PURPOSE: Mechanical circulatory support (MCS) has emerged as a lifesaving therapy for patients with advanced and end-stage heart failure. Sadly, MCS therapy is limited by a paradoxical coagulopathy accompanied by both thrombosis and bleeding. We hypothesized that shear-mediated alterations of platelet hemostatic function, i.e. integrin expression, procoagulant activity, and aggregation, mechanistically drive MCS-related coagulopathy. METHODS: Human platelets were exposed to shear stress in a hemodynamic shearing device (30-70 dyn/cm2, 10 min). Integrin αIIbβ3 & GPIb surface expression/activation, phosphatidylserine externalization (PSE) and microparticles (MPs) were quantified by flow cytometry. Platelet procoagulant activity was verified by thrombin generation assay. Platelet aggregation was measured by optical aggregometry. RESULTS: Shear stress exposure induced notable PSE, simultaneously promoting thrombin generation on platelets and MP. Paradoxically, shear-mediated platelet activation (SMPA) did not induce integrin αIIbβ3 activation. Moreover, high shear (70 dyn/cm2) prevented activation and upregulation of αII2bβ3 mediated by biochemical agonists. Aggregometry findings further validate flow cytometry results, as high shear did not promote aggregation, rather decreased ADP- and TRAP-6 induced aggregation. Likewise, SMPA led to the evident reduction of GPIb surface expression, as indicated by significant drop of GPIb+ platelet number and their fluorescence intensity (73.5 ± 2.9% & 953.1 ± 101.0 AU vs. 94.3 ± 0.7% & 1620 ± 72.4 AU for intact platelets; M ± SEM, ANOVA, p ≤ 0.05). Shear-mediated decrease of GPIb expression along with evident augmentation of GPIb- & αIIbβ3-positive MPs (3.3 ± 0.6% & 12.5 ± 2.8%, respectively) supports integrin shedding as an operative mechanism. CONCLUSION: SMPA promotes platelet PSE and procoagulant MP generation, thus facilitating thrombin formation and driving prothrombosis. Yet, shear stress did not promote platelet aggregation, rather impaired agonist-induced platelet aggregation via integrin αIIbβ3 and GPIb shedding from the platelets into MPs. This dichotomic effect of shear on platelets mechanistically defines the paradoxical prothrombotic state with a concomitant propensity of bleeding in MCS patients.
|Original language||English (US)|
|Journal||The Journal of heart and lung transplantation : the official publication of the International Society for Heart Transplantation|
|State||Published - Apr 1 2020|
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine
- Cardiology and Cardiovascular Medicine