Coincident Fluorescence-Burst Analysis of the Loading Yields of Exosome-Mimetic Nanovesicles with Fluorescently-Labeled Cargo Molecules

The possible targeting functionality and low immunogenicity of exosomes and exosome-like nanovesicles make them promising as drug-delivery carriers. To tap into this potential, accurate non-destructive methods to load them and characterize their contents are of utmost importance. However, the small size, polydispersity, and aggregation of nanovesicles in solution make quantitative characterizations of their loading particularly challenging. Here, an ad-hoc methodology is developed based on burst analysis of dual-color confocal fluorescence microscopy experiments, suited for quantitative characterizations of exosome-like nanovesicles and of their fluorescently-labeled loading. It is applied to study exosome-mimetic nanovesicles derived from animal extracellular-vesicles and human red blood cell detergent-resistant membranes, loaded with fluorescently-tagged dUTP cargo molecules. For both classes of nanovesicles, successful loading is proved and by dual-color coincident fluorescence burst analysis, size statistics and loading yields are retrieved and quantified. The procedure affords single-vesicle characterizations well-suited for the investigation of a variety of cargo molecules and biological nanovesicle combinations besides the proof-of-principle demonstrations of this study. The results highlight a powerful characterization tool essential for optimizing the loading process and for advanced engineering of biomimetic nanovesicles for therapeutic drug delivery.

Extracellular vesicles and energy metabolism

Glycolytic enzymes are among the most frequently identified proteins in proteomics of exosomes/extracellular vesicles. This review brings up the possibility that exosomes/extracellular vesicles during their life-time in bodily fluids power important energy-consuming functions by glycolytic conversion of glucose or fructose into ATP. It was seen that prostasomes (exosomes of the prostate) could produce ATP by glycolysis and that the produced ATP quickly was consumed by adjacent prostasomal ATPases. The glycolytic ATP production appeared to be coupled to self-sustaining energy requirements. It will also be discussed how a failure in this machinery (lowered activity of ATPases) with a resultant polluting leakage of extracellular ATP could affect cancer development.

Tracing Cellular Origin of Human Exosomes Using Multiplex Proximity Extension Assays

Extracellular vesicles (EVs) are membrane-coated objects such as exosomes and microvesicles, released by many cell-types. Their presence in body fluids and the variable surface composition and content render them attractive potential biomarkers. The ability to determine their cellular origin could greatly move the field forward. We used multiplex proximity extension assays (PEA) to identify with high specificity and sensitivity the protein profiles of exosomes of different origins, including seven cell lines and two different body fluids. By comparing cells and exosomes, we successfully identified the cells originating the exosomes. Furthermore, by principal component analysis of protein patterns human milk EVs and prostasomes released from prostate acinar cells clustered with cell lines from breast and prostate tissues, respectively. Milk exosomes uniquely expressed CXCL5, MIA, and KLK6, whereas prostasomes carried NKX31, GSTP1, and SRC, highlighting that EVs originating from different origins express distinct proteins. In conclusion, PEA provides a powerful protein screening tool in exosome research, for purposes of identifying the cell source of exosomes, or new biomarkers in diseases such as cancer and inflammation.

Detecting individual extracellular vesicles using a multicolor in situ proximity ligation assay with flow cytometric readout

Flow cytometry is a powerful method for quantitative and qualitative analysis of individual cells. However, flow cytometric analysis of extracellular vesicles (EVs), and the proteins present on their surfaces has been hampered by the small size of the EVs – in particular for the smallest EVs, which can be as little as 40 nm in diameter, the limited number of antigens present, and their low refractive index. We addressed these limitations for detection and characterization of EV by flow cytometry through the use of multiplex and multicolor in situ proximity ligation assays (in situ PLA), allowing each detected EV to be easily recorded over background noise using a conventional flow cytometer. By targeting sets of proteins on the surface that are specific for distinct classes of EVs, the method allows for selective recognition of populations of EVs in samples containing more than one type of EVs. The method presented herein opens up for analyses of EVs using flow cytometry for their characterization and quantification.

Malignant cell-derived extracellular vesicles express different chromogranin epitopes compared to prostasomes

BACKGROUND

Prostasomes are nanosized extracellular vesicles exocytosed by prostate epithelial cells. They have been assigned many roles propitious to sperm in favor of fertilization. Prostatic cancer cells can also produce and secrete extracellular vesicles.

