.9% of all glaucoma cases. The most common cause of NVG is ischaemic central retinal vein occlusion (iCRVO). NVG frequently results in blindness and painful end-stage glaucomatous damage leading to the need for enucleation. Currently, there is no preventive therapy for NVG following iCRVO. Rescue treatments have severe drawbacks. Accordingly, there is a great need for preventing the often visually devastating outcomes of NVG. The STRONG study is designed to test whether the topically active anti-angiogenic agent aganirsen is able to inhibit the formation of neovascularisation leading to the development of secondary NVG in eyes with iCRVO. At the same time, STRONG will provide important information on the natural course of iCRVO and NVG in a large and well-characterised cohort of such patients.

Methods/design

This protocol describes a phase II/III, prospective, randomised, placebo-controlled, double-masked, three-armed multicentre study for the investigation of aganirsen, a new topical treatment for iCRVO in order to prevent NVG. The study will evaluate the efficacy of two different doses of this newly developed antisense oligonucleotide formulated in an eye emulsion to avoid new vessel formation by blocking insulin receptor substrate-1 (IRS)-1. This leads to subsequent down-regulation of both angiogenic as well as proinflammatory growth factors such as vascular endothelial growth factor (VEGF) and tumour necrosis factor (TNF). Eligible patients (n = 333) will be treated with topical aganirsen or placebo for a period of 24 weeks. They will also be invited to participate in substudies involving analysis of gonioscopic images, detection of biomarkers for NVG and risk factors for iCRVO.

Discussion

The STRONG study has the potential to offer a new treatment modality for patients suffering from iCRVO with a high risk of developing NVG. The topical administration can reduce patients’ burden and risk related to rescue treatment, such as destructive laser treatment or enucleation, but requires a high level of patient compliance.

Trial registration

EudraCT: 2014-000239-18; ClinicalTrials.gov, ID: NCT02947867. (Registered on 15 October 2016); see also http://strong-nvg.com.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-1861-3) contains supplementary material, which is available to authorized users.

The potential impact of recent insights into proteomic changes associated with glaucoma

INTRODUCTION

Glaucoma, a major ocular neuropathy, is still far from being understood on a molecular scale. Proteomic workflows revealed glaucoma associated alterations in different eye components. By using state-of-the-art mass spectrometric (MS) based discovery approaches large proteome datasets providing important information about glaucoma related proteins and pathways could be generated. Corresponding proteomic information could be retrieved from various ocular sample species derived from glaucoma experimental models or from original human material (e.g. optic nerve head or aqueous humor). However, particular eye tissues with the potential for understanding the disease's molecular pathomechanism remains underrepresented. Areas covered: The present review provides an overview of the analysis depth achieved for the glaucomatous eye proteome. With respect to different eye regions and biofluids, proteomics related literature was found using PubMed, Scholar and UniProtKB. Thereby, the review explores the potential of clinical proteomics for glaucoma research. Expert commentary: Proteomics will provide important contributions to understanding the molecular processes associated with glaucoma. Sensitive discovery and targeted MS approaches will assist understanding of the molecular interplay of different eye components and biofluids in glaucoma. Proteomic results will drive the comprehension of glaucoma, allowing a more stringent disease hypothesis within the coming years.

Plasma citrate concentration: a possible biomarker for glaucoma in children

OBJECTIVES

The main aim of the present study was to examine a possible role of plasma and urine citrate levels as glaucoma indicators in school-aged children with glaucoma diagnosis.

PATIENTS

34 school-aged children with a glaucoma diagnosis (mean age 15.69±1.86 years) were qualified for the study group and 34 patients with no ophthalmological ailments were qualified for the control group (mean age 16.1±1.98 years). Plasma and urine citrate levels in the study and the control group (Kruskal-Wallis test) were compared.

RESULTS

Plasma citrate levels in the study (16.33±4.51 mg/L) and the control group (19.11±3.66 mg/L) were different; the statistical significance (p=0.0036). Plasma citrate concentrations were significantly lower in the study group in comparison with the control group. There were no statistically important differences between the study group (291.12±259.13 mg/24 hours; 275.82±217.57 mg/g) and the control group (434.88±357.66 mg/24 hours; 329.81±383.27 mg/g) including urine citrate level (p=0.052) and urine citrate to creatine ratio (p=0.4667).

CONCLUSION

Plasma citrate concentration might be considered as glaucoma biomarker in paediatric population.

Analysis of Clinical Factors Associated with Retinal Morphological Changes in Patients with Primary Sjögren's Syndrome

Purpose

To investigate clinical factors associated with abnormal retinal morphologies in patients with primary Sjögren's syndrome (pSS).

