Vision protection and robust axon regeneration in glaucoma models by membrane-associated Trk receptors

[Gene therapy for visual function recovery]

Glaucoma is an age-related neurodegenerative disease and the leading cause of blindness, but currently no fundamental treatment has been present. The main treatment is to reduce intraocular pressure, which is expected to delay the progression of the disease. However, there are many glaucoma patients for whom progression cannot be controlled by lowering intraocular pressure alone, and the development of a fundamental treatment is required. Meanwhile, the clinical application of gene therapy is increasing worldwide. Various gene therapy vectors are still being developed, and technological change is much faster in this field. Gene therapy has already been clinically applied to several neurodegenerative diseases, but gene therapy for glaucoma has not yet been established. Our group is investigating the development of a new treatment for glaucoma by gene therapy using neurotrophic factor signaling. And we aim not only to suppress disease progression by neuroprotection, but also to recover the visual function by axonal regeneration.

Emerging therapeutic strategies for optic nerve regeneration

The optic nerve, comprising axons from retinal ganglion cells (RGCs), is a component of the central nervous system (CNS) that generally exhibits a limited regeneration capacity following injury in mature mammals, resulting in permanent vision loss. Here, we summarize recent advances in interventions targeting cell-intrinsic and cell-extrinsic mechanisms to enhance RGC axon regeneration. Additionally, we summarize strategies for guiding the reconnection of regenerating axons with brain visual targets, aiming to restore partial visual function. Given the advent of high-throughput screening techniques and multiomics analyses, we discuss how these emerging methodologies deepen our understanding of regenerative mechanisms and expedite the development of innovative therapeutic approaches. Lastly, we explore the translational potential of these strategies in achieving clinically meaningful vision recovery.

Emerging strategies targeting genes and cells in glaucoma

Glaucoma comprises a heterogeneous set of eye conditions that cause progressive vision loss. Glaucoma has a complex etiology, with different genetic and non-genetic risk factors that differ across populations. Although difficult to diagnose in early stages, compromised cellular signaling, dysregulation of genes, and homeostatic imbalance are common precursors to injury and subsequent death of retinal ganglion cells (RGCs). Lowering intraocular pressure (IOP) remains the primary approach for managing glaucoma but IOP alone does not explain all glaucoma risks. Orthogonal approaches such as large-scale genetic screening, combined with studies of animal models have been instrumental in identifying genes and molecular pathways involved in glaucoma pathogenesis. Cell type dependent vulnerability among RGCs can reveal genetic basis for specific visual deficits. A growing body of knowledge and availability of modern tools to perform targeted assessments of cellular health in different animal models facilitate development of effective and timely interventions for vision rescue. This review highlights recent findings on genes, molecules, and cell types in the context of glaucoma pathophysiology and treatment.

Gene therapy for glaucoma: Targeting key mechanisms

Glaucoma is a group of optic neuropathies characterised by progressive retinal ganglion cell (RGC) degeneration and is the leading cause of irreversible blindness worldwide. Current treatments for glaucoma focus on reducing intraocular pressure (IOP) with topical medications. However, many patients do not achieve sufficient IOP reductions with such treatments. Patient compliance to dosing schedules also poses a significant challenge, further limiting their effectiveness. While surgical options exist for resistant cases, these are invasive and carry risks of complications. Thus, there is a critical need for better strategies to prevent irreversible vision loss in glaucoma. Gene therapy holds significant promise in this regard, offering potential long-term solutions by targeting the disease's underlying causes at a molecular level. Gene therapy strategies for glaucoma primarily target the two key hallmarks of the disease: elevated IOP and RGC death. This review explores key mechanisms underlying these hallmarks and discusses the current state of gene therapies targeting them. In terms of IOP reduction, this review covers strategies aimed at enhancing extracellular matrix turnover in the conventional outflow pathway, targeting fibrosis, regulating aqueous humor production, and targeting myocilin for gene-specific therapy. Neuroprotective strategies explored include targeting neurotrophic factors and their receptors, reducing oxidative stress and mitochondrial dysfunction, and preventing Wallerian degeneration. This review also briefly highlights key research priorities for advancing gene therapies for glaucoma through the clinical pipeline, such as refining delivery vectors and improving transgene regulation. Addressing these priorities will be essential for translating advancements from preclinical models into effective clinical therapies for glaucoma.

