Optic vesicle-like structures derived from human pluripotent stem cells facilitate a customized approach to retinal disease treatment

Cellular and circuit remodeling of the primate foveal midget pathway after acute photoreceptor loss

The retinal fovea in human and nonhuman primates is essential for high acuity and color vision. Within the fovea lies specialized circuitry in which signals from a single cone photoreceptor are largely conveyed to one ON and one OFF type midget bipolar cell (MBC), which in turn connect to a single ON or OFF midget ganglion cell (MGC), respectively. Restoring foveal vision requires not only photoreceptor replacement but also appropriate reconnection with surviving ON and OFF MBCs and MGCs. However, our current understanding of the effects of cone loss on the remaining foveal midget pathway is limited. We thus used serial block-face electron microscopy to determine the degree of plasticity and potential remodeling of this pathway in adult Macaca fascicularis several months after acute photoreceptor loss upon photocoagulation. We reconstructed MBC structure and connectivity within and adjacent to the region of cone loss. We found that MBC dendrites within the scotoma retracted and failed to reach surviving cones to form new connections. However, both surviving cones and ON and OFF MBC dendrites at the scotoma border exhibited remodeling, suggesting that these neurons can demonstrate plasticity and rewiring at maturity. At six months postlesion, disconnected OFF MBCs clearly lost output ribbon synapses with their postsynaptic partners, whereas the majority of ON MBCs maintained their axonal ribbon numbers, suggesting differential timing or extent in ON and OFF midget circuit remodeling after cone loss. Our findings raise rewiring considerations for cell replacement approaches in the restoration of foveal vision.

Application of eye organoids in the study of eye diseases

The eyes are one of the most important sensory organs in the human body. Currently, diseases such as limbal stem cell deficiency, cataract, retinitis pigmentosa and dry eye seriously threaten the quality of people's lives, and the treatment of advanced blinding eye disease and dry eye is ineffective and costly. Thus, new treatment modalities are urgently needed to improve patients' symptoms and suffering. In recent years, stem cell-derived three-dimensional structural organoids have been shown to mimic specific structures and functions similar to those of organs in the human body. Currently, 3D culture systems are used to construct organoids for different ocular growth and development models and ocular disease models to explore their physiological and pathological mechanisms. Eye organoids can also be used as a platform for drug screening. This paper reviews the latest research progress in regard to eye organoids (the cornea, lens, retina, lacrimal gland, and conjunctiva).

Induction of astrocyte reactivity promotes neurodegeneration in human pluripotent stem cell models

Reactive astrocytes are known to exert detrimental effects upon neurons in several neurodegenerative diseases, yet our understanding of how astrocytes promote neurotoxicity remains incomplete, especially in human systems. In this study, we leveraged human pluripotent stem cell (hPSC) models to examine how reactivity alters astrocyte function and mediates neurodegeneration. hPSC-derived astrocytes were induced to a reactive phenotype, at which point they exhibited a hypertrophic profile and increased complement C3 expression. Functionally, reactive astrocytes displayed decreased intracellular calcium, elevated phagocytic capacity, and decreased contribution to the blood-brain barrier. Subsequently, co-culture of reactive astrocytes with a variety of neuronal cell types promoted morphological and functional alterations. Furthermore, when reactivity was induced in astrocytes from patient-specific hPSCs (glaucoma, Alzheimer's disease, and amyotrophic lateral sclerosis), the reactive state exacerbated astrocytic disease-associated phenotypes. These results demonstrate how reactive astrocytes modulate neurodegeneration, significantly contributing to our understanding of a role for reactive astrocytes in neurodegenerative diseases.

Rapid and efficient generation of mature retinal organoids derived from human pluripotent stem cells via optimized pharmacological modulation of Sonic hedgehog, activin A, and retinoic acid signal transduction

Human retinal organoids have become indispensable tools for retinal disease modeling and drug screening. Despite its versatile applications, the long timeframe for their differentiation and maturation limits the throughput of such research. Here, we successfully shortened this timeframe by accelerating human retinal organoid development using unique pharmacological approaches. Our method comprised three key steps: 1) a modified self-formed ectodermal autonomous multizone (SEAM) method, including dual SMAD inhibition and bone morphogenetic protein 4 treatment, for initial neural retinal induction; 2) the concurrent use of a Sonic hedgehog agonist SAG, activin A, and all-trans retinoic acid for rapid retinal cell specification; and 3) switching to SAG treatment alone for robust retinal maturation and lamination. The generated retinal organoids preserved typical morphological features of mature retinal organoids, including hair-like surface structures and well-organized outer layers. These features were substantiated by the spatial immunostaining patterns of several retinal cell markers, including rhodopsin and L/M opsin expression in the outermost layer, which was accompanied by reduced ectopic cone photoreceptor generation. Importantly, our method required only 90 days for retinal organoid maturation, which is approximately two-thirds the time necessary for other conventional methods. These results indicate that thoroughly optimized pharmacological interventions play a pivotal role in rapid and precise photoreceptor development during human retinal organoid differentiation and maturation. Thus, our present method may expedite human retinal organoid research, eventually contributing to the development of better treatment options for various degenerative retinal diseases.

Towards Stem/Progenitor Cell-Based Therapies for Retinal Degeneration

Retinal degeneration (RD) is a leading cause of blindness worldwide and includes conditions such as retinitis pigmentosa (RP), age-related macular degeneration (AMD), and Stargardt's disease (STGD). These diseases result in the permanent loss of vision due to the progressive and irreversible degeneration of retinal cells, including photoreceptors (PR) and the retinal pigment epithelium (RPE). The adult human retina has limited abilities to regenerate and repair itself, making it challenging to achieve complete self-replenishment and functional repair of retinal cells. Currently, there is no effective clinical treatment for RD. Stem cell therapy, which involves transplanting exogenous stem cells such as retinal progenitor cells (RPCs), embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), and mesenchymal stem cells (MSCs), or activating endogenous stem cells like Müller Glia (MG) cells, holds great promise for regenerating and repairing retinal cells in the treatment of RD. Several preclinical and clinical studies have shown the potential of stem cell-based therapies for RD. However, the clinical translation of these therapies for the reconstruction of substantial vision still faces significant challenges. This review provides a comprehensive overview of stem/progenitor cell-based therapy strategies for RD, summarizes recent advances in preclinical studies and clinical trials, and highlights the major challenges in using stem/progenitor cell-based therapies for RD.

