Prospects for the application of Müller glia and their derivatives in retinal regenerative therapies

Single-cell RNA sequencing highlights a significant retinal Müller glial population in dry age-related macular degeneration

The main challenge in dissecting the cells and pathways involved in the pathogenesis of age-related macular degeneration (AMD) is the highly heterogeneous and dynamic nature of the retinal microenvironment. This study aimed to describe the comprehensive landscape of the dry AMD (dAMD) model and identify the key cell cluster contributing to dAMD. We identified a subset of Müller cells that express high levels of Sox2, which play crucial roles in homeostasis and neuroprotection in both mouse models of AMD and patients with dAMD. Additionally, the number of Sox2+ Müller cells decreased significantly during the progression of AMD, indicating these cells were damaged and underwent cell death. Interestingly, ferroptosis and apoptosis were identified as contributors to the damage of Sox2+ Müller cells. Our findings are potentially valuable not only for advancing the current understanding of dAMD progression but also for the development of treatment strategies through the protection of Müller cells.

Lycii Fructus and Chrysanthemum Flos, a Chinese medicine herbal pair, ameliorates retinal degeneration of mice induced by sodium iodate and protects Müller cells from oxidative stress

ETHNOPHARMACOLOGICAL RELEVANCE

The combination of Lycii Fructus (LF) and Chrysanthemum Flos (CF) is a well-known herbal pair utilized in Chinese medicine for the treatment of retinal degeneration diseases commonly found in the elderly, such as age-related macular degeneration (AMD). However, the precise mechanisms of action mechanism and active constituents responsible for the therapeutic effects of the LF-CF herbal pair in improving AMD remain unknown.

AIM OF THE STUDY

This study aims to evaluate the effect of the LF-CF herbal pair on alleviating retinal damage and apoptosis in Müller cells of a dry AMD mouse model, especially its role in enhancing oxidative stress in the retina. Moreover, it endeavors to clarify the underlying action mechanisms and identify the bioactive ingredients in the LF - CF herbal pair that act on Müller cells to alleviate oxidative stress.

MATERIALS AND METHODS

A mice model of dry AMD was established through intraperitoneal administration of sodium iodate. Various solvents were employed to prepare extracts of the LF-CF herbal pair. The impact of these solvent extracts on ameliorating oxidative damage and determination of oxidation index in the retina was assessed. The ability of LF-CF herbal pair on regulating Nrf2/HO-1 signaling pathway in model mice was also detected. The MIO-M1 cell cultures were employed to assess the impact of extracts on protecting cells from oxidative damage caused by sodium iodate. The cell cultures were also utilized to investigate the potential mechanism of action and identify the active components involved.

RESULTS

The LF-CF herbal pair extracts showed evident protective effects on the mouse retina against sodium iodate-induced oxidative damage. They maintained retinal structural integrity and inhibited apoptosis. Among the extracts, the aqueous and 70 % ethanol ones were more effective in preventing retina injury. These two extracts enhanced antioxidant enzyme activity, reduced oxidative products in the experimental mice's retina, reversing the down-regulation of glutamine synthetase (a Müller cell marker). In vitro, the aqueous and 70 % ethanol extracts of the LF-CF herbal pair also protected MIO-M1 cells from sodium iodate-induced oxidative stress via regulating caspase-dependent and Nrf2/HO-1 signaling pathways. Lycium barbarum polysaccharides and luteolin are likely the active ingredients responsible for these effects.

CONCLUSIONS

The LF-CF herbal pair demonstrated the ability to mitigate oxidative stress in the retina and suppress apoptosis in Müller cells through the regulation of caspase-dependent and Nrf2/HO-1 signaling pathways. These findings contribute to the growing body of scientific evidences supporting the potential of LF-CF herbal pair as a viable therapeutic option or preventive measure for dry AMD.

Müller Glial-Derived Small Extracellular Vesicles Mitigate RGC Degeneration by Suppressing Microglial Activation via Cx3cl1-Cx3cr1 Signaling

Retinal ganglion cell (RGC) degeneration leads to irreversible blindness. Müller glia (MG) play pivotal roles in retinal homeostasis and disease through paracrine signaling. Small extracellular vesicles (sEVs) are bioactive nanomaterials derived from all types of live cells and are recognized as a potential strategy for neuroprotective therapy. The aim of this study is to investigate the potential roles of MG-derived sEVs (MG-sEVs) in a mouse model of optic nerve injury (ONC). It is found that MG-sEVs treatment effectively mitigates RGC degeneration and suppresses microglial activation, thereby improves visual function in ONC mice. Retinal transcriptomic analysis reveals a strong correlation between C-x3-c motif chemokine ligand 1 (Cx3cl1)-mediated glial activation and inflammation. Subsequently, it is confirmed that the expression levels of Cx3cl1 and proinflammatory cytokines are significantly decreased in retinas treated with MG-sEVs. The components analysis of MG-sEVs cargo identifies that miR-125b-5p and miR-16-5p target Cx3cl1 gene to regulate its expression. It is also observed that Cx3cl1 colocalizes on the microglia of transgenic C-x3-c motif chemokine receptor 1 (Cx3Cr1)-GFP mice. In conclusion, MG-sEVs mitigate RGC degeneration by suppressing microglial activation via Cx3cl1-Cx3cr1 signaling. This research provides additional opportunities for the treatment of RGC degeneration.

Müller cells trophism and pathology as the next therapeutic targets for retinal diseases

Müller cells are a crucial retinal cell type involved in multiple regulatory processes and functions that are essential for retinal health and functionality. Acting as structural and functional support for retinal neurons and photoreceptors, Müller cells produce growth factors, regulate ion and fluid homeostasis, and facilitate neuronal signaling. They play a pivotal role in retinal morphogenesis and cell differentiation, significantly contributing to macular development. Due to their radial morphology and unique cytoskeletal organization, Müller cells act as optical fibers, efficiently channeling photons directly to the photoreceptors. In response to retinal damage, Müller cells undergo specific gene expression and functional changes that serve as a first line of defense for neurons, but can also lead to unwarranted cell dysfunction, contributing to cell death and neurodegeneration. In some species, Müller cells can reactivate their developmental program, promoting retinal regeneration and plasticity-a remarkable ability that holds promising therapeutic potential if harnessed in mammals. The crucial and multifaceted roles of Müller cells-that we propose to collectively call "Müller cells trophism"-highlight the necessity of maintaining their functionality. Dysfunction of Müller cells, termed "Müller cells pathology," has been associated with a plethora of retinal diseases, including age-related macular degeneration, diabetic retinopathy, vitreomacular disorders, macular telangiectasia, and inherited retinal dystrophies. In this review, we outline how even subtle disruptions in Müller cells trophism can drive the pathological cascade of Müller cells pathology, emphasizing the need for targeted therapies to preserve retinal health and prevent disease progression.

