Transplantation of BDNF-secreting mesenchymal stem cells provides neuroprotection in chronically hypertensive rat eyes

Development of a novel SupraChoroidal-to-Optic-NervE (SCONE) drug delivery system

PURPOSE

Targeted drug delivery to the optic nerve head may be useful in the preclinical study and later clinical management of optic neuropathies, however, there are no FDA-approved drug delivery systems to achieve this. The purpose of this work was to develop an optic nerve head drug delivery technique.

METHODS

Different strategies to approach the optic nerve head were investigated, including standard intravitreal and retroorbital injections. A novel SupraChoroidal-to-Optic-NervE (SCONE) delivery was optimized by creating a sclerotomy and introducing a catheter into the suprachoroidal space. Under direct visualization, the catheter was guided to the optic nerve head. India ink was injected. The suprachoroidal approach was performed in New Zealand White rabbit eyes in vivo (25 animals total). Parameters, including microneedle size and design, catheter design, and catheter tip angle, were optimized ex vivo and in vivo.

RESULTS

Out of the candidate optic nerve head approaches, intravitreal, retroorbital, and suprachoroidal approaches were able to localize India ink to within 2 mm of the optic nerve. The suprachoroidal approach was further investigated, and after optimization, was able to deposit India ink directly within the optic nerve head in up to 80% of attempts. In eyes with successful SCONE delivery, latency and amplitude of visual evoked potentials was not different than the naïve untreated eye.

CONCLUSIONS

SCONE delivery can be used for targeted drug delivery to the optic nerve head of rabbits without measurable toxicity measured anatomically or functionally. Successful development of this system may yield novel opportunities to study optic nerve head-specific drug delivery in animal models, and paradigm-shifting management strategies for treating optic neuropathies.

TRANSLATIONAL RELEVANCE

Here we demonstrate data on a new method for targeted delivery to the optic nerve head, addressing a significant unmet need in therapeutics for optic neuropathies.

Encapsulated cell technology: Delivering cytokines to treat posterior ocular diseases

Encapsulated cell technology (ECT) is a targeted delivery method that uses the genetically engineered cells in semipermeable polymer capsules to deliver cytokines. Thus far, ECT has been extensively utilized in pharmacologic research, and shows enormous potentials in the treatment of posterior segment diseases. Due to the biological barriers within the eyeball, it is difficult to attain effective therapeutic concentration in the posterior segment through topical administration of drug molecules. Encouragingly, therapeutic cytokines provided by ECT can cross these biological barriers and achieve sustained release at the desired location. The encapsulation system uses permeable materials that allow growth factors and cytokines to diffuse efficiently into retinal tissue. Moreover, the ECT based treatment can be terminated timely when we need to retrieve the implant, which makes the therapy reversible and provides a safer alternative for intraocular gene therapy. Meanwhile, we also place special emphasis on optimizing encapsulation materials and enhancing preservation techniques to achieve the stable release of growth factors and cytokines in the eyeball. This technology holds great promise for the treatment of patients with dry AMD, RP, glaucoma and MacTel. These findings would enrich our understandings of ECT and promote its future applications in treatment of degenerative retinopathy. This review comprises articles evaluating the exactness of artificial intelligence-based formulas published from 2000 to March 2024. The papers were identified by a literature search of various databases (PubMed/MEDLINE, Google Scholar, Cochrane Library and Web of Science).

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.

Cell-Based Therapies for Glaucoma

Glaucomatous optic neuropathy (GON) is the major cause of irreversible visual loss worldwide and can result from a range of disease etiologies. The defining features of GON are retinal ganglion cell (RGC) degeneration and characteristic cupping of the optic nerve head (ONH) due to tissue remodeling, while intraocular pressure remains the only modifiable GON risk factor currently targeted by approved clinical treatment strategies. Efforts to understand the mechanisms that allow species such as the zebrafish to regenerate their retinal cells have greatly increased our understanding of regenerative signaling pathways. However, proper integration within the retina and projection to the brain by the newly regenerated neuronal cells remain major hurdles. Meanwhile, a range of methods for in vitro differentiation have been developed to derive retinal cells from a variety of cell sources, including embryonic and induced pluripotent stem cells. More recently, there has been growing interest in the implantation of glial cells as well as cell-derived products, including neurotrophins, microRNA, and extracellular vesicles, to provide functional support to vulnerable structures such as RGC axons and the ONH. These approaches offer the advantage of not relying upon the replacement of degenerated cells and potentially targeting earlier stages of disease pathogenesis. In order to translate these techniques into clinical practice, appropriate cell sourcing, robust differentiation protocols, and accurate implantation methods are crucial to the success of cell-based therapy in glaucoma. Translational Relevance: Cell-based therapies for glaucoma currently under active development include the induction of endogenous regeneration, implantation of exogenously derived retinal cells, and utilization of cell-derived products to provide functional support.

Erythropoietin in Glaucoma: From Mechanism to Therapy

Glaucoma can cause irreversible vision loss and is the second leading cause of blindness worldwide. The disease mechanism is complex and various factors have been implicated in its pathogenesis, including ischemia, excessive oxidative stress, neurotropic factor deprivation, and neuron excitotoxicity. Erythropoietin (EPO) is a hormone that induces erythropoiesis in response to hypoxia. However, studies have shown that EPO also has neuroprotective effects and may be useful for rescuing apoptotic retinal ganglion cells in glaucoma. This article explores the relationship between EPO and glaucoma and summarizes preclinical experiments that have used EPO to treat glaucoma, with an aim to provide a different perspective from the current view that glaucoma is incurable.

A bibliometric analysis of the application of stem cells in glaucoma research from 1999 to 2022

Background: Glaucoma, a neurodegenerative disease of the retina, is the leading cause of irreversible blindness. Stem cells have therapeutic potential for glaucoma. However, few bibliometric studies have been published in this field. Concerning a visual map, this article aims to characterize the research context, cooperation relationship, hotspots, and trends concerning the application of stem cells in glaucoma research. Methods: Publications focusing on stem cell research and glaucoma were retrieved from the Web of Science Core Collection. VOSviewer, CiteSpace, Microsoft Excel, and Scimago Graphica were used to map the contributions of countries or regions, authors, organizations, and journals. Journal Impact Factor data were obtained from the Web of Science Core Collection. We analyzed the tendencies, hotspots, and knowledge networks using VOSviewer, and CiteSpace. Results: We analyzed 518 articles published from 1999 through 2022. In the first decade, the number of articles in this field increased slowly, and there was a marked acceleration in publication frequency after 2010. The United States, China, and England were the main contributors. Yiqin Du was the most prolific author, and among the top 10 prolific writers, Keith R. Martin's work was cited most frequently. Investigative Ophthalmology and Visual Science, Experimental Eye Research, and Cornea published the most articles in this domain. The three most commonly co-cited journals were Investigative Ophthalmology and Visual Science, Experimental Eye Research, and Proceedings of the National Academy of Sciences of the United States of America. The Central South University, the University of Pittsburgh, and the National Institutes of Health National Eye Institute were highly prolific institutions in this research area. Our keywords analysis with VOSviewer suggested directions of future research and yielded the following recent key themes, extracellular vesicles, exosomes, mitochondria, growth factors, oxidative stress, and ocular diseases. Four co-cited references had a citation burst duration until 2022. Conclusion: With improvements in overall quality of life and demographic transitions toward population aging, research and clinical focus on eye care has increased, with glaucoma as a key area of emphasis. This study added to our understanding of the global landscape and Frontier hotspots in this field.