Characterization of the development of the high-acuity area of the chick retina

The fovea is a small region within the central retina that is responsible for our high acuity daylight vision. Chickens also have a high acuity area (HAA), and are one of the few species that enables studies of the mechanisms of HAA development, due to accessible embryonic tissue and methods to readily perturb gene expression. To enable such studies, we characterized the development of the chick HAA using single molecule fluorescent in situ hybridization (smFISH), along with more classical methods. We found that Fgf8 provides a molecular marker for the HAA throughout development and into adult stages, allowing studies of the cellular composition of this area over time. The radial dimension of the ganglion cell layer (GCL) was seen to be the greatest at the HAA throughout development, beginning during the period of neurogenesis, suggesting that genesis, rather than cell death, creates a higher level of retinal ganglion cells (RGCs) in this area. In contrast, the HAA acquired its characteristic high density of cone photoreceptors post-hatching, which is well after the period of neurogenesis. We also confirmed that rod photoreceptors are not present in the HAA. Analyses of cell death in the developing photoreceptor layer, where rods would reside, did not show apoptotic cells, suggesting that lack of genesis, rather than death, created the "rod-free zone" (RFZ). Quantification of each cone photoreceptor subtype showed an ordered mosaic of most cone subtypes. The changes in cellular densities and cell subtypes between the developing and mature HAA provide some answers to the overarching strategy used by the retina to create this area and provide a framework for future studies of the mechanisms underlying its formation.

Modeling inherited retinal diseases using human induced pluripotent stem cell derived photoreceptor cells and retinal pigment epithelial cells

Since the discovery of induced pluripotent stem cell (iPSC) technology, there have been many attempts to create cellular models of inherited retinal diseases (IRDs) for investigation of pathogenic processes to facilitate target discovery and validation activities. Consistency remains key in determining the utility of these findings. Despite the importance of consistency, quality control metrics are still not widely used. In this review, a toolkit for harnessing iPSC technology to generate photoreceptor, retinal pigment epithelial cell, and organoid disease models is provided. Considerations while developing iPSC-derived IRD models such as iPSC origin, reprogramming methods, quality control metrics, control strategies, and differentiation protocols are discussed. Various iPSC IRD models are dissected and the scientific hurdles of iPSC-based disease modeling are discussed to provide an overview of current methods and future directions in this field.

A highly reproducible and efficient method for retinal organoid differentiation from human pluripotent stem cells

Human pluripotent stem cell (hPSC)-derived retinal organoids are three-dimensional cellular aggregates that differentiate and self-organize to closely mimic the spatial and temporal patterning of the developing human retina. Retinal organoid models serve as reliable tools for studying human retinogenesis, yet limitations in the efficiency and reproducibility of current retinal organoid differentiation protocols have reduced the use of these models for more high-throughput applications such as disease modeling and drug screening. To address these shortcomings, the current study aimed to standardize prior differentiation protocols to yield a highly reproducible and efficient method for generating retinal organoids. Results demonstrated that through regulation of organoid size and shape using quick reaggregation methods, retinal organoids were highly reproducible compared to more traditional methods. Additionally, the timed activation of BMP signaling within developing cells generated pure populations of retinal organoids at 100% efficiency from multiple widely used cell lines, with the default forebrain fate resulting from the inhibition of BMP signaling. Furthermore, given the ability to direct retinal or forebrain fates at complete purity, mRNA-seq analyses were then utilized to identify some of the earliest transcriptional changes that occur during the specification of these two lineages from a common progenitor. These improved methods also yielded retinal organoids with expedited differentiation timelines when compared to traditional methods. Taken together, the results of this study demonstrate the development of a highly reproducible and minimally variable method for generating retinal organoids suitable for analyzing the earliest stages of human retinal cell fate specification.

Recapitulation and investigation of human brain development with neural organoids

Organoids are 3D cultured tissues derived from stem cells that resemble the structure of living organs. Based on the accumulated knowledge of neural development, neural organoids that recapitulate neural tissue have been created by inducing self-organized neural differentiation of stem cells. Neural organoid techniques have been applied to human pluripotent stem cells to differentiate 3D human neural tissues in culture. Various methods have been developed to generate neural tissues of different regions. Currently, neural organoid technology has several significant limitations, which are being overcome in an attempt to create neural organoids that more faithfully recapitulate the living brain. The rapidly advancing neural organoid technology enables the use of living human neural tissue as research material and contributes to our understanding of the development, structure and function of the human nervous system, and is expected to be used to overcome neurological diseases and for regenerative medicine.

Inherited Retinal Diseases and Retinal Organoids as Preclinical Cell Models for Inherited Retinal Disease Research

Inherited retinal diseases (IRDs) are a large group of genetically and clinically diverse blinding eye conditions that result in progressive and irreversible photoreceptor degeneration and vision loss. To date, no cures have been found, although strides toward treatments for specific IRDs have been made in recent years. To accelerate treatment discovery, retinal organoids provide an ideal human IRD model. This review aims to give background on the development and importance of retinal organoids for the human-based in vitro study of the retina and human retinogenesis and retinal pathologies. From there, we explore retinal pathologies in the context of IRDs and the current landscape of IRD treatment discovery. We discuss the usefulness of retinal organoids in this context (as a patient-derived cell model for IRDs) to precisely understand the pathogenesis and potential mechanisms behind a specific IRD-causing variant of interest. Finally, we discuss the importance and promise of retinal organoids in treatment discovery for IRDs, now and in the future.

Pluripotent stem cell-derived models of retinal disease: Elucidating pathogenesis, evaluating novel treatments, and estimating toxicity

Blindness poses a growing global challenge, with approximately 26% of cases attributed to degenerative retinal diseases. While gene therapy, optogenetic tools, photosensitive switches, and retinal prostheses offer hope for vision restoration, these high-cost therapies will benefit few patients. Understanding retinal diseases is therefore key to advance effective treatments, requiring in vitro models replicating pathology and allowing quantitative assessments for drug discovery. Pluripotent stem cells (PSCs) provide a unique solution given their limitless supply and ability to differentiate into light-responsive retinal tissues encompassing all cell types. This review focuses on the history and current state of photoreceptor and retinal pigment epithelium (RPE) cell generation from PSCs. We explore the applications of this technology in disease modelling, experimental therapy testing, biomarker identification, and toxicity studies. We consider challenges in scalability, standardisation, and reproducibility, and stress the importance of incorporating vasculature and immune cells into retinal organoids. We advocate for high-throughput automation in data acquisition and analyses and underscore the value of advanced micro-physiological systems that fully capture the interactions between the neural retina, RPE, and choriocapillaris.

Disruption of Circadian Clock Induces Abnormal Mammary Morphology and Aggressive Basal Tumorigenesis by Enhancing LILRB4 Signaling

Epidemiological studies have shown that circadian rhythm disruption (CRD) is associated with the risk of breast cancer. However, the role of CRD in mammary gland morphology and aggressive basal mammary tumorigenesis and the molecular mechanisms underlying CRD and cancer risk remain unknown. To investigate the effect of CRD on aggressive tumorigenesis, a genetically engineered mouse model that recapitulates the human basal type of breast cancer was used for this study. The effect of CRD on mammary gland morphology was investigated using wild-type mice model. The impact of CRD on the tumor microenvironment was investigated using the tumors from LD12:12 and CRD mice via scRNA seq. ScRNA seq was substantiated by multiplexing immunostaining, flow cytometry, and realtime PCR. The effect of LILRB4 immunotherapy on CRD-induced tumorigenesis was also investigated. Here we identified the impact of CRD on basal tumorigenesis and mammary gland morphology and identified the role of LILRB4 on CRD-induced lung metastasis. We found that chronic CRD disrupted mouse mammary gland morphology and increased tumor burden, and lung metastasis and induced an immunosuppressive tumor microenvironment by enhancing LILRB4a expression. Moreover, CRD increased the M2-macrophage and regulatory T-cell populations but decreased the M1-macrophage populations. Furthermore, targeted immunotherapy against LILRB4 reduced CRD-induced immunosuppressive microenvironment and lung metastasis. These findings identify and implicate LILRB4a as a link between CRD and aggressive mammary tumorigenesis. This study also establishes the potential role of the targeted LILRB4a immunotherapy as an inhibitor of CRD-induced lung metastasis.

