Exosomes Derived from Nerve Stem Cells Loaded with FTY720 Promote the Recovery after Spinal Cord Injury in Rats by PTEN/AKT Signal Pathway

Neural Stem Cell-Derived Small Extracellular Vesicles: key Players in Ischemic Stroke Therapy - A Comprehensive Literature Review

Ischemic stroke, being a prominent contributor to global disability and mortality, lacks an efficacious therapeutic approach in current clinical settings. Neural stem cells (NSCs) are a type of stem cell that are only found inside the nervous system. These cells can differentiate into various kinds of cells, potentially regenerating or restoring neural networks within areas of the brain that have been destroyed. This review begins by providing an introduction to the existing therapeutic approaches for ischemic stroke, followed by an examination of the promise and limits associated with the utilization of NSCs for the treatment of ischemic stroke. Subsequently, a comprehensive overview was conducted to synthesize the existing literature on the underlying processes of neural stem cell-derived small extracellular vesicles (NSC-sEVs) transplantation therapy in the context of ischemic stroke. These mechanisms encompass neuroprotection, inflammatory response suppression, and endogenous nerve and vascular regeneration facilitation. Nevertheless, the clinical translation of NSC-sEVs is hindered by challenges such as inadequate targeting efficacy and insufficient content loading. In light of these limitations, we have compiled an overview of the advancements in utilizing modified NSC-sEVs for treating ischemic stroke based on current methods of extracellular vesicle modification. In conclusion, examining NSC-sEVs-based therapeutic approaches is anticipated to be prominent in both fundamental and applied investigations about ischemic stroke.

Advances in extracellular vesicle-based combination therapies for spinal cord injury

Spinal cord injury is a severe insult to the central nervous system that causes persisting neurological deficits. The currently available treatments involve surgical, medical, and rehabilitative strategies. However, none of these techniques can markedly reverse neurological deficits. Recently, extracellular vesicles from various cell sources have been applied to different models of spinal cord injury, thereby generating new cell-free therapies for the treatment of spinal cord injury. However, the use of extracellular vesicles alone is still associated with some notable shortcomings, such as their uncertainty in targeting damaged spinal cord tissues and inability to provide structural support to damaged axons. Therefore, this paper reviews the latest combined strategies for the use of extracellular vesicle-based technology for spinal cord injury, including the combination of extracellular vesicles with nanoparticles, exogenous drugs and/or biological scaffold materials, which facilitate the targeting ability of extracellular vesicles and the combinatorial effects with extracellular vesicles. We also highlight issues relating to the clinical transformation of these extracellular vesicle-based combination strategies for the treatment of spinal cord injury.

Clinical applications of stem cell-derived exosomes

Although stem cell-based therapy has demonstrated considerable potential to manage certain diseases more successfully than conventional surgery, it nevertheless comes with inescapable drawbacks that might limit its clinical translation. Compared to stem cells, stem cell-derived exosomes possess numerous advantages, such as non-immunogenicity, non-infusion toxicity, easy access, effortless preservation, and freedom from tumorigenic potential and ethical issues. Exosomes can inherit similar therapeutic effects from their parental cells such as embryonic stem cells and adult stem cells through vertical delivery of their pluripotency or multipotency. After a thorough search and meticulous dissection of relevant literature from the last five years, we present this comprehensive, up-to-date, specialty-specific and disease-oriented review to highlight the surgical application and potential of stem cell-derived exosomes. Exosomes derived from stem cells (e.g., embryonic, induced pluripotent, hematopoietic, mesenchymal, neural, and endothelial stem cells) are capable of treating numerous diseases encountered in orthopedic surgery, neurosurgery, plastic surgery, general surgery, cardiothoracic surgery, urology, head and neck surgery, ophthalmology, and obstetrics and gynecology. The diverse therapeutic effects of stem cells-derived exosomes are a hierarchical translation through tissue-specific responses, and cell-specific molecular signaling pathways. In this review, we highlight stem cell-derived exosomes as a viable and potent alternative to stem cell-based therapy in managing various surgical conditions. We recommend that future research combines wisdoms from surgeons, nanomedicine practitioners, and stem cell researchers in this relevant and intriguing research area.

