Name: live-cell imaging of platelet degranulation and secretion under flow
Uploaded: 2017-07-10T10:00:00
Description: Watch this Scientific Journal Video about Live-cell Imaging of Platelet Degranulation and Secretion Under Flow at JoVE.com

CM acknowledges financial support from the International Patient Organization for C1-Inhibitor Deficiencies (HAEi), Stichting Vrienden van Het UMC Utrecht, and the Landsteiner Foundation for Blood Transfusion Research (LSBR).

The local Medical Ethical Committee of the University Medical Center Utrecht approved the drawing of blood for ex vivo research purposes, including those of this study.
1. Solution Preparation
<ol>
	<li>Prepare a 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) Tyrode&#39;s buffer by dissolving 10 mM HEPES, 0.5 mM Na2HPO4, 145 mM NaCl, 5 mM KCl, 1 mM MgSO4, and 5.55 mM D-glucose in distilled water.
	<ol>
		<li>Make two vari...

<ol>
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L., Flaumenhaft, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Platelet+granule+exocytosis:+a+comparison+with+chromaffin+cells.">Platelet granule exocytosis: a comparison with chromaffin cells.</a> Front Endocrinol (Lausanne). 4, 11 (2013).</li><li>May, B., Menkens, I., Westermann, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+release+of+serotonin+and+histamine+from+blood+platelets+of+the+rabbit+by+aliphatic+and+aromatic+amines.">Differential release of serotonin and histamine from blood platelets of the rabbit by aliphatic and aromatic amines.</a> Life Sci. 6 (19), 2079-2085 (1967).</li><li>Schmaier, A. H., Smith, P. M., Colman, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Platelet+C1-+inhibitor.+A+secreted+alpha-granule+protein.">Platelet C1- inhibitor. A secreted alpha-granule protein.</a> J. Clin. Invest. 75 (1), 242-250 (1985).</li><li>Battinelli, E. M., Markens, B. A., Italiano, J. E., 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=Release+of+angiogenesis+regulatory+proteins+from+platelet+alpha+granules:+modulation+of+physiologic+and+pathologic+angiogenesis.">Release of angiogenesis regulatory proteins from platelet alpha granules: modulation of physiologic and pathologic angiogenesis.</a> Blood. 118 (5), 1359-1369 (2011).</li><li>Kamykowski, J., Carlton, P., Sehgal, S., Storrie, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+immunofluorescence+mapping+reveals+little+functional+coclustering+of+proteins+within+platelet+&#945;-granules.">Quantitative immunofluorescence mapping reveals little functional coclustering of proteins within platelet &#945;-granules.</a> Blood. 118 (5), 1370-1373 (2011).</li><li>Sakariassen, K. S., Aarts, P. A., de Groot, P. G., Houdijk, W. P., Sixma, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+perfusion+chamber+developed+to+investigate+platelet+interaction+in+flowing+blood+with+human+vessel+wall+cells,+their+extracellular+matrix,+and+purified+components.">A perfusion chamber developed to investigate platelet interaction in flowing blood with human vessel wall cells, their extracellular matrix, and purified components.</a> J Lab Clin Med. 102 (4), 522-535 (1983).</li><li>Van Aelst, B., Feys, H. B., Devloo, R., Vandekerckhove, P., Compernolle, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+Flow+Chambers+Using+Reconstituted+Blood+to+Model+Hemostasis+and+Platelet+Transfusion+In+Vitro.">Microfluidic Flow Chambers Using Reconstituted Blood to Model Hemostasis and Platelet Transfusion In Vitro.</a> J Vis Exp. (109), (2016).</li><li>Nesbitt, W. S., Westein, E., 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=A+shear+gradient-dependent+platelet+aggregation+mechanism+drives+thrombus+formation.">A shear gradient-dependent platelet aggregation mechanism drives thrombus formation.</a> Nat Med. 15 (6), 665-673 (2009).</li><li>Mitchell, J. L., Lionikiene, A. S., 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=Polyphosphate+colocalizes+with+factor+XII+on+platelet-bound+fibrin+and+augments+its+plasminogen+activator+activity.">Polyphosphate colocalizes with factor XII on platelet-bound fibrin and augments its plasminogen activator activity.</a> Blood. 128 (24), 2834-2845 (2016).</li><li>Park, Y., Schoene, N., Harris, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mean+platelet+volume+as+an+indicator+of+platelet+activation:+methodological+issues.">Mean platelet volume as an indicator of platelet activation: methodological issues.</a> Platelets. 13 (5-6), 301-306 (2002).</li><li>Sixma, J. J., de Groot, P. G., van Zanten, H., IJsseldijk, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+perfusion+chamber+to+detect+platelet+adhesion+using+a+small+volume+of+blood.">A new perfusion chamber to detect platelet adhesion using a small volume of blood.</a> Thromb Res. 92, S43-S46 (1998).</li><li>Slack, S. M., Turitto, V. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flow+chambers+and+their+standardization+for+use+in+studies+of+thrombosis.+On+behalf+of+the+Subcommittee+on+Rheology+of+the+Scientific+and+Standardization+Committee+of+the+ISTH.">Flow chambers and their standardization for use in studies of thrombosis. On behalf of the Subcommittee on Rheology of the Scientific and Standardization Committee of the ISTH.</a> Thromb Haemost. 72 (5), 777-781 (1994).</li><li>Oreopoulos, J., Berman, R., Browne, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spinning-disk+confocal+microscopy:+present+technology+and+future+trends.">Spinning-disk confocal microscopy: present technology and future trends.</a> Methods Cell Biol. 123, 153-175 (2014).</li><li>Nishibori, M., Cham, B., McNicol, A., Shalev, A., Jain, N., Gerrard, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+protein+CD63+is+in+platelet+dense+granules,+is+deficient+in+a+patient+with+Hermansky-Pudlak+syndrome,+and+appears+identical+to+granulophysin.">The protein CD63 is in platelet dense granules, is deficient in a patient with Hermansky-Pudlak syndrome, and appears identical to granulophysin.</a> J. Clin. Invest. 91 (4), 1775-1782 (1993).</li><li>Ruiz, F. A., Lea, C. R., Oldfield, E., Docampo, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+platelet+dense+granules+contain+polyphosphate+and+are+similar+to+acidocalcisomes+of+bacteria+and+unicellular+eukaryotes.">Human platelet dense granules contain polyphosphate and are similar to acidocalcisomes of bacteria and unicellular eukaryotes.</a> J. Biol. Chem. 279 (43), 44250-44257 (2004).</li><li>Tersteeg, C., Fijnheer, R., 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=Keeping+von+Willebrand+Factor+under+Control:+Alternatives+for+ADAMTS13.">Keeping von Willebrand Factor under Control: Alternatives for ADAMTS13.</a> Semin Thromb Hemost. 42 (1), 9-17 (2016).</li><li>Tersteeg, C., de Maat, S., 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=Plasmin+cleavage+of+von+Willebrand+factor+as+an+emergency+bypass+for+ADAMTS13+deficiency+in+thrombotic+microangiopathy.">Plasmin cleavage of von Willebrand factor as an emergency bypass for ADAMTS13 deficiency in thrombotic microangiopathy.</a> Circulation. 129 (12), 1320-1331 (2014).</li><li>Basir, A., de Groot, P., 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+Hemocompatibility+Testing+of+Dyneema+Purity+Fibers+in+Blood+Contact.">In Vitro Hemocompatibility Testing of Dyneema Purity Fibers in Blood Contact.</a> Innovations (Phila). 10 (3), 195-201 (2015).</li></ol>

