Platelet P2Y(12) receptor influences the vessel wall response to arterial injury and thrombosis.

BACKGROUND: Platelets are believed to play an important role in atherogenesis and the vessel response to vascular injury. The P2Y(12) receptor (P2Y(12)) plays a central role in amplifying platelet aggregation, dense granule and alpha-granule secretion, P-selectin expression, microparticle formation, and procoagulant membrane changes, regardless of the activating stimulus. We hypothesized that P2Y(12) deficiency might reduce the vessel wall response to vascular injury as well as thrombosis in murine vascular injury models. METHODS AND RESULTS: P2Y(12)-deficient (-/-) mice and littermate controls (+/+) were bred on a C57 BL/6 background. In vivo murine models of arterial injury were employed alone and in combination with bone marrow transplantation to investigate the role of P2Y(12) in the vessel wall response to arterial injury and thrombosis. At 21 days after ferric chloride injury, neointima formation in P2Y(12)(-/-) arteries was significantly less than that observed in control strain arteries (P<0.025). In agreement with this, the intima-media ratio was significantly greater in femoral wire-injured arteries from P2Y(12)(+/+) compared with P2Y(12)(-/-) animals (P<0.05). Bone marrow transplantation was used to examine the importance of vessel wall P2Y(12) versus platelet P2Y(12). Analysis of arterial sections from chimeric animals at 21 days after injury revealed a smaller intima-media ratio in -/- to +/+ animals than in the positive (+/+ to +/+) control group (P<0.01). CONCLUSIONS: These data demonstrate a role for platelet P2Y(12) in the vessel wall response to arterial injury and thrombosis. This illustrates the manner in which platelets may contribute to atherogenesis and restenosis.

Changes in the mechanical and adhesive behaviour of human neutrophils on cooling in vitro.

Changes in the rheological properties of neutrophils may influence flow in microvessels that are cooled below normal body temperature. We investigated the effects of temperature on the mechanical and adhesive properties of human neutrophils by measuring transit times for individual cells flowing through 8-microm-pores in filters, and adhesion to P-selectin for cells perfused over a monolayer of activated platelets. Pore transit time increased as temperature was decreased from 37 degrees C to 0 degrees C. Upon rapid cooling, there was an instantaneous increase attributable to changes in aqueous viscosity. Interestingly, at 10 degrees C specifically, there was an additional increase in transit time, which was abolished by the inhibitor of actin polymerization, cytochalasin B. This meant that by 15 min, transit time at 10 degrees C was greater than at 0 degrees C. Most adherent cells on P-selectin were rolling, rather than stationary, at 10, 26 or 37 degrees C. The velocity of rolling slowed with decreasing temperature. The total number of adherent cells decreased with increasing wall shear rate, but for a given shear rate there was relatively little effect of temperature on attachment. However, when adhesion at 10, 26 or 37 degrees C was compared at equal shear stress (taking into account fluid viscosity), adhesion was greatest at 10 degrees C. Measurements of immunofluorescence showed that exposure to 10 degrees C gradually increased expression of beta2-integrin CD11b/CD18, but this did not cause transformation to stationary adhesion with time in the flow assay. Thus, neutrophils show an anomalous rheological response around 10 degrees C, which may impair local microcirculation in the cold. On rewarming, "activated" cells might inhibit recovery or become released into the systemic circulation.