Revealing the clinical potential of high-resolution organoids

The symbiotic interplay of organoid technology and advanced imaging strategies yields innovative breakthroughs in research and clinical applications. Organoids, intricate three-dimensional cell cultures derived from pluripotent or adult stem/progenitor cells, have emerged as potent tools for in vitro modeling, reflecting in vivo organs and advancing our grasp of tissue physiology and disease. Concurrently, advanced imaging technologies such as confocal, light-sheet, and two-photon microscopy ignite fresh explorations, uncovering rich organoid information. Combined with advanced imaging technologies and the power of artificial intelligence, organoids provide new insights that bridge experimental models and real-world clinical scenarios. This review explores exemplary research that embodies this technological synergy and how organoids reshape personalized medicine and therapeutics.

Toward Retinal Organoids in High-Throughput

Human retinal organoids recapitulate the cellular diversity, arrangement, gene expression, and functional aspects of the human retina. Protocols to generate human retinal organoids from pluripotent stem cells are typically labor intensive, include many manual handling steps, and the organoids need to be maintained for several months until they mature. To generate large numbers of human retinal organoids for therapy development and screening purposes, scaling up retinal organoid production, maintenance, and analysis is of utmost importance. In this review, we discuss strategies to increase the number of high-quality retinal organoids while reducing manual handling steps. We further review different approaches to analyze thousands of retinal organoids with currently available technologies and point to challenges that still await to be overcome both in culture and analysis of retinal organoids.

Retinal Organoids: A Next-Generation Platform for High-Throughput Drug Discovery

Retinal diseases are leading causes of blindness globally. Developing new drugs is of great significance for preventing vision loss. Current drug discovery relies mainly on two-dimensional in vitro models and animal models, but translation to human efficacy and safety is biased. In recent years, the emergence of retinal organoid technology platforms, utilizing three-dimensional microenvironments to better mimic retinal structure and function, has provided new platforms for exploring pathogenic mechanisms and drug screening. This review summarizes the latest advances in retinal organoid technology, emphasizing its application advantages in high-throughput drug screening, efficacy and toxicity evaluation, and translational medicine research. The review also prospects the combination of emerging technologies such as organ-on-a-chip, 3D bioprinting, single cell sequencing, gene editing with retinal organoid technology, which is expected to further optimize retinal organoid models and advance the diagnosis and treatment of retinal diseases.

Advances in the engineering of the outer blood-retina barrier: From in-vitro modelling to cellular therapy

The outer blood-retina barrier (oBRB), crucial for the survival and the proper functioning of the overlying retinal layers, is disrupted in numerous diseases affecting the retina, leading to the loss of the photoreceptors and ultimately of vision. To study the oBRB and/or its degeneration, many in vitro oBRB models have been developed, notably to investigate potential therapeutic strategies against retinal diseases. Indeed, to this day, most of these pathologies are untreatable, especially once the first signs of degeneration are observed. To cure those patients, a current strategy is to cultivate in vitro a mature oBRB epithelium on a custom membrane that is further implanted to replace the damaged native tissue. After a description of the oBRB and the related diseases, this review presents an overview of the oBRB models, from the simplest to the most complex. Then, we propose a discussion over the used cell types, for their relevance to study or treat the oBRB. Models designed for in vitro applications are then examined, by paying particular attention to the design evolution in the last years, the development of pathological models and the benefits of co-culture models, including both the retinal pigment epithelium and the choroid. Lastly, this review focuses on the models developed for in vivo implantation, with special emphasis on the choice of the material, its processing and its characterization, before discussing the reported pre-clinical and clinical trials.

Development of a simplified human embryonic stem cell-based retinal pre-organoid model for toxicity evaluations of common pollutants

OBJECTIVE

To explore the retinal toxicity of pharmaceuticals and personal care products (PPCPs), flame retardants, bisphenols, phthalates, and polycyclic aromatic hydrocarbons (PAHs) on human retinal progenitor cells (RPCs) and retinal pigment epithelial (RPE) cells, which are the primary cell types at the early stages of retinal development, vital for subsequent functional cell type differentiation, and closely related to retinal diseases.

MATERIALS AND METHODS

After 23 days of differentiation, human embryonic stem cell (hESC)-based retinal pre-organoids, containing RPCs and RPE cells, were exposed to 10, 100, and 1000 nM pesticides (butachlor, terbutryn, imidacloprid, deltamethrin, pendimethalin, and carbaryl), flame retardants (PFOS, TBBPA, DBDPE, and TDCIPP), PPCPs (climbazole and BHT), and other typical pollutants (phenanthrene, DCHP, and BPA) for seven days. Then, mRNA expression changes were monitored and compared.

RESULTS

(1) The selected pollutants did not show strong effects at environmental and human-relevant concentrations, although the effects of flame retardants were more potent than those of other categories of chemicals. Surprisingly, some pollutants with distinct structures showed similar adverse effects. (2) Exposure to pollutants induced different degrees of cell detachment, probably due to alterations in extracellular matrix and/or cell adhesion.

CONCLUSIONS

In this study, we established a retinal pre-organoid model suitable for evaluating multiple pollutants' effects, and pointed out the potential retinal toxicity of flame retardants, among other pollutants. Nevertheless, the potential mechanisms of toxicity and the effects on cell detachment are still unclear and deserve further exploration. Additionally, this model holds promise for screening interventions aimed at mitigating the detrimental effects of these pollutants.

