Therapeutic effect of bone marrow mesenchymal stem cells on laser-induced retinal injury in mice

Mesenchymal stem cells and mesenchymal stem cell-derived exosomes: a promising strategy for treating retinal degenerative diseases

Mesenchymal stem cells (MSCs) have emerged as a promising therapeutic strategy in regenerative medicine, demonstrating significant potential for clinical applications. Evidence suggests that MSCs not only exhibit multipotent differentiation potential but also exert critical therapeutic effects in retinal degenerative diseases via robust paracrine mechanisms. MSCs protect retinal cells from degenerative damage by modulating inflammation, inhibiting apoptosis, alleviating oxidative stress, and suppressing cell death pathways. Furthermore, MSCs contribute to retinal structural and functional stability by facilitating vascular remodeling and donating mitochondria to retinal cells. Of particular interest, MSC-derived exosomes have gained widespread attention as a compelling cell-free therapy. Owing to their potent anti-inflammatory, anti-apoptotic, and vascular-stabilizing properties, exosomes show significant promise for the treatment of retinal degenerative diseases.

Stem Cell-Based Therapies for Glaucoma Treatment: A Review Bridging the Gap in Veterinary Patients

Retinal diseases are characterized by progressive damage to retinal cells, leading to irreversible vision loss. Among these, glaucoma stands out as a multifactorial neurodegenerative disease involving elevated intraocular pressure, retinal ganglion cell apoptosis, and optic nerve damage, ultimately resulting in blindness in both humans and dogs. Stem cell-based therapies have emerged as a promising therapeutic option for such conditions due to their regenerative and neuroprotective potential. These therapies, particularly those based on mesenchymal stem cells, offer the potential to repair and protect retinal tissues through the bioactive molecules (growth factors, cytokines, chemokines) secreted, their secretome. However, research in this field, especially on the use of umbilical cord mesenchymal stem cells' secretome, remains sparse. Most clinical trials focus on human glaucomatous patients, leaving a significant gap in veterinary patients' application, especially in dogs, with additional research being needed to determine its usefulness in canine glaucoma treatment. Future studies should aim to evaluate these therapies across both human and veterinary contexts, broadening treatment possibilities for glaucoma.

Treatment of dry age-related macular degeneration: A review

Age-related macular degeneration is a global disease with a significant societal impact. The advent of anti-vascular endothelial growth factor therapy (anti-VEGF) has revolutionised the treatment of neovascular age-related macular degeneration (nAMD). Dry age-related macular degeneration (dAMD) is being investigated for possible therapeutic options. The therapeutic categories undergoing clinical trials include complement pathway inhibitors, visual cycle modulators, reduction of toxic byproducts, antioxidative therapy, neuroprotective agents, laser therapy, surgical options, gene therapy, stem cell therapy, and miscellaneous treatments. Two intravitreal anti-complement factors (pegcetacoplan and avacincaptad pegol) have recently shown phase 3 clinical trial evidence of a reduction in the growth of geographic atrophy. In this review, we provide an update on treatment options currently undergoing clinical research trials for the management of dAMD and preventing the progression of Geographic Atrophy (GA).

Intravitreal Administration of Retinal Organoids-Derived Exosomes Alleviates Photoreceptor Degeneration in Royal College of Surgeons Rats by Targeting the Mitogen-Activated Protein Kinase Pathway

Increasing evidence suggests that exosomes are involved in retinal cell degeneration, including their insufficient release; hence, they have become important indicators of retinopathies. The exosomal microRNA (miRNA), in particular, play important roles in regulating ocular and retinal cell functions, including photoreceptor maturation, maintenance, and visual function. Here, we generated retinal organoids (ROs) from human induced pluripotent stem cells that differentiated in a conditioned medium for 60 days, after which exosomes were extracted from ROs (Exo-ROs). Subsequently, we intravitreally injected the Exo-RO solution into the eyes of the Royal College of Surgeons (RCS) rats. Intravitreal Exo-RO administration reduced photoreceptor apoptosis, prevented outer nuclear layer thinning, and preserved visual function in RCS rats. RNA sequencing and miRNA profiling showed that exosomal miRNAs are mainly involved in the mitogen-activated protein kinase (MAPK) signaling pathway. In addition, the expression of MAPK-related genes and proteins was significantly decreased in the Exo-RO-treated group. These results suggest that Exo-ROs may be a potentially novel strategy for delaying retinal degeneration by targeting the MAPK signaling pathway.

