Neuroprotection of retinal ganglion cells by a novel gene therapy construct that achieves sustained enhancement of brain-derived neurotrophic factor/tropomyosin-related kinase receptor-B signaling

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.

Intravitreal AAV2 gene delivery to feline retinal ganglion cells

Effective strategies for the neuroprotection and preservation of retinal ganglion cells (RGCs) remain elusive in the management of glaucoma. A spontaneous genetic model of glaucoma has been identified in cats and extensively characterized as a viable translational model, with eye size and anatomy similar to humans. In this study we sought to establish initial proof of concept for gene delivery to feline RGCs via intravitreal injection of AAV2 in normal cats. Pre-retinal, posterior vitreal injection of AAV2/2-CMV-GFP, was performed overlying the area centralis in 5 adult cats. Immunosuppressive oral prednisolone was administered perioperatively and gradually tapered over 6-10wks post-injection. Ophthalmic examination was performed pre- and post-injection. The GFP reporter expression and morphological effects of viral transduction on the retina were monitored in vivo using confocal scanning laser ophthalmoscopy (cSLO) and optical coherence tomography (OCT), respectively (Spectralis OCT-HRA, Heidelberg), at 1-2wk intervals over 6-10wks. Full-field electroretinograms (ERG) and visual evoked potentials (VEP) were recorded at baseline and post-injection. Retinas were examined by histology and immunolabeling for the RGC marker RBPMS and Müller cell and astrocyte marker SOX9, and GFP expression was examined in the retina, optic nerve (ON), optic tract and lateral geniculate nucleus (LGN). GFP+ retinal cells and RGC axons were visualized by cSLO at 1-2 weeks post-injection. No retinal morphological changes were observed by OCT in vivo but 3/5 eyes exhibited mild retinal inflammation on histology. Retinal and ON function were preserved in injected eyes compared to baseline and untreated eyes. GFP expression was predominantly identified in RBPMS+ RGC cells as well as SOX9+ Müller cells. GFP fluorescence was observed throughout RGC nerve fiber tract in the central visual pathway. Peak transduction in RGCs (up to ∼ 20 %) was observed in the regions with high GFP expression, but < 1 % of RGCs expressed GFP across the whole retina. Our data provide proof of concept that pre-retinal injection of AAV2/2 may represent a feasible platform for gene delivery to feline RGCs in vivo but highlight a need for further refinement to improve RGC transduction efficiency and control low-grade retinal inflammation.

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.

Visual stimulation and brain-derived neurotrophic factor (BDNF) have protective effects in experimental autoimmune uveoretinitis

AIMS

To investigate the therapeutic potential of visual stimulation (VS) and BDNF in murine experimental autoimmune uveoretinitis (EAU).

MAIN METHODS

Mice were immunized by subcutaneous injection of interphotoreceptor retinoid-binding protein in Freund's complete adjuvant and intravenous injection of pertussis toxin, and were then exposed to high-contrast VS 12 h/day (days 1-14 post-immunization). EAU severity was assessed by examining clinical score, visual acuity, inflammatory markers, and immune cells in the retina. The transcriptome of activated retinal cells was determined by RNA-seq using RNA immunoprecipitated in complex with phosphorylated ribosomal protein S6. The retinal levels of protein products of relevant upregulated genes were quantified. The effect of BDNF on EAU was tested in unstimulated mice by its daily topical ocular administration (days 8-14 post-immunization).

KEY FINDINGS

VS attenuated EAU development and decreased the expression of pro-inflammatory cytokines/chemokines and numbers of immune cells in the retina (n = 10-20 eyes/group for each analysis). In activated retinal cells of control mice (n = 30 eyes/group), VS upregulated genes encoding immunomodulatory neuropeptides, of which BDNF and vasoactive intestinal peptide (VIP) also showed increased mRNA and protein levels in the retina of VS-treated EAU mice (n = 6-10 eyes/group for each analysis). In unstimulated EAU mice, BDNF treatment mimicked the protective effects of VS by modulating the inflammatory and stem cell properties of Müller cells (n = 5 eyes/group for each analysis).

SIGNIFICANCE

VS effectively suppresses EAU, at least through enhancing retinal levels of anti-inflammatory and neuroprotective factors, VIP and BDNF. Our findings also suggest BDNF as a promising therapeutic agent for uveitis treatment.

Molecular Mechanisms of Glaucoma Pathogenesis with Implications to Caveolin Adaptor Protein and Caveolin-Shp2 Axis

Glaucoma is a common retinal disorder characterized by progressive optic nerve damage, resulting in visual impairment and potential blindness. Elevated intraocular pressure (IOP) is a major risk factor, but some patients still experience disease progression despite IOP-lowering treatments. Genome-wide association studies have linked variations in the Caveolin1/2 (CAV-1/2) gene loci to glaucoma risk. Cav-1, a key protein in caveolae membrane invaginations, is involved in signaling pathways and its absence impairs retinal function. Recent research suggests that Cav-1 is implicated in modulating the BDNF/TrkB signaling pathway in retinal ganglion cells, which plays a critical role in retinal ganglion cell (RGC) health and protection against apoptosis. Understanding the interplay between these proteins could shed light on glaucoma pathogenesis and provide potential therapeutic targets.

Advances in Neuroprotection in Glaucoma: Pharmacological Strategies and Emerging Technologies

Glaucoma is a major global health concern and the leading cause of irreversible blindness worldwide, characterized by the progressive degeneration of retinal ganglion cells (RGCs) and their axons. This review focuses on the need for neuroprotective strategies in glaucoma management, addressing the limitations of current treatments that primarily target intraocular pressure (IOP) reduction. Despite effective IOP management, many patients continue to experience RGC degeneration, leading to irreversible blindness. This review provides an overview of both pharmacological interventions and emerging technologies aimed at directly protecting RGCs and the optic nerve, independent of IOP reduction. Pharmacological agents such as brimonidine, neurotrophic factors, memantine, Ginkgo biloba extract, citicoline, nicotinamide, insulin, and resveratrol show promise in preclinical and early clinical studies for their neuroprotective properties. Emerging technologies, including stem cell therapy, gene therapy, mitochondrial-targeted therapies, and nanotechnologies, offer innovative approaches for neuroprotection and regeneration of damaged RGCs. While these interventions hold significant potential, further research and clinical trials are necessary to confirm their efficacy and establish their role in clinical practice. This review highlights the multifaceted nature of neuroprotection in glaucoma, aiming to guide future research and clinical practice toward more effective management of glaucoma-induced neurodegeneration.

Review: Neuroprotective Nanocarriers in Glaucoma

Glaucoma stands as a primary cause of irreversible blindness globally, characterized by the progressive dysfunction and loss of retinal ganglion cells (RGCs). While current treatments primarily focus on controlling intraocular pressure (IOP), many patients continue to experience vision loss. Therefore, the research focus has shifted to therapeutic targets aimed at preventing or delaying RGC death and optic nerve degeneration to slow or halt disease progression. Traditional ocular drug administration, such as eye drops or oral medications, face significant challenges due to the eye's unique structural and physiological barriers, which limit effective drug delivery. Invasive methods like intravitreal injections can cause side effects such as bleeding, inflammation, and infection, making non-invasive delivery methods with high bioavailability very desirable. Nanotechnology presents a promising approach to addressing these limitations in glaucoma treatment. This review summarizes current approaches involving neuroprotective drugs combined with nanocarriers, and their impact for future use.