Exosome-mediated repair of spinal cord injury: a promising therapeutic strategy

Spinal cord injury (SCI) is a catastrophic injury to the central nervous system (CNS) that can lead to sensory and motor dysfunction, which seriously affects patients' quality of life and imposes a major economic burden on society. The pathological process of SCI is divided into primary and secondary injury, and secondary injury is a cascade of amplified responses triggered by the primary injury. Due to the complexity of the pathological mechanisms of SCI, there is no clear and effective treatment strategy in clinical practice. Exosomes, which are extracellular vesicles of endoplasmic origin with a diameter of 30-150 nm, play a critical role in intercellular communication and have become an ideal vehicle for drug delivery. A growing body of evidence suggests that exosomes have great potential for repairing SCI. In this review, we introduce exosome preparation, functions, and administration routes. In addition, we summarize the effect and mechanism by which various exosomes repair SCI and review the efficacy of exosomes in combination with other strategies to repair SCI. Finally, the challenges and prospects of the use of exosomes to repair SCI are described.

Hydrogel-encapsulated extracellular vesicles for the regeneration of spinal cord injury

Spinal cord injury (SCI) is a critical neurological condition that may impair motor, sensory, and autonomous functions. At the cellular level, inflammation, impairment of axonal regeneration, and neuronal death are responsible for SCI-related complications. Regarding the high mortality and morbidity rates associated with SCI, there is a need for effective treatment. Despite advances in SCI repair, an optimal treatment for complete recovery after SCI has not been found so far. Therefore, an effective strategy is needed to promote neuronal regeneration and repair after SCI. In recent years, regenerative treatments have become a potential option for achieving improved functional recovery after SCI by promoting the growth of new neurons, protecting surviving neurons, and preventing additional damage to the spinal cord. Transplantation of cells and cells-derived extracellular vesicles (EVs) can be effective for SCI recovery. However, there are some limitations and challenges related to cell-based strategies. Ethical concerns and limited efficacy due to the low survival rate, immune rejection, and tumor formation are limitations of cell-based therapies. Using EVs is a helpful strategy to overcome these limitations. It should be considered that short half-life, poor accumulation, rapid clearance, and difficulty in targeting specific tissues are limitations of EVs-based therapies. Hydrogel-encapsulated exosomes have overcome these limitations by enhancing the efficacy of exosomes through maintaining their bioactivity, protecting EVs from rapid clearance, and facilitating the sustained release of EVs at the target site. These hydrogel-encapsulated EVs can promote neuroregeneration through improving functional recovery, reducing inflammation, and enhancing neuronal regeneration after SCI. This review aims to provide an overview of the current research status, challenges, and future clinical opportunities of hydrogel-encapsulated EVs in the treatment of SCI.

Fingolimod (FTY720) Hinders Interferon-γ-Mediated Fibrotic Scar Formation and Facilitates Neurological Recovery After Spinal Cord Injury

Following spinal cord injury (SCI), fibrotic scar inhibits axon regeneration and impairs neurological function recovery. It has been reported that T cell-derived interferon (IFN)-γ plays a pivotal role in promoting fibrotic scarring in neurodegenerative disease. However, the role of IFN-γ in fibrotic scar formation after SCI has not been declared. In this study, a spinal cord crush injury mouse was established. Western blot and immunofluorescence showed that IFN-γ was surrounded by fibroblasts at 3, 7, 14, and 28 days post-injury. Moreover, IFN-γ is mainly secreted by T cells after SCI. Further, in situ injection of IFN-γ into the normal spinal cord resulted in fibrotic scar formation and inflammation response at 7 days post-injection. After SCI, the intraperitoneal injection of fingolimod (FTY720), a sphingosine-1-phosphate receptor 1 (S1PR1) modulator and W146, an S1PR1 antagonist, significantly reduced T cell infiltration, attenuating fibrotic scarring via inhibiting IFN-γ/IFN-γR pathway, while in situ injection of IFN-γ diminished the effect of FTY720 on reducing fibrotic scarring. FTY720 treatment inhibited inflammation, decreased lesion size, and promoted neuroprotection and neurological recovery after SCI. These findings demonstrate that the inhibition of T cell-derived IFN-γ by FTY720 suppressed fibrotic scarring and contributed to neurological recovery after SCI.

