Complement mediated apoptosis leads to the loss of retinal ganglion cells in animal model of glaucoma

The complement system and diabetic retinopathy

Diabetic retinopathy (DR) is one of the common microvascular complications of diabetes mellitus and is the main cause of visual impairment in diabetic patients. The pathogenesis of DR is still unclear. The complement system, as an important component of the innate immune system in addition to defending against the invasion of foreign microorganisms, is involved in the occurrence and development of DR through 3 widely recognized complement activation pathways, the complement regulatory system, and many other pathways. Molecules such as C3a, C5a, and membrane attacking complex, as important molecules of the complement system, are involved in the pathologenesus of DR, either through direct damaging effects or by activating cells (microglia, macroglia, etc.) in the retinal microenvironment to contribute to the pathological damage of DR indirectly. We review the integral association of the complement system and DR to further understand the pathogenesis of DR and possibly provide a new strategy for itstreatment.

Addressing neurodegeneration in glaucoma: Mechanisms, challenges, and treatments

Glaucoma is the leading cause of irreversible blindness globally. The disease causes vision loss due to neurodegeneration of the retinal ganglion cell (RGC) projection to the brain through the optic nerve. Glaucoma is associated with sensitivity to intraocular pressure (IOP). Thus, mainstay treatments seek to manage IOP, though many patients continue to lose vision. To address neurodegeneration directly, numerous preclinical studies seek to develop protective or reparative therapies that act independently of IOP. These include growth factors, compounds targeting metabolism, anti-inflammatory and antioxidant agents, and neuromodulators. Despite success in experimental models, many of these approaches fail to translate into clinical benefits. Several factors contribute to this challenge. Firstly, the anatomic structure of the optic nerve head differs between rodents, nonhuman primates, and humans. Additionally, animal models do not replicate the complex glaucoma pathophysiology in humans. Therefore, to enhance the success of translating these findings, we propose two approaches. First, thorough evaluation of experimental targets in multiple animal models, including nonhuman primates, should precede clinical trials. Second, we advocate for combination therapy, which involves using multiple agents simultaneously, especially in the early and potentially reversible stages of the disease. These strategies aim to increase the chances of successful neuroprotective treatment for glaucoma.

In a novel autoimmune and high-pressure glaucoma model a complex immune response is induced

Background

The neurodegenerative processes leading to glaucoma are complex. In addition to elevated intraocular pressure (IOP), an involvement of immunological mechanisms is most likely. In the new multifactorial glaucoma model, a combination of high IOP and optic nerve antigen (ONA) immunization leads to an enhanced loss of retinal ganglion cells accompanied by a higher number of microglia/macrophages in the inner retina. Here, we aimed to evaluate the immune response in this new model, especially the complement activation and the number of T-cells, for the first time. Further, the microglia/macrophage response was examined in more detail.

Methods

Six-week-old wildtype (WT+ONA) and βB1-connective tissue growth factor high-pressure mice (CTGF+ONA) were immunized with 1 mg ONA. A wildtype control (WT) and a CTGF group (CTGF) received NaCl instead. Six weeks after immunization, retinae from all four groups were processed for immunohistology, RT-qPCR, and flow cytometry, while serum was used for microarray analyses.

Results

We noticed elevated numbers of C1q+ cells (classical complement pathway) in CTGF and CTGF+ONA retinae as well as an upregulation of C1qa, C1qb, and C1qc mRNA levels in these groups. While the complement C3 was only increased in CTGF and CTGF+ONA retinae, enhanced numbers of the terminal membrane attack complex were noted in all three glaucoma groups. Flow cytometry and RT-qPCR analyses revealed an enhancement of different microglia/macrophages markers, including CD11b, especially in CTGF and CTGF+ONA retinae. Interestingly, increased retinal mRNA as well as serum levels of the tumor necrosis factor α were found throughout the different glaucoma groups. Lastly, more T-cells could be observed in the ganglion cell layer of the new CTGF+ONA model.

Conclusion

These results emphasize an involvement of the complement system, microglia/macrophages, and T-cells in glaucomatous disease. Moreover, in the new multifactorial glaucoma model, increased IOP in combination with autoimmune processes seem to enforce an additional T-cell response, leading to a more persistent pathology. Hence, this new model mimics the pathomechanisms occurring in human glaucoma more accurately and could therefore be a helpful tool to find new therapeutic approaches for patients in the future.

The Role of Complement Dysregulation in Glaucoma

Glaucoma is a progressive neurodegenerative disease characterized by damage to the optic nerve that results in irreversible vision loss. While the exact pathology of glaucoma is not well understood, emerging evidence suggests that dysregulation of the complement system, a key component of innate immunity, plays a crucial role. In glaucoma, dysregulation of the complement cascade and impaired regulation of complement factors contribute to chronic inflammation and neurodegeneration. Complement components such as C1Q, C3, and the membrane attack complex have been implicated in glaucomatous neuroinflammation and retinal ganglion cell death. This review will provide a summary of human and experimental studies that document the dysregulation of the complement system observed in glaucoma patients and animal models of glaucoma driving chronic inflammation and neurodegeneration. Understanding how complement-mediated damage contributes to glaucoma will provide opportunities for new therapies.

Glaucoma: from pathogenic mechanisms to retinal glial cell response to damage

Glaucoma is a neurodegenerative disease of the retina characterized by the irreversible loss of retinal ganglion cells (RGCs) leading to visual loss. Degeneration of RGCs and loss of their axons, as well as damage and remodeling of the lamina cribrosa are the main events in the pathogenesis of glaucoma. Different molecular pathways are involved in RGC death, which are triggered and exacerbated as a consequence of a number of risk factors such as elevated intraocular pressure (IOP), age, ocular biomechanics, or low ocular perfusion pressure. Increased IOP is one of the most important risk factors associated with this pathology and the only one for which treatment is currently available, nevertheless, on many cases the progression of the disease continues, despite IOP control. Thus, the IOP elevation is not the only trigger of glaucomatous damage, showing the evidence that other factors can induce RGCs death in this pathology, would be involved in the advance of glaucomatous neurodegeneration. The underlying mechanisms driving the neurodegenerative process in glaucoma include ischemia/hypoxia, mitochondrial dysfunction, oxidative stress and neuroinflammation. In glaucoma, like as other neurodegenerative disorders, the immune system is involved and immunoregulation is conducted mainly by glial cells, microglia, astrocytes, and Müller cells. The increase in IOP produces the activation of glial cells in the retinal tissue. Chronic activation of glial cells in glaucoma may provoke a proinflammatory state at the retinal level inducing blood retinal barrier disruption and RGCs death. The modulation of the immune response in glaucoma as well as the activation of glial cells constitute an interesting new approach in the treatment of glaucoma.

Lovastatin promotes the self-renewal of murine and primate spermatogonial stem cells

The spermatogonial stem cell (SSC) niche is critical for SSC maintenance and subsequent spermatogenesis. Numerous reproductive hazards impair the SSC niche, thereby resulting in aberrant SSC self-renewal and male infertility. However, promising agents targeting the impaired SSC niche to promote SSC self-renewal are still limited. Here, we screen out and assess the effects of Lovastatin on the self-renewal of mouse SSCs (mSSCs). Mechanistically, Lovastatin promotes the self-renewal of mSSCs and inhibits its inflammation and apoptosis through the regulation of isoprenoid intermediates. Remarkably, treatment by Lovastatin could promote the proliferation of undifferentiated spermatogonia in the male gonadotoxicity model generated by busulfan injection. Of note, we demonstrate that Lovastatin could enhance the proliferation of primate undifferentiated spermatogonia. Collectively, our findings uncover that lovastatin could promote the self-renewal of both murine and primate SSCs and have implications for the treatment of certain types of male infertility using small compounds.

