Work pertinent to this study was supported in part by National Institutes of Health (NIH) National Heart, Lung, and Blood Institute grants HL082808, HL123984 (R.L.), and F31HL134241 (M.E.Q.). Funding also provided by NIH National Institute of General Medical Sciences grant T32GM008367 (M.E.Q.); and pilot grant funds from Children&#8217;s Healthcare of Atlanta and Emory University Pediatric Flow Cytometry Core. The authors would like to thank Dr. Hans Deckmyn for sharing the 6B4 antibody, and the Emory Children&#39;s Pediatric Research Center Flow Cytometry Core for technical support.

All methods using donor-derived human platelets described herein were approved by the Institutional Review Board of Emory University/Children&#39;s Healthcare of Atlanta.
1. Blood Draw and Platelet Isolation
<ol>
	<li>Draw human blood from consenting healthy adult donors via venipuncture on the day of the experiment into 3.8% trisodium citrate. One 4.5 mL tube of blood is sufficient to yield enough platelet rich plasma (PRP) for 20-25 conditions in donors whose platelet counts are close to 250 x 103 per &#956;L. 
	NOTE: Avoid drawing blood via narrow gauge needles (smaller than 21 G).</li>
	<li>Prepare PRP via centrifugation at 22 &#176;C and 140 x g for 12 min with a long brake. This will result in two distinct layers, with red blood cells at the bottom and the light colored PRP at the top.</li>
	<li>Isolate the top, cloudy, yellow layer of PRP via careful pipetting through a pipette tip cut at a 45&#176; angle and obtain the platelet count via a complete blood count (CBC).</li>
	<li>If necessary, wash platelets in PIPES-buffered saline (150 mM NaCl, 20 mM PIPES) in the presence of prostaglandin E1 (PGE1) and resuspend in Tyrode&#39;s buffer (134 mM NaCl, 0.34 mM Na2HPO4, 2.9 mM KCl, 1 mM MgCl2, 5 mM glucose, 12 mM NaHCO3, 20 mM HEPES, pH 7.35) with 5 mM glucose, otherwise, proceed to step 1.5. The following steps describe the washing in brief.
	<ol>
		<li>Adjust PRP volume to 10 mL with PIPES-buffered saline and add 0.6 &#956;M PGE1.</li>
		<li>Centrifuge for 8 min at 1,900 x g, then discard supernatant and let the platelet pellet sit in 400 &#956;L of Tyrode&#39;s and glucose solution for 5 min.</li>
		<li>Gently resuspend the platelet pellet and keep it undisturbed for 30 min.</li>
	</ol>
	</li>
	<li>Adjust the platelet count to ~250 x 103 platelets per &#956;L with pooled human platelet-poor plasma (PPP) and maintain the suspension at 22 &#176;C undisturbed or under gentle rotation.</li>
</ol>
2. Ligand and uniform shear treatment
NOTE: All steps in section 2 that require pipetting should be done slowly, so as not to introduce any shear.
<ol>
	<li>Add the desired antibody or ligand to the PRP or washed platelets and mix gently by pipetting up and down or stirring with a pipette tip. Leave it undisturbed at room temperature for 5-10 min. Add an equivalent volume of PPP or Tyrode&#39;s buffer to a negative control.</li>
	<li>Turn on the cone-plate viscometer, set the plate temperature to 22 &#176;C and allow time to let the plate reach this temperature.</li>
	<li>Pipette the treated PRP or washed platelets onto the temperature-controlled cone-plate viscometer directly at the center of the plate. Ensure that all of the sample is deposited between the cone and plate at the point of contact, and not on the outside of the cone&#8217;s rim.</li>
	<li>Shear at an appropriate rate and duration.
	<ol>
		<li>Calculate shear as indicated by the viscometer manual, or as previously shown15,16.</li>
		<li>Determine shear rate from viscosity and desired shear stress via Newton&#39;s law of viscosity; <img alt="Equation 1" src="/files/ftp_upload/59704/59704eq1.jpg" />; plasma viscosity is 1.5-1.6 centipoise (cP)17. For example, a normal shear range for human circulation is 5-30 dyn/cm2 and shear should be applied on the single digit minute time scale.</li>
	</ol>
	</li>
	<li>Lift the cone off of the plate slighlty (~2 mm) so that the sample remains in contact with both the plate and cone, and use a gel-loading or other long pipette tip to collect 5-10 &#956;L from the center of the sample volume.</li>
	<li>Incubate the sheared samples with the desired markers for 20 min at room temperature. For markers of phosphatidylserine, &#946;-galactose, and P-selectin exposure use Lactadherin C2 domain (LactC2) at 0.08 &#956;M18, Erythrina cristagalli lectin (ECL) at 6.25 &#956;g/mL, and anti-P-selectin antibody (20 &#181;g/mL), respectively.</li>
	<li>Fix samples in 2% paraformaldehyde for 20 min at RT prior to dilution or cold storage, and proceed to step 3.1 or store samples at 4 &#176;C for no longer than 12 h.</li>
</ol>
3. Detection of surface markers and crosslinking via flow cytometry
<ol>
	<li>Analyze the sample via flow cytometry, collecting at least 20,000 events for each condition.</li>
	<li>Quantitate signal strength of the fluorescent markers using the height value for the intensity of each fluorophore, or the geometric mean fluorescence intensity (MFI).</li>
	<li>If aiming to detect platelet crosslinking following shear treatment, analyze the sample on an imaging-capable flow cytometer and quantitate crosslinking by area and aspect ratio parameters.
	<ol>
		<li>Plot a histogram of area and/or aspect ratio.</li>
		<li>Use a negative control with bovine serum albumin (BSA) or vehicle to draw a gate excluding most fully circular events (this gate is usually drawn at an aspect ratio ~0.819,20) and quantitate the percentage of events inside of this gate. Events with a lower aspect ratio are more likely to be crosslinked.</li>
	</ol>
	</li>
</ol>

