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JoVE Journal Biology

Biology

Isolation and Analysis of Traceable and Functionalized Extracellular Vesicles from the Plasma and Solid Tissues

Published: October 17, 2022 doi: 10.3791/63990
Automatic Translation
*1,2, *1,3, 1,2, 1,4, 1,5, 1, 2, 1,6, 1
1State Key Laboratory of Military Stomatology & National Clinical Research Center for Oral Diseases & Shaanxi International Joint Research Center for Oral Diseases, Center for Tissue Engineering, School of Stomatology, The Fourth Military Medical University, 2Department of Orthodontics, School of Stomatology, The Fourth Military Medical University, 3Department of VIP Dental Care, School of Stomatology, The Fourth Military Medical University, 4School of Basic Medicine, The Fourth Military Medical University, 5College of Life Science, Northwest University, 6Xi'an Institute of Tissue Engineering and Regenerative Medicine
* These authors contributed equally

Summary

The present protocol describes a method to extract extracellular vesicles from the peripheral blood and solid tissues with subsequent profiling of surface antigens and protein cargos.

Abstract

Circulating and tissue-resident extracellular vesicles (EVs) represent promising targets as novel theranostic biomarkers, and they emerge as important players in the maintenance of organismal homeostasis and the progression of a wide spectrum of diseases. While the current research focuses on the characterization of endogenous exosomes with the endosomal origin, microvesicles blebbing from the plasma membrane have gained increasing attention in health and sickness, which are featured by an abundance of surface molecules recapitulating the membrane signature of parent cells. Here, a reproducible procedure is presented based on differential centrifugation for extracting and characterizing EVs from the plasma and solid tissues, such as the bone. The protocol further describes subsequent profiling of surface antigens and protein cargos of EVs, which are thus traceable for their derivations and identified with components related to potential function. This method will be useful for correlative, functional, and mechanistic analysis of EVs in biological, physiological, and pathological studies.

Introduction

Extracellular vesicles (EVs) have been proposed to define cell-released lipid bilayer-enclosed extracellular structures1, which play important roles in various physiological and pathological events2. EVs released by healthy cells can be broadly divided into two main categories, namely exosomes (or small EVs) formed through an intracellular endocytic trafficking pathway3 and microvesicles (or large EVs) developed by the outward budding of the plasma membrane of the cell4. While many studies focus on the function of EVs collected from cultured cells in vitro5, EVs derived from the circulation or tissues are more complex and heterogeneous, which have the advantage of reflecting the true state of the organism in vivo6. Furthermore, nearly all kinds of tissues can produce EVs in vivo, and these EVs can act as messengers within the tissue or be transferred by various body fluids, especially the peripheral blood, to facilitate systemic communication7. EVs in the circulation and tissues are also targets for disease diagnosis and treatment8.

Whereas exosomes have been intensively studied in recent years, microvesicles also have important biological functions, which can be easily extracted without ultracentrifugation, thus promoting basic and clinical research9. Notably, a critical issue regarding EVs isolated from the circulation and tissues is that they are derived from different cell types10. Since microvesicles are blebbed from the plasma membrane and featured by an abundance of cell surface molecules9, using parent cell membrane markers to identify the cellular origin of these EVs is feasible. Specifically, the flow cytometry (FC) technique can be applied to detect membrane markers. Moreover, researchers can isolate the EVs and make further analyses based on the functional cargos.

The present protocol provides a thorough procedure for extracting and characterizing EVs from in vivo samples. The EVs are isolated via differential centrifugation, and the characterization of EVs includes morphological identification via nanoparticle tracking analysis (NTA) and transmission electron microscopy (TEM), origin analysis via FC, and protein cargo analysis via western blot. The blood plasma and maxillary bone of mice are used as representatives. Researchers can refer to this protocol for EVs from other sources and make corresponding modifications.

