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From the Department of Hematology, University Hospital, Utrecht, The Netherlands.
Correspondence to Dr Philip G. de Groot, University Hospital Utrecht, Department of Hematology (G03.647), PO Box 85500, 3508 GA Utrecht, The Netherlands. E-mail jvelde{at}digd.azu.nl
| Abstract |
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Key Words: platelet adhesion platelet detachment von Willebrand factor collagen
| Introduction |
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The effect of the shear rate on platelet adhesion has been studied for most adhesive proteins.2,3 No shear optimum was found for collagen type III, ECM, and surface-coated vWF: Increased shear rate leads to increased adhesion up to 2000 s-1, and adhesion remains unchanged above this shear rate.3 Fibronectin showed an optimum at 300 s-1,4 laminin at 800 s-1,5 and thrombospondin at 1500 s-1.6 Adhesion to fibrinogen/fibrin showed a broad shear optimum between 500 and 1000 s-1, with a gradual decrease toward 50% of the optimum at 2000 s-1.7 It is currently unclear whether this shear optimum is determined to a larger extent by adhesion or detachment of platelets. In the current study, we have measured the detachment of platelets from various adhesive proteins and from ECM to shed some light on this question.
| Methods |
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Coating and Spraying of the Coverslips
Glass coverslips (Menzel Gläser 18x18 mm) were
cleaned overnight by a chromium trioxide solution and rinsed with
distilled water before spraying. Monomeric collagen type III was
solubilized in 50 mmol/L acetic acid and spray-coated with
a density of 30 µg/cm2 on glass
coverslips with a retouching airbrush (Badger model 100, Badger Brush
Co).11 After the spraying procedure, the collagen
surface was incubated for 1 hour with 1% human albumin in PBS
(10 mmol/L phosphate buffer, pH 7.4, .15 mol/L NaCl)
to block further protein binding.
Human endothelial cells derived from umbilical veins were isolated and cultured as described before.12,13 For the experiments described, endothelial cells were cultured on glass coverslips, previously coated with gelatin. To isolate the extracellular matrix, cells were grown to confluence and exposed to 0.1 mol/L NH4OH for 3 to 5 minutes at room temperature. The cell layer was completely removed by this procedure, leaving the extracellular matrix intact.14 The extracellular matrix was washed three times with PBS before use.
Platelet adhesion to adsorbed adhesive proteins (vWF, fibronectin, laminin, fibrinogen) was studied by using square glass microcapillaries (Microcell, The Wilmad Glass Company Inc). Coating was performed by incubating the microcapillaries with 25 µL of purified vWF (10 µg/mL), fibronectin (300 µg/mL), laminin (100 µg/mL), and fibrinogen (100 µg/mL) in PBS for 1 hour, followed by a 15-minute incubation with 1% human albumin solution in PBS to block further protein binding. The concentration chosen for the coating of the capillaries is the concentration of the different proteins that gives optimal platelet adhesion. After coating, microcapillaries were kept in PBS until perfusion. In separate experiments it was shown that the coated proteins remain bound to the surfaces during the perfusion experiments.
Perfusion Studies
Perfusion studies over ECM and collagen type III were carried
out in a specially devised small parallel plate perfusion chamber with
well-defined rheological characteristics devised to accommodate a glass
coverslip.15 Whole blood obtained by
venipuncture from healthy volunteer donors was
anticoagulated with 0.1 vol 200 U/mL LMWH(LMWH-blood) or 0.1 vol
110 mmol/L trisodium citrate (citrated blood). Citrated
blood was use for platelet adhesion studies to vWF, fibronectin,
fibrinogen, and endothelial cell extracellular matrix.
