Grafted c-kit+/SSEA1- eye-wall progenitor cells delay retinal degeneration in mice by regulating neural plasticity and forming new graft-to-host synapses

Stem cell factor protects against chronic ischemic retinal injury by modulating on neurovascular unit

Retinal ischemia is a significant factor in various vision-threatening diseases, but effective treatments are currently lacking. This study explores the potential of stem cell factor (SCF) in regulating the neurovascular unit as a therapeutic intervention for retinal ischemic diseases. A chronic retinal ischemia model was established in Brown Norway rats using bilateral common carotid artery occlusion (BCCAO). Subsequent SCF treatment resulted in a remarkable recovery of retinal function, as indicated by electroretinogram, light/dark transition test, and optokinetic head tracking test results. Histological examination demonstrated a significant increase in the number of retinal neurons and an overall thickening of the retina. Immunofluorescence confirmed these findings and further demonstrated that SCF treatment regulated retinal remodeling. Notably, SCF treatment ameliorated the disrupted expression of synaptic markers in the control group's BCCAO rats and suppressed the activation of Müller cells and microglia. Retinal whole-mount analysis revealed a significant improvement in the abnormalities in retinal vasculature following SCF treatment. Transcriptome sequencing analysis revealed that SCF-induced transcriptome changes were closely linked to the Wnt7 pathway. Key members of the Wnt7 pathway, exhibited significant upregulation following SCF treatment. These results underscore the protective role of SCF in the neurovascular unit of retinal ischemia rats by modulating the Wnt7 pathway. SCF administration emerges as a promising therapeutic strategy for retinal ischemia-related diseases, offering potential avenues for future clinical interventions.

Identifying Hmga2 preserving visual function by promoting a shift of Müller glia cell fate in mice with acute retinal injury

BACKGROUND

Unlike in lower vertebrates, Müller glia (MG) in adult mammalian retinas lack the ability to reprogram into neurons after retinal injury or degeneration and exhibit reactive gliosis instead. Whether a transition in MG cell fate from gliosis to reprogramming would help preserve photoreceptors is still under exploration.

METHODS

A mouse model of retinitis pigmentosa (RP) was established using MG cell lineage tracing mice by intraperitoneal injection of sodium iodate (SI). The critical time point for the fate determination of MG gliosis was determined through immunohistochemical staining methods. Then, bulk-RNA and single-cell RNA seq techniques were used to elucidate the changes in RNA transcription of the retina and MG at that time point, and new genes that may determine the fate transition of MG were screened. Finally, the selected gene was specifically overexpressed in MG cells through adeno-associated viruses (AAV) in the mouse RP model. Bulk-RNA seq technique, immunohistochemical staining methods, and visual function testing were used to elucidate and validate the mechanism of new genes function on MG cell fate transition and retinal function.

RESULTS

Here, we found the critical time point for MG gliosis fate determination was 3 days post SI injection. Hmga2 was screened out as a candidate regulator for the cell fate transition of MG. After retinal injury caused by SI, the Hmga2 protein is temporarily and lowly expressed in MG cells. Overexpression of Hmga2 in MG down-regulated glial cell related genes and up-regulated photoreceptor related genes. Besides, overexpressing Hmga2 exclusively to MG reduced MG gliosis, made MG obtain cone's marker, and retained visual function in mice with acute retinal injury.

CONCLUSION

Our results suggested the unique reprogramming properties of Hmga2 in regulating the fate transition of MG and neuroprotective effects on the retina with acute injury. This work uncovers the reprogramming ability of epigenetic factors in MG.

Sstr2 Defines the Cone Differentiation-Competent Late-Stage Retinal Progenitor Cells in the Developing Mouse Retina

Cone cell death is a characteristic shared by various retinal degenerative disorders, such as cone-rod dystrophy, Stargardt disease, achromatopsia, and retinitis pigmentosa. This leads to conditions like color blindness and permanently impaired visual acuity. Stem cell therapy focused on photoreceptor replacement holds promise for addressing these conditions. However, identifying surface markers that aid in enriching retinal progenitor cells (RPCs) capable of differentiating into cones remains a complex task. In this study, we employed single-cell RNA sequencing to scrutinize the transcriptome of developing retinas in C57BL/6J mice. This revealed the distinctive expression of somatostatin receptor 2 (Sstr2), a surface protein, in late-stage RPCs exhibiting the potential for photoreceptor differentiation. In vivo lineage tracing experiments verified that Sstr2+ cells within the late embryonic retina gave rise to cones, amacrine and horizontal cells during the developmental process. Furthermore, Sstr2+ cells that were isolated from the late embryonic mouse retina displayed RPC markers and exhibited the capability to differentiate into cones in vitro. Upon subretinal transplantation into both wild-type and retinal degeneration 10 (rd10) mice, Sstr2+ cells survived and expressed cone-specific markers. This study underscores the ability of Sstr2 to enrich late-stage RPCs primed for cone differentiation to a large extent. It proposes the utility of Sstr2 as a biomarker for RPCs capable of generating cones for transplantation purposes.

