Recent advances in genetically modified animal models of glaucoma and their roles in drug repositioning

Exploring the Ocular Surface Microbiome and Tear Proteome in Glaucoma

Although glaucoma is a leading cause of irreversible blindness worldwide, its pathogenesis is incompletely understood, and intraocular pressure (IOP) is the only modifiable risk factor to target the disease. Several associations between the gut microbiome and glaucoma, including the IOP, have been suggested. There is growing evidence that interactions between microbes on the ocular surface, termed the ocular surface microbiome (OSM), and tear proteins, collectively called the tear proteome, may also play a role in ocular diseases such as glaucoma. This study aimed to find characteristic features of the OSM and tear proteins in patients with glaucoma. The whole-metagenome shotgun sequencing of 32 conjunctival swabs identified Actinobacteria, Firmicutes, and Proteobacteria as the dominant phyla in the cohort. The species Corynebacterium mastitidis was only found in healthy controls, and their conjunctival microbiomes may be enriched in genes of the phospholipase pathway compared to glaucoma patients. Despite these minor differences in the OSM, patients showed an enrichment of many tear proteins associated with the immune system compared to controls. In contrast to the OSM, this emphasizes the role of the proteome, with a potential involvement of immunological processes in glaucoma. These findings may contribute to the design of new therapeutic approaches targeting glaucoma and other associated diseases.

Protection against Oxidative Stress by Coenzyme Q10 in a Porcine Retinal Degeneration Model

Oxidative stress plays an important role in neurodegenerative diseases, including glaucoma. Therefore, we analyzed if the antioxidant coenzyme Q10 (CoQ10), which is also commercially available, can prevent retinal degeneration induced by hydrogen peroxide (H2O2) in a porcine organ culture model. Retinal explants were cultivated for eight days, and H2O2 (500 µM, 3 h) induced the oxidative damage. CoQ10 therapy was applied (700 µM, 48 h). Retinal ganglion cells (RGCs) and microglia were examined immunohistologically in all groups (control, H2O2, H2O2 + CoQ10). Cellular, oxidative, and inflammatory genes were quantified via RT-qPCR. Strong RGC loss was observed with H2O2 (p ≤ 0.001). CoQ10 elicited RGC protection compared to the damaged group at a histological (p ≤ 0.001) and mRNA level. We detected more microglia cells with H2O2, but CoQ10 reduced this effect (p = 0.004). Cellular protection genes (NRF2) against oxidative stress were stimulated by CoQ10 (p ≤ 0.001). Furthermore, mitochondrial oxidative stress (SOD2) increased through H2O2 (p = 0.038), and CoQ10 reduced it to control level. Our novel results indicate neuroprotection via CoQ10 in porcine retina organ cultures. In particular, CoQ10 appears to protect RGCs by potentially inhibiting apoptosis-related pathways, activating intracellular protection and reducing mitochondrial stress.

Neuroprotective effects of acteoside in a glaucoma mouse model by targeting Serta domain-containing protein 4

AIM

To explore the therapeutic effect and main molecular mechanisms of acteoside in a glaucoma model in DBA/2J mice.

METHODS

Proteomics was used to compare the differentially expressed proteins of C57 and DBA/2J mice. After acteoside administration in DBA/2J mice, anterior segment observation, intraocular pressure (IOP) monitoring, electrophysiology examination, and hematoxylin and eosin staining were used to analyze any potential effects. Immunohistochemistry (IHC) assays were used to verify the proteomics results. Furthermore, retinal ganglion cell 5 (RGC5) cell proliferation was assessed with cell counting kit-8 (CCK-8) assays. Serta domain-containing protein 4 (Sertad4) mRNA and protein expression levels were measured by qRT-PCR and Western blot analysis, respectively.

RESULTS

Proteomics analysis suggested that Sertad4 was the most significantly differentially expressed protein. Compared with the saline group, the acteoside treatment group showed decreased IOP, improved N1-P1 wave amplitudes, thicker retina, and larger numbers of cells in the ganglion cell layer (GCL). The IHC results showed that Sertad4 expression levels in DBA/2J mice treated with acteoside were significantly lower than in the saline group. Acteoside treatment could improve RGC5 cell survival and reduce the Sertad4 mRNA and protein expression levels after glutamate injury.

CONCLUSION

Sertad4 is differentially expressed in DBA/2J mice. Acteoside can protect RGCs from damage, possibly through the downregulation of Sertad4, and has a potential use in glaucoma treatment.

Drug Treatment Attenuates Retinal Ganglion Cell Death by Inhibiting Collapsin Response Mediator Protein 2 Phosphorylation in Mouse Models of Normal Tension Glaucoma

Normal tension glaucoma (NTG) is a progressive neurodegenerative disease in glaucoma families. Typical glaucoma develops because of increased intraocular pressure (IOP), whereas NTG develops despite normal IOP. As a subtype of open-angle glaucoma, NTG is characterized by retinal ganglion cell (RGC) degeneration, gradual loss of axons, and injury to the optic nerve. The relationship between glutamate excitotoxicity and oxidative stress has elicited great interest in NTG studies. We recently reported that suppressing collapsin response mediator protein 2 (CRMP2) phosphorylation in S522A CRMP2 mutant (CRMP2 KIKI) mice inhibited RGC death in NTG mouse models. This study evaluated the impact of the natural compounds huperzine A (HupA) and naringenin (NAR), which have therapeutic effects against glutamate excitotoxicity and oxidative stress, on inhibiting CMRP2 phosphorylation in mice intravitreally injected with N-methyl-D-aspartate (NMDA) and GLAST mutant mice. Results of the study demonstrated that HupA and NAR significantly reduced RGC degeneration and thinning of the inner retinal layer, and inhibited the elevated CRMP2 phosphorylation. These treatments protected against glutamate excitotoxicity and suppressed oxidative stress, which could provide insight into developing new effective therapeutic strategies for NTG.

Drug combination of topical ripasudil and brimonidine enhances neuroprotection in a mouse model of optic nerve injury

PURPOSE

To determine whether combination of topical ripasudil and brimonidine has more effective neuroprotection on retinal ganglion cells (RGCs) following injury to axons composing the optic nerve.

