Alessandra d&#8217;Azzo holds the Jewelers for Children (JFC) Endowed Chair in Genetics and Gene Therapy. This work was supported in part by NIH grants R01GM104981, RO1DK095169, and CA021764, the Assisi Foundation of Memphis, and the American Lebanese Syrian Associated Charities.

All procedures in mice were performed according to animal protocols approved by the St. Jude Children&#8217;s Research Hospital Institutional Animal Care and Use Committee and National Institutes of Health guidelines.
1. Preparation of solutions and media
<ol>
	<li>Prepare digestion solution by mixing 15.4 mL of PBS with 2.5 mL of 20 mg/mL collagenase P (5 mg/mL final concentration), 2 mL of 11 U/mL dispase II (1.2 U/mL final concentration), and 100 &#181;L of 1.0 M CaCl2 (5 mM final concentration).</li>
	<li>Prepare 500 mL of primary fibroblasts medium (DMEM complete) by mixing 440 mL of DMEM with 50 mL of FBS (10%), 5.0 mL of pen/strep (100 U/mL and 100 &#181;g/mL, respectively) and 5.0 mL of glutamine supplement (2 mM). Filter-sterilize the medium with a 0.22 &#181;m pore size vacuum filter.</li>
	<li>Prepare exosome-free serum by overnight ultracentrifugation of FBS in 38.5 mL polypropylene tubes at 100,000 x g at 4 &#176;C and transfer the supernatant to a new tube.</li>
	<li>Prepare 500 mL of exosome-free medium by mixing 440 mL of DMEM with 50 mL of exosome-free serum (10%), 5 mL of pen/strep (100 U/mL and 100 &#181;g/mL), and 5 mL of glutamine supplement (2 mM). Filter-sterilize the medium with a 0.22 &#181;m pore size vacuum filter.</li>
	<li>Prepare 0.5 M Tris-HCl (pH 7.4) by dissolving 6.057 g of Tris base in 90 mL of dH2O and adjusting the pH to 7.4 with HCl. Adjust the volume to 100 mL with dH2O.</li>
	<li>Prepare 10 mM Tris-HCl (pH 7.4)/1 mM Mg(Ac)2 solution (sucrose working solution) by mixing 97.9 mL of dH2O with 2 mL of 0.5 M Tris-HCl (pH = 7.4) and 100 &#181;L of 1 M Mg(Ac)2. Add protease inhibitors to the solution just before use and keep the solution on ice.</li>
	<li>Prepare sucrose density gradient solutions on ice according to Table 1. These solutions are sufficient to prepare two sucrose gradient tubes.</li>
	<li>Prepare 100% TCA by adding 40 mL of dH2O to 100 g of TCA powder and mix until fully dissolved. Adjust the final volume with dH2O to 100 mL.</li>
	<li>Prepare 80% ethanol by mixing 20 mL of dH2O with 80 mL of 100% ethanol.</li>
	<li>Prepare western blot running buffer by mixing 1.8 L of dH2O with 200 mL of 10x running buffer.</li>
	<li>Prepare western blot transfer buffer by mixing 1.4 L of dH2O with 200 mL of 10x transfer buffer and 400 mL of methanol. Precool the transfer buffer to 4 &#176;C.</li>
	<li>Prepare 20x Tris-buffered saline (TBS) by dissolving 122 g of Tris base and 180 g of sodium chloride in 850 mL of dH2O (pH 8.0). Adjust the volume to 1 L with dH2O.</li>
	<li>Prepare blocking buffer by dissolving 5 g of nonfat dry milk with 1 mL of 10% Tween-20, 5 mL of 20x TBS, and 94 mL of dH2O.</li>
	<li>Prepare antibody buffer by dissolving 3 g of BSA with 1 mL of 10% Tween-20, 5 mL of 20x TBS, and 94 mL of dH2O.</li>
	<li>Prepare washing buffer by mixing 100 mL of 20x TBS and 20 mL of 10% Tween-20 (10x) with 1.88 L of dH2O.</li>
	<li>Prepare developing solution by mixing 1 volume of luminol/enhance with 1 volume of stable peroxide buffer.</li>
</ol>
2. Dissection of gastrocnemius (GA) mouse muscle15,16
<ol>
	<li>Prepare 50 mL tubes containing 10 mL PBS on ice.</li>
	<li>Euthanize the mice in a CO2 chamber followed by cervical dislocation.</li>
	<li>Remove the gastrocnemius muscle from both legs and transfer them to the tube with PBS on ice. 
	NOTE: Remove the soleus muscle from the GA muscle before transferring the GA muscle to PBS.</li>
</ol>
3. Mouse primary fibroblast isolation and culture
<ol>
	<li>Weigh the muscles and transfer them to a 10 cm dish under a biosafety hood. Mince the muscles with scalpels until it becomes a fine paste.</li>
	<li>Transfer the finely minced muscle paste to a 50 mL tube and add 3.5x volume/mg tissue of digestion solution to the tube and incubate for 45 min at 37 &#176;C. Mix the suspension thoroughly with a 5 mL pipet every 10 min (this will aid in complete dissociation). 
	NOTE: Alternatively, a tissue dissociator can be used for this step.</li>
	<li>Add 20 mL of DMEM complete to the cell suspension to inactivate the digestion solution. Transfer to a 70 &#181;m nylon cell strainer placed on a 50 mL tube. Collect the flow-through and wash the cell strainer with an additional 5 mL of DMEM complete.</li>
	<li>Centrifuge the cell suspension at 300 x g at room temperature (RT) for 10 min and carefully remove the supernatant.</li>
	<li>Resuspend the pellet in 10 mL of DMEM complete and seed the cells into a 10 cm dish.</li>
	<li>Culture the cells at 37 &#176;C, 5% CO2, 3% O2 (passage 0 or P0). 
	NOTE: 1) These cultures need to be maintained at a low oxygen level to ensure physiological-like conditions (O2 level in skeletal muscle is around 2.5%)17. 2) The passage number (e.g., P0) of a cell culture is a record of the number of times the culture has been subcultured. 3) Primary fibroblasts at P0 are routinely cultured until 100% confluency plus 1 day (and only for P0). This is to purge other types of cells and assure that the cells present in the culture are only fibroblasts, depleted of myogenic cells based on microscope examination. The skeletal muscle from an adult animal at 2 months of age contains about 2% myogenic progenitors4. In addition, myogenic progenitors usually do not attach to the uncoated dishes; therefore, they are lost during subculturing18,19,20. Myogenic cells require a different medium (F10) supplemented with 20% FBS and basic fibroblast growth factor (bFGF)18. In DMEM complete, medium fibroblasts have a higher proliferation rate than the myogenic cells, which results in the elimination of these contaminating cells before the first passage.</li>