Extracellular Vesicles: Therapeutic Potential in Central Nervous System Trauma by Regulating Cell Death

CNS (central nervous system) trauma, which is classified as SCI (spinal cord injury) and TBI (traumatic brain injury), is gradually becoming a major cause of accidental death and disability worldwide. Many previous studies have verified that the pathophysiological mechanism underlying cell death and the subsequent neuroinflammation caused by cell death are pivotal factors in the progression of CNS trauma. Simultaneously, EVs (extracellular vesicles), membrane-enclosed particles produced by almost all cell types, have been proven to mediate cell-to-cell communication, and cell death involves complex interactions among molecules. EVs have also been proven to be effective carriers of loaded bioactive components to areas of CNS trauma. Therefore, EVs are promising therapeutic targets to cure CNS trauma. However, the link between EVs and various types of cell death in the context of CNS trauma remains unknown. Therefore, in this review, we summarize the mechanism underlying EV effects, the relationship between EVs and cell death and the pathophysiology underlying EV effects on the CNS trauma based on information in published papers. In addition, we discuss the prospects of applying EVs to the CNS as feasible therapeutic strategies for CNS trauma in the future.

Neural stem cell-derived extracellular vesicles: The light of central nervous system diseases

Central nervous system (CNS) diseases are the leading cause of death worldwide. By performing compensatory functions and improving the inflammatory microenvironment, the transplantation of neural stem cells (NSCs) can promote functional recovery from brain injury, aging, brain tumours, and other diseases. However, the ability of NSCs to differentiate into neurons is limited, and they are associated with a risk of tumourigenicity. NSC-derived extracellular vesicles (NSC-EVs) can modulate the local microenvironment of the nervous system as well as distant neuronal functions. Thus, cell-free therapy may be a novel remedy for CNS disorders. This article reviews the characteristics, contents, and mechanisms of action of NSC-EVs as well as their roles and application prospects in various CNS diseases.

A swift expanding trend of extracellular vesicles in spinal cord injury research: a bibliometric analysis

Extracellular vesicles (EVs) in the field of spinal cord injury (SCI) have garnered significant attention for their potential applications in diagnosis and therapy. However, no bibliometric assessment has been conducted to evaluate the scientific progress in this area. A search of articles in Web of Science (WoS) from January 1, 1991, to May 1, 2023, yielded 359 papers that were analyzed using various online analysis tools. These articles have been cited 10,842 times with 30.2 times per paper. The number of publications experienced explosive growth starting in 2015. China and the United States led this research initiative. Keywords were divided into 3 clusters, including "Pathophysiology of SCI", "Bioactive components of EVs", and "Therapeutic effects of EVs in SCI". By integrating the average appearing year (AAY) of keywords in VoSviewer with the time zone map of the Citation Explosion in CiteSpace, the focal point of research has undergone a transformative shift. The emphasis has moved away from pathophysiological factors such as "axon", "vesicle", and "glial cell" to more mechanistic and applied domains such as "activation", "pathways", "hydrogels" and "therapy". In conclusions, institutions are expected to allocate more resources towards EVs-loaded hydrogel therapy and the utilization of innovative materials for injury mitigation.

