Induced pluripotent stem cells generate both retinal ganglion cells and photoreceptors: therapeutic implications in degenerative changes in glaucoma and age-related macular degeneration

Integration and Differentiation of Transplanted Human iPSC-Derived Retinal Ganglion Cell Precursors in Murine Retinas

Optic neuropathy such as glaucoma, stemming from retinal ganglion cell (RGC) degeneration, is a leading cause of visual impairment. Given the substantial loss of RGCs preceding clinical detection of visual impairment, cell replacement therapy emerges as a compelling treatment strategy. Human-induced pluripotent stem cells (hiPSCs) serve as invaluable tools for exploring the developmental processes and pathological mechanisms associated with human RGCs. Utilizing a 3D stepwise differentiation protocol for retinal organoids, we successfully differentiated RGC precursors from hiPSCs harboring a BRN3B-GFP RGC reporter, verified by GFP expression. Intravitreal transplantation of enriched RGC precursors into healthy or N-methyl-D-aspartate (NMDA)-injured mice demonstrated their survival, migration, and integration into the proper retinal layer, the ganglion cell layer, after 3 weeks. Notably, these transplanted cells differentiated into marker-positive RGCs and extended neurites. Moreover, enhanced cell survival was observed with immunosuppressive and anti-inflammatory treatments of the host prior to transplantation. These data underscore the potential of transplanted RGC precursors as a promising therapeutic avenue for treating degenerative retinal diseases resulting from RGC dysfunction.

Cell replacement with stem cell-derived retinal ganglion cells from different protocols

Glaucoma, characterized by a degenerative loss of retinal ganglion cells, is the second leading cause of blindness worldwide. There is currently no cure for vision loss in glaucoma because retinal ganglion cells do not regenerate and are not replaced after injury. Human stem cell-derived retinal ganglion cell transplant is a potential therapeutic strategy for retinal ganglion cell degenerative diseases. In this review, we first discuss a 2D protocol for retinal ganglion cell differentiation from human stem cell culture, including a rapid protocol that can generate retinal ganglion cells in less than two weeks and focus on their transplantation outcomes. Next, we discuss using 3D retinal organoids for retinal ganglion cell transplantation, comparing cell suspensions and clusters. This review provides insight into current knowledge on human stem cell-derived retinal ganglion cell differentiation and transplantation, with an impact on the field of regenerative medicine and especially retinal ganglion cell degenerative diseases such as glaucoma and other optic neuropathies.

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.

Reproducible generation of human retinal ganglion cells from banked retinal progenitor cells: analysis of target recognition and IGF-1-mediated axon regeneration

The selective degeneration of retinal ganglion cells (RGCs) is a common feature in glaucoma, a complex group of diseases, leading to irreversible vision loss. Stem cell-based glaucoma disease modeling, cell replacement, and axon regeneration are viable approaches to understand mechanisms underlying glaucomatous degeneration for neuroprotection, ex vivo stem cell therapy, and therapeutic regeneration. These approaches require direct and facile generation of human RGCs (hRGCs) from pluripotent stem cells. Here, we demonstrate a method for rapid generation of hRGCs from banked human pluripotent stem cell-derived retinal progenitor cells (hRPCs) by recapitulating the developmental mechanism. The resulting hRGCs are stable, functional, and transplantable and have the potential for target recognition, demonstrating their suitability for both ex vivo stem cell approaches to glaucomatous degeneration and disease modeling. Additionally, we demonstrate that hRGCs derived from banked hRPCs are capable of regenerating their axons through an evolutionarily conserved mechanism involving insulin-like growth factor 1 and the mTOR axis, demonstrating their potential to identify and characterize the underlying mechanism(s) that can be targeted for therapeutic regeneration.

Survival of Neural Progenitors Derived from Human Embryonic Stem Cells Following Subretinal Transplantation in Rodents

Purpose: To examine the survival of neural progenitors (NPs) cells derived from human embryonic stem cells (hESCs) following subretinal (SR) transplantation in rodents. Methods: hESCs engineered to express enhanced green fluorescent protein (eGFP) were differentiated in vitro toward an NP fate using a 4-week protocol. State of differentiation was characterized by quantitative-PCR. NPs in suspension (75,000/μl) were transplanted to the SR-space of Royal College of Surgeons (RCS) rats (n = 66), nude-RCS rats (n = 18), and NOD scid gamma (NSG) mice (n = 53). Success of engraftment was determined at 4 weeks post-transplant by in vivo visualization of GFP-expression using a properly filtered rodent fundus camera. Transplanted eyes were examined in vivo at set time points using the fundus camera, and in select cases, by optical coherence tomography imaging, and after enucleation, by retinal histology and immunohistochemistry. Results: In RCS rats, cell rejection was observed in 29% of eyes at 6 weeks, rising to 92% at 8 weeks. In the more immunodeficient nude-RCS rats, the rejection rate was still high reaching 62% of eyes at 6 weeks post-transplant. Following transplantation in highly immunodeficient NSG mice, survival of the hESC-derived NPs was much improved, with 100% survival at 9 weeks and 72% at 20 weeks. A small number of eyes that were followed past 20 weeks showed survival also at 22 weeks. Conclusions: Immune status of recipient animals influences transplant survival. Highly immunodeficient NSG mice provide a better model for studying long-term survival, differentiation, and possible integration of hESC-derived NPs. Clinical Trial Registration numbers: NCT02286089, NCT05626114.

Differential Susceptibility of Fetal Retinal Pigment Epithelial Cells, hiPSC- Retinal Stem Cells, and Retinal Organoids to Zika Virus Infection

Zika virus (ZIKV) causes microcephaly and congenital eye disease. The cellular and molecular basis of congenital ZIKV infection are not well understood. Here, we utilized a biologically relevant cell-based system of human fetal retinal pigment epithelial cells (FRPEs), hiPSC-derived retinal stem cells (iRSCs), and retinal organoids to investigate ZIKV-mediated ocular cell injury processes. Our data show that FRPEs were highly susceptible to ZIKV infection exhibiting increased apoptosis, whereas iRSCs showed reduced susceptibility. Detailed transcriptomics and proteomics analyses of infected FRPEs were performed. Nucleoside analogue drug treatment inhibited ZIKV replication. Retinal organoids were susceptible to ZIKV infection. The Asian genotype ZIKV exhibited higher infectivity, induced profound inflammatory response, and dysregulated transcription factors involved in retinal organoid differentiation. Collectively, our study shows that ZIKV affects ocular cells at different developmental stages resulting in cellular injury and death, further providing molecular insight into the pathogenesis of congenital eye disease.