	<li>Rinse the P0 cells with PBS when 100% confluent plus 1 day. Add 1 mL of trypsinization solution and incubate at 37 &#176;C, 5% CO2, 3% O2 to detach the cells. Stop the enzymatic activity by using 10 mL of DMEM complete.</li>
	<li>Centrifuge the cells at 300 x g for 10 min at RT and resuspend the pellet in 20 mL of DMEM complete and seed into a 15 cm dish (passage 1 or P1). The cells are grown until 80%&#8211;90% confluency and can be expanded until passage 3. 
	NOTE: Depending on the downstream experiments passage 1, passage 2 (P2) or passage 3 (P3) can be used.</li>
</ol>
4. Seeding of cells and collection of conditioned medium
<ol>
	<li>Wash the fibroblasts (P1, P2, or P3) with 10 mL of PBS, add 2.5 mL of trypsinization solution to the cells and incubate at 37 &#176;C, 5% CO2, 3% O2. Stop enzymatic activity by using 10 mL of DMEM complete. 
	NOTE: After passage 4, primary cells are discarded and should not be used for further experiments, as they change characteristics.</li>
	<li>Collect the cells and centrifuge at 300 x g at RT for 10 min.</li>
	<li>Resuspended the cell pellet in 10 mL of exosome-free medium and count the cells.</li>
	<li>Seed the cells at 1.5&#8211;2.0 x 106 cells per dish (15 cm) and incubate at 37 &#176;C, 5% CO2, 3% O2.</li>
	<li>Collect the conditioned medium between 16&#8211;24 h in 50 mL tubes on ice. 
	NOTE: If cells are not 80% confluent, fresh exosomal free medium can be added again and collected after an additional 16&#8211;24 h period. The two collections can be combined for further processing.</li>
</ol>
5. Purification of exosomes using differential and ultra-centrifugation
NOTE: All steps are performed at 4 &#176;C or on ice. Balance the tube with a tube filled with water when needed.
<ol>
	<li>Centrifuge the conditioned medium at 300 x g for 10 min for removal of live cells and transfer the supernatant to a new 50 mL tube.</li>
	<li>Remove dead cells by centrifugation at 2,000 x g for 10 min and transfer the supernatant to a 38.5 mL polypropylene tube.</li>
	<li>Centrifuge the supernatant at 10,000 x g for 30 min for the removal of organelles, apoptotic bodies, and membrane fragments. Transfer the supernatant to a 38.5 mL ultra-clear tube.</li>
	<li>Ultracentrifuge the supernatant at 100,000 x g for 1.5 h to pellet the exosomes.</li>
	<li>Carefully discard the supernatant, leaving approximately 1 mL of conditioned medium, and wash the exosome pellet in a total volume of 30 mL of ice-cold PBS.</li>
	<li>Centrifuge at 100,000 x g for 1.5 h and carefully discard the supernatant by pipetting, being careful not to disturb the exosomal pellet.</li>
	<li>Resuspend the pellet in ice-cold PBS (~25 &#956;L per 15 cm dish) and measure the protein concentration using the BCA protein assay kit and a microplate reader at 562 nm. 
	NOTE: The protein concentration is measured by a 1:2 dilution with 0.1% Triton-X100 in dH2O. The yield of exosomes from a 15 cm dish (20 mL of conditioned medium) of primary fibroblasts at 80% confluency is ~3&#8211;4 &#956;g.</li>
</ol>
6. Characterization of exosomes by sucrose density gradient
<ol>
	<li>Load the sucrose gradient in a 13 mL ultra-clear tube by pipetting (from the bottom up) the following: 1.5 mL of 2.0 M, 2.5 mL of 1.3 M, 2.5 mL of 1.16 M, 2.0 mL of 0.8 M, and 2.0 mL of 0.5 M sucrose solutions.</li>
	<li>Mix 30&#8211;100 &#181;g of exosomes with 0.25 M sucrose solution and adjust the volume to 1 mL.</li>
	<li>Load carefully the exosomes on top of the gradients and ultra-centrifuge the samples for 2.5 h at 100,000 x g and 4 &#176;C.</li>
	<li>Remove the tubes from the ultra-centrifuge and place them on ice and collect 1.0 mL fractions starting from the top of the gradient. Transfer them to 1.7 mL tubes on ice.</li>
	<li>Add 110 &#181;L of 100% TCA to each tube, mix well, and incubate for 10 min at RT.</li>
	<li>Centrifuge for 10 min at 10,000 x g and RT and carefully discard the supernatant.</li>
	<li>Resuspend the pellet in 500 &#181;L of pre-cooled 80% ethanol and leave the samples to wash for 10 min at -20 &#176;C.</li>
	<li>Centrifuge for 10 min at 10,000 x g and 4 &#176;C and discard the supernatant.</li>
	<li>Dry the pellet for 10&#8211;15 min at RT and resuspend the pellet in PBS for in vitro experiments. Measure the protein concentration using BCA protein assay kit or resuspend the pellet directly in 14.5 &#181;L of dH2O, 5 &#181;L of 4x Laemmli buffer, and 0.5 &#181;L of 1 M DTT for western blot analyses.</li>
</ol>
7. Exosome detection by western blot analysis
<ol>
	<li>Mix 5&#8211;10 &#181;g of exosomes from step 5.7 with 5 &#181;L of 4x Laemmli buffer, and 0.5 &#181;L of 1 M DTT, then adjust the final volume to 20 &#181;L with dH2O. Heat all samples, including those in step 6.9, for 5 min at 98 &#176;C.</li>
	<li>Load the samples into a 10% TGX stain-free gel and load the protein ladders according to the manufacturer&#8217;s recommendations. 
	NOTE: Choose the percentage of the gel according to the molecular weight of the protein of interest.</li>
	<li>Run the gel at 100 V for ~1 h in running buffer until the loading dye is at the bottom of the gel. 
	NOTE: The run time may vary according to the equipment used or type and percentage of gel.</li>
	<li>Image the gel. Images of the stain-free gels are used as the loading control for immunoblots.</li>
	<li>Transfer the gel using a PVDF membrane for 1.5 h at 80 V or overnight at 30 V at 4 &#176;C.</li>
	<li>Block the membranes in blocking buffer for 1 h at RT.</li>
	<li>Incubate the membranes for specific antibodies (Table 2) in antibody buffer overnight at 4 &#176;C with agitation.</li>
	<li>Wash the membranes in washing buffer and incubate the membranes with the appropriate secondary antibodies (Table 2) for 1 h at RT with agitation.</li>
	<li>Wash the membranes in washing buffer and image the membranes using develop solution and a camera-based imager. Alternatively, use an X-ray film to develop the membranes.</li>
</ol>

