Epiretinal transplantation of human bone marrow mesenchymal stem cells rescues retinal and vision function in a rat model of retinal degeneration

New frontiers in retinal transplantation

New frontiers about retinal cell transplantation for retinal degenerative diseases start from the idea that acting on stem cells can help regenerate retinal layers and establish new synapses among retinal cells. Deficiency or alterations of synaptic input and neurotrophic factors result in trans-neuronal degeneration of the inner retinal cells. Thus, the disruption of photoreceptors takes place. However, even in advanced forms of retinal degeneration, a good percentage of the ganglion cells and the inner nuclear layer neurons remain intact. This phenomenon provides evidence for obtaining retinal circuitry through the transplantation of photoreceptors into the subretinal region. The eye is regarded as an optimal organ for cell transplantation because of its immunological privilege and the relatively small number of cells collaborating to carry out visual activities. The eyeball's immunological privilege, characterized by the suppression of delayed-type hypersensitivity responses in ocular tissues, is responsible for the low rate of graft rejection in transplant patients. The main discoveries highlight the capacity of embryonic stem cells (ESCs) and induced pluripotent stem cells to regenerate damaged retinal regions. Recent progress has shown significant enhancements in transplant procedures and results. The research also explores the ethical ramifications linked to the utilization of stem cells, emphasizing the ongoing issue surrounding ESCs. The analysis centers on recent breakthroughs, including the fabrication of three-dimensional retinal organoids and the innovation of scaffolding for cell transportation. Moreover, researchers are currently assessing the possibility of CRISPR and other advanced gene editing technologies to enhance the outcomes of retinal transplantation. The widespread use of universally recognized safe surgical and imaging methods enables retinal transplantation and monitoring of transplanted cell growth toward the correct location. Currently, most therapy approaches are in the first phases of development and necessitate further research, including both pre-clinical and clinical trials, to attain favorable visual results for individuals suffering from retinal degenerative illnesses.

Retinitis Pigmentosa and Therapeutic Approaches: A Systematic Review

Background: Retinitis pigmentosa (RP) is a group of hereditary retinal dystrophies characterized by progressive degeneration of photoreceptor cells, which results in debilitating visual impairment. This systematic review aims to evaluate the efficacy and safety of emerging treatment modalities for RP, including gene therapy, mesenchymal-cell-based approaches, and supplementary interventions. Methods: A comprehensive search of electronic databases was conducted to identify relevant studies published up to February 2024. Studies reporting outcomes of treatment interventions for RP, including randomized controlled trials, non-randomized studies, and case series, were included. Data extraction and synthesis were performed according to predefined criteria, focusing on assessing the quality of evidence and summarizing key findings. Results: The search yielded 13 studies meeting inclusion criteria, encompassing diverse treatment modalities and study designs. Gene therapy emerged as a promising therapeutic approach, with several studies reporting favorable outcomes regarding visual function preservation and disease stabilization. Mesenchymal-cell-based therapies also demonstrated potential benefits, although evidence remains limited and heterogeneous. Supplementary interventions, including nutritional supplements and neuroprotective agents, exhibited variable efficacy, with conflicting findings across studies. Conclusions: Despite the lack of definitive curative treatments, emerging therapeutic modalities promise to slow disease progression and preserve visual function in individuals with RP. However, substantial gaps in evidence and heterogeneity in study methodologies underscore the need for further research to elucidate optimal treatment strategies, refine patient selection criteria, and enhance long-term outcomes. This systematic review provides a comprehensive synthesis of current evidence and highlights directions for future research to advance the care and management of individuals with RP.

MIR96 Has Good Potential to Differentiate Human Bone Marrow-Derived Mesenchymal Stem Cells into Photoreceptor-Like Cells

OBJECTIVES

MicroRNAs play an important role in the development and function of neuron cells. Among these, the miRNA known as MIR96 is abundantly expressed in mammalian retina and significantly affects differentiation, maturation, and survival of human photoreceptor cells. In this study, a mimic to miRNA-96 was transfected into human bone marrowderived mesenchymal stem cells to explore the biological functions of MIR96 at differentiation processing.

MATERIALS AND METHODS

A mimic to miRNA-96 and a competitive control were transfected into human bone marrow-derived mesenchymal stem cells using Lipofectamine. After 24 and 48 hours, we evaluated changes in expression levels of genes associated with neural progenitor and photoreceptor differentiation (OTX2, NRL, protein kinase C, SLC1A1, and recoverin) by real-time polymerase chain reaction. In addition, we measured expression of mRNA and protein of the CRX gene (neuroretinal progenitor cell marker) and the RHO gene (terminal differentiation marker) using real-time polymerase chain reaction and immunocytochemistry, respectively.

RESULTS

Real-time polymerase chain reaction results showed increased levels of RHO and recoverin mRNA after 24 hours in transfected cells. In addition, mRNA levels of OTX2, CRX, NRL, RHO, recoverin, and protein kinase C increased after 48 hours in transfected cells. Immunocytochemistry results confirmed these findings by demonstrating RHO and CRX at both 24 and 48 hours in transfected cells.

CONCLUSIONS

Control of the expression of MIR96 can be a good strategy to promote cell differentiation and can be used in cell therapy for retinal degeneration. Our results showed that human bone marrow-derived mesenchymal stem cells can differentiate into photoreceptor cells after transfection with MIR96. These results support therapeutic use of MIR96 in retinal degeneration and suggest human bone marrowderived mesenchymal stem cells as a promising tool for interventions.

Therapeutic Potential of Oral-Derived Mesenchymal Stem Cells in Retinal Repair

The retina has restricted regeneration ability to recover injured cell layer because of reduced production of neurotrophic factors and increased inhibitory molecules against axon regrowth. A diseased retina could be regenerated by repopulating the damaged tissue with functional cell sources like mesenchymal stem cells (MSCs). The cells are able to release neurotrophic factors (NFs) to boost axonal regeneration and cell maintenance. In the current study, we comprehensively explore the potential of various types of stem cells (SCs) from oral cavity as promising therapeutic options in retinal regeneration. The oral MSCs derived from cranial neural crest cells (CNCCs) which explains their broad neural differentiation potential and secret rich NFs. They are comprised of dental pulp SCs (DPSCs), SCs from exfoliated deciduous teeth (SHED), SCs from apical papilla (SCAP), periodontal ligament-derived SCs (PDLSCs), gingival MSCs (GMSCs), and dental follicle SCs (DFSCs). The Oral MSCs are becoming a promising source of cells for cell-free or cell-based therapeutic approach to recover degenerated retinal. These cells have various mechanisms of action in retinal regeneration including cell replacement and the paracrine effect. It was demonstrated that they have more neuroprotective and neurotrophic effects on retinal cells than immediate replacement of injured cells in retina. This could be the reason that their therapeutic effects would be weakened over time. It can be concluded that neuronal and retinal regeneration through these cells is most likely due to their NFs that dramatically suppress oxidative stress, inflammation, and apoptosis. Although, oral MSCs are attractive therapeutic options for retinal injuries, more preclinical and clinical investigations are required.

