A central role of GPIb-IX in the procoagulant function of platelets that is independent of the 45-kDa GPIbalpha N-terminal extracellular domain.
Activated platelets become procoagulant and efficiently promote the conversion of prothrombin to thrombin. A role of the GPIb-V-IX complex has long been postulated in view of the decreased prothrombin consumption in Bernard-Soulier patients. We evaluated the impact of GPIb-V-IX deficiency and the requirement for the GPIbalpha extracellular domain. In GPIbbeta(-/-) mice, thrombin generation was profoundly decreased in tissue factor- or collagen-related peptide (CRP)-activated platelet-rich plasma and in washed platelets supplemented with normal plasma or with FVa, FXa, and prothrombin. Phosphatidylserine (PS) exposure was similarly decreased in response to thrombin, CRP, or CRP + PAR4 peptide despite a normal platelet phospholipid composition. The hypothesis that these defects originate from lack of the GPIbalpha N-terminal domain was evaluated after its removal from normal mouse and human platelets with Nk protease or O-sialoglycoprotein endopeptidase. Unexpectedly, the treated platelets exhibited normal thrombin generation and PS exposure, indicating that GPIb-V-IX regulates procoagulant activity independently of its GPIbalpha-binding region. These results suggested a more general structuring role through intracellular cytoskeleton-anchoring portions regulating responses leading to PS exposure. This hypothesis was supported by the decreased calcium mobilization observed in GPIbbeta(-/-) platelets in response to several agonists, some acting independently of GPIb, in contrast to the normal calcium responses in Nk protease-treated platelets.
Ravanat
Catherine
C
INSERM UMR_S 949, Etablissement Français du Sang-Alsace (EFS-Alsace), Université de Strasbourg, Strasbourg, France.
Strassel
Catherine
C
Hechler
Béatrice
B
Schuhler
Simone
S
Chicanne
Gaëtan
G
Payrastre
Bernard
B
Gachet
Christian
C
Lanza
François
F
D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D005434:Flow Cytometry; D053804:Granzymes / Q000378:metabolism; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D010718:Phosphatidylserines / Q000378:metabolism; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000502:physiology*; D017434:Protein Structure, Tertiary; D013917:Thrombin / Q000378:metabolism
D008562:Membrane Glycoproteins; D010718:Phosphatidylserines; D019038:Platelet Glycoprotein GPIb-IX Complex; C094990:adhesion receptor; D053804:Granzymes; D013917:Thrombin; D002118:Calcium