Methods

One-hundred-thirty patients with pSS who underwent immunoserological tests, minor salivary gland biopsies, and optical coherence tomography examinations were retrospectively analyzed. Risk factors for abnormally reduced peripapillary retinal nerve fiber layer (pRNFL) and macular ganglion cell–inner plexiform layer (mGCIPL) thicknesses were evaluated, as well as the correlation between clinical factors and pRNFL and mGCIPL thicknesses.

Results

Anti-Sjögren's syndrome type B (SSB) antibody positivity (P = 0.048) was identified as a risk factor associated with abnormally reduced pRNFL thickness, and anti-SSB positivity (P = 0.005) and erythrocyte sedimentation rate (ESR) level (P = 0.031) were identified as risk factors associated with an abnormally reduced mGCIPL thickness as revealed by multivariate logistic regression analysis. There was a significant negative correlation between anti-SSB antibody levels and the thickness of pRNFL and mGCIPL. The thicknesses of pRNFL and mGCIPL were significantly reduced in anti-SSB–positive eyes when compared to anti-SSB–negative eyes (P < 0.05). However, histopathologic grading was not associated with the pRNFL and mGCIPL thicknesses.

Conclusion

Anti-SSB antibody positivity and ESR levels may be useful for predicting an abnormally reduced pRNFL or mGCIPL thickness in patients with pSS. Our results may provide clinical evidence to substantiate the association between aberrant autoimmunity and inner retinal changes in patients with pSS.

Autoimmune aspects in glaucoma

The pathogenesis of glaucoma, a common neurodegenerative disease, involves an immunologic component. Studies demonstrate changes of autoantibody concentrations against retinal and optic nerve head antigens in glaucoma patients. Furthermore we found antibody deposits in human glaucomatous retinae in a pro-inflammatory environment. Clinical studies showed up regulated, but also significantly down-regulated autoantibody levels. These antibodies belong to the natural autoimmunity. The upregulation of autoantibodies can be associated with fatal conditions, but several studies demonstrate that natural autoantibodies entail also neuroprotective characteristics and influence the protein expression of neuroretinal cells. A misbalance in the physiological equilibrium may shift from regulatory immunity into a neuroinflammatory degenerative process, what may lead to a predisposition to glaucoma. However, the protective nature of autoantibodies and the molecular mechanisms underlying the very sensitive equilibrium of natural autoimmunity between autoaggression and neuroprotection offer promising target sites for new therapeutic approaches. Finally, the changes in antibody profiles represent a new opportunity as highly sensitive and specific biomarkers for diagnostics purposes.

Analysis of toll-like receptor rs4986790 polymorphism in Saudi patients with primary open angle glaucoma

BACKGROUND

To investigate whether SNP rs4986790 in toll-like receptors (TLRs) is a risk factor for primary open angle glaucoma (POAG) in a Saudi population.

MATERIALS AND METHODS

A cohort of 85 unrelated POAG patients and 95 unrelated control subjects from Saudi Arabia were genotyped utilizing Taq-Man® assay. The association between mutant genotypes and various clinical indices important for POAG was investigated.

RESULTS

Among cases, the normal pattern (A/A) was detected in 70 (82.4%) of the subjects, A/G in 14 (16.5%) and G/G in one subject only (1.2%). Among controls, prevalence of the genotype (A/A) was detected in 86 (90.5%), the (A/G) genotype in 8 (8.4%) and homozygous mutated genotype (G/G) in 1 (1.1%) subjects. Comparing cases to controls, the odds ratio of having heterozygous mutation (A/G) was 2.15 [95% CI: 0.853-5.417], which was not significant (p = 0.114). The odds ratio of having homozygous mutation (G/G) was 1.22 [95% CI: 0.075-19.99], which was statistically non-significant (p = 0.568). Likewise, the presence of the mutated allele (G) was non-significantly different between cases and controls (p = 0.154). Comparing cases to controls as regards co-morbidity with other systemic diseases, there were no statistically significant differences between groups in all assessed diseases except for a family history of glaucoma (p = 0.014) Conclusions: In conclusion, we could not detect any direct link between genotypes or allele frequencies of SNP rs4986790 in the TLR4 gene and POAG. In contrast, genotype (A/A) may be protective against POAG especially among individuals with no family history of glaucoma.

Retinal ganglion cell death in glaucoma: Exploring the role of neuroinflammation

In clinical glaucoma, as well as in experimental models, the loss of retinal ganglion cells occurs by apoptosis. This final event is preceded by inflammatory responses involving the activation of innate and adaptive immunity, with retinal and optic nerve resident glial cells acting as major players. Here we review the current literature on the role of neuroinflammation in neurodegeneration, focusing on the inflammatory molecular mechanisms involved in the pathogenesis and progression of the optic neuropathy.