METHODS

Topical ripasudil, brimonidine, or mixture of both drugs were administered to adult mice after optic nerve injury (ONI). The influence of drug conditions on RGC health were evaluated by the quantifications of surviving RGCs, phosphorylated p38 mitogen-activated protein kinase (phospho-p38), and expressions of trophic factors and proinflammatory mediators in the retina.

RESULTS

Topical ripasudil and brimonidine suppressed ONI-induced RGC death respectively, and mixture of both drugs further stimulated RGC survival. Topical ripasudil and brimonidine suppressed ONI-induced phospho-p38 in the whole retina. In addition, topical ripasudil suppressed expression levels of TNFα, IL-1β and monocyte chemotactic protein-1 (MCP-1), whereas topical brimonidine increased the expression level of basic fibroblast growth factor (bFGF).

CONCLUSIONS

Combination of topical ripasudil and brimonidine may enhance RGC protection by modulating multiple signaling pathways in the retina.

Molecular pathways in experimental glaucoma models

Glaucoma is a complex and progressive disease that primarily affects the optic nerve axons, leading to irreversible vision loss. Although the exact molecular mechanisms underlying glaucoma pathogenesis are not fully understood, it is believed that except increased intraocular pressure, a combination of genetic and environmental factors play a role in the development of the disease. Animal models have been widely used in the study of glaucoma, allowing researchers to better understand the underlying mechanisms of the disease and test potential treatments. Several molecular pathways have been implicated in the pathogenesis of glaucoma, including oxidative stress, inflammation, and excitotoxic-induced neurodegeneration. This review summarizes the most important knowledge about molecular mechanisms involved in the glaucoma development. Although much research has been done to better understand the molecular mechanisms underlying this disease, there is still much to be learned to develop effective treatments and prevent vision loss in those affected by glaucoma.

Circumlimbal suture and laser burns: Comparison between two different chronic glaucoma models

OBJECTIVES

Glaucoma is a multifactorial optic neuropathy with a high rate of irreversible visual loss, and its pathogenesis is complex and still unclear. Elevated intraocular pressure (IOP) is well recognized as the sole modifiable risk factor for the development of glaucoma in the majority of cases. This study aims to compare 2 different methods of inducing chronic ocular hypertension by circumlimbal suture or by laser burns in degree and lasting time of the IOP, different status of the retina and retinal ganglion cells (RGCs), and changes of the microstructure of neurons.

METHODS

The chronic ocular hypertension models were induced by 2 different ways. One kind of the models was built by unilateral circumlimbal suture (10/0) implantation (suture group), another kind of model was built by laser burns at trabecular meshwork and episcleral veins (laser group). The untreated contralateral eye served as the control group. Changes in IOP were observed and regularly monitored in the 2 groups of rats. HE staining was applied to observe the retinal and optic nerve pathology. Transmission electron microscope (TEM) was used to observe the mitochondrial morphology. RGCs were specifically labeled with Brn3b antibody and counted. The expression of caspase-3 was detected by Western blotting to clarify the apoptosis of RGCs.

RESULTS

Compared with the control group, IOP were significantly increased in the suture group and the laser group (both P<0.05). The suture group induced a 1.5-fold elevation of IOP, and sustained for 8 weeks. The laser group induced a 2-fold elevation of IOP for 12 weeks. Both methods could cause RGCs loss (both P<0.05), which were verified by pathology and immune staining of Brn3b. The expressions of caspase-3 were also increased (both P<0.05). The mitochondrial morphology became more fragment, which changed from long shape to round and small one under TEM in 2 models. For comparison, the pathology changes of retinal structure in suture group were not obviously than those in the laser group.

CONCLUSIONS

Circumlimbal suture can build an effective model of chronic elevated IOP and induce glaucomatous pathologic changes similar to those in the laser photocoagulation, but the pathologic changes are milder than those in laser photocoagulation. Compare with translimbal laser photocoagulation, equipment and skill demand for circumlimbal suture is less.

Retinal ganglion cell repopulation for vision restoration in optic neuropathy: a roadmap from the RReSTORe Consortium

Retinal ganglion cell (RGC) death in glaucoma and other optic neuropathies results in irreversible vision loss due to the mammalian central nervous system's limited regenerative capacity. RGC repopulation is a promising therapeutic approach to reverse vision loss from optic neuropathies if the newly introduced neurons can reestablish functional retinal and thalamic circuits. In theory, RGCs might be repopulated through the transplantation of stem cell-derived neurons or via the induction of endogenous transdifferentiation. The RGC Repopulation, Stem Cell Transplantation, and Optic Nerve Regeneration (RReSTORe) Consortium was established to address the challenges associated with the therapeutic repair of the visual pathway in optic neuropathy. In 2022, the RReSTORe Consortium initiated ongoing international collaborative discussions to advance the RGC repopulation field and has identified five critical areas of focus: (1) RGC development and differentiation, (2) Transplantation methods and models, (3) RGC survival, maturation, and host interactions, (4) Inner retinal wiring, and (5) Eye-to-brain connectivity. Here, we discuss the most pertinent questions and challenges that exist on the path to clinical translation and suggest experimental directions to propel this work going forward. Using these five subtopic discussion groups (SDGs) as a framework, we suggest multidisciplinary approaches to restore the diseased visual pathway by leveraging groundbreaking insights from developmental neuroscience, stem cell biology, molecular biology, optical imaging, animal models of optic neuropathy, immunology & immunotolerance, neuropathology & neuroprotection, materials science & biomedical engineering, and regenerative neuroscience. While significant hurdles remain, the RReSTORe Consortium's efforts provide a comprehensive roadmap for advancing the RGC repopulation field and hold potential for transformative progress in restoring vision in patients suffering from optic neuropathies.

