Rodent models of glaucoma

Agreement of tonometer for measuring intraocular pressure in Wistar rats: a systematic review

Glaucoma is the most common cause of irreversible blindness in the world. It is associated with elevated intraocular pressure (IOP). Fluctuations in tonometer readings have implications for glaucoma research, where accurate IOP measurements are vital for evaluating disease progression and treatment efficacy. Researchers should carefully select the appropriate tonometer and consider biases associated with different tonometers. Validation against standard measurements can improve IOP measurement accuracy in rat models. In conclusion, this systematic review will emphasize on the importance of selecting the appropriate tonometer for IOP measurement in rat models, considering potential biases and their implications for glaucoma research. Accurate and consistent IOP measurement in rat models is crucial for understanding glaucoma pathophysiology and developing effective treatments. This systematic review aims to assess agreement among tonometers used for measuring IOP in Wistar rat models primarily focusing on TonoLab, TonoVet, and Tono-pen. The review was conducted using PRISMA guidelines. Two articles were included for qualitative synthesis. The studies compared manometric IOP with TonoLab, rebound tonometer, and Tono-pen XL readings. It was observed that TonoLab consistently underestimated IOP, while Tono-pen XL tended to overestimate IOP compared to manometric measurements. The study's findings will help researchers in making decisions about tonometer selection, leading to more reliable outcomes in glaucoma research using rat models. Further research, specifically RCT's (randomized controlled trial) is needed to confirm the results and enhance IOP measurement precision in rat models.

Modeling complex age-related eye disease

Modeling complex eye diseases like age-related macular degeneration (AMD) and glaucoma poses significant challenges, since these conditions depend highly on age-related changes that occur over several decades, with many contributing factors remaining unknown. Although both diseases exhibit a relatively high heritability of >50%, a large proportion of individuals carrying AMD- or glaucoma-associated genetic risk variants will never develop these diseases. Furthermore, several environmental and lifestyle factors contribute to and modulate the pathogenesis and progression of AMD and glaucoma. Several strategies replicate the impact of genetic risk variants, pathobiological pathways and environmental and lifestyle factors in AMD and glaucoma in mice and other species. In this review we will primarily discuss the most commonly available mouse models, which have and will likely continue to improve our understanding of the pathobiology of age-related eye diseases. Uncertainties persist whether small animal models can truly recapitulate disease progression and vision loss in patients, raising doubts regarding their usefulness when testing novel gene or drug therapies. We will elaborate on concerns that relate to shorter lifespan, body size and allometries, lack of macula and a true lamina cribrosa, as well as absence and sequence disparities of certain genes and differences in their chromosomal location in mice. Since biological, rather than chronological, age likely predisposes an organism for both glaucoma and AMD, more rapidly aging organisms like small rodents may open up possibilities that will make research of these diseases more timely and financially feasible. On the other hand, due to the above-mentioned anatomical and physiological features, as well as pharmacokinetic and -dynamic differences small animal models are not ideal to study the natural progression of vision loss or the efficacy and safety of novel therapies. In this context, we will also discuss the advantages and pitfalls of alternative models that include larger species, such as non-human primates and rabbits, patient-derived retinal organoids, and human organ donor eyes.

MicroRNA-93 promotes the pathogenesis of glaucoma by inhibiting matrix metalloproteinases as well as up-regulating extracellular matrix and Rho/ROCK signaling pathways

Objective

To investigate the effect and potential molecular mechanism of microRNA-93 (miR-93) on retinal ganglion cells (RGCs) apoptosis as well as retinal damage in acute glaucoma mice.

Methods

RGCs apoptosis were induced by oxygen-glucose deprivation and reperfusion (OGD/R). The pro-apoptotic effect of miR-93 was evaluated by transfecting miR-93 mimics or miR-93 inhibitor into OGD/R-induced RGCs. The viability and apoptosis of RGCs were determined by MTT assay and flow cytometry. Mouse model of acute glaucoma were successfully induced via high intraocular pressure (IOP), and then these model animals were randomly divided into vehicle group, miR-93 mimics group or miR-93 inhibitor group (n = 10), using healthy mice as normal control. Histopathologic changes of retinal tissue were evaluated by Hematoxylin and Eosin (H&E) staining method. Moreover, cell counts of retinal ganglion cell layer and mean thickness of different layers were also determined. Quantitative real-time PCR (qPCR) and western blotting analysis were used to detect the mRNA and protein expression levels of extracellular matrix (ECM), matrix metalloproteinases (MMPs) and Rho/ROCK signaling pathway.

Results

miR-93 mimics significantly decreased or promoted the viability and apoptosis of OGD/R-induced RGCs, respectively. In addition, miR-93 mimics significantly exacerbated the degree of retinal tissue damage in mice with acute glaucoma, which was accompanied by a decrease in the number of ganglion cell layer (GCL) cells and the thickness of different tissue layers. Moreover, miR-93 mimics significantly increased IOP in mice with acute glaucoma. Significantly, miR-93 inhibitors significantly reversed the above changes. In addition, results of Western blot analysis showed that miR-93 mimics increased and decreased the expression of ECM-associated and MMP-associated proteins, respectively, by activating the Rho/ROCK signaling pathway. In contrast, miR-93 significantly decreased and increased the expression of ECM-associated and MMP-associated proteins, and suppressed the expression of Rho/ROCK signaling pathway-related proteins.

Conclusion

miR-93 can promote the development of glaucoma by activating Rho/ROCK signaling pathway to mediate the accumulation of ECM-related proteins as well as the down-regulation of MMP-related proteins.

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.

Durable 3D murine ex vivo retina glaucoma models for optical coherence tomography

Durable and standardized phantoms with optical properties similar to native healthy and disease-like biological tissues are essential tools for the development, performance testing, calibration and comparison of label-free high-resolution optical coherence tomography (HR-OCT) systems. Available phantoms are based on artificial materials and reflect thus only partially ocular properties. To address this limitation, we have performed investigations on the establishment of durable tissue phantoms from ex vivo mouse retina for enhanced reproduction of in vivo structure and complexity. In a proof-of-concept study, we explored the establishment of durable 3D models from dissected mouse eyes that reproduce the properties of normal retina structures and tissue with glaucoma-like layer thickness alterations. We explored different sectioning and preparation procedures for embedding normal and N-methyl-D-aspartate (NMDA)-treated mouse retina in transparent gel matrices and epoxy resins, to generate durable three-dimensional tissue models. Sample quality and reproducibility were quantified by thickness determination of the generated layered structures utilizing computer-assisted segmentation of OCT B-scans that were acquired with a commercial HR-OCT system at a central wavelength of 905 nm and analyzed with custom build software. Our results show that the generated 3D models feature thin biological layers close to current OCT resolution limits and glaucoma-like tissue alterations that are suitable for reliable HR-OCT performance characterization. The comparison of data from resin-embedded tissue with native murine retina in gels demonstrates that by utilization of appropriate preparation protocols, highly stable samples with layered structures equivalent to native tissues can be fabricated. The experimental data demonstrate our concept as a promising approach toward the fabrication of durable biological 3D models suitable for high-resolution OCT system performance characterization supporting the development of optimized instruments for ophthalmology applications.

Stable Gastric Pentadecapeptide BPC 157-Possible Novel Therapy of Glaucoma and Other Ocular Conditions

Recently, stable gastric pentadecapeptide BPC 157 therapy by activation of collateral pathways counteracted various occlusion/occlusion-like syndromes, vascular, and multiorgan failure, and blood pressure disturbances in rats with permanent major vessel occlusion and similar procedures disabling endothelium function. Thereby, we revealed BPC 157 cytoprotective therapy with strong vascular rescuing capabilities in glaucoma therapy. With these capabilities, BPC 157 therapy can recover glaucomatous rats, normalize intraocular pressure, maintain retinal integrity, recover pupil function, recover retinal ischemia, and corneal injuries (i.e., maintained transparency after complete corneal abrasion, corneal ulceration, and counteracted dry eye after lacrimal gland removal or corneal insensitivity). The most important point is that in glaucomatous rats (three of four episcleral veins cauterized) with high intraocular pressure, all BPC 157 regimens immediately normalized intraocular pressure. BPC 157-treated rats exhibited normal pupil diameter, microscopically well-preserved ganglion cells and optic nerve presentation, normal fundus presentation, nor- mal retinal and choroidal blood vessel presentation, and normal optic nerve presentation. The one episcleral vein rapidly upgraded to accomplish all functions in glaucomatous rats may correspond with occlusion/occlusion-like syndromes of the activated rescuing collateral pathway (azygos vein direct blood flow delivery). Normalized intraocular pressure in glaucomatous rats corresponded to the counteracted intra-cranial (superior sagittal sinus), portal, and caval hypertension, and aortal hypotension in occlusion/occlusion-like syndromes, were all attenuated/eliminated by BPC 157 therapy. Furthermore, given in other eye disturbances (i.e., retinal ischemia), BPC 157 instantly breaks a noxious chain of events, both at an early stage and an already advanced stage. Thus, we further advocate BPC 157 as a therapeutic agent in ocular disease.

