Extracellular vesicle-mediated transfer of genetic information between the hematopoietic system and the brain in response to inflammation

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.

Exosomes as new players in metabolic organ cross-talk

Blood glucose homeostasis requires a constant communication between insulin-secreting and insulin-sensitive cells. A wide variety of circulating factors, including hormones, cytokines and chemokines work together to orchestrate the systemic response of metabolic organs to changes in the nutritional state. Failure in the coordination between these organs can lead to a rise in blood glucose levels and to the appearance of metabolic disorders such as diabetes mellitus. Exosomes are small extracellular vesicles (EVs) that are produced via the endosomal pathway and are released from the cells upon fusion of multivesicular bodies with the plasma membrane. There is emerging evidence indicating that these EVs play a central role in cell-to-cell communication. The interest in exosomes exploded when they were found to transport bioactive proteins, messenger RNA (mRNAs) and microRNA (miRNAs) that can be transferred in active form to adjacent cells or to distant organs. In this review, we will first outline the mechanisms governing the biogenesis, the cargo upload and the release of exosomes by donor cells as well as the uptake by recipient cells. We will then summarize the studies that support the novel concept that miRNAs and other exosomal cargo components are new important vehicles for metabolic organ cross-talk.

Exosomes Mediate Epithelium-Mesenchyme Crosstalk in Organ Development

Organ development requires complex signaling by cells in different tissues. Epithelium and mesenchyme interactions are crucial for the development of skin, hair follicles, kidney, lungs, prostate, major glands, and teeth. Despite myriad literature on cell-cell interactions and ligand-receptor binding, the roles of extracellular vesicles in epithelium-mesenchyme interactions during organogenesis are poorly understood. Here, we discovered that ∼100 nm exosomes were secreted by the epithelium and mesenchyme of a developing tooth organ and diffused through the basement membrane. Exosomes were entocytosed by epithelium or mesenchyme cells with preference by reciprocal cells rather than self-uptake. Exosomes reciprocally evoked cell differentiation and matrix synthesis: epithelium exosomes induce mesenchyme cells to produce dentin sialoprotein and undergo mineralization, whereas mesenchyme exosomes induce epithelium cells to produce basement membrane components, ameloblastin and amelogenenin. Attenuated exosomal secretion by Rab27a/b knockdown or GW4869 disrupted the basement membrane and reduced enamel and dentin production in organ culture and reduced matrix synthesis and the size of the cervical loop, which harbors epithelium stem cells, in Rab27a^ash/ash mutant mice. We then profiled exosomal constituents including miRNAs and peptides and further crossed all epithelium exosomal miRNAs with literature-known miRNA Wnt regulators. Epithelium exosome-derived miR135a activated Wnt/β-catenin signaling and escalated mesenchymal production of dentin matrix proteins, partially reversible by Antago-miR135a attenuation. Our results suggest that exosomes may mediate epithelium-mesenchyme crosstalk in organ development, suggesting that these vesicles and/or the molecular contents they are transporting may be interventional targets for treatment of diseases or regeneration of tissues.

[MiRNAs: new actors in the physiopathology of multiple sclerosis]

Multiple sclerosis (MS) is an auto-immune demyelinating disorder characterized by a chronic neuro-inflammatory process associated with an infiltration of the central nervous system (CNS) by autoreactive lymphocytes. The etiology of the disease remains unclear but the recent discovery of a dysregulated miRNA network in both cells and extracellular fluids of MS patients has brought new insights on the pathophysiological mechanisms involved in this disorder. miRNAs can induce a T cell polarization towards a pathological Th17 or Th1 phenotype and a deleterious activation of microglia, the CNS-resident macrophages. We provide here a review of the most recent data regarding miRNA dysregulation and pathophysiological roles in MS patients and in the animal model of MS, EAE (experimental autoimmune encephalomyelitis). Moreover, we discuss the putative clinical value of miRNAs as a novel biomarker and diagnostic tool for MS.

Immunometabolism of human autoimmune diseases: from metabolites to extracellular vesicles

Immunometabolism focuses on the mechanisms regulating the impact of metabolism on lymphocyte activity and autoimmunity outbreak. The adipose tissue is long known to release adipokines, either pro- or anti-inflammatory factors bridging nutrition and immune function. More recently, adipocytes were discovered to also release extracellular vesicles (EVs) containing a plethora of biological molecules, including metabolites and microRNAs, which can regulate cell function/metabolism in distant tissues, suggesting that immune regulatory function by the adipose tissue may be far more complex than originally thought. Moreover, EVs were also identified as important mediators of immune cell-to-cell communication, adding a further microenvironmental mechanism of plasticity to fine-tune specific lymphocyte responses. This Review will first focus on the known mechanisms by which metabolism impacts immune function, presenting a systemic (nutrition and long-ranged adipokines) and a cellular point of view (metabolic pathway derangement in autoimmunity). It will then discuss the new discoveries concerning how EVs may act as nanometric vehicles integrating immune/metabolic responses at the level of the extracellular environment and affecting pathological processes.

Chronic Oxidative Stress, Mitochondrial Dysfunction, Nrf2 Activation and Inflammation in the Hippocampus Accompany Heightened Systemic Inflammation and Oxidative Stress in an Animal Model of Gulf War Illness