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I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Snapshots of hemodynamics: an aid for clinical research and graduate education. , (2010).</li><li>Liang, X., 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=Specific+inhibition+of+ectodomain+shedding+of+glycoprotein+Ibalpha+by+targeting+its+juxtamembrane+shedding+cleavage+site.">Specific inhibition of ectodomain shedding of glycoprotein Ibalpha by targeting its juxtamembrane shedding cleavage site.</a> Journal of Thrombosis and Haemostasis. 11 (12), 2155-2162 (2013).</li><li>Samsel, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+flow+cytometry+for+morphologic+and+phenotypic+characterization+of+rare+circulating+endothelial+cells.">Imaging flow cytometry for morphologic and phenotypic characterization of rare circulating endothelial cells.</a> Cytometry Part B: Clinical Cytometry. 84 (6), 379-389 (2013).</li><li>Basiji, D. 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The authors have nothing to disclose.

The protocol described in this manuscript allows quick and versatile assessment of the effect of laminar shear on platelet and cell surface receptors. The specific representative results presented here underscore how the effects of multimeric or bivalent ligands can be affected by shear flow. In addition to this application, a uniform shear assay has broad applications in observing shear-dependent effects. In the absence of a known ligand-receptor pair, a uniform shear assay can also detect the effects of shear on factor...

