Exosomes - beyond stem cells for restorative therapy in stroke and neurological injury

Stem Cell-Derived Exosomes and Nanovesicles: Promotion of Cell Proliferation, Migration, and Anti-Senescence for Treatment of Wound Damage and Skin Ageing

Extracellular vesicles (EVs), such as exosomes, are nano-sized vesicles derived from endocytic membranes and contain biomolecules such as proteins, lipids, RNAs, and DNAs for the transfer of signals to recipient cells, playing significant roles in cell-to-cell communication. Discovery of exosomes has attracted attention for possible use as next generation therapies in clinical applications; however, several studies suggest that cells secrete exosomes that perform as mediators in the tumor niche and play several roles in tumorigenesis, angiogenesis, and metastasis. Recently, stem cell-derived exosomes have been suggested as a desirable source for regenerative medicine due to their roles in the promotion of angiogenesis via migratory and proliferative mechanisms. This review is aimed at demonstrating the present knowledge of stem cell-derived exosomes and cell-engineered nanovesicles (CNVs) as proliferative, migratory, and anti-senescent therapeutic biomaterial for use in tissue regeneration; wound healing and anti-ageing are explained. We conclude this review by discussing the future perspectives of stem cell-derived exosomes and CNVs as a platform in therapeutic strategies for treatment of wound damage and skin aging.

Extracellular vesicles: A bright star of nanomedicine

Extracellular vesicles (EVs) have unique structural, compositional, and morphological characteristics as well as predominant physiochemical stability and biocompatibility properties. They play a crucial role in pathophysiological regulation, and also have broad prospects for clinical application in the diagnosis, prognosis, and therapy of disease, and tissue regeneration and repair. Herein, the biosynthesis and physiological functions and current methods for separation and identification of EVs are summarized. Specifically, engineered EVs may be used to enhance targeted therapy in cancer and repair damaged tissues, and they may be developed as an individualized imaging diagnostic reagent, among other potential applications. We will focus on reviewing recent studies on engineered EVs in which alterations enhanced their therapeutic capability or diagnostic imaging potential via physical, chemical, and biological modification approaches. This review will clarify the superior biological functions and powerful therapeutic potential of EVs, particularly with regard to new designs based on EVs and their utilization in a new generation of nanomedicine diagnosis and treatment platforms.

Early single-dose exosome treatment improves neurologic outcomes in a 7-day swine model of traumatic brain injury and hemorrhagic shock

BACKGROUND

Early single-dose treatment with human mesenchymal stem cell-derived exosomes promotes neuroprotection and promotes blood-brain barrier integrity in models of traumatic brain injury (TBI) and hemorrhagic shock (HS) in swine. The impact of an early single dose of exosomes on late survival (7 days), however, remains unknown. We sought to evaluate the impact of early single-dose exosome treatment on neurologic outcomes, brain lesion size, inflammatory cytokines, apoptotic markers, and mediators of neural plasticity in a 7-day survival model.

METHODS

Yorkshire swine were subjected to a severe TBI (8-mm cortical impact) and HS (40% estimated total blood volume). After 1 hour of shock, animals were randomized (n = 4/cohort) to receive either lactated Ringer's (5 mL) or lactated Ringer's with exosomes (1 × 10 exosome particles). After an additional hour of shock, animals were resuscitated with normal saline. Daily neurologic severity scores were compared. At 7 days following injury, lesion size, inflammatory markers, and mediators of inflammation (NF-κB), apoptosis (BAX), and neural plasticity (brain-derived neurotrophic factor) in brain tissue were compared between groups.

RESULTS

Exosome-treated animals had significantly lower neurologic severity scores (first 4 days; p < 0.05) and faster neurologic recovery. At 7 days, exosome-treated animals had significantly smaller (p < 0.05) brain lesion sizes. Exosome-treated animals also had significantly lower levels of inflammatory markers (interleukin [IL]-1, IL-6, IL-8, and IL-18) and higher granulocyte-macrophage colony-stimulating factor levels compared with the control animals, indicating specific impacts on various cytokines. The BAX and NF-κB levels were significantly lower (p < 0.05) in exosome-treated animals, while brain-derived neurotrophic factor levels were significantly higher (p < 0.05) in the exosome-treated animals.

CONCLUSION

In a large animal model of TBI and HS, early single-dose exosome treatment attenuates neurologic injury, decreases brain lesion size, inhibits inflammation and apoptosis, and promotes neural plasticity over a 7-day period.

The Function of Astrocyte Mediated Extracellular Vesicles in Central Nervous System Diseases

Astrocyte activation plays an important role during disease-induced inflammatory response in the brain. Exosomes in the brain could be released from bone marrow (BM)-derived stem cells, neuro stem cells (NSC), mesenchymal stem cells (MSC), etc. We summarized that exosomes release and transport signaling to the target cells, and then produce function. Furthermore, we discussed the pathological interactions between astrocytes and other brain cells, which are related to brain diseases such as stroke, Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS) disease, multiple sclerosis (MS), psychiatric, traumatic brain injury (TBI), etc. We provide up-to-date, comprehensive and valuable information on the involvement of exosomes in brain diseases, which is beneficial for basic researchers and clinical physicians.

Wg secreted by conventional Golgi transport diffuses and forms Wg gradient whereas Wg tethered to extracellular vesicles do not diffuse

Wingless (Wg)/Wnt family proteins are essential for animal development and adult homeostasis. Drosophila Wg secreted from the dorsal-ventral (DV) midline in wing discs forms a concentration gradient that is shaped by diffusion rate and stability of Wg. To understand how the gradient of extracellular Wg is generated, we compared the secretion route of NRT-Wg, an artificial membrane-tethered form of Wg that is supposedly not secreted but still supports fly development, to that of wild-type Wg. We found that wild-type Wg is secreted by both conventional Golgi transport and via extracellular vesicles (EVs), and NRT-Wg can be also secreted via EVs. Furthermore, wild-type Wg secreted by Golgi transport diffused and formed Wg gradient but Wg-containing EVs did not diffuse at all. In case of Wg stability, Sol narae (Sona), a metalloprotease that cleaves Wg, contributes to generate a steep Wg gradient. Interestingly, Wg was also produced in the presumptive wing blade region, which indicates that NRT-Wg on EVs expressed in the blade allows the blade cells to proliferate and differentiate without Wg diffused from the DV midline. We propose that EV-associated Wg induces Wg signaling in autocrine and juxtaposed manners whereas Wg secreted by Golgi transport forms gradient and acts in the long-range signaling, and different organs differentially utilize these two types of Wg signaling for their own development.

COVID-19 therapy with mesenchymal stromal cells (MSC) and convalescent plasma must consider exosome involvement: Do the exosomes in convalescent plasma antagonize the weak immune antibodies?

Exosome extracellular vesicles as biologic therapy for COVID-19 are discussed for two areas. The first involves the growing use of mesenchymal stromal cells (MSCs) for the profound clinical cytokine storm and severe pneumonia in COVID-19 patients. Instead, it is recommended to treat alternatively with their MSC-released exosomes. This is because many reports in the literature and our data have shown that the release of exosomes from the in vivo administered MSC is actually responsible for their beneficial effects. Further, the exosomes are superior, simpler and clinically more convenient compared to their parental MSC. Additionally, in the context of COVID-19, the known tendency of MSC to intravascularly aggregate causing lung dysfunction might synergize with the pneumonia aspects, and the tendency of MSC peripheral vascular micro aggregates might synergize with the vascular clots of the COVID-19 disease process, causing significant central or peripheral vascular insufficiency. The second exosome therapeutic area for severe COVID-19 involves use of convalescent plasma for its content of acquired immune antibodies that must consider the role in this therapy of contained nearly trillions of exosomes. Many of these derive from activated immune modulating cells and likely can function to transfer miRNAs that acting epigenetically to also influence the convalescent plasma recipient response to the virus. There is sufficient evidence, like recovery of patients with antibody deficiencies, to postulate that the antibodies actually have little effect and that immune resistance is principally due to T cell mechanisms. Further, COVID-19 convalescent plasma has remarkably weak beneficial effects if compared to what was expected from many prior studies. This may be due to the dysfunctional immune response to the infection and resulting weak Ab that may be impaired further by antagonistic exosomes in the convalescent plasma. At the least, pre selection of plasma for the best antibodies and relevant exosomes would produce the most optimum therapy for very severely affected COVID-19 patients.

