Loss Of Retinal Ganglion Cell Axons Research Articles

The Mechanisms of Neuroprotection by Topical Rho Kinase Inhibition in Experimental Mouse Glaucoma and Optic Neuropathy.

The purpose of this study was to delineate the neuroprotective mechanisms of topical 2% ripasudil (Rip), a Rho kinase (ROCK) inhibitor. In 340 mice, scheduled 2% Rip or balanced salt solution (BSS) saline drops were intermittently, unilaterally delivered. Intracameral microbead glaucoma (GL) injection increased intraocular pressure (IOP) from 1day to 6 weeks (6W), whereas other mice underwent optic nerve (ON) crush. Retinal ganglion cell (RGC) loss was assessed using retinal wholemount anti-RNA Binding Protein with Multiple Splicing (RBPMS) labeling and ON axon counts. Axonal transport was quantified with β-amyloid precursor protein (APP) immunolocalization. Micro-Western (Wes) analysis quantified protein expression. Immunofluorescent expression of ROCK pathway molecules, quantitative astrocyte structural changes, and ON biomechanical strains (explanted eyes) were evaluated. ROCK activity assays were conducted in separate ON regions. At 6W GL, mean RGC axon loss was 6.6 ± 13.3% in Rip and 36.3 ± 30.9% in BSS (P = 0.04, n = 10/group). RGC soma loss after crush was lower with Rip (68.6 ± 8.2%) than BSS (80.5 ± 5.7%, P = 0.006, n = 10/group). After 6W GL, RGC soma loss was lower with Rip (34 ± 5.0%) than BSS (51 ± 8.1%, P = 0.03, n = 10/group). Axonal transport of APP within the unmyelinated ON (UON) was unaffected by Rip. Maximum principal mechanical strains increased similarly in Rip and BSS-treated mice. Retinal ROCK 1 and 2 activity was reduced by Rip in GL eyes. The pROCK2/ROCK2 protein ratio rose in the retina of BSS GL eyes, but not in Rip GL eyes. Topical Rip reduced RGC loss in GL and ON crush, with suppression of ROCK signaling in the retina and ON. The neuroprotection mechanisms appear to involve effects on both RGC and astrocyte responses to IOP elevation.

Non-glaucomatous Optic Disc Cupping: A Brief Review

Although optic disc cupping is mostly seen in glaucoma patients, it can occur in non-glaucomatous optic neuropathies (NGON). The characteristics of NGON are cupping toxic optic neuropathies, optic neuritis, compressive ischemia, and hereditary nature. The basic components of optic disc cupping are prelaminar and laminar. Prelaminar thinning, which seemed to be non-specific, occurs in all types of retinal ganglion cell axon loss; such as compressive, ischemic, and inflammatory events; glaucoma; and aging. This form of cupping is usually shallow, with less excavation of the optic disc. Laminar type of cupping which is a clinically profound type of cupping, may damage peripapillary scleral and lamina cribrosa. Sometimes experienced clinicians cannot clearly distinguish glaucomatous from non-glaucomatous cupping. The non-glaucomatous optic neuropathy has more neuroretinal rim pallor with less excavation of the disc than in glaucoma. It also involves central visual acuity and color vision in primary levels with visual field defects aligned vertically and respecting the midline. Evaluation of the patient’s medical records, disease presentation, ocular function, and examination are also crucial. Secondary examinations, including visual field examination and optical coherence tomography (OCT) or neuroimaging, facilitate the disease’s differentiation. This review presents the methods of examining a patient with an increased cup-to-disc ratio.

Telmisartan Reduces Axon Degeneration in Mice With Experimental Glaucoma.

