Retinal Ganglion Cell Death In Glaucoma Research Articles

IL1A enhances TNF-induced retinal ganglion cell death.

Glaucoma is a neurodegenerative disease that leads to the death of retinal ganglion cells (RGCs). A growing body of literature suggests a role for neuroinflammation in RGC death after glaucoma-relevant insults. For instance, it was shown that deficiency of three proinflammatory cytokines, complement component 1, subcomponent q ( C1q ), interleukin 1 alpha ( Il1a ), and tumor necrosis factor ( Tnf ), resulted in near complete protection of RGCs after two glaucoma-relevant insults, optic nerve injury and ocular hypertension. While TNF and C1Q have been extensively investigated in glaucoma-relevant model systems, the role of IL1A in RGC is not as well defined. Thus, we investigated the direct neurotoxicity of IL1A on RGCs in vivo. Intravitreal injection of IL1A did not result in RGC death at either 14 days or 12 weeks after insult. Consistent with previous studies, TNF injection did not result in significant RGC loss at 14 days but did after 12 weeks. Interestingly, IL1A+TNF resulted in a relatively rapid RGC death, driving significant RGC loss two weeks after injection. JUN activation and SARM1 have been implicated in RGC death in glaucoma and after cytokine insult. Using mice deficient in JUN or SARM1, we show RGC loss after IL1A+TNF insult is JUN-independent and SARM1-dependent. Furthermore, RNA-seq analysis showed that RGC death by SARM1 deficiency does not stop the neuroinflammatory response to IL1A+TNF. These findings indicate that IL1A can potentiate TNF-induced RGC death after combined insult is likely driven by a SARM1-dependent RGC intrinsic signaling pathway.

Müller cells under hydrostatic pressure modulate retinal cell survival via TRPV1/PLCγ1 complex-mediated calcium influx in experimental glaucoma.

Glaucoma, an irreversible blinding eye disease, is currently unclear whose pathological mechanism is. This study investigated how transient receptor potential cation channel subfamily V member 1 (TRPV1), 1-phosphatidylinositol 4,5-bisphosphate phosphodiesterase gamma-1 (PLCγ1), and P2X purinoceptor 7 (P2X7) modulate the levels of intracellular calcium ions (Ca2+) and adenosine triphosphate (ATP) in Müller cells and retinal ganglion cells (RGCs) under conditions of elevated intraocular pressure (IOP). Müller cells were maintained at hydrostatic pressure (HP). TRPV1- and PLCG1-silenced Müller cells and P2X7-silenced RGCs were constructed by transfection with short interfering RNA (siRNAs). RGCs were cultured with the conditioned media of Müller cells under HP. A mouse model of chronic ocular hypertension (COH) was established and used to investigate the role of TRPV1 in RGCs in vivo. Müller cells and RGCs were analyzed by ATP release assays, intracellular calcium assays, CCK-8 assays, EdU (5-ethynyl-2'-deoxyuridine) staining, TUNEL staining, flow cytometry, and transmission electron microscopy. In vivo changes in inner retinal function were evaluated by hematoxylin and eosin (H&E) staining and TUNEL staining. Western blot analyses were performed to measure the levels of related proteins. Our data showed that HP increased the levels of ATP and Ca2+ influx in Müller cells, and those increases were accompanied by the upregulation of TRPV1 and p-PLCγ1 expression. Suppression of TRPV1 or PLCG1 expression in Müller cells significantly decreased the ATP levels and intracellular Ca2+ accumulation induced by HP. Knockdown of TRPV1, PLCG1, or P2X7 significantly decreased apoptosis and autophagy in RGCs cultured in the conditioned media of HP-treated Müller cells. Moreover, TRPV1 silencing decreased RGC apoptosis and autophagy in the in vivo model of COH. Collectively, inhibition of TRPV1/PLCγ1 and P2X7 expression may be a useful therapeutic strategy for managing RGC death in glaucoma.