Worldwide, thrombosis is a leading cause of death and morbidity, and platelets play a central role in its development. This work describes a method for the live-cell imaging of platelet degranulation under flow. It is generally assumed that, when platelets become activated, all granular contents are directly released into solution. The accompanying results suggest that this is not necessarily the case. During adhesion and degranulation, platelets retain a significant amount of polyphosphate (Figure 4). A...

Platelets are anucleate cells that circulate in the blood stream. Their main function is to seal vascular breaches at sites of injury and to prevent blood loss. At these sites of injury, subendothelial collagen fibers become exposed and are subsequently covered by the multimeric protein, von Willebrand factor (VWF). VWF interacts with the platelets in circulation in a mechanism that depends upon the glycoprotein Ib&#945;-IX-V complex on the cell surface1, slowing down the speed of the platelets. This is particularly important at high shear rates. The platelets subsequently undergo morphological changes while receiving activating impulses from collagen. This leads to irreversible spreading and eventually to platelet aggregation. Both processes depend upon the secretion of granule contents to facilitate platelet-platelet crosstalk. Amongst others, platelet &#945;-granules contain fibrinogen and VWF to assist platelet adhesion and to bridge platelets together in an integrin-dependent manner. The platelet-dense granules contain inorganic compounds2, including calcium and adenosine diphosphate (ADP), which help to reinforce platelet activation. Furthermore, platelets contain mediators of (allergic) inflammation3, complement-controlling proteins4, and angiogenesis factors5,6, raising the questions of whether and how these contents are differentially released under varying conditions.
Since the 1980s, the study of platelet function in flow models has been valuable to the investigation of thrombotic mechanisms7. Since then, much technical progress has been made, and flow models that include fibrin formation are currently developed to assay the hemostatic potential of therapeutic platelet concentrates ex vivo8 or to investigate the influence of disturbances in shear rates on thrombus morphology9. The differences in the molecular and cell-biological mechanisms that drive stable adhesion and physiological thrombus formation (hemostasis) versus pathological thrombus formation (thrombosis) may be very subtle and motivate the development of flow models that allow for the real-time visualization of these subcellular processes.
An example of a process for which such a setup would be valuable is the (re)distribution of intracellular polyphosphate and the recruitment of clotting factors to uncover the time-dependent impact that this has on fibrin ultrastructure10. Studies are often limited to end-point analyses. The main aim of the described method is to enable the real-time visual investigation of dynamic subcellular processes that take place during platelet activation under flow.