MSC exosomes and MSC exosomes loaded with LncRNA H19 as nanotherapeutics regulate the neurogenetic potential of Müller Glial Cells in dry age-related macular degeneration

In retinal degeneration diseases such as dry age-related macular degeneration (AMD), Müller Glial Cells (MGCs) in mammals undergo a process of reactive gliosis leading to the progression of dry AMD. Here, It is demonstrated that exosomes derived from mesenchymal stem cells (MSC exosomes) and MSC exosomes loaded with LncRNA H19, acting as nanotherapeutics, can be regulated by MGCs in dry AMD. In the in vivo study, MSC exosomes were administered via intravitreal injection. MSC exosomes effectively redirected MGCs from gliosis to dedifferentiation and alleviated MGCs-to-epithelial transition by inhibiting oxidative stress in mice with dry AMD induced by NaIO3. In the in vitro study, MSC exosomes promoted MGCs dedifferentiation by activating Wnt/β-catenin signaling pathway and prevented oxidative stress-induced MGCs gliosis and MGCs-to-epithelial transition by inhibiting TGFβ1 signaling pathway. MSC exosomes loaded with LncRNA H19 enhanced the activation of Wnt/β-catenin signaling pathway and the inhibition of the TGFβ1 signaling pathway compared with MSC exosomes. These results suggest that MSC exosomes regulate the neurogenetic potential of MGCs by redirecting MGCs from gliosis to dedifferentiation and alleviating the transformation of MGCs to epithelial cells through regulating oxidative stress. Regulating LncRNA H19 in MGCs to promote mammalian retinal regeneration in dry AMD was suggested for the first time.

Investigating Müller glia reprogramming in mice: a retrospective of the last decade, and a look to the future

Müller glia, as prominent glial cells within the retina, plays a significant role in maintaining retinal homeostasis in both healthy and diseased states. In lower vertebrates like zebrafish, these cells assume responsibility for spontaneous retinal regeneration, wherein endogenous Müller glia undergo proliferation, transform into Müller glia-derived progenitor cells, and subsequently regenerate the entire retina with restored functionality. Conversely, Müller glia in the mouse and human retina exhibit limited neural reprogramming. Müller glia reprogramming is thus a promising strategy for treating neurodegenerative ocular disorders. Müller glia reprogramming in mice has been accomplished with remarkable success, through various technologies. Advancements in molecular, genetic, epigenetic, morphological, and physiological evaluations have made it easier to document and investigate the Müller glia programming process in mice. Nevertheless, there remain issues that hinder improving reprogramming efficiency and maturity. Thus, understanding the reprogramming mechanism is crucial toward exploring factors that will improve Müller glia reprogramming efficiency, and for developing novel Müller glia reprogramming strategies. This review describes recent progress in relatively successful Müller glia reprogramming strategies. It also provides a basis for developing new Müller glia reprogramming strategies in mice, including epigenetic remodeling, metabolic modulation, immune regulation, chemical small-molecules regulation, extracellular matrix remodeling, and cell-cell fusion, to achieve Müller glia reprogramming in mice.

Postnatal development of rat retina: a continuous observation and comparison between the organotypic retinal explant model and in vivo development

JOURNAL/nrgr/04.03/01300535-202503000-00033/figure1/v/2024-06-17T092413Z/r/image-tiff The organotypic retinal explant culture has been established for more than a decade and offers a range of unique advantages compared with in vivo experiments and cell cultures. However, the lack of systematic and continuous comparison between in vivo retinal development and the organotypic retinal explant culture makes this model controversial in postnatal retinal development studies. Thus, we aimed to verify the feasibility of using this model for postnatal retinal development studies by comparing it with the in vivo retina. In this study, we showed that postnatal retinal explants undergo normal development, and exhibit a consistent structure and timeline with retinas in vivo. Initially, we used SOX2 and PAX6 immunostaining to identify retinal progenitor cells. We then examined cell proliferation and migration by immunostaining with Ki-67 and doublecortin, respectively. Ki-67- and doublecortin-positive cells decreased in both in vivo and explants during postnatal retinogenesis, and exhibited a high degree of similarity in abundance and distribution between groups. Additionally, we used Ceh-10 homeodomain-containing homolog, glutamate-ammonia ligase (glutamine synthetase), neuronal nuclei, and ionized calcium-binding adapter molecule 1 immunostaining to examine the emergence of bipolar cells, Müller glia, mature neurons, and microglia, respectively. The timing and spatial patterns of the emergence of these cell types were remarkably consistent between in vivo and explant retinas. Our study showed that the organotypic retinal explant culture model had a high degree of consistency with the progression of in vivo early postnatal retina development. The findings confirm the accuracy and credibility of this model and support its use for long-term, systematic, and continuous observation.

Experimental Framework for Assessing Mouse Retinal Regeneration Through Single-Cell RNA-Sequencing

Retinal degenerative diseases including age-related macular degeneration and glaucoma are estimated to currently affect more than 14 million people in the United States, with an increased prevalence of retinal degenerations in aged individuals. An expanding aged population who are living longer forecasts an increased prevalence and economic burden of visual impairments. Improvements to visual health and treatment paradigms for progressive retinal degenerations slow vision loss. However, current treatments fail to remedy the root cause of visual impairments caused by retinal degenerations-loss of retinal neurons. Stimulation of retinal regeneration from endogenous cellular sources presents an exciting treatment avenue for replacement of lost retinal cells. In multiple species including zebrafish and Xenopus, Müller glial cells maintain a highly efficient regenerative ability to reconstitute lost cells throughout the organism's lifespan, highlighting potential therapeutic avenues for stimulation of retinal regeneration in humans. Here, we describe how the application of single-cell RNA-sequencing (scRNA-seq) has enhanced our understanding of Müller glial cell-derived retinal regeneration, including the characterization of gene regulatory networks that facilitate/inhibit regenerative responses. Additionally, we provide a validated experimental framework for cellular preparation of mouse retinal cells as input into scRNA-seq experiments, including insights into experimental design and analyses of resulting data.

Automated In Vivo Phenotypic Screening Platform for Identifying Factors that Affect Cell Regeneration Kinetics

Various strategies for replacing retinal neurons lost in degenerative diseases are under investigation, including stimulating the endogenous regenerative capacity of Müller Glia (MG) as injury-inducible retinal stem cells. Inherently regenerative species, such as zebrafish, have provided key insights into mechanisms regulating MG dedifferentiation to a stem-like state and the proliferation of MG and MG-derived progenitor cells (MGPCs). Interestingly, promoting MG/MGPC proliferation is not sufficient for regeneration, yet mechanistic studies are often focused on this measure. To fully account for the regenerative process, and facilitate screens for factors regulating cell regeneration, an assay for quantifying cell replacement is required. Accordingly, we adapted an automated reporter-assisted phenotypic screening platform to quantify the pace of cellular regeneration kinetics following selective cell ablation in larval zebrafish. Here, we detail a method for using this approach to identify chemicals and genes that control the rate of retinal cell regeneration following selective retinal cell ablation.

