Characteristics of Progenitor Cells Derived from Adult Ciliary Body in Mouse, Rat, and Human Eyes

Adult stem cells in the eye: Identification, characterisation, and therapeutic application in ocular regeneration - A review

Adult stem cells, present in various parts of the human body, are undifferentiated cells that can proliferate and differentiate to replace dying cells within tissues. Stem cells have specifically been identified in the cornea, trabecular meshwork, crystalline lens, iris, ciliary body, retina, choroid, sclera, conjunctiva, eyelid, lacrimal gland, and orbital fat. The identification of ocular stem cells broadens the potential therapeutic strategies for untreatable eye diseases. Currently, stem cell transplantation for corneal and conjunctival diseases remains the most common stem cell-based therapy in ocular clinical management. Lens epithelial stem cells have been applied in the treatment of paediatric cataracts. Several early-phase clinical trials for corneal and retinal regeneration using ocular stem cells are also underway. Extensive preclinical studies using ocular stem cells have been conducted, showing encouraging outcomes. Ocular stem cells currently demonstrate great promise in potential treatments of eye diseases. In this review, we focus on the identification, characterisation, and therapeutic application of adult stem cells in the eye.

A systematic review on the effects of ROCK inhibitors on proliferation and/or differentiation in human somatic stem cells: A hypothesis that ROCK inhibitors support corneal endothelial healing via acting on the limbal stem cell niche

Rho kinase inhibitors (ROCKi) have attracted growing multidisciplinary interest, particularly in Ophthalmology where the question as to how they promote corneal endothelial healing remains unresolved. Concurrently, stem cell biology has rapidly progressed in unravelling drivers of stem cell (SC) proliferation and differentiation, where mechanical niche factors and the actin cytoskeleton are increasingly recognized as key players. There is mounting evidence from the study of the peripheral corneal endothelium that supports the likelihood of an internal limbal stem cell niche. The possibility that ROCKi stimulate the endothelial SC niche has not been addressed. Furthermore, there is currently a paucity of data that directly evaluates whether ROCKi promotes corneal endothelial healing by acting on this limbal SC niche located near the transition zone. Therefore, we performed a systematic review examining the effects ROCKi on the proliferation and differentiation of human somatic SC, to provide insight into its effects on various human SC populations. An appraisal of electronic searches of four databases identified 1 in vivo and 58 in vitro studies (36 evaluated proliferation while 53 examined differentiation). Types of SC studied included mesenchymal (n = 32), epithelial (n = 11), epidermal (n = 8), hematopoietic and other (n = 8). The ROCK 1/2 selective inhibitor Y-27632 was used in almost all studies (n = 58), while several studies evaluated ≥2 ROCKi (n = 4) including fasudil, H-1152, and KD025. ROCKi significantly influenced human somatic SC proliferation in 81% of studies (29/36) and SC differentiation in 94% of studies (50/53). The present systemic review highlights that ROCKi are influential in regulating human SC proliferation and differentiation, and provides evidence to support the hypothesis that ROCKi promotes corneal endothelial division and maintenance via acting on the inner limbal SC niche.

Traumatic optic neuropathy: a review of current studies

Traumatic optic neuropathy (TON) is a serious complication of craniofacial trauma that directly or indirectly damages the optic nerve and can cause severe vision loss. The incidence of TON has been gradually increasing in recent years. Research on the protection and regeneration of the optic nerve after the onset of TON is still at the level of laboratory studies and which is insufficient to support clinical treatment of TON. And, due to without clear guidelines, there is much ambiguity regarding its diagnosis and management. Clinical interventions for TON include observation only, treatment with corticosteroids alone, or optic canal (OC) decompression (with or without steroids). There is controversy in clinical practice concerning which treatment is the best. A review of available studies shows that the visual acuity of patients with TON can be significantly improved after OC decompression surgery (especially endoscopic transnasal/transseptal optic canal decompression (ETOCD)) with or without the use of corticosteroids. And new findings of laboratory studies such as mitochondrial therapy, lipid change studies, and other studies in favor of TON therapy have also been identified. In this review, we discuss the evolving perspective of surgical treatment and experimental study.

Evaluation of the Potential Effects of Retinol and Alginate/Gelatin-Based Scaffolds on Differentiation Capacity of Mouse Mesenchymal Stem Cells (MSCs) into Retinal Cells

Background and Objectives

Retinal stem cells (RSCs) resided in ciliary epithelium have shown to possess a high capacity to self-renew and differentiate into retinal cells. RSCs could be induced to differentiate when they are exposed to stimuli like natural compounds and suitable contexts such as biomaterials. The aim of this study was to examine the effects of Retinol and alginate/gelatin-based scaffolds on differentiation potential of mesenchymal stem cells (MSCs) originated from mouse ciliary epithelium.

Methods and Results

MSCs were extracted from mouse ciliary epithelium, and their identity was verified by detecting specific surface antigens. To provide a three-dimensional in vitro culture system, 2% alginate, 0.5% gelatin and the mixed alginate-gelatin hydrogels were fabricated and checked by SEM. Retinol treatment was performed on MSCs expanded on alginate/gelatin hydrogels and the survival rate and the ability of MSCs to differentiate were examined through measuring expression alterations of retina-specific genes by ICC and qPCR. The cell population isolated from ciliary epithelium contained more than 93.4% cells positive for MSC-specific marker CD105. Alginate/gelatin scaffolds showed to provide an acceptable viability (over 70%) for MSC cultures. Retinol treatment could induce a high expression of rhodopsin protein in MSCs expanded in alginate and alginate-gelatin mixtures. An elevated presentation of Nestin, RPE65 and Rhodopsin genes was detected in retinol-treated cultures expanded on alginate and alginate-gelatin scaffolds.

Conclusions

The results presented here elucidate that retinol treatment of MSCs grown on alginate scaffolds would promote the mouse ciliary epithelium-derived MSCs to differentiate towards retinal neurons.