Identifying new drugs and targets to treat rapidly elevated intraocular pressure for angle closure and secondary glaucomas to curb visual impairment and prevent blindness

A multitude of pharmacological compounds have been shown to lower and control intraocular pressure (IOP) in numerous species of animals and human subjects after topical ocular dosing or via other routes of administration. Most researchers have been interested in finding drug candidates that exhibit a relatively long duration of action from a chronic therapeutic use perspective, for example to treat ocular hypertension (OHT), primary open-angle glaucoma and even normotensive glaucoma. However, it is equally important to seek and characterize treatment modalities which offer a rapid onset of action to help provide fast relief from quickly rising IOP that occurs in certain eye diseases. These include acute angle-closure glaucoma, primary angle-closure glaucoma, uveitic and inflammatory glaucoma, medication-induced OHT, and other secondary glaucomas induced by eye injury or infection which can cause partial or complete loss of eyesight. Such fast-acting agents can delay or prevent the need for ocular surgery which is often used to lower the dangerously raised IOP. This research survey was therefore directed at identifying agents from the literature that demonstrated ocular hypotensive activity, normalizing and unifying the data, determining their onset of action and rank ordering them on the basis of rapidity of action starting within 30-60 min and lasting up to at least 3-4 h post topical ocular dosing in different animal species. This research revealed a few health authority-approved drugs and some investigational compounds that appear to meet the necessary criteria of fast onset of action coupled with significant efficacy to reduce elevated IOP (by ≥ 20%, preferably by >30%). However, translation of the novel animal-based findings to the human conditions remains to be demonstrated but represent viable targets, especially EP2-receptor agonists (e.g. omidenepag isopropyl; AL-6598; butaprost), mixed activity serotonin/dopamine receptor agonists (e.g. cabergoline), rho kinase inhibitors (e.g. AMA0076, Y39983), CACNA2D1-gene product inhibitors (e.g. pregabalin), melatonin receptor agonists, and certain K+-channel openers (e.g. nicorandil, pinacidil). Other drug candidates and targets were also identified and will be discussed.

Recently Approved Drugs for Lowering and Controlling Intraocular Pressure to Reduce Vision Loss in Ocular Hypertensive and Glaucoma Patients

Serious vision loss occurs in patients affected by chronically raised intraocular pressure (IOP), a characteristic of many forms of glaucoma where damage to the optic nerve components causes progressive degeneration of retinal and brain neurons involved in visual perception. While many risk factors abound and have been validated for this glaucomatous optic neuropathy (GON), the major one is ocular hypertension (OHT), which results from the accumulation of excess aqueous humor (AQH) fluid in the anterior chamber of the eye. Millions around the world suffer from this asymptomatic and progressive degenerative eye disease. Since clinical evidence has revealed a strong correlation between the reduction in elevated IOP/OHT and GON progression, many drugs, devices, and surgical techniques have been developed to lower and control IOP. The constant quest for new pharmaceuticals and other modalities with superior therapeutic indices has recently yielded health authority-approved novel drugs with unique pharmacological signatures and mechanism(s) of action and AQH drainage microdevices for effectively and durably treating OHT. A unique nitric oxide-donating conjugate of latanoprost, an FP-receptor prostaglandin (PG; latanoprostene bunod), new rho kinase inhibitors (ripasudil; netarsudil), a novel non-PG EP2-receptor-selective agonist (omidenepag isopropyl), and a form of FP-receptor PG in a slow-release intracameral implant (Durysta) represent the additions to the pharmaceutical toolchest to mitigate the ravages of OHT. Despite these advances, early diagnosis of OHT and glaucoma still lags behind and would benefit from further concerted effort and attention.

An optimized method for retrograde labelling and quantification of rabbit retinal ganglion cells

Rabbits are a commonly used animal model in glaucoma research, but their application has been limited by the techniques used to assess optic nerve injury (ONI). Our study devised an optimized method for retrograde labelling and analysing rabbit retinal ganglion cells (RGCs). This method involved improvements over the conventional method regarding the stereotaxic device, the positioning of superior colliculi, the target of axonal tracer delivery, and the visualization and analysis of labelled RGCs. To evaluate its efficacy, eight New Zealand White rabbits were divided into naïve and ONI groups. Unilateral limbal buckling surgery was performed in each animal of the ONI group to induce chronic ocular hypertension (OHT). The animals of both groups were injected with indocyanine green (ICG) into the interstice between the superior colliculus and occipital lobe on each side of the brain, and their eyes were examined by confocal scanning laser ophthalmoscopy (CSLO) after 48 h. The acquired images were then analysed to quantify the number of ICG-labelled RGCs in these eyes and their loss induced by OHT. To verify the identity and changes of the labelled RGCs, the retinas of the rabbits were subjected to immunofluorescence analyses. In addition, three animals were subjected to a second ICG labelling after 12 months to determine the influence of this procedure on the long-term viability of the labelled RGCs. Our results showed that ICG-labelled RGCs were detected by CSLO throughout the retinas of all animals. These RGCs showed a distinctly higher density below the ONH and were defective in sectorial areas in OHT eyes. Their average number in the cell counting area was 3989.2 ± 414.2 and 4023.3 ± 603.4 in the right and left eyes, respectively, of the naïve animals and 2590.9 ± 1474.2 and 3966.7 ± 24.0 in the OHT and non-OHT eyes, respectively, of the ONI animals. Immunofluorescence analyses showed positive staining with Brn3a and RBPMS in the ICG-labelled RGCs and sectorial defects of the cells in the OHT eyes, similarly as observed by CSLO. The second ICG labelling after 12 months in three animals showed no appreciable changes in RGC density compared with the first one. In summary, the optimized method of rabbit RGC retrograde labelling is reliable and accurate in both naïve and ONI animals and offers an approach for longitudinal observation of RGCs in the same eyes, which suggests its potential as a powerful tool for glaucoma and optic nerve research.

