Differential Involvement of ERK2 and p38 in Platelet Adhesion to Collagen

Abstract

We investigated the role of two MAP kinases, ERK2 and p38, in platelet adhesion and spreading over collagen matrix in static and blood flow conditions. P38 was involved in collagen-induced platelet adhesion and spreading in static adhesion conditions, whereas ERK2 was not. In blood flow conditions, with shear rates of 300 or 1500 s–1, ERK2 and p38 displayed differential involvement in platelet adhesion, depending on the presence or absence of the von Willebrand factor (vWF). Low collagen coverage densities (0.04 μg/cm2) did not support vWF binding. During perfusions over this surface, platelet adhesion was not affected by the inhibition of ERK2 phosphorylation by PD 98059. However, abolishing p38 activation by SB 203580 treatment reduced platelet adhesion by 67 ± 9% at 300 s–1 and 56 ± 2% at 1500 s–1. In these conditions, the p38 activity required for platelet adhesion depends on the α2β1 collagen receptor. At higher collagen coverage densities (0.8 μg/cm2) supporting vWF binding, the inhibition of ERK2 activity by PD 98059 decreased adhesion by 47 ± 6% at 300 s–1 and 72 ± 3% at 1500 s–1, whereas p38 inhibition had only a small effect. The ERK2 activity required for platelet adhesion was dependent on the interaction of vWF with GPIb. In conclusion, ERK2 and p38 have complementary effects in the control of platelet adhesion to collagen in a shear stress-dependent manner. We investigated the role of two MAP kinases, ERK2 and p38, in platelet adhesion and spreading over collagen matrix in static and blood flow conditions. P38 was involved in collagen-induced platelet adhesion and spreading in static adhesion conditions, whereas ERK2 was not. In blood flow conditions, with shear rates of 300 or 1500 s–1, ERK2 and p38 displayed differential involvement in platelet adhesion, depending on the presence or absence of the von Willebrand factor (vWF). Low collagen coverage densities (0.04 μg/cm2) did not support vWF binding. During perfusions over this surface, platelet adhesion was not affected by the inhibition of ERK2 phosphorylation by PD 98059. However, abolishing p38 activation by SB 203580 treatment reduced platelet adhesion by 67 ± 9% at 300 s–1 and 56 ± 2% at 1500 s–1. In these conditions, the p38 activity required for platelet adhesion depends on the α2β1 collagen receptor. At higher collagen coverage densities (0.8 μg/cm2) supporting vWF binding, the inhibition of ERK2 activity by PD 98059 decreased adhesion by 47 ± 6% at 300 s–1 and 72 ± 3% at 1500 s–1, whereas p38 inhibition had only a small effect. The ERK2 activity required for platelet adhesion was dependent on the interaction of vWF with GPIb. In conclusion, ERK2 and p38 have complementary effects in the control of platelet adhesion to collagen in a shear stress-dependent manner. The adhesion and aggregation of platelets in response to vascular injury plays a key role in hemostasis and thrombosis. Fibrillar collagen is the most abundant thrombogenic molecule among the macromolecular constituents of the subendothelial layer. Following exposure to collagen, platelets rapidly adhere, spread, become active, and then aggregate (1Rauterberg J. Jaeger E. Althaus M. Curr. Top. Pathol. 1993; : 163-192PubMed Google Scholar, 2Baumgartner H.R. Tschopp T.B. Weiss H.J. Thromb. Haemostasis. 1977; 37: 17-28Crossref PubMed Google Scholar). This interaction of collagen with platelets is both direct and indirect. Under the high shear stress conditions found in small arteries, the von Willebrand factor (vWF), 1The abbreviations used are: vWF, von Willebrand factor; PAK, p21-activated kinase; ERK, extracellular signal-regulated kinase; JNK, c-Jun N-terminal kinase; Hsp, heat-shock protein; LT, lethal toxin; BSA, bovine serum albumin; PBS, phosphate-buffered saline; TRITC, tetramethylrhodamine isothiocyanate; GP, glycoprotein; mAb, monoclonal antibody; FITC, fluorescein isothiocyanate; MEK, mitogen-activated protein kinase/extracellular signal-regulated kinase kinase; MAP, mitogen-activated protein. 