Aggregation reroutes molecules from a recycling to a vesicle-mediated secretion pathway during reticulocyte maturation

Exosome-like Systems: From Therapies to Vaccination for Cancer Treatment and Prevention-Exploring the State of the Art

Cancer remains one of the main causes of death in the world due to its increasing incidence and treatment difficulties. Although significant progress has been made in this field, innovative approaches are needed to reduce tumor incidence, progression, and spread. In particular, the development of cancer vaccines is currently ongoing as both a preventive and therapeutic strategy. This concept is not new, but few vaccines have been approved in oncology. Antigen-based vaccination emerges as a promising strategy, leveraging specific tumor antigens to activate the immune system response. However, challenges persist in finding suitable delivery systems and antigen preparation methods. Exosomes (EXs) are highly heterogeneous bilayer vesicles that carry several molecule types in the extracellular space. The peculiarity is that they may be released from different cells and may be able to induce direct or indirect stimulation of the immune system. In particular, EX-based vaccines may cause an anti-tumor immune attack or produce memory cells recognizing cancer antigens and inhibiting disease development. This review delves into EX composition, biogenesis, and immune-modulating properties, exploring their role as a tool for prevention and therapy in solid tumors. Finally, we describe future research directions to optimize vaccine efficacy and realize the full potential of EX-based cancer immunotherapy.

Extracellular vesicles in cancer therapy: Roles, potential application, and challenges

Extracellular vesicles (EVs) have emerged as a novel cell-free strategy for the treatment of many diseases including cancer as they play important roles in cancer development and progression. Considering their natural capacity to facilitate cell-to-cell communication as well as their high physiochemical stability and biocompatibility, EVs serve as superior delivery systems for a wide range of therapeutic agents, including medicines, nanomaterials, nucleic acids, and proteins. Therefore, EVs-based cancer therapy is of greater interest to researchers. Mounting studies indicate that EVs can be improved in efficiency, specificity, and safety for cancer therapy. However, their heterogeneity of physicochemical properties and functions is not fully understood, hindering the achievement of bioactive EVs with high yield and purity. Herein, we paid more attention to the EVs applications and their significance in cancer therapy.

Biology and function of exosomes in tumor immunotherapy

Exosomes are nano-scale extracellular vesicles that are found widely in various biological fluids. As messengers, exosomes deliver characteristic biological information from donor cells, facilitating their accumulation and subsequent transfer of information to tumor immune cells. Immunotherapy is a cutting-edge strategy for cancer therapy, but it has not yet reached its full potential owing to severe side effects and limited efficacy. Exosomes possess antigens and immunostimulatory molecules and can serve as cell-free vaccines to induce antitumor immunity. In addition, given their stability, low immunogenicity, and targeting ability, exosomes represent ideal drug delivery systems in tumor immunotherapy by delivering cargoes, including non-coding ribonucleic acids (RNAs), membrane proteins, chemotherapeutic agents, and immune cell death inducers. Exosomes can also be engineered to precisely target tumor cells. However, as a rising star in tumor immunotherapy, exosomes are also impeded by some challenges, including the lack of uniform technical standards for their isolation and purification, the need to improve exosomal cargo loading for efficient exosome delivery, and the expansion of clinical trials, which are currently in their infancy. Long-term, multi-center, and large-scale clinical trials are needed to evaluate the performance of exosomes in the future. Nonetheless, exosomes have demonstrated encouraging performance in tumor immunotherapy. In this review, we summarize the potential and challenges of exosomes in tumor immunotherapy, with the aim to shed light on exosomes as new-era tumor immunotherapy tools.

Unraveling the Intricate Roles of Exosomes in Cardiovascular Diseases: A Comprehensive Review of Physiological Significance and Pathological Implications

Exosomes, as potent intercellular communication tools, have garnered significant attention due to their unique cargo-carrying capabilities, which enable them to influence diverse physiological and pathological functions. Extensive research has illuminated the biogenesis, secretion, and functions of exosomes. These vesicles are secreted by cells in different states, exerting either protective or harmful biological functions. Emerging evidence highlights their role in cardiovascular disease (CVD) by mediating comprehensive interactions among diverse cell types. This review delves into the significant impacts of exosomes on CVD under stress and disease conditions, including coronary artery disease (CAD), myocardial infarction, heart failure, and other cardiomyopathies. Focusing on the cellular signaling and mechanisms, we explore how exosomes mediate multifaceted interactions, particularly contributing to endothelial dysfunction, oxidative stress, and apoptosis in CVD pathogenesis. Additionally, exosomes show great promise as biomarkers, reflecting differential expressions of NcRNAs (miRNAs, lncRNAs, and circRNAs), and as therapeutic carriers for targeted CVD treatment. However, the specific regulatory mechanisms governing exosomes in CVD remain incomplete, necessitating further exploration of their characteristics and roles in various CVD-related contexts. This comprehensive review aims to provide novel insights into the biological implications of exosomes in CVD and offer innovative perspectives on the diagnosis and treatment of CVD.

Haematopoietic cell-derived exosomes in cancer development and therapeutics: From basic science to clinical practice

BACKGROUND

The tumour microenvironment (TME) is a specialised niche involving intercellular communication among cancer cells and various host cells. Among the host cells, the quantity and quality of immune cells within the TME play essential roles in cancer development and management. The immunologically suppressive, so-called 'cold' TME established by a series of tumour-host interactions, including generating immunosuppressive cytokines and recruiting regulatory host immune cells, is associated with resistance to therapies and worse clinical outcomes.

MAIN BODY

Various therapeutic approaches have been used to target the cold TME, including immune checkpoint blockade therapy and adoptive T-cell transfer. A promising, less explored therapeutic strategy involves targeting TME-associated exosomes. Exosomes are nanometer-sized, extracellular vesicles that transfer material from donor to recipient cells. These particles can reprogram the recipient cells and modulate the TME. In particular, exosomes from haematopoietic cells are known to promote or suppress cancer progression under specific conditions. Understanding the effects of haematopoietic cell-secreted exosomes may foster the development of therapeutic exosomes (tExos) for personalised cancer treatment. However, the development of exosome-based therapies has unique challenges, including scalable production, purification, storage and delivery of exosomes and controlling batch variations. Clinical trials are being conducted to verify the safety, feasibility, availability and efficacy of tExos.

CONCLUSION

This review summarises our understanding of how haematopoietic cell-secreted exosomes regulate the TME and antitumour immunity and highlights present challenges and solutions for haematopoietic cell-derived exosome-based therapies.