Cell-Specific Expression of Human SIRT1 by Gene Therapy Reduces Retinal Ganglion Cell Loss Induced by Elevated Intraocular Pressure

SIRT1 prevents retinal ganglion cell (RGC) loss in several acute and subacute optic neuropathy models following pharmacologic activation or genetic overexpression. We hypothesized that adeno-associated virus (AAV)-mediated overexpression of SIRT1 in RGCs in a chronic ocular hypertension model can reduce RGC loss, thereby preserving visual function by sustained therapeutic effect. A control vector AAV-eGFP and therapeutic vector AAV-SIRT1 were constructed and optimized for transduction efficiency. A magnetic microbead mouse model of ocular hypertension was optimized to induce a time-dependent and chronic loss of visual function and RGC degeneration. Mice received intravitreal injection of control or therapeutic AAV in which a codon-optimized human SIRT1 expression is driven by a RGC selective promoter. Intraocular pressure (IOP) was measured, and visual function was examined by optokinetic response (OKR) weekly for 49 days following microbead injection. Visual function, RGC survival, and axon numbers were compared among control and therapeutic AAV-treated animals. AAV-eGFP and AAV-SIRT1 showed transduction efficiency of ~ 40%. AAV-SIRT1 maintains the transduction of SIRT1 over time and is selectively expressed in RGCs. Intravitreal injections of AAV-SIRT1 in a glaucoma model preserved visual function, increased RGC survival, and reduced axonal degeneration compared with the control construct. Over-expression of SIRT1 through AAV-mediated gene transduction indicates a RGC-selective component of neuroprotection in multiple models of acute optic nerve degeneration. Results here show a neuroprotective effect of RGC-selective gene therapy in a chronic glaucoma model characterized by sustained elevation of IOP and subsequent RGC loss. Results suggest that this strategy may be an effective therapeutic approach for treating glaucoma, and warrants evaluation for the treatment of other chronic neurodegenerative diseases.

Regional differences of the sclera in the ocular hypertensive rat model induced by circumlimbal suture

PURPOSE

To describe the regional differences of the sclera in ocular hypertension (OHT) models with the inappropriate extension of the ocular axis.

METHODS

To discover the regional differences of the sclera at the early stage, OHT models were established using circumlimbal suture (CS) or sclerosant injection (SI). Axial length (AL) was measured by ultrasound and magnetic resonance imaging. The glaucoma-associated distinction was determined by intraocular pressure (IOP) and retrograde tracing of retinal ganglion cells (RGCs). The central thickness of the ganglion cell complex (GCC) was measured by optical coherence tomography. RGCs and collagen fibrils were detected using a transmission electron microscope, furthermore, anti-alpha smooth muscle actin (αSMA) was determined in the early stage after the operation.

RESULTS

Compared with the control group, the eyes in OHT models showed an increased IOP (P < 0.001 in the CS group, P = 0.001 in the SI group), growing AL (P = 0.026 in the CS group, P = 0.043 in the SI group), reduction of central RGCs (P < 0.001 in the CS group, P = 0.017 in the SI group), thinning central GCC (P < 0.001 in the CS group), and a distinctive expression of αSMA in the central sclera in the early 4-week stage after the operation (P = 0.002 in the CS group). Compared with the SI group, the eye in the CS group showed a significantly increased AL (7.1 ± 0.4 mm, P = 0.031), reduction of central RGCs (2121.1 ± 87.2 cells/mm², P = 0.001), thinning central GCC (71.4 ± 0.8 pixels, P = 0.015), and a distinctive expression of αSMA (P = 0.005). Additionally, ultrastructural changes in RGCs, scleral collagen fibers, and collagen crimp were observed in the different regions. Increased collagen volume fraction in the posterior segment of the eyeball wall (30.2 ± 3.1%, P = 0.022) was observed by MASSON staining in the CS group.

CONCLUSION

Regional differences of the sclera in the ocular hypertensive rat model induced by CS may provide a reference for further treatment of scleral-related eye disorders.

RAGE and its ligand amyloid beta promote retinal ganglion cell loss following ischemia-reperfusion injury

Introduction

Glaucoma is a progressive neurodegenerative disease associated with age. Accumulation of amyloid-beta (Aß) proteins in the ganglion cell layer (GCL) and subsequent retinal ganglion cell (RGC) loss is an established pathological hallmark of the disease. The mechanism through which Aß provokes RGC loss remains unclear. The receptor for the advanced glycation end product (RAGE), and its ligand Aß, have been shown to mediate neuronal loss via internalizing Aß within the neurons. In this study, we investigated whether the RAGE-Aß axis plays a role in RGC loss in experimental glaucoma.

Methods

Retinal ischemia was induced by an acute elevation of intraocular pressure in RAGE^-/- and wild-type (WT) control mice. In a subset of animals, oligomeric Aß was injected directly into the vitreous of both strains. RGC loss was assessed using histology and biochemical assays. Baseline and terminal positive scotopic threshold (pSTR) were also recorded.

Results

Retinal ischemia resulted in 1.9-fold higher RGC loss in WT mice compared to RAGE^-/- mice (36 ± 3% p < 0.0001 vs. 19 ± 2%, p = 0.004). Intravitreal injection of oligomeric Aß resulted in 2.3-fold greater RGC loss in WT mice compared to RAGE^-/- mice, 7-days post-injection (55 ± 4% p = 0.008 vs. 24 ± 2%, p = 0.02). We also found a significant decline in the positive scotopic threshold response (pSTR) amplitude of WT mice compared to RAGE^-/- (36 ± 3% vs. 16 ± 6%).

Discussion

RAGE^-/- mice are protected against RGC loss following retinal ischemia. Intravitreal injection of oligomeric Aß accelerated RGC loss in WT mice but not RAGE^-/-. A co-localization of RAGE and Aß, suggests that RAGE-Aß binding may contribute to RGC loss.

Mechanisms of retinal ganglion cell injury following acute increases in intraocular pressure

The maintenance of intraocular pressure (IOP) is critical to preserving the pristine optics required for vision. Disturbances in IOP can directly impact the optic nerve and retina, and inner retinal injury can occur following acute and chronic IOP elevation. There are a variety of animal models that have been developed to study the effects of acute and chronic elevation of IOP on the retina, retinal ganglion cell (RGC) morphology, intracellular signaling, gene expression changes, and survival. Acute IOP models induce injury that allows for the study of RGC response to well characterized injury and potential recovery. This review will focus on the initial impact of acute IOP elevation on RGC injury and recovery as these early responses may be the best targets for potential therapeutic interventions to promote RGC survival in glaucoma.

Microglia: Friends or Foes in Glaucoma? A Developmental Perspective

Glaucoma is the most prevalent form of optic neuropathy where a progressive degeneration of retinal ganglion cells (RGCs) leads to irreversible loss of vision. The mechanism underlying glaucomatous degeneration remains poorly understood. However, evidence suggests that microglia, which regulate RGC numbers and synaptic integrity during development and provide homeostatic support in adults, may contribute to the disease process. Hence, microglia represent a valid cellular target for therapeutic approaches in glaucoma. Here, we provide an overview of the role of microglia in RGC development and degeneration in the backdrop of neurogenesis and neurodegeneration in the central nervous system and discuss how pathological recapitulation of microglia-mediated developmental mechanisms may help initiate or exacerbate glaucomatous degeneration.