Biofabrication of Artificial Stem Cell Niches in the Anterior Ocular Segment

The anterior segment of the eye is a complex set of structures that collectively act to maintain the integrity of the globe and direct light towards the posteriorly located retina. The eye is exposed to numerous physical and environmental insults such as infection, UV radiation, physical or chemical injuries. Loss of transparency to the cornea or lens (cataract) and dysfunctional regulation of intra ocular pressure (glaucoma) are leading causes of worldwide blindness. Whilst traditional therapeutic approaches can improve vision, their effect often fails to control the multiple pathological events that lead to long-term vision loss. Regenerative medicine approaches in the eye have already had success with ocular stem cell therapy and ex vivo production of cornea and conjunctival tissue for transplant recovering patients' vision. However, advancements are required to increase the efficacy of these as well as develop other ocular cell therapies. One of the most important challenges that determines the success of regenerative approaches is the preservation of the stem cell properties during expansion culture in vitro. To achieve this, the environment must provide the physical, chemical and biological factors that ensure the maintenance of their undifferentiated state, as well as their proliferative capacity. This is likely to be accomplished by replicating the natural stem cell niche in vitro. Due to the complex nature of the cell microenvironment, the creation of such artificial niches requires the use of bioengineering techniques which can replicate the physico-chemical properties and the dynamic cell-extracellular matrix interactions that maintain the stem cell phenotype. This review discusses the progress made in the replication of stem cell niches from the anterior ocular segment by using bioengineering approaches and their therapeutic implications.

Transplantation Efficacy of Human Ciliary Epithelium Cells from Fetal Eye and Lin-ve Stem Cells from Umbilical Cord Blood in the Murine Retinal Degeneration Model of Laser Injury

A number of degenerative conditions affecting the neural retina including age-related macular degeneration have no successful treatment, resulting in partial or complete vision loss. There are a number of stem cell replacement strategies for recovery of retinal damage using cells from variable sources. However, literature is still deficit in the comparison of efficacy of types of stem cells. The purpose of the study was to compare the therapeutic efficacy of undifferentiated cells, i.e., lineage negative stem cells (Lin-ve SC) with differentiated neurosphere derived from ciliary epithelium (CE) cells on retinal markers associated with laser-induced retinal injury. Laser-induced photocoagulation was carried out to disrupt Bruch’s membrane and retinal pigmented epithelium in C57BL/6 mouse model. Lineage negative cells were isolated from human umbilical cord blood, whereas neurospheres were derived from CE of post-aborted human eyeballs. The cells were then transplanted into subretinal space to study their effect on injury. Markers of neurotropic factors, retina, apoptosis, and proliferation were analyzed after injury and transplantation. mRNA expression was also analyzed by real-time polymerase chain reaction at 1 week, and 3-month immunohistochemistry was evaluated at 1-week time point. CE cell transplantation showed enhanced differentiation of rods and retinal glial cells. However, Lin-ve cells exerted paracrine-dependent modulation of neurotrophic factors, which is possibly mediated by antiapoptotic and proliferative effects. In conclusion, CE transplantation showed superior regenerative outcome in comparison to Lin-ve SC for rescue of artificially injured rodent retinal cells. It is imperative that this source for transplantation may be extensively studied in various doses and additional retinal degeneration models for prospective clinical applications.

Let-7, Lin28 and Hmga2 Expression in Ciliary Epithelium and Retinal Progenitor Cells

Purpose

Ciliary epithelium (CE) of adult mammalian eyes contains quiescent retinal progenitor/stem cells that generate neurospheres in vitro and differentiate into retinal neurons. This ability doesn't evolve efficiently probably because of regulatory mechanisms, such as microRNAs (miRNAs) that control pluripotent, progenitor, and differentiation genes. Here we investigate the presence of Let-7 miRNAs and its regulator and target, Lin28 and Hmga2, in CE cells from neurospheres, newborns, and adult tissues.

Methods

Newborn and adult rats CE cells were dissected into pigmented and nonpigmented epithelium (PE and NPE). Newborn PE cells were cultured with growth factors to form neurospheres and we analyzed Let-7, Lin28a, and Hmga2 expression. During the neurospheres formation, we added chemically modified single-stranded oligonucleotides designed to bind and inhibit or mimic endogenous mature Let-7b and Let-7c. After seven days in culture, we analyzed neurospheres size, number and expression of Let-7, Lin28, and Hmga2.

Results

Let-7 miRNAs were expressed at low rates in newborn CE cells with significant increase in adult tissues, with higher levels on NPE cells, that does not present the stem cells reprogramming ability. The Lin28a and Hmga2 protein and transcripts were more expressed in newborns than adults cells, opposed to Let-7. Neurospheres presented higher Lin28 and Hmga2 expression than newborn and adult, but similar Let-7 than newborns. Let-7b inhibitor upregulated Hmga2 expression, whereas Let-7c mimics upregulated Lin28 and downregulated Hmga2.

Conclusions

This study shows the dynamic of Lin28-Let-7-Hmga regulatory axis in CE cells. These components may develop different roles during neurospheres formation and postnatal CE cells.

Human Fetal Pigmented Ciliary Epithelium Stem Cells have Regenerative Capacity in the Murine Retinal Degeneration Model of Laser Injury

BACKGROUND

Retinal degeneration and related eye disorders have limited treatment interventions. Since stem cell therapy has shown promising results, ciliary epithelium (CE) derived stem cells could be a better choice given the fact that cells from eye niche can better integrate with the degenerating retina, rewiring the synaptic damage.

OBJECTIVE

To test the effect of human fetal pigmented ciliary epithelium-derived neurospheres in the mouse model of laser-induced retinal degeneration.

METHODS

C57 male mice were subjected to retinal injury by Laser photocoagulation. Human fetal pigmented ciliary epithelium was obtained from post-aborted human eyeballs and cultured with epidermal growth factor (rhEGF) and fibroblast growth factor (rhFGF). The six day neurospheres were isolated, dissociated and transplanted into the subretinal space of the laser injured mice at the closest proximity to Laser shots. Mice were analyzed for functional vision through electroretinogram (ERG) and sacrificed at 1 week and 12 week time points. Retinal, Neurotropic, Apoptotic and proliferation markers were analysed using real-time polymerase chain reaction (PCR).

RESULTS

The CE neurospheres showed an increase in the expression of candidate genes analyzed in the study at 1 week time point, which sustained for longer time point of 12 weeks.

CONCLUSION

We showed the efficacy of human CE cells in the regeneration of retinal degeneration in murine model for the first time. CE cells need to be explored comprehensively both in disease and degeneration.