Pathological mechanisms of neuroimmune response and multitarget disease-modifying therapies of mesenchymal stem cells in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disease characterized by the degeneration of dopaminergic neurons in the substantia nigra (SN); the etiology and pathological mechanism of the disease are still unclear. Recent studies have shown that the activation of a neuroimmune response plays a key role in the development of PD. Alpha-synuclein (α-Syn), the primary pathological marker of PD, can gather in the SN and trigger a neuroinflammatory response by activating microglia which can further activate the dopaminergic neuron's neuroimmune response mediated by reactive T cells through antigen presentation. It has been shown that adaptive immunity and antigen presentation processes are involved in the process of PD and further research on the neuroimmune response mechanism may open new methods for its prevention and therapy. While current therapeutic regimens are still focused on controlling clinical symptoms, applications such as immunoregulatory strategies can delay the symptoms and the process of neurodegeneration. In this review, we summarized the progression of the neuroimmune response in PD based on recent studies and focused on the use of mesenchymal stem cell (MSC) therapy and challenges as a strategy of disease-modifying therapy with multiple targets.

Mesenchymal stromal/stem cell (MSC)-derived exosomes in clinical trials

Mesenchymal stromal/stem cells (MSCs) are widely utilized in cell therapy because of their robust immunomodulatory and regenerative properties. Their paracrine activity is one of the most important features that contribute to their efficacy. Recently, it has been demonstrated that the production of various factors via extracellular vesicles, especially exosomes, governs the principal efficacy of MSCs after infusion in experimental models. Compared to MSCs themselves, MSC-derived exosomes (MSC-Exos) have provided significant advantages by efficiently decreasing unfavorable adverse effects, such as infusion-related toxicities. MSC-Exos is becoming a promising cell-free therapeutic tool and an increasing number of clinical studies started to assess the therapeutic effect of MSC-Exos in different diseases. In this review, we summarized the ongoing and completed clinical studies using MSC-Exos for immunomodulation, regenerative medicine, gene delivery, and beyond. Additionally, we summarized MSC-Exos production methods utilized in these studies with an emphasis on MSCs source, MSC-Exos isolation methods, characterization, dosage, and route of administration. Lastly, we discussed the current challenges and future directions of exosome utilization in different clinical studies as a novel therapeutic strategy.

Mesenchymal Stromal Cells and their EVs as Potential Leads for SARSCoV2 Treatment

In December 2019, a betacoronavirus was isolated from pneumonia cases in China and rapidly turned into a pandemic of COVID-19. The virus is an enveloped positive-sense ssRNA and causes a severe respiratory syndrome along with a cytokine storm, which is the main cause of most complications. Therefore, treatments that can effectively control the inflammatory reactions are necessary. Mesenchymal Stromal Cells and their EVs are well-known for their immunomodulatory effects, inflammation reduction, and regenerative potentials. These effects are exerted through paracrine secretion of various factors. Their EVs also transport various molecules such as microRNAs to other cells and affect recipient cells' behavior. Scores of research and clinical trials have indicated the therapeutic potential of EVs in various diseases. EVs also seem to be a promising approach for severe COVID-19 treatment. EVs have also been used to develop vaccines since EVs are biocompatible nanoparticles that can be easily isolated and engineered. In this review, we have focused on the use of Mesenchymal Stromal Cells and their EVs for the treatment of COVID-19, their therapeutic capabilities, and vaccine development.

Mesenchymal-Stem-Cell-Based Strategies for Retinal Diseases

Retinal diseases are major causes of irreversible vision loss and blindness. Despite extensive research into their pathophysiology and etiology, pharmacotherapy effectiveness and surgical outcomes remain poor. Based largely on numerous preclinical studies, administration of mesenchymal stem cells (MSCs) as a therapeutic strategy for retinal diseases holds great promise, and various approaches have been applied to the therapies. However, hindered by the retinal barriers, the initial vision for the stem cell replacement strategy fails to achieve the anticipated effect and has now been questioned. Accumulating evidence now suggests that the paracrine effect may play a dominant role in MSC-based treatment, and MSC-derived extracellular vesicles emerge as a novel compelling alternative for cell-free therapy. This review summarizes the therapeutic potential and current strategies of this fascinating class of cells in retinal degeneration and other retinal dysfunctions.

Stem Cell-based Therapeutic and Diagnostic Approaches in Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative impairment mainly recognized by memory loss and cognitive deficits. However, the current therapies against AD are mostly limited to palliative medications, prompting researchers to investigate more efficient therapeutic approaches for AD, such as stem cell therapy. Recent evidence has proposed that extensive neuronal and synaptic loss and altered adult neurogenesis, which is perceived pivotal in terms of plasticity and network maintenance, occurs early in the course of AD, which exacerbates neuronal vulnerability to AD. Thus, regeneration and replenishing the depleted neuronal networks by strengthening the endogenous repair mechanisms or exogenous stem cells and their cargoes is a rational therapeutic approach. Currently, several stem cell-based therapies as well as stem cell products like exosomes, have shown promising results in the early diagnosis of AD.

OBJECTIVE

This review begins with a comparison between AD and normal aging pathophysiology and a discussion on open questions in the field. Next, summarizing the current stem cell-based therapeutic and diagnostic approaches, we declare the advantages and disadvantages of each method. Also, we comprehensively evaluate the human clinical trials of stem cell therapies for AD.