PurposeThe purpose of this study was to determine if treatment with telmisartan, an angiotensin II type 1 receptor blocker (ARB), protects against retinal ganglion cell (RGC) degeneration in a mouse glaucoma model with induced elevation of intraocular pressure (IOP).MethodsIOP elevation was induced by injection of polystyrene microbeads into the anterior chamber of the right eye of 3-month-old C57BL/6J mice, with the left eye serving as contralateral control. Starting the day of microbead injection, mice were maintained on solid food pellets with or without incorporated telmisartan. IOP was measured by Tono Lab tonometry prior to and weekly after microbead injection. Twelve weeks postinjection, mice were euthanized to obtain optic nerves for analysis of RGC axons. The total numbers of optic nerve axons were determined manually and automatedly using AxonJ. Degenerating axons were counted manually.ResultsIOP elevation induced by microbead injection was similar in magnitude and duration in vehicle and telmisartan-fed mice, although IOP was reduced 5.8% in uninjected mice treated with telmisartan (P = 0.0027). Axon loss determined by manual and automated methods was greater in vehicle compared to telmisartan-treated mice (manual: 9.5% vs. 1.8%, P = 0.044; automated: 14.2% vs. 2.9%, P = 0.0375). An increase in the percent of axons undergoing degeneration was observed in nerves from microbead-injected eyes that was greater in vehicle-treated compared to telmisartan-treated mice (49.0% vs. –0.58%, P = 0.0019).ConclusionsElevation of IOP by microbead injection led to loss of RGC axons in vehicle-treated mice that was largely prevented by telmisartan treatment, suggesting a neuroprotective effect of telmisartan.

Chronic demyelination exacerbates neuroaxonal loss in patients with MS with unilateral optic neuritis.

ObjectiveTo examine the effect of chronic demyelination in the optic nerve of patients with MS on progressive loss of retinal ganglion cell (RGC) axons.MethodsProgressive retinal nerve fiber layer (RNFL) loss, as measured by optical coherence tomography, was longitudinally examined in 51 patients with MS with a history of unilateral optic neuritis (ON) and 25 normal controls. Patients were examined annually with a median of 4-year follow-up. Pairwise intereye comparison was performed between ON and fellow non-ON (NON) eyes of patients with MS using the linear mixed-effects model and survival analysis. The latency asymmetry of multifocal visual evoked potential (mfVEP) was used to determine the level of demyelination in the optic nerve.ResultsAlthough both ON and NON eyes demonstrate significantly faster loss of RGC axons compared with normal subjects, ON eyes with severe chronic demyelination show accelerated thinning in the RNFL in the temporal sector of the optic disc (temporal RNFL [tRNFL]) compared with fellow eyes (evidenced by both the linear mixed-effects model and survival analysis). Furthermore, progressive tRNFL thinning is associated with the degree of optic nerve demyelination and reflects the topography of pathology in the optic nerve. More rapid axonal loss in ON eyes is also functionally evidenced by mfVEP amplitude reduction, which correlates with the level of optic nerve demyelination.ConclusionsAlthough the effect of demyelination on axonal survival has been demonstrated in experimental studies, our results provide first clinically meaningful evidence that chronic demyelination is associated with progressive axonal loss in human MS.

Artificial intelligence and deep learning in glaucoma: Current state and future prospects.

Over the past few years, there has been an unprecedented and tremendous excitement for artificial intelligence (AI) research in the field of Ophthalmology; this has naturally been translated to glaucoma-a progressive optic neuropathy characterized by retinal ganglion cell axon loss and associated visual field defects. In this review, we aim to discuss how AI may have a unique opportunity to tackle the many challenges faced in the glaucoma clinic. This is because glaucoma remains poorly understood with difficulties in providing early diagnosis and prognosis accurately and in a timely fashion. In the short term, AI could also become a game changer by paving the way for the first cost-effective glaucoma screening campaigns. While there are undeniable technical and clinical challenges ahead, and more so than for other ophthalmic disorders whereby AI is already booming, we strongly believe that glaucoma specialists should embrace AI as a companion to their practice. Finally, this review will also remind ourselves that glaucoma is a complex group of disorders with a multitude of physiological manifestations that cannot yet be observed clinically. AI in glaucoma is here to stay, but it will not be the only tool to solve glaucoma.

Pathophysiological basis of low contrast visual acuity loss in multiple sclerosis.