<table border="0" cellpadding="0" cellspacing="0" width="1340">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES)&#160;</td>
			<td style="width:295px;">VWR</td>
			<td style="width:227px;">441476L</td>
			<td style="width:372px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Na2HPO4</td>
			<td style="width:295px;">Sigma</td>
			<td style="width:227px;">S-0876</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NaCl</td>
			<td style="width:295px;">Sigma</td>
			<td style="width:227px;">31434</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">KCl</td>
			<td style="width:295px;">Sigma</td>
			<td style="width:227px;">31248</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">MgSO4</td>
			<td style="width:295px;">Merck KGaA</td>
			<td style="width:227px;">1.05886</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">D-glucose</td>
			<td style="width:295px;">Merck KGaA</td>
			<td style="width:227px;">1.04074</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Prostacyclin&#160;</td>
			<td style="width:295px;">Cayman Chemical</td>
			<td style="width:227px;">18220</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tri-sodium citrate</td>
			<td style="width:295px;">Merck KGaA</td>
			<td style="width:227px;">1.06448</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Citric acid&#160;</td>
			<td style="width:295px;">Merck KGaA</td>
			<td style="width:227px;">1.00244</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cover glasses</td>
			<td style="width:295px;">Menzel-Gl&#228;ser</td>
			<td style="width:227px;">BBAD02400500#A</td>
			<td>24x50mm, No. 1 = 0.13-0.16 mm thickness.</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:447px;">Chromosulfuric acid (2% CrO3)</td>
			<td style="width:295px;">Riedel de Haen</td>
			<td>07404</td>
			<td>CAS [65272-70-0].</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Von Willebrand factor (VWF)</td>
			<td style="width:295px;">in-house purified</td>
			<td style="width:227px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Fibrinogen</td>
			<td style="width:295px;">Enzyme Research Laboratories</td>
			<td style="width:227px;">FIB3L</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">4 well dish, non-treated</td>
			<td style="width:295px;">Thermo Scientific</td>
			<td style="width:227px;">267061</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Human Serum Albumin Fraction V</td>
			<td style="width:295px;">Haem Technologies Inc.</td>
			<td style="width:227px;">823022</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Blood collection tubes, 9 ml, 9NC Coagulation Sodium Citrate 3.2%</td>
			<td style="width:295px;">Greiner Bio-One</td>
			<td style="width:227px;">455322</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Cell analyser&#160;</td>
			<td style="width:295px;">Abbott Diagnostics</td>
			<td style="width:227px;">CELL-DYN hematology analyzer</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Paraformaldehyde</td>
			<td style="width:295px;">Sigma</td>
			<td>30525-89-4&#160;</td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">Syringe pump</td>
			<td style="width:295px;">Harvard Apparatus, Holliston, MA</td>
			<td style="width:227px;">Harvard apparatus 22</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">10 mL syringe with 14.5 mm diameter</td>
			<td style="width:295px;">BD biosciences</td>
			<td style="width:227px;">305959</td>
			<td>Luer-Lok syringe</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">Anti-CD63-biotin&#160;</td>
			<td style="width:295px;">Abcam&#160;</td>
			<td style="width:227px;">AB134331</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">Anti-CD62P-biotin&#160;</td>
			<td style="width:295px;">R&#38;D Systems</td>
			<td style="width:227px;">Dy137</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">4&#8217;,6-Diamidino-2-phenylindole dihydrochloride (DAPI)</td>
			<td style="width:295px;">Polysciences Inc.&#160;</td>
			<td style="width:227px;">9224</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Streptavidin, Alexa Fluor 488 conjugate</td>
			<td>Thermo Scientific</td>
			<td>S11223&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Immersion oil</td>
			<td>Zeiss</td>
			<td>444963-0000-000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Detergent solution</td>
			<td>Unilever, Biotex</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Glycine</td>
			<td>Sigma</td>
			<td>56-40-6&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Polyvinyl alcohol</td>
			<td style="width:295px;">Sigma</td>
			<td>9002-89-5</td>
			<td>Mowiol 40-88.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tris hydrochloride</td>
			<td style="width:295px;">Sigma</td>
			<td>1185-53-1&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1,4-Diazabicyclo[2.2.2]octane (DABCO)</td>
			<td style="width:295px;">Sigma</td>
			<td>280-57-9</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sheep Anti-hVWF pAb</td>
			<td>Abcam&#160;</td>
			<td style="width:227px;">AB9378</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">Alexa fluor 488-NHS</td>
			<td style="width:295px;">Thermo Scientific</td>
			<td style="width:227px;">A20000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Glycerol</td>
			<td style="width:295px;">Sigma-Aldrich</td>
			<td style="width:227px;">15523-1L-R</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">Parafinn film</td>
			<td style="width:295px;">Bemis</td>
			<td style="width:227px;">PM-996</td>
			<td>4 in. x 125 ft. Roll.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">Silicone sheet non-reinforced</td>
			<td style="width:295px;">Nagor</td>
			<td style="width:227px;">NA 500-1</td>
			<td>200mmx150mmx0.125mm.</td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:447px;">Customized cut silicone sheet with perfusion and vacuum channels</td>
			<td style="width:295px;">in-house made</td>
			<td style="width:227px;"></td>
			<td>Made of Silicone sheet non-reinforced (Nagor, NA 500-1)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">1.5 mL tubes</td>
			<td style="width:295px;">Eppendorf AG</td>
			<td style="width:227px;">T9661-1000AE</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">Fluorescent microscope</td>
			<td style="width:295px;">Zeiss Observer Z1&#160;</td>
			<td style="width:227px;"></td>
			<td>Equiped with LED excitation lights.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">Microscope software</td>
			<td style="width:295px;">Zeiss ZEN 2</td>
			<td style="width:227px;">blue edition</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">18 G needle (18 G x 1 1/2&#34;)</td>
			<td style="width:295px;">BD biosciences</td>
			<td>305196</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">NaCl</td>
			<td style="width:295px;">Riedel de Haen</td>
			<td style="width:227px;">31248375</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">Tris</td>
			<td style="width:295px;">Roche</td>
			<td style="width:227px;">10708976</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">Plastic pasteur pipet</td>
			<td style="width:295px;">VWR</td>
			<td style="width:227px;">612-1681</td>
			<td>&#160;7 ml non sterile, graduated up to 3ml.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">Silicone tubing</td>
			<td style="width:295px;">VWR</td>
			<td style="width:227px;">228-0656</td>
			<td>Inner diamete. x Outer diameter x Wall thickness = 1.02 x 2.16 x 0.57 mm.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:447px;">Microscope slides</td>
			<td style="width:295px;">Thermo Scientific</td>
			<td style="width:227px;">ABAA000001##12E</td>
			<td>76 x 26 x 1 mm, ground edges 45&#176;, frosted end.</td>
		</tr>
	</tbody>
</table>