Synaptic or Non-synaptic? Different Intercellular Interactions with Retinal Ganglion Cells in Optic Nerve Regeneration

Axons of adult neurons in the mammalian central nervous system generally fail to regenerate by themselves, and few if any therapeutic options exist to reverse this situation. Due to a weak intrinsic potential for axon growth and the presence of strong extrinsic inhibitors, retinal ganglion cells (RGCs) cannot regenerate their axons spontaneously after optic nerve injury and eventually undergo apoptosis, resulting in permanent visual dysfunction. Regarding the extracellular environment, research to date has generally focused on glial cells and inflammatory cells, while few studies have discussed the potentially significant role of interneurons that make direct connections with RGCs as part of the complex retinal circuitry. In this study, we provide a novel angle to summarize these extracellular influences following optic nerve injury as "intercellular interactions" with RGCs and classify these interactions as synaptic and non-synaptic. By discussing current knowledge of non-synaptic (glial cells and inflammatory cells) and synaptic (mostly amacrine cells and bipolar cells) interactions, we hope to accentuate the previously neglected but significant effects of pre-synaptic interneurons and bring unique insights into future pursuit of optic nerve regeneration and visual function recovery.

Thalidomide-based inhibitor for TNF-α: designing and Insilico evaluation

Background

Inflammatory diseases are the vast array of disorders caused by inflammation. During most inflammatory events, many cytokines expressions were modulated, and one such cytokine is tumor necrosis factor-alpha (TNF-α). TNF-α is mainly secreted by monocytes and macrophages. Notably, it has been proposed as a therapeutic target for several diseases. The anti-TNF biology approach is mainly based on monoclonal antibodies. The fusion protein and biosimilars are prevalent in treating inflammation for decades. Only a few small molecule inhibitors are available to inhibit the expression of TNF-α, and one such promising drug was thalidomide. Therefore, the study was carried out to design thalidomide-based small molecule inhibitors for TNF-α. The main objective of our study is to design thalidomide analogs to inhibit TNF-α using the insilico approach.

Results

Several thalidomide analogs were designed using chemsketch. After filtration of compounds through ‘Lipinski rule of 5’ by Molinspiration tool, as a result, five compounds were selected. All these compounds were subjected to molecular docking, and the study showed that all five compounds had good binding energy. However, based on ADMET predictions, two compounds (S3 and S5) were eliminated.

Conclusions

Our preliminary results suggest that S1, S2, S4 compounds showed potential ligand binding capacity with TNF-α and, interestingly, with limited or no toxicity. Our preliminary investigation and obtained results have fashioned more interest for further in vitro studies.

Retinal Organoid Technology: Where Are We Now?

It is difficult to regenerate mammalian retinal cells once the adult retina is damaged, and current clinical approaches to retinal damages are very limited. The introduction of the retinal organoid technique empowers researchers to study the molecular mechanisms controlling retinal development, explore the pathogenesis of retinal diseases, develop novel treatment options, and pursue cell/tissue transplantation under a certain genetic background. Here, we revisit the historical background of retinal organoid technology, categorize current methods of organoid induction, and outline the obstacles and potential solutions to next-generation retinal organoids. Meanwhile, we recapitulate recent research progress in cell/tissue transplantation to treat retinal diseases, and discuss the pros and cons of transplanting single-cell suspension versus retinal organoid sheet for cell therapies.

Advances in Regeneration of Retinal Ganglion Cells and Optic Nerves

Glaucoma, the second leading cause of blindness worldwide, is an incurable neurodegenerative disorder due to the dysfunction of retinal ganglion cells (RGCs). RGCs function as the only output neurons conveying the detected light information from the retina to the brain, which is a bottleneck of vision formation. RGCs in mammals cannot regenerate if injured, and RGC subtypes differ dramatically in their ability to survive and regenerate after injury. Recently, novel RGC subtypes and markers have been uncovered in succession. Meanwhile, apart from great advances in RGC axon regeneration, some degree of experimental RGC regeneration has been achieved by the in vitro differentiation of embryonic stem cells and induced pluripotent stem cells or in vivo somatic cell reprogramming, which provides insights into the future therapy of myriad neurodegenerative disorders. Further approaches to the combination of different factors will be necessary to develop efficacious future therapeutic strategies to promote ultimate axon and RGC regeneration and functional vision recovery following injury.

What Is New in Glaucoma: From Treatment to Biological Perspectives

Glaucoma is a chronic silent disease and an irreversible cause of blindness worldwide. Research has made many efforts to improve disease control and especially to anticipate both early diagnosis and treatment of advanced stages of glaucoma. In terms of prevention, networking between professionals and nonprofessionals is an important goal to disseminate information and help diagnose the disease early. On the other hand, the most recent approaches to treat glaucoma outcomes in its advanced stages include electrical stimulation, stem cells, exosomes, extracellular vesicles, and growth factors. Finally, neuronal plasticity-based rehabilitation methods are being studied to reeducate patients in order to stimulate their residual visual capacity. This review provides an overview of new approaches to future possible glaucoma treatment modalities and gives insight into the perspectives available nowadays in this field.