Protective effect of 14-3-3 antibodies on stressed neuroretinal cells via the mitochondrial apoptosis pathway

Background

Previous studies demonstrate changes of autoantibody concentrations against retinal and optic nerve head antigens in the serum of glaucoma patients in comparison to healthy persons. These antibodies belong to the natural autoimmunity. Previous studies showed up regulated, but also significantly down-regulated autoantibody levels. These antibodies have the ability to influence protein profiles of neuroretinal cells and possibly hold neuroprotective potential, as we have been able to demonstrate before. Aim of this study was to analyse the serum and antibody effect of glaucoma patients on neuroretinal cells in more detail and also determine the impact of antibodies found down-regulated in glaucoma patients on the pathogenesis of the neurodegenerative disease glaucoma.

Methods

Neuroretinal cells (RGC-5) were incubated with serum either from glaucoma patients or healthy controls for 24 h. Mass spectrometric analysis was performed after cell lysis. Furthermore the neuroretinal cells were preincubated with different and concentrations of 14-3-3 antibodies (0.005, 0.1, 0.5, 1, 5 and 10 μg/ml) and then stressed with H2O2, staurosporine or glutamate. Viability tests were performed with crystal violet and ROS tests with DCFH-DA. Antibody location in the cell after antibody incubation was performed with immunoccytochemical methods. Additionally mass spectrometric analysis was performed with the cells after antibody incubation.

Results

Protein expression analysis with Maldi-Orbitrap MS showed changes in the expression level of regulatory proteins in cells incubated with glaucoma serum, e.g. an up-regulation of 14-3-3 and a down-regulation of Calmodulin. After preincubation of the cells with anti-14-3-3 antibody and stressing the cells, we detected an increase in viability of up to 22 % and a decrease in reactive oxygen species (ROS) of up to 31 %. Proteomic 1 analysis involvement of the mitochondrial apoptosis pathway in this protective effect and immunohistochemical analysis showed an antibody uptake in the cells.

Conclusion

We found significant effects of serum antibodies on proteins of neuroretinal cells especially of the mitochondrial apoptosis pathway. Furthermore we detected a protective potential of antibodies down-regulated in glaucoma patients. The changed autoantibodies belong to the natural autoimmunity. We conclude that changes in the natural autoimmunity of patients with glaucoma can negatively impact regulatory functions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12886-015-0044-9) contains supplementary material, which is available to authorized users.

Contribution of microglia-mediated neuroinflammation to retinal degenerative diseases

Retinal degenerative diseases are major causes of vision loss and blindness worldwide and are characterized by chronic and progressive neuronal loss. One common feature of retinal degenerative diseases and brain neurodegenerative diseases is chronic neuroinflammation. There is growing evidence that retinal microglia, as in the brain, become activated in the course of retinal degenerative diseases, having a pivotal role in the initiation and propagation of the neurodegenerative process. A better understanding of the events elicited and mediated by retinal microglia will contribute to the clarification of disease etiology and might open new avenues for potential therapeutic interventions. This review aims at giving an overview of the roles of microglia-mediated neuroinflammation in major retinal degenerative diseases like glaucoma, age-related macular degeneration, and diabetic retinopathy.

Pharmacotherapy of glaucoma

Glaucoma is a group of diseases involving the optic nerve and associated structures, which is characterized by progressive visual field loss and typical changes of the optic nerve head (ONH). The only known treatment of the disease is reduction of intraocular pressure (IOP), which has been shown to reduce glaucoma progression in a variety of large-scale clinical trials. Nowadays, a relatively wide array of topical antiglaucoma drugs is available, including prostaglandin analogues, carbonic anhydrase inhibitors, beta-receptor antagonists, adrenergic agonists, and parasympathomimetics. In clinical routine, this allows for individualized treatment taking risk factors, efficacy, and safety into account. A major challenge is related to adherence to therapy. Sustained release devices may help minimize this problem but are not yet available for clinical routine use. Another hope arises from non-IOP-related treatment concepts. In recent years, much knowledge has been gained regarding the molecular mechanisms that underlie the disease process in glaucoma. This also strengthens the hope that glaucoma therapy beyond IOP lowering will become available. Implementing this concept with clinical trials remains, however, a challenge.

Relationship between retinal morphological findings and autoantibody profile in primary Sjögren's syndrome

PURPOSE

To investigate the morphological changes of the retina measured with the Cirrus high-definition optical coherence tomography in patients with primary Sjögren's syndrome (pSS).