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.

Dental pulp stem cells retain mesenchymal phenotype despite differentiation toward retinal neuronal fate in vitro

Dental pulp stem cells (DPSCs) are an easily accessible, heterogenous source of mesenchymal stem cells (MSCs) that are derived from the neural crest. Evidence suggests that they have neurotrophic qualities in their undifferentiated state and can also be differentiated into neuronal and retinal cell types. There is growing interest in using DPSCs in cell-based therapies to treat glaucoma and blinding retinal diseases. However, careful characterization of these cells is necessary as direct intravitreal and subretinal MSC transplantation is known to lead to deleterious glial reaction and fibrosis. In this study, we provide evidence for the mesenchymal-predominant nature of DPSCs and show that DPSCs maintain their mesenchymal phenotype despite upregulating mature retinal markers under retinal differentiation conditions. CD56, which was previously thought to be a specific marker of neural crest lineage, is robustly co-expressed with mesenchymal markers and may not be adequate for isolating a subpopulation of neural crest cells in DPSCs. Therefore, identification of more specific markers is required to elucidate the heterogeneity of the population and to successfully isolate a putative neural stem cell population before DPSCs can be used for retinal therapy.

A novel glaucoma approach: Stem cell regeneration of the trabecular meshwork

Glaucoma is the leading cause of global irreversible blindness, necessitating research for new, more efficacious treatment options than currently exist. Trabecular meshwork (TM) cells play an important role in the maintenance and function of the aqueous outflow pathway, and studies have found that there is decreased cellularity of the TM in glaucoma. Regeneration of the TM with stem cells has been proposed as a novel therapeutic option by several reports over the last few decades. Stem cells have the capacity for self-renewal and the potential to differentiate into adult functional cells. Several types of stem cells have been investigated in ocular regenerative medicine: tissue specific stem cells, embryonic stem cells, induced pluripotent stem cells, and adult mesenchymal stem cells. These cells have been used in various glaucoma animal models and ex vivo models and have shown success in IOP homeostasis and TM cellularity restoration. They have also demonstrated stability without serious side effects for a significant period of time. Based on current knowledge of TM pathology in glaucoma and existing literature regarding stem cell regeneration of this tissue, we propose a human clinical study as the next step in understanding this potentially revolutionary treatment paradigm. The ability to protect and replace TM cells in glaucomatous eyes could change the field forever.

Brain-Derived Neurotrophic Factor-Mediated Neuroprotection in Glaucoma: A Review of Current State of the Art

Retinal ganglion cells (RGCs) are neurons of the visual system that are responsible for transmitting signals from the retina to the brain via the optic nerve. Glaucoma is an optic neuropathy characterized by apoptotic loss of RGCs and degeneration of optic nerve fibers. Risk factors such as elevated intraocular pressure and vascular dysregulation trigger the injury that culminates in RGC apoptosis. In the event of injury, the survival of RGCs is facilitated by neurotrophic factors (NTFs), the most widely studied of which is brain-derived neurotrophic factor (BDNF). Its production is regulated locally in the retina, but transport of BDNF retrogradely from the brain to retina is also crucial. Not only that the interruption of this retrograde transport has been detected in the early stages of glaucoma, but significantly low levels of BDNF have also been detected in the sera and ocular fluids of glaucoma patients, supporting the notion that neurotrophic deprivation is a likely mechanism of glaucomatous optic neuropathy. Moreover, exogenous NTF including BDNF administration was shown reduce neuronal loss in animal models of various neurodegenerative diseases, indicating the possibility that exogenous BDNF may be a treatment option in glaucoma. Current literature provides an extensive insight not only into the sources, transport, and target sites of BDNF but also the intracellular signaling pathways, other pathways that influence BDNF signaling and a wide range of its functions. In this review, the authors discuss the neuroprotective role of BDNF in promoting the survival of RGCs and its possible application as a therapeutic tool to meet the challenges in glaucoma management. We also highlight the possibility of using BDNF as a biomarker in neurodegenerative disease such as glaucoma. Further we discuss the challenges and future strategies to explore the utility of BDNF in the management of glaucoma.

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

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

Stem Cell-Based Regeneration and Restoration for Retinal Ganglion Cell: Recent Advancements and Current Challenges

Glaucoma is a group of irreversible blinding eye diseases characterized by the progressive loss of retinal ganglion cells (RGCs) and their axons. Currently, there is no effective method to fundamentally resolve the issue of RGC degeneration. Recent advances have revealed that visual function recovery could be achieved with stem cell-based therapy by replacing damaged RGCs with cell transplantation, providing nutritional factors for damaged RGCs, and supplying healthy mitochondria and other cellular components to exert neuroprotective effects and mediate transdifferentiation of autologous retinal stem cells to accomplish endogenous regeneration of RGC. This article reviews the recent research progress in the above-mentioned fields, including the breakthroughs in the fields of in vivo transdifferentiation of retinal endogenous stem cells and reversal of the RGC aging phenotype, and discusses the obstacles in the clinical translation of the stem cell therapy.

Cell-based therapy for ocular disorders: A promising frontier

As the ocular disorders causing long-term blindness or optical abnormalities of the ocular tissue affect the quality of life of patients to a large extent, awareness of their corresponding pathogenesis and the earlier detection and treatment need more consideration. Though current therapeutics result in desirable outcomes, they do not offer an inclusive solution for development of visual impairment to blindness. Accordingly, stem cells, because of their particular competencies, have gained extensive attention for application in regenerative medicine of ocular diseases. In the last decades, a wide spectrum of stem cells surrounding mesenchymal stem/stromal cells (MSC), neural stem cells (NSCs), and embryonic/induced pluripotent stem cells (ESCs/iPSCs) accompanied by Müller glia, ciliary epithelia-derived stem cells, and retinal pigment epithelial (RPE) stem cells have been widely investigated to report their safety and efficacy in preclinical models and also human subjects. In this regard, in the first interventions, RPE cell suspensions were successfully utilized to ameliorate visual defects of the patients suffering from age-related macular degeneration (AMD) after subretinal transplantation. Herein, we will explain the pathogenesis of ocular diseases and highlight the novel discoveries and recent findings in the context of stem cell-based therapies in these disorders, focusing on the in vivo reports published during the last decade.

Retinal Ganglion Cell Transplantation: Approaches for Overcoming Challenges to Functional Integration

As part of the central nervous system, mammalian retinal ganglion cells (RGCs) lack significant regenerative capacity. Glaucoma causes progressive and irreversible vision loss by damaging RGCs and their axons, which compose the optic nerve. To functionally restore vision, lost RGCs must be replaced. Despite tremendous advancements in experimental models of optic neuropathy that have elucidated pathways to induce endogenous RGC neuroprotection and axon regeneration, obstacles to achieving functional visual recovery through exogenous RGC transplantation remain. Key challenges include poor graft survival, low donor neuron localization to the host retina, and inadequate dendritogenesis and synaptogenesis with afferent amacrine and bipolar cells. In this review, we summarize the current state of experimental RGC transplantation, and we propose a set of standard approaches to quantifying and reporting experimental outcomes in order to guide a collective effort to advance the field toward functional RGC replacement and optic nerve regeneration.