Addressing neurodegeneration in glaucoma: Mechanisms, challenges, and treatments

Glaucoma is the leading cause of irreversible blindness globally. The disease causes vision loss due to neurodegeneration of the retinal ganglion cell (RGC) projection to the brain through the optic nerve. Glaucoma is associated with sensitivity to intraocular pressure (IOP). Thus, mainstay treatments seek to manage IOP, though many patients continue to lose vision. To address neurodegeneration directly, numerous preclinical studies seek to develop protective or reparative therapies that act independently of IOP. These include growth factors, compounds targeting metabolism, anti-inflammatory and antioxidant agents, and neuromodulators. Despite success in experimental models, many of these approaches fail to translate into clinical benefits. Several factors contribute to this challenge. Firstly, the anatomic structure of the optic nerve head differs between rodents, nonhuman primates, and humans. Additionally, animal models do not replicate the complex glaucoma pathophysiology in humans. Therefore, to enhance the success of translating these findings, we propose two approaches. First, thorough evaluation of experimental targets in multiple animal models, including nonhuman primates, should precede clinical trials. Second, we advocate for combination therapy, which involves using multiple agents simultaneously, especially in the early and potentially reversible stages of the disease. These strategies aim to increase the chances of successful neuroprotective treatment for glaucoma.

Mesenchymal stem cells for repairing glaucomatous optic nerve

Glaucoma is a common and complex neurodegenerative disease characterized by progressive loss of retinal ganglion cells (RGCs) and axons. Currently, there is no effective method to address the cause of RGCs degeneration. However, studies on neuroprotective strategies for optic neuropathy have increased in recent years. Cell replacement and neuroprotection are major strategies for treating glaucoma and optic neuropathy. Regenerative medicine research into the repair of optic nerve damage using stem cells has received considerable attention. Stem cells possess the potential for multidirectional differentiation abilities and are capable of producing RGC-friendly microenvironments through paracrine effects. This article reviews a thorough researches of recent advances and approaches in stem cell repair of optic nerve injury, raising the controversies and unresolved issues surrounding the future of stem cells.

AAV-mediated gene therapies for glaucoma and uveitis: are we there yet?

Glaucoma and uveitis are non-vascular ocular diseases which are among the leading causes of blindness and visual loss. These conditions have distinct characteristics and mechanisms but share a multifactorial and complex nature, making their management challenging and burdensome for patients and clinicians. Furthermore, the lack of symptoms in the early stages of glaucoma and the diverse aetiology of uveitis hinder timely and accurate diagnoses, which are a cause of poor visual outcomes under both conditions. Although current treatment is effective in most cases, it is often associated with low patient adherence and adverse events, which directly impact the overall therapeutic success. Therefore, long-lasting alternatives with improved safety and efficacy are needed. Gene therapy, particularly utilising adeno-associated virus (AAV) vectors, has emerged as a promising approach to address unmet needs in these diseases. Engineered capsids with enhanced tropism and lower immunogenicity have been proposed, along with constructs designed for targeted and controlled expression. Additionally, several pathways implicated in the pathogenesis of these conditions have been targeted with single or multigene expression cassettes, gene editing and silencing approaches. This review discusses strategies employed in AAV-based gene therapies for glaucoma and non-infectious uveitis and provides an overview of current progress and future directions.

Lessons From The Glaucoma Foundation Think Tank 2023: A Patient-Centric Approach to Glaucoma

PRCIS

The main takeaways also included that BIG DATA repositories and AI are important combinatory tools to foster novel strategies to prevent and stabilize glaucoma and, in the future, recover vision loss from the disease.

PURPOSE

To summarize the main topics discussed during the 28th Annual Glaucoma Foundation Think Tank Meeting "A Patient-Centric Approach to Glaucoma" held in New York on June 9 and 10, 2023.

METHODS

The highlights of the sessions on BIG DATA, genetics, modifiable lifestyle risk factors, female sex hormones, and neuroprotection in the field of primary open angle glaucoma (POAG) were summarized.

RESULTS

The researchers discussed the importance of BIG DATA repositories available at national and international levels for POAG research, including the United Kingdom Biobank. Combining genotyped large cohorts worldwide, facilitated by artificial intelligence (AI) and machine-learning approaches, led to the milestone discovery of 312 genome-wide significant disease loci for POAG. While these loci could be combined into a polygenic risk score with clinical utility, Think Tank meeting participants also provided analytical epidemiological evidence that behavioral risk factors modify POAG polygenetic risk, citing specific examples related to caffeine and alcohol use. The impact of female sex hormones on POAG pathophysiology was discussed, as was neuroprotection and the potential use of AI to help mitigate specific challenges faced in clinical trials and speed approval of neuroprotective agents.

CONCLUSIONS

The experts agreed on the importance of genetics in defining individual POAG risk and highlighted the additional crucial role of lifestyle, gender, blood pressure, and vascular risk factors. The main takeaways also included that BIG DATA repositories and AI are important combinatory tools to foster novel strategies to prevent and stabilize glaucoma and, in the future, recover vision loss from the disease.

Genes as drugs for glaucoma: latest advances

PURPOSE OF REVIEW

To provide the latest advances on the future use of gene therapy for the treatment of glaucoma.

RECENT FINDINGS

In preclinical studies, a number of genes have been shown to be able to reduce elevated intraocular pressure (IOP), and to exert neuroprotection of the retinal ganglion cells. These genes target various mechanisms of action and include among others: MMP3 , PLAT, IκB, GLIS, SIRT, Tie-2, AQP1. Some of these as well as some previously identified genes ( MMP3, PLAT, BDNF, C3, TGFβ, MYOC, ANGPTL7 ) are starting to move onto drug development. At the same time, progress has been made in the methods to deliver and control gene therapeutics (advances in these areas are not covered in this review).

SUMMARY

While preclinical efforts continue in several laboratories, an increasing number of start-up and large pharmaceutical companies are working on developing gene therapeutics for glaucoma ( Sylentis, Quetera/Astellas, Exhaura, Ikarovec, Genentech, Regeneron, Isarna, Diorasis Therapeutics ). Despite the presence of generic medications to treat glaucoma, given the size of the potential world-wide market (∼$7B), it is likely that the number of companies developing glaucoma gene therapies will increase further in the near future.

rAAV-compatible human mini promoters enhance transgene expression in rat retinal ganglion cells

Recombinant adeno-associated viral vectors (rAAV) are the safest and most effective gene delivery platform to drive the treatment of many inherited eye disorders in well-characterized animal models. The use in rAAV of ubiquitous promoters derived from viral sequences such as CMV/CBA (chicken β-actin promoter with cytomegalovirus enhancer) can lead to unwanted side effects such as pro-inflammatory immune responses and retinal cytotoxicity, thus reducing therapy efficacy. Thus, an advance in gene therapy is the availability of small promoters, that potentiate and direct gene expression to the cell type of interest, with higher safety and efficacy. In this study, we used six human mini-promoters packaged in rAAV2 quadruple mutant (Y-F) to test for transduction of the rat retina after intravitreal injection. After four weeks, immunohistochemical analysis detected GFP-labeled cells in the ganglion cell layer (GCL) for all constructs tested. Among them, Ple25sh1, Ple25sh2 and Ple53 promoted a widespread reporter-transgene expression in the GCL, with an increased number of GFP-expressing retinal ganglion cells when compared with the CMV/CBA vector. Moreover, Ple53 provided the strongest levels of GFP fluorescence in both cell soma and axons of retinal ganglion cells (RGCs) without any detectable adverse effects in retina function. Remarkably, a nearly 50-fold reduction in the number of intravitreally injected vector particles containing Ple53 promoter, still attained levels of transgene expression similar to CMV/CBA. Thus, the tested MiniPs show great potential for protocols of retinal gene therapy in therapeutic applications for retinal degenerations, especially those involving RGC-related disorders such as glaucoma.