METHODS

One hundred ninety six eyes of 196 patients with pSS and 200 eyes of 200 age and sex-matched normal controls were enrolled. Patients with pSS were divided into four subgroups based on their presence of autoantibodies (antinuclear antibody (ANA), anti-Ro/SSA, and anti-La/SSB). Peripapillary retinal nerve fiber layer (pRNFL) thickness, macular ganglion cell-inner plexiform layer (mGCIPL) thickness, and optic nerve head parameters were compared between groups.

RESULTS

Compared with controls, a significant decrease was observed in the average, inferior, and temporal thicknesses of pRNFL and in the minimum, superotemporal, inferonasal, inferior, and inferotemporal thicknesses of mGCIPL of eyes with pSS (all P < 0.05). In subgroup analyses, all eyes with positive tested autoantibodies [ANA(+), anti-Ro/SSA(+), anti-La/SSB(+)] showed a significant decrease of mGCIPL thicknesses, except for the superonasal portion, compared with eyes with any positivity for autoantibody (all P < 0.05). There was a negative linear relationship between the number of positive autoantibodies and average and inferior pRNFL thicknesses or all mGCIPL parameters, except for the superonasal portion, with a Spearman correlation analysis in patients with pSS (all P < 0.05).

CONCLUSIONS

Compared with controls, eyes with pSS showed thinning of pRNFL and mGCIPL thicknesses. The degree of thinning correlated with increased numbers of the positive autoantibody.

A decade of proteomics studies of glaucomatous neurodegeneration

Glaucoma is a leading cause of blindness; however, limited understanding of the molecular mechanisms involved in optic nerve degeneration hinders the development of improved treatment strategies. Proteomics techniques that combine the protein chemistry, MS, and bioinformatics offer the opportunity to shed light on molecular mechanisms so that new treatment strategies can be developed for immunomodulation, neuroprotection, neurorescue, neuroregeneration, and function gain in glaucoma. The proteomics technologies also hold great promise for biomarker discovery, another important goal of glaucoma research. As much as developing new treatment strategies, molecular biomarkers are strongly needed for early diagnosis of glaucoma, prediction of its prognosis, and monitoring the responses to new treatments. It is now a decade that the proteomics analysis techniques have been using to move glaucoma research forward. This review will focus on valuable applications of proteomics in the field of glaucoma research and highlight the power of this analytical toolbox in translational and clinical research toward better characterization and improved treatment of glaucomatous neurodegeneration and discovery of glaucoma-related molecular biomarkers.

Biomarkers of primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is a primary neuronal disease of the optic nerve without a definable cause, and is often associated with increased intraocular pressure. Worldwide, POAG is the second leading cause of blindness; there are 45 million people today with POAG and bilateral blindness is present in 4.5 million of these. In order to elucidate the possible etiologic factors in POAG, we have cataloged all known biomarkers in the aqueous humor, trabecular meshwork, optic nerve and blood into four categories, namely extracellular matrix (ECM), cell signaling molecules, aging/stress and immunity-related changes. We present a theoretical model to show possible signaling pathways of the ECM, cell signaling and innate immune response through activation of Toll-like receptor 4. Our article suggests that ECM and innate immune biomarkers are the lead candidates for developing the 'POAG biomarker signature'. We suggest that current research is critical to pinpoint the causes of the disease so that new treatment modalities can become available for better regulation of the intraocular pressure and neuroprotection of the optic nerve.

Apoptotic retinal ganglion cell death in an autoimmune glaucoma model is accompanied by antibody depositions

Glaucoma is characterized by death of retinal ganglion cells (RGC), but its cause is still unknown. We used an autoimmune glaucoma model to study (1) apoptosis, (2) antibody occurrence, and (3) gliosis by immunohistochemistry. Rats were immunized with optic nerve homogenate (ONA). At 8 days no significant apoptosis or difference in RGCs was noted, but ONA retinas had a significantly higher GFAP(+) area (p = 0.02). At 14 days, significantly more TUNEL(+) (p = 0.0002) and caspase 3(+) (p = 0.004) were detected in ONA animals, but no difference in RGC density. Distinct IgM and IgG deposits (p = 0.04) were observed in ONA retinas. At 22 days, a significantly higher number of TUNEL(+) cells (p = 0.0002), caspase 3(+) cells (p = 0.0007), and concurrent a lower RGC density (p = 0.04) was noted in ONA animals. IgM and IgG deposits were observed in the ganglion cell layer of ONA retinas. The largest percentage of GFAP(+) area in the ONA group was observed at 22 days (p = 0.02). This data suggest that immunization with ocular antigens leads to apoptotic retinal ganglion cell death. Based on the co-localization of antibody deposits and apoptotic cells, we conclude that antibodies are engaged in eliciting RGC apoptosis in this animal model.