ObjectiveThere is currently an urgent need for reliable clinical biomarkers of remyelination to be used in Phase 2 and Phase 3 clinical trials. Low contrast visual acuity (LCVA) has been suggested as a functional measure of the integrity of the visual pathway. Therefore, the aim of this study was to elucidate the potential contribution of axonal loss and demyelination to LCVA loss in MS patients.MethodIn this study, 50 consecutive relapsing remitting MS patients with a previous history of unilateral optic neuritis were enrolled. Using the linear regression model, we assessed the relative contribution of multifocal Visual Evoked Potentials (mfVEP) latency and Retinal Nerve Fiber Layer (RNFL) thickness to LCVA deficit.ResultsIntereye asymmetry of mfVEP latency and RNFL thickness correlated significantly with intereye asymmetry of LCVA (P < 0.001). A linear regression model demonstrated increased predictive power of LCVA when mfVEP latency and RNFL thinning were combined (reaching R 2 = 0.67) and confirmed a higher predictive value of RNFL thinning compared to mfVEP latency delay for both contrast levels. However, elimination of subjects with severe axonal loss dramatically increased the relative contribution of mfVEP latency, with contribution of RNFL thickness losing significance for both 1.25% and 2.5% LCVA.InterpretationWhile retinal ganglion cell axonal loss is a superior predictor of LCVA, the degree of demyelination contributes significantly to worsening of LCVA, particularly when patients with severe axonal loss are excluded. These results support the feasibility of using LCVA as a functional biomarker in remyelination therapy trials, providing appropriate patient's selection criteria are implemented.

Regional Retinal Ganglion Cell Axon Loss in a Murine Glaucoma Model.

PurposeTo determine if retinal ganglion cell (RGC) axon loss in experimental mouse glaucoma is uniform in the optic nerve.MethodsExperimental glaucoma was induced for 6 weeks with a microbead injection model in CD1 (n = 78) and C57BL/6 (B6, n = 68) mice. From epoxy-embedded sections of optic nerve 1 to 2 mm posterior to the globe, total nerve area and regional axon density (axons/1600 μm2) were measured in superior, inferior, nasal, and temporal zones.ResultsControl eyes of CD1 mice have higher axon density and more total RGCs than control B6 mice eyes. There were no significant differences in control regional axon density in all mice or by strain (all P > 0.2, mixed model). Exposure to elevated IOP caused loss of RGC in both strains. In CD1 mice, axon density declined without significant loss of nerve area, while B6 mice had less density loss, but greater decrease in nerve area. Axon density loss in glaucoma eyes was not significantly greater in any region in either mouse strain (both P > 0.2, mixed model). In moderately damaged CD1 glaucoma eyes, and CD1 eyes with the greatest IOP elevation exposure, density loss differed by region (P = 0.05, P = 0.03, mixed model) with the greatest loss in the temporal and superior regions, while in severely injured B6 nerves superior loss was greater than inferior loss (P = 0.01, mixed model, Bonferroni corrected).ConclusionsThere was selectively greater loss of superior and temporal optic nerve axons of RGCs in mouse glaucoma at certain stages of damage. Differences in nerve area change suggest non-RGC responses differ between mouse strains.

Distribution pattern of axonal cytoskeleton proteins in the human optic nerve head.

Glaucoma is one of the leading causes of blindness in the developed world. It is a progressive optic neuropathy where structural loss of retinal ganglion cell (RGC) axons corresponds with functional visual field defect. Glaucoma is distinguished from other optic neuropathies by its selective loss of RGC axons. Superior and inferior peripheral nerve sectors are found to be most vulnerable to pressure induced injury whereas the inner temporal sector is most resilient (Quigley et al., 1988). Pathogenesis behind the preferential axonal damage pattern is still poorly understood.

Experimental scleral cross-linking increases glaucoma damage in a mouse model

The purpose of this study was to assess the effect of a scleral cross-linking agent on susceptibility to glaucoma damage in a mouse model.CD1 mice underwent 3 subconjunctival injections of 0.5 M glyceraldehyde (GA) in 1 week, then had elevated intraocular pressure (IOP) induced by bead injection. Degree of cross-linking was measured by enzyme-linked immunosorbent assay (ELISA), scleral permeability was measured by fluorescence recovery after photobleaching (FRAP), and the mechanical effects of GA exposure were measured by inflation testing. Control mice had buffer injection or no injection in 2 separate glaucoma experiments. IOP was monitored by Tonolab and retinal ganglion cell (RGC) loss was measured by histological axon counting. To rule out undesirable effects of GA, we performed electroretinography and detailed histology of the retina. GA exposure had no detectable effects on RGC number, retinal structure or function either histologically or electrophysiologically. GA increased cross-linking of sclera by 37% in an ELISA assay, decreased scleral permeability (FRAP, p = 0.001), and produced a steeper pressure–strain behavior by in vitro inflation testing. In two experimental glaucoma experiments, GA-treated eyes had greater RGC axon loss from elevated IOP than either buffer-injected or control eyes, controlling for level of IOP exposure over time (p = 0.01, and 0.049, multivariable regression analyses). This is the first report that experimental alteration of the sclera, by cross-linking, increases susceptibility to RGC damage in mice.