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Muscle Dissection in mouse Available from: <a target="_blank" href="https://www.youtube.com/watch?v=Wh0gXfrHaH8">https://www.youtube.com/watch?v=Wh0gXfrHaH8</a> (2016)</li><li>Mas-Bargues, C., 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=Relevance+of+oxygen+concentration+in+stem+cell+culture+for+regenerative+medicine.">Relevance of oxygen concentration in stem cell culture for regenerative medicine.</a> International Journal of Molecular Sciences. 20 (5), 1195 (2019).</li><li>Bois, P. R., Grosveld, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=FKHR+(FOX01a)+is+required+for+myotube+fusion+of+primary+mouse+myoblasts.">FKHR (FOX01a) is required for myotube fusion of primary mouse myoblasts.</a> The EMBO Journal. 22 (5), 1147-1157 (2003).</li><li>Machida, S., Spangenburg, E. E., Booth, F. 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None of the authors have any conflicts of interest to declare.

A critical step for the successful isolation of exosomes from the culture media, as outlined in this protocol, is the proper establishment and maintenance of primary mouse fibroblast cultures from adult skeletal muscle. These cultures need to be maintained at a low oxygen level to ensure physiological-like conditions (O2 level in skeletal muscle is ~2.5%)15. Primary fibroblasts will change characteristics when passed in culture too many times. Hence, a low passage number is imperative f...

Exosomes are heterogeneous extracellular vesicles ranging in size from 30&#8211;150 nm. They are established key players in physiological and pathological processes, given their ubiquitous distribution in tissues and organs1,2. Exosomes carry a complex cargo of proteins, lipids, DNA types, and RNA types, which vary according to the type of cells from which they are derived1,2,3. Exosomes are enriched in proteins that have different functions (i.e., tetraspanins, including CD9 and CD63) are responsible for fusion events. For example, heat shock proteins HSP70 and HSP90 are involved in antigen binding and presentation. Additionally, Alix, Tsg101, and flotillin participate in exosome biogenesis and release and are widely used as markers of these nanovesicles2,3,4.
Exosomes also contain a variety of RNAs (i.e., microRNAs, long noncoding RNAs, ribosomal RNAs) that can be transferred to recipient cells, where they influence downstream signaling3. Being enclosed by a single unit membrane, exosome bioactivity depends not only on the cargo of proteins and nucleic acids, but also on lipid components of the limiting membrane1. Exosomal membranes are enriched in phosphatidylserine, phosphatidic acid, cholesterol, sphingomyelin, arachidonic acid, and other fatty acids, all of which can influence exosome stability and membrane topology2,3. As a result of the cargo and lipid arrangement, exosomes initiate signaling pathways in receiving cells and participate in the maintenance of normal tissue physiology1,2,4,5. Under certain pathological conditions (i.e., neurodegeneration, fibrosis, and cancer), they have been shown to trigger and propagate pathological stimuli4,6,7,8,9,10,11.
Owing to their ability to propagate signals to neighboring or distant sites, exosomes have become valuable biomarkers for the diagnosis or prognosis of disease conditions. In addition, exosomes have been used experimentally as vehicles of therapeutic compounds2,12. The potential application of these nanovesicles in the clinic makes the isolation method increasingly important in order to achieve maximum yield, purity, and reproducibility. Different techniques for the isolation of exosomes have been developed and implemented. Generally, exosomes can be isolated from conditioned cell culture media or body fluids by differential centrifugation, size exclusion chromatography, and immune capture (using commercially available kits). Each approach has unique advantages and disadvantages that have been discussed previously1,2,13,14.
The outlined protocol focuses on the 1) isolation and culture of primary fibroblasts from adult mouse gastrocnemius muscle and 2) purification and characterization of exosomes released into the culture medium by these cells. A well-established protocol for the isolation of exosomes from primary fibroblasts for functional studies is currently lacking. Primary fibroblasts do not secrete large amounts of exosomes, making the isolation and purification process challenging. This protocol describes the purification of large amounts of pure exosomes from large culture volumes while maintaining their morphological integrity and functional activity. Purified exosomes obtained from conditioned medium have been used successfully in in vitro uptake experiments to induce specific signaling pathways in recipient cells. They have also been used for comparative proteomic analyses of exosomal cargos from multiple biological samples4.