Drug Discovery Strategies for Inherited Retinal Degenerations

Inherited retinal degeneration is a group of blinding disorders afflicting more than 1 in 4000 worldwide. These disorders frequently cause the death of photoreceptor cells or retinal ganglion cells. In a subset of these disorders, photoreceptor cell death is a secondary consequence of retinal pigment epithelial cell dysfunction or degeneration. This manuscript reviews current efforts in identifying targets and developing small molecule-based therapies for these devastating neuronal degenerations, for which no cures exist. Photoreceptors and retinal ganglion cells are metabolically demanding owing to their unique structures and functional properties. Modulations of metabolic pathways, which are disrupted in most inherited retinal degenerations, serve as promising therapeutic strategies. In monogenic disorders, great insights were previously obtained regarding targets associated with the defective pathways, including phototransduction, visual cycle, and mitophagy. In addition to these target-based drug discoveries, we will discuss how phenotypic screening can be harnessed to discover beneficial molecules without prior knowledge of their mechanisms of action. Because of major anatomical and biological differences, it has frequently been challenging to model human inherited retinal degeneration conditions using small animals such as rodents. Recent advances in stem cell-based techniques are opening new avenues to obtain pure populations of human retinal ganglion cells and retinal organoids with photoreceptor cells. We will discuss concurrent ideas of utilizing stem-cell-based disease models for drug discovery and preclinical development.

Neuroprotection in neurodegenerations of the brain and eye: Lessons from the past and directions for the future

Background

Neurological and ophthalmological neurodegenerative diseases in large part share underlying biology and pathophysiology. Despite extensive preclinical research on neuroprotection that in many cases bridges and unifies both fields, only a handful of neuroprotective therapies have succeeded clinically in either.

Main body

Understanding the commonalities among brain and neuroretinal neurodegenerations can help develop innovative ways to improve translational success in neuroprotection research and emerging therapies. To do this, analysis of why translational research in neuroprotection fails necessitates addressing roadblocks at basic research and clinical trial levels. These include optimizing translational approaches with respect to biomarkers, therapeutic targets, treatments, animal models, and regulatory pathways.

Conclusion

The common features of neurological and ophthalmological neurodegenerations are useful for outlining a path forward that should increase the likelihood of translational success in neuroprotective therapies.

Genetic inhibition of collapsin response mediator protein-2 phosphorylation ameliorates retinal ganglion cell death in normal-tension glaucoma models

Glaucoma is a neurodegenerative disorder caused by the death of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) is a cause of glaucoma. However, glaucoma often develops with normal IOP and is known as normal-tension glaucoma (NTG). Glutamate neurotoxicity is considered as one of the significant causes of NTG, resulting in excessive stimulation of retinal neurons via the N-methyl-D-aspartate (NMDA) receptors. The present study examined the phosphorylation of collapsin response mediator protein-2 (CRMP2), a protein that is abundantly expressed in neurons and involved in their development. In two mouse models, NMDA-injection and glutamate/aspartate transporter (GLAST) mutant, CRMP2 phosphorylation at the cyclin-dependent kinase-5 (Cdk5) site was elevated in RGCs. We confirmed that the decrease in the number of RGCs and thickness of the inner retinal layer (IRL) could be suppressed after NMDA administration in CRMP2KI/KI mice with genetically inhibited CRMP2 phosphorylation. Next, we investigated GLAST heterozygotes (GLAST+/-) with CRMP2KI/KI (GLAST+/-;CRMP2KI/KI) and GLAST knockout (GLAST-/-) mice with CRMP2KI/KI (GLAST-/-;CRMP2KI/KI) mice and compared them with GLAST+/- and GLAST-/- mice. pCRMP2 (S522) inhibition significantly reduced RGC loss and IRL thinning. These results suggest that the inhibition of CRMP2 phosphorylation could be a novel strategy for treating NTG.

Sodium Hyaluronate-Induced Ocular Hypertension in Rats Damages the Direction-Selective Circuit and Inner/Outer Retinal Plexiform Layers

Purpose

To assess the changes in retinal morphology in a rat model of chronic glaucoma induced by ocular hypertension.

Methods

Intraocular pressure (IOP) was surgically increased through weekly injections of sodium hyaluronate (HYA) in the anterior eye chamber of the left eye of male Wistar rats, whereas the right eyes were sham operated (salt solution). During the 10-week experimental period, IOP was measured weekly with a rebound tonometer. Retinal cryosections were prepared for histological/immunohistochemical analysis and morphometry.

Results

IOP was higher in HYA-treated eyes than in sham-operated eyes along the 10-week period, which was significant from the fourth to the nineth week. Ocular hypertension in HYA-treated eyes was associated with morphologic and morphometric changes in bipolar cells, ON-OFF direction-selective ganglion cells, ON/OFF starburst amacrine cells, and inner plexiform layer sublamina.

Conclusions

Serial HYA treatment in the rat anterior eye chamber results in mild-to-moderate elevated and sustained IOP and ganglion cell death, which mimics most human open-angle glaucoma hallmarks. The reduced number of direction-selective ganglion cells and starburst amacrine cells accompanied by a deteriorated ON/OFF plexus in this glaucoma model could lend insight to the abnormalities in motion perception observed in patients with glaucoma.

Treatment of Glaucoma with Natural Products and Their Mechanism of Action: An Update

Glaucoma is one of the leading causes of irreversible blindness. It is generally caused by increased intraocular pressure, which results in damage of the optic nerve and retinal ganglion cells, ultimately leading to visual field dysfunction. However, even with the use of intraocular pressure-lowering eye drops, the disease still progresses in some patients. In addition to mechanical and vascular dysfunctions of the eye, oxidative stress, neuroinflammation and excitotoxicity have also been implicated in the pathogenesis of glaucoma. Hence, the use of natural products with antioxidant and anti-inflammatory properties may represent an alternative approach for glaucoma treatment. The present review highlights recent preclinical and clinical studies on various natural products shown to possess neuroprotective properties for retinal ganglion cells, which thereby may be effective in the treatment of glaucoma. Intraocular pressure can be reduced by baicalein, forskolin, marijuana, ginsenoside, resveratrol and hesperidin. Alternatively, Ginkgo biloba, Lycium barbarum, Diospyros kaki, Tripterygium wilfordii, saffron, curcumin, caffeine, anthocyanin, coenzyme Q10 and vitamins B3 and D have shown neuroprotective effects on retinal ganglion cells via various mechanisms, especially antioxidant, anti-inflammatory and anti-apoptosis mechanisms. Extensive studies are still required in the future to ensure natural products' efficacy and safety to serve as an alternative therapy for glaucoma.