Impairment of visual function and retinal ER stress activation in Wfs1-deficient mice.

Wolfram syndrome is an early onset genetic disease (1/180,000) featuring diabetes mellitus and optic neuropathy, associated to mutations in the WFS1 gene. Wfs1−/− mouse model shows pancreatic beta cell atrophy, but its visual performance has not been investigated, prompting us to study its visual function and histopathology of the retina and optic nerve. Electroretinogram and visual evoked potentials (VEPs) were performed in Wfs1−/− and Wfs1+/+ mice at 3, 6, 9 and 12 months of age. Fundi were pictured with Micron III apparatus. Retinal ganglion cell (RGC) abundance was determined from Brn3a immunolabeling of retinal sections. RGC axonal loss was quantified by electron microscopy in transversal optic nerve sections. Endoplasmic reticulum stress was assessed using immunoglobulin binding protein (BiP), protein disulfide isomerase (PDI) and inositol-requiring enzyme 1 alpha (Ire1α) markers. Electroretinograms amplitudes were slightly reduced and latencies increased with time in Wfs1−/− mice. Similarly, VEPs showed decreased N+P amplitudes and increased N-wave latency. Analysis of unfolded protein response signaling revealed an activation of endoplasmic reticulum stress in Wfs1 −/− mutant mouse retinas. Altogether, progressive VEPs alterations with minimal neuronal cell loss suggest functional alteration of the action potential in the Wfs1 −/− optic pathways.

Scleral Permeability Varies by Mouse Strain and Is Decreased by Chronic Experimental Glaucoma

To determine differences in scleral permeability, as measured by diffusion of macromolecules, by using fluorescence recovery after photobleaching (FRAP), with reference to differences by mouse strain, scleral region, and the effect of experimental glaucoma. In three mouse strains (B6, CD1, and B6 mice with mutation in collagen 8α2 [Aca23]), we used FRAP to measure the diffusion of fluorescein isothiocyanate-dextran, molecular weight 40 kDa, into a photobleached zone of sclera. Scleral regions near the optic nerve head (peripapillary) and two successively more anterior regions were compared. Sclera from mouse eyes subjected to chronically elevated intraocular pressure after bead injection into the anterior chamber were compared to fellow eye controls. FRAP data were compared against estimated retinal ganglion cell axon loss in glaucomatous eyes. Diffusion rates of dextran molecules in the sclera were significantly greater in Aca23 and B6 mice than in CD1 mice in a multivariate model adjusted for region and axial length (P < 0.0001). Dextran diffusion significantly decreased in glaucomatous eyes, and the decline increased with greater axon loss (P = 0.0003, multivariable model). Peripapillary scleral permeability was higher in CD1 than B6 and Aca23 mice (P < 0.05, multivariable model, adjusted by Bonferroni). Measurement of the diffusion rates of dextran molecules in the sclera showed that glaucoma leads to decreased scleral permeability in all three mouse strains tested. Among mouse strains tested, those that were more susceptible to glaucomatous loss of retinal ganglion cells had a lower scleral permeability at baseline.

Is there a link between open‐angle glaucoma and dementia?

Previous research has suggested an association between dementia and glaucoma through common risk factors or mechanisms. Our aim was to evaluate the longitudinal relationship between open-angle glaucoma (OAG) and incident dementia. The Three-City-Bordeaux-Alienor study is a population-based cohort of 812 participants with a 3-year follow-up period. All participants were aged 72 years or older. An eye examination was performed on all subjects. An OAG was determined based on optic nerve damage and visual field loss. Incident dementia was actively screened for and confirmed by a neurologist. A total of 41 participants developed dementia over the 3-year follow-up period. Future incident dementia cases had an increased prevalence of OAG (17.5% vs 4.5% for nondemented participants, p = 0.003). After adjustment for age, gender, education, family history of glaucoma, vascular comorbidities, and apolipoprotein ε4, our results showed that participants with an OAG were four times more likely to develop dementia during the 3-year follow-up period (odds ratio = 3.9, 95% confidence interval = 1.5-10.4, p = 0.0054). An increased risk of dementia was also associated with 2 markers of optic nerve degeneration (vertical cup:disk ratio and minimal rim:disk ratio). However, no association was found between a high intraocular pressure and/or the use of intraocular pressure-lowering medications and incident dementia. If the association between OAG and dementia is confirmed, direct and noninvasive quantification of the amount of retinal ganglion cell axonal loss may be a useful biomarker of cerebral axonal loss in the future. It may also offer new breakthroughs in understanding the underlying pathophysiological mechanisms of both diseases.