Effects of Adult Müller Cells and Their Conditioned Media on the Survival of Stem Cell-Derived Retinal Ganglion Cells

Retinal neurons, particularly retinal ganglion cells (RGCs), are susceptible to the degenerative damage caused by different inherited conditions and environmental insults, leading to irreversible vision loss and, ultimately, blindness. Numerous strategies are being tested in different models of degeneration to restore vision and, in recent years, stem cell technologies have offered novel avenues to obtain donor cells for replacement therapies. To date, stem cell-based transplantation in the retina has been attempted as treatment for photoreceptor degeneration, but the same tools could potentially be applied to other retinal cell types, including RGCs. However, RGC-like cells are not an abundant cell type in stem cell-derived cultures and, often, these cells degenerate over time in vitro. To overcome this limitation, we have taken advantage of the neuroprotective properties of Müller glia (one of the main glial cell types in the retina) and we have examined whether Müller glia and the factors they secrete could promote RGC-like cell survival in organoid cultures. Accordingly, stem cell-derived RGC-like cells were co-cultured with adult Müller cells or Müller cell-conditioned media was added to the cultures. Remarkably, RGC-like cell survival was substantially enhanced in both culture conditions, and we also observed a significant increase in their neurite length. Interestingly, Atoh7, a transcription factor required for RGC development, was up-regulated in stem cell-derived organoids exposed to conditioned media, suggesting that Müller cells may also enhance the survival of retinal progenitors and/or postmitotic precursor cells. In conclusion, Müller cells and the factors they release promote organoid-derived RGC-like cell survival, neuritogenesis, and possibly neuronal maturation.

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.

Differentiation of retinal organoids from human pluripotent stem cells

Human pluripotent stem cells (hPSCs) possess the remarkable ability to differentiate into any cell type of the body, including those of the retina. Through the differentiation of these cells as retinal organoids, it is now possible to model the spatial and temporal development of the human retina using hPSCs, in which retinal progenitor cells produce the entire repertoire of retinal cells, first differentiating into retinal ganglion cells and ending with mature photoreceptors, bipolar cells, and Müller glia. Importantly, retinal organoids self-assemble into laminated structures that recapitulate the layering of the human retina with a retinal ganglion cell layer lining the inner layer and a distinctly separate photoreceptor layer occupying the outer layers. This organoid technology has provided access to human tissue for developmental and disease modeling, as well as translational applications such as high throughput drug screening and cell replacement therapies. However, the differentiation of retinal organoids does require some expertise and multiple strategies produce inconsistent results. Here, we describe in detail a well-established and relatively simple method for the generation of retinal organoids.

Physiologic maturation is both extrinsically and intrinsically regulated in progenitor-derived neurons

During development, newly-differentiated neurons undergo several morphological and physiological changes to become functional, mature neurons. Physiologic maturation of neuronal cells derived from isolated stem or progenitor cells may provide insight into maturation in vivo but is not well studied. As a step towards understanding how neuronal maturation is regulated, we studied the developmental switch of response to the neurotransmitter GABA, from excitatory depolarization to inhibitory hyperpolarization. We compared acutely isolated retinal ganglion cells (RGCs) at various developmental stages and RGCs differentiated in vitro from embryonic retinal progenitors for the effects of aging and, independently, of retinal environment age on their GABAA receptor (GABAAR) responses, elicited by muscimol. We found that neurons generated in vitro from progenitors exhibited depolarizing, immature GABA responses, like those of early postnatal RGCs. As progenitor-derived neurons aged from 1 to 3 weeks, their GABA responses matured. Interestingly, signals secreted by the early postnatal retina suppressed acquisition of mature GABA responses. This suppression was not associated with changes in expression of GABAAR or of the chloride co-transporter KCC2, but rather with inhibition of KCC2 dimerization in differentiating neurons. Taken together, these data indicate GABA response maturation depends on release of inhibition by developmentally regulated diffusible signals from the retina.

Stem Cell Transplantation Therapy for Retinal Degenerative Diseases

In the past decade, progress in the research on human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) has provided the solid basis to derive retinal pigment epithelium, photoreceptors, and ganglion cells from hESCs/iPSCs for transplantation therapy of retinal degenerative diseases (RDD). Recently, the iPSC-derived retinal pigment epithelium cells have achieved efficacy in treating patients with age-related macular degeneration (AMD). However, there is still much work to be done about the differentiation of hESCs/iPSCs into clinically required retinal cells and improvement in the methods to deliver the cells into the retina of patients. Here we will review the research advances in stem cell transplantation in animal studies and clinical trials as well as propose the challenges for improving the clinical efficacy and safety of hESCs/iPSCs-derived retinal neural cells in treating retinal degenerative diseases.

Recapitulating developmental mechanisms for retinal regeneration

Degeneration of specific retinal neurons in diseases like glaucoma, age-related macular degeneration, and retinitis pigmentosa is the leading cause of irreversible blindness. Currently, there is no therapy to modify the disease-associated degenerative changes. With the advancement in our knowledge about the mechanisms that regulate the development of the vertebrate retina, the approach to treat blinding diseases through regenerative medicine appears a near possibility. Recapitulation of developmental mechanisms is critical for reproducibly generating cells in either 2D or 3D culture of pluripotent stem cells for retinal repair and disease modeling. It is the key for unlocking the neurogenic potential of Müller glia in the adult retina for therapeutic regeneration. Here, we examine the current status and potential of the regenerative medicine approach for the retina in the backdrop of developmental mechanisms.

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.

Differentiation of retinal ganglion cells from induced pluripotent stem cells: a review

Glaucoma is a common optic neuropathy that is characterized by the progressive degeneration of axons and the loss of retinal ganglion cells (RGCs). Glaucoma is one of the leading causes of irreversible blindness worldwide. Current glaucoma treatments only slow the progression of RGCs loss. Induced pluripotent stem cells (iPSCs) are capable of differentiating into all three germ layer cell lineages. iPSCs can be patient-specific, making iPSC-derived RGCs a promising candidate for cell replacement. In this review, we focus on discussing the detailed approaches used to differentiate iPSCs into RGCs.

Retinal Ganglion Cell Replacement: Current Status and Challenges Ahead

The neurons of the retina can be affected by a wide variety of inherited or environmental degenerations that can lead to vision loss and even blindness. Retinal ganglion cell (RGC) degeneration is the hallmark of glaucoma and other optic neuropathies that affect millions of people worldwide. Numerous strategies are being trialed to replace lost neurons in different degeneration models, and in recent years, stem cell technologies have opened promising avenues to obtain donor cells for retinal repair. Stem cell-based transplantation has been most frequently used for the replacement of rod photoreceptors, but the same tools could potentially be used for other retinal cell types, including RGCs. However, RGCs are not abundant in stem cell-derived cultures, and in contrast to the short-distance wiring of photoreceptors, RGC axons take a long and intricate journey to connect with numerous brain nuclei. Hence, a number of challenges still remain, such as the ability to scale up the production of RGCs and a reliable and functional integration into the adult diseased retina upon transplantation. In this review, we discuss the recent advancements in the development of replacement therapies for RGC degenerations and the challenges that we need to overcome before these technologies can be applied to the clinic. Developmental Dynamics 248:118-128, 2019. © 2018 Wiley Periodicals, Inc.