Müller glial cells located in the peripheral retina are more susceptible to high pressure: implications for glaucoma

BackgroundGlaucoma, a progressive neurodegenerative disease, is a leading cause of irreversible vision loss worldwide. This study aims to elucidate the critical role of Müller glia (MG) in the context of retinal ganglion cell (RGC) death, particularly focusing on the influence of peripheral MG sensitivity to high pressure (HP).MethodsCo-cultures of porcine RGCs with MG were isolated from both the central and peripheral regions of pig retinas and subjected to both normal and HP conditions. Mass spectrometry analysis of the MG-conditioned medium was conducted to identify the proteins released by MG under all conditions.ResultsPeripheral MG were found to secrete a higher quantity of neuroprotective factors, effectively promoting RGC survival under normal physiological conditions. However, under HP conditions, co-cultures with peripheral MG exhibited impaired RGC survival. Moreover, under HP conditions, peripheral MG significantly upregulated the secretion of proteins associated with apoptosis, oxidative stress, and inflammation.ConclusionsThis study provides robust evidence suggesting the involvement of MG in RGC death in glaucoma, thus paving the way for future therapeutic investigations.

Saffron and glaucoma. Effects of active components of an old natural neuroprotector

Glaucoma is a neurodegenerative disease characterized by the loss of retinal ganglion cells (RGCs). An increase in the intraocular pressure is the principal risk factor but controlling this pressure does not always prevent glaucomatous damage, so other harmful factors would be implicated in this pathologic process. Several mechanisms have been proposed that leads to the RGC death in glaucoma, including glutamate excitotoxicity, aggregation of misfolded proteins, mitochondrial dysfunction, oxidative stress, neurotrophic deprivation, and neuroinflammation, among others. Therefore, early diagnosis of neurodegeneration, understanding of its pathogenic mechanisms, and the development of new neuroprotective therapies represent major challenges for treating this disease.During the inflammatory process that occurs in glaucoma, retinal glial cells, both microglia and macroglia (Müller cells and astrocytes), become activated and release factors that can be neuroprotective in some cases and neurodegenerative in others. Cytokine‐ and chemokine‐mediated signalling engages in the neuroinflammatory process that leads to retinal ganglion cell (RGC) damage in glaucoma. Thus, a substance with anti‐inflammatory activity may protect against RGC degeneration.Increasing evidence from both experimental models and clinical studies in patients supports the neuroprotective effect of saffron components in neurodegenerative conditions and in retinal neurodegenerative pathologies, due to its important anti‐inflammatory, anti‐apoptotic, and antioxidant properties.This talk overviews the published studies that analysed the neuroprotective and anti‐inflammatory effects of saffron and its main components in both clinical trials and experimental models of glaucoma. All findings indicate that oral administration of saffron extract could be beneficial in glaucoma by decreasing the neuroinflammation associated with increased intraocular pressure, reducing microglial activation, regulating the production of proinflammatory cytokines, and preventing retinal ganglion cell death.

A bibliometric analysis of apoptosis in glaucoma.

Glaucoma is the first irreversible and second blindness disease, which is characterized by the death of retinal ganglion cells (RGCs) and degeneration of the optic nerve. Previous works have indicated that apoptosis is the main reason for RGC death in glaucoma. Although many studies have investigated the mechanism of apoptosis and different strategies targeting apoptosis to protect the RGCs and finally recover the impaired vision in the glaucoma. However, the global trend and hotspots of apoptosis in glaucoma have not been well illustrated and discussed. Documents were extracted from the Web of Science Core Collection on November 2, 2022. We selected articles and reviews published in English from January 1, 1999 to November 1, 2022 to perform visual analysis and statistical analysis of countries, institutions, authors, references and keywords by VOSviewer 1.6.18 and CiteSpace 5.8. The publications about apoptosis in glaucoma show an increasing trend over time. Besides, the authors, institutions in the US and China published the most numbers of articles with the highest citation, which may be leading the research in the field of apoptosis in glaucoma. Last, series of advanced research results, technology and treatment for glaucoma, such as the discovery of key regulatory mechanisms on RGC apoptosis are emerging and will provide precise strategies for the treatment of glaucoma. This research will broaden our comprehension about the role of apoptosis in the process of glaucoma, and provide guidelines for us in basic research and disease treatment in the further.