Mesenchymal Stem Cell-Derived Exosomes: A Novel Approach to Diabetes-Associated Cognitive Impairment

The progression of diabetes frequently results in a myriad of neurological disorders, including ischemic stroke, depression, blood-brain barrier impairment, and cognitive dysfunction. Notably, diabetes-associated cognitive impairment, a prevalent comorbidity during the course of diabetes, progressively affects patients' cognitive abilities and may reciprocally influence diabetes management, thereby severely impacting patients' quality of life. Extracellular vesicles, particularly nanoscale exosomes, have garnered considerable attention in recent years. These exosomes carry and transfer various functional molecules, such as proteins, lipids, and diverse non-coding RNAs, serving as novel regulators and communicators in intercellular interactions. Of particular interest, mesenchymal stem cell-derived exosomes (MSC-Exos) have been reported to traverse the blood-brain barrier and ameliorate intracerebral pathologies. This review elucidates the role of MSC-Exos in diabetes-related cognitive impairment, with a focus on their applications as biomarkers, modulation of neuronal regeneration and synaptic plasticity, anti-inflammatory properties, antioxidative effects, and their involvement in regulating the functionality of β-amyloid proteins during the course of cognitive impairment. The immense therapeutic potential of MSC-Exos in the treatment of diabetes-induced cognitive dysfunction is emphasized.

Chaperonin CCT controls extracellular vesicle production and cell metabolism through kinesin dynamics

Cell proteostasis includes gene transcription, protein translation, folding of de novo proteins, post-translational modifications, secretion, degradation and recycling. By profiling the proteome of extracellular vesicles (EVs) from T cells, we have found the chaperonin complex CCT, involved in the correct folding of particular proteins. By limiting CCT cell-content by siRNA, cells undergo altered lipid composition and metabolic rewiring towards a lipid-dependent metabolism, with increased activity of peroxisomes and mitochondria. This is due to dysregulation of the dynamics of interorganelle contacts between lipid droplets, mitochondria, peroxisomes and the endolysosomal system. This process accelerates the biogenesis of multivesicular bodies leading to higher EV production through the dynamic regulation of microtubule-based kinesin motors. These findings connect proteostasis with lipid metabolism through an unexpected role of CCT.

(Patho)Physiology of Glycosylphosphatidylinositol-Anchored Proteins I: Localization at Plasma Membranes and Extracellular Compartments

Glycosylphosphatidylinositol (GPI)-anchored proteins (APs) are anchored at the outer leaflet of plasma membranes (PMs) of all eukaryotic organisms studied so far by covalent linkage to a highly conserved glycolipid rather than a transmembrane domain. Since their first description, experimental data have been accumulating for the capability of GPI-APs to be released from PMs into the surrounding milieu. It became evident that this release results in distinct arrangements of GPI-APs which are compatible with the aqueous milieu upon loss of their GPI anchor by (proteolytic or lipolytic) cleavage or in the course of shielding of the full-length GPI anchor by incorporation into extracellular vesicles, lipoprotein-like particles and (lyso)phospholipid- and cholesterol-harboring micelle-like complexes or by association with GPI-binding proteins or/and other full-length GPI-APs. In mammalian organisms, the (patho)physiological roles of the released GPI-APs in the extracellular environment, such as blood and tissue cells, depend on the molecular mechanisms of their release as well as the cell types and tissues involved, and are controlled by their removal from circulation. This is accomplished by endocytic uptake by liver cells and/or degradation by GPI-specific phospholipase D in order to bypass potential unwanted effects of the released GPI-APs or their transfer from the releasing donor to acceptor cells (which will be reviewed in a forthcoming manuscript).

Microfluidic Technology for the Isolation and Analysis of Exosomes

Exosomes are lipid-bilayer enclosed vesicles with diameters of 30-150 nm, which play a pivotal role in cell communication by transporting their cargoes such as proteins, lipids, and genetic materials. In recent years, exosomes have been under intense investigation, as they show great promise in numerous areas, especially as bio-markers in liquid biopsies. However, due to the high heterogeneity and the nano size of exosomes, the separation of exosomes is not easy. This review will deliver an outline of the conventional methods and the microfluidic-based technologies for exosome separation. Particular attention is devoted to microfluidic devices, highlighting the efficiency of exosome isolation by these methods. Additionally, this review will introduce advances made in the integrated microfluidics technologies that enable the separation and analysis of exosomes.

Delineating the role of extracellular vesicles in cancer metastasis: A comprehensive review

Extracellular vesicles (EVs) are subcellular messengers that aid in the formation and spread of cancer by enabling tumor-stroma communication. EVs develop from the very porous structure of late endosomes and hold information on both the intrinsic “status” of the cell and the extracellular signals absorbed by the cells from their surroundings. These EVs contain physiologically useful components, including as nucleic acids, lipids, and proteins, which have been found to activate important signaling pathways in tumor and tumor microenvironment (TME) cells, aggravating tumor growth. We highlight critical cell biology mechanisms that link EVS formation to cargo sorting in cancer cells in this review.Sorting out the signals that control EVs creation, cargo, and delivery will aid our understanding of carcinogenesis. Furthermore, we reviewed how cancer development and spreading behaviors are affected by coordinated communication between malignant and non-malignant cells. Herein, we studied the reciprocal exchanges via EVs in various cancer types. Further research into the pathophysiological functions of various EVs in tumor growth is likely to lead to the discovery of new biomarkers in liquid biopsy and the development of tumor-specific therapies.

Perspectives and Challenges on the Potential Use of Exosomes in Bioartificial Pancreas Engineering

Exosomes are enclosed within a single outer membrane and exemplify a specific subtype of secreted vesicles. Exosomes transfer signalling molecules, including microRNAs (miRNAs), messenger RNA (mRNA), fatty acids, proteins, and growth factors, making them a promising therapeutic tool. In routine bioartificial pancreas fabrication, cells are immobilized in polymeric hydrogels lacking attachment capability for cells and other biological cues. In this opinion article, we will discuss the potential role that exosomes and their specific biofactors may play to improve and sustain the function of this bioartificial construct. We will particularly discuss the challenges associated with their isolation and characterization. Since stem cells are an attractive source of exosomes, we will present the advantages of using exosomes in place of stem cells in medical devices including the bioartificial pancreas. We will provide literature evidence of active biofactors in exosomes to support their incorporation in the matrix of encapsulated islets. This will include their potential beneficial effect on hypoxic injury to encapsulated islets. In summary, we propose that the biofactors contained in secreted exosomes have significant potential to enhance the performance of islets encapsulated in polymeric material hydrogels with perm-selective properties to provide immunoisolation for islet transplants as an insulin delivery platform in diabetes.