Neuroinflammation Treatment via Targeted Delivery of Nanoparticles

The lack of effective treatments for most neurological diseases has prompted the search for novel therapeutic options. Interestingly, neuroinflammation is emerging as a common feature to target in most CNS pathologies. Recent studies suggest that targeted delivery of small molecules to reduce neuroinflammation can be beneficial. However, suboptimal drug delivery to the CNS is a major barrier to modulate inflammation because neurotherapeutic compounds are currently being delivered systemically without spatial or temporal control. Emerging nanomaterial technologies are providing promising and superior tools to effectively access neuropathological tissue in a controlled manner. Here we highlight recent advances in nanomaterial technologies for drug delivery to the CNS. We propose that state-of-the-art nanoparticle drug delivery platforms can significantly impact local CNS bioavailability of pharmacological compounds and treat neurological diseases.

Exosome-Derived LncRNAs in Lung Cancer

As extracellular vesicles, exosomes are released from most cells to perform cell–cell communication. Recent studies have shown that exosomes could be released into tumor microenvironment and blood to promote tumor progression through packaging and transmitting various bioactive molecules, such as cholesterol, proteins, lipids, miRNAs, mRNAs, and long non-coding RNAs (lncRNAs) to distant cells. LncRNAs have emerged as a major class of non-coding transcripts. A lot of LncRNAs have been discovered during the past few years of research on genomics. They have been proven to participate in various biological functions and disease processes through multiple mechanisms. In this review, we analyzed the role of exosome-derived lncRNAs in lung carcinogenesis and metastasis. We also highlight opportunities for the clinical potential of exosomes with specific lncRNAs as biomarkers and therapeutic intervention in lung cancer.

Pleiotropic Effects of Exosomes as a Therapy for Stroke Recovery

Stroke is the leading cause of disability, and stroke survivors suffer from long-term sequelae even after receiving recombinant tissue plasminogen activator therapy and endovascular intracranial thrombectomy. Increasing evidence suggests that exosomes, nano-sized extracellular membrane vesicles, enhance neurogenesis, angiogenesis, and axonal outgrowth, all the while suppressing inflammatory reactions, thereby enhancing functional recovery after stroke. A systematic literature review to study the association of stroke recovery with exosome therapy was carried out, analyzing species, stroke model, source of exosomes, behavioral analyses, and outcome data, as well as molecular mechanisms. Thirteen studies were included in the present systematic review. In the majority of studies, exosomes derived from mesenchymal stromal cells or stem cells were administered intravenously within 24 h after transient middle cerebral artery occlusion, showing a significant improvement of neurological severity and motor functions. Specific microRNAs and molecules were identified by mechanistic investigations, and their amplification was shown to further enhance therapeutic effects, including neurogenesis, angiogenesis, axonal outgrowth, and synaptogenesis. Overall, this review addresses the current advances in exosome therapy for stroke recovery in preclinical studies, which can hopefully be preparatory steps for the future development of clinical trials involving stroke survivors to improve functional outcomes.

Extracellular Vesicles as Innovative Tool for Diagnosis, Regeneration and Protection against Neurological Damage

Extracellular vesicles (EVs) have recently attracted a great deal of interest as they may represent a new biosignaling paradigm. According to the mode of biogenesis, size and composition, two broad categories of EVs have been described, exosomes and microvesicles. EVs have been shown to carry cargoes of signaling proteins, RNA species, DNA and lipids. Once released, their content is selectively taken up by near or distant target cells, influencing their behavior. Exosomes are involved in cell–cell communication in a wide range of embryonic developmental processes and in fetal–maternal communication. In the present review, an outline of the role of EVs in neural development, regeneration and diseases is presented. EVs can act as regulators of normal homeostasis, but they can also promote either neuroinflammation/degeneration or tissue repair in pathological conditions, depending on their content. Since EV molecular cargo constitutes a representation of the origin cell status, EVs can be exploited in the diagnosis of several diseases. Due to their capability to cross the blood–brain barrier (BBB), EVs not only have been suggested for the diagnosis of central nervous system disorders by means of minimally invasive procedures, i.e., “liquid biopsies”, but they are also considered attractive tools for targeted drug delivery across the BBB. From the therapeutic perspective, mesenchymal stem cells (MSCs) represent one of the most promising sources of EVs. In particular, the neuroprotective properties of MSCs derived from the dental pulp are here discussed.

Exosome-Mimetic Supramolecular Vesicles with Reversible and Controllable Fusion and Fission*

The fusion and fission behaviors of exosomes are essential for the cell-to-cell communication. Developing exosome-mimetic vesicles with such behaviors is of vital importance, but still remains a big challenge. Presented herein is an artificial supramolecular vesicle that exhibits redox-modulated reversible fusion-fission functions. These vesicles tend to fuse together and form large-sized vesicles upon oxidation, undergo a fission process and then return to small-sized vesicles through reduction. Noteworthy, the aggregation-induced emission (AIE) characteristics of the supramolecular building blocks enable the molecular configuration during vesicular transformation to be monitored by fluorescence technology. Moreover, the presented vesicles are excellent nanocarrier candidates to transfer siRNA into cancer cells.

Stem Cell-Derived Exosomes as Treatment for Stroke: a Systematic Review

BACKGROUND

The therapeutic potential of stem cells may largely be mediated by paracrine factors contained in exosomes released from intracellular endosomes. A systematic review was performed to identify the effects of stem cell-derived exosomes for their ability to induce restorative effects in animal models of stroke.

METHODS

PubMed, Scopus, and ISI Web of Science databases were searched for all available articles testing stem cell-derived exosomes as therapeutic interventions in animal models of stroke until April 2020. The STAIR scale was used to assess the quality of the included studies.

RESULTS

A total of 994 published articles were identified in the systematic search. After screening for eligibility, a total of 16 datasets were included. Type of cerebral ischemia was transient in majority studies and most studies used rat or mice adipose tissue-derived stem cells/bone marrow-derived stem cells. Eight studies indicated improved functional recovery while 8 were able to show reduced infarct volume as a result of exosome therapy. The beneficial effects were mainly attributed to reduced inflammation and oxidative stress, enhanced neurogenesis, angiogenesis, and neurite remodeling. Also, 4 studies demonstrated that exosomes hold great promise as an endogenous drug delivery nano-system.

CONCLUSION

In preclinical studies, use of stem cell-derived exosomes is strongly associated with improved neurological recovery and reduced brain infarct volume following stroke. Improved preclinical study quality in terms of treatment allocation reporting, randomization and blinding will accelerate needed progress towards clinical trials that should assess feasibility and safety of this therapeutic approach in humans. Graphical abstract.

Exosomes in Sepsis

Sepsis is a severe state of infection with high mortality. Pathogen-associated molecular patterns and damage-associated molecular patterns (DAMPs) initiate dysregulated systemic inflammation upon binding to pattern recognition receptors. Exosomes are endosome-derived vesicles, which carry proteins, lipids and nucleic acids, and facilitate intercellular communications. Studies have shown altered contents and function of exosomes during sepsis. In sepsis, exosomes carry increased levels of cytokines and DAMPs to induce inflammation. Exosomal DAMPs include, but are not limited to, high mobility group box 1, heat shock proteins, histones, adenosine triphosphate, and extracellular RNA. Exosomes released during sepsis have impact on multiple organs, including the lungs, kidneys, liver, cardiovascular system, and central nervous system. Here, we review the mechanisms of inflammation caused by exosomes, and their contribution to multiple organ dysfunction in sepsis.

Strategies for scalable manufacturing and translation of MSC-derived extracellular vesicles

Mesenchymal Stem/Stromal Cells (MSCs) are a well-studied cellular therapy with many clinical trials over the last few decades to treat a range of therapeutic indications. Recently, extracellular vesicles secreted by MSCs (MSC-EVs) have been shown to recapitulate many of the therapeutic effects of the MSCs themselves. While research in MSC-EVs has exploded, it is still early in their development towards a clinical therapy. One of the main challenges in cellular therapy, which will clearly also be a challenge in MSC-EV manufacturing, is developing a scalable, cGMP-compatible manufacturing paradigm. Therefore, the focus of this review is to identify some key MSC-EV manufacturing considerations such as the selection of critical raw materials, manufacturing platforms, and critical quality attribute assays. Addressing these issues early in research and development will accelerate clinical product development, clinical trials, and commercial therapies of MSC-EVs.