New insight of complement system in the process of vascular calcification

The complement system defences against pathogenic microbes and modulates immune homeostasis by interacting with the innate and adaptive immune systems. Dysregulation, impairment or inadvertent activation of complement system contributes to the pathogenesis of some autoimmune diseases and cardiovascular diseases (CVD). Vascular calcification is the pivotal pathological basis of CVD, and contributes to the high morbidity and mortality of CVD. Increasing evidences indicate that the complement system plays a key role in chronic kidney diseases, atherosclerosis, diabetes mellitus and aging-related diseases, which are closely related with vascular calcification. However, the effect of complement system on vascular calcification is still unclear. In this review, we summarize current evidences about the activation of complement system in vascular calcification. We also describe the complex network of complement system and vascular smooth muscle cells osteogenic transdifferentiation, systemic inflammation, endoplasmic reticulum stress, extracellular matrix remodelling, oxidative stress, apoptosis in vascular calcification. Hence, providing a better understanding of the potential relationship between complement system and vascular calcification, so as to provide a direction for slowing the progression of this burgeoning health concern.

Enhanced glaucomatous damage accompanied by glial response in a new multifactorial mouse model

Introduction

Glaucoma is a complex, multifactorial neurodegenerative disease, which can lead to blindness if left untreated. It seems that, among others, immune processes, elevated intraocular pressure (IOP), or a combination of these factors are responsible for glaucomatous damage. Here, we combined two glaucoma models to examine if a combination of risk factors (IOP and immune response) results in a more severe damage of retinal ganglion cells (RGCs) and the optic nerves as well as an additional glia activation.

Methods

Six-week-old wildtype (WT+ONA) and βB1-Connective Tissue Growth Factor (CTGF) mice (CTGF+ONA) were immunized with 1 mg ONA (optic nerve antigen). A WT and a CTGF control group (CTGF) received sodium chloride instead. IOP was measured before and every two weeks after immunization. After six weeks, electroretinogram (ERG) measurements were performed. Then, retinae and optic nerves were processed for (immuno-) histology. Further, mRNA levels of corresponding genes in optic nerve and retina were analyzed via RT-qPCR.

Results

Six weeks after immunization, the IOP in CTGF and CTGF+ONA mice was increased. The optic nerve of CTGF+ONA animals displayed the most severe cell inflammation, demyelination, and macroglia activation. Fewer numbers of oligodendrocytes were only observed in WT+ONA optic nerves, while more apoptotic cells triggered by the extrinsic pathway could be revealed in all three glaucoma groups. The number of microglia/macrophages was not altered within the optic nerves of all groups. The loss of neuronal cells, especially RGCs was most pronounced in CTGF+ONA retinae in the central part and this was accompanied by an enhanced activation of microglia/macrophages. Also, Müller cell activation could be noted in CTGF and CTGF+ONA retinae.

Discussion

In this new model, an additive degeneration could be noted in optic nerves as well as in the number of RGCs. These results suggest a potential additive role of high IOP and immune factors in glaucoma development, which will aid for understanding this multifactorial disease more precisely in the future.

Complement C3a receptor inactivation attenuates retinal degeneration induced by oxidative damage

Retinal degeneration causes vision loss and threatens the health of elderly individuals worldwide. Evidence indicates that the activation of the complement system is associated with retinal degeneration. However, the mechanism of complement signaling in retinal degeneration needs to be further studied. In this study, we show that the expression of C3 and C3a receptor (C3ar1) is positively associated with the inflammatory response and retinal degeneration. Genetic deletion of C3 and pharmacological inhibition of C3ar1 resulted in the alleviation of neuroinflammation, prevention of photoreceptor cell apoptosis and restoration of visual function. RNA sequencing (RNA-seq) identified a C3ar1-dependent network shown to regulate microglial activation and astrocyte gliosis formation. Mechanistically, we found that STAT3 functioned downstream of the C3-C3ar1 pathway and that the C3ar1-STAT3 pathway functionally mediated the immune response and photoreceptor cell degeneration in response to oxidative stress. These findings reveal an important role of C3ar1 in oxidative-induced retinal degeneration and suggest that intervention of the C3ar1 pathway may alleviate retinal degeneration.

The Complement System, Aging, and Aging-Related Diseases

The complement system is a part of the immune system and consists of multiple complement components with biological functions such as defense against pathogens and immunomodulation. The complement system has three activation pathways: the classical pathway, the lectin pathway, and the alternative pathway. Increasing evidence indicates that the complement system plays a role in aging. Complement plays a role in inflammatory processes, metabolism, apoptosis, mitochondrial function, and Wnt signaling pathways. In addition, the complement system plays a significant role in aging-related diseases, including Alzheimer’s disease, age-related macular degeneration, and osteoarthritis. However, the effect of complement on aging and aging-related diseases is still unclear. Thus, a better understanding of the potential relationship between complement, aging, and aging-related diseases will provide molecular targets for treating aging, while focusing on the balance of complement in during treatment. Inhibition of a single component does not result in a good outcome. In this review, we discussed the research progress and effects of complement in aging and aging-related diseases.

Serum complement component 3, complement component 4 and complement component 1q levels predict progressive visual field loss in older women with primary angle closure glaucoma

AIM

To evaluate the association between serum levels of complement component (C) 3, C4 and C1q and visual field (VF) loss in patients with primary angle closure glaucoma (PACG).

METHODS

In this prospective cohort study, a total of 308 patients with PACG were included. The patients were followed up every 6 months (at least 2 years), with clinical examination and VF testing. Based on their sex and age, the subjects were stratified into male and female subgroups, and by age at <60 and ≥60 years per subgroup.

RESULTS

One hundred twenty-three (39.94%) patients showed glaucoma VF progression. The serum levels of C3, C4 and C1q were significantly lower (p<0.05) in the progression group compared with the non-progression group in the ≥60 years female subgroup. In female patients with age ≥60 years, (1) lower levels of baseline C3 (HR=0.98, p<0.001), C4 (HR=0.96, p=0.01) and C1q levels (HR=0.99, p=0.003) were associated with a greater risk of VF progression; (2) patients with lower C3 levels had significantly (p<0.05) higher rates of VF loss progression, similar to those with lower C4 and lower C1q levels; and (3) the generalised additive model revealed a negative correlation between baseline C3 (p<0.001), C4 (p<0.001) and C1q (p<0.001) levels with the risk of VF progression. No statistical significance was observed in the male (<60 and ≥60 years) and female (<60 years) subgroups.

CONCLUSION

Decreased C3, C4 and C1q levels at baseline were significantly associated with a greater risk of VF loss progression only in older women with PACG.

Emerging opportunities for C3 inhibition in the eye

The eye presents a unique opportunity for complement component 3 (C3) therapeutics. Drugs can be delivered directly to specific parts of the eye, and growing evidence has established a pivotal role for C3 in age-related macular degeneration (AMD). Emerging data show that C3 may be important to the pathophysiology of other eye diseases as well. This article will discuss the location of C3 expression in the eye as well as the preclinical and clinical data regarding C3's functions in AMD. We will provide a comprehensive review of developing C3 inhibitors for the eye, including the Phase 2 and 3 data for the C3 inhibitor pegcetacoplan as a treatment for the geographic atrophy of AMD. Developing evidence also points toward C3 as a therapeutic target for stages of AMD preceding geographic atrophy. We will also discuss data illuminating C3's relationship to other eye diseases, such as Stargardt disease, diabetic retinopathy, and glaucoma. In addition to being a converging point and centerpiece of the complement cascade, C3 has broad effects as a multifaceted controller of opsonophagocytosis, microglia/macrophage recruitment, and downstream terminal pathway activity. C3 is a crucial player in the pathophysiology of AMD but also seems to have importance in other diseases that are major causes of blindness. Directions for further investigation will be highlighted, as culminating evidence suggests that we may be approaching an era of C3 therapeutics for the eye.

