Role of exosomes/microvesicles in the nervous system and use in emerging therapies

Molecular Characterization of Peripheral Extracellular Vesicles in Clinically Isolated Syndrome: Preliminary Suggestions from a Pilot Study

Extracellular vesicles (EVs), nanoparticles originated from different cell types, seem to be implicated in several cellular activities. In the Central Nervous System (CNS), glia and neurons secrete EVs and recent studies have demonstrated that the intercellular communication mediated by EVs has versatile functional impact in the cerebral homeostasis. This essential role may be due to their proteins and RNAs cargo that possibly modify the phenotypes of the targeted cells. Despite the increasing importance of EVs, little is known about their fluctuations in physiological as well as in pathological conditions. Furthermore, only few studies have investigated the contents of contemporary EVs subgroups (microvesicles, MVs and exosomes, EXOs) with the purpose of discriminating between their features and functional roles. In order to possibly shed light on these issues, we performed a pilot study in which MVs and EXOs extracted from serum samples of a little cohort of subjects (patients with the first clinical evidence of CNS demyelination, also known as Clinically Isolated Syndrome and Healthy Controls) were submitted to deep small-RNA sequencing. Data were analysed by an in-home bioinformatics platform. In line with previous reports, distinct classes of non-coding RNAs have been detected in both the EVs subsets, offering interesting suggestions on their origins and functions. We also verified the feasibility of this extensive molecular approach, thus supporting its valuable use for the analysis of circulating biomarkers (e.g., microRNAs) in order to investigate and monitor specific diseases.

Transmission of α-synuclein-containing erythrocyte-derived extracellular vesicles across the blood-brain barrier via adsorptive mediated transcytosis: another mechanism for initiation and progression of Parkinson's disease?

Parkinson’s disease (PD) pathophysiology develops in part from the formation, transmission, and aggregation of toxic species of the protein α-synuclein (α-syn). Recent evidence suggests that extracellular vesicles (EVs) may play a vital role in the transport of toxic α-syn between brain regions. Moreover, increasing evidence has highlighted the participation of peripheral molecules, particularly inflammatory species, which may influence or exacerbate the development of PD-related changes to the central nervous system (CNS), although detailed characterization of these species remains to be completed. Despite these findings, little attention has been devoted to erythrocytes, which contain α-syn concentrations ~1000-fold higher than the cerebrospinal fluid, as a source of potentially pathogenic α-syn. Here, we demonstrate that erythrocytes produce α-syn-rich EVs, which can cross the BBB, particularly under inflammatory conditions provoked by peripheral administration of lipopolysaccharide. This transport likely occurs via adsorptive-mediated transcytosis, with EVs that transit the BBB co-localizing with brain microglia. Examination of microglial reactivity upon exposure to α-syn-containing erythrocyte EVs in vitro and in vivo revealed that uptake provoked an increase in microglial inflammatory responses. EVs derived from the erythrocytes of PD patients elicited stronger responses than did those of control subjects, suggesting that inherent characteristics of EVs arising in the periphery might contribute to, or even initiate, CNS α-syn-related pathology. These results provide new insight into the mechanisms by which the brain and periphery communicate throughout the process of synucleinopathy pathogenesis.

Multiple Sclerosis Treatments Affect Monocyte-Derived Microvesicle Production

Microvesicles (MVs) are released by immune cells especially of the myeloid lineage upon stimulation with ATP on its cognate receptor P2X7, both in physiological and pathological conditions. In multiple sclerosis (MS) the role of MVs remains little investigated. We aimed to compare the release of MVs in peripheral blood monocytes from MS patients with healthy donors (HDs) and to see how current MS treatment may affect such a production. We also assessed the treatment effect on M1 and M2 monocyte polarization and on the inflammasome components. Spectrophotometric quantification was performed to compare monocyte-derived MVs from 20 untreated relapsing-remitting MS patients and 20 HDs and to evaluate the effect of different treatments. Subgroups of nine interferon-beta and of five teriflunomide-treated MS patients were evaluated at baseline and after 2, 6, and 12 months of treatment. Six MS patients taking Fingolimod, after switching from a first-line therapy, were included in the study and analyzed only at 12 months of treatment. MVs analysis revealed that monocytes from MS patients produced vesicles in higher amounts than controls. All treatments reduced vesicle production but only teriflunomide was associated with a downregulation of purinergic P2X7 receptor and inflammasome components expression. The therapies modulated mRNA expression of both M1 and M2 monocyte markers. Our results, suggesting new molecular targets for drugs currently used in MS, may potentially provide useful novel evidence to approach the disease.

Therapeutic Role and Drug Delivery Potential of Neuroinflammation as a Target in Neurodegenerative Disorders

Neuroinflammation, the condition associated with the hyperactivity of immune cells within the CNS (central nervous system), has recently been linked to a host range of neurodegenerative disorders. Targeting neuroinflammation could be of prime importance as recent research highlights the beneficial aspects associated with modulating the inflammatory mediators associated with the CNS. One of the main obstructions in neuroinflammatory treatments is the hindrance posed by the blood-brain barrier for the delivery of drugs. Hence, research has focused on novel modes of transport for drugs to cross the barrier through drug delivery and nanotechnology approaches. In this Review, we highlight the therapeutic advancement made in the field of neurodegenerative disorders by focusing on the effect neuroinflammation treatment has on these conditions.

Extracellular vesicles in coronary artery disease

Membrane vesicles released in the extracellular space are composed of a lipid bilayer enclosing soluble cytosolic material and nuclear components. Extracellular vesicles include apoptotic bodies, exosomes, and microvesicles (also known previously as microparticles). Originating from different subcellular compartments, the role of extracellular vesicles as regulators of transfer of biological information, acting locally and remotely, is now acknowledged. Circulating vesicles released from platelets, erythrocytes, leukocytes, and endothelial cells contain potential valuable biological information for biomarker discovery in primary and secondary prevention of coronary artery disease. Extracellular vesicles also accumulate in human atherosclerotic plaques, where they affect major biological pathways, including inflammation, proliferation, thrombosis, calcification, and vasoactive responses. Extracellular vesicles also recapitulate the beneficial effect of stem cells to treat cardiac consequences of acute myocardial infarction, and now emerge as an attractive alternative to cell therapy, opening new avenues to vectorize biological information to target tissues. Although interest in microvesicles in the cardiovascular field emerged about 2 decades ago, that for extracellular vesicles, in particular exosomes, started to unfold a decade ago, opening new research and therapeutic avenues. This Review summarizes current knowledge on the role of extracellular vesicles in coronary artery disease, and their emerging potential as biomarkers and therapeutic agents.