Matrix Metalloproteinases and Glaucoma

Matrix metalloproteinases (MMPs) are enzymes that decompose extracellular matrix (ECM) proteins. MMPs are thought to play important roles in cellular processes, such as cell proliferation, differentiation, angiogenesis, migration, apoptosis, and host defense. MMPs are distributed in almost all intraocular tissues and are involved in physiological and pathological mechanisms of the eye. MMPs are also associated with glaucoma, a progressive neurodegenerative disease of the eyes. MMP activity affects intraocular pressure control and apoptosis of retinal ganglion cells, which are the pathological mechanisms of glaucoma. It also affects the risk of glaucoma development based on genetic pleomorphism. In addition, MMPs may affect the treatment outcomes of glaucoma, including the success rate of surgical treatment and side effects on the ocular surface due to glaucoma medications. This review discusses the various relationships between MMP and glaucoma.

Histological and molecular characterization of glaucoma model induced by one or two injections of microbeads to the anterior chamber of mice

PURPOSE

To characterize glaucoma-induced damage following injections of plastic microbeads into the anterior chamber of mice.

METHODS

Mice were divided into three groups: a single plastic microbeads injection (n = 21); two consecutive plastic microbead injections to the right eye at 1-week intervals, 4 of which with two consecutive saline injections in the left eye (n = 15); and an additional control group of two consecutive saline injections at 1-week intervals (n = 6). Intraocular pressure (IOP) was measured weekly. Retinal thickness, ganglion cells (RGCs) and axonal loss, inflammatory and gliosis reactions were measured at week four. Molecular analysis using qRT-PCR in the microbeads injection groups focused on expression levels of inflammation and glaucoma-related genes.

RESULTS

Mean IOP following single injection at 4 weeks was significantly elevated compared to baseline in injected eyes (14.5 ± 3.3 mmHg vs. 11.1 ± 2.5 mmHg, respectively, p = 0.003) and not in fellow eyes (13.2 ± 2.9 mmHg vs. 12.2 ± 2.9, respectively, NS). Six (35.3%) bead-injected eyes had IOP ≥ 17 mmHg compared with 2 (11.8%) saline-injected control eyes. Retinal thickness in injected and fellow eyes was 193.7 ± 15.5 µm and 223.9 ± 15.5 µm, respectively (p = 0.03). RGC loss in injected and fellow eyes was 16.0 ± 0.5 and 17.6 ± 0.7 cells per 200 µm, respectively (p = 0.005). Retinal gliosis, axonal loss and inflammatory cell infiltration to the bead-injected eyes were noted. Molecular analysis following double injection showed STAT3 expression decreased in the glaucoma-induced optic nerves (0.69 ± 0.3 vs. 1.16 ± 0.3, p = 0.04), but increased in the glaucoma-induced retinae (p = 0.05) versus saline; retinal IL-1β decreased significantly (0.04 ± 0.04 vs. 0.36 ± 0.2, p = 0.02). TNF-α, NFkB and SOD-1 expression did not change.

CONCLUSION

One/two injections of microbeads elevated IOP, with measurable neuronal damage. An inflammatory response was detected in the injured retina and optic nerve. The therapeutic significance of these findings should be explored.

CCN2/CTGF—A Modulator of the Optic Nerve Head Astrocyte

In primary open-angle glaucoma (POAG), a neurodegenerative disease of the optic nerve (ON) and leading cause of blindness, the optic nerve head (ONH) undergoes marked structural extracellular matrix (ECM) changes, which contribute to its permanent deformation and to degeneration of ON axons. The remodeling process of the ECM causes changes in the biomechanical properties of the ONH and the peripapillary sclera, which is accompanied by an increased reactivity of the resident astrocytes. The molecular factors involved in the remodeling process belong to the Transforming growth factor (TGF)-β superfamily, especially TGF-β2. In previous publications we showed that TGF-β2 induced ECM alterations are mediated by Cellular Communication Network Factor (CCN)2/Connective Tissue Growth Factor (CTGF) and recently we showed that CCN2/CTGF is expressed by astrocytes of the ON under normal conditions. In this study we wanted to get a better understanding of the function of CCN2/CTGF under normal and pathologic conditions. To this end, we analyzed the glial lamina and peripapillary sclera of CCN2/CTGF overexpressing mice and studied the effect of CCN2/CTGF and increasing substratum stiffness on murine ON astrocytes in vitro. We observed enhanced astrocyte reactivity in the ONH, increased ECM protein synthesis in the peripapillary sclera and increased Ccn2/Ctgf expression in the ONH during the pathologic development in situ. CCN2/CTGF treatment of primary murine ON astrocytes induced a higher migration rate, and increase of ECM proteins including fibronectin, elastin and collagen type III. Furthermore, the astrocytes responded to stiffer substratum with increased glial fibrillary acidic protein, vimentin, actin and CCN2/CTGF synthesis. Finally, we observed the reinforced appearance of CCN2/CTGF in the lamina cribrosa of glaucomatous patients. We conclude that reactive changes in ONH astrocytes, induced by the altered biomechanical characteristics of the region, give rise to a self-amplifying process that includes increased TGF-β2/CCN2/CTGF signaling and leads to the synthesis of ECM molecules and cytoskeleton proteins, a process that in turn augments the stiffness at the ONH. Such a scenario may finally result in a vicious circle in the pathogenesis of POAG. The transgenic CTGF-overexpressing mouse model might be an optimal model to study the chronic pathological POAG changes in the ONH.

Angiotensin II related glial cell activation and necroptosis of retinal ganglion cells after systemic hypotension in glaucoma

The purpose of this study was to design an animal model mimicking glaucoma with hemodynamic instability and to identify involvement of angiotensin II (AngII) and associated changes of the retina. Systemic hypotension was induced in Sprague–Dawley rats by oral hydrochlorothiazide administration. Rats were sacrificed at 4, 8, and 12-week time points. AngII and receptor levels were examined in the serum and retina. To examine the relationship between glia activation and associated RGC death, biochemical analysis of GFAP, Iba-1, and necroptosis associated factors such as TNFα, receptor-interacting protein (RIP) 1, 3, and inactive caspase 8 were explored. To investigate the difference in RGC death mechanism, JNK inhibitor or RIP3 inhibitor were given intraperitoneally to rats with ocular hypertension and systemic hypotension both to identify the pathway mainly involved. AngII and receptors were increased in the serum and retina of systemic hypotensive rat. At 4, 8, and 12 weeks after hypotension induction, glial activation was increased as indicated by GFAP and Iba-1 staining. TNFα, RIP3 were elevated. and downregulation of inactive caspase 8 was apparent in the retina of hypotensive rat. Electron microscopy revealed that necroptosis of RGC was gradually increased after systemic hypotension. Following intraperitoneal JNK inhibitor or RIP3 inhibitor administration, RGC loss was attenuated in systemic hypotensive rats but not in ocular hypertensive rats. In conclusion, AngII is involved in glial activation and associated RGC necroptosis following systemic hypotension. This pathway represents a novel and distinct cell death mechanism when compared to that involved in elevated intraocular pressure.

The Role of Axonal Transport in Glaucoma

Glaucoma is a neurodegenerative disease that affects the retinal ganglion cells (RGCs) and leads to progressive vision loss. The first pathological signs can be seen at the optic nerve head (ONH), the structure where RGC axons leave the retina to compose the optic nerve. Besides damage of the axonal cytoskeleton, axonal transport deficits at the ONH have been described as an important feature of glaucoma. Axonal transport is essential for proper neuronal function, including transport of organelles, synaptic components, vesicles, and neurotrophic factors. Impairment of axonal transport has been related to several neurodegenerative conditions. Studies on axonal transport in glaucoma include analysis in different animal models and in humans, and indicate that its failure happens mainly in the ONH and early in disease progression, preceding axonal and somal degeneration. Thus, a better understanding of the role of axonal transport in glaucoma is not only pivotal to decipher disease mechanisms but could also enable early therapies that might prevent irreversible neuronal damage at an early time point. In this review we present the current evidence of axonal transport impairment in glaucomatous neurodegeneration and summarize the methods employed to evaluate transport in this disease.

