OC 28.1 - Myosin light chain 6 (Myl6) interacts with kindlin-3 and is required to support integrin αIIbβ3 activation in platelets

Background: Kindlin-3 in platelets plays an essential role in supporting integrin αIIbβ3 activation, platelet spreading, aggregation, and clot retraction by binding to the integrin β3 cytoplasmic tail. However, the mechanism by which kindlin-3 mediates the crosstalk between integrin αIIbβ3 and myosin in platelets remains unknown.

Aims: To examine the role of Myl6 in supporting integrin αIIbβ3 activation in platelets.

Methods: Myl6fl/flPF4-Cre mice, with a deficiency of Myl6 in the megakaryocyte lineage, were generated, and integrin αIIbβ3 activation in Myl6-deficient platelets was analyzed.

Results: We identified a novel kindlin-3 binding protein, Myl6, an essential light chain of myosin in platelets. Myl6fl/flPF4-Cre mice exhibited significant macrothrombocytopenia resulting from defective proplatelet formation. In the absence of Myl6, integrin αIIbβ3 activation in platelets was significantly suppressed, and platelet aggregation was substantially impaired. Interestingly, the deficiency of Myl6 in platelets preferentially affected the binding of a multivalent ligand compared to a monovalent ligand to integrin αIIbβ3 upon activation, indicating that Myl6 may contribute to the avidity modulation of integrin αIIbβ3 by binding to kindlin-3. Furthermore, blood coagulation ability was impaired in Myl6fl/flPF4-Cre mice, and consistently, these mice exhibited defects in both hemostatic and thrombotic functions.

Conclusion(s): In summary, these results suggest that Myl6, as a novel kindlin-3 binding partner, is required to support integrin αIIbβ3 activation in platelets, playing an important role in both hemostasis and thrombosis.