Shear-induced integrin signaling in platelet phosphatidylserine exposure, microvesicle release, and coagulation

Abstract

It is currently unclear why agonist-stimulated platelets require shear force to efficiently externalize the procoagulant phospholipid phosphatidylserine (PS) and release PS-exposed microvesicles (MVs). We reveal that integrin outside-in signaling is an important mechanism for this requirement. PS exposure and MV release were inhibited in β platelets or by integrin antagonists. The impaired MV release and PS exposure in β platelets were rescued by expression of wild-type β but not a Gα binding-deficient β mutant (EEE to AAA), which blocks outside-in signaling but not ligand binding. Inhibition of Gα or Src also diminished agonist/shear-dependent PS exposure and MV release, further indicating a role for integrin outside-in signaling. PS exposure in activated platelets was induced by application of pulling force via an integrin ligand, which was abolished by inhibiting Gα-integrin interaction, suggesting that Gα-dependent transmission of mechanical signals by integrins induces PS exposure. Inhibition of Gα delayed coagulation in vitro. Furthermore, inhibition or platelet-specific knockout of Gα diminished laser-induced intravascular fibrin formation in arterioles in vivo. Thus, β integrins serve as a shear sensor activating the Gα-dependent outside-in signaling pathway to facilitate platelet procoagulant function. Pharmacological targeting of Gα-integrin interaction prevents occlusive thrombosis in vivo by inhibiting both coagulation and platelet thrombus formation.

SARS-CoV-2 binds platelet ACE2 to enhance thrombosis in COVID-19

“…In addition, SARS-CoV-2 and its Spike protein directly stimulated Factor V and XIII release as well as LPAs formation. SARS-CoV-2 failed to induce PS exposure, which is consistent with previous reports that suggest that platelet activators are inefficient in inducing PS exposure in the absence of a shear force [84].…”

Characterization and function of medium and large extracellular vesicles from plasma and urine by surface antigens and Annexin V

“…The results indicated the validity of the differential centrifugation method (Biro et al, 2003;. Pang et al (2018) reported that integrin outside-in signaling is an important mechanism for microvesicle formation, in which the procoagulant phospholipid phosphatidylserine (PS) is efficiently externalized to release PS-exposed microvesicles (MVs). These plateletderived Annexin V positive MVs were induced by application of a pulling force via an integrin ligand such as shear stress.…”

Procoagulant Phosphatidylserine-Exposing Platelets in vitro and in vivo

“…Anywhere from 20 to 40% of C+T-stimulated platelets become PS-exposing, with a wide variation between donors; singly, these agonists are not as potent, with a smaller proportion of PS-exposing platelets being formed (56). ADP or thromboxane A 2 (TxA 2 ) (using the stable mimetic U46619) does not play a major role (23,33), while shear forces are effective (57,58). The non-physiological, non-receptor-mediated ionophores A23187, and ionomycin, that directly increase Ca 2+ cyt , are the most potent stimulators of PS exposure, with typically >90% of platelets taking on the procoagulant phenotype (19,56).…”