Mesenchymal stem cell-derived extracellular vesicle-based therapies protect against coupled degeneration of the central nervous and vascular systems in stroke

Stem cell-based treatments have been suggested as promising candidates for stroke. Recently, mesenchymal stem cells (MSCs) have been reported as potential therapeutics for a wide range of diseases. In particular, clinical trial studies have suggested MSCs for stroke therapy. The focus of MSC treatments has been directed towards cell replacement. However, recent research has lately highlighted their paracrine actions. The secretion of extracellular vesicles (EVs) is offered to be the main therapeutic mechanism of MSC therapy. However, EV-based treatments may provide a wider therapeutic window compared to tissue plasminogen activator (tPA), the traditional treatment for stroke. Exosomes are nano-sized EVs secreted by most cell types, and can be isolated from conditioned cell media or body fluids such as plasma, urine, and cerebrospinal fluid (CSF). Exosomes apply their effects through targeting their cargos such as microRNAs (miRs), DNAs, messenger RNAs, and proteins at the host cells, which leads to a shift in the behavior of the recipient cells. It has been indicated that exosomes, in particular their functional cargoes, play a significant role in the coupled pathogenesis and recovery of stroke through affecting the neurovascular unit (NVU). Therefore, it seems that exosomes could be utilized as diagnostic and therapeutic tools in stroke treatment. The miRs are small endogenous non-coding RNA molecules which serve as the main functional cargo of exosomes, and apply their effects as epigenetic regulators. These versatile non-coding RNA molecules are involved in various stages of stroke and affect stroke-related factors. Moreover, the involvement of aging-induced changes to specific miRs profile in stroke further highlights the role of miRs. Thus, miRs could be utilized as diagnostic, prognostic, and therapeutic tools in stroke. In this review, we discuss the roles of stem cells, exosomes, and their application in stroke therapy. We also highlight the usage of miRs as a therapeutic choice in stroke therapy.

Measurement and standardization challenges for extracellular vesicle therapeutic delivery vectors

Extracellular vesicles (EVs), such as exosomes and microvesicles, are nonreplicating lipid bilayer particles shed by most cell types which have the potential to revolutionize the development and efficient delivery of clinical therapeutics. This article provides an introduction to the landscape of EV-based vectors under development for the delivery of protein- and nucleic acid-based therapeutics. We highlight some of the most pressing measurement and standardization challenges that limit the translation of EVs to the clinic. Current challenges limiting development of EVs for drug delivery are the lack of: standardized cell-based platforms for the production of EV-based therapeutics; EV reference materials that allow researchers/manufacturers to validate EV measurements and standardized measurement systems for determining the molecular composition of EVs.

Exosomes: Beyond stem cells for cardiac protection and repair

The adult human heart has limited regenerative capacity; hence, stem cell therapy has been investigated as a potential approach for cardiac repair. However, a large part of the benefit of the injection of stem and progenitor cells into injured hearts is mediated by secreted factors. Exosomes-nano-sized secreted extracellular vesicles of endosomal origin-have emerged as key signaling organelles in intercellular communication, and are now viewed as the key regenerative constituent of the secretome of stem and progenitor cells. Exosomes released from mesenchymal stem cells, cardiac-derived progenitor cells, embryonic stem cells, induced pluripotent stem cells (iPSCs), and iPSC-derived cardiomyocytes exhibit cardioprotective, immunomodulatory, and reparative abilities. This concise review discusses the therapeutic benefit of exosomes secreted by stem and progenitor cells in preclinical models of ischemic heart disease.

Characterization of brain-derived extracellular vesicles reveals changes in cellular origin after stroke and enrichment of the prion protein with a potential role in cellular uptake

Extracellular vesicles (EVs) are important means of intercellular communication and a potent tool for regenerative therapy. In ischaemic stroke, transient blockage of a brain artery leads to a lack of glucose and oxygen in the affected brain tissue, provoking neuronal death by necrosis in the core of the ischaemic region. The fate of neurons in the surrounding penumbra region depends on the stimuli, including EVs, received during the following hours. A detailed characterization of such stimuli is crucial not only for understanding stroke pathophysiology but also for new therapeutic interventions. In the present study, we characterize the EVs in mouse brain under physiological conditions and 24 h after induction of transient ischaemia in mice. We show that, in steady-state conditions, microglia are the main source of small EVs (sEVs), whereas after ischaemia the main sEV population originates from astrocytes. Brain sEVs presented high amounts of the prion protein (PrP), which were further increased after stroke. Moreover, EVs were enriched in a proteolytically truncated PrP fragment (PrP-C1). Because of similarities between PrP-C1 and certain viral surface proteins, we studied the cellular uptake of brain-derived sEVs from mice lacking (PrP-KO) or expressing PrP (WT). We show that PrP-KO-sEVs are taken up significantly faster and more efficiently than WT-EVs by primary neurons. Furthermore, microglia and astrocytes engulf PrP-KO-sEVs more readily than WT-sEVs. Our results provide novel information on the relative contribution of brain cell types to the sEV pool in murine brain and indicate that increased release of sEVs by astrocytes together with elevated levels of PrP in sEVs may play a role in intercellular communication at early stages after stroke. In addition, amounts of PrP (and probably PrP-C1) in brain sEVs seem to contribute to regulating their cellular uptake.

Extracellular vesicles from human iPSC-derived neural stem cells: miRNA and protein signatures, and anti-inflammatory and neurogenic properties

Grafting of neural stem cells (NSCs) derived from human induced pluripotent stem cells (hiPSCs) has shown promise for brain repair after injury or disease, but safety issues have hindered their clinical application. Employing nano-sized extracellular vesicles (EVs) derived from hiPSC-NSCs appears to be a safer alternative because they likely have similar neuroreparative properties as NSCs and are amenable for non-invasive administration as an autologous or allogeneic off-the-shelf product. However, reliable methods for isolation, characterization and testing the biological properties of EVs are critically needed for translation. We investigated signatures of miRNAs and proteins and the biological activity of EVs, isolated from hiPSC-NSCs through a combination of anion-exchange chromatography (AEC) and size-exclusion chromatography (SEC). AEC and SEC facilitated the isolation of EVs with intact ultrastructure and expressing CD9, CD63, CD81, ALIX and TSG 101. Small RNA sequencing, proteomic analysis, pathway analysis and validation of select miRNAs and proteins revealed that EVs were enriched with miRNAs and proteins involved in neuroprotective, anti-apoptotic, antioxidant, anti-inflammatory, blood-brain barrier repairing, neurogenic and Aβ reducing activities. Besides, EVs comprised miRNAs and/or proteins capable of promoting synaptogenesis, synaptic plasticity and better cognitive function. Investigations using an in vitro macrophage assay and a mouse model of status epilepticus confirmed the anti-inflammatory activity of EVs. Furthermore, the intranasal administration of EVs resulted in the incorporation of EVs by neurons, microglia and astrocytes in virtually all adult rat and mouse brain regions, and enhancement of hippocampal neurogenesis. Thus, biologically active EVs containing miRNAs and proteins relevant to brain repair could be isolated from hiPSC-NSC cultures, making them a suitable biologic for treating neurodegenerative disorders.

Potential therapeutic application of mesenchymal stem cell-derived exosomes in SARS-CoV-2 pneumonia

BACKGROUND

The outbreak of a new virus known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has now become the main health concern all over the world. Since effective antiviral treatments have not been developed until now, SARS-CoV-2 is severely affecting countries and territories around the world.

METHODS

At the present review, articles in PubMed were searched with the following terms: mesenchymal stem cells, exosomes, coronavirus, and SARS-CoV-2, either alone or in a combination form. The most relevant selected functions were mesenchymal stem cell-derived exosomes and SARS-CoV-2 virus infection.

RESULTS

SARS-CoV-2 could damage pulmonary cells and induce secretion of different types of inflammatory cytokines. In the following, these cytokines trigger inflammation that damages the lungs and results in lethal acute respiratory distress syndrome (ARDS). The main characteristic of ARDS is the onset of inflammation in pulmonary, hyaline formation, pulmonary fibrosis, and edema. Mesenchymal stem cell-derived exosomes (MSC-Exo) are believed to have anti-inflammatory effects and immune-modulating capacity as well as the ability to induce tissue regeneration, suggesting a significant therapeutic opportunity that could be used to SARS-CoV-2 pneumonia treatment. Besides, exosomes may serve as a biomarker, drug delivery system, and vaccine for the management of the patient with SARS-CoV-2.

CONCLUSION

MSC-Exo may serve as a promising tool in the treatment of SARS-CoV-2 pneumonia. However, further work needs to be carried out to confirm the efficacy of exosomes in the treatment of SARS-CoV-2 pneumonia.