EphA4/ephrinA3 reverse signaling induced Müller cell gliosis and production of pro-inflammatory cytokines in experimental glaucoma

Previous work showed that ephrinA3/EphA4 forward signaling contributed to retinal ganglion cell (RGC) damage in experimental glaucoma. Since up-regulated patterns of ephrinA3 and EphA4 were observed in Müller cells and RGCs, an EphA4/ephrinA3 reverse signaling may exist in Müller cells of chronic ocular hypertension (COH) retina. We investigated effects of EphA4/ephrinA3 reverse signaling activation on Müller cells in COH retina. Intravitreal injection of the ephrinA3 agonist EphA4-Fc increased glial fibrillary acidic protein (GFAP) levels in normal retinas, suggestive of Müller cell gliosis, which was confirmed in purified cultured Müller cells treated with EphA4-Fc. These effects were mediated by intracellular STAT3 signaling pathway as phosphorylated STAT3 (p-STAT3) levels and ratios of p-STAT3/STAT3 were significantly increased in both COH retinas and EphA4-Fc intravitreally injected retinas, as well as in EphA4-Fc treated purified cultured Müller cells. The increase of GFAP protein levels in EphA4-Fc-injected retinas and EphA4-Fc treated purified cultured Müller cells could be partially eliminated by stattic, a selective STAT3 blocker. Co-immunoprecipitation results testified to the presence of interaction between ephrinA3 and STAT3/p-STAT3. In addition, intravitreal injection of EphA4-Fc or EphA4-Fc treatment of cultured Müller cells significantly up-regulated mRNA and protein contents of pro-inflammatory cytokines. Moreover, intravitreal injection of EphA4-Fc increased the number of apoptotic RGCs, which could be reversed by the tyrosine kinase blocker PP2. Overall, EphA4/ephrinA3 reverse signaling may induce Müller cell gliosis and increases release of pro-inflammatory factors, which could contribute to RGC death in glaucoma. Inhibition of EphA4/ephrinA3 signaling may provide an effective neuroprotection in glaucoma.

Saffron benefits for eye diseases

AbstractGlaucoma is a neurodegenerative disease characterized by the loss of retinal ganglion cells (RGCs). An increase in the intraocular pressure is the principal risk factor but controlling this pressure does not always prevent glaucomatous damage, so other harmful factors would be implicated in this pathologic process. Several mechanisms have been proposed that leads to the RGC death in glaucoma, including glutamate excitotoxicity, aggregation of misfolded proteins, mitochondrial dysfunction, oxidative stress, neurotrophic deprivation, and neuroinflammation, among others. Therefore, early diagnosis of neurodegeneration, understanding of its pathogenic mechanisms, and the development of new neuroprotective therapies represent major challenges for treating this disease.During the inflammatory process that occurs in glaucoma, retinal glial cells, both microglia and macroglia (Müller cells and astrocytes), become activated and release factors that can be neuroprotective in some cases and neurodegenerative in others. Cytokine‐ and chemokine‐mediated signalling engages in the neuroinflammatory process that leads to retinal ganglion cell (RGC) damage in glaucoma. Thus, a substance with anti‐inflammatory activity may protect against RGC degeneration.Increasing evidence from both experimental models and clinical studies in patients supports the neuroprotective effect of saffron components in neurodegenerative conditions and in retinal neurodegenerative pathologies, due to its important anti‐inflammatory, anti‐apoptotic, and antioxidant properties.This study investigated the neuroprotective and anti‐inflammatory effects of a hydrophilic saffron extract standardized to 3% crocin content in a mouse model of unilateral, laser‐induced ocular hypertension (OHT). For this purpose, morphological signs of microglial activation and the expression of P2RY12, which demonstrates the increased microglial activation, were analysed. In addition, the possible regulation of cytokine and myokine production was also studied. Treatment with saffron extract decreased microglial signs of activation including reduction of microglial cell numbers and morphological features of its activation, including decrease soma size and process retraction, both in OHT and in contralateral eyes. In addition, also partially reversed OHT‐induced down‐regulation of P2RY12 and prevented retinal ganglion cell death in OHT eyes. Furthermore, most of the concentration of proinflammatory cytokines (IL‐1β, IFN‐γ, TNF‐α, and IL‐17), anti‐inflammatory cytokines (IL‐4 and IL‐10), Brain‐derived Neurotrophic Factor (BDNF), Vascular Endothelial Growth Factor (VEGF), and fractalkine were unaffected in response to laser‐induced OHT in both the OHT eye and its contralateral eye in animals treated with saffron extracts. Only IL‐6 levels were significantly increased in the OHT eye one day after laser induction compared with the control group.These results differed from those observed in this OHT glaucoma model in animals untreated with saffron, where microglial activation and down‐regulation of P2RY12 was more intense, and the significant changes in cytokine levels in both eyes in response to IOP increase were observed.All these findings indicate that oral administration of saffron extract could be beneficial in glaucoma by decreasing the neuroinflammation associated with increased intraocular pressure, reducing microglial activation, regulating the production of proinflammatory cytokines, VEGF, and fractalkine and preventing retinal ganglion cell death.

