Differential regulation of platelet aggregation and aminophospholipid exposure by calpain.

Aggregation, exposure of procoagulant phospholipids and shedding of microparticles are platelet responses that depend on activating conditions. To determine how these different responses are interconnected, we simultaneously measured fibrinogen (Fg) binding and aminophospholipid exposure on activated platelets by means of flow cytometry. Low calcium ionophore (A23187) concentrations induced Fg binding but not annexin V binding.

Integrin alpha(IIb)beta3 signals lead cofilin to accelerate platelet actin dynamics.

Cofilin, in its Ser3 dephosphorylated form, accelerates actin filament turnover in cells. We report here the role of cofilin in platelet actin assembly. Cofilin is primarily phosphorylated in the resting platelet as evidenced by a specific antibody directed against its Ser3 phosphorylated form.

Thiosulfinates inhibit platelet aggregation and microparticle shedding at a calpain-dependent step.

Thiosulfinates (TSs) are sulfur compounds generated through the processing of different Allium species with antiplatelet property. To further define this platelet inhibitory effect we studied diallyl-TS (Al2TS), dipropyl-TS (Pr2TS). and dimethyl-TS (Me2TS) on platelet responses.

Implication of protein S thrombin-sensitive region with membrane binding via conformational changes in the gamma-carboxyglutamic acid-rich domain.

In the vitamin K-dependent protein family, only protein S (PS) contains a thrombin-sensitive region (TSR), located between the domain containing the gamma-carboxyglutamic acid and the first epidermal growth factor-like domain. To better define the role of TSR in the PS molecule, we expressed a recombinant human PS (rHPS) and its analogue lacking TSR (rTSR-less), and prepared factor Xa- and thrombin-cleaved rHPS. A peptide reproducing TSR (TSR-peptide) was also synthesized in an attempt to obtain direct evidence of the domain involvement in PS anticoagulant activity.

The platelet release reaction: granules' constituents, secretion and functions.

Although anucleated, blood platelets are highly organized cells rich in different types of organelles. Three specific granule populations store different types of constituents, some of which are at high concentrations. Platelets thus transport some specific compounds through the whole body.

A new approach in the study of the molecular and cellular events implicated in heparin-induced thrombocytopenia. Formation of leukocyte-platelet aggregates.

Heparin-induced thrombocytopenia (HIT), a relatively common complication of heparin therapy, results of platelet activation, via the receptor for the Fc domain of IgG (FcgammaRIIa), by heparin-dependent-antibodies, commonly directed against the heparin-platelet factor 4 (H-PF4) antigenic complex. Our strategy was to use whole blood allowing the study of leukocyte-platelet interactions. Experiments were performed with blood from healthy donors incubated with HIT patients' plasma and different concentrations of heparin.

Platelets induce human umbilical vein endothelial cell proliferation through P-selectin.

We studied whether platelets could participate in the endothelial cell monolayer regeneration in the case of a vessel damage. Incorporation of [3H]-thymidine into the DNA of human umbilical vein endothelial cells (HUVECs) was measured after 48 h of co-incubation with platelets. The effect of platelets was compared to that of platelet-free supernatants from thrombin-activated platelets that had secreted their active granule constituents.

Calpain controls the balance between protein tyrosine kinase and tyrosine phosphatase activities during platelet activation.

Protein phosphorylation was studied during platelet stimulation in two ranges of ionized [Ca2+]. At ionized [Ca2+]i< or = 1 microM, proteins were phosphorylated. At ionized [Ca2+]i > or = 4 microM, phosphoproteins disappeared.