Western blot patterns of serum autoantibodies against optic nerve antigens in dogs with goniodysgenesis-related glaucoma

OBJECTIVE

To investigate whether differences existed between clinically normal dogs and dogs with goniodysgenesis-related glaucoma (GDRG) in serum autoantibodies against optic nerve antigens.

ANIMALS

16 dogs with GDRG, 17 healthy dogs with unremarkable pectinate ligament and iridocorneal angle morphology, and 13 euthanized dogs with no major ocular abnormalities or underlying diseases.

PROCEDURES

Western blotting was performed with optic nerve extracts from the euthanized dogs as an antigen source and serum from clinically normal dogs and dogs with GDRG as a primary antibody (autoantibody) source. Blots were evaluated for presence and density of bands.

RESULTS

Multiple bands were identified on western blots from all dogs with GDRG and all clinically normal dogs, with a high degree of variability among individual dogs. Dogs with GDRG were significantly more likely than healthy dogs to have bands present at 38, 40, and 68 kDa. Dogs with GDRG had significant increases in autoreactivity at 40 and 53 kDa and a significant decrease in autoreactivity at 48 kDa.

CONCLUSIONS AND CLINICAL RELEVANCE

Significant differences in serum autoantibodies against optic nerve antigens were found in dogs with versus without GDRG. Although it remains unclear whether these differences were part of the pathogenesis of disease or were sequelae to glaucomatous changes, these findings provide support for the hypothesis that immune-mediated mechanisms play a role in the development or progression of GDRG. However, the high degree of variability among individual dogs and the considerable overlap between groups suggest that the clinical usefulness of this technique for distinguishing dogs with GDRG from clinically normal dogs is likely limited.

Biomarkers in primary open angle glaucoma

Glaucoma, a leading cause of blindness worldwide, is currently defined as a disturbance of the structural or functional integrity of the optic nerve that causes characteristic atrophic changes in the optic nerve, which may lead to specific visual field defects over time. This disturbance usually can be arrested or diminished by adequate lowering of intraocular pressure (IOP). Glaucoma can be divided roughly into two main categories, ‘ open angle ’ and ‘ closed angle ’ glaucoma.Open angle, chronic glaucoma tends to progress at a slower rate and patients may not notice loss of vision until the disease has progressed significantly. Primary open angle glaucoma(POAG) is described distinctly as a multifactorial optic neuropathy that is chronic and progressive with a characteristic acquired loss of optic nerve fibers. Such loss develops in the presence of open anterior chamber angles, characteristic visual field abnormalities, and IOP that is too high for the healthy eye. It manifests by cupping and atrophy of the optic disc, in the absence of other known causes of glaucomatous disease. Several biological markers have been implicated with the disease. The purpose of this study was to summarize the current knowledge regarding the non-genetic molecular markers which have been predicted to have an association with POAG but have not yet been validated.

Status and perspectives of neuroprotective therapies in glaucoma: the European Glaucoma Society White Paper

Glaucoma, a chronic progressive neuropathy and the most frequent cause of irreversible blindness worldwide, is commonly treated by medication or surgery aimed at lowering intraocular pressure. In view of the limited therapeutic options, the European Glaucoma Society (EGS) sponsored two Think Tank Meetings with the goal of assessing the current status and the overall perspectives for neuroprotective treatment strategies in glaucoma. The results of the meetings are summarized in this EGS White Paper.

Does autoimmunity play a part in the pathogenesis of glaucoma?

Glaucoma is a chronic neurodegenerative disease and one of the leading causes of blindness. Several risk factors have been described, e.g. an elevated intraocular pressure (IOP), oxidative stress or mitochondrial dysfunction. Additionally, alterations in serum antibody profiles of glaucoma patients, upregulation (e.g. anti-HSP60, anti-MBP) and downregulation (e.g. anti-14-3-3), have been described, but it still remains elusive if the autoantibodies seen in glaucoma are an epiphenomenon or causative. However, it is known that elicited autoimmunity causes retinal ganglion cell loss resulting in glaucomatous-like damage and according to the autoaggressive nature of some autoantibodies we found antibody deposits in human glaucomatous retinae in a pro-inflammatory environment. Furthermore, glaucomatous serum has the potential to influence neuroretinal cell regulatory processes. Importantly, we demonstrate that some autoantibodies hold neuroprotective potential for neuroretinal cells. The protective nature of autoantibodies and the molecular mechanisms underlying the very sensitive equilibrium between autoaggression and protection remain subject of future examinations and offer promising target sites for new therapeutic approaches. Additionally, the changes in antibody profiles could be used as highly sensitive and specific marker for diagnostics purposes. Early diagnosis and intervention in risk patients would offer the chance of early treatment and to slow down the progression of glaucoma and delay the resulting blindness.