Glia in tissue engineering: From biomaterial tools to transplantation

Glia are imperative in nearly every function of the nervous system, including neurotransmission, neuronal repair, development, immunity, and myelination. Recently, the reparative roles of glia in the central and peripheral nervous systems have been elucidated, suggesting a tremendous potential for these cells as novel treatments to central nervous system disorders. Glial cells often behave as 'double-edged swords' in neuroinflammation, ultimately deciding the life or death of resident cells. Compared to glia, neuronal cells have limited mobility, lack the ability to divide and self-renew, and are generally more delicate. Glia have been candidates for therapeutic use in many successful grafting studies, which have been largely focused on restoring myelin with Schwann cells, olfactory ensheathing glia, and oligodendrocytes with support from astrocytes. However, few therapeutics of this class have succeeded past clinical trials. Several tools and materials are being developed to understand and re-engineer these grafting concepts for greater success, such as extra cellular matrix-based scaffolds, bioactive peptides, biomolecular delivery systems, biomolecular discovery for neuroinflammatory mediation, composite microstructures such as artificial channels for cell trafficking, and graft enhanced electrical stimulation. Furthermore, advances in stem cell-derived cortical/cerebral organoid differentiation protocols have allowed for the generation of patient-derived glia comparable to those acquired from tissues requiring highly invasive procedures or are otherwise inaccessible. However, research on bioengineered tools that manipulate glial cells is nowhere near as comprehensive as that for systems of neurons and neural stem cells. This article explores the therapeutic potential of glia in transplantation with an emphasis on novel bioengineered tools for enhancement of their reparative properties. STATEMENT OF SIGNIFICANCE: Neural glia are responsible for a host of developmental, homeostatic, and reparative roles in the central nervous system but are often a major cause of tissue damage and cellular loss in insults and degenerative pathologies. Most glial grafts have employed Schwann cells for remyelination, but other glial with novel biomaterials have been employed, emphasizing their diverse functionality. Promising strategies have emerged, including neuroimmune mediation of glial scar tissues and facilitated migration and differentiation of stem cells for neural replacement. Herein, a comprehensive review of biomaterial tools for glia in transplantation is presented, highlighting Schwann cells, astrocytes, olfactory ensheating glia, oligodendrocytes, microglia, and ependymal cells.

Extrinsic electric field modulates neuronal development and increases photoreceptor population in retinal organoids

Introduction

Considering the significant role played by both intrinsic and extrinsic electric fields in the growth and maturation of the central nervous system, the impact of short exposure to external electric fields on the development and differentiation of retinal organoids was investigated.

Methods

Retinal organoids derived from human embryonic stem cells were used at day 80, a key stage in their differentiation. A single 60-minute exposure to a biphasic electrical field was administered to assess its influence on retinal cell populations and maturation markers. Immunohistochemistry, qPCR, and RNA sequencing were employed to evaluate cell type development and gene expression changes.

Results

Electrical stimulation significantly enhanced neuronal development and increased the population of photoreceptors within the organoids. RNA sequencing data showed upregulated expression of genes related to rod photoreceptors, Müller cells, horizontal cells, and amacrine cells, while genes associated with retinal pigment epithelium and retinal ganglion cells were downregulated. Variations in development and maturation were observed depending on the specific parameters of the applied electric field.

Discussion

These findings highlight the significant impact of extrinsic electrical fields on early retinal development and suggest that optimizing electrical field parameters could effectively address certain limitations in retinal organoid technology, potentially reducing the reliance on chemicals and small molecules.

Organoids and organoid extracellular vesicles-based disease treatment strategies

Organoids are "mini-organs" that self-organize and differentiate from stem cells under in vitro 3D culture conditions, mimicking the spatial structure and function of tissues in vivo. Extracellular vesicles (EVs) are nanoscale phospholipid bilayer vesicles secreted by living cells, rich in bioactive molecules, with excellent biocompatibility and low immunogenicity. Compared to EVs, organoid-derived EVs (OEVs) exhibit higher yield and enhanced biological functions. Organoids possess stem cell characteristics, and OEVs are capable of delivering active substances, making both highly promising for medical applications. In this review, we provide an overview of the fundamental biological principles of organoids and OEVs, and discuss their current applications in disease treatment. We then focus on the differences between OEVs and traditional EVs. Subsequently, we present methods for the engineering modification of OEVs. Finally, we critically summarize the advantages and challenges of organoids and OEVs. In conclusion, we believe that a deeper understanding of organoids and OEVs will provide innovative solutions to complex diseases.

Exosome-loaded degradable polymeric microcapsules for the treatment of vitreoretinal diseases

The therapeutic benefits of many cell types involve paracrine mechanisms. Inspired by the paracrine functions of exosomes and the sustained degradation properties of microcapsules, here we report the therapeutic benefits of exosome-loaded degradable poly(lactic-co-glycolic acid) microcapsules with micrometric pores for the treatment of vitreoretinal diseases. On intravitreal injection in a mouse model of retinal ischaemia-reperfusion injury, microcapsules encapsulating mouse mesenchymal-stem-cell-derived exosomes settled in the inferior vitreous cavity, released exosomes for over one month as they underwent degradation and led to the restoration of retinal thickness to nearly that of the healthy retina. In mice and non-human primates with primed mycobacterial uveitis, intravitreally injected microcapsules loaded with exosomes from monkey regulatory T cells resulted in a substantial reduction in the levels of inflammatory cells. The exosome-encapsulating microcapsules, which can be lyophilised, may offer alternative treatment options for vitreoretinal diseases.

Dysregulated energy and protein homeostasis and the loss of GABAergic amacrine cells in aging retina

Aging is a major risk factor for the development or the worsening of retinal degenerative conditions. The intricate network of the neural retina determined that the retinal aging is a complicated process. The aim of this study is to delineate the transcriptomic changes of major retinal neurons during aging in C57BL/6 mice at single-cell level. We analyzed the transcriptional profiles of the photoreceptor, bipolar, amacrine, and Müller glial cells of 1.5-2 and 24-30 months old mice using single-cell RNA sequencing technique. We selectively confirmed the differences in gene expression using immunofluorescence staining and RNA in situ hybridization analysis. We found that each retinal cell type had unique changes upon aging. However, they all showed signs of dysregulated glucose and energy metabolism, and perturbed proteostasis. In particular, old Müller glia exhibited the most profound changes, including the upregulation of cell metabolism, stress-responses, antigen-presentation and immune responses and metal ion homeostasis. The dysregulated gliogenesis and differentiation was confirmed by the presence of Müller glia expressing rod-specific genes in the inner nuclear layer and the outer plexiform layer of the old retina. We further pinpointed the specific loss of GABAergic amacrine cells in old retina. Our study emphasized changes of amacrine and Müller glia during retinal aging, provided resources for further research on the molecular and cellular regulatory mechanisms underlying aging-associated retinal deterioration.

Mitochondrial transfer between BMSCs and Müller promotes mitochondrial fusion and suppresses gliosis in degenerative retina

Mitochondrial dysfunction and Müller cells gliosis are significant pathological characteristics of retinal degeneration (RD) and causing blinding. Stem cell therapy is a promising treatment for RD, the recently accepted therapeutic mechanism is cell fusion induced materials transfer. However, whether materials including mitochondrial transfer between grafted stem cells and recipient's cells contribute to suppressing gliosis and mechanism are unclear. In present study, we demonstrated that bone marrow mesenchymal stem cells (BMSCs) transferred mitochondria to Müller cells by cell fusion and tunneling nanotubes. BMSCs-derived mitochondria (BMSCs-mito) were integrated into mitochondrial network of Müller cells, improving mitochondrial function, reducing oxidative stress and gliosis, which protected visual function partially in the degenerative rat retina. RNA sequencing analysis revealed that BMSCs-mito increased mitochondrial DNA (mtDNA) content and facilitated mitochondrial fusion in damaged Müller cells. It suggests that mitochondrial transfer from BMSCs remodels Müller cells metabolism and suppresses gliosis; thus, delaying the degenerative progression of RD.