Therapeutic strategies for glaucoma and optic neuropathies

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

CGMP Compliant Microfluidic Transfection of Induced Pluripotent Stem Cells for CRISPR-Mediated Genome Editing

Inherited retinal degeneration is a term used to describe heritable disorders that result from the death of light sensing photoreceptor cells. Although we and others believe that it will be possible to use gene therapy to halt disease progression early in its course, photoreceptor cell replacement will likely be required for patients who have already lost their sight. While advances in autologous photoreceptor cell manufacturing have been encouraging, development of technologies capable of efficiently delivering genome editing reagents to stem cells using current good manufacturing practices (cGMP) are needed. Gene editing reagents were delivered to induced pluripotent stem cells (iPSCs) using a Zephyr microfluidic transfection platform (CellFE). CRISPR-mediated cutting was quantified using an endonuclease assay. CRISPR correction was confirmed via digital PCR and Sanger sequencing. The resulting corrected cells were also karyotyped and differentiated into retinal organoids. We describe use of a novel microfluidic transfection platform to correct, via CRISPR-mediated homology-dependent repair (HDR), a disease-causing NR2E3 mutation in patient-derived iPSCs using cGMP compatible reagents and approaches. We show that the resulting cell lines have a corrected genotype, exhibit no off-target cutting, retain pluripotency and a normal karyotype and can be differentiated into retinal tissue suitable for transplantation. The ability to codeliver CRISPR/Cas9 and HDR templates to patient-derived iPSCs without using proprietary transfection reagents will streamline manufacturing protocols, increase the safety of resulting cell therapies, and greatly reduce the regulatory burden of clinical trials.

Reliability of human retina organoid generation from hiPSC-derived neuroepithelial cysts

The possible applications for human retinal organoids (HROs) derived from human induced pluripotent stem cells (hiPSC) rely on the robustness and transferability of the methodology for their generation. Standardized strategies and parameters to effectively assess, compare, and optimize organoid protocols are starting to be established, but are not yet complete. To advance this, we explored the efficiency and reliability of a differentiation method, called CYST protocol, that facilitates retina generation by forming neuroepithelial cysts from hiPSC clusters. Here, we tested seven different hiPSC lines which reproducibly generated HROs. Histological and ultrastructural analyses indicate that HRO differentiation and maturation are regulated. The different hiPSC lines appeared to be a larger source of variance than experimental rounds. Although previous reports have shown that HROs in several other protocols contain a rather low number of cones, HROs from the CYST protocol are consistently richer in cones and with a comparable ratio of cones, rods, and Müller glia. To provide further insight into HRO cell composition, we studied single cell RNA sequencing data and applied CaSTLe, a transfer learning approach. Additionally, we devised a potential strategy to systematically evaluate different organoid protocols side-by-side through parallel differentiation from the same hiPSC batches: In an explorative study, the CYST protocol was compared to a conceptually different protocol based on the formation of cell aggregates from single hiPSCs. Comparing four hiPSC lines showed that both protocols reproduced key characteristics of retinal epithelial structure and cell composition, but the CYST protocol provided a higher HRO yield. So far, our data suggest that CYST-derived HROs remained stable up to at least day 200, while single hiPSC-derived HROs showed spontaneous pathologic changes by day 200. Overall, our data provide insights into the efficiency, reproducibility, and stability of the CYST protocol for generating HROs, which will be useful for further optimizing organoid systems, as well as for basic and translational research applications.

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.

Factors Affecting Stem Cell-Based Regenerative Approaches in Retinal Degeneration

Inherited and age-associated vision loss is often associated with degeneration of the cells of the retina, the light-sensitive layer at the back of the eye. The mammalian retina, being a postmitotic neural tissue, does not have the capacity to repair itself through endogenous regeneration. There has been considerable excitement for the development of cell replacement approaches since the isolation and development of culture methods for human pluripotent stem cells, as well as the generation of induced pluripotent stem cells. This has now been combined with novel three-dimensional organoid culture systems that closely mimic human retinal development in vitro. In this review, we cover the current state of the field, with emphasis on the cell delivery challenges, role of the recipient immunological microenvironment, and challenges related to connectivity between transplanted cells and host circuitry both locally and centrally to the different areas of the brain.

Self-formation of concentric zones of telencephalic and ocular tissues and directional retinal ganglion cell axons

The telencephalon and eye in mammals are originated from adjacent fields at the anterior neural plate. Morphogenesis of these fields generates telencephalon, optic-stalk, optic-disc, and neuroretina along a spatial axis. How these telencephalic and ocular tissues are specified coordinately to ensure directional retinal ganglion cell (RGC) axon growth is unclear. Here, we report self-formation of human telencephalon-eye organoids comprising concentric zones of telencephalic, optic-stalk, optic-disc, and neuroretinal tissues along the center-periphery axis. Initially-differentiated RGCs grew axons towards and then along a path defined by adjacent PAX2+ VSX2+ optic-disc cells. Single-cell RNA sequencing of these organoids not only confirmed telencephalic and ocular identities but also identified expression signatures of early optic-disc, optic-stalk, and RGCs. These signatures were similar to those in human fetal retinas. Optic-disc cells in these organoids differentially expressed FGF8 and FGF9; FGFR inhibitions drastically decreased early RGC differentiation and directional axon growth. Through the RGC-specific cell-surface marker CNTN2 identified here, electrophysiologically excitable RGCs were isolated under a native condition. Our findings provide insight into the coordinated specification of early telencephalic and ocular tissues in humans and establish resources for studying RGC-related diseases such as glaucoma.

Establishing Functional Retina in a Dish: Progress and Promises of Induced Pluripotent Stem Cell-Based Retinal Neuron Differentiation

The human eye plays a critical role in vision perception, but various retinal degenerative diseases such as retinitis pigmentosa (RP), glaucoma, and age-related macular degeneration (AMD) can lead to vision loss or blindness. Although progress has been made in understanding retinal development and in clinical research, current treatments remain inadequate for curing or reversing these degenerative conditions. Animal models have limited relevance to humans, and obtaining human eye tissue samples is challenging due to ethical and legal considerations. Consequently, researchers have turned to stem cell-based approaches, specifically induced pluripotent stem cells (iPSCs), to generate distinct retinal cell populations and develop cell replacement therapies. iPSCs offer a novel platform for studying the key stages of human retinogenesis and disease-specific mechanisms. Stem cell technology has facilitated the production of diverse retinal cell types, including retinal ganglion cells (RGCs) and photoreceptors, and the development of retinal organoids has emerged as a valuable in vitro tool for investigating retinal neuron differentiation and modeling retinal diseases. This review focuses on the protocols, culture conditions, and techniques employed in differentiating retinal neurons from iPSCs. Furthermore, it emphasizes the significance of molecular and functional validation of the differentiated cells.

Retinal organoid and gene editing for basic and translational research

The rapid evolution of two technologies has greatly transformed the basic, translational, and clinical research in the mammalian retina. One is the retinal organoid (RO) technology. Various induction methods have been created or adapted to generate species-specific, disease-specific, and experimental-targeted retinal organoids (ROs). The process of generating ROs can highly mimic the in vivo retinal development, and consequently, the ROs resemble the retina in many aspects including the molecular and cellular profiles. The other technology is the gene editing, represented by the classical CRISPR-Cas9 editing and its derivatives such as prime editing, homology independent targeted integration (HITI), base editing and others. The combination of ROs and gene editing has opened up countless possibilities in the study of retinal development, pathogenesis, and therapeutics. We review recent advances in the ROs, gene editing methodologies, delivery vectors, and related topics that are particularly relevant to retinal studies.