Damage-associated molecular patterns in trauma

In 1994, the "danger model" argued that adaptive immune responses are driven rather by molecules released upon tissue damage than by the recognition of "strange" molecules. Thus, an alternative to the "self versus non-self recognition model" has been provided. The model, which suggests that the immune system discriminates dangerous from safe molecules, has established the basis for the future designation of damage-associated molecular patterns (DAMPs), a term that was coined by Walter G. Land, Seong, and Matzinger. The pathological importance of DAMPs is barely somewhere else evident as in the posttraumatic or post-surgical inflammation and regeneration. Since DAMPs have been identified to trigger specific immune responses and inflammation, which is not necessarily detrimental but also regenerative, it still remains difficult to describe their "friend or foe" role in the posttraumatic immunogenicity and healing process. DAMPs can be used as biomarkers to indicate and/or to monitor a disease or injury severity, but they also may serve as clinically applicable parameters for optimized indication of the timing for, i.e., secondary surgeries. While experimental studies allow the detection of these biomarkers on different levels including cellular, tissue, and circulatory milieu, this is not always easily transferable to the human situation. Thus, in this review, we focus on the recent literature dealing with the pathophysiological importance of DAMPs after traumatic injury. Since dysregulated inflammation in traumatized patients always implies disturbed resolution of inflammation, so-called model of suppressing/inhibiting inducible DAMPs (SAMPs) will be very briefly introduced. Thus, an update on this topic in the field of trauma will be provided.

Assessment of Long-Term Effects of Sports-Related Concussions: Biological Mechanisms and Exosomal Biomarkers

Concussion or mild traumatic brain injury (mTBI) in athletes can cause persistent symptoms, known as post-concussion syndrome (PCS), and repeated injuries may increase the long-term risk for an athlete to develop neurodegenerative diseases such as chronic traumatic encephalopathy (CTE), and Alzheimer's disease (AD). The Center for Disease Control estimates that up to 3.8 million sport-related mTBI are reported each year in the United States. Despite the magnitude of the phenomenon, there is a current lack of comprehensive prognostic indicators and research has shown that available monitoring tools are moderately sensitive to short-term concussion effects but less sensitive to long-term consequences. The overall aim of this review is to discuss novel, quantitative, and objective measurements that can predict long-term outcomes following repeated sports-related mTBIs. The specific objectives were (1) to provide an overview of the current clinical and biomechanical tools available to health practitioners to ensure recovery after mTBIs, (2) to synthesize potential biological mechanisms in animal models underlying the long-term adverse consequences of mTBIs, (3) to discuss the possible link between repeated mTBI and neurodegenerative diseases, and (4) to discuss the current knowledge about fluid biomarkers for mTBIs with a focus on novel exosomal biomarkers. The conclusions from this review are that current post-concussion clinical tests are not sufficiently sensitive to injury and do not accurately quantify post-concussion alterations associated with repeated mTBIs. In the current review, it is proposed that current practices should be amended to include a repeated symptom inventory, a cognitive assessment of executive function and impulse control, an instrumented assessment of balance, vestibulo-ocular assessments, and an improved panel of blood or exosome biomarkers.

A Two-Dimensional Affinity Capture and Separation Mini-Platform for the Isolation, Enrichment, and Quantification of Biomarkers and Its Potential Use for Liquid Biopsy

Biomarker detection for disease diagnosis, prognosis, and therapeutic response is becoming increasingly reliable and accessible. Particularly, the identification of circulating cell-free chemical and biochemical substances, cellular and subcellular entities, and extracellular vesicles has demonstrated promising applications in understanding the physiologic and pathologic conditions of an individual. Traditionally, tissue biopsy has been the gold standard for the diagnosis of many diseases, especially cancer. More recently, liquid biopsy for biomarker detection has emerged as a non-invasive or minimally invasive and less costly method for diagnosis of both cancerous and non-cancerous diseases, while also offering information on the progression or improvement of disease. Unfortunately, the standardization of analytical methods to isolate and quantify circulating cells and extracellular vesicles, as well as their extracted biochemical constituents, is still cumbersome, time-consuming, and expensive. To address these limitations, we have developed a prototype of a portable, miniaturized instrument that uses immunoaffinity capillary electrophoresis (IACE) to isolate, concentrate, and analyze cell-free biomarkers and/or tissue or cell extracts present in biological fluids. Isolation and concentration of analytes is accomplished through binding to one or more biorecognition affinity ligands immobilized to a solid support, while separation and analysis are achieved by high-resolution capillary electrophoresis (CE) coupled to one or more detectors. When compared to other existing methods, the process of this affinity capture, enrichment, release, and separation of one or a panel of biomarkers can be carried out on-line with the advantages of being rapid, automated, and cost-effective. Additionally, it has the potential to demonstrate high analytical sensitivity, specificity, and selectivity. As the potential of liquid biopsy grows, so too does the demand for technical advances. In this review, we therefore discuss applications and limitations of liquid biopsy and hope to introduce the idea that our affinity capture-separation device could be used as a form of point-of-care (POC) diagnostic technology to isolate, concentrate, and analyze circulating cells, extracellular vesicles, and viruses.

Small extracellular vesicles secreted by human iPSC-derived MSC enhance angiogenesis through inhibiting STAT3-dependent autophagy in ischemic stroke

Background

Small extracellular vesicles (sEV) secreted by mesenchymal stem cells (MSC) derived from human induced pluripotent stem cells (iPSC, iMSC-sEV) are considered to have great potential in treating ischemic diseases. Angiogenesis play an important role in post-stroke recovery. However, no studies have yet been conducted to systemically examine the effect and the underlying mechanism of iMSC-sEV on angiogenesis under brain ischemia conditions.

Methods

Ischemic stroke model was performed in rats induced by middle cerebral artery occlusion (MCAO), and the pro-angiogenic capacity of iMSC-sEV was measured. The in vitro effects of iMSC-sEV on the migration and tube formation of endothelial cells were investigated, respectively. Autophagy and autophagy-related signaling pathway were detected in vivo and in vitro.

Results

We found that iMSC-sEV significantly reduced infarct volume, enhanced angiogenesis, and alleviated long-term neurological deficits in rats after stroke. We also demonstrated that iMSC-sEV increased migration and tube formation of endothelial cells in vitro. A further mechanism study revealed that the pro-angiogenic effect of iMSC-sEV was correlated with a reduction in autophagy. Furthermore, iMSC-sEV significantly activated signal transducer and activator of transcription 3 (STAT3), and suppression of STAT3 abolished iMSC-sEV-induced inhibition of autophagy and promotion of angiogenesis in vivo and in vitro.

Conclusions

Taken together, our data indicate that iMSC-sEV promote angiogenesis after ischemic stroke, potentially, by inhibiting autophagy, a process that is partially dependent on STAT3 activation.

Exosomal long noncoding RNA LNMAT2 promotes lymphatic metastasis in bladder cancer

Patients with bladder cancer (BCa) with clinical lymph node (LN) metastasis have an extremely poor prognosis. VEGF-C has been demonstrated to play vital roles in LN metastasis in BCa. However, approximately 20% of BCa with LN metastasis exhibits low VEGF-C expression, suggesting a VEGF-C-independent mechanism for LN metastasis of BCa. Herein, we demonstrate that BCa cell-secreted exosome-mediated lymphangiogenesis promoted LN metastasis in BCa in a VEGF-C-independent manner. We identified an exosomal long noncoding RNA (lncRNA), termed lymph node metastasis-associated transcript 2 (LNMAT2), that stimulated human lymphatic endothelial cell (HLEC) tube formation and migration in vitro and enhanced tumor lymphangiogenesis and LN metastasis in vivo. Mechanistically, LNMAT2 was loaded to BCa cell-secreted exosomes by directly interacting with heterogeneous nuclear ribonucleoprotein A2B1 (hnRNPA2B1). Subsequently, exosomal LNMAT2 was internalized by HLECs and epigenetically upregulated prospero homeobox 1 (PROX1) expression by recruitment of hnRNPA2B1 and increasing the H3K4 trimethylation level in the PROX1 promoter, ultimately resulting in lymphangiogenesis and lymphatic metastasis. Therefore, our findings highlight a VEGF-C-independent mechanism of exosomal lncRNA-mediated LN metastasis and identify LNMAT2 as a therapeutic target for LN metastasis in BCa.

BMSC-derived exosomes alleviate smoke inhalation lung injury through blockade of the HMGB1/NF-κB pathway

AIMS

To investigate the role of bone marrow mesenchymal stem cell (BMSC)-derived exosomes in smoke inhalation lung injury.

MAIN METHODS

In this study, we initially isolated exosomes from BMSCs and identified them by western blot and transmission electron microscopy. BMSC-derived exosomes were then used to treat in vitro and in vivo models of smoke inhalation lung injury. Pathologic alterations in lung tissue, the levels of inflammatory factors and apoptosis-related factors, and the expression of HMGB1 and NF-κB were determined to evaluate the therapeutic effect of BMSC-derived exosomes.