Mechanoreceptors are proteins that respond to mechanical stimuli, such as pressure or mechanical perturbation/deformation. For some mechanoreceptors, sensing these mechanical perturbations is explicit to the function of the cell types in which they are expressed. Take, for example, the stretch receptors in baroreceptor neurons; these mechanosensitive ion channels regulate blood pressure by sensing vascular &#34;stretch&#34;1,2. In the inner ear, ion channels on hair cells detect mechanical deformations caused by sound waves3, and cutaneous low threshold mechanoreceptors (LTMRs) facilitate the transmission of tactile information4. In other cases, mechanoreceptors provide important information to the cell for the establishment of adhesion or growth. Cells can sense the rigidity of their local environment, and may rely on contractile forces via the actin cytoskeleton and integrins to dictate growth or spreading5,6.
When studying receptor-ligand interactions in cell or tissue-based models, common assays exist which can quickly and accurately report the effects of altering temperature, pH, ligand concentration, tonicity, membrane potential, and many other parameters which can vary in vivo. However, these same assays may fall short when it comes to detecting the contribution of mechanical force to receptor activation. Whether cells are sensing their microenvironment, detecting sound waves, or responding to stretch, one thing the aforementioned mechanoreceptors have in common is that they are participating in interactions where the ligand, receptor, or both, are anchored to a surface. Assays developed to test the effects of mechanical forces on receptor interactions often reflect this paradigm. Microfluidics and flow chambers are used to study the effects of shear flow on cells and receptors7,8. These types of experiments have the advantage of allowing fine-tuning of shear rates via established flow speeds. Other techniques employ fluorescent molecular probes to detect forces applied by cells on ligand-rich surfaces, yielding an accurate readout of the magnitude and orientations of forces involved in the interaction9,10.
In addition to mechanosensation occurring where one or both partners are anchored to a surface, shear stress may affect proteins and cells in solution. This is often observed in blood cells/proteins which are constantly in the circulation, and may manifest via activation of mechanoreceptors that are normally surface-anchored11, or through exposure of target sequences which would be occluded under static conditions12. However, relatively fewer techniques assay the effects of shear force on particles in solution. Some in-solution approaches introduce shear via vortexing cells in fluid suspension with varying speeds and durations, although these approaches may not allow a very precise determination of the shear stress generated. Rotational viscometers measure viscosity by applying a specific shear force to fluids. Herein we describe an applied method for determining the effect of specific laminar shear rates on cells or cell fragments in solution.
One of the most highly expressed proteins on the platelet surface is the glycoprotein (GP) Ib-IX complex. GPIb-IX is the primary receptor for the plasma protein von Willebrand Factor (VWF). Together, this receptor-ligand pair has long been recognized as the foundation of the platelet response to shear stress13. In the event of vascular damage, VWF binds to exposed collagen in the sub-endothelial matrix14, thus recruiting platelets to the site of injury via the VWF-GPIb-IX interaction. VWF engagement to its binding site in the GPIb&#945; subunit if GPIb-IX under physiological shear stress induces unfolding of a membrane-proximal mechanosensory domain (MSD) which in turn activates GPIb-IX15. In a recent study, we have shown that antibodies against GPIb&#945;, like those generated in many immune thrombocytopenia (ITP) patients, are also capable of inducing platelet signaling via MSD unfolding under shear stress11. However, unlike VWF, which facilitates shear-induced GPIb-IX activation by immobilizing the complex under normal circulation, the bivalent antibodies are able to crosslink platelets via GPIb-IX and unfold the MSD in circulation. In this way, a mechanoreceptor which is normally activated by surface immobilization under shear can be activated in solution. In the present report, we will demonstrate how a viscometer-based uniform shear assay was leveraged to detect the effects of specific levels of shear stress on receptor activation in solution.

<table><tbody><tr><td>APC anti-human CD62P (P-Selectin)</td><td>BioLegend</td><td>304910</td><td></td></tr><tr><td>Brookfield Cap 2000+ Viscometer</td><td>Brookfield</td><td>-</td><td></td></tr><tr><td>FITC-conjugated Erythrina cristagalli lectin (ECL)</td><td>Vector Labs</td><td>FL-1141</td><td></td></tr><tr><td>Pooled Normal Human Plasma</td><td>Precision Biologic</td><td>CCN-10</td><td></td></tr><tr><td>Vacutainer Light Blue Blood Collection Tube (Sodium Citrate)</td><td>BD</td><td>369714</td><td></td></tr><tr><td>Vacutainer Blood Collection Set, 21G x &amp;frac34;&quot; Needle</td><td>BD</td><td>367287</td><td></td></tr></tbody></table>

a uniform shear assay for human platelet and cell surface receptors via cone-plate viscometry

Many biological cells/tissues sense the mechanical properties of their local environments via mechanoreceptors, proteins that can respond to forces like pressure or mechanical perturbations. Mechanoreceptors detect their stimuli and transmit signals via a great diversity of mechanisms. Some of the most common roles for mechanoreceptors are in neuronal responses, like touch and pain, or hair cells which function in balance and hearing. Mechanosensation is also important for cell types which are regularly exposed to shear stress such as endothelial cells, which line blood vessels, or blood cells which experience shear in normal circulation. Viscometers are devices that detect the viscosity of fluids. Rotational viscometers may also be used to apply a known shear force to fluids. The ability of these instruments to introduce uniform shear to fluids has been exploited to study many biological fluids including blood and plasma. Viscometry may also be used to apply shear to the cells in a solution, and to test the effects of shear on specific ligand-receptor pairs. Here, we utilize cone-plate viscometry to test the effects of endogenous levels of shear stress on platelets treated with antibodies against the platelet mechanosensory receptor complex GPIb-IX.

