Extracellular Vesicles Derived from Epidural Fat-Mesenchymal Stem Cells Attenuate NLRP3 Inflammasome Activation and Improve Functional Recovery After Spinal Cord Injury

Applications of Stem Cell-Derived Extracellular Vesicles in Nerve Regeneration

Extracellular vesicles (EVs), including exosomes, microvesicles, and other lipid vesicles derived from cells, play a pivotal role in intercellular communication by transferring information between cells. EVs secreted by progenitor and stem cells have been associated with the therapeutic effects observed in cell-based therapies, and they also contribute to tissue regeneration following injury, such as in orthopaedic surgery cases. This review explores the involvement of EVs in nerve regeneration, their potential as drug carriers, and their significance in stem cell research and cell-free therapies. It underscores the importance of bioengineers comprehending and manipulating EV activity to optimize the efficacy of tissue engineering and regenerative therapies.

Molars to Medicine: A Focused Review on the Pre-Clinical Investigation and Treatment of Secondary Degeneration following Spinal Cord Injury Using Dental Stem Cells

Spinal cord injury (SCI) can result in the permanent loss of mobility, sensation, and autonomic function. Secondary degeneration after SCI both initiates and propagates a hostile microenvironment that is resistant to natural repair mechanisms. Consequently, exogenous stem cells have been investigated as a potential therapy for repairing and recovering damaged cells after SCI and other CNS disorders. This focused review highlights the contributions of mesenchymal (MSCs) and dental stem cells (DSCs) in attenuating various secondary injury sequelae through paracrine and cell-to-cell communication mechanisms following SCI and other types of neurotrauma. These mechanistic events include vascular dysfunction, oxidative stress, excitotoxicity, apoptosis and cell loss, neuroinflammation, and structural deficits. The review of studies that directly compare MSC and DSC capabilities also reveals the superior capabilities of DSC in reducing the effects of secondary injury and promoting a favorable microenvironment conducive to repair and regeneration. This review concludes with a discussion of the current limitations and proposes improvements in the future assessment of stem cell therapy through the reporting of the effects of DSC viability and DSC efficacy in attenuating secondary damage after SCI.

Role of epidural fat in the local milieu: what we know and what we don't

PURPOSE

Traditionally, the epidural fat (EF) is known as a physical buffer for the dural sac against the force and a lubricant facilitating the relative motion of the latter on the osseous spine. Along with the development of the studies on EF, controversies still exist on vital questions, such as the underlying mechanism of the spinal epidural lipomatosis. Meanwhile, the scattered and fragmented researches hinder the global insight into the seemingly dispensable tissue.

METHODS

Herein, we reviewed literature on the EF and its derivatives to elucidate the dynamic change and complex function of EF in the local milieu, especially at the pathophysiological conditions. We start with an introduction to EF and the current pathogenic landscape, emphasizing the interlink between the EF and adjacent structures. We generally categorize the major pathological changes of the EF into hypertrophy, atrophy, and inflammation.

RESULTS AND CONCLUSIONS

It is acknowledged that not only the EF (or its cellular components) may be influenced by various endogenic/exogenic and focal/systematic stimuli, but the adjacent structures can also in turn be affected by the EF, which may be a hidden pathogenic clue for specific spinal disease. Meanwhile, the unrevealed sections, which are also the directions the future research, are proposed according to the objective result and rational inference. Further effort should be taken to reveal the underlying mechanism and develop novel therapeutic pathways for the relevant diseases.

Understanding exosomes: Part 2-Emerging leaders in regenerative medicine

Exosomes are the smallest subset of extracellular signaling vesicles secreted by most cells with the ability to communicate with other tissues and cell types over long distances. Their use in regenerative medicine has gained tremendous momentum recently due to their ability to be utilized as therapeutic options for a wide array of diseases/conditions. Over 5000 publications are currently being published yearly on this topic, and this number is only expected to dramatically increase as novel therapeutic strategies continue to be developed. Today exosomes have been applied in numerous contexts including neurodegenerative disorders (Alzheimer's disease, central nervous system, depression, multiple sclerosis, Parkinson's disease, post-traumatic stress disorders, traumatic brain injury, peripheral nerve injury), damaged organs (heart, kidney, liver, stroke, myocardial infarctions, myocardial infarctions, ovaries), degenerative processes (atherosclerosis, diabetes, hematology disorders, musculoskeletal degeneration, osteoradionecrosis, respiratory disease), infectious diseases (COVID-19, hepatitis), regenerative procedures (antiaging, bone regeneration, cartilage/joint regeneration, osteoarthritis, cutaneous wounds, dental regeneration, dermatology/skin regeneration, erectile dysfunction, hair regrowth, intervertebral disc repair, spinal cord injury, vascular regeneration), and cancer therapy (breast, colorectal, gastric cancer and osteosarcomas), immune function (allergy, autoimmune disorders, immune regulation, inflammatory diseases, lupus, rheumatoid arthritis). This scoping review is a first of its kind aimed at summarizing the extensive regenerative potential of exosomes over a broad range of diseases and disorders.

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.