Retinal ganglion cell loss in an ex vivo mouse model of optic nerve cut is prevented by curcumin treatment

Retinal ganglion cell (RGC) loss is a pathologic feature common to several retinopathies associated to optic nerve damage, leading to visual loss and blindness. Although several scientific efforts have been spent to understand the molecular and cellular changes occurring in retinal degeneration, an effective therapy to counteract the retinal damage is still not available. Here we show that eyeballs, enucleated with the concomitant optic nerve cut (ONC), when kept in PBS for 24 h showed retinal and optic nerve degeneration. Examining retinas and optic nerves at different time points in a temporal window of 24 h, we found a thinning of some retinal layers especially RGC's layer, observing a powerful RGC loss after 24 h correlated with an apoptotic, MAPKs and degradative pathways dysfunctions. Specifically, we detected a time-dependent increase of Caspase-3, -9 and pro-apoptotic marker levels, associated with a strong reduction of BRN3A and NeuN levels. Importantly, a powerful activation of JNK, c-Jun, and ERK signaling (MAPKs) were observed, correlated with a significant augmented SUMO-1 and UBC9 protein levels. The degradation signaling pathways was also altered, causing a significant decrease of ubiquitination level and an increased LC3B activation. Notably, it was also detected an augmented Tau protein level. Curcumin, a powerful antioxidant natural compound, prevented the alterations of apoptotic cascade, MAPKs, and SUMO-1 pathways and the degradation system, preserving the RGC survival and the retinal layer thickness. This ex vivo retinal degeneration model could be a useful method to study, in a short time window, the effect of neuroprotective tools like curcumin that could represent a potential treatment to contrast retinal cell death.

Deletion of transcription factor AP-2β from the developing murine trabecular meshwork region leads to progressive glaucomatous changes

Glaucoma is one of the leading causes of irreversible blindness and can result from abnormalities in anterior segment structures required for aqueous humor outflow, including the trabecular meshwork (TM) and Schlemm's canal (SC). Transcription factors such as AP-2β play critical roles in anterior segment development. Here, we show that the Mgp-Cre knock-in (Mgp-Cre.KI) mouse can be used to target the embryonic periocular mesenchyme giving rise to the TM and SC. Fate mapping of male and female mice indicates that AP-2β loss causes a decrease in iridocorneal angle cells derived from Mgp-Cre.KI-expressing populations compared to controls. Moreover, histological analyses revealed peripheral iridocorneal adhesions in AP-2β mutants that were accompanied by a decrease in expression of TM and SC markers, as observed using immunohistochemistry. In addition, rebound tonometry showed significantly higher intraocular pressure (IOP) that was correlated with a progressive significant loss of retinal ganglion cells, reduced retinal thickness, and reduced retinal function, as measured using an electroretinogram, in AP-2β mutants compared with controls, reflecting pathology described in late-stage glaucoma patients. Importantly, elevated IOP in AP-2β mutants was significantly reduced by treatment with latanoprost, a prostaglandin analog that increases unconventional outflow. These findings demonstrate that AP-2β is critical for TM and SC development, and that these mutant mice can serve as a model for understanding and treating progressive human primary angle-closure glaucoma.

An inducible rodent glaucoma model that exhibits gradual sustained increase in intraocular pressure with distinct inner retina and optic nerve inflammation

Glaucoma is a chronic and progressive neurodegenerative disease of the optic nerve resulting in loss of retinal ganglion cells (RGCs) and vision. The most prominent glaucoma risk factor is increased intraocular pressure (IOP), and most models focus on reproducing this aspect to study disease mechanisms and targets. Yet, current models result in IOP profiles that often do not resemble clinical glaucoma. Here we introduce a new model that results in a gradual and sustained IOP increase over time. This approach modifies a circumlimbal suture method, taking care to make the sutures 'snug' instead of tight, without inducing an initial IOP spike. This approach did not immediately affect IOPs, but generated gradual ocular hypertension (gOHT) as the sutures tighten over time, in comparison to loosely sutured control eyes (CON), resulting in an average 12.6 mmHg increase in IOP at 17 weeks (p < 0.001). Corresponding characterization revealed relevant retinal and optic nerve pathology, such as thinning of the retinal nerve fiber layer, decreased optokinetic response, RGC loss, and optic nerve head remodeling. Yet, angles remained open, with no evidence of inflammation. Corresponding biochemical profiling indicated significant increases in TGF-β2 and 3, and IL-1 family cytokines in gOHT optic nerve tissues compared to CON, with accompanying microglial reactivity, consistent with active tissue injury and repair mechanisms. Remarkably, this signature was absent from optic nerves following acute ocular hypertension (aOHT) associated with intentionally tightened sutures, although the resulting RGC loss was similar in both methods. These results suggest that the pattern of IOP change has an important impact on underlying pathophysiology.

Age and intraocular pressure in murine experimental glaucoma

Age and intraocular pressure (IOP) are the two most important risk factors for the development and progression of open-angle glaucoma. While IOP is commonly considered in models of experimental glaucoma (EG), most studies use juvenile or adult animals and seldom older animals which are representative of the human disease. This paper provides a concise review of how retinal ganglion cell (RGC) loss, the hallmark of glaucoma, can be evaluated in EG with a special emphasis on serial in vivo imaging, a parallel approach used in clinical practice. It appraises the suitability of EG models for the purpose of in vivo imaging and argues for the use of models that provide a sustained elevation of IOP, without compromise of the ocular media. In a study with parallel cohorts of adult (3-month-old, equivalent to 20 human years) and old (2-year-old, equivalent to 70 human years) mice, we compare the effects of elevated IOP on serial ganglion cell complex thickness and individual RGC dendritic morphology changes obtained in vivo. We also evaluate how age modulates the impact of elevated IOP on RGC somal and axonal density in histological analysis as well the density of melanopsin RGCs. We discuss the challenges of using old animals and emphasize the potential of single RGC imaging for understanding the pathobiology of RGC loss and evaluating new therapeutic avenues.

Cell-Based Neuroprotection of Retinal Ganglion Cells in Animal Models of Optic Neuropathies

Retinal ganglion cells (RGCs) comprise a heterogenous group of projection neurons that transmit visual information from the retina to the brain. Progressive degeneration of these cells, as it occurs in inflammatory, ischemic, traumatic or glaucomatous optic neuropathies, results in visual deterioration and is among the leading causes of irreversible blindness. Treatment options for these diseases are limited. Neuroprotective approaches aim to slow down and eventually halt the loss of ganglion cells in these disorders. In this review, we have summarized preclinical studies that have evaluated the efficacy of cell-based neuroprotective treatment strategies to rescue retinal ganglion cells from cell death. Intraocular transplantations of diverse genetically nonmodified cell types or cells engineered to overexpress neurotrophic factors have been demonstrated to result in significant attenuation of ganglion cell loss in animal models of different optic neuropathies. Cell-based combinatorial neuroprotective approaches represent a potential strategy to further increase the survival rates of retinal ganglion cells. However, data about the long-term impact of the different cell-based treatment strategies on retinal ganglion cell survival and detailed analyses of potential adverse effects of a sustained intraocular delivery of neurotrophic factors on retina structure and function are limited, making it difficult to assess their therapeutic potential.

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.

Intravitreally Injected Methylene Blue Protects Retina against Acute Ocular Hypertension in Rats

Purpose: To assess the neuroprotective effects of methylene blue (MB) in a rat model of acute ocular hypertension (AOH) and explore its possible mechanisms.Methods: Our AOH rat model was obtained with anterior chamber perfusion for 60 min. After that, 100 μM MB was injected into the vitreous cavity immediately after injury. Electroretinogram, fundus photography, optical coherence tomography (OCT) and retina morphology examination were utilized to quantify retinal damage before surgery, as well as 7, 14 and 28 days after. The average number of surviving retinal ganglion cells (RGCs) was counted after fluorescent retrograde labelling with 4% DiI. And TUNEL assay was used to investigate retinal cell apoptosis at 24 hours after AOH. Nrf2 and BACE1 in the retina were determined by RT-qPCR analysis.Results: AOH did produce a severe degeneration effect on the whole retinal layer. Intravitreally injected MB maintained certain retinal thickness after AOH, reduced the destruction of electroretinograms, and enhanced RGCs survival. The average number of TUNEL-labelled cells statistically reduced in the MB-treated retina tissue compared with retina treated with normal saline. The relative mRNA level of Nrf2 was also much higher in the MB-treated retinas after AOH, and the expression of BACE1 had a decline in the AOH + MB group.Conclusions: MB can protect the retina from AOH injury and the possible mechanism might involve the inhibition of BACE1 expression and the activation of Nrf2 antioxidant pathway.