Extracellular Vesicles and Hepatocellular Carcinoma: Opportunities and Challenges

The incidence of hepatocellular carcinoma (HCC) is increasing worldwide. Extracellular vesicles (EVs) contain sufficient bioactive substances and are carriers of intercellular information exchange, as well as delivery vehicles for nucleic acids, proteins and drugs. Although EVs show great potential for the treatment of HCC and their role in HCC progression has been extensively studied, there are still many challenges such as time-consuming extraction, difficult storage, easy contamination, and low drug loading rate. We focus on the biogenesis, morphological characteristics, isolation and extraction of EVs and their significance in the progression of HCC, tumor invasion, immune escape and cancer therapy for a review. EVs may be effective biomarkers for molecular diagnosis of HCC and new targets for tumor-targeted therapy.

An Emerging Frontier in Intercellular Communication: Extracellular Vesicles in Regeneration

Regeneration requires cellular proliferation, differentiation, and other processes that are regulated by secreted cues originating from cells in the local environment. Recent studies suggest that signaling by extracellular vesicles (EVs), another mode of paracrine communication, may also play a significant role in coordinating cellular behaviors during regeneration. EVs are nanoparticles composed of a lipid bilayer enclosing proteins, nucleic acids, lipids, and other metabolites, and are secreted by most cell types. Upon EV uptake by target cells, EV cargo can influence diverse cellular behaviors during regeneration, including cell survival, immune responses, extracellular matrix remodeling, proliferation, migration, and differentiation. In this review, we briefly introduce the history of EV research and EV biogenesis. Then, we review current understanding of how EVs regulate cellular behaviors during regeneration derived from numerous studies of stem cell-derived EVs in mammalian injury models. Finally, we discuss the potential of other established and emerging research organisms to expand our mechanistic knowledge of basic EV biology, how injury modulates EV biogenesis, cellular sources of EVs in vivo, and the roles of EVs in organisms with greater regenerative capacity.

Role of Exosomes and its emerging therapeutic applications in the pathophysiology of Non-Infectious disease

Exosomes are a type of small Extracellular Vesicles (EVs) and play crucial roles in cancer and other diseases. Exosomes role in various diseases has been studied as they regulate intercellular communication and are obtained from almost any part of the body. Exosomes use is complicated in diseases as they promote pathogenesis but also act as a very good therapeutic agent in most diseases. The presence of a complex molecular cargo consisting of nucleic acids (DNA, RNA, miRNA, siRNA, etc.,) makes it a very good delivery agent and acts as a biomarker for many cancers, cardiovascular and neurodegenerative diseases. They can be used to selectively target cells and activate immune cell responses depending on the source obtained. Exosomes based immunotherapy is an area of gaining importance due to the proteins present in them and their specificity to the targeted cells. The role of exosomes in the diagnosis and treatment of non-infectious diseases is discussed in detail in this article.

Targeting the liver X receptor with dendrogenin A differentiates tumour cells to secrete immunogenic exosome-enriched vesicles

Tumour cells are characterized by having lost their differentiation state. They constitutively secrete small extracellular vesicles (sEV) called exosomes when they come from late endosomes. Dendrogenin A (DDA) is an endogenous tumour suppressor cholesterol‐derived metabolite. It is a new class of ligand of the nuclear Liver X receptors (LXR) which regulate cholesterol homeostasis and immunity. We hypothesized that DDA, which induces tumour cell differentiation, inhibition of tumour growth and immune cell infiltration into tumours, could functionally modify sEV secreted by tumour cells. Here, we have shown that DDA differentiates tumour cells by acting on the LXRβ. This results in an increased production of sEV (DDA‐sEV) which includes exosomes. The DDA‐sEV secreted from DDA‐treated cells were characterized for their content and activity in comparison to sEV secreted from control cells (C‐sEV). DDA‐sEV were enriched, relatively to C‐sEV, in several proteins and lipids such as differentiation antigens, “eat‐me” signals, lipidated LC3 and the endosomal phospholipid bis(monoacylglycero)phosphate, which stimulates dendritic cell maturation and a Th1 T lymphocyte polarization. Moreover, DDA‐sEV inhibited the growth of tumours implanted into immunocompetent mice compared to control conditions. This study reveals a pharmacological control through a nuclear receptor of exosome‐enriched tumour sEV secretion, composition and immune function. Targeting the LXR may be a novel way to reprogram tumour cells and sEV to stimulate immunity against cancer.

Roles of the Exosomes Derived From Myeloid-Derived Suppressor Cells in Tumor Immunity and Cancer Progression

Tumor immunity is involved in malignant tumor progression. Myeloid-derived suppressor cells (MDSCs) play an irreplaceable role in tumor immunity. MDSCs are composed of immature myeloid cells and exhibit obvious immunomodulatory functions. Exosomes released by MDSCs (MDSCs-Exos) have similar effects to parental MDSCs in regulating tumor immunity. In this review, we provided a comprehensive description of the characteristics, functions and mechanisms of exosomes. We analyzed the immunosuppressive, angiogenesis and metastatic effects of MDSCs-Exos in different tumors through multiple perspectives. Immunotherapy targeting MDSCs-Exos has demonstrated great potential in cancers and non-cancerous diseases.

Reticulocyte Maturation

Changes to the membrane proteins and rearrangement of the cytoskeleton must occur for a reticulocyte to mature into a red blood cell (RBC). Different mechanisms of reticulocyte maturation have been proposed to reduce the size and volume of the reticulocyte plasma membrane and to eliminate residual organelles. Lysosomal protein degradation, exosome release, autophagy and the extrusion of large autophagic–endocytic hybrid vesicles have been shown to contribute to reticulocyte maturation. These processes may occur simultaneously or perhaps sequentially. Reticulocyte maturation is incompletely understood and requires further investigation. RBCs with membrane defects or cation leak disorders caused by genetic variants offer an insight into reticulocyte maturation as they present characteristics of incomplete maturation. In this review, we compare the structure of the mature RBC membrane with that of the reticulocyte. We discuss the mechanisms of reticulocyte maturation with a focus on incomplete reticulocyte maturation in red cell variants.

Exosomes as a new frontier of cancer liquid biopsy

Liquid biopsy, characterized by minimally invasive detection through biofluids such as blood, saliva, and urine, has emerged as a revolutionary strategy for cancer diagnosis and prognosis prediction. Exosomes are a subset of extracellular vesicles (EVs) that shuttle molecular cargoes from donor cells to recipient cells and play a crucial role in mediating intercellular communication. Increasing studies suggest that exosomes have a great promise to serve as novel biomarkers in liquid biopsy, since large quantities of exosomes are enriched in body fluids and are involved in numerous physiological and pathological processes. However, the further clinical application of exosomes has been greatly restrained by the lack of high-quality separation and component analysis methods. This review aims to provide a comprehensive overview on the conventional and novel technologies for exosome isolation, characterization and content detection. Additionally, the roles of exosomes serving as potential biomarkers in liquid biopsy for the diagnosis, treatment monitoring, and prognosis prediction of cancer are summarized. Finally, the prospects and challenges of applying exosome-based liquid biopsy to precision medicine are evaluated.