Hypoxic Processes Induce Complement Activation via Classical Pathway in Porcine Neuroretinas

Considering the fact that many retinal diseases are yet to be cured, the pathomechanisms of these multifactorial diseases need to be investigated in more detail. Among others, oxidative stress and hypoxia are pathomechanisms that take place in retinal diseases, such as glaucoma, age-related macular degeneration, or diabetic retinopathy. In consideration of these diseases, it is also evidenced that the immune system, including the complement system and its activation, plays an important role. Suitable models to investigate neuroretinal diseases are organ cultures of porcine retina. Based on an established model, the role of the complement system was studied after the induction of oxidative stress or hypoxia. Both stressors led to a loss of retinal ganglion cells (RGCs) accompanied by apoptosis. Hypoxia activated the complement system as noted by higher C3⁺ and MAC⁺ cell numbers. In this model, activation of the complement cascade occurred via the classical pathway and the number of C1q⁺ microglia was increased. In oxidative stressed retinas, the complement system had no consideration, but strong inflammation took place, with elevated TNF, IL6, and IL8 mRNA expression levels. Together, this study shows that hypoxia and oxidative stress induce different mechanisms in the porcine retina inducing either the immune response or an inflammation. Our findings support the thesis that the immune system is involved in the development of retinal diseases. Furthermore, this study is evidence that both approaches seem suitable models to investigate undergoing pathomechanisms of several neuroretinal diseases.

Immune Responses in the Glaucomatous Retina: Regulation and Dynamics

Glaucoma is a multifactorial disease resulting in progressive vision loss due to retinal ganglion cell (RGC) dysfunction and death. Early events in the pathobiology of the disease include oxidative, metabolic, or mechanical stress that acts upon RGC, causing these to rapidly release danger signals, including extracellular ATP, resulting in micro- and macroglial activation and neuroinflammation. Danger signaling also leads to the formation of inflammasomes in the retina that enable maturation of proinflammatory cytokines such IL-1β and IL-18. Chronic neuroinflammation can have directly damaging effects on RGC, but it also creates a proinflammatory environment and compromises the immune privilege of the retina. In particular, continuous synthesis of proinflammatory mediators such as TNFα, IL-1β, and anaphylatoxins weakens the blood–retina barrier and recruits or activates T-cells. Recent data have demonstrated that adaptive immune responses strongly exacerbate RGC loss in animal models of the disease as T-cells appear to target heat shock proteins displayed on the surface of stressed RGC to cause their apoptotic death. It is possible that dysregulation of these immune responses contributes to the continued loss of RGC in some patients.

Neuroinflammatory Mechanisms of Mitochondrial Dysfunction and Neurodegeneration in Glaucoma

The exact mechanism of retinal ganglion cell loss in the pathogenesis of glaucoma is yet to be understood. Mitochondrial damage-associated molecular patterns (DAMPs) resulting from mitochondrial dysfunction have been linked to Leber's hereditary optic neuropathy and autosomal dominant optic atrophy, as well as to brain neurodegenerative diseases. Recent evidence shows that, in conditions where mitochondria are damaged, a sustained inflammatory response and downstream pathological inflammation may ensue. Mitochondrial damage has been linked to the accumulation of age-related mitochondrial DNA mutations and mitochondrial dysfunction, possibly through aberrant reactive oxygen species production and defective mitophagy. The present review focuses on how mitochondrial dysfunction may overwhelm the ability of neurons and glial cells to adequately maintain homeostasis and how mitochondria-derived DAMPs trigger the immune system and induce neurodegeneration.

Immunological and molecular basics of the primary open angle glaucoma pathomechanism

Glaucoma is a degenerative process of the optic nerve. Increased intraocular pressure is believed to be the main factor leading to the glaucomatous damage. The in vitro and in vivo animal glaucoma research models provide insight into the molecular changes in the retina in response to the injury factor. The damage is a complex process incorporating molecular and immunological changes. Such changes involve NF kB activity and complement activation. The processes affect the human antigen, JNK, MAPK, p53, MT2 and DBA/2J molecular pathways, activate the autophagy processes and compromise neuroprotective mechanisms. Activation and inhibition of immunological responses contribute to cell injury. The immunological mechanisms of glaucomatous degeneration include glial response, the complement, tumor necrosis factor α (TNF-α) pathways and toll-like receptors athways. Oxidative stress and excitotoxicity are factors contributing to cell death in glaucoma. The authors present an up-to-date review of the mechanisms involved and update on research focusing on a possible innovative glaucoma treatment.

Glaucoma and neuroinflammation: An overview

Glaucoma is an optic neuropathy characterized by well-defined optic disc morphological changes (i.e., cup enlargement, neuroretinal border thinning, and notching, papillary vessel modifications) consequent to retinal ganglion cell loss, axonal degeneration, and lamina cribrosa remodeling. These modifications tend to be progressive and are the main cause of functional damage in glaucoma. Despite the latest findings about the pathophysiology of the disease, the exact trigger mechanisms and the mechanism of degeneration of retinal ganglion cells and their axons have not been completely elucidated. Neuroinflammation may play a role in both the development and the progression of the disease as a result of its effects on retinal environment and retinal ganglion cells. We summarize the latest findings about neuroinflammation in glaucoma and examine the connection between risk factors, neuroinflammation, and retinal ganglion cell degeneration.

Increased ratios of complement factors C3a to C3 in aqueous humor and serum mark glaucoma progression

INTRODUCTION

We recently performed a combined analysis of publicly available proteomic studies of aqueous humor (AH) of patients with primary open angle glaucoma (POAG). This analysis revealed changes in complement protein concentrations in the AH of progressive POAG patients, which suggested that the complement system may play a role in POAG progression. As the proteomic studies could not provide information on the activity of the complement system, we addressed this question in the current study.

METHODS

Blood serum and AH were obtained from 30 patients: 10 progressive POAG, 10 stable POAG and, as controls, 10 cataract patients. Glaucoma patients with a visual field Mean Deviation (MD) change of at least 1.0 dB/year were considered progressive; a MD change of less than 0.5 dB/year was considered stable. The ratio between the levels of complement factors C3a and C3 was used as indicator for activation of the complement cascade. The factors were measured with commercially available ELISA kits.

RESULTS

AH levels of complement factors C3 and C3a did not significantly differ between groups. In serum, complement factor C3 did not differ between groups whereas C3a was significantly elevated in progressive POAG patients compared to controls (p < 0.05). The resulting complement C3a/C3 ratio was significantly higher in progressive POAG patients in both AH (p < 0.05) and serum (p < 0.01), and this ratio significantly correlated between the two body fluids (p < 0.001). Furthermore, there was a strong correlation between disease progression and C3a/C3 activation ratio both in AH (p < 0.01) and in serum (p < 0.001). The higher the complement C3a/C3 ratio, the faster the disease progression.

CONCLUSION

Significant increases in AH and serum complement C3a/C3 ratios were observed in progressive POAG patients but not in stable POAG patients. Furthermore, the complement C3a/C3 ratio correlated strongly with the rate of disease progression in both AH and serum. These findings suggest that activation of the complement system plays a role in glaucoma progression and that progressive glaucoma patients may have systemic changes in complement activation.

Complement peptide C3a receptor 1 promotes optic nerve degeneration in DBA/2J mice

BACKGROUND

The risk of glaucoma increases significantly with age and exposure to elevated intraocular pressure, two factors linked with neuroinflammation. The complement cascade is a complex immune process with many bioactive end-products, including mediators of inflammation. Complement cascade activation has been shown in glaucoma patients and models of glaucoma. However, the function of complement-mediated inflammation in glaucoma is largely untested. Here, the complement peptide C3a receptor 1 was genetically disrupted in DBA/2J mice, an ocular hypertensive model of glaucoma, to test its contribution to neurodegeneration.