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Protocol

The animal experiments were performed in accordance with the Guidelines of Institutional Animal Care and Use Committee of the Fourth Military Medical University and the ARRIVE guidelines. For the present study, 8-week-old C57Bl/6 mice (no preference for either females or males) were used. The steps involved in isolating plasma and tissue EVs are illustrated in Figure 1. The plasma is taken as a representative to describe the EV isolation procedure from body fluids. The maxillary bone is taken as a representative to explain the EV isolation procedure from the solid tissues.

1. Preparation of the plasma and the maxillary bone samples

  1. Prepare the plasma samples following the steps below.
    1. Determine the body weight of the mouse using a standard laboratory balance.
    2. Add 20 µL, 2 mg/mL of heparin to a 1.5 mL centrifuge tube and use the mixer device (see Table of Materials) to let the heparin attach to the wall of the tube.
      NOTE: Anticoagulation tubes can also be used directly to collect the blood.
    3. Anesthetize the mouse by intraperitoneal injection of 50 mg/kg of pentobarbital sodium (see Table of Materials). Grab the neck of the mouse with the thumb and forefinger, then fix the tail and the left hind leg with the little finger and inject the pentobarbital sodium with a 1 mL injection syringe after exposing the belly.
    4. Confirm that the mouse is properly anesthetized based on the absence of corneal reflex and limb reaction when the footpad is pinched.
    5. Shave the hair on the face and eyelashes of the eyes with curved scissors.
    6. Grab the neck skin of the mouse and press the skin around the eyes to the back of the neck so that the eyeball protrudes. Use ophthalmic tweezers to quickly clamp the eyeball, and collect the outflow of blood with the 1.5 mL centrifuge tubes prepared in step 1.1.2. Sacrifice the mouse by dislocating the cervical vertebra.
      CAUTION: Be careful with the hairs and eyelashes because they may cause hemolysis.
    7. Gently turn the tube upside down several times to prevent blood clotting.
      CAUTION: Turn the tube upside down as soon as possible.
    8. Centrifuge the blood sample for 15 min at 1,200 x g at 4 °C.
    9. Carefully transfer the supernatant to new and clean 1.5 mL centrifuge tubes, and use the plasma sample immediately or store it at 4 °C for a few hours.
    10. Dilute the supernatant with an equal volume of 1x phosphate-buffered saline (PBS) and mix well.
      ​NOTE: The protocol provided above to collect the plasma is fatal. The blood can also be collected through subclavian vein puncture11 without sacrificing the mouse.
  2. Prepare the maxillary bone samples following the steps below.
    1. Isolate the maxillary bone with ophthalmic tweezers and scissors and wash them with PBS to get rid of soft tissues with tweezers.
    2. Put the maxillary bone into 1.5 mL centrifuge tubes and cut the bone into small pieces (the size must be less than 1 mm in diameter) with scissors. Add a certain amount of Liberase (5 µg/mL, see Table of Materials) to cover the tissue (usually 1 mL for bone samples from an 8-week-old mouse), and then incubate for 30 min at 37 °C.
    3. Centrifuge the sample at 800 x g for 10 min at 4 °C.
    4. Carefully transfer the supernatant with a pipette to new and clean 1.5 mL centrifuge tubes.

2. Extraction of EVs

  1. Centrifuge the samples (prepared in step 1.1.10 and step 1.2.4) for 15 min at 2,500 x g (4 °C) to remove large cell debris and remaining platelets.
  2. Carefully transfer the supernatants to new and clean 1.5 mL centrifuge tubes and centrifuge for 30 min at 16,800 x g (4 °C).
    NOTE: The centrifugation speed can be set to over 10,000 x g to extract EVs12. The higher the speed of the centrifuge, the more quantity of EVs can be obtained. Because the speed limit of the centrifuge we used is 16,800 x g (see Table of Materials), we chose this speed in this protocol.
  3. Discard the supernatant and resuspend the pellets in each tube with 1 mL of PBS. Centrifuge for 30 min at 16,800 x g (4 °C).
  4. Discard the supernatant and resuspend the pellets in each tube with 50 µL of PBS. Store these samples at 4 °C for only less than 24 h, or preferably use immediately for the following analyses (steps 3-5).
    ​CAUTION: Storage at -80 °C is unacceptable, as this will reduce the concentration of EVs and increase the particle sizes of EVs13, thus influencing the following analysis of EVs.

