Characterization of the Role of Integrin α5β1 in Platelet Function, Hemostasis, and Experimental Thrombosis

Abstract

Objective: Integrins are key regulators of various platelet functions. The pathophysiological importance of most platelet integrins has been investigated, with the exception of α5β1, a receptor for fibronectin. The aim of this study was to characterize the role of α5β1 in megakaryopoiesis, platelet function, and to determine its importance in hemostasis and arterial thrombosis. Approach and results: We generated a mouse strain deficient for integrin α5β1 on megakaryocytes and platelets (PF4Cre-α5-/-). PF4Cre-α5-/- mice were viable, fertile and presented no apparent signs of abnormality. Megakaryopoiesis appears unaltered as evidence by a normal megakaryocytes morphology and development, which is in agreement with a normal platelet count. Expression of the main platelet receptors and the response of PF4Cre-α5-/- platelets to a series of agonists were all completely normal. Adhesion and aggregation of PF4Cre-α5-/- platelets under shear flow on fibrinogen, laminin or von Willebrand factor were unimpaired. In contrast, PF4Cre-α5-/- platelets displayed a marked decrease in adhesion, activation and aggregation on fibrillar cellular fibronectin and collagen. PF4Cre-α5-/- mice presented no defect in a tail-bleeding time assay and no increase in inflammatory bleeding in a reverse passive Arthus model and a lipopolysaccharide pulmonary inflammation model. Finally, no defects were observed in three distinct experimental models of arterial thrombosis based on ferric chloride-induced injury of the carotid artery, mechanical injury of the abdominal aorta or laser-induced injury of mesenteric vessels. Conclusion: In summary, this study shows that platelet integrin α5β1 is a key receptor for fibrillar cellular fibronectin but is dispensable in hemostasis and arterial thrombosis.

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

“…We recently reported that α5β1 does not seem to play a major role in arterial thrombosis as PF4Cre-α5 -/- mice did not display reduced thrombosis in three different in vivo models (ferric chloride injury of the carotid artery, mechanical lesion of the abdominal aorta and laser lesion of mesenteric arterioles). 35 Concerning α6β1, our group observed that PF4Cre-α6 -/- mice are protected against thrombosis in in vivo models using a mechanical or laser lesion. 36 This protection reached the same level as in the PF4Cre-β1 -/- mice mentioned above, 36 suggesting that the platelet β1 integrin with greatest importance in arterial thrombosis is α6β1.…”

“…Indeed, perfusion of whole blood from mice genetically deficient in α5 in the platelet linage (PF4Cre-α5 -/- ) over collagen, a surface that does not activate α5β1, resulted in a reduced thrombus volume as compared to that following perfusion of whole blood from control mice. 35 This suggests that α5β1 contributes to thrombus formation through an interaction with plasma fibronectin. However, the same effect was not observed using human blood perfused over collagen in the presence of an anti-α5 blocking antibody.…”

“… 105 There are currently no antithrombotic agents targeting any of the other four platelet integrins. Since αvβ3 and α5β1 do not play major roles in experimental arterial thrombosis 35 ( Online Supplementary Figure S2E, F ), they are unlikely to be suitable targets for antithrombotic therapy. With regard to integrin α2β1, a reduction in thrombus formation was reported, 96 , 97 indicating that this receptor could represent a potential antithrombotic target.…”

The Novel Role of Noncoding RNAs in Modulating Platelet Function: Implications in Activation and Aggregation

“…The most abundant and best-characterized integrin is αIIbβ3 [58]. Recently, the importance of α5β1 in hemostasis under normal and inflammatory conditions has also been better defined [59]. Various agonists may modulate the affinity of integrins for their ligands, thereby reinforcing platelet activation [57].…”

Illustrated Abstracts of the 5th EUPLAN International Conference

“…We and others identified a role for integrin α5β1 in platelet adhesion, activation and aggregation on fibronectin in vitro . In FeCl 3 -, forceps- and laser-injury models of arterial thrombosis, mice invalidated for the platelet α5β1 present a normal profile of thrombus formation [ 3 ]. Furthermore, the normal tail-bleeding time favors no major role of this integrin in hemostasis.…”