Genetic engineering and the eye

The transformative potential of genetic engineering in ophthalmology is remarkable, promising new treatments for a wide range of blinding eye diseases. The eye is an attractive target organ for genetic engineering approaches, in part due to its relatively immune-privileged status, its accessibility, and the ease of monitoring of efficacy and safety. Consequently, the eye has been at the forefront of genetic engineering advances in recent years. The development of Clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9), base editors, prime editors, and transposases have enabled efficient and specific gene modification. Ocular gene therapy continues to progress, with recent advances in delivery systems using viral / non-viral vectors and novel promoters and enhancers. New strategies to achieve neuroprotection and neuroregeneration are evolving, including direct in-vivo cell reprogramming and optogenetic approaches. In this review, we discuss recent advances in ocular genetic engineering, examine their current therapeutic roles, and explore their potential use in future strategies to reduce the growing burden of vision loss and blindness.

Immunomodulation by the combination of statin and matrix-bound nanovesicle enhances optic nerve regeneration

Modulating inflammation is critical to enhance nerve regeneration after injury. However, clinically applicable regenerative therapies that modulate inflammation have not yet been established. Here, we demonstrate synergistic effects of the combination of an HMG-CoA reductase inhibitor, statin/fluvastatin and critical components of the extracellular matrix, Matrix-Bound Nanovesicles (MBV) to enhance axon regeneration and neuroprotection after mouse optic nerve injury. Mechanistically, co-intravitreal injections of fluvastatin and MBV robustly promote infiltration of monocytes and neutrophils, which lead to RGC protection and axon regeneration. Furthermore, monocyte infiltration is triggered by elevated expression of CCL2, a chemokine, in the superficial layer of the retina after treatment with a combination of fluvastatin and MBV or IL-33, a cytokine contained within MBV. Finally, this therapy can be further combined with AAV-based gene therapy blocking anti-regenerative pathways in RGCs to extend regenerated axons. These data highlight novel molecular insights into the development of immunomodulatory regenerative therapy.

Managing Ocular Surface Disease in Glaucoma Treatment: A Systematic Review

Ocular surface disease (OSD) is a frequent disabling challenge among patients with glaucoma who use benzalkonium chloride (BAK)-containing topical glaucoma medications for prolonged periods. In this comprehensive review, we evaluated the prevalence of OSD and its management, focusing on both current and future alternatives. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) criteria were used to assess a) the impact of active ingredients and preservatives on the ocular surface and b) the efficacy of preservative-free (PF) alternatives and adjunctive therapies. BAK-containing glaucoma medications were found to significantly contribute to OSD by increasing corneal staining, reducing tear film stability, and elevating ocular surface disease index (OSDI) scores. Transitioning to PF formulations or those with less cytotoxic preservatives, such as Polyquad® and SofZia®, demonstrated a marked improvement in OSD symptoms. In particular, the use of adjunct cyclosporine A, through its anti-inflammatory and enhanced tear film stability actions, was shown to be very beneficial to the ocular surface. Therefore, the most effective management of OSD is multi-factorial, consisting of switching to PF or less cytotoxic medications, adjunct use of cyclosporine A, and early incorporation of glaucoma surgical treatments such as laser trabeculoplasty, trabeculectomy, glaucoma drainage devices, or minimally invasive glaucoma surgery (MIGS).

Membrane-anchored intracellular insulin receptor or insulin-like growth factor-1 receptor elicits ligand-independent downstream signaling

Neurodegenerative diseases including glaucoma affect insulin signaling, and insulin treatment has been shown to reverse the neurodegenerative loss of dendritic complexity in retinal ganglion cells. Therefore, strategies for enhancing or maintaining insulin signaling are worth pursuing to establish new therapies for these diseases. In the present study, we generated constitutively active insulin receptor (F-iIR) and insulin-like growth factor-1 receptor (F-iIGF1R) using a system that forces membrane localization of the intracellular domains of these receptors by farnesylation. Immunohistochemistry and Western blot analysis revealed that F-iIR and F-iIGF1R caused the activation of ERK and AKT in the absence of ligands in vitro. Our results suggest that in vivo effects of F-iIR and F-iIGF1R on the progression of neurodegenerative diseases should be investigated in the future.