METHODS

A null allele of C3ar1 was backcrossed into DBA/2J mice. Development of iris disease, ocular hypertension, optic nerve degeneration, retinal ganglion cell activity, loss of RGCs, and myeloid cell infiltration in C3ar1-deficient and sufficient DBA/2J mice were compared across multiple ages. RNA sequencing was performed on microglia from primary culture to determine global effects of C3ar1 on microglia gene expression.

RESULTS

Deficiency in C3ar1 lowered the risk of degeneration in ocular hypertensive mice without affecting intraocular pressure elevation at 10.5 months of age. Differences were found in the percentage of mice affected, but not in individual characteristics of disease progression. The protective effect of C3ar1 deficiency was then overcome by additional aging and ocular hypertensive injury. Microglia and other myeloid-derived cells were the primary cells identified that express C3ar1. In the absence of C3ar1, microglial expression of genes associated with neuroinflammation and other immune functions were differentially expressed compared to WT. A network analysis of these data suggested that the IL10 signaling pathway is a major interaction partner of C3AR1 signaling in microglia.

CONCLUSIONS

C3AR1 was identified as a damaging neuroinflammatory factor. These data help suggest complement activation causes glaucomatous neurodegeneration through multiple mechanisms, including inflammation. Microglia and infiltrating myeloid cells expressed high levels of C3ar1 and are the primary candidates to mediate its effects. C3AR1 appeared to be a major regulator of microglia reactivity and neuroinflammatory function due to its interaction with IL10 signaling and other immune related pathways. Targeting myeloid-derived cells and C3AR1 signaling with therapies is expected to add to or improve neuroprotective therapeutic strategies.

Complement-Mediated Microglial Phagocytosis and Pathological Changes in the Development and Degeneration of the Visual System

The focus of this review is the role of complement-mediated phagocytosis in retinal and neurological diseases affecting the visual system. Complement activation products opsonize synaptic material on neurons for phagocytic removal, which is a normal physiological process during development, but a pathological process in several neurodegenerative diseases and conditions. We discuss the role of complement in the refinement and elimination of synapses in the retina and lateral geniculate nucleus, both during development and in disease states. How complement and aberrant phagocytosis promotes injury to the visual system is discussed primarily in the context of multiple sclerosis, where it has been extensively studied, although the role of complement in visual dysfunction in other diseases such as stroke and traumatic brain injury is also highlighted. Retinal diseases are also covered, with a focus on glaucoma and age-related macular degeneration. Finally, we discuss the potential of complement inhibitory strategies to treat diseases affecting the visual system.

Preservation of optic nerve structure by complement inhibition in experimental glaucoma

Glaucoma is characterized by a progressive damage of the retina and the optic nerve. Despite a huge research interest, the exact pathomechanisms are still unknown. In the experimental autoimmune glaucoma model, rats develop glaucoma-like damage of the retina and the optic nerve after immunization with an optic nerve antigen homogenate (ONA). An early activation of the complement system, even before optic nerve degeneration, was reported in this model. Here, we investigated the effects of a monoclonal antibody against complement factor C5 on optic nerves. Rats were immunized with ONA and compared to controls. In one eye of some ONA animals, the antibody against C5 was intravitreally injected (15 μmol: ONA + C5-I or 25 μmol: ONA + C5-II) before immunization and then every 2 weeks. After 6 weeks, optic nerves were processed for histology (n = 6/group). These analyses demonstrated that the intravitreal therapy reduced the depositions of the membrane attack complex compared to ONA animals (ONA + C5-I: p = 0.005; ONA + C5-II: p = 0.002). Cellular infiltration was significantly reduced in the ONA + C5-I group (p = 0.003), but not in ONA + C5-II tissues (p = 0.41). Furthermore, SMI-32 staining revealed that neurofilament was preserved in both treatment groups compared to ONA optic nerves (both p = 0.002). A decreased amount of microglia was found in treated animals in comparison to the ONA group (ONA + C5-I: p = 0.03; ONA + C5-II: p = 0.009). We observed, for the first time, that a complement system inhibition could prevent optic nerve damage in an autoimmune glaucoma model. Therefore, complement inhibition could serve as a new therapeutic tool for glaucoma.

Associations between Blood Cell Profiles and Primary Open-Angle Glaucoma: A Retrospective Case-Control Study

PURPOSE

We aimed to evaluate whether the neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), lymphocyte-to-monocyte ratio (LMR), and systemic immune inflammation index (SII) were associated with primary open-angle glaucoma (POAG).

MATERIALS AND METHODS

This retrospective case-control study included 240 patients with POAG and 300 age- and sex-matched control subjects. Complete ophthalmological examination and blood count measurements were performed for all subjects.

RESULTS

The values of NLR, PLR, and SII in the POAG group were significantly increased compared with the control group (p < 0.001; p = 0.012; p < 0.001). However, the LMR value was lower in the POAG patients than in the control group (p < 0.001). When we divided the subjects into different age and gender subgroups, the NLR and SII values in the POAG patients were always higher than those in the control group. In the comparison of laboratory parameters in POAG subjects stratified according to severity, we also found that NLR and SII increased with the severity. The receiver operating characteristic (ROC) analysis revealed that the areas under the ROC curve of NLR, PLR, LMR, and SII to predict patients with POAG were found to be 0.627, 0.569, 0.382, and 0.986, respectively. The best cutoff point of NLR was 1.998 with a sensitivity of 59.8% and a specificity of 63.0%, and the SII was 947.365 with a sensitivity of 95.4% and a specificity of 95.7%. Multivariable logistic regression analysis showed that NLR was positively associated with mean deviation; moreover, NLR and SII were independent indicators correlated with POAG (OR 1.502; 95% CI 1.227-1.839; p < 0.001; OR 1.02; 95% CI 1.009-1.021; p < 0.001).

CONCLUSION

We speculated that elevated NLR and SII might serve as readily available inflammatory predictors in POAG patients.

The role of protein disulphide-isomerase A3 as autoantigen in the pathogenesis of autoimmune thyroiditis and related brain damage in adult mice

Autoimmune thyroiditis (AIT)-related brain damage is one of most severe extrathyroidal manifestations of AIT, but the mechanism remains unclear. In this study, we confirmed that protein disulfide-isomerase A3 (PDIA3) is expressed in both thyroid and brain tissues of mouse, and found the significantly increased serum levels of anti-PDIA3 antibody (PDIA3Ab) in classical mouse models of thyroiditis. In addition, we investigated the PDIA3-specific autoimmune reaction in thyroid and brain tissues in a mouse model with high-serum PDIA3Ab induced by immunization with recombinant PDIA3 protein. PDIA3-immunized mice had elevated serum thyrotropin and impaired learning and memory. PDIA3-expressing cells had IgG deposition, and IgG colocalized with C3 in the thyroid and brain tissues of PDIA3-immunized mice, resulting in membrane attack complex formation. Our results suggest that PDIA3 protein may be a common autoantigen shared by the thyroid and brain tissues and involve in the thyroidal and intracerebral damage through activating complement system.

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.

Decreased Serum Levels of Complement C3 Reflect Complement System Dysregulation in Patients With Primary Open-angle Glaucoma: Results From a Pilot Study

PURPOSE

To evaluate the serum complement component (C)3 concentration in patients with primary open-angle glaucoma (POAG) and to investigate the association between C3 levels and POAG severity.