The ins and outs of microvesicles

Microvesicles are a heterogeneous group of membrane-enclosed vesicles that are released from cells into the extracellular space by the outward budding and pinching of the plasma membrane. These vesicles are loaded with multiple selectively sorted proteins and nucleic acids. Although interest in the clinical potential of microvesicles is increasing, there is only limited understanding of different types of microvesicles and the mechanisms involved in their formation. Here, we describe what is presently known about this expanding and complex field of research focusing on the mechanism of biogenesis, cargo loading, and release of microvesicles.

Adipocyte-Endothelium Crosstalk in Obesity

Obesity is characterized by pathological adipose tissue (AT) expansion. While healthy AT expansion enhances systemic insulin sensitivity, unhealthy AT expansion through increased adipocyte size is associated with insulin resistance, fibrosis, hypoxia, and reduced adipose-derived adiponectin secretion. The mechanisms causing the unhealthy AT expansion are not fully elucidated; yet, dysregulated crosstalk between cells within the AT is an important contributor. Evidence from animal and human studies suggests a crucial role of the crosstalk between vascular endothelium (the innermost cell type in blood vessels) and adipocytes for metabolic homeostasis. Arterial endothelial cells are directly involved in maintaining normal organ functions through local blood flow regulation. The endothelial-dependent regulation of blood flow in AT is hampered in obesity, which negatively affects the adipocyte. Moreover, endothelial cells secrete extracellular vesicles (EVs) that target adipocytes in vivo. The endothelial EVs secretion is hampered in obesity and may be affected by the adipocyte-derived adipokine adiponectin. Adiponectin targets the vascular endothelium, eliciting organ-protective functions through binding to T-cadherin. The reduced obesity-induced adiponectin binding of T-cadherin reduces endothelial EV secretion. This affects endothelial health and cell-cell communication between AT cells and distant organs, influencing systemic energy homeostasis. This review focuses on the current understanding of endothelial and adipocyte crosstalk. We will discuss how obesity changes the AT environment and how these changes contribute to obesity-associated metabolic disease in humans. Particularly, we will describe and discuss the EV-dependent communication and regulation between adipocytes, adiponectin, and the endothelial cells regulating systemic energy homeostasis in health and metabolic disease in humans.

Exosomes and extracellular vesicles as liquid biopsy biomarkers in diffuse large B-cell lymphoma: Current state of the art and unmet clinical needs

Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin's lymphoma, and it constitutes biologically heterogeneous entities. Standard first-line therapies cure ~60% of patients, the rest being either refractory or experiencing relapse. Currently, there are no robust predictive biomarkers of therapeutic response. Heterogeneity of DLBCL is partly explained by the cell of origin (COO), ie, germinal centre B cell or activated B cell, with the latter exhibiting worse prognosis. While gene expression profiling (GEP) is the gold standard for determining COO, surrogate immunohistochemical algorithms are used clinically, but show significant discordance with GEP. Recently, additional genetic subgroups with different prognoses have been reported. However, the tools/expertise required for analysis prohibit widespread deployment. Liquid biopsy-based assays show promise in providing clinically actionable information, are noninvasive and facilitate serial sampling to assess mechanisms of therapy resistance. Circulating, cell-free DNA analysis has shown enhanced sensitivity for detecting molecular alterations, but this modality cannot determine alterations of the tumor proteome or on signalling pathways. Exosomes are endosomally derived vesicles, are found in high abundance in body fluids and are readily isolated using a variety of methods. Tumour-derived exosomes can yield data regarding genetic, transcriptional, and proteomic changes useful for diagnosis, prognosis, and therapy of DLBCL. At present, standardized techniques for isolating exosomes are lacking and discriminating between exosomes from neoplastic and normal B cells is challenging. Refinements in isolation procedures are required to realize their full potential as precision medicine tools to provide comprehensive information on disease subtypes, identify prognostic factors, allow real-time monitoring of therapy response and delineate novel drug targets.

Exosomes

Exosomes are small, single-membrane, secreted organelles of ∼30 to ∼200 nm in diameter that have the same topology as the cell and are enriched in selected proteins, lipids, nucleic acids, and glycoconjugates. Exosomes contain an array of membrane-associated, high-order oligomeric protein complexes, display pronounced molecular heterogeneity, and are created by budding at both plasma and endosome membranes. Exosome biogenesis is a mechanism of protein quality control, and once released, exosomes have activities as diverse as remodeling the extracellular matrix and transmitting signals and molecules to other cells. This pathway of intercellular vesicle traffic plays important roles in many aspects of human health and disease, including development, immunity, tissue homeostasis, cancer, and neurodegenerative diseases. In addition, viruses co-opt exosome biogenesis pathways both for assembling infectious particles and for establishing host permissiveness. On the basis of these and other properties, exosomes are being developed as therapeutic agents in multiple disease models.

Membrane-bound extracellular vesicles secreted by parasitic protozoa: cellular structures involved in the communication between cells

The focus of this review is a group of structures/organelles collectively known as extracellular vesicles (EVs) that are secreted by most, if not all, cells, varying from mammalian cells to protozoa and even bacteria. They vary in size: some are small (100-200 nm) and others are larger (> 200 nm). In protozoa, however, most of them are small or medium in size (200-400 nm). These include vesicles from different origins. We briefly review the biogenesis of this distinct group that includes (a) exosome, which originates from the multivesicular bodies, an important component of the endocytic pathway; (b) ectosome, formed from a budding process that takes place in the plasma membrane of the cells; (c) vesicles released from the cell surface following a process of patching and capping of ligand/receptor complexes; (d) other processes where tubules secreted by the parasite subsequently originate exosome-like structures. Here, special emphasis is given to EVs secreted by parasitic protozoa such as Leishmania, Trypanosoma, Plasmodium, Toxoplasma, Cryptosporidium, Trichomonas, and Giardia. Most of them have been characterized as exosomes that were isolated using several approaches and characterized by electron microscopy, proteomic analysis, and RNA sequencing. The results obtained show clearly that they present several proteins and different types of RNAs. From the functional point of view, it is now clear that the secreted exosomes can be incorporated by the parasite itself as well as by mammalian cells with which they interact. As a consequence, there is interference both with the parasite (induction of differentiation, changes in infectivity, etc.) and with the host cell. Therefore, the EVs constitute a new system of transference of signals among cells. On the other hand, there are suggestions that exosomes may constitute potential biotechnology tools and are important players of what has been designated as nanobiotechnology. They may constitute an important delivery system for gene therapy and molecular-displaying cell regulation capabilities when incorporated into other cells and even by interfering with the exosomal membrane during its biogenesis, targeting the vesicles via specific ligands to different cell types. These vesicles may reach the bloodstream, overflow through intercellular junctions, and even pass through the central nervous system blood barrier. There is evidence that it is possible to interfere with the composition of the exosomes by interfering with multivesicular body biogenesis.