3. Morphological identification of EVs

  1. Perform NTA analysis.
    1. According to the amount of EVs (roughly judged by the size of pellets, the particles of 50 µL plasma are the minimum), transfer 5-50 µL of resuspension (step 2.4), dilute in 10 mL of buffer solution (PBS filtered with 0.22 µm filter), and mix with 1 mL micro pipettor tips sufficiently. Use this final suspension for particle measurement.
    2. Use a sterile 1 mL syringe to inject at least 5 mL of distilled water with a moderate and constant speed until the number of particles displayed on the detection interface is less than five.
      NOTE: After injecting 1 mL of distilled water through the whole channel, the number of particles is directly shown on the detection interface. If the number is still over five, continue injecting 1 mL of distilled water until the criteria are met.
    3. Reconstitute 1 µL of calibration solution in 1 mL of distilled water to generate a primary solution, and then take 100 µL of the primary solution to 25 mL of distilled water to prepare a standard stock solution (1:250,000). Store this working reagent at 4 °C for 1 week.
    4. Calibrate the NTA instrument with the standard stock solution (step 3.1.3). Inject 1-5 mL of the working calibration solution with a 1 mL sterile syringe to flush the machine channel until the number of particles displayed on the detection interface is between 50-400 (preferably around 300). Run the calibration program.
    5. Repeat step 3.1.2 to flush the machine channel before each sample measurement.
    6. Use a sterile 1 mL syringe to inject at least 2 mL of buffer solution to flush the machine channel at a constant speed until the number of particles displayed on the detection interface is less than 10.
    7. Inject 1 mL of the EV sample prepared in step 3.1.1 with a moderate and constant speed (the recommended speed is 0.5-1 mL/s).
      NOTE: The optimal particle concentration is making the number of particles displayed on the detection interface range from 50-400, preferably around 300. If the number of particles is too high, repeat step 3.1.2 to flush the machine channel immediately to avoid particle retention at the channel wall and adjust the concentration of the EV sample with step 3.1.1, then repeat from step 3.1.5.
    8. Conduct the particle analysis and generate the analysis reports according to the manufacturer's instructions (see Table of Materials).
    9. If the sample is precious, pump back the EV sample with the 1 mL syringe and collect them in 1.5 mL centrifuge tubes. Repeat step 2.2 to extract the EVs.
    10. After detecting all samples, inject at least 2 mL of buffer solution to the machine channel and then inject at least 5 mL of distilled water until the number of particles displayed on the detection interface is less than five.
    11. Use a sterile 5 mL syringe to inject at least 10 mL of air at a constant speed (the recommended speed is 1 mL/s) to remove the water in the channel.
  2. Perform TEM analysis.
    NOTE: Perform the following steps with fresh EV resuspensions. The formvar-carbon coated electron microscope grid has two sides, with the working side being luminous in the center grids. The minimum volume of plasma to extract the EVs for the below procedure is 50 µL.
    1. Mix the EV sample (step 2.4) with an equal volume of 4% paraformaldehyde (PFA). Deposit 4 µL of the EVs on one grid and incubate for 15 min at room temperature (RT).
    2. Put four drops of PBS (one drop is equal to 50 µL) on a sheet of polyethylene film (see Table of Materials). Transfer the grids with clean microscopic tweezers and wash the working side of the grid in PBS from one drop to another.
    3. Use filter papers to remove extra PBS that remained in the grids.
    4. Incubate the working side of the grid into 1% phosphotungstic acid (see Table of Materials) for 2 min and then repeat step 3.2.2.
      CAUTION: Since phosphotungstic acid is poisonous, this procedure needs to be operated in the fume hood, and redundant phosphotungstic acid needs to be specifically recycled rather than discarded directly.
    5. Put the grids face up in a 10 cm dish covered with filter papers. The grids can be stored at RT for several years.
    6. Observe the grids under an electron microscope following the manufacturer's instructions (see Table of Materials).
      ​NOTE: To ensure the single particles are observed, the concentration of the EVs must be adjusted, and the suspension needs to be clear without obvious turbidity. Before dropping, the sample should be well mixed. The representative TEM and NTA analyses are shown in Figure 2.

