This research was funded by Instituto de Salud Carlos III, Ministerio de Econom&#237;a y Competitividad, co-funded by the ESF European Social Fund and the ERDF European Regional Development Fund (MS16/00124; CP16/00124); by the PROGRAMA JUNIOR del proyecto TALENT PLUS, construyendo SALUD, generando VALOR (JUNIOR01/18), financed by the sustainable tourism tax of the Balearic Islands; by the Direcci&#243; General d&#39;Investigaci&#243;, Conselleria d&#39;Investigaci&#243;, Govern Balear (FPI/2046/2017); by the FOLIUM postdoctoral program (FOLIUM 17/01) within the FUTURMed, financed at 50% by the sustainable tourism tax of the Balearic Islands and at 50% by the ESF; and by the Comissio de Docencia i Investigacio de la Fundacio Banc de Sang i Teixits de les Illes Balears (CDI21/03).

NOTE: Cartilage explants were obtained from the IdISBa Biobank (IB 1995/12 BIO) in compliance with institutional guidelines after ethical approval of the project by the CEI-IB (IB 3656118 PI).
1. Column preparation
<ol>
	<li>Equilibrate columns following the manufacturer&#39;s instructions or as follows:
	<ol>
		<li>Remove the column cap and equilibrate the column. Remove the storage buffer by elution.</li>
		<li>Wash the column 3 times with 2.5 mL of phosphate-buffered saline (PBS). During each wash, wait for the column to absorb the whole volume. 
		&#8203;NOTE: Do not let the column dry.</li>
		<li>Cover the column with the cap after the last wash and until sample preparation.</li>
	</ol>
	</li>
</ol>
2. EV labeling
NOTE: This EV labeling protocol uses a PL-EV sample previously isolated by size exclusion chromatography (SEC) with previously described conditions21,22. However, any EV sample from any source may be used with this protocol.
<ol>
	<li>Concentrate the EV sample and the control (PBS) using a concentrating tube.
	<ol>
		<li>Place the samples in a 15 mL or 500 &#181;L concentrating tube, depending on the starting volume of the EV sample starting. Centrifuge the tubes according to the manufacturer&#39;s instructions until an almost-dry sample is obtained. 
		NOTE: The control sample is necessary to check for any dye background. Although this method does not require any specific initial volume, it should be considered that around 10% of particles will be lost during purification steps.&#160;</li>
	</ol>
	</li>
	<li>Resuspend the concentrated samples with diluent C. Resuspend EV samples with 200 &#181;L and the control group with 100 &#181;L and transfer them to new 1.5 mL centrifuge tubes.</li>
	<li>Separate the EV sample into two aliquots of 100 &#181;L. Mark one with dye and use it as treatment (PKH-PL-EV); leave the other unmarked but process it (NTA-PL-EV) like the EV sample and use it to quantify the EV concentration by NTA.</li>
	<li>Prepare 2x dye solution, resulting in 8 &#181;M PKH26 solution in diluent C.</li>
	<li>Mix 1 &#181;L of 1 mM PKH26 linker per 125 &#181;L of diluent C in the sample. Prepare a volume required to add to the samples in a 1:1 ratio.</li>
	<li>Add 2x dye solution to PKH-PL-EV and control samples in a 1:1 ratio to achieve 1x dye concentration and 4 &#181;M PKH26 concentration. Add the same volume of PBS to the NTA-PL-EV sample. Incubate for 5 min at room temperature.</li>
	<li>Add 5% bovine serum albumin-PBS solution to the samples in a 1:1 ratio and ensure that the final volume is ~400 &#181;L. 
	NOTE: This step allows the removal of nonspecific dye interactions or unbound dye.</li>
	<li>Proceed to separate the labeled EVs from the unbound dye and nonspecific interactions of the dye with the column.</li>
</ol>
3. Labeled-EV isolation
<ol>
	<li>Remove the cap from the column, add 400 &#181;L of the sample (PKH-PL-EV, NTA-PL-EV, or control), and discard all eluted liquid.</li>
	<li>Wait for the sample to enter the column completely before proceeding to the next step. Add 600 &#181;L of PBS and discard all eluted liquid.</li>
	<li>Wait for the PBS to enter the column completely before proceeding to the next step. Add 600 &#181;L of PBS and collect a fraction of 600 &#181;L in a 1.5. mL centrifuge tube (EVs or control). 
	NOTE: These steps are needed to remove the excess dye from the samples. Another separation by column is needed to obtain purer EVs. Thus, the following steps should be performed in a new equilibrated column (step 4.1.) or the same column after an initial washing step (step 4.2).</li>
	<li>Prepare the column for a new EV separation step to obtain purer EVs. If it is a new column, repeat steps 2.1. and 2.2. If it is the same column, wash the column with 2.5 mL of 20% isopropanol and then repeat steps 2.1 and 2.2.</li>
	<li>Add 600 &#181;L of previously eluted EVs obtained in step 2.5 to the column and discard the eluted volume. Wait for the liquid to enter the column completely before proceeding to the next step.</li>