New perspectives of immunomodulation and neuroprotection in glaucoma

Glaucoma is the neurodegenerative disease of retinal ganglion cells. The main risk factor for glaucoma is increased intraocular pressure. The processes leading to cell death due to presence of the injury factor comprise multiple molecular mechanisms, as well as the immunological response. The knowledge of immunological mechanisms occurring in glaucomatous degeneration makes it possible to introduce glaucoma treatment modulating the cellular degradation. The glaucoma treatment of the future will make it possible not only to lower the intraocular pressure, but also to moderate the intracellular mechanisms in order to prevent retinal cell degeneration. Citicoline is a drug modulating glutamate excitotoxicity that is already in use. Rho kinase inhibitors were found to stimulate neurite growth and axon regeneration apart from lowering intraocular pressure. The complementary action of brimonidine is to increase neurotrophic factor (NTF) concentrations and inhibit glutamate toxicity. Immunomodulatory therapies with antibodies and gene therapies show promising effects in the current studies. The supplementation of NTFs prevents glaucomatous damage. Resveratrol and other antioxidants inhibit reactive oxygen species formation. Cell transplantation of stem cells, Schwann cells and nerve extracts was reported to be successful so far. Our review presents the most promising new strategies of neuroprotection and immunomodulation in glaucoma.

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

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

Protection of retinal ganglion cells in glaucoma: Current status and future

Glaucoma is a neuropathic disease that causes optic nerve damage, loss of retinal ganglion cells (RGCs), and visual field defects. Most glaucoma patients have no early signs or symptoms. Conventional pharmacological glaucoma medications and surgeries that focus on lowering intraocular pressure are not sufficient; RGCs continue to die, and the patient's vision continues to decline. Recent evidence has demonstrated that neuroprotective approaches could be a promising strategy for protecting against glaucoma. In the case of glaucoma, neuroprotection aims to prevent or slow down disease progression by mitigating RGCs death and optic nerve degeneration. Notably, new pharmacologic medications such as antiglaucomatous agents, antibiotics, dietary supplementation, novel neuroprotective molecules, neurotrophic factors, translational methods such as gene therapy and cell therapy, and electrical stimulation-based physiotherapy are emerging to attenuate the death of RGCs, or to make RGCs resilient to attacks. Understanding the roles of these interventions in RGC protection may offer benefits over traditional pharmacological medications and surgeries. In this review, we summarize the recent neuroprotective strategy for glaucoma, both in clinical trials and in laboratory research.

Interaction Between Mesenchymal Stem Cells and Retinal Degenerative Microenvironment

Retinal degenerative diseases (RDDs) are a group of diseases contributing to irreversible vision loss with yet limited therapies. Stem cell-based therapy is a promising novel therapeutic approach in RDD treatment. Mesenchymal stromal/stem cells (MSCs) have emerged as a leading cell source due to their neurotrophic and immunomodulatory capabilities, limited ethical concerns, and low risk of tumor formation. Several pre-clinical studies have shown that MSCs have the potential to delay retinal degeneration, and recent clinical trials have demonstrated promising safety profiles for the application of MSCs in retinal disease. However, some of the clinical-stage MSC therapies have been unable to meet primary efficacy end points, and severe side effects were reported in some retinal “stem cell” clinics. In this review, we provide an update of the interaction between MSCs and the RDD microenvironment and discuss how to balance the therapeutic potential and safety concerns of MSCs' ocular application.

Human mesenchymal stem cell therapy promotes retinal ganglion cell survival and target reconnection after optic nerve crush in adult rats

BACKGROUND

Optic-nerve injury results in impaired transmission of visual signals to central targets and leads to the death of retinal ganglion cells (RGCs) and irreversible vision loss. Therapies with mesenchymal stem cells (MSCs) from different sources have been used experimentally to increase survival and regeneration of RGCs.

METHODS

We investigated the efficacy of human umbilical Wharton's jelly-derived MSCs (hWJ-MSCs) and their extracellular vesicles (EVs) in a rat model of optic nerve crush.

RESULTS

hWJ-MSCs had a sustained neuroprotective effect on RGCs for 14, 60, and 120 days after optic nerve crush. The same effect was obtained using serum-deprived hWJ-MSCs, whereas transplantation of EVs obtained from those cells was ineffective. Treatment with hWJ-MSCs also promoted axonal regeneration along the optic nerve and reinnervation of visual targets 120 days after crush.

CONCLUSIONS

The observations showed that this treatment with human-derived MSCs promoted sustained neuroprotection and regeneration of RGCs after optic nerve injury. These findings highlight the possibility to use cell therapy to preserve neurons and to promote axon regeneration, using a reliable source of human MSCs.

Human Dental Pulp Stem Cells (DPSCs) Therapy in Rescuing Photoreceptors and Establishing a Sodium Iodate-Induced Retinal Degeneration Rat Model

BACKGROUND

Different methods have been used to inject stem cells into the eye for research. We previously explored the intravitreal route. Here, we investigate the efficacy of intravenous and subretinal-transplanted human dental pulp stem cells (DPSCs) in rescuing the photoreceptors of a sodium iodate-induced retinal degeneration model.

METHODS

Three groups of Sprague Dawley rats were used: intervention, vehicle group and negative control groups (n = 6 in each). Intravenous injection of 60 mg/kg sodium iodate (day 0) induced retinal degeneration. On day 4 post-injection of sodium iodate, the rats in the intervention group received intravenous DPSC and subretinal DPSC in the right eye; rats in the vehicle group received subretinal Hank's balance salt solution and intravenous normal saline; while negative control group received nothing. Electroretinogram (ERG) was performed to assess the retinal function at day 0 (baseline), day 4, day 11, day 18, day 26, and day 32. By the end of the study at day 32, the rats were euthanized, and both their enucleated eyes were sent for histology.

RESULTS

No significant difference in maximal ERG a-wave (p = 0.107) and b-wave, (p = 0.153) amplitude was seen amongst the experimental groups. However, photopic 30 Hz flicker amplitude of the study eye showed significant differences in the 3 groups (p = 0.032). Within the intervention group, there was an improvement in 30 Hz flicker ERG response of all 6 treated right eyes, which was injected with subretinal DPSC; while the 30 Hz flicker ERG of the non-treated left eyes remained flat. Histology showed improved outer nuclear layer thickness in intervention group; however, findings were not significant compared to the negative and vehicle groups.

CONCLUSION

Combination of subretinal and intravenous injection of DPSCs may have potential to rescue cone function from a NaIO₃-induced retinal injury model.

High Correlation between Glaucoma Treatment with Topical Prostaglandin Analogs and BDNF Immunoreactivity in Human Retina

PURPOSE

To examine the expression of brain-derived neurotrophic factor (BDNF) and its high-affinity receptor, tropomyosin-related kinase receptor-B (TrkB), in normal and glaucomatous human retinas.