Current Perspectives on In Vivo Noninvasive Tracking of Extracellular Vesicles with Molecular Imaging

Clinical and preclinical in vivo tracking of extracellular vesicles (EVs) are a crucial tool for the development and optimization of EV-based diagnosis and treatment. EVs have gained interest due to their unique properties that make them excellent candidates for biological applications. Noninvasive in vivo EV tracking has allowed marked progress towards elucidating the mechanisms and functions of EVs in real time in preclinical and clinical studies. In this review, we summarize several molecular imaging methods that deal with EVs derived from different cells, which have allowed investigations of EV biodistribution, as well as their tracking, delivery, and tumor targeting, to determine their physiological functions and to exploit imaging-derived information for EV-based theranostics.

Exosome-Based Delivery of miR-124 in a Huntington's Disease Model

Objective

Huntington’s disease (HD) is a genetic neurodegenerative disease that is caused by abnormal CAG expansion. Altered microRNA (miRNA) expression also causes abnormal gene regulation in this neurodegenerative disease. The delivery of abnormally downregulated miRNAs might restore normal gene regulation and have a therapeutic effect.

Methods

We developed an exosome-based delivery method to treat this neurodegenerative disease. miR-124, one of the key miRNAs that is repressed in HD, was stably overexpressed in a stable cell line. Exosomes were then harvested from these cells using an optimized protocol. The exosomes (Exo-124) exhibited a high level of miR-124 expression and were taken up by recipient cells.

Results

When Exo-124 was injected into the striatum of R6/2 transgenic HD mice, expression of the target gene, RE1-Silencing Transcription Factor, was reduced. However, Exo-124 treatment did not produce significant behavioral improvement.

Conclusion

This study serves as a proof of concept for exosome-based delivery of miRNA in neurodegenerative diseases.

Exosomes in human atherosclerosis: An ultrastructural analysis study

Cell-to-cell communication, or signaling, is absolutely essential in orchestrating the activities of cells in multicellular organisms, to grow, develop, detect environmental changes and compensate for them in an internal, coordinated fashion. In the last few years, a considerable amount of new data have demonstrated the occurrence of a sophisticated intercellular signaling pathway based on the release of specialized vesicular structures, called exosomes, whose secretion appears to be regulated by various natural and experimental stimuli, physiological states, and disease processes. In the cardiovascular system, the study of exosomes is still in its infancy. Here, we aim to provide the first ultrastructural evidence for the presence of exosomes in human atherosclerotic plaque. We demonstrate by means of transmission electron microscopy that both lesional smooth muscle cells and endothelial cells are able to generate these membraneous microvesicles within specific compartments of the cell, called multivesicular bodies. Notably, in our series no signs of apoptosis have been detected in vascular cells secreting exosomes and no evidence of calcification has been observed associated with these structures in the extracellular space. Our results suggest the possible existence of a new mechanism of intercellular communication in the plaque milieu.

Tracking Extracellular Vesicles Delivery and RNA Translation Using Multiplexed Reporters

Elucidating extracellular vesicle (EV; e.g., exosomes, microvesicles) delivery and translation of its RNA cargo with an accurate spatiotemporal resolution is critical in helping understand EV's role under normal and pathological conditions. We here describe a multiplexed fluorescent and bioluminescent reporter strategy to simultaneously monitor and quantify EV delivery, as well as EV-RNA translation in EV-recipient cells.

Exosomes in Parkinson's Disease

Exosomes, nano-sized extracellular vesicles secreted by most cell types, are found in all kinds of biological fluids and tissues, including the central nervous system (CNS). The proposed functions of these vesicles include roles in cell-cell signaling, removal of cellular debris, and transfer of pathogens between cells. Many studies have revealed that exosomes derived from the CNS occur in the cerebrospinal fluid and peripheral body fluids, and their contents are altered during disease, making them an appealing target for biomarker development in Parkinson's disease (PD). Exosomes have been shown to spread toxic α-synuclein (αsyn) between cells and induce apoptosis, which suggests a key mechanism underlying the spread of αsyn aggregates in the brain and the acceleration of pathology in PD. However, potential neuroprotective roles of exosomes in PD have also been reported. On the treatment side, as drug delivery vehicles, exosomes have been used to deliver small interfering RNAs and catalase to the brain, and have shown clear therapeutic effects in a mouse model of PD. These features of exosomes in PD make them extremely interesting from the point of view of developing novel diagnostic and therapeutic approaches.

Function of neural stem cells in ischemic brain repair processes

Hypoxic/ischemic injury is the single most important cause of disabilities in infants, while stroke remains a leading cause of morbidity in children and adults around the world. The injured brain has limited repair capacity, and thereby only modest improvement of neurological function is evident post injury. In rodents, embryonic neural stem cells in the ventricular zone generate cortical neurons, and adult neural stem cells in the ventricular-subventricular zone of the lateral ventricle produce new neurons through animal life. In addition to generation of new neurons, neural stem cells contribute to oligodendrogenesis. Neurogenesis and oligodendrogenesis are essential for repair of injured brain. Much progress has been made in preclinical studies on elucidating the cellular and molecular mechanisms that control and coordinate neurogenesis and oligodendrogenesis in perinatal hypoxic/ischemic injury and the adult ischemic brain. This article will review these findings with a focus on the ventricular-subventricular zone neurogenic niche and discuss potential applications to facilitate endogenous neurogenesis and thereby to improve neurological function post perinatal hypoxic/ischemic injury and stroke.