Effects of lighting environment on the degeneration of retinal ganglion cells in glutamate/aspartate transporter deficient mice, a mouse model of normal tension glaucoma

Lighting conditions may affect the development of retinal degenerative diseases such as macular degeneration. In this study, to determine whether the lighting environment affects the progression of degeneration of retinal ganglion cells (RGCs), we examined glutamate/aspartate transporter (GLAST) heterozygous (GLAST^+/-) mice, a mouse model of normal tension glaucoma. GLAST^+/- mice were reared under a 12-h light-dark cycle (Light/Dark) or complete darkness (Dark/Dark) condition after birth. The total RGC number in the Dark/Dark group was significantly decreased compared with the Light/Dark group at 3 weeks old, while the number of osteopontin-positive αRGCs were similar in both groups. At 6 and 12 weeks old, the total RGC number were not significantly different in both conditions. In addition, the retinal function examined by multifocal electroretinogram were similar at 12 weeks old. These results suggest that lighting conditions may regulate the progression of RGC degeneration in some types of glaucoma.

Therapeutic Drugs and Devices for Tackling Ocular Hypertension and Glaucoma, and Need for Neuroprotection and Cytoprotective Therapies

Damage to the optic nerve and the death of associated retinal ganglion cells (RGCs) by elevated intraocular pressure (IOP), also known as glaucoma, is responsible for visual impairment and blindness in millions of people worldwide. The ocular hypertension (OHT) and the deleterious mechanical forces it exerts at the back of the eye, at the level of the optic nerve head/optic disc and lamina cribosa, is the only modifiable risk factor associated with glaucoma that can be treated. The elevated IOP occurs due to the inability of accumulated aqueous humor (AQH) to egress from the anterior chamber of the eye due to occlusion of the major outflow pathway, the trabecular meshwork (TM) and Schlemm’s canal (SC). Several different classes of pharmaceutical agents, surgical techniques and implantable devices have been developed to lower and control IOP. First-line drugs to promote AQH outflow via the uveoscleral outflow pathway include FP-receptor prostaglandin (PG) agonists (e.g., latanoprost, travoprost and tafluprost) and a novel non-PG EP2-receptor agonist (omidenepag isopropyl, Eybelis^®). TM/SC outflow enhancing drugs are also effective ocular hypotensive agents (e.g., rho kinase inhibitors like ripasudil and netarsudil; and latanoprostene bunod, a conjugate of a nitric oxide donor and latanoprost). One of the most effective anterior chamber AQH microshunt devices is the Preserflo^® microshunt which can lower IOP down to 10–13 mmHg. Other IOP-lowering drugs and devices on the horizon will be also discussed. Additionally, since elevated IOP is only one of many risk factors for development of glaucomatous optic neuropathy, a treatise of the role of inflammatory neurodegeneration of the optic nerve and retinal ganglion cells and appropriate neuroprotective strategies to mitigate this disease will also be reviewed and discussed.

Apolipoprotein E-Containing Lipoproteins and LRP1 Protect From NMDA-Induced Excitotoxicity Associated With Reducing α2-Macroglobulin in Müller Glia

Purpose

Optic nerve damage leads to impairment of visual functions. We previously demonstrated that apolipoprotein E-containing lipoproteins (E-LPs) protect retinal ganglion cells (RGCs) from degeneration in a glaucoma model of glutamate/aspartate transporter-deficient mice. This study aimed to determine whether E-LPs protect RGCs from N-methyl-d-aspartate (NMDA)-induced excitotoxicity, and to investigate the details of an indirect neuroprotective mechanism of E-LPs by reducing α2-macroglobulin, which interferes with the neuroprotective effect of E-LPs, in Müller glia.

Methods

Excitotoxicity was caused by intravitreal injection of NMDA, and then retinae were subjected to immunoblotting or quantitative reverse transcription-PCR. Primary cultures of mouse mixed retinal cells and mouse Müller glia were used for evaluating the effects of E-LPs on the expression of α2-macroglobulin.

Results

Intravitreal injection of E-LPs protected the optic nerve from degeneration and attenuated the increase in α2-macroglobulin in aqueous humor and retina of rats. E-LPs directly decreased the expression and secretion of α2-macroglobulin in primary cultures of Müller glia; this decrease in production of α2-macroglobulin was blocked by knockdown of the low-density lipoprotein receptor-related protein 1 (LRP1) with small interfering RNA. E-LPs promoted the phosphorylation of STAT3, whereas Stattic, an inhibitor of STAT3, restored the expression of α2-macroglobulin decreased by E-LPs.

Conclusions

In addition to our previous findings of the protection of RGCs by E-LPs, the new observations in Müller glia indicate that a reduction of the intraocular α2-macroglobulin, regulated by the E-LP-LRP1-STAT3 pathway, might be an additional protective mechanism against excitotoxicity in the retina.

Looking for In Vitro Models for Retinal Diseases

Retina is a layered structure of the eye, composed of different cellular components working together to produce a complex visual output. Because of its important role in visual function, retinal pathologies commonly represent the main causes of visual injury and blindness in the industrialized world. It is important to develop in vitro models of retinal diseases to use them in first screenings before translating in in vivo experiments and clinics. For this reason, it is important to develop bidimensional (2D) models that are more suitable for drug screening and toxicological studies and tridimensional (3D) models, which can replicate physiological conditions, for investigating pathological mechanisms leading to visual loss. This review provides an overview of the most common retinal diseases, relating to in vivo models, with a specific focus on alternative 2D and 3D in vitro models that can replicate the different cellular and matrix components of retinal layers, as well as injury insults that induce retinal disease and loss of the visual function.

