Thrombasthenic mice generated by replacement of the integrin αIIb gene: demonstration that transcriptional activation of this megakaryocytic locus precedes lineage commitment

The relative importance of platelet integrins in hemostasis, thrombosis and beyond

Integrins are heterodimeric transmembrane receptors composed of α and β chains, with an N-terminal extracellular domain forming a globular head corresponding to the ligand binding site. Integrins regulate various cellular functions including adhesion, migration, proliferation, spreading and apoptosis. On platelets, integrins play a central role in adhesion and aggregation on subendothelial matrix proteins of the vascular wall, thereby ensuring hemostasis. Platelet integrins belong either to the β1 family (α2β1, α5β1 and α6β1) or to the β3 family (αIIbβ3 and αvβ3). On resting platelets, integrins can engage their ligands when the latter are immobilized but not in their soluble form. The effects of various agonists promote an inside-out signal in platelets, increasing the affinity of integrins for their ligands and conveying a modest signal reinforcing platelet activation, called outside-in signaling. This outside-in signal ensures platelet adhesion, shape change, granule secretion and aggregation. In this review, we examine the role of each platelet integrin in hemostatic plug formation, hemostasis and arterial thrombosis and also beyond these classical functions, notably in tumor metastasis and sepsis.

Functional consequences of integrin gene mutations in mice

Integrins are cell-surface receptors responsible for cell attachment to extracellular matrices and to other cells. The application of mouse genetics has significantly increased our understanding of integrin function in vivo. In this review, we summarize the phenotypes of mice carrying mutant integrin genes and compare them with phenotypes of mice lacking the integrin ligands.