Figure 1 outlines how the trigger model of GPIb-IX activation, initially introduced to explain shear-dependent receptor activation when anchored to the vessel wall, may also support activation of platelets crosslinked by a multivalent ligand. Figure 2 shows readouts of human platelet activation treated by two antibodies targeting the N-terminal domain of GPIb-IX (6B4 and 11A8), and one control antibody (normal IgG) under sheared and static conditions. In <strong...

Watch this Scientific Journal Video about A Uniform Shear Assay for Human Platelet and Cell Surface Receptors via Cone-plate Viscometry at JoVE.com

A Uniform Shear Assay for Human Platelet and Cell Surface Receptors via Cone-plate Viscometry

We describe an in-solution method to apply uniform shear to platelet surface receptors using cone-plate viscometry. This method may also be used more broadly to apply shear to other cell types and cell-fragments and need not target a specific ligand-receptor pair.

Many biological cells/tissues sense the mechanical properties of their local environments via mechanoreceptors, proteins that can respond to forces like ...

a-uniform-shear-assay-for-human-platelet-cell-surface-receptors-via

Research

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Biology

7.6K Views.  Children's Healthcare of Atlanta. We describe an in-solution method to apply uniform shear to platelet surface receptors using cone-plate viscometry. This method may also be used more broadly to apply shear to other cell types and cell-fragments and need not target a specific ligand-receptor pair.

Video: A Uniform Shear Assay for Human Platelet and Cell Surface Receptors via Cone-plate Viscometry

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 ...

Enhancing Targeted Cancer Diagnosis by Quantifying Single-Cell Mechanics

Shear Assay Protocol for the Determination of Single-Cell Material Properties

Irregular biomechanics are a hallmark of cancer biology subject to extensive study. The mechanical properties of a cell are similar to those of a material. A cell's resistance to stress and strain, its relaxation time, and its elasticity are all properties that can be derived and compared to other types of cells. Quantifying the mechanical properties of cancerous (malignant) versus normal (non-malignant) cells allows researchers to further uncover the biophysical fundamentals of this disease. While the mechanical properties of cancer cells are known to consistently differ from the mechanical properties of normal cells, a standard experimental procedure to deduce these properties from cells in culture is lacking. 
This paper outlines a procedure to quantify the mechanical properties of single cells in vitro using a fluid shear assay. The principle behind this assay involves applying fluid shear stress onto a single cell and optically monitoring the resulting cellular deformation over time. Cell mechanical properties are subsequently characterized using digital image correlation (DIC) analysis and fitting an appropriate viscoelastic model to the experimental data generated from the DIC analysis. Overall, the protocol outlined here aims to provide a more effective and targeted method for the diagnosis of difficult-to-treat cancers.

Author Spotlight: Shear Assay Protocol for the Determination of Single-Cell Material Properties  

This protocol outlines the quantification of the mechanical properties of cancerous and non-cancerous cell lines in vitro. Conserved differences in the mechanics of cancerous and normal cells can act as a biomarker that may have implications in prognosis and diagnosis.

Irregular biomechanics are a hallmark of cancer biology subject to extensive study. The mechanical properties of a cell are similar to those of a ...