MATERIALS AND METHODS

This study enrolled 190 consecutive POAG patients and 204 normal control subjects. A detailed eye and systematic examination, including intraocular pressure, gonioscopy, fundus photography, A-scan ultrasound, visual field testing, electrocardiograms, x-rays, liver function, renal function, infectious disease, etc., and measurement of serum C3 concentration by immunoturbidimetry, was performed. The subgroups were classified according to age (17 to 29, 30 to 49, 50 to 69, 70+ y), sex, and visual field: mild (MD≤6 dB), moderate (6 dB<MD≤12 dB), and severe (MD>12 dB) glaucoma.

RESULTS

The serum C3 level of the POAG (95.63±17.71 mg/dL) was ∼20.93% lower than that of the control group (115.65±22.19 mg/dL) (P<0.001). A similar result was observed when serum levels of C3 were compared between the POAG and control groups with respect to age and sex. The mean serum C3 level was lowest in the severe POAG group (85.18±19.62 mg/dL), followed by the moderate POAG group (96.62±12.63 mg/dL) and the mild POAG group (110.44±14.89 mg/dL) (P<0.001). Multiple logistic regression analyses revealed a significant correlation between the C3 levels and the vertical cup-disc ratio (B=-0.373, P=0.026), C3 levels and MD (B=-0.546, P=0.001). Logistic regression analyses revealed that serum C3 levels were associated (odds ratio=0.939, 95% CI=0.901-0.979, P=0.003) with severity of POAG.

CONCLUSIONS

The POAG patients had decreased C3 levels, which were further negatively associated with POAG severity, suggesting the involvement of C3 in the pathomechanisms of POAG.

A small peptide antagonist of the Fas receptor inhibits neuroinflammation and prevents axon degeneration and retinal ganglion cell death in an inducible mouse model of glaucoma

BACKGROUND

Glaucoma is a complex, multifactorial disease where apoptosis, microglia activation, and inflammation have been linked to the death of retinal ganglion cells (RGCs) and axon degeneration. We demonstrated previously that FasL-Fas signaling was required for axon degeneration and death of RGCs in chronic and inducible mouse models of glaucoma and that Fas activation triggered RGC apoptosis, glial activation, and inflammation. Here, we investigated whether targeting the Fas receptor with a small peptide antagonist, ONL1204, has anti-inflammatory and neuroprotective effects in a microbead-induced mouse model of glaucoma.

METHODS

Intracameral injection of microbeads was used to elevate intraocular pressure (IOP) in Fas-deficient (Faslpr) mice and WT C57BL/6J mice that received an intravitreal injection of the Fas inhibitor, ONL1204 (2 μg/1 μl) (or vehicle only), on day 0 or day 7 after microbead injection. The IOP was monitored by rebound tonometry, and at 28 days post-microbead injection, Brn3a-stained RGCs and paraphenylenediamine (PPD)-stained axons were analyzed. The effects of ONL1204 on retinal microglia activation and the expression of inflammatory genes were analyzed by immunostaining of retinal flatmounts and quantitative PCR (qPCR).

RESULTS

Rebound tonometry showed equivalent elevation of IOP in all groups of microbead-injected mice. At 28 days post-microbead injection, the RGC and axon counts from microbead-injected Faslpr mice were equivalent to saline-injected (no IOP elevation) controls. Treatment with ONL1204 also significantly reduced RGC death and loss of axons in microbead-injected WT mice when compared to vehicle-treated controls, even when administered after IOP elevation. Confocal analysis of Iba1-stained retinal flatmounts and qPCR demonstrated that ONL1204 also abrogated microglia activation and inhibited the induction of multiple genes implicated in glaucoma, including cytokines and chemokines (GFAP, Caspase-8, TNFα, IL-1β, IL-6, IL-18, MIP-1α, MIP-1β, MIP-2, MCPI, and IP10), components of the complement cascade (C3, C1Q), Toll-like receptor pathway (TLR4), and inflammasome pathway (NLRP3).

CONCLUSIONS

These results serve as proof-of-principal that the small peptide inhibitor of the Fas receptor, ONL1204, can provide robust neuroprotection in an inducible mouse model of glaucoma, even when administered after IOP elevation. Moreover, Fas signaling contributes to the pathogenesis of glaucoma through activation of both apoptotic and inflammatory pathways.

Immune Mediated Degeneration and Possible Protection in Glaucoma

The underlying pathomechanisms for glaucoma, one of the most common causes of blindness worldwide, are still not identified. In addition to increased intraocular pressure (IOP), oxidative stress, excitotoxicity, and immunological processes seem to play a role. Several pharmacological or molecular/genetic methods are currently investigated as treatment options for this disease. Altered autoantibody levels were detected in serum, aqueous humor, and tissue sections of glaucoma patients. To further analyze the role of the immune system, an IOP-independent, experimental autoimmune glaucoma (EAG) animal model was developed. In this model, immunization with ocular antigens leads to antibody depositions, misdirected T-cells, retinal ganglion cell death and degeneration of the optic nerve, similar to glaucomatous degeneration in patients. Moreover, an activation of the complement system and microglia alterations were identified in the EAG as well as in ocular hypertension models. The inhibition of these factors can alleviate degeneration in glaucoma models with and without high IOP. Currently, several neuroprotective approaches are tested in distinct models. It is necessary to have systems that cover underlying pathomechanisms, but also allow for the screening of new drugs. In vitro models are commonly used, including single cell lines, mixed-cultures, and even organoids. In ex vivo organ cultures, pathomechanisms as well as therapeutics can be investigated in the whole retina. Furthermore, animal models reveal insights in the in vivo situation. With all these models, several possible new drugs and therapy strategies were tested in the last years. For example, hypothermia treatment, neurotrophic factors or the blockage of excitotoxity. However, further studies are required to reveal the pressure independent pathomechanisms behind glaucoma. There is still an open issue whether immune mechanisms directly or indirectly trigger cell death pathways. Hence, it might be an imbalance between protective and destructive immune mechanisms. Moreover, identified therapy options have to be evaluated in more detail, since deeper insights could lead to better treatment options for glaucoma patients.

C3- and CR3-dependent microglial clearance protects photoreceptors in retinitis pigmentosa

Silverman et al. demonstrate that complement activation features prominently in retinitis pigmentosa in close association with activated microglia. This response mediates adaptive neuroprotection for photoreceptors by facilitating a C3-CR3–dependent clearance of apoptotic photoreceptors by microglial phagocytosis.

Complement activation has been implicated as contributing to neurodegeneration in retinal and brain pathologies, but its role in retinitis pigmentosa (RP), an inherited and largely incurable photoreceptor degenerative disease, is unclear. We found that multiple complement components were markedly up-regulated in retinas with human RP and the rd10 mouse model, coinciding spatiotemporally with photoreceptor degeneration, with increased C3 expression and activation localizing to activated retinal microglia. Genetic ablation of C3 accelerated structural and functional photoreceptor degeneration and altered retinal inflammatory gene expression. These phenotypes were recapitulated by genetic deletion of CR3, a microglia-expressed receptor for the C3 activation product iC3b, implicating C3-CR3 signaling as a regulator of microglia–photoreceptor interactions. Deficiency of C3 or CR3 decreased microglial phagocytosis of apoptotic photoreceptors and increased microglial neurotoxicity to photoreceptors, demonstrating a novel adaptive role for complement-mediated microglial clearance of apoptotic photoreceptors in RP. These homeostatic neuroinflammatory mechanisms are relevant to the design and interpretation of immunomodulatory therapeutic approaches to retinal degenerative disease.