KEY FINDINGS

We found that BMSC-derived exosomes could alleviate the injury caused by smoke inhalation. Smoke inhalation increased the levels of inflammatory factors and apoptosis-related factors and the expression of HMGB1 and NF-κB, and these increases were reversed by BMSC-derived exosomes. HMGB1 overexpression abrogated the exosome-induced decreases in inflammatory factors, apoptosis-related factors and NF-κB.

SIGNIFICANCE

Collectively, these results indicate that BMSC-derived exosomes can effectively alleviate smoke inhalation lung injury by inhibiting the HMGB1/NF-κB pathway, suggesting that exosome, a noncellular therapy, is a potential therapeutic strategy for inhalation lung injury.

Multimodal imaging of hair follicle bulge-derived stem cells in a mouse model of traumatic brain injury

Traumatic brain injury (TBI) is a devastating event for which current therapies are limited. Stem cell transplantation may lead to recovery of function via different mechanisms, such as cell replacement through differentiation, stimulation of angiogenesis and support to the microenvironment. Adult hair follicle bulge-derived stem cells (HFBSCs) possess neuronal differentiation capacity, are easy to harvest and are relatively immune-privileged, which makes them potential candidates for autologous stem cell-based therapy. In this study, we apply in vivo multimodal, optical and magnetic resonance imaging techniques to investigate the behavior of mouse HFBSCs in a mouse model of TBI. HFBSCs expressed Luc2 and copGFP and were examined for their differentiation capacity in vitro. Subsequently, transduced HFBSCs, preloaded with ferumoxytol, were transplanted next to the TBI lesion (cortical region) in nude mice, 2 days after injury. Brains were fixed for immunohistochemistry 58 days after transplantation. Luc2- and copGFP-expressing, ferumoxytol-loaded HFBSCs showed adequate neuronal differentiation potential in vitro. Bioluminescence of the lesioned brain revealed survival of HFBSCs and magnetic resonance imaging identified their localization in the area of transplantation. Immunohistochemistry showed that transplanted cells stained for nestin and neurofilament protein (NF-Pan). Cells also expressed laminin and fibronectin but extracellular matrix masses were not detected. After 58 days, ferumoxytol could be detected in HFBSCs in brain tissue sections. These results show that HFBSCs are able to survive after brain transplantation and suggest that cells may undergo differentiation towards a neuronal cell lineage, which supports their potential use for cell-based therapy for TBI.

Evaluation of M2-like macrophage enrichment after diffuse traumatic brain injury through transient interleukin-4 expression from engineered mesenchymal stromal cells

BACKGROUND

Appropriately modulating inflammation after traumatic brain injury (TBI) may prevent disabilities for the millions of those inflicted annually. In TBI, cellular mediators of inflammation, including macrophages and microglia, possess a range of phenotypes relevant for an immunomodulatory therapeutic approach. It is thought that early phenotypic modulation of these cells will have a cascading healing effect. In fact, an anti-inflammatory, "M2-like" macrophage phenotype after TBI has been associated with neurogenesis, axonal regeneration, and improved white matter integrity (WMI). There already exist clinical trials seeking an M2-like bias through mesenchymal stem/stromal cells (MSCs). However, MSCs do not endogenously synthesize key signals that induce robust M2-like phenotypes such as interleukin-4 (IL-4).

METHODS

To enrich M2-like macrophages in a clinically relevant manner, we augmented MSCs with synthetic IL-4 mRNA to transiently express IL-4. These IL-4 expressing MSCs (IL-4 MSCs) were characterized for expression and functionality and then delivered in a modified mouse TBI model of closed head injury. Groups were assessed for functional deficits and MR imaging. Brain tissue was analyzed through flow cytometry, multi-plex ELISA, qPCR, histology, and RNA sequencing.

RESULTS

We observed that IL-4 MSCs indeed induce a robust M2-like macrophage phenotype and promote anti-inflammatory gene expression after TBI. However, here we demonstrate that acute enrichment of M2-like macrophages did not translate to improved functional or histological outcomes, or improvements in WMI on MR imaging. To further understand whether dysfunctional pathways underlie the lack of therapeutic effect, we report transcriptomic analysis of injured and treated brains. Through this, we discovered that inflammation persists despite acute enrichment of M2-like macrophages in the brain.

CONCLUSION

The results demonstrate that MSCs can be engineered to induce a stronger M2-like macrophage response in vivo. However, they also suggest that acute enrichment of only M2-like macrophages after diffuse TBI cannot orchestrate neurogenesis, axonal regeneration, or improve WMI. Here, we also discuss our modified TBI model and methods to assess severity, behavioral studies, and propose that IL-4 expressing MSCs may also have relevance in other cavitary diseases or in improving biomaterial integration into tissues.

Exosomes: roles and therapeutic potential in osteoarthritis

Exosomes participate in many physiological and pathological processes by regulating cell-cell communication, which are involved in numerous diseases, including osteoarthritis (OA). Exosomes are detectable in the human articular cavity and were observed to change with OA progression. Several joint cells, including chondrocytes, synovial fibroblasts, osteoblasts, and tenocytes, can produce and secrete exosomes that influence the biological effects of targeted cells. In addition, exosomes from stem cells can protect the OA joint from damage by promoting cartilage repair, inhibiting synovitis, and mediating subchondral bone remodeling. This review summarizes the roles and therapeutic potential of exosomes in OA and discusses the perspectives and challenges related to exosome-based treatment for OA patients in the future.

miR-23a-3p-abundant small extracellular vesicles released from Gelma/nanoclay hydrogel for cartilage regeneration

Articular cartilage has limited self-regenerative capacity and the therapeutic methods for cartilage defects are still dissatisfactory in clinic. Recent studies showed that exosomes derived from mesenchymal stem cells promoted chondrogenesis by delivering bioactive substances to the recipient cells, indicating exosomes might be a novel method for repairing cartilage defect. Herein, we investigated the role and mechanism of human umbilical cord mesenchymal stem cells derived small extracellular vesicles (hUC-MSCs-sEVs) on cartilage regeneration. In vitro results showed that hUC-MSCs-sEVs promoted the migration, proliferation and differentiation of chondrocytes and human bone marrow mesenchymal stem cells (hBMSCs). MiRNA microarray showed that miR-23a-3p was the most highly expressed among the various miRNAs contained in hUC-MSCs-sEVs. Our data revealed that hUC-MSCs-sEVs promoted cartilage regeneration by transferring miR-23a-3p to suppress the level of PTEN and elevate expression of AKT. Moreover, we fabricated Gelatin methacrylate (Gelma)/nanoclay hydrogel (Gel-nano) for sustained release of sEVs, which was biocompatible and exhibited excellent mechanical property. In vivo results showed that hUC-MSCs-sEVs containing Gelma/nanoclay hydrogel (Gel-nano-sEVs) effectively promoted cartilage regeneration. These results indicated that Gel-nano-sEVs have a promising capacity to stimulate chondrogenesis and heal cartilage defects, and also provided valuable data for understanding the role and mechanism of hUC-MSCs-sEVs in cartilage regeneration.

Extracellular Vesicles as Therapeutics for Brain Injury and Disease

Extracellular vesicles (EVs) are gaining tremendous importance in comprehending central nervous system (CNS) function and treating neurological disorders because of their role in intercellular communication and reparative processes, and suitability as drug delivery vehicles. Since EVs have lipid membranes, they cross the blood-brain barrier easily and communicate with target neurons and glia even deep inside the brain. EVs from various sources have been isolated, characterized, and tailored for promoting beneficial effects in conditions, such as brain injury and disease. Particularly, EVs isolated from mesenchymal stem cells and neural stem cells have shown promise for alleviating brain dysfunction after injury or disease. Such properties of stem cell-derived EVs have great importance for clinical applications, as EV therapy can avoid several concerns typically associated with cell therapy. This minireview confers the competence of EVs for improving brain function by modulating CNS injury and disease.

Strategies and prospects of effective neural circuits reconstruction after spinal cord injury

Due to the disconnection of surviving neural elements after spinal cord injury (SCI), such patients had to suffer irreversible loss of motor or sensory function, and thereafter enormous economic and emotional burdens were brought to society and family. Despite many strategies being dealing with SCI, there is still no effective regenerative therapy. To date, significant progress has been made in studies of SCI repair strategies, including gene regulation of neural regeneration, cell or cell-derived exosomes and growth factors transplantation, repair of biomaterials, and neural signal stimulation. The pathophysiology of SCI is complex and multifaceted, and its mechanisms and processes are incompletely understood. Thus, combinatorial therapies have been demonstrated to be more effective, and lead to better neural circuits reconstruction and functional recovery. Combinations of biomaterials, stem cells, growth factors, drugs, and exosomes have been widely developed. However, simply achieving axon regeneration will not spontaneously lead to meaningful functional recovery. Therefore, the formation and remodeling of functional neural circuits also depend on rehabilitation exercises, such as exercise training, electrical stimulation (ES) and Brain-Computer Interfaces (BCIs). In this review, we summarize the recent progress in biological and engineering strategies for reconstructing neural circuits and promoting functional recovery after SCI, and emphasize current challenges and future directions.