Gene and cell-based therapies for retinal and optic nerve disease

Leading causes of blindness worldwide include neurodegenerative diseases of the retina, which cause irreversible loss of retinal pigment epithelium (RPE) and photoreceptors, and optic neuropathies, which result in retinal ganglion cell (RGC) death. Because photoreceptor and RGCs do not spontaneously regenerate in mammals, including humans, vision loss from these conditions is, at present, permanent. Recent advances in gene and cell-based therapies have provided new hope to patients affected by these conditions. This chapter reviews the current state and future of these approaches to treating ocular neurodegenerative disease. Gene therapies for retinal degeneration and optic neuropathies primarily focus on correcting known pathogenic mutations that cause inherited conditions to halt progression. There are multiple retinal and optic neuropathy gene therapies in clinical trials, and one retinal gene therapy is approved in the United States, Canada, Europe, and Australia. Cell-based therapies are mutation agnostic and have the potential to repopulate neurons regardless of the underlying etiology of degeneration. While photoreceptor cell replacement is nearing a human clinical trial, RPE transplantation is currently in phase I/II clinical trials. RGC replacement faces numerous logistical challenges, but preclinical research has laid the foundation for functional repair of optic neuropathies to be feasible.

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.

The Role of Retinal Ganglion Cell Structure and Function in Glaucoma

Glaucoma, a leading cause of irreversible blindness globally, primarily affects retinal ganglion cells (RGCs). This review dives into the anatomy of RGC subtypes, covering the different underlying theoretical mechanisms that lead to RGC susceptibility in glaucoma, including mechanical, vascular, excitotoxicity, and neurotrophic factor deficiency, as well as oxidative stress and inflammation. Furthermore, we examined numerous imaging methods and functional assessments to gain insight into RGC health. Finally, we investigated the current possible neuroprotective targets for RGCs that could help with future glaucoma research and management.

Gene therapies and gene product-based drug candidates for normalizing and preserving tissue functions in animal models of ocular hypertension and glaucoma

More than 76 million people worldwide are afflicted with the neurodegenerative eye diseases described and grouped together as glaucoma. A common feature amongst the many forms of glaucoma is chronically elevated intraocular pressure (IOP) within the anterior chamber of the eye that physically damages the retina, optic nerve and parts of the brain connected with visual perception. The mediators of the contusing raised IOP responsible for such damage and loss of vision include locally released inflammatory agents, tissue remodeling enzymes and infiltrating immune cells which damage the retinal ganglion cell (RGC) axons and eventually kill a significant number of the RGCs. Additional culprits include genetic defects of the patient that involve aberrations in receptors, enzymes and/or endogenous ligands and possible over- or under-production of the latter. Other genetic abnormalities may include issues with signal transduction machinery within key cells of critical tissues in the front (e.g. trabecular meshwork [TM] and Schlemm's canal [SC]) and back of the eye (e.g. retinal ganglion cells and their axons). Genome-wide associated studies (GWAS) coupled with next generation sequencing have provided powerful linkage of certain gene defects and polymorphic variants to the onset and progression of diseases of the tissues involved in fluid dynamics in the TM and SC, and many retinal elements (lamina cribosa, optic nerve head) at the back of the eye which cause ocular hypertension (OHT) and glaucomatous optic neuropathy (GON), respectively. Despite the availability of some drugs, fluid drainage microshunts and full surgical techniques to lower and control intraocular pressure, the major modifiable biomarker of open-angle and other forms of glaucoma, their side-effect profiles, less than optimum effectiveness and short duration of action present opportunities to clinically manage the glaucomas with next generation of treatments with high therapeutic indices, including gene therapies. Thus, identification, characterization and deployment of genetic data coupled with traditional drug discovery and novel gene replacement, gene editing and genetic engineering technologies may provide some solutions to the aforementioned problems. These aspects will be discussed in this article.

Novel frontiers in neuroprotective therapies in glaucoma: Molecular and clinical aspects

In the last years, neuroprotective therapies have attracted the researcher interests as modern and challenging approach for the treatment of neurodegenerative diseases, aimed at protecting the nervous system from injuries. Glaucoma is a neurodegenerative disease characterized by progressive excavation of the optic nerve head, retinal axonal injury and corresponding vision loss that affects millions of people on a global scale. The molecular basis of the pathology is largely uncharacterized yet, and the therapeutic approaches available do not change the natural course of the disease. Therefore, in accordance with the therapeutic regimens proposed for other neurodegenerative diseases, a modern strategy to treat glaucoma includes prescription of drugs with neuroprotective activities. With respect to this, several preclinical and clinical investigations on a plethora of different drugs are currently ongoing. In this review, first, the conceptualization of the rationale for the adoption of neuroprotective strategies for retina is summarized. Second, the molecular aspects highlighting glaucoma as a neurodegenerative disease are reported. In conclusion, the molecular and pharmacological properties of most promising direct neuroprotective drugs used to delay glaucoma progression are examined, including: neurotrophic factors, NMDA receptor antagonists, the α2-adrenergic agonist, brimonidine, calcium channel blockers, antioxidant agents, nicotinamide and statins.

Therapeutic strategies for glaucoma and optic neuropathies

Glaucoma is a neurodegenerative eye disease that causes permanent vision impairment. The main pathological characteristics of glaucoma are retinal ganglion cell (RGC) loss and optic nerve degeneration. Glaucoma can be caused by elevated intraocular pressure (IOP), although some cases are congenital or occur in patients with normal IOP. Current glaucoma treatments rely on medicine and surgery to lower IOP, which only delays disease progression. First-line glaucoma medicines are supported by pharmacotherapy advancements such as Rho kinase inhibitors and innovative drug delivery systems. Glaucoma surgery has shifted to safer minimally invasive (or microinvasive) glaucoma surgery, but further trials are needed to validate long-term efficacy. Further, growing evidence shows that adeno-associated virus gene transduction and stem cell-based RGC replacement therapy hold potential to treat optic nerve fiber degeneration and glaucoma. However, better understanding of the regulatory mechanisms of RGC development is needed to provide insight into RGC differentiation from stem cells and help choose target genes for viral therapy. In this review, we overview current progress in RGC development research, optic nerve fiber regeneration, and human stem cell-derived RGC differentiation and transplantation. We also provide an outlook on perspectives and challenges in the field.

The Association of Physical Activity with Glaucoma and Related Traits in the UK Biobank

PURPOSE

To examine the association of physical activity (PA) with glaucoma and related traits, to assess whether genetic predisposition to glaucoma modified these associations, and to probe causal relationships using Mendelian randomization (MR).

DESIGN

Cross-sectional observational and gene-environment interaction analyses in the UK Biobank. Two-sample MR experiments using summary statistics from large genetic consortia.

PARTICIPANTS

UK Biobank participants with data on self-reported or accelerometer-derived PA and intraocular pressure (IOP; n = 94 206 and n = 27 777, respectively), macular inner retinal OCT measurements (n = 36 274 and n = 9991, respectively), and glaucoma status (n = 86 803 and n = 23 556, respectively).

METHODS

We evaluated multivariable-adjusted associations of self-reported (International Physical Activity Questionnaire) and accelerometer-derived PA with IOP and macular inner retinal OCT parameters using linear regression and with glaucoma status using logistic regression. For all outcomes, we examined gene-PA interactions using a polygenic risk score (PRS) that combined the effects of 2673 genetic variants associated with glaucoma.

MAIN OUTCOME MEASURES

Intraocular pressure, macular retinal nerve fiber layer (mRNFL) thickness, macular ganglion cell-inner plexiform layer (mGCIPL) thickness, and glaucoma status.

RESULTS

In multivariable-adjusted regression models, we found no association of PA level or time spent in PA with glaucoma status. Higher overall levels and greater time spent in higher levels of both self-reported and accelerometer-derived PA were associated positively with thicker mGCIPL (P < 0.001 for trend for each). Compared with the lowest quartile of PA, participants in the highest quartiles of accelerometer-derived moderate- and vigorous-intensity PA showed a thicker mGCIPL by +0.57 μm (P < 0.001) and +0.42 μm (P = 0.005). No association was found with mRNFL thickness. High overall level of self-reported PA was associated with a modestly higher IOP of +0.08 mmHg (P = 0.01), but this was not replicated in the accelerometry data. No associations were modified by a glaucoma PRS, and MR analyses did not support a causal relationship between PA and any glaucoma-related outcome.