Regeneration of periodontal bone defects with mesenchymal stem cells in animal models. Systematic review and meta-analysis

The aim of this study was to evaluate the efficacy of mesenchymal stem cells (MSCs) in the regeneration of periodontal bone defects in animal models. A systematic review and meta-analysis were conducted following the PRISMA guidelines, and the study was recorded in PROSPERO under reference number CDR42021247462. The PICO question was: is periodontal regeneration (cementum, periodontal ligament and alveolar bone) with MSCs more effective than other techniques? Three groups were considered: Group 1: MSCs alone or mixed with regenerative materials. Group 2: only regenerative materials. Group 3: no regenerative material nor MSCs. The search was conducted using MeSH with a total of 18 articles for qualitative analysis and 5 for quantitative analysis. For the meta-analysis, a modification of the effect size algorithm was developed, which considered a comparison of means between treatments using the Student's t sample distribution. When comparing the effect size between Group 1 and Group 2, the effect size for the new cementum was 2.83 mm with an estimated confidence interval of 95% (CI 95%) between 0.48 and 5.17 mm. When considering the fit to a random-effects model, the combined variance (τ²) was 6.1573 mm, with a standard deviation (SD) of 5.6008 mm and a percentage of total heterogeneity I² of 92.33% (p < 0.0001). For new bone, the effect size was 0.88 mm, CI 95% - 0.25 to 2.01 mm, τ² = 1.3108 mm (SD = 1.2021 mm) and I² = 80.46%, p = 0.0004). With regard to the new periodontal ligament, it was not possible for the meta-analysis to be performed. MSCs have a greater capacity for tissue regeneration in root cementum than in alveolar bone compared to other regenerative materials.

Stimulation of C-Kit+ Retinal Progenitor Cells by Stem Cell Factor Confers Protection Against Retinal Degeneration

C-kit/CD117, expressed in a series of tissue-specific progenitor cells, plays an important role in tissue regeneration and tissue homeostasis. We previously demonstrated that organoid-derived c-kit⁺ retinal progenitor cells can facilitate the restoration of degenerated retina. Meanwhile, we have identified a population of endogenous c-kit⁺ cells in retinas of adult mouse. However, the exact role of these cells in retinal degeneration remains unclear. Here, we demonstrated that stimulation of endogenous c-kit⁺ cells by stem cell factor (SCF) conferred protection against retinal degeneration. Retinal degeneration was induced by intravitreal injection of N-methyl-D-aspartate (NMDA). NMDA challenge increased the total number of c-kit⁺ cells in the retinal ganglion cell layer (GCL), while deregulated the protein level of SCF, which was mainly expressed in Müller cells. Both flash electroretinogram (fERG) and light/dark transition tests showed that intravitreal injection of SCF effectively improved the visual function of NMDA-treated mice. Mechanistically, SCF administration not only prevented the loss of retinal ganglion cells (RGCs), but also maintained the function of RGCs as quantified by fERG. Further, we performed transcriptome sequencing analysis of the retinal cells isolated from SCF-treated mice and the parallel control. Gene Ontology analysis showed that SCF-induced transcriptome changes were closely correlated with eye development-related pathways. Crystallins and several protective factors such as Pitx3 were significantly upregulated by SCF treatment. Our results revealed the role of SCF stimulated c-kit⁺ cells in the protection of RGCs in NMDA-treated mice, via inhibiting the loss of RGCs. Administration of SCF can act as a potent strategy for treating retinal degeneration-related diseases.

Retinal Organoid Technology: Where Are We Now?

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

Synaptic repair and vision restoration in advanced degenerating eyes by transplantation of retinal progenitor cells

Stem cell transplantation shows enormous potential for treatment of incurable retinal degeneration (RD). To determine if and how grafts connect with the neural circuits of the advanced degenerative retina (ADR) and improve vision, we perform calcium imaging of GCaMP5-positive grafts in retinal slices. The organoid-derived C-Kit⁺/SSEA1^- (C-Kit⁺) retinal progenitor cells (RPCs) become synaptically organized and build spontaneously active synaptic networks in three major layers of ADR. Light stimulation of the host photoreceptors elicits distinct neuronal responses throughout the graft RPCs. The graft RPCs and their differentiated offspring cells in inner nuclear layer synchronize their activities with the host cells and exhibit presynaptic calcium flux patterns that resemble intact retinal neurons. Once graft-to-host network is established, progressive vision loss is stabilized while control eyes continually lose vision. Therefore, transplantation of organoid-derived C-Kit⁺ RPCs can form functional synaptic networks within ADR and it holds promising avenue for advanced RD treatment.