Human primary retinal cells as an in-vitro model for investigating defective signalling caused by OPTN mutants associated with glaucoma

Studies carried out on the pathogenesis of glaucoma using murine cell lines and animal models require to be validated in human cells. Therefore, we explored the possibility of using human primary retinal cells (hPRCs) in culture as a model for molecular studies and testing of potential therapeutic drugs. For this purpose, central retinal tissue, obtained from the enucleated eyes of patients with anterior staphyloma, was digested with trypsin and grown in a medium containing supplements (basic fibroblast growth factor and fetal bovine serum). hPRCs at passage 1 and 2, show expression of either GFAP, a glial cell marker, or β-III tubulin, a retinal ganglion cell (RGC)-specific marker. But at passages 3-5 nearly all of hPRCs express several RGC-specific markers (Brn3 proteins, Thy-1, β-III tubulin, RBPMS and NeuN) but not GFAP. Expression of these markers indicated that these cells may have functional properties of RGCs. As RGCs are sensitive to glaucoma-associated mutants of OPTN, we analysed the survival of hPRCs upon overexpression of OPTN mutants. Glaucoma-associated mutants, E50K-OPTN and M98K-OPTN, induced significantly higher cell death in hPRCs compared to WT-OPTN, whereas an amyotrophic lateral sclerosis-associated mutant, E478G-OPTN, did not. TBK1 inhibitor Amlexanox protected hPRCs from E50K-OPTN and M98K-OPTN induced cell death. M98K-OPTN induced cell death was suppressed by inhibitors of CaMKKβ and AMPK in hPRCs as well as in 661W, a mouse cell line that expresses several markers of RGCs and RGC precursor cells. Our results suggest that hPRCs under appropriate culture condition show RGC-like properties. These cells can be used to explore the molecular mechanisms of cell death relevant for glaucoma pathogenesis and for testing of cytoprotective compounds.

Citicoline Modulates Glaucomatous Neurodegeneration Through Intraocular Pressure-Independent Control

Glaucoma is a neurodegenerative disease that causes progressive, irreversible vision loss. Currently, intraocular pressure (IOP) is the only modifiable risk factor for glaucoma. However, glaucomatous degeneration may continue despite adequate IOP control. Therefore, there exists a need for treatment that protects the visual system, independent of IOP. This study sought, first, to longitudinally examine the neurobehavioral effects of different magnitudes and durations of IOP elevation using multi-parametric magnetic resonance imaging (MRI), optokinetics and histology; and, second, to evaluate the effects of oral citicoline treatment as a neurotherapeutic in experimental glaucoma. Eighty-two adult Long Evans rats were divided into six groups: acute (mild or severe) IOP elevation, chronic (citicoline-treated or untreated) IOP elevation, and sham (acute or chronic) controls. We found that increasing magnitudes and durations of IOP elevation differentially altered structural and functional brain connectivity and visuomotor behavior, as indicated by decreases in fractional anisotropy in diffusion tensor MRI, magnetization transfer ratios in magnetization transfer MRI, T1-weighted MRI enhancement of anterograde manganese transport, resting-state functional connectivity, visual acuity, and neurofilament and myelin staining along the visual pathway. Furthermore, 3 weeks of oral citicoline treatment in the setting of chronic IOP elevation significantly reduced visual brain integrity loss and visual acuity decline without altering IOP. Such effects sustained after treatment was discontinued for another 3 weeks. These results not only illuminate the close interplay between eye, brain, and behavior in glaucomatous neurodegeneration, but also support a role for citicoline in protecting neural tissues and visual function in glaucoma beyond IOP control.

Retinal Genomic Fabric Remodeling after Optic Nerve Injury

Glaucoma is a multifactorial neurodegenerative disease, characterized by degeneration of the retinal ganglion cells (RGCs). There has been little progress in developing efficient strategies for neuroprotection in glaucoma. We profiled the retina transcriptome of Lister Hooded rats at 2 weeks after optic nerve crush (ONC) and analyzed the data from the genomic fabric paradigm (GFP) to bring additional insights into the molecular mechanisms of the retinal remodeling after induction of RGC degeneration. GFP considers three independent characteristics for the expression of each gene: level, variability, and correlation with each other gene. Thus, the 17,657 quantified genes in our study generated a total of 155,911,310 values to analyze. This represents 8830x more data per condition than a traditional transcriptomic analysis. ONC led to a 57% reduction in RGC numbers as detected by retrograde labeling with 1,1'-dioctadecyl-3,3,3,3'-tetramethylindocarbocyanine perchlorate (DiI). We observed a higher relative expression variability after ONC. Gene expression stability was used as a measure of transcription control and disclosed a robust reduction in the number of very stably expressed genes. Predicted protein-protein interaction (PPI) analysis with STRING revealed axon and neuron projection as mostly decreased processes, consistent with RGC degeneration. Conversely, immune response PPIs were found among upregulated genes. Enrichment analysis showed that complement cascade and Notch signaling pathway, as well as oxidative stress and kit receptor pathway were affected after ONC. To expand our studies of altered molecular pathways, we examined the pairwise coordination of gene expressions within each pathway and within the entire transcriptome using Pearson correlations. ONC increased the number of synergistically coordinated pairs of genes and the number of similar profiles mainly in complement cascade and Notch signaling pathway. This deep bioinformatic study provided novel insights beyond the regulation of individual gene expression and disclosed changes in the control of expression of complement cascade and Notch signaling functional pathways that may be relevant for both RGC degeneration and remodeling of the retinal tissue after ONC.

Mesenchymal Stem Cell-Based Therapy for Retinal Degenerative Diseases: Experimental Models and Clinical Trials

Retinal degenerative diseases, such as age-related macular degeneration, retinitis pigmentosa, diabetic retinopathy or glaucoma, represent the main causes of a decreased quality of vision or even blindness worldwide. However, despite considerable efforts, the treatment possibilities for these disorders remain very limited. A perspective is offered by cell therapy using mesenchymal stem cells (MSCs). These cells can be obtained from the bone marrow or adipose tissue of a particular patient, expanded in vitro and used as the autologous cells. MSCs possess potent immunoregulatory properties and can inhibit a harmful inflammatory reaction in the diseased retina. By the production of numerous growth and neurotrophic factors, they support the survival and growth of retinal cells. In addition, MSCs can protect retinal cells by antiapoptotic properties and could contribute to the regeneration of the diseased retina by their ability to differentiate into various cell types, including the cells of the retina. All of these properties indicate the potential of MSCs for the therapy of diseased retinas. This view is supported by the recent results of numerous experimental studies in different preclinical models. Here we provide an overview of the therapeutic properties of MSCs, and their use in experimental models of retinal diseases and in clinical trials.