Macrophage/microglia polarization for the treatment of diabetic retinopathy

Macrophages/microglia are immune system defense and homeostatic cells that develop from bone marrow progenitor cells. According to the different phenotypes and immune responses of macrophages (Th1 and Th2), the two primary categories of polarized macrophages/microglia are those conventionally activated (M1) and alternatively activated (M2). Macrophage/microglial polarization is a key regulating factor in the development of inflammatory disorders, cancers, metabolic disturbances, and neural degeneration. Macrophage/microglial polarization is involved in inflammation, oxidative stress, pathological angiogenesis, and tissue healing processes in ocular diseases, particularly in diabetic retinopathy (DR). The functional phenotypes of macrophages/microglia affect disease progression and prognosis, and thus regulate the polarization or functional phenotype of microglia at different DR stages, which may offer new concepts for individualized therapy of DR. This review summarizes the involvement of macrophage/microglia polarization in physiological situations and in the pathological process of DR, and discusses the promising role of polarization in personalized treatment of DR.

Ocular tropism of SARS-CoV-2 in animal models with retinal inflammation via neuronal invasion following intranasal inoculation

Although ocular manifestations are reported in patients with COVID-19, consensus on ocular tropism of SARS-CoV-2 is lacking. Here, we infect K18-hACE2 transgenic mice with SARS-CoV-2 using various routes. We observe ocular manifestation and retinal inflammation with production of pro-inflammatory cytokines in the eyes of intranasally (IN)-infected mice. Intratracheal (IT) infection results in dissemination of the virus from the lungs to the brain and eyes via trigeminal and optic nerves. Ocular and neuronal invasions are confirmed using intracerebral (IC) infection. Notably, the eye-dropped (ED) virus does not cause lung infection and becomes undetectable with time. Ocular and neurotropic distribution of the virus in vivo is evident in fluorescence imaging with an infectious clone of SARS-CoV-2-mCherry. The ocular tropic and neuroinvasive characteristics of SARS-CoV-2 are confirmed in wild-type Syrian hamsters. Our data can improve the understanding regarding viral transmission and clinical characteristics of SARS-CoV-2 and help in improving COVID-19 control procedures.

Potential therapeutic strategies for photoreceptor degeneration: the path to restore vision

Photoreceptors (PRs), as the most abundant and light-sensing cells of the neuroretina, are responsible for converting light into electrical signals that can be interpreted by the brain. PR degeneration, including morphological and functional impairment of these cells, causes significant diminution of the retina's ability to detect light, with consequent loss of vision. Recent findings in ocular regenerative medicine have opened promising avenues to apply neuroprotective therapy, gene therapy, cell replacement therapy, and visual prostheses to the challenge of restoring vision. However, successful visual restoration in the clinical setting requires application of these therapeutic approaches at the appropriate stage of the retinal degeneration. In this review, firstly, we discuss the mechanisms of PR degeneration by focusing on the molecular mechanisms underlying cell death. Subsequently, innovations, recent developments, and promising treatments based on the stage of disorder progression are further explored. Then, the challenges to be addressed before implementation of these therapies in clinical practice are considered. Finally, potential solutions to overcome the current limitations of this growing research area are suggested. Overall, the majority of current treatment modalities are still at an early stage of development and require extensive additional studies, both pre-clinical and clinical, before full restoration of visual function in PR degeneration diseases can be realized.

Intravitreal and subretinal syngeneic bone marrow mononuclear stem cell transplantation improves photoreceptor survival but does not ameliorate retinal function in two rat models of retinal degeneration

PURPOSE

To study and compare effects of syngeneic bone marrow mononuclear stem cells (BM-MNCs) transplants on inherited retinal degeneration in two animal models with different etiologies: the RCS and the P23H-1 rats. To compare the safety and efficacy of two methods of intraocular delivery: subretinal and/or intravitreal.

METHODS

A suspension of BM-MNCs was injected subretinally or intravitreally in the left eyes of P23H-1 and RCS rats at post-natal day (P) 21. At different survival intervals after the injection: 7, 15, 30 or 60 days, the retinas were cross-sectioned, and photoreceptor survival and glial cell responses were investigated using immunodetection of cones (anti-cone arrestin), synaptic connections (anti-bassoon), microglia (anti-Iba-1), astrocytes and Müller cells (anti-GFAP). Electroretinographic function was also assessed longitudinally.

RESULTS

Intravitreal injections (IVIs) or subretinal injections (SRIs) of BM-MNCs did not produce adverse effects. The transplanted cells survived for up to 15 days but did not penetrate the retina. Both IVIs and SRIs increased photoreceptor survival, decreased synaptic degeneration and glial fibrillary acidic protein (GFAP) expression in Müller cells but did not modify microglial cell activation and migration or the electroretinographic responses.

CONCLUSIONS

Intravitreal and subretinal syngeneic BM-MNCs transplantation decreases photoreceptor degeneration and shows anti-gliotic effects on Müller cells but does not ameliorate retinal function. Moreover, syngeneic BM-MNCs transplants are more effective than the xenotransplants of these cells. BM-MNC transplantation has potential therapeutic effects that merit further investigation.

The Inability of Ex Vivo Expanded Mesenchymal Stem/Stromal Cells to Survive in Newborn Mice and to Induce Transplantation Tolerance

An encounter of the developing immune system with an antigen results in the induction of immunological areactivity to this antigen. In the case of transplantation antigens, the application of allogeneic hematopoietic cells induces a state of neonatal transplantation tolerance. This tolerance depends on the establishment of cellular chimerism, when allogeneic cells survive in the neonatally treated recipient. Since mesenchymal stem/stromal cells (MSCs) have been shown to have low immunogenicity and often survive in allogeneic recipients, we attempted to use these cells for induction of transplantation tolerance. Newborn (less than 24 h old) C57BL/6 mice were injected intraperitoneally with 5 × 10⁶ adipose tissue-derived MSCs isolated from allogeneic donors and the fate and survival of these cells were monitored. The impact of MSC application on the proportion of cell populations of the immune system and immunological reactivity was assessed. In addition, the survival of skin allografts in neonatally treated recipients was tested. We found that in vitro expanded MSCs did not survive in neonatal recipients, and the living MSCs were not detected few days after their application. Furthermore, there were no significant changes in the proportion of individual immune cell populations including CD4⁺ cell lineages, but we detected an apparent shift to the production of Th1 cytokines IL-2 and IFN-γ in neonatally treated mice. However, skin allografts in the MSC-treated recipients were promptly rejected. These results therefore show that in vitro expanded MSCs do not survive in neonatal recipients, but induce a cytokine imbalance without induction of transplantation tolerance.