Biosafety of a 3D-printed intraocular lens made of a poly(acrylamide-co-sodium acrylate) hydrogel in vitro and in vivo

AIM

To assess the biosafety of a poly(acrylamide-co-sodium acrylate) hydrogel (PAH) as a 3D-printed intraocular lens (IOL) material.

METHODS

The biosafety of PAH was first evaluated in vitro using human lens epithelial cells (LECs) and the ARPE19 cell line, and a cell counting kit-8 (CCK-8) assay was performed to investigate alterations in cell proliferation. A thin film of PAH and a conventional IOL were intraocularly implanted into the eyes of New Zealand white rabbits respectively, and a sham surgery served as control group. The anterior segment photographs, intraocular pressure (IOP), blood parameters and electroretinograms (ERG) were recorded. Inflammatory cytokines in the aqueous humor, such as TNFα and IL-8, were examined by ELISA. Cell apoptosis of the retina was investigated by TUNEL assay, and macroPAHge activation was detected by immunostaining.

RESULTS

PAH did not slow cell proliferation when cocultured with human LECs or ARPE19 cells. The implantation of a thin film of a 3D-printed IOL composed of PAH did not affect the IOP, blood parameters, ERG or optical structure in any of the three experimental groups (n=3 for each). Both TNFα and IL-8 in the aqueous humor of PAH group were transiently elevated 1wk post-operation and recovered to normal levels at 1 and 3mo post-operation. Iba1⁺ macroPAHges in the anterior chamber angle in PAH group were increased markedly compared to those of the control group; however, there was no significant difference compared to those in the IOL group.

CONCLUSION

PAH is a safe material for 3D printing of personal IOLs that hold great potential for future clinical applications.

KIT ligand produced by limbal niche cells under control of SOX10 maintains limbal epithelial stem cell survival by activating the KIT/AKT signalling pathway

Homeostasis and function of limbal epithelial stem cells (LESCs) rely on the limbal niche, which, if dysfunctional, leads to limbal epithelial stem cell deficiency (LSCD) and impaired vision. Hence, recovery of niche function is a principal therapeutic goal in LSCD, but the molecular mechanisms of limbal niche homeostasis are still largely unknown. Here, we report that the neural crest transcription factor SOX10, which is expressed in neural crest‐derived limbal niche cells (LNCs), is required for LNCs to promote survival of LESCs both in vivo and in vitro. In fact, using mice with a Sox10 mutation and in vitro coculture experiments, we show that SOX10 in LNCs stimulates the production of KIT ligand (KITL), which in turn activates in LESCs the KIT‐AKT signalling pathway that protects the cells against activated CASPASE 3‐associated cell death. These results suggest that SOX10 and the KITL/KIT‐AKT pathway play key roles in limbal niche homeostasis and LESC survival. These findings provide molecular insights into limbal niche function and may point to rational approaches for therapeutic interventions in LSCD.

SCF/SCFR signaling plays an important role in the early morphogenesis and neurogenesis of human embryonic neural retina

The stem cell factor receptor (SCFR) has been demonstrated to be expressed in the neural retina of mice, rat and human for decades. Previous reports indicated that the SCFR correlates with glia differentiation of late retinal progenitor cells (RPCs), retinal vasculogenesis and homeostasis of the blood-retinal barrier. However, the role of SCF/SCFR signaling in the growth and development of the neural retina (NR), especially in the early embryonic stage, remains poorly understood. Here, we show that SCF/SCFR signaling orchestrates invagination of the human embryonic stem cell (hESC)-derived NR via regulation of cell cycle progression, cytoskeleton dynamic and apical constriction of RPCs in the ciliary marginal zone (CMZ). Furthermore, activation of SCF/SCFR signaling promotes neurogenesis in the central-most NR via acceleration of the migration of immature ganglion cells and repressing apoptosis. Our study reveals an unreported role for SCF/SCFR signaling in controlling ciliary marginal cellular behaviors during early morphogenesis and neurogenesis of the human embryonic NR, providing a new potential therapeutic target for human congenital eye diseases such as anophthalmia, microphthalmia and congenital high myopia.