Effects of topical prostaglandin drops on angiogenesis in an in ovo chick chorioallantoic membrane model

BACKGROUND

To investigate the effects of bimatoprost, latanoprost and travoprost on angiogenesis in the chick chorioallantoic membrane (CAM) model in ovo.

MATERIALS AND METHODS

Fifty fertilized specific-pathogen-free chick eggs were used in this preclinical, prospective, experimental embryo study. Eggs were randomly distributed into 5 groups of ten eggs. Eggs were placed in the incubator after disinfection of their shells with alcohol and monitored appropriate temperature and humidity. On the 3rd day of incubation, a small window was opened on the eggshell. Bimatoprost in group 1, latanoprost in group 2, travoprost in group 3, bevacizumab in group 4, phosphate-buffered-saline (PBS) used in group 5 was applied by injection to CAM. The sterile film was glued onto the broken part of the shell and the eggs were placed in the incubator again. On the 8th day of incubation, eggs were opened and vascular structures on CAMs were examined. Digital photographs were taken, analysed in the ImageJ open source image processing software and differences between groups were evaluated. Thereafter, VEGF (Vascular endothelial growth factor) levels were measured appropriately in the embryo samples.

RESULTS

All embryos in the prostaglandin groups and the PBS control group were observed to have life signs confirmed by heart rate. In 8 embryos in the bevacizumab group, no life signs were confirmed, while 2 embryos with life signs showed severe hypoplasia. Vascular density, number of vessels and VEGF levels in the bimatoprost, latanoprost and travoprost groups, there were statistically significantly higher than the PBS control group.

CONCLUSION

This study demonstrates that topical prostaglandin drops increase angiogenesis in the chick CAM model in ovo.

Inflammation in Glaucoma: From the back to the front of the eye, and beyond

The pathophysiology of glaucoma is complex, multifactorial and not completely understood. Elevated intraocular pressure (IOP) and/or impaired retinal blood flow may cause initial optic nerve damage. In addition, age-related oxidative stress in the retina concurrently with chronic mechanical and vascular stress is crucial for the initiation of retinal neurodegeneration. Oxidative stress is closely related to cell senescence, mitochondrial dysfunction, excitotoxicity, and neuroinflammation, which are involved in glaucoma progression. Accumulating evidence from animal glaucoma models and from human ocular samples suggests a dysfunction of the para-inflammation in the retinal ganglion cell layer and the optic nerve head. Moreover, quite similar mechanisms in the anterior chamber could explain the trabecular meshwork dysfunction and the elevated IOP in primary open-angle glaucoma. On the other hand, ocular surface disease due to topical interventions is the most prominent and visible consequence of inflammation in glaucoma, with a negative impact on filtering surgery failure, topical treatment efficacy, and possibly on inflammation in the anterior segment. Consequently, glaucoma appears as an outstanding eye disease where inflammatory changes may be present to various extents and consequences along the eye structure, from the ocular surface to the posterior segment, and the visual pathway. Here we reviewed the inflammatory processes in all ocular structures in glaucoma from the back to the front of the eye and beyond. Our approach was to explain how para-inflammation is necessary to maintain homoeostasis, and to describe abnormal inflammatory findings observed in glaucomatous patients or in animal glaucoma models, supporting the hypothesis of a dysregulation of the inflammatory balance toward a pro-inflammatory phenotype. Possible anti-inflammatory therapeutic approaches in glaucoma are also discussed.

Topical ripasudil stimulates neuroprotection and axon regeneration in adult mice following optic nerve injury

Optic nerve injury induces optic nerve degeneration and retinal ganglion cell (RGC) death that lead to visual disturbance. In this study, we examined if topical ripasudil has therapeutic potential in adult mice after optic nerve crush (ONC). Topical ripasudil suppressed ONC-induced phosphorylation of p38 mitogen-activated protein kinase and ameliorated RGC death. In addition, topical ripasudil significantly suppressed the phosphorylation of collapsin response mediator protein 2 and cofilin, and promoted optic nerve regeneration. These results suggest that topical ripasudil promotes RGC protection and optic nerve regeneration by modulating multiple signaling pathways associated with neural cell death, microtubule assembly and actin polymerization.

Suppression of Oxidative Stress as Potential Therapeutic Approach for Normal Tension Glaucoma

Glaucoma is a neurodegenerative disease of the eye, which involves degeneration of retinal ganglion cells (RGCs): the output neurons of the retina to the brain, which with their axons comprise the optic nerve. Recent studies have shown the possible involvement of oxidative stress in the pathogenesis of glaucoma, especially in the subtype of normal tension glaucoma. Basic experiments utilizing rodent and primate models of glaucoma revealed that antioxidants protect RGCs under various pathological conditions including glutamate neurotoxicity and optic nerve injury. These results suggested that existing drugs and food factors may be useful for prevention and hence therapy of glaucoma. In this review, we highlight some therapeutic candidates, particularly those with antioxidant properties, and discuss the therapeutic potential of RGC protection by modulating gene expressions that prevent and ameliorate glaucoma.

Changes of Ocular Dimensions as a Marker of Disease Progression in a Murine Model of Pigmentary Glaucoma

Purpose

The elevation of intraocular pressure (IOP), a major risk factor in glaucoma, is an important parameter tracked in experimental models of this disease. However, IOP measurement in laboratory rodents is challenging and may not correlate with some key pathological events that occur in the development of glaucoma. The aims of this study were to quantify changes in ocular morphology in DBA/2J mice that develop spontaneous, age-dependent, pigmentary glaucoma and to check the possible correlation of these parameters with IOP.