	<li>Add 400 &#181;L of PBS and discard all eluted volume. Wait for the liquid to enter the column completely before proceeding to the next step.</li>
	<li>Add 600 &#181;L of PBS and collect a fraction of 600 &#181;L in a 1.5 mL centrifuge tube. Use the EVs and control samples for further analyses or store them overnight at 4 &#7506;C.</li>
	<li>Store the used columns for future use.
	<ol>
		<li>Wash the column with 25 mL of 20% isopropanol and discard the eluted volume. Wash the column 3 times with 2.5 mL of PBS.</li>
		<li>Add the storage buffer removed in step 1.1.1 and wait for the buffer to enter the column. Cover the column with the cap and store at 4 &#7506;C until subsequent use.</li>
	</ol>
	</li>
</ol>
4. EV quantification
<ol>
	<li>Prepare 1:1,000 dilutions of the NTA-PL-EV sample and the initial PL-EV sample as described by the following two steps.
	<ol>
		<li>Prepare 1 mL of 1:10 diluted NTA-PL-EV and 1 mL of 1:10 diluted initial PL-EV with PBS filtered through a 0.2 &#181;m filter.</li>
		<li>Prepare 1 mL of a 1:100 dilution of the previous diluted samples with PBS filtered through a 0.2 &#181;m filter.</li>
	</ol>
	</li>
	<li>Inject the 1:1,000 diluted NTA-PL-EV sample or the initial PL-EV sample using a sterile syringe into the NTA pump. Follow the manufacturer&#39;s instructions and recommendations for particle concentration and size distribution determination. 
	&#8203;NOTE: As EV concentration depends on the sample starter volume, it may be necessary to read intermediate dilutions and make adjustments to obtain a correct NTA determination.</li>
</ol>
5. EVs used as a treatment for inflammation-driven OA
<ol>
	<li>Wash the cartilage twice with PBS and excise it using a 3 mm diameter biopsy punch under sterile conditions. 
	NOTE: Perform the procedure from steps 5.1 to 5.6 in a cell culture hood.</li>
	<li>Place the explants in 96-well culture plates with DMEM-F12 medium supplemented with 1% penicillin-streptomycin at 37 &#7506;C, 5% CO2, and 80% humidity.
	<ol>
		<li>To establish an inflammation-driven OA model, supplement the cell culture medium with 10 ng/mL oncostatin M and 2 ng/mL tumor necrosis factor-alpha (TNF&#945;).</li>
	</ol>
	</li>
	<li>Treat the explants with 1 &#215; 109 particles/well of labeled EVs (PKH-PL-EV) or control in cell culture medium supplemented with oncostatin M and TNF&#945;. 
	NOTE: Measure the volume of the sample containing 1 &#215; 109 particles/well and use the same volume for the control.</li>
	<li>Remove the medium from the 96-well cell culture plates containing cartilage explants. Add 200 &#181;L of the cell culture medium described in step 5.3 to each well. 
	NOTE: If the 96-well plates have been in contact with fetal bovine serum (FBS), wash each well three times with 200 &#181;L of PBS to remove any EVs from the FBS.</li>
	<li>Stop the in vitro assay at different times: 0, 1, 2, 3, 4, and 5 h.</li>
	<li>Wash the cell culture wells containing the cartilage explants twice with 200 &#181;L of PBS.</li>
	<li>Add 100 &#181;L of 4% paraformaldehyde (PFA) to the tissue to fix it for 3 h at 4 &#7506;C. 
	&#8203;NOTE: Steps involving PFA should be performed in a fume hood following the Safety Data Sheet recommendations.</li>
	<li>Remove the PFA, add 100 &#181;L of PBS, store the fixed tissue at 4 &#176;C, and process the samples within 48 h.</li>
</ol>
6. Microscopy preparation and visualization
NOTE: This histological procedure consists of dehydration, paraffin embedding, and rehydration steps. These steps may reduce overall dye fluorescence (a limitation mentioned in the datasheet for PKH26). Therefore, other procedures, such as frozen sectioning, may be more suitable for EV visualization by confocal microscopy.
<ol>
	<li>Embed the fixed tissues in paraffin blocks. Cut the tissue into 6 &#181;m-thick sections.</li>
	<li>Deparaffinize the tissue sections. 
	NOTE: All steps using xylene should be performed in a fume hood.
	<ol>
		<li>Immerse the tissue sections in xylene for 30 min, 100% ethanol for 2 min, 96% ethanol for 2 min, 75% ethanol for 1 min, and finally in distilled water for 30 s.</li>
	</ol>
	</li>
	<li>Permeabilize the tissue sections.
	<ol>
		<li>Prepare a 0.1% Triton-0.1% sodium citrate solution to permeabilize the tissue. Add a 20 &#181;L drop to each tissue section and incubate for 10 min at room temperature. Wash each section twice with 20 &#181;L of PBS.</li>
	</ol>
	</li>
	<li>On a microscopic slide, add a drop of mounting medium containing 4&#8242;,6-diamidino-2-phenylindole (DAPI) with an aqueous mounting medium for preserving fluorescence. Cover the slide containing 3 tissue sections from step 6.3.1.</li>
	<li>Incubate the slides overnight at room temperature, protected from light.</li>
	<li>Store at 4 &#176;C, protected from light until confocal microscopy.</li>
</ol>