Small extracellular vesicles of organoid-derived human retinal stem cells remodel Müller cell fate via miRNA: A novel remedy for retinal degeneration

Remodeling retinal Müller glial fate, including gliosis inhibition and pro-reprogramming, represents a crucial avenue for treating degenerative retinal diseases. Stem cell transplantation exerts effects on modulating retinal Müller glial fate. However, the optimized stem cell products and the underlying therapeutic mechanisms need to be investigated. In the present study, we found that retinal progenitor cells from human embryonic stem cell-derived retinal organoids (hERO-RPCs) transferred extracellular vesicles (EVs) into Müller cells following subretinal transplantation into RCS rats. Small EVs from hERO-RPCs (hERO-RPC-sEVs) were collected and were found to delay photoreceptor degeneration and protect retinal function in RCS rats. hERO-RPC-sEVs were taken up by Müller cells both in vivo and in vitro, and inhibited gliosis while promoting early dedifferentiation of Müller cells. We further explored the miRNA profiles of hERO-RPC-sEVs, which suggested a functional signature associated with neuroprotection and development, as well as the regulation of stem cell and glial fate. Mechanistically, hERO-RPC-sEVs might regulate the fate of Müller cells by miRNA-mediated nuclear factor I transcription factors B (NFIB) downregulation. Collectively, our findings offer novel mechanistic insights into stem cell therapy and promote the development of EV-centered therapeutic strategies.

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.

MicroRNA profile of extracellular vesicles released by Müller glial cells

Introduction

As with any other radial glia in the central nervous system, Müller glia derive from the same neuroepithelial precursors, perform similar functions, and exhibit neurogenic properties as radial glia in the brain. Müller glial cells retain progenitor-like characteristics in the adult human eye and can partially restore visual function upon intravitreal transplantation into animal models of glaucoma. Recently, it has been demonstrated that intracellular communication is possible via the secretion of nano-sized membrane-bound extracellular vesicles (EV), which contain bioactive molecules like microRNA (miRNA) and proteins that induce phenotypic changes when internalised by recipient cells.

Methods

We conducted high-throughput sequencing to profile the microRNA signature of EV populations secreted by Müller glia in culture and used bioinformatics tools to evaluate their potential role in the neuroprotective signalling attributed to these cells.

Results

Sequencing of miRNA within Müller EV suggested enrichment with species associated with stem cells such as miR-21 and miR-16, as well as with miRNA previously found to play a role in diverse Müller cell functions in the retina: miR-9, miR-125b, and the let-7 family. A total of 51 miRNAs were found to be differentially enriched in EV compared to the whole cells from which EV originated. Bioinformatics analyses also indicated that preferential enrichment of species was demonstrated to regulate genes involved in cell proliferation and survival, including PTEN, the master inhibitor of the PI3K/AKT pathway.

Discussion

The results suggest that the release by Müller cells of miRNA-enriched EV abundant in species that regulate anti-apoptotic signalling networks is likely to represent a significant proportion of the neuroprotective effect observed after the transplantation of these cells into animal models of retinal ganglion cell (RGC) depletion. Future studies will seek to evaluate the modulation of putative genes as well as the activation of these pathways in in vitro and in vivo models following the internalisation of Müller-EV by target retinal neurons.

MicroRNA-152-3p and MicroRNA-196a-5p Are Downregulated When Müller Cells Are Promoted by Components of the Internal Limiting Membrane: Implications for Macular Hole Healing

Müller cells play a critical role in the closure of macular holes, and their proliferation and migration are facilitated by the internal limiting membrane (ILM). Despite the importance of this process, the underlying molecular mechanism remains underexplored. This study investigated the effects of ILM components on the microRNA (miRNA) profile of Müller cells. Rat Müller cells (rMC-1) were cultured with a culture insert and varying concentrations of ILM component coatings, namely, collagen IV, laminin, and fibronectin, and cell migration was assessed by measuring cell-free areas in successive photographs following insert removal. MiRNAs were then extracted from these cells and analyzed. Mimics and inhibitors of miRNA candidates were transfected into Müller cells, and a cell migration assay and additional cell viability assays were performed. The results revealed that the ILM components promoted Müller cell migration (p < 0.01). Among the miRNA candidates, miR-194-3p was upregulated, whereas miR-125b-1-3p, miR-132-3p, miR-146b-5p, miR-152-3p, miR-196a-5p, miR-542-5p, miR-871-3p, miR-1839-5p, and miR-3573-3p were significantly downregulated (p < 0.05; fold change > 1.5). Moreover, miR-152-3p and miR-196a-5p reduced cell migration (p < 0.05) and proliferation (p < 0.001), and their suppressive effects were reversed by their respective inhibitors. In conclusion, miRNAs were regulated in ILM component-activated Müller cells, with miR-152-3p and miR-196a-5p regulating Müller cell migration and proliferation. These results serve as a basis for understanding the molecular healing process of macular holes and identifying potential new target genes in future research.

Effects of Apelin on the fibrosis of retinal tissues and Müller cells in diabetes retinopathy through the JAK2/STAT3 signalling pathway

Retinal fibrosis was a key characteristic of diabetes retinopathy (DR). Apelin was found to be a candidate for tissue fibrosis. Nevertheless, the role of Apelin in the Müller cells in DR remains unclear. This study identified the function and mechanism of Apelin in Müller cells and the fibrosis of retinal tissue. Western blot was carried out to detect the Apelin, GFAP, Collagen I, α-SMA, JAK2 and STAT3 protein levels. Masson staining was performed to display the histopathological changes in retinal tissue of diabetic mellitus (DM) rats. The immunofluorescence staining was conducted to evaluate the Apelin levels in the retinal tissue. The levels of GFAP, Collagen I and α-SMA in the retinal tissue of DM rats was visualised by the immunohistochemistry staining. The results showed that Apelin, GFAP, Collagen I andα-SMA expression was prominently elevated in the retinal tissue of DM rats and high glucose (HG)-exposed Müller cells. The results of Masson staining showed that the epiretinal fibrotic membrane was observed in DM rats. Apelin knockdown declined the GFAP, Collagen I andα-SMA levels. Besides, the protein levels of p-JAK2 and p-STAT3 were elevated in the HG-treated Müller cells, while Apelin knockdown declined them. FLLL32 treatment neutralised the role of Apelin. In conclusion, Apelin facilitated the fibrogenic activity of Müller cells through activating the JAK2/STAT3 signalling pathway, and thus inducing the retinal fibrosis in DR.