Extracellular vesicle mimetics: Novel alternatives to extracellular vesicle-based theranostics, drug delivery, and vaccines

Extracellular vesicles are nano-sized spherical bilayered proteolipids encasing various components. Cells of all domains of life actively release these vesicles to the surroundings including various biological fluids. These extracellular vesicles are known to play pivotal roles in numerous pathophysiological functions. Extracellular vesicles have distinct characteristics, like high biocompatibility, safety, and nano-sized diameters that allow efficient drug loading capacity and long blood circulation half-life. These characteristics of extracellular vesicles have engrossed many scientists to harness them as new tools for novel delivery systems. This review will highlight the current state of the arts and problems of such extracellular vesicle-based theranostics, drug delivery and vaccines, and introduce "extracellular vesicle mimetics" as the novel alternative of extracellular vesicles. We hope to provide insights into the potential of extracellular vesicle mimetics as superior substitute to the natural extracellular vesicles that can be applied to theranostics, drug delivery, and vaccines against various diseases.

Imaging and Intracellular Tracking of Cancer-Derived Exosomes Using Single-Molecule Localization-Based Super-Resolution Microscope

Exosomes are small membrane vesicles secreted by cells and enriched with plenty of proteins. Considering their significant roles in different physical activities and potential value for diagnostic drug delivery, researchers have put great efforts in in vitro tracking and content analysis of exosomes. Recently, the emergence of different kinds of super-resolution microscopy provides powerful tools for exosome study. Here, we demonstrate the application of single-molecule localization based super-resolution imaging technique in the imaging and tracking of cancer-derived exosomes. In the experiment, first, cancer-derived exosomes are extracted from the culture media of tumor cells. Then the exosome membrane receptors are labeled with photoswitchable probes, which allow super-resolution imaging of these membrane receptors via photoactivated localization microscopy (PALM) or stochastic optical reconstruction microscopy (STORM). By using human breast cancer cell-derived exosomes, we demonstrated simultaneous dual-color PALM/STORM imaging of two kinds of membrane receptors on the exosome membrane. Moreover, the successful labeling and imaging of exosomes make it possible to observe the interaction between cancer-derived exosomes and normal cells. Meanwhile, we realized the colocalization of cancer-derived exosomes and lysosomes in recipient cells with PALM/STORM imaging. Since exosomes play a vital role in intercellular communications, we anticipate that the presented PALM/STORM-based imaging and tracking of exosomes holds a great potential in the investigation of the mechanism of exosome-mediated cancer metastasis.

Profile of Exosomal and Intracellular microRNA in Gamma-Herpesvirus-Infected Lymphoma Cell Lines

Exosomes are small vesicles released from cells, into which microRNAs (miRNA) are specifically sorted and accumulated. Two gamma-herpesviruses, Kaposi sarcoma-associated herpesvirus (KSHV) and Epstein-Barr virus (EBV), encode miRNAs in their genomes and express virus-encoded miRNAs in cells and exosomes. However, there is little information about the detailed distribution of virus-encoded miRNAs in cells and exosomes. In this study, we thus identified virus- and host-encoded miRNAs in exosomes released from KSHV- or EBV-infected lymphoma cell lines and compared them with intracellular miRNAs using a next-generation sequencer. Sequencing analysis demonstrated that 48% of the annotated miRNAs in the exosomes from KSHV-infected cells originated from KSHV. Human mir-10b-5p and mir-143-3p were much more highly concentrated in exosomes than in cells. Exosomes contained more nonexact mature miRNAs that did not exactly match those in miRBase than cells. Among the KSHV-encoded miRNAs, miRK12-3-5p was the most abundant exact mature miRNA in both cells and exosomes that exactly matched those in miRBase. Recently identified EXOmotifs, nucleotide motifs that control the loading of miRNAs into exosomes were frequently found within the sequences of KSHV-encoded miRNAs, and the presence of the EXOmotif CCCT or CCCG was associated with the localization of miRNA in exosomes in KSHV-infected cells. These observations suggest that specific virus-encoded miRNAs are sorted by EXOmotifs and accumulate in exosomes in virus-infected cells.

Microvesicles as Vehicles for Tissue Regeneration: Changing of the Guards

PURPOSE OF REVIEW

Microvesicles (MVs) have been recognised as mediators of stem cell function, enabling and guiding their regenerative effects.

RECENT FINDINGS

MVs constitute one unique size class of extracellular vesicles (EVs) directly shed from the cell plasma membrane. They facilitate cell-to-cell communication via intercellular transfer of proteins, mRNA and microRNA (miRNA). MVs derived from stem cells, or stem cell regulatory cell types, have proven roles in tissue regeneration and repair processes. Their role in the maintenance of healthy tissue function throughout the life course and thus in age related health span remains to be elucidated.

SUMMARY

Understanding the biogenesis and mechanisms of action of MVs may enable the development of cell-free therapeutics capable of assisting in tissue maintenance and repair for a variety of age-related degenerative diseases. This review critically evaluates recent work published in this area and highlights important new findings demonstrating the use of MVs in tissue regeneration.

Neural Stem Cells and Ischemic Brain

Stroke activates neural stem cells in the ventricular-subventricular zone (V/SVZ) of the lateral ventricle, which increases neuroblasts and oligodendrocyte progenitor cells (OPCs). Within the ischemic brain, neural stem cells, neuroblasts and OPCs appear to actively communicate with cerebral endothelial cells and other brain parenchymal cells to mediate ischemic brain repair; however, stroke-induced neurogenesis unlikely plays any significant roles in neuronal replacement. In this mini-review, we will discuss recent findings how intercellular communications between stroke-induced neurogenesis and oligodendrogenesis and brain parenchymal cells could potentially facilitate brain repair processes.

Exosomes in developmental signalling

In order to achieve coordinated growth and patterning during development, cells must communicate with one another, sending and receiving signals that regulate their activities. Such developmental signals can be soluble, bound to the extracellular matrix, or tethered to the surface of adjacent cells. Cells can also signal by releasing exosomes – extracellular vesicles containing bioactive molecules such as RNA, DNA and enzymes. Recent work has suggested that exosomes can also carry signalling proteins, including ligands of the Notch receptor and secreted proteins of the Hedgehog and WNT families. Here, we describe the various types of exosomes and their biogenesis. We then survey the experimental strategies used so far to interfere with exosome formation and critically assess the role of exosomes in developmental signalling.