METHODS

Human retinas were collected from 8 donors who had been clinically diagnosed and treated for glaucoma, and from 9 control donors. Immunohistochemical analysis for BDNF and TrkB was performed. The percent of each retina expressing BDNF and TrkB was quantified for the total retinal thickness, and separately for the retinal ganglion cell (RGC) complex + retinal nerve fiber layer (RNFL). The expression of each protein was correlated with clinical outcomes obtained from the subject's ocular histories.

RESULTS

There was no significant difference in BDNF or TrkB expression when comparing glaucomatous and control retinas. Correlation analysis revealed a significant relationship between BDNF expression and the use of prostaglandin analogs. TrkB expression was highly correlated with the last-measured intraocular pressure (IOP), the use of carbonic anhydrase inhibitors, the use of beta blockers, and the total number of drugs used for the treatment of glaucoma.

CONCLUSION

Topical drugs used to treat glaucoma were associated with an increase in retinal BDNF and TrkB expression in human retina, independent of IOP, which may represent molecular evidence of neuroprotective pathway activation.

Towards stem cell-based neuronal regeneration for glaucoma

Glaucoma is a neurodegenerative disease as a leading cause of global blindness. Retinal ganglion cell (RGC) apoptosis and optic nerve damage are the main pathological changes. Patients have elevated intraocular pressure and progressive visual field loss. Unfortunately, current treatments for glaucoma merely stay at delaying the disease progression. As a promising treatment, stem cell-based neuronal regeneration therapy holds potential for glaucoma, thereby great efforts have been paid on it. RGC regeneration and transplantation are key approaches for the future treatment of glaucoma. A line of studies have shown that a variety of cells can be used to regenerate RGCs, including embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), mesenchymal stem cells (MSCs), and retinal progenitor cells (RPCs). In this review, we overview the current progress on the regeneration of pluripotent stem cell-derived RGCs and outlook the perspective and challenges in this field.

Effects of Varying Intranasal Treatment Regimens in ST266-Mediated Retinal Ganglion Cell Neuroprotection

INTRODUCTION

Previous studies have shown that intranasally administered ST266, a novel biological secretome of amnion-derived multipotent progenitor cells containing multiple growth factors and anti-inflammatory cytokines, attenuated visual dysfunction and prevented retinal ganglion cell (RGC) loss in experimental optic neuritis. Long-term effects and dose escalation studies examined here have not been reported previously.

METHODS

Optic neuritis was induced in the multiple sclerosis model experimental autoimmune encephalomyelitis (EAE). EAE and control mice were treated once or twice daily with intranasal placebo/vehicle or ST266 beginning after onset of optic neuritis for either 15 days or continuously until sacrifice. Visual function was assessed by optokinetic responses (OKRs). RGC survival and optic nerve inflammation and demyelination were measured.

RESULTS

Both once and twice daily continuous intranasal ST266 treatment from disease onset to 56 days after EAE induction significantly increased OKR scores, decreased RGC loss, and reduced optic nerve inflammation and demyelination compared with placebo (saline, nonspecific protein solution, or cell culture media)-treated EAE mice. ST266 treatment given for just 15 days after disease onset, then discontinued, only delayed OKR decreases, and had limited effects on RGC survival and optic nerve inflammation 56 days after disease induction.

CONCLUSIONS

ST266 is a potential neuroprotective therapy to prevent RGC damage, and intranasal delivery warrants further study as a novel mechanism to deliver protein therapies for optic neuropathies. Results suggest that once daily ST266 treatment is sufficient to sustain maximal benefits and demonstrate that neuroprotective effects promoted by ST266 are specific to the combination of factors present in this complex biologic therapy.

[The influence of long-term retinal protective therapy on glaucoma progression according to structural and functional tests]

PURPOSE

To evaluate the influence of prolonged neuroprotective therapy on disease progression in patients with primary open-angle glaucoma (POAG) with compensated intraocular pressure (IOP).

MATERIAL AND METHODS

The study included 147 patients with stages I-II POAG (249 eyes) who were randomized into the main (69 patients, 119 eyes) and control groups (78 patients, 130 eyes). Patients of the main group underwent retinalamin treatment course every 6 months. Patients were examined before enrolling and then every 3 months during the 24-months follow-up including optical coherence tomography (OCT; RNFL - retinal nerve fiber layer, NRR - neuroretinal rim, GCL - ganglion cell layer) and static perimetry (MD - mean deviation, PSD - pattern standard deviation).

RESULTS

Visual acuity and refraction did not change in either group (p>0.05). IOP increased in the control group (p=0.033). There was no difference between the groups by the 24th month (p=0.87). No MD changes were noted in the main (p=0.45) and control groups (p=0.27). PSD changed in the main (4.84±3.21 and 6.01±2.584 dB in the beginning and the end, respectively, p=0.0004) and the control groups (3.46±2.23 and 5.86±2.26 dB, respectively; p<0.0001). The groups differed in MD and PSD initially (p=0.15; p=0.02) and became equal by the end (p=0.59; p=0.53). RNFL did not change significantly in the main group (p=0.078) and decreased from 83.5±22.47 to 76.7±20.7 µm in the control group (p=0.001); no differences between the groups were noted in the beginning (p=0.276) or in the end of the study (p=0.524). NRR increased in the main group from 222±88.94 to 231±99.3 (p=0.012), and decreased in the control group from 248±87.09 to 234±96.2 (p=0.0006); no differences were found between groups in the beginning or in the end of the study (p=0.109; p=0.909). GCL thickness did not change either in the main, or in the control group (p=0.211; p=0.16), with no difference between the group noted in the beginning or the end of the study (p=0.44; p=0.51).

CONCLUSION

Regular treatment with retinalamin arrests the development of glaucomatous optic neuropathy. Longer-term research is required to study its influence on the visual function and the quality of life.

Articulation recovery in ALS patients after lineage-negative adjuvant cell therapy - preliminary report

Background: Amyotrophic lateral sclerosis (ALS) is one of the most frequently occurring neurodegenerative diseases affecting speech and swallowing. This preliminary study aimed to investigate whether an autologous lineage-negative stem/progenitor cell therapy applied to ALS patients affects the level of selected trophic and proinflammatory factors, and subsequently improves the articulation. Methods: We enrolled 12 patients with sporadic ALS, who underwent autologous bone marrow-derived lineage negative (LIN^-) cells administration into cerebrospinal fluid (CSF). We evaluated patients' articulation using the Frenchay Dysarthria Assessment on days 0 and 28 following the LIN^- cells administration. Concentrations of various factors (BDNF, NGF, ANGP-2, VEGF, PDGF-AA, PEDF, COMP-FH, CRP, C3, C4) in CSF were quantified by multiplex fluorescent bead-based immunoassays in the samples collected on the day of LIN^- cells administration and 28 days later. On top of this, we assessed levels of BDNF and NGF in the patients' plasma on the day of the injection, three, seven days and three months after the treatment. Results: Of the 12 patients who received the LIN^- cell therapy 8 showed short-termed improvement in articulatory functions (group I), which was particularly noticeable in better phonation time, lips and soft palate performance, swallowing reflex and voice loudness. Four patients (group II) did not show substantial improvement. CSF concentrations of BDNF, ANGP-2 and PDGF-AA in group I decreased significantly 28 days after LIN^- cells administration. The highest concentration levels of BDNF in group II and NGF in both groups in blood plasma were observed on day 3 following the injection. Conclusions: The outcomes of the LIN^- cell application in ALS treatment of articulatory organs are promising. The procedure proved to be safe and feasible. A short-lasting trophic effect of autologous LIN^- administration could encourage repeated cell's application in order to sustain their beneficial effects, however this approach needs further investigation.