The combination of bFGF and CHIR99021 maintains stable self-renewal of mouse adult retinal progenitor cells

BACKGROUND

Millions of people are affected with retinal diseases that eventually cause blindness, and retinal progenitor cell (RPC) transplantation is a promising therapeutic avenue. However, RPC expansion and the underlying regulation mechanisms remain elusive.

METHODS

Adult mouse neural RPCs (mNRPCs) were isolated and amplified with the combination of basic fibroblast growth factor (bFGF) and glycogen synthase kinase 3 (GSK3) inhibitor CHIR99021. The progenitor characteristics were evaluated with RT-PCR, immunocytochemistry (ICC), western blot, flow cytometry, and transcriptome analysis prior to transplantation. By treating cells with or without bFGF and CHIR99021 at different time points, the mechanism for mNRPCs' self-renewal was investigated by transcriptome analysis and western blot assay.

RESULTS

mNRPCs were self-renewing in the presence of bFGF and CHIR99021 and showed prominent RPC characteristics. bFGF was essential in promoting cell cycle by facilitating G1/S and G2/M transitions. bFGF combined with CHIR99021 activated the non-canonical Wnt5A/Ca²⁺ pathway and form a calcium homeostasis. In addition, the self-renewing mNRPCs could differentiate into rod photoreceptor-like cells and retinal pigment epithelium (RPE)-like cells by in vitro induction. When green fluorescent protein (GFP)-labeled cells were transplanted into the subretinal space (SRS) of Pde6b (rd1) mice (also known as RD1 mice, or rodless mice), the cells survived for more than 12 weeks and migrated into the retina. Parts of the recipient retina showed positive expression of photoreceptor marker rhodopsin. Transplanted cells can migrate into the retina, mainly into the inner cell layer (INL) and ganglion cell layer (GCL). Some cells can differentiate into astrocytes and amacrine cells. Cultured mNRPCs did not form tumors after transplanted into NOD/SCID mice for 6 months.

CONCLUSIONS

Present study developed an approach to maintain long-term self-renewal of RPCs from adult retinal tissues and revealed that activation of the non-canonical Wnt5A/Ca²⁺ pathway may participate in regulating RPC self-renewal in vitro. This study presents a very promising platform to expand RPCs for future therapeutic application.

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.

Prospective applications of induced pluripotent stem cells in military medicine

Soldiers involved in combat operations worldwide may be subjected to a wide array of tissue-specific injuries of varying degrees, thereby undergoing complicated medical treatments and prolonged rehabilitations. In many cases involving inadequate recovery, soldiers are further mentally traumatized as they can no longer serve their beloved country. In addition, many severe injuries can lead to soldiers being incapacitated for life and unable to perform even the most basic day-to-day activities. Present therapy for combat injuries is majorly aimed at alleviating pain and limiting further tissue damage from secondary infections. Cell-based therapy using stem cells is a promising tissue regenerative source, which will help our soldiers to recuperate from the severe injuries, and in some cases, even continue their service for the country after complete recovery. In this context, we would like to discuss the yet fully untapped potential of induced pluripotent stem cells (iPSCs) in regenerative medicine on the battlefield. In this review, we shall try to explore the rationale behind the use of these cells for military medicine, as well as the conventional and novel approaches to produce them for therapeutic applications. We shall also attempt to elucidate the evolving trends of battlefield injuries throughout history and the ongoing research on regeneration of tissues of specific interest using iPSCs and their potential role in combat medicine in the future. Additionally, we shall also discuss the concept of stem cell bio-banking for military personnel as a personalized safeguard against crippling and traumatic combat injuries.

Autologous stem cell therapy for inherited and acquired retinal disease

The mammalian retina, derived from neural ectoderm, has little regenerative potential. For conditions where irreversible retinal pigment epithelium or photoreceptor cell loss occurs, advanced techniques are required to restore vision. Inherited retinal dystrophies and some acquired conditions, such as age-related macular degeneration, have a similar end result of photoreceptor cell death leading to debilitating vision loss. These diseases stand to benefit from future regenerative medicine as dietary recommendations and current pharmacologic therapy only seek to prevent further disease progression. Cell-based strategies, such as autologously derived induced pluripotent stem cells, have come a long way in overcoming previous technical and ethical concerns. Clinical trials for such techniques are already underway. These trials and the preceding preclinical studies will be discussed in the context of retinal disease.

Direct cell fate conversion of human somatic stem cells into cone and rod photoreceptor-like cells by inhibition of microRNA-203

Stem cell-based photoreceptor differentiation strategies have been the recent focus of therapies for retinal degenerative diseases. Previous studies utilized embryonic stem (ES) cells and neural retina differentiation cocktails, including DKK1 and Noggin. Here, we show a novel microRNA-mediated strategy of retina differentiation from somatic stem cells, which are potential allogeneic cell sources. Human amniotic epithelial stem cells (AESCs) and umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) treated with a retina differentiation cocktail induced gene expressions of retina development-relevant genes. Furthermore, microRNA-203 (miR-203) is abundantly expressed in human AESCs and human UCB-MSCs. This miR-203 is predicted to target multiple retina development-relevant genes, particularly DKK1, CRX, RORβ, NEUROD1, NRL and THRB. The inhibition of miR-203 induced a retina differentiation of AESCs and UCB-MSCs. Moreover, successive treatments of anti-miR-203 led to the expression of both mature photoreceptor (PR) markers, rhodopsin and opsin. In addition, we determined that CRX, NRL and DKK1 are direct targets of miR-203 using a luciferase assay. Thus, the work presented here suggests that somatic stem cells can potentially differentiate into neural retina cell types when treated with anti-miR-203. They may prove to be a source of both PR subtypes for future allogeneic stem cell-based therapies of non-regenerative retina diseases.