Different behaviour of Müller cells according to their location in the retina: Possible relation with the differential susceptibility of retinal ganglion cells in glaucoma

AbstractPurpose: Glaucoma is a neurodegenerative disease and the leading cause of irreversible blindness in the world. Increased intraocular pressure (IOP) is considered a major risk factor. When visual problems are first detected in patients with glaucoma, half of the retinal ganglion cells (RGCs) have already died, principally in the peripheral retina. Müller glia (MG), which are the main macroglial cells in the retina, play prominent physiological and pathological roles. The change of MG to a reactive phenotype initiates signalling cascades that may serve a neuroprotective role, but may also promote damaging effects on RGCs. Our main hypothesis is that MG exert an important role in RGCs death in glaucoma, being the MG in the periphery the most sensitive to intraocular pressure, promoting the death of RGCs.Methods: Survival of RGCs was analysed by immunocytochemistry in porcine primary co‐cultures of RGCs and MG from central and peripheral retina under control and elevated hydrostatic pressure (EHP) conditions. The conditioned media (CM) from MG primary cultures from central and peripheral retina were collected and analysed by mass spectrometry to identify and quantify proteins in all experimental conditions.Results: We demonstrated that in control condition MG secret neuroprotective factors, and in EHP MG contribute to RGC death. MG from central retina are less sensitive to EHP since RGCs survival further decrease in co‐culture with MG from peripheral retina. Moreover, stretch‐activated nonselective TRPV4 cation channels present in MG are differently activated by the pressure depending of their location within the retina. Proteomic analysis from CM of MG revealed differential protein expression levels, being more pronounced in the CM from MG from peripheral retina under EHP. The proteins identified are mainly associated to apoptosis, oxidative stress, inflammation and angiogenesis.Conclusions: The different sensitivity of the RGCs to IOP in glaucoma could be related with the different activation of neighbouring MG.

GSK872 and necrostatin-1 protect retinal ganglion cells against necroptosis through inhibition of RIP1/RIP3/MLKL pathway in glutamate-induced retinal excitotoxic model of glaucoma

BackgroundGlaucoma, the major cause of irreversible blindness worldwide, is characterized by progressive degeneration of retinal ganglion cells (RGCs). Current treatments for glaucoma only slow or partially prevent the disease progression, failing to prevent RGCs death and visual field defects completely. Glutamate excitotoxicity via N-methyl-d-aspartic acid (NMDA) receptors plays a vital role in RGCs death in glaucoma, which is often accompanied by oxidative stress and NLRP3 inflammasome activation. However, the exact mechanisms remain unclear.MethodsThe glutamate-induced R28 cell excitotoxicity model and NMDA-induced mouse glaucoma model were established in this study. Cell counting kit-8, Hoechst 33342/PI dual staining and lactate dehydrogenase release assay were performed to evaluate cell viability. Annexin V-FITC/PI double staining was used to detect apoptosis and necrosis rate. Reactive oxygen species (ROS) and glutathione (GSH) were used to detect oxidative stress in R28 cells. Levels of proinflammatory cytokines were measured by qRT-PCR. Transmission electron microscopy (TEM) was used to detect necroptotic morphological changes in RGCs. Retinal RGCs numbers were detected by immunofluorescence. Hematoxylin and eosin staining was used to detect retinal morphological changes. The expression levels of RIP1, RIP3, MLKL and NLRP3 inflammasome-related proteins were measured by immunofluorescence and western blotting.ResultsWe found that glutamate excitotoxicity induced necroptosis in RGCs through activation of the RIP1/RIP3/MLKL pathway in vivo and in vitro. Administration of the RIP3 inhibitor GSK872 and RIP1 inhibitor necrostatin-1 (Nec-1) prevented glutamate-induced RGCs loss, retinal damage, neuroinflammation, overproduction of ROS and a decrease in GSH. Furthermore, after suppression of the RIP1/RIP3/MLKL pathway by GSK872 and Nec-1, glutamate-induced upregulation of key proteins involved in NLRP3 inflammasome activation, including NLRP3, pro-caspase-1, cleaved-caspase-1, and interleukin-1β (IL-1β), was markedly inhibited.ConclusionsOur findings suggest that the RIP1/RIP3/MLKL pathway mediates necroptosis of RGCs and regulates NLRP3 inflammasome activation induced by glutamate excitotoxicity. Moreover, GSK872 and Nec-1 can protect RGCs from necroptosis and suppress NLRP3 inflammasome activation through inhibition of RIP1/RIP3/MLKL pathway, conferring a novel neuroprotective treatment for glaucoma.