An immune response to the avascular lens following wounding of the cornea involves ciliary zonule fibrils

The lens and central cornea are avascular. It was assumed that the adult lens had no source of immune cells and that the basement membrane capsule surrounding the lens was a barrier to immune cell migration. Yet, microfibril‐associated protein‐1 (MAGP1)‐rich ciliary zonules that originate from the vasculature‐rich ciliary body and extend along the surface of the lens capsule, form a potential conduit for immune cells to the lens. In response to cornea debridement wounding, we find increased expression of MAGP1 throughout the central corneal stroma. The immune cells that populate this typically avascular region after wounding closely associate with this MAGP1‐rich matrix. These results suggest that MAGP1‐rich microfibrils support immune cell migration post‐injury. Using this cornea wound model, we investigated whether there is an immune response to the lens following cornea injury involving the lens‐associated MAGP1‐rich ciliary zonules. Our results provide the first evidence that following corneal wounding immune cells are activated to travel along zonule fibers that extend anteriorly along the equatorial surface of the lens, from where they migrate across the anterior lens capsule. These results demonstrate that lens‐associated ciliary zonules are directly involved in the lens immune response and suggest the ciliary body as a source of immune cells to the avascular lens.

The peripheral eye: A neurogenic area with potential to treat retinal pathologies?

Numerous degenerative diseases affecting visual function, including glaucoma and retinitis pigmentosa, are produced by the loss of different types of retinal cells. Cell replacement therapy has emerged as a promising strategy for treating these and other retinal diseases. The retinal margin or ciliary body (CB) of mammals has been proposed as a potential source of cells to be used in degenerative conditions affecting the retina because it has been reported it might hold neurogenic potential beyond embryonic development. However, many aspects of the origin and biology of the CB are unknown and more recent experiments have challenged the capacity of CB cells to generate different types of retinal neurons. Here we review the most recent findings about the development of the marginal zone of the retina in different vertebrates and some of the mechanisms underlying the proliferative and neurogenic capacity of this fascinating region of the vertebrates eye. In addition, we performed experiments to isolate CB cells from the mouse retina, generated neurospheres and observed that they can be expanded with a proliferative ratio similar to neural stem cells. When induced to differentiate, cells derived from the CB neurospheres start to express early neural markers but, unlike embryonic stem cells, they are not able to fully differentiate in vitro or generate retinal organoids. Together with previous reports on the neurogenic capacity of CB cells, also reviewed here, our results contribute to the current knowledge about the potentiality of this peripheral region of the eye as a therapeutic source of functional retinal neurons in degenerative diseases.

The current state of stem cell therapy for ocular disease

Herein, we review the safety, efficacy, regulatory standards and ethical implications of the use of stem cells in ocular disease. A literature review was conducted, registered clinical trials reviewed, and expert opinions sought. Guidelines and codes of conduct from international societies and professional bodies were also reviewed. Collated data is presented on current progress in the field of ocular regenerative medicine, future challenges, the clinical trial process and ethical considerations in stem cell therapy. A greater understanding of the function and location of ocular stem cells has led to rapid advances in possible therapeutic applications. However, in the context of significant technical challenges and potential long-term complications, it is imperative that stem cell practices operate within formal clinical trial frameworks. While there remains broad scope for innovation, ongoing evidence-based review of potential interventions and the development of standardized protocols are necessary to ensure patient safety and best practice in ophthalmic care.

Stem Cell Sources and Their Potential for the Treatment of Retinal Degenerations

Stem cells offer unprecedented opportunities for the development of strategies geared toward the treatment of retinal degenerative diseases. A variety of cellular sources have been investigated for various potential clinical applications, including tissue regeneration, disease modeling, and screening for non–cell-based therapeutic agents. As the field transitions from more than a decade of preclinical research to the first phase I/II clinical trials, we provide a concise overview of the stem cell sources most commonly used, weighing their therapeutic potential on the basis of their technical strengths/limitations, their ethical implications, and the extent of the progress achieved to date. This article serves as a framework for further in-depth analyses presented in the following chapters of this Special Issue.

Using Electrical Stimulation to Enhance the Efficacy of Cell Transplantation Therapies for Neurodegenerative Retinal Diseases: Concepts, Challenges, and Future Perspectives

Disease or trauma-induced loss or dysfunction of neurons in any central nervous system (CNS) tissue will have a significant impact on the health of the affected patient. The retina is a multilayered tissue that originates from the neuroectoderm, much like the brain and spinal cord. While sight is not required for life, neurodegeneration-related loss of vision not only affects the quality of life for the patient but also has societal implications in terms of health care expenditure. Thus, it is essential to develop effective strategies to repair the retina and prevent disease symptoms. To address this need, multiple techniques have been investigated for their efficacy in treating retinal degeneration. Recent advances in cell transplantation (CT) techniques in preclinical, animal, and in vitro culture studies, including further evaluation of endogenous retinal stem cells and the differentiation of exogenous adult stem cells into various retinal cell types, suggest that this may be the most appropriate option to replace lost retinal neurons. Unfortunately, the various limitations of CT, such as immune rejection or aberrant cell behavior, have largely prevented this technique from becoming a widely used clinical treatment option. In parallel with the advances in CT methodology, the use of electrical stimulation (ES) to treat retinal degeneration has also been recently evaluated with promising results. In this review, we propose that ES could be used to enhance CT therapy, whereby electrical impulses can be applied to the retina to control both native and transplanted stem cell behavior/survival in order to circumvent the limitations associated with retinal CT. To highlight the benefits of this dual treatment, we have briefly outlined the recent developments and limitations of CT with regard to its use in the ocular environment, followed by a brief description of retinal ES, as well as described their combined use in other CNS tissues.

Alteration in cellular turnover and progenitor cell population in lacrimal glands from thrombospondin 1-/- mice, a model of dry eye

The purpose of this study was to investigate the changes that occur in the lacrimal glands (LGs) in female thrombospondin 1 knockout (TSP1^-/-) mice, a mouse model of the autoimmune disease Sjogren's syndrome. The LGs of 4, 12, and 24 week-old female TSP1^-/- and C57BL/6J (wild type, WT) mice were used. qPCR was performed to measure cytokine expression. To study the architecture, LG sections were stained with hematoxylin and eosin. Cell proliferation was measured using bromo-deoxyuridine and immunohistochemistry. Amount of CD47 and stem cell markers was analyzed by western blot analysis and location by immunofluorescence microscopy. Expression of stem cell transcription factors was performed using Mouse Stem Cell Transcription Factors RT² Profiler PCR Array. Cytokine levels significantly increased in LGs of 24 week-old TSP1^-/- mice while morphological changes were detected at 12 weeks. Proliferation was decreased in 12 week-old TSP1^-/- mice. Three transcription factors were overexpressed and eleven underexpressed in TSP1^-/- compared to WT LGs. The amount of CD47, Musashi1, and Sox2 was decreased while the amount of ABCG2 was increased in 12 week-old TSP1^-/- mice. We conclude that TSP1 is necessary for maintaining normal LG homeostasis. Absence of TSP1 alters cytokine levels and stem cell transcription factors, LG cellular architecture, decreases cell proliferation, and alters amount of stem cell markers.

