Advances in Regeneration of Retinal Ganglion Cells and Optic Nerves

CCR5-overexpressing mesenchymal stem cells protect against experimental autoimmune uveitis: insights from single-cell transcriptome analysis

Autoimmune uveitis is a leading cause of severe vision loss, and animal models provide unique opportunities for studying its pathogenesis and therapeutic strategies. Here we employ scRNA-seq, RNA-seq and various molecular and cellular approaches to characterize mouse models of classical experimental autoimmune uveitis (EAU), revealing that EAU causes broad retinal neuron degeneration and marker downregulation, and that Müller glia may act as antigen-presenting cells. Moreover, EAU immune response is primarily driven by Th1 cells, and results in dramatic upregulation of CC chemokines, especially CCL5, in the EAU retina. Accordingly, overexpression of CCR5, a CCL5 receptor, in mesenchymal stem cells (MSCs) enhances their homing capacity and improves their immunomodulatory outcomes in preventing EAU, by reducing infiltrating T cells and activated microglia and suppressing Nlrp3 inflammasome activation. Taken together, our data not only provide valuable insights into the molecular characteristics of EAU but also open an avenue for innovative MSC-based therapy.

Diabetic Retinopathy: New Treatment Approaches Targeting Redox and Immune Mechanisms

Diabetic retinopathy (DR) represents a severe complication of diabetes mellitus, characterized by irreversible visual impairment resulting from microvascular abnormalities. Since the global prevalence of diabetes continues to escalate, DR has emerged as a prominent area of research interest. The development and progression of DR encompass a complex interplay of pathological and physiological mechanisms, such as high glucose-induced oxidative stress, immune responses, vascular endothelial dysfunction, as well as damage to retinal neurons. Recent years have unveiled the involvement of genomic and epigenetic factors in the formation of DR mechanisms. At present, extensive research explores the potential of biomarkers such as cytokines, molecular and cell therapies, antioxidant interventions, and gene therapy for DR treatment. Notably, certain drugs, such as anti-VEGF agents, antioxidants, inhibitors of inflammatory responses, and protein kinase C (PKC)-β inhibitors, have demonstrated promising outcomes in clinical trials. Within this context, this review article aims to introduce the recent molecular research on DR and highlight the current progress in the field, with a particular focus on the emerging and experimental treatment strategies targeting the immune and redox signaling pathways.

Mesenchymal stem cells for repairing glaucomatous optic nerve

Glaucoma is a common and complex neurodegenerative disease characterized by progressive loss of retinal ganglion cells (RGCs) and axons. Currently, there is no effective method to address the cause of RGCs degeneration. However, studies on neuroprotective strategies for optic neuropathy have increased in recent years. Cell replacement and neuroprotection are major strategies for treating glaucoma and optic neuropathy. Regenerative medicine research into the repair of optic nerve damage using stem cells has received considerable attention. Stem cells possess the potential for multidirectional differentiation abilities and are capable of producing RGC-friendly microenvironments through paracrine effects. This article reviews a thorough researches of recent advances and approaches in stem cell repair of optic nerve injury, raising the controversies and unresolved issues surrounding the future of stem cells.

Cell replacement with stem cell-derived retinal ganglion cells from different protocols

Glaucoma, characterized by a degenerative loss of retinal ganglion cells, is the second leading cause of blindness worldwide. There is currently no cure for vision loss in glaucoma because retinal ganglion cells do not regenerate and are not replaced after injury. Human stem cell-derived retinal ganglion cell transplant is a potential therapeutic strategy for retinal ganglion cell degenerative diseases. In this review, we first discuss a 2D protocol for retinal ganglion cell differentiation from human stem cell culture, including a rapid protocol that can generate retinal ganglion cells in less than two weeks and focus on their transplantation outcomes. Next, we discuss using 3D retinal organoids for retinal ganglion cell transplantation, comparing cell suspensions and clusters. This review provides insight into current knowledge on human stem cell-derived retinal ganglion cell differentiation and transplantation, with an impact on the field of regenerative medicine and especially retinal ganglion cell degenerative diseases such as glaucoma and other optic neuropathies.

