Proteomic Profiling of Two Distinct Populations of Extracellular Vesicles Isolated from Human Seminal Plasma.

Body fluids contain many populations of extracellular vesicles (EV) that differ in size, cellular origin, molecular composition, and biological activities. EV in seminal plasma are in majority originating from prostate epithelial cells, and hence are also referred to as prostasomes. Nevertheless, EV are also contributed by other accessory sex glands, as well as by the testis and epididymis. In a previous study, we isolated EV from seminal plasma of vasectomized men, thereby excluding contributions from the testis and epididymis, and identified two distinct EV populations with diameters of 50 and 100 nm, respectively. In the current study, we comprehensively analyzed the protein composition of these two EV populations using quantitative Liquid Chromatography-Mass Spectrometry (LC-MS/MS). In total 1558 proteins were identified. Of these, ≈45% was found only in the isolated 100 nm EV, 1% only in the isolated 50 nm EV, and 54% in both 100 nm and 50 nm EV. Gene ontology (GO) enrichment analysis suggest that both originate from the prostate, but with distinct biogenesis pathways. Finally, nine proteins, including KLK3, KLK2, MSMB, NEFH, PSCA, PABPC1, TGM4, ALOX15B, and ANO7, with known prostate specific expression and alternate expression levels in prostate cancer tissue were identified. These data have potential for the discovery of EV associated prostate cancer biomarkers in blood.

A novel three step protocol to isolate extracellular vesicles from plasma or cell culture medium with both high yield and purity.

Extracellular vesicles (EV) are membrane encapsulated nanoparticles that can function in intercellular communication, and their presence in biofluids can be indicative for (patho)physiological conditions. Studies aiming to resolve functionalities of EV or to discover EV-associated biomarkers for disease in liquid biopsies are hampered by limitations of current protocols to isolate EV from biofluids or cell culture medium. EV isolation is complicated by the >105-fold numerical excess of other types of particles, including lipoproteins and protein complexes. In addition to persisting contaminants, currently available EV isolation methods may suffer from inefficient EV recovery, bias for EV subtypes, interference with the integrity of EV membranes, and loss of EV functionality. In this study, we established a novel three-step non-selective method to isolate EV from blood or cell culture media with both high yield and purity, resulting in 71% recovery and near to complete elimination of unrelated (lipo)proteins. This EV isolation procedure is independent of ill-defined commercial kits, and apart from an ultracentrifuge, does not require specialised expensive equipment.

Bystander T-Cells Support Clonal T-Cell Activation by Controlling the Release of Dendritic Cell-Derived Immune-Stimulatory Extracellular Vesicles.

Extracellular vesicles (EV) that are released by immune cells are studied intensively for their functions in immune regulation and are scrutinized for their potential in human immunotherapy, for example against cancer. In our search for signals that stimulate the release of functional EV by dendritic cells we observed that LPS-activated human monocyte-derived dendritic cells (moDC) changed their morphological characteristics upon contact with non-cognate activated bystander T-cells, while non-activated bystander T-cells had no effect. Exposure to activated bystander T-cells also stimulated the release of EV-associated proteins by moDC, particularly CD63, and ICAM-1, although the extent of stimulation varied between individual donors. Stimulation of moDC with activated bystander T-cells also increased the release of EV-associated miR155, which is a known central modulator of T-cell responses. Functionally, we observed that EV from moDC that were licensed by activated bystander T-cells exhibited a capacity for antigen-specific T-cell activation. Taken together, these results suggest that non-cognatei interactions between DC and bystander T-cells modulates third party antigen-specific T-cell responses via EV.

Antigen Presentation by Extracellular Vesicles from Professional Antigen-Presenting Cells.