Ocular stem cells: a status update!

Stem cells are unspecialized cells that have been a major focus of the field of regenerative medicine, opening new frontiers and regarded as the future of medicine. The ophthalmology branch of the medical sciences was the first to directly benefit from stem cells for regenerative treatment. The success stories of regenerative medicine in ophthalmology can be attributed to its accessibility, ease of follow-up and the eye being an immune-privileged organ. Cell-based therapies using stem cells from the ciliary body, iris and sclera are still in animal experimental stages but show potential for replacing degenerated photoreceptors. Limbal, corneal and conjunctival stem cells are still limited for use only for surface reconstruction, although they might have potential beyond this. Iris pigment epithelial, ciliary body epithelial and choroidal epithelial stem cells in laboratory studies have shown some promise for retinal or neural tissue replacement. Trabecular meshwork, orbital and sclera stem cells have properties identical to cells of mesenchymal origin but their potential has yet to be experimentally determined and validated. Retinal and retinal pigment epithelium stem cells remain the most sought out stem cells for curing retinal degenerative disorders, although treatments using them have resulted in variable outcomes. The functional aspects of the therapeutic application of lenticular stem cells are not known and need further attention. Recently, embryonic stem cell-derived retinal pigment epithelium has been used for treating patients with Stargardts disease and age-related macular degeneration. Overall, the different stem cells residing in different components of the eye have shown some success in clinical and animal studies in the field of regenerative medicine.

Stem cell treatment of degenerative eye disease

Stem cell therapies are being explored extensively as treatments for degenerative eye disease, either for replacing lost neurons, restoring neural circuits or, based on more recent evidence, as paracrine-mediated therapies in which stem cell-derived trophic factors protect compromised endogenous retinal neurons from death and induce the growth of new connections. Retinal progenitor phenotypes induced from embryonic stem cells/induced pluripotent stem cells (ESCs/iPSCs) and endogenous retinal stem cells may replace lost photoreceptors and retinal pigment epithelial (RPE) cells and restore vision in the diseased eye, whereas treatment of injured retinal ganglion cells (RGCs) has so far been reliant on mesenchymal stem cells (MSC). Here, we review the properties of non-retinal-derived adult stem cells, in particular neural stem cells (NSCs), MSC derived from bone marrow (BMSC), adipose tissues (ADSC) and dental pulp (DPSC), together with ESC/iPSC and discuss and compare their potential advantages as therapies designed to provide trophic support, repair and replacement of retinal neurons, RPE and glia in degenerative retinal diseases. We conclude that ESCs/iPSCs have the potential to replace lost retinal cells, whereas MSC may be a useful source of paracrine factors that protect RGC and stimulate regeneration of their axons in the optic nerve in degenerate eye disease. NSC may have potential as both a source of replacement cells and also as mediators of paracrine treatment.

Cellular strategies for retinal repair by photoreceptor replacement

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

Transplantation of mesenchymal stem cells promotes tissue regeneration in a glaucoma model through laser-induced paracrine factor secretion and progenitor cell recruitment

Among bone marrow cells, hematopoietic and mesenchymal components can contribute to repair damaged organs. Such cells are usually used in acute diseases but few options are available for the treatment of chronic disorders. In this study, we have used a laser-induced model of open angle glaucoma (OAG) to evaluate the potential of bone marrow cell populations and the mechanisms involved in tissue repair. In addition, we investigated laser-induced tissue remodeling as a method of targeting effector cells into damaged tissues. We demonstrate that among bone marrow cells, mesenchymal stem cells (MSC) induce trabecular meshwork regeneration. MSC injection into the ocular anterior chamber leads to far more efficient decrease in intraocular pressure (IOP) (p < .001) and healing than hematopoietic cells. This robust effect was attributable to paracrine factors from stressed MSC, as injection of conditioned medium from MSC exposed to low but not to normal oxygen levels resulted in an immediate decrease in IOP. Moreover, MSC and their secreted factors induced reactivation of a progenitor cell pool found in the ciliary body and increased cellular proliferation. Proliferating cells were observed within the chamber angle for at least 1 month. Laser-induced remodeling was able to target MSC to damaged areas with ensuing specific increases in ocular progenitor cells. Thus, our results identify MSC and their secretum as crucial mediators of tissue repair in OAG through reactivation of local neural progenitors. In addition, laser treatment could represent an appealing strategy to promote MSC-mediated progenitor cell recruitment and tissue repair in chronic diseases.

Mobilizing endogenous stem cells for retinal repair

Irreversible vision loss is most often caused by the loss of function and subsequent death of retinal neurons, such as photoreceptor cells-the cells that initiate vision by capturing and transducing signals of light. One reason why retinal degenerative diseases are devastating is that, once retinal neurons are lost, they don't grow back. Stem cell-based cell replacement strategy for retinal degenerative diseases are leading the way in clinical trials of transplantation therapy, and the exciting findings in both human and animal models point to the possibility of restoring vision through a cell replacement regenerative approach. A less invasive method of retinal regeneration by mobilizing endogenous stem cells is, thus, highly desirable and promising for restoring vision. Although many obstacles remain to be overcome, the field of endogenous retinal repair is progressing at a rapid pace, with encouraging results in recent years.

Gene expression-based comparison of the human secretory neuroepithelia of the brain choroid plexus and the ocular ciliary body: potential implications for glaucoma

Background

The neuroepithelia of the choroid plexus (CP) in the brain and the ciliary body (CB) of the eye have common embryological origins and share similar micro-structure and functions. The CP epithelium (CPE) and the non-pigmented epithelium (NPE) of the CB produce the cerebrospinal fluid (CSF) and the aqueous humor (AH) respectively. Production and outflow of the CSF determine the intracranial pressure (ICP); production and outflow of the AH determine the intraocular pressure (IOP). Together, the IOP and ICP determine the translaminar pressure on the optic disc which may be involved in the pathophysiology of primary open angle glaucoma (POAG). The aim of this study was to compare the molecular machinery of the secretory neuroepithelia of the CP and CB (CPE versus NPE) and to determine their potential role in POAG.

Methods

We compared the transcriptomes and functional annotations of healthy human CPE and NPE. Microarray and bioinformatic studies were performed using an Agilent platform and the Ingenuity Knowledge Database (IPA).