Mesenchymal Stem Cell-Derived Exosomes Improve Functional Recovery in Rats After Traumatic Brain Injury: A Dose-Response and Therapeutic Window Study

Background. Mesenchymal stem cell (MSC)-derived exosomes play a critical role in regenerative medicine. Objective. To determine the dose- and time-dependent efficacy of exosomes for treatment of traumatic brain injury (TBI). Methods. Male rats were subjected to a unilateral moderate cortical contusion. In the dose-response study, animals received a single intravenous injection of exosomes (50, 100, 200 µg per rat) or vehicle, with treatment initiated at 1 day after injury. In the therapeutic window study, animals received a single intravenous injection of 100 µg exosomes or vehicle starting at 1, 4, or 7 days after injury. Neurological functional tests were performed weekly after TBI for 5 weeks. Spatial learning was measured on days 31 to 35 after TBI using the Morris water maze test. Results. Compared with the vehicle, regardless of the dose and delay in treatment, exosome treatment significantly improved sensorimotor and cognitive function, reduced hippocampal neuronal cell loss, promoted angiogenesis and neurogenesis, and reduced neuroinflammation. Exosome treatment at 100 µg per rat exhibited a significant therapeutic effect compared with the 50- or 200-µg exosome groups. The time-dependent exosome treatment data demonstrated that exosome treatment starting at 1 day post-TBI provided a significantly greater improvement in functional and histological outcomes than exosome treatments at the other 2 delayed treatments. Conclusions. These results indicate that exosomes have a wide range of effective doses for treatment of TBI with a therapeutic window of at least 7 days postinjury. Exosomes may provide a novel therapeutic intervention in TBI.

Extracellular Vesicle-Mediated Delivery of Circular RNA SCMH1 Promotes Functional Recovery in Rodent and Nonhuman Primate Ischemic Stroke Models

BACKGROUND

Stroke is a leading cause of adult disability that can severely compromise the quality of life of patients, yet no effective medication currently exists to accelerate rehabilitation. A variety of circular RNA (circRNA) molecules are known to function in ischemic brain injury. Lentivirus-based expression systems have been widely used in basic studies of circRNAs, but safety issues with such delivery systems have limited exploration of the potential therapeutic roles for circRNAs.

METHODS

Circular RNA SCMH1 (circSCMH1) was screened from the plasma of patients with acute ischemic stroke by using circRNA microarrays. Engineered rabies virus glycoprotein-circSCMH1-extracellular vesicles were generated to selectively deliver circSCMH1 to the brain. Nissl staining was used to examine infarct size. Behavioral tasks were performed to evaluate motor functions in both rodent and nonhuman primate ischemic stroke models. Golgi staining and immunostaining were used to examine neuroplasticity and glial activation. Proteomic assays and RNA-sequencing data combined with transcriptional profiling were used to identify downstream targets of circSCMH1.

RESULTS

CircSCMH1 levels were significantly decreased in the plasma of patients with acute ischemic stroke, offering significant power in predicting stroke outcomes. The decreased levels of circSCMH1 were further confirmed in the plasma and peri-infarct cortex of photothrombotic stroke mice. Beyond demonstrating proof-of-concept for an RNA drug delivery technology, we observed that circSCMH1 treatment improved functional recovery after stroke in both mice and monkeys, and we discovered that circSCMH1 enhanced the neuronal plasticity and inhibited glial activation and peripheral immune cell infiltration. CircSCMH1 binds mechanistically to the transcription factor MeCP2 (methyl-CpG binding protein 2), thereby releasing repression of MeCP2 target gene transcription.

CONCLUSIONS

Rabies virus glycoprotein-circSCMH1-extracellular vesicles afford protection by promoting functional recovery in the rodent and the nonhuman primate ischemic stroke models. Our study presents a potentially widely applicable nucleotide drug delivery technology and demonstrates the basic mechanism of how circRNAs can be therapeutically exploited to improve poststroke outcomes.

Extracellular vesicle-mediated transfer of miR-21-5p from mesenchymal stromal cells to neurons alleviates early brain injury to improve cognitive function via the PTEN/Akt pathway after subarachnoid hemorrhage

Patients with subarachnoid hemorrhage (SAH) often suffer from cognitive function impairments even when they have received proper treatment, such as the clipping or coiling of aneurysms, and this causes problems with returning to work and burdens the family. Increasing attention has been paid to mesenchymal stem cell (MSC)-derived extracellular vesicle (MSC-EV) as promising therapeutic vesicles for stroke management. In this study, we explored the potential role of MSC-EV in a rat model of SAH. We observed that MSC-EV ameliorated early brain injury (EBI) after SAH by reducing the apoptosis of neurons and that SAH induced an increase in the expression level of miR-21 in the prefrontal cortex and hippocampus. In addition, using miRNA profiling and CSF sequencing data from the exRNA Atlas, we demonstrated that EV-derived miR-21 protected neurons from apoptosis and alleviated SAH-induced cognitive dysfunction. The neuroprotective role of MSC-EV was abrogated by miR-21 knockdown or the administration of MK2206, a PTEN/Akt inhibitor. Overall, our results suggest that MSC-EV promotes neuronal survival and alleviates EBI after SAH through transferring miR-21 to recipient neurons.

Surface functionalization strategies of extracellular vesicles

Extracellular vesicles (EVs) are lipid-protein bilayer vesicular constructs secreted to the extracellular spaces by cells. All cells secrete EVs as a regular biological process that appears to be conserved throughout the evolution. Owing to the rich molecular cargo of EVs with specific lipid and protein content and documented role in cellular communication, EVs have been exploited as a versatile agent in the biomedical arena, including as diagnostic, drug delivery, immunomodulatory, and therapeutic agents. With these multifaceted applications in the biomedical field, the functionalization of EVs to add diverse functionality has garnered rapid attention. EVs can be functionalized with an exogenous imaging and targeting moiety that allows for the target specificity and the real-time tracking of EVs for diagnostic and therapeutic applications. Importantly, such added functionalities can be used to explore EVs' biogenesis pathway and their role in cellular communication, which can lead to a better understanding of EVs' cellular mechanisms and processes. In this report, we have reviewed the existing surface functionalization strategies of EVs and broadly classified them into three major approaches: physical, biological, and chemical approaches. The physical approach of EV functionalization includes methods like sonication, extrusion, and freeze-thaw that can change the surface properties of EVs via membrane rearrangements. The biological approach includes genetically and metabolically engineering cells to express protein or cargo molecules of interest in secreted EVs. The chemical approach includes different facile click type chemistries that can be used to covalently conjugate the EV lipid or protein construct with different linker groups for diverse functionality. Different chemistries like thiol-maleimide, EDC/NHS, azide-alkyne cycloaddition, and amidation chemistry have been discussed to functionalize EVs. Finally, a comparative discussion of all approaches has been done focusing on the significance of each approach. The collective knowledge of the major approach of surface functionalization can be used to improve the limitation of one technique by combining it with another. An optimized surface functionalization approach developed accordingly can efficiently add required functionality to EVs while maintaining their natural integrity.

Exosomes as mediators of neuron-glia communication in neuroinflammation

In recent years, a type of extracellular vesicles named exosomes has emerged that play an important role in intercellular communication under physiological and pathological conditions. These nanovesicles (30-150 nm) contain proteins, RNAs and lipids, and their internalization by bystander cells could alter their normal functions. This review focuses on recent knowledge about exosomes as messengers of neuron-glia communication and their participation in the physiological and pathological functions in the central nervous system. Special emphasis is placed on the role of exosomes under toxic or pathological stimuli within the brain, in which the glial exosomes containing inflammatory molecules are able to communicate with neurons and contribute to the pathogenesis of neuroinflammation and neurodegenerative disorders. Given the small size and characteristics of exosomes, they can cross the blood-brain barrier and be used as biomarkers and diagnosis for brain disorders and neuropathologies. Finally, although the application potential of exosome is still limited, current studies indicate that exosomes represent a promising strategy to gain pathogenic information to identify therapeutically targets and biomarkers for neurological disorders and neuroinflammation.

Enhanced therapeutic effects of MSC-derived extracellular vesicles with an injectable collagen matrix for experimental acute kidney injury treatment

BACKGROUND

Mesenchymal stem cell (MSC)-derived extracellular vesicles (EVs) have been shown to have therapeutic potential for ischemic diseases and are considered an alternative to cell therapy. However, the low retention and poor stability of EVs post-transplantation in vivo remain obstacle prior to the clinical application of EVs.