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M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Confounding+factors+in+vesicle+uptake+studies+using+fluorescent+lipophilic+membrane+dyes.">Confounding factors in vesicle uptake studies using fluorescent lipophilic membrane dyes.</a> Journal of Extracellular Vesicles. 6 (1), 1388731 (2017).</li><li>Mortati, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+study+of+extracellular+vesicles+migration+in+cartilage-derived+osteoarthritis+samples+using+real-time+quantitative+multimodal+nonlinear+optics+imaging.">In vitro study of extracellular vesicles migration in cartilage-derived osteoarthritis samples using real-time quantitative multimodal nonlinear optics imaging.</a> Pharmaceutics. 12 (8), 1-18 (2020).</li></ol>

The authors have no conflicts of interest to disclose.

EV imaging helps to understand EV properties, such as their release and uptake mechanisms. Their imaging allows the monitoring of their biodistribution and the characterization of their pharmacokinetic properties as drug vehicles. However, EV imaging and tracking may be difficult due to their small sizes, although many imaging devices and labeling techniques have been developed to help researchers monitor EVs under in vitro and in vivo conditions23,24...

Osteoarthritis (OA) is an articular degenerative disease that implies a progressive and irreversible inflammation and destruction of the extracellular matrix of the articular cartilage1. Although various forms of arthritis have numerous treatments2,3,4, these are restricted by their side effects and limited efficacy. Tissue engineering techniques using autologous chondrocyte implantation are routinely applied for the regenerative treatment of injured cartilage in early OA cartilage lesions4. Cell-based therapies are restricted mainly due to the limited number of phenotypically stable chondrocytes or chondroprogenitors capable of effectively repairing the cartilage3. Therefore, the development of new therapeutic strategies to prevent disease progression and regenerate large cartilage lesions is of paramount importance.
Extracellular vesicles (EVs) have been suggested as a treatment for OA by different authors5,6. EVs are membranous bodies secreted by the majority of cell types, are involved in intercellular signaling, and have been shown to exert stem cells&#39; therapeutic effects7,8,9, due to which they have recently elicited interest in regenerative medicine10. EVs derived from mesenchymal stromal cells (MSCs) are the main therapeutic EVs investigated for OA, although other joint-related cells have been used as EV sources, e.g., chondroprogenitors or immune cells11,12.
Platelet concentrates, such as platelet lysates (PLs), are used to enhance wound healing in different injuries, such as corneal ulcers13,14,15 or in tendon tissue regeneration16, because of the hypothesis that the EV component of platelet concentrates may be responsible for these effects17. Some studies related to joint-related diseases use platelet-derived EVs (PL-EVs) as a treatment to ameliorate osteoarthritic conditions. PL-EVs improve chondrocyte proliferation and cell migration by activating the Wnt/&#946;-catenin pathway18, promoting the expression of chondrogenic markers in osteoarthritic chondrocytes19, or showing higher levels of chondrogenic proteins and fewer tissular abnormalities in osteoarthritic rabbits treated with PL-EVs18.
EVs contain proteins, lipids, and nucleic acids that are liberated to the target cell, establishing cell-to-cell communication, which is the main feature related to their therapeutic applications20. The effects of EVs depend on their reaching cells and subsequent cargo release. This effect can be confirmed indirectly by changes caused in cells, such as metabolic activity or gene expression modification. However, these methods do not allow the visualization of how EVs reach cells to exert their function. Thus, this paper presents a method to label these PL-derived EVs to be used as a treatment for inflammation-driven OA cartilage explants. Confocal microscopy was used to monitor EV uptake and progression to the chondrocytes present in the explants in a time-lapse of 5 h.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Material</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1.5 mL Centrifuge tube</td>