LMWH-blood was used for platelet adhesion to laminin and collagen
because for these surfaces the presence of cations is necessary for
optimal adhesion. Whole blood was prewarmed at 37°C for 5 minutes and
then drawn from a container through the chamber for 5 minutes at
different wall shear rates with the use of a syringe and an automated
syringe pump (Harvard Apparatus). Some of the coverslips
were then taken from the chamber for evaluation as described below. The
other coverslips were subjected to a brief perfusion at variable
shear rates with 10 mmol/L HEPES buffer, pH 7.4, containing
0.15 mol/L NaCl (HBS) during 1 minute (viscosity HEPES buffer
0.75±0.01 cpoise). These coverslips were then taken from the chamber,
rinsed in HBS, fixed in 0.5% glutaraldehyde/PBS,
dehydrated in methanol, and stained with May-GrünwaldGiemsa as
previously described.16 Platelet adhesion was
evaluated with a light microscope, and the coverage was measured with
an image analyzer (AMS 40 to 10). A homogeneous
coverage of platelets was always observed. Fixation, staining, and
evaluation for the square microcapillaries was identical. The
microscope was focused on the upper glass wall of the capillary.
Adhesion was expressed as the percentage of the surface covered with
platelets. The effect of the applied shear stress during the second
perfusion was presented as attached platelets remaining
after the second perfusion. This effect was expressed as percentage of
the platelet coverage obtained after the first perfusion (not
subjected to the 1-minute perfusion with HBS). In some experiments,
spread and dendritic platelets were counted. For this purpose, five
duplicate fields at a magnification of 400x were imaged and printed,
and the total number of spread and dendritic cells was counted.
Dendritic and spread cells were recognized by eye. The mean area of a
dendritic cell was 8.2±2.2 µ2 and the mean
area of a spread cell 42.1±11.3 µ2, indicating
that clear distinction had been achieved.
Perfusions were also performed with glass microcapillaries coated by adsorption with vWF, fibronectin, laminin, and fibrinogen as described. This procedure was followed to reach very high shear rates. Perfusions were performed with a single passage, drawing blood from a container through the tube at various wall shear rates as described above. Perfusions were directly followed by a 1-minute flush of HBS at varying shear stress as described above.
Scanning Electron Microscopy
For scanning electron microscopy, coverslips with platelets
fixed for 1 hour with 2% glutaraldehyde/PBS at room
temperature were postfixed in 1% osmium tetroxide for 1 hour,
dehydrated in a graded series of ethanol, and dried by the critical
point procedure, using CO2 as transitional fluid.
The samples were sputter-coated with a thin layer of gold and viewed in
a scanning electron microscope (Cam Scan S2).
| Results |
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Morphology of the Remaining Platelets
Intuitively, one does expect that platelets that are more
spread out will be less easily removed at high shear rates. At very
high shear rates, damage to adherent cells may occur, which may lead to
spuriously low results. We therefore quantified the morphology of
adherent platelets on various surfaces after the detachment
experiment and compared it with the morphology before the experiment.
The results are shown in Fig 2A
through
2D. For all four surfaces, dendritic platelets detached more
quickly than spread platelets. This finding was most pronounced for
fibronectin (Fig 2B
). The detachment of spread platelets tended to
be linear with the shear stress. Of note is the presence of some
dendritic platelets still present on vWF at high shear stress.
Spread platelets remaining on fibrinogen and vWF at the highest
shear stress regularly contained a central hole. This hole is shown in
more detail in the scanning electron micrograph (Fig 3
).
Immunofluorescence staining of fibrinogen
demonstrated that these holes showed exactly the same staining as the
surface surrounding the attached platelets, suggesting that part of
the platelet had completely disappeared and that the underlying
surface coat had become accessible to the fluorescent antibody
(data not shown).
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Platelet Detachment From the ECM
Platelet adhesion studies to the ECM were performed at 100 and
300 s-1, giving a surface coverage of
16.5±3.4% and 34.8±1.6%, respectively (Table 1
). Detachment studies were performed in
the single-pass small perfusion chamber, in which a maximum shear
stress of 30 dyne/cm2 could be attained. A flush
with HBS lasting 1 minute at this shear stress caused a small but
significant decrease in surface coverage to 87.5±0.9% of the control
value when platelet adhesion was caused by flowing blood at a wall
shear rate of 300 s-1. A remaining attachment of
57.8±4.7% of control was found when the adhesion had occurred at 100
s-1. When platelet spreading at 300
s-1 was prevented by using a high concentration
of dRGDW (100 µmol/L), platelet adhesion was
decreased to 12.1±0.9%, but the subsequent platelet detachment
was increased, so that 56.6±6.0% of control remained attached to the
ECM (Table 2
).