Treatment of agitation in people with Alzheimer's dementia: Rationale for the clinical investigation of AVP-923 (dextromethorphan/quinidine)

Background: Dementia and glaucoma have been hypothesized to be connected, through common risk factors or common mechanisms. Our aim was to evaluate the longitudinal relationship between open-angle glaucoma (OAG) and incident dementia.Methods: The 3C Bordeaux-Alienor study is a population-based cohort of 812 participants aged 72 years and over, followed-up three years. An eye examination was performed and OAG was classified according to optic nerve damage and visual field loss. Incident dementia was actively screened and confirmed by a neurologist. Results: A total of 41 participants developed a dementia over the three-year followup. Future incident dementia cases had more often a diagnosis of OAG (in 17.5% vs 4.5% for non-demented, p1⁄40.003). After adjustment for age, gender, education, family history of glaucoma, vascular comorbidities, and apolipoprotein e4, OAG participants had a nearly four-time increased risk of developing dementia over the three years of follow-up (OR1⁄43.8, 95%CI 1.5-10.1, p1⁄40.006). An increased risk of dementia was also evidenced for two markers of optic nerve degeneration (vertical cup:disc ratio and minimal rim:disc ratio) whereas no association was found between ocular hypertension and incident dementia. Conclusions: If this association between OAG and dementia is confirmed, direct and non-invasive quantification of the amount of retinal ganglion cell axonal loss might represent a useful biomarker of cerebral axonal loss in the future. It may also offer new breakthroughs in the understanding of the pathophysiological mechanisms underlying both diseases.

Ectopic Vesicular Glutamate Release at the Optic Nerve Head and Axon Loss in Mouse Experimental Glaucoma

Although clinical and experimental observations indicate that the optic nerve head (ONH) is a major site of axon degeneration in glaucoma, the mechanisms by which local retinal ganglion cell (RGC) axons are injured and damage spreads among axons remain poorly defined. Using a laser-induced ocular hypertension (LIOH) mouse model of glaucoma, we found that within 48 h of intraocular pressure elevation, RGC axon segments within the ONH exhibited ectopic accumulation and colocalization of multiple components of the glutamatergic presynaptic machinery including the vesicular glutamate transporter VGLUT2, several synaptic vesicle marker proteins, glutamate, the soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex and active zone cytomatrix components, as well as ultrastructurally identified, synaptophysin-containing vesicles. Ectopic vesicle exocytosis and glutamate release were detected in acute preparations of the LIOH ONH. Immunolocalization and analysis using the ionotropic receptor channel-permeant cation agmatine indicated that ONH axon segments and glia expressed glutamate receptors, and these receptors were more active after LIOH compared with controls. Pharmacological antagonism of glutamate receptors and neuronal activity resulted in increased RGC axon sparing in vivo. Furthermore, in vivo RGC-specific genetic disruption of the vesicular glutamate transporter VGLUT2 or the obligatory NMDA receptor subunit NR1 promoted axon survival in experimental glaucoma. As the inhibition of ectopic glutamate vesicular release or glutamate receptivity can independently modify the severity of RGC axon loss, synaptic release mechanisms may provide useful therapeutic entry points into glaucomatous axon degeneration.

Experimental glaucoma models

AbstractPurpose To introduce in vivo methods for experimental glaucoma research.Methods Animal models with natural elevation of intraocular pressure (IOP) and genetic manipulation to raise IOP will be discussed. Experimental elevation of IOP in rats and mice will be presented in more detail.Results Up to 30% of retinal ganglion cell (RGC) loss during a 3‐week period can be achieved with rat laser photocoagulation model. Similarly, experimental elevation of IOP in mice can result in up to 30% RGC axon loss in the optic nerve with a 6‐week follow‐up.Conclusion The age and strain of animals should be considered in experimental glaucoma research.