Elevated Hydrostatic Pressure Causes Retinal Degeneration Through Upregulating Lipocalin-2

Elevation of intraocular pressure is a major risk factor for glaucoma development, which causes the loss of retinal ganglion cells (RGCs). Lipocalin 2 (Lcn2) is upregulated in glaucomatous retinae; however, whether Lcn2 is directly involved in glaucoma is debated. In this study, retinal explant cultures were subjected to increased water pressure using a two-chamber culture device, and Lcn2 protein levels were examined by immunoblotting. In situ TdT-mediated dUTP nick and labeling (TUNEL) and glial fibrillary acidic protein (GFAP) immunohistochemical assays were performed to assess apoptosis and gliosis, respectively. The neurotoxicity of Lcn2 in the retinal explant culture was determined with exogenous administration of recombinant Lcn2. The Lcn2 protein levels, percentage of TUNEL-positive cells, and GFAP-positive area were significantly higher in retinae cultured under 50 cm H₂O pressure loads compared to those cultured under 20 cm H₂O. We found that Lcn2 exhibited neurotoxicity in retinae at dose of 1 μg/ml. The negative effects of increased hydrostatic pressure were attenuated by the iron chelator deferoxamine. This is the first report demonstrating the direct upregulation of Lcn2 by elevating hydrostatic pressure. Modulating Lcn2 and iron levels may be a promising therapeutic approach for retinal degeneration.

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.

Ion-Complex Microcrystal Formulation Provides Sustained Delivery of a Multimodal Kinase Inhibitor from the Subconjunctival Space for Protection of Retinal Ganglion Cells

Glaucoma is the leading cause of irreversible blindness worldwide. Elevated intraocular pressure (IOP) is one of the major risk factors for glaucoma onset and progression, and available pharmaceutical interventions are exclusively targeted at IOP lowering. However, degeneration of retinal ganglion cells (RGCs) may continue to progress despite extensive lowering of IOP. A complementary strategy to IOP reduction is the use of neuroprotective agents that interrupt the process of cell death by mechanisms independent of IOP. Here, we describe an ion complexation approach for formulating microcrystals containing ~50% loading of a protein kinase inhibitor, sunitinib, to enhance survival of RGCs with subconjunctival injection. A single subconjunctival injection of sunitinib-pamoate complex (SPC) microcrystals provided 20 weeks of sustained retina drug levels, leading to neuroprotection in a rat model of optic nerve injury. Furthermore, subconjunctival injection of SPC microcrystals also led to therapeutic effects in a rat model of corneal neovascularization. Importantly, therapeutically relevant retina drug concentrations were achieved with subconjunctival injection of SPC microcrystals in pigs. For a chronic disease such as glaucoma, a formulation that provides sustained therapeutic effects to complement IOP lowering therapies could provide improved disease management and promote patient quality of life.

Evaluation of the Effectiveness of a Chronic Ocular Hypertension Mouse Model Induced by Intracameral Injection of Cross-Linking Hydrogel

Background: Glaucoma is an irreversible and blinding neurodegenerative disease that is characterized by progressive loss of retinal ganglion cells. The current animal models of glaucoma fail to provide a chronic elevated intraocular pressure and cannot maintain the optical media clarity for a long time, which brings some difficulties to the study of glaucoma. Here, we developed a new chronic ocular hypertension model of mice induced by cross-linking hydrogel intracameral injection.

Methods: C57BL/6J mice aged 6–8 weeks were randomly divided into the control group and the operation group. The mice of the operation group were injected with cross-linking hydrogel to induce ocular hypertension. Intraocular pressure was measured preoperatively, 3 days after surgery, and weekly until the end of the study. Flash visual evoked potential (F-VEP) was used to observe optic nerve function at different times (preoperatively and 2, 4, and 6 weeks) after chronic ocular hypertension (COH). Retinal TNF-α, IL-1β, and IL-17A protein expression were measured by western blotting in the control group and in mice at 2, 4, and 6 weeks after COH. Microglial cell activation was evaluated by immunofluorescence staining and western blotting. Apoptosis and loss of retinal ganglion cells after 2, 4, and 6 weeks of intracameral injection of cross-linking hydrogel were observed by the TUNEL assay and Brn3a protein labeling. The loss of optic nerve axons in COH mice was evaluated by neurofilament heavy polypeptide protein labeling.

Results: Intracameral injection of the cross-linking hydrogel induces increased intraocular pressure (IOP) to a mean value of 19.3 ± 4.1 mmHg, which was sustained for at least 8 weeks. A significant difference in IOP was noted between COH mice and sham-operation mice (p < 0.0001). The success rate was 75%. The average amplitude of F-VEP in mice with COH was reduced (p = 0.0149, 0.0012, and 0.0009 at 2, 4, and 6 weeks after COH vs. the control group, respectively), and the average latent period in mice with COH was longer (p = 0.0290, <0.0001, and <0.0001 at 2, 4, and 6 weeks after COH vs. the control group, respectively) compared with that in the control group. TNF-α, IL-1β, IL-17A, Iba-1, and CD68 protein expression increased in COH mice. During the processing of COH, the number of microglial cells increased along with cellular morphological changes of rounder bodies and thicker processes compared with the control group. Apoptosis of retinal ganglion cells (RGCs) was clearly observed in mice at 2, 4, and 6 weeks after COH (p = 0.0061, 0.0012, <0.0001, and 0.0371 at 2, 4, and 6 weeks after COH vs. the control group, respectively). The RGC density decreased significantly in the COH mice compared with the control group (p = 0.0042, 0.0036, and <0.0001 at 2, 4, and 6 weeks after COH vs. the control group, respectively). There was a significant loss of optic nerve axons in mice after intracameral injection of cross-linking hydrogel (p = 0.0095, 0.0002, and <0.0001 at 2, 4, and 6 weeks after COH vs. the control group, respectively).

Conclusions: A single intracameral injection of cross-linking hydrogel can effectively induce chronic ocular hypertension in mice, which causes progressive loss of retinal ganglion cells, increased expression levels of inflammatory cytokines and microglial cell activation, and deterioration of optic nerve function.

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.

Increased episcleral venous pressure in a mouse model of circumlimbal suture induced ocular hypertension

PURPOSE

To investigate changes in aqueous humor dynamics during intraocular pressure (IOP) elevation induced by circumlimbal suture in mice.

METHODS

Ocular hypertension (OHT) was induced by applying a circumlimbal suture behind the limbus in male adult C57BL6/J mice. In the OHT group, the suture was left in place for an average of 8 weeks (n = 10, OHT group). In the sham control group the suture was cut at 2 days (n = 9, sham group) and in the naïve control group (n = 5) no suture was implanted. IOP was measured at baseline across 3 days, 1 h post-suture implantation, and at the chronic endpoint. Anterior segments were assessed using optical coherence tomography (OCT). Episcleral venous pressure (EVP), total outflow facility (C), uveoscleral outflow (Fu) and aqueous humor flow rate (Fin) were determined using a constant-flow infusion model.

RESULTS

All aqueous dynamic and chronic IOP outcome measures showed no difference between sham and naïve controls (p > 0.05) and thus these groups were combined into a single control group. IOP was elevated in OHT group compared with controls (p < 0.01). Chronic suture implantation did not change pupil size, anterior chamber depth or iridocorneal angles (p > 0.05). EVP was significantly higher in OHT eyes compared to control eyes (p < 0.01). There was no statistical difference in C, Fu and Fin between groups (p > 0.05). A significant linear correlation was found between IOP and EVP (R² = 0.35, p = 0.001).

CONCLUSIONS

Circumlimbal suture implantation in mouse eyes results in chronic IOP elevation without angle closure. Chronic IOP elevation is likely to reflect higher EVP.

Ovariectomy worsens visual function after mild optic nerve crush in rodents

Glaucoma is the leading cause of irreversible blindness worldwide, and women represent roughly 60% of the affected population. Early menopause and estrogen signaling defects are risk factors for glaucoma. Recently, we found that surgical menopause exacerbated visual dysfunction in an ocular hypertension model of glaucoma. Here, we investigated if surgical menopause exacerbated visual dysfunction in a model of direct retinal ganglion cell (RGC) damage via optic nerve crush (ONC). Female Long Evans rats (n = 12) underwent ovariectomy (OVX) to induce surgical menopause or Sham surgery. Eight weeks post-surgery, baseline visual function was assessed via optomotor response. Afterwards, rats underwent monocular ONC. Visual function was assessed at 4, 8, and 12 weeks post-ONC. At 12 weeks, retinal function via electroretinography and retinal nerve fiber layer (RNFL) thickness via optical coherence tomography were measured. Visual acuity was reduced after ONC (p < 0.001), with surgical menopausal animals having 31.7% lower visual acuity than Sham animals at 12 weeks (p = 0.01). RNFL thinning (p < 0.0001) and decreased RGC function (p = 0.0016) occurred at 12 weeks in ONC groups. Surgical menopause worsens visual acuity after direct RGC damage using an ONC model. This demonstrates that surgical menopause plays a role in visual function after injury.