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Platelet Detachment From Collagen Type III
Platelets adhere to collagen type III at 100 and 300
s-1, with formation of aggregates. Surface
coverage was 4.6±0.2% and 15.4±0.5%, respectively. A brief flush
with HBS for 1 minute at 30 dyne/cm2 had no
effect at all at 300 s-1 but caused a
significant reduction to 59.7±4.1% of the control when adhesion had
occurred at 100 s-1 (Table 1
). When platelet
aggregation and platelet spreading were prevented at 300
s-1 with use of dRGDW, platelet adhesion
increased considerably, as has been published
before.17 A perfusion with HBS during 1 minute at
30 dyne/cm2 resulted in only a slight
nonsignificant decrease toward 87.6±11.3% of control (Table 2
).
Effect of the Shear Rate at Which Platelets Have Adhered on the
Subsequent Detachment
The studies on platelet detachment from the ECM and collagen
type III showed the importance of the initial shear rate at which
platelets had attached for the subsequent detachment at high shear
stress. We have studied this detachment in detail also for fibronectin,
laminin, fibrinogen, and vWF. The results are summarized in Fig 4
, which shows the results on ECM and
collagen type III (Table 1
) as well, for comparison. The percentage of
platelets that remains attached after a 1-minute flush at a shear
stress of 2.2 (fibronectin and laminin) or 30
dyne/cm2 (fibrinogen, vWF, ECM, and collagen type
III) increased sharply in the range between 100 and 600
s-1. For ECM and collagen type III, almost no
detachment was observed by 300 s-1. Fibronectin
was studied only up to a shear rate of 300 s-1
because the adhesion decreases strongly above this shear
rate.4
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Effect of the Time Period Between the Two Perfusions on
Detachment
Dendritic cells were removed more easily than spread cells. In
time, platelets showed an increased tendency to spread. Therefore,
we studied the influence of the perfusion time of the first run on the
detachment of platelets. The results are summarized in Fig 5
, which shows that after 3 minutes'
perfusion, 65% of the platelets detached in the second flush.
After 5 minutes, the percentage of detached platelets decreased to
56%, while after 10 minutes, only 19% of the platelets were
detached with the second flush.
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| Discussion |
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Relation Between Shear Stress and Detachment
We have studied the detachment of platelets that adhered under
flow from a series of adhesive surfaces and adhesive proteins. We
found, on the basis of a shear rate for adhesion of 300
s-1, that there was a hierarchy, with ECM and
collagen type III as the surfaces to which platelets were attached
most firmly, von Willebrand factor and fibrinogen as a second
group with firm attachment, and fibronectin and laminin as the proteins
with the least firm attachment. The results that we observed on
platelets adhering to fibrinogen after 5 minutes' flow at 300
s-1 were in the same range as the results of Jen
et al17 after 12 minutes' adhesion from
platelet-rich plasma under static conditions. Detachment was
linear, with the shear stress with half-maximal detachment at 26
dyne/cm2. The results on fibronectin, laminin,
and von Willebrand factor were somewhat different. Detachment
was linear with the logarithm of the shear stress. A likely explanation
may be that platelets are spread to a larger degree on fibrinogen.
As seen in Fig 2A
, at least 40% of the platelets are fully spread
out on fibrinogen, which corresponds to a large proportion of the
surface coverage. Spread platelets are removed in a linear relation
to the shear stress, and this dominated the overall picture in the case
of fibrinogen to a larger extent than for the other adhesive
proteins.
Relation Between Morphology and Detachment
The platelets that remained attached to fibrinogen and vWF
were fully spread, and high stress (50 dyne/cm2)
caused mechanical damage, with a central hole where part of the
platelet had been torn away. This may indicate that the central
part of a spread platelet is less strongly attached to the surface
than the periphery. Also, on other surfaces, spread platelets
remained attached relatively better than dendritic platelets. Jen
et al17 suggested on the basis of their results
on fibrinogen that the degree of spreading is the main determinant of
platelet detachment. Our current results confirm this observation
when a single shear rate is selected for adhesion and when a single
surface is studied. This does not mean, however, that detachment is
completely determined by the degree of spreading. Closer study of Fig 2
shows that at a shear rate at which all dendritic platelets have
disappeared from fibronectin, 50% remain still attached to fibrinogen
or vWF. Also, perfusion studies depicted in Fig 4
indicate that
dendritic platelets may remain fully attached when they have
adhered at high shear rates, since up to 30% of the adhering
platelets is dendritic and no detachment occurs even at the highest
shear stress.