Memory and mood dysfunction are the key symptoms of Gulf war illness (GWI), a lingering multi-symptom ailment afflicting >200,000 veterans who served in the Persian Gulf War-1. Research probing the source of the disease has demonstrated that concomitant exposures to anti-nerve gas agent pyridostigmine bromide (PB), pesticides, and war-related stress are among the chief causes of GWI. Indeed, exposures to GWI-related chemicals (GWIR-Cs) and mild stress in animal models cause memory and mood impairments alongside reduced neurogenesis and chronic low-level inflammation in the hippocampus. In the current study, we examined whether exposure to GWIR-Cs and stress causes chronic changes in the expression of genes related to increased oxidative stress, mitochondrial dysfunction, and inflammation in the hippocampus. We also investigated whether GWI is linked with chronically increased activation of Nrf2 (a master regulator of antioxidant response) in the hippocampus, and inflammation and enhanced oxidative stress at the systemic level. Adult male rats were exposed daily to low-doses of PB and pesticides (DEET and permethrin), in combination with 5 min of restraint stress for 4 weeks. Analysis of the hippocampus performed 6 months after the exposure revealed increased expression of many genes related to oxidative stress response and/or antioxidant activity (Hmox1, Sepp1, and Srxn1), reactive oxygen species metabolism (Fmo2, Sod2, and Ucp2) and oxygen transport (Ift172 and Slc38a1). Furthermore, multiple genes relevant to mitochondrial respiration (Atp6a1, Cox6a1, Cox7a2L, Ndufs7, Ndufv1, Lhpp, Slc25a10, and Ucp1) and neuroinflammation (Nfkb1, Bcl6, Csf2, IL6, Mapk1, Mapk3, Ngf, N-pac, and Prkaca) were up-regulated, alongside 73–88% reduction in the expression of anti-inflammatory genes IL4 and IL10, and nuclear translocation and increased expression of Nrf2 protein. These hippocampal changes were associated with elevated levels of pro-inflammatory cytokines and chemokines (Tnfa, IL1b, IL1a, Tgfb, and Fgf2) and lipid peroxidation byproduct malondialdehyde in the serum, suggesting the presence of an incessant systemic inflammation and elevated oxidative stress. These results imply that chronic oxidative stress, inflammation, and mitochondrial dysfunction in the hippocampus, and heightened systemic inflammation and oxidative stress likely underlie the persistent memory and mood dysfunction observed in GWI.

The role of extracellular vesicles in malaria biology and pathogenesis

In the past decade, research on the functions of extracellular vesicles in malaria has expanded dramatically. Investigations into the various vesicle types, from both host and parasite origin, has revealed important roles for extracellular vesicles in disease pathogenesis and susceptibility, as well as cell–cell communication and immune responses. Here, work relating to extracellular vesicles in malaria is reviewed, and the areas that remain unknown and require further investigations are highlighted.

Remote control of BBB: A tale of exosomes and microRNA

Exosome-mediated intercellular communication has become an emerging field of human health and diseases. A recent study published by Cell Research reports that in zebrafish neurons can remotely regulate blood-brain barrier integrity by delivering miR-132 through secretion of exosomes.

Mesenchymal Stem Cell Derived Extracellular Vesicles: A Role in Hematopoietic Transplantation?

Mesenchymal stem cells (MSCs) are a heterogeneous cellular population containing different progenitors able to repair tissues, support hematopoiesis, and modulate immune and inflammatory responses. Several clinical trials have used MSCs in allogeneic hematopoietic stem cell transplantation (allo-HSCT) to prevent hematopoietic stem cell (HSC) engraftment failure, reduce aplasia post chemotherapy, and to control graft versus host disease (GvHD). The efficacy of MSCs is linked to their immune suppressive and anti-inflammatory properties primarily due to the release of soluble factors. Recent studies indicate that most of these effects are mediated by extracellular vesicles (EVs). MSC-EVs have therefore therapeutic effects in regenerative medicine, tumor inhibition, and immune-regulation. MSC-EVs may offer specific advantages for patient safety, such as lower propensity to trigger innate and adaptive immune responses. It has been also shown that MSC-EVs can prevent or treat acute-GvHD by modulating the immune-response and, combined with HSCs, may contribute to the hematopoietic microenvironment reconstitution. Finally, MSC-EVs may provide a new potential therapeutic option (e.g., transplantation, gene therapy) for different diseases, particularly hematological malignancies. In this review, we will describe MSC and MSC-EVs role in improving allo-HSCT procedures and in treating GvHD.

Engineered Exosomes as Vehicles for Biologically Active Proteins

Exosomes represent an attractive vehicle for the delivery of biomolecules. However, mechanisms for loading functional molecules into exosomes are relatively unexplored. Here we report the use of the evolutionarily conserved late-domain (L-domain) pathway as a mechanism for loading exogenous proteins into exosomes. We demonstrate that labeling of a target protein, Cre recombinase, with a WW tag leads to recognition by the L-domain-containing protein Ndfip1, resulting in ubiquitination and loading into exosomes. Our results show that Ndfip1 expression acts as a molecular switch for exosomal packaging of WW-Cre that can be suppressed using the exosome inhibitor GW4869. When taken up by floxed reporter cells, exosomes containing WW-Cre were capable of inducing DNA recombination, indicating functional delivery of the protein to recipient cells. Engineered exosomes were administered to the brain of transgenic reporter mice using the nasal route to test for intracellular protein delivery in vivo. This resulted in the transport of engineered exosomes predominantly to recipient neurons in a number of brain regions, including the olfactory bulb, cortex, striatum, hippocampus, and cerebellum. The ability to engineer exosomes to deliver biologically active proteins across the blood-brain barrier represents an important step for the development of therapeutics to treat brain diseases.

Astrocyte-shed extracellular vesicles regulate the peripheral leukocyte response to inflammatory brain lesions

Brain injury induces a peripheral acute cytokine response that directs the transmigration of leukocytes into the brain. Because this brain-to-peripheral immune communication affects patient recovery, understanding its regulation is important. Using a mouse model of inflammatory brain injury, we set out to find a soluble mediator for this phenomenon. We found that extracellular vesicles (EVs) shed from astrocytes in response to intracerebral injection of interleukin-1β (IL-1β) rapidly entered into peripheral circulation and promoted the transmigration of leukocytes through modulation of the peripheral acute cytokine response. Bioinformatic analysis of the protein and microRNA cargo of EVs identified peroxisome proliferator-activated receptor α (PPARα) as a primary molecular target of astrocyte-shed EVs. We confirmed in mice that astrocytic EVs promoted the transmigration of leukocytes into the brain by inhibiting PPARα, resulting in the increase of nuclear factor κB (NF-κB) activity that triggered the production of cytokines in liver. These findings expand our understanding of the mechanisms regulating communication between the brain and peripheral immune system and identify astrocytic EVs as a molecular regulator of the immunological response to inflammatory brain damage.