The initiation and maintenance of adaptive immunity require multifaceted modes of communication between different types of immune cells, including direct intercellular contact, secreted soluble signaling molecules, and extracellular vesicles (EVs). EVs can be formed as microvesicles directly pinched off from the plasma membrane or as exosomes secreted by multivesicular endosomes. Membrane receptors guide EVs to specific target cells, allowing directional transfer of specific and complex signaling cues. EVs are released by most, if not all, immune cells. Depending on the type and status of their originating cell, EVs may facilitate the initiation, expansion, maintenance, or silencing of adaptive immune responses. This review focusses on EVs from professional antigen-presenting cells, their demonstrated and speculated roles, and their potential for cancer immunotherapy.

Prostasomes as a source of diagnostic biomarkers for prostate cancer.

New biomarkers are needed to improve the diagnosis of prostate cancer. Similarly to healthy cells, prostate epithelial cancer cells produce extracellular vesicles (prostasomes) that can be isolated from seminal fluid, urine, and blood. Prostasomes contain ubiquitously expressed and prostate-specific membrane and cytosolic proteins, as well as RNA. Both quantitative and qualitative changes in protein, mRNA, long noncoding RNA, and microRNA composition of extracellular vesicles isolated from prostate cancer patients have been reported. In general, however, the identified extracellular vesicle-associated single-marker molecules or combinations of marker molecules require confirmation in large cohorts of patients to validate their specificity and sensitivity as prostate cancer markers. Complications include variable factors such as prostate manipulation and urine flux, as well as masking by ubiquitously expressed free molecules and extracellular vesicles from tissues other than the prostate. Herein, we propose that the most promising methods include comprehensive combinational screening for (mutant) RNA in prostasomes that are immunoisolated with antibodies targeting prostate-specific epitopes.

Resolving sorting mechanisms into exosomes.

The complexity of mechanisms driving protein sorting into exosomes is only beginning to emerge. In a paper recently published in Cell Research, Roucourt et al. report that trimming of heparan sulfate side chains of syndecans by endosomal heparanase facilitates sorting into exosomes by the formation of tight syndecan clusters that are recruited by the multivalent adaptor syntenin to the ALIX-ESCRT sorting machinery at endosomes.

Prostasomes: extracellular vesicles from the prostate.

The term 'prostasomes' is generally used to classify the extracellular vesicles (EVs) released into prostatic fluid by prostate epithelial cells. However, other epithelia within the male reproductive tract also release EVs that mix with 'true' prostasomes during semen emission or ejaculation. Prostasomes have been proposed to regulate the timing of sperm cell capacitation and induction of the acrosome reaction, as well as to stimulate sperm motility where all three are prerequisite processes for spermatozoa to attain fertilising capacity. Other proposed functions of prostasomes include interfering with the destruction of spermatozoa by immune cells within the female reproductive tract. On the other hand, it is unclear whether the distinct presumed functions are performed collectively by a single type of prostasome or by separate distinct sub-populations of EVs. Moreover, the exact molecular mechanisms through which prostasomes exert their functions have not been fully resolved. Besides their physiological functions, prostasomes produced by prostate tumour cells have been suggested to support prostate cancer spread development, and prostasomes in peripheral blood plasma may prove to be valuable biomarkers for prostate cancer.

MHC class II antigen presentation by dendritic cells regulated through endosomal sorting.

For the initiation of adaptive immune responses, dendritic cells present antigenic peptides in association with major histocompatibility complex class II (MHCII) to naïve CD4(+) T lymphocytes. In this review, we discuss how antigen presentation is regulated through intracellular processing and trafficking of MHCII. Newly synthesized MHCII is chaperoned by the invariant chain to endosomes, where peptides from endocytosed pathogens can bind. In nonactivated dendritic cells, peptide-loaded MHCII is ubiquitinated and consequently sorted by the ESCRT machinery to intraluminal vesicles of multivesicular bodies, ultimately leading to lysosomal degradation. Ubiquitination of newly synthesized MHCII is blocked when dendritic cells are activated, now allowing its transfer to the cell surface. This mode of regulation for MHCII is a prime example of how molecular processing and sorting at multivesicular bodies can determine the expression of signaling receptors at the plasma membrane.

Endothelial cells require miR-214 to secrete exosomes that suppress senescence and induce angiogenesis in human and mouse endothelial cells.