4. Origin analysis of EVs

NOTE: The identification of the cellular origin of EVs requires the application of antibodies for typical cell membrane markers. The minimum plasma volume to extract the EVs for the below procedure is 300 µL. Based on the lipid bilayer structures of EVs, membrane dye can be used to mark them. For blood plasma samples, CD18 for lymphocytes14 is chosen for representation. For maxillary bone samples, osteoclast-associated receptor (OSCAR) for osteoclasts15 is selected as an example. Before the FC, ensure the flow cytometer is adapted to the measurement of EVs16, as the lower size limit is largely different between distinct flow cytometers.

  1. Resuspend samples (step 2.4) with 500 µL of PBS and transfer 50 µL into a new and clean 1.5 mL centrifuge tube as a blank control (tube A) and another 50 µL into a new and clean 1.5 mL centrifuge tube as a simple staining tube for FITC (tube B). Add 0.5 µL of membrane dye to the primary tube for membrane staining. Incubate for 5 min at RT.
  2. Centrifuge the primary tube for 30 min at 16,800 x g (4 °C). Discard the supernatant and resuspend the pellets with 200 µL of PBS.
  3. Divide each 50 µL sample into four 1.5 mL centrifuge tubes for simple staining tubes for PE (tube C), surface marker staining (tube D), and secondary antibody only controls (tube E).
  4. Add the primary antibody of OSCAR in bone EV samples as well as CD18 antibody in plasma EV samples (see Table of Materials) to tube B (step 4.1) and tube D (step 4.3) separately (diluted at 1:100). Incubate for 1 h at 4 °C.
  5. Centrifuge the tubes for 30 min at 16,800 x g (4 °C). Discard the supernatant, resuspend the pellets with 500 µL of PBS, and then centrifuge again for 30 min at 16,800 x g (4 °C) to remove the extra primary antibodies.
  6. Discard the supernatant and resuspend the pellets with 50 µL of PBS, followed by adding FITC-conjugated secondary antibodies (see Table of Materials), respectively (diluted at 1:200) (tube E). Add the same secondary antibodies to tube B (step 4.1) and tube D (step 4.3). Incubate all the tubes for 1 h, at 4 °C in the dark.
    NOTE: Direct fluorescence-conjugated labeling antibodies can also be used to process the FC detection with proper isotype controls.
  7. Dilute one drop of 0.2, 0.5, and 1 µm sized beads (see Table of Materials) suspension respectively into 1 mL of PBS, and run each size beads first to make sure of the gate chosen for EVs. Set the threshold of the flow cytometer to search for the beads and EV population by using a suitable forward scatter (FSC) and side scatter (SSC).
    1. Set the terminal condition as calculating 100,000 membrane-dyed particles. Analyze the sample via a flow cytometer under the manufacturer's instructions (see Table of Materials). The representative results are shown in Figure 3.
      ​NOTE: NTA equipment with fluorescence channels can also be used for origin analysis, and the sample preparation is the same as FC.

5. Protein content analysis of EVs

NOTE: The analysis of the protein content within EVs is performed via western blot. For example, the plasma and bone EVs were selected to analyze 6-phosphogluconate dehydrogenase (PGD) and pyruvate kinase M2 (PKM2) for metabolic status. Golgin84 (the Golgi organelle) was used as a negative control, and Flotillin (membrane protein), Caveolin (integral protein of caveolae), and β-actin (the cytoskeleton)17 were used as a positive control in EVs compared to cell samples. Mitofilin and α-Actinin-4 were chosen as large EV markers, while CD9 and CD81 were chosen as small EV markers to demonstrate the EV subpopulations18. Apoa1 was selected as a plasma lipoparticle marker19. For the respective reagent details, see Table of Materials.