Development of a three-dimensional organoid model to explore early retinal phenotypes associated with Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by the accumulation of Aβ plaques and neurofibrillary tangles, resulting in synaptic loss and neurodegeneration. The retina is an extension of the central nervous system within the eye, sharing many structural similarities with the brain, and previous studies have observed AD-related phenotypes within the retina. Three-dimensional retinal organoids differentiated from human pluripotent stem cells (hPSCs) can effectively model some of the earliest manifestations of disease states, yet early AD-associated phenotypes have not yet been examined. Thus, the current study focused upon the differentiation of hPSCs into retinal organoids for the analysis of early AD-associated alterations. Results demonstrated the robust differentiation of retinal organoids from both familial AD and unaffected control cell lines, with familial AD retinal organoids exhibiting a significant increase in the Aβ42:Aβ40 ratio as well as phosphorylated Tau protein, characteristic of AD pathology. Further, transcriptional analyses demonstrated the differential expression of many genes and cellular pathways, including those associated with synaptic dysfunction. Taken together, the current study demonstrates the ability of retinal organoids to serve as a powerful model for the identification of some of the earliest retinal alterations associated with AD.

Bankable human iPSC-derived retinal progenitors represent a valuable source of multipotent cells

Retinal progenitor cells (RPCs) are the source of all retinal cell types during retinogenesis. Until now, the isolation and expansion of RPCs has been at the expense of their multipotency. Here, we report simple methods and media for the generation, expansion, and cryopreservation of human induced pluripotent stem-cell derived-RPCs (hiRPCs). Thawed and passed hiRPCs maintained biochemical and transcriptional RPC phenotypes and their ability to differentiate into all retinal cell types. Specific conditions allowed the generation of large cultures of photoreceptor precursors enriched up to 90% within a few weeks and without a purification step. Combined RNA-seq analysis between hiRPCs and retinal organoids identified genes involved in developmental or degenerative retinal diseases. Thus, hiRPC lines could provide a valuable source of retinal cells for cell-based therapies or drug discovery and could be an advanced cellular tool to better understand retinal dystrophies.

Next generation organoid engineering to replace animals in cancer drug testing

Cancer therapies have several clinical challenges associated with them, namely treatment toxicity, treatment resistance and relapse. Due to factors ranging from patient profiles to the tumour microenvironment (TME), there are several hurdles to overcome in developing effective treatments that have low toxicity that can mitigate emergence of resistance and occurrence of relapse. De novo cancer development has the highest drug attrition rates with only 1 in 10,000 preclinical candidates reaching the market. To alleviate this high attrition rate, more mimetic and sustainable preclinical models that can capture the disease biology as in the patient, are required. Organoids and next generation 3D tissue engineering is an emerging area that aims to address this problem. Advancement of three-dimensional (3D) in vitro cultures into complex organoid models incorporating multiple cell types alongside acellular aspects of tissue microenvironments can provide a system for therapeutic testing. Development of microfluidic technologies have furthermore increased the biomimetic nature of these models. Additionally, 3D bio-printing facilitates generation of tractable ex vivo models in a controlled, scalable and reproducible manner. In this review we highlight some of the traditional preclinical models used in cancer drug testing and debate how next generation organoids are being used to replace not only animal models, but also some of the more elementary in vitro approaches, such as cell lines. Examples of applications of the various models will be appraised alongside the future challenges that still need to be overcome.

Self-formation of concentric zones of telencephalic and ocular tissues and directional retinal ganglion cell axons

The telencephalon and eye in mammals are originated from adjacent fields at the anterior neural plate. Morphogenesis of these fields generates telencephalon, optic-stalk, optic-disc, and neuroretina along a spatial axis. How these telencephalic and ocular tissues are specified coordinately to ensure directional retinal ganglion cell (RGC) axon growth is unclear. Here, we report the self-formation of human telencephalon-eye organoids comprising concentric zones of telencephalic, optic-stalk, optic-disc, and neuroretinal tissues along the center-periphery axis. Initially-differentiated RGCs grew axons towards and then along a path defined by adjacent PAX2+ optic-disc cells. Single-cell RNA sequencing of CONCEPT organoids not only confirmed telencephalic and ocular identities but also identified expression signatures of early optic-disc, optic-stalk, and RGCs. These signatures were similar to those in human fetal retinas. Optic-disc cells in CONCEPT organoids differentially expressed FGF8 and FGF9 ; FGFR inhibitions drastically decreased RGC differentiation and directional axon growth. Through the identified RGC-specific cell-surface marker CNTN2, electrophysiologically-excitable RGCs were isolated under a native condition. Our findings provide insight into the coordinated specification of early telencephalic and ocular tissues in humans and establish resources for studying RGC-related diseases such as glaucoma.

Impact statement

A human telencephalon-eye organoid model that exhibited axon growth and pathfinding from retinal ganglion cell (RGC) axons is reported; via cell surface marker CNTN2 identified using scRNA-seq, early RGCs were isolated under a native condition.

Generation of iPSC-derived human forebrain organoids assembling bilateral eye primordia

Induced pluripotent stem cell-derived brain organoids enable the developmental complexities of the human brain to be deconstructed. During embryogenesis, optic vesicles (OVs), the eye primordium attached to the forebrain, develop from diencephalon. However, most 3D culturing methods generate either brain or retinal organoids individually. Here we describe a protocol to generate organoids with both forebrain entities, which we call OV-containing brain organoids (OVB organoids). In this protocol, we first induce neural differentiation (days 0-5) and collect neurospheres, which we culture in a neurosphere medium to initiate their patterning and further self-assembly (days 5-10). Then, upon transfer to spinner flasks containing OVB medium (days 10-30), neurospheres develop into forebrain organoids with one or two pigmented dots restricted to one pole, displaying forebrain entities of ventral and dorsal cortical progenitors and preoptic areas. Further long-term culture results in photosensitive OVB organoids constituting complementary cell types of OVs, including primitive corneal epithelial and lens-like cells, retinal pigment epithelia, retinal progenitor cells, axon-like projections and electrically active neuronal networks. OVB organoids provide a system to help dissect interorgan interactions between the OVs as sensory organs and the brain as a processing unit, and can help model early eye patterning defects, including congenital retinal dystrophy. To conduct the protocol, experience in sterile cell culture and maintenance of human induced pluripotent stem cells is essential; theoretical knowledge of brain development is advantageous. Furthermore, specialized expertise in 3D organoid culture and imaging for the analysis is needed.

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.

Emerging strategies of engineering retinal organoids and organoid-on-a-chip in modeling intraocular drug delivery: current progress and future perspectives

Retinal diseases are a rising concern as major causes of blindness in an aging society; therapeutic options are limited, and the precise pathogenesis of these diseases remains largely unknown. Intraocular drug delivery and nanomedicines offering targeted, sustained, and controllable delivery are the most challenging and popular topics in ocular drug development and toxicological evaluation. Retinal organoids (ROs) and organoid-on-a-chip (ROoC) are both emerging as promising in-vitro models to faithfully recapitulate human eyes for retinal research in the replacement of experimental animals and primary cells. In this study, we review the generation and application of ROs resembling the human retina in cell subtypes and laminated structures and introduce the emerging engineered ROoC as a technological opportunity to address critical issues. On-chip vascularization, perfusion, and close inter-tissue interactions recreate physiological environments in vitro, whilst integrating with biosensors facilitates real-time analysis and monitoring during organogenesis of the retina representing engineering efforts in ROoC models. We also emphasize that ROs and ROoCs hold the potential for applications in modeling intraocular drug delivery in vitro and developing next-generation retinal drug delivery strategies.