Detachment as Determinant of Shear Resistance
As mentioned in the introduction, adhesion to various proteins
shows a clear-cut hierarchy regarding the shear rate. Fibronectin has a
shear optimum at 300 s-1 and laminin at 800
s-1.4,5 For von
Willebrand factor, ECM, and collagen type III, no shear optimum
was observed.3 Adhesion to fibrin(ogen) showed a
broad shear optimum between 500 and 1000 s-1,
with a gradual decrease toward 50% of the optimum at 2000
s-1.7 Comparison of the
shear rate dependence of adhesion with the detachment data observed at
a shear rate of 300 s-1 shows considerable
discrepancy. Laminin and fibronectin show similar detachment, but their
shear optima are different. vWF and fibrinogen have approximately
similar detachment but a different shear optimum for adhesion. This
observation suggests that the adhesion optimum is not primarily
determined by the detachment.
Detachment From Complex Matrices
The detachment from ECM and collagen type III was minimal when
adhesion occurred at 300 s-1. This is most
likely due to the fact that several different adhesive interactions are
involved in both of these cases. Adhesion to collagen type III is
dependent on vWF and on direct interactions between collagen type III
and platelet receptors. Platelet adhesion to collagen type III
leads to thrombus formation. It is striking that a shear stress of 30
dyne/cm2 has an effect neither on adhesion nor on
thrombus formation once thrombi had formed during 5 minutes' perfusion
at 300 s-1.
Platelet spreading on ECM is known to be mediated by GPIIb-IIIa.20 Adhesion in the presence of the GPIIb-IIIa blocking peptide dRGDW gave a decrease in platelet adhesion and a pronounced increase in detachment. On collagen type III, a surface on which GPIIb-IIIa interaction and spreading are not important, detachment was not affected by dRGDW, although thrombus formation was completely abolished, with a rise in platelet adhesion as the consequence of the higher platelet concentration in the marginal layer, as has been reported before.21
In conclusion, platelet detachment is determined by the shear rate at which adhesion occurred, the adhesive surface, and the degree of spreading, in that order of importance. Complex matrices are better able to retain platelets on their surface than single proteins. Adhesion is a complex process determined only to a limited extent by detachment of platelets that have adhered as dendritic or spread platelets.
| Selected Abbreviations and Acronyms |
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| Acknowledgments |
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Received November 25, 1996; accepted April 21, 1997.
| References |
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2. Sixma JJ, van Zanten GH, Banga JD, Nieuwenhuis HK, De Groot PG. Platelet adhesion. Semin Hematol. 1995;32:16.[Medline] [Order article via Infotrieve]
3.
Wu YP, van Breugel HHFI, Lankhof H, Wise RJ, Handin
RI, de Groot PG, Sixma JJ. Platelet adhesion to multimeric
and dimeric von Willebrand factor and to collagen type III
preincubated with von Willebrand factor. Arterioscler
Thromb Vasc Biol. 1996;16:611620.
4.
Beumer S, IJsseldijk MJW, De Groot PG, Sixma JJ.
Platelet adhesion to fibronectin in flow: dependence on surface
concentration and shear rate, role of membrane GP IIb/IIIa, and VLA-5
and inhibition by heparin. Blood. 1994;84:37243733.
5.
Hindriks GA, IJsseldijk MJW, Sonnenberg A, Sixma JJ,
De Groot PG. Platelet adhesion to laminin: role of
Ca2+ and Mg2+ ions, shear
rate, and platelet membrane glycoproteins.
Blood. 1992;79:928935.
6. Agbanyo FR, Sixma JJ, De Groot PG, Languino LR, Plow EF. Thrombospondin-platelet interactions: role of divalent cations, wall shear rate and platelet membrane glycoproteins. J Clin Invest. 1993;92:288296.