			<td>SPL life sciences</td>
			<td>PLC60015</td>
			<td></td>
		</tr>
		<tr>
			<td>1 mL Syringe BD Plastipak</td>
			<td>BD</td>
			<td>303174</td>
			<td></td>
		</tr>
		<tr>
			<td>2-Propanol (Isopropanol)</td>
			<td>Panreac AppliChem</td>
			<td>1.310.901.211</td>
			<td>Prepared at 20% with Milli-Q water</td>
		</tr>
		<tr>
			<td>96-well culture plate</td>
			<td>SPL life sciences</td>
			<td>PLC30096</td>
			<td></td>
		</tr>
		<tr>
			<td>Absolute ethanol Pharmpur</td>
			<td>Scharlab</td>
			<td>ET0006005P</td>
			<td>Used to prepare 96% and 75% ethanol with Milli-Q water</td>
		</tr>
		<tr>
			<td>Biopsy Punch with plunger 3 mm</td>
			<td>Scandidact</td>
			<td>MTP-33-32</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine serum&#160;Albumin (BSA)</td>
			<td>Sigma-Aldrich</td>
			<td>A7030</td>
			<td>Prepared at 5% with PBS</td>
		</tr>
		<tr>
			<td>Cartilage explants</td>
			<td>IdISBa Biobank</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Concentrating tube 15 mL Nanosep 100 kD Omega</td>
			<td>Pall</td>
			<td>MCP100C41</td>
			<td></td>
		</tr>
		<tr>
			<td>Concentrating tube 500 &#181;L Nanosep 100 kD Omega</td>
			<td>Pall</td>
			<td>OD003C33</td>
			<td></td>
		</tr>
		<tr>
			<td>Cover glass 24 x 60 mm</td>
			<td>Deltalab</td>
			<td>D102460</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM-F12 -GlutaMAX medium</td>
			<td>Biowest</td>
			<td>L0092</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s PBS (1x)</td>
			<td>Capricorn Scientific</td>
			<td>PBS-1A</td>
			<td></td>
		</tr>
		<tr>
			<td>Embedded paraffin tissue blocks</td>
			<td>IdISBa Biobank</td>
			<td></td>
			<td>Fee for service</td>
		</tr>
		<tr>
			<td>Exo-spin mini-HD columns</td>
			<td>Cell guidance systems</td>
			<td>EX05</td>
			<td></td>
		</tr>
		<tr>
			<td>Feather S35 Microtome Blade</td>
			<td>Feather</td>
			<td>43037</td>
			<td></td>
		</tr>
		<tr>
			<td>Filtropur S 0.2 &#181;m syringe filter</td>
			<td>Sarstedt</td>
			<td>83.1826.001</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluoroshield with DAPI</td>
			<td>Sigma-Aldrich</td>
			<td>F-6057</td>
			<td></td>
		</tr>
		<tr>
			<td>Oncostatin M Human</td>
			<td>Sigma-Aldrich</td>
			<td>O9635-10UG</td>
			<td>Prepare a stock solution to a final concentration of 0.1 &#181;g/&#181;L diluten in PBS-0.1% BSA</td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Sigma-Aldrich</td>
			<td>8.18715.1000</td>
			<td>Prepared at 4% with PBS and stored at 4 &#176;C</td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin Solution 100x</td>
			<td>Biowest</td>
			<td>L0022</td>
			<td></td>
		</tr>
		<tr>
			<td>PKH26 Red Fluorescent Cell Linker Kit for General Cell Membrane Labeling</td>
			<td>Sigma-Aldrich</td>
			<td>MINI26</td>
			<td>PKH26 and Dliuent C included</td>
		</tr>
		<tr>
			<td>Sodium citrate dihydrate</td>
			<td>Scharlab</td>
			<td>SO019911000</td>
			<td></td>
		</tr>
		<tr>
			<td>Superfrost Plus Microscope Slides</td>
			<td>Thermo Scientific</td>
			<td>J1800AMNZ</td>
			<td></td>
		</tr>
		<tr>
			<td>TNF&#945;</td>
			<td>R&#38;D systems</td>
			<td>210-TA-005</td>
			<td>Prepare a stock solution to a final concentration of 0.01 &#181;g/&#181;L diluted in PBS-0.1% BSA</td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma-Aldrich</td>
			<td>T8787</td>
			<td>Used to prepare a 0.1% Triton-0.1% sodium citrate solution with Milli-Q water</td>
		</tr>
		<tr>
			<td>Xylene</td>
			<td>Scharlab</td>
			<td>XI0050005P</td>
			<td></td>
		</tr>
		<tr>
			<td>Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge 5430 R</td>
			<td>Eppendorf</td>
			<td>5428000210</td>
			<td>F-45-48-11 rotor</td>
		</tr>
		<tr>
			<td>NanoSight NS300</td>
			<td>Malvern</td>
			<td>NS300</td>
			<td>Device with embedded laser at &#955;= 532 nm and camera sCMOS</td>
		</tr>
		<tr>
			<td>Shandon Finesse 325 Manual Microtome</td>
			<td>Thermo Scientific&#8482;</td>
			<td>A78100101</td>
			<td></td>
		</tr>
		<tr>
			<td>TCS-SPE confocal microscope</td>
			<td>Leica Microsystems</td>
			<td>5200000271</td>
			<td></td>
		</tr>
	</tbody>
</table>

labeling of extracellular vesicles for monitoring migration and uptake in cartilage explants