Signaling between endothelial cells, endothelial progenitor cells, and stromal cells is crucial for the establishment and maintenance of vascular integrity and involves exosomes, among other signaling pathways. Exosomes are important mediators of intercellular communication in immune signaling, tumor survival, stress responses, and angiogenesis. The ability of exosomes to incorporate and transfer messenger RNAs (mRNAs) encoding for "acquired" proteins or micro RNAs (miRNAs) repressing "resident" mRNA translation suggests that they can influence the physiological behavior of recipient cells. We demonstrate that miR-214, an miRNA that controls endothelial cell function and angiogenesis, plays a dominant role in exosome-mediated signaling between endothelial cells. Endothelial cell-derived exosomes stimulated migration and angiogenesis in recipient cells, whereas exosomes from miR-214-depleted endothelial cells failed to stimulate these processes. Exosomes containing miR-214 repressed the expression of ataxia telangiectasia mutated in recipient cells, thereby preventing senescence and allowing blood vessel formation. Concordantly, specific reduction of miR-214 content in exosome-producing endothelial cells abolishes the angiogenesis stimulatory function of the resulting exosomes. Collectively, our data indicate that endothelial cells release miR-214-containing exosomes to stimulate angiogenesis through the silencing of ataxia telangiectasia mutated in neighboring target cells.

Extracellular vesicles: exosomes, microvesicles, and friends.

Cells release into the extracellular environment diverse types of membrane vesicles of endosomal and plasma membrane origin called exosomes and microvesicles, respectively. These extracellular vesicles (EVs) represent an important mode of intercellular communication by serving as vehicles for transfer between cells of membrane and cytosolic proteins, lipids, and RNA. Deficiencies in our knowledge of the molecular mechanisms for EV formation and lack of methods to interfere with the packaging of cargo or with vesicle release, however, still hamper identification of their physiological relevance in vivo. In this review, we focus on the characterization of EVs and on currently proposed mechanisms for their formation, targeting, and function.

Distinct lipid compositions of two types of human prostasomes.

Prostasomes are vesicles secreted by prostate epithelial cells and found in abundance in seminal plasma. They regulate aspects of sperm cell function and are also thought to prevent immune-mediated destruction of sperm cells within the female reproductive tract. In a previous study, we isolated two distinct populations of prostasomes, differing both in size and protein composition, from the seminal fluid of vasectomized men. In the current study, we characterized the lipid content of these two prostasome populations. Both prostasome types had an unusual lipid composition, with high levels of sphingomyelin (SM), cholesterol, and glycosphingolipids at the expense of, in particular, phosphatidylcholine. The different classes of glycerophospholipids consisted mainly of mono-unsaturated species. The sphingosine-based lipids, SM and the hexosylceramides, were characterized by a near absence of unsaturated species. The two types of prostasome differed in lipid composition, particularly with regard to the relative contributions of SM and hexosylceramides. Potential implications of the lipid compositions of prostasomes for the mechanisms of their formation and function are discussed.

Spermatozoa recruit prostasomes in response to capacitation induction.

Seminal plasma contains various types of extracellular vesicles, including 'prostasomes'. Prostasomes are small vesicles secreted by prostatic epithelial cells that can be recruited by and fuse with sperm cells in response of progesterone that is released by oocyte surrounding cumulus cells. This delivers Ca(2+) signaling tools that allow the sperm cell to gain hypermotility and undergo the acrosome reaction. Conditions for binding of prostasomes to sperm cells are however unclear. We found that classically used prostasome markers are in fact heterogeneously expressed on distinct populations of small and large vesicles in seminal plasma. To study interactions between prostasomes and spermatozoa we used the stallion as a model organism. A homogeneous population of ~60nm prostasomes was first separated from larger vesicles and labeled with biotin. Binding of biotinylated prostasomes to individual live spermatozoa was then monitored by flow cytometry. Contrary to assumptions in the literature, we found that such highly purified prostasomes bound to live sperm only after capacitation had been initiated, and specifically at pH ≥7.5. Using fluorescence microscopy, we observed that prostasomes bound primarily to the head of live sperm. We propose that in vivo, prostasomes may bind to sperm cells in the uterus, to be carried in association with sperm cells into oviduct and to fuse with the sperm cell only during the final approach of the oocyte. This article is part of a Special Issue entitled: An Updated Secretome.