An effective pharmacological hydrogel induces optic nerve repair and improves visual function

Irreversible eye lesions, such as glaucoma and traumatic optic neuropathy, can cause blindness; however, no effective treatments exist. The optic nerve, in particular, lacks the capacity to spontaneously regenerate, requiring the development of an effective approach for optic nerve repair, which has proven challenging. Here, we demonstrate that a combination of the small molecules 3BDO and trichostatin A (TSA)-which regulate mTOR and HDAC, respectively-packaged in thermosensitive hydrogel for 4-week-sustained release after intravitreal injection, effectively induced optic nerve regeneration in a mouse model of optic nerve crush injury. Moreover, this combination of 3BDO and TSA also protected axon projections and improved visual responses in an old mouse model (11 months old) of glaucoma. Taken together, our data provide a new, local small molecule-based treatment for the effective induction of optic nerve repair, which may represent a foundation for the development of pharmacological methods to treat irreversible eye diseases.

Aldose reductase is a potential therapeutic target for neurodegeneration

Neurodegeneration is a complex process involving various inflammatory mediators and cellular responses. Aldose reductase (AR) is a key enzyme in the polyol pathway, which converts glucose to sorbitol. Beyond its metabolic role, AR has also been found to play a significant role in modulating neuroinflammation. This review aims to provide an overview of the current knowledge regarding the involvement of AR inhibition in attenuating neuroinflammation and complications from diabetic neuropathies. Here, we review the literature regarding AR and neuropathy/neurodegeneration. We discuss the mechanisms underlying the influence of AR inhibitors on ocular inflammation, beta-amyloid-induced neurodegeneration, and optic nerve degeneration. Furthermore, potential therapeutic strategies targeting AR in neurodegeneration are explored. The understanding of AR's role in neurodegeneration may lead to the development of novel therapeutic interventions for other neuroinflammatory disorders.

Therapeutic strategies for glaucoma and optic neuropathies

Glaucoma is a neurodegenerative eye disease that causes permanent vision impairment. The main pathological characteristics of glaucoma are retinal ganglion cell (RGC) loss and optic nerve degeneration. Glaucoma can be caused by elevated intraocular pressure (IOP), although some cases are congenital or occur in patients with normal IOP. Current glaucoma treatments rely on medicine and surgery to lower IOP, which only delays disease progression. First-line glaucoma medicines are supported by pharmacotherapy advancements such as Rho kinase inhibitors and innovative drug delivery systems. Glaucoma surgery has shifted to safer minimally invasive (or microinvasive) glaucoma surgery, but further trials are needed to validate long-term efficacy. Further, growing evidence shows that adeno-associated virus gene transduction and stem cell-based RGC replacement therapy hold potential to treat optic nerve fiber degeneration and glaucoma. However, better understanding of the regulatory mechanisms of RGC development is needed to provide insight into RGC differentiation from stem cells and help choose target genes for viral therapy. In this review, we overview current progress in RGC development research, optic nerve fiber regeneration, and human stem cell-derived RGC differentiation and transplantation. We also provide an outlook on perspectives and challenges in the field.

Trim9 regulates the directional differentiation of retinal Müller cells to retinal ganglion cells

OBJECTIVES

Glaucoma is a leading cause of irreversible blindness, and effective therapies to reverse the visual system damage caused by glaucoma are still lacking. Recently, the stem cell therapy enable the repair and regeneration of the damaged retinal neurons, but challenges regarding the source of stem cells remain. This study aims to investigate a protocol that allows the dedifferentiation of Müller cells into retinal stem cells, following by directed differentiation into retinal ganglion cells with high efficiency, and to provide a new method of cellular acquisition for retinal stem cells.

METHODS

Epidermal cell growth factor and fibroblast growth factor 2 were used to induce the dedifferentiation of rat retinal Müller cells into retinal neural stem cells. Retinal stem cells derived from Müller cells were infected with a Trim9 overexpression lentiviral vector (PGC-FU-Trim9-GFP), and the efficiency of viral infection was assessed by fluorescence microscopy and flow cytometry. Retinoic acid and brain-derived neurotrophic factor treatments were used to induce the differentiation of the retinal stem cells into neurons and glial cells with or without the overexpression of Trim9. The expressions of each cellular marker (GLAST, GS, rhodopsin, PKC, HPC-1, Calbindin, Thy1.1, Brn-3b, Nestin, Pax6) were detected by immunofluorescence, PCR/real-time RT-PCR or Western blotting.

RESULTS

Rat retinal Müller cells expressed neural stem cells markers (Nestin and Pax6) with the treatment of epidermal cell growth factor and fibroblast growth factor 2. The Thy1.1 positive cell rate of retinal stem cells overexpressing Trim9 was significantly increased, indicating their directional differentiation into retinal ganglion cells after treatment with retinoic acid and brain-derived neurotrophic factor.