A lab-on-a-chip model of glaucoma

AIMS

We developed a glaucoma-on-a-chip model to evaluate the viability of retinal ganglion cells (RGCs) against high pressure and the potential effect of neuroprotection.

METHODS

A three-layered chip consisting of interconnecting microchannels and culture wells was designed and fabricated from poly-methyl methacrylate sheets. The bottom surface of the wells was modified by air plasma and coated with different membranes to provide a suitable extracellular microenvironment. RGCs were purified from postnatal Wistar rats by magnetic assisted cell sorting up to 70% and characterized by flow cytometry and immunocytochemistry. The cultured RGCs were exposed to normal (15 mmHg) or elevated pressure (33 mmHg) for 6, 12, 24, 36, and 48 hr, with and without adding brain-derived neurotrophic factor (BDNF) or a novel BDNF mimetic (RNYK).

RESULTS

Multiple inlet ports allow culture media and gas into the wells under elevated hydrostatic pressure. PDL/laminin formed the best supporting membrane. RGC survival rates were 85%, 78%, 70%, 67%, and 61% under normal pressure versus 40%, 22%, 18%, 12%, and 10% under high pressure at 6, 12, 24, 36, and 48 hr, respectively. BDNF and RNYK separately reduced RGC death rates about twofold under both normal and elevated pressures.

CONCLUSION

This model recapitulated the effects of elevated pressure over relatively short time periods and demonstrated the neuroprotective effects of BDNF and RNYK.

Efficacy, Drug Sensitivity, and Safety of a Chronic Ocular Hypertension Rat Model Established Using a Single Intracameral Injection of Hydrogel into the Anterior Chamber

Background

Chronic ocular hypertension (COH) models mostly focus on changes in intraocular pressure (IOP) and loss of retinal ganglion cells (RGCs). The present study evaluated important glaucoma-related changes in visual function, response to common ocular hypotensive drugs, and safety for our previously developed rat model.

Material/Methods

The model was established through a single injection of hydrogel into the anterior chambers. Efficacy was assessed through F-VEP by measuring latency and amplitude of P1. We evenly divided 112 rats into 4 groups: control and COH at 2, 4, and 8 weeks. Response to 5 common drugs (brimonidine, timolol, benzamide, pilocarpine, and bimatoprost) were each tested on 6 rats and assessed using difference in IOP. Safety assessment was conducted through histological analysis of 24 rats evenly divided into 4 groups of control and COH at 2, 4, and 8 weeks. Corneal endothelial cells (CECs) of 24 additional rats were used to determine toxic effects through TUNEL and CCK-8 assays.

Results

P1 latency and amplitude of VEP demonstrated the model is effective in inducing optic nerve function impairment. Only the drug pilocarpine failed to have an obvious hypotensive effect, while the other 4 were effective. CECs at 2, 4, and 8 weeks showed no significant differences from control groups in results of histological analysis, TUNEL, and CCK-8 assays.

Conclusions

A single injection of hydrogel into the anterior chamber is effective for modeling COH, can respond to most commonly used hypotensive drugs, and is non-toxic to the eyes.

Longitudinal outcomes of circumlimbal suture model-induced chronic ocular hypertension in Sprague-Dawley albino rats

PURPOSE

To characterise longitudinal structural and functional changes in albino Sprague-Dawley rats following circumlimbal suture ocular hypertension (OHT) induction.

METHODS

Ten-week-old rats (n = 24) underwent suture implantation around the limbal region in both eyes. On the next day, the suture was removed from one eye (control eyes) and left intact in the other eye (OHT eyes) of each animal. Intraocular pressure (IOP) was monitored weekly twice for the next 15 weeks. Optical coherence tomography (OCT) and electroretinogram (ERG) were measured at baseline and weeks 4, 8, 12, and 15, and eyes were then collected for histological assessment.

RESULTS

Sutured eyes (n = 12) developed IOP elevation of ~ 50% in the first 2 weeks that was sustained at ~ 25% above the control eye up to week 15 (p = 0.001). Animals with insufficient IOP elevation (n = 6), corneal changes (n = 3), and attrition (n = 3) were excluded from the analysis. OHT eyes developed significant retinal nerve fibre layer (RNFL) thinning (week 4: - 19 ± 14%, p = 0.10; week 8: - 17 ± 12%, p = 0.04; week 12: - 16 ± 10%, p = 0.04, relative to baseline) and reduction in retinal ganglion cell (RGC) density (- 32 ± 26%, p = 0.02). At week 15, both inner (9 ± 7%, p = 0.01) and outer retinal layer thicknesses (6.0 ± 5%, p = 0.001) showed a mild increase in thicknesses. The positive scotopic threshold response (- 28 ± 25%, p = 0.04) and a-wave were significantly reduced at week 12 (- 35 ± 21%; p = 0.04), whereas b-wave was not significantly affected (week 12: - 18 ± 27%, p = 0.24).

CONCLUSION

The circumlimbal suture model produced a chronic, moderate IOP elevation in an albino strain that led to RNFL thinning and reduced RGC density along with the reductions in ganglion and photoreceptoral cell functions. There was a small thickening in both outer and inner retinal layers.

New antiglaucomatous agent for the treatment of open angle glaucoma: Polymeric inserts for drug release and in vitro and in vivo study

A benzamidine derivative from diminazene was tested for a novel activity: treatment of primary open-angle glaucoma. This drug was incorporated into mucoadhesive polymeric inserts prepared using chitosan (Chs) and chondroitin sulfate (CS). Of current interest is the mucoadhesion, which increases the contact time with the ocular surface, resulting in improved bioavailability; also, the inserts are made to act as a prolonged release system. In the present work the inserts were prepared by the solvent casting method using different polymeric proportions (30:70, 50:50, 75:25% w/w Chs:CS and 100% Chs). Thermal analysis and infrared spectroscopy both demonstrated physical dispersion of the active drug. The most promising was the 50:50% Chs:CS which demonstrated that it was not fragile and has an in vitro release profile of up to 180 minutes. In addition, it presented greater adhesion strength in relation to the other formulations. These physicochemical results corroborate the in vivo tests performed. In this sense, we also demonstrated that the treatment with the 50:50% insert can control the intraocular pressure (IOP) for at least 3 weeks and prevents damage to the retinal ganglion cells (RGCs) compared to the placebo insert. Thus, this indicates thus that the new drug is quite viable and promising in glaucoma treatment.

An In Vitro Bovine Cellular Model for Human Schlemm's Canal Endothelial Cells and Their Response to TGFβ Treatment

Purpose

Due to the limited availability of primary human Schlemm's canal (SC) endothelial cells, we aimed to develop an in vitro cellular model using the angular aqueous plexus (AAP) cells from bovine eyes.

Methods

We harvested a mixture of cells from the trabecular meshwork region including AAP loops from multiple donors, followed by puromycin treatment and immunostaining of Von Willebrand factor and vascular endothelial (VE)-cadherin to confirm identity. Previously identified differentially expressed genes in glaucomatous SC cells were examined in non-glaucomatous SC cells (n = 3) under 0% or 15% equibiaxial strain for 24 hours using droplet digital polymerase chain reaction (ddPCR) and analyzed using the Ingenuity Pathway Analysis (IPA) software application to identify upstream regulators. To compare the cellular responses to candidate regulators of these mechanoresponsive genes, AAP and human SC cells (n = 3) were treated with 5 or 10 ng/mL transforming growth factor beta-2 (TGFβ2) for 24 or 48 hours, followed with expression profiling using real-time PCR or ddPCR.