1The abbreviations used are: vWF, von Willebrand factor; PAK, p21-activated kinase; ERK, extracellular signal-regulated kinase; JNK, c-Jun N-terminal kinase; Hsp, heat-shock protein; LT, lethal toxin; BSA, bovine serum albumin; PBS, phosphate-buffered saline; TRITC, tetramethylrhodamine isothiocyanate; GP, glycoprotein; mAb, monoclonal antibody; FITC, fluorescein isothiocyanate; MEK, mitogen-activated protein kinase/extracellular signal-regulated kinase kinase; MAP, mitogen-activated protein. which binds to newly exposed collagen fibers, is required to capture flowing platelets (3Savage B. Saldivar E. Ruggeri Z.M. Cell. 1996; 84: 289-297Abstract Full Text Full Text PDF PubMed Scopus (1008) Google Scholar) via the GPIb-IX-V complex on the platelet surface. This interaction (vWF-GPIb) cannot support the assembly of a stable platelet thrombus. Subsequent firm platelet adhesion and activation are mediated by two major surface receptors for collagen, the integrin α2β1 and glycoprotein VI (4Farndale R.W. Sixma J.J. Barnes M.J. De Groot P.G. J. Thromb. Haemostasis. 2004; 2: 561-573Crossref PubMed Scopus (299) Google Scholar, 5Watson S.P. Gibbins J. Immunol. Today. 1998; 19: 260-264Abstract Full Text Full Text PDF PubMed Scopus (166) Google Scholar, 6Siljander P.R-M. Farndale R.W. Gresele P. Page C.P. Fuster V. Vermylen J. Platelets in Thrombotic and Non-thrombotic Disorders: Pathophysiology, Pharmacology, and Therapeutics. Cambridge University Press, Cambridge, UK2002: 158-178Google Scholar). The relative contributions of these two receptors to collagen-mediated adhesion are unclear, and various models have been proposed (7Saelman E.U. Nieuwenhuis H.K. Hese K.M. De Groot P.G. Heijmen H.F. Sage E.H. Williams S. McKeown L. Gralnick H.R. Sixma J.J. Blood. 1994; 83: 1244-1250Crossref PubMed Google Scholar). According to the two-site, two-step model, the major candidate for involvement in platelet deposition and stabilization on collagen is α2β1, with GPVI mediating activation and initiating the signaling pathway involved in thrombus formation (8Moroi M. Jung S.M. Shinmyozu K. Tomiyama Y. Ordinas A. Diaz-Ricart M. Blood. 1996; 88: 2081-2092Crossref PubMed Google Scholar). Platelet activation leads to an increase in the affinity of α2β1, which in turn leads to an increase in adhesion stability. Another model has been proposed in which the absence of functional GPVI impairs adhesion under static and shear conditions (9Nieswandt B. Brakebusch C. Bergmeier W. Schulte V. Bouvard D. Mokhtari-Nejad R. Lindhout T. Heemskerk J.W. Zirngibl H. Fassler R. EMBO J. 2001; 20: 2120-2130Crossref PubMed Scopus (442) Google Scholar, 10Goto S. Tamura N. Handa S. Arai M. Kodama K. Takayama H. Circulation. 2002; 106: 266-272Crossref PubMed Scopus (110) Google Scholar). In this model, GPVI initiates signaling pathways, leading to the activation of the α2β1 integrin and of other integrins involved in firm adhesion at sites of vascular injury (11Nieswandt S. Watson S.P. Blood. 2003; 102: 449-461Crossref PubMed Scopus (895) Google Scholar). However, the intracellular signaling pathway occurring during platelet adhesion and spreading on collagen is poorly understood. The small GTP-binding proteins Cdc42/Rac and the effector p21-activated kinases (PAKs) play an important role in the spreading of platelet lamellipodia over the collagen matrix (12Suzuki-Inoue K. Yatomi Y. Asazuma N. Kainoh M. Tanaka T. Satoh K. Ozaki Y. Blood. 2001; 98: 3708-3716Crossref PubMed Scopus (73) Google Scholar), and the Cdc42/Rac-dependent activation of PAK involves cortactin (13Vidal C. Geny B. Melle J. Jandrot-Perrus M. Fontenay-Roupie M. Blood. 2002; 100: 4462-4469Crossref PubMed Scopus (131) Google Scholar). A model of intracellular events during α2β1-mediated platelet spreading has been described recently (14Inoue O. Suzuki-Inoue K. Dean W.L. Frampton J. Watson S.P. J. Cell Biol. 2003; 160: 769-780Crossref PubMed Scopus (203) Google Scholar). In this model, the α2β1 integrin mediates the activation of Src family kinases and Syk upstream from phospholipase Cγ2 and the Ca2+ mobilization required for platelet spreading. A second pathway may also involve phosphorylation of the tyrosine kinase focal adhesion kinase. MAP kinases are involved in signaling for cell adhesion and spreading. They belong to a serine/threonine kinase family that includes the extracellular signal-regulated kinase (ERK), the c-Jun N-terminal kinase (JNK), and p38 MAP kinase (15Rossomando A.J. Payne D.M. Weber M.J. Sturgill T.W. Proc. Natl. Acad. Sci. U. S. A. 1989; 86: 6940-6943Crossref PubMed Scopus (287) Google Scholar). In proliferative cells, MAP kinase signaling is essential for normal cell adhesion and spreading and is regulated by growth factors and integrins (16Cobb M.H. Boulton T.G. Robbins D.J. Cell Regul. 