Establishment of a human induced pluripotent stem cell derived alveolar organoid for toxicity assessment

Alveolar epithelial cells (AECs) are vulnerable to injury, which can result in epithelial hyperplasia, apoptosis, and chronic inflammation. In this study, we developed human induced pluripotent stem cell (hiPS) cell-derived AECs (iAECs) and the iAECs based organoids (AOs) for testing AEC toxicity after chemical exposure. HiPS cells were cultured for 14 days with differentiation medium corresponding to each step, and the iAECs-based AOs were maintained for another 14 days. SFTPC and AQP5 were expressed in the AOs, and mRNA levels of SOX9, NKX2.1, GATA6, HOPX, and ID2 were increased. The AOs were exposed for 24 h to nine chemical substances, and IC₅₀ values of the nine chemicals were determined using MTT assay. When the correlations between iAECs 2D culture and AOs 3D culture were calculated using Pearson's correlation coefficient r value, the nine chemicals that caused a significant decrease of cell viability in 3D culture were found to be highly correlated in 2D culture. The cytotoxicity and nitric oxide release in AO cultured with macrophages were then investigated. When AOs with macrophages were exposed to sodium chromate for 24 h, the IC₅₀ value and nitric oxide production were higher than when the AOs were exposed alone. Taken together, the AO-based 3D culture system provides a useful platform for understanding biological characteristics of AECs and modeling chemical exposures.

hPSC-derived RPE transplantation for the treatment of macular degeneration

Macular degeneration (MD) is a group of diseases characterized by irreversible and progressive vision loss. Patients with MD suffer from severely impaired central vision, especially elderly people. Currently, only one type of MD, wet age-related macular degeneration (AMD), can be treated with anti-vascular endothelium growth factor (VEGF) drugs. Other types of MD remain difficult to treat. With the advent of human pluripotent stem cells (hPSCs) and their differentiation into retinal pigmented epithelium (RPE), it is promising to treat patients with MD by transplantation of hPSC-derived RPE into the subretinal space. In this review, the current progress in hPSC-derived RPE transplantation for the treatment of patients with MD is described from bench to bedside, including hPSC differentiation into RPE and the characterization and usage of hPSC-derived RPE for transplantation into patients with MD.

Pluripotent stem cell-derived retinal organoid/cells for retinal regeneration therapies: A review

In recent decades, many researchers have attempted to restore vision via transplantation of retina/retinal cells in eyes with retinal degeneration. The advent of induced pluripotent stem cells (iPSC) and retinal organoid induction technologies has boosted research on retinal regeneration therapy. Although the recognition of functional integration of graft photoreceptor cells in the host retina from 2006 has been disputed a decade later by the newly evidenced phenomenon denoted as "material transfer," several reports support possible reconstruction of the host-graft network in the retinas of both end-stage degeneration and in progressing degeneration cases. Based on proof of concept (POC) studies in animal models, a clinical study was conducted in Kobe, Japan in 2020 and showed the feasibility of cell-based therapy using iPSC retinal organoid technology. Although the graft potency of human embryonic stem (ES)/iPS cell-derived retinal organoid/retinal cells has been suggested by previous studies, much is still unknown regarding host capability, that is, how long-standing human degenerating retinas are capable of rewiring with transplanted cells. This review summarizes past POC studies on photoreceptor replacement therapy and introduces some new challenges to maximize the possible efficacy in future human clinical studies of regenerative therapy.

Automating iPSC generation to enable autologous photoreceptor cell replacement therapy

BACKGROUND

Inherited retinal degeneration is a leading cause of incurable vision loss in the developed world. While autologous iPSC mediated photoreceptor cell replacement is theoretically possible, the lack of commercially available technologies designed to enable high throughput parallel production of patient specific therapeutics has hindered clinical translation.

METHODS

In this study, we describe the use of the Cell X precision robotic cell culture platform to enable parallel production of clinical grade patient specific iPSCs. The Cell X is housed within an ISO Class 5 cGMP compliant closed aseptic isolator (Biospherix XVivo X2), where all procedures from fibroblast culture to iPSC generation, clonal expansion and retinal differentiation were performed.

RESULTS

Patient iPSCs generated using the Cell X platform were determined to be pluripotent via score card analysis and genetically stable via karyotyping. As determined via immunostaining and confocal microscopy, iPSCs generated using the Cell X platform gave rise to retinal organoids that were indistinguishable from organoids derived from manually generated iPSCs. In addition, at 120 days post-differentiation, single-cell RNA sequencing analysis revealed that cells generated using the Cell X platform were comparable to those generated under manual conditions in a separate laboratory.

CONCLUSION

We have successfully developed a robotic iPSC generation platform and standard operating procedures for production of high-quality photoreceptor precursor cells that are compatible with current good manufacturing practices. This system will enable clinical grade production of iPSCs for autologous retinal cell replacement.

Self-organization, quality control, and preclinical studies of human iPSC-derived retinal sheets for tissue-transplantation therapy

Three-dimensional retinal organoids (3D-retinas) are a promising graft source for transplantation therapy. We previously developed self-organizing culture for 3D-retina generation from human pluripotent stem cells (hPSCs). Here we present a quality control method and preclinical studies for tissue-sheet transplantation. Self-organizing hPSCs differentiated into both retinal and off-target tissues. Gene expression analyses identified the major off-target tissues as eye-related, cortex-like, and spinal cord-like tissues. For quality control, we developed a qPCR-based test in which each hPSC-derived neuroepithelium was dissected into two tissue-sheets: inner-central sheet for transplantation and outer-peripheral sheet for qPCR to ensure retinal tissue selection. During qPCR, tissue-sheets were stored for 3-4 days using a newly developed preservation method. In a rat tumorigenicity study, no transplant-related adverse events were observed. In retinal degeneration model rats, retinal transplants differentiated into mature photoreceptors and exhibited light responses in electrophysiology assays. These results demonstrate our rationale toward self-organizing retinal sheet transplantation therapy.

