Platelet hyperreactivity and a prothrombotic phenotype in mice with a gain-of-function mutation in phospholipase Cgamma2.
BACKGROUND
Agonist-induced platelet activation involves different signaling pathways leading to the activation of phospholipase C (PLC) beta or PLCgamma2. Activated PLC produces inositol 1,4,5-trisphosphate and diacylglycerol, which trigger Ca(2+) mobilization and the activation of protein kinase C, respectively. PLCbeta is activated downstream of Gq-coupled receptors for soluble agonists with only short interaction times in flowing blood. In contrast, PLCgamma2 becomes activated downstream of receptors that interact with immobilized ligands such as the collagen receptor glycoprotein (GP) VI or activated integrins.


OBJECTIVE
We speculated that PLCgamma2 activity might be optimized for sustained but submaximal signaling to control relatively slow platelet responses. To test this hypothesis, we analyzed platelets from mice heterozygous for a gain-of-function mutation in the Plcg2 gene (Plcg2(Ali5/+)).


RESULTS
Plcg2(Ali5/+) platelets showed enhanced Ca(2+) mobilization, integrin activation, granule secretion and phosphatidylserine exposure upon GPVI or C-type lectin-like receptor-2 stimulation. Furthermore, integrin alpha(IIb)beta(3) outside-in signaling was markedly enhanced in the mutant platelets, as shown by accelerated spreading on different matrices and faster clot retraction. These defects translated into virtually unlimited thrombus formation on collagen under flow in vitro and a prothrombotic phenotype in vivo.


CONCLUSIONS
These results demonstrate that the enzymatic activity of PLCgamma2 is tightly regulated to ensure efficient but limited platelet activation at sites of vascular injury.
Elvers
M
M
Chair of Vascular Medicine, University Clinic, and Rudolf Virchow Center, DFG Research Center for Experimental Biomedicine, University of Würzburg, Germany.
Pozgaj
R
R
Pleines
I
I
May
F
F
Kuijpers
M J E
MJ
Heemskerk
J M W
JM
Yu
P
P
Nieswandt
B
B
D000818:Animals; D001792:Blood Platelets / Q000201:enzymology / Q000502:physiology*; D005434:Flow Cytometry; D006579:Heterozygote; D051379:Mice; D009154:Mutation; D010641:Phenotype; D051966:Phospholipase C gamma / Q000235:genetics / Q000378:metabolism*; D010974:Platelet Aggregation; D013927:Thrombosis / Q000235:genetics*
D051966:Phospholipase C gamma