In Vivo Sublayer Analysis of Human Retinal Inner Plexiform Layer Obtained by Visible-Light Optical Coherence Tomography

PurposeGrowing evidence suggests that dendrite retraction or degeneration in a subpopulation of the retinal ganglion cells (RGCs) may precede detectable soma abnormalities and RGC death in glaucoma. Visualization of the lamellar structure of the inner plexiform layer (IPL) could advance clinical management and fundamental understanding of glaucoma. We investigated whether visible-light optical coherence tomography (vis-OCT) could detect the difference in the IPL sublayer thicknesses between small cohorts of healthy and glaucomatous subjects.MethodWe imaged nine healthy and five glaucomatous subjects with vis-OCT. Four of the healthy subjects were scanned three times each in two separate visits, and five healthy and five glaucoma subjects were scanned three times during a single visit. IPL sublayers were manually segmented using averaged A-line profiles.ResultsThe mean ages of glaucoma and healthy subjects are 59.6 ± 13.4 and 45.4 ± 14.4 years (P = 0.02.) The visual field mean deviations (MDs) are −26.4 to −7.7 dB in glaucoma patients and −1.6 to 1.1 dB in healthy subjects (P = 0.002). Median coefficients of variation (CVs) of intrasession repeatability for the entire IPL and three sublayers are 3.1%, 5.6%, 6.9%, and 5.6% in healthy subjects and 1.8%, 6.0%, 7.7%, and 6.2% in glaucoma patients, respectively. The mean IPL thicknesses are 36.2 ± 1.5 µm in glaucomatous and 40.1 ± 1.7 µm in healthy eyes (P = 0.003).ConclusionsIPL sublayer analysis revealed that the middle sublayer could be responsible for the majority of IPL thinning in glaucoma. Vis-OCT quantified IPL sublayers with good repeatability in both glaucoma and healthy subjects.

Glaucoma Pathogenesis and Neurotrophins: Focus on the Molecular and Genetic Basis for Therapeutic Prospects.

Retinal ganglion cell (RGC) degeneration is a major feature of glaucoma pathology. Neuroprotective approaches that delay or halt the progression of RGC loss are needed to prevent vision loss which can occur even after conventional medical or surgical treatments to lower intraocular pressure. The aim of this review was to examine the progress in genetics and cellular mechanisms associated with endoplasmic reticulum (ER) stress, RGC dysfunction and cell death pathways in glaucoma. Here, we review the involvement of neurotrophins like brain derived neurotrophic factor (BDNF) and its high affinity receptor tropomyosin receptor kinase (TrkB) in glaucoma. The role of ER stress markers in human and animal retinas in health and disease conditions is also discussed. Further, we analysed the literature highlighting genetic linkage in the context of primary open angle glaucoma and suggested mechanistic insights into potential therapeutic options relevant to glaucoma management. The literature review of the neurobiology underlying neurotrophin pathways, ER stress and gene associations provide critical insights into association of RGCs death in glaucoma. Alteration in signalling pathway is associated with increased risk of misfolded protein aggregation in ER promoting RGC apoptosis. Several genes that are linked with neurotrophin signalling pathways have been reported to be associated with glaucoma pathology. Understanding genetic heterogeneity and involvement of neurotrophin biology in glaucoma could help to understand the complex pathophysiology of glaucoma. Identification of novel molecular targets will be critical for drug development and provide neuroprotection to the RGCs and optic nerve.