CONCLUSIONS

Higher overall PA level and greater time spent in moderate and vigorous PA were not associated with glaucoma status but were associated with thicker mGCIPL. Associations with IOP were modest and inconsistent. Despite the well-documented acute reduction in IOP after PA, we found no evidence that high levels of habitual PA are associated with glaucoma status or IOP in the general population.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

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.

Reduced Plasma BDNF Levels in Normal Tension Glaucoma Compared to Open Angle Glaucoma

PRCIS

The study suggests that a low level of systemic BDNF may contribute to the pathogenesis of glaucoma in an IOP-independent manner.

AIMS

To evaluate differences in systemic brain-derived neurotrophic factor (BDNF) levels between primary open angle glaucoma (POAG) patients and normal tension glaucoma (NTG) patients.

METHODS

This study collected blood samples from 260 NTG patients, 220 age-matched POAG patients, and 120 age-matched cataract patients (as controls). BDNF levels were measured with an antibody-conjugated bead assay system (Luminex).

RESULTS

We found that plasma BDNF levels in the NTG group were significantly lower than in the POAG and cataract control groups. There was no significant difference between the POAG and cataract groups.

CONCLUSION

This result suggests that a low level of systemic BDNF may contribute to the pathogenesis of glaucoma in an IOP-independent manner.

The Neuroprotective Effect of Activation of Sigma-1 Receptor on Neural Injury by Optic Nerve Crush

Purpose

This study aimed to explore the neuroprotective effects of sigma-1 receptor (S1R) on optic nerve crush (ONC) mice by upregulating its expression through intravitreal injection of adeno-associated virus (AAV).

Methods

The animals were divided into four groups. Mice that underwent ONC were administered an intravitreal injection with blank vector (ONC group), with AAV targeting downregulation of S1R (S1R-sh group), or with AAV targeting overexpression of S1R (S1R-AAV group). Mice in the control group underwent intravitreal injection with blank vector. The thickness of each layer of the retina was measured through optical coherence tomography, and the apoptotic rate of retinal neurons was determined using the TUNEL assay. The expression levels of brain-derived neurotrophic factor (BDNF) and S1R were quantified through western blot. Electroretinogram (ERG) was performed to evaluate the visual function.

Results

The thickness of the total retina (P = 0.001), ganglion cell layer (P = 0.017), and inner nuclear layer (P = 0.002) in S1R-AAV group was significantly thicker than that of the ONC group. The number of retinal apoptotic cells in the S1R-AAV group was 23% lower than that in the ONC group (P = 0.002). ERG results showed that, compared to the ONC group, the amplitudes of the a- and b-waves were higher in the S1R-AAV group (a-wave, P < 0.001; b-wave, P = 0.007). Western blot showed that the expression of BDNF in the S1R-AAV group was higher than that in the ONC group (P < 0.001).

Conclusions

Activation of S1R in the retina through intravitreal injection of AAV can effectively maintain the retina structure, promote neuronal cell survival, and protect visual function.

Emerging Gene Therapy Technologies for Retinal Ganglion Cell Neuroprotection

ABSTRACT

Optic neuropathies encompass a breadth of diseases that ultimately result in dysfunction and/or loss of retinal ganglion cells (RGCs). Although visual impairment from optic neuropathies is common, there is a lack of effective clinical treatments. Addressing a critical need for novel interventions, preclinical studies have been generating a growing body of evidence that identify promising new drug-based and cell-based therapies. Gene therapy is another emerging therapeutic field that offers the potential of specifically and robustly increasing long-term RGC survival in optic neuropathies. Gene therapy offers additional benefits of driving improvements following a single treatment administration, and it can be designed to target a variety of pathways that may be involved in individual optic neuropathies or across multiple etiologies. This review explores the history of gene therapy, the fundamentals of its application, and the emerging development of gene therapy technology as it relates to treatment of optic neuropathies.

Neuroprotection in glaucoma: Mechanisms beyond intraocular pressure lowering

Glaucoma is a common, complex, multifactorial neurodegenerative disease characterized by progressive dysfunction and then loss of retinal ganglion cells, the output neurons of the retina. Glaucoma is the most common cause of irreversible blindness and affects ∼80 million people worldwide with many more undiagnosed. The major risk factors for glaucoma are genetics, age, and elevated intraocular pressure. Current strategies only target intraocular pressure management and do not directly target the neurodegenerative processes occurring at the level of the retinal ganglion cell. Despite strategies to manage intraocular pressure, as many as 40% of glaucoma patients progress to blindness in at least one eye during their lifetime. As such, neuroprotective strategies that target the retinal ganglion cell and these neurodegenerative processes directly are of great therapeutic need. This review will cover the recent advances from basic biology to on-going clinical trials for neuroprotection in glaucoma covering degenerative mechanisms, metabolism, insulin signaling, mTOR, axon transport, apoptosis, autophagy, and neuroinflammation. With an increased understanding of both the basic and clinical mechanisms of the disease, we are closer than ever to a neuroprotective strategy for glaucoma.

Elevated Intraocular Pressure and Glaucomatous Optic Neuropathy: Genes to Disease Mechanisms, Therapeutic Drugs, and Gene Therapies

This review article focuses on the pathogenesis of and genetic defects linked with chronic ocular hypertension (cOHT) and glaucoma. The latter ocular disease constitutes a group of ocular degenerative diseases whose hallmark features are damage to the optic nerve, apoptotic demise of retinal ganglion cells, disturbances within the brain regions involved in visual perception and considerable visual impairment that can lead to blindness. Even though a number of pharmaceuticals, surgical and device-based treatments already exist addressing cOHT associated with the most prevalent of the glaucoma types, primary open-angle glaucoma (POAG), they can be improved upon in terms of superior efficacy with reduced side-effects and with longer duration of activity. The linkage of disease pathology to certain genes via genome-wide associated studies are illuminating new approaches to finding novel treatment options for the aforementioned ocular disorders. Gene replacement, gene editing via CRISPR-Cas9, and the use of optogenetic technologies may replace traditional drug-based therapies and/or they may augment existing therapeutics for the treatment of cOHT and POAG in the future.

Postsynaptic neuronal activity promotes regeneration of retinal axons

The wiring of visual circuits requires that retinal neurons functionally connect to specific brain targets, a process that involves activity-dependent signaling between retinal axons and their postsynaptic targets. Vision loss in various ophthalmological and neurological diseases is caused by damage to the connections from the eye to the brain. How postsynaptic brain targets influence retinal ganglion cell (RGC) axon regeneration and functional reconnection with the brain targets remains poorly understood. Here, we established a paradigm in which the enhancement of neural activity in the distal optic pathway, where the postsynaptic visual target neurons reside, promotes RGC axon regeneration and target reinnervation and leads to the rescue of optomotor function. Furthermore, selective activation of retinorecipient neuron subsets is sufficient to promote RGC axon regeneration. Our findings reveal a key role for postsynaptic neuronal activity in the repair of neural circuits and highlight the potential to restore damaged sensory inputs via proper brain stimulation.

Adeno-associated virus mediated gene therapy for neuroprotection of retinal ganglion cells in glaucoma

Glaucoma is a group of diseases typically characterized by the degeneration of the optic nerve and is one of the world's leading causes of blindness. Although there is no cure for glaucoma, reducing intraocular pressure is an approved treatment to delay optic nerve degeneration and retinal ganglion cell (RGC) death in most patients. Recent clinical trials have evaluated the safety and efficacy of gene therapy vectors for the treatment of inherited retinal degenerations (IRDs), and the results are promising, generating enthusiasm for the treatment of other retinal diseases. While there have been no reports on successful clinical trials for gene therapy-based neuroprotective treatment of glaucoma, and only a few studies assessing the efficacy of gene therapy vectors for the treatment of Leber hereditary optic neuropathy (LHON), the potential for neuroprotective treatment of glaucoma and other diseases affecting RGCs is still widely recognized. Here, we review recent progress and cover current limitations pertaining to targeting RGCs with adeno-associated virus-based gene therapy for the treatment of glaucoma.