Obstacles and opportunities in the functional analysis of extracellular vesicle RNA - an ISEV position paper

The release of RNA-containing extracellular vesicles (EV) into the extracellular milieu has been demonstrated in a multitude of different in vitro cell systems and in a variety of body fluids. RNA-containing EV are in the limelight for their capacity to communicate genetically encoded messages to other cells, their suitability as candidate biomarkers for diseases, and their use as therapeutic agents. Although EV-RNA has attracted enormous interest from basic researchers, clinicians, and industry, we currently have limited knowledge on which mechanisms drive and regulate RNA incorporation into EV and on how RNA-encoded messages affect signalling processes in EV-targeted cells. Moreover, EV-RNA research faces various technical challenges, such as standardisation of EV isolation methods, optimisation of methodologies to isolate and characterise minute quantities of RNA found in EV, and development of approaches to demonstrate functional transfer of EV-RNA in vivo. These topics were discussed at the 2015 EV-RNA workshop of the International Society for Extracellular Vesicles. This position paper was written by the participants of the workshop not only to give an overview of the current state of knowledge in the field, but also to clarify that our incomplete knowledge – of the nature of EV(-RNA)s and of how to effectively and reliably study them – currently prohibits the implementation of gold standards in EV-RNA research. In addition, this paper creates awareness of possibilities and limitations of currently used strategies to investigate EV-RNA and calls for caution in interpretation of the obtained data.

High-throughput sequencing of two populations of extracellular vesicles provides an mRNA signature that can be detected in the circulation of breast cancer patients

Extracellular vesicles (EVs) contain a wide range of RNA types with a reported prevalence of non-coding RNA. To date a comprehensive characterization of the protein coding transcripts in EVs is still lacking. We performed RNA-Sequencing (RNA-Seq) of 2 EV populations and identified a small fraction of transcripts that were expressed at significantly different levels in large oncosomes and exosomes, suggesting they may mediate specialized functions. However, these 2 EV populations exhibited a common mRNA signature that, in comparison to their donor cells, was significantly enriched in mRNAs encoding E2F transcriptional targets and histone proteins. These mRNAs are primarily expressed in the S-phase of the cell cycle, suggesting that they may be packaged into EVs during S-phase. In silico analysis using subcellular compartment transcriptome data from the ENCODE cell line compendium revealed that EV mRNAs originate from a cytoplasmic RNA pool. The EV signature was independently identified in plasma of patients with breast cancer by RNA-Seq. Furthermore, several transcripts differentially expressed in EVs from patients versus controls mirrored differential expression between normal and breast cancer tissues. Altogether, this largest high-throughput profiling of EV mRNA demonstrates that EVs carry tumor-specific alterations and can be interrogated as a source of cancer-derived cargo.

The role of exosomes in CNS inflammation and their involvement in multiple sclerosis

Multiple sclerosis (MS) is a putative autoimmune disease of the central nervous system (CNS) in which autoreactive immune cells recognizing myelin antigens lead to demyelination and axonal injury. Mechanisms relevant to the pathogenesis of MS have not been fully elucidated, particularly those underlying initiation of immune system dysfunction. For example, it is not known how reactivity against CNS components is generated within the peripheral immune system. In this review, we propose that a significant contribution to the immunoregulatory events may derive from a cell-to-cell communication system involving the production, secretion and transfer of extracellular vesicles known as exosomes. Herein, we discuss in detail the biogenesis and roles of these cell surface-generated vesicles from the standpoint of receptors and their cargo, microRNA. It is well known that exosomes can cross the blood-brain barrier and thus may contribute to the spread of brain antigens to the periphery. Further understanding of exosome-dependent mechanisms in MS should provide a novel angle to the analysis of the pathogenesis of this disease. Finally, we launch the idea that exosomes and their contents may serve as biomarkers in MS.

Regulation of T Cell Activation and Differentiation by Extracellular Vesicles and Their Pathogenic Role in Systemic Lupus Erythematosus and Multiple Sclerosis

How autoreactive tissue-infiltrated effector T cells are induced and sustained in autoimmune disease, usually dominated by the Th1 and Th17 subsets, is still largely unknown. In organ-specific autoimmunity, self-reactive T cells initially activated by dendritic cells (DCs) in the lymph nodes migrate and infiltrate into the target tissues where their reactivation by peripheral tissue antigen is a prerequisite for effector cytokine production and tissue destruction. The target tissue microenvironment, as well as the local microenvironment at the immune synapse formed by T cells that encounter cognate antigen presenting cells (APCs) shave recently emerged as critical factors in shaping the differentiation and function of self-reactive effector T cells, providing the signals required for their activation in the form of the self-antigen and cytokine milieu. Moreover, depending on the specific microenvironment, self-reactive effector T cells have the ability to change their phenotype, especially Th17 and regulatory T (Treg) cells, which are characterized by the highest instability. In this context, cell-derived extracellular vesicles, i.e., vesicles carrying cytosolic proteins and nucleic acids protected by a phospholipid bilayer, as well as membrane-associated proteins, with the ability to spread throughout the body by means of biological fluids, are emerging as key mediators in intercellular communications and in the modulation of the microenvironment. In this review, we will discuss recent findings implicating extracellular vesicles (EVs) at different steps of CD4+ T cell differentiation to specific effectors, with a focus on the Th17/Treg balance and its alterations in systemic lupus erythematosus and multiple sclerosis.

Mesenchymal stem cell-derived extracellular vesicles ameliorate inflammation-induced preterm brain injury

OBJECTIVE

Preterm brain injury is a major cause of disability in later life, and may result in motor, cognitive and behavioural impairment for which no treatment is currently available. The aetiology is considered as multifactorial, and one underlying key player is inflammation leading to white and grey matter injury. Extracellular vesicles secreted by mesenchymal stem/stromal cells (MSC-EVs) have shown therapeutic potential in regenerative medicine. Here, we investigated the effects of MSC-EV treatment on brain microstructure and maturation, inflammatory processes and long-time outcome in a rodent model of inflammation-induced brain injury.

METHODS

3-Day-old Wistar rats (P3) were intraperitoneally injected with 0.25mg/kg lipopolysaccharide or saline and treated with two repetitive doses of 1×10⁸ cell equivalents of MSC-EVs per kg bodyweight. Cellular degeneration and reactive gliosis at P5 and myelination at P11 were evaluated by immunohistochemistry and western blot. Long-term cognitive and motor function was assessed by behavioural testing. Diffusion tensor imaging at P125 evaluated long-term microstructural white matter alterations.