Lipoxin A4 delays the progression of retinal degeneration via the inhibition of microglial overactivation

BACKGROUND

Retinal degeneration (RD) is characterized by progressive photoreceptor degeneration, and emerging evidence has demonstrated that activated microglia-mediated inflammation exacerbates the progression of RD. Lipoxin A4 (LXA4) is an endogenous neuroprotective lipid mediator, but the potential therapeutic roles of LXA4 in RD have not been evaluated.

METHODS

Electroretinogram (ERG) recordings and behavioral tests were used to analyze whether the intravitreal injection (IVI) of LXA4 restored visual function in RD1 mice. Immunostaining, qPCR, western blotting and mouse cytokine arrays using an ex-vivo retinal explant model were successively performed to explore the mechanisms underlying the effects of LXA4.

RESULTS

The key rate-limiting enzyme in LXA4 biosynthesis and the LXA4 receptor were substantially downregulated in end-stage RD1 retinas. LXA4 maintained visual function in RD1 mice from postnatal days 15-21 (PN15 to PN21). Moreover, LXA4 modulated microglial activities, significantly inhibited proinflammatory gene expression, and thereby attenuated photoreceptor apoptosis.

CONCLUSIONS

LXA4 delayed the progression of RD, and thus, the use of LXA4 might be a novel approach for ameliorating dysfunction in neurodegenerative disorders.

Rescue of Retinal Degeneration in rd1 Mice by Intravitreally Injected Metformin

Retinitis pigmentosa (RP) is a progressive hereditary retinal degenerative disease in which photoreceptor cells undergo degeneration and apoptosis, eventually resulting in irreversible loss of visual function. Currently, no effective treatment exists for this disease. Neuroprotection and inflammation suppression have been reported to delay the development of RP. Metformin is a well-tested drug used to treat type 2 diabetes, and it has been reported to exert beneficial effects in neurodegenerative diseases, such as Parkinson’s disease and Alzheimer’s disease. In the present study, we used immunofluorescence staining, electroretinogram (ERG) recordings and RNA-Seq to explore the effects of metformin on photoreceptor degeneration and its mechanism in rd1 mice. We found that metformin significantly reduced apoptosis in photoreceptors and delayed the degeneration of photoreceptors and rod bipolar cells in rd1 mice, thus markedly improving the visual function of rd1 mice at P14, P18, and P22 when tested with a light/dark transition test and ERG. Microglial activation in the outer nuclear layer (ONL) of the retina of rd1 mice was significantly suppressed by metformin. RNA-Seq showed that metformin markedly downregulated inflammatory genes and upregulated the expression of crystallin proteins, which have been demonstrated to be important neuroprotective molecules in the retina, revealing the therapeutic potential of metformin for RP treatment. αA-crystallin proteins were further confirmed to be involved in the neuroprotective effects of metformin in a Ca²⁺ ionophore-damaged 661W photoreceptor-like cell line. These data suggest that metformin exerts a protective effect in rd1 mice via both immunoregulatory and new neuroprotective mechanisms.

Organoid-derived C-Kit+/SSEA4- human retinal progenitor cells promote a protective retinal microenvironment during transplantation in rodents

Stem cell therapy may replace lost photoreceptors and preserve residual photoreceptors during retinal degeneration (RD). Unfortunately, the degenerative microenvironment compromises the fate of grafted cells, demanding supplementary strategies for microenvironment regulation. Donor cells with both proper regeneration capability and intrinsic ability to improve microenvironment are highly desired. Here, we use cell surface markers (C-Kit⁺/SSEA4⁻) to effectively eliminate tumorigenic embryonic cells and enrich retinal progenitor cells (RPCs) from human embryonic stem cell (hESC)-derived retinal organoids, which, following subretinal transplantation into RD models of rats and mice, significantly improve vision and preserve the retinal structure. We characterize the pattern of integration and materials transfer following transplantation, which likely contribute to the rescued photoreceptors. Moreover, C-Kit⁺/SSEA4⁻ cells suppress microglial activation, gliosis and the production of inflammatory mediators, thereby providing a healthier host microenvironment for the grafted cells and delaying RD. Therefore, C-Kit⁺/SSEA4⁻ cells from hESC-derived retinal organoids are a promising therapeutic cell source.

Stem cell transplantation to treat retinal degeneration could be limited by the degenerative microenvironment. Here, the authors show that C-Kit⁺/SSEA4^– progenitor cells enriched from human embryonic stem cell derived retinal organoids protect retinal structure, suppress microglial activation, gliosis and inflammation.