Method

Eye morphology was evaluated with MRI in DBA/2J, DBA/2J-Gpnmb⁺/SjJ, and C57BL/6J female mice ages 3, 6, 9, 12, and 15 months. The animals were anesthetized with isoflurane. A planar receive-only surface coil (inner diameter = 10 mm) was placed over each animal’s left eye and the image was acquired with a 7T small animal-dedicated magnetic resonance tomograph and T2-weighted TurboRARE sequence. Ocular dimensions were manually quantitated using OsiriX software. IOP was measured with rebound tonometry.

Results

In the control animals, no age-related changes in the ocular morphology were noted. Since 6 months of age, the anterior chamber deepening and elongation of the eyeballs of DBA/2J mice was detectable. We found a significant, positive correlation between IOP and axial length, anterior chamber area, or anterior chamber width in C57BL/6J mice but not in DBA/2J mice. However, after excluding the measurements performed in the oldest DBA/2J mice (i.e. analyzing only the animals ages 3 to 12 months), we demonstrated a significant positive correlation between IOP and anterior chamber width.

Conclusion

High-resolution magnetic resonance imaging of the eye area in mice enables reproducible and consistent measures of key dimensions of the eyeball. We observed age-dependent alterations in the eye morphology of DBA/2J mice that mostly affected the anterior chamber. We also demonstrated a correlation between some of the ocular dimensions and the IOP of C57Bl/6J mice and DBA/2J mice with moderately advanced glaucomatous pathology.

Neuroprotective Strategies for Retinal Ganglion Cell Degeneration: Current Status and Challenges Ahead

The retinal ganglion cells (RGCs) are the output cells of the retina into the brain. In mammals, these cells are not able to regenerate their axons after optic nerve injury, leaving the patients with optic neuropathies with permanent visual loss. An effective RGCs-directed therapy could provide a beneficial effect to prevent the progression of the disease. Axonal injury leads to the functional loss of RGCs and subsequently induces neuronal death, and axonal regeneration would be essential to restore the neuronal connectivity, and to reestablish the function of the visual system. The manipulation of several intrinsic and extrinsic factors has been proposed in order to stimulate axonal regeneration and functional repairing of axonal connections in the visual pathway. However, there is a missing point in the process since, until now, there is no therapeutic strategy directed to promote axonal regeneration of RGCs as a therapeutic approach for optic neuropathies.

Normal tension glaucoma-like degeneration of the visual system in aged marmosets

The common marmoset (Callithrix jacchus) is a non-human primate that provides valuable models for neuroscience and aging research due to its anatomical similarities to humans and relatively short lifespan. This study was carried out to examine whether aged marmosets develop glaucoma, as seen in humans. We found that 11% of the aged marmosets presented with glaucoma-like characteristics; this incident rate is very similar to that in humans. Magnetic resonance imaging showed a significant volume loss in the visual cortex, and histological analyses confirmed the degeneration of the lateral geniculate nuclei and visual cortex in the affected marmosets. These marmosets did not have elevated intraocular pressure, but showed an increased oxidative stress level, low cerebrospinal fluid (CSF) pressure, and low brain-derived neurotrophic factor (BDNF) and TrkB expression in the retina, optic nerve head and CSF. Our findings suggest that marmosets have potential to provide useful information for the research of eye and the visual system.

Cholinergic nervous system and glaucoma: From basic science to clinical applications

The cholinergic system has a crucial role to play in visual function. Although cholinergic drugs have been a focus of attention as glaucoma medications for reducing eye pressure, little is known about the potential modality for neuronal survival and/or enhancement in visual impairments. Citicoline, a naturally occurring compound and FDA approved dietary supplement, is a nootropic agent that is recently demonstrated to be effective in ameliorating ischemic stroke, traumatic brain injury, Parkinson's disease, Alzheimer's disease, cerebrovascular diseases, memory disorders and attention-deficit/hyperactivity disorder in both humans and animal models. The mechanisms of its action appear to be multifarious including (i) preservation of cardiolipin, sphingomyelin, and arachidonic acid contents of phosphatidylcholine and phosphatidylethanolamine, (ii) restoration of phosphatidylcholine, (iii) stimulation of glutathione synthesis, (iv) lowering glutamate concentrations and preventing glutamate excitotoxicity, (v) rescuing mitochondrial function thereby preventing oxidative damage and onset of neuronal apoptosis, (vi) synthesis of myelin leading to improvement in neuronal membrane integrity, (vii) improving acetylcholine synthesis and thereby reducing the effects of mental stress and (viii) preventing endothelial dysfunction. Such effects have vouched for citicoline as a neuroprotective, neurorestorative and neuroregenerative agent. Retinal ganglion cells are neurons with long myelinated axons which provide a strong rationale for citicoline use in visual pathway disorders. Since glaucoma is a form of neurodegeneration involving retinal ganglion cells, citicoline may help ameliorate glaucomatous damages in multiple facets. Additionally, trans-synaptic degeneration has been identified in humans and experimental models of glaucoma suggesting the cholinergic system as a new brain target for glaucoma management and therapy.

Differential effects of N-acetylcysteine on retinal degeneration in two mouse models of normal tension glaucoma

N-acetylcysteine (NAC) is widely used as a mucolytic agent and as an antidote to paracetamol overdose. NAC serves as a precursor of cysteine and stimulates the synthesis of glutathione in neural cells. Suppressing oxidative stress in the retina may be an effective therapeutic strategy for glaucoma, a chronic neurodegenerative disease of the retinal ganglion cells (RGCs) and optic nerves. Here we examined the therapeutic potential of NAC in two mouse models of normal tension glaucoma, in which excitatory amino-acid carrier 1 (EAAC1) or glutamate/aspartate transporter (GLAST) gene was deleted. EAAC1 is expressed in retinal neurons including RGCs, whereas GLAST is mainly expressed in Müller glial cells. Intraperitoneal administration of NAC prevented RGC degeneration and visual impairment in EAAC1-deficient (knockout; KO) mice, but not in GLAST KO mice. In EAAC1 KO mice, oxidative stress and autophagy were suppressed with increased glutathione levels by NAC treatment. Our findings suggest a possibility that systemic administration of NAC may be available for some types of glaucoma patients.