Enhanced insight into the autoimmune component of glaucoma: IgG autoantibody accumulation and pro-inflammatory conditions in human glaucomatous retina

BACKGROUND

There is accumulating evidence that autoimmune components, such as autoantibodies and autoantibody depositions, play a role in the pathogenesis of neurodegenerative diseases like Alzheimeŕs disease or Multiple Sclerosis. Due to alterations of autoantibody patterns in sera and aqueous humor, an autoimmune component is also assumed in the pathogenesis of glaucoma, a common reason for irreversible blindness worldwide. So far there has been no convincing evidence that autoantibodies are accumulated in the retina of glaucoma patients and that the local immune homeostasis might be affected.

METHODS AND RESULTS

Six human glaucomatous donor eyes and nine samples from donors with no recorded ocular disease were included. Antibody microarrays were used to examine the patterns of pro-inflammatory proteins and complement proteins. Analysis of TNF-α and interleukin levels revealed a slight up-regulation exclusively in the glaucomatous group, while complement protein levels were not altered. IgG autoantibody accumulations and/or cellular components were determined by immunohistology (n = 4 per group). A significantly reduced number of retinal ganglion cells was found in the glaucomatous group (healthy: 104±7 nuclei/mm, glaucoma: 67±9 nuclei/mm; p = 0.0007). Cell loss was accompanied by strong retinal IgG autoantibody accumulations, which were at least twice as high as in healthy subjects (healthy: 5.0±0.5 IgG deposits/100 cells, glaucoma: 9.4±1.9 IgG deposits/100 cells; p = 0.004). CD27(+) cells and CD27(+)/IgG(+) plasma cells were observed in all glaucomatous subjects, but not in controls.

CONCLUSION

This work provides serious evidence for the occurrence of IgG antibody deposition and plasma cells in human glaucomatous retina. Moreover, the results suggest that these IgG deposits occurred in a pro-inflammatory environment which seems to be maintained locally by immune-competent cells like microglia. Thereby, glaucoma features an immunological involvement comparable to other neurodegenerative diseases, but also shows a multifactorial pathomechanism, which diverges and might be linked to the specific nature of both eye and retina.

A proteomics view of the molecular mechanisms and biomarkers of glaucomatous neurodegeneration

Despite improving understanding of glaucoma, key molecular players of neurodegeneration that can be targeted for treatment of glaucoma, or molecular biomarkers that can be useful for clinical testing, remain unclear. Proteomics technology offers a powerful toolbox to accomplish these important goals of the glaucoma research and is increasingly being applied to identify molecular mechanisms and biomarkers of glaucoma. Recent studies of glaucoma using proteomics analysis techniques have resulted in the lists of differentially expressed proteins in human glaucoma and animal models. The global analysis of protein expression in glaucoma has been followed by cell-specific proteome analysis of retinal ganglion cells and astrocytes. The proteomics data have also guided targeted studies to identify post-translational modifications and protein-protein interactions during glaucomatous neurodegeneration. In addition, recent applications of proteomics have provided a number of potential biomarker candidates. Proteomics technology holds great promise to move glaucoma research forward toward new treatment strategies and biomarker discovery. By reviewing the major proteomics approaches and their applications in the field of glaucoma, this article highlights the power of proteomics in translational and clinical research related to glaucoma and also provides a framework for future research to functionally test the importance of specific molecular pathways and validate candidate biomarkers.

Immunoproteomic analysis of potential serum biomarker candidates in human glaucoma

PURPOSE

Evidence supporting the immune system involvement in glaucoma includes increased titers of serum antibodies to retina and optic nerve proteins, although their pathogenic importance remains unclear. This study using an antibody-based proteomics approach aimed to identify disease-related antigens as candidate biomarkers of glaucoma.

METHODS

Serum samples were collected from 111 patients with primary open-angle glaucoma and an age-matched control group of 49 healthy subjects without glaucoma. For high-throughput characterization of antigens, serum IgG was eluted from five randomly selected glaucomatous samples and analyzed by linear ion trap mass spectrometry (LC-MS/MS). Serum titers of selected biomarker candidates were then measured by specific ELISAs in the whole sample pool (including an additional control group of diabetic retinopathy).