Schwann Cell-Derived Exosomal Vesicles: A Promising Therapy for the Injured Spinal Cord

Exosomes are nanoscale-sized membrane vesicles released by cells into their extracellular milieu. Within these nanovesicles reside a multitude of bioactive molecules, which orchestrate essential biological processes, including cell differentiation, proliferation, and survival, in the recipient cells. These bioactive properties of exosomes render them a promising choice for therapeutic use in the realm of tissue regeneration and repair. Exosomes possess notable positive attributes, including a high bioavailability, inherent safety, and stability, as well as the capacity to be functionalized so that drugs or biological agents can be encapsulated within them or to have their surface modified with ligands and receptors to imbue them with selective cell or tissue targeting. Remarkably, their small size and capacity for receptor-mediated transcytosis enable exosomes to cross the blood-brain barrier (BBB) and access the central nervous system (CNS). Unlike cell-based therapies, exosomes present fewer ethical constraints in their collection and direct use as a therapeutic approach in the human body. These advantageous qualities underscore the vast potential of exosomes as a treatment option for neurological injuries and diseases, setting them apart from other cell-based biological agents. Considering the therapeutic potential of exosomes, the current review seeks to specifically examine an area of investigation that encompasses the development of Schwann cell (SC)-derived exosomal vesicles (SCEVs) as an approach to spinal cord injury (SCI) protection and repair. SCs, the myelinating glia of the peripheral nervous system, have a long history of demonstrated benefit in repair of the injured spinal cord and peripheral nerves when transplanted, including their recent advancement to clinical investigations for feasibility and safety in humans. This review delves into the potential of utilizing SCEVs as a therapy for SCI, explores promising engineering strategies to customize SCEVs for specific actions, and examines how SCEVs may offer unique clinical advantages over SC transplantation for repair of the injured spinal cord.

Mesenchymal stem cell-derived extracellular vesicles therapy in traumatic central nervous system diseases: a systematic review and meta-analysis

Although there are challenges in treating traumatic central nervous system diseases, mesenchymal stem cell-derived extracellular vesicles (MSC-EVs) have recently proven to be a promising non-cellular therapy. We comprehensively evaluated the efficacy of mesenchymal stem cell-derived extracellular vesicles in traumatic central nervous system diseases in this meta-analysis based on preclinical studies. Our meta-analysis was registered at PROSPERO (CRD42022327904, May 24, 2022). To fully retrieve the most relevant articles, the following databases were thoroughly searched: PubMed, Web of Science, The Cochrane Library, and Ovid-Embase (up to April 1, 2022). The included studies were preclinical studies of mesenchymal stem cell-derived extracellular vesicles for traumatic central nervous system diseases. The Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE)'s risk of bias tool was used to examine the risk of publication bias in animal studies. After screening 2347 studies, 60 studies were included in this study. A meta-analysis was conducted for spinal cord injury (n = 52) and traumatic brain injury (n = 8). The results indicated that mesenchymal stem cell-derived extracellular vesicles treatment prominently promoted motor function recovery in spinal cord injury animals, including rat Basso, Beattie and Bresnahan locomotor rating scale scores (standardized mean difference [SMD]: 2.36, 95% confidence interval [CI]: 1.96-2.76, P < 0.01, I² = 71%) and mouse Basso Mouse Scale scores (SMD = 2.31, 95% CI: 1.57-3.04, P = 0.01, I² = 60%) compared with controls. Further, mesenchymal stem cell-derived extracellular vesicles treatment significantly promoted neurological recovery in traumatic brain injury animals, including the modified Neurological Severity Score (SMD = -4.48, 95% CI: -6.12 to -2.84, P < 0.01, I² = 79%) and Foot Fault Test (SMD = -3.26, 95% CI: -4.09 to -2.42, P = 0.28, I² = 21%) compared with controls. Subgroup analyses showed that characteristics may be related to the therapeutic effect of mesenchymal stem cell-derived extracellular vesicles. For Basso, Beattie and Bresnahan locomotor rating scale scores, the efficacy of allogeneic mesenchymal stem cell-derived extracellular vesicles was higher than that of xenogeneic mesenchymal stem cell-derived extracellular vesicles (allogeneic: SMD = 2.54, 95% CI: 2.05-3.02, P = 0.0116, I² = 65.5%; xenogeneic: SMD: 1.78, 95%CI: 1.1-2.45, P = 0.0116, I² = 74.6%). Mesenchymal stem cell-derived extracellular vesicles separated by ultrafiltration centrifugation combined with density gradient ultracentrifugation (SMD = 3.58, 95% CI: 2.62-4.53, P < 0.0001, I² = 31%) may be more effective than other EV isolation methods. For mouse Basso Mouse Scale scores, placenta-derived mesenchymal stem cell-derived extracellular vesicles worked better than bone mesenchymal stem cell-derived extracellular vesicles (placenta: SMD = 5.25, 95% CI: 2.45-8.06, P = 0.0421, I² = 0%; bone marrow: SMD = 1.82, 95% CI: 1.23-2.41, P = 0.0421, I² = 0%). For modified Neurological Severity Score, bone marrow-derived MSC-EVs worked better than adipose-derived MSC-EVs (bone marrow: SMD = -4.86, 95% CI: -6.66 to -3.06, P = 0.0306, I² = 81%; adipose: SMD = -2.37, 95% CI: -3.73 to -1.01, P = 0.0306, I² = 0%). Intravenous administration (SMD = -5.47, 95% CI: -6.98 to -3.97, P = 0.0002, I² = 53.3%) and dose of administration equal to 100 μg (SMD = -5.47, 95% CI: -6.98 to -3.97, P < 0.0001, I² = 53.3%) showed better results than other administration routes and doses. The heterogeneity of studies was small, and sensitivity analysis also indicated stable results. Last, the methodological quality of all trials was mostly satisfactory. In conclusion, in the treatment of traumatic central nervous system diseases, mesenchymal stem cell-derived extracellular vesicles may play a crucial role in promoting motor function recovery.