Neurosteroids and oxysterols as potential therapeutic agents for glaucoma and Alzheimer's disease.

Glaucoma is one of the most frequent causes of visual impairment worldwide and involves selective damage to retinal ganglion cells (RGCs) resulting in degeneration of neural pathways connecting retina to visual cortex. It is of interest that similarities in pathological changes have been described in Alzheimer's disease (AD), the most common cause of progressive memory loss and dementia in older people. Accumulation of amyloid-beta (Abeta) and hyperphosphorylated tau is thought to contribute to apoptotic neuronal death in Alzheimer's disease, and similar changes have been linked to apoptotic RGC death in glaucoma. Both glaucoma and Alzheimer's disease also suffer from a lack of effective treatments prompting a search for novel therapeutic interventions. Neurosteroids (NSs) (including oxysterols) are endogenous molecules synthesized in the nervous system from cholesterol that can modulate glutamate and GABA receptors, the primary mediators of fast excitatory and inhibitory neurotransmission in the brain, respectively. Because changes in the glutamate and GABA neurotransmitter systems contribute to the pathogenesis of AD and glaucoma, NSs are possible therapeutic targets for these disorders. In this review, we present recent evidence supporting pathological links between Alzheimer's disease and glaucoma, and focus on the possible role of NSs in these diseases and how NSs might be developed for therapeutic purposes.

Non-amyloidogenic effects of α2 adrenergic agonists: implications for brimonidine-mediated neuroprotection.

The amyloid beta (Aβ) pathway is strongly implicated in neurodegenerative conditions such as Alzheimer's disease and more recently, glaucoma. Here, we identify the α2 adrenergic receptor agonists (α2ARA) used to lower intraocular pressure can prevent retinal ganglion cell (RGC) death via the non-amyloidogenic Aβ-pathway. Neuroprotective effects were confirmed in vivo and in vitro in different glaucoma-related models using α2ARAs brimonidine (BMD), clonidine (Clo) and dexmedetomidine. α2ARA treatment significantly reduced RGC apoptosis in experimental-glaucoma models by 97.7% and 92.8% (BMD, P<0.01) and 98% and 92.3% (Clo, P<0.01)) at 3 and 8 weeks, respectively. A reduction was seen in an experimental Aβ-induced neurotoxicity model (67% BMD and 88.6% Clo, both P<0.01, respectively), and in vitro, where α2ARAs significantly (P<0.05) prevented cell death, under both hypoxic (CoCl2) and stress (UV) conditions. In experimental-glaucoma, BMD induced ninefold and 25-fold and 36-fold and fourfold reductions in Aβ and amyloid precursor protein (APP) levels at 3 and 8 weeks, respectively, in the RGC layer, with similar results with Clo, and in vitro with all three α2ARAs. BMD significantly increased soluble APPα (sAPPα) levels at 3 and 8 weeks (2.1 and 1.6-fold) in vivo and in vitro with the CoCl2 and UV-light insults. Furthermore, treatment of UV-insulted cells with an sAPPα antibody significantly reduced cell viability compared with BMD-treated control (52%), co-treatment (33%) and untreated control (27%). Finally, we show that α2ARAs modulate levels of laminin and MMP-9 in RGCs, potentially linked to changes in Aβ through APP processing. Together, these results provide new evidence that α2ARAs are neuroprotective through their effects on the Aβ pathway and sAPPα, which to our knowledge, is the first description. Studies have identified the need for α-secretase activators and sAPPα-mimetics in neurodegeneration; α2ARAs, already clinically available, present a promising therapy, with applications not only to reducing RGC death in glaucoma but also other neurodegenerative processes involving Aβ.

Down-regulation of semaphorin 3F in rat retinal ganglion cells in response to optic nerve crush.