Bone marrow-derived mononuclear stem cells in the treatment of retinal degenerations

Retinal degenerative diseases affecting the outer retina in its many forms (inherited, acquired or induced) are characterized by photoreceptor loss, and represent currently a leading cause of irreversible vision loss in the world. At present, there are very few treatments capable of preventing, recovering or reversing photoreceptor degeneration or the secondary retinal remodeling, which follows photoreceptor loss and can also cause the death of other retinal cells. Thus, these diseases are nowadays one of the greatest challenges in the field of ophthalmological research. Bone marrow derived-mononuclear stem cell transplantation has shown promising results for the treatment of photoreceptor degenerations. These cells may have the potential to slow down photoreceptor loss, and therefore should be applied in the early stages of photoreceptor degenerations. Furthermore, because of their possible paracrine effects, they may have a wide range of clinical applications, since they can potentially impact on several retinal cell types at once and photoreceptor degenerations can involve different cells and/or begin in one cell type and then affect adjacent cells. The intraocular injection of bone marrow derived-mononuclear stem cells also enhances the outcomes of other treatments aimed to protect photoreceptors. Therefore, it is likely that future investigations may combine bone marrow derived-mononuclear stem cell therapy with other systemic or intraocular treatments to obtain greater therapeutic effects in degenerative retinal diseases.

Intravenous infusion of small umbilical cord mesenchymal stem cells could enhance safety and delay retinal degeneration in RCS rats

Background

Human umbilical cord mesenchymal stem cells (UCMSCs) transplantation is a promising therapy for the treatment of retinitis pigmentosa (RP). However, intravenously infused cells may be blocked in the lung, increasing the risk of vascular obstruction, which needs to be optimized to further improve safety and efficacy.

Methods

We derived small UCMSCs (S-UCMSCs) from filtering UCMSCs with a 10-μm filter, and compared with UCMSCs by flow cytometry, directional differentiation culture and transcriptome sequencing. Then the S-UCMSCs and UCMSCs were intravenously infused in the Royal College Surgeons (RCS) rats to evaluate the safety and the efficacy.

Results

The diameter of S-UCMSCs ranged from 5.568 to 17.231 μm, with an average diameter of 8.636 ± 2.256 μm, which was significantly smaller than that of UCMSCs. Flow cytometry, immunofluorescence and transcriptome sequencing demonstrated that the S-UCMSCs and UCMSCs were the same kind of MSCs, and the S-UCMSCs were more proliferative. After the S-UCMSCs and UCMSCs were intravenously infused into the Royal College of Surgeons (RCS) rats at a dose of 1 × 10⁶ cells/rat, the S-UCMSCs blocked in the lungs were significantly fewer and disappeared more quickly than UCMSCs. The b wave of the flash electroretinogram was improved at 7 d, and the retinal outer nuclear layer thickness was thicker at 7 d and 14 d. The expression level of inflammation was inhibited, and the expression level of neurotrophic factors was upregulated in the retina and serum after transplantation.

Conclusions

S-UCMSCs intravenous infusion was safer than UCMSCs and could delay retinal degeneration and protect visual function in RCS rats, which may be a preferable therapeutic approach for RP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-021-02171-3.

Retinoic acid and taurine enhance differentiation of the human bone marrow stem cells into cone photoreceptor cells and retinal ganglion cells

Degeneration and apoptotic death of the photoreceptor cell-layer of retina are a major cause of irreversible blindness in the development era. The stem cell replacement therapy is one of the strategies for the retinal repairing. In addition, exogenous signals critically contribute to the direction of lineage decisions that causes the fate-restricted photoreceptor progenitors from stem cell progeny in culture. It has been found that epidermal growth factor (EGF), taurine, and retinoic acid (RA) initially act in the instructive as well as lineage-restricted way in the progenitor lineage for producing neuroretinal cells or photoreceptor like cells from stem cell. The study aims to investigate the effect of RA and taurine in differentiation of the human bone marrow stem cell into cone photoreceptors cells and retinal ganglion cells. Mesenchymal stem cell was derived from human bone marrow of the term delivery. Therefore, the cultured cells have been treated with Dulbecco's modified Eagle's medium (DMEM)/high glucose (H⁺ ). After the four-cell passage, basal medium was replaced with DMEM/F12 complemented with 50 μmol/L taurine, RA (1 µM) and EGF (1 µg/ml). Subsequently cellular change morphology was detected following 7 and 14 days. Then, gene expression of neuroretinal and photoreceptor cell biomarkers (CRX, OTX2, PKC-α, recoverin, and Rho) were examined by quantitative polymerase chain reaction (Q-PCR). Also, cells were cultured, fixed, and then immunocytochemical analyzed. Primary antibodies included CRX and Rho. Cellular morphology demonstrated spindle elongated morphology. Taurine alone and combination of RA upregulate neuroretinal and photoreceptor cell biomarkers in messenger RNA and protein levels but along with EGF have not significant effect. Our data showed that taurine combination with RA can differentiate bone marrow mesenchymal stem cells into neuroretinal or photoreceptor like cells in vitro that can offer an attractive treatment ground for transplantation in the cell-replacement therapy for some forms of the retinal degeneration.

Drug Delivery via the Suprachoroidal Space for the Treatment of Retinal Diseases

The suprachoroidal space (SCS), a potential space between the sclera and choroid, is becoming an applicable method to deliver therapeutics to the back of the eye. In recent years, a vast amount of research in the field has been carried out, with new discoveries in different areas of interest, such as imaging, drug delivery methods, pharmacokinetics, pharmacotherapies in preclinical and clinical trials and advanced therapies. The SCS can be visualized via advanced techniques of optical coherence tomography (OCT) in eyes with different pathologies, and even in healthy eyes. Drugs can be delivered easily and safely via hollow microneedles fitted to the length of the approximate thickness of the sclera. SCS injections were found to reach greater baseline concentrations in the target layers compared to intravitreal (IVT) injection, while agent clearance was faster with highly aqueous soluble molecules. Clinical trials with SCS injection of triamcinolone acetonide (TA) were executed with promising findings for patients with noninfectious uveitis (NIU), NIU implicated with macular edema and diabetic macular edema (DME). Gene therapy is evolving rapidly with viral and non-viral vectors that were found to be safe and efficient in preclinical trials. Here, we review these novel different aspects and new developments in clinical treatment of the posterior segment of the eye.