Therapeutic Potential of Mesenchymal Stem Cells and Their Secretome in the Treatment of Glaucoma

Glaucoma represents a group of progressive optic neuropathies characterized by gradual loss of retinal ganglion cells (RGCs), the neurons that conduct visual information from the retina to the brain. Elevated intraocular pressure (IOP) is considered the main reason for enhanced apoptosis of RGCs in glaucoma. Currently used therapeutic agents are not able to repopulate and/or regenerate injured RGCs and, therefore, are ineffective in most patients with advanced glaucoma. Accordingly, several new therapeutic approaches, including stem cell-based therapy, have been explored for the glaucoma treatment. In this review article, we emphasized current knowledge regarding molecular and cellular mechanisms responsible for beneficial effects of mesenchymal stem cells (MSCs) and their secretome in the treatment of glaucoma. MSCs produce neurotrophins and in an exosome-dependent manner supply injured RGCs with growth factors enhancing their survival and regeneration. Additionally, MSCs are able to generate functional RGC-like cells and induce proliferation of retinal stem cells. By supporting integrity of trabecular meshwork, transplanted MSCs alleviate IOP resulting in reduced loss of RGCs. Moreover, MSCs are able to attenuate T cell-driven retinal inflammation providing protection to the injured retinal tissue. In summing up, due to their capacity for neuroprotection and immunomodulation, MSCs and their secretome could be explored in upcoming clinical studies as new therapeutic agents for glaucoma treatment.

Transplantation of Retinal Ganglion Cells Derived from Male Germline Stem Cell as a Potential Treatment to Glaucoma

Glaucoma is characterized by retinal ganglion cell (RGC) degeneration and is the second leading cause of blindness worldwide. However, current treatments such as eye drop or surgery have limitations and do not target the loss of RGC. Regenerative therapy using embryonic stem cells (ESCs) holds a promising option, but ethical concern hinders clinical applications on human subjects. In this study, we employed spermatogonial stem cells (SSCs) as an alternative source of ESCs for cell-based regenerative therapy in mouse glaucoma model. We generated functional RGCs from SSCs with a two-step protocol without applying viral transfection or chemical induction. SSCs were first dedifferentiated to embryonic stem-like cells (SSC-ESCs) that resemble ESCs in morphology, gene expression signatures, and stem cell properties. The SSC-ESCs then differentiated toward retinal lineages. We showed SSC-ESC-derived retinal cells expressed RGC-specific marker Brn3b and functioned as bona fide RGCs. To allow in vivo RGC tracing, Brn3b-EGFP reporter SSC-ESCs were generated and the derived RGCs were subsequently transplanted into the retina of glaucoma mouse models by intravitreal injection. We demonstrated that the transplanted RGCs could survive in host retina for at least 10 days after transplantation. SSC-ESC-derived RGCs can thus potentially be a novel alternative to replace the damaged RGCs in glaucomatous retina.

Effects of a combinatorial treatment with gene and cell therapy on retinal ganglion cell survival and axonal outgrowth after optic nerve injury

After an injury, axons in the central nervous system do not regenerate over large distances and permanently lose their connections to the brain. Two promising approaches to correct this condition are cell and gene therapies. In the present work, we evaluated the neuroprotective and neuroregenerative potential of pigment epithelium-derived factor (PEDF) gene therapy alone and combined with human mesenchymal stem cell (hMSC) therapy after optic nerve injury by analysis of retinal ganglion cell survival and axonal outgrowth. Overexpression of PEDF by intravitreal delivery of AAV2 vector significantly increased Tuj1-positive cells survival and modulated FGF-2, IL-1ß, Iba-1, and GFAP immunostaining in the ganglion cell layer (GCL) at 4 weeks after optic nerve crush, although it could not promote axonal outgrowth. The combination of AAV2.PEDF and hMSC therapy showed a higher number of Tuj1-positive cells and a pronounced axonal outgrowth than unimodal therapy after optic nerve crush. In summary, our results highlight a synergistic effect of combined gene and cell therapy relevant for future therapeutic interventions regarding optic nerve injury.

Influence of Lineage-Negative Stem Cell Therapy on Articulatory Functions in ALS Patients

Introduction

Amyotrophic lateral sclerosis (ALS) is a fatal, neurodegenerative disease, leading to loss of muscle strength and motor control. Impaired speech and swallowing lower the quality of life and consequently may induce acute respiratory failure. Bone marrow-derived stem and progenitor cells (SPCs) may be a valuable source of trophic factors. In this study, we assessed whether adjuvant cellular therapy could affect the levels of selected neurotrophins and proinflammatory factors in the cerebrospinal fluid (CSF) and subsequently prevent the deterioration of articulation.

Materials and Methods

The study group consisted of 32 patients with sporadic ALS who underwent autologous lineage-negative (Lin⁻) stem cell intrathecal administration to the spinal canal. Lin⁻ cells were aspirated from the bone marrow and isolated using immunomagnetic beads and a lineage cell depletion kit. Patients were examined for articulatory functions by means of the Voice Handicap Index (VHI) questionnaire and Frenchay Dysarthria Assessment (FDA). In parallel, we carried out the analysis of selected trophic and proinflammatory factors in CSF utilizing multiplex fluorescent bead-based immunoassays.

Results

Of the 32 patients who received the Lin⁻ progenitor cell therapy, 6 (group I) showed improvement in articulatory functions, 23 remained stable (group II), and 3 deteriorated (group III) on the 28^th day. The improvement was particularly noticeable in a better cough reflex, laryngeal time, and dribble reflex. A statistically significant lower level of brain-derived neurotrophic factor (BDNF) was observed on day 0 in group I compared to group II. The CSF concentrations of C-reactive protein (CRP) in group I significantly decreased 7 days after Lin⁻ SPC transplantation. On the contrary, a significant increase in the tumor necrosis factor receptor (TNF-R) level was confirmed among patients from group I with improvement of dribble and coughing reflex, tongue movements, and respiration on the 7^th day, as well as on day 28 including dribble reflex solely.

Conclusions

An application of Lin⁻ stem cells could potentate the beneficial humoral effect. The prevention of deterioration of articulatory functions in ALS patients after applying adjuvant Lin⁻ stem cell therapy seems to be promising. Although the procedure is safe and feasible, it requires further in-depth studies.