METHODS

We assessed using ELISA, the surface expression of chromogranin proproteins on prostasomes and malignant extracellular vesicles of four different prostate cancer cell-lines, two hormone sensitive and two hormone refractory. We used a panel of chromogranin A and chromogranin B antibodies against peptides in-between hypothetical cleavage sites along the proproteins.

RESULTS

A diverging pattern of chromogranin peptides was apparent when comparing prostasomes and malignant extracellular vesicles indicating a phenotypical change. We also compared western blot patterns (prostasomes and malignant extracellular vesicles) for selected antibodies that displayed high absorbances in the ELISA. Western blot analyses revealed various cleavage patterns of those proproteins that were analyzed in prostasomes and extracellular vesicles.

CONCLUSION

Chromogranins are constituents of not only prostasomes but also of malignant prostate cell-derived extracellular vesicles with different amino acid sequences exposed at the membrane surface giving rise to a mosaic pattern. These findings may be of relevance for designing new assays for detection or even possible treatment of prostate cancers.

Prostasomes from four different species are able to produce extracellular adenosine triphosphate (ATP)

BACKGROUND

Prostasomes are extracellular vesicles. Intracellularly they are enclosed by another larger vesicle, a so called "storage vesicle" equivalent to a multivesicular body of late endosomal origin. Prostasomes in their extracellular context are thought to play a crucial role in fertilization.

METHODS

Prostasomes were purified according to a well worked-out schedule from seminal plasmas obtained from human, canine, equine and bovine species. The various prostasomes were subjected to SDS-PAGE separation and protein banding patterns were compared. To gain knowledge of the prostasomal protein systems pertaining to prostasomes of four different species proteins were analyzed using a proteomic approach. An in vitro assay was employed to demonstrate ATP formation by prostasomes of different species.

RESULTS

The SDS-PAGE banding pattern of prostasomes from the four species revealed a richly faceted picture with most protein bands within the molecular weight range of 10-150kDa. Some protein bands seemed to be concordant among species although differently expressed and the number of protein bands of dog prostasomes seemed to be distinctly fewer. Special emphasis was put on proteins involved in energy metabolic turnover. Prostasomes from all four species were able to form extracellular adenosine triphosphate (ATP). ATP formation was balanced by ATPase activity linked to the four types of prostasomes.

CONCLUSION

These potencies of a possession of functional ATP-forming enzymes by different prostasome types should be regarded against the knowledge of ATP having a profound effect on cell responses and now explicitly on the success of the sperm cell to fertilize the ovum.

GENERAL SIGNIFICANCE

This study unravels energy metabolic relationships of prostasomes from four different species.

Human prostasomes express glycolytic enzymes with capacity for ATP production

Prostasomes are prostate-derived, exosome-like microvesicles that transmit signaling complexes between the acinar epithelial cells of the prostate and sperm cells. The vast majority of prostasomes have a diameter of 30-200 nm, and they are generally surrounded by a classical membrane bilayer. Using a selected proteomic approach, it became increasingly clear that prostasomes harbor distinct subsets of proteins that may be linked to adenosine triphosphate (ATP) metabolic turnover that in turn might be of importance in the role of prostasomes as auxiliary instruments in the fertilization process. Among the 21 proteins identified, most of the enzymes of anaerobic glycolysis were represented, and three of the glycolytic enzymes present are among the top 10 proteins found in most exosomes, once again linking prostasomes to the exosome family. Other prostasomal enzymes involved in ATP turnover were adenylate kinase, ATPase, 5'-nucleotidase, and hexose transporters. The identified enzymes in their prostasomal context were operational for ATP formation when supplied with substrates. The net ATP production was low due to a high prostasomal ATPase activity that could be partially inhibited by vanadate that was utilized to profile the ATP-forming ability of prostasomes. Glucose and fructose were equivalent as glycolytic substrates for prostasomal ATP formation, and the enzymes involved were apparently surface located on prostasomes, since an alternative substrate not being membrane permeable (glyceraldehyde 3-phosphate) was operative, too. There is no clear-cut function linked to this subset of prostasomal proteins, but some possible roles are discussed.

Proteomic analysis of prostate cancer metastasis-derived prostasomes

BACKGROUND

The secretory epithelial cells of the prostate gland use sophisticated vehicles in the form of prostasomes to relay important information to sperm cells in semen. This prostasome-forming and secretory ability of the epithelial cells is also preserved in poorly differentiated prostate cancer cells. The aim of the present investigation was to conduct a proteomic analysis of metastasis-derived prostasomes.