7.
Hantgan RR, Hindriks G, Taylor R, Sixma JJ, De Groot
PG. Glycoprotein Ib, von Willebrand factor, and
glycoprotein IIb/IIIa are all involved in platelet
adhesion to fibrin in flowing whole blood. Blood. 1990;76:345353.
8. Tetteroo PAT, Lansdorp PM, Leeksma OC, von dem Borne AE. Monoclonal antibodies against human platelet glycoprotein IIIa. Br J Haematol. 1983;55:509522.[Medline] [Order article via Infotrieve]
9. Houdijk WPM, Sakariassen KS, Nievelstein PFEM, Sixma JJ. Role of factor VIII-von Willebrand factor and fibronectin in the interaction of platelets in flowing blood with monomeric and fibrillar collagen types I and III. J Clin Invest. 1985;75:531540.
10. Van Mourik JA, Mochtar IA. Purification of human anti-hemophilic factor (factor VIII) by gel-chromatography. Biochim Biophys Acta. 1970;221:677679.[Medline] [Order article via Infotrieve]
11. Muggli R, Baumgartner HR, Tschopp TB, Keller H. Automated microdensitometry and protein assay as a measure for platelet adhesion and aggregation on collagen-coated slides under controlled flow conditions. J Lab Clin Med. 1980;95:195207.[Medline] [Order article via Infotrieve]
12. Jaffe EA, Nachman RL, Becker CG, Minick CR. Culture of human endothelial cells derived from umbilical veins: identification by morphologic and immunologic criteria. J Clin Invest. 1973;52:27452756.
13. Willems C, Astaldi GCB, de Groot PG, Jansen MC, Consalves MD, Zeijlemaker WP, van Mourik JA, van Aken WG. Media conditioned by cultured human vascular endothelial cells inhibit the growth of vascular smooth muscle cells. Exp Cell Res. 1982;139:191197.[Medline] [Order article via Infotrieve]
14. Sixma JJ, Nievelstein PFEM, Zwaginga JJ, De Groot PG. Adhesion of blood platelets to the extracellular matrix of cultured human endothelial cells. Ann N Y Acad Sci. 1987;516:3951.[Medline] [Order article via Infotrieve]
15. van Zanten GH, Saelman EUM, Schut-Heese KM, Wu Y-P, Slootweg PJ, Nieuwenhuis HK. Platelet adhesion to collagen type IV under flow conditions. Blood. 1996;85:38623871.
16.
Nievelstein PFEM, d'Alessio PA, Sixma JJ. Fibronectin
in platelet adhesion to human collagen types I and III: use of
nonfibrillar and fibrillar collagen in flowing blood studies.
Arteriosclerosis. 1988;8:200206.
17.
Jen CJ, Li HM, Wang JS, Chen HI, Usami S. Flow-induced
detachment of adherent platelets from fibrinogen-coated surface.
Am J Physiol. 1996;270:H160H166.
18. Baumgartner HR. The role of blood flow in platelet adhesion, fibrin deposition, and formation of mural thrombi. Microvasc Res. 1973;5:167179.[Medline] [Order article via Infotrieve]
19. Sakariassen KS, Aarts PAMM, De Groot PG, Houdijk WPM, Sixma JJ. A perfusion chamber developed to investigate platelet interaction in flowing blood with human vessel wall cells, their extracellular matrix and purified components. J Lab Clin Med. 1983;102:522535.[Medline] [Order article via Infotrieve]
20. Weiss HJ, Turitto VT, Baumgartner HR. Further evidence that glycoprotein IIb-IIIa mediates platelet spreading on subendothelium. Thromb Haemost. 1991;65:202205.[Medline] [Order article via Infotrieve]
21.
Saelman EUM, Hese KM, Nieuwenhuis HK, Uzan A, Cavero I,
Marguerie G, Sixma JJ, de Groot PG. Aggregate formation is more
strongly inhibited at higher shear rates by dRGDW, a synthetic
RGD-containing peptide. Arterioscler Thromb. 1993;13:11641170.
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