Transplanted Erythropoietin-Expressing Mesenchymal Stem Cells Promote Pro-survival Gene Expression and Protect Photoreceptors From Sodium Iodate-Induced Cytotoxicity in a Retinal Degeneration Model

Mesenchymal stem cells (MSC) are highly regarded as a potential treatment for retinal degenerative disorders like retinitis pigmentosa and age-related macular degeneration. However, donor cell heterogeneity and inconsistent protocols for transplantation have led to varied outcomes in clinical trials. We previously showed that genetically-modifying MSCs to express erythropoietin (MSC^EPO) improved its regenerative capabilities in vitro. Hence, in this study, we sought to prove its potential in vivo by transplanting MSCs^EPO in a rat retinal degeneration model and analyzing its retinal transcriptome using RNA-Seq. Firstly, MSCs^EPO were cultured and expanded before being intravitreally transplanted into the sodium iodate-induced model. After the procedure, electroretinography (ERG) was performed bi-weekly for 30 days. Histological analyses were performed after the ERG assessment. The retina was then harvested for RNA extraction. After mRNA-enrichment and library preparation, paired-end RNA-Seq was performed. Salmon and DESeq2 were used to process the output files. The generated dataset was then analyzed using over-representation (ORA), functional enrichment (GSEA), and pathway topology analysis tools (SPIA) to identify enrichment of key pathways in the experimental groups. The results showed that the MSC^EPO-treated group had detectable ERG waves (P <0.05), which were indicative of successful phototransduction. The stem cells were also successfully detected by immunohistochemistry 30 days after intravitreal transplantation. An initial over-representation analysis revealed a snapshot of immune-related pathways in all the groups but was mainly overexpressed in the MSC group. A subsequent GSEA and SPIA analysis later revealed enrichment in a large number of biological processes including phototransduction, regeneration, and cell death (P_adj <0.05). Based on these pathways, a set of pro-survival gene expressions were extracted and tabulated. This study provided an in-depth transcriptomic analysis on the MSC^EPO-treated retinal degeneration model as well as a profile of pro-survival genes that can be used as candidates for further genetic enhancement studies on stem cells.

Extracellular Vesicles from Human Adipose-Derived Mesenchymal Stem Cells: A Review of Common Cargos

In recent years, the interest in adipose tissue mesenchymal cell–derived extracellular vesicles (AT-MSC-EVs) has increasingly grown. Numerous articles support the potential of human AT-MSC-EVs as a new therapeutic option for treatment of diverse diseases in the musculoskeletal and cardiovascular systems, kidney, skin, and immune system, among others. This approach makes use of the molecules transported inside of EVs, which play an important role in cell communication and in transmission of macromolecules. However, to our knowledge, there is no database where essential information about AT-MSC-EVs cargo molecules is gathered for easy reference. The aim of this study is to describe the different molecules reported so far in AT-MSC- EVs, their main molecular functions, and biological processes in which they are involved. Recently, the presence of 591 proteins and 604 microRNAs (miRNAs) has been described in human AT-MSC-EVs. The main molecular function enabled by both proteins and miRNAs present in human AT-MSC-EVs is the binding function. Signal transduction and gene silencing are the biological processes in which a greater number of proteins and miRNAs from human AT-MSC-EVs are involved, respectively. In this review we highlight the therapeutics effects of AT-MSC-EVs related with their participation in relevant biological processes including inflammation, angiogenesis, cell proliferation, apoptosis and migration, among others.

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

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

Retinal cell transplantation in retinitis pigmentosa

Retinitis pigmentosa is the most common hereditary retinal disease. Dietary supplements, neuroprotective agents, cytokines, and lately, prosthetic devices, gene therapy, and optogenetics have been employed to slow down the retinal degeneration or improve light perception. Completing retinal circuitry by transplanting photoreceptors has always been an appealing idea in retinitis pigmentosa. Recent developments in stem cell technology, retinal imaging techniques, tissue engineering, and transplantation techniques have brought us closer to accomplish this goal. The eye is an ideal organ for cell transplantation due to a low number of cells required to restore vision, availability of safe surgical and imaging techniques to transplant and track the cells in vivo, and partial immune privilege provided by the subretinal space. Human embryonic stem cells, induced pluripotential stem cells, and especially retinal organoids provide an adequate number of cells at a desired developmental stage which may maximize integration of the graft to host retina. However, stem cells must be manufactured under strict good manufacturing practice protocols due to known tumorigenicity as well as possible genetic and epigenetic stabilities that may pose a danger to the recipient. Immune compatibility of stem cells still stands as a problem for their widespread use for retinitis pigmentosa. Transplantation of stem cells from different sources revealed that some of the transplanted cells may not integrate the host retina but slow down the retinal degeneration through paracrine mechanisms. Discovery of a similar paracrine mechanism has recently opened a new therapeutic path for reversing the cone dormancy and restoring the sight in retinitis pigmentosa.

The Chemokine Receptors Ccr5 and Cxcr6 Enhance Migration of Mesenchymal Stem Cells into the Degenerating Retina

Cell therapy approaches hold great potential for treating retinopathies, which are currently incurable. This study addresses the problem of inadequate migration and integration of transplanted cells into the host retina. To this end, we have identified the chemokines that were most upregulated during retinal degeneration and that could chemoattract mesenchymal stem cells (MSCs). The results were observed using a pharmacological model of ganglion/amacrine cell degeneration and a genetic model of retinitis pigmentosa, from both mice and human retinae. Remarkably, MSCs overexpressing Ccr5 and Cxcr6, which are receptors bound by a subset of the identified chemokines, displayed improved migration after transplantation in the degenerating retina. They also led to enhanced rescue of cell death and to preservation of electrophysiological function. Overall, we show that chemokines released from the degenerating retinae can drive migration of transplanted stem cells, and that overexpression of chemokine receptors can improve cell therapy-based regenerative approaches.

In vivo retinal imaging in translational regenerative research

Regenerative translational studies must include a longitudinal assessment of the changes in retinal structure and function that occur as part of the natural history of the disease and those that result from the studied intervention. Traditionally, retinal structural changes have been evaluated by histological analysis which necessitates sacrificing the animals. In this review, we describe key imaging approaches such as fundus imaging, optical coherence tomography (OCT), OCT-angiography, adaptive optics (AO), and confocal scanning laser ophthalmoscopy (cSLO) that enable noninvasive, non-contact, and fast in vivo imaging of the posterior segment. These imaging technologies substantially reduce the number of animals needed and enable progression analysis and longitudinal follow-up in individual animals for accurate assessment of disease natural history, effects of interventions and acute changes. We also describe the benefits and limitations of each technology, as well as outline possible future directions that can be taken in translational retinal imaging studies.