Results

Based on gene expression profiles, we found many similar functions for the CPE and NPE including molecular transport, neurological disease processes, and immunological functions. With commonly-used selection criteria (fold-change > 2.5, p-value < 0.05), 14% of the genes were expressed significantly differently between CPE and NPE. When we used stricter selection criteria (fold-change > 5, p-value < 0.001), still 4.5% of the genes were expressed differently, which yielded specific functions for the CPE (ciliary movement and angiogenesis/hematopoiesis) and for the NPE (neurodevelopmental properties). Apart from a few exceptions (e.g. SLC12A2, SLC4A4, SLC4A10, KCNA5, and SCN4B), all ion transport protein coding genes involved in CSF and AH production had similar expression profiles in CPE and NPE. Three POAG disease genes were expressed significantly higher in the CPE than the NPE, namely CDH1, CDKN2B and SIX1.

Conclusions

The transcriptomes of the CPE and NPE were less similar than we previously anticipated. High expression of CSF/AH production genes and candidate POAG disease genes in the CPE and NPE suggest that both might be involved in POAG.

Retinal stem cells and regeneration of vision system

The vertebrate retina is a well-characterized model for studying neurogenesis. Retinal neurons and glia are generated in a conserved order from a pool of mutlipotent progenitor cells. During retinal development, retinal stem/progenitor cells (RPC) change their competency over time under the influence of intrinsic (such as transcriptional factors) and extrinsic factors (such as growth factors). In this review, we summarize the roles of these factors, together with the understanding of the signaling pathways that regulate eye development. The information about the interactions between intrinsic and extrinsic factors for retinal cell fate specification is useful to regenerate specific retinal neurons from RPCs. Recent studies have identified RPCs in the retina, which may have important implications in health and disease. Despite the recent advances in stem cell biology, our understanding of many aspects of RPCs in the eye remains limited. PRCs are present in the developing eye of all vertebrates and remain active in lower vertebrates throughout life. In mammals, however, PRCs are quiescent and exhibit very little activity and thus have low capacity for retinal regeneration. A number of different cellular sources of RPCs have been identified in the vertebrate retina. These include PRCs at the retinal margin, pigmented cells in the ciliary body, iris, and retinal pigment epithelium, and Müller cells within the retina. Because PRCs can be isolated and expanded from immature and mature eyes, it is possible now to study these cells in culture and after transplantation in the degenerated retinal tissue. We also examine current knowledge of intrinsic RPCs, and human embryonic stems and induced pluripotent stem cells as potential sources for cell transplant therapy to regenerate the diseased retina.

Emerging novel roles of neuropeptide Y in the retina: from neuromodulation to neuroprotection

Neuropeptide Y (NPY) and NPY receptors are widely expressed in the central nervous system, including the retina. Retinal cells, in particular neurons, astrocytes, and Müller, microglial and endothelial cells express this peptide and its receptors (Y1, Y2, Y4 and/or Y5). Several studies have shown that NPY is expressed in the retina of various mammalian and non-mammalian species. However, studies analyzing the distribution of NPY receptors in the retina are still scarce. Although the physiological roles of NPY in the retina have not been completely elucidated, its early expression strongly suggests that NPY may be involved in the development of retinal circuitry. NPY inhibits the increase in [Ca(2+)]i triggered by elevated KCl in retinal neurons, protects retinal neural cells against toxic insults and induces the proliferation of retinal progenitor cells. In this review, we will focus on the roles of NPY in the retina, specifically proliferation, neuromodulation and neuroprotection. Alterations in the NPY system in the retina might contribute to the pathogenesis of retinal degenerative diseases, such as diabetic retinopathy and glaucoma, and NPY and its receptors might be viewed as potentially novel therapeutic targets.

Does the adult human ciliary body epithelium contain "true" retinal stem cells?

Recent reports of retinal stem cells being present in several locations of the adult eye have sparked great hopes that they may be used to treat the millions of people worldwide who suffer from blindness as a result of retinal disease or injury. A population of proliferative cells derived from the ciliary body epithelium (CE) has been considered one of the prime stem cell candidates, and as such they have received much attention in recent years. However, the true nature of these cells in the adult human eye has still not been fully elucidated, and the stem cell claim has become increasingly controversial in light of new and conflicting reports. In this paper, we will try to answer the question of whether the available evidence is strong enough for the research community to conclude that the adult human CE indeed harbors stem cells.

Adult ciliary epithelial stem cells generate functional neurons and differentiate into both early and late born retinal neurons under non-cell autonomous influences

Background

The neural stem cells discovered in the adult ciliary epithelium (CE) in higher vertebrates have emerged as an accessible source of retinal progenitors; these cells can self-renew and possess retinal potential. However, recent studies have cast doubt as to whether these cells could generate functional neurons and differentiate along the retinal lineage. Here, we have systematically examined the pan neural and retinal potential of CE stem cells.

Results

Molecular and cellular analysis was carried out to examine the plasticity of CE stem cells, obtained from mice expressing green fluorescent protein (GFP) under the influence of the promoter of the rod photoreceptor-specific gene, Nrl, using the neurospheres assay. Differentiation was induced by specific culture conditions and evaluated by both transcripts and protein levels of lineage-specific regulators and markers. Temporal pattern of their levels were examined to determine the expression of genes and proteins underlying the regulatory hierarchy of cells specific differentiation in vitro. Functional attributes of differentiation were examined by the presence of current profiles and pharmacological mobilization of intracellular calcium using whole cell recordings and Fura-based calcium imaging, respectively. We demonstrate that stem cells in adult CE not only have the capacity to generate functional neurons, acquiring the expression of sodium and potassium channels, but also respond to specific cues in culture and preferentially differentiate along the lineages of retinal ganglion cells (RGCs) and rod photoreceptors, the early and late born retinal neurons, respectively. The retinal differentiation of CE stem cells was characterized by the temporal acquisition of the expression of the regulators of RGCs and rod photoreceptors, followed by the display of cell type-specific mature markers and mobilization of intracellular calcium.

Conclusions

Our study demonstrates the bonafide retinal potential of adult CE stem cells and suggests that their plasticity could be harnessed for clinical purposes once barriers associated with any lineage conversion, i.e., low efficiency and fidelity is overcome through the identification of conducive culture conditions.