Intraocular Pressure-Lowering and Retina-Protective Effects of Exosome-Rich Conditioned Media from Human Amniotic Membrane Stem Cells in a Rat Model of Glaucoma

Glaucoma is one of the most devastating eye diseases, since the disease can develop into blindness and no effective therapeutics are available. Although the exact mechanisms and causes of glaucoma are unknown, increased intraocular pressure (IOP) has been demonstrated to be an important risk factor. Exosomes are lipid nanoparticles secreted from functional cells, including stem cells, and have been found to contain diverse functional molecules that control body function, inhibit inflammation, protect and regenerate cells, and restore damaged tissues. In the present study, exosome-rich conditioned media (ERCMs) were attained via hypoxic culture (2% O₂) of human amniotic membrane mesenchymal stem cells (AMMSCs) and amniotic membrane epithelial stem cells (AMESCs) containing 50 times more exosome particles than normoxic culture (20% O₂) medium (NCM). The exosome particles in ERCM were confirmed to be 77 nm in mean size and contain much greater amounts of growth factors (GFs) and neurotrophic factors (NFs) than those in NCM. The glaucoma-therapeutic effects of ERCMs were assessed in retinal cells and a hypertonic (1.8 M) saline-induced high-IOP animal model. CM-DiI-labeled AMMSC exosomes were found to readily penetrate the normal and H₂O₂-damaged retinal ganglion cells (RGCs), and AMMSC-ERCM not only facilitated retinal pigment epithelial cell (RPEC) proliferation but also protected against H₂O₂- and hypoxia-induced RPEC insults. The IOP of rats challenged with 1.8 M saline increased twice the normal IOP (12-17 mmHg) in a week. However, intravitreal injection of AMMSC-ERCM or AMESC-ERCM (3.9-4.5 × 10⁸ exosomes in 10 μL/eye) markedly recovered the IOP to normal level in 2 weeks, similar to the effect achieved with platelet-derived growth factor-AB (PDGF-AB, 1.5 μg), a reference material. In addition, AMMSC-ERCM, AMESC-ERCM, and PDGF-AB significantly reversed the shrinkage of retinal layers, preserved RGCs, and prevented neural injury in the glaucoma eyes. It was confirmed that stem cell ERCMs containing large numbers of functional molecules such as GFs and NFs improved glaucoma by protecting retinal cells against oxidative and hypoxic injuries in vitro and by recovering IOP and retinal degeneration in vivo. Therefore, it is suggested that stem cell ERCMs could be a promising candidate for the therapy of glaucoma.

Gene therapy strategies for glaucoma from IOP reduction to retinal neuroprotection: progress towards non-viral systems

Glaucoma is the result of the gradual death of retinal ganglion cells (RGCs) whose axons form the optic nerve. Elevated intraocular pressure (IOP) is a major risk factors thatcontributes to RGC apoptosis and axonal loss at the lamina cribrosa, resulting in progressive reduction and eventual anterograde-retrograde transport blockade of neurotrophic factors. Current glaucoma management mainly focuses on pharmacological or surgical lowering of IOP, to manage the only modifiable risk factor. Although IOP reduction delays disease progression, it does not address previous and ongoing optic nerve degeneration. Gene therapy is a promising direction to control or modify genes involved in the pathophysiology of glaucoma. Both viral and non-viral gene therapy delivery systems are emerging as promising alternatives or add-on therapies to traditional treatments for improving IOP control and provide neuroprotection. The specific spotlight on non-viral gene delivery systems shows further progress towards improving the safety of gene therapy and implementing neuroprotection by targeting specific tissues and cells in the eye and specifically in the retina.

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

Activation of neurotrophic factor signaling is a promising therapy for neurodegeneration. However, the transient nature of ligand-dependent activation limits its effectiveness. In this study, we solved this problem by inventing a system that forces membrane localization of the intracellular domain of tropomyosin receptor kinase B (iTrkB), which results in constitutive activation without ligands. Our system overcomes the small size limitation of the genome packaging in adeno-associated virus (AAV) and allows high expression of the transgene. Using AAV-mediated gene therapy in the eyes, we demonstrate that iTrkB expression enhances neuroprotection in mouse models of glaucoma and stimulates robust axon regeneration after optic nerve injury. In addition, iTrkB expression in the retina was also effective in an optic tract transection model, in which the injury site is near the superior colliculus. Regenerating axons successfully formed pathways to their brain targets, resulting in partial recovery of visual behavior. Our system may also be applicable to other trophic factor signaling pathways and lead to a significant advance in the field of gene therapy for neurotrauma and neurodegenerative disorders, including glaucoma.

7,8-Dihydroxiflavone protects retinal ganglion cells and promotes axonal regeneration through TrkB signaling pathway followed by AKT and ERK activation

The aim of this study was to investigate the effects of 7,8-dihydroxyflavone (7,8-DHF) in protecting retinal ganglion cells (RGCs) and promoting axonal regeneration, and to explore its potential molecular mechanisms. We used three-dimensional retinal culture system and optic nerve crush (ONC) rat models in this study. The pro-axonal regenerative effect of 7,8-DHF was determined with light microscopy observation and immunofluorescence staining of Thy1.1 and GAP43. The RGC protective function of 7,8-DHF was detected by RBPMS immunofluorescent staining and TUNEL staining. The inhibition effect of 7,8-DHF on astrocyte activation was measured using GFAP immunofluorescence and Western blotting. The protein levels of p-TrkB, p-AKT and p-ERK was examined by Western blotting and immunohistochemistry. Our results revealed that 7,8-DHF significantly promoted the average density and length of regenerated neurites and suppressed the apoptosis of GCL cells in three-dimensional culture system and significantly increased the number of RBPMS-positive cells and inhibited the GFAP expression and apoptosis of GCL cells in ONC rats. Our results also revealed that 7,8-DHF activates TrkB, AKT and ERK proteins in vivo, however, these activations can be inhibited byANA-12. In conclusion, 7,8-DHF protects RGCs and promotes axonal regeneration through the TrkB signaling pathway followed by AKT and ERK activation.

Improving adeno-associated viral (AAV) vector-mediated transgene expression in retinal ganglion cells: comparison of five promoters

Recombinant adeno-associated viral vectors (AAVs) are an effective system for gene transfer. AAV serotype 2 (AAV2) is commonly used to deliver transgenes to retinal ganglion cells (RGCs) via intravitreal injection. The AAV serotype however is not the only factor contributing to the effectiveness of gene therapies. Promoters influence the strength and cell-selectivity of transgene expression. This study compares five promoters designed to maximise AAV2 cargo space for gene delivery: chicken β-actin (CBA), cytomegalovirus (CMV), short CMV early enhancer/chicken β-actin/short β-globulin intron (sCAG), mouse phosphoglycerate kinase (PGK), and human synapsin (SYN). The promoters driving enhanced green fluorescent protein (eGFP) were examined in adult C57BL/6J mice eyes and tissues of the visual system. eGFP expression was strongest in the retina, optic nerves and brain when driven by the sCAG and SYN promoters. CBA, CMV, and PGK had moderate expression by comparison. The SYN promoter had almost exclusive transgene expression in RGCs. The PGK promoter had predominant expression in both RGCs and AII amacrine cells. The ubiquitous CBA, CMV, and sCAG promoters expressed eGFP in a variety of cell types across multiple retinal layers including Müller glia and astrocytes. We also found that these promoters could transduce human retina ex vivo, although expression was predominantly in glial cells due to low RGC viability. Taken together, this promoter comparison study contributes to optimising AAV-mediated transduction in the retina, and could be valuable for research in ocular disorders, particularly those with large or complex genetic cargos.