METHODOLOGY

Peer-reviewed reports were extracted through Embase, PubMed, and Google Scholar until 2021.

RESULTS

With several ongoing clinical trials, stem cells and their derivatives (e.g., exosomes) are an emerging and encouraging field in diagnosing and treating neurodegenerative diseases. Although stem cell therapies have been successful in animal models, numerous clinical trials in AD patients have yielded unpromising results, which we will further discuss.

Current Development, Obstacle and Futural Direction of Induced Pluripotent Stem Cell and Mesenchymal Stem Cell Treatment in Degenerative Retinal Disease

Degenerative retinal disease is one of the major causes of vision loss around the world. The past several decades have witnessed emerging development of stem cell treatment for retinal disease. Nevertheless, sourcing stem cells remains controversial due to ethical concerns and their rarity. Furthermore, induced pluripotent stem cells (iPSCs) and mesenchymal stem cells (MSCs) are both isolated from patients’ mature tissues; thus, issues such as avoiding moral controversy and adverse events related to immunosuppression and obtaining a large number of cells have opened a new era in regenerative medicine. This review focuses on the current application and development, clinical trials, and latest research of stem cell therapy, as well as its limitations and future directions.

Retina stem cells, hopes and obstacles

Retinal degeneration is a major contributor to visual dysfunction worldwide. Although it comprises several eye diseases, loss of retinal pigment epithelial (RPE) and photoreceptor cells are the major contributors to their pathogenesis. Early therapies included diverse treatments, such as provision of anti-vascular endothelial growth factor and many survival and trophic factors that, in some cases, slow down the progression of the degeneration, but do not effectively prevent it. The finding of stem cells (SC) in the eye has led to the proposal of cell replacement strategies for retina degeneration. Therapies using different types of SC, such as retinal progenitor cells (RPCs), embryonic SC, pluripotent SCs (PSCs), induced PSCs (iPSCs), and mesenchymal stromal cells, capable of self-renewal and of differentiating into multiple cell types, have gained ample support. Numerous preclinical studies have assessed transplantation of SC in animal models, with encouraging results. The aim of this work is to revise the different preclinical and clinical approaches, analyzing the SC type used, their efficacy, safety, cell attachment and integration, absence of tumor formation and immunorejection, in order to establish which were the most relevant and successful. In addition, we examine the questions and concerns still open in the field. The data demonstrate the existence of two main approaches, aimed at replacing either RPE cells or photoreceptors. Emerging evidence suggests that RPCs and iPSC are the best candidates, presenting no ethical concerns and a low risk of immunorejection. Clinical trials have already supported the safety and efficacy of SC treatments. Serious concerns are pending, such as the risk of tumor formation, lack of attachment or integration of transplanted cells into host retinas, immunorejection, cell death, and also ethical. However, the amazing progress in the field in the last few years makes it possible to envisage safe and effective treatments to restore vision loss in a near future.

SDF-1/CXCR4 Augments the Therapeutic Effect of Bone Marrow Mesenchymal Stem Cells in the Treatment of Lipopolysaccharide-Induced Liver Injury by Promoting Their Migration Through PI3K/Akt Signaling Pathway

Mesenchymal stem cells (MSCs) are thought to have great potential in the therapy of acute liver injury. It is possible that these cells may be regulated by the stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor-4 (CXCR4) signaling axis, which has been shown to promote stem cells migration in the inflammation-associated diseases. However, the effects of SDF-1/CXCR4 axis on the MSCs-transplantation-based treatment for acute liver injury and the underlying mechanisms are largely unknown. In this study, we sought to determine whether SDF-1/CXCR4 would augment the therapeutic effect of bone marrow mesenchymal stem cells (BMSCs) by promoting their migration, which may result from activating the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway, in a rat acute liver injury model induced by lipopolysaccharide (LPS). We found that BMSCs transplantation markedly attenuated liver injury and improved the survival of LPS-treated rats. Of interest, overexpression of CXCR4 in BMSCs could substantially promote their migration both in vitro and in vivo, and result in even better therapeutic effects. This might be attributed to the activation of PI3K/Akt signaling pathway in BMSCs that is downstream of CXCR4, as demonstrated by the use of the CXCR4 antagonist AMD3100 and PI3K pathway inhibitor LY294002 assays in vitro and in vivo. Together, our results unraveled a novel molecular mechanism for the therapeutic effect of BMSCs for the treatment of acute liver injury, which may shed a new light on the clinical application of BMSCs for acute liver failure.