Glaucoma: now and beyond

The glaucomas are a group of conditions leading to irreversible sight loss and characterised by progressive loss of retinal ganglion cells. Although not always elevated, intraocular pressure is the only modifiable risk factor demonstrated by large clinical trials. It remains the leading cause of irreversible blindness, but timely treatment to lower intraocular pressure is effective at slowing the rate of vision loss from glaucoma. Methods for lowering intraocular pressure include laser treatments, topical medications, and surgery. Although modern surgical innovations aim to be less invasive, many have been introduced with little supporting evidence from randomised controlled trials. Many cases remain undiagnosed until the advanced stages of disease due to the limitations of screening and poor access to opportunistic case finding. Future research aims to generate evidence for intraocular pressure-independent neuroprotective treatments, personalised treatment through genetic risk profiling, and exploration of potential advanced cellular and gene therapies.

The New Era of Therapeutic Strategies for the Treatment of Retinitis Pigmentosa: A Narrative Review of Pathomolecular Mechanisms for the Development of Cell-Based Therapies

Retinitis pigmentosa, defined more properly as cone-rod dystrophy, is a paradigm of inherited diffuse retinal dystrophies, one of the rare diseases with the highest prevalence in the worldwide population and one of the main causes of low vision in the pediatric and elderly age groups. Advancements in and the understanding of molecular biology and gene-editing technologies have raised interest in laying the foundation for new therapeutic strategies for rare diseases. As a consequence, new possibilities for clinicians and patients are arising due to the feasibility of treating such a devastating disorder, reducing its complications. The scope of this review focuses on the pathomolecular mechanisms underlying RP better to understand the prospects of its treatment using innovative approaches.

TRIM9 promotes Müller cell-derived retinal stem cells to differentiate into retinal ganglion cells by regulating Atoh7

Glaucoma is a multifactorial, irreversible blinding eye disease characterized by a large number of retinal ganglion cell (RGC) deaths. Müller cell-derived retinal stem cells (RSCs) can be induced to differentiate into RGCs under certain conditions. This study aimed to explore the regulatory effect and mechanism of TRIM9 on the differentiation of Müller cell-derived stem cells into RGCs. First, episcleral vein cauterization was used to induce high intraocular pressure (IOP) rat model. Next, Müller cells were isolated from rat retina, identified and induced to dedifferentiate into RSCs. Finally, RSCs were intervened with lentivirus PGC-FU-TRIM9-GFP transfection or siRNA Atoh7 and induced to redifferentiate into RGCs. In vivo, TRIM9 was highly expressed and Müller cells proliferated abnormally in the high IOP rat model. In vitro, S-100, GFAP, vimentin, and GS were positively expressed in Müller cells isolated from rat retina, and the purity of cells was 97.17%. Under the stimulation of cytokines, the proliferative capacity of the cells and the expression of Nestin and Ki67 gradually increased with the prolongation of culture time. Furthermore, RSCs transfected with the lentiviral vector PGC-FU-TRIM9-GFP displayed a striking morphological feature of long neurites. Additionally, there was a remarkable increase in the fluorescence intensity of Brn-3b and Thy1.1, accompanied by elevated mRNA and protein expression levels of Brn-3b, Thy1.1, and Atoh7. After knocking down Atoh7, the effect of TRIM9 on the above indicators was reversed. TRIM9 might promote the differentiation of Müller cells into RGCs by regulating the expression of Atoh7.

Low-dose radiation induces unstable gene expression in developing human iPSC-derived retinal ganglion organoids

The effects of low-dose radiation on undifferentiated cells carry important implications. However, the effects on developing retinal cells remain unclear. Here, we analyzed the gene expression characteristics of neuronal organoids containing immature human retinal cells under low-dose radiation and predicted their changes. Developing retinal cells generated from human induced pluripotent stem cells (iPSCs) were irradiated with either 30 or 180 mGy on days 4-5 of development for 24 h. Genome-wide gene expression was observed until day 35. A knowledge-based pathway analysis algorithm revealed fluctuations in Rho signaling and many other pathways. After a month, the levels of an essential transcription factor of eye development, the proportion of paired box 6 (PAX6)-positive cells, and the proportion of retinal ganglion cell (RGC)-specific transcription factor POU class 4 homeobox 2 (POU4F2)-positive cells increased with 30 mGy of irradiation. In contrast, they decreased after 180 mGy of irradiation. Activation of the "development of neurons" pathway after 180 mGy indicated the dedifferentiation and development of other neural cells. Fluctuating effects after low-dose radiation exposure suggest that developing retinal cells employ hormesis and dedifferentiation mechanisms in response to stress.

Genetic and epigenetic regulators of retinal Müller glial cell reprogramming

Background

Retinal diseases characterized with irreversible loss of retinal nerve cells, such as optic atrophy and retinal degeneration, are the main causes of blindness. Current treatments for these diseases are very limited. An emerging treatment strategy is to induce the reprogramming of Müller glial cells to generate new retinal nerve cells, which could potentially restore vision.

Main text

Müller glial cells are the predominant glial cells in retinae and play multiple roles to maintain retinal homeostasis. In lower vertebrates, such as in zebrafish, Müller glial cells can undergo cell reprogramming to regenerate new retinal neurons in response to various damage factors, while in mammals, this ability is limited. Interestingly, with proper treatments, Müller glial cells can display the potential for regeneration of retinal neurons in mammalian retinae. Recent studies have revealed that dozens of genetic and epigenetic regulators play a vital role in inducing the reprogramming of Müller glial cells in vivo. This review summarizes these critical regulators for Müller glial cell reprogramming and highlights their differences between zebrafish and mammals.

Conclusions

A number of factors have been identified as the important regulators in Müller glial cell reprogramming. The early response of Müller glial cells upon acute retinal injury, such as the regulation in the exit from quiescent state, the initiation of reactive gliosis, and the re-entry of cell cycle of Müller glial cells, displays significant difference between mouse and zebrafish, which may be mediated by the diverse regulation of Notch and TGFβ (transforming growth factor-β) isoforms and different chromatin accessibility.

Cell-Based Therapies for Glaucoma

Glaucomatous optic neuropathy (GON) is the major cause of irreversible visual loss worldwide and can result from a range of disease etiologies. The defining features of GON are retinal ganglion cell (RGC) degeneration and characteristic cupping of the optic nerve head (ONH) due to tissue remodeling, while intraocular pressure remains the only modifiable GON risk factor currently targeted by approved clinical treatment strategies. Efforts to understand the mechanisms that allow species such as the zebrafish to regenerate their retinal cells have greatly increased our understanding of regenerative signaling pathways. However, proper integration within the retina and projection to the brain by the newly regenerated neuronal cells remain major hurdles. Meanwhile, a range of methods for in vitro differentiation have been developed to derive retinal cells from a variety of cell sources, including embryonic and induced pluripotent stem cells. More recently, there has been growing interest in the implantation of glial cells as well as cell-derived products, including neurotrophins, microRNA, and extracellular vesicles, to provide functional support to vulnerable structures such as RGC axons and the ONH. These approaches offer the advantage of not relying upon the replacement of degenerated cells and potentially targeting earlier stages of disease pathogenesis. In order to translate these techniques into clinical practice, appropriate cell sourcing, robust differentiation protocols, and accurate implantation methods are crucial to the success of cell-based therapy in glaucoma. Translational Relevance: Cell-based therapies for glaucoma currently under active development include the induction of endogenous regeneration, implantation of exogenously derived retinal cells, and utilization of cell-derived products to provide functional support.