CONCLUSIONS

In this study, rat retinal Müller cells are dedifferentiated into retinal stem cells successfully, and Trim9 promotes the directional differentiation from retinal stem cells to retinal ganglion cells effectively.

Context-Dependent Effects of the Ketogenic Diet on Retinal Ganglion Cell Survival and Axonal Regeneration After Optic Nerve Injury

Purpose: There is increasing interest in nonpharmacologic approaches to protect retinal ganglion cells (RGCs) after injury and enhance the efficacy of therapeutic molecules. Accumulating evidence demonstrates neuroprotection by the high-fat low-carbohydrate ketogenic diet (KD) in humans and animal models of neurologic diseases. However, no studies to date have examined whether the KD protects RGCs and promotes axonal regrowth after traumatic injury to the optic nerve (ON) or whether it increases efficacy of experimental proregenerative molecules. In this study, we investigated whether the KD promoted RGC survival and axonal regeneration after ON injury in the presence and absence of neuroprotective Wnt3a ligand. Methods: Adult mice were placed on a KD or control diet before ON crush injury and remained on the diet until the end of the experiment. Nutritional ketosis was confirmed by measuring serum beta-hydroxybutyrate levels. Mice were intravitreally injected with Wnt3a ligand or phosphate-buffered saline (PBS), and RGC survival, function, axonal regeneration, and inflammatory responses were measured. Results: Mice fed the KD showed increased RGC survival and reduced inflammatory cells in PBS-injected mice. Also, mice fed the KD had increased RGC functional responses but not increased RGC numbers in the presence of Wnt3a, indicating that the KD did not enhance the prosurvival effect of Wnt3a. The KD did not promote axonal regeneration in the presence or absence of Wnt3a. Conclusions: The KD has a complex protective effect after ON injury and cotreatment with Wnt3a. This work sets the foundation for studies identifying underlying molecular mechanisms.

The Neuroprotective Effect of Activation of Sigma-1 Receptor on Neural Injury by Optic Nerve Crush

Purpose

This study aimed to explore the neuroprotective effects of sigma-1 receptor (S1R) on optic nerve crush (ONC) mice by upregulating its expression through intravitreal injection of adeno-associated virus (AAV).

Methods

The animals were divided into four groups. Mice that underwent ONC were administered an intravitreal injection with blank vector (ONC group), with AAV targeting downregulation of S1R (S1R-sh group), or with AAV targeting overexpression of S1R (S1R-AAV group). Mice in the control group underwent intravitreal injection with blank vector. The thickness of each layer of the retina was measured through optical coherence tomography, and the apoptotic rate of retinal neurons was determined using the TUNEL assay. The expression levels of brain-derived neurotrophic factor (BDNF) and S1R were quantified through western blot. Electroretinogram (ERG) was performed to evaluate the visual function.

Results

The thickness of the total retina (P = 0.001), ganglion cell layer (P = 0.017), and inner nuclear layer (P = 0.002) in S1R-AAV group was significantly thicker than that of the ONC group. The number of retinal apoptotic cells in the S1R-AAV group was 23% lower than that in the ONC group (P = 0.002). ERG results showed that, compared to the ONC group, the amplitudes of the a- and b-waves were higher in the S1R-AAV group (a-wave, P < 0.001; b-wave, P = 0.007). Western blot showed that the expression of BDNF in the S1R-AAV group was higher than that in the ONC group (P < 0.001).

Conclusions

Activation of S1R in the retina through intravitreal injection of AAV can effectively maintain the retina structure, promote neuronal cell survival, and protect visual function.

Genome-wide analysis of genetic pleiotropy and causal genes across three age-related ocular disorders

Age-related macular degeneration (AMD), cataract, and glaucoma are leading causes of blindness worldwide. Previous genome-wide association studies (GWASs) have revealed a variety of susceptible loci associated with age-related ocular disorders, yet the genetic pleiotropy and causal genes across these diseases remain poorly understood. By leveraging large-scale genetic and observational data from ocular disease GWASs and UK Biobank (UKBB), we found significant pairwise genetic correlations and consistent epidemiological associations among these ocular disorders. Cross-disease meta-analysis uncovered seven pleiotropic loci, three of which were replicated in an additional cohort. Integration of variants in pleiotropic loci and multiple single-cell omics data identified that Müller cells and astrocytes were likely trait-related cell types underlying ocular comorbidity. In addition, we comprehensively integrated eye-specific gene expression quantitative loci (eQTLs), epigenomic profiling, and 3D genome data to prioritize causal pleiotropic genes. We found that pleiotropic genes were essential in nerve development and eye pigmentation, and targetable by aflibercept and pilocarpine for the treatment of AMD and glaucoma. These findings will not only facilitate the mechanistic research of ocular comorbidities but also benefit the therapeutic optimization of age-related ocular diseases.