A Gal-MµS Device to Evaluate Cell Migratory Response to Combined Galvano-Chemotactic Fields

Electric fields have been studied extensively in biomedical engineering (BME) for numerous regenerative therapies. Recent studies have begun to examine the biological effects of electric fields in combination with other environmental cues, such as tissue-engineered extracellular matrices (ECM), chemical gradient profiles, and time-dependent temperature gradients. In the nervous system, cell migration driven by electrical fields, or galvanotaxis, has been most recently studied in transcranial direct stimulation (TCDS), spinal cord repair and tumor treating fields (TTF). The cell migratory response to galvano-combinatory fields, such as magnetic fields, chemical gradients, or heat shock, has only recently been explored. In the visual system, restoration of vision via cellular replacement therapies has been limited by low numbers of motile cells post-transplantation. Here, the combinatory application of electrical fields with other stimuli to direct cells within transplantable biomaterials and/or host tissues has been understudied. In this work, we developed the Gal-MµS device, a novel microfluidics device capable of examining cell migratory behavior in response to single and combinatory stimuli of electrical and chemical fields. The formation of steady-state, chemical concentration gradients and electrical fields within the Gal-MµS were modeled computationally and verified experimentally within devices fabricated via soft lithography. Further, we utilized real-time imaging within the device to capture cell trajectories in response to electric fields and chemical gradients, individually, as well as in combinatory fields of both. Our data demonstrated that neural cells migrated longer distances and with higher velocities in response to combined galvanic and chemical stimuli than to either field individually, implicating cooperative behavior. These results reveal a biological response to galvano-chemotactic fields that is only partially understood, as well as point towards novel migration-targeted treatments to improve cell-based regenerative therapies.

The use of induced pluripotent stem cells for studying and treating optic neuropathies

PURPOSE OF REVIEW

The present review aims to provide an update of applications of induced pluripotent stem cells (iPSCs) for disease modeling, cell/gene therapy, and drug screening for optic neuropathies.

RECENT FINDINGS

Degeneration of retinal ganglion cells (RGCs) is a characteristic of optic neuropathies. Human iPSCs can serve as a model to investigate disease pathology and potential repair mechanisms. In recent years, significant progress has been made in generating RGCs from iPSCs. Various groups have reported the potential of iPSCs for modeling optic neuropathies, such as glaucoma. The literature also highlights the potential to use iPSC-derived cells for high-throughput drug and toxicity screening.

SUMMARY

The present review summarizes current work in the field of iPSCs in optic neuropathies. Future studies to characterize iPSC-derived RGCs in a more in-depth manner will help expand the use of iPSCs to model and treat optic neuropathic diseases. Furthermore, iPSC modeling can be used in drug development by offering a new avenue to test novel therapeutic drugs for optic neuropathies.

Glaucoma: Biological Trabecular and Neuroretinal Pathology with Perspectives of Therapy Innovation and Preventive Diagnosis

Glaucoma is a common degenerative disease affecting retinal ganglion cells (RGC) and optic nerve axons, with progressive and chronic course. It is one of the most important reasons of social blindness in industrialized countries. Glaucoma can lead to the development of irreversible visual field loss, if not treated. Diagnosis may be difficult due to lack of symptoms in early stages of disease. In many cases, when patients arrive at clinical evaluation, a severe neuronal damage may have already occurred. In recent years, newer perspective in glaucoma treatment have emerged. The current research is focusing on finding newer drugs and associations or better delivery systems in order to improve the pharmacological treatment and patient compliance. Moreover, the application of various stem cell types with restorative and neuroprotective intent may be found appealing (intravitreal autologous cellular therapy). Advances are made also in terms of parasurgical treatment, characterized by various laser types and techniques. Moreover, recent research has led to the development of central and peripheral retinal rehabilitation (featuring residing cells reactivation and replacement of defective elements), as well as innovations in diagnosis through more specific and refined methods and inexpensive tests.

Regulated differentiation of WERI-Rb-1 cells into retinal neuron-like cells

The encouraging response and improved survival of acute promyelocytic leukemia patients following retinoic acid treatment has rendered differentiation therapy an attractive option in cancer treatment. Given that terminal differentiation represents a considerable barrier in retinoblastoma tumorigenesis and that retinoblastoma has a significantly higher spontaneous degeneration rate compared with other tumors (1,000-fold change), differentiation therapy represents a promising alternative in the treatment of retinoblastoma. However, the full differentiation potential of retinoblastoma still unknown. The present study was designed to investigate the extend differentiation of the classical retinoblastoma cell line WERI-Rb-1 (W-RBCs). Several critical cell signaling pathways and key genes related to cell proliferation and differentiation were comprehensively regulated to control the fate of W-RBCs. Various strategies were applied to optimize simple and time-saving methods to induce W-RBCs into different types of retinal neuron-like cells (RNLCs) in vitro. Further, the tumorigenesis of these differentiated W-RBCs was tested in nude mice in vivo. W-RBCs were found to inherently express both retinal progenitor cell- and embryonic stem cell-related genes or proteins. Moreover, the addition of antagonists of critical cell signals (Wnt, Nodal, BMP4 and Notch), even without atonal bHLH transcription factor 7 gene transfection, could directly induce W-RBCs into RNLCs, and especially into photoreceptor-like and retinal ganglion-like cells. Interestingly, the differentiated cells showed remarkably poorer tumorigenesis in vivo. These findings may offer new insights on the oriented differentiation of W-RBCs into RNLCs with low tumorigenicity and provide potential targets for retinoblastoma differentiation therapy.

Retinoid acid and taurine promote NeuroD1-induced differentiation of induced pluripotent stem cells into retinal ganglion cells

Induced pluripotent stem cells (iPSCs) possess the capacity to differentiate into multiple cell types including retinal neurons. Despite substantial progress in the transcriptional regulation of iPSC differentiation process, the efficiency of generation of retinal neurons from iPSCs is still low. In this study, we investigated the role of transcription factor NeuroD1 in the differentiation of iPSCs into retinal neurons. We observed that retrovirus-mediated NeuroD1 overexpression in iPSCs increased the efficiency of neuronal differentiation. Immunostaining analysis showed that NeuroD1 overexpression increased the expression of retina ganglion cell markers including Islet-1, Math5, Brn3b, and Thy1.2. Retinoid acid (RA) and taurine further improved the differentiation efficiency of iPSCs overexpressing NeuroD1. However, RA and taurine did not promote differentiation in the absence of NeuroD1 overexpression. Together, our study provides new evidence in transcription factor-regulated stem cell differentiation in vitro.