Recent advancements in the study of breast cancer exosomes as mediators of intratumoral communication

Breast cancer is a heterogeneous disease, with a morbidity rate of 27.8% and a mortality rate of 15% among women population worldwide. Understanding how this cancer develops and the mechanisms behind tumor progression and chemoresistance is of utmost importance. Exosomes mediate communication in a population of heterogeneous tumoral cells. They have a cargo composed of oncogenes and oncomiRs which change the transcriptomic scenario of their targeted cells and activate numerous tumor-promoting signaling pathways. Exosomes secreted by breast cancer cells lead to enhanced cell proliferation, replicative immortality, angiogenesis, invasion, migration, and chemoresistance. Studying exosomes from this perspective offers more in depth understanding of breast malignancy and may aid in the future development of early diagnostic, prognostic and therapeutic options. We present the latest findings in this area and offer practical solutions which may further stimulate the much-needed research of exosome in breast cancer.

Advances in exosome isolation methods and their applications in proteomic analysis of biological samples

Exosomes are membrane-bound vesicles secreted by cells, and contain various important biological molecules, such as lipids, proteins, messenger RNAs, microRNAs, and noncoding RNAs. Emerging evidence demonstrates that proteomic analysis of exosomes is of great significance in studying metabolic diseases, tumor metastasis, immune regulation, and so forth. However, exosome proteomic analysis has high requirements with regard to the purity of collected exosomes. Here recent advances in the methods for isolating exosomes and their applications in proteomic analysis are summarized. Graphical abstract.

Stimulated release of intraluminal vesicles from Weibel-Palade bodies

Weibel-Palade bodies (WPBs) are secretory granules that contain von Willebrand factor and P-selectin, molecules that regulate hemostasis and inflammation, respectively. The presence of CD63/LAMP3 in the limiting membrane of WPBs has led to their classification as lysosome-related organelles. Many lysosome-related organelles contain intraluminal vesicles (ILVs) enriched in CD63 that are secreted into the extracellular environment during cell activation to mediate intercellular communication. To date, there are no reports that WPBs contain or release ILVs. By light microscopy and live-cell imaging, we show that CD63 is enriched in microdomains within WPBs. Extracellular antibody recycling studies showed that CD63 in WPB microdomains can originate from the plasma membrane. By cryo-electron tomography of frozen-hydrated endothelial cells, we identify internal vesicles as novel structural features of the WPB lumen. By live-cell fluorescence microscopy, we directly observe the exocytotic release of EGFP-CD63 ILVs as discrete particles from individual WPBs. WPB exocytosis provides a novel route for release of ILVs during endothelial cell stimulation.

Role of extracellular vesicles in stem cell biology

The extracellular vesicles (EVs) are membrane vesicles carrying proteins, nucleic acids, and bioactive lipids of the cell of origin. These vesicles released within the extracellular space and entering into the circulation may transfer their cargo to neighboring or distant cells and induce phenotypical and functional changes that may be relevant in several physiopathological conditions. In an attempt to define the biological properties of EVs, several investigations have focused on their cargo and on the effects elicited in recipient cells. EVs have been involved in modulation of tumor microenvironment and behavior, as well as in the immune and inflammatory response. In the present review, we address the paracrine action of EVs released by stem cells and their potential involvement in the activation of regenerative programs in injured cells.

HOPS-dependent endosomal fusion required for efficient cytosolic delivery of therapeutic peptides and small proteins

Protein therapeutics represent a significant and growing component of the modern pharmacopeia, but their potential to treat human disease is limited because most proteins fail to traffic across biological membranes. Recently, we discovered a class of cell-permeant miniature proteins (CPMPs) containing a precisely defined, penta-arginine (penta-Arg) motif that traffics readily to the cytosol and nucleus of mammalian cells with efficiencies that rival those of hydrocarbon-stapled peptides active in animals and man. Like many cell-penetrating peptides (CPPs), CPMPs enter the endocytic pathway; the difference is that CPMPs containing a penta-Arg motif are released efficiently from endosomes, while other CPPs are not. Here, we seek to understand how CPMPs traffic from endosomes into the cytosol and what factors contribute to the efficiency of endosomal release. First, using two complementary cell-based assays, we exclude endosomal rupture as the primary means of endosomal escape. Next, using an RNA interference screen, fluorescence correlation spectroscopy, and confocal imaging, we identify VPS39-a gene encoding a subunit of the homotypic fusion and protein-sorting (HOPS) complex-as a critical determinant in the trafficking of CPMPs and hydrocarbon-stapled peptides to the cytosol. Although CPMPs neither inhibit nor activate HOPS function, HOPS activity is essential to efficiently deliver CPMPs to the cytosol. CPMPs localize within the lumen of Rab7+ and Lamp1+ endosomes and their transport requires HOPS activity. Overall, our results identify Lamp1+ late endosomes and lysosomes as portals for passing proteins into the cytosol and suggest that this environment is prerequisite for endosomal escape.

Exosomes: Isolation, Analysis, and Applications in Cancer Detection and Therapy

Exosomes are cell-derived small extracellular vesicles that are naturally secreted by all types of cells and widely distributed in various biofluids. They carry a variety of key bioactive molecules (e.g., nucleic acids, proteins, growth factors, cytokines) from their parent cells and convey them to neighboring or even distant cells through circulation. In recent years, tumor-derived exosomes have attracted great interest from investigators because they actively participate in nearly all aspects of tumor development and facilitate both tumor growth and metastasis through exosome-mediated intercellular communication. The vesicular contents are increasingly considered potential biomarkers for tumor diagnoses and prognosis. With the progress made in isolation and analytical technologies, the functions of exosomes and their contents in tumor development are also becoming clearer. In this review article we describe the recent developments in exosome isolation techniques and analysis of exosomal contents. We also address their applications in cancer detection and therapy.