MATERIALS AND METHODS

We investigated prostasomes from vertebral metastases of prostate cancer by 2-dimensional electrophoresis and matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) protein characterization.

RESULTS

Twenty-five unique protein spots were identified by MALDI-TOF and another five proteins were determined by mass spectrometry (MS)/MS. Annexins A1, A3 and A5, as well as dimethylarginine dimethylaminohydrolase 1 were among the identified proteins. The annexins and dimethylarginine dimethylaminohydrolase 1 found in cancer-derived prostasomes can act, among others, as angiogenic factors and can increase the vascular development in the neighbourhood of the tumour.

CONCLUSION

Cancer-derived prostasomes may play an important role in the interaction between tumour cells and their environment.

Human prostasomes contain chromosomal DNA

BACKGROUND

The aim of this study was to perform a comprehensive evaluation of the occurrence of DNA in human prostasomes.

METHODS

Prostasomes were purified from seminal fluid (seminal prostasomes) and from PC-3-cells (PC-3 cell prostasomes). DNA extracted from both sources of prostasomes was visualized on agarose gels. Further, the DNA was cloned and sequenced (13 clones from seminal prostasomal DNA and 16 clones from PC-3 cell prostasomal DNA) and identified by alignment in the BLAST-nucleotide search database. In order to decide if the DNA was internally or externally located in/on prostasomes, prostasomes were treated with nuclease (DNase) and A(260) was measured before and after treatment. Additionally, flow cytometric studies were performed with membrane permeable and membrane impermeable DNA stains.

RESULTS

We identified human chromosomal DNA in purified prostasomes from both sources and treatment with DNase demonstrated that the prostasome-shielded DNA was protected from enzyme attack. Membrane-permeable DNA stain raised the fluorescence contrary to membrane-impermeable stain. Clearly discernible nucleic acid of prostasomes was separated on 1% agarose gel yielding DNA fragments of about 13 kbp and below with a marked band at about 1 kbp. Cloning and sequencing of 13 fragments from seminal prostasomes and 16 from PC-3 cell prostasomes revealed a chromosomal origin of the DNA. In purified seminal prostasomes, 4 out of 13 DNA clones featured gene sequences (31%). The corresponding figure for PC3-derived prostasomes was 4 out of 16 clones featuring gene sequences (25%).

CONCLUSION

Human prostasomes contain chromosomal DNA. Both nuclease treatment and differential DNA stainings indicated an inside location of the prostasomal DNA. Our findings suggest a DNA-delivery function of prostasomes to sperm cells.

Serum antibodies against prostasomal clusterin in prostate cancer patients

OBJECTIVE

Clusterin is a ubiquitous secretory sulphated glycoprotein present in prostasomes. It is an anti-apoptotic mediator in prostate cancer and is among the most frequently occurring prostasomal proteins immunogenic in prostate cancer patients. The aim of the present study was to investigate the occurrence of anti-clusterin antibodies in the serum of patients with prostate cancer and whether there is a relationship between anti-clusterin antibody titres and other clinico-pathological variables.

MATERIAL AND METHODS

Serum samples were collected from 391 consecutive patients with suspected prostate cancer (150 benign prostate and 241 prostate cancer). The patients' serum samples were used in an ELISA where microtitre wells were coated with purified clusterin from serum of a healthy volunteer. Flow cytometric studies of clusterin and prostasomes were performed.

RESULTS

Flow cytometric analyses revealed the presence of clusterin on the surface of seminal prostasomes. Anti-clusterin ELISA titres in sera of patients did not differ significantly from those of a control group. A significant "inverse" correlation existed between anti-clusterin ELISA titres and lymph node metastases (p = 0.047), but only 11 out of 161 patients had metastases. These titres correlated significantly with total prostate (p = 0.021) and transitional zone (p = 0.015) volumes of the patients.

CONCLUSIONS

The correlation between serum anti-clusterin antibody titres and other clinico-pathological variables was generally weak in prostate cancer patients, although clusterin has been assigned an important role in tumourigenesis and progression of prostate cancer. However, the anti-clusterin antibody titre appeared to be related to prostate volume, correlating to both transitional zone volume and total volume of the prostate.