NLR family pyrin domain containing 3 (NLRP3) inflammasomes and peripheral neuropathic pain - Emphasis on microRNAs (miRNAs) as important regulators

Neuropathic pain is caused by the lesion or disease of the somatosensory system and can be initiated and/or maintained by both central and peripheral mechanisms. Nerve injury leads to neuronal damage and apoptosis associated with the release of an array of pathogen- or damage-associated molecular patterns to activate inflammasomes. The activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome contributes to neuropathic pain and may represent a novel target for pain therapeutic development. In the current review, we provide an up-to-date summary of the recent findings on the involvement of NLRP3 inflammasome in modulating neuropathic pain development and maintenance, focusing on peripheral neuropathic conditions. Here we provide a detailed review of the mechanisms whereby NLRP3 inflammasomes contribute to neuropathic pain via (1) neuroinflammation, (2) apoptosis, (3) pyroptosis, (4) proinflammatory cytokine release, (5) mitochondrial dysfunction, and (6) oxidative stress. We then present the current research literature reporting on the antinociceptive effects of several natural products and pharmacological interventions that target activation, expression, and/or regulation of NLRP3 inflammasome. Furthermore, we emphasize the effects of microRNAs as another regulator of NLRP3 inflammasome. In conclusion, we summarize the possible caveats and future perspectives that might provide successful therapeutic approaches against NLRP3 inflammasome for treating or preventing neuropathic pain conditions.

The research landscape of immunology research in spinal cord injury from 2012 to 2022

Background

Spinal cord injury (SCI) is defined as traumatic damage to the spinal cord, affecting over three million patients worldwide, and there is still no treatment for the injured spinal cord itself. In recent years, immunology research on SCI has been published in various journals.

Methods

To systematically analyze the research hotspots and dynamic scientific developments of immunology research in SCI, we conducted a bibliometric and knowledge map analysis to help researchers gain a global perspective in this research field.

Results

The bibliometric study we completed included 1788 English-language papers published in 553 journals by 8861 authors from 1901 institutions in 66 countries/regions. Based on the references and keyword analysis, researchers in the past 10 years have mainly focused on the research directions of "monocyte chemoattractor protein 1," "nitric oxide," "pain," and "nitric oxide synthase" related to immunological research in SCI. However, with the development of other new directions such as "extracellular vesicles" (2019-2022), "Regenerative medicine" (2019-2022), "stromal cells" (2018-2022), "motor recovery" (2019-2022), and "glial activation" (2019-2022). Researchers prefer to study the application of regenerative strategies in SCI, the mechanism of extracellular vesicles in the development of SCI, the activation of spinal glial cells in SCI, and the pathways of motor recovery. This bibliometric analysis of immunology research in SCI summarizes the current status of this research field. The relationship between extracellular vesicles, regenerative medicine, stromal cells, motor recovery, and glial activation is currently a major research frontier. Further research and cooperation worldwide need to be enhanced.

Conclusion

We believe that our research can help researchers quickly grasp the current hotspot of immunology research in SCI and determine a new direction for future research.

Buyang Huanwu Decoction promotes the neurological recovery of traumatic spinal cord injury via inhibiting apoptosis, inflammation, and oxidative stress

BACKGROUND

The incidence rate of spinal cord injury (SCI) is increasing, and the mortality or disability rate caused by SCI remains high in the world. Buyang Huanwu Decoction (BYHWD) is a kind of Traditional Chinese medicine, and it is believed to be effective in several kinds of nervous system diseases. Whether BYHWD could improve SCI and the potential function mechanism remain unclear.

METHODS

SCI animal model was established by damaging T10 spinal cord. Animals experiments included five groups as follows: Sham, SCI, SCI+BYHWD, SCI+mesenchymal stromal cells (MSCs), and SCI+BYHWD+MSCs. H₂ O₂ -treated cells (100 µM, 6 h) were used to simulate SCI damage in vitro, which included five groups as follows: control, H₂ O₂ , H₂ O₂ +BYHWD, H₂ O₂ +MSCs, and H₂ O₂ +BYHWD+MSCs. The behavioral function was evaluated with Tarlov and inclined plated test score. Western blot analysis and immunohistochemical staining were used to detect protein expression. The levels of superoxide dismutase (SOD), catalase (CAT), malondiadehyde (MDA), interleukin (IL)-1β, tumor necrosis factor-α, and IL-6 in serum were measured with commercial enzyme-linked immunosorbent assay kits. terminal deoxynucleotidyl transferase dUTP nick end labeling staining and flow cytometry were performed to measure apoptosis in vivo and in vitro levels. Gene expression profiling analysis was performed to analyze differential expression genes.

RESULTS

BYHWD suppressed apoptosis and accelerating cell proliferation after SCI. Recovery of neurofunction, inhibition of inflammatory response, and oxidative condition were achieved by BYHWD and MSCs. The expression levels of gp130/Janus kinase/signal transducers and activator of transcription (JAK/STAT) were suppressed by BYHWD and MSCs, both in vivo and in vitro. BYHWD and MSCs markedly promoted cells viability and inhibited apoptosis. Greater gene expression difference was observed between group control and H₂ O₂ through gene expression profiling analysis. The recovery effects of traumatic SCI by BYHWD were similar to MSCs, and synergies effects were observed in several items.

CONCLUSION

BYHWD could increase Tarlov score and Basso, Beatie, and Bresnahan functional score, inhibit apoptosis, inflammatory response, and oxidative condition after SCI. The expression level of gp130/JAK/STAT axis was suppressed by BYHWD. BYHWD might be a new therapeutic strategy for the prevention or treatment of SCI.