Extracellular vesicles (EVs) are used in different studies to prove their potential as a cell-free treatment due to their cargo derived from their cellular source, such as platelet lysate (PL). When used as treatment, EVs are expected to enter the target cells and effect a response from these. In this research, PL-derived EVs have been studied as a cell-free treatment for osteoarthritis (OA). Thus, a method was set up to label EVs and test their uptake on cartilage explants. PL-derived EVs are labeled with the lipophilic dye PKH26, washed twice through a column, and then tested in an in vitro inflammation-driven&#160;OA model for 5 h after particle quantification by nanoparticle tracking analysis (NTA). Hourly, cartilage explants are fixed, paraffined, cut into 6 &#181;m sections to mount on slides, and observed under a confocal microscope. This allows verification of whether EVs enter the target cells (chondrocytes) during this period and analyze their direct effect.

A schematic overview for EV labeling and uptake monitoring is displayed in Figure 1. The particle concentration and EV size detected by NTA in Table 1 show that the EV concentration decreases during the process due to the purification step performed twice after labeling with the column. However, the amount obtained is in the optimal range of the number of particles to use for treatment. This particle concentration is used to calculate the volume of PKH-PL-EV and control that...

Watch this Scientific Journal Video about Labeling of Extracellular Vesicles for Monitoring Migration and Uptake in Cartilage Explants at JoVE.com

Labeling of Extracellular Vesicles for Monitoring Migration and Uptake in Cartilage Explants

Here, we present a protocol to label platelet lysate-derived extracellular vesicles to monitor their migration and uptake in cartilage explants used as a model for osteoarthritis.

Extracellular vesicles (EVs) are used in different studies to prove their potential as a cell-free treatment due to their cargo derived from their ...

labeling-extracellular-vesicles-for-monitoring-migration-uptake

Research

JoVE Journal

Bioengineering

2.4K Views.  University of the Balearic Islands. Here, we present a protocol to label platelet lysate-derived extracellular vesicles to monitor their migration and uptake in cartilage explants used as a model for osteoarthritis. 

Video: Labeling of Extracellular Vesicles for Monitoring Migration and Uptake in Cartilage Explants

Non-contact, Label-free Monitoring of Cells and Extracellular Matrix using Raman Spectroscopy

Non-destructive, non-contact and label-free technologies to monitor cell and tissue cultures are needed in the field of biomedical research.1-5 However, currently available routine methods require processing steps and alter sample integrity. Raman spectroscopy is a fast method that enables the measurement of biological samples without the need for further processing steps. This laser-based technology detects the inelastic scattering of monochromatic light.6 As every chemical vibration is assigned to a specific Raman band (wavenumber in cm-1), each biological sample features a typical spectral pattern due to their inherent biochemical composition.7-9 Within Raman spectra, the peak intensities correlate with the amount of the present molecular bonds.1 Similarities and differences of the spectral data sets can be detected by employing a multivariate analysis (e.g. principal component analysis (PCA)).10
Here, we perform Raman spectroscopy of living cells and native tissues. Cells are either seeded on glass bottom dishes or kept in suspension under normal cell culture conditions (37 &deg;C, 5% CO2) before measurement. Native tissues are dissected and stored in phosphate buffered saline (PBS) at 4 &deg;C prior measurements. Depending on our experimental set up, we then either focused on the cell nucleus or extracellular matrix (ECM) proteins such as elastin and collagen. For all studies, a minimum of 30 cells or 30 random points of interest within the ECM are measured. Data processing steps included background subtraction and normalization.

Raman spectroscopy is a suitable technique for the non-contact, label-free analysis of living cells, tissue-engineered constructs and native tissues. Source-specific spectral fingerprints can be generated and analyzed using multivariate analysis.

Non-destructive, non-contact and label-free technologies to monitor cell and tissue cultures are needed in the field of biomedical research.1-5 However, ...

Mass Cytometry: Protocol for Daily Tuning and Running Cell Samples on a CyTOF Mass Cytometer