Empowering Mesenchymal Stem Cells for Ocular Degenerative Disorders

Multipotent mesenchymal stem cells (MSCs) have been employed in numerous pre-clinical and clinical settings for various diseases. MSCs have been used in treating degenerative disorders pertaining to the eye, for example, age-related macular degeneration, glaucoma, retinitis pigmentosa, diabetic retinopathy, and optic neuritis. Despite the known therapeutic role and mechanisms of MSCs, low cell precision towards the targeted area and cell survivability at tissue needing repair often resulted in a disparity in therapeutic outcomes. In this review, we will discuss the current and feasible strategy options to enhance treatment outcomes with MSC therapy. We will review the application of various types of biomaterials and advances in nanotechnology, which have been employed on MSCs to augment cellular function and differentiation for improving treatment of visual functions. In addition, several modes of gene delivery into MSCs and the types of associated therapeutic genes that are important for modulation of ocular tissue function and repair will be highlighted.

Methods to Induce Chronic Ocular Hypertension: Reliable Rodent Models as a Platform for Cell Transplantation and Other Therapies

Glaucoma, a form of progressive optic neuropathy, is the second leading cause of blindness worldwide. Being a prominent disease affecting vision, substantial efforts are being made to better understand glaucoma pathogenesis and to develop novel treatment options including neuroprotective and neuroregenerative approaches. Cell transplantation has the potential to play a neuroprotective and/or neuroregenerative role for various ocular cell types (e.g., retinal cells, trabecular meshwork). Notably, glaucoma is often associated with elevated intraocular pressure, and over the past 2 decades, several rodent models of chronic ocular hypertension (COH) have been developed that reflect these changes in pressure. However, the underlying pathophysiology of glaucoma in these models and how they compare to the human condition remains unclear. This limitation is the primary barrier for using rodent models to develop novel therapies to manage glaucoma and glaucoma-related blindness. Here, we review the current techniques used to induce COH-related glaucoma in various rodent models, focusing on the strengths and weaknesses of the each, in order to provide a more complete understanding of how these models can be best utilized. To so do, we have separated them based on the target tissue (pre-trabecular, trabecular, and post-trabecular) in order to provide the reader with an encompassing reference describing the most appropriate rodent COH models for their research. We begin with an initial overview of the current use of these models in the evaluation of cell transplantation therapies.

The Krüppel-Like Factor Gene Target Dusp14 Regulates Axon Growth and Regeneration

Purpose

Adult central nervous system (CNS) neurons are unable to regenerate their axons after injury. Krüppel-like transcription factor (KLF) family members regulate intrinsic axon growth ability in vitro and in vivo, but mechanisms downstream of these transcription factors are not known.

Methods

Purified retinal ganglion cells (RGCs) were transduced to express exogenous KLF9, KLF16, KLF7, or KLF11; microarray analysis was used to identify downstream genes, which were screened for effects on axon growth. Dual-specificity phosphatase 14 (Dusp14) was further studied using genetic (siRNA, shRNA) and pharmacologic (PTP inhibitor IV) manipulation to assess effects on neurite length in vitro and survival and regeneration in vivo after optic nerve crush in rats and mice.

Results

By screening genes regulated by KLFs in RGCs, we identified Dusp14 as a critical gene target limiting axon growth and regeneration downstream of KLF9's ability to suppress axon growth in RGCs. The KLF9-Dusp14 pathway inhibited activation of mitogen-activated protein kinases normally critical to neurotrophic signaling of RGC survival and axon elongation. Decreasing Dusp14 expression or disrupting its function in RGCs increased axon growth in vitro and promoted survival and optic nerve regeneration after optic nerve injury in vivo.

Conclusions

These results link intrinsic and extrinsic regulators of axon growth and suggest modulation of the KLF9-Dusp14 pathway as a potential approach to improve regeneration in the adult CNS after injury.

Perspectives of Autologous Mesenchymal Stem-Cell Transplantation in Macular Hole Surgery: A Review of Current Findings

The main treatment available for idiopathic macular holes is represented by pars plana vitrectomy with internal limiting membrane peeling. However, late-stage macular holes are affected by a higher risk of surgical failure. Although adjuvant techniques can be employed, a satisfactory functional recovery is difficult to achieve in refractory macular holes. Given their neuroprotective and antiapoptotic properties, mesenchymal stem cells (MSCs) may represent an appealing approach to treat these extreme cases. The purpose of this review is to highlight the findings regarding healing mechanisms exerted by mesenchymal stem cells and preliminary application in cases of refractory macular holes. When compared with MSCs, MSC-derived exosomes may represent a feasible alternative, given their reduced risk of undesired proliferation and easiness of use.

Novel stem cell and gene therapy in diabetic retinopathy, age related macular degeneration, and retinitis pigmentosa

Degenerative retinal disease leads to significant visual morbidity worldwide. Diabetic retinopathy and macular degeneration are leading causes of blindness in the developed world. While current therapies for these diseases slow disease progression, stem cell and gene therapy may also reverse the effects of these, and other, degenerative retinal conditions. Novel therapies being investigated include the use of various types of stem cells in the regeneration of atrophic or damaged retinal tissue, the prolonged administration of neurotrophic factors and/or drug delivery, immunomodulation, as well as the replacement of mutant genes, and immunomodulation through viral vector delivery. This review will update the reader on aspects of stem cell and gene therapy in diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa and other less common inherited retinal dystrophies. These therapies include the use of adeno-associated viral vector-based therapies for treatment of various types of retinitis pigmentosa and dry age-related macular degeneration. Other potential therapies reviewed include the use of mesenchymal stem cells in local immunomodulation, and the use of stem cells in generating structures like three-dimensional retinal sheets for transplantation into degenerative retinas. Finally, aspects of stem cell and gene therapy in diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, and other less common inherited retinal dystrophies will be reviewed.

Preclinical Evaluation of Long-Term Neuroprotective Effects of BDNF-Engineered Mesenchymal Stromal Cells as Intravitreal Therapy for Chronic Retinal Degeneration in Rd6 Mutant Mice

This study aimed to investigate whether the transplantation of genetically engineered bone marrow-derived mesenchymal stromal cells (MSCs) to overexpress brain-derived neurotrophic factor (BDNF) could rescue the chronic degenerative process of slow retinal degeneration in the rd6 (retinal degeneration 6) mouse model and sought to identify the potential underlying mechanisms. Rd6 mice were subjected to the intravitreal injection of lentivirally modified MSC-BDNF or unmodified MSC or saline. In vivo morphology, electrophysiological retinal function (ERG), and the expression of apoptosis-related genes, as well as BDNF and its receptor (TrkB), were assessed in retinas collected at 28 days and three months after transplantation. We observed that cells survived for at least three months after transplantation. MSC-BDNF preferentially integrated into the outer retinal layers and considerably rescued damaged retinal cells, as evaluated by ERG and immunofluorescence staining. Additionally, compared with controls, the therapy with MSC-BDNF was associated with the induction of molecular changes related to anti-apoptotic signaling. In conclusion, BDNF overexpression observed in retinas after MSC-BDNF treatment could enhance the neuroprotective properties of transplanted autologous MSCs alone in the chronically degenerated retina. This research provides evidence for the long-term efficacy of genetically-modified MSC and may represent a strategy for treating various forms of degenerative retinopathies in the future.