<table>
	<tbody>
		<tr>
			<td>10 cm dishes</td>
			<td>Midwest Scientific, TPP</td>
			<td>TP93100</td>
			<td></td>
		</tr>
		<tr>
			<td>15 cm dishes</td>
			<td>Midwest Scientific</td>
			<td>TP93150</td>
			<td></td>
		</tr>
		<tr>
			<td>BCA protein assay kit</td>
			<td>Thermo Fisher Scientific, Pierce</td>
			<td>23225</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine serum albumin Fraction V</td>
			<td>Roche</td>
			<td>10735094001</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2</td>
			<td>Sigma</td>
			<td>C1016-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge 5430R with rotors FA-35-6-30/ FA-45-48-11</td>
			<td>Eppendorf</td>
			<td>022620659/5427754008</td>
			<td></td>
		</tr>
		<tr>
			<td>Chemidoc MP imaging system</td>
			<td>BioRad</td>
			<td>12003154</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase P</td>
			<td>Sigma, Roche</td>
			<td>11 213 857 001</td>
			<td>100 mg</td>
		</tr>
		<tr>
			<td>cOmplete protease inhibitor cocktail</td>
			<td>Millipore/Sigma, Roche</td>
			<td>11697498001</td>
			<td></td>
		</tr>
		<tr>
			<td>Criterion Blotter with plate electrodes</td>
			<td>BioRad</td>
			<td>1704070</td>
			<td></td>
		</tr>
		<tr>
			<td>Criterion TGX stain-free protein gel</td>
			<td>BioRad</td>
			<td>5678034</td>
			<td>10% 18-well, midi-gel</td>
		</tr>
		<tr>
			<td>Criterion vertical electrophoresis cell (midi)</td>
			<td>BioRad</td>
			<td>NC0165100</td>
			<td></td>
		</tr>
		<tr>
			<td>Dispase II</td>
			<td>Sigma, Roche</td>
			<td>04 942 078 001</td>
			<td>neutral protease, grade II</td>
		</tr>
		<tr>
			<td>Dithiothreitol</td>
			<td>Sigma/Millipore, Roche</td>
			<td>10708984001</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#8217;s Modification Eagles Medium</td>
			<td>Corning</td>
			<td>15-013-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#8217;s Phosphate Buffered Saline</td>
			<td>Corning</td>
			<td>21-031-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol 200 proof</td>
			<td>Pharmco by Greenfield Global</td>
			<td>111000200</td>
			<td></td>
		</tr>
		<tr>
			<td>Falcon 50 mL conical centrifuge tubes</td>
			<td>Corning</td>
			<td>352070</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Gibco</td>
			<td>10437-028</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluostar Omega multi-mode microplate reader</td>
			<td>BMG Labtech</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>GlutaMAX supplement</td>
			<td>Thermo Fisher Scientific, Gibco</td>
			<td>35050-061</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrochloric acid</td>
			<td>Fisher Scientific</td>
			<td>A144S-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Immobilon-P Transfer membranes</td>
			<td>Millipore</td>
			<td>IPVH00010</td>
			<td></td>
		</tr>
		<tr>
			<td>Laemmli sample buffer (4x)</td>
			<td>BioRad</td>
			<td>1610747</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium acetate solution</td>
			<td>Sigma</td>
			<td>63052-100ml</td>
			<td></td>
		</tr>
		<tr>
			<td>Non-fat dry milk</td>
			<td>LabScientific</td>
			<td>M-0842</td>
			<td></td>
		</tr>
		<tr>
			<td>O2/CO2 incubator</td>
			<td>Sanyo</td>
			<td>MC0-18M</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin</td>
			<td>Thermo Fisher Scientific, Gibco</td>
			<td>15140-122</td>
			<td>10,000 U/ml</td>
		</tr>
		<tr>
			<td>Premium microcentrifuge tubes</td>
			<td>Fisher Scientific, Midwest Scientific</td>
			<td>AVSC1510</td>
			<td>1.7 mL</td>
		</tr>
		<tr>
			<td>Protected disposable scalpels</td>
			<td>Fisher Scientific, Aspen Surgical Bard-Parker</td>
			<td>372610</td>
			<td></td>
		</tr>
		<tr>
			<td>Running buffer</td>
			<td>BioRad</td>
			<td>1610732</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride</td>
			<td>Fisher Scientific, Fisher Chemical</td>
			<td>S271-3</td>
			<td></td>
		</tr>
		<tr>
			<td>Stericup Quick release-GP sterile vacuum filtration system</td>
			<td>Millipore</td>
			<td>S2GPU05RE</td>
			<td>500 mL</td>
		</tr>
		<tr>
			<td>Sterile cell strainer (70 mm)</td>
			<td>Fisher Scientific, Fisher brand</td>
			<td>22-363-548</td>
			<td></td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Fisher Scientific, Fisher Chemical</td>
			<td>S5-500</td>
			<td></td>
		</tr>
		<tr>
			<td>SuperSignal west Femto</td>
			<td>Thermo Fisher Scientific</td>
			<td>34096</td>
			<td></td>
		</tr>
		<tr>
			<td>Thin wall Polypropylene tubes</td>
			<td>Beckman Coulter</td>
			<td>326823</td>
			<td></td>
		</tr>
		<tr>
			<td>Transfer buffer</td>
			<td>BioRad</td>
			<td>16110734</td>
			<td></td>
		</tr>
		<tr>
			<td>Trichloroacetic Acid</td>
			<td>Sigma</td>
			<td>91228-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris base</td>
			<td>BioRad</td>
			<td>1610719</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton-X100 solution</td>
			<td>Sigma</td>
			<td>93443-100mL</td>
			<td></td>
		</tr>
		<tr>
			<td>TrypLE Express Enzyme</td>
			<td>Thermo Fisher Scientific, Gibco</td>
			<td>12604-013</td>
			<td>No phenol red</td>
		</tr>
		<tr>
			<td>Tween-20</td>
			<td>BioRad</td>
			<td>#1610781</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultra-centrifuge Optima XPM</td>
			<td>Beckman Coulter</td>
			<td>A99842</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultra-clear tube (14x89 mm)</td>
			<td>Beckman Coulter</td>
			<td>344059</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultra-clear tubes (25x89 mm)</td>
			<td>Beckman Coulter</td>
			<td>344058</td>
			<td></td>
		</tr>
		<tr>
			<td>Water bath Isotemp 220</td>
			<td>Fisher Scientific</td>
			<td>FS220</td>
			<td></td>
		</tr>
	</tbody>
</table>