In recent years, the rapid analysis of single cells has commonly been performed using flow cytometry and fluorescently-labeled antibodies. However, the issue of spectral overlap of fluorophore emissions has limited the number of simultaneous probes. In contrast, the new CyTOF mass cytometer by DVS Sciences couples a liquid single-cell introduction system to an ICP-MS.1 Rather than fluorophores, chelating polymers containing highly-enriched metal isotopes are coupled to antibodies or other specific probes.2-5 Because of the metal purity and mass resolution of the mass cytometer, there is no "spectral overlap" from neighboring isotopes, and therefore no need for compensation matrices. Additionally, due to the use of lanthanide metals, there is no biological background and therefore no equivalent of autofluorescence. With a mass window spanning atomic mass 103-203, theoretically up to 100 labels could be distinguished simultaneously. Currently, more than 35 channels are available using the chelating reagents available from DVS Sciences, allowing unprecedented dissection of the immunological profile of samples.6-7
Disadvantages to mass cytometry include the strict requirement for a separate metal isotope per probe (no equivalent of forward or side scatter), and the fact that it is a destructive technique (no possibility of sorting recovery). The current configuration of the mass cytometer also has a cell transmission rate of only ~25%, thus requiring a higher input number of cells.
Optimal daily performance of the mass cytometer requires several steps. The basic goal of the optimization is to maximize the measured signal intensity of the desired metal isotopes (M) while minimizing the formation of oxides (M+16) that will decrease the M signal intensity and interfere with any desired signal at M+16. The first step is to warm up the machine so a hot, stable ICP plasma has been established. Second, the settings for current and make-up gas flow rate must be optimized on a daily basis. During sample collection, the maximum cell event rate is limited by detector efficiency and processing speed to 1000 cells/sec. However, depending on the sample quality, a slower cell event rate (300-500 cells/sec) is usually desirable to allow better resolution between cells events and thus maximize intact singlets over doublets and debris. Finally, adequate cleaning of the machine at the end of the day helps minimize background signal due to free metal.

The steps necessary for daily tuning and optimization of the performance of a CyTOF mass cytometer are described. Comments on optimal sample preparation and flow rate are discussed

In recent years, the rapid analysis of single cells has commonly been performed using flow cytometry and fluorescently-labeled antibodies. However, the ...

Quantification and Size-profiling of Extracellular Vesicles Using Tunable Resistive Pulse Sensing

Extracellular vesicles (EVs), including &#8216;microvesicles&#8217; and &#8216;exosomes&#8217;, are highly abundant in bodily fluids. Recent years have witnessed a tremendous increase in interest in EVs. EVs have been shown to play important roles in various physiological and pathological processes, including coagulation, immune responses, and cancer. In addition, EVs have potential as therapeutic agents, for instance as drug delivery vehicles or as regenerative medicine. Because of their small size (50 to 1,000 nm) accurate quantification and size profiling of EVs is technically challenging.
This protocol describes how tunable resistive pulse sensing (tRPS) technology, using the qNano system, can be used to determine the concentration and size of EVs. The method, which relies on the detection of EVs upon their transfer through a nano sized pore, is relatively fast, suffices the use of small sample volumes and does not require the purification and concentration of EVs. Next to the regular operation protocol an alternative approach is described using samples spiked with polystyrene beads of known size and concentration. This real-time calibration technique can be used to overcome technical hurdles encountered when measuring EVs directly in biological fluids.

Extracellular vesicles play important roles in physiological and pathological processes, including coagulation, immune responses, and cancer or as potential therapeutic agents in drug delivery or regenerative medicine. This protocol presents methods for the quantification and size characterization of isolated and non-isolated extracellular vesicles in various fluids using tunable resistive pulse sensing.

Extracellular vesicles (EVs), including &#8216;microvesicles&#8217; and &#8216;exosomes&#8217;, are highly abundant in bodily fluids. Recent years have ...

Paper-based Devices for Isolation and Characterization of Extracellular Vesicles

Extracellular vesicles (EVs), membranous particles released from various types of cells, hold a great potential for clinical applications. They contain nucleic acid and protein cargo and are increasingly recognized as a means of intercellular communication utilized by both eukaryote and prokaryote cells. However, due to their small size, current protocols for isolation of EVs are often time consuming, cumbersome, and require large sample volumes and expensive equipment, such as an ultracentrifuge. To address these limitations, we developed a paper-based immunoaffinity platform for separating subgroups of EVs that is easy, efficient, and requires sample volumes as low as 10 &#956;l. Biological samples can be pipetted directly onto paper test zones that have been chemically modified with capture molecules that have high affinity to specific EV surface markers. We validate the assay by using scanning electron microscopy (SEM), paper-based enzyme-linked immunosorbent assays (P-ELISA), and transcriptome analysis. These paper-based devices will enable the study of EVs in the clinic and the research setting to help advance our understanding of EV functions in health and disease.

This protocol details a method to isolate extracellular vesicles (EVs), small membranous particles released from cells, from as little as 10 &#956;l serum samples. This approach circumvents the need for ultracentrifugation, requires only a few minutes of assay time, and enables the isolation of EVs from samples of limited volumes.

Extracellular vesicles (EVs), membranous particles released from various types of cells, hold a great potential for clinical applications. They contain ...