Proteomics study of human cord blood reticulocyte-derived exosomes

Reticulocyte-derived exosomes (Rex), extracellular vesicles of endocytic origin, were initially discovered as a cargo-disposal mechanism of obsolete proteins in the maturation of reticulocytes into erythrocytes. In this work, we present the first mass spectrometry-based proteomics of human Rex (HuRex). HuRex were isolated from cultures of human reticulocyte-enriched cord blood using different culture conditions and exosome isolation methods. The newly described proteome consists of 367 proteins, most of them related to exosomes as revealed by gene ontology over-representation analysis and include multiple transporters as well as proteins involved in exosome biogenesis and erythrocytic disorders. Immunoelectron microscopy validated the presence of the transferrin receptor. Moreover, functional assays demonstrated active capture of HuRex by mature dendritic cells. As only seven proteins have been previously associated with HuRex, this resource will facilitate studies on the role of human reticulocyte-derived exosomes in normal and pathological conditions affecting erythropoiesis.

Cellular mechanisms responsible for cell-to-cell spreading of prions

Prions are infectious agents that cause fatal neurodegenerative diseases. Current evidence indicates that they are essentially composed of an abnormally folded protein (PrPSc). These abnormal aggregated PrPSc species multiply in infected cells by recruiting and converting the host PrPC protein into new PrPSc. How prions move from cell to cell and progressively spread across the infected tissue is of crucial importance and may provide experimental opportunity to delay the progression of the disease. In infected cells, different mechanisms have been identified, including release of infectious extracellular vesicles and intercellular transfer of PrPSc-containing organelles through tunneling nanotubes. These findings should allow manipulation of the intracellular trafficking events targeting PrPSc in these particular subcellular compartments to experimentally address the relative contribution of these mechanisms to in vivo prion pathogenesis. In addition, such information may prompt further experimental strategies to decipher the causal roles of protein misfolding and aggregation in other human neurodegenerative diseases.

To be or not to be... secreted as exosomes, a balance finely tuned by the mechanisms of biogenesis

The release of extracellular vesicles such as exosomes provides an attractive intercellular communication pathway. Exosomes are 30- to 150-nm membrane vesicles that are generated in endosomal compartment and act as intercellular mediators in both physiological and pathological context. Despite the growing interest in exosome functions, the mechanisms responsible for their biogenesis and secretion are still not completely understood. Knowledge about these mechanisms is important because they control the composition, and hence the function and secretion, of exosomes. Exosomes are produced as intraluminal vesicles in extremely dynamic endosomal organelles, which undergo various maturation processes in order to form multivesicular endosomes. Notably, the function of multivesicular endosomes is balanced between exosome secretion and lysosomal degradation. In the present review, we present and discuss each intracellular trafficking pathway that has been reported or proposed as regulating exosome biogenesis, with a particular focus on the importance of endosomal dynamics in sorting out cargo proteins to exosomes and to the secretion of multivesicular endosomes. An overall picture reveals several key mechanisms, which mainly act at the crossroads of endosomal pathways as regulatory checkpoints of exosome biogenesis.

Exosomal cargo-loading and synthetic exosome-mimics as potential therapeutic tools

Exosomes are nano-sized vesicles that serve as mediators for intercellular communication through the delivery of cargo, including protein, lipids, nucleic acids or other cellular components, to neighboring or distant cells. Exosomal cargo may vary in response to different physiological or pathological conditions. The endosomal sorting complex required for transport (ESCRT) family has been widely accepted as a key mechanism in biogenesis and cargo sorting. On the other hand, accumulating evidence show that ESCRT-independent pathways exist. Due to the critical role of exosomes in intercellular communications in delivering cargo to recipient cells, exosomes have been investigated as a vector for the delivery of endogenous or exogenous cargo for therapeutic purposes. But the number of exosomes produced by cells is limited, which hampers their application. Synthetic exosome-mimics have been fabricated and investigated as a therapeutic tool for drug delivery. This review focuses on ESCRT-independent regulation of cargo loading into exosomes, including lipid raft and ceramide-mediated mechanisms, and reported exosomes or exosome-mimics with therapeutic effects.

New Technologies for Analysis of Extracellular Vesicles

Extracellular vesicles (EVs) are diverse, nanoscale membrane vesicles actively released by cells. Similar-sized vesicles can be further classified (e.g., exosomes, microvesicles) based on their biogenesis, size, and biophysical properties. Although initially thought to be cellular debris, and thus under-appreciated, EVs are now increasingly recognized as important vehicles of intercellular communication and circulating biomarkers for disease diagnoses and prognosis. Despite their clinical potential, the lack of sensitive preparatory and analytical technologies for EVs poses a barrier to clinical translation. New analytical platforms including molecular ones are thus actively being developed to address these challenges. Recent advances in the field are expected to have far-reaching impact in both basic and translational studies. This article aims to present a comprehensive and critical overview of emerging analytical technologies for EV detection and their clinical applications.

Shedding light on the cell biology of extracellular vesicles

Extracellular vesicles are a heterogeneous group of cell-derived membranous structures comprising exosomes and microvesicles, which originate from the endosomal system or which are shed from the plasma membrane, respectively. They are present in biological fluids and are involved in multiple physiological and pathological processes. Extracellular vesicles are now considered as an additional mechanism for intercellular communication, allowing cells to exchange proteins, lipids and genetic material. Knowledge of the cellular processes that govern extracellular vesicle biology is essential to shed light on the physiological and pathological functions of these vesicles as well as on clinical applications involving their use and/or analysis. However, in this expanding field, much remains unknown regarding the origin, biogenesis, secretion, targeting and fate of these vesicles.

Atg5 Disassociates the V1V0-ATPase to Promote Exosome Production and Tumor Metastasis Independent of Canonical Macroautophagy

Autophagy and autophagy-related genes (Atg) have been attributed prominent roles in tumorigenesis, tumor growth, and metastasis. Extracellular vesicles called exosomes are also implicated in cancer metastasis. Here, we demonstrate that exosome production is strongly reduced in cells lacking Atg5 and Atg16L1, but this is independent of Atg7 and canonical autophagy. Atg5 specifically decreases acidification of late endosomes where exosomes are produced, disrupting the acidifying V₁V₀-ATPase by removing a regulatory component, ATP6V1E1, into exosomes. The effect of Atg5 on exosome production promotes the migration and in vivo metastasis of orthotopic breast cancer cells. These findings uncover mechanisms controlling exosome release and identify means by which autophagy-related genes can contribute to metastasis in autophagy-independent pathways.