Integrative Single-Cell Transcriptomics and Epigenomics Mapping of the Fetal Retina Developmental Dynamics

The underlying mechanisms that determine gene expression and chromatin accessibility in retinogenesis are poorly understood. Herein, single-cell RNA sequencing and single-cell assay for transposase-accessible chromatin sequencing are performed on human embryonic eye samples obtained 9-26 weeks after conception to explore the heterogeneity of retinal progenitor cells (RPCs) and neurogenic RPCs. The differentiation trajectory from RPCs to 7 major types of retinal cells are verified. Subsequently, diverse lineage-determining transcription factors are identified and their gene regulatory networks are refined at the transcriptomic and epigenomic levels. Treatment of retinospheres, with the inhibitor of RE1 silencing transcription factor, X5050, induces more neurogenesis with the regular arrangement, and a decrease in Müller glial cells. The signatures of major retinal cells and their correlation with pathogenic genes associated with multiple ocular diseases, including uveitis and age-related macular degeneration are also described. A framework for the integrated exploration of single-cell developmental dynamics of the human primary retina is provided.

Extrusion bioprinting of cellular aggregates improves mesenchymal stem cell proliferation and differentiation

3D extrusion bioprinting brings the prospect of stem cell-based therapies in regenerative medicine. These bioprinted stem cells are expected to proliferate and differentiate to form the desired organoids into 3D structures, which is critical for complex tissue construction. However, this strategy is hampered by low reproducible cell number and viability, and organoid immaturity due to incomplete differentiation of stem cells. Hence, we apply a novel extrusion-based bioprinting process with cellular aggregates (CA) bioink, in which the encapsulated cells are precultured in hydrogels to undergo aggregation. In this study, alginate-gelatin-collagen (Alg-Gel-Col) hydrogel containing mesenchymal stem cells (MSCs) were precultured for 48 h to form CA bioink and resulted in high cell viability and printing fidelity. Meanwhile, MSCs in CA bioink showed high proliferation, stemness and lipogenic differentiative potential in contrast to that in single cell (SC) bioink and hanging drop cell spheroid (HDCS) bioink, which indicated the considerable potential for complex tissue construction. In addition, the printability and efficacy of human umbilical cord MSCs (hUC-MSCs) were further confirmed the translational potential of this novel bioprinting method.

The Role of Nrf2/sMAF Signalling in Retina Ageing and Retinal Diseases

Age-related diseases, such as Parkinson's disease, Alzheimer's disease, cardiovascular diseases, cancers, and age-related macular disease, have become increasingly prominent as the population ages. Oxygen is essential for living organisms, but it may also cause disease when it is transformed into reactive oxygen species via biological processes in cells. Most of the production of ROS occurs in mitochondrial complexes I and III. The accumulation of ROS in cells causes oxidative stress, which plays a crucial role in human ageing and many diseases. Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a key antioxidant transcription factor that plays a central role in many diseases and ageing in general. It regulates many downstream antioxidative enzymes when cells are exposed to oxidative stress. A basic-region leucine zipper (bZIP) transcription factor, MAF, specifically the small MAF subfamily (sMAFs), forms heterodimers with Nrf2, which bind with Maf-recognition elements (MAREs) in response to oxidative stress. The role of this complex in the human retina remains unclear. This review summarises the current knowledge about Nrf2 and its downstream signalling, especially its cofactor-MAF, in ageing and diseases, with a focus on the retina. Since Nrf2 is the master regulator of redox homeostasis in cells, we hypothesise that targeting Nrf2 is a promising therapeutic approach for many age-related diseases.

Application of IPSC and Müller glia derivatives in retinal degenerative diseases

Retinal degenerative diseases cause blindness characterized by a progressive decline in the number and function of retinal pigment epithelium (RPE), photoreceptor cells, and ganglion cells. Such diseases include retinitis pigmentosa (RP), glaucomatous optic neuropathy, age-related macular degeneration and diabetic optic neuropathy. Recent studies have demonstrated that Müller glial cells (MGCs), an endogenous alternative source of retinal neurons, are important glial cells involved in retinal development, damage, and regeneration, making it an excellent target for retinal nerve regeneration. Although hardly differentiate into neuron cells, transplanted MGCs have been shown to induce partial recovery of visual function in experimental retinal degenerative models. This improvement is possibly attributed to the release of neuroprotective factors that derived from the MGCs. With the development of the therapeutic usage of pluripotent stem cell, application of induced pluripotent stem cells (iPSCs) or embryonic stem cells (ESCs) originated derivation of MGCs have been widely used in retinal degenerative disease model such as glaucoma and retinitis pigmentosa model. This chapter summarized the relevant research and mechanisms and provided a broader application and research prospects for effective treatments in retinal degenerative diseases.

Activation of retinal glial cells contributes to the degeneration of ganglion cells in experimental glaucoma

Elevation of intraocular pressure (IOP) is a major risk factor for neurodegeneration in glaucoma. Glial cells, which play an important role in normal functioning of retinal neurons, are well involved into retinal ganglion cell (RGC) degeneration in experimental glaucoma animal models generated by elevated IOP. In response to elevated IOP, mGluR I is first activated and Kir4.1 channels are subsequently inhibited, which leads to the activation of Müller cells. Müller cell activation is followed by a complex process, including proliferation, release of inflammatory and growth factors (gliosis). Gliosis is further regulated by several factors. Activated Müller cells contribute to RGC degeneration through generating glutamate receptor-mediated excitotoxicity, releasing cytotoxic factors and inducing microglia activation. Elevated IOP activates microglia, and following morphological and functional changes, these cells, as resident immune cells in the retina, show adaptive immune responses, including an enhanced release of pro-inflammatory factors (tumor neurosis factor-α, interleukins, etc.). These ATP and Toll-like receptor-mediated responses are further regulated by heat shock proteins, CD200R, chemokine receptors, and metabotropic purinergic receptors, may aggravate RGC loss. In the optic nerve head, astrogliosis is initiated and regulated by a complex reaction process, including purines, transmitters, chemokines, growth factors and cytokines, which contributes to RGC axon injury through releasing pro-inflammatory factors and changing extracellular matrix in glaucoma. The effects of activated glial cells on RGCs are further modified by the interplay among different types of glial cells. This review is concluded by presenting an in-depth discussion of possible research directions in this field in the future.