3D Hydrogel Scaffolds for Articular Chondrocyte Culture and Cartilage Generation

Human articular cartilage is highly susceptible to damage and has limited self-repair and regeneration potential. Cell-based strategies to engineer cartilage tissue offer a promising solution to repair articular cartilage. To select the optimal cell source for tissue repair, it is important to develop an appropriate culture platform to systematically examine the biological and biomechanical differences in the tissue-engineered cartilage by different cell sources. Here we applied a three-dimensional (3D) biomimetic hydrogel culture platform to systematically examine cartilage regeneration potential of juvenile, adult, and osteoarthritic (OA) chondrocytes. The 3D biomimetic hydrogel consisted of synthetic component poly(ethylene glycol) and bioactive component chondroitin sulfate, which provides a physiologically relevant microenvironment for in vitro culture of chondrocytes. In addition, the scaffold may be potentially used for cell delivery for cartilage repair in vivo. Cartilage tissue engineered in the scaffold can be evaluated using quantitative gene expression, immunofluorescence staining, biochemical assays, and mechanical testing. Utilizing these outcomes, we were able to characterize the differential regenerative potential of chondrocytes of varying age, both at the gene expression level and in the biochemical and biomechanical properties of the engineered cartilage tissue. The 3D culture model could be applied to investigate the molecular and functional differences among chondrocytes and progenitor cells from different stages of normal or aberrant development.

Cartilage repair represents an unmet medical challenge and cell-based approaches to engineer human articular cartilage are a promising solution. Here, we describe three-dimensional (3D) biomimetic hydrogels as an ideal tool for the expansion and maturation of human articular chondrocytes.

Human articular cartilage is highly susceptible to damage and has limited self-repair and regeneration potential. Cell-based strategies to engineer ...

3D Magnetic Stem Cell Aggregation and Bioreactor Maturation for Cartilage Regeneration

Cartilage engineering remains a challenge due to the difficulties in creating an in vitro functional implant similar to the native tissue. An approach recently explored for the development of autologous replacements involves the differentiation of stem cells into chondrocytes. To initiate this chondrogenesis, a degree of compaction of the stem cells is required; hence, we demonstrated the feasibility of magnetically condensing cells, both within thick scaffolds and scaffold-free, using miniaturized magnetic field sources as cell attractors. This magnetic approach was also used to guide aggregate fusion and to build scaffold-free, organized, three-dimensional (3D) tissues several millimeters in size. In addition to having an enhanced size, the tissue formed by magnetic-driven fusion presented a significant increase in the expression of collagen II, and a similar trend was observed for aggrecan expression. As the native cartilage was subjected to forces that influenced its 3D structure, dynamic maturation was also performed. A bioreactor that provides mechanical stimuli was used to culture the magnetically seeded scaffolds over a 21-day period. Bioreactor maturation largely improved chondrogenesis into the cellularized scaffolds; the extracellular matrix obtained under these conditions was rich in collagen II and aggrecan. This work outlines the innovative potential of magnetic condensation of labeled stem cells and dynamic maturation in a bioreactor for improved chondrogenic differentiation, both scaffold-free and within polysaccharide scaffolds.

Chondrogenesis from stem cells requires fine tuning the culture conditions. Here, we present a magnetic approach for condensing cells, an essential step to initiate chondrogenesis. In addition, we show that dynamic maturation in a bioreactor applies mechanical stimulation to the cellular constructs and enhances cartilaginous extracellular matrix production.

Cartilage engineering remains a challenge due to the difficulties in creating an in vitro functional implant similar to the native tissue. An approach ...

Comparable Decellularization of Fetal and Adult Cardiac Tissue Explants as 3D-like Platforms for In Vitro Studies

Current knowledge of extracellular matrix (ECM)-cell communication translates to large two-dimensional (2D) in vitro culture studies where ECM components are presented as a surface coating. These culture systems constitute a simplification of the complex nature of the tissue ECM that encompasses biochemical composition, structure, and mechanical properties. To better emulate the ECM-cell communication shaping the cardiac microenvironment, we developed a protocol that allows for the decellularization of the whole fetal heart and adult left ventricle tissue explants simultaneously for comparative studies. The protocol combines the use of a hypotonic buffer, a detergent of anionic surfactant properties, and DNase treatment without any requirement for specialized skills or equipment. The application of the same decellularization strategy across tissue samples from subjects of various age is an alternative approach to perform comparative studies. The present protocol allows the identification of unique structural differences across fetal and adult cardiac ECM mesh and biological cellular responses. Furthermore, the herein methodology demonstrates a broader application being successfully applied in other tissues and species with minor adjustments, such as in human intestine biopsies and mouse lung.

The cardiac extracellular matrix (ECM) is a complex network of molecules that orchestrate key processes in tissues and organs while enduring physiological remodeling throughout life. Standardized decellularization of fetal and adult hearts permits comparative experimental studies of both tissues in a 3D context by capturing native architecture and biomechanical properties.

Current knowledge of extracellular matrix (ECM)-cell communication translates to large two-dimensional (2D) in vitro culture studies where ECM components ...