RESULTS

LC-MS/MS analysis of IgG elutes revealed a complex panel of proteins, including those detectable only in glaucomatous samples. Interestingly, many of these antigens corresponded to upregulated retinal proteins previously identified in glaucomatous donors (or that exhibited increased methionine oxidation). Moreover, additional analysis detected a greater immunoreactivity of the patient sera to glaucomatous retinal proteins (or to oxidatively stressed cell culture proteins), thereby suggesting the importance of disease-related protein modifications in autoantibody production/reactivity. As a narrowing-down strategy for selection of initial biomarker candidates, we determined the serum proteins overlapping with the retinal proteins known to be up-regulated in glaucoma. Four of the selected 10 candidates (AIF, cyclic AMP-responsive element binding protein, ephrin type-A receptor, and huntingtin) exhibited higher ELISA titers in the glaucomatous sera.

CONCLUSIONS

A number of serum proteins identified by this immunoproteomic study of human glaucoma may represent diseased tissue-related antigens and serve as candidate biomarkers of glaucoma.

Evaluation of presumptive biomarkers of oxidative stress, immune response and apoptosis in primary open-angle glaucoma

There is growing interest on the correlation among oxidative stress, inflammation, apoptosis and primary open-angle glaucoma initiation and progression. Reactive oxygen species are formed in the eyes following a wide variety of stressors, and are largely implicated in glaucoma pathogenesis. Immune-inflammatory response mediators have recently become a target of ophthalmologic concern, including glaucoma. Much attention has been derived to the role of specific pro and anti-apoptotic molecules in glaucoma. This article reviews the early evidence suggesting that reactive oxygen species, immune inflammatory response mediators, and apoptogenic molecules are engaged in glaucoma disease. Moreover, further research concerning the functions, effectors and signaling pathways of the above molecules and their interactions, may lead to specifically develop targeted screening tools based on presumptive biomarkers and surrogate endpoints against primary open-angle glaucoma progression and blindness.

Serum and antibodies of glaucoma patients lead to changes in the proteome, especially cell regulatory proteins, in retinal cells

Purpose

Previous studies show significantly specifically changed autoantibody reactions against retinal antigens in the serum of glaucoma and ocular hypertension (OHT) patients in comparison to healthy people. As pathogenesis of glaucoma still is unknown the aim of this study was to analyze if the serum and antibodies of glaucoma patients interact with neuroretinal cells.

Methods

R28 cells were incubated with serum of patients suffering from primary open angle glaucoma (POAG), normal tension glaucoma (NTG) or OHT, POAG serum after antibody removal and serum from healthy people for 48 h under a normal or an elevated pressure of 15000 Pa (112 mmHg). RGC5 cells were additionally incubated with POAG antibodies under a normal pressure. Protein profiles of the R28 cells were measured with Seldi-Tof-MS, protein identification was performed with Maldi-TofTof-MS. Protein analysis of the RGC5 cells was performed with ESI-Orbitrap MS. Statistical analysis including multivariate statistics, variance component analysis as well as calculating Mahalanobis distances was performed.

Results

Highly significant changes of the complex protein profiles after incubation with glaucoma and OHT serum in comparison to healthy serum were detected, showing specific changes in the cells (e.g. Protein at 9192 Da (p<0.001)). The variance component analysis showed an effect of the serum of 59% on the cells. The pressure had an effect of 11% on the cells. Antibody removal led to significantly changed cell reactions (p<0.03). Furthermore, the incubation with POAG serum and its antibodies led to pro-apoptotic changes of proteins in the cells.

Conclusions

These studies show that the serum and the antibodies of glaucoma patients significantly change protein expressions involved in cell regulatory processes in neuroretinal cells. These could lead to a higher vulnerability of retinal cells towards stress factors such as an elevated IOP and eventually could lead to an increased apoptosis of the cells as in glaucoma.

The Immunology of Glaucoma

The presence of specific antibodies and T cells that are specific in patients with glaucoma supports the idea that the immune system may play an important role in the initiation and/or sustainment of glaucomatous optic neuropathy, at least in some patients. At present, our understanding regarding immunological mechanisms associated with glaucomatous optic neuropathy is far from satisfactory. In this review, we examined evidence suggesting involvement of autoimmune responses in the pathogenesis of glaucoma. These include detection of autoantibodies and T cells and expression of cytokines and stress proteins in patients with glaucoma. Although immune responses are thought to be detrimental, some responses may exert a protective effect against neurodegenerative damage. Likely, the balance between positive and negative regulators determines the survival or demise of cells. It is vital that research continues to elucidate the roles of the immune system in glaucomatous neurodegeneration and the possibility of alternative modalities of treatment. These studies may also provide valuable molecular biomarkers for the diagnosis and identification of a specific cohort of patients with glaucoma, that is, those with normal-tension glaucoma.