  1. Resuspend the pellets (step 2.4) in 50 µL of RIPA lysis buffer, and incubate for 30 min on ice.
  2. Quantify the protein concentrations of all samples in the 96-well microplate by the BCA protein assay following the manufacturer's instructions (see Table of Materials).
    1. Dilute the 2 mg/mL of bovine serum albumin (BSA) with 0.9% of normal saline (NS) (containing 0.9% (w/v) of sodium chloride) into 0.5 mg/mL. Add the 0.5 mg/mL of BSA and 0.9% of NS into three duplicated wells with certain volumes, as shown in Table 1.
    2. Drop 2 µL of the samples (step 5.1) and add 18 µL of NS into three duplicated wells separately.
    3. Prepare a working solution by mixing BCA Reagent A with Reagent B (50:1 Reagent A:B). Add 200 µL of the working solution to each well and shake gently for 30 s.
    4. Incubate the 96-well microplate for 20-25 min at 37 °C.
    5. Measure the OD at 596 nm by the spectrophotometer (see Table of Materials).
    6. Export the data.
    7. Draw a standard curve and calculate the protein concentration of the samples.
  3. According to the results, dilute the samples to 1 µg/µL with 0.9% of NS and 5x SDS-PAGE loading buffer (250 mM Tris·HCl, pH 6.8, 10% SDS, 30% (v/v) Glycerol, 10 mM DTT, 0.05% (w/v) Bromophenol blue, see Table of Materials). Seal the tubes with film tightly and heat for 5 min at 100 °C.
  4. Load the samples and the protein ladder into a gradient concentration of 4%-20% Hepes-Tris gel (see Table of Materials).
    NOTE: Choose the gel percentage according to the molecular weight of the proteins of interest.
  5. Run the gel in the running buffer at 80 V until the proteins form a line, and then switch to 120 V for 1 h until the loading dye is at the bottom of the gel.
    NOTE: The run time may vary according to the equipment used or the type and concentration of the gel.
  6. Transfer the gel to the polyvinylidene fluoride (PVDF) membrane (see Table of Materials), pre-incubated in methyl alcohol for 20 s. Use a wet transfer system to transfer for 1 h at 200 mA.
    CAUTION: Ensure that there is no bubble inside the transfer system and keep the PVDF membrane wet.
    NOTE: The transfer time may vary according to the molecular weight of the target protein; 1 KD usually needs 1 min.
  7. Prepare 5% BSA blocking buffer by adding 2.5 g of BSA (see Table of Materials) in 50 mL of Tris-buffered saline-Tween (TBST) (2 mL of Tween added in 2 L of PBS solution) into a 50 mL centrifuge tube. Agitate until the powder is dissolved. Block the membranes in this buffer for 2 h at RT with agitation.
  8. Incubate the membranes with specific primary antibodies diluted with TBST into proper concentration (Mitofilin, 1:1000; α-Actinin-4, 1:1000; CD9, 1:1000; CD81, 1:1000; Apoa1, 1:1000; Golgin84, 1:1000; Flotillin-1, 1:1000; Caveolin-1, 1:1000; PGD, 1:1000; PKM2, 1:1000; β-actin, 1:3000) overnight at 4 °C.
  9. Wash the membranes in the washing buffer (2 mL of Tween added in 2 L of PBS solution) four times (15 min each time), and incubate the membranes with the suitable secondary antibodies at 1:4000 for 1 h at RT with agitation.
  10. Wash the membranes in the washing buffer four times (15 min each time), and image the membranes using the Chemiluminescence Kit and a gel imaging system (see Table of Materials).