Methodologic Quality of Studies on Prognostic Factors for Primary Open-angle Glaucoma Progression Measured by Visual Field Deterioration

Glaucoma is a chronic, slowly progressing, and asymptomatic optic neuropathic disorder with a great variety of causes that involve gradual retinal ganglion cell axon loss. The disease is the second most common cause of blindness in the industrialized world. Once vision loss develops it is irreversible-although in many cases further loss can be slowed if adequate treatment is provided. If not treated, glaucoma can lead to complete vision loss in the affected eye. Primary open-angle glaucoma (POAG) is the most prevalent form of the disease in the industrialized countries, representing 94% of all glaucomas. In a Spanish study of 569 individuals, the prevalence of POAG was 2.1% (99% confidence interval 1.9%-2.3%) in the age range between 40 and 79 years. Assessing glaucomatous damage progression remains one of the most important and challenging aspects in glaucoma management. In addition, a better understanding of clinical risk factors for glaucoma worsening may help us to develop new strategies to improve glaucoma care. Over the past 2 decades, many studies have addressed the issue of risk factors associated with or predicting for glaucoma progression. Although many studies have attempted to identify the prognostic factors capable of predicting the course of POAG, the results have been varied and in some cases contradictory, and are thus of scant practical utility. This study was designed to evaluate the methodologic quality of the studies published in the literature on the prognostic factors for POAG progression measured by visual field deterioration.

Inflammatory demyelination induces axonal injury and retinal ganglion cell apoptosis in experimental optic neuritis

Optic neuritis is an inflammatory disease of the optic nerve that often occurs in patients with multiple sclerosis and leads to permanent visual loss mediated by retinal ganglion cell (RGC) damage. Optic neuritis occurs with high frequency in relapsing-remitting experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, with significant loss of RGCs. In the current study, mechanisms of RGC loss in this model were examined to determine whether inflammation-induced axonal injury mediates apoptotic death of RGCs. RGCs were retrogradely labeled by injection of fluorogold into superior colliculi of 6–7 week old female SJL/J mice. EAE was induced one week later by immunization with proteolipid protein peptide. Optic neuritis was detected by inflammatory cell infiltration on histological examination as early as 9 days after immunization, with peak incidence by day 12. Demyelination occurred 1–2 days after inflammation began. Loss of RGC axons was detected following demyelination, with significant axonal loss occurring by day 13 post-immunization. Axonal loss occurred prior to loss of RGC bodies at day 14. Apoptotic cells were also observed at day 14 in the ganglion cell layer of eyes with optic neuritis, but not in control eyes. Together these results suggest that inflammatory cell infiltration mediates demyelination and leads to direct axonal injury in this model of experimental optic neuritis. RGCs die by an apoptotic mechanism triggered by axonal injury. Potential neuroprotective therapies to prevent permanent RGC loss from optic neuritis will likely need to be initiated prior to axonal injury to preserve neuronal function.

Reduced Retina Microglial Activation and Improved Optic Nerve Integrity with Minocycline Treatment in the DBA/2J Mouse Model of Glaucoma

In the context of the retinal ganglion cell (RGC) axon degeneration in the optic nerve that occurs in glaucoma, microglia become activated, then phagocytic, and redistribute in the optic nerve head. The authors investigated the potential contribution of retinal microglia activation to glaucoma progression in the DBA/2J chronic mouse glaucoma model. The authors treated 6-week-old DBA/2J mice for 25 weeks with minocycline, a tetracycline derivative known to reduce microglia activation and to improve neuronal survival in other models of neurodegenerative disease. They quantified RGC numbers and characterized microglia activation, gliosis, and both axonal integrity and retrograde tracer transport by RGCs in mice systemically treated with minocycline or vehicle only. Minocycline reduced microglial activation and improved RGC axonal transport and integrity, yet it had no effect on the characteristic age-related ocular changes that lead to chronically elevated pressure and did not alter Müller or astrocyte gliosis. Specifically, minocycline increased the fraction of microglia with resting ramified morphology and reduced levels of Iba1 mRNA and protein, a microglia-specific calcium ligand linked to activation. The reduction in microglial activation was coupled to significant improvement in RGC axonal transport, as measured by neuronal retrograde tracing from the superior colliculus. Finally, minocycline treatment significantly decoupled RGC axon loss from increased intraocular pressure. These observations suggest that in glaucoma, retina and optic nerve head microglia activation may be a factor in the early decline in function of the optic nerve and its subsequent degeneration.