Cancer Research

Laminar Flow-based Assays to Investigate Leukocyte Recruitment on Cultured Vascular Cells and Adherent Platelets

The recruitment of leukocytes upon injury or inflammation to sites of injury or tissue damage has been investigated during recent decades and has resulted in the concept of the leukocyte adhesion cascade. However, the exact molecular mechanisms involved in leukocyte recruitment have not yet been fully identified. Since leukocyte recruitment remains an important subject in the field of infection, inflammation, and (auto-) immune research, we present a straightforward laminar flow-based assay to study underlying mechanisms of the adhesion, de-adhesion, and transmigration of leukocytes under venous and arterial flow regimes. The in vitro assay can be used to study the molecular mechanisms that underlie the interactions between leukocytes and their cellular partners in different models of vascular inflammation. This protocol describes a laminar flow-based assay using a parallel-flow chamber and an inverted phase contrast microscope connected to a camera to study the interactions of leukocytes and endothelial cells or platelets, which can be visualized and recorded then analyzed offline. Endothelial cells, platelets, or leukocytes can be pretreated with inhibitors or antibodies to determine the role of specific molecules during this process. Shear conditions, i.e. arterial or venous shear stress, can be easily adapted by the viscosity and flow rate of the perfused fluids and the height of the channel.

Leukocytes avidly interact with vascular cells and platelets after vessel wall injury or during inflammation. Here, we describe a straightforward laminar flow-based assay to characterize the molecular mechanisms that underlie the interactions between leukocytes and their cellular partners.

The recruitment of leukocytes upon injury or inflammation to sites of injury or tissue damage has been investigated during recent decades and has resulted ...

Immunology and Infection

Turbidimetry on Human Washed Platelets: The Effect of the Pannexin1-inhibitor Brilliant Blue FCF on Collagen-induced Aggregation

Turbidimetry is a laboratory technique that is applied to measure the aggregation of platelets suspended in either plasma (platelet-rich plasma, PRP) or in buffer (washed platelets), by the use of one or a combination of agonists. The use of washed platelets separated from their plasma environment and in the absence of anticoagulants allows for studying intrinsic platelet properties. Among the large panel of agonists, arachidonic acid (AA), adenosine di-phosphate (ADP), thrombin and collagen are the most frequently used. The aggregation response is quantified by measuring the relative optical density (OD) over time of platelet suspension under continuous stirring. Platelets in homogeneous suspension limit the passage of light after the addition of an agonist, platelet shape change occurs producing a small transitory increase in OD. Following this initial activation step, platelet clots form gradually, allowing the passage of light through the suspension as a result of decreased OD. The aggregation process is ultimately expressed as a percentage, compared to the OD of platelet-poor plasma or buffer. Rigorous calibration is thus essential at the beginning of each experiment. As a general rule: calibration to 0% is set by measuring the OD of a non-stimulated platelet suspension while measuring the OD of the suspension medium containing no platelets represents a value of 100%. Platelet aggregation is generally visualized as a real-time aggregation curve. Turbidimetry is one of the most commonly used laboratory techniques for the investigation of platelet function and is considered as the historical gold standard and used for the development of new pharmaceutical agents aimed at inhibiting platelet aggregation. Here, we describe detailed protocols for 1) preparation of human washed platelets and 2) turbidimetric analysis of collagen-induced aggregation of human washed platelets pretreated with the food dye Brilliant Blue FCF that was recently identified as an inhibitor of Pannexin1 (Panx1) channels.

We describe a straightforward method for the isolation of washed platelets from human blood followed by agonist-induced platelet aggregation measurements by turbidimetry. As an example we apply this method for studying the aggregation response of human platelets to collagen after a pre-incubation with the Pannexin1 channel inhibitor Brilliant Blue FCF.

Turbidimetry is a laboratory technique that is applied to measure the aggregation of platelets suspended in either plasma (platelet-rich plasma, PRP) or ...

Medicine

Investigating von Willebrand Factor Pathophysiology Using a Flow Chamber Model of von Willebrand Factor-platelet String Formation