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Representative Results

According to the experimental workflow, EVs can be extracted from the peripheral blood and solid tissues (Figure 1). The maxillary bone of a mouse aged 8 weeks is approximately 0.1 ± 0.05 g, and about 300 µL of plasma can be collected from the mouse. Following the protocol steps, 0.3 mg and 3 µg of EVs can be collected, respectively. As analyzed by TEM and NTA, the typical morphological characteristics of EVs are round cup-shaped membrane vesicles with a diameter ranging from 50-300 nm (Figure 2). FC can detect the membrane dye-labeled EVs under useful controls, and FC analysis shows the percentages of specific membrane markers expressed on EVs that implies their origin from parent cells (Figure 3). Western blot analysis shows the expression of PGD and PKM2, respectively, as a representative of protein content in plasma EVs and bone EVs, indicating the metabolic status (Figure 4). Negative expression of Golgin84 in EVs is also detected with the presence of Mitofilin, α-Actinin-4, Flotillin-1, Caveolin-1, and β-actin, which is commonly enriched in plasma membrane-derived large EVs (microvesicles). The small EV marker CD9 can also be detected, while CD81 expression is low or absent, with a lack of Apoa1 existence in the plasma EVs (Figure 4).

Figure 1
Figure 1: Illustration of the protocol to extract EVs. (A) The steps to extract peripheral blood plasma EVs with differential centrifugation. (B) The steps to extract tissue EVs with differential centrifugation. Please click here to view a larger version of this figure.

Figure 2
Figure 2: Morphological identification of EVs. (A) Representative transmission electron microscope (TEM) image displaying the morphology of EVs. Scale bar = 200 nm. (B) Representative nanoparticle tracking analysis (NTA) images and quantification results show the size distribution and particle number of EVs. Please click here to view a larger version of this figure.

Figure 3
Figure 3: Origin analysis of EVs. (A) The different sets of tubes with different controls of the experiment. (B) The distribution of 1 µm, 0.5 µm, and 0.2 µm size beads showed in the scatted graph. (C) Representative density graphs showing PBS (tube A), the simple staining of EVs (tube B), the simple staining of membrane dye (tube C), and double staining of the EV samples (tube D). (D) Flow cytometric analysis of the percentage of CD18 positive EVs in blood plasma EVs in red compared with the secondary antibody only control in black. (E) Flow cytometric analysis of the percentage of OSCAR positive EVs from bone samples in red compared with the secondary antibody only control in black. Please click here to view a larger version of this figure.

Figure 4
Figure 4: Protein content analysis of EVs. (A) Representative western blot of plasma EV images showing the presence of 6-phosphogluconate dehydrogenase (PGD) and Mitofilin, α-Actinin-4, CD9, Flotillin-1, Caveolin-1, and β-actin in plasma EVs and the negative expression of CD81, Golgin84, and Apoa1. (B) Representative western blot of bone EV images showing the presence of pyruvate kinase M2 (PKM2) and Mitofilin, α-Actinin-4, CD9, CD81, Flotillin-1, Caveolin-1, and β-actin in bone EVs and the negative expression of Golgin84. Please click here to view a larger version of this figure.

Number 1 2 3 4 5 6 7 8
BSA (µL) 0 1 2 4 8 12 16 20
NS (µL) 20 19 18 16 12 8 4 0

Table 1: Standard working solution of BCA assay. Add the 0.5 mg/mL of BSA and 0.9% of NS into three duplicated wells, as shown in the table.

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Discussion

When studying the features, the fate, and the function of EVs, it is crucial to isolate EVs with high yield and low contamination. Various methods exist to extract EVs, such as density gradient centrifugation (DGC), size-exclusion chromatography (SEC), and immunocapture assays4,20. Here, one of the most commonly used methods, differential centrifugation, was used; the advantages of this are that it is not time consuming, it generates a high yield of EVs with easy isolation from limited samples, and the ability to modify the method based on the sample source used. For analyzing the function of circulating EVs, it's better to choose the blood plasma, which can better reflect the real state of EVs in vivo, rather than the serum. This is because many platelet-derived EVs will be released during the process of clot formation for collecting serum21, while platelets are removed via centrifugation before isolation of EVs from the plasma22. It must be noted that the choice of anticoagulation for plasma EV isolation is still controversial. The anticoagulant mechanism of heparin is more closely related to physiology; the EVs isolated thus might be more reflective of the in vivo status. It must be mentioned that heparin will cause false negative PCR reads and block EV uptake by cells23,24. Other anticoagulation reagents, such as EDTA or sodium citrate, also have their shortages, including biotoxicity, affecting the chemical properties of plasma and the platelets. Collectively, given the above information, heparin is selected in this study. To remove the platelets, the samples were centrifuged at the speed of 2,500 x g before 16,800 x g, which may remove some large EVs. Additionally, considering that many EVs within the viscous plasma will attach to platelets and get removed, it is suggested to dilute the plasma with an equal volume of PBS before removing platelets through centrifugation to improve the yield of EVs. Of note, it's better to use a sucrose gradient with ultracentrifugation to purify the EVs to remove the soluble protein contaminations, such as protein polymers21.