Engineering strategies and optimized delivery of exosomes for theranostic application in nerve tissue

Severe injuries or diseases affecting the peripheral and central nervous systems can result in impaired organ function and permanent paralysis. Conventional interventions, such as drug administration and cell-based therapy, exhibit limited effectiveness due to their inability to preserve post-implantation cell survival and impede the deterioration of adjacent tissues. Exosomes have recently emerged as powerful tools for tissue repair owing to their proteins and nucleic acids, as well as their unique phospholipid properties, which facilitate targeted delivery to recipient cells. Engineering exosomes, obtained by manipulating the parental cells or directly functionalizing exosomes, play critical roles in enhancing regenerative repair, reducing inflammation, and maintaining physiological homeostasis. Furthermore, exosomes have been shown to restore neurological function when used in combination with biomaterials. This paper primarily focuses on the engineering strategies and delivery routes of exosomes related to neural research and emphasizes the theranostic application of optimized exosomes in peripheral nerve, traumatic spinal cord, and brain injuries. Finally, the prospects of exosomes development and their combination with other approaches will be discussed to enhance our knowledge on their theranostic effectiveness in neurological diseases.

Research progress of exosomes as drug carriers in cancer and inflammation

Extracellular vesicles (EVs) could be produced by most cells and play an important role in disease development. As a subtype of EVs, exosomes exhibit suitable size, rich surface markers and diverse contents, making them more appealing as potential drug carriers. Compared with traditional synthetic nanoparticles, exosomes possess superior biocompatibility and much lower immunogenicity. This work reviewed the most up-to-date research progress of exosomes as carriers for nucleic acids, proteins and small molecule drugs for cancer and inflammation management. The drug loading strategies and potential cellular uptake behaviour of exosomes are highlighted, trying to provide reference for future exosome design and application.

The Exosome-Mediated PI3K/Akt/mTOR Signaling Pathway in Neurological Diseases

As major public health concerns associated with a rapidly growing aging population, neurodegenerative diseases (NDDs) and neurological diseases are important causes of disability and mortality. Neurological diseases affect millions of people worldwide. Recent studies have indicated that apoptosis, inflammation, and oxidative stress are the main players of NDDs and have critical roles in neurodegenerative processes. During the aforementioned inflammatory/apoptotic/oxidative stress procedures, the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway plays a crucial role. Considering the functional and structural aspects of the blood-brain barrier, drug delivery to the central nervous system is relatively challenging. Exosomes are nanoscale membrane-bound carriers that can be secreted by cells and carry several cargoes, including proteins, nucleic acids, lipids, and metabolites. Exosomes significantly take part in the intercellular communications due to their specific features including low immunogenicity, flexibility, and great tissue/cell penetration capabilities. Due to their ability to cross the blood-brain barrier, these nano-sized structures have been introduced as proper vehicles for central nervous system drug delivery by multiple studies. In the present systematic review, we highlight the potential therapeutic effects of exosomes in the context of NDDs and neurological diseases by targeting the PI3K/Akt/mTOR signaling pathway.

Exosomes combined with biomaterials in the treatment of spinal cord injury

Spinal cord injury (SCI) is a serious and disabling disease with a high mortality rate. It often leads to complete or partial sensory and motor dysfunction and is accompanied by a series of secondary outcomes, such as pressure sores, pulmonary infections, deep vein thrombosis in the lower extremities, urinary tract infections, and autonomic dysfunction. Currently, the main treatments for SCI include surgical decompression, drug therapy, and postoperative rehabilitation. Studies have shown that cell therapy plays a beneficial role in the treatment of SCI. Nonetheless, there is controversy regarding the therapeutic effect of cell transplantation in SCI models. Meanwhile exosomes, as a new therapeutic medium for regenerative medicine, possess the advantages of small size, low immunogenicity, and the ability to cross the blood-spinal cord barrier. Certain studies have shown that stem cell-derived exosomes have anti-inflammatory effects and can play an irreplaceable role in the treatment of SCI. In this case, it is difficult for a single treatment method to play an effective role in the repair of neural tissue after SCI. The combination of biomaterial scaffolds and exosomes can better transfer and fix exosomes to the injury site and improve their survival rate. This paper first reviews the current research status of stem cell-derived exosomes and biomaterial scaffolds in the treatment of SCI respectively, and then describes the application of exosomes combined with biomaterial scaffolds in the treatment of SCI, as well as the challenges and prospects.