The road to restore vision with photoreceptor regeneration

Neuroretinal diseases are the predominant cause of irreversible blindness worldwide, mainly due to photoreceptor loss. Currently, there are no radical treatments to fully reverse the degeneration or even stop the disease progression. Thus, it is urgent to develop new biological therapeutics for these diseases on the clinical side. Stem cell-based treatments have become a promising therapeutic for neuroretinal diseases through the replacement of damaged cells with photoreceptors and some allied cells. To date, considerable efforts have been made to regenerate the diseased retina based on stem cell technology. In this review, we overview the current status of stem cell-based treatments for photoreceptor regeneration, including the major cell sources derived from different stem cells in pre-clinical or clinical trial stages. Additionally, we discuss herein the major challenges ahead for and potential new strategy toward photoreceptor regeneration.

Bone Marrow-Derived Mononuclear Cell Transplants Decrease Retinal Gliosis in Two Animal Models of Inherited Photoreceptor Degeneration

Inherited photoreceptor degenerations are not treatable diseases and a frequent cause of blindness in working ages. In this study we investigate the safety, integration and possible rescue effects of intravitreal and subretinal transplantation of adult human bone-marrow-derived mononuclear stem cells (hBM-MSCs) in two animal models of inherited photoreceptor degeneration, the P23H-1 and the Royal College of Surgeons (RCS) rat. Immunosuppression was started one day before the injection and continued through the study. The hBM-MSCs were injected in the left eyes and the animals were processed 7, 15, 30 or 60 days later. The retinas were cross-sectioned, and L- and S- cones, microglia, astrocytes and Müller cells were immunodetected. Transplantations had no local adverse effects and the CD45+ cells remained for up to 15 days forming clusters in the vitreous and/or a 2–3-cells-thick layer in the subretinal space after intravitreal or subretinal injections, respectively. We did not observe increased photoreceptor survival nor decreased microglial cell numbers in the injected left eyes. However, the injected eyes showed decreased GFAP immunoreactivity. We conclude that intravitreal or subretinal injection of hBM-MSCs in dystrophic P23H-1 and RCS rats causes a decrease in retinal gliosis but does not have photoreceptor neuroprotective effects, at least in the short term. However, this treatment may have a potential therapeutic effect that merits further investigation.

Cytokine interplay among the diseased retina, inflammatory cells and mesenchymal stem cells - a clue to stem cell-based therapy

Retinal degenerative disorders, such as diabetic retinopathy, retinitis pigmentosa, age-related macular degeneration or glaucoma, represent the most common causes of loss of vision and blindness. In spite of intensive research, treatment options to prevent, stop or cure these diseases are limited. Newer therapeutic approaches are offered by stem cell-based therapy. To date, various types of stem cells have been evaluated in a range of models. Among them, mesenchymal stem/stromal cells (MSCs) derived from bone marrow or adipose tissue and used as autologous cells have been proposed to have the potential to attenuate the negative manifestations of retinal diseases. MSCs delivered to the vicinity of the diseased retina can exert local anti-inflammatory and repair-promoting/regenerative effects on retinal cells. However, MSCs also produce numerous factors that could have negative impacts on retinal regeneration. The secretory activity of MSCs is strongly influenced by the cytokine environment. Therefore, the interactions among the molecules produced by the diseased retina, cytokines secreted by inflammatory cells and factors produced by MSCs will decide the development and propagation of retinal diseases. Here we discuss the interactions among cytokines and other factors in the environment of the diseased retina treated by MSCs, and we present results supporting immunoregulatory and trophic roles of molecules secreted in the vicinity of the retina during MSC-based therapy.

Treatment with Stem Cells from Human Exfoliated Deciduous Teeth and Their Derived Conditioned Medium Improves Retinal Visual Function and Delays the Degeneration of Photoreceptors

Retinitis pigmentosa (RP) is a hereditary disease characterized by degeneration and the loss of photoreceptors. Stem cell-based therapy has emerged as a promising strategy for treating RP. Stem cells from exfoliated deciduous teeth (SHEDs), a type of mesenchymal stem cell from human exfoliated deciduous teeth, have the potential to differentiate into photoreceptor-like cells under specific induction in vitro. It has been confirmed that through paracrine secreta, SHEDs exert neurotrophic, angiogenic, immunoregulatory, and antiapoptotic functions in injured tissues. This study was designed to determine whether retinal-differentiated SHEDs and the conditioned medium derived from SHEDs (SHEDs-CM) have therapeutic effects in a mouse model of RP. The results showed that both SHEDs and SHEDs-CM improved electroretinogram responses, ameliorated photoreceptor degeneration, and maintained the structure of the outer segments of photoreceptors. The therapeutic effects were related to antiapoptotic activity of SHEDs and SHEDs-CM. Thus, SHEDs may be a promising stem cell source for treating retinal degeneration.

Therapeutic Strategies for Attenuation of Retinal Ganglion Cell Injury in Optic Neuropathies: Concepts in Translational Research and Therapeutic Implications

Retinal ganglion cell (RGC) death is the central and irreversible endpoint of optic neuropathies. Current management of optic neuropathies and glaucoma focuses on intraocular pressure-lowering treatment which is insufficient. As such, patients are effectively condemned to irreversible visual impairment. This review summarizes experimental treatments targeting RGCs over the last decade. In particular, we examine the various treatment modalities and determine their viability and limitations in translation to clinical practice. Experimental RGC treatment can be divided into (1) cell replacement therapy, (2) neuroprotection, and (3) gene therapy. For cell replacement therapy, difficulties remain in successfully integrating transplanted RGCs from various sources into the complex neural network of the human retina. However, there is significant potential for achieving full visual restoration with this technique. Neuroprotective strategies, in the form of pharmacological agents, nutritional supplementation, and neurotrophic factors, are viable strategies with encouraging results from preliminary noncomparative interventional case series. It is important to note, however, that most published studies are focused on glaucoma, with few treating optic neuropathies of other etiologies. Gene therapy, through the use of viral vectors, has shown promising results in clinical trials, particularly for diseases with specific genetic mutations like Leber's hereditary optic neuropathy. This treatment technique can be further extended to nonhereditary diseases, through transfer of genes promoting cell survival and neuroprotection. Crucially though, for gene therapy, teratogenicity remains a significant issue in translation to clinical practice.