Retinitis Pigmentosa: Novel Therapeutic Targets and Drug Development

Retinitis pigmentosa (RP) is a heterogeneous group of hereditary diseases characterized by progressive degeneration of retinal photoreceptors leading to progressive visual decline. It is the most common type of inherited retinal dystrophy and has a high burden on both patients and society. This condition causes gradual loss of vision, with its typical manifestations including nyctalopia, concentric visual field loss, and ultimately bilateral central vision loss. It is one of the leading causes of visual disability and blindness in people under 60 years old and affects over 1.5 million people worldwide. There is currently no curative treatment for people with RP, and only a small group of patients with confirmed RPE65 mutations are eligible to receive the only gene therapy on the market: voretigene neparvovec. The current therapeutic armamentarium is limited to retinoids, vitamin A supplements, protection from sunlight, visual aids, and medical and surgical interventions to treat ophthalmic comorbidities, which only aim to slow down the progression of the disease. Considering such a limited therapeutic landscape, there is an urgent need for developing new and individualized therapeutic modalities targeting retinal degeneration. Although the heterogeneity of gene mutations involved in RP makes its target treatment development difficult, recent fundamental studies showed promising progress in elucidation of the photoreceptor degeneration mechanism. The discovery of novel molecule therapeutics that can selectively target specific receptors or specific pathways will serve as a solid foundation for advanced drug development. This article is a review of recent progress in novel treatment of RP focusing on preclinical stage fundamental research on molecular targets, which will serve as a starting point for advanced drug development. We will review the alterations in the molecular pathways involved in the development of RP, mainly those regarding endoplasmic reticulum (ER) stress and apoptotic pathways, maintenance of the redox balance, and genomic stability. We will then discuss the therapeutic approaches under development, such as gene and cell therapy, as well as the recent literature identifying novel potential drug targets for RP.

Extracellular vesicles in the retina - putative roles in physiology and disease

The retina encompasses a network of neurons, glia and epithelial and vascular endothelia cells, all coordinating visual function. Traditionally, molecular information exchange in this tissue was thought to be orchestrated by synapses and gap junctions. Recent findings have revealed that many cell types are able to package and share molecular information via extracellular vesicles (EVs) and the technological advancements in visualisation and tracking of these delicate nanostructures has shown that the role of EVs in cell communication is pleiotropic. EVs are released under physiological conditions by many cells but they are also released during various disease stages, potentially reflecting the health status of the cells in their cargo. Little is known about the physiological role of EV release in the retina. However, administration of exogenous EVs in vivo after injury suggest a neurotrophic role, whilst photoreceptor transplantation in early stages of retina degeneration, EVs may facilitate interactions between photoreceptors and Müller glia cells. In this review, we consider some of the proposed roles for EVs in retinal physiology and discuss current evidence regarding their potential impact on ocular therapies via gene or cell replacement strategies and direct intraocular administration in the diseased eye.

Assessing Rewiring of the Retinal Circuitry by Electroretinogram (ERG) After Inner Retinal Lesion in Adult Zebrafish

Adult zebrafish respond to retinal injury with a regenerative response that replaces damaged neurons with Müller glia-derived regenerated neurons. The regenerated neurons are functional, appear to make appropriate synaptic connections, and support visually mediated reflexes and more complex behaviors. Curiously, the electrophysiology of damaged, regenerating, and regenerated zebrafish retina has only recently been examined. In our previous work, we demonstrated that electroretinogram (ERG) recordings of damaged zebrafish retina correlate with the extent of the inflicted damage and that the regenerated retina at 80 days post-injury exhibited ERG waveforms consistent with functional visual processing. In this paper we describe the procedure for obtaining and analyzing ERG recordings from adult zebrafish previously subjected to widespread lesions that destroy inner retinal neurons and engage a regenerative response that restores retinal function, in particular the synaptic connections between photoreceptor axon terminals and the dendritic trees of retinal bipolar neurons.

Does senescence play a role in age-related macular degeneration?

Advanced age is the most established risk factor for developing age-related macular degeneration (AMD), one of the leading causes of visual impairment in the elderly, in Western and developed countries. Similarly, after middle age, there is an exponential increase in pathologic molecular and cellular events that can induce senescence, traditionally defined as an irreversible loss of the cells' ability to divide and most recently reported to also occur in select post-mitotic and terminally differentiated cells, such as neurons. Together these facts raise the question as to whether or not cellular senescence, may play a role in the development of AMD. A number of studies have reported the effect of ocular-relevant inducers of senescence using primarily in vitro models of poorly polarized, actively dividing retinal pigment epithelial (RPE) cell lines. However, in interpretating the data, the fidelity of these culture models to the RPE in vivo, must be considered. Fewer studies have explored the presence and/or impact of senescent cells in in vivo models that present with phenotypic features of AMD, leaving this an open field for further investigation. The goal of this review is to discuss current thoughts on the potential role of senescence in AMD development and progression, with consideration of the model systems used and their relevance to human disease.

Release of VAMP5-positive extracellular vesicles by retinal Müller glia in vivo

Cell-cell interactions in the central nervous system are based on the release of molecules mediating signal exchange and providing structural and trophic support through vesicular exocytosis and the formation of extracellular vesicles. The specific mechanisms employed by each cell type in the brain are incompletely understood. Here, we explored the means of communication used by Müller cells, a type of radial glial cells in the retina, which forms part of the central nervous system. Using immunohistochemical, electron microscopic, and molecular analyses, we provide evidence for the release of distinct extracellular vesicles from endfeet and microvilli of retinal Müller cells in adult mice in vivo. We identify VAMP5 as a Müller cell-specific SNARE component that is part of extracellular vesicles and responsive to ischemia, and we reveal differences between the secretomes of immunoaffinity-purified Müller cells and neurons in vitro. Our findings suggest extracellular vesicle-based communication as an important mediator of cellular interactions in the retina.

Hotspots and trends in ophthalmology in recent 5 years: Bibliometric analysis in 2017–2021

Purpose

The purpose of this study was to investigate the hotspots and research trends of ophthalmology research.

Method

Ophthalmology research literature published between 2017 and 2021 was obtained in the Web of Science Core Collection database. The bibliometric analysis and network visualization were performed with the VOSviewer and CiteSpace. Publication-related information, including publication volume, citation counts, countries, journals, keywords, subject categories, and publication time, was analyzed.

Results

A total of 10,469 included ophthalmology publications had been cited a total of 7,995 times during the past 5 years. The top countries and journals for the number of publications were the United States and the Ophthalmology. The top 25 global high-impact documents had been identified using the citation ranking. Keyword co-occurrence analysis showed that the hotspots in ophthalmology research were epidemiological characteristics and treatment modalities of ocular diseases, artificial intelligence and fundus imaging technology, COVID-19-related telemedicine, and screening and prevention of ocular diseases. Keyword burst analysis revealed that “neural network,” “pharmacokinetics,” “geographic atrophy,” “implementation,” “variability,” “adverse events,” “automated detection,” and “retinal images” were the research trends of research in the field of ophthalmology through 2021. The analysis of the subject categories demonstrated the close cooperation relationships that existed between different subject categories, and collaborations with non-ophthalmology-related subject categories were increasing over time in the field of ophthalmology research.

Conclusions

The hotspots in ophthalmology research were epidemiology, prevention, screening, and treatment of ocular diseases, as well as artificial intelligence and fundus imaging technology and telemedicine. Research trends in ophthalmology research were artificial intelligence, drug development, and fundus diseases. Knowledge from non-ophthalmology fields is likely to be more involved in ophthalmology research.