Long-term results after limited macular translocation surgery for wet age-related macular degeneration

Purpose

To evaluate the long-term results of limited macular translocation (LMT) surgery with radial chorioscleral outfolding in patients with wet age-related macular degeneration (AMD) and subfoveal choroidal neovascularization (CNV). In addition, to identify the factors associated with the final best-corrected visual acuity (BCVA).

Methods

The medical records of 20 eyes of 20 consecutive patients (65.2±9.8 years) who had undergone LMT for the treatment of wet AMD and were followed for at least 5 years, were reviewed. The surgical outcomes including the BCVA, degree of foveal displacement, and complications were recorded.

Results

The mean foveal displacement was 1332 ± 393 μm after the LMT. The CNV was removed in 16 eyes and photocoagulated in 4 eyes. The mean preoperative VA was 0.83 ± 0.33 logMAR units which significantly improved to 0.59 ± 0.37 logMAR units at 1 year after the surgery (P = 0.015). This BCVA was maintained at 0.59 ± 0.41 logMAR units on the final examination. The final BCVA was significantly correlated with that at 1 year after the surgery (r = 0.83, P<0.001). Multiple linear regression analysis showed that the final BCVA was significantly correlated with the BCVA at 1 year after the surgery (P<0.001), a recurrence of a CNV (P = 0.001), and the age (P = 0.022).

Conclusions

LMT improves the BCVA significantly at 1 year, and the improved BCVA lasted for at least 5 years. These results indicate that the impaired function of the sensory retina at the fovea can recover on the new RPE after the displacement for at least 5 years. The ability to maintain good retinal function on the new RPE for a long period is important for future treatments of CNVs such as the transplantation of RPE cells and stem cells.

HiPSC-derived retinal ganglion cells grow dendritic arbors and functional axons on a tissue-engineered scaffold

Numerous therapeutic procedures in modern medical research rely on the use of tissue engineering for the treatment of retinal diseases. However, the cell source and the transplantation method are still a limitation. Previously, it was reported that a self-organizing three-dimensional neural retina can be induced from human-induced pluripotent stem cells (hiPSCs). In this study, we disclose the generation of retinal ganglion cells (RGCs) from the neural retina and their seeding on a biodegradable poly (lactic-co-glycolic acid) (PLGA) scaffold to create an engineered RGC-scaffold biomaterial. Moreover, we explored the dendritic arbor, branching point, functional axon and action potential of the biomaterial. Finally, the cell-scaffold was transplanted into the intraocular environment of rabbits and rhesus monkeys.

STATEMENT OF SIGNIFICANCE

As a part of the mammalian central nervous system (CNS), the retinal ganglion cell (RGC) shows little regenerative capacity. With the use of medical biomaterial for cells seeding and deliver, a new domain is now emerging that uses tissue engineering therapy for retinal disease. However, previous studies utilized RGCs from rodent model, which has limitations for human disease treatment. In the present study, we generated RGCs from hiPSCs-3D neural retina and then seeded these RGCs on PLGA scaffold to create an engineered RGC-scaffold biomaterial. Moreover, we assessed the transplantation method for biomaterial in vivo. Our study provides a technique to produce the engineered human RGC-scaffold biomaterial.

Novel Regulatory Mechanisms for the SoxC Transcriptional Network Required for Visual Pathway Development

What pathways specify retinal ganglion cell (RGC) fate in the developing retina? Here we report on mechanisms by which a molecular pathway involving Sox4/Sox11 is required for RGC differentiation and for optic nerve formation in mice in vivo, and is sufficient to differentiate human induced pluripotent stem cells into electrophysiologically active RGCs. These data place Sox4 downstream of RE1 silencing transcription factor in regulating RGC fate, and further describe a newly identified, Sox4-regulated site for post-translational modification with small ubiquitin-related modifier (SUMOylation) in Sox11, which suppresses Sox11's nuclear localization and its ability to promote RGC differentiation, providing a mechanism for the SoxC familial compensation observed here and elsewhere in the nervous system. These data define novel regulatory mechanisms for this SoxC molecular network, and suggest pro-RGC molecular approaches for cell replacement-based therapies for glaucoma and other optic neuropathies.SIGNIFICANCE STATEMENT Glaucoma is the most common cause of blindness worldwide and, along with other optic neuropathies, is characterized by loss of retinal ganglion cells (RGCs). Unfortunately, vision and RGC loss are irreversible, and lead to bilateral blindness in ∼14% of all diagnosed patients. Differentiated and transplanted RGC-like cells derived from stem cells have the potential to replace neurons that have already been lost and thereby to restore visual function. These data uncover new mechanisms of retinal progenitor cell (RPC)-to-RGC and human stem cell-to-RGC fate specification, and take a significant step toward understanding neuronal and retinal development and ultimately cell-transplant therapy.

Generation of Functional Human Retinal Ganglion Cells with Target Specificity from Pluripotent Stem Cells by Chemically Defined Recapitulation of Developmental Mechanism

Glaucoma is a complex group of diseases wherein a selective degeneration of retinal ganglion cells (RGCs) lead to irreversible loss of vision. A comprehensive approach to glaucomatous RGC degeneration may include stem cells to functionally replace dead neurons through transplantation and understand RGCs vulnerability using a disease in a dish stem cell model. Both approaches require the directed generation of stable, functional, and target-specific RGCs from renewable sources of cells, that is, the embryonic stem cells and induced pluripotent stem cells. Here, we demonstrate a rapid and safe, stage-specific, chemically defined protocol that selectively generates RGCs across species, including human, by recapitulating the developmental mechanism. The de novo generated RGCs from pluripotent cells are similar to native RGCs at the molecular, biochemical, functional levels. They also express axon guidance molecules, and discriminate between specific and nonspecific targets, and are nontumorigenic. Stem Cells 2017;35:572-585.