Dynamics of dendritic cell-derived vesicles: high-resolution flow cytometric analysis of extracellular vesicle quantity and quality.

Nano-sized membrane vesicles are secreted by many cell types. These vesicles can serve as carriers of cellular information. DC-derived vesicles can be targeted to other immune cells and modify their function. Accurate analysis of quantitative and qualitative changes in EV production by DC upon different activation stimuli is needed to further reveal the immune regulatory properties of DC-derived EVs. However, methods for reliable quantification of individual EVs and for analysis of the heterogeneity of EV populations are limited. With our recently developed high-resolution flow cytometry-based method, we can perform a high-throughput, multiparameter, and quantitative analysis of individual EVs. With the use of this novel technique, we show that despite previous assumptions, stimulation with bacterial LPS increases EV release by DC. Furthermore, we demonstrate heterogeneity in DC-derived EVs regarding their buoyant density and MHC class II content. Finally, we show that cognate interaction between LPS-stimulated DC and CD4(+) T cells affects both the quantity and quality of LPS DC-derived EVs present in the culture supernatant. These data indicate that flow cytometry-based analysis of individual EVs is a valuable, novel tool to study the dynamics of EV secretion and composition, offering great opportunities to unveil the function of immune cell-derived EVs.

Vesiclepedia: a compendium for extracellular vesicles with continuous community annotation.

Extracellular vesicles (EVs) are membraneous vesicles released by a variety of cells into their microenvironment. Recent studies have elucidated the role of EVs in intercellular communication, pathogenesis, drug, vaccine and gene-vector delivery, and as possible reservoirs of biomarkers. These findings have generated immense interest, along with an exponential increase in molecular data pertaining to EVs. Here, we describe Vesiclepedia, a manually curated compendium of molecular data (lipid, RNA, and protein) identified in different classes of EVs from more than 300 independent studies published over the past several years. Even though databases are indispensable resources for the scientific community, recent studies have shown that more than 50% of the databases are not regularly updated. In addition, more than 20% of the database links are inactive. To prevent such database and link decay, we have initiated a continuous community annotation project with the active involvement of EV researchers. The EV research community can set a gold standard in data sharing with Vesiclepedia, which could evolve as a primary resource for the field.

Deep sequencing of RNA from immune cell-derived vesicles uncovers the selective incorporation of small non-coding RNA biotypes with potential regulatory functions.

Cells release RNA-carrying vesicles and membrane-free RNA/protein complexes into the extracellular milieu. Horizontal vesicle-mediated transfer of such shuttle RNA between cells allows dissemination of genetically encoded messages, which may modify the function of target cells. Other studies used array analysis to establish the presence of microRNAs and mRNA in cell-derived vesicles from many sources. Here, we used an unbiased approach by deep sequencing of small RNA released by immune cells. We found a large variety of small non-coding RNA species representing pervasive transcripts or RNA cleavage products overlapping with protein coding regions, repeat sequences or structural RNAs. Many of these RNAs were enriched relative to cellular RNA, indicating that cells destine specific RNAs for extracellular release. Among the most abundant small RNAs in shuttle RNA were sequences derived from vault RNA, Y-RNA and specific tRNAs. Many of the highly abundant small non-coding transcripts in shuttle RNA are evolutionary well-conserved and have previously been associated to gene regulatory functions. These findings allude to a wider range of biological effects that could be mediated by shuttle RNA than previously expected. Moreover, the data present leads for unraveling how cells modify the function of other cells via transfer of specific non-coding RNA species.

Fluorescent labeling of nano-sized vesicles released by cells and subsequent quantitative and qualitative analysis by high-resolution flow cytometry.