METHODS

This study was designed to investigate whether collagen matrix could increase the retention and stability of EVs and further improve the therapeutic effects in murine acute kidney injury (AKI) model. EVs were isolated from human placental MSCs (hP-MSC-EVs) and encapsulated in a collagen matrix. Then, we investigated whether collagen matrix can prolong the retention of EVs in vivo, further enhancing the therapeutic efficiency of EVs in AKI.

RESULTS

Our results indicated that collagen matrix could effectively encapsulate EVs, significantly increase the stability of EVs, and promote the sustained release of EVs. Collagen matrix has improved the retention of EVs in the AKI model, which was proved by Gaussia luciferase (Gluc) imaging. The application of collagen matrix remarkably facilitated the proliferation of renal tubular epithelial cells in AKI compared with EVs alone. Moreover, collagen matrix could further augment the therapeutic effects of hP-MSC-EVs as revealed by angiogenesis, fibrosis and apoptosis, and functional analysis. Finally, we found that EVs play a therapeutic role by inhibiting endoplasmic reticulum (ER) stress.

CONCLUSIONS

Collagen matrix markedly enhanced the retention of EVs and further augmented the therapeutic effects of EVs for AKI. This strategy for improving the efficacy of EVs therapy provides a new direction for cell-free therapy.

Mesenchymal Stromal Cell-Derived Small Extracellular Vesicles Induce Ischemic Neuroprotection by Modulating Leukocytes and Specifically Neutrophils

Background and Purpose- Small extracellular vesicles (sEVs) obtained from mesenchymal stromal cells (MSCs) were shown to induce neurological recovery after focal cerebral ischemia in rodents and to reverse postischemic lymphopenia in peripheral blood. Since peripheral blood cells, especially polymorphonuclear neutrophils (PMNs), contribute to ischemic brain injury, we analyzed brain leukocyte responses to sEVs and investigated the role of PMNs in sEV-induced neuroprotection. Methods- Male C57Bl6/j mice were exposed to transient intraluminal middle cerebral artery occlusion. After reperfusion, vehicle or sEVs prepared from conditioned media of MSCs raised from bone marrow samples of 3 randomly selected healthy human donors were intravenously administered. sEVs obtained from normoxic and hypoxic MSCs were applied. PMNs were depleted in vehicle and MSC-sEV-treated mice. Neurological deficits, ischemic injury, blood-brain barrier integrity, peripheral blood leukocyte responses, and brain leukocyte infiltration were evaluated over 72 hours. Results- sEV preparations of all 3 donors collected from normoxic MSCs significantly reduced neurological deficits. Preparations of 2 of these donors significantly decreased infarct volume and neuronal injury. sEV-induced neuroprotection was consistently associated with a decreased brain infiltration of leukocytes, namely of PMNs, monocytes/macrophages, and lymphocytes. sEVs obtained from hypoxic MSCs (1% O₂) had similar effects on neurological deficits and ischemic injury as MSC-sEVs obtained under regular conditions (21% O₂) but also reduced serum IgG extravasation-a marker of blood-brain barrier permeability. PMN depletion mimicked the effects of MSC-sEVs on neurological recovery, ischemic injury, and brain PMN, monocyte, and lymphocyte counts. Combined MSC-sEV administration and PMN depletion did not have any effects superior to PMN depletion in any of the readouts examined. Conclusions- Leukocytes and specifically PMNs contribute to MSC-sEV-induced ischemic neuroprotection. Individual MSC-sEV preparations may differ in their neuroprotective activities. Potency assays are urgently needed to identify their therapeutic efficacy before clinical application. Visual Overview- An online visual overview is available for this article.

Targeting High Mobility Group Box 1 in Subarachnoid Hemorrhage: A Systematic Review

Aneurysmal subarachnoid hemorrhage (aSAH) is a complex and potentially deadly disease. Neurosurgical clipping or endovascular coiling can successfully obliterate ruptured aneurysms in almost every case. However, despite successful interventions, the clinical outcomes of aSAH patients are often poor. The reasons for poor outcomes are numerous, including cerebral vasospasm (CVS), post-hemorrhagic hydrocephalus, systemic infections and delayed cerebral ischemia. Although CVS with subsequent cerebral ischemia is one of the main contributors to brain damage after aSAH, little is known about the underlying molecular mechanisms of brain damage. This review emphasizes the importance of pharmacological interventions targeting high mobility group box 1 (HMGB1)-mediated brain damage after subarachnoid hemorrhage (SAH) and CVS. We searched Pubmed, Ovid medline and Scopus for "subarachnoid hemorrhage" in combination with "HMGB1". Based on these criteria, a total of 31 articles were retrieved. After excluding duplicates and selecting the relevant references from the retrieved articles, eight publications were selected for the review of the pharmacological interventions targeting HMGB1 in SAH. Damaged central nervous system cells release damage-associated molecular pattern molecules (DAMPs) that are important for initiating, driving and sustaining the inflammatory response following an aSAH. The discussed evidence suggested that HMGB1, an important DAMP, contributes to brain damage during early brain injury and also to the development of CVS during the late phase. Different pharmacological interventions employing natural compounds with HMGB1-antagonizing activity, antibody targeting of HMGB1 or scavenging HMGB1 by soluble receptors for advanced glycation end products (sRAGE), have been shown to dampen the inflammation mediated brain damage and protect against CVS. The experimental data suggest that HMGB1 inhibition is a promising strategy to reduce aSAH-related brain damage and CVS. Clinical studies are needed to validate these findings that may lead to the development of potential treatment options that are much needed in aSAH.

Treatment with Mesenchymal-Derived Extracellular Vesicles Reduces Injury-Related Pathology in Pyramidal Neurons of Monkey Perilesional Ventral Premotor Cortex

Functional recovery after cortical injury, such as stroke, is associated with neural circuit reorganization, but the underlying mechanisms and efficacy of therapeutic interventions promoting neural plasticity in primates are not well understood. Bone marrow mesenchymal stem cell-derived extracellular vesicles (MSC-EVs), which mediate cell-to-cell inflammatory and trophic signaling, are thought be viable therapeutic targets. We recently showed, in aged female rhesus monkeys, that systemic administration of MSC-EVs enhances recovery of function after injury of the primary motor cortex, likely through enhancing plasticity in perilesional motor and premotor cortices. Here, using in vitro whole-cell patch-clamp recording and intracellular filling in acute slices of ventral premotor cortex (vPMC) from rhesus monkeys (Macaca mulatta) of either sex, we demonstrate that MSC-EVs reduce injury-related physiological and morphologic changes in perilesional layer 3 pyramidal neurons. At 14-16 weeks after injury, vPMC neurons from both vehicle- and EV-treated lesioned monkeys exhibited significant hyperexcitability and predominance of inhibitory synaptic currents, compared with neurons from nonlesioned control brains. However, compared with vehicle-treated monkeys, neurons from EV-treated monkeys showed lower firing rates, greater spike frequency adaptation, and excitatory:inhibitory ratio. Further, EV treatment was associated with greater apical dendritic branching complexity, spine density, and inhibition, indicative of enhanced dendritic plasticity and filtering of signals integrated at the soma. Importantly, the degree of EV-mediated reduction of injury-related pathology in vPMC was significantly correlated with measures of behavioral recovery. These data show that EV treatment dampens injury-related hyperexcitability and restores excitatory:inhibitory balance in vPMC, thereby normalizing activity within cortical networks for motor function.SIGNIFICANCE STATEMENT Neuronal plasticity can facilitate recovery of function after cortical injury, but the underlying mechanisms and efficacy of therapeutic interventions promoting this plasticity in primates are not well understood. Our recent work has shown that intravenous infusions of mesenchymal-derived extracellular vesicles (EVs) that are involved in cell-to-cell inflammatory and trophic signaling can enhance recovery of motor function after injury in monkey primary motor cortex. This study shows that this EV-mediated enhancement of recovery is associated with amelioration of injury-related hyperexcitability and restoration of excitatory-inhibitory balance in perilesional ventral premotor cortex. These findings demonstrate the efficacy of mesenchymal EVs as a therapeutic to reduce injury-related pathologic changes in the physiology and structure of premotor pyramidal neurons and support recovery of function.