Utilizing extracellular vesicles as a drug delivery system in glaucoma and RGC degeneration

Retinal diseases are the leading cause of blindness, resulting in irreversible degeneration and death of retinal neurons. One such cell type, the retinal ganglion cell (RGC), is responsible for connecting the retina to the rest of the brain through its axons that make up the optic nerve and is the primary cell lost in glaucoma and traumatic optic neuropathy. To date, different therapeutic strategies have been investigated to protect RGCs from death and preserve vision, yet currently available strategies are restricted to treating neuron loss by reducing intraocular pressure. A major barrier identified by these studies is drug delivery to RGCs, which is in large part due to drug stability, short duration time at target, low delivery efficiency, and undesired off-target effects. Therefore, a delivery system to deal with these problems is needed to ensure maximum benefit from the candidate therapeutic material. Extracellular vesicles (EV), nanocarriers released by all cells, are lipid membranes encapsulating RNAs, proteins, and lipids. As they naturally shuttle these encapsulated compounds between cells for communicative purposes, they may be exploitable and offer opportunities to overcome hurdles in retinal drug delivery, including drug stability, drug molecular weight, barriers in the retina, and drug adverse effects. Here, we summarize the potential of an EV drug delivery system, discussing their superiorities and potential application to target RGCs.

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.

Future directions of glaucoma treatment: emerging gene, neuroprotection, nanomedicine, stem cell, and vascular therapies

PURPOSE OF REVIEW

The aim of this article is to summarize current research on novel gene, stem cell, neuroprotective, nanomedicine, and vascular therapies for glaucoma.

RECENT FINDINGS

Gene therapy using viral vectors and siRNA have been shown to reduce intraocular pressure by altering outflow and production of aqueous humor, to reduce postsurgical fibrosis with few adverse effects, and to increase retinal ganglion cell (RGC) survival in animal studies. Stem cells may treat glaucoma by replacing or stimulating proliferation of trabecular meshwork cells, thus restoring outflow facility. Stem cells can also serve a neuroprotective effect by differentiating into RGCs or preventing RGC loss via secretion of growth factors. Other developing neuroprotective glaucoma treatments which can prevent RGC death include nicotinamide, the NT-501 implant which secretes ciliary neurotrophic factor, and a Fas-L inhibitor which are now being tested in clinical trials. Recent studies on vascular therapy for glaucoma have focused on the ability of Rho Kinase inhibitors and dronabinol to increase ocular blood flow.

SUMMARY

Many novel stem cell, gene, neuroprotective, nanomedicine, and vascular therapies have shown promise in preclinical studies, but further clinical trials are needed to demonstrate safety and efficacy in human glaucomatous eyes. Although likely many years off, future glaucoma therapy may take a multifaceted approach.

Optic nerve regeneration: Potential treatment approaches

The optic nerve, predominantly constituted by the axons of retinal ganglion cells (RGCs), lacks the ability to regenerate and re-establish function after injury. RGCs are crucial for visual function, and thus, RGC death contributes to the development of numerous progressive neurodegenerative optic neuropathies including glaucoma, ischemic optic neuropathy, and optic neuritis. Regenerating optic nerve axons poses numerous challenges due to factors such as the intricate and inhibitory conditions that exist within their environment, intrinsic breaks to regeneration, and the geometric tortuosity that offers physical hindrance to axon growth. However, recent research advancements offer hope for clinically meaningful regeneration for those who suffer from optic nerve damage. In this review, we highlight the current treatment approaches for optic nerve axon regeneration.

Glial cells as a promising therapeutic target of glaucoma: beyond the IOP

Glial cells, a type of non-neuronal cell found in the central nervous system (CNS), play a critical role in maintaining homeostasis and regulating CNS functions. Recent advancements in technology have paved the way for new therapeutic strategies in the fight against glaucoma. While intraocular pressure (IOP) is the most well-known modifiable risk factor, a significant number of glaucoma patients have normal IOP levels. Because glaucoma is a complex, multifactorial disease influenced by various factors that contribute to its onset and progression, it is imperative that we consider factors beyond IOP to effectively prevent or slow down the disease's advancement. In the realm of CNS neurodegenerative diseases, glial cells have emerged as key players due to their pivotal roles in initiating and hastening disease progression. The inhibition of dysregulated glial function holds the potential to protect neurons and restore brain function. Consequently, glial cells represent an enticing therapeutic candidate for glaucoma, even though the majority of glaucoma research has historically concentrated solely on retinal ganglion cells (RGCs). In addition to the neuroprotection of RGCs, the proper regulation of glial cell function can also facilitate structural and functional recovery in the retina. In this review, we offer an overview of recent advancements in understanding the non-cell-autonomous mechanisms underlying the pathogenesis of glaucoma. Furthermore, state-of-the-art technologies have opened up possibilities for regenerating the optic nerve, which was previously believed to be incapable of regeneration. We will also delve into the potential roles of glial cells in the regeneration of the optic nerve and the restoration of visual function.