Heterozygous Meg2 Ablation Causes Intraocular Pressure Elevation and Progressive Glaucomatous Neurodegeneration

Glaucomatous neurodegeneration represents one of the major causes of irreversible blindness worldwide. Yet, the detailed molecular mechanisms that initiate optic nerve damage and retinal ganglion cell (RGC) loss are not fully understood. Members of the protein tyrosine phosphatase (PTP) superfamily are key players in numerous neurodegenerative diseases. In order to investigate the potential functional relevance of the PTP megakaryocyte 2 (Meg2) in retinal neurodegeneration, we analyzed Meg2 knockout (KO) and heterozygous (HET)-synonym protein-tyrosine phosphatase non-receptor type 9 (Ptpn9)-mice. Interestingly, via global microarray and quantitative real-time PCR (RT-qPCR) analyses of Meg2 KO and HET retinae, we observed a dysregulation of several candidate genes that are highly associated with retinal degeneration and intraocular pressure (IOP) elevation, the main risk factor for glaucoma. Subsequent IOP measurements in Meg2 HET mice verified progressive age-dependent IOP elevation. Ultrastructural analyses and immunohistochemistry showed severe optic nerve degeneration accompanied by a dramatic loss of RGCs. Additionally, HET mice displayed reactive micro-/macrogliosis and early activation of the classical complement cascade with pronounced deposition of the membrane attack complex (MAC) in the retina and optic nerve. When treated with latanoprost, significant IOP lowering prevented RGC loss and microglial invasion in HET mice. Finally, electroretinogram (ERG) recordings revealed reduced a- and b-wave amplitudes, indicating impaired retinal functionality in Meg2 HET mice. Collectively, our findings indicate that the heterozygous loss of Meg2 in mice is sufficient to cause IOP elevation and glaucomatous neurodegeneration. Thus, Meg2 HET mice may serve as a novel animal model to study the pathomechanism involved in the onset and progression of glaucoma.

Neuroprotective effects of overexpressed microRNA-200a on activation of glaucoma-related retinal glial cells and apoptosis of ganglion cells via downregulating FGF7-mediated MAPK signaling pathway

Glaucoma is a progressive optic neuropathy and is one of the leading causes of blindness in the industrialized countries. The involvement of microRNAs (miRs) has been implicated in regulating the complex biological responses to changes in intraocular pressure. However, the therapeutic role of miR-200a on glaucoma has not been well studied yet. In this study, we confirmed the role of miR-200a in glaucoma progression and identified the related mechanism. Microarray expression profiles were used to screen the glaucoma-related genes. The relationship between miR-200a and FGF7 was validated by bioinformatics analysis and dual-luciferase reporter gene assay. Glaucoma-related parameters including the expression of CD11b and iNOS, activation of Muller cells, and apoptosis of retinal ganglion cells (RGCs) in the mouse model were measured by immunohistochemistry, MTT assay and TUNEL assay, respectively. miR-200a was reduced in glaucoma, whereas FGF7 was robustly induced. Thereby, we speculated that FGF7 was negatively regulated by miR-200a. Downregulated miR-200a could activate the MAPK signaling pathway following elevations in ERK, JNK, p38 and Bax expression and reduction in Bcl-2 expression. In the mouse model, downregulated miR-200a increased the expression of CD11b and iNOS and the apoptosis of RGCs, but stimulated the inactivation of Muller cells. However, the above-mentioned alternations induced by downregulated miR-200a were reversed after FGF7 repression. miR-200a can inhibit the FGF7-mediated MAPK signaling pathway and play a protective role on improving the glaucoma-induced optical nerve injury.

Modulation of the Immune System for the Treatment of Glaucoma

Background:

At present intraocular pressure (IOP) lowering therapies are the only approach to treat glaucoma. Neuroprotective strategies to protect the retinal ganglion cells (RGC) from apoptosis are lacking to date. Substantial amount of research concerning the role of the immune system in glaucoma has been performed in the recent years. This review aims to analyse changes found in the peripheral immune system, as well as selected local changes of retina immune cells in the glaucomatous retina.

Methods:

By dividing the immune system into the innate and the adaptive immune system, a systematic literature research was performed to find recent approaches concerning the modulation of the immune system in the context of glaucoma. Also ClinicalTrials.gov was assessed to identify studies with a translational context.

Results:

We found that some aspects of the immune system, such as changes in antibody levels, changes in toll like receptor signalling, T cells and retinal microglial cells, experience more research activity than other areas such as changes in dendritic cells or macrophages. Briefly, results from clinical studies revealed altered immunoreactivities against retinal and optic nerve antigens in sera and aqueous humor of glaucoma patients and point toward an autoimmune involvement in glaucomatous neurodegeneration and RGC death. IgG accumulations along with plasma cells were found localised in human glaucomatous retinae in a pro-inflammatory environment possibly maintained by microglia. Animal studies show that antibodies (e.g. anti- heat shock protein 60 and anti-myelin basic protein) elevated in glaucoma patients provoke autoaggressive RGC loss and are associated with IgG depositions and increased microglial cells. Also, studies addressing changes in T lymphocytes, macrophages but also local immune responses in the retina have been performed and also hold promising results.

Conclusions:

This recapitulation of recent literature demonstrates that the immune system definitely plays a role in the pathogenesis of glaucoma. Multiple changes in the peripheral innate as well as adaptive immune system have been detected and give room for further research concerning valuable therapeutic targets. We conclude that there still is a great need to bring together the results derived from basic research analysing different aspects of the immune system in glaucoma to understand the immune context of the disease. Furthermore local immune changes in the retina of glaucoma patients still leave room for further therapeutic targets

Microglia in the Retina: Roles in Development, Maturity, and Disease

Microglia, the primary resident immune cell type, constitute a key population of glia in the retina. Recent evidence indicates that microglia play significant functional roles in the retina at different life stages. During development, retinal microglia regulate neuronal survival by exerting trophic influences and influencing programmed cell death. During adulthood, ramified microglia in the plexiform layers interact closely with synapses to maintain synaptic structure and function that underlie the retina's electrophysiological response to light. Under pathological conditions, retinal microglia participate in potentiating neurodegeneration in diseases such as glaucoma, retinitis pigmentosa, and age-related neurodegeneration by producing proinflammatory neurotoxic cytokines and removing living neurons via phagocytosis. Modulation of pathogenic microglial activation states and effector mechanisms has been linked to neuroprotection in animal models of retinal diseases. These findings have led to the design of early proof-of-concept clinical trials with microglial modulation as a therapeutic strategy.

Subtype-specific response of retinal ganglion cells to optic nerve crush

Glaucoma is a neurodegenerative disease with retinal ganglion cell (RGC) loss, optic nerve degeneration and subsequent vision loss. There are about 30 different subtypes of RGCs whose response to glaucomatous injury is not well characterized. The purpose of this study was to evaluate the response of 4 RGC subtypes in a mouse model of optic nerve crush (ONC). In this study, we also evaluated the pattern of axonal degeneration in RGC subtypes after nerve injury. We found that out of the 4 subtypes, transient-Off α RGCs are the most susceptible to injury followed by On-Off direction selective RGCs (DSGC). Non-image forming RGCs are more resilient with ipRGCs exhibiting the most resistance of them all. In contrast, axons degenerate irrespective of their retinal soma after ONC injury. In conclusion, we show that RGCs have subtype specific cell death response to ONC injury and that RGC axons disintegrate in an autonomous fashion undergoing Wallerian degeneration. These discoveries can further direct us towards effective diagnostic and therapeutic approaches to treat optic neuropathies, such as glaucoma.

The innate immunity of guinea pigs against highly pathogenic avian influenza virus infection

H5N1 avian influenza viruses are a major pandemic concern. In contrast to the highly virulent phenotype of H5N1 in humans and many animal models, guinea pigs do not typically display signs of severe disease in response to H5N1 virus infection. Here, proteomic and transcriptional profiling were applied to identify host factors that account for the observed attenuation of A/Tiger/Harbin/01/2002 (H5N1) virulence in guinea pigs. RIG-I and numerous interferon stimulated genes were among host proteins with altered expression in guinea pig lungs during H5N1 infection. Overexpression of RIG-I or the RIG-I adaptor protein MAVS in guinea pig cell lines inhibited H5N1 replication. Endogenous GBP-1 expression was required for RIG-I mediated inhibition of viral replication upstream of the activity of MAVS. Furthermore, we show that guinea pig complement is involved in viral clearance, the regulation of inflammation, and cellular apoptosis during influenza virus infection of guinea pigs. This work uncovers features of the guinea pig innate immune response to influenza that may render guinea pigs resistant to highly pathogenic influenza viruses.