Neural stem/progenitor cell-derived extracellular vesicles: A novel therapy for neurological diseases and beyond

As bilayer lipid membrane vesicles secreted by neural stem/progenitor cells (NSCs), NSC-derived extracellular vesicles (NSC-EVs) have attracted growing attention for their promising potential to serve as novel therapeutic agents in treatment of neurological diseases due to their unique physicochemical characteristics and biological functions. NSC-EVs exhibit advantages such as stable physical and chemical properties, low immunogenicity, and high penetration capacity to cross blood-brain barrier to avoid predicaments of the clinical applications of NSCs that include autoimmune responses, ethical/religious concerns, and the problematic logistics of acquiring fetal tissues. More importantly, NSC-EVs inherit excellent neuroprotective and neuroregenerative potential and immunomodulatory capabilities from parent cells, and display outstanding therapeutic effects on mitigating behavioral alterations and pathological phenotypes of patients or animals with neurological diseases. In this review, we first comprehensively summarize the progress in functional research and application of NSC-EVs in different neurological diseases, including neurodegenerative diseases, acute neurological diseases, dementia/cognitive dysfunction, and peripheral diseases. Next, we provide our thoughts on current limitations/concerns as well as tremendous potential of NSC-EVs in clinical applications. Last, we discuss future directions of further investigations on NSC-EVs and their probable applications in both basic and clinical research.

Extracellular vesicles from human umbilical cord mesenchymal stem cells reduce lipopolysaccharide-induced spinal cord injury neuronal apoptosis by mediating miR-29b-3p/PTEN

OBJECTIVE

This study investigated the molecular mechanism of whether hUC-MSCs-EVs repressed PTEN expression and activated the PI3K/AKT pathway through miR-29b-3p, thus inhibiting LPS-induced neuronal injury.

METHODS

hUC-MSCs were cultured and then identified. Cell morphology was observed. Alizarin red, oil red O, and alcian blue staining were used for inducing osteogenesis, adipogenesis, and chondrogenesis. EVs were extracted from hUC-MSCs and identified by transmission electron microscope observation and Western blot. SCI neuron model was established by 24h lipopolysaccharide (LPS) induction. After the cells were cultured with EVs without any treatment, uptake of EVs by SCI neurons, miR-29b-3p expression, cell viability, apoptosis, caspase-3, cleaved caspase-3, caspase 9, Bcl-2, PTEN, PI3K, AKT, and p-Akt protein levels, caspase 3 and caspase 9 activities, and inflammatory factors IL-6 and IL-1β levels were detected by immunofluorescence labeling, RT-qPCR, MTT, flow cytometry, Western blot, caspase 3 and caspase 9 activity detection kits, and ELISA. The binding sites between PTEN and miR-29b-3p were predicted by the database and verified by dual-luciferase assay.

RESULTS

LPS-induced SCI cell model was successfully established, and hUC-MSCs-EVs inhibited LPS-induced apoptosis of injured spinal cord neurons. EVs transferred miR-29b-3p into LPS-induced injured neurons. miR-29b-3p silencing reversed EV effects on reducing LPS-induced neuronal apoptosis. miR-29b-3p reduced LPS-induced neuronal apoptosis by targeting PTEN. After EVs-miR-inhi and si-PTEN treatment, inhibition of the PI3K/AKT pathway reversed hUC-MSCs-EVs effects on reducing LPS-induced neuronal apoptosis.

CONCLUSION

hUC-MSCs-EVs activated the PI3K/AKT pathway by carrying miR-29b-3p into SCI neurons and silencing PTEN, thus reducing neuronal apoptosis.