RESULTS

MSC-EV treatment significantly ameliorated inflammation-induced neuronal cellular degeneration reduced microgliosis and prevented reactive astrogliosis. Short-term myelination deficits and long-term microstructural abnormalities of the white matter were restored by MSC-EV administration. Morphological effects of MSC-EV treatment resulted in improved long-lasting cognitive functions INTERPRETATION: MSC-EVs ameliorate inflammation-induced cellular damage in a rat model of preterm brain injury. MSC-EVs may serve as a novel therapeutic option by prevention of neuronal cell death, restoration of white matter microstructure, reduction of gliosis and long-term functional improvement.

Exosomes, an Unmasked Culprit in Neurodegenerative Diseases

Exosomes are extracellular nanovesicles (30–100 nm) generated from endosomal membranes and known to be released by all cell lineages of the Central Nervous System (CNS). They constitute important vesicles for the secretion and transport of multilevel information, including signaling, toxic, and regulatory molecules. Initially thought to have a function merely in waste disposal, the involvement of exosomes in neuronal development, maintenance, and regeneration through its paracrine and endocrine signaling functions has drawn particular attention in recent years. These vesicles, being involved in the clearance and cell-to-cell spreading of toxic molecules, have been naturally implicated in aging, and in several neurodegenerative diseases associated with pathological conversion of proteins, as well as in the transport of other disease-associated molecules, such as nucleic acids or pro-inflammatory cytokines. Our understanding of such unique form of communication may provide not only answers about (patho)physiological processes in the brain, but can also offer means to exploit these vesicles as vehicles for the delivery of biologically relevant molecules or as tools to monitor brain diseases in a non-invasive way. A promising field in expansion, the study of exosomes and related extracellular vesicles has just commenced to unveil their potential as therapeutic tools for brain disorders as well as biomarkers of disease state.

RNA-mediated communication between helminths and their hosts: The missing links

Small RNAs have been discovered in a wide variety of extracellular environments and are now thought to participate in communication between cells and even between different organisms and species. Helminths are parasitic worms that generally reside in extracellular niches in their hosts and can establish chronic infection through the release of immunomodulatory factors. Recent work has demonstrated that Extracellular RNA (exRNA) may be another class of immunomodulator secreted by helminths. Here we will detail what is known about small RNA pathways in helminth pathogens (focusing on nematodes) and mammalian hosts. We will then explore the computational challenges with identifying RNA-RNA interactions between 2 different species and the paradigm of RNA-RNA co-evolution that accompanies this. Finally we explore the lingering questions that require further investigation to understand the properties of exRNA that would enable it to function as an immunomodulator.

Re-Engineering Extracellular Vesicles as Smart Nanoscale Therapeutics

In the past decade, extracellular vesicles (EVs) have emerged as a key cell-free strategy for the treatment of a range of pathologies, including cancer, myocardial infarction, and inflammatory diseases. Indeed, the field is rapidly transitioning from promising in vitro reports toward in vivo animal models and early clinical studies. These investigations exploit the high physicochemical stability and biocompatibility of EVs as well as their innate capacity to communicate with cells via signal transduction and membrane fusion. This review focuses on methods in which EVs can be chemically or biologically modified to broaden, alter, or enhance their therapeutic capability. We examine two broad strategies, which have been used to introduce a wide range of nanoparticles, reporter systems, targeting peptides, pharmaceutics, and functional RNA molecules. First, we explore how EVs can be modified by manipulating their parent cells, either through genetic or metabolic engineering or by introducing exogenous material that is subsequently incorporated into secreted EVs. Second, we consider how EVs can be directly functionalized using strategies such as hydrophobic insertion, covalent surface chemistry, and membrane permeabilization. We discuss the historical context of each specific technology, present prominent examples, and evaluate the complexities, potential pitfalls, and opportunities presented by different re-engineering strategies.

Extracellular Vesicles Isolated from the Leaf Apoplast Carry Stress-Response Proteins

Exosomes are extracellular vesicles (EVs) that play a central role in intercellular signaling in mammals by transporting proteins and small RNAs. Plants are also known to produce EVs, particularly in response to pathogen infection. The contents of plant EVs have not been analyzed, however, and their function is unknown. Here, we describe a method for purifying EVs from the apoplastic fluids of Arabidopsis (Arabidopsis thaliana) leaves. Proteomic analyses of these EVs revealed that they are highly enriched in proteins involved in biotic and abiotic stress responses. Consistent with this finding, EV secretion was enhanced in plants infected with Pseudomonas syringae and in response to treatment with salicylic acid. These findings suggest that EVs may represent an important component of plant immune responses.

Isolation of Exosomes and Microvesicles from Cell Culture Systems to Study Prion Transmission

Extracellular vesicles (EVs) are composed of microvesicles and exosomes. Exosomes are small membrane vesicles (40-120 nm sized) of endosomal origin released in the extracellular medium from cells when multivesicular bodies fuse with the plasma membrane, whereas microvesicles (i.e., shedding vesicles, 100 nm to 1 μm sized) bud from the plasma membrane. Exosomes and microvesicles carry functional proteins and nucleic acids (especially mRNAs and microRNAs) that can be transferred to surrounding cells and tissues and can impact multiple dimensions of the cellular life. Most of the cells, if not all, from neuronal to immune cells, release exosomes and microvesicles in the extracellular medium, and all biological fluids including blood (serum/plasma), urine, cerebrospinal fluid, and saliva contain EVs.Prion-infected cultured cells are known to secrete infectivity into their environment. We characterized this cell-free form of prions and showed that infectivity was associated with exosomes. Since exosomes are produced by a variety of cells, including cells that actively accumulate prions, they could be a vehicle for infectivity in body fluids and could participate to the dissemination of prions in the organism. In addition, such infectious exosomes also represent a natural, simple, biological material to get key information on the abnormal PrP forms associated with infectivity.In this chapter, we describe first a method that allows exosomes and microvesicles isolation from prion-infected cell cultures and in a second time the strategies to characterize the prions containing exosomes and their ability to disseminate the prion agent.