To date, the common methods of characterizing EVs include NTA, TEM, FC16, and western blot, among others25. In addition, because of the alteration of morphology and quantity of EVs after being restored in different conditions13, we suggest processing the detection as soon as possible after extraction of the EVs. Besides, Görgens et al. have recommended to use PBS supplemented with human albumin and trehalose (PBS-HAT) for better preservation than pure PBS26. Morphological identification of EVs via NTA and TEM must be performed immediately after the extraction procedure, otherwise the shape of EVs may change27. Furthermore, Cryo-EM can be used28 for advanced morphological observation of EVs, which has the benefits of better preserving the shape with higher resolution. Besides NTA, the concentration of particles can also be quantified by FC with the help of a known amount of counting beads29, but this method is not very stable, and the sensitivity to small particles is low for FC. Moreover, because of the swarm detection of small particles with FC30, it's better to use NTA for size determinations. Similarly, the origin of EVs can also be analyzed by NTA with fluorescence filters. Compared with FC, NTA is more sensitive to smaller particles and has the potential advantage of recycling the sample for other experiments. One advantage of using FC is that the specific subtypes of EVs can be enriched with fluorochrome-conjugated membrane antibodies28. Also, the function of specific surface antigens can be studied via loss-of-function experiments, such as using neutralizing antibodies28. Alternatively, 1% Triton X-100 can be used to destroy the lipid raft of EVs membrane, thus as a control for detecting membrane signals31. Furthermore, researchers can use the specific membrane characteristics to create targeted drug carriers32.

Western blot is extensively used for analyzing the protein contents in EVs. Several markers such as Mitofilin, caveolin, and α-Actinin-418 have been recommended as candidates to identify large EVs in recent studies; CD9 is enriched in small EVs rather than in large EVs, and CD81, CD63, and Syntenin-1 are extensively abundant in small EVs18. As for the results of the Western blot, markers such as Mitofilin and CD9 are variable in different animal conditions. It can be assumed that the isolated EVs represent a mixed population, in which large EVs are one major subpopulation. To verify the purity of EVs, it is suggested that the detection of organelle/nuclear proteins, such as Lamin B or Golgin84, be added as the negative control. As for plasma EVs, according to our results, Apoa1 representing lipoparticles is not enriched in the collected EVs. One limitation of this method is that it is hard to distinguish the proteins on the surface from those within the vesicle. Therefore, enzyme-linked immunosorbent assay (ELISA) can be applied for membrane protein analysis as supplementary experiments. Moreover, with the development of high-throughput sequencing, researchers can take advantage of proteomic mapping33 to analyze the protein composition of EVs, with the target proteins also needing to be verified by western blot.

In summary, this study provides a feasible protocol to isolate and characterize circulatory and tissue EVs, including an analysis of their cell sources and protein contents, which helps to establish a basis for further functional experiments.

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Disclosures

The authors have no conflicts of interest to disclose.

Acknowledgments

This work was supported by grants from the National Natural Science Foundation of China (32000974, 81870796, 82170988, and 81930025) and the China Postdoctoral Science Foundation (2019M663986 and BX20190380). We are grateful for the assistance of the National Experimental Teaching Demonstration Center for Basic Medicine (AMFU).