Von Willebrand factor (VWF) is a multimeric glycoprotein coagulation factor that mediates platelet adhesion and aggregation at sites of endothelial damage and that carries factor VIII in the circulation. VWF is synthesized by endothelial cells and is either released constitutively into the plasma or is stored in specialized organelles, called Weibel-Palade bodies (WPBs), for on-demand release in response to hemostatic challenge. Procoagulant and proinflammatory stimuli can rapidly induce WPB exocytosis and VWF release. The majority of VWF released by endothelial cells circulates in the plasma; however, a proportion of VWF is anchored to the endothelial cell surface. Under conditions of physiological shear, endothelial-anchored VWF can bind to platelets, forming a VWF-platelet string that may represent the nidus of thrombus formation. A flow chamber system can be used to visually observe the release of VWF from endothelial cells and the subsequent platelet capture in a manner that is reproducible and relevant to the pathophysiology of VWF-mediated thrombus formation. Using this methodology, endothelial cells are cultured in a flow chamber and are subsequently stimulated with secretagogues to induce WPB exocytosis. Washed platelets are then perfused over the activated endothelium. The platelets are activated and subsequently bind to elongated VWF strings in the direction of fluid flow. Using extracellular histones as a procoagulant and proinflammatory stimulus, we observed increased VWF-platelet string formation on histone-treated endothelial cells compared to untreated endothelial cells. This protocol describes a quantitative, visual, and real-time assessment of the activation of VWF-platelet interactions in models of thrombosis and hemostasis.

In this paper, we describe a method to assess endothelial von Willebrand factor release and the subsequent platelet capture under fluid shear stress in response to inflammatory stimuli using an in vitro flow chamber system.

Von Willebrand factor (VWF) is a multimeric glycoprotein coagulation factor that mediates platelet adhesion and aggregation at sites of endothelial damage ...

Platform for Assessing Platelet Function in Trauma and Transfusion

Microfluidics in Assessing Platelet Function

Microfluidics incorporate physiologically relevant substrates and flows that mimic the vasculature and are, therefore, a valuable tool for studying aspects of thrombosis and hemostasis. At high-shear environments simulating arterial flow, a microfluidic assay facilitates the study of platelet function, as platelet-rich thrombi form in a localized stenotic region of a flow channel. Utilizing devices that allow for small sample volume can additionally aid in evaluating platelet function under flow from volume-limited patient samples or animal models. Studying trauma patient samples or samples following platelet product transfusion may aid in directing therapeutic strategies for patient populations in which platelet function is critical. Effects of platelet inhibition via pharmacological agents can also be studied in this model. The objective of this protocol is to establish a microfluidic platform that incorporates physiologic flow, biological surfaces, and relevant hemostatic mechanisms to assess platelet function with implications for the study of trauma induced coagulopathy and transfusion medicine.

Platelet function under flow can be assessed and simulated hemostatic resuscitation can be modeled using a microfluidic device, which has applications in trauma and transfusion medicine.

Microfluidics incorporate physiologically relevant substrates and flows that mimic the vasculature and are, therefore, a valuable tool for studying ...

Imaging Single Platelet Migration Using a Three-Layer Coating System

An In Vitro Assay to Study Platelet Migration Using RGD-Functionalized Avidin-Biotin Tethers

Despite being anucleated cell fragments, platelets are now widely recognized for their multifaceted abilities. Not only do they form blood clots to prevent bleeding after injury, but they also fight infections and maintain vascular integrity during inflammatory diseases. While hemostatic plugs require the collective activation and aggregation of platelets, their role in protecting inflamed blood vessels is performed at the single-cell level. In this context, recent data have shown that platelets can migrate autonomously, a process dependent on the mechanosensing of their adhesive environment. Here, a detailed protocol for imaging single platelet migration is presented, utilizing a three-layer coating system consisting of a poly-L-lysine graft poly(ethylene glycol) (PLL-PEG)-biotin backbone (1), a fluorescent avidin linker (2), and biotin-cyclic Arg-Gly-Asp (cRGD) (3) as the platelet integrin-binding motif. This reductionist approach allows precise control of substrate adhesion properties and serves as a simple, standardized in vitro assay to study the mechanisms underlying platelet migration. The results indicate that migrating platelets binding to cRGD exert forces capable of disrupting the avidin-biotin bond. Furthermore, the density of biotin-cRGD significantly influences both platelet spreading and migration.

A detailed protocol for imaging single migrating platelets using RGD-functionalized avidin-biotin tethers with tunable density is provided, revealing that platelets generate enough force to rupture the avidin-biotin bond.

Despite being anucleated cell fragments, platelets are now widely recognized for their multifaceted abilities. Not only do they form blood clots to ...