Real-time Visualization and Analysis of Chondrocyte Injury Due to Mechanical Loading in Fully Intact Murine Cartilage Explants

Homeostasis of articular cartilage depends on the viability of resident cells (chondrocytes). Unfortunately, mechanical trauma can induce widespread chondrocyte death, potentially leading to irreversible breakdown of the joint and the onset of osteoarthritis. Additionally, maintenance of chondrocyte viability is important in osteochondral graft procedures for optimal surgical outcomes. We present a method to assess the spatial extent of cell injury/death on the articular surface of intact murine synovial joints after application of controlled mechanical loads or impacts. This method can be used in comparative studies to investigate the effects of different mechanical loading regimens, different environmental conditions or genetic manipulations, as well as different stages of cartilage degeneration on short- and/or long-term vulnerability of in situ articular chondrocytes. The goal of the protocol introduced in the manuscript is to assess the spatial extent of cell injury/death on the articular surface of murine synovial joints. Importantly, this method enables testing on fully intact cartilage without compromising native boundary conditions. Moreover, it allows for real-time visualization of vitally stained articular chondrocytes and single image-based analysis of cell injury induced by application of controlled static and impact loading regimens. Our representative results demonstrate that in healthy cartilage explants, the spatial extent of cell injury depends sensitively on load magnitude and impact intensity. Our method can be easily adapted to investigate the effects of different mechanical loading regimens, different environmental conditions or different genetic manipulations on the mechanical vulnerability of in situ articular chondrocytes.

We present a method to assess the spatial extent of cell injury/death on the articular surface of intact murine joints after application of controlled mechanical loads or impacts. This method can be used to investigate how osteoarthritis, genetic factors and/or different loading regimens affect the vulnerability of in situ chondrocytes.

Homeostasis of articular cartilage depends on the viability of resident cells (chondrocytes). Unfortunately, mechanical trauma can induce widespread ...

Evaluation of the Storage Stability of Extracellular Vesicles

Extracellular vesicles (EVs) are promising targets in current research, to be used as drugs, drug-carriers, and biomarkers. For their clinical development, not only their pharmaceutical activity is important but also their production needs to be evaluated. In this context, research focuses on the isolation of EVs, their characterization, and their storage. The present manuscript aims at providing a facile procedure for the assessment of the effect of different storage conditions on EVs, without genetic manipulation or specific functional assays. This makes it possible to quickly get a first impression of the stability of EVs under a given storage condition, and EVs derived from different cell sources can be compared easily. The stability measurement is based on the physicochemical parameters of the EVs (size, particle concentration, and morphology) and the preservation of the activity of their cargo. The latter is assessed by the saponin-mediated encapsulation of the enzyme beta-glucuronidase into the EVs. Glucuronidase acts as a surrogate and allows for an easy quantification via the cleavage of a fluorescent reporter molecule. The present protocol could be a tool for researchers in the search for storage conditions that optimally retain EV properties to advance EV research toward clinical application.

Here we present a readily applicable protocol to assess the storage stability of extracellular vesicles, a group of naturally occurring nanoparticles produced by cells. The vesicles are loaded with glucuronidase as a model enzyme and stored under different conditions. After storage, their physicochemical parameters and the activity of the encapsulated enzyme are evaluated.

Extracellular vesicles (EVs) are promising targets in current research, to be used as drugs, drug-carriers, and biomarkers. For their clinical ...

A Human 3D Extracellular Matrix-Adipocyte Culture Model for Studying Matrix-Cell Metabolic Crosstalk

The extracellular matrix (ECM) plays a central role in regulating tissue homeostasis, engaging in crosstalk with cells and regulating multiple aspects of cellular function. The ECM plays a particularly important role in adipose tissue function in obesity, and alterations in adipose tissue ECM deposition and composition are associated with metabolic disease in mice and humans. Tractable in vitro models that permit dissection of the roles of the ECM and cells in contributing to global tissue phenotype are sparse. We describe a novel 3D in vitro model of human ECM-adipocyte culture that permits study of the specific roles of the ECM and adipocytes in regulating adipose tissue metabolic phenotype. Human adipose tissue is decellularized to isolate ECM, which is subsequently repopulated with preadipocytes that are then differentiated within the ECM into mature adipocytes. This method creates ECM-adipocyte constructs that are metabolically active and retain characteristics of the tissues and patients from which they are derived. We have used this system to demonstrate disease-specific ECM-adipocyte crosstalk in human adipose tissue. This culture model provides a tool for dissecting the roles of the ECM and adipocytes in contributing to global adipose tissue metabolic phenotype and permits study of the role of the ECM in regulating adipose tissue homeostasis.

We describe a 3D human extracellular matrix-adipocyte in vitro culture system that permits dissection of the roles of the matrix and adipocytes in contributing to adipose tissue metabolic phenotype.

The extracellular matrix (ECM) plays a central role in regulating tissue homeostasis, engaging in crosstalk with cells and regulating multiple aspects of ...