Astrocyte Differentiation of Human Pluripotent Stem Cells: New Tools for Neurological Disorder Research

Astrocytes have a central role in brain development and function, and so have gained increasing attention over the past two decades. Consequently, our knowledge about their origin, differentiation and function has increased significantly, with new research showing that astrocytes cultured alone or co-cultured with neurons have the potential to improve our understanding of various central nervous system diseases, such as amyotrophic lateral sclerosis, Alzheimer’s disease, or Alexander disease. The generation of astrocytes derived from pluripotent stem cells (PSCs) opens up a new area for studying neurologic diseases in vitro; these models could be exploited to identify and validate potential drugs by detecting adverse effects in the early stages of drug development. However, as it is now known that a range of astrocyte populations exist in the brain, it will be important in vitro to develop standardized protocols for the in vitro generation of astrocyte subsets with defined maturity status and phenotypic properties. This will then open new possibilities for co-cultures with neurons and the generation of neural organoids for research purposes. The aim of this review article is to compare and summarize the currently available protocols and their strategies to generate human astrocytes from PSCs. Furthermore, we discuss the potential role of human-induced PSCs derived astrocytes in disease modeling.

Clinical Trials in Retinal Dystrophies

Research development is burgeoning for genetic and cellular therapy for retinal dystrophies. These dystrophies are the focus of many research efforts due to the unique biology and accessibility of the eye, the transformative advances in ocular imaging technology that allows for in vivo monitoring, and the potential benefit people would gain from success in the field – the gift of renewed sight. Progress in the field has revealed the immense complexity of retinal dystrophies and the challenges faced by researchers in the development of this technology. This study reviews the current trials and advancements in genetic and cellular therapy in the treatment of retinal dystrophies and also discusses the current and potential future challenges.

Enriched retinal ganglion cells derived from human embryonic stem cells

Optic neuropathies are characterised by a loss of retinal ganglion cells (RGCs) that lead to vision impairment. Development of cell therapy requires a better understanding of the signals that direct stem cells into RGCs. Human embryonic stem cells (hESCs) represent an unlimited cellular source for generation of human RGCs in vitro. In this study, we present a 45-day protocol that utilises magnetic activated cell sorting to generate enriched population of RGCs via stepwise retinal differentiation using hESCs. We performed an extensive characterization of these stem cell-derived RGCs by examining the gene and protein expressions of a panel of neural/RGC markers. Furthermore, whole transcriptome analysis demonstrated similarity of the hESC-derived RGCs to human adult RGCs. The enriched hESC-RGCs possess long axons, functional electrophysiological profiles and axonal transport of mitochondria, suggestive of maturity. In summary, this RGC differentiation protocol can generate an enriched population of functional RGCs from hESCs, allowing future studies on disease modeling of optic neuropathies and development of cell therapies.

Modeling autosomal dominant optic atrophy using induced pluripotent stem cells and identifying potential therapeutic targets

Background

Many retinal degenerative diseases are caused by the loss of retinal ganglion cells (RGCs). Autosomal dominant optic atrophy is the most common hereditary optic atrophy disease and is characterized by central vision loss and degeneration of RGCs. Currently, there is no effective treatment for this group of diseases. However, stem cell therapy holds great potential for replacing lost RGCs of patients. Compared with embryonic stem cells, induced pluripotent stem cells (iPSCs) can be derived from adult somatic cells, and they are associated with fewer ethical concerns and are less prone to immune rejection. In addition, patient-derived iPSCs may provide us with a cellular model for studying the pathogenesis and potential therapeutic agents for optic atrophy.

Methods

In this study, iPSCs were obtained from patients carrying an OPA1 mutation (OPA1^+/−-iPSC) that were diagnosed with optic atrophy. These iPSCs were differentiated into putative RGCs, which were subsequently characterized by using RGC-specific expression markers BRN3a and ISLET-1.

Results

Mutant OPA1^+/−-iPSCs exhibited significantly more apoptosis and were unable to efficiently differentiate into RGCs. However, with the addition of neural induction medium, Noggin, or estrogen, OPA1^+/−-iPSC differentiation into RGCs was promoted.

Conclusions

Our results suggest that apoptosis mediated by OPA1 mutations plays an important role in the pathogenesis of optic atrophy, and both noggin and β-estrogen may represent potential therapeutic agents for OPA1-related optic atrophy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0264-1) contains supplementary material, which is available to authorized users.

Delivery strategies for treatment of age-related ocular diseases: From a biological understanding to biomaterial solutions

Age-related ocular diseases, such as age-related macular degeneration (AMD), diabetic retinopathy, and glaucoma, result in life-long functional deficits and enormous global health care costs. As the worldwide population ages, vision loss has become a major concern for both economic and human health reasons. Due to recent research into biomaterials and nanotechnology major advances have been gained in the field of ocular delivery. This review provides a summary and discussion of the most recent strategies employed for the delivery of both drugs and cells to the eye to treat a variety of age-related diseases. It emphasizes the current challenges and limitations to ocular delivery and how the use of innovative materials can overcome these issues and ultimately provide treatment for age-related degeneration and regeneration of lost tissues. This review also provides critical considerations and an outlook for future studies in the field of ophthalmic delivery.

Research on induced pluripotent stem cells and the application in ocular tissues

Induced pluripotent stem cells (iPSCs) were firstly induced from mouse fibroblasts since 2006, and then the research on iPSCs had made great progress in the following years. iPSCs were established from different somatic cells through DNA, RNA, protein or small molecule pathways and transduction vehicles. With continuous improvement of technology on reprogramming, the induction of iPSCs became more secure and effective, and showed enormous promise for clinical applications. We reviewed different reprogramming of somatic cells, four kinds of pathways of reprogramming and three types of transduction vehicles, and discuss the research of iPSCs in ophthalmology and the prospect of iPSCs applications.