The role of microglia in the progression of glaucomatous neurodegeneration- a review

Glaucoma is a serious leading cause of irreversible blindness worldwide. Reducing intraocular pressure (IOP) does not always stop glaucomatous neurodegeneration and the optic nerve may continue to be damaged in the normal IOP. Microglial activity has been recognized to play essential roles in pathogenesis of the central nervous system (CNS) as well as retinal ganglion cell (RGC) survival. The relationship between the neurodegeneration and the microglia cells in glaucoma is very complicated and still remains unclear. In the present review, we summarize the recent studies of mechanisms of microglia in glaucoma neurodegeneration, which might provide new ways to treat glaucoma.

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.

Intravitreal injection of β-crystallin B2 improves retinal ganglion cell survival in an experimental animal model of glaucoma

Purpose of this study was to investigate firstly specific proteomic changes within the retina in the course of an animal glaucoma model and to identify secondly new approaches for neuroprotective, therapeutic options in glaucoma by addressing those specific changes. Intraocular pressure was elevated through cauterization of episcleral veins in adult Sprague Dawley rats. Molecular and morphological changes were surveyed using mass spectrometry, optical coherence tomography as well as immunohistochemical cross section- and flat mount stainings. By quantifying more than 1500 retinal proteins, it was found that the HspB5 protein and numerous beta-crystallins showed a uniform and unique shifting expression pattern as a result of different periods of elevated IOP exposure. Crystallins showed a significant downregulation (p<0.05) after 3 weeks of elevated IOP and an upregulation after 7 weeks. Counteracting those typical changes, an intravitreal injection of β-crystallin B2 at the time of IOP elevation was found to reduce retinal ganglion cell loss (p<0.05), decrease of the retinal nerve fiber layer (p<0.05) and impairment of the optic nerve. Ultimately, proteomic data revealed that β-crystallin B2 might influence calcium-depended cell signaling pathways with severe effect on apoptosis and gene regulation. In this context especially annexin A5, calcium-transporting ATPase 1 and various histone proteins seem to play a major role.

Targeting the complement system for the management of retinal inflammatory and degenerative diseases

The retina, an immune privileged tissue, has specialized immune defense mechanisms against noxious insults that may exist in diseases such as age-related macular degeneration (AMD), diabetic retinopathy (DR), uveoretinitis and glaucoma. The defense system consists of retinal innate immune cells (including microglia, perivascular macrophages, and a small population of dendritic cells) and the complement system. Under normal aging conditions, retinal innate immune cells and the complement system undergo a low-grade activation (parainflammation) which is important for retinal homeostasis. In disease states such as AMD and DR, the parainflammatory response is dysregulated and develops into detrimental chronic inflammation. Complement activation in the retina is an important part of chronic inflammation and may contribute to retinal pathology in these disease states. Here, we review the evidence that supports the role of uncontrolled or dysregulated complement activation in various retinal degenerative and angiogenic conditions. We also discuss current strategies that are used to develop complement-based therapies for retinal diseases such as AMD. The potential benefits of complement inhibition in DR, uveoretinitis and glaucoma are also discussed, as well as the need for further research to better understand the mechanisms of complement-mediated retinal damage in these disease states.

Simultaneous Complement Response via Lectin Pathway in Retina and Optic Nerve in an Experimental Autoimmune Glaucoma Model

Glaucoma is a multifactorial disease and especially mechanisms occurring independently from an elevated intraocular pressure (IOP) are still unknown. Likely, the immune system contributes to the glaucoma pathogenesis. Previously, IgG antibody depositions and retinal ganglion cell (RGC) loss were found in an IOP-independent autoimmune glaucoma model. Therefore, we investigated the possible participation of the complement system in this model. Here, rats were immunized with bovine optic nerve homogenate antigen (ONA), while controls (Co) received sodium chloride (n = 5–6/group). After 14 days, RGC density was quantified on flatmounts. No changes in the number of RGCs could be observed at this point in time. Longitudinal optic nerve sections were stained against the myelin basic protein (MBP). We could note few signs of degeneration processes. In order to detect distinct complement components, retinas and optic nerves were labeled with complement markers at 3, 7, 14, and 28 days and analyzed. Significantly more C3 and MAC depositions were found in retinas and optic nerves of the ONA group. These were already present at day 7, before RGC loss and demyelination occurred. Additionally, an upregulation of C3 protein was noted via Western Blot at this time. After 14 days, quantitative real-time PCR revealed significantly more C3 mRNA in the ONA retinas. An upregulation of the lectin pathway-associated mannose-serine-protease-2 (MASP2) was observed in the retinas as well as in the optic nerves of the ONA group after 7 days. Significantly more MASP2 in retinas could also be observed via Western Blot analyses at this point in time. No effect was noted in regard to C1q. Therefore, we assume that the immunization led to an activation of the complement system via the lectin pathway in retinas and optic nerves at an early stage in this glaucoma model. This activation seems to be an early response, which then triggers degeneration. These findings can help to develop novel therapy strategies for glaucoma patients.

Visual and Ocular Manifestations of Alzheimer's Disease and Their Use as Biomarkers for Diagnosis and Progression

Alzheimer's disease (AD) is the most common form of dementia affecting the growing aging population today, with prevalence expected to rise over the next 35 years. Clinically, patients exhibit a progressive decline in cognition, memory, and social functioning due to deposition of amyloid β (Aβ) protein and intracellular hyperphosphorylated tau protein. These pathological hallmarks of AD are measured either through neuroimaging, cerebrospinal fluid analysis, or diagnosed post-mortem. Importantly, neuropathological progression occurs in the eye as well as the brain, and multiple visual changes have been noted in both human and animal models of AD. The eye offers itself as a transparent medium to cerebral pathology and has thus potentiated the development of ocular biomarkers for AD. The use of non-invasive screening, such as retinal imaging and visual testing, may enable earlier diagnosis in the clinical setting, minimizing invasive and expensive investigations. It also potentially improves disease management and quality of life for AD patients, as an earlier diagnosis allows initiation of medication and treatment. In this review, we explore the evidence surrounding ocular changes in AD and consider the biomarkers currently in development for early diagnosis.

[Complement activation after induction of ocular hypertension in an animal model]

BACKGROUND

Although an elevated intraocular pressure (IOP) is known as the main risk factor for glaucoma, many studies also showed an involvement of the immune system in this disease. In this study we investigated if a moderate increase in IOP leads to activation of the complement system.

METHODS

The IOP was elevated experimentally in the left eye of rats, whereas the fellow eye served as the control. The IOP was measured at regular intervals. The number of retinal ganglion cells (RGC) was quantified via NeuN staining. To evaluate the activation of the complement system staining for C3, membrane attack complex (MAC), and mannose-binding lectin (MBL) was performed. Furthermore, we investigated possible glia activation (GFAP and vimentin) and apoptosis (Bax).

RESULTS

A moderate elevation of the IOP was noted from day 11 after induction of ocular hypertension (OHT) until the end of the study (28 days, p = 0.0005). In the OHT-group significantly fewer RGCs (p = 0.02) were detected. Additionally, we noted significant C3 and MAC activation in the ganglion cell layer (C3, p = 0.001 and MAC, p = 0.02) as well as in the total retina (C3, p = 0.002 and MAC, p = 0.012). An activation via the lectin pathway by MBL staining could not be detected (p = 0.40). At this point in time no alterations with regard to glia cells were noted (GFAP, p = 0.97 and vimentin, p = 0.99). No apoptosis via Bax pathway could be observed (p = 0.90).