Exosomes as Naturally Occurring Vehicles for Delivery of Biopharmaceuticals: Insights from Drug Delivery to Clinical Perspectives

Exosomes as nanosized vesicles are emerging as drug delivery systems for therapeutics owing to their natural origin, their ability to mediate intercellular communication, and their potential to encapsulate various biological molecules such as proteins and nucleic acids within the lipid bilayer membrane or in the lumen. Exosomes contain endogenous components (proteins, lipids, RNA) that could be used to deliver cargoes to target cells, offering an opportunity to diagnose and treat various diseases. Owing to their ability to travel safely in extracellular fluid and to transport cargoes to target cells with high efficacy, exosomes offer enhanced delivery of cargoes in vivo. However, several challenges related to the stabilization of the exosomes, the production of sufficient amounts of exosomes with safety and efficacy, the efficient loading of drugs into exosomes, the clearance of exosomes from circulation, and the transition from the bench scale to clinical production may limit their development and clinical use. For the clinical use of exosomes, it is important to understand the molecular mechanisms behind the transport and function of exosome vesicles. This review exploits techniques related to the isolation and characterization of exosomes and their drug delivery potential to enhance the therapeutic outcome and stabilization methods. Further, routes of administration, clinical trials, and regulatory aspects of exosomes will be discussed in this review.

Emerging Role of Exosomes in Retinal Diseases

Retinal diseases, the leading causes of vison loss and blindness, are associated with complicated pathogeneses such as angiogenesis, inflammation, immune regulation, fibrous proliferation, and neurodegeneration. The retina is a complex tissue, where the various resident cell types communicate between themselves and with cells from the blood and immune systems. Exosomes, which are bilayer membrane vesicles with diameters of 30–150 nm, carry a variety of proteins, lipids, and nucleic acids, and participate in cell-to-cell communication. Recently, the roles of exosomes in pathophysiological process and their therapeutic potential have been emerging. Here, we critically review the roles of exosomes as possible intracellular mediators and discuss the possibility of using exosomes as therapeutic agents in retinal diseases.

A Promising Strategy for Non-Arteritic Anterior Ischemic Optic Neuropathy: Intravitreal Mesenchymal Stem Cell Exosome

Non-arteritic anterior ischemic optic neuropathy (NAION) is a leading cause of optic nerverelated permanent visual impairment among individuals of over 50 years of age after glaucoma. Due to perplexing disorder regarding its pathogenesis, there is still no widely accepted and established treatment plan. Mesenchymal stem cells (MSCs) are one of the rare stem cell types that therapeutic agents for immunomodulation and ischemic tissue repair in clinical practice. However, there are certain disadvantages in using MSCs, such as potential tumorigenicity, need for autologous collection, and short survival time. Previous evidence suggested that MSC-exosome significantly attenuated post-ischemic neuronal damage and induced long-term neuroprotection associated with enhanced angiogenesis in MSCs. Therefore, we hypothesized that the intravitreal administration of MSC-exosome could be a potentially effective therapeutic approach for NAION by using a similar mechanism via promoting angiogenesis, neuro-regeneration, and neurological recovery, suppressing oxidative stress and reducing apoptosis, and suppressing inflammation and immunity based on its biological structure and function in NAION. Questions that need to be answered before testing clinically include dose regimen, injection frequency, the optimal duration of treatment, and duration of medication.

Human Dental Pulp Stem Cells (DPSCs) Therapy in Rescuing Photoreceptors and Establishing a Sodium Iodate-Induced Retinal Degeneration Rat Model

BACKGROUND

Different methods have been used to inject stem cells into the eye for research. We previously explored the intravitreal route. Here, we investigate the efficacy of intravenous and subretinal-transplanted human dental pulp stem cells (DPSCs) in rescuing the photoreceptors of a sodium iodate-induced retinal degeneration model.

METHODS

Three groups of Sprague Dawley rats were used: intervention, vehicle group and negative control groups (n = 6 in each). Intravenous injection of 60 mg/kg sodium iodate (day 0) induced retinal degeneration. On day 4 post-injection of sodium iodate, the rats in the intervention group received intravenous DPSC and subretinal DPSC in the right eye; rats in the vehicle group received subretinal Hank's balance salt solution and intravenous normal saline; while negative control group received nothing. Electroretinogram (ERG) was performed to assess the retinal function at day 0 (baseline), day 4, day 11, day 18, day 26, and day 32. By the end of the study at day 32, the rats were euthanized, and both their enucleated eyes were sent for histology.

RESULTS

No significant difference in maximal ERG a-wave (p = 0.107) and b-wave, (p = 0.153) amplitude was seen amongst the experimental groups. However, photopic 30 Hz flicker amplitude of the study eye showed significant differences in the 3 groups (p = 0.032). Within the intervention group, there was an improvement in 30 Hz flicker ERG response of all 6 treated right eyes, which was injected with subretinal DPSC; while the 30 Hz flicker ERG of the non-treated left eyes remained flat. Histology showed improved outer nuclear layer thickness in intervention group; however, findings were not significant compared to the negative and vehicle groups.

CONCLUSION

Combination of subretinal and intravenous injection of DPSCs may have potential to rescue cone function from a NaIO₃-induced retinal injury model.

Stem Cell Based Exosomes: Are They Effective in Disease or Health?