Empowering Mesenchymal Stem Cells for Ocular Degenerative Disorders

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

Differentiation of Stem Cells from Human Exfoliated Deciduous Teeth into Retinal Photoreceptor-Like Cells and Their Sustainability In Vivo

Retinal degeneration is characterized by the progressive loss of photoreceptors, and stem cell therapy has become a promising strategy. Many studies have reported that mesenchymal stem cell transplantation can sustain retinal structure and prolong retinal functions based on two mechanisms. One is cell replacement, and the other is the paracrine action of stem cells. Cells from human exfoliated deciduous teeth (SHEDs) show characteristics typical of mesenchymal stem cells. They are derived from the neural crest and are a potential cellular source for neural regeneration in stem cell therapy. In this study, we explored the potential of SHEDs to be induced towards the retinal photoreceptor phenotype and to be sustainable in an animal model of retinal degeneration. A factor-cocktail protocol was used to induce SHEDs towards retinal photoreceptors for 24 days, and the characteristics of the induced cells were identified in terms of morphological changes, biomarker expression and subcellular distribution, and calcium influx. SHEDs were labeled with firefly luciferase for in vivo tracking by bioluminescent imaging and then transplanted into the subretinal space of mice. Our results showed that SHEDs successfully transdifferentiated into photoreceptor-like cells, which displayed neuron-like morphology, and expressed specific genes and proteins associated with retinal precursors, photoreceptor precursors, and mature photoreceptors. In addition, calcium influx was significantly greater in the retinal-induced than in noninduced SHEDs. In vivo tracking confirmed at least 2 weeks of good survival by bioluminescent imaging and 3 months of sustainability of SHEDs by histological analysis. We conclude that SHEDs have the potential to transdifferentiate into retinal photoreceptor-like cells in vitro and maintain good viability in vivo after transplantation into mice with a normal immune system. This demonstrates preliminary success in generating photoreceptor-like cells from SHEDs and applying SHEDs in treating retinal degeneration.

Evaluation of visual function in Royal College of Surgeon rats using a depth perception visual cliff test

Preserving of vision is the main goal in vision research. The presented research evaluates the preservation of visual function in Royal College of Surgeon (RCS) rats using a depth perception test. Rats were placed on a stage with one side containing an illusory steep drop ("cliff") and another side with a minimal drop ("table"). Latency of stage dismounting and the percentage of rats that set their first foot on the "cliff" side were determined. Nondystrophic Long-Evans (LE) rats were tested as control. Electroretinogram and histology analysis were used to determine retinal function and structure. Four-week-old RCS rats presented a significantly shorter mean latency to dismount the stage compared with 6-week-old rats (mean ± standard error, 13.7 ± 1.68 vs. 20.85 ± 6.5 s, P = 0.018). Longer latencies were recorded as rats aged, reaching 45.72 s in 15-week-old rats (P &lt; 0.00001 compared with 4-week-old rats). All rats at the age of 4 weeks placed their first foot on the table side. By contrast, at the age of 8 weeks, 28.6% rats dismounted on the cliff side and at the age of 10 and 15 weeks, rats randomly dismounted the stage to either table or cliff side. LE rats dismounted the stage faster than 4-week-old RCS rats, but the difference was not statistically significant (7 ± 1.58 s, P = 0.057) and all LE rats dismounted on the table side. The latency to dismount the stage in RCS rats correlated with maximal electroretinogram b-wave under dark and light adaptation (Spearman's rho test = -0.603 and -0.534, respectively, all P &lt; 0.0001), outer nuclear layer thickness (Spearman's rho test = -0.764, P = 0.002), and number of S- and M-cones (Spearman's rho test = -0.763 [P = 0.002], and -0.733 [P = 0.004], respectively). The cliff avoidance test is an objective, quick, and readily available method for the determination of RCS rats' visual function.

In vivo MRI assessment of bioactive magnetic iron oxide/human serum albumin nanoparticle delivery into the posterior segment of the eye in a rat model of retinal degeneration

Background

Retinal degeneration diseases affect millions of patients worldwide and lead to incurable vision loss. These diseases are caused by pathologies in the retina and underlying choroid, located in the back of the eye. One of the major challenges in the development of treatments for these blinding diseases is the safe and efficient delivery of therapeutics into the back of the eye. Previous studies demonstrated that narrow size distribution core–shell near infra-red fluorescent iron oxide (IO) nanoparticles (NPs) coated with human serum albumin (HSA, IO/HSA NPs) increase the half-life of conjugated therapeutic factors, suggesting they may be used for sustained release of therapeutics. In the present study, the in vivo tracking by MRI and the long term safety of IO/HSA NPs delivery into the suprachoroid of a rat model of retinal degeneration were assessed.

Results

Twenty-five Royal College of Surgeons (RCS) pigmented rats received suprachoroidal injection of 20-nm IO/HSA NPs into the right eye. The left eye was not injected and used as control. Animals were examined by magnetic resonance imaging (MRI), electroretinogram (ERG) and histology up to 30 weeks following injection. IO/HSA NPs were detected in the back part of the rats’ eyes up to 30 weeks following injection by MRI, and up to 6 weeks by histology. No significant differences in retinal structure and function were observed between injected and non-injected eyes. There was no significant difference in the weight of IO/HSA NP-injected animals compared to non-injected rats.

Conclusions

MRI could track the nanoparticles in the posterior segment of the injected eyes demonstrating their long-term persistence, and highlighting the possible use of MRI for translational studies in animals and in future clinical studies. Suprachoroidal injection of IO/HSA NPs showed no sign of adverse effects on retinal structure and function in a rat model of retinal degeneration, suggesting that suprachoroidal delivery of IO/HSA NPs is safe and that these NPs may be used in future translational and clinical studies for extended release drug delivery at the back of the eye.

Electronic supplementary material

The online version of this article (10.1186/s12951-018-0438-y) contains supplementary material, which is available to authorized users.

A Promising Tool in Retina Regeneration: Current Perspectives and Challenges When Using Mesenchymal Progenitor Stem Cells in Veterinary and Human Ophthalmological Applications