Comparing the transcriptome of developing native and iPSC-derived mouse retinae by single cell RNA sequencing

We report the generation and analysis of single-cell RNA-Seq data (> 38,000 cells) from mouse native retinae and induced pluripotent stem cell (iPSC)-derived retinal organoids at four matched stages of development spanning the emergence of the major retinal cell types. We combine information from temporal sampling, visualization of 3D UMAP manifolds, pseudo-time and RNA velocity analyses, to show that iPSC-derived 3D retinal organoids broadly recapitulate the native developmental trajectories. However, we observe relaxation of spatial and temporal transcriptome control, premature emergence and dominance of photoreceptor precursor cells, and susceptibility of dynamically regulated pathways and transcription factors to culture conditions in retinal organoids. We demonstrate that genes causing human retinopathies are enriched in cell-type specifying genes and identify a subset of disease-causing genes with expression profiles that are highly conserved between human retinae and murine retinal organoids. This study provides a resource to the community that will be useful to assess and further improve protocols for ex vivo recapitulation and study of retinal development.

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.

Optic cup morphogenesis across species and related inborn human eye defects

The vertebrate eye is shaped as a cup, a conformation that optimizes vision and is acquired early in development through a process known as optic cup morphogenesis. Imaging living, transparent teleost embryos and mammalian stem cell-derived organoids has provided insights into the rearrangements that eye progenitors undergo to adopt such a shape. Molecular and pharmacological interference with these rearrangements has further identified the underlying molecular machineries and the physical forces involved in this morphogenetic process. In this Review, we summarize the resulting scenarios and proposed models that include common and species-specific events. We further discuss how these studies and those in environmentally adapted blind species may shed light on human inborn eye malformations that result from failures in optic cup morphogenesis, including microphthalmia, anophthalmia and coloboma.

Comprehensive characterization of fetal and mature retinal cell identity to assess the fidelity of retinal organoids

Characterizing cell identity in complex tissues such as the human retina is essential for studying its development and disease. While retinal organoids derived from pluripotent stem cells have been widely used to model development and disease of the human retina, there is a lack of studies that have systematically evaluated the molecular and cellular fidelity of the organoids derived from various culture protocols in recapitulating their in vivo counterpart. To this end, we performed an extensive meta-atlas characterization of cellular identities of the human eye, covering a wide range of developmental stages. The resulting map uncovered previously unknown biomarkers of major retinal cell types and those associated with cell-type-specific maturation. Using our retinal-cell-identity map from the fetal and adult tissues, we systematically assessed the fidelity of the retinal organoids in mimicking the human eye, enabling us to comprehensively benchmark the current protocols for retinal organoid generation.

Autophagy disruption reduces mTORC1 activation leading to retinal ganglion cell neurodegeneration associated with glaucoma

Autophagy dysfunction has been associated with several neurodegenerative diseases including glaucoma, characterized by the degeneration of retinal ganglion cells (RGCs). However, the mechanisms by which autophagy dysfunction promotes RGC damage remain unclear. Here, we hypothesized that perturbation of the autophagy pathway results in increased autophagic demand, thereby downregulating signaling through mammalian target of rapamycin complex 1 (mTORC1), a negative regulator of autophagy, contributing to the degeneration of RGCs. We identified an impairment of autophagic-lysosomal degradation and decreased mTORC1 signaling via activation of the stress sensor adenosine monophosphate-activated protein kinase (AMPK), along with subsequent neurodegeneration in RGCs differentiated from human pluripotent stem cells (hPSCs) with a glaucoma-associated variant of Optineurin (OPTN-E50K). Similarly, the microbead occlusion model of glaucoma resulting in ocular hypertension also exhibited autophagy disruption and mTORC1 downregulation. Pharmacological inhibition of mTORC1 in hPSC-derived RGCs recapitulated disease-related neurodegenerative phenotypes in otherwise healthy RGCs, while the mTOR-independent induction of autophagy reduced protein accumulation and restored neurite outgrowth in diseased OPTN-E50K RGCs. Taken together, these results highlight an important balance between autophagy and mTORC1 signaling essential for RGC homeostasis, while disruption to these pathways contributes to neurodegenerative features in glaucoma, providing a potential therapeutic target to prevent neurodegeneration.

Modeling inducible neuropathologies of the retina with differential phenotypes in organoids

Neurodegenerative diseases remain incompletely understood and therapies are needed. Stem cell-derived organoid models facilitate fundamental and translational medicine research. However, to which extent differential neuronal and glial pathologic processes can be reproduced in current systems is still unclear. Here, we tested 16 different chemical, physical, and cell functional manipulations in mouse retina organoids to further explore this. Some of the treatments induce differential phenotypes, indicating that organoids are competent to reproduce distinct pathologic processes. Notably, mouse retina organoids even reproduce a complex pathology phenotype with combined photoreceptor neurodegeneration and glial pathologies upon combined (not single) application of HBEGF and TNF, two factors previously associated with neurodegenerative diseases. Pharmacological inhibitors for MAPK signaling completely prevent photoreceptor and glial pathologies, while inhibitors for Rho/ROCK, NFkB, and CDK4 differentially affect them. In conclusion, mouse retina organoids facilitate reproduction of distinct and complex pathologies, mechanistic access, insights for further organoid optimization, and modeling of differential phenotypes for future applications in fundamental and translational medicine research.

Retinal Ganglion Cells in a Dish: Current Strategies and Recommended Best Practices for Effective In Vitro Modeling of Development and Disease

The ability to derive retinal ganglion cells (RGCs) from human pluripotent stem cells (hPSCs) provides an extraordinary opportunity to study the development of RGCs as well as cellular mechanisms underlying their degeneration in optic neuropathies. In the past several years, multiple approaches have been established that allow for the generation of RGCs from hPSCs, with these methods greatly improved in more recent studies to yield mature RGCs that more faithfully recapitulate phenotypes within the eye. Nevertheless, numerous differences still remain between hPSC-RGCs and those found within the human eye, with these differences likely explained at least in part due to the environment in which hPSC-RGCs are grown. With the ultimate goal of generating hPSC-RGCs that most closely resemble those within the retina for proper studies of retinal development, disease modeling, as well as cellular replacement, we review within this manuscript the current effective approaches for the differentiation of hPSC-RGCs, as well as how they have been applied for the investigation of RGC neurodegenerative diseases such as glaucoma. Furthermore, we provide our opinions on the characteristics of RGCs necessary for their use as effective in vitro disease models and importantly, how these current systems should be improved to more accurately reflect disease states. The establishment of characteristics in differentiated hPSC-RGCs that more effectively mimic RGCs within the retina will not only enable their use as effective models of RGC development, but will also create a better disease model for the identification of mechanisms underlying the neurodegeneration of RGCs in disease states such as glaucoma, further facilitating the development of therapeutic approaches to rescue RGCs from degeneration in disease states.

Human Retinal Organoids in Therapeutic Discovery: A Review of Applications

Human embryonic stem cells (hESCs)- and induced pluripotent stem cells (hiPSCs)-derived retinal organoids (ROs) are three-dimensional laminar structures that recapitulate the developmental trajectory of the human retina. The ROs provide a fascinating tool for basic science research, eye disease modeling, treatment development, and biobanking for tissue/cell replacement. Here we review the previous studies that paved the way for RO technology, the two most widely accepted, standardized protocols to generate ROs, and the utilization of ROs in medical discovery. This review is conducted from the perspective of basic science research, transplantation for regenerative medicine, disease modeling, and therapeutic development for drug screening and gene therapy. ROs have opened avenues for new technologies such as assembloids, coculture with other organoids, vasculature or immune cells, microfluidic devices (organ-on-chip), extracellular vesicles for drug delivery, biomaterial engineering, advanced imaging techniques, and artificial intelligence (AI). Nevertheless, some shortcomings of ROs currently limit their translation for medical applications and pose a challenge for future research. Despite these limitations, ROs are a powerful tool for functional studies and therapeutic strategies for retinal diseases.