1991; 2: 965-978Crossref PubMed Scopus (428) Google Scholar). In platelets, ERK2, JNK1, and p38 are present and activated by various agonists (17Nadal F. Levy-Toledano S. Grelac F. Caen J.P. Rosa J.-P. Bryckaert M. J. Biol. Chem. 1997; 272: 22381-22384Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar, 18Bugaud F. Nadal-Wollbold F. Levy-Toledano S. Rosa J.-P. Bryckaert M. Blood. 1999; 94: 3800-3805Crossref PubMed Google Scholar, 19Canobbio I. Reineri S. Sinigaglia F. Balduini C. M. Thromb. Haemostasis. 2004; PubMed Google Scholar), role in and ERK2 has been to involved in the of collagen-induced platelet and the activation of by vWF and D. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, D. M. R. M. F. Cell. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar, S. M. A. Jandrot-Perrus M. Rosa J.-P. Bryckaert M. 2004; PubMed Scopus Google Scholar). ERK2 activation collagen-induced platelet by kinase activation E. C. H. De R. Vermylen J. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). In the of a mitogen-activated protein kinase/extracellular signal-regulated kinase kinase lethal by collagen and C. M. E. A. S. I. De R. Vermylen J. Heemskerk J.W. M. Blood. 2003; PubMed Scopus Google Scholar). also Ca2+ in platelets Sage J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). In to these ERK2, Watson and Watson S.P. J. 1996; PubMed Scopus Google Scholar) that inhibition of the pathway not the activation of platelet activation has been to dependent on Src kinases not MAP kinases R. F. T. F. Watson S.P. Blood. 2004; PubMed Scopus Google Scholar). The other MAP p38, is involved in collagen-induced platelet aggregation J. L. S. Barnes M.J. Farndale R.W. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar) and activity P. Farndale R.W. P. S. Heemskerk J.W. Thromb. Biol. 2001; PubMed Scopus Google Scholar). has role in We investigated the of p38 and ERK2 in platelet adhesion and spreading over a collagen matrix in static and blood flow conditions. We found that both p38 and ERK2 involved in platelet The role of p38 in platelet adhesion and spreading was of blood flow and involved the α2β1 In the role of ERK2 was dependent on blood flow and We for the complementary for ERK2 and p38 in platelet adhesion to collagen under flow conditions. collagen, and vWF from The MAP kinase PD 98059 and SB from was from The MAP and from The the of p38 MAP kinase was from and that the of from and from The the of was from Cell from and from to from and from from M. The the integrin was by B. The which the of the vWF to was described T. C. D. Vermylen J. Blood. 1999; 94: PubMed Google Scholar). which the of vWF to collagen, was from and Platelet blood was in from of for at to blood was from in with the of the was by blood at for at and platelets by differential The platelet was in and Platelet platelets at in the presence of with SB 203580 PD 98059 or in with collagen or to or μg/cm2) for at was to effects of SB 203580 and PD 98059 on in phosphate-buffered adhesion was in with bovine serum in Platelet deposition was by an described J. Cell Biol. 1996; PubMed Scopus Google Scholar). and blood in a by at with of or collagen, coverage densities of and platelet adhesion not thrombus to the blood at in the presence of SB 203580 PD 98059 or In was to effects of SB 203580 and PD 98059 on and and with for at in the presence or absence of a MAP kinase blood A. H. C. M. Vermylen J. Blood. 2003; PubMed Scopus Google Scholar) of the of the was over the for with a at shear rates of 300 or 1500 s–1. platelets in PBS, with in PBS, and They then by in at and for with They with an and surface, from The by platelets was and S. P. E. M. R. M. F. F. A. and M. Platelet adhesion is relative surface coverage to the of of with or SB 203580 PD 98059 lethal or a control on collagen with a surface of They for at with and by for with or with to and S. Bryckaert M. E. J. Cell Sci. 2004; PubMed Scopus Google Scholar). Platelets and and on a at and to platelet to described S. M. A. Jandrot-Perrus M. Rosa J.