Extracellular Vesicles in Molecular Diagnostics: An Overview with a Focus on CNS Diseases

All known cells continuously release nanoscale lipid membrane-enclosed packets. These packets, termed extracellular vesicles (EVs), bear the signature of their cells of origin. These vesicles can be detected in just about every type of biofluid tested, including blood, urine, and cerebrospinal fluid. The majority comes from normal cells, but disease cells also release them. There is a great interest in collecting and analyzing EVs in biofluids as diagnostics for a wide spectrum of central nervous system diseases. Here, we will review the state of central nervous system EV research in terms of molecular diagnostics and biomarkers.

Exosomal formulation enhances therapeutic response of celastrol against lung cancer

Celastrol (CEL), a plant-derived triterpenoid, is a known inhibitor of Hsp90 and NF-κB activation pathways and has recently been suggested to be of therapeutic importance in various cancers. However, the molecular mechanisms of celastrol-mediated effects in lung cancer are not systematically studied. Moreover, it suffers from poor bioavailability and off-site toxicity issues. This study aims to study the effect of celastrol loaded into exosomes against two non-small cell-lung carcinoma (NSCLC) cell lines and explore the molecular mechanisms to determine the proteins governing the cellular responses. We observed that celastrol inhibited the proliferation of A549 and H1299 NSCLC cells in a time- and concentration-dependent manner as indexed by MTT assay. Mechanistically, CEL pre-treatment of H1299 cells completely abrogated TNFα-induced NF-κB activation and upregulated the expression of ER-stress chaperones Grp 94, Grp78, and pPERK. These changes in ER-stress mediators were paralleled by an increase in apoptotic response as evidenced by higher annexin-V/PI positive cells evaluated by FACS and immunoblotting which showed upregulation of the ER stress specific pro-apoptotic transcription factor, GADD153/CHOP and alteration of Bax/Bcl2 levels. Exosomes loaded with CEL exhibited enhanced anti-tumor efficacy as compared to free CEL against lung cancer cell xenograft. CEL did not exhibit any gross or systemic toxicity in wild-type C57BL6 mice as determined by hematological and liver and kidney function test. Together, our data demonstrate the chemotherapeutic potential of CEL in lung cancer and that exosomal formulation enhances its efficacy and reduces dose related toxicity.

The hnRNP family: insights into their role in health and disease

Heterogeneous nuclear ribonucleoproteins (hnRNPs) represent a large family of RNA-binding proteins (RBPs) that contribute to multiple aspects of nucleic acid metabolism including alternative splicing, mRNA stabilization, and transcriptional and translational regulation. Many hnRNPs share general features, but differ in domain composition and functional properties. This review will discuss the current knowledge about the different hnRNP family members, focusing on their structural and functional divergence. Additionally, we will highlight their involvement in neurodegenerative diseases and cancer, and the potential to develop RNA-based therapies.

Loss of tumor suppressive microRNA-31 enhances TRADD/NF-κB signaling in glioblastoma

Glioblastomas (GBMs) are deadly tumors of the central nervous system. Most GBM exhibit homozygous deletions of the CDKN2A and CDKN2B tumor suppressors at 9p21.3, although loss of CDKN2A/B alone is insufficient to drive gliomagenesis. MIR31HG, which encodes microRNA-31 (miR-31), is a novel non-coding tumor suppressor positioned adjacent to CDKN2A/B at 9p21.3. We have determined that miR-31 expression is compromised in >72% of all GBM, and for patients, this predicts significantly shortened survival times independent of CDKN2A/B status. We show that miR-31 inhibits NF-κB signaling by targeting TRADD, its upstream activator. Moreover, upon reintroduction, miR-31 significantly reduces tumor burden and lengthens survival times in animal models. As such, our work identifies loss of miR-31 as a novel non-coding tumor-driving event in GBM.

Blood biomarkers for brain injury: What are we measuring?

Accurate diagnosis for mild traumatic brain injury (mTBI) remains challenging, as prognosis and return-to-play/work decisions are based largely on patient reports. Numerous investigations have identified and characterized cellular factors in the blood as potential biomarkers for TBI, in the hope that these factors may be used to gauge the severity of brain injury. None of these potential biomarkers have advanced to use in the clinical setting. Some of the most extensively studied blood biomarkers for TBI include S100β, neuron-specific enolase, glial fibrillary acidic protein, and Tau. Understanding the biological function of each of these factors may be imperative to achieve progress in the field. We address the basic question: what are we measuring? This review will discuss blood biomarkers in terms of cellular origin, normal and pathological function, and possible reasons for increased blood levels. Considerations in the selection, evaluation, and validation of potential biomarkers will also be addressed, along with mechanisms that allow brain-derived proteins to enter the bloodstream after TBI. Lastly, we will highlight perspectives and implications for repetitive neurotrauma in the field of blood biomarkers for brain injury.

Extracellular Vesicles in Physiology, Pathology, and Therapy of the Immune and Central Nervous System, with Focus on Extracellular Vesicles Derived from Mesenchymal Stem Cells as Therapeutic Tools

Extracellular vesicles (EVs) are membrane-surrounded structures released by most cell types. They are characterized by a specific set of proteins, lipids and nucleic acids. EVs have been recognized as potent vehicles of intercellular communication to transmit biological signals between cells. In addition, pathophysiological roles of EVs in conditions like cancer, infectious diseases and neurodegenerative disorders are well established. In recent years focus has been shifted on therapeutic use of stem cell derived-EVs. Use of stem cell derived-EVs present distinct advantage over the whole stem cells as EVs do not replicate and after intravenous administration, they are less likely to trap inside the lungs. From the therapeutic perspective, the most promising cellular sources of EVs are mesenchymal stem cells (MSCs), which are easy to obtain and maintain. Therapeutic activity of MSCs has been shown in numerous animal models and the beneficial paracrine effect of MSCs may be mediated by EVs. The various components of MSC derived-EVs such as proteins, lipids, and RNA might play a specific therapeutic role. In this review, we characterize the role of EVs in immune and central nervous system (CNS); present evidences for defective signaling of these vesicles in neurodegeneration and therapeutic role of EVs in CNS.

