Photoreceptor cells from mouse ES cells by co-culture with chick embryonic retina

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.

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.

Recent Advances in Retinal Stem Cell Therapy

Purpose of review

Progress in stem cell research for blinding diseases over the past decade is now being applied to patients with retinal degenerative diseases and soon perhaps, glaucoma. However, the field still has much to learn about the conversion of stem cells into various retinal cell types, and the potential delivery methods that will be required to optimize the clinical efficacy of stem cells delivered into the eye.

Recent findings

Recent groundbreaking human clinical trials have demonstrated both the opportunities and current limitations of stem cell transplantation for retinal diseases. New progress in developing in vitro retinal organoids, coupled with the maturation of bio-printing technology, and non-invasive high-resolution imaging have created new possibilities for repairing and regenerating the diseased retina and rigorously validating its clinical impact in vivo.

Summary

While promising progress is being made, meticulous clinical trials with cells derived using good manufacturing practice, novel surgical methods, and improved methods to derive all of the neuronal cell types present in the retina will be indispensable for developing stem cell transplantation as a paradigm shift for the treatment of blinding diseases.

Cellular responses following retinal injuries and therapeutic approaches for neurodegenerative diseases

Retinal neurodegenerative diseases like age-related macular degeneration, glaucoma, diabetic retinopathy and retinitis pigmentosa each have a different etiology and pathogenesis. However, at the cellular and molecular level, the response to retinal injury is similar in all of them, and results in morphological and functional impairment of retinal cells. This retinal degeneration may be triggered by gene defects, increased intraocular pressure, high levels of blood glucose, other types of stress or aging, but they all frequently induce a set of cell signals that lead to well-established and similar morphological and functional changes, including controlled cell death and retinal remodeling. Interestingly, an inflammatory response, oxidative stress and activation of apoptotic pathways are common features in all these diseases. Furthermore, it is important to note the relevant role of glial cells, including astrocytes, Müller cells and microglia, because their response to injury is decisive for maintaining the health of the retina or its degeneration. Several therapeutic approaches have been developed to preserve retinal function or restore eyesight in pathological conditions. In this context, neuroprotective compounds, gene therapy, cell transplantation or artificial devices should be applied at the appropriate stage of retinal degeneration to obtain successful results. This review provides an overview of the common and distinctive features of retinal neurodegenerative diseases, including the molecular, anatomical and functional changes caused by the cellular response to damage, in order to establish appropriate treatments for these pathologies.

Bladder cancer cell in co-culture induces human stem cell differentiation to urothelial cells through paracrine FGF10 signaling

Fibroblast growth factor 10 (FGF10) is required for embryonic epidermal morphogenesis including brain development, lung morphogenesis, and initiation of limb bud formation. In this study, we investigated the role of FGF10 as a lead induction factor for stem cell differentiation toward urothelial cell. To this end, human multipotent stem cell in vitro system was employed. Human amniotic fluid stem cells were co-cultured with immortalized bladder cancer lines to induce directed differentiation into urothelial cells. Urothelial markers, uroplakin II, III, and cytokeratin 8, were monitored by RT-PCR, immunocytochemistry, and Western blot analysis. Co-cultured stem cells began to express uroplakin II, III, and cytokeratin 8. Targeted FGF10 gene knockdown from bladder cancer cells abolished the directed differentiation. In addition, when FGF10 downstream signaling was blocked with the Mek inhibitor, the co-culture system lost the capacity to induce urothelial differentiation. Exogenous addition of recombinant FGF10 protein promoted stem cell differentiation into urothelium cell lineage. Together, this report suggests that paracrine FGF10 signaling stimulates the differentiation of human stem cell into urothelial cells. Current study provides insight into the potential role of FGF10 as a lead growth factor for bladder regeneration and its therapeutic application for bladder transplantation.