Exosomes are nano-sized vesicles involved in intercellular communication via delivery of molecules including lipids, nucleic acids, proteins, or other cellular components to distant or neighboring sites. Their ability to pass biological barriers, stability in physiological fluids without degradation, and distinctive affinity to target cells make exosomes very remarkable therapeutic vehicles. Virus-based approaches are some of the most widely used gene therapy methods; however, there are many issues need to be clarified such as high immunogenicity. Using of the exosomes procures the functional transfer of their cargo with minimal intervention from the immune system and it has been reported to be secure and well-tolerated. When the regenerative medicine is taken into consideration, stem cell-based approaches have been aimed to utilize but the general efficacy and safety profile of stem cell therapy has still not been enlightened. At this point, stem cell-derived exosomes exhibit a way to procure cell-free regenerative medicine with their unique characteristics. Exosomes are considered as appropriate and highly stable biological nano-vectors taking part in a wide variety of healthy and pathological processes for advanced targeted therapies. However, there are still crucial obstacles to achieve efficient isolation of large amount of specific and pure exosomes. Thus, large-scale exosome production under good manufacturing practice is required. The purpose of this review is to focus on stem cell-based exosomes for gene delivery and to introduce synthetic exosome-mimics as a potential alternative in the field of targeted gene therapies. Further, we aim to highlight the biobanking and large-scale manufacturing methods of exosomes.

Mesenchymal stem cell-derived exosomes for clinical use

Mesenchymal stem/stromal cells (MSCs) are commonly used as a source of cellular therapy due to their strong immunosuppressive and regenerative effects. One of the key mechanisms of MSC efficacy appears to derive from their paracrine activity. Recently, it has been shown that the secretion of different factors through extracellular vesicles known as exosomes, orchestrate the principle mechanisms of action of MSCs after infusion. The use of MSC-derived exosomes may provide considerable advantages over their counterpart live cells, potentially reducing undesirable side effects including infusional toxicities. In this review, we examine clinical trials of MSC-derived exosomes currently in progress for gene delivery, regenerative medicine, and immunomodulation. In addition, we summarize the limitations and clinical potential of this cell-free therapeutic strategy.

Towards stem cell-based neuronal regeneration for glaucoma

Glaucoma is a neurodegenerative disease as a leading cause of global blindness. Retinal ganglion cell (RGC) apoptosis and optic nerve damage are the main pathological changes. Patients have elevated intraocular pressure and progressive visual field loss. Unfortunately, current treatments for glaucoma merely stay at delaying the disease progression. As a promising treatment, stem cell-based neuronal regeneration therapy holds potential for glaucoma, thereby great efforts have been paid on it. RGC regeneration and transplantation are key approaches for the future treatment of glaucoma. A line of studies have shown that a variety of cells can be used to regenerate RGCs, including embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), mesenchymal stem cells (MSCs), and retinal progenitor cells (RPCs). In this review, we overview the current progress on the regeneration of pluripotent stem cell-derived RGCs and outlook the perspective and challenges in this field.

Stem Cell Ophthalmology Treatment Study (SCOTS): Bone Marrow-Derived Stem Cells in the Treatment of Age-Related Macular Degeneration

Background: Dry age-related macular degeneration (AMD) is one of the leading causes of vision loss in older patients. The macula accumulates drusen with loss of retinal pigment epithelial cells and photoreceptors. Abnormal subretinal neovascularization is absent. There is no effective drug therapy for dry AMD and a large proportion of patients progress to legal blindness from macular atrophy. The Stem Cell Ophthalmology Treatment Study (SCOTS) was conducted to assess the effect of bone marrow-derived stem cells (BMSCs) on dry AMD and other retinal and optic nerve diseases. Methods: Thirty-two eyes were treated with BMSC per the protocols in SCOTS. Provision of BMSCs in Arm 1 was via retrobulbar (RB), sub-tenons (ST) and intravenous (IV); Arm 2 via intravitreal, RB, ST and IV; Arm 3 via subretinal and IV. Patient age averaged 78 years old and ranged from 69 to 90. Visual acuity preoperatively ranged from counting fingers to 20/50-2 with an average preoperative LogMAR of 1.125. Results: Following treatment, 20 of 32 (63%) of eyes experienced improvement in visual acuity averaging 27.6% on LogMAR and ranging from 2.5% to 44.6%. The mean improvement in LogMAR was 0.963 with a standard deviation (SD) of 0.42. The visual acuity remained stable in 34% of treated eyes. One eye continued to worsen as a consequence of disease progression. The results showed high statistical significance with p ≤ 0.001. The procedures were conducted safely, and no complications were observed. Conclusion: Treatment of dry AMD with BMSC using the protocols developed in the SCOTS clinical trial has shown statistically significant clinical benefit improving visual acuity and potentially delaying visual loss in the disease.