An emerging role of inflammasomes in spinal cord injury and spinal cord tumor

Spinal cord injury (SCI) and spinal cord tumor are devastating events causing structural and functional impairment of the spinal cord and resulting in high morbidity and mortality; these lead to a psychological burden and financial pressure on the patient. These spinal cord damages likely disrupt sensory, motor, and autonomic functions. Unfortunately, the optimal treatment of and spinal cord tumors is limited, and the molecular mechanisms underlying these disorders are unclear. The role of the inflammasome in neuroinflammation in diverse diseases is becoming increasingly important. The inflammasome is an intracellular multiprotein complex and participates in the activation of caspase-1 and the secretion of pro-inflammatory cytokines such as interleukin (IL)-1β and IL-18. The inflammasome in the spinal cord is involved in the stimulation of immune-inflammatory responses through the release of pro-inflammatory cytokines, thereby mediating further spinal cord damage. In this review, we highlight the role of inflammasomes in SCI and spinal cord tumors. Targeting inflammasomes is a promising therapeutic strategy for the treatment of SCI and spinal cord tumors.

Mesenchymal stem cells in the treatment of spinal cord injury: Mechanisms, current advances and future challenges

Spinal cord injury (SCI) has considerable impact on patient physical, mental, and financial health. Secondary SCI is associated with inflammation, vascular destruction, and subsequent permanent damage to the nervous system. Mesenchymal stem cells (MSCs) have anti-inflammatory properties, promoting vascular regeneration and the release neuro-nutrients, and are a promising strategy for the treatment of SCI. Preclinical studies have shown that MSCs promote sensory and motor function recovery in rats. In clinical trials, MSCs have been reported to improve the American Spinal Injury Association (ASIA) sensory and motor scores. However, the effectiveness of MSCs in treating patients with SCI remains controversial. MSCs promote tumorigenesis and ensuring the survival of MSCs in the hostile environment of SCI is challenging. In this article we examine the evidence on the pathophysiological changes occurring after SCI. We then review the underlying mechanisms of MSCs in the treatment of SCI and summarize the potential application of MSCs in clinical practice. Finally, we highlight the challenges surrounding the use of MSCs in the treatment of SCI and discuss future applications.

Mechanism of spinal cord injury regeneration and the effect of human neural stem cells-secretome treatment in rat model

BACKGROUND

Globally, complete neurological recovery of spinal cord injury (SCI) is still less than 1%, and 90% experience permanent disability. The key issue is that a pharmacological neuroprotective-neuroregenerative agent and SCI regeneration mechanism have not been found. The secretomes of stem cell are an emerging neurotrophic agent, but the effect of human neural stem cells (HNSCs) secretome on SCI is still unclear.

AIM

To investigate the regeneration mechanism of SCI and neuroprotective-neuroregenerative effects of HNSCs-secretome on subacute SCI post-laminectomy in rats.

METHODS

An experimental study was conducted with 45 Rattus norvegicus, divided into 15 normal, 15 control (10 mL physiologic saline), and 15 treatment (30 μL HNSCs-secretome, intrathecal T10, three days post-traumatic). Locomotor function was evaluated weekly by blinded evaluators. Fifty-six days post-injury, specimens were collected, and spinal cord lesion, free radical oxidative stress (F2-Isoprostanes), nuclear factor-kappa B (NF-κB), matrix metallopeptidase 9 (MMP9), tumor necrosis factor-alpha (TNF-α), interleukin-10 (IL-10), transforming growth factor-beta (TGF-β), vascular endothelial growth factor (VEGF), B cell lymphoma-2 (Bcl-2), nestin, brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF) were analyzed. The SCI regeneration mechanism was analyzed using partial least squares structural equation modeling (PLS SEM).

RESULTS

HNSCs-secretome significantly improved locomotor recovery according to Basso, Beattie, Bresnahan (BBB) scores and increased neurogenesis (nestin, BDNF, and GDNF), neuroangiogenesis (VEGF), anti-apoptotic (Bcl-2), anti-inflammatory (IL-10 and TGF-β), but decreased pro-inflammatory (NF-κB, MMP9, TNF-α), F2-Isoprostanes, and spinal cord lesion size. The SCI regeneration mechanism is valid by analyzed outer model, inner model, and hypothesis testing in PLS SEM, started with pro-inflammation followed by anti-inflammation, anti-apoptotic, neuroangiogenesis, neurogenesis, and locomotor function.

CONCLUSION

HNSCs-secretome as a potential neuroprotective-neuroregenerative agent for the treatment of SCI and uncover the SCI regeneration mechanism.

Regenerative Effects of Exosomes-Derived MSCs: An Overview on Spinal Cord Injury Experimental Studies

Spinal cord injury (SCI) is a devastating condition usually induced by the initial mechanical insult that can lead to permanent motor and sensory deficits. At present, researchers are investigating potential therapeutic strategies to ameliorate the neuro-inflammatory cascade that occurs post-injury. Although the use of mesenchymal stromal/stem (MSCs) as a potential therapy in application to regenerative medicine promoted anti-inflammatory and neuroprotective effects, several disadvantages limit their use. Therefore, recent studies have reported the effects of exosomes-derived MSCs (MSC-EXOs) as an innovative therapeutic option for SCI patients. It is noteworthy that MSC-EXOs can maintain the integrity of the blood-spinal cord barrier (BSCB), promoting angiogenic, proliferative, and anti-oxidant effects, as well as immunomodulatory, anti-inflammatory, and antiapoptotic properties. Therefore, in this study, we summarized the preclinical studies reported in the literature that have shown the effects of MSC-EXOs as a new molecular target to counteract the devastating effects of SCI.