We provide a protocol for a high-resolution flow cytometry-based method for quantitative and qualitative analysis of individual nano-sized vesicles released by cells, as developed and previously described by our group. The method involves (i) bright fluorescent labeling of cell-derived vesicles and (ii) flow cytometric analysis of these vesicles using an optimized configuration of the commercially available BD Influx flow cytometer. The method allows the detection and analysis of fluorescent cell-derived vesicles of ∼100 nm. Integrated information can be obtained regarding the light scattering, quantity, buoyant density and surface proteins of these nano-sized vesicles. This method can be applied in nanobiology to study basic aspects of cell-derived vesicles. Potential clinical applications include the detailed analysis of vesicle-based biomarkers in body fluids and quality control analysis of (biological) vesicles used as therapeutic agents. Isolation, fluorescent labeling and purification of vesicles can be done within 24 h. Flow cytometer setup, calibration and subsequent data acquisition can be done within 2-4 h by an experienced flow cytometer operator.

Quantitative and qualitative flow cytometric analysis of nanosized cell-derived membrane vesicles.

Nanosized cell-derived membrane vesicles are increasingly recognized as therapeutic vehicles and high-potential biomarkers for several diseases. Currently available methods allow bulk analysis of vesicles but are not suited for accurate quantification and fail to reveal phenotypic heterogeneity in membrane vesicle populations. For such analyses, single vesicle-based, multiparameter, high-throughput methods are needed. We developed a fluorescence-based, high-resolution flow cytometric method for quantitative and qualitative analysis of nanosized membrane vesicles. Proof of principle was obtained by single-particle analysis of virions and liposomes. Further validation was obtained by quantification of cell-derived nanosized membrane vesicles from cell cultures and body fluids. An important aspect was that the technology was extended to detect specific proteins on individual vesicles. This allowed identification of exosome subsets and phenotyping of individual exosomes produced by dendritic cells (DCs) undergoing different modes of activation. The described technology allows quantitative, multiparameter, and high-throughput analysis of a wide variety of nanosized particles and has broad applications. FROM THE CLINICAL EDITOR: The authors developed a fluorescence-based, high-resolution flow cytometric method for quantitative and qualitative analysis of nanosized cell-derived membrane vesicles that are increasingly recognized both as therapeutic vehicles and high-potential biomarkers for several diseases. A high throughput, easily available, and sensitive detection method such as the one discussed here is a critically important prerequisite for further refinements of this technology.

Identification of distinct populations of prostasomes that differentially express prostate stem cell antigen, annexin A1, and GLIPR2 in humans.

In addition to sperm cells, seminal fluid contains various small membranous vesicles. These include prostasomes, membrane vesicles secreted by prostate epithelial cells. Prostasomes have been proposed to perform a variety of functions, including modulation of (immune) cell activity within the female reproductive tract and stimulation of sperm motility and capacitation. How prostasomes mediate such diverse functions, however, remains unclear. In many studies, vesicles from the seminal plasma have been categorized collectively as a single population of prostasomes; in fact, they more likely represent a heterogeneous mixture of vesicles produced by different reproductive glands and secretory mechanisms. We here characterized membranous vesicles from seminal fluid obtained from vasectomized men, thereby excluding material from the testes or epididymides. Two distinct populations of vesicles with characteristic sizes (56 ± 13 nm vs. 105 ± 25 nm) but similar equilibrium buoyant density (∼1.15 g/ml) could be separated by using the distinct rates with which they floated into sucrose gradients. Both types of vesicle resembled exosomes in terms of their buoyant density, size, and the presence of the ubiquitous exosome marker CD9. The protein GLIPR2 was found to be specifically enriched in the lumen of the smaller vesicles, while annexin A1 was uniquely associated with the surface of the larger vesicles. Prostate stem-cell antigen (PSCA), a prostate-specific protein, was present on both populations, thereby confirming their origin. PSCA was, however, absent from membrane vesicles in the seminal fluid of some donors, indicating heterogeneity of prostasome characteristics between individuals.