-P. Bryckaert M. 2004; PubMed Scopus Google Scholar). Platelets in and at for was by by to The protein to and with by with are ± for at was with for Platelet p38 MAP investigated the role of MAP kinases p38 and ERK2 in platelet deposition on collagen at a of or to or in the presence or absence of SB 203580 and PD 98059 In conditions, control platelets or platelets with with to effects of the on At a collagen of the of platelet deposition by ± 2% platelets platelets for the with SB 203580 to 67 ± 3% In at higher collagen coverage platelet deposition was not affected the MAP kinase deposition to for the with with other and p38 and with of not In investigated the of phosphorylation of ERK2 and p38 required for activity in the presence and absence of and was only in platelets on the higher of collagen μg/cm2) and was by PD 98059. was the of collagen used SB 203580 p38 activity not p38 the of phosphorylation of an of p38, the heat-shock protein not was by SB In static adhesion conditions, of the adhesion was to interaction the We investigated the role of p38 in adhesion aggregation the and of MAP in the presence or absence of the that interaction was not involved at this of collagen μg/cm2) and that the inhibition of adhesion with was of which is involved in platelet adhesion only The of SB 203580 in the presence and absence of the that p38 affected platelet adhesion not platelet that p38 plays a major role in collagen-induced platelet adhesion, whereas ERK2 has only a small effect. Platelet p38 MAP ERK2 investigated the of p38 and ERK2 in platelet spreading over a collagen matrix μg/cm2) under conditions in which MAP kinases have been to involved in platelet was with and lamellipodia In the presence of PD 98059 the formation of and the spreading of In platelet spreading was by SB 203580 platelets We the surface of platelet with in an to these SB 203580 platelet spreading by ± whereas PD 98059 had ± platelet spreading in the presence of not p38 is involved in platelet whereas ERK2 is not. The of p38 in Platelet on and and activation of the small are required for platelet spreading (13Vidal C. Geny B. Melle J. Jandrot-Perrus M. Fontenay-Roupie M. Blood. 2002; 100: 4462-4469Crossref PubMed Scopus (131) Google Scholar). We investigated the role of p38 and ERK2 in by the which The of platelets to collagen had by ± In these conditions, SB 203580 and PD 98059 did not the in response to p38 is involved in platelet spreading not in We then used from C. and from C. to the small protein required for platelet spreading was involved in p38 and whereas and proteins E. E. von C. M. P. D. B. P. M. J. P. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar, L. M. C. 1999; 2: Google Scholar). and decreased the collagen-induced by and also collagen-induced of the most of involved in lamellipodia formation In these conditions, p38 phosphorylation was by and that p38 activation is dependent on This and the activation of other small p38 phosphorylation and by two pathways, both of which are required for spreading. of p38 and ERK2 in Platelet to under investigated the of p38 and ERK2 in blood in conditions of collagen coverage and platelet adhesion not thrombus was over collagen at a or high shear to was with to PD 98059 and SB 203580 from effects on and on We adhesion at 1500 s–1 in the presence and absence of We found that only a role in blood flow not of blood over collagen at coverage the p38 decreased collagen-induced platelet adhesion by 67 ± and 56 ± 2% at 300 and 1500 s–1, with the other p38 SB not In the had ± or ± of shear and p38 is also involved in collagen-induced platelet adhesion under shear conditions. The inhibition by SB 203580 of platelet deposition in both static and shear conditions that p38 of shear conditions and also of We investigated the of p38 and ERK2 at a higher of collagen μg/cm2) at a shear stress of 300 or 1500 s–1. SB 203580 ± platelet adhesion at 1500 s–1. PD 98059 reduced platelet adhesion by 47 ± 6% at 300 s–1 and by 72 ± 3% at 1500 s–1. inhibition was with of two of and at 1500 s–1 not ERK2 is involved in platelet adhesion at higher collagen and the involvement of ERK2 to on shear conditions. of Platelet α2β1 and in MAP and Platelet that activated ERK2 and p38 are involved in platelet adhesion via We investigated the of the collagen α2β1 and interaction in platelet adhesion and MAP kinase activation in stress conditions We vWF was on collagen at and