Mesenchymal stem cell-derived extracellular vesicles as a new therapeutic strategy for ocular diseases

Mesenchymal stem cells (MSCs) have attracted considerable attention for their activity in the treatment of refractory visual disorders. Since MSCs were found to possess the beneficial effects by secreting paracrine factors rather than direct differentiation, MSC-derived extracellular vesicles (EVs) were widely studied in various disease models. MSCs generate abundant EVs, which act as important mediators by exchanging protein and genetic information between MSCs and target cells. It has been confirmed that MSC-derived EVs possess unique anti-inflammatory, anti-apoptotic, tissue repairing, neuroprotective, and immunomodulatory properties, similar to their parent cells. Upon intravitreal injection, MSC-derived EVs rapidly diffuse through the retina to alleviate retinal injury or inflammation. Due to possible risks associated with MSC transplantation, such as vitreous opacity and pathological proliferation, EVs appear to be a better choice for intravitreal injection. Small size EVs can pass through biological barriers easily and their contents can be modified genetically for optimal therapeutic effect. Hence, currently, they are also explored for the possibility of serving as drug delivery vehicles. In the current review, we describe the characteristics of MSC-derived EVs briefly, comprehensively summarize their biological functions in ocular diseases, and discuss their potential applications in clinical settings.

Human umbilical cord mesenchymal stem cells derived-exosomes in diseases treatment

Exosomes are extracellular vesicles with the size of 40-100 nm in diameter and a density of 1.13-1.19 g/mL, containing proteins, mRNAs, miRNAs, and DNAs. Exosomes change the recipient cells biochemical features through biomolecules delivery and play a role in cellular communication. These vesicles are produced from body fluids and different cell types like mesenchymal stem cells (MSCs). Evidence suggests that mesenchymal stem cells-derived exosome (MSC-EXO) exhibit functions similar to MSCs with low immunogenicity and no tumorization. MSCs can also be isolated from a variety of sources including human umbilical cord (HUC). Because of the non-invasive collection method, higher proliferation and lower immunogenicity, HUCMSC-EXO has been frequently used in regenerative medicine and various diseases treatment compared to the other MSC-EXO resources. This review aimed to investigate the applications of HUCMSC-EXO in different diseases.

Empowering Mesenchymal Stem Cells for Ocular Degenerative Disorders

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

Effects of mesenchymal stem cells and their exosomes on the healing of large and refractory macular holes

PURPOSE

To assess the efficacy of mesenchymal stem cells (MSCs) and MSC-derived exosomes (MSC-Exos) to promote the healing of large and refractory macular holes (MHs).

METHODS

Seven patients (age 51-75 years old) with large and long-standing idiopathic MHs underwent vitrectomy, internal limiting membrane peeling, MSC (two patients) or MSC-Exo (five patients) intravitreal injection, and heavy silicon oil, air, 20% SF6, or 14% C3F8 tamponade. The MSCs were isolated from human umbilical cord tissue, and MSC-Exos were isolated from the supernatants of cultured MSCs using sequential ultracentrifugation.

RESULTS

Five eyes underwent pars plana vitrectomy (PPV) only, while two underwent PPV combined with cataract surgery. Six MHs were closed, while one remained in a flat-open state. The best-corrected visual acuity (BCVA) was improved in five patients with MH closure and remained unchanged in one patient with MH closure who had a 4-year history of MH. A fibrotic membrane was observed on the surface of the retina in one patient who underwent MSC therapy. One patient who received a higher dose of MSC-Exos exhibited an inflammatory reaction.

CONCLUSIONS

MSC and MSC-Exo therapy may promote functional and anatomic recovery from MH. MSC-Exo therapy may be a useful and safe method for improving the visual outcomes after surgery for refractory MHs.

Intraperitoneal administration of adipose tissue-derived stem cells for the rescue of retinal degeneration in a mouse model via indigenous CNTF up-regulation by IL-6

As the world's population begins to age, retinal degeneration is an increasing problem, and various treatment modalities are being developed. However, there have been no therapies for degenerative retinal conditions that are not characterized by neovascularization. We investigated whether transplantation of mouse adipose tissue-derived stem cells (mADSC) into the intraperitoneal space has a rescue effect on NaIO3 -induced retinal degeneration in mice. In this study, mADSC transplantation recovered visual function and preserved the retinal outer layer structure compared to the control group without any integration of mADSC into the retina. Moreover, endogenous ciliary neurotrophic factor (CNTF) was elevated in the retinas of mADSC-treated mice. We found that lipopolysaccharide (LPS) or LPS-stimulated monocyte supernatant induced the secretion of granulocyte colony stimulating factor (GCSF), CD54, CXCL10, interleukin-6 (IL-6), and CCL5 from the mADSC by cytokine array. Network inference was conducted to investigate signaling networks related to CNTF regulation. Based on bioinformatics data, the expression of IL-6 was related to the expression of CNTF. Additionally, intravitreal injection of IL-6 in rats produced up-regulation of endogenous CNTF in the retina. mADSC had a rescue effect on retinal degeneration through the up-regulation of endogenous CNTF by IL-6. Thus, transplantation of mADSC could be a potential treatment option for retinal degeneration.