Human embryonic stem cell applications for retinal degenerations

Loss of vision in severe retinal degenerations often is a result of photoreceptor cell or retinal pigment epithelial cell death or dysfunction. Cell replacement therapy has the potential to restore useful vision for these individuals especially after they have lost most or all of their light-sensing cells in the eye. A reliable, well-characterized source of retinal cells will be needed for replacement purposes. Human embryonic stem cells (ES cells) can provide an unlimited source of replacement retinal cells to take over the function of lost cells in the eye. The author's intent for this review is to provide an historical overview of the field of embryonic stem cells with relation to the retina. The review will provide a quick primer on key pathways involved in the development of the neural retina and RPE followed by a discussion of the various protocols out in the literature for generating these cells from non-human and human embryonic stem cells and end with in vivo application of ES cell-derived photoreceptors and RPE cells.

Enhanced generation of retinal progenitor cells from human retinal pigment epithelial cells induced by amniotic fluid

BACKGROUND

Retinal progenitor cells are a convenient source of cell replacement therapy in retinal degenerative disorders. The purpose of this study was to evaluate the expression patterns of the homeobox genes PAX6 and CHX10 (retinal progenitor markers) during treatment of human retinal pigment epithelium (RPE) cells with amniotic fluid (AF), RPE cells harvested from neonatal cadaver globes were cultured in a mixture of DMEM and Ham's F12 supplemented with 10% FBS. At different passages, cells were trypsinized and co-cultured with 30% AF obtained from normal fetuses of 1416 weeks gestational age.

RESULTS

Compared to FBS-treated controls, AF-treated cultures exhibited special morphological changes in culture, including appearance of spheroid colonies, improved initial cell adhesion and ordered cell alignment. Cell proliferation assays indicated a remarkable increase in the proliferation rate of RPE cells cultivated in 30% AF-supplemented medium, compared with those grown in the absence of AF. Immunocytochemical analyses exhibited nuclear localization of retinal progenitor markers at a ratio of 33% and 27% for CHX10 and PAX6, respectively. This indicated a 3-fold increase in retinal progenitor markers in AF-treated cultures compared to FBS-treated controls. Real-time PCR data of retinal progenitor genes (PAX6, CHX10 and VSX-1) confirmed these results and demonstrated AF's capacity for promoting retinal progenitor cell generation.

CONCLUSION

Taken together, the results suggest that AF significantly promotes the rate of retinal progenitor cell generation, indicating that AF can be used as an enriched supplement for serum-free media used for the in vitro propagation of human progenitor cells.

Adult retinal stem cells revisited

Recent advances in retinal stem cell research have raised the possibility that these cells have the potential to be used to repair or regenerate diseased retina. Various cell sources for replacement of retinal neurons have been identified, including embryonic stem cells, the adult ciliary epithelium, adult Müller stem cells and induced pluripotent stem cells (iPS). However, the true stem cell nature of the ciliary epithelium and its possible application in cell therapies has now been questioned, leaving other cell sources to be carefully examined as potential candidates for such therapies. The need for identification of the ontogenetic state of grafted stem cells in order to achieve their successful integration into the murine retina has been recognized. However, it is not known whether the same requirements may apply to achieve transplant cell integration into the adult human eye. In addition, the existence of natural barriers for stem cell transplantation, including microglial accumulation and abnormal extracellular matrix deposition have been demonstrated, suggesting that several obstacles need to be overcome before such therapies may be implemented. This review addresses recent scientific developments in the field and discusses various strategies that may be potentially used to design cell based therapies to treat human retinal disease.

In vitro and in vivo differentiation of human embryonic stem cells into retina-like organs and comparison with that from mouse pluripotent epiblast stem cells

Correctly inducing the differentiation of pluripotent hESCs to a specific lineage with high purity is highly desirable for regenerative cell therapy. Our first effort to perform in vitro differentiation of hESCs resulted in a limited recapitulation of the ocular tissue structures. When undifferentiated hESCs were placed in vivo into the ocular tissue, in this case into the vitreous cavity, 3-dimensional retina-like structures reminiscent of the invagination of the optic vesicle were generated. Immunohistochemical analysis confirmed the presence of both a neural retina-like cell layer and a retinal pigmented epithelium-like cell layer, possibly equivalent to the developing E12.5 mouse retina. Furthermore, mouse epiblast-derived stem cells, which are reported to share some characteristics with hESCs, but not with mouse ESCs, also generated retinal anlage-like structures in vivo. hESC-derived retina-like structures present a novel therapeutic possibility for retinal diseases and also provide a novel experimental system to study early human eye development.