Understanding the bone marrow microenvironment in hematologic malignancies: A focus on chemokine, integrin, and extracellular vesicle signaling

Signaling between leukemia cells and nonhematopoietic cells in the bone marrow microenvironment contributes to leukemia cell growth and survival. This complicated extrinsic mechanism of chemotherapy resistance relies on a number of pathways and factors, some of which have yet to be determined. Research on cell-cell crosstalk the bone marrow microenvironment in acute leukemia was presented at the 2016 annual Therapeutic Advances in Childhood Leukemia (TACL) investigator meeting. This review summarizes the mini-symposium proceedings and focuses on chemokine signaling via the cell surface receptor CXCR4, adhesion molecule signaling via integrin α4, and crosstalk between leukemia cells and the bone marrow microenvironment that is mediated through extracellular vesicles.

Epigenetic inheritance of acquired traits through sperm RNAs and sperm RNA modifications

Once deemed heretical, emerging evidence now supports the notion that the inheritance of acquired characteristics can occur through ancestral exposures or experiences and that certain paternally acquired traits can be 'memorized' in the sperm as epigenetic information. The search for epigenetic factors in mammalian sperm that transmit acquired phenotypes has recently focused on RNAs and, more recently, RNA modifications. Here, we review insights that have been gained from studying sperm RNAs and RNA modifications, and their roles in influencing offspring phenotypes. We discuss the possible mechanisms by which sperm become acquisitive following environmental-somatic-germline interactions, and how they transmit paternally acquired phenotypes by shaping early embryonic development.

Elucidation of Exosome Migration across the Blood-Brain Barrier Model In Vitro

The delivery of therapeutics to the central nervous system (CNS) remains a major challenge in part due to the presence of the blood-brain barrier (BBB). Recently, cell-derived vesicles, particularly exosomes, have emerged as an attractive vehicle for targeting drugs to the brain, but whether or how they cross the BBB remains unclear. Here, we investigated the interactions between exosomes and brain microvascular endothelial cells (BMECs) in vitro under conditions that mimic the healthy and inflamed BBB in vivo. Transwell assays revealed that luciferase-carrying exosomes can cross a BMEC monolayer under stroke-like, inflamed conditions (TNF-α activated) but not under normal conditions. Confocal microscopy showed that exosomes are internalized by BMECs through endocytosis, co-localize with endosomes, in effect primarily utilizing the transcellular route of crossing. Together, these results indicate that cell-derived exosomes can cross the BBB model under stroke-like conditions in vitro. This study encourages further development of engineered exosomes as drug delivery vehicles or tracking tools for treating or monitoring neurological diseases.

Appearance of claudin-5+ leukocytes in the central nervous system during neuroinflammation: a novel role for endothelial-derived extracellular vesicles

BACKGROUND

The mechanism of leukocyte transendothelial migration (TEM) across the highly restrictive blood-brain barrier (BBB) remains enigmatic, with paracellular TEM thought to require leukocytes to somehow navigate the obstructive endothelial tight junctions (TJs). Transient interactions between TJ proteins on the respective leukocyte and endothelial surfaces have been proposed as one mechanism for TEM. Given the expanding role of extracellular vesicles (EVs) in intercellular communication, we investigated whether EVs derived from brain microvascular endothelial cells (BMEC) of the BBB may play a role in transferring a major TJ protein, claudin-5 (CLN-5), to leukocytes as a possible basis for such a mechanism during neuroinflammation.

METHODS

High-resolution 3D confocal imaging was used to highlight CLN-5 immunoreactivity in the central nervous system (CNS) and on leukocytes of mice with the neuroinflammatory condition experimental autoimmune encephalomyelitis (EAE). Both Western blotting of circulating leukocytes from wild-type mice and fluorescence imaging of leukocyte-associated eGFP-CLN-5 in the blood and CNS of endothelial-targeted, Tie-2-eGFP-CLN-5 transgenic mice were used to confirm the presence of CLN-5 protein on these cells. EVs were isolated from TNF-α-stimulated BMEC cultures and blood plasma of Tie-2-eGFP-CLN-5 mice with EAE and evaluated for CLN-5 protein by Western blotting and fluorescence-activated cell sorting (FACS), respectively. Confocal imaging and FACS were used to detect binding of endothelial-derived EVs from these two sources to leukocytes in vitro. Serial electron microscopy (serial EM) and 3D contour-based surface reconstruction were employed to view EV-like structures at the leukocyte:BBB interface in situ in inflamed CNS microvessels.

RESULTS

A subpopulation of leukocytes immunoreactive for CLN-5 on their surface was seen to infiltrate the CNS of mice with EAE and reside in close apposition to inflamed vessels. Confocal imaging of immunostained samples and Western blotting established the presence of CLN-5+ leukocytes in blood as well, implying these cells are present prior to TEM. Moreover, imaging of inflamed CNS vessels and the associated perivascular cell infiltrates from Tie-2-eGFP-CLN-5 mice with EAE revealed leukocytes bearing the eGFP label, further supporting the hypothesis CLN-5 is transferred from endothelial cells to circulating leukocytes in vivo. Western blotting of BMEC-derived EVs, corresponding in size to both exosomes and microvesicles, and FACS analysis of plasma-derived EVs from Tie-2-eGFP-CLN-5 mice with EAE validated expression of CLN-5 by EVs of endothelial origin. Confocal imaging and FACS further revealed both PKH-67-labeled EVs from cultured BMECs and eGFP-CLN-5+ EVs from plasma of Tie-2-eGFP-CLN-5 mice with EAE can bind to leukocytes. Lastly, serial EM and 3D contour-based surface reconstruction revealed a close association of EV-like structures between the marginating leukocytes and BMECs in situ during EAE.

CONCLUSIONS

During neuroinflammation, CLN-5+ leukocytes appear in the CNS, and both CLN-5+ leukocytes and CLN-5+ EVs are detected in the blood. As endothelial cells transfer CLN-5+ to leukocytes in vivo, and EVs released from BMEC bind to leukocytes in vitro, EVs may serve as the vehicles to transfer CLN-5 protein at sites of leukocyte:endothelial contact along the BBB. This action may be a prelude to facilitate TEM through the formation of temporary TJ protein bridges between these two cell types.