isolation and characterization of exosomes from skeletal muscle fibroblasts

Exosomes are small extracellular vesicles released by virtually all cells and secreted in all biological fluids. Many methods have been developed for the isolation of these vesicles, including ultracentrifugation, ultrafiltration, and size exclusion chromatography. However, not all are suitable for large scale exosome purification and characterization. Outlined here is a protocol for establishing cultures of primary fibroblasts isolated from adult mouse skeletal muscles, followed by purification and characterization of exosomes from the culture media of these cells. The method is based on the use of sequential centrifugation steps followed by sucrose density gradients. Purity of the exosomal preparations is then validated by western blot analyses using a battery of canonical markers (i.e., Alix, CD9, and CD81). The protocol describes how to isolate and concentrate bioactive exosomes for electron microscopy, mass spectrometry, and uptake experiments for functional studies. It can easily be scaled up or down and adapted for exosome isolation from different cell types, tissues, and biological fluids.

This protocol is suitable for the purification of exosomes from large volumes of conditioned medium in a cost-effective manner. The procedure is highly reproducible and consistent. Figure 1 shows transmission electron microscopy (TEM) image of exosomes purified from the culture medium of mouse primary fibroblasts. Figure 2 shows the protein expression pattern of canonical exosomal markers, and the absence of cytosolic (LDH) and ER (calnexin) protein contaminants...

Watch this Scientific Journal Video about Isolation and Characterization of Exosomes from Skeletal Muscle Fibroblasts at JoVE.com

Isolation and Characterization of Exosomes from Skeletal Muscle Fibroblasts

This protocol illustrates the 1) the isolation and culture of primary fibroblasts from the adult mouse gastrocnemius muscle as well as 2) purification and characterization of exosomes using a differential ultracentrifugation method combined with sucrose density gradients followed by western blot analyses.

Exosomes are small extracellular vesicles released by virtually all cells and secreted in all biological fluids. Many methods have been developed for the ...

isolation-characterization-exosomes-from-skeletal-muscle

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Biology

3.2K Views.  St. Jude Children's Research Hospital. This protocol illustrates the 1) the isolation and culture of primary fibroblasts from the adult mouse gastrocnemius muscle as well as 2) purification and characterization of exosomes using a differential ultracentrifugation method combined with sucrose density gradients followed by western blot analyses.

Video: Isolation and Characterization of Exosomes from Skeletal Muscle Fibroblasts

Adult and Embryonic Skeletal Muscle Microexplant Culture and Isolation of Skeletal Muscle Stem Cells

Cultured embryonic and adult skeletal muscle cells have a number of different uses. The micro-dissected explants technique described in this chapter is a robust and reliable method for isolating relatively large numbers of proliferative skeletal muscle cells from juvenile, adult or embryonic muscles as a source of skeletal muscle stem cells. The authors have used micro-dissected explant cultures to analyse the growth characteristics of skeletal muscle cells in wild-type and dystrophic muscles. Each of the components of tissue growth, namely cell survival, proliferation, senescence and differentiation can be analysed separately using the methods described here. The net effect of all components of growth can be established by means of measuring explant outgrowth rates. The micro-explant method can be used to establish primary cultures from a wide range of different muscle types and ages and, as described here, has been adapted by the authors to enable the isolation of embryonic skeletal muscle precursors.
Uniquely, micro-explant cultures have been used to derive clonal (single cell origin) skeletal muscle stem cell (SMSc) lines which can be expanded and used for in vivo transplantation. In vivo transplanted SMSc behave as functional, tissue-specific, satellite cells which contribute to skeletal muscle fibre regeneration but which are also retained (in the satellite cell niche) as a small pool of undifferentiated stem cells which can be re-isolated into culture using the micro-explant method.

The micro-dissected explants technique is a robust and reliable method for isolating proliferative skeletal muscle cells from juvenile, adult or embryonic muscles as a source of skeletal muscle stem cells. Uniquely, these cells have been clonally derived to produce skeletal muscle stem cell lines used for in vivo transplantation.

Cultured embryonic and adult skeletal muscle cells have a number of different uses. The micro-dissected explants technique described in this chapter is a ...