Biogenesis and function of ESCRT-dependent extracellular vesicles

From bacteria to humans, cells secrete a large variety of membrane-bound extracellular vesicles. Only relatively recently has it however started to become clear that the exovesicular transport of proteins and RNAs is important for normal physiology and numerous pathological conditions. Extracellular vesicles can be formed through the release of the intralumenal vesicles of multivesicular endosomes as so-called exosomes, or through direct, ectosomal, budding from the cell surface. Through their ability to promote the bending of membranes away from the cytoplasm, the components of the Endosomal Sorting Complex Required for Transport (ESCRT) have been implicated in both exo- and ectosomal biogenesis. Studies of the ESCRT machinery may therefore provide important insights into the formation and function of extracellular vesicles. In the present review, we first describe the cell biological mechanisms through which ESCRT components contribute to the biogenesis of different types of extracellular vesicles. We then discuss how recent functional studies have started to uncover important roles of ESCRT-dependent extracellular vesicles in a wide variety of processes, including the transport of developmental signaling molecules and embryonic morphogenesis, the regulation of social behavior and host-pathogen interactions, as well as the etiology and progression of neurodegenerative pathologies and cancer.

The Methods of Choice for Extracellular Vesicles (EVs) Characterization

In recent years, extracellular vesicles (EVs) have become a subject of intense study. These membrane-enclosed spherical structures are secreted by almost every cell type and are engaged in the transport of cellular content (cargo) from parental to target cells. The impact of EVs transfer has been observed in many vital cellular processes including cell-to-cell communication and immune response modulation; thus, a fast and precise characterization of EVs may be relevant for both scientific and diagnostic purposes. In this review, the most popular analytical techniques used in EVs studies are presented with the emphasis on exosomes and microvesicles characterization.

Prions on the run: How extracellular vesicles serve as delivery vehicles for self-templating protein aggregates

Extracellular vesicles (EVs) are actively secreted, membrane-bound communication vehicles that exchange biomolecules between cells. EVs also serve as dissemination vehicles for pathogens, including prions, proteinaceous infectious agents that cause transmissible spongiform encephalopathies (TSEs) in mammals. Increasing evidence accumulates that diverse protein aggregates associated with common neurodegenerative diseases are packaged into EVs as well. Vesicle-mediated intercellular transmission of protein aggregates can induce aggregation of homotypic proteins in acceptor cells and might thereby contribute to disease progression. Our knowledge of how protein aggregates are sorted into EVs and how these vesicles adhere to and fuse with target cells is limited. Here we review how TSE prions exploit EVs for intercellular transmission and compare this to the transmission behavior of self-templating cytosolic protein aggregates derived from the yeast prion domain Sup 35 NM. Artificial NM prions are non-toxic to mammalian cell cultures and do not cause loss-of-function phenotypes. Importantly, NM particles are also secreted in association with exosomes that horizontally transmit the prion phenotype to naive bystander cells, a process that can be monitored with high accuracy by automated high throughput confocal microscopy. The high abundance of mammalian proteins with amino acid stretches compositionally similar to yeast prion domains makes the NM cell model an attractive model to study self-templating and dissemination properties of proteins with prion-like domains in the mammalian context.

New insights into the function of Rab GTPases in the context of exosomal secretion

In the last two decades, extracellular vesicle-mediated communication between cells has become a major field in cell biology. However, the function of extracellular vesicles is far from clear, especially due to the disparity of released vesicles by cells. Basically, one must consider vesicles budding from the cell plasma membrane (ectosomes) and vesicles released upon fusion of an endosomal multivesicular compartment (exosomes). Moreover, even for exosomes, we report and discuss here the possibility that different routes regulated by specific Rab GTPases might produce exosomes having various biologic functions.

The role of the miR-17-92 cluster in neurogenesis and angiogenesis in the central nervous system of adults

It is well known that neurogenesis is not the only concern for the fully functional recovery after brain or spinal cord injury, as it has been shed light on the critical role of angiogenesis in improving neurological functional recovery. Angiogenesis and neurogenesis coordinately interact with each other in the developing and adult brain, during which they may respond to similar mediators and receptors, in which they share a common posttranscriptional regulator: the miR-17-92 cluster. The miR-17-92 cluster was initially described as an oncogene and was later demonstrated to drive key physiological and pathological responses during development and diseases respectively. It has been reported that the miR-17-92 cluster regulates both neurogenesis and angiogenesis. The miR-17-92 cluster modulates neural progenitor cells proliferation not only during development but also during neurological disorders such as stroke. It has also been shown that the endothelial miR-17-92 cluster regulates angiogenesis during embryonic stage and adulthood. In this review, we have discussed the actions of the miR-17-92 cluster in neuronal and vascular plasticity, and its potential as a novel therapeutic strategy for CNS injury. © 2016 Wiley Periodicals, Inc.

Horizontal Transmission of Cytosolic Sup35 Prions by Extracellular Vesicles

Prions are infectious protein particles that replicate by templating their aggregated state onto soluble protein of the same type. Originally identified as the causative agent of transmissible spongiform encephalopathies, prions in yeast (Saccharomyces cerevisiae) are epigenetic elements of inheritance that induce phenotypic changes of their host cells. The prototype yeast prion is the translation termination factor Sup35. Prions composed of Sup35 or its modular prion domain NM are heritable and are transmitted vertically to progeny or horizontally during mating. Interestingly, in mammalian cells, protein aggregates derived from yeast Sup35 NM behave as true infectious entities that employ dissemination strategies similar to those of mammalian prions. While transmission is most efficient when cells are in direct contact, we demonstrate here that cytosolic Sup35 NM prions are also released into the extracellular space in association with nanometer-sized membrane vesicles. Importantly, extracellular vesicles are biologically active and are taken up by recipient cells, where they induce self-sustained Sup35 NM protein aggregation. Thus, in mammalian cells, extracellular vesicles can serve as dissemination vehicles for protein-based epigenetic information transfer.

IMPORTANCE

Prions are proteinaceous infectious particles that propagate by templating their quaternary structure onto nascent proteins of the same kind. Prions in yeast act as heritable epigenetic elements that can alter the phenotype when transmitted to daughter cells or during mating. Prion activity is conferred by so-called prion domains often enriched in glutamine and asparagine residues. Interestingly, many mammalian proteins also contain domains with compositional similarity to yeast prion domains. We have recently provided a proof-of-principle demonstration that a yeast prion domain also retains its prion activity in mammalian cells. We demonstrate here that cytosolic prions composed of a yeast prion domain are also packaged into extracellular vesicles that transmit the prion phenotype to bystander cells. Thus, proteins with prion-like domains can behave as proteinaceous information molecules that exploit the cellular vesicle trafficking machinery for intercellular long-distance dissemination.

Extracellular vesicle microRNAs: biomarker discovery in various diseases based on RT-qPCR

In recent years, biomarker discovery based on extracellular microRNAs (miRNAs), especially exosome miRNAs, has drawn wide attention. While exosome isolation and identification technologies are increasingly sophisticated, the preanalytical process of exosome miRNAs seems to be no longer a crucial problem. Though next-generation sequencing, microarray and digital PCR have been recommended as good downstream analytical platforms for exosome miRNA quantification, they are still more constrained in clinical utility compared with RT-qPCR method at present. In this review, we will trace back to the origin and summarize current studies of biomarker discovery based on extracellular vesicle miRNAs, and provide an overview and latest developments of RT-qPCR-based data normalization, in order to further assist the development of translational medicine.