Results

We found that the isolated AAP cells displayed uniform cobblestone-like morphology and positive expression of two endothelial markers. In stretched SC cells, nine glaucoma-related genes were upregulated, and IPA implicated TGFβ as a potential upstream regulator. The effects of TGFβ2 treatment were similar for both AAP and SC cells in a dose- and time-dependent manner, activating TGFBR1 and SMAD2, inhibiting BMP4, and altering expression of three glaucoma-related genes (DCN,EZR, and CYP1B1).

Conclusions

Bovine AAP cells may serve as an alternative cellular model of human SC cells.

Translational Relevance

These AAP cells may be used to study the functional pathways related to the outflow facility.

Gabor patterns as stimuli in a rodent visual attention task

BACKGROUND

Gabor patterns are defined as the product of a sinusoid function and a Gaussian envelope and are commonly used in visual and attentional research due to their ability to selectively stimulate the primary visual cortex. The aim of this study was to investigate whether Gabor patterns can be used as visual stimuli in the rodent continuous performance test (rCPT), a newly developed task to study attentional function and impulsivity.

METHODS

Sixteen male C57BL/6 J mice were trained in the rCPT using Gabor patterns as visual stimuli and their performance was compared to sixteen mice that were trained using traditional high-contrast pattern stimuli. Mice were compared during training, baseline, and a variable stimulus duration probe.

RESULTS

The Gabor pattern group required more training sessions to reach criteria than the group with high-contrast patterns. At baseline, the Gabor pattern group showed a higher false alarm rate and a lower discriminability index. As task difficulty increased during the variable stimulus duration probe, differences between groups became more pronounced. Specifically, the Gabor pattern group showed decreased hit rate and discriminability index, as well as increased false alarm rate and premature responses compared to the high-contrast pattern group.

CONCLUSION

This feasibility study showed that it is possible to use Gabor patterns as visual stimuli in the rCPT, although it increases task demands. We discuss the differences between Gabor patterns and high-contrast patterns in the context of translatability of animal models in visual and cognitive research and give two examples of applicability.

AxoNet: A deep learning-based tool to count retinal ganglion cell axons

In this work, we develop a robust, extensible tool to automatically and accurately count retinal ganglion cell axons in optic nerve (ON) tissue images from various animal models of glaucoma. We adapted deep learning to regress pixelwise axon count density estimates, which were then integrated over the image area to determine axon counts. The tool, termed AxoNet, was trained and evaluated using a dataset containing images of ON regions randomly selected from whole cross sections of both control and damaged rat ONs and manually annotated for axon count and location. This rat-trained network was then applied to a separate dataset of non-human primate (NHP) ON images. AxoNet was compared to two existing automated axon counting tools, AxonMaster and AxonJ, using both datasets. AxoNet outperformed the existing tools on both the rat and NHP ON datasets as judged by mean absolute error, R2 values when regressing automated vs. manual counts, and Bland-Altman analysis. AxoNet does not rely on hand-crafted image features for axon recognition and is robust to variations in the extent of ON tissue damage, image quality, and species of mammal. Therefore, AxoNet is not species-specific and can be extended to quantify additional ON characteristics in glaucoma and potentially other neurodegenerative diseases.

Adaptive optics two-photon microscopy enables near-diffraction-limited and functional retinal imaging in vivo

In vivo fundus imaging offers non-invasive access to neuron structures and biochemical processes in the retina. However, optical aberrations of the eye degrade the imaging resolution and prevent visualization of subcellular retinal structures. We developed an adaptive optics two-photon excitation fluorescence microscopy (AO-TPEFM) system to correct ocular aberrations based on a nonlinear fluorescent guide star and achieved subcellular resolution for in vivo fluorescence imaging of the mouse retina. With accurate wavefront sensing and rapid aberration correction, AO-TPEFM permits structural and functional imaging of the mouse retina with submicron resolution. Specifically, simultaneous functional calcium imaging of neuronal somas and dendrites was demonstrated. Moreover, the time-lapse morphological alteration and dynamics of microglia were characterized in a mouse model of retinal disorder. In addition, precise laser axotomy was achieved, and degeneration of retinal nerve fibres was studied. This high-resolution AO-TPEFM is a promising tool for non-invasive retinal imaging and can facilitate the understanding of a variety of eye diseases as well as neurodegenerative disorders in the central nervous system.

Visualization of the Retina in Intact Eyes of Mice and Ferrets Using a Tissue Clearing Method

Purpose

Visualization of specific cells and structures in intact organs would greatly facilitate our knowledge about pathological changes; therefore, a tissue clearing method applicable to the intact eye may be valuable. Here we report a novel imaging method for the retina using the hyperhydration-based tissue clearing technique CUBIC (Clear, Unobstructed Brain/Body Imaging Cocktails and Computational Analysis).

Methods

Eyes of Institute of Cancer Research (ICR) mice, C57BL/6 mice, and normally pigmented sable ferrets (Mustela putorius furo) were used. Intact eyes were subjected to CUBIC, melanin bleaching with H₂O₂, and immunostaining. Images of the retina in intact eyes were taken using epifluorescence microscopes and confocal microscopes.

Results

The combination of melanin bleaching and CUBIC efficiently made the eyes of C57BL/6 mice transparent. By combining melanin bleaching, CUBIC, and immunostaining, we succeeded in visualization of retinal structures from the outside of the intact eyes of mice. Furthermore, we found that our methods were applicable not only to mouse eyes but also to ferret eyes, which are much larger than those of mice.

Conclusions

Our method was useful for visualizing specific cells and structures in the retina of intact eyes with single-cell resolution without making tissue sections.

Translational Relevance

This simple and efficient method can be applicable to various rodent models, including those associated with glaucoma or myopia, and will facilitate evaluating the effects of novel therapy for relevant eye diseases by visualizing changes from the retina to the sclera at both molecular and macroscopic levels simultaneously in a whole-eye preparation.

A subacute model of glaucoma based on limbal plexus cautery in pigmented rats

Glaucoma is a neurodegenerative disorder characterized by the progressive functional impairment and degeneration of the retinal ganglion cells (RGCs) and their axons, and is the leading cause of irreversible blindness worldwide. Current management of glaucoma is based on reduction of high intraocular pressure (IOP), one of its most consistent risk factors, but the disease proceeds in almost half of the patients despite such treatments. Several experimental models of glaucoma have been developed in rodents, most of which present shortcomings such as high surgical invasiveness, slow learning curves, damage to the transparency of the optic media which prevents adequate functional assessment, and variable results. Here we describe a novel and simple method to induce ocular hypertension in pigmented rats, based on low-temperature cauterization of the whole circumference of the limbal vascular plexus, a major component of aqueous humor drainage and easily accessible for surgical procedures. This simple, low-cost and efficient method produced a reproducible subacute ocular hypertension with full clinical recovery, followed by a steady loss of retinal ganglion cells and optic axons, accompanied by functional changes detected both by electrophysiological and behavioral methods.

Effect of ocular hypertension on the pattern of retinal ganglion cell subtype loss in a mouse model of early-onset glaucoma

Glaucoma is a neurodegenerative disease with elevated intraocular pressure as one of the major risk factors. Glaucoma leads to irreversible loss of vision and its progression involves optic nerve head cupping, axonal degeneration, retinal ganglion cell (RGC) loss, and visual field defects. Despite its high global prevalence, glaucoma still remains a major neurodegenerative disease. Introduction of mouse models of experimental glaucoma has become integral to glaucoma research due to well-studied genetics as well as ease of manipulations. Many established inherent and inducible mouse models of glaucoma are used to study the molecular and physiological progression of the disease. One such model of spontaneous mutation is the nee model, which is caused by mutation of the Sh3pxd2b gene. In both humans and mice, mutations disrupting function of the SH3PXD2B adaptor protein cause a developmental syndrome including secondary congenital glaucoma. The purpose of this study was to characterize the early onset nee glaucoma phenotype on the C57BL/6J background and to evaluate the pattern of RGC loss and axonal degeneration in specific RGC subtypes. We found that the B6.Sh3pxd2b^nee mutant animals exhibit glaucoma phenotypes of elevated intraocular pressure, RGC loss and axonal degeneration. Moreover, the non-image forming RGCs survived longer than the On-Off direction selective RGCs (DSGC), and the axonal death in these RGCs was independent of their respective RGC subtype. In conclusion, through this study we characterized an experimental model of early onset glaucoma on a C57BL/6J background exhibiting key glaucoma phenotypes. In addition, we describe that RGC death has subtype-specific sensitivities and follows a specific pattern of cell death under glaucomatous conditions.