Mitochondrial Isolation from Skeletal Muscle

Mitochondria are organelles controlling the life and death of the cell. They participate in key metabolic reactions, synthesize most of the ATP, and regulate a number of signaling cascades2,3. Past and current researchers have isolated mitochondria from rat and mice tissues such as liver, brain and heart4,5. In recent years, many researchers have focused on studying mitochondrial function from skeletal muscles.
Here, we describe a method that we have used successfully for the isolation of mitochondria from skeletal muscles 6. Our procedure requires that all buffers and reagents are made fresh and need about 250-500 mg of skeletal muscle. We studied mitochondria isolated from rat and mouse gastrocnemius and diaphragm, and rat extraocular muscles. Mitochondrial protein concentration is measured with the Bradford assay. It is important that mitochondrial samples be kept ice-cold during preparation and that functional studies be performed within a relatively short time (~1 hr). Mitochondrial respiration is measured using polarography with a Clark-type electrode (Oxygraph system) at 37&deg;C7. Calibration of the oxygen electrode is a key step in this protocol and it must be performed daily. Isolated mitochondria (150 &mu;g) are added to 0.5 ml of experimental buffer (EB). State 2 respiration starts with addition of glutamate (5mM) and malate (2.5 mM). Then, adenosine diphosphate (ADP) (150 &mu;M) is added to start state 3. Oligomycin (1 &mu;M), an ATPase synthase blocker, is used to estimate state 4. Lastly, carbonyl cyanide p-[trifluoromethoxy]-phenyl-hydrazone (FCCP, 0.2 &mu;M) is added to measurestate 5, or uncoupled respiration 6. The respiratory control ratio (RCR), the ratio of state 3 to state 4, is calculated after each experiment. An RCR &ge;4 is considered as evidence of a viable mitochondria preparation.
In summary, we present a method for the isolation of viable mitochondria from skeletal muscles that can be used in biochemical (e.g., enzyme activity, immunodetection, proteomics) and functional studies (mitochondrial respiration).

This protocol describes a procedure to study the respiration of mitochondria isolated from skeletal muscles. This method was adapted from Scorrano et al. (2007). The mitochondrial isolation procedure requires about 2 hours. The mitochondrial respiration can be completed in about 1 hour.

Mitochondria are organelles controlling the life and death of the cell. They participate in key metabolic reactions, synthesize most of the ATP, and ...

Purification of Progenitors from Skeletal Muscle

Skeletal muscle contains multiple progenitor populations of distinct embryonic origins and developmental potential. Myogenic progenitors, usually residing in a "satellite cell position" between the myofiber plasma membrane and the laminin-rich basement membrane that ensheaths it, are self-renewing cells that are solely committed to the myogenic lineage1,2. We have recently described a second class of vessel associated progenitors that can generate myofibroblasts and white adipocytes, which responds to damage by efficiently entering proliferation and provides trophic support to myogenic cells during tissue regeneration3,4. One of the most trusted assays to determine the developmental and regenerative potential of a given cell population relies on their isolation and transplantation5-7. To this end we have optimized protocols for their purification by flow cytometry from enzymatically dissociated muscle, which we will outline in this article. The populations obtained using this method will contain either myogenic or fibro/adipogenic colony forming cells: no other cell types are capable of expanding in vitro or surviving in vivo delivery. However, when these populations are used immediately after the sort for molecular analysis (e.g qRT-PCR) one must keep in mind that the freshly sorted subsets may contain other contaminant cells that lack the ability of forming colonies or engrafting recipients.

Method for the enzymatic dissociation, surface labeling and purification by flow cytometry of fibro/adipogenic and myogenic progenitors from murine skeletal muscle.

Skeletal muscle contains multiple progenitor populations of distinct embryonic origins and developmental potential. Myogenic progenitors, usually residing ...

Isolation and Characterization of RNA-Containing Exosomes

The field of exosome research is rapidly expanding, with a dramatic increase in publications in recent years. These small vesicles (30-100 nm) of endocytic origin were first proposed to function as a way for reticulocytes to eradicate the transferrin receptor while maturing into erythrocytes1, and were later named exosomes. Exosomes are formed by inward budding of late endosomes, producing multivesicular bodies (MVBs), and are released into the environment by fusion of the MVBs with the plasma membrane2. Since the first discovery of exosomes, a wide range of cells have been shown to release these vesicles. Exosomes have also been detected in several biological fluids, including plasma, nasal lavage fluid, saliva and breast milk3-6. Furthermore, it has been demonstrated that the content and function of exosomes depends on the originating cell and the conditions under which they are produced. A variety of functions have been demonstrated for exosomes, such as induction of tolerance against allergen7,8, eradication of established tumors in mice9, inhibition and activation of natural killer cells10-12, promotion of differentiation into T regulatory cells13, stimulation of T cell proliferation14 and induction of T cell apoptosis15. Year 2007 we demonstrated that exosomes released from mast cells contain messenger RNA (mRNA) and microRNA (miRNA), and that the RNA can be shuttled from one cell to another via exosomes. In the recipient cells, the mRNA shuttled by exosomes was shown to be translated into protein, suggesting a regulatory function of the transferred RNA16. Further, we have also shown that exosomes derived from cells grown under oxidative stress can induce tolerance against further stress in recipient cells and thus suggest a biological function of the exosomal shuttle RNA17. Cell culture media and biological fluids contain a mixture of vesicles and shed fragments. A high quality isolation method for exosomes, followed by characterization and identification of the exosomes and their content, is therefore crucial to distinguish exosomes from other vesicles and particles. Here, we present a method for the isolation of exosomes from both cell culture medium and body fluids. This isolation method is based on repeated centrifugation and filtration steps, followed by a final ultracentrifugation step in which the exosomes are pelleted. Important methods to identify the exosomes and characterize the exosomal morphology and protein content are highlighted, including electron microscopy, flow cytometry and Western blot. The purification of the total exosomal RNA is based on spin column chromatography and the exosomal RNA yield and size distribution is analyzed using a Bioanalyzer.

This paper demonstrates methods for the isolation, purification and detection of exosomes, as well as techniques for analysis of their molecular content. These methods are adaptable for exosome isolation from both cell culture media and biological fluids, and can beyond analysis of molecular content also be useful in functional studies.