Upregulation ofEphB2andephrin-B2at the Optic Nerve Head of DBA/2J Glaucomatous Mice Coincides with Axon Loss

To identify genes with upregulated expression at the optic nerve head (ONH) that coincides with retinal ganglion cell (RGC) axon loss in glaucomatous DBA/2J mice. To further demonstrate that the proteins encoded by these genes bind to RGC axons and influence fundamental axon physiology. In situ hybridization and cell-type-specific immunolabeling were performed on ONH sections from DBA/2J mice (3 to 11 months old) and C57Bl/6NCrl mice (10 months old). EphB2-Fc and ephrin-B2-Fc chimeric proteins were applied to adult RGC axons in vitro and in vivo at the ONH to demonstrate protein binding on axons. EphB2-Fc or control Fc protein was applied in a bath or locally to axons preloaded with the calcium indicator Fluo-4-AM, and changes in intra-axonal calcium were determined. EphB2 and ephrin-B2 were specifically upregulated at the ONH of DBA/2J mice starting at 9 months of age, but not in age-matched C57Bl/6NCrl mice or in DBA/2J animals that did not have axon loss. EphA4 was also present at the ONH, but no difference in expression was detected between unaffected and affected animals. EphB2 was expressed by F4/80(+), MOMA2(+), ED1(-) macrophage-like cells, ephrin-B2 was expressed by Iba-1(+) microglia and GFAP(+) astrocytes, whereas EphA4 was expressed by GFAP(+) astrocytes. EphB2-Fc and ephrin-B2-Fc protein bound to RGC axons in culture and to ONH RGC axons in vivo. Adult RGC axons in vitro elevated intra-axonal calcium in response to EphB2-Fc but not to control Fc protein. The expression of EphB2 and ephrin-B2 is upregulated at the ONH of glaucomatous DBA/2J mice coinciding with RGC axon loss. The direct binding of EphB2 and ephrin-B2 on adult RGC axons at the ONH and the ability of EphB2 to elevate intra-axonal calcium indicate that these proteins may affect RGC axon physiology in the setting of glaucoma and thus affect the development or progression of the disease.

Transforming growth factor‐β‐regulated gene transcription and protein expression in human GFAP‐negative lamina cribrosa cells

Primary open-angle glaucoma (POAG) is a progressive optic neuropathy, which is a major cause of worldwide visual impairment and blindness. Pathological hallmarks of the glaucomatous optic nerve head (ONH) include retinal ganglion cell axon loss and extracellular matrix (ECM) remodeling of the lamina cribrosa layer. Transforming growth factor-beta (TGF-beta) is an important pro-fibrotic modulator of ECM metabolism, whose levels are elevated in human POAG lamina cribrosa tissue compared with non-glaucomatous controls. We hypothesize that in POAG, lamina cribrosa (LC) glial cells respond to elevated TGF-beta, producing a remodeled ONH ECM. Using Affymetrix microarrays, we report the first study examining the effect of TGF-beta1 on global gene expression profiles in glial fibrillary acidic acid (GFAP)-negative LC glial cells in vitro. Prominent among the differentially expressed genes were those with established fibrogenic potential, including CTGF, collagen I, elastin, thrombospondin, decorin, biglycan, and fibromodulin. Independent TaqMan and Sybr Green quantitative PCR analysis significantly validated genes involved in regulation of cell proliferation (platelet-derived growth factor [PDGF-alpha]), angiogenesis (vascular endothelial growth factor [VEGF]), ECM accumulation and degradation (CTGF, IL-11, and ADAMT-S5), and growth factor binding (ESM-1). Bioinformatic analysis of the ESM-1 promoter identified putative Smad and Runx transcription factor binding sites, and luciferase assays confirmed that TGF-beta1 drives transcription of the ESM-1 gene. TGF-beta1 induces expression and release of ECM components in LC cells, which may be important in regulating matrix remodeling in the lamina cribrosa. In disease states such as POAG, the LC cell may represent an important pro-fibrotic cell type and an attractive target for novel therapeutic strategies.