Continuous non-cell autonomous reprogramming to generate retinal ganglion cells for glaucomatous neuropathy

Glaucoma, where the retinal ganglion cells (RGCs) carrying the visual signals from the retina to the visual centers in the brain are progressively lost, is the most common cause of irreversible blindness. The management approaches, whether surgical, pharmacological, or neuroprotective do not reverse the degenerative changes. The stem cell approach to replace dead RGCs is a viable option but currently faces several barriers, such as the lack of a renewable, safe, and ethical source of RGCs that are functional and could establish contacts with bona fide targets. To address these barriers, we have derived RGCs from the easily accessible adult limbal cells, reprogrammed to pluripotency by a non-nucleic acid approach, thus circumventing the risk of insertional mutagenesis. The generation of RGCs from the induced pluripotent stem (iPS) cells, also accomplished non-cell autonomously, recapitulated the developmental mechanism, ensuring the predictability and stability of the acquired phenotype, comparable to that of native RGCs at biochemical, molecular, and functional levels. More importantly, the induced RGCs expressed axonal guidance molecules and demonstrated the potential to establish contacts with specific targets. Furthermore, when transplanted in the rat model of ocular hypertension, these cells incorporated into the host RGC layer and expressed RGC-specific markers. Transplantation of these cells in immune-deficient mice did not produce tumors. Together, our results posit retinal progenitors generated from non-nucleic acid-derived iPS cells as a safe and robust source of RGCs for replacing dead RGCs in glaucoma.

Optimized Culture System to Induce Neurite Outgrowth From Retinal Ganglion Cells in Three-Dimensional Retinal Aggregates Differentiated From Mouse and Human Embryonic Stem Cells

PURPOSE

To establish a practical research tool for studying the pathogenesis of retinal ganglion cell (RGC) diseases, we optimized culture procedures to induce neurite outgrowth from three-dimensional self-organizing optic vesicles (3D-retinas) differentiated in vitro from mouse and human embryonic stem cells (ESCs).

MATERIALS AND METHODS

The developing 3D-retinas isolated at various time points were placed on Matrigel-coated plates and cultured in media on the basis of the 3D-retinal culture or the retinal organotypic culture protocol. The number, length, and morphology of the neurites in each culture condition were compared.

RESULTS

First, we confirmed that Venus-positive cells were double-labeled with a RGC marker, Brn3a, in the 3D-retina differentiated from Fstl4::Venus mouse ESCs, indicating specific RGC-subtype differentiation. Second, Venus-positive neurites grown from these RGC subsets were positive for beta-III tubulin and SMI312 by immunohistochemistry. Enhanced neurite outgrowth was observed in the B27-supplemented Neurobasal-A medium on Matrigel-coated plates from the optic vesicles isolated after 14 days of differentiation from mouse ESCs. For the differentiated RGCs from human ESCs, we obtained neurite extension of >4 mm by modifying Matrigel coating and the culture medium from the mouse RGC culture.

CONCLUSION

We successfully optimized the culture conditions to enhance lengthy and high-frequency neurite outgrowth in mouse and human models. The procedure would be useful for not only developmental studies of RGCs, including maintenance and projection, but also clinical, pathological, and pharmacological studies of human RGC diseases.

Importance of the stem cell microenvironment for ophthalmological cell-based therapy

Cell therapy is a promising treatment for diseases that are caused by cell degeneration or death. The cells for clinical transplantation are usually obtained by culturing healthy allogeneic or exogenous tissue in vitro. However, for diseases of the eye, obtaining the adequate number of cells for clinical transplantation is difficult due to the small size of tissue donors and the frequent needs of long-term amplification of cells in vitro, which results in low cell viability after transplantation. In addition, the transplanted cells often develop fibrosis or degrade and have very low survival. Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPS) are also promising candidates for cell therapy. Unfortunately, the differentiation of ESCs can bring immune rejection, tumorigenicity and undesired differentiated cells, limiting its clinical application. Although iPS cells can avoid the risk of immune rejection caused by ES cell differentiation post-transplantation, the low conversion rate, the risk of tumor formation and the potentially unpredictable biological changes that could occur through genetic manipulation hinder its clinical application. Thus, the desired clinical effect of cell therapy is impaired by these factors. Recent research findings recognize that the reason for low survival of the implanted cells not only depends on the seeded cells, but also on the cell microenvironment, which determines the cell survival, proliferation and even reverse differentiation. When used for cell therapy, the transplanted cells need a specific three-dimensional structure to anchor and specific extra cellular matrix components in addition to relevant cytokine signaling to transfer the required information to support their growth. These structures present in the matrix in which the stem cells reside are known as the stem cell microenvironment. The microenvironment interaction with the stem cells provides the necessary homeostasis for cell maintenance and growth. A large number of studies suggest that to explore how to reconstruct the stem cell microenvironment and strengthen its combination with the transplanted cells are key steps to successful cell therapy. In this review, we will describe the interactions of the stem cell microenvironment with the stem cells, discuss the importance of the stem cell microenvironment for cell-based therapy in ocular diseases, and introduce the progress of stem cell-based therapy for ocular diseases.

Cellular strategies for retinal repair by photoreceptor replacement

Loss of photoreceptors due to retinal degeneration is a major cause of blindness in the developed world. While no effective treatment is currently available, cell replacement therapy, using pluripotent stem cell-derived photoreceptor precursor cells, may be a feasible future treatment. Recent reports have demonstrated rescue of visual function following the transplantation of immature photoreceptors and we have seen major advances in our ability to generate transplantation-competent donor cells from stem cell sources. Moreover, we are beginning to realise the possibilities of using endogenous populations of cells from within the retina itself to mediate retinal repair. Here, we present a review of our current understanding of endogenous repair mechanisms together with recent progress in the use of both ocular and pluripotent stem cells for the treatment of photoreceptor loss. We consider how our understanding of retinal development has underpinned many of the recent major advances in translation and moved us closer to the goal of restoring vision by cellular means.

Tapping Stem Cells to Target AMD: Challenges and Prospects

Human pluripotent stem cells (hPSCs) are increasingly gaining attention in biomedicine as valuable resources to establish patient-derived cell culture models of the cell type known to express the primary pathology. The idea of "a patient in a dish" aims at basic, but also clinical, applications with the promise to mimic individual genetic and metabolic complexities barely reflected in current invertebrate or vertebrate animal model systems. This may particularly be true for the inherited and complex diseases of the retina, as this tissue has anatomical and physiological aspects unique to the human eye. For example, the complex age-related macular degeneration (AMD), the leading cause of blindness in Western societies, can be attributed to a large number of genetic and individual factors with so far unclear modes of mutual interaction. Here, we review the current status and future prospects of utilizing hPSCs, specifically induced pluripotent stem cells (iPSCs), in basic and clinical AMD research, but also in assessing potential treatment options. We provide an outline of concepts for disease modelling and summarize ongoing and projected clinical trials for stem cell-based therapy in late-stage AMD.