live-cell imaging of platelet degranulation and secretion under flow

Blood platelets are essential players in hemostasis, the formation of thrombi to seal vascular breaches. They are also involved in thrombosis, the formation of thrombi that occlude the vasculature and injure organs, with life-threatening consequences. This motivates scientific research on platelet function and the development of methods to track cell-biological processes as they occur under flow conditions.
A variety of flow models are available for the study of platelet adhesion and aggregation, two key phenomena in platelet biology. This work describes a method to study real-time platelet degranulation under flow during activation. The method makes use of a flow chamber coupled to a syringe-pump setup that is placed under a wide-field, inverted, LED-based fluorescence microscope. The setup described here allows for the simultaneous excitation of multiple fluorophores that are delivered by fluorescently labeled antibodies or fluorescent dyes. After live-cell imaging experiments, the cover glasses can be further processed and analyzed using static microscopy (i.e., confocal microscopy or scanning electron microscopy).

Figure 1 shows images of the flow chamber and experimental setup; the position and dimensions of the silicon sheet; and tubing connections. Figure 2 provides details on the dimensions of the flow chamber. Figure 3 and Movie 1 show a time-series of images of platelet adhesion and spreading on immobilized VWF. CD63 is a transmembrane protein that is inserted into the membrane of intrac...

Watch this Scientific Journal Video about Live-cell Imaging of Platelet Degranulation and Secretion Under Flow at JoVE.com

Live-cell Imaging of Platelet Degranulation and Secretion Under Flow

This work describes a fluorescence microscopy-based method for the study of platelet adhesion, spreading, and secretion under flow. This versatile platform enables the investigation of platelet function for mechanistic research on thrombosis and hemostasis.

Blood platelets are essential players in hemostasis, the formation of thrombi to seal vascular breaches. They are also involved in thrombosis, the ...