Illuminating the physiology of extracellular vesicles

Extracellular vesicles play a crucial role in intercellular communication by transmitting biological materials from donor cells to recipient cells. They have pathophysiologic roles in cancer metastasis, neurodegenerative diseases, and inflammation. Extracellular vesicles also show promise as emerging therapeutics, with understanding of their physiology including targeting, distribution, and clearance therefore becoming an important issue. Here, we review recent advances in methods for tracking and imaging extracellular vesicles in vivo and critically discuss their systemic distribution, targeting, and kinetics based on up-to-date evidence in the literature.

Illuminating the physiology of extracellular vesicles

Extracellular vesicles play a crucial role in intercellular communication by transmitting biological materials from donor cells to recipient cells. They have pathophysiologic roles in cancer metastasis, neurodegenerative diseases, and inflammation. Extracellular vesicles also show promise as emerging therapeutics, with understanding of their physiology including targeting, distribution, and clearance therefore becoming an important issue. Here, we review recent advances in methods for tracking and imaging extracellular vesicles in vivo and critically discuss their systemic distribution, targeting, and kinetics based on up-to-date evidence in the literature.

Extracellular vesicles and intercellular communication within the nervous system

Extracellular vesicles (EVs, including exosomes) are implicated in many aspects of nervous system development and function, including regulation of synaptic communication, synaptic strength, and nerve regeneration. They mediate the transfer of packets of information in the form of nonsecreted proteins and DNA/RNA protected within a membrane compartment. EVs are essential for the packaging and transport of many cell-fate proteins during development as well as many neurotoxic misfolded proteins during pathogenesis. This form of communication provides another dimension of cellular crosstalk, with the ability to assemble a "kit" of directional instructions made up of different molecular entities and address it to specific recipient cells. This multidimensional form of communication has special significance in the nervous system. How EVs help to orchestrate the wiring of the brain while allowing for plasticity associated with learning and memory and contribute to regeneration and degeneration are all under investigation. Because they carry specific disease-related RNAs and proteins, practical applications of EVs include potential uses as biomarkers and therapeutics. This Review describes our current understanding of EVs and serves as a springboard for future advances, which may reveal new important mechanisms by which EVs in coordinate brain and body function and dysfunction.

Delivery of Therapeutic Proteins via Extracellular Vesicles: Review and Potential Treatments for Parkinson's Disease, Glioma, and Schwannoma

Extracellular vesicles present an attractive delivery vehicle for therapeutic proteins. They intrinsically contain many proteins which can provide information to other cells. Advantages include reduced immune reactivity, especially if derived from the same host, stability in biologic fluids, and ability to target uptake. Those from mesenchymal stem cells appear to be intrinsically therapeutic, while those from cancer cells promote tumor progression. Therapeutic proteins can be loaded into vesicles by overexpression in the donor cell, with oligomerization and membrane sequences increasing their loading. Examples of protein delivery for therapeutic benefit in pre-clinical models include delivery of: catalase for Parkinson's disease to reduce oxidative stress and thus help neurons to survive; prodrug activating enzymes which can convert a prodrug which crosses the blood-brain barrier into a toxic chemotherapeutic drug for schwannomas and gliomas; and the apoptosis-inducing enzyme, caspase-1 under a Schwann cell specific promoter for schwannoma. This therapeutic delivery strategy is novel and being explored for a number of diseases.

Exosomes in stroke pathogenesis and therapy

Stroke is one of the leading causes of death and disability worldwide. Stroke recovery is orchestrated by a set of highly interactive processes that involve the neurovascular unit and neural stem cells. Emerging data suggest that exosomes play an important role in intercellular communication by transferring exosomal protein and RNA cargo between source and target cells in the brain. Here, we review these advances and their impact on promoting coupled brain remodeling processes after stroke. The use of exosomes for therapeutic applications in stroke is also highlighted.

Extracellular Vesicles in Brain Tumor Progression

Brain tumors can be viewed as multicellular 'ecosystems' with increasingly recognized cellular complexity and systemic impact. While the emerging diversity of malignant disease entities affecting brain tissues is often described in reference to their signature alterations within the cellular genome and epigenome, arguably these cell-intrinsic changes can be regarded as hardwired adaptations to a variety of cell-extrinsic microenvironmental circumstances. Conversely, oncogenic events influence the microenvironment through their impact on the cellular secretome, including emission of membranous structures known as extracellular vesicles (EVs). EVs serve as unique carriers of bioactive lipids, secretable and non-secretable proteins, mRNA, non-coding RNA, and DNA and constitute pathway(s) of extracellular exit of molecules into the intercellular space, biofluids, and blood. EVs are also highly heterogeneous as reflected in their nomenclature (exosomes, microvesicles, microparticles) attempting to capture their diverse origin, as well as structural, molecular, and functional properties. While EVs may act as a mechanism of molecular expulsion, their non-random uptake by heterologous cellular recipients defines their unique roles in the intercellular communication, horizontal molecular transfer, and biological activity. In the central nervous system, EVs have been implicated as mediators of homeostasis and repair, while in cancer they may act as regulators of cell growth, clonogenicity, angiogenesis, thrombosis, and reciprocal tumor-stromal interactions. EVs produced by specific brain tumor cell types may contain the corresponding oncogenic drivers, such as epidermal growth factor receptor variant III (EGFRvIII) in glioblastoma (and hence are often referred to as 'oncosomes'). Through this mechanism, mutant oncoproteins and nucleic acids may be transferred horizontally between cellular populations altering their individual and collective phenotypes. Oncogenic pathways also impact the emission rates, types, cargo, and biogenesis of EVs, as reflected by preliminary analyses pointing to differences in profiles of EV-regulating genes (vesiculome) between molecular subtypes of glioblastoma, and in other brain tumors. Molecular regulators of vesiculation can also act as oncogenes. These intimate connections suggest the context-specific roles of different EV subsets in the progression of specific brain tumors. Advanced efforts are underway to capture these events through the use of EVs circulating in biofluids as biomarker reservoirs and to guide diagnostic and therapeutic decisions.

