An integrin α(IIb)β(3) intermediate affinity state mediates biomechanical platelet aggregation

Integrins are membrane receptors mediating cell adhesion and mechanosensing. The structure-function relationship of integrins remains incompletely understood, despite the extensive studies due to its importance to basic cell biology and translational medicine. Using fluorescence dual biomembrane force probe, microfluidics and cone-and-plate rheometry, we applied precisely-controlled mechanical stimulations to platelets and identified an intermediate state of integrin α(IIb)β(3), which is characterized by an ectodomain conformation, ligand affinity and bond lifetimes that are all intermediate between the well-known inactive and active states. This intermediate state is induced by ligand engagement of GPIbα via a mechano-signaling pathway and potentiates the outside-in mechano-signaling of α(IIb)β(3) for further transition to the active state during integrin mechanical affinity maturation. Our work reveals distinct α(IIb)β(3) state transitions in response to biomechanical and biochemical stimuli, and identifies a role for the α(IIb)β(3) intermediate state in promoting biomechanical platelet aggregation.