Concise review: Current understanding of extracellular vesicles to treat neuropathic pain

Extracellular vesicles (EVs) including exosomes are vesicular vesicles with phospholipid bilayer implicated in many cellular interactions and have the ability to transfer multiple types of cargo to cells. It has been found that EVs can package various molecules including proteins and nucleic acids (DNA, mRNA, and noncoding RNA). The discovery of EVs as carriers of proteins and various forms of RNA, such as microRNAs (miRNA) and long noncoding RNAs (lncRNA), has raised great interest in the field of drug delivery. Despite the underlying mechanisms of neuropathic pain being unclear, it has been shown that uncontrolled glial cell activation and the neuroinflammation response to noxious stimulation are important in the emergence and maintenance of neuropathic pain. Many studies have demonstrated a role for noncoding RNAs in the pathogenesis of neuropathic pain and EVs may offer possibilities as carriers of noncoding RNAs for potential in neuropathic pain treatment. In this article, the origins and clinical application of EVs and the mechanism of neuropathic pain development are briefly introduced. Furthermore, we demonstrate the therapeutic roles of EVs in neuropathic pain and that this involve vesicular regulation of glial cell activation and neuroinflammation.

Native and engineered exosomes for inflammatory disease

Exosomes are extracellular vesicles which carry specific molecular information from donor cells and act as an intercellular communication vehicle, which have emerged as a novel cell-free strategy for the treatment of many diseases including inflammatory disease. Recently, rising studies have developed exosome-based strategies for novel inflammation therapy due to their biocompatibility and bioactivity. Researchers not only use native exosomes as therapeutic agents for inflammation, but also strive to make up for the natural defects of exosomes through engineering methods to improve and update the property of exosomes for enhanced therapeutic effects. The engineered exosomes can improve cargo-loading efficiency, targeting ability, stability, etc., to achieve combined and diverse treatment strategies in inflammation diseases. Herein, a comprehensive overview of the recent advances in application studies of native and engineered exosomes as well as the engineered methods is provided. Meanwhile, potential application prospects, possible challenges, and the development of clinical researches of exosome treatment strategy are concluded from plentiful examples, which may be able to provide guidance and suggestions for the future research and application of exosomes.

Extracellular vesicle therapy for traumatic central nervous system disorders

Traumatic central nervous system (CNS) disorders have catastrophic effects on patients, and, currently, there is no effective clinical treatment. Cell transplantation is a common treatment for traumatic CNS injury in animals. In recent years, an increasing number of studies have reported that the beneficial effect of transplanted cells for CNS repair is mediated primarily through the extracellular vesicles (EVs) secreted by the cells, in which microRNAs play a major role. Accordingly, numerous studies have evaluated the roles and applications of EVs secreted by different cell types in neurological diseases. Furthermore, due to their unique biological features, EVs are used as disease biomarkers and drug delivery systems for disease prevention and treatment. We discuss current knowledge related to EVs, focusing on the mechanism underlying their effects on traumatic CNS diseases, and summarize existing research on the potential clinical utility of EVs as disease biomarkers and drug delivery systems.

The Role of Exosomes and Exosomal Noncoding RNAs From Different Cell Sources in Spinal Cord Injury

Spinal cord injury (SCI) not only affects the quality of life of patients but also poses a heavy burden on their families. Therefore, it is essential to prevent the occurrence of SCI; for unpreventable SCI, it is critical to develop effective treatments. In recent years, various major breakthroughs have been made in cell therapy to protect and regenerate the damaged spinal cord via various mechanisms such as immune regulation, paracrine signaling, extracellular matrix (ECM) modification, and lost cell replacement. Nevertheless, many recent studies have shown that the cell therapy has many disadvantages, such as tumorigenicity, low survival rate, and immune rejection. Because of these disadvantages, the clinical application of cell therapy is limited. In recent years, the role of exosomes in various diseases and their therapeutic potential have attracted much attention. The same is true for exosomal noncoding RNAs (ncRNAs), which do not encode proteins but affect transcriptional and translational processes by targeting specific mRNAs. This review focuses on the mechanism of action of exosomes obtained from different cell sources in the treatment of SCI and the regulatory role and therapeutic potential of exosomal ncRNAs. This review also discusses the future opportunities and challenges, proposing that exosomes and exosomal ncRNAs might be promising tools for the treatment of SCI.

Human Epidural AD–MSC Exosomes Improve Function Recovery after Spinal Cord Injury in Rats

Spinal cord injury (SCI) interferes with the normal function of the autonomic nervous system by blocking circuits between the sensory and motor nerves. Although many studies focus on functional recovery after neurological injury, effective neuroregeneration is still being explored. Recently, extracellular vesicles such as exosomes have emerged as cell-free therapeutic agents owing to their ability of cell-to-cell communication. In particular, exosomes released from mesenchymal stem cells (MSCs) have the potential for tissue regeneration and exhibit therapeutic effectiveness in neurological disorders. In this study, we isolated exosomes from human epidural adipose tissue-derived MSCs (hEpi AD–MSCs) using the tangential flow filtration method. The isolated exosomes were analyzed for size, concentration, shape, and major surface markers using nanoparticle tracking analysis, transmission electron microscopy, and flow cytometry. To evaluate their effect on SCI recovery, hEpi AD–MSC exosomes were injected intravenously in SCI-induced rats. hEpi AD–MSC exosomes improved the locomotor function of SCI-induced rats. The results of histopathological and cytokine assays showed that hEpi AD–MSC exosomes regulated inflammatory response. Genetic profiling of the rat spinal cord tissues revealed changes in the expression of inflammation-related genes after exosome administration. Collectively, hEpi AD–MSC exosomes are effective in restoring spinal functions by reducing the inflammatory response.