Analyzing Platelet Phosphatidylserine and Microvesicle Release

Procoagulant Platelet Characterization by Measuring Phosphatidylserine Exposure and Microvesicle Release from Human Purified Platelets

Activated platelets promote coagulation primarily by exposing the procoagulant phospholipid phosphatidylserine (PS) on their outer membrane surfaces and releasing PS-expressing microvesicles that retain the original membrane architecture and cytoplasmic components of their originating cells. The accessibility of phosphatidylserine facilitates the binding of major coagulation factors, significantly amplifying the catalytic efficiency of coagulation enzymes, while microvesicle release acts as a pivotal mediator of intercellular signaling. Procoagulant platelets play a crucial role in clot stabilization during hemostasis, and their increased proportion in the bloodstream correlates with an increased risk of thrombosis. It has also been shown that platelet microvesicles are rich in growth factors that promote wound healing and inflammatory modulation. Analyzing phosphatidylserine exposure and microvesicle release using flow cytometry poses significant challenges due to their small size and the limited number of positive events for markers of interest. Despite considerable advances in the last decade, methods for assessing phosphatidylserine exposure and microvesicle release remain a work in progress. Unfortunately, no single universally applicable protocol exists, and several factors must be evaluated to determine the most appropriate methodology for each specific application. Here, we describe a detailed protocol for isolating washed platelets from human blood, followed by collagen and/or thrombin activation, to measure the exposure of phosphatidylserine and microvesicle release that characterize procoagulant platelets. This protocol is designed to facilitate the initial preparation of platelet-rich plasma and the isolation of washed platelets. Finally, phosphatidylserine exposure and microvesicle release are quantified by flow cytometry, enabling the identification of procoagulant platelets.

Procoagulant platelet formation has been correlated with an increased risk of thrombosis. Presented here is a precise protocol for isolating washed platelets from human blood, intended to quantify the exposure of phosphatidylserine and microvesicle release, which are distinctive features of procoagulant platelets.

Activated platelets promote coagulation primarily by exposing the procoagulant phospholipid phosphatidylserine (PS) on their outer membrane surfaces and ...

Isolating Quiescent Platelets for Metabolic Research

Preparation of Washed Human Platelets for Quantitative Metabolic Flux Studies

Platelets are blood cells that play an integral role in hemostasis and the innate immune response. Platelet hyper- and hypoactivity have been implicated in metabolic disorders, increasing risk for both thrombosis and bleeding. Platelet activation and metabolism are tightly linked, with the numerous methods to measure the former but relatively few for the latter. To study platelet metabolism without the interference of other blood cells and plasma components, platelets must be isolated, a process that is not trivial because of platelets shear sensitivity and ability to irreversibly activate. Presented here is a protocol for platelet isolation (washing) that produces quiescent platelets that are sensitive to stimulation by platelet agonists. Successive centrifugation steps are used with the addition of platelet inhibitors to isolate platelets from whole blood and resuspend them in a controlled, isosmotic buffer. This method reproducibly produces 30%&#8211;40% recovery of platelets from whole blood with low activation as measured by markers of granule secretion and integrin activity. Platelet count and fuel concentration can be precisely controlled to allow the user to probe a variety of metabolic situations.

Platelet metabolism is of interest, particularly as it relates to the role of platelet hyper- and hypoactivity in bleeding and thrombotic disorders. Isolating platelets from plasma is necessary for some metabolic assays; presented here is a method for isolating of intracellular metabolites from washed platelets.

Platelets are blood cells that play an integral role in hemostasis and the innate immune response. Platelet hyper- and hypoactivity have been implicated ...

The Effects of Shear Stress on Platelets Treated with Antibodies Against Mechanosensory Receptors

Source: Quach, M. E. et al., <a href="https://app.jove.com/v/59704">A Uniform Shear Assay for Human Platelet and Cell Surface Receptors via Cone-plate Viscometry.</a> J. Vis. Exp.&#160;(2019)
This video demonstrates the method to assess the impact of shear stress on platelets. Antibody treatment induces dissociation and conformational changes in mechanoreceptor complexes, activating the platelets and expressing markers on the surface. These markers are observed via immunostaining and flow cytometry.