Exosomes in osteoarthritis and cartilage injury: advanced development and potential therapeutic strategies

Articular cartilage injury is a common clinical problem, which can lead to joint dysfunction, significant pain, and secondary osteoarthritis (OA) in which major surgical procedures are mandatory for treatment. Exosomes, as endosome-derived membrane-bound vesicles, participating in intercellular communications in both physiological and pathophysiological conditions, have been attached great importance in many fields. Recently, the significance of exosomes in the development of OA has been gradually concerned, while the therapeutic value of exosomes in cartilage repair and OA treatment has also been gradually revealed. The functional difference of different types and derivations of exosomes are determined by their specific contents. Herein, we provide comprehensive understanding on exosome and OA, including how exosomes participating in OA, the therapeutic value of exosomes for cartilage injury/OA, and related bioengineering strategies for future therapeutic design.

The dual character of exosomes in osteoarthritis: Antagonists and therapeutic agents

Exosomes have gained increasing attention as they participate in cell cross-talk in pathological environments and are functional paracrine factors of therapeutic stem cells. Osteoarthritis (OA) is a common age-related degenerative joint disease, leading to a debilitating lifestyle for sufferers. However, currently no drugs on the market promote cartilage repair, and the patients usually have to undergo arthroplasty in the late stage of OA. Although significant progress has been made in the development of stem cells for the treatment of OA and cartilage injury, problems like immune rejection remain. Recently, increasing evidence has demonstrated that exosomes from the joint microenvironment ("negative" exosomes) could play vital and complicated roles in the progression of OA. Moreover, exosomes from therapeutic cells ("therapeutic" exosomes) have also shown enormous potential for OA therapy/cartilage repair. Here, we first discuss the definition and biological background of exosomes. Then, we critically examine the roles of the "negative" exosomes in OA-affected joint. Then, we will cover the potential of the "therapeutic" exosomes for OA therapy/cartilage repair. Next, the recent progress of tissue engineering with exosomes, especially for OA therapy/cartilage repair, will also be discussed. Finally, the limitations and opportunities of exosome-based OA therapy will be outlined. STATEMENT OF SIGNIFICANCE: As natural extracellular vesicles, exosomes participate in the intercellular communication. On the basis of biological characteristics of exosomes, exosomes have their two sides for osteoarthritis (OA). On the one hand, exosomes in the OA microenvironment are involved in pathology of OA. On the other hand, exosomes from therapeutic cells have the potential as advanced strategies for OA therapy. In addition, the development of tissue engineering technology is beneficial to the exosome-based OA therapy. According to the latest research status, exosomes are of great significance and interest for the personalized and precision treatment of OA in the future, despite the limitations and challenges.

Therapeutic potential of KLF2-induced exosomal microRNAs in pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a severe disorder of lung vasculature that causes right heart failure. Homoeostatic effects of flow-activated transcription factor Krüppel-like factor 2 (KLF2) are compromised in PAH. Here, we show that KLF2-induced exosomal microRNAs, miR-181a-5p and miR-324-5p act together to attenuate pulmonary vascular remodelling and that their actions are mediated by Notch4 and ETS1 and other key regulators of vascular homoeostasis. Expressions of KLF2, miR-181a-5p and miR-324-5p are reduced, while levels of their target genes are elevated in pre-clinical PAH, idiopathic PAH and heritable PAH with missense p.H288Y KLF2 mutation. Therapeutic supplementation of miR-181a-5p and miR-324-5p reduces proliferative and angiogenic responses in patient-derived cells and attenuates disease progression in PAH mice. This study shows that reduced KLF2 signalling is a common feature of human PAH and highlights the potential therapeutic role of KLF2-regulated exosomal miRNAs in PAH and other diseases associated with vascular remodelling.

C-C chemokine receptor type 2-overexpressing exosomes alleviated experimental post-stroke cognitive impairment by enhancing microglia/macrophage M2 polarization

BACKGROUND

Human-derived mesenchymal stromal cells have been shown to improve cognitive function following experimental stroke. The activity of exosomes has been verified to be comparable to the therapeutic effects of mesenchymal stromal cells. However, the effects of exosomes derived from human umbilical cord mesenchymal stem cells (HUC-MSCs) (Exo^Ctrl) on post-stroke cognitive impairment (PSCI) have rarely been reported. Moreover, whether exosomes derived from C-C chemokine receptor type 2 (CCR2)-overexpressing HUC-MSCs (Exo^CCR2) can enhance the therapeutic effects on PSCI and the possible underlying mechanisms have not been studied.

AIM

To investigate the effects of Exo^Ctrl on PSCI and whether Exo^CCR2 can enhance therapeutic effects on PSCI.

METHODS

Transmission electron microscopy, qNano^® particles analyzer, and Western blotting were employed to determine the morphology and CCR2 expression of Exo^Ctrl or Exo^CCR2. ELISA was used to study the binding capacity of exosomes to CC chemokine ligand 2 (CCL2) in vivo. After the intravenous injection of Exo^Ctrl or Exo^CCR2 into experimental rats, the effect of Exo^Ctrl and Exo^CCR2 on PSCI was assessed by Morris water maze. Remyelination and oligodendrogenesis were analyzed by Western blotting and immunofluorescence microscopy. QRT-PCR and immunofluorescence microscopy were conducted to compare the microglia/macrophage polarization. The infiltration and activation of hematogenous macrophages were analyzed by Western blotting and transwell migration analysis.

RESULTS

CCR2-overexpressing HUC-MSCs loaded the CCR2 receptor into their exosomes. The morphology and diameter distribution between Exo^Ctrl and Exo^CCR2 showed no significant difference. Exo^CCR2 bound significantly to CCL2 but Exo^Ctrl showed little CCL2 binding. Although both Exo^CCR2 and Exo^Ctrl showed beneficial effects on PSCI, oligodendrogenesis, remyelination, and microglia/macrophage polarization, Exo^CCR2 exhibited a significantly superior beneficial effect. We also found that Exo^CCR2 could suppress the CCL2-induced macrophage migration and activation in vivo and in vitro, compared with Exo^Ctrl treated group.

CONCLUSION

CCR2 over-expression enhanced the therapeutic effects of exosomes on the experimental PSCI by promoting M2 microglia/macrophage polarization, enhancing oligodendrogenesis and remyelination. These therapeutic effects are likely through suppressing the CCL2-induced hematogenous macrophage migration and activation.

Aptamer-guided extracellular vesicle theranostics in oncology

In the past decade, the study of exosomes, nanosized vesicles (50-150 nm) released into the extracellular space via the fusion of multivesicular bodies with the plasma membrane, has burgeoned with impressive achievements in theranostics applications. These nanosized vesicles have emerged as key players in homeostasis and in the pathogenesis of diseases owing to the variety of the cargos they can carry, the nature of the molecules packaged inside the vesicles, and the robust interactions between exosomes and target cells or tissues. Accordingly, the development of exosome-based liquid biopsy techniques for early disease detection and for monitoring disease progression marks a new era of precision medicine in the 21st century. Moreover, exosomes possess intrinsic properties - a nanosized structure and unique "homing effects" - that make them outstanding drug delivery vehicles. In addition, targeted exosome-based drug delivery systems can be further optimized using active targeting ligands such as nucleic acid aptamers. Indeed, the aptamers themselves can function as therapeutic and/or diagnostic tools based on their attributes of unique target-binding and non-immunogenicity. This review aims to provide readers with a current picture of the research on exosomes and aptamers and their applications in cancer theranostics, highlighting recent advances in their transition from the bench to the clinic.

Charge Detection Mass Spectrometry Measurements of Exosomes and other Extracellular Particles Enriched from Bovine Milk

The masses of particles in a bovine milk extracellular vesicle (EV) preparation enriched for exosomes were directly determined for the first time by charge detection mass spectrometry (CDMS). In CDMS, both the mass-to-charge ratio (m/z) and z are determined simultaneously for individual particles, enabling mass determinations for particles that are far beyond the mass limit (∼1.0 MDa) of conventional mass spectrometry (MS). Particle masses and charges span a wide range from m ∼ 2 to ∼90 MDa and z ∼ 50 to ∼1300 e (elementary charges) and are highly dependent upon the conditions used to extract and isolate the EVs. EV particles span a continuum of masses, reflecting the highly heterogeneous nature of these samples. However, evidence for unique populations of particles is obtained from correlation of the charges and masses. An analysis that uses a two-dimensional Gaussian model, provides evidence for six families of particles, four of which having masses in the range expected for exosomes. Complementary proteomics measurements and electron microscopy (EM) imaging are used to further characterize the EVs and confirm that these samples have been enriched in exosomes. The ability to characterize such extremely heterogeneous mixtures of large particles with rapid, sensitive, and high-resolution MS techniques is critical to ongoing analytical efforts to separate and purify exosomes and exosome subpopulations. Direct measurement of each particle's mass and charge is a new means of characterizing the physical and chemical properties of exosomes and other EVs.