Ephrin-A3 suppresses Wnt signaling to control retinal stem cell potency

The ciliary epithelium (CE) of adult mammals has been reported to provide a source of retinal stem cells (RSCs) that can give rise to all retinal cell types in vitro. A recent study, however, suggests that CE-derived cells possess properties of pigmented ciliary epithelial cells and display little neurogenic potential. Here we show that the neurogenic potential of CE-derived cells is negatively regulated by ephrin-A3, which is upregulated in the CE of postnatal mice and presents a strong prohibitory niche for adult RSCs. Addition of ephrin-A3 inhibits proliferation of CE-derived RSCs and increases pigment 349 cell 359. In contrast, absence of ephrin-A3 promotes proliferation and increases expression of neural progenitor cell markers and photoreceptor progeny. The negative effects of ephrin-A3 on CE-derived RSCs are mediated through activation of an EphA4 receptor and suppression of Wnt3a/β-catenin signaling. Together, our data suggest that CE-derived RSCs contain the intrinsic machinery to generate photoreceptors and other retinal neurons, while the CE of adult mice expresses negative regulators that prohibit the proliferation and neural differentiation of RSCs. Manipulating ephrin and Wnt/β-catenin signaling may, thus, represent a viable approach in activating the endogenous neurogenic potential of CE-derived RSCs for treating photoreceptor damage and retinal degenerative disorders.

Neuro-protection of retinal stem cells transplantation combined with copolymer-1 immunization in a rat model of glaucoma

Glaucoma is a chronic, neurodegenerative disease that often leads to blindness. A common treatment is to reduce intraocular pressure (IOP), but this approach does not halt visual loss caused by the death of retinal ganglion cells (RGCs). Therefore, there is an important need for therapies that protect against RGCs degeneration. The present study in a rat glaucoma model aimed to determine whether retinal stem cells (RSCs) transplantation plus vaccination with a glatiramer acetate copolymer-1 (COP-1) could confer neuroprotection. Rats were immunized with COP-1 on the same day as IOP induction by argon laser photocoagulation of the episcleral veins and limbal plexus. RSCs were cultured and transplanted intravitreally 1week after laser treatment. The expression of brain-derived neurotrophic factor (BDNF) and insulin-like growth factor I (IGF-I) was detected by immunohistochemical staining, RT-PCR, and western blotting. RGCs survival was assessed by TUNEL staining and RGCs counting. We found that the expression of BDNF and IGF-I in the RSCs/COP-1 group was significantly higher than in other groups (P<0.05). In addition, the number of the apoptotic RGCs in the RSCs/COP-1 group was notably lower than in other groups (P<0.05), and the number of RGCs in the RSCs/COP-1 group was higher than in other groups (P<0.05). We conclude, therefore, that the combined effects between RSCs transplantation and COP-1 immunization protect RGCs from apoptosis in our rat model of glaucoma. The increase in levels of secreted BDNF and IGF-I may be one of the mechanisms underlying the neuro-protection of RGCs.

Distinct neurogenic potential in the retinal margin and the pars plana of mammalian eye

Unlike many other vertebrates, a healthy mammalian retina does not grow throughout life and lacks a ciliary margin zone capable of actively generating new neurons. The isolation of stem-like cells from the ciliary epithelium has led to speculation that the mammalian retina and/or surrounding tissues may retain neurogenic potential capable of responding to retinal damage. Using genetically altered mouse lines with varying degrees of retinal ganglion cell loss, we show that the retinal margin responds to ganglion cell loss by prolonging specific neurogenic activity, as characterized by increased numbers of Atoh7(LacZ)-expressing cells. The extent of neurogenic activity correlated with the degree of ganglion cell deficiency. In the pars plana, but not the retinal margin, cells remain proliferative into adulthood, marking the junction of pars plana and retinal margin as a niche capable of producing proliferative cells in the mammalian retina and a potential cellular source for retinal regeneration.

Gene expression and functional annotation of the human ciliary body epithelia

Purpose

The ciliary body (CB) of the human eye consists of the non-pigmented (NPE) and pigmented (PE) neuro-epithelia. We investigated the gene expression of NPE and PE, to shed light on the molecular mechanisms underlying the most important functions of the CB. We also developed molecular signatures for the NPE and PE and studied possible new clues for glaucoma.

Methods

We isolated NPE and PE cells from seven healthy human donor eyes using laser dissection microscopy. Next, we performed RNA isolation, amplification, labeling and hybridization against 44×k Agilent microarrays. For microarray conformations, we used a literature study, RT-PCRs, and immunohistochemical stainings. We analyzed the gene expression data with R and with the knowledge database Ingenuity.

Results

The gene expression profiles and functional annotations of the NPE and PE were highly similar. We found that the most important functionalities of the NPE and PE were related to developmental processes, neural nature of the tissue, endocrine and metabolic signaling, and immunological functions. In total 1576 genes differed statistically significantly between NPE and PE. From these genes, at least 3 were cell-specific for the NPE and 143 for the PE. Finally, we observed high expression in the (N)PE of 35 genes previously implicated in molecular mechanisms related to glaucoma.

Conclusion

Our gene expression analysis suggested that the NPE and PE of the CB were quite similar. Nonetheless, cell-type specific differences were found. The molecular machineries of the human NPE and PE are involved in a range of neuro-endocrinological, developmental and immunological functions, and perhaps glaucoma.

Nestin expressing progenitor cells during establishment of the neural retina and its vasculature

In order to test if nestin is a useful marker for various types of progenitor cells, we explored nestin expression in the retina during development. Nestin expression was co-evaluated with bromodeoxyuridine (BrdU) labeling and Griffonia simplicifolia isolectin B4 (GSIB4) histochemistry. Nestin immunoreactivity appears in cell soma of dividing neural progenitor cells and their leading processes in retinas from embryonic day (E) 13 to E20, in accordance with a BrdU-labeled pattern. At postnatal day (P) 5, it is restricted to the end feet of Müller cells. BrdU-labeled nuclei were mainly in the inner part of the inner nuclear layer in postnatal neonates. The retinal vessels demarcated with GSIB4-positive endothelial cells were first distributed in the nerve fiber layer from P3. Afterward the vascular branches sprouted and penetrated deeply into the retina. The endothelial cells positive for GSIB4 and the pericytes in the microvessels were additionally immunoreactive for nestin. Interestingly, the presumed migrating microglial cells showing only GSIB4 reactivity preceded the microvessels throughout the neuroblast layer during vascular sprouting and extension. These findings may suggest that nestin expression represents the proliferation and movement potential of the neural progenitor cells as well as the progenitor cells of the endothelial cell and the pericyte during retinal development. Thus, Müller glial cells might be potential neural progenitor cells of the retina, and the retinal microvasculature established by both the endothelial and the pericyte progenitor cells via vasculogenesis along microglia migrating routes sustains its angiogenic potential.