The overall goal of this experiment is to track platelet degranulation and secretion under flow using live-cell imaging. This method can help to answer key questions in the field of platelet biology. The main advantage of this technique is that it enables a versatile investigation of platelet contents at the subcellular level in live cells.Though this method can provide insight into platelet function, it can also be applied to other cell types such as mast cells. In general, individuals new to this method, will struggle because of problems with platelet isolation in a form of preactivation. We first had the idea for this method when we realized that platelet secretion could only be evaluated at end point stages.Real time images provide information of the release kinetics of platelet granular release. The procedure of platelet isolation will be demonstrated by Silvia Pignatelli, a student in our institute. Next, Arjan Barendrecht will demonstrate the real-time imaging experiments.To begin, degrease cover glasses by incubating them overnight in undiluted chromosulfuric acid. The next day, rinse them with distilled water. Then place then overnight at 60 degrees Celsius in an oven, to dry.Next, place a drop of water on a laboratory bench and adhere a 10 centimeter by 15 centimeter strip of a paraffin film on top of the drop by removing the air between the bench and the film. Then pipette 80 microliter drops of 10 microgram per milliliter von Willebrand factor or 100 microgram per milliliter fibrinogen onto the paraffin film. Place the dry cover glasses onto the drops and incubate them for one and a half hours at room temperature.Next, add three milliliters of blocking buffer into each well of a four well plate. Transfer the cover glasses with the coated side up into individual wells of the plate. Incubate them overnight at four degrees Celsius.Centrifuge nine milliliters of citrated whole blood for 15 minutes at 160 time G without a break. Then use a plastic Pasteur pipette to collect the supernatant containing the platelet-rich plasma. Add a one part of acid citrate dextrose to nine parts of the platelets by volume to prevent platelet preactivation.Then centrifuge the platelets for 15 minutes at 400 times G without a break. Next, remove the supernatant, leaving a platelet pellet. Then resuspend the pellet carefully in HEPES Tyrode buffer at a pH of 6.5 back to the original volume of the platelet sample.Then, add Prostacyclin to the resuspended platelets. Immediately centrifuge the sample and then remove the supernatant. Resuspend the pellet carefully in HEPES Tyrode buffer at a pH of 7.4.Next, place the washed platelets into a cell analyzer and count the number of platelets. Adjust the number of platelets in the sample to a concentration of 150, 000 platelets per microliter with HEPES Tyrode buffer at a pH of 7.4. After resuspension, leave the platelets to recover for 30 minutes at room temp prior to the experiment.Cover the top of the flow chamber with distilled water and place a customized silicone sheet with the smooth side down on the water. Float the sheet into position by removing excess water while keeping the sheet in position. Incubate the flow chamber for one hour at 60 degrees Celsius to evaporate the residual water and to firmly adhere the silicone sheet to the flow chamber.With the plastic Pasteur pipette, add a drop of HEPES Tyrode buffer at a pH of 7.4 onto the flow channel. Then place the prepared cover glass with the coated side down, onto the flow channel. Turn on the vacuum pump to a pressure of around 10 kilopascals and attach the vacuum pump to the vacuum connection of the flow chamber.Add 10 micrograms per milliliter DAPI stain to the washed platelets, and wrap the tube containing the platelets in aluminum foil. Then incubate them for 30 minutes at 37 degrees Celsius. To prevent platelet activation, add prostacyclin at a final concentration of 10 nanograms per milliliter and immediately centrifuge the platelets for 15 minutes at 400 times G without using the brake to remove unbound DAPI.Reconstitute the platelet pellet and HEPES Tyrode buffer at a pH of 7.4 to the original volume with a concentration of 150, 000 platelets per microliter. Then, turn on the fluorescence microscope and load the microscope software. Set up the imaging parameters as described in table one of the accompanying text protocol.Block the inlet tubing by connecting a 10 milliliter syringe and aspirating blocking buffer into the inlet tubing. Block for 15 minutes at room temperature and then rinse the inlet tubing by aspirating HEPES Tyrode buffer 7.4 into the inlet tubing. Connect the blocked inlet tubing and the untreated outlet tubing to the inlet and outlet of the chamber.Then connect the 10 milliliter syringe to the outlet tubing. Place a drop of immersion oil on a 100 times objective and mount the chamber on the microscope with the glass surface facing downwards. Next, place the inlet tubing into a tube containing HEPES Tyrode buffer at a pH of 7.4.Manually pull the plunger of the syringe connected to the outlet tubing to pull the solution through the chamber and remove the air from the system. Then place the syringe into the syringe pump and run the pump briefly to tighten the plunger and ensure stable flow. With the flow system now ready, add the antibodies and or dyes to the platelet suspension and mix carefully.Then squeeze the inlet tubing and move it from the buffer to the tube containing the labeled platelets. Select live visualization in the software. Focus the microscope on the cover glass surface and start the pump at 484 microliters per minute.Run the pump until the platelets reach the flow chamber. Next, reduce the flow rate to 7.5 microliters per minute. Monitor the cover glass surface.Once the first platelet starts to adhere, focus the microscope on this platelet and start recording by initiating the experiment in the software. Record for 30 minutes and then stop the syringe pump. Save the microscope raw data files containing all the metadata.When needed, export the movies to the MOV H 264 compressed or AVI uncompressed. Save separate frames as JPEG or TIF files. When finished imaging, remove the chamber from the microscope, clean the immersion oil from the glass, disconnect the vacuum and carefully remove the cover glass from the chamber with an 18 gauge needle.Place the cover slide with the cells directed upwards in a new four well plate on top of a tissue prewetted with distilled water. Then pipette 750 microliters of a fixative solution on top of the cover glass and incubate it for one hour at room temperature in the dark. In case the samples cannot be analyzed directly, store them in 0.5%paraformaldehyde at four degrees Celsius to ensure stable fixation.This shows the time series of platelet adhesion and spreading on glass slides coated with immobilized von Willebrand factor. Shown in green in CD63, a transmembrane protein which is mobilized onto the platelet surface in a time-dependent manner. Similarly, shown in orange, P-selectin is also a transmembrane protein inserted in the membrane of intracellular alpha-granules arresting platelets.Following a flow experiment, confocal fluorescence microscopy can be used to produce a tilt series of the platelet adhesion. Seen here, CD63 is mainly located at the central granulomere while P-selectin is distributed over the entire cell body and appears concentrated at the edges. In these experiments, platelets, which do not have nuclear DNA, were preincubated with DAPI, which appears blue.In this case, DAPI stains the polyphosphates and dense granules. Appearing later as green staining, is the time dependent mobilization of CD63 onto the platelet surface. Despite clear signs of dense granule release, single cell analysis shows that polyphosphate is retained within or on the outside of these platelets.Once mastered, this technique can be done in six hours for four individual flow experiments. While attempting this procedure, it's important to prevent platelet preactivation. This can be achieved by careful manipulation of the cell suspension.Following this procedure, other methods like confocal microscopy can be used to obtain additional insight into the three dimensional distribution of target molecules. After watching this video, you should have a good understanding of how to study platelet function under flow at a single cell level.

live-cell-imaging-of-platelet-degranulation-and-secretion-under-flow

Research

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Biology

Live Cell Imaging of F-actin Dynamics via Fluorescent Speckle Microscopy (FSM)

In this protocol we describe the use of Fluorescent Speckle Microscopy (FSM) to capture high-resolution images of actin dynamics in PtK1 cells. A unique advantage of FSM is its ability to capture the movement and turnover kinetics (assembly/disassembly) of the F-actin network within living cells. This technique is particularly useful in deriving quantitative measurements of F-actin dynamics when paired with computer vision software (qFSM).  We describe  the selection, microinjection and visualization of fluorescent actin probes in living cells. Importantly, similar procedures are applicable to visualizing other macomolecular assemblies. FSM has been demonstrated for microtubules, intermediate filaments, and adhesion complexes.  

Live Cell Imaging of F-actin Dynamics via Fluorescent Speckle Microscopy FSM

Selection, microinjection, and imaging of fluorescently-labeled F-actin via fluorescent speckle microscopy (FSM).

In this protocol we describe the use of Fluorescent Speckle Microscopy (FSM) to capture high-resolution images of actin dynamics in PtK1 cells. A unique ...