Functions of Exosomes and Microbial Extracellular Vesicles in Allergy and Contact and Delayed-Type Hypersensitivity

Extracellular vesicles, such as exosomes, are newly recognized intercellular conveyors of functional molecular mechanisms. Notably, they transfer RNAs and proteins between different cells that can then participate in the complex pathogenesis of allergic and related hypersensitivity responses and disease mechanisms, as described herein. This review highlights this important new appreciation of the in vivo participation of such extracellular vesicles in the interactions between allergy-mediating cells. We take into account paracrine epigenetic exchanges mediated by surrounding stromal cells and the endocrine receipt of exosomes from distant cells via the circulation. Exosomes are natural ancient nanoparticles of life. They are made by all cells and in some form by all species down to fungi and bacteria, and are present in all fluids. Besides a new focus on their role in the transmission of genetic regulation, exosome transfer of allergens was recently shown to induce allergic inflammation. Importantly, regulatory and tolerogenic exosomes can potently inhibit allergy and hypersensitivity responses, usually acting nonspecifically, but can also proceed in an antigen-specific manner due to the coating of the exosome surface with antibodies. Deep analysis of processes mediated by exosomes should result in the development of early diagnostic biomarkers, as well as allergen-specific, preventive and therapeutic strategies. These will likely significantly diminish the risks of current allergen-specific parenteral desensitization procedures, and of the use of systemic immunosuppressive drugs. Since extracellular vesicles are physiological, they can be fashioned for the specific delivery of therapeutic molecular instructions through easily tolerated, noninvasive routes, such as oral ingestion, nasal administration, and perhaps even inhalation.

Increased Brain-Specific MiR-9 and MiR-124 in the Serum Exosomes of Acute Ischemic Stroke Patients

The aims of this study were to examine the alternation in serum exosome concentrations and the levels of serum exosomal miR-9 and miR-124, two brain-specific miRNAs, in acute ischemic stroke (AIS) patients and to explore the predictive values of these miRNAs for AIS diagnosis and damage evaluation. Sixty-five patients with AIS at the acute stage were enrolled and 66 non-stroke volunteers served as controls. Serum exosomes isolated by ExoQuick precipitations were characterized by transmission electron microscopy, nanoparticle-tracking analysis and western blotting. The levels of exosomal miR-9 and miR-124 were determined by real-time quantitative PCR. Compared with controls, the concentration of serum exosomes and the median levels of serum exosomal miR-9 and miR-124 were significantly higher in AIS patients (p<0.01). The levels of both miR-9 and miR-124 were positively correlated with National Institutes of Health Stroke Scale (NIHSS) scores, infarct volumes and serum concentrations of IL-6. The areas under the curve for exosomal miR-9 and miR-124 were 0.8026 and 0.6976, respectively. This proof of concept study suggests that serum exosomal miR-9 and miR-124 are promising biomarkers for diagnosing AIS and evaluating the degree of damage caused by ischemic injury. However, further studies are needed to explore the potential roles of the exosomes released from brain tissues in post stroke complications.

Extracellular vesicles — new tool for joint repair and regeneration

Cell-derived extracellular vesicles (EVs), present in synovial fluid and cartilage extracellular matrix (ECM), are involved in joint development and in the regulation of joint homeostasis. Although the exact function of EVs in these processes remains incompletely defined, the knowledge already acquired in this field suggests a role for these EVs as biomarkers of joint disease, and as a new tool to restore joint homeostasis and enhance articular tissue regeneration. In addition to direct injection of therapeutic EVs into the target site, surface coating of scaffolds and embedding of EVs in hydrogels might also lead to novel therapeutic possibilities. Based on the existing literature of EVs in synovial fluid and articular tissues, and investigation of the molecular factors (including microRNAs) active in joint homeostasis (or during its disturbance), we postulate novel perspectives for the implementation of EVs as a regenerative medicine approach in joint repair.

Therapeutic and diagnostic applications of extracellular vesicles

During the past two decades, extracellular vesicles (EVs) have been identified as important mediators of intercellular communication, enabling the functional transfer of bioactive molecules from one cell to another. Consequently, it is becoming increasingly clear that these vesicles are involved in many (patho)physiological processes, providing opportunities for therapeutic applications. Moreover, it is known that the molecular composition of EVs reflects the physiological status of the producing cell and tissue, rationalizing their exploitation as biomarkers in various diseases. In this review the composition, biogenesis and diversity of EVs is discussed in a therapeutic and diagnostic context. We describe emerging therapeutic applications, including the use of EVs as drug delivery vehicles and as cell-free vaccines, and reflect on future challenges for clinical translation. Finally, we discuss the use of EVs as a biomarker source and highlight recent studies and clinical successes.

Extracellular vesicles and viruses: Are they close relatives?

Extracellular vesicles (EVs) released by various cells are small phospholipid membrane-enclosed entities that can carry miRNA. They are now central to research in many fields of biology because they seem to constitute a new system of cell-cell communication. Physical and chemical characteristics of many EVs, as well as their biogenesis pathways, resemble those of retroviruses. Moreover, EVs generated by virus-infected cells can incorporate viral proteins and fragments of viral RNA, being thus indistinguishable from defective (noninfectious) retroviruses. EVs, depending on the proteins and genetic material incorporated in them, play a significant role in viral infection, both facilitating and suppressing it. Deciphering the mechanisms of EV-cell interactions may facilitate the design of EVs that inhibit viral infection and can be used as vehicles for targeted drug delivery.

Sources and Functions of Extracellular Small RNAs in Human Circulation

Various biotypes of endogenous small RNAs (sRNAs) have been detected in human circulation, including microRNAs, transfer RNAs, ribosomal RNA, and yRNA fragments. These extracellular sRNAs (ex-sRNAs) are packaged and secreted by many different cell types. Ex-sRNAs exhibit differences in abundance in several disease states and have, therefore, been proposed for use as effective biomarkers. Furthermore, exosome-borne ex-sRNAs have been reported to elicit physiological responses in acceptor cells. Exogenous ex-sRNAs derived from diet (most prominently from plants) and microorganisms have also been reported in human blood. Essential issues that remain to be conclusively addressed concern the (a) presence and sources of exogenous ex-sRNAs in human bodily fluids, (b) detection and measurement of ex-sRNAs in human circulation, (c) selectivity of ex-sRNA export and import, (d) sensitivity and specificity of ex-sRNA delivery to cellular targets, and (e) cell-, tissue-, organ-, and organism-wide impacts of ex-sRNA-mediated cell-to-cell communication. We survey the present state of knowledge of most of these issues in this review.