Required Time for Migration of Bone Marrow-derived Cells to Dental Pulp after Bone Marrow Transplantation

INTRODUCTION

This study aimed to evaluate the time required for bone marrow-derived cells (BMDCs) from transgenic green fluorescent protein (GFP)+ donor mice (GFP+ mice) to migrate into the dental pulp of wild-type GFP- recipient mice (GFP- mice) by using bone marrow transplantation (BMT) as an in vivo model for tracking BMDCs from GFP+ mice (GFP+ BMDCs).

METHODS

GFP+ BMDCs were injected into irradiated GFP- mice. Maxillary arches, tibiae, and femora from GFP- mice were isolated and processed at 24 hours, 48 hours, 4, 7, and 14 days, and 7 weeks after BMT. Confocal laser microscopy analyses were performed to assess the presence of GFP+ BMDCs in the dental pulp, and flow cytometry of BM was performed to confirm the efficiency of engraftment of GFP+ BMDCs.

RESULTS

Confocal laser microscopy analyses evidenced the presence of GFP+ BMDCs in the dental pulp of GFP- mice from 14 days to 7 weeks after BMT. There was no presence of GFP+ BMDCs at 24 hours, 48 hours, 4 days, and 7 days. Flow cytometry of the BM of GFP- mice demonstrated a constant increase in the presence of GFP+ BMDCs at 24 hours, 48 hours, and 4 days after BMT, which stabilized from 7 days to 7 weeks.

CONCLUSIONS

The study demonstrated the presence of GFP+ BMDCs in the dental pulp from 14 days to 7 weeks after BMT and the feasibility of using GFP+ animals and BMT as an in vivo model for tracking GFP+ BMDCs.

Overview of retinal differentiation potential of mesenchymal stem cells: A promising approach for retinal cell therapy

Retinal disease caused by retinal cell apoptosis leads to irreversible vision loss. Stem cell investigation efforts have been made to solve and cure retinal disorders. There are several sources of stem cells which have been used in these experiments. Numerous studies demonstrated that transplanted stem cells can migrate into and integrate in different layers of retina. Among these, mesenchymal stem cells (MSCs) were considered a promising source for cell therapy. Here, we review the literature assessing the potential of MSCs to differentiate into retinal cells in vivo and in vitro as well as their clinical application. However, more investigation is required to define the protocols that optimize stem cell differentiation and their functional integration in the retina.

Exosomes derived from MSCs ameliorate retinal laser injury partially by inhibition of MCP-1

Although accumulated evidence supports the notion that mesenchymal stem cells (MSCs) act in a paracrine manner, the mechanisms are still not fully understood. Recently, MSC-derived exosomes (MSC-Exos), a type of microvesicle released from MSCs, were thought to carry functional proteins and RNAs to recipient cells and play therapeutic roles. In the present study, we intravitreally injected MSCs derived from either mouse adipose tissue or human umbilical cord, and their exosomes to observe and compare their functions in a mouse model of laser-induced retinal injury. We found that both MSCs and their exosomes reduced damage, inhibited apoptosis, and suppressed inflammatory responses to obtain better visual function to nearly the same extent in vivo. Obvious down-regulation of monocyte chemotactic protein (MCP)-1 in the retina was found after MSC-Exos injection. In vitro, MSC-Exos also down-regulated MCP-1 mRNA expression in primarily cultured retinal cells after thermal injury. It was further demonstrated that intravitreal injection of an MCP-1-neutralizing antibody promoted the recovery of retinal laser injury, whereas the therapeutic effect of exosomes was abolished when MSC-Exos and MCP-1 were administrated simultaneously. Collectively, these results suggest that MSC-Exos ameliorate laser-induced retinal injury partially through down-regulation of MCP-1.

Research progress of stem cells on glaucomatous optic nerve injury

Glaucoma, the second leading cause of blindness, is an irreversible optic neuropathy. The mechanism of optic nerve injury caused by glaucoma is undefined at present. There is no effective treatment method for the injury. Stem cells have the capacity of self-renewal and differentiation. These two features have made them become the research focus on improving the injury at present. This paper reviews the application progress on different types of stem cells therapy for optic nerve injury caused by glaucoma.

An ex vivo gene therapy approach in X-linked retinoschisis

PURPOSE

X-linked retinoschisis (XLRS) is juvenile-onset macular degeneration caused by haploinsufficiency of the extracellular cell adhesion protein retinoschisin (RS1). RS1 mutations can lead to either a non-functional protein or the absence of protein secretion, and it has been established that extracellular deficiency of RS1 is the underlying cause of the phenotype. Therefore, we hypothesized that an ex vivo gene therapy strategy could be used to deliver sufficient extracellular RS1 to reverse the phenotype seen in XLRS. Here, we used adipose-derived, syngeneic mesenchymal stem cells (MSCs) that were genetically modified to secrete human RS1 and then delivered these cells by intravitreal injection to the retina of the Rs1h knockout mouse model of XLRS.