Development and regulation of exosome-based therapy products

Recently, various innovative therapies involving the ex vivo manipulation and subsequent reintroduction of exosome-based therapeutics into humans have been developed and validated, although no exosome-based therapeutics have yet to be brought into the clinic. Exosomes are nanosized vesicles secreted by many cells that utilize them for cell-to-cell communications to facilitate transport of proteins and genetic material. Comprised of cellular membranes with multiple adhesive proteins on their surface, exosomes offer distinct advantages that exceptionally position them as highly effective drug carriers. Additionally, exosomes can exert unique biological activity reflective of their origin that may be used for therapy of various diseases. In fact, exosomes have benefits of both synthetic nanocarriers and cell-mediated drug delivery systems, and avoid their limitations. This concise review highlights the recent developments in exosome-based drug delivery systems and the main regulatory considerations for using this type of therapeutic in clinic. WIREs Nanomed Nanobiotechnol 2016, 8:744-757. doi: 10.1002/wnan.1395 For further resources related to this article, please visit the WIREs website.

Exosomes and other extracellular vesicles in neural cells and neurodegenerative diseases

The function of human nervous system is critically dependent on proper interneuronal communication. Exosomes and other extracellular vesicles are emerging as a novel form of information exchange within the nervous system. Intraluminal vesicles within multivesicular bodies (MVBs) can be transported in neural cells anterogradely or retrogradely in order to be released into the extracellular space as exosomes. RNA loading into exosomes can be either via an interaction between RNA and the raft-like region of the MVB limiting membrane, or via an interaction between an RNA-binding protein-RNA complex with this raft-like region. Outflow of exosomes from neural cells and inflow of exosomes into neural cells presumably take place on a continuous basis. Exosomes can play both neuro-protective and neuro-toxic roles. In this review, we characterize the role of exosomes and microvesicles in normal nervous system function, and summarize evidence for defective signaling of these vesicles in disease pathogenesis of some neurodegenerative diseases.

Exosomes for repair, regeneration and rejuvenation

INTRODUCTION

Application of regenerative medicine strategies for repair of organs/tissue impacted by chronic disease is an active subject for product development. Such methodologies emphasize the role of stem cells as the active biological ingredient. However, recent developments in elucidating mechanisms of action of these therapies have focused on the role of paracrine, 'action-at-a-distance' modus operandi in mediating the ability to catalyze regenerative outcomes without significant site-specific engraftment. A salient component of this secreted regenerative milieu are exosomes: 40-100 nm intraluminal vesicles that mediate transfer of proteins and nucleic acids across cellular boundaries.

AREAS COVERED

Here, we synthesize recent studies from PubMed and Google Scholar highlighting how cell-based therapeutics and cosmeceutics are transitioning towards the secretome generally and exosomes specifically as a principal modulator of regenerative outcomes.

EXPERT OPINION

Exosomes contribute to organ development and mediate regenerative outcomes in injury and disease that recapitulate observed bioactivity of stem cell populations. Encapsulation of the active biological ingredients of regeneration within non-living exosome carriers may offer process, manufacturing and regulatory advantages over stem cell-based therapies.

Microvesicles in the brain: Biomarker, messenger or mediator?

Microvesicles (MVs) are cell-derived vesicles produced after membrane remodeling of eukaryotic cells during activation or apoptosis. MVs are considered a novel biomarker/messenger for many diseases. Neurons, astrocytes, microglia, as well as neural stem cells, have been described to release MVs, many studies have demonstrated the involvement of platelets and endothelial MVs in some central nervous diseases. This review is focused on understanding the role of MVs in the brain; new findings demonstrated that MVs can contribute to the onset and progression of some neurodegenerative and neuroinflammatory diseases, as well as to the development and regeneration of the nervous system.

Promoting brain remodeling to aid in stroke recovery

Endogenous brain repair after stroke involves a set of highly interactive processes, such as angiogenesis, neurogenesis, oligodendrogenesis, synaptogenesis, and axonal outgrowth, which together orchestrate neurological recovery. During the past several years, there have been advances in our understanding of miRNAs and histone deacetylases (HDACs) in brain repair processes after stroke. Emerging data indicate the important role of exosomes for intercellular communication in promoting coupled brain remodeling processes. These advances will likely have a major impact on the development of restorative therapies for ischemic brain repair, consequently leading to improvement of neurological function. In this review, we provide an update on our current understanding of cellular and molecular mechanisms of miRNAs, exosomes, and HDACs in brain restorative processes after stroke.

Circulating microparticles reflect treatment effects and clinical status in multiple sclerosis

AIM

To evaluate whether circulating microparticles (MPs) derived from three cell subtypes (platelets, total leukocytes or monocytes) obtained from multiple sclerosis (MS) patients were modulated depending on the clinical status and to investigate the effect of treatments on MP levels.

PATIENTS & METHODS

The MP counts were assessed with flow cytometry.

RESULTS

The platelet-derived MP level was higher in untreated MS patients than controls. Relapsing-remitting patients showed the highest levels in the three subtypes of MP while secondary progressive patients presented similar levels to those of healthy controls. Treatments had significant effects increasing the three subtypes of MP counts.

CONCLUSION

We suggest that MPs play a role in MS pathogenesis, reflecting disease status with an increment of their shedding during inflammatory periods and turning to baseline during chronic progressive degeneration.

Neuronal Differentiation of Human Mesenchymal Stem Cells Using Exosomes Derived from Differentiating Neuronal Cells

Exosomes deliver functional proteins and genetic materials to neighboring cells, and have potential applications for tissue regeneration. One possible mechanism of exosome-promoted tissue regeneration is through the delivery of microRNA (miRNA). In this study, we hypothesized that exosomes derived from neuronal progenitor cells contain miRNAs that promote neuronal differentiation. We treated mesenchymal stem cells (MSCs) daily with exosomes derived from PC12 cells, a neuronal cell line, for 1 week. After the treatment with PC12-derived exosomes, MSCs developed neuron-like morphology, and gene and protein expressions of neuronal markers were upregulated. Microarray analysis showed that the expression of miR-125b, which is known to play a role in neuronal differentiation of stem cells, was much higher in PC12-derived exosomes than in exosomes from B16-F10 melanoma cells. These results suggest that the delivery of miRNAs contained in PC12-derived exosomes is a possible mechanism explaining the neuronal differentiation of MSC.