Platelet Adhesion and Aggregation Under Flow using Microfluidic Flow Cells

Platelet aggregation occurs in response to vascular injury where the extracellular matrix below the endothelium has been exposed. The platelet adhesion cascade takes place in the presence of shear flow, a factor not accounted for in conventional (static) well-plate assays. This article reports on a platelet-aggregation assay utilizing a microfluidic well-plate format to emulate physiological shear flow conditions. Extracellular proteins, collagen I or von Willebrand factor are deposited within the microfluidic channel using active perfusion with a pneumatic pump. The matrix proteins are then washed with buffer and blocked to prepare the microfluidic channel for platelet interactions. Whole blood labeled with fluorescent dye is perfused through the channel at various flow rates in order to achieve platelet activation and aggregation. Inhibitors of platelet aggregation can be added prior to the flow cell experiment to generate IC50 dose response data.

The platelet adhesion cascade takes place in the presence of shear flow, a factor not accounted for in conventional (static) well-plate assays. This article reports on a platelet-aggregation assay utilizing a microfluidic well-plate format to emulate physiological shear flow conditions.

Platelet aggregation occurs in response to vascular injury where the extracellular matrix below the endothelium has been exposed. The platelet adhesion ...

Live-cell Imaging and Quantitative Analysis of Embryonic Epithelial Cells in Xenopus laevis

Embryonic epithelial cells serve as an ideal model to study morphogenesis where multi-cellular tissues undergo changes in their geometry, such as changes in cell surface area and cell height, and where cells undergo mitosis and migrate. Furthermore, epithelial cells can also regulate morphogenetic movements in adjacent tissues1. A traditional method to study epithelial cells and tissues involve chemical fixation and histological methods to determine cell morphology or localization of particular proteins of interest. These approaches continue to be useful and provide "snapshots" of cell shapes and tissue architecture, however, much remains to be understood about how cells acquire specific shapes, how various proteins move or localize to specific positions, and what paths cells follow toward their final differentiated fate. High resolution live imaging complements traditional methods and also allows more direct investigation into the dynamic cellular processes involved in the formation, maintenance, and morphogenesis of multicellular epithelial sheets. Here we demonstrate experimental methods from the isolation of animal cap tissues from Xenopus laevis embryos to confocal imaging of epithelial cells and simple measurement approaches that together can augment molecular and cellular studies of epithelial morphogenesis.

Live-cell Imaging and Quantitative Analysis of Embryonic Epithelial Cells in Xenopus laevis

Xenopus embryonic epithelia are an ideal model system to study cell behaviors such as polarity development and shape change during epithelial morphogenesis. Traditional histology of fixed samples is increasingly being complemented by live-cell confocal imaging. Here we demonstrate methods to isolate frog tissues and visualize live epithelial cells and their cytoskeleton using live-cell confocal microscopy.

Embryonic epithelial cells serve as an ideal model to study morphogenesis where multi-cellular tissues undergo changes in their geometry, such as changes ...

Two- and Three-Dimensional Live Cell Imaging of DNA Damage Response Proteins

Double-strand breaks (DSBs) are the most deleterious DNA lesions a cell can encounter. If left unrepaired, DSBs harbor great potential to generate mutations and chromosomal aberrations1. To prevent this trauma from catalyzing genomic instability, it is crucial for cells to detect DSBs, activate the DNA damage response (DDR), and repair the DNA. When stimulated, the DDR works to preserve genomic integrity by triggering cell cycle arrest to allow for repair to take place or force the cell to undergo apoptosis. The predominant mechanisms of DSB repair occur through nonhomologous end-joining (NHEJ) and homologous recombination repair (HRR) (reviewed in2). There are many proteins whose activities must be precisely orchestrated for the DDR to function properly. Herein, we describe a method for 2- and 3-dimensional (D) visualization of one of these proteins, 53BP1.
The p53-binding protein 1 (53BP1) localizes to areas of DSBs by binding to modified histones3,4, forming foci within 5-15 minutes5. The histone modifications and recruitment of 53BP1 and other DDR proteins to DSB sites are believed to facilitate the structural rearrangement of chromatin around areas of damage and contribute to DNA repair6. Beyond direct participation in repair, additional roles have been described for 53BP1 in the DDR, such as regulating an intra-S checkpoint, a G2/M checkpoint, and activating downstream DDR proteins7-9. Recently, it was discovered that 53BP1 does not form foci in response to DNA damage induced during mitosis, instead waiting for cells to enter G1 before localizing to the vicinity of DSBs6. DDR proteins such as 53BP1 have been found to associate with mitotic structures (such as kinetochores) during the progression through mitosis10.
In this protocol we describe the use of 2- and 3-D live cell imaging to visualize the formation of 53BP1 foci in response to the DNA damaging agent camptothecin (CPT), as well as 53BP1's behavior during mitosis. Camptothecin is a topoisomerase I inhibitor that primarily causes DSBs during DNA replication. To accomplish this, we used a previously described 53BP1-mCherry fluorescent fusion protein construct consisting of a 53BP1 protein domain able to bind DSBs11. In addition, we used a histone H2B-GFP fluorescent fusion protein construct able to monitor chromatin dynamics throughout the cell cycle but in particular during mitosis12. Live cell imaging in multiple dimensions is an excellent tool to deepen our understanding of the function of DDR proteins in eukaryotic cells.