Glaucoma is characterized by degeneration of optic nerve axons and death of retinal ganglion cells (RGCs). Nerve crush and axotomy of the optic nerve are studied as models of RGC death in glaucoma and of axon regeneration. The mechanisms underlying the response of RGCs to axonal injury remain unclear, however. We have now examined the effects of optic nerve crush on the expression of members of the semaphorin family of neuronal guidance proteins in the rat retina. The expression of semaphorin 3F (Sema3F) in the retina was down-regulated at both the mRNA and protein levels at 7 days after optic nerve injury, whereas that of Sema3A, Sema3B or Sema3C remained unaffected. Immunohistofluorescence analysis and laser capture microdissection followed by reverse transcription-polymerase chain reaction analysis revealed that this loss of Sema3F expression occurred in the RGC layer of the retina. Furthermore, antibody-mediated neutralization of secreted Sema3F in retinal organ culture resulted in down-regulation of neuron-specific βIII-tubulin (Tuj-1 antigen), a marker of RGCs. Our results suggest that Sema3F may contribute to the regulation of RGC function or survival and therefore warrants further investigation as a potential mediator of neuroprotection. Copyright © 2016 John Wiley & Sons, Ltd.

P16INK4a Upregulation Mediated by SIX6 Defines Retinal Ganglion Cell Pathogenesis in Glaucoma

Glaucoma, a blinding neurodegenerative disease, whose risk factors include elevated intraocular pressure (IOP), age, and genetics, is characterized by accelerated and progressive retinal ganglion cell (RGC) death. Despite decades of research, the mechanism of RGC death in glaucoma is still unknown. Here, we demonstrate that the genetic effect of the SIX6 risk variant (rs33912345, His141Asn) is enhanced by another major POAG risk gene, p16INK4a (cyclin-dependentkinase inhibitor 2A, isoform INK4a). Wefurther show that the upregulation of homozygous SIX6 risk alleles (CC) leads to an increase in p16INK4a expression, with subsequent cellular senescence, as evidenced in a mouse model of elevated IOP and inhuman POAG eyes. Our data indicate that SIX6 and/or IOP promotes POAG by directly increasing p16INK4a expression, leading to RGC senescence in adult human retinas. Our study provides important insights linking genetic susceptibility to the underlying mechanism of RGC death and provides a unified theory of glaucoma pathogenesis.

Arundic acid attenuates retinal ganglion cell death by increasing glutamate/aspartate transporter expression in a model of normal tension glaucoma.

Glaucoma is the second leading cause of blindness worldwide and is characterized by gradual visual impairment owing to progressive loss of retinal ganglion cells (RGCs) and their axons. Glutamate excitotoxicity has been implicated as a mechanism of RGC death in glaucoma. Consistent with this claim, we previously reported that glutamate/aspartate transporter (GLAST)-deficient mice show optic nerve degeneration that is similar to that observed in glaucoma. Therefore, drugs that upregulate GLAST may be useful for neuroprotection in glaucoma. Although many compounds are known to increase the expression of another glial glutamate transporter, EAAT2/GLT1, few compounds are shown to increase GLAST expression. Arundic acid is a glial modulating agent that ameliorates delayed ischemic brain damage by attenuating increases in extracellular glutamate. We hypothesized that arundic acid neuroprotection involves upregulation of GLAST. To test this hypothesis, we examined the effect of arundic acid on GLAST expression and glutamate uptake. We found that arundic acid induces GLAST expression in vitro and in vivo. In addition, arundic acid treatment prevented RGC death by upregulating GLAST in heterozygous (GLAST+/−) mice. Furthermore, arundic acid stimulates the human GLAST ortholog, EAAT1, expression in human neuroglioblastoma cells. Thus, discovering compounds that can enhance EAAT1 expression and activity may be a novel strategy for therapeutic treatment of glaucoma.

Retinal ganglion cell apoptotic pathway in glaucoma: Initiating and downstream mechanisms.

Apoptosis of retinal ganglion cells (RGCs) in glaucoma causes progressive visual field loss, making it the primary cause of irreversible blindness worldwide. Elevated intraocular pressure and aging, the main risk factors for glaucoma, accelerate RGC apoptosis. Numerous pathways and mechanisms were found to be involved in RGC death in glaucoma. Neurotrophic factors deprivation is an early event. Oxidative stress, mitochondrial dysfunction, inflammation, glial cell dysfunction, and activation of apoptotic pathways and prosurvival pathways play a significant role in RGC death in glaucoma. The most important among the involved pathways are the MAP-kinase pathway, PI-3 kinase/Akt pathway, Bcl-2 family, caspase family, and IAP family.