Ex Vivo Integration of Human Stem Retinal Ganglion Cells into the Mouse Retina

Cell replacement therapies may be key in achieving functional recovery in neurodegenerative optic neuropathies diseases such as glaucoma. One strategy that holds promise in this regard is the use of human embryonic stem cell and induced pluripotent stem-derived retinal ganglion cells (hRGCs). Previous hRGC transplantation studies have shown modest success. This is in part due to the low survival and integration of the transplanted cells in the host retina. The field is further challenged by mixed assays and outcome measurements that probe and determine transplantation success. Thefore, we have devised a transplantation assay involving hRGCs and mouse retina explants that bypasses physical barriers imposed by retinal membranes. We show that hRGC neurites and somas are capable of invading mouse explants with a subset of hRGC neurites being guided by mouse RGC axons. Neonatal mouse retina explants, and to a lesser extent, adult explants, promote hRGC integrity and neurite outgrowth. Using this assay, we tested whether suppmenting cultures with brain derived neurotrophic factor (BDNF) and the adenylate cyclase activator, forskolin, enhances hRGC neurite integration, neurite outgrowth, and integrity. We show that supplementing cultures with a combination BDNF and forskolin strongly favors hRGC integrity, increasing neurite outgrowth and complexity as well as the invasion of mouse explants. The transplantation assay presented here is a practical tool for investigating strategies for testing and optimizing the integration of donor cells into host tissues.

Advances in cell therapies using stem cells/progenitors as a novel approach for neurovascular repair of the diabetic retina

BACKGROUND

Diabetic retinopathy, a major complication of diabetes mellitus, is a leading cause of sigh-loss in working age adults. Progressive loss of integrity of the retinal neurovascular unit is a central element in the disease pathogenesis. Retinal ischemia and inflammatory processes drive interrelated pathologies such as blood retinal barrier disruption, fluid accumulation, gliosis, neuronal loss and/or aberrant neovascularisation. Current treatment options are somewhat limited to late-stages of the disease where there is already significant damage to the retinal architecture arising from degenerative, edematous and proliferative pathology. New preventive and interventional treatments to target early vasodegenerative and neurodegenerative stages of the disease are needed to ensure avoidance of sight-loss.

MAIN BODY

Historically, diabetic retinopathy has been considered a primarily microvascular disease of the retina and clinically it is classified based on the presence and severity of vascular lesions. It is now known that neurodegeneration plays a significant role during the pathogenesis. Loss of neurons has been documented at early stages in pre-clinical models as well as in individuals with diabetes and, in some, even prior to the onset of clinically overt diabetic retinopathy. Recent studies suggest that some patients have a primarily neurodegenerative phenotype. Retinal pigment epithelial cells and the choroid are also affected during the disease pathogenesis and these tissues may also need to be addressed by new regenerative treatments. Most stem cell research for diabetic retinopathy to date has focused on addressing vasculopathy. Pre-clinical and clinical studies aiming to restore damaged vasculature using vasoactive progenitors including mesenchymal stromal/stem cells, adipose stem cells, CD34+ cells, endothelial colony forming cells and induced pluripotent stem cell derived endothelial cells are discussed in this review. Stem cells that could replace dying neurons such as retinal progenitor cells, pluripotent stem cell derived photoreceptors and ganglion cells as well as Müller stem cells are also discussed. Finally, challenges of stem cell therapies relevant to diabetic retinopathy are considered.

CONCLUSION

Stem cell therapies hold great potential to replace dying cells during early and even late stages of diabetic retinopathy. However, due to the presence of different phenotypes, selecting the most suitable stem cell product for individual patients will be crucial for successful treatment.

Microbiota and Ocular Diseases

Recent advances have identified significant associations between the composition and function of the gut microbiota and various disorders in organ systems other than the digestive tract. Utilizing next-generation sequencing and multiomics approaches, the microbial community that possibly impacts ocular disease has been identified. This review provides an overview of the literature on approaches to microbiota analysis and the roles of commensal microbes in ophthalmic diseases, including autoimmune uveitis, age-related macular degeneration, glaucoma, and other ocular disorders. In addition, this review discusses the hypothesis of the "gut-eye axis" and evaluates the therapeutic potential of targeting commensal microbiota to alleviate ocular inflammation.