In vitro Model Systems for Studies Into Retinal Neuroprotection

Therapy development for neurodegenerative diseases of the retina constitutes a major unmet medical need, and this may be particularly relevant for inherited diseases of the retina, which are largely untreatable to this day. Therapy development necessitates appropriate models to improve the understanding of the underlying degenerative mechanisms, as well as for the testing and evaluation of novel treatment approaches. This review provides an overview of various in vitro model systems used to study retinal neuroprotection. The in vitro methods and technologies discussed range from primary retinal cell cultures and cell lines, to retinal organoids and organotypic retinal explants, to the cultivation of whole eyeballs. The advantages and disadvantages of these methods are compared and evaluated, also in view of the 3R principles (i.e., the refinement, reduction, and replacement of live animal testing), to identify suitable in vitro alternatives for in vivo experimentation. The article further expands on the use of in vitro models to test and evaluate neuroprotective treatments and to aid the development of retinal drug delivery systems. Among the pharmacological agents tested and characterized in vitro are such that interfere with aberrant cyclic guanosine monophosphate (cGMP) -signaling or such that inhibit the activities of poly (ADP-ribose) polymerase (PARP), histone deacetylases (HDAC), calpain-type proteases, as well as unfolded protein response-related stress. We then introduce nanoparticle-based drug delivery systems and discuss how different in vitro systems may be used to assess their efficacy in the treatment of retinal diseases. The summary provides a brief comparison of available in vitro models and relates their advantages and limitations to the various experimental requirements, for instance, for studies into disease mechanisms, novel treatments, or retinal toxicity. In many cases, combinations of different in vitro models may be required to obtain a comprehensive view of the efficacy of a given retinal neuroprotection approach.

Gene-independent therapeutic interventions to maintain and restore light sensitivity in degenerating photoreceptors

Neurodegenerative retinal diseases are a prime cause of blindness in industrialized countries. In many cases, there are no therapeutic treatments, although they are essential to improve patients' quality of life. A set of disease-causing genes, which primarily affect photoreceptors, has already been identified and is of major interest for developing gene therapies. Nevertheless, depending on the nature and the state of the disease, gene-independent strategies are needed. Various strategies to halt disease progression or maintain function of the retina are under research. These therapeutic interventions include neuroprotection, direct reprogramming of affected photoreceptors, the application of non-coding RNAs, the generation of artificial photoreceptors by optogenetics and cell replacement strategies. During recent years, major breakthroughs have been made such as the first optogenetic application to a blind patient whose visual function partially recovered by targeting retinal ganglion cells. Also, RPE cell transplantation therapies are under clinical investigation and show great promise to improve visual function in blind patients. These cells are generated from human stem cells. Similar therapies for replacing photoreceptors are extensively tested in pre-clinical models. This marks just the start of promising new cures taking advantage of developments in the areas of genetic engineering, optogenetics, and stem-cell research. In this review, we present the recent therapeutic advances of gene-independent approaches that are currently under clinical evaluation. Our main focus is on photoreceptors as these sensory cells are highly vulnerable to degenerative diseases, and are crucial for light detection.

Regulations of Retinal Inflammation: Focusing on Müller Glia

Retinal inflammation underlies multiple prevalent retinal diseases. While microglia are one of the most studied cell types regarding retinal inflammation, growing evidence shows that Müller glia play critical roles in the regulation of retinal inflammation. Müller glia express various receptors for cytokines and release cytokines to regulate inflammation. Müller glia are part of the blood-retinal barrier and interact with microglia in the inflammatory responses. The unique metabolic features of Müller glia in the retina makes them vital for retinal homeostasis maintenance, regulating retinal inflammation by lipid metabolism, purine metabolism, iron metabolism, trophic factors, and antioxidants. miRNAs in Müller glia regulate inflammatory responses via different mechanisms and potentially regulate retinal regeneration. Novel therapies are explored targeting Müller glia for inflammatory retinal diseases treatment. Here we review new findings regarding the roles of Müller glia in retinal inflammation and discuss the related novel therapies for retinal diseases.

Suppression of transient receptor potential melastatin 7 regulates pluripotency, proliferation, and differentiation of mouse embryonic stem cells via mechanistic target of rapamycin-extracellular signal-regulated kinase activation

Mouse embryonic stem cells (mESCs) are a widely used model for their diverse availability in studying early embryonic development and their application in regenerative treatment of various intractable diseases. Transient receptor potential melastatin 7 (Trpm7) regulates Ca²⁺ as a nonselective ion channel and is essential for early embryonic development; however, the precise role of Trpm7 in mESCs has not been clearly elucidated. In this study, we showed that the inhibition of Trpm7 affects the pluripotency and self-renewal of mESCs. We found that short hairpin RNA (shRNA)-mediated suppression of Trpm7 resulted in decreased expression of transcriptional regulators, Oct4 and Sox2, which maintain stemness in mESCs. In addition, Trpm7 knockdown led to alterations in the basic properties of mESCs, such as decreased proliferation, cell cycle arrest at the G0/G1 phase, and increased apoptosis. Furthermore, embryoid body (EB) formation and teratoma formation assays revealed abnormal regulation of differentiation due to Trpm7 knockdown, including the smaller size of EBs, elevated ectodermal differentiation, and diminished endodermal and mesodermal differentiation. We found that EB Day 7 samples displayed decreased intracellular Ca²⁺ levels compared to those of the scrambled group. Finally, we identified that these alterations induced by Trpm7 knockdown occurred due to decreased phosphorylation of mechanistic target of rapamycin (mTOR) and subsequent activation of extracellular signal-regulated kinase (ERK) in mESCs. Our findings suggest that Trpm7 could be a novel regulator for maintaining stemness and modulating the differentiation of mESCs.

Insights Into Central Nervous System Glial Cell Formation and Function From Zebrafish

The term glia describes a heterogenous collection of distinct cell types that make up a large proportion of our nervous system. Although once considered the glue of the nervous system, the study of glial cells has evolved significantly in recent years, with a large body of literature now highlighting their complex and diverse roles in development and throughout life. This progress is due, in part, to advances in animal models in which the molecular and cellular mechanisms of glial cell development and function as well as neuron-glial cell interactions can be directly studied in vivo in real time, in intact neural circuits. In this review we highlight the instrumental role that zebrafish have played as a vertebrate model system for the study of glial cells, and discuss how the experimental advantages of the zebrafish lend themselves to investigate glial cell interactions and diversity. We focus in particular on recent studies that have provided insight into the formation and function of the major glial cell types in the central nervous system in zebrafish.

Retinal Stem/Progenitor Cells Derived From Adult Müller Glia for the Treatment of Retinal Degeneration

Over the past two decades, progress in our understanding of glial function has been revolutionary. Within the retina, a subset of glial cells termed the “Müller glia (MG),” have been demonstrated to play key roles in retinal homeostasis, structure and metabolism. Additionally, MG have also been shown to possess the regenerative capacity that varies across species. In teleost fish, MG respond to injury by reprogramming into stem-like cells capable of regenerating lost tissue. The expression of stem/progenitor cell markers has been demonstrated broadly in mammalian MG, including human MG, but their in vivo regenerative capacity appears evolutionarily limited. Advances in stem cell therapy have progressively elucidated critical mechanisms underlying innate MG reprogramming in teleost fish, which have shown promising results when applied to rodents. Furthermore, when cultured ex vivo, MG from mammals can differentiate into several retina cell types. In this review, we will explore the reparative and regenerative potential of MG in cellular therapy approaches, and outline our current understanding of embryonic retinal development, the stem-cell potential of MG in adult vertebrate retina (including human), and microenvironmental cues that guide MG reprogramming.