Reactive gliosis along the visual system in rodent models of ocular hypertension

AbstractGlaucoma is a complex disease that causes the loss of retinal ganglion cells (RGCs) and eventually blindness. The mechanisms leading to the progressive RGC death in glaucoma are still a matter of debate. It is known that the main risk factor is an elevated intraocular pressure (IOP) that triggers the initial insult: presumably a crush‐like injury to the RGC axons at the level of the optic nerve head. Current research indicates that neuroinflammation, mediated by the activation of glial cells and the release of cytokines, pro‐inflammatory and neurotoxic molecules, plays an important role in the pathogenesis of glaucoma, aggravating and spreading the initial insult. Ocular hypertension in rats and mice causes permanent damage to the outer and inner retinal layers that cannot be the result of RGC axonal damage and may thus be secondary to an ischemic or neurotoxic insult. Ocular hypertension also induces a glial response that may affect the whole visual system. Activated microglial and macroglial cells are found not only in the ocular hypertensive but also in the contralateral retina and these cells may be the mediators of neuroprotective or neurotoxic reactions to injury.

Therapeutic targets in glaucoma

AbstractGlaucoma leads to irreversible blindness and is characterized by changes in the optic disc and the visual field. The elevated intraocular pressure is considered the most important factor responsible for the glaucomatous optic neuropathy. There are multiple factors involved in the development of retinal ganglion cell death. The goal of glaucoma treatment is to preserve the visual field of patients and prevent the loss of visual function that is associated with the disease (European Guidelines). We should focus at least on three separate targets of glaucoma treatment (Brubaker RF. Survey of Ophthalmology 2003: Three targets for glaucoma management): Intraocular pressure (IOP), outflow facility, and the retinal ganglion cell (RGC). Elevated IOP is still the primary risk factor for the development and progression of glaucoma, and many studies have shown that IOP reduction can limit the progression of glaucoma and slow the loss of visual function. IOP lowering can be beneficial for normal‐tension as well as high‐tension glaucoma patients, and it may also prevent or delay the onset of visual field loss and optic disk damage in individuals with ocular hypertension. The second target of glaucoma treatment is outflow facility. In a healthy eye, aqueous production (flow) equals aqueous outflow through the trabecular and uveoscleral outflow pathways. Any imbalance between flow and outflow results in a change in IOP, yet even a transient elevation of IOP may cause significant glaucomatous damage. The third target of glaucoma treatment is the RGC itself. RGC death in glaucoma might have many causes, including vascular insufficiency, blockage of axonal transport, diffusion of toxic agents into the nerve cell, or initiation of apoptosis. Treatment that aims to directly protect the RGC from every possible insult might be the ultimate treatment for glaucoma because a strategy of neuroprotection could preserve the visual function of patients regardless of the etiology of their glaucoma.

Chronic and Acute Models of Retinal Neurodegeneration TrkA Activity Are Neuroprotective whereas p75NTR Activity Is Neurotoxic through a Paracrine Mechanism

In normal adult retinas, NGF receptor TrkA is expressed in retinal ganglion cells (RGC), whereas glia express p75(NTR). During retinal injury, endogenous NGF, TrkA, and p75(NTR) are up-regulated. Paradoxically, neither endogenous NGF nor exogenous administration of wild type NGF can protect degenerating RGCs, even when administered at high frequency. Here we elucidate the relative contribution of NGF and each of its receptors to RGC degeneration in vivo. During retinal degeneration due to glaucoma or optic nerve transection, treatment with a mutant NGF that only activates TrkA, or with a biological response modifier that prevents endogenous NGF and pro-NGF from binding to p75(NTR) affords significant neuroprotection. Treatment of normal eyes with an NGF mutant-selective p75(NTR) agonist causes progressive RGC death, and in injured eyes it accelerates RGC death. The mechanism of p75(NTR) action during retinal degeneration due to glaucoma is paracrine, by increasing production of neurotoxic proteins TNF-α and α(2)-macroglobulin. Antagonists of p75(NTR) inhibit TNF-α and α(2)-macroglobulin up-regulation during disease, and afford neuroprotection. These data reveal a balance of neuroprotective and neurotoxic mechanisms in normal and diseased retinas, and validate each neurotrophin receptor as a pharmacological target for neuroprotection.