Characterization of Progenitor Cells during Canine Retinal Development

We identify the presence of progenitor cells during retinal development in the dog, as this species represents a natural model for studying several breed-specific degenerative retinal disorders. Antibodies to detected progenitor cells (Pax6, C-kit, and nestin) and ganglion cells (BDNF, Brn3a, and Thy1) were used in combination with H3 for the purpose of identifying proliferating cells. Pax6, nestin, C-kit, and H3 were localized mainly in the neuroblastic layer of the retina during the embryonic stage. During the fetal stage, proteins were expressed in the inner neuroblastic layer (INL) as well as in the outer neuroblastic layer; BDNF, Thy1, and Brn3a were also expressed in the INL. During the neonatal stage only C-kit was not expressed. Proliferating cells were present in both undifferentiated and differentiated retina. These results suggest that, during canine retinogenesis, progenitor cells are distributed along the retina and some of these cells remain as progenitor cells of the ganglion cells during the first postnatal days.

Retinal stem cells transplantation combined with copolymer-1 immunization reduces interferon-gamma levels in an experimental model of glaucoma

AIM

To explore the effect of immunization with copolymer-1 (COP-1) and retinal stem cells (RSCs) transplantation on interferon-gamma (IFN-γ) levels in a rat experimental glaucoma model.

METHODS

An experimental glaucoma was induced by argon laser photocoagulation of the episcleral veins and limbal plexus in the right eye of rats. Immediately following glaucoma induction, rats were immunized with COP-1. RSCs were cultured and transplanted intravitreally into the eyes of glaucoma model animals 1 week post-laser treatment. Six experimental groups were used: COP-1/RSC, PBS/RSC, COP-1/PBS, PBS/PBS, glaucoma model group, and a normal control group. The concentration of IFN-γ in aqueous humor (AH) and serum was measured by enzyme-linked immunosorbent assay (ELISA) in each of the six groups. Retinal ganglion cell (RGC) survival was assessed by quantifying apoptosis using Hoechst staining.

RESULTS

Concentrations of IFN-γ in AH and serum of rats that had undergone glaucoma induction were higher than those of non-induced control rats. The concentrations of IFN-γ in AH and serum of the COP-1/RSCs treated group were determined to be 2371.9ng/L and 710.9ng/L, respectively, which were significantly lower than those in the other treated groups (P<0.05). In fact, IFN-γ levels in the dual treated group were reduced to background levels. The COP-1/RSC group had lower number of apoptotic RGCs than the other three experimental groups (P<0.05).

CONCLUSION

The reduced levels of IFN-γ in AH and serum of the COP-1/RSC group may be related to synergistic effects between RSCs transplantation and COP-1 immune modulation. It is likely that the lower levels of IFN-γ prevented RGCs glaucomatous apoptosis.

Pigment epithelial cells isolated from human peripheral iridectomies have limited properties of retinal stem cells

PURPOSE

The identification of cells with properties of retinal progenitor cells (RPCs) in the adult human ciliary margin (CM) prompted a number of studies of their proliferative and differentiation potential. One of the remaining challenges is to find a feasible method of isolating RPCs from the patient's eye. In the human CM, only the iris pigment epithelium (IPE) is easily obtained by a minimally invasive procedure. In the light of recent studies questioning the existence of RPCs in the adult mammalian CM, we wanted to assess the potential of the adult human IPE as source of RPCs.

METHODS

The IPE were isolated from peripheral iridectomies during glaucoma surgery, and IPE and ciliary body (CB) epithelium were also isolated from post-mortem tissue. Cells were cultivated in sphere-promoting conditions or as monolayers. Whole-tissue samples, undifferentiated and differentiated cells were studied by immunocytochemistry, RT-PCR and transmission electron microscopy.

RESULTS

The adult human IPE, like the CB, expressed markers of RPCs such as Pax6, Sox2 and Nestin in vivo. Both sphere-promoting and monolayer cultures preserved this phenotype. However, both IPE/CB cultures expressed markers of differentiated epithelial cells such as Claudin, microphtalmia-associated transcription factor (MITF) and Cytokeratin-19. Ultrastructurally, IPE spheres displayed epithelial-like junctions and contained mature melanosomes. After induced differentiation, IPE-derived cells showed only partial neuronal differentiation expressing β-III-tubulin, Map-2 and Rhodopsin, whereas no mature glial markers were found.

CONCLUSION

Proliferative cells with some properties of RPCs can be isolated from the adult human IPE by peripheral iridectomies. Yet, many cells retain properties of differentiated epithelial cells and lack central properties of somatic stem cells.

Promises of stem cell therapy for retinal degenerative diseases

With the development of stem cell technology, stem cell-based therapy for retinal degeneration has been proposed to restore the visual function. Many animal studies and some clinical trials have shown encouraging results of stem cell-based therapy in retinal degenerative diseases. While stem cell-based therapy is a promising strategy to replace damaged retinal cells and ultimately cure retinal degeneration, there are several important challenges which need to be overcome before stem cell technology can be applied widely in clinical settings. In this review, different types of donor cell origins used in retinal treatments, potential target cell types for therapy, methods of stem cell delivery to the eye, assessments of potential risks in stem cell therapy, as well as future developments of retinal stem cells therapy, will be discussed.

In situ dividing and phagocytosing retinal microglia express nestin, vimentin, and NG2 in vivo

Background

Following injury, microglia become activated with subsets expressing nestin as well as other neural markers. Moreover, cerebral microglia can give rise to neurons in vitro. In a previous study, we analysed the proliferation potential and nestin re-expression of retinal macroglial cells such as astrocytes and Müller cells after optic nerve (ON) lesion. However, we were unable to identify the majority of proliferative nestin⁺ cells. Thus, the present study evaluates expression of nestin and other neural markers in quiescent and proliferating microglia in naïve retina and following ON transection in adult rats in vivo.

Methodology/Principal Findings

For analysis of cell proliferation and cells fates, rats received BrdU injections. Microglia in retinal sections or isolated cells were characterized using immunofluorescence labeling with markers for microglia (e.g., Iba1, CD11b), cell proliferation, and neural cells (e.g., nestin, vimentin, NG2, GFAP, Doublecortin etc.). Cellular analyses were performed using confocal laser scanning microscopy. In the naïve adult rat retina, about 60% of resting ramified microglia expressed nestin. After ON transection, numbers of nestin⁺ microglia peaked to a maximum at 7 days, primarily due to in situ cell proliferation of exclusively nestin⁺ microglia. After 8 weeks, microglia numbers re-attained control levels, but 20% were still BrdU⁺ and nestin⁺, although no further local cell proliferation occurred. In addition, nestin⁺ microglia co-expressed vimentin and NG2, but not GFAP or neuronal markers. Fourteen days after injury and following retrograde labeling of retinal ganglion cells (RGCs) with Fluorogold (FG), nestin⁺NG2⁺ microglia were positive for the dye indicating an active involvement of a proliferating cell population in phagocytosing apoptotic retinal neurons.