Retinal ganglion cell loss is accompanied by antibody depositions and increased levels of microglia after immunization with retinal antigens

Background

Antibodies against retinal and optic nerve antigens are detectable in glaucoma patients. Recent studies using a model of experimental autoimmune glaucoma demonstrated that immunization with certain ocular antigens causes an immun-mediated retinal ganglion cell loss in rats.

Methodology/Principal Findings

Rats immunized with a retinal ganglion cell layer homogenate (RGA) had a reduced retinal ganglion cell density on retinal flatmounts (p = 0.007) and a lower number of Brn3⁺retinal ganglion cells (p = 0.0001) after six weeks. The autoreactive antibody development against retina and optic nerve was examined throughout the study. The levels of autoreactive antibodies continuously increased up to 6 weeks (retina: p = 0.004; optic nerve: p = 0.000003). Additionally, antibody deposits were detected in the retina (p = 0.02). After 6 weeks a reactive gliosis (GFAP density: RGA: 174.7±41.9; CO: 137.6±36.8, p = 0.0006; %GFAP⁺ area: RGA: 8.5±3.4; CO: 5.9±3.6, p = 0.006) as well as elevated level of Iba1⁺ microglia cells (p = 0.003) was observed in retinas of RGA animals.

Conclusions/Significance

Our findings suggest that these antibodies play a substantial role in mechanisms leading to retinal ganglion cell death. This seems to lead to glia cell activation as well as the invasion of microglia, which might be associated with debris clearance.

The immune response in glaucoma: a perspective on the roles of oxidative stress

Neurodegenerative insults and glial activation during glaucomatous neurodegeneration initiate an immune response to restore tissue homeostasis and facilitate tissue cleaning and healing. However, increasing risk factors over a chronic and cumulative period may lead to a failure in the regulation of innate and adaptive immune response pathways and represent a route for conversion of the beneficial immunity into a neuroinflammatory degenerative process contributing to disease progression. Oxidative stress developing through the pathogenic cellular processes of glaucoma, along with the aging-related component of oxidative stress, likely plays a critical role in shifting the physiological equilibrium. This review aims to provide a perspective on the complex interplay of cellular events during glaucomatous neurodegeneration by proposing a unifying scheme that integrates oxidative stress-related risk factors with the altered regulation of immune response in glaucoma.

Immunological mechanisms in glaucoma

Glaucoma is one of the most frequent causes of blindness worldwide. The elevated intraocular pressure does not explain glaucoma in all patients but can be considered as a risk factor of the disease. There are some evidences that autoimmune mechanisms may be involved in this disorder. This review attempts to demonstrate the findings about autoimmune mechanisms in glaucoma patients. Consistent up- and down-regulations in the autoantibody profiles against ocular antigens are present in glaucoma patients. These changes in natural autoimmunity could be found in independent study populations and might be a promising tool for glaucoma detection.

Sera of glaucoma patients show autoantibodies against myelin basic protein and complex autoantibody profiles against human optic nerve antigens

BACKGROUND

The aim of this study was to gain more information about the possible immunological mechanisms in glaucoma. We analyzed the complex autoantibody patterns against human optic nerve antigens in sera of patients with glaucoma and tried to identify important antigens.

METHODS

Sera of 133 patients were included: healthy control subjects (n = 44), primary open-angle glaucoma (n = 44), and normal tension glaucoma patients (n = 45). The sera were tested against Western blots of human optic nerve, and antibody bands were visualized with chloronaphthol. IgG antibody patterns were analyzed by multivariate statistical techniques, and the most significant antigens were identified by mass spectrometry (Maldi-TOFTOF).

RESULTS

All subjects, even healthy ones, showed different and complex antibody patterns. Glaucoma groups showed specific up- and down-regulations of antibody reactivities compared to the control group. The multivariate analysis of discriminance found significant differences (P < 0.05) in IgG antibody profiles against human optic nerve antigens between both glaucoma groups and healthy subjects. The identified antigens include: myelin basic protein (up-regulated in the POAG group), glial fibrillary acidic protein (down-regulated in the glaucoma groups), and vimentin (down-regulated in the glaucoma groups in comparison to controls).

CONCLUSIONS

Using human optic nerve antigen, we were able to demonstrate that complex IgG autoantibody patterns exist in sera of patients with glaucoma. Large correlations between the given and our previous studies using bovine optic nerve antigens could be seen. Furthermore, anti-myelin basic protein antibodies, which can also be detected in patients with multiple sclerosis, were found in sera of glaucoma patients.