Transferring intercellular signals and traits between cancer cells: extracellular vesicles as "homing pigeons"

Extracellular vesicles are cell-derived vesicles, which can transport various cargos out of cells. From their cell of origin, the content molecules (proteins, non-coding RNAs including miRNAs, DNA and others) can be delivered to neighboring or distant cells and as such extracellular vesicles can be regarded as vehicles of intercellular communication or "homing pigeons". Extracellular vesicle shuttling is able to actively modulate the tumor microenvironment and can partake in tumor dissemination. In various diseases, including cancer, levels of extracellular vesicle secretion are altered resulting in different amounts and/or profiles of detectable vesicular cargo molecules and these distinct content profiles are currently being evaluated as biomarkers. Apart from their potential as blood-derived containers of specific biomarkers, the transfer of extracellular vesicles to surrounding cells also appears to be involved in the propagation of phenotypic traits. These interesting properties have put extracellular vesicles into the focus of many recent studies.Here we review findings on the involvement of extracellular vesicles in transferring traits of cancer cells to their surroundings and briefly discuss new data on oncosomes, a larger type of vesicle. A pressing issue in cancer treatment is rapidly evolving resistance to many initially efficient drug therapies. Studies investigating the role of extracellular vesicles in this phenomenon together with a summary of the technical challenges that this field is still facing, are also presented. Finally, emerging areas of research such as the analysis of the lipid composition on extracellular vesicles and cutting-edge techniques to visualise the trafficking of extracellular vesicles are discussed.

How Our Other Genome Controls Our Epi-Genome

Eukaryotes and prokaryotes produce extracellular nanovescicles that contain RNAs and other molecules that they exploit to communicate. Recently, inter-kingdom crosstalk was demonstrated between humans and bacteria through fecal microRNAs. We suggest here how bacteria interact with humans via RNAs within membrane vesicles to alter our epigenome, thus filling the gap and closing the circle. At the same time, there are indications that there could be a wider inter-kingdom communication network that might encompass all known kingdoms. Now that the connection with our other genome has been established, we also should begin to explore the 'social' network that we have around us.

Extracellular vesicles: interneural shuttles of complex messages

A core function of neural cells is the exchange and integration of information. Extracellular vesicles such as exosomes and microvesicles recently entered the scene of neuroscience as novel vehicles transmitting complex signals between neural cells. Carrying a defined but mixed cargo of biomolecules, extracellular vesicles possess versatile biological activities with the ability to profoundly modulate the molecular configuration and behaviour of target cells. Extracellular vesicles are suggested to carry out functions during neural development and maintenance, they appear to spread neuropathology and furthermore, convey neuroprotection and regeneration. Understanding the molecular mechanisms of this sophisticated cellular crosstalk will fundamentally improve our insight in complex intercellular processes in the healthy and diseased nervous system.

Extracellular vesicles in neurodegenerative disease - pathogenesis to biomarkers

To develop effective disease-modifying therapies for neurodegenerative diseases, reliable markers of diagnosis, disease activity and progression are a research priority. The fact that neurodegenerative pathology is primarily associated with distinct subsets of cells in discrete areas of the CNS makes the identification of relevant biomarker molecules a challenge. The trafficking of macromolecules from the CNS to the cerebrospinal fluid and blood, mediated by extracellular vesicles (EVs), presents a promising source of CNS-specific biomarkers. EVs are released by almost all cell types and carry a cargo of protein and nucleic acid that varies according to the cell of origin. EV output changes with cell status and reflects intracellular events, so surface marker expression can be used to identify the cell type from which EVs originate. EVs could, therefore, provide an enriched pool of information about core neuropathogenic, cell-specific processes. This Review examines the current knowledge of the biology and function of EVs, discusses the evidence for their involvement in the pathogenesis of neurodegenerative diseases, and considers their potential as biomarkers of disease.

Oligodendrocyte progenitor programming and reprogramming: Toward myelin regeneration

Demyelinating diseases such as multiple sclerosis (MS) are among the most disabling and cost-intensive neurological disorders. The loss of myelin in the central nervous system, produced by oligodendrocytes (OLs), impairs saltatory nerve conduction, leading to motor and cognitive deficits. Immunosuppression therapy has a limited efficacy in MS patients, arguing for a paradigm shift to strategies that target OL lineage cells to achieve myelin repair. The inhibitory microenvironment in MS lesions abrogates the expansion and differentiation of resident OL precursor cells (OPCs) into mature myelin-forming OLs. Recent studies indicate that OPCs display a highly plastic ability to differentiate into alternative cell lineages under certain circumstances. Thus, understanding the mechanisms that maintain and control OPC fate and differentiation into mature OLs in a hostile, non-permissive lesion environment may open new opportunities for regenerative therapies. In this review, we will focus on 1) the plasticity of OPCs in terms of their developmental origins, distribution, and differentiation potentials in the normal and injured brain; 2) recent discoveries of extrinsic and intrinsic factors and small molecule compounds that control OPC specification and differentiation; and 3) therapeutic potential for motivation of neural progenitor cells and reprogramming of differentiated cells into OPCs and their likely impacts on remyelination. OL-based therapies through activating regenerative potentials of OPCs or cell replacement offer exciting opportunities for innovative strategies to promote remyelination and neuroprotection in devastating demyelinating diseases like MS. This article is part of a Special Issue entitled SI:NG2-glia(Invited only).

