Key result
MRP4 deficiency in mice delayed arterial occlusion, prolonged tail bleeding time, and increased blood loss compared with wild-type mice, indicating a role in promoting platelet aggregation.
Why the study?
Does MRP4 deletion impair platelet activation and thrombus formation in mice?
Does MRP4 deletion impair platelet activation and thrombus formation in mice?
MRP4 promotes platelet aggregation by modulating the cAMP-protein kinase A signaling pathway, identifying it as a potential target for novel antiplatelet agents.
MRP4 modulates platelet reactivity in vitro; leaves open its viability as an antithrombotic target pending in vivo studies.
Molecules that reduce the level of cyclic adenosine 5'-monophosphate (cAMP) in the platelet cytosol, such as adenosine 5'-diphosphate (ADP) secreted from dense granules, trigger platelet activation. Therefore, any change in the distribution and/or availability of cyclic nucleotides or ADP may interfere with platelet reactivity. In this study, we evaluated the role of multidrug resistance protein 4 (MRP4, or ABCC4), a nucleotide transporter, in platelet functions in vivo and in vitro by investigating MRP4-deficient mice. MRP4 deletion resulted in a slight increase in platelet count but had no impact on platelet ultrastructure. In MRP4-deficient mice, the arterial occlusion was delayed and the tail bleeding time was prolonged. In a model of platelet depletion and transfusion mimicking a platelet-specific knockout, mice injected with MRP4(-/-) platelets also showed a significant increase in blood loss compared with mice injected with wild-type platelets. Defective thrombus formation and platelet activation were confirmed in vitro by studying platelet adhesion to collagen in flow conditions, integrin αIIbβ3 activation, washed platelet secretion, and aggregation induced by low concentrations of proteinase-activated receptor 4-activating peptide, U46619, or ADP. We found no role of MRP4 in ADP dense-granule storage, but MRP4 redistributed cAMP from the cytosol to dense granules, as confirmed by increased vasodilator-stimulated phosphoprotein phosphorylation in MRP4-deficient platelets. These data suggest that MRP4 promotes platelet aggregation by modulating the cAMP-protein kinase A signaling pathway, suggesting that MRP4 might serve as a target for novel antiplatelet agents.
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Decouture et al. (2015) studied MRP4 deficiency (animal model). MRP4 deficiency vs. Wild-type mice was evaluated on Platelet function, arterial occlusion, and bleeding time. MRP4 deficiency in mice delayed arterial occlusion, prolonged tail bleeding time, and increased blood loss compared with wild-type mice, indicating a role in promoting platelet aggregation.
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