The field of exosome research is rapidly expanding, with a dramatic increase in publications in recent years. These small vesicles (30-100 nm) of ...

Isolation and Culture of Individual Myofibers and their Satellite Cells from Adult Skeletal Muscle

Muscle regeneration in the adult is performed by resident stem cells called satellite cells. Satellite cells are defined by their position between the basal lamina and the sarcolemma of each myofiber. Current knowledge of their behavior heavily relies on the use of the single myofiber isolation protocol. In 1985, Bischoff described a protocol to isolate single live fibers from the Flexor Digitorum Brevis (FDB) of adult rats with the goal to create an in vitro system in which the physical association between the myofiber and its stem cells is preserved 1. In 1995, Rosenblattmodified the Bischoff protocol such that myofibers are singly picked and handled separately after collagenase digestion instead of being isolated by gravity sedimentation 2, 3. The Rosenblatt or Bischoff protocol has since been adapted to different muscles, age or conditions 3-6. The single myofiber isolation technique is an indispensable tool due its unique advantages. First, in the single myofiber protocol, satellite cells are maintained beneath the basal lamina. This is a unique feature of the protocol as other techniques such as Fluorescence Activated Cell Sorting require chemical and mechanical tissue dissociation 7. Although the myofiber culture system cannot substitute for in vivo studies, it does offer an excellent platform to address relevant biological properties of muscle stem cells. Single myofibers can be cultured in standard plating conditions or in floating conditions. Satellite cells on floating myofibers are subjected to virtually no other influence than the myofiber environment. Substrate stiffness and coating have been shown to influence satellite cells' ability to regenerate muscles 8, 9 so being able to control each of these factors independently allows discrimination between niche-dependent and -independent responses. Different concentrations of serum have also been shown to have an effect on the transition from quiescence to activation. To preserve the quiescence state of its associated satellite cells, fibers should be kept in low serum medium 1-3. This is particularly useful when studying genes involved in the quiescence state. In serum rich medium, satellite cells quickly activate, proliferate, migrate and differentiate, thus mimicking the in vivo regenerative process 1-3. The system can be used to perform a variety of assays such as the testing of chemical inhibitors; ectopic expression of genes by virus delivery; oligonucleotide based gene knock-down or live imaging. This video article describes the protocol currently used in our laboratory to isolate single myofibers from the Extensor Digitorum Longus (EDL) muscle of adult mice (6-8 weeks old).

Isolation and culture of myofibers is the gold standard in vitro system to study the transition of satellite cells through quiescence, activation and differentiation. Importantly, the single myofiber culture system preserves the myofiber/stem cell association, which is an essential component of the muscle stem cell niche.

Muscle  regeneration in the adult is performed by resident stem cells called satellite  cells. Satellite cells are defined by  their position between the ...

Isolation of Blood-vessel-derived Multipotent Precursors from Human Skeletal Muscle

Since the discovery of mesenchymal stem/stromal cells (MSCs), the native identity and localization&#160;of MSCs have been obscured by their retrospective isolation in culture. Recently, using fluorescence-activated cell sorting (FACS), we and other researchers prospectively identified and purified three subpopulations of multipotent precursor cells associated with the vasculature of human skeletal muscle. These three cell populations: myogenic endothelial cells (MECs), pericytes (PCs), and adventitial cells (ACs), are localized respectively to the three structural layers of blood vessels: intima, media, and adventitia. All of these human blood-vessel-derived stem cell (hBVSC) populations not only express classic MSC markers but also possess mesodermal developmental potentials similar to typical MSCs. Previously, MECs, PCs, and ACs have been isolated through distinct protocols and subsequently characterized in separate studies. The current isolation protocol, through modifications to the isolation process and adjustments in the selective cell surface markers, allows us to simultaneously purify all three hBVSC subpopulations by FACS from a single human muscle biopsy. This new method will not only streamline the isolation of multiple BVSC subpopulations but also facilitate future clinical applications of hBVSCs for distinct therapeutic purposes.

Blood vessels within human skeletal muscle harbor several multi-lineage precursor populations that are ideal for regenerative applications. This isolation method allows simultaneous purification of three multipotent precursor cell populations respectively from three structural layers of blood vessels: myogenic endothelial cells from intima, pericytes from media, and adventitial cells from adventitia.

Since the discovery of mesenchymal stem/stromal cells (MSCs), the native identity and localization&#160;of MSCs have been obscured by their retrospective ...

Isolation of Mitochondria from Minimal Quantities of Mouse Skeletal Muscle for High Throughput Microplate Respiratory Measurements

Dysfunctional skeletal muscle mitochondria play a role in altered metabolism observed with aging, obesity and Type II diabetes. Mitochondrial respirometric assays from isolated mitochondrial preparations allow for the assessment of mitochondrial function, as well as determination of the mechanism(s) of action of drugs and proteins that modulate metabolism. Current isolation procedures often require large quantities of tissue to yield high quality mitochondria necessary for respirometric assays. The methods presented herein describe how high quality purified mitochondria (~ 450 &#181;g) can be isolated from minimal quantities (~75-100 mg) of mouse skeletal muscle for use in high throughput respiratory measurements. We determined that our isolation method yields 92.5&#177; 2.0% intact mitochondria by measuring citrate synthase activity spectrophotometrically. In addition, Western blot analysis in isolated mitochondria resulted in the faint expression of the cytosolic protein, GAPDH, and the robust expression of the mitochondrial protein, COXIV. The absence of a prominent GAPDH band in the isolated mitochondria is indicative of little contamination from non-mitochondrial sources during the isolation procedure. Most importantly, the measurement of O2 consumption rate with micro-plate based technology and determining the respiratory control ratio (RCR) for coupled respirometric assays shows highly coupled (RCR; &#62;6 for all assays) and functional mitochondria. In conclusion, the addition of a separate mincing step and significantly reducing motor driven homogenization speed of a previously reported method has allowed the isolation of high quality and purified mitochondria from smaller quantities of mouse skeletal muscle that results in highly coupled mitochondria that respire with high function during microplate based respirometirc assays.