Electroacupuncture ameliorates inflammatory response induced by retinal ischemia-reperfusion injury and protects the retina through the DOR-BDNF/Trkb pathway

Objectives: Retinal ischemia-reperfusion injury (RIRI) is the common pathological basis of many ophthalmic diseases in the later stages, and inflammation is the primary damage mechanism of RIRI. Our study aimed to assess whether electroacupuncture (EA) has a protective effect against RIRI and to elucidate its related mechanisms. Methods: A high-intraocular pressure (HIOP) model was used to simulate RIRI in Wistar rats. EA was applied to the EA1 group [Jingming (BL1) + Shuigou (GV26)] and the EA2 group [Jingming (BL1) + Hegu (LI4)] respectively for 30 min starting immediately after the onset of reperfusion and repeated (30 min/time) at 12 h and then every 24 h until days 7 after reperfusion. The pathological changes in the retina were observed by H and E staining after HIOP. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining was utilized to observe retinal cell apoptosis. The mRNA expression of IL1-β, TNF-α, IL-4, IL-10, δ-opioid receptor (DOR), brain-derived neurotrophic factor (BDNF), and tropomyosin-related kinase B (TrkB) in the retina was measured by quantitative real-time PCR. Results: HIOP caused structural disorders of the retina, decreased RGCs, and increased retinal cell apoptosis. At 1 and 3 days of RIRI, retinal apoptotic cells in the EA group were significantly reduced, while there was no distinct difference in the EA group compared with the HIOP group at 7 days of RIRI. Compared with that in the HIOP group, the expression of anti-inflammatory factors, DOR and TrkB was increased, and the expression of pro-inflammatory factors was decreased in the EA group. In contrast, HIOP had no appreciable effect on BDNF expression. Conclusion: EA at Jingming (BL1) and Shuigou (GV26) or at Jingming (BL1) and Hegu (LI4) may inhibit RIRI induced inflammation through activating the DOR-BDNF/TrkB pathway to protect the retina, especially the pair of Jingming (BL1) and Shuigou (GV26) has better inhibitory effects on inflammation.

Intravitreal Injection of AAV for the Transduction of Mouse Retinal Ganglion Cells

The injection of therapies into the eye is common practice, both clinically and pre-clinically. The most straightforward delivery route is via an intravitreal injection, which introduces the treatment into the largest cavity at the posterior of the eye. This technique is frequently used to deliver gene therapies, including those containing recombinant adeno-associated viral vectors (AAVs), to the back of the eye to enable inner retinal targeting. This chapter provides detailed methodology on how to successfully perform an intravitreal injection in mice. The chapter covers vector preparation considerations, advice on how to minimize vector loss in the injection device, and ways to reduce vector reflux from the eye when administering a therapy. Finally, a protocol is provided on common retinal histology processing techniques to assess vector-mediated expression in retinal ganglion cells. It is hoped that this chapter will enable researchers to carry out effective and consistent intravitreal injections that transduce the inner retinal surface while avoiding common pitfalls.

Developments in the Treatment of Leber Hereditary Optic Neuropathy

PURPOSEOF REVIEW

To outline the current landscape of treatments for Leber hereditary optic neuropathy (LHON) along the therapeutic delivery pipeline, exploring the mechanisms of action and evidence for these therapeutic approaches.

RECENT FINDINGS

Treatments for LHON can be broadly classified as either mutation-specific or mutation-independent. Mutation-specific therapies aim to correct the underlying mutation through the use of a gene-editing platform or replace the faulty mitochondrial DNA-encoded protein by delivering the wild-type gene using a suitable vector. Recent gene therapy clinical trials assessing the efficacy of allotopically expressed MT-ND4 for the treatment of LHON due to the m.11778G > A mutation in MT-ND4 have shown positive results when treated within 12 months of symptom onset. Mutation-independent therapies can have various downstream targets that aim to improve mitochondrial respiration, reduce mitochondrial stress, inhibit or delay retinal ganglion cell apoptosis, and/or promote retinal ganglion cell survival. Idebenone, a synthetic hydrosoluble analogue of co-enzyme Q10 (ubiquinone), is the only approved treatment for LHON. Mutation-independent approaches to gene therapy under pre-clinical investigation for other neurodegenerative disorders may have the potential to benefit patients with LHON. Although approved treatments are presently limited, innovations in gene therapy and editing are driving the expansion of the therapeutic delivery pipeline for LHON.

Advanced Therapy and Clinical Trials to Treat Patients with Optic Nerve Diseases

Optic nerve diseases include a wide variety of pathogenic conditions triggering injury or dysfunction of the optic nerves that lead to visual impairment or blindness in one or both eyes. Despite their pathogenic variety, most of them proceed through common mechanisms that allow them to investigate together. Nevertheless, roles of the cells, tissues, genes, growth factors, and proteins, and all underlying pathophysiological mechanisms need to be studied fully for better management of each optic nerve disease. This review presents a collection of information regarding ongoing and completed clinical trials (CT) of advanced therapies that deliver stem cell and gene therapy treatments as drugs to patients with optic nerve diseases as well as successes and failures achieved in treating these patients in the last few years. These drugs seem safe from creating neurotoxicity. It describes outcomes of a bibliographic search for stem cell therapy, gene therapy, and neuroprotection-based CT registered in the International ClinicalTrials.gov, the European EudraCT, and the Spanish REEC database, and related papers published in the PUBMED database by applying different search terminologies. This review overall informs the patients of optic neurodiseases that advanced therapies are progressing successfully in search of effective and safe treatments for them.

Neuroprotection in Glaucoma: Basic Aspects and Clinical Relevance

Glaucoma is a neurodegenerative disease that affects primarily the retinal ganglion cells (RGCs). Increased intraocular pressure (IOP) is one of the major risk factors for glaucoma. The mainstay of current glaucoma therapy is limited to lowering IOP; however, controlling IOP in certain patients can be futile in slowing disease progression. The understanding of potential biomolecular processes that occur in glaucomatous degeneration allows for the development of glaucoma treatments that modulate the death of RGCs. Neuroprotection is the modification of RGCs and the microenvironment of neurons to promote neuron survival and function. Numerous studies have revealed effective neuroprotection modalities in animal models of glaucoma; nevertheless, clinical translation remains a major challenge. In this review, we select the most clinically relevant treatment strategies, summarize preclinical and clinical data as well as recent therapeutic advances in IOP-independent neuroprotection research, and discuss the feasibility and hurdles of each therapeutic approach based on possible pathogenic mechanisms. We also summarize the potential therapeutic mechanisms of various agents in neuroprotection related to glutamate excitotoxicity.

Brain-derived neurotrophic factor is a regulator of synaptic transmission in the adult visual thalamus

Brain-derived neurotrophic factor (BDNF) is an important regulator of circuit development, neuronal survival, and plasticity throughout the nervous system. In the visual system, BDNF is produced by retinal ganglion cells (RGCs) and transported along their axons to central targets. Within the dorsolateral geniculate nucleus (dLGN), a key RGC projection target for conscious vision, the BDNF receptor tropomyosin receptor kinase B (TrkB) is present on RGC axon terminals and postsynaptic thalamocortical (TC) relay neuron dendrites. Based on this, the goal of this study was to determine how BDNF modulates the conveyance of signals through the retinogeniculate (RG) pathway of adult mice. Application of BDNF to dLGN brain slices increased TC neuron spiking evoked by optogenetic stimulation of RGC axons. There was a modest contribution to this effect from a BDNF-dependent enhancement of TC neuron intrinsic excitability including increased input resistance and membrane depolarization. BDNF also increased evoked vesicle release from RGC axon terminals, as evidenced by increased amplitude of evoked excitatory postsynaptic currents (EPSCs), which was blocked by inhibition of TrkB or phospholipase C. High-frequency stimulation revealed that BDNF increased synaptic vesicle pool size, release probability, and replenishment rate. There was no effect of BDNF on EPSC amplitude or short-term plasticity of corticothalamic feedback synapses. Thus, BDNF regulates RG synapses by both presynaptic and postsynaptic mechanisms. These findings suggest that BNDF influences the flow of visual information through the retinogeniculate pathway.NEW & NOTEWORTHY Brain-derived neurotrophic factor (BDNF) is an important regulator of neuronal development and plasticity. In the visual system, BDNF is transported along retinal ganglion cell (RGC) axons to the dorsolateral geniculate nucleus (dLGN), although it is not known how it influences mature dLGN function. Here, BDNF enhanced thalamocortical relay neuron responses to signals arising from RGC axons in the dLGN, pointing toward an important role for BDNF in processing signals en route to the visual cortex.