Extracellular vesicle-derived miR-511-3p from hypoxia preconditioned adipose mesenchymal stem cells ameliorates spinal cord injury through the TRAF6/S1P axis

Extracellular vesicle (EV) from hypoxic adipose tissue-derived mesenchymal stem cells (AD-MSCs) play critical roles in spinal cord injury (SCI) by transferring miRNAs to target cells through fusion with the cell membrane. However, the role of miR-511-3p within the AD-MSCs -derived EV in SCI is largely unknown. Western blotting results demonstrated the secretion of EVs derived from AD-MSCs under hypoxia (Hyp-EVs) was more than those under normoxia (Nor-EVs), and miR-511-3p expression was more enriched in Hyp-EVs. PC12 cells were stimulated with lipopolysaccharide (LPS) to induce cell damage. AD-MSCs were transfected with miR-511-3p mimic or miR-511-3p inhibitor to induce EVs-miR-511-3p overexpression or silencing. Cells treated with Hyp-EVs-miR-511-3p mimic reduced LPS-induced apoptosis, alleviated inflammation and promoted proliferation, while cells treated with Hyp-EVs-miR-511-3p inhibitor aggravated LPS-induced apoptosis and inflammation, and suppressed proliferation. Luciferase reporter gene assay revealed tumor necrosis factor receptor-associated factor 6 (TRAF6) was a target downstream gene of miR-511-3p. A series of gain- and loss-of-function experiments verified that TRAF6 could antagonize the effects of Hyp-EVs-miR-511-3p on inflammation, cell apoptosis and viability. Furthermore, cells treated with CYM5541, an agonist of sphingosine-1-phosphate receptor 3 (S1PR3), reversed the inhibitory effect of Hyp-EVs-miR-511-3p mimic on S1PR3 expression, inflammation and cell apoptosis. Finally, intravenously injection of Hyp-EVs-miR-511-3p mimic into SCI model rats obviously reduced inflammation and promoted neurological function recovery. In conclusion, EVs-derived miR-511-3p from hypoxia preconditioned AD-MSCs ameliorates SCI via TRAF6/S1P/NF-κB pathway, which indicates that miR-511-3p may be a potential therapeutic target for SCI.

Extracellular Vesicles in the Pathogenesis, Treatment, and Diagnosis of Spinal Cord Injury: A Mini-Review

BACKGROUND

Benefiting from in-depth research into stem cells, extracellular vesicles (EVs), which are byproducts of cells and membrane-wrapped microvesicles (30-120 nm) containing lipids, proteins, and nucleic acids, may cast light on the research and development of therapeutics capable of improving the neurological recovery of spinal cord injury (SCI) animals. However, the mechanistic modes of action for EVs in alleviating the lesion size of SCI remain to be solved, thus presenting a tremendous gap existing in translation from the laboratory to the clinic.

OBJECTIVE

The purpose of this minireview was to cover a wide range of basic views on EVs involved in SCI treatment, including the effects of EVs on the pathogenesis, treatment, and diagnosis of spinal cord injury.

METHODS

We searched databases (i.e., PubMed, Web of Science, Scopus, Medline, and EMBASE) and acquired all accessible articles published in the English language within five years. Studies reporting laboratory applications of EVs in the treatment of SCI were included and screened to include studies presenting relevant molecular mechanisms.

RESULTS

This review first summarized the basic role of EVs in cell communication, cell death, inflammatory cascades, scar formation, neuronal regrowth, and angiogenesis after SCI, thereby providing insights into neuroprotection and consolidated theories for future clinical application of EVs.

CONCLUSION

EVs participate in an extremely wide range of cell activities, play a critical role in cell communication centring neurons, and are considered potential therapies and biomarkers for SCI. miRNAs are the most abundant nucleic acids shipped by EVs and effluent cytokines, and they may represent important messengers of EVs and important factors in SCI treatment.

NLRP3 downregulation enhances engraftment and functionality of adipose-derived stem cells to alleviate erectile dysfunction in diabetic rats

BACKGROUND

The transplantation of adipose-derived stem cells (ASCs) is a most promising treatment for diabetic erectile dysfunction (DMED). However, the effect of high glucose on the post-transplantation survival of stem cells limits the efficacy of ASCs transplantation. Prolonging the survival time of ASCs in vivo after transplantation is a key issue in the utilization of ASCs for DMED. Herein, we aimed to investigate the therapeutic effect of ASCs by downregulating NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) as well as its mechanism of action in DMED.

METHODS

ASCs were obtained by isolating subcutaneous fat from SD rats and were identified using lipogenic and osteogenic differentiation assays, as well as flow cytometric analysis. The shNLRP3 lentivirus with the best downregulating effect was screened, and shNLRP3 lentivirus (LV-shNLRP3) was transfected into ASCs (ASCs^shNLRP3) to detect apoptosis and the reactive oxygen species (ROS) levels in each group under high glucose conditions. In DMED rats, ASCs^LV-shNLRP3, ASCs^LV-control, or phosphate buffered saline (PBS) were administrated via intra-cavernous injection, and normal rats served as normal controls. One week post-injection, animal imaging was performed to track the ASCs. Four weeks post-injection, erectile function was evaluated by measuring the intra-cavernosal pressure and mean arterial pressure. Corpus cavernosum pyroptosis and endothelial function were examined by western blotting and immunofluorescence.

RESULTS

NLRP3-mediated pyroptosis might be a pathogenic mechanism of ED and DMED. ASCs were isolated successfully. Thereafter, the LV-shNLRP3 with the highest transfection efficiency was selected and used to modify ASCs successfully. LV-shNLRP3 could protect ASCs paracrine function under hyperglycemia through anti-apoptosis and anti-ROS deposition mechanisms. Furthermore, ASCs^LV-shNLRP3 showed an advantage in the suppression of pyroptosis compared to ASCs^LV-control. The ASCs^LV-shNLRP3 group had improved cavernous endothelial function and smooth muscle injury, thus reversing erectile function, and was superior to the ASCs^LV-control group.