higher coverage densities or μg/cm2) blood At collagen only small of vWF of vWF at higher μg/cm2) This that the involvement of p38 in adhesion depends on α2β1, whereas that of ERK2 depends on interaction We investigated the of p38 inhibition on platelet adhesion to collagen μg/cm2) in the presence of to the integrin α2β1, to the or to the for the vWF on We found that platelet adhesion by ± whereas inhibition ± and ± was with or the small of vWF In the presence of the p38 platelet adhesion was by ± that p38 is required for the of A of inhibition was in the presence of ± In and the on platelet adhesion of was by p38 ± with in the presence or absence of the p38 The p38 and the role of p38 in platelet adhesion is dependent on the collagen We investigated the of and the collagen in the ERK2 activation required for platelet adhesion in conditions of higher collagen μg/cm2) at a shear stress of 1500 s–1. and platelet adhesion by ± and ± whereas only inhibition ± In the presence of the platelet adhesion was by ± that the of ERK2 is not dependent on of inhibition with and in the presence ± ± and absence ± ± of the that the involvement of ERK2 was dependent on This that ERK2 and p38 play in platelet adhesion over collagen matrix under static and shear conditions. The involvement of p38 in platelet adhesion and spreading is of shear the α2β1 and is by the GPVI signaling the involvement of ERK2 in platelet adhesion is dependent on shear stress and We also that a small activated not p38 phosphorylation and by two pathways, both of which are required for platelet spreading. In has been collagen with platelet the intracellular signaling involved in platelet adhesion and spreading on poorly MAP activated during adhesion and spreading in proliferative have been described K. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar). In platelets activated by a p38 activation has been to involved in adhesion to P. S. V. R. D. R. C. Thromb. Haemostasis. 2002; PubMed Scopus Google Scholar). In this that two MAP kinases, ERK2 and p38, activated during adhesion to collagen in static conditions and that only p38 was required for adhesion and spreading. p38 on platelet adhesion not on platelet α2β1 has been to involved in platelet deposition on of platelets to collagen of control platelets B. L. R. R. W. J. Blood. PubMed Google Scholar). also platelet adhesion or deposition on collagen, whereas has T. J. M. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). The of involvement of the vWF in the static adhesion of platelets at collagen densities of and not and the involvement of p38 only at a collagen of that signaling via the collagen receptors and are during platelet deposition at and high collagen Platelet spreading on the was recently to the activation of Src kinases and phospholipase Cγ2 (14Inoue O. Suzuki-Inoue K. Dean W.L. Frampton J. Watson S.P. J. Cell Biol. 2003; 160: 769-780Crossref PubMed Scopus (203) Google Scholar). We that the role of p38 in adhesion depends on α2β1, that platelet spreading via α2β1 involves p38 of that the of p38, and In cells, the p38 by growth factor the required for formation via the S. Bryckaert M. E. J. Cell Sci. 2004; PubMed Scopus Google Scholar). In platelets, aggregation leads to the activation of p38 and MAP protein kinase and the phosphorylation of in Y. S. J. L. Blood. 1994; 84: PubMed Google Scholar). In model, the p38 was not involved in on collagen, the of two and p38 both of which are involved in platelet spreading. The activation of a small and of PAK is required for and spreading on (12Suzuki-Inoue K. Yatomi Y. Asazuma N. Kainoh M. Tanaka T. Satoh K. Ozaki Y. Blood. 2001; 98: 3708-3716Crossref PubMed Scopus (73) Google Scholar). Src family kinases and the are involved in this (12Suzuki-Inoue K. Yatomi Y. Asazuma N. Kainoh M. Tanaka T. Satoh K. Ozaki Y. Blood. 2001; 98: 3708-3716Crossref PubMed Scopus (73) Google Scholar). In proliferative cells, the activation and p38 activation is The activation of p38 has been to dependent on of T. K. Tamura K. K. H. Y. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar) and to involve the serine/threonine kinase PAK J. 2001; PubMed Google Scholar). activation was in this not and investigated the activation and p38 and lethal (13Vidal C. Geny B. Melle J. Jandrot-Perrus M. Fontenay-Roupie M. Blood. 