Using exosomes, naturally-equipped nanocarriers, for drug delivery

Exosomes offer distinct advantages that uniquely position them as highly effective drug carriers. Comprised of cellular membranes with multiple adhesive proteins on their surface, exosomes are known to specialize in cell-cell communications and provide an exclusive approach for the delivery of various therapeutic agents to target cells. In addition, exosomes can be amended through their parental cells to express a targeting moiety on their surface, or supplemented with desired biological activity. Development and validation of exosome-based drug delivery systems are the focus of this review. Different techniques of exosome isolation, characterization, drug loading, and applications in experimental disease models and clinic are discussed. Exosome-based drug formulations may be applied to a wide variety of disorders such as cancer, various infectious, cardiovascular, and neurodegenerative disorders. Overall, exosomes combine benefits of both synthetic nanocarriers and cell-mediated drug delivery systems while avoiding their limitations.

Peripheral blood biomarkers in multiple sclerosis

Multiple sclerosis is the most common autoimmune disorder affecting the central nervous system. The heterogeneity of pathophysiological processes in MS contributes to the highly variable course of the disease and unpredictable response to therapies. The major focus of the research on MS is the identification of biomarkers in biological fluids, such as cerebrospinal fluid or blood, to guide patient management reliably. Because of the difficulties in obtaining spinal fluid samples and the necessity for lumbar puncture to make a diagnosis has reduced, the research of blood-based biomarkers may provide increasingly important tools for clinical practice. However, currently there are no clearly established MS blood-based biomarkers. The availability of reliable biomarkers could radically alter the management of MS at critical phases of the disease spectrum, allowing for intervention strategies that may prevent evolution to long-term neurological disability. This article provides an overview of this research field and focuses on recent advances in blood-based biomarker research.

The role of exosomes in peripheral nerve regeneration

Peripheral nerve injuries remain problematic to treat, with poor functional recovery commonly observed. Injuries resulting in a nerve gap create specific difficulties for axonal regeneration. Approaches to address these difficulties include autologous nerve grafts (which are currently the gold standard treatment) and synthetic conduits, with the latter option being able to be impregnated with Schwann cells or stem cells which provide an appropriate micro-environment for neuronal regeneration to occur. Transplanting stem cells, however, infers additional risk of malignant transformation as well as manufacturing difficulties and ethical concerns, and the use of autologous nerve grafts and Schwann cells requires the sacrifice of a functioning nerve. A new approach utilizing exosomes, secreted extracellular vesicles, could avoid these complications. In this review, we summarize the current literature on exosomes, and suggest how they could help to improve axonal regeneration following peripheral nerve injury.

Visualization and tracking of tumour extracellular vesicle delivery and RNA translation using multiplexed reporters

Accurate spatiotemporal assessment of extracellular vesicle (EV) delivery and cargo RNA translation requires specific and robust live-cell imaging technologies. Here we engineer optical reporters to label multiple EV populations for visualization and tracking of tumour EV release, uptake and exchange between cell populations both in culture and in vivo. Enhanced green fluorescence protein (EGFP) and tandem dimer Tomato (tdTomato) were fused at NH₂-termini with a palmitoylation signal (PalmGFP, PalmtdTomato) for EV membrane labelling. To monitor EV-RNA cargo, transcripts encoding PalmtdTomato were tagged with MS2 RNA binding sequences and detected by co-expression of bacteriophage MS2 coat protein fused with EGFP. By multiplexing fluorescent and bioluminescent EV membrane reporters, we reveal the rapid dynamics of both EV uptake and translation of EV-delivered cargo mRNAs in cancer cells that occurred within 1-hour post-horizontal transfer between cells. These studies confirm that EV-mediated communication is dynamic and multidirectional between cells with delivery of functional mRNA.

Extracellular vesicles (EVs) act as a conduit for intercellular communication through the exchange of cellular materials without direct cell-to-cell contacts. Here the authors develop a multiplexed reporter system that allows monitoring of EV exchange, cargo delivery and protein translation between different cell populations.

Extracellular vesicles and their synthetic analogues in aging and age-associated brain diseases

Multicellular organisms rely upon diverse and complex intercellular communications networks for a myriad of physiological processes. Disruption of these processes is implicated in the onset and propagation of disease and disorder, including the mechanisms of senescence at both cellular and organismal levels. In recent years, secreted extracellular vesicles (EVs) have been identified as a particularly novel vector by which cell-to-cell communications are enacted. EVs actively and specifically traffic bioactive proteins, nucleic acids, and metabolites between cells at local and systemic levels, modulating cellular responses in a bidirectional manner under both homeostatic and pathological conditions. EVs are being implicated not only in the generic aging process, but also as vehicles of pathology in a number of age-related diseases, including cancer and neurodegenerative and disease. Thus, circulating EVs-or specific EV cargoes-are being utilised as putative biomarkers of disease. On the other hand, EVs, as targeted intercellular shuttles of multipotent bioactive payloads, have demonstrated promising therapeutic properties, which can potentially be modulated and enhanced through cellular engineering. Furthermore, there is considerable interest in employing nanomedicinal approaches to mimic the putative therapeutic properties of EVs by employing synthetic analogues for targeted drug delivery. Herein we describe what is known about the origin and nature of EVs and subsequently review their putative roles in biology and medicine (including the use of synthetic EV analogues), with a particular focus on their role in aging and age-related brain diseases.