Here, we present a modification of a previously reported method that allows for the isolation of high quality and purified mitochondria from smaller quantities of mouse skeletal muscle. This procedure results in highly coupled mitochondria that respire with high function during microplate based respirometirc assays.

Dysfunctional skeletal muscle mitochondria play a role in altered metabolism observed with aging, obesity and Type II diabetes. Mitochondrial ...

Isolation of Intact Mitochondria from Skeletal Muscle by Differential Centrifugation for High-resolution Respirometry Measurements

Mitochondria are involved in cellular energy metabolism and use oxygen to produce energy in the form of adenosine triphosphate (ATP). Differential centrifugation at low- and high-speed is commonly used to isolate mitochondria from tissues and cultured cells. Crude mitochondrial fractions obtained by differential centrifugation are used for respirometry measurements. The differential centrifugation technique is based on the separation of organelles according to their size and sedimentation velocity. The isolation of mitochondria is performed immediately after tissue harvesting. The tissue is immersed in an ice-cold homogenization medium, minced using scissors and homogenized in a glass homogenizer with a loose-fitting pestle. The differential centrifugation technique is efficient, fast and inexpensive and the mitochondria obtained by differential centrifugation are pure enough for respirometry assays. Some of the limitations and disadvantages of isolated mitochondria, based on differential centrifugation, are that the mitochondria can be damaged during the homogenization and isolation procedure and that large amounts of the tissue biopsy or cultured cells are required for the mitochondrial isolation.

Here, a quadriceps muscle specimen is taken from an anaesthetized pig and mitochondria are isolated by differential centrifugation. Then, the respiratory rates of mitochondrial respiratory chain complexes I, II and IV are determined using high-resolution respirometry.

Mitochondria are involved in cellular energy metabolism and use oxygen to produce energy in the form of adenosine triphosphate (ATP). Differential ...

Isolation and Characterization of Adult Cardiac Fibroblasts and Myofibroblasts

Cardiac fibrosis in response to injury is a physiological response to wound healing. Efforts have been made to study and target fibroblast subtypes that mitigate fibrosis. However, fibroblast research has been hindered due to the lack of universally acceptable fibroblast markers to identify quiescent as well as activated fibroblasts. Fibroblasts are a heterogenous cell population, making them difficult to isolate and characterize. The presented protocol describes three different methods to enrich fibroblasts and myofibroblasts from uninjured and injured mouse hearts. Using a standard and reliable protocol to isolate fibroblasts will enable the study of their roles in homeostasis as well as fibrosis modulation.

Obtaining a pure population of fibroblasts is crucial to studying their role in wound repair and fibrosis. Described here is a detailed method to isolate fibroblasts and myofibroblasts from uninjured and injured mouse hearts followed by characterization of their purity and functionality by immunofluorescence, RTPCR, fluorescence-assisted cell sorting, and collagen gel contraction.

Cardiac fibrosis in response to injury is a physiological response to wound healing. Efforts have been made to study and target fibroblast subtypes that ...

Isolation of Human Ventricular Cardiomyocytes from Vibratome-Cut Myocardial Slices

The isolation of ventricular cardiac myocytes from animal and human hearts is a fundamental method in cardiac research. Animal cardiomyocytes are commonly isolated by coronary perfusion with digestive enzymes. However, isolating human cardiomyocytes is challenging because human myocardial specimens usually do not allow for coronary perfusion, and alternative isolation protocols result in poor yields of viable cells. In addition, human myocardial specimens are rare and only regularly available at institutions with on-site cardiac surgery. This hampers the translation of findings from animal to human cardiomyocytes. Described here is a reliable protocol that enables efficient isolation of ventricular myocytes from human and animal myocardium. To increase the surface-to-volume ratio while minimizing cell damage, myocardial tissue slices 300 &#181;m thick are generated from myocardial specimens with a vibratome. Tissue slices are then digested with protease and collagenase. Rat myocardium was used to establish the protocol and quantify yields of viable, calcium-tolerant myocytes by flow-cytometric cell counting. Comparison with the commonly used tissue-chunk method showed significantly higher yields of rod-shaped cardiomyocytes (41.5 &#177; 11.9 vs. 7.89 &#177; 3.6%, p &#60; 0.05). The protocol was translated to failing and non-failing human myocardium, where yields were similar as in rat myocardium and, again, markedly higher than with the tissue-chunk method (45.0 &#177; 15.0 vs. 6.87 &#177; 5.23 cells/mg, p &#60; 0.05). Notably, with the protocol presented it is possible to isolate reasonable numbers of viable human cardiomyocytes (9&#8211;200 cells/mg) from minimal amounts of tissue (&#60;50 mg). Thus, the method is applicable to healthy and failing myocardium from both human and animal hearts. Furthermore, it is possible to isolate excitable and contractile myocytes from human tissue specimens stored for up to 36 h in cold cardioplegic solution, rendering the method particularly useful for laboratories at institutions without on-site cardiac surgery.

Presented is a protocol for the isolation of human and animal ventricular cardiomyocytes from vibratome-cut myocardial slices. High yields of calcium-tolerant cells (up to 200 cells/mg) can be obtained from small amounts of tissue (&#60;50 mg). The protocol is applicable to myocardium exposed to cold ischemia for up to 36 h.

The isolation of ventricular cardiac myocytes from animal and human hearts is a fundamental method in cardiac research. Animal cardiomyocytes are commonly ...