Mesenchymal stromal cell therapy for damaged retinal ganglion cells, is gold all that glitters?

Mesenchymal stromal cells are an excellent source of stem cells because they are isolated from adult tissues or perinatal derivatives, avoiding the ethical concerns that encumber embryonic stem cells. In preclinical models, it has been shown that mesenchymal stromal cells have neuroprotective and immunomodulatory properties, both of which are ideal for central nervous system treatment and repair. Here we will review the current literature on mesenchymal stromal cells, focusing on bone marrow mesenchymal stromal cells, adipose-derived mesenchymal stromal cells and mesenchymal stromal cells from the umbilical cord stroma, i.e., Wharton's jelly mesenchymal stromal cells. Finally, we will discuss the use of these cells to alleviate retinal ganglion cell degeneration following axonal trauma.

Genetic Manipulation and Selection of Mouse Mesenchymal Stem Cells for Delivery of Therapeutic Factors In Vivo

Bone marrow-derived mesenchymal stem cells (MSCs) hold great potential as an ex vivo cellular system for delivery of therapeutic proteins to the diseased or damaged central nervous system (CNS). This adult stem cell population has considerable translational potential for autologous transplantation due to lack of ethical concerns, accessibility, multipotent nature, and plasticity. Here we describe a methodology and outline a strategy using lentiviral vectors for producing lines of MSCs hypersecreting neurotrophic growth factors (e.g., brain-derived neurotrophic factor (BDNF) and/or glial cell line-derived neurotrophic factor (GDNF)) together with a reporter protein such as green fluorescent protein (GFP) that may be used for in vitro and in vivo neuroprotection bioassays. This approach provides exciting opportunities for basic research and proof-of-concept studies.

Stemming retinal regeneration with pluripotent stem cells

Cell replacement therapy is a promising treatment for irreversible retinal cell death in diverse diseases, such as age-related macular degeneration (AMD), Stargardt's disease, retinitis pigmentosa (RP) and glaucoma. These diseases are all characterized by the degeneration of one or two retinal cell types that cannot regenerate spontaneously in humans. Aberrant retinal pigment epithelial (RPE) cells can be observed through optical coherence tomography (OCT) in AMD patients. In RP patients, the morphological and functional abnormalities of RPE and photoreceptor layers are caused by a genetic abnormality. Stargardt's disease or juvenile macular degeneration, which is characterized by the loss of the RPE and photoreceptors in the macular area, causes central vision loss at an early age. Loss of retinal ganglion cells (RGCs) can be observed in patients with glaucoma. Once the retinal cell degeneration is triggered, no treatments can reverse it. Transplantation-based approaches have been proposed as a universal therapy to target patients with various concomitant diseases. Both the replacement of dead cells and neuroprotection are strategies used to rescue visual function in animal models of retinal degeneration. Diverse retinal cell types derived from pluripotent stem cells, including RPE cells, photoreceptors, RGCs and even retinal organoids with a layered structure, provide unlimited cell sources for transplantation. In addition, mesenchymal stem cells (MSCs) are multifunctional and protect degenerating retinal cells. The aim of this review is to summarize current findings from preclinical and clinical studies. We begin with a brief introduction to retinal degenerative diseases and cell death in diverse diseases, followed by methods for retinal cell generation. Preclinical and clinical studies are discussed, and future concerns about efficacy, safety and immunorejection are also addressed.

Pluripotent Stem Cell-Based Approaches to Explore and Treat Optic Neuropathies

Sight is a major sense for human and visual impairment profoundly affects quality of life, especially retinal degenerative diseases which are the leading cause of irreversible blindness worldwide. As for other neurodegenerative disorders, almost all retinal dystrophies are characterized by the specific loss of one or two cell types, such as retinal ganglion cells, photoreceptor cells, or retinal pigmented epithelial cells. This feature is a critical point when dealing with cell replacement strategies considering that the preservation of other cell types and retinal circuitry is a prerequisite. Retinal ganglion cells are particularly vulnerable to degenerative process and glaucoma, the most common optic neuropathy, is a frequent retinal dystrophy. Cell replacement has been proposed as a potential approach to take on the challenge of visual restoration, but its application to optic neuropathies is particularly challenging. Many obstacles need to be overcome before any clinical application. Beyond their survival and differentiation, engrafted cells have to reconnect with both upstream synaptic retinal cell partners and specific targets in the brain. To date, reconnection of retinal ganglion cells with distal central targets appears unrealistic since central nervous system is refractory to regenerative processes. Significant progress on the understanding of molecular mechanisms that prevent central nervous system regeneration offer hope to overcome this obstacle in the future. At the same time, emergence of reprogramming of human somatic cells into pluripotent stem cells has facilitated both the generation of new source of cells with therapeutic potential and the development of innovative methods for the generation of transplantable cells. In this review, we discuss the feasibility of stem cell-based strategies applied to retinal ganglion cells and optic nerve impairment. We present the different strategies for the generation, characterization and the delivery of transplantable retinal ganglion cells derived from pluripotent stem cells. The relevance of pluripotent stem cell-derived retinal organoid and retinal ganglion cells for disease modeling or drug screening will be also introduced in the context of optic neuropathies.

Pronounced synergistic neuroprotective effect of GDNF and CNTF on axotomized retinal ganglion cells in the adult mouse

Neuroprotection is among the potential treatment options for glaucoma and other retinal pathologies characterized by the loss of retinal ganglion cells (RGCs). Here, we examined the impact of a neural stem (NS) cell-based intravitreal co-administration of two neuroprotective factors on the survival of axotomized RGCs. To this aim we used lentiviral vectors to establish clonal NS cell lines ectopically expressing either glial cell line-derived neurotrophic factor (GDNF) or ciliary neurotrophic factor (CNTF). The modified NS cell lines were intravitreally injected either separately or as a 1:1 mixture into adult mice one day after an optic nerve lesion, and the number of surviving RGCs was determined in retinal flat-mounts two, four and eight weeks after the lesion. For the transplantation experiments, we selected a GDNF- and a CNTF-expressing NS cell line that promoted the survival of axotomized RGCs with a similar efficacy. Eight weeks after the lesion, GDNF-treated retinas contained 3.8- and CNTF-treated retinas 3.7-fold more RGCs than control retinas. Of note, the number of surviving RGCs was markedly increased when both factors were administered simultaneously, with 14.3-fold more RGCs than in control retinas eight weeks after the lesion. GDNF and CNTF thus potently and synergistically rescued RGCs from axotomy-induced cell death, indicating that combinatorial neuroprotective approaches represent a promising strategy to effectively promote the survival of RGCs under pathological conditions.