2002; 100: 4462-4469Crossref PubMed Scopus (131) Google Scholar). on a surface was in the presence of these In these conditions, p38 that p38 phosphorylation is dependent on a small In platelets, p38 activation and both of which are required for are dependent on We for the that in blood flow conditions and at collagen coverage p38 is involved in adhesion, whereas ERK2 plays only a The of p38 to of shear and the vWF have been to p38 in platelet aggregation I. Reineri S. Sinigaglia F. Balduini C. M. Thromb. Haemostasis. 2004; PubMed Google Scholar). In collagen conditions, at shear rates high in only small of vWF to collagen, that p38 effects on adhesion via the collagen receptors and by the for platelet adhesion to and 1500 which was dependent on the collagen α2β1 This with that both and α2β1 to adhesion under flow in these shear stress conditions I. H. Lindhout T. Farndale R.W. Heemskerk J. Blood. 2004; PubMed Scopus Google Scholar) may to the of collagen vWF binding, the of collagen at this of collagen In platelet α2β1 is essential for platelet at high shear stress A. P. J. Thromb. 2004; 2: PubMed Scopus Google Scholar). B. M.H. Ruggeri Z.M. Blood. 1999; 94: PubMed Google Scholar) that α2β1 inhibition platelet adhesion to collagen had on to We cannot the of collagen from collagen, leading to the activation of adhesion by signaling to in collagen have been to to in vWF A. P. J. Thromb. 2004; 2: PubMed Scopus Google Scholar). In conditions in have that collagen may of an increase in the matrix activity of and activated H. N. Y. Acad. Sci. PubMed Scopus Google Scholar). that α2β1 plays a major role in these conditions. At a collagen μg/cm2) adhesion not thrombus formation B. M.H. Ruggeri Z.M. Blood. 1999; 94: PubMed Google Scholar), ERK2 was involved in platelet adhesion, and role to on shear In static conditions, ERK2 had on platelet adhesion, whereas at 1500 s–1, adhesion was by in the presence of the This static adhesion and blood flow by the presence of the vWF, involved in ERK2 in blood At higher collagen the vWF was to the collagen and adhesion on interaction and to a on collagen receptors that of the of ERK2 on adhesion was dependent on the This was by the inhibition of adhesion in the presence of and increase to the of the are two the platelet adhesion to a or The interaction involved in platelet adhesion may on at two pathways, with the major pathway dependent on ERK2 activation and the second of ERK2 ERK2 activity may not by PD 98059. whereas adhesion at 300 s–1 was dependent on α2β1 and to a on interaction not the inhibition of adhesion by PD 98059 was and on This that ERK2 plays a major role in platelet adhesion to the for the that the role of ERK2 in platelet adhesion under shear conditions is dependent on the In the vWF has been to and to platelet aggregation via ERK2 activation D. J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). In collagen model, two of and interaction platelet adhesion via ERK2, that ERK2 plays a major role in adhesion and thrombus However, in platelets, Watson and R. F. T. F. Watson S.P. Blood. 2004; PubMed Scopus Google Scholar) that ERK2 was not involved in adhesion to collagen in blood flow conditions. these models may for the the role of ERK2 at high shear are with the involvement of the ERK2 pathway in platelet aggregation on collagen under flow conditions in via the platelet C. M. E. A. S. I. De R. Vermylen J. Heemskerk J.W. M. Blood. 2003; PubMed Scopus Google Scholar) and in platelets, the pathway and the vWF to collagen are involved in platelet activation and the of via the MAP kinase the role of ERK2 at high shear dependent on interaction and the role of ERK2 dependent on the in C. M. E. A. S. I. De R. Vermylen J. Heemskerk J.W. M. Blood. 2003; PubMed Scopus Google Scholar) are two and complementary pathways, both of which to platelet thrombus In conclusion, the differential involvement of ERK2 and p38 in adhesion during the of blood over a collagen matrix In models of small of collagen are exposed and vWF cannot In these conditions, platelets via collagen receptors and this adhesion is dependent on In of at high shear rates in collagen are exposed and vWF In this model, platelets via glycoprotein and vWF to This is dependent on ERK2 activation by adhesion to the collagen receptor. We B. for We also C. for and A. is in of the