Exosomes as drug delivery vehicles for Parkinson's disease therapy

Exosomes are naturally occurring nanosized vesicles that have attracted considerable attention as drug delivery vehicles in the past few years. Exosomes are comprised of natural lipid bilayers with the abundance of adhesive proteins that readily interact with cellular membranes. We posit that exosomes secreted by monocytes and macrophages can provide an unprecedented opportunity to avoid entrapment in mononuclear phagocytes (as a part of the host immune system), and at the same time enhance delivery of incorporated drugs to target cells ultimately increasing drug therapeutic efficacy. In light of this, we developed a new exosomal-based delivery system for a potent antioxidant, catalase, to treat Parkinson's disease (PD). Catalase was loaded into exosomes ex vivo using different methods: the incubation at room temperature, permeabilization with saponin, freeze-thaw cycles, sonication, or extrusion. The size of the obtained catalase-loaded exosomes (exoCAT) was in the range of 100-200nm. A reformation of exosomes upon sonication and extrusion, or permeabilization with saponin resulted in high loading efficiency, sustained release, and catalase preservation against proteases degradation. Exosomes were readily taken up by neuronal cells in vitro. A considerable amount of exosomes was detected in PD mouse brain following intranasal administration. ExoCAT provided significant neuroprotective effects in in vitro and in vivo models of PD. Overall, exosome-based catalase formulations have a potential to be a versatile strategy to treat inflammatory and neurodegenerative disorders.

ATP13A2/PARK9 regulates secretion of exosomes and α-synuclein

Kufor-Rakeb syndrome (KRS) is caused by loss-of-function mutations in ATP13A2 (PARK9) and characterized by juvenile-onset parkinsonism, pyramidal signs, and cognitive decline. Previous studies suggested that PARK9 deficiency causes lysosomal dysfunction and α-synuclein (α-syn) accumulation, whereas PARK9 overexpression suppresses toxicity of α-syn. However, the precise mechanism of PARK9 effect on lysosomes and α-syn has been unknown. Here, we found that overexpressed PARK9 localized to multivesicular bodies (MVBs) in the human H4 cell line. The results from patient fibroblasts showed that loss of PARK9 function leads to decreased number of the intraluminal vesicles in MVBs and diminished release of exosomes into culture media. By contrast, overexpression of PARK9 results in increased release of exosomes in H4 cells and mouse primary cortical neurons. Moreover, loss of PARK9 function resulted in decreased secretion of α-syn into extracellular space, whereas overexpressed PARK9 promotes secretion of α-syn, at least in part via exosomes. Finally, we found that PARK9 regulates exosome biogenesis through functional interaction with the endosomal sorting complex required for transport machinery. Together, these data suggest the involvement of PARK9 in the biogenesis of exosomes and α-syn secretion and raise a possibility that disruption of these pathways in patients with KRS contributes to the disease pathogenesis.

Emerging roles of extracellular vesicles in the nervous system

Information exchange executed by extracellular vesicles, including exosomes, is a newly described form of intercellular communication important in the development and physiology of neural systems. These vesicles can be released from cells, are packed with information including signaling proteins and both coding and regulatory RNAs, and can be taken up by target cells, thereby facilitating the transfer of multilevel information. Recent studies demonstrate their critical role in physiological processes, including nerve regeneration, synaptic function, and behavior. These vesicles also have a sinister role in the propagation of toxic amyloid proteins in neurodegenerative conditions, including prion diseases and Alzheimer's and Parkinson's diseases, in inducing neuroinflammation by exchange of information between the neurons and glia, as well as in aiding tumor progression in the brain by subversion of normal cells. This article provides a summary of topics covered in a symposium and is not meant to be a comprehensive review of the subject.

Dysfunction of platelet-derived growth factor receptor α (PDGFRα) represses the production of oligodendrocytes from arylsulfatase A-deficient multipotential neural precursor cells

The membrane-bound receptor for platelet-derived growth factor A (PDGFRα) is crucial for controlling the production of oligodendrocytes (OLs) for myelination, but regulation of its activity during OL differentiation is largely unknown. We have examined the effect of increased sulfated content of galactosylceramides (sulfatides) on the regulation of PDGFRα in multipotential neural precursors (NPs) that are deficient in arylsulfatase A (ASA) activity. This enzyme is responsible for the lysosomal hydrolysis of sulfatides. We show that sulfatide accumulation significantly impacts the formation of OLs via deregulation of PDGFRα function. PDGFRα is less associated with detergent-resistant membranes in ASA-deficient cells and showed a significant decrease in AKT phosphorylation. Rescue experiments with ASA showed a normalization of the ratio of long versus short sulfatides, restored PDGFRα levels, corrected its localization to detergent-resistant membranes, increased AKT phosphorylation, and normalized the production of OLs in ASA-deficient NPs. Moreover, our studies identified a novel mechanism that regulates the secretion of PDGFRα in NPs, in glial cells, and in the brain cortex via exosomal shedding. Our study provides a first step in understanding the role of sulfatides in regulating PDGFRα levels in OLs and its impact in myelination.

Interactions between cancer cells and normal cells via miRNAs in extracellular vesicles

MicroRNAs (miRNAs) exhibit many functions in biological activities. Recent studies have shown that miRNAs exist outside cells and are transferred between cells. Extracellular miRNAs are protected from ribonucleases found in body fluids through binding to specific proteins or by being encapsulated in lipid bilayer vesicles. Here, we review the mechanisms of the secretion and uptake as well as the functions of extracellular miRNAs, particularly those encapsulated in extracellular vesicles. Extracellular vesicles are related to cancer progression, and some miRNAs in extracellular vesicles are associated with cancer cells. We describe the transfer of cancer-related miRNAs between cancer cells and non-cancerous cells. Finally, we discuss the anticipated applications of miRNAs present in extracellular vesicles in diagnostics and therapeutics.

Neuroepigenomics: Resources, Obstacles, and Opportunities

Long-lived post-mitotic cells, such as the majority of human neurons, must respond effectively to ongoing changes in neuronal stimulation or microenvironmental cues through transcriptional and epigenomic regulation of gene expression. The role of epigenomic regulation in neuronal function is of fundamental interest to the neuroscience community, as these types of studies have transformed our understanding of gene regulation in post-mitotic cells. This perspective article highlights many of the resources available to researchers interested in neuroepigenomic investigations and discusses some of the current obstacles and opportunities in neuroepigenomics.