Abstract
Integrin αIIbβ3 plays a central role in the adhesion and aggregation of platelets and thus is essential for hemostasis and thrombosis. Integrin activation requires the transmission of a signal from the small cytoplasmic tails of the α or β subunit to the large extracellular domains resulting in conformational changes of the extracellular domains to enable ligand binding. Hydrogen peroxide-inducible clone-5 (Hic-5), a member of the paxillin family, serves as a focal adhesion adaptor protein associated with αIIbβ3 at its cytoplasmic tails. Previous studies suggested Hic-5 as a novel regulator of integrin αIIbβ3 activation and platelet aggregation in mice. To assess this in more detail, we generated Hic-5-null mice and analyzed activation and aggregation of their platelets in vitro and in vivo. Surprisingly, lack of Hic-5 had no detectable effect on platelet integrin activation and function in vitro and in vivo under all tested conditions. These results indicate that Hic-5 is dispensable for integrin αIIbβ3 activation and consequently for arterial thrombosis and hemostasis in mice.
Highlights
Vessel wall injury results in the exposure of the subendothelial extracellular matrix which initiates stable platelet adhesion and aggregation [1,2]. These processes are crucial for normal hemostasis, but in diseased vessels they may lead to pathological thrombus formation and infarction of vital organs [3]
Platelet adhesion and aggregation are mediated by integrins, heterodimeric transmembrane receptors composed of α and β subunits that are expressed in a low affinity state under resting conditions
We used embryonic stem cells provided by CSD, a collaborative team at the Children's Hospital Oakland Research Institute, and the University of California at Davis, within the Knockout Mouse Program (KOMP) with a knockout first approach targeting exon 1 of the Tgfb1i1 gene leading to efficient loss of Hydrogen peroxide-inducible clone-5 (Hic-5) protein in Tgfb1i1+/- mice
Summary
Vessel wall injury results in the exposure of the subendothelial extracellular matrix which initiates stable platelet adhesion and aggregation [1,2]. We generated Hic-5-null (Tgfb1i1-/-) mice and found, in stark contrast to the study by KimKaneyama et al [14], unaltered platelet integrin function in vitro and in vivo. For adhesion to vWF, cover slips were coated with rabbit anti-human vWF antibody at 4°C o/n, washed with PBS, blocked for 1 h with 1% BSA in H2O and incubated with 100 μl murine serum obtained from control mice.
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