Retinogenesis in a Dish: Bibliometric Analysis and Visualization of Retinal Organoids From 2011 to 2022

Retinal organoid (RO) is the three-dimensional (3D) retinal culture derived from pluripotent or embryonic stem cells which recapitulates organ functions, which was a revolutionary milestone in stem cell technology. The purpose of this study is to explore the hotspots and future directions on ROs, as well as to better understand the fields of greatest research opportunities. Eligible publications related to RO from 2011 to 2022 were acquired from the Web of Science (WoS) Core Collection database. Bibliometric analysis was performed by using software including VOSviewer, CiteSpace, and ArcGIS. A total of 520 articles were included, and the number of annual publications showed a rapid increase with an average rate of 40.86%. The United States published the most articles (241/520, 46.35%) with highest total citation frequencies (5,344). University College London (UK) contributed the largest publication output (40/520, 7.69%) and received highest total citation frequencies. Investigative Ophthalmology & Visual Science was the most productive journal with 129 articles. Majlinda Lako contributed the most research with 32 articles, while Olivier Goureau has the strongest collaboration work. Research could be subdivided into four keyword clusters: "culture and differentiation," "morphogenesis and modeling," "gene therapy," and "transplantation and visual restoration," and evolution of keywords was identified. Last decade has witnessed the huge progress in the field of RO, which is a young and promising research area with extensive and in-depth studies. More attention should be paid to RO-related models and therapies based on specific retinal diseases, especially inherited retinopathies.

Differentiation of Human Embryonic/Induced-Pluripotent Stem Cells to Retinal Ganglion Cells

The generation of retinal ganglion cells (RGCs) differentiated from human embryonic stem cell (hESC) or induced-pluripotent stem cells (iPSC) could aid with understanding of human RGC development, neuronal biology, drug discovery, potential cell-based therapies, and gene regulation. Here, we present a protocol for differentiation of hESC to RGCs using a 40-day protocol, significantly shorter than typical retinal organoids while still yielding cells with RGC-enriched markers and show physiological and morphological properties typical of RGCs.

Bulk RNA sequencing analysis of developing human induced pluripotent cell-derived retinal organoids

Retinogenesis involves the transformation of the anterior developing brain into organized retinal lamellae coordinated by intricate gene signalling networks. This complex process has been investigated in several model organisms such as birds, fish, mammals and amphibians, yet many facets of retinal development are different in humans and remain unexplored. In this regard, human pluripotent stem cell (hPSC)-derived 3D retinal organoids and Next Generation Sequencing (NGS) have emerged as key technologies that have facilitated the discovery of previously unknown details about cell fate specification and gene regulation in the retina. Here we utilized hPSCs integrated with fluorescent reporter genes (SIX6-p2A-eGFP/CRX-p2A-h2b-mRuby3) to generate retinal organoids and carry out bulk RNA sequencing of samples encompassing the majority of retinogenesis (D0-D280). This data set will serve as a valuable reference for the vision research community to characterize differentially expressed genes in the developing human eye.

Generation and Differentiation of Induced Pluripotent Stem Cells from Mononuclear Cells in An Age-Related Macular Degeneration Patient

OBJECTIVE

We aimed to generate induced pluripotent stem cells (iPSCs)-derived retinal pigmented epithelium (RPE) cells from peripheral blood mononuclear cells (PBMCs) and age-related macular degeneration (AMD) patient to provide potential cell sources for both basic scientific research and clinical application.

MATERIALS AND METHODS

In this experimental study, PBMCs were isolated from the whole blood of a 70-year-old female patient with AMD and reprogrammed into iPSCs by transfection of Sendai virus that contained Yamanaka factors (OCT4, SOX2, KLF4, and c-MYC). Flow cytometry, real-time quantitative polymerase chain reaction (qPCR), karyotype analysis, embryoid body (EB) formation, and teratoma detection were performed to confirm that AMD-iPSCs exhibited full pluripotency and maintained a normal karyotype after reprogramming. AMD-iPSCs were induced into RPE cells by stepwise induced differentiation and specific markers of RPE cells examined by immunofluorescence and flow cytometry.

RESULTS

The iPSC colonies started to form on three weeks post-infection. AMD-iPSCs exhibited typical morphology including roundness, a large nucleus, sparse cytoplasm, and conspicuous nucleoli. QPCR data showed that AMDiPSCs expressed pluripotency markers (endo-OCT4, endo-SOX2, NANOG and REX1). Flow cytometry indicated 99.7% of generated iPSCs was TRA-1-60 positive. Methylation sequencing showed that the regions of OCT4 and NANOG promoter were demethylated in iPSCs. EBs and teratomas formation assay showed that iPSCs had strong differentiation potential and pluripotency. After a series of inductions with differentiation mediums, a monolayer of AMDiPSC- RPE cells was observed on day 50. The AMD-iPSC-RPEs highly expressed specific RPE markers (MITF, ZO-1, Bestrophin, and PMEL17).

CONCLUSION

A high quality iPSCs could be established from the PBMCs obtained from elderly AMD patient. The AMDiPSC displayed complete pluripotency, enabling for scientific study, disease modeling, pharmacological testing, and therapeutic applications in personalized medicine. Collectively, we successfully differentiated the iPSCs into RPE with native RPE characteristics, which might provide potential regenerative treatments for AMD patients.

Development of Müller cell-based 3D biomimetic model using bioprinting technology

Müller cells are the principal glial cells for the maintenance of structural stability and metabolic homeostasis in the human retina. Although variousin vitroexperiments using two-dimensional (2D) monolayer cell cultures have been performed, the results provided only limited results because of the lack of 3D structural environment and different cellular morphology. We studied a Müller cell-based 3D biomimetic model for use in experiments on thein vivo-like functions of Müller cells within the sensory retina. Isolated primary Müller cells were bioprinted and a 3D-aligned architecture was induced, which aligned Müller cell structure in retinal tissue. The stereographic and functional characteristics of the biomimetic model were investigated and compared to those of the conventional 2D cultured group. The results showed the potential to generate Müller cell-based biomimetic models with characteristic morphological features such as endfeet, soma, and microvilli. Especially, the 3D Müller cell model under hyperglycemic conditions showed similar responses as observed in thein vivodiabetic model with retinal changes, whereas the conventional 2D cultured group showed different cytokine and growth factor secretions. These results show that our study is a first step toward providing advanced tools to investigate thein vivofunction of Müller cells and to develop complete 3D models of the vertebrate retina.