Abstract Number: PB1770
Meeting: ISTH 2020 Congress
Theme: Role of Hemostatic System in Cancer, Inflammation and Immunity » Coagulation Proteins Beyond Hemostasis
Background: : PKa contributes to contact-activated thrombin formation and, in turn, hemostasis by acceleration the activation of factor XII to XIIa when exposed to negatively charged surfaces on medical devices or biologic substances such as polyP, RNA, DNA, and collagen. However, PKa’s contribution to platelet activation has not been studied.
Aims: To examine the mechanism(s) and significance by which PKa potentiates platelet aggregation induced by ADP.
Methods:
Human platelet: blood was collected into 3.8% sodium citrate (w/v) 1:10, centrifuged 141 x g/12 min (PRP, platelet rich plasma) and 350 x g/15 min (PPP, platelet poor plasma).
Platelet activation: ADP-induced platelet activation was measured in a lumi-aggregometer (Chronolog). PRP also were incubated with Fluo-4/AM and calcium mobilization was measured in the confocal microscope.
Immunoblot studies: platelets were lysed, separated by SDS-PAGE and transferred onto nitrocellulose membrane and immunoblotted with anti-phospho-p38, anti-p38 MAPK antibody, anti-phospho-ERK or anti-ERK antibody or anti-AKT monoclonal antibody.
Results: PKa potentiates platelet responses to subthreshold doses of ADP (2 µM) by proteolysis of the G-protein-coupled receptor PAR-1, although PKa itself does not induce platelet aggregation. The potentiation is mediated by the integrin αIIbβ3 through interactions with the KGD/KGE sequence motif in PKa. PKa binds integrin αIIbβ3 to position it for PAR-1 hydrolysis and leads to the amplification of the phosphorylation of Src, AkTS473, ERK1/2, and p38 MAPK, and to Ca2+ mobilization initiated with subthreshold doses of ADP. The effect of PKa is blocked by specific antagonists of PAR-1 (SCH 19197) and αIIbβ3 (abciximab) and by synthetic peptides containing the KGD and KGE sequence motifs of PKa. Further, recombinant plasma kallikrein inhibitor, rBbKI, blocks this entire mechanism.
Conclusions: These findings indicate a new function for PKa. Formation of PKa lowers the threshold for ADP-induced platelet activation. The present observations are consistent with the notion that PKa is a risk factor for cardiovascular disease.
To cite this abstract in AMA style:
Oliva MLV, Ottaiano TF, Andrade SS, Juliano MA, Girão MJBC, Schmaier AH, Wlodawer A, Maffei FHdA. Human Plasma Kallikrein (PKa) Potentiates ADP-Induced Platelet Activation [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/human-plasma-kallikrein-pka-potentiates-adp-induced-platelet-activation/. Accessed April 17, 2024.« Back to ISTH 2020 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/human-plasma-kallikrein-pka-potentiates-adp-induced-platelet-activation/