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 g/cm 2 ) 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 ␣2␤1 collagen receptor. At higher collagen coverage densities (0.8 g/cm 2 ) 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 (1, 2). 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), 1 which binds to newly exposed collagen fibers, is required to capture flowing platelets (3) 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 ␣2␤1 and glycoprotein VI (4 -6). The relative contributions of these two receptors to collagen-mediated adhesion are unclear, and various models have been proposed (7). According to the two-site, two-step model, the major candidate for involvement in platelet deposition and stabilization on collagen is ␣2␤1, with GPVI mediating activation and initiating the signaling pathway involved in thrombus formation (8). Platelet activation leads to an increase in the affinity of ␣2␤1, 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 (9, 10). In this model, GPVI initiates signaling pathways, leading to the activation of the ␣2␤1 integrin and of other integri...

Dietary α-Linolenic Acid Inhibits Arterial Thrombus Formation, Tissue Factor Expression, and Platelet Activation

“…Because the MAP kinase p38 plays a crucial role in collagen-induced, as well as thrombininduced, platelet activation and adhesion, the effect of ALA on p38 phosphorylation in isolated platelets was investigated. 38,39 ALA decreased collagen-and thrombin-induced p38 activation, an effect that may well account for the reduced aggregation observed in ALA-treated platelets. Taken together, these observations may provide an explanation for the remaining difference in occlusion times observed between the 2 groups after treatment with an inhibitory anti-TF antibody.…”

Thrombin stimulation of p38 MAP kinase in human platelets is mediated by ADP and thromboxane A2 and inhibited by cGMP/cGMP-dependent protein kinase

“…Similar observations have been made in the case of ERK activation. 16 p38 has been shown to mediate platelet adhesion in static as well as flow conditions on low-collagen-density surfaces, 17 and platelet aggregation induced by low collagen, U46619, 18 and thrombin 8 concentrations. However, these studies relied on the use of p38 inhibitors (SB202190, SB203580), but unfortunately did not use appropriate controls such as the inactive analog SB202474.…”

Enhanced Levels of Soluble CD40 Ligand Exacerbate Platelet Aggregation and Thrombus Formation Through a CD40-Dependent Tumor Necrosis Factor Receptor–Associated Factor-2/Rac1/p38 Mitogen-Activated Protein Kinase Signaling Pathway

“…Consistent with its role in sCD40L-induced shape change and platelet priming, p38 MAPK has been shown to be an important regulator of actin polymerization and platelet spreading. 35 Whether enhanced levels of sCD40L seen in patients with ACS are a consequence of increased platelet activation or a predetermining cause of these complications (or perhaps both) is still unknown. Here, we provide novel evidence demonstrating a direct correlation between enhanced levels of sCD40L and thrombosis.…”