Extracellular Vesicles and a Novel Form of Communication in the Brain

In numerous neurodegenerative diseases, the interplay between neurons and glia modulates the outcome and progression of pathology. One particularly intriguing mode of interaction between neurons, astrocytes, microglia, and oligodendrocytes is characterized by the release of extracellular vesicles that transport proteins, lipids, and nucleotides from one cell to another. Notably, several proteins that cause disease, including the prion protein and mutant SOD1, have been detected in glia-derived extracellular vesicles and observed to fuse with neurons and trigger pathology in vitro. Here we review the structural and functional characterization of such extracellular vesicles in neuron-glia interactions. Furthermore, we discuss possible mechanisms of extracellular vesicle biogenesis and release from activated glia and microglia, and their effects on neurons. Given that exosomes, the smallest type of extracellular vesicles, have been reported to recognize specific cellular populations and act as carriers of very specialized cargo, a thorough analysis of these vesicles may aid in their engineering in vitro and targeted delivery in vivo, opening opportunities for therapeutics.

Induction of α-synuclein aggregate formation by CSF exosomes from patients with Parkinson's disease and dementia with Lewy bodies

Extracellular α-synuclein has been proposed as a crucial mechanism for induction of pathological aggregate formation in previously healthy cells. In vitro, extracellular α-synuclein is partially associated with exosomal vesicles. Recently, we have provided evidence that exosomal α-synuclein is present in the central nervous system in vivo. We hypothesized that exosomal α-synuclein species from patients with α-synuclein related neurodegeneration serve as carriers for interneuronal disease transmission. We isolated exosomes from cerebrospinal fluid from patients with Parkinson's disease, dementia with Lewy bodies, progressive supranuclear palsy as a non-α-synuclein related disorder that clinically overlaps with Parkinson's disease, and neurological controls. Cerebrospinal fluid exosome numbers, α-synuclein protein content of cerebrospinal fluid exosomes and their potential to induce oligomerization of α-synuclein were analysed. The quantification of cerebrospinal fluid exosomal α-synuclein showed distinct differences between patients with Parkinson's disease and dementia with Lewy bodies. In addition, exosomal α-synuclein levels correlated with the severity of cognitive impairment in cross-sectional samples from patients with dementia with Lewy bodies. Importantly, cerebrospinal fluid exosomes derived from Parkinson's disease and dementia with Lewy bodies induce oligomerization of α-synuclein in a reporter cell line in a dose-dependent manner. Our data suggest that cerebrospinal fluid exosomes from patients with Parkinson's disease and dementia with Lewy bodies contain a pathogenic species of α-synuclein, which could initiate oligomerization of soluble α-synuclein in target cells and confer disease pathology.

Proteomics of extracellular vesicles: Exosomes and ectosomes

Almost all bacteria, archaea, and eukaryotic cells shed extracellular vesicles either constitutively or in a regulated manner. These nanosized membrane vesicles are spherical, bilayered proteolipids that harbor specific subsets of proteins, DNAs, RNAs, and lipids. Recent research has facilitated conceptual advancements in this emerging field that indicate that extracellular vesicles act as intercellular communicasomes by transferring signals to their target cell via surface ligands and delivering receptors and functional molecules. Recent progress in mass spectrometry-based proteomic analyses of mammalian extracellular vesicles derived from diverse cell types and body fluids has resulted in the identification of several thousand vesicular proteins that provide us with essential clues to the molecular mechanisms involved in vesicle cargo sorting and biogenesis. Furthermore, cell-type- or disease-specific vesicular proteins help us to understand the pathophysiological functions of extracellular vesicles and contribute to the discovery of diagnostic and therapeutic target proteins. This review focuses on the high-throughput mass spectrometry-based proteomic analyses of mammalian extracellular vesicles (i.e., exosomes and ectosomes), EVpedia (a free web-based integrated database of high-throughput data for systematic analyses of extracellular vesicles; http://evpedia.info), and the intravesicular protein-protein interaction network analyses of mammalian extracellular vesicles. The goal of this article is to encourage further studies to construct a comprehensive proteome database for extracellular vesicles that will help us to not only decode the biogenesis and cargo-sorting mechanisms during vesicle formation but also elucidate the pathophysiological roles of these complex extracellular organelles.

Syntenin and syndecan in the biogenesis of exosomes

Cells communicate with their environment in various ways, including by secreting vesicles. Secreted vesicles are loaded with proteins, lipids and RNAs that compose 'a signature' of the cell of origin and potentially can reprogram recipient cells. Secreted vesicles recently gained in interest for medicine. They represent potential sources of biomarkers that can be collected from body fluids and, by disseminating pathogenic proteins, might also participate in systemic diseases like cancer, atherosclerosis and neurodegeneration. The mechanisms controlling the biogenesis and the uptake of secreted vesicles are poorly understood. Some of these vesicles originate from endosomes and are called 'exosomes'. In this review, we recapitulate recent insight on the role of the syndecan (SDC) heparan sulphate proteoglycans, the small intracellular adaptor syntenin and associated regulators in the biogenesis and loading of exosomes with cargo. SDC-syntenin-associated regulators include the endosomal sorting complex required for transport accessory component ALG-2-interacting protein X, the small GTPase adenosine 5'-diphosphate-ribosylation factor 6, the lipid-modifying enzyme phospholipase D2 and the endoglycosidase heparanase. All these molecules appear to support the budding of SDC-syntenin and associated cargo into the lumen of endosomes. This highlights a major mechanism for the formation of intraluminal vesicles that will be released as exosomes.

A TRP Channel Senses Lysosome Neutralization by Pathogens to Trigger Their Expulsion

Vertebrate cells have evolved elaborate cell-autonomous defense programs to monitor subcellular compartments for infection and to evoke counter-responses. These programs are activated by pathogen-associated pattern molecules and by various strategies intracellular pathogens employ to alter cellular microenvironments. Here, we show that, when uropathogenic E. coli (UPEC) infect bladder epithelial cells (BECs), they are targeted by autophagy but avoid degradation because of their capacity to neutralize lysosomal pH. This change is detected by mucolipin TRP channel 3 (TRPML3), a transient receptor potential cation channel localized to lysosomes. TRPML3 activation then spontaneously initiates lysosome exocytosis, resulting in expulsion of exosome-encased bacteria. These studies reveal a cellular default system for lysosome homeostasis that has been co-opted by the autonomous defense program to clear recalcitrant pathogens.