Models and treatments for traumatic optic neuropathy and demyelinating optic neuritis

Pathologies of the optic nerve could result as primary insults in the visual tract or as secondary deficits due to inflammation, demyelination, or compressing effects of the surrounding tissue. The extent of damage may vary from mild to severe, differently affecting patient vision, with the most severe forms leading to complete uni- or bilateral visual loss. The aim of researchers and clinicians in the field is to alleviate the symptoms of these, yet uncurable pathologies, taking advantage of known and novel potential therapeutic approaches, alone or in combinations, and applying them in a limited time window after the insult. In this review, we discuss the epidemiological and clinical profile as well as the pathophysiological mechanisms of two main categories of optic nerve pathologies, namely traumatic optic neuropathy and optic neuritis, focusing on the demyelinating form of the latter. Moreover, we report on the main rodent models mimicking these pathologies or some of their clinical aspects. The current treatment options will also be reviewed and novel approaches will be discussed.

A Chronic Ocular-Hypertensive Rat Model induced by Injection of the Sclerosant Agent Polidocanol in the Aqueous Humor Outflow Pathway

Background: To induce a moderate chronic ocular hypertension (OHT) by injecting polidocanol, a foamed sclerosant drug, in the aqueous humor outflow pathway. Methods: Intraocular pressure (IOP) was monitored for up to 6 months. Pattern and full-field electroretinogram (PERG and ERG) were recorded and retinal ganglion cells (RGC) and retinal nerve fiber layer (RNFL) thickness were assessed in vivo with optical coherence tomography (OCT) and ex vivo using Brn3a immunohistochemistry. Results: In the first 3 weeks post-injection, a significant IOP elevation was observed in the treated eyes (18.47 ± 3.36 mmHg) when compared with the control fellow eyes (12.52 ± 2.84 mmHg) (p < 0.05). At 8 weeks, 65% (11/17) of intervention eyes had developed an IOP increase >25% over the baseline. PERG responses were seen to be significantly reduced in the hypertensive eyes (2.25 ± 0.24 µV) compared to control eyes (1.44 ± 0.19 µV) (p < 0.01) at week 3, whereas the ERG components (photoreceptor a-wave and bipolar cell b-wave) remained unaltered. By week 24, RNFL thinning and cell loss in the ganglion cell layer was first detected (2/13, 15.3%) as assessed by OCT and light microscopy. Conclusions: This novel OHT rat model, with moderate levels of chronically elevated IOP, and abnormal PERG shows selective functional impairment of RGC.

Experimental Models of Glaucoma: A Powerful Translational Tool for the Future Development of New Therapies for Glaucoma in Humans-A Review of the Literature

Glaucoma is a common complex disease that leads to irreversible blindness worldwide. Even though preclinical studies showed that lowering intraocular pressure (IOP) could prevent retinal ganglion cells loss, clinical evidence suggests that lessening IOP does not prevent glaucoma progression in all patients. Glaucoma is also becoming more prevalent in the elderly population, showing that age is a recognized major risk factor. Indeed, recent findings suggest that age-related tissue alterations contribute to the development of glaucoma and have encouraged exploration for new treatment approaches. In this review, we provide information on the most frequently used experimental models of glaucoma and describe their advantages and limitations. Additionally, we describe diverse animal models of glaucoma that can be potentially used in translational medicine and aid an efficient shift to the clinic. Experimental animal models have helped to understand the mechanisms of formation and evacuation of aqueous humor, and the maintenance of homeostasis of intra-ocular pressure. However, the transfer of pre-clinical results obtained from animal studies into clinical trials may be difficult since the type of study does not only depend on the type of therapy to be performed, but also on a series of factors observed both in the experimental period and the period of transfer to clinical application. Conclusions: Knowing the exact characteristics of each glaucoma experimental model could help to diminish inconveniences related to the process of the translation of results into clinical application in humans.

Review of rodent hypertensive glaucoma models

Glaucoma is a neurodegenerative disease characterized by the progressive loss of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) is a primary risk factor for the development and progression of glaucoma. Rodent models of glaucoma have greatly improved our understanding of the pathophysiology of glaucoma and served as a useful tool to investigate neuroprotective agents. An ideal glaucoma animal model should be easy to induce, reproducible, biologically plausible and predictable. Of the available animal models of glaucoma, rodents are commonly studied because they have a relatively short life span and can be genetically altered. A successful hypertensive glaucoma model should induce structural glaucomatous changes: including loss of retinal nerve fibres, retinal ganglion cells and optic-disc cupping along with IOP elevation. The level and duration of IOP elevation should be titratable depending on the targeted glaucomatous damage. This review summarizes the outcomes of induced rodent hypertensive glaucoma models including intracameral injection of microbeads, laser photocoagulation, episcleral vein cauterization, injection of hypertonic saline and hyaluronic acid. We aim to provide a detailed overview of each of the models with a focus on parameters that defines a successful glaucoma model. The induced IOP elevation and duration of elevation varied among the different models and strain of rodent; nonetheless, they all achieved a sustainable raised IOP with corresponding RGC loss. The limitations of each model are discussed.

Differential Misfolding Properties of Glaucoma-Associated Olfactomedin Domains from Humans and Mice

Mutations in myocilin, predominantly within its olfactomedin (OLF) domain, are causative for the heritable form of open angle glaucoma in humans. Surprisingly, mice expressing Tyr423His mutant myocilin, corresponding to a severe glaucoma-causing mutation (Tyr437His) in human subjects, exhibit a weak, if any, glaucoma phenotype. To address possible protein-level discrepancies between mouse and human OLFs, which might lead to this outcome, biophysical properties of mouse OLF were characterized for comparison with those of human OLF. The 1.55 Å resolution crystal structure of mouse OLF reveals an asymmetric 5-bladed β-propeller that is nearly indistinguishable from previous structures of human OLF. Wild-type and selected mutant mouse OLFs mirror thermal stabilities of their human OLF counterparts, including characteristic stabilization in the presence of calcium. Mouse OLF forms thioflavin T-positive aggregates with a similar end-point morphology as human OLF, but amyloid aggregation kinetic rates of mouse OLF are faster than human OLF. Simulations and experiments support the interpretation that kinetics of mouse OLF are faster because of a decreased charge repulsion arising from more neutral surface electrostatics. Taken together, phenotypic differences observed in mouse and human studies of mutant myocilin could be a function of aggregation kinetics rates, which would alter the lifetime of putatively toxic protofibrillar intermediates.

Neuroprotective effects of topical coenzyme Q10 + vitamin E in mechanic optic nerve injury model

PURPOSE

We aimed to create mechanic optic nerve injury model in rats and investigate the neuroprotective effects of topical Coenzyme Q10 + Vitamin E (CoQ + Vit.E) molecules on retinal ganglion cells.

METHODS

Mechanic optic nerve injury model was created in the right eyes of rats (n = 12). Rats were divided into two groups: glaucoma model with sham treatment and topical CoQ + Vit.E treatment. Treatment was applied for 4 weeks. Glial fibrillary acidic protein, Brn-3a antibody, and anti-Iba1 were examined by immunohistochemistry. Glial fibrillary acidic protein, Bax, Bcl-xL, and Tfam protein expression were measured by Western blot analysis.

RESULTS

The number of Brn-3a-positive retinal ganglion cell was 15.0 ± 1.0 (min: 14, max: 16) in sham treatment group and 22.2 ± 4.8 (min: 18, max: 29) in topical CoQ10 + Vit.E treatment group. The protection of Brn-3a in CoQ10 + Vit.E was statistically significant (p < 0.05). Glial fibrillary acidic protein-positive astroglial counts were recorded as 11.7 ± 2.1 (min: 10, max: 14) in sham treatment and 2.5 ± 1.5 (min: 1, max: 4) in topical CoQ10 + Vit.E treatment group (p < 0.05). Topical CoQ10 + Vit.E treatment also decreased Iba1 expression in the retina of mechanic optic nerve injury groups. CoQ10 + Vit.E treatment prevented apoptotic cell death by increasing Bcl-xL protein expression. Also, CoQ10 + Vit.E preserved Tfam protein expression in the retina.

CONCLUSION

This study has shown that in glaucoma treatment the neuron protecting effect of topical CoQ10 + Vit.E molecules can be valuable.