Conclusions/Significance

The current study provides evidence that in adult rat retina, a specific resident population of microglia expresses proteins of immature neural cells that are involved in injury-induced cell proliferation and phagocytosis while transdifferentiation was not observed.

CNS targets support and sustain differentiation of cultured neuronal and retinal progenitor cells

Superior colliculus (SC) is the target of retinal neurons, allowing them to form connections. Cultured stem cells/progenitors can potentially be used as donor tissue to reconstruct degenerated retina including perhaps replacing lost ganglion cells in glaucoma. In which case, it will be essential for these cells to integrate with the central nervous system targets. Here, we have investigated if the mid-brain region containing superior colliculus (SC) provides a permissive environment for the survival and differentiation of neural progenitors, including retinal progenitor cells propagated in cultures. Neural (NPCs) and retinal progenitor cells (RPCs) from green fluorescent protein (GFP) transgenic mice were cultured. Passage two through four neural and retinal progenitor cells were subsequently cocultured with the SC organotypic slices and maintained in culture for 17 and eight days respectively. Differentiation of the neurons was studied by immunocytochemistry for retinotypic neuronal markers. Retinal progenitor cells cocultured with SC slices were able to differentiate into various neuronal morphologies. Some cocultured progenitor cells differentiated into neurons as suggested by class III β tubulin immunoreactivity. In addition, specific retinotypic neuronal differentiation of RPC was detected by immunoreactivity for calbindin and PKC. SC provides a permissive environment that supports survival and differentiation of the progenitor cells.

Using stem cells to mend the retina in ocular disease

Retinal degenerative diseases are the leading cause of incurable blindness worldwide. Furthermore, existing pharmacological and surgical interventions are only partially effective in halting disease progression, thus adjunctive neuroprotective strategies are desperately needed to preserve vision. Stem cells appear to possess inherent neuroprotective abilities, at least in part by providing neurotrophic support to injured neurons. Advances in stem cell biology offer the hope of new therapies for a broad range of neurodegenerative conditions, including those of the retina. Experimental cell-mediated therapies also hint at the tantalizing possibility of achieving retinal neuronal replacement and regeneration, once cells are lost to the disease process. This article summarizes the latest advances in cell therapies for neuroprotection and regeneration in neurodegenerative pathologies of both the inner and outer retina.

Activation of retinal stem cells in the proliferating marginal region of RCS rats during development of retinitis pigmentosa

Retinal stem cells (RSCs) have been demonstrated at the proliferating marginal regions from the pars plana of ciliary body to the ciliary marginal zone (CMZ) in adult lower vertebrates and mammals. Investigations in the lower vertebrates have provided some evidence that RSCs can proliferate following retinal damage; however, the evidence that this occurs in mammals is not clear. In this study, we explored RSCs proliferation potential of adult mammalian in proliferating marginal regions of Royal College of Surgeons (RCS) rats, an animal model for retinitis pigmentosa (RP). The proliferation was evaluated using BrdU labeling, and Chx-10 as markers to discern progenitor cell of CMZ in Long-Evan's and RCS rats at different postnatal day (PND) after eye opening. We found that few Chx-10 and BrdU labeled cells in the proliferating marginal regions of Long-Evan's rats, which significantly increased in RCS rats at PND30 and PND60. Consistent with this, Chx-10/Vimentin double staining cells in the center retina of RCS rats increased significantly at PND30 after eye opening. In addition, mRNA expression of Shh, Ptch1 and Smo was up-regulated in RCS rats at PND60 compared to age-matched Long-Evan's rats, which revealed Shh/ptc pathway involving in the activation of RSCs. These results suggest that RSCs in the mammalian retinal proliferating marginal regions has the potential to regenerate following degeneration.

Stem cells for neuroprotection in glaucoma

Stem cell transplantation is currently being explored as a therapy for many neurodegenerative diseases including glaucoma. Cellular therapies have the potential to provide chronic neuroprotection after a single treatment, and early results have been encouraging in models of spinal cord injury and Parkinson's disease. Stem cells may prove ideal for use in such treatments as they can accumulate at sites of injury in the central nervous system (CNS) and may also offer the possibility of targeted treatment delivery. Numerous stem cell sources exist, with embryonic and fetal stem cells liable to be superseded by adult-derived cells as techniques to modify the potency and differentiation of somatic cells improve. Possible neuroprotective mechanisms offered by stem cell transplantation include the supply of neurotrophic factors and the modulation of matrix metalloproteinases and other components of the CNS environment to facilitate endogenous repair. Though formidable challenges remain, stem cell transplantation remains a promising therapeutic approach in glaucoma. In addition, such studies may also provide important insights relevant to other neurodegenerative diseases.

CD133+ adult human retinal cells remain undifferentiated in Leukaemia Inhibitory Factor (LIF)

Background

CD133 is a cell surface marker of haematopoietic stem and progenitor cells. Leukaemia inhibitory factor (LIF), sustains proliferation and not differentiation of embryonic stem cells. We used CD133 to purify adult human retinal cells and aimed to determine what effect LIF had on these cultures and whether they still had the ability to generate neurospheres.

Methods

Retinal cell suspensions were derived from adult human post-mortem tissue with ethical approval. With magnetic automated cell sorting (MACS) CD133⁺ retinal cells were enriched from post mortem adult human retina. CD133⁺ retinal cell phenotype was analysed by flow cytometry and cultured cells were observed for proliferative capacity, neuropshere generation and differentiation with or without LIF supplementation.

Results

We demonstrated purification (to 95%) of CD133⁺ cells from adult human postmortem retina. Proliferating cells were identified through BrdU incorporation and expression of the proliferation markers Ki67 and Cyclin D1. CD133⁺ retinal cells differentiated whilst forming neurospheres containing appropriate lineage markers including glia, neurons and photoreceptors. LIF maintained CD133⁺ retinal cells in a proliferative and relatively undifferentiated state (Ki67, Cyclin D1 expression) without significant neurosphere generation. Differentiation whilst forming neurospheres was re-established on LIF withdrawal.

Conclusion

These data support the evidence that CD133 expression characterises a population of cells within the resident adult human retina which have progenitor cell properties and that their turnover and differentiation is influenced by LIF. This may explain differences in retinal responses observed following disease or injury.