CONCLUSIONS

NLRP3 Inflammasome-mediated pyroptosis might be involved in DMED formation. Intra-cavernous injection of ASCs^LV-shNLRP3 could suppress cavernosal pyroptosis, contributing to improved erectile function in DMED rats.

Advanced approaches to regenerate spinal cord injury: The development of cell and tissue engineering therapy and combinational treatments

Spinal cord injury (SCI) is a central nervous system (CNS) devastate event that is commonly caused by traumatic or non-traumatic events. The reinnervation of spinal cord axons is hampered through a myriad of devices counting on the damaged myelin, inflammation, glial scar, and defective inhibitory molecules. Unfortunately, an effective treatment to completely repair SCI and improve functional recovery has not been found. In this regard, strategies such as using cells, biomaterials, biomolecules, and drugs have been reported to be effective for SCI recovery. Furthermore, recent advances in combinatorial treatments, which address various aspects of SCI pathophysiology, provide optimistic outcomes for spinal cord regeneration. According to the global importance of SCI, the goal of this article review is to provide an overview of the pathophysiology of SCI, with an emphasis on the latest modes of intervention and current advanced approaches for the treatment of SCI, in conjunction with an assessment of combinatorial approaches in preclinical and clinical trials. So, this article can give scientists and clinicians' clues to help them better understand how to construct preclinical and clinical studies that could lead to a breakthrough in spinal cord regeneration.

Bone Marrow Mesenchymal Stem Cell-Derived Exosomes Accelerate Functional Recovery After Spinal Cord Injury by Promoting the Phagocytosis of Macrophages to Clean Myelin Debris

Macrophage phagocytosis contributes predominantly to processing central nervous system (CNS) debris and further facilitates neurological function restoration after CNS injury. The aims of this study were to evaluate the effect of bone marrow mesenchymal stem cells (BMSC)-derived exosomes (BMSC-Exos) on the phagocytic capability of macrophages to clear myelin debris and to investigate the underlying molecular mechanism during the spinal cord injury (SCI) process. This work reveals that monocyte-derived macrophages (MDMs) infiltrating into the SCI site could efficiently engulf myelin debris and process phagocytic material. However, the phagocytic ability of macrophages to clear tissue debris is compromised after SCI. The administration of BMSC-Exos as an approach for SCI treatment could rescue macrophage normal function by improving the phagocytic capability of myelin debris internalization, which is beneficial for SCI repair, as evidenced by better axon regrowth and increased hindlimb locomotor functional recovery in a rodent model. Examination of macrophage treatment with BMSC-Exos revealed that BMSC-Exos could promote the capacity of macrophages to phagocytose myelin debris in vitro and could create a regenerative microenvironment for axon regrowth. In addition, we confirmed that BMSC-Exo treatment resulted in improved phagocytosis of engulfed myelin debris by promoting the expression of macrophage receptor with collagenous structure (MARCO) in macrophages. The inhibition of MARCO with PolyG (a MARCO antagonist) impaired the effect of BMSC-Exos on the phagocytic capacity of macrophages and resulted in compromised myelin clearance at the lesion site, leading to further tissue damage and impaired functional healing after SCI. In conclusion, these data indicated that targeting the phagocytic ability of macrophages may have therapeutic potential for the improvement in functional healing after SCI. The administration of BMSC-Exos as a cell-free immune therapy strategy has wide application prospects for SCI treatment.

Spinal Cord Repair: From Cells and Tissue Engineering to Extracellular Vesicles

Spinal cord injury (SCI) is a debilitating condition, often leading to severe motor, sensory, or autonomic nervous dysfunction. As the holy grail of regenerative medicine, promoting spinal cord tissue regeneration and functional recovery are the fundamental goals. Yet, effective regeneration of injured spinal cord tissues and promotion of functional recovery remain unmet clinical challenges, largely due to the complex pathophysiology of the condition. The transplantation of various cells, either alone or in combination with three-dimensional matrices, has been intensively investigated in preclinical SCI models and clinical trials, holding translational promise. More recently, a new paradigm shift has emerged from cell therapy towards extracellular vesicles as an exciting "cell-free" therapeutic modality. The current review recapitulates recent advances, challenges, and future perspectives of cell-based spinal cord tissue engineering and regeneration strategies.

Stem cell-derived exosomes as a cell free therapy against spinal cord injury

Recent evidence suggests that stem cell therapy has beneficial effects on spinal cord injury. It was subsequently established that these beneficial effects may be mediated through release of paracrine factors, a kind of extracellular vesicle known as exosomes. Stem cell-secreted nano-sized exosomes have shown great potential to reduce apoptosis and inflammation, enhance angiogenesis, and improve functional behavioral recovery following spinal cord injury. This review summarizes current knowledge about the influence of exosomes derived from stem cells on spinal cord protection and regeneration with their molecular mechanisms after injury.