Otx2 enhances transdifferentiation of Müller cells-derived retinal stem cells into photoreceptor-like cells

Retinal Müller glial cells have the potential of neurogenic retinal progenitor cells, and could reprogram into retinal-specific cell types such as photoreceptor cells. How to promote the differentiation of Müller cells into photoreceptor cells represents a promising therapy strategy for retinal degeneration diseases. This study aimed to enhance the transdifferentiation of rat Müller cells-derived retinal stem cells (MC-RSCs) into photoreceptor-like cells and explore the signalling mechanism. We dedifferentiated rat Müller cells into MC-RSCs which were infected with Otx2 overexpression lentivirus or control. The positive rate of photoreceptor-like cells among MC-RSCs treated with Otx2 overexpression lentivirus was significantly higher compared to control. Furthermore, pre-treatment with Crx siRNA, Nrl siRNA, or GSK-3 inhibitor SB-216763 reduced the positive rate of photoreceptor-like cells among MC-RSCs treated with Otx2 overexpression lentivirus. Finally, Otx2 induced photoreceptor precursor cells were injected into subretinal space of N-methyl-N-nitrosourea induced rat model of retinal degeneration and partially recovered retinal degeneration in the rats. In conclusion, Otx2 enhances transdifferentiation of MC-RSCs into photoreceptor-like cells and this is associated with the inhibition of Wnt signalling. Otx2 is a potential target for gene therapy of retinal degenerative diseases.

Bone Marrow CD133+ Stem Cells Ameliorate Visual Dysfunction in Streptozotocin-induced Diabetic Mice with Early Diabetic Retinopathy

Diabetic retinopathy (DR), one of the leading causes of vision loss worldwide, is characterized by neurovascular disorders. Emerging evidence has demonstrated retinal neurodegeneration in the early pathogenesis of DR, and no treatment has been developed to prevent the early neurodegenerative changes that precede detectable microvascular disorders. Bone marrow CD133+ stem cells with revascularization properties exhibit neuroregenerative potential. However, whether CD133+ cells can ameliorate the neurodegeneration at the early stage of DR remains unclear. In this study, mouse bone marrow CD133+ stem cells were immunomagnetically isolated and analyzed for the phenotypic characteristics, capacity for neural differentiation, and gene expression of neurotrophic factors. After being labeled with enhanced green fluorescent protein, CD133+ cells were intravitreally transplanted into streptozotocin (STZ)-induced diabetic mice to assess the outcomes of visual function and retina structure and the mechanism underlying the therapeutic effect. We found that CD133+ cells co-expressed typical hematopoietic/endothelial stem/progenitor phenotypes, could differentiate to neural lineage cells, and expressed genes of robust neurotrophic factors in vitro. Functional analysis demonstrated that the transplantation of CD133+ cells prevented visual dysfunction for 56 days. Histological analysis confirmed such a functional improvement and showed that transplanted CD133+ cells survived, migrated into the inner retina (IR) over time and preserved IR degeneration, including retina ganglion cells (RGCs) and rod-on bipolar cells. In addition, a subset of transplanted CD133+ cells in the ganglion cell layer differentiated to express RGC markers in STZ-induced diabetic retina. Moreover, transplanted CD133+ cells expressed brain-derived neurotrophic factors (BDNFs) in vivo and increased the BDNF level in STZ-induced diabetic retina to support the survival of retinal cells. Based on these findings, we suggest that transplantation of bone marrow CD133+ stem cells represents a novel approach to ameliorate visual dysfunction and the underlying IR neurodegeneration at the early stage of DR.

Autologous stem cell therapy for inherited and acquired retinal disease

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

Evidence for a retinal progenitor cell in the postnatal and adult mouse

Progress in cell therapy for retinal disorders has been challenging. Recognized retinal progenitors are a heterogeneous population of cells that lack surface markers for the isolation of live cells for clinical implementation. In the present application, our objective was to use the stem cell factor receptor c-Kit (CD117), a surface marker, to isolate and evaluate a distinct progenitor cell population from retinas of postnatal and adult mice. Here we report that, by combining traditional methods with fate mapping, we have identified a c-Kit-positive (c-Kit⁺) retinal progenitor cell (RPC) that is self-renewing and clonogenic in vitro, and capable of generating many cell types in vitro and in vivo. Based on cell lineage tracing, significant subpopulations of photoreceptors in the outer nuclear layer and bipolar, horizontal, amacrine and Müller cells in the inner nuclear layer are the progeny of c-Kit⁺ cells in vivo. The RPC progeny contributes to retinal neurons and glial cells, which are responsible for the conversion of light into visual signals. The ability to isolate and expand in vitro live c-Kit⁺ RPCs makes them a future therapeutic option for retinal diseases.