Low-density lipoprotein mimics blood plasma-derived exosomes and microvesicles during isolation and detection

Circulating extracellular vesicles have emerged as potential new biomarkers in a wide variety of diseases. Despite the increasing interest, their isolation and purification from body fluids remains challenging. Here we studied human pre-prandial and 4 hours postprandial platelet-free blood plasma samples as well as human platelet concentrates. Using flow cytometry, we found that the majority of circulating particles within the size range of extracellular vesicles lacked common vesicular markers. We identified most of these particles as lipoproteins (predominantly low-density lipoprotein, LDL) which mimicked the characteristics of extracellular vesicles and also co-purified with them. Based on biophysical properties of LDL this finding was highly unexpected. Current state-of-the-art extracellular vesicle isolation and purification methods did not result in lipoprotein-free vesicle preparations from blood plasma or from platelet concentrates. Furthermore, transmission electron microscopy showed an association of LDL with isolated vesicles upon in vitro mixing. This is the first study to show co-purification and in vitro association of LDL with extracellular vesicles and its interference with vesicle analysis. Our data point to the importance of careful study design and data interpretation in studies using blood-derived extracellular vesicles with special focus on potentially co-purified LDL.

Introduction to Extracellular Vesicles: Biogenesis, RNA Cargo Selection, Content, Release, and Uptake

Extracellular vesicles are a heterogeneous group of membrane-limited vesicles loaded with various proteins, lipids, and nucleic acids. Release of extracellular vesicles from its cell of origin occurs either through the outward budding of the plasma membrane or through the inward budding of the endosomal membrane, resulting in the formation of multivesicular bodies, which release vesicles upon fusion with the plasma membrane. The release of vesicles can facilitate intercellular communication by contact with or by internalization of contents, either by fusion with the plasma membrane or by endocytosis into "recipient" cells. Although the interest in extracellular vesicle research is increasing, there are still no real standards in place to separate or classify the different types of vesicles. This review provides an introduction into this expanding and complex field of research focusing on the biogenesis, nucleic acid cargo loading, content, release, and uptake of extracellular vesicles.

Is It worth Considering Circulating microRNAs in Multiple Sclerosis?

New evidence has highlighted that miRNA production and trafficking can be dysregulated in both autoimmmune and neurological disorders. Multiple sclerosis (MS) in particular is an autoimmune pathology leading to neurodegeneration. Profiling studies performed on cells derived from MS patients have described a dysregulated network of miRNAs in both immune and neural cells. Interestingly, new evidence has emerged showing that circulating miRNAs are also dysregulated in MS body fluids, including plasma/serum and cerebrospinal fluid. This review summarizes the current scientific theories on the function of this altered circulating miRNA network. It builds up new insights about miRNA transfer mechanisms including extracellular vesicle trafficking involved in cell-to-cell communication and the possible physiopathological functions of these transfers in MS. Finally, this review proposes that monitoring altered miRNA expression levels could serve as a potential biomarker read-out of MS subtype and severity.

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.

Neurovesicles in Brain Development

Long before the nervous system is organized into electrically active neural circuits, connectivity emerges between cells of the developing brain through extracellular signals. Extracellular vesicles that shuttle RNA, proteins, and lipids from donor cells to recipient cells are candidates for mediating connectivity in the brain. Despite the abundance of extracellular vesicles during brain development, evidence for their physiological functions is only beginning to materialize. Here, we review evidence of the existence, content, and functions of extracellular vesicles in brain development.

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.

Implications of Extracellular Vesicle Transfer on Cellular Heterogeneity in Cancer: What Are the Potential Clinical Ramifications?

The functional and phenotypic heterogeneity of tumor cells represents one of the greatest challenges in the successful treatment of cancer patients, because it increases the risk that certain individual tumor cells possess the ability to, for example, metastasize or to tolerate cytotoxic drugs. This heterogeneity in cellular behavior is driven by genetic and epigenetic changes and environmental differences. Recent studies suggest that an additional layer of complexity of tumor heterogeneity exists, based on the ability of cells to share functional biomolecules through local and systemic transfer of extracellular vesicles (EV), with profound effects on cellular behavior. The transfer of functional biomolecules between various populations of tumor cells and between tumor cells and nontumor cells has large consequences for both the tumor cells and the microenvironment that support the cellular behavior of tumor cells, and therefore for the clinical outcome of cancer. Here, we discuss the latest findings on EV transfer and the potential implications of EV-mediated local and systemic transmission of phenotypic behavior, particularly in the context of tumor heterogeneity, metastatic disease, and treatment response. Cancer Res; 76(8); 2071-5. ©2016 AACR.

Mesenchymal stem cell-derived exosomes from different sources selectively promote neuritic outgrowth

Mesenchymal stem cells (MSCs) obtained from bone marrow (BM) have been shown to promote neuronal growth and survival. However, the comparative effects of MSCs of different sources, including menstrual MSCs (MenSCs), BM, umbilical cord and chorion stem cells on neurite outgrowth have not yet been explored. Moreover, the modulatory effects of MSCs may be mediated by paracrine mechanisms, i.e. by molecules contained in the MSC secretome that includes soluble factors and extracellular vesicles such as microvesicles and/or exosomes. The biogenesis of microvesicles, characterized by a vesicle diameter of 50 to 1000 nm, involves membrane shedding while exosomes, of 30 to 100 nm in diameter, originate in the multivesicular bodies within cells. Both vesicle types, which can be harvested from the conditioned media of cell cultures by differential centrifugation steps, regulate the function of target cells due to their molecular content of microRNA, mRNA, proteins and lipids. Here, we compared the effect of human menstrual MSCs (MenSCs) mediated by cell-cell contact, by their total secretome or by secretome-derived extracellular vesicles on neuritic outgrowth in primary neuronal cultures. The contact of MenSCs with cortical neurons inhibited neurite outgrowth while their total secretome enhanced it. The extracellular vesicle fractions showed a distinctive effect: while the exosome-enriched fraction enhanced neurite outgrowth, the microvesicle-enriched fraction displayed an inhibitory effect. When we compared exosome fractions of different human MSC sources, MenSC exosomes showed superior effects on the growth of the longest neurite in cortical neurons and had a comparable effect to BM-SC exosomes on neurite outgrowth in dorsal root ganglia neurons. Thus, the growth-stimulating effects of exosomes derived from MenSCs as well as the opposing effects of both extracellular vesicle fractions provide important information regarding the potential use of MenSCs as therapeutic conveyors in neurodegenerative pathologies.