Molecular and Functional Characterization of BDNF-Overexpressing Human Retinal Pigment Epithelial Cells Established by Sleeping Beauty Transposon-Mediated Gene Transfer

More and more patients suffer from multifactorial neurodegenerative diseases, such as age-related macular degeneration (AMD). However, their pathological mechanisms are still poorly understood, which complicates the development of effective therapies. To improve treatment of multifactorial diseases, cell-based gene therapy can be used to increase the expression of therapeutic factors. To date, there is no approved therapy for dry AMD, including late-stage geographic atrophy. We present a treatment option for dry AMD that transfers the brain-derived neurotrophic factor (BDNF) gene into retinal pigment epithelial (RPE) cells by electroporation using the plasmid-based Sleeping Beauty (SB) transposon system. ARPE-19 cells and primary human RPE cells were co-transfected with two plasmids encoding the SB100X transposase and the transposon carrying a BDNF transcription cassette. We demonstrated efficient expression and secretion of BDNF in both RPE cell types, which were further increased in ARPE-19 cell cultures exposed to hydrogen peroxide. BDNF-transfected cells exhibited lower apoptosis rates and stimulated neurite outgrowth in human SH-SY5Y cells. This study is an important step in the development of a cell-based BDNF gene therapy that could be applied as an advanced therapy medicinal product to treat dry AMD or other degenerative retinal diseases.

New strategies for neuro protection in glaucoma

Glaucoma is a progressive, irreversible loss of retinal ganglion cells (RGCs) and axons that results in characteristic optic atrophy and corresponding progressive visual field defect. The exact mechanisms underlying glaucomatous neuron loss are not clear. The main risk factor for glaucoma onset and development is high intraocular pressure (IOP), however traditional IOP-lowering therapies are often not sufficient to prevent degeneration of RGCs and the vision loss may progress, indicating the need for complementary neuroprotective therapy. This review summarizes the progress for neuro protection in glaucoma in recent 5 years, including modulation of neuroinflammation, gene and cell therapy, dietary supplementation, and sustained-release system.

Systemic Beta-Hydroxybutyrate Affects BDNF and Autophagy into the Retina of Diabetic Mice

Background: Diabetic retinopathy (DR) is a neurovascular disease, characterized by a deficiency of brain-derived neurotrophic factor (BDNF), a regulator of autophagy. Beta-hydroxybutyrate (BHB), previously reported as a protective agent in DR, has been associated with BDNF promotion. Here, we investigated whether systemic BHB affects the retinal levels of BDNF and local autophagy in diabetic mice with retinopathy; Methods: C57BL/6J mice were administered with intraperitoneal (i.p.) streptozotocin (STZ) (75 mg/kg) injection to develop diabetes. After 2 weeks, they received i.p. injections of BHB (25−50−100 mg/kg) twice a week for 10 weeks. Retinal samples were collected in order to perform immunofluorescence, Western blotting, and ELISA analysis; Results: BHB 50 mg/kg and 100 mg/kg significantly improved retinal BDNF levels (p < 0.01) in diabetic mice. This improvement was negatively associated with autophagosome−lysosome formations (marked by LC3B and ATG14) and to higher levels of connexin 43 (p < 0.01), a marker of cell integrity. Moreover, BHB administration significantly reduced M1 microglial activation and autophagy (p < 0.01); Conclusions: The systemic administration of BHB in mice with DR improves the retinal levels of BDNF, with the consequent reduction of the abnormal microglial autophagy. This leads to retinal cell safety through connexin 43 restoration.

An EPO-loaded multifunctional hydrogel synergizing with adipose-derived stem cells restores neurogenic erectile function via enhancing nerve regeneration and penile rehabilitation

Neurogenic erectile dysfunction (nED) is one of the most common and intractable postoperative complications of rectal and prostate cancer surgery and sometimes accompanies patients lifelong. The transplantation of stem cells has been proved a promising way for treatment. However, the therapeutic efficacy is severely impaired by excessive cell loss and death and poor accumulation in the injury site along with the traditional implantation strategy. Herein, an EPO-loaded multifunctional hydrogel was designed. The hydrogels' adhesive property and mechanical strength were enhanced by adding catechol-catechol adducts, thus significantly improving adipose-derived stem cells (ADSC) retention and rescuing cell loss in the injury site. Meanwhile, the sustained release of EPO effectively ameliorated the viability and paracrine activity of ADSC, leading to enhanced migration of Schwann cells and differentiation of PC12 cells in vivo. On a bilateral cavernous nerve injury rat model, the present stem cell-EPO-hydrogel implanted strategy could significantly alleviate erectile dysfunction. The higher expression of Tuj1 and lower expression of GFAP in the major pelvic ganglia (MPG) indicated the acceleration of neural differentiation while the suppressing development of astrocytes. Also, the combined therapy restored the expression levels of eNOs, nNOs, and α-SMA in penile tissues, suggesting the rehabilitation of the penis. Further analysis of Masson trichrome staining and apoptosis evaluation of the corpus cavernosum showed the preservation of vascular endothelium content and the prevention of penile fibrosis after denervation. Overall, we believe that this combined strategy presents a promising way not only for restoring neurogenic erectile function but also for the clinical translation of stem cell therapy.

Treadmill exercise promotes retinal astrocyte plasticity and protects against retinal degeneration in a mouse model of light-induced retinal degeneration

Exercise is an effective neuroprotective intervention that preserves retinal function and structure in several animal models of retinal degeneration. However, the retinal cell types governing exercise-induced neuroprotection remain elusive. Previously, we found exercise-induced retinal neuroprotection was associated with increased levels of retinal brain-derived neurotrophic factor (BDNF) and required intact signal transduction with its high-affinity receptor, tropomyosin kinase B (TrkB). Brain studies have shown astrocytes express BDNF and TrkB and that decreased BDNF-TrkB signaling in astrocytes contributes to neurodegeneration. Additionally, exercise has been shown to alter astrocyte morphology. Using a light-induced retinal degeneration (LIRD) model, we investigated how exercise influences retinal astrocytes in adult male BALB/c mice. Treadmill exercise in dim control and LIRD groups had increased astrocyte density, GFAP labeling, branching, dendritic endpoints, and arborization. Meanwhile, inactive LIRD animals had significant reductions in all measured parameters. Additionally, exercised groups had increased astrocytic BDNF expression that was visualized using proximity ligase assay. Isolated retinal astrocytes from exercised LIRD groups had significantly increased expression of a specific isoform of TrkB associated with cell survival, TrkB.FL. Conversely, inactive LIRD isolated retinal astrocytes had significantly increased expression of TrkB.T1, which has been implicated in neuronal cell death. Our data indicate exercise not only alters retinal astrocyte morphology but also promotes specific BDNF-TrkB signaling associated with cell survival and protection during retinal degeneration. These findings provide novel insights into the effects of treadmill exercise on retinal astrocyte morphology and cellular expression, highlighting retinal astrocytes as a potential cell type involved in BDNF-TrkB signaling.