Comparisons of Extracellular Vesicles from Human Epidural Fat-Derived Mesenchymal Stem Cells and Fibroblast Cells

Extracellular vesicles (EVs) are generated and secreted by cells into the circulatory system. Stem cell-derived EVs have a therapeutic effect similar to that of stem cells and are considered an alternative method for cell therapy. Accordingly, research on the characteristics of EVs is emerging. EVs were isolated from human epidural fat-derived mesenchymal stem cells (MSCs) and human fibroblast culture media by ultracentrifugation. The characterization of EVs involved the typical evaluation of cluster of differentiation (CD antigens) marker expression by fluorescence-activated cell sorting, size analysis with dynamic laser scattering, and morphology analysis with transmission electron microscopy. Lastly, the secreted levels of cytokines and chemokines in EVs were determined by a cytokine assay. The isolated EVs had a typical size of approximately 30–200 nm, and the surface proteins CD9 and CD81 were expressed on human epidural fat MSCs and human fibroblast cells. The secreted levels of cytokines and chemokines were compared between human epidural fat MSC-derived EVs and human fibroblast-derived EVs. Human epidural fat MSC-derived EVs showed anti-inflammatory effects and promoted macrophage polarization. In this study, we demonstrated for the first time that human epidural fat MSC-derived EVs exhibit inflammatory suppressive potency relative to human fibroblast-derived EVs, which may be useful for the treatment of inflammation-related diseases.

Adipose Extracellular Vesicles in Intercellular and Inter-Organ Crosstalk in Metabolic Health and Diseases

Adipose tissue (AT) is a highly heterogeneous and dynamic organ that plays important roles in regulating energy metabolism and insulin sensitivity. In addition to its classical roles in nutrient sensing and energy storage/dissipation, AT secretes a large number of bioactive molecules (termed adipokines) participating in immune responses and metabolic regulation through their paracrine and/or endocrine actions. Adipose-derived extracellular vesicles (ADEVs), including exosomes, microvesicles (MVs), and apoptotic bodies, have recently emerged as a novel class of signal messengers, mediating intercellular communications and inter-organ crosstalk. In AT, ADEVs derived from adipocytes, immune cells, mesenchymal stem cells, endothelial cells are actively involved in modulation of immune microenvironment, adipogenesis, browing of white adipose tissue, adipokine release and tissue remodeling. Furthermore, ADEVs exert their metabolic actions in distal organs (such as liver, skeletal muscle, pancreas and brain) by sending genetic information (mainly in the form of microRNAs) to their target cells for regulation of gene expression. Here, we provide an updated summary on the nature and composition of ADEVs, and their pathophysiological functions in regulating immune responses, whole-body insulin sensitivity and metabolism. Furthermore, we highlight the latest clinical evidence supporting aberrant production and/or function of ADEVs as a contributor to obesity-related chronic inflammation and metabolic complications and discuss the opportunities and challenges in developing novel therapies by targeting ADEVs.

Mesenchymal stem cell-derived exosomes: therapeutic opportunities and challenges for spinal cord injury

Spinal cord injury (SCI) often leads to serious motor and sensory dysfunction of the limbs below the injured segment. SCI not only results in physical and psychological harm to patients but can also cause a huge economic burden on their families and society. As there is no effective treatment method, the prevention, treatment, and rehabilitation of patients with SCI have become urgent problems to be solved. In recent years, mesenchymal stem cells (MSCs) have attracted more attention in the treatment of SCI. Although MSC therapy can reduce injured volume and promote axonal regeneration, its application is limited by tumorigenicity, a low survival rate, and immune rejection. Accumulating literature shows that exosomes have great potential in the treatment of SCI. In this review, we summarize the existing MSC-derived exosome studies on SCI and discuss the advantages and challenges of treating SCI based on exosomes derived from MSCs.

Therapeutic Application of Exosomes in Inflammatory Diseases

Immunomodulation is on the cusp of being an important therapy for treating many diseases, due to the significant role of the immune system in defending the human body. Although the immune system is an essential defense system, overactivity can result in diverse sicknesses such as inflammation and autoimmune disease. Exosomes are emerging as a state-of-the-art therapeutic strategy for treating an overactive immune system. Thus, in this review, we will thoroughly review therapeutic applications of exosomes in various inflammatory and autoimmune diseases. Finally, issues for an outlook to the future of exosomal therapy will be introduced.

Extracellular vesicles derived from head and neck squamous cells carcinoma inhibit NLRP3 inflammasomes

The content of tumor-derived extracellular vesicles (EVs) can regulate the tumor microenvironment and functionally acts in favor of cancer aggressiveness. To better elucidate the role of EVs in the interplay between immune system and tumor microenvironment, the purpose of this study was to analyze the effect of head and neck squamous cells carcinoma (HNSCC)-derived EVs on the modulation of inflammasomes - mediators of pyroptosis and secretion of inflammatory factors by macrophages. Our results showed that macrophages treated with the Vesicular Secretome Fraction (VSF) isolated from patient-derived HNSCC presented a reduction in the secretion of mature IL-1β and caspase-1 without affecting cell viability. An analysis of the protein content of HNSCC-derived VSF by antibody array revealed that some of the most expressed proteins share a correlation with Transforming Growth Factor-beta (TGF-β) activity. Since TGF-β is related to the inhibition of the NF-kB-related pathways, including those required for the priming phase of the inflammasomes, we sought to evalute the interference of the VSF in the induction of inflammasome components. In fact, HNSCC-derived VSF inhibited the induction of pro-IL-1β and pro-caspase-1 proteins and NLRP3 gene expression during the priming phase of inflammasome activation. Thus, our findings contribute to a better understanding of how tumor-derived EVs modulate inflammatory response by demonstrating their role in inhibiting NLRP3 inflammasomes.

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Vesicular Secretome Fraction (VSF) from HNSCC inhibits macrophage responses to the NLRP3 inflammasomes agonists.

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HNSCC-derived VSF is enriched with proteins correlated with the Transforming Growth Factor-b pathway.

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HNSCC-derived VSF affects the priming phase of inflammasome activation.