This protocol describes a method for visualizing a DNA double-strand break signaling protein activated in response to DNA damage as well as its localization during mitosis.

Double-strand breaks (DSBs) are the most deleterious DNA lesions a cell can encounter. If left unrepaired, DSBs harbor great potential to generate ...

Live Cell Imaging of Early Autophagy Events: Omegasomes and Beyond

Autophagy is a cellular response triggered by the lack of nutrients, especially the absence of amino acids. Autophagy is defined by the formation of double membrane structures, called autophagosomes, that sequester cytoplasm, long-lived proteins and protein aggregates, defective organelles, and even viruses or bacteria. Autophagosomes eventually fuse with lysosomes leading to bulk degradation of their content, with the produced nutrients being recycled back to the cytoplasm. Therefore, autophagy is crucial for cell homeostasis, and dysregulation of autophagy can lead to disease, most notably neurodegeneration, ageing and cancer.	
	Autophagosome formation is a very elaborate process, for which cells have allocated a specific group of proteins, called the core autophagy machinery. The core autophagy machinery is functionally complemented by additional proteins involved in diverse cellular processes, e.g. in membrane trafficking, in mitochondrial and lysosomal biology. Coordination of these proteins for the formation and degradation of autophagosomes constitutes the highly dynamic and sophisticated response of autophagy. Live cell imaging allows one to follow the molecular contribution of each autophagy-related protein down to the level of a single autophagosome formation event and in real time, therefore this technique offers a high temporal and spatial resolution.	
	Here we use a cell line stably expressing GFP-DFCP1, to establish a spatial and temporal context for our analysis. DFCP1 marks omegasomes, which are precursor structures leading to autophagosomes formation. A protein of interest (POI) can be marked with either a red or cyan fluorescent tag. Different organelles, like the ER, mitochondria and lysosomes, are all involved in different steps of autophagosome formation, and can be marked using a specific tracker dye. Time-lapse microscopy of autophagy in this experimental set up, allows information to be extracted about the fourth dimension, i.e. time. Hence we can follow the contribution of the POI to autophagy in space and time.

Time-lapse microscopy of fluorescently labeled autophagy markers allows monitoring of the dynamic autophagy response with high temporal resolution. Using specific autophagy and organelle markers in a combination of 3 different colors, we can follow the contribution of a protein to autophagosome formation in a robust spatial and temporal context.

Autophagy is a  cellular response triggered by the lack of nutrients, especially the absence of  amino acids. Autophagy is defined by the formation of ...

Studying the Protein Quality Control System of D. discoideum Using Temperature-controlled Live Cell Imaging

The complex lifestyle of the social amoebae Dictyostelium discoideum makes it a valuable model for the study of various biological processes. Recently, we showed that D. discoideum is remarkably resilient to protein aggregation and can be used to gain insights into the cellular protein quality control system. However, the use of D. discoideum as a model system poses several challenges to microscopy-based experimental approaches, such as the high motility of the cells and their susceptibility to photo-toxicity. The latter proves to be especially challenging when studying protein homeostasis, as the phototoxic effects can induce a cellular stress response and thus alter to behavior of the protein quality control system. 
Temperature increase is a commonly used way to induce cellular stress. Here, we describe a temperature-controllable imaging protocol, which allows observing temperature-induced perturbations in D. discoideum. Moreover, when applied at normal growth temperature, this imaging protocol can also noticeably reduce photo-toxicity, thus allowing imaging with higher intensities. This can be particularly useful when imaging proteins with very low expression levels. Moreover, the high mobility of the cells often requires the acquisition of multiple fields of view to follow individual cells, and the number of fields needs to be balanced against the desired time interval and exposure time.

Studying the Protein Quality Control System of D. discoideum Using Temperature-controlled Live Cell Imaging

The social amoebae Dictyostelium discoideum has recently been established as a system to study protein misfolding and proteostasis. Here, we describe a new imaging-based methodology to study temperature-induced protein aggregation and the cellular stress response in D. discoideum.

The complex lifestyle of the social amoebae Dictyostelium discoideum makes it a valuable model for the study of various biological processes. Recently, we ...

Mixed Primary Cultures of Murine Small Intestine Intended for the Study of Gut Hormone Secretion and Live Cell Imaging of Enteroendocrine Cells

The gut is the largest endocrine organ of the body, with hormone-secreting enteroendocrine cells located along the length of the gastrointestinal epithelium. Despite their physiological importance, enteroendocrine cells represent only a small fraction of the epithelial cell population and in the past, their characterization has presented a considerable challenge resulting in a reliance on cell line models. Here, we provide a detailed protocol for the isolation and culture of mixed murine small intestinal cells. These primary cultures have been used to identify the signaling pathways underlying the stimulation and inhibition of gut peptide secretion in response to a number of nutrients and neuropeptides as well as pharmacological agents. Furthermore, in combination with the use of transgenic fluorescent reporter mice, we have demonstrated that these primary cultures become a powerful tool for the examination of fluorescently-tagged enteroendocrine cells at the intracellular level, using methods such as patch clamping and single-cell calcium and cAMP-FRET imaging.

This protocol describes the isolation and culture of mixed murine small intestinal cells. These primary intestinal cultures enable the investigation of signaling pathways underlying gut peptide secretion using a number of techniques.

The gut is the largest endocrine organ of the body, with hormone-secreting enteroendocrine cells located along the length of the gastrointestinal ...

