Prostacyclin reverses platelet stress fibre formation causing platelet aggregate instability

• Published in: Scientific reports Vol. 7; no. 1; pp. 5582 - 11
• Main Authors: Yusuf, M. Z., Raslan, Z., Atkinson, L., Aburima, A., Thomas, S. G., Naseem, K. M., Calaminus, S. D. J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 17-07-2017; Nature Publishing Group; Nature Portfolio
• Subjects: 14; 14/19; 14/63; 692/4019/592/1339; 692/4019/592/75/593/567; 96/95; Actin; Animals; Blood Platelets - chemistry; Blood Platelets - drug effects; Blood Platelets - metabolism; Colforsin - pharmacology; Cyclic AMP-Dependent Protein Kinases - metabolism; Cytoskeleton; Epoprostenol - pharmacology; Fibers; Fibrinogen; Forskolin; Guanosine triphosphate; Humanities and Social Sciences; Humans; Kinases; Molecular modelling; multidisciplinary; Myosin; Nodules; Phosphorylation; Platelet Aggregation - drug effects; Platelet Aggregation Inhibitors - pharmacology; Platelets; Prostacyclin; Protein kinase A; rhoA GTP-Binding Protein - metabolism; RhoA protein; Science; Science (multidisciplinary); Spreading; Stress Fibers - drug effects; Thromboembolism; Thrombosis
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-05817-9

Prostacyclin (PGI
2
) modulates platelet activation to regulate haemostasis. Evidence has emerged to suggest that thrombi are dynamic structures with distinct areas of differing platelet activation. It was hypothesised that PGI
2
could reverse platelet spreading by actin cytoskeletal modulation, leading to reduced capability of platelet aggregates to withstand a high shear environment. Our data demonstrates that post-flow of PGI
2
over activated and spread platelets on fibrinogen, identified a significant reduction in platelet surface area under high shear. Exploration of the molecular mechanisms underpinning this effect revealed that PGI
2
reversed stress fibre formation in adherent platelets, reduced platelet spreading, whilst simultaneously promoting actin nodule formation. The effects of PGI
2
on stress fibres were mimicked by the adenylyl cyclase activator forskolin and prevented by inhibitors of protein kinase A (PKA). Stress fibre formation is a RhoA dependent process and we found that treatment of adherent platelets with PGI
2
caused inhibitory phosphorylation of RhoA, reduced RhoA GTP-loading and reversal of myosin light chain phosphorylation. Phospho-RhoA was localised in actin nodules with PKA type II and a number of other phosphorylated PKA substrates. This study demonstrates that PGI
2
can reverse key platelet functions after their initial activation and identifies a novel mechanism for controlling thrombosis.