Visual impairment is a common ailment of the current world population, with more exposure to CCD screens and fluorescent lighting, approximately 285 billion people suffer from this deficiency and 13% of those are considered clinically blind. More common causes for visual impairment include age-related macular degeneration (AMD), glaucoma and diabetic retinopathy (Zhu et al. Molecular Medicine Reports, 2015; Kolb et al. 2007; Machalińska et al. Current Eye Research, 34(9),748-760, 2009) among a few. As cases of retinal and optic nerve diseases rise, it is vital to find a treatment, which has led to investigation of the therapeutic potential of various stem cells types (Bull et al. Investigative Opthalmology & Visual Science, 50(9), 4244, 2009; Bull et al. Investigative Opthalmology & Visual Science, 49(8), 3449, 2008; Yu et al. Biochemical and Biophysical Research Communications, 344(4), 1071-1079, 2006; Na et al. Graefe's Archive for Clinical and Experimental Ophthalmology, 247(4), 503-514, 2008). In previous studies, some of the stem cell variants used include human Muller SCs and bone marrow derived SCs. Some of the regenerative potential characteristics of mesenchymal progenitor stem cells (MSCs) include their multilineage differentiation potential, their immunomodulatory effects, their high proliferative activity, they can be easily cultured in vitro, and finally their potential to synthesize and secrete membrane derived vesicles rich in growth factors, mRNA and miRNA which possibly aid in regulation of tissue damage regeneration. These facts alone, explain why MSCs are so widely used in clinical trials, 350 up to date (Switonski, Reproductive Biology, 14(1), 44-50, 2014). Animal studies have demonstrated that sub-retinal transplantation of MSCs delays retinal degeneration and preserves retinal function through trophic response (Inoue et al. Experimental Eye Research, 85(2), 234-241, 2007). Umbilical cord derived MSCs (UC/MSCs) have also been shown to contain neuroprotective features of ganglion cells in rat studies (Zwart et al. Experimental Neurology, 216(2), 439-448, 2009). This review aims to present current MSC therapies in practice, as well as their retinal regeneration potential in animal models, and their innovative prospects for treatment of human retinal diseases.

Establishing a Surgical Procedure for Rhesus Epiretinal Scaffold Implantation with HiPSC-Derived Retinal Progenitors

Background

To develop an effective surgical procedure for cellular scaffold epiretinal implantation in rhesus, facilitating subsequent epiretinal stem cell transplantation.

Methods

Retinal progenitors were seeded onto a poly(lactic-co-glycolic) acid (PLGA) scaffold. First, the cellular scaffolds were delivered by 18G catheter or retinal forceps into rabbit epiretinal space (n = 50). Then, the cell survival rate was evaluated by Cell Counting Kit-8 (CCK-8). Second, three methods of scaffold fixation, including adhesion after gas-liquid exchange (n = 1), tamponade by hydrogel (n = 1), and fixation by retinal tacks (n = 4), were performed in rhesus monkeys. After one month, fundus photography and SD-OCT were performed to assess the outcomes, and histological examination was performed to evaluate proliferation.

Results

The cell survival rate was significantly higher in the catheter group. Follow-up examination showed that retinal tack fixation was the only method to maintain the scaffolds attached to host retina for at least 3 weeks, which is the minimal time required for cell integration. Histological staining demonstrated slight glial fibrillary acidic protein (GFAP) accumulation in the retinal tack insertion area.

Conclusions

The established surgical procedure offers a new insight into research of epiretinal cell replacement therapy in rhesus eyes. The successful delivery and long-term fixation provide a prerequisite for cell migration and integration.

The suprachoroidal space as a route of administration to the posterior segment of the eye

The suprachoroidal space (SCS) is a potential space between the sclera and choroid that traverses the circumference of the posterior segment of the eye. The SCS is an attractive site for drug delivery because it targets the choroid, retinal pigment epithelium, and retina with high bioavailability, while maintaining low levels elsewhere in the eye. Indeed, phase III clinical trials are investigating the safety and efficacy of SCS drug delivery. Here, we review the anatomy and physiology of the SCS; methods to access the SCS; kinetics of SCS drug delivery; strategies to target within the SCS; current and potential clinical indications; and the safety and efficacy of this approach in preclinical animal studies and clinical trials.

Cellular Reparative Mechanisms of Mesenchymal Stem Cells for Retinal Diseases

The use of multipotent mesenchymal stem cells (MSCs) has been reported as promising for the treatment of numerous degenerative disorders including the eye. In retinal degenerative diseases, MSCs exhibit the potential to regenerate into retinal neurons and retinal pigmented epithelial cells in both in vitro and in vivo studies. Delivery of MSCs was found to improve retinal morphology and function and delay retinal degeneration. In this review, we revisit the therapeutic role of MSCs in the diseased eye. Furthermore, we reveal the possible cellular mechanisms and identify the associated signaling pathways of MSCs in reversing the pathological conditions of various ocular disorders such as age-related macular degeneration (AMD), retinitis pigmentosa, diabetic retinopathy, and glaucoma. Current stem cell treatment can be dispensed as an independent cell treatment format or with the combination of other approaches. Hence, the improvement of the treatment strategy is largely subjected by our understanding of MSCs mechanism of action.

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.

Progranulin increases phagocytosis by retinal pigment epithelial cells in culture

Retinal pigment epithelium (RPE) cells take part in retinal preservation, such as phagocytizing the shed photoreceptor outer segments (POS), every day. The incomplete phagocytic function accelerates RPE degeneration and formation of the toxic by-product lipofuscin. Excessive lipofuscin accumulation is characteristic of various blinding diseases in the human eye. Progranulin is a cysteine-rich protein that has multiple biological activities, and it has a high presence in the retina. Progranulin has been recognized to be involved in macrophage phagocytosis in the brain. The purpose of this study is to determine whether progranulin influences phagocytosis by RPE cells. All experiments were performed on primary human RPE (hRPE) cells in culture. pHrodo was used to label the isolated porcine POS, and quantification of pHrodo fluorescence was used to determine the degree of phagocytosis. Western blotting and immunohistochemistry of key proteins involved in phagocytosis were used to clarify the mechanism of progranulin. Progranulin increased RPE phagocytosis in hydrogen peroxide-treated and nontreated RPE cells. The phosphorylated form of Mer tyrosine kinase, which is important for POS internalization, was significantly increased in the progranulin-exposed cells. This increase was attenuated by SU11274, an inhibitor of hepatic growth factor receptor. Under the oxidative stress condition, exposure to progranulin led to an approximately twofold increase in integrin alpha-v, which is associated with the first step in recognition of POS by RPE cells. These results suggest that progranulin could be an effective stimulator for RPE phagocytosis and could repair RPE function. © 2017 Wiley Periodicals, Inc.

Progress of stem/progenitor cell-based therapy for retinal degeneration

Retinal degeneration (RD), such as age-related macular degeneration (AMD) and retinitis pigmentosa, is one of the leading causes of blindness. Presently, no satisfactory therapeutic options are available for these diseases principally because the retina and retinal pigmented epithelium (RPE) do not regenerate, although wet AMD can be prevented from further progression by anti-vascular endothelial growth factor therapy. Nevertheless, stem/progenitor cell approaches exhibit enormous potential for RD treatment using strategies mainly aimed at the rescue and replacement of photoreceptors and RPE. The sources of stem/progenitor cells are classified into two broad categories in this review, which are (1) ocular-derived progenitor cells, such as retinal progenitor cells, and (2) non-ocular-derived stem cells, including embryonic stem cells, induced pluripotent stem cells, and mesenchymal stromal cells. Here, we discuss in detail the progress in the study of four predominant stem/progenitor cell types used in animal models of RD. A short overview of clinical trials involving the stem/progenitor cells is also presented. Currently, stem/progenitor cell therapies for RD still have some drawbacks such as inhibited proliferation and/or differentiation in vitro (with the exception of the RPE) and limited long-term survival and function of grafts in vivo. Despite these challenges, stem/progenitor cells represent the most promising strategy for RD treatment in the near future.