Application of Membrane and Cell Wall Selective Fluorescent Dyes for Live-Cell Imaging of Filamentous Fungi

The application of membrane and cell wall selective fluorescent dyes for live-cell imaging analyses of organelle dynamics in fungal cells started two decades ago and since then continues to contribute greatly to our understanding of the filamentous fungal lifestyle. This paper provides a practical guide for the utilization of the two membrane dyes FM 1-43 and FM 4-64 and the four cell wall stains Calcofluor White M2R, Solophenyl Flavine 7GFE 500, Pontamine Fast Scarlet 48 and Congo Red. The focus is on their low-dose application to ascertain artefact-free staining, their co-imaging properties, and their quantitative evaluation. The presented methods are applicable to all filamentous fungal samples that can be prepared in the described ways. The fundamental staining approaches can serve as starting points for adaptations to species that might require different cultivation conditions. First, biophysical and biochemical properties are reviewed as their understanding is essential for using these dyes as truly vital fluorescent stains. Secondly, step-by-step protocols are presented that detail the preparation of various fungal sample types for fluorescent live-cell imaging. Finally, example experiments illustrate different approaches to: (1) identify defects in the spatio-temporal organization of endocytosis in genetic mutants, (2) comparatively characterize shared and distinct co-localization of GFP-labeled target proteins in the endocytic pathway, (3) identify morphogenetic cell wall defects in a genetic mutant, and (4) monitor cell wall biogenesis in real time.

Vital fluorescent dyes are essential tools for live-cell imaging analyses in modern fungal cell biology. This paper details the application of established and lesser-known fluorescent dyes for tracking plasma membrane dynamics, endo-/exocytosis and cell wall morphogenesis in filamentous fungi.

The application of membrane and cell wall selective fluorescent dyes for live-cell imaging analyses of organelle dynamics in fungal cells started two ...

Super-Resolution Live Cell Imaging of Subcellular Structures

There has long been a crucial tradeoff between spatial and temporal resolution in imaging. Imaging beyond the diffraction limit of light has traditionally been restricted to be used only on fixed samples or live cells outside of tissue labeled with strong fluorescent signal. Current super-resolution live cell imaging techniques require the use of special fluorescence probes, high illumination, multiple image acquisitions with post-acquisition processing, or often a combination of these processes. These prerequisites significantly limit the biological samples and contexts that this technique can be applied to.
Here we describe a method to perform super-resolution (~140 nm XY-resolution) time-lapse fluorescence live cell imaging in situ. This technique is also compatible with low fluorescent intensity, for example, EGFP or mCherry endogenously tagged at lowly expressed genes. As a proof-of-principle, we have used this method to visualize multiple subcellular structures in the Drosophila testis. During tissue preparation, both the cellular structure and tissue morphology are maintained within the dissected testis. Here, we use this technique to image microtubule dynamics, the interactions between microtubules and the nuclear membrane, as well as the attachment of microtubules to centromeres.
This technique requires special procedures in sample preparation, sample mounting and immobilizing of specimens. Additionally, the specimens must be maintained for several hours after dissection without compromising cellular function and activity. While we have optimized the conditions for live super-resolution imaging specifically in Drosophila male germline stem cells (GSCs) and progenitor germ cells in dissected testis tissue, this technique is broadly applicable to a variety of different cell types. The ability to observe cells under their physiological conditions without sacrificing either spatial or temporal resolution will serve as an invaluable tool to researchers seeking to address crucial questions in cell biology.

Presented here is a protocol for super-resolution live-cell imaging in intact tissue. We have standardized the conditions for imaging a highly sensitive adult stem cell population in its native tissue environment. This technique involves balancing temporal and spatial resolution to allow for the direct observation of biological phenomena in live tissue.

There has long been a crucial tradeoff between spatial and temporal resolution in imaging. Imaging beyond the diffraction limit of light has traditionally ...

Immunophenotyping and Cell Sorting of Human MKs from Human Primary Sources or Differentiated In Vitro from Hematopoietic Progenitors

Megakaryocyte (MK) differentiation encompasses a number of endomitotic cycles that result in a highly polyploid (reaching even&#160;&#62;64N) and extremely large cell (40-60 &#181;m). As opposed to the fast-increasing knowledge in megakaryopoiesis at the cell biology and molecular level, the characterization of megakaryopoiesis by flow cytometry is limited to the identification of mature MKs using lineage-specific surface markers, while earlier MK differentiation stages remain unexplored. Here, we present an immunophenotyping strategy that allows the identification of successive MK differentiation stages, with increasing ploidy status, in human primary sources or in vitro cultures with a panel integrating MK specific and non-specific surface markers. Despite its size and fragility, MKs can be immunophenotyped using the above-mentioned panel and enriched by fluorescence-activated cell sorting under specific conditions of pressure and nozzle diameter. This approach facilitates multi-Omics studies, with the aim to better understand the complexity of megakaryopoiesis and platelet production in humans. A better characterization of megakaryopoiesis may pose fundamental in the diagnosis or prognosis of lineage-related pathologies and malignancy.

Immunophenotyping and Cell Sorting of Human MKs from Human Primary Sources or Differentiated In Vitro from Hematopoietic Progenitors

Here, we present an immunophenotyping strategy for the characterization of megakaryocyte differentiation, and show how that strategy allows the sorting of megakaryocytes at different stages with a fluorescence-activated cell sorter. The methodology can be applied to human primary tissues, but also to megakaryocytes generated in culture in vitro.