Covalent Organic Framework (COF): A Drug and Carrier to Attenuate Retinal Ganglion Cells Death in an Acute Glaucoma Mouse Model

Purpose: We aim to investigate the use of covalent organic framework (COF) nanoparticles in the local treatment of glaucoma, both as a means of protecting retinal ganglion cells (RGCs), and as a carrier for delayed release of the medication rapamycin following a single intravitreal injection. Methods: a water-dispersible COF, and a COF-based nanoplatform for rapamycin release (COF-Rapa) was constructed. C57BL/6J mice were randomly divided into four groups: intravitreal injection of 1.5 µL normal saline (NS), COF (0.67 ng/µL), rapamycin (300 µM) or COF-Rapa (0.67 ng/µL-300 µM), respectively. The ischemia–reperfusion (I/R) model was established to mimic high intraocular pressure (IOP)-induced retinal injury in glaucoma. Labeling of RGCs by Fluoro-Gold and retinal electroretinogram were used to evaluate retinal function. Immunohistochemistry and Western blotting analyses of retinas were performed. Results: COF nanoparticles were delivered in vitro and in vivo. Six weeks after the COF injection, the number of RGCs was unaffected. In addition, the number of RBPMS-positive RGCs, GFAP-positive astrocytes and Iba1-positive microglia did not differ from the normal control. COF could effectively reduce RGCs death, improve phototransduction function and alleviate the overactivation of microglia compared to NS control after retinal I/R injury. Within six weeks, the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway in the retinas could be inhibited by a single intravitreal injection of COF-Rapa. Compared with single COF administration, COF-Rapa significantly reduced the inflammatory reaction after retinal I/R injury. Conclusions: COF may act as both an RGC protection agent and a carrier for prolonged rapamycin release. This research may lead to the development of novel RGC protection agents and drug delivery techniques, as well as the creation of multifunctional COF-based biomaterials for glaucoma retinopathy.

From Bench to Bedside-Delivering Gene Therapy for Leber Hereditary Optic Neuropathy

Leber hereditary optic neuropathy (LHON) is a rare, maternally inherited mitochondrial disorder that presents with severe bilateral sequential vision loss, due to the selective degeneration of retinal ganglion cells (RGCs). Since the mitochondrial genetic basis for LHON was uncovered in 1988, considerable progress has been made in understanding the pathogenetic mechanisms driving RGC loss, which has enabled the development of therapeutic approaches aimed at mitigating the underlying mitochondrial dysfunction. In this review, we explore the genetics of LHON, from bench to bedside, focusing on the pathogenetic mechanisms and how these have informed the development of different gene therapy approaches, in particular the technique of allotopic expression with adeno-associated viral vectors. Finally, we provide an overview of the recent gene therapy clinical trials and consider the unanswered questions, challenges, and future prospects.

Advancing precision medicines for ocular disorders: Diagnostic genomics to tailored therapies

Successful sequencing of the human genome and evolving functional knowledge of gene products has taken genomic medicine to the forefront, soon combining broadly with traditional diagnostics, therapeutics, and prognostics in patients. Recent years have witnessed an extraordinary leap in our understanding of ocular diseases and their respective genetic underpinnings. As we are entering the age of genomic medicine, rapid advances in genome sequencing, gene delivery, genome surgery, and computational genomics enable an ever-increasing capacity to provide a precise and robust diagnosis of diseases and the development of targeted treatment strategies. Inherited retinal diseases are a major source of blindness around the world where a large number of causative genes have been identified, paving the way for personalized diagnostics in the clinic. Developments in functional genetics and gene transfer techniques has also led to the first FDA approval of gene therapy for LCA, a childhood blindness. Many such retinal diseases are the focus of various clinical trials, making clinical diagnoses of retinal diseases, their underlying genetics and the studies of natural history important. Here, we review methodologies for identifying new genes and variants associated with various ocular disorders and the complexities associated with them. Thereafter we discuss briefly, various retinal diseases and the application of genomic technologies in their diagnosis. We also discuss the strategies, challenges, and potential of gene therapy for the treatment of inherited and acquired retinal diseases. Additionally, we discuss the translational aspects of gene therapy, the important vector types and considerations for human trials that may help advance personalized therapeutics in ophthalmology. Retinal disease research has led the application of precision diagnostics and precision therapies; therefore, this review provides a general understanding of the current status of precision medicine in ophthalmology.

From Bench to Bed: The Current Genome Editing Therapies for Glaucoma

Glaucoma is a group of optic neuropathies featured by degeneration of retinal ganglion cells and loss of their axons in the optic nerve. The only currently approved therapies focus on lowering intraocular pressure with medication and surgery. Over the previous few decades, technological advances and research progress regarding pathogenesis has brought glaucomatous gene therapy to the forefront. In this review, we discuss the three current genome editing methods and potential disease mechanisms of glaucoma. We further summarize different genome editing strategies that are being developed to target a number of glaucoma-related genes and pathways from four aspects including strategies to lower intraocular pressure, neuroprotection, RGC and optic nerve neuro-regeneration, and other strategies. In summary, genome therapy is a promising therapy for treating patients with glaucoma and has great potential to be widely applied in clinical practice.

Newer advances in medical management of glaucoma

The burden of irreversible vision loss from Glaucoma continues to rise. While the disease pathogenesis is not well understood, intraocular pressure (IOP) is the only modifiable risk factor identified to prevent glaucomatous vision loss. Medical management remains the first-line of treatment in most adult glaucomas and the evolution of medical therapy for glaucoma has followed an exponential curve. This review tracks the rapid development of new medications and drug delivery systems in the recent years. Introduction of Rho kinase inhibitors with an entirely new mechanism of action from that of the currently used anti glaucoma medications has been a significant milestone. Latanoprostene Bunod is a novel, single molecule which provides two active metabolites that work through two different pathways for reducing intra ocular pressure. Bimatoprost implants and travoprost punctum plugs attempt to ease chronic medication use in glaucoma patients. Nanotechnology is an evolving route of drug delivery. Role of cannabinoids in medical management of glaucoma remain equivocal. The relatively short term effect on IOP, the risks of developing tolerance and side effects impacting patients' neurocognitive health greatly outweigh the potential benefit. Research on Latrunculin B, Adenosine receptor agonists, Specific gene silencing and Stem cell therapy are poised to make an impact on glaucoma treatment. While there is some evidence to support the role of Brimonidine in neuroprotection, further research is needed to clarify the role of Memantine and Neurotrophins. Evidence for benefit from dietary supplementation with Alpha lipoic acid, Forskolin , and Ginko Biloba is limited.

Chronic Chemogenetic Activation of the Superior Colliculus in Glaucomatous Mice: Local and Retrograde Molecular Signature

One important facet of glaucoma pathophysiology is axonal damage, which ultimately disrupts the connection between the retina and its postsynaptic brain targets. The concurrent loss of retrograde support interferes with the functionality and survival of the retinal ganglion cells (RGCs). Previous research has shown that stimulation of neuronal activity in a primary retinal target area-i.e., the superior colliculus-promotes RGC survival in an acute mouse model of glaucoma. To build further on this observation, we applied repeated chemogenetics in the superior colliculus of a more chronic murine glaucoma model-i.e., the microbead occlusion model-and performed bulk RNA sequencing on collicular lysates and isolated RGCs. Our study revealed that chronic target stimulation upon glaucomatous injury phenocopies the a priori expected molecular response: growth factors were pinpointed as essential transcriptional regulators both in the locally stimulated tissue and in distant, unstimulated RGCs. Strikingly, and although the RGC transcriptome revealed a partial reversal of the glaucomatous signature and an enrichment of pro-survival signaling pathways, functional rescue of injured RGCs was not achieved. By postulating various explanations for the lack of RGC neuroprotection, we aim to warrant researchers and drug developers for the complexity of chronic neuromodulation and growth factor signaling.