CONCLUSION

The results suggest that the complement system is involved in the loss of RGCs even by a moderate IOP elevation which was indicated by significantly more C3 and MAC depositions in the OHT group.

[CFH gene polymorphism in primary open-angle glaucoma patients]

AIM

to study the CFH T402H polymorphism in glaucoma patients and controls.

MATERIAL AND METHODS

Genetic analysis was performed in 68 patients with primary open-angle glaucoma (POAG) of various severity. The control group consisted of 30 participants. Venous whole blood samples were obtained. From them, leukocytes were isolated and human genomic DNA extracted for further PCR.

RESULTS

None of the patients from either group was homozygous for the 402H allele. With ganglion cells death (i.e. at later stages of the disease), the percentage of homozygotes that carry no CFH polymorphism increases up to 65%, while that of heterozygotes decreases down to 35%.

CONCLUSION

As shown, most of early and advanced POAG patients are heterozygotes. At these stages of the disease own ganglion cells are very likely to be damaged. Further progression, however, is associated with a gradual decrease in heterozygotes (down to 35%) due to a substantial loss of neuroepithelial cells and suppression of the autoimmune response which has lost its target.

Unraveling the molecular repertoire of tears as a source of biomarkers: beyond ocular diseases

Proteomics and metabolomics investigations of body fluids present several challenges for biomarker discovery of several diseases. The search for biomarkers is actually conducted in different body fluids, even if the ideal biomarker can be found in an easily accessible biological fluid, because, if validated, the biomarker could be sought in the healthy population. In this regard, tears could be considered an optimum material obtained by noninvasive procedures. In the past years, the scientific community has become more interested in the study of tears for the research of new biomarkers not only for ocular diseases. In this review, we provide a discussion on the current state of biomarkers research in tears and their relevance for clinical practice, and report the main results of clinical proteomics studies on systemic and eye diseases. We summarize the main methods for tear samples analyses and report recent advances in "omics" platforms for tears investigations. Moreover, we want to take stock of the emerging field of metabolomics and lipidomics as a new and integrated approach to study protein-metabolites interplay for biomarkers research, where tears represent a still unexplored and attractive field.

The complex role of neuroinflammation in glaucoma

Glaucoma is a multifactorial neurodegenerative disorder affecting 80 million people worldwide. Loss of retinal ganglion cells and degeneration of their axons in the optic nerve are the major pathological hallmarks. Neuroinflammatory processes, inflammatory processes in the central nervous system, have been identified in human glaucoma and in experimental models of the disease. Furthermore, neuroinflammatory responses occur at early stages of experimental glaucoma, and inhibition of certain proinflammatory pathways appears neuroprotective. Here, we summarize the current understanding of neuroinflammation in the central nervous system, with emphasis on events at the optic nerve head during early stages of glaucoma.

Sublytic C5b-9 triggers glomerular mesangial cell apoptosis via XAF1 gene activation mediated by p300-dependent IRF-1 acetylation

The apoptosis of glomerular mesangial cells (GMCs) in rat Thy-1 nephritis (Thy-1N), a model of human mesangioproliferative glomerulonephritis (MsPGN), is accompanied by sublytic C5b-9 deposition. However, the mechanism by which sublytic C5b-9 induces GMC apoptosis is unclear. In the present studies, the effect of X-linked inhibitor of apoptosis-associated factor 1 (XAF1) expression on GMC apoptosis and the role of p300 and interferon regulatory factor-1 (IRF-1) in mediating XAF1 gene activation were determined, both in the GMCs induced by sublytic C5b-9 (in vitro) and in the renal tissues of rats with Thy-1N (in vivo). The in vitro studies demonstrated that IRF-1-enhanced XAF1 gene activation and its regulation by p300-mediated IRF-1 acetylation were involved in GMC apoptosis induced by sublytic C5b-9. The element of IRF-1 binding to XAF1 promoter and two acetylated sites of IRF-1 protein were also revealed. In vivo, silence of p300, IRF-1 or XAF1 genes in the renal tissues diminished GMC apoptosis and secondary GMC proliferation as well as urinary protein secretion in Thy-1N rats. Together, these data implicate that sublytic C5b-9 induces the expression of both p300 and IRF-1, as well as p300-dependent IRF-1 acetylation that may contribute to XAF1 gene activation and subsequent GMC apoptosis in Thy-1N rats.

Complement expression in the retina is not influenced by short-term pressure elevation

PURPOSE

To determine whether short-term pressure elevation affects complement gene expression in the retina in vitro and in vivo.

METHODS

Muller cell (TR-MUL5) cultures and organotypic retinal cultures from adult mice and monkeys were subjected to either 24-h or 72-h of pressure at 0, 15, 30, and 45 mmHg above ambient. C57BL/6 mice were subjected to microbead-induced intraocular pressure (IOP) elevation for 7 days. RNA and protein were extracted and used for analysis of expression levels of complement component genes and complement component 1, q subcomponent (C1q) and complement factor H (CFH) immunoblotting.

RESULTS

mRNA levels of complement genes and C1q protein levels in Muller cell cultures remained the same for all pressure levels after exposure for either 24 or 72 h. In primate and murine organotypic cultures, pressure elevation did not produce changes in complement gene expression or C1q and CFH protein levels at either the 24-h or 72-h time points. Pressure-related glial fibrillary acidic protein (GFAP) mRNA expression changes were detected in primate retinal organotypic cultures (analysis of variance [ANOVA]; p<0.05). mRNA expression of several other genes changed as a result of time in culture. Eyes subjected to microbead-induced IOP elevation had no differences in mRNA expression of complement genes and C1q protein levels (ANOVA; p>0.05 for both) with contralateral control and naïve control eyes.

CONCLUSIONS

Short-term elevation of pressure in vitro as well as short-term (1 week) IOP elevation in vivo does not seem to dramatically alter complement system gene expression in the retina. Prolonged expression to elevated pressure may be necessary to affect the complement system expression.

Deficiency of complement component 5 ameliorates glaucoma in DBA/2J mice

Background

Glaucoma is an age-related neurodegenerative disorder involving the loss of retinal ganglion cells (RGCs), which results in blindness. Studies in animal models have shown that activation of inflammatory processes occurs early in the disease. In particular, the complement cascade is activated very early in DBA/2J mice, a widely used mouse model of glaucoma. A comprehensive analysis of the role of the complement cascade in DBA/2J glaucoma has not been possible because DBA/2J mice are naturally deficient in complement component 5 (C5, also known as hemolytic complement, Hc), a key mediator of the downstream processes of the complement cascade, including the formation of the membrane attack complex.

Methods

To assess the role of C5 in DBA/2J glaucoma, we backcrossed a functional C5 gene from strain C57BL/6J to strain DBA/2J for at least 10 generations. The prevalence and severity of glaucoma was evaluated using ocular examinations, IOP measurements, and assessments of optic nerve damage and RGC degeneration. To understand how C5 affects glaucoma, C5 expression was assessed in the retinas and optic nerves of C5-sufficient DBA/2J mice, using immunofluorescence.

Results

C5-sufficient DBA/2J mice developed a more severe glaucoma at an earlier age than standard DBA/2J mice, which are therefore protected by C5 deficiency. Components of the membrane attack complex were found to be deposited at sites of axonal injury in the optic nerve head and associated with RGC soma in the retina.

Conclusion

C5 plays an important role in glaucoma, with its deficiency lessening disease severity. These results highlight the importance of fully understanding the role of the complement cascade in neurodegenerative diseases. Inhibiting C5 may be beneficial as a therapy for human glaucoma.