Terpenoid natural products exert neuroprotection via the PI3K/Akt pathway

PI3K/Akt, an essential signaling pathway widely present in cells, has been shown to be relevant to neurological disorders. As an important class of natural products, terpenoids exist in large numbers and have diverse backbones, so they have a great chance to be identified as neuroprotective agents. In this review, we described and summarized recent research for a range of terpenoid natural products associated with the PI3K/Akt pathway by classifying their basic chemical structures of the terpenes, identified by electronic searches on PubMed, Web of Science for research, and Google Scholar websites. Only articles published in English were included. Our discussion here concerned 16 natural terpenoids and their mechanisms of action, the associated diseases, and the methods of experimentation used. We also reviewed the discovery of their chemical structures and their derivatives, and some compounds have been concluded for their structure–activity relationships (SAR). As a result, terpenoids are excellent candidates for research as natural neuroprotective agents, and our content will provide a stepping stone for further research into these natural products. It may be possible for more terpenoids to serve as neuroprotective agents in the future.

The PI3K/AKT signalling pathway in inflammation, cell death and glial scar formation after traumatic spinal cord injury: Mechanisms and therapeutic opportunities

Objects

Traumatic spinal cord injury (TSCI) causes neurological dysfunction below the injured segment of the spinal cord, which significantly impacts the quality of life in affected patients. The phosphoinositide 3kinase/serine‐threonine kinase (PI3K/AKT) signaling pathway offers a potential therapeutic target for the inhibition of secondary TSCI. This review summarizes updates concerning the role of the PI3K/AKT pathway in TSCI.

Materials and Methods

By searching articles related to the TSCI field and the PI3K/AKT signaling pathway, we summarized the mechanisms of secondary TSCI and the PI3K/AKT signaling pathway; we also discuss current and potential future treatment methods for TSCI based on the PI3K/AKT signaling pathway.

Results

Early apoptosis and autophagy after TSCI protect the body against injury; a prolonged inflammatory response leads to the accumulation of pro‐inflammatory factors and excessive apoptosis, as well as excessive autophagy in the surrounding normal nerve cells, thus aggravating TSCI in the subacute stage of secondary injury. Initial glial scar formation in the subacute phase is a protective mechanism for TSCI, which limits the spread of damage and inflammation. However, mature scar tissue in the chronic phase hinders axon regeneration and prevents the recovery of nerve function. Activation of PI3K/AKT signaling pathway can inhibit the inflammatory response and apoptosis in the subacute phase after secondary TSCI; inhibiting this pathway in the chronic phase can reduce the formation of glial scar.

Conclusion

The PI3K/AKT signaling pathway has an important role in the recovery of spinal cord function after secondary injury. Inducing the activation of PI3K/AKT signaling pathway in the subacute phase of secondary injury and inhibiting this pathway in the chronic phase may be one of the potential strategies for the treatment of TSCI.

Therapeutic Effect of Exosomes Derived From Stem Cells in Spinal Cord Injury: A Systematic Review Based on Animal Studies

Objective

A systematic review of the role of stem cell-derived exosomes in repairing spinal cord injury (SCI) and the existing problems in animal experiments to provide a reference for better animal experiments and clinical studies in the future.

Method

Three electronic databases, namely PubMed, Web of Science, and Ovid-Embase were searched. The studies were retrieved from inception to October 2021. Two researchers independently screened the literature, extracted data, and evaluated the methodological quality based on the inclusion criteria.

Results and Discussion

Thirty-two studies were incorporated into the final analyses. Exosomes derived from stem cells could not only significantly improve the motor function of animals with SCI, but also significantly increase the expression of anti-inflammatory factors IL-4 and IL-10 and anti-apoptotic protein Bcl-2, while significantly lowering the pro-inflammatory factor IL-1β and TNF-α and the expression of the apoptotic protein BAX. However, the mechanism of exosome-mediated SCI repair, as well as the best source and dosage remain unknown. In addition, there are still some issues with the design, implementation, and reporting of animal experiments in the included studies. Therefore, future research should further standardize the implementation and reporting of animal studies and fully explore the best strategies for exosomes to repair SCI so as to promote the translation of preclinical research results to clinical research better and faster.