METHODS

MSCs were electroporated with two transgene expression systems (cytomegalovirus (CMV)-controlled constitutive and doxycycline-induced Tet-On controlled inducible), both driving expression of human RS1 cDNA. The stably transfected cells, using either constitutive mesenchymal stem cell (MSC) or inducible MSC cassettes, were assayed for their RS1 secretion profile. For single injection studies, 100,000 genetically modified MSCs were injected into the vitreous cavity of the Rs1h knockout mouse eye at P21, and data were recorded at 2, 4, and 8 weeks post-injection. The control groups received either unmodified MSCs or vehicle injection. For the multiple injection studies, the mice received intravitreal MSC injections at P21, P60, and P90 with data collection at P120. For the single- and multiple-injection studies, the outcomes were measured with electroretinography, optokinetic tracking responses (OKT), histology, and immunohistochemistry.

RESULTS

Two lines of genetically modified MSCs were established and found to secrete RS1 at a rate of 8 ng/million cells/day. Following intravitreal injection, RS1-expressing MSCs were found mainly in the inner retinal layers. Two weeks after a single injection of MSCs, the area of the schisis cavities was reduced by 65% with constitutive MSCs and by 83% with inducible MSCs, demonstrating improved inner nuclear layer architecture. This benefit was maintained up to 8 weeks post-injection and corresponded to a significant improvement in the electroretinogram (ERG) b-/a-wave ratio at 8 weeks (2.6 inducible MSCs; 1.4 untreated eyes, p<0.05). At 4 months after multiple injections, the schisis cavity areas were reduced by 78% for inducible MSCs and constitutive MSCs, more photoreceptor nuclei were present (700/µm constitutive MSC; 750/µm inducible MSC; 383/µm untreated), and the ERG b-wave was significantly improved (threefold higher with constitutive MSCs and twofold higher with inducible MSCs) compared to the untreated control group.

CONCLUSIONS

These results establish that extracellular delivery of RS1 rescues the structural and functional deficits in the Rs1h knockout mouse model and that this ex vivo gene therapy approach can inhibit progression of disease. This proof-of-principle work suggests that other inherited retinal degenerations caused by a deficiency of extracellular matrix proteins could be targeted by this strategy.

Revisiting the role of erythropoietin for treatment of ocular disorders

Erythropoietin (EPO) is a glycoprotein hormone conventionally thought to be responsible only in producing red blood cells in our body. However, with the discovery of the presence of EPO and EPO receptors in the retinal layers, the EPO seems to have physiological roles in the eye. In this review, we revisit the role of EPO in the eye. We look into the biological role of EPO in the development of the eye and the physiologic roles that it has. Apart from that, we seek to understand the mechanisms and pathways of EPO that contributes to the therapeutic and pathological conditions of the various ocular disorders such as diabetic retinopathy, retinopathy of prematurity, glaucoma, age-related macular degeneration, optic neuritis, and retinal detachment. With these understandings, we discuss the clinical applications of EPO for treatment of ocular disorders, modes of administration, EPO formulations, current clinical trials, and its future directions.

Thermally labile components of aqueous humor potently induce osteogenic potential in adipose-derived mesenchymal stem cells

Adipose-derived mesenchymal stem cells (ASCs) hold promise for use in cell-based therapies. Their intrinsic anti-inflammatory properties are potentially useful for treatments of inflammatory conditions such as uveitis, while their ability to differentiate along multiple cell lineages suggests use in regenerating damaged or degenerated tissue. However, how ASCs will respond to the intraocular environment is poorly studied. We have recently reported that aqueous humor (AH), the fluid that nourishes the anterior segment of the eye, potently increases alkaline phosphatase (ALP) activity of ASCs, indicating osteogenic differentiation. Here, we expand on our previous findings to better define the nature of this response. To this end, we cultured ASCs in the presence of 0, 5, 10, and 20% AH and assayed them for ALP activity. We found ALP activity correlates with increasing AH concentrations from 5 to 20%, and that longer treatments result in increased ALP activity. By using serum free media and pretreating AH with dextran-coated charcoal, we found that serum and charcoal-adsorbable AH components augment but are not required for this response. Further, by heat-treating the AH, we established that thermally labile components are required for the osteogenic response. Finally, we showed myocilin, a protein present in AH, could induce ALP activity in ASCs. However, this was to a lesser extent than untreated 5% AH, and myocilin could only partially rescue the effect after heat treatment, documenting there were additional thermally labile constituents of AH involved in the osteogenic response. Our work adds to the understanding of the induction of ALP in ASCs following exposure to AH, providing important insight in how ASCs will be influenced by the ocular environment. In conclusion, increased osteogenic potential upon exposure to AH represents a potential challenge to developing ASC cell-based therapies directed at the eye.