Therapeutic efficacy of neural stem cells originating from umbilical cord-derived mesenchymal stem cells in diabetic retinopathy

The aim of this study was to evaluate the effects of intravitreal injection of neural stem cells (NSCs) originating from human umbilical cord-derived mesenchymal stem cells (UC-MSCs) on neurodegeneration of diabetic retinopathy (DR) in rats. UC-MSCs were isolated and passaged, followed by induction to NSCs in neural differentiation medium. Four weeks following NSC transplantation, treatment attenuated retinal vascular dysfunction compared with non-treated rats, and BDNF and Thy-1 expression was significantly higher in the treated group than in the control group. Treatment of diabetic rats with NSCs prevented the decrease in BDNF levels caused by diabetes. The average leakage of Evans Blue (EB) dye in the treated group was significantly less than that in the control group. These morphological improvements were accompanied by a restoration of vision, as documented by F-ERG. NSCs originating from MSCs demonstrated a neuroprotective effect by increasing the number of surviving RGCs and significantly reducing the progression of DR. Thus, transplantation of NSCs could be a novel strategy for the treatment of neurodegeneration in DR.

Combined transplantation of human mesenchymal stem cells and human retinal progenitor cells into the subretinal space of RCS rats

Retinitis pigmentosa (RP) is one of hereditary retinal diseases characterized by the loss of photoreceptors. Cell transplantation has been clinically applied to treat RP patients. Human retinal progenitor cells (HRPCs) and human bone marrow-derived mesenchymal stem cells (HBMSCs) are the two commonly and practically used stem cells for transplantation. Since combined transplantation could be a promising way to integrate the advantages of both stem cell types, we transplanted HRPCs and HBMSCs into the subretinal space (SRS) of Royal College of Surgeons (RCS) rats. We report that HRPCs/HBMSCs combined transplantation maintains the electroretinogram results much better than HRPCs or HBMSCs single transplantations. The thickness of outer nuclear layer also presented a better outcome in the combined transplantation. Importantly, grafted cells in the combination migrated better, both longitudinally and latitudinally, than single transplantation. The photoreceptor differentiation of grafted cells in the retina of RCS rats receiving combined transplantation also showed a higher ratio than single transplantation. Finally, activation of microglia and the gliosis of Müller cells were more effectively suppressed in combined transplantation, indicating better immunomodulatory and anti-gliosis effects. Taken together, combining the transplantation of HRPCs and HBMSCs is a more effective strategy in stem cell-based therapy for retinal degenerative diseases.

Signal Factors Secreted by 2D and Spheroid Mesenchymal Stem Cells and by Cocultures of Mesenchymal Stem Cells Derived Microvesicles and Retinal Photoreceptor Neurons

We aim to identify levels of signal factors secreted by MSCs cultured in 2D monolayers (2D-MSCs), spheroids (spheroids MSCs), and cocultures of microvesicles (MVs) derived from 2D-MSCs or spheroid MSCs and retinal photoreceptor neurons. We seeded 2D-MSCs, spheroid MSCs, and cells derived from spheroids MSCs at equal numbers. MVs isolated from all 3 culture conditions were incubated with 661W cells. Levels of 51 signal factors in conditioned medium from those cultured conditions were quantified with bead-based assay. We found that IL-8, IL-6, and GROα were the top three most abundant signal factors. Moreover, compared to 2D-MSCs, levels of 11 cytokines and IL-2Rα were significantly increased in conditioned medium from spheroid MSCs. Finally, to test if enhanced expression of these factors reflects altered immunomodulating activities, we assessed the effect of 2D-MSC-MVs and 3D-MSC-MVs on CD14+ cell chemoattraction. Compared to 2D-MSC-MVs, 3D-MSC-MVs significantly decreased the chemotactic index of CD14+ cells. Our results suggest that spheroid culture conditions improve the ability of MSCs to selectively secrete signal factors. Moreover, 3D-MSC-MVs also possessed an enhanced capability to promote signal factors secretion compared to 2D-MSC-MVs and may possess enhanced immunomodulating activities and might be a better regenerative therapy for retinal degenerative diseases.

Adult Human Peripheral Blood Mononuclear Cells Are Capable of Producing Neurocyte or Photoreceptor-Like Cells That Survive in Mouse Eyes After Preinduction With Neonatal Retina

: Adult human peripheral blood mononuclear cells (hPBMCs) exhibit pluripotency in vitro and so may be a valuable cell source for regenerative therapies. The efficacy of such therapies depends on the survival, differentiation, migration, and integration capacity of hPBMCs in specific tissues. In this study, we examined these capacities of transplanted hPBMCs in mouse retina as well functional improvement after transplant. We isolated hPBMCs and preinduced them for 4 days in media preconditioned with postnatal day 1 rat retina explants. Preinduction increased the proportions of hPBMCs expressing neural stem cell, neural progenitor cell, or photoreceptor markers as revealed by immunofluorescent staining, flow cytometry, and quantitative real-time polymerase chain reaction. Preinduced hPBMCs were transplanted into the subretinal space of retinal degenerative slow (RDS) and retinal degeneration 1 (RD1) mice. At 1, 3, and 6 months after transplantation, treated eyes of RDS mice were collected and cell phenotype was studied by immunofluorescent staining. Preinduced hPBMCs survived in the subretinal space; migrated away from the injection site and into multiple retinal layers; and expressed neural stem cell, neuronal, and photoreceptor markers. Finally, we assessed RD1 retinal function after subretinal transplantation and found significant improvement at 3 months after transplantation. The ease of harvesting, viability in vivo, capacity to express neuronal and photoreceptor proteins, and capacity for functional enhancement suggest that hPBMCs are potential candidates for cell replacement therapy to treat retinal degenerative diseases.

SIGNIFICANCE

This study provides support for the use of peripheral blood mononuclear cells (PBMCs) as a potential source of pluripotent stem cells for treating retinal degeneration. First, this study demonstrated that PBMCs can differentiate into retinal neuron-like cells in vitro and in vivo. Second, some transplanted cells expressed markers for neural progenitors, mature neurons, or photoreceptors at 1, 3, and 6 months after subretinal injection. Finally, this study showed that PBMC transplantation can improve the function of a degenerated retina.