Physical exercise and glaucoma: a review on the roles of physical exercise on intraocular pressure control, ocular blood flow regulation, neuroprotection and glaucoma-related mental health

The benefits of physical exercise on health and well-being have been studied in a wide range of systemic and ocular diseases, including glaucoma, a progressive optic neuropathy characterized by accelerated apoptosis of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) and insufficient ocular perfusion have been postulated to be the two main theories in glaucoma development and progression. The effects of exercise in these two aspects have been demonstrated by numerous researches. A review in 2009 focusing on these two theories concluded that exercise results in transient IOP reduction but an inconsistent elevation in ocular perfusion. However, the majority of the studies had been conducted in healthy subjects. Over the past decade, technological advancement has brought forth new and more detailed evidence regarding the effects of exercise. Moreover, the neuroprotective effect of exercise by upregulation of neurotrophin and enhancement of mitochondrial function has been a focus of interest. Apart from visual impairment, the mental health issues in patients with glaucoma, which include anxiety and depression, should also be addressed. In this review, we mainly focus on publications from the recent years, so as to provide a comprehensive review on the impact of physical exercise on IOP, ocular perfusion, neuroprotection and mental health in patients with glaucoma.

Human Mesenchymal Stem Cells Expressing Erythropoietin Enhance Survivability of Retinal Neurons Against Oxidative Stress: An In Vitro Study

Retinal degeneration is a prominent feature in ocular disorders. In exploring possible treatments, Mesenchymal Stem Cells (MSCs) have been recognized to yield therapeutic role for retinal degenerative diseases. Studies have also displayed that erythropoietin (EPO) administration into degenerative retina models confers significant neuroprotective actions in limiting pathological cell death. In this study, we aimed to use MSCs to deliver EPO and to evaluate the ability of EPO to rescue retinal neurons from dying upon reactive oxidative stress induction. We derived human MSCs from Wharton's jelly (hWJMSCs) of the umbilical cord and cells were transduced with lentivirus particles encoding EPO and a reporter gene of green fluorescent protein (GFP). The supernatants of both transduced and non-transduced cells were collected and used as a pre-conditioning medium for Y79 retinoblastoma cells (retinal neuron cell line) following exposure to glutamate induction. Retinal cells exposed to glutamate showed reduced mitochondrial depolarization and enhanced improvement in cell viability when incubated with pre-conditioned media of transduced cells. Our results established a proof-of-concept that MSCs could be used as a candidate for the delivery of EPO therapeutic gene in the treatment of retinal degenerations.

The effect of trabeculectomy on serum brain-derived neurotrophic factor levels in primary open-angle glaucoma

PURPOSE

We aimed to investigate the effect of trabeculectomy on serum brain-derived neurotrophic factor (BDNF) levels. Our secondary goal was to compare serum and aqueous humor (AH) BDNF levels in primary open-angle glaucoma (POAG) and control subjects.

METHODS

This prospective, cross-sectional study consists of 20 eyes of with advanced-stage POAG who had trabeculectomy and 19 eyes of age- and sex-matched control healthy subjects who had cataract surgery. Serum and AH samples were obtained preoperatively in trabeculectomy group and control subjects. Serum samples were obtained at the third postoperative month in both groups.

RESULTS

The aqueous humor and serum levels of BDNF at the surgery day were found to be strongly positive correlated (r = 0.868; p < 0.001). Serum and AH BDNF levels of POAG cases were significantly lower than control subjects at the surgery day (respectively p = 0.038, p = 0.011). In POAG cases, serum BDNF levels significantly increased at the third month after trabeculectomy while there was not a significant difference in control subjects with cataract surgery (p < 0.001; p = 0.717 respectively).

CONCLUSION

Trabeculectomy was found to have a positive effect on serum BDNF levels in POAG cases.

Adult Stem Cell-Based Strategies for Peripheral Nerve Regeneration

Peripheral nerve injuries (PNI) occur as the result of sudden trauma and can lead to life-long disability, reduced quality of life, and heavy economic and social burdens. Although the peripheral nervous system (PNS) has the intrinsic capacity to regenerate and regrow axons to a certain extent, current treatments frequently show incomplete recovery with poor functional outcomes, particularly for large PNI. Many surgical procedures are available to halt the propagation of nerve damage, and the choice of a procedure depends on the extent of the injury. In particular, recovery from large PNI gaps is difficult to achieve without any therapeutic intervention or some form of tissue/cell-based therapy. Autologous nerve grafting, considered the "gold standard" is often implemented for treatment of gap formation type PNI. Although these surgical procedures provide many benefits, there are still considerable limitations associated with such procedures as donor site morbidity, neuroma formation, fascicle mismatch, and scarring. To overcome such restrictions, researchers have explored various avenues to improve post-surgical outcomes. The most commonly studied methods include: cell transplantation, growth factor delivery to stimulate regenerating axons and implanting nerve guidance conduits containing replacement cells at the site of injury. Replacement cells which offer maximum benefits for the treatment of PNI, are Schwann cells (SCs), which are the peripheral glial cells and in part responsible for clearing out debris from the site of injury. Additionally, they release growth factors to stimulate myelination and axonal regeneration. Both primary SCs and genetically modified SCs enhance nerve regeneration in animal models; however, there is no good source for extracting SCs and the only method to obtain SCs is by sacrificing a healthy nerve. To overcome such challenges, various cell types have been investigated and reported to enhance nerve regeneration.In this review, we have focused on cell-based strategies aimed to enhance peripheral nerve regeneration, in particular the use of mesenchymal stem cells (MSCs). Mesenchymal stem cells are preferred due to benefits such as autologous transplantation, routine isolation procedures, and paracrine and immunomodulatory properties. Mesenchymal stem cells have been transplanted at the site of injury either directly in their native form (undifferentiated) or in a SC-like form (transdifferentiated) and have been shown to significantly enhance nerve regeneration. In addition to transdifferentiated MSCs, some studies have also transplanted ex-vivo genetically modified MSCs that hypersecrete growth factors to improve neuroregeneration.

Glaucoma, Stem Cells, and Gene Therapy: Where Are We Now?

Glaucoma is the second most common cause of blindness, affecting 70∼80 million people around the world. The death of retinal ganglion cells (RGCs) is the main cause of blindness related to this disease. Current therapies do not provide enough protection and regeneration of RGCs. A novel opportunity for treatment of glaucoma is application of technologies related to stem cell and gene therapy. In this perspective we will thus focus on emerging approaches to glaucoma treatment including stem cells and gene therapy.

Glaucoma and the brain: Trans-synaptic degeneration, structural change, and implications for neuroprotection

A recent hypothesis to enter the literature suggests that glaucoma is a neurodegenerative disease. The basis for this has been the finding of central nervous system changes in glaucoma patients on histology and neuroimaging. It is known that retinal ganglion cell pathology of any cause leads to anterograde and retrograde retinal ganglion cell degeneration, as well as trans-synaptic (transneuronal) anterograde degeneration. Trans-synaptic degeneration has been demonstrated in a range of optic neuropathies including optic nerve transection, optic neuritis, and hereditary optic neuropathies. More recently, similar changes have been confirmed in glaucoma patients using the neuroimaging techniques of voxel-based morphometry and diffusion tensor imaging. Some studies have reported brain changes in glaucoma outside the retino-geniculo-cortical pathway; however, these are preliminary and exploratory in nature. Further research is required to identify whether the degenerative brain changes in glaucoma are entirely secondary to the optic neuropathy or whether there is additional primary central nervous system pathology. This has critical implications for neuroprotective and regenerative treatment strategies and our basic understanding of glaucoma.