Properties of procoagulant platelets: defining and characterizing the subpopulation binding a functional prothrombinase.
OBJECTIVE
The goal of this study was to define and characterize the subpopulation of platelets capable of regulating the functional interactions of factors Va (FVa) and Xa (FXa) on the thrombin-activated platelet surface.


RESULTS
Flow cytometric analyses were used to define and characterize platelet subpopulations. At a concentration of thrombin known to elicit maximal platelet activation, platelet-derived FVa release, and prothrombinase assembly/function, only a subpopulation of platelets was positive for FVa and FXa binding. An additional subpopulation bound lower levels of FVa but little, if any, FXa. Fluorescence microscopy analyses confirmed these data. Phenotypically, platelets capable of binding FXa were more highly reticulated and demonstrated significantly increased expression of several key adhesion molecules, including P-selectin, glycoprotein Ibα, and integrins α(IIb) and β(3). This platelet subpopulation was also defined by the expression of a nondissociable, membrane-bound pool of functional platelet-derived FVa, which made up ≈35% to 50% of the total membrane-bound cofactor.


CONCLUSIONS
The ability of activated platelets to support thrombin generation is defined by a subpopulation of platelets expressing a nondissociable pool of platelet-derived FVa and increased adhesive receptor density. This subpopulation is hypothesized to play a significant role in regulating both normal hemostasis and pathological thrombus formation because the adherent properties of platelets and their ability to mount and sustain a procoagulant response are crucial steps in both of these processes.
Department of Biochemistry, University of Vermont College of Medicine, Burlington, Vt 05405, USA.
Ammon M
AM
Fager
Jeremy P
JP
Wood
Beth A
BA
Bouchard
Ping
P
Feng
Paula B
PB
Tracy
D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001777:Blood Coagulation; D001792:Blood Platelets / Q000201:enzymology*; D015943:Factor Va / Q000378:metabolism*; D015951:Factor Xa / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D039421:Integrin alpha2 / Q000097:blood; D039661:Integrin beta3 / Q000097:blood; D008562:Membrane Glycoproteins / Q000097:blood; D008856:Microscopy, Fluorescence; D008875:Middle Aged; D019007:P-Selectin / Q000097:blood; D010641:Phenotype; D015539:Platelet Activation; D010973:Platelet Adhesiveness; D019038:Platelet Glycoprotein GPIb-IX Complex; D011485:Protein Binding; D013917:Thrombin / Q000378:metabolism*
C056564:ITGA2B protein, human; C061248:ITGB3 protein, human; D039421:Integrin alpha2; D039661:Integrin beta3; D008562:Membrane Glycoproteins; D019007:P-Selectin; D019038:Platelet Glycoprotein GPIb-IX Complex; C094990:adhesion receptor; D015943:Factor Va; D013917:Thrombin; D015951:Factor Xa