Investigating the role of Src family kinases in αIIbβ3-mediated platelet signalling

Abstract

αIIbβ3 is the major integrin expressed in platelets and plays a critical role in platelet aggregation and cessation of bleeding. Signalling via this integrin is critically dependent on the Src-family-kinases of which there are eight members, several of which are expressed in platelets. Platelets also express G protein-coupled receptors which signal through their G proteins, however some evidence for dependence on both Src family kinases and other platelet receptors exists. In this thesis, I have demonstrated that there are differential levels of expression of SFKs in mouse and human platelets. Further to this, utilising mouse models, I demonstrate that Src plays a critical positive role in αIIbβ3-mediated spreading on fibrinogen, with Lyn playing a negative role, potentially downstream of Src. In contrast, individual Src-family-kinases do not appear to play a role in clot retraction or tail bleeding assays, despite the Src-family-kinase inhibitor, Dasatinib having a significant effect. Finally, I demonstrate that both Gi-coupled receptors in human platelets are critically dependent on Src family kinases and αIIbβ3 for signalling, Interestingly, neither receptor stimulates tyrosine phosphorylation of Src family kinases in platelets. This suggests a role for the basal phosphorylation of Src-family-kinases which may be dependent on αIIbβ3-mediated signalling.