TY - JOUR

T1 - Megakaryocyte-specific RhoA deficiency causes macrothrombocytopenia and defective platelet activation in hemostasis and thrombosis

AU - Pleines, Irina

AU - Hagedorn, Ina

AU - Gupta, Shuchi

AU - May, Frauke

AU - Chakarova, Lidija

AU - van Hengel, Jolanda

AU - Offermanns, Stefan

AU - Krohne, Georg

AU - Kleinschnitz, Christoph

AU - Brakebusch, Cord

AU - Nieswandt, Bernhard

PY - 2011/11/1

Y1 - 2011/11/1

N2 - Vascular injury initiates rapid platelet activation that is critical for hemostasis, but it also may cause thrombotic diseases, such as myocardial infarction or ischemic stroke. Reorganizations of the platelet cytoskeleton are crucial for platelet shape change and secretion and are thought to involve activation of the small GTPase RhoA. In this study, we analyzed the in vitro and in vivo consequences of megakaryocyte- and platelet-specific RhoA gene deletion in mice. We found a pronounced macrothrombocytopenia in RhoA-deficient mice, with platelet counts of approximately half that of wild-type controls. The mutant cells displayed an altered shape but only a moderately reduced life span. Shape change of RhoA-deficient platelets in response to G(13)-coupled agonists was abolished, and it was impaired in response to G(q) stimulation. Similarly, RhoA was required for efficient secretion of a and dense granules downstream of G(13) and G(q). Furthermore, RhoA was essential for integrin-mediated clot retraction but not for actomyosin rearrangements and spreading of activated platelets on fibrinogen. In vivo, RhoA deficiency resulted in markedly prolonged tail bleeding times but also significant protection in different models of arterial thrombosis and in a model of ischemic stroke. Together, these results establish RhoA as an important regulator of platelet function in thrombosis and hemostasis.

AB - Vascular injury initiates rapid platelet activation that is critical for hemostasis, but it also may cause thrombotic diseases, such as myocardial infarction or ischemic stroke. Reorganizations of the platelet cytoskeleton are crucial for platelet shape change and secretion and are thought to involve activation of the small GTPase RhoA. In this study, we analyzed the in vitro and in vivo consequences of megakaryocyte- and platelet-specific RhoA gene deletion in mice. We found a pronounced macrothrombocytopenia in RhoA-deficient mice, with platelet counts of approximately half that of wild-type controls. The mutant cells displayed an altered shape but only a moderately reduced life span. Shape change of RhoA-deficient platelets in response to G(13)-coupled agonists was abolished, and it was impaired in response to G(q) stimulation. Similarly, RhoA was required for efficient secretion of a and dense granules downstream of G(13) and G(q). Furthermore, RhoA was essential for integrin-mediated clot retraction but not for actomyosin rearrangements and spreading of activated platelets on fibrinogen. In vivo, RhoA deficiency resulted in markedly prolonged tail bleeding times but also significant protection in different models of arterial thrombosis and in a model of ischemic stroke. Together, these results establish RhoA as an important regulator of platelet function in thrombosis and hemostasis.

KW - Animals

KW - Bleeding Time

KW - Blood Platelets

KW - Brain Infarction

KW - Calcium Signaling

KW - Cell Shape

KW - Cell Size

KW - Clot Retraction

KW - GTP-Binding Protein alpha Subunits, G12-G13

KW - GTP-Binding Protein alpha Subunits, Gq-G11

KW - Hemostasis

KW - Kinetics

KW - Megakaryocytes

KW - Mice

KW - Mice, Knockout

KW - Platelet Activation

KW - Platelet Count

KW - Thrombocytopenia

KW - Thrombosis

KW - rho GTP-Binding Proteins

U2 - 10.1182/blood-2011-08-372193

DO - 10.1182/blood-2011-08-372193

M3 - Journal article

C2 - 22045984

VL - 119

SP - 1054

EP - 1063

JO - Blood

JF - Blood

SN - 0006-4971

IS - 4

ER -