Materials

Name Company Catalog Number Comments
4% paraformaldehyde  Biosharp 143174 Transmission electron microscope
Alexa fluor 488 anti-goat secondary antibody Yeason 34306ES60 Flow cytometry
Alexa fluor 488 anti-rabbit secondary antibody Invitrogen A11008 Flow cytometry
Anti-CD18 antibody Abcam ab131044 Flow cytometry
Anti-CD81 antibody Abcam ab109201 Western blot
anti-CD9 antibody Huabio ET1601-9 Western blot
Anti-Mitofilin antibody Abcam ab110329 Western blot
APOA1 Rabbit pAb Abclone A14211 Western blot
BCA protein assay kit TIANGEN PA115 Western blot
BLUeye Prestained Protein Ladder Sigma-Aldrich 94964-500UL Western blot
Bovine serum albumin MP Biomedical 218072801 Western blot
Caveolin-1 antibody Santa Cruz Biotechnology sc-53564 Western blot
CellMask Orange plasma membrane stain Invitrogen C10045 Flow cytometry
Chemiluminescence Amersham Biosciences N/A Western blot
Curved operating scissor JZ Surgical Instrument J21040 EV isolation
Electronic balance Zhi Ke ZK-DST EV isolation
Epoch spectrophotometer BioTek N/A Western blot
Eppendorf tubes Eppendorf 3810X EV isolation
Flotillin-1 antibody PTM BIO PTM-5369 Western blot
Gel imaging system Tanon 4600 Western blot
Golgin84 Novus nbp1-83352 Western blot
Grids - Formvar/Carbon Coated - Copper 200 mesh Polysciences 24915 Transmission electron microscope
Heparin Solution StemCell  7980 EV isolation
Liberase Research Grade Sigma-Aldrich 5401127001 EV isolation
Microscopic tweezer JZ Surgical Instrument JD1020 EV isolation
NovoCyte flow cytometer ACEA N/A Flow cytometry
Omni-PAGE Hepes-Tris Gels Hepes 4~20%, 10 wells Epizyme LK206 Western blot
OSCAR(D-19) antibody Santa Cruz Biotechnology SC-34235 Flow cytometry
PBS (2x) ZHHC PW013 Western blot
Pentobarbital sodium Sigma-Aldrich 57-33-0 Anesthetization
Peroxidase AffiniPure Goat Anti-Mouse IgG (H+L) Jacson 115-035-003 Western blot
Peroxidase AffiniPure Goat Anti-Rabbit IgG (H+L) Jacson 111-035-003 Western blot
Phosphotungstic acid RHAWN 12501-23-4 Transmission electron microscope
PKM2(d78a4) xp rabbit  mab  Cell Signaling 4053t Western blot
Polyethylene (PE) film Xiang yi 200150055 Transmission electron microscope
Polyvinylidene fluoride membranes  Roche 3010040001 Western blot
Protease inhibitors Roche 4693132001 Western blot
Recombinant anti-PGD antibody Abcam ab129199 Western blot
RIPA lysis buffer Beyotime P0013 Western blot
SDS-PAGE loading buffer (5x) Cwbio CW0027S Western blot
Size beads Invitrogen F13839 Flow cytometry
Tabletop High-Speed Micro Centrifuges Hitachi CT15E EV isolation
Transmission electron microscope HITACHI H-7650 Transmission electron microscope
Tween-20 MP Biomedicals 19472 Western blot
Vortex Mixer Genie Scientific Industries SI0425 EV isolation
ZetaView BASIC NTA - Nanoparticle Tracking Video Microscope PMX-120 Particle Metrix N/A Nanoparticle tracking analysis
α-Actinin-4 Rabbit mAb Abclone A3379 Western blot
β-actin Cwbio CW0096M Western blot

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References

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Isolation and Analysis of Traceable and Functionalized Extracellular Vesicles from the Plasma and Solid Tissues
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Cao, Y., Qiu, J. Y., Chen, D., Li,… More

Cao, Y., Qiu, J. Y., Chen, D., Li, C. Y., Xing, S. J., Zheng, C. X., Liu, X., Jin, Y., Sui, B. D. Isolation and Analysis of Traceable and Functionalized Extracellular Vesicles from the Plasma and Solid Tissues. J. Vis. Exp. (188), e63990, doi:10.3791/63990 (2022).

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