The concept of gene therapy for glaucoma: the dream that has not come true yet

Gene therapies, despite of being a relatively new therapeutic approach, have a potential to become an important alternative to current treatment strategies in glaucoma. Since glaucoma is not considered a single gene disease, the identified goals of gene therapy would be rather to provide neuroprotection of retinal ganglion cells, especially, in intraocular-pressure-independent manner. The most commonly reported type of vector for gene delivery in glaucoma studies is adeno-associated virus serotype 2 that has a high tropism to retinal ganglion cells, resulting in long-term expression and low immunogenic profile. The gene therapy studies recruit inducible and genetic animal models of optic neuropathy, like DBA/2J mice model of high-tension glaucoma and the optic nerve crush-model. Reported gene therapy-based neuroprotection of retinal ganglion cells is targeting specific genes translating to growth factors (i.e., brain derived neurotrophic factor, and its receptor TrkB), regulation of apoptosis and neurodegeneration (i.e., Bcl-xl, Xiap, FAS system, nicotinamide mononucleotide adenylyl transferase 2, Digit3 and Sarm1), immunomodulation (i.e., Crry, C3 complement), modulation of neuroinflammation (i.e., erythropoietin), reduction of excitotoxicity (i.e., CamKIIα) and transcription regulation (i.e., Max, Nrf2). On the other hand, some of gene therapy studies focus on lowering intraocular pressure, by impacting genes involved in both, decreasing aqueous humor production (i.e., aquaporin 1), and increasing outflow facility (i.e., COX2, prostaglandin F2α receptor, RhoA/RhoA kinase signaling pathway, MMP1, Myocilin). The goal of this review is to summarize the current state-of-art and the direction of development of gene therapy strategies for glaucomatous neuropathy.

Exploring the current use of animal models in glaucoma drug discovery: where are we in 2023?

INTRODUCTION

Animal models are widely used in glaucoma-related research. Since the elevated intraocular pressure (IOP) is a major risk factor underlying the disease pathogenesis, animal models with high IOP are commonly used. However, models are also used to represent the clinical context of glaucomatous changes developing despite a normal IOP.

AREAS COVERED

Herein, the authors discuss the various factors that contribute to the quality of studies using animal models based on the evaluation of studies published in 2022. The factors affecting the quality of studies using animal models, such as the animal species, age, and sex, are discussed, along with various methods and outcomes of studies involving different animal models of glaucoma.

EXPERT OPINION

Translating animal research data to clinical applications remains challenging. Our observations in this review clearly indicate that many studies lack scientific robustness not only in their experiment conduct but also in data analysis, interpretation, and presentation. In this context, ensuring the internal validity of animal studies is the first step in quality assurance. External validity, however, is more challenging, and steps should be taken to satisfy external validity at least to some extent.

Neuroprotection and axon regeneration by novel low-molecular-weight compounds through the modification of DOCK3 conformation

Dedicator of cytokinesis 3 (DOCK3) is an atypical member of the guanine nucleotide exchange factors (GEFs) and plays important roles in neurite outgrowth. DOCK3 forms a complex with Engulfment and cell motility protein 1 (Elmo1) and effectively activates Rac1 and actin dynamics. In this study, we screened 462,169 low-molecular-weight compounds and identified the hit compounds that stimulate the interaction between DOCK3 and Elmo1, and neurite outgrowth in vitro. Some of the derivatives from the hit compound stimulated neuroprotection and axon regeneration in a mouse model of optic nerve injury. Our findings suggest that the low-molecular-weight DOCK3 activators could be a potential therapeutic candidate for treating axonal injury and neurodegenerative diseases including glaucoma.