Neural regeneration and cell replacement: a view from the eye

Neuronal degenerations in the retina are leading causes of blindness. Like most other areas of the CNS, the neurons of the mammalian retina are not replaced following degeneration. However, in nonmammalian vertebrates, endogenous repair processes restore neurons very efficiently, even after complete loss of the retina. We describe the phenomenon of retinal regeneration in nonmammalian vertebrates and attempts made in recent years to stimulate similar regenerative processes in the mammalian retina. In addition, we review the various strategies employed to replace lost neurons in the retina and the recent use of stem cell technologies to address problems of retinal repair.

Stem-cell therapy in retinal disease

PURPOSE OF REVIEW

Stem-cell research is being investigated for the treatment of retina diseases. Cell replacement strategies have the potential to improve vision in patients who were previously considered to be untreatable. This review summarizes progress within the field and obstacles which must be overcome to make stem-cell therapy a viable treatment for select retinal disease.

RECENT FINDINGS

Researchers have demonstrated that stem-cell transplants can survive, migrate, differentiate, and integrate within the retina. Stem cells from various developmental stages have been used in these experiments, including embryonic stem cells, neural stem cells, mesenchymal stem cells, retinal stem cells, and adult stem cells from the ciliary margin. Not only can these transplants adopt retina-like morphologies and phenotypes, but they have also shown evidence of synaptic reconnection and visual recovery in both animal and human studies. Still, work must be done to achieve higher yields of functioning retinal neurons and to promote better integration within the host retina.

SUMMARY

Although many obstacles remain, stem-cell-based therapy is a promising treatment to restore vision in patients with retina disease.

Generation of motor neurons by coculture of retinoic acid-pretreated embryonic stem cells with chicken notochords

Understanding neuroectoderm formation and its subsequent diversification to functional neural subtypes remains elusive. We have shown here for the first time that embryonic stem cells (ESCs) can differentiate into neurons and motor neurons (MNs) by using a coculture embryonic notochord model in vitro. Mouse ESCs were induced to form neural precursors via timed exposure to retinoic acid (RA) using the 4-/4+ RA protocol. These cells were then cocultured with alginate bead-encapsulated notochords isolated from Hamburger and Hamilton stage 6-10 chick embryos. The use of notochord alone was not able to induce neural differentiation from ESCs, and, therefore, notochord does not possess neural inducing activity. Hence, the most successful neuronal cells and MN differentiation was only observed following the coculture of RA-pretreated ESCs with notochord. This resulted in a significantly greater number of cells expressing microtubule-associated protein-2 (MAP2), HB9, choline acetyltransferase (ChAT) and MN-specific genes. While further characterization of these differentiated cells will be essential before transplantation studies commence, these data illustrate the effectiveness of embryonic notochord coculture in providing valuable molecular cues for directed differentiation of ESCs toward an MN lineage.

Embryonic stem cells reduce liver fibrosis in CCl4-treated mice

We transplanted undifferentiated embryonic stem (ES) cells into the spleens of carbon tetrachloride (CCl₄)-treated mice to determine their effects on liver fibrosis. Carbon tetrachloride at 0.5 ml/kg of body weight was injected intraperitoneally into C57BL/6 mice twice weekly for up to 20 weeks. Four weeks after the first injection, the mice were divided into two groups and those in group 1 received 1 × 10⁵ ES cells genetically labelled with enhanced green fluorescent protein (GFP) in the spleens, while group 2 mice received 0.1 ml of phosphate-buffered saline. In group 1, GFP-immunopositive cells were retained and found in areas of fibrosis in the liver, and reduced liver fibrosis was observed as compared with group 2. Secondary transplantation of ES cells at 12 weeks after the initial transplantation enhanced the reduction in liver fibrosis. No teratoma formation or uncontrolled growth of ES cells in organs, including the liver and spleen, was observed in any of the mice. In the livers of group 1 mice, metalloproteinase 9-immunopositive cells derived from ES cells as well as those from the recipient were observed. These cells were also found to be immunopositive for the hepatoblast marker Delta-like (DlK-1), a member of the DlK-1 family of transmembrane proteins. These results suggest that ES-based cell therapy is potentially useful for liver fibrosis treatment and that reduction in CCl₄-induced liver fibrosis by transplantation of ES cells may be related closely to the emergence of metalloproteinase-producing hepatoblast-like cells.

Cell transplantation strategies for retinal repair

Cell transplantation is a novel therapeutic strategy to restore visual responses to the degenerate adult neural retina and represents an exciting area of regenerative neurotherapy. So far, it has been shown that transplanted postmitotic photoreceptor precursors are able to functionally integrate into the adult mouse neural retina. In this review, we discuss the differentiation of photoreceptor cells from both adult and embryonic-derived stem cells and their potential for retinal cell transplantation. We also discuss the strategies used to overcome barriers present in the degenerate neural retina and improve retinal cell integration. Finally, we consider the future translation of retinal cell therapy as a therapeutic strategy to treat retinal degeneration.

Strategies for retinal repair: cell replacement and regeneration

The retina, like most other regions of the central nervous system, is subject to degeneration from both genetic and acquired causes. Once the photoreceptors or inner retinal neurons have degenerated, they are not spontaneously replaced in mammals. In this review, we provide an overview of retinal development and regeneration with emphasis on endogenous repair and replacement seen in lower vertebrates and recent work on induced mammalian retinal regeneration from Müller glia. Additionally, recent studies demonstrating the potential for cellular replacement using postmitotic photoreceptors and embryonic stem cells are also reviewed.

A review of in vivo animal studies in retinal prosthesis research

BACKGROUND

The development of a functional retinal prosthesis for acquired blindness is a great challenge. Rapid progress in the field over the last 15 years would not have been possible without extensive animal experimentation pertaining to device design and fabrication, biocompatibility, stimulation parameters and functional responses. This paper presents an overview of in vivo animal research related to retinal prosthetics, and aims to summarize the relevant studies.

METHODS

A Pubmed search of the English language literature was performed. The key search terms were: retinal implant, retinal prosthesis, artificial vision, rat, rabbit, cat, dog, sheep, pig, minipig. In addition a manual search was performed based on references quoted in the articles retrieved through Pubmed.

RESULTS

We identified 50 articles relevant to in vivo animal experimentation directly related to the development of a retinal implant. The highest number of publications related to the cat (n = 18).

CONCLUSION

The contribution of animal models to the development of retinal prosthetic devices has been enormous, and has led to human feasibility studies. Grey areas remain regarding long-term tissue-implant interactions, biomaterials, prosthesis design and neural adaptation. Animals will continue to play a key role in this rapidly evolving field.

Concise Review: The Potential of Stem Cells for Auditory Neuron Generation and Replacement

Sensory hair cells in the mammalian cochlea are sensitive to many insults including loud noise, ototoxic drugs, and ageing. Damage to these hair cells results in deafness and sets in place a number of irreversible changes that eventually result in the progressive degeneration of auditory neurons, the target cells of the cochlear implant. Techniques designed to preserve the density and integrity of auditory neurons in the deafened cochlea are envisaged to provide improved outcomes for cochlear implant recipients. This review examines the potential of embryonic stem cells to generate new neurons for the deafened mammalian cochlea, including the directed differentiation of stem cells toward a sensory neural lineage and the engraftment of exogenous stem cells into the deafened auditory system. Although still in its infancy the aim of this therapy is to restore a critical number of auditory neurons, thereby improving the benefits derived from a cochlear implant.

Promoted differentiation of cynomolgus monkey ES cells into hepatocyte-like cells by co-culture with mouse fetal liver-derived cells

AIM: To explore whether a co-culture of cynomolgus monkey embryonic stem (cES) cells with embryonic liver cells could promote their differentiation into hepatocytes.

METHODS: Mouse fetal liver-derived cells (MFLCs) were prepared as adherent cells from mouse embryos on embryonic d (ED) 14, after which undifferentiated cES cells were co-cultured with MFLCs. The induction of cES cells along a hepatic lineage was examined in MFLC-assisted differentiation, spontaneous differentiation, and growth factors (GF) and chemicals-induced differentiations (GF-induced differentiation) using retinoic acid, leukemia inhibitory factor (LIF), FGF2, FGF4, hepatocyte growth factor (HGF), oncostatin M (OSM), and dexamethasone.

RESULTS: The mRNA expression of α-fetoprotein, albumin (ALB), α-1-antitrypsin, and hepatocyte nuclear factor 4α was observed earlier in the differentiating cES cells co-cultured with MFLCs, as compared to cES cells undergoing spontaneous differentiation and those subjected to GF-induced differentiation. The expression of cytochrome P450 7a1, a possible marker for embryonic endoderm-derived mature hepatocytes, was only observed in cES cells that had differentiated in a co-culture with MFLCs. Further, the disappearance of Oct3/4, a representative marker of an undifferentiated state, was noted in cells co-cultured with MFLCs, but not in those undergoing spontaneous or GF-induced differentiation. Immunocytochemical analysis revealed an increased ratio of ALB-immunopositive cells among cES cells co-cultured with MFLCs, while glycogen storage and urea synthesis were also demonstrated.

CONCLUSION: MFLCs showed an ability to induce cES cells to differentiate toward hepatocytes. The co-culture system with MFLCs is a useful method for induction of hepatocyte-like cells from undifferentiated cES cells.

Auditory hair cell explant co-cultures promote the differentiation of stem cells into bipolar neurons

Auditory neurons, the target neurons of the cochlear implant, degenerate following a sensorineural hearing loss. The goal of this research is to direct the differentiation of embryonic stem cells (SCs) into bipolar auditory neurons that can be used to replace degenerating neurons in the deafened mammalian cochlea. Successful replacement of auditory neurons is likely to result in improved clinical outcomes for cochlear implant recipients. We examined two post-natal auditory co-culture models with and without neurotrophic support, for their potential to direct the differentiation of mouse embryonic SCs into characteristic, bipolar, auditory neurons. The differentiation of SCs into neuron-like cells was facilitated by co-culture with auditory neurons or hair cell explants, isolated from post-natal day five rats. The most successful combination was the co-culture of hair cell explants with whole embryoid bodies, which resulted in significantly greater numbers of neurofilament-positive, neuron-like cells. While further characterization of these differentiated cells will be essential before transplantation studies commence, these data illustrate the effectiveness of post-natal hair cell explant co-culture, at providing valuable molecular cues for directed differentiation of SCs towards an auditory neuron lineage.

Cynomolgus monkey embryonic stem cell lines express green fluorescent protein

We successfully established cynomolgus monkey embryonic stem (cES) cell lines expressing enhanced green fluorescent protein (GFP) by introducing a GFP-encoding gene under cytomegalovirus immediate early enhancer (CMVIE) promoter regulation into cES cells. The cells maintained the ability of in vitro differentiation toward ectodermal, mesodermal, and endodermal lineages, and produced teratomas composed of tissues derived from the three embryonic germ layers when transplanted into severe combined immunodeficient disease mice. GFP expression was also observed in the differentiated cells. These GFP-expressing cES cell lines are considered useful for basic research, including cell transplantation.

Transplantation of embryonic stem cell-derived neural stem cells for spinal cord injury in adult mice

AIMS

To investigate the efficacy of embryonic stem cell-derived neural stem cells (NSCs) for spinal cord injury (SCI) in mice and whether a combination treatment with thyroid hormone provides a more effective ES cell-based therapy.

METHODS

Nestin-positive NSCs were induced from undifferentiated mouse ES cells by a step-by-step culture and used as grafts. Thirty-six mice were subjected to an SCI at Th10 and divided into three groups of 12. Graft cells were transplanted into the injury site 10 days after injury. Group 1 mice were left under observation without receiving graft cells, while mice in Group 2 received 2 x 104 graft cells, and those in Group 3 received 2 x 104 graft cells and were treated with a continuous intraperitoneal injection of thyroxin using osmotic mini-pumps. Behavioral improvement was assessed by a scoring system throughout the experimental period until post-transplantation day (PD) 28.

RESULTS

Mice in Groups 2 and 3 demonstrated an improved behavioral function, as compared to those in Group 1 after PD 14. There was no significant difference in behavioral recovery between Groups 2 and 3.

CONCLUSIONS